GB2131439A - Coating composition for polypropylene resins - Google Patents

Abstract

A coating composition for polypropylene resins is disclosed principally comprising a chlorinated polyolefin (I) obtained by chlorinating, to a degree within a range from 10 to 50 wt%, a polyolefin which is modified with one or two or more kinds of compounds selected from unsaturated polybasic carboxylic acids and their acid anhydrides and is of a saponification value between 6 and 60; and a compound or a resin (II) which has at least two epoxy groups per molecule.

Description

SPECIFICATION Coating composition for polypropylene resins This invention relates to a coating composition usable for protecting and beautifying a polypropylene resin such as polypropylene, an ethylene propylene copolymer, an ethylene propylenediene copolymer, and more particularly to a coating composition which is satisfactory in respect to adhesiveness to the polypropylene resin, appearance, gasoline-resistance, bending-resistance, shockresistance, moisture-resistance and water-resistance, when applied to a sheet or a moulded product made of the polypropylene resin.

Polypropylene resins are widely in use as industrial materials for various electrical household appliances and vehicle parts on account of their light weights and low prices in addition to their excellent properties with respect to, for example, chemical-resistance, ozone-resistance, heatresistance and water-resistance. The demands for them on these products are expected to greatly increase in the future. Despite such advantageous features, however, the applications of polypropylene resins are confined within a limited range. In the case of vehicle parts, for example, while efforts to reduce weight for energy-saving results in increased use of varied kinds of plastics year after year, the use of polypropylene resins still remains limited to some of the parts.One of the reasons hindering the polypropylene resins from a wider range of applications resides in the fact that the resin is non-polar and crystalline which make it extremely difficult to apply a coating or adhesive materials thereof. There has been a strong need, therefore, for some coating composition that excels in adhesiveness to polypropylene resins. Heretofore, application of a print or an adhesive to a polypropylene resin has been carried out through treatments such as a corona discharge process in an attempt to attain an improved adhesion. However, conventional methods have been incapable of uniformly treating a product having a complex surface shape. To solve this problem, therefore, there have been proposed varied kinds of primer coating compositions with good adhesion to polypropylene.These primers include, for example, primer compositions which comprise a cyclized rubber, an aromatic petroleum resin, an oil-soluble phenolic resin, a coumarone-indene resin and a chlorinated polyolefin as disclosed in Japanese Patent Publications No. Sho 49-18089 and No. Sho. 49-5214. However, they have had such shortcomings that their adhesion to an upper coating layer is insufficient although they have sufficient adhesion to the polypropylene and that their solvent resistance is insufficient even if they have sufficient adhesion to both the polypropylene and the upper coating layer. Products to be coated such as motor vehicles, autobicycles and the like adapted for outdoor use are desired these days to be coated with some coating material that has a strong gasoline resistance as well as strong adhesion and strong weather resistance.To meet this requirement, there have been proposed various coating compositions including, for example, a coating composition obtained by blending a chlorinated polyolefin, an acrylic copolymer containing a basic nitrogen and an epoxy resin as disclosed by Japanese Patent Application Laid-Open No. Sho 56-76433 and a coating composition obtained by blending epoxy resin with a copolymer of chlorinated polyolefin, an acrylic monomer containing a basic nitrogen and another acrylic monomer as disclosed by Japanese Patent Application Laid-Open No. Sho 56-50971. However, in order to obtain a satisfactory coating performance, the quantity of the chlorinated polyolefin contained in the coating resin must be reduced.As a result of this limitation, the compositions of the prior art have presented a problem in that they do not have sufficient adhesion to polypropylene resins in general although they have adequate adhesion to some specific polypropylene resins.

We have attempted to solve these problems. As a result of our research we noted the reactivity of carboxyl groups or acid an hydride groups upon epoxy groups. Then, we discovered that a coating composition principally comprising a chlorinated polyolefin (I) prepared by chlorinating, to a degree within a range from 10 to 50 wt.%, a polyolefin which is of a saponification value between 6 and 60 and which is denatured with one or two or more compounds selected from unsaturated polybasic carboxylic acids and their acid anhydrides and a compound or a resin (II) which has at least two epoxy groups per molecule has excellent gasoline resistance as well as excellent adhesion, appearance, bending-resistance, shock-resistance, moisture-resistance and water-resistance when applied to a polypropylene resin.The present invention has derived from that discovery.

