JP2668195B2 - Precoat metal coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoat metal coating composition which has both hardness and workability and forms a coating film having excellent stain resistance.

[0002]

2. Description of the Related Art Conventionally, the so-called post-coat method, in which a metal plate is formed by cutting, bending, or the like, and then coated, is applied to home appliances, kitchen appliances, office equipment, and the like. However, this post-coating method has a problem that not only is the coating workability poor, but also it is difficult to uniformly coat the entire surface when the object to be coated has a complicated shape. Therefore, a plate-shaped or coil-shaped metal plate such as a galvanized steel plate, a cold-rolled steel plate, or an aluminum plate is preliminarily painted, and after the coating film is cured, the painted plate is formed and processed. The "PCM" method has been adopted. However, PCM
Processability of the coating film that can follow the elongation and bending of the metal material during molding (ie, flexibility)
At the same time, after the molding process, coating film properties such as high hardness and stain resistance, which are inconsistent with the processability, are required, and a paint for PCM satisfying both of these properties has not yet been developed. For example, Japanese Patent Publication No. 61-32351 and Japanese Patent Publication No. 62-34273 disclose a polyester-melamine resin-based paint for PCM which has a well-balanced coating film hardness and processability. Stain resistance to ash and mustard was insufficient.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the prior art and provides a coating film formed by the PCM method with processability and high hardness and stain resistance which are contradictory to it. An object of the present invention is to provide a coating composition for use.

[0004]

That is, the present invention provides: (A) a polyester resin having a number average molecular weight of 10,000 to 25,000, a glass transition temperature of 5 to 40 ° C., and a hydroxyl value of 5 to 15; (B-1) an imino group-type melamine resin having an average of 1.8 to 4.8 butoxy groups per triazine ring,
(B-2) a melamine resin obtained by mixing a complete methoxy group type melamine resin at a weight ratio of (B-1) / (B-2) = 50/50 to 90/10, and A) /
(B) = 70/30 to 85/15 With respect to 100 parts by weight of the polyester-melamine resin mixed, (C) the amine block of the sulfonic acid compound is 0.5 to
An object of the present invention is to provide a coating composition for precoat metal (PCM), which is blended in 2 parts by weight.

Hereinafter, the present invention will be described in detail. The coating composition of the present invention contains a polyester resin (A), a melamine resin (B) as a crosslinking agent thereof, an acid catalyst (C), and an organic solvent as essential components, and further contains various pigments and additives as necessary.
It contains a modified resin, a plasticizer and the like. The polyester resin (A) is produced by condensation polymerization of a polybasic acid and a polyhydric alcohol by a conventional method. In the production, the molecular weight is adjusted by using benzoic acid or the like as a terminal blocking agent. You may. This polybasic acid includes aromatic polybasic acids such as phthalic acid, terephthalic acid, isophthalic acid and trimellitic acid, and aliphatic polybasic acids such as oxalic acid, malonic acid, succinic acid, adipic acid and sebacic acid, and other cycloacids. Typical examples thereof include pentanedicarboxylic acid, hexahydrophthalic acid, hexahydrotrimellitic acid, and acid anhydrides thereof. Further, as the polyhydric alcohol, ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, butylene glycol, pentanediol, hexanediol,
Representative examples include trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, and sorbitol. Polyester resin (A)
Is an appropriate combination of these polybasic acids and polyhydric alcohols,
The number average molecular weight (hereinafter, referred to as “Mn”) obtained by the reaction is from 10,000 to 25,000, preferably 12,000.
The resin has a glass transition temperature (hereinafter, referred to as “Tg”) of 5 to 40 ° C., preferably 10 to 35; and a hydroxyl value of 5 to 15, preferably 7 to 13. When Mn is larger than the above range, it is difficult to dissolve in an organic solvent and the coating workability is deteriorated. Conversely, when Mn is small, workability such as cutting and bending and stain resistance are unfavorably reduced. On the other hand, if the Tg is higher than the above range, the workability such as cutting and bending is reduced, and if the Tg is lower, the hardness and the stain resistance are undesirably reduced. On the other hand, if the hydroxyl value is larger than the above range, the workability such as cutting and bending is reduced, and if the hydroxyl value is smaller, the hardness and solvent resistance are lowered, which is not preferable. In addition,
The acid value of the polyester resin is not particularly limited,
Generally, 10 or less is preferable.

