JP3514199B2 - Pre-coated steel sheet excellent in environmental harmony and corrosion resistance of processed part and method of manufacturing the same - Google Patents

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 excellent in environmental friendliness and corrosion resistance in a worked part, and a method for producing the same. 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 The pre-coated steel sheets currently used are
In order to secure corrosion resistance, a chemical conversion treatment containing chromium is performed, and a chromium-based rust preventive pigment is contained in the undercoat coating film (for example, JP-A-7-316497). However, these pre-coated steel sheets have recently been regarded as problematic due to the generation of pollution due to elution of highly toxic chromium.

To address such a problem, Japanese Patent Laid-Open No. 8-319
In Japanese Patent No. 437, it is stated that by adding a basic phosphite-based rust preventive pigment in an undercoat coating film, a non-toxic precoated steel sheet excellent in corrosion resistance can be obtained. Also,
JP-A-8-11257 describes that a pollution-free precoated steel sheet excellent in 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, these pollution-free precoated steel sheets have almost the same corrosion resistance as the conventional chromium-based rust preventive pigments in terms of the corrosion resistance of the flat surface portion, the scratched portion (cross cut portion) and the end surface. Although equivalent performance is obtained,
According to the investigation by the present inventors, it has been found that the corrosion resistance of the portion subjected to severe processing is inferior to that using the conventional chromium-based rust preventive pigment. Since the pre-coated steel sheet is used as a product after being processed, the corrosion resistance of the processed part is very important.

It is also conceivable to use a polyester-melamine-based coating film having improved workability as the top coating film in order to improve the corrosion resistance of the precoated steel sheet at the processed portion.
Although such a pre-coated steel sheet has improved corrosion resistance in the worked portion, it has a problem of poor coating film hardness. Therefore, the object of the present invention is to solve the problems of the prior art,
An object of the present invention is to provide an environment-friendly precoated steel sheet that can obtain excellent properties such as corrosion resistance of a processed part without adding a chromium-based rust preventive pigment in the coating film, and a method for producing the same.

[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. On the surface of the zinc-based plated steel sheet on which is formed, by forming an undercoat coating film in which multiple types of specific rust preventive additive components are added in combination, and by forming an overcoat coating film on the upper layer, environmental friendliness and processed parts A precoated steel sheet having excellent corrosion resistance can be obtained, and preferably, as a top coating film, a polyol is used as a main component, and a curing agent and mainly naphthalene 2,6-dicarboxylic acid and / or its lower alkyl ester are reacted with an alcohol component. By forming a coating film with a coating composition containing the polyester compound obtained in this way, we can see that a precoated steel sheet with particularly excellent corrosion resistance in the processed part can be obtained. Out was.

The present invention has been made on the basis of such findings, and its features are as follows. [1] Silica fine particles and water or water as a binder
Dispersible organic polymer, oxygenate (excluding chromate)
A pre-coated steel sheet having an undercoat coating film formed on the surface of a zinc-based plated steel sheet having a chemical conversion coating film containing one or more selected from the above, and further having an overcoat coating film formed thereon. There, the undercoat coating contains the following components (a) and (b) as a rust-preventive additive component, (a) Ca component (provided that the salt and other components added as the component (b) below) C contained as a part of Ca-containing compound
(including a): 1 to 8.4 parts by weight in terms of Ca based on 100 parts by weight of resin solids (b) SiO ₂ and / or silicate: amount of SiO ₂ converted based on 100 parts by weight of resin solids. 1 to 35 parts by weight and the compounding amount of the rust preventive additive components (a) and (b) (however, C
Ca equivalent amount for a component, the total resin solids of SiO ₂ and / or SiO ₂ in terms of the amount of the silicate) 1
A pre-coated steel sheet excellent in environmental compatibility and corrosion resistance in the worked part, characterized in that it is 5 to 100 parts by weight with respect to 00 parts by weight.

[2] Silica fine particles and water as a binder thereof
Soluble or water-dispersible organic polymer, oxyacid salt (however, chromium
(Excluding acid salts) , an undercoat coating film is formed on the surface of the zinc-based plated steel sheet on which a chemical conversion coating film containing one or more selected from A precoated steel sheet on which an overcoat film is formed, wherein the undercoat film contains the following components (a) to (c) as a rust preventive addition component, and (a) Ca component (however, the following (b) Salt added as a component of C, salt added as a component of (c) below, and other C
a is included as Ca contained as a part of the compound): 1 to 8.4 in terms of Ca based on 100 parts by weight of resin solid content.
Parts by weight (b) SiO ₂ and / or silicate: 1-35 parts by weight in terms of SiO _{2 with} respect to 100 parts by weight of resin solids (c) molybdate, tungstate, phosphite,
1 type or 2 types or more selected from borate and metaborate: 1 to 50 parts by weight with respect to 100 parts by weight of resin solid content, and the compounding amount of the rust-preventive additive components (a) to (c). (However, Ca
The total amount of the components is Ca equivalent amount, and SiO ₂ and / or silicate is the SiO ₂ equivalent amount).
A pre-coated steel sheet excellent in environmental friendliness and corrosion resistance of the processed part, characterized in that it is 5 to 100 parts by weight with respect to 0 parts by weight.

