JP2001026745A - Coating composition for precoated steel plate, precoated steel plate excellent in forming processability and creak resistance, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of providing precoated steel plates having high coating film hardness and axcellent forming processability under severe forming process conditions, and also excellent in creak resistance, by including a specific polyester compound, a curing agent and organic resin beads, etc., in a specific proportion. SOLUTION: This composition is obtained by mainly including, based on the resin solid content, (A) 1-15 wt.% of a polyester compound with the main recurring unit of formula I ((n) is 2 to 10; R is a polyoxymethylene, neopentylene or the like; and R' is formula II or the like), (B) 40 to 90 wt.% of a polyol except the component A, and (C) 9 to 50 wt.% of a curing agent comprising, pref. a blocked polyisocyanate compound, and including (D) 0.3 to 30 pts.wt. of organic resin beads pref. such as of a urethane resin with an average particle diameter of pref. 0.1 to 10 μm (a value converted to the diameter of a sphere having the same volume), based on 100 pts.wt. of the resin composition (weight of the coating composition except the component D) on a solid basis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a paint composition, a precoated steel sheet using the paint composition, and a method for producing the same. 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 Conventionally, paints for pre-coated steel sheets include:
A polyester resin or an epoxy resin is mainly used for the outer surface undercoat and the back surface paint, and a polyester, acrylic, vinyl, etc. paint is used for the outer surface topcoat. The most common outer coating on the outer surface is a polyester resin coating composed of a combination of a polyester resin (main component) and a melamine compound (curing agent). Hardness. However, when this outer surface top coat is applied to a pre-coated steel sheet having strict performance requirements, particularly a pre-coated steel sheet for home appliances, the obtained performance cannot be said to be sufficient.

One of the important performances required for a precoated steel sheet is squeak resistance. In other words, when a pre-coated steel sheet processed like an indoor partition is used in combination with a metal frame such as aluminum, when an external force is applied by pressing by hand or the like, the metal frame comes into contact with the pre-coated steel sheet. Sound (squeaking sound)
The precoated steel sheet is required to have such a performance that it does not easily generate such "squeak noise". However, the conventional paint for pre-coated steel sheet has not sufficiently satisfied such required characteristics.

[0004] Conventionally, a coating composition for a coating film capable of satisfying a high degree of processability and coating film hardness has been disclosed in, for example, Japanese Patent Application Laid-Open No. 7-1995.
In 233349, a coating composition containing a polyol as a main component and an isocyanate compound and / or an amino resin as a curing agent is obtained by reacting naphthalene-2,6-dicarboxylic acid and / or a lower alkyl ester thereof with an alcohol component. There has been proposed a coating composition for a precoated steel sheet to which a polyester compound to be added is added.

[0005]

However, Japanese Patent Laid-Open No.
In the coating composition of No. 233349, although a coating film having good workability (for example, bending workability) and hardness can be obtained, the above-described squeak noise resistance (characteristics in which squeak noise is unlikely to occur) is as described above. Satisfactory performance cannot be obtained. Conventionally, it is generally thought that increasing the hardness of the coating film is effective in reducing the squeak noise and improving the squeak noise resistance. There is a problem that is lost.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a precoat having high coating film hardness, high formability in severe forming, and excellent squeak noise resistance. An object of the present invention is to provide a coating composition for a precoated steel sheet that can obtain a steel sheet. Another object of the present invention is to provide a precoated steel sheet using the above-described coating composition and having excellent coating film hardness, moldability, and squeaking noise resistance. Still another object of the present invention is to provide a method for producing the above-mentioned precoated steel sheet.

[0007]

Means for Solving the Problems The inventors of the present invention have studied to solve the above-mentioned problems and obtain a precoated steel sheet having excellent performance. As a result, a polyol is used as a main component, and a curing agent, mainly a naphthalene -2,6-dicarboxylic acid and / or
Or a coating composition containing a polyester compound obtained by reacting a lower alkyl ester thereof with an alcohol component, and further preferably forming a coating film with a coating composition to which an appropriate amount of organic resin beads is added. By forming an undercoating film and an overcoating film on the surface of the galvanized steel sheet that has been subjected to the chemical conversion treatment, and by forming the overcoating film with the above-mentioned coating composition, the coating film hardness, moldability and moldability are improved. It has been found that a pre-coated steel sheet having both excellent squeak noise can be obtained.

