TRANSFERRING SMALL ELECTRQSTATOGRAPHIC

TONER PARTICLES TO A THERMOPLASTIC BEARING RECEIVER

Field of the Invention

This invention relates to an improved method of non-electrostatically transferring dry toner particles which comprise a toner binder and have a particle size of less than 8 micrometers from the surface of an element to a receiver. More particularly, the invention relates to a thermally assisted method of transferring such toner particles where the particles are carried on the surface of an element which has a surface layer comprising a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and a surface energy of not greater than approximately 47 dynes/cm to a receiver which comprises a substrate having a polymeric coating on a surface of the substrate in which the polymeric coating is a blend of particular thermoplastic addition polymers which have a Tg which is less than approximately 10 ^β C above the Tg of the toner binder and the surface energy of the thermoplastic polymer coating is approximately 38 to 43 dynes/cm by contacting the toner particles with the receiver which is heated to a temperature such that the temperature of the thermoplastic polymer coating during transfer is at least approximately 5 ^β C above the Tg of the thermoplastic addition polymers in the blend. After transfer, the receiver is immediately separated from the element while the temperature of the thermoplastic polymer coating is maintained at a temperature which is above the Tg of the thermoplastic addition polymers.

Description of the Prior Art

In an electrostatographic copy machine, an electrostatic latent image is formed on an element. That image is developed by the application of an oppositely charged toner to the element. The image- forming toner on the element is then transferred to a receiver where it is permanently fixed, typically by heat fusion. The transfer of the toner to the receiver is usually accomplished electrostatically by means of an electrostatic bias between the receiver and the element.

In order to produce copies of very high resolution and low granularity, it is necessary to use toner particles that have a very small particle size, i.e., less than about 8 micrometers. (Particle size herein refers to mean volume weighted diameter as measured by conventional diameter measuring devices such as a Coulter Multisizer, sold by Coulter, Inc. Mean volume weighted diameter is the sum of the mass of each particle times the diameter of a spherical particle of equal mass and density, divided by total particle mass.) However, it has been found that it is very difficult to electrostatically transfer such fine toner particles from the element to the receiver, especially when they are less than 6 micrometers in diameter. That is, fine toner particles frequently do not transfer from the element with reasonable efficiency. Moreover, those particles which do transfer frequently fail to transfer to a position on the receiver that is directly opposite their position on the element, but rather, under the influence of coulombic forces, tend to scatter, thus lowering the resolution of the transferred image and increasing the grain and mottle. Thus, high resolution images of low granularity require very small particles, however, images having high resolution and low granularity have

not been attainable using electrostatically assisted transfer.

In order to avoid this problem, it has become necessary to transfer the toner from the element to the receiver by non-electrostatic processes. One such process is the thermally assisted transfer process where the receiver is heated, typically to about 60 to about 90 ^C C, and is pressed against the toner particles on the element. The heated receiver sinters the toner particles causing them to stick to each other and to the receiver thereby effecting the transfer of the toner from the element to the receiver. The element and receiver are then separated and the toner image is fixed, e.g., thermally fused to the receiver. For details, see U.S. Patent No. 4,927,727, titled "Thermally Assisted Transfer of Small Electro- statographic Toner Particles".

While the thermally assisted transfer process does transfer very small particles without the scattering that occurs with electrostatic transfer processes, it is sometimes difficult to transfer all of the toner particles by this process. The toner particles that are directly on the element often experience a greater attractive force to the element than they do to the receiver and to other toner particles that are stacked above them, and the heat from the receiver may have diminished to such an extent by the time it reaches the toner particles next to the element that it does not sinter them. As a result, the toner particles that are in contact with the element may not transfer. Attempts to solve this problem by coating the element with a release agent have not proven to be successful because the process tends to wipe the release agent off the element into the developer which degrades both the developer and

the development process. Moreover, because the process tends to wipe the release agent off the element, the application of additional release agent to the element is periodically required in order to prevent the toner particles from adhering to the element during transfer.

An alternative approach to removing all of the toner particles from the element is to use a receiver that has been coated with a thermoplastic polymer. During transfer, the toner particles adhere to or become partially or slightly embedded in the thermoplastic polymer coating and are thereby removed from the element. However, it has been found that many thermoplastics that are capable of removing all of the toner particles also tend to adhere to the element. This, of course, not only seriously impairs image quality but it may also damage both the element and the receiver. Moreover, it has not been possible to predict with any degree of certainty which thermoplastic polymers would remove all of the toner particles from the element without sticking to the element during transfer and subsequent separation of the receiver from the element and which ones would not. In U.S. Patent No. 4,968,578, entitled "Method of Non-Electrostatically Transferring Toner", it is disclosed that if such small sized toner particles are transferred to a receiver formed of a substrate or a support which has been coated with a thermoplastic polymer having a layer of a release agent on the thermoplastic polymer coating and the receiver is heated above the Tg of the thermoplastic polymer during transfer, the release agent will prevent the thermoplastic polymer coating from adhering to the element but it will not prevent the toner from transferring to the thermoplastic polymer coating on the receiver and virtually all of the toner

will transfer to the receiver. This constitutes a significant advancement in the art because it is now possible not only to obtain the high image quality that was not previously attainable when very small toner particles were transferred electrostatically but, in addition, the problem of incomplete transfer is avoided. In addition, several other advantages are provided by this process. One such advantage is that copies made by this process can be given a more uniform gloss because all of the receiver is coated with a thermoplastic polymer which can be made glossy while, in receivers that are not coated with a thermoplastic polymer, only those portions of the receiver that are covered with toner can be made glossy and the level of gloss varies with the amount of toner. Another advantage of the process is that when the toner is fixed, it is driven more or less intact into the thermoplastic polymer coating rather than being flattened and spread out over the receiver. This also results in a higher resolution image and less grain. Finally, in images made using this process, light tends to reflect from behind the embedded toner particles that are in the thermoplastic layer which causes the light to diffuse more making the image appear less grainy.

For all of the benefits and advantages provided by this process, however, the application of a release agent to the thermoplastic polymer coating on the receiver in order to prevent the thermoplastic polymer coating from adhering to the surface of the element during transfer and subsequent separation of the receiver from the element creates several problems. One such problem is that the release agent tends to transfer to and build up on the element or photoconductor thereby degrading image quality and causing potential damage to both the element and the

receiver. Another problem is that the release agent tends to allow the thermoplastic polymer coating to separate from the support or substrate, especially during or after finishing, due to a reduction in the adhesion strength of the thermoplastic polymer coating to the receiver support caused by the tendency of the release agent, which has a lower surface energy than the thermoplastic polymer coating and hence a lesser predilection to adhere to the receiver support than the thermoplastic polymer coating, to migrate through the thermoplastic polymer coating to the interfacial region between the thermoplastic polymer coating and the support and to cause the thermoplastic polymer coating to separate from the support. It has also been found that the release agent reduces the gloss of the finished image. Finally, the addition of a release agent to the thermoplastic polymer coating adds to the overall cost of the process.

Accordingly, it would be desirable to be able to provide a thermally assisted transfer process for transferring dry toner particles having a particle size of less than 8 micrometers from an element to a receiver in which a thermoplastic polymer coated receiver is utilized such that all of the benefits and advantages afforded by the use of a thermoplastic polymer coated receiver in a thermally assisted transfer process are retained, including the transfer of virtually all of the toner particles from the element to the receiver, but one which does not require the use of a coating or layer of a release agent on the thermoplastic polymer coating on the receiver substrate (or the element) in order to prevent the receiver from adhering to the element during transfer and subsequent separation from the element.

Applicant has found a transfer process whereby fine toner particles having a particle size of

less than 8 micrometers can be transferred from the surface of an element to a thermoplastic polymer coated receiver with virtually 100% toner transfer efficiency using the thermally assisted method of transfer in the absence of a layer or a coating of a release agent on the thermoplastic polymer coating on the receiver substrate in order to prevent the thermoplastic polymer coating from sticking or adhering to the element surface during transfer of the toner particles from the surface of the element to the thermoplastic polymer coated receiver and during the subsequent separation of the receiver from the element if (i) the surface layer of the element on which the toner particles are carried and from which they are to be transferred to the receiver comprises a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and has a surface energy of not more than approximately 47 dynes/cm, preferably from about 40 to 45 dynes/cm; (ii) the thermoplastic polymer coating on the receiver substrate to which the very fine, small toner particles are to be transferred comprises a thermoplastic addition polymer or mixture of such polymers, typically having weight average molecular weights in the range of from approximately 20,000 to 500,000, which have a glass transition temperature or Tg which is less than approximately 10 ^β C above the Tg of the toner binder and the surface energy of the thermoplastic polymer coating on the substrate is approximately 38 to 43 dynes/cm, and (iii) the receiver is heated to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate is at least approximately 15 ^β C above the Tg of the thermoplastic addition polymer during toner transfer and the temperature of the receiver is maintained at a temperature such that the

temperature of the thermoplastic polymer coating is above the Tg of the thermoplastic polymer immediately following transfer during the time when the receiver separates from the element. Applicant also has found that such fine toner particles can be transferred from the surface of an element to a thermoplastic polymer coated receiver with virtually 100% toner transfer efficiency using the thermally assisted method of transfer in the absence of a layer or a coating of a release agent on the thermoplastic polymer coating on the receiver substrate when the thermoplastic polymer coating on the receiver substrate is formed of or comprises a thermoplastic condensation polymer, as distinguished from and in contrast to, a thermoplastic addition polymer if (i) the surface layer of the element on which the toner particles are carried and from which they are to be transferred to the receiver comprises a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and has a surface energy of not more than approximately 47 dynes/cm, preferably from about 40 to 45 dynes/cm; (ii) the thermoplastic polymer coating on the receiver substrate to which the very fine toner particles are to be transferred is a thermoplastic condensation polymer and has a glass transition temperature or Tg which is less than approximately 10 ^β C above the Tg of the toner binder, and (iii) the receiver is heated to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate is at least approximately 5°C above the Tg of the thermoplastic polymer during toner transfer and the temperature of the receiver is maintained at a temperature such that the temperature of the thermoplastic polymer coating is above the Tg of the thermoplastic condensation polymer immediately

following transfer during the time when the receiver separates from the element.

