JP3143316B2 - Painted metal plate with yuzu skin appearance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a painted metal plate having a citron skin appearance which is excellent in hardness, workability, stain resistance and chemical resistance. It is used as a constituent material of products, indoor and outdoor building materials, and other articles.

[0002]

2. Description of the Related Art In recent years, the use of so-called pre-coated metal plates, which have been painted before molding, has been increasing. According to this pre-coated metal plate, it is not necessary to apply a coating after molding, so that it is possible to omit various processes and reduce capital investment, for example, in a manufacturer using the metal plate.

Conventionally, as a method for producing this kind of precoated metal sheet, a method of applying a solvent-based paint to a metal sheet material using a roll has been mainly used. But with this method,
There is a problem that only a single-color smooth coating surface can be obtained. In addition, the pre-coated metal sheet is punched, bent,
Since the appearance of the product remains as it is after processing such as drawing, a high balance between workability and hardness is required, but in the method using the conventional solvent-based paint, workability and hardness are generally It is difficult to balance. Therefore, in the case of a pre-coated metal sheet using a solvent-based paint, those having excellent workability tend to be easily scratched because the film is soft, while those having high hardness tend to have poor workability.

[0004] In order to solve such a problem and at the same time take into account environmental issues in recent years, recently, a solventless powder coating has been used and sprayed onto the surface of a metal plate with a gun. Pre-coated metal sheet (powder pre-coated)
Have also been used. According to this method, there is no need to impart solvent solubility to the resin in the paint, so that the hardness and hardness are lower than when a solvent-based paint is used.
A pre-coated metal plate with excellent workability balance can be obtained, and on the surface of it a so-called "yuzu skin" can be formed, which has the same solid feeling as conventional electrostatic coating or solvent spray coating as after-coating. There are benefits. However, the production speed is usually 20 m / min. And the production speed of the solvent-based paint 60 to 100 m / min. It has the disadvantages of being much slower and of lower productivity.

Therefore, in order to deal with such a problem,
JP-A-3-38280 and JP-A-3-3828
In JP-A No. 1 (1994), there is proposed a technique of manufacturing a pre-coated metal plate by dispersing a powder coating material in a dispersion medium to form a slurry, applying the slurry to a metal plate by a roll coater, and performing heat treatment. According to this, since it is not necessary to spray the powder coating on the surface of the metal plate, the coating efficiency is improved by blowing off part of the powder coating once applied with the compressed air for spraying the coating. In addition, since the production speed is higher than that of the powder precoat described above by coating with a roll coater, productivity is enhanced.

[0006]

However, in the technology described in each of the above publications, the viscosity of the dispersed paint is low, so that the pick-up (lifting of the paint to a roll) is sufficiently performed when coating with a roll coater. Therefore, there is a problem that a coating defect easily occurs. In addition, when using a coating line for coating and baking ordinary solvent-based paints, the furnace length is not sufficient, and the so-called `` armpit '' in which by-products generated in the baking hardening process break through the film surface and evaporate. There is a problem that it easily occurs. In the case of the powder precoat described above, the leveling property (the property of trying to be smooth) differs depending on the paint, which determines the yuzu skin shape, and the appearance is almost determined by the particle size of the powder. It is difficult to control the skin appearance of citron.

[0007] The present invention addresses the above-mentioned problems in the prior art, and provides a yuzu skin appearance that has the same solid feeling as in the case of using powder precoat or aftercoat powder or solvent spray coating. It is an object of the present invention to provide a highly productive solvent-based coated metal sheet which can exhibit a good balance of hardness, workability, stain resistance, etc., and can arbitrarily control the surface appearance of citron.

[0008]

The inventors of the present invention have studied the above problems and found that organic particles having a different surface tension from a resin and a cross-linking agent (particularly organic particles that are not dissolved in a solvent) are contained in a coating composition. Is preferable), the repelling pattern can be formed, and if such a paint is applied and baked as an undercoating resin coating layer, and then a resin coating layer is provided on the upper layer, it is used in the case of powder pre-coating. It has been found that a skin appearance can be obtained. In that case, it was also found that by changing the thickness of the undercoat resin coating layer, it was possible to obtain citron skin of any size.

