JP2022071536A - Welding can repair paint composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition for repairing a weld can, which is excellent in coating film performance such as processability, corrosion resistance and water resistance, and also has excellent blocking resistance.
SOLUTION: A polyester resin (A), a melamine resin (B), a resin having an aromatic ring structure, having a number average molecular weight in the range of 10,000 to 20,000 and a glass transition temperature in the range of 51 to 100 ° C. A coating composition for repairing a welded can containing C) and an acid catalyst (D). Preferably, it further contains a solvent composition (E) comprising a solvent (E1) having a boiling point of less than 100 ° C., a solvent (E2) having a boiling point in the range of 100 ° C. to 120 ° C., and a solvent (E3) having a boiling point of more than 120 ° C.
[Selection diagram] None

Description

The present invention relates to a coating composition for repairing welded cans.

Metal is exposed on the welded portion (inner surface side of the can) of a three-piece can or the like, and in painting a can having a welded portion, a paint for repairing a welded can is used on the welded portion.

Initially, epoxy resin-based repair paints were common, but workability, corrosion resistance, etc. were insufficient, and polyester resin-based repair paints have been developed to improve workability.

For example, Patent Document 1 describes (A) a polyester resin having a glass transition point (Tg) in the range of 10 to 50 ° C. and a number average molecular weight (Mn) in the range of 10,000 to 20,000, and (B) thermosetting. It contains (A): (B) 90:10 to 60:40 in weight ratio of the sex resin, and contains (C) a defoaming agent, (D) a rocking agent and (E) a solvent. Disclosed is an inner surface correction paint for a welding can, which is characterized by the above.

Further, Patent Document 2 includes a polyester resin having a number average molecular weight of 3,000 to 30,000 and a glass transition temperature of 5 to 110 ° C. as a paint for repairing a laminated can. The paint is disclosed.

However, the paints described in Patent Documents 1 and 2 may have insufficient corrosion resistance and blocking resistance even if they have good processability.

Japanese Unexamined Patent Publication No. 2002-129906 Japanese Unexamined Patent Publication No. 2004-210844

An object to be solved by the present invention is to provide a coating composition for repairing weld cans, which is excellent in coating film performance such as processability, corrosion resistance, and water resistance, and is also excellent in blocking resistance.

As a result of diligent studies to solve the above problems, the present inventors have a polyester resin and a melamine resin having a specific range of number average molecular weight and a glass transition temperature, a specific range of number average molecular weight, and an aromatic ring structure. It has been found that the above-mentioned problems can be solved by the coating composition for repairing welded cans containing a resin and an acid catalyst, and the present invention has been completed.

That is, the present invention relates to the following contents.

1. 1. A polyester resin (A), a melamine resin (B), a resin (C) having an aromatic ring structure, and an acid having a number average molecular weight in the range of 10,000 to 20,000 and a glass transition temperature in the range of 51 to 100 ° C. A coating composition for repairing a welded can containing a catalyst (D).

2. 2. Item 2. The coating composition for repairing a weld can according to Item 1, wherein the melamine resin (B) is a methyl etherified melamine resin.

3. 3. Item 2. The coating composition for repairing a welded can according to Item 1 or 2 above, wherein the acid catalyst (D) is a sulfonic acid compound or an amine neutralized product of the sulfonic acid compound.

4. Based on the total solid content of the polyester resin (A), the melamine resin (B) and the resin (C) having an aromatic ring structure, the polyester resin (A) is 60 to 90% by mass, and the melamine resin (B) is 5 to 40% by mass. %, 3 to 20% by mass of the resin (C) having an aromatic ring structure, and 0.1 to 3% by mass of the acid catalyst (D). thing.

5. Claim 1 further contains a solvent composition (E) comprising a solvent (E1) having a boiling point of less than 100 ° C., a solvent (E2) having a boiling point in the range of 100 ° C. to 120 ° C., and a solvent (E3) having a boiling point of more than 120 ° C. The coating composition for repairing a welding can according to any one of 4 to 4.

