JP2006182967A - Coating composition and coated metal plate using the same and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating composition capable of producing thick-coated film, which can give a coated film having good rough surface appearance formed by granule and excellent anti-blocking ability, anti-tacking ability, etc. <P>SOLUTION: A coating composition comprises 100 pts.wt. of a binder ingredient containing (A) a hydroxy-containing polyester resin having a hydroxy value of 5-95 mgKOH/g and (B) a block isocyanate compound, 0.5-20 pts.wt. of at least one resin granules selected from (C) a melamine-formaldehyde resin, a benzoguanamine-formaldehyde resin and a urea-formaldehyde resin, and (D) 0.5-50 pts.wt. of resin particles having an average particle size of 8-70 μm, the resin being other than a melamine-formaldehyde resin, a benzoguanamine-formaldehyde resin and a urea-formaldehyde resin. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides a coating composition capable of forming a thick film coating film even by baking at a high temperature for a short time, and capable of forming a coating film excellent in hardness, workability, corrosion resistance, blocking resistance, tack resistance, etc., and the coating composition The present invention relates to a coated metal plate using an object and a method for producing the painted metal plate.

  2. Description of the Related Art Conventionally, pre-coated metal sheets that are coated by continuous coating such as coil coating can be manufactured at low cost, and are therefore widely used for building materials such as roofs and walls and for processing equipment such as audio, refrigerators, and partitions. In these fields, in order to further expand sales channels, improvements in design and long-term durability are required. Conventionally, as a pre-coated steel sheet suitable for these purposes, there is a PVC steel sheet. This is a coating of a polyvinyl chloride sol paint on a metal plate with a thick film. Embossing is performed on the formed film to provide design, and the thick film is excellent in durability. However, since the polyvinyl chloride sol paint generates dioxins when the coating film is baked, environmental pollution becomes a problem, and the development of alternative products has been demanded.

  However, since the coil coating is applied at a high speed, baking at a high temperature for a short time is required. However, with a commonly used paint, there is a problem that if the film is thickened, there will be a crack during baking, When the film is thickened, there is a problem that the processability of the coating film is lowered.

  In order to solve these problems, a coating composition in which resin fine particles are added to a binder component composed of a polyester resin having a high molecular weight and a low glass transition temperature and a blocked polyisocyanate compound blocked with ε-caprolactam has been proposed (Patent Document 1). reference.). With this technique, it was possible to form a film excellent in workability and blocking resistance, and to prevent the occurrence of cracking even when a thick film was applied. This coating film has fine irregularities formed on the surface, and can obtain a coating film having an appearance that is similar to the embossed steel sheet by the polyvinyl chloride sol paint, and can be used as an alternative to the embossed steel sheet.

  However, since the coating film is soft, it is necessary to pay attention to tack resistance particularly at high temperatures, and it is necessary to consider the usage environment and the storage conditions of the coated coil.

Also, instead of the usual two-coat film, a three-coat film is formed by sequentially forming a primer film, an intermediate coat film and a top coat film. In addition, it was proposed to use a coating film having a shrinkage pattern as the top coating film (see Patent Document 2).
In the coating film obtained by this method, very fine wrinkles are formed on the surface of the coating film, and light can be irregularly reflected to obtain a unique appearance with almost no gloss.

  However, in some cases, an uneven appearance formed by particles as in Patent Document 1 is required, and in this case, the method of Patent Document 1 is used. In particular, when high workability is required, it is considered that the top coat film of Patent Document 1 is formed on the primer film and the intermediate coat film disclosed in Patent Document 2 to form a three-coat film. The tack resistance at a high temperature was further lowered as compared with the case of the 2-coat coating film. In addition, when fine particles of ordinary organic resin (about 0.5 to 8 μm) and a silica-based matting agent were added to improve the tack resistance, workability and designability were greatly reduced.

JP 2000-7988 A JP 2000-204483 A

  An object of the present invention is to provide a coating composition that can be applied to a thick film, has a good uneven appearance formed by particles, and can form a coating film excellent in blocking resistance, tack resistance, etc. Is to provide things.

