KR20120116359A - Optical sheet, optical unit, backlight unit and liquid crystal display device - Google Patents

Abstract

PURPOSE: A light spread sheet, an optical unit, a backlight unit, and a liquid crystal display device are provided to more improve the reflection and refraction of light by using resin beads. CONSTITUTION: A light spread sheet(31) includes a transparent base layer(41) and a light spread layer(42). The light spread sheet is laminated on a surface of the base layer. The light spread sheet includes resin beads(51) in a binder(52). A refractive index of the resin beads is greater than 1.50. A primary polymer of the resin beads is a copolymer of a styrene monomer and an acrylic monomer.

Description

Diffusion sheet, optical unit, backlight unit and liquid crystal display {OPTICAL SHEET, OPTICAL UNIT, BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a light diffusion sheet, an optical unit including the light diffusion sheet, a backlight unit including the optical unit, and a liquid crystal display device including the backlight unit.

Liquid crystal displays are widely used as flat panel displays utilizing features such as thin, light weight, and low power consumption, and their use is expanding year by year as display devices such as mobile phones, portable information terminal devices, personal computers, and televisions. In recent years, the characteristics required for the liquid crystal display include high brightness, wide viewing angle, energy saving, and thin weight, and the like, and the demand for high brightness is particularly high.

The conventional general liquid crystal display device has a liquid crystal display element and the backlight unit arrange | positioned at the back side of a liquid crystal display element (for example, refer Unexamined-Japanese-Patent No. 2005-106959). The liquid crystal display element has a structure in which a liquid crystal cell is sandwiched between a surface side polarizing plate and a back side polarizing plate, and is driven by various display modes. The backlight unit illuminates a liquid crystal display element from the back surface side, and the backlight unit of edge light type and a direct type | mold is popular. These conventional backlight units have a light source, a light guide plate which guides light rays from the light source to the side of the liquid crystal display element, and an optical unit disposed on the side of the liquid crystal display element of the light guide plate. The optical unit is for incidence of light rays from the light guide plate efficiently and uniformly on the entire surface of the back side of the liquid crystal display element. For example, an optical diffusion sheet for diffusing light rays from the light guide plate and a transmitted light beam are refracted toward the normal direction. The prism sheet etc. which are made to make are provided.

Japanese Patent Publication No. 2005-106959

Since a conventional liquid crystal display device has a light diffusion sheet, a prism sheet, and the like as described above, some degree of high brightness has been achieved, but further high brightness of the liquid crystal display device is required today. A high gain prism sheet has been developed for the purpose of improving the brightness of a liquid crystal display device and the like. For example, the high gain prism sheet by which the product name "BEF2-G2-MR-155" by Sumitomo 3M Co., Ltd. was put on is commercialized. The high gain prism sheet is a prism sheet made of a high refractive index material. Thus, although the high gain prism sheet is commercialized, the light-diffusion sheet matched with the high gain prism sheet has not been developed, and the effect of improving the brightness by the high gain prism sheet could not be brought out. In addition, further thinning of liquid crystal display devices is required today.

The present invention provides a light diffusing sheet for realizing further high brightness and thinning of a liquid crystal display device, an optical unit including the light diffusing sheet, a backlight unit including the optical unit, and further high brightness and thinning. It is an object to provide a liquid crystal display device.

The light diffusion sheet of the present invention

A transparent base layer,

Light-diffusion layer laminated | stacked on the surface of this base material layer, and having resin beads in a binder

A light diffusion sheet comprising:

The refractive index of the resin beads is characterized in that 1.50 or more.

Since the refractive index of the resin beads of the light diffusion sheet is larger than that of the resin beads of the conventional light diffusion sheet, the reflection and refraction of light rays caused by the resin beads are larger than in the prior art. Therefore, when the said light-diffusion sheet is incorporated in a liquid crystal display device, the brightness of a liquid crystal display device can be made higher than before. As a result, the backlight unit can be thinned, and further, the liquid crystal display can be thinned. Moreover, even if it is a high gain prism sheet which has a certain refractive index, by standing each refractive index of the binder of the said light-diffusion sheet, and resin beads, the standing of the light beam by the high gain prism sheet in the vertical direction can be implement | achieved.