[0008] The present invention has been made based on such knowledge, and the characteristic configuration thereof is as follows. [1] The following (a) to (c) are the main components, and the organic resin beads have a solid content of 0.3 to 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the organic resin beads). ~
A coating composition for a precoated steel sheet, wherein 30 parts by weight are blended. B) General formula (1)

Embedded image A) a polyester compound having as a main repeating unit: 1 to 15% by weight in the resin solid content b) Polyol other than the above a): 40 to 90% by weight in the resin solid content c) Curing agent: resin solid content 9-50% by weight in medium ratio

[2] The coating composition for precoated steel sheet according to the above [1], wherein the curing agent is a blocked polyisocyanate compound. [3] In the coating composition according to the above [1] or [2], the average particle size of the organic resin beads (however, the average particle size is calculated by converting the organic resin beads into a sphere having the same volume, and the diameter of the sphere is determined by the organic resin. (Average particle size assuming the particle size of beads) is 0.1 to 10 μm.

[4] The coating composition according to any one of [1] to [3] above, wherein the organic resin beads are methacrylic acid resin beads,
A coating composition for a precoated steel sheet, which is at least one selected from acrylic resin beads, urea resin beads, and urethane resin beads. [5] The coating composition according to any one of [1] to [3], wherein the organic resin beads are urea resin beads.

[6] A precoated steel sheet having a chemical conversion treatment on at least one surface of a galvanized steel sheet having an undercoat film and an overcoat film, wherein the overcoat film is as follows:
To (c) as the main component, and 0.3 to 30 parts by weight of organic resin beads in a proportion of solid content relative to 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the organic resin beads). A pre-coated steel sheet having excellent moldability and squeak noise resistance, characterized in that it is a coating film formed by applying a coating composition. B) General formula (1)

Embedded image A) a polyester compound having as a main repeating unit: 1 to 15% by weight in the resin solid content b) Polyol other than the above a): 40 to 90% by weight in the resin solid content c) Curing agent: resin solid content 9-50% by weight in medium ratio

[7] In the precoated steel sheet according to the above [6],
A precoated steel sheet having excellent moldability and squeak noise resistance, wherein a curing agent in a coating composition for forming an overcoat film is a blocked polyisocyanate compound. [8] In the precoated steel sheet of the above [6] or [7], the average particle size of the organic resin beads contained in the overcoat film (however, the average particle size is calculated by converting the organic resin beads into a sphere having the same volume, Average particle size when the diameter of the sphere is the particle size of the organic resin beads)
A precoated steel sheet having excellent formability and squeak noise resistance, characterized in that the steel sheet has a thickness of 0.1 to 10 µm.

[9] In the precoated steel sheet according to any one of the above [6] to [8], the organic resin beads contained in the overcoat film are methacrylic acid resin beads, acrylic resin beads, urea resin beads, and urethane resin beads. 1 selected from
Pre-coated steel sheet excellent in formability and squeak noise resistance characterized by being at least one kind. [10] The precoated steel sheet according to any one of [6] to [8], wherein the organic resin beads contained in the overcoat film are urea resin beads, and are excellent in moldability and squeak noise resistance. Pre-coated steel sheet.

[11] The method for producing a precoated steel sheet according to any one of the above [6] to [10], wherein a coating composition for an undercoat film is applied on at least one surface of a zinc-based plated steel sheet which has been subjected to a chemical conversion treatment. After the application, the coating composition 1 is baked in a temperature range of 180 to 260 ° C. at the ultimate plate temperature, and then contains the following a) to c) as main components, and the organic resin beads have a solid content of 1%.
After applying 0.3 to 30 parts by weight of the coating composition for the overcoating film with respect to 00 parts by weight (however, the weight of the coating composition excluding the organic resin beads), a) the general formula (1)

Embedded image A) a polyester compound having as a main repeating unit: 1 to 15% by weight in the resin solid content b) Polyol other than the above a): 40 to 90% by weight in the resin solid content c) Curing agent: resin solid content A method for producing a precoated steel sheet having excellent formability and resistance to squeak noise, wherein baking treatment is performed at a temperature of 180 to 260 ° C. at a sheet temperature of 9 to 50% by weight at a medium ratio.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limiting the same will be described below. The coating composition for a precoated steel sheet according to the present invention comprises, as main components, a) a specific polyester compound, b) a polyol excluding the above a), and c) a hardening agent, and an organic resin as a squeak-resistance improving agent. The beads are blended at a specific ratio. First, the polyester compound (a) is a polyester compound having the following general formula (1) as a main repeating unit.

