JPH1129745A - Coating composition, formation of coating film, coated article, and reflector for lighting fixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating compsn. which forms a coating film with a high reflectance by mixing a resin with a silica aerogel. SOLUTION: A resin 1 is pref. a powder coating material contg. an inorg. component. esp. a white pigment. Pref., the silica aerogel 2 is contained in an amt. of 0.1-10 wt.% of the compsn. and has a refractive index after the hydrophobizing treatment is 1.008-1.18. A thermosetting powder coating material (e.g. the one based on an epoxy-polyester resin) or a thermoplastic powder coating material (e.g. the one based on polyvinyl chloride or a polyamide) is used as the resin. The inorg. component is a white pigment (e.g. silica or titanium dioxide). A coating film 4 formed on the surface of a substrate 3 comprises a matrix formed from the resin 1 and particles of the silica aerogel 3 dispersed therein. Since the aerogel 2 has a low refractive index and the difference in refractive index between the aerogel and the matrix is large, light causes the total reflection in a wide angle at an interface. The reflectance in the visible to infrared region is high, enhancing the efficiency of a lighting fixture and suppressing the temp. increase of a reflector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition, a method for forming a coating film using the coating composition, a coated article having a coating film formed from the coating composition, and a reflector for lighting equipment.

[0002]

2. Description of the Related Art In recent years, in order to meet market needs such as energy saving, development of lighting fixtures aiming at high efficiency and compact lighting has been promoted. In a lighting fixture using a reflector, it is necessary to increase the reflectance of the reflector in order to achieve an improvement in lighting efficiency.

[0003] Therefore, conventionally, a paint prepared by blending a white pigment such as silica, calcium carbonate, magnesium sulfate, magnesium carbonate, or titanium dioxide in a resin component such as polyester, polyurethane, or epoxy resin for coating a reflector such as a lighting fixture. Is used to produce a white reflector having a high reflectance. However, the reflectance of a paint prepared by blending such a white pigment is limited because the white pigment particles themselves have absorption of a specific wavelength, and responds to the above-described demand for improvement in illumination efficiency. Was not enough.

[0004] In the case of lighting fixtures, especially downlights, the need to make them shallower and the rise in the temperature of the upper part of the reflector due to high airtightness and high heat insulation of the house have become problems. Further, as a light reflection sheet used for a liquid crystal backlight or the like, as described in JP-A-4-296819, fine bubbles are contained in a film substrate, and light is scattered by the bubbles to whiten. What has been provided. However, since this light reflection sheet is not a paint, it cannot be applied to, for example, a reflector for lighting equipment.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and provides a coating composition, a coating film forming method, and a coated article capable of obtaining a coating film having high reflectance. It is another object of the present invention to provide a reflector for a lighting fixture that has a high reflectance even in an infrared region, can increase the fixture efficiency of the lighting fixture, and can suppress a rise in temperature. .

[0006]

According to the present invention, there is provided a coating composition comprising a mixture of a resin and silica airgel. According to a second aspect of the present invention, the resin is a powder coating.

[0007] The invention of claim 3 is characterized in that the powder coating contains an inorganic component. The invention according to claim 4 is characterized in that the inorganic component is a white pigment. The invention of claim 5 is characterized in that the content of the silica airgel is 0.1% by weight to 10% by weight based on the total amount of the composition.

According to a sixth aspect of the present invention, the silica airgel has a refractive index of 1.008 to 1.18. The invention of claim 7 is characterized in that the silica airgel has been subjected to a hydrophobic treatment. The coating film forming method according to the present invention is characterized in that the coating composition is electrostatically coated and baked to form a coating film in which silica airgel is dispersed in a resin.

A coated article according to the present invention is characterized in that a coating film of the above-mentioned coating composition is formed on the surface of a substrate. The reflector for lighting equipment according to the present invention is characterized in that a coating film of the above-mentioned coating composition is formed on a surface of a metal substrate.

[0010]

Embodiments of the present invention will be described below. The coating composition of the present invention is prepared as a mixture of the resin 1 and the silica airgel 2, and the coating film 4 formed on the surface of the substrate 3 by the coating composition is, as shown in FIG. The particles of the silica airgel 2 are dispersed and exist in the matrix. Silica airgel 2
Is transparent, the light refractive index is as small as air, and the refractive index difference between the silica airgel 2 and the matrix of the resin 1 is large. Therefore, at the interface between the matrix of the resin 1 and the silica airgel 2, light causes total reflection at a wide angle,
A coating film 4 having a high reflectance can be obtained.

