JPH11181969A - Highly reflective surface treated plate with excellent stain resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain excellent reflectivity against sunlight by providing a reflecting layer containing inorganic ceramics particles rich with reflectivity on the surface and the remainder composed of organic resin, and laminating photocatalyst layer on the reflecting layer. SOLUTION: Paint composition in which inorganic ceramics particles excellent in reflectivity against radiation energy from sunlight and organic resin are dispersed in a solvent is spread on the surface of a base plate made of metal plate, plastics, or the like, to form a reflecting layer. Sol liquid in which photocatalyst paricles containing combination of titanium oxide and crystalline zirconium titanate are dispersed, as it is, or paint composition in which colloidal silica, chromate, and the like are added to the sol liquid is spread on the reflecting layer, so as to form a high reflectivity surface treated plate. Consequently, the surface is hardly polluted, and excellent heat insulating property against the sunlight can be maintained for a long term.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reflective surface-treated plate mainly used as a building material such as a building roof or wall.

[0002]

2. Description of the Related Art As measures against earthquake disasters in houses and the like, it has been desired to reduce the weight of roofing materials in addition to structural reinforcement. Roofing materials include roofing materials made of new ceramic materials, metal roofing materials, etc., in addition to Japanese tiles. Approximately 1/3 of the weight of this. However, the metal roofing material has a problem that heat generated by sunlight is easily transmitted to the attic, and the room becomes hot.

[0003] In order to suppress heat transmission, there is a method of bonding a heat insulating material to the back surface of a metal roofing material. However, in order to adopt a procedure of bonding a heat insulating material after forming a metal plate, manufacturing is performed. There are problems that the process is complicated and that initial costs are high due to high material costs. There is also a method of applying a heat-insulating paint, but this paint uses ceramics containing a large number of vacuum bubbles as a pigment, and there are restrictions such as the need to apply a very thick paint.
Not suitable for general use.

Japanese Patent Application Laid-Open No. Sho 58-124159 discloses a reflector for a solar heat collector, in which a coating film is formed with a paint comprising a metal fine powder of aluminum, copper, brass or the like and a binder. This reflector realizes high sunlight reflectance by using a paint mixed with flaky metal powder. However, when dust and exhaust gas floating in the outside adhere to the surface and become contaminated, there is a problem that the reflectance of sunlight is remarkably reduced and the absorption of radiant heat is increased.

When a semiconductor such as titanium oxide (TiO ₂ ) or zinc oxide (ZnO) is irradiated with light having an energy larger than its band gap in the coexistence of air, these semiconductors are excited to be an n-type semiconductor. It shows the action of decomposing organic substances. This is known as photocatalysis ("Surface" Vol. 25 No. 8, pages 477-49).
5, (1987)), and these particles having a photocatalytic function (hereinafter simply referred to as “photocatalyst particles”) are applied to decompose and remove harmful substances and the like. Also, the photocatalyst particles are
It is also known that when irradiated with ultraviolet rays, a superhydrophilic surface having a contact angle with water close to 0 ° is formed (“Nat”).
ure "Vol. 388, p. 431, (1997)).

[0006]

The problem to be solved by the present invention is to solve the above-mentioned problems, and it is difficult to attach dirt to the surface of the performance required for exterior materials for building materials such as roofing materials. Another object of the present invention is to provide a highly reflective surface-treated plate capable of maintaining excellent reflectance to sunlight for a long period of time.

[0007]

The gist of the present invention resides in a highly reflective surface-treated plate excellent in stain resistance described in the following (1) and (2).

(1) Excellent in stain resistance, characterized in that the surface comprises a reflective layer containing inorganic ceramic particles having a high reflectivity and a balance substantially composed of an organic resin, and a photocatalytic layer thereon. Highly reflective surface treated plate.

(2) The photocatalytic layer contains a combination of titanium oxide and crystalline zirconium titanate, and has high reflectivity excellent in stain resistance as described in (1) above. Surface treatment plate.

