GB2070045A

GB2070045A - Method of making abrasion resistant polyurethane coated rigid plastics

Info

Publication number: GB2070045A
Application number: GB8104720A
Authority: GB
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1980-02-14
Filing date: 1981-02-16
Publication date: 1981-09-03
Also published as: FR2476103B1; FR2476103A1; JPS56131635A; GB2070045B; JPH0225936B2

Abstract

A method of making an abrasion resistant polyurethane coated rigid plastics transparency comprising the steps of: a. preparing a single phase liquid reaction mixture comprising an aliphatic or cycloaliphatic diisocyanate and a substantially equivalent amount of polyol such that the resulting polyurethane has a durometer value at 21 DEG C of from Shore A 50 to Shore D 80 and a molecular weight between branch points of from about 400 to about 13,000; b. casting said reaction mixture into a mold having a cavity at least about 5 mils (0.1 millimeters) thick and comprising one ply of a rigid transparent plastics to which the polyurethane coating will adhere; and c. curing said reaction mixture at a sufficiently rapid rate to form an abrasion resistant polyurethane coating with substantially no warpage or degradation of the rigid plastics ply. t

Description

SPECIFICATION Method of making abrasion resistant polyurethane coated rigid plastics The present invention relates to a method of making abrasion resistant polyurethane coated rigid plastics.

U.S. Patent No. 4,079,160 to Phillipson teaches an optical element, such as an eyeglass lens, formed of a typical rigid polymeric substrate of relatively low scratch resistance coated on at least one surface with a relatively soft, resilient and tough, transparent polymeric material.

U.S. Patent No. 4,174,240 to Mulier teaches laminates wherein glass or glass-like plastics are coated with a transparent film 0.1 to 5 millimeters thick formed from a polyurethane polyurea containing 1 to 20 percent by weight urea groups and 0.001 to 10 percent by weight lateral --COOH groups.

The present invention involves the use of relatively soft, resilient branched polyester polyurethanes as abrasion resistant coatings on rigid plastic materials. The present invention further involves a method of casting such polyurethane compositions against a rigid plastic substrate and curing in place at a sufficiently rapid rate to avoid warpage and deterioration of the rigid plastic surface which can result from prolonged exposure to the isocyanate at high temperatures.

According to the present invention a method is provided for making an abrasion resistant polyurethane coated rigid plastic transparency comprising the steps of: a. preparing a single phase liquid reaction mixture comprising an aliphatic diisocyanate and substantially equivalent amount of polyol such that the resulting polyurethane has a durometer value at 21 OC of from Shore A 50 to Shore D 80 and a molecular weight between branch points of from about 400 to about 13,000; b. casting said reaction mixture into a mold having a cavity at least about 5 mils (0.1 millimeters) thick and comprising one ply of a rigid transparent plastic to which the polyurethane coating will adhere; and c. curing said reaction mixture at a sufficiently rapid rate to form an abrasion resistant polyurethane coating with substantially no warpage or degradation of the rigid plastic ply. The coated plastics are especially useful as aircraft transparencies.

The following is an embodiment of the invention.

A castable, fast-curing branched aliphatic polyester polyurethane is prepared from a reaction mixture of an aliphatic organic diisocyanate and a substantially equivalent proportion of polyol. The polyol contains polyester, which may include polycarbonate, segments and may further comprise a low molecular weight diol chain extender, e.g. one containing up to 10 carbon atoms. Sufficient catalyst is added to cure the polyurethane composition before the diisocyanate deteriorates the rigid plastic surface. Butyl stannoic acid is preferred because it provides rapid cure at elevated temperatures with good pot life at lower temperatures according to U.S. Patent No. 4,131,605 the disclosure of which is incorporated herein by reference.

The diisocyanate is preferably a cycloaliphatic diisocyanate such as for example 4,4'-methylenebis-(cyclohexyl isocyanate). Polyurethanes prepared from aliphatic isocyanates, particularly cycloaliphatic diisocyanates, have high impact resistance over a wide temperature range and are not adversely affected by ultraviolet light. In addition to the most preferred diisocyanate, 4,4'-methylene- bis-(cyclohexyl isocyanate), other suitable aliphatic diisocyanates are 1,4 cyclohexyl diisocyanate, 4,4' isopropylidene-bis-(cyclohexyl isocyanate), isophorone diisocyanate, and other dinuclear cycloaliphatic diisocyanates formed through an alkylidene bridging group of from 1 to 3 carbon atoms.

