JPH09156028A - Coated metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated metal plate suitable for building material and kitchen apparatus, having high hardness, excellent flaw resistance and stain resistance, and excellent workability. SOLUTION: On at least one face of a metal plate, a chemically converted film is provided. On its upper layer, a precoating film having a high molecular polyester resin as a main component is provided. Further, the upper layer is coated with a coating composition having, as a main component, a vehicle which contains 50-75 pts.wt. of acrylic resin having a hydroxyl group value of 60-110mgKOH/g and a glass transition temperature of 70-110 deg.C, and 50-25 pts.wt. of melamine resin, and is baked so as to form a coated metal plate having a film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal sheet having high hardness, excellent scratch resistance, stain resistance and durability, and also excellent impact resistance and workability. A coated metal plate that is resistant to scratches and dirt when applied to equipment, storage containers, exterior materials for various home appliances, door materials, etc., and has long-term durability against chemical erosion due to acidic or alkaline substances. It is about.

[0002]

2. Description of the Related Art Metal plates, particularly stainless steel plates, are often used as building materials, kitchen equipment, housings, exterior materials for various home appliances, and door materials. In that case, if the metal plate is used as it is as a bare material, contaminants such as fingerprints and oils and fats are likely to adhere to the metal plate, and it is difficult to remove it.

Therefore, in order to prevent the adherence of pollutants while facilitating the appearance of the metal plate and to facilitate the removal of adhered pollutants, polyester resin clear paint, fluororesin clear paint, acrylic resin clear paint, etc. A method of coating the surface of a metal plate with metal is generally used.

[0004]

However, a coated metal sheet coated with a polyester resin-based clear paint is excellent in workability, but is poor in scratch resistance due to its low coating hardness and is also resistant to stains. Is also inferior. A coated metal sheet coated with a fluororesin-based clear paint is excellent in workability and stain resistance, but is inferior in scratch resistance due to its low coating hardness. Further, the conventional coated metal plate coated with a clear acrylic resin-based paint has a problem that it is poor in workability and the coating film hardness, scratch resistance and stain resistance are not sufficient.

The present invention has been made in order to solve the problems in the prior art, and has a high hardness, an excellent scratch resistance, a stain resistance and a durability, which are optimal for the above-mentioned applications. It is an object of the present invention to provide a coated metal plate having excellent impact resistance and workability.

[0006]

Means for Solving the Problems As a result of studying a coating resin having the above characteristics, the present inventors have found that an acrylic resin having a specific hydroxyl value and a glass transition temperature and a melamine resin are bonded at a specific ratio. The resin-based coating makes it possible to optimize the hardness, stain resistance, and chemical resistance, and by using a high-molecular polyester resin for the undercoat, sufficient impact resistance and It was found that the workability can be secured.

The present invention has been made on the basis of such knowledge, and a chemical conversion treatment film and an undercoating mainly composed of a polymer polyester resin formed as an upper layer on at least one surface of a metal plate. A film and a coating film formed on the upper layer thereof, which has a hydroxyl value of 60 to 110 mg KO.
A coating composition containing a color-developing agent as a main component containing 50 to 75 parts by weight of an acrylic resin having H / g and a glass transition temperature of 70 to 110 ° C. and 50 to 25 parts by weight of a melamine resin is applied and baked. A coated metal plate having a coating film formed by the above.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

The main coating composition of the present invention comprises a melamine resin and an acrylic resin having a specific hydroxyl value and glass transition temperature as the main components of the color developing agent.

This acrylic resin reacts with a melamine resin to form a crosslink structure having a very high hardness. Therefore, an acrylic resin having a hydroxyl group in its side chain or an acrylic resin having a hydroxyl group and a carboxyl group in its side chain is used. Use resin.

For introducing a hydroxyl group into an acrylic resin,
As the acrylic monomer having a hydroxyl group, for example,
Hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, N-
Examples include methylol acrylic amine.

Examples of the acrylic monomer having a carboxyl group for introducing a carboxyl group into the acrylic resin include acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, and substituted derivatives thereof.

Further, as an acrylic monomer to be copolymerized with the above-mentioned acrylic monomer having a hydroxyl group or a carboxyl group in order to form a crosslink structure having an extremely high hardness, for example, (meth) acrylic Methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n- (meth) acrylate
Butyl, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, n-octyl (meth) acrylate, isoponyl (meth) acrylate, etc. (Meth) acrylic acid alkyl ester type ethylenic monomers, further ethylenic monomers copolymerizable with these monomers, and (meth) acrylonitrile,
Styrene and the like can be mentioned.