Thus, means now exist for non-electro- statically transferring very small, fine toner particles having a particle size of less than 8 micrometers from the surface of an element to a receiver using a thermally assisted method of transfer in which a thermoplastic polymer coated receiver can be utilized such that all of the aforementioned benefits and advantages afforded by the use of a thermoplastic polymer coated receiver are retained, including the transfer of virtually all of the toner particles from the element to the receiver, and one which does not require the use of a coating or a layer of a release agent on the thermoplastic polymer coating in order to prevent the receiver from adhering to the element during toner transfer and subsequent separation of the receiver from the element. This achievement constitutes a much needed and long sought after improvement in the thermally assisted transfer process .

However, there is one problem or disadvantage inherent in the process regarding the use of high molecular weight thermoplastic addition polymers or mixtures of such polymers having weight average molecular weights in the range of from approximately 20,000 to 500,000 to form the polymeric coating on the receiver substrates which are used in the process. The problem resides in the fact that when such high molecular weight thermoplastic addition polymers are used to form the polymeric coatings, the receiver must be heated to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate is at least approximately 15°C above the Tg of the thermoplastic addition polymer or polymers which form the coating in order for the coating material to melt and/or soften or flow sufficiently

enough to permit the toner particles to adhere to or to become slightly or partially embedded in the polymer coating during toner transfer so that all or virtually all of the toner can be removed from the element surface during transfer. This is undesirable because ideally it is most advantageous and desirable to heat the receiver to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate is at or just slightly above the Tg of the thermoplastic polymer during toner transfer when removing the toner particles from the element because the higher the temperature to which the thermoplastic polymer coating must be heated above the Tg of the thermoplastic polymeric material which forms the polymer coating in order for the thermoplastic polymer coating to melt and/or flow sufficiently enough to permit the toner particles to adhere to or become slightly or partially embedded in the polymer coating during toner transfer, the greater the tendency of the thermoplastic polymer coating to adhere to the element surface during transfer when it contacts the element. Also, the higher the temperature to which the thermoplastic polymer coating must be heated above the Tg of the thermoplastic polymeric material which forms the polymer coating in order for the thermoplastic polymer coating to melt or soften sufficiently enough for the toner particles to adhere to or become partially embedded in the polymer coating during toner transfer, the greater the tendency of the toner particles to melt and flow or blend together into a localized mass during transfer instead of remaining sintered or fused at localized regions on the individual toner particle surfaces which are in contact with one another during toner transfer and deposition on the polymer coating which is a requirement of the thermally assisted transfer

process. Further, the higher the temperature to which the thermoplastic polymer coating must be heated above the Tg of the thermoplastic polymeric material which forms the polymer coating in order for the thermoplastic polymer coating to melt sufficiently enough for the toner particles to adhere to or become partially embedded in the polymer coating during toner transfer, the greater the risk of damage to the element due to a softening of the element caused by the additional heat when the receiver contacts the element during transfer. Still further, the higher the temperature to which the thermoplastic polymer coating must be heated above the Tg of the thermoplastic polymeric material which forms the polymer coating in order for the thermoplastic polymer coating to melt and/or flow sufficiently enough for the toner particles to adhere to or become partially embedded in the polymer coating during toner transfer, the greater the risk of the toner melting and adhering or fusing to the element surface during toner transfer, especially where the coating is heated to a temperature which approaches or exceeds about 25 ^β C above the Tg of the polymeric material. Finally, the higher the temperature to which the thermoplastic polymer coating must be heated above the Tg of the thermoplastic polymeric material which forms the polymer coating during toner transfer, the greater the risk of blistering the receiver substrate during transfer. Conversely, if the receiver is heated to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate is less than approximately 15 ^β C above the Tg of the thermoplastic addition polymer or polymers during toner transfer, typically less than 50% and, more typically, less than 10% of the toner particles will transfer from the element surface to the thermoplastic polymer coating during toner transfer.

Accordingly, it would be highly desirable to be able to provide a thermally assisted transfer process for transferring dry toner particles having a particle size of less than 8 micrometers from the surface of an element to a thermoplastic polymer coated receiver in which thermoplastic addition polymers can be utilized to form the thermoplastic polymer coating on the receiver substrate such that all of the previously mentioned benefits and advantages afforded by the use of such a thermoplastic polymer coated receiver can be retained, including the transfer of virtually all of the toner particles from the element to the receiver in the absence of a coating or layer of a release agent on the thermoplastic polymer coating in order to prevent the receiver from adhering to the element during toner transfer and subsequent separation of the receiver from the element, and one in which the temperature of the thermoplastic polymer coating on the receiver substrate does not have to be heated to a temperature that is at least approximately 15°C above the Tg of the polymeric material which forms the polymer coating during toner transfer in order for the thermoplastic polymer coating to melt and/or flow sufficiently enough to permit the toner particles to adhere to or become partially embedded in the polymer coating during transfer so that all of the aforementioned problems associated with the use of such high transfer temperatures can be avoided. It should be noted that the use of thermoplastic addition polymers as the polymeric material with which to form the receiver coatings is highly desirable and very important in the thermally assisted transfer process when toner binders are used in the process which are also made of thermoplastic addition polymers because of the increased tendency of the toner binder material to adhere to or become

partially or slightly embedded in the polymer coating during toner transfer due to the natural affinity of the materials for each other. The present invention provides such a process. it has now been found that by using, as the thermoplastic polymer coating materials with which to form the thermoplastic polymer receiver coatings used in the thermally assisted method of transfer, a blend or mixture of certain high and low molecular weight thermoplastic addition polymers, in specific amounts, that toner particles having a particle size of less than 8 micrometers can be transferred from the surface of an element to the thermoplastic polymer coated receiver with virtually 100% toner transfer efficiency using the thermally assisted method of transfer without having to apply a coating or a layer of a release agent to the toner contacting surface of the thermoplastic polymer coating on the receiver substrate prior to toner transfer in order to prevent the thermoplastic polymer coating from adhering or sticking to the element surface during transfer of the toner particles from the surface of the element to the thermoplastic polymer coated receiver and during the subsequent separation of the receiver from the element and, further, without having to heat the thermoplastic polymer coating on the receiver substrate to a temperature such that the temperature of the thermoplastic polymer coating must be at least approximately 15°C above the Tg of the thermoplastic addition polymers which form the polymer coating during toner transfer in order for the thermoplastic polymer coating to melt and/or flow sufficiently enough to permit the sintered toner particles to adhere to or become partially embedded in the thermoplastic polymer coating during toner transfer. By utilizing such a blend as the polymeric coating material, it has been found that the thermoplastic

polymer coating on the receiver substrate only has to be heated to a temperature such that its temperature during toner transfer is only approximately at least about 5 ^β C above the Tg of the thermoplastic addition polymers which make up or form the polymeric blend in order for the polymer coating to soften sufficiently enough to allow the toner particles to stick to or become partially embedded in the coating during transfer. This is a significant achievement because now not only can thermoplastic addition polymers be used as the thermoplastic receiver coating materials in the thermally assisted transfer process, but, because the temperature to which the thermoplastic polymer coating must be heated during toner transfer has been reduced, all of the aforementioned problems associated with the use of higher transfer temperatures such as the increased risk of thermal degradation to the element during toner transfer, the increased tendency for the toner particles to melt and flow together into a localized mass during toner transfer, the increased risk of the toner particles adhering to and damaging the element during toner transfer and the increased risk of blistering to the receiver substrate during transfer are avoided. Specifically, the foregoing achievements and advantages are obtained by blending together to form, as the polymeric receiver coating used in the thermally assisted transfer method, a blend of:

(a) from about 40 to about 90 percent by weight based on the total weight of the blend of a thermoplastic addition polymer having a weight average molecular weight of from about 20,000 to 500,000, a number average molecular weight of from about 5000 to 50,000, and a ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 20:1; and

(b) from about 10 to about 60 percent by weight based on the total weight of the blend of a thermoplastic addition polymer having a weight average molecular weight of from about 1000 to 20,000, a number average molecular weight of from about 500 to 5000, and of ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 10:1;

wherein the Tg of the thermoplastic addition polymers in the blend is less than approximately 10°C above the Tg of the toner binder and non-electrostatically transferring the dry toner particles which comprise a toner binder and have a particle size of less than 8 micrometers from the surface of an element which has a surface layer comprising a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and a surface energy of not greater than approximately 47 dynes/cm, preferably from about 40 to 45 dynes/cm, to a receiver which comprises a substrate having a polymeric coating on a surface of the substrate comprising a blend of the aforedescribed thermoplastic addition polymers and where the surface energy of the thermoplastic polymer coating is approximately 38 to 43 dynes/cm and contacting the toner particles with the receiver which is heated to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate is at least approximately 5 ^β C above the Tg of the thermoplastic addition polymers whereby virtually all of the toner particles are transferred from the surface of the element to the thermoplastic polymer coating on the receiver substrate and the thermoplastic polymer coating is prevented from adhering to the element surface during transfer in the absence of a layer or a coating of a release agent on the thermoplastic polymer coating and separating the

receiver from the element while the temperature of the thermoplastic polymer coating is maintained above the Tg of the thermoplastic addition polymers in the blend.

