JP2001191447A - Precoat steel panel excellent in environmental affinity and processing part corrosion resistance and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a precoat steel panel capable of affording excellent characteristics inclusive of processing part corrosion resistance even if a chromium type rustproof pigment is not added to a coating film. SOLUTION: A precoat steel panel is constituted by forming an undercoat film on the surface of a galvanized steel panel having a chemical forming treatment film containing silica fine particles and a binder therefore formed thereon and foaming a topcoat film on the undercoat film. The undercoat film contains 1-30 parts by weight per 100 parts by weight of a resin solid of a Ca component (a) in terms of Ca, 1-35 parts by weight per 100 parts by weight of a resin solid of SiO2 and/or silicate (b) in terms of SiO2, 1-30 parts by weight per 100 parts by weight of a resin solid of phosphoric acid and/or phosphate (c) in terms of PO4 and, if necessary, 1-50 parts by weight per 100 parts by weight of a resin solid of one or more molybdate or tungstate (d) as rustproof additives and the sum total of the compounding amounts of the rustproof additives (a)-(d) is 5-100 parts by weight of 100 parts by weight of a resin solid.

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 having excellent environmental friendliness and corrosion resistance in a processed part, and a method for producing the same. The precoated steel sheet of the present invention is suitable for, for example, home electric appliances and building materials, and can also be used for automobiles.

[0002]

2. Description of the Related Art Currently used precoated steel sheets are:
In order to ensure corrosion resistance, a chemical conversion treatment containing chromium is performed, and a chromium-based rust-preventive pigment is contained in the undercoat film (for example, JP-A-7-316497). However, recently, there is a concern that such precoated steel sheets may cause pollution due to elution of highly toxic chromium.

To solve such a problem, Japanese Patent Application Laid-Open No. 8-319
Japanese Patent No. 437 discloses that a pre-coated steel sheet which is non-toxic and excellent in corrosion resistance can be obtained by including a basic phosphite-based rust-preventive pigment in an undercoating film. Also,
JP-A-8-11257 states that a pollution-free precoated steel sheet excellent in corrosion resistance can be obtained by including an isocyanate compound and a phosphoric acid-based rust preventive pigment in an undercoating film.

[0004]

However, these non-polluting pre-coated steel sheets have almost the same corrosion resistance of flat portions, scratches (cross-cut portions) and end faces as those using conventional chromium-based rust preventive pigments. Although the same performance can be obtained,
According to the investigation by the present inventors, it has been found that the corrosion resistance of the parts subjected to severe processing is inferior to those 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.

[0005] Further, in order to improve the corrosion resistance of the processed portion of the precoated steel sheet, it is conceivable to use a polyester-melamine-based coating film with improved workability as an overcoating film.
Such a precoated steel sheet has a problem in that the corrosion resistance of the processed portion is improved, but the hardness of the coating film is inferior. Therefore, an object of the present invention is to solve such problems of the prior art,
It is an object of the present invention to provide an environmentally friendly precoated steel sheet capable of obtaining excellent properties such as corrosion resistance in a processed part without adding a chromium-based rust preventive pigment in a coating film, and a method for producing the same.

[0006]

Means for Solving the Problems The inventors of the present invention have studied to solve the above problems and obtain a precoated steel sheet exhibiting excellent performance. As a result, a chemical conversion coating containing fine silica particles and a binder thereof has been obtained. On the surface of the galvanized steel sheet on which is formed, an undercoating film is formed by adding several kinds of specific rust-preventive additive components in combination, and an overcoating film is formed on the undercoating film, thereby achieving environmental friendliness and processing. Pre-coated steel sheet with excellent corrosion resistance can be obtained, and also preferably as a top coat,
Forming a paint-blended coating film comprising a polyol as a main component, a curing agent, and a polyester compound obtained by reacting naphthalene 2,6-dicarboxylic acid and / or a lower alkyl ester thereof with an alcohol component. As a result, it has been found that a precoated steel sheet having particularly excellent corrosion resistance in the processed portion can be obtained.

The present invention has been made based on such findings, and the features thereof are as follows. [1] A precoated steel sheet in which an undercoat film is formed on the surface of a zinc-based plated steel sheet on which a chemical conversion coating containing silica fine particles and a binder is formed, and an overcoat film is further formed thereon. The undercoating film contains the following components (a) to (c) as rust preventive additives, (a) Ca component (however, a salt added as a component of the following (b), the following (c) Salts and other C added as components of
(Including Ca contained as a part of a-containing compound): 1 to 30 parts by weight in terms of Ca based on 100 parts by weight of resin solids. (b) SiO ₂ and / or silicate: 100 parts by weight of resin solids 1-35 parts by weight in terms of SiO ₂ amount relative part (c) phosphoric acid and / or phosphate: at PO ₄ equivalent amount relative to the resin solid content of 100 parts by weight to 30 parts by weight and the (a) To (c) the amount of the rust preventive additive component (however, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
A precoated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part, which is 5 to 100 parts by weight based on parts by weight.

