GB1597995A

GB1597995A - Coating composition

Info

Publication number: GB1597995A
Application number: GB18831/78A
Authority: GB
Original assignee: Nippon Sheet Glass Co Ltd; Sumitomo Chemical Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd; Sumitomo Chemical Co Ltd
Priority date: 1977-05-10
Filing date: 1978-05-10
Publication date: 1981-09-16
Also published as: FR2390481A1; IT7868057A0; FR2390481B1; DE2820391C2; DE2820391A1

Description

(54) COATING COMPOSITION (71) We, SUMITOMO CHEMICAL COMPANY, LIMITED, a Japanese Body Corporate, of No. 13, Kitahama 5-chome, Higashi-ku, Osaka-shi, Osaka-fu, Japan, and NIPPON SHEET GLASS CO., Ltd., a Japanese Body Corporate, of No. 8, Dosho-machi 14-chome, Higashi-ku, Osaka-shi, Osaka-fu, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a coating composition and to a method for improving the surface hardness of various articles by applying coating composition to them.

The coating composition is useful for improving the surface properties, such as surface hardness and chemical resistance, of for example plastics products, wooden products and metallic products, preferably after forming an undercoating layer having an excellent adhesion on the products in question. The coated articles may preferably be produced by applying an undercoat onto the surface of an article, baking the undercoated article, applying the coating composition thereto, and then baking the article.

Plastics, for example plastics such as polycarbonate, polymethyl methacrylate, polystyrene and polyvinyl chloride, are useful for many applications because of their light weight, easy processability and high impact resistance. However, these materials have inferior abrasion resistance and solvent resistance and their surfaces are readily injured by rubbing and easily swollen or dissolved by solvent contact.

To overcome these defects, it has been proposed to coat the surface of the plastics with various thermosetting resins, such as melamine resin, thermosetting acrylic resin, polyester resin, polyurethane resin, or silicone resin. However, these proposals have not been one hundred percent successful, taking into account all the desired properties, such as surface hardness, abrasion resistance, hot water resistance and weatherability. When the hardness of the coating film is increased, a loss of flexibility occa sionally results and cracking of the film when tested for hot water resistance.

The invention provides a method for the improvement of the surface hardness of a base material which comprises coating the base material with an under-coating composition comprising (1) a polymer having a repeating structural unit of the formula:

wherein R4 and Rd are each hydrogen, an alkyl group having from 1 to 5 carbon atoms, or a carboxyl group, and X is a side chain containing a carboxyl or amino group, or (2) a polymer having a repeating structural unit of the formula:

wherein R and R7 ar each hydrogen, an alkyl group having from 1 to 5 carbon atoms, or a carboxyl group, and Y is a side chain containing a hydroxy group, and a repeating structural unit of the formula::

wherein Rs and R9 are each hydrogen, an alkyl group having from 1 to 5 carbon atoms or a carboxyl group, and Z is a side chain containing a substituted amino, epoxy or tetrahydrofuryl group, and then coating the resulting coated material with a top coating composition (sometimes referred to herein as a "silicon coating composition"), comprising a solution in a solvent, of a first component (A) which consists of the co-partial hydrolysis product of a tetraalkoxysilane of the formula Si(ORl), wherein R1 is an alkyl group having from 1 to 4 carbon atoms and an organic silicon compound of the formula:: R"2Si(OR3)~l, wherein n is 1, 2 or 3, R2 is a hydrocarbyl group having from 1 to 6 carbon atoms and R3 is an alkyl group having from l to 4 carbon atoms, and/or a mixture of the partial hydrolysis product of a tetraalkoxysilane as defined above and the partial hydrolysis product of an organic silicon compound as defined above, the partial hydrolysis or co-partial hydrolysis products of the tetraalkoxysilane (calculated as SiO2) and organic silicon compound (calculated as Rn2SiOm wherein m = (4-n)/2 being present in a ratio of from 5/95 to 95/5 by weight; and from 10 to 400 parts by weight per 100 parts by weight of the first component (calculated as SiO2 for the partial or co-partial hydrolysis product of the tetraalkoxysilane and as 1L2SiOm for the partial or co-partial hydrolysis product of the organic silicon compound) of a second component (B), which is X a copolymer of an alkyl acrylate and/or an alkyl methacrylate with a hydroxyalkyl acrylate and/or a hydroxy-alkyl methacrylate; XI a copolymer of at least one of an N,N-dialkyi- aminoalkyl acrylate, an N,N-dialkylaminoalkyl methacrylate, an N,N-dialkylacrylamide and an N,N-dialkylmethacrylaniide with at least one of a hydroxyalkyl acrylate, a hydroxyalkyl methacrylate, an alkyl acrylate and an alkyl methacrylate;XII a monomer or oligomer having two or more hydroxy groups, or a mixture of two or more com ponents X, XI, XII and optionally up to 300 parts by weight on the aforesaid basis of a third component (C) which is an etherified methylolamine, provided that when the component (B) is the monomer or oligomer having two or more hydroxy groups, the etherified methylolmelamine is also present, in an amount of from 0.5 to 1.5 gram equivalents per gram equivalent of the monomer or oligomer.

Certain related top-coating compositions are described and claimed in British Specification No. 1501243, but most of the top-coating compositions are novel, and the invention includes a coating composition which comprises a solution in a solvent, of a first component (A) which consists of the co-partial hydrolyis product of a tetraalkoxysilane of the formula Si(OR1), wherein R1 is an alkyl group having from 1 to 4 carbon atoms and an organic silicon compound of the formula: Ra2Si(OR3)4..

wherein n is 1, 2 or 3, R2 is a hydrocarbyl group having from 1 to 6 carbon atoms and R3 is an alkyl group having from 1 to 4 carbon atoms, and/or a mixture of the partial hydrolysis product of a tetraalkoxysilane as defined above and the partial hydrolysis product of an organic silicon compound, as defined above the partial hydrolysis or co-partial hydrolysis products of the tetraalkoxysilane (calculated as SiO2) and organ silicon compound (calculated as Ra2SiO.m wherein m = (4-n)/2) being present in a ratio of from 5/95 to 95/5 by weight; and from 10 to 400 parts by weight per 100 parts by weight of the first component (calculated as SiO2 for the partial or co-partial hydrolysis product of the tetraalkoxysilane and as Ra2SiOm for the partial or co-partial hydrolysis product of the organic silicon compound) of second component (B), which is X a copolymer of at least one of an N,N-dialkylaminoalkyl acrylate, an N,N-dialkylaminoalkyl methacrylate, an N,N-dialkylacrylamide and an N,N-dialkylmethacrylamide with at least one of a hydroxyalkyl acrylate, a hydroxyalkyl methacrylate, and alkyl acrylate and an alkyl methacrylate;XI a monomer or oligomer having two or more hydroxy groups, or a mixture of components X and XI, and optionally up to 300 parts by weight on the aforesaid basis of a third component (C) which is an etherified methylolmelamine, provided that when the component (B) is the monomer or oligomer having two or more hydroxy groups, the etherilied methylolmelamine is also present, in an amount of from 0.5 to 1.5 gram equivalents per gram equivalent of the monomer or oligomer.

rhe coating compositions may be applied to the surface of various products, such as plastics products, wooden products, metallic products, or the like, to give a surface layer having excellent surface hardness.

When the undercoating composition and subsequent top coating composition are applied and then baked, there is obtained a coated product having good abrasion resistance adhesion to the base material.

Suitable examples of the tetraalkoxysilane present in the component (A) of the top coating composition are the compounds of the formula: Si(ORl), wherein the alkoxy group: 091 is methoxy, ethoxy, propoxy or butoxy. Suitable examples of the organic silicon compound present in the component (A) are the compounds of the formula: R,2Si(ORS),, wherein the hydrocarbon group: R2 is methyl, ethyl, propyl, butyl, pentyl, hexyl, vinyl, allyl or phenyl, and the alkyl group: R3 is methyl, ethyl, propyl or butyl.

