JPH10324844A - Coating composition for precoated steel sheet, precoated steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition which can give a coating film excellent in processability, hardness, stainproofness and scratch resistance by including a specified amount of a specified polyester compound, a specified polyol and a curing agent being a mixture of a plurality of specified blocked polyisocyanate compounds and using a resin component as the principal component. SOLUTION: This composition comprises 1-18 wt.%, based on the resin solid matter, polyester compound mainly consisting of repeating units of a polyol of the formula, a polyol other than the polyol of the formula and a curing agent being a mixture comprising a blocked polyisocyanate obtained from at least one member selected among 4,4'-diphenylmethane, isophorone, tolylene, xylylene diisocyanates, etc., and a blocked polyisocyanate obtained from at least one member selected among (trimethyl)hexamethylene, and hydrogenated 4,4'-diphenylmethane diisocyanates, etc. In the formula, n is an integer; R is a 1-10 C alkylene, 1,4-cyclohexylenedimethyl, neopentylene or polyoxyalkylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosetting coating composition for a precoated steel sheet which is required to have high hardness, high workability and stain resistance, a precoated steel sheet having a coating film made of the coating composition, and a precoated steel sheet. It relates to a manufacturing method. The precoated steel sheet of the present invention is suitable for, for example, home electric appliances and building materials, and can also be used for automobiles.

[0002]

2. Description of the Related Art Paints for precoated steel sheets are required to have many properties such as high hardness, high workability, stain resistance, chemical resistance, water resistance, and high definition. Among these properties, hardness and workability, which are important properties, are mutually contradictory properties, but their required levels are high. The term "workability" as used herein refers to less damage to the coating film in the process of bending, cutting, drawing, etc. when processing a flat steel sheet into various shapes, elongation and flexibility of the coating film itself. It can be said that the larger the degree is, the better the workability is. In particular, regarding the bending workability, the degree of workability differs depending on the thickness of the object to be coated, that is, the steel plate.

For example, a T-shaped bending test (12.2.2 of JIS G3312) often used for evaluating bending workability.
In accordance with), in the inside of a steel plate, n sample plates of the same thickness are sandwiched and bent, and this bent portion is observed with a loupe, and the minimum number of sandwiches that does not cause coating film cracking is evaluated as an evaluation value. It is displayed as 1T, 2T. The elongation of the outermost circumference in this T-bending is expressed by the following equation: ε = (t / 2) / (r + t / 2) where ε: elongation strain (%) of the outermost circumference t: sheet thickness ( mm) r: R (mm) inside the bent portion Therefore, if the evaluation value of the T-shaped bending test is the same, the thinner the plate thickness, the larger the elongation strain (%) of the outermost periphery and the smaller the curvature of the processed portion. It means that it is excellent in workability.

[0004] The above-described T-bending test is generally used as a method for evaluating the workability of a coated steel sheet. However, the pressing and roll forming processes performed industrially by a home appliance manufacturer and the like are compared with the T-bending test. The processing history, processing speed, etc. are different, and the processing conditions are more severe. The machining history here refers to the machining process up to the final machining level. Even if the final machining level is the same, R
Is large, the strain generated by the processing is dispersed throughout the R portion, and the load on the coating film is small. On the other hand, if the radius R inside the bent portion is small at the initial stage of the processing, the strain generated by the processing is concentrated on the small R portion, and the load on the coating film increases.
Therefore, T, which performs close contact bending after U-shaped bending,
Compared to the V-shaped bending test, the one subjected to close bending after V-shaped bending has a large load on the coating film even at the same final processing level, and is useful as a simple evaluation of severe processing.

[0005] On the other hand, the higher the hardness, the better in terms of improving the durability of the coating film, but the higher the hardness, the lower the workability. In general, precoated steel sheets are required to have excellent corrosion resistance and scratch resistance. Here, the term "corrosion resistance" means that, after being molded as a product, there is little or no rusting of the coating film or rust from the object to be coated in a use environment. The term “scratch resistance” means that scratches due to friction with a molding machine during molding (molding flaws) and scratches due to conveyance after molding processing (handling flaws) are unlikely to occur.

Heretofore, polyester resins and epoxy resins have been mainly used for the undercoat and the backcoat on the outer surface, and polyester, acrylic and vinyl paints have been used as the outer coat for the precoated steel sheet. ing. The most common outer surface top coating is a polyester resin coating composed of a combination of a polyester resin (main component) and a melamine compound (curing agent).
Hardness is obtained by a melamine compound. However, this outer surface top coat is a pre-coated steel plate with strict performance requirements,
In particular, the performance of precoated steel sheets for home appliances and the like is not always sufficient, and improvement in performance has been desired.

In response to such a demand, for example,
No. 234,752, an attempt has been made to obtain a coating film which satisfies both flexibility and coating film hardness at a high level by reacting a polyester resin with a melamine resin (curing agent) imparted with orientation by modification. I have. JP-A-7-316497 also discloses a coating composition containing polyol as a main component and an isocyanate compound and / or an amino resin as a curing agent for the purpose of obtaining a coating film having high workability and coating film hardness. In particular, there has been proposed a coating composition for a precoated steel sheet to which a polyester compound obtained by reacting 1,4-cyclohexanedicarboxylic acid and / or a lower alkyl ester thereof with an alcohol component is added.

[0008]

However, among these prior arts, the technique disclosed in Japanese Patent Application Laid-Open No. Hei 6-234,752 involves a long process of synthesizing a modified melamine resin. Is difficult. Also, Japanese Patent Application Laid-Open
In the technology of No. 316497, no consideration is given to the improvement of the coating film performance including the coating film's stain resistance. However, it is impossible to obtain a coating film which satisfies all of the coating film hardness, workability, and stain resistance, for example, inferior in paintability, or inferior in processability even though the coating film hardness and stain resistance can be secured.

Conventionally, a wax (lubricant) is generally added to a coating film in order to improve the scratch resistance at the time of molding, and the wax may be a carnauba wax, palm oil or the like. Natural and synthetic waxes are used. However, in the conventional coating film to which these lubricants are added, the waxes floating on the coating film surface fall off by contact with other substances, and stain the contacted surface. There are problems such as agglomeration on the coating film surface, clouding of the coating film, generation of cissing, eye holes, etc. on the coated surface.

[0010] Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, to satisfy both the workability and hardness of a coating film even at a relatively thin plate thickness, and to improve the stain resistance. Another object of the present invention is to provide an excellent coating composition for a precoated steel sheet. Another object of the present invention is to provide a precoated steel sheet having high coating film hardness and excellent stain resistance, and excellent workability in which the coating film is hardly cracked even in severe molding. It is in.

Further, another object of the present invention is to not only have high coating film hardness, excellent workability and stain resistance, but also
An object of the present invention is to provide a pre-coated steel sheet having excellent corrosion resistance. Further, another object of the present invention is to not only have high coating film hardness and excellent workability and stain resistance, but also have excellent scratch resistance, and further, clouding of the coating film surface due to aggregation of wax and the like. An object of the present invention is to provide a precoated steel sheet that does not occur. Still another object of the present invention is to provide a manufacturing method capable of inexpensively and efficiently producing the above-mentioned precoated steel sheet.

[0012]

Means for Solving the Problems The present inventors have repeatedly studied to obtain a coating composition for a precoated steel sheet having excellent performance which can solve the above-mentioned problems. A polyisocyanate compound as an agent,
Mainly 1,4-cyclohexanedicarboxylic acid and / or
Alternatively, in a paint compounding system containing a polyester compound obtained by reacting the lower alkyl ester with an alcohol component, at least one blocked polyisocyanate compound selected from two specific blocked polyisocyanate compound groups as a curing agent. By mixing and using the isocyanate compound, a coating film excellent in both processability, coating film hardness and stain resistance can be obtained, and this coating film is also excellent in other properties such as glossiness. I found something.

As the precoated steel sheet to which the above specific coating composition is applied, a precoated steel sheet in which an undercoat film and an overcoat film of the above coating composition are formed on the surface of a galvanized steel sheet which has been subjected to a chemical conversion treatment is used. It is preferable, and particularly, in such a precoated steel sheet, that a particularly excellent moldability can be obtained by forming a coating film having specific physical properties as an undercoat coating film, and that an appropriate amount of Excellent corrosion resistance can be obtained by adding strontium chromate, and excellent scratch resistance can be obtained by adding an appropriate amount of wax to the overcoat film, and clouding of the coating film surface due to aggregation of the wax. It turned out to be difficult to occur.

The present invention has been made on the basis of such findings, and the characteristic configuration thereof is as follows. [1] b) General formula (1)

Embedded image 1 to 18% by weight of a polyester compound having as a main repeating unit in a resin solid content; b) a polyol other than the above a); and c) a polyisocyanate of the following group (a) and its derivatives. A blocked polyisocyanate compound obtained by blocking one or more of the obtained polyisocyanate compounds and one or more polyisocyanate compounds selected from the following polyisocyanates of the group (b) and derivatives thereof A curing agent mixed with the obtained blocked polyisocyanate compound (a) 4,4'-diphenylmethane diisocyanate,
Isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene-1,5
-Diisocyanate (b) a coating composition for a precoated steel sheet mainly containing a resin component consisting of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylylene diisocyanate Stuff.