  As a result of intensive studies to solve the above problems, the present inventors have found that a binder component composed of a hydroxyl group-containing polyester resin and a blocked polyisocyanate compound and resin fine particles having an average particle size in the range of 8 to 70 μm By adding particles of at least one resin selected from the group consisting of melamine-formaldehyde resin, benzoguanamine-formaldehyde resin, and urea-formaldehyde resin to the coating system comprising, tackiness, particularly at a high temperature of about 40 ° C. The inventors have found that tackiness can be remarkably improved and have completed the present invention.

  Thus, the present invention is based on 100 parts by weight of a binder component consisting of (A) a hydroxyl group-containing polyester resin having a hydroxyl value of 5 to 95 mgKOH / g and (B) a blocked polyisocyanate compound, and (C) melamine-formaldehyde resin, benzoguanamine. -0.5-20 parts by weight of particles of at least one resin selected from the group consisting of formaldehyde resins and urea-formaldehyde resins, and (D) resins other than melamine-formaldehyde resins, benzoguanamine-formaldehyde resins and urea-formaldehyde resins It is related with the coating composition characterized by containing 0.5-50 weight part of resin microparticles | fine-particles which are average particle diameters in the range of 8-70 micrometers.

  In the present invention, a primer coating and a coating with the coating composition are sequentially formed on a metal plate whose surface may be subjected to chemical conversion treatment, or a primer coating, an intermediate coating, and the above The present invention relates to a coated metal plate characterized in that a coating film formed by a coating composition is sequentially formed.

  Furthermore, the present invention provides a primer paint on a metal plate whose surface may be subjected to chemical conversion treatment, after coating and baking it so that the dry film thickness is 0.5 to 10 μm. The coating composition according to any one of the above is applied so that the dry film thickness is 15 to 45 μm, and baking is performed within a range of 15 to 120 seconds at a raw material maximum temperature of 160 to 260 ° C., Alternatively, the primer coating is applied on a metal plate whose surface may be subjected to chemical conversion treatment so that the dry film thickness is 0.5 to 10 μm and baked. After coating and baking to a thickness of ˜45 μm, the coating composition according to any one of claims 1 to 3 is applied so that the dry film thickness is 15 to 45 μm, and the maximum material temperature is reached. Is baked in the range of 15 to 120 seconds at 160 to 260 ° C. It is related with the manufacturing method of the coating metal plate characterized by performing.

  The coating composition of the present invention comprises a melamine-formaldehyde resin and a benzoguanamine in a coating system comprising a binder component comprising a hydroxyl group-containing polyester resin and a blocked polyisocyanate compound and resin fine particles having an average particle size in the range of 8 to 70 μm. -By adding particles of at least one resin selected from the group consisting of formaldehyde resin and urea-formaldehyde resin, the tack property, particularly the tack property at a high temperature of about 40 ° C, is remarkably improved, and a good uneven pattern The coated metal plate of 2 coats or 3 coats obtained by using the coating composition of the present invention can be used for building materials and household appliances. It can be used as an alternative to conventional PVC steel sheets.

  The coating composition of the present invention comprises at least one resin particle (C) selected from the group consisting of a hydroxyl group-containing polyester resin (A), a blocked polyisocyanate compound (B), a melamine-formaldehyde resin, and a urea-formaldehyde resin. ) And resin particles other than melamine-formaldehyde resin and urea-formaldehyde resin, which contain resin fine particles (D) having an average particle diameter in the range of 8 to 70 μm.

Hydroxyl-containing polyester resin (A)
The hydroxyl group-containing polyester resin as the component (A) in the composition of the present invention is a polyester resin having a hydroxyl group in the molecule, and is an oil-free polyester resin, an oil-modified alkyd resin, or a modified product of these resins such as a urethane-modified resin. Examples include polyester resins, urethane-modified alkyd resins, and epoxy-modified polyester resins.

  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. In general, as the urethane-modified resin, those having a modification degree such that the amount of the polyisocyanate compound forming the urethane-modified resin is 30% by weight or less with respect to the urethane-modified resin can be preferably 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.

  Among the polyester resins described above, particularly preferred are oil-free polyester resins.

