JP2009210731A - Combined light-reflective film having high heat radiating capacity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combined light-reflective film which exhibits a heat radiating effect sufficiently even when arranged in a narrow space in a liquid crystal display component and efficiently radiates the heat from a semiconductor light-emitting diode to mitigate a heat spot and effectively restrain temperature irregularity on a liquid crystal display screen; and to provide a liquid crystal display apparatus comprising the same. <P>SOLUTION: The combined light-reflective film is characterized in that a graphite sheet having 600-1,800 W/(m K) thermal conductivity in the planar direction and 10-50 μm thickness is bonded to one side of a light-reflective film having 30-60 μm thickness and 1.0-1.4 specific gravity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to heat dissipation of liquid crystal display components mounted on electronic devices and precision devices, and more particularly to a composite reflective film that efficiently dissipates heat generated from a semiconductor light emitting diode (hereinafter referred to as LED) and a liquid crystal display device having the same. .

  Liquid crystal display devices mounted on electronic devices and precision devices include a liquid crystal unit, LEDs serving as liquid crystal light sources, a light guide plate that uniformly emits light generated from the LEDs, a diffusion film that achieves uniform surface brightness, It is composed of a prism sheet having a light condensing effect toward the front of the screen, and a reflection film that reflects light generated from the LED to the liquid crystal side. These materials generally have low thermal conductivity (about 0.1 to 0.2 W / m · K) and cannot effectively release heat from the LED, and heat spots are likely to occur around the LED. The optical properties of materials used in liquid crystals are highly controlled, and when this heat causes a dimensional change, the optical properties change drastically, resulting in color unevenness on the liquid crystal screen. There was a problem. There is also a problem that the screen is not displayed because the liquid crystal undergoes a phase transition from the liquid crystal phase to the liquid phase by heat from the light source. With the progress of higher brightness and higher density mounting of LEDs, there is a long-awaited appearance of a system that can effectively dissipate the heat generated from the LEDs and reduce the heat spot. In view of such a problem, for example, in Patent Document 1, the entire liquid crystal display device is covered with a casing made of aluminum or a galvanized steel plate to dissipate heat.

In small mobile devices that are required to be small and light, heat radiating sheets such as graphite sheets are used as heat spreader materials. The graphite sheet has greatly different thermal and electrical properties in the ab plane direction and the c axis direction, and the anisotropy of thermal conductivity in the ab plane direction and the c axis direction reaches 50 to 400 times. The purpose of the graphite heat-dissipating sheet is to diffuse the generated heat quickly and widely using such properties. In Patent Document 2, a reflective layer is provided between a thermoplastic polyester foam sheet having an average bubble shape of 100 μm or less, a thickness of 200 μm or more, and a specific gravity of 0.7 or less, and a graphite sheet. Trying to give a heat dissipation effect.
JP 2007-183634 A JP 2004-101893 A

  When heat radiation of the liquid crystal display device is performed in a case of aluminum or galvanized steel plate, there are the following problems. The thermal conductivity value of aluminum is 237 W / m · K, and the thermal conductivity value of the galvanized steel sheet is not as large as 20 W / m · K. In order to obtain a sufficient heat diffusion effect, It was necessary to increase the thickness. While small mobile devices are being thinned by several microns, they are unsuitable for the purpose of reducing the thickness of the entire liquid crystal member, and the weight of the entire liquid crystal display device also increases.

  When the polyester foam sheet described in Patent Document 2 is used, there are the following problems. Polyester has a low thermal conductivity (about 0.2 W / m · K), and when this polyester is foamed, an air layer with a lower thermal conductivity (about 0.025 W / m · K) is interposed inside the polyester. Therefore, the value of heat conduction is further reduced. When this foam sheet is used as a reflective film, the above-mentioned polyester foam sheet acts as a heat insulating material, and heat generated from the LED is not sufficiently transmitted to the graphite, resulting in a problem that the heat spot of the LED is hardly improved. Further, as disclosed in the embodiments of the invention, an expanded graphite sheet is used as the graphite sheet, but the expanded graphite sheet is generally thicker than 70 μm, and as described above, the entire liquid crystal display device It was unsuitable for the purpose of reducing the thickness.

