JPH0474367B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applicable to adherends such as plastics and metals by applying one coat directly onto the adherend without using a primer.
-Coat) Coating resin compositions useful as binders for paints. [Prior Art] In recent years, in the automobile industry, the use of plastics for automobile parts has been rapidly progressing in order to reduce the weight of car bodies, prevent rust, and offer greater freedom in design. Plastic materials used for automobiles include non-polar polyolefin resins such as polypropylene and polyethylene; polyamide resins, polybutylene terephthalate resins, polyurethane resins, unsaturated polyester resins, FRP, polycarbonate resins, mixed plastics thereof, reinforced plastics, etc. can be mentioned. Many of these plastics are generally difficult to paint, and in particular, non-polar polyolefin resins are painted through complicated work steps such as pretreatment (oxidation treatment), undercoating, and topcoating. The same thing can be said about package resins, steel frames, steel plates, etc. for buildings other than automobiles, equipment, home appliances, etc., and multiple coating steps including undercoating and topcoating are performed on the adherend. [Problems with the Prior Art] In particular, we will discuss paints for polyolefin resin base materials that are difficult to paint. Paints based on chlorinated polyolefin resins have a rating of 1 for polyethylene and polypropylene.
Although it adheres temporarily, there are major problems in terms of long-term stability, paint workability, etc. That is, when used for a long period of time, chlorine is released over time and the paint film tends to yellow or change in quality, and the weather resistance of the paint film is problematic, so it has not been put to practical use as a paint resin. Even if polyolefin resin is subjected to some pre-treatment before painting (physical treatment such as surface polishing, chromic acid mixture treatment, solvent treatment, plasma treatment, corona treatment, etc.), it is not possible to form a coating film with good adhesion. Have difficulty. As a method for improving the above-mentioned problems, especially weather resistance, (1) a paint has been proposed in which a general-purpose acrylic resin is blended with a chlorinated polyolefin resin or an unsaturated polycarboxylic acid or its acid anhydride-modified chlorinated polyolefin; (Unexamined Japanese Patent Publication No. 57-198764,
JP-A Nos. 60-123565 and 61-860), the compatibility between the chlorinated polyolefin and the acrylic resin is insufficient, and the effect of improving weather resistance is also insufficient. (2) Paint resin obtained by polymerizing acrylic monomer in the presence of chlorinated polyolefin resin (JP-A-56-
50971, Japanese Patent Publication No. 61-12940) (3) An epoxy compound having two or more epoxy groups per molecule obtained by polymerizing a monomer mixture containing a functional group-containing acrylic monomer in the presence of a chlorinated polyolefin. or paint containing epoxy resin (JP-A-56-50971) (4) Chlorinated polyolefin modified with unsaturated polycarboxylic acid or its acid anhydride and epoxy having two or more epoxy groups per molecule Paints containing compounds or epoxy resins (JP-A-60-
Although various proposals have been made, such as No. 22383), the improvement effect is insufficient and there are problems with the weather resistance of the coating film. [Specific means for solving the problems] The present invention provides an inert solvent in which a hydrogenated product (A) of a styrene-butadiene-styrene block copolymer is dissolved. Contains 50% by weight or more of an acrylic ester or methacrylic ester having a group,
In addition, a vinyl monomer (B) containing a vinyl monomer having a hydroxyl group in a proportion of 0.5 to 20% by weight or an α,β-unsaturated carboxylic acid or its acid anhydride in a proportion of 0.1 to 10% by weight is polymerized. The present invention provides a resin composition for coating material obtained by the method. [However, the weight ratio (A/B) of component (A) and component (B) is
It is 2/8 to 7/3. ] Methods for producing styrene-butadiene-styrene block copolymers are well known to those skilled in the art;
A typical procedure is disclosed in US Pat. No. 3,265,765 (August 9, 1966). By hydrogenating the intramolecular double bonds of this block copolymer of styrene and butadiene, an elastomer with improved thermal stability can be obtained. The production of such hydrogenated block copolymers is known, for example, from the Japanese Patent Publication Publication No. 42
−8704, Special Publication No. 1977-6636, Special Publication No. 1977-20504
It is described in the specifications of Japanese Patent Publication No. 48-3555, etc. In addition, several compositions using these hydrogenated substances have been proposed, such as JP-A-50-14742, JP-A-52-65551, and JP-A-60-60.