  In addition, the polyester resin (A) has a number average molecular weight of 2,000 to 20,000, particularly 3,000 to 3,000, from the viewpoint of balance such as processability, hardness, curability and resistance to cracking of the resulting coating film. The glass transition temperature (Tg point) is in the range of −40 ° C. to 40 ° C., particularly −25 to 15 ° C., and the hydroxyl value is 5 to 95 mgKOH / g, particularly 20 to. Polyester resins that are in the range of 65 mg KOH / g are preferred.

  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.

Blocked polyisocyanate compound (B)
The blocked polyisocyanate compound as the component (B) in the composition of the present invention is used as a curing agent for the hydroxyl group-containing polyester resin (A), and a part or all of the isocyanate groups of the polyisocyanate compound are blocked. It is made by blocking with.

  Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; cyclic aliphatic diisocyanates such as hydrogenated xylylene diisocyanate and isophorone diisocyanate; tolylene diisocyanate and 4,4′-diphenylmethane diisocyanate. Aromatic diisocyanates such as: triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4′-dimethyl An organic polyisocyanate itself, such as a polyisocyanate compound having three or more isocyanate groups, such as diphenylmethane-2,2 ', 5,5'-tetraisocyanate, or the like Each organic polyisocyanates with polyhydric alcohol, an adduct of low molecular weight polyester resin or water, etc., or cyclic polymer of the organic polyisocyanate comrades described above, even and an isocyanate-biuret, or the like.

  Moreover, as blocking agents, phenols such as phenol, cresol, xylenol; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam; methanol, ethanol, n-propyl alcohol, isopropyl Alcohols such as alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol; formamidoxime, acetoaldoxime, Such as acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime Of oxime; dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, a blocking agent such as active methylene of acetylacetone. Among these, lactam-based blocking agents, particularly ε-caprolactam, are highly effective in improving the resistance to cracking when the coating film is heat-cured, and are preferably used when thick coating is required.

  In the composition of the present invention, the polyester resin (A) as the binder component and the blocked polyisocyanate compound (B) are: blocked isocyanate group in the blocked polyisocyanate compound (B) / hydroxyl group in the polyester resin (A). Is preferably in the range of 0.7 to 1.2, particularly 0.8 to 1.05. When the ratio is less than 0.7, the curability of the coating film is decreased, or the hydroxyl groups remaining in the coating film are increased, the water resistance of the coating film is decreased and the corrosion resistance is easily deteriorated. When the ratio is larger than 1.2, an unnecessary curing reaction due to isocyanate groups remaining in the coating film may progress after coating, and a problem may occur that cracking of the processed portion of the coating film may progress with time.

Resin particles (C)
The resin particles which are the component (C) of the coating composition of the present invention are particles of at least one resin selected from the group consisting of melamine-formaldehyde resin, benzoguanamine-formaldehyde resin and urea-formaldehyde resin, and average particles Those having a diameter of about 0.1 to 20 μm are generally commercially available, and those in this range have the effect of increasing the tack resistance and the coating film hardness without deteriorating the processability and designability of the coating film. It was confirmed that there was. Examples of commercially available products include Eposter S, S6, S12, M05, M30 (all manufactured by Nippon Shokubai Co., Ltd.), Chrysozyplast PL 100-R (produced by Chryso), PERGOPAK HP, M , M2, M3, M4, and M5 (all are all manufactured by ALBEMARLE).

  The compounding amount of the resin particles (C) is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the binder component comprising the polyester resin (A) and the blocked polyisocyanate compound (B). Within the range of the part. When the blending amount of the resin fine particles (C) is small, the effect of improving the tack resistance of the coating film decreases.

Resin particles (D)
The resin particles which are the component (D) of the coating composition of the present invention are particles of a resin different from the melamine-formaldehyde resin, benzoguanamine-formaldehyde resin and urea-formaldehyde resin, and have an average particle diameter of 8 to 70 μm, preferably Are fine resin particles having a particle size of 15 to 60 μm, and contribute to improving the blocking resistance of the cured coating film. The resin particles (D) are preferably those that do not completely melt at the time of coating film curing (baking and curing conditions for the coating film). Here, “not completely melted” means that the resin particles 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 (D) is less than 8 μm, the effect of improving the blocking resistance of the coating film is not sufficient, but may be added for other effects, for example, improvement of resistance to cracking. On the other hand, when it exceeds 70 μm, the appearance of the coating film and the coating workability deteriorate.