[0009] Further, as a result of studying to obtain the same hardness, workability, stain resistance and chemical resistance balance as that of the powder precoat, the resin of the upper resin coating layer has a glass transition temperature of 20 ° C or more. It has been found that it is effective to use a copolymerized polyester resin having a number average molecular weight of 5000 or more.

[0010] Based on these findings, the coated metal sheet exhibiting the yuzu skin appearance according to the present invention is characterized in that it is configured as follows to achieve the above object. That is, a resin, a cross-linking agent, and a resin that is molten at a temperature at which a cross-linking reaction between the resin and the cross-linking agent proceeds or is in a solution state, as an undercoat resin coating layer on the metal plate on which the base treatment is performed. And a crosslinking agent having a different surface tension from the dry weight of the resin composition of the resin coating layer.
A coating composition containing 0% by weight of organic particles is applied and baked to form a coating layer, and as a top coating resin coating layer on the coating layer, the glass transition temperature is 20 ° C. or higher and the number average molecular weight is 5000 or higher. And a coating layer formed by applying and baking a coating composition containing a polyester resin and an amino resin and / or an isocyanate compound.

Next, the components of the present invention described above will be described.
This will be described in detail. (1) Metal plate Especially if it is a material used for ordinary pre-coated metal plate
Not limited. Specifically, steel sheets, plated steel sheets (zinc-based
Jack, aluminum plating, tin plating, lead plating, etc.),
An aluminum plate, a copper plate and the like are suitable. For plated steel sheets,
10g / m^Two~ 100g / m^TwoWhat is
It is desirable to use. (2) Undercoating The undercoating is not particularly limited as long as it is a commonly used undercoating of a metal plate.
Absent. Chemical conversion treatment such as zinc phosphate treatment and iron phosphate treatment, and coating
Chromate such as mold chromate treatment and electrolytic chromate treatment
Treatment is suitable, and a commercially available chemical solution is used as it is.
Alternatively, it can be used after dilution. Such as zinc phosphate
In the chemical conversion treatment, the amount deposited on one side is 0.5 g / m ^Two~ 1.5g /
m^Two5 mg / m for chromate treatment^Two~ 100g / m
^TwoIt is. (3) Undercoating resin coating layer The undercoating resin coating layer is composed of a resin, a crosslinking agent, and a predetermined organic substance.
And a coating composition containing particles. This place
The coating composition is not an essential component, but will be described later.
Other pigments. Also, there is no
Although this type of solvent is also included, this kind of solvent
Since it is not present in the resin coating layer,
Just mention it. Resin which is the main component of "resin" undercoat resin coating layer
Are polyester, polyurethane, epoxy,
If it is a resin commonly used for solvent-based paints such as krill-based paints,
It is not limited to. However, it is preferable from the viewpoint of workability.
It is a polyester-based or polyurethane-based resin. Also,
If strong adhesion to the substrate is required, use epoxy
Or polyester, epoxy and polyurethane
In some cases, a combination of system resins is used.

From the viewpoint of processability, corrosion resistance and adhesion, the ratio of the resin in the dry film is 30% based on the total dry film weight.
It is preferably from 80 to 80% by weight, more preferably from 35 to 70% by weight. "Cross-linking agent" As a cross-linking agent used for forming a thermosetting resin coating layer by reaction with the above-mentioned resin, an amino resin such as a melamine resin, a urea resin, a benzoguanamine resin, or an isocyanate compound (blocked Isocyanate compounds).

The weight ratio of these crosslinking agents in the dry film is 10 to 10 parts by weight based on the total weight of the resin and the crosslinking agent.
30 parts by weight are preferred. If the amount of the cross-linking agent is 10 parts by weight or less, not only the workability, adhesion and corrosion resistance are not sufficiently exhibited, but also the appearance of citron skin cannot be sufficiently obtained. This is because the property is reduced. "Organic particles" Organic particles are an essential component for forming the yuzu skin appearance. The types of organic particles are as follows
Must meet the requirements of I and II, and
It is desirable that the condition of III is satisfied.

