JPH0780403A - Resin-coated steel plate with superb press-forming, and coating properties and corrosion-protective effect and its manufacture - Google Patents

Abstract

PURPOSE:To provide a resin-coated steel plate with superb press-forming and coating properties and corrosion-protective effect, used most suitably for an automotive, home electric applicances and construction as well as a method of preparing the plate. CONSTITUTION:This resin-coated steel plate has a compound resin coat applied at a cohesive quantity of 0.2 to 3g/m<2> which is based mainly on polyester resin with a hydroxyl group contained in a molecule and 1 to 10wt.% of an isocyanate curing agent which reacts chemically with such a hydroxyl group as a resin component, and also contains 0.5 to 4wt.% of polyethylene wax particle. In addition, the form of the polyethylene wax is held in the coat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated steel sheet having excellent press formability, paintability and corrosion resistance, which is suitably used for automobiles, household electric appliances, building materials and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Generally, when pressing a steel plate,
Press oil is applied to the surface of the steel sheet to improve its workability. However, if such a press oil is applied to the surface of the steel sheet, the press oil is scattered during the press working of the steel sheet, which deteriorates the working environment or causes pollution problems, and further, degreasing after the press working. There are problems such as requiring a process.

Therefore, various steel sheet surface treatment methods have been proposed in order to obtain good press workability without using press oil. For example, a mill bond coating or a wax coating is formed on the steel plate surface, or an emulsion or aqueous solution of a resin containing an inorganic or organic solid lubricant is used as a surface treatment agent, which is applied to the steel plate surface and dried. Then, a method of forming a resin coating film is known. In particular,
The latter method is widely used as a surface treatment method for products that are strongly processed or for products that require degreasing after processing and require painting.

As such a method, for example, Japanese Patent Laid-Open No.
Japanese Unexamined Patent Publication No. 3-0171 discloses a surface treatment method using a surface treatment agent obtained by adding an epoxy resin to a carboxylated polyolefin resin.
Japanese Unexamined Patent Publication No. 89 describes a method of using a surface treatment agent obtained by adding fluorine-based resin particles as a solid lubricant to a urethane-modified polyolefin resin.

However, according to the surface treatment method in which the fluorine-based resin particles are contained as the solid lubricant in the resin coating, the surface of the fluorine-based resin particles is inactive, so that the adhesiveness with the resin forming the coating is high. Poorly, the fluorine-based resin particles in the coating film are wound around the roll during production and adhere to the product, deteriorating the appearance of the product and the coatability after processing. On the other hand, JP-A-3
No. 13367 describes a method of incorporating polyethylene wax particles as a solid lubricant into a resin film. When the wax has a softening point of 120 ° C. or lower, baking is performed at a temperature of 120 ° C. or higher during film formation. When it is carried out, the wax particles are softened and the wax is concentrated on the surface of the coating film, and although the effect as a lubricant is obtained, the paintability and corrosion resistance after processing are markedly lowered. Therefore, in order to perform the baking at 120 ° C. or lower, it is necessary to use a low temperature curing agent, but there are few kinds thereof and there is a problem in the stability of the resin during storage.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems in the above-mentioned conventional resin-coated steel sheet, and is press-formability suitable for use in automobiles, household electric appliances, building materials and the like. An object of the present invention is to provide a resin-coated steel sheet having excellent paintability and corrosion resistance, and a method for producing the same.

[0007]

A resin-coated steel sheet having excellent press formability, coatability and corrosion resistance according to the present invention contains a polyester resin having a hydroxyl group in the molecule and an isocyanate curing agent in an amount of 1 to 10% by weight. A composite resin coating mainly containing a resin component and containing 0.5 to 4% by weight of polyethylene wax particles is formed on the surface of the steel sheet at a deposition amount of 0.2 to 3 g / m ² , and the shape of the polyethylene wax is It is characterized by being retained in the coating.

According to the present invention, such a resin-coated steel sheet contains a polyester resin having a hydroxyl group in the molecule and 1 to 10% by weight of an isocyanate curing agent in terms of solid content, that is, in terms of resin coating. The surface treatment agent containing polyethylene wax particles in an amount of 0.5 to 4% by weight is mainly applied to the surface of the steel sheet, and is heated and dried at a temperature not higher than the softening point of the polyethylene wax.
It can be obtained by forming a composite resin film at a rate of 0.2 to 3 g / m ² .