[2] In the coating composition of the above [1],
(a) blocked polyisocyanate compounds obtained by blocking at least one polyisocyanate compound selected from the group consisting of polyisocyanates and derivatives thereof
(A), the blending ratio of the blocked polyisocyanate compound (B) obtained by blocking at least one polyisocyanate compound selected from the group (b) of polyisocyanates and derivatives thereof, (A) /
(B) = 70/30 to 30/70, a coating composition for a precoated steel sheet. [3] In the coating composition of the above [1] or [2], the curing agent of c) is the isocyanate group [NCO] in the curing agent, the polyester compound of a) and the hydroxyl group [OH] of the polyol of b). ], And the molar ratio [NCO] / [OH] is 0.8 to 1.2.

[4] In the coating composition according to any one of the above [1] to [3], a blocked composition obtained by blocking a polyisocyanate compound selected from the group (a) polyisocyanates and derivatives thereof. The polyisocyanate compound is any of an isocyanurate form, an adduct form, and a prepolymer, and is a blocked polyisocyanate compound obtained by blocking a polyisocyanate compound selected from the group (b) polyisocyanates and derivatives thereof. Is a burette body, an isocyanurate body,
A paint composition for a precoated steel sheet, which is one of an adduct body and a prepolymer.

[5] In the coating composition according to any one of the above [1] to [4], the polyol other than a) is used in an amount of 2 per molecule.
Having at least one hydroxyl group and having a number average molecular weight of 1500 to 1
2000 or more acrylic resins and / or two or more hydroxyl groups in one molecule and a number average molecular weight of 1000 to 80
A coating composition for a precoated steel sheet, which is a polyester resin of No. 00. [6] A precoated steel sheet having a coating film formed by applying the coating composition according to any one of [1] to [5].

[7] A precoated steel sheet having an undercoating film and an overcoating film on the surface of a galvanized steel sheet subjected to a chemical conversion treatment, wherein the overcoating film is any one of the above-mentioned [1] to [5]. A precoated steel sheet having excellent hardness and workability, characterized in that it is a coating film formed by applying a coating composition. [8] In the precoated steel sheet of the above [7], the undercoat film has a breaking strength of 50 kg / cm ² or more and a breaking elongation of 50% or more measured as a film having a width of 5 mm and a thickness of 8 ± 1 μm. Precoated steel sheet with excellent hardness and workability.

[9] The precoated steel sheet according to the above [8], wherein the undercoat film is a film formed by applying a coating composition containing a bisphenol A-added polyester resin as a main component. Pre-coated steel sheet with excellent workability. [10] In the precoated steel sheet of the above-mentioned [7], the undercoating film contains strontium chromate in an amount of 0.1% per 1 μm of film thickness.
A precoated steel sheet excellent in hardness and workability, characterized in that it contains from 0.6 to 0.26 g / m ² . [11] The precoated steel sheet according to the above [10], wherein the undercoating film is a coating film formed by applying a coating composition containing a polyester resin as a main component, and has excellent hardness and workability. Pre-coated steel sheet.

[12] In the precoated steel sheet according to any one of the above [7] to [11], the undercoat film has a dry film thickness of 2 to 12 μm.
m, a precoated steel sheet having excellent hardness and workability. [13] In the precoated steel sheet according to the above [7], the top coating film contains wax in a proportion of 100 parts by weight of the coating composition in terms of solid content (however, the weight of the coating composition excluding the wax).
A precoated steel sheet having excellent hardness and workability, characterized by containing 3 to 30 parts by weight. [14] The precoated steel sheet according to the above [13], wherein the wax contained in the overcoat film has a melting point of 100 ° C or more, and is excellent in hardness and workability.

[15] The precoated steel sheet according to [13] or [14], wherein the wax contained in the overcoat film is a mixture of polyethylene wax and polytetrafluoroethylene, and is excellent in hardness and workability. Pre-coated steel sheet. [16] After applying the coating composition for an undercoat coating film on the surface of the galvanized steel sheet which has been subjected to the chemical conversion treatment, 180 to 260
Baking at the ultimate plate temperature of 180 ° C., and then applying the coating composition of any of the above [1] to [5] for the top coat, and then baking at the ultimate plate temperature of 180 to 260 ° C. A method for producing a precoated steel sheet having excellent hardness and workability.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The coating composition for a precoated steel sheet according to the present invention comprises (a) a specific polyester compound, (b) a polyol other than the above (a), and (c) two specific blocked polyisocyanate compounds as a curing agent. A coating composition comprising, as a main component, a resin component comprising a curing agent obtained by mixing at least one kind of blocked polyisocyanate compound selected from each group. First, the polyester compound (a) is a polyester compound having the following general formula (1) as a main repeating unit.

Embedded image

As the acid component for obtaining the polyester compound (a), 1,4-cyclohexanedicarboxylic acid and / or its lower alkyl ester are mainly used, and a part of them is terephthalic acid, isophthalic acid, naphthalene or the like. Dicarboxylic acids such as -2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid and diphenyldicarboxylic acid, or lower alkyl esters of these dicarboxylic acids can be substituted. Examples of the lower alkyl ester include a methyl ester and an ethyl ester having 1 to 2 carbon atoms. However, even in this case, it is desirable that the main component of 1,4-cyclohexanedicarboxylic acid be 85 mol% or more of the entire acid component, and the ratio of the other compound to be replaced be suppressed to less than 15 mol%.

As the alcohol component for obtaining the polyester compound (a), a diol is mainly used. As this diol, an aliphatic diol, an alicyclic diol or the like can be used. For example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexane Dimethanol and the like. Further, as the alcohol component, a trihydric or higher polyhydric alcohol may be used in addition to the above-mentioned diol. 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.

The polyester compound (a) has a number average molecular weight of 2 in terms of styrene measured by GPC.
It is preferable to use those having a molecular weight of 000 or less, more preferably 1000 or less. Styrene-equivalent number average molecular weight of 200
If it exceeds 0, a remarkable effect due to the addition of the polyester compound cannot be obtained, and the appearance of the coating film, hardness, workability, and the like become insufficient. The amount of the polyester compound (a) is from 1 to 18% by weight, preferably from 2 to 15% by weight, and more preferably from 3 to 10% by weight, based on the solid content of the resin. If the amount of the polyester compound is less than 1% by weight, the effect of improving the coating film performance is not remarkable, and the superiority of the conventional material in the coating film performance is small. On the other hand, if the compounding amount exceeds 18% by weight, the coating film performance, particularly the flexibility, is reduced.

Next, an acrylic resin or a polyester resin can be used as the polyol in the above item b). The acrylic resin as the polyol (b) is not particularly limited as long as it is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of 1500 to 12,000. Is preferably from 1700 to 10000. Hydroxyl groups in the acrylic resin molecule are randomly arranged in the acrylic resin main chain, and when the number average molecular weight is less than 1500, the processability is significantly reduced. On the other hand, if the number average molecular weight exceeds 12,000, the viscosity becomes high, so that an excess of a diluting solvent is required, and the proportion of the resin in the coating material is reduced, so that an appropriate coating film cannot be obtained. Further, the compatibility with other compounding components is significantly reduced. The number average molecular weight of the acrylic resin is determined by gel permeation chromatography (hereinafter, referred to as “gel permeation chromatography”).
GPC) as measured in terms of polyester.

The acrylic resin is a copolymer obtained by subjecting (meth) acryl having a hydroxyl group to an acrylic ester or a methacrylic ester by a heat reaction in a known manner. As acrylic monomer and methacrylic monomer,
For example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, and the like can be used. Examples of the acrylates and methacrylates include, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylic acid-
n-Butyl, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, and the like can be used. Commercially available acrylic resins include “Almatex” (manufactured by Mitsui Toatsu Chemicals, Inc.) and “Desmophen”
(Sumitomo Bayer Urethane Co., Ltd.), "Dianal"
(Manufactured by Mitsubishi Rayon Co., Ltd.).

The polyester resin as the polyol (b) is not particularly limited as long as it has at least two hydroxyl groups in one molecule and has a number average molecular weight of 1,000 to 8,000. The preferred number average molecular weight range is from 1200 to 7000, more preferably 15
00 to 6000. The hydroxyl group in the molecule of the polyester resin may be at either the terminal or the side chain in the molecule. If the number average molecular weight of the polyester resin is less than 1,000, the processability will be significantly reduced. On the other hand, if the number average molecular weight exceeds 8000, the viscosity becomes high, so that an excess of a diluting solvent is required, and the proportion of the resin in the coating material is reduced, so that an appropriate coating film cannot be obtained. Further, the compatibility with other compounding components is significantly reduced. The number average molecular weight of the polyester resin is a molecular weight in terms of polystyrene measured by GPC.

The polyester resin is a copolymer obtained by heating and reacting a polybasic acid component and a polyhydric alcohol by a known method. As the polybasic acid component, for example, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used. Examples of the polyhydric alcohol include, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, Glycerin, pentaerythritol, trimethylolpropane, trimethylolethane and the like can be used. Commercially available polyester resins include “Almatex” (manufactured by Mitsui Toatsu Chemicals, Inc.), “alkynol” (manufactured by Sumitomo Bayer Urethane Co., Ltd.), “desmophen” (manufactured by Sumitomo Bayer Urethane Co., Ltd.), Byron (manufactured by Toyobo Co., Ltd.) and the like.

The above-mentioned polyester compound (a) and the above-mentioned (b)
The polyol forms a cured coating film by reaction with the curing agent of the above item c). As the curing agent of the above (c), the following (a)
A blocked polyisocyanate compound obtained by blocking one or more polyisocyanate compounds selected from a group of polyisocyanates and derivatives thereof,
A curing agent mixed with a blocked polyisocyanate compound obtained by blocking one or more polyisocyanate compounds selected from the following polyisocyanates (b) and derivatives thereof is used.

