3,772,236 Patented Nov. 13, 1973

United States Patent Office 2 object of this invention to provide an improved dispersion s: "...... A 2,236 composition containing high molecular weight polytetra POLYFLUOROCARBONMOISTURECURING POLY fluoroethylene particles and thermosetting resin material URETHANE POLYVINYLBUTYRALDISPERSION with the dispersion composition being particularly stable; CoMPOSITION FOR LOW FRICTION COATINGS the method of preparing this composition; and, the method Cornelius Soons, Scheemda, Netherlands, assignor to of applying this composition to substrates to form low No Drawing.Acheson Continuation-in-part Industries, Inc., Port of Huron,application Mich Ser. No. friction coatings. : 872,765, Oct. 30, 1969, which is a continuation-in-part Other objects, features and advantages of the present ... of application Ser. No. 645,612, June 13, 1967, both invention will become apparent from the subsequent now abandoned. This application Nov. 9, 1971, Ser. O description and the appended claims. No. 197,101. . . . . Int, C. C08f 45/24 SUMMARY OF THE INVENTION U.S. C.260. 29.6FE. . . . . 11. Claims I have now found that by the use of a specific moisture curing polyurethane resin, together with polyvinyl butyral ABSTRACT OF THE DISCLOSURE 15 resin, in combination with polytetrafluoroethylene parti Stabilized dispersions of polytetrafluoroethylene parti cles, having a molecular weight greater than 500,000, a cles in a water-containing moisture curing polyurethane stable dispersion with long storage life can be obtained, polymer solution suitable for use in preparing low-friction which more nearly duplicates the protective properties of protective coatings, methods of preparing such dispersions 20 pure fused polytetrafluoroethylene without the fusion tem and methods of applying these dispersions to substrates to perature limitations. Heretofore those skilled in the art form low-friction coatings. have been unable to attain a dispersion composition having the advantages of this invention, and which composition CROSS REFERENCE TO RELATED APPLICATION includes a moisture curing polyurethane resin. 25 Also, in order to overcome the above deficiencies, I This application is a continuation-in-part of copending have now discovered a method of forming an adherent, U.S. application Ser. No. 872,765, filed Oct. 30, 1969, protective, and low-friction coating of polytetrafluoro now-abandoned; which latter application is in turn a ethylene particles firmly bonded to a substrate by a poly continuation-in-part of copending U.S. application, Ser. urethane resin, such coating being formed from a hereto No. 645,612, filed June 13, 1967, now abandoned, entitled fore unobtainable, highly stable, water-containing disper “Polytetrafluoroethylene-Moisture Curing Polyurethane sion including said polyurethane resin and polytetrafluoro Polyvinyl Butyral-Dispersion Composition For Low Fric ethylene particles. tion Coatings." DESCRIPTION OF THE PREFERRED BACKGROUND OF THE INVENTION 35 EMBODIMENTS ... For many years the ability of polytetrafluoroethylene The desired dispersion may be obtained by preparing a resin to form low-friction objects and shapes has been composition of polytetrafluoroethylene particles in a solu known and utilized...More recently, formation of similar tion of modified polyurethane polymer in a water low-friction, and protective surface-coatings on various 40 containing medium. substrates has also been desired. The earliest attempts to The amount of polyurethane resinous component form such coatings resulted in procedures which required present, relative to the polytetrafluoroethylene is in Sufi the application of polytetrafluoroethylene particles to the cient quantity to act as the continuous phase and binder substrate and fusion of the applied particles at high tem holding the polytetrafluoroethylene particles to the Sub peratures, in the order of 680-750 F. Such high fusion strate surface. temperatures severely limit the wide use of such coating It has surprisingly and completely unexpectedly been methods. In order to avoid such high fusion tempera found that this modified polyurethane resin component is tures several inventors: have proposed the use of resin effective when formulated with the polytetrafluoroethylene bonded polytetrafluoroethylene particles, with the resin as in the presence of substantial amounts of water. Normally a matrix, to, form the-coatings. Typical of such coatings 50 a moisture curing polyurethane resin of the type herein are those of U.S. Pat. 3,293,203 (the disclosure of which after described would not be considered