JPH11129388A - Precoating metal plate with excellent flaw resistance, processability and durability, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a procoating metal plate having excellent performance of both a processability and a flaw resistance, and an excellent durability resulting from the performances against a corrosion, coating film deterioration or the like caused by a flaw or a crack of the coating film, and a method for manufacturing the metal plate. SOLUTION: A conversion treated layer executed at least on one side surface of a molten Zn-plated steel sheet or molten Al-Zn alloy-plated steel sheet is coated with a primary coating paint containing an epoxy resin A, one type or more of curing agents B selected from an amino resin and an isocyanate compound, and elastomer fine particles C having a mean particle size of 0.01 to 5 μm and a glass transition temperature of a rubber part of 20 deg.C or lower and not compatible with cured substances of the resin A and the agent B as main components of a coating film forming resin, on the upper layer of the primary paint with an overcoating paint. In this case, a resin solid content ratio in the primary paint is A/B=60/40 to 95/5, 1 to 50 pts.wt. of the particles C per 100 pts.wt. of the resin solid content obtained by totally calculating the resin A and the agent B is contained, and further a glass transition temperature of the cured primary paint is 20 to 110 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated metal sheet having excellent scratch resistance, workability, impact resistance, durability and the like, which is used for construction materials, automobiles, home electric appliances and the like. During processing and molding, during construction, and even during use, the coating film is less likely to cause scratches, processing, and impact cracks, and is also excellent against coating film deterioration and corrosion caused by scratching and cracking of the coating film The present invention relates to a durable pre-coated metal plate.

[0002]

2. Description of the Related Art In recent years, prepainted steel sheets are often used as painted steel sheets for building materials, automobiles, home electric appliances and the like. In the base steel sheet of such pre-coated steel sheet,
Galvanized steel sheets, and more recently, aluminum-zinc alloy-plated steel sheets are often used. Recently, high workability is required for coating films of such precoated steel sheets. This is due to the fact that galvanized steel and especially aluminum
Pre-coated steel sheet with zinc alloy plated steel sheet as a base, when bent or stretched during processing and molding, cracks occur in the plating, so the coating film on it also breaks and the coating film cracks and the base steel sheet is often exposed However, such coating cracks not only impair the appearance, but also cause moisture, oxygen, corrosive ions, etc. to easily reach the base steel sheet in the damaged portion of plating, causing corrosion to occur and concentrating corrosion for a short period of time. This causes a problem that rust and peeling of the coating film occur.

[0003] In response to such demands, improvement in coating film processability has been attempted by increasing the breaking elongation of the coating film. Conventionally, it is necessary to lower the cross-link density of
By lowering the (glass transition temperature), the extensibility and flexibility of the coating film have been increased, and the processability has been improved.

On the other hand, recently, Tg and molecular weight differing from each other have been increasing.
Balancing processability and scratch resistance by using a coating resin blended with more than one type of base resin, or by applying a coating using a base resin modified using block copolymerization or graft copolymerization. It has been practiced to obtain pre-coated steel sheets.

[0005]

However, in the above-mentioned method for enhancing the elongation and flexibility of the coating film, the workability is enhanced, and at the same time, the breaking strength of the coating film, the adhesion to the base, the water resistance, the anticorrosion performance, etc. are improved. To reduce the scratch resistance and corrosion resistance,
Performance such as chemical resistance has been sacrificed.

[0006] In the case of a pre-coated steel sheet in which the workability and the scratch resistance are balanced as described above, the workability, the scratch resistance, and the durability still tend to contradict each other. Although it is superior to the pre-coated steel sheet coated with a coating film whose Tg has been lowered, both performances cannot be sufficiently improved. An object of the present invention is to use a hot-dip galvanized steel sheet or a hot-dip aluminum-zinc alloy-plated steel sheet as an underlayer, and to have excellent performance in both workability and scratch resistance, and as a result, corrosion caused by scratches or cracks in the coating film. It is an object of the present invention to provide a precoated metal sheet having excellent durability against deterioration of the coating film and the like, and a method for producing the same.

[0007]

In order to solve the above problems and achieve the object, the present invention uses the following means.

(1) The metal sheet of the present invention comprises an epoxy resin (A) and an amino resin on a chemical conversion treatment layer applied to at least one surface of a hot-dip galvanized steel sheet or a hot-dip aluminum-zinc alloy-plated steel sheet. One or more curing agents selected from isocyanate compounds (B), the average particle size is 0.01 to 5 μm, the glass transition temperature of the rubber portion is 20 ° C. or less, and the (A) Fine particles which are incompatible with the cured product obtained by curing (B)
... (C) a pre-coated metal plate obtained by coating an undercoat paint containing, as a main component of a resin for forming a coating film, and an overcoat paint on the undercoat paint, wherein (A) and (B) in the undercoat paint ) Is (A) / (B) = 60/40.
(C) is contained in an amount of 1 to 50 parts by weight per 100 parts by weight of the total resin solid content of (A) and (B), and the glass transition temperature of the cured undercoat film is 20 to 95/5.
It is a precoated metal plate excellent in scratch resistance, workability and durability, which is characterized by being at a temperature of up to 110 ° C.

(2) The metal sheet of the present invention is characterized in that the elastomer fine particles (C) are dispersed in the undercoating film, and the metal plate according to the above (1) is scratch-resistant, processable and durable. It is a pre-coated metal plate with excellent properties.

(3) In the metal plate of the present invention, the rubber portion of the elastomer fine particles (C) in the undercoat paint has an acrylic resin as a main component and the surface thereof has a carboxyl group, an epoxy group, a hydroxyl group, and an amino group. Characterized by being modified with a resin having at least one functional group selected from the group consisting of groups, having excellent scratch resistance, processability and durability as described in (1) or (2) above. It is a pre-coated metal plate.