(A) 4,4'-diphenylmethane diisocyanate (hereinafter referred to as MDI), isophorone diisocyanate (hereinafter referred to as IPDI), tolylene diisocyanate (hereinafter referred to as TDI), xylylene diisocyanate (hereinafter referred to as XDI), naphthylene -1,
5-diisocyanate (hereinafter referred to as NDI) (b) Hexamethylene diisocyanate (hereinafter HDI)
), Trimethylhexamethylene diisocyanate (hereinafter referred to as TMDI), hydrogenated 4,4'-diphenylmethane diisocyanate (hereinafter referred to as hydrogenated MDI),
Hydrogenated tolylene diisocyanate (hereinafter referred to as hydrogenated TDI), hydrogenated xylylene diisocyanate (hereinafter referred to as hydrogenated X)
DI)

As described above, as the curing agent,
By using a curing agent mixed with a blocked polyisocyanate compound obtained by blocking at least one type of polyisocyanate compound selected from the group (b) of polyisocyanates and derivatives thereof,
A coating film having excellent coating film hardness, processability, and stain resistance can be obtained. The reason why a coating film excellent in both film hardness, workability and stain resistance can be obtained by using a curing agent in which two or more different blocked polyisocyanate compounds are mixed is as described below. This is considered to be due to a synergistic effect of mixing two kinds of blocked polyisocyanate compounds having properties and using such a curing agent in combination with the polyester compound of the above-mentioned a). Not always clear.

One of the reasons that can be presumed is that a curing agent obtained by mixing two kinds of blocked polyisocyanate compounds having different properties as described below is used, and that a combination of the above-mentioned alcohol component and acid component is used. Due to the synergistic effect of the action such as the orientation of the polyester compound of the above a), even at a relatively thin plate thickness, 180 °
The crosslinking density, which greatly affects the elongation of the coating film and the stain resistance that can withstand close contact bending, is controlled in a well-balanced manner.

Of the polyisocyanates and their derivatives of the above groups (a) and (b), those of the group (a) are relatively rigid curing agents and those of the group (b) are relatively soft. Although it can be classified into each of the curing agent components, these (a) group or (b)
When a blocked polyisocyanate compound of a polyisocyanate or a derivative thereof selected from the group is used alone, a coating film having a high degree of coating hardness, workability and stain resistance cannot be obtained, Only a coating film inferior to at least one of the properties can be obtained. On the contrary,
(a) a relatively rigid curing agent component selected from the group and (b)
By using a mixture with a relatively soft curing agent component selected from the group, excellent coating film performance as described above can be obtained.

The blocked polyisocyanate compound (A) obtained by blocking at least one polyisocyanate compound selected from the group (a) polyisocyanate and its derivative, and the polyisocyanate compound (b) The mixing ratio with the blocked polyisocyanate compound (B) obtained by blocking at least one polyisocyanate compound selected from isocyanates and derivatives thereof is (A) / (B) in terms of solids weight ratio. = 70 / 30-30 / 70,
More desirably, it is preferably 60/40 to 40/60. When the weight ratio of the solid content (A) / (B) exceeds 70/30, high coating film hardness and excellent workability cannot be obtained in a well-balanced manner, and the impact resistance is also poor. On the other hand, if the weight ratio of the solid content of (A) / (B) is less than 30/70, sufficient stain resistance cannot be obtained. Therefore, in any case, it is difficult to obtain a coating film having excellent coating film hardness, workability, and stain resistance.

In the coating composition of the present invention, the above (a)
A blocked polyisocyanate compound obtained by blocking a polyisocyanate compound selected from the group consisting of a polyisocyanate and a derivative thereof is any of an isocyanurate form, an adduct form, and a prepolymer; The blocked polyisocyanate compound obtained by blocking a polyisocyanate compound selected from isocyanates and derivatives thereof is preferably any one of a burette body, an isocyanurate body, an adduct body, and a prepolymer.

The curing agent of (c) is a molar ratio [NCO] of the isocyanate group [NCO] of the blocked polyisocyanate compound and the total of the hydroxyl group [OH] of the polyester compound of (a) and the polyol of (b). /
[OH] is 0.8 to 1.2, preferably 0.85 to 1.
It is preferable to mix them so as to be 15. [NCO] /
When the molar ratio of [OH] is less than 0.8, curing of the coating film is insufficient, and desired coating film hardness and strength cannot be obtained. on the other hand,
When the molar ratio of [NCO] / [OH] exceeds 1.2, a side reaction between excess isocyanate groups or between an isocyanate group and a urethane bond occurs, thereby deteriorating the processability of the coating film.

Further, the coating composition of the present invention may contain a curing catalyst such as trimethylenediamine, tin octoate, dibutyltin dilaurate, 2-ethylhexoate lead, etc., depending on the purpose and application; calcium carbonate, kaolin, clay, Pigments such as titanium oxide, talc, barium sulfate, mica, red iron oxide, manganese blue, carbon black, aluminum powder, and pearl mica; and other various additives such as an antifoaming agent and a flow stopper can be appropriately compounded.

The composition of the coating composition of the present invention has been described above. In actual use, these are dissolved in an organic solvent and used. As the organic solvent used, for example,
Methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 100 (manufactured by Exxon Chemical), Solvesso 150 (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, ethyl acetate, butyl acetate, petroleum ether, petroleum naphtha and the like. In preparing the coating composition, an ordinary dispersing machine or kneading machine such as a sand grind mill, a ball mill, and a blender can be selected and used, and the respective components can be blended.

There are no particular restrictions on the type of steel sheet to be coated with the coating composition for a pre-coated steel sheet of the present invention. Usually, however, cold-rolled steel sheets and various types of coated steel sheets (for example, hot-dip galvanized steel sheets, electrogalvanized steel sheets, etc.) Steel sheets, composite galvanized steel sheets, chrome-plated steel sheets, etc.) are coated on steel sheets that have been subjected to a chemical conversion treatment such as phosphate treatment or chromate treatment. By coating the steel sheet surface which has been subjected to the chemical conversion treatment, the adhesion of the coating film to the steel sheet is improved and the corrosion resistance is also improved. In order to further improve the adhesion between the coating film and the steel sheet using the coating composition of the present invention and to increase the corrosion resistance, a primer coat may be applied as a base. Epoxy or polyester coatings are suitable as such primer coats. Further, a rust preventive pigment may be added to the primer coat in order to further improve the corrosion resistance.
This primer coat can be omitted.

The coating method of the coating composition of the present invention is not particularly limited, but it is preferably applied by a method such as roll coater coating or curtain flow coating. After coating, the coating film is baked by heating means such as hot air heating, infrared heating, induction heating, etc., and the resin is crosslinked to obtain a cured coating film. The baking treatment at the time of heating and curing is about 30 at about 200 to 250 ° C.
About 2 to 3 minutes is appropriate. The thickness of the cured coating film thus formed is usually about 15 to 25 μm, but is not particularly limited thereto.

The coating composition of the present invention is preferably used as a two-coat two-bake or three-coat three-bake topcoat, but is not limited thereto. When using the three-coat three-bake method, it is preferable to apply an intermediate coat between the coating with the coating composition of the present invention and the primer coat so as to be used in the usual three-coat three-bake. .

Further, in order to obtain a precoated steel sheet having particularly excellent hardness and workability, an undercoating film is formed on the surface of a galvanized steel sheet which has been subjected to a chemical conversion treatment such as a phosphate treatment or a chromate treatment. It is preferable to form an overcoat film comprising the above-mentioned coating composition of the present invention on the upper layer. As a zinc-based plated steel sheet that becomes the base steel sheet of this pre-coated steel sheet,
Hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, electro-galvanized steel sheet, hot-dip Zn-55% Al alloy coated steel sheet, hot-dip Zn-5% Al alloy coated steel sheet, Zn-Ni alloy-coated steel sheet, Zn-Co gold-plated steel sheet , Zn-Cr alloy plated steel sheet, composite zinc-based plated steel sheet (for example, Electric Z
n-SiO ₂ dispersion plating steel plate) various galvanized steel sheet or the like can be used.

In the forming process such as relatively gentle bending, the workability becomes better as the degree of elongation and flexibility of the coating film itself increases, but in the severe forming process such as drawing, the coating film becomes harder. In addition to the elongation and flexibility, the strength that can withstand the stress during deformation processing is an important factor in obtaining excellent workability. Therefore, in order to obtain high workability and high hardness performance by combining the undercoating film and the overcoating film, the elongation and strength of the undercoating film are important, and the undercoating film has a width of 5 mm.
It is preferred that the film has physical properties such that the breaking strength measured as a film having a thickness of 8 ± 1 μm and a breaking elongation of 50 mm / cm ² or more and 50% or more. If any one of the physical property values falls below the above lower limit value, the desired effect due to the combination with the overcoat film cannot be obtained.