The refractive index of the said binder may be 1.49 or more and 1.51 or less, and the refractive index of the said resin beads may be 1.52 or more and 1.59 or less. In that case, since the refractive index of the resin beads of the said light-diffusion sheet is larger than the refractive index of the resin beads of the conventional light-diffusion sheet, reflection and refraction of the light beam by resin beads become larger than before, and the brightness | luminance of a liquid crystal display device becomes high.

In the light diffusion sheet, a value obtained by subtracting the refractive index of the binder from the refractive index of the resin beads may be 0.06 or more and 0.08 or less. In that case, since the reflection and refraction of the light beam by the resin beads become larger, the luminance of the liquid crystal display device becomes further higher.

The main polymer of the resin beads may be a copolymer of a (meth) acrylic monomer and a styrene monomer. In that case, it is easy to set the refractive index of the resin beads to 1.52 or more and 1.59 or less, or to set the value obtained by subtracting the refractive index of the binder from the refractive index of the resin beads to 0.06 or more and 0.08 or less.

40 mass parts or more and 230 mass parts or less may be sufficient as the compounding quantity with respect to 100 mass parts of binders of the said resin beads. In that case, since the reflection and refraction of the light beam by the resin beads become larger, the luminance of the liquid crystal display device becomes further higher.

The haze value of the light diffusion sheet may be 78% or more and 93% or less. In that case, since the reflection and refraction of the light beam by the resin beads become larger, the luminance of the liquid crystal display device becomes further higher.

The average particle diameter of the said resin beads may be 2 micrometers or more and 5 micrometers or less. In that case, since the reflection and refraction of the light beam by the resin beads become larger, the luminance of the liquid crystal display device becomes further higher.

The resin beads may be polydisperse beads. In that case, since the reflection and refraction of the light beam by the resin beads become larger, the luminance of the liquid crystal display device becomes further higher.

In order to realize further high brightness and thinning of the liquid crystal display device, the optical diffusing sheet and one prism sheet superposed on the surface side of the light diffusing sheet are provided, and the optical unit whose refractive index of the prism sheet is 1.50 or more is used as a liquid crystal. It can be used as one component of a display apparatus. Similarly, in order to realize further high brightness and thinning of the liquid crystal display device, the light diffusing sheet and two prism sheets overlapping the surface side of the light diffusing sheet are provided. The optical unit which is arrange | positioned so that it may cross | intersect and whose refractive index of these two prism sheets is 1.50 or more can be used as one component of a liquid crystal display device. In that case, if the refractive index of each prism sheet is 1.55 or more and 1.70 or less, the brightness | luminance of a liquid crystal display device will become high further. In addition, the thinning of the liquid crystal display device is realized.

In addition, in order to realize further high brightness and thinning of the liquid crystal display device, a backlight having a light source, a light guide plate on which light rays from the light source enter and exit the incident light, and a corresponding optical unit laminated on the light guide plate The unit can be used as one component of the liquid crystal display device.

Moreover, the liquid crystal display device which has the said backlight unit and the liquid crystal display element arrange | positioned on the prism sheet of this backlight unit is also one aspect of this invention.

The present invention provides a light diffusing sheet for realizing further high brightness and thinning of a liquid crystal display device, an optical unit including the light diffusing sheet, a backlight unit including the optical unit, and further high brightness and thinning. A liquid crystal display device can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the cross section of the liquid crystal display device of embodiment of this invention.
FIG. 2 is a diagram for explaining the progress of light rays in the liquid crystal display of FIG. 1.

EMBODIMENT OF THE INVENTION Below, embodiment of this invention is described with reference to drawings.

(Configuration of Liquid Crystal Display)

The liquid crystal display device 1 of FIG. 1 has a liquid crystal display element 10 and a backlight unit 20. The liquid crystal display element 10 is an element for displaying information using light, and has a structure in which the liquid crystal cell 12 is sandwiched between the front side polarizing plate 11 and the back side reflective polarizing plate 13. The back-side reflective polarizing plate 13 transmits the polarization component in one direction of light and reflects the remaining polarization component.

The backlight unit 20 is an edge light type backlight unit which is disposed on the rear surface side of the liquid crystal display element 10 and illuminates the liquid crystal display element 10 from the rear side, and includes a light source 21, a light guide plate 22, and an optical unit. Has a unit 23.

