JPH06313152A - Coating composition - Google Patents

Abstract

(57) [Summary] [Structure] Two types of hydroxyl group-containing polyester resins differing in number average molecular weight, hydroxyl value and glass transition point, and the difference in glass transition point falls within a specific range, a block polyisocyanate compound, and an average polymerization. A coating composition containing a specific amount of a melamine resin having a degree of 1.1 to 3. [Effect] By combining two kinds of hydroxyl group-containing polyester resins having different physical properties and two kinds of curing agent components, a low Tg network structure with a large inter-crosslinking molecular weight and a high Tg network structure with a small inter-crosslinking molecular weight A coating film having the following special network structure is formed, and a coating film excellent in high workability and high durability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition for precoat coating, and in particular, it has a good coating hardness, good workability immediately after coating, and adhesion of the coating over time at the processing location. The present invention relates to a coating composition which gives a coating film which is good and is also excellent in weather resistance, stain resistance and chemical resistance.

[0002]

2. Description of the Related Art A so-called pre-coated metal plate obtained by previously coating a metal material such as an aluminum plate, a steel plate, a galvanized steel plate, etc. does not need to be coated again after processing such as bending, It has been widely used in recent years.

In such a precoated metal plate,
Good workability is required so that cracks or cracks in the coating film do not occur even when processing such as bending is performed. Further, it is required that the coating film does not come off at the processed portion even after a lapse of time. Further, not only processability but also performance such as weather resistance, stain resistance, and chemical resistance is required depending on the application.

However, the conventional coating composition cannot provide a coating film having sufficient hardness and simultaneously satisfying the workability, weather resistance, stain resistance, chemical resistance and the like.

Therefore, vigorous efforts have been made to develop paints that provide coating films that simultaneously satisfy such characteristics. For example, JP-A-2-242867 discloses that (A) a hydroxyl group-containing resin, (B) an amino resin, and (C) a block polyisocyanate compound as the main components, and a reaction between the (C) component and the (A) component. Disclosed is a thermosetting coating composition having an initiation temperature in the range of -20 ° C to + 50 ° C based on the reaction initiation temperature of the components (A) and (B). However, according to the study of the present inventors, in the coating composition disclosed in JP-A-2-242867, although the stain resistance and the chemical resistance are good, the crosslinking density becomes high and sufficient processability is obtained. However, at the same time, there is a drawback in that the phenomenon of deterioration of the processed portion with time occurs.

Further, JP-A-2-58671 discloses a metal-coated urethane baking coating composition comprising a hydroxyl group-containing polyester resin, a blocked isocyanate compound, an organic tin compound, an organic solvent and a coating additive. There is. However, this coating composition has drawbacks such as deterioration of the processed portion over time and poor stain resistance.

Therefore, the object of the present invention is to have a good coating film hardness, good workability immediately after coating, and to prevent peeling of the coating film at the processed portion even after a lapse of time. It is intended to provide a coating composition which gives a coating film having excellent properties, stain resistance and chemical resistance.

[0008]

As a result of earnest research in view of the above problems, the present inventor has found that two kinds of polyester resins having different number average molecular weights, hydroxyl values and glass transition points are used as paint main components and cured. If a block polyisocyanate compound and a melamine resin are used in combination as an agent component, good coating film hardness can be obtained, workability immediately after coating is good, and peeling occurs in the coating film at the processed portion over time. Without occurring, weather resistance, stain resistance,
The present invention has been completed by discovering that a coating film having excellent chemical resistance can be formed.

That is, the coating composition of the present invention comprises (a) a first hydroxyl group-containing polyester resin having a number average molecular weight of 8500 to 30000 and a hydroxyl value of 2 to 15, and (b) a number average molecular weight of
A second hydroxyl group-containing polyester resin having a hydroxyl value of 1500 to 8000 and a hydroxyl value of 16 to 120, (c) a block polyisocyanate compound, and (d) a melamine resin having an average degree of polymerization of 1.1 to 3 Glass transition point Tg ₁ of (a) and the above components
The glass transition point Tg ₂ of (b) satisfies the following formula: 0 <| Tg ₁ −Tg ₂ | ≦ 20, and the blending amount of each component is a weight ratio of solid content, (a) / (b) = 95/5 to 40/60, (c) / (d) = 95/5 to 5/95, and [(a) + (b)] / [(c) + (d)] = 9/1 to 7 It is characterized by being / 3.

The present invention will be described in detail below. In the present invention, the following two types of hydroxyl group-containing polyester resins (a) and (b) are used. These two types of polyester resins (a) and (b) are both ester reaction products of a polyhydric alcohol and a polybasic acid or an anhydride thereof, each containing an amount of a hydroxyl group having a hydroxyl value described below. It has in the molecule.

(A) First Hydroxyl Group-Containing Polyester Resin Polyhydric alcohols that can be used for producing the first hydroxyl group-containing polyester resin include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol,
Polypropylene glycol, neopentyl glycol,
1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 2,2-dimethyl-3-hydroxypropionate,
N, N-bis (2-hydroxyethyl) dimethylhytantoin, polytetramethylene ether glycol, ε-caprolactone, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, trimethylolbutane,
Hexanetriol, pentaerythritol, dipentaerythritol, tris (hydroxyethyl) isocyanate, 1,9-nonanediol and the like can be mentioned.

