FIELD OF THE INVENTION

This invention relates generally to coatings of versatile application and utility, providing broad-spectrum protection, lubricity, and many other performance-enhancing qualities to a wide variety of substrates.

The invention relates to a coating or sheath that comprises at least two sequentially applied layers: a primer layer of a suitable binder resin that is bonded to the surface of a substrate, and a layer or layers of particles of poly (fluorinated ethylene) (PFE) fixed over the resin. In particular, the coating may comprise particles of poly(tetrafluoroethylene) (PTFE) . The specific examples herein employ particles of that material, "PTFE". Other members of the PFE family of materials, such as fluorinated ethylene propylene (FEP) and perfluoroalkoxy (PFA), are also useful in the practice of the invention.

BACKGROUND OF THE INVENTION

Since the appearance of poly.(tetrafluoroethylene)

(PTFE) more than fifty years ago, its uses have been limited by some of its several remarkable qualities.

For example, nothing much adheres to it. Hardly anything attacks it, much less reacts with it.

Heating PTFE to the temperature at which it fuses, starting at about 350°C, allows coatings to be applied to some substrates. But the process itself, involving relatively high temperatures, eliminates many applications, and some of PTFE's renowned lubricity is lost in that process.

There are materials on the market such as, for example, the Emralon products sold by Acheson, Inc., which have the disadvantage of achieving adhesion of particles of PTFE to a substrate by physically encapsulating the PTFE and surrounding the particles with a binder material. These and other similar products are typically a mix of PTFE particles and binder material resulting in a coating which contains the encapsulated PTFE particles distributed throughout the coating so that, as the ratio of PTFE to binder in the mix is increased, less of the adhesive binder is present to strengthen the bond with the substrate and to provide strong shear resistance in the coating itself.

Also, since these products, which are often called "suspended particle coatings", depend upon encapsulation of the PTFE, the extent of enrichment of the coating material with PTFE is limited. The ratio of particles to resin must be reasonable. The critical particle volume concentration, that is, the ratio beyond which mechanical integrity is compromised, would be in the range of 40% to 60% and preferably 50% or less. Therefore, the surface area of these suspended particle coatings cannot be represented by more than about 50% PTFE. This requirement dictates that corrosion resistance, coefficient of friction and other such benefits are likewise limited by the characteristics of the encapsulating binder resin itself which constitutes about 50% or more of the surface of the coating.

In addition to suspended particle coatings, there are "stratified particle coatings" available which provide a surface which is nearly 100% PTFE. In the stratified coating process, a two step curing

procedure is used in which, during the second curing, the PTFE particles 'float' to the surface of the coating and constitute all or nearly all of the coating's surface. But for this 'float' to occur, the second curing must take place at about 315°C. This requirement severely limits the range and variety of substrates as well as the applications for which stratified particle coatings are useful.

By contrast, the coatings of the present invention are 100% binder resin at the interface with the substrate and 100% PTFE at the coating surface. They are processed at moderately elevated or even room temperatures and can be applied by almost anyone to almost any substrate and in most environments.

In addition, these other products typically utilize PTFE materials which are in powder or granular form and have particle sizes in the range of 0.5 μm to 10 μm and even larger - much larger than those of the examples hereafter given of the present invention which are PTFE particles from aqueous dispersions with particle sizes in the 0.05 μm to 0.5 μm range. The larger particle sizes of these other products produce a relatively irregular or micro-lumpy surface, limiting the utility or range of utilization to those applications in which the poorer appearance and performance are acceptable.

Most practioners will recognize that resin-based coatings which adhere well and resist shear when applied to stainless steels will produce similar or better results on many other substrates. Some of the substrates used in the examples that follow are stainless steel needles and, more particularly, stainless steel surgical needles which, in use, are subjected to repeated severe shear stress.

Minimum coating thicknesses of the other available products are typically in excess of 10 μm, and, for coatings on steels, and especially stainless steels, grit or sand-blasting is recommended to prepare the substrate for optimal adhesion of the coatings. Many of the other coatings require application by the vendor since specialty equipment and skills are said to be required and because, in some cases, proprietary processes are used. Finally, other products often require burnishing prior to use for removal of the exterior layer of the binder-resin which encapsulates the lubricating particles.

The industry which manufactures needles used in surgery prizes surface lubricity to minimize the effort required to penetrate tissues, enhance stitching precision, and minimize trauma to tissues in the wound-closure process.

Prior to the present invention, one standard treatment for surgical needles was, as it had been for several decades, the application of a coating of a silicone, polydimethysiloxane (PDMS), or other similar material. Even in the most recent iterations of that process, the coating remains mobile to a large extent and does not adhere to or become more than a tenuous part of the needle's surface. In use, after one or a few punctures, much of the coating sloughs off into the wound, and lubricity is lost.

Some prior art purports to solve the surface lubricity problem but provides only impractical or relatively ephemeral coatings. For example, a method of coating PTFE on a surgical needle is described in U.S. Patent Number 3,700,489. The method requires the use of partially pyrolyzed PTFE which is subsequently

vaporized under vacuum and condensed on the surface of a surgical needle. Japanese patent publication number J6-2101-236-A discloses a needle coated with silicone based materials.

