JP2006302876A - Direct type backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct type backlight device which has high degree of luminance balance and high luminance while high rate of effective use of light flux is maintained and which cannot be easily affected by an environment. <P>SOLUTION: The direct type backlight device has a reflecting plate 4, a plurality of linear light sources 3, a plurality of optical diffusion sheets 21 and 22, and a diffusion sheet 1 sequentially in this order. In the faces of the optical outgoing side of each optical diffusion sheets 21 and 22, a prism stripe of concavo-convex structure column whose Rz value is 200 μm or less is formed. The board thickness of each optical diffusion sheets 21 and 22 are respectively 0.4-5.0 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direct type backlight device. More specifically, the present invention relates to a direct type backlight device having good luminance and luminance uniformity, low cost and good moisture resistance.

  Conventionally, as a backlight device for a liquid crystal display, a device using a cold cathode tube as a light source has been 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 backlight device having a structure in which a cold cathode tube of a thin tube is arranged on the end side of a light guide plate, and light incident from the end surface is repeatedly reflected in the light guide plate and emitted to the main surface of the light guide plate.

  On the other hand, the direct type backlight device has a configuration in which a plurality of cold-cathode tubes arranged in parallel, a reflector provided on the back surface of the cold-cathode tube, and a light diffusing plate forming a light emitting surface are combined. In contrast to the edge light type, since the number of cold cathode fluorescent lamps can be increased, the light emitting surface can be easily brightened. However, the direct type backlight device has a problem that the luminance uniformity of the light emitting surface is poor. In particular, the periodic luminance unevenness that occurs because the luminance is increased directly above the cold cathode tube is a serious problem. That is, when the luminance uniformity of the light emitting surface of the backlight device is poor, display unevenness occurs on the display screen of the liquid crystal display.

  Various measures have been taken to improve the luminance uniformity of the direct type backlight device. For example, a striped pattern or dot-shaped light quantity correction pattern is printed on a light diffusing plate, and a method (illustrated in Patent Document 1) for reducing a light beam emitted directly above a fluorescent tube, or a wave-shaped reflecting plate is used. There has been proposed a technique (Patent Document 2) for focusing the reflected light from the reflecting plate to a region corresponding to the middle between the fluorescent tube and the fluorescent tube. However, when the light intensity correction pattern is printed as a means of improving the luminance uniformity, a part of the light beam is cut off, so that the utilization rate of the light beam emitted from the fluorescent tube is reduced and sufficient luminance cannot be obtained. was there. In addition, when the corrugated reflector is used, there is a problem that the configuration of the device becomes complicated and the manufacturing cost of the backlight device increases.

  Conventionally, a light diffusing plate used in a direct type backlight device is often made of a material in which a light diffusing agent is dispersed in a transparent resin. However, in order to improve the luminance uniformity, the concentration of the light diffusing agent is adjusted. There is a problem that the brightness is lowered when it is raised. In order to solve this problem, it has been proposed to form a concavo-convex structure such as a prism shape on the surface of the light diffusing plate so as to have a diffusion effect due to the surface shape without lowering the luminance (Patent Documents 3, 4, and 5). . However, the luminance uniformity cannot be improved by simply forming a prismatic pattern on the surface of the light diffusion plate.

  In addition, in order to maintain a luminance uniformity and to obtain a thin and high-brightness direct-type backlight, a technique using a diffusion plate divided into two sheets has been proposed (Patent Document 6). However, when this technique is used, light is attenuated by two light diffusing plates, so that the objective of obtaining a high-brightness backlight has not been sufficiently fulfilled.

  In order to project the light beam of the direct type backlight device onto the entire surface of the liquid crystal panel with high luminance, a diffusion plate and several optical sheets are set between the light source of the backlight device and the liquid crystal panel. Among optical sheets, a prism sheet having a prism section with a fine cross-sectional sawtooth shape on a transparent sheet having a thickness of about 50 μm to 300 μm is used in most direct type backlight devices that require high luminance. .

  However, in order to form a fine and precise prism row, the prism sheet uses an expensive shape imparting roll due to the necessity of precision processing, and further presses the roll against the sheet accurately. There is a problem that the cost of the backlight device and thus the liquid crystal display increases because the manufacturing cost is expensive for two reasons, that is, it is difficult to improve the production speed and the yield, such as transferring the shape. .

  In addition, the prism sheet is often made of a material having a high hygroscopic property to form the fine prism-like rows as described above, and is easily deformed thinly. There was also a problem of causing unevenness.

  Such a problem occurs not only when a linear light source is used as the light source but also when a point light source such as an LED is used.

JP-A-6-273760 JP 2001-174813 A JP-A-5-333333 JP-A-8-297202 JP 2000-182418 A JP-A-10-104622

  The present invention relates to an improvement of a direct type backlight device, obtains a high effective luminous flux, further suppresses periodic luminance unevenness of a light emitting surface, has a good balance between luminance and luminance uniformity, and is suitable for the environment. The purpose of the present invention is to provide a means that can realize a backlight that is hardly affected at low cost.