There are no particular restrictions on the main component of the coating composition for forming the undercoat film, but from the viewpoint of processability and adhesion between the topcoat film and the chemical conversion film, polyester resins and epoxy resins are preferred. It is preferable to use a coating composition mainly composed of an epoxy-modified polyester resin such as a polyurethane resin, a urethane-based resin, or a bisphenol A-added polyester resin. Further, two or more of these resins may be used as a mixture. Examples of the resin used for the epoxy modification of the polyester resin include bisphenol A or bisphenol F type epoxy resin, and in addition, epihalohydrin (eg, epichlorohydrin) in the presence of a base catalyst (eg, potassium hydroxide). Hydrin)
(Eg, novolak type epoxy resin) and the like obtained by reacting the compound with an aldehyde (eg, formaldehyde) and a condensate of monohydric phenol or polyhydric polyphenol.

Usually, the physical properties of the undercoating film vary depending on the Tg of the resin used as the main component of the coating composition. However, in general, a coating film made of an epoxy-based undercoating paint has high breaking strength but breaks due to the molecular structure of the resin. The elongation is small, while a coating film made of a polyester-based undercoat or a urethane-based undercoat has a large breaking elongation but a small breaking strength. On the other hand, since the undercoating film formed of the coating composition containing the bisphenol A-added polyester resin as the main component has the molecular structure of both of the above resins, the breaking strength and the breaking elongation can be obtained in a well-balanced manner. Particularly preferred from the viewpoint of processability.

When the undercoat film is formed of a coating composition mainly composed of a polyester resin (including a modified polyester resin such as bisphenol A-added polyester resin. The same applies hereinafter), the undercoat film must have the above physical properties. To achieve this, the polyester resin has a number average molecular weight of 10
00 to 50,000, more preferably 3000 to 4000
It is desirable to use those having a value of 0, particularly preferably in the range of 5,000 to 30,000. When the number average molecular weight of the polyester resin is less than 1,000, the above-mentioned physical properties cannot be obtained due to insufficient elongation of the coating film, and the effect of improving the coating film performance is not sufficient. On the other hand, when the number average molecular weight exceeds 50,000, the coating composition becomes high in viscosity, so that an excess of a diluting solvent is required, and the proportion of the resin in the coating decreases, so that an appropriate coating film cannot be obtained. Furthermore, the compatibility with the blended components is significantly reduced.

When a bisphenol A-added polyester resin is used as the main component of the coating composition, the content of bisphenol A in the bisphenol A-added polyester resin is 1 to 70% by weight, more preferably 3 to 70% by weight, based on the resin solid content. -60% by weight, particularly preferably 5-50% by weight
It is desirable that If the content of bisphenol A in the bisphenol A-added polyester resin is less than 1% by weight, the effect of improving the strength of the coating film cannot be sufficiently obtained, and the effect of improving the performance of the coating film is not remarkable. On the other hand, when the content of bisphenol A exceeds 70% by weight, sufficient elongation of the coating film cannot be obtained.

Examples of the polyhydric alcohol for obtaining the polyester resin include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin,
Sorbitol, annitol, trimethylolethane,
Examples include trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, and the like, and a combination of two or more of these polyhydric alcohols can also be used.

The polybasic acid components for obtaining the polyester resin include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, hymic anhydride, trimellitic anhydride, and trimellit. Acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride , 1,4-cyclohexanedicarboxylic acid, etc., and these polybasic acid components can be used in combination of two or more.

As a curing agent used in a coating composition for an undercoat film, a polyisocyanate compound or an amino resin can be used. Also, two or more of these may be used as a mixture. Examples of the polyisocyanate compound used as a curing agent include aromatic diisocyanates such as xylylene diisocyanate, tolylene diisocyanate, and 4,4'-diphenylmethane diisocyanate;
Aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate;
Alicyclic diisocyanates such as isophorone diisocyanate; or a polymer of these diisocyanates or an adduct thereof with a polyhydric alcohol; and a blocking agent (for example, phenolic, lactam, alcohol, mercaptan, imine, (Amine-based, imidazole-based or oxime-based blocking agents) and the like. Further, as a dissociation catalyst for these blocked polyisocyanate compounds, tin octoate, dibutyltin dilaurate, 2-ethylhexoate lead and the like can be used.

Examples of the amino resin used as a curing agent include, for example, condensates of formaldehyde or paraformaldehyde alkyletherified with a lower alcohol and urea, dicyandiamide, aminotriazine and the like. Methylol urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, and the like. As the curing catalyst, acids such as hydrochloric acid, monoalkyl phosphate, and P-toluenesulfonic acid, or salts of these acids with tertiary amines or secondary amine compounds can be used.

Various additives such as rust preventive pigments can be appropriately added to the coating composition for the undercoating film according to the purpose and application. In particular, in order to improve the corrosion resistance of the entire coating film. The addition of a rust-preventive pigment is effective. As the rust-preventive pigment to be contained in the undercoat coating film, it is conceivable to use fine powder of a hardly soluble chromate such as strontium chromate, zinc chromate, barium chromate, etc., from the viewpoint that long-term corrosion resistance can be maintained. Is most preferred.

When strontium chromate is added to the undercoat film, the content thereof is 0.06 to 1 μm in thickness.
It is preferably 0.26 g / m ² . The content of strontium chromate is 0.06 g / m per 1 μm of film thickness.
^If it is less than ² , a sufficient corrosion resistance improvement effect cannot be obtained, while
If it exceeds 0.26 g / m ² , workability will be reduced. The dry film thickness of the undercoat film is preferably 2 to 12 μm.
When the film thickness is less than 2 μm, the effect of improving the workability by providing an undercoating film having specific physical properties or the effect of improving the corrosion resistance by providing the undercoating film to which strontium chromate is added cannot be sufficiently obtained. 12μm thick
If it exceeds 300, both the processability and the hardness of the coating film decrease.

An overcoat consisting of the above-described coating composition of the present invention is formed on the undercoat as described above. An appropriate amount of wax can be added to the coating composition for forming the overcoating film in order to improve the scratch resistance of the coating film. As this wax, a natural wax or a synthetic wax can be used. As the natural wax, for example, carnauba wax, paraffin wax, microcrystalline wax and the like can be used, and as a commercially available product, slip aid SL-506 is used.
(Manufactured by San Nopco), Slip Aid SL-523 (manufactured by San Nopco), Rio Flat W-7467 (manufactured by Toyo Ink Mfg.), High Desper-6413 (manufactured by Gifu Shellac) and the like.

As the synthetic wax, polyethylene wax or the like can be used, and commercially available products include Despalon 510-10X (manufactured by Kusumoto Kasei Co., Ltd.) and Paint Additive 371FP (manufactured by Matsushita Sangyo Co., Ltd.).
As the synthetic wax, a mixed wax can be used. Among them, a mixed wax of polyethylene wax and polytetrafluoroethylene (resin fine particles) is particularly preferable. As commercially available products of this mixed wax, Hydespar 4252 (manufactured by Gifu Shellac Co., Ltd.), SHAMROC
KS600 (manufactured by SHAMROCK) and the like. These waxes are used alone or in combination of two or more, and impart lubricity to the coating film.

The amount of the wax in the coating composition is preferably 0.3 to 30 parts by weight, based on 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the wax) in terms of solid content. Is from 0.3 to 20 parts by weight, more preferably from 0.5 to 10 parts by weight. 0.3% wax
If the amount is less than parts by weight, the effect of improving the lubricity of the coating film is not sufficient. On the other hand, if the amount of the wax exceeds 30 parts by weight, the wax is remarkably precipitated in the coating composition during low-temperature storage (winter), and the precipitated wax agglomerates may cause cissing and dents during the formation of the coating film. As a result, serious defects occur as a precoated steel sheet.

As described above, the amount of the wax in the coating composition is important from the viewpoint of imparting lubricity to the coating film, but from the viewpoint of preventing the coating film from fogging, the melting point of the wax is important. It is preferable to use a wax having a melting point of 100 ° C. or more in order to obtain a coating film having a large influence and a small haze. That is, if the melting point of the wax used is less than 100 ° C., the surface of the coating film becomes cloudy and the appearance of the coating film deteriorates. If the melting point of the wax is less than 100 ° C., the scratch resistance tends to deteriorate.

The above-mentioned various additives can be appropriately blended with the coating composition for the overcoat film in addition to the wax according to the purpose and application. The dry film thickness of the top coat is preferably 10 to 35 μm. 10 μm thick
If the thickness is less than the above, there is a possibility that the overall coating performance as a top coat may not be sufficiently obtained, while if the thickness exceeds 35 μm, the hardness of the coating decreases.

In actually using the coating compositions for forming the top coat and the undercoat, these are dissolved in an organic solvent before use. Examples of the organic solvent to be used include methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 100 (manufactured by Exxon Chemical), Solvesso 150 (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, ethyl acetate, butyl acetate, petroleum ether, petroleum naphtha and the like. . In preparing the coating composition, an ordinary dispersing machine or kneading machine such as a sand grind mill, a ball mill, and a blender can be selected and used, and the respective components can be blended.

The method of applying the coating composition (each coating composition for undercoating and topcoating) for producing the precoated steel sheet of the present invention is not particularly limited, but is preferably roll coater coating, curtain flow coating. It is preferable to apply by a method such as painting. After the coating composition is applied to both the undercoat film and the topcoat film, the coating film 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 film. The baking treatment at the time of heat-curing the undercoating film is usually performed at a plate temperature of about 180 to 260 ° C. for about 30 seconds to 1 minute. The baking treatment for heating and curing the top coat is usually performed at a plate temperature of about 180 to 260 ° C. for about 30 seconds to 3 minutes. In addition, the above-mentioned precoated steel sheet may form a coating film (for example, a clear coating film) on the top coating film, and may be used in three coats and three bake.