(4) In the metal plate according to the present invention, the elastomer fine particles (C) in the undercoating film are composed of a core portion including a rubber portion and a shell portion whose surface is modified with a resin having a functional group. The precoated metal sheet according to any one of the above (1) to (3), having a core-shell structure having excellent scratch resistance, workability, and durability.

(5) The metal plate according to the present invention, wherein the epoxy resin (A) in the undercoat paint has a number average molecular weight of 1,000 to 1,000.
The precoated metal sheet according to any one of the above (1) to (4), which is excellent in scratch resistance, workability, and durability, characterized in that it is 3000.

(6) The metal sheet of the present invention is characterized in that the plated steel sheet as a base is a molten aluminum-zinc alloy plated steel sheet containing 1 to 60% by weight of aluminum. The precoated metal sheet according to any one of (5), which is excellent in scratch resistance, workability, and durability.

(7) The metal plate of the present invention is characterized in that the overcoating paint comprises a vinylidene fluoride resin or a polyester resin as a main component of a resin for forming a coating film. A precoated metal sheet excellent in scratch resistance, workability and durability according to any one of the above.

(8) The metal plate of the present invention is characterized in that the undercoat film has a dry film thickness of 8 to 30 μm.
Scratch resistance according to any one of the above (1) to (7),
It is a pre-coated metal plate with excellent workability and durability.

(9) In the production method of the present invention, the undercoated paint and the overcoated paint having the resin composition for forming a coating film according to any one of the above (1) to (8) are coated on the plated steel sheet as a base. In a method of producing a pre-coated metal sheet by painting, a chemical conversion treatment is applied to at least one surface of a plated steel sheet, and an undercoat paint is applied on the chemical conversion treatment layer.
Heated for 0 to 180 seconds, steel plate temperature is 150 ° C or higher and 300
C. and baking the base coat to a temperature below 150 ° C., and further applying a top coat to the upper layer of the plated steel sheet to which the base coat has been baked, followed by heating for 30 to 180 seconds to reduce the steel sheet temperature to 150 ° C.
And baking at a temperature of not less than 300 ° C. and less than 300 ° C., which is a method for producing a precoated metal sheet excellent in scratch resistance, workability and durability.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors, based on a hot-dip galvanized steel sheet or a hot-dip aluminum-zinc alloy-plated steel sheet, have excellent performances in both workability and scratch resistance. In order to obtain a pre-coated metal plate having excellent durability against corrosion, coating film deterioration, and the like caused by cracks and cracks, the following findings have been obtained as a result of intensive studies.

In order to improve the workability of the precoated metal sheet, it is necessary to prevent the coating film from cracking when bent or stretched. However, with regard to a galvanized steel sheet and particularly a precoated steel sheet having an aluminum-zinc alloy-plated steel sheet as a base, cracking occurs in plating due to such processing.

Therefore, in order to prevent the coating film on the plating crack from stretching and breaking, it is necessary to greatly increase the breaking elongation of the coating film. In addition, the adhesion, the water resistance, the anticorrosion performance and the like are deteriorated, so that the performances such as scratch resistance, corrosion resistance and chemical resistance are sacrificed.

In the present invention, when cracks occur in the plating, the development of the cracks in the undercoating film thereon is suppressed to a minimum, thereby suppressing the occurrence of cracks on the surface of the overcoating film. It is not necessary to increase the elongation as compared with the conventional one, and as a result, it is possible to use an undercoat film with high breaking strength, substrate adhesion, water resistance, corrosion resistance, and both workability and scratch resistance, durability A precoated metal sheet having excellent heat resistance can be obtained.

Such an effect can be obtained by dispersing the elastomer fine particles in an undercoat film mainly composed of an epoxy resin. Conventionally, there has been proposed a method of dispersing flexible elastomer fine particles in a hard epoxy resin to improve both performance and impact resistance and breaking strength performance, but the mechanism is as follows. It has been estimated. That is, even if minute cracks occur in the resin due to stress such as tension, (1) the effect of absorbing deformation energy by stretching or tearing the elastomer particles in the crack portion, and (2) the tip of the crack Due to the effect of plastic deformation in the region and blunting of the crack tip, crack growth can be suppressed and resin destruction can be prevented (Nakamura Yoshinobu et al., Journal of the Adhesion Society of Japan, Vo
l. 24, no. 5, page 186 (1988)).

However, in order for such a mechanism to be exhibited in a galvanized steel sheet or a pre-coated metal sheet having an aluminum-zinc alloy-plated steel sheet as a base, the resin for forming a coating film in the undercoat paint has a specific composition. In addition, it has been found that the glass transition temperature of the undercoat film must be under appropriate conditions, and the present invention has been achieved.

Based on the above findings, the present inventors have determined that the resin composition of the undercoating film in which the elastomer fine particles are dispersed is applied to the base plated steel sheet, and the coating conditions (steel sheet heating temperature, baking time) In order to adjust the physical properties of the coating film to a specified range, to find a pre-coated metal plate excellent in scratch resistance, workability and durability and a method for producing the same,
The present invention has been completed.

That is, the present invention can provide a precoated metal sheet having excellent scratch resistance, workability and durability by limiting the coating film and the production conditions of the precoated metal sheet to the following ranges.

Hereinafter, the reasons for limiting the coating of the precoated metal sheet of the present invention and the reasons for limiting the manufacturing conditions will be described.