It is preferable to use a powder coating as the resin component of the coating composition. Since the powder coating has a solid content of 100% resin and does not contain an organic solvent or the like, the silica airgel which has been subjected to the hydrophobic treatment does not shrink due to the action of the organic solvent or the like and becomes cloudy. Here, the powder coating is a solid that is not contained in the coating such as an organic solvent or water, but is mixed only with a film-forming component, and is epoxy-based, epoxy-polyester-based, polyester-based, and acrylic. And thermosetting powder coatings such as acrylic, polyester and the like, and thermoplastic powder coatings such as polyvinyl chloride, polyethylene, polyamide, fluorine and modified polyolefin. In the present invention, the powder coating is not limited to a specific one, and at least one of the above powder coatings can be used.

In these powder coatings, an inorganic component can be contained in order to whiten the coating film and improve the diffuse reflectance. In order to increase the reflectance of the coating film, it is preferable to form a white coating film even among light colors,
Therefore, as the inorganic component, silica, titanium dioxide, magnesium sulfate, magnesium carbonate, white pigments such as calcium carbonate can be used, and these may be used alone,
Alternatively, two or more kinds can be used as a mixture. The content of these inorganic components is not particularly limited, but may be 5% by weight or more and 25% by weight based on the total amount of the coating composition.
A range of less than is preferred.

The silica airgel used in the present invention comprises a porous skeleton of silica, and is disclosed in US Pat.
Nos. 827 and 4432956 and 46108
No. 63, a wet gel compound comprising a silica skeleton obtained by hydrolysis and polymerization of an alkoxysilane (also referred to as silicon alkoxide or alkyl silicate) is converted into an alcohol or carbon dioxide. In the presence of a solvent (dispersion medium) such as above, the solvent can be produced by drying in a supercritical state at or above the supercritical point of the solvent. Also, U.S. Pat.
As provided in JP-A Nos. 7 and 5124364, they can be similarly produced using sodium silicate as a raw material. Here, Japanese Patent Application Laid-Open No. Hei 5-279011,
As disclosed in JP-A-7-138375, a silica airgel is made hydrophobic by subjecting a gel compound obtained by hydrolysis and polymerization of alkoxysilane to a hydrophobizing treatment using a hydrophobizing agent. Is preferably provided. This hydrophobizing treatment step can be performed before the supercritical drying of the gel compound or during the supercritical drying of the gel compound. As the hydrophobizing agent,
Hexamethyldisilazane, hexamethyldisiloxane,
Trimethylchlorosilane, trimethylmethoxysilane,
Trimethylethoxysilane, triethylethoxysilane, triethylmethoxysilane, dimethyldimethoxysilane, dimethyldichlorosilane, dimethyldiethoxysilane, methyltrichlorosilane, and organic silane compounds such as ethyltrichlorosilane.In addition to these, acetic acid, Organic compounds such as carboxylic acids such as formic acid and succinic acid, and alkyl halides such as methyl chloride can be exemplified. As described above, the hydrophobic silica airgel imparted with hydrophobicity makes it difficult for moisture, water, and the like to penetrate, and the performance such as the refractive index and the light transmittance hardly deteriorates.

The refractive index of the silica aerogel comprising the porous skeleton of silica can be freely changed by the mixing ratio of the raw materials of the silica aerogel, but the refractive index difference from the resin component is set to a large value. In order to ensure the performance such as transparency of the silica airgel, 1.008-
It is preferable to use silica airgel whose refractive index is adjusted to the range of 1.18. By making the refractive index very small in this way, the difference in the refractive index between the resin component (the refractive index of the resin is generally in the range of 1.3 to 1.7) becomes large, and at the interface between the resin component and the silica airgel, Light can be totally reflected at a wide angle, and the light reflectance increases.

Here, the content of the silica airgel is preferably 0.1% by weight or more and 10% by weight or less, more preferably 1% by weight or more and 5% by weight or less based on the total amount of the coating composition. is there. When the content of the silica airgel is less than 0.1% by weight, it is difficult to obtain a coating film having a high reflectance, and when the content of the silica airgel exceeds 10% by weight, the coating film performance such as mechanical strength is poor. It is not preferable because it may be caused. When the powder coating is used as the resin, the particle size of the silica airgel is approximately the same as the average particle size of a general powder coating of several tens of μm from the viewpoint of the compatibility with the powder coating. Those having an average particle size of several tens μm are preferred.

