JPH11199800A - Powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating compsn. which can form a coating film excellent in surface state, adhesivenss, processibiltiy, water resistance, curability, corrosion resistance, taste retention, etc., and having a low potassium permangante consumption. SOLUTION: This compsn. contains (A) a bisphenol epoxy resin having an epoxy equivalent of 500 or higher but lower than 2,000, a number average mol.wt. of 1,000 or higher but lower than 3,000, and a ratio of Mw/Mn of 1.8 or lower, (B) a bisphenol epoxy resin having an epoxy equivalent of 2,000-5,000 and a number average mol.wt. of 3,000-8,000, (C) an acid-anhydride-group-contg. polyester resin having a number average mol.wt. of 3,400-12,000, a total acid value of 30-90 mgKOH/g, an acid anhydride group equivalent of 2,000-6,000 g/equivalent, and a softening point of 50-140 deg.C, and (D) a cure catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating composition having excellent curability in short-time baking, and a method for coating the inner and outer surfaces of a can, a can lid processed portion, and a can body weld with the powder coating composition. About.

[0002]

2. Description of the Related Art
BACKGROUND ART Metal cans such as edible cans and beverage cans are coated with paint for cans to prevent metal elution and corrosion of the cans. As a paint used, a liquid paint in which a resin such as an epoxy resin or a vinyl chloride resin is dissolved or dispersed in a solvent is generally used.

[0003] In recent years, the organic solvent contained in these liquid paints volatilizes into the air at the time of coating, causing a problem of causing air pollution and the organic solvent remaining in the coating film on the inner surface of the can.
Since this has a problem in terms of hygiene that it is transferred to the contents of the can by heat sterilization, the shift to a pollution-free and solvent-free paint is being rapidly promoted.

[0004] In addition, conventionally known powders are generally made of unsuitable materials for sanitary use inside food cans and beverage cans. Therefore, the development of a powder coating that cures in a short time baking suitable for a coating for the inner surface of a can that is in direct contact with food and beverages is desired because good smooth coating surface, corrosion resistance, and processability of can making cannot be obtained. ing.

Accordingly, the present inventors have developed a can which can form a coating film having excellent coating surface condition, adhesion, workability, water resistance, curability, corrosion resistance, flavor retention and the like even with a short baking time. As a paint composition for cans, previously containing a bisphenol-type epoxy resin, a low molecular weight organic acid component having two or more trimellitic anhydride residues as a curing agent, and choline chloride as a curing catalyst. A powder coating composition has been proposed (see JP-A-8-3514). However, in the composition of this proposal, although the reactivity of the epoxy resin and the curing agent in a short time is improved, a part of the low molecular weight component in the epoxy resin still remains unreacted in the coating film, When this composition is applied to form a coating for the inner surface of a can, the low molecular weight epoxy resin component is easily extracted into the contents of the can, the flavor retention is reduced, and the consumption of potassium permanganate in the water extract is reduced. There is a problem that the amount becomes large.

[0006] For the same purpose, the present inventors have previously prepared a bisphenol type epoxy resin and a low molecular weight organic acid component or a high acid value having at least two trimellitic anhydride residues as a curing agent. And a powder coating composition for cans containing the above polyester resin and a metal salt of an organic carboxylic acid as a curing catalyst (see JP-A-8-92505).
However, also in this composition, the low molecular weight component in the epoxy resin remains in the coating film as described above, so that the flavor retention is reduced and the consumption of potassium permanganate in the water extract becomes large. is there.

[0007] The inventors of the present invention have found that the water extraction liquid permanganate has excellent properties such as a coated surface condition, adhesion, workability, water resistance, curability, corrosion resistance, and the like, and has a good flavor retention. As a result of intensive research to develop a powder coating composition for cans that can form a coating film with low potassium consumption, this time, a combination of epoxy resin with narrow molecular weight distribution and high molecular weight epoxy resin was used. The inventors have found that the above object can be achieved by using a specific acid anhydride group-containing polyester resin as an agent, and have completed the present invention.

[0008]

That is, the present invention provides:
(A) the epoxy equivalent is 500 or more and less than 2,000, the number average molecular weight is 1,000 or more and less than 3,000, the ratio of weight average molecular weight / number average molecular weight is 1.8 or less, and Bisphenol-type epoxy resin having a softening point of 50 to 140 ° C, (B) an epoxy equivalent of 2000 to 5,
000 and a number average molecular weight of 3,000 to 8,000
A bisphenol-type epoxy resin having a softening point of 50 to 140 ° C., (C) an acid component containing 80 to 100 mol% of an aromatic dicarboxylic acid in an acid component, and an aliphatic diol in an alcohol component of 92 to 100%. A number-average molecular weight of 3, obtained by reacting with an alcohol component containing 100 mol%.
000-10,000, hydroxyl value 10-40mgKOH
/ G of a polyester resin (a) having a molecular weight of 400 to 700 and containing at least two carboxylic acid anhydride groups in a molecule of the ester compound (b) with respect to 1 mol of the hydroxyl group in the resin (a). The acid anhydride group in (b) is 1.5 to
The number-average molecular weight is 3,400 to 12,000, and the total acid value is 30 to 90 mg KO, which is reacted at a ratio of 3.0 mol.
H / g, an acid anhydride group equivalent of 2,000 to 6,000 g / equivalent, containing an acid anhydride group-containing polyester resin having a softening point of 50 to 140 ° C. and (D) a curing catalyst, wherein the polyester resin (C) An object of the present invention is to provide a powder coating composition characterized in that the equivalent ratio of the acid anhydride group to the total of epoxy groups in all epoxy resins is in the range of 0.5 / 1 to 2/1.