Specifications such as No. 4225 contain hydrogenated styrene/conjugated diene block copolymer mixed with hydrocarbon oil, rosin ester adhesive, α-olefin polymer, wax, ethylene/vinyl acetate copolymer, etc. A composition is disclosed. Such hydrogen additives are available from Shell Chemical
It is sold by Kraton Company under the grade name of Kraton G-, for example, under the code name #1652. Inert organic solvents for dissolving this hydrogenated styrene-butadiene-styrene block copolymer include aromatic hydrocarbons such as toluene, xylene, and chlorobenzene, ketones such as methyl ethyl ketone and methyl isobutyl ketone, ethyl acetate, butyl acetate, etc. esters, chlorinated solvents such as carbon tetrachloride, tetralin, mineral spirits, and mixed solvents thereof are used. This inert organic solvent is capable of dissolving the hydrogenated styrene-butadiene-styrene block copolymer and the vinyl monomer of component (B), and is sufficient to dissolve components (A) and (B). The amount used is usually 50 to 2000% by weight of the sum of the two. Component (B): The vinyl monomer of component (B) is mainly composed of an acrylic ester having an alkyl group or a cyclohexyl group having 1 to 8 carbon atoms or its methacrylic ester equivalent, and has a hydroxyl group. Contains 0.5 to 20% by weight of vinyl monomer or 0.1 to 10% by weight of α,β-unsaturated carboxylic acid or its acid anhydride, including styrene, acrylonitrile, divinylbenzene, butanediol Acrylic ester or its methacrylic ester equivalent having an acrylic group or cyclohexyl group having 1 to 8 carbon atoms may contain other vinyl monomers such as diacrylate and acrylamide in a proportion of 50% by weight or less Examples include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-acrylate
Butyl, t-butyl acrylate, cyclohexyl acrylate and their methacrylate equivalents can be used. These acrylates contribute to improving the weather resistance, adhesion to the substrate, and hardness of the resulting film. As the α,β-unsaturated carboxylic acid or its acid anhydride, acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, crotonic acid, fumaric acid, and maleic anhydride are used. In addition, when it is a polybasic acid such as maleic acid or fumaric acid,
It may also be a half alkyl ester thereof. These unsaturated acids are used in a proportion of 0.1 to 10% by weight in component (B). Also, the sum of component (A) and component (B)
It is used in a proportion of 0.01 to 5% by weight. Examples of the vinyl monomer having a hydroxyl group include hydroxyethyl acrylate, hydroxypropyl acrylate, butadienol monoacrylate, polyethylene glycol monoacrylate,
Examples of these methacrylate equivalents include N-methylolacrylamide, allyl alcohol, hydroxyethyl vinyl ether, hydroxyethyl butyl maleate, and ε-caprolactone-modified acrylate. These vinyl monomers having hydroxyl groups are 0.5 to 20% by weight in component (B), and 0.1 to 20% by weight of the sum of components (A) and (B).
Used at a rate of 10% by weight. These unsaturated acids and vinyl monomers having hydroxyl groups enable the crosslinking reaction of hydrogenated styrene/butadiene/styrene copolymers. Polymerization: Polymerization is carried out by dropping the vinyl monomer component (B) in which a polymerization initiator has been dissolved into a solution of a hydrogenated styrene/butadiene/styrene block copolymer in an inert organic solvent. Alternatively, it can be carried out by gradually dropping the mixture and heating it to 65 to 150°C while stirring.
Polymerization time is 1 to 24 hours. Examples of the polymerization initiator include organic peroxides and azonitrile. Organic peroxides include alkyl peroxides, aryl peroxides, acyl peroxides, aroyl peroxides, ketone peroxides, peroxycarbonates, peroxycarboxylates, and the like.
Alkyl peroxides include diisopropyl peroxide, ditertiary butyl peroxide,
tertiary butyl hydroperoxide, dicumyl peroxide as aryl peroxide,
Cumyl hydroperoxide, acyl peroxide is dilauroyl peroxide, aroyl peroxide is dibenzoyl peroxide,
Examples of the ketone peroxide include methyl ethyl ketone peroxide and cyclohexanone peroxide. Examples of azonitrile include azobisisobutyronitrile and azobisisopropionitrile. Component (A), the hydrogenated styrene/butadiene/styrene block copolymer, is important for the adhesion of the coating film to the adhesive.
