JP2007134281A - Backlight unit and liquid crystal display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit requiring no specific pattern formation corresponding to various light sources, and to provide a liquid crystal display device incorporating the backlight unit. <P>SOLUTION: The backlight unit has a light source, a reflecting part disposed at least on the back side of the light source to reflect light from the light source, a light diffusing part disposed on the front side of the light source to diffuse light from the light source, which enters the diffusing part directly or by being reflected by the reflecting part, The diffusing part contains at least one anisotropic diffusion medium in which a quantity of linearly transmitted light differs depending on the angle of incidence of light from the light source. This backlight unit is incorporated in the liquid crystal display device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight unit for illuminating a liquid crystal display unit or the like from behind, and more particularly to a direct type backlight unit.

The liquid crystal display device is a display device that is visible by illumination from a normal backlight because it is not self-luminous. There are two types of backlights, an edge light type and a direct type. In the edge light type, a light source is arranged at the edge portion of a light guide plate made of a transparent acrylic plate or the like, and light from the light source is emitted in the front direction of the light guide plate by a light guide plate, a reflection plate, a diffusion film, etc. It is mainly used for small and medium-sized displays. On the other hand, the direct type irradiates light from a light source arranged directly below the display screen through a reflection plate and a diffusion plate, and is used in applications that require high brightness and large display devices.
As shown in FIG. 1, this direct type backlight has light sources arranged at regular intervals on the bottom of a box-shaped housing (not shown), and is reflected on the inside of the housing other than the installation position of the light diffusion portion. The part is arranged. On the upper side of the housing, the opening of the box is arranged so that the light diffusion part covers the gap from the light source. The light diffusing unit diffuses light that is directly incident from the light source or light that is reflected from the light source and guided by the reflecting unit, and emits light of uniform intensity from the upper surface of the diffusion plate. It is indispensable.
As the light source, a cold cathode tube or an LED is used, and an aluminum or silver vapor deposition film or a synthetic resin film or plate containing a large amount of white pigment such as titanium oxide on the surface or inside thereof is used for the reflection portion. As the light diffusing portion, a transparent synthetic resin plate is generally used in which resin or inorganic fine particles having a refractive index different from that of the resin are dispersed on the surface or inside thereof.

  By the way, in this direct type backlight, since the light emitting part of the light source is arranged in a discrete state, when viewed through a normal light diffusion part, the luminance of the part where the light source exists directly below is brighter than its surroundings, A so-called lamp image in which the shape of the light source is raised can be seen. Therefore, various ideas have been devised to suppress this and make the luminance of the entire surface uniform. In Patent Document 1, a light reflection pattern corresponding to the distance to the light source is formed in the light diffusing section. In Patent Document 2, the surface facing the light source of the light diffusing section is changed according to the distance from the light source. Unevenness is formed. Further, in Patent Document 3, a light diffusing unit is provided in which a light control dot pattern having a predetermined total light transmittance and a haze value is printed in a predetermined shape and size at a predetermined position in the light projecting direction of the light source. It is shown. Here, the ink for forming the light control dot pattern is prepared by blending a light shielding agent and a diffusing agent at a predetermined blending concentration. Furthermore, in order to correct the difference in luminance between the high pressure side and the low pressure side in the cold cathode tube as the light source, in addition to the normal diffusion part agent, another diffusion part agent is directly disposed only on the upper side of the high pressure side with high luminance. An example is shown in US Pat. In many of these attempts, it is necessary to form a specific pattern on the surface of the light diffusing member in accordance with the shape and position of the light source, and the fabrication is very troublesome. There was a problem that it was greatly damaged. And it was necessary to prepare the light-diffusion part which consists of a light-diffusion member which has a different pattern for every model of backlight.

  The light diffusing member has not been used for lighting fixtures and building materials for a long time, but is also widely used in recent displays, particularly LCDs. The light diffusion mechanism of these members includes scattering due to irregularities formed on the surface (surface scattering), scattering due to a difference in refractive index between the matrix resin and the filler dispersed therein (internal scattering), and surface scattering. This is due to both internal scattering. However, the diffusion performance of these light diffusing members is generally isotropic, and even if the incident angle is slightly changed, the diffusion characteristics of the transmitted light are not greatly different.

  However, there has been proposed a light control plate that can selectively scatter only incident light from a specific angle (see, for example, Patent Document 5). This special light diffusing member, which is a light control plate, has a specific direction in a resin composition composed of a plurality of compounds having one or more photopolymerizable carbon-carbon double bonds in molecules having different refractive indexes. A plastic sheet cured by irradiating with ultraviolet rays, and only incident light having a specific angle with respect to the sheet is selectively scattered.