The partial hydrolysis products of the tetraalkoxysilane and the organic silicon compound may be obtained by hydrolyzing them either separately or together in a solvent, such as a mixed solvent or water and an alcohol, in the presence of an acid (e.g. hydrochloric, phosphoric and sulfuric acid, oxalic and maleic acid, acetic and formic acid).Alternatively, the partial hydrolysis products may be produced by hydrolyzing directly a silicon chloride or mixed chloride (e.g. SiC14 or RnSiCl4) and accordingly the term partial hydrolysis products" as used herein is not intended to imply that the products are necessarily obtained by hydrolyzing rhe stated compounds, and the partial hydrolysis products" may be obtained by hydrolyzmg any suitable starting material. Generally speaking, it is more preferable to cohydrolyze a mixture of the silicon compounds rather than hydrolyzing separately each of the silicon compounds and mixing the products.The partial hydrolysis products of the silicon compounds thus obtained contain the partial hydrolyzate of the tetraalkoxysilane (calculated as SiO2) and the partial hydrolyzate of the organic silicon compound (calculated as Rn2SiOm wherein m is (4-,)/2) in the ratio of 5/95 to 95/5 by weight, preferably 30/70 to 80/20; by weight. When the partial hydrolyzate of the tetraalkoxysilane is present in an amount of less than 5% by weight, the coating film formed from the coating composition has low hardness and loses abrasion resistance so that it cannot be practically used, and on the other hand, when more than 95% by weight is present, the coating film has low flexibility and tends to crack.

The acrylic copolymer-X used as the component (B) in the present coating composition may be obtained by subjecting an alkyl (meth)acrylate and a hydroxyalkyl (meth)acrylate to a bulk polymerization, emulsion polymerization, suspension polymerization or solution polymerization in the presence of a radical polymerization initiator, such as azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, or the like. Alkyl (meth)acrylate includes esters of (meth)acrylic acid with an alcohol having from 1 to 18 carbon atoms, for example, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, or the like. Hydroxyalkyl (meth)acrylate includes for example, 2-hydroxyethyl (methacrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acryplate, glycerol mono(meth)acrylate), or the like.The ratio of alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate, units present in the acrylic copolymer-X, is not critical but is preferably from 90/10 to 10/90 weight, for optimum adhesion between the coating film and the undercoating layer and flexibility of the coating film.

The acrylic copolymer-XI may be obtained by subjecting one or more N,Ndialkylaminoalkyl (meth)acrylates or an N,N-dialkyl(meth)acrylamides to copolymerization with one or more hydroxyalkyl (meth)acrylates or alkyl (meth)acrylates.

The polymerization may be carried out by bulk polymerization, emulsion polymerization, suspension polymerization or solution polymerization in the presence of a radical polymerization initiator, for example azobisisobutyronitrile, benzoyl peroxide or a ditert-butyl peroxide.

Examples of suitable N,N-dialkylaminoalkyl (meth)acrylates are 2-(N,N dimethylamino ) ethyl (meth ) acrylate, 2- (N,N-diethylamino )ethyl ethyl (meth ) acrylate and 3- (3N,N-diethylamino )propyl (meth)acrylate.

Examples of suitable N,N-dialkyl (meth)acrylamides are N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, and N,N-dibutyl (meth)acrylamide.

Examples of suitable hydroxyalkyl (meth)acylates are 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth) acrylate, glycerol mono (meth)acrylate, and polyethyleneglycol mono(meth)acrylate.

Examples of suitable alkyl (meth)acrylates are methyl (meth)acrylate, ethyl (meth ) acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate.

The ratio of N,N-dialkylaminoalkyl (meth)acrylate and/or N,N-dialkyl (meth)acrylamide to hydroxyalkyl (meth)acrylate and/or alkyl (meth)acrylate, units in the acrylic copolymer-XI, is not critical, but is preferably from 95/5 to 10/90, for optimum adhesion between the coating film and the undercoating layer flexibility of the coating film.

Suitable examples of polyols for use as component B (XII) are ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, (1,3-, 1,4- or 2,3-) butanediol, 1,6-hexanediol, 1,8-octanediol, l,l0-decanediol, neopentyl glycol, pentaerythritol, glycerin, sorbitol, and polyethylene glycol, polypropylene glycol and an ethylene glycol-propylene glycol copolymer. These polyols have a molecular weight of less than 500. When a polyol having a molecular weight of 500 or more is used, the coating film tends to show lower surface hardness and abrasion resistance, although its flexibility is increased.

One or more of the acrylic copolymer-X, acrylic copolymer-XI and the polyol XII are incorporated together with the silicon containing component (A) into the top coating composition of the invention.

In the top coating composition, the total amount of the component (B) is from 10 to 400 parts by weight, preferably 20 to 250 parts by weight, per 100 parts by weight of the component (A) wherein the weight of the partially hydrolyzed tetraalkoxysilane is calculated as SlO2 and the weight of the partially hydrolyzed organic silicon compound is calculated as R,32SiOm. When the amount of the component (B) is smaller than 10 parts by weight, the coating film obtained has poor adhesion and also a low flexibility which results in cracking and on the other hand, when the amount of the component (B) is more than 400 parts by weight, the coating film has an inferior hardness.

In order te give both excellent hardness and excellent flexibility to the coating film, it is preferable to include in the composition an etherified methylolmelamine [component (C)].

Many suitable etherified methylolmelamines are disclosed in the literature and some are commercially available. Suitable examples of etherified methylolmelamines are hexamethylolmelamine, pentamethylolmelamine, tetramethylolmelamine, some or all of the methylol groups of which may be methylated, ethylated, propylated or butylated. Particularly suitable examples are a hexa(alkoxymethyl)melamine, such as hexa (methoxymethyl ) melamine, hexa (ethoxymethyl ) melamine, hexa (propoxymethyl) melamine, hexa (isopropoxymethyl ) melamine, hexa (butoxymethyl )melamine, or hexa (cyclohexyloxymethyl )melamine.

These etherified methylolmelamines may be used alone or in a combination of two or more thereof in an amount of O to 300 parts by weight per 100 parts by weight of the component (A) (calculated as SiO2 and RX2SiOm) When the amount of the etherified methylolmelamine is more than 300 parts by weight, the coating film has inferior hardness and a low adhesion after being dipped in hot water and subjected to a weatherability test. When the polyol is used as the component (B), it is essential to use the etherified methylolmelamine. When the polyol is used in an amount excess to that of the etherified methylolmelamine, the unreacted polyol remains in the coating film, which results in lowering of the hardness and durability of the coating film.

When the amount of the polyol is too small, the coating film loses flexibility and tends to crack.

Therefore, when the polyol is used as component B, the etherified methylolmelamine is also used, the ratio of the two being 1:05-1.5 by gram equivalent, preferably 1:0.8-1.2 by gram equivalent (etherified methylolmelamine:polyol). In order to give both hardness and flexibility to the coating film and to regulate the viscosity of the coating liquid, it is preferable to pre-condense the etherified methylolmelamine and rhe polyol and then add the resulting pre-condensate to the component (A), rather than to add them to the component (A) separately.

We have also found that the amount of the partial hydrolysis product of tetraalkoxysilane present in the coating composition has a large effect on the hardness of the top coating film. When the amount of the partial hydrolysis product of the tetraalkoxysilane is large, the coating film has good hardness and abrasion resistance, but inferior flexibility, and tends to crack. When the amount of the partial hydrolyzate of tetraalkoxysilane is small, the coating film has poor hardness and abrasion resistance.

When the polyol is used as the component (B), the amount of the partial hydrolysis product tetraalkoxysilane (calculated as SiO2) is preferably from 6 to 45% by weight based upon the total weight of the solid components in the top coating composition.

The solvent used in the preparation of the top coating composition may be for example alcohol, a ketone, an ester, an ethylene glycol monoalkyl ether, an ether, a halogenated compound, a carboxylic acid, an aromatic compound, or a mixture of two or more thereof. Particularly suitable examples of the solvent are lower alcohols (for example methanol, ethanol, propanol or butanol), ethylene glycol monoalkyl ethers (for example 2-methoxyethanol, 2-ethoxyethanol or 2-butoxyethanol), lower aliphatic carboxylic acids (for example formic acid, acetic acid or propionic acid), aromatic compounds (for example toluene or xylene) esters (for example ethyl acetate or butyl acetate), and mixtures of these solvents. Sufficient solvent is used to provide a solids content of the coating composition of from 5 to 50% by weight.