(1) Coating of pre-coated metal plate a. Coated Steel Sheet As the coated steel sheet used in the precoated metal sheet of the present invention, a hot-dip galvanized steel sheet or a hot-dip aluminum-zinc alloy-plated steel sheet containing 1 to 60% by weight of molten aluminum is used.

Although these plated steel sheets have the highest corrosion resistance, they cannot prevent the formation of an initial alloy layer at the interface between the plating and the base steel sheet during production, and the alloy layer is very hard and brittle, so that the steel sheet is extremely hard and brittle. There is a disadvantage that the work is inferior in workability because the work is easily broken by the work, and the cracks form cracks throughout the plating.

In particular, in a hot-dip galvanized steel sheet containing 1 to 60% of aluminum, the corrosion resistance of the hot-dip galvanized steel sheet is more excellent than that of the hot-dip galvanized steel sheet. About twice as thick, the workability is further inferior, and the width of the cracks generated on the plating surface during processing is too large to be able to follow the elongation of the coating film on top of it, and the coating film cracks easily occur, so the corrosion resistance of the processed part may be inferior Had been a problem.

However, in the undercoat coating film of the present invention, even if cracks occur at the interface with the undercoat, the cracks of the coating film do not reach the upper portion of the coating film due to the effect of the elastomer fine particles in the coating film. Therefore, the precoated metal sheet of the present invention can maintain higher workability and corrosion resistance than before.
In particular, when coated on a hot-dip aluminum-zinc alloy-coated steel sheet containing 1 to 60% of aluminum, the corrosion resistance can be improved more than that of the hot-dip galvanized steel sheet while maintaining the workability at the same level as the hot-dip galvanized steel sheet. A coated steel sheet having excellent properties can be obtained. Further, such a tendency is remarkable in a molten aluminum-zinc alloy plated steel sheet containing about 55% of aluminum. It is appropriate that the plating amount is 3 to 30 μm on one side. If the thickness is smaller than that, the corrosion resistance is insufficient, and if the thickness is larger, the workability is inferior.

The metal component of the plating used in the precoated metal sheet of the present invention is preferably aluminum or zinc having the above composition, but the impurities of unavoidable impurities such as Si and Fe do not impair the effects of the present invention. Mixing in the range is acceptable.

B. Chemical conversion coating A chemical conversion coating is formed on the surface of the above-mentioned steel sheet in order to secure adhesion to the coating film. The chemical conversion coating may be formed by a pre-coating treatment suitable for each steel sheet.
In addition to those formed by application or spraying of phosphates and silane coupling agents, activation by acid or alkali such as phosphoric acid, nitric acid, hydrofluoric acid, etc., those formed by composite oxide coating treatment and electrolytic treatment May be. In addition, before the chemical conversion treatment, Ni may be attached by electric or chemical plating to enhance the adhesion of the treatment.

The thickness of the chemical conversion coating is not particularly limited in the present invention.
g / m ² is desirable. If it is less than 5 mg / m ² , sufficient corrosion resistance and adhesion between the base plated steel sheet and the coating film cannot be obtained.
On the other hand, if it exceeds 100 mg / m ² , the effect is saturated. At the time of the treatment of other phosphates, silicates and the like described above, it may be determined appropriately.

C. Undercoat paint The undercoat paint applied to the plated steel sheet on which the above chemical conversion coating is applied is specified in a paint film obtained by curing an epoxy resin with one or more curing agents selected from amino resins and isocyanate compounds. Particle size (average particle size: 0.01 to 5μ)
m), a rubber transition temperature of the rubber portion (20 ° C. or lower) and elastomer fine particles incompatible with the cured product are dispersed.

Examples of the epoxy resin for dispersing such an elastomer include a bisphenol type epoxy resin derived from bisphenol A or bisphenol F and epichlorohydrin, a novolak type epoxy resin derived from novolak phenol and epichlorohydrin, and biphenol. Resins having a skeleton such as dihydroxynaphthalene, dicyclopentadiene, etc., aliphatic epoxy resins obtained by adding ethylene oxide or propylene oxide to bisphenol A or bisphenol F and then reacting with epichlorohydrin, and copolymerization of the above epoxy resins Combined, further modified to the above epoxy resin with amine or glycol, and with ring opening of polyoxycarboxylic acid, butyl lactone, caprolactone, etc. Those which are obtained by grafting on branched by,
Then, a blend of the above epoxy resin and the like can be used. Furthermore, commercially available epoxy resins such as Epicoat (registered trademark of Yuka Shell Epoxy Co., Ltd.), Epototo (registered trademark of Toto Kasei Co., Ltd.), and Epoki (registered trademark of Mitsui Toatsu Chemicals, Inc.) can also be used. Among them, a bisphenol-type epoxy resin obtained from bisphenol A or bisphenol F is particularly preferable from the viewpoint of the breaking strength of the coating resin and the adhesion to the base.

The molecular weight of the epoxy resin used is as follows:
Although a number average molecular weight of about 350 to about 10,000 can be used, it is preferably 1000 to 300.
0. When the molecular weight is less than 1,000, the epoxy resin reacts with the elastomer fine particles to completely become incompatible, and the desired crack resistance may not be obtained. On the other hand, when the molecular weight exceeds 3,000, the elastomer fine particles may not be contained in the epoxy resin. In this case, the elastomer does not stably disperse, and aggregation between the elastomers occurs, and similarly, the desired crack resistance cannot be obtained.

In order to obtain an elastomer-dispersed coating film excellent in processability and scratch resistance using such an epoxy resin, it is necessary to cure the resin with an amino resin, an isocyanate compound, or a mixture thereof.