SUMMARY OF THE INVENTION

The invention provides a coating for a substrate and a method for coating a substrate. In one embodiment, the method comprises the steps of cleaning and preparing a substrate and of applying a layer of a bonding resin to the cleaned and prepared surface of a substrate; subsequently coating the bonding resin with a layer of PTFE particles, and performing any necessary added step or steps to bond the PTFE coating to the bonding-resin coated substrate. Optionally, the PTFE coated substrate may be overcoated with a film of a super-lubricious material.

The only PFE material used in the experiments on which this invention is based has been PTFE from commercially available aqueous dispersions. However, it is contemplated that any dispersion of any member of the poly(fluorinated ethylene) family of materials can be used to practice the invention as long as the solvent used in the dispersion is not also the solvent used in the binder-resin layer.

The invention provides a very thin and thus, virtually non-dimensional, shear-resistant coating of particles on the substrate, with many desirable characteristics. The coating may be controlled to be as thin as the size of the particles themselves, or about 0.5 μm, for example, when using dispersions of particles in the 0.05 μm to 0.5 μm size range. Thicker coats may be obtained by application of multiple coats, should that be desirable.

The particles adhere to the resin prime coat by a combination of semi-encapsulation within the binder and by what is believed to be chemical bonding of functional groups on the PTFE, such as carboxylate (COOH) or hydroxylate (OH), with groups such as amines, amides, carboxylates or hydroxylates on the binder resin.

The strength of the coatings' resistance to shear forces is demonstrated in the puncture performance test results of the present invention applied to surgical needles. In addition, wettability of the coatings of the present invention is significantly less than in other available materials. Contact angles in the 120° range have been measured on the surfaces of materials coated with methods of the present invention.

In one embodiment, the invention relates to a substrate or product having a stable, shear-resistant coating applied thereto wherein the coating comprises a resin binder layer coated on the surface of the substrate and bonded to the substrate; and a layer of poly (fluorinated ethylene) particles fixed on the resin binder layer wherein the particles are deposited on the resin from a surfactant-free aqueous disper¬ sion; wherein the particles have sizes in the range of from about 0.05 μm to about 0.5 μm; and wherein the layer of particles is up to about lOμm thick.

In another embodiment, the product of the first embodiment is coated repeatedly with additional layers of poly (fluorinated ethylene) particles. In still another embodiment, it is contemplated that an aqueous dispersion of larger sized particles may be used and the resulting very thin layer or layers of particles may exceed about 25 μm in thickness.

In still another embodiment of the invention it is contemplated that the surfaces of an electrically conductive wire implant may be coated with one or more layers of poly(fluorinated ethylene) particles according to the invention to thereby give the implant a coating that provides electrical insulation, mechanical protection and corrosion resistance under use conditions. It is contemplated that the coating particles have sizes in the range of from about 0.05 μm to about 0.5 μm and that the layer or layers of particles have a total thickness in the range of from about 1 μm to about 250 μ .

WL2n it is appropriate, as an optional final step, the product may be further coated with a film of super-lubricant such as a perfluoropolyether or PDMS, applied over the final layer of particles.

The characteristics of a PTFE particle surface coupled with the ease of application provided by the present invention give rise to a broad variety of uses in industrial, commercial, military and household settings. In effect, any surface to which a suitable bonding resin can be made to adhere may now, after coating with PTFE particles, exhibit many of the features of PTFE itself.

THE DRAWINGS

Fig. 1 is a graph which plots the puncture per¬ formance of a random selection of ten specimens of a widely used silicone-coated surgical needle, commonly considered the industry standard, compared with ten needles coated in accordance with Example 2, below, of the present invention wherein each needle was used repeatedly for 10 successive penetrations. The force

required to penetrate a tissue surrogate (Porvair), from first to tenth puncture, for each of the two kinds of needles, was measured with a penetrometer, and the chart reports and compares their performances.

Fig. 2 is a graph of averages that were derived from the data plotted in Fig. 1. Each entry of Fig. 2 is based on the average of the pressures required by each of the ten similar needles for that particular penetration number.

DETAILED DESCRIPTION OF THE INVENTION

THE PROCESS OF THE INVENTION

AS APPLIED TO A STAINLESS STEEL SUBSTRATE:

AS APPLIED TO A POLYAMIDE SUBSTRATE: AND

AS APPLIED TO A POLYESTER SUBSTRATE

Most practitioners recognize that, if a coating adheres and functions well on stainless steel, it will do so on many other surfaces with which the coating technology is compatible. One preferred embodiment of the invention provides coated stainless steel needles that have a highly lubricious PTFE coating. The PTFE coating is sufficiently stable and resistant so that it will withstand autoclaving and other high-temperature or strong-chemical exposure. This coating may be used on many articles including, for example, surgical instruments, hypodermic needles, implants, catheters, drains, parts of aircraft, spacecraft and other machinery, etc.