[0010] Various types of plated metal plates and painted metal plates are often used for roofs and walls of buildings from the viewpoint of corrosion resistance and landscape. Depending on the application, plastics and the like are also used. The highly reflective surface-treated plate of the present invention comprises inorganic metal particles having excellent reflection characteristics for radiation energy from sunlight and organic materials on the surface of such a metal plate or plastics (hereinafter simply referred to as “substrate”). A coating film containing a resin (hereinafter, also simply referred to as a “reflection layer”) is provided to prevent the propagation of heat energy from sunlight.

The radiant energy of sunlight passing through the atmosphere is mainly transmitted as a short-wavelength electromagnetic wave in the range of 0.2 to 2.5 μm. An object whose temperature rises by absorbing the energy as heat emits energy as an electromagnetic wave having a longer wavelength than this. For example, the radiant energy radiated from the surface heated to the temperature of the object surface of 80 to 100 ° C. is in the infrared region of 2.5 to 20 μm.
In order to construct a highly efficient reflector, it is preferable that the reflector has a high radiation energy reflectivity (small absorbance) and a high energy emissivity from the reflector. In other words, the surface that reflects sunlight has a reflectance of about 1 for radiation having a wavelength of 2.5 μm or less, and a wavelength of 2.5 μm from the surface.
It is desirable that the emissivity of energy of m or more has a characteristic close to 1. In the surface-treated plate of the present invention, highly reflective particles having the above-described spectral performance are contained in a coating material, and a coating film is formed on the surface using an organic resin as a binder.

When the surface of the reflective layer is contaminated, the reflectivity deteriorates. When the surface-treated plate is used outdoors, dirt gradually adheres to organic substances having poor water wettability attached to hydrophobic surfaces having poor water wettability, and is recognized as contaminants. Therefore, in order to prevent contamination, it is effective to prevent contaminants from adhering to the surface and to improve the water wettability of the surface.

In the surface-treated plate of the present invention, photocatalyst particles are held on the reflective layer, and organic matter is decomposed by the photocatalytic reaction. Furthermore, the surface of the reflective layer is made hydrophilic so that even if contaminants adhere, they are washed away during precipitation. Utilizing these effects, the reflectivity of the reflective layer is permanently maintained in a good state.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail.

Reflective layer: As the highly reflective inorganic ceramic particles contained in the reflective layer, those having a reflectance of 0.7 or more with respect to radiation having a wavelength of 2.5 μm or less are preferable. When the reflectance is less than 0.7, the reflection of sunlight on the reflection layer becomes insufficient. More preferably, it is 0.8 or more. As the highly reflective inorganic ceramic particles, those having an emissivity of energy of wavelength of 2.5 μm or more of 0.7 or more are preferable. When the emissivity is less than 0.7, heat radiation from the reflective layer becomes insufficient. More preferably, the emissivity is 0.8 or more.

The inorganic ceramic particles having these properties include cordierite (2MgO.2Al ₂ O _3.
5SiO), zirconia (ZrO ₂ ), magnesia (M
gO), alumina (Al ₂ O ₃ ), boron nitride (hBN,
Inorganic ceramic particles such as cBN) are preferred. The reflectance of these particles in the wavelength range of 0.3 to 2.5 μm can be measured using a commercially available visible / ultraviolet absorption spectrum measuring instrument, and the emissivity in the wavelength range of 2.5 μm or more is commercially available. Can be measured using a Fourier transform infrared spectrometer. As the inorganic ceramic particles having high reflectivity, one kind of the above-mentioned particles may be used, or two or more kinds may be used in combination.

The size of the highly reflective inorganic ceramic particles is preferably 30 μm or less in terms of the median diameter by mass. Further, it is desirable that the thickness be 35% or less of the thickness of the reflection layer. This is because the smaller the particle size, the better the shielding property against sunlight. More preferably, it is 15 μm or less.

The reflectivity to sunlight increases as the content of the inorganic ceramic particles increases. For this reason, it is preferable that the content be 30% by weight or more based on the weight of the reflective layer. When the content of the highly reflective inorganic ceramic particles is less than this, the shielding property against sunlight may be insufficient. It is more preferably at least 50% by weight.
If the content of the highly reflective inorganic ceramic particles exceeds 90% by weight, the cohesive strength as a coating film and the adhesion to a substrate are reduced. Therefore, the upper limit of the content is preferably set to 90% by weight.

