JP2001243819A - White painted metal plate excellent in light reflecting property and workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high reflectance painted metal plate having an undercoat film containing rust prevention pigment formed on the metal surface and having a topcoat film whose main component is a polyester resin containing TiO2 powder of white collar pigment formed on the undercoat film. SOLUTION: TiO2 powder of white collar pigment is added in undercoat film and a specific gravity N of topcoat film is maintained in a condition described in an inequality: 1.75<N<2.3 and L value of color tone measurement based on JIS Z 8722 is maintained greater than 90 and gloss value measured with 60 degree miller surface gloss method is maintained greater than 80. Topcoat film containing 20-35 parts by weight of a curing agent whose main component is melamine against 100 parts by weight of polyester resin is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white-painted metal plate having a two-layer coating film on the surface to be used, the reflectance of which is increased.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for energy-saving products for electric appliances. As a part of this, lighting fixtures capable of obtaining the same brightness with low power consumption have been developed. In the case of the development of this lighting fixture having a reflector, it is important to develop a reflector having a high reflectivity together with the development of a power saving bulb. This reflection plate has been partly adopted because it is formed by forming a painted metal plate and has relatively high reflectance and is inexpensive.

[0003] Of these coated metal plates, those which are widely used in the past have an undercoating film containing a chromium-based rust-preventive pigment formed on the surface of the metal plate, on which silica and calcium carbonate are formed as white pigments. A coated metal plate on which an overcoating film made of a resin paint such as polyester, polyurethane, or epoxy is blended with one or more kinds of powders such as magnesium sulfate, magnesium carbonate, and titanium dioxide. When TiO ₂ powder is used as the white pigment of the top coating material on this white painted metal plate, 80 to 100 parts by weight, and specific gravity of the coating film of 1.7 to 1.75 with respect to 100 parts by weight of the resin.
And the gloss is 88, but the L value in the color tone measurement according to JIS Z 8722 is 86, which is insufficient, and the reflectance at the wavelength of 450 nm and 550 nm, which is the main wavelength of the fluorescent lamp light, is 76 to 80% and 81. % Was difficult to achieve.
Even when formed in a coating containing chromium-based anticorrosive pigment and TiO ₂ powder in the undercoat coating film of the coated metal plate, the content of the anticorrosive pigment and the TiO ₂ powder is TiO ₂ / proof Since the rust pigment is 0.2 to 1.0, the gloss is 88, but the L value in the color tone measurement according to JIS Z 8722 is 8
7, which is not enough, and the wavelength 450n which is the main wavelength of the fluorescent light beam
m, the reflectance at 550 nm is 78-81%, 82%
It was difficult to do this.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coated metal plate having improved reflectivity by increasing whiteness and gloss.

[0005]

According to the present invention, an undercoating film containing a rust-preventive pigment is formed on the surface of a metal plate, and a polyester resin containing TiO ₂ powder of a white pigment is formed on the undercoating film. In the coated metal plate on which the top coat is formed, a white pigment TiO ₂ powder is added to the undercoat and the specific gravity N of the top coat is 1.75 <N <2.
3. L value in color tone measurement according to JIS Z8722 is 90
Super, gloss by the 60-degree specular gloss method was set to more than 80.

[0006]

The present inventors have conducted various studies to develop a coated metal plate having high whiteness and gloss. As a result, TiO ₂
It has been found that the addition of a powder makes it possible to improve the whiteness and gloss of the top coat. The rust preventive pigment used in the undercoat film must be a chromium-based one such as strontium chromate or zinc chromate in terms of anticorrosion performance, so that the color of the undercoat film is yellow. If the overcoating film formed thereon has a large hiding power, the undercoating color tone does not affect the color tone of the overcoating film, but in the case of a white coating film, the hiding power is inferior. And the color tone became yellowish. However, TiO ₂
When the powder is contained, the color tone becomes close to white, so that the color tone of the overcoat film becomes white. Further, since the hiding power is improved by the addition of the TiO ₂ powder, the gloss increases, and accordingly, the gloss of the overcoat film also increases.

When the content ratio of the rust preventive pigment and the TiO ₂ powder in the undercoat coating film is TiO ₂ powder / rust preventive pigment = 3 to 8, the corrosion resistance and the L value in the color tone measurement according to JIS Z 8722 are harmonized. Preferably TiO ₂ powder / rust preventive pigment =
It is good to be 4-6. The coating resin may be a known resin, for example, a polyester resin, an epoxy resin, or a mixture thereof. The coating thickness is 3 to 15 μm, preferably 6 to 9 μm.