  As a result of intensive studies to solve the problems in the previous period, the present inventors surprisingly found that at least one main surface of a light diffusing plate in which the effect of improving the brightness uniformity is not sufficient in a direct type backlight device. By combining the technology to provide a specific concavo-convex structure with the technology to arrange multiple diffusers that may reduce the brightness, there is no expensive prism sheet, high brightness and good brightness uniformity, and environmental impact It has been found that a backlight device that is difficult to be obtained is obtained, and the present invention has been completed based on this finding.

  Specifically, in the direct type backlight device, the plate thickness of each light diffusion plate is 0.4 mm to 5.0 mm, respectively, and a part or all of at least one main surface of the at least one light diffusion plate In addition, it was found that a low-cost and high-brightness backlight device can be obtained by using one having an uneven structure with an Rz value of 200 μm or less, and the present invention has been completed based on this finding.

That is, the present invention
(1) A direct backlight comprising a plurality of light sources, a reflecting plate for reflecting light from the light source, and a plurality of light diffusing plates arranged in the order of the reflecting plate, the light source, and the plurality of light diffusing plates. The apparatus has a thickness of 0.4 mm to 5.0 mm for each light diffusion plate, and unevenness having an Rz value of 200 μm or less on a part or all of at least one main surface of at least one light diffusion plate. A direct-type backlight device characterized by having a structure;
(2) The shape of the concavo-convex structure having an Rz value of 200 μm or less is a sawtooth-shaped prism array having a cross-sectional triangular shape and a plurality of linear prisms whose apex angles are 60 to 170 degrees arranged in parallel. The direct-type backlight device, wherein a dimension of a bottom surface portion of the prism in a width direction (a direction orthogonal to a longitudinal direction of the linear prism: a short direction of the linear prism) is 20 μm to 700 μm,
(3) The plurality of light sources are a plurality of linear light sources arranged in parallel, and among the light diffusion plates having the prism array, the ridge line direction of the prism array of at least one light diffusion plate is linear. The direct type backlight device characterized in that the angle formed with the longitudinal direction of the light source is 60 degrees or less,
(4) The direct-type backlight device, wherein the concavo-convex structure having an Rz value of 200 μm or less is provided only on the surface of the light diffusion plate far from the light source,
(5) At least one light diffusion plate is made of a material in which a light diffusing agent is dispersed in a transparent resin. The total light transmittance of the dispersion is 60% or more and 95% or less, and haze is 40% or more and 94%. The direct type backlight device, characterized in that: (6) the direct light type backlight device, wherein the light source is a point light source;
Is to provide.
Furthermore, as a preferred embodiment of the present invention,
(7) The direct type backlight device described above, wherein the transparent resin used for the light diffusion plate has a water absorption of 0.25% or less.

  The direct type backlight device of the present invention has a high effective luminous flux utilization rate without using an expensive and non-moisture-resistant prism sheet, and the periodic luminance unevenness of the light emitting surface is suppressed. According to the present invention, it is possible to provide a backlight device that is low in cost, high in luminance, good in luminance uniformity, and hardly affected by the environment.

  The present invention provides a direct-type back including a plurality of light sources, a reflecting plate that reflects light from the light source, and a plurality of light diffusing plates arranged in the order of the reflecting plate, the light source, and the plurality of light diffusing plates. A light device, wherein each light diffusion plate has a thickness of 0.4 mm to 5.0 mm, and at least one main surface of at least one light diffusion plate has an Rz value of 200 μm or less. A direct type backlight device having an uneven structure.

FIG. 1 is a schematic perspective view of an embodiment of a direct type backlight device of the present invention.
The direct type backlight device according to this aspect includes a plurality of linear light sources 3 arranged in parallel, a reflecting plate 4 that reflects light from the linear light source 3, direct light from the linear light source 3, and a reflecting plate. Diffusing and irradiating light reflected from the light diffusing plate 21, diffusing and irradiating light emitted from the light diffusing plate 21, and a diffusion sheet 1 provided on the side of the light diffusing plate 22 far from the linear light source 3. It has.

  In the light diffusing plate 21, a prism array having a sawtooth cross section in which a plurality of linear prisms having apex angles 51 are arranged substantially in parallel is provided on the surface far from the linear light source 3. In the light diffusing plate 22, a prism array having a sawtooth cross section in which a plurality of linear prisms having apex angles 52 are arranged substantially in parallel is provided on the surface far from the linear light source 3.

  In this embodiment, the prism array having the concavo-convex structure is formed only on one surface of the light diffusing plate, but it may be formed on both surfaces thereof. Moreover, although the prism row | line | column which is an uneven structure was formed in the surface far from a linear light source, you may form in the surface near the linear light source. Moreover, although the prism row | line | column which is an uneven | corrugated structure was formed in each of several light diffusing plates, you may form an uneven | corrugated structure only in any one light diffusing plate. Moreover, although the prism row | line was employ | adopted as an uneven structure, it is not limited to this.