Summary of the Invention

Thus, in accordance with the present invention there is provided a method of non—electrostatically transferring dry toner particles which comprise a toner binder and which have a particles size of less than 8 micrometers from the surface of an element which has a surface layer which comprises a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric resin matrix and a surface energy of not greater than approximately 47 dynes/cm to a receiver which comprises a substrate having a polymeric coating on a surface of the substrate in which the polymeric coating comprises a blend of:

(i) from about 40 to 90 percent by weight based on the total weight of the blend of a thermoplastic addition polymer having a weight average molecular weight from about 20,000 to 500,000, a number average molecular weight of from about 5000 to 50,000, and a ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 20:1; and

(ii) from about 10 to about 60 percent by weight based on the total weight of the blend of a thermoplastic addition polymer having a weight average molecular weight of from about 1000 to 20,000, a number average molecular weight of from about 500 to 5000, and a ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 10:1;

wherein the Tg of the thermoplastic addition polymers in the blend is less than approximately 10°C above the Tg of the toner binder and the surface energy of the thermoplastic polymer coating is approximately 38 to 43 dynes/cm which comprises:

(A) contacting said toner particles with said thermoplastic polymer coating on said receiver;

(B) heating said receiver to a temperature such that the temperature of said thermoplastic polymer coating on said receiver during said transferring is at least approximately 5°C above the Tg of said thermoplastic addition polymers; and

(C) separating said receiver from said element at a temperature above the Tg of said thermoplastic addition polymers,

whereby virtually all of said toner particles are transferred from the surface of said element to said thermoplastic polymer coating on said receiver.

Description of the Preferred Embodiments In the method of this invention, the transfer of toner particles from the element to the receiver is accomplished non—electrostatically using a receiver which comprises a substrate having a polymeric coating which comprises a blend of:

(i) from about 40 to about 90 percent by weight based on the total weight of the blend of a thermoplastic addition polymer having a weight average molecular weight of from about 20,000 to 500,000, a number average molecular weight of from about 5000 to 50,000, and a ratio of weight average molecular weight

to number average molecular weight in the range of from about 1:1 to 20:1; and

(ii) from about 10 to about 60 percent by weight based on the total weight of the blend of a thermoplastic addition polymer having a weight average molecular weight of from about 1000 to 20,000, a number average molecular weight of from about 500 to 5000, and a ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 10:1

on a surface of the substrate in which the thermoplastic polymer coating has a surface energy in the range of from approximately 38 to 43 dynes/cm and the Tg of the thermoplastic addition polymers in the blend is less than approximately 10°C above the Tg of the toner binder. The upper surface, or surface layer, of the element on which the toner particles which are to be transferred are carried, comprises a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and the surface of the element has a surface energy of not greater than approximately 47 dynes/cm, preferably from about 40 to 45 dynes/cm. The receiver is heated to a temperature such that the temperature of the thermoplastic polymer coating on the receiver substrate during transfer is at least approximately 5°C above the glass transition temperature, Tg, of the thermoplastic addition polymers in the blend. After transfer, the receiver is immediately separated from the element while the temperature of the receiver is maintained at a temperature which is above the Tg of the thermoplastic addition polymers. As a result of the unique selection and combination of materials which form the thermoplastic polymer coatings and surface layers of the elements used in the practice of

the process of the present invention, the interrelationship of the respective surface energies of the thermoplastic polymer coatings and element surfaces used in the practice of the process of the present invention, and the heating temperatures which are employed during contact of the receiver with the element during toner transfer and during the subsequent separation of the receiver from the element, it is possible to transfer virtually 1007o of the toner particles from the element to the receiver using the thermally assisted method of transfer without having to use a coating or a layer of a release agent on the thermoplastic polymer coating in order to prevent the thermoplastic polymer coating from adhering to the element surface during transfer and subsequent separation of the receiver from the element.

In addition, by using as the polymeric material with which to form the thermoplastic polymer coatings on the receiver substrates used in the practice of the process of the present invention, a blend of the aforedescribed thermoplastic addition polymers in the aforestated amounts, the thermoplastic polymer coating only has to be heated to a temperature which is approximately at least about 5 ^β C above the Tg of the thermoplastic addition polymers which form the blend during toner transfer in order for the polymer coating to soften sufficiently enough to permit the toner particles to stick to or become slightly embedded in the polymer coating during transfer. As mentioned previously, this avoids potential damage to the element during toner transfer, potential melting of the toner particles into a localized mass during toner transfer, adhesion of the toner particles to the surface of the element and potential blistering of the receiver substrate during toner transfer.

The molecular weight distribution of the thermoplastic addition polymers which are used in the practice of the process of the present invention can be expressed by the value of weight average molecular weight/number average molecular weight (Mw/Mn) .

The weight average molecular weight (Mw) and the number average molecular weight (Mn) may be determined by various measuring methods. The measuring method used in the present invention is described below.

A number average molecular weight Mn is a value obtained by adding products of Mi (molecular weight) and

Ni/Σ Ni i

(number fraction of molecular weight Mi) from 0 it ∞ as to i where Ni is the number of molecules having a molecular weight Mi, and can be defined by the formula

? MiNi i=l

Mn =

S Ni i=l

This is an average as to number of molecules. On the contrary, weight average molecular weight Mw where great importance is attached to the contribution of high molecular weight materials to an average molecular weight is defined as follows:

Mi ² Ni

_ ⁼ l

Mn = ϊ MiNi i=l

According to the present invention both weight average molecular weights and number average molecular weights were determined or measured by gel permeation chromatography, or GPC, using a Waters Gel Permeation Chromatograph, Model R401. Columns of m-styragel with pore sizes of 10 6, 105, 104, and

10 A were eluted with THF (tetrahydrofuran) . A universal polystyrene calibration curve was used and therefore the molecular weight results reported are not the absolute values but polystyrene equivalent molecular weights.

It has been found that if the percentage of the higher molecular weight thermoplastic addition polymer in the total blend or mixture exceeds approximately 90 percent by weight of the total weight of the blend, the polymeric coating will not flow and/or soften sufficiently enough at the toner transfer temperatures, i.e., approximately at least

5°C above the Tg of the addition polymers in the blend to permit the toner particles to adhere to or become partially embedded in the thermoplastic polymer coating and poor transfer efficiency results. On the other hand, it has also been found that if the percentage of the higher molecular weight thermoplastic addition polymer in the total blend or mixture is present in an amount which is less than approximately 40 percent by weight based on the total weight of the blend, the polymeric coating is brittle and tends to flake off the receiver substrate prior to toner transfer.

The present invention constitutes an improvement in the thermally assisted method of non-electrostatically transferring very small toner particles from the surface of an element to a thermoplastic polymer coated receiver where the toner particles which are carried on the surface of the element are transferred non-electrostatically to the

receiver which is heated, but not heated sufficiently to melt the particles. As is taught in previously mentioned U.S. Application Serial No. 230,381 entitled "Improved Method of Non—Electrostatically Transferring Toner" filed August 9, 1988, it is not necessary or desirable to melt the toner particles in order to achieve their transfer, but that merely fusing the toner particles to each other at their points of contact, i.e. localized regions on the individual toner particle surfaces which are in contact either with one another or with the surface upon which such a particle is transferred or deposited, is adequate to accomplish a complete, or nearly complete, transfer of the particles. Thus, the toner is not fixed during transfer, but instead is fixed at a separate location away from the element. In this manner, the higher temperatures required for fixing the toner do not negatively affect or damage the element. Since the heat required to merely sinter the toner particles at their points of contact is much lower than the heat needed to fix the toner, the element is not damaged by high temperatures during transfer.

-The term "sinter" or "sintering" as used herein in relation to toner particles employed in the practice of the present invention has reference to bonding or fusion that is thermally achieved at locations of contact existing either between adjacent toner particles or between toner particles and an adjacent surface. The term "sinter" and equivalent forms is distinguished for present purposes from a term such as "melts", "melting", "melt", "melt fusion" or "heat fusion". In heat fusion, in response to sufficiently applied thermal energy, toner particles tend to lose their discrete individual identities and melt and blend together into a localized mass, as when a toner powder is heat fused and thereby bonded or fixed to a receiver.

The crux of the present invention resides in the fact that it has now been found that very fine toner particles, i.e. toner particles having a particle size of less than 8 micrometers, and more typically, 3 to 5 micrometers, can be non- electrostatically transferred with virtually 100% transfer efficiency from the surface of an element to the surface of a thermoplastic polymer coated receiver using the thermally assisted method of transfer, but without the necessity of having to apply a coating or a layer of a release agent to the thermoplastic polymer coating prior to toner transfer in order to prevent the thermoplastic polymer coating from adhering to the element surface during and immediately following toner transfer when the receiver separates from the element and that by using as the polymeric material for forming the thermoplastic polymeric coating on the receiver substrate used in the thermally assisted process of the present invention a polyblend or mixture of certain thermoplastic addition polymers in certain specified amounts, that the thermoplastic polymer coating only has to be heated to a temperature such that its temperature during toner transfer need only be at least about 5 ^β C above the Tg of the thermoplastic addition polymers in the blend in order for the coating to soften sufficiently enough to allow the toner particles to adhere to the coating during transfer. As stated previously, this avoids potential damage to the element surface, the receiver substrate and melting of the toner particles into a localized mass during transfer often caused by higher transfer temperatures . Due to the result of the interrelationship between the unique selection and combination of materials which form the thermoplastic polymer coatings, the materials which comprise the thermoplastic binder resin matrices of the surface layers of the elements which are used in the thermally

assisted transfer process of the present invention, the interrelationship which exists between the respective surface energies of the thermoplastic polymer coatings and the surface layers of the elements used in the thermally assisted transfer process of the present invention to each other, and the heating temperatures employed during contact of the thermoplastic polymer coated receiver with the element surface during toner transfer and subsequent separation of the receiver from the element, not only can very fine toner particles having a particle size of less than 8 micrometers be non-electrostatically transferred with virtually 100% transfer efficiency from the element surface to the thermoplastic polymer coated receiver without the necessity of having to apply a coating or a layer of a release agent to the thermoplastic polymer coating prior to toner transfer in order to prevent the thermoplastic polymer coating from adhering to the element surface during and immediately following toner transfer when the receiver separates from the element but, in addition, transfer can be carried out at a temperature wherein the temperature of the thermoplastic polymer coating only has to be slightly above the Tg of the thermoplastic addition polymers which make up or comprise the polymeric coating.

