GB2117273A

GB2117273A - Color stabilized water- dispersed polyurethane coating on vinyl surfaces

Info

Publication number: GB2117273A
Application number: GB08307245A
Authority: GB
Inventors: Peter Loewrigkeit; Shmuel Dabi
Original assignee: Witco Chemical Corp
Current assignee: Witco Corp
Priority date: 1982-03-26
Filing date: 1983-03-16
Publication date: 1983-10-12
Also published as: DE3310966A1; NL8300776A; BE896256A; FR2523991A1; IT1163163B; NL188755B; GB2117273B; DE3310966C2; IT8320303A0; FR2523991B1; GB8307245D0

Abstract

A polyurethane coated polyvinyl chloride or vinyl chloride co-polymer which resists discoloration is provided by coating the substrate surface with an aqueous dispersed polyurethane treated with a mono-acid halide, mono-acid anhydride, carbethoxy cyclic imide or monoisocyanate. The coated composite even when subjected to temperatures in excess of 100 degrees C for extended periods resists discoloration and remains thermo-color stable with extended use.

Description

SPECIFICATION Color stabilised polyurethane coated vinyl chloride polymer or copolymer This invention relates to aqueous based polyurethane coatings on polyvinyl chloride or Co- polymer substrates. More particularly, this invention relates to providing an aqueous based polyurethane coating on the polymer substrate wherein the composite resists discloration at temperatures of 1000 to 1500C.

Generally, films of aqueous polyurethane dispersions tend to become discolored on heat aging at temperatures up to about 1500C, but are quite color stable at temperatures up to about 700 to 1000C. Vinyl chloride polymers on the other hand, are generally color stable, even at temperatures of 1 50C for extended periods.

When a vinyl chloride polymer is coated with an aqueous based (water soluble or dispersible) polyurethane, however, the composite discolors at temperatures as low as 700C.

In Hermann, U.S. 3,923,713, granted December 2, 1975, it is proposed to add organic monoisocyanate, an antioxidant and a U.V.

absorber to a urethane adhesive for plastic bonding to prevent gas-fade yellowing. Such use achieved a certain level of stability for the adhesive.

The art desired that a urethane as a coating be provided to a polyvinyl chloride or copolymer surface, which coating as well as the substrate would not discolor with extended use, or when subjected to high temperatures during and after the manufacturing process.

It would therefore be desirable to provide a urethane coated polyvinyl chloride or copolymer in which discoloration at temperatures up to about 1500C is not a problem.

Broadly speaking, the present invention may be said to comprise adding a compound selected from: (1) a mono-acid halide; (2) an acid anhydride; (3) a carbethoxy cyclic imide; and (4) a mono-isocyanate; to an aqueous urethane latex, and applying same to a polyvinyl chloride surface, to produce a urethane coated polyvinyl chloride or copolymer composite which is resistant to thermal discoloration. The foregoing compounds are amine capping or blocking agents and represent those compounds which are effective in the present invention. The mechanism involved is not completely understood, however it is considered that one function of these compounds is the capping of whatever amines are present in the polyurethane latex.

Therefore, in one aspect there is provided a color stabilized polyurethane coated polyvinyl chloride or vinyl chloride copolymer surface, the polyurethane and the polyvinyl chloride each being substantially color stable at above 1000C but becoming discolored at 1000C when combined, comprising: the polyvinyl chloride or copolymer surface; and a coating cured on the surface, the coating comprising a water-dispersed latex of the polyurethane, the dispersed polyurethane being treated with at least one treatment compound selected from a mono-acid halide, mono-acid anhydride, carbethoxy cyclic imide or mono-isocyanate.

In another aspect, the present invention may broadly be said to comprise a method for providing the present color-stable urethane coated vinyl chloride polymer, whereby a water soluble or dispersible isocyanate terminated prepolymer is dispersed in water and treated with a mono acid halide, monoacid anhydride, a monoisocyanate, a carbethoxy cyclic imide, or mixtures thereof. This latex product is then coated onto a polyvinyl chloride or copolymer surface and cured thereon.

Thus, a second aspect of the invention provides a method of preparing a color stabilized polyurethane coated polyvinyl chloride or vinyl chloride copolymer surface, the polyurethane and the polyvinyl chloride or copolymer each being substantially color stable at above 1000C but becoming discolored at 1000C when combined, the method comprising: a. preparing a water dispersion or latex of the polyurethane; b. treating the dispersed polyurethane of step (a) with one or more of a mono-acid halide, mono-acid anhydride, carbethoxy cyclic imide or monoisocyanate; c. applying the product of step (b) to the polymer surface; and d. drying the coating on the surface.