Furthermore, as an optical member (not shown) for improving luminance, any one of the following two types of members may be installed on the side of the diffusion sheet 1 far from the linear light source 3.
(1) An optical laminate having a cholesteric liquid crystal layer in which the helical pitch of liquid crystal molecules continuously changes on a transparent substrate, and the formula Rth = {(nx + ny) / 2−nz} × d (where nx, ny Represents a refractive index in two directions perpendicular to each other perpendicular to the thickness direction, and nx> ny, nz represents a refractive index in the thickness direction, and d represents a film thickness). A laminate including a retardation element having a thickness of 20 nm to -1000 nm and a quarter-wave plate.
(2) A reflective polarizer using birefringence proposed in Japanese Patent No. 3448626.

  The linear light source used in the present invention is not particularly limited, and a cold cathode tube, a hot cathode tube, a linearly arranged LED, a combination of an LED and a light guide, and the like can be used. At this time, the cold cathode tube or the hot cathode tube may be U-shaped, N-shaped or W-shaped in addition to the linear shape. A cold cathode tube is preferable in terms of luminance uniformity as a light source, and a combination of LEDs arranged in a linear form, and an LED and a light guide is preferable in terms of color reproducibility. When using a linear array of LEDs or a combination of LEDs and light guides, if there are a plurality of arrayed LED pairs or combinations of LEDs and light guides, it can be considered as a linear array. Assume that there are multiple light sources that can be used.

  The distance between the centers of the linear light sources is not particularly limited, but is preferably 15 mm or more and 150 mm or less, and more preferably 20 mm or more and 100 mm or less. If it is smaller than the above numerical range, the power consumption becomes too large, and if it is larger than the above numerical range, the luminance uniformity deteriorates. The distance between the center of the linear light source and the surface of the light diffusing plate closest to the light source that is closer to the light source is not particularly limited, but is preferably 5 mm to 30 mm, and more preferably 5 mm to 25 mm. . If it is smaller than the above numerical range, the luminance uniformity deteriorates, and if it is larger than the above numerical range, the luminance deteriorates.

  In this embodiment, a linear light source is employed as the light source, but a configuration in which a plurality of point light sources such as LEDs are arranged can be employed. In this case, the point light sources such as LEDs can be arranged regularly or randomly. However, the point light sources are preferably arranged regularly, for example, in a lattice shape. When a point light source is used as the light source, the distance between the centers of the point light sources is preferably 15 mm or more and 150 mm or less, and preferably 20 mm or more and 100 mm or less for the same reason as in the case of the linear light source. It is more preferable that The distance between the center of the point light source and the surface of the light diffusing plate closer to the point light source is preferably 5 mm or more and 30 mm or less for the same reason as in the case of the linear light source. More preferably, it is 25 mm or less.

  The reflecting plate is not particularly limited, but a white or silver colored resin, metal, or the like can be used. The color is preferably white from the viewpoint of improving the brightness uniformity, and the material is preferably a resin from the viewpoint of weight reduction.

  The light diffusing plate used in the device of the present invention is used for improving the luminance uniformity, adjusting the light emission direction, and improving the luminance of the backlight device. In particular, a light diffusing plate having a concavo-convex structure on the surface is excellent in adjusting the light emission direction, and thus has a great effect of improving luminance. The light diffusing plate has a light incident surface and a light emitting surface, and light from the linear light source is incident on the light incident surface on the side closer to the light source, and within the light diffusing plate or at least of the light incident surface or the light emitting surface. In the unevenness provided on one side, the light is diffused and emitted from the light exit surface far from the light source.

  The brightness uniformity can be improved by using a plurality of light diffusion plates. If the number is one, the luminance uniformity may not be sufficiently improved. In order to improve the balance between brightness and brightness uniformity, and to obtain a lighter and lower cost backlight device, the number of light diffusion plates used is preferably 2 to 4, more preferably 2 to 3 preferable.

  The shortest distance between adjacent light diffusion plates is preferably 0 mm or more and 50 mm or less, more preferably 0 mm or more and 40 mm or less, and further preferably 0 mm or more and 20 mm or less. If this interval is larger than the above numerical range, the luminance of the backlight device may decrease.

  Although nothing is preferably disposed between the plurality of light diffusion plates, an optical sheet such as a prism sheet or a diffusion sheet may be disposed.

  In the backlight device of the present invention, it is preferable that at least one main surface of at least one light diffusing plate has a concavo-convex structure. Luminance can be sufficiently improved by providing a light diffusing plate having an uneven structure. The number of light diffusion plates having a concavo-convex structure is preferably 1 to 4 in order to appropriately restrict the light emission direction and thereby ensure luminance even in a direction greatly inclined from the normal direction of the emission surface. Three to three are more preferable.