The top coating composition may be applied to a base material preferably after application of an undercoating composition as mentioned hereinafter, and the coating is then baked. After top coating, heating is carried out to cure the coating, at a temperature higher than TOOC, but lower than the heat deformation temperature of the base material (for a polycarbonate resin, the heat deformation temperature being in the range of 120 to 1600C) for 10 to 200 minutes to give a coating film having excellent hardness and adhesion.In order to lower the curing temperature or to shorten the curing time, it is preferable to use a curing accelerator, such as acids (for example hydrochloric acid, phosphoric acid or toluenesulfonic acid), ammonium salts (for example ammonium chloride, ammonium nitrate or ammonium thiocyanate), organic amines, metal salts of organic carboxylic acids, metal salts of thiocyanic acid, metal salts of nitrous acids, metal salts of boric acid, organic tin compounds, or the like.

Optionally, a commercially available flowicontrolling agent, such as an alkylene oxidedimethylsiloxane block copolymer (for example NUC Silicone Y-70D6, a trade name of Nippon Unicar Co.) may also be used. These curing accelerator and flow-controlling agent may be used in a small amount, and usually, the curing accelerator may be used in an amount of 0.1 to 5% by weight based on the weight of solid components in the coating composition and the flow controlling agent may be used in an amount of 0.01 to 0.1% by weight based on the total weight of the coating composition.

The top coating may be carried out by a conventional coating method, such as dipping, spray coating, roller coating or flow coating, and after coating, the resultant is cured by heating at 700 C or higher to give a coating film having excellent hardness, flexibility and chemical resistance. The thickness of the top coating layer (after curing) is preferably in the range of 3 to 50 micron, more preferably 5 to 20 micron.

In order to increase the adhesion between the top coating layer and the base material, it is preferable to previously apply an undercoating composition to the base material.

The undercoating composition comprises the polymer (1) or the polymer (2) as mentioned hereinbefore. The polymer (1) contains at least 5 mole%, preferably 20 to 100 mole%, of the repeating structural unit of the formula (I), and the polymer (2) contains at least 2.5 mole%, preferably 10 to 90 mole%, of structural units of the formula (II) and the formula (III).

The polymer (1) may contain in addition to the repeating structural units of formula (I), repeating structural units of formula (II).

The copolymer (1) may be prepared by polymerizing a vinyl monomer (i) as mentioned hereinafter alone or by copolymerizing the vinyl monomer (i) and another monomer which is copolymerizable with the vinyl monomer (i) by a conventional polymerization method.

Suitable examples of the vinyl monomer (i) are acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid, maleic acid, itaconic acid, aminomethyl acrylate, aminomethyl methacrylate, acrylamide, methacrylamide, crotonamide, or the like, which may be used alone or in a mixture of two or more thereof.

The other monomer copolymerizable with the vinyl monomer (i) or the vinyl monomers (ii) and (iii) as mentioned hereinafter includes any compound having at least one ethylenically unsaturated bond in the molecule, for example, olefins (for example ethylene), diolefins (for example, butadiene), vinyl compounds (for example vinyl chloride, vinylidene chloride or acrylonitrile), acrylic or methacrylic acid esters (for example methyl (meth)acrylate, ethyl (meth)acrylate, (meth)acrylamides (for example N,N-dimethyl (meth)acrylamide), or the like, which may be used alone or in a combination of two or more thereof.

Suitable examples of the polymer (1) are a copolymer comprising from 90 ro 5% by weight of one or more N,N-dialkylaminoalkyl(meth)acrylate or N,N-dialkyl (meth)acrylamide monomer units, 10 to 50% by weight of methyl methacrylate units and 0 to 85% by weight of units of at least one vinyl compound copolymerizable with these monomers. This copolymer is particularly useful when the base material to be coated is a polycarbonate resin article.

The polymer (2) may be prepared by copolymerizing the vinyl monomer (ii) and the vinyl monomer (iii) as mentioned hereinafter, optionally together with one or more other monomers copolymerizable with these vinyl monomer (ii) and (iii) as mentioned hereinbefore by a conventional polymerization method.

Suitable examples of the vinyl monomer (ii) are allyl alcohol, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N- (2-hydroxyethyl) acrylamide, N,Ndihydroxymethylacrylamide, N,N-di (2-hydroxyethyl ) methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxylpropyl methacrylate, 1,4-butylene glycol monoacrylate, 1,4-butylene glycol monomethacrylate, glycerol monomethacrylate, hydroxyallyl methacrylate, polyethylene glycol monoacrylate, polypropylene glycol monomethacrylate, hydroxymethylaminomethyl acrylate, hydroxymethylaminoethyl methacrylate, 2-hydroxyethylaminomethyl acrylate, 2-(2'hydroxyethylamino ) ethyl methacrylate, N,N-di (hydroxymethyl ) aminomethyl acrylate, N,N-di (hydroxymethyl ) aminomethyl methacrylate, and N,N-di (2-hydroxyethyl ) - aminomethyl acrylate, which may be used alone or in a combination of two or more thereof.

Suitable examples of the vinyl monomer (iii) are acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid, maleic acid, itaconic acid, acrylamide, methacrylamide, crotonamide, N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, Nethylmethacrylamide, N-propylacrylamide, N-butylacrylamide, N - tert - butylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-dethylacrylamide, N,N-diethylmethacrylamide, N,N-dipropylmethacrylamide, N,N-dibutylacrylamide, N,N-dibutylmethacrylamide, N-butoxymethylacrylamide, N -iso - butoxymethylmethacrylamide, 2-(N-methylamino)ethyl acrylate, 2-dierhylamino)ethyl methacrylate, 2 - (N,N - dimethylamino)ethyl acrylate, 2 - (N,N - dimethylamino)ethyl methacrylate, 2 - (N,N - diethylamino)ethyl acrylate, 2 - (N,N - diethylamino)ethyl methacrylate, 2 - (N,N - dibutylamino)ethyl acrylate, 2 - (N,N - dibutylamino)ethyl methacrylate, 3 - (N,N - diethylamino)propyl acrylate, 3 - (N,N - diethyl- amino)propyl methacrylate, 2 - (N,N - dibutylamino)propyl acrylate, 2 - (N,Ndibutylamino)propyl methacrylate, 3-(N,N-dibutylamino)propyl methacrylate, allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, tetrahydrofurfuryl acrylate and tetrahydrofurfuryl methacrylate, which may be used alone or in a combination of two or more thereof.

It is not necessarily required to incorporate a crosslinking agent into the undercoating composition. However, when the top coating composition is applied to the base material coated with the undercoating composition, the organic solvent contained in the top coating composition occasionally corrodes the undercoat layer, which results in lowering of the adhesion of the coating film to the base material. In order to prevent such a corrosion of the undercoat with the solvent, it is preferable to incorporate a crosslinking agent into the undercoating composition. The crosslinking agent may be for example an alkyleneglycol di(meth)acrylate, an alkyl-etherfied methvlolmelamine, a polyalkyleneglycol di(meth)acrylate, or pentaervthritol diacrylate. Hexa tmethovvmethyl)melamine and hexa (butoxymethyl )melamine are particularly preferred. These crosslinking agents may be used alone or in a combination of two or more thereof. Ihe crosslinking agent may be used in an amount of 0.05 to 0.7 equivalents, preferably 0.2 to 0.4 equivalents, per equivalent of the functional groups (for example, carboxyl, amino, substituted amino, hydroxy, epoxy or tetrahydrofuryl) in the polymer (1) or polymer (2).

A crosslinking catalyst is used together with the crosslinking agent. Suitable examples of crosslinking catalysts are hydrochloric acid, ammonium chloride, ammo nium nitrate, and ammonium thiocyanate. The crosslinking catalyst may preferably be used in an amount of 0.05 to 0.8 gram equivalents per gram equivalent of the crosslinking agent.