[2] The surface of a galvanized steel sheet on which a chemical conversion coating containing silica fine particles and a binder is formed,
An undercoating film is formed, and further a precoated steel sheet having an overcoating film formed thereon, wherein the undercoating film contains the following components (a) to (d) as rust preventive additive components, a) Ca component (however, a salt added as a component of the following (b), a salt added as a component of the following (c), a salt added as a component of the following (d), and other Ca-containing compounds (Including Ca contained as a part): 1 to 30 parts by weight in terms of Ca with respect to 100 parts by weight of resin solid content (b) SiO ₂ and / or silicate: SiO with respect to 100 parts by weight of resin solid content ₂ to 35 parts by weight (c) phosphoric acid and / or phosphate: 1 to 30 parts by weight of PO ₄ equivalent to 100 parts by weight of resin solids (d) molybdate and tungstate , Phosphite,
One or more selected from borates and metaborates: 1 to 50 parts by weight per 100 parts by weight of resin solids and the amount of the rust preventive additive component (a) to (d) (However, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
A precoated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part, which is 5 to 100 parts by weight based on parts by weight.

[3] In the pre-coated steel sheet according to the above [1] or [2], the overcoating film has the following resin components a) to b)
A pre-coated steel sheet having excellent environmental friendliness and corrosion resistance in processed parts, characterized in that it is a coating film formed by applying a coating composition containing (c). B) General formula (1)

Embedded image B) a polyester resin and / or an acrylic resin: 40 to 90% by weight in a resin solid content c) a 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 base resin component in the coating composition forming the undercoat film is a polyester resin and / or an epoxy-modified polyester resin. The film thickness is 2
A pre-coated steel sheet excellent in environmental friendliness and corrosion resistance in a processed part, characterized in that the thickness is up to 20 µm.

[5] The surface of a galvanized steel sheet on which a chemical conversion coating containing silica fine particles and a binder is formed,
It contains the following components (a) to (c) as rust preventive additives, (a) Ca component (however, a salt added as a component of the following (b), a salt added as a component of the following (c) And other C
(Including Ca contained as a part of a-containing compound): 1 to 30 parts by weight in terms of Ca based on 100 parts by weight of resin solids. (b) SiO ₂ and / or silicate: 100 parts by weight of resin solids 1-35 parts by weight in terms of SiO ₂ amount relative part (c) phosphoric acid and / or phosphate: at PO ₄ equivalent amount relative to the resin solid content of 100 parts by weight to 30 parts by weight and the (a) To (c) the amount of the rust preventive additive component (however, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
5 to 100 parts by weight of the coating composition for the undercoating film is applied, followed by baking treatment at the ultimate plate temperature of 180 to 260 ° C., and then applying the coating composition for the topcoating film. After that, a baking treatment is performed at a plate temperature of 180 to 260 ° C., thereby producing a precoated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part.

[6] The surface of a galvanized steel sheet on which a chemical conversion coating containing silica fine particles and a binder is formed,
It contains the following components (a) to (d) as rust preventive additives, (a) Ca component (however, a salt added as a component of the following (b), a salt added as a component of the following (c) (Including the salt added as a component of the following (d) and Ca contained as a part of other Ca-containing compounds): 1 to 30 parts by weight in terms of Ca with respect to 100 parts by weight of resin solid content (b ) SiO ₂ and / or silicate: 1 to 35 parts by weight in terms of SiO _{2 based} on 100 parts by weight of resin solids (c) Phosphoric acid and / or phosphate: based on 100 parts by weight of resin solids 1 to 30 parts by weight in terms of PO ₄ (d) molybdate, tungstate, phosphite,
One or more selected from borates and metaborates: 1 to 50 parts by weight per 100 parts by weight of resin solids and the amount of the rust preventive additive component (a) to (d) (However, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
5 to 100 parts by weight of the coating composition for the undercoating film is applied, followed by baking treatment at the ultimate plate temperature of 180 to 260 ° C., and then applying the coating composition for the topcoating film. After that, a baking treatment is performed at a plate temperature of 180 to 260 ° C., thereby producing a precoated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limiting the same will be described below. The pre-coated steel sheet of the present invention is a coated steel sheet in which a base coat and a top coat containing a specific component are formed on the surface of a galvanized steel sheet on which a chemical conversion coating containing a specific component is formed. Various types of galvanized steel sheets, such as a hot-dip galvanized steel sheet, a galvannealed steel sheet, an electrogalvanized steel sheet, and a hot-dip Zn-Al alloy-coated steel sheet, can be used as the zinc-coated steel sheet serving as the base steel sheet.

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

The chemical conversion coating formed on the surface of the galvanized steel sheet is a chemical conversion coating containing fine silica particles (fine powder) and a binder. As the silica fine particles, for example, one or more selected from wet silica (colloidal silica) and dry silica (fumed silica) having a primary particle size of about 1 to 100 nm can be used. By blending such silica fine particles in the chemical conversion coating, the adhesion, the scratch resistance, and the corrosion resistance of the upper layer of the chemical conversion coating to the resin film (undercoat) can be increased.

The binder may be, for example, one or more selected from water-soluble or water-dispersible organic polymers and oxyacid salts (excluding chromates). . 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, and vanadate. By blending such a binder in the chemical conversion treatment film, it is possible to enhance the bonding between the silica fine particles (the cohesive failure resistance of the film) and the adhesion of the silica fine particles to the base metal.

Further, the chemical conversion treatment solution contains a Zr compound, Ti
Compound 1 or Hf compound (for example, fluoro complex salt)
Seeds or two or more kinds can be added as additives, and they can be contained in the chemical conversion coating. The mixing ratio of the silica fine particles and the binder is desirably in the range of silica fine particles / binder = 1 / 0.01 to 1/10 in terms of the solid content weight ratio. When the compounding ratio of the silica fine particles to the compounding amount of the silica fine particles is less than 0.01, the bondability between the silica fine particles (the cohesive failure resistance of the film) and the adhesion of the silica fine particles to the base metal are inferior. Further, when the compounding ratio of the binder to the compounding amount of the silica fine particles is more than 10, the adhesion, the scratch resistance, and the corrosion resistance with the resin film (undercoat) on the chemical conversion treatment film are inferior.