usable by one is incorporated herein by reference), and Dawe et al. U.S. skilled in the art in a composition containing water. Pat. 2,976,257, where various thermosetting resins in com The polyurethane resinous component useful in this in bination with various, stabilizers and resin modifiers are vention is a combination of (1) a high molecular weight, used to form coating compositions which may be cured at moisture curing, reaction product of polyester and poly temperatures below those needed to sinter polytetrafluoro 55 isocyanate, i.e., polyurethane polymer, and (2) a poly ethylene to form coatings. The polyurethane described in vinyl butyral resin dissolved in an organic solvent or in Table 1, Example 4 of the Dawe et al. patent is a drying solvent blends. This combination of resinous material is oil modified with isocyanate and, not a moisture curing unusual and produces unexpected action in that, contrary polyurethane composition as in the instant patent to all previously known information, substantial amounts application...... 60 of water can be added to this combination, for example, Moreover, the Dawe et al. dispersions due to problems as an aqueous polytetrafluoroethylene dispersion, without in the area of stability were unsuitable for use as a one adversely affecting the useful storage life, curing action, package dispersion composition having a shelf life of or bonding properties of the urethane polymer. several months...... " , ", , . . . . " The coating compositions of this invention contain, both Other polytetrafluoroethylene-resinous binder coating 65 water and organic solvents, and this carrier medium does compositions have been developed in which no external not react with the polyurethane component to produce an heating is required to form adherent coatings. Such coat abnormally short storage life; in fact, coating composi ings as in U.S. Pats. 3,154,506 and 3,055,852, which utilize tions of this invention have been stored for periods of cellulosic resins to form adherent low-friction coatings, several months, and found to remain satisfactory for use. are limited in their protective properties by the inherent 70 The exact reason for such an unexpected result is un properties of the resinous binders. Accordingly, it is an known, but it is speculated that this may be the result of 3,772,236 3 some interaction between the urethane polymer and the tion and such additional organic solvents as may be added vinyl resin modifier. during the compounding operations to control drying The polytetrafluoroethylene particles useful in this in rates, solvency, etc. The preferred organic solvents are vention are those which have been condensed or pluralized blended mixtures of methyl ethyl ketone, n-butyl acetate to such an extent that they are normally solid and are and 4-methoxy-4-methyl-pentanone-2. dispersible in a liquid medium of water or an organic Formulation of stable dispersions requires the presence suspending agent such as hydrocarbons, alcohols, esters, of the polymeric stablilizer, polyvinyl butyral, such as ketones, etc., and have a particle size of about 0.1 to "Butvar B-76,' a product of the Monsanto Co. about 3 microns, and have a molecular weight in the The relative proportions of the various ingredients is range of about 500,000 to about 10 million. Typical of the O an important factor in the successfull operation of this in polymers are those produced by procedures described in vention. The total non-volatile solids content of the dis the U.S. Pats. 2,534,058 and 2,478,229. persion composition should not be over about 25% by It is preferred to employ an aqueous suspension of weight and the preferred maximum is about 14%. As is colloidal polytetrafluoroethylene as the source of the poly obvious to those skilled in the coating art, the lower limit tetrafluoroethylene particles. An especially suitable start 5 of total solids content is not critical and may be varied by ing material for this invention is the aqueous suspension additions of organic solvents to suit the method of appli containing 60% polytetrafluoroethylene particles having a cation. For some applications, such as dispensing from size in the range of about 0.1 to about 3 microns, avail internally pressurized containers (aerosol bomb type), the able under the trade name "Teflon. 