I. Different in surface tension from resin and crosslinking agent II. Those whose melting point is lower than the reaction temperature between the resin and the crosslinking agent III. It does not dissolve in the solvent contained in the paint before baking,
What is dispersed in a paint in a solid state, a suspended state or an emulsified state. Here, the surface tension is, as is well known, an energy per unit area of a formed surface (surface Gibbs free energy). It can be easily measured by the contact angle between the distilled water and the surface when the distilled water is dropped on the surface. A contact angle of 0 ° means that the surface is completely wet with distilled water, while a contact angle of 180 ° means that the surface is not wet at all. Since it is difficult to easily measure the surface tension of the particles by the contact angle, in the present invention, after the organic particles are once melted to form a film, the contact angle between the film and distilled water is measured. Thereby, the contact angle of the organic particles was determined.

Regarding condition II, the melting point of the organic particles is 1
The temperature is preferably from 00 ° C to 180 ° C. Melting point 100 °
Those having a C or less have poor stability in the paint, may increase the viscosity of the paint, and have poor citron skin shape upon baking. Further, when the melting point is 180 ° C. or more, the particles are not yet melted at the time when the curing reaction starts, and the desired citron skin shape cannot be obtained. Preferably 130 ° C to 1
It is in the range of 60 ° C.

Further, regarding the condition III, the particle diameter of the organic particles is preferably 3 μm to 60 μm in a state where the particles in a solid state or a suspended or emulsified state are dispersed in a paint. If the particle size is more than or less than this, the texture forming citron skin becomes uneven or a desirable surface skin cannot be obtained. More preferably, 10 to 50
μm.

Preferred as such organic particles are waxes. From the viewpoint of availability and cost, polyethylene wax, polypropylene wax,
Synthetic waxes such as polyamide waxes are particularly preferred.
In addition, the number average molecular weight is 300-1000
0, particularly preferably 500 to 6000. The type of polyethylene wax or polypropylene wax is polyethylene or polyethylene homopolymer, or polypropylene or polypropylene copolymer, and 0.5 to 40% by weight of the comonomer unit is derived from a saturated or unsaturated monocarboxylic acid or an amide thereof. Such copolymer units include acrylic acid,
It is a group of methacrylic acid, maleic acid, fumaric acid, acrylamide, stearic acid or stearamide. Further, particles in a suspended or emulsified state of a fatty acid ester are also preferred.

The weight ratio of the organic particles in the dry film is as follows:
0.5 to the dry weight of the resin composition in the resin coating layer
The content was limited to 7.0% by weight, but if it is less than 0.5% by weight, a unique citron skin appearance cannot be obtained, and if it exceeds 7.0% by weight, the surface irregularities become extremely large, and the appearance deteriorates. In addition to this, there is a fear that workability may be reduced. In order to prevent the metal plate which is the "pigment" base from being corroded, the undercoat resin coating layer generally contains a rust preventive pigment. From the same viewpoint, in the present invention, the rust preventive pigment is usually contained in the undercoat resin coating layer. Examples of such a rust-preventive pigment include chromate-based, phosphate-based, molybdate-based, and vanadate-based rust-preventive pigments.

Examples of the chromate-based rust preventive pigments include strontium chromate, zinc chromate, calcium chromate, and barium chromate. Strontium chromate or zinc chromate is preferred from the viewpoint of the dissolution rate. Further, as phosphate-based rust preventive pigments, there are zinc phosphate and calcium phosphate-based rust preventive pigments, and as molybdate-based rust preventive pigments, there are calcium molybdate-based, calcium molybdate-based and aluminum phosphomolybdate-based rust-proof pigments. Although there are rust-preventive pigments, it is difficult to use them alone in terms of rust-preventive power, and it is desirable to use them together with chromate-based rust-preventive pigments.

The amount of the rust preventive pigment to be added is 4 to 60% by weight based on the dry weight of the resin coating layer. If it is less than 4% by weight, the corrosion resistance is reduced, and if it exceeds 60% by weight, the workability is reduced. Preferably it is 7 to 50% by weight, more preferably 15 to 40% by weight.