The amount of the chemical conversion film deposited is 5 to 200 mg / m ^{2 in} terms of Si of silica fine particles contained as a component.
It is preferable to be within the range. 5mg / m
^If it is less than ² , the adhesion to the base metal and the corrosion resistance will be poor, while if it is more than 200 g / m ² , the adhesion to the resin coating (undercoat) on the chemical conversion coating will be inferior. Although there is no particular limitation on the treatment method for forming the chemical conversion treatment film, a chemical conversion treatment solution is generally coated with a roll coater and then dried. In this drying, the film is usually dried at a plate temperature of about 50 to 150 ° C. by a heating means such as hot air heating, infrared heating, induction heating or the like.

Next, the undercoat film formed on the chemical conversion film will be described. As the base resin of the coating composition for forming the undercoat coating film, for example, one or more of an epoxy-modified polyester resin such as a polyester resin, an epoxy resin, and a bisphenol A-added polyester resin may be used. Although it is possible, a polyester resin and / or an epoxy-modified polyester resin are particularly preferable from the viewpoint of processability.

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

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

When the undercoat film is formed of 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 undercoat film has the above-mentioned physical properties. In order to make the number average molecular weight of the polyester resin 1000 to 50,000, more preferably 3
000-40000, particularly preferably 5000-300
It is desirable to use one in the range of 00. If the number average molecular weight of the polyester resin is less than 1,000, the above properties are not obtained because the elongation of the coating film is insufficient, and the improvement of the coating film performance is not sufficient. On the other hand, when the number average molecular weight exceeds 50,000, the coating composition becomes high in viscosity, so that an excess of a diluting solvent is required, and the proportion of the resin in the coating decreases, so that an appropriate coating film cannot be obtained. Further, the compatibility with other compounding components is significantly reduced.

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

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

The polybasic acid component for obtaining the polyester resin includes phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, hymic anhydride, trimic anhydride, Melitic 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 thereof include acids, 1,4-cyclohexanedicarboxylic acid, and the like. Two or more 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 and the like can be used. Further, two or more of these may be used as a mixture. Examples of the polyisocyanate compound used as a curing agent include: aromatic diisocyanates such as xylylene diisocyanate, tolylene diisocyanate, and 4,4'-diphenylmethane diisocyanate; aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; isophorone diisocyanate Alicyclic diisocyanates such as, for example; multimers of these diisocyanates or adducts with polyhydric alcohols; and blocking agents such as phenol, lactam, alcohol, mercaptan, imine, and amine. , Or an imidazole-based or oxime-based blocking agent).
Further, as a dissociation catalyst for these blocked polyisocyanate compounds, tin octoate, dibutyltin dilaurate, 2-ethylhexoate lead and the like can be used.

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

In the undercoating film, as an antirust additive component,
(a) Ca component (however, a salt added as a component of the following (b), a salt added as a component of the following (c), a salt added as a component of the following (d) and other Ca-containing compounds (B) SiO ₂ and / or silicate, (c) phosphoric acid and / or phosphate, and more preferably (d) a salt such as molybdate. Seeds or two or more kinds are blended.

The form of addition of the Ca component to the undercoat film is not particularly limited, and it can be added as calcium metal and / or a Ca-containing compound. Examples of the Ca-containing compound include calcium oxide, calcium hydroxide, calcium silicate, calcium carbonate, calcium phosphate, a simple salt containing only calcium as a cation such as calcium molybdate, and the like.
A double salt containing a cation other than calcium and calcium, such as zinc, calcium / magnesium phosphate, calcium / zinc molybdate, or the like, or two or more of these may be added.

Therefore, as the Ca component,
A salt (for example, calcium silicate) added as a component of (b), a salt (for example, calcium phosphate, calcium phosphate / zinc or the like) added as a component of (c), and a salt added as a component of (d) above Ca (eg, calcium molybdate, calcium tungstate, calcium phosphite, calcium borate, etc.) may be included as a part of the salt. It is considered that the Ca component blended in the undercoat film elutes in an environment where corrosion is likely to occur, thereby forming a protective film at an early stage, and has a function of suppressing further progress of corrosion.

The content of the Ca component in the undercoating film is 1 to 30 parts by weight in terms of Ca based on 100 parts by weight of the resin solids. If the content of Ca component (calculated in terms of Ca) is less than 1 part by weight per 100 parts by weight of the resin solids, the self-repair effect of the coating film by calcium is poor. In addition, the adhesion between the coating films is reduced. In addition, when a part or all of the Ca component blended in the undercoat film is Ca contained in the salt added as the component (b) to (d), the content of the Ca component is It goes without saying that the Ca-conversion amount of the Ca-containing salt is included.

SiO ₂ as a rust preventive additive in the undercoating film
And / or the addition of silicates has an 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.

[0033] The content of SiO ₂ and / or silicate in the undercoat film is determined based on 100 parts by weight of the resin solid content.
And 1-35 parts by weight O ₂ equivalent amount. Resin solids 100
If the content of SiO ₂ and / or silicate with respect to parts by weight (in terms of SiO ₂ ) is less than 1 part by weight, the effect of the addition is not recognized, while if it exceeds 35 parts by weight, the adhesion of the coating film is reduced. In addition, the coating film is easily peeled off during processing. Also,
When SiO ₂ is added, its average particle size is 10 μm.
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, so that the corrosion resistance is improved.