According to the present invention, a polyester resin having a hydroxyl group in the molecule is used as a main resin component in the surface treatment agent. Such a polyester resin is generally produced by a condensation reaction of a polybasic acid (which may contain an unsaturated polybasic acid) and a polyhydric alcohol. For example, as the polybasic acid, Examples thereof include phthalic acid, terephthalic acid, tetrachlorophthalic anhydride, succinic acid, adipic acid, sebacic acid, azelaic acid, trimellitic anhydride, and rosin maleic anhydride, and examples of the polyhydric alcohol include: Ethylene glycol, glycerin, neopentyl glycol,
Pentaerythritol, sorbitol, glycerin monoallyl, etc. can be mentioned.

In the present invention, commercially available products can be preferably used as such polyester resins. Examples of such commercially available products include saturated polyester resins such as Byron 23CS, Byron 29CS, Byron 29XS, Byron 20SS, Byron 29SS,
(Manufactured by Toyobo Co., Ltd.) and the like. In the present invention, the saturated polyester resin is preferably used as described above, but an unsaturated polyester resin is also used if necessary.

Further, according to the present invention, the surface treatment agent contains an isocyanate curing agent. Thus, according to the present invention, together with the polyester resin having a hydroxyl group in the molecule, as a curing agent that reacts with the hydroxyl group, a surface treatment agent containing an isocyanate curing agent is applied to the surface of the steel sheet, which is By drying, it is possible to form a resin film formed by curing a polyester-based resin, and thus having the desired film strength and increasing the temperature of the mold and the sliding surface pole in press forming of strong processing. It is possible to obtain a resin-coated steel sheet in which scratches and black discoloration are suppressed against pressure and which is further excellent in corrosion resistance, coatability, and coatability after processing.

Other than the above isocyanate-based curing agents, epoxy-based, melamine-based, and styrene-based curing agents are known as curing agents for polyester resins. However, when these are used as curing agents, they are obtained. Resin coated steel sheet is inferior in paintability. In addition, since the hardness of the formed coating increases and the elongation decreases, the resin cannot follow the deformation of the steel sheet during processing, and the coating peels off.

However, when an isocyanate curing agent is used according to the present invention, this isocyanate curing agent reacts with the hydroxyl group of the polyester resin to form a urethane bond, and this urethane bond adheres to the coating film. It is believed that it contributes to the paintability and ensures excellent paintability.

In the present invention, the isocyanate curing agent has a high reactivity with the hydroxyl group of the polyester resin and a good compatibility with the polyester resin, and is cured at a temperature not higher than the softening point of the polyethylene wax. Those having good liquid stability in which the reaction occurs are preferably used.

Examples of such an isocyanate curing agent include, for example, Millionate MT, Millionate N, Coronate T, Coronate HL, Coronate L, Coronate HK, Coronate EH, Coronate 2030, Coronate 2067, Suprasec 3240, and Suprasec 3333.
40, Daltsec 1350, Daltsec 2170,
Dartsec 2280, (Japan Polyurethane Industry Co., Ltd.)
Manufactured) and the like.

In the present invention, the amount of such an isocyanate curing agent is preferably in the range of 1 to 10% by weight in terms of solid content in the surface treatment agent. When the isocyanate curing agent is less than 1% by weight in the surface treatment agent, the curing of the polyester resin is insufficient,
The required film strength cannot be obtained. On the other hand, if it exceeds 10% by weight, the coating film becomes too hard, and the coating film is likely to peel during press molding. Particularly, in the present invention, the isocyanate curing agent is preferably in the range of 1 to 5% by weight in the surface treatment agent.

The resin-coated steel sheet according to the present invention is mainly composed of a polyester resin containing the above isocyanate curing agent as a curing agent, and contains polyethylene wax particles in an amount of 0.5.
Applying a surface treatment agent containing ~ 4 wt% to the surface of the steel sheet,
After drying, the amount of resin coating that retains the shape of polyethylene wax in the coating is 0.2 to 3 g /
It can be obtained by forming with m ² .

Therefore, the resin-coated steel sheet according to the present invention contains, on the surface of the steel sheet, mainly a polyester resin containing the above-mentioned isocyanate-based curing agent as a curing agent and 0.5 to 4% by weight of polyethylene wax particles, Among them, the composite coating in which the shape of polyethylene wax is retained is formed at the rate of the attached amount of 0.2 to 3 g / m ² .