Further, pigments other than rust-preventive pigments are appropriately used in the undercoating resin coating layer. When the desired color tone cannot be obtained with the overcoat resin layer alone, or when the undercoat resin layer has sufficient adhesion or hardness (the result is that the hardness of the undercoat layer affects the hardness of the final product) ), Titanium oxide as a white pigment or silica or kaolin as an extender may be appropriately used.
However, in this case, the pigment is blended so that the total weight of the pigment is 12 to 55% by weight based on the total weight of the dry film. If the content is less than 12% by weight, sufficient corrosion resistance, adhesion and hardness cannot be obtained, and if it exceeds 55% by weight, the workability is significantly reduced. (4) Topcoat Resin Coating Layer The topcoat resin coating layer is formed of a coating composition containing a predetermined polyester resin and an amino resin and / or an isocyanate compound as a crosslinking agent. In this case, the coating composition may contain a pigment, which is not an essential component but will be described later. "Polyester resin" The polyester resin used for the overcoat resin coating layer has a glass transition temperature of 2 as described above.
A polyester resin having a number average molecular weight of 5,000 or more at 0 ° C. or more. If the glass transition temperature is lower than 20 ° C., sufficient curing and stain resistance cannot be obtained, and the number average molecular weight is 5,000.
If it is less than 30, sufficient workability cannot be obtained. Preferably, the glass transition temperature is 30 ° C or more and 90 ° C or less,
The number average molecular weight is from 7000 to 30,000.

Particularly preferred is a gas transition temperature of 40 °.
Number average molecular weight of 10,000 to 25 at C or more and 80 ° C or less
Of a copolymerized polyester resin obtained by introducing 0.1 to 5 moles of a metal sulfonate base to the total acid or alcohol component into the basic polyester skeleton hardly soluble in a general-purpose organic solvent. Alternatively, a resin composition which is dissolved or dispersed in a solvent mainly containing isophorone and / or 1-methyl-2-pyrrolidone is used.

Here, the general-purpose organic solvent means a solvent having a solubility parameter in the range of 7.5 to 11.5, for example, toluene, xylene, cellosolve acetate, cyclohexanone, methyl ethyl ketone, isophorone or Solvesso (registered trademark). There are solvents used as paint thinners.

In addition, the term “sparingly soluble” refers to a temperature around room temperature (10
(35 ° C.) means that the solubility is less than 10% by weight even in a solvent. When the base resin dissolves in the solvent at room temperature or more at about 10% by weight or more, the solvent-type paint can be manufactured by directly dissolving in the solvent, and thus it cannot be said that the resin is hardly soluble. Such a soluble polyester resin has a poor balance between hardness and processability.

When workability at a low temperature is particularly required, it is effective to incorporate a copolymerized polyester resin (polyester resin B) having a glass transition temperature of 10 ° C. or less and a number average molecular weight of 5,000 or more. It is.

In this case, the metal sulfonic acid base is added to the polyester basic skeleton which is hardly soluble in the above-mentioned general-purpose organic solvent in an amount of 0.1.
0 to 40 parts by weight of the polyester resin B is blended with 50 to 70 parts by weight of the copolymerized polyester resin (polyester resin A) introduced by 1 to 5.0 mol,
It is important to use 70 to 90 parts by weight of both resins A and B in total. If the blending amount of the polyester resin B is too large, the hardness and stain resistance decrease. "Crosslinking agent" Examples of a crosslinking agent used for forming a thermosetting resin coating layer by reaction with the above-mentioned resin include amino resins such as melamine resin, urea resin and benzoguanamine resin or isocyanate compounds (blocked isocyanate). Compounds are also preferred.