The organic resin functions as a binder for holding the highly reflective inorganic ceramic particles. As this resin, any one of various organic resins such as an acrylic resin, a polyester resin, a silicone resin, a urethane resin, an epoxy resin, a polyolefin resin, and a fluorine resin can be used. As the binder resin, one of the above resins may be used, or a mixture of two or more may be used. The organic resin is preferably contained in an amount of 10% by weight or more based on the weight of the reflective layer in order to secure a binder effect on the inorganic ceramics. 70
When the content is contained by weight, the effect as a binder is saturated. Therefore, the upper limit is preferably set to 70% by weight.

The meaning that the remainder substantially consists of an organic resin means that, in addition to the above-mentioned highly reflective inorganic ceramic particles and the organic resin, extender pigments such as silica, titania or alumina may be used in the reflective layer. And a crosslinking agent such as a melamine-based compound, an isocyanate-based compound, a benzoguanamine-based compound, or an epoxy-based compound. Thereby, the adhesion between the substrate surface and the organic resin as the binder can be improved, and the cohesive strength of the coating film itself can be increased. In addition, if the pigment has a refractive index close to that of the organic resin, even if the pigment is contained in the reflection layer, the effect on the transparency to visible light is small, so that the color tone of the coating on the substrate can be maintained.

The thickness of the reflection layer is preferably 3 to 200 μm. When the thickness of the reflective layer is less than 3 μm, the reflectivity is poor. The upper limit of the thickness of the reflective layer is not particularly limited, but if it is too thick, the workability is deteriorated.

Photocatalyst layer: The photocatalyst layer on the reflection layer contains photocatalyst particles. As the photocatalyst particles, known semiconductor particles having a photocatalytic function can be used. Among them, a semiconductor of titanium oxide or zinc oxide is preferable because of its excellent photocatalytic function. Further, as the photocatalyst particles, those containing a combination of titanium oxide and crystalline zirconium titanate are more preferable. This combined body is not simply a mixture of crystalline zirconium titanate and titanium oxide, but is a combination of both via a Ti—O—Zr bond. By arranging titanium oxide and zirconium titanate in this manner, the photocatalytic function can be greatly improved as compared with the case where the photocatalyst particles of titanium oxide alone are used.

The above-mentioned conjugate of titanium oxide and crystalline zirconium titanate can be obtained, for example, by firing a reaction product of a titanium compound and a zirconium compound in an air atmosphere.

The smaller the size of the photocatalyst particles, the better.
There is no particular limitation, and it may be 1 μm or less, which is usually obtained. The size of the crystallite constituting the photocatalyst particles is preferably 5 to 50 nm. The crystallite size is calculated from the diffraction peak from the (101) plane of the anatase crystal obtained by X-ray diffraction. If the crystallite size exceeds 50 nm, the photocatalytic activity is undesirably reduced. The smaller the crystallite size is, the better the photocatalytic activity is. Therefore, the crystallite size may be as small as possible.

The thickness of the photocatalyst layer is preferably in the range of 50 nm to 3 μm. If the thickness of the photocatalyst layer is less than 50 nm, a sufficient antifouling effect cannot be obtained. Photocatalyst layer thickness is 3
If it exceeds μm, the antifouling effect is saturated and the workability in molding the surface-treated plate may be impaired.

The photocatalyst particles are preferably contained in the photocatalyst layer in an amount of 10 to 90% by weight based on the weight of the photocatalyst layer. If the content of the photocatalyst particles is less than 10% by weight, a sufficient antifouling effect cannot be obtained. 90% by weight photocatalyst particles
If it exceeds, the antifouling effect saturates and becomes expensive, which impairs economic efficiency.

In the photocatalyst layer, in addition to the above photocatalyst particles,
In order to improve the strength and adhesion of the film, silicone resin, fluorine resin, colloidal silica, colloidal alumina, chromate, chromate, phosphoric acid, phosphate, etc.
It may be contained up to 90% by weight based on the weight of the photocatalyst layer.