Meanwhile, it has been known, from Japanese Patent Publication No. Sho. 50-10916, that a poly-a-olefin chlorine compound that contains carboxyl group is usable as a primer or a primary coating material. However, this compound does not have the required solvent-resistance.

The above stated chlorinated polyolefin (I) to be prepared in accordance with the invention by chlorinating a polyolefin which is denatured with one or two or more compounds selected from unsaturated polybasic carboxylic acids and their acid anhydrides can be manufactured in accordance with a suitable known method. In one example of such a known method, a polyolefin resin such as a crystalline polypropylene, an amorphous polypropylene, polybutene-1, polypentene-1,4methylpentene-1, a low density or high density polyethylene, and an ethylenepropylene copolymer is thermally fused either singly or in a state of mixture of two or more kinds of them. If necessary, its viscosity may be reduced by a thermal decomposition process.A polyolefin fused resin thus obtained is denatured with an unsaturated polybasic carboxylic acid or its acid anhydride in the presence of a radical-generating agent in either a batch process or a continuous process. The denatured resin is dispersed or melted in a chlorinated solvent. Following that, a reaction is carried out by blowing chlorine gas in at a temperature between 50 and 1 200C either in the presence of a catalyst or under irradiation of ultraviolet rays and under pressure or under atmospheric pressure to obtain the chlorinated polyolefin (I).

The radical-generating agent used in the denaturing reaction is for example, a peroxide such as di-tert-butyl peroxide, a tert-butyl hydroperoxide, dicumyl peroxide, benzoyi peroxide, tert-butyl peroxy benzoate, methyl ethyl ketone peroxide, a di-tert-butyl or di-perphthalate or an azo nitrile such as azobis-iso-butyro nitrile or azo-bis-iso-propio nitrile. The unsaturated poiybasic carboxylic acid and the acid an hydride used in the denaturing reaction are, for example, maleic acid, maleic anhydride, citraconic acid, citraconic an hydride, fumaric acid, mesaconic acid, itaconic acid, itaconic anhydride, aconitic acid and aconitic anhydride.

In accordance with this invention, the saponification value of the polyolefin denatured by the unsaturated carboxylic acid and its acid an hydride is at least 6 and preferably between 10 and 60. With a saponification value which is too low, the effect obtainable from bridging with the epoxy resin would be decreased and, as a result, the solvent resistance would lower. If the saponification value is too high on the other hand, the adhesion to polypropylene resins would degrade. The degree of chlorination of the chlorinated polyolefin (I) which is prepared by chlorinating the polyolefin denatured with the unsaturated polybasic carboxylic acid and its an hydride is between 10 wt% and 50 wt% and preferably within the range from 1 5 to 35 wt%.If the chlorination degree is lower than 10 wt% the condition in the form of a solution would degrade while, if the chlorination degree is higher than 50 wt.% adhesion to polypropylene resins would become insufficient.

The compound or resin (II) which has at least two epoxy groups per molecule and to be used in accordance with this invention preferably has good mutual solubility with the chlorinated polyolefin (I) which is obtained by chlorinating the polyolefin denatured with the unsaturated polybasic carboxylic acid anhydride. The compound of resin (II) may be selected from bis-phenol A or polyhydric alcohol of the glycidyl ether type such as ethylene glycol glycidyl ether, propylene glycol glycidyl ether, glycerol polyglycidyl ether and sorbitol polyglycidyl ether; a cycloaliphatic epoxy resin obtained by oxidizing an olefin with a per-acid; an acrylic epoxy compound obtained by copolymerizing glycidyl meta-acrylate and meta-acrylate; and other compounds or resins that have at least two epoxy groups in each molecule.

In accordance with this invention, the chlorinated polyolefin (I) obtained by chlorinating the denatured polyolefin which is denatured with the above stated unsaturated polybasic carboxylic acids and their acid anhydrides and the compound or resin (II) which has epoxy groups are blended preferably in the ratio expressed in part by weight of 100:0.5-50. If the compound or resin (II) having epoxy groups is in a ratio not exceeding 0.5, sufficient solvent-resistance cannot be obtained. If the ratio exceeds 50, the adhesion to sheets or molded products made of polypropylene resins would become too low.