The phosphoric acid and / or phosphate compounded in the undercoating film has a function of forming a protective film between the metal and the eluting metal (eg, zinc as a plating component). It is thought that it exerts. Phosphoric acid and phosphates are not particularly limited in terms of the phosphate ion skeleton and the degree of condensation. Therefore, the phosphate may be any of a normal salt, a dihydrogen salt and a monohydrogen salt, and the normal salt includes all condensed phosphates such as polyphosphate in addition to orthophosphate. Phosphates also include double salts thereof.

The content of phosphoric acid and / or phosphate in the undercoat film is determined based on PO ₄
The equivalent amount is 1 to 30 parts by weight. Phosphoric acid and / or phosphate content relative to 100 parts by weight of resin solids (PO ₄
When the amount is less than 1 part by weight, the effect of the addition is not recognized. On the other hand, when the amount exceeds 30 parts by weight, the adhesion of the coating film is reduced and the coating film is easily peeled off during processing.

The rust-preventive additives contained in these undercoat films do not contain harmful substances and have the effect of increasing the corrosion resistance of the paint film. Is markedly improved when the Ca component, SiO ₂ and / or silicate, phosphoric acid and / or phosphate are added in combination, and the stability of the protective film formed from these three components is specifically increased. It is thought to be due to being expensive.

Here, the Ca conversion amount of the Ca component and Si
The ratio of the Ca component of the Ca component to the total amount of O ₂ and / or silicate in terms of SiO ₂ is preferably 15 to 80% by weight. If the ratio of the Ca component in the Ca component is less than 15% by weight or more than 80% by weight, the Ca component and SiO
There is a tendency that the effect of improving the corrosion resistance of the processed portion by adding ₂ and / or silicate in combination is inferior.

In the present invention, one or more selected from molybdates, tungstates, phosphites, borates, and metaborates may be further added as a fourth rust preventive additive in the undercoating film. Two or more kinds can be added, whereby the corrosion resistance of the processed portion can be further improved. Examples of the molybdate include zinc molybdate, calcium molybdate, calcium zinc molybdate, and the like, and one or more thereof 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, and zinc calcium tungstate, and one or more of them can be used. Calcium acid is preferred.
Although the kind of the phosphite is not particularly limited, a phosphite of an alkaline earth metal, aluminum or zinc is preferable, and one or more of these phosphites can be used. Among them, phosphites of alkaline earth metals such as calcium and magnesium are particularly preferable.

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

The content of one or more rust preventive additives selected from molybdates, tungstates, phosphites, borates and metaborates in the undercoat film is determined by the resin. 1 to 50 parts by weight based on 100 parts by weight of the solid content. If the content of the rust-preventive additive component relative to 100 parts by weight of the resin solids is less than 1 part by weight, the effect of the addition is not recognized. On the other hand, if it exceeds 50 parts by weight, the adhesion of the coating film is reduced, The coating film is easily peeled.

The fourth rust preventive additive also contains no harmful substances and has an effect of improving corrosion resistance.
The combined addition of the components (a) to (c) to the undercoating film together with the rust-preventive additive component significantly improves the corrosion resistance of the processed portion. The reason is that these fourth rust-preventive additive components include
It is considered that this is because there is a function of further improving the barrier properties of the stable protective film formed by the rust-preventive additive components (a) to (c).

The above (a) to (c) in the undercoat film
The amount of the rust-preventive additive component (except for the Ca component
a, Si for SiO ₂ and / or silicate
O ₂ equivalent, phosphoric acid and / or phosphate
₄ equivalents), and when the rust preventive additive component (d) is blended, the total of the rust preventive additive components (a) to (d) is based on 100 parts by weight of the resin solid content. And 5 to 100 parts by weight. If the total amount of the rust-preventive additive component is less than 5 parts by weight based on 100 parts by weight of the resin solid content, sufficient corrosion resistance in the processed part cannot be obtained, while if it exceeds 100 parts by weight, there is a problem in workability.

In addition, depending on the purpose and application, a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate, and lead 2-ethylhexoate; Pigments such as calcium, kaolin, clay, titanium oxide, talc, barium sulfate, mica, red iron oxide, manganese blue, carbon black, aluminum powder, and pearl mica; and other additives such as defoaming agents and anti-flow agents as appropriate Can be blended.

The thickness of the undercoat film is preferably in the range of 2 to 20 μm. If the film thickness is less than 2 μm, sufficient corrosion resistance cannot be obtained, while if it exceeds 20 μm, workability is insufficient. In actually using the coating composition for forming the undercoat film, these are dissolved in an organic solvent before use. As the organic solvent to be used, for example, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone,
Solvesso 100 (trade name, manufactured by Exxon Chemical), Solvesso 150 (trade name, manufactured by Exxon Chemical), Solvesso 200 (trade name, manufactured by Exxon Chemical), toluene, xylene, methyl cellosolve, butyl cellosolve, cellosolve acetate, butyl cellosolve acetate Carbitol, ethyl carbitol, butyl carbitol, ethyl acetate, butyl acetate, petroleum ether, petroleum naphtha and the like.

In preparing the coating composition for the undercoat coating film, a conventional dispersing machine or kneading machine such as a sand grind mill, a ball mill, or a blender can be selected and used, and each component can be blended. . There is no particular limitation on the method of applying the undercoating film, but it is preferable to apply the coating composition by a method such as roll coater coating or curtain flow coating. After applying the coating composition for the undercoat coating on the surface of the zinc-based plated steel sheet on which the above-mentioned chemical conversion coating has been formed, hot air heating, infrared heating, induction heating and other heating means, usually about 180 to 260 ° C. A baking process is performed at the reached plate temperature for about 30 seconds to 1 minute.