It is a component that contributes to bending resistance and impact resistance, and the polymer of component (B) greatly affects the hardness, solvent resistance, weather resistance, abrasion resistance, etc. of the coating film, and all coating films. In terms of performance balance, (A)/(B) is 2/8 to 7/3
(weight ratio). If (A)/(B) is less than 2/8, the adhesion to the substrate becomes too poor. Conversely, if it exceeds 7/3, solvent resistance and gasoline resistance will deteriorate. Resin for paints The resins obtained by the above polymerization include hydrogenated styrene/butadiene/styrene block copolymers, vinyl monomer copolymers, vinyl monomer grafted hydrogenated styrene/butadiene/styrene block copolymers, etc. It is a homogeneously mixed polymer alloy. Since the product obtained by polymerization is a solution in which this paint resin is dissolved in an organic solvent, a paint may be prepared by adding a pigment, a dispersant, a leveling agent, a crosslinking agent, etc. to this solution. Alternatively, after removing the organic solvent, a new organic solvent, pigment, dispersant, etc. may be added to form a paint, or a necessary amount of organic solvent for adjusting the viscosity may be partially removed from the resin solution. ,
Alternatively, it may be added to the resin solution and then blended with pigments and the like to form a paint. One-coat paint: An example of the composition of a paint that can be applied directly to a substrate is shown below. (a) 100 parts by weight of the coating resin of the present invention (b) 0 to 50 parts by weight of a crosslinking agent (c) 100 to 5000 parts by weight of an organic solvent for dissolving the resins of components (a) and (b) above (d) Pigment: 10 to 300 parts by weight (e) Other optional components: 0 to 10 parts by weight. However, the crosslinking agent of component (b) above is added for the purpose of improving the hardness and gasoline resistance of the coating film, and it is a resin having a functional group that reacts with a carboxyl group or a hydroxyl group, and an epoxy group. polyepoxides having isocyanate groups; polyurethane resins, polyester resins, blocked polyisocyanates having isocyanate groups; reactive functional groups (-
OH, -COOH) acrylic resin, amino resin, etc. can be used. Specific examples of crosslinking agents include (1) self-reactive compounds such as methanol, ethanol, n-
Amino resins such as melanin resins or urea resins modified with alcohols such as butanol and isobutanol, and compounds containing polymerizable unsaturated groups (for example, polyesters such as trimethylolpropane triacrylate, polyethylene glycol diacrylate, and pentaerythritol triacrylate) Functional acrylate; Epoxy acrylate or methacrylate obtained by esterifying the epoxy group of an epoxy compound with acrylic acid or methacrylic acid; Polyurethane acrylate or methacrylate obtained by reacting a polyisocyanate compound described below with an acrylate or methacrylate having a hydroxyl group; Examples include acrylic resins obtained by copolymerizing acrylic monomers having functional groups such as carboxyl groups, hydroxyl groups, amino groups, and methylol groups. In addition, (2) polyisocyanate compounds (for example,
Aromatic diisocyanates or fatty acid diisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexane 1,4-diisocyanate, and addition of these with diols, triols, etc. polyisocyanates, chain trimers, cyclic trimers, etc.) and the isocyanate groups contained in the above-mentioned polyisocyanate compounds are substituted with lower alcohols, ε-caprolactam, methyl ethiketoxime, diethyl Examples include blocked isocyanate compounds blocked with blocking agents such as malonate and phenol. Furthermore, (3) epoxy compounds include compounds containing one or more, especially two or more, epoxy groups in the molecule, and mixtures thereof, such as 2,2-bis(4-hydroxyphenyl)propane(bis). Phenol A), bis(4-hydroxyphenyl)