[0063]

【Example】

[Example 1] Compounds (1) to (3) used in this example
Examples of the synthesis of polyols and polyols (1) to (4) are shown below. Compound (1): Polyester compound In a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer, 1,4-cyclohexanedicarboxylic acid dimethyl ester (trans isomer ratio 20%, Towa Chemical Industry Co., Ltd.) 200 parts by weight) and 13 parts of ethylene glycol
0 parts by weight, titanium tetra-n-butoxide 0.5
Charge 3 parts by weight, raise the reaction temperature to 240 ° C,
It took about 5 hours to distill out 64 parts by weight of methanol to complete the reaction. Thus, compound (1) was obtained. This compound (1) is a white wax-like solid at room temperature, and has a mass spectrum (hereinafter abbreviated as FD-MS) by an electrolytic desorption / ionization method.
The molecular weight obtained by was 260.

Compound (2): Polyester compound In a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer, 1,4-cyclohexanedicarboxylic acid dimethyl ester (trans isomer ratio 99%, Towa Kasei Kogyo Co., Ltd.) 200 parts by weight, ethylene glycol 13
0 parts by weight, titanium tetra-n-butoxide 0.5
Charge 3 parts by weight, raise the reaction temperature to 240 ° C,
It took about 5 hours to distill out 64 parts by weight of methanol to complete the reaction. Thus, compound (2) was obtained. This compound (2) is a white wax-like solid at room temperature, and FD-M
The molecular weight determined by S was 260.

Compound (3): Polyester compound In a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer, 1,4-cyclohexanedicarboxylic acid dimethyl ester (trans isomer ratio 20%, Towa Chemical Industry Co., Ltd.) 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 raised to 240 ° C., and about 5 hours were required. Then, 64 parts by weight of methanol was distilled off to complete the reaction. Thus, compound (3) was obtained.
This compound (3) is a white waxy solid at room temperature.
The molecular weight determined by D-MS was 372.

Polyol (1) A polyester resin having a number average molecular weight of about 2,000 was used. Polyol (2) A polyester resin having a number average molecular weight of about 3000 was used. Polyol (3) A polyester resin having a number average molecular weight of about 5000 was used. -Polyol (4) An acrylic resin having a number average molecular weight of about 3000 was used. The chemical structural formulas of the compounds (1) to (3) described above are shown below.

Compound (1)

Embedded image

Compound (2)

Embedded image

Compound (3)

Embedded image

The following curing agents were used. HDI prepolymer (blocked polyisocyanate compound belonging to group (b) defined by the present invention): NCO content about 7% by weight, resin solids content about 75% by weight HDI isocyanurate (defined by the present invention ( b) blocked polyisocyanate compounds belonging to the group): NC
O content about 11% by weight, resin solids content about 75% by weight Hydrogenated MDI prepolymer (blocked polyisocyanate compound belonging to group (b) defined by the present invention): NCO
TDI prepolymer (blocked polyisocyanate compound belonging to group (a) defined by the present invention): NCO content: about 4% by weight, resin solids: about 50% by weight % By weight IPDI isocyanurate (as defined in the present invention (a)
Group of blocked polyisocyanate compounds): N
CO content about 8% by weight, resin solids content about 65% by weight MDI adduct (blocked isocyanate compound belonging to group (a) defined by the present invention): NCO content about 7
Weight%, resin solid content about 70% by weight

Compounds (1) to (3) described above, polyol
(1) to (4) and adjusting the coating composition using the curing agent,
This coating composition was applied to a steel sheet to produce precoated steel sheets of the present invention examples and comparative examples as shown below, and the coating film performance was examined. The results are shown in Tables 1 to 12 together with the composition of the coating composition and the like.

Invention Example 1 To 3.0 parts of the above compound (1), 40 parts of cyclohexanone was added and stirred for 12 hours. At this time, the compound (1) used was crushed by a crusher to 250 μm or less. With respect to the cyclohexanone dispersion of the compound (1) thus obtained, 55.3 parts of the polyol (1) was used as a curing agent, and hydrogenated as a blocked polyisocyanate compound of the group (b) defined by the present invention as a curing agent. 20. MDI prepolymer
9 parts, 20.9 parts of IPDI isocyanurate, which is a blocked polyisocyanate compound of the group (a) defined by the present invention, 100 parts of rutile-type titanium oxide, and dibutyltin dilaurate (hereinafter referred to as DBTDL) 10
% Cyclohexanone solution, 10.0 parts acronal 4
4.8 parts of 50% F (manufactured by BASF Corporation) cyclohexanone solution was blended and dispersed for about 30 minutes using a sand mill containing glass beads having a diameter of about 1 mm. Further, cyclohexanone was added to adjust the nonvolatile content to 60% to obtain a desired coating composition. This coating composition,
Hot-dip galvanized steel sheet (plate thickness: 0.5 μm) with chromate treatment and polyester-based primer (film thickness: about 5 μm)
mm, 0.4 mm) with a bar coater so as to have a dry film thickness of 15 to 18 μm, and baked in a hot air drying furnace at 230 ± 5 ° C. for 60 seconds to obtain a precoated steel sheet.

Inventive Examples 2 to 4 In the same combination of the compound, polyol and curing agent as in Inventive Example 1, the content of compound (1) was changed, and the formulations shown in Table 1 were the same as in Inventive Example 1. Was adjusted to obtain the desired coating composition. The ratio of the compound (1) in the resin solid content was 5.0% by weight in Examples 2, 3, and 4 of the present invention, respectively.
0.0 wt% and 18.0 wt%. The coating composition was applied to a steel sheet and baked in the same manner as in Example 1 of the present invention to obtain a precoated steel sheet.

Examples 5 to 10 of the present invention As a curing agent, a TDI prepolymer which is a blocked polyisocyanate compound of the group (a) defined by the present invention, I
One of PDI isocyanurate and MDI adduct is mixed with one of HDI prepolymer, HDI isocyanurate and hydrogenated MDI prepolymer which is also a blocked polyisocyanate compound of group (b) The same preparation as in Example 1 of the present invention was carried out using the obtained curing agent with the composition shown in Table 1, to obtain the intended coating composition. The coating composition was applied to a steel sheet and baked in the same manner as in Example 1 of the present invention to obtain a precoated steel sheet.

Inventive Examples 11 to 17 Compounds (2) and (3) are used as polyester compounds, and TDI prepolymers, IPDIs, which are blocked polyisocyanate compounds of group (a) defined by the present invention, are used as curing agents. One of an isocyanurate and an MDI adduct, and one of an HDI prepolymer, an HDI isocyanurate and a hydrogenated MDI prepolymer which is also a blocked polyisocyanate compound of group (b)
The same preparation as in Example 1 of the present invention was carried out using the curing agent mixed with the seed and in the composition shown in Table 3, to obtain the intended coating composition.
This coating composition was applied to a steel sheet and baked in the same manner as in Inventive Example 1 to obtain a precoated steel sheet.

Comparative Example 1 To 3.0 parts of compound (1), 40 parts of cyclohexanone was added and stirred for 12 hours. At this time, the compound (1) used was crushed by a crusher to 250 μm or less. 54.6 parts of polyol (1), 42.4 parts of hydrogenated MDI prepolymer as a curing agent, 100 parts of rutile type titanium oxide as a curing agent were added to the cyclohexanone dispersion of compound (1) thus obtained. After mixing 10.0 parts of DBTDL 10% cyclohexanone solution and 4.8 parts of Acronal 4F 50% cyclohexanone solution, they were dispersed for about 30 minutes using a sand mill containing glass beads having a diameter of about 1 mm. Further, cyclohexanone was added to adjust the nonvolatile content to 60% to obtain a desired coating composition.
The prepared coating composition is coated on a hot-dip galvanized steel sheet (thickness: 0.5 mm, 0.4 mm) that has been subjected to chromate treatment and a polyester-based primer (thickness: about 5 μm) to have a dry film thickness of 15 to 18 μm. Was coated with a bar coater and baked in a hot air drying oven at 230 ± 5 ° C. for 60 seconds to obtain a precoated steel sheet.