In the water-based coating composition of the present invention, the polyester resin as the substrate resin has a relatively high molecular weight and a high Tg, so that both processability and water resistance can be achieved at the same time. Further, it is presumed that the corrosion resistance is improved by improving the adhesiveness because it has a resin having an aromatic ring. Further, since it is an acid-catalyzed melamine resin curable type, it is presumed that the curability is good and the blocking resistance is also improved.

As described above, according to the present invention, it is possible to obtain a coating film having excellent coating film performance such as processability, corrosion resistance and water resistance, and to provide a coating composition for repairing weld cans which is also excellent in blocking resistance. ..

The present invention comprises a polyester resin (A), a melamine resin (B), and a resin having an aromatic ring structure, in which the number average molecular weight is in the range of 10,000 to 20,000 and the glass transition temperature is in the range of 51 to 100 ° C. C) and a welding can repair coating composition containing an acid catalyst (D) (hereinafter, may be abbreviated as the present coating composition).

Hereinafter, the contents of the present invention will be described in detail.

<Paint composition for repairing welding cans>
Polyester resin (A)
The polyester resin (A) is synthesized by directly esterifying an acid component and an alcohol component by a transesterification reaction, and has a large molecular weight and a relatively high glass transition in order to obtain sufficient processability and water resistance. It is preferable to have a temperature (Tg), the number average molecular weight is 10,000 to 20,000, particularly 10,000 to 18,000, and the glass transition temperature (Tg) is in the range of 50 to 100 ° C., particularly 55 to 95 ° C. Is preferable.

In the present specification, the number average molecular weight is measured by gel permeation chromatography (GPC) by the following molecular weight measuring method using a standard polystyrene calibration curve.

For the number average molecular weight, the holding time (holding capacity) measured by a gel permeation chromatograph (“HLC8120GPC” manufactured by Tosoh Corporation) using tetrahydrofuran as a solvent is converted based on the number average molecular weight of polystyrene. It is the value that was set. Four columns, "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000XL" (all manufactured by Tosoh Corporation, trade name) are used and moved. Phase; tetrahydrofuran, measurement temperature; 40 ° C., flow rate; 1 ml / min, detector; RI conditions.

The hydroxyl value is preferably in the range of 1 to 20, particularly 3 to 15 mgKOH / g, from the viewpoint of crosslinkability and water resistance.

Examples of the acid component constituting the polyester resin (A) include phthalic acid anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid anhydride, hexahydrohydric acid anhydride, hexahydroisophthalic acid, hexahydroterephthalic acid, succinic acid and fumaric acid. Examples thereof include one or more dibasic acids selected from adipic acid, sebacic acid, maleic anhydride, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid and the like, and lower alkyl esterified products of these acids.

Further, if necessary, monobasic acids such as benzoic acid, crotonic acid and pt-butylbenzoic acid, trivalent or higher polybasic acids such as trimellitic anhydride, methylcyclohexcentricarboxylic acid and pyromellitic anhydride are also available. Can be used together.

These acid components can be used alone or in combination of two or more.

Examples of the alcohol component constituting the polyester resin (A) include ethylene glycol, diethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and 2-methyl-1,3-propanediol. , 3-Methylpentanediol, 1,4-hexanediol, 1,6-hexanediol, 1,4-dimethylolcyclohexane and other dihydric alcohols.

Further, if necessary, a trihydric or higher polyhydric alcohol such as glycerin, trimethylolethane, trimethylolpropane, or pentaerythritol can also be used in combination.

These alcohol components can be used alone or in combination of two or more.

When the acid component and the alcohol component are synthesized by a direct esterification method or an ester exchange method by a conventional method, if the reaction is carried out under the condition that the carboxyl group is excessive with respect to the hydroxyl group, the carboxyl group is mainly contained. If a polyester resin is obtained and the reaction is carried out under the condition that the hydroxyl group is excessive with respect to the carboxyl group, a polyester resin containing a hydroxyl group as a main component can be obtained. Further, by adding an acid anhydride to the polyester resin containing the hydroxyl group as a main component, the amount of the hydroxyl group and the carboxyl group in the resin can be adjusted.

