JP2808705B2 - Precoated steel sheet and paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a precoated steel sheet which can be suitably used for building interior and exterior materials, home electric appliances, appliances, automobile interior materials, and the like, and a top layer of the precoated steel sheet. The present invention relates to a coating composition to be applied, and more particularly to a matte precoated steel sheet which can be produced by high-speed coating and has excellent decorativeness, workability, and scratch resistance.

[Related Art] In recent years, in the industry of manufacturing products such as interior and exterior materials for buildings, home appliances, appliances, and interior materials for automobiles, there has been a strong demand for matte pre-coated steel sheets having a more luxurious feel.

In response to such demands, several matte precoated steel sheets have been developed. One of them is particle size 5 or
A paint containing an inorganic powder such as silica or alumina having a particle size of 20 μm is applied to a steel sheet.
A coating containing a thermoplastic resin powder of μm nylon, polypropylene or the like is applied to a steel plate. Among these, pre-coated steel sheet to which paint containing inorganic powder is applied,
The appearance is merely matte. The texture is the same as that of a normal coated steel sheet, and the steel sheet has a sensation of cracks, which is not sufficient in terms of decorativeness.

On the other hand, the pre-coated steel sheet to which the paint containing the thermoplastic resin powder is applied has a semi-matte appearance, has a matte texture, and is slightly higher in quality than the pre-coated steel sheet to which the paint containing the inorganic powder is applied. Show feeling. However,
This pre-coated steel sheet also has the sensation of cracking of the steel sheet and is insufficient in the matting property.

By the way, as a decorative paint for concrete wall surfaces and plastic base materials, a paint containing crosslinked and cured colored elastic polymer beads (spherical powder) and a urethane resin binder is known. This paint gives the substrate a multicolored, super-matte appearance and a soft, cross-like feel.

[Problems to be Solved by the Invention] Therefore, the present inventors consider that a high-grade pre-coated steel sheet excellent in decorativeness can be obtained by applying a coating containing the above-mentioned crosslinked and cured colored polymer beads and a urethane resin binder to the steel sheet. Thought.

However, since this paint is a two-part curable paint, it is necessary to mix the two parts at the time of painting. Further, since the usable time after mixing is as short as 2 to 4 hours, workability is poor.
In addition, the baking temperature for curing the coating film is determined by discoloration (yellowing) and cracking of the coating film due to thermal deterioration of the binder resin.
In order to prevent peeling or the like, it is necessary to keep the temperature to 120 to 140 ° C. at the most, so that the baking time takes a long time of 20 to 30 minutes. For this reason, it is not possible to manufacture a precoated steel sheet using the paint online at high speed and high efficiency.

Accordingly, an object of the present invention is to provide a matte pre-coated steel sheet which is excellent in workability and scratch resistance as a pre-coated steel sheet, can be manufactured by high-speed coating, and a one-component high-speed paint coating composition applied thereto. To provide things.

[Means for Solving the Problems] The matte precoated steel sheet of the present invention has a number average molecular weight of 10,000 to 30,000 and a glass transition temperature of 10 to 10,000.
A curing agent based on a polyester resin and / or an acrylic polyester resin having a temperature of 60 ° C. and an OH value of 5 or more, and blocked with an alkyl etherified melamine resin and / or an oxime blocking agent. And having as a top layer a coating film formed from a coating composition in which a crosslinked and cured colored spherical resin powder having an average particle diameter of 20 to 150 μm is mixed in a coating solid content at a ratio of 30 to 80% by volume. It is characterized by the following.

Further, the coating composition of the present invention has a number average molecular weight of 1000.
Based on a polyester resin and / or an acrylic polyester resin having a glass transition temperature of 10 to 60 ° C. and an OH value of 5 or more, based on an alkyl etherified melamine resin and / or an oxime resin. Isocyanate compounds blocked with a blocking agent are compounded as a curing agent, and crosslinked and cured colored spherical resin powder having an average particle diameter of 20 to 150 μm is compounded at a ratio of 30 to 80% by volume in the solid content of the paint. It is assumed that.

 Hereinafter, the present invention will be described in more detail.

The present inventors have conducted intensive studies to obtain a matte precoated steel sheet which has excellent workability as a precoated steel sheet and can be manufactured by high-speed coating, and a one-part high-speed coating composition applicable to the same. did. As a result, it has been found that the intended purpose can be achieved by using a paint in which a specific colored spherical resin powder is mixed with a specific hardening agent in a specific base resin.