Almost any type of substrate can be used to make the coated receiver used in this invention, including paper, film, and particularly transparent film, which is useful in making transparencies. The substrate must not melt, soften, or otherwise lose its mechanical integrity during transfer or fixing of the toner. A good substrate should not absorb the thermoplastic polymer, but should permit the thermoplastic polymer to stay on its surface and form a good bond to the surface. Substrates having smooth surfaces will, of course, result in a better image

quality. A flexible substrate is particularly desirable, or even necessary, in many electrostato— graphic copy machines. A substrate is required in this invention because the thermoplastic coating must soften during transfer and fixing of the toner particles to the receiver, and without a substrate the thermoplastic coating would warp or otherwise distort, or form droplets, destroying the image.

In preparing the polymeric coatings of this invention, a thermoplastic addition polymer having a weight average molecular weight of from about 20,000 to 500,000, a number average molecular weight of from about 5000 to 50,000, a ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 20:1, and a glass transition temperature or Tg which is less than approximately 10 ^β C above the Tg of the toner binder is mechanically mixed together with a thermoplastic addition polymer having a weight average molecular weight of from about 1000 to 20,000, a number average molecular weight of from about 500 to 5000, a ratio of weight average molecular weight to number average molecular weight in the range of from about 1:1 to 10:1, and a glass transition temperature or Tg which is less than approximately 10°C above the Tg of the toner binder to form a mixture or a blend of the polymers in which the first described thermoplastic addition polymer is present in the blend in an amount of from about 40 to about 90 percent by weight based on the total weight of the blend and the other thermoplastic addition polymer is present in the blend in an amount of from about 10 to about 60 percent by weight based on the total weight of the blend to provide a thermoplastic polymer coating which has a surface energy of from about 38 to about 43 dynes/cm. The term "glass transition temperature" or "Tg" as used herein means the temperature or

temperature range at which a polymer changes from a solid to a viscous liquid or rubbery state. This temperature (Tg) can be measured by differential thermal analysis as disclosed in Mott, N.F. and Davis, E.A. Electronic Processes in Non-Crystalline

Material. Belfast, Oxford University Press, 1971. p. 192.

The term "surface energy" of a material as used herein means the energy needed or required to create a unit surface area of that material to an air interface. Surface energy can be measured by determining the contact angles of droplets of two different liquids, e.g., diiodomethane and distilled water on the surface of the material and adding the polar and dispersive contributions to the surface and by using the approximation of Girifalco and Good for the interfacial energy as described in Fowkes, F. "Contact Angle, Wettability, and Adhesion", in: Advances in Chemistry Series (Washington, D.C., American Chemical Society, 1964) p. 99-111.

In addition to the foregoing requirements, the thermoplastic addition polymers must be sufficiently adherent to the substrate so that they will not peel off when the receiver is heated. They must also be sufficiently adherent to the toner so that transfer of the toner occurs. The thermoplastic polymer coating also should be abrasion resistant and flexible enough so that it will not crack when the receiver is bent. A good thermoplastic polymer should not shrink or expand very much, so that it does not warp the receiver or distort the image, and it is preferably transparent so that it does not detract from the clarity of the image. Further, the thermoplastic addition polymers used to form the polymer blend must be miscible with each other. The thermoplastic addition polymers advantageously should have a Tg that is less than

approximately 10 ^β C above the Tg of the toner binder, which preferably has a Tg of about 50 to about 100°C, so that the toner particles can be pressed into the surface of the thermoplastic polymer coating during transfer thereby becoming slightly or partially embedded therein, in contrast to being completely or nearly completely encapsulated in the thermoplastic polymer coating. Preferably, the Tg of the thermoplastic addition polymers is below the Tg of the toner binder, but polymers having a Tg up to approximately 10°C above the Tg of the toner binder can be used at higher nip speeds when the toner is removed from the nip before it can melt. Melting of the toner in the nip should be avoided as it may cause the toner to adhere to the element or to damage the element. Since fixing of the toner on the receiver usually requires the fusing of the toner, fixing occurs at a higher temperature than transfer and fixing softens or melts both the toner and the thermoplastic polymer coating. A suitable Tg for the thermoplastic addition polymers is about 40 to about 80 ^β C, and preferably about 45 to about 60 ^β C, as polymers having a lower Tg may be too soft in warm weather and may clump or stick together, and polymers having a higher Tg may not soften enough to pick up all of the toner. Other desirable properties include thermal stability and resistance to air oxidation and discoloration.

Thermoplastic addition polymers which can be used in the practice of the present invention can be chosen from among polymers of acrylic and methacrylic acid, including poly(alkylacrylates), poly(alkylmethacrylates), and the like, wherein the alkyl moiety contains 1 to about 10 carbon atoms; styrene containing polymers, and the like.

For example, such polymers can comprise a polymerized blend containing on a 100 weight percent

combined weight basis, about 40 to about 85 weight percent of styrene and about 15 to about 60 weight percent of a lower alkyl acrylate or methacrylate having 1 to about 6 carbon atoms in the alkyl moiety, such as methyl, ethyl, isopropyl, butyl, and the like. Typical styrene—containing polymers prepared from such a copolymerized blend as above indicated are copolymers prepared fro *m a monomeric blend which comprises on a 100 weight percent basis about 40 to about 80 weight percent styrene or styrene homolog, such as vinyl toluene, tert—butyl styrene, α-methylstyrene, and the like, a halogenated styrene such as p—chlorostyrene, an alkoxy—substituted styrene in which the alkoxy group contains from about 1 to 6 carbon atoms such as, for example, p—methoxy—styrene, and about 20 to about 60 weight percent of a lower alkyl acrylate or methacrylate. Especially preferred copolymers are polyvinyl(toluene-co-n-butyl acrylate), polyvinyl(toluene-co—isobutyl methacrylate), polyvinyl(styrene-co-n—butyl acrylate), polyvinyl(methacrylate-co-isobutyl methacrylate) and α-methylstyrene-vinyltoluene.

Examples of such polymers which are presently available commercially include various styrene butylacrylates such as Pliotone 2003 and Pliotone 2015, both of which are available from Goodyear, and an α-methylstyrene—vinyltoluene copolymer marketed by Hercules Company under the tradename Piccotex 100. The thermoplastic coating on the receiver can be formed in a variety of ways, including solvent coating, extruding, and spreading from a water latex. The resulting thermoplastic polymer coating on the substrate is preferably about 5 to about 30 micrometers in thickness, and more preferably about 2 to about 20 micrometers in thickness, as thinner layers may be insufficient to transfer all of the toner from the element and thicker layers are

unnecessary and may result in warpage of the receiver, may tend to delaminate, may embrittle, or may result in a loss of image sharpness.

As mentioned previously, one of the criteria to the successful practice of the process of the present invention is that the surface energies of the thermoplastic polymer coatings on the receiver substrates used in the process of the invention be in a range of from approximately 38 to 43 dynes/cm. In general, thermoplastic polymer coatings which meet this requirement can be attained by selecting, as thermoplastic addition polymers for forming the thermoplastic polymer coatings on the receiver substrates, thermoplastic addition polymers which have a glass transition temperature or Tg that is less than approximately 10°C above the Tg of the toner binder and a surface energy of from approximately 38 to 43 dynes/cm. In most instances, or generally, this will provide a thermoplastic polymer coated receiver which will have a polymer coating which has the requisite surface energy (i.e., from approximately 38 to 43 dynes/cm). However, it may sometimes happen that when thermoplastic addition polymers possessing the required glass transition temperature and surface energy are blended together to form a polymeric coating on the substrate, a thermoplastic polymer coated receiver may be produced which has a surface energy which is either somewhat greater than approximately 43 dynes/cm or somewhat less than approximately 38 dynes/cm due to a change in surface energy brought about during the application of the polymer blend onto the substrate. While the cause of this change in surface energy is not completely understood at this time, in the situation where the polymeric blend is melt extruded onto the substrate, it may be due to a thermal degradation of the polymers during the melt extrusion process and changes in the

degree of crystallinity as the polymeric materials cool through their melting points. Therefore, it is recommended that the surface energy for any given thermoplastic polymer coated receiver which is to be used in the practice of the present process be determined or measured using the above mentioned contact angle procedure prior to using it in carrying out the process of the present invention.

As was stated previously, in the past a layer or a coating of a release agent was formed on the thermoplastic polymer coating of a coated receiver which was used in the thermally assisted transfer process to prevent the thermoplastic polymer coating from adhering or sticking to the element surface during toner transfer and subsequent separation of the thermoplastic polymer coated receiver from the element.