Next, the overcoat film formed on the undercoat film will be described. In the present invention, there is no particular restriction on the configuration of the overcoating film, and as the main resin, one or more of polyester resin, acrylic resin, fluororesin and the like can be used. In order to obtain it, a top coat is used as a resin component, i) a specific polyester compound, and b)
A coating composition containing a specific polyol excluding (i) and (c) a specific curing agent (preferably containing these as a main component resin) is applied to form a coating film formed by baking treatment. preferable. By forming such a specific top coat, particularly excellent corrosion resistance in the processed portion can be obtained by the combined effect with the above-mentioned undercoat.

Hereinafter, the specific top coat will be described. First, the polyester compound (a) is a polyester compound having the following general formula (1) as a repeating unit.

Embedded image

The polyester compound (a) can be obtained by reacting naphthalene-2,6-dicarboxylic acid as an acid component and / or a lower alkyl ester thereof with an alcohol component. The acid component for obtaining the polyester compound of the above a) includes naphthalene-2,
6-Dicarboxylic acids and / or lower alkyl esters thereof are mainly used, and some of them are dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene-2,7-dicarboxylic acid and diphenyldicarboxylic acid, or the dicarboxylic acids of these dicarboxylic acids. It can be replaced by a lower alkyl ester or the like. Examples of the lower alkyl ester include a methyl ester and an ethyl ester having 1 to 2 carbon atoms. However, even in this case, naphthalene-2,6-dicarboxylic acid, which is the main component, accounts for 8% of the entire acid component.
It is desirable that the content be 5 mol% or more, and the proportion of the other compound to be replaced be suppressed to less than 15 mol%.

As the alcohol component for obtaining the polyester compound (a), a diol is mainly used. As this diol, an aliphatic diol, an alicyclic diol, or the like can be used. For example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexane Dimethanol and the like. Further, polyoxyalkylene glycol, particularly polyethylene glycol having a number average molecular weight of 1,000 or less (hereinafter abbreviated as PEG), or a number average molecular weight of 1
000 or less polytetraethylene glycol (hereinafter, P
TG) can also be used. Further, these may be used as a mixture.

As the alcohol component, a polyhydric alcohol having a valency of 3 or more may be used in addition to the diol described above. Examples of the polyhydric alcohol include triethylene glycol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane.
The acid component and the alcohol component react as described above to produce the polyester compound (a). In particular, when PEG having a number average molecular weight of 1000 or less or PTG having a number average molecular weight of 1000 or less is used, a polyester compound having an ether bond is produced.

The polyester compound (a) used in the present invention can be obtained by a usual polyester production method such as a transesterification method or a direct esterification method. Usually, the acid component and the alcohol component react at a molar ratio of 1: 2, and therefore, in order to perform the reaction efficiently, it is desirable to mix the acid component and the alcohol component at a molar ratio as close as possible to 1: 2. Further, the polyester compound can be used either alone or in combination of two or more.

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

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

The amount of the polyester compound (a) is from 1 to 15% by weight, preferably from 2 to 12% by weight, more preferably from 3 to 10% by weight, based on the solid content of the resin. 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 polyol in the above item b). The acrylic resin which is the polyol of the above (b),
The compound is not particularly limited as long as it has at least two hydroxyl groups in one molecule and has a number average molecular weight of 1500 to 12000, but a preferable range of the number average molecular weight is 1700 to 10000. Hydroxyl groups in the acrylic resin molecule are randomly arranged in the acrylic resin main chain, and when the number average molecular weight is less than 1500, the processability is significantly reduced. On the other hand, if the number average molecular weight exceeds 12,000, the viscosity becomes high, so that an excess of a diluting solvent is required, and the proportion of the resin in the coating material is reduced, so that an appropriate coating film cannot be obtained. Further, the compatibility with other compounding components is significantly reduced. The number average molecular weight of the acrylic resin is a molecular weight in terms of polyester measured by gel permeation chromatography (hereinafter, referred to as GPC).

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

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

The polyester resin is a copolymer obtained by heating and reacting a polybasic acid component and a polyhydric alcohol by a known method. As the polybasic acid component, for example, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used. Further, as the polyhydric alcohol, for example,
Ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, glycerin, pentaerythritol, trimethylolpropane, trimethyl glycol Methylolethane or the like can be used. “Almatex” is a commercially available polyester resin.
(Trade name, manufactured by Mitsui Toatsu Chemicals, Inc.), “Alkinol”
(Trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), "desmophen" (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.),
"Byron" (trade name, manufactured by Toyobo Co., Ltd.) and the like.

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

As the curing agent of the above (c), an isocyanate compound and / or an amino resin can be used.
As the isocyanate compound, an isocyanate compound obtained by a general production method can be used. Among them, phenol, cresol, aromatic secondary amine, and tertiary alcohol, which can be used as a one-pack type paint, are particularly preferable. Polyisocyanate compounds blocked with a blocking agent such as lactam, oxime and the like are preferred. By using this blocked polyisocyanate compound, storage with one liquid becomes possible, and use as a paint for a precoated steel sheet is facilitated.

