GB2082606A

GB2082606A - Coated polycarbonate

Info

Publication number: GB2082606A
Application number: GB8125945A
Authority: GB
Original assignee: Anic SpA
Current assignee: Anic SpA
Priority date: 1980-08-29
Filing date: 1981-08-25
Publication date: 1982-03-10
Also published as: DE3134157C2; DK356881A; AT381322B; SE450002B; ZA815428B; NL8104013A; ATA374681A; JPS5775857A; IT8024354A0; CH655733A5; BR8105413A; BE890097A; GB2082606B; DE3134157A1; IT1141029B; FR2489345A1; FR2489345B1; DK163821B; NO156204B; NO812854L

Abstract

Improved coatings on polycarbonate are formed by polymerizing a mixture containing (1) an oligomer or a reactive resin having a molecular weight between 400 and 4,000 and containing at least two acrylic groups per molecule, and (2) an N-vinyl derivative of straight-chain or cyclic secondary amide, the polymerization being carried out in the presence of a photoinitiator.

Description

SPECIFICATION Coated polycarbonate This invention relates to coated polycarbonate such as coated polycarbonate of Bisphenol A.

Polycarbonates have excellent properties such as transparency, shock resistance and tensile strength.

However, the surface of polycarbonate has a poor resistance to abrasion and scratching and a poor resistance to solvents. More particularly, the surface of polycarbonate, due to the effect of weathering agents or even gentle contact with other materials, becomes scratched and tends to become opaque. Some methods have been suggested for overcoming these defects. These methods are based on the use of particular coatings based on siloxane or melamine resins. These coatings involve cost problems. Also, they are difficult to use and have unsatisfactory properties, since they are in the form of varnishes in solvents and generally require a heat treatment to bring about cross-linking, this treatment being such as to jeopardize the properties of the polycarbonate, more particularly the impact resistance thereof.

We have found a polycarbonate coating which has good properties as to adhesion, hardness and abrasion resistance.

According to the present invention, there is provided polycarbonate having on a surface thereof a coating of a copolymer of (a) an oligomer or reactive resin having a molecular weight of from 400 to 4000 and containing at least two acrylic groups, and (b) an N-vinyl derivative of a linear or cyclic secondary amine.

The present invention also provides a process for forming a coating on a surface of polycarbonate, which comprises coating the surface with a mixture of (a) an oligomer or reactive resin having a molecular weight of from 400 to 4000 and containing at least two acrylic groups, and (b) an N-vinyl derivative of a linear or cyclic secondary amide; and copolymerising the components of the mixture, in the presence of a photoinitiator, by exposure of the mixture to radiation.

The polymerisation mixture may contain, moreover, reactive compounds having a low molecular weight (less than 4000) and containing at least a functional group of acrylate type, methacrylate type, maleate type or fumarate type. Examples of such compounds are butanediol diacrylate, ethyl hexyl acrylate, dimethyl maleate, diethyl fumarate and ethylene glycol diacrylate.

The method of the invention as compared with conventional procedures, enables the mixture to be completely hardened at room temperature without modifying the properties of the polycarbonate, such as its shock resistance and its transparency.

The oligomer used is preferably (a) a urethane resin containing, at the ends of the molecule, at least two acrylic groups; (b) a resin obtained by oligomerising acrylic momomer(s) functionalised by at least two acrylic groups per molecule; or (c) a resin obtained by condensing a saturated or unsaturated dicarboxylic acid with a glycol and subsequently esterifying their terminal hydroxy groups with acrylic acid.

Examples of resins (a) above are the condensation product of one mol of hexamethylene diisocyanate with two mols of trimethylolpropane diacrylate; the condensation product of one mol of hexamethylene diisocyanate with two mols of hydroxyethyl diacrylate; and the condensation product of one mol of toluene diisocyanate with two mols of hydroxyethyl acrylate.

