KR20080077105A - Direct type backlight device - Google Patents

Abstract

Provided are a light diffusion plate and a direct type backlight device having improved luminance and luminance uniformity. A direct backlight unit comprising a plurality of linear light sources arranged in parallel, a reflecting plate for reflecting the light, and a light diffusing plate for diffusing and emitting direct and reflected light from the linear light source, wherein the light diffusing plate includes: And a substantially flat light incidence surface and a light emission surface for diffusing and exiting light incident from the light incidence surface, wherein the light emission surface extends substantially parallel to the longitudinal direction of the linear light source, A prism array having a plurality of linear prisms formed of concave or convex triangles, each of the two inclined surfaces of each of the linear prisms having the same angle as the light incident surface, and the position of the linear prism is As the distance from the linear light source closest to the linear prism increases, the angle increases continuously or stepwise Direct type backlight device.

Description

Direct type backlight unit {DIRECTLY-BELOW TYPE BACKLIGHT DEVICE}

The present invention relates to a direct type backlight device. More specifically, the present invention relates to a direct type backlight device having high luminance and high luminance uniformity ratio.

Background Art Conventionally, as a backlight device for a liquid crystal display, a device using a cold cathode tube as a light source is widely used, and there are a method called an edge light type and a method called a direct type. The edge light type is a device in which a cold cathode tube of a capillary tube is arranged at the end of the light guide plate, and light incident from the end surface is repeatedly reflected in the light guide plate and outputs to the main surface of the light guide plate. On the other hand, the direct type | mold apparatus consists of the structure which combined the plurality of cold cathode tubes arrange | positioned in parallel, the reflecting plate provided in the back of a cold cathode tube, and the light-diffusion plate which forms a light emitting surface. In contrast to the edge light type, this apparatus can increase the number of cold cathode tubes used, so that the light emitting surface can be easily made high.

However, the direct type backlight device has a problem that the luminance uniformity of the light emitting surface is bad. In particular, the periodic luminance unevenness generated due to the high luminance just above the cold cathode tube is a major problem. That is, since the luminance uniformity of the device light emitting surface is bad, display unevenness occurs on the display screen of the liquid crystal display.

In the direct backlight device, it is possible to improve the luminance uniformity by reducing the gap between the cold cathode tubes, but for this purpose, the number of cold cathode tubes must be increased, resulting in an increase in power consumption during lighting. In addition, although the brightness uniformity can be improved by increasing the distance between the cold cathode tube and the light diffusion plate, in this case, the device becomes thicker, and the thinning of the liquid crystal display could not be realized.

In addition, in order to improve the brightness uniformity, various measures have been conventionally taken. For example, a method of reducing the luminous flux radiated directly on the cold cathode tube by printing a stripe or dot shape light quantity correction pattern on the surface of the light diffusion plate (Patent Document 1: Japanese Patent Laid-Open No. 6-273760); Using a corrugated reflector, a method of converging the reflected light from the reflector into a region corresponding to the middle between the cold cathode tube and the neighboring cold cathode tube (Patent Document 2: Japanese Patent Laid-Open No. 2001-174813) has been proposed. .

However, as a means for improving the luminance uniformity, printing of the light quantity correction pattern cuts off a part of the light flux, so that the utilization rate of the light flux emitted by the cold cathode tube is lowered, resulting in a problem that sufficient luminance cannot be obtained. In addition, there is a problem that the configuration of the device becomes complicated when the waveform reflector is used.

In addition, although the material which disperse | distributed the light-diffusion agent to the transparent resin may be used for the light-diffusion plate used for a direct type | mold, the problem that a brightness will fall when the density | concentration of a light-diffusion agent is raised in order to improve the brightness uniformity is also a problem. There was. In order to solve this problem, it is proposed to form a prism shape or the like on the surface of the light diffusion plate and to have a diffusion effect by the surface shape without lowering the luminance (Patent Documents 3, 4 and 5, respectively). Japanese Patent Application Laid-Open No. 5-333333, Japanese Patent Application Laid-Open No. 8-297202, and Japanese Patent Application Laid-Open No. 2000-182418). However, the improvement of the brightness uniformity was not enough only by forming the prism shape pattern on the surface of the light diffusion plate.

Disclosure of the Invention

Problems to be Solved by the Invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a direct type backlight device having improved luminance and luminance uniformity.

Means to solve the problem

MEANS TO SOLVE THE PROBLEM As a result of carrying out detailed examination so that the said subject might be solved, surprisingly, in a direct backlight device, such as a direct backlight device, only by providing a cross-sectional sawtooth prism array in the light exit surface of a light-diffusion plate. Although the effect of improving the brightness uniformity is not sufficient, it has been found that by making the prism array into a specific shape, a device having high brightness and high brightness uniformity can be obtained, and thus, the present invention has been completed based on this knowledge.

Specifically, the prism array is formed such that the angle between the two inclined surfaces and the light incidence surface constituting the linear prism of the cross-sectional triangle shape is the same, and the angle between these inclined surfaces and the light incidence surface is the closest position. It has been found that by forming it so as to become larger as it moves away from the linear light source, it is possible to improve the luminance and the luminance uniformity.