The weight ratio of these cross-linking agents in the dry film is 10 to 30 with respect to 100 parts by weight of the total weight of the resin and the cross-linking agent.
It is preferred to use parts by weight. This is because when the amount of the crosslinking agent is 10 parts by weight or less, the workability, adhesion and corrosion resistance are not sufficiently exhibited, and when the amount is 30 parts by weight or less, the workability decreases. The "pigment" top-coating resin coating layer is used not only for various properties such as workability and hardness but also for giving a beautiful appearance to the coated metal plate, and accordingly, various pigments are appropriately used according to the purpose. For example, coloring pigments such as titanium oxide, iron oxide and phthalocyanine blue are used. An extender such as silica or kaolin may be added depending on the use. In that case, the amount of the pigment to be added is suitably 70 to 120% by weight based on the total weight of the resin and the crosslinking agent (the weight of the solid content of the resin composition). If the addition amount is less than this, the concealing property is not sufficient, and if the addition amount is too large, the processability decreases.

[0028]

According to the above arrangement, since the coating composition for forming the undercoat resin coating layer on the metal plate subjected to the undercoat treatment contains organic particles having a surface tension different from that of the resin and the crosslinking agent. In the state after the application and baking, a repelled pattern is formed. Then, by providing the overcoating resin coating layer on the undercoating resin coating layer on which the repelling pattern is formed, it is possible to obtain a yuzu skin appearance with a firm feeling like a powder precoat.

In this case, as a resin constituting the coating material for forming the overcoating resin coating layer, a copolymerized polyester resin having a glass transition temperature of 20 ° C. or more and a number average molecular weight of 5,000 or more was used, so that The same hardness, workability, stain resistance and chemical resistance balance as the body precoat can be obtained.

Further, in the coated metal plate of the present invention,
In any of the undercoating and the overcoating, a resin coating layer is formed by applying a solvent-based coating composition containing the above-described coating composition to a solvent using a roll coater and then baking, so that efficient production can be achieved. Becomes Also, in that case, it is possible to arbitrarily control the yuzu skin appearance of the surface by appropriately changing the thickness of the undercoat resin coating layer.

[0031]

Embodiments of the present invention will be described below. In Examples and Comparative Examples described below, “parts”
All indicate parts by weight. [Examples 1 to 4, Comparative Examples 1 to 6] As shown in FIG. 1, a coating type chromate treatment is applied to a 0.5 mm thick hot-dip galvanized steel plate (metal plate) a (NRC300 manufactured by Nippon Paint Co., Ltd.). Was applied in an amount of about 30 mg / m ² on one side, and an undercoat resin coating layer b containing organic particles was applied and baked on the upper layer.

In forming the undercoating resin coating layer b, a resin composition having the following composition and a rust preventive pigment are mixed and dispersed using a disper, and then the organic particles (No. 1 to 6) were used, and the resulting coating material was redispersed. With respect to the contact angle of the organic particles in the same table, a value measured after forming the organic particles on the film was used. In this case, cyclohexanone was used as the solvent. Here, Tg is the glass transition temperature, M
n shows a number average molecular weight, respectively.

<Resin Composition> Polyester Resin 1 (Tg = 32 ° C., Mn = 6600) 45 parts Polyester Resin 2 (Tg = 5 ° C., Mn = 9500) 43 {hexamethoxymethylated melamine (crosslinking agent) 12 〃 (manufactured by Mitsui Cyanamid Co., Ltd .; trade name: Cymel 303) amine block of dodecylbenzene (catalyst for crosslinking reaction) 0.5〃 <rust-proof pigment> strontium chromate 25 〃 Aluminum phosphomolybdate 10〃 (manufactured by Kikuchi Color Co., Ltd., trade name: LF BOSEI PM-308)

[0034]

[Table 1]

After the undercoating resin layer b is formed in this manner, the overcoating resin coating layer 1 or 2 having the following composition is formed thereon.
(In FIG. 1, the overcoat resin coating layer is indicated by the symbol c.).

<Overcoat Resin Coating Layer 1> Polyester A (Tg = 33 ° C., Mn = 9000) 80 parts Hexamethoxymethylated melamine 20 << Amine block of paratoluenesulfonic acid 1 >> Titanium oxide 100 >> Layer 2> Polyester A (Tg = 15 ° C., Mn = 4000) 80 parts Hexamethoxymethylated melamine 20 << Amine block of paratoluenesulfonic acid 1 >> Titanium oxide 100 >> Here, the above-mentioned undercoat resin coating layer and each The baking of the overcoat resin coating layer was performed under the following conditions.