Polyglycidyl ethers of polyhydric phenols such as methane and 1,1-bis(4-hydroxyphenyl)ethane, polyglycidyl ethers of polyhydric alcohols such as glycerin, pentaerythritol, and trimethylolpropane, and glycidyl ethers of polyalkylene polyethers. Examples include glycidyl ether, polyhydric carboxylic acid, so-called diglycidyl ester of dimer acid, and the like. In addition, olefins such as epoxy compounds obtained by oxidizing polybutadiene with peracid, acrylic epoxy compounds obtained by copolymerizing with glycidyl acrylate or glycidyl methacrylate, and phenol novolak-type compounds obtained by the reaction of phenol with formalin are also available. Examples include epoxy compounds and modified products thereof. These crosslinking agents may be used alone or in combination of two or more. Furthermore, these crosslinking agents may be mixed with active hydrogen-containing resins such as acrylic resins, polyester resins, and polyurethane resins having functional groups such as carboxyl groups, hydroxyl groups, amino groups, and imino groups that react chemically. As the organic solvent for component (c), those exemplified as solvents for dissolving the hydrogenated styrene/butadiene/styrene block copolymer can be used. Component (d) pigments include inorganic and organic pigments commonly used in paints, such as titanium dioxide,
Examples include carbon black, talc, kaolin, calcium carbonate, magnesium carbonate, barium sulfate, iron oxide, cyanine blue, and quinacridone red. Other optional components of component (e) include leveling agents, anti-settling agents, dispersants, ultraviolet absorbers, chlorinated polyolefins, cyclized rubber, petroleum resins, antifoaming agents,
Antioxidants are available. Paints are manufactured by using a known pigment dispersion machine such as an attritor or sand mill to disperse pigments in part or all of the resin component, then adding the remaining resin component, organic solvent, and paint additives to form a predetermined amount. Manufactured by adjusting the viscosity to . As the means for applying the paint, any known painting method such as air spray, air atomization electrostatic, electrostatic atomization electrostatic coating, etc. can be used. Dry at room temperature for 30 minutes to 24 hours, or dry at 60 minutes to 24 hours.
Heat at 140°C for 5 to 60 minutes to form a coating film. Adhesives to be coated include steel plates, stainless steel, aluminum, polyamide resin, polybutylene terephthalate resin, ABS resin, polyurethane resin, polyvinyl chloride, polycarbonate resin, unsaturated polyester resin, polypropylene resin, polystyrene, acrylic resin, and Nylene oxide resin and mixed plastics thereof,
Further, these reinforced plastic resins and metallized plastics in which a plating film or a metal vapor deposition film of copper, nickel, chromium, zinc, etc. is formed on the surface of these resins can be used. [Effects of the Invention] The paint obtained using the paint resin of the present invention can be applied directly to adherends without a primer, and can produce a paint film with a good balance of weather resistance, gasoline resistance, adhesion, and flexibility. give. Furthermore, since it provides a coating film with excellent adhesion to both metals and plastics, it can be applied to both steel sheet materials and plastic materials at the same time. [Example] Hereinafter, the present invention will be explained in detail with reference to Examples. (Manufacture of molded products) Example 1 Hydrogenated styrene/butadiene/styrene block copolymer “Krayton G-” manufactured by Shell Chemical Co., Ltd.
1652” (trade name) 25 parts by weight, ethylene (74% by weight)/propylene copolymer rubber with a Mooney viscosity of 32
25 parts by weight and propylene/ethylene (7% by weight) block copolymer manufactured by Mitsubishi Yuka Co., Ltd. (MFR45g/
10 minutes) 50 parts by weight were mixed for 2 minutes using a Kawada Seisakusho super mixer, and PCM manufactured by Ikegai Iron Works Co., Ltd.
The composition was kneaded and granulated at 220°C using a twin-screw kneader to form pellets. Each composition was molded using a screw-in-line injection molding machine at 240°C with a wall thickness of 2 mm and a size of 100 cm.
A 100 cm test piece was molded. Example 2 The propylene/ethylene block copolymer (EP) described above was used alone and injection molded to form a test piece. Example 3 Polyamide resin material 1013RW-1 (Ube Industries, Ltd.)
A test piece was molded using an injection molding machine at 280°C. Example 4 A test piece was molded from polybutylene terephthalate resin (PBT) material 5201X11 (manufactured by Toray Industries, Inc., trade name) using an injection molding machine at 250°C. Example 5 ABS resin material Lustran240 (Mitsubishi Monsanto Chemical Co., Ltd.)