The light source 21 arranges a plurality of light emitting diodes on a straight line. The light guide plate 22 is wedge-shaped and has a rectangular plane when viewed from the surface of the liquid crystal display device 1, and one side of the rectangle is disposed to face the entire light source 21. Although not shown, a member that reflects light rays is provided on a side surface of the light guide plate 22 that does not face the light source 21. Although not shown on the rear surface of the light guide plate 22, a member for reflecting light rays is provided. The light guide plate 22 emits the light rays incident from the light source 21 to the optical unit 23 by the member reflecting the light rays described above.

The optical unit 23 is disposed on the surface on the side of the liquid crystal display element 10 of the light guide plate 22, and from the light guide plate 22 so that the light beam is incident perpendicularly to the entire surface of the rear surface of the liquid crystal display element 10. The incident light beams are diffused and emitted to the liquid crystal display device 10. Specifically, the optical unit 23 refracts the light diffusing sheet 31 for diffusing the light incident from the light guide plate 22 and the light diffused by the light diffusing sheet 31 to the liquid crystal display element 10. It has a first prism sheet 32 and a second prism sheet 33 running substantially vertically. Each of the light diffusion sheet 31, the first prism sheet 32, and the second prism sheet 33 is superposed in order from the rear surface side of the liquid crystal display device 1 to the surface side as shown in FIG. have.

The light diffusion sheet 31 diffuses the light incident from the light guide plate 22 and exits the first prism sheet 32 so that the light is incident on the entire surface of the rear surface of the liquid crystal display element 10. The light diffusion sheet 31 includes a base layer 41, a light diffusion layer 42 stacked on the front side of the base layer 41, and a sticking preventing layer 43 stacked on the back side of the base layer 41. Have The detailed structure of the light-diffusion sheet 31 is mentioned later.

The first prism sheet 32 is a high gain prism sheet, which refracts light rays incident from the light diffusion sheet 31 and exits the second prism sheet 33. The second prism sheet 33 is a high-gain prism sheet. The second prism sheet 33 is a high-gain prism sheet, which refracts the light rays incident from the first prism sheet 32 so that the light beams travel substantially perpendicular to the back surface of the liquid crystal display element 10. It is emitted to the element 10. The 1st prism sheet 32 and the 2nd prism sheet 33 are equipped with the base material layer and the processus | protrusion line which consists of several protrusion prism part laminated | stacked on the surface of this base material layer.

As thickness (height from the lower surface to the apex of a protrusion prism part) of the 1st prism sheet 32 and the 2nd prism sheet 33, 50 micrometers or more and 200 micrometers or less are preferable, and 100 micrometers or more and 180 micrometers or less are more preferable. Moreover, as a space | interval (pitch) between the protrusion prism parts in the 1st prism sheet 32 and the 2nd prism sheet 33, 30 micrometers or more and 100 micrometers or less are preferable, and 40 micrometers or more and 60 micrometers or less are more preferable. Moreover, as a right angle of a protrusion prism part, 85 degrees or more and 95 degrees or less are preferable. The refractive index of the 1st prism sheet 32 and the 2nd prism sheet 33 is 1.50 or more, and 1.55 or more and 1.70 or less are preferable. In addition, the refractive index of a prism sheet says the refractive index of a prism part. Further high brightness can be achieved by using the prism sheets 32 and 33 having such a structure in combination with the light diffusion sheet 31. Moreover, the 1st prism sheet 32 and the 2nd prism sheet 33 also refract the light beam from the direction which forms an angle of about 33-34 degrees with the normal line of a board | substrate in the back surface side to the surface side of the normal line. The conventional prism sheet refracts light rays from a direction forming an angle of about 30 to 31 degrees with the normal of the substrate to the surface side of the normal. That is, the first prism sheet 32 and the second prism sheet 33 have a higher capability than the conventional prism sheet with respect to the function of vertically standing the light rays incident in the oblique direction with respect to the back surface of the substrate. Each of the 1st prism sheet 32 and the 2nd prism sheet 33 is a high-gain prism sheet by which the product name of "BEF2-G2-MR-155" made by Sumitomo 3M Co., Ltd. was affixed, for example.

(Configuration of Light Diffusion Sheet)

The light diffusion sheet 31 is an optical sheet that diffuses and emits the incident light, and as described above, the light diffusion layer 42 laminated on the surface side of the base layer 41, the base layer 41, It has the sticking prevention layer 43 laminated | stacked on the back surface side of the base material layer 41. As shown in FIG.