Substrate: The type of substrate on which the reflective layer and the photocatalyst layer are provided need not be particularly limited, and various types of known cold-rolled steel sheets, hot-rolled steel sheets, stainless steel sheets, aluminum sheets and other metal sheets, Various types of plastic plates, plates obtained by subjecting the surfaces of these metal plates or plastic plates to various known plating, and the like can be used. When a plated product is used as a substrate, a plating product of a known plating type such as a Zn-based or Al-based plating plate by a known method such as electroplating, hot-dip plating, or electroless plating can be applied. The plated substrate may be subjected to a known chromate treatment or phosphate conversion treatment for the purpose of further improving rust prevention and the like. Further, the substrate may be one obtained by applying a coating to the above-mentioned various plates. The type of painting is optional,
Those coated with a known roll coat, dip coat or the like can be used.

The method for producing the highly reflective surface-treated plate of the present invention, which is excellent in stain resistance, is not particularly limited. However, the above-mentioned inorganic ceramic particles and organic resin are dispersed in a solvent to form a coating composition. A coating material is applied to the substrate surface and dried to form a reflective layer, and then the sol liquid in which the photocatalyst particles are dispersed is used as it is, or the colloidal silica, chromate, or the like is added to form a coating composition, It is preferable to apply it on the reflective layer and dry it.

As the solvent, water, toluene, xylene,
Usually used ones such as cyclohexane and methyl ethyl ketone may be appropriately selected and used. The coating composition may contain a thickening agent such as synthetic finely powdered silica, carboxymethylcellulose, polyvinyl alcohol, and organic bentonite, and a dispersant such as polyacrylic acid and salts thereof, and naphthalenesulfonic acid. The coating method of the coating composition may be performed by a known method, for example, a method such as spray coating, roll coating, curtain flow coating, and bar coating can be applied. After coating, dried by known methods such as hot air oven, induction heating oven,
What is necessary is just to cool by a well-known method. When the substrate is a metal plate, these processes can be efficiently manufactured by using a general two-coat, two-bake continuous coating metal plate manufacturing facility.

[0031]

EXAMPLES (Example 1) Mass median diameter 3 μm, 2.5 μm
0.75, 2.5 for the reflectance of radiation of wavelength below m
45 parts by weight of cordierite powder, which is an inorganic ceramic particle having an emissivity of 0.85 μm or more and having a spectral characteristic of 0.85, and 55 parts by weight of a polyester resin are dispersed and mixed using a ball mill together with an appropriate amount of cyclohexanone as a solvent. A coating composition for forming a reflective layer (hereinafter, referred to as a “cordierite-containing coating”) was obtained. Further, a coating composition (hereinafter referred to as “titanium oxide-containing coating agent”) for forming a photocatalyst layer was prepared by mixing 50 parts by weight of a titanium oxide sol and 50 parts by weight of a commercially available water glass coating material.

The above-mentioned cordierite-containing paint was roll-coated on a hot-dip galvanized steel sheet having a sheet thickness of 0.8 mm to a dry film thickness of about 10 μm, and dried at 250 ° C. for 40 seconds. Thereafter, the above-mentioned titanium oxide-containing coating agent was dip-coated so as to have a dry film thickness of 1 μm, and dried at 180 ° C. for 70 seconds to obtain a surface-treated plate (sample A) of the present invention.

(Comparative Example 1) A polyester resin and a solvent as a solvent were used in place of the coating composition for forming the reflective layer used in Example 1 on the same hot-dip galvanized steel sheet as used in Example 1. Using a coating composition containing an appropriate amount of cyclohexanone, the composition was applied to a dry film thickness of about 10 μm and dried. Thereafter, the above-mentioned titanium oxide-containing coating agent was treated under the same conditions as in Example 1 to obtain a sample L.

Comparative Example 2 A hot-dip galvanized steel sheet similar to that used in Example 1 was coated with a cordierite-containing paint having the same composition as described in Example 1 in the same manner as described in Example 1. By applying and drying, a sample M having only a reflective layer on the substrate was obtained.

Comparative Example 3 A titanium oxide-containing coating agent having the same composition as described in Example 1 was coated on a hot-dip galvanized steel sheet similar to that used in Example 1, as described in Example 1. Sample N having only a photocatalyst layer on the substrate was obtained by directly applying and drying under the same conditions.

Each of the samples obtained by the above treatments was measured for the lightness L of the treated surface using a color difference meter in accordance with the method specified in JIS-Z-8722, and then exposed outdoors for three months and re-surfaced. Was measured, and subjected to a reflection evaluation test for sunlight as it was without removing surface dirt.