  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 and the like can be mentioned, and in particular, the particles of at least one resin selected from the group consisting of polyamide resin, polyacrylonitrile resin, and acrylic resin are resistant to blocking. The improvement effect is large and preferable. These can be used alone or in combination.

  The compounding amount of the resin fine particles (D) is 0.5 to 50 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the binder component comprising the polyester resin (A) and the blocked polyisocyanate compound (B). Within the range of the part. When the blending amount of the resin fine particles (D) is less than 0.5 parts by weight, the effect of improving the blocking resistance of the coating film is not sufficient. On the other hand, when it exceeds 50 parts by weight, the workability and coating workability of the coating film are deteriorated. To do.

  The coating composition of the present invention comprises at least one resin particle (C) selected from the group consisting of a hydroxyl group-containing polyester resin (A), a blocked polyisocyanate compound (B), a melamine-formaldehyde resin, and a urea-formaldehyde resin. ) And resin particles (D) other than melamine-formaldehyde resin, benzoguanamine-formaldehyde resin, and urea-formaldehyde resin, usually containing an organic solvent, and if necessary, an inorganic powder , Curing catalyst, coloring pigment, glitter pigment; additives such as a lubricity imparting agent, an antifoaming agent, a coating surface conditioner, and an anti-settling agent known per se for coatings may be contained. In particular, the lubricity imparting agent is preferably added in order to improve the scratch resistance of the coating film, and is added in an amount of about 0.5 to 30 parts by weight, particularly about 0.5 to 10 parts by weight based on 100 parts by weight of the binder component. Suitable examples of the lubricity-imparting agent include polyethylene wax, fluorine wax, carnauba wax, lanolin wax and the like.

  The organic solvent is blended as necessary for improving the paintability of the composition of the present invention, and can be used to dissolve or disperse the polyester resin (A) and the blocked polyisocyanate compound (B). Specifically, for example, xylene, aromatic hydrocarbon solvents such as high boiling point aromatic petroleum hydrocarbon solvents; ketone solvents such as cyclohexanone and isophorone; butyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol mono Ester solvents such as ethyl 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 Bets can be, with preference high-boiling aromatic petroleum hydrocarbon solvent. These organic solvents can be used alone or in admixture of two or more.

  Examples of the inorganic powder include talc, clay, silica, mica, alumina, barium sulfate, calcium carbonate and the like, and these can be used alone or in combination. As the inorganic powder, silica is particularly preferable.

  By blending the inorganic powder, it is possible to improve the tack resistance of the coating surface, but if too much is added, the processability and design properties of the coating will be reduced, so when blending this powder The blending amount is 30 parts by weight or less, preferably 0.1 to 20 parts by weight, particularly preferably 0, based on 100 parts by weight of the binder component comprising the polyester resin (A) and the blocked polyisocyanate compound (B). Suitably within the range of 2 to 10 parts by weight.

  The curing catalyst is blended as necessary to promote the curing reaction between the polyester resin (A) and the blocked polyisocyanate compound (B), and a curing catalyst that promotes dissociation of the blocking agent is suitable. As suitable curing catalysts, for example, tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide And organometallic catalysts such as lead 2-ethylhexanoate.

  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.

  When titanium white is blended to form a light-colored coating film, the blending amount is within the range of 50 to 120 parts by weight with respect to 100 parts by weight of the total of resin (A) and compound (B). Is preferable from the viewpoints of concealability and processability.

  As the bright pigment that can be used as necessary, bright pigments usually used in the paint field, such as aluminum powder, copper powder, nickel powder, coated mica powder having pearly luster, and bright graphite, etc. At least one can be mentioned.

  The coating composition of the present invention can be applied to various objects to be coated such as metal plates, plastics, glass plates, etc., but when producing a coated metal plate, the metal plate is used as the object to be coated. Is done. Examples of the metal plate used as the object to be coated include untreated metal plates such as cold-rolled steel plates, galvanized steel plates, and aluminum plates; phosphate treatment, chromate treatment, Examples of the metal plate include chemical conversion treatment such as chromium phosphate treatment and zirconium treatment. Among them, a zinc-based plated steel sheet that has been subjected to no treatment or chemical treatment can be preferably used.

