JP2010073476A - Backlight unit, and liquid crystal display provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device maintaining uniform display performance in a display screen, by uniformizing heat amount distribution emitted from a light source of a backlight in a plane on a light-emitting side, and to provide a liquid crystal display provided with the device. <P>SOLUTION: The backlight unit 10 includes the light source 11, and a light guide member 15 for guiding light from the light source 11 and emitting a planar light. A translucent thermal diffusion sheet 21 is arranged so as to cover an entire emission surface 15b, in front of the optical path of the emission surface 15b of the light guide member 15 for emitting the planar light. The liquid crystal display 100 is constituted of the backlight unit 10, and a liquid crystal panel 20 arranged on a light-emitting side of the backlight unit 10, and having a liquid crystal cell 20 with polarizing plates arranged on the front and back surfaces. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a backlight unit and a liquid crystal display device including the backlight unit.

  With the recent increase in the screen size of liquid crystal display devices, the demand for display quality has become increasingly severe. In a liquid crystal display device, since the optical characteristics of various optical sheets change depending on temperature, the display screen may change due to environmental temperature or change over time, and its behavior has begun to be regarded as important. A liquid crystal display device is configured by arranging a backlight unit having a cold cathode ray tube, a light emitting diode (LED), or the like as a light source on the back of a liquid crystal panel having liquid crystal cells. In this liquid crystal display device, the heat generated from the light source of the backlight unit (including heat transfer between the members and the heat ray (infrared) component contained in the light source light) is transmitted to the liquid crystal panel, and the liquid crystal panel has a local temperature. Generate a distribution. Then, white display spots and color unevenness are displayed on the display surface of the liquid crystal panel in a strip shape or a diagonal shape, and the display quality of the liquid crystal display device is degraded. This phenomenon is particularly prominent in the case of a side-edge type backlight unit in which a light source is disposed on the side of the display surface to guide light to the entire display surface. Accordingly, various improvements have been made to reduce this temperature change.

  For example, Patent Document 1 discloses a configuration in which a high thermal conductivity sheet (polymer film) is provided on a polarizing plate provided on the front and back surfaces of a liquid crystal cell, and an optical compensation sheet disposed between the liquid crystal cell and the polarizing plate. The structure made into the adhesive sheet is described. However, even if a sheet with high thermal conductivity is placed in contact with the liquid crystal cell, the heat from the light source of the backlight unit is not sufficiently diffused, and the liquid crystal panel is still heated locally, affecting the optical characteristics. There was a thing.

  When a part of the liquid crystal panel is locally heated, the optical properties such as the heated polarizing plate and the retardation value of the optical compensation sheet change, causing light leakage and uneven color during black display. To do. Also, in the liquid crystal cell, the thermal expansion of the heated portion is larger than the thermal expansion of the non-heated portion, and the entire liquid crystal panel is subjected to local internal stress, which also changes the optical characteristics of various optical sheets. It was supposed to occur.

Further, as a technique for distributing heat not on the liquid crystal panel side but on the backlight unit side, for example, Patent Document 2 describes a configuration in which heat from a light source of the backlight unit is dispersed by a heat diffusion plate. However, this heat diffusion plate is made of an aluminum plate or a copper plate, and is laid on the bottom side of the backlight unit. Therefore, heat from the light source cannot be dispersed to the liquid crystal panel side, and changes in optical characteristics of each optical sheet of the liquid crystal panel cannot be prevented.
Japanese Patent Laid-Open No. 2002-40241 JP 2005-37814 A

  Therefore, the present invention is provided with a backlight device and a backlight device capable of keeping the display performance in the display screen uniform by making the distribution of heat emitted from the light source of the backlight uniform within the surface on the light emitting side. An object is to provide a liquid crystal display device.

The present invention has the following configuration.
(1) A backlight unit having a light source and a light guide member that guides light from the light source to emit planar light,
A backlight unit in which a light diffusing sheet having translucency is disposed so as to cover the entire emission surface in front of an optical path of an emission surface that emits planar light of the light guide member.