As the melamine resin (B), an imino group type melamine resin (B-1) having an average of 1.8 to 4.8 butoxy groups and 1.0 or more imino groups per triazine ring (B-1). ). By using the imino group-type melamine resin having a butoxy group in the above range, the stain resistance to tobacco, mustard, etc. is improved. In addition, the imino group type melamine resin (B-1) is a melamine resin having a butoxy group and an imino group on the triazine ring, and if the butoxy group and the imino group have the number in the above-described range, the remaining portions may be used. Melamine resins having a methoxy group, a propoxy group, a methylol group or the like can also be used. Further, in the present invention, a coating film having excellent stain resistance can be obtained by using the imino group-type melamine resin (B-1). However, in order to improve solvent resistance, a complete methoxy-type melamine resin is further added. (B-2) is used in combination. The mixing ratio of the imino group type melamine resin (B-1) and the complete methoxy group type melamine resin (B-2) is (B-
1) / (B-2) = 50/50 to 90/10 is suitable. If the former is larger than the above range, the effect of improving the solvent resistance is not sufficiently exhibited, and if the former is smaller, the stain resistance, which is one of the objects of the present invention, is undesirably reduced. The mixing ratio of the polyester resin (A) and the melamine resin (B) composed of (B-1) and (B-2) is (A) / (B) = 70/30 to 85/15 by weight. , Preferably 75/25 to 80/20. If the amount of the polyester resin (A) is more than the above range, the stain resistance, hardness, solvent resistance and the like will be reduced.

The amine block (C) of the sulfonic acid compound as the acid catalyst is composed of dodecylbenzenesulfonic acid,
Paratoluenesulfonic acid, dinonylnaphthalenedisulfonic acid, sulfonic acid compounds such as methanesulfonic acid, isopropanolamine, diethylamine, diisopropylamine, di-n-propylamine, diisobutylamine,
It is blocked with an amine compound such as di-n-butylamine, morpholine, N-methylmorpholine, N, N-dimethylallylamine, N-methylpiperidine, pyridine, etc., and temporarily blocks the catalytic action to form a coating film. At the time of baking, the amine compound serving as a blocking agent is dissociated by heat, and at that time, the function as a catalyst is exhibited only. The amine block (C) of the sulfonic acid compound is dissociated by baking near the surface of the coating film, and the concentration of the active acid catalyst is increased due to volatilization of the amine. The concentration of the active acid catalyst is low because it is difficult to get outside. As a result, self-condensation of the melamine resin tends to occur near the surface of the coating film, the melamine resin concentrates toward the coating film surface, and a crosslinked layer is formed, so that the coating film surface has excellent stain resistance. The hardness inside the coating is not so high compared to the vicinity of the coating surface,
It is considered to be flexible.

When a sulfonic acid compound which is not amine-blocked is used, the difference in the acid catalyst concentration between the inside of the coating film and the vicinity of the coating film surface is small. Does not occur. The compounding amount of the amine block body (C) of the sulfonic acid compound is determined by the polyester resin (A), the above-mentioned (B-1) and (B-2)
Is 0.5 to 2 parts by weight, preferably 0.8 to 1.5 parts by weight, based on 100 parts by weight of the mixture of the melamine resin (B) consisting of Amine block of sulfonic acid compound (C)
If the content is more than the above range, the workability and the like will decrease, and if it is less, the hardness and stain resistance will decrease, which is not preferable. Examples of the organic solvent include aromatic hydrocarbons such as toluene and xylene, alcohols such as butanol, propanol, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether, and esters such as butyl acetate, methoxyethyl acetate, and ethoxyethyl acetate. Various organic solvents usually used for coating materials, such as ketones such as methyl ethyl ketone, methyl isobutyl ketone, isophorone and cyclohexanone, can be used.
Further, as the pigment to be blended as needed, it is used for ordinary paints such as coloring pigments such as titanium oxide, carbon black, iron oxide, phthalocyanine blue, and extender pigments such as calcium carbonate, talc, barium sulfate, kaolin and clay. Various pigments can be used.