Next, a method for forming a coating film using the above-described coating composition containing silica airgel will be described. When a powder coating is used as the resin, a coating film can be formed by applying a general powder coating process. That is, as shown in FIG. 2A, the powder coating 1a and the silica airgel 2 charged by the charging gun 7 are sprayed onto the surface of the electrically grounded substrate 3 to form a coating powder layer. Electrostatic coating is performed, and this is baked at the baking temperature of the powder coating 1a (a temperature lower than the melting temperature of the silica airgel 2) to make only the powder coating 1a into a semi-molten state. In the process of cooling the paint 1a, the silica airgel 2 is taken into the coating film of the resin 1 by the powder paint 1a, and as shown in FIG.
The coating film 4 in which the silica airgel 2 is dispersed and present can be formed on the surface of the substrate 3.
It is possible to obtain a coated product in which a coating film 4 in which silica airgel is dispersed is formed on the surface.

Here, this coated product can be used in various fields, but by using a metal substrate such as an aluminum plate or a zinc steel plate as a base material and forming a reflective coating film on the surface of the metal substrate, A white reflector for lighting equipment can be manufactured. The reflection plate formed by providing the reflection coating made of the coating composition containing silica airgel as described above can obtain a high reflectance by the coating and improve the lighting fixture efficiency. In addition, a reflective coating made of a coating composition containing silica airgel has a high reflectance of infrared light, and can reflect infrared light with high efficiency. It is possible to suppress a temperature rise on the upper surface of the plate. When the metal substrate is used as the base material in this way, the present invention can be applied not only to a reflector for a lighting device but also to a guard rail having a good surface light reflectivity.

In the case where a plastic sheet is used as a base material and a reflection coating is formed on the surface of the plastic sheet to produce a light reflection sheet for a liquid crystal backlight or the like, a conductive sheet or a grounding sheet which can be grounded. It is necessary to use an antistatic sheet. A general plastic sheet is an electrical insulator having a volume resistivity of usually 10 ¹² to 10 ¹⁶ Ωcm. However, a polymer electrolyte or conductive fine particles are uniformly dispersed in the sheet, and a conductive treatment is applied to the surface of the sheet. By applying, a conductive sheet can be obtained. For example, conductive carbon or carbon fiber is kneaded into a sheet of general-purpose resin such as polyethylene or polyester, or conductive fine powder is dispersed on the surface of a sheet of general-purpose resin such as polyethylene or polyester to conduct electricity. Dispersion type with a conductive resin layer formed on the surface, semiconductor thin film, metal thin film,
There is a thin film type in which a multilayer film or the like is formed. Examples of the semiconductor thin film include indium tin oxide (ITO), tin oxide, cadmium tin oxide, and copper iodide, and examples of the metal thin film include gold, palladium, platinum, silver, aluminum, and chromium. The conductive level only needs to be such that grounding is possible, and it is preferable that the volume resistivity is 10 ⁸ Ωcm or less, or the surface resistance is 10 ¹¹ Ω or less.

[0019]

The present invention will be described below in detail with reference to examples. (Example 1) Polyester-based powder coating material (average particle size 40μ)
m, containing 10% by weight of barium sulfate as a white pigment) 97
Parts by weight and silica airgel powder (average particle size 50 μm,
A coating composition was prepared by mixing 3 parts by weight of a refractive index of 1.03).

Then, grounding was performed using a zinc steel plate of 70 × 150 × 1 mm as a base material, and the above-mentioned coating composition was electrostatically applied to the surface thereof using a corona discharge type charging gun. Next, this was baked at 180 ° C. for 15 minutes to form a coating film. The average thickness of the obtained coating film was 65 μm. Here, the above-mentioned powdered silica airgel used was obtained by the following method. First, an oligomer of tetramethoxysilane ("Methylsilicate 5" manufactured by Colcoat Co., Ltd.)
1 ": average molecular weight = about 470), ethanol, water, 15
A sol solution was prepared by mixing N ammonia water at a molar ratio of 1: 43: 20: 0.20, and the sol solution was left to gel to obtain a gel compound. Next, this gel-like compound is heated and stirred at 40 ° C. for about 2 hours in an ethanol solution of hexamethyldisilazane (reagent of Toray Dow Corning Silicone Co., Ltd.) at a concentration of 0.2 mol / liter, thereby performing a hydrophobic treatment. went. Next, this hydrophobized gel-like compound is placed in carbon dioxide at 18 ° C. and 55 atm, and an operation of replacing ethanol in the gel-like compound with carbon dioxide is performed for about 2 hours. Supercritical drying was performed for about 24 hours at 40 ° C. and 80 atm, which is the supercritical condition, to obtain a powdery silica airgel comprising a porous skeleton of silica. This was ground to obtain a powdery silica airgel.

