JP2003025497A - Pre-coated steel plate which is excellent in environmental harmony, worked section anticorrosive property, and worked section adhesion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pre-coated steel plate wherein excellent worked section anticorrosive property and worked section adhesion being equivalent to those of a highly anticorrosive chrome based pre-coated steel plate can be obtained without adding a chrome based rustproof pigment in the coating film. SOLUTION: An undercoating film is formed on the surface of a zinc-based plated steel plate wherein a chemical conversion treatment film containing a silica particle and its binder is formed. In addition, a finish coating film is formed on the upper layer of the undercoating film for this pre-coated steel plate. In this case, the finish coating film contains 1 to 20 pts.wt. of a rustproof additive component comprising one kind or two kinds or more of organic compounds selected from among a molybdate, or a molybdate and triazoles, thiols, thiadiazoles, thiazoles, and thiurams, based on 100 pts.wt. of a resin solid portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated steel sheet which is excellent in environmental friendliness, corrosion resistance of a worked part and adhesion of a worked part. The precoated steel sheet of the present invention is suitable for, for example, home appliances and building materials, and can also be used for automobiles.

[0002]

2. Description of the Related Art Conventionally widely used precoated steel sheets are subjected to a chemical conversion treatment containing chromium in order to ensure corrosion resistance, and a chromium-based rust preventive pigment is contained in the undercoating coating film (for example, JP-A-7-316497
issue). However, recently, from the viewpoint of environmental protection, there is a demand for the development of a chromium-free precoated steel sheet containing no highly toxic chromium.

In response to such a demand, for example, Japanese Patent Laid-Open No. 8-
Japanese Patent No. 3194437 discloses that a basic phosphite-based rust preventive pigment is contained in an undercoating coating film to obtain a precoated steel sheet that is chromium-free and has excellent corrosion resistance. Further, JP-A-8-11257 discloses that a chromium-free precoated steel sheet having excellent corrosion resistance can be obtained by incorporating an isocyanate compound and a phosphoric acid-based rust preventive pigment in an undercoat coating film.

[0004]

However, in order to obtain corrosion resistance equivalent to that of a chromium-based precoated steel sheet having high corrosion resistance in these conventional chromium-free precoated steel sheets, it is necessary to add a large amount of rust preventive additive in the undercoat coating film. ,Also,
As a result, even if the corrosion resistance of the flat portion and the end surface which are not processed is secured, there is a problem that the corrosion resistance of the processed portion and the adhesion of the coating film are deteriorated. Since the precoated steel sheet is used as a product after being subjected to processing, it can be said that the corrosion resistance and the coating film adhesion of the processed portion are very important characteristics.

Therefore, an object of the present invention is to solve the problems of the prior art, and to provide excellent corrosion resistance to a processed portion as high as that of a chromium-based precoated steel sheet even if a chromium-based rust preventive pigment is not added to the coating film. Another object of the present invention is to provide an environmentally friendly pre-coated steel sheet that can provide processing adhesion.

[0006]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems and obtain a precoated steel sheet having excellent performance, and as a result, a chemical conversion coating film containing silica fine particles and a binder thereof. By forming an undercoating film on the surface of the zinc-based plated steel sheet on which is formed, and forming an overcoating film containing a specific rust-preventive additive component on the upper layer, environmental friendliness and corrosion resistance of the processed part and processing adhesion It was found that an excellent precoated steel sheet was obtained.

The present invention has been made on the basis of such findings, and its features are as follows. [1] A precoated steel sheet in which an undercoat coating film is formed on the surface of a zinc-based plated steel sheet on which a chemical conversion treatment film containing silica fine particles and a binder thereof is formed, and further, an overcoat coating film is formed on the upper layer thereof. A precoated steel sheet excellent in environmental harmony, corrosion resistance of processed part and adhesion of processed part, characterized in that the top coating film contains 1 to 20 parts by weight of molybdate based on 100 parts by weight of resin solid content.

[2] On the surface of a zinc-based plated steel sheet on which a chemical conversion treatment film containing fine silica particles and a binder thereof is formed,
An undercoat coating film is formed, which is a precoated steel sheet having a topcoat coating film formed thereon, wherein the topcoat coating film is a molybdate salt, triazoles, thiols,
A total of 1 part by weight of a rust preventive additive component consisting of one or more organic compounds selected from thiadiazoles, thiazoles and thiurams per 100 parts by weight of resin solids.
A pre-coated steel sheet excellent in environmental friendliness, corrosion resistance of the processed part and adhesion of the processed part, characterized by containing 20 to 20 parts by weight.

[3] In the precoated steel sheet according to [1] or [2], the undercoat coating film contains molybdate in an amount of 5 to 50 parts by weight based on 100 parts by weight of the resin solid content. Pre-coated steel sheet with excellent harmony, corrosion resistance in the processed part and adhesion to the processed part.