Examples of resins (b) above are an oligomer containing monomeric units deriving from the copolymerization of methyl acrylate, ethyl acrylate and glycidyl acrylate, the oligomer being reacted with an amount of acrylic acid which is stoichiometric relative to the glycidyl group, thus forming an acrylated acrylic resin; and an oligomer obtained by copolymerizing methyl acrylate with ethyl acrylate and 2-hydroxyethyl acrylate, the oligomer being reacted with acrylic acid to form an acrylated acrylic resin.

An example of resin (c) above is an oligomer obtained by condensation of maleic acid anhydride, adipic acid and ethylene glycol, the oligomer, which has two terminal hydroxy groups, being subsequently esterified with acrylic acid.

Examples of N-vinyl derivatives of straight-chain or cyclic secondary amides are N-vinyl pyrrolidone, N-vinyl caprolactam, N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl-propionamide and N-vinyl-N-methyl propionamide.

The quantity of N-vinyl compound which is present in the mixture is preferably from 5 to 60% by weight of the mixture.

The photoinitiators used are compounds capable of producing free radicals under the action of UV radiation. Examples of these are benzoin isopropyl ether, benzion ethyl ether, benzyl dimethyl ketal, benzophenone, 2,2-dimethyl-2-phenyl acetophenone, 2-chlorothioxanthone and anthraquinone.

The mixture is preferably spread on the polycarbonate by spreading, spraying or dipping. The thickness of the coating is preferably from 5 to 200 microns.

The UV radiation used for the cross-linking of the mixture can easily be produced by using mercury-vapour lamps overating under medium or high pressures. It is possible to use also other types of radiations (e.g.

electron rays and X-rays).

The possible uses for the coated polycarbonate are manifold. Thus, for example, they can be used as transparent slabs, machine parts and various other articles. As a matter of fact, the coated polycarbonate has the basic and inherent properties of the polycarbonates (i.e. shock resistance, transparency and resistance to high temperatures) and very good surface properties such as resistance to scratching, to abrasion, to solvents, to radiation and to hydrolysis, so that outdoor use of the composite material is possible, since it can withstand weathering agents and contact with other chemicals as well.

The invention will now be illustrated by the following Examples.

Example 1 A urethane-acrylic resin (Resin A), obtained by condensing one mol of hexamethylene diisocyanate with two mols of trimethylolpropane diacrylate, was used. The resin had a viscosity at 25"C of 13,500 cps and an acrylicfunctionality of 4. The resin was used to propose the following composition: Resin A . 80 parts by weight N-vinyl pyrrolidone . . 20 parts by weight Benzyl-methyl ketal . 5 parts by weight The mixture had a viscosity at 25"C of 830 cps. It was spread over sample plates cut from a planar extruded slab of a typical commercial polycarbonate so as to form a coating having a thickness of 30 microns. For this operation a film-spreader K-Control Coaterwith spiral bars was used.The coating was cross-linked by passing the sample plates in air through a UV tunnel equipped with a mercury vapour lamp having a power of 80 W/cm and placed at a distance of 11 cm from the surface to be cross-linked, the speed of the conveyor being 24 metres per minute. The surface hardness (König Hardness, FN Unichim No. 91) and the scratch resistance of the plates was measured as a function of the number of passes through the tunnel. The resistance to scratching was measured by reading the minimum load (in grams) which is necessary to scratch the surface with a diamond point with an angle of 1200 under conditions of a slow rectilinear motion.

The results given in the following Table were obtained.

TABLE 1 No. of passes König Hardness Resistance to scratching (s) (g) 2 169 26 4 170 29 8 176 32 12 178 33 16 181 34 20 185 35 It can be seen that the surface has a high hardness and a high resistance to scratching even after 2 passes.