Example 2 A coating composition was prepared by mixing 99 parts by weight of a polyester powder coating (same as in Example 1) and 1 part by weight of silica airgel (same as in Example 1). Thereafter, in the same manner as in Example 1, a coating film having an average thickness of 65 μm was formed on the surface of the zinc steel sheet. Example 3 A coating composition was prepared by mixing 95 parts by weight of a polyester-based powder coating (same as in Example 1) and 5 parts by weight of silica airgel (same as in Example 1). Thereafter, the average film thickness was 65 μm on the surface of the zinc steel sheet in the same manner as in Example 1.
m was formed.

Example 4 A 100 μm-thick transparent conductive sheet (“High Beam B” manufactured by Toray Industries, Inc.) as a substrate:
Polyester substrate), and the same coating composition as in Example 1 was used. Thereafter, a coating film was formed on the surface of the transparent conductive sheet in the same manner as in Example 1. The average thickness of the obtained coating film was 65 μm.

Comparative Example 1 A zinc steel sheet was produced in the same manner as in Example 1 except that only the polyester-based powder coating (same as in Example 1) was used as the coating composition (no silica airgel was used). A film having an average film thickness of 65 μm was formed on the surface of. (Comparative Example 2) Except that only the polyester-based powder coating (same as in Example 1) was used as the coating composition (without using silica airgel), a transparent conductive sheet ( (Same as in Example 4), a coating film having an average film thickness of 65 μm was formed.

With respect to the coating films prepared in Examples 1 to 4 and Comparative Examples 1 and 2, the total light reflectance and the diffuse reflectance were measured with a self-recording spectrophotometer (U-4000, manufactured by Hitachi, Ltd.). Visible light wavelength 555 nm and infrared light wavelength 10
Table 1 shows the total light reflectance and diffuse reflectance for 00 nm. 3 and 4 show the measurement results of the total light reflectance and the diffuse reflectance from the visible light region to the infrared light region for Example 1 and Comparative Example 1. FIG.

[0025]

[Table 1]

As can be seen from Table 1 and FIGS. 3 and 4, the reflectance of the reflective paint of the embodiment is higher than that of the comparative example in the whole range from the visible light range to the infrared light range. Is confirmed. (Example 5) Downlight lighting equipment ("LB74386" manufactured by Matsushita Electric Works, Ltd .: lamp LDS100V60W
W.KM) by electrostatically applying the coating composition prepared in Example 1 to the inner surface of an aluminum reflector.
A coating film having an average thickness of 65 μm was formed.

Example 6 The coating composition prepared in Example 2 was electrostatically coated on the inner surface of an aluminum reflector of a downlight illuminator (same as in Example 5) to obtain an average film thickness. A coating film of 65 μm was formed. (Comparative Example 3) Downlight lighting fixture (same as Example 5)
The average film thickness was 65 μm by electrostatically applying the coating composition of Comparative Example 1 to the inner surface of the aluminum reflector of
Was formed.

For the lighting fixtures of Examples 5 and 6 and Comparative Example 3, the fixture efficiency and the temperature of the upper surface of the reflector were measured. Light emitted from the lamp of the light source in the lighting equipment is reflected or refracted through a reflector or the like and comes out of the lighting equipment.
At this time, part of the light is absorbed by the lighting fixtures, resulting in loss,
Due to this loss, less light is effectively used. An indicator of this standard is the efficiency of the instrument, as defined by JIS C
The luminous flux emitted from the lamp of the light source and the luminous flux emitted from the lighting fixture are measured by the method according to 8105, and the fixture efficiency can be obtained from the following equation.

Fixture efficiency (%) = (light flux emitted from lighting equipment / luminous flux emitted from lamp) × 100 Further, the temperature of the upper surface of the reflection plate is determined by turning on the lamp and leaving it until the temperature becomes constant. It was used for measurement.
Table 2 shows the results.