The additives to be added as required include various additives used for ordinary paints such as a pigment dispersant, an antisettling agent, an antifoaming agent, a leveling agent, an ultraviolet absorber and an antibacterial agent. Can be used. The coating composition of the present invention comprises the components described above, and the compounding amount of the organic solvent is adjusted so that the coating viscosity becomes 40 to 200 seconds (Ford Cup No. 4 / room temperature) according to the coating workability. The amount is appropriate. The amount of the pigment is suitably from 0 to 60% by weight, preferably from 20 to 50% by weight, based on the solid content of the paint. The amount of the additive is suitably from 0 to 5% by weight, preferably from 1 to 3% by weight, based on the solid content of the paint. It is suitable for the coating composition of the present invention that such constituent components are kneaded and dispersed to obtain a pigment dispersity of 10 μm or less by a grind gauge A method. Next, a method of manufacturing the PCM will be described. If necessary, various surface treatments such as chromic acid type surface treatment, phosphate type surface treatment, etc., and further various types of primer such as epoxy type primer, polyester type primer, etc., galvanized steel plate, cold rolled steel plate, aluminum plate, etc. The coating composition of the present invention is applied to each of the various metal plates by a continuous coating means such as a reverse type or natural type roll coater or a flow coater so that the dry film thickness is about 10 to 30 μm, preferably 15 to 25 μm. , Maximum plate temperature (hereinafter referred to as "PMT") 50-120 at 200-250 ° C
Baking for a short time of 2 seconds to form a cured coating film, PCM
To manufacture. The line speed is 10 to 100 m /
Min is appropriate.

[0010]

EFFECT OF THE INVENTION The coating composition of the present invention is a coating composition for PCM, which has both processability and high-hardness coating film performance, and can provide a coating film excellent in stain resistance and solvent resistance against tobacco, mustard, etc. It is suitable as.

[0011]

The present invention will be described below in more detail with reference to examples. In the examples, "parts" and "%" are shown by weight.

Examples 1 to 8 and Comparative Examples 1 to 9 Chromate-treated electrogalvanized steel sheet having a thickness of 0.5 mm and a polyester resin-based primer ["V Knit # 160 Primer" (trade name, manufactured by Dainippon Paint Co., Ltd.)] The dry film thickness 5μ
m and baked and cured at a PMT of 204 ° C. for 40 seconds. Next, the coating compositions shown in Tables 1 and 2 were reverse roll coated so that the dry film thickness was 20 μm, and baked and dried at PMT232 ° C. for 60 seconds in a hot air drying oven to produce PCM. For the coated plates obtained in Examples 1 to 8 and Comparative Examples 1 to 9, gloss, pencil hardness,
Tests of workability, stain resistance, and solvent resistance were performed, and the results are shown in Tables 1 and 2 below. In addition, each test method and evaluation criteria were performed as follows. Mitsuzawa: 60 degree specular gloss is JIS K 5400
Was measured in accordance with the method described above. ：: 80 or more, Δ: 75 to 79, ×: 74 or less Pencil hardness: Measured according to the method of JIS K5400. ：: F or more, Δ: HB, ×: B or less Workability: The coated plate was subjected to a T-bend test at 20 ° C., and the presence or absence of cracks was determined with a 10-fold loupe. ○: 0T to 2T, △: 3T, ×: 4T or more Contamination resistance (1): Apply mustard dissolved in water to a coated plate, and
After standing at ℃ for 24 hours, it was washed with a neutral detergent to determine the degree of contamination. ◯: Very little or no coloration, Δ: Slightly coloration, X: Severe coloration Contamination resistance (2): Burn tobacco in a sealed container containing a coated plate, leave it for 24 hours, and then neutral detergent And the degree of contamination was determined. ：: very slight or no coloring, △: slightly colored, ×: severely colored Solvent resistance: 1 greased gauze impregnated with xylene
The appearance of the coating film after rubbing 00 times and the degree of stain on the gauze were determined. ⊚: The primer layer is not exposed and the gauze stain is small. ○: The primer layer is not exposed, but the gauze stain is large, Δ: 50 to
Exposing the primer layer with 100 rubs, ×: Exposing the primer layer with less than 50 rubs

As apparent from Table 1, Examples 1 to 8, which are the coating compositions of the present invention, had excellent coating properties in terms of workability, hardness, stain resistance, solvent resistance and the like. on the other hand,
Comparative Examples 1 and 7 using a polyester resin having a small Mn
Had poor stain resistance and poor workability. Further, in Comparative Examples 2 and 8 using a complete butoxy group type melamine resin having 6 butoxy groups in the triazine ring, the stain resistance was poor. In Comparative Example 3 using a completely methoxy group type melamine resin, the stain resistance was poor. In Comparative Example 4 in which the polyester resin was excessive, the stain resistance and solvent resistance were poor, and in Comparative Example 5, in which the melamine resin was excessive, the workability was poor. Further, in Comparative Examples 6 and 9 in which a sulfonic acid compound which was not blocked was used, gloss and stain resistance were poor.