In another aspect, the present invention may broadly be said to comprise a method for providing a non-discoloring urethane coated polyvinyl chloride surface, said method comprising dispersing an isocyanate terminated prepolymer in water and rapidly adding less than a stoichiometric amount of a polyamine as a chainextender and then treating the resultant product with one or mixtures of a mono-acid halide, mono-acid anhydride, carbethoxy cyclic imide and mono-isocyanate. The final latex is applied to a polyvinyl chloride surface and cured on said surface to form a color stabilized urethane coated polymer composite.Although the polyamine competitively reacts with the --NCO much faster than water, when the --NCO terrminated prepolymer is dispersed in water some amine terminated urethane is formed regardless of the rapid addition of the amine chain extender.

Accordingly, a third aspect of the invention provides a method of preparing a color stabilised polyurethane coated polyvinyl chloride or vinyl chloride copolymer, the polyurethane and the polyvinyl chloride each being substantially color stable at above 1000C but becoming discolored at 1000C when combined, the method comprising: a. preparing a water dispersion or latex of an isocyanate terminated prepolymer; b. rapidly adding less than a stoichiometric amount of a polyamine as a chain exender to give the polyurethane as a latex; c. treating the dispersed polyurethane of step (b) with one or more of a mono-acid halide, mono-acid an hydride, carbethoxy cyclic imide or monoisocyanate; d. applying the product of step (c) to the polymer surface; and e. drying the coating on the surface.

The compounds useful pursuant to the invention, to be added to the water dispersed polyurethane, include (1) a mono-acid halide, preferably a mono-acid chloride, such as paratoluene-sulfonyl chloride, but also benzoyl chloride, butyryl chloride or hexanoyl chloride; (2) an acid anhydride, such as the mono-acid an hydrides, including acetic anhydride, propionic anhydride, butyric anhydride, and benzoic anhydride; (3) a carbethoxy cyclic imide, particularly the substituted imides and most preferably aryl mono-imides, such as Ncarbethoxy pthalimide; and (4) a monoisocyanate, both alkyl and aryl isocyanates such as phenyl isocyanate, p-chlorophenyl isocyanate cyclohexyl isocyanate or octadecyl isocyanate.

Also, the reaction product of polyisocyanate with a mono-alcohol to form a monoisocyanate. The aforesaid compounds are effective in very small amounts of from about 1 to 5% by weight and as low as 1 to 3% by weight based on the weight of the polyurethane in the latex. Larger quantities do not appear to impart any additional advantage.

By the present invention, both the polyvinyl chloride or copolymer substrate and the polyurethane to be coated thereon are relatively thermally color-stable. However, when the polyurethane is not treated as described herein, the coated composite is not color-stable. It is indeed surprising and unexpected that only certain capping compounds as herein described are effective in the present color-stable composite.

To prepare the polyurethanes, any polyisocyanate may be used. Typical aromatic polyisocyanates include m-phenylene diisocyanate, p-phenylene diisocyanate, polymethylene polyphenyl isocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, dianisidine diisocyanate, ditolylene diisocyanate, naphthalene-1 ,5-diisocyanate, diphenylene -4,4'diisocyanate; such as xylylene-1 ,3-diisocyanate, bis(4-isocyanatophenyl) methane, bis(3-methyl4-isocyanatophenyl) methane, 4,4'diphenylpropane diisocyanate; and aliphatic diisocyanates, such as isophorone diisocyanate, hexamethylene diisocyanate, and 4,4' (isocyanato cyclohexyl) methane.

Preferred aromatic polyisocyanates used in the practice of the invention are 2,4- and 2,6-toluene diisocyanates and methylene bridged polyphenyl polyisocyanate mixtures which have functionality of from about to about 4.

The polyhydroxyl compounds of polyols can be either low or high molecular weight materials and in general will have average hydroxyl values as determined by ASTM designation E-222-67, method B, between about 1000 and 10, and preferably between about 500 and 50. The term "polyol" is meant to include materials having an average of two or more hydroxyl groups per molecule.