  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 generally used. However, since the coating composition of the present invention can be coated with a thick film, a non-chromium chemical conversion treatment having a low environmental impact such as zirconium treatment is performed. The chemical conversion-treated zinc-based plated steel sheet can be used.

  The primer coating film is formed on the metal plate which may be subjected to the above chemical conversion treatment, and if necessary, an intermediate coating film is formed on the primer coating film, and then the coating material of the present invention is formed on the coating film. A coated metal plate can be obtained by coating and baking and curing the composition. In the case where it is used as an alternative to a PVC steel sheet or in applications where high corrosion resistance is required, a three-coat coating film in which an intermediate coating film is sandwiched between a primer coating film and a top coating film is preferable.

  As the primer coating film, a coating film obtained from a polyester primer or an epoxy primer is suitable. As a primer coating for forming a primer coating, a non-polluting non-chromium primer coating that does not contain harmful pigments such as chromium anticorrosive pigments such as strontium chromate, zinc chromate and calcium chromate is used. A coating film can be formed. Examples of rust preventive pigments used in non-chromium primer paints include zinc oxide, zinc phosphate, phosphorous zinc silicate, aluminum zinc phosphate, calcium zinc phosphate, zinc phosphite, calcium phosphite, aluminum phosphite Cyanamide zinc calcium, zinc treated aluminum polyphosphate, aluminum tripolyphosphate, zinc calcium molybdate, zinc molybdate, zinc phosphomolybdate, aluminum phosphomolybdate, calcium ion-exchanged amorphous silica fine particles, etc. These can be used alone or in admixture of two or more.

  In particular, a non-polluted coated steel sheet can be obtained by combining a non-chromium-based chemical conversion-treated zinc-plated steel sheet and a non-polluting non-chromium primer coating film, but this combination usually gives the corrosion resistance of the coated steel sheet. Will fall. However, since the coating composition of the present invention can be coated with a thick film and is excellent in the workability of the obtained coating film, it is possible to suppress a decrease in the corrosion resistance of not only the flat portion but also the processed portion.

  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 further improves by setting it as the 3 coat coating film which pinched | interposed the intermediate coating film between the primer coating film and the 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 1-50 weight part of hardening | curing 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 30 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 fine particles, 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 coating of the coating composition of the present invention on the primer coating or intermediate coating can be performed using, for example, roll coating, curtain flow coating, dip coating, spray coating, etc., and the coating film at that time Although the thickness is not particularly limited, in the case of coil coating continuously applied by roll coating or the like, usually, the material maximum temperature (PMT) is set to 160 to 260 ° C. for 15 to 120 seconds. The baking conditions within a range of 20 to 90 seconds at PMT 190 to 240 ° C. are particularly suitable, and the film thickness at that time is 15 to 45 μm, preferably about 17 to 35 μm as a dry film thickness. ing.

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

Primer paint production example 1
Byron EP-2940 (Note 1) 266.7 parts (80 parts by solids), Cymel 303 (Note 2) 20 parts, Aluminum tripolyphosphate 30 parts, Titanium white 20 parts and Neicure 5225 (Note 3) 2.0 parts And an appropriate amount of cyclohexanone / swazol 1500 (manufactured by Maruzen Petrochemical Co., Ltd., aromatic high-boiling solvent) = 50/50 until a tube (particle diameter of coarse pigment particles) becomes 10 microns or less. Dispersion gave primer paint P1.
(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 paint production example 2
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 amine neutralized solution of dodecylbenzene sulfonic acid, curing catalyst, active ingredient 25%) manufactured by Industrieise Co., Ltd. and the above mixed solvent are uniformly mixed for adjusting the viscosity of the paint, and the viscosity of the paint is 90 seconds (Ford Cup # 4 , 25 ° C.) intermediate coating B1 was obtained.