Comparative Example 2 Comparative Example in which the IPDI isocyanurate alone was used as a curing agent (other components and amounts were almost the same as Comparative Example 1).
The same preparation as in Comparative Example 1 was performed with the composition shown in Table 5 to obtain the desired coating composition. This coating composition was applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet. Comparative Examples 3 and 4 Comparative examples in which a hydrogenated MDI prepolymer and an IPDI isocyanurate compound were used alone as curing agents (other components and amounts were almost the same as those of Example 2 of the present invention). The same operation as in Comparative Example 1 was performed with the above composition to obtain the desired coating composition. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 5 and 6 Comparative examples in which a hydrogenated MDI prepolymer and an IPDI isocyanurate compound were used alone as curing agents (other components and amounts were almost the same as those of Example 3 of the present invention). The same operation as in Comparative Example 1 was performed with the composition shown in No. 5 to obtain the desired coating composition. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 7 to 10 Polyol (1) as a polyol, compound (1) as a polyester compound, and one of HDI prepolymer, HDI isocyanurate, TDI prepolymer and MDI adduct as a curing agent This is a comparative example in which each type of blocked polyisocyanate compound was used alone, and the same operation as in Comparative Example 1 was performed with the composition shown in Table 5 to obtain a target coating composition. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 11 and 12 Comparative examples in which a hydrogenated MDI prepolymer and a TDI prepolymer were used alone as curing agents (other components and amounts were almost the same as those of Example 11 of the present invention). And the same operation as in Comparative Example 1 was carried out using the composition shown in (1) to obtain the desired coating composition. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 13 and 14 Comparative examples using the HDI isocyanurate compound and the MDI adduct compound alone as the curing agent (other components and compounding amounts are almost the same as those of the inventive example 15). The same operation as in Comparative Example 1 was performed with the indicated composition to obtain the desired coating composition. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 15 and 16 Comparative examples in which HDI isocyanurate and IPDI isocyanurate alone were used alone as curing agents (other components and compounding amounts were almost the same as those of Example 17 of the present invention). And the same operation as in Comparative Example 1 was carried out using the composition shown in (1) to obtain the desired coating composition. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 17 and 18 Comparative examples in which the content of compound (1) was changed in the same combination of the compound, polyol and curing agent as in Example 1 of the present invention. Were prepared in the same manner as in the above to obtain a desired coating composition. The ratio of the compound (1) in the resin solid content was 0.3% by weight and 20.0% by weight in Comparative Examples 17 and 18, respectively. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 19 and 20 This is a comparative example in which the combination of the curing agent was changed in the same compounds and polyols as those of Example 15 of the present invention. Was obtained. In Comparative Example 19, the combination of the curing agent in the coating composition was the HDI isocyanurate compound and the hydrogenated MDI prepolymer,
In Comparative Example 20, an IPDI isocyanurate and an MDI adduct were used. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

Comparative Examples 21 and 22 Comparative examples in which the same compound, polyol and curing agent as in Example 2 of the present invention were used but the blending ratio between the hydrogenated MDI prepolymer as the curing agent and the IPDI isocyanurate was changed. Yes, the same adjustments as in Comparative Example 1 were performed with the formulations shown in Table 11 to obtain the desired coating composition. The curing agent ratio (A) / (B) in the coating composition was 20/80 in Comparative Example 21, and Comparative Example 2
In No. 2, the ratio was 80/20. Comparative Example 1
Coating and baking were performed on the steel sheet in the same manner as in the above to obtain a precoated steel sheet.

Comparative Examples 23 and 24 In the same combination of the compound, polyol and curing agent as in Example 6 of the present invention, an isocyanate group [NC
O] and the hydroxyl group [O] in the compound (1) and the polyol (1).
H] and Comparative Example 1 in which the molar ratio [NCO] / [OH] was changed, and the same adjustment as in Comparative Example 1 was performed with the composition shown in Table 11 to obtain a target coating composition. The molar ratio [NCO] / [OH] in the coating composition was 0.7 in Comparative Example 23 and 1.3 in Comparative Example 24. These coating compositions were applied to a steel sheet and baked in the same manner as in Comparative Example 1 to obtain a precoated steel sheet.

The conditions and evaluation methods of each characteristic test and the like performed in this example are shown below. (1) Appearance The quality of the surface properties of the coating film after baking was visually judged. (2) Gloss The 60 ° specular reflectance (%) was measured based on JIS K5400 7.6 and evaluated as follows. ：: Glossiness of 80 or more ○: Glossiness of 70 or more and less than 80 Δ: Glossiness of 60 or more and less than 70 ×: Glossiness of less than 60 (3) Pencil hardness JIS K5400 8.
4.2 based on the hardness limit that does not scratch (however,
H + indicates H to 2H, and F + indicates F to H).

(4) Workability (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 cracking of the coating film was used as an evaluation value, and the number of sheets was indicated with T, such as 1T, 2T, and 3T. The evaluation of the workability was performed on both steel plates having a thickness of 0.5 mm and a thickness of 0.4 mm as follows. Workability 1: Plate thickness 0.5 mm (0.45 to 0.50 mm)
Uses hot-dip galvanized steel sheet. Workability 2: Sheet thickness 0.4 mm (0.35 to 0.40 mm)
Uses hot-dip galvanized steel sheet

(5) Impact resistance Using a Dupont impact tester, JIS K5400 8.
According to 3.2, a load of 1.0 kg or 1.5 kg is dropped onto the coating film from a height of a maximum of 50 cm, and when observed with a 30-power loupe, the coating film has a maximum height at which cracks on the coating film surface are not seen. The value multiplied by the load was used as the evaluation value.

(6) Solvent resistance (number of MEK rubbing times) The surface of the coating film was rubbed with a load of 1.0 kg using gauze impregnated with methyl ethyl ketone, and the number of times of one reciprocation was counted as the number of times until the primer was exposed. Expressed. However, the upper limit was set to 100 times.

(7) Stain Resistance (Marking Pen Stain Resistance) In accordance with JIS K5400 8.10, the surface of the coating film is painted with a red and black quick-drying oil-based marking pen in a room at 20 ° C., and after 24 hours And a cotton wool containing a 50/50 solution of petroleum benzene / ethanol and wiped with
(= [L, a, b values after test]-[L, a, b before test]
Value] (4.2 of JIS Z8722).
The measurement was performed using a spectrometer according to ◎: ΔE is 0 or more to less than 5 ：: ΔE is 5 or more to less than 15 Δ: ΔE is 15 or more to less than 25 ×: ΔE is 25 or more

[0092]

[Table 1]

[0093]

[Table 2]

[0094]

[Table 3]

[0095]

[Table 4]

[0096]

[Table 5]

[0097]

[Table 6]

[0098]

[Table 7]

[0099]

[Table 8]

[0100]

[Table 9]

[0101]

[Table 10]

[0102]

[Table 11]

[0103]

[Table 12]

According to Tables 1 to 12, the present invention example is excellent in hardness, workability and stain resistance even when the steel sheet thickness is 0.5 mm and 0.4 mm, and also in gloss and solvent resistance. Are better. On the other hand, Comparative Examples 1 to 16 are comparative examples in which the blocked polyisocyanate compound of any one of the groups (a) and (b) defined by the present invention was used alone. Comparative example is 0.5mm thick
In the case of, although the hardness and workability are balanced to some extent by the effect of the polyester compound showing anisotropy, in many cases the stain resistance is poor, and if the stain resistance is excellent, Workability and impact resistance at a thickness of 0.4 mm are insufficient.

Comparative Examples 17 and 18 are comparative examples in which the compounding amount of the polyester compound was out of the range of the present invention. Among them, those in which the compounding amount of the polyester compound was too small were inferior in the coating film hardness and stain resistance. . On the other hand, when the amount of the polyester compound is too large, the smoothness of the coating film surface is reduced, and accordingly, the glossiness is reduced and the stain resistance is reduced due to the physical action. In Comparative Examples 19 and 20, a curing agent obtained by mixing two kinds of blocked polyisocyanate compounds in the same group among the blocked polyisocyanate compounds of the groups (a) and (b) defined by the present invention was used. These are comparative examples, and all of the comparative examples are not balanced in hardness, workability, and stain resistance, and are inferior in at least one of the characteristics.

Comparative Examples 21 and 22 are comparative examples in which the blending ratio (curing agent ratio) of the blocked polyisocyanates of the groups (a) and (b) deviated from the range defined in claim 2 of the present application. In any of the comparative examples, the hardness of the coating film, the workability, and the stain resistance are not balanced, and at least one of the characteristics is inferior. In Comparative Examples 23 and 24, the molar ratio [N] of the isocyanate group [NCO] in the curing agent to the hydroxyl group [OH] in the polyester compound of b) and the polyol of b) was used.
CO] / [OH] are comparative examples that deviate from the range defined in claim 3 of the present application. In each comparative example, the balance of the coating film hardness, workability, and stain resistance is not balanced. In any case, one of the characteristics is inferior.

[Example 2] A sheet thickness of 0.5 m, which is a base steel sheet
m hot-dip galvanized steel sheet (coating weight per side: 3
0 g / m ² ), and a coating type chromate-based treating agent (“Surfcoat NRC300” manufactured by Nippon Paint Co., Ltd.)
To form an undercoating film with the coating composition for an undercoating film shown in Tables 15 and 16, and further overcoat with a coating composition for a topcoating film as shown in Table 17 A desired precoated steel sheet was obtained by forming a film. Tables 18 and 19 show the performance of these precoated steel sheets together with the production conditions. The coating compositions A-1 to A-4 and B-1 to B-4 for the undercoat shown in Tables 15 and 16 and the coating composition C-1 for the topcoat shown in Table 17 are as follows. Was adjusted.

(1) Coating composition for undercoat coating film (1-1) Preparation of polyester resins a-1 to a-4 A reaction vessel equipped with a heating device, a stirrer, a rectification tower, a decompression device, and a thermometer Was charged with dimethyl terephthalate, dimethyl isophthalate, adipic acid, ethylene glycol, neopentyl glycol, 1,6-hexanediol and manganese acetate in a composition as shown in Table 13, and in a nitrogen atmosphere, at 160 to 220 ° C. The transesterification reaction was performed by gradually increasing the temperature over about 4 hours at a temperature to distill off methanol. Further, under a reduced pressure of 0.5 to 5.0 mmHg, a polycondensation reaction was performed at 260 ° C. for about 2 hours to obtain polyester resins a-1 to a-4 shown in Table 13. The obtained polyester resin was dissolved in a mixed solvent of cyclohexanone / solvesso 150 (weight ratio: 50/50) to obtain a nonvolatile content of 40/50.
%. Further, the molecular weight of the polyester resin was adjusted by the polycondensation reaction time. The molecular weight was measured by gel permeation chromatography, and the number average molecular weight in terms of polystyrene was measured.