The undercoating composition is usually diluted for use with a diluent to a concentration at which it can be applied. Examples of diluents are alcohols (for example methanol, ethanol), ethers (for example ethylene glycol monomethyl ether), ketones (for example methyl ethyl ketone), and esters (for example, methyl acetate, ethyl acetate), which may be used alone or in the form of a mixed solvent of two or more thereof.

A suitable concentration of polymer (1) or polymer (2) in the undercoating composition after dilution is from 0.1 to 10% by weight, preferably from 0.5 to 5% by weight.

The undercoating composition may optionally contain a small amount of conventional additives such as a flow-controlling agent.

The undercoating composition containing the polymer (1) or the polymer (2) as the main ingredient and optionally a crosslinking agent, a crosslinking catalyst, a diluent and a flow-controlling agent may be applied to the surface of a base material by a conventional coating method, such as dipping, spray coating, roller coating or flow coating. It is then dried and may optionally be cured by heating at a temperature lower than the heat deformation temperature of the base material to give an undercoating film. The undercoating film may preferably have a thickness of 0.1 to 1 micron.

When the top coating composition is applied to the undercoat the functional groups such as hydroxyl, carboxyl and amino in the undercoating film react with the silicon components in the top coating composition, and thereby, the top coating film adheres strongly to the base material via the undercoating film.

Suitable base materials on which the coating composition of the invention may be used include synthetic resins (for example polycarbonate resin, polymethyl methacrylic resin, polystyrene resin or polyvinyl chloride resin), metallized products produced by depositing a metal (for example aluminum) onto a resin sheet (for example a polymethacrylate sheet), plated products produced by plating a metal (for example chromium) onto a resin (for example ABS resin), metals (for example aluminum or iron), coated products of plastics or metals, or the like.Since the components of rhe undercoating composition and the top coating composition of the present invention have excellent transparency, these compositions are particularly useful for coating clear plastics such as polycarbonates and for finishing the surface of metallized products or plated products in order to give them good abrasion resistance.

The composition is particularly suitable for use on polycarbonate resins, for example, bisphenol type polycarbonate (for example 4,4'-isopropylidenediphenol polycarbonate), the polycarbonates disclosed in U.S. Patent 3,305,520 and Crystofer and Fox, "Polycarbonates", pages 161-176 (1962), and diethylene glycol bisallylcarbonate.

The present invention is illustrated by the following Examples, but is not limited thereto. In Examples, "%" and "part" mean % by weight and part by weight unless specified otherwise.

Examples 1 to 11 and Reference Examples 1 to 4.

(1) Preparation of a solution of cohydrolyzation products of tetraethoxysilane and methyltriethoxysilane (Component I): Tetraethoxysilane (66.7 g) and methyltriethoxysilane (33.3 g) were dissolved in isopropyl alcohol (70 g) and 0.û5 N hydrochloric acid (30 g) was added to the solution, and the mixture was stirred at room temperature to effect hydrolysis. After the reaction, the mixture was matured at room temperature for 20 hours or more.

The resulting solution contained a partial hydrolyzate of tetraethoxysilane (9.6%, calculated as SiO2) and a partial hydrolyzate of methyltriethoxysilane (6.3%, calcu lated as CSiO1.5) 5) (SiO2:CH3SiO1., = 60:40).

(2) Preparation of a solution of cohydrolyzation products of tetraethoxysilane and methyltriethoxysilane (Component II): A reactor provided with a reflux condenser was charged with isopropyl alcohol (68 g), tetraethoxysilane (38 g) and methyltriethoxysilane (72 g). To the mixture was added 0.05 N hydrochloric acid (36 g), and the mixture was heated with stirring at a reflux temperature for 5 hours to effect hydrolysis. After the reaction, the reaction mixture was cooled to room temperature to give a cohydrolyzation solution which contained a partial hydrolyzate of tetraethoxysilane (5.1%, calculated as six2) and a partial hydrolyzate of methyltriethoxysilane (12.6%, calculated as CHsSiOl6) (Si02:CHsSi01, = 29:71).

(3) Preparation of a solution of cohydrolyzation products of tetraethoxysilane and dimethyldiethoxysilane (Component III): Tetraethoxysilane (83.3 g) and dimethyldiethoxysilane (16.7 g) were dissolved in isopropyl alcohol (70 g) and 0.05 N hydrochloric acid (30 g) was added to the solution and the mixture was stirred at room temperature to effect hydrolysis. After the reaction, the mixture was matured at room temperature for 20 hours or more. The resulting solution contained a partial hydrolyzate of tetraethoxysilane (12%, calculated as SiO2) and a partial hydrolyzate of dimethyldiethoxysilane (4.2%, calculated as (GH3)2SiO) (SiO2:(CH3)2SiO = 74:26).

(4) Preparation of a solution of cohydrolyzation products of tetraethoxysilane, methyltriethoxysilane and trimethylethoxysilane (Component IV): Tetraethoxysilane (83.3 g), methyltriethoxysilane (14 g) and trimethylethoxysilane (2.7 g) were dissolved in ethyl alcohol (70 g) and 0.05 N hydrochloric acid (30 g) was added to the solution, and the mixture was stirred at room temperature to effect hydrolysis. After the reaction, the resulting mixture was matured at room temperature for 20 hours or more.The resulting solution contained a partial hydrolyzate of tetraethoxysilane (12%, calculated as Six2), a partial hydrolyzate of methyltriethoxysilane (2.6, calculated as CH3SiOl) and a partial hydrolyzate of trimethylethoxysilane (0.9%, calculated as (CH3),SiO,,) s) [SiO2:CH3SiOl s (CH,),SiO,,) = 77:23].

(5) Preparation of a solution of cohydrolyzation products of tetraethoxysiiane and methyltriethoxysilane (Component V): Tetraethoxysilane (88 g) and methyltriethoxysilane (16 g) were dissolved in isopropyl alcohol (60 g) and 0.05 N hydrochloric acid (36 g) was added to the solution, and the mixture was stirred at room temperature to effect hydrolysis. After the reaction, the mixture was matured at room temperature for 20 hours or more. The resulting solution contained a partial hydrolyzate of tetraethoxysilane (12.8%, calculated as SiO2) and a partial hydrolyzate of methyltriethoxysilane (3.0%, calculated as CH;8SiOl.6) (SiO2:CH3SiOl s: = 81:19).

(6) Preparation of acrylic copolymer-I: a) Butyl acrylate (40 g), 2-hydroxyethyl methacrylate (10 g) and azobisisobutyronitrile (0.5 g) were dissolved in ethyl alcohol (300 g). The mixture was stirred at 700C for 5 hours under nitrogen gas to effect polymerization. After the reaction was completed, the reaction mixture was poured into petroleum ether and thereby the unreacted monomer was removed to give Copolymer (a).

b) Ethyl acrylate (50 g) and 3-hydroxypropyl methacrylate (10 g) were copolymerized in the same manner as described in the above a) to give Copolymer (b).

(7) Preparation of acrylic copolymer-II: c) 2-N-,N-Dimethylamino ) ethyl methacrylate (4 g), 2-hydroxyethyl methacrylate (2 g), butyl acrylate (14 g) and benzoyl peroxide (0.2 g) were dissolved in ethylene glycol monoethyl ether (80 g). The mixture was stirred at 850C for 4 hours and further at 1000C for 30 minutes under nitrogen gas to give a solution of Copolymer (c).

d) N,N-Dimethylacrylamide (4 g), 2-hydroxyethyl methacrylate (2 g) and butyl acrylate (14 g) were copolymerized in the same manner as described in the above c) to give a solution of Copolymer (d).

(8) Preparation of a solution of each pre-condensate of hexa(methoxymethyl)melamine and 1,4-butanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol.

a) An 85% phosphoric acid (0.2 ml) was added to hexa(methoxymethyl)melamine (78 g) and 1,4-butanediol (54 g) (gram equivalent ratio = 1:1), and the mixture was reacted at 13e-140"C to give a prepolymer having a molecular weight of about 5,000. To the reaction product was added ethyl cellosolve to give Pre-condensate Solution (a) having a solid content of 75%.

b) Hexa(methoxymethyl)melamine (78 g) and 1,6-hexanediol (71 g) (gram equivalent ratio = 1:1) were condensed in the same manner as described in the above a) to give Pre-condensate Solution (b) having a solid content of 96%.

c) Hexa(methoxymethyl)melamine (65 g) and diethylene glycol (53 g) (gram equivalent ratio = 1:1) were reacted likewise to give a prepolymer having a molecular weight of about 30,000. To the prepolymer was added 2-ethoxyethanol to give Precondensate Solution (c) having a solid content of 96%.

d) An 85% phosphoric acid (0.2 ml) was added to hexa(methoxyethyl)melamine (260 g) and triethylene glycol (300 g) (gram equivalent ratio = 1.1).