Production Example 3
Byron KS-1480V (polyester resin manufactured by Toyobo Co., Ltd., number average molecular weight 8,200, glass transition temperature 5 ° C., hydroxyl value 28 mgKOH / g) 80 parts dissolved in 120 parts cyclohexanone / swazole 1500 = 50/50 mixed solvent As a result, a resin solution q having a solid content of 40% was obtained. To 75 parts of the resin solution, 40 parts of Taipei CR-95 (manufactured by Ishihara Sangyo Co., Ltd., titanium white pigment), 6 parts of carbon black pigment, and 30 parts of the mixed solvent were mixed, and pigment dispersion was performed to obtain a pigment paste.

  To 141 parts of the obtained pigment paste, 125 parts of resin solution q, 26.7 parts of Desmodur BL-3175 (manufactured by Sumitomo Bayer Urethane Co., Ltd., trade name, blocked polyisocyanate compound, solid content of about 75%) and formate TK-1 (manufactured by Takeda Pharmaceutical Company Limited, trade name, dissociation catalyst of blocked polyisocyanate compound, solid content of about 10%) 2.0 parts and the above-mentioned mixed solvent for paint viscosity adjustment are uniformly mixed to obtain a paint viscosity An intermediate coating B2 for 90 seconds (Ford Cup # 4, 25 ° C.) was obtained.

Topcoat Examples 1 to 7 and Comparative Examples 1 to 3
Each of the top coats was obtained by coating with the composition shown in Table 1 below. The amount of each composition in Table 1 is indicated by the solid content weight. In addition, at the time of making the top coat of each Example and Comparative Example, titanium white, which is a white pigment, was dispersed. Further, a mixed solvent of cyclohexanone / swazol 1500 = 50/50 was used for adjusting the viscosity of the paint, and the paint viscosity was adjusted to about 90 seconds (Ford Cup # 4, 25 ° C.). In Table 1, the equivalent ratio of blocked isocyanate group in the blocked polyisocyanate compound / hydroxyl group in the polyester resin in the binder component of each top coat (abbreviated as “NCO / OH equivalent ratio” in Table 1) Show).

  The raw materials for each note in Table 1 are as follows.

  The polyester resins shown in (* 1) to (* 6) in Table 1 are polyester resins manufactured by Toyobo Co., Ltd., and have the property values shown in Table 2 below.

(* 7) Desmodur TPLS2957: HDI isocyanurate type polyisocyanate compound manufactured by Sumitomo Bayer Urethane Co., Ltd., blocked with ε-caprolactam.
(* 8) Desmodur BL-3175: HDI isocyanurate-type polyisocyanate compound blocked by methyl ethyl ketoxime manufactured by Sumitomo Bayer Urethane Co., Ltd.
(* 9) Formate TK-1: An organic tin-based curing catalyst manufactured by Takeda Pharmaceutical Company Limited.
(* 10) Taopeque CR-95: Titanium white pigment manufactured by Ishihara Sangyo Co., Ltd.
(* 11) PERGOPAK M3: manufactured by ALBEMAR, urea-formaldehyde resin particles, average particle size of about 6 to 8.5 μm.
(* 12) Eposter S12: manufactured by Nippon Shokubai Co., Ltd., melamine-formaldehyde resin particles, average particle diameter of about 1 to 2 μm.
(* 13) Eposter MS: manufactured by Nippon Shokubai Co., Ltd., benzoguanamine-formaldehyde resin particles, average particle size of about 1 to 3 μm.
(* 14) Tuftic A-20: manufactured by Toyobo Co., Ltd., polyacrylonitrile resin fine particles, average particle size of about 26 μm.
(* 15) Orgasol 2002ES-3: ARKEMA, nylon 12 resin fine particles, average particle size of about 30 μm.
(* 16) TEXTURE 5380W: Shamrock Technologies, Inc., polypropylene resin fine particles, average particle size of about 40 μm.
(* 17) Cefral lube WR: manufactured by Central Glass Co., Ltd., trade name, polytetrafluoroethylene powder, average particle size of about 5 μm.
(* 18) Syloid 308: manufactured by GRACE, silica fine powder, average particle size of about 5 μm.

