JPH1148405A - Coating composition and precoating metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition for forming a coating film exhibiting excellent flaw resistance for scarcely damaging such as handling damage or flaw at the time of working and assembling by incorporating excellent workability for scarcely damaging such as crack of the film even in the case of severely molding and working. SOLUTION: The coating composition comprises 1 to 5 wt.% of polyester compound having a chemical structure represented by a formula in total solid content of the composition, polyvinylidene fluoride resin and acrylic resin in such a manner that the total sum of the respective compounds is 40 wt.% or more of the overall solid content of the composition. The composition is adapted to the precoating steel sheet and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition capable of obtaining a coating film having excellent workability and scratch resistance, and a precoated metal sheet coated with the coating composition. A paint composition and a pre-coat coated with this paint composition, which hardly cause damages such as coating film cracks, and which do not easily cause damage such as handling scratches during processing and transportation and scratches during processing and assembly. Related to metal plates.

[0002]

2. Description of the Related Art The market demand for durability of pre-coated steel sheets used for building exterior materials such as roofs and exterior wall materials is increasing, and long-term stable durability is required. It has become. Fluororesin-based paints containing 70% or more of polyvinylidene fluoride have been developed as paints to meet such demands. Fluororesin-based coated steel sheets formed as a coating film have excellent weather resistance and are suitable for general outdoor use. Because of its excellent workability compared to painted steel sheets for automobiles, it is used in building exterior materials requiring durability. On the other hand, this fluororesin-based coated steel sheet has a drawback that the coating film is easily scratched at the time of construction or in the environment after the construction because the coating film hardness is lower than that of a general outdoor painted steel sheet.

[0003]

To improve the scratch resistance of the fluororesin coating film, a hard aggregate is added to the organic coating film to increase the apparent hardness of the coating film.
Attempts have been made to impart scratch resistance and abrasion resistance to the coating film, and in JP-A-61-236869, glass fiber is blended with a fluororesin-based coating material to improve the strength and hardness of the coating film. A paint having improved scratch resistance and abrasion resistance is disclosed.

In Japanese Patent Publication No. Hei 6-88371, addition of fluororesin fine particles into a coating film makes it possible to
In Japanese Patent Publication No. 7-65016, by adding acrylic resin fine particles of a specific composition to a coating film, it is possible to improve wear resistance while suppressing abrasion of a forming roll, a shearing blade and the like at the time of forming and cutting, respectively. A painted metal plate is disclosed. However, in these prior arts, the forming roll is worn out during the forming process of the coated metal sheet, and the level of the scratch resistance of the coating film is not always sufficiently satisfactory. Sufficient coating film performance has not been obtained, for example, the workability level is reduced.

[0005] Accordingly, an object of the present invention is to provide a coating film such as a pre-coated steel sheet, which has excellent workability which does not easily cause damages such as coating film cracks even when subjected to severe molding. An object of the present invention is to provide a coating composition exhibiting excellent scratch resistance, which hardly causes damage such as scratches and scratches during processing and assembly, and a precoated metal sheet coated with the coating composition.

[0006]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems, and as a result, a coating film formed by a coating composition having the following composition has been coated on a precoated metal plate. It has been found that the processability and the scratch resistance are highly satisfied. That is, the characteristics of the coating composition and the precoated metal plate of the present invention are as follows.

[1] a) a polyester compound having a chemical structure represented by the general formula (1) is used in an amount of 1 to 15% by weight based on the total solid content of the coating composition;

Embedded image B) It contains polyvinylidene fluoride resin and c) an acrylic resin, and the total of the above components a), b) and c) is at least 40% by weight in the total solid content of the coating composition. A characteristic coating composition. [2] A pre-coated metal plate having a coating having a thickness of 5 to 35 μm formed by applying the coating composition according to [1] on at least one surface of a metal plate or a plated metal plate. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The coating composition of the present invention is a coating composition comprising a) a specific polyester compound, b) a polyvinylidene fluoride resin, and c) an acrylic resin. First, the polyester compound of the above a) is a polyester compound having a chemical structure represented by the following general formula (1).