Examples of the amino resin include melamine resin, benzoguanamine resin, urea resin and the like. These resins are obtained by reacting an amino compound such as melamine or benzoguanamine with formaldehyde, and then etherifying a part or all of the methylol group with a monohydric alcohol having 1 to 4 carbon atoms such as methanol, propanol and butanol. Obtained. In particular, it is preferable that 2 to 6 methylol groups per melamine molecule are etherified. If the number is less than 2, the compatibility with the epoxy resin decreases. Specific examples of such melamine resins include butylated melamine resins such as Melan 22 (manufactured by Hitachi Chemical Co., Ltd.) and Super Becamine J-820-60 (manufactured by Dainippon Ink and Chemicals, Inc.), Cymel 325, Methylated melamine resin such as Cymel 303 (both manufactured by Mitsui Cyanamid Co., Ltd.), Cymel 254
(Manufactured by Mitsui Cyanamid Co., Ltd.) and alkyl etherified melamine resins such as methyl / butyl mixed melamine resins.

On the other hand, aliphatic polyamines such as ethylenediamine, triethylenetetramine and hexamethylenediamine; aromatic polyamines such as metaphenylenediamine and diaminodiphenylmethane; and secondary or secondary polyamines such as triethanolamine and benzyldimethylamine. When a curing agent such as an acid anhydride such as tertiary amine, tetrahydrophthalic anhydride or dodecenyl succinic anhydride, an imidazole compound such as imidazole or 2-phenylimidazole, dicyandiamide or a derivative thereof, or an organic acid dihydrazide such as adipic dihydrazide is used. As a coating film, processability is poor and unsuitable.

As the isocyanate compound, an isocyanate compound obtained by a general production method is used. Considering the application as a coating for pre-coated steel sheets, phenol, cresol,
Resins blocked with aromatic secondary amines, tertiary alcohols, lactams, oximes and the like are desirable. More preferably, hexamethylene diisocyanate and its derivatives, tolylene diisocyanate and its derivatives,
-Diphenylmethane diisocyanate and its derivatives, xylylene diisocyanate and its derivatives, isophorone diisocyanate and its derivatives, trimethylhexamethylene diisocyanate and its derivatives,
Norbornene diisocyanate and its derivatives can be mentioned. Further, commercially available isocyanate compounds such as Sumidur (registered trademark of Sumitomo Bayer Urethane Co., Ltd.), Desmodur (registered trademark of Sumitomo Bayer Urethane Co., Ltd.) and Coronate (registered trademark of Nippon Polyurethane Co., Ltd.) can also be used.

The resin solid content ratio between the epoxy resin and the curing agent is preferably from 60/40 to 95/5. If the ratio of the epoxy resin is greater than this, the flexibility of the cured product is reduced, so the workability is reduced, and if the amount of the curing agent is increased, the breaking strength of the cured product is insufficient and the scratch resistance is reduced. is there. More preferably, it is 70/30 to 90/10. Comparing the amino resin and the isocyanate compound, the isocyanate compound is more preferable because it does not affect the dispersion of the elastomer. When an amino resin is used as a curing agent, depending on the combination with an epoxy resin, dispersion of the elastomer is inhibited by a self-condensation reaction of the amino resin, and a desired processability may not be obtained. Even when the amino resin and the isocyanate compound are used in combination, higher processability can be obtained by increasing the ratio of the isocyanate compound. In addition, among amino resins, a methylated melamine resin which is not easily self-condensed tends to obtain good performance.

As the elastomer fine particles used in the present invention, carboxyl-modified NBR rubber fine particles, acrylic elastomer fine particles, silicone rubber fine particles and the like can be used. Nipol (registered trademark of Zeon Corporation), staphyloid (registered by Takeda Pharmaceutical Company Limited) Commercially available elastomer fine particles such as (trademark) can also be used. The average particle size is
It is 0.01-5 μm. When the thickness is less than 0.01 μm, crazes (micro cracks) for developing workability are not sufficiently generated, and large cracks are easily generated during processing. On the other hand, if the thickness exceeds 5 μm, the unevenness of the coating film becomes conspicuous, impairs the appearance, and lowers the mechanical strength of the coating film.
Scratch property etc. decrease. More preferably, it is 0.
1 to 0.5 μm.

Further, the glass transition temperature of the rubber portion of the elastomer fine particles must be 20 ° C. or less. The elastomer fine particles often have a core-shell structure in which the surface thereof is covered with a resin having a high functional group concentration in order to increase the adhesion to the coating epoxy resin. Also in this case, since the effect of preventing cracks of the elastomer fine particles is exhibited by the soft rubber portion of the core portion, the glass transition temperature (Tg) of the core portion is preferably 20 ° C. or lower, more preferably 0 ° C. or lower. If the glass transition temperature is higher than that, the plasticity of the elastomer is small, and the effect of improving the processability is small.

Such elastomer fine particles need to be incompatible with a cured product obtained by curing an epoxy resin with at least one resin selected from an amino resin and an isocyanate compound. This is because, when the elastomer is compatible with the cured product, the Tg of the cured product is reduced, and the physical properties of the coating film, particularly, the breaking strength is reduced. As the kind of the elastomer, acrylic elastomer fine particles are preferable. Elastomer microparticles such as carboxyl-modified NBR rubber microparticles and silicone rubber microparticles tend to be more compatible with epoxy resins and their cured products than acrylic elastomers, and as a result, their performance as cured products is likely to be reduced. is there.

In the undercoat paint applied to the precoated metal plate of the present invention, the rubber portion of the elastomer fine particles in the paint has an acrylic resin as a main component and the surface thereof has a carboxyl group, an epoxy group, a hydroxyl group, And a resin having at least one functional group selected from the group of amino groups.