Further, the present invention provides a method for coating a can, characterized in that the above powder coating composition is applied to the inner or outer surface of the can and baked.

[0010] The present invention also provides a method for repairing and coating a processed can lid, characterized in that the powder coating composition is applied to the processed can lid and baked.

Further, the present invention provides a method for coating a can body welding portion of a can, characterized in that the above powder coating composition is applied to a can body welding portion and baked.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, each component in the powder coating composition of the present invention will be further described.

Bisphenol type epoxy resin (A) In the composition of the present invention, the epoxy resin of the component (A) comprises:
The epoxy equivalent is 500 or more and less than 2,000, preferably in the range of 600 to 1,500, and the number average molecular weight is 1,000 or more and less than 3,000, preferably 1,20.
0 to 2,500, the ratio of weight average molecular weight / number average molecular weight (hereinafter sometimes abbreviated as “Mw / Mn ratio”) is 1.8 or less, and the softening point is 50 to 2,500. 14
It is a bisphenol type epoxy resin at a temperature of 0 ° C, preferably 80 to 130 ° C.

When the epoxy equivalent of the epoxy resin (A) is less than 500, the blocking resistance during storage of the powder coating material is deteriorated, and when it is 2,000 or more, the heat flow during heat curing of the powder coating material is reduced. The corrosion resistance of the resulting coating film is liable to be lowered. When the number average molecular weight of the epoxy resin (A) is less than 1,000, the adhesion and workability of the resulting coating film after a water resistance test are liable to be reduced. Fluidity decreases, and the smoothness and corrosion resistance of the resulting cured coating film tend to decrease. Mw / M of epoxy resin (A)
When the n ratio exceeds 1.8, the molecular weight distribution of the epoxy resin is widened and low molecular weight components are increased, so that the consumption of potassium permanganate of the aqueous extract of the obtained coating film is increased. The softening point of the epoxy resin (A) is 5
If the temperature is lower than 0 ° C., the powder coating tends to block during storage, while if the temperature exceeds 140 ° C., poor kneading occurs during coating, or the heat fluidity during heat curing of the powder coating deteriorates, resulting in a smooth surface. It becomes difficult to obtain a proper coating film.

The above bisphenol type epoxy resin (A)
Is, for example, epihalohydrin, bisphenols and optionally saturated aliphatic monocarboxylic acid, dibasic acid,
It can be obtained by reacting a modifier such as a polymerized fatty acid. As the epihalohydrin used as a raw material, epichlorohydrin is particularly preferred. As bisphenols, for example, bis (4-hydroxyphenyl) methane [abbreviation, bisphenol F], 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4
-Hydroxyphenyl) propane [abbreviation, bisphenol A], 2,2-bis (4-hydroxyphenyl) butane [abbreviation, 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 and the like can be mentioned. For the inner surface of the can,
Of these, bisphenol A and bisphenol F are preferable from the viewpoint of hygiene.

In the production of the above-mentioned bisphenol type epoxy resin, a modifying agent optionally used is preferable from the viewpoint of processability of a coating film from which dimer acid which is a polymerizable fatty acid is obtained. Dimer acid is a dimerized higher unsaturated fatty acid such as a purified vegetable oil fatty acid obtained from a drying oil or a semi-drying oil, and the unsaturated fatty acid is mainly a C ₁₈ unsaturated fatty acid such as linoleic acid. Linolenic acid, oleic acid and the like. The dimer acid is mainly composed of a dimer of the unsaturated fatty acid, but may contain other oligomers such as a trimer or a monomer fatty acid depending on the case.

Examples of the epoxy resin (A) include ZX1519 manufactured by Toto Kasei Co., Ltd.

Bisphenol type epoxy resin (B) In the composition of the present invention, the epoxy resin of the component (B) is
The epoxy equivalent is in the range of 2,000 to 5,000, preferably 2,000 to 4,000, and the number average molecular weight is 3,000 to 8,000, preferably 4,000 to 4,000.
7,000 and the softening point is 50-140.
It is a bisphenol type epoxy resin in the range of 80 ° C, preferably 80 to 130 ° C. The epoxy resin (B)
It is preferable that the compound does not substantially contain a compound having a molecular weight of less than 800.

When the epoxy equivalent of the epoxy resin (B) is less than 2,000, the processability of the coating film tends to decrease, while when it exceeds 5,000, the curability decreases and the resulting coating film becomes harder. Water resistance and corrosion resistance are likely to deteriorate. When the number average molecular weight of the epoxy resin (B) is less than 3,000, the processability of the obtained coating film is liable to decrease, while when the number average molecular weight exceeds 8,000, the heat resistance of the powder coating during heat curing is reduced. The thermal fluidity is reduced, and the smoothness and corrosion resistance of the obtained coating film are apt to be reduced. If the softening point of the epoxy resin (B) is less than 50 ° C., the powder coating tends to be blocked during storage, while if it exceeds 140 ° C., poor kneading may occur at the time of coating, or the powder coating may be heated. The heat fluidity at the time of curing becomes poor, and it becomes difficult to obtain a smooth coating film.

The above bisphenol type epoxy resin (B)
As the raw material for the production, the same one as the raw material for the production of the epoxy resin (A) can be used.

