JP2009099336A - Coated metal plate for led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflecting plate for an inexpensive LED having high thermal conductivity and excellent processability. <P>SOLUTION: A thermosetting white resin film with a crosslinked density of 0.5 to 2.5×10<SP>-3</SP>mol/cc, which includes 10 to 40 vol% white pigment particulates wherein a thermal conductivity is 1 W/mK or more and a peak of an excited spectrum is 460 to 480 nm and also includes at least a kind out of polyethylene wax, carnauba wax, and microcrystalline wax, is applied on at least one surface of a chemical film of a metal plate having the chemical films on both surfaces. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coated metal plate that is inexpensive and excellent in workability and heat dissipation as a reflector for LED in a liquid crystal display or lighting such as a personal computer or a television.

  Conventionally, as a reflection plate, (1) a film-coated metal plate obtained by attaching a white film having fine bubbles to a metal plate using an adhesive or the like (see, for example, Patent Document 1), (2) barium sulfate or alumina A coated metal plate (for example, see Patent Document 2) containing a highly reflective substance such as hollow glass beads has been proposed. Moreover, as a reflecting plate with good heat dissipation, (3) a resin-coated metal plate (see, for example, Patent Document 3) in which one surface is a white film and the opposite surface is a heat dissipation film has been proposed.

  In recent years, a light source such as a liquid crystal display or an illumination such as a personal computer or a television has been changed from a cold cathode tube to an LED. This is because the cold-cathode tube contains mercury, so there is concern about the environmental impact at the time of disposal. In addition, LEDs are a completely new type of solid-state light source using semiconductors, which are compact, long-life, power-saving, mercury-free, This is because it has many unprecedented features such as light source color and brightness.

  An LED (Light Emitting Diode) is an element that emits light (spontaneous light emission) by recombination of minority carriers injected when a pure bias is applied to a pn junction of a semiconductor. The light emitting material is a compound semiconductor, and commercially available materials include mainly Group III-IV GaAlAs: red, AlInGaP: yellow, AlInGaP: orange, InGaN: green, InGaN: blue.

  In addition, for white LEDs, multi-chip type equipped with chips of R (red), G (green) and B (blue), which are the three primary colors of light, and LEDs emitting blue or ultraviolet light are excited. A one-chip type that excites a phosphor as a light source for use is known. In general, the latter is formed by sealing a LED with a phosphor-containing resin in which a yellow phosphor such as YAG is dispersed in a transparent resin such as an epoxy resin, and effectively converts the light emitted from the ultraviolet region of the LED to yellow, White light is obtained by mixing with blue. This is the mainstream of current white LEDs because the device itself emits white light and only controls the current, so that control is relatively simple and inexpensive white light can be obtained.

In addition, in recent years, blue LEDs have been developed, and R (red), G (green), and B (blue), which are the three primary colors of light, have been arranged, so that white LEDs have been realized and conventional incandescent bulbs, fluorescent lamps, etc. As a next-generation energy-saving illumination light source that replaces the LED, the application of LEDs is rapidly spreading. The LED has a high directivity, low drive current, and space-saving characteristics, but the size of the element is as small as a few millimeters square, so for example to obtain the desired brightness as a lighting device. Requires a large number of elements. Therefore, when viewed as a whole as a device, there is a problem such as a decrease in luminous efficiency of the element due to heat generation.

JP-A-10-177805 JP 2005-96405 A Japanese Patent Laid-Open No. 2004-160979

  In the case of the film-coated metal plate of (1), the total cost is due to the problem of wrinkle generation at the bent part during molding, the problem of moldability that causes film peeling, and the film is thick, and a film pasting process is required. There is a problem that is very high. In particular, when the film is used in an LED, there are problems that the film has poor thermal conductivity because it contains many fine bubbles, and that the film is thick and heat is likely to be trapped. That is, if heat is trapped in the reflector, the deterioration of the LED sealing resin is promoted, and the long life, which is an advantage of the LED, is hindered, making it unsuitable as a reflector for LED.

  In the case of the coated metal plate (2), although a relatively low-cost reflector can be provided, the description regarding the base resin is not sufficient, and when implemented as a reflector for LED, it is applied at the time of molding such as drilling or bending. Cracking or peeling of the film may occur, scratches may occur on the coating film, and there may be processing problems. Depending on the white pigment fine particles contained, the thermal conductivity of the coating film is poor, and the deterioration of the sealing resin is accelerated like the film. Therefore, the long life, which is an advantage of LED, is hindered, and it is not suitable as a reflector for LED.