30.” total solids content may be below 1%, and broadly as low The polyurethane component useful in this invention is 20 as about 0.1%. unique. Although it is normally a moisture curing ma The polytetrafluoroethylene solids may comprise about terial, when used following the teachings of this invention, 20% to about 70% of the total solids, the preferred range the presence of the water in the aqueous polytetrafluoro being from about 35% to about 50% by weight. ethylene suspension does not prematurely cure the resin The polyvinyl butyral may comprise about 10% to ous component. Urethane polymers useful in this inven 25 about 40% by weight of the total solids, the preferred tion are the urethane surface coating materials supplied range being from about 25% to about 35%. by Dyestuffs Division of Imperial Chemical Industries The polyurethane polymer or resin constitutes at least Limited under the trade names "Daltosec 1150' and "Dal 10% of the total solids, and more specifically about 10% tosec 1250.' These maetrials are described as follows: to 70%. . "Daltosec 1150.-A 50% by weight solution, in a mix 30 Regarding the method of mixing the various ingredi ture of n-butyl acetate and "Pentoxone', of a moisture ents, it has been found that conventional mixers such as curing polyester-polyisocyanate reaction product having a propeller stirrers, and the like, are satisfactory provided viscosity of 2.5 poise at 25 C., isocyanate value 2.5% and a uniformly mixed dispersion is obtained. A suitable volatile organic isocyanate content below 0.5%. method of mixing is to blend the polyurethane resin solu "Daltosec 1250.-A 50% solution, in a mixture of n tion with any desired diluting solvents, followed by the butyl-acetate and "Pentoxone,' of a moisture curing poly addition, with blending, of the resin modifier and finally esterpolyisocyanate reaction product having a viscosity of adding the polytetrafluoroethylene component. 7.5 poise at 25 C., isocyanate value 4.5% and volatile The products of this invention may be applied to vari organic isocyanate content below 0.5%.' ous Substrates by brushing, atomizing, spraying, dipping A moisture curing reaction product of polyester and 40 and the like. One particularly useful method is to apply polyisocyanate usable in this invention is further defined the coating from internally pressurized spray containers, and delimited as being comprised of a solution in a sol commonly called "aerosols' or “aerosol bombs.' The vent inert to isocyanates of an isocyanate-ended polyure coatings of this invention are best applied in relatively thane of average molecular weight more than 1000, which thin layers. For most purposes a coating thickness of is soluble in said solvent and which is obtained by reaction about 0.1 to about 1.5 mils is satisfactory. Multiple coat of a polyhydroxy compound of molecular weight more ings may be used, with solvent removal between coatings, than 400 and a polyisocyanate in amount sufficient to pro to obtain thicker layers. - vide at least 1.05 isocyanate groups for each hydroxyl After the desired coating thickness is obtained, the coat group present, and polymerized organic diisocyanate hav ing is finally cured. This curing may be done at room ing isocyanurate rings, in which the proportions of poly 50 temperature or accelerated by heating the coated articles. urethane to polymerized diisocyanate by weight lie be At normal room temperatures, periods of time of 6 to 24 tween the limits of 1:12 and 12:1. A useful polyurethane hours are required for coatings to cure. This time can be for the invention may also be further characterized as a substantially shortened by heating, at temperatures of reaction product of an aromatic diisocyanate with a poly 80-120° C. Additional drying time may be required to esterification product of an aliphatic dicarboxylic acid and 55 develop the maximum hardness of these coatings. at least one aliphatic diol and the polymerized organic In order to further illustrate the invention, the follow diisocyanate is a polymerized monocyclic aromatic diiso ing examples are provided. It is to be understood, how cyanate. See U.S. Pat. 3,454,533 which discloses other types of moisture curing polyurethane resins which are ever, that the examples are included for illustrative pur usable in this invention. 60 poses and are not intended to be limiting of the scope of The particular solvents, n-butyl acetate and "Pent the invention as set forth in the subjoined claims. oxone,' used with the polyurethane resin are not critical Example I and could be substituted for by other solvents; however, from a preferred standpoint and ease of usage said par A dispersion was prepared by mixing with a propeller ticular solvents would be present. 65 mixer 12.8 parts of the polyurethane solution, Daltosec The fluid or liquid carrier media for the dispersions of 1250, with 18.2 parts of Pentoxone and 143.6 parts of this invention are combinations of water and organic methyl ethyl ketone. 