The term "release agent" as used herein has reference to a coatable material or substance which, when present at the time when two surfaces are contacted together, either prevents bonding or sticking from occurring between such surfaces or, if bonding does occur, causes a bond of such a low strength to result that the two surfaces can subsequently be separated without leaving any substantial fragments of one surface embedded in the other. Examples of suitable compounds or substances which were heretofore used as release agents to form a layer or coating of a release agent on such thermoplastic polymer coated receivers include non—polar compounds such as metal salts of organic fatty acids, for example, zinc stearate, nickel stearate and zinc palmitate, siloxane copolymers such as poly[4,4'-isopropylidenediphenylene-co—block- poly(dimethylsiloxanediyl)] sebacate, fluorinated hydrocarbons, perfluorinated polyolefins, and the like. The layer of release agent was formed on the thermoplastic polymer layer or coating by solvent

coating, rubbing on a powdered or liquid release agent, or other method. A preferred method was to apply both the release agent and the thermoplastic polymer together to the substrate. This was done by dissolving both the thermoplastic polymer and the release agent in a suitable non—polar solvent. If the release agent had a lower surface energy than the thermoplastic polymer, the release agent came to the surface of the thermoplastic polymer coating as the solvent evaporated. A solution where the release agent was present in concentrations of from about 1 to about 5% by weight of the combined weight of the thermoplastic polymer and the release agent was typically used. However, formation of the layer of release agent could also be accomplished by mixing the release agent into a melt with the thermoplastic polymer and extruding the melt directly onto the substrate. Such a melt might comprise from about 1 to about 5%. by weight of the release agent and from about 95 to about 99% by weight of the thermoplastic polymer. As the melt solidified on the substrate, the release agent came to the surface because the release agent had a lower surface energy than that of the thermoplastic polymer and a layer of the release agent was thus formed on the surface of the thermoplastic polymer coating or layer. A release agent was selected which not only had a surface energy which was lower than the surface energy of the thermoplastic polymer coating to which it was applied, but one which also had a surface energy which was less than the surface energy of the element surface on which the toner particles were carried. Typically, a release agent was selected which had a surface energy of less than 40 dynes/cm to insure that the release agent would have a surface energy which was less than both the thermoplastic polymer coating and the element surface. Because the surface energy of the release

agent was lower than both that of the thermoplastic polymer coating and the element surface, the release agent was able to form an interface between the surface of the element and the thermoplastic polymer coating which prevented contact or intimate contact between the surface of the element and the polymer coating and thereby prevented the thermoplastic polymer coating from adhering or sticking to the element surface during toner transfer and during the subsequent separation of the receiver from the element. Thus, the thermoplastic polymer coating was prevented from adhering to the element surface during transfer and separation. If the release layer was applied over the thermoplastic coating it was preferably about 30A to about 1 micrometer thick because thinner layers might not prevent the thermoplastic coating from adhering to the element, and the toner may not penetrate into the thermoplastic coating if the layer was thicker. If desired, coating aids, such as polymethylphenylsiloxane having a methyl to phenyl ratio of 23:1 sold by Dow-Corning Company under the trade designation "DC 510", which is a surfactant, can be added to the thermoplastic polymer coating materials used in the practice of the present invention to facilitate a more uniform coating of the polymer blend onto the substrate. This can be done, for example, by dissolving both the blend of thermoplastic addition polymers and the coating aid in a non-polar solvent, coating the polymeric blend and coating aid containing solvent solution onto the surface of the substrate, and thereafter evaporating the solvent from the receiver, or by mixing the coating aid into a melt with the thermoplastic polymeric blend and extruding the melt directly onto the surface of the substrate. Other materials which may be used as coating aids in the practice of the

present invention, in addition to the aforedescribed surfactant, can include many of the same substances or compounds which were previously described herein as being suitable release agents for forming a coating or a layer on a thermoplastic polymer coated receiver, e.g., polysiloxanes, metal salts of organic fatty acids, and the like.

However, when such substances or compounds are employed as coating aids in the practice of the present invention, they are used in such small amounts or concentrations that they are precluded from functioning as release agents. For example, if such a material is to be used as a coating aid in the practice of the present invention, it is dissolved in a non—polar solvent along with the blend of thermoplastic polymer coating materials in an amount such that the amount of the material present in the solution will be approximately 0.5% by weight of the combined weight of the thermoplastic polymer blend and the release agent, or less, and preferably from about .01 to about .05% by weight based on the combined weight of the thermoplastic polymer blend and the release agent. Likewise, if such a material is to be used as a coating aid in the practice of the present invention and is mixed into a melt with the thermoplastic addition polymer blend, the material will be present in the melt in an amount not exceeding approximately 0.57β by weight of the melt, and preferably from about .01 to about .05% by weight of the melt. In both instances, the concentration of the material in the solution and the melt is not sufficient enough to come to the surface of the thermoplastic polymer coating upon evaporation of the solvent or solidification of the melt and form a continuous layer or coating of the material on the thermoplastic polymer coating surface so as to produce a thermoplastic polymer coating having a layer of a

release agent on the polymer coating having a surface energy lower than that of the thermoplastic polymer coating. Thus, the material is precluded from serving as a release agent for the thermoplastic polymer coating because in general concentrations of such a material of at least about 1% by weight of the combined weight of the thermoplastic polymeric blend and the material in a solvent solution of the polymeric blend and a concentration of such a material of about 1%. by weight of a melt comprising such a material and a thermoplastic polymeric blend is required to form a continuous film or a layer of the material on the surface of the thermoplastic polymer coating upon evaporation of the solvent and solidification of the melt. In no instance, however, will such a compound be present in the thermoplastic polymer coating of a polymer coated receiver used in the practice of the present invention in an amount exceeding approximately 0.5% by weight based on the total weight of the combined thermoplastic polymer coating material and the coating aid material. Thus, although some amount or portion of the coating aid material which is present in the thermoplastic polymer coating may be present at the surface of the thermoplastic polymer coating, it will not be present on the surface of the polymer coating as a continuous film or layer so as to form a layer of a release agent on the polymer coating.

Alternatively, the coating aid material can be applied directly to a suitable substrate, such as paper, for example, as by melt extrusion, for example, prior to the formation or application of the thermoplastic polymer coating on the substrate, to form a coating or a layer of the material on the substrate between the substrate and the subsequently applied thermoplastic polymer layer. Coating materials such as polyethylene and polypropylene are

examples of suitable materials which can be so applied to the surface of a substrate to facilitate a more uniform coating of the polymer blend on the receiver substrate. Such materials also serve as sealing layers for the substrate to impart a smooth surface to the substrate in addition to serving as a coating aid for the thermoplastic polymeric blend. In general, the thickness of such a coating on the substrate may range from about .0001 to about 30 microns, and preferably from about 5 to about 30 microns.

If extrusion is used as the method of forming the thermoplastic polymer coating on the receiver substrate, generally the extrusion conditions are determined by the thermal properties of the polymers such as melt viscosity and melting point. One may extrude a molten layer comprised of a blend or mixture of the thermoplastic addition polymers as above characterized upon one face or surface of a receiver substrate of the type described above using suitable extrusion temperatures. If it is desired to apply a coating aid directly to the substrate prior to applying the thermoplastic polymer coating to the substrate, the coating aid can be melt extruded onto the substrate prior to extruding the thermoplastic polymeric blend onto the substrate, or it can be co-extruded with the polymer mixture.

In the process of this invention, the receiver is preheated to a temperature such that the temperature of the receiver during transfer will be adequate to fuse the toner particles at their points of contact but will not be high enough to melt the toner particles, or to cause contacting toner particles to coalesce or flow together into a single mass. It is important also that the receiver be heated to a temperature such that the temperature of the thermoplastic polymer coating on the substrate is at least approximately 5 ^C C above the Tg of the

thermoplastic addition polymers in the polymer blend during transfer as it generally has been found that if the temperature of the thermoplastic polymer coating is not maintained at a temperature which is at least about 5 ^β C above the Tg of the thermoplastic addition polymers in the polymer blend during transfer, less than 50%, and more typically less than 10%, of the toner particles will transfer from the element surface to the thermoplastic polymer coating during transfer. While it is imperative that the receiver be heated to a temperature such that the temperature of the thermoplastic polymer coating will be at least about 5°C above the Tg of the thermoplastic addition polymers in the polymer blend during transfer, caution must be exercised to make sure that the receiver is not heated to a temperature so high that the toner particles will melt and flow or blend together into a localized mass. In practice, it has generally been found to be prudent not to heat the receiver to a temperature whereby the temperature of the thermoplastic polymer coating during transfer approaches or exceeds a temperature which is approximately 25 ^β C above the Tg of the thermoplastic addition polymers in the polymer blend. This is because of the increased tendency of the thermoplastic polymer coating to adhere to the element surface as the temperature of the thermoplastic polymer coating rises to a level which approaches or exceeds approximately 25°C above the Tg of the thermoplastic addition polymers.

The temperature range necessary to achieve these conditions depends upon the time that the receiver resides in the nip and the heat capacity of the receiver. In most cases, if the temperature of the thermoplastic polymer coating immediately after it contacts the element is below the Tg of the toner binder, but above a temperature that is 20 degrees

below that Tg, the toner particles will be fused or sintered at their points of contact and the temperature of the thermoplastic polymer coating will be at a temperature that is approximately at least about 5°C above the Tg of the thermoplastic addition polymers. Or, stated another way, if the front surface of the thermoplastic polymer coating on the receiver substrate is preheated to a temperature such that the temperature of the thermoplastic polymer coating is from about 60 to 90 ^β C when it is in contact with the toner particles on the surface of the element during transfer, the temperature of the thermoplastic polymer coating will be at a temperature that is approximately at least 5 ^C C above the Tg of the thermoplastic addition polymers in the polymer blend and the toner particles will be fused or sintered at their points of contact during transfer. However, receiver temperatures up to approximately 10 ^β C above the Tg of the toner binder are tolerable when nip time is small or the heat capacity of the receiver is low. Although either side of the receiver can be heated, it is preferable to conductively heat only the back surface of the receiver, i.e., the substrate surface or side of the receiver which does not contact the toner particles, such as by contacting the substrate with a hot shoe or a heated compression roller, as this is more energy efficient than heating the thermoplastic polymer coated surface of the receiver using a non—conductive source of heat such as, for example, a heat lamp or a plurality of heat lamps, or an oven which results in a less efficient absorption of the heat by the thermoplastic polymer coating. Furthermore, it is easier to control the temperature of that surface, and it usually avoids damage to the receiver. The preheating of the receiver must be accomplished before the heated thermoplastic polymer coating portion of the receiver contacts the element

because the length of time during which the receiver is in the nip region when the toner particles are being contacted with the receiver and transferred to the thermoplastic polymer coating on the receiver substrate is so brief (i.e., typically less than 0.25 second, and usually 0.1 second or less), that it would be extremely difficult, if not impossible, to heat the receiver to the temperatures required for the successful transfer of the toner particles to the thermoplastic polymer coating if the receiver was heated only in the nip. Thus, if a backup roller, which presses the receiver against the element, is used to heat the receiver, the receiver must be wrapped around the backup roller sufficiently so that the receiver is heated to the proper temperature before it enters the nip. The backup or compression rollers which can be used in the practice of the process of the present invention to create an appropriate nip for acceptable toner transfer can be hard or compliant (i.e., resilient) rollers.