The base material layer 41 is a transparent layer which can transmit light rays, and is formed of resin. The resin is, for example, an acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather resistant vinyl chloride, or the like. 10 micrometers or more and 400 micrometers or less are preferable, and, as for the average thickness of the base material layer 41, 20 micrometers or more and 130 micrometers or less are more preferable. By making the average thickness more than 10 micrometers, the base material layer 41 can have the strength which a curvature does not produce. Moreover, by making the average thickness into 400 micrometers or less, thickness reduction of the liquid crystal display device 1 is implement | achieved, and the brightness | luminance of the liquid crystal display device 1 can fully be ensured.

The light diffusion layer 42 includes a resin beads 51 having a high refractive index and a binder 52 for fixing in a state where the resin beads 51 are dispersed. The resin beads 51 are also dispersed and arranged on the surface of the light diffusing layer 42, whereby irregularities in a fine and disordered state are provided on the surface of the light diffusing layer 42. Due to the unevenness and the interface between the resin beads 51 and the binder 52, the function of diffusing the light rays appears larger.

The refractive index of the resin beads 51 is 1.50 or more, 1.52 or more and 1.59 or less are preferable, and 1.55 or more and 1.57 or less are more preferable. Since the refractive index of the resin beads in the conventional light diffusion sheet is about 1.49, the refractive index of the resin beads 51 of this embodiment is larger than the conventional one.

The main polymer for forming the resin beads 51 is not particularly limited, and acrylic resins, acrylonitrile resins, polyurethanes, polyvinyl chlorides, polystyrenes, polyacrylonitriles, polyamides, and the like can be used. The copolymer of an acryl-type monomer and a styrene-type monomer is preferable, and the crosslinked (meth) acryl-styrene type copolymer obtained from a (meth) acrylic-type monomer, a styrene-type monomer, and a crosslinkable monomer is more preferable. By using the main polymer which introduce | transduced the styrene frame | skeleton into a (meth) acrylic frame | skeleton, the refractive index of the resin beads 51 becomes high, and it can further raise refractive index by setting it as a crosslinked structure. Moreover, when acrylic resin (acryl polyol etc.) is used for the binder 52, since it has the same acryl skeleton, the resin beads 51 are uniformly dispersed in the binder 52, and front brightness can be raised more.

Examples of the (meth) acrylic monomers include acrylic acid and derivatives of acrylic acid such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate and undecyl acrylate. , Dodecyl acrylate, glycidyl acrylate, methoxyethyl acrylate, propoxy acrylate, butoxyethyl acrylate, methoxydiethylene acrylate, ethoxydiethylene glycol acrylate, methoxy ethylene glycol acrylate, butoxy triethylene glycol acrylate , Methoxy dipropylene glycol acrylate, phenoxy ethyl acrylate, phenoxy diethylene glycol acrylate, phenoxy tetraethylene glycol acrylate, benzyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, dicyclopentenyl acrylate, dicyclopentenyl acrylate Ethyl, acrylic N-vinyl-2-pyrrolidone, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxy-3-phenyloxypropyl acrylate, glycidyl acrylate, acrylonitrile, acrylamide, N -Methylol acrylamide, diacetone acrylamide or derivatives of methacrylic acid and methacrylic acid, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate Hexyl methacrylate, heptyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, glycidyl methacrylate, methoxyethyl methacrylate, Propoxyethyl methacrylate, butoxyethyl methacrylate, methoxydiethylene glycol methacrylate, ethoxy methacrylate diethylene glycol, methacrylic acid methoxyethylene glycol, methacrylic acid butoxy triethylene glycol, methacrylate methacrylate Sidipropylene glycol, phenoxy ethyl methacrylate, phenoxy diethylene glycol methacrylate, phenoxy tetraethylene glycol methacrylate, benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, dimethacrylate Cyclopentenyl, dicyclopentenyloxyethyl methacrylate, methacrylic acid N-vinyl-2-pyrrolidone, methacrylonitrile, methacrylamide, N-methylol methacrylamide, methacrylic acid 2-hydroxy Ethyl, methacrylate hydroxypropyl, methacrylate hydroxybutyl, methacrylic acid 2-hydroxy-3-phenyloxypropyl and the like. These can be used 1 type or in combination of 2 or more types.

Styrene derivatives, such as styrene, (alpha) -methylstyrene, vinyltoluene, and p-t-butyl styrene, are mentioned as said (meth) acrylic-type monomer. These can be used 1 type or in combination of 2 or more types.