These polyhydric alcohols may be used alone or in combination with
A combination of two or more species can be used. When two or more kinds are used in combination, it is particularly preferable to combine ε-caprolactone with other polyhydric alcohol. In this case, the amount of ε-caprolactone is preferably 20 to 60 mol% of the total amount of polyhydric alcohol. If the amount of ε-caprolactone is less than 20 mol%, the workability is deteriorated. On the other hand, when the amount of ε-caprolactone exceeds 60 mol%, the stain resistance decreases and the desired coating film hardness cannot be obtained. More preferably, it is 30 to 60 mol%.

As the polybasic acid or its anhydride, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, Hymic acid anhydride, trimellitic acid, trimellitic acid anhydride, pyromellitic acid, pyromellitic acid anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, Examples thereof include succinic acid, succinic anhydride, lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1,4-dicarboxylic acid and endo acid anhydride.

These polybasic acids or their anhydrides may be used alone or in combination of two or more. In particular, it is preferable to use isophthalic acid alone or to use isophthalic acid in combination with other polybasic acid or its anhydride. The mixing amount of isophthalic acid is 2 of the total amount of polybasic acid or its anhydride.
It is preferably 0 to 100 mol%. If the amount of isophthalic acid is less than 20 mol%, the weather resistance will decrease. More preferably, it is 30 to 100 mol%.

In the present invention, a hydroxyl group-containing polyester resin synthesized from the above-mentioned polyhydric alcohol and polybasic acid or its anhydride is further added to a long-chain monoepoxide (for example, Cardura E: Shell Chemical Co., Ltd., or AO
EX24: manufactured by Daicel Chemical Industries, Ltd. may also be used after being modified.

The number average molecular weight of the first hydroxyl group-containing polyester resin is 8500 to 30,000, and the hydroxyl value is 2 to 15.

When the number average molecular weight is less than 8500, the adhesion of the coating film at the processed portion is lowered, and particularly, the adhesion of the coating film after a lapse of about one year (coating adhesion with time) is greatly reduced. . Further, if the number average molecular weight exceeds 30,000, the coating workability becomes poor. Preferred number average molecular weight is 10,000 to 20
It is 000.

In the present invention, the number average molecular weight of the resin is measured by gel permeation chromatography (GPC method) using SHODEXKF-803 (manufactured by Tosoh Corporation) as a column and tetrahydrofuran as a solvent. It was done.

With respect to the hydroxyl value, if it is less than 2, the coating film cross-linking density at the time of bake hardening is lowered and the chemical resistance is lowered. On the other hand, if it exceeds 15, resin synthesis becomes difficult. The preferred hydroxyl value range is 3 to 10. The hydroxyl value in the present invention is measured by the method of JIS K-1557 (6.4).

The hydroxyl value can be adjusted by changing the molar ratio of the hydroxyl group of the polyhydric alcohol to the carboxyl group of the polybasic acid or its anhydride. Specifically, by changing the ratio of the hydroxyl group of the polyhydric alcohol and the carboxyl group of the polybasic acid or its anhydride, the hydroxyl value can be defined within the above range.

(B) Second hydroxyl group-containing polyester resin The number average molecular weight of the second hydroxyl group-containing polyester resin is 15
It is from 00 to 8000, and the hydroxyl value is from 16 to 120.

If the number average molecular weight of the second hydroxyl group-containing polyester resin is less than 1,500, the processability is lowered. Further, if the number average molecular weight exceeds 8,000, the chemical resistance is lowered. The preferred number average molecular weight is 3000 to 7000.

With respect to the hydroxyl value, if it is less than 16, the cross-linking density of the coating film at the time of bake hardening is lowered and the chemical resistance becomes poor. Further, when it exceeds 120, hydroxyl groups remain in the coating film after baking and curing, and the chemical resistance is lowered.
The preferred hydroxyl value range is 16 to 50.

The second hydroxyl group-containing polyester resin can be produced from the polyhydric alcohol used in the production of the first hydroxyl group-containing polyester resin and a polybasic acid or an anhydride thereof. And the composition of the polyhydric alcohol, the polybasic acid or the anhydride thereof is controlled to have a number average molecular weight and a hydroxyl value different from those of the first polyester resin.

Also in the production of the second hydroxyl group-containing polyester resin, ε-caprolactone is used as at least a part of the component of the polyhydric alcohol, and isophthalic acid is used as a part of the component of the polybasic acid or its anhydride. Is preferred. The compounding amount of ε-caprolactone in the whole polyhydric alcohol and the compounding amount of isophthalic acid in the whole polybasic acid or its anhydride are preferably the same as those in the case of the first hydroxyl group-containing polyester resin.

In the present invention, the above-mentioned two types of hydroxyl group-containing polyester resins (a) and (b) are used in combination. The two types of hydroxyl group-containing polyester resins differ not only in the number average molecular weight and the hydroxyl value. , Glass transition point (Tg)
Is also different.