In one preferred embodiment, the process for coating stainless steel needles according to the invention comprises:

1) Cleaning and preparing the surfaces of the needles;

2) Applying a layer of a bonding resin;

3) Applying a coating of an essentially surfactant free aqueous dispersion of

PTFE particles; and,

4) Optionally, applying a film of a super-lubricious material.

To coat a stainless steel surgical needle, the surface should be clean and prepared to provide strong and uniform adhesion of the resin binder layer. In the examples that follow, preliminary cleaning was done with acetone. Otl r suitable solvents might be used, including, for example chloroform, carbon tetrachloride, simple alcohols or fluorinated solvents.

In the preferred method for preparation (the heating preparation method) , the needles are heated to ~200°C for 5 to 10 minutes and immediately coated with the resin binder material.

Other acceptable methods of preparation (chemical preparation methods) are exemplified as follows: the needles are immersed for -10 minutes at -75°C in a bath of the following composition, for example:

Sodium dichromate 31 parts by weight Sulfuric acid (cone.) 50 " " " Water 170"

Alternatively, the needles may be immersed and agitated for from a few minutes to overnight in a solution containing 12 parts of sodium hydroxide, 12 parts of water and 76 parts of ethyl alcohol.

The preparation materials, processes and time requirements will differ, of course, depending upon the composition of the surfaces to be prepared and the nature and extent of their contamination.

In lieu of the above procedures, satisfactory results are obtained when the surfaces to be coated are slightly abraded (abrasion preparation method), for example by tumbling, sanding, or sand blasting with from about 600 to about 800 grit abrasive. They are then cleaned in acetone, preferably under ultrasonification, and finally, rinsed in deionized (DI) water and dried at about 60°C prior to application of the resin binder lryer.

Next, a coating of bonding resin is applied. The resin preferably is applied as a solution in an appro¬ priate solvent. Suitable bonding resins include epoxies, polyethylene, polyacetal, polyamide-imide, polyimide, poly(phenylene sulfides), phenolics, silicones, polyesters, polyurethanes, poly(vinylidene chloride), poly(vinyl chloride), polyacrylates, polyphenylsulfides, polyethersulfones, polysulfones, polyvinyl acetates, and polyvinyl chlorides, among others.

As regards each bonding resin material, the time, temperature, and duration of the application process may be tailored to suit the specific substrate, the particular resin systems, the desired coating thick¬ ness, and its intended use. Solvents, solvent systems, or other vehicles for the several resin materials should be selected from among those recom¬ mended by the sources of the resin. Shell Chemical Co. of Houston, Texas, for example, lists approxi¬ mately 20 solvents for certain classes of its resins

that are useful in the practice of the invention. Depending upon the boiling points of the solvents used, for example, the thickness of the coatings will vary; and withdrawal speed from the resin solution, rates and amplitudes of agitation or tumbling etc., and the power and temperature of forced air systems if used, should be adjusted accordingly to produce the appropriate coating thickness. Aqueous systems are also available and are useful.

The parameters that govern film thickness in the immersion (dip) coating process are: 1) concentration of the resin in the solution and, 2) speed of withdrawal.

Several factors provide means for controlling coating thickness and preventing adhesion among products during batch processing. They include, for example, a) concentration of the resin in the solvent system, b) choice of solvents for curing times and temperatures, c) rate and amplitude of agitation, tumbling or similar induced movements, and d) rates and temperatures of air flow over the products after withdrawal from the resin-binder solution.

When the resin and curing agent are separate, the resin and curing agent materials are mixed and then applied together in a thin coat by spraying, dipping, swabbing, brushing, rolling, or other convenient means. Depending upon the nature of the substrate and the intended use, the resin coating may be as thin as about 0.2 μm to about 0.3 μm.

Next, the resin coating is dried, cured, or permitted to cure, at from atmospheric pressure and ambient temperature to the specific conditions

required by the resin and curing agent combination selected.

Next, the surface is coated with a layer of PTFE particles from a surfactant-free (SF), aqueous dispersion of PTFE. All examples given hereafter utilize particles so derived. The basic dispersions from which surfactant-free materials may be made are obtainable from, for example, the E.I. du Pont de Nemours Corporation or ICI Americas Inc., both of Wilmington, Delaware. Suitable dispersion products that are obtainable from du Pont include Grade 30B, TE-3170, FEP 120, and PFA 335 , among others. Suitable dispersion products that are obtainable from ICI include AD-1. The SF PTFE coating of the present invention may be applied by spraying, brushing, dipping, rolling, swabbing or other convenient means. The coating may be applied in layers as thin as 0.2 μm - 0.3 μm, which is the approximate size of the particles in some of the commercially available dispersions.

Thicker coatings with good mechanical integrity can be provided by repeating the application of resin binder and the application of the SF PTFE particle layer. The previous coating should be dried, at ambient or elevated temperatures, to remove water from the coating before the application of successive coatings.