(1-2) Preparation of bisphenol A-added polyester resin b-1 to b-4 A reaction vessel equipped with a heating device, a stirrer, a rectification tower, a decompression device and a thermometer was prepared as shown in Table 14. Charge dimethyl terephthalate, dimethyl isophthalate, ethylene glycol, ethylene oxide 2 mol adduct of bisphenol A and manganese acetate, and raise the temperature stepwise in a nitrogen atmosphere at a temperature of 160 to 220 ° C for about 4 hours. Then, a transesterification reaction was performed, and methanol was distilled off. Further, under a reduced pressure of 0.5 to 5.0 mmHg,
The polycondensation reaction was performed at 60 ° C. for about 2 hours to obtain bisphenol A-added polyester resins b-1 to b-4 shown in Table 14. The obtained bisphenol A-added polyester resin was mixed with cyclohexanone / solvesso 150 in a mixed solvent (weight ratio: 50).
/ 50) to prepare a nonvolatile content of 40%. Also,
The molecular weight of the bisphenol A-added polyester resin was adjusted by the polycondensation reaction time. The molecular weight was measured by gel permeation chromatography, and the number average molecular weight in terms of polystyrene was measured.

(1-3) Coating Compositions A-1 to A- for Undercoat Film
4, Production of B-1 to B-4 The polyester resins a-1 to a- obtained in the above (1-1) and (1-2)
4. Coating compositions A-1 to A-4 and B-1 to B-4 are produced using bisphenol A-added polyester resins b-1 to b-4 in the proportions shown in Tables 15 and 16. did. Strontium chromate as a pigment was added to these coating compositions and dispersed by a sand mill until the pigment particle size became 5 μm or less. Tables 15 and 16 show the amounts of strontium chromate per 1 μm of the dry film thickness. The elongation at break and the breaking strength of each undercoat film were 5 m in width from each coating composition.
m, a free film (film piece) having a thickness of 8 ± 1 μm was prepared, and the free film was stretched at a pulling speed of 10 mm / cm by a Tensilon tensile tester manufactured by Orientec.
It was measured in min.

(2) Coating composition for overcoating film The polyester resin of compound (1) used in the above [Example 1], polyester resin, curing agent, pigment, curing catalyst in the mixing ratio shown in Table 17 After blending the additives and the additives, the mixture was dispersed for about 30 minutes using a sand mill containing glass beads having a diameter of about 1 mm. Further, cyclohexanone was added to adjust the nonvolatile content to 60%, thereby producing a coating composition C-1.

The conditions and evaluation methods of each characteristic test and the like performed in this example are shown below. (1) Appearance Same as [Example 1] (2) Pencil hardness Same as [Example 1]

(3) Workability 3 (Bending workability) At room temperature of 20 ° C., the V-shaped bending of the steel sheet was previously performed at a speed of 10 mm / min using the V-shaped bending mold shown in FIG. After that, 180 ° contact bending (0T bending) test and 1T
A bending test was performed, the surface of the coating film in the processed portion was observed with a 30-fold loupe, and the presence or absence of minute pinholes or cracks in the coating film was examined. A: No fine pinholes or cracks were observed on the coating film surface. ：: 1 to 5 fine pinholes / cm were observed on the coating film surface. B: 6 to 20 minute pinholes / cm were observed on the coating film surface. C: More than 20 pinholes / cm were observed on the coating film surface, and cracks were also observed.

(4) Adhesion (cross-cut peeling) test (JI
(Based on 8.5 (adhesion) of SK 5400) 10 times at 1 mm intervals on the cured coating film surface using a cutter knife.
100 squares were cut in a range of mm × 10 mm, and an adhesive tape was pressed on the squares, and then vigorously peeled off, and the state of peeling of the squares was observed and evaluated according to the following criteria. ◎: No peeling of the coating film ○: 90 or more and less than 100 crossing residuals △: 80 or more and less than 90 crossing residuals ×: less than 80 crossing residuals

[0115]

[Table 13]

[0116]

[Table 14]

[0117]

[Table 15]

[0118]

[Table 16]

[0119]

[Table 17]

[0120]

[Table 18]

[0121]

[Table 19]

According to Tables 18 and 19, by forming an overcoating film comprising the coating composition of the present invention on the upper layer of the undercoating film having specific physical properties, particularly excellent workability (bending workability). It can be seen that a precoated steel sheet having evaluated workability) and coating film hardness can be obtained.

[Example 3] The thickness of the base steel sheet was 0.5 m.
m hot-dip galvanized steel sheet (coating weight per side: 3
0 g / m ² ), and a coating type chromate-based treating agent (“Surfcoat NRC300” manufactured by Nippon Paint Co., Ltd.)
To form an undercoat with the coating composition for the undercoat shown in Table 20, and further form a topcoat with the coating composition for the overcoat shown in Table 21 Thus, a desired precoated steel sheet was obtained. Table 2 shows the performance of these precoated steel sheets together with the manufacturing conditions.
2, shown in Table 23. Coating compositions P-1 to P-4 for undercoating films shown in Table 20 and coating compositions for overcoating films shown in Table 21
C-2 was adjusted as follows.

(1) Coating composition for undercoat coating film The resin component and the pigment were mixed in the mixing ratio shown in Table 20, and dispersed by a sand mill until the pigment particle size became 5 μm or less. ~ P-4 was produced.

(2) Coating composition for top coat The polyester resin, the curing agent, the pigment, the curing catalyst and the additives are added to the compound (1) used in the above [Example 1] in the mixing ratio shown in Table 21. Was dispersed in a sand mill containing glass beads having a diameter of about 1 mm for about 30 minutes. Further, by adding cyclohexanone, the nonvolatile content becomes 60%.
% To prepare a coating composition C-2.

The test method and evaluation method of the performance test of the precoated steel sheet will be described below. (1) Appearance Same as [Example 1] (2) Pencil hardness Same as [Example 1]

(3) Workability (Bendability) At room temperature of 20 ° C., JIS G 3312.
After bending the steel plate in advance using the bending vise specified in 2 (Bending test), the steel plate was bent 180 °, and the coating surface of the processed part was observed with a 30-fold loupe. The presence or absence of (cracks) was examined and evaluated according to the following criteria. A: No fine pinholes or cracks were observed on the coating film surface. ：: 1 to 5 fine pinholes / cm were observed on the coating film surface. B: 6 to 20 minute pinholes / cm were observed on the coating film surface. C: More than 20 pinholes / cm were observed on the coating film surface, and cracks were also observed.

(4) Adhesion (cross-cut peeling) test Same as in [Example 2] (5) Flat plate corrosion resistance (based on 9.1 (salt water spray resistance) of JIS K 5400) Apply tape seals on the top and bottom,
Test pieces were prepared such that the cut ends on the right and left sides were upper burrs (cut from the non-painted surface side) and lower burrs (cut from the painted surface side), respectively, and were subjected to a salt spray test (SST) for 240 hours. Thereafter, a tape peeling test was performed on the cut end portion of the upper burr of the test piece, and the corrosion resistance was evaluated according to the following criteria. ：: Peeling of the coating from the cut end is less than 3 mm ：: Peeling of the coating from the cut end is 3 mm or more and less than 5 mm ：: Peeling of the coating from the cut end is 5 mm or more and less than 10 mm ×: Cut end 10mm or more of film peeling from

[0129]

[Table 20]

[0130]

[Table 21]

[0131]

[Table 22]

[0132]

[Table 23]

According to Tables 22 and 23, a precoated steel sheet having particularly excellent corrosion resistance was formed by forming an overcoating film comprising the coating composition of the present invention on the undercoating film to which an appropriate amount of strontium chromate was added. Is obtained.

[Example 4] The thickness of the base steel sheet was 0.5 m.
m hot-dip galvanized steel sheet (coating weight per side: 3
0 g / m ² ), and then subjected to a coating type chromate treatment (the amount of chromium adhered in terms of chromium metal: 30 mg / m ² ).
On top of that, a polyester-based primer with a dry film thickness of 5 μm
After the application, a baking treatment was performed at an ultimate plate temperature of 215 ° C. and a baking time of 60 seconds to form an undercoating film. Further, a coating composition for an overcoating film shown in Table 17 was formed thereon. After applying the wax to which the wax shown in Table 24 was added, a baking treatment was performed at a reaching plate temperature of 230 ° C. and a baking time of 60 seconds to form an overcoat film to obtain a desired precoated steel sheet. Table 25 shows the performance of these precoated steel sheets together with the production conditions.

The test method and the evaluation method of the performance test of the precoated steel sheet are described below. (1) Appearance Same as [Example 1] (2) Pencil hardness Same as [Example 1]

(3) Abrasion of forming rolls Roll forming machine (roll material: steel-chrome plating)
For a test piece of size 10 cm x 30 cm,
Forming was performed under a roll forming condition of a processing speed of 2 m / min and a processing step number of eight steps. The surface of the coating film after the formation was observed and evaluated as follows. ：: No abnormality at all △: Slight scratch ×: Abnormal

(4) Cylindrical drawing workability Using a cylindrical drawing machine, for a test piece of size 10 cm × 10 cm, sample size: 90φ, die: 42.4
φ5R, plunger: 40.4φ4R, hold pressure:
Molding was performed under a 2.0-ton cylindrical drawing condition, and the coating film surface after the molding was observed and evaluated as follows. ：: No abnormality Δ: Slight scratch ×: Abnormal (5) Repeated abrasion Using a repeated abrasion machine, the number of times until the coating film was scratched was measured and evaluated.