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

When a polyisocyanate compound is used as a curing agent, the compounding ratio [NCO / OH] of the isocyanate group of the polyisocyanate compound to the hydroxyl group of the polyester compound of (a) and the polyol of (b) is 0.8. To 1.2, more preferably 0.90 to 1.10
It is desirable to be within the range. If the molar ratio of [NCO / OH] is less than 0.8, curing of the coating film is insufficient, and desired coating film hardness and strength cannot be obtained. On the other hand, [NCO / O
When the molar ratio of [H] exceeds 1.2, a side reaction occurs between the excess isocyanate groups or between the isocyanate group and the urethane compound, and the processability of the coating film deteriorates.

As the amino resin as a curing agent, urea,
Resins obtained by reacting benzoguanamine, melamine, etc. with formaldehyde, and those obtained by alkyl etherifying these with alcohols such as methanol and butanol can be used. Specifically, a methylated urea resin, n
-Butylated benzoguanamine resin, methylated melamine resin, n-butylated melamine resin, iso-butylated melamine resin, and the like. Furthermore, “Symel” (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.), “ Meran ”
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 and the polyester compound of the above (a) and the above (ii)
The mixing ratio (weight ratio of solid content) with the polyol was [polyester compound] + [polyol] / [amino resin]: 9
5/5 to 65/35, preferably 90/10 to 75/2
Preferably, the ratio is 5. The compounding amount of the curing agent in the above item (c) is set to 9 to 50% by weight in the resin solid content.
If the amount of the curing agent is less than 9% by weight, the hardness of the coating film is insufficient, while if it exceeds 50% by weight, the processability is insufficient. In addition, an appropriate amount of wax can be added to the overcoat film according to the purpose and use. As this wax, a natural wax or a synthetic wax can be used.

Further, depending on the purpose and application, a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate, and lead 2-ethylhexoate; Pigments such as calcium, kaolin, clay, titanium oxide, talc, barium sulfate, mica, red iron oxide, manganese blue, carbon black, aluminum powder, and pearl mica; and other additives such as defoaming agents and anti-flow agents as appropriate Can be blended. It is preferable that the thickness of the overcoat film is 10 to 20 μm. If the film thickness is less than 10 μm, there is a possibility that the overall coating performance as a topcoat film may not be sufficiently obtained, while if the film thickness exceeds 20 μm, the coating film hardness decreases.

In actually using a coating composition for forming a top coat, these are dissolved in an organic solvent before use. Examples of the organic solvent to be used include methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 100 (trade name, manufactured by Exxon Chemical Co., Ltd.), Solvesso 150 (trade name, manufactured by Exxon Chemical Co., Ltd.) and Solvesso 200 (trade name, 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 adjusting the coating composition for the top coat, a sand grind mill,
An ordinary dispersing machine or kneading machine such as a ball mill or a blender can be selected and used, and each component can be blended.

The method of applying the top coat is not particularly limited, but preferably the coating composition is applied by a method such as roll coater coating or curtain flow coating. After applying the coating composition for the top coat on the above-mentioned undercoat, the coat is baked by a heating means such as hot air heating, infrared heating or induction heating to crosslink the resin to obtain a cured coating. In the baking treatment for heat-curing the top coat, usually, the maximum attained plate temperature is about 180 to 260 ° C., and baking is performed in this temperature range for about 30 seconds to 3 minutes. In addition, the pre-coated steel sheet of the present invention may be formed by further forming a coating film (for example, a clear coating film) on the top coating film, and may be used in three coats and three bake.

[0069]

EXAMPLE A 0.5 mm thick hot-dip galvanized steel sheet (coating weight per side: 30 g / m ² ) as a base steel sheet was degreased, and then colloidal silica: 5 parts by weight, ammonium orthophosphate: 1 part by weight, Polyacrylic acid: 1 part by weight,
Water: a conversion treatment liquid having a composition of 93 parts by weight 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. to form a chemical conversion treatment film. A polyester resin having a composition shown in Table 1 was further coated thereon with a coating composition for an undercoat film adjusted to the composition shown in Tables 2 to 5 so as to have a predetermined dry film thickness. (Achieved plate temperature) A baking treatment was performed at 215 ° C. and a baking time of 60 seconds to form an undercoat film, and a coating composition for a topcoat film having a composition shown in Table 6 having a dry film thickness of 15 μm was further formed thereon Then, a baking treatment was performed at a baking temperature (attained plate temperature) of 230 ° C. and a baking time of 60 seconds to form a topcoat film, and precoated steel sheets of the present invention and comparative examples were obtained. Tables 7 and 8 show the performances of these precoated steel sheets.

The coating compositions for undercoat films shown in Tables 2 to 5 were prepared as follows. [Coating composition for undercoat film] (1) Preparation of polyester resin Dimethyl terephthalate was added to a reaction vessel equipped with a heating device, a stirrer, a rectification tower, a decompression device, and a thermometer with the composition shown in Table 1. , Is charged with dimethyl isophthalate, ethylene glycol, neopentyl glycol and manganese acetate, and at a temperature of 160 to 220 ° C in a nitrogen atmosphere,
The temperature was increased stepwise over about 4 hours to perform a transesterification reaction, and methanol was distilled off. Furthermore, 0.5 to 5.0
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%. Further, the molecular weight of the polyester resin was adjusted by the polycondensation reaction time. The molecular weight was measured by gel permeation chromatography, and the number average molecular weight in terms of polystyrene was measured.