That is, according to the present invention, the following is provided:

[1] a plurality of linear light sources arranged in parallel, a reflecting plate for reflecting light from the linear light source, and a light diffusing plate for diffusing and emitting direct light from the linear light source and the reflected light from the reflecting plate In one direct type backlight device, the light diffusing plate is provided on a substantially flat light incident surface for incident light from the linear light source and on a surface opposite to the light incident surface, and the light incident from the light incident surface. And a light exit surface for diffusing the light exit surface, the light exit surface extending substantially parallel to the longitudinal direction of the linear light source, and having a plurality of linear prisms formed of a concave or convex triangle in cross section. A prism array, the angle between each of the two inclined surfaces of each linear prism and the light incidence surface is the same; And the angle increases continuously or stepwise as the value moves away from the linear light source closest to the linear prism.

In this case, when the angle is continuously increased, the angle is increased for each linear prism. Incidentally, when the angle is increased stepwise, each region 1 in the case where the region 1 including a certain amount of linear prism and the region 2 adjacent to the side away from the linear light source in the region 1 are provided. , The angles of the linear prisms in 2 are equal to each other, and the angle of the linear prisms in the area 2 is larger than the angle of the linear prisms in the area 1.

[2] The direct type backlight device described in [1], wherein the light diffusing plate comprises a transparent resin, wherein an angle formed between each inclined surface of the arbitrary linear prism and the light incident surface is X (°). W (mm) is the distance between the vertex of the linear prism having the inclined surface and the position when the center of the linear light source at the position closest to the linear prism is projected on the light incident surface; The distance between the center of the linear light source and the light incidence plane is a (mm), the distance between the center of the inclined plane and the light incidence plane is b (mm), and the first and second linear forms are close to the inclined plane. A direct backlight unit, characterized in that the relation of formula (1) is established at least a part of the light exit surface when the distance between the centers of the light sources is P (mm) and the refractive index of the transparent resin is n.

[Equation 1]

[3] The direct type backlight device described in [2], wherein the emission surface is composed of a plurality of regions, each of the regions having a plurality of the linear prisms, and in each region, an inclined surface of the linear prism. An angle between each of the light incidence planes and the light incidence plane is the same, and in each of the regions, at least one linear prism satisfies Equation (1).

Effects of the Invention

The direct type backlight device of the present invention is high in luminance and brightness uniformity and is useful as a backlight of a display device such as a liquid crystal display.

1 is a longitudinal sectional view showing an example of a direct type backlight device of the present invention;

2 is a longitudinal cross-sectional view showing the relationship between the linear light source and the light diffusion plate in the direct type backlight device of the present invention;

3 is a longitudinal cross-sectional view showing an enlarged region R1 of FIG. 2;

4 is a perspective view showing an outline of the relationship between a light diffusing plate, a linear light source and a reflecting plate in the direct type backlight device of the present invention;

5 is a schematic longitudinal sectional view showing a light diffuser plate and a linear light source in the direct type backlight device of the present invention in order to explain the meanings of the equations (1) and (2);

FIG. 6 is an enlarged partial cross-sectional view of a region 50 in FIG. 5. FIG.

Implement the invention  Best form for

The direct type backlight device of the present invention includes a plurality of linear light sources arranged in parallel, a reflecting plate for reflecting light from the linear light source, and a specific light which diffuses and emits the direct light from the linear light source and the reflected light from the reflecting plate. A diffuser plate is provided.

Although the linear light source used for this invention is not specifically limited, A cold cathode tube, a hot cathode tube, LED (light emitting diode) arrange | positioned linearly, the combination of LED and a light guide can be used. In this case, the cold cathode tube or the hot cathode tube has a U-shape in which, in addition to the straight line, two parallel tubes are connected in one semi-circle and are integrated, and three parallel tubes are connected in two semi-circles and are integrally formed. It is possible to use a magnetic shape or a W-shaped shape in which four parallel tubes are connected to three substantially semicircles and are integrated. When using these three shape light sources, let the distance between the centers of the parallel part of a pipe be the distance P between the centers of adjacent linear light sources.

The linear cathode light source is preferably a cold cathode tube in terms of luminance uniformity, and a combination of LEDs, LEDs and light guides arranged in a linear form is preferable in terms of luminous efficiency. When using LEDs arranged in a linear form or a combination of LEDs and light guides, a plurality of linear light sources are referred to when there are a plurality of sets of a series of LEDs arranged or a combination of LEDs and light guides.

Although the reflecting plate used for this invention is not specifically limited, Resin, metal, etc. which were colored in white or silver can be used, A color is preferable in order to improve brightness uniformity, and a resin is preferable at the point of weight reduction. The reflecting plate can be provided in the position opposite to the light-diffusion plate of a linear light source like the reflecting plate 3 shown in FIG. 1, and the reflecting plate 403 shown in FIG.

The light diffusing plate used for this invention is provided in the substantially flat light incident surface which injects the light from a linear light source, and the surface on the opposite side to the said light incident surface, and diffuses the light incident from the said light incidence surface, and emits it. A light exit surface is provided. The light incidence surface is a substantially flat flat surface having no unevenness, and a specific structure is provided on the light emission surface. Here, a substantially flat flat surface is a surface whose center line average surface roughness Ra is 5 micrometers or less, Preferably it is 3 micrometers or less, More preferably, it is 1 micrometer or less.