Embedded image

The polyester compound (a) can be obtained by reacting naphthalene-2,6-dicarboxylic acid as an acid component and / or a lower alkyl ester thereof with an alcohol component. The acid component for obtaining the polyester compound of the above a) includes naphthalene-2,
6-Dicarboxylic acids and / or lower alkyl esters thereof are mainly used, and some of them are dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene-2,7-dicarboxylic acid and diphenyldicarboxylic acid, or the dicarboxylic acids of these dicarboxylic acids. It can be replaced by a lower alkyl ester or the like. 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, naphthalene-2,6-dicarboxylic acid, which is the main component, accounts for 8% of the entire acid component.
It is desirable that the content be 5 mol% or more, and the proportion of the other compound to be replaced be suppressed to less than 15 mol%.

As the alcohol component for obtaining the polyester compound (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, polyoxyalkylene glycol, particularly polyethylene glycol having a number average molecular weight of 1,000 or less (hereinafter abbreviated as PEG), or a number average molecular weight of 1
000 or less polytetraethylene glycol (hereinafter, P
TG) can also be used. Further, these may be used as a mixture.

Further, as the alcohol component, 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 acid component and the alcohol component react as described above to produce the polyester compound (a). In particular, when PEG having a number average molecular weight of 1000 or less or PTG having a number average molecular weight of 1000 or less is used, a polyester compound having an ether bond is produced.

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 formed by the combination of the acid component and the alcohol component as described above exhibits anisotropy when observed with a polarizing microscope. It is considered that the coating film containing such a polyester compound achieves toughness of the coating film even after baking due to an action such as alignment, which is a characteristic of the liquid crystal compound, and this is considered to contribute to the improvement of the coating film hardness and workability. Can be

When the above PEG or PTG is used as an alcohol component, it reacts with an acid component to form a polyester compound having an ether bond. The polyester compound having an ether bond has a reduced viscosity of 0.20.
dl / g or less is desirable. Reduced viscosity is 0.2
If it exceeds 0 dl / g, the solubility in a solvent and the compatibility with a polyol, a curing agent and the like are remarkably reduced, and the coating film performance becomes insufficient. The reduced viscosity was determined by measuring the sample with phenol /
It is a value obtained by dissolving in a solution of tetrachloroethane (weight ratio: 60/40) and measuring at 25 ° C. using an Ubbelohde viscometer. When a polyester compound having this ether bond is used, a toughness is imparted to a crosslinked structure by a combination of a flexible ether chain and a rigid naphthalene skeleton, and this contributes to an improvement in coating film hardness and workability. it is conceivable that.

The amount of the polyester compound (a) is 1 to 15% by weight, preferably 2 to 12% by weight, more preferably 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 amount exceeds 15% by weight, the flexibility of the coating film decreases.

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 an acrylic monomer or methacrylic monomer having a hydroxyl group to an acrylate or methacrylate ester by heating in a known manner. As the acrylic monomer and methacryl monomer having a hydroxyl group, for example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate and the like can be used. Also,
As acrylic acid esters and methacrylic acid esters,
For example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, methacrylic acid 2-ethylhexyl and the like can be used. As the commercially available acrylic resin, "Almatex" (Mitsui Toatsu Chemical Co., Ltd.)
Desmophen) (Sumitomo Bayer Urethane Co., Ltd.)
And "Dianal" (manufactured by Mitsubishi Rayon Co., Ltd.).

The polyester 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 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. Further, as the polyhydric alcohol, 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, trimethyl glycol Methylolethane or the like can be used. “Almatex” is a commercially available polyester resin.
(Mitsui Toatsu Chemical Co., Ltd.), "Alkinol" (Sumitomo Bayer Urethane Co., Ltd.), "Desmophen" (Sumitomo Bayer Urethane Co., Ltd.), "Byron" (Toyobo Co., Ltd.), etc. is there.