Among the bisphenol type epoxy resins (B), commercially available resins not modified with a modifying agent include:
For example, Epikote # 1007, Epikote # 1009, Epikote # 1
010 (all of which are manufactured by Yuka Shell Epoxy Co., Ltd., trade name) and Epototo YD-6020 (trade name, manufactured by Toto Kasei Co., Ltd.).

In the powder coating composition of the present invention, the epoxy resin contains the above-mentioned bisphenol type epoxy resin (A) and bisphenol type epoxy resin (B) as essential components. Mold epoxy resin can be blended.

The novolak type epoxy resin includes:
For example, various novolak epoxy resins such as a phenol novolak epoxy resin, a cresol novolak epoxy resin, and a phenol glyoxal epoxy resin having a large number of epoxy groups in a molecule can be used.

As a commercial product of the above novolak type epoxy resin, phenol novolak type is EPPN-2.
01 (trade name, manufactured by Nippon Kayaku Co., Ltd.), and the cresol novolak type is Epicoat # 180S
65, # 180H65 (both manufactured by Yuka Shell Epoxy, trade name), EOCN-102S, -10
3S and -104S (both are Nippon Kayaku Co., Ltd.)
Manufactured, trade name), Epototh YDCN-701, -70
2, -703, and -704 (all, manufactured by Toto Kasei Co., Ltd., trade names).

The compounding amount of each epoxy resin in the composition of the present invention is suitably in the following range, assuming that the compounding amount of all epoxy resins is 100 parts by weight. Epoxy resin (A): 20 to 80 parts by weight, preferably 30 to 70 parts by weight, Epoxy resin (B): 20 to 80 parts by weight, preferably 30 to 70 parts by weight, Novolak type epoxy resin: 0 to 40 parts by weight , Preferably 0 to 30 parts by weight.

Acid anhydride group-containing polyester resin (C) In the composition of the present invention, the acid anhydride group-containing polyester resin (C) serves as a curing agent for the epoxy resin, and contains a specific acid component and an alcohol component. Is reacted with an ester compound (b) containing two or more carboxylic acid anhydride groups in the molecule to thereby introduce an acid anhydride group into the resin. It is a group-containing polyester resin.

The polyester resin (a) comprises an acid component containing an aromatic dicarboxylic acid in the acid component in an amount of 80 to 100 mol% and an alcohol component containing an aliphatic diol in the amount of 92 to 1%.
It is a polyester resin obtained by reacting with an alcohol component containing 00 mol%.

Examples of the aromatic dicarboxylic acid in the acid component include phthalic anhydride, isophthalic acid, terephthalic acid and the like, and lower alkyl esters of these acids. These can be used alone or in combination of two or more.

As the acid component, in addition to the aromatic dicarboxylic acid, other acids can be used in combination, if necessary. Examples of the acid that can be used in combination include tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, and fumaric acid. , Adipic acid,
Azelaic acid, sebacic acid, dodecanedioic acid, maleic anhydride, 1,3-cyclohexanedicarboxylic acid, 1,4-
Non-aromatic dicarboxylic acids such as cyclohexanedicarboxylic acid; monobasic acids such as benzoic acid, crotonic acid and pt-butylbenzoic acid; trimellitic anhydride, pyromellitic anhydride, methylcyclohexentricarboxylic acid, and pyromellitic anhydride And tribasic or higher polybasic acids, and lower alkyl esters of these acids.
The ratio of the aromatic dicarboxylic acid in the acid component is 80 mol%.
When the proportion of the aromatic dicarboxylic acid is less than 80 mol%, generally, the produced resin tends to be softened, and it is difficult to balance the softening point of the resin with the coating film performance. .

As the alcohol component to be reacted with the acid component, for example, ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, 2-methyl-1,2
3-propanediol, 2-ethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-butyl-1,3-propanediol,
1,2-butanediol, 1,3-butanediol,
1,4-butanediol, neopentyl glycol, 3
-Methyl-1,5-pentanediol, 1,5-pentanediol, 1,4-hexanediol, 1,6-hexanediol, 2,5-hexanediol, ester diol 204 (manufactured by Union Carbide), etc. Can be mentioned. These can be used alone or in combination of two or more. As an alcohol component,
In addition to the above-mentioned aliphatic diols, alcohols that can be used as required include alicyclic or aromatic diols such as 1,4-cyclohexanedimethanol and hydrogenated bisphenol A; glycerin, trimethylolethane, trimethylolpropane, pentane Examples include trihydric or higher polyhydric alcohols such as erythritol, mannitol, and sorbitol. It is preferable that the amount of the aliphatic diol in the alcohol component is 92 mol% or more. If the amount is less than 92 mol%, the resin has many branches and the processability of the obtained coating film tends to be deteriorated.

The polyester resin (a) can be prepared by directly reacting the above-mentioned acid component and alcohol component by a direct esterification method or a transesterification method. That is, the acid component and the alcohol component may be polycondensed in excess of a hydroxyl group to form a hydroxyl-terminated polyester resin. This reaction can be promoted by pressurizing or depressurizing operation, or by flowing an inert gas. Further, at the time of the reaction, an organic metal catalyst such as di-n-butyltin oxide or the like can be used as an esterification catalyst. In general, the direct esterification method is advantageously used industrially, and the transesterification method is advantageously used when the reaction is carried out without applying pressure. However, the reaction can be appropriately performed depending on conditions and the like.

