JP2006219731A - Coating material composition for rear surface of precoated metal and precoated metal obtained by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating material composition for the rear surface of a precoated metal with which a low gloss coating film having excellent coating work efficiency, workability, blocking resistance or the like can be formed on the rear surface of a precoated metal, and to provide a precoated metal which is obtained by using the coating material composition, has a low gloss coating film on the rear surface, and has excellent workability, blocking resistance or the like. <P>SOLUTION: The coating composition for the rear surface of a precoated metal is provided which contains resin fine particles (C) with the average particle diameter in the range of 5 to 50 μm in an amount of 1 to 30 pts.wt. based on 100 pts.wt. of binder components composed of a hydroxy group-containing resin (A) and a crosslinking agent (B). The precoated metal is provided which is obtained by using the coating material composition and has a low gloss coating film formed on the rear surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coating composition for a back surface of a pre-coated metal excellent in coating workability, workability, blocking resistance, and the like, and a pre-coated metal using this coating composition.

  Pre-coated metal (sometimes abbreviated as “PCM”) is a metal flat plate (cut or coiled) that has been pre-coated prior to molding, and is applied after the desired product has been molded. It may be distinguished from post-coating, and is often used for building materials such as roofs and walls, and for processing equipment such as audio, refrigerators, partitions, etc., and is advantageous in terms of economy, energy saving, and resource saving compared to post-coating. It is seen.

  Pre-coating metal is generally applied to both front and back surfaces, and the surface side is the outer surface of the product after molding, and the appearance of the coating film, physical performance (hardness, adhesion, scratch resistance, (Bendability, etc.), anticorrosion, weather resistance, and other paints are applied. The coating process uses a two-coat, two-bake method using a primer and a top coat, and a primer, an intermediate coat and a top coat. A 3-coat 3-bake method is employed. On the other hand, since the back surface is located inside the product after the molding process, the appearance of the coating film and the weather resistance as much as the front surface side are not required, and the coating is a 1-coat 1-bake method using only the back-surface paint in consideration of economy. It is common. However, physical performance equivalent to or better than the surface (adhesion, bending workability, etc.) and anticorrosion properties are necessary, and as a coating for the back side of pre-coated metal, for example, a vinyl chloride resin that is insoluble or hardly soluble in organic solvents in the coating There has been proposed a paint capable of forming a coating film having excellent physical performance and anticorrosion properties even by a 1-coat 1-bake method by blending powder (Patent Document 1). Further, in applications where corrosion resistance is required, a 2-coat 2-bake method using a primer and a back surface coating is also employed.

  Pre-coated metal ideally has the same appearance (gloss and color tone) on the front and back surfaces, but the back surface of the pre-coated metal is inside the processed product after molding and is rarely seen. For example, if only two types of paint for the back surface, ie, high-gloss back surface paint and low-gloss back surface paint are prepared, and the surface has a relatively high gloss, the back surface is coated with a high-gloss back surface. When the surface gloss is relatively low, the number of paints used is often reduced and the economy is improved by applying a low-gloss backside paint on the back side.

  Of these, low-gloss coatings for back surfaces have been manufactured by blending inorganic powders such as silica, which have a gloss-reducing effect. However, coating workability is reduced due to increased viscosity, bending workability is reduced, and blocking resistance is reduced. In some cases, defects such as gloss transfer due to inferiority occur. Gloss transfer due to poor blocking resistance means that a pre-coated metal with different surface gloss and back side gloss is coiled, and when high pressure is applied while the front and back sides are in contact, This refers to a phenomenon in which the gloss is lowered and the gloss on the low gloss surface is increased, and the gloss appears to be transferred from the high gloss surface to the low gloss surface. This phenomenon is caused by pressing a low-gloss surface having fine irregularities against a relatively smooth high-gloss surface, so that fine irregularities of the low-gloss surface bite into the high-gloss surface and the smoothness is lowered. It is considered that the fine unevenness of the low gloss surface is crushed and smoothed by the smooth high gloss surface. When this phenomenon occurs, the surface gloss of the pre-coated metal changes while it is stored in a coiled state, and the gloss transfer becomes uneven because the change in gloss is particularly noticeable in parts that are locally loaded. Since uneven gloss transfer occurs, it becomes impossible to supply a homogeneous product.

JP-A-61-228069

  An object of the present invention is to provide a coating composition for a back surface of a pre-coated metal capable of forming a low gloss coating film excellent in coating workability, workability, blocking resistance, etc. on the back surface of the pre-coated metal, and An object of the present invention is to provide a precoat metal having a low gloss coating film on the back surface and excellent workability, blocking resistance and the like using this coating composition.

  As a result of intensive studies to solve the above problems, the present inventors have found that a binder component comprising a hydroxyl group-containing resin and a crosslinking agent contains resin fine particles having an average particle diameter in the range of 5 to 50 μm. By using the composition, it was found that a low-gloss coating film with significantly improved coating workability, workability, blocking resistance and the like could be formed, and the present invention was completed.

  That is, the present invention is based on 100 parts by weight of a binder component composed of the hydroxyl group-containing resin (A) and the crosslinking agent (B), and the resin fine particles (C) having an average particle diameter in the range of 5 to 50 μm are 1 to 30 weights. By providing a part, a coating composition for a back surface of a pre-coated metal capable of forming a low gloss coating film excellent in coating workability, workability, blocking resistance and the like is provided.

  In addition, the present invention sequentially forms a primer coating and a top coating, or a primer coating, an intermediate coating and a top coating on the surface of a metal plate which may be subjected to chemical conversion treatment on the front surface and / or the back surface. On the back surface, based on 100 parts by weight of the binder component comprising the hydroxyl group-containing resin (A) and the crosslinking agent (B), the resin fine particles (C) having an average particle diameter in the range of 5 to 50 μm are 1 to 30 weights. By forming a low-gloss coating film using a coating composition containing a part, a precoat metal having a low-gloss coating film on the back surface and excellent in processability, blocking resistance and the like is provided.

  In addition, the present invention sequentially forms a primer coating and a top coating, or a primer coating, an intermediate coating and a top coating on the surface of a metal plate which may be subjected to chemical conversion treatment on the front surface and / or the back surface. And, on the back surface, based on 100 parts by weight of the binder film composed of the primer coating film and the hydroxyl group-containing resin (A) and the crosslinking agent (B), the resin fine particles having an average particle diameter in the range of 5 to 50 μm (C ) Pre-coated metal excellent in workability, blocking resistance, anticorrosion, etc., having a low gloss coating on the back surface by sequentially forming a low gloss coating using a coating composition containing 1 to 30 parts by weight I will provide a.

  The coating composition of the present invention has excellent coating workability and can form a low-gloss coating film excellent in workability, blocking resistance, etc. on the back surface of the steel sheet for precoat metal, and thus excellent processing. A low-gloss pre-coated metal having high properties and blocking resistance can be obtained.

  The coating composition of the present invention comprises resin fine particles (C) 1 having an average particle diameter in the range of 5 to 50 μm based on 100 parts by weight of a binder component comprising a hydroxyl group-containing resin (A) and a crosslinking agent (B). It is a coating composition for the back surface of the precoat metal characterized by containing -30 weight part.