[0009]

Embedded image

Cyclohexane-1,4-dicarboxylic acid is mainly used as an acid component for obtaining the polyester compound of the above-mentioned a), and a part of them is replaced with terephthalic acid, isophthalic acid and naphthalene-2,7- It can also be replaced with dicarboxylic acids such as dicarboxylic acids and diphenyldicarboxylic acids, or lower alkyl esters of these dicarboxylic acids. As lower alkyl esters,
Examples thereof include methyl esters and ethyl esters having 1 to 2 carbon atoms. However, even in this case, the main component cyclohexane-1,4-dicarboxylic acid accounts for 85% of the total acid component.
Mol% or more, and the ratio of other compounds to be replaced is 1
It is desirable to keep it to less than 5 mol%.

As the alcohol component for obtaining the polyester compound of the above (a), a polyalkylene glycol having 10 or less carbon atoms, preferably a polyalkylene glycol having 6 or less carbon atoms can be used. Further, these may be used as a mixture. Also, as the alcohol component,
In addition to the glycol components described above, trihydric or higher polyhydric alcohols may be used. Examples of the polyhydric alcohol include triethylene glycol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane.

The above-mentioned acid component and alcohol component react with each other to produce the polyester compound (a).
The polyester compound (a) used in the present invention can be obtained by a usual polyester production method such as a transesterification method or a direct esterification method. Usually, the acid component and the alcohol component react at a molar ratio of 1: 2, and therefore, in order to perform the reaction efficiently, it is desirable to mix the acid component and the alcohol component at a molar ratio as close as possible to 1: 2. Further, the polyester compound can be used either alone or in combination of two or more.

When the polyester compound (a) alone is observed while raising the temperature from room temperature to 200 ° C. or higher, the polyester compound exhibits the orientation characteristic of the thermotropic liquid crystal. It is thought that it has contributed to the improvement. The compounding amount of the polyester compound (a) is 1 to 15% by weight based on the total solid content of the coating composition. The above-mentioned polyester compound is blended in order to obtain the desired coating film performance of the present invention without deteriorating the molding processability of the coating film. Is not obtained enough. On the other hand, if the compounding amount exceeds 15% by weight, the solubility in a solvent and the compatibility with other resin components become insufficient, so that the coating film performance deteriorates.

The polyvinylidene fluoride resin (b) has a weight average molecular weight of 300,000 to 700,000,
Those having a melting point of 150 to 180 ° C are particularly preferred. As such a polyvinylidene fluoride resin, for example, “Kynar 500” (weight average molecular weight: 350,000, melting point: 160 to 165 ° C.) manufactured by Nippon Penwald Co., Ltd. can be exemplified. As the acrylic resin of (c), those having a number average molecular weight of 1,000 to 2,000 are particularly preferable. The acrylic resin used in the present invention can be obtained by, for example, polymerizing (or copolymerizing) at least one of the following monomers (including at least one acrylic monomer) by an ordinary method.

(1) Hydroxymethyl acrylate, hydroxymethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, N-methylol acryl Ethylene monomer having hydroxyl group such as amine (2) Ethylene monomer having carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid and maleic acid

(3) Methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, n-propyl acrylate, n-butyl acrylate,
Ethylene monomers copolymerizable with the above-mentioned monomers (1) and (2), such as isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-dodecyl acrylate, etc. (4) Styrene, α-methyl Styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt
Styrene derivatives such as tert-butylstyrene Further, among these monomers, by using a monomer having a functional group such as a hydroxyl group or a carboxyl group, a cross-linking reaction with another reactable component is possible.

The acrylic resin of the above (c) does not need to be self-crosslinkable, but when it is made to be self-crosslinkable, a so-called crosslinkable monomer having two or more radically polymerizable unsaturated bonds in the molecule is used. To be included. Examples of the radical polymerizable monomer include ethylene glycol diacrylate,
Ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,
4-butanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, glycerol diacrylate, 1,1 , 1
-Trishydroxydimethylethane diacrylate,
1,1,1-trishydroxydimethylethane triacrylate, 1,1,1-trishydroxydimethylpropane diacrylate, 1,1,1-trishydroxydimethylpropane triacrylate, 1,1,1-trishydroxydimethylpropane diacrylate Methacrylate, 1,
Examples thereof include polymerizable unsaturated compounds such as 1,1-trishydroxydimethylpropane trimethacrylate, diallyl terephthalate, diallyl phthalate, glycidyl acrylate, glycidyl methacrylate, triallyl cyanurate, and triallyl isocyanurate. Crosslinkable monomers can be added up to 20% by weight of the acrylic resin.