FIG. 4 is a diagram schematically showing a cross section of a reflection evaluation test apparatus for sunlight. Except for the sample loading portion of the heat retaining container 6, heat is blocked from entering and exiting by a heat insulating material. Each sample was stuck on the upper surface of the heat insulation container 6 prepared for each sample with the reflective layer 2 facing outward. A thermocouple 4 is mounted on the back surface of the sample 1 and connected to an external recorder so that a temperature change of the sample can be recorded. The heat-insulating container to which each sample was attached was placed outdoors, and the reflective layer 2 was exposed to sunlight 7
Were placed in the same direction at the same angle, and the temperature rise on the back surface of the steel sheet after the start of exposure to sunlight was measured.

Table 1 shows the change in lightness of each sample before and after exposure.
FIG. 1 shows the results of the reflection evaluation test.

[0039]

[Table 1]

As shown in Table 1, samples A and N having a photocatalyst layer on the surface showed only a slight change in the surface brightness even after three months of outdoor exposure, and showed good stain resistance. Obtained.

As can be seen from FIG. 1, Sample A, which is an example of the present invention, has a slower rate of temperature rise after the start of the reflectivity evaluation test than Samples L, M, and N, which are comparative materials. Temperature was also low. The temperature rise rate of the sample M is slower than that of the samples L and N but faster than that of the sample A, and the temperature in the steady state is higher than that of the sample A. This is because dirt attached during outdoor exposure absorbs sunlight and the temperature on the back surface of the steel plate increases. Samples L and N did not have a reflective layer, and the temperature of the back surface of the steel plate was higher than those of Samples A and M.

Example 2 Mass median diameter was 5 μm, 2.5
The reflectance for radiation having a wavelength of less than μm is 0.9, 2.5.
60 parts by weight of boron nitride and 40 parts by weight of a polyurethane resin having a spectral characteristic of an emissivity of 0.9 having a wavelength of μm or more were mixed with cyclohexanone: toluene: xylene in a volume ratio of 1: 1: 1. The mixture was diluted with a liquid and dispersed and mixed using a paint shaker to obtain a coating composition (hereinafter referred to as "boron nitride-containing coating") for forming a reflective layer having a dry solid content of 50% by weight. On the same hot-dip galvanized steel sheet as used in Example 1, the above-mentioned boron nitride-containing paint was roll-coated so that the dry film thickness was about 10 μm,
A drying treatment was performed at 240 ° C. for 40 seconds. Then, the titanium oxide-containing coating agent described in Example 1 was applied and dried under the same conditions as in Example 1 so that the dry film thickness was 1 μm, and the surface-treated plate (Sample B) of the present invention was obtained. Obtained.

Example 3 10 parts by weight of crystalline zirconium titanate and 90 parts by weight of titanium oxide were mixed, fired at 500 ° C. for 2 hours in the air, pulverized, and dispersed in water to obtain a solid matter of 10%. A weight percent slurry was made. This slurry was adjusted to pH 10 using sodium hydroxide, and subjected to a hydrothermal treatment at 150 ° C. for 3 hours in an autoclave. afterwards,
The pH was adjusted to 7 by adding nitric acid having a concentration of 60%, and the mixture was filtered to obtain a zirconium titanate-titanium oxide conjugate. A commercially available water glass-based coating agent is mixed with the zirconium titanate-titanium oxide conjugate so as to have a solid content of 50% by weight, and a coating composition for forming a photocatalytic layer (hereinafter, referred to as a coating composition).
"Zirconium titanate-titanium oxide coating agent") was obtained. On the same hot-dip galvanized steel sheet as used in Example 1, a boron nitride-containing paint was applied in the same manner as in Example 2 so as to have a dry film thickness of 10 μm.
After drying, the above-mentioned zirconium titanate-titanium oxide-based coating agent was roll-coated so as to have a dry film thickness of 1 μm, and dried at 180 ° C. for 60 seconds to obtain a surface-treated plate (sample C) of the present invention. Was.