  As a material for producing this light control plate, the above-mentioned “resin composition comprising a plurality of compounds having at least one photopolymerizable carbon-carbon double bond in a molecule having a difference in the respective refractive indexes” In addition to the above, compositions containing urethane acrylate oligomers are disclosed (for example, see Patent Documents 6 to 8). Further, a combination of compound A having a polymerizable carbon-carbon double bond in the molecule and compound B having no polymerizable carbon-carbon double bond having a refractive index difference of 0.01 or more with this A , Compounds having a plurality of polymerizable carbon-carbon double bonds in the molecule and having a refractive index difference of 0.01 or more before and after curing (for example, see Patent Document 9), and radical polymerization A combination of a functional compound and a cationically polymerizable compound having a vinyl ether as a functional group is also disclosed (see, for example, Patent Document 10).

  The incident angle dependence of the scattering characteristics that these light control plates can selectively scatter only incident light from a specific angle is shown in FIG. This is observed when the light control plate is rotated around the line projected on the surface of the light control plate with the linear light source arranged above it. On the other hand, when rotating around a line orthogonal to the projection line of the linear light source, the incident angle dependence of the scattering characteristic is hardly seen, or it is rotated around the projection line of the previous linear light source. The incident angle dependency of the scattering characteristic that is significantly different from the case is obtained.

JP-A-6-273760 Japanese Patent Laid-Open No. 6-273663 JP 2005-1117023 A Japanese Patent Laid-Open No. 7-288023 JP-A-1-77001 Japanese Patent Laid-Open No. 1-1147405 JP-A-1-147406 JP-A-2-54201 Japanese Patent Laid-Open No. 3-109501 JP-A-6-9714

  The present invention has been made in view of the above situation, and a backlight unit using an anisotropic diffusion medium that does not require specific pattern formation according to various light sources, and a liquid crystal display incorporating the backlight unit. The object is to provide an apparatus.

  The backlight unit of the present invention includes a light source, a reflective portion disposed on at least the back side of the light source that reflects light from the light source, and disposed on the front side of the light source and reflected directly or by the reflective portion. And a light diffusing unit that diffuses the incident light from the light source, and the light diffusing unit includes at least one anisotropic diffusion medium having a different amount of linearly transmitted light depending on an incident angle of the light from the light source. It is characterized by that.

  The anisotropic diffusion medium of the present invention is obtained by curing a composition containing a photocurable compound and has a scattering center axis.

  The light diffusing section of the present invention has at least a light diffusing medium formed by laminating at least one layer made of the anisotropic diffusing medium, and may be configured to include other light diffusing media in some cases. To do.

  The light source of the present invention is characterized by using one or a plurality of cold cathode tubes and LEDs.

  The liquid crystal display device of the present invention is characterized in that the backlight unit is disposed on the back surface of the liquid crystal display unit.

  The anisotropic diffusion medium used for the light diffusion portion of the backlight unit of the present invention has a scattering center axis, and selectively receives light incident from a direction within a certain polar angle range surrounding the scattering center axis. Since the light is scattered, it is possible to obtain uniform emitted light from the light diffusing portion without forming a specific pattern provided on the light diffusing member immediately above according to the shape of the light source. Therefore, not only the labor and expense of pattern formation become unnecessary, but also applicable to many types of backlight units, it is possible to reduce the cost by reducing the types of members.

  The backlight unit of the present invention uses an anisotropic diffusion medium as one of the light diffusing members constituting the light diffusing portion shown in FIG. As this anisotropic diffusion medium, a medium having a scattering center axis is preferably used. In this anisotropic diffusion medium, the direction of the incident angle at which the scattering of the incident light is the strongest and the direction of the strongest incident light that is incident on the anisotropic diffusion medium from the light source are substantially matched, so that the strong incident light is The amount of light in this direction is reduced by being strongly scattered, while incident light in the other directions is transmitted without being scattered. As a result, the in-plane uniformity of the amount of light transmitted through the light diffusion portion is increased.

  An anisotropic scattering medium having a scattering central axis is a so-called anisotropic scattering characteristic in which the light scattering characteristic changes when the incident angle is changed, and exhibits substantially symmetry about the scattering central axis. Therefore, the former stage will be described using the scattering center axis. By aligning the direction of the strongest incident light incident on the anisotropic diffusion member from the light source with the scattering center axis, the light diffusion having the anisotropic diffusion medium is performed. This means that the in-plane uniformity of the amount of light transmitted through the portion is increased.