[3] In the precoated steel sheet according to the above [1] or [2], the top coating film has the following resin components as a) to
A precoated steel sheet excellent in environmental harmony and corrosion resistance in a processed part, which is a coating film formed by applying a coating composition containing c). B) General formula (1)

[Chemical 2] A repeating unit of 1 to 15% by weight in the resin solid content b) Polyester resin and / or acrylic resin: 40 to 90% by weight in the resin solid content c) Curing agent Isocyanate compound and / or amino resin: 9 to 50% by weight in the resin solid content

[4] In the precoated steel sheet according to any one of the above [1] to [3], the main resin component in the coating composition forming the undercoat coating film is a polyester resin and / or an epoxy modified polyester resin, Film thickness is 2
A pre-coated steel sheet having excellent environmental compatibility and corrosion resistance in the worked part, which is characterized by having a thickness of up to 20 μm. [ 5 ] On any of the precoated steel sheets of [ 1 ] to [ 4 ] above
In the chemical conversion coating, the fine silica particles and the binder are mixed.
The ratio is a solid content weight ratio of silica fine particles / binder = 1/0.
Environmental harmony and addition characterized by 01 to 1/10
Pre-coated steel sheet with excellent corrosion resistance. [ 6 ] On the precoated steel sheet according to any of the above [ 1 ] to [ 5 ]
In addition, the amount of the chemical conversion coating adhered to the silica particles is
Environment characterized by a calculated amount of 5 to 200 mg / m ^2.
Pre-coated steel sheet with excellent harmony and corrosion resistance in the processed area.

[ 7 ] Silica fine particles and water as a binder thereof
Soluble or water-dispersible organic polymer, oxyacid salt (however, chromium
On the surface of the zinc-plated steel sheet on which a chemical conversion treatment film containing one or more selected from (excluding acid salts) is formed, the following (a) and ( It contains the component b), and (a) the Ca component (however, the salt added as the component of the following (b) and the C contained as part of other Ca-containing compounds)
(including a): 1 to 8.4 parts by weight in terms of Ca based on 100 parts by weight of resin solids (b) SiO ₂ and / or silicate: amount of SiO ₂ converted based on 100 parts by weight of resin solids. 1 to 35 parts by weight and the compounding amount of the rust preventive additive components (a) and (b) (however, C
Ca equivalent amount for a component, the total resin solids of SiO ₂ and / or SiO ₂ in terms of the amount of the silicate) 1
After coating a coating composition for an undercoating coating of 5 to 100 parts by weight with respect to 00 parts by weight, baking treatment is performed at an ultimate plate temperature of 180 to 260 ° C., and then a coating composition for a topcoating coating is prepared. A method for producing a precoated steel sheet excellent in environmental harmony and corrosion resistance in a worked part, characterized by performing a baking treatment at an ultimate plate temperature of 180 to 260 ° C. after coating.

[ 8 ] Silica fine particles and water as a binder thereof
Soluble or water-dispersible organic polymer, oxyacid salt (however, chromium
(Excluding acid salts)), on the surface of the zinc-based plated steel sheet on which the chemical conversion treatment film containing one or more selected from the following (a) to ( (a) Ca component (provided that the salt added as the component (b) below, the salt added as the component (c) below, and other C).
a is included as Ca contained as a part of the compound): 1 to 8.4 in terms of Ca based on 100 parts by weight of resin solid content.
Parts by weight (b) SiO ₂ and / or silicate: 1-35 parts by weight in terms of SiO _{2 with} respect to 100 parts by weight of resin solids (c) molybdate, tungstate, phosphite,
1 type or 2 types or more selected from borate and metaborate: 1 to 50 parts by weight with respect to 100 parts by weight of resin solid content, and the compounding amount of the rust-preventive additive components (a) to (c). (However, Ca
The total amount of the components is Ca equivalent amount, and SiO ₂ and / or silicate is the SiO ₂ equivalent amount).
After coating a coating composition for an undercoating coating in an amount of 5 to 100 parts by weight with respect to 0 parts by weight, a baking treatment is performed at an ultimate plate temperature of 180 to 260 ° C., and then a coating composition for a topcoating coating is prepared. A method for producing a precoated steel sheet excellent in environmental harmony and corrosion resistance in a worked part, characterized by performing a baking treatment at an ultimate plate temperature of 180 to 260 ° C. after coating. [ 9 ] In the manufacturing method of [ 7 ] or [ 8 ] above , the chemical conversion
The blending ratio of silica fine particles and binder in the treated film is solid content.
Silica fine particles / binder = 1 / 0.01 to 1/1 by weight ratio
0 for environmental compatibility and corrosion resistance of processed parts
Excellent pre-coated steel sheet manufacturing method. [ 10 ] The manufacturing method according to any one of the above [ 7 ] to [ 9 ]
The amount of chemical conversion coating adhered is the amount of silica particles converted to Si.
Environmental harmonization characterized by 5 to 200 mg / m ²
Of precoated steel sheet with excellent corrosion resistance and corrosion resistance

[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 pre-coated steel sheet of the present invention is a coated steel sheet in which an undercoat coating film and a top coating film containing specific components are formed on the surface of a zinc-based plated steel sheet on which a chemical conversion treatment film containing specific components is formed. Various zinc-based plated steel sheets such as a hot-dip galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, an electrogalvanized steel sheet, and a hot-dip Zn-Al alloy plated steel sheet can be used as the zinc-based plated steel sheet serving as the base steel sheet.