To increase the thickness of the PTFE coating alone, repeat only the application of the SF PTFE particle layer. Attempting to apply a thicker PTFE particle coating in one application is likely to result in cracking of the surface due to the pressures of capillary contraction during drying.

In the first four examples that follow, surgical needles were coated to produce a highly lubricious PTFE surface. A very low friction perfluoropolyether, (PFPE), was applied over the PTFE layer, and the solvent allowed to evaporate. Other materials, including additional PTFE, may be applied over the PTFE coating, in layers, to achieve a wide array of functional and physical characteristics.

Examples of very low friction materials that may be applied over the PTFE layer, and that are capable of forming chemical and/or physical bonds with the PTFE layer, include, for example:

1) Perfluoropolyethers (PFPE) containing . functional groups such as, for example, Z-DOL (hydroxyl groups), Z-DIAC (carboxylate groups), and Z-DISOC (isocyanate groups). Z-DOL, Z-DIAC and Z-DISOC are products of The Montecatini Edison Company of Italy. As an example, a low-friction PFPE film may be composed of a 10% solution of Z-DIAC in Freon, which solution was used in Example 1.

2) Long chain fatty acids and alcohols, e.g., stearic acid, palmitic acid, and alcohols such as hexadecanol. Amines and amides of these same fatty acids are also useful.

3) Silicone compounds, such as aminofunctional polymeric silanes and other silicone based materials.

As an example, a low-friction PDMS film could include a duplex film composed of reactive as well as neutral PDMS, such as a solution of 5 parts of PS 513 (aminobutyldimethyl terminated polydimethylsiloxane), 5 parts of PS 047 (trimethylsiloxy terminated polydimethylsiloxane), and 90 parts of chloroform, which solution was used in Example 2. These

particular materials, with the "PS" designation, are available from the Petrarch Systems division of Huls America, Inc. of Piscataway, New Jersey. The unbonded portion of all the above superlubricious material can be removed by finding an appropriate solvent.

With a resin-bonded coating of PTFE-rich material, and a film of very-low friction lubricant over the PTFE layer, the force required for the initial punctures of a surgical needle through a skin surrogate approximates that for the industry standard. However, all subsequent punctures of needles coated according to the present invention - for as long as the surgeon may wish to use the needle - require efforts only slightly greater than did the initial punctures, resulting in a more effective, reliable and relatively consistent performance.

In one embodiment of this invention a stratum, which may be a monolayer or multilayer, of PTFE particles of relatively uniform size in the 0.2 μm to

0.3 μm range, is applied to a resin coated needle or other substrate. In this embodiment, in addition to benefitting from the usual PTFE characteristics, the substrate is protected from ultraviolet radiation in the 185 μm to 400 μm range since, even in a monolayer configuration, PTFE particles in the 0.2 μm to 0.3 μm range, it has been observed, scatter or deflect ≥99% of incident ultraviolet radiation. Better protection from ultraviolet radiation will be provided, it is believed, by thicker layers of PTFE coatings.

In the case of surgical needles, such as are described in the first four Examples below, no particu- lar benefit would accrue to the needle by having the substrate protected from ultraviolet light. However,

the inventive coating can be used to coat a wide variety of materials including, for example, wood, certain plastics, fabrics, etc. which, if protected from ultraviolet light, could be expected to have the benefit of enhanced long term stability and life.

The invention will now be demonstrated in greater detail in the following six examples. Throughout, all temperatures are in degrees Celsius and all parts and percentages are by weight, as is, unless otherwise specified.

The surgical needles used in the first four examples that follow were manufactured by Ethicon, Inc. of New Jersey and are generally considered the standard in the industry.

In a fifth example and a sixth example, the substrate coated is polyamide dental floss and polyester (Dacron) surgical suture, respectively. The dental floss used in Example 5 was manufactured by Johnson & Johnson Co. of New Jersey. The surgical suture used in Example 6 was manufactured by Ethicon Inc. of New Jersey.

The bonding resin used to coat the surgical needles was different in each of the four examples. In Example 1, a polyamide resin was used; in Example 2, an epoxy/polyamide was used; and in Example 3, an epoxy resin, mercaptan hardener and a tertiary amine accelerator system were used. The polyamide resin used in Example 1 was du Pont's Elvamide 8063. The epoxy Epon 1007F, and the polyamide V-40, both from the Shell Chemical Company, were used in Example 2. The epoxy resin Epon 828 from the Shell Chemical Company, the mercaptan hardener Capcure 3-800 and the accelerator EH-30, both from the Henkel Corp. of

Ambler, Pennsylvania, were used in Example 3. The resin used in Example 4 was a polyurethane resin from TACC International of Rockland, Massachusetts designated CR-3200WS.

The surfactant-free (SF) dispersions of PTFE used in all the Examples were prepared from a commercially available product from the du Pont Corporation and identified as du Pont Grade 30B. Grade 30B (also identified as Teflon 30B) is described by DuPont as containing approximately 60 percent (by total weight) of 0.05 μm to 0.5 μm PTFE (polytetrafluoroethylene) resin particles suspended in water.