  According to this backlight unit, by disposing the heat diffusion sheet over the entire light emitting surface of the light guide member, the heat from the light source can be dispersed throughout the light emitting surface, and local temperature changes can occur. It is possible to make the configuration difficult to occur. In other words, the heat from the light source of the backlight can be dispersed by the heat diffusion sheet, and the entire surface of the light exit surface is made to have a uniform temperature distribution without locally applying heat from the light source to the surface light irradiation target. Can do.

(2) The backlight unit according to (1),
A backlight unit in which the thermal diffusion sheet includes highly thermally conductive particles in a resin sheet.

  According to this backlight unit, it is possible to easily obtain a heat diffusion sheet having a uniform thermal conductivity by dispersing the high thermal conductivity particles in the resin sheet.

(3) The backlight unit according to (1),
The backlight unit in which the thermal diffusion sheet has a thermal conductive layer containing highly thermal conductive particles on at least one surface of a resin sheet.

  According to this backlight unit, by forming a heat conductive layer containing high heat conductive particles on at least one surface of the resin sheet, a heat conductive layer can be provided in a post process on a resin sheet prepared in advance, It is divided and high efficiency is achieved. Moreover, the thermal conductivity of the thermal diffusion sheet can be appropriately adjusted by changing the thickness of the thermal conductive layer.

(4) The backlight unit according to (2) or (3),
The backlight unit in which the high thermal conductivity particles include one of aluminum nitride and an indium compound.

  According to this backlight unit, high thermal conductivity can be obtained in a small amount by using aluminum nitride and an indium compound for the high thermal conductivity particles.

(5) The backlight unit according to (1),
The backlight unit, wherein the thermal diffusion sheet has a high thermal conductive thin film on at least one side of a resin sheet.

  According to this backlight unit, by forming a highly thermally conductive thin film, the film thickness can be easily controlled, and the thermal conductivity can be set with high accuracy.

(6) The backlight unit according to any one of (2) to (5),
The backlight unit in which the resin sheet contains triacetylcellulose, acrylic, or polyethylene terephthalate as a main component.

  According to this backlight unit, the resin sheet can be configured using a high-functional material that is industrially supplied at low cost.

(7) The backlight unit according to any one of (1) to (6),
A backlight unit in which the thermal diffusion sheet has a thermal conductivity of 1 to 10 W / (m · K).

  According to this backlight unit, heat dispersion from the light source is improved by setting the thermal conductivity in the above range.

(8) The backlight unit according to any one of (1) to (7),
A backlight unit in which the light source is disposed at at least one side end of the light guide member.

  According to this backlight unit, when the light source is a side-edge type arranged at the side end of the light guide member, the heat from the light source tends to increase locally, Dispersing throughout makes it difficult for local temperature changes to occur.

(9) The backlight unit according to (8),
A backlight unit in which an outer edge portion of the heat diffusion sheet is in contact with a rear casing of the backlight unit.

  According to this backlight unit, the heat transferred to the heat diffusion sheet can be quickly removed by bringing the outer edge portion of the heat diffusion sheet into contact with the rear casing, so that a uniform temperature distribution can be obtained. .

(10) The backlight unit according to any one of (1) to (9);
A liquid crystal panel having a liquid crystal cell disposed on the light emitting side of the backlight unit and having polarizing plates disposed on the front and back surfaces;
A liquid crystal display device.

  According to this liquid crystal display device, it is possible to prevent the optical characteristics (eg, retardation value) of the polarizing plate of the liquid crystal panel from changing in temperature by preventing the heat generated from the light source from being locally transmitted to the liquid crystal panel. Can be prevented. Thereby, display quality is improved without causing display unevenness on the display screen due to the elapsed time from the start of lighting of the light source.