[0030]

[Table 2]

As can be seen from Table 2, the lighting fixture of the embodiment using the reflection plate having the coating film of the present invention has high fixture efficiency due to the high light reflectance of the lamp, and has high infrared light efficiency. As a result, it is confirmed that there is a heat insulation effect of suppressing a temperature rise on the upper surface of the reflection plate.

[0032]

As described above, the coating composition according to the present invention comprises a mixture of a resin and silica airgel, and the resin and silica airgel have a large difference in refractive index, and the interface between the resin and silica airgel is large. The light causes total reflection and a coating film having a high reflectance can be obtained.

In the second aspect of the present invention, since the powder coating is used as the resin, the powder coating does not contain an organic solvent or the like, and the silica airgel subjected to the hydrophobic treatment shrinks due to the action of the organic solvent or the like. And no cloudiness. The invention according to claims 3 and 4 uses a powder coating containing a white pigment as the powder coating.
A white coating film can be formed by the white pigment, and the reflectance of the coating film can be further increased by improving the diffuse reflectance.

Further, the invention of claim 5 provides that the content of the silica airgel is 0.1% by weight to 1% by weight based on the total amount of the composition.
Since it is set to 0% by weight, a coating film having a high reflectance can be obtained without lowering the coating film performance such as mechanical strength. Further, in the invention of claim 6, since the silica airgel having a refractive index of 1.008 to 1.18 is used, the performance such as transparency of the silica airgel can be ensured, and the silica airgel can be used with resin. Can be set large, and the light reflectance increases.

According to the seventh aspect of the present invention, since the silica airgel used is a hydrophobized one, the silica airgel absorbs and absorbs water, and the performance such as the refractive index and the light transmittance deteriorates. That can be prevented. The coating film forming method according to the present invention, by electrostatically coating the coating composition, and baking it,
Since a coating film in which silica airgel is dispersed in a resin is formed, a coating film having high reflectance in which silica airgel is dispersed can be easily formed by an electrostatic coating process.

The coated article according to the present invention is obtained by forming a coating film of the above-mentioned coating composition on the surface of a substrate, and is capable of obtaining a coated article having a coating film having high light reflectance. It is. The reflector for a lighting device according to the present invention is obtained by forming a coating film of the above-described coating composition on the surface of a metal substrate, and the coating film has a reflectance in a whole range from a visible light region to an infrared light region. The fixture efficiency of the lighting fixture can be increased by the high reflectance in the visible light region, and the temperature rise of the reflector can be suppressed by the high reflectance in the infrared light region.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an embodiment of a coated product of the present invention.

FIG. 2 shows an example of an embodiment of a method for forming a coating film according to the present invention, in which (a) is a schematic view showing a process of electrostatic coating, and (b) is a cross-sectional view of the obtained coated product. It is.

FIG. 3 is a graph showing the relationship between total light reflectance and diffuse reflectance and wavelength in Example 1.

FIG. 4 is a graph showing the relationship between total light reflectance and diffuse reflectance and wavelength in Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resin 2 Silica airgel 3 Substrate 4 Coating

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Yokokawa 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works, Ltd. Inventor Hiroshi Takasaka 1048 Kazuma Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Works Co., Ltd. (72) Inventor Nankai Nakazawa 2-5-5 Sumida, Hirakata-shi, Osaka Inside Otani National Electric Co., Ltd. 2-5, Sumida, Hirakata City, Otani National Electric Corporation

Claims (10)

[Claims] 1. A coating composition comprising a mixture of a resin and silica airgel. 2. The coating composition according to claim 1, wherein the resin is a powder coating. 3. The coating composition according to claim 2, wherein the powder coating contains an inorganic component. 4. The coating composition according to claim 3, wherein the inorganic component is a white pigment. 5. The coating composition according to claim 1, wherein the content of the silica airgel is 0.1% by weight to 10% by weight based on the total amount of the composition. 6. The silica airgel has a refractive index of 1.
The coating composition according to any one of claims 1 to 5, wherein the composition is 008 to 1.18. 7. The coating composition according to claim 1, wherein the silica airgel has been subjected to a hydrophobic treatment. 8. An electrostatic coating of the coating composition according to claim 1, and baking the coating composition.
A coating film forming method comprising forming a coating film in which silica airgel is dispersed in a resin. 9. A coated article comprising a substrate and a coating film of the coating composition according to claim 1 formed on a surface of the substrate. 10. A reflector for a lighting fixture, comprising a metal substrate and a coating film of the coating composition according to claim 1 formed on a surface of the metal substrate.