The amount of the polyol (b) is 40 to 90% by weight based on the resin solid content. If the amount of the polyol is less than 40% by weight, the workability of the coating film cannot be sufficiently ensured, while if it exceeds 90% by weight, the hardness of the coating film becomes insufficient.

As the curing agent (c), a blocked polyisocyanate compound and / or an amino resin can be used. As the polyisocyanate compound, a polyisocyanate compound obtained by a general production method can be used. Among them, phenol, cresol, an aromatic secondary amine, Polyisocyanate compounds blocked with blocking agents such as secondary alcohols, lactams and oximes are preferred. By using this blocked polyisocyanate compound, storage with one liquid becomes possible, and use as a paint for a precoated steel sheet is facilitated.

More preferred polyisocyanate compounds include non-yellowing hexamethylene diisocyanate (hereinafter abbreviated as HDI) and its derivatives, tolylene diisocyanate (hereinafter abbreviated as TDI) and its derivatives, and 4,4'- Diphenylmethane diisocyanate (hereinafter abbreviated as MDI) and its derivatives, xylylene diisocyanate (hereinafter abbreviated as XDI) and its derivatives, isophorone diisocyanate (hereinafter abbreviated as IPDI) and its derivatives, trimethylhexamethylene diisocyanate (hereinafter abbreviated as TMDI) ) And its derivatives,
Examples include hydrogenated TDI and its derivatives, hydrogenated MDI and its derivatives, hydrogenated XDI and its derivatives, and the like. Further, commercially available isocyanate compounds such as “Sumidur” (manufactured by Sumitomo Bayer Urethane Co., Ltd.), “Desmodur” (manufactured by Sumitomo Bayer Urethane Co., Ltd.) and “Coronate” (manufactured by Nippon Polyurethane Co., Ltd.) can also be used. .

When a polyisocyanate compound is used as a curing agent, the compounding ratio [NCO / OH] of the isocyanate group of the polyisocyanate compound with the hydroxyl group of the polyester compound of (a) and the polyol of (b) is 0.8. To 1.2, more preferably 0.90 to 1.10
It is desirable to be within the range. If the molar ratio of [NCO / 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, [NCO / O
When the molar ratio of [H] exceeds 1.2, a side reaction occurs between the excess isocyanate groups or between the isocyanate group and the urethane compound, and the processability of the coating film deteriorates.

As the amino resin as a curing agent, urea,
Resins obtained by reacting benzoguanamine, melamine, etc. with formaldehyde, and those obtained by alkyl etherifying these with alcohols such as methanol and butanol can be used. Specifically, a methylated urea resin, n
-Butylated benzoguanamine resin, methylated melamine resin, n-butylated melamine resin, iso-butylated melamine resin, and the like. Furthermore, “Symel” (Mitsui Cyanamid Co., Ltd.) and “Uban”
Commercially available amino resins such as "Sumimar" (manufactured by Mitsui Toatsu Chemicals, Inc.) (manufactured by Sumitomo Chemical Co., Ltd.) and "Melan" (manufactured by Hitachi Chemical Co., Ltd.) can also be used.

When an amino resin is used as the curing agent, the amino resin and the polyester compound of the above (a) and the above (ii)
The mixing ratio (weight ratio of solid content) with the polyol was [polyester compound] + [polyol] / [amino resin]: 9
5 / 5-65-35, preferably 90 / 10-75-2
Preferably, the ratio is 5. The compounding amount of the curing agent in the above item (c) is 9 to 50% by weight in terms of the resin solid content. If the amount of the curing agent is less than 9% by weight, the hardness of the coating film is insufficient, while if it exceeds 50% by weight, the processability is insufficient.

An appropriate amount of organic resin beads is blended in the coating composition, and the organic resin beads impart squeak resistance to the coating film. As the organic resin beads, for example, MM
A (methacrylic acid) resin beads, acrylic resin beads,
There are urea resin beads, urethane resin beads, and the like. One of these can be used alone, or two or more can be used in combination. In particular, when a urea resin is used, particularly excellent squeak resistance can be obtained.