  The uneven structure on the surface of the light diffusion plate of the present invention has a maximum height Rz value of 200 μm or less. If the Rz value exceeds 200 μm, the processing becomes difficult, so that the uneven structure cannot be formed uniformly, and the luminance uniformity deteriorates. In order to further improve the balance between the luminance and the luminance uniformity of the backlight device and make the processing of the light diffusion plate easier, it is more preferable that the uneven structure on the surface of the light diffusion plate has an Rz value of 2 μm or more and 200 μm or less. The thickness is more preferably 4 μm or more and 150 μm or less, and most preferably 8 μm or more and 100 μm or less.

  In the present invention, the maximum surface height Rz value and the arithmetic average height Ra are determined in accordance with JIS B 0601 from a cross-sectional curve that appears at the cut surface when a target surface is cut by a plane perpendicular to the target surface. A roughness curve obtained by removing a component longer than the wavelength with a phase compensation high-pass filter can be obtained, or can be directly read using an ultradeep shape measuring microscope or the like.

  The shape of the concavo-convex structure is not particularly limited, but may be a shape that narrows the light emission direction, such as a hemispherical protrusion, a conical protrusion, a pyramidal protrusion, a saddle-shaped lenticular lens, and a prism pattern with a sawtooth cross section. . When the concavo-convex structure is a prismatic pattern having a sawtooth cross section, the balance between luminance and luminance uniformity can be made suitable. At this time, the vertex angle of each linear prism constituting the prism row can be set to 60 degrees to 170 degrees. Thereby, the balance between luminance and luminance uniformity can be made suitable. The apex angle is more preferably 80 ° to 150 °, and further preferably 90 ° to 120 °. If the apex angle is too small, the average luminance is lowered, and if the apex angle is too large, the luminance uniformity may be deteriorated.

  The prism array having a sawtooth cross section has a configuration in which a plurality of linear prisms having a triangular cross section perpendicular to the longitudinal direction are arranged substantially in parallel. As a configuration of this prism array, a cross section cut in a direction perpendicular to the longitudinal direction forms a shape in which triangular linear prisms are connected, or a triangular linear prism is connected to form a V-shaped groove. Such a shape, or a shape in which a horizontal portion exists between the bottoms of triangular linear prisms can be used. Among these, a configuration in which triangular bases are connected to form a V-shaped groove is preferable in order to diffuse light appropriately. The shape of the triangle is not particularly limited as long as it is within the range of the above-described apex angle, but is preferably an isosceles triangle so that the luminance in the front direction of the liquid crystal display is the highest.

  In the present invention, the dimension in the width direction (width dimension) of the bottom portion of the linear prism constituting the prism row is preferably 20 μm or more and 700 μm or less, more preferably 30 μm or more and 500 μm or less, and 40 μm or more and 400 μm. More preferably, it is as follows. If the width dimension is less than the above numerical range, the shape may be difficult due to the fine shape, or the light diffusion effect may be reduced. When the width dimension exceeds the above numerical range, the light diffusion becomes rough, and there is a possibility that luminance unevenness occurs.

  The surface of the prism row of the light diffusing plate can be roughened and the direction in which the light is emitted can be more varied within an appropriate range. In that case, the arithmetic average height Ra when the prism surface is measured at 20 μm in the direction perpendicular to the longitudinal direction is preferably 0.08 μm or more and 3 μm or less, more preferably 0.09 μm or more and 2 μm or less. More preferably, it is 1 μm or more and 1 μm or less. When Ra is in the preferred range, the light emission direction can be appropriately diversified.

  In the backlight device of the present invention, when a linear light source is used as the light source, when the light diffusion plate has a prism row, the ridge line direction of the prism row of at least one light diffusion plate is the longitudinal direction of the linear light source. The angle formed with the direction is preferably 60 degrees or less. This angle is more preferably 50 degrees or less, and further preferably 45 degrees or less. By setting the angle formed by the longitudinal direction of the linear light source and the ridge line direction of the prism row within the above range, luminance unevenness can be reduced.

  In the case of using a point light source as the light source, when the uneven structure formed on each light diffusion plate is a prism array, the longitudinal direction of the linear prism of one light diffusion plate and the longitudinal direction of another light diffusion plate It is preferable to arrange a plurality of light diffusing plates so that the directions intersect. In this case, for example, these directions may intersect each other at 60 °.

  There is no particular limitation on the method for forming the concavo-convex structure having an Rz value of 200 μm or less on the surface of the light diffusing plate used in the apparatus of the present invention. For example, the concavo-convex structure having an Rz value of 200 μm or less is formed on the flat light diffusing plate surface. Alternatively, an uneven structure having an Rz value of 200 μm or less can be formed simultaneously with the formation of the light diffusing plate. There is no particular limitation on the method for forming a concavo-convex structure with an Rz value of 200 μm or less on the surface of a flat light diffusing plate. For example, it can be performed by cutting, or a photo-curing resin is applied to transfer the shape of a mold. It can also be cured in the state. When a light diffusing plate is produced by extrusion molding and a concavo-convex structure having an Rz value of 200 μm or less is formed at the same time, it can be extruded by using a deformed die having the shape of the concavo-convex structure, or embossed after extrusion. Thus, a concavo-convex structure can also be formed. In the case where the light diffusing plate is produced by casting and the prism row is formed at the same time, a casting mold having a concavo-convex structure can be used. When the light diffusing plate is produced by injection molding and the concavo-convex structure is formed at the same time, a mold having the concavo-convex structure can be used.