The resistance to scratching of an uncoated sample plate was 6.2 g so that it can be appreciated that the coating considerably improves the resistance of the plates to scratching. The adhesion of the coating to the plates, measured after 20 tunnel passes was 100%. Also, the adhesion of adhesive tape to the coating (measurement through FN Unichim No.37 grid) was 100%. These two adhesion tests are referred to hereinbelow as "adhesion without tape" and "adhesion with tape", respectively. The resistance to shocks of the coated plates was equal to that (75 kg.cm/cm2) of the uncoated plates. The same is true of their transparency.

For determining the impact resistance of the plates, the Izod method, ASTM-D-256, was used.

Accelerated ageing tests were carried out in a Weatherometer (WOM) and by immersion of the plates in water. The results given in the following Table 2 were obtained.

TABLE 2 After 1,000 hours in the WOM Adhesion without tape 100% Adhesion with tape 100% Scratch resistance 379 Colour unaffected After 10 days in water at 23"C Adhesion without tape 100% Adhesion with tape 100% Scratch resistance 319 Colour unaffected It can thus be seen that there are no visible alterations in the plates during the ageing test and the water immersion test. The same tests were repeated, using a plate coated with a coating composed of resin A alone. The coating had the same properties as tabulated above, but its adhesion was zero. This shows that the presence of both the resin and the vinyl amide are necessary in order that the expected properties may be obtained.

The resistance of the coated plates to abrasion was measured with a Taber Abrasion-meter having CS 1 OF grinding wheels, according to ASTM-D10 44. A determination of the extent of abrasion was carried out by an optical method, namely the ASTM 1003 Haze test. The results which have been obtained for various cycles of treatment, employing plates coated with resin A and vinyl pyrrolidone, in comparison with a commercial polycarbonate coated with a siloxane varnish coating, given in the following Table 3.

TABLE 3 Haze test (%) No. of Polycarbonate + Resin Commercial cycles Resin A+vinyl pyrrolidone Polycarbonate 10 1.2 1.2 20 2.5 1.6 40 3.8 3.9 60 5.0 5.6 100 7.5 10.0 150 10.8 15.6 200 13.9 26.8 Polycarbonate as such, under these conditions, displays, even after 10 cycles, a value in the Haze test higher than 20%. These results show that the composition described above has a high abrasion resistance, namely a resistance which is higher than that of the commercial varnish coated articles.

Example 2 Using the same procedure as in the previous Example, a mixture having the following composition was prepared: Resin A . 50 parts by weight Vinyl pyrrolidone . . 50 parts by weight Benzyl dimethyl ketal 5 parts by weight The mixture had a viscosity at 25"C of 75 cps. It was spread on plates as used in Example 1 so as to form a coating having a thickness of 30 microns. After 20 UV-tunnel passes, the coating had the following properties: König Hardness .. . 176s Adhesion without tape . 100% Adhesion with tape . . 100% Resistance to scratching . 24 g.

The resistance to shock and the transparency of the coated sample plates were the same as those of the uncoated sample plates. When a different amount of the photoinitiator was used, and when a nitrogen atmosphere was used, the coated plates, after 20 passes, had the properties given in the following Table 4.

TABLE 4 Hardness Adhesion Resistance to without with scratching tape tape (s) (%) (%) (g) Benzyl dimethyl ketal 181 100 100 22 (2 parts) Benzyl dimethyl ketal 189 100 100 26 (2 parts) +N2 atmosphere It can be seen that, within the limits above, the concentration of the initiator and the presence of nitrogen do not involve any appreciable variations in the properties of the coated plates.

Example 3 The procedure was the same as in Example 1. A mixture having the following composition was prepared Resin A . 60 parts byweight N-vinyl caprolactam .. ....40 parts by weight Benzyl dimethyl ketal . .. 5 parts by weight The mixture had a viscosity at 25"C of 230 cps. It was spread on polycarbonate plates so as to form a coating having a thickness of 30 microns. After 20 UV-tunnel passes, the coating had the following properties: König Hardness . 180 s Adhesion without tape 100% Adhesion with tape 100% Resistance to Scratching 27 g.