When the glass transition point of the first hydroxyl group-containing polyester resin is Tg ₁ (° C) and the glass transition point of the second hydroxyl group-containing polyester resin is Tg ₂ (° C), in the present invention, Tg ₁ And Tg ₂ is 20 ° C. or less.
If the difference between Tg ₁ and Tg ₂ exceeds 20 ° C, the workability decreases.
Either Tg ₁ or Tg ₂ may be larger. Therefore, the relationship between Tg ₁ and Tg ₂ is represented by the following formula: 0 <| Tg ₁ −Tg ₂ | ≦ 20. Preferably, the difference between Tg ₁ and Tg ₂ is 2 to
It shall be 10 ° C or lower.

(C) Blocked Polyisocyanate Compound In the present invention, as the blocked polyisocyanate, non-yellowing type aliphatic polyfunctional isocyanate such as hexamethylene diisocyanate (HMDI) and alicyclic polyfunctional isocyanate such as isophorone diisocyanate (IPDI) are used. ,
And diphenylmethane-4,4'-diisocyanate (MD
Partially or completely blocked functional groups of polyisocyanate compounds such as I) and hydrogenated MDI are used.

As the blocking agent, acetone oxime,
Cyclohexanone oxime, acetophenone oxime,
Oxime-based blocking agents such as benzophenone oxime,
Further, a blocking agent such as methyl acetoacetate, ethyl acetoacetate, and methanol can be used.

It is also possible to use aromatic monoalcohols, hydroxy tertiary amines, phenols, cresols, and lactam type blocking agents. By using an oxime-based blocking agent or a blocking agent other than the above-mentioned oxime-based blocking agents, yellowing of the coating film can be prevented.

As the blocked polyisocyanate compound, I blocked with methyl ethyl ketone oxime can be used.
PDI is preferred.

(D) Melamine resin As the melamine resin, an alkoxymethyl melamine resin can be used. Specifically, a methylated melamine resin, an ethylated melamine resin, an n-butylated melamine resin, an isobutylated melamine resin and the like using a methoxy group, an ethoxy group, an n-butoxy group, an isobutoxy group or the like as an alkoxy group can be mentioned. .

The average degree of polymerization of the melamine resin is 1.1-3. If the average degree of polymerization is less than 1.1, the stain resistance decreases. On the other hand, when it exceeds 3, workability is deteriorated. The preferred average degree of polymerization is 1.1 to 2.6. The melamine resin of the present invention can be synthesized by a known method.

In the present invention, the average degree of polymerization of the melamine resin refers to the degree of connection of triazine nuclei in the melamine resin.

Next, the blending amount of each component will be described.
The amounts of the first hydroxyl group-containing polyester resin (a), the second hydroxyl group-containing polyester resin (b), the blocked polyisocyanate compound (c), and the melamine resin (d) are as follows.

Mixing ratio (a) of the first hydroxyl group-containing polyester resin (a) and the second hydroxyl group-containing polyester resin (b)
/ (B) is 95/5 to 40/60 by weight ratio based on solid content
Is. When the compounding ratio (a) / (b) is less than 40/60 (that is, when the component (b) is too much), the workability tends to be lowered. On the other hand, if (a) / (b) exceeds 95/5 (that is, if the amount of component (a) is too large), the viscosity becomes high and the amount of solvent in the paint and at the time of painting increases, resulting in poor workability in painting. To do. More preferable range of (a) / (b) is 95/5 to 50
/ 50.

The weight ratio (c) / (d) of the blocked polyisocyanate (c) and the melamine resin (d) is 95/5 to 5/9.
It is 5. If (c) / (d) is less than 5/95, the workability is deteriorated. On the other hand, if (c) / (d) exceeds 95/5, the stain resistance decreases. The preferred range of (c) / (d) is 4/6 to 6
/ 4.

A weight ratio of the total amount of the two hydroxyl group-containing polyester resins (a) and (b) and the total amount of the block polyisocyanate (c) which is a curing agent component and the melamine resin (d) [(a) + (B)] / [(c) + (d)] is 9/1 to 7/3. If this ratio is less than 7/3, workability becomes poor. On the other hand, if it exceeds 9/1, the coating film is not sufficiently cured, and good coating film hardness cannot be obtained. Preferred [(a) +
(b)] / [(c) + (d)] is 70/30 to 85/15.