7.2 parts of polyvinyl butyral (But liquids having suitable solvency. The relative proportion var B-76) was dissolved in this mixture. 16.7 parts of an of water to organic liquid is not critical. The water may aqueous dispersion containing 60% polytetrafluoroethyl be introduced as such, or by using an aqueous dispersion 70 ene (Teflon 30) was added to the solution and mixed till of polytetrafluoromethylene particles. The organic sol uniform. This composition was then sprayed on degreased vents used are those present in the urethane polymer Solu steel panels using a De Vilbiss spray gun, Model MBC with a No. 30 tip and an air pressure between 25 and 50 1 Pentoxone is the Shell Chemical Co. trade name for the ketoether: 4 methoxy-4-methyl-pentanone-2. 75 pounds per square inch...... 3,772,236 5 6 These coated panels were airdried for 24 hours, and particles such as for example other fluorinated ethylene the following properties were observed on examination: polymer particles may be used or there may be used Thickness.------0.6 mil. fluorocarbon polymer particles selected from the group Coefficient of friction.------0.07. consisting of fluorinated and fluoro-chlorinated polymers Flex test (bending around a 4-inch man of Ca-C4 olefins. drel) ------Passed. While it will be apparent that the preferred embodi Impact test (28. in... lubs:) ------Do. ments of the invention disclosed are well calculated to Appearance ------Hard, smooth, fulfill the objects above stated, it will be appreciated that f : ...... glossy film. the invention is susceptible to modification, variation and 10 change without departing from the proper scope or fair Example II meaning of the subjoined claims. A dispersion was prepared as in Example I using the What is claimed is: following materials: 1. A stable, one package, dispersion composition con : - ...... Parts by weight sisting essentially of: Daltosec 1250------25.6 15 (a) fluorocarbon polymer particles selected from the Pentoxone ------36.4 group consisting of fluorinated and fluoro-chlorinated Methyl ethyl ketone.------132.2 polymers of Ca-Ca olefins said particles being in Butvar B-76------14.4 aqueous Suspension, and said particles being present Teflon 30------33.4 in an amount of about 20% to about 70% by weight total solids, 242.0 (b) a polyurethane resin component dissolved in a sol vent material, said component consisting essen I This dispersion was then diluted 1 part to 1 part with tially of additional methyl ethyl ketone to spraying consistency (1) at least one moisture curing polyester-poly and applied to steel panels as in Example I. The coated 25 isocyanate reaction product having a viscosity panels, after air curing for 24 hours, had a coefficient of of about 2% poise to about 7% poise at 25 C., friction of 0.087 and had a smooth, hard, semi-gloss an isocyanate value of about 2%% to about appearance. 4/2, and a volatile organic isocyanate content ...... Example III below about 72%, said reaction product being A dispersion was prepared as in Example I using the 30 comprised of an isocyanate-ended polyurethane following materials: of average molecular weight more than 1000, Parts by weight which is soluble in said solvent and which is ob Daltosec 1250------12.8 tained by reaction of a polyhydroxy compound Pentoxone ------18.2 of molecular weight more than 400 and a poly Methylethylketone------143.6 35 isocyanate in amount sufficient to provide at Butvar B-76------7.2 least 1.05 isocyanate groups for each hydroxyl Teflon 30------66.6 group present and polymerized organic diso . This dispersion was then diluted 3 parts to 1 part of cyanate having isocyanurate rings, in which the methyl ethyl-ketone and applied to steel panels as in 40 proportions of polyurethane to polymerized di Example I...The coated, panels after air curing 24 hours isocyanate by weight lie between the limits of were examined and found to have a hard, smooth Sur 1.12 and 12:1, and wherein the polyurethane is a reaction product of an aromatic diisocyanate face, slightly dull in appearance and a coefficient of fric with a polyesterification product of an aliphatic tion of 0.087...... - dicarboxylic acid and at least one aliphatic diol ' ...... Example IV and the polymerized organic diisocyanate is a A 30-gram portion of the dispersion of Example I was polymerized monocyclic aromatic diisocyanate, inserted into a 6-ounce aerosol container preloaded with said reaction product being present in an amount a proprietary blend of fluorinated hydrocarbon propellant of about 10% to about 70% by weight of total and enamel solvent known under the trade name of "En solids, and amel Type Omnipak” of the Sprayon Products Co. The 50 (2) polyvinyl butyral resin present in an amount dispersion was then sprayed from this container onto of about 10% to about 40% by weight of total degreased steel panels. After curing for about 72 hours at solids, and room temperature, the coated panels were examined and (c) an inert fluid carrier material, said composition found to have a smooth, hard, glossy and adherent coat having a total solids content of (a), (b), and (c) ing with a low coefficient of fiction. 