JPH10193509A - Manufacturing method of pre-coated steel sheet with excellent weather resistance - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To manufacture a precoated steel sheet with good weather resistance by using an inexpensive polyacrylic resin paint. SOLUTION: A copolymer obtained by copolymerizing a polymerizable monomer component essentially containing a polymerizable UV-stable monomer, a cycloalkyl group-containing polymerizable monomer, and a hydroxyl group-containing polymerizable monomer. Acrylic polyol is blended with an aminoplast resin or a polyisocyanate compound as a crosslinking agent, and a coating obtained by dissolving or dispersing these in a solvent is applied to at least one surface of a steel sheet so that the coating thickness is 5 μm or more and 40 μm or less. Then, bake at 150 ° C. or more and less than 300 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a weather-resistant precoated steel sheet used for home appliances, building materials, automobiles and the like.

[0002]

2. Description of the Related Art Steel sheets are generally used after being painted. The purpose of this coating is to protect the base steel plate while at the same time increasing its durability and beautifying it. Painted steel sheets are used for everything from large structures such as buildings, ships, bridges, etc. to various machines, automobiles, furniture, small appliances and household goods, but the painting of these steel sheets is generally called post-coating. Performed after processing and assembly. However, in the field of building materials and home appliances, there is a transition to a method of processing and assembling a so-called pre-coated painted steel plate. In this precoated steel sheet, a polyacrylic resin or the like having workability is used as a paint so that the coating film is not peeled off during processing.

[0003]

However, a conventional polyacrylic resin coating film cannot provide sufficient weather resistance while maintaining workability. Note that the weather resistance refers to durability performance against a change in appearance due to deterioration or deterioration of a resin due to irradiation of sunlight or wind and rain when using a coated steel sheet outdoors. On the other hand, a fluororesin-based coating film has sufficient weather resistance, but its cost is much higher than that of a polyacrylic resin-based coating material.

[0004] The present invention has been made in order to solve the aforementioned problems.
An object of the present invention is to provide a method for producing a precoated steel sheet in which good weather resistance is added to an inexpensive polyacrylic resin paint.

[0005]

According to the present invention, there is provided a polymerizable monomer component essentially comprising a polymerizable ultraviolet-stable monomer, a cycloalkyl group-containing polymerizable monomer, and a hydroxyl group-containing polymerizable monomer. An acrylic resin or a polyisocyanate compound as a cross-linking agent is blended with a copolymerized acrylic polyol obtained by copolymerizing the above, and a coating obtained by dissolving or dispersing these in a solvent is coated on at least one surface of a steel sheet. 5
This is a method for producing a precoated steel sheet having excellent weather resistance, characterized in that the coated steel sheet is coated so as to have a thickness of not less than μm and not more than 40 μm and baked at a temperature of not less than 150 ° C. and less than 300 ° C.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method for producing a precoated steel sheet according to the present invention will be described in more detail.

First, the coating resin component in the present invention comprises a copolymerized acrylic polyol containing a polymer component for improving weather resistance. As essential polymerizable monomer components, a polymerizable UV-stable monomer containing a functional group such as a hindered amine having a UV-stabilizing ability and a cycloalkyl group-containing polymer having a functional group necessary for improving the weather resistance of the resin And a hydroxyl group-containing polymerizable monomer.

[0008] The polymerizable ultraviolet-stable monomer is an essential compound for imparting excellent weather resistance to the copolymer. In particular, at least a sterically hindered piperidinyl group and a polymerizable unsaturated group are present in the molecule. One having one is awarded, and among them, the substance represented by the general formula (1) is most typically used.

[0009]

Embedded image

In the general formula (1), R ₁ is a hydrogen atom or a cyano group, R ₂ and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and X is an imino group or an oxygen atom. , Y represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or —CO—CR ₂ ＣＨCHR ₃ (wherein R ₂
· R ₃ has the same meaning as before).

Illustratively, the specific compound name will be used as an example. As the polymerizable UV-stable monomer, for example, 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine , 4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-
(Meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4- (meth) acryloylamino-1,2,2,6,6-pentamethylpiperidine,
-Cyano-4- (meth) acryloylamino-2,2,
6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,
6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 1-
Crotonoyloxy-2,2,6,6-tetramethylpiperidine and the like can be mentioned, and one or more of these can be used.

Examples of the cycloalkyl group-containing polymerizable monomer include cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, and tertiary butylcyclohexyl (meth) acrylate. Two or more can be used.

Next, examples of the hydroxyl group-containing polymerizable monomer include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and caprolactone-modified hydroxy (meth) acrylate. Two or more can be used.