The polyols include low molecular weight diols, triols and higher alcohols, low molecular weight amide containing polyols and higher polymeric polyols such as polyester polyols, polyether polyols and hydroxy-containing acrylic interpoiymers.

The low molecular weight diols, triols and higher alcohols useful in the instant invention are known in the art. They have hydroxyl values of 200 or above, usually within the range of 1 500 to 200. Such materials include aliphatic polyols, particularly alkylene polyols containing from 2 to 1 8 cabon atoms. Examples include ethylene glycol, 1,4-butanediol, 1,6-hexanediol; cycioaliphatic polyols such as 1,2cyclohexanediol, cyclohexane dimethanol and higher alcohols include trimethylol propane, dimethylol propionic acid, glycerol and oxyalkylate glycerol.

When flexible and elastomeric properties are desired, the partially reacted NCO-containing polymer should preferably contain at least a portion of a higher molecular weight polymeric polyol. Such a polymeric polyol should be predominantly linear (that is, absence of trifunctional or higher functionality ingredients) to avoid gelling of the resultant polymeric product and should have a hydroxyl value of 200 or less, preferably within the range of about 1 50 to 30.

Any suitable polyalkylene ether polyol may be used including those which have the following structural formula:

where the substituent R is hydrogen or lower alkyl including mixed substituents, and n is typically from 2 to 6 and m is from 2 to 100 or even higher. Included are poly(oxytetramethylene) glycols, poly(oxyethylene) glycols, polyoxy- propylene glycols and the reaction product of ethylene glycol with a mixture of propylene oxide and ethylene oxide.

Also useful are polyether polyols formed from the oxyalkylation of various polyols, for example, glycols such as ethylene glycol, 1 6-hexanediol, Bisphenol A, and the like or higher polyols, such as trimethylol propane, pentaerythritoi and the like. Polyols of higher functionality which can be utilized as indicated can be made, for instance, by oxyalkylation of compounds such as sorbitol or sucrose. One commonly utilized oxyalkylation method is by reacting a polyol with an alkylene oxide, in the presence of an acidic or basic catalyst.

Besides poly(oxyalkylene) glyols, any suitable polyhydric polythioether may be used, for example, the condensation product of thioglycol or the reaction product of a polyhydric alcohol, such as disclosed herein for the preparation of hydroxyl polyesters, with thioglycol or any other suitable glycol.

Polyester polyols are preferred as a polymeric polyol component in the practice of the invention.

The polyester polyols can be prepared by the polyesterification of organic polycarboxylic acids or anhydrides thereof with organic polyols.

Usually, the polycarboxylic acids and polyols are aliphatic or aromatic dibasic acids and diols.

The diols which are usually employed in making the polyester include alkylene glycols, such as ethylene glycol and butylene glycol, neopentyl glycol and other glycols such as hydrogenated Bisphenol A, cyclohexane diol, cyclohexane dimethanol, caprolactone diol (for example, the reaction product of caprolactone and ethylene glycol), hydroxyalkylated bisphenols, poly-ether glycols, for example, poly(oxytetramethylene) glycol. However, other diols of various types and, as indicated, polyols of higher functionality can also be utilized. Such higher polyols can include, for example, trimethylol propane, trimethylol ethane and pentaerythritol, as well as higher molecular weight polyols such as those produced by oxyalkylating low molecular weight polyols.An example of such high molecular weight polyol is the reaction product of 20 moles of ethylene oxide per mole of trimethylol propane.

The acid component of the polyester preferably consists primarily of monomeric carboxylic acids or anhydrides having 2 to 1 8 carbon atoms per molecule. Among the acids which are useful are phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, glutaric acid, chlorendic acid, tetrachlorophthalic acid, and other dicarboxylic acids of varying types.

Larger amounts of a monobasic acid such as benzoic acid may be combined with sucrose to make effectively polyfunctional sucrose benzoate.

This polyfunctional material can then be reacted with various other ingredients and isocyanates to form polyurethanes having enhanced durability.

Also, there may be employed higher polycarboxylic acids such as trimellitic acid and tricarballylic acid (where acids are referred to above, it is understood that the anhydrides of those acids which form anhydrides can be used in place of the acid). Also, lower alkyl esters of acids such as dimethyl glutarate can be used. It is preferred that the polyester include an aliphatic dicarboxylic acid as at least part of the acid component.