The light-diffusion plate used for this invention is equipped with the prism array which has two or more triangular linear prism which consists of cross-sectional concave shape or convex shape in the light emission surface. Here, the prism array will be described using, for example, the light diffusion plate 401 shown in FIG. 4. As shown in FIG. 4, the prism array 401B is provided on the light exit surface of the light diffusion plate 401. The prism array 401B is composed of a plurality of linear prisms 401A substantially parallel to each other, and a cross section perpendicular to the longitudinal direction of the linear prisms 401A is formed in a sawtooth shape. In addition, in FIG. 4, for the purpose of extremely schematic illustration, the prism array is represented as being composed of a plurality of uniform linear prisms, but the light diffuser in the direct type backlight device of the present invention has a specific shape as described below. To have.

Here, in the cross-sectional concave linear prism, in the cross section perpendicular to the longitudinal direction of the linear prism constituting the prism array as in the region U2 shown in Fig. 1 (hereinafter simply referred to as "array cross section"), , An area between the peaks T in the neighboring drawings. In addition, the linear prism of a convex cross section means the area | region between the curved parts V in a neighboring figure in the cross section of an array like the area | region U1 shown in FIG. In the present invention, in the case where the array unit is viewed as a concave shape or as a convex shape, the above conditions are satisfied when at least one of the following conditions is satisfied.

In the direct backlight device of the present invention, the light diffusion plate is disposed such that the longitudinal direction of the linear prism extends substantially parallel to the longitudinal direction of the linear light source. Here, substantially parallel has shown the case where the angle which the longitudinal direction of a linear prism and the longitudinal direction of a linear light source make is 5 degrees or less.

In the light diffusion plate, the angle between each of the two inclined planes of the linear prism and the light incidence plane is the same, and as the distance from the linear light source closest to the position of the linear prism is increased, the angle is continuously or stepwise. Gets bigger Here, in the case where the angle between the two inclined planes and the light incidence plane is the same, the cross-sectional shape of the linear prism is an isosceles triangle (that is, a cross section corresponding to two inclined planes of one linear prism). Two line segments in a cross-sectional surface constitute two sides which are symmetrical in an isosceles triangle. In this case, the two inclined surfaces are composed of two inclined surfaces that do not become parallel to the light incidence surface when the linear prism is selected to be an isosceles triangle in cross section. With such a configuration, the light diffusing plate can be easily designed and manufactured, and the luminance angle of the direct type backlight device as a product can be increased, and the viewing angle can be made somewhat wider. In addition, in this invention, the angle formed by each of the two inclined surfaces of the linear prism and the light incidence surface is "equal" when the difference of angles is less than 1 degrees. In some cases, the vertices of the linear prism may be rounded, but in this case, the angle represents the angle formed by the linear portions of the two inclined surfaces constituting the linear prism and the light incidence surface.

Such a prism array will be described in detail with reference to FIG. 1. The direct backlight device shown in FIG. 1 includes linear light sources 2a and 2b arranged in parallel, a reflecting plate 3, and a light diffusing plate 1. The light diffusion plate 1 diffuses the light incident surface 5 which enters the direct light from the linear light sources 2a and 2b and the reflected light from the reflecting plate 3, and the light which entered the light incident surface 5. And a light exit surface 10 to exit. The prism array 4 is formed on the light exit surface 10. The prism array 4 has a plurality of linear prisms in the form of concave isosceles triangles. In each linear prism, the angle which each of the two inclined surfaces which comprise it and the light incidence surface 5 make is the same. As the linear prism is farther from the linear light source in the immediate vicinity, the angle between the two inclined surfaces and the light incident surface 5 constituting the linear prism becomes larger.

The above configuration will be described in more detail with reference to several linear prisms in the prism array 4 as an example. In FIG. 1, the prism array 4 includes a linear prism composed of an inclined surface 6a and an inclined surface 6b, a linear prism composed of an inclined surface 7a and an inclined surface 7b, and an inclined surface 8a and an inclined surface. The linear prism comprised by (8b) and the linear prism comprised by the inclined surface 9a and the inclined surface 9b are included. The angle between each of the inclined surface 6a and the inclined surface 6b and the light incident surface 5 is the same angle X1, and the angle between each of the inclined surface 7a and the inclined surface 7b and the light incident surface 5 is the same angle X2 The angle formed by each of the inclined surface 8a and the inclined surface 8b and the light incident surface 5 is the same angle X3, and the angle formed by each of the inclined surface 9a and the inclined surface 9b and the light incident surface 5 is the same. Angle X4. The relationship between the angles X1 to X4 is an angle X1 < angle X2 < angle X3 < angle X4, and the larger the distance from the linear light source 2a is, the larger the angle becomes.

In the prism array, the area of the inclined surface constituting the linear prism may be uniform or different as in the example shown in FIG. 1.

In the example shown in FIG. 1, the angle which the inclination surface and light-incidence surface which comprise a linear prism make is increasing continuously as it moves away from a linear light source. In other words, the angles of the adjacent linear prisms are different from each other, and the farther from the linear light source, the larger the angle. However, the form of this invention is not limited to this, The said angle may become large step by step. That is, a plurality of regions defined by a line parallel to the linear light source are defined on the light exit surface, and a plurality of linear prisms having the same angle between the inclined plane and the light incidence plane are successively provided in each region. As the region is farther from the linear light source, the angle may be larger. In this aspect, when the width dimension of the region is smaller than the width dimension of the linear light source (hereinafter referred to as G), the effect of improving the luminance uniformity can be further increased.