As a crosslinkable monomer, divinylbenzene, ethylene glycol dimethacrylate, 1, 3- butylene glycol dimethacrylate, 1, 4- butanediol dimethacrylate, 1, 5- pentanediol methacrylate, 1, 6 -Hexanediol dimethacrylate, neopentyl glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, tripropylene glycol dimethacrylate, etc. are mentioned. have. These can be used 1 type or in combination of 2 or more types.

The main polymer may further contain other monomers in addition to the (meth) acrylic monomer, the styrene monomer and the crosslinkable monomer. Examples of other monomers include vinyl acetate, vinyl chloride, maleic anhydride, maleic acid, maleic acid esters, fumaric acid, fumaric acid esters, triaryl isocyanurates, and the like.

Resin beads which use the said copolymer as a main polymer can be obtained, for example by suspension-polymerizing the mixture of each monomer in presence of a polymerization initiator. This suspension polymerization can usually be performed in aqueous media, such as water or a mixture of water and alcohol.

The shape of the said resin beads 51 is not specifically limited, For example, spherical shape, a cubic shape, needle shape, rod shape, fusiform shape, plate shape, scale shape, fiber shape, etc. are mentioned, Especially, The spherical shape which is excellent in light diffusivity is preferable.

2 micrometers or more and 5 micrometers or less are preferable, and, as for the average particle diameter of the said resin beads 51, 2.5 micrometers or more and 4 micrometers or less are more preferable. By using the particle | grains of such an average particle diameter, light diffusivity etc. can be improved. In addition, the average particle diameter in this invention means what averaged the particle diameter of 30 particle | grains extracted randomly from the particle | grains observed with the electron microscope of 1000 times magnification. In addition, a particle diameter is defined as a ferret diameter (interval when sandwiching a projection image in a parallel line in a constant direction).

It is preferable that the resin beads 51 are polydisperse beads, and the variation coefficient of the particle diameter is preferably 20% or more and 40% or less. By using such polydisperse beads, light diffusivity, furthermore, front brightness and the like can be improved.

Moreover, as for the compounding quantity with respect to 100 mass parts of the binder 52 of the resin beads 51 contained in the light-diffusion layer 42, 40 mass parts or more and 230 mass parts or less are preferable, and 45 mass parts or more and 100 mass parts or less are more preferable. Preferably, 60 mass parts or less are more preferable. The compounding quantity of the resin beads 51 is determined according to the size of an average particle diameter so that light diffusivity can be exhibited more.

The binder 52 is usually obtained by curing the base polymer with a curing agent. In the binder 52, a plasticizer, a dispersant, various leveling agents, an ultraviolet absorber, an antioxidant, a viscosity modifier, a lubricant, a light stabilizer, or the like may be appropriately blended. This binder 52 arranges and fixes the resin beads 51 to substantially the same density on the whole surface of the base material layer 41 by the base polymer which is a main component.

The base polymer is not particularly limited, and examples thereof include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamideimide, epoxy resins, ultraviolet curable resins, and the like. Or it can mix and use 2 or more types. In particular, as the base polymer, a polyol having high processability and capable of easily forming the light diffusion layer 42 by means such as coating is preferable. Moreover, since the base polymer used for the binder 52 needs to transmit light, it becomes transparent, and colorless transparent is especially preferable.

As said polyol, polyester polyol or (meth) acryl polyol is preferable, and (meth) acryl polyol is more preferable. The binder 52 which uses such a polyester polyol or an acryl polyol as a base polymer has high weather resistance, and can suppress yellowing of the light-diffusion layer 42 and the like. Moreover, when using the copolymer containing the (meth) acrylic-type monomer mentioned above as resin beads 51, dispersibility becomes high by using a (meth) acryl polyol, and front brightness can be raised. Either one of the polyester polyol and the acrylic polyol may be used, or both of them may be used.

The number of hydroxyl groups in the polyester polyol and (meth) acrylic polyol is not particularly limited as long as it is two or more per molecule, but when the hydroxyl value in the solid content is 10 or less, the crosslinking score is decreased, and the solvent resistance, water resistance, heat resistance, and surface hardness are reduced. There exists a tendency for film physical properties, such as these, to fall.