  That is, the present invention provides (1) a polymer graphite sheet obtained by heat-treating a polymer film on one side of a reflective film having a thickness of 30 μm to 60 μm and a specific gravity of 1.0 to 1.4. (2) The composite reflective film according to (1), wherein aluminum or silver is vapor-deposited on one side or both sides of the reflective film, (3) The reflective film is preferably made of at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, and acrylic. Furthermore, (4) the graphite sheet has a thermal conductivity in the plane direction of 600 W / m · K to 1800 W / m · K and a thickness of 10 μm to 50 μm. 3) the composite reflective film according to any one of the above, (5) the liquid crystal display device having the composite reflective film according to any one of (1) to (4), (6) a liquid crystal display panel, a light guide plate, and a reflective film. The present invention relates to the liquid crystal display device according to (5), characterized in that the layers are laminated in the order of graphite.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the composite reflective film which thermally radiates the heat_generation | fever from LED efficiently, and a liquid crystal display device having the same.

  The reflective film of the present invention will be described below. Since the liquid crystal display itself is not a light emitter, it can be displayed by installing a light source called a backlight from the back side or the edge side and irradiating light. The edge type backlight employs a light guide plate method that uniformly irradiates the entire liquid crystal display using a light guide plate that uniformly propagates and diffuses light. In this illumination method, a reflective film is provided under the light guide plate in order to efficiently reflect the light diffused from the light guide plate to the liquid crystal screen side. This provides a function of reducing the loss of light from the light source and brightening the liquid crystal screen.

  The reflective film is formed by depositing aluminum or silver on one side or both sides of a thermoplastic polymer film such as polyethylene terephthalate, polypropylene, polycarbonate, and acrylic. As the vapor deposition method, a vacuum vapor deposition method, a sputtering method, an ion plating method, or the like is used. The thickness of the vapor deposition layer is usually in the range of about 20 nm to 200 nm. When the thickness is less than 20 nm, the reflectivity is poor, and even when the thickness exceeds 200 nm, no further improvement in the reflectivity is observed. As the amount of heat received is increased, workability is inferior, and the amount of metal used is increased, which is economically inferior. Moreover, 30-60 micrometers is preferable as a total thickness of a reflective film, and 40-50 micrometers is more preferable. When the thickness is less than 30 μm, it becomes difficult to ensure the flatness of the film, and uneven brightness tends to occur. On the other hand, when the thickness is larger than 60 μm, the thickness may be too large to be used as a reflective film in a liquid crystal display device of a small electronic device. Moreover, 1.0-1.4 are preferable and, as for the specific gravity of a reflective film, 1.1-1.3 are more preferable. When the specific gravity is less than 1.0, there are more fine bubbles contained in the polymer film as the base material, and those with larger bubble sizes are contained. Such problems appear. If the specific gravity is greater than 1.4, it may contain a large amount of inorganic filler, or the generation of fine bubbles may be insufficient, and problems such as reduced film stability and reduced reflectance will also appear. come.

  In general, graphite sheets are widely used as thermal diffusion / heat dissipation materials, heat-resistant sealing materials, gaskets, fuel cell separators, etc. because of their excellent heat resistance, chemical resistance, thermal conductivity, electrical conductivity, and low gas permeability. in use. There are two methods for producing a graphite sheet used for thermal diffusion and heat dissipation as described below.

  One of them is a method generally called an expanded graphite method. This is a sheet-like graphite film obtained by rolling expanded graphite produced when natural graphite lead is treated with a strong acid such as sulfuric acid to form an intercalation compound, and this is heated and expanded (hereinafter referred to as the present invention). Then, the graphite sheet produced by this method is called an expanded graphite sheet).

  Such an expanded graphite sheet exhibits a thermal conductivity of about 100 to 400 W / m · K in the planar direction and is used as a heat dissipation material. In the expanded graphite sheet viewed as a heat dissipation material, (1) it is difficult to achieve a thermal conductivity of 400 W / m · K or more, (2) it is difficult to produce a thin film of 50 μm or less, (3) machine There is a disadvantage that it is inferior to a typical characteristic. Therefore, in order to increase the heat transport amount, it is necessary to increase the thickness of the film.

  The second method for producing graphite used for thermal diffusion and heat dissipation is to use a polymer film as a raw material and carbonize and graphitize it to produce a graphite sheet. Examples of the polymer used for such a purpose include a thermosetting polymer film, and examples thereof include polyimide, polyamideimide, polybenzimidazole, polyamide, and polyoxazole.