In all of the examples, surfactants were removed from the dispersion by dialysis, although other methods such as centrifugation or ultrafiitration could also be employed. In the examples, the disper¬ sions were tested for completeness of the removal of surfactants by measuring the surface tension of the cleaned dispersion since dispersions free of surfactants have surface tensions equivalent to that of water. Depending upon the procedure used and the extent to which the surfactants are removed, various degrees of concentration of PTFE particles in the resulting dispersion will be achieved.

The SF PTFE dispersion that was used in each example had a pH of about 10, a solids content of about 30% and a surface tension of about 55 to 60 dynes per centimeter.

The needles were dip coated in the SF PTFE dispersion and the concentration of the dispersion and withdrawal speed were adjusted to produce a coating thickness of from about 1 μm to about 10 μm. The approximate withdrawal speed used was from about 1mm

to about 3mm per second. After dipping and agitation in the SF PTFE dispersion for a few seconds, the needles were withdrawn and allowed to dry and cure at ambient to elevated temperatures for appropriate times as suggested by the examples.

In order to measure the lubricity of the coated surfaces of the needles, the pin-on-flat test apparatus was used. In this method, the pin is held stationary and the flat moves in a reciprocating motion. The frictional force required to keep the pin stationary when pressed against a moving surface is monitored and the friction coefficient, which equals the frictional force divided by the applied load, is calculated. Using the pin-on-flat method, tests were conducted on glass surfaces coated with the disclosed formulations. Typically, the friction coefficients of PTFE coatings deposited following the procedures described in Examples 1 through 4 were measured in the range between 0.04 and 0.07, irrespective of the resin type used as a primer. The application of the top coat, composed of either the PFPE solution or the PDMS mixture in solution to the PTFE coatings resulted in lowering the coefficient of friction to exceptionally low values in the 0.02 to 0.04 range.

EXAMPLE 1 USE OF A POLYAMIDE RESIN PRIMER

Cleaning and Etching Surσical Needles

In this example, stainless steel surgical needles were cleaned by immersion and agitation in acetone for several minutes, following which they were heated at about 200°C for about 5 to 10 minutes and immediately dipped into the polyamide solution.

Applying a Polvamide Resin to the Surgical Needles

In this case, du Pont's Elvamide 8063 polyamide was selected. A solution was prepared by dissolving 5 parts of the resin in 95 parts of methyl alcohol. The needles were then dipped in the resin solution and withdrawn at a speed adjusted to produce a film thickness of from about 5 μm to 10 μm; in this case the withdrawal speed was from about 1mm to about 3mm per second. Solvent was then removed by drying the resin-coated needles at ≥ 105 ^β C.

Applying SF PTFE Coatings To The Bonding Resin Coated Surgical Needles

The bonding-resin coated needles were then dipped into the PTFE coating material previously described, which was composed of about 30% PTFE solids and about 70% deionized (DI) water. The needles were dipped into the coating and then withdrawn at a speed of about 1mm to 3mm per second, resulting in a coating thickness of from about 1 μm to 10 μm. The residual water in the coating was removed from the coated needles by heating the needles at about 110°C.

Fusing The Bonding Resin To The Needles And To The PTFE Overcoating

To fuse the resin to the surfaces of the needles and to the PTFE coating, the needles were heated at from about 160°C to about 165°C, the melting point of

Elvamide resin, for approximately ten minutes following the PTFE dip coating.

Applying A Very Low-Friction Surface As A TOP Coat

To apply a low friction top coating, the coated needles were dipped in a 10% Freon solution of the perfluoropolyether (Z-DIAC) lubricant previously described. An excess of unbounded Z-DIAC material was removed by rinsing with Freon.

EXAMPLE 2 USE OF AN EPOXY-POLYAMIDE RESIN PRIMER

Cleaning and Etching The Surgical Needles

In this example, stainless steel surgical needles were cleaned by immersion and agitation in acetone for several minutes following which they were heated at about 200°C for about 10 minutes and immediately dipped into the epoxy/polyamide resin solution.

Applying An EpoxV/Polvamide Bonding Resin

To The Needles and Curing

The needles were coated with an epoxy/polyamide resin system.

An epoxy/polyamide solution was prepared by dissolving 5 parts of epoxy resin and 5 parts of polyamide resin in 90 parts of chloroform. In this example, the epoxy resin chosen was Epon 1007F epoxy, and the polyamide resin was V-40 polyamide, both from Shell Chemical Co.

The needles were dip-coated in the bonding resin solution using a speed of withdrawal that produced a coating with a thickness of from 5 μ to 10 μm.

Solvents were then removed from the resin coating by air-drying the needles, following which, the needles were heated in an oven at 100 ^β C for about 30 minutes in order to cure the resin coating. The needles were then cooled at room temperature.

Applying SF PTFE Coating To The Bonding Resin Coated Needles

The resin coated needles were then dipped into the SF PTFE dispersion previously described, which was composed of about 30% PTFE particles and about 70% DI water and then withdrawn at the speed of about 1mm to 3mm per second to produce a dry film of from about 1 μm to about 10 μm in thickness. The water in the PTFE coating was removed by heating the needles at about 110°C.