In the case of using acrylic elastomer fine particles, it is better to add a functional group such as a carboxyl group, an epoxy group, a hydroxyl group, or an amino group to the acrylic in order to increase the affinity with the epoxy resin, and the crack progresses. The effect of suppressing is high, and the effect of improving workability is high. In that case, a method of copolymerizing an acrylic monomer and a monomer having a functional group to impart a functional group to the entire acrylic elastomer, and a method of using a core-shell structure in which only the surface of ordinary acrylic monomer fine particles is modified with a functional group There is,
The latter is more preferable because the acrylic rubber in the core portion has a low Tg and also has a high affinity with the epoxy resin.

Whether or not the elastomer is compatible with the cured product can be confirmed by the change in Tg of the cured product. When the elastomer is compatible with the cured product, the resin having a significantly lower Tg than the cured product is mixed with the cured product, so that the Tg of the cured product decreases. The Tg can be determined, for example, by measuring the main dispersion peak using a dynamic viscoelasticity measuring device. Further, for simplicity, the cured product is observed with an electron microscope, and it can be seen from the fact that the elastomer is clearly separated from the cured product.

The amount of the elastomer added to the cured product has an optimum value depending on the type of the elastomer and the cured product and the amount of the other additives. , 1 to 50% by weight. If the amount is too small, the effect of adding the elastomer does not appear, and the crack resistance is poor.If the amount is too large, the cured product cannot maintain a continuous phase, the strength and durability of the cured product are reduced, and the scratch resistance as a coating film is reduced. Adhesion and durability are reduced. Further, it is preferably 5 to 30% by weight. As a method of dispersing the elastomer fine particles in the coating film, in addition to the method of dispersing the elastomer fine particles directly in the coating material and dispersing it in the coating film by applying and curing the same, the elastomer fine particles were dispersed in the resin. A method is also possible in which an epoxy resin (for example, Epototo YR-593 manufactured by Toto Kasei Co., Ltd.) is used as a starting material, and a coating material using the same is applied and cured in the same manner to be dispersed in the coating film.

In any case, the glass transition temperature of the undercoat as a cured coating must be from 20 to 110 ° C. If the temperature is lower than 20 ° C., the coating film strength is inferior, and the coating film has insufficient scratch resistance and durability.
For that purpose, it is necessary that the Tg of the cured product in which the elastomer fine particles are not dispersed is 20 ° C. or more, and that the coating film Tg does not decrease by adding the elastomer fine particles. On the other hand, if the temperature is higher than 110 ° C., the flexibility of the cured product is too low, so that even if an elastomer is added, the processability becomes insufficient. More preferably, the glass transition temperature of the undercoat film is 50 to 100 ° C.

The dry film thickness of the undercoat film is suitably from 5 to 50 μm. If the amount is less than that, the corrosion resistance of the processed portion is inferior. If the thickness is more than that, coating defects are generated and the workability is also inferior, which is not preferable. Further, in the coating film in which the elastomer fine particles of the present invention are dispersed, there is an optimum value in a place where the thickness of the dry film to be applied as a usual undercoating film is 3 to 5 μm, and it is preferable to apply 8 to 30 μm. This is because when the thickness is 8 μm or more, the prevention of crack propagation is further enhanced. However, even if the thickness is more than 30 μm, the effect of preventing the crack from growing is not significantly improved. In the undercoating film of the present invention, in addition to the above-mentioned essential components, rust-preventive pigments, coloring pigments, constitutional facial agents, solvents, curing catalysts, plasticizers, desiccants, dispersants, antioxidants, etc. Can be blended. As the rust preventive pigment, silica or a chromate compound can be used, but it is preferable to add a chromate compound. As the chromate compound, zinc chromate, strontium chromate, calcium chromate, barium chromate, and the like are suitable, and the content thereof is suitably 1 to 60% by weight in the solid content of the coating film. If the amount is less than that, the corrosion resistance decreases, and if it is more than that, the workability decreases.

More preferably, when the strontium chromate pigment is contained in an amount of 20 to 40% by weight, the workability and the corrosion resistance of the processed portion are most excellent.

As the color pigment, for example, titanium oxide,
Examples include carbon black, iron oxide, lead chromate, metal powder, calcined pigment, pearl pigment and the like. Examples of the extender include calcium carbonate, clay, talc, antimony trioxide, barium sulfate, kaolin and the like.
Further, scaly aggregates can be added to prevent permeation of corrosive substances, and powder or fiber-based aggregates such as ceramics and glass can be added to further enhance the effect of preventing damage.
Further, as an additive, for example, an antifoaming agent, a pigment dispersant,
An anti-sagging agent, an anti-scratch agent and the like can be mentioned. As the solvent, for example, toluene, xylene, ethyl acetate, butyl acetate, cellosolve solvent, methyl isobutyl ketone, methyl ethyl ketone, diisobutyl ketone, isophorone,
And cyclohexanone.

As the undercoat paint of the present invention, a polyester paint may be used in addition to the above epoxy paint. d. Topcoat Film An overcoat film is formed on the undercoat film.
Further, the reason for forming the overcoat film is to make up for the following problems of the undercoat film.

1) Epoxy resin (base material of undercoating film) is inferior in weather resistance.

2) Epoxy resin is inferior in flexibility, and cracks are likely to occur in the processed part.

3) When a colored rust-preventive pigment or the like is blended in the undercoat film, the color of the undercoat film cannot be easily changed when the paint film is colored for the purpose of imparting design.