The amines which can be employed in chain extending the present aqueous polyurethanes can be primary or secondary (having an available H) diamines or polyamines in which the radicals attached to the nitrogen atoms can be saturated or unsaturated, aliphatic alicyclic, aromatic, aromatic-substituted aliphatic, aliphaticsubstituted aromatic or heterocyclic. Mixed amines in which the radicals such as, for example, aromatic and aliphatic can be employed.

Exemplary of suitable aliphatic and alicyclic diamines are the following: ethylene diamine, 1,2propylene diamine, 1,8-menthane, diamine, isophorone diamine, propane-2,2-cyclohexyl amine, methane-bis-(4-cyclohexyl amine), and

wherex=1 to 10.

Aromatic diamines such as the phenylene diamines and the toluene diamines can be employed. Exemplary of the aforesaid amines are: o-phenylene diamine and p-tolylene diamine. Nalkyl and N-aryl derivatives of the above amines can be employed such as, for example, N,N'dimethyl-o-phenylene diamine, N,N'-di-p-tolyl-m phenylene diamine, and p-aminodiphenylamine.

Polynuclear aromatic diamines can be employed in which the aromatic rings are attached by means of a valence bond, such as, for example, 4,4'-biphenyl diamine, methlene dianiline and monochloromethylene dianiline.

As known in the art, the amount of polyamine may be up to 100% equivalent of NCO groups present in the prepolymer, but it is preferred to employ less than the stoichiometric amount.

Excess polyamine may be added but serves no useful purpose in this invention.

Vinyi substrates usefuj pursuant to the present invention include the broad range of vinyl chloride polymers and copolymers with vinyl acetate or acrylic acid, for instance, or vinylidene chloride, as well known in the art. Surprisingly, it was found that polyvinyl chloride and copolymer substrates which were not first heat stabilized were nevertheless rendered color stable by the urethane coating of the present invention.

When the aforedescribed coating is applied to the polyvinyl chloride or copolymer substrate, with or without the known stabilizers such as the cadmium/barium type, for instance, no significant discoloration occurs and both the coating and substrate remain color stable with heat aging, as shown in the following specific examples.

Example I Hydroxy terminated poly hexanediol adipate, having an OH number of 112, weighing 1 99g was melted at 800 C. Dimethylol propionic acid, 24.6g, and 4,4'-di(isocyanato cyclohexyl)-methane, 1 52g, were added and the temperature was reduced to 600C. Acetone, 95.39 and triethylamine 18.69 were charged. The mixture was stirred at 650C for 4 hours, to give a prepolymer with 3.3% freee NCO. The prepolymer was dispersed in 750g water and further chain extended with 7.59 ethylenediamine.

A. A sheet of dried film cast from the foregoing dispersion did not become discolored after aging for 5 days at 1 000C in a convection oven.

B. A sheet of white plasticized P.V.C. which also did not discolor after aging for 5 days at 1 000C in a convection oven, was coated with the resulting latex, then aged at 1 000C. After 24 hours, the composite turned yellow, and after 4 days it turned to purple.

C. The above latex was treated with 9.4g of phenyl isocyante (PhNCO) (2.3% based on solid polymer), at room temperature for one hour and coated on the same P.V.C. used in B above. No discoloration was noted after aging for 5 days at 1 000C. Slight yellowing appeared only after 7 days at this temperature.

Example II A latex as in Example I was coated on light brown P.V.C. and aged at 1000C for seven days.

The light color became very dark. When the latex was treated, as in Example I, with 1.0% ptoluene-sulfonyl)-chloride (in place of the PhNCO), no change in color was noted after 8 days at 1000C.

Example Ill Toluene diisocyanate (TDI) was partially reacted with methanol (1:1 molar ratio) to leave one free NCO group capable of reacting with amine end groups. When added to the urethane latex in Example I, this product reduced discoloration of the vinyl composite as effectively as PhNCO.

Example IV Example I was repeated, substituting 1% Ncarbethoxy-phthalimide for the PhNCO. The treated urethane was coated onto a copolymer of vinyl chloride and vinyl acetate. The coated substrate was tested at 1000C for seven days. No significant discoloration was observed.

Example V Example I was repeated, adding 1 0g of adipic acid dihydrazide and 7.5g ethylenediamine to chain-extend the dispersed polyurethane. The resultant latex was treated with butyric anhydride in place of phenyl isocyanate and coated on a P.V.C. substrate. The composite resisted thermal discoloration as in Example I.