Hydroxyl-containing resin (A)
The hydroxyl group-containing resin (A) in the composition of the present invention is a resin having a hydroxyl group in the molecule, and is usually used for thermosetting paints such as polyester resins, acrylic resins, epoxy resins, and phenol resins. The known resins can be used, and these hydroxyl group-containing resins are used alone or in admixture of two or more. Among these, at least one hydroxyl group-containing resin selected from a hydroxyl group-containing polyester resin and a hydroxyl group-containing epoxy resin can be preferably used.

  The hydroxyl group-containing polyester resin is a polyester resin having a hydroxyl group in the molecule, and is an oil-free polyester resin, an oil-modified alkyd resin, and modified products of these resins, such as a urethane-modified polyester resin, a urethane-modified alkyd resin, and an epoxy-modified polyester. Resin etc. are mentioned.

  The oil-free polyester resin is an esterified product of a polybasic acid component and a polyhydric alcohol component. Examples of the polybasic acid component include one or more selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride, and the like. Dibasic acids and lower alkyl esterified products of these acids are mainly used, and if necessary, monobasic acids such as benzoic acid, crotonic acid, pt-butylbenzoic acid, trimellitic anhydride, methylcyclohexericarboxylic acid , Tribasic or higher polybasic acids such as pyromellitic anhydride are used in combination. Examples of the polyhydric alcohol component include divalent compounds such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, and 1,6-hexanediol. Alcohol is mainly used, and a trihydric or higher polyhydric alcohol such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol can be used in combination as necessary. These polyhydric alcohols can be used alone or in admixture of two or more. The esterification or transesterification reaction of both components can be carried out by a method known per se.

  In addition to the acid component and alcohol component of the oil-free polyester resin, the alkyd resin is obtained by reacting an oil fatty acid by a method known per se. Examples of the oil fatty acid include coconut oil fatty acid, soybean oil fatty acid, Examples thereof include linseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, and kiri oil fatty acid. The oil length of the alkyd resin is preferably 30% or less, particularly about 5 to 20%.

  As the urethane-modified polyester resin, the oil-free polyester resin or the low-molecular weight oil-free polyester resin obtained by reacting an acid component and an alcohol component used in the production of the oil-free polyester resin, a polyisocyanate compound and Examples thereof include those reacted by a method known per se. The urethane-modified alkyd resin is obtained by reacting the alkyd resin or a low molecular weight alkyd resin obtained by reacting each component used in the production of the alkyd resin with a polyisocyanate compound by a method known per se. Things are included. Polyisocyanate compounds that can be used in the production of urethane-modified polyester resins and urethane-modified alkyd resins include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4 ′. -Methylenebis (cyclohexyl isocyanate), 2,4,6-triisocyanatotoluene and the like. As the urethane-modified resin, generally, a resin having a modification degree in which the amount of the polyisocyanate compound forming the urethane-modified resin is 0.1 to 30% by weight with respect to the urethane-modified resin can be suitably used. .

  As an epoxy-modified polyester resin, a polyester resin produced from each component used in the production of the polyester resin is used, a reaction product of a carboxyl group of this resin and an epoxy group-containing resin, a hydroxyl group in the polyester resin and an epoxy resin The reaction product by reaction, such as addition of a polyester resin and an epoxy resin, condensation, grafting, etc., such as the product which couple | bonded the hydroxyl group in it through the polyisocyanate compound, can be mentioned. In general, the degree of modification in the epoxy-modified polyester resin is preferably such that the amount of the epoxy resin is 0.1 to 30% by weight with respect to the epoxy-modified polyester resin.

  Of the polyester resins described above, particularly preferred are oil-free polyester resins and alkyd resins.

  In addition, the hydroxyl group-containing polyester resin has a hydroxyl value in the range of 40 to 140 mgKOH / g, particularly 60 to 120 mgKOH / g, from the viewpoint of the balance of processability, hardness, curability and resistance to cracking of the resulting coating film. The number average molecular weight is in the range of 1,000 to 20,000, particularly 3,000 to 15,000, and the glass transition temperature (Tg point) is −40 ° C. to 100 ° C., particularly −20 to 20 ° C. It is preferably within the range of 80 ° C.

  The hydroxyl group-containing epoxy resin is an epoxy resin having a hydroxyl group in the molecule, a bisphenol type epoxy resin, a novolac type epoxy resin, and a modified epoxy resin in which various modifiers are reacted with the epoxy group or the hydroxyl group in these epoxy resins. And so on. In the production of the modified epoxy resin, the modification time with the modifier is not particularly limited, and it may be modified in the middle of the epoxy resin production or in the final stage of the epoxy resin production.

  The bisphenol-type epoxy resin is, for example, a resin obtained by condensing epichlorohydrin and bisphenol to a high molecular weight in the presence of a catalyst such as an alkali catalyst, if necessary, epichlorohydrin and bisphenol, and if necessary, an alkali catalyst or the like. Any of resins obtained by condensing into a low molecular weight epoxy resin in the presence of a catalyst and polyaddition reaction of the low molecular weight epoxy resin and bisphenol may be used.

  Examples of the bisphenol include bis (4-hydroxyphenyl) methane [bisphenol F], 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], 2, 2-bis (4-hydroxyphenyl) butane [bisphenol B], bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, p- (4-hydroxyphenyl) phenol, oxybis (4-hydroxyphenyl), sulfonylbis (4-hydroxyphenyl), 4,4′-dihydroxybenzophenone, bis (2-hydroxynaphthyl) methane, etc. Bisphenol A and bisphenol F are preferably used . The bisphenols can be used alone or as a mixture of two or more.

  As commercial products of bisphenol type epoxy resins, for example, Epicoat 828, 812, 815, 820, 834, 1001, 1004, 1007, 1009, 1010 manufactured by Japan Epoxy Resin Co., Ltd .; Asahi Ciba Araldite AER6099 manufactured by the company, and Epomic R-309 manufactured by Mitsui Chemicals.

  Examples of the novolak type epoxy resin that can be used as the epoxy resin include various novolak type epoxy resins such as a phenol novolak type epoxy resin, a cresol novolak type epoxy resin, and a phenol glyoxal type epoxy resin having a large number of epoxy groups in the molecule. Can be mentioned.

  As the modified epoxy resin, for example, an epoxy ester resin obtained by reacting a dry oil fatty acid with the bisphenol type epoxy resin or novolak type epoxy resin; and a polymerizable unsaturated monomer component containing acrylic acid or methacrylic acid is reacted. Epoxy acrylate resin; Urethane modified epoxy resin reacted with isocyanate compound; Amino group or quaternary ammonium by reacting amine compound with epoxy group in bisphenol type epoxy resin, novolac type epoxy resin or various modified epoxy resins Examples thereof include an amine-modified epoxy resin into which a salt is introduced.

  Among the epoxy resins described above, bisphenol type epoxy resins are particularly preferable.

In addition, the hydroxyl group-containing epoxy resin has a number average molecular weight of 1,000 to 20,000, particularly 2,000 to 10, in terms of the balance of processability, hardness, curability and resistance to cracking of the resulting coating film. Within the range of 1,000.
In the present invention, the glass transition temperature (Tg) is determined by differential thermal analysis (DTA), and the number average molecular weight is measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.