Undercoat resin coating layer Furnace temperature: 320 ° C., maximum plate temperature (PMT): 2
16 ° C, baking time: 30 seconds, dry film thickness (average value): 7μ
m to 8 μm Top coat resin coating layer Furnace temperature: 350 ° C, Maximum plate temperature (PMT): 2
32 ° C., baking time: 38 seconds, dry film thickness: 18 μm to 19
The change in performance due to the combination of the undercoat resin coating layer thus formed and each of the overcoat resin coating layers was investigated. Table 2 shows the results.

[0038]

[Table 2]

The evaluation items shown in Table 2 are as follows. 1. Bending workability Indicated by the minimum number of sandwiching plates that does not cause cracks with a 10-fold loupe. For example, 0T indicates that close contact bending is possible, and 1T indicates that when the plate to be measured is bent, it can be bent without cracking until the distance between the bent plates becomes equal to the thickness of the same plate. It is shown that. Therefore, the larger the numerical value, the lower the workability. Since this bending workability varies depending on the temperature, here, 20 ° C. and 5 ° C.
Were measured at two different test temperatures. 2. Pencil hardness Based on the scar method (JIS K5400), the coating film was drawn using Mitsubishi Uni (trade name), and the hardness at which the scratches were formed was examined. At that time, each rank of pencil hardness (for example, 2H, H,
F etc.) were evaluated in two stages. Specifically, it is as follows.

2. Hard ← 2H, 2H ⁻ , H ⁺ , H, H ⁻ , F ⁺ , F, F ⁻ , HB ⁺ , HB → soft Nail scratch resistance The coating film surface was strongly rubbed with nails, and the scratch condition was evaluated.
The meanings of the symbols in Table 2 relating to the nail flaw resistance are as follows.

◎: no flaws, ○: slight flaws, Δ: flaw remaining easily recognized, ×: marked flaws Red magic stain (stain resistance) Red magic ink manufactured by Uchida Yoko was applied to the coating film, left for 24 hours, wiped off with a gauze impregnated with ethanol, and evaluated for remaining condition. The meanings of the symbols in Table 2 are as follows.

◎: no adhesion trace, ○: slight adhesion trace Alkali resistance The glass was immersed in a 5% NaOH solution at 25 ° C. and a 60% RH atmosphere for 24 hours, and the glossiness before and after the test was evaluated. The meanings of the symbols in Table 2 are as follows.

◎: good, ：: normal Boiling water resistance The coated metal plate was immersed in boiling water for 3 hours, and the surface gloss, blisters, peeling, etc. were visually observed. The meanings of the symbols in Table 2 are as follows.

：: good, ×: gloss reduction or blister generation Appearance The feeling of citron skin was visually evaluated. The meanings of the symbols in Table 2 are as follows.

：: good, ：: normal, ×: poor As shown in Table 2 above, in Examples 1 to 4,
Good results were obtained in all evaluation items of hardness, nail flaw resistance, stain resistance, alkali resistance, boiling water resistance and appearance. On the other hand, Comparative Examples 1, 2 and 6 have a problem in appearance, and Comparative Examples 3 to 6 are inferior in nail flaw resistance and stain resistance to Examples 1 to 4. Was done.
Further, it was also found that the workability (particularly the workability at a low temperature) was not sufficient in all of the comparative examples. [Examples 5 to 8, Comparative Examples 7 to 11] After degreasing an aminium plate (metal plate) having a thickness of 0.6 mm, a coating type chromate treatment (adhesion amount: 40 mg / m ² ) was performed, and the following composition was further applied. To form an undercoat resin film layer.

<Undercoat Resin Coating Layer> Polyester Resin C (Tg = 18 ° C., Mn = 7000) 85 parts Hexamethylene diisocyanate 15 {(ε-caprolactam block type) dibutyltin dilaurate 0.5} propyl stearate 0} Titanium oxide (TiO ₂ ) 29 {Strontium chromate 11} Then, on this undercoat resin coating layer, overcoat resin coating layers 3 to 10 having the following compositions are formed, respectively, and each of them is the same as in Examples 1 to 4. Was tested. In this case, conditions such as baking of the undercoat resin coating layer and each of the overcoat resin coating layers are as follows.