Coating composition (and coating of precoated steel sheet)
The amount of the organic resin beads in the composition is 0.3 to 30 parts by weight, preferably 0 to 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the organic resin beads) in terms of solid content. 0.3 to 20 parts by weight, more preferably 0.5 to 10 parts by weight
Parts by weight, most preferably 1.1 to 8 parts by weight. If the amount of the organic resin beads is less than 0.3 parts by weight, the squeaking resistance of the coating film is not sufficiently improved. On the other hand, when the compounding amount of the organic resin beads exceeds 30 parts by weight, the precipitation of the organic resin beads in the coating composition during low-temperature storage (winter) is remarkable,
Agglomerates of the precipitated organic resin beads cause repelling and dents during coating film formation, and cause serious defects as a precoated steel sheet.

There is no limitation on the shape of the organic resin beads, and any shape such as a column shape (for example, a column shape), a fibrous shape, a needle shape, and other irregular shapes can be used in addition to a spherical shape or a shape similar thereto. Can be. Further, the average particle size of the organic resin beads mixed in the coating composition is preferably in the range of 0.1 to 10 μm. Here, the average particle diameter of the organic resin beads refers to an average particle diameter when the diameter of the organic resin beads is converted into a sphere having the same volume and the diameter of the sphere is regarded as the particle diameter of the organic resin beads. If the average particle size of the organic resin beads is less than 0.1 μm, the squeaking resistance of the coating film is not sufficiently improved. On the other hand, when the average particle size of the organic resin beads exceeds 10 μm, the processability of the coating film is reduced.

Further, depending on the purpose and application, the coating composition may contain a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate, lead 2-ethylhexoate, silica, 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 an anti-flow agent can be appropriately compounded.

In preparing the coating composition, a conventional disperser or kneader such as a sand grind mill, a ball mill, or a blender may be selected and used, and the above-mentioned components may be blended. Although there is no particular limitation on the type of steel sheet to be coated with the coating composition for pre-coated steel sheet of the present invention,
Normally, the surface of cold-rolled steel sheets and various types of galvanized steel sheets (for example, hot-dip galvanized steel sheets, electrogalvanized steel sheets, composite galvanized steel sheets, chromium-coated steel sheets, etc.) is subjected to a chemical conversion treatment such as phosphate treatment or chromate treatment. Painted on steel plate. 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 enhance 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 heat curing is about 180-260 ° C and about 30
About 2 to 3 minutes is appropriate. The thickness of the cured coating film thus formed is usually about 10 to 35 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 necessarily 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. . In addition, in order to obtain a pre-coated steel sheet having particularly excellent coating film hardness, formability, squeak noise resistance, etc., a zinc-based steel that has been subjected to a chemical conversion treatment such as a phosphate treatment or a chromate treatment as described below is used. It is preferable to form an undercoat film on the surface of the plated steel sheet, and to form an overcoat film comprising the above-mentioned coating composition of the present invention on the upper layer.

Hereinafter, the precoated steel sheet of the present invention using the above coating composition will be described. The precoated steel sheet of the present invention is a coated steel sheet in which an undercoat film and an overcoat film are formed on at least one surface (a steel sheet surface subjected to a chemical conversion treatment) of a galvanized steel plate subjected to a chemical treatment. As the zinc-based galvanized steel sheet to be the base steel sheet, there are hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, electro-galvanized steel sheet, hot-dip Zn
-55% Al alloy plated steel sheet, hot-dip Zn-5% Al alloy plated steel sheet, Zn-Ni alloy plated steel sheet, Zn-Co alloy plated steel sheet, Zn-Cr alloy plated steel sheet, composite zinc-based plated steel sheet (for example, electric Zn- Various types of galvanized steel sheets, such as SiO ₂ dispersion-coated steel sheets, can be used. In addition, particularly for applications requiring corrosion resistance, molten Zn
It is preferable to use a -55% Al alloy plated steel sheet or a hot-dip Zn-5% Al alloy plated steel sheet.

The surface of such a zinc-based plated steel sheet is subjected to a chemical conversion treatment such as a phosphate treatment and a chromate treatment.
An undercoat film and an overcoat film are sequentially formed thereon.
By forming a coating film on the plated steel sheet surface which has been subjected to the chemical conversion treatment as described above, the adhesion of the coating film to the steel sheet surface is improved, and the corrosion resistance is also improved.