Cross-linking agent (B)
The crosslinking agent (B) can be used without particular limitation as long as it can be cured by reacting with the hydroxyl group-containing resin (A) by heating. Among them, amino resins and blocked polyisocyanate compounds can be used. At least one kind of cross-linking agent selected from can be suitably used.

  Examples of the amino resin include methylolated amino resins obtained by reacting amino components such as melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, and dicyandiamide with aldehyde. Examples of the aldehyde used in the above reaction include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. Moreover, what etherified the said methylolated amino resin with suitable alcohol can also be used as an amino resin. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.

  The blocked polyisocyanate compound is a compound obtained by blocking free isocyanate groups of a polyisocyanate compound with a blocking agent.

  Examples of the polyisocyanate compound before blocking include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as hydrogenated xylylene diisocyanate or isophorone diisocyanate; Organic diisocyanates such as aromatic diisocyanates such as 4'-diphenylmethane diisocyanate itself, or adducts of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins or water, or organic diisocyanates as described above. Examples thereof include cyclized polymers and isocyanurate biurets.

  Examples of the blocking agent for blocking the isocyanate group include phenols such as phenol, cresol and xylenol; ε-caprolactam; lactams such as δ-valerolactam and γ-butyrolactam; methanol, ethanol, n-, i- or t- Alcohols such as butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol; formamidoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, Oximes such as cyclohexane oxime; dimethyl malonate, diethyl malonate, ethyl acetoacetate, acetyl The blocking agent such as active methylene, such as acetone can be preferably used. By mixing the polyisocyanate compound and the blocking agent, free isocyanate groups of the polyisocyanate compound can be easily blocked.

  The mixing ratio of the hydroxyl group-containing resin (A) and the crosslinking agent (B) is within the range of hydroxyl group-containing resin (A) / crosslinking agent (B) = 50/50 to 95/5. It is preferable from points, such as property, workability, sclerosis | hardenability, and it is preferable to exist in the range of hydroxyl-containing resin (A) / crosslinking agent (B) = 60 / 40-90 / 10 especially.

Resin fine particles (C)
The resin fine particles (C) are resin fine particles having an average particle diameter of 5 to 50 μm, preferably 10 to 40 μm, and contribute to improving the blocking resistance of the cured coating film. The resin fine particles (C) are preferably those that do not completely melt when the coating is cured (baking and curing conditions for the coating), but here “not completely melted” means that they are not melted at all. And a state in which the peripheral surface of each fine particle is partially covered with the melt by being partially melted.

  If the average particle diameter of the resin fine particles (C) is less than 5 μm, the effect of improving the blocking resistance of the coating film is not sufficient, but it may be added for other effects such as improvement of resistance to cracking. On the other hand, if it exceeds 50 μm, the unevenness of the coating film surface on the back surface becomes large, so that gloss transfer is likely to occur, and the blocking resistance decreases. In addition, when roll coating, which is a general coating method for pre-coated metal, resin fine particles having a large particle diameter cannot pass through the gap between the rolls, which may cause poor coating workability.

  Examples of the resin type of the resin fine particles (C) include polyamide resins such as nylon 6, nylon 11, and nylon 12; polyimide resin, polyethylene resin, polypropylene resin, polyvinylidene fluoride resin, polytetrafluoroethylene, polyacrylonitrile resin, acrylic Resin, polyurethane resin, phenol resin, silicon resin, etc., among which at least one selected from the group consisting of polyamide resin, polyimide resin, polyacrylonitrile resin, acrylic resin, polyurethane resin, phenol resin, silicon resin Resin is preferable, and it is particularly preferable that it is particles of at least one resin selected from the group consisting of polyamide resin, polyacrylonitrile resin and acrylic resin, because the effect of improving blocking resistance is large. These resin fine particles (C) can be used alone or in combination.

  The compounding amount of the resin fine particles (C) is in the range of 1 to 30 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the binder component comprising the hydroxyl group-containing resin (A) and the crosslinking agent (B). It is. When the blending amount of the resin fine particles (C) is less than 1 part by weight, the effect of improving the blocking resistance of the coating film is not sufficient, while when it exceeds 30 parts by weight, the workability of the coating film and the coating workability are deteriorated.

  The coating composition of the present invention can consist essentially of the hydroxyl group-containing resin (A), the crosslinking agent (B), and the resin fine particles (C), but usually contains an organic solvent, and if necessary, Inorganic powder (D), lubricity imparting agent (E) known per se for coatings, curing catalyst, coloring pigment, glitter pigment, rust preventive pigment, organic resin fiber, glass beads, antifoaming agent, coating surface adjusting agent Further, it may contain an anti-settling agent.

  The organic solvent is blended as necessary for improving the paintability of the composition of the present invention, and can be used that can dissolve or disperse the hydroxyl group-containing resin (A) and the crosslinking agent (B). Specifically, for example, aromatic hydrocarbon solvents such as xylene and high boiling aromatic petroleum hydrocarbon solvents; ketone solvents such as cyclohexanone and isophorone; butyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl Examples include ester solvents such as ether acetate; alcohol solvents such as n-butanol and isobutanol; ether alcohol solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether. Boiling point Family petroleum hydrocarbon solvents are preferred. These organic solvents can be used alone or in admixture of two or more.

Inorganic powder (D)
Examples of the inorganic powder (D) include talc, clay, silica, mica, alumina, barium sulfate, calcium carbonate and the like, and these can be used alone or in combination. Among these, silica and talc are preferable as the inorganic powder.

  The amount of the inorganic powder (D) is 1 to 30 parts by weight, preferably 5 to 25 parts by weight, particularly preferably based on 100 parts by weight of the binder component comprising the hydroxyl group-containing resin (A) and the crosslinking agent (B). Is in the range of 10 to 20 parts by weight. If the blending amount of the inorganic powder (D) is 1 part by weight or less, the effect of improving the tack resistance of the coating film surface is not sufficient. On the other hand, if it exceeds 30 parts by weight, the workability and coating workability of the coating film are deteriorated.

Lubricating agent (E)
The lubricity-imparting agent (E) is preferably added to improve the scratch resistance of the coating film, and is 0.05 to 10 parts by weight, particularly 0.1 to 5 parts by weight, based on 100 parts by weight of the binder component. As a preferable lubricity imparting agent, for example, polyethylene wax, polypropylene wax, fluorine wax, carnauba wax, lanolin wax, microcrystalline wax, montan wax and the like can be mentioned.

  The said curing catalyst is mix | blended as needed in order to accelerate | stimulate the crosslinking reaction of hydroxyl-containing resin (A) and a crosslinking agent (B).

  For example, when an amino resin is used as the crosslinking agent (B) to crosslink the hydroxyl group-containing resin (A) and the amino resin, an acid catalyst is suitable, and among them, a sulfonic acid compound is preferably used. Representative examples of the sulfonic acid compounds include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and the like, and among them, p-toluenesulfonic acid, dodecylbenzenesulfonic acid. Is preferred. The acid catalyst may be partially or wholly neutralized with a secondary amine or a tertiary amine, and is preferably neutralized from the viewpoint of storage stability of the coating composition. .

  In addition, when a blocked polyisocyanate is used as the crosslinking agent (B) to crosslink the hydroxyl group-containing resin (A) and the blocked polyisocyanate, a curing catalyst that promotes dissociation of the blocking agent is suitable, and is suitable. Examples of the curing catalyst include tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, and 2-ethylhexane. Examples thereof include organometallic catalysts such as lead acid.