In the present invention, various pigments can be added to the above-mentioned essential components. As the pigment, (1) a metal foil pigment, for example, an aluminum foil having a particle size of 10 to 45 μm, mica foil, bronze foil, tin foil, gold foil, silver foil, copper foil, metal titanium foil, stainless steel foil, nickel foil, chrome Foil, and alloy foil of the above-mentioned metals, metal foil coated with plastic, foil-shaped phthalocyanine blue, etc. or cobalt sulfide, manganese sulfide, titanium sulfide, (2)
Inorganic pigments such as Sicotrans Red L2915D, Sicotrans Yellow L1915, 1916 (all manufactured by Ciba-Geigy) and other inorganic transparent iron oxides, carbon black,
Titanium dioxide, yellow iron oxide, red iron oxide, and (3) organic pigments such as organic Chromophtal red A2B (manufactured by Ciba Geigy), and dark colors such as red, blue, purple, black, and brown. Thus, for example, transparent pigments such as Orazole Black RL, Orazole Red B, Orazole Yellow 3R (all manufactured by Ciba Geigy), cyanine blue, cyanine green, quinacdrine, indanthrone, isoindolinone, pererin, anthravirimidine. Pigments such as benzimidazolone can be used. The amount of the pigment added is 1 based on 100 parts by weight of the total of the solid components (a) to (d).
It is preferably not more than 00 parts by weight.

In order to improve the lubricity of the coating film,
If necessary, wax, powder such as polyethylene and fluorinated polyethylene, and lubricant such as molybdenum disulfide can be added. The lubricant can be added in an amount of 10 parts by weight or less, with the total of the solid components of components (a) to (d) being 100 parts by weight.

Further, a curing catalyst such as dodecylbenzene sulfonic acid, a benzophenol-based ultraviolet absorber, a phenol-based or sulfide-based antioxidant, a surface modifier such as silicone or an organic polymer, an anti-sagging agent, and a thickener. Additives such as agents and rust preventives such as fumed silica can also be used. These additives can be added in an amount of 5 parts by weight or less, based on 100 parts by weight of the total solid components (a) to (d).

Further, in order to adjust the viscosity of the paint, aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene and chlorobenzene, aliphatic hydrocarbons such as cyclohexane, ethylcyclohexane and perchloroethylene, ethyl acetate and butyl acetate. , Esters such as isobutyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ketones such as diacetoalcohol, ethers such as carbitol acetate and butyl carbitol, dioxane, tetrahydrofuran, dimethylformamide, nitropropane, Solvents usually used in the field of paints such as styrene and mineral spirit can be appropriately selected and used alone or as a mixture. The solid content during coating is preferably 30 to 80%.

To disperse each of the above components, a device such as a paint shaker, a dissolver, a ball mill, a sand grind mill, or a kneader, which is usually used in the production of paint, can be used.

The members which can be coated with the coating composition of the present invention are mainly cold-rolled steel sheets, galvanized steel sheets (zinc-iron, zinc-aluminum, zinc-manganese, zinc-cobalt, zinc- (Including alloys such as nickel-chromium, zinc-nickel-cobalt, and zinc-nickel). In addition, conductive members such as stainless steel plate, aluminum plate, copper plate, brass plate, FRP, polyethylene, polypropylene, polyamide, vinyl chloride,
The coating composition of the present invention also includes a non-conductive material such as vinylidene chloride, polycarbonate, polyurethane, or various rubbers containing a conductive material, or a non-conductive member provided with conductivity by electroless plating or the like. Can be used for painting. Further, it can be applied to a material in which a conductive material and a non-conductive material are integrated by adhesion, fixation, or the like. Degreasing, chemical conversion treatment, etc. can be performed on each member as necessary.

The coating composition of the present invention can be coated by a conventional coating method such as air spray coating, airless coating, electrostatic coating and brush coating. It is also possible to adopt gravure coating method, roll coating method, curtain flow coating method, bar coating method, offset gravure coating method, etc., which are excellent in coating thickness (coating thickness) accuracy and coating surface smoothness. it can. When the roll coating method is adopted, either a top feed method for supplying paint between the applicator roll and the pickup roll or a bottom feed method for supplying paint to the coater pan can be adopted.

The maximum baking temperature of the coating film is 19
It is preferably 0 to 230 ° C. and about 30 to 70 seconds.

[0047]

In the present invention, since two kinds of polyester resins having different number average molecular weights, hydroxyl values and glass transition points are used as the main components of the coating material, when the coating film is cured,
A high molecular weight network structure having a high breaking elongation and a low molecular weight network structure having a relatively high tensile strength are simultaneously formed,
Moreover, it is considered that these two types of network structures intrude into each other to form a so-called mutual intrusion network structure.

Further, in the coating composition of the present invention, since the block polyisocyanate compound and the melamine resin are used together as the curing agent component, the urethane bond introduced by the block polyisocyanate compound increases the cohesive force to increase the tensile strength. At the same time, the cross-linking reaction by the melamine resin can impart good hardness and stain resistance to the coating film.

As described above, in the present invention, since two kinds of polyester resins having different glass transition points are cured by two kinds of curing agent components, the above-mentioned interpenetrating network structure is formed and the inside of the coating film is formed. Stress is relieved. Further, as described above, since two types of curing agent components, that is, a polyisocyanate compound and a melamine resin, are used, it has the advantages of each curing agent component,
It is possible to achieve both high cohesive strength and high breaking elongation. As a result, a well-balanced coating film can be obtained by controlling the hardness and elongation of the coating film.