[0138]

[Table 24]

[0139]

[Table 25]

According to Table 25, a precoated steel sheet having excellent scratch resistance can be obtained by forming an overcoating film of the coating composition of the present invention in which an appropriate amount of wax was added to the upper layer of the undercoating film. I understand.

[0141]

As described above, the coating composition for a pre-coated steel sheet of the present invention can highly satisfy both workability and coating film hardness and can obtain a coating film having extremely excellent stain resistance. . Therefore, the precoated steel sheet having such a coating film is extremely useful as a material for home electric appliances and building materials. In addition, a precoated steel sheet in which an undercoating film and an overcoating film of the coating composition of the present invention are formed on the surface of a zinc-coated steel sheet subjected to a chemical conversion treatment, excellent workability,
Has coating film hardness, coating appearance, and adhesion. Also, among them, the precoated steel sheet having an undercoat film having specific physical properties has particularly excellent workability, and the precoated steel sheet having an undercoat film to which an appropriate amount of strontium chromate is added is particularly excellent. Pre-coated steel sheet with corrosion resistance, and further formed with a top coat coated with an appropriate amount of wax, has particularly excellent scratch resistance, and has the property that clouding of the coating film surface due to aggregation of the wax hardly occurs. ing. Therefore, these precoated steel sheets are extremely useful as precoated steel sheets used in parts requiring high coating film hardness and formability in applications such as home appliances, building materials, and automobiles. In addition, these precoated steel sheets are industrially extremely useful in that they can be manufactured by a simpler method than before.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a mold and a processing method for V-shaped bending.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 6, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

Embedded image 1 to 18% by weight of a polyester compound having as a main repeating unit in a resin solid content; b) a polyol other than the above a); and c) a polyisocyanate of the following group (a) and its derivatives. A blocked polyisocyanate compound obtained by blocking one or more of the obtained polyisocyanate compounds and one or more polyisocyanate compounds selected from the following polyisocyanates of the group (b) and derivatives thereof A curing agent mixed with the obtained blocked polyisocyanate compound (a) 4,4'-diphenylmethane diisocyanate,
Isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthoquinone data Ren 1,5
-Diisocyanate (b) a coating composition for a precoated steel sheet mainly containing a resin component consisting of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylylene diisocyanate Stuff.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The present invention has been made on the basis of such findings, and the characteristic configuration thereof is as follows. [1] b) General formula (1)

Embedded image 1 to 18% by weight of a polyester compound having as a main repeating unit in a resin solid content; b) a polyol other than the above a); and c) a polyisocyanate of the following group (a) and its derivatives. A blocked polyisocyanate compound obtained by blocking one or more of the obtained polyisocyanate compounds and one or more polyisocyanate compounds selected from the following polyisocyanates of the group (b) and derivatives thereof A curing agent mixed with the obtained blocked polyisocyanate compound (a) 4,4'-diphenylmethane diisocyanate,
Isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthoquinone data Ren 1,5
-Diisocyanate (b) a coating composition for a precoated steel sheet mainly containing a resin component consisting of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylylene diisocyanate Stuff.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

(A) 4,4'-diphenylmethane diisocyanate (hereinafter referred to as MDI), isophorone diisocyanate (hereinafter referred to as IPDI), tolylene diisocyanate (hereinafter referred to as TDI), xylylene diisocyanate (hereinafter referred to as XDI), naphthene data Ren -1,
5-diisocyanate (hereinafter referred to as NDI) (b) Hexamethylene diisocyanate (hereinafter HDI)
), Trimethylhexamethylene diisocyanate (hereinafter referred to as TMDI), hydrogenated 4,4'-diphenylmethane diisocyanate (hereinafter referred to as hydrogenated MDI),
Hydrogenated tolylene diisocyanate (hereinafter referred to as hydrogenated TDI), hydrogenated xylylene diisocyanate (hereinafter referred to as hydrogenated X)
DI)

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08G 18/72 C08G 18/72 W (72) Inventor Masaru Sagiyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Masaaki Yamashita, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Inventor Yasuyuki Kajita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Inventor Hiroyuki Kato 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Kenichi Sasaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan 1-2 ) Inventor Keiichi Kotani 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Yasuhiro Toyoda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Mamoru Ehara 4-1-1-15 Minamishinagawa, Shinagawa-ku, Tokyo Nippon Paint Co., Ltd. Tokyo Office (72) Inventor Katsuyoshi Tanaka 4-1-1 Minamishinagawa, Shinagawa-ku, Tokyo No. 15 Nippon Paint Co., Ltd. Tokyo office

Claims (16)

[Claims] 1. A) General formula (1) 1 to 18% by weight of a polyester compound having as a main repeating unit in a resin solid content; b) a polyol other than the above a); and c) a polyisocyanate of the following group (a) and its derivatives. A blocked polyisocyanate compound obtained by blocking one or more of the obtained polyisocyanate compounds and one or more polyisocyanate compounds selected from the following polyisocyanates of the group (b) and derivatives thereof A curing agent mixed with the obtained blocked polyisocyanate compound (a) 4,4'-diphenylmethane diisocyanate,
Isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene-1,5
-Diisocyanate (b) a coating composition for a precoated steel sheet mainly containing a resin component consisting of hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylylene diisocyanate Stuff. 2. A blocked polyisocyanate compound (A) obtained by blocking at least one polyisocyanate compound selected from the group (a) polyisocyanates and derivatives thereof, and a polyisocyanate group (b). The mixing ratio of the blocked polyisocyanate compound (B) obtained by blocking at least one polyisocyanate compound selected from isocyanates and derivatives thereof is (A) / (B) = The coating composition for a precoated steel sheet according to claim 1, wherein the coating composition has a ratio of 70/30 to 30/70. 3. The molar ratio [NCO] / [C] of the curing agent of (c) to the total of the isocyanate group [NCO] in the curing agent and the hydroxyl group [OH] in the polyester compound of (a) and the polyol of (b). OH] is 0.8 to 1.2. The coating composition for a precoated steel sheet according to claim 1 or 2, wherein the coating composition is 0.8 to 1.2. 4. A blocked polyisocyanate compound obtained by blocking a polyisocyanate compound selected from the group (a) polyisocyanates and derivatives thereof, wherein the blocked polyisocyanate compound is selected from the group consisting of an isocyanurate compound, an adduct compound and a prepolymer. And a blocked polyisocyanate compound obtained by blocking a polyisocyanate compound selected from the group (b) polyisocyanates and derivatives thereof is a buret, isocyanurate,
4. The coating composition for a precoated steel sheet according to claim 1, which is one of an adduct body and a prepolymer. 5. The method according to claim 1, wherein the polyol other than (a) is 2 per molecule.
Having at least one hydroxyl group and having a number average molecular weight of 1500 to 1
2000 or more acrylic resins and / or two or more hydroxyl groups in one molecule and a number average molecular weight of 1000 to 80
The coating composition for a pre-coated steel sheet according to claim 1, which is a polyester resin of No. 00. 6. A precoated steel sheet having a coating film formed by applying the coating composition according to claim 1, 2, 3, 4, or 5. 7. A precoated steel sheet having an undercoat film and an overcoat film on the surface of a galvanized steel sheet which has been subjected to a chemical conversion treatment, wherein the overcoat film is formed on the surface thereof.
Or a precoated steel sheet excellent in hardness and workability, which is a coating film formed by applying the coating composition according to 5. 8. An undercoating film having a width of 5 mm and a thickness of 8 ± 1 μm.
The breaking strength measured as a 50 m / m film is 50 kg / c.
precoated steel sheet excellent in hardness and workability according to claim 7, and elongation at break in m ² or more is equal to or less than 50%. 9. The hardness and processability according to claim 8, wherein the undercoating film is a coating film formed by applying a coating composition containing a bisphenol A-added polyester resin as a main component. Excellent pre-coated steel sheet. 10. The pre-coated steel sheet according to claim 7, wherein the undercoat film contains strontium chromate in an amount of 0.06 to 0.26 g / m ² per 1 μm of film thickness. 11. The precoat having excellent hardness and workability according to claim 10, wherein the undercoat coating is a coating formed by applying a coating composition containing a polyester resin as a main component. steel sheet. 12. The undercoat film having a dry film thickness of 2 to 12 μm.
The precoated steel sheet excellent in hardness and workability according to claim 7, 8, 9, 10 or 11. 13. The overcoating film is characterized by containing 0.3 to 30 parts by weight of wax with respect to 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the wax) in terms of solid content. A precoated steel sheet having excellent hardness and workability according to claim 7. 14. The precoated steel sheet having excellent hardness and workability according to claim 13, wherein the melting point of the wax contained in the overcoat film is 100 ° C. or higher. 15. The precoated steel sheet having excellent hardness and workability according to claim 13, wherein the wax contained in the top coat is a mixture of polyethylene wax and polytetrafluoroethylene. 16. After applying a coating composition for an undercoat coating film on the surface of a galvanized steel sheet subjected to a chemical conversion treatment,
A baking treatment is performed at an ultimate plate temperature of 0 to 260 ° C., and then, after the coating composition according to claim 1, 2, 3, 4, or 5 is applied for a top coat, an ultimate plate temperature of 180 to 260 ° C. A method for producing a precoated steel sheet having excellent hardness and workability, characterized by baking treatment.