The shock resistance and the transparency of the sample plates were the same as those of the pure polycarbonate.

Example 4 A mixture having the following composition was prepared: Resin A . 70 parts byweight N-vinyl pyrrolidone . . 15 parts by weight Methyl maleate . 15 parts by weig ht Benzoin ethyl ether 5 parts by weight The mixture was spread on polycarbonate plates in a thickness of 30 microns, and, upon cross-linking by 20 UV-tunnel passes, the coating obtained had the following properties: K6nig Hardness . 177s Adhesion without tape 100% Adhesion with tape . 100% Resistance to Scratching 28 g The shock resistance and the transparency of the plates were the same as those of uncoated polycarbonate.

Example 5 There is used a resin of acryl-acrylate type (Resin B), obtained by copolymerising methyl acrylate with ethyl acrylate and glycidyl acrylate to form a terpolymer in which the three monomers are present in the molar proportions 55:35:10, respectively. The terpolymer is reacted with a stoichiometric amount of acrylic acid relative to the glycidyl group, thus forming an acryl-acrylate type resin having an average molecular weight, M,, of 1650. The resin was used to form a mixture having the following composition: Resin B . 50 parts by weight Butanediol diacrylate . 30 parts by weight N-vinyl pyrrolidone . . 20 parts by weight Benzyl dimethyl ketal 5 parts by weight The mixture had a viscosity at 25"C of 330 cps. It was spread on polycarbonate sample plates to a thickness of 30 microns.After 20 UV-tunnel passes, the coating had the following properties: Kong hardness . . 149s Adhesion without tape . 100% Adhesion with tape . . 100% Resistance to Scratching 18 g.

The shock resistance and the transparency of the plates were the same as those of uncoated polycarbonate.

An accelerated ageing test in a WOM and an immersion test in water were carried out as in Example 1. The results given in following Table 5 were obtained.

TABLE 5 After 1,000 hours in WOM Adhesion without tape 100% Adhesion with tape 100% Resistance to Scratching 17 9 Colour unaffected After 10 days in water at 23"C Adhesion without tape 100% Adhesion with tape 100% Resistance to scratching 14 9 Colour unaffected These results shows that there are no appreciable alterations of the sample plates in the two tests. When the tests were repeated under the same conditions, but without any N-vinyl pyrrolidone in the mixture, the coatings had the same properties but their adhesion to the plate was nil.

Example 6 Using resin B of Example 5, the following blend was prepared: Resin B . 30 parts by weight Ethylene glycol diacrylate . 20 parts by weight - Vinyl pyrrolidone . . 50 parts by weight Benzoin ethyl ether 5 parts by weight The mixture had a viscosity at 25"C of 85 cps. After 20 UV-tunnel passes of polycarbonate plates coated to a thickness of 30 microns, the coating had the following properties: Konig hardness . 147s Adhesion without tape 100% Adhesion with tape 100% Resistance to Scratching 13 g.

The other properties of the coated plates were found to be similar to those of the previous Example.

Example 7 Resin A of Example 1 was used to form the following mixture: Resin A . 70 parts byweight N-vinyl-N-methyl butyramide 30 parts by weight Benzyl-dimethyl-ketal 5 parts by weight A coating having a thickness of 5 microns was formed on polycarbonate plates and, after 10 UV-tunnel passes, the coatings had the following properties: Kong hardness . 162s Adhesion without tape 100% Adhesion with tape 100% Resistance to Scratching 18 g.

The other properties of the coated plates were similar to those of Example 1.

Example 8 The same mixture as used in Example 1 was spread in different thicknesses on three sample plates of commercial polycarbonate of different brands. These sample plates had the following resistances to scratching: Sample No. . . 6.2 9 Sample No. 2 ........ . . 7.5 9 Sample No.3 ......