An example of a direct type backlight device including a light diffusion plate in which the angle increases step by step will be described with reference to FIGS. 2 and 3. In the direct type backlight device shown in FIG. 2, a plurality of linear light sources 2 are provided in parallel with a gap P, and are separated from them, and direct light from the linear light sources 2 and a reflecting plate (not shown). The light diffusion plate 1 which diffuses and emits the reflected light from ()) is provided. In FIG. 2, the region partitioned by R1 represents one repetitive unit of the stepwise angle change of the linear prism of the light diffusion plate.

3 is an enlarged view illustrating the region R1. The repeating unit U3 occupies the range extending Px0.5 to the left and right (direction to the adjacent linear light source) centering on the linear light source 2. In the repeating unit U3, the regions l ₁ , l ₂ ..., Left and right in order from the region closest to the linear light source ₂ . , l _{s -1} , l _s are specified. In each of the areas l ₁ -l _s , the angle between each of the inclined planes of the linear prism and the light incidence plane is the same. The angles X ₁ to X _s formed between the inclined plane and the light incidence plane constituting the linear prism in each of the regions l ₁ to l _s are the angle X ₁ <angle X ₂ <. <Angle X _{s -1} <angle X _s . By setting it as such a structure, the effect of this invention, such as being able to raise a brightness uniformity, can be acquired. In this embodiment, the value of preferred S is not particularly limited, but is P / (4G) or more, and more preferably S is P / (2G) or more.

Although the thickness of the light-diffusion plate used for this invention is not specifically limited, It is preferable that it is 0.4 mm-5 mm, and it is more preferable that it is 0.8 mm-4 mm. If the thickness is too small, devising for suppressing warping due to its own weight, such as forming a large number of posts, is necessary. In addition, when the thickness is too large, molding becomes difficult.

In the present invention, the pitch of the linear prism of the light diffusion plate, that is, the distance between the peaks or curved portions of the adjacent linear prisms is preferably 20 µm or more and 700 µm or less, more preferably 30 µm or more and 500 µm or less, 40 It is more preferable that they are more than 400 micrometers. If the pitch is too small, the shape is fine, so that the shape may be difficult to be applied, or the light diffusion effect may be lowered. If the pitch is too large, light diffusion becomes rough, which may cause luminance unevenness. In addition, a pitch may be nonuniform or uniform in a prism array like the example shown in FIG.

In this invention, the surface of the prism array of a light-diffusion plate can be harmonized, and the direction which light exits can be made more diversified within an appropriate range. In that case, it is preferable that center line average surface roughness Ra when the surface of a linear prism is measured 20 micrometers orthogonally with respect to a longitudinal direction is 0.08 micrometer or more and 3 micrometers or less, It is more preferable that they are 0.09 micrometer or more and 2 micrometer or less, It is more preferable that they are 0.1 micrometer or more and 1 micrometer or less. By making Ra into a preferable range, the emission direction of light can be made more diversified, and the emission direction of light can not be made too diverse.

Although the material of the light-diffusion plate used for this invention is not specifically limited, It can be set as the composition containing glass, resin, and resin. As a composition containing resin or resin, the mixture of 2 or more types of resins which are difficult to mix, or the thing which disperse | distributed the light-diffusion agent to transparent resin, etc. can be used. Among these, a resin containing a resin or a resin is preferable because it is light and easy to mold, and it is particularly preferable to disperse the light diffusing agent in the transparent resin in view of easy adjustment of the total light transmittance and the base. In addition, forming the whole light-diffusion plate containing a prism array part by disperse | distributing a light-diffusion agent to transparent resin, and adjusting the whole light-diffusion plate to the same total light transmittance and a base is the direction of the light which exits from a light-diffusion plate It is more preferable because it can be made more diverse.

There is no restriction | limiting in particular in content of the light-diffusion agent of the thing which disperse | distributed the light-diffusion agent to transparent resin, Although it can select suitably according to the thickness of a light-diffusion plate, the linear light source spacing of a backlight, etc., the total light transmittance of a dispersion is 60% normally. It is preferable to adjust content of a light diffusing agent so that it may become 100% or more, and it is more preferable to adjust content of a light diffusing agent so that it may become 80% or more and 100% or less, and it is 90% or more and 100% or less. It is more preferable to adjust the content of. It is preferable to adjust content of a light-diffusion agent so that a haze may be 0% or more and 95% or less, and it is more preferable to adjust content of a light-diffusion agent so that it may become 0% or more and 90% or less. The luminance can be further improved by setting the total light transmittance to 60% or more and the haze to 95% or less. The luminance uniformity can be further improved by setting the total light transmittance to 100% or less and the haze to 0% or more. The total light transmittance in this case is a value measured with a 2 mm thick flat plate on both sides according to JIS K7361-1, and haze is a value measured with a 2 mm thick flat plate on both sides according to JIS K7136.

