The present invention relates to a process for manufacturing toner resins in the presence of peroxides.

Electrographic methods comprise the use of a heated roller for fixing electrostatic latent images, which are visualized with the use of a dry development toner. In these methods it is desired that the minimum temperature for fixing be low and the temperature causing offset to the heated roller be high. A low fixing temperature can be obtained by using polymeric material of low molecular weight. However, the use of a low molecular weight polymer alone as the dry development toner material has the disadvantage that it causes blocking. In addition, high molecular weight polymer is essential to imparting high temperature offset properties to a dry development toner. Thus, a dry toner must consist of polymers (hereinafter described as toner resins) having both a low molecular weight and a high molecular weight in order to provide fixability at low temperatures, offset properties and anti-blocking properties.

The present invention relates to a process for manufacturing high molecular weight toner resins by polymerizing at least one polymerizable vinyl monomer in the presence of at least one polyfunctional polymerization initiator having at least one peroxide functionality and at least one unsaturated functionality.

A similar process is known from GB-A-2 232 160. However, the polyfunctional polymerization initiators disclosed in the British publication need to be phlegmatized and phlegmatizers have undesirable effects on the performance of dry development toner. Furthermore, the initiators disclosed do not give total conversion from monomer to

polymer. Processes comparable to the British process are known from EP-A-0351929 and EP-A-0354466. These processes are attended with the same d sadvantages as mentioned above for the British process.

In the process of the present invention the polyfunctional polymerization initiator is an organic peroxide represented by the general formula:

(I)

or

hydrogen, and Ri is an alkylene group having from 1 to 22 carbon atoms, a sec-alkylene group having from 2 to 22 carbon atoms, or a tert-a kylene group having from 3 to 22 carbon atoms and n is an integer from 0 to 5, the organic peroxide being present in the process in an amount of 0.001 to 2 wt%. The organic peroxides of the present invention have the advantage of not needing to be phlegmatized. Therefore, dry development toners comprising high molecular weight toner resins of the present invention have a good offset resistance. Furthermore, the use of the organic peroxides of the present invention results in nearly complete conversion to polymer. Obtained are polymers having a molecular weight which is as high as or even higher than that of the polymers obtained by the process disclosed in the British publication.

Preferably, Z in the general formula I represents a hydrogen atom. More preferably, the organic peroxide is 4-isopropenylcumyl tert-butyl peroxide.

Of course, two or more of the organic peroxides represented by formula I may be used simultaneously in the process of the present invention.

From JP 5 9204 643 it is known to copolymerize the present organic peroxides together with unsaturated monomers. The organic peroxide therefor reacts with its double bond, resulting in copolymers containing peroxide groups. In the present invention, this is not the case, the organic peroxide being used as an initiator. Accordingly, the peroxide group is decomposed, resulting in polymers with essentially no peroxide groups present in the polymer. SU 887 578, JP 6 0011 349, JP 6 0011 539, and JP 6 0013 828 disclose similar processes as described in JP 5 9204643.

The organic peroxides of the present invention may be prepared in a manner as described in M.A. Dikii, V.A. Puchin, S.A. Voronov, V.S. Tokarev, 0.1. Gevus (Lvov. Politekh. Inst., Lvov, USSR), Zh. Org. Khim., 1981, 17 (2), 337-9.

Suitable polymerizable monomers include aromatic vinyl monomers, such as styrene and styrene homologues or substituted styrenes, including Cι_8 alkylstyrenes, al oxy-substituted styrenes, halogen-substituted styrenes; acrylic or methacrylic monomers, such as Cι_8 alkyl (meth)acrylates, aryl (meth)acrylates, hydroxyl-containing (meth)acrylates, amino-containing ( eth)acrylates, epoxy-containing (meth)acrylates, and ( eth)acrylic acids and derivatives thereof; vinyl esters, such as vinyl acetate and vinyl propionate; aliphatic hydrocarbon monomers, such as butadiene; vinyl ethers, such as vinylmethyl ether, vinylethyl ether, and vinyl-iso-butyl ether; vinyl

ketones, such as vinylmethyl ketone, vinylhexyl ketone, and methyl isopropenyl ketone; N-vinyl compounds, such as N-vinylpyrrole, N- vinylcarbazole, N-vinylindole, and N-vinylpyrrolidine; and mixtures thereof.

Preferred polymerizable monomers are styrene, alkyl (meth)acrylates (more particularly, methyl, ethyl, butyl, and 2-ethylhexyl (meth)acrylates), (meth)acrylic acids, vinyl esters, aliphatic hydrocarbon monomers, and mixtures thereof.

More preferably, copolymers of styrene and alkyl (meth)aerylates are prepared by the process of the present invention.

It is preferred to carry out the polymerization process at a temperature not lower than 60°C and not higher than 160°C. More preferably, the process is carried out at a temperature of 110 ^o -140°C.

The process of the invention may be carried out using any known polymerization technique, such as solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, and combinations thereof.