In the present invention, the whiteness of the overcoat film is determined by using TiO.
Rather than content ₂ powder, defined by the coating density. This is because, when the TiO ₂ powder is dispersed in the coating material, air is entrained, voids are generated, and the pigment density is small if the porosity is high even if the pigment content is large. On the other hand, when the pigment density is defined by the specific gravity of the coating film, the pigment density is proportional to the magnitude. Therefore, the content of the TiO ₂ powder is adjusted in the top coat to make the specific gravity N of the coat larger than 1.75 and smaller than 2.3. If the specific gravity N of the coating film is smaller than 1.75, the concealing power is inferior.
In some cases, the L value in the color tone measurement by Z 8722 cannot be made larger than 90. On the other hand, when the specific gravity N of the coating film is greater than 2.3, the L value increases, but the workability of the coating film decreases. In order to set the specific gravity N of the coating film to 1.75 <N <2.3, the content of TiO ₂ powder should be 1 to 100 parts by weight of the resin.
The amount may be 00 to 160 parts by weight, preferably 130 to 150 parts by weight. It is preferable to use TiO ₂ powder that has been surface-treated with Al ₂ O ₃ , SiO ₂ , ZrO ₂ or the like in order to improve the dispersibility of the resin.

When the L value is larger than 90, JIS
It is preferable that the b value (indicator of yellowish and bluish) in the color tone measurement by Z 8722 is set to a range larger than −1 and smaller than 1. If it is -1 or less, the bluish color becomes strong, and if it is 1 or more, the yellow color becomes strong. In order to set the b value in the above range, the average particle diameter of the TiO ₂ powder is 0.2 to 0.3 μm.
It is preferred to use If the average particle size is too small, blue light having a short wavelength is well absorbed, so that it appears bluish. If the average particle size is too large, yellow to red light is scattered to appear yellowish. Alternatively, the pigment may be adjusted by adding a pigment having a color tone having a complementary color relationship, such as red bengalara and navy blue. When the gloss by the 60-degree specular gloss method is 80 or less,
The sharpness of the color tone is insufficient, a dull feeling is produced, and the reflectance is low. In order to achieve a gloss of more than 80, it is preferable to cause a self-condensation reaction of the melamine resin to occur on the coating film surface using a melamine resin having poor compatibility with the polyester resin as the main resin. Here, the use of a melamine resin having poor compatibility with the polyester resin as the main resin is because when a melamine resin having excellent compatibility with the polyester resin as the main resin is used,
This is because the probability of the reaction between the functional group of the polyester resin, which is the main resin, and the functional group of the melamine resin increases, so that the melamine resin hardly appears on the surface of the coating film and the self-condensation reaction hardly occurs on the surface of the coating film. Since the melamine resin concentrated on the surface of the coating film by self-condensation is present as a clear layer on the surface layer of the coating film, the gloss becomes higher than that when the resin is not concentrated on the surface of the coating film.

[0010] The resin of the overcoating film is mainly composed of a polyester resin, and the overcoating film contains 20 to 35 parts of a curing agent mainly containing a melamine resin per 100 parts by weight of the polyester resin. Parts by weight, preferably 25 to
It is preferably formed by a paint to which 30 parts by weight are added.
When the melamine resin is added, as described above, the melamine resin concentrates on the surface of the coating film and improves the gloss. If the amount of the melamine resin is less than 20 parts by weight, the amount of the melamine resin concentrated on the surface of the coating film is small, so that the gloss is reduced. As the melamine resin, a methylated melamine resin, a butylated melamine resin, and the like are preferable.

Polyester resin is composed of polybasic acid and polyvalent alcohol.
It is obtained by polycondensation with
The basic acid may be divalent or higher valent aromatic or aliphatic type
Acid anhydrides, for example, maleic acid, maleic anhydride
Acid, adipic acid, sebacic acid, succinic acid, isophthalic acid
Typified by acids, phthalic anhydride, terephthalic acid, etc.
And the polyvalent alcohol is C_Two~ C₆Arco with more than two valencies
For example, ethylene glycol, diethylene
Glycol, propylene glycol, triethylene glycol
Cole, neopentyl glycol, 1,6-hexanedi
Representative of allol, glycerin, trimethylolethane, etc.
Is what is done. Processability of coating film, TiO _TwoPigment dispersion
Considering the properties, etc., the dibasic acid and the divalent alcohol
Polycondensates are preferred. Coating thickness is 10-25μm, preferred
Or 15 to 18 μm.

The metal plate is not particularly limited, and may be, for example, a cold-rolled steel plate, a hot-dip galvanized steel plate, an electro-galvanized steel plate, a zinc alloy-plated steel plate, a stainless steel plate, a copper-plated steel plate, an aluminum plate, or the like.