  Examples of the color pigment that can be used as necessary include color pigments commonly used in the paint field, such as white pigments such as titanium white and zinc white; cyanine blue; cyanine green; organic reds such as azo and quinacridone. Pigments: organic yellow pigments such as benzimidazolone-based, isoindolinone-based, isoindoline-based, and quinophthalone-based materials; inorganic colored pigments such as titanium yellow, bengara, carbon black, yellow lead, and various fired pigments.

  Examples of the bright pigments that can be used as necessary include bright pigments commonly used in the paint field, such as aluminum powder, copper powder, nickel powder, coated mica powder having pearly luster, and bright graphite. Can be mentioned.

  Examples of the rust preventive pigment that can be used as necessary include chromium-based rust preventive pigments such as strontium chromate, calcium chromate, zinc chromate, zinc potassium chromate, and barium chromate; ions such as calcium ion-exchanged silica. Exchanged silica, zinc phosphate, magnesium phosphate, zinc phosphite, aluminum phosphite, calcium phosphite, aluminum tripolyphosphate, zinc molybdate, oil absorption in the range of 30 to 200 ml / 100 g, preferably 60 to 180 ml / 100 g and Non-chromium rust preventive pigments such as small oil absorption silica fine powder having a pore volume in the range of 0.05 to 1.2 ml / g, preferably 0.2 to 1 ml / g.

  Examples of the metal plate used as an object to be coated of the coating composition of the present invention include untreated metal plates such as cold-rolled steel plates, galvanized steel plates, and aluminum plates; Metal plates formed by chemical conversion treatment such as acid treatment, chromate treatment, chromium phosphate treatment, zirconium treatment, etc. can be mentioned. Among them, galvanized steel sheets that have not been treated or have been subjected to chemical conversion treatment are preferably used. Can do.

  Examples of galvanized steel sheets include hot dip galvanized steel sheets, electrogalvanized steel sheets, iron-zinc alloy plated steel sheets, nickel-zinc alloy plated steel sheets, aluminum-zinc alloy plated steel sheets, and these galvanized steel sheets. The chemical conversion treatment zinc-plated steel plate etc. which give a process can be mentioned. As the chemical conversion treatment, zinc phosphate treatment or chromate treatment is common, but a chemical conversion treatment zinc-based plated steel sheet subjected to zirconium treatment or the like may be used.

  The chemical conversion treatment is generally performed on both the front and back surfaces of the metal plate, but may be performed only on either the front surface or the back surface.

  A primer coating film is formed on the surface of the metal plate that may be subjected to the above chemical conversion treatment, and an intermediate coating film is formed on the primer coating film as necessary. A coated metal plate can be obtained by forming a top coat film on the top and, if necessary, forming a primer coat film on the back surface, and then forming a coat film with the coating composition of the present invention.

  As the primer coating film, a coating film obtained from a polyester primer coating or an epoxy primer coating is suitable. As the primer paint for forming the primer coating film, a chromium-based primer containing a chromium-based anticorrosive pigment such as strontium chromate, zinc chromate, calcium chromate may be used, or low pollution that does not contain these chromium-based anticorrosive pigments. Non-chromium primer paints may be used. Examples of rust preventive pigments used in non-chromium primer paints include zinc oxide, zinc phosphate, magnesium phosphate, zinc zinc silicate, aluminum zinc phosphate, calcium zinc phosphate, zinc phosphite, calcium phosphite, Aluminum phosphite, calcium cyanamide, zinc-treated aluminum polyphosphate, aluminum tripolyphosphate, zinc calcium molybdate, zinc molybdate, zinc phosphomolybdate, aluminum phosphomolybdate, calcium ion-exchanged amorphous silica fine particles These may be used alone or in combination of two or more.

  In particular, a low pollution type coated steel sheet can be obtained by combining a chemically treated zinc-coated steel sheet subjected to non-chromium chemical conversion treatment and a low pollution non-chromium primer coating film.

  The primer coating is not particularly limited, and can be performed using, for example, roll coating, curtain flow coating, dip coating, spray coating, and the coating film thickness is not particularly limited. However, a dry film thickness of about 0.5 to 10 μm, preferably about 1 to 8 μm is suitable. When roll coating is performed, a baking condition of about 10 to 120 seconds is suitable so that the maximum material temperature (PMT) is 150 to 260 ° C.

  Moreover, corrosion resistance and workability are further improved by forming a three-coat coating film in which an intermediate coating film is sandwiched between a primer coating film and a top coating film.

  Since the intermediate coating film is preferably excellent in processability and needs to have excellent adhesion to the primer coating film and the top coating film, a polyester resin is used as the intermediate coating film. And what used the binder component as what mix | blended about 1-50 weight part of crosslinking agents, such as a melamine resin and a blocked polyisocyanate compound, with respect to 100 weight part of epoxy resins is suitable. Among them, those particularly suitable in terms of processability and cost are exemplified by using a polyester resin and a melamine resin as a binder component, and the polyester resin has a glass transition temperature of −40 to 40 ° C. and a number average molecular weight of 5,000. Examples include those containing a polyester resin having ˜50,000 and a hydroxyl value of 2 to 100 mg KOH / g in an amount of 50% by weight or more based on the total polyester resin component.

  In addition to the binder component, the intermediate coating usually contains an organic solvent, and if necessary, organic resin fine particles, inorganic powder, curing catalyst, coloring pigment, inorganic pigment, rust preventive pigment, antifoaming agent, coating surface It may contain a regulator, an anti-settling agent, and the like.

  The film thickness of the intermediate coating film is 10 to 45 μm as a dry film thickness, preferably about 15 to 40 μm from the viewpoint of coating workability. Two or more layers may be applied.

  The coating of the intermediate coating is not particularly limited, and can be performed using, for example, roll coating, curtain flow coating, immersion coating, spray coating, etc. About 10 to 120 seconds is suitable so that the maximum material temperature (PMT) is 150 to 260 ° C.

  The top coat film is preferably excellent in coating film appearance, weather resistance, and processability, and is preferably excellent in adhesion to the primer coating film and the intermediate coating film. As the top coat, a binder component obtained by blending a hydroxyl group-containing resin such as a hydroxyl group-containing polyester resin or a hydroxyl group-containing acrylic resin with a crosslinking agent such as a melamine resin or a blocked polyisocyanate compound is suitable. What mix | blended about 1-100 weight part of crosslinking agents, such as a melamine resin and a blocked polyisocyanate compound, with respect to 100 weight part of containing polyester resins is suitable. Usually, an organic solvent is blended in addition to this binder component, and further, if necessary, organic resin fine particles, organic resin fibers, inorganic powder, colored pigment, glitter pigment, rust preventive pigment, glass beads, lubricity imparting agent. Further, it may contain a curing catalyst, an antifoaming agent, a coating surface conditioner, an antisettling agent and the like.

  For example, roll coating, curtain flow coating, dip coating, spray coating, etc. can be used to apply the top coating onto the primer coating or intermediate coating, and the coating film thickness is also particularly limited. However, in the case of coil coating that is continuously applied by roll coating or the like, usually, a material reaching maximum temperature (PMT) of 160 to 260 ° C. is suitable for about 15 to 120 seconds. In particular, baking conditions within a range of 20 to 90 seconds at a PMT of 190 to 250 ° C. are suitable, and the film thickness at that time is 10 to 45 μm, preferably about 15 to 35 μm as a dry film thickness.