Undercoat Resin Coating Layer Same as in Examples 1-4 and Comparative Examples 1-6. Top coat resin coating layer Furnace temperature: 340 ° C, PMT: 224 ° C, baking time: 42 seconds, dry film thickness: 17 µm to 18
μm <Top coating resin coating layer 3 (Example 5)> Polyester resin D (Tg = 23 ° C., Mn = 10000) 80 parts Methyl / butyl mixed melamine 20 {dodecylbenzenesulfonic acid 1.6} TiO ₂ 100} silica 1.9% <Overcoat resin coating layer 4 (Example 6)> Polyester resin E (Tg = 55 ° C, Mn = 17000) 80 parts Hexamethoxymethylated melamine 15 {Butylated melamine 1.5} Dodecylbenzenesulfonic acid 1.0% (A-DBSA) TiO ₂ 90 ° <Overcoating resin coating layer 5 (Example 7)> Polyester resin F (Tg = 60 ° C., Mn = 17000) 86 parts Imino group-containing melamine 13 〃 butylated melamine 1.0〃 TiO ₂ 100 〃 However, as constituents of a next of said polyester resin F A.

Acid component: terephthalic acid 70 mol% isophthalic acid 20 1,4-cyclohexanedicarboxylic acid 7 pyromellitic acid 1.5 5-sodium 5-sulfoterephthalate 1.5 alcohol component: ethylenegolicol 70 mol% 1 , 3-propanediol 3 {neopentyl glycol 25} glycerin 2} The polyester resin F can be dissolved in cyclohexane, but is dissolved in toluene, xylene and Solvesso 150 (trade name) which is a petroleum solvent. Did not.

<Overcoat Resin Coating Layer 6 (Example 8)> Polyester Resin F 60 parts Polyester Resin G (Tg = 5 ° C., Mn = 15000) 22 {hexamethoxymethylated melamine 16} butylated melamine 2} dodecylbenzene Sulfonic acid 1 {TiO ₂ 95} <Top coating resin coating layer 7 (Comparative Example 7)> Polyester resin H (Tg = 13 ° C, Mn = 13000) 80 {Hexamethoxymethylated melamine (HMMM) 20} Paratoluenesulfonic acid 1 TiO ₂ 99 〃 <Overcoat resin coating layer 8 (Comparative Example 8)> Polyester resin F 92 〃HMMM 8 ＡA-DBSA 1 〃TiO ₂ 100 〃 <Overcoat resin coating layer 9 (Comparative Example 9)> Polyester resin E 65 〃 HMMM 35 〃 A-DBSA 1 〃 TiO ₂ 100 〃 <the overcoat resin Layer 10 (Comparative Example 10)> Polyester resin F 45 〃 polyester resin G 40 〃 HMMM 15 〃 A-DBSA 1 〃 TiO ₂ 100 〃 <overcoat resin coating layer 11 (Comparative Example 11)> Polyester resin F 72 〃 polyester resin G 12 {HMMM 16} A-DBSA 1 {TiO ₂ 100} Table 3 shows the results of tests performed after the formation of these overcoat resin coating layers 3 to 11.

[0050]

[Table 3]

As can be seen from Table 3, according to Examples 5 to 8 of the present invention, it was confirmed that good performance balance was obtained in all evaluation items including workability. On the other hand, the hardness and stain resistance of Comparative Example 7 were reduced, the boiling water was reduced in Comparative Example 8, the workability was decreased in Comparative Example 9, and the hardness and stain resistance were decreased in Comparative Example 10, respectively. Further, in Comparative Example 11, it was found that low-temperature workability, hardness and stain resistance were slightly reduced. As the reason, in the case of Comparative Example 7, the Tg of the polyester resin was low, and in the case of Comparative Example 8, the crosslinking was insufficient.
On the contrary, it is considered that the cross-linking is excessive in Comparative Example 9, that the amount of the polyester resin having a low Tg is large in Comparative Example 10, and that the effect of adding the polyester resin having a low Tg is small in Comparative Example 11. Can be