  FIG. 2A shows an example in which a conventional isotropic diffusion plate is used for the light diffusion portion. When light from the light source passes through the light diffusion part, the distance is close and the linear transmitted light intensity is the strongest in the direction directly above the light source, but in the area of the isotropic diffuser that falls between the two light sources, the distance from the light source Therefore, the amount of incident light is relatively weak, and thus the lamp image can be seen by being emitted relatively weakly. On the other hand, in FIG. 2B in which the anisotropic diffusion medium used in the present invention in which the scattering center axis coincides with the normal direction is used for the light diffusion portion, the diffusion is strong in the portion directly above the light source, so However, in the region of the anisotropic diffusion medium that falls between the two light sources, the amount of light that is incident on the anisotropic diffusion medium in an oblique direction and transmitted is large.

  The anisotropic diffusion plate used in the present invention is made of a cured product of a composition containing a photocurable compound, and the internal structure of the one having a scattering center axis is a minute region 5 as shown in FIG. Many are formed. In FIG. 3, the minute region 5 is schematically illustrated in a columnar shape, but the shape is not particularly limited, such as a circular shape, a polygonal shape, or an indefinite shape. These minute regions 5 are formed by irradiating ultraviolet rays parallel to each other from a point light source arranged in the normal S direction of the anisotropic diffusion medium 4, and these minute regions are all parallel to the normal S direction. Is formed.

  The optical micrograph of the AA sectional view in FIG. 3 is shown in FIG. 4A, and the optical micrograph of the BB sectional view is shown in FIG. 4B. It can be confirmed that the minute region 5 exists in both the sectional views. In the anisotropic diffusion medium of FIG. 3, since the microregion 5 exists in any cross section as described above, light scattering characteristics can be obtained for incident light from any direction.

  In the present invention, since the in-plane uniformity of the light emitted from the light diffusion portion of the backlight unit is required, an anisotropic diffusion plate having the characteristics shown in FIG. 3 is essential.

  As an index for evaluating the light scattering characteristics of the light diffusing medium, diffuse transmittance, parallel light transmittance, and haze normally indicated by JIS-K7105 and JIS-K7136 are used. These are measured by irradiating light from the normal direction under the condition that the sample is brought into close contact with the integrating sphere and there is no light leakage, and measurement by arbitrarily changing the incident angle is not assumed. In other words, there is no officially recognized method for evaluating the incident angle dependence of the diffusion characteristics of anisotropic diffusion media. Therefore, in order to measure the optical characteristics of the anisotropic diffusion medium used in the present invention, as shown in FIG. 7, a sample is arranged between a light source (not shown) and the light receiver 6, and a straight line L on the sample surface is obtained. The incident angle dependence of the linearly transmitted light was evaluated based on the measurement principle of measuring the amount of light entering the light receiver 6 through the sample while changing the angle with respect to the center. As a specific apparatus, a commercially available haze meter, goniophotometer, or spectrophotometer in which a rotatable sample holder is provided between the light source and the light receiving unit can be used. Although the light quantity value obtained here is only relative, a measurement result as shown in FIG. 8 can be obtained as the angle dependency of the linear transmitted light quantity.

  Although this result does not represent the direct light scattering characteristic, it can be said that the light scattering characteristic is generally shown because the diffuse transmitted light quantity increases conversely when the linear transmitted light quantity decreases. Therefore, the angle dependence of the light scattering characteristic will be described below using the linear transmitted light amount.

  FIG. 9 is a schematic cross-sectional view for explaining the incident angle dependence of the linear transmitted light amount transmitted through the anisotropic diffusion medium shown in FIG. 3 by the linear transmitted light amount measured by the above measuring method. In FIG. 9, the code | symbol 5 represents the rod-shaped hardening area | region typically, and the rod-shaped hardening area | region has extended in the normal line S direction here. When light enters from above and exits downward from the anisotropic diffusion medium, the incident light I0 incident from the normal S direction, that is, the extending direction of the rod-shaped cured region, passes through the anisotropic diffusion medium. Therefore, the corresponding linear transmitted light amount is small. In FIG. 9, this is represented by a transmitted light vector T0 having the same direction as I0 and having a magnitude proportional to the linear transmitted light amount. Next, with respect to the incident light I1 inclined by a certain angle from the incident light I0, the corresponding linearly transmitted light amount increases, so that the transmitted light vector T1 is larger than T0. Furthermore, in the incident light I2 from an angle deeper than the incident light I1, the corresponding transmitted light vector T2 is larger than T1.