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.

Further, as the binder, water-soluble or water-dispersible organic polymer, oxyacid salt (however, chromate is excluded) using one or more selected from among. 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 g / 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, the undercoat coating film formed as 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 or more kinds of polyester resin, epoxy resin, epoxy modified polyester resin such as bisphenol A-added polyester resin, etc. may be used. However, a polyester resin and / or an epoxy-modified polyester resin is particularly preferable from the viewpoint of processability.

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 component of the coating composition, the content of bisphenol A in this bisphenol A-added polyester resin is 1 to 70% by weight, more preferably, the resin solid content. It is desirable that the amount is 3 to 60% by weight, particularly preferably 5 to 50% by weight. When the content of bisphenol A in the bisphenol A-added polyester resin is less than 1% by weight, 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, when the content of bisphenol A exceeds 70% by weight, the elongation of the coating film cannot be sufficiently 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 the 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.

In the undercoat coating film, as a rust preventive additive component,
(a) Ca component (however, a salt added as a component of (b) below, a salt added as a component of (c) below, and other C)
including Ca contained as part of the a-containing compound),
(b) SiO ₂ and / or silicate, more preferably,
(c) One or more kinds of salts such as molybdate are blended.

The form of addition of the Ca component in the undercoat coating film is not particularly limited, and it can be added as a compound containing calcium metal and / or Ca. As the Ca-containing compound, in addition to calcium oxide, calcium hydroxide, single salts containing only calcium as a cation such as calcium silicate, calcium carbonate, calcium molybdate, and further, calcium molybdate / zinc, etc. A double salt containing calcium and a cation other than calcium may be added, or two or more of these may be added.

Therefore, as the Ca component,
a salt added as a component of (b) (for example, calcium silicate), a salt added as a component of the above (c) (for example, calcium molybdate, calcium tungstate, calcium phosphite, calcium borate, etc.) It may be Ca contained as a part. It is considered that the Ca component blended in the undercoat coating film has a function of forming a protective film at an early stage by being eluted in an environment where corrosion is likely to occur and suppressing further progress of corrosion.

The content of the Ca component in the undercoat coating film is 1 to 8.4 in terms of Ca based on 100 parts by weight of the resin solid content.
Parts by weight. If the content of Ca component (calculated amount) is less than 1 part by weight relative to 100 parts by weight of the resin solid content, the self-repairing effect of the coating film by calcium is poor, while 8.4
When it exceeds the weight part, the elution amount of calcium becomes excessive and the adhesiveness between the coating films deteriorates. In addition, a part or all of the Ca component mixed in the undercoat coating film, the above (b) and (c)
When it is Ca contained in the salt added as a component of
It goes without saying that the content of the Ca component includes the Ca equivalent amount of the salt containing Ca.

SiO _{2 is} used as an anticorrosive additive in the undercoating film.
And / or adding silicate has a C effect on the corrosion resistance.
This is because the effect of adding the component a can be enhanced. There is no particular restriction on SiO ₂ and / or the addition form of the silicate into the undercoat paint film, as such colloidal SiO ₂ for SiO _2, also for the silicate is added as calcium silicate be able to.

The content of SiO ₂ and / or silicate in the undercoat coating film is Si based on 100 parts by weight of the resin solid content.
The amount is 1 to 35 parts by weight in terms of O ₂ . Resin solid content 100
If the content of SiO ₂ and / or silicate with respect to parts by weight (SiO ₂ conversion amount) is less than 1 part by weight, the effect of addition is not observed, while if it exceeds 35 parts by weight, the adhesion of the coating film decreases. , The coating film is easily peeled off during processing. Also,
When SiO ₂ is added, the average particle size is 10μ.
m or less is preferable. By setting the average particle diameter of SiO ₂ to 10 μm or less, the surface area of SiO ₂ is increased, and thus the corrosion resistance is improved.

The rust-preventive additive component to be added to these undercoat coating films does not contain harmful substances and has the effect of enhancing the corrosion resistance of the coating film. It is considered that the reason for the remarkable improvement is that, when the Ca component and SiO ₂ and / or silicate are added together, the stability of the protective film formed from these two components is specifically high. Here, SiO ₂ of Ca equivalent amount and SiO ₂ and / or silicate of said Ca components
The ratio of the Ca conversion amount of the Ca component to the total conversion amount is preferably 15 to 80% by weight. When the ratio of the Ca component in terms of Ca is less than 15% by weight and more than 80% by weight, the effect of improving the corrosion resistance of the worked part due to the combined addition of the Ca component and SiO ₂ and / or silicate tends to be poor.