[0050]

The present invention will be described in more detail by the following specific examples. Synthesis Example 1 A polybasic acid component and a polyhydric alcohol component shown in Table 1 were placed in a reaction vessel, and a polymerization catalyst of 0.05
Add dibutyltin oxide in the amount of wt.% To 150-20
The esterification was carried out at 0 ° C. for 4 hours. In addition, the blending amounts of the polybasic acid component and the polyhydric alcohol component in Table 1 are represented by mol%.

Subsequently, the pressure in the reaction vessel was reduced to 1 mmHg over 1 hour, and the pressure was further reduced to 0.3 mmHg, and the reaction was continued at 250 ° C. for 3 hours to synthesize a hydroxyl group-containing polyester resin a1.

The physical properties (number average molecular weight, glass transition point and hydroxyl value) of the obtained polyester resin a1 were measured by the following methods. The results are shown in Table 1.

Number average molecular weight Measured by GPC (gel permeation chromatography). Here, a GPC column (SHODEX KF-803) manufactured by Toyo Soda Co., Ltd. is used as the column.
Was used, and tetrahydrofuran was used as a solvent.

Glass transition point (Tg) It was measured using TMA-100 manufactured by Seiko Instruments Inc.

Hydroxyl value (OHV) It was measured by the method of JIS K-1557 (6.4).

Cyclohexanone / Solvesso 150 (manufactured by MC Chemical Co.) was used as a hydroxyl group-containing polyester resin a1.
A varnish was prepared by dissolving it in a solvent of 8/2. Nonvolatile content in varnish of hydroxyl group-containing polyester resin a1 [NV
The value of (%)] is also shown in Table 1.

Synthesis Examples 2 to 14 In the same manner as in Synthesis Example 1, a hydroxyl group-containing polyester resin was prepared from the polybasic acid component and polyhydric alcohol component shown in Table 1.
a2-a7 and b1-b7 were synthesized. Further, in the same manner as in Synthesis Example 1, each resin was dissolved in a solvent to obtain a varnish. Table 1 shows the physical properties of each hydroxyl group-containing polyester resin and the value of the nonvolatile content [NV (%)] in the varnish.

Table 1 (Part 1) Synthetic Example No. 1 2 3 4 5 6 7 Resin symbol a1 a2 a3 a4 a5 a6 a7 Acid component Isophthalic acid 20 50 100 100 75 50 50 Orthophthalic acid 80 50 0 0 0 0 0 Adipine Acid 0 0 0 0 25 50 50 Total 100 100 100 100 100 100 100 Alcohol component NPG ⁽¹⁾ 60 40 35 60 35 50 52 EG ⁽²⁾ 19 39 4 19 4 39 6 ε-CL ⁽³⁾ 20 20 60 20 60 10 38 HD ⁽⁴⁾ − − − − − − − TMP ⁽⁵⁾ 0.25 0.25 1.0 0.25 0.25 0.25 2.0 Total 99.25 99.25 100 99.25 99.25 99.25 98.0 Physical properties Number average molecular weight (× 10 ⁴ ) 3 2 0.85 2 3 2 0.85 Tg (℃) ⁽⁶⁾ 10 10 20 20 -10 10 0 OHV ⁽⁷⁾ 4 4 15 6 4 6 20 NV (%) ⁽⁸⁾ 40 40 40 40 40 40 40 40

Table 1 (Part 2) Synthesis Example No. 1 2 3 4 5 6 7 Resin symbol b1 b2 b3 b4 b5 b6 b7 Acid component Isophthalic acid 20 50 50 100 100 20 50 Orthophthalic acid 80 50 50 0 0 80 50 Adipine Acid 0 0 0 0 0 0 0 Total 100 100 100 100 100 100 100 Alcohol component NPG ⁽¹⁾ 70 70 55 40 35 29 20 EG ⁽²⁾ 9 9 39 4 4 30 8 ε-CL ⁽³⁾ 20 20 5 55 60 0 50 HD ⁽⁴⁾ − − − − − 40 − TMP ⁽⁵⁾ 1 1 1 1 1 1 22 Total 100 100 100 100 100 100 100 Physical property number Average molecular weight (Mn) (× 10 ³ ) 3 5 8 7 8 3 1.5 Tg (℃) ⁽⁶⁾ 15 20 40 0 2 0 12 OHV ⁽⁷⁾ 47 26 16 18 16 47 120 NV (%) ⁽⁸⁾ 50 50 50 50 50 50 50

Table 1 Note: (1) Neopentyl glycol. (2) It is ethylene glycol. (3) Epsilon caprolactone. (4) It is 1,6-hexanediol. (5) It is trimethylolpropane. (6) Glass transition point (° C). (7) It has a hydroxyl value. (8) Indicates the weight percentage of the nonvolatile content.

Examples 1 to 11 and Comparative Examples 1 to 14 Zinc phosphate treated with a zinc phosphate treating agent (Surfdyne ZS9100, manufactured by Nippon Paint Co., Ltd.) on 0.4 mm thick galvanized steel sheets. Then, a coating type chromate treatment agent (Surfcoat NRC-00, Nippon Paint Co., Ltd.)
Manufactured).