  Such a graphite sheet (hereinafter, the graphite sheet produced by this method is referred to as a polymer graphite sheet in the present invention) exhibits very high thermal conductivity in the planar direction and is used as a heat dissipation material. The polymer graphite sheet viewed as a heat dissipation material has (1) a very high thermal conductivity of 600 to 1800 W / m · K, (2) it is possible to produce a thin sheet, and a sheet of 50 μm or less is also easy It has the advantage that it can be manufactured, and (3) it has excellent mechanical properties.

  The graphite sheet used in the present invention is desirably as thin as possible from the viewpoint of reducing the thickness of the entire liquid crystal display device, and the thickness is preferably 50 μm or less, more preferably 40 μm or less. In order to ensure a sufficient amount of heat transport in a thin thickness, the value of the thermal conductivity in the plane direction is preferably 600 W / m · K or more, more preferably 800 W / m · K or more, most preferably 1000 W. / M · K or more is desirable. For this reason, polymer graphite is preferred as the graphite sheet used in the present invention.

  First, the polymer graphite sheet used in the present invention will be described. As a polymer film used as a raw material for polymer graphite sheets, carbon atoms remain as carbonaceous films after pyrolysis and recombine simultaneously with pyrolysis to form an intermediate state between polymer and carbon called carbon precursor. Need to form. In order to obtain a good graphite sheet, the polymer film is preferably a thermosetting polymer. For example, a good graphite sheet can be obtained with thermosetting films such as polyimide, polyamideimide, polybenzimidazole, polyamide, and polyoxazole. In particular, it is one of the most preferred polymer raw materials because a high-quality graphite fill can be obtained from a polyimide film by processing at a high temperature of 2400 ° C. or higher.

  The polyimide film is produced by casting an organic solvent solution of polyamic acid, which is a polyimide precursor, on a support such as an endless belt or a stainless drum, followed by drying and imidization. As a method for producing the polyamic acid, a known method can be used. Usually, at least one aromatic dianhydride and at least one diamine are dissolved in a substantially equimolar amount in an organic solvent, The obtained polyamic acid organic solvent solution is produced by stirring under controlled temperature conditions until polymerization of the acid dianhydride and diamine is completed. Any known method can be used as the polymerization method.

  A well-known method can be used about the method of manufacturing a polyimide film from these polyamic-acid solutions. This method includes a thermal imidization method and a chemical imidization method. The chemical curing method comprises a polyamic acid organic solvent solution, a dehydrating agent typified by an acid anhydride such as acetic anhydride, an imidation catalyst typified by a tertiary amine such as isoquinoline, β-picoline, and pyridine. It is a method of acting. A thermal imidization method may be used in combination with the chemical imidization method.

  Next, a method for producing the polymer graphite sheet used in the present invention will be described. The polymer graphite sheet can be produced by subjecting a polymer film to a heat treatment and passing through carbonization and graphitization processes. Hereinafter, specific production examples will be described.

  First, a polymer film as a raw material is carbonized by preheating, for example, in an inert gas, preferably in a nitrogen gas, to prepare a carbonized film. Preheating is usually performed at a temperature of about 1000 ° C. In the preheating stage, it is effective to apply a pressure in the plane direction so that the film does not break so that the orientation of the polymer film as a raw material is not lost.

  Next, the carbonized film obtained by the above method is set in a horizontal ultrahigh temperature furnace using, for example, a graphite heater, and graphitized. Graphitization is preferably carried out in an inert gas, but argon is most suitable as the inert gas, and it is more preferable to add a small amount of helium to the argon. The treatment temperature is preferably 2400 ° C. or higher, and more preferably 2700 ° C. or higher, in that a purer graphite sheet can be obtained. In order to create an extremely high temperature of 2400 ° C. or higher, an electric current is usually passed directly to a graphite heater, and heating is performed using the juule heat.

  Graphitization occurs by converting a carbonized film produced by carbonization by preheating to a graphite structure, but in order to cause graphitization smoothly, carbon-carbon bond cleavage and recombination occur with minimal energy. It is preferable to set such conditions. The molecular orientation of the polymer film as a raw material affects the carbon arrangement of the carbonized film, and the carbon arrangement has the effect of reducing the energy of carbon-carbon bond cleavage and recombination during graphitization. Therefore, by designing the molecules so that the molecules of the polymer film as a raw material are highly oriented, it becomes possible to graphitize at a low temperature and to produce a high-quality graphite sheet.