Further, as other polymerizable monomers, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, t-butyl (meth) acrylate, 2- (Meth) acrylic acid alkyl esters such as ethylhexyl (meth) acrylate, epoxy group-containing unsaturated monomers such as glycidyl (meth) acrylate, (meth) acrylimide, N, N'-dimethylaminoethyl (meth) acrylate, Nitrogen-containing unsaturated monomers such as vinylpyridine and vinylimidazole; aromatic unsaturated monomers such as styrene, α-methylstyrene and vinyltoluene; vinylesters such as vinyl acetate; vinylesters such as vinylether and (meth) acrylonitrile; Examples include saturated cyanide compounds Bets can be, can be used alone or in combination selected from these groups as necessary.

The copolymerization of the above-mentioned polymerizable monomer components is not particularly limited, but the content ratio of each monomer component is preferably 0.1 to 10.0. % By weight, cycloalkyl group-containing polymerizable monomer 5.0 to 9
7.9% by weight, hydroxyl group-containing polymerizable monomer 2.0 to 35.
It is preferable to constitute 100% by weight of the copolymerized acrylic polyol within the range of 0% by weight and 0 to 92.9% by weight of the other polymerizable monomers.

An aminoplast resin or a polyisocyanate compound is blended as a crosslinking agent.

Examples of the aminoplast resin include methyletherified melamine resin, butyletherified melamine resin, butyletherified benzoguanamine resin, and butyletherified cyclohexylbenzoguanamine resin. The blend of the aminoplast resin and the copolymerized acrylic polyol is preferably 10 to 100% by weight of the acrylic polyol.

Further, as the polyisocyanate compound,
It suffices if the molecule contains two or more isocyanate groups. For example, trimethylene diisocyanate, 1.6-
Hexamethylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and adduct polyisocyanate compounds such as trimethylolpropane adduct, buret, and isocyanurate, which are derivatives of these diisocyanates, further include isocyanate compounds And a blocked polyisocyanate compound in which the isocyanate group is blocked with a compound such as ε-caprolactam, phenol, cresol, oxime, or alcohol. The blend of the polyisocyanate compound and the acrylic polyol is preferably such that the isocyanate group is 0.3 to 2.0 mol per 1 mol of the OH group in the acrylic polyol.

It is preferable that the composition is mixed with a curing catalyst such as dodecylbenzene sulfonic acid, a color pigment such as titanium white, a leveling effect agent, an antioxidant, an ultraviolet absorber and the like to form a paint.

The paint is applied on at least one side of the steel sheet which has been subjected to chemical conversion treatment or undercoating so that the coating film thickness is 5 to 40 μm. If the thickness of the coating film is less than 5 μm, poor appearance such as color loss and insufficient weather resistance are caused. On the other hand, when the film thickness is 4
If it exceeds 0 μm, workability will be insufficient. Preferably 7 to 2
The thickness is preferably 5 μm.

After the application, it is baked at 150 ° C. or more and less than 300 ° C., and is cured and dried. Baking temperature is 150 ℃
If it is less than 3, the solvent in the paint will not be sufficiently volatilized and the coating will be insufficiently cured, and if it is more than 300 ° C., the resin component will be thermally degraded, and it will not be suitable as a product due to a reduction in workability.

As a method for applying the coating, a roll coater, a curtain flow coater, a roller curtain coater, an electrostatic coating machine, a brush, a blade coater, a die coater or the like is used to apply a coating to a required film thickness, and then cured and dried. The method is preferably drying at room temperature or curing and drying in a hot air oven, induction heating oven, near infrared oven, far infrared oven, energy ray curing oven, or the like.

The steel sheets include cold-rolled steel sheets, hot-rolled steel sheets, galvanized steel sheets, galvannealed steel sheets, zinc-iron alloy coated steel sheets, zinc-aluminum alloy coated steel sheets, aluminum-coated steel sheets, chromium-coated steel sheets, nickel Plated steel sheet,
Examples include a zinc-nickel alloy-plated steel plate, a tin-plated steel plate, a stainless steel plate, an aluminum-plated stainless steel plate, a lead-plated stainless steel plate, and a zinc-plated stainless steel plate.

The pretreatment of the steel sheet includes water washing, hot water washing, pickling, alkali degreasing, grinding, polishing, chromate treatment, zinc phosphate treatment, composite oxide film treatment and the like. It is good to do. The conditions for the pre-coating treatment may be appropriately selected.

Further, if necessary, an undercoat paint is applied on a steel plate and cured and dried to form an undercoat film layer. Examples of the undercoat paint include polyester-based, epoxy-based, and urethane-based paints.