Further, to promote and accelerate a bridging reaction between the epoxy groups and the carboxyl groups or acid anhydride groups, it is preferable to add some basic catalysts selected from tertiary amines such as pyridine, iso-quinoline, quinoline, N,N-dimethyl cyclohexyl amine, tri-ethyl amine, benzyl methyl amine, 1 ,8-diazobicyclo-undecen-7 and their amine salts; octylic acid tin oxide; and BF3-mono-ethylamine. The addition quantity of the additive is from 0.05 wt% to 5.0 wt% based on the solid content of the chlorinated polyolefin (I), though it is not limited to that range. In cases where the acid an hydride groups are employed, a polyol such as ethylene glycol, tri-methylol propane or polypropylene glycol, may be added as reaction initiator.As for drying of a coating applied, it is preferable to allow the coating film to harden at a temperature between room temperature and 1 500 C.

The solvent to be used for the coating composition according to the invention is most preferably an aromatic solvent. In addition to them, such solvents as esters, ketones and alcohols may be used in a state of being partly mixed in the solvent. Further, an inorganic pigment such as titanium dioxide or talc or an organic pigment may be also used.

It is a feature of the present invention to obtain a coating material system by bridging, with the compound or resin (II) having epoxy groups, the chlorinated polyolefin (I) which is obtained by chlorinating a polyolefin denatured by means of carboxyl groups or acid anhydride groups. The coating material system according to the invention has a strong adhesion to polypropylene resins which have been difficult to coat. Besides, it excels in other properties over conventional coating materials.

With the coating composition according to the present invention applied to the surface of a sheet or moulded product made of a polypropylene resin, a finished coat can be obtained with one coating process by drying the coating composition at a temperature between room temperature and 1 500C after allowing it to be dried by air at room temperature. The coating which is thus applied excels in appearance, solvent-resistance, water-resistance, chemical-resistance, bending-resistance and shockresistance. Besides, compared with other one coat finishing coating materials used for the same purpose, the coating compound according to the invention much excels in adhesion to the base material to which the coating is applied.This coating composition is not only applicable to polypropylene resins but also applicable to the base materials such as various plastics, wood and concrete.

The coating composition of the invention is also usable as a primary coating material. In that event, the coating material to be applied on top of the invented coating compound according to the present invention is preferably for example, urethane coating materials, epoxy resin coating materials and alkyd resin coating materials. Compared with a finish coat using the conventional primary coating material, the finish coat obtained with the coating composition according to the invention, thus used as primer excels in gasoline-resistance, moisture-resistance property, water-resistance, chemicalresistance, bending-resistance and shock-resistance. Besides, in that instance, it shows strong adhesion both to the base material and the upper or finish coating material.

The following examples further illustrate the present invention.

Example 1 A three-necked distillation flask which is equipped with a stirrer, a dropping funnel and a cooling tube for causing a monomer to flow back was employed. Into this flask was put 500 g of isotactic polypropylene the melt viscosity of which was about 2600 cps at 1 800 C. The polypropylene was completely melted in an oil bath which was kept at a constant temperature of 1 800 C. Nitrogen replacement of the inside of the flask was carried out for 10 minutes. After that, 20 g of maleic an hydride was poured over a period of five minutes with stirring. Then, 2 g of di-tert-butyl peroxide which was dissolved in 10 ml of heptane was poured from the dropping funnel over a period of about 30 minutes.At this time, the system thus arranged was kept at 1 800C. After the reaction was allowed to further continue for about one hour, non-reacted maleic anhydride was removed over a period of about 30 minutes while pressure inside the flask was reduced by means of an aspirator. The saponification value of the reaction product thus obtained was 26. Following that, 300 g of this product was put into a reaction boiler which is provided with glass lining. To this was added 5 1 of carbon tetrachloride. They were thoroughly dissolved at 11 O0C under pressure of 2 kg/cm2. After that, gaseous chlorine was blown in from the bottom of the reaction boiler with irradiation of ultraviolet rays until a chlorination degree of 24 wt% was obtained.Upon completion of the reaction, the carbon tetrachloride which was used as solvent was removed by evaporator and was replaced with toluene.