In the present invention, the transparent resin is a resin having a total light transmittance of 70% or more, as measured by a 2 mm thick plate that is smooth on both sides according to JIS K7361-1. For example, polyethylene, propylene-ethylene copolymer, polypropylene, polystyrene, and aromatic vinyl type. Copolymers of monomers with (meth) acrylic acid alkyl esters having lower alkyl groups, polyethylene terephthalates, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymers, polycarbonates, acrylic resins, resins having alicyclic structures, and the like. . Among these, the water absorption of a copolymer of an aromatic vinyl monomer containing 10% or more of a polycarbonate, polystyrene, an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester having a lower alkyl group or a resin having an alicyclic structure is 0.25%. Since the following resin is few in deformation | transformation by moisture absorption, it is preferable at the point which can obtain the large light-diffusion plate with little warpage. The resin having an alicyclic structure is more preferable because it has good fluidity, can efficiently manufacture a large light diffusing plate, and can form a prism array having a specific shape as designed. The compound which mixed resin which has an alicyclic structure, and a light-diffusion agent has the high permeability and high diffusivity required for a light-diffusion plate, and since chromaticity is favorable, it can be used suitably. In addition, the said (meth) acrylic acid has shown methacrylic acid and acrylic acid.

Resin which has alicyclic structure is resin which has alicyclic structure in main chain and / or side chain. From the viewpoint of mechanical strength, heat resistance and the like, resins containing an alicyclic structure in the main chain are particularly preferable. Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From a viewpoint of mechanical strength, heat resistance, etc., a cycloalkane structure and a cycloalkene structure are preferable, and the cycloalkane structure is the most preferable especially. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but the mechanical strength, heat resistance and light diffusion plate of the carbon atoms in the range of usually 4-30, preferably 5-20, more preferably 5-15 Formability properties are highly balanced and desirable. Although the ratio of the repeating unit which has an alicyclic structure in resin which has an alicyclic structure may be suitably selected according to a use purpose, it is 50 weight% or more normally, Preferably it is 70 weight% or more, More preferably, it is 90 weight% or more. . When the ratio of the repeating unit which has alicyclic structure is too small, heat resistance falls and it is unpreferable. In addition, repeating units other than the repeating unit which has an alicyclic structure in resin which has an alicyclic structure are suitably selected according to a use purpose.

Specific examples of the resin having an alicyclic structure include (1) a ring-opening polymer of a norbornene-based monomer and a ring-opening copolymer of a norbornene-based monomer with another monomer capable of ring-opening copolymerization with these, and hydrogenated products thereof and norbornene-based monomers Norbornene-based polymers such as an addition polymer and an addition copolymer of norbornene-based monomers with other monomers copolymerizable therewith; (2) Monocyclic cyclic olefin polymer and its hydrogenated substance; (3) a cyclic conjugated diene polymer and its hydrogenated substance; (4) Polymers of vinyl alicyclic hydrocarbon monomers and copolymers of vinyl alicyclic hydrocarbon monomers with other monomers copolymerizable with these, and hydrogenated substances thereof and hydrogenated compounds of aromatic rings of polymers of vinyl aromatic monomers And vinyl alicyclic hydrocarbon-based polymers such as hydrogenated products of aromatic rings of copolymers of vinyl aromatic monomers with other monomers copolymerizable therewith; Etc. can be mentioned. Among these, norbornene-based polymers and vinyl alicyclic hydrocarbon-based polymers are preferable from the viewpoint of heat resistance, mechanical strength, and the like, and ring-opening polymer hydrogenated polymers of norbornene-based monomers, norbornene-based monomers, and others capable of ring-opening copolymerization with these The ring-opening copolymer hydrogenated substance with a monomer, the hydrogenated substance of the aromatic ring which is a polymer of a vinyl aromatic monomer, and the hydrogenated substance of the aromatic ring of the copolymer of a vinyl aromatic monomer and another monomer copolymerizable with this are more preferable.

The light diffusing agent used for the light diffusing plate is a particle having a property of diffusing light rays, and classified into inorganic fillers and organic fillers. As the inorganic filler, specifically, silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, or a mixture thereof can be used. As a specific material of the organic filler, acrylic resin, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, benzoguanamine resin and the like can be used. have. Among these, the fine particles composed of polystyrene resin, polysiloxane resin or crosslinked material thereof are particularly suitably used because they do not have high dispersibility, high heat resistance and coloring (yellowing) during molding. Since the microparticles | fine-particles which consist of a crosslinked material of polysiloxane resin are excellent by heat resistance, it can use it more suitably.

Although the shape of the light-diffusion agent used for a light-diffusion plate is not specifically limited, For example, spherical shape, a cubic shape, needle shape, rod shape, fusiform shape, plate shape, scale fragment shape, fiber shape, etc. are mentioned, Especially, Sphere-shaped beads capable of isotropically diffusing the light are preferable.

The light diffusing agent is used in the form contained in the transparent resin.

Although the refractive index of the transparent resin which comprises the light-diffusion plate of this invention is not specifically limited, It can be set as the range of 1.2-2.0.