  In the present invention, the gloss of the coating film was evaluated according to the 60 ° specular gloss of JIS K5600-4-7 (1999). The low-gloss paint composition of the present invention is suitable as a paint to be applied on the back surface when a relatively low-gloss coating film (for example, 60 ° specular gloss is 35 or less) is formed on the surface of a pre-coated metal. In addition, it is possible to obtain a pre-coated metal that has less uncomfortable feeling on the back surface and is excellent in workability and blocking resistance.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Hereinafter, both “parts” and “%” are based on weight.

Synthetic synthesis example 1 of polyester resin
740 parts of phthalic anhydride, 498 parts of isophthalic acid, 145 parts of adipic acid in a reaction tank using a normal polyester resin production apparatus equipped with a heating device, a stirrer, a reflux device, a water separator, a rectifying column, a thermometer, 735 parts of neopentyl glycol and 236 parts of 1.6-hexanediol were charged and heated. After the raw material was melted, stirring was started, the reaction temperature was raised to 230 ° C., and the condensed water produced by maintaining at 230 ° C. for 2 hours was distilled out of the system through a rectifying column. Subsequently, 90 parts of xylol was added to the reaction vessel and the reaction was continued by switching to the solvent condensation method. When the acid value reached 5 mgKOH / g, the reaction was terminated and cooled. After cooling, 1414 parts of xylol was added to obtain a polyester resin solution A1 having a solid content of 60%. The obtained resin had a hydroxyl value of 79 mgKOH / g and a number average molecular weight of about 1,300.

Synthesis example 2
In Synthesis Example 1, the raw material composition initially charged in the reaction vessel was 592 parts of phthalic anhydride, 747 parts of isophthalic acid, 145 parts of adipic acid, 735 parts of neopentyl glycol, 295 parts of 1.6-hexanediol and 68 parts of trimethylolpropane. A polyester resin solution A2 having a solid content of 60% was obtained in the same manner except that the composition was obtained. The obtained resin had a hydroxyl value of 42 mgKOH / g and a number average molecular weight of about 2,100.

Manufacture example 1 of coating for back side
133 parts of polyester resin solution A1 synthesized in Synthesis Example 1 and 33 parts of Uban 20SE60 (Mitsui Toatsu Chemical Co., Ltd., butyl etherified melamine resin solution, solid content 60%) in a resin mixture of Solvesso 100 (manufactured by Esso Petrochemicals, In a solution obtained by mixing 30 parts of a high boiling petroleum solvent) and 5 parts of butanol, 79 parts of titanium white JR-701 (manufactured by Teica, titanium white pigment), 1 part of carbon black pigment, 20 parts of strontium chromate pigment, 30 parts of precipitated barium sulfate is pigment-dispersed, 10 parts of tough AR650M (manufactured by Toyobo Co., Ltd., acrylic resin fine particles, average particle diameter of about 30 μm) and high flat T-15P (manufactured by Gifu Shellac Manufacturing Co., Ltd., polyethylene wax, average) Add 10 parts of particle size 4μm, solid content 15%, and add Silicia 445 (Fuji Silysia) Co., Ltd., silica fine powder) was added to adjust the 60 ° specular gloss to 10 to obtain a paint base R1 for the back surface.

The 60 ° specular gloss was measured by applying a back coating base to a zirconium-treated hot-dip galvanized steel sheet with a thickness of 0.35 mm with a bar coater so that the dry coating amount was 9 g / m ^2. The coating film obtained by baking for 30 seconds under the condition that the PMT (material maximum temperature reached) is 220 ° C., according to the measuring method of 60 ° specular gloss specified in JIS K5600-4-7 (1999). I did it.

Production Example 2
133 parts of polyester resin solution A1 synthesized in Synthesis Example 1 and 33 parts of Uban 20SE60 (Mitsui Toatsu Chemical Co., Ltd., butyl etherified melamine resin solution, solid content 60%) in a resin mixture of Solvesso 100 (manufactured by Esso Petrochemicals, In a solution obtained by mixing 30 parts of a high-boiling petroleum solvent and 5 parts of butanol, 79 parts of titanium white JR-701 (manufactured by Teica, titanium white pigment), 1 part of carbon black pigment, 30 parts of precipitated barium sulfate 10 parts of Tuftic AR650M (Toyobo Co., Ltd., acrylic resin fine particles, average particle size of about 30 μm) and Hi-flat T-15P (Gifu Shellac Manufacturing Co., Ltd., polyethylene wax, average particle size of 4 μm, solid content) 15%) and 10 parts are added, and further Silicia 445 (manufactured by Fuji Silysia Co., Ltd., silica fine powder) is added to form 60 °. Adjusts to surface glossiness is 10, to obtain the back paint base R2.

Production Example 3
In Production Example 1, the amount of addition of Toughtic AR650M was changed from 10 parts to 30 parts, and production was carried out in the same manner as in Production Example 1 except that 60 ° specular gloss was adjusted to 2 with Silicia 445. Obtained.

Production Example 4
In Production Example 1, 20 parts of PERGOPAK M3 (manufactured by ALBEMALLE, urea-formaldehyde resin particles, average particle size of about 6 to 8.5 μm) is blended in place of 10 parts of addition amount of tuftic AR650M. Was produced in the same manner as in Production Example 1 except that the 60 ° specular gloss was adjusted to 5 to obtain a back surface paint base R4.

Production Example 5
In Production Example 1, instead of 10 parts of Tufic AR650M, 5 parts of Orgasol 2002ES-3 (manufactured by ARKEMA, nylon 12 resin fine particles, average particle diameter of about 30 μm) was blended, and 60 parts were added by Silicia 445. A production was carried out in the same manner as in Production Example 1 except that the mirror glossiness was adjusted to 22, to obtain a back surface paint base R5.

Production Example 6
In Production Example 1, instead of 10 parts of tuftic AR650M, 1 part of TEXTURE 5380W (manufactured by Shamrock Technologies, Inc., polypropylene resin fine particles, average particle diameter of about 40 μm) and 5 parts of tuftic AR650M were blended, and 60 ° specular gloss by Silicia 445 Was prepared in the same manner as in Production Example 1 except that the value was adjusted to 8, and a back surface paint base R6 was obtained.

Production Example 7
Epicote 1007 (Japan Epoxy Resin, bisphenol A type epoxy resin, number average molecular weight 2900, epoxy equivalent of about 2250) is subjected to addition reaction of trimellitic anhydride, hydroxyl value of about 190 mgKOH / g, acid value of about 40 mgKOH / g 75 parts of a methyl ethyl ketone solution having a solid content of 40%, and Byron KS-1480V (polyester resin manufactured by Toyobo Co., Ltd., number average molecular weight 8,200, glass transition temperature 5 ° C., hydroxyl value 28 mg KOH / g) 1500 = 20 parts of Solvesso 100 and 5 parts of butanol were mixed in 138 parts of a resin solution dissolved in a mixed solvent of 50/50 and adjusted to a solid content of 40% and 25 parts of a resin solution of 60% solids Uban 20SE60. In the solution obtained, titanium white JR-7 161 parts, 0.8 parts of carbon black pigment, 15 parts of aluminum tripolyphosphate and 23 parts of precipitated barium sulfate were pigment-dispersed, Olgasol 2002ES-3 (manufactured by Arkema, nylon 12 resin fine particles, average particle diameter About 30 μm) and 5 parts of High Flat T-15P (Gifu Shellac Manufacturing Co., Ltd., polyethylene wax, average particle size 4 μm, solid content 15%) are added, and Silicia 445 (Fuji Silysia, silica fine powder) is added. Was added to adjust the 60 ° specular gloss to 5 to obtain a backside paint base R7.