[4] In the precoated steel sheet according to [1] or [2], the undercoat coating film is one selected from molybdate and triazoles, thiols, thiadiazoles, thiazoles, thiurams. Alternatively, a rust preventive additive component composed of two or more kinds of organic compounds is added to the resin solid content 100
A pre-coated steel sheet excellent in environmental compatibility, corrosion resistance of the processed part and adhesion of the processed part, which is characterized by containing a total of 5 to 50 parts by weight with respect to the parts by weight.

[5] In the precoated steel sheet according to any one of the above [1] to [4], the top coating film has the following a) and b)
A pre-coated steel sheet excellent in environmental harmony, corrosion resistance in the processed part and adhesion to the processed part, which is a coating film formed by applying a coating composition containing the. A) Polyester resin and / or acrylic resin: 40 to 90% by mass in the resin solid content b) Isocyanate compound and / or amino resin as a curing agent: 9 to 50% by mass in the resin solid content

[6] In the precoated steel sheet according to any one of the above [1] to [5], the main resin component in the coating composition for forming the undercoat coating film is a polyester resin and / or an epoxy modified polyester resin. A pre-coated steel sheet that is excellent in environmental friendliness, corrosion resistance of the processed part and adhesion of the processed part.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and the reasons for limitation thereof will be described below. The precoated steel sheet of the present invention forms an undercoat coating film on the surface of a zinc-based plated steel sheet on which a chemical conversion coating containing specific components is formed, and forms an overcoat coating film containing a specific rust preventive addition component on the upper layer thereof. It is a painted steel plate. As the zinc-based plated steel sheet to be the base steel sheet, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, electrogalvanized steel sheet,
Various zinc-based plated steel sheets such as hot-dip Zn-Al alloy plated steel sheet can be used.

Further, as the zinc-based plated steel sheet, one which has been subjected to surface conditioning treatment after zinc-based plating can be used in order to enhance the adhesion with the chemical conversion coating. This surface conditioning treatment may use either an acidic treatment liquid or an alkaline treatment liquid. The treatment method may be dipping, spraying, or the like.

The chemical conversion treatment film formed on the surface of the zinc-based plated steel sheet is a chemical conversion treatment film containing silica fine particles (fine powder) and a binder thereof. As the silica fine particles, for example, one kind or two or more kinds selected from wet silica (colloidal silica) and dry silica (fumed silica) having a primary particle diameter of about 1 to 100 nm can be used. By incorporating such silica fine particles into the chemical conversion treatment film, it is possible to enhance the adhesion to the resin film (undercoating film) on the chemical conversion treatment film, scratch resistance, and corrosion resistance.

As the binder, for example, one or more selected from water-soluble or water-dispersible organic polymers and oxyacid salts (excluding chromate) can be used. . Examples of the water-soluble or water-dispersible organic polymer include poly (meth) acrylic acid and polyvinyl alcohol. Examples of the oxyacid salt include phosphate, molybdate, tungstate, vanadate, and the like. By compounding such a binder in the chemical conversion treatment film, the bondability between silica fine particles (cohesion failure resistance of the film) and the adhesion of the silica fine particles to the base metal can be enhanced.

The chemical conversion treatment liquid contains Zr compound and Ti.
Compound, Hf compound (eg, fluoro complex salt) 1
It is possible to add one kind or two or more kinds as additives and to include them in the chemical conversion treatment film. The compounding ratio of the silica fine particles and the binder is preferably in the range of silica fine particles / binder = 1 / 0.01 to 1/10 in terms of solid content weight ratio. If the blending ratio of the binder to the blending amount of silica fine particles: 1 is less than 0.01, the binding properties between silica fine particles (cohesive failure resistance of the coating) and the adhesion of the silica fine particles to the base metal are poor. Further, when the compounding ratio of the silica fine particles to the compounding ratio of 1 is more than 10, the adhesion with the resin film (undercoating film) as the upper layer of the chemical conversion treatment film, scratch resistance, and corrosion resistance are poor.

The amount of the chemical conversion coating adhered is 5 to 200 mg / m ^{2 in} terms of Si equivalent of silica fine particles contained as a component.
It is preferable to set it as the range. This adhesion amount is 5 mg / m
^When it is less than ² , the adhesion to the base metal and the corrosion resistance are poor, while when it exceeds 200 mg / m ² , the adhesion to the resin film (undercoating film) as the upper layer of the chemical conversion treatment film is poor. The treatment method for forming the chemical conversion treatment film is not particularly limited, but generally, the chemical conversion treatment liquid is roll coater-coated and then dried. In this drying, the coating is usually dried at a reached plate temperature of about 50 to 150 ° C. by heating means such as hot air heating, infrared heating, and induction heating.

Next, preferable conditions of the undercoat coating film formed on the upper layer of the above chemical conversion coating will be described. As the main resin of the coating composition for forming the undercoat coating film,
For example, one kind or two or more kinds of epoxy modified polyester resin such as polyester resin, epoxy resin, and bisphenol A-added polyester resin can be used, but from the viewpoint of processability, the polyester resin and / or the epoxy modified polyester is used. Resins are particularly preferred.