When the content of polyethylene wax particles in the resin coating is less than 0.5% by weight, the lubricity and press moldability of the obtained coating are not sufficiently improved, while when it exceeds 4% by weight. Although there is no particular problem in terms of lubrication performance, the adhesion between the coating film and the steel sheet obtained becomes poor, the coating film peels off during press working, and the corrosion resistance after working becomes poor. Further, with respect to paintability as well, the adhesion between the coating and the paint is reduced. Particularly, in the present invention, the amount of polyethylene wax particles in the resin coating is 1 to 3.
It is preferably in the weight%.

The polyethylene wax particles used in the present invention preferably have a softening point in the range of 125 to 200 ° C. When the softening point is lower than 125 ° C,
When the die temperature rises during pressing, the wax softens and liquefies, causing the liquid to run out between the steel plate and die,
Workability deteriorates. Further, when the softening point is higher than 200 ° C., the wax does not soften due to the increase of the mold temperature during the press working, so that good lubricating performance cannot be obtained.

Further, in the present invention, when the surface treatment agent is applied to the surface of a steel sheet and then dried to form a resin film, the drying temperature is set to be equal to or lower than the softening point of the polyethylene wax particles. As a result, the shape of the polyethylene wax particles dispersed in the film after the molded product of the resin film is maintained, and the lubricity of the film is further improved.

Further, when degreasing is performed as a pretreatment for coating the product after press working, the polyethylene wax particles are separated from the coating surface by the degreasing, and the diameter of the coating surface is from 0.1 to 1. Many pinholes of 3 μm are generated. The pinhole exerts an anchoring effect to remarkably improve the adhesion between the resin film and the paint during painting. Such pinholes are often generated by degreasing using a solvent, and the above effect can be more effectively exhibited. As a solvent used for such degreasing, for example,
Examples thereof include trichloroethylene, trichloroethane, acetone and the like. Also, by alkaline degreasing,
Similar effects can be obtained by controlling the pH and temperature of the degreasing liquid.

The effect of generating pinholes in the above resin coating is even greater and useful when performing electrodeposition coating after pressing. That is, the pinhole improves the uniform current-carrying property at the time of electrodeposition coating, and as a result, the local concentration of the current is eliminated, and the coating appearance is significantly improved.

In order to maximize the effect of such polyethylene wax particles, the polyethylene wax particles are
The particle size is preferably in the range of 0.1 to 3 μm. When the particle size exceeds 3 μm, it becomes difficult to disperse the particles uniformly in the surface treatment agent, and as a result, the adhesion of the obtained coating film to the steel sheet and the adhesion to the coating material deteriorate. On the other hand, the size of polyethylene wax particles is 0.1μ
If it is smaller than m, the effect of improving the lubricity and corrosion resistance of the above-mentioned coating due to the addition of polyethylene wax particles cannot be obtained.

In the present invention, commercially available products can be preferably used as the above-mentioned polyethylene wax, and as such commercially available products, for example, Disparlon SE210-15T, SE1020-7TN, SE47.
8-10T, SE470-10T, SE480-10
T, SR510-10X, SE1020-7X (Kusumoto Kasei Co., Ltd.), etc. can be mentioned.

In the present invention, the amount of such composite resin coating adhered to the steel sheet is in the range of 0.2 to 3 g / m ² .
When the adhesion amount of the composite resin film is less than 0.2 g / m ² , the required lubrication effect cannot be obtained in the heavy working, and the required corrosion resistance and paintability cannot be obtained after the working. However, when the adhesion amount of the composite resin coating exceeds 3 g / m ² , the peeling amount of the composite resin coating increases in the press working of the steel sheet, and for example, in the press molding, the release coating accumulates in the mold and the press forming Cause trouble.

In the present invention, the steel sheet material is not particularly limited, but for example, zinc or zinc alloy plated steel sheet, those obtained by subjecting these steel sheets to chemical conversion treatment such as chromate treatment or phosphate treatment are preferable. Used for.

[0028]

As described above, according to the present invention, a polyester resin containing an isocyanate curing agent is mainly used and a surface treatment agent containing polyethylene wax particles is applied to the surface of a steel sheet to give a polyethylene wax having a softening point. By drying at the temperature below, it is possible to perform press forming of strong working without applying a press oil, and to form a composite resin film having excellent corrosion resistance and coatability.