To cure the resin and to enhance adhesion of the PTFE particles, the needles were heated at from about 100°C to about 110 ^β C for approximately 20 minutes following the PTFE dip coating.

Applying A Very Low-Friction Surface As A TOP Coat

In order to apply a low friction top coating, the coated needles were dipped into the polydimethylsiloxane (PDMS) lubricant previously described. After removal of the solvent from the coated needles, the needles were heated at from about 100°C to about 110 ^C C for about 5 minutes to ensure bonding of the reactive siloxane to the PTFE coating. An excess of unbo nded PDMS was removed by rinsing with chloroform.

EXAMPLE 3

USE OF AN EPOXY WITH A CURING AGENT

AND AN ACCELERATOR AS THE RESIN PRIMER

Cleaning And Etching The Needles

In this example, stainless steel surgical needles were cleaned by immersion and agitation in acetone for several minutes. Following the cleaning step, the needles were immersed for 10 minutes at a temperature of about 75°C in a bath composed of 31 parts sodium dichromate, 50 parts of concentrated sulfuric acid, and 170 parts of water. Next, the needles were rinsed in deionized water and dried in an oven at about 60°C.

Applying An Epoxy/Mercaptan/Tertiarv Amine Accelerator Resin Binder System To The Needles and Curing

The needles were then coated with a solution containing epoxy resin, mercaptan hardener, and tertiary amine accelerator. In this example, the epoxy resin selected was Epon 828, from Shell Chemical Co. The mercaptan hardener was Capcure 3-800 and the accelerator was EH-30, both of the latter from the Henkel Corp.

The bonding resin coating solution was prepared by dissolving 1 part of EH-30, 10 parts of Capcure 3-800, and 10 parts of Epon 828 in 180 parts of chloroform. The needles were coated by dipping them in the solution followed by air drying at room temperature for about 10 minutes.

Applying SF PTFE Coating To Bonding Resin Coated Needles

The bonding resin coated needles were then dipped into the SF PTFE dispersion previously described, which was composed of about 30% PTFE solids and 70% DI water. The needles were dipped into the dispersion and then withdrawn at a speed of about 1mm to 3mm per second. The water in the PTFE coating was removed by heating at about 100°C for about 10 minutes and then cooling to room temperature. The needles were then ready to be top-coated.

Applying A Very Low-Friction Mat ^e rial As A TOP Coat

To apply a low friction top coating, the PTFE coated needles were dipped into the polydimethylsiloxane (PDMS) lubricant previously described. After removal of the solvent, the needles were dried and heated at about 100°C for about 5 minutes to ensure bonding of the reactive siloxane to the PTFE coating. An excess of unbonded PDMS was removed as indicated in the previous examples.

EXAMPLE 4

USE OF A POLYURETHANE RESIN PRIMER

Preparing The Needles

In this example, stainless steel surgical needles were cleaned by immersion and agitation in acetone for several minutes. Following the cleaning step, the needles were heated at about 200°C for about 5 to 10 minutes, and allowed to cool to room temperature.

Applying a Polyurethane Resin to the Needles and Curing

The needles were then coated with a polyurethane solution which was prepared by mixing one part of water reducible polyurethane resin with one part of DI water. In this example, the polyurethane resin chosen was CR-3200 WS from TACC International Co. The needles were coated by dipping in the polyurethane solution followed by air drying at room temperature for about ten minutes.

Applying a SF PTFE Coating to the Resin Coated Needles

The polyurethane coated needles were then dipped into the SF PTFE dispersion previously described, which was composed of about 30% PTFE solids and 70% DI water. The needles were dipped into the dispersion and then withdrawn at a speed of about 1mm to 3mm per second. Residual water was removed by heating the needles for about 10 minutes at about 100°C.

Applying a Very Low-Friction Material as a TOP Coat

A low friction top coating composed of a 1:1 mixture of neutral and reactive PDMS was applied as described in the previous Examples.

Push- ull Penetration Testing Of The Needles

In order to compare the penetration ability of a surgical needle when used for successive penetrations, the point of the needle and a portion of the needle's length was pushed through a tissue surrogate (Porvair) . The needle was then removed and reinserted to the same extent, but at different locations on the

tissue surrogate, for a total of ten penetrations. The force required for each penetration was measured using a penetrometer that was made by the Chatillon Corp. of Greensboro, North Carolina and identified as Dial Push-Pull Gage, Model DPP.

The result of one series of tests is set forth in graph form in Figure 1 and Figure 2. The series of tests was made using ten needles selected at random made according to Example 2 and, as a control, ten identical but silicone coated needles, selected at random, all of which were manufactured by Ethicon, Inc.

In Figure 1, the force required for a penetration of each needle is plotted against its puncture number. The plots for the needles of the invention are entered in dotted lines and the plots for the controls are entered in solid lines.

In Figure 2, the average force for penetration of a needle of the invention, based on the ten tests, is plotted against the penetration number. Similarly, the average force for penetration of a control needle, based on the ten tests, is plotted against the penetration number.