The mixture was reacted at 130--1400C until 42.7 g of a distillate were obtained.

To the prepolymer thus obtained was added 2-ethoxyethanol to give Pre-condensate.

Solution (d) having a solid content of 96%.

e) An 85% phosphoric acid (0.4 ml) was added to hexa(methoxymethyl)melamine (520 g) and tetraethylene glycol (800 g) (gram equivalent ratio = 1:1).

The mixture was reacted at 130L-140"C until 86 g of a distillate were obtained.

To the prepolymer thus obtained was added ethyl cellosolve to give Pre-condensate Solution (e) having a solid content of 96%.

(9) Preparation of the coating composition: To the solution of Component I, Component II and Component V were added hexa(methoxymethyl)melamine and polyol or a pre-condensate thereof, a curing accelerator, a flow-controlling agent, etc. To the mixture was added ethyl cellosolve so that the solid content becomes 10 to 40% to give the coating compositions as shown in Table 1.

(10) Coating and tests of the properties of the coated products: Polycarbonate sheet (thickness: 3 mm) was washed and coated with the aboveobtained coating compositions. The coated products were cured with a hot-air drier at 1300C for 2 hours. The polycarbonate sheets thus coated were subjected to the following tests: (i) Adhesion: This was tested by so-called "cross-cut tape test". That is, the coating film was cross-cut by making each 11 parallel lines of nicks with a knife at intervals of 1 mm in horizontal and vertical directions so that a hundred cells having an area of 1 mm2 were formed, and thereon was bonded an adhesive cellulose tape. The cellulose tape was then peeled off. The adhesion of the coating film was evaluated by the number of the remaining cells.

(ii) Abrasion resistance: Steel wool test: the surface was rubbed with &num;0000 steel wool. The abrasion resistance was evaluated according to the following scale.

A: No scratch made on the surface even by strong rubbing.

B: A few scratches made by strong rubbing.

C: Scratches made even by weak rubbing.

Taber abrasion test: It was tested in accordance with ASTM D-1044 by using a Taber abrader (wheel: CS-1OF, load: 500 g). The abrasion resistance was evaluated by a haze (%) after rotating the wheel 500 times.

(iii) Boiling water resistance: The surfaces to be tested were immersed in boiling water for 60 minutes, and thereafter, the state of the coating film was observed.

(iv) Flexibility: A sample (50 mm X 100 mm X thickness 0.7 mm) was bent at a radius of 15 mm at room temperature. The flexibility was evaluated by the ocurrence of cracks.

(v) Heat cycle test: A sample was kept in turn at -200C and at 80"C for each 2 hours. This was repeated ten times, and thereafter, the state of the coating film was observed.

These test results are shown in Table 2.

TABLE 1

Component A Components B and C I II V Etherified (Solid (Solid (Solid methylolmelamine Polyol Pre-condensate Solution content content content (Component C) (Component B) (Components B and C) 15.9%) 17.7%) 15.8%) Part by Part by Part by Part by Example No. weight weight weight Part by weight Kind weight Kind Part by weight Ex. 1 100 - - 21 1,4-Butanediol 14 - Ex. 2 100 - 9 Glycerin 4 - Ex. 3 - - 100 11 Neopentyl 9 - glycol Ref. Ex. 1 100 - - 35 - - - Ref. Ex. 2 100 - - - 1,4-Butanediol 35 - Ex. 4 100 - - - - - a 103 Ex. 5 - 100 - - - - a 17 Ex. 6 - - 100 - - - a 38 Ref. Ex. 3 - - 100 - - - a 1 Ex. 7 - 100 - - - - b 9 Ex. 8 - - 100 - - - b 20 Ref. Ex. 4 - 100 - - - - b 101 Ex. 9 100 - - - - - c 17 Ex. 10 100 - - - - - d 17 Ex. 11 100 - - - - - e 17 [Note]: (1) Etherified methylolmelamine is hexa (methoxymethyl) melamine. .

(2) The Pre-condensate Solution (a) has a solid content of 75%, and the Pre-condensate Solution (b), (c), (d) and (e) have a solid content of 96% TABLE 2

Properties Abrasion resistance Appearance after Steel wool Taber test Boiling water Example No. curing Adhesion test (Haze: %) resistance Flexibility Heat cycle test Ex. 1 Good 100/100 A 29 Good Yes Good Ex. 2 " " A 18 " " " Ex. 3 " " A 15 " " " Ref. Ex. 1 Crack " A 22 Increased crack No Increased crack Ref. Ex. 2 " " A 30 " " " Ex. 4 Good " B 35 Good Yes Good Ex. 5 " " A 30 " " " Ex. 6 " " A 13 " " " Ref. Ex. 3 Crack " A 5 Increased crack No Increased crack Ex. 7 Good " A 28 Good Yes Good Ex. 8 " " A 7 " " " Ref. Ex. 4 " " C 42 " " " Ex. 9 " " A 20 " " " Ex. 10 " " A 18 " " " Ex. 11 " " B 23 " " " Example 12.

To a mixture of ethylene glycol monoethylether (320 g), 2-hydroxyethyl methacrylate (36 g) and dimethylaminoethyl methacrylate (44 g) was added azobisisobuytronitrile (0.4 g), and the mixture was reacted at 900C to give a solution of a copolymer of 2-hydroxyethyl methacrylate and dimethylaminoethyl methacrylate).

To the silicon Component I (100 parts) were added the copolymer solution obtained above (40 parts), Pre-condensate Solution (a) (10 parts), a curing accelerator and a flow-controlling agent to give a coating composition. The coating composition thus obtained was applied to a previously washed polycarbonate sheet (thickness: 3 mm). The coated product was cured with a hot-air drier at 1300C for 2 hours. The coating film thus prepared showed steel wool test: A, and excellent boiling water resistance and flexibility.

In the following Examples 13 to 35 and Reference Examples 5 to 11, the Components I to V, Copolymers (a) to (d) and Pre-condensate Solutions (a) to (e) as prepared in the above Examples 1 to 11 were used. Besides, the under coating compositions were prepared as follows: a) 2-Hydroxyethyl methacrylate (76 g), dimethylaminoethyl methacrylate (4 g) and azobisisobutyronitrile (0.4 g) were dissolved in ethylene glycol monoethylether (320 g), and the mixture was stirred at 90"C for 4 hours under nitrogen gas to effect copolymerization. To the resulting solution (100 g) were added hexa(methoxymethyl)melamine (2.8 g), ammonium chloride (0.18 g), ethylene glycol monoethylether (900 g) and a small amount of a flow-controlling agent to give Under Coating Composition (a).

b) 2-Hydroxyethyl methacrylate (36 g), dimethylaminoethyl methacrylate (14 g), methyl methacrylate (50 g) and azobisisobutyronitrile (0.4 g) were dissolved in ethylene glycol monoethylether (320 g), and the mixture was stirred at 90"C for 4 hours under nitrogen gas to effect copolymerization. To the resulting solution (100 g) were added hexa(methoxymethyl)melamine (1.3 g), ammonium chloride (0.18 g), ethylene glycol monoethylether (900 g) and a small amount of a flow-controlling agent to give Under Coating Composition (b).

Examples 13 to 17 and Reference Examples 5 to 8.

A previously washed polycarbonate sheet was coated with the above Under Coating Composition (a) except Reference Example 8. The coated products were cured with a hot-air drier at 1300C for 10 minutes to give under coating films having a thickness of about 0.5 micron.