Production Example 8 (for comparative example)
133 parts of polyester resin solution A1 synthesized in Synthesis Example 1 and 33 parts of Uban 20SE60 (Mitsui Toatsu Chemical Co., Ltd., butyl etherified melamine resin solution, solid content 60%) in a resin mixture of Solvesso 100 (manufactured by Esso Petrochemicals, In a solution obtained by mixing 30 parts of a high boiling petroleum solvent) and 5 parts of butanol, 79 parts of titanium white JR-701 (manufactured by Teica, titanium white pigment), 1 part of carbon black pigment, 20 parts of strontium chromate pigment, 30 parts of precipitated barium sulfate is pigment-dispersed, 10 parts of High Flat T-15P (Gifu Shellac Manufacturing Co., Ltd., polyethylene wax, average particle size 4 μm, solid content 15%) is added, and Silicia 445 (Fuji Silysia) is added. , Silica fine powder) is added to adjust the 60 ° specular gloss to 10, and the back surface paint base R 8 was obtained.

Production Example 9 (for comparative example)
133 parts of polyester resin solution A1 synthesized in Synthesis Example 1 and 33 parts of Uban 20SE60 (Mitsui Toatsu Chemical Co., Ltd., butyl etherified melamine resin solution, solid content 60%) in a resin mixture of Solvesso 100 (manufactured by Esso Petrochemicals, In a solution obtained by mixing 30 parts of a high boiling petroleum solvent) and 5 parts of butanol, 79 parts of titanium white JR-701 (manufactured by Teica, titanium white pigment), 1 part of carbon black pigment, 20 parts of strontium chromate pigment, 30 parts of precipitated barium sulfate is pigment-dispersed, 0.5 parts of Toughtic AR650M (Toyobo Co., Ltd., acrylic resin fine particles, average particle diameter of about 30 μm) and High Flat T-15P (Gifu Shellac Manufacturing Co., Ltd., polyethylene wax) 10 parts of an average particle diameter of 4 μm and a solid content of 15%), and further Silicia 445 (Fuji Silysi A silica fine powder manufactured by A Co., Ltd.) was added to adjust the 60 ° specular gloss to 10 to obtain a backside paint base R9.

Production Example 10 (for comparative example)
133 parts of polyester resin solution A1 synthesized in Synthesis Example 1 and 33 parts of Uban 20SE60 (Mitsui Toatsu Chemical Co., Ltd., butyl etherified melamine resin solution, solid content 60%) in a resin mixture of Solvesso 100 (manufactured by Esso Petrochemicals, In a solution obtained by mixing 30 parts of a high-boiling petroleum solvent) and 5 parts of butanol, 79 parts of titanium white JR-701 (manufactured by Teica, titanium white pigment), 1 part of carbon black pigment, 20 parts of strontium chromate pigment, and 30 parts of precipitated barium sulfate was mixed, and the pigment was dispersed with a shaker. 10 parts of Toughtic AR650MZ (manufactured by Toyobo Co., Ltd., acrylic resin fine particles, average particle diameter of about 60 μm) and Hi-flat T-15P (manufactured by Gifu Shellac Manufacturing Co., Ltd.) 10 parts of polyethylene wax, average particle size 4 μm, solid content 15%) Shea 445 (manufactured by Fuji Silysia Co., Ltd., silica fine powder) was added to adjust the 60 ° specular gloss to 10, and a back surface paint base R10 was obtained.

Primer paint production example 11
Byron EP-2940 (Note 1) 266.7 parts (80 parts in solids) dissolved in 20 parts of a mixed solvent of cyclohexanone / swazol 1500 (manufactured by Maruzen Petrochemical Co., Ltd., aromatic petroleum-based high boiling solvent) = 50/50 In this resin solution, 30 parts of aluminum tripolyphosphate and 20 parts of titanium white JR-701 (manufactured by Teika Co., Ltd., titanium white pigment) are mixed and dispersed with a shaker to give 20 parts of Cymel 303 (Note 2) and a natural cure. By adding 2.0 parts of 5225 (Note 3), a primer paint P1 was obtained.
(Note 1) Byron EP-2940: manufactured by Toyobo Co., Ltd., an epoxy-modified polyester resin solution having a solid content of 30%, the number average molecular weight of the resin is about 10,000, and the glass transition temperature is about 72 ° C.
(Note 2) Cymel 303: manufactured by Nippon Cytec Industries, Ltd., low-nuclear methylated melamine resin, solid content of about 100%.
(Note 3) Neicure 5225: manufactured by King Industries, USA, amine neutralized solution of dodecylbenzenesulfonic acid, curing catalyst.

Intermediate coating production example 12
Byron KS-1460V (polyester resin manufactured by Toyobo Co., Ltd., number average molecular weight 15,000, glass transition temperature 7 ° C., hydroxyl value 11 mg KOH / g) 75 parts of cyclohexanone / swazole 1500 = 50/50 mixed solvent 112.5 parts To obtain a resin solution p having a solid content of 40%. To 75 parts of the resin solution, 50 parts of Taipei CR-95 (manufactured by Ishihara Sangyo Co., Ltd., titanium white pigment), 4 parts of carbon black pigment and 25 parts of the mixed solvent were mixed, and pigment dispersion was performed to obtain a pigment paste.

  To 154 parts of the obtained pigment paste, 112.5 parts of resin solution p, Cymel 303 (Nippon Cytec Industries, low-nuclear methylated melamine resin, solid content of about 100%), 25 parts of Neicure 5225 (King, USA) 2 parts of an amine neutralized solution of dodecylbenzenesulfonic acid, curing catalyst, active ingredient 25%) manufactured by Industrieise Co., Ltd. was added and stirred to obtain an intermediate coating material B1.

Topcoat production example 13
50 parts of the polyester resin solution A2 having a solid content of 60% obtained in Synthesis Example 2, 50 parts of Taipei CR-95 (Ishihara Sangyo Co., Ltd., titanium white pigment), 4 parts of carbon black pigment, and 1500 of cyclohexanone / swazole (Maruzen) 25 parts of 50/50 mixed solvent (manufactured by Petrochemical Co., Ltd., aromatic petroleum-based high-boiling solvent) was mixed, and pigment dispersion was performed to obtain a pigment paste.

  To 154 parts of the obtained pigment paste, 75 parts of polyester resin solution A2, 25 parts of Cymel 303 (manufactured by Nippon Cytec Industries, Ltd., low-nucleated methylated melamine resin, solid content of about 100%), NACURE 5225 (King Industries, USA) 2 parts by amine, neutralized amine solution of dodecylbenzenesulfonic acid, curing catalyst, active ingredient 25%) and 15 parts of silicia 445 (manufactured by Fuji Silysia Co., Ltd., silica fine powder) were added to obtain a top coat T1. .