In the present invention, one or more molybdates, tungstates, phosphites, borates, and metaborates are further added to the undercoat film as a third rust preventive addition component. Two or more kinds can be added, whereby the corrosion resistance of the processed part can be further improved. Examples of the molybdate include zinc molybdate, calcium molybdate, zinc calcium molybdate, and the like, and one or more of them can be used. Among them, zinc molybdate and calcium molybdate are particularly preferable. It is suitable.

Examples of the tungstate include zinc tungstate, calcium tungstate, zinc calcium tungstate and the like, and one or more of them can be used. Among them, zinc tungstate and tungsten are particularly preferable. Calcium acid is preferred.
The type of phosphite is not particularly limited, but phosphite of alkaline earth metal, aluminum, or zinc is preferable, and one or more of these phosphites can be used. Of these, phosphite salts of alkaline earth metals such as calcium and magnesium are particularly preferable.

Examples of the borate include calcium borate, barium borate, zinc borate and the like, and examples of the metaborate include calcium metaborate, barium metaborate and the like, or one of them. Two or more kinds can be used, but among them, calcium borate, barium borate, and barium metaborate are particularly preferable.

The content of the one or more rust preventive addition components selected from molybdate, tungstate, phosphite, borate and metaborate in the undercoat coating film is the resin. The solid content is 1 to 50 parts by weight based on 100 parts by weight. If the content of the above-mentioned rust-preventive additive component is less than 1 part by weight with respect to 100 parts by weight of the resin solid content, the addition effect is not recognized, while if it exceeds 50 parts by weight, the adhesion of the coating film is deteriorated, and during processing The coating film is easy to peel off.

These third rust-preventive additive components also contain no harmful substances and have the effect of enhancing corrosion resistance.
The combined addition of the anticorrosive components (a) and (b) into the undercoat coating film significantly improves the corrosion resistance of the processed part. The reason is that these third rust preventive additive components are
It is considered that this is because it has a function of further enhancing the barrier property of the stable protective film formed by the rust-preventive additive components (a) and (b).

In addition, the above (a) and
Compounding amount of rust preventive additive component (b) (however, for Ca component
Is equivalent to Ca, SiO_TwoAnd / or for silicates
SiO _Two(Converted amount), and the addition of rust prevention additive in (c) above.
When the components are mixed, the rust preventive additive components (a) to (c) above
The total is 5 to 100 parts by weight for 100 parts by weight of resin solids.
The quantity is to be used. Addition of rust prevention to 100 parts by weight of resin solids
If the total amount of the components is less than 5 parts by weight, sufficient processing area resistance
The foodability is not obtained, on the other hand, if it exceeds 100 parts by weight, it is processable.
Cause problems.

Further, in the coating composition for the undercoating film, a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate or lead 2-ethylhexoate, carbonic acid, depending on the purpose and use, 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 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 μ, workability is insufficient. In actually using the coating composition for forming the undercoat coating film, these are dissolved in an organic solvent before use. 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.

In preparing the coating composition for the 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. In the present invention, there is no particular restriction on the constitution of the top coating film, and as the main resin, one or more of polyester resin, acrylic resin, fluororesin and the like can be used, but particularly excellent performance is obtained. In order to obtain the above, the top coating film is used as a resin component a) a specific polyester compound, and b) the above a).
A coating composition formed by applying a coating composition containing a specific polyol other than (c) and a specific curing agent (preferably containing these as a main component resin) and baking the composition may be formed. preferable. 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, the polyester compound (a) is a polyester compound having the following general formula (1) as a repeating unit.

[Chemical 3]

The polyester compound (a) can be obtained by reacting the acid component naphthalene-2,6-dicarboxylic acid and / or its lower alkyl ester with the alcohol component. As the acid component for obtaining the polyester compound of the above b), naphthalene-2,
6-dicarboxylic acid and / or its lower alkyl ester is mainly used, but a part of them is used as a dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,7-dicarboxylic acid, diphenyldicarboxylic acid, or a dicarboxylic acid thereof. It can also be replaced with a lower alkyl ester or the like. Examples of the lower alkyl ester include methyl ester and ethyl ester having 1 to 2 carbon atoms. However, even in this case, the main component naphthalene-2,6-dicarboxylic acid is 8% of the entire acid component.
It is desirable that the amount is 5 mol% or more, and the ratio of other compounds to be replaced is less than 15 mol%.

A diol is mainly used as the alcohol component for obtaining the above-mentioned a) polyester compound. Aliphatic diols, alicyclic diols and the like can be used as this diol, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexane. Examples include dimethanol. 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
(Abbreviated as TG) can also be used. Moreover, you may use these, mixing them.