Figure 2 shows that in a first penetration the needle of the invention requires a greater force than the standard needle and it is not until the third penetration that the force required is about the same as that for the standard needle. Thereafter, the force required for penetration by the needle of the invention remains virtually constant as compared with force required for penetration required by the standard needle. The penetration . force of the standard needle eventually becomes as much as two or three times its initial effort.

EXAMPLE 5 APPLYING COATINGS TO DENTAL FLOSS

Preparing The Floss

In this example, polyamide dental floss was cleaned by immersion in acetone for several minutes. The solvent was removed by air drying at room temperature.

Applying a Polyamide Binder-Resin to Polvamide Dental Floss

The cleaned dental floss was then coated with a polyamide resin solution. The solution was prepared by dissolving 5 parts of du Pont's Elvamide 8063 polyamide resin in 95 parts of methyl alcohol. The floss was then immersed in the resin solution and withdrawn, as a single strand, at the rate of several inches per minute to produce a coating thickness of from about 5 μm to 10 μm. Solvent was removed during withdrawal by exposing the strand to warm air in the temperature range of from about 30°C to about 60°C.

Applying SF PTFE Coatings to the Binder-Resin Coated Dental Floss

The polyamide coated dental floss was then immersed in the SF PTFE coating material previously described, which was composed of about 30% PTFE solids in water. A single strand of dental floss was then withdrawn at the rate of several inches per minute resulting in a PTFE coating thickness of from about 1 μm to about 5 μm. Solvent removal was accomplished by exposing the strand to air in the temperature range of from about 60°C to about 100°C.

EXAMPLE 6 COATING SURGICAL SUTURE

Preparing The Suture

In this example, a strand of polyester (Dacron) suture was cleaned by immersion in acetone for several minutes. The solvent was removed by air drying at room temperature.

Applying a Polyamide Binder-Resin to the Suture

The cleaned suture was then coated with a polyamide resin. A solution of du Pont's Elvamide 8063 polyamide resin was prepared by dissolving 5 parts of the resin in 95 parts of methyl alcohol. The suture was then immersed in the resin solution and withdrawn at the rate of several inches per minute to produce a resin coating of from about 5 μm to 10 μm in thickness. Solvent was removed during withdrawal by exposing the strand to warm air in the temperature range of from about 30° to about 60°C.

Applying a SF PTFE coating to the Binder-Resin layer

The polyamide-coated suture was then immersed in the SF PTFE coating material previously described, which was composed of about 30% PTFE solids in water. The suture was then withdrawn at the rate of several inches per minute resulting in a PTFE coating thickness of from about 1 μm to 5 μm. Solvent removal was accomplished by exposing the suture to air in the temperature range of from about 60°C to about 100°C.

CONCLUSION STAINLESS STEEL NEEDLES

The results of the push-pull testing demonstrate that previous state of the art silicone-coated stainless steel surgical needles have a coating that remains mobile to a large extent and does not adhere to or become more than a tenuous part of the needle's surface. In use, after one or a few punctures, surface lubricity is lost as much of the coating sloughs off. The sloughed off coating can often be observed with the unaided eye. It appears as a whitish collar which forms at that place on the tested needle where penetration stopped.

On the other hand, the coated needle of the invention sets a new standard for the industry. The needle of the invention provides a stable layer of PTFE, well bonded to the stainless steel needle. The PTFE itself may become a substrate for a surface coating of a super-lubricious material. Initial punctures of such needles then approximate the historical standard as regards efforts required for initial penetrations of tissue. But all subsequent punctures, for as long as the surgeon may wish to use the needle, require efforts only slightly greater than the initial punctures, resulting in a more effective, reliable and relatively invariant performance with little or no evidence of sloughing.

DENTAL FLOSS AND DENTAL TAPE

Experimentation with the present invention has disclosed that the tendency of bacteria, food particles and other debris to adhere to and accumulate or grow on the surfaces of teeth can be reduced

significantly by enhancing the lubricity and inertness of the tooth surfaces.

Example 5, illustrates a process whereby dental floss is coated with a polyamide resin-binder and then coated with a layer of SF PTFE. The product resulting from the process has the benefits of, a) reduced fraying, and b) reduced frictional resistance in use.

Similarly, a highly lubricious, inert and effective coating may be applied to teeth by use of appropriately configured instruments composed of wood, plastic or other material, such as and including interdental cleaners similar to those presently produced and sold by Johnson & Johnson Co., when such instruments are coated in accordance with the processes of the present invention. Such instruments can be used to clean and then coat the areas between the teeth and beneath the gum line where bacteria and debris most often accumulate and where ordinary brushing is least effective.

In addition, and most importantly, during use, particles of PTFE transfer from the floss to the surfaces of teeth, especially the surfaces between teeth and in otherwise less accessible areas such as surfaces of teeth beneath the gums. Particles of PTFE have the property of, c) inhibiting the initiation, and/or adhesion and/or growth of bacteria, including the bacteria associated with the production of plaque, on the areas on which PTFE particles adhere. The transferred particles also impart the property of, d) facilitating removal of plaque that may or does form on the areas covered by the PTFE particles.