Examples of the acid anhydride that reacts with the polyester resin mainly containing the hydroxyl group include phthalic anhydride, succinic anhydride, maleic anhydride, hexahydrophthalic anhydride, trimellitic anhydride and the like.

In the above method, the reaction by the direct esterification method or the transesterification method can be promoted by a pressurization or depressurization operation or by inflowing an inert gas. Further, an organometallic catalyst such as di-n-butyltin oxide can be used as an esterification catalyst in the reaction.

The polyester resin (A) may be any of an oil-free polyester resin, an oil-modified alkyd resin, or a modified product of these resins, for example, a urethane-modified polyester resin, a urethane-modified alkyd resin, or the like.

Melamine resin (B)
The melamine resin is a resin obtained by subjecting melamine to formaldehyde in a condensation reaction, and is usually a resin obtained by further etherifying the remaining methylol groups with alcohol.

Before the etherification reaction, the melamine resin usually contains (1) residual amino group (-NH ₂ ), (2) iminomethylol group (-NHCH ₂ OH), and (3) dimethylol amino as functional groups. There is a group [-N (CH ₂ OH) ₂ ].

As the melamine resin (B), for example, a monohydric alcohol having 1 to 8 carbon atoms in part or all of the methylol group of the methylolated melamine, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, etc. Examples thereof include partially etherified or fully etherified melamine resins etherified with n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.

As the melamine resin (B), a resin in which all the methylol groups are etherified or partially etherified and the methylol groups and imino groups remain can also be used. Specific examples thereof include alkyl etherified melamines such as methyl etherified melamine, ethyl etherified melamine, and butyl etherified melamine, which can be used alone or in combination of two or more.

Of the above, a methyl etherified melamine resin obtained by methyl etherifying at least a part of a methylol group can be preferably used from the viewpoint of blocking resistance.

As the melamine resin (B), a commercially available product can be used.

Specific examples of the commercially available product include Cymel 202, Cymel 232, Cymel 235, Cymel 238, Cymel 254, Cymel 266, Cymel 267, Cymel 272, Cymel 285, Cymel 301, Cymel 303, Cymel 325, and Cymel. 327, Cymel 350, Cymel 370, Cymel 701, Cymel 703, Cymel 1141 [all manufactured by Ornex Co., Ltd.] and the like can be mentioned.

Resin (C) having an aromatic ring structure
The resin (C) having an aromatic ring structure can be used without particular limitation as long as it has an aromatic ring structure in the resin. Specific examples thereof include bisphenol type epoxy resin, novolak type epoxy resin, xylene resin, benzoguanamine resin, and phenol resin.

The number average molecular weight of the resin (C) having an aromatic ring is preferably in the range of 500 to 5000, more preferably 600 to 4500, from the viewpoint of water resistance and corrosion resistance.

By containing the resin (C) having an aromatic ring structure, it is possible to improve the corrosion resistance by improving the water resistance and the adhesion to the material.

As the bisphenol type epoxy resin, for example, a resin obtained by reacting a bisphenol compound with epichlorohydrin (for example, epichlorohydrin or the like) can be used.

Commercially available bisphenol type epoxy resins include, for example, "jER827", "jER828", "jER828EL", "jER828XA", "jER834", "jER1007" (all manufactured by Mitsubishi Chemical Corporation), "EPICLON840", and "EPICLON840". -S "," EPICLON850 "," EPICLON850-S "," EPICLON850-CRP "," EPICLON850-LC "(above, manufactured by DIC)," Epototo YD-127 "," Epototo YD-128 "(above, day) Bisphenol A type epoxy resin such as "Rikaresin BPO-20E", "Rikaresin BEO-60E" (manufactured by Shin Nihon Rika Co., Ltd.); "jER806", "jER807" (above, Mitsubishi Chemical) ), "EPICLON 830", "EPICLON 830-S", "EPICLON 835" (above, manufactured by DIC), "Epototo YDF-170" (manufactured by Nittetsu Chemical & Materials), etc. be able to.

Examples of the novolak type epoxy resin include phenol novolac type epoxy resin, cresol novolak type epoxy resin, and novolak type epoxy resin such as phenol glioxal type epoxy resin having a large number of epoxy groups in the molecule.