Preparation Examples 8-18 and Comparative Examples 4-8
A primer coating was applied onto a 0.5 mm thick hot-dip galvanized steel sheet subjected to chromate treatment with a bar coater and baked for 30 seconds so that the maximum material temperature reached 220 ° C. to obtain a primer-coated steel sheet. On this primer-coated steel sheet, an intermediate coating was applied with a bar coater and baked for 30 seconds so that the maximum material arrival temperature was 220 ° C. to obtain an intermediate-coated steel sheet. Each top coat obtained in Examples 1 to 7 and Comparative Examples 1 to 3 is applied onto this intermediate coated steel sheet with a bar coater and baked for 60 seconds so that the maximum material temperature reaches 220 ° C. A steel plate was obtained. The primer coating, intermediate coating, top coating, and film thickness (dry film thickness, μm) of each coating used in each example and comparative example are as shown in Table 3, and primer coating P2 is KP color 8000 primer (Kansai). (Epoxy resin primer for pre-coated steel sheet containing chromate rust preventive pigment, manufactured by Paint Co.).

Test method Waki resistance: The appearance of the coated surface (30 cm × 30 cm) of the coated steel sheet was observed with the naked eye and evaluated according to the following criteria.
○: No occurrence of foam (foaming) on the coated surface.
Δ: Slight wrinkles (foaming) are observed on the coated surface.
X: Occurrence of remarkable cracks (foaming) is observed on the coated surface.

  Pencil hardness: A pencil scratch test specified in JIS K-5400 8.4.2 (1990) was performed on the coated steel sheet, and evaluation by tearing was performed.

Impact resistance: In a room at 20 ° C., according to JIS K-5400 8.3.2 (1990) DuPont impact resistance test, weight drop weight 500 g, striker tip diameter 1/2 inch, drop weight height An impact was applied to the coated surface of the coated steel sheet under the condition of a length of 50 cm. Then, a cellophane adhesive tape was attached to the impacted part, and the degree of peeling of the coating film when the tape was instantaneously peeled was evaluated according to the following criteria.
○: No peeling is observed on the coated surface.
Δ: Slight peeling is observed on the coated surface.
X: Significant peeling is observed on the coated surface.

  Bending workability: In a room at 20 ° C., the test plate was bent 180 degrees with the coating surface removed, and the T number at which no cracking occurred at the bent portion was displayed. The number of T is 0T when bending 180 degrees without anything inside the bent part, 1T when bending a sheet of the same thickness as the test plate, 2T The number of sheets is 2T,... 4 is 4T.

Tackiness of the coated surface: The coated surface of each coated steel sheet left in a constant temperature room at 20 ° C. and a constant temperature room at 40 ° C. for 1 hour was touched with a finger, and the degree of adhesion of the coated surface was evaluated according to the following criteria.
A: Adhesive feeling is not recognized on the coated surface.
○: Slight tackiness is recognized on the coated surface, but in a practical range.
Δ: Adhesive feeling is considerably recognized on the coated surface.
X: Adhesive feeling is remarkably recognized on the coated surface.

Blocking resistance: KP color 1510 beige (manufactured by Kansai Paint Co., Ltd., polyester resin-based back coating for precoated steel sheets) on a 0.5 mm thick electrogalvanized steel sheet with chromate treatment Then, it was baked for 30 seconds so that the maximum material temperature reached 220 ° C. to obtain a KP color 1510 coated plate. This coated plate of KP color 1510 was cut to a size of 5 cm × 5 cm, and the coated surface of each coated steel plate having a size of 5 cm × 5 cm was superposed on the coated surface, and the pressure was 80 kg / cm ² at 50 ° C. After maintaining for 24 hours, the ease of peeling when peeling both coated plates was evaluated according to the following criteria.
◎: Both coated plates are not attached, and leave just by tilting.
○: Both coated plates are slightly adhered, but easily peeled off by hand, and practical range.
(Triangle | delta): Although both coating plates have adhered quite a little, it can peel off by a coating film without damage.
X: Both coated plates are strongly adhered and cannot be peeled off by hand, or even if peeled by hand, the coating film is damaged.

Alkali resistance: The test plate was immersed in an aqueous 5% sodium hydroxide solution heated to 30 ° C. for 24 hours, pulled up, visually observed on the coated surface, and evaluated according to the following criteria.
○: No change is observed on the painted surface.
Δ: Slight whitening or swelling is observed on the coated surface.
X: Whitening or swelling is remarkably observed on the coated surface.