When using a polyol as a base polymer as mentioned above, as a hardening | curing agent, hexamethylene diisocyanate, isoprone diisocyanate, and xylene diisocyanate are preferable, hexamethylene diisocyanate is more preferable, and adduct type hexamethylene diisocyanate is preferable. More preferred. Use of these curing agents increases the curing reaction rate of the polymer composition. This improvement in the curing reaction rate contributes to the uniform dispersibility of the resin beads in the binder. Moreover, in order to improve more uniform dispersibility etc., it is more preferable to use combining (meth) acryl polyol and hexamethylene diisocyanate.

As refractive index of the binder 52, 1.49 or more and 1.51 or less are preferable. Moreover, as a value which subtracted the refractive index of the said binder 52 from the refractive index of the said resin beads 51, 0.06 or more and 0.08 or less are preferable.

The sticking prevention layer 43 is composed of a binder and beads dispersed in the binder. As the binder, the same components as those of the binder 52 of the light diffusion layer 42 may be mentioned. Moreover, inorganic beads and organic beads are mentioned as a bead material. In addition, although the thickness (thickness of the binder part except beads) of this sticking prevention layer 43 is not specifically limited, For example, it can be made into about 1 micrometer or more and about 10 micrometers or less.

The compounding quantity of the beads in this sticking prevention layer 43 becomes comparatively small quantity, the beads are mutually disperse | distributed in a binder, and most of the beads protrude a very small amount from the binder at the lower end. Therefore, when this light-diffusion sheet 31 is laminated | stacked with the light-guide plate 22, the lower end of the protruding bead abuts on the surface of the light-guide plate 22, and the whole surface of the back surface of the light-diffusion sheet 31 is light-guide plate 22 ) Does not touch. Thereby, sticking of the light-diffusion sheet 31 and the light guide plate 22 is prevented, and the luminance nonuniformity of the screen of a liquid crystal display device is suppressed.

Next, the manufacturing method of the light-diffusion sheet 31 is demonstrated. The manufacturing method of the said light-diffusion sheet 31 manufactures the coating liquid for light-diffusion layers by mixing resin beads 51 with (a) the composition (base polymer, hardening | curing agent, etc.) which comprise the binder 52, for example. The step of laminating | stacking the light-diffusion layer 42 by apply | coating this process and (b) this coating liquid for light-diffusion layers to the surface of the base material layer 41, and (c) sticking by mixing beads to the polymer composition which comprises a binder. And a step of laminating the sticking prevention layer 43 by applying the coating solution for the anti-sticking layer to the back surface of the base layer 41 (d).

(Beam progression)

Next, advancing of the light beam in the liquid crystal display device 1 of this embodiment is demonstrated. The light beam is generated when the light source 21 emits light, and as shown in FIG. 2, the light beam A from the light source 21 is guided by the light guide plate 22 to the optical unit 23, and the light of the optical unit 23 is generated. It is scattered by the diffusion sheet 31 and enters the first prism sheet 32 from the entire surface of the back surface of the first prism sheet 32. The light beam A incident on the first prism sheet 32 is refracted by the first prism sheet 32, thereby standing upright in the direction perpendicular to the back surface of the liquid crystal display element 10, whereby the second prism sheet Proceed to (33). The light ray A which has propagated to the second prism sheet 33 is further refracted by the second prism sheet 33 to stand up, and is incident substantially perpendicularly to the back surface of the liquid crystal display element 10. In this way, the light ray A from the backlight unit 20 is incident on the liquid crystal display element 10.

Since the back side reflective polarizing plate 13 is provided on the back side of the liquid crystal display element 10, a part of the light beam A incident on the liquid crystal display element 10 passes through the back side reflective polarizing plate 13, and the remainder Reflected on the side of the backlight unit 20. The light ray A transmitted through the back side reflective polarizing plate 13 passes through the liquid crystal cell 12 and the surface side polarizing plate 11 in order and exits to the surface side of the liquid crystal display device 1. The light beam A reflected on the side of the backlight unit 20 is reflected by the reflecting member of the light guide plate 22 and, as described above, passes through the optical unit 23 and enters the liquid crystal display element 10 again. do.