Co., Ltd. (trade name) was molded into test pieces using an injection molding machine at 200°C. Example 6 The ABS resin test piece of Example 5 was subjected to micropore chrome electroplating to obtain a test piece. Example 7 A test piece was prepared by cutting an unsaturated polyester resin material (SMC) N12 (manufactured by Takeda Pharmaceutical Co., Ltd., trade name). (Resin production example) Example 1 100 parts of Kraton G-1652 (hydrogenated styrene-butadiene-styrene block copolymer manufactured by Shell Chemical Co., Ltd.) as component (A) was placed in a flask equipped with a condenser, a thermometer, and a stirrer. , 200 parts of toluene were charged, and the temperature was raised to 95°C under a nitrogen gas atmosphere. To this, methyl methacrylate 80 is added as component (B).
20 parts of n-butyl methacrylate, 1 part of methacrylic acid, 1 part of benzoyl peroxide and 50 parts of toluene were added dropwise over 3 hours.
After 12 hours at °C, polymerization was completed to obtain coating resin A of the present invention. Example 3 A coating resin C was obtained in the same manner as in Example 1, except that 50 parts of methyl methacrylate, 30 parts of cyclohexyl methacrylate, 20 parts of ethyl acrylate, and 1 part of methacrylic acid were used as component (B). Example 4 Paint resin D was obtained in the same manner as in Example 1, except that 40 parts of methyl methacrylate, 20 parts of ethyl acrylate, 30 parts of cyclohexyl methacrylate, and 10 parts of 2-hydroxyethyl methacrylate were used as component (B). Comparative Example 1 160 parts of Kraton G-1652 as component (A), (B)
A coating resin F was obtained in the same manner as in Example 1 using 20 parts of methyl methacrylate, 20 parts of n-butyl methacrylate, and 1 part of methacrylic acid as components. Comparative Example 2 20 parts of Kraton G-1652 as component (A), (B)
Ingredients: 90 parts of methyl methacrylate, 40 parts of ethyl acrylate, cyclohexyl methacrylate
Coating resin G was obtained in the same manner as in Example 1, except that 50 parts and 1 part of methacrylic acid were used. Example 6 As component (B), 80 parts of methyl methacrylate, n
- Example 1 except that 15 parts of butyl methacrylate and 5 parts of 2-hydroxyethyl acrylate were used.
Resin H for paint was obtained in the same manner as above. Example 7 As component (B), 80 parts of methyl methacrylate, n
A coating resin I was obtained in the same manner as in Example 1, except that 10 parts of -butyl methacrylate and 10 parts of 2-hydroxypropyl methacrylate were used. Example 8 Coating resin J was prepared in the same manner as in Example 1 except that 50 parts of methyl methacrylate, 30 parts of cyclohexyl methacrylate, 10 parts of ethyl acrylate, 20 parts of styrene and 10 parts of N-methylolmethacryamide were used as component (B). I got it. Example 9 Paint resin K was obtained in the same manner as in Example 1, except that 80 parts of methyl methacrylate, 40 parts of ethyl acrylate, 60 parts of cyclohexyl methacrylate and 20 parts of 2-hydroxyethyl methacrylate were used as component (B). Example 10 As component (B), 40 parts of methyl methacrylate, 20 parts of ethyl acrylate, 20 parts of cyclohexyl methacrylate, and ε-caprolactone modified methacrylate "Plaxel FM-" manufactured by Daicel Chemical Co., Ltd.
Paint resin L was obtained in the same manner as in Example 1, except that 10 parts of 1" (trade name) were used. Comparative example 3 As component (A), 20 parts of Taleyton G-1652, (B)
Ingredients: 90 parts of methyl methacrylate, 40 parts of ethyl acrylate, cyclohexyl methacrylate
50 parts and 2-hydroxyethyl methacrylate
Resin M for coating material was obtained in the same manner as in Example 1 except that 10 parts of the resin was used.