Polyols useful according to the present invention may be liquid at room temperature or soluble in the reaction mixture. Preferred polyols include polycaprolactone diols and triols of molecular weight about 300 to 2000, polybutylene adipate diols and polycarbonate diols of molecular weight about 100 to 2000. Preferred chain extenders include such low molecular weight polyols as for example 1,4 butanediol, 1,6 hexanediol, 1,12 dodecanediol and 1,4 cyclohexanedimethanol. The combination and molecular weights of polyols are chosen to meet the criterion that the branched polyurethanes formed therefrom are abrasion-resistant and have a molecular weight between branch points of from about 400 to 13,000, preferably above about 3200, more preferably above about 6000.A particularly preferred polyol comprises polycaprolactone triol of molecular weight 300 to 1000 made by ring opening epsilon caproiactone with trimethylolpropane and polycaprolactone diol of molecular weight about 300 to 1200.

The aliphatic diisocyanate and polyol are preferably mixed together under vacuum in a reaction kettle until the reaction mixture is single phase and well degassed. The reaction mixture further comprises a catalyst, preferably butyl stannoic acid when the mixture is to be cast by gravity feed and pot life is important, dissolved in a polyol compatible with the reaction mixture. The catalyst is preferably added to a level of about 100 to 1000 parts per miliion based on the weight of isocyanate polyol reaction mixture and is most preferably dissolved in the reactant polyol.

The reaction mixture is preferably cast into a mold comprising a ply of a rigid plastic such as polycarbonate, acrylic or rigid polyurethane spaced from a second ply, typically glass coated with a material from which the polyurethane will release. The reaction mixture is then cured in place against the rigid plastic sheet at temperatures from about 175 to 2750F (about 79 to 1 350C), preferably about 2250F (about 1 070C) for about 1 hour or longer to yield an abrasion resistant coating preferably about 5 to 50 mils (about 0.1 to 1.3 millimeters) on the plastic sheet without warpage or interface deterioration from diisocyanate typically resulting from longer exposures at such temperatures.

The present invention will be more fully understood from the descriptions of the illustrative specific examples which follow.

EXAMPLE I The following components are mixed together to yield a colorless, transparent, single phase, low viscosity reaction mixture at room temperature: Equivalent Equivalent Weight Component Weight Ratio Percent Polycaprolactone triol 102.6 0.22 5.9 Polycaprolactone diol 270 0.73 51.9 Polycaprolactone diol 505 0.05 7.5 (containing 1 percent butyl stannoic acid) 4,4'-methylene-bis-(cyclohexyl isocyanate) 131 1.00 34.6 The reaction mixture is cast into a mold comprising an 1/8 inch (about 3 millimeters) thick polycarbonate sheet and a release coated glass sheet. The reaction mixture cures to form an abrasion resistant polyurethane which has a calculated urethane content of about 1 5.7 percent and a theoretical molecular weight between branch points of about 3400.

EXAMPLE II A polyurethane composition is cast onto polycarbonate and cured at elevated temperature for use as an interior surface-of an aircraft transparency. The composition comprises: Molecular Weight Component Weight Percent Polycaprolactone triol 900 17.59 Polycaprolactone diol 550 43.91 Polycaprolactone diol (containing 1% butyl stannoic acid) 1000 7.22 4,4'-methylene-bis-(cyclohexyl isocyanate) 262 31.28 The resulting polyurethane has a urethane content of about 14.1 percent, a molecular weight between branch points of about 2510, no hard segment and a Shore A durometer value of 56 at 700F (21 OC). The coating exhibits a haze increase of only 0.9 percent after 1000 cycles on a Taber Abraser.

EXAMPLE Ill A polyurethane composition is cast and cured as in the previous example for use as an interior surface of an aircraft transparency. The composition comprises: Molecular Weight Component Weight Percent Polycaprolactone triol 900 9.34 Polycaprolactone diol 1200 48.13 1,4 butanediol 90 6.98 Butyl stanoic acid (dissolved in above 1,4 butanediol) .06 4,4'-methylene-bis-(cyclohexyl isocyanate) 262 35.49 The resulting polyurethane has a urethane content of about 1 5.9 percent, a molecular weight between branch points of about 6600, 27.3 percent hard segment and a Shore A durometer value of 72. The coating exhibits a haze increase of 0.8 percent after 1000 cycles on a Taber Abraser compared with 31 percent for uncoated polycarbonate after only 100 cycles.

EXAMPLE IV A polyurethane composition is cast and cured as in the previous examples. The composition provides a stiffer coating to reduce water spotting in exterior use and further comprises ultraviolet light and oxidation stabilizers. The composition comprises: Molecular Weight Component Weight Percent Trimethylolpropane 135 0.87 Polycaprolactone diol 1000 46.45 Cyclohexanedimethanol 144 12.83 Butyl stannoic acid (dissolved in above cyclohexane dimethanol) - 0.06 4,4'-methyiene-bis-(cyclohexyl isocyanate) 262 37.80 Tinuvin 328 (substituted benzotriazole ultraviolet light stabilizer) - 1.0 Irganox 1035 (high molecular weight, hindered phenolic antioxidant) - 1.0 The resulting polyurethane has a urethane content of about 17.0 percent, a molecular weight between branch points of about 10,500, a hard segment of about 39.4 percent and a Shore A durometer value of 67. The coating exhibits a haze increase of 2.2 percent after 300 cycles on a Bayer Sand Abrader.