As with any thermally assisted method of transfer, it has been found that pressure aids in the transfer of the toner to the receiver, and an average nip pressure of about 135 to about 5000 kPa is preferred, as when a roller nip region is used to apply such pressures , or when such pressure are applied by a platen or equivalent. Lower pressures may result in less toner being transferred and higher pressures may damage the element and can cause slippage between the element and the receiver, thereby degrading the image.

As a result of the combination of contact time and temperature, and applied pressure, the toner particles are transferred from the element surface to the adjacent thermoplastic polymer coating surface on the receiver substrate. In all cases, the applied contacting pressure is exerted against the outside

face or substrate side of the receiver opposite the thermoplastic polymer coated side or surface of the receiver and the side or face of the element opposite to the element surface on which the toner particles are carried.

Also, as mentioned previously, it is important that the temperature of the receiver be maintained at a temperature which is above the Tg of the thermoplastic addition polymers during separation of the receiver from the element immediately after the toner particles are transferred to the thermoplastic polymer coating on the receiver so that the receiver will separate from the element while hot without the thermoplastic polymer coating adhering to the element surface during separation.

In any case, the toner must not be fixed during transfer but must be fixed instead at a separate location that is not in contact with the element. In this way, the element is not exposed to high temperatures and the toner is not fused to the element. Also, the use of the lower temperatures during transfer means that the transfer process can be much faster, with 40 meters/minute or more being feasible. Typically, after transfer of the toner particles from the element to the receiver and subsequent separation of the receiver from the element, the developed toner image is heated to a temperature sufficient to fuse it to the receiver. A present preference is to heat the image-bearing thermoplastic polymer coating surface on the receiver until it reaches or approaches its glass transition temperature and then place it in contact "ύth a heated ferrotyping material which raises the tei. 3rature or maintains it above its glass transition temperature while a force is applied which urges the ferrotyping material toward the thermoplastic layer with

sufficient pressure to completely or nearly completely embed the toner image in the heated layer. This serves to substantially reduce visible relief in the image and impart a smoothness to the coated layer on the receiver. The ferrotyping material, which conveniently can be in the form of a web or belt, and the receiver sheet can be pressed together by a pair of pressure rollers, at least one of which is heated, to provide substantial pressure in the nip. A pressure of at least approximately 690 kPa should be applied, however, better results are usually achieved with pressures of approximately 2100 kPa, typically in excess of about 6,900 kPa, particularly with multilayer color toner images. The ferrotyping web or belt can be made of a number of materials including both metals and plastics. For example, a highly polished stainless steel belt, as electroformed nickel belts, and a chrome plated brass belt both have good ferrotyping and good release characteristics. In general, better results are obtained, however, with conventional polymeric support materials such as polyester, cellulose acetate and polypropylene webs, typically having a thickness of approximately 2-5 mils. Materials marketed under the trademarks Estar, Mylar and a polyamide film distributed by Dupont under the trademark apton-H, which optionally can be coated with a release agent to enhance separation, are especially useful ferrotyping materials. In addition, metal belts coated with heat resistant, low surface energy polymers, such as highly crosslinked polysiloxanes, also are effective ferrotyping materials. After the image—bearing thermoplastic coated surface has been contacted with the ferrotyping material and the toner image has been embedded in the heated thermoplastic coating or layer, the layer is allowed to cool to well below its glass transition temperature while it is still in contact with the

ferrotyping material. After cooling, the layer is separated from the ferrotyping material.

Either halftone or continuous tone images can be transferred with equal facility using the process of this invention. Because the electrostatic image on the element is not significantly disturbed during transfer it is possible to make multiple copies from a single imagewise exposure.

Toners useful in the practice of this invention are dry toners having a particle size of less than 8 micrometers, and preferably 5 micrometers or less. The toners must contain a thermoplastic binder in order to be fusible.

The polymers useful as toner binders in the practice of the present invention can be used alone or in combination and include those polymers conventionally employed in electrostatic toners. Useful polymers generally have a Tg of from about 40 to 120°C, preferably from about 50 to 100 ^β C. Preferably, toner particles prepared from these polymers have a relatively high caking temperature, for example, higher than about 60°C, so that the toner powders can be stored for relatively long periods of time at fairly high temperatures without having individual particles agglomerate and clump together. The melting point or temperature of useful polymers preferably is within the range of from about 65 ^β C to about 200°C so that the toner particles can readily be fused to the receiver to form a permanent image. Especially preferred polymers are those having a melting point within the range of from about 65° to about 120°C.

Among the various polymers which can be employed in the toner particles of the present invention are polycarbonates, resin-modified maleic alkyd polymers, polyamides, phenol—formaldehyde polymers and various derivatives thereof, polyester

condensates, modified alkyd polymers, aromatic polymers containing alternating methylene and aromatic units such as described in U.S. Patent No. 3,809,554 and fusible crosslinked polymers and described in U.S. Reissue Patent No. 31,072.

Typical useful toner polymers include certain polycarbonates such as those described in U.S. Patent No. 3,694,359, which include polycarbonate materials containing an alkylidene diarylene moiety in a recurring unit and having from 1 to about 10 carbon atoms in the alkyl moiety. Other useful polymers having the above—described physical properties include polymeric esters of acrylic and methacrylic acid such as poly(alkyl acrylate), and poly(alkyl methacrylate) wherein the alkyl moiety can contain from 1 to about 10 carbon atoms. Additionally, other polyesters having the aforementioned physical properties also are useful. Among such other useful polyesters are copolyesters prepared from terephthalic acid (including substituted terephthalic acid), a bis(hydroxyalkoxy)phenylalkane having from 1 to 4 carbon atoms in the alkoxy radical and from 1 to 10 carbon atoms in the alkane moiety (which also can be a halogen-substituted alkane), and an alkylene glycol having from 1 to 4 carbon atoms in the alkylene moiety. Other useful polymers are various styrene-containing polymers. Such polymers can comprise, e.g., a polymerized blend of from about 40 to about 100% by weight of styrene, from 0 to about 45% by weight of a lower alkyl acrylate or methacrylate having from 1 to about 4 carbon atoms in the alkyl moiety such as methyl, ethyl, isopropyl, butyl, etc. and from about 5 to about 50% by weight of another vinyl monomer other than styrene, for example, a higher alkyl acrylate or methacrylate having from about 6 to 20 or more carbon atoms in the alkyl group. Typical styrene-containing polymers prepared

from a copolymerized blend as described hereinabove are copolymers prepared from a monomeric blend of 40 to 60% by weight styrene or styrene homolog, from about 20 to about 50% by weight of a lower alkyl acrylate or methacrylate and from about 5 to about 30% by weight of a higher alkyl acrylate or methacrylate such as ethylhexyl acrylate (e.g., styrene—butyl acrylate-ethylhexyl acrylate copolymer). Preferred fusible styrene copolymers are those which are covalently crosslinked with a small amount of a divinyl compound such as divinylbenzene. A variety of other useful styrene-containing toner materials are disclosed in U.S. Patent Nos . 2,917,460; Re 25,316; 2,788,288; 2,638,416; 2,618,552 and 2,659,670. Especially preferred toner binders are polymers and copolymers of styrene or a derivative of styrene and an acrylate, preferably butylacrylate.

Useful toner particles can simply comprise the polymeric particles but it is often desirable to incorporate addenda in the toner such as waxes, colorants, release agents, charge control agents, and other toner addenda well known in the art. The toner particle also can incorporate carrier material so as to form what is sometimes referred to as a "single component developer." The toners can also contain magnetizable material, but such toners are not preferred because they are available in only a few colors and it is difficult to make such toners in the small particles sizes required in this invention. If a colorless image is desired, it is not necessary to add colorant to the toner particles. However, more usually a visibly colored image is desired and suitable colorants selected from a wide variety of dyes and pigments such as disclosed for example, in U.S. Reissue Patent No. 31,072 are used. A particularly useful colorant for toners to be used in black-and-white electrophotographic copying

machines is carbon black. Colorants in the amount of about 1 to about 30 percent, by weight, based on the weight of the toner can be used. Often about 8 to 16 percent, by weight, of colorant is employed. Charge control agents suitable for use in toners are disclosed for example in U.S. Patent Nos. 3,893,935; 4,079,014; 4,323,634 and British Patent Nos. 1,501,065 and 1,420,839. Charge control agents are generally employed in small quantities such as about 0.01 to about 3, weight percent, often 0.1 to 1.5 weight percent, based on the weight of the toner.

Toners used in this invention can be mixed with a carrier vehicle. The carrier vehicles, which can be used to form suitable developer compositions, can be selected from a variety of materials. Such materials include carrier core particles and core particles overcoated with a thin layer of film-forming resin. Examples of suitable resins are described in U.S. Patent Nos. 3,547,822; 3,632,512; 3,795,618; 3,898,170; 4,545,060; 4,478,925; 4,076,857; and 3,970,571.

The carrier core particles can comprise conductive, non—conductive, magnetic, or non—magnetic materials, examples of which are disclosed in U.S. Patent Nos. 3,850,663 and 3,970,571. Especially useful in magnetic brush development schemes are iron particles such as porous iron particles having oxidized surfaces, steel particles, and other "hard" or "soft" ferromagnetic materials such as gamma ferric oxides or ferrites, such as ferrites of barium, strontium, lead, magnesium, or aluminum. See for example, U.S. Patent Nos. 4,042,518; 4,478,925; and 4,546,060.