  The thickness of the light diffusing plate of the present invention is 0.4 mm to 5.0 mm. If the thickness is smaller than the above numerical range, not only is it easy to deform due to moisture absorption, but a device for suppressing deflection due to its own weight, such as the formation of a large number of support columns, is required, and the cost of the backlight increases. If the thickness exceeds the above numerical range, molding becomes difficult and the weight of the backlight also increases. Furthermore, from the viewpoint of balancing the stability of the shape due to the influence of humidity, the ease of molding, and the lightness of the backlight, the thickness of the light diffusing plate is more preferably from 0.8 mm to 4.0 mm. More preferably, it is from 0.0 mm to 3.5 mm.

  The material of the light diffusing plate may be glass, transparent resin, a mixture of two or more resins difficult to mix, a material in which a light diffusing agent is dispersed in transparent resin, and the like, but is not particularly limited. Among these, a resin is preferable because of light weight and easy molding, and a material in which a light diffusing agent is dispersed in a transparent resin is preferable because adjustment of total light transmittance and haze is easy. Moreover, since it is easy to recycle, a thermoplastic transparent resin can be suitably used.

  In the present invention, the transparent resin refers to a resin having a total light transmittance of 70% or more measured with a 2 mm thick plate smooth on both sides according to JIS K7361-1.

  Further, in the case of a light diffusing plate having a concavo-convex structure, it is preferable to produce a thermoplastic resin by injection molding because it can be easily molded in a short time. It is formed with a transparent resin dispersed with a light diffusing agent up to the uneven structure part and adjusted so that the entire light diffusing plate has the same total light transmittance and haze, further improving the light diffusibility, This is preferable because the luminance uniformity can be improved.

  The content of the light diffusing agent in which the light diffusing agent is dispersed in a transparent resin is not particularly limited, and can be appropriately selected according to the thickness of the light diffusing plate, the linear light source interval of the backlight, etc. It is preferable to adjust the content of the light diffusing agent so that the total light transmittance of the dispersion is 60% to 95%, and the content of the light diffusing agent is adjusted to be 65% to 95%. More preferably. It is preferable to adjust the content of the light diffusing agent so that the haze is 40% or more and 94% or less, and it is more preferable to adjust the content of the light diffusing agent so as to be 50% or more and 94% or less. The brightness can be further improved by setting the total light transmittance to 60% or more and the haze to 94% or less, and the brightness uniformity can be further improved by setting the total light transmittance to 95% or less and the haze to 40% or more. Can be improved.

  The total light transmittance in this case is a value measured with a 2 mm thick plate smooth on both sides according to JIS K7361-1, and the haze is a value measured with a 2 mm thick plate smooth on both sides according to JIS K7136.

  By arranging one or more light diffusing plates having a total light transmittance of 60% or more and 95% or less and a haze of 40% or more and 94% or less, the brightness and luminance uniformity can be improved in a balanced manner. By arranging two, the luminance uniformity can be improved while keeping the luminance high.

  Examples of the transparent resin constituting the light diffusion plate used in the present invention include polyethylene, propylene-ethylene copolymer, polypropylene, polystyrene, an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester having a lower alkyl group. Copolymer, polyethylene terephthalate, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, resin having an alicyclic structure, and the like. Among these, a copolymer of an aromatic vinyl monomer containing 10% or more of an aromatic vinyl monomer such as polycarbonate, polystyrene or styrene and a (meth) acrylic acid alkyl ester having a lower alkyl group Alternatively, a resin having a water absorption rate of 0.25% or less, such as a resin having an alicyclic structure, is preferable in that a large light diffusing plate with less warpage can be obtained because deformation due to moisture absorption is small. A resin having an alicyclic structure is more preferable because it has good fluidity and can efficiently produce a large light diffusion plate. A compound in which a resin having an alicyclic structure and a light diffusing agent are mixed has both high permeability and high diffusibility necessary for a light diffusing plate, and has good chromaticity, so that it can be suitably used.

  The resin having an alicyclic structure is a resin having an alicyclic structure in the main chain and / or side chain. From the viewpoint of mechanical strength, heat resistance, etc., a resin containing an alicyclic structure in the main chain is particularly preferred. Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From the viewpoint of mechanical strength, heat resistance, etc., a cycloalkane structure or a cycloalkene structure is preferable, and among them, a cycloalkane structure is most preferable. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The properties of heat resistance and moldability of the light diffusing plate are highly balanced and suitable.