[0052]

As described above, according to the present invention, since the organic material particles having a surface tension different from that of the resin and the cross-linking agent are contained in the coating material for forming the undercoat resin coating layer, a yuzu having a sense of solidity is provided. A painted metal plate having a skin appearance is obtained. Also,
Glass transition temperature of 20 ° C on the undercoat resin coating layer
A coating composition containing a copolymerized polyester resin having a number average molecular weight of 5,000 or more was coated and baked to form an overcoating resin coating layer. The hardness, workability, stain resistance, and chemical resistance were equivalent to those of a powder precoat. A coated metal plate excellent in balance of properties and the like can be obtained. Furthermore, since the roll coating method can be used when performing undercoating and overcoating,
It can be produced efficiently, and the size of yuzu skin on the surface can be arbitrarily adjusted by changing the thickness of the undercoat resin coating layer.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a painted metal plate having a citron skin appearance according to the embodiment, which is used for explaining the embodiment of the present invention.

[Explanation of symbols]

 a: Metal plate (galvanized steel plate) b: Undercoat resin coating layer c: Top coating resin coating layer

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B32B 15/08 B32B 15/08 G (72) Inventor Kaoru Yoshida 4-33 Kitahama, Chuo-ku, Osaka City, Osaka Sumitomo Metal Industries (72) Inventor Kenji Ikishima 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture Sumitomo Metal Industries Co., Ltd. (72) Inventor Hiroyuki Susumu 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka No. Sumitomo Metal Industries, Ltd. (56) References JP-A-3-245877 (JP, A) JP-B-47-29179 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/00-7/26 B32B 15/08

Claims (4)

(57) [Claims] An undercoating resin coating layer is formed on a metal plate which has been subjected to an undercoating treatment, as a resin, a cross-linking agent, and at a temperature at which a cross-linking reaction between the resin and the cross-linking agent proceeds or is in a solution state. And coating and baking a coating composition containing organic particles having a surface tension different from that of the resin and the cross-linking agent and containing 0.5 to 7.0% by weight based on the dry weight of the resin composition of the resin coating layer. Coating composition comprising a polyester resin having a glass transition temperature of 20 ° C. or more and a number average molecular weight of 5,000 or more, and an amino resin and / or an isocyanate compound, as an overcoat resin coating layer on the upper layer. A coated metal plate having a yuzu skin appearance, characterized in that a coating layer formed by applying and baking is provided. 2. The overcoating resin coating layer comprises 90 to 70 parts by weight of a copolymerized polyester resin having a glass transition temperature of 40 ° C. or more and a number average molecular weight of 5,000 or more, and 10 to 30 parts by weight of an amino resin and / or an isocyanate compound. And a coating layer obtained by applying and baking a coating composition containing 70 to 120 parts by weight of one or more pigments based on 100 parts by weight of the total of these components.
A painted metal plate exhibiting the citron skin appearance described in 1. 3. The polyester resin having a glass transition temperature of 40 ° C. or higher and a number average molecular weight of 5,000 or higher contained in the overcoat resin coating layer is contained in a basic skeleton of a copolymer polyester resin which is hardly soluble in general-purpose organic solvents. 3. Yuzu skin appearance according to claim 1 or 2, characterized in that it is a copolymerized polyester resin (polyester resin A) obtained by introducing 0.1 to 5.0 mol of a sulfonic acid metal base with respect to all alcohol components. A painted metal plate. 4. A resin composition for forming an overcoating resin coating layer, comprising the copolymerized polyester resin (polyester resin A) according to claim 3 and a glass transition temperature of 10 ° C.
The following is a blend with a polyester resin having a number average molecular weight of 5000 or more (polyester resin B), and the blending ratio of these polyester resins A: B is 50 to 70: 0 by weight.
-40 and the sum of both resins A and B is 70-
The coated metal sheet exhibiting a citron skin appearance according to any one of claims 1 to 3, which is 90 parts by weight.