As described above, the overcoat film has a film appearance,
It is selected in consideration of weather resistance, durability and the like. Lacquer-based and oil-based coatings can also be used.Synthetic resin-based coatings include polyester-amino resin-based coatings, polyester-isocyanate compound-based coatings, fluororesin-based coatings, and silicone-polyester resins. A commonly used overcoating film such as a coating film, an acrylic resin coating film, an acrylic-siloxane resin coating film, or a silicone resin coating film can be used. However, in order to maximize the high workability of the undercoat film, it is necessary to use a high workability for the overcoat film, and it is necessary to use vinylidene fluoride resin or polyester resin as the main resin for forming the film. Components are preferred.

The dry coating thickness of the top coat is 10 to 50 μm.
m is preferable. When the coating thickness is less than 10 μm, the film thickness becomes thin, and the wear resistance, corrosion resistance, and chemical resistance are reduced. On the other hand, if the thickness of the coating film exceeds 50 μm, coating film defects are likely to appear at the time of coating, and workability is also reduced. However, the top coat may be applied in two or more coatings, in which case the coating may be 50 μm or less at a time, and the upper limit of the preferable thickness of the top coating is (50 × n) μm (n: top coating). Number of coatings).

Further, powder such as ceramics and glass, or fiber-based aggregate may be added, or elastomer fine particles may be added to prevent damage.

That is, regarding the scratch resistance, in the present invention, the effect of the adhesion between the undercoating film and the base plating is great, but the toughening of the overcoating film by using the above additives is required. Thereby, the stress on the undercoat film is reduced, the breakage and peeling of the film are reduced, and the scratch resistance can be further improved. If necessary, a plasticizer, a desiccant, a dispersant, a curing catalyst, an antioxidant, a pigment, a solvent, and the like can be added to the overcoating film. It is effective to add.

As the pigment, extender pigments, rust preventive pigments, and lubricants can be added in addition to various color pigments.

By adjusting the resin composition for forming a coating film and the physical properties of the coating film, a precoated steel sheet having excellent scratch resistance, workability and durability can be obtained.

The precoated steel sheet having such characteristics can be manufactured by the following manufacturing method.

(2) Manufacturing process of pre-coated metal sheet (Manufacturing method) An undercoat and an overcoat having the above-mentioned resin composition for forming a coating film on the above-mentioned hot-dip galvanized steel sheet or hot-dip aluminum-zinc alloy-plated steel sheet. In a method of producing a pre-coated metal sheet by painting a steel sheet, at least one surface of a plated steel sheet is subjected to a chemical conversion treatment, and an undercoating paint is applied on the chemical conversion treatment layer, and then 30 to 180
It is baked so that the temperature of the steel sheet becomes 150 ° C. or more and less than 300 ° C. by heating for seconds. Next, after further applying an overcoat to the upper layer, the coating is heated for 30 to 180 seconds and baked so that the steel sheet temperature becomes 150 ° C. or more and less than 300 ° C.

A. Temperature of steel sheet and baking time during undercoating When the steel sheet temperature is lower than 150 ° C, the drying and curing of the coating film components are insufficient. On the other hand, when the temperature exceeds 300 ° C, thermal deterioration of the coating film components starts. If the baking time is less than 30 seconds, the drying and curing of the components of the coating film are insufficient, and the curing speed of the resin is higher than the evaporation speed of the solvent, so that the coating film is liable to have defects such as cracks and the appearance is easily deteriorated. , 180 seconds, thermal degradation of coating film components starts. Accordingly, the temperature of the steel sheet when applying the undercoat paint is 150 ° C. or more and less than 300 ° C., and the baking time is 30 to 180 seconds. b. When the steel sheet temperature is less than 150 ° C., the drying and curing of the coating film components are insufficient. On the other hand, when the steel plate temperature exceeds 300 ° C., thermal degradation of the coating film components starts. If the baking time is less than 30 seconds, the drying and curing of the components of the coating film are insufficient, and the curing speed of the resin is higher than the evaporation speed of the solvent, so that the coating film is liable to have defects such as cracks and the appearance is easily deteriorated. , 180 seconds, thermal degradation of coating film components starts. Therefore, the temperature of the steel sheet when the top coat is further applied is 150 ° C. or more and less than 300 ° C., and the baking time is 30 to 180 seconds.

The coating method is not particularly limited, and may be a roll coating method, a curtain flow coater method, a roller curtain flow coater method, a blade coater method, a die coater method, an electrostatic coating method, a spraying method, etc., which are generally performed conventionally. A painting method can be applied.

The baking method is also performed by heating in a hot blast stove, an induction heating furnace, a near-infrared furnace or the like.

Further, the method of forming the chemical conversion treatment layer applied to the base plated steel sheet is not particularly limited as described above.
That is, it may be formed by a pre-coating treatment suitable for each steel sheet.

The effects of the present invention will be proved by the following examples.

[0069]

EXAMPLES An undercoating composition shown in Tables 1 to 3 was prepared.
After applying various types of steel sheets (all 0.5 mm thick) to a coating type chromate treatment or a phosphate treatment, an undercoat is applied under the conditions shown in Tables 4 to 6, followed by baking treatment,
The coated steel plate (Examples of the present invention: Nos. 1 to 47 (including 2 'and 3'), Comparative Examples: Nos. 1 to 11) was subjected to the following various tests. did.

Table 4 shows the test results (coating film properties and performance).
To # 6.