  The composite method with the reflective film of the present invention will be described below. As a method for combining the reflective film and the graphite sheet, there is a method in which the reflective film and the graphite sheet are mechanically contacted by directly caulking the liquid crystal display device, the LED, the light guide plate, the reflective film, and the graphite sheet with a casing. In this case, however, an air layer is interposed between the reflective film and the graphite sheet, which may cause a large thermal resistance. When the air layer is interposed, the amount of heat transferred from the LED to the graphite sheet is reduced, and thus the LED temperature rise suppressing effect is reduced.

  Next, conjugation through an adhesive layer is conceivable. Examples of the material for the adhesive layer include acrylic, silicone, epoxy, and polyimide resins. In order to cope with use in a narrow space, the thickness range is preferably 30 μm or less, more preferably 20 μm or less, and most preferably 10 μm or less. When the adhesive layer is interposed, there is almost no air layer between the reflective film and the graphite sheet, but the thermal conductivity of the adhesive layer is very small compared to the thermal conductivity in the surface direction of graphite (usually 0.1 to 1 W). Therefore, when bonded using an adhesive layer with the same thickness as the graphite layer, the apparent thermal conductivity is actually reduced to half the value of the thermal conductivity of the graphite layer used. To do. For example, when a graphite sheet with a thermal conductivity of 800 W / m · K and a thickness of 40 μm is joined via a 40 μm adhesive layer, it is the same as when a graphite layer with a thickness of 80 μm and a thermal conductivity of 400 W / m · K is joined directly. Only the effect will be obtained. However, if the thickness of the pressure-sensitive adhesive layer is made as thin as possible, the decrease in thermal conductivity due to the presence of the adhesive layer can be minimized. For this reason as well, when joining the graphite sheet using the adhesive layer, it is preferable to make the thickness of the adhesive layer as thin as possible.

  It is known that the adhesive strength becomes smaller as the adhesive layer becomes thinner, but in the case of the present invention, it is also possible to reinforce the adhesive strength by caulking the graphite sheet joined to the reflective film with a casing, It is possible to achieve a sufficient adhesive force even with an adhesive layer having a low adhesive strength. Covering the entire liquid crystal display device of the present invention with a casing of aluminum or galvanized steel sheet described in Patent Document 1 is also preferable in terms of further enhancing the heat dissipation effect of the LED.

  As another method, there is a method in which a polyethylene terephthalate layer is coated on the surface of a graphite sheet by a method such as vapor deposition and coating, and then a polyethylene terephthalate layer is vapor-deposited in aluminum to produce a composite reflective film.

  When combining a reflective film and a graphite sheet, it is preferable that the reflective film and the graphite sheet have the same size as much as possible. For example, even if the graphite sheet is bonded only to a portion close to the LED, an LED temperature rise suppressing effect appears. Therefore, the size of the graphite sheet to be joined may be changed according to the installation situation.

  In addition, the insulation process at the time of using as a liquid crystal display element is demonstrated below. Since the graphite sheet has electrical conductivity, in order to use it in an electronic device, it is common to form a protective film layer, that is, an insulating layer on the surface for the purpose of preventing a short circuit due to contact with a component. In the composite reflective film of the present invention, when the graphite sheet is exposed inside the device, it is better to provide a protective film layer on the graphite. The protective film is preferably a tape in which an acrylic, silicone, epoxy, or polyimide adhesive or adhesive is formed on one side of a film such as polyimide, polyethylene terephthalate, polyethylene, polypropylene, or polyester. Further, it may be a hot melt type (thermoplastic) tape such as polyester.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
(Method for producing graphite sheet A)
In a DMF (dimethylformamide) solution in which 1 equivalent of 4,4′-oxydianiline was dissolved, 1 equivalent of pyromellitic dianhydride was dissolved to obtain a polyamic acid solution (18.5 wt%). While this solution was cooled, an imidation catalyst containing 1 equivalent of acetic anhydride, 1 equivalent of isoquinoline, and DMF was added to the carboxylic acid group contained in the polyamic acid to degas. Next, this mixed solution was applied onto an aluminum foil so as to have a predetermined thickness after drying. The mixed solution layer on the aluminum foil was dried at 120 ° C. for 240 seconds using a hot air oven and a far-infrared heater to obtain a gel film having self-supporting properties. The gel film was peeled off from the aluminum foil and fixed to the frame. Further, the gel film was heated stepwise in a hot air oven at 120 ° C. for 30 seconds, 275 ° C. for 40 seconds, 400 ° C. for 43 seconds, 450 ° C. for 50 seconds, and a far infrared heater at 460 ° C. for 23 seconds. And dried. As described above, a polyimide film A having a thickness of 75 μm (elasticity 3.1 GPa, water absorption 2.5%, birefringence 0.10, linear expansion coefficient 3.0 × 10 ⁻⁵ / ° C.) was produced.