  For all the incident light inclined from the incident light I0, the transmitted light quantity is expressed by a vector in the same manner as described above, and a curve having symmetry as shown by a broken line in FIG. Furthermore, when the same examination is performed on other cross sections including the incident light I0, the same broken line curve as that of FIG. 9 is obtained for all the cross sections. That is, when the tips of the transmitted light vectors obtained in all directions are connected, a bell-shaped curved surface having a scattering center axis in the normal S direction as shown in FIG. 10 is obtained.

  The anisotropic diffusion medium of the present invention is not limited only to the above-described embodiment. For example, as shown in FIG. 11, the anisotropic diffusion medium having a direction P inclined at an arbitrary angle from the normal S direction is used. It is also possible to use an ionic diffusion medium.

  FIG. 12 is a schematic cross-sectional view for explaining the incident angle dependence of the amount of linearly transmitted light that passes through the anisotropic diffusion medium shown in FIG. In FIG. 12, reference numeral 5 schematically shows a rod-like hardened region. When this anisotropic diffusion medium is examined in the same manner as described above, the incident light I0 from the P direction, which is the extending direction of the rod-shaped hardened region, and the transmission light corresponding to the incident light I1 and I2 tilted with respect thereto. If the tips of the light vectors T0, T1, and T2 are connected, the curve shown by the broken line in FIG. 12 is obtained, and if the tips of the transmitted light vectors are connected in the same manner for all cross sections including the incident light I0, FIG. A bell-shaped curved surface having a scattering center axis in the direction P is obtained.

  In addition, there exists what formed the parallel plate-shaped structure like FIG. 5 in what is corresponded to the light control board known from before. FIG. 6A shows an optical micrograph of the cross section along the line AA in FIG. 5 and FIG. 6B shows an optical micrograph of the cross section along the line BB. Although a structure extending in the thickness direction is confirmed, it can be seen only homogeneously by observation of the cross section along the line BB. In the anisotropic diffusion medium having such a structure, incident angle anisotropy of light scattering characteristics is observed for incident light parallel to the AA line, but incident light parallel to the BB line is observed. On the other hand, almost no incident angle anisotropy is observed.

  The anisotropic diffusion medium manufactured using a linear light source exhibits the incident angle dependency shown in FIG. 8, but this is only when the sample is rotated around the specific straight line L shown in FIG. However, when the sample is rotated around a straight line orthogonal to the straight line L in the sample plane, the incident angle dependency of the linear transmitted light amount is hardly shown, or a completely different aspect is exhibited. That is, regarding the light control plate produced by irradiating light from a linear light source in the same direction as the straight line L shown in FIG. 13, the angle dependency of the linear transmitted light amount when the light control plate is rotated around the straight line L is As shown by the solid line in FIG. 14, when rotated about the straight line M orthogonal to the straight line L, completely different incident angle dependency is shown as shown by the broken line.

  The symmetry in the present invention refers to the difference between the maximum value and the minimum value of the amount of linear transmitted light in the region where the incident light is in the plus side, ΔR, and the incident angle of the incident light in the direction P in FIG. The negative side is represented by ΔL, which means a case where the relationship of 0.5 ≦ (ΔR / ΔL) ≦ 2 is established.

  The anisotropic diffusion medium used in the backlight unit of the present invention is produced by irradiating a composition containing a photocurable compound with parallel rays from the direction of the straight line P and curing the composition. As the direction of the straight line P, the inclination from the normal line of the medium is preferably within 45 °, more preferably within 30 °, and further preferably within 15 °. It is also a preferred form of the present invention that this straight line P coincides with the normal line. When light is irradiated from a deep inclination of 45 ° or more, the absorption efficiency of the irradiated light is poor, which is disadvantageous in manufacturing, and the linearly transmitted light amount in an arbitrary incident surface including the straight line P shown in the present invention depends on the incident angle. This is not preferable because it is highly possible that the identity of the sex cannot be maintained. As is clear from FIG. 12, when the inclination with respect to the normal line in the direction P is large, even if the incident light beams I2 are inclined with respect to the direction P by the same angle, the optical path length in the anisotropic diffusion medium This is because they differ significantly from each other, resulting in a difference in the amount of transmitted light T2.