  In the case of the resin-coated metal plate of (3) above, the white film has a high absorbency with respect to infrared rays, and the heat from the absorbed infrared rays is radiated from the coating film on the opposite side through the metal plate to improve heat dissipation. However, since the resin film is inherently inferior in heat conductivity to metals, the heat inside the white film cannot be quickly transferred to the metal plate. Deterioration of the stop resin is promoted and the long life, which is an advantage of the LED, is hindered, making it unsuitable as a reflector for LED.

  Furthermore, in the case of the resin-coated metal plate of the above (3), it is described that by setting the upper limit of the molecular weight of the base resin, the cross-linking density of the film becomes high, and as a result, the film becomes hard and scratch resistance is improved. Yes. However, the crosslinking density is not mainly determined by the size of the molecular weight, but greatly depends on the reaction point (the number of functional groups of the base resin that reacts with the crosslinking agent). Control is not sufficient, and there are problems in processing that may cause cracking or peeling of the coating film or scratching the coating film during molding such as drilling or bending for use as a reflector for LED. It is not suitable as a reflector for LED.

  Therefore, there is a strong demand for a reflector that is low in cost and good in workability and heat dissipation (here, thermal conductivity) for LEDs.

  For these reasons, the present inventors provide a chemical conversion film on a metal plate, and pay attention to the crosslinking density of the thermosetting resin film that has not been studied in detail and the thermal conductivity of the white pigment fine particles contained therein. As a result, it has been found that processability and heat dissipation can be improved, and further research has been made to complete the present invention.

That is, according to the first aspect of the present invention, a thermosetting white resin film is formed on a chemical film on at least one surface of a metal plate having a chemical film on both sides, and the crosslink density of the thermosetting white resin film is 0. A coated metal plate for LED, which is 0.5 to 2.5 × 10 ⁻³ mol / cc, and further contains 10 to 40 vol% of white pigment fine particles with respect to the thermosetting white resin film. .

  The invention according to claim 2 is the coated metal plate for LED according to claim 1, wherein the white pigment fine particles have a thermal conductivity of 1 W / mK or more.

  The invention as set forth in claim 3 is characterized in that the thermosetting white resin film contains at least one of polyethylene wax, carnauba wax, and microcrystalline wax. It is.

  The invention according to claim 4 is the coated metal plate for LED according to claims 1 to 3, wherein the thermosetting white resin film contains a fluorescent material having an excitation spectrum peak of 460 to 480 nm. .

  The coated metal plate of the present invention has good processability and heat dissipation, and is particularly preferably used as a reflector for LEDs such as a liquid crystal display or illumination using an LED light source.

  In the present invention, the base metal plate is not particularly limited, for example, an aluminum plate, a stainless steel plate, a low carbon steel, a high carbon steel, a steel plate made of a low alloy steel used for a high strength steel plate, or the like, or A plated steel sheet having a surface plated with these steel sheets as a base material is used. In particular, it has sufficient strength to form and hold lighting devices and reflecting members, has sufficient moldability during drawing and bending, and dissipates heat generated inside more quickly to the outside. A 1000-series, 3000-series, and 5000-series aluminum plate having excellent thermal conductivity is preferable.

  The chemical conversion film provided on the aluminum material has a coating type and a reactive type, and is not particularly limited, but a reactive chemical film having good adhesion is used for both the aluminum and the resin film. The reactive chemical conversion film is specifically a film formed with a treatment liquid such as phosphate chromate, chromate chromate, zirconium phosphate, and titanium phosphate. In particular, a phosphoric acid chromate-treated film is preferable in terms of cost and versatility.

The thermosetting white resin film provided on the chemical conversion film has a crosslinking density of 0.5 to 2.5 × 10 ⁻³ mol / cc. When the crosslinking density is less than 0.5 × 10 ⁻³ mol / cc, the degree of crosslinking of the coating film is rough, and the coating film is easily deformed but weakened. . When the cross-linking density exceeds 2.5 × 10 ⁻³ mol / cc, the degree of cross-linking of the coating film is dense and scratches are difficult to enter, but the coating film is difficult to deform and is easily cracked, resulting in poor workability. The crosslink density is calculated from the absolute temperature at T: equilibrium storage elastic modulus and the measured value of E ′: equilibrium storage elastic modulus using the following equation of rubber elasticity.

n = E '/ 3RT

n: Crosslink density (mol / cc)
R: Gas constant (8.314 × 10 ⁷ , erg.deg / mol)
T: absolute temperature at equilibrium storage modulus (° K)
E ′: equilibrium storage elastic modulus (dyne / cm ² )

When the molecular weight between the crosslinking points is small and the number of crosslinking points is large, it can be said that the equilibrium storage elastic modulus is high and the crosslinking density is high.