A solution of Component I, Component II, Component III or Component IV, Copolymer (a) or Copolymer (b), and optionally hexa (butoxymethyl)melamine, a curing accelerator and a flow-controlling agent were mixed in the ratio as shown in Table 3. The mixtures were dissolved in a mixture of n-butanol (60 parts), acetic acid (40 parts) and xylene (20 parts) to give coating compositions.

The coating compositions obtained above were applied to under-coated polycarbonate sheets, except Reference Example 8, and the resulting products were cured with a hot-air drier at 1300C for 2 hours to give top coating films having a thickness of about 10 micron. The coating films thus obtained were subjected to various tests, and the properties of the coating films are shown in Table 4. In these tests, adhesion and abrasion resistance were tested in the same manner as described in Examples 1 to 11. The boiling water resistance was tested by immersing the surfaces to be tested in hot water at 800C for 2 hours and thereafter observing the state of the coating film.The heat cycle test was carried out by immersing in turn a sample into boiling water at 80"C for 10 seconds and ice-salt water at -200C for 10 seconds (this being repeated ten times) and then observing the state of the coating film.

In these examples and reference examples, bisphenol type polycarbonate sheet and diethylene glycol bisallylcarbonate sheet were used as the polycarbonate sheet. In both sheets, same results were obtained.

TABLE 3

Component (B) Component (C) Component (A) (Acrylic copolymer-I) [Hexa(butoxymethyl) (100 parts by malamine] Example No. Under coating weight) Kind Part by weight (Part by weight) Additives Ex. 13 Yes I a 4 2 U Ex. 14 " II a 10 10 Ex. 15 " III a 6 - V Ref. Ex. 5 " I - - - U Ref. Ex. 6 " III - - - V Ex. 16 " IV a 20 - W Ex. 17 " IV b 15 5 " Ref. Ex. 7 " IV - - - " Ref. Ex. 8 No IV - - - " [Note]: U: Sodium acetate (0.4 part) V: Potassium thiocyanate (0.4 part) and NUC Silicone Y-7006 (a surfactant sold by Nippon Unicar Co.) (0.2 part) W: Sodium acetate (0.4 part) and NUC Silicone Y-7006 (0.2 part) TABLE 4

Appearance Abrasion Boiling water Example No. after curing Adhesion resistance resistance Heat cycle test Ex. 13 Good 100/100 A Good Good Ex. 14 ,, ,, B Ex. 15 " " A. " " Ref. Ex. 5 Slight crack " ,, A Increased crack Increased crack Ref. Ex. 6 Good ,, A Good Crack Ex. 16 " " A ,, Good Ex. 17 ,, ,, A Ref. Ex. 7 Slight crack ,, A Increased crack Increased crack Ref. Ex. 8 Good 0/100 * Peeled off | Peeled off [Note]@: *) Owing to the inferior adhesion, the coating film was peelcd off by rubbing with the steel wool.

Examples 18 to 21 and Reference Example 9.

A solution of Component I, Copolymer (c) or Copolymer (d), and optionally methlyated methylolmelamine and a curing accelerator (sodium acetate, 0.4 part) were mixed in the ratio as shown in Table 5. The mixture is dissolved in a mixture of isopropanol (20 parts), acetic acid (10 parts) and ethyl cellosolve (20 parts) to give coating compositions.

The coating compositions were applied to polycarbonate sheets which were pre viously washed and coated with Under Coating Composition (a) as in Examples 13 17. The coated products were cured with a hot-air drier at 1300C for one hour. The coating films thus produced were subjected to various tests, and the properties of the coating films are shown in Table 5. In the tests, the boiling water resistance was tested by immersing the surfaces to be tested in boiling water at 600 C for 30 minutes and thereafter observing the state of the coating film, and other tests were done in the same manner as described in Examples 1 to 11.

In these examples and reference examples, bisphenol type polycarbonate sheet and diethylene glycol bisallylcarbonate sheet were used as the polycarbonate sheet.

In both sheets, same results were obtained.

TABLE 5

Component (B) (Copolymer Component (A) solution) Before boiling water resistance After boiling water resistance test (Solid content Melamine** 15.9%) Part by Part by Abrasion Abrasion Example No. Part by weight Kind* weight weight Appearance Adhesion resistance Appearance Adhesion resistance Ex. 18 100 c 50 - Good 100/100 A Good 100/100 A Ex. 19 " c 10 - " " A " " A Ref. Ex. 9 " - - - Crack 0/100 A Increased 0/100 A crack Ex. 20 " d 50 - Good 100/100 A Good 100/100 A Ex. 21 " c 50 15 " " A " " A [Note]: *) The copolymer (c) and (d) have both a solid content of 20%.

**) The melamine is a 70% solution of a methylated methylolmelamine in ethylene glycol monoethyl ether (Suminal M 55, a trade name of Sumitomo Chemical Company, Limited).

Examples 22 to 35 and Reference Examples 10 to 11.

A solution of Component I, Component II or Component V, hexa(methoxymethyl)melamine [Component (C)], a polyol [Component (B)] or its Pre-condensatse Solution (a) to (e) and a curing accelerator were mixed in the ratio as shown in Table 6. To the mixture was added ethylene glycol monoethyl ether so that the solid content thereof became 10 to 40% to give coating compositions.

The coating compositions were applied to polycarbonate sheets which were previously washed and coated with Under Coating Compoosition (a) or (b), except Examples 27 and 31. The coated products were cured with a hot-air drier at 130 C for 2 hours. The properties of the coating films thus prepared were tested in the same manner as described in Examples 1 to 11, and the results are shown in Table 7.

In these examples and reference examples, bisphenol type polycarbonate sheet and diethyleneglycol bisallylcarbonate sheet were used as the polycarbonate sheet.

For both sheets, the same results were obtained.

TABLE 6

Components (B) and (C) (Pre-condensate) Component (A) [Hexa(methoxymethyl) (100 parts by melamine] Example No. Under coating weight) Kind Part by weight (Part by weight) Additives Ex. 22 a I 1,4-Butanediol 14 21 P Ex. 23 a I Glycerin 4 9 P Ex. 24 a V Neopentyl glycol 9 11 Q Ref. Ex. 10 a I - - 35 P Ex. 25 a I 1,4-Butanediol 55 - P Ex. 26 a I a 103 - P Ex. 27 - I a 103 - P Ex. 28 b II a 17 - P Ex. 29 a V a 38 - R Ref. Ex. 11 b V a 1 - P Ex. 30 a V b 20 - P Ex. 31 - V b 20 - P Ex. 32 b I b 105 - P Ex. 33 a I c 17 - R Ex. 34 a I d 17 - R Ex. 35 a I e 17 - R [Note]: P: Ammonium thiocyanate (0.7 part) Q: P-toluenesulfonic acid (0.2 part) R: Ammonium nitrate (0.5 part) TABLE 7

Before boiling water resistance Abrasion resistance After boiling water resistance test Steel wool Taber test** Abrasion Head cycle Example No. Appearance Adhesion test (Haze: %) Appearance Adhesion resistance Flexibility test Ex. 22 Good 100/100 A 29 Good 100/100 A Yes Good Ex. 23 " " A 18 " " A " " Ex. 24 " " A 15 " " A " " Ref. Ex. 10 Crack " A 22 Increased " A NO Increased crack crack Ex. 25 Good " B 40 Good " B Yes Good Ex. 26 " " B 35 " " B " " Ex. 27 " " B 35 " 0/100 * " " Ex. 28 " " A 30 " 100/100 A " " Ex. 29 " " A 13 " " A " " Ref. Ex. 11 Crack " A 5 Increased " A No Increased crack crack Ex. 30 Good " A 7 Good " A Yes Good Ex. 31 " " A 7 " 0/100 * " " Ex. 32 " " B 42 " 100/100 B " " Ex. 33 " " A 20 " " A " " Ex. 34 " " A 20 " " A " " Ex. 35 " " A 23 " " A " " [Note]: *) The coating film had inferior adhesion, and hence, it was peeled off by rubbing with steel wool.

**) The untreated polycarbon sheet had a haze of 45 to 50%.

Example 36.

Copolymers or homopolymers were prepared by using a co-monomer or monomer, a solvent and a polymerization initiator as shown in Table 8. To the copolymers or homopolymers were added a crosslinking agent, a curing accelerator and a solvent as shown in Table 9 to give Under Coating Compositions (c) to (1).