  According to the backlight unit of the present invention and the liquid crystal display device including the backlight unit, the heat quantity distribution emitted from the light source of the backlight is made uniform in the plane on the light emission side, and the display performance in the display screen is made uniform. Can be kept in.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram of a main part of a liquid crystal display device for explaining an embodiment of the present invention.
As shown in the figure, the liquid crystal display device 100 includes a backlight unit 10 and a liquid crystal panel 20. The backlight unit 10 includes a light source 11 such as a cold cathode ray tube or an LED element, a reflector 13 that covers the light source 11, and light from the light source 11 is reflected directly or by the reflector 13 and is input to the side light incident surface 15a. Further, a prism sheet 17 having a triangular prism array formed on one surface, a light diffusing sheet 19, and a heat diffusion member are provided on the light emitting surface 15b side of the light guiding member 15. Sheets 21 are stacked in this order. In addition, a metal rear casing 23 is disposed on the opposite side of the light guide member 15 from the light emitting side 15b, and the inner surface of the rear casing 23 is mirror-finished or painted white to function as a reflector with high reflectivity. To do. The prism sheet 17 and the light diffusing sheet 21 are not limited to the number in the illustrated example, and can be appropriately changed such that an arbitrary number is installed.

  The light guide member 15 is made of a translucent resin material, and a triangular prism array arranged in a direction orthogonal to the arrangement direction of the triangular prism array of the prism sheet 17 is formed on the back surface 15c opposite to the light emitting surface 15b. Has been. In the illustrated example, the light source 11 is disposed on one side surface of the light guide member 15, but the light source 11 may be disposed on both side surfaces of the light guide member 15.

  The light guide member 15 and the triangular prism array of the prism sheet 17 are not limited to this, and an appropriate prism shape such as a quadrangular pyramid or a trapezoidal cross section is applicable.

  As shown in FIG. 2A, the thermal diffusion sheet 21 includes a thermal diffusion sheet 21A including high thermal conductivity particles in the resin sheet, and a thermal conductive layer including high thermal conductivity particles as illustrated in FIG. 2B. 25 is provided on one side (or both sides) of the resin sheet 27 having translucency, or as shown in FIG. 2C, the high thermal conductive thin film 29 is applied to the resin sheet having translucency. The thermal diffusion sheet 21 </ b> C on one side (or both sides) can be used. In addition, the density of the high thermal conductivity particles and the thickness of the high thermal conductivity thin film are adjusted so that the thermal conductivity of each of the thermal diffusion sheets 21A, 21B, and 21C is in the range of 1 to 10 W / (m · K). ing. The thermal conductivity of the thermal diffusion sheet 21 is required to be higher than that of the protective film of the polarizing plate, and the thermal conductivity of the commonly used protective film is 0.17 to 0.33 W / ( m · K), it is desirable to set the above thermal conductivity range. The thermal conductivity can be measured with a thermal conductivity measuring device such as UNITHERM2021 (manufactured by ANTER, disc heat flow meter ASTM E1530 compliant). Moreover, a thermal expansion coefficient can be measured with linear thermal expansion coefficient measuring apparatuses, such as SL-2000M (made by Shinagawa white brick company).

  By disposing the heat diffusion sheet 21 (21A, 21B, 21C) over the entire light emission side of the backlight unit 10, heat generated from the light source 11 is dispersed, and the side of the liquid crystal panel 20 near the light source 11 is locally increased. It can prevent warming. As shown in FIG. 3, the outer edge portion 21 a of the thermal diffusion sheet 21 is held in contact with the rear casing 23 of the backlight unit 10, thereby transferring heat to the rear casing 23. That is, the rear casing 23 functions as a heat sink, so that heat can be dispersed and dissipated more quickly and reliably.