(2) Production of Rust Preventive Additive Component PG-1 for Undercoating Film Rust preventive additive component PG-1 was prepared so as to have the composition shown in Tables 2 to 5. The preparation procedure is as follows: first, zinc oxide dispersed in water is heated to 50 ° C., and zinc orthophosphate is formed by adding phosphoric acid, and then calcium carbonate and nitric acid are added, further sodium silicate is added, and water washing is performed. After filtration and drying, the mixture was pulverized. (3) Production of coating composition for undercoat coating film Using the polyester resin obtained in the above (1), Table 2
-Coating compositions P-1 to P-23 were produced in the proportions shown in Table 5. These coating compositions contained rust preventive additives and were dispersed by a sand mill until the particle size became 5 μm or less.

The coating composition for a top coat shown in Table 6 is as follows:
The adjustment was performed as follows. [Coating composition for top coat] (1) Preparation of polyester compound In a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer, naphthalene-2,6-dicarboxylic acid dimethyl ether (hereinafter referred to as "2. , 6-NDCM ") in 0.5 mo
1.02 mol of 1,1,4-butanediol
Heated and melted at 00 ° C. Thereafter, 0.06 mol% of titanium tetra-n-butoxide as a catalyst was added to 2,6-NDCM, and the reaction temperature was gradually increased to 240 ° C.
To a theoretical amount of 32 g of methanol (1.0 m
ol) was distilled off when the reaction was completed. Thus, 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.

Embedded image

(2) Preparation of Polyester Polyol 174.6 parts of dimethyl terephthalate was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device, and a thermometer.
213.4 parts of dimethyl isophthalate, 93.0 parts of ethylene glycol and 52.0 parts of neopentyl glycol
And 1.5 parts of a manganese acetate catalyst, and a transesterification reaction was carried out at 180 to 210 ° C. in a nitrogen atmosphere to distill off methanol. Further, 6.1 parts of trimethylolpropane is added, and while heating to 250 ° C., 10 mmHg
The polymerization reaction was carried out by gradually reducing the pressure until then, and the nonvolatile content was adjusted to 70% with a cyclohexanone solvent. Thus, a polyester polyol was obtained. The obtained polyester polyol had 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) Preparation of paint composition for top coat The curing agent, pigment and curing catalyst are added to the polyester compound and polyester polyol obtained in the above (1) and (2) in the proportions shown in Table 6. After the addition of 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, by adding cyclohexanone to adjust the nonvolatile content to 60%, the coating composition C-
1, C-2 was manufactured.

The test method and evaluation method of the performance test of the precoated steel sheet are described below. (1) Pencil hardness JIS K 5400 8.
The test was performed based on No. 4 and showed a hardness limit at which the coating film was not damaged.

(2) Cylindrical drawing workability Using a cylindrical drawing machine, a sample size of 90φ and a die of 42.4 were applied to a test piece having a size of 10 cm × 10 cm.
φ5R, plunger: 40.4φ4R, hold pressure:
Molding was performed under a 2.0-ton cylindrical drawing condition, and the coating film surface after the molding was observed and evaluated as follows. ：: No abnormality at all △: Slight scratch generation observed ×: Clear scratch generation observed (abnormal)

(3) Corrosion Resistance of Processed Part (1) After a salt spray test (SST test) was performed on the 2T bent test piece for 480 hours, an adhesive tape was stuck to and peeled from the 2T bent part, and the 2T bent part was peeled off. The peeling rate (area ratio:%) of the coating film was measured and evaluated as follows. ：: Film peeling rate of 10% or less △: Film peeling rate of more than 10%, 50% or less ×: Film peeling rate of more than 50%

(4) Corrosion resistance of cross-cut portion (1) After performing a salt spray test (SST test) on a test piece having a cross-cut reaching the substrate for 480 hours, the maximum blister width of the cross-cut portion was measured. Was evaluated as follows. ○: Maximum blister width is less than 3 mm △: Maximum blister width is 3 to 5 mm ×: Maximum blister width exceeds 5 mm

(5) Corrosion resistance of processed part (2) A combined cycle test was performed on the 2T bending test piece for 300 times.
After performing the cycle, an adhesive tape is stuck to and peeled from the 2T bent portion, and the peeling rate (area ratio:
%) And evaluated according to 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 hours).
This was repeated with one cycle of 0 ° C., 2 h) and hot air drying (30 ° C., 2 h). ：: Film peeling rate of 10% or less △: Film peeling rate of more than 10%, 50% or less ×: Film peeling rate of more than 50%

(6) Corrosion resistance of cross-cut part (2) After 300 cycles of a composite cycle test were performed on a test piece having a cross-cut reaching the substrate, the maximum blister width of the cross-cut part was measured and evaluated as follows. did. In addition, the combined cycle test method is a salt spray (30 ° C., 0.1 mL).
5 h), wet (30 ° C., 95 ± 3% RH, 0.5 h),
Hot air drying (50 ° C, 2h), hot air drying (30 ° C, 2h)
This was repeated as one cycle. ：: Maximum blister width is less than 3 mm △: Maximum blister width is 3 to 5 mm ×: Maximum blister width is more than 5 mm (7) Environmental harmony ○: No chromium-based compound in coating film ×: Chromium-based compound in coating film including

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

[Table 3]

[0085]

[Table 4]

[0086]

[Table 5]

[0087]

[Table 6]

[0088]

[Table 7]

[0089]

[Table 8]

[0090]