Next, a 75 μm-thick polyimide film A is sandwiched between graphite plates, heated to 1000 ° C. in a nitrogen atmosphere using an electric furnace, and then heat-treated at 1000 ° C. for 1 hour for carbonization (carbonization treatment). I did it. This carbonized film was designated as carbonized film A. Subsequently, the obtained carbonized film A of 200 mm × 200 mm was sandwiched from above and below by plate-like smooth graphite of 270 mm × 270 mm × 3 mm, and heated to 3000 ° C. in a 300 mm × 300 mm × 60 mm graphite container, Graphite was produced. The graphite after heat treatment was compressed in the thickness direction with a press machine (product number NSF-50 type) manufactured by Shindo Metal Industry Co., Ltd. to obtain a graphite sheet A having a thickness of 40 μm.
(Method for producing graphite sheet B)
A graphite sheet B having a thickness of 25 μm was produced in the same manner as the graphite sheet A except that a polyimide film having a thickness of 50 μm was used instead of a thickness of 75 μm as a starting film material.
(Graphite sheet C)
The graphite sheet C is a graphite sheet (λ70 μm product) manufactured by Geltech Co., Ltd.
(Measurement of thermal conductivity of graphite sheet)
The thermal conductivity of the above graphite sheets A and B was calculated from the following equation (1).

λ = α × d × Cp (1)
In Equation (1), λ represents thermal conductivity, α represents thermal diffusivity, d represents density, and Cp represents specific heat capacity. In addition, the thermal diffusivity, density, and specific heat capacity of a graphite sheet can be calculated | required by the method shown below.
(Measurement of thermal diffusivity in the film surface direction by the optical AC method)
The progress of graphitization was determined by measuring the thermal diffusivity in the film surface direction. The higher the thermal diffusivity, the more remarkable the graphitization. The thermal diffusivity was measured at 10 Hz in an atmosphere of 20 ° C. by cutting a graphite sheet into a 4 × 40 mm sample shape using a thermal diffusivity measuring device (LaserPit) manufactured by ULVAC-RIKO Co., Ltd. using an optical alternating current method. .
(Density measurement of graphite sheet)
The density of the graphite sheet was calculated by dividing the weight (g) of the graphite sheet by the volume (cm ³ ) calculated by the product of the vertical, horizontal and thickness of the graphite sheet. In addition, the average value measured by arbitrary 10 points | pieces was used for the thickness of a graphite sheet. The higher the density, the more remarkable the graphitization.
(Measurement of graphite sheet thickness)
As a method for measuring the thickness of the graphite sheet, a film of 50 mm × 50 mm was measured using a thickness gauge (HEIDENHAIN-CERTO) manufactured by HEIDENHAIN Co., Ltd., at a room temperature of 25 ° C., at any 10 points, The average was taken as the measured value.
(Specific heat measurement of graphite sheet)
The specific heat of the graphite sheet was measured using a differential scanning calorimeter (DSC220CU) manufactured by SII Nano Technology Co., Ltd. under a temperature rising condition of 10 ° C./min from 20 ° C. to 260 ° C. The value shown in the table is the specific heat at 50 ° C. In addition, about the specific heat of the graphite sheet C, the catalog value was applied.

  Table 1 shows the thermal diffusivity, density, thickness, specific heat, and thermal conductivity of graphite sheets A, B, and C obtained by the above method.