The top coat of the precoated steel sheet of the present invention is
The above-mentioned coating composition, i.e., a) a specific polyester compound, b) a polyol excluding the above a), and c) a curing agent as main components, and organic resin beads as a squeak-resistance improving agent. The composition was formed by applying the coating composition blended in the ratio of 1 and baking. It is preferable that the thickness of the overcoat film is 10 to 20 μm. If the film thickness is less than 10 μm, there is a possibility that the overall coating film performance as a topcoat film may not be sufficiently obtained.
If it exceeds m, the hardness of the coating film decreases.

The base material of the coating composition for forming the undercoat film of the precoated steel sheet of the present invention is not particularly limited.
From the viewpoint of processability and adhesion between the top coat and the chemical conversion coating, it is preferable to use a coating composition containing a polyester resin, an epoxy resin or a urethane resin as a main component. Further, two or more of these resins may be used as a mixture. A polyisocyanate compound or an amino resin can be used as a curing agent used in a coating composition for an undercoat film. 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; and aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate. An alicyclic diisocyanate such as isophorone diisocyanate; a polymer of these diisocyanates or an adduct thereof with a polyhydric alcohol; and a blocking agent (for example, phenol-based, lactam-based, alcohol-based, mercaptan-based, or imine-based). , An amine-based, imidazole-based or oxime-based blocking agent) 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 a condensate of formaldehyde or paraformaldehyde alkyletherified with a lower alcohol and urea, dicyandiamide, aminotriazine and the like. Examples include methylol urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, and butoxylated methylol benzoguanamine. Further, as a curing catalyst, hydrochloric acid, monoalkyl phosphate, P-
Acids such as toluenesulfonic acid or salts of these acids with tertiary or secondary amine compounds can be used.

The thickness of the undercoat film is preferably 2 to 12 μm. If the film thickness is less than 2 μm, the effect of improving workability and corrosion resistance cannot be sufficiently obtained, while if the film thickness exceeds 12 μm, both the workability and the coating film hardness decrease.

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 such as a sand grind mill, a ball mill, or a blender or a kneading machine is selected and used, and each component can be blended.

There are no particular restrictions on the method of applying the coating composition (each coating composition for undercoating and topcoating) when producing the precoated steel sheet of the present invention, but preferably a roll coater coating or 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 heating and curing the undercoat film is usually performed at a maximum temperature of about 180 to 260 ° C.,
Baking is performed in this temperature range for about 30 seconds to 1 minute. The baking treatment for heat-curing the top coat is usually performed at a maximum temperature of about 180 to 260 ° C. and baking for about 30 seconds to 3 minutes in this temperature range. In addition, the pre-coated steel sheet of the present invention may be formed by further forming a coating film (for example, a clear coating film) on the top coating film, and may be used in three coats and three bake.

[0050]

EXAMPLE A 0.5 mm thick hot-dip galvanized steel sheet (coated weight per side: 30 g / m ² ) as a base steel sheet was degreased, and then subjected to a coating type chromate treatment (chromium coated amount in terms of chromium metal: 30 mg). / M ² ), and a polyester-based primer is applied thereon so as to have a dry film thickness of 5 μm, and then a baking temperature (attained plate temperature) of 215 ° C. and a baking time of 6 hours.
An undercoating film was formed by performing a baking treatment for 0 second, and a coating composition having the beads shown in Table 2 added to the coating composition for the overcoating film shown in Table 1 was applied thereon. A baking treatment was performed at a temperature (attained plate temperature) of 230 ° C. and a baking time of 60 seconds to form an overcoat film, and precoated steel sheets of the present invention and comparative examples were obtained. Tables 3 to 6 show the performance of these precoated steel sheets together with the production conditions.

The coating compositions A to A for the overcoating film shown in Table 1
C was adjusted as follows. [Coating composition for top coat] (1) Preparation of polyester compound f-1 Naphthalene-2,6-dicarboxylate dimethyl ether (hereinafter referred to as "dimethylether") was prepared in a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer. , "2,6-NDCM") in 0.5 mo
l, 1.05 mol of diethylene glycol
Heated and melted at 0 ° C. Thereafter, titanium tetra-n-butoxide was used as a catalyst in 0.2 to 2,6-NDCM.
10 mol% was added, the reaction temperature was increased stepwise to 240 ° C., and a theoretical amount of 32 g of methanol (1.0 mol
The reaction was completed when l) was distilled off. Thus, a polyester compound f-1 was obtained. The reduced viscosity of this polyester compound was 0.05 dl / g.