The coating composition of the present invention is a polyester resin curable by baking at 190 to 250 ° C. for about 30 to 120 seconds by dealcoholation with melamine resin, bicondensation reaction with dehydration, and urethanation reaction with isocyanate. Contains acrylic polyester resin as base. This base resin has a number average molecular weight of 10,000 to 30,000, a glass transition temperature (Tg) of 10 to 60 ° C., and an OH value of 5 or more.

When the number average molecular weight of the base resin is less than 10,000, the formed coating film is hard and brittle, and the coating film is easily cracked or peeled at the time of forming a precoated steel sheet.
On the other hand, when the molecular weight exceeds 30,000, although dispersibility of the colored spherical resin powder in the coating liquid is deteriorated, although it is preferable in terms of processability, coating becomes difficult.

Further, when the glass transition temperature of the base resin is less than 10 ° C., the coating film becomes soft, and although the workability is good, the coating film is easily scratched by scratching. On the other hand, if the temperature of the glass point exceeds 60 ° C, the formed coating film becomes hard and brittle, and the coating film loses the soft touch of the cross tone, and at the same time, the coating film cracks or peels off during the precoat steel sheet forming process Is more likely to occur.

Further, when the OH value of the base resin is less than 5, the bonding strength of the coating film to the colored spherical resin powder becomes weak, and the resin powder is easily peeled off by scratching.
Value must be at least 5.

The base resin is, for example, succinic acid, adipic acid,
Azelaic acid, sebacic acid, maleic acid, fumaric acid, terephthalic acid, trimellitic acid, acrylic acid, methacrylic acid, itaconic acid, acrylic ester, methacrylic acid ester, one kind of carboxylic acid such as itaconic acid ester or esters thereof or Two or more, ethylene glycol, propylene glycol, trimethylene glycol,
Condensation with one or more polyols such as trimethylolpropane, cyclohexanediol, diethylene glycol, dipropylene glycol, cyclohexanediol, 1,3-butanediol, 1,5 pentanediol, and the like in a conventional manner under an excess of hydroxyl groups It is obtained by doing.

The curing agent for curing the base resin is an alkyl etherified melamine resin and / or a blocked isocyanate compound.

Examples of the alkyl etherified melamine resin include a condensation product of melamine and formaldehyde alkyl etherified with an alkyl alcohol such as methanol, ethanol, and n-butanol. Examples of the blocked isocyanate compound include methyl ethyl ketoxime, formaldehyde oxime,
Non-yellowing hexamethylene diisocyanate blocked with an oxime-based blocking agent such as acetaldehyde ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexanone, and its buret type and isocyanurate prepolymers.

The base resin and the curing agent react by heating to form a crosslinked coating film. In order to obtain a cured film satisfactory in terms of processability and scratch resistance, when using an alkyl etherified melamine resin as a curing agent, 10 parts by weight to 70 parts by weight based on 100 parts by weight of the base resin. Is appropriate. When a blocked isocyanate is used as a curing agent, the amount of the regenerated isocyanate group of the blocked product is preferably 0.5 mol to 1.5 mol per 1 mol of the hydroxyl group of the base resin.

When the crosslinked and cured colored resin powder (beads) blended in the paint satisfies the following conditions, a more excellent matte precoated steel sheet can be obtained.

First, the average particle size of the crosslinked and cured colored spherical resin powder is
20 to 150 μm, and the compounding ratio is 30% of the solid content of the coating film.
Or 80% by volume. Average particle size is 20μm
If it is less than 150 Å, a coating film having a soft feeling of cloth tone cannot be obtained, and if it exceeds 150 μm, it becomes a rough and uneven coating film, and the decorativeness is deteriorated. If the amount is less than 30% by volume, a coating film having a matte appearance cannot be obtained,
Gloss is caused. On the other hand, when the amount exceeds 80% by volume, cracks are formed in the formed coating film.

The resin powder is composed of one or more resins of known epoxy resins, acrylic urethane resins, polyester resins, polyurethane resins, acrylic resins and / or modified resins thereof. In order to improve the stability and improve the adhesion in the formed coating film and prevent the peeling from the coating film due to scratching, the same resin type as the paint base resin or the curing material of the present invention is used. It is preferable that these are included. The powder is colored to a desired color by a pigment or a dye,
Two or more different colored materials can be blended in the paint.

The coating composition of the present invention comprises toluene, Solvesso 15
The viscosity can be adjusted using at least one solvent such as 0, methyl isobutyl ketone, cyclohexanone, ethyl cellosolve, isophorone, cellosolve acetate and the like. When an alkyl etherified melamine resin is used as a curing agent, it is preferable to appropriately mix a p-toluenesulfonic acid-based acidic catalyst in order to promote curing.