Other known capping compounds, such as ethylene carbonate, phenylchloroformate, and butyrolactone, for instance, were added to the latex of Example I. After testing at 1000C for several days, both the coating and the substrate (composite) had discolored in each case.

In addition to the components mentioned above, the compositions ordinarily contain optional ingredients, including any of the various pigments ordinarily utilized in coatings of this general class. In addition, various fillers, plasticizers, anti-oxidants, flow control agents, surfactants, cross-linking agents and other such formulating additives can be employed in many instances.

The urethane compositions herein can be applied by any conventional method, including brushing, dipping, flow coating electrodeposition, electrostatic spraying, and the like, but they are most often applied by air spraying. The usuals spray techniques and equipment are utilized. The coatings of the present invention can be applied over virtually any vinyl substrate.

Included herein by reference is the priority application , USSN 362330, a copy of which is filed herewith.

Claims

1. A color stabilized polyurethane coated polyvinyl chloride or vinyl chloride copolymer surface, the polyurethane and the polyvinyl chloride each being substantially color stable at above 1000C but becoming discolored at 1000C when combined, comprising: the polyvinyl chloride or copolymer surface; and a coating cured on the surface, the coating comprising a water-dispersed latex of the polyurethane, the dispersed polyurethane being treated with at least one treatment compound selected from a monoacid halide, mono-acid anhydride, carbethoxy cyclic imide or mono-isocyanate.

2. A coated surface as claimed in Claim 1, wherein the treatment compound is present in an amount of from 1 to 3% by weight based on the weight of the latex.

3. A coated surface as claimed in Claim 1 or Claim 2, wherein the treatment compound is a monoisocyanate.

4. A coated surface as claimed in Claim 1 or Claim 2, wherein the treatment compound is Ncarbethoxy phthalimide.

5. A coated surface as claimed in Claim 1 or Claim 2, wherein the treatment compound is ptoluene sulfonyl chloride.

6. A method of preparing a color stabilized polyurethane coated polyvinyl chloride or vinyl chloride copolymer surface, the polyurethane and the polyvinyl chloride or copolymer each being substantially color stable at above 1 0000 but becoming discolored at 1000C when combined, the method comprising: a. preparing a water dispersion or latex of the polyurethane; b. treating the dispersed polyurethane of step (a) with one or more of a mono-acid halide, mono-acid anhydride, carbethoxy cyclic imide or monoisocyanate; c. applying the product of step (b) to the polymer surface; and d. drying the coating on the surface.

7. A method as claimed in Claim 6, wherein the compound used in step (b) is present in an amount of 1 to 3% by weight based on the weight of the latex or dispersion.

8. A method as claimed in Claim 6 or Claim 7, wherein the compound used in step (b) is a carbethoxy mono-cyclic imide.

9. A method as claimed in Claim 6 or Claim 7, wherein the compound used in step (b) is a monoisocyanate.

10. A method as claimed in Claim 6 or Claim 7, wherein the compound used in step (b) is ptoluene sulfonyl chloride.

11. A method of preparing a color stabilised polyurethane coated polyvinyl chloride or vinyl chloride copolymer, the polyurethane and the polyvinyl chloride each being substantially color stable at above 1 000C but becoming discolored at 1 000C when combined, the method comprising: a. preparing a water dispersion or latex of an isocyanate terminated prepolymer; b. rapidly adding less than a stoichiometric amount of a polyamine as a chain extender to give the polyurethane as a latex; c. treating the dispersed polyurethane of step (b) with one or more of a mono-acid halide, mono-acid anhydride, carbethoxy cyclic imide or monoisocyanate; d. applying the product of step (c) to the polymer surface; and e. drying the coating of the surface.

12. A method as claimed in Claim 11 wherein the compound used in step (c) is present in an amount of 1 to 3% by weight based on the weight of the polyurethane latex.

13. A method as claimed in Claim 11 or Claim 12 wherein the compound used in step (c) is as claimed in any one of Claims 8, 9 or 10.

14. A method of preparing a color stabilised polyurethane coated polyvinyl chloride, or vinyl chloride copolymer, substantially as described in any one of Examples I to III and V, or IV respectively.

1 5. A polyurethane coated polyvinyl chloride or vinyl chloride copolymer whenever made by a method as claimed in any one of Claims 6 to 14.