  As the form of the light diffusion part of the present invention, an anisotropic diffusion medium alone, a structure in which an anisotropic diffusion medium is laminated on a transparent substrate, or a structure in which a transparent substrate is laminated on both sides of an anisotropic diffusion medium can be provided. is there. As the transparent substrate, the higher the transparency, the better, and the total light transmittance (JIS K7361-1) is 80% or more, more preferably 85% or more, most preferably 90% or more. The haze value (JIS K7136) is preferably 3.0 or less, more preferably 1.0 or less, and most preferably 0.5 or less. A transparent plastic film, a glass plate, or the like can be used, but a plastic film is preferable because it is thin, light, difficult to break, and has excellent productivity. Specifically, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), polycarbonate (PC), polyarylate, polyimide (PI), aromatic polyamide, polysulfone (PS), polyethersulfone ( PES), cellophane, polyethylene (PE), polypropylene (PP), polyvinyl alcohol (PVA), cycloolefin resin and the like can be mentioned, and these can be used alone or in combination or further laminated. The thickness of the substrate is 1 μm to 5 mm, preferably 10 to 500 μm, and more preferably 50 to 150 μm in consideration of use and productivity.

The anisotropic diffusion medium used in the present invention is obtained by curing a composition containing a photocurable compound. As the form of this composition, (A) a form containing a photopolymerizable compound alone, ( B) A form including a mixture of a plurality of photopolymerizable compounds, (C) a form including a mixture of a single or a plurality of photopolymerizable compounds and a polymer compound having no photopolymerizability, and the like. In any of the above forms (A) to (C), as described above, as a result of the formation of a micron-order fine structure having a different refractive index in the anisotropic scattering layer by light irradiation, incidence of a linearly transmitted light amount. It is thought that angular dependence can be expressed.
Therefore, in the form (A), the photopolymerizable compound preferably has a large refractive index change before and after the photopolymerization. In the forms (B) and (C), as the photopolymerizable compound, A combination of a plurality of materials having different refractive indexes is preferable. From the viewpoint of effectively obtaining the effects of the present invention, the refractive index change and the difference in refractive index are preferably 0.01 or more, more preferably 0.05 or more, and 0.10. It is still more preferable that it is above.

The photopolymerizable compound contains a photopolymerizable compound selected from radically polymerizable or cationically polymerizable functional groups, oligomers, and monomers and a photoinitiator, and is cured by irradiation with ultraviolet rays and visible light. It has the property to do.
Further, as a method for producing a sufficient refractive index difference in the photopolymerizable compound, fluorine atoms (F) may be introduced in order to reduce the refractive index, and sulfur (S) may be used in order to increase the refractive index. ), Bromine atoms (Br), and various metal atoms may be introduced. In order to increase the refractive index of the anisotropic diffusion medium, ultrafine particles made of a metal oxide having a high refractive index such as titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), tin oxide (SnO _X ), etc. It is also effective to add functional ultrafine particles into which a photopolymerizable functional group such as an acrylic group or an epoxy group is introduced into the photopolymerizable compound.

  The radically polymerizable compound mainly contains one or more unsaturated double bonds in the molecule. For example, an acrylic oligomer called by the name of epoxy acrylate, urethane acrylate, polyester acrylate, silicone acrylate, etc., and 2 -Ethylhexyl acrylate, phenoxyethyl acrylate, isonorbornyl acrylate, 2-hydroxyethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2-perfluorooctyl-ethyl acrylate, triethylene glycol diacrylate, 1,6- Hexanediol diacrylate, 1,9-nonanediol diacrylate, trimethylolpropane triacrylate, EO modified trimethylolpropane triacrylate, pentaerythritol Li acrylate, pentaerythritol tetra acrylate, acrylate monomers such as dipentaerythritol hexaacrylate.

  As the cationic polymerizable compound, a compound having at least one epoxy group, vinyl ether group or oxetane group in the molecule can be used. Examples of the compound having an epoxy group include bisphenol A, hydrogenated bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetrachlorobisphenol A, tetrabromobisphenol A, and the like. Polyglycidyl ethers of novolak resins such as diglycidyl ethers, phenol novolak, cresol novolak, brominated phenol novolak, orthocresol novolak, ethylene glycol, butanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane , Diglycidyl ethers of alkylene glycols such as EO adducts of bisphenol A, glycidyl esters of hexahydrophthalic acid Glycidyl esters such as diglycidyl esters of Le and dimer acids. Furthermore, alicyclic epoxy compounds such as 3,4-epoxycyclohexanemethyl-3 ′, 4′-epoxycyclohexylcarboxylate, 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene, 3- Oxetane compounds such as ethyl-3- (hydroxymethyl) -oxetane, and vinyl ether compounds such as diethylene glycol divinyl ether and trimethylolpropane trivinyl ether can also be used.