55 solvent free basis, of less than about 25% by weight ...... Example V. of the composition. 2. The composition of claim 1 further characterized in The following materials were combined as in Example that said particles are present in an amount of I to produce a coating composition: about 35% to about 50% by weight of total solids, : ...... is Parts by weight 60 said resin component is present in an amount of Daltosec. 1150. ------12.7 about 10% to about 40% by weight of total solids, and Pentoxone ------18.2 said polyvinyl butyral is present in an amount of Methyl ethyl ketone------143.6 about 25% to about 35% by weight of total solids. Butvar B-76------7.3 3. The composition of claim 1 wherein said resin com Teflon 30------16.7 65 ponent is in solution in a solvent mixture of n-butyl This dispersion was then plied to steel panels and acetate and 4-methoxy-4-methyl-pentanone-2. to rubber'strips, and cured to form smooth, tough, adher 4. The composition of claim 1 wherein the total solids ent, low-friction coatings. . . : ...", content is from about 0.1% to about 25% by weight. By the term moisture curing it is meant a urethane 5. The composition of claim 4 wherein said polyure component or reaction product containing excess isocy 70. thane resin component is further characterized as being a anate groups which dries by reaction with moisture in 50% by weight solution, in a mixture of n-butyl acetate the air'...... - and 4-methoxy-4-methyl-pentanone-2, of a moisture cur It is also workable herein in this invention to use fluoro ing polyester-polyisocyanate reaction product having a carbon polymer particles besides polytetrafluoroethylene 7. viscosity of 2.5 poise at 25 C. and an isocyanate value 3,772,236 7 8 of 2.5%, and a volatile organic isocyanate content below which the proportions of polyurethane to po 0.5%. lymerized diisocyanate by weight lie between the 6. The composition of claim 4 wherein said poly limits of 1:12 and 12:1, said reaction product urethane resin component is further characterized as being being present in an amount of about 10% to a 50% solution, in a mixture of n-butyl acetate and 4 about 70% by weight of total solids, and methoxy-4-methyl-pentanone-2, of a moisture curing poly (2) polyvinyl butyral resin present in an amount ester-polyisocyanate reaction product having a viscosity of about 10% to about 40% by weight of total of 7.5 poise at 25 C. and an isocyanate value of 4.5% solids, and and a volatile organic isocyanate content below 0.5%. (c) an inert fluid carrier material, said composition 7. A stable, one package, dispersion composition con O having a total solids content of (a), (b), and (c) sisting essentially of: solvent free basis, of less than about 25% by weight (a) fluorocarbon polymer particles selected from the of the composition, wherein said polyurethane resin group consisting of fluorinated and fluoro-chlorinated component is further characterized as being a .50% polymers of C-C olefins said particles being in solution in a mixture of n-butyl acetate and 4-me aqueous suspension, and said particles being present 5 thoxy-4-methylpentanone-2, of a moisture curing in an amount of about 20% to about 70% by weight polyester-polyisocyanate reaction product having a of total solids, viscosity of 7.5 poise at 25 C. and an isocyanate (b) a polyurethane resin component dissolved in a sol value of 4.5% and a volatile organic isocyanate con vent material, said component consisting essentially tent below 0.5%. of 20 9. A stable, one package, dispersion composition con (1) at least one moisture curing polyester-poly sisting essentially of: isocyanate reaction product, said reaction prod (a) fluorocarbon polymer particles selected from the uct being comprised of an isocyanate-ended group consisting of fluorinated and fluoro-chlorinated polyurethane of average molecular weight more polymers of C-C olefins, said particles being in than 1000, which is