The polyester resin (a) has a number average molecular weight of 3,000 to 10,000, preferably 5,000 to 5,000.
It is a polyester resin having a 9,000 hydroxyl value of 10 to 40 mg KOH / g, preferably 10 to 25 mg KOH / g.
The mixing ratio of the acid component and the alcohol component, the type of each component, and the like are appropriately selected.

When the number average molecular weight of the polyester resin (a) is less than 3,000, the coating strength of the resulting coating film tends to be insufficient, while the number average molecular weight is 10,000 or less.
If it exceeds 00, the adhesion of the obtained coating film to the object to be coated, water resistance, and corrosion resistance tend to be reduced. When the hydroxyl value is less than 10 mgKOH / g, the amount of acid anhydride groups in a polyester resin obtained by reacting the ester value with the ester compound (b) decreases, and the curability of the coating film obtained decreases. On the other hand, while the hydroxyl value is 4
If it exceeds 0 mgKOH / g, the degree of branching of the polyester resin increases, and the processability of the resulting coating film tends to decrease.

In order to obtain the acid anhydride group-containing polyester resin (C) in the composition of the present invention, the ester compound (b) to be reacted with the polyester resin (a) has two or more carboxylic acid anhydride groups in the molecule. Containing molecular weight 400-
Any ester compound of 700, preferably 400 to 600 can be used without particular limitation.

If the number of carboxylic anhydride groups in the ester compound (b) is less than 2 in one molecule, the acid anhydride group-containing polyester resin (C) cannot be obtained. Also, 2
It is difficult to obtain an ester compound having a molecular weight of less than 400 as an ester compound containing two or more carboxylic acid anhydride groups, while if the molecular weight of the ester compound (b) exceeds 700, the reactivity with the polyester resin (a) is increased. Tends to decrease.

Typical examples of the ester compound (b) include:
The compound represented by the following formula (1) can be mentioned.

R (-OX) _k (1) In the formula, R is a divalent alkylene group having 2 to 6 carbon atoms or a trivalent alkanetriyl group, and X is a group represented by the following formula (2). Represents the trimellitic anhydride residue represented, and k represents 2 or 3.

[0038]

Embedded image

The compound represented by the formula (1) can be an esterified product of alkylene glycol having 2 to 6 carbon atoms or trivalent alkanetriol and trimellitic anhydride.

The alkylene glycol having 2 to 6 carbon atoms includes ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 1,6 -Hexanediol and the like, among which ethylene glycol is particularly preferred. Examples of the trivalent alkanetriol include glycerin, 1,2,3-butanetriol, 1,1,1-trimethylolpropane,
Examples thereof include 1,2,6-hexanetriol, and among them, glycerin is particularly preferable.

The reaction between the polyester resin (a) and the ester compound (b) to obtain the acid anhydride group-containing polyester resin (C) is carried out by converting the hydroxyl group in the polyester resin (a) to the ester compound (b). This is a reaction for introducing an acid anhydride group into a resin by reacting the acid anhydride group, and can be performed by a conventionally known esterification method. The mixing ratio of the polyester resin (a) and the ester compound (b) in the above reaction is such that the ratio of the acid anhydride group to the hydroxyl group is excessive, and the acid anhydride group is usually 1.5 to 1 mol per mol of the hydroxyl group.
The ratio is 2.5 mol, preferably 1.7 to 2.3 mol.

In the present invention, the acid anhydride group-containing polyester resin (C) has a number average molecular weight of 3,400 to 12,0.
00, preferably in the range of 6,000-10,000, the total acid number is in the range of 30-90 mgKOH / g, preferably 35-65 mgKOH / g, and the acid anhydride equivalent is 2,000-6,000. 2,000 g / equivalent, preferably 3,
Suitably, it is in the range of 000 to 5,500 g / equivalent and the softening point is in the range of 50 to 140 ° C, preferably 80 to 130 ° C.

The above acid anhydride group-containing polyester resin (C)
In the case where the number average molecular weight is less than 3,400, the coating strength and workability of the obtained coating film are liable to decrease. On the other hand, when the number average molecular weight exceeds 12,000, the coating of the obtained coating film is Adhesion with objects, water resistance, and corrosion resistance are likely to decrease. When the total acid value of the resin (C) is less than 30 mgKOH / g, the curability is reduced, and the water resistance of the obtained coating film is apt to decrease. On the other hand, the coating film obtained when the total acid value exceeds 70 mgKOH / g The workability of the steel is reduced. When the equivalent weight of the acid anhydride group in the resin (C) is less than 2,000 g / equivalent, the processability of the obtained coating film tends to be reduced,
On the other hand, if it exceeds 6,000 g / equivalent, the curability of the coating film tends to decrease. When the softening point of the resin (C) is less than 50 ° C., the resin (C) tends to be blocked during storage, while
If the temperature exceeds 140 ° C, poor kneading may occur during coating.
During heating and curing, there is a problem that the resin (C) is less likely to be melted, and the curability is poor, and the smoothness of the coated surface is liable to be reduced.

Curing catalyst (D) As the curing catalyst (D), any catalyst can be used as long as it can accelerate the reaction between the epoxy resin and the polyester resin (C) during the heat curing of the powder coating composition of the present invention. Examples thereof include choline chloride, metal salts of organic carboxylic acids, and imidazole compounds.