Examples of the resin used for the epoxy modification of the polyester resin include bisphenol A or bisphenol F type epoxy resin, and other than this,
Obtained by reacting an epihalohydrin (eg epichlorohydrin) with a condensate of an aldehyde (eg formaldehyde) and a monohydric phenol or a polyhydric polyphenol in the presence of a base catalyst (eg potassium hydroxide). Phenol derivative epoxy resin (for example,
Novolak type epoxy resin) and the like can also be used.

Generally, the physical properties of the undercoating coating film vary depending on the Tg of the resin used as the main component of the coating composition. Generally, from the molecular structure of the resin, the coating film of the epoxy-based undercoating coating material has a large breaking strength, but is broken. On the other hand, the elongation is small, whereas the coating film made of the polyester undercoat paint or the urethane undercoat paint has a large breaking elongation but a small breaking strength. On the other hand, the undercoat coating film formed by a coating composition containing an epoxy-modified polyester resin such as a bisphenol A-added polyester resin as a main resin has both the molecular structures of the above-mentioned resins, so that the breaking strength and the breaking elongation are Is obtained in a well-balanced manner, and is particularly preferable from the viewpoint of high workability which is the object of the present invention.

When the undercoating film is formed from a coating composition containing a polyester resin (including an epoxy-modified polyester resin such as a bisphenol A-added polyester resin; the same applies hereinafter) as a main resin, the undercoating film should have the above physical properties. In order to obtain a polyester resin having a number average molecular weight of 1,000 to 50,000, more preferably 3
000 to 40,000, particularly preferably 5000 to 300
It is desirable to use one in the range of 00. When the number average molecular weight of the polyester resin is less than 1,000, the above-mentioned physical properties cannot be obtained because the elongation of the coating film is insufficient, and the coating film performance is not sufficiently improved. On the other hand, when the number average molecular weight exceeds 50,000, the coating composition becomes highly viscous and an excessive amount of diluting solvent is required, and the proportion of the resin in the coating is reduced, so that a proper coating film cannot be obtained. Furthermore, the compatibility with other compounding ingredients is significantly reduced.

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

As the polyhydric alcohol for obtaining the above polyester resin, 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 thereof include trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, and dipentaerythritol, and two or more kinds of these polyhydric alcohols can be used in combination.

As the polybasic acid component for obtaining the polyester resin, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, hymic acid anhydride, and triamic acid Mellitic 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 Examples of the acid include 1,4-cyclohexanedicarboxylic acid, and two or more kinds of these polybasic acid components can be used in combination.

As the curing agent used in the coating composition for the undercoat coating film, a polyisocyanate compound, an amino resin or the like can be used. Moreover, you may use these 2 or more types in 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; isophorone diisocyanate. Alicyclic diisocyanates such as; or multimers of these diisocyanates or adducts with polyhydric alcohols, and the like, and these blocking agents (for example, phenol-based, lactam-based, alcohol-based, mercaptan-based, imine-based, amine-based , Imidazole-based or oxime-based blocking agents) and the like.
As the dissociation catalyst for these blocked polyisocyanate compounds, tin octoate, dibutyltin dilaurate, lead 2-ethylhexoate, etc. can be used.

The amino resin used as the curing agent includes, for example, a condensate of formaldehyde or paraformaldehyde alkylated with a lower alcohol, and urea, dicyandiamide, aminotriazine or the like. Examples thereof include methylol urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine. Further, as the curing catalyst, hydrochloric acid, phosphoric acid monoalkyl ester, P-
Acids such as toluenesulfonic acid or salts of these acids with tertiary amines or secondary amine compounds can be used.

It is preferable that a molybdate is contained in the undercoat film as a rust preventive addition component. This molybdate exhibits anticorrosion performance (self-repair performance) due to the passivation effect. That is, the molybdate forms a dense oxide on the surface of the plating film together with dissolved oxygen in a corrosive environment, and this blocks the corrosion starting point to suppress the corrosion reaction. There is no limitation on the skeleton and the degree of condensation of molybdate, and examples thereof include orthomolybdate, paramolybdate, and metamolybdate. Further, it includes all salts such as single salt and double salt, and examples of the double salt include phosphomolybdate.

In addition to the molybdate, a rust preventive additive component composed of one or more kinds of organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles and thiurams is added in combination. As a result, particularly excellent corrosion resistance can be obtained. While molybdates exhibit anticorrosion performance (self-repairing performance) due to passivation, organic compounds such as triazoles, thiols, thiadiazoles, thiazoles, and thiurams exhibit anticorrosion performance (self-repairing performance) by adsorption. Therefore, a rust preventive additive component consisting of one or more organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles and thiurams and a molybdate are obtained. By adding multiple, the anticorrosive action of each rust-preventive additive component becomes complex,
As a result, a higher level of anticorrosion performance can be obtained.

As described above, the organic compounds of triazoles, thiols, thiadiazoles, thiazoles and thiurams exhibit anticorrosion performance (self-repairing performance) due to the adsorption action. That is, zinc or aluminum eluted by corrosion is adsorbed by polar groups containing nitrogen and sulfur in these organic compounds to form an inactive film, which blocks the corrosion starting point and suppresses the corrosion reaction.