（実施例１）
図２を参照して幅６０ｍｍ×４０ｍｍの液晶表示装置の反射フィルム背面に幅６０ｍｍ×４０ｍｍ×厚み１０μｍのアクリル系接着剤(寺岡製作所製５６０１)を介して幅６０ｍｍ×４０ｍｍ×厚み４０μｍグラファイトシートＡが接続されている。この液晶表示装置を厚み０．２ｍｍのアルミニウム製筐体で覆い、ＬＥＤに５０ｍＷの出力を与え、定常状態になった時の画面表面の温度Ｔ_Ｈ１〜Ｔ_Ｈ１１を測定した。温度測定には熱電対を用いて行ない、測定は大気圧下２３℃で行なった。なお、測定点はＰ_１を原点として、Ｐ_２：５ｍｍ、Ｐ_３：１０ｍｍ、Ｐ_４：１５ｍｍ、Ｐ_５：２０ｍｍ、Ｐ_６：２５ｍｍ、Ｐ_７：３０ｍｍ、Ｐ_８：３５ｍｍ、Ｐ_９：４０ｍｍ、Ｐ_１０：４５ｍｍ、Ｐ_１１：５０ｍｍの距離である。結果を表２に示した。

Example 1
Referring to FIG. 2, 60 mm × 40 mm × 40 μm thick graphite sheet A is placed on the back surface of a reflective film of a liquid crystal display device having a width of 60 mm × 40 mm through an acrylic adhesive (5601 manufactured by Teraoka Seisakusho) having a width of 60 mm × 40 mm × thickness 10 μm. Is connected. The liquid crystal display device was covered with an aluminum casing having a thickness of 0.2 mm, an output of 50 mW was applied to the LED, and the temperatures T _{H1 to} T _H11 of the screen surface when the steady state was reached were measured. The temperature was measured using a thermocouple, and the measurement was performed at 23 ° C. under atmospheric pressure. The measurement point as origin _{P 1, P 2: 5mm,} P 3: 10mm, P 4: 15mm, P 5: 20mm, P 6: 25mm, P 7: 30mm, P 8: 35mm, P 9: 40mm , P ₁₀ : 45 mm, P ₁₁ : 50 mm. The results are shown in Table 2.

（実施例２）
図３を参照して幅６０ｍｍ×４０ｍｍの液晶表示装置の反射フィルム背面に幅６０ｍｍ×４０ｍｍ×厚み１０μｍのアクリル系接着剤(寺岡製作所製５６０１)を介して幅６０ｍｍ×４０ｍｍ×厚み２５μｍのグラファイトシートＢが接続されている。この液晶表示装置を厚み０．２ｍｍのアルミニウム製筐体で覆い、ＬＥＤに５０ｍＷの出力を与え、定常状態になった時の画面表面の温度Ｐ_Ｐ１〜Ｐ_Ｐ１１を測定した。温度測定には熱電対を用いて行ない、測定は大気圧下２３℃で行なった。なお、測定点はＰ_１を原点として、Ｐ_２：５ｍｍ、Ｐ_３：１０ｍｍ、Ｐ_４：１５ｍｍ、Ｐ_５：２０ｍｍ、Ｐ_６：２５ｍｍ、Ｐ_７：３０ｍｍ、Ｐ_８：３５ｍｍ、Ｐ_９：４０ｍｍ、Ｐ_１０：４５ｍｍ、Ｐ_１１：５０ｍｍの距離である。結果を表２に示した。

(Example 2)
Referring to FIG. 3, a graphite sheet having a width of 60 mm × 40 mm and a thickness of 25 μm is provided on the back surface of a reflective film of a liquid crystal display device having a width of 60 mm × 40 mm via an acrylic adhesive (5601 manufactured by Teraoka Seisakusho) having a width of 60 mm × 40 mm × 10 μm. B is connected. This liquid crystal display device was covered with an aluminum casing having a thickness of 0.2 mm, an output of 50 mW was given to the LED, and the temperatures P _{P1 to} P _P11 of the screen surface when the steady state was reached were measured. The temperature was measured using a thermocouple, and the measurement was performed at 23 ° C. under atmospheric pressure. The measurement point as origin _{P 1, P 2: 5mm,} P 3: 10mm, P 4: 15mm, P 5: 20mm, P 6: 25mm, P 7: 30mm, P 8: 35mm, P 9: 40mm , P ₁₀ : 45 mm, P ₁₁ : 50 mm. The results are shown in Table 2.

(Comparative Example 1)
Referring to FIG. 4, the temperature T _H1 of the screen surface when the output of 50 mW is applied to the LED of the liquid crystal display device having a width of 60 mm × 40 mm covered with the aluminum casing having a thickness of 0.2 mm and the steady state is reached. ~ _TH11 was measured. The temperature was measured using a thermocouple, and the measurement was performed at 23 ° C. under atmospheric pressure. The measurement point as origin _{P 1, P 2: 5mm,} P 3: 10mm, P 4: 15mm, P 5: 20mm, P 6: 25mm, P 7: 30mm, P 8: 35mm, P 9: 40mm , P ₁₀ : 45 mm, P ₁₁ : 50 mm. The results are shown in Table 2.