The resin-coated steel sheet having high lubricity, high corrosion resistance, and high paintability according to the present invention can be directly coated after pressing, and can be degreased for electrodeposition coating.

[0030]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. In the following, as a raw material steel plate, a chromate-treated hot-dip galvanized steel plate (zinc adhesion amount 90 g
/ M ² and the amount of deposited chromium of 40 mg / m ² ) were used. In addition, except for Example 1, as an isocyanate curing agent,
Coronate HL was used. The isocyanate curing agents used in Example 1 are noted in Table 1.

Example 1 A polyester resin (Vylon 23CS) was added with each of the isocyanate curing agents shown in Table 1 in an amount of 0.5 to 15% by weight.
2% by weight of polyethylene wax (particle size 1-2 μm, softening point 140) in terms of total solids content after blending
(° C.) The particles were dispersed to prepare a surface treatment agent. This surface treatment agent was applied to the surface of the raw steel sheet with a squeezing roll so that the dry adhesion amount was 1 g / m ^2, and dried at 120 ° C. to form a resin film, thereby obtaining a resin-coated steel sheet.

For comparison, the same polyester resin as above was blended with 5% by weight of an epoxy, melamine or styrene curing agent to prepare a surface treating agent, which was used in the same manner as above. As a result, a resin-coated steel sheet was obtained. Each surface-treated steel sheet thus obtained was subjected to a sliding test, a press test, a salt spray test and a coating test to examine the dynamic friction coefficient, mold galling resistance, corrosion resistance and coating adhesion.

The coefficient of kinetic friction was determined from the load due to sliding at a pressure of 150 kg using a sliding tester. The mold galling resistance and blackening resistance were visually examined for mold galling and black discoloration on the sliding surface of the molded product after press molding using a single-shot press tester. In addition, the corrosion resistance is JIS Z 23
According to the method described in No. 71, a salt spray test was conducted and examined. Regarding the coating film adhesion, after the acrylic and melamine alkyd coatings were applied, the adhesion of the coating film was examined by cross-cutting and cross-cutting Erichsen. The results are shown in Table 1.

[0034]

[Table 1]

Example 2 As in Example 1, a polyester resin (Vylon 29) was used.
CS) is mixed with 5% by weight of an isocyanate curing agent, and a polyethylene wax having a particle diameter of 0.1 to 3 μm (softening point 15
(0 ° C.) was dispersed in an amount of 2% by weight in terms of the total solid content after the film formation to prepare a surface treatment agent.

For comparison, a polyethylene wax having a particle size of less than 0.1 μm and a polyethylene wax having a particle size of more than 4 μm (each having a softening point of 150 ° C.) were used in an amount of 2% by weight, and a surface treatment agent was similarly prepared. Prepared. The amount of these surface treatment agents applied to the surface of the raw steel sheet in a dry amount of 1 g /
It was applied with a squeezing roll so as to have m ² and dried at 140 ° C. to form a resin film, thereby obtaining a resin-coated steel sheet. Various characteristics of the resin-coated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 2.

[0037]

[Table 2]

Example 3 As in Example 1, a polyester resin (Vylon 29) was used.
CS) was mixed with 5% by weight of an isocyanate curing agent, and a polyethylene wax having a particle diameter of 1 to 2 μm (softening point 160
C) is 0 to 5% by weight in terms of total solid content after film formation.
Was dispersed to prepare a surface treatment agent.

This surface treatment agent was applied to the surface of the raw steel sheet with a squeezing roll so that the dry adhesion amount was 1 g / m ^2, and 15
A resin coating was formed by drying at 0 ° C. to obtain a resin-coated steel sheet Various properties of the resin-coated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 3.

[0040]

[Table 3]

Example 4 As in Example 1, a polyester resin (Vylon 20)
CS) was mixed with 5% by weight of an isocyanate curing agent, and a polyethylene wax having a particle diameter of 1 to 2 μm (softening point 100
˜250 ° C.) was dispersed in an amount of 2% by weight in terms of the total solid content after the film formation to prepare a surface treatment agent.

This surface treatment agent was applied to the surface of the material steel sheet with a squeezing roll so that the dry adhesion amount was 1 g / m ^2, and
A resin coating was formed by drying at ~ 300 ° C to obtain a resin-coated steel sheet. Various characteristics of the resin-coated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 4.