Commercially available novolak type epoxy resins include, for example, "jER152", "jER154" (all manufactured by Mitsubishi Chemical Co., Ltd.), EPPN-201 (manufactured by Nippon Kayaku Co., Ltd.), and Epototo YDPN-638. Examples of the cresol novolac type (manufactured by Nittetsu Chemical & Materials Co., Ltd.) include "jER180S65", "jER180H65" (all manufactured by Mitsubishi Chemical Co., Ltd.), EOCN-102S, -103S, and -104S (all of which are manufactured by Mitsubishi Chemical Co., Ltd.). Other novolak type epoxy resins such as Nippon Kayaku Co., Ltd.), Epototo YDCN-701, -702, -703, -704 (all manufactured by Nittetsu Chemical & Materials Co., Ltd.), for example. Epoxy ZX-1071T, ZX-1015, ZX-1247, YDG-414S (all of which are manufactured by Nittetsu Chemical & Materials Co., Ltd.) and the like can be mentioned.

Examples of the xylene resin include a reaction product of xylene and formaldehyde; a reaction product of mesitylene and formaldehyde; a reaction product of xylene, phenol and formaldehyde; and the like. If necessary, resins modified with phenols such as phenols and bifunctional phenols such as parat-butylphenol can also be used.

Commercially available xylene resins can be appropriately used, and specific examples thereof include "Nicanol LL", "Nicanol LL", "Nicanol L", "Nicanol H", "Nicanol G", and "Nicanol Y-50". "Niknol Y-100", (above, trade name, manufactured by Fudo Co., Ltd.) and the like can be mentioned.

Specific examples of the benzoguanamine resin include methyl etherified benzoguanamine resins such as Mycoat 102, 105 and 106 [all manufactured by Ornex] and BL-60 [manufactured by Sanwa Chemical Co., Ltd .]; Cymel 1123 [ Mixed etherified benzoguanamine resin of methyl ether and ethyl ether such as [Ornex]; mixed etherified benzoguanamine of methyl ether and butyl ether such as Mycoat 136 [Ornex], BX-4000 [Sanwa Chemical] Resins; butyl etherified benzoguanamine resins such as Mycoat 1128 [manufactured by Ornex]; and the like can be mentioned.

Examples of the phenol resin include a resol-type phenol resin obtained by subjecting phenols such as phenol compounds and bisphenol A to aldehydes such as formaldehyde in a condensation reaction in the presence of a reaction catalyst to introduce a methylol group. Can be done.

Examples of the phenols include bifunctional phenol compounds such as o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol; coal acid, m-cresol, and the like. Trifunctional phenolic compounds such as m-ethylphenol, 3,5-xylenol, and m-methoxyphenol; tetrafunctional phenolic compounds such as bisphenol A and bisphenol F; Can be used.

Examples of the aldehydes include formaldehyde, paraformaldehyde, trioxane and the like.

As the alcohol used for alkyl etherifying a part of the methylol group of the methylolated phenol resin, a monohydric alcohol having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms can be preferably used. .. Suitable monohydric alcohols include methanol, ethanol, n-propanol, n-butanol, isobutanol and the like.
The resin (C) having an aromatic ring structure can be used alone or in combination of two or more.

Acid catalyst (D)
The present coating composition contains an acid catalyst (D) in order to accelerate the curing reaction.

The acid catalyst (D) includes, for example, an acid catalyst such as a carboxyl group-containing compound, a phosphoric acid compound, paratoluene sulfonic acid, dodecylbenzene sulfonic acid, dinonylnaphthalene sulfonic acid, dinonylnaphthalenedisulfonic acid, and cumene sulfonic acid, or an acid catalyst thereof. Examples thereof include an amine neutralized product of an acid.

Of the above, from the viewpoint of crosslinkability, the sulfonic acid compound or the amine neutralized product of the sulfonic acid compound can be preferably used.