  Photoinitiators that can polymerize radically polymerizable compounds include benzophenone, 2,4-diethylthioxanthone, benzoin isopropyl ether, 2,2-diethoxyacetophenone, benzyldimethyl ketal, 2,2-dimethoxy-1,2 -Diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpho Linopropanone-1, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, bis (cyclopentadienyl) -bis (2,6- Difluoro-3- (pyr-1-yl) titanium, 2-benzyl-2-dimethylamino 1- (4-morpholinophenyl) - butanone -1,2,4,6- trimethyl benzoyl diphenyl phosphine oxide, and the like.

  A photoinitiator capable of polymerizing a cationically polymerizable compound is a compound capable of generating an acid upon irradiation with light and polymerizing the above-mentioned cationically polymerizable compound with the generated acid. Salts and metallocene complexes are preferably used. As the onium salt, a diazonium salt, a sulfonium salt, an iodonium salt, a phosphonium salt, a selenium salt, or the like is used, and an anion such as BF4-, PF6-, AsF6-, or SbF6- is used as these counter ions. Specific examples include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, (4-methoxyphenyl) phenyliodonium hexafluoroantimonate, bis (4-t-butylphenyl) iodonium hexafluorophosphate, (η5- Isopropylbenzene) (η5-cyclopentadienyl) iron (II) hexafluorophosphate and the like.

  In addition, it is preferable that a photoinitiator is mix | blended by 0.01 weight part or more and 10 weight part or less with respect to 100 weight part of photopolymerizable compounds. This is because if it is less than 0.01 part by weight, the photocuring property is lowered, and if it exceeds 10 parts by weight, only the surface is cured and the internal curability is lowered. The photoinitiator is more preferably blended in an amount of 0.1 to 7 parts by weight with respect to 100 parts by weight of the photopolymerizable compound, preferably 0.1 to 5 parts by weight. More preferably, it is blended.

  As a composition containing a photocurable compound, a polymer resin having no photopolymerizability can be used together with the photopolymerizable compound. Polymer resins that can be used here include acrylic resin, styrene resin, styrene-acrylic copolymer, polyurethane resin, polyester resin, epoxy resin, cellulose resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer, polyvinyl Examples include butyral resin. These polymer resins and photopolymerizable compounds are required to have sufficient compatibility before photopolymerization, and various organic solvents, plasticizers, etc. are used to ensure this compatibility. It is also possible. In addition, when using an acrylate as a photopolymerizable compound, it is preferable from a compatible point to select as a polymer resin from an acrylic resin.

  The method for curing the composition containing the photopolymerizable compound is not particularly limited. For example, there is a method in which the composition is provided in a sheet form on a substrate and irradiated with parallel rays such as ultraviolet rays from a predetermined direction. Can be mentioned. Thereby, the aggregate | assembly of the some rod-shaped hardening area | region extended in parallel with the irradiation direction of a parallel ray as shown, for example in FIG. 3 can be formed.

  As a method of providing the composition in a sheet form on the substrate, a normal coating method or printing method is applied. Specifically, air doctor coating, bar coating, blade coating, knife coating, reverse coating, transfer roll coating, gravure roll coating, kiss coating, cast coating, spray coating, slot orifice coating, calendar coating, dam coating, dip coating Coating such as die coating, intaglio printing such as gravure printing, printing such as stencil printing such as screen printing, and the like can be used. Further, when the composition has a low viscosity, a weir having a certain height can be provided around the substrate, and the composition can be cast in the dam.

  As a light source used for irradiating parallel rays such as ultraviolet rays, a short arc ultraviolet lamp is usually used. Specifically, a high pressure mercury lamp, a low pressure mercury lamp, a metahalide lamp, a xenon lamp, or the like can be used. The shape of the fine structure formed by light irradiation differs depending on the shape of the light emitting surface, and a light source having a rod-like light emitting surface forms a plate-like fine structure, whereas a parallel light source used for resist exposure When is used, a rod-like microstructure is formed. In the present invention, any can be used, but the latter is preferred. In the case of producing a small size, it is possible to irradiate from a sufficiently long distance using an ultraviolet spot light source as a point light source.