The very small toner particles that are required in this invention can be prepared by a variety of processes well—known to those skilled in

the art including spray-drying, grinding, and suspension polymerization.

As indicated above, the process of this invention is applicable to the formation of color copies. If a color copy is to be made, successive latent electrostatic images are formed on the element, each representing a different color, and each image is developed with a toner of a different color and is transferred to a receiver. Typically, but not necessarily, the images will correspond to each of the three primary colors, and black as a fourth color if desired. After each image has been transferred to the receiver, it can be fixed on the receiver, although it is preferable to fix all of the transferred images together in a single step. For example, light reflected from a color photograph to be copied can be passed through a filter before impinging on a charged photoconductor so that the latent electrostatic image on the photoconductor corresponds to the presence of yellow in the photograph. That latent image can be developed with a yellow toner and the developed image can be transferred to a receiver. Light reflected from the photograph can then be passed through another filter to form a latent electrostatic image on the photoconductor which corresponds to the presence of magenta in the photograph, and that latent image can then be developed with a magenta toner which can be transferred to the same receiver. The process can be repeated for cyan (and black, if desired) and then all of the toners on the receiver can be fixed in a single step.

The image-bearing element from which the toner particles are transferred upon contact with the thermoplastic polymer coated receiver sheet of the invention can include any of the electrostatographic elements well known in the art, including electrophotographic or dielectric elements such as

dielectric recording elements, and the like with the proviso that the toner contacting surface layer of the element, i.e., the surface layer of the element on which the toner particles are carried comprises a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and has a surface energy of not greater than approximately 47 dynes/cm, preferably from about 40 to 45 dynes/cm. The use of such an element has been found to be essential to the practice of the present process in order to achieve virtually 100 percent transfer of the very small toner particles while at the same time preventing the thermoplastic polymer coated receiver from adhering to the element during transfer and subsequent separation of the receiver from the element without resorting to the use of a release agent coated on or otherwise applied to the thermoplastic polymer coating on the receiver substrate, prior to toner contact and toner transfer.

The image—bearing element can be in the form of a drum, a belt, a sheet or other shape and can be a single use material or a reusable element. Reusable elements are preferred because they are generally less expensive. Of course, reusable elements must be thermally stable at the temperature of transfer for the duration of the transfer process.

A present preference is to employ a photoconductive element for the element used in toner particle or toner image transfer. The photoconductive element is preferably conventional in structure, function and operation, such as is used, for example, in a conventional electrophotographic copying apparatus. The element is conventionally imaged. For example, an electrostatic latent image-charge pattern is formed on the photoconductive element which can consist of one or more photoconductive layers

deposited on a conductive support. By treating the charge pattern with, or applying thereto, a dry developer containing charged toner particles, the latent image is developed. The toner pattern is then transferred to a receiver in accordance with the practice of the present invention and subsequently fused or fixed to the receiver.

Various types of photoconductive elements are known for use in electrophotographic imaging processes. In many conventional elements, the active photoconductive components are contained in a single layer composition. This composition is typically affixed, for example, to a conductive support during the electrophotographic imaging process. Among the many different kinds of photoconductive compositions which may be employed in the typical single active layer photoconductive elements are inorganic photoconductive materials such as vacuum evaporated selenium, particulate zinc oxide dispersed in a polymeric binder, homogeneous organic photoconductive compositions composed of an organic photoconductor solubilized in a polymeric binder, and the like.

Other useful photoconductive insulating compositions which may be employed in a single active layer photoconductive element are the high—speed heterogeneous or aggregate photoconductive compositions described in U.S. Patent No. 3,732,180. These aggregate-containing photoconductive compositions have a continuous electrically insulating polymer phase containing a finely-divided, particulate, co-crystalline complex of (i) at least one pyrylium-type dye salt and (ii) at least one polymer having an alkylidene diarylene group in a recurring unit.

In addition to the various single active layer photoconductive insulating elements such as

those described above, various "multi-layer" photoconductive insulating elements have been described in the art. These kinds of elements, also referred to as "multi-active" or "multi-active-layer" photoconductive elements, have separate charge generation and charge transport layers as are appreciated by those familiar with the art. The configuration and principles of operation of multi—active photoconductive elements are known as are methods for their preparation having been described in a number of patents, for example, in U.S. Patent Nos. 4,175,960; 4,111,693; and 4,578,334. Another configuration suitable for the imaging of elements in the practice of the process of the invention is the "inverted multi—layer" form in which a charge- transport layer is coated on the conductive substrate and a charge-generation layer is the surface layer. Examples of inverted multi—layer elements are disclosed, for example, in U.S. Patent No. 4,175,960. It should be understood that, in addition to the principal layers which have been discussed, i.e., the conductive substrate and the charge—generation and the charge-transport layers, the photoconductive elements which can be used in the practice of the present invention may also contain other layers of known utility, such as subbing layers to improve adhesion of contiguous layers and barrier layers to serve as an electrical barrier layer between the conductive layer and the photoconductive composition. The charge-generation and charge-transport layers also can contain other addenda such as leveling agents, surfactants and plasticizers to enhance various physical properties. In addition, addenda such as contrast control agents to modify the electrophotographic response of the element can be incorporated in the charge-transport layers .

In all instances, however, it is essential that the surface layer of the electrostatographic element of choice comprise a film-forming, electrically insulating polyester or polycarbonate thermoplastic polymeric binder resin matrix and have a surface energy of not more than about 47 dynes/cm, preferably from about 40—45 dynes/cm. As indicated above, the surface energy of the element surface can be readily and easily determined or measured by one skilled in the art using the contact angle procedure disclosed in the aforementioned Fowkes, F. "Contact Angle, Wettability, and Adhesion." in: Advances in Chemical Series (Washington, D.C., American Chemical Society, 1964) p. 99-111. Examples of suitable polymers are the condensation polymers of polyester or polycarbonate resins which may comprise the surface layer of the electrostatographic elements which can be used in the process of the present invention include poly[4,4'- (2-norbornylidene)bis-phenoxy azelate-co-terephthalate] and poly[4,4'-(2-isopropylidene)bisphenoxy carbonate].

Examples of other useful polyester and/or polycarbonate binder resins which may be suitable for use in the present invention, include those disclosed in U.S. Patent Nos. 4,284,699, 4,175,960; 3,615,414; 4,350,751; 3,679,407; 3,684,502; and 3,873,311.

However, since the surface energy of the toner particle carrying surface of the element is largely, if not completely or nearly completely determined by the surface energy of the thermoplastic polyester or polycarbonate materials which comprise the thermoplastic binder resin matrices of the surface layers of the elements used in the practice of the process of the present invention, it is important that the polyester and/or polycarbonate binder resins which comprise the thermoplastic binder resin matrices of the surface layers of the element used in the practice

of the present invention have a surface energy not exceeding approximately 47 dynes/cm, and preferably from about 40 to about 45 dynes/cm.

A presently preferred photoconductive element is a near infrared sensitive inverted multi—layer photoconductive element made from fluorine-substituted titanyl tetrafluorophthalocyanine pigments which is disclosed in U.S. Patent No. 4,701,396.

The invention is illustrated by the following examples .

In these examples, transfer was accomplished by simultaneously passing a thermoplastic polymeric coated receiver and an element, the surface of which had thereon a transferable toner image comprised of very fine toner particles through the nip region of a pair of hard compression rollers which were oppositely rotating with respect to each other, whereby the thermoplastic polymer coating on the receiver was contacted against the toner particles on the element surface while the thermoplastic polymer coating on the receiver was heated to a temperature sufficient to sinter the toner particles at their locations of contact to each other. Heating of the receiver was accomplished by heating the roller contacting the opposed face of the thermoplastic polymer coating, i.e., the substrate face or side of the receiver. The other roller, which contacted the opposed face of the element surface, i.e., the face or side of the element on which the toner particles were not carried, was at ambient temperature (i.e., temperatures usually in the range of about 20 to about 30°C). Suitable contacting pressures were applied to the compression rollers during contact of the element and the receiver as they passed through the nip region created by the rollers. In these examples, the contacting pressures were applied to the compression rollers by means of two piston shafts in contact with and driving the

unheated roller against the heated roller. The pressures are expressed as air pressures rather than nip pressures. Air pressures are a more precisely determined quantity and are scaled linearly to the nip pressure.

Example 1 A receiver suitable for use in the practice of the present invention was prepared as follows. A thermoplastic polymeric blend comprising 80 percent by weight of a commercially available styrene butylacrylate copolymer having a Tg of approximately 57 ^C C, a weight average molecular weight of approximately 84,000, a number average molecular weight of approximately 35,000 and a ratio of weight average molecular weight to number average molecular weight of approximately 2.4 marketed by Goodyear under the tradename "Pliotone 2015" and 20 percent by weight of an α—methylstyrene—vinyltoluene copolymer having a Tg of approximately 54°C, a weight average molecular weight of approximately 3200, a number average molecular weight of approximately 2500 and a ratio of weight average molecular weight to number average molecular weight of approximately 1.28 marketed by Hercules Company under the tradename "Piccotex 100" was dissolved in methylene chloride containing 0.03 percent by weight (based on the total weight of the solution) of polymethylphenylsiloxane having a methyl to phenyl ratio of 23:1 marketed by Dow-Corning Company under the trade designation "DC 510", forming a 10 percent by weight solution of the polymeric blend. Polymethylphenylsiloxane is a surfactant and functions as a coating aid for the polymeric blend. A polyethylene coated flexible paper having a surface roughness average of 0.45 micrometers, as measured by a Surtronic 3 Profilometer obtained from Rank Taylor Hobson, P.O. Box 36, Guthlaxton Street, Leicester LE205P, England, marketed as "Photofinishing Stock

486V" by Eastman Kodak Company which had been corona treated to increase surface tension and therefore adhesion was coated with the solution and the solvent was evaporated to form a thermoplastic coating on the paper approximately 10 micrometers thick. The thermoplastic polymer coating on the receiver had a surface energy of approximately 41 dynes/cm.