A previously washed polycarbonate sheet was coated with the Under Coating Compositions (c) to (1). The coated products were cured with a hot-air drier at 130 C for 10 minutes. The polycarbonate sheets under-coated with Under Coating Compositions (c) to (1) were coated with the coating composition as prepared in Example 29, and the resulting products were cured at 130 C for 2 hours likewise.

The coating films showed an excellent adhesion after boiling water resistance test.

In this example, bisphenol type polycarbonate sheet and diethylene glycol bisallylcarbonate sheet were used as the polycarbonate sheet. In both sheets, the same results were obtained.

TABLE 8

Co-monomer or monomer Solvent Weight Weight Weight Weight Polymer Kind (g) Kind (g) Kind (g) Kind (g) c 2-Hydroxyethyl 36 Dimethylaminoethyl 44 - - 2-ethoxyethanol 320 methacrylate methacrylate d " 20 " 20 Methyl methacrylate 60 " " e " 51.5 Acrylic acid 28.5 - - " " f " 38 Glycidyl metha- 42 - - " " crylate g " 51.7 Acrylamide 28.3 - - 2-ethoxyethanol 200 + water 100 h " 45 N-Methylol- 35 - - 2-ethoxyethanol 320 acrylamide i " 40 Tetrahydrofurfuryl 52 - - " 360 methacrylate j Acrylamide 20 " 50 - - 2-ethoxyethanol 230 + water 100 k " 50 - - - - Water 200 l Acrylic acid 20 - - - - " " TABLE 8 (continued)

Polymerization initiator Polymerization conditions weight Temperature Time Polymer Kind (g) ( C) (hr) c Azobisisobutyronitrile 0.4 90 2 d " " " " e " " " " f " " 80 4 g ,, ,, ,, 6 h " " " " i " 0.5 " 2 j " 0.4 90 " k Ammonium persulfate 0.5 80 1 Ammonium peroxide ,, 90 TABLE 9

Copolymer or homopolymer Crosslinking agent Curing accelerator Solvent Under coating composition Kind Weight (g) Kind Weight (g) Kind Weight (g) Kind Weight (g) c c 100 Hexa(metoxy- 1.4 NH4Cl 0.19 2-ethoxyethanol 900 methyl)melamine d d " " 0.7 " 0.10 " " e e " " 1.9 " 0.27 " " f f " " 1.4 " 0.20 " " g g " " 1.9 " 0.27 2-ethoxyethanol 675 + water 225 h h " " 1.7 " 0.24 2-ethoxyethanol 900 i i " " 1.3 " 0.18 " " j j " " 1.4 " 0.20 2-ethoxyethanol 675 + water 225 k k " " 2.0 " 0.08 2-ethoxyethanol 300 + water 600 l l " " 1.0 " 0.05 2-ethoxyethanol 150 + water 300 Example 37.

An under coating composition and a silicic coating composition were prepared as follows: (1) Preparation of an under coating composition: 2- (N,N-Dimethylamino)ethyl methacrylate (7 g), methyl methacrylate (8 g), 2-hydroxyethyl methacrylate (5 g) and benzoyl peroxide (0.2 g) were dissolved in ethylene glycol monoethyl ether (80 g), and the mixture was stirred at 850C for 4 hours and further at 1000C for 30 minutes under nitrogen gas to effect copolymerization. To the resulting solution (10 parts) was added ethylene glycol monoethylether (90 parts) to give a copolymer solution for under coating.

(2) Preparation of a silicic coating composition: Tetraethoxysilane (66.7 g) and methyltrimethoxysilane (33. 3 g) were dissolved in isopropyl alcohol (70 g), and thereto was added 0.05 N hydrochloric acid (30 g).

The mixture was stirred at room temperature to effect hydrolysis. After the reaction, the resulting mixture was matured at room temperature for 20 hours or more. To a solution of a partial hydrolyzate of silicon compounds (100 parts) and the copolymer solution for under coating (30 parts) obtained above were dissolved in a mixture of n-butanol (80 parts), acetic acid (40 parts) and sodium acetate (û.4 part) to give a coating composition.

A polycarbonate sheet (thickness: 2 mm) was washed with a neutral detergent and then with water and coated with the under coating composition obtained above.

The coated product was cured with a hot-air drier at 1300 C for 30 minutes. The under-coated polycarbonate sheet was coated with the silicic coating composition obtained above, and the resulting product was cured with a hot-air drier at 13010C for 2 hours. The thus treated polycarbonate sheet had a clear, smooth surface, which was not injured even by strongly scratching with a finger nail and had a good surface hardness (abrasion resistance by the steel wool test: no scratch) and also had a good adhesion (the cross-cut tape test: no peeling off, 100/100).

In this example, bisphenol type polycarbonate sheet and diethylene glycol bisallylcarbonate sheet were used as the polycarbonate sheet. For both sheets, the same results were obtained.

Example 38.

A silicic coating composition was prepared in the same manner as described in Example 37 except that a copolymer of butyl acrylate and 2-hydroxyethyl methacrylate (ratio by weight: 4/1 (6 parts) was used instead of the copolymer solution for under coating (30 parts). A polycarbonate sheet was treated in the same manner as in Example 37. The thus treated polycarbonate sheet had a clear, smooth surface, a good adhesion (the cross-cut tape test: 100/100) and a good surface hardness (abrasion resistance by the steel wool test: no scratch).

Example 39.

A polymethyl methacrylate sheet (thickness: 2 mm), one surface of which was mirror-finished by depositing aluminum thereon in a vacuum, was coated with the same under coating composition as used in Example 37. The coated product was cured at 80"C for 60 minutes. The resulting sheet was further coated with the same silicic coating composition as used in Example 38, and the resulting product was cured at 800C for 2 hours. The polymethyl methacrylate sheet thus treated had no haze, was clear on both surfaces, had good adhesion (the cross-cut tape test: 100/100), good surface hardness (the steel wool test: no scratch) on both surfaces, and both sides of the sheet acted as mirrors.

Reference Example 12.

A polymethyl methacrylate sheet was treated in the same manner as described in Example 39 except that the under coating composition was not used. The polymethyl methacrylate sheet thus treated had good adhesion (the cross-cut tape test: 100/100) to the surface which was not covered with aluminum, but the aluminumcoated surface showed poor adhesion (the cross-cut tape test: 0/100) and had poor surface hardness (the steel wool test: scratches, wherein the deposited metal was removed and hence the sheet showed through).

Example 40.

An aluminum sheet (thickness: 1 mm, JIS A 1050 P) was coated with the under coating composition as used in Example 37, and the coated product was cured at 140"C for 30 minutes. The under-coated aluminum sheet was further coated with the silicic coating composition as used in Example 38, and the resulting product was cured at 13û C for 2 hours. The aluminum sheet thus treated had no haze and a smooth surface and had a good adhesion (the cross-cut tape test: 100/100) and had good surface hardness (the steel wool test: no scratch).