The parallel rays irradiated on the sheet of the composition must include a wavelength capable of polymerizing and curing the photopolymerizable compound, and usually uses light of a wavelength around 365 nm from a mercury lamp. Is done. When fabricating the anisotropic diffusion medium for use in the present invention using this wavelength range, it is preferred that as the illumination intensity is in the range of 0.01 to 100 mW / cm ^2, more preferably 0.1~20mW / cm ² range. If the illuminance is 0.01 mW / cm ² or less, it takes a long time to cure, resulting in poor production efficiency. If the illuminance is 100 mW / cm ² or more, the photo-curing compound is cured too quickly and no structure is formed. This is because the light scattering characteristics of the above cannot be expressed.

  It should be noted that one or both surfaces of the composition provided on the sheet is irradiated with light for the purpose of accelerating the curing of the composition containing the photocurable compound upon light irradiation or controlling the strength of the light scattering property. May be covered with a transparent flexible sheet, and the composition provided in the form of a sheet may be heated before and after light irradiation.

  In the backlight unit of the present invention, the anisotropic diffusion medium described above is used for the light diffusing portion. In order to make the in-plane luminance of the backlight more uniform, the conventional isotropic diffusion is used. It is also possible to use by overlapping media or prism lenses, and there is a method in which anisotropic diffusion media, isotropic diffusion media are ordered from the side close to the light source, or vice versa, There is a method of laminating various light diffusion media on both sides as necessary to form a light diffusion member. As another method, there is a method of providing a gap (air layer) between a light diffusing member including an anisotropic diffusing medium and another light diffusing member.

  The backlight unit of the present invention is required to maintain a predetermined positional relationship between the light source and the liquid crystal cell for a long period of time. In particular, in a backlight applied to a large screen, it is essential that the light diffusing portion does not deform even under the influence of heat or the like from the light source. In order to give the light diffusing portion a certain level of rigidity, a plate formed of a material such as an acrylic resin, a polycarbonate resin, or a norbornene resin can be used for the light diffusing member.

  As the light source used in the backlight unit of the present invention, a cold cathode tube, an LED, or the like is preferably used. As for the LED, one that emits white light alone can be used. However, in applications that place importance on color purity, three types of LEDs that emit primary colors of R (red), G (green), and B (blue) are used. Are preferably combined and dispersed.

(Example of production of anisotropic diffusion medium)
A partition wall having a height of 0.2 mm was formed with a curable resin on the entire periphery of the edge of a PET film (trade name: A4300, manufactured by Toyobo Co., Ltd.) having a thickness of 75 μm and a size of 76 × 26 mm. The following ultraviolet curable resin composition was dropped into this and covered with another PET film.
・ 50 parts by weight of 2- (perfluorooctyl) -ethyl acrylate (fluorine content 61%, manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light acrylate FA-108)
・ 1,9-nonanediol diacrylate 50 parts by weight (fluorine-free, manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light acrylate 1.9ND-A)
-4-hydroxy-2-methyl-1-phenylpropan-1-one 4 parts by weight (Ciba Specialty Chemicals, trade name: Darocur 1173)
An irradiation intensity of 30 mW is perpendicular to the epi-illumination irradiation unit of a UV spot light source (manufactured by Hamamatsu Photonics, Inc., product name: L2859-01) with respect to a liquid film having a thickness of 0.2 mm sandwiched between both surfaces of the PET film. An anisotropic diffusion medium having a large number of rod-shaped minute regions as shown in FIG.

(Production example of light diffusion plate)
A linear UV light source with a light emission length of 125 mm (Nihon UV Machine Co., Ltd.) placed in the direction perpendicular to the long side of the PET film in an ultraviolet curable composition sandwiched between the same PET films as in the production example of the anisotropic diffusion medium. (Product name: handy UV device HUV-1000), UV rays having the same irradiation intensity as in the production example of the anisotropic diffusion medium are vertically irradiated to form plate-like regions having different refractive indexes as shown in FIG. A light diffusing plate having was obtained.

  Using a goniophotometer (trade name: GP-5, manufactured by Murakami Color Co., Ltd.), the light receiving part is fixed at a position where it receives straight light from the light source, and the anisotropic diffusion obtained in the above production example is placed on the sample holder in the meantime. A medium and a light diffusing plate were set. As shown in FIG. 13, the sample was rotated with the short side direction of the sample as the rotation axis (L), and the amount of linear transmitted light corresponding to each incident angle was measured, and this was named “short side axis rotation”. Next, once remove the sample from the sample holder, rotate it 90 degrees in the plane and set it again, this time measure the linear transmitted light amount with the long side of the slide glass as the rotation axis (M). Long side axis rotation ”.