An electrostatic latent image of a black and white silver halide negative, consisting of both continuous tone and alpha—numeric regions, was formed by standard electrophotographic techniques on the surface of an inverted multilayer photoconductive element which had a toner contacting surface comprising a polycarbonate binder resin of poly(oxycarbonyloxy-l,4-phenylenebicyclo[2.2.l]hept- 2—ylidene—1,4-phenylene) and a surface energy of approximately 43 dynes/cm, developed and transferred to the receiver using the thermally assisted transfer method of the present invention. The electrostatic image was developed with a dry electrographic toner in combination with a magnetic carrier consisting of a polymer coated ferrite core material approximately 30 micrometers in diameter. The toner particles were comprised of a polystyrene binder having a Tg of approximately 62°C, marketed as "Piccotoner 1221" by Hercules Company, and contained 8.0 weight percent carbon black marketed by Cabot Corporation as "Sterling R" and 0.2 weight percent of a quaternary ammonium charge control agent sold by Onyx Chemical Company as "Ammonyx 4002". The toner particles had a median volume weighted diameter of approximately 3.5 micrometers. Transfer was accomplished by passage through the nip region of a pair of compression rollers. The roller contacting the substrate side or face of the receiver opposite the thermoplastic polymer coated side or face of the receiver was heated to a temperature of approximately 110°C while the

other roller which contacted the face or side of the element opposite the element surface on which the toner particles were carried was at ambient temperature so that the front surface of the receiver, i.e., the thermoplastic polymer coating was heated to a temperature that was about 110 ^β C prior to transfer. The temperature of the thermoplastic polymer coating during transfer was approximately 65°C. The passage speed was 1.25 cm/second. Air pressure to the unheated compression roller was approximately 276 kPa. During passage through the nip region of the rollers, the heated front surface of the receiver, i.e. the thermoplastic polymer coating, was contacted with the toner particles on the surface of the photoconductive element and the particles transferred to the receiver. The receiver and the photoconductive element were separated immediately after transfer while hot and prior to fixing the transferred image. After transfer, the toner image was ferrotyped by casting it against a sheet of Kapton-H and passing the thermoplastic polymer coated receiver bearing the transferred toner image partially embedded in the surface thereof and the Kapton-H through a pair of hard compression rollers oppositely rotating with respect to each other one of which was heated to a temperature of 120 ^β C and the other being unheated. The ferrotyping sheet contacted the heated roller. The process speed was approximately 2.54 cm/second.

The transfer efficiency, i.e., the percentage of toner that transferred from the element to the receiver was excellent (i.e., greater than 99.9 percent) and the element readily separated from the receiver after the transfer process was completed. Substantially the same results can be obtained when a photoconductive element which has a toner contacting surface comprising a polyester or a substituted polyester binder resin such as

poly[4,4'—(2—norbornylidene)bis-phenoxy-azelate-co- terephthalate] is substituted for the photoconductive element described above and the process is repeated.

Example 2

Example 1 was repeated except that the thermoplastic polymer coating on the receiver substrate consisted of a polymeric blend comprising 70 percent by weight of the commercially available styrene butylacrylate copolymer "Pliotone 2015" marketed by Goodyear and 30 percent by weight of the α-methylstyrene—vinyltoluene copolymer "Piccotex 100" marked by Hercules Company. Transfer efficiency was excellent (i.e. transfer efficiency was greater than 99.9 percent) and the element separated readily from the receiver after the transfer process was completed.

Example 3 Example 1 was repeated except that the thermoplastic polymer coating on the receiver substrate consisted of a polymeric blend comprising 60 percent by weight of a commercially available styrene butylacrylate copolymer marketed by Goodyear under the tradename "Pliotone 2003" having a Tg of approximately 57 ^β C, a weight average molecular weight of approximately 171,000, a number average molecular weight of approximately 52,000 and a ratio of weight average molecular weight to number average molecular weight of approximately 3.5, and 40 percent by weight of the α—methylstyrene— inyltoluene copolymer marketed by Hercules Company under the tradename "Piccotex 100" having a Tg of approximately 54 ^β C, a weight average molecular weight of approximately 3200, a number average molecular weight of approximately

2500 and a ratio of weight average molecular weight to number average molecular weight of approximately

1.28. In addition, the thermoplastic polymer coating was heated to temperature that was about 120 ^β C prior to toner transfer and the temperature of the coating during transfer was approximately 65 ^β C. Also, the surface energy of the thermoplastic coating was approximately 43.3 dynes/cm. The transfer efficiency was poor (i.e., less than 50 percent). However, the element readily separated from the receiver after the transfer process was completed. This examples does not fall within the scope of the invention because the surface energy of the thermoplastic polymer coating was too high, i.e., greater than approximately 43 dynes/cm.

Example 4

Example 1 was repeated except that the thermoplastic polymer coating on the receiver substrate consisted of a polymeric blend comprising 60 percent by weight of a commercially available styrene butylacrylate copolymer marketed by Goodyear under the designation "95J APR-7446" having a Tg of approximately 57°C, a weight average molecular weight of approximately 147,000, a number average molecular weight of approximately 51,000 and a ratio of weight average molecular weight to number average molecular weight of approximately 2.9 and 40 percent by weight of the α-methylstyrene-vinyltoluene copolymer marketed by Hercules Company under the tradename "Piccotex 100" having a Tg of approximately 54 ^β C, a weight average molecular weight of approximately 3200, a number average molecular weight of approximately 2500 and a ratio of weight average molecular weight to number average molecular weight of approximately 1.28. In addition, the surface energy of the thermoplastic coating was approximately 45 dynes/cm. The transfer efficiency was poor (i.e., less than 50 percent) and the element adhered to the receiver

during transfer. This example does not fall within the scope of the invention because the surface energy of the thermoplastic polymer coating was too high, i.e., greater than approximately 43 dynes/cm.

Example 5 Example 1 was repeated except that the thermoplastic polymer coating on the receiver substrate consisted of a polymeric blend comprising 70 percent by weight of the commercially available styrene butylacrylate copolymer marketed by Goodyear under the tradename "Pliotone 2015" having a Tg of approximately 57 ^β C, a weight average molecular weight of approximately 84,000, a number average molecular weight of approximately 35,000 and a ratio of weight average molecular weight to number average molecular weight of approximately 2.4, and 30 percent by weight of the α—methylstyrene—vinyltoluene copolymer marketed by Hercules Company under the tradename "Piccotex 100" having a Tg of approximately 54°C, a weight average molecular weight of approximately 3200, a number average molecular weight of approximately 2500 and a ratio of weight average molecular weight to number average molecular weight of approximately 1.28. In addition, the surface energy of the thermoplastic coating was approximately 41 dynes/cm and the thermoplastic polymer coating was only heated to a temperature that was about 96°C prior to toner transfer so that the temperature of the polymer coating during transfer was approximately 58 ^β C. Also, the transferred toner image was not ferrotyped by casting it against a sheet of Kapton—H after transfer and separation as was the transferred toner image in Example 1. Transfer efficiency was poor (i.e. less than

50%). This examples does not fall within the scope of the invention because the temperature of the

thermoplastic polymer coating during transfer was less than approximately 5 ^β C above the Tg of the thermoplastic addition polymers in the polymeric blend.

Example 7

A receiver suitable for use in the present invention was prepared according to the process set forth in Example 1 except that the thermoplastic polymer coating on the receiver substrate consisted of a polymeric blend comprising 70 percent by weight of the commercially available styrene butylacrylate copolymer "Pliotone 2015" marketed by Goodyear and 30 percent by weight of the α-methylstyrene- vinyltoluene copolymer "Piccotex 100" marketed by Hercules Company. The Tg of the "Pliotone 2015" was approximately 57°C and the Tg of the "Piccotex 100" was approximately 54°C. The thermoplastic polymer coating on the receiver had a surface energy of approximately 41 dynes/cm. The receiver and an inverted multilayer photoconductive element as described in Example 1 on which no developed toner image was carried were passed through the nip region of a pair of compression rollers as in Example 1 except that the roller contacting the substrate side or face of the receiver opposite the thermoplastic polymer coated side of the receiver was heated to a temperature of approximately 140°C while the other roller which contacted the face or> side of the element opposite the element surface on which toner particles normally would be carried was at ambient temperature so that the front surface of the receiver, i.e., the thermoplastic polymer coating was heated to a temperature that was about 80°C during the time when toner transfer would have occured had a developed toner image been present on the element surface. This was done to demonstrate the effects of heating the thermoplastic polymer coating to a temperature such

that its temperature during transfer was approximately 25°C above the Tg of the thermoplastic addition polymers in the polymeric blend. Passage speed at transfer pressure were the same as in Example 1. It was observed that the thermoplastic polymer coated receiver completely adhered to the element surface during passage through the nip region of the rollers.

Example 8 An attempt was made to prepare a receiver suitable for use in the practice of the present invention according to the procedure set forth in Example 1 except that only the low molecular weight "Piccotex 100" thermoplastic addition polymer described in Example 1 was used as the sole polymeric material for forming the polymeric coating on the receiver substrate. A suitable receiver could not be made using the "Piccotex 100" copolymer as the sole thermoplastic polymeric material because it became brittle and flaked off the paper substrate soon after it was coated onto the paper thereby demonstrating that very low molecular weight thermoplastic addition polymers cannot be used by themselves to form a polymeric coating for the receivers used in the practice of the present invention.