As the alcohol component, a polyhydric alcohol having a valence of 3 or more may be used in addition to the above-mentioned diol. Examples of the polyhydric alcohol include triethylene glycol, glycerin, pentaerythritol, trimethylolpropane, trimethylolethane and the like.
The above-mentioned acid component and alcohol component react with each other 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 above-mentioned a) polyester compound used in the present invention can be obtained by a general 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. Therefore, in order to carry out the reaction efficiently, it is desirable to mix the acid component and the alcohol component in a molar ratio as close as possible to 1: 2. The polyester compound may be used alone or in combination of two or more.

The polyester compound produced by the combination of the acid component and the alcohol component as described above exhibits anisotropy when observed with a polarizing microscope. A coating film containing such a polyester compound is considered to contribute to the improvement of coating film hardness and processability even after baking, due to the action such as the orientation which is a characteristic of the liquid crystal compound, the toughness of the coating film. To be

When the above-mentioned PEG or PTG is used as the alcohol component, it reacts with the acid component to produce a polyester compound having an ether bond. The polyester compound having an ether bond has a reduced viscosity of 0.20.
It is preferably dl / g or less. Reduced viscosity is 0.2
When it exceeds 0 dl / g, the solubility in a solvent and the compatibility with a polyol, a curing agent, etc. are remarkably reduced, and the coating film performance becomes insufficient. In addition, the reduced viscosity of the sample is phenol /
It is a value measured by dissolving it in a solution of tetrachloroethane (weight ratio: 60/40) and using an Ubbelohde viscometer at 25 ° C. When this polyester compound having an ether bond is used, toughness is imparted to the crosslinked structure due to the combination of a flexible ether chain and a rigid naphthalene skeleton, which is believed to contribute to the improvement of coating film hardness and processability. To be

The blending amount of the polyester compound (a) is 1 to 15% by weight, preferably 2 to 12% by weight, and more preferably 3 to 10% by weight in the resin solid content. If the blending amount of the polyester compound is less than 1% by weight, the effect of improving the coating film performance is not remarkable, while if the blending amount exceeds 15% by weight, the flexibility of the coating film decreases.

Next, an acrylic resin and / or a polyester resin can be used as the above-mentioned polyol). The acrylic resin which is the polyol of the above (b) is
It 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, but the preferable range of the number average molecular weight is 1700 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 a polyester-equivalent molecular weight measured by gel permeation chromatography (hereinafter referred to as GPC).

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 (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 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 amount of the above-mentioned polyol) is 40 to 90% by weight in terms of the resin solid content. If the content of the polyol is less than 40% by weight, the workability of the coating film cannot be sufficiently secured, while if it exceeds 90% by weight, the coating film hardness becomes insufficient.

An isocyanate compound and / or an amino resin can be used as the curing agent of the above (c).
As the isocyanate compound, an isocyanate compound obtained by a general production method can be used, and among them, particularly usable as a one-pack type paint, phenol, cresol, aromatic secondary amine, tertiary alcohol Polyisocyanate compounds blocked with a blocking agent such as lactam, lactam and oxime are preferred. 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 a curing agent, the compounding ratio [NCO / OH] of the isocyanate group of the polyisocyanate compound and the hydroxyl group of the polyester compound of the above (a) and the polyol of the above (2) is 0.8 in molar ratio. ~ 1.2, more preferably 0.90 to 1.10
It is desirable to set the range to. If the molar ratio of [NCO / 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, [NCO / O
When the molar ratio of [H] 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" (product name, manufactured by Mitsui Cyanamid Co., Ltd.), "Uban" (product name, manufactured by Mitsui Toatsu Chemicals, Inc., "Sumimar" (product 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 amino resin, the polyester compound of the above a) and the above b) are used.
The compounding ratio (weight ratio of solid content) of the polyol of [polyester compound] + [polyol] / [amino resin]: 9
5/5 to 65/35, preferably 90/10 to 75/2
A ratio of 5 is preferable. The content of the curing agent in the above (c) is 9 to 50% by weight in the resin solid content.
If the compounding amount of this curing agent is less than 9% by weight, the coating film hardness will be insufficient, while if it exceeds 50% by weight, the processability will be insufficient. 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 may be added depending on the purpose and use; 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 actually using the coating composition for forming the overcoat coating film, these are dissolved in an organic solvent 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 adjusting the coating composition for the top coating film, a sand grind mill,
A normal dispersing machine such as a ball mill or a blender or a kneading machine can be selected and used to blend the respective components.

There are no particular restrictions on the method of applying the top coat, 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.