As a base coat, Superlac D1
FP-01 primer (manufactured by Nippon Paint Co., Ltd.) was applied by the bar coating method. The amount applied is 5 after the weight is dried.
It was set to g / m ² . Maximum temperature reached 200 ℃ after undercoating
It was baked for 50 seconds.

Any of the hydroxyl group-containing polyester resins a1 to a7 synthesized in the above Synthesis Examples 1 to 7 as the component (a), and the hydroxyl group containing polyester resins b1 to b7 synthesized in the above Synthesis Examples 8 to 14 as the component (b). One of the components (c),
A coating material was prepared according to the formulation shown in Table 2 by using the following components (d), pigments, additives and catalysts. Here, cyclohexanone was added as a solvent in each of the examples, and the non-volatile content of each paint was adjusted to 55% by weight. Table 2
The numbers in the compounding amount column of each component in are the components (a) to (d).
The parts by weight of the respective components are shown when the total solid content is 100 parts by weight.

Component (c) C2513: Coronate 2513, a block polyisocyanate compound manufactured by Nippon Polyurethane Industry Co., Ltd.,
The nonvolatile content is 80% by weight. C2507: Coronate 2507, a block polyisocyanate compound manufactured by Nippon Polyurethane Industry Co., Ltd.,
The nonvolatile content is 80% by weight.

Component (d) Cy325: Cymel 325, a methylated melamine resin manufactured by Mitsui Cyanamid Co., Ltd., having an average degree of polymerization of 2.3 and a nonvolatile content of 80% by weight. Cy370: Cymel 370 is a methylated melamine resin manufactured by Mitsui Cyanamid Co., Ltd., having an average degree of polymerization of 2.6 and a nonvolatile content of 88% by weight. Cy235: Cymel 235, a methyl butyl mixed melamine resin manufactured by Mitsui Cyanamid Co., Ltd., with an average degree of polymerization of 1.
4, non-volatile content 100% by weight. U220: Uban 220, a butylated melamine resin manufactured by Mitsui Toatsu Chemicals, Inc., having an average degree of polymerization of 3.3 and a nonvolatile content of 6
It is 0% by weight.

Pigment titanium CR-91, manufactured by Ishihara Sangyo Co., Ltd. was used.

The catalyst dibutyltin laurate was used. The amount added is from component (a)
The amount was 0.1 part by weight based on 100 parts by weight of the total solid content of (d).

Additive Modablo (acrylic defoamer, Mitsubishi Monsanto Co., Ltd.)
Manufactured) was used. This addition amount is 100 parts by weight of the paint [(a)
+ (B) + (c) + (d) + pigment + catalyst (dibutyltin laurate) + solvent (cyclohexanone)].

Table 2 Example No. Example 1 Example 2 Example 3 Example 4 Example 5 Component (a) Resin symbol a3 a1 a2 a3 a4 Mn ⁽¹⁾ 8500 30000 20000 8500 20000 OHV ⁽²⁾ 15 4 4 15 6 Isophthalic acid 100 20 50 100 100 ε-CL ⁽³⁾ 0 20 20 0 18 Tg ⁽⁴⁾ 0 10 10 2 20 Compounding amount ⁽⁵⁾ 76 76 76 70 76 Component (b) Resin symbol b4 b1 b2 b1 b3 Mn ⁽¹⁾ 7000 3000 5000 3000 8000 OHV ⁽²⁾ 18 47 26 47 16 Tg ⁽⁴⁾ 2 15 20 15 40 Compounding amount ⁽⁵⁾ 4 4 4 10 4 Tg difference (° C) 2 5 10 15 20 composition ( c) Type C2513 C2513 C2513 C2513 C2513 Compounding amount ⁽⁵⁾ 10 1 19 10 10 Component (d) Type Cy325 Cy235 Cy325 Cy325 Cy325 Compounding amount ⁽⁵⁾ 10 19 1 10 10 (c) / (d) 50/50 95 / 5 5/95 50/50 50/50 Pigment ⁽⁶⁾ 100 100 100 100 100 Catalyst ⁽⁷⁾ 0.1 0.1 0.1 0.1 0.1

Table 2 (Part 2) Example No. Example 6 Example 7 Example 8 Example 9 Example 10 Component (a) Resin symbol a5 a7 a1 a4 a4 Mn ⁽¹⁾ 30000 8500 30000 20000 20000 OHV ^{(2 )} 4 20 4 6 6 Isophthalic acid 75 50 20 100 100 ε-CL ⁽³⁾ 60 38 20 19 19 Tg ⁽⁴⁾ -10 0 10 20 20 Compounding amount ⁽⁵⁾ 76 76 76 40 28 Component (b) Resin symbol b4 b2 b7 b4 b4 Mn ⁽¹⁾ 7000 5000 1500 7000 7000 OHV ⁽²⁾ 18 26 120 18 18 Tg ⁽⁴⁾ 0 20 12 2 2 Compounding amount ⁽⁵⁾ 4 4 4 4 40 42 Tg difference (° C) 10 20 2 2 2 component (c) type C2507 C2513 C2513 C2513 C2513 compounding amount ⁽⁵⁾ 10 10 10 10 27 component (d) type Cy235 Cy325 Cy325 Cy325 Cy325 compounding amount ⁽⁵⁾ 10 10 10 10 3 (c) / (d) 95/5 50/50 50/50 50/50 10/90 Pigment ⁽⁶⁾ 100 100 100 100 100 Catalyst ⁽⁷⁾ 0.1 0.1 0.1 0.1 0.1