Of the above organic compounds, triazoles include 1,2,4-triazole, 3-amino-1,
2,4-triazole, 3-mercapto-1,2,4-
Triazole, 5-amino-3-mercapto-1,2,
4-triazole, 1H-benzotriazole, etc.
The thiols include 1,3,5-triazine-
2,4,6-trithiol, 2-mercaptobenzimidazole and the like, and thiadiazoles include 5-
Amino-2-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole and the like, and thiazoles include 2-N, N-diethylthiobenzothiazole and 2-mercapto. Examples thereof include benzothiazoles, and examples of thiurams include tetraethylthiuram disulfide. One or more organic compounds selected from these triazoles, thiols, thiadiazoles, thiazoles and thiurams can be added as a rust preventive addition component.

Here, a rust preventive additive component (y) consisting of molybdate (x) and one or more organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles and thiurams. ) And the blending ratio is
It is suitable that the weight ratio of solids is (x) / (y) = 1/99 to 99/1, more preferably 10/90 to 90/10, and further preferably 20/80 to 80/20. . With such a blending ratio, different anticorrosive effects can be effectively combined.

The rust-preventive additives added to the undercoating film as described above do not contain harmful substances and have the effect of enhancing the corrosion resistance of the coating film. The compounding amount (total compounding amount) of the above-mentioned rust preventive additive component in the undercoat coating film is 5 to 50 parts by weight with respect to 100 parts by weight of the resin solid content. If the amount of the rust preventive additive component is less than 5 parts by weight with respect to 100 parts by weight of the resin solid content, the effect of improving the corrosion resistance of the processed part by adding the rust preventive additive component cannot be sufficiently obtained, while if it exceeds 50 parts by weight. It causes a problem in workability.

Further, in the coating composition for the undercoating film, a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate, lead 2-ethylhexoate, etc., depending on the purpose and use; calcium carbonate; , Kaolin, clay, titanium oxide, talc, barium sulfate, mica, rouge, manganese blue, carbon black, aluminum powder, pearl mica and other pigments; other additives such as defoaming agents and anti-flow agents can do.

The thickness of the undercoat coating film is preferably in the range of 2 to 20 μm. When the film thickness is less than 2 μm, sufficient corrosion resistance cannot be obtained, while when it exceeds 20 μm, workability is insufficient. In actually using the coating composition for forming the undercoat coating film, these are dissolved in an organic solvent and / or water before use. Examples of the organic solvent used include methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 100 (trade name, manufactured by Exxon Chemical Co., Ltd.), Solvesso 150 (trade name, manufactured by Exxon Chemical Co., Ltd.), Solvesso 200 (trade name, Exxon Chemical Co., Ltd.). And 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 a coating composition for an undercoat coating film, a conventional disperser or kneader such as a sand grind mill, a ball mill or a blender can be selected and used to blend the respective components. . There are no particular restrictions on the method of applying the undercoat coating film, but it is preferable to apply the coating composition by a method such as roll coater coating or curtain flow coating. After coating the coating composition for an undercoating film on the surface of the zinc-based plated steel sheet on which the above-mentioned chemical conversion treatment film is formed, it is usually heated to about 180 to 260 ° C. by heating means such as hot air heating, infrared heating, and induction heating. A baking process is performed at the ultimate plate temperature for about 30 seconds to 1 minute.

Next, the top coat film formed as the upper layer of the above-mentioned bottom coat film will be described. As the base resin of the top coating film, one or more of polyester resin, acrylic resin, fluororesin and the like can be used, but in order to obtain particularly excellent performance, the top coating film is used as a resin component. A) A coating composition formed by applying a coating composition containing a specific polyol and b) a specific curing agent (preferably containing these as a main component resin) and baking it. Is preferred. By forming such a specific top coat film, particularly excellent processed portion corrosion resistance can be obtained due to the combined effect with the above-mentioned under coat film.

The specific top coat film will be described below. First, an acrylic resin and / or a polyester resin can be used as the polyol of the above (a). The acrylic resin, which is the polyol (a), 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 12000. Is preferably 1
It is 700 to 10,000. The hydroxyl groups in the molecule of the acrylic resin are randomly arranged in the main chain of the acrylic resin, and if the number average molecular weight is less than 1500, the processability is remarkably reduced. On the other hand, when the number average molecular weight exceeds 12000, the viscosity becomes high, and therefore an excessive amount of diluting solvent is required, and the ratio of the resin in the paint is reduced, so that an appropriate coating film cannot be obtained. Furthermore, the compatibility with other compounding ingredients is significantly reduced. The number average molecular weight of the acrylic resin is
Gel permeation chromatography (hereinafter GP
It is the polyester-equivalent molecular weight measured by C).