[0066]

[Examples] After degreasing a hot-dip galvanized steel sheet having a thickness of 0.5 mm (plating adhesion amount per one side: 30 g / m ² ) which is a base steel sheet, colloidal silica: 5 parts by weight, ammonium orthophosphate: 1 part by weight, Polyacrylic acid: 1 part by weight,
Water: 93 parts by weight of a chemical conversion treatment liquid having a composition was applied so that the dry film adhesion amount was 65 mg / m ² in terms of Si, followed by a drying treatment at an ultimate plate temperature of 80 ° C. to form a chemical conversion treatment film, A polyester resin having a composition shown in Table 1 was used to apply a coating composition for an undercoating film having a composition shown in Tables 2 to 5 to a predetermined dry film thickness, and then the baking temperature was set. (Achieved plate temperature) 215 ° C., baking treatment for 60 seconds is performed to form an undercoat coating film, and a coating composition for the top coating film having the composition shown in Table 6 is dried thereon to a dry film thickness of 15 μm. After being applied so as to obtain a precoat steel sheet of the present invention example and the comparative example, a top coating film was formed by performing a baking treatment at a baking temperature (reaching plate temperature) of 230 ° C. and a baking time of 60 seconds. The performance of these precoated steel sheets is shown in Tables 7 and 8.

The coating compositions for undercoat coating films shown in Tables 2 to 5 were prepared as follows. [Coating composition for undercoating film] (1) Preparation of polyester resin Dimethyl terephthalate having the composition shown in Table 1 was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device and a thermometer. , Dimethyl isophthalate, ethylene glycol, neopentyl glycol and manganese acetate are charged, and the temperature is 160 to 220 ° C. in a nitrogen atmosphere.
The temperature was raised stepwise over about 4 hours to carry out a transesterification reaction to distill off methanol. Furthermore, 0.5 to 5.0
A polycondensation reaction was performed at 260 ° C. for about 2 hours under reduced pressure of 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 rust-preventive additive component PG-1 for undercoat film The rust-preventive additive component PG-1 was prepared so as to have the composition shown in Tables 2 to 5. The preparation procedure was as follows. First, calcium carbonate dispersed in water was heated to 50 ° C, sodium silicate was added, washed with water, filtered, dried, and then pulverized. (3) Production of coating composition for undercoat coating film Using the polyester resin obtained in (1) above, Table 2
~ Coating compositions P-1 to P-24 were produced in the blending ratios shown in Table 5. These coating compositions contained a rust preventive additive component and were dispersed by a sand mill until the particle size became 5 μm or less.

The coating composition for the top coating film shown in Table 6 is
It adjusted as follows. [Coating composition for top coating film] (1) Preparation of polyester compound In a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer, naphthalene-2,6-dicarboxylic acid dimethyl ether (hereinafter referred to as "2 , 6-NDCM ”)
1.02 mol of 1,1,4-butanediol was added and 2
It was heated and melted at 00 ° C. Then, titanium tetra-n-butoxide was added as a catalyst in an amount of 0.06 mol% with respect to 2,6-NDCM, and the reaction temperature was gradually increased to 240 ° C.
32g of theoretical amount of methanol (1.0m
ol) was distilled off, the reaction was terminated. As a result, a polyester compound was obtained. The reduced viscosity of this polyester compound was 0.04 dl / g.

The chemical structural formula of this polyester compound is shown below.

[Chemical 4]

(2) Preparation of polyester polyol In a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device and a thermometer, 174.6 parts of dimethyl terephthalate,
213.4 parts of dimethyl isophthalate, 93.0 parts of ethylene glycol, 52.0 parts of neopentyl glycol.
And 1.5 parts of a manganese acetate catalyst were charged, and a transesterification reaction was performed at 180 to 210 ° C. in a nitrogen atmosphere to distill off methanol. Furthermore, 6.1 parts of trimethylolpropane was added, and the mixture was heated to 250 ° C. and heated to 10 mmHg.
The polymerization reaction was carried out by gradually reducing the pressure until the non-volatile content was adjusted to 70% with a cyclohexanone solvent. Thus, a polyester polyol was obtained. The obtained polyester polyol has a number average molecular weight (Mn) determined by GPC.
Was 3000, and the hydroxyl value determined by the phthalic anhydride-pyridine method was 60.0 mgKOH / g.

(3) Production of coating composition for top coating film A curing agent, a pigment, and a curing catalyst are added to the polyester compounds and polyester polyols obtained in the above (1) and (2) at the compounding ratios shown in Table 6. After the addition of the additive and the additives, the mixture was dispersed for about 30 minutes using a sand mill containing glass beads having a diameter of about 1 mm. Further, cyclohexanone was added to adjust the nonvolatile content to 60%, and the coating composition C-
1 and C-2 were manufactured.