The above choline chloride has the chemical formula [HOCH ₂ C]
H ₂ N (CH ₃ ) ₃ ] ⁺ .Cl ⁻ . The metal salt of an organic carboxylic acid is preferably a compound having 5 carbon atoms.
To 24 fatty acid metal salts are preferred.
-Tin ethylhexanoate, tin laurate, dibutyltin dioctylate, dibutyltin dilaurate, zinc 2-ethylhexanoate, lithium stearate and the like. Examples of the imidazole compound include, for example, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-undecylimidazole,
2-heptadecylimidazole, 2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1
-Cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole,
1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 2,4-diamino-6 -[2-methylimidazolyl- (1)]-ethyl S-triazine, 2,4-diamino-6- [2-undecylimidazolyl- (1)]-
Ethyl S-triazine, 1-dodecyl-2-methyl-3
-Benzylimidazolium chloride, 1,3-dibenzyl-2-methylimidazolium chloride, and the like. Among the above curing catalysts, choline chloride and tin 2-ethylhexanoate are particularly preferred.

In the powder coating composition of the present invention, the compounding ratio of the epoxy resins (A) and (B) and the novolak type epoxy resin compounded as required with the acid anhydride group-containing polyester resin (C) is as follows: Equivalent of acid anhydride group in polyester resin (C) / epoxy group in total epoxy resin from the viewpoints of curability of paint, adhesion to can body, processability, water resistance, corrosion resistance, flavor retention, etc. The ratio is usually between 0.5 / 1 and
A range of 2/1, preferably 0.7 / 1 to 1.3 / 1 is appropriate.

In the composition of the present invention, the mixing ratio of the curing catalyst (D) is not particularly limited. However, from the viewpoint of the catalytic effect, the smoothness of the coating film obtained, the water resistance, etc., the total epoxy resin is usually used. 0.01 to 5 parts by weight based on 100 parts by weight of the total of the resin and the acid anhydride group-containing polyester resin (C).
It is preferable that the amount be in the range of 0.1 parts by weight, more preferably 0.1 to 2.0 parts by weight.

The powder coating composition of the present invention is blended with the epoxy resin (A), the epoxy resin (B), the acid anhydride group-containing polyester resin (C), the curing catalyst (D), and if necessary. It may be composed only of a novolak type epoxy resin, but if necessary, a known coating surface improving agent, solid waxes, coloring pigment, extender pigment, and a softening point of 5
It may contain a modified resin at 0 to 140 ° C.

It is advantageous to mix fine silica powder or fine aluminum oxide powder as an extender, since the fluidity of the paint powder is improved. The silica fine powder and the aluminum oxide fine powder can be blended alone or as a mixture. The total amount of both is the total epoxy resin component and the acid anhydride group-containing polyester resin (C). Is preferably in the range of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the total.

In order to obtain the powder coating composition of the present invention, the components forming the composition of the present invention are treated with a conventional kneader or extruder at a temperature at which the thickening and gelling phenomena do not occur. , Time conditions, usually at 50-160 ° C
Melting and kneading under conditions of ~ 60 seconds, cooling, pulverizing,
A classifier may be used, and a powder coating having a desired particle size distribution can be obtained. Usually, the particle size of the powder coating is preferably about 1 to 80 μm.

Examples of the metal material forming the can to which the powder coating composition of the present invention is applied include untreated steel sheets, tin-plated steel sheets, galvanized steel sheets, chromium-plated steel sheets, steel sheets, phosphate-treated steel sheets, and chromic acid-treated steel sheets. Examples include a steel plate, an untreated aluminum plate, and a chromic acid-treated aluminum plate. The coating of the composition of the present invention on a metal material can be performed by, for example, electrostatic coating.
A cured coating film can be formed by baking and drying at a temperature of about 7 to 180 seconds.

The powder coating composition of the present invention is used for coating the inner surface of a can and the outer surface of a can. Examples of the coating on the inner surface and the outer surface of the can include, for example, coating on the inner and outer surfaces of a two-piece can or three-piece can, coating on a sheet metal plate forming a can body and a lid, and sheet-like forming a coating film. Repair coating of the can lid processing part which cut the metal plate and processed it as a can lid, cut the sheet-like metal plate with the coating film formed, cut both ends, welded the can body welding part on the inner and outer surface of the can (side seam Part) repair painting.

In the powder coating composition of the present invention, by using a bisphenol A type epoxy resin or a bisphenol F type epoxy resin as the epoxy resin (A) and the epoxy resin (B) component, a material having no problem in hygiene can be obtained. The composition can be applied to the inner surface of a two-piece can because of its good inner surface coating property and workability.

The powder coating composition of the present invention has a cured coating film thickness of:
In the general part of the inner surface of the can and the outer surface of the can, usually 2 to 20μ
m, for repair painting of the can lid processing part, usually 15 to 50
In the repair coating of the side seam portion of the can body, the coating is usually performed in the range of 30 to 100 μm in order to sufficiently cover the welding step.

[0055]

The present invention will be described more specifically with reference to the following examples.

Hereinafter, both “parts” and “%” are based on weight.

Production of acid anhydride group-containing polyester resin (C)
The alcohol component shown in granulation Production Examples 1 to 11 the following Table 1, stirrer, heater, thermometer, nitrogen gas inlet tube, were charged into a stainless steel pressure reactor equipped with a fractionating apparatus and distill water reservoir, stirred and The temperature was raised to 160 ° C. while the contents were in a solution state.