The acrylic resin is a copolymer obtained by heating and reacting an acrylic or methacrylic monomer having a hydroxyl group with an acrylic ester or a methacrylic ester by a known method. As the acrylic monomer and methacrylic monomer having a hydroxyl group, for example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, etc. can be used. Also,
As acrylic acid ester and methacrylic acid ester,
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 or the like can be used. Commercially available acrylic resins include "ALMATEX" (trade name, manufactured by Mitsui Toatsu Kagaku Co., Ltd.), "Desmofen" (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), and "Dynar" (trade name) , Mitsubishi Rayon Co., Ltd., etc.

The polyester resin, which is the polyol (a), 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 number average molecular weight is preferably 1200 to 7,000, more preferably 15
It is from 00 to 6000. The hydroxyl group in the molecule of the polyester resin may be at either the terminal or side chain in the molecule. If the number average molecular weight of the polyester resin is less than 1000, the workability is significantly reduced. On the other hand, when the number average molecular weight exceeds 8000, the viscosity becomes high and an excessive amount of diluting solvent is required, and the proportion of the resin in the paint is reduced, so that an appropriate coating film cannot be obtained. Furthermore, the compatibility with other compounding ingredients is significantly reduced. The number average molecular weight of the polyester resin is a polystyrene equivalent molecular weight 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, etc. 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, tri Methylolethane or the like can be used. As a commercially available polyester resin, "ALMATEX"
(Product name, manufactured by Mitsui Toatsu Chemicals, Inc.), "Alkynol"
(Product name, Sumitomo Bayer Urethane Co., Ltd.), "Desmofen" (Product name, Sumitomo Bayer Urethane Co., Ltd.),
"Byron" (trade name, manufactured by Toyobo Co., Ltd.) is available.

The blending amount of the above-mentioned a) polyol in the top coating film is preferably 40 to 90% by mass in the resin solid content. If the content of this polyol is less than 40% by mass, the workability of the coating film cannot be sufficiently secured, while
If it exceeds 90 mass%, the coating film hardness will be insufficient.

An isocyanate compound and / or an amino resin can be used as the curing agent in the above (b).
As the isocyanate compound, a polyisocyanate compound obtained by a general production method can be used, and among them, particularly, it can be used as a one-pack type coating material,
A polyisocyanate compound blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam or oxime is preferable. By using this blocked polyisocyanate compound, it is possible to store it in one liquid, and it becomes easy to use it as a paint for precoated steel sheet.

Further, more preferable polyisocyanate compounds include non-yellowing hexamethylene diisocyanate (hereinafter abbreviated as HDI) and its derivatives, tolylene diisocyanate (hereinafter abbreviated as TDI) and its derivatives, 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. Furthermore, "Sumijour" (product name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), "Desmodur" (product name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), "Coronate" (product name, manufactured by Nippon Polyurethane Co., Ltd.) Commercially available isocyanate compounds such as can also be used.

When a polyisocyanate compound is used as the curing agent, the compounding ratio [NC of the isocyanate group of the polyisocyanate compound and the hydroxyl group of the polyol (a) above]
It is desirable that the molar ratio of [O / OH] is 0.8 to 1.2, more preferably 0.90 to 1.10. [N
If the molar ratio [CO / OH] is less than 0.8, the coating film is insufficiently cured, 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 occurs between the excess isocyanate groups or between the isocyanate groups and the urethane compound, and the workability of the coating film deteriorates.

As the amino resin which is a curing agent, urea,
Resins obtained by the reaction of benzoguanamine, melamine, and the like with formaldehyde, and those obtained by alkylating them with alcohols such as methanol and butanol can be used. Specifically, methylated urea resin, n
Examples thereof include butylated benzoguanamine resin, methylated melamine resin, n-butylated melamine resin, and iso-butylated melamine resin. Furthermore, "Cymel" (trade name, manufactured by Mitsui Cyanamid Co., Ltd.), "Uban" (trade name, manufactured by Mitsui Toatsu Chemicals, Inc.), "Sumimar" (trade name, manufactured by Sumitomo Chemical Co., Ltd.), "Melan"
Commercially available amino resins such as (trade name, manufactured by Hitachi Chemical Co., Ltd.) can also be used.

When an amino resin is used as the curing agent, the compounding ratio (weight ratio of solid content) of the amino resin and the polyol of the above item a) is [polyol] / [amino resin]: 95/5.
The ratio is preferably 65/35, more preferably 90/10 to 75/25. The amount of the curing agent in (b) above is
The proportion in the resin solid content is preferably 9 to 50% by mass. If the compounding amount of this curing agent is less than 9% by mass, the coating film hardness will be insufficient, while if it exceeds 50% by mass, the processability will be insufficient.

In the present invention, a molybdate is contained in the top coating film as a rust preventive addition component. The details of the molybdate and the anticorrosion mechanism are the same as those described above for the undercoating film, and the molybdate exhibits anticorrosion performance (self-repairing performance) by the passivation action. In addition to the molybdate, by adding a rust preventive additive component composed of one or more organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles, and thiurams in combination, Particularly excellent corrosion resistance is obtained.