The test method and evaluation method for the performance test of the precoated steel sheet will be described below. (1) Pencil hardness JIS K 5400 8. using Mitsubishi pencil "Uni".
The test was carried out based on No. 4 and showed a hardness limit at which the coating film was not scratched. (2) Cylindrical drawing process Using a cylindrical drawing machine, for a test piece of size 10 cm x 10 cm, sample size: 90φ, die: 42.4
φ5R, Plunger: 40.4 φ4R, Hold pressure:
Molding was performed under a cylindrical drawing condition of 2.0 ton, the coating film surface after the molding was observed, and evaluated by the following. ◯: No abnormality at all Δ: Slight scratches were found ×: Clear scratches were found (abnormal)

(3) Corrosion resistance of processed part (1) A salt spray test (SST test) was carried out on a 2T bent test piece for 480 hours, and then an adhesive tape was attached to and peeled from the 2T bent part. The peeling rate (area ratio:%) of the coating film 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) Corrosion resistance of cross-cut part (1) A salt spray test (SST test) was carried out for 480 hours on a test piece containing a cross-cut reaching the base, and then the maximum blistering width of the cross-cut part was measured. It was 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

(5) Corrosion resistance of processed part (2) 300 cycles of combined cycle test for 2T bent test pieces
After carrying out the cycle, the adhesive tape was adhered to and peeled from the 2T bent portion, and the peeling rate of the coating film at the 2T bent portion (area ratio:
%) Was measured and evaluated by the following. The combined cycle test method was salt spray (30 ° C., 0.5 h), wet (30 ° C., 95 ± 3% RH, 0.5 h), hot air drying (5
This was repeated with 0 cycle, 2 hours) and hot air drying (30 degrees, 2 hours) as one cycle. ◯: 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%

(6) Corrosion resistance of cross-cut part (2) After performing a combined cycle test for 300 cycles on a test piece containing a cross-cut reaching the base, the maximum blistering width of the cross-cut part was measured and evaluated by the following. did. The combined cycle test method was salt spray (30 ° C, 0.
5h), wet (30 ° C, 95 ± 3% RH, 0.5h),
Hot air drying (50 ° C, 2h), hot air drying (30 ° C, 2h)
Was set as one cycle, and this was repeated. ◯: Maximum swelling width is less than 3 mm Δ: Maximum swelling width is 3 to 5 mm ×: Maximum swelling width is more than 5 mm (7) Environmental compatibility ○: Chromium-based compound is not included in coating film ×: Chromium-based compound in coating film including

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

[Table 4]

[0082]

[Table 5]

[0083]

[Table 6]

[0084]

[Table 7]

[0085]

[Table 8]

[0086]

As described above, the precoated steel sheet of the present invention is excellent in environmental friendliness, cross-cut portion corrosion resistance, processed portion corrosion resistance, coating film hardness and forming workability,
Therefore, it is extremely useful as a pre-coated steel sheet used for parts requiring high environmental friendliness, cross-cut portion corrosion resistance, processed portion corrosion resistance, coating film hardness and forming workability in applications such as home electric appliances, building materials and automobiles.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C09D 5/08 C09D 5/08 167/00 167/00 (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo (56) References JP-A-5-84466 (JP, A) JP-A-7-118871 (JP, A) JP-A-10-44306 (JP, A) JP-A-11-57609 ( (58) Fields surveyed (Int.Cl. ⁷ , DB name) B05D 1/00-7/26 B32B 1/00-35/00 C09D 1/00-10/00 C09D 101/00-201 / 10 C23C 28/00

Claims (10)