The solid content composition ratios of the polyester resin (A), the melamine resin (B), the resin (C) having an aromatic ring structure, and the acid catalyst (D) in the present coating composition are the polyester resin (A) and the melamine resin (B). Based on the total solid content of the resin (C) having an aromatic ring structure, the polyester resin (A) is 60 to 90% by mass, particularly 65 to 85% by mass, and the melamine resin (B) is 5 to 40% by mass. Especially in the case of 10 to 30% by mass, the resin (C) having an aromatic ring structure is 3 to 20% by mass, particularly 5 to 15% by mass, and the acid catalyst (D) (for example, an amine neutralized product of a sulfonic acid compound). The remaining sulfonic acid compound from which the amine has been removed from this neutralized product) is in the range of 0.1 to 3% by mass, particularly 0.3 to 2% by mass, that is, processability, water resistance, corrosion resistance, and blocking resistance. It is preferable from the viewpoint of.

The present coating composition contains a polyester resin (A), a melamine resin (B), a resin (C) having an aromatic ring structure, and an acid catalyst (D), but is usually used from the viewpoint of coatability and the like. A solvent is mixed. Further, if necessary, other resins can be blended for the purpose of modifying the coating film, and further, pigments such as coloring pigments and extender pigments; antiaggregating agents, leveling agents, defoaming agents, waxes. It can also contain additives for paints such as.

As the solvent, a solvent capable of dissolving or dispersing each component such as the above components (A), (B), (C), (D) and other resins used as needed can be used. ..

Specifically, for example, hydrocarbon solvents such as toluene, xylene, and high boiling petroleum hydrocarbons, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone, ethyl acetate, butyl acetate, and ethylene glycol monoethyl ether. Examples thereof include ester solvents such as acetate and diethylene glycol monoethyl ether acetate, alcohol solvents such as methanol, ethanol and butanol, alcohol ether solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether. , These can be used alone or in combination of two or more.

It is preferable to use two or more of the above solvents in combination, and it is resistant to containing the solvent composition (E) that further satisfies the following requirements in addition to the essential components (A), (B), (C) and (D). It is preferable from the viewpoint of improving the blocking property.

The solvent composition (E) comprises a solvent (E1) having a boiling point of less than 100 ° C., a solvent (E2) having a boiling point in the range of 100 ° C. to 120 ° C., and a solvent (E3) having a boiling point of more than 120 ° C. A solvent composition that meets the requirements of 30 to 60% by mass of the solvent (E1), 25 to 70% by mass of the solvent (E2), and 15% by mass of the solvent (E3) based on the total amount of (E2) and (E3). be.

When the solvent composition (E) is contained, the content thereof is 90 to 70 mass by mass with respect to the total solid content of the polyester resin (A), the melamine resin (B) and the resin (C) having an aromatic ring structure. %, In particular, it is preferably in the range of 85 to 75% by mass from the viewpoint of improving blocking resistance and coating workability.

The coating composition for repairing a welded can of the present invention can be used for repairing a seam of any welded can known per se. The seam may be formed by either lap welding or butt welding.

The coating composition for repairing a weld can of the present invention can also be applied to a welded portion obtained by polymerization laser welding, butt laser welding, or the like. In particular, the thickness of the welded portion obtained by butt laser welding or the like is substantially the same as the thickness of the material, and since there is no welding step seen in the welded portion of polymerized welding, it is easy to cover with the repair paint.

Various surface-treated steel plates are used as the metal plates that make up the welding can. The surface-treated steel sheet is one or two types of surface treatment such as zinc plating, tin plating, nickel plating, nickel tin plating, electrolytic chromium acid treatment, and chromium acid treatment, which are obtained by annealing a cold-rolled steel sheet and then secondary cold-rolling. You can use the one that has done the above. Further, an aluminum-coated steel sheet that has been plated with aluminum, crimped with aluminum, or the like can also be used. The thickness of the metal plate varies depending on the type of metal, the use or size of the container, but generally, a metal plate having a thickness of 0.10 to 0.50 mm, particularly 0.10 to 0.30 mm is preferably used. Can be done.

The metal plate used for welding cans is preferably laminated with a resin film or painted with a paint in advance, except for the edge portion to be welded. As the paint coated on the metal plate, a conventionally known paint used for metal coating can be used. The film thickness of the coating film coated with the resin film laminate or the paint is generally preferably in the range of 3 to 50 μm, particularly preferably in the range of 5 to 40 μm.