In the production of the light diffusing plate used in the present invention, there is no particular limitation on the method of forming the specific prism array on the surface thereof. For example, the prism array can be formed on the surface of the flat light diffusing plate, or In addition, the prism array may be formed simultaneously with the molding of the light diffusion plate. There is no restriction | limiting in particular as a method of forming a prism array on the surface of a plate-shaped light-diffusion plate, For example, it is possible by cutting by using the tool which can form the linear prism of a desired shape, or photocuring resin It can also apply | coat and harden | cure in the state which transferred the mold of a desired shape. When the light diffusing plate is produced by extrusion molding and at the same time forming a prism array, it can be extruded using a release die having a desired prism array shape, or the prism is formed by embossing after extrusion. It is also possible to form an array. When the light diffusing plate is produced by casting and simultaneously forming a prism array, a casting type capable of forming a desired prism array shape can be used. When the light diffusing plate is produced by injection molding, and a prism array is formed at the same time, a mold capable of forming the shape of a desired prism array can be used. The mold used when forming a prism array by mold transfer to a photocuring resin, extrusion by a release die, embossing, casting, or injection molding forms a desired linear prism. It can be obtained by cutting into a metal member of a mold using a tool that can be used, or by electroforming onto a member on which a desired shape is formed.

In the direct type backlight device of the present invention, the light diffusing plate comprises a transparent resin, and the linear prism having the inclined plane of the angle between each inclined plane and the light incidence plane of an arbitrary linear prism is X (°) and the inclined plane. The distance between the vertex of and the position when the center of the linear light source at the position closest to the linear prism is projected on the light incidence plane is W (mm), and the distance between the center of the linear light source and the light incidence plane. A (mm), the distance between the center of the inclined surface and the light incident surface b (mm), the distance between the center of the linear light source closest to the first and second inclined surface P (mm), the transparent When the refractive index of the resin is n, it is preferable that the relationship of formula (1) is established in order to set the direct backlight device having a high luminance uniformity. Moreover, it is preferable that these parameters satisfy | fill the relationship of Formula (2) in order to further raise luminance uniformity.

[Equation 2]

[Equation 3]

When the parameter satisfies Expression (1), preferably Expression (2), one of the two inclined planes constituting the linear prism causes light from the linear light source to be perpendicular to the light incident plane. Let go. Therefore, when the parameter satisfies the formula (1), preferably the formula (2), the emission of light in the direction perpendicular to the light incidence plane is ensured, so that good luminance and brightness uniformity can be obtained.

Here, the meaning of said Formula (1)-(2) is demonstrated with reference to drawings. In simple terms, these equations (1) to (2) show that when a light diffusing plate is observed from the light exit surface side, images of a plurality of linear light sources are confirmed between the linear light sources, and the direct type backlight device has a high brightness and luminance. The conditions which enable the homogeneity to be good are shown.

Hereinafter, it demonstrates more concretely. 5 and 6 are schematic diagrams for explaining the significance of the above formulas (1) to (2), wherein FIG. 5 is a cross-sectional view of the direct type backlight device, and FIG. 6 shows a portion 50 showing two linear prisms. An enlarged view of. In such a direct type backlight device, the following virtual state is examined. That is, from the upper side to the lower side in FIG. 5, in other words, from the light exit surface (here, virtually the light incident plane) formed with a linear prism formed of an isosceles triangle having a convex cross section, the light incident plane composed of a flat plane ( Here, the light emitting surface will be virtually assumed. Hereinafter, the case where light perpendicular to the lower surface is incident toward the "lower surface" will be examined.

For example, taking two incident lights I1 and I2 as an example, light incident on the right side of the linear prism is refracted at the right side and the bottom side of the linear prism, so that the distance of (a + b) from the center position of the right side is On the separated surface, the position of the horizontal distance along the middle side in the equation (1) is reached. The value of the middle side is a function of X only if P, a, b and n are integers.

Here, when these arrival positions overlap one, that is, when the horizontal distances to the arrival positions are the same as W1 and W2, and the linear light sources are arranged at such overlap positions, the light emitted from the linear light sources is coarse. The path of the virtual light represented by the line is traced backwards, and the light exits in a direction perpendicular to the upper side from the right side of the linear prism. This relationship holds even for all linear prisms not shown. That is, when the middle side and W are equal, light is emitted in a direction perpendicular to the lower surface than one surface of the linear prism on the front side of the light diffusion plate, so that the luminance uniformity and the luminance can be greatly improved. However, as a result of the present inventor's examination, it turned out that it has a sufficient effect even if it is a little shift | deviated from the vertical direction when the light emission direction becomes it. As for the range which has sufficient effect, it is preferable that the moving distance of the virtual incident light to the horizontal direction is within 0.2 times of P, and it is more preferable that it is within 0.1 times of P.

In addition, in the middle side of Formula (1)-(2), the part of bxtan (X- to sin (x) / n)) is the original which the light perpendicular | vertical to the light-diffusion plate injects from the linear prism side. When considering the state opposite to the above, it is the horizontal distance that light reaches from the prism plane to the lower surface, and the portion of a × tan (sin ⁻¹ to sin (X / n)) considers the same state. It is the horizontal distance that light reaches from the lower surface to the same surface as the center of the light source. Summarizing the above results, equations (1) and (2) are obtained.

It is preferable that the above equation is satisfied on the entire surface of the light diffusion plate, but the above-mentioned preferable effect can be obtained even if not satisfied on the entire surface of the light diffusion plate. For example, as described above, when the angle between the inclined surface and the light incident surface constituting the linear prism is gradually increased, at least one linear prism, preferably in the center of the region, in each of the plurality of regions. Even when the linear prism to satisfy the condition of the above equation can be obtained a desirable effect.

Specifically, for example, in the example shown in FIG. 3, in each of the regions l ₁ to l _s , in the at least one linear prism, when the relationship of the formula (1) or (2) is established, a preferable effect Can be obtained.