The acrylic resin used in the present invention is
For example, it can be produced by a radical polymerization reaction by dropping a mixture of the above acrylic monomer components and a radical polymerization initiator into a heated organic solvent over a predetermined period of time and then maintaining the temperature at a constant temperature for a predetermined period of time. .

The acrylic resin produced in this way is
It is necessary that the hydroxyl value is in the range of 60 to 110 mgKOH / g and the glass transition temperature is in the range of 70 to 110 ° C.

When the hydroxyl value is less than 60 mgKOH / g, the crosslink density of the coating film is low, so that the strength and hardness of the coating film are insufficient. On the other hand, when it exceeds 110 mgKOH / g, the flexibility of the coating film is poor. Therefore, a problem occurs in impact resistance, inferior in bake hardenability, and unreacted groups remain in the coating film even after curing, so that chemical resistance and stain resistance also decrease.

When the glass transition temperature is less than 70 ° C., the strength and hardness of the coating film are insufficient, while when it exceeds 110 ° C., the flexibility of the coating film is poor and the impact resistance is insufficient. Poor paintability and bake hardenability.

Further, the acrylic resin has a number average molecular weight of 3
The range of 000 to 10,000 is preferable.

When it is less than 3,000, the bake hardenability is poor, and the coating film hardness tends to be insufficient. On the other hand, when it is more than 10,000, the resin is hard to dissolve in the solvent and the solid content of the coating is low, resulting in poor coatability.

The melamine resin to be blended with the acrylic resin is obtained by reacting melamine with formaldehyde and then etherifying a part or all of the methylol group with a monohydric alcohol such as methanol, ethanol, propanol or butanol. It is an alkyl etherified melamine. As the melamine resin, a methylated melamine resin, a butylated melamine resin, or a methylated-butylated mixed melamine resin is particularly preferable.

The coating composition used in the present invention comprises the above acrylic resin (A) and melamine resin (B) as the main components of the color-developing agent, and the solid content of the component (A) is 50.
To 75 parts by weight and component (B) in the range of 50 to 25 parts by weight, more preferably 60 to 70 parts by weight of component (A) and 40 to 30 parts by weight of component (B).
When the amount of the component (B) is less than 25 parts by weight, the coating film hardness is insufficient, and the chemical resistance and stain resistance are poor. On the other hand, when it is more than 50 parts by weight, the flexibility is poor, so that there is a problem in impact resistance. Occurs.

Next, a method of manufacturing the coated metal plate of the present invention will be described. First of all, as the coated metal plate to be used,
In addition to cold-rolled steel plates, stainless steel plates, and aluminum plates, various metal plates such as steel plates plated with zinc, zinc-based alloys, aluminum, chromium, nickel, or these alloys can be used.

A chemical conversion treatment film is formed on the surface of the above metal plate in order to secure adhesion to the coating film. The chemical conversion coating may be formed by a pre-coating treatment suitable for each metal plate, such as coating or spraying with a chromate, a phosphate or a silane coupling agent, or an acid such as phosphoric acid, nitric acid or hydrofluoric acid or an alkali. In addition to those formed by activation treatment or the like, those formed by electrolytic treatment may be used.

The undercoating film is applied to enhance the adhesion between the metal plate and the topcoating film and to improve the bending workability and impact resistance of the coating film system. In order to ensure such performance, it is necessary to form a coating film containing a high-molecular type polyester resin as a main component, and it is particularly preferable to use a high-molecular polyester resin having a molecular weight of 5000 or more as a main component.
When the molecular weight is less than 5000, workability and impact resistance are poor.

As the paint for forming this undercoating film, commercially available paints having a high molecular polyester resin as a main component can be used, and a melamine resin or an isocyanate compound is used as a curing agent. Those contained are preferred. When high corrosion resistance and coating adhesion are required, epoxy and acrylic components in the undercoat coating,
Other additive components can be added.

The dry film thickness of the undercoat film is preferably about 5 to 20 μm in order to obtain the above effects.