Similarly, toothbrush bristles composed of polyamide, when coated in accordance with the process

described for coating polyamide dental floss, provide the benefits mentioned for dental floss above and, in addition, coat and smooth the exposed ends of the bristles resulting in less irritation to soft tissues during use. The toothbrush bristles resulting from the process also have improved resistance to the initiation, and/or adhesion and/or growth of bacteria on their surfaces.

Of course, the dental floss or the toothbrush bristles may be composed of an appropriate material other than polyamide. It is only necessary that the material be one that may be properly coated by a suitable resin-binder according to the invention.

SURGICAL SUTURES

Example 6 illustrates a process whereby surgical sutures composed of silk, cotton, linen, polyamide, polyester, polypropylene or any other appropriate material or combination of such materials may be coated with an appropriate binder-resin layer and then coated with a continuous coating of PTFE particles.

The products resulting from the process have the advantages of, a) lower coefficients of friction on their surfaces, b) greater ease of use from less force required to draw the suture through tissues, c) greater hydrophobicity, d) lower wettability, e) reduced micro-trauma to penetrated tissues, f) greater resistance to the initiation, and/or adhesion, and/or growth of bacteria, g) reduced flow, by capillarity, of fluids on the surface of the sutures, h) reduced formation of adhesions with surrounding tissues during the healing processes, i) enhanced ease of removal of sutures, j) improved knot-tying quality, and, k) improved knot-holding quality.

Dental floss suitable for coating according to the invention can be in the form of a monofilament or it can be in woven form. Likewise, suture suitable for coating according to the invention can be in the form of a monofilament or it can be in woven form.

Similarly, fibers, filaments, thread, yarns, strings, lines, ropes, fabrics, etc. composed of any material to which any of the selected resins adheres may be coated with a resin-binder coating which is then coated with a SF PTFE coating, thus providing the benefits and characteristics of a PTFE surface, including those set out in the paragraph above.

Some Examples Of Characteristics

And Uses Of The Invention

The invention provides surfaces which: 1) have among the lowest coefficients of friction available, 2) are essentially chemically inert, 3) are highly hydrophobic, having a contact angle in the neighborhood of 120°; 4) have low surface-free energy, so that dirt and debris tend not to adhere and are readily removed, 5) are odorless and tasteless, 6) increasingly, as the thickness of the PTFE coating increases, are electrically insular, 7) have very low surface wettability as a consequence of reduced surface free energy, 8) have a very broad functional thermal envelope, similar to that described for Teflon, except that the thermal envelope may be limited by the characteristics of the primer coating, 9) are generally recognized as acceptable for contact with human blood and tissues as well as food and food packages, 10) with layering, can probably inhibit or prevent the formation, adhesion and accumulation of ice on most substrates, 11) are protected from

ultraviolet radiation and, as a consequence of this and the hydrophobicity feature: 12) are highly resistant to weathering; 13) may be colored by dyes having appropriate functional groups in their structures, although the dye may be affected by weathering even though the substrate is protected, and, 14) may be applied without special training, equipment or facilities by almost anyone to almost any substrate and in most environments.

The invention can be used to provide its benefits to such disparate surfaces as: a) wood and wood products such as paper, cardboard, building materials, furniture, etc., where resistance to weathering is important, b) textile products such as curtains draperies, tents, flags, sails, parachutes, clothing, handbags, etc., the utility and length of service of which would be improved with improved resistance to ultraviolet radiation, c) those whose utility is enhanced with freedom from debris, such as helicopter rotors and propellers, etc. d) aircraft surfaces subjected to exhaust and other corrosives, contami¬ nants, debris, formations of ice, etc., e) those which need to be water and stain-proof and easy to keep clean, such as TVs, computers, aircraft interiors, etc. f) injection molds which are improved by a non-dimensional, solid-state release agent, g) hinges and sliders in sensitive instruments, machines, etc. where friction, vibration and energy required are reduced and where a wide thermal envelope may be helpful, h) surfaces of surgical instruments and other devices which may benefit from surfaces and edges with low friction, freedom from debris and staining and the ability to be implanted, i) tubes, drains, catheters, pipes, etc. especially those of small diameter where enhanced flow rates as well as the other benefits of

PTFE may be helpful, j) the multitude of other materials and products used in industrial commercial, military and household settings where the characteris¬ tics of PTFE may be practically available using the methods and materials of the present invention, including, for example, bearings, seals, pumps, impellers, slurry tanks, punches, extrusion screws, wear plates, air and hydraulic power tools, automotive components such as carburetor parts and brake mechanisms, computer mechanisms and components, food processing machinery, aerospace and aircraft hardware, naval and undersea hardware, chemical processing equipment, welding nozzles and equipment, electronic components, fasteners, printing equipment, slides and chutes, paper handling equipment, shafts, lock mechanisms, solenoid plungers, vending equipment, gears, and copying machines.