The coating composition for repairing a weld can of the present invention can be applied by any means to the weld seam of the weld can, but it is generally preferable to apply the coating composition by spray coating. In a welding can using a resin film laminated plate or a metal plate coated with paint, it is preferable to apply the repair paint so as to straddle the resin laminated film layer on both sides of the seam or the coating film layer coated with the paint.

The coating film thickness of the coating composition for repairing welded cans of the present invention is preferably in the range of 3 to 15 μm, particularly preferably 4 to 13 μm.

The heat-curing of the coating composition for repairing a weld can of the present invention is preferably carried out by heating at a temperature of 170 to 220 ° C., particularly 180 to 210 ° C. for 10 to 60 seconds, particularly 15 to 40 seconds.

Hereinafter, the present invention will be described in more detail with reference to Examples. Here, "parts" and "%" mean "parts by mass" and "% by mass", respectively. The mass part of the raw material in the following production examples, examples and comparative examples represents the mass part of the solid content (or may be referred to as an active ingredient) of the raw material.

<Manufacturing of paint composition>
The polyester resin (A), the melamine resin (B), the resin (C) having an aromatic ring structure, and the acid catalyst (D) are adjusted to have the solid content mass ratio and the solvent composition shown in Table 1 to obtain mass solids. Each coating composition No. with a component concentration of 20%. Obtained 1 to 15. The solvent of Cymel 327 (B1) and Cymel 370 (B2) was isobutanol (boiling point 108 ° C.), and the amount brought in from these was subtracted from toluene to adjust the mass solid content concentration. Paint composition No. 12 to 15 are for comparative examples.

Further, for comparative examples, the coating composition No. As No. 16, an epoxy resin-based paint having the following composition was also prepared.

Epoxy resin paint: jER1009 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Co., Ltd.) 85 parts / Amidia P-138 (butylated urea resin, manufactured by DIC) 15 parts / dodecylbenzenesulfonic acid 1 part Solvent composition is toluene / The mass solid content concentration was adjusted to 20% with butyl acetate / methyl ethyl ketone = 1/1/1 (mass ratio).

The details of each raw material in the table are as follows.

Polyester resin (A)
Polyester resin (A1): UE9200 (number average molecular weight 15000, glass transition temperature 65 ° C., hydroxyl value 6 mgKOH / g, manufactured by Unitika Ltd.)
Polyester resin (A2): Byron 200 (number average molecular weight 17,000, glass transition temperature 67 ° C., hydroxyl value 6 mgKOH / g, manufactured by Toyobo Co., Ltd.)
Polyester resin (A3): UE3360 (number average molecular weight 5000, glass transition temperature 55 ° C., hydroxyl value 25 mgKOH / g, manufactured by Unitika Ltd.)
Polyester resin (A4): Byron 600 (number average molecular weight 16000, glass transition temperature 47 ° C., hydroxyl value 7 mgKOH / g, manufactured by Toyobo Co., Ltd.)
Melamine resin (B)
Melamine resin (B1): Cymel 327 (imino group-containing methyl etherified melamine resin, manufactured by Ornex)
Melamine resin (B2): Cymel 370 (methyl etherified melamine resin containing methylol group, manufactured by Ornex)
Melamine resin (B3): Cymel 303 (full methyl etherified melamine resin, manufactured by Ornex)
Resin (C) having an aromatic ring structure
Resin having an aromatic ring structure (C1): jER1007 (bisphenol A type epoxy resin, number average molecular weight 2900, manufactured by Mitsubishi Chemical Corporation)
Resin having an aromatic ring structure (C2): jER154 (phenol novolac type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
Resin having an aromatic ring structure (C3): Nikanol LL (xylene formaldehyde resin, manufactured by Fudo Co., Ltd.)
Resin having an aromatic ring structure (C4): BX-4000 (benzoguanamine resin, manufactured by Sanwa Chemical Co., Ltd.)
Acid catalyst (D)
Acid catalyst (D1): Dodecylbenzenesulfonic acid Acid catalyst (D2): Paratoluenesulfonic acid Acid catalyst (D3): Phosphorus Solvent composition Solvent composition a: Methylethylketone 50 parts / Toluene 40 parts / Swazole 1000 (*) 5 parts / Solvent composition b: Methyl ethyl ketone 20 parts / Toluene 70 parts / Swazole 1000 5 parts / Butyl acetate 5 parts Solvent composition c: Methyl ethyl ketone 20 parts / Toluene 60 parts / Swazole 1000 10 parts / Butyl acetate 10 parts Swazole 1000 (* ): Aromatic hydrocarbon solvent, boiling point 160-170 ℃, manufactured by Maruzen Petrochemical Co., Ltd. <Preparation of test plate>
Each of the coating compositions prepared above was spray-coated on a cold-rolled steel sheet having a thickness of 0.30 mm so as to have a film thickness of 10 μm, and dried at a plate temperature of 200 ° C. for 30 seconds to obtain each test plate. ..