【table】

[Table] Paint manufacturing example Resin A to M (solid content) 35 parts or 25 parts Cross-linked resin 0 or 5 parts Toluene 40 parts Titanium oxide 25 parts Mix and disperse in a sand mill for 1 hour. A paint having the composition shown in 2 was obtained. Details of the components shown in Table 2 are as follows. Blocked isocyanate compound: Coronate
2507 (manufactured by Nippon Polyurethane Co., Ltd., product name, solid content 75
%) Polyisocyanate compound: Sumidyur N-
75 (manufactured by Sumitomo Bayer Urethane Co., Ltd., product name, solid content
75%, 1,6-hexamethylene diisocyanate trimer) Isobutylated melamine resin: Supervecamine L-116-70 (manufactured by Nippon Reichhold Co., Ltd., trade name, solid content 70%) Bisphenol A type epoxy compound : Epicote 834 (manufactured by Yuka Ciel Epoxy Co., Ltd., product name, solid content
100%) Evaluation of paint Coating on plastic: After degreasing the surface of the sheet obtained in Molded Product Production Examples 1 to 4 and 7 for 1 minute with 1,1,1-trichloroethane vapor, the rest was treated with isopropyl alcohol. After 1 minute of immersion in water and air drying for 1 minute, the paint prepared above was diluted with toluene to an appropriate viscosity, and then spray coated to a film thickness of 40 to 45 μm and dried. (Application examples 1, 2, 7 and comparative application examples 1 and 2 are
Bake at 80℃ for 30 minutes. Application examples 4 and 6 and comparative application example 3 were baked at 150℃ for 30 minutes, application examples 8 and 9 were baked at 140℃.
Bake for 30 minutes and dry. ) (Coating on steel plate) A cold-rolled steel plate measuring 0.8 mm x 70 mm x 150 mm was treated with zinc phosphate using Bonderite #3004 (trade name, manufactured by Nihon Parkerizing Co., Ltd.) and spray-painted with the above paint. Evaluation of paint film Gloss: Measured using 60 degree specular reflectance Hardness: Measured using a pencil hardness meter Adhesion: Using a cutter knife, 11 lines were drawn vertically and horizontally at 1 mm intervals, reaching the material, and the resulting 100
Cellophane tape was attached to each square and when it was removed all at once, the coating film could not be peeled off and the evaluation was based on the number of squares that remained. Evaluation criteria is 100/100
(○, excellent), 99/100 - 80/100 (△, acceptable), 79/100
~50/100 (x, poor), 49/100 ~ 0/100 (xx, extremely poor). Bending resistance: The condition of the coating film was examined by bending it 180° using a 1/2φ inch mandrel. ○ (pass), × (fail) Gasoline resistance: The test plate was immersed in gasoline for 1 hour, and changes in the coating film, such as discoloration and staining, swelling, and peeling, were evaluated. Evaluation criteria are ◎ (no change;
Excellent), ○ (slight change; fair), △ (swelling that is a practical problem), × (significant change, peeling;
(Not allowed) Moisture resistance Place the test plate in a sealed box adjusted to a temperature of 50±1℃ and a relative humidity of 98% or higher, and check the appearance of the coating film after 240 hours.
Check for blisters. The evaluation criteria are: Good appearance, no bulges: ○ (excellent), bulges (less than 0.2 mm in diameter): △ (acceptable), bulges (diameter 0.2 mm or more): × (unacceptable)

【table】

[Table] * Except for adhesion, the base material used in Example 1 was used.

Claims (1)

[Scope of Claims] 1. Acrylic acid ester having an alkyl group or cyclohexyl group having 1 to 8 carbon atoms or Contains 50% by weight or more of methacrylic acid ester, and
Obtained by polymerizing a vinyl monomer (B) containing 0.5 to 20% by weight of a vinyl monomer having a hydroxyl group or 0.1 to 10% by weight of an α,β-unsaturated carboxylic acid or its acid anhydride. Resin composition for paint. [However, the weight ratio (A/B) of component (A) and component (B) is 2/8 to 7/3. 2. The resin composition for paint according to claim 1, wherein the inert organic solvent is toluene or xylene. 3. The resin composition for paint according to claim 2, wherein the vinyl monomer having a hydroxyl group is bidroxyethyl methacrylate. 4. The resin composition for paint according to claim 1, wherein the α,β-unsaturated acid is methacrylic acid. 5. Claim 1, characterized in that the inert organic solvent is used in a ratio of 50 to 2000 parts by weight based on 100 parts by weight of the total resin content of components (A) and (B).
The resin composition for coatings described in .