soluble in said solvent and 25 aqueous suspension, and said particles being present which is obtained by reaction of a polyhydroxy in an amount of about 20% to about 70% by weight compound of molecular weight more than 400 of total solids, and a polyisocyanate in amount sufficient to (b) a polyurethane resin component dissolved in a provide at least 1.05 isocyanate groups for each solvent material, said component consisting essen hydroxy group present, and polymerized organic 30 tially of . . . diisocyanate having isocyanurate rings, in which (1) at least one moisture curing polyester-polyiso the proportions of polyurethane to polymerized cyanate reaction product having a viscosity of diisocyanate by weight lie between the limits of about 2% poise to about 7% poise at 25 C., 1:12 and 12:1, said reaction product being pres an isocyanate value of about 2/2% to about ent in an amount of about 10% to about 70% 4%%, and a volatile organic isocyanate by weight of total solids, and content below about .2%, said reaction (2) polyvinyl butyral resin present in an amount product being comprised of an isocyanate-ended of about 10% to about 40% by weight of total polyurethane of average molecular weight more solids, and than 1000, which is soluble in said solvent and (c) an inert fluid carrier material, said composition 40 which is obtained by reaction of a polyhydroxy having a total solids content of (a), (b), and (c) compound of molecular weight more than 400 solvent free basis, of less than about 25% by weight and a polyisocyanate in amount sufficient to pro of the composition, wherein said polyurethane resin vide at least 1.05 isocyanate groups for each component is further characterized as being a 50%, hydroxyl group present, and polymerized or by weight solution, in a mixture of n-butyl acetate ganic diisocyanate having isocyanurate rings, in and 4-methoxy-4-methyl-pentanone-2, of a moisture which the proportions of polyurethane to po curing polyesterpolyisocyanate reaction product hav lymerized diisocyanate by weight lie between the ing a viscosity of 2.5 poise at 25° C. and an iso limits of 1:12 and 12:1, said reaction product cyanate value of 2.5% and a volatile organic iso 50 being present in an amount of about 10% to cyanate content below 0.5%. about 70% by weight of total solids, and 8. A stable, one package, dispersion composition con (2) polyvinyl butyral resin present in an amount sisting essentially of less than about 40% by weight of total solids, (a) fluorocarbon polymer particles selected from the and group consisting of fluorinated and fluoro-chlorinated 55 (c) an inert fluid carrier material, said composition polymers of C-C olefins, said particles being in having a total solids content of (a), (b), and (c) aqueous suspension, and said particles being present solvent free basis, of less than about 25% by weight in an amount of about 20% to about 70% by weight of the composition. of total solids, 10. The composition of claim 1 wherein said particles (b) a polyurethane resin component dissolved in a sol 60 are polytetrafluoroethylene particles. bent material, said component consisting essen 11. The composition of claim 9 wherein said particles tially of are polytetrafluoroethylene particles. (1) at least one moisture curing polyester-poly isocyanate reaction product, said reaction prod References Cited uct being comprised of an isocyanate-ended 65 UNITED STATES PATENTS polyurethane of average molecular weight more than 1000, which is soluble in said solvent and 2,976,257 3/1961 Dawe et al.------260-29.6F which is obtained by reaction of a polyhydroxy 3,454,533 7/1969 Derrigan et al.----260-75 NR compound of molecular weight more than 400 HAROLD D. ANDERSON, Primary Examiner and a polyisocyanate in amount sufficient to pro 70 vide at least 1.05 isocyanate groups for each U.S. C1, X.R. hydroxyl group present, and polymerized or 117-132 CF, 16.1 KP, 161 UZ; 260-29.6 NR, 29.6 RB, ganic diisocyanate having isocyanurate rings, in 859 R ...... UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,772, 236 Dated November 13, 1973

Inventor(s) Cornelius Soons It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Column 3, line 29, change "maetrials' to --materials--. Column 6, line 20, before "total" insert --of--. Column 6, line 28, after '4-1/2" insert --%--. Column 6, line 41, change "1. 12' to -- 1:12--.

Signed and sealed this l6th day of April

(SEAL) Atte St : EDWARD i.FLETCHER, JR. - C. MARSHALL, DANN Atte sting Officer Commissioner of Patents

FORM PO-1050 (10-69) UscdMMad c 6037 6-roeg U.S. GOVERNMENT PRINTNG OFFICE: 9ss O-366-334