Here, the thermal diffusion sheets 21A and 21B shown in FIGS. 2 (a) and 2 (b) will be described.
As the high thermal conductivity particles, various high thermal conductivity particles can be used in order to improve the thermal conductivity of the resin sheet. For example, aluminum nitride and an indium compound are preferably used. In addition, silicon nitride, boron nitride, magnesium nitride, silicon carbide, aluminum oxide, silicon oxide, zinc oxide, magnesium oxide, carbon, diamond, metal, and the like can be used. Moreover, in order not to impair the transparency of the resin sheet, it is desirable to use transparent particles. When a cellulose acetate film is used as the resin sheet, the blending amount of the high thermal conductivity particles is preferably 5 to 100 parts by mass with respect to 100 parts by mass of cellulose acetate. When the blending amount is less than 5 parts by mass, improvement in heat conduction is poor, and filling exceeding 50 parts by mass is difficult in terms of productivity and the cellulose acetate film becomes brittle. The average particle size of the high thermal conductivity particles is 0.05 to 80 μm, preferably 0.1 to 10 μm. Spherical particles may be used, or acicular particles may be used.

  As the resin sheet, it is preferable to use a polymer film having a light transmittance of 80% or more. Examples of polymer films include cellulose polymers, norbornene polymers such as trade name Arton (manufactured by JSR Co., Ltd.) and trade name Zeonex (manufactured by Nippon Zeon Co., Ltd.), polymethyl methacrylate, acrylic resin, polyethylene terephthalate, Examples include polycarbonate. As the cellulose polymer, a cellulose ester is preferable, and a lower fatty acid ester of cellulose is more preferable. Lower fatty acid means a fatty acid having 6 or less carbon atoms. The number of carbon atoms is preferably 2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulose butyrate). Cellulose acetate is preferred as the cellulose ester, and examples thereof include diacetyl cellulose and triacetyl cellulose. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used.

  Further, the viscosity average degree of polymerization (DP) of the resin sheet is preferably 250 or more, and more preferably 290 or more. The resin sheet preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.3 to 1.65, and most preferably 1.4 to 1.6. preferable. As the resin sheet used here, a cellulose acetate film having an acetylation degree of 59.0 to 61.5% is preferably used. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).

[Manufacture of thermal diffusion sheet]
Hereinafter, the case where a cellulose acetate film is used as a base sheet of a thermal diffusion sheet will be specifically described. It is preferable to produce a cellulose acetate film by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose acetate is dissolved in an organic solvent. The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain. The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

  Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogenated hydrocarbon hydrogen atoms substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a representative halogenated hydrocarbon. Two or more organic solvents may be mixed and used.

  A cellulose acetate solution can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent. The amount of cellulose acetate is adjusted so that it is contained in an amount of 10 to 40% by mass in the resulting solution. The amount of cellulose acetate is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent). The solution can be prepared by stirring cellulose acetate and an organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, cellulose acetate and an organic solvent are placed in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 110 ° C.

  Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure. When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid. It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall. Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

  A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose acetate with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method. In the cooling dissolution method, first, cellulose acetate is gradually added to an organic solvent with stirring at room temperature. The amount of cellulose acetate is preferably adjusted so as to be contained in the mixture at 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

  The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of cellulose acetate and organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

  Furthermore, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), cellulose acetate is dissolved in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath. The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. . A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

  In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container. In addition, according to differential scanning calorimetry (DSC), a 20 mass% solution obtained by dissolving cellulose acetate (acetylation degree: 60.9%, viscosity average polymerization degree: 299) in methyl acetate by a cooling dissolution method was 33. There exists a quasi-phase transition point between a sol state and a gel state in the vicinity of ° C., and a uniform gel state is obtained below this temperature. Therefore, this solution needs to be stored at a temperature equal to or higher than the pseudo phase transition temperature, preferably about the gel phase transition temperature plus about 10 ° C. However, this pseudo phase transition temperature varies depending on the degree of acetylation of cellulose acetate, the degree of viscosity average polymerization, the concentration of the solution, and the organic solvent used.