Production Example 14
50 parts of the polyester resin solution A2 having a solid content of 60% obtained in Synthesis Example 2, 50 parts of Taipei CR-95 (Ishihara Sangyo Co., Ltd., titanium white pigment), 4 parts of carbon black pigment, and 1500 of cyclohexanone / swazole (Maruzen) 25 parts of 50/50 mixed solvent (manufactured by Petrochemical Co., Ltd., aromatic petroleum-based high-boiling solvent) was mixed, and pigment dispersion was performed to obtain a pigment paste.

  To 154 parts of the obtained pigment paste, 75 parts of polyester resin solution A2, 25 parts of Cymel 303 (manufactured by Nippon Cytec Industries, Ltd., low-nucleated methylated melamine resin, solid content of about 100%), NACURE 5225 (King Industries, USA) 2 parts by amine, neutralized amine solution of dodecylbenzene sulfonic acid, curing catalyst, active ingredient 25%), ORGASOL 2002ES-3 (manufactured by ARKEMA, nylon 12 resin fine particles, average particle size of about 30 μm) 12 parts, 2 parts of high flat T-15P (Gifu Shellac Manufacturing Co., Ltd., polyethylene wax, average particle size 4 μm, solid content 15%) and 7 parts of Siricia 445 (Fuji Silysia Co., silica fine powder) are added. A top coat T2 was obtained.

Production Example 15
100 parts of the polyester resin solution A2 having a solid content of 60% obtained in Synthesis Example 2 was mixed with 10 parts of xylol, 70 parts of titanium white and 5 parts of phthalocyanine blue, and the pigment was dispersed with a shaker. Next, 42 parts of the polyester resin solution A2, 15 parts of Cymel 303 (Nippon Cytec Industries, Ltd., low-nuclear methylated melamine resin, solid content of about 100%), Nacure 5225 (manufactured by King Industries, USA) 2 parts neutralized product of secondary amine of dodecylbenzene sulfonic acid), 3.5 parts of di-normal butylamine and 10 parts of silicia 445 (manufactured by Fuji Silysia Co., Ltd., silica fine powder), and stirred uniformly to top coat T3 Got.

Create test coating
Preparation Examples 1 to 7 and Comparative Examples 1 to 3 of Coating Plate for Back Surface
The back coating R1, R3 to R10 was applied to a zirconium-treated hot-dip galvanized steel sheet having a thickness of 0.35 mm with a bar coater so that the dry coating amount was 9 g / m ^2. ) Was baked for 30 seconds under the condition of 220 ° C. to obtain each test coated plate. In addition, the primer coating P1 is applied to a zirconium-treated hot-dip galvanized steel sheet having a thickness of 0.35 mm so that the dry coating amount is 9 g / m ² , and the PMT (material maximum temperature reached) is 210 ° C. After being baked for 25 seconds, the back coating material R2 is applied with a bar coater so that the dry coating amount is 9 g / m ² , and the PMT (material maximum temperature reached) is 220 ° C. for 30 seconds. Baking was performed to obtain a test coated plate.

  Each test coated plate was tested according to the following test method. The obtained results are shown in Table 1 below.

Test method 60 ° specular gloss: measured according to JIS K5600-4-7 (1999).

Appearance of coating film: The coated plate was visually evaluated.
(Double-circle): The unevenness | corrugation of the coating-film surface is uniform, and a coarse grain is not recognized.
○: Concavities and convexities on the surface of the coating film are uniform, but slightly coarse particles are observed.
(Triangle | delta): The unevenness | corrugation of the coating-film surface is uneven, and a coarse grain is recognized considerably.
X: The unevenness | corrugation of the coating-film surface is uneven and a coarse grain is recognized remarkably.

Workability: Cut the painted plate into 70x150mm size, and at the room temperature of 20 ° C, with the coated plate surface outside and two 0.35mm thick steel plates inside the folded part The plate was bent 180 degrees in a vise (2T processing), and the state of the coating film in the bent portion was visually observed and evaluated according to the following criteria. As the coated plate, two types were used: a coated plate that was not treated after coating (initial stage) and a painted plate that was immersed in boiling water for 20 hours after coating (secondary). In the following tests for processing adhesion, impact resistance, and scratch resistance, two types of coated plates, an initial and a secondary, were used.
A: No cracking or peeling of the coating is observed in the processed part.
○: Slight cracking or peeling of the coating film is observed in the processed part,
(Triangle | delta): The crack or peeling of a coating film is recognized considerably in a process part,
X: The crack or peeling of a coating film is recognized remarkably in a process part.

Work adhesion: In the above workability test, cellophane adhesive tape is affixed to the folded part of the 2T processed painted plate, and when the tape is peeled off instantaneously, the degree of peeling of the coating film on the folded part is as follows. It was evaluated by.
A: No peeling of the coating film is observed in the processed part.
○: Peeling of the coating film is slightly observed in the processed part,
Δ: Peeling of the coating film is considerably recognized in the processed part,
X: Peeling of the coating film is remarkably observed in the processed part.

Impact resistance: Painted according to JIS K5600-5-3-6 (1999) DuPont impact resistance test under conditions of weight drop weight 500g, striker tip diameter 1/2 inch, drop weight height 50cm. An impact was given to the painted surface of the board. Then, a cellophane adhesive tape was applied to the part where the impact on the coating surface was applied, and the peeled state of the coating film was evaluated when the tape was instantaneously peeled off.
A: No peeling of the coating film is observed on the coated surface.
○: Peeling of the coating film is slightly observed on the coated surface,
Δ: Peeling of the coating film is considerably observed on the coated surface,
X: Peeling of the coating film is remarkably observed on the coated surface.

Scratch resistance: Using a coin scratch tester (manufactured by Kayaku Giken Kogyo Co., Ltd.) at a room temperature of 20 ° C. while pressing the edge of a 10-yen copper coin at a 45 ° angle and applying a load of 3 kg. The degree of scratching was evaluated when a 10-yen copper coin was pulled about 30 mm at a speed of 10 mm / second to scratch the coated surface.
◎: No metal substrate is found in the scratched portion ○: Metal substrate is slightly seen in the scratched portion △: Metal substrate is considerably seen in the scratched portion ×: Most of the coating is on the scratched portion You can see the metal base clearly.

Corrosion resistance: After the coated plate was cut into a size of 70 × 150 mm, the back surface and the cut surface were sealed with a rust preventive paint. Next, a cross-cut reaching the substrate is put in the substantially central part of the painted plate, and a 2T-folded portion is applied to a location approximately 1 cm from the end of the painted plate, which is used as a test plate. And subjected to a salt spray test. The salt spray test time was 500 hours, the degree of rust generation was evaluated for the processed parts, and the average blister width was evaluated for the cross-cut parts based on the following criteria.
Rust generation degree in the processed part ◎: No rust generation in the processed part,
○: It is recognized that the degree of occurrence of rust is less than 10% of the length of the processed part,
Δ: The degree of occurrence of rust is 10% or more and less than 30% of the length of the processed part.
X: The degree of occurrence of rust is 30% or more of the length of the processed part,
Average swelling width of the cross cut part ◎: No swelling is observed in the cross cut part.
○: The average swelling width on one side from the cut wound is less than 1 mm.
(Triangle | delta): The average swelling width | variety of one side from a cut crack is 1 mm or more and less than 5 mm,
X: The average swelling width of one side from the cut flaw is 5 mm or more.