(Tests and Evaluation Methods) (1) Structure of Elastomer Fine Particles and Cured Product Whether or not the elastomer fine particles are compatible with the cured product was examined using a dynamic viscoelasticity measuring apparatus. A free film having a thickness of 10 μm was formed between the coating film containing and not containing the elastomer fine particles, and the Tg of the coating film was obtained from the peak of tan δ of the dynamic viscoelasticity. Tg when elastomer fine particles are added
However, those which did not decrease by 1.0 ° C. or more as compared with when they were not added were regarded as incompatible.

(2) Scratch resistance The scratch resistance of the coating film was determined by changing the hardness of the pencil lead according to the method of JIS-K5400 8.4.1 (1995). Examination was made by peeling from the substrate, and the hardness at which peeling of the coating film was not observed two or more times in five tests was defined as the pencil hardness of the coating film. Pencil hardness of 6H or more passed, 6H
Those less than were rejected.

(3) Processability After bending at 180 ° in a room at 20 ° C., the portion was immersed in boiling water for 3 hours, pulled up and dried for 24 hours, and then subjected to a tape peeling test of the bent portion. Here, the evaluation was based on the minimum number of plate scissors in which no peeling of the coating film was observed. In this evaluation, 0 to 2 sheets were passed, and 3 or more sheets were rejected.

(4) Impact resistance A DuPont impact test was performed according to the method of JIS-K5400 (1995). In a room at 20 ° C., with the steel sheet facing upward (coating surface), drop a 1000 g weight from above onto the coating surface, immerse the portion in boiling water for 3 hours, then pull up and dry for 24 hours After that, a tape peeling test was performed. The highest drop height at which no peeling of the coating film was observed was evaluated. In this evaluation, 30 cm or more was passed, 30
cm was rejected.

(5) Corrosion Resistance A test was conducted according to the method of 9.1 of JIS-K5400 (1995). As shown in FIG.
2 below the center of the coated steel sheet cut to a size of 50 mm
T bend processing was performed, and four sides and the back were covered with tar epoxy paint. In the evaluation, a tape peeling test was performed on the coating film of the T-bend processed part after 1000 hours of the salt spray test, and a film having a coating film peeling rate of 20% or less was judged to be acceptable.

[0076]

[Table 1]

[0077]

[Table 2]

[0078]

[Table 3]

[0079]

[Table 4]

[0080]

[Table 5]

[0081]

[Table 6]

The meanings of the symbols in Tables 1 to 6 relating to the production conditions (items (1) to (11)) for each coated steel sheet to be tested are as follows.

1) Base steel sheet ZN: hot-dip galvanized steel sheet (Al: 0.1% by weight), G
F: Hot-dip 5% Al-Zn-plated steel sheet (Al: 4.6% by weight), GL: Hot-dip 55% Al-Zn-plated steel sheet (A
l: 55% by weight), AL: Hot-dip Al-plated steel sheet (A
l: 100% by weight), EG: Electro-Zn plated steel sheet (Al: 0% by weight) 2) Chemical conversion treatment P: Phosphate treatment (PB-3308, manufactured by Nippon Parkerizing Co., Ltd., film weight 1.5g / m) ² ), Cr: Chromate treatment (ZMR1415A, manufactured by Nippon Parkerizing Co., Ltd., film weight 40 mg / m ² ) 3) Epoxy resin E-1: Bisphenol A (EPICLON-105)
0, manufactured by Dainippon Ink and Chemicals, Inc.), E-2: bisphenol A (EPICLON-4050, manufactured by Dainippon Ink and Chemicals, Inc.), E-3: bisphenol A (EP
ICLON-7050, Dainippon Ink and Chemicals, Inc.
E-4: Bisphenol A (EPICLON-H)
M091, Dainippon Ink and Chemicals, Inc.), E-5:
Bisphenol A / F co-condensed epoxy (EPICLON-
7070-50M, manufactured by Dainippon Ink and Chemicals, Inc.)
E-6: Modified epoxy (EPICLON-P-439,
E-7: Modified epoxy (EPICLON-P-415, manufactured by Dainippon Ink and Chemicals, Inc.), E-8: Modified epoxy (FLEP-41)
0C, manufactured by Toray Thiokol Co., Ltd.), E-9: acrylic rubber-dispersed epoxy (YR-693, manufactured by Toto Kasei Co., Ltd.) 4) Curing agent H-1: methylated melamine resin (Cymel 303, Mitsui Cyanamid Co., Ltd.) )), H-2: Butylated melamine resin (Uban 20SE60, Mitsui Toatsu Chemicals, Inc.)
), H-3: isocyanate compound (Epokey EPR)
130, manufactured by Mitsui Toatsu Chemical Co., Ltd.), H-4: isocyanate compound (Desmodur TPLS-2957, manufactured by Sumitomo Bayer Urethane Co., Ltd.), H-5: dimethylethanolamine 5) Elastomer A-1: acrylic rubber (YR-693, Toto Kasei Co., Ltd.
A-2) carboxyl group-modified acrylic rubber (Staphyloid AC-3881, manufactured by Takeda Pharmaceutical Co., Ltd.)
A-3: Acrylic rubber (Staphyroid AC-335)
5, Takeda Pharmaceutical Co., Ltd.), A-4: Acrylic rubber (Staphyroid GM-0405, Takeda Pharmaceutical Co., Ltd.)
A-5): Acrylic rubber (Staphyroid GM-0)
A-1, Acrylic rubber (Microgel S-5005, Nippon Paint Co., Ltd.)
A-7: Acrylic rubber (Microgel S-50)
03, Nippon Paint Co., Ltd.), A-8: carboxyl group-modified NBR rubber (XER-91P, Nippon Synthetic Rubber Co., Ltd.) 6) Rubber type AC: acrylic, BN: carboxyl terminal NBR 7) mixed solvent cyclohexanone / Xylene / solvesso = 50/30
/ 20 (% by weight) 8) Titanium oxide R-820 (manufactured by Ishihara Sangyo Co., Ltd.) 9) Rust preventive pigment B-1: strontium chromate, B-2: calcium chromate, B-3: zinc chromate (ZTO),
B-4: Silica 10) Additive C-1: Leveling agent (Polyflow S, manufactured by Kyoeisha Chemical Co., Ltd.), C-2: Scratched alumina aggregate (AA-
05, manufactured by Sumitomo Chemical Co., Ltd.) 11) Top coat paint D-1: polyester resin paint (KP color 1406,
D-2: Vinylidene fluoride resin paint (Uniflon K, manufactured by Nippon Paint Co., Ltd.), D-
3: Silicone modified polyester resin paint (DIF S-
30, manufactured by Nippon Paint Co., Ltd.) As is clear from the results of the above examples, the resin composition for forming the coating film, the physical properties of the coating film, or the production conditions were out of the range of the present invention. The coated steel sheets 1 to 11 were rejected in any of scratch resistance, workability, and corrosion resistance.