The weight ratio of polyvinylidene fluoride resin to acrylic resin (weight ratio of resin solids) is [polyvinylidene fluoride resin]: [acrylic resin] = 90: 10 to 40: 6.
It is preferably set to 0. When the weight ratio of the polyvinylidene fluoride resin to the acrylic resin exceeds 90:10, the thixotropy increases, and coating with a roll coater becomes difficult, resulting in a coating film having an uneven finish and poor coating film appearance. On the other hand, if the weight ratio of the polyvinylidene fluoride resin to the acrylic resin is less than 40:60, the coating film adhesion is remarkably deteriorated with time, and the weather resistance is also unpreferably reduced.

The polyester compound a), the polyvinylidene fluoride resin b), and the acrylic resin c)
The coating compositions (a), (b) and (c) are blended so that the total of the coating compositions is 40% by weight or more based on the total solid content. If the total of components a), b) and c) is less than 40% by weight in the total solid content of the coating composition, the desired coating film performance cannot be sufficiently obtained.

In the coating composition of the present invention, in addition to the essential components described above, coloring pigments, extender pigments, other additives, and the like can be added as necessary, depending on the purpose and application.
For example, curing catalysts such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate, lead 2-ethylhexoate, calcium carbonate, kaolin, clay, titanium oxide, talc, barium sulfate, mica, red iron oxide, manganese blue Pigments such as carbon black, aluminum powder, and pearl mica, and various additives such as an antifoaming agent and an anti-flow agent can be selected and blended.

The composition of the coating composition of the present invention has been described above. In actual use, these are dissolved in an organic solvent before use. As the organic solvent used, for example,
Methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 100 (manufactured by Exxon Chemical), solvesso 200 (manufactured by Exxon Chemical), toluene, xylene, methyl cellosolve, butyl cellosolve, cellosolve acetate, butyl cellosolve acetate, carbitol, ethyl carbitol, butyl carbitol, Examples include ethyl acetate, butyl acetate, petroleum ether, petroleum naphtha, and the like. In preparing the coating composition, a conventional dispersing machine or kneading machine such as a sand grind mill, a ball mill or a blender is selected and used, and each component can be blended.

The coating composition of the present invention is particularly useful for coating a precoated steel sheet. In this case, the steel sheet to be coated is a galvanized steel sheet produced by a melting method or an electrolytic method. , A zinc-based 5% aluminum alloy-plated steel sheet, a zinc-based 55% aluminum alloy-plated steel sheet, and the like, an aluminum-plated steel sheet, a stainless steel sheet, a cold-rolled steel sheet, and the like. In addition to these steel plates or plated steel plates, metal plates such as aluminum plates (including aluminum alloy plates) can also be used as coating targets.

In the coating, the surface of the metal plate to be coated is subjected to a chemical conversion treatment such as a phosphate treatment and a chromate treatment.
It is preferable to apply a coating composition thereon. By coating on the metal plate surface that has been subjected to the chemical conversion treatment as described above, the adhesion of the coating film to the metal plate surface is improved and the corrosion resistance is also improved. In addition, a primer coating film can be formed on the surface of the metal plate that has been subjected to the chemical conversion treatment, and coating can be performed thereon.

The method of applying the coating composition to the surface of the metal plate is not particularly limited, but preferably applied by a method such as roll coater coating or curtain flow coating. After application,
The coating is baked by a heating means such as hot air heating, infrared heating, induction heating or the like, and the resin is crosslinked to obtain a cured coating. The baking treatment is preferably performed at a baking temperature of 200 to 250 ° C. for about 40 seconds to 3 minutes.