(Comparative Example 4) On the same hot-dip galvanized steel sheet as used in Example 1, a boron nitride-containing paint was applied in the same manner as in Example 2 so as to have a dry film thickness of 10 μm. It dried at 70 degreeC for 70 second, and obtained the sample P which has only a reflective layer.

Comparative Example 5 A zirconium titanate-titanium oxide-based coating agent was applied directly on the same substrate as in Example 4 so as to have a dry film thickness of 1 μm, and dried at 180 ° C. for 60 seconds. A sample R having only the photocatalyst layer thereon was obtained.

Width 150 from Samples A, B, C, P and R
A test piece having a length of 300 mm and a length of 300 mm was cut out, and thermocouples for temperature measurement were attached to the front and back surfaces of each test piece, and each was attached to the upper surface of the heat retaining container 6 as shown in FIG. These are installed on the roof of the building so that the test surface (surface having a reflective layer and a photocatalyst layer) is exposed to solar radiation at the same angle in the same direction in the south direction, and for 6 months from June to November Exposure was outdoors. At noon every day during the exposure period, the lightness of the test surface was measured using a simple portable color difference meter and the temperature difference between the front and back surfaces of the test piece (hereinafter referred to as “ΔT”) was measured for one month each. The average value was obtained to evaluate the stain resistance and the reflectance to solar radiation. It was determined that the greater the ΔT, the better the reflectance to solar radiation.

FIG. 3 shows the transition of the brightness of each test piece. As shown in FIG. 3, the test surfaces of Samples A, B, C and R having a photocatalytic layer on the surface showed excellent stain resistance. Above all, the samples C and R using the zirconium titanate-titanium oxide-based coating agent as the photocatalyst particles had particularly good stain resistance. The test surface of the sample P used in Example 1 and having no photocatalytic layer on the surface gradually became soiled during the exposure period.

FIG. 2 shows the transition of ΔT of each test piece. As shown in FIG. 2, the sample having the reflective layer in the range defined by the present invention exhibited good heat shielding properties. In particular, Samples B and C using the boron nitride-based coating composition excellent in reflectivity and emissivity for the reflective layer exhibited more excellent heat shielding properties than Sample A using cordierite. In sample C using the zirconium titanate-titanium oxide-based coating composition for the photocatalyst layer, dirt was less likely to adhere than sample B, and stable heat shielding was exhibited over a long period of time. In comparison, the sample P in which the boron nitride-based coating composition was used for the reflective layer but the photocatalytic layer was not provided had excellent heat shielding properties immediately after the start of exposure, but stains adhered to the surface during the exposure period, The heat insulation gradually deteriorated. Sample R, in which a photocatalytic layer composed of a zirconium titanate-titanium oxide-based coating composition was directly provided on a substrate without providing a reflective layer, was not preferable.

[0049]

EFFECT OF THE INVENTION The highly reflective surface-treated plate of the present invention, which is excellent in stain resistance, is not only light in weight but also hardly contaminated on the surface, and maintains excellent heat shielding property against sunlight for a long time without maintenance. it can. Further, since the productivity is high, it can be supplied at low cost. The surface-treated plate of the present invention has the above characteristics, and is particularly suitable as a building material exterior material such as a roof material or a wall material.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of measuring the heat shielding properties of a surface-treated plate of the present invention and a comparative example.

FIG. 2 is a diagram showing a transition of a temperature difference between the front and back surfaces of a test piece after outdoor exposure.

FIG. 3 is a diagram showing a change in brightness of a test surface after outdoor exposure.

FIG. 4 is a sectional view of an apparatus for measuring the performance of a surface-treated plate.

[Explanation of symbols]

1 ... sample, 2 ... photocatalyst layer, 3 ... reflection layer, 4
... Substrate, 5 ... Thermocouple, 6 ... Insulated container, 7
..Recorder, 8 ... sunlight.

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI B32B 7/02 103 B32B 7/02 103

Claims (2)

[Claims] 1. A reflective layer comprising, on a surface thereof, highly reflective inorganic ceramic particles and a balance substantially composed of an organic resin,
A highly reflective surface treated plate having excellent contamination resistance, comprising a photocatalyst layer thereon. 2. The highly reflective surface treatment with excellent contamination resistance according to claim 1, wherein the photocatalyst layer contains a combination of titanium oxide and crystalline zirconium titanate. Board.