Table 2 ( No. 3) Example No. Example 11 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Component (a) Resin symbol a4 a1 a2 a3 a4 Mn ⁽¹⁾ 20000 30000 20000 8000 20000 OHV ^{(2 )} 6 4 4 15 6 Isophthalic acid 100 20 50 100 100 ε-CL ⁽³⁾ 19 20 20 60 19 Tg ⁽⁴⁾ 20 10 10 0 20 Compounding amount ⁽⁵⁾ 72 80 80 80 80 Component (b) Resin symbol b4 − − − − Mn ⁽¹⁾ 7000 − − − − OHV ⁽²⁾ 18 − − − − Tg ⁽⁴⁾ 2 − − − − Blending amount ⁽⁵⁾ 18 − − − − Tg difference (° C) 2 − − − − Component (c) type C2513 C2513 C2513 − C2513 Compound amount ⁽⁵⁾ 5 10 1-20 Component (d) type Cy325 U220 Cy325 Cy325 − Compound amount ⁽⁵⁾ 5 10 19 20 − (c) / (d) 50 / 50 50/50 95/5 100/0 0/100 Pigment ⁽⁶⁾ 100 100 100 100 100 Catalyst ⁽⁷⁾ 0.1 0.5 0.5 0.5 0.5

Table 2 (Part 4) Example No. Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Component (a) Resin symbol --- a3 Mn ⁽¹⁾ --- 8000 OHV ^{(2 )} − − − − 15 Isophthalic acid − − − − 100 ε-CL ⁽³⁾ − − − − 0 Tg ⁽⁴⁾ − − − − 0 Compounding amount ⁽⁵⁾ − − − − 60 Component (b) Resin symbol b1 b2 b3 b4 b5 Mn ⁽¹⁾ 3000 5000 8000 7000 8000 OHV ⁽²⁾ 47 26 16 18 15 Tg ⁽⁴⁾ 15 20 40 00 Compounding amount ⁽⁵⁾ 80 80 80 80 20 Tg difference (° C) − − − − 0 component (c) type C2513 C2513 − C2513 C2513 compounding amount ⁽⁵⁾ 10 19 − 20 10 component (d) type Cy325 Cy325 Cy325 − Cy325 compounding amount ⁽⁵⁾ 10 120 − 10 (c) / (d) 50 / 50 5/95 100/0 0/100 50/50 Pigment ⁽⁶⁾ 100 100 100 100 100 Catalyst ⁽⁷⁾ 0.5 0.5 0.5 0.5 0.5

Table 2 ( No. 5) Example No. Comparative Example 10 Comparative Example 11 Comparative Example 12 Comparative Example 13 Comparative Example 14 Component (a) Resin symbol a3 a1 a4 a6 a3 Mn ⁽¹⁾ 8000 30000 20000 20000 8500 OHV ^{(2 )} 15 4 6 6 15 Isophthalic acid 100 20 100 50 100 ε-CL ⁽³⁾ 0 20 19 100 Tg ⁽⁴⁾ 0 10 20 10 0 Compounding amount ⁽⁵⁾ 76 76 76 76 76 76 Component (b) Resin symbol b3 b3 b2 b6 b4 Mn ⁽¹⁾ 8000 8000 5000 3000 7000 OHV ⁽²⁾ 15 16 26 47 18 Tg ⁽⁴⁾ 40 40 20 0 2 Mixing amount ⁽⁵⁾ 4 4 4 4 4 Tg difference (° C) 40 30 0 10 2 component (c) type C2513 C2513 C2513 C2507 − compounding amount ⁽⁵⁾ 1 19 10 10 − component (d) type Cy370 Cy325 U220 Cy325 U220 compounding amount ⁽⁵⁾ 19 1 10 10 20 (c) / (d) 95 / 5 5/95 50/50 50/50 50/50 Pigment ⁽⁶⁾ 100 100 100 100 100 Catalyst ⁽⁷⁾ 0.5 0.5 0.5 0.5 0.1

Table 2 Notes: (1) Number average molecular weight. (2) It has a hydroxyl value. (3) ε-caprolactone, and the number represents the mol% of ε-caprolactone in the polyhydric alcohol used in the synthesis of component (a). (4) Glass transition point (° C). (5) When the total solid content of the components (a) to (d) is 100 parts by weight, the blending amount of each component is expressed in parts by weight. (6) Titanium CR-91 (manufactured by Ishihara Sangyo Co., Ltd.)
When the total solid content of (a) to (d) is 100 parts by weight, the blending amount is expressed in parts by weight. (7) It is dibutyltin laurate, and the compounding amount is expressed in parts by weight when the total solid content of the components (a) to (d) is 100 parts by weight.