The thickness of the cured coating film of the pre-coated metal plate thus formed is desirably 5 to 35 μm, and more desirably 15 to 25 μm. Coating thickness 5μm
If it is less than 30, scratch resistance, chemical resistance, performance such as weather resistance cannot be sufficiently obtained, while if the coating thickness exceeds 35 μm, not only coating workability and coating appearance are reduced, but also Bending workability and scratch resistance are inferior, and the cost increases, which is not preferable. The coating composition of the present invention has two coats and two coats.
The use as a top coat of a bake system or a 3-coat / 3-bake system is particularly preferred. In the case of using the three-coat three-bake method, an intermediate coating film used in the usual three-coat three-bake is formed between the coating film of the coating composition of the present invention and the primer coating film.

[0026]

EXAMPLES The methods for synthesizing the polyester compounds (1) and (2), the method for preparing the coating composition, the structure of the steel sheet to be coated, and the method for manufacturing the precoated steel sheet used in this example are described below.

[Synthesis of Polyester Compound] Synthesis of Polyester Compound (1) Cyclohexane-1,4-dicarboxylic acid dimethyl ether (trans isomer ratio) was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer. 99%, manufactured by Towa Kasei Kogyo Co., Ltd.) 200 parts by weight, ethylene glycol 13
0 parts by weight, titanium tetra-n-butoxide 0.5
3 parts by weight were charged, the reaction temperature was gradually increased to 200 ° C., and it took about 5 hours to distill out 64 parts by weight of methanol to complete the reaction. Thus, a polyester compound (1) was obtained. This polyester compound is at room temperature (23
C), and was a white crystalline solid, and the number average molecular weight determined by GPC was 326.

Synthesis of Polyester Compound (2) Cyclohexane-1,4-dicarboxylic acid dimethyl ether (trans isomer ratio 20%, Towa Chemical Industry Co., Ltd.) was placed in a reaction vessel equipped with a heating device, stirrer, rectification tower and thermometer. 200 parts by weight), 248 parts by weight of 1,6-hexanediol, and 0.53 parts by weight of titanium tetra-n-butoxide. The reaction temperature was gradually increased to 200 ° C. Over time, 64 parts by weight of methanol were distilled off to complete the reaction. Thus, a polyester compound (2) was obtained. This polyester compound was a white crystalline solid at room temperature (23 ° C.), and had a number average molecular weight of 618 as determined by GPC.

The above polyester compounds (1) and (2)
The chemical structural formula of is shown below. Polyester compound (1)

Embedded image

Polyester compound (2)

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[Preparation of coating composition] To 3 parts by weight of the polyester compound (1), 40 parts by weight of cyclohexanone was added.
Stir for 12 hours. At this time, the polyester compound (1)
Used was crushed by a crusher to 250 μm or less. Polyester compound (1) thus obtained
Was added with a base resin composed of a polyvinylidene fluoride resin and an acrylic resin, a solvent, and a pigment, and the mixture was mixed with a sand mill to obtain a coating composition 1.
Hereinafter, coating compositions 2 to 5 were prepared in the same manner. Table 1 shows the compositions of these coating compositions. In addition, the compounding quantity of the polyester compound of Table 1 is a value which does not contain cyclohexanone. In addition, as the coating composition of the comparative example, each component was blended at a ratio shown in Table 1 to obtain coating compositions 6 to 8.

[Steel to be Coated] As the steel sheet to be coated, a hot-dip galvanized steel sheet (a coating weight per side: 130 g / m 2)
^2), zinc -5% aluminum alloy plated steel sheet (per side coating weight: 130 g / m ^2), -55% zinc aluminum -1.6% silicon alloy plated steel sheet (per side coating weight: 100 g / m ²⁾ Was used. The thickness of each plated steel sheet was all 0.35 mm.

[Production of pre-coated steel sheet] Each of the above-mentioned plated steel sheets is subjected to a coating type chromate treatment so that the chromium equivalent in terms of chromium metal becomes 30 mg / m ² , and then Nippon Paint which is an epoxy resin-based primer is used as a base coat. After applying “UNIFRON P-640 primer” manufactured by Co., Ltd. so that the dry coating film thickness becomes 5 μm, baking treatment is performed under the conditions of a reaching plate temperature of 210 ° C. and a baking time of 60 seconds, and further prepared as a top coat. After applying the above-mentioned coating compositions 1 to 8 to a predetermined dry film thickness, the ultimate plate temperature 245
C. and a baking time of 60 seconds, followed by water cooling to obtain a precoated steel sheet. The precoated steel sheet obtained as described above was subjected to various characteristic tests as described below. Tables 2 and 3 show the results together with the configuration of the precoated steel sheet.