The chemical structural formula of the polyester compound f-1 is shown below.

Embedded image

(2) Preparation of polyester compound f-2 0.5 mol of 2,6-NDCM and 1 part of 1,4-butanediol were placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer. 0.02 mol was added and melted by heating at 200 ° C. Thereafter, as a catalyst, titanium tetra-n-butoxide was added at 0.06 mol% to 2,6-NDCM, and the reaction temperature was gradually increased to 240 ° C., and 32 g (1.0 mol) of a theoretical amount of methanol was obtained. The reaction was completed when distilling was completed. Thus, a polyester compound f-2 was obtained. The reduced viscosity of this polyester compound was 0.04 dl / g.

The chemical structural formula of the polyester compound f-2 is shown below.

Embedded image

(3) Production of a coating composition for a top coat film The polyester compound f- obtained in the above (1) and (2)
After blending a polyol (polyester resin), a curing agent, a pigment, a curing catalyst, and an additive in the blending ratio shown in Table 1 with 1, f-2, about 1 mm using a sand mill containing glass beads having a diameter of about 1 mm. Dispersed for 30 minutes. further,
Cyclohexanone was added to adjust the nonvolatile content to 60%, and coating compositions A and B were produced.

Further, as a paint composition for a top coat as a comparative example, a polyol (polyester resin), a curing agent, a pigment, a curing catalyst and an additive were blended in the blending ratios as shown in Table 1, and then the diameter was reduced. The mixture was dispersed for about 30 minutes using a sand mill containing 1 mm glass beads. Further, cyclohexane was added to adjust the non-volatile content to 60%, thereby producing a coating composition C.

The test method and evaluation method of the performance test of the precoated steel sheet will be described below. (1) Appearance The quality of the surface properties of the coating film after baking was visually judged. (2) Pencil hardness Use Mitsubishi pencil "Uni" and meet JIS K 5400-8.
The test was performed based on No. 4 and showed a hardness limit at which the coating film was not damaged.

(3) 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 at all ○: No scratch was found even when visually observed, but 10
When observed with a loupe, slight scratching is observed. Δ: Slight scratch generation is observed when visually observed. ×: Clear scratches are observed (abnormal).

(4) Squeaking Noise Resistance The degree of generation of "squeaking noise" when a precoated steel sheet was brought into contact with aluminum as a frame material and a force was applied by hand was evaluated as follows. ：: No sound ○: Sound is generated when pressed for the first time, but no sound is generated even after the second press. Δ: A sound is generated when the button is first pressed, and a sound is generated when the button is pressed after the second time, but no sound is generated by the fifth time. ×: A sound is generated when the button is pressed for the first time, and a sound is continuously generated even when the button is pressed repeatedly thereafter (a sound is generated when the button is pressed for the fifth time and thereafter).

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

[0063]

[Table 4]

[0064]

[Table 5]

[0065]

[Table 6]

[0066]

As described above, according to the coating composition of the present invention, it is possible to obtain a coating film excellent in all of squeak noise resistance, coating film hardness, molding processability and coating film appearance. Therefore, the precoated steel sheet having such a coating film is extremely useful as a material for home electric appliances, building materials, automobiles and the like.

In particular, the precoated steel sheet of the present invention in which an undercoating film and an overcoating film of the above-mentioned coating composition are formed on the surface of a zinc-coated steel sheet which has been subjected to a chemical conversion treatment, has a squeaking resistance, a coating film hardness, and a High properties are obtained in both processability and appearance of coating film, so home appliances, building materials,
It is extremely useful as a pre-coated steel sheet used in parts requiring high squeaking noise resistance, coating film hardness, moldability, and coating film appearance in applications such as automobiles. Further, the precoated steel sheet of the present invention is industrially extremely useful in that it can be manufactured by a simpler method than before.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Keiji Yoshida, Inventor, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Yasuyuki Kajita 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Japan In-tube (72) Inventor Hiroyuki Kato 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Inside the Steel Pipe Co., Ltd. (72) Inventor Katsuyoshi Tanaka 4-1-1, Minamishinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. Tokyo Office F-term (reference) 4D075 AE03 BB28Z CA05 DB02 DB05 DC01 DC10 DC12 DC18 EC07 EC24 EC53 4J038 CG032 CG142 DA142 DD001 DD061 DG002 KA03 MA02 MA14 PB05 PB07 PB09 PC02