EXAMPLE V A polyurethane composition comprising the following components is prepared for use as in Example IV.

Molecular Weight Component Weight Percent Trimethylolpropane 135 0.98 Polycaprolactone diol 1000 37.52 Cyclohexanedimethanol 144 16.65 Butyl stannoic acid (dissolved in above cyclohexane dimethanol) - 0.06 4,4'-methylene-bis-(cyclohexyl isocyanate) 262 42.79 Tinuvin 328 - 1.0 Irganox 1035 - 1.0 The resulting polyurethane has a urethane content of about 1 9.3 percent, a molecular weight between branch points of about 9400, a hard segment of about 50.5 percent and a Shore D durometer value of 80. The coating exhibits a haze increase of 8.1 percent after 300 cycles on a Bayer Sand Abrader.

EXAMPLE VI A polyurethane composition comprising the following components is cast and cured as in the previous examples: Molecular Weight Component Weight Percent Polycaprolactone triol 900 50.27 1,4 butane diol 90 6.40 4,4'-methylene-bis-(cyclohexyl isocyanate) 262 41.75 Polycaprolactone diol (containing 1% butyl stannoic acid) 1000 1.57 The resulting polyurethane has a urethane content of about 1 8.5 percent, a molecular weight between branch points of about 1200, a hard segment of about 24.8 percent and a Shore D durometer value of 62 at 700F (21 bC). The coating exhibits a haze increase of 9.0 percent after 300 cycles on a Bayer Sand Abrader.

The above examples are offered to illustrate the present invention. Various modifications, such as the coating of other rigid plastics, such as acrylic and rigid polyurethanes, are included within the scope of the invention, which is defined by the following claims.

Claims

1. A method for making an abrasion resistant polyurethane coated rigid plastic transparency comprising the steps of: a. preparing a single phase liquid reaction mixture comprising an aliphatic diisocyanate and a substantially equivalent amount of polyol such that the resulting polyurethane has a durometer value at 21 OC of from Shore A 50 to Shore D 80 and a molecular weight between branch points of from about 400 to about 13,000; b. casting said reaction mixture into a mold having a cavity at least about 5 mils (0.1 millimeters) thick and comprising one ply of a rigid transparent plastic to which the polyurethane coating will adhere; and c. curing said reaction mixture at a sufficiently rapid rate to form an abrasion resistant polyurethane coating with substantially no warpage or degradation of the rigid plastic ply.

2. A method according to claim 1 wherein the polyol comprises a polyester diol or triol, polycarbonate diol or triol, a monomeric polyol or mixtures thereof.

3. A method according to claim 1 wherein the polyol comprises a polycaprolactone diol or triol of molecular weight 300 to 2000, polybutylene adipate diol, polycarbonate polyol of molecular weight 100 to 2000, butanediol, 1,6 hexanediol, 1,12 dodecanediol, cyclohexane dimethanol or trimethylolpropane.

4. A method according to any of claims 1 to 3, wherein the aliphatic diisocyanate is 4,4'methylene-bis-(cyclohexyl isocyanate).

5. A method according to claim 4 wherein the polyol comprises a polycaprolactone triol of molecular weight 300 to 900 or a polycaprolactone diol of molecular weight 500 to 1200.

6. A method according to any of claims 1 to 5 wherein the rigid plastic is polycarbonate, acrylic or polyurethane having a Shore D durometer value of greater than about 85 at about 21 OC.

7. A method according to any of claims 1 to 6 wherein the reaction mixture includes a catalyst.

8. A method according to claim 7 wherein the catalyst is added to a level of about 100 to about 1000 parts per million.

9. A method according to claim 7 or 8 wherein the catalyst is dissolved in the reactant polyol.

10. A method according to claim 7, 8 or 9 wherein the catalyst is butyl stannoic acid.

11. A method according to any of claims 1 to 10, wherein the ply of rigid transparent plastic is spaced from a ply from which the polyurethane will release.

12. A method according to any of claims 1 to 11 , wherein the reaction mixture is cured at from about 790C to about 1 350C for at least one hour.

13. A method according to claim 12 wherein the reaction mixture is cured at about 1 070C.

14. A method according to any of claims 1 to 13 wherein the coating is about 0.1 to about 1.3 millimeters thick.

1 5. A method according to any of claims 1 to 14 wherein the polyurethane has a molecular weight above about 3200.

16. A method according to claim 1 5 wherein the molecular weight is above about 6000.

17. A method of making an abrasion resistant polyurethane coated rigid plastic transparency, substantially as herein described with reference to and as illustrated in any of the Examples.

1 8. An abrasion resistant polyurethane coated rigid plastic transparency prepared according to the method of any of claims 1 to 17.