(effect)

As mentioned above, the light-diffusion sheet 31 of this embodiment is the light-diffusion layer 42 which contains the resin beads 51 which have a high refractive index, and the binder 52 whose refractive index is preferably 1.49 or more and 1.51 or less. Has Since the refractive index of the resin beads in the conventional light-diffusion sheet is about 1.49 as mentioned above, the refractive index of the resin beads 51 of this embodiment is larger than the conventional one. Therefore, the reflection or refraction of the light beam by the resin beads 51 of this embodiment becomes larger than before. As a result, the light-diffusion sheet 31 of this embodiment matches with the 1st prism sheet 32 and the 2nd prism sheet 33 which are high gain prism sheets, and the 1st prism sheet 32 and the 2nd prism sheet The effect of improving the luminance by (33) can be brought out. Therefore, the brightness | luminance of the liquid crystal display device 1 of this embodiment becomes higher than before, and the high luminance requested | required by society is implement | achieved.

Moreover, since the 1st prism sheet 32 and the 2nd prism sheet 33 are high gain prism which consists of a high refractive index material, the ratio of the light which reflects among the light rays which advanced to the back surface of this prism sheet becomes high. However, according to the light diffusion sheet 31, since the light reflection by the resin beads 51 is large, the light reflected by the prism sheet to the side of the light diffusion layer 42 is the first by the light diffusion layer 42. The prism sheet 32 and the second prism sheet 33 are reflected again. Therefore, the utilization efficiency of a light beam improves compared with the past, and further high luminance of the liquid crystal display device 1 is implement | achieved.

And since high brightness of a liquid crystal display device is implement | achieved, the backlight unit 20 can be made thin, and also thickness of a liquid crystal display device can be realized. In addition, with the light diffusion sheet 31 of the present embodiment, the luminance of the liquid crystal display device 1 of the present embodiment is uniformized within the screen while maintaining a high state. Therefore, the backlight unit 20 can be concealed from the surface side. Further, by adjusting the refractive indices of the binder of the light diffusion sheet 31 and the resin beads, even in a high gain prism sheet having a certain refractive index, standing in the vertical direction of the light beam by the high gain prism sheet can be realized.

As haze value of the said light-diffusion sheet, 78% or more and 93% or less are preferable, and 80% or more and 90% or less are more preferable. By having such a relatively high haze value, the front brightness of the liquid crystal display device 1 becomes further high. In addition, a "haze value" is a value measured based on JIS-K-7105.

As mentioned above, since the liquid crystal display device 1 of this embodiment has the light-diffusion sheet 31 containing the resin beads 51 of the high refractive index larger than the refractive index of the conventional resin beads, society demands Additional high brightness is realized. Therefore, the liquid crystal display device 1 of this embodiment is useful as a high brightness display device of various sizes including, for example, 2 inches to 22 inches. That is, the liquid crystal display device 1 of this embodiment is useful as display apparatuses, such as a mobile telephone, a smart phone, an onboard machine, a game machine, a tablet personal computer, a mobile personal computer, a notebook personal computer, and a monitor.

(Modified example)

In the above-described embodiment, the optical unit 23 includes the first prism sheet 32 and the second prism sheet 33. However, the optical unit 23 may have only the first prism sheet 32 as the prism sheet. Moreover, the said light-diffusion sheet does not need to have a sticking prevention layer.

In the above-described embodiment, the backlight unit 20 is an edge light type backlight unit. However, the backlight unit 20 may be a direct type backlight unit. When the backlight unit 20 is a direct type backlight unit, even if the optical unit 23 has only the first prism sheet 32 as the prism sheet, the light beam can be diffused very largely. As a result, high luminance of the liquid crystal display device required by society can be realized.

In addition, in the above-mentioned embodiment, although the light source 21 arrange | positions several light emitting diodes on a straight line, the light source 21 may be a rod-shaped cold cathode tube. Moreover, in the above-mentioned embodiment, although the light guide plate 22 is wedge-shaped, the light guide plate 22 may be a flat plate type. Thus, the form of the backlight unit 20 including the light source 21 and the light guide plate 22 is not limited to the form mentioned above.

In addition, in the above-mentioned embodiment, although the liquid crystal display element 10 has the back side reflective polarizing plate 13, the liquid crystal display element 10 has a polarizing plate which does not have a reflection function instead of the back side reflective polarizing plate 13. You may be.