(57) [Claims] 1. Silica fine particles and water-soluble binder thereof
Or water-dispersible organic polymer, oxyacid salt (however, chromate
(Excluding the above) , an undercoat coating film is formed on the surface of a zinc-based plated steel sheet on which a chemical conversion treatment film containing one or more selected from A precoated steel sheet, wherein the undercoating film has the following (a) and (b) as a rust-preventive additive component:
(A) Ca component (however, C added as a part of the salt and other Ca-containing compounds added as the component (b) below).
(including a): 1 to 8.4 parts by weight in terms of Ca based on 100 parts by weight of resin solids (b) SiO ₂ and / or silicate: amount of SiO ₂ converted based on 100 parts by weight of resin solids. 1 to 35 parts by weight and the compounding amount of the rust preventive additive components (a) and (b) (however, C
Ca equivalent amount for a component, the total resin solids of SiO ₂ and / or SiO ₂ in terms of the amount of the silicate) 1
A pre-coated steel sheet excellent in environmental compatibility and corrosion resistance in the worked part, characterized in that it is 5 to 100 parts by weight with respect to 00 parts by weight. 2. Silica fine particles and a water-soluble binder thereof
Or water-dispersible organic polymer, oxyacid salt (however, chromate
(Excluding the above) , an undercoat coating film is formed on the surface of the zinc-based plated steel sheet on which a chemical conversion treatment film containing one or more selected from A precoated steel sheet, wherein the undercoat coating contains the following components (a) to (c) as a rust preventive addition component, and (a) Ca component (however, a salt added as a component of the following (b)) , Salts and other C added as components of (c) below
a is included as Ca contained as a part of the compound): 1 to 8.4 in terms of Ca based on 100 parts by weight of resin solid content.
Parts by weight (b) SiO ₂ and / or silicate: 1-35 parts by weight in terms of SiO _{2 with} respect to 100 parts by weight of resin solids (c) molybdate, tungstate, phosphite,
1 type or 2 types or more selected from borate and metaborate: 1 to 50 parts by weight with respect to 100 parts by weight of resin solid content, and the compounding amount of the rust-preventive additive components (a) to (c). (However, Ca
The total amount of the components is Ca equivalent amount, and SiO ₂ and / or silicate is the SiO ₂ equivalent amount).
A pre-coated steel sheet excellent in environmental friendliness and corrosion resistance of the processed part, characterized in that it is 5 to 100 parts by weight with respect to 0 parts by weight. 3. The top coating film as a resin component, the following a)
To C), which is a coating film formed by applying a coating composition containing (3) to (3). B) General formula (1) A repeating unit of 1 to 15% by weight in the resin solid content b) Polyester resin and / or acrylic resin: 40 to 90% by weight in the resin solid content c) Curing agent Isocyanate compound and / or amino resin: 9 to 50% by weight in the resin solid content 4. A base resin component in a coating composition for forming an undercoating film is a polyester resin and / or an epoxy-modified polyester resin, and the film thickness of the undercoating film is 2 to 20.
The precoated steel sheet according to claim 1, 2 or 3, which is excellent in environmental compatibility and corrosion resistance of the processed portion. 5. A silica fine particle and a binder in a chemical conversion coating.
The compounding ratio of the solid content is silica fine particles / binder = 1
/0.01-1/10, It is characterized by the above-mentioned.
For environmental harmony and corrosion resistance of processed parts as described in 1, 2, 3 or 4.
Excellent pre-coated steel sheet. 6. The amount of the chemical conversion coating adhered is that of silica fine particles.
5 to 200 mg / m in terms of Si ^Two Is characterized by
The environmental harmony according to claim 1, 2, 3, 4 or 5.
Pre-coated steel sheet with excellent corrosion resistance in the processed area. 7. Silica fine particles and water-soluble binder thereof
Or water-dispersible organic polymer, oxyacid salt (however, chromate
The following components (a) and (b) are contained as rust preventive addition components on the surface of the zinc-based plated steel sheet on which the chemical conversion treatment film containing one or more selected from , (A) Ca component (however, C added as a part of the salt and other Ca-containing compounds added as the component (b) below)
(including a): 1 to 8.4 parts by weight in terms of Ca based on 100 parts by weight of resin solids (b) SiO ₂ and / or silicate: amount of SiO ₂ converted based on 100 parts by weight of resin solids. 1 to 35 parts by weight and the compounding amount of the rust preventive additive components (a) and (b) (however, C
Ca equivalent amount for a component, the total resin solids of SiO ₂ and / or SiO ₂ in terms of the amount of the silicate) 1
After coating a coating composition for an undercoating coating of 5 to 100 parts by weight with respect to 00 parts by weight, baking treatment is performed at an ultimate plate temperature of 180 to 260 ° C., and then a coating composition for a topcoating coating is prepared. A method for producing a precoated steel sheet excellent in environmental harmony and corrosion resistance in a worked part, characterized by performing a baking treatment at an ultimate plate temperature of 180 to 260 ° C. after coating. 8. Silica fine particles and water-soluble binder thereof
Or water-dispersible organic polymer, oxyacid salt (however, chromate
The following components (a) to (c) are contained as rust preventive addition components on the surface of the zinc-based plated steel sheet on which the chemical conversion treatment film containing one or more selected from , (A) Ca component (however, the salt added as the component (b) below, the salt added as the component (c) below, and other C)
a is included as Ca contained as a part of the compound): 1 to 8.4 in terms of Ca based on 100 parts by weight of resin solid content.
Parts by weight (b) SiO ₂ and / or silicate: 1-35 parts by weight in terms of SiO _{2 with} respect to 100 parts by weight of resin solids (c) molybdate, tungstate, phosphite,
1 type or 2 types or more selected from borate and metaborate: 1 to 50 parts by weight with respect to 100 parts by weight of resin solid content, and the compounding amount of the rust-preventive additive components (a) to (c). (However, Ca
The total amount of the components is Ca equivalent amount, and SiO ₂ and / or silicate is the SiO ₂ equivalent amount).
After coating a coating composition for an undercoating coating in an amount of 5 to 100 parts by weight with respect to 0 parts by weight, a baking treatment is performed at an ultimate plate temperature of 180 to 260 ° C., and then a coating composition for a topcoating A method for producing a precoated steel sheet excellent in environmental harmony and corrosion resistance in a worked part, characterized by performing a baking treatment at an ultimate plate temperature of 180 to 260 ° C. after coating. 9. A silica fine particle and a binder in a chemical conversion coating.
The compounding ratio of the solid content is silica fine particles / binder = 1
8. It is /0.01-1/10, It is characterized by the above-mentioned.
Or a pre-coated product with excellent environmental compatibility and corrosion resistance in the processed part
Manufacturing method of coated steel sheet. 10. The amount of the chemical conversion coating adhered is silica fine particles.
5 to 200 mg / m in terms of Si ^Two Characterized by being
The environmental compatibility and the processed part resistance according to claim 7, 8 or 9.
A method for producing a precoated steel sheet having excellent corrosion resistance.