The overcoat film is formed by applying the above-mentioned coating composition on the undercoat film and then baking it. The dry film thickness of the top coat film is preferably 2 to 10 μm. If the film thickness is less than 2 μm, the hard coating film does not form a continuous film, and the scratch resistance, stain resistance, and chemical resistance of the coating film deteriorate. On the other hand, when the film thickness exceeds 10 μm, the coating film becomes brittle, and bending workability and impact resistance deteriorate.

If necessary, a plasticizer, a desiccant, a dispersant, a curing catalyst and the like can be added to the coating composition used for forming the top coating film or the under coating film, especially at high temperature. When baking, it is effective to add an antioxidant.

The coating method of these paints is not particularly limited, and the roll coater method, which has been generally used in the past,
A coating method such as a curtain flow coater method or a die coater method can be applied.

[0030]

[Example] A stainless steel plate or a galvalume steel plate (each having a plate thickness of 0.5 mm) was subjected to a coating type chromate treatment or a silane coupling treatment as a chemical conversion treatment,
Then, a clear coating of a high molecular polyester resin as an undercoating coating (trade name “Precolor P-
20 clear ", molecular weight 5,000 to 10,000), polyester resin-based paint (NOF Co., Ltd., product number" No.
3800 ", molecular weight 2000-4000), epoxy resin-based paint (Nippon Yushi Co., Ltd., product number" WP-3 "), and then applied plate temperature: 220 ° C, baking time: 40 seconds After baking, the coating composition prepared as described below was applied as a top coat, and baking was performed (baking time: 90 seconds), and the obtained coated metal plate was subjected to the following various tests.

Table 1 shows the composition and characteristics of the acrylic resin copolymer used in the top coating composition, and Table 2 shows the composition of the top coating composition.

[0032]

[Table 1]

[0033]

[Table 2]

The top coating composition was produced as follows. (1) Production of Acrylic Resin Copolymer A four-necked flask equipped with a thermometer, a reflux condenser, a stirrer, a dropping funnel, and a nitrogen gas introducing tube was charged with 20 parts by weight of Solvesso # 100 under a nitrogen gas stream. -Butanol (10 parts by weight) was charged, and the mixture was heated to reflux with stirring, and the monomer and polymerization initiator mixture (dropping component) 55 having the composition shown in Table 1 was added.
Parts by weight were dripped at a constant speed from the dropping funnel over 24 hours.
After dripping, hold under reflux for 2 hours, then solves #
After 15 parts by weight of 100 was added and cooled, filtration was performed with a 200-mesh wire mesh to obtain solutions of acrylic resin copolymers A-1 to A-8 having the characteristics shown in Table 1, respectively.

The number average molecular weight of each acrylic resin copolymer was measured by gel permeation chromatography using a calibration curve of standard polystyrene.

(2) Manufacture of Topcoat Coating Composition According to the blending ratio shown in Table 2, the acrylic resin copolymer and a part of the mixed solvent are mixed, and then a melamine resin and an acid catalyst are added and stirred. , Mixed. Then, the remaining mixed solvent is appropriately added to adjust the viscosity to Ford Cup No. 4 in 1
The paint T- shown in Table 2 was adjusted to 20 ± 10 seconds (25 ° C).
1 to T-10 were obtained.

In Table 2, T-1 to T-4 are paints of the present invention, and T-5 to T-10 are paints outside the scope of the present invention.

[Test / Evaluation Method] The coating film performance of the coated metal plate was evaluated as follows. (1) Pencil hardness test According to the method of 8.4.1 (1993) of JIS-K5400, the scratch resistance of the coating film was examined by scratching the coating film when the hardness of the pencil core was changed, The maximum hardness at which no scratch was observed on the coating film was defined as the pencil hardness of the coating film. A pencil hardness of 4H or more was passed, and a pencil hardness of less than 4H was rejected.

(2) Coating film adhesion test (cross-cut tape method) The test piece was immersed in boiling water for 2 hours and then allowed to stand in a room at 20 ° C. for 2 hours, followed by JIS-K5400 8.
In accordance with the method of 5.2 (1993), using a cutter knife in a room at 20 ° C., make a 1 mm square, 10 × 10 square grid-shaped scratch that reaches the groundwork, and then use cellophane adhesive tape on the grid. Then, the cellophane tape was immediately peeled off from the coating film surface, and the number of grids of the coating film that remained without peeling off was measured. Then, the number of cross-cuts of the coating film remaining without peeling off was evaluated as 100, and the number of 99 or less was evaluated as unacceptable.