Upon coating the plates with the mixture in different thicknesses and after 20 UV cross-linking passes, the coating had the properties given in the following Table 6.

TABLE 6 Sample 5 microns thickness 30 microns thickness No. Resistance to Adhesion Resistance to Adhesion Scratching with tape Scratching with tape (9) (%) (9) (%) 1 16 100 35 100 2 13 100 32 100 3 13 100 30 100 These results show that the adhesion is not influenced by the thickness, whereas the resistance to scratching is increased as the film thickness is increased.

Example 9 A resin C of polyester acrylate type was used. This resin was obtained by polycondensing a mixture of one mol of maleic acid anhydridewith one mol of adipic acid and 3 mols of ethylene glycol. The product thus obtained was esterified by reacting it with acrylic acid to obtain a semi-solid resin having an Mn of 460 and an acrylic functionality of 2. This resin was used to form the following mixture: Resin C . 70 parts by weight N-vinyl pyrrolidone . . 30 parts by weight Benzyl dimethyl ketal 5 parts by weight The mixture, spread to a thickness of 30 microns on polycarbonate plates and UV-cross-linked by 20 tunnel passes, gave coatings having the following properties: Konig hardness . 172s Adhesion without tape . 100% Adhesion with tape . . 100% Resistance to Scratching 22 g.

The other properties of the sample plates were similar to those of Example 1. The test was repeated without adding the vinyl amide. The coated sample plates obtained has similar properties to the foregoing plates, but the adhesion of the coatings to the plates was nil.

Claims

1. Polycarbonate having on a surface thereof a coating of a copolymer of (a) an oligomer or reactive resin having a molecular weight of from 400 to 4000 and containing at least two acrylic groups, and (b) an N-vinyl derivative of a linear or cyclic secondary amine.

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2. Coated polycarbonate as claimed in claim 1, wherein the oligomer is a urethane resin containing at least two terminal acrylic groups.

3. Coated polycarbonate as claimed in claim 1, wherein the oligomer is one obtained by oligomerising acrylic monomer(s) functionalised with at least two acrylic groups.

4. Coated polycarbonate as claimed in claim 1, wherein the oligomer is a resin obtained by condensing a saturated or unsaturated dicarboxylic acid with a glycol and by subsequently esterfying the terminal hydroxy groups of the condensate with acrylic acid.

5. Coated polycarbonate as claimed in any of claims 1 to 4, wherein the N-vinyl derivative of a secondary amine is N-vinyl pyrrolidone, N-vinyl caprolactain, N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl propionamide or N-vinyl-N-methyl propionamide.

6. Coated polycarbonate as claimed in claim 1, substantially as described in any of the foregoing Examples.

7. A process for forming a coating on a surface of polycarbonate, which comprises coating the surface with a mixture of (a) an oligomer or reactive resin having a molecular weight of from 400 to 4000 and containing at least two acrylic groups, and (b) an N-vinyl derivative of a linear or cyclic secondary amide; and copolymerising the components of the mixture, in the presence of a photoinitiator, by exposure of the mixture to radiation.

8. A process according to claim 7, wherein the amount of component (b) in the mixture is from 5 to 60% by weight, based on the weight of the mixture.

9. A process according to claim 7 or 8, wherein the photoinitiator is benzoin isopropyl ether, benzoin ethyl ether, benzyl dimethyl ketal, benzophenone, 2,2-dimethyl-2-phenyl acetophenone, 2- chlorothioxanthone or anthraquinone.

10. A process according to any of claims 7 to 9, wherein the radiation is UV radiation.

11. A process according to any of claims 7 to 10, wherein the mixture contains a reactive compound having a molecular weight of less than 400 and containing at least one functional group of acrylate type, methacrylate type, maleate type or fumarate type.

12. Coated polycarbonate prepared buy a process according to any of claims 7 to 12.

12. A process according to claim 7, substantially as described in any of the foregoing Examples.