  Therefore, the crosslinking density of the coating film alone is achieved by a combination of the molecular weight of the resin to be used, the type and amount of the functional group, the type and amount of the crosslinking agent to be contained, the amount of the catalyst, and the baking conditions. That is, when the molecular weight of the resin used is large, the crosslinking density is low, the number of functional groups of the base resin and the crosslinking agent is large (the number of crosslinking points increases) or the baking temperature is high (the crosslinking proceeds and the number of crosslinking points increases). The crosslink density is increased.

  The thermosetting resin and the crosslinking agent used for the thermosetting white resin film are not particularly limited as long as the result satisfies the crosslinking density. For example, 1 type (s) or 2 or more types, such as a fluorine resin, an acrylic resin, a polyester resin, an epoxy resin, are used. Further, the crosslinking agent having a function of reacting with the functional group of the resin and curing the paint is not particularly limited. For example, 1 type (s) or 2 or more types, such as a melamine-type resin, a urea-type resin, and blocked isocyanate, are used.

  The thermosetting white resin film contains white pigment fine particles. The white pigment fine particles in the present invention are not particularly limited as long as the thermosetting resin film is white. For example, hollow glass beads, white organic resin fine particles, alumina, silica, glass, barium sulfate, titanium oxide, calcium carbonate, etc. Is mentioned. Particularly preferably, the white pigment fine particles having a thermal conductivity of 1 W / mK or more are used. Since the thermal conductivity of the single thermosetting resin film is about 0.1 W / mK, the addition of white pigment fine particles having good thermal conductivity improves the thermal conductivity (heat dissipation). Moreover, the content rate of the said white pigment fine particle is 10-40 vol% with respect to a thermosetting white resin film. When the content is less than 10 vol%, the absolute amount of the high thermal conductive fine particles is small, so that the thermal conductivity is not sufficiently improved. When the content exceeds 40 vol%, the white pigment fine particles are excessive, the coating film is hard and brittle, and the workability is lowered.

  The white pigment fine particles preferably have an average particle size of 0.1 to 1.0 μm. When the average particle size is less than 0.1 μm, the particle size is smaller than the wavelength of visible light (0.38 to 0.78 μm), so that the visible light is hardly reflected by the fine particles and the reflectivity is lowered. When the average particle diameter exceeds 1.0 μm, when the same vol%, the number of particles that reflect visible light decreases and the reflectivity decreases.

  The thermosetting white resin film contains at least one of polyethylene wax, carnauba wax, and microcrystalline wax, thereby improving processability. As an addition amount, it is preferable that it is 20 wt% or less with respect to a thermosetting white resin film. When the lubricity imparting component exceeds 20 wt%, the processability such as generation of coating film residue and cracking of the coating film tends to occur.

  The thermosetting white resin film is improved in reflectivity by containing a fluorescent substance having an excitation spectrum peak of 460 to 480 nm. White LEDs, which are currently the mainstream, are generally sealed with a phosphor-containing resin in which a yellow phosphor such as YAG is dispersed in a transparent resin such as an epoxy resin to effectively emit light in the ultraviolet region of the LED. It is converted to yellow, and white light is obtained by mixing with the original blue color. Therefore, in the case of an LED light source, a LED having a strong emission peak (blue light) at a wavelength different from that of a conventional cold-cathode tube type fluorescent lamp, that is, 460 to 480 nm, and being excited at this wavelength is included in the LED. The blue light of the light source can be used effectively.

  The film thickness of the thermosetting resin film is preferably 25 to 120 μm. If the film thickness is less than 25 μm, the film is not sufficiently concealed and the reflectivity is inferior, making it unsuitable as a reflector. When the film thickness exceeds 120 μm, the workability decreases, or the thermal resistance of the coating film due to the thickness increases, resulting in a decrease in heat dissipation.

  In addition, the thermosetting white resin film paint used in the present invention includes a solvent, a leveling agent, a pigment dispersant, and an armpit prevention, which are usually used in paints to ensure paintability and general performance as a precoat material. You may use an agent etc. suitably.

   Hereinafter, the present invention will be described in detail with reference to examples. An aluminum plate (material: JIS A5052, plate thickness: 0.6 mm) is degreased with a commercially available aluminum degreasing agent, washed with water, and then treated with a commercially available phosphoric acid chromate treatment solution. In addition, an organic solvent, a catalyst, white pigment fine particles having different thermal conductivities, a melamine resin as a curing agent, and an acrylic paint made of an acrylic resin as a base resin so that the film thickness becomes 70 μm by a roll coater under the conditions shown in Table 1. The paint was applied and baked at 200 ° C. PMT (maximum ultimate plate temperature). In this way, a coated metal plate schematically shown in cross section in FIG. 1 was produced. In the figure, 1 is a thermosetting white resin film, 2 is a chemical conversion film, and 3 is a metal plate.