Each of the obtained coating materials was used to coat the undercoat coating film by the bar coating method. The thickness of the coating film was 32 g / m ² in terms of film weight after drying. This coating reaches the highest temperature 2
A test piece was obtained by baking at 30 ° C. for 60 seconds.

The hardness, workability, aging-promoted coating adhesion, stain resistance, chemical resistance, and weather resistance of the obtained test pieces were evaluated by the following methods. The results are shown in Table 3.

(1) Coating hardness Hardness was evaluated by the scratch method of JIS K5400 8.4.2.

(2) Machinability A plurality of test pieces having the same coating film are superposed, and the superposed test pieces are bent by a vise with the coated surface facing outward and tested. The crack (crack) generated in the bent portion of the outer test piece was observed, and the minimum number of overlaps (T
Number)

(3) Adhesion property of accelerated coating film After the workability test of (2) above, a test piece having a crack in the bent portion was immersed in boiling water for 2 hours to expand the original crack. It was indicated by the minimum T number of the test pieces that were not tested.

(4) Contamination resistance Apply blue magic ink (made by guitar) to the coating film and apply
After being left for 24 hours in a humidity of 73% at a temperature of ℃, it was wiped with ethanol to visually check whether or not the mark of the magic ink remains, and evaluated according to the following criteria. ◯: No ink remains at all. Δ: Some residual trace of ink is recognized. X: A trace of ink remains completely.

(5) Chemical resistance The test piece was immersed in 5% hydrochloric acid kept at 20 ° C. for 24 hours,
After pulling up, it was visually inspected whether blister was generated on the surface of the coating film, and evaluated according to the following criteria. ◯: No discoloration or blister was observed. △: 8F based on ASTMD714 blister generation standard
Occurrence of blister of ~ 6F was observed. ×: 6M in ASTMD714 blister generation standard
Generation of the above blisters was observed.

(6) Weather resistance Using an accelerated weather resistance tester, a sunshine weatherometer, the gloss after 1000 hours of test was measured with a gloss meter, and the gloss retention rate obtained by the following formula was evaluated. . Gloss retention (%) = [Gloss after test / Gloss before test] ×
100 ○: The gloss retention rate is 80% or more. Δ: The gloss retention rate is 60% or more and less than 80%. X: The gloss retention rate is less than 60%.

[0083] Table 3 time coating Example No. film hardness workability adhesion stain resistance chemical resistance weather resistance Example 1 2H 4T 4T ○ ○ ○ Example 2 2H 4T 4T ○ ○ ○ Example 3 2H 4T 4T ○ ○ ○ Example 4 2H 4T 4T ○ ○ ○ Example 5 2H 4T 4T ○ ○ ○ Example 6 2H 4T 4T ○ ○ ○ Example 7 2H 5T 5T ○ ○ ○ Example 8 2H 4T 4T ○ ○ ○ Example 9 2H 4T 4T ○ ○ ○ Example 10 2H 4T 4T ○ ○ ○ Example 11 2H 4T 4T ○ ○ ○ ~ △ Comparative Example 1 2H 3T 6T ○ ○ ○ Comparative Example 2 2H 4T 7T ○ ○ ○ Comparative Example 3 2H 5T 8T ○ ○ ○ Comparative Example 4 H 3T 6T × Δ × Comparative Example 5 2H 7T 8T ○ ○ ○ Comparative Example 6 2H 6T 8T ○ ○ ○ Comparative Example 7 2H 6T 8T ○ ○ ○ Comparative Example 8 H 6T 8T × ○ ○ Comparative Example 9 2H T 6T ○ ○ △ Comparative Example 10 2H 5T 7T ○ ○ ○ Comparative Example 11 2H 4T 7T ○ ○ △ Comparative Example 12 2H 6T 8T ○ ○ △ Comparative Example 13 2H 4T 6T △ ○ × Comparative Example 14 2H 6T 8T ○ △ ×

[0084]

As described above in detail, the coating film of the coating composition of the present invention has good hardness, good workability immediately after coating, and the coating film at the processed portion even after a long time. It does not peel off and has excellent weather resistance, stain resistance, and chemical resistance.

The coating composition of the present invention is suitable as a coating for precoated metal plates for various applications.

Claims (1)

[Claims] 1. A first hydroxyl group-containing polyester resin having a number average molecular weight of 8500 to 30000 and a hydroxyl value of 2 to 15, and (b) a number average molecular weight of 1500 to 8000 and a hydroxyl value of 16 to
120 second hydroxyl group-containing polyester resin, (c) block polyisocyanate compound, (d) average degree of polymerization is 1.
1 to 3 of the melamine resin, the glass transition point Tg ₁ of the component (a) and the glass transition point Tg ₂ of the component (b) are represented by the following formula: 0 <| Tg ₁ −Tg ₂ | ≦ 20 While satisfying the conditions, the blending amount of each component is a solid content weight ratio of (a) / (b) = 95/5 to 40/60, (c) / (d) = 95/5 to 5/95, and [(A) + (b)] / [(c) + (d)] = 9/1 to 7/3: A coating composition.