  A cellulose acetate film is produced from the prepared cellulose acetate solution (dope) by a solvent cast method. At that time, in order to control the thermal conductivity of the cellulose acetate film, highly thermally conductive particles are added to the dope. Moreover, it is preferable to add a retardation increasing agent to the dope.

  As described above, in order to control the thermal conductivity, as shown in FIG. 2 (b), the thermal conductive layer 25 containing highly thermal conductive particles is provided on at least one surface of the resin sheet (cellulose acetate film) 27. It may be provided separately. The heat conductive layer 25 may be provided by co-casting a polymer containing highly heat conductive particles with cellulose acetate, or may be provided by applying to a cellulose acetate film.

  The dope is cast on a drum or band and the solvent is evaporated to form a sheet. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. The casting and drying methods in the solvent casting method are described in U.S. Pat. Nos. 2,336,310, 2,367,603, 2,429,078, 2,429,297, 2,429,978, 2,607,704, 2,739,69, British Patent 6,407,331, No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained sheet can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

  A plasticizer can be added to the cellulose acetate film in order to improve mechanical properties or increase the drying rate. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred. The addition amount of the plasticizer is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass of the amount of the cellulose ester.

  A degradation inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the cellulose acetate film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by mass of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by mass. When the addition amount is less than 0.01% by mass, the effect of the deterioration preventing agent is hardly recognized. When the added amount exceeds 1% by mass, bleeding-out (bleeding) of the deterioration preventing agent to the film surface may be observed. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

Next, the thermal diffusion sheet 21C shown in FIG.
The thermal diffusion sheet 21 </ b> C uses the cellulose acetate film described above as the resin sheet 27, and the high thermal conductive thin film 29 is formed on at least one surface of the resin sheet 27. As the material of the high thermal conductive thin film 29, aluminum oxide or aluminum nitride can be used. The high thermal conductive thin film 29 is a thin film formed by a publicly known and broadly defined vacuum thin film manufacturing technique such as a vacuum vapor deposition method, a reactive vapor deposition method, a sputtering method, or a plasma CVD method. According to this thermal diffusion sheet 21C, the thickness of the high thermal conductive thin film 29 can be uniformly formed with high accuracy, and a desired thermal conductivity can be reliably obtained.

  In addition, when using the thermal diffusion sheet 21 as a transparent protective film such as the light diffusion sheet 19, it is preferable to subject the thermal diffusion sheet 21 to a surface treatment. As the surface treatment, corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment or ultraviolet irradiation treatment is performed. It is particularly preferable that the acid treatment or the alkali treatment, that is, the saponification treatment is performed on the heat diffusion sheet 21.

  As described above, according to the backlight unit 10, the heat distribution in the backlight unit 10 can be made uniform even when compared with the conventional configuration in which a heat dissipation mechanism is provided in the light source device, and the light emission The heat distribution at the time can be made more uniform. Thereby, when irradiating light to the liquid crystal panel 20, giving a local heat distribution with respect to the liquid crystal panel 20 is prevented. Moreover, it is only necessary to provide the thermal diffusion sheet 21 at the top of the backlight unit 10, and the thermal diffusion sheet 21 can be easily installed. The arrangement position of the heat diffusion sheet 21 is not limited to the configuration shown in FIG. 1, and may be any position as long as it is in front of the light path of the light emitting surface 15 b of the light guide member 15. In addition to the side edge type backlight unit, the heat distribution is made uniform in the same manner as described above for a direct type backlight unit in which a plurality of cold cathode ray tubes and LEDs are arranged on the back surface of the liquid crystal panel. The effect is demonstrated.