Claims (11)

[Claims] 1. Organic resin beads containing the following components a) to c) as main components and having a solid content of 0 to 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the organic resin beads). 3. A coating composition for a pre-coated steel sheet, which is mixed in an amount of 3 to 30 parts by weight. B) General formula (1) A) a polyester compound having as a main repeating unit: 1 to 15% by weight in the resin solid content b) Polyol other than the above a): 40 to 90% by weight in the resin solid content c) Curing agent: resin solid content 9-50% by weight in medium ratio 2. The coating composition for a precoated steel sheet according to claim 1, wherein the curing agent is a blocked polyisocyanate compound. 3. Average particle diameter of organic resin beads (however, average particle diameter: average particle diameter when converting the organic resin beads into a sphere having the same volume and defining the diameter of the sphere as the particle diameter of the organic resin beads) The coating composition for a precoated steel sheet according to claim 1 or 2, wherein the particle size is 0.1 to 10 µm. 4. The method according to claim 1, wherein the organic resin beads are at least one selected from methacrylic acid resin beads, acrylic resin beads, urea resin beads, and urethane resin beads. Paint composition for precoated steel sheet. 5. The coating composition for a precoated steel sheet according to claim 1, wherein the organic resin beads are urea resin beads. 6. A pre-coated steel sheet having an undercoat film and an overcoat film on at least one side of a galvanized steel sheet which has been subjected to a chemical conversion treatment, wherein the overcoat film has the following components a) to c) as main components: And applying a coating composition in which 0.3 to 30 parts by weight of the organic resin beads are blended in a solid content ratio with respect to 100 parts by weight of the coating composition (however, the weight of the coating composition excluding the organic resin beads). A pre-coated steel sheet with excellent formability and squeak noise resistance, characterized by being a coating film formed by forming. B) General formula (1) A) a polyester compound having as a main repeating unit: 1 to 15% by weight in the resin solid content b) Polyol other than the above a): 40 to 90% by weight in the resin solid content c) Curing agent: resin solid content 9-50% by weight in medium ratio 7. The precoated steel sheet according to claim 6, wherein the curing agent in the coating composition for forming the overcoat film is a blocked polyisocyanate compound. . 8. The average particle size of the organic resin beads contained in the overcoat film (however, the average particle size: the organic resin beads are converted into spheres of the same volume, and the diameter of the spheres is calculated as the particle size of the organic resin beads. 8. The precoated steel sheet according to claim 6, wherein the precoated steel sheet has excellent formability and squeak noise resistance. 9. The organic resin beads contained in the overcoat film are selected from methacrylic acid resin beads, acrylic resin beads, urea resin beads, and urethane resin beads.
9. The precoated steel sheet according to claim 6, 7 or 8, which is excellent in formability and squeak noise resistance. 10. The organic resin beads contained in the overcoat film are urea resin beads.
7. A precoated steel sheet excellent in formability and squeak noise resistance according to 7 or 8. 11. The method for producing a precoated steel sheet according to claim 6, 7, 8, 9 or 10, wherein at least one surface of the galvanized steel sheet which has been subjected to a chemical conversion treatment is used as a coating composition for an undercoat film. After applying, 180-260 at reached plate temperature
B) in a temperature range of 100 ° C., and then 100 parts by weight of the coating composition containing the following a) to c) as main components and the organic resin beads in a solid content ratio (however, except for the organic resin beads). After applying a coating composition for a top coat coated in an amount of 0.3 to 30 parts by weight with respect to (weight), a) the general formula (1) A) a polyester compound having as a main repeating unit: 1 to 15% by weight in the resin solid content b) Polyol other than the above a): 40 to 90% by weight in the resin solid content c) Curing agent: resin solid content 9 to 50% by weight in a medium ratio. A method for producing a precoated steel sheet having excellent formability and resistance to squeak noise, wherein baking treatment is performed at a temperature of 180 to 260 ° C. at a reached sheet temperature.