The details of the organic compounds such as triazoles, thiols, thiadiazoles, thiazoles and thiurams and the anticorrosion mechanism are the same as those described above with respect to the undercoat coating film, and the molybdate provides an anticorrosion property by the passivation action ( Self-repairing performance), whereas the triazoles, thiols, thiadiazoles, thiazoles, thiurams organic compounds exhibit corrosion resistance (self-repairing performance) by adsorption, and therefore, By adding a molybdate and a rust-preventive additive component consisting of one or more organic compounds selected from the above triazoles, thiols, thiadiazoles, thiazoles, and thiurams, the respective anti-corrosion agents are added. The anticorrosion effect of the rust-added components becomes complex, and as a result, a higher level of anticorrosion performance is obtained. Is will be.

Here, a rust preventive additive component (y) consisting of molybdate (x) and one or more organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles and thiurams. ) And the blending ratio is
It is suitable that the weight ratio of solids is (x) / (y) = 1/99 to 99/1, more preferably 10/90 to 90/10, and further preferably 20/80 to 80/20. . With such a blending ratio, different anticorrosive effects can be effectively combined.

The rust-preventive-additive components mixed in the above-mentioned top coating film do not contain harmful substances and have the action of enhancing the corrosion resistance of the coating film. The compounding amount (total compounding amount) of the rust preventive additive component in the top coating film is 1 to 20 parts by weight with respect to 100 parts by weight of the resin solid content. If the amount of the rust-preventive additive component is less than 1 part by weight based on 100 parts by weight of the resin solid content, sufficient corrosion resistance of the processed part cannot be obtained, while if it exceeds 20 parts by weight, there is a problem in workability. Further, an appropriate amount of wax may be blended in the top coat film depending on the purpose and application. As this wax, a natural wax or a synthetic wax can be used.

Further, in the coating composition for the top coating film, a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate or lead 2-ethylhexoate, carbonic acid; Pigments such as calcium, kaolin, clay, titanium oxide, talc, barium sulfate, mica, rouge, manganese blue, carbon black, aluminum powder, pearl mica; and various additives such as defoaming agent and anti-flow agent It can be blended. The thickness of the top coating film is preferably 10 to 20 μm. If the film thickness is less than 10 μm, the overall coating film performance as an overcoat film may not be sufficiently obtained, while if the film thickness exceeds 20 μm, the coating film hardness decreases.

In the actual use of the coating composition for forming the top coating film, these are dissolved in an organic solvent and / or water before use. As the organic solvent used,
For example, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 100 (trade name, manufactured by Exxon Chemical Co., Ltd.), Solvesso 150 (trade name, manufactured by Exxon Chemical Co., Ltd.), Solvesso 200 (trade name, manufactured by Exxon Chemical Co., Ltd.), 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 can be mentioned. In adjusting the coating composition for the top coating film, a conventional disperser such as a sand grind mill, a ball mill, or a blender or a kneader can be selected and used, and each component can be blended.

There are no particular restrictions on the method of applying the top coat film, but it is preferable to apply the coating composition by a method such as roll coater coating or curtain flow coating. After coating the coating composition for an overcoat on the above-mentioned undercoat, the coating is baked by a heating means such as hot air heating, infrared heating, induction heating and the like to crosslink the resin to obtain a cured coating. The baking treatment for heat-curing the top coating film is usually performed at a maximum reached plate temperature of about 180 to 260 ° C., and baking is performed for about 30 seconds to 3 minutes within this temperature range. The precoated steel sheet of the present invention may be used in 3 coats and 3 bake by further forming a coating film (for example, a clear coating film) on the top coating film.

[0055]

[Embodiment] [Embodiment 1] Base steel sheet having a thickness of 0.5 mm
Hot-dip galvanized steel sheet (Amount of coating on one side: 30
After degreasing (g / m ² ), a chemical conversion treatment liquid having the composition shown in Table 1 was applied so that the dry film adhesion amount was 65 mg / m ² in terms of Si, and then a drying treatment was performed at an ultimate plate temperature of 80 ° C. A chemical conversion coating (chrome-free coating) was formed. Also, for some of the comparative examples, as a chromium-based chemical conversion treatment, a coating type chromate "Surf Coat" manufactured by Nippon Paint Co., Ltd.
NRC300 ″ was applied at 50 mg / m ² in terms of Cr, and the same drying treatment was performed to form a chromium-based chemical conversion coating. Table 2 was formed on the chemical conversion coating thus formed. A polyester resin having the composition shown in Table 3 was used to adjust the composition shown in Table 3, and a rust preventive additive component shown in Table 4 was added to the composition, if necessary, to prepare a coating composition for an undercoating film having a dry film thickness of 5 μm. After coating so that a baking temperature (achievement plate temperature) of 215 ° C. and a baking time of 60 seconds are applied to form an undercoat coating film, and the composition shown in Table 5 is adjusted thereon. The coating composition for the top coating film containing the anticorrosive additive component shown in Table 4 had a dry film thickness of 15 μm.
After coating so that the baking temperature (reached plate temperature) 230
A baking treatment was performed at a temperature of 60 ° C. for a baking time of 60 seconds to form an overcoat coating film, and pre-coated steel sheets of Examples of the present invention and Comparative Examples were obtained.
The performances of these precoated steel sheets are shown in Tables 6 and 7 together with their film configurations.