Each test plate obtained above was tested based on the following test method. The results are also shown in Table 1.

Workability The test plate was folded in half with a cold-rolled steel sheet having a thickness of 0.30 mm sandwiched between two spacers, and the processed portion was observed with an optical microscope.
〇: No cracks or peeling in the coating film △: Fine cracks occur in the coating film ×: Cracks occur in the coating film and part of it is peeled off Immerse the water resistant test plate in water and 125 After the treatment at ° C. for 30 minutes, the whitening state of the coating film was visually observed and evaluated according to the following criteria.
〇: No whitening is observed △: Partial whitening is observed ×: Significant whitening is observed Corrosion resistance A test coated plate that has been subjected to the same bending process as the workability test after covering the unpainted surface with tape. , Citric acid and sodium chloride were immersed in a mixed aqueous solution in which 3% each was dissolved, left at 40 ° C. for 2 weeks, and then the coated surface condition was visually observed and evaluated according to the following criteria.
〇: No corrosion is observed △: Slight corrosion is observed ×: Corrosion is considerably observed Blocking resistance Each coating composition prepared above is applied to a cold rolled steel sheet with a thickness of 0.30 mm to a film thickness of 10 μm. After spray-painting two sheets and drying them in a box oven set at 80 ° C. for 30 seconds, the coated surfaces of the two plates were overlapped with each other, and a load of 200 g / dm2 was applied and left for 1 minute.
⊚: Two test plates are easily peeled off and no trace is observed. 〇: Two test plates are easily peeled off, but slight traces are observed. △: There is resistance to peeling off the two test plates. , Marks are clearly visible ×: There is strong resistance to peel off the two test plates, and some of the coating film peels off.

It is possible to provide a coating composition for repairing a weld can, which is excellent in coating film performance such as processability, corrosion resistance, and water resistance, and is also excellent in blocking resistance.

Claims (5)

A polyester resin (A), a melamine resin (B), a resin (C) having an aromatic ring structure, and an acid having a number average molecular weight in the range of 10,000 to 20,000 and a glass transition temperature in the range of 51 to 100 ° C. A coating composition for repairing a welded can containing a catalyst (D). The coating composition for repairing a weld can according to claim 1, wherein the melamine resin (B) is a methyl etherified melamine resin. The coating composition for repairing a welded can according to claim 1 or 2, wherein the acid catalyst (D) is a sulfonic acid compound or an amine neutralized product of the sulfonic acid compound. Based on the total solid content of the polyester resin (A), the melamine resin (B) and the resin (C) having an aromatic ring structure, the polyester resin (A) is 60 to 90% by mass, and the melamine resin (B) is 5 to 40% by mass. %, The resin (C) having an aromatic ring structure (C) 3 to 20% by mass, and the acid catalyst (D) 0.1 to 3% by mass. thing. Claim 1 further contains a solvent composition (E) comprising a solvent (E1) having a boiling point of less than 100 ° C., a solvent (E2) having a boiling point in the range of 100 ° C. to 120 ° C., and a solvent (E3) having a boiling point of more than 120 ° C. The coating composition for repairing a welding can according to any one of 4 to 4.