Into this reaction vessel were charged フ of terephthalic acid in the amount shown in Table 1 below and dibutyltin oxide as a reaction catalyst, the reactor was closed, and nitrogen gas for pressurization was introduced to introduce 2 kg. / Cm ² . As the temperature in the reactor increases, the pressure in the reactor also increases, but when the temperature reaches 240 ° C., the pressure is 3.5 kg / cm ^2.
The pressure in the reactor was adjusted while introducing nitrogen gas so that The temperature and pressure in the reactor were adjusted so that the temperature at the top of the fractionation device did not exceed 150 ° C., and the reaction was continued while the generated condensed water was stored in the distillate storage tank. 1.5 hours after the temperature reached 240 ° C., when the amount of condensed water distilled out exceeded 90% of the theoretical value, the system was cooled to 180 ° C.
When the pressure became, the system pressure was released.

Next, the remaining amount of terephthalic acid and other acid components shown in Table 1 below is charged into the reactor, and the temperature at the top of the fractionating apparatus is not higher than 100 ° C., and the condensation generated by the nitrogen gas stream is performed. Gradually remove water 2
The temperature was raised to 40 ° C., and the esterification reaction was continued at that temperature. At any time during the reaction, a sample of the reaction product was collected, and the acid value of the reaction product was measured by a method of titration with a 1/10 normal alcoholic KOH solution using pyridine as a solvent, and this value was within a predetermined range. Thereafter, the content was cooled to 190 ° C. to obtain each polyester resin (a) having a hydroxyl group at a terminal. The number average molecular weight, hydroxyl value and acid value of each resin (a) are shown in Table 1 below.

Next, each ester compound (b) containing a carboxylic acid anhydride group was added to the reactor, and the mixture was stirred for 2 hours to carry out an addition reaction to obtain each acid anhydride group-containing polyester resin (C). The acid anhydride group-containing polyester resins obtained in Production Examples 8 to 11 are comparative resins.

The name, number average molecular weight, total acid value, acid anhydride equivalent, and softening point of each resin (C) are shown in Table 1 below. The amount of each component in Table 1 is indicated by a molar amount.

Further, (note) in Table 1 has the following meaning.

(Note 1) Ester compound (b) -1: an ester compound having two trimellitic anhydride residues in one molecule, represented by the following formula, and having a molecular weight of 410.

X—O—CH ₂ CH ₂ —O—X In the above formula, X represents a trimellitic anhydride residue represented by the above formula (2).

(Note 2) Ester compound (b) -2: An ester compound having three trimellitic anhydride residues in one molecule and represented by the following formula, and having a molecular weight of 614.

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In the above formula, X represents a trimellitic anhydride residue represented by the above formula (2).

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[Table 1]

Production of Powder Coating Example 1 ZX1519 ( manufactured by Toto Kasei Co., Ltd., number average molecular weight of about 1,
740, epoxy equivalent about 850, Mw / Mn ratio = 1.5
7, bisphenol A type epoxy resin, softening point about 95
C) 26 parts, Epototo YD177 (Toto Kasei Co., Ltd.)
Dimer acid-modified bisphenol-type epoxy resin having a product name, a product name, a number average molecular weight of about 3340, an epoxy equivalent of about 2,000, and a softening point of about 100 ° C., abbreviated as “YD177” in Tables 2 and 3 below) 14 parts, 166 1.0 part of polyester resin C-1 obtained in Production Example 1 above, Carplex FPS500 (manufactured by Shionogi Pharmaceutical Co., Ltd., silica fine powder, abbreviated as “FPS500” in Tables 2 and 3 below) , Choline chloride 1.0 part and Modaflow powder (manufactured by Monsanto, USA, powdery surface conditioner)
After dry-blending 2.1 parts, Buscon Kneader PR
The mixture was melt-kneaded at 46 (manufactured by Bus). Then, after cooling, a particle size of 5 to 75 μm and an average particle size of about 4 were determined using a pulverizer and a classifier.
A powder coating of 0 μm was obtained.

Examples 2 to 10 and Comparative Examples 1 to 11 The procedure of Example 1 was repeated, except that the raw materials were mixed as shown in Table 2 below.
m, each powder coating having an average particle size of about 40 μm.

Examples 11 to 20 and Comparative Examples 12 to 22 In Example 1, the raw materials were mixed as shown in Table 3 below, and a powder having a particle size of 1 to 30 μm and an average particle size of about 15 μm was obtained by a pulverizer and a classifier. Each powder coating was obtained in the same manner as in Example 1 except for coating.

(Note) in Tables 2 and 3 below has the following meanings.

(Note 1) and (Note 2) have the same meaning as described above.

(Note 3) YDCN704: Toto Kasei Co., Ltd.
Product name “Epototo YDCN704”, number average molecular weight about 1300, epoxy equivalent about 206, softening point about 94 ° C
Novolak type epoxy resin.

(Note 4) E1004: manufactured by Yuka Shell Epoxy Co., Ltd., trade name “Epicoat 1004”, number average molecular weight: about 1400, epoxy equivalent: about 920, softening point: about 97 ° C.
Bisphenol A type epoxy resin.

(Note 5) YD6020: Toto Kasei Co., Ltd.
Product name “Epototo YD6020”, number average molecular weight about 7,000, epoxy equivalent about 3,500, softening point about 1
Bisphenol type epoxy resin at 20 ° C.

Test Method Each of the powder coatings obtained in Examples 1 to 10 and Comparative Examples 1 to 11 was tested according to the following method (1) in order to test the suitability of the side seam portion on the inner surface of the can for repair coating. A painted plate was created.