WHAT WE CLAIM IS: 1. A method for the improvement of the surface hardness of a base material which comprises coating the base material with an under-coating composition comprising (1) A polymer having a repeating structural unit of the formula:

wherein R4 and R5 are each hydrogen, an alkyl group having from 1 to 5 carbon atoms, or a carboxyl group, and X is a side chain containing a carboxyl or amino group, or (2) a polymer having a repeating structural unit of the formula:

wherein R6 and Rt are each hydrogen, an alkyl group having from 1 to 5 carbon atoms or a carboxyl group, and Y is a side chain containing a hydroxy group, and a repeating structural unit of the formula::

wherein R8 and R9 are each hydrogen, an alkyl group having from 1 to 5 carbon atoms or a carboxyl group, and Z is a side chain containing a substituted amino, epoxy or tetrahydrofuryl group, and then coating the resulting coated material with a composition comprising a solution in a solvent, of a first component (A) which consists of the co-partial hydrolysis product of a tetraalkoxysilane of the formula Si(OR1), wherein Rl is an alkyl group having from 1 to 4 carbon atoms and an organic silicon compound of the formula:: Rn2Si(OR3)4~; wherein n is 1, 2 or 3, R2 is a hydrocarbyl group having from 1 to 6 carbon atoms and R3 is an alkyl group having from 1 to 4 carbon atoms, and/or a mixture of the partial hydrolysis product of a tetraalkoxsilane as defined above and the partial hydrolysis product of an organic silicon compound as defined above, the partial hydrolysis or co-partial hydrolysis products of the tetraalkoxysilane (calculated as SiO2) and organic silicon compound (calculated as R2SiOffi wherein m = (4-n)/2) being present in a ratio of from 5/95 to 95/5 by weight; and from 10 to 400 parts by weight per 100 parts by weight of the first component (calculated as SiO2 for the partial or co-partial hydrolysis product of the tetraalkoxysilane and as Rn2SiOI for the partial or co-partial hydrolysis product of the organic silicon compound) of a second component (B), which is X a copolymer of an alkyl acrylate and/or an alkyl methacrylate with a hydroxyalkyl acrylate and/or a hydroxyalkyl methacrylate; XI a copolymer of at least one of an N,N-dialkylaminoalkyl acrylate, an N,N-dialkylaminoalkyl methacrylate, an N,N-dialkylacrylamide and an N,N-dialkylmethacrylmide with at least one of a hydroxyalkyl acrylate, a hydroxyalkyl methacrylate, an alkyl acrylate and an alkyl methacrylate; XII a monomer or

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 40. An aluminum sheet (thickness: 1 mm, JIS A 1050 P) was coated with the under coating composition as used in Example 37, and the coated product was cured at 140"C for 30 minutes. The under-coated aluminum sheet was further coated with the silicic coating composition as used in Example 38, and the resulting product was cured at 13û C for 2 hours. The aluminum sheet thus treated had no haze and a smooth surface and had a good adhesion (the cross-cut tape test: 100/100) and had good surface hardness (the steel wool test: no scratch). WHAT WE CLAIM IS:

1. A method for the improvement of the surface hardness of a base material which comprises coating the base material with an under-coating composition comprising (1) A polymer having a repeating structural unit of the formula:

oligomer having two or more hydroxy groups, or a mixture of two or more components X, XI, XII; and optionally up to 300 parts by weight on the aforesaid basis of a third component (C) which is an etherified methylolmelamine, provided that when the component (B) is the monomer or oligomer having two or more hydroxy groups, the etherified methylolamine is also present, in an amount of from 0.5 to 1.5 gram equivalents per gram equivalent of the monomer or oligomer.

2. A method as claimed in claim 1, wherein n in the formula: Rll2Si(OR3)^~n is 1.

3. A method according to claim 1 or claim 2, wherein the partial or co-partial hydrolysis products of the tetraalkoxysilane (calculated as SiO,) and the partial or co-partial hydrolysis products of the organic silicon compound (calculated as Rg2SiO) are present in ratio of from 30/70 to 80/20 by weight.

4. A method as claimed in any one of claims 1 to 3, wherein the component (B) comprises a copolymer of an alkyl (meth)acrylate and a hydroxyalkyl (meth)acrylate in a ratio of from 10/90 to 90/10 by weight.

S. A method as claimed in any one of claims 1 to 3, wherein the component (B) is a copolymer of at least one of an N,N-dialkylaminoalkyl (meth)acrylate and an N,N-dialkyl-(meth)acrylamide with at least one of a hydroxyalkyl (meth)acrylate and an alkyl (meth)acrylate in a ratio of 95/

5 to 10/90 by weight.

6. A method as claimed in any one of claims 1 to 5 wherein the component (B) contains the monomer or oligomer having two or more hydroxy groups.

7. A method as claimed in any one of claims 1 to 6 wherein the second coating composition comprises from 20 to 250 parts by weight of component (B) per 100 parts by weight of the component (A), the basis of the parts being as defined in claim 1.

8. A method as claimed in any one of the preceding claims, wherein the polymer including the repeating structural unit (I) is a copolymer consisting of from 90 to 5% by weight of at least one of an N,N-dialkylaminoalky1 acrylate, an N,N-dialkylaminoalkyl methacrylate, an N,N-dialkylacrylamide and an N,N-dialkylmethacrylamide, from 10 to 50% by weight of methyl methacrylate and from 0 to 85% by weight of at least one vinyl compound which is copolymerizable with the other monomers present.

9. A method as claimed in any one of claims 1 to 8, wherein the material coated is a polycarbonate, polymethyl methacrylate, polystyrene, polyvinyl chloride or aluminum.

10. A method as claimed in any one of the preceding claims, wherein the undercoating composition comprises a polymer having a repeating structural unit of the formula (I), and the said polymer also comprises a repeating structural unit of the formula (II) as defined in claim 1.

11. A method of producing a coated article substantially as hereinbefore described in any one of the Examples, excluding the reference Examples.

12. A coated article when made by a method as claimed in any one of claims 1 to 11.

13. An article as claimed in claim 12, wherein the material coated is a polycarbonate.

14. A coating composition which comprises a solution in a solvent of, a first component (A) which consists of the co-partial hydrolysis product of a tetraalkoxysilane of the formula Si(OR1)4 wherein R1 is an alkyl group having from 1 to 4 carbon atoms and an organic silicon compound of the formula:: R,2Si(OR')4n wherein n is 1, 2 or 3, R2 is a hydrocarbyl group having from 1 to 6 carbon atoms and R' is an alkyl group having from 1 to 4 carbon atoms, and/or a mixture of the partial hydrolysis product of a tetralkoxysilane as defined above and the partial hydrolysis product of an organic silicon compound, as defined above the partial hydrolysis or co-partial hydrolysis products of the tetraalkoxysilane (calculated as SiO2) and organic silicon compound (calculated as Ra2SiOm wherein m = (4~n)/2) being present in a ratio of from 5/95 to 95/5 by weight; and from 10 to 400 parts by weight per 100 parts by weight ot the first component (calculated as SiO2 for the partial or co-partial hydrolysis product of the tetraalkoxysilane and as Rn2SiOm for the partial or co partial hydrolysis product of the organic silicon compound) of second component (B), which is X a copolymer of at least one of an N,N-dialkylaminoalkyl acrylate, an N,N-dialkylaminoalkyl methacrylate, an N,N-dialkylacrylamide and an N,N-dialkylmethacrylamide with at least one of a hydroxyalkyl acrylate, a hydroxy methacrylate, and alkyl acrylate and an alkyl methacrylate;XI a monomer or oligomer having two or more hydroxy groups, or a mixture of com ponents X and XI, and optionally up to 300 parts by weight on the aforesaid basis of a third component (C) which is an etherified methylolmelamine, provided that when the component (B) is the monomer or oligomer having two or more hydroxy groups, the etherified methylolmelamine is also present, in an amount of from 0.5 to 1.5 gram equivalents per gram equivalent of the monomer or oligomer.

15. A composition as claimed in claim 13, wherein n in the formula: R,2Si(OR3),, is 1.

16. A composition according to claim 13 or claim 14, wherein the partial or co-partial hydrolysis products of the tetraalkoxysilane (calculated as SiO2) and the partial or co-partial hydrolysis products of the organic silicon compound (calculated as R"2SiO) ar epresent in ratio of from 30/70 to 80/20 by weight.

17. A composition as claimed in any one of claims 14 to 16, wherein the component (B) is a copolymer of at least one of an N,N-dialkylaminoalkyl (meth)acrylate and an N,N-dialkyl (meth)acrylamide with at least one of a hydroxyalkyl (meth)acrylate and an alkyl (meth)acrylate in a ratio of 95/5 to 10/90 by weight.

18. A composition as claimed in any one of claims 14 to 17, wherein the component (B) contains the monomer or oligomer having two or more hydroxy groups.

19. A composition as claimed in any one of claims 14 to 18, comprising from 20 to 250 parts by weight of component (B) per 100 parts by weight of the component (A), the basis of the parts being as defined in claim 1.

20. A coating composition as claimed in claim 14, and substantially as hereinbefore described in any one of the Examples, excluding the reference Examples.

21. A composition as claimed in any one of claims 14 to 20, when made by a method substantially as hereinbefore described in any one of the specific Examples.