As described above, the precoated steel sheet of the present invention is excellent in environmental harmony, corrosion resistance in the cross cut portion, corrosion resistance in the processed portion, coating film hardness, and moldability.
For this reason, it is extremely useful as a precoated steel sheet used for parts requiring high environmental harmony, corrosion resistance in a cross-cut portion, corrosion resistance in a processed portion, coating film hardness, and moldability in applications such as home appliances, building materials, and automobiles.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Matsuzaki, Inventor 1-1-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan F-term (reference) in this steel pipe Co., Ltd. GB07 GB32 GB48 JA20B JB02 JB02B JB20A JK06 JK12 JM02A JM02B JM02C YY00B YY00C

Claims (6)

[Claims] 1. A pre-coated steel sheet in which an undercoat film is formed on the surface of a galvanized steel sheet on which a chemical conversion coating film containing silica fine particles and a binder is formed, and an overcoat film is further formed thereon. The undercoating film contains the following components (a) to (c) as rust preventive additives, and (a) a Ca component (provided that a salt added as a component of the following (b), Salts and other C added as components of c)
(Including Ca contained as a part of a-containing compound): 1 to 30 parts by weight in terms of Ca based on 100 parts by weight of resin solids. (b) SiO ₂ and / or silicate: 100 parts by weight of resin solids 1-35 parts by weight in terms of SiO ₂ amount relative part (c) phosphoric acid and / or phosphate: at PO ₄ equivalent amount relative to the resin solid content of 100 parts by weight to 30 parts by weight and the (a) To (c) the amount of the rust preventive additive component (however, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
A pre-coated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part, which is 5 to 100 parts by weight based on parts by weight. 2. A pre-coated steel sheet in which an undercoat film is formed on the surface of a galvanized steel sheet on which a chemical conversion coating film containing silica fine particles and a binder is formed, and an overcoat film is further formed thereon. The undercoating film contains the following components (a) to (d) as rust preventive additives, and (a) a Ca component (provided that a salt added as a component of the following (b), salt added as a component of c), salt added as a component of the following (d) and Ca contained as a part of other Ca-containing compounds): Ca conversion to 100 parts by weight of resin solid content (B) SiO ₂ and / or silicate: 1 to 35 parts by weight in terms of SiO _{2 based} on 100 parts by weight of resin solids (c) Phosphoric acid and / or phosphate: 1-30 parts by weight PO ₄ equivalent amount relative to the resin solid content of 100 parts by weight (d) molybdate , Tungstate, phosphite,
One or more selected from borates and metaborates: 1 to 50 parts by weight per 100 parts by weight of resin solids and the amount of the rust preventive additive component (a) to (d) (However, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
A pre-coated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part, which is 5 to 100 parts by weight based on parts by weight. 3. An overcoat film as a resin component which comprises:
3. The precoated steel sheet according to claim 1, wherein the coated steel sheet is a coating film formed by applying a coating composition containing (c). B) General formula (1) B) a polyester resin and / or an acrylic resin: 40 to 90% by weight in a resin solid content c) a curing agent Isocyanate compound and / or amino resin: 9 to 50% by weight in the resin solid content 4. The base resin component in a coating composition for forming an undercoat film is a polyester resin and / or an epoxy-modified polyester resin, and the thickness of the undercoat film is 2 to 20.
The precoated steel sheet according to claim 1, 2 or 3, which is excellent in environmental friendliness and corrosion resistance in a processed part. 5. The surface of a galvanized steel sheet on which a chemical conversion coating containing silica fine particles and a binder thereof is formed, contains the following components (a) to (c) as rust preventive additives, ) Ca component (however, a salt added as a component of the following (b), a salt added as a component of the following (c), and other C
(Including Ca contained as a part of a-containing compound): 1 to 30 parts by weight in terms of Ca based on 100 parts by weight of resin solids. (b) SiO ₂ and / or silicate: 100 parts by weight of resin solids 1-35 parts by weight in terms of SiO ₂ amount relative part (c) phosphoric acid and / or phosphate: at PO ₄ equivalent amount relative to the resin solid content of 100 parts by weight to 30 parts by weight and the (a) To (c) the amount of the rust preventive additive component (however, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
5 to 100 parts by weight of the coating composition for the undercoating film is applied, followed by baking treatment at the ultimate plate temperature of 180 to 260 ° C., and then applying the coating composition for the topcoating film. After that, a baking treatment is performed at a plate temperature of 180 to 260 ° C., thereby producing a precoated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part. 6. The surface of a galvanized steel sheet on which a chemical conversion coating containing silica fine particles and a binder is formed, contains the following components (a) to (d) as rust preventive additives, ) Ca component (however, a salt added as a component of the following (b), a salt added as a component of the following (c), a salt added as a component of the following (d), and a part of other Ca-containing compounds (B) SiO ₂ and / or silicate: SiO _{2 with} respect to 100 parts by weight of resin solids. (C) phosphoric acid and / or phosphate: 1 to 30 parts by weight in terms of PO _{4 based} on 100 parts by weight of resin solids (d) molybdate, tungstate, Phosphite,
One or more selected from borates and metaborates: 1 to 50 parts by weight per 100 parts by weight of resin solids and the amount of the rust preventive additive component (a) to (d) (However, Ca
Ca equivalent amount for components, SiO ₂ and / or SiO ₂ in terms of the amount of the silicate, total resin solids of PO ₄ equivalent amount) for phosphoric acid and / or phosphate content 100
5 to 100 parts by weight of the coating composition for the undercoating film is applied, followed by baking treatment at the ultimate plate temperature of 180 to 260 ° C., and then applying the coating composition for the topcoating film. After that, a baking treatment is performed at a plate temperature of 180 to 260 ° C., thereby producing a precoated steel sheet having excellent environmental friendliness and corrosion resistance in a processed part.