The coating composition for the undercoat coating shown in Table 3 is
It adjusted as follows. (1) Preparation of polyester resin In a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device and a thermometer, dimethyl terephthalate, dimethyl isophthalate, ethylene glycol, neopentyl are blended as shown in Table 2. A glycol and a manganese acetate catalyst were charged, and the temperature was raised stepwise in a nitrogen atmosphere at a temperature of 160 to 220 ° C. for about 4 hours to carry out a transesterification reaction to distill off methanol. Furthermore, 0.5-
Polycondensation reaction was performed at 260 ° C. for about 2 hours under a reduced pressure of 5.0 mmHg to obtain a polyester resin. The obtained polyester resin was dissolved in a mixed solvent of cyclohexanone / Solvesso 150 (weight ratio 50/50) to prepare a nonvolatile content of 40%. The molecular weight of the polyester resin was adjusted by the polycondensation reaction time. As for the molecular weight, the number average molecular weight in terms of polystyrene was measured using gel permeation chromatography. (2) Production of coating composition for undercoat coating film Using the polyester resin obtained in (1) above, Table 3
A coating composition was produced in the compounding ratio as shown in. Among these coating compositions, those to which the rust preventive additive component was added were dispersed by a sand mill until the particle size of the rust preventive additive component became 5 μm or less.

The coating composition for the top coating film shown in Table 5 is
It adjusted as follows. A curing agent, a pigment, a curing catalyst, in a blending ratio as shown in Table 5 in the polyester polyol,
Approximately 1m in diameter after compounding additive and rust preventive additive
It was dispersed for about 30 minutes using a sand mill containing m glass beads. Further, cyclohexanone was added to adjust the nonvolatile content to 60%, and a coating composition was produced.

The test method and evaluation method for the performance test of the precoated steel sheet will be described below. (1) Appearance The appearance after coating was visually observed and evaluated by the following. ◯: No abnormality X: Smooth and uniform appearance cannot be obtained.

(2) Cross-Cut Section Corrosion Resistance After performing a salt spray test (SST test) on a test piece containing a cross-cut reaching the base for 480 hours, the maximum blistering width of the cross-cut section was measured. evaluated. ◯: Maximum swell width is less than 3 mm Δ: Maximum swell width is 3 to 5 mm ×: Maximum swell width is more than 5 mm

(3) Corrosion resistance of processed part A salt spray test (SST test) was performed on a 2T bent test piece for 480 hours, and then an adhesive tape was attached to and peeled from the 2T bent part to form a coating film on the 2T bent part. The peeling rate (area ratio:%) was measured and evaluated by the following. ◯: Coating film peeling rate is 10% or less Δ: Coating film peeling rate is over 10%, 50% or less ×: Coating film peeling rate is over 50%

(4) Adhesion to processed part Adhesive tape was adhered to and peeled from the 2T bent part of a 2T bent test piece, and the peeling rate (area ratio:%) of the coating film at the 2T bent part was measured. did. ◯: Coating film peeling rate of 10% or less Δ: Coating film peeling rate of more than 10% and 50% or less ×: Coating film peeling rate of more than 50% (5) Environmental harmony ○: No chromium compound is contained in the coating film ×: The coating contains chromium compounds

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5]

[0067]

[Table 6]

[0068]

[Table 7]

[Example 2] Inventive Example and Comparative Example under the same conditions as in [Example 1] except that the rust-preventive additive components shown in Table 8 were used in the undercoating film and the overcoating film. Example precoated steel sheets were manufactured and their respective performances were evaluated. The results are shown in Tables 9 and 10 together with the film constitution of each precoated steel sheet.

The test method and evaluation method for the performance test of the precoated steel sheet will be described below. (1) Appearance: same as in [Example 1] (2) Cross-cut portion Corrosion resistance After performing a salt spray test (SST test) for 750 hours on a test piece containing a cross-cut reaching the base, The maximum blistering width was measured and evaluated by the following. ◯: Maximum swell width is less than 3 mm Δ: Maximum swell width is 3 to 5 mm ×: Maximum swell width is more than 5 mm

(3) Corrosion resistance of processed part A salt spray test (SST test) was performed on a 2T bent test piece for 750 hours, and then an adhesive tape was attached to and peeled from the 2T bent part to form a coating film of the 2T bent part. The peeling rate (area ratio:%) was measured and evaluated by the following. ◯: Coating film peeling rate of 10% or less Δ: Coating film peeling rate of more than 10%, 50% or less ×: Coating film peeling rate of more than 50% (4) Adhesion of processed part: Same as [Example 1] (5) Environment Harmony: Same as [Example 1]

[0072]

[Table 8]

[0073]

[Table 9]

[0074]

[Table 10]

[0075]

As described above, the precoated steel sheet of the present invention is chromium-free and has excellent corrosion resistance and adhesion of the processed portion as high as a chromium-based precoated steel sheet having high corrosion resistance. , It is extremely useful as a chrome-free precoated steel sheet used in parts requiring high corrosion resistance of processed parts and adhesion of processed parts in applications such as building materials and automobiles.