On the other hand, in the present invention example No. satisfying the conditions of the present invention. The coated steel sheets of Nos. 1 to 47 (including Nos. 2 ′ and 3 ′) are excellent in scratch resistance, workability, and corrosion resistance. Example No. 1 of the present invention that satisfies the optimum conditions of physical properties or production 1
0, 11, 2 ', 3', 23, 25, 26, 28, 29
Has better properties (scratch resistance, processability and durability)
have.

[0085]

According to the present invention described above, by specifying the resin composition for forming the coating film, the physical properties of the coating film, and the production conditions, both the scratch resistance and the workability are excellent, and the durability is also improved. An excellent pre-coated metal plate can be provided.

The precoated metal sheet of the present invention has an industrial utility value such as being applicable to building materials, automobiles, home appliances, etc., which require high scratch resistance, workability, and durability for the coating film. large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the appearance of a test piece used for corrosion resistance evaluation according to an example of the present invention.

Claims (9)

[Claims] 1. An epoxy resin (A), an amino resin, or an isocyanate compound, on a chemical conversion treatment layer applied to at least one surface of a hot-dip galvanized steel sheet or a hot-dip aluminum-zinc alloy-plated steel sheet. One or more curing agents (B), average particle size: 0.01 to 5 μm, glass transition temperature of rubber part is 20 ° C. or less, and (A) is cured by (B) A pre-coated metal plate obtained by applying an undercoat paint containing (C) an elastomer fine particle incompatible with the cured product as a main component of a resin for forming a coating film, and an overcoat paint on an upper layer thereof; The resin solid content ratio of (A) and (B) in the undercoat paint is (A) / (B) = 60/40 to 95/5, and the total resin solid content of (A) and (B) is 100% by weight. (C) 1 to 50 weight per part Including further glass transition temperature of the cured undercoating film is characterized in that it is a 20 to 110 ° C., scratch resistance, processability and Durable precoated metal sheet. 2. The precoated metal sheet according to claim 1, wherein the undercoating film has elastomer fine particles (C) dispersed therein, wherein the precoated metal sheet has excellent scratch resistance, workability, and durability. 3. The rubber part of the elastomer fine particles (C) in the undercoat paint has an acrylic resin as a main component and its surface is selected from the group consisting of a carboxyl group, an epoxy group, a hydroxyl group, and an amino group. 3. The precoated metal sheet according to claim 1, wherein the precoated metal sheet is modified with a resin having at least one or more kinds of functional groups and has excellent scratch resistance, workability, and durability. 4. The elastomer fine particles (C) in the undercoating film have a core-shell structure comprising a core part including a rubber part and a shell part whose surface is modified with a resin having a functional group. The precoated metal sheet according to any one of claims 1 to 3, which is excellent in scratch resistance, workability, and durability. 5. The epoxy resin (A) in the undercoat paint
5. The precoated metal sheet according to claim 1, wherein the number-average molecular weight of the precoated metal sheet is excellent in scratch resistance, workability, and durability. 6. 6. The scratch-resistant steel according to claim 1, wherein the plated steel sheet serving as a base is a molten aluminum-zinc alloy plated steel sheet containing 1 to 60% by weight of aluminum. Pre-coated metal sheet with excellent workability, workability and durability. 7. The scratch resistance and processing according to claim 1, wherein the top coat contains vinylidene fluoride resin or polyester resin as a main component of the resin for forming a coating film. Pre-coated metal sheet with excellent durability and durability. 8. The undercoating film having a dry film thickness of 8 to 30.
The precoated metal sheet according to any one of claims 1 to 7, wherein the precoated metal sheet has excellent scratch resistance, workability, and durability. 9. The method according to claim 1, wherein the plated steel sheet serving as a base is provided with
9. A method for producing a precoated metal sheet by applying an undercoat paint and an overcoat paint having the resin composition for forming a coating film according to any one of claims 1 to 8, wherein at least one surface of the plated steel sheet is subjected to a chemical conversion treatment. After applying the undercoat on the treatment layer, 30 to 1
A step of heating for 80 seconds and baking so that the steel sheet temperature becomes 150 ° C. or more and less than 300 ° C. After further applying a top coat to the upper layer of the plated steel sheet where the undercoat is baked, heating for 30 to 180 seconds Baking the steel sheet so that the temperature of the steel sheet becomes 150 ° C. or more and less than 300 ° C. A method for producing a pre-coated metal sheet having excellent scratch resistance, workability, and durability.