  The results of Example 1 and Comparative Example 1 are summarized in FIG. By joining the graphite sheet A to the reflective film, the heat spots appearing around the LEDs were alleviated, and the temperature unevenness in the screen was also suppressed.

(Comparative Example 2)
Referring to FIG. 5, in addition to the configuration of Example 1, a polyester foam having a width of 60 mm × 40 mm × thickness of 200 μm was sandwiched between the light guide plate and the reflective film. An output of 50 mW was given to the LED, and the temperatures P _{P1 to} P _P11 on the screen surface when the steady state was reached were measured. The temperature was measured using a thermocouple, and the measurement was performed at 23 ° C. under atmospheric pressure. The measurement point as origin _{P 1, P 2: 5mm,} P 3: 10mm, P 4: 15mm, P 5: 20mm, P 6: 25mm, P 7: 30mm, P 8: 35mm, P 9: 40mm , P ₁₀ : 45 mm, P ₁₁ : 50 mm. The results are shown in Table 2.

  The results of Example 1 and Comparative Example 2 are summarized in FIG. When a 200 μm polyester foam was interposed between the reflective film and the light guide plate, the effect of joining the graphite sheets was significantly lost.

(Comparative Example 3)
Referring to FIG. 6, in addition to the configuration of Example 1, instead of graphite sheet A, a graphite sheet C having a width of 60 mm × 40 mm × thickness of 70 μm and an acrylic adhesive having a width of 60 mm × 40 mm × thickness of 10 μm (5601 manufactured by Teraoka Seisakusho) It was made to join to a reflective film via. An output of 50 mW was given to the LED, and the temperatures P _{P1 to} P _P11 on the screen surface when the steady state was reached were measured. The temperature was measured using a thermocouple, and the measurement was performed at 23 ° C. under atmospheric pressure. The measurement point as origin _{P 1, P 2: 5mm,} P 3: 10mm, P 4: 15mm, P 5: 20mm, P 6: 25mm, P 7: 30mm, P 8: 35mm, P 9: 40mm , P ₁₀ : 45 mm, P ₁₁ : 50 mm. The results are shown in Table 2.

  The results of Example 1 and Comparative Example 3 are summarized in FIG. When the expanded graphite sheet was used, sufficient heat spot suppression effect and temperature unevenness suppression effect could not be obtained.

It is the schematic which shows an example of the composite reflective film concerning this invention, and a liquid crystal display device. It is the schematic which shows the further another example of the composite reflective film concerning this invention, and a liquid crystal display device. It is the schematic which shows the further another example of the composite reflective film concerning this invention, and a liquid crystal display device. It is the schematic which shows an example of a typical liquid crystal display device. It is the schematic which shows an example of a typical liquid crystal display device. It is the schematic which shows an example of a typical liquid crystal display device. 4 is a graph showing temperature distribution on the screen surface in Example 1 and Comparative Example 1. 6 is a graph showing temperature distribution on the screen surface in Example 1 and Comparative Example 2. 6 is a graph showing temperature distribution on the screen surface in Example 1 and Comparative Example 3.

Explanation of symbols

1 LCD panel 2 LED
3 Light guide plate 4 Reflective film 5 Graphite sheet A
6 Aluminum cover 7 Acrylic adhesive 8 Graphite sheet B
9 Foamed polyester 10 Graphite sheet C

Claims (6)

  A composite comprising a polymer graphite sheet obtained by heat-treating a polymer film on one side of a reflective film having a thickness of 30 μm to 60 μm and a specific gravity of 1.0 to 1.4 Reflective film.   The composite reflective film according to claim 1, wherein aluminum or silver is vapor-deposited on one side or both sides of the reflective film.   The composite reflective film according to claim 1, wherein the reflective film is made of at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, and acrylic.   The composite according to any one of claims 1 to 3, wherein the graphite sheet has a thermal conductivity in a planar direction of 600 W / m · K to 1800 W / m · K and a thickness of 10 µm to 50 µm. Reflective film.   The liquid crystal display device which has a composite reflective film in any one of Claims 1-4.   6. The liquid crystal display device according to claim 5, wherein a liquid crystal display panel, a light guide plate, a reflective film, and graphite are laminated in this order.

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