The coating composition of the present invention includes a ball mill, a disper,
It can be manufactured using a mixer such as a sand mill.

As the precoated steel sheet of the present invention, a cold-rolled steel sheet, a galvanized steel sheet, or a sheet subjected to a chemical conversion treatment with a phosphate, a chromate or the like can be used as an original sheet. In addition, an epoxy resin-based, urethane resin-based, urethane-modified epoxy resin-based, polyester resin-based primer or the like can be formed to improve the adhesion between the paint and the steel plate.

To produce the pre-coated steel sheet of the present invention, the above-mentioned coating composition is applied on the above-mentioned steel sheet by a roll coater or the like,
Heat and cure in a hot air drying oven. The thickness of the coating is from 20 to
80 μm is appropriate. During heat hardening, the ultimate temperature of the steel sheet is 190
A rapid curing of about 30 to 120 seconds at a temperature of 250 to 250 ° C is possible.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples of the present invention. In the following examples, the amounts of each component are parts by weight of solid content unless otherwise specified.

Examples 1 to 7 and Comparative Examples 1 to 4 A chromate conversion treatment was carried out on an electrogalvanized steel sheet (sheet thickness 0.5 mm) having a coating weight of 20 g / m ^{2 with} a coating weight of 50 mg / m ^{2 in} terms of metallic chromium. (Kansai Paint Co., Ltd. Cosmer 15
0), and a urethane-modified epoxy resin primer (WP-3 manufactured by NOF CORPORATION) was roll-coated to a thickness of 5 μm and baked. The topcoat paint is a colored spherical resin powder (blue powder / white powder / red powder = 3/5/2 (volume ratio)) in the resin blending system shown in Table 1.
Were mixed at the ratios shown in Table 1 and thinner (solvesso 150 /
An appropriate amount of methyl isobutyl ketone / cyclohexanone / ethyl cellosolve (4/2/2/2 (weight ratio)) was added, and the mixture was sufficiently dispersed using a sand mill. The obtained paint was applied on the above-mentioned base material using a roll coater so as to have a dry film thickness of 40 μm, and dried and baked in a hot air oven at 260 ° C. for 45 seconds.

Table 2 shows the performance of the paint obtained as described above and the performance of the coated plate.

As is clear from Table 2, Examples 1 to 7 of the present invention
Provides a matte precoated steel sheet which is excellent in workability as a precoated steel sheet and can be manufactured by high-speed coating. However, Comparative Examples 1 to 4 were all inferior in paint and coating film performance.

[Effects of the Invention] As described above, the pre-coated steel sheet of the present invention is excellent in pre-coating having a super-matte appearance and a soft touch feeling, in which the coating film is hardly peeled or scratched during bending, handling and transportation. It is a steel plate. Therefore, the precoated steel sheet of the present invention can be advantageously used as a material for high-end products requiring decorativeness and decorative durability, such as interior and exterior materials for buildings, home electric appliances, objects, and interior materials for automobiles.

In addition, the coating composition of the present invention is one-part, so that it has good workability and achieves high-speed coating.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Keiichi Kotani 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Hirofumi Asakawa 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Inside Kokan Co., Ltd. (72) Inventor Hiroshi Ishimura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Kokan Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 15/08 B05D 7 / 14 C09D 167/02 C09D 175/04 C08F 299/04

Claims (2)

(57) [Claims] (1) a number average molecular weight of 10,000 to 30,000;
Based on a polyester resin and / or an acrylic polyester resin having a glass transition temperature of 10 to 60 ° C. and an OH value of 5 or more, which is blocked with an alkyl etherified melamine resin and / or an oxime blocking agent. Isocyanate compound as a curing agent, crosslinked and cured average particle size 20 to 15
0-μm colored spherical resin powder in the solid content of the coating 30-80
A precoated steel sheet having, as an uppermost layer, a coating film formed from a coating composition blended at a ratio of% by volume. (2) a number average molecular weight of 10,000 to 30,000;
Based on a polyester resin and / or an acrylic polyester resin having a glass transition temperature of 10 to 60 ° C. and an OH value of 5 or more, which is blocked with an alkyl etherified melamine resin and / or an oxime blocking agent. Isocyanate compound as a curing agent, crosslinked and cured average particle size 20 to 15
0-μm colored spherical resin powder in the solid content of the coating 30-80
A coating composition characterized by being blended in a ratio of volume%.