Method for Preparing Coated Plate (1) Each of the powder coatings obtained in Examples 1 to 10 and Comparative Examples 1 to 11 was electrostatically coated on a # 25 tin plate so that the dry coating thickness was about 45 μm. Each of the coated plates was baked and cured under the condition that the plate temperature was maintained at 190 to 200 ° C. for 30 seconds.

For each of the powder coatings obtained in Examples 11 to 20 and Comparative Examples 12 to 22, a coated plate was prepared according to the following method (2) in order to test the suitability for coating the inner surface of the can body of the can. Created.

(2) Each of the powder coatings obtained in Examples 12 to 20 and Comparative Examples 12 to 22 was electrostatically coated on a # 25 tin plate so that the dry coating thickness became about 15 μm. , 220-230 ° C. for 60 seconds for baking and curing to prepare each coated plate.

For each of the coated plates obtained by the above methods (1) and (2), the coated surface condition, gel fraction, workability,
The water resistance, water resistance (general part), adhesion, and the adhesion after the water resistance test of the processed portion were tested according to the following methods.

Coated surface condition: The coated surface of the coated plate was visually observed and evaluated according to the following criteria. ：: The entire coated surface is smooth and no foaming is observed. Δ: Slight unevenness is observed on the entire coated surface and small foaming is observed. X: Slight unevenness is observed on the entire coated surface and large foaming is observed. Can be

Gel fraction: A coated plate having a weight of W ₂ was placed in a flask, and methyl ethyl ketone / coated area of the coated plate = 1.
After adding methyl ethyl ketone so as to be 00 cc / 100 cm ² and performing extraction for 1 hour while heating under reflux, the coated plate was taken out, dried at 120 ° C. for 30 minutes, and cooled to room temperature.
The weight W ₃ was measured. The weight before tinplate application of paints to the coated plate and W _1, gel fraction (%) was calculated by the following equation. Gel fraction (%) = {(W ₃ −W ₁ ) / (W ₂ −W ₁ )}
× 100 Workability: A 180 ° bent part with the coating surface facing out at the lower part of the coated plate, and using a special goby fold type Dupont impact tester, the contact surface is flat at this bent part and weighs 1 kg. The length of the crack in the coating film at the bent portion caused when the iron weight of Example 1 was dropped from a height of 50 cm was measured and evaluated according to the following criteria. ◎: less than 5 mm ：: 5 mm or more and less than 10 mm Δ: 10 mm or more and less than 20 mm ×: 20 mm or more.

Water resistance of the processed part: The coated plate subjected to the above test of the workability was immersed in deionized water at 125 ° C. for 35 minutes in an autoclave, pulled up, and the crack length of the coating film was measured. The evaluation was performed based on the evaluation criteria of the workability test.

Water resistance (general part): The coated plate was immersed in deionized water at 125 ° C. for 35 minutes in an autoclave and pulled up. The whitening state of the coating film was observed and evaluated according to the following criteria. ◎: No whitening is observed in the coating film. ：: Slight whitening is observed in the coating film. か な り: Significant whitening is observed in the coating film. X: Significant whitening is observed in the coating film.

Adhesion: 11 cuts each in the vertical and horizontal directions with a knife of about 1.5 mm in width were applied to the coating film of the coated plate using a knife, and a 24 mm wide cellophane adhesive tape was adhered to it and peeled off strongly. The coating film at the gobang eye portion was observed and evaluated according to the following criteria. ◎: No peeling is observed at all. ○: Slight peeling is observed. Δ: Considerable peeling is observed. X: Remarkable peeling is observed.

Adhesion after water resistance test: The coated plate was immersed in deionized water at 125 ° C. for 35 minutes in an autoclave and pulled up.
Put 11 cuts on each side, 24mm
A cellophane pressure-sensitive adhesive tape having a width was adhered to the film, and the coating film at the gobang portion when strongly peeled was observed. The evaluation was performed based on the evaluation criteria of the adhesion test.

Can Body for Corrosion Resistance and Flavor Retention Test
Preparation of a can body with a side seam part repaired and painted on a can body # 25 A solution type epoxy-phenol resin paint for the can inner surface is painted to a dry film thickness of 5 μm, leaving a margin for welding on a tin plate # 25. And baking to form a cured coating film. The coated plate was welded to a three-piece can body, and Examples 1 to 10 and Comparative Examples 1 to 1 were welded to the inner surface of the welded can body.
Each of the powder coatings obtained in 1 was electrostatically coated so that the dry film thickness was about 45 μm and the coating width was about 15 mm.
Each can body which was baked and cured under the condition of maintaining the temperature at 0 ° C. for 30 seconds and repair-painted was prepared.

Preparation of Can Body of Two-Piece Can Each of the powder coatings obtained in Examples 11 to 20 and Comparative Examples 12 to 22 has a dry film thickness of about 15 μm on the inner surface of a steel two-piece can having a capacity of 250 cc. 215
It was baked and cured at 60 ° C. for 60 seconds to prepare a two-piece can body.

Each of the test liquids was put into the repair-painted can body and the two-piece can body, and the test solution was subjected to the following corrosion resistance and flavor retention test. The upper and lower lids of the repair-painted can body were tightened, and the upper lid of a two-piece can body was tightly wound.