In each of the above parameters, X may take a value of 0 to 90 degrees. Although the value of W is not specifically limited, It is preferable that it is 15-150 mm, and it is more preferable that it is 20-100 mm. The value of a is not particularly limited and may be designed in consideration of the thickness and brightness uniformity of the direct backlight device, preferably 5 to 30 mm, and more preferably 5 to 25 mm. Moreover, it is preferable that the value of b is 0.4-5 mm.

Each said parameter X, W, a, and b is specifically measured as shown in FIG. In the example shown in FIG. 1, X is angle X1-X4, W is the distance between centers of the linear light source 2a and the linear light source 2b, and a is the linear light source 2a or the linear light source. It is the distance from (2b) to the light incident surface 5, and b is the distance shown by the arrows b1-b4.

The direct type backlight device of the present invention includes the linear light source, the reflecting plate, and the light diffusing plate as essential components, but may be modified within an equivalent range, and in addition to these essential components, any configuration It can contain elements. For example, the diffusion sheet and the prism sheet may be provided far from the light source of the light diffusion plate in order to improve the brightness and the brightness uniformity. In addition, in order to improve luminance, the following reflective polarizers may be provided away from the light sources of the two kinds of sheets. As said reflective polarizer, the reflective polarizer which used the difference of the reflectance of the polarization component by Brewster's angle (for example, described in Unexamined-Japanese-Patent No. 6-508449 (corresponding publication: international publication brochure WO92 / 22838)). ; Reflective polarizer using selective reflection characteristics by cholesteric liquid crystal; Specifically, the laminated body of the film which consists of a cholesteric liquid crystal, and a quarter wave plate (for example, Unexamined-Japanese-Patent No. 3-45906 (corresponding publication: US Pat. No. 5,235,443)); Reflective polarizers (such as those described in Japanese Patent Application Laid-Open No. 2-308106) in which fine metal line-like patterns are constructed; At least two kinds of polymer films are laminated and described in a reflective polarizer (for example, Japanese Patent Application Laid-Open No. 9-506837 (corresponding publication: International Publication Pamphlet WO95 / 17303)) utilizing anisotropy of reflectance by refractive index anisotropy. ); Reflective polarizers (eg, those described in US Pat. No. 5,825,543) having a sea island structure formed of at least two polymers in the polymer film and utilizing anisotropy of reflectance due to refractive anisotropy; Reflective polarizers (eg, those described in Japanese Patent Application Laid-Open No. 11-509014 (corresponding publication: International Publication Pamphlet WO97 / 41484)) in which particles are dispersed in a polymer film and use the anisotropy of reflectance due to refractive anisotropy; Inorganic particles are dispersed in the polymer film, and reflecting polarizer using anisotropy of reflectance based on the scattering ability difference by size (for example, Japanese Patent Application Laid-Open No. 9-297204 (corresponding publication: US Patent Specification No. 5,995,183)) Described in); Etc. can be used.

Although the use of the direct type backlight device of this invention is not specifically limited, It can use suitably as a backlight in display apparatuses, such as a liquid crystal display.

Hereinafter, although this invention is demonstrated in detail with reference to an Example and a comparative example, this invention is not limited to these.

(Example 1)

99.85 parts by weight of a resin having an alicyclic structure as a transparent resin (manufactured by Nippon Xeon Co., Ltd., Zeonoa 1060R, refractive index 1.53), and a fine particle of a crosslinked product of a polysiloxane resin as a light diffusing agent (GE Toshiba Silicone Co., Tospearl 120) From the pallet of the composition which mixed 0.15 weight part, the light-diffusion plate 1 of external shape 310mm x 280mm and thickness of about 2.0mm in which the prism shape was transferred to the surface by injection molding was produced using the metal mold | die which provided the predetermined prism shape. It was. On one surface of the light diffusion plate 1, a prism array having the shape shown in Table 1 was formed in parallel with the long side, and the other was a flat surface. This light-diffusion plate had 93% of the total light transmittance, and 93% of haze.

Next, a reflecting sheet (Tsujiden Co., Ltd. product name RF188) was bonded to the bottom and side surfaces of the housing having an opening having a width of 300 mm at the front, a width of 200 mm at the rear, and an 18 mm depth to form a reflecting plate, and a diameter of 3 mm and a length of 360 mm. Eight cold cathode tubes are spaced 1.5 mm apart from the bottom surface, and the center-to-center distance is set to 25 mm, parallel to the longitudinal direction of the opening, and parallel to the depth direction at equal intervals. The light diffusing plate 1 was provided such that the prism array was located on the light exit surface side in parallel with the cold cathode tube. On top of this, a light diffusion sheet (produced by Kimoto Co., Ltd., product name 188GM-2), a reflecting polarizer using birefringence (product of Sumitomos Rem Co., product name DBEF-D), and a polarizing plate were mounted in this order, and the direct type backlight device was mounted. Produced.

Subsequently, the cold cathode tube was turned on so that the tube current was 6.5 mA, and 100 luminance was measured at equal intervals on the short center line by using a two-dimensional color distribution measuring instrument (product name: CA1500W manufactured by Konica Minolta Co.). ) And Eq. (4), the average luminance La and the luminance equalizer Lu were calculated. The average luminance was 3743 cd / m 2 and the luminance uniformity was 1.3.