Solvent resistance: In a room at 20 ° C., the coated surface state after applying a load of about 1 kg / cm ^{2 to} the coated surface with gauze soaked with methyl ethyl ketone and reciprocating the length of about 5 cm 50 times. Was visually evaluated according to the following criteria.
○: No change is observed on the painted surface.
Δ: Whitening or swelling of the coating film is not observed, but scratches are observed on the coated surface.
X: Whitening or swelling of the coating film is observed.

Corrosion resistance: Cross-cut scratches reaching the metal surface with a knife are applied to the coated surface of the coated steel plate, and this coated steel plate is subjected to a salt spray test for 1000 hours in accordance with the salt spray test specified in JIS Z-2371. Evaluation was based on the width of rust or swelling.
A: Maximum width of rust or swelling is less than 1 mm on one side.
○: The maximum width of rust or swelling is 1 mm or more and less than 3 mm on one side.
Δ: The maximum width of rust or swelling is 3 mm or more and less than 9 mm on one side.
X: The maximum width of rust or swelling is 9 mm or more on one side.

Claims (10)

  (A) Based on 100 parts by weight of a binder component comprising a hydroxyl group-containing polyester resin having a hydroxyl value of 5 to 95 mg KOH / g and (B) a blocked polyisocyanate compound, (C) melamine-formaldehyde resin, benzoguanamine-formaldehyde resin and urea -0.5-20 parts by weight of particles of at least one resin selected from the group consisting of formaldehyde resin and (D) particles of resin other than melamine-formaldehyde resin, benzoguanamine-formaldehyde resin and urea-formaldehyde resin A coating composition comprising 0.5 to 50 parts by weight of resin fine particles having an average particle diameter in the range of 8 to 70 μm.   The coating composition according to claim 1, wherein the equivalent ratio of blocked isocyanate group in the blocked polyisocyanate compound (B) / hydroxyl group in the hydroxyl group-containing polyester resin (A) is in the range of 0.7 to 1.2.   The coating composition according to claim 1 or 2, wherein the hydroxyl group-containing polyester resin (A) has a number average molecular weight of 2,000 to 20,000 and a glass transition temperature of -40 ° C to 40 ° C.   The coating composition according to any one of claims 1 to 3, wherein the resin fine particles (D) are particles of at least one resin selected from the group consisting of a polyamide resin, a polyacrylonitrile resin and an acrylic resin.   Further, the lubricity imparting agent (E) is contained in an amount of 0.5 to 30 parts by weight based on 100 parts by weight of the binder component composed of the hydroxyl group-containing polyester resin (A) and the blocked polyisocyanate compound (B). The coating composition of any one of Claims 1-4.   6. A coating comprising a primer coating and a coating formed by the coating composition according to any one of claims 1 to 5 on a metal plate, the surface of which may be subjected to chemical conversion treatment. Metal plate.   A primer coating, an intermediate coating, and a coating of the coating composition according to any one of claims 1 to 5 are sequentially formed on a metal plate that may be subjected to chemical conversion treatment on the surface. Characteristic painted metal plate.   After applying the primer paint on the metal plate which may be subjected to chemical conversion treatment on the surface so that the dry film thickness is 0.5 to 10 μm, and baking it, any one of claims 1 to 5 A coated metal plate, characterized in that the coating composition described above is applied so that the dry film thickness is 15 to 45 μm, and is baked for 15 to 120 seconds so that the maximum material temperature reaches 160 to 260 ° C. Manufacturing method.   The primer coating is applied on a metal plate that may be subjected to chemical conversion treatment on the surface so that the dry film thickness is 0.5 to 10 μm, and after baking, the intermediate coating is dried to a film thickness of 10 to 45 μm. After coating and baking, the coating composition according to any one of claims 1 to 5 is applied so that the dry film thickness is 15 to 45 μm, and the maximum material temperature reaches 160. Baking is performed for 15 to 120 seconds so that it may become -260 degreeC, The manufacturing method of the coating metal plate characterized by the above-mentioned. The intermediate coating 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., a number average molecular weight of 5,000 to 50,000, and a hydroxyl value of 2 The method for producing a coated metal sheet according to claim 9, wherein the polyester resin of 30 mg KOH / g is contained in an amount of 50% by weight or more based on the total polyester resin component.