[0043]

[Table 4]

Example 5 As in Example 1, a polyester resin (Vylon 29
5% by weight of an isocyanate-based curing agent was added to SS), and a polyethylene wax having a particle diameter of 1 to 2 μm (softening point 180
2% by weight in terms of the total solid content after film formation was dispersed to prepare a surface treatment agent.

This surface treatment agent is applied to the surface of the raw steel sheet by a squeezing roll so that the dry adhesion amount becomes 0.2 to 3 g / m ^2, and dried at 160 ° C. to form a resin film, and resin coating. A steel plate was obtained. Various characteristics of the resin-coated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 5.

[0046]

[Table 5]

Example 6 As in Example 1, a polyester resin (Vylon 29) was used.
XS) was mixed with 5% by weight of an isocyanate curing agent, and a polyethylene wax having a particle diameter of 1 to 2 μm (softening point 150
2% by weight in terms of the total solid content after film formation was dispersed to prepare a surface treatment agent.

This surface treatment agent was applied to the surface of the raw steel sheet with a squeezing roll so that the dry adhesion amount was 1 g / m ^2, and
The resin-coated steel sheet was obtained by drying at 0 ° C to form a resin film. After vapor degreasing with trichloroethane or alkali spray degreasing (liquid temperature 55 ° C.) on this resin-coated steel sheet, electrodeposition coating was carried out. The results are shown in Table 6.

[0049]

[Table 6]

The electrodeposition coating was carried out using acrylic cation electrodeposition coating (Aqua No. 4800) manufactured by NOF CORPORATION. The coating conditions and the evaluation of coating film physical properties after coating are shown below. [Coating conditions] Bath temperature 28 ° C Polar ratio (+/-) 1/4 to 1/6 energizing time 2 minutes Energizing voltage 160 to 230V Coating film thickness 25 μm Washing with water Shower with water Washing conditions 180 ° C x 20 minutes

[Evaluation of physical properties of coating film] Cross-cut test: After coating, cut a cross-cut at 1 mm intervals on a steel plate,
The peeling of the coating film was investigated by a tape peeling test. Erichsen test: Using an Erichsen tester, the coated steel sheet was extruded by 4.5 mm, and then the state of cracking of the coating film was investigated. DuPont impact test: DuPont impact tester (height 300
mm × weight 500 g × punch diameter ½ inch), an impact test was carried out to investigate the occurrence of cracks in the coating film and the coating film peeling by the tape peeling test. Salt spray test (SST): A flat plate was cross-cut at 60 °, and the swelling width of the coating film after 240 hours of the salt spray test and the peeling of the coating film by a tape peeling test and the occurrence of red rust were investigated.

Claims (6)

[Claims] 1. Polyethylene wax particles mainly composed of a polyester resin having a hydroxyl group in the molecule and a resin component containing 1 to 10% by weight of an isocyanate curing agent.
The amount of composite resin coating containing 5-4% by weight is 0.2-3
A resin-coated steel sheet, which is formed on the surface of the steel sheet at a rate of g / m ² and retains the shape of polyethylene wax in the coating. 2. The particle size of polyethylene wax particles is 0.1.
The resin-coated steel sheet according to claim 1, wherein the resin-coated steel sheet is in the range of 3 μm to 3 μm. 3. A polyethylene wax particle having a softening point of 12
The resin-coated steel sheet according to claim 1, which is in the range of 5 to 200 ° C. 4. A polyester resin having a hydroxyl group in the molecule and an isocyanate curing agent 1 to 10 in terms of solid content.
A resin composition containing 0.5% by weight of polyethylene wax particles as a main component, a surface treatment agent containing 0.5-4% by weight of polyethylene wax particles is applied to the surface of a steel sheet and dried by heating at a temperature not higher than the softening point of the polyethylene wax. A method for producing a resin-coated steel sheet, which comprises forming a composite resin coating film at a rate of 0.2 to 3 g / m ² of coating amount. 5. A polyethylene wax particle having a particle diameter of 0.1.
The method for producing a resin-coated steel sheet according to claim 4, wherein the resin-coated steel sheet is in the range of 3 to 3 μm. 6. A polyethylene wax particle having a softening point of 12
It exists in the range of 5-200 degreeC, The manufacturing method of the resin coated steel plate of Claim 4 characterized by the above-mentioned.