[0091] Corrosion resistance:
The 0% pine juice was hot-packed at 98 ° C., tightly wound, stored at 37 ° C. for 6 months, opened, observed for corrosion on the inner surface, and evaluated according to the following criteria. ：: No corrosion is observed Δ: Slight corrosion is observed ×: Corrosion is remarkable

Flavor retention: Using each of the above can bodies,
Tap water was filled with 250 cc of water treated with activated carbon, tightly wound, sterilized at 125 ° C. for 30 minutes, stored at 37 ° C. for 6 months, then subjected to a flavor test, and evaluated according to the following criteria. ：: No change is observed at all. ○: Slight change is observed. Δ: A considerable change is observed. X: Remarkable change is observed.

Potassium permanganate consumption: Each can body was filled with 250 cc of deionized water, wound tightly, and treated at 125 ° C. for 30 minutes. The consumption of potassium permanganate (KMnO ₄ ) was measured according to (Ministry of Health and Welfare No. 434). This consumption is expressed in ppm.

The powder coating materials obtained in each of the examples and comparative examples were tested for powder fluidity and powder storability based on the following methods.

Powder flowability: temperature 20 ° C., humidity 60% RH
The angle of repose of the powder coating was measured under the following conditions. The evaluation was performed according to the following criteria. ：: angle of repose is 45 degrees or less Δ: angle of repose exceeds 45 degrees and 50 degrees or less ×: angle of repose exceeds 50 degrees

Powder storability: After storing the powder coating in an atmosphere at 40 ° C. for 7 days, it was taken out and the condition was examined.

◎: No lump was observed at all. ○: Lump was observed but loosened easily with fingers. △: Powder coating was fused and loosened with fingers, but uniform powder was not obtained. ×: Powder Paint is fused and cannot be loosened with fingers.

The results of these tests are shown in Tables 2 and 3 below.

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[Table 2]

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[Table 3]

[0101]

[Table 4]

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[Table 5]

[0103]

The powder coating composition of the present invention has excellent curability in low-temperature and short-time baking, and has good coating surface condition, adhesion, processability, water resistance, corrosion resistance, flavor retention and the like on a substrate. Excellent,
In addition, a coating film that consumes less potassium permanganate can be formed. The coating composition of the present invention uses a specific acid anhydride group-containing polyester resin as a curing agent to be combined with an epoxy resin, and can achieve both curability and coating film performance. In addition, as the epoxy resin, a mixture of a high molecular weight epoxy resin and an epoxy resin having a narrow molecular weight distribution and a low molecular weight component is used, so that the coating film performance can be further improved, and further, potassium permanganate is used. A coating film with low consumption can be formed.

Further, the composition of the present invention has almost no residual solvent, and by selecting a material, can form a coating film having no hygiene problem even if it comes into direct contact with foods and beverages as a coating film on the inner surface of the can. . Further, the composition of the present invention can form a coating film having excellent coating performance without foaming during curing even in repair coating of a can lid processed portion and a can body side seam portion.

Further, since the composition of the present invention is a powder coating, there is an effect that there is no problem of air pollution due to volatilization of the organic solvent at the time of coating.

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Claims (7)

[Claims] (A) When the epoxy equivalent is 500 or more,
000, the number average molecular weight is 1,000 or more and less than 3,000, the ratio of weight average molecular weight / number average molecular weight is 1.8 or less, and the softening point is 50 to 140 ° C.
Bisphenol type epoxy resin, (B) epoxy equivalent is 2,000-5,000, and number average molecular weight is 3.0.
00-8,000 and softening point of 50-140 ° C
A bisphenol-type epoxy resin, (C) an acid component containing an aromatic dicarboxylic acid in the acid component in an amount of 80 to 100 mol%, and an aliphatic diol in the alcohol component in an amount of 92 to 10;
By reacting with an alcohol component containing 0 mol%,
Number average molecular weight 3,000-10,000, hydroxyl value 10
A polyester resin (a) having a molecular weight of 4 to 40 mgKOH / g containing two or more carboxylic anhydride groups in the molecule.
The ester compound (b) of the resin (a) is reacted at a ratio of 1.5 to 3.0 mol of the acid anhydride group in the ester compound (b) with respect to 1 mol of the hydroxyl group in the resin (a). , Number average molecular weight 3,400-12,000, total acid value 3
0 to 90 mgKOH / g, acid anhydride equivalent 2,000 to
6,000 g / equivalent, containing an acid anhydride group-containing polyester resin having a softening point of 50 to 140 ° C. and (D) a curing catalyst, wherein acid anhydride groups in the polyester resin (C) / epoxy groups in all epoxy resins Equivalent ratio to total 0.5 / 1 ~
A powder coating composition characterized by being in the range of 2/1. 2. An ester compound (b) represented by the following formula (1):
The polyester resin according to claim 1, which is a compound represented by the formula: R (-OX) _k (1) In the formula, R is a divalent alkylene group having 2 to 6 carbon atoms or a trivalent alkanetriyl group, and X is represented by the following formula (2). Represents a trimellitic anhydride residue, and k represents 2 or 3. 3. The powder coating composition according to claim 1, further comprising a novolak type epoxy resin. 4. The powder coating composition according to claim 1, further comprising silica fine powder or aluminum oxide fine powder. 5. A method for coating cans, which comprises applying the powder coating composition according to claim 1 to the inner or outer surface of the can and baking it. 6. A method for repairing and coating a can lid processed part, comprising applying the powder coating composition according to claim 1 to a can lid processed part and baking it. 7. A method for coating a can body welding portion of a can, comprising coating and baking the powder coating composition according to claim 1 on the can body welding portion.