The conditions and evaluation methods of each characteristic test performed in this example are shown below. (1) Pencil hardness JIS K5400 using Mitsubishi pencil "Uni".
The test was carried out based on 4.2 and showed a hardness limit at which no damage was caused and a hardness limit at which no peeling occurred. (2) Bending workability 12.2.2 of JIS G3312 (based on bending resistance)
Was bent in a room at 20 ° C. by using a bending vise specified in (1) above, and n pieces of the same sample plate were sandwiched inside and bent by a press. 3 bends
Observation was performed using a magnifying glass with a magnification of 0, and the minimum number of sandwiched sheets (n sheets) that did not cause cracks in the coating film was used as an evaluation value, and the number of sheets was indicated with a T, such as 1T, 2T, and 3T. 0 to 2T was judged as acceptable (○), and 3T or more was judged as unacceptable (x).

(3) Abrasion of Coating Film During Roll Forming A test piece having a width of 10 mm and a length of 300 mm was formed using a roll forming machine having a roll shape as shown in FIG. An 8-stage roll former having a steel chrome plating roll was used as a roll forming machine, and the forming was performed at a forming speed of 1.5 m / min. After the molding, the surface of the coating film of the test piece was visually observed and evaluated as follows. ○: No abnormality △: Slight scratch ×: Abnormal (4) Taber abrasion Using a wear tester (A type made by TOYOSEKI), CS-10 was used as the wear wheel, and a load of 1 kg was applied to the wear wheel. In addition, it was tested and evaluated by the number of rotations until the primer was exposed. In this evaluation, less than 1000 rotations were rejected (x), and more than 1000 rotations were passed (o). The worn wheel was used after being polished every 200 rotations.

(5) Sand Falling Abrasion A test was conducted by dropping No. 4 silica sand based on ASTM-D968, and the sand falling amount until the primer was exposed was evaluated. In this evaluation, less than 40L was judged as failed (x), and more than 40L was judged as acceptable (o). (6) Chemical resistance 5% sulfuric acid aqueous solution, 5%
5% each in hydrochloric acid aqueous solution and 5% sodium hydroxide aqueous solution
After immersion for 00 hours, take out, observe the coating film surface,
The following was evaluated. ：: No abnormality at all △: Slight discoloration or swelling ×: Abnormal

According to Tables 2 and 3, the precoated steel sheet of the comparative example is inferior in at least one of scratch resistance, abrasion resistance, workability and chemical resistance, whereas the present invention has It can be seen that the example precoated steel sheet is excellent in all these features.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

According to the coating composition of the present invention described above, the coating composition of a pre-coated steel sheet has excellent workability which does not easily cause damage such as coating film cracking even when subjected to severe molding. In addition, a coating film having excellent scratch resistance, which hardly causes damage such as handling scratches and scratches during processing and assembly, can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a roll shape of a roll forming machine used in a coating film wear test using a forming roll.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C09D 127/16 C09D 127/16 133/06 133/06 (72) Inventor Yasuhide Yoshida 1-1-1 Marunouchi, Chiyoda-ku, Tokyo No. 2 Inside Nippon Kokan Co., Ltd. (72) Inventor Mamoru Ehara 4-1-1-15 Minamishinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. Tokyo Office (72) Inventor Katsuyoshi Tanaka 4-chome Minamishinagawa, Shinagawa-ku, Tokyo No. 1-15 Japan Paint Co., Ltd. Tokyo Office

Claims (2)

[Claims] (1) A polyester compound having a chemical structure represented by the general formula (1) is used in an amount of 1 to 15% by weight based on the total solid content of a coating composition. B) It contains polyvinylidene fluoride resin and c) an acrylic resin, and the total of the above components a), b) and c) is at least 40% by weight in the total solid content of the coating composition. A characteristic coating composition. 2. A precoated metal having a coating having a thickness of 5 to 35 μm formed by applying the coating composition according to claim 1 on at least one surface of a metal plate or a plated metal plate. Board.