Average Luminance La = (L1 + L2) / 2 Formula (3)

Luminance equalization Lu = ((L1-L2) / La) × 100 (4)

    (L1: average of the luminance maximum values in the vertical fluctuation of the luminance)

    (L2: Average of minimum luminance values in vertical fluctuations in luminance)

The luminance uniformity is an index indicating the uniformity of luminance, and the smaller this number is, the higher the luminance uniformity is.

(Example 2)

The light diffusing plate 2 was produced in the same manner as in Example 1 except that a predetermined prism shape different from that used in Example 1 was used as the mold. The prism array of the shape shown in Table 1 was formed in one surface of this light-diffusion plate 2 in parallel with a long side, and the other was planar.

The direct type backlight device was produced and evaluated similarly to Example 1 except having used the said light diffusing plate 2 instead of the light diffusing plate 1. The average luminance was 3755 cd / m 2 and the luminance uniformity was 1.3.

(Example 3)

The light diffusing plate 3 was produced in the same manner as in Example 1 except that a predetermined prism shape different from that used in Example 1 was used as the mold. The prism array of the shape shown in Table 1 was formed in one surface of this light-diffusion plate 3 in parallel with a long side, and the other was planar.

A direct type backlight device was produced and evaluated in the same manner as in Example 1 except that the light diffusing plate 3 was used instead of the light diffusing plate 1. The average luminance was 3832 cd / m 2 and the luminance uniformity was 0.9.

(Comparative Example 1)

The light diffusing plate 4 was produced in the same manner as in Example 1 except that a predetermined prism shape different from that used in Example 1 was used as the mold. The prism array of the shape shown in Table 1 was formed in one surface of this light-diffusion plate 4 in parallel with the long side, and the other was planar.

A direct type backlight device was produced and evaluated in the same manner as in Example 1 except that the light diffusing plate 4 was used instead of the light diffusing plate 1. The average brightness was 3396 cd / m 2 and the brightness uniformity was 3.5.

(Comparative Example 2)

The light diffusion plate 5 was produced in the same manner as in Example 1 except that a predetermined prism shape different from that used in Example 1 was used as the mold. The prism array of the shape shown in Table 1 was formed in one surface of this light-diffusion plate 5 in parallel with a long side, and the other was planar.

A direct type backlight device was produced and evaluated in the same manner as in Example 1 except that the light diffusing plate 5 was used instead of the light diffusing plate 1. The average brightness was 3527 cd / m 2 and the brightness uniformity was 2.0.

The measurement result in each Example and a comparative example is put together in Table 2, and is shown.

TABLE 1

In Table 1, "l ₁ -l ₁₀ " shows the width | variety (mm) of the area | region 1-area 10, respectively, and "X ₁ -X ₁₀ " shows the inclined surface and light incidence of the linear prism in area 1-area 10, respectively. represents the angle (°) of the surface, "b ₁ to b _10" denotes a distance (mm) between the center and the light incident surface of the slope of the linear prisms in the first-region 10 each area, "width" is The width | variety (mm) of the linear prism in area | region 1-area | region 10 is shown.

TABLE 2

From the result of Table 2, in the Example (Examples 1-3) with respect to the direct type backlight device of this invention, it turns out that favorable result is obtained in brightness | luminance and brightness | luminance uniformity. On the other hand, in Comparative Examples 1 and 2, it can be seen that sufficient results are not obtained in both of the average brightness and the brightness uniformity. In addition, "(circle)" in Table 2 has shown that the member is used.

Claims (3)

A direct backlight having a plurality of linear light sources arranged in parallel, a reflecting plate for reflecting light from the linear light source, and a light diffusing plate for diffusing and radiating the direct light from the linear light source and the reflected light from the reflecting plate. As a device, The light diffusing plate is provided on a substantially flat light incident surface for incident light from the linear light source and a surface opposite to the light incident surface, and emits light by diffusing light incident from the light incident surface. With cotton, The light exit surface includes a prism array having a plurality of linear prisms extending in substantially parallel to the longitudinal direction of the linear light source and composed of a triangular concave or convex triangle. The angle between each of the two inclined surfaces of each linear prism and the light incident surface is the same, The position of the linear prism is that the angle is increased continuously or stepwise as it moves away from the linear light source closest to the linear prism. Direct type backlight device, characterized in that. The method of claim 1, The light diffusion plate comprises a transparent resin, The angle formed between each inclined plane of the linear prism and the light incident plane is X (°), W (mm) is the distance between the vertex of the linear prism having the inclined surface and the position when the center of the linear light source at the position closest to the linear prism is projected on the light incident surface; The distance between the center of the linear light source and the light incident surface is a (mm), B (mm) the distance between the center of the inclined surface and the light incident surface, P (mm), the distance between the centers of the linear light sources closest to the inclined surface and the second light source; When the refractive index of the transparent resin is n, the relationship of the formula (1) is established in at least part of the light exit surface Direct type backlight device, characterized in that. [Equation 1]

The method of claim 2, The exit surface is composed of a plurality of areas, Each of said regions has a plurality of said linear prisms, Within each area, the angle between each inclined plane of the linear prism and the light incidence plane is the same, In each of the regions, at least one linear prism satisfies Equation 1 above. Direct type backlight device, characterized in that.

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