Through this process, a 20 wt% toluene solution of a chlorinated polypropylene which was denatured with the maleic anhydride was obtained.

Example 2 The same method as in Example 1 was carried out using 500 g of the same isotactic polypropylene, 30 g of maleic anhydride and 2 g of di-tert-butyl peroxide. By this, a maleic an hydride denatured polypropylene of a saponification value of 37 was obtained. After that, a chlorination reaction was carried out in a manner similar to Example 1 to obtain a 20 wt% toluene solution of the maleic anhydride denatured polypropylene of a chlorination degree of 24 wt%.

Example 3 500 g of the isotactic polypropylene which was used in Example 1, 40 g of maleic anhydride and 3 g of di-tert-butyl peroxide were used. In this case, the maleic anhydride and the di-tert-bytyl peroxide were graduaily and simultaneously added over a period of about 30 minutes. With the exception of that, the same method as in Example 1 was carried out to obtain a polypropylene which was denatured with a maleic anhydride and was of a saponification value of 49. Then, a chlorination reaction was carried out in a manner similar to Example 1 to obtain a 20 wt% toluene solution of a maleic anhydride denatured, chlorinated polypropylene of a chlorination degree of 26 wt%.

Example 4 500 g of an ethylene-propylene copolymer which contains 4.2 wt% of ethylene and was of melt viscosity about 5000 cps at 1 800 C; 30 g of maleic anhydride; and 3 g of di-tert-butyl peroxide were used. The maleic anhydride and the di-tert-butyl peroxide were simultaneously and gradually added over a period of about 30 minutes at a reaction temperature of 200"C. With the exception of that, the same method was carried out as in Example 1 to obtain a maleic anhydride denatured ethylenpropylene copolymer. The saponification value of this denatured copolymer was 32. Then, a chlorination reaction was carried out in a manner similar to the reaction carried out in Example 1. A 20 wt% toluene solution of a chlorinated ethylene-propylene copolymer which was denatured with a maleic anhydride was obtained.The chlorination degree of this product was 24 wt%.

Example 5 A sand mill was used. 30 g of titanium dioxide was mixed in 350 g of the chlorinated product (a 20 wt% toluene solution) obtained in Example 2. Then, a pigment was dispersed by operating the sand mill over a period of one hour. After that, 11 g of "Epikote 828" (a product of Shell Chemical Co., Ltd.) which was an epoxy resin and was a condensate of bisphenol A and epichloro-hydrine of epoxy equivalent between 1 84 and 1 94 was added. Further added was 7 g of a 10 wt% xylene solution of an amine catalyst called U-Cat-SA-No. 1 02 (a product of San-Abbot Co., Ltd.) which was used as a reaction promoter. A product which was thus obtained was diluted to a suitable viscosity and was sprayed upon a polypropylene plate (2x50x80 mm) the surface of which had been washed with toluene.The sprayed coating was allowed to air dry at room temperature for 1 5 minutes and, after that, was forcedly dried at 130"C over a period of 30 minutes. It was then left intact at room temperature for 7 days. The coating thus obtained was then subjected to tests to obtain test results as shown in Table 1.

Example 6 350 g of the chlorinated product (a 20 wt% toluene solution) which was obtained in Example 2 and 30 g of titanium dioxide were mixed. A pigment was dispersed by operating a sand mill for one hour. After that, 10 g of an epoxy resin called "Denacol Ex-61 1" (a product of Nagase a Co., Ltd.) which was a sorbitol-poly-glycidyl ether and was of epoxy equivalent 1 70 and which was dissolved in 20 g of ethyl acetate was added. Then, 7 g of a 10 wt% xylene solution of "U-Cat-SA-No. 102" was added as a reaction promoter. A test plate was prepared in the same manner as in Example 5. The coating thus applied to the test plate was subjected to tests, the results of which were as shown in Table 1.