[0014]

Table 1 Example 1 Coating composition 1 2 3 4 5 6 7 8 Polyester type ABCDAAAAA resin ¹⁾ Compounding amount 75 75 75 80 75 75 75 75 Butoxyimino Type (i) ( i) (i) (i) (ii) (iii) (i) (i) Basic melamine resin ²⁾ content 25 25 25 20 25 25 20 13 Complete methoxy group melamine resin ⁴⁾ Content 5 12 Sulfonic acid Compound amine Amount 1 1 1 1 1 1 1 1 1 block ⁵⁾ Titanium dioxide 100 100 100 100 100 100 100 100 Organic solvent ⁷⁾ Amount 170 200 170 145 170 170 170 170 Coating performance gloss ○ ○ ○ ○ ○ ○ ○ ○ Pencil hardness ○ ○ ○ ○ ○ ○ ○ ○ Workability ○ ○ ○ ○ ○ ○ ○ ○ Contamination resistance Mustard ○ ○ ○ ○ ○ ○ ○ ○ Tobacco ○ ○ ○ ○ ○ ○ ○ ○ Solvent resistance ○ ○ ○ ○ ○ ○ ◎ ◎

[0015]

[Table 2] Table 2Comparative example Coating composition 1 2 3 4 5 6 7 8 9 Polyester type EAAAAAAAAA Resin ¹⁾ Compounding amount 75 75 75 90 60 75 75 75 75 Butoxyimid Type (i) (i) (i) (i) (i) (i) No.-based melamine Content 25 10 40 25 20 20 Resin ²⁾  Complete butoxy-based melamine content 25 20Resin ³⁾  Complete methoxy-based melamine content 25 25 55 Resin ⁴⁾  Amine of sulfone oxide compounding amount 1 1 1 1 1 1 1Block body ⁵⁾  Non-blown amount of sulfonated compound 1 1 ⁶⁾ Titanium dioxide content 100 100 100 100 100 100 100 100 100 Organic solvent ⁷⁾ Amount 133 170 170 145 170 170 133 170 170 Film performance Gloss ○ ○ ○ ○ ○ × ○ ○ × Pencil hardness ○ ○ ○ △ ○ ○ ○ ○ ○ Processability △ ○ ○ ○ × ○ △ ○ ○ Stain resistance mustard × × × × ○ × × × × tobacco × × × × ○ × × × × Solvent resistance ◎ △ ◎ × ○ ○ ◎ ○ ○ Note 1) Polyester resin Polyester resin was produced according to the mixing ratio of polybasic acid and polyhydric alcohol shown in Table 3 below.

[0016]

Table 3 (Unit: mol%) Type of polyester resin ABCD E Polybasic acid terephthalic acid 40 40 30 54 40 Isophthalic acid 42 42 50 30 42 Sebacic acid 18 18 20 16 18 Polyhydric alcohol ethylene glycol 44 44 50 34 44 Neopentyl glycol 33 33 25 45 33 Diethylene glycol 23 23 25 21 22 Trimethylolpropane 1 Characteristic Mn × 10 ⁴ 1.4 2.0 1.4 1.2 0.7 Tg (° C) 20 20 10 35 20 Hydroxyl value 10 7 10 13 25 Note 2) Melamine resin The melamine resin used has the properties shown in Table 4 below.

[0017]

Table 4 Types of melamine resin (i) (ii) (iii) Average number of butoxy groups of 3.8 2.2 3.1 per triazine ring Average number of imino groups of 2.0 1.2 2.4 per triazine ring Polymerization degree 6 6 2 Note 3 ) Degree of polymerization 2 * 4) Degree of polymerization 2 * 5) Morpholine block of dodecylbenzenesulfonic acid * 6) Dodecylbenzenesulfonic acid * 7) Mixing of (50:40:10) of Solvesso # 150, cyclohexyne and isophorone solvent

Claims (1)

(57) [Claims] 1. (A) Number average molecular weight 10,000 to 2
5,000, glass transition temperature 5 to 40 ° C, hydroxyl value 5
15 polyester resins, and (B) (B-1) an imino group-type melamine resin having an average of 1.8 to 4.8 butoxy groups per triazine ring.
(B-2) a melamine resin obtained by mixing a complete methoxy group type melamine resin at a weight ratio of (B-1) / (B-2) = 50/50 to 90/10; A) / (B) = 70/30 to 85/15 100 parts by weight of the mixed polyester / melamine resin, and (C) the amine block of the sulfonic acid compound is 0.5 to
A coating composition for a pre-coated metal, which is characterized by containing 2 parts by weight.