A performance test was performed on the obtained coated metal plate excellent in workability and heat dissipation by the following test method.
(Reflective)
The total reflectance is a multi-light source spectrocolorimeter MSC-IS-2DH manufactured by Suga Test Instruments Co., Ltd. (using an integrating sphere, diffuse light illumination 8 ° direction light reception), and the total reflectance at a wavelength of 550 nm (including a regular reflection component). ) Was expressed as a percentage when a BaSO ₄ white plate was used as a standard plate. Since it is used as a reflector for LEDs such as lighting and liquid crystal panels, ◎: Total reflectance is 95% or more, ○: 90% or more and less than 95%, Δ: 85% or more and less than 90%, ×: less than 85%, Evaluation was made according to the criteria.
(Processability)
The processability was 180 ° 2T bending with the evaluation surface on the outside, and the resin film layer was visually observed for cracks. ◎: No crack of coating film, ○: Minor coating film cracked, Δ: Small coating Evaluation was made based on the criteria that the film was cracked but could be used, and x: a large coating film was cracked and not usable.
Further, after observing the crack, the cellophane tape was closely attached to the bent part, and the peeling condition of the coating film was observed when the tape was suddenly peeled. ○: No peeling, Δ: Slight peeling but usable, ×: The evaluation was based on the standard of unusable due to many peeling.
(Heat dissipation)
For heat dissipation, the case was prepared by the following method, the temperature inside the case was measured, and the temperature difference from the metal film affixed with the white film was calculated. A: Lowering temperature 5 ° C or higher, ○: Lowering temperature 3 ° C or higher, 5 ° C Less than, (triangle | delta): The temperature of 1 degreeC or more and less than 3 degreeC, and x: Evaluation of the temperature of less than 1 degreeC. In addition, when the fall temperature with respect to a white film was less than 1 degreeC, since the heat problem was not solved, it was made unusable. A casing with a bottom surface of 150 mm x 150 mm and a height of 200 mm is produced from the obtained coated metal plate having excellent workability and heat dissipation. Here, as an example, only the top surface of the casing is used in order to achieve the same state as the liquid crystal display device. A 60 W incandescent bulb with a higher heat quantity than the white LED was used for reducing the test time. The produced housing is shown in FIG. In the figure, 4 is glass, 5 is liquid crystal, 6 is an acrylic diffuser plate, 7 is a light source (60 W incandescent bulb), 8 is a reflector, 9 is a thermosetting white resin film, and 10 is a metal plate. A hole was drilled in this case, a 60 W incandescent bulb was attached as a light source, and electricity was emitted to generate light and heat, and the ambient temperature inside the case when the temperature inside the case reached a steady state was measured.
(Lubricity)
Lubricity is measured by a friction coefficient with a Bowden friction tester. ○: Less than 0.10, △: More than 0.10 and less than 0.30 can be used, ×: Not usable at 0.30 or more Evaluation based on the criteria.

  The obtained performance test results are shown in Table 1. As is clear from the results shown in Table 1, Examples 1 to 20 of the present invention are all good in reflectivity, workability, heat dissipation, and lubricity. On the other hand, No. which is a comparative example. 21-24 are inferior in reflectivity, workability, heat dissipation, and lubricity, and are unsuitable as LED reflectors. That is, no. No. 21 is inferior in workability because the crosslink density of the thermosetting resin is low. No. No. 22 is inferior in workability because the crosslink density of the thermosetting resin is high. No. No. 23 is inferior in reflectivity because the content of white pigment fine particles is small. No. No. 24 is inferior in processability due to the high white pigment fine particle content.

It is sectional drawing which shows typically the coating metal plate excellent in workability and heat dissipation of this invention. It is sectional drawing which shows typically the liquid crystal display device using the reflecting plate of this invention.

Explanation of symbols

1 Thermosetting white resin film 2 Chemical conversion film 3 Metal plate 4 Glass 5 Liquid crystal 6 Acrylic diffuser plate 7 Light source (60 W incandescent bulb)
8 Reflector 9 Thermosetting white resin film 10 Metal plate

Claims (4)

A thermosetting white resin film is formed on the chemical film on at least one surface of the metal plate having a chemical film on both sides, and the crosslink density of the thermosetting white resin film is 0.5 to 2.5 × 10 ^{−. A} coated metal plate for LED, which is ³ mol / cc, and further contains 10 to 40 vol% of white pigment fine particles in the thermosetting white resin film.   The coated metal plate for LED according to claim 1, wherein the white pigment fine particles have a thermal conductivity of 1 W / mK or more.   3. The painted metal plate for LED according to claim 1, wherein the thermosetting white resin film contains at least one of polyethylene wax, carnauba wax, and microcrystalline wax.   4. The coated metal plate for LED according to claim 1, wherein the thermosetting white resin film contains a fluorescent material having an excitation spectrum peak of 460 to 480 nm.

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