Example 7 30 g of titanium dioxide was mixed in 350 g of the chlorinated product (a 20 wt% toluene solution). A pigment was dispersed by means of a sand mill for one hour. Following this, 10.4 g of "Chisso NOX CX-22 1" (a product of Chisso Co., Ltd.) which was a cyclic aliphatic epoxy resin of epoxy equivalent 131-145 was added. Then, 7 g of a 10 wt% xylene solution of "U-Cat SA-No. 102" was added as a reaction promotor. A reaction product thus obtained was diluted with an aromatic solvent to a suitable viscosity. The diluted product was then sprayed upon a polypropylene plate (2x50x80 mm) the surface of which had been washed with toluene. A sprayed coating thus obtained was allowed to dry at room temperature for about 30 minutes.After that, the coating was forcedly dried at 800C for 30 minutes and then was left intact at room temperature for a period of 7 days. Following that, the coating was subjected to tests to obtain test results as shown in Table 1.

Example 8 30 g of titanium dioxide was mixed in 350 g of the chlorinated product (a 20 wt% toluene solution) which was obtained in Example 4. A pigment was dispersed by means of a sand mill for one hour. Then, 7.8 g of an epoxy resin called "Denacol EX-42 1" (a product of Nagase a Co., Ltd) which was di-glycerol-poly-glycidyl ether of epoxy equivalent 1 55 and was dissolved in 20 g of ethyl acetate was added. 7 g of a 10 wt% "U-Cat SA-No. 102" was then added as a reaction promoter. A product thus obtained was diluted to a suitable viscosity with an aromatic solvent. The surface of a polypropylene plate measuring 2x50x80 mm was coated with the diluted product by spraying. The coating was allowed to air dry at room temperature for about 1 5 minutes.After that, the coating was forcedly dried at 1 200C for 30 minutes. Further, the coating was left intact at room temperature over a period of 7 days before it was tested. The test results were as shown in Table 1.

Comparison Example 1 30 g of titanium dioxide was mixed in 350 g of the chlorinated product (a 20% toluene solution) which was obtained in Example 2. A pigment was dispersed by operating a sand mill over a period of one hour. After that, the product was diluted to a suitable viscosity with an aromatic solvent.

Meanwhile, the surface of a polypropylene plate (2x50x80 mm) was washed with toluene. The plate was then coated with the diluted product by spraying. The coating thus obtained was allowed to air dry at room temperature for 1 5 minutes and then was forcedly dried at 1 300C for 30 minutes. Further, the coating was left intact over a period of 7 days. The dried coating was tested. Test results thus obtained were as shown in Table 1.

Comparison Example 2 30 g of titanium dioxide was mixed in 350 g of a 20 wt% toluene solution of a chlorinated polypropylene called "Superchlon 803L" (a product of Sanyo Kokusaku Pulp Co., Ltd), a chlorination degree was 26 wt%). A pigment was dispersed by operating a sand mill over a period of one hour.

Then, 11 g of "Epikote 828" was mixed in. To the mixture was added 7 g of a 10 wt% xylene solution of "U-Cat SA-No. 1 02" as a reaction promoter. The product thus obtained was diluted to a suitable viscosity with an aromatic solvent. Meanwhile, the surface of a polypropylene plate (2x50x80 mm) was washed with toluene. The diluted product was applied by spraying to the polypropylene plate to coat the latter. The coating thus applied was allowed to air dry at room temperature for about 1 5 minutes and, after that, was forcedly dried at 1 300C for 30 minutes. The coating was further allowed to air dry at room temperature over a period of 7 days before it was subjected to tests. Test results were as shown in Table 1.