(3) Impact Deformation Test (DuPont Type) By applying the method of JIS-K5400, 8.3.2 (1993), the coating surface of the test piece is directed upward under the conditions of 1 kg weight and 50 cm height. Test the case and the downward case,
The impact deformation resistance was evaluated according to the following criteria. ⊚: No peeling of cellophane tape (pass) O: Peeling area of cellophane tape is 10% or less (pass) Δ: Peeling area of cellophane tape exceeds 10% and less than 50% (fail) ×: Cellophane tape peeling area 50% or more (fail)

(4) Scratch resistance test After rubbing back and forth 10 times with 5 layers of gauze under a load of 200 g, the degree of scratches on the surface of the coating film was observed and evaluated according to the following criteria. ⊚: No scratches are recognized (pass) O: Slight scratches are recognized (pass) Δ: Scratches are slightly clearly recognized (fail) X: Scratches are clearly recognized (failure)

(5) Chemical resistance test According to the method of JIS-A5707, 1 ml of 5% nitric acid, 5% sulfuric acid and 5% sodium hydroxide aqueous solution was dropped on the coating film, and the temperature and humidity were kept at 20 ° C. and 50 RH%. After leaving it in the room for 24 hours, it was washed with water and dried, and the change of the coating film surface was visually observed and evaluated according to the following criteria. ◯: No change on the coating film surface (pass) Δ: Slight discoloration or swelling is observed on the coating film surface (fail) ×: Clear discoloration, swelling or peeling is observed on the coating film surface (fail)

(6) Carbon Contamination Resistance Test 1 ml of a dispersion of carbon black / water = 5/95 (weight ratio) was dropped on the coating film, and kept in a constant temperature and humidity chamber at 20 ° C. and 50 RH% for 24 hours. After leaving it to stand, it was washed with water and dried, and the degree of discoloration on the surface of the coating film was visually observed and evaluated according to the following criteria. ◎: No traces are recognized (pass) ○: Slight traces are recognized (pass) △: Traces are slightly conspicuous (fail) ×: Traces remain thick (fail)

(7) Workability test In a room at 20 ° C., the coated surface of each test piece cut into a width of 5 cm is placed outside, and three coated metal plates identical to the test piece are sandwiched inside and bent 180 degrees in close contact. I went.
Then, sufficiently attach the cellophane adhesive tape to the bent portion, immediately after peeling off the cellophane tape from the coating surface,
The peeling condition of the coating film was observed. Then, the workability was evaluated according to the following criteria. ⊚: No peeling of cellophane tape (pass) O: Peeling area of cellophane tape is 10% or less (pass) Δ: Peeling area of cellophane tape exceeds 10% and less than 50% (fail) ×: Cellophane tape peeling area 50% or more (failed) Table 3 shows the manufacturing conditions of the coated metal sheet of each example and the results of the above various tests.

[0045]

[Table 3]

As is clear from the results of the above examples,
The coated metal plates of Comparative Examples 1 to 8, which are out of the conditions of the present invention,
It fails in any of the test items of coating hardness, impact resistance, scratch resistance, chemical resistance, carbon stain resistance, and workability.

On the other hand, the coated metal sheets of Examples 1 to 6 of the present invention showed performances exceeding the acceptance criteria in all test items including scratch resistance and impact resistance.

[0048]

As described above, according to the present invention, a coating film having high hardness, excellent scratch resistance, stain resistance and durability as well as impact resistance and workability is provided. Building materials,
It is possible to manufacture a coated metal plate that is optimal for kitchen equipment, storage containers, exterior materials for various home appliances, door materials, etc.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Okuma 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A metal plate on at least one surface of which (1) a chemical conversion treatment film, (2) an undercoating film mainly composed of a polymer polyester resin formed on the upper layer thereof, and (3) further formed on the upper layer thereof. The coating film has a hydroxyl value of 60 to 110 m.
50 to 75 parts by weight of acrylic resin having gKOH / g and a glass transition temperature of 70 to 110 ° C., and melamine resin 50 to 25
A coated metal plate, comprising: a coating composition formed by applying and baking a coating composition containing, as a main component, a color-developing agent containing 10 parts by weight.