Suitable solvents used in solution polymerization include cycloalkanes, such as cyclohexane; aromatic hydrocarbons, such as benzene, toluene, xylene, ethylbenzene, and cu ene; esters, such as ethyl acetate and butyl acetate; ethers, such as methyleellosolve, ethylcellosolve and butylcellosolve; and the like. Preferred among these to obtain high molecular weight polymer are cycloalkanes and aromatic hydrocarbons.

Suspension polymerization can be carried out in an aqueous medium, as known in the art.

This invention relates also to dry development toners comprising the high molecular weight toner resin produced by the process of the present invention. Dry development toners of the present invention have a good offset resistance.

The dry development toner comprising said high molecular weight toner resin may further contain one or more other components. It preferably contains one or more lower molecular weight toner resins. Preferably, toner resins of a molecular weight of 3000 to 50000 are present, such as styrene/acrylic copolymers, polyester resins, ^' polyepoxide resins, polyurethane resins, and the like. Among these, styrene/acrylic copolymers and polyester resins are preferred.

In preferred embodiments said low molecular weight toner resin can be prepared beforehand, either separately or simultaneously with the preparation of said high molecular weight toner resin. In other words, dry development toner may be produced by blending, in a solution or in the melted state, the high and low molecular weight toner resins being prepared separately beforehand; or by polymerizing said monomer to a high molecular weight toner resin in the presence of a low molecular weight toner resin and the organic peroxide of the present invention. In another embodiment, said low molecular weight toner resin may be produced by polymerizing in bulk or in solution at least one precursor monomer for a low molecular weight toner resin in the presence of a high molecular weight polymer. For instance, a high molecular weight polymer is dissolved in said precursor monomer, which precursor monomer is then polymerized to obtain a low molecular weight polymer. The polymerizing of said precursor monomer is by bulk polymerization or solution polymerization rather than suspension polymerization, because when using the former two techniques, one can remarkably reduce the amount of the polymerization initiator to provide the same molecular weight and, therefore, can remedy or reduce objectionable

influences (such as excessive charging of toner, environmental instability, and so on) caused by the presence of initiator residues.

In these dry development toners, the low and high molecular weight toner resins may be blended or used in bonded form, such as through covalent bonding. In these dry development toners, the content of the high molecular weight toner resin is usually 10-50 wt%, preferably 15-45 wt%, and that of the low molecular weight toner resin 50-90 wt%, preferably 55-85 wt%, based on the total weight of these toner resins.

In addition to the high and low molecular weight toner resins generally present in an amount of 50 to 95 wt%, the dry development toner may contain one or more known colorants in an amount of 5 to 10 wt%, magnetic powders in an amount of 0 to 50 wt%, and other additives, -such as charge controllers and lubricants in an amount of 0 to 5 wt%. Colorants may be inorganic or organic pigments, such as carbon black, iron black, benzidine yellow, quinacridone pigments, rhodamine B, phthalocyanine pigments, and the like. Preferred magnetic powders are powders of ferromagnetic metals and compounds such as iron, cobalt, nickel, magnetite, hematite, ferrite, and the like.

The dry development toner may be prepared by dry blending these components and then melting them under kneading, followed by crushing, finely pulverizing with a grinder, and finally classifying to obtain particles of 5-20 microns diameter.

The dry development toner may be optionally mixed with one or more carrier particles, such as iron powder, glass beads, nickel powder, ferrite, and the like, and used as a developer for electrical latent images. Besides, hydrophobic colloidal silica powder may be used to improve flowability of the powders.

The invention will be further illustrated by the following examples which are not to be construed as limiting the invention in any way. The scope of the invention is to be determined from the claims appended hereto.

Examples

Polymerization process

Several ampoules,- 2.5 cm ³ in volume, were 80% filled with a monomer mixture of 80 wt% styrene and 20 wt% butyl acrylate, in which mixture different peroxides in an amount of 0.75 meq active oxygen groups/lOOg were dissolved. The ampoules were sealed under nitrogen and immersed in a pre-heated oil bath. Each two hours an ampoule was taken from the oil bath and analysed for monomer conversion and polymer molecular weight. The results obtained after 10 hours of polymerization have been reported in Table I.

Polymer evaluation method

* Conversion into polymer (%) : The amount of residual monomer was determined by gas chromatography to calculate the conversion.

* Molecular weight (Mw, Mn, Mw/Mn) : A calibration curve was prepared by using polystyrene as standard to determine the molecular weight of a polymer according to GPC (Gel Permeation Chromatography).

In table I, Examples 1-3 are carried out with an organic peroxide according to the invention. Examples A-E are comparative examples using organic peroxides disclosed in GB-A-2 232 160.

Table I

Tx 171: 4-isopropenylcumyl tert-butyl peroxide

TBNBF: n-butyl tert-butyl peroxy fumarate

Px 12: 2,2-bis(4,4-di-tert-butylperoxycyclohexyl )propane

Mw: weight-average molecular weight Mn: number-average molecular weight

It can be understood from the results shown in Table I that the peroxide of the present invention (Ex. 1-3) is able to convert a styrene/butylacrylate monomer mixture more completely at a higher molecular weight than the other two peroxides (Ex. A-E), under the same reaction conditions. Further, the peroxides of the present invention are able to be applied at higher temperatures than the other mentioned peroxides thus enabling reactor output to be increased.