  The proportion of the repeating unit having an alicyclic structure in the resin having an alicyclic structure may be appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90%. % By weight or more. When the ratio of the repeating unit having an alicyclic structure is too small, the heat resistance is lowered, which is not preferable. 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 the intended purpose.

  Specific examples of the resin having an alicyclic structure include (1) a ring-opening polymer of a norbornene monomer and a ring-opening of the norbornene monomer and other monomers capable of ring-opening copolymerization with this. Norbornene polymers such as copolymers, addition products of these hydrogenated products, norbornene monomers, and addition copolymers of norbornene monomers with other monomers copolymerizable therewith (2) a monocyclic olefin polymer and a hydrogenated product thereof; (3) a cyclic conjugated diene polymer and a hydrogenated product thereof; (4) a polymer of a vinyl alicyclic hydrocarbon monomer and Copolymers of vinyl alicyclic hydrocarbon monomers and other monomers copolymerizable therewith, as well as hydrogenated products thereof, aromatic ring hydrogen of polymers of vinyl aromatic monomers Additives and other vinyl aromatic monomers copolymerizable therewith Vinyl alicyclic hydrocarbon polymers such as hydrogenated products of the aromatic rings of the copolymer and the amount thereof; and the like. Among these, from the viewpoints of heat resistance, mechanical strength, and the like, norbornene-based polymers and vinyl alicyclic hydrocarbon-based polymers are preferable, ring-opening polymer hydrogenated norbornene-based monomers, norbornene-based single monomers Ring-opening copolymer hydrogenated product of this product with other ring-opening copolymerizable monomers, vinyl aromatic monomer hydrogenated aromatic vinyl monomer and vinyl aromatic monomer More preferred is a hydrogenated aromatic ring of a copolymer of the above and other monomers copolymerizable therewith.

  The light diffusing agent used for the light diffusing plate is a particle having a property of diffusing light, and is roughly classified into an inorganic filler and an organic filler. Specifically, silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, or a mixture thereof can be used as the inorganic filler. Specific examples of the organic filler include acrylic resin, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, and benzoguanamine resin. Among these, fine particles made of polystyrene resin, polysiloxane resin, or cross-linked products thereof can be used particularly suitably because they have high dispersibility, high heat resistance, and no coloration (yellowing) during molding. . Fine particles made of a cross-linked product of polysiloxane resin are more suitable for use because they are superior in heat resistance.

  The shape of the light diffusing agent used in the light diffusing plate is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, and a fiber shape. Spherical beads that can be isotropic are preferred. The light diffusing agent is contained in a transparent resin and is used after being macroscopically dispersed uniformly and spaced apart.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Production Example 1>
Resin having an alicyclic structure as a transparent resin [Nippon Zeon Co., Ltd., ZEONOR 1060R, water absorption 0.01%] 99.7 parts by weight, and fine particles comprising a crosslinked product of a polysiloxane polymer as a light diffusing agent [ GE Toshiba Silicone Co., Ltd., Tospearl 120] 0.3 parts by weight was mixed, kneaded with a twin-screw extruder, extruded into a strand, and cut with a pelletizer to produce pellets 1 for a light diffusion plate. From this light diffusion plate pellet, a 100 mm × 50 mm test plate having a smooth thickness of 2 mm on both sides was molded using an injection molding machine [clamping force 1000 kN]. The total light transmittance and haze of this test plate were measured using an integrating sphere color difference turbidimeter according to JIS K7361-1 and JIS K7136. The total light transmittance was 85%, and the haze was 92%.

<Production Example 2>
Resin having an alicyclic structure [Nippon ZEON Co., Ltd., ZEONOR 1060R water absorption 0.01%] fine particles composed of 99.2 parts by weight and a cross-linked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120 The pellet 4 for light diffusing plate was produced in the same manner as in Production Example 1 except that 0.8 part by weight was used, and the total light transmittance and haze were measured in the same manner as in Production Example 1. Was 65% and haze was 92%.

<Production Example 3>
Styrene-methyl methacrylate copolymer resin [manufactured by Nippon Steel Chemical Co., Ltd., Estyrene MS-600, water absorption 0.20%] fine particles comprising 99.8 parts by weight of a cross-linked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120] 0.2 parts by weight was mixed to produce a light diffusion plate pellet 5 in the same manner as in Production Example 1, and the total light transmittance and haze were measured in the same manner as in Production Example 1, The total light transmittance was 83% and the haze was 91%.

<Example 1>
Using the injection molding machine (clamping force 4410 kN) from the light diffusion plate pellet 1, a prism row having a cross-sectional shape in which isosceles triangles with a pitch of 70 μm and an apex angle of 110 degrees are connected is formed in parallel with the longitudinal direction. A light diffusion plate having a thickness of 2 mm and a thickness of 407 mm × 305 mm was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. When the surface of the molded light diffusion plate was observed with an ultra-deep microscope, the maximum height Rz value was 24 μm.