It should be noted that polyacryl, polyester, and the like are provided between the undercoat film and the polyacryl resin-containing film layer of the present invention.
The formation of an intermediate coating film layer such as an epoxy coating film may be performed.

[0027]

EXAMPLES Examples of the method for producing a precoated steel sheet according to the present invention will be described.

4-methacryloyloxy-2,2,6
3 parts of 6-tetramethylpiperidine, 20 parts of cyclohexyl methacrylate, 1 part of stearyl methacrylate
0 parts, 15 parts of butyl acrylate, 5.5 parts of methyl methacrylate, 2 parts of hydroxyethyl acrylate
Parts, acrylic acid resin consisting of 4.5 parts of acrylic acid and 2 parts of azobisisobutylnitrile, Desmodur BL3175 (manufactured by Sumitomo Bayer Urethane) as a curing agent in OH / NCO = 1: 1 equivalent as a curing agent, and curing catalyst As dibutylene urearate at a resin solids ratio of 250
ppm, and titanium white CR-9 as a color pigment
5 (manufactured by Ishihara Sangyo Co., Ltd.) is mixed so that PWC becomes 40%
Paint. Next, 4 μm of an epoxy-based primer was applied on a hot-dip galvanized steel sheet which had been subjected to alkali degreasing and chromate treatment, cured at 200 ° C. and dried, and then coated with the paint, and baked by a high-frequency induction heating method. Table 1 shows the coating film thickness and the baking temperature (PMT). The workability and weather resistance of the obtained precoated steel sheet were evaluated under the following conditions.

1) Workability In accordance with JIS G 3312, evaluation was made at the limit of cracks in the coating film after bending by 180 degrees. For example, 0T means that there is no crack due to close bending.

2) Weather Resistance As an accelerated weather resistance test, a sunshine weather meter (SWOM) was used to measure and evaluate a chromaticity difference (ΔE) and a gloss retention (GR) before and after the test for 3000 hours. The chromaticity difference is measured using a chromaticity measuring instrument, and ΔE of 2.0 or less is judged to be good. The gloss retention is measured by a 60-degree reflectometer, and 50% or more is judged to be good.

As is clear from Table 1, the precoated steel sheet manufactured by the method of the present invention was a product excellent in workability and weather resistance.

[0032]

[Table 1]

[0033]

According to the present invention, a precoated steel sheet which is inexpensive and excellent in workability and weather resistance can be manufactured. By applying this to home appliances and building materials, etc.,
Product quality can be improved and manufacturing costs can be reduced.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C23C 28/00 C23C 28/00 C (72) Inventor Ryoji Nishioka 20-1 Shintomi, Futtsu Nippon Steel Corporation Technology Development Division (72) Inventor Masashi Takasugi 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works (72) Inventor Masaya Yoshida 5-8 Nishiobari-cho, Suita-shi, Osaka Japan Catalyst Co., Ltd. Suita Works (72) Inventor Takao Minami 5-8 Nishiburi-cho, Suita-shi, Osaka, Japan Inside Nihon Shokubai Suita Manufacturing Co., Ltd. (72) Inventor Mitsuo Nakazaki 5-8, Nishi-Motomachi-cho, Suita-shi, Osaka Pref.

Claims (3)

[Claims] 1. A copolymer obtained by copolymerizing a polymerizable monomer component essentially containing a polymerizable UV-stable monomer, a cycloalkyl group-containing polymerizable monomer, and a hydroxyl group-containing polymerizable monomer. An aminoplast resin or a polyisocyanate compound is compounded as a crosslinking agent in the polymerized acrylic polyol, and a coating material obtained by dissolving or dispersing the compound in a solvent is coated on at least one surface of the steel sheet so that the coating film thickness is 5 μm or more and 40 μm or less. A method for producing a precoated steel sheet having excellent weather resistance, which is applied and baked at a temperature of 150 ° C. or more and less than 300 ° C. 2. The polymerizable ultraviolet-stable monomer is represented by the following general formula (1): wherein R ₁ is a hydrogen atom or a cyano group, and R ₂ and R ₃ are each independently A hydrogen atom or an alkyl group having 1 to 2 carbon atoms, X represents an imino group or an oxygen atom, Y represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, or -CO-CR ₂ ＣＨCHR ₃ (wherein R _{2 represents}
· R ₃ the method of manufacturing the pre-coated painted steel sheet excellent in weather resistance according to claim 1, which is manifested in the same sense)] as before. Embedded image 3. The precoated steel sheet having excellent weather resistance according to claim 1 or 2, wherein the steel sheet is subjected to chemical conversion treatment and / or undercoating before applying the coating material to the steel sheet. Production method.