Continuation of front page (51) Int.Cl. ⁷ identification code FI theme code (reference) C09D 7/12 C09D 7/12 133/00 133/00 161/20 161/20 163/00 163/00 167/00 167 / 00 175/04 175/04 201/00 201/00 C23C 22/07 C23C 22/07 22/40 22/40 28/00 28/00 C (72) Inventor Keiji Yoshida 1 Marunouchi 1-chome, Chiyoda-ku, Tokyo No. 2 Nihon Steel Pipe Co., Ltd. (72) Inventor Akira Matsuzaki 1-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Masaaki Yamashita 1-1-2, Marunouchi, Chiyoda-ku, Tokyo No. Nihon Kokan Co., Ltd. (72) Inventor Keiichi Kotani 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa NKK Steel Sheet Co., Ltd. (72) Inventor Yasuyuki Kajita Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa 6-1 F-Terms in NKK Steel Co., Ltd. (reference) 4D075 AE03 BB73X BB87X CA02 CA03 CA13 CA33 DA06 DB05 DB07 DC01 DC10 DC11 DC18 EA07 EB16 EB19 EB20 EB22 EB32 EB33 EB34 EB35 EB38 EB45 EB56 EC 01 EC03 EC07 EC15 EC54 4F100 AA20B AA33C AA33D AB03A AB18A AB20C AH03C AH03D AK01C AK01D AK25D AK41C AK41D AL05D AL06C AR00C BA04 BA07 BA10A BA10D CA02D CA14C CA14D DE01B EH71A EJ68B GB07 GB48 JB02 JL00 JL11 YY00C YY00D 4J038 CG141 CH121 DA142 DA162 DA172 DB061 DB471 DD041 DG111 DG191 HA246 JB35 JC02 JC07 JC18 KA03 KA05 NA03 NA12 NA27 PA07 PC02 4K026 AA12 AA13 BA01 BA03 BB06 BB08 CA16 CA18 CA23 CA29 CA30 CA31 CA39 CA41 DA02 EB08 EB11 4K044 AA02 AB02 BA10 BA11 BA14 CA18 CA11 BC21 BA11 BC02 BB04 BB04

Claims (6)

[Claims] 1. A precoated steel sheet having an undercoat coating film formed on the surface of a zinc-based plated steel sheet on which a chemical conversion treatment film containing silica fine particles and a binder thereof is formed, and further forming an overcoat coating film on the upper layer thereof. The above-mentioned top coating film contains molybdate in a resin solid content of 100.
A pre-coated steel sheet excellent in environmental harmony, corrosion resistance of processed part and adhesion of processed part, characterized by containing 1 to 20 parts by weight relative to parts by weight. 2. A precoated steel sheet having an undercoat coating film formed on the surface of a zinc-based plated steel sheet on which a chemical conversion treatment film containing silica fine particles and a binder thereof is formed, and further forming an overcoat coating film on the upper layer thereof. The above-mentioned top coating film comprises molybdate and a rust preventive additive component consisting of one or more organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles and thiurams. A pre-coated steel sheet excellent in environmental friendliness, corrosion resistance of the processed part and adhesion of the processed part, characterized by containing 1 to 20 parts by weight in total with respect to 100 parts by weight of the resin solid content. 3. The undercoating film contains molybdate in an amount of 5 to 50 parts by weight based on 100 parts by weight of the resin solid content, and the environmental compatibility and the corrosion resistance of the processed part according to claim 1 or 2. And a precoated steel sheet with excellent adhesion to the processed part. 4. The undercoating film comprises a molybdate and a rust preventive additive component comprising one or more organic compounds selected from triazoles, thiols, thiadiazoles, thiazoles and thiurams. The resin solid content of 10
A total of 5 to 50 parts by weight relative to 0 parts by weight, the precoated steel sheet having excellent environmental compatibility, corrosion resistance of the processed part, and adhesion of the processed part according to claim 1 or 2. 5. The environment according to claim 1, 2, 3 or 4, wherein the top coating film is a coating film formed by applying a coating composition containing the following a) and b). Pre-coated steel sheet with excellent harmony, corrosion resistance in the processed part and adhesion to the processed part. A) Polyester resin and / or acrylic resin: 40 to 90% by mass in the resin solid content b) Isocyanate compound and / or amino resin as a curing agent: 9 to 50% by mass in the resin solid content 6. The main resin component in a coating composition for forming an undercoat coating film is a polyester resin and / or an epoxy-modified polyester resin, according to claim 1, 2, 3, 4 or 5. Pre-coated steel sheet with excellent environmental friendliness, corrosion resistance in the processed part and adhesion to the processed part.