  A reflector sheet (RF188, manufactured by Tsujiden Co., Ltd.) is attached to the bottom of a milky white plastic case with an inner width of 400 mm, a depth of 300 mm, and a depth of 18 mm. The reflector is 4 mm away from the reflector and has a diameter of 4 mm. Twelve 420 mm cold-cathode tubes were arranged with a distance between the centers of the cold-cathode tubes of 25 mm, the vicinity of the electrode portion was fixed with a silicone sealant, and an inverter was attached. With the above light diffusion plate as the first sheet, the prism row is parallel to the cold cathode tube and on the opposite side, and the distance between the cold cathode tube center and the surface of the light diffusion plate closer to the cold cathode tube is It installed so that it might be set to 14 mm. Furthermore, the light diffusing plate created by the same method on the side far from the light source is stacked in the same direction as the second sheet, and further, a diffusion sheet (Light Up 100GM3 manufactured by Kimoto Co., Ltd.) is added to the layer containing the light diffusing agent from the light diffusing plate. One was installed so that it might be on the far side. A reflective polarizer (DBEF-M manufactured by Sumitomo 3M Limited) using birefringence was installed thereon, and a polarizing plate was further attached.

Next, a tube current of 6 mA and a tube voltage of 330 Vrms were applied to light the cold cathode tube, and using a two-dimensional color distribution measuring device, the luminance at 100 points was measured at equal intervals on the center line in the longitudinal direction. The luminance average value La and the luminance uniformity Lu were obtained according to 1 and Equation 2. At this time, the luminance average value was 3025 cd / m ² and the luminance uniformity was 0.9.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance uniformity Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average brightness maximum value just above a plurality of cold-cathode tubes installed L2: Average minimum value sandwiched between maximum values

  The luminance uniformity is an index indicating the uniformity of luminance. When the luminance uniformity is poor, the numerical value becomes large. Further, the light diffusion plate and the optical sheet thereon were removed from a commercially available 20-inch liquid crystal television, and instead, the two light diffusion plates, the diffusion sheet, the reflective polarizer, and the polarizing plate were attached in the same order. After this television was left at 40 ° C. and 95% RH for 72 hours, a signal for displaying a white screen was given to the entire surface, and the backlight was turned on to observe the image. As a result, no unevenness was observed in the image.

<Example 2>
Evaluation was performed in the same manner as in Example 1 except that a second light diffusion plate obtained using a resin having an alicyclic structure not containing a light diffusing agent (Zeonor 1060R pellets) was used. . The average luminance value was 3205 cd / m ² , and the luminance uniformity was 1.2. As in Example 1, no unevenness was observed in the observed image after standing under high humidity.

<Example 3>
The same as Example 1 except that the light diffusing plate obtained by using the light diffusing agent-containing styrene-methyl methacrylate copolymer resin (MS resin) pellet of Production Example 3 is used for the first and second sheets. And evaluated. The Rz value of the diffusion plate was 23.5 μm. The luminance average value was 3196 cd / m ² and the luminance uniformity was 1.1. As in Example 1, no unevenness was observed in the observed image after standing under high humidity.

<Example 4>
Evaluation was performed in the same manner as in Example 1 except that a second light diffusion plate obtained by using a mold having no prism array and a smooth surface was used. The luminance average value was 3095 cd / m ² , and the luminance uniformity was 2.0. As in Example 1, no unevenness was observed in the observed image after standing under high humidity.

<Example 5>
From the light diffusion plate pellet 1, using an injection molding machine (clamping force 4410 kN), a prism row having a cross-sectional shape in which isosceles triangles with a pitch of 70 μm and an apex angle of 110 degrees are connected to each other is formed of a rectangular light diffusion plate. Directions of angles of 30 degrees and -30 degrees formed with the longitudinal direction (the directions of 30 degrees and -30 degrees are directions of 30 degrees on one side and 30 degrees on the other side with respect to the longitudinal direction) A light diffusion plate having a thickness of 2 mm and a thickness of 407 mm × 305 mm was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. When the surface of the molded light diffusion plate was observed with an ultra-deep microscope, the maximum height Rz value was 24 μm.

Next, a 0.5 mm aluminum plate is laid on the bottom of the milky white plastic case for heat dissipation, and a reflective sheet (RF 188, manufactured by Tsujiden Co., Ltd.) is pasted thereon to form a reflective plate, and the bottom of the reflective plate is cooled. A white chip type LED (NCCWO22S manufactured by Nichia Chemical Co., Ltd .: size: 7.2 × 11.2 × 4.7 mm) instead of the cathode tube is used as a point light source, and the center is evenly and squarely 30 mm both vertically and horizontally. Installed in an array, wired so that a direct current can be supplied to the electrode section, and the two light diffusion plates installed on the upper part of the prism array and the longitudinal direction of the backlight are at the angle of the first sheet Example 1 except that two light diffusion plates were provided such that the light diffusion plate was oriented at +30 degrees and the second light diffusion plate was oriented at −30 degrees. And evaluated. FIG. 2 shows the configuration of the backlight device according to this example. The direction of the prism row formed on the lower light diffusion plate in the figure intersects with the direction of the prism row formed on the upper light diffusion plate in the drawing, and the angle formed is 60 degrees. It is. In this example, the luminance average value was 5130 cd / m ² , and the luminance uniformity in the short direction directly above the LED was 1.8. As in Example 1, no unevenness was observed in the observed image after standing under high humidity.