<Verification of effects>
FIG. 4 is an explanatory view showing a temperature change after lighting the light source of the side edge type backlight unit not including the heat diffusion sheet, (a) shows the temperature measurement position of the backlight unit, and (b) shows the elapsed time. A graph of temperature change is shown. The backlight unit used in the experiment is a backlight unit for a 17-inch liquid crystal display device, and is a side edge type in which light sources are arranged on both sides of the screen.
In this backlight unit, after the light source is turned on, the temperature starts to rise from a room temperature of about 25 ° C., and the positions of the upper left P1 and lower right P2 of the screen, which are the light exit surfaces, are close to the light source. The heating rate is faster than the position P3. When 30 minutes have elapsed since lighting, the temperature difference ΔT between the positions of the screen ends P1, P2 and the position of the screen center P3 is about 10 ° C. On the other hand, according to the configuration of the backlight unit 10 shown in FIG. 1, the temperature difference ΔT can be suppressed to about 5 ° C., and light leakage during black display on the display screen can be achieved even when assembled in a liquid crystal display device. In addition, image defects such as white display spots and uneven color were not visually recognized.

It is a principal part cross-section block diagram of the liquid crystal display device for describing one Embodiment of this invention. It is sectional drawing of a thermal diffusion sheet, Comprising: (a) is a thermal diffusion sheet which contains highly heat-conductive particle | grains in a resin sheet, (b) is a resin sheet which has a light-transmitting property about the heat conductive layer containing highly heat-conductive particle. (C) is sectional drawing of the thermal diffusion sheet which has a highly heat conductive thin film on the single side | surface (or both surfaces) of a translucent resin sheet. It is a partial cross section figure which shows a mode that the outer edge part of a thermal-diffusion sheet is hold | maintained in the state which contacted the rear casing of the backlight unit. It is explanatory drawing which shows the temperature change after the light source lighting of the side edge type backlight unit which does not contain a thermal diffusion sheet, (a) shows the temperature measurement position of a backlight unit, (b) shows the temperature change with elapsed time. It is a graph to show.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Backlight unit 11 Light source 15 Light guide member 15a Light incident surface 15b Light output surface 17 Prism sheet 19 Light diffusion sheet 20 Liquid crystal panel 21 Thermal diffusion sheet 21A Thermal diffusion sheet 21B Thermal diffusion sheet 21C Thermal diffusion sheet 23 Rear casing 25 Thermal conduction Layer 27 Resin sheet 29 High thermal conductive thin film 100 Liquid crystal display device

Claims (10)

A backlight unit having a light source and a light guide member that guides light from the light source and emits planar light,
A backlight unit in which a light diffusing sheet having translucency is disposed so as to cover the entire emission surface in front of an optical path of an emission surface that emits planar light of the light guide member. The backlight unit according to claim 1,
A backlight unit in which the thermal diffusion sheet includes highly thermally conductive particles in a resin sheet. The backlight unit according to claim 1,
The backlight unit in which the thermal diffusion sheet has a thermal conductive layer containing highly thermal conductive particles on at least one surface of a resin sheet. The backlight unit according to any one of claims 2 and 3,
The backlight unit in which the high thermal conductivity particles include one of aluminum nitride and an indium compound. The backlight unit according to claim 1,
The backlight unit, wherein the thermal diffusion sheet has a high thermal conductive thin film on at least one side of a resin sheet. The backlight unit according to any one of claims 2 to 5,
The backlight unit in which the resin sheet contains triacetylcellulose, acrylic, or polyethylene terephthalate as a main component. The backlight unit according to any one of claims 1 to 6,
A backlight unit in which the thermal diffusion sheet has a thermal conductivity of 1 to 10 W / (m · K). The backlight unit according to any one of claims 1 to 7,
A backlight unit in which the light source is disposed at at least one side end of the light guide member. The backlight unit according to claim 8,
A backlight unit in which an outer edge portion of the heat diffusion sheet is in contact with a rear casing of the backlight unit. The backlight unit according to any one of claims 1 to 9, and
A liquid crystal panel having a liquid crystal cell disposed on the light emitting side of the backlight unit and having polarizing plates disposed on the front and back surfaces;
A liquid crystal display device.

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