  The general coating film performance of Examples 1 to 7 is excellent in workability, impact resistance, and coating film appearance as compared with the performance of the conventional backside coating film shown in Comparative Examples 1 to 3, and there is no problem in other performances. It was a level.

Production Example 13 of Surface Paint Plate 13
Primer paint P1 is applied to a zirconium-treated hot-dip galvanized steel sheet having a thickness of 0.35 mm so that the dry coating amount is 9 g / m ² , and the PMT (material maximum temperature reached) is 210 ° C. After baking for 2 seconds, top coat T1 is applied onto the primer coating so that the dry coating amount is 30 g / m ² and baking is performed for 30 seconds under the condition that PMT (material maximum temperature reached) is 220 ° C. The coated steel plate K1 was obtained. The gloss of the coating film was 20.

Production Example 14
Primer paint P1 is applied to a zirconium-treated hot-dip galvanized steel sheet having a thickness of 0.35 mm so that the dry coating amount is 9 g / m ² , and the PMT (material maximum temperature reached) is 210 ° C. After baking for 2 seconds, the intermediate coating material B1 is applied onto the primer coating so that the dry coating amount is 34 g / m ² and the PMT (material maximum temperature reached) is 210 ° C. for 25 seconds. After baking, the top coating T2 is applied onto the intermediate coating film so that the dry coating amount is 34 g / m ² and baked for 30 seconds under the condition that the PMT (material maximum temperature reached) is 230 ° C. The coated steel plate K2 was obtained. The coating film was a matte coating film having fine irregularities and having a design property, and the glossiness of the coating film was 5.8.

Production Example 15
Primer paint P1 is applied to a zirconium-treated hot-dip galvanized steel sheet having a thickness of 0.35 mm so that the dry coating amount is 9 g / m ² , and the PMT (material maximum temperature reached) is 210 ° C. After baking for 2 seconds, the intermediate coating material B1 is applied onto the primer coating so that the dry coating amount is 34 g / m ² and the PMT (material maximum temperature reached) is 210 ° C. for 25 seconds. After baking, the top coating T3 is applied onto the intermediate coating film so that the dry coating amount is 38 g / m ² and baked for 30 seconds under the condition that the PMT (material maximum temperature reached) is 230 ° C. The coated steel plate K3 was obtained. The coating film was a matte coating film having a design and having a hazy pattern, and the glossiness of the coating film was 1.5.

Blocking resistance test The surface coating plate obtained above and the coating plate coated with the back surface coating material prepared in Examples 1 to 6 and Comparative Example 1 were each cut to a size of 5 cm × 5 cm, and the surface coating was applied. After the plate was overlaid for 24 hours under the conditions of a temperature of 40 ° C. and a load of 80 kg / cm ² so that the back coating film of the coating plate on which the top coating film of the plate and the coating film by the back coating were formed contacted each other, After peeling off the two test plates, the state of the top coat film was observed and evaluated according to the following criteria. The results are shown in Table 2 below.
A: No abnormality is observed on the painted surface.
A: Gloss unevenness is slightly observed on the coated surface, but recovers within one day at room temperature.
(Triangle | delta): Gloss unevenness is recognized by the coating surface and it does not recover even if it is left at room temperature for 1 day.
X: Gloss significantly different from the gloss before the test, or marked gloss unevenness is observed on the coated surface, and it does not recover even if left at room temperature for 1 day.

The anti-blocking properties of Examples 1 to 7 were superior to the conventional back coating films shown in Comparative Examples 1 to 3, and were at a level with no problem.

Claims (14)

  Based on 100 parts by weight of the binder component composed of the hydroxyl group-containing resin (A) and the crosslinking agent (B), 1-30 parts by weight of resin fine particles (C) having an average particle diameter in the range of 5-50 μm are contained. A coating composition for the back side of a pre-coated metal characterized by The coating composition for the back surface of the precoat metal according to claim 1, wherein the hydroxyl group-containing resin (A) is a hydroxyl group-containing polyester resin having a hydroxyl value of 40 to 140 mgKOH / g. The coating composition for the back surface of the precoated metal according to claim 1 or 2, wherein the hydroxyl group-containing resin (A) is in the range of a number average molecular weight of 1,000 to 20,000 and a glass transition temperature of -40 to 100 ° C. The coating composition for the back surface of the precoat metal according to any one of claims 1 to 3, wherein the crosslinking agent (B) is at least one crosslinking agent selected from a blocked polyisocyanate compound and an amino resin.   The coating material for the back surface of the precoat metal according to any one of claims 1 to 4, wherein the resin fine particles (C) are particles of at least one resin selected from the group consisting of a polyamide resin, a polyacrylonitrile resin, and an acrylic resin. Composition.   The inorganic powder (D) is further contained in an amount of 1 to 30 parts by weight based on 100 parts by weight of the binder component comprising the hydroxyl group-containing resin (A) and the crosslinking agent (B). The coating composition for the back surface of the precoat metal according to item 1.   The coating composition for the back surface of the precoat metal according to claim 6, wherein the inorganic powder (D) is silica.   Furthermore, the lubricity imparting agent (E) is contained in an amount of 0.05 to 10 parts by weight based on 100 parts by weight of the binder component comprising the hydroxyl group-containing resin (A) and the crosslinking agent (B). The coating composition for back surfaces of the precoat metal of any one of -7.   The coating composition according to any one of claims 1 to 8, wherein a primer coating and a top coating are sequentially formed on the surface of a metal plate that may be subjected to chemical conversion treatment on the front and / or back. A pre-coated metal, characterized in that a film is formed.   The primer coating film and the top coating film are sequentially formed on the surface of the metal plate that may be subjected to chemical conversion treatment on the front surface and / or the back surface, and the primer coating film and the any one of claims 1 to 8 are formed on the back surface. A pre-coated metal, wherein a coating film of the coating composition is sequentially formed.   The primer coating film, the intermediate coating film and the top coating film are sequentially formed on the surface of the metal plate which may be subjected to chemical conversion treatment on the front surface and / or the back surface, and the back surface according to any one of claims 1 to 8. A pre-coated metal, characterized in that a film is formed of the coating composition.   A primer coating film, an intermediate coating film, and a top coating film are sequentially formed on the surface of the metal plate which may be subjected to chemical conversion treatment on the front surface and / or the back surface, and the primer coating film on the back surface and any one of claims 1 to 8. A pre-coated metal, wherein a coating of the coating composition according to item 1 is sequentially formed.   The intermediate coating that forms the intermediate coating film has a polyester resin and a melamine resin or a blocked polyisocyanate compound as a binder component, and the polyester resin has a glass transition temperature of −40 to 40 ° C. and a number average molecular weight of 5,000 to 50, The precoated metal according to claim 11 or 12, wherein the polyester resin having a 000 and a hydroxyl value of 2 to 100 mgKOH / g is contained in an amount of 50% by weight or more based on the total polyester resin component. The precoat metal according to any one of claims 9 to 13, wherein the gloss value of the top coat film on the surface is 1 to 35 in terms of 60 ° specular gloss.