<Comparative Example 1>
Evaluation was performed in the same manner as in Example 1 except that both the first and second light diffusing plates obtained using a mold having no prism array and a smooth surface were used. The luminance average value was 2482 cd / m ² and the luminance uniformity was 2.0. As in Example 1, no unevenness was observed in the observed image after standing under high humidity.

<Comparative Example 2>
Evaluation was performed in the same manner as in Example 1 except that only the first light diffusion plate was used and the second light diffusion plate was not used. The luminance average value was 3205 cd / m ² , and the luminance uniformity was 5.5. As in Example 1, no unevenness was observed in the observed image after standing under high humidity.

<Comparative Example 3>
In the same manner as in Example 1 except that only the first light diffusing plate was used, the second light diffusing plate was not used, and a prism sheet (BEFII manufactured by Sumitomo 3M Limited) was used instead. Evaluation was performed. The luminance average value was 3323 cd / m ² , and the luminance uniformity was 0.9. As in Example 1, large unevenness was observed in the observed image after being left under high humidity.

<Comparative example 4>
Evaluation was performed in the same manner as in Example 5 except that only the first light diffusion plate was used and the second light diffusion plate was not used. The luminance average value was 5330 cd / m ² , and the luminance uniformity was 6.8. As in Example 5, no unevenness was observed in the observed image after standing under high humidity.

  The configuration and measurement results of Examples 1 to 5 are shown in Table 1, and the configuration and measurement results of Comparative Examples 1 to 4 are shown in Table 2.

In Examples 1 to 4, without using an expensive prism sheet having low moisture resistance, the average luminance is 3000 cd / m ² or more and the luminance uniformity is 2.0 or less, which is not much different from Comparative Example 1 using a prism sheet. The display is uneven and the display is not observed after being left under high humidity. In addition, when none of the light diffusion plates has a fine structure as in Comparative Example 1, the luminance is low, and when only one light diffusion plate is used as in Comparative Example 2, the luminance uniformity is not good. . In Comparative Example 3 using one light diffusing plate and a prism sheet, display unevenness occurs after leaving under high humidity. Furthermore, as shown in Example 5, even when the light source is an LED, good uniformity is obtained, and display unevenness after being left under high humidity is not observed.

  According to the direct type backlight device of the present invention, it is possible to improve the average luminance and the luminance uniformity, and the moisture resistance is good. Therefore, when the direct type backlight is incorporated in the liquid crystal display device, it has high image quality. A liquid crystal display screen that is not easily affected can be obtained.

It is the perspective view of the direct type backlight apparatus of this invention, and its one part enlarged view. 10 is a perspective view schematically showing a direct type backlight device according to Embodiment 5. FIG.

Explanation of symbols

1 Diffusion sheet 3 Linear light source (light source)
4 Reflecting plates 21, 22 Light diffusing plates 51, 52

Claims (6)

A direct type backlight device configured by arranging a plurality of light sources, a reflecting plate for reflecting light from the light source, and a plurality of light diffusing plates in the order of the reflecting plate, the light source, and the plurality of light diffusing plates. And
The thickness of each light diffusion plate is 0.4 mm to 5.0 mm, respectively.
A direct-type backlight device having a concavo-convex structure having an Rz value of 200 μm or less on a part or all of at least one main surface of at least one light diffusion plate. The direct type backlight device according to claim 1,
The shape of the concavo-convex structure with an Rz value of 200 μm or less is a cross-sectional sawtooth prism array in which a plurality of linear prisms having a triangular cross section and an apex angle of 60 to 170 degrees are arranged in parallel.
The direct-type backlight device, wherein a dimension in a width direction of a bottom surface portion of the linear prism is 20 μm to 700 μm. A direct type backlight device according to claim 2,
The plurality of light sources are a plurality of linear light sources arranged in parallel,
Of the light diffusion plates having a prism row, the angle between the ridge line direction of the prism row of at least one light diffusion plate and the longitudinal direction of the linear light source is 60 degrees or less. Light equipment. The direct type backlight device according to claim 1, 2, or 3,
The direct-type backlight device, wherein the uneven structure having an Rz value of 200 μm or less is provided only on the surface of the light diffusing plate that is far from the light source. The direct type backlight device according to claim 1, 2, 3 or 4,
At least one light diffusion plate is made of a material in which a light diffusing agent is dispersed in a transparent resin, and the total light transmittance of the dispersion is 60% or more and 95% or less, and haze is 40% or more and 94% or less. A direct-type backlight device characterized by that. 6. The direct type backlight device according to claim 1, 2, 4, or 5, wherein the light source is a point light source.

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