  FIG. 15 and FIG. 16 show the relationship between the incident angle measured with respect to the two rotation axes and the linear transmitted light amount for the anisotropic diffusion medium and the light diffusion plate, respectively. In the anisotropic diffusion medium, both the short-side axis rotation and the long-side axis rotation include a small mountain at an incident angle of 0 °, and the change rate of the linear transmitted light amount is a deep valley shape of about 0.9, and is almost symmetrical. I understand that. However, the light diffusing plate shows a deep valley shape similar to that of an anisotropic diffusion medium by rotating the short side axis. With the long side axis rotation, the amount of linear transmitted light is the size of the valley of the short side axis rotation even if the incident angle is changed. It showed selective light scattering properties with little change.

It is a partial schematic diagram of the backlight unit of the present invention. (A) It is a schematic diagram at the time of using the conventional isotropic diffuser for a light-diffusion part. (B) It is a schematic diagram at the time of using an anisotropic diffusion medium for a light-diffusion part. It is a schematic diagram which shows an example of the structure of the anisotropic diffusion medium used for this invention. (A) It is an optical micrograph which shows the AA line cross section in FIG. (B) It is an optical microscope photograph which shows the BB line cross section (cross section orthogonal to an AA line cross section) in FIG. It is a schematic diagram which shows an example of the structure of the conventional light control board. (A) It is an optical microscope photograph which shows the AA line cross section (cross section perpendicular | vertical to the direction of a linear light source) in the light control board of FIG. (B) It is an optical microscope photograph which shows the BB line cross section (cross section parallel to the direction of a linear light source) in the light control board of FIG. It is a schematic diagram which shows the evaluation method of the incident angle dependence of the linear transmitted light quantity of an anisotropic diffusion medium (when only the straight line L is made into a rotating shaft). It is a graph which shows the relationship between the incident angle and linear transmitted light quantity in evaluation of the incident angle dependence of the linear transmitted light quantity of an anisotropic diffusion medium. FIG. 4 is a schematic cross-sectional view illustrating the incident angle dependence of the linearly transmitted light amount that passes through the anisotropic diffusion medium of FIG. 3. It is a schematic diagram explaining the incident angle dependence of the linear transmitted light amount which permeate | transmits the anisotropic diffusion medium of FIG. It is a schematic diagram which shows other embodiment of an anisotropic diffusion medium. It is typical sectional drawing explaining the incident angle dependence of the linearly transmitted light quantity which permeate | transmits the anisotropic diffusion medium of FIG. It is a schematic diagram which shows the evaluation method of the incident angle dependence of the linear transmitted light amount of the conventional light control board (when the straight lines L and M are made into the rotating shaft). It is a graph which shows the relationship between the incident angle and the linear transmitted light amount in evaluation of the incident angle dependence of the linear transmitted light amount of the conventional light control board. It is a graph which shows the incident angle dependence of the linearly transmitted light quantity in the manufacture example of an anisotropic diffusion medium. It is a graph which shows the incident angle dependence of the linearly transmitted light quantity in the manufacture example of the conventional light control board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusion part 2 Light source 3 Reflection part 4 Anisotropic diffusion medium 5 Rod-shaped hardening area | region 6 Light-receiving part I Incident light T Transmitted light P Incident direction S Normal line of anisotropic diffusion medium surface

Claims (9)

A light source;
A reflecting portion disposed on at least the back side of the light source for reflecting light from the light source;
A light diffusing section that is disposed on the front side of the light source and diffuses light from the light source that is incident directly or reflected by the reflecting section;
The light diffusing unit includes at least one anisotropic diffusing medium having a linearly transmitted light amount that varies depending on an incident angle of light from the light source.   The backlight unit according to claim 1, wherein the anisotropic diffusion medium is obtained by curing a composition containing a photocurable compound and has a scattering center axis.   2. The backlight unit according to claim 1, wherein the light diffusing unit is configured by a light diffusing medium in which at least one layer made of the anisotropic diffusing medium is stacked.   2. The back according to claim 1, wherein the light diffusion portion includes a light diffusion medium formed by laminating at least one layer made of the anisotropic diffusion medium, and another light diffusion medium. Light unit.   The backlight unit according to claim 1, wherein the light source is surrounded by the reflecting portion except for the front side of the light source.   The backlight unit according to claim 1, wherein the light source is a cold cathode tube.   The backlight unit according to claim 1, wherein the light source is a light emitting diode (LED).   The backlight unit according to claim 7, wherein the LED is a unit that produces white light by combining a red light emitting diode (R), a green light emitting diode (G), and a blue light emitting diode (B).   A liquid crystal display device, wherein the backlight unit is disposed on a back surface of the liquid crystal display unit.

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