Table 1 Comparison Comparison Example 5 Example 6 Example 7 Example 8 Example 1 Example 2 Adhesion (checkered, cellophane adhesive tape) 100/100 100/100 100/100 100/100 100/100 100/100 Gasoline resistance No abnor- No abnor- No abnor- No abnor- Coating Coating (Nisseki Regular) mality mality mality mality was dis- was dis happened happened happened happened solved solved Gloss (600 mirror) 91 90 91 93 92 90 reflection Pencil hardnass F H H H HB B Bending resistance Good Good Good Good Good Good Shock resistance Good Good Good Good Good Good Water resistance No abnor- No abnor- No abnor- No abnor- Decrease Decrease (500 C) mality mality mality mality in gloss in gloss Moisture resistance No abnor- No abnor- No abnor- No abnor- Decrease Decrease (500C, 98% RH) mality mality mality mality in gloss in gloss Test Procedures Adhesion: On the surface of the coating, 100 sections of a checkered pattern were cut into through the whole coating layer thickness at intervals of 1 mm. A cellophane adhesive tape was tightly applied to the checkered pattern and then was peeled off at an angle of 1 800. Then, the number of checker sections remaining not peeled was counted.

Gasoline resistance The coating was scratched to draw X marks deep through the whole coating layer thickness. The test plate was then immersed in an ordinary gasoline and was left there at 250C for two hours. The condition of the coating was examined after the lapse of two hours.

Bending resistance The coated test plate was bent 1 800 by means of a 1/2 inch diameter mandrel. Then, the condition of the coating was examined.

Shock resistance A dupont type impact tester was used. A hitting core of 1/2 inch with a load of 500 g were used.

It was allowed to fall from above at a distance of 50 cm for hitting on the surface and at a distance of 25 cm for hitting on the reverse side.

Water resistance The coated test plate was immersed in warm water of 500C over a period of 240 hours. The condition of the coating was examined after the end of the immersion period.

Moisture resistance The coated test plate was left at 500C and under an atmosphere of relative humidity exceeding 98% over a period of 240 hours. The condition of the coating was examined after the lapse of the test period.

Example 9 200 g of the chlorinated product (a 20 wt% toluene solution) which was obtained in Example 1, 4 g of titanium dioxide, 0.1 g of carbon black and 1.6 g of "Epikote 828" were mixed. A pigment was dispersed by operating a sand mill over a period of one hour. After that, the product which was thus obtained was diluted to a suitable degree with an aromatic solvent. A polypropylene plate which measured 2x50x80 mm was washed with toluene. The diluted product was then applied to the polypropylene plate by spraying to have a coating formed to a thickness between 5 and 10 y. After the lapse of several minutes, a two-liquid hardening type urethane paint (manufactured by Nippon Oils a Fats Co., Ltd) was then sprayed on top of the coating to make the coating thickness between 30 and 40 u. The coating was then allowed to air dry at room temperature for 1 5 minutes. A forced drying process was then carried out at 800C for a period of 30 minutes. After the forced drying, the coating was left intact at room temperature over a period of 24 hours before it was subjected to tests. The coating thus obtained excelled in gasoline resistance, bending resistance, shock resistance, moisture resistance, water resistance, etc. as well as in adhesion.

Claims (1)

1. Claims

   1. A coating composition comprising (I) a chlorinated polyolefin obtained by chlorinating a polyolefin, which is modified with at least one compound selected from unsaturated polybasic carboxylic acids and acid anhydrides thereof and has a saponification value of 6 to 60, in a range of 10 wt% to 50 wt% and (II) a compound and/or resin which has at least two epoxy groups per molecule thereof.

   2. A coating composition according to claim 1, wherein the carboxyl group and/or acid anhydride group of the chlorinated modified polyolefin (I) and the epoxy group of the epoxy group containing compound and/or resin (II) are subjected to a cross-linking reaction.

   3. A coating composition according to claim 2, wherein the cross-linking reaction is effected in the presence of a catalyst such as a tertiary amine.

   4. A coating composition according to claim 2, wherein the cross-linking reaction is initiated by addition of a polyol.

   5. A coating composition according to any of claims 1 to 4, which includes an aromatic hydrocarbon solvent optionally together with an ester solvent, ketone solvent or alcohol solvent.

   6. A coating composition according to any of claims 1 to 5, which includes an inorganic pigment such as titanium dioxide or talc.

   7. A coating composition according to any of claims 1 to 6 which is applied to a substrate comprising plastics, wood or concrete.

   9. A coating composition according to claim 7, applied to polypropylene.

   10. A coating composition according to claim 9 wherein the chlorinated modified polyolefin (I) and the epoxy group containing compound and/or resin (II) are contained in a weight ratio of 100:0.5-50.