The coated metal sheet of the present invention may be manufactured in the same manner as a conventional coated metal sheet. For example, a metal plate is subjected to a reactive or coating type chromate treatment, and then a base coat is applied by a roll coat method, a carte coat method, a spray method, etc., and then baked and dried. An undercoating film is formed, and then an overcoating material is applied on the undercoating film by the same method, and baked and dried to form an overcoating film.

[0014]

EXAMPLE A hot-dip galvanized steel sheet (plated weight: 45 g / m ² (one side)) having a thickness of 0.6 mm was subjected to a coating-type chromate treatment, and then a polyester-based resin was used as a main component, and the weight of the resin was 100%. 81.8 parts by weight of TiO ₂ powder having an average particle diameter of 0.25μm surface-treated with Al ₂ O ₃ with respect to parts,
An undercoat paint of a polyester resin to which 18.2 parts by weight of a strontium chromate rust preventive pigment was added was applied to a dry film thickness of 7 μm, and was baked at 215 ° C. for 40 seconds and dried. Thereafter, a polyester resin composed of isophthalic acid, which is a dibasic acid, and neopentyl glycol, which is a divalent alcohol, is used as a main component. 100 parts by weight of the polyester resin is subjected to surface treatment with Al ₂ O _3. Table 1 obtained by adding 130 parts by weight of a TiO ₂ powder having an average particle size of 0.25 μm and a melamine resin (a mixture of butylated melamine resin / methylated melamine resin = 3/7 by weight) in various ratios. The top coats A to K shown above were applied so that all of them had a dry film thickness of 17 μm.
Bake dry for 2 seconds. Then, the following test was performed on the obtained coated steel sheet. Table 2 shows the results.

(1) Coating film specific gravity measurement test Measurement was carried out using a potassium iodide solution by the floatation / sedimentation method specified in JIS K7112. (2) L value measurement test A spectrophotometer [CM-37 manufactured by Minolta Co., Ltd.] of a mechanism employing a method for measuring an object color specified in JIS Z 8722.
00d, light source: C], and the L value of the top coat was measured. (3) Gloss measurement test The specular photometer [manufactured by Suga Test Instruments Co., Ltd.] was used to measure the 60 ° specular gloss of the overcoated film.

(4) Reflectivity measurement test The spectrophotometer used in the L value measurement test has a wavelength of 450 nm.
The reflectance at 550 nm was measured, and those with a reflectance of 82% or more at both wavelengths were evaluated with the symbol ○, and those with less than 82% were evaluated with the symbol x. (5) Coating workability test Two sheets of the same thickness were sandwiched between the same coating on the other side of the test piece left in a constant temperature room at a temperature of 20 ° C. by 180 °.
After the bending test (2T) was performed, those having no cracks in the bent portions were evaluated with the symbol ○, and those having cracks were evaluated with the symbol x.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

As described above, an undercoating film containing a rust-preventive pigment is formed on the surface of a metal plate, and an overcoating film mainly composed of a polyester resin containing TiO ₂ powder of a white pigment is formed thereon. In the coated metal plate on which the film is formed, while adding TiO ₂ powder of a white pigment to the undercoat film,
The specific gravity N of the top coat is 1.75 <N <2.3, JIS
When the L value in the color tone measurement according to Z 8722 exceeds 90 and the gloss by the 60-degree specular gloss method exceeds 80, the reflectance of the overcoat film becomes 82% or more. When the top coat contains 20 to 35 parts by weight of a curing agent containing melamine as a main component with respect to 100 parts by weight of the polyester resin, the L value becomes 9
It tends to be more than 0 and gloss more than 80.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Nakamura 7th, Takatani-Shimmachi, Ichikawa-shi, Chiba F-term (reference) 4D075 AE03 BB94Z CB04 DA06 DB02 DC18 EA05 EB35 EB45 4F100 AA20B AA20C AB01A AH03C AK41C AR00B BA03 BA07 BA10A BA10C CA13B CA13C CA14B DE01B DE01C EH46B GB90 JL01 JL10C JN06 JN21 JN21C YY00C 4J038 NA01 DB02 DD02DB01

Claims (2)

[Claims] An undercoating film containing a rust-preventive pigment was formed on the surface of a metal plate, and an overcoating film mainly composed of a polyester-based resin containing TiO ₂ powder of a white pigment was formed thereon. In the coated metal plate, TiO ₂ powder as a white pigment is added to the undercoat film, and the specific gravity N of the overcoat film is 1.75 <N <2.3, JIS Z872
Light reflectivity characterized by having an L value of more than 90 in the color tone measurement by 2, and a gloss of more than 80 by the 60-degree specular gloss method,
White painted metal plate with excellent workability. 2. The overcoating film according to claim 1, wherein a curing agent containing melamine as a main component is used in an amount of from 20 to 100 parts by weight of the polyester resin.
The white painted metal sheet according to claim 1, which is contained in an amount of 35 parts by weight.