(Example)

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is described in detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

Example 1

As a base material layer, the transparent polyethylene terephthalate film of 100 micrometers in thickness was used. As a polymer composition for light-diffusion layers, the polymer composition which consists of 100 parts of binders (acryl polyol and adduct type hexamethylene diisocyanate type hardening | curing agent), 50 parts of resin beads, and a solvent was used. The number of copies which shows the compounding quantity of each composition is the mass ratio of solid content conversion. The light-diffusion sheet of Example 1 was obtained by laminating | stacking 5g / m <^2> (solid content conversion) the polymer composition for light-diffusion layers on the surface of this base material layer by the gravure coat method. The refractive index of the binder was 1.49 The resin beads used were those containing a crosslinked (meth) acryl-styrene copolymer obtained by suspension polymerization as a main polymer. The refractive index of this resin beads was 1.56, and the average particle diameter was 3.0 µm (30% variation coefficient).

EXAMPLES 2-10

The light-diffusion sheets of Examples 2-10 were obtained like Example 1 except having used the binder of the refractive index shown in Table 1, and the refractive index, average particle diameter, and additional resin beads shown in Table 1.

Comparative Example 1

The light-diffusion sheet of Comparative Example 1 was obtained in the same manner as in Example 1 except that acrylic resin beads (refractive index 1.49) formed by suspension polymerization were used as the resin beads.

Comparative Example 2

The light-diffusion sheet of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that the compounding amount of the resin beads was 100 parts by mass.

[Comparative Example 3]

The light-diffusion sheet of Comparative Example 3 was obtained in the same manner as in Comparative Example 1 except that a binder having a refractive index of 1.42 was used.

[Evaluation of Characteristics]

The haze value of these light-diffusion sheets was measured using the light-diffusion sheet of the said Examples 1-10, and the light-diffusion sheet of Comparative Examples 1-3. Moreover, these light-diffusion sheets were actually incorporated in the edge light type backlight unit, and the front brightness was measured. The results are shown in Table 1 below. In addition, the backlight unit has a structure in which two prism sheets are superposed on the surface side of the light diffusion sheet, and the two prism sheets are arranged so that the ridge lines cross each other. In addition, "BEF2-G2-MR-155" by Sumitomo 3M Co., Ltd. was used for the said prism sheet. The evaluation results are shown in Table 1. In addition, front brightness is shown by the relative value which made Example 1 100.0%.

As shown in the said Table 1, the light-diffusion sheets of Examples 1-10 show the high haze value and front brightness, and have the outstanding optical characteristic compared with the light-diffusion sheet of the comparative example using the conventional beads.

The light diffusion sheet, the optical unit, and the backlight unit of the present invention are useful as members constituting the liquid crystal display device. Moreover, the liquid crystal display device of this invention is useful as display apparatuses, such as a mobile telephone and a personal computer.

One… Liquid crystal display device 10. Liquid crystal display device
11 ... Surface-side polarizing plate 12... Liquid crystal cell
13 ... Back-side reflective polarizer 20.. Backlight unit
21 ... Light source 22. Light guide plate
23 ... Optical unit 31... Light diffusion sheet
32 ... First prism sheet 33... Second prism sheet
41... Substrate layer 42. Light diffusion layer
43 ... Anti-sticking layer 51... Resin beads
52 ... bookbinder

Claims (13)

A transparent base layer,
Light-diffusion layer laminated | stacked on the surface of this base material layer, and having resin beads in a binder
A light diffusion sheet comprising:
The refractive index of the said resin beads is 1.50 or more, The light-diffusion sheet characterized by the above-mentioned. The refractive index of the said binder is 1.49 or more and 1.51 or less,
A light diffusion sheet having a refractive index of the resin beads of 1.52 or more and 1.59 or less. The light diffusion sheet according to claim 1, wherein a value obtained by subtracting the refractive index of the binder from the refractive index of the resin beads is 0.06 or more and 0.08 or less. The light diffusion sheet according to claim 1, wherein the main polymer of the resin beads is a copolymer of a (meth) acrylic monomer and a styrene monomer. The light diffusion sheet according to claim 1, wherein a compounding amount of 40 parts by mass to 230 parts by mass with respect to 100 parts by mass of the binder of the resin beads is used. The light diffusion sheet according to claim 1, wherein the haze value is 78% or more and 93% or less. The light diffusing sheet according to claim 1, wherein an average particle diameter of the resin beads is 2 µm or more and 5 µm or less. The light diffusion sheet according to claim 1, wherein the resin beads are polydisperse beads. The light diffusion sheet according to claim 1,
It is provided with one prism sheet superposed on the surface side of this light-diffusion sheet,
The refractive index of the said prism sheet is 1.50 or more, The optical unit characterized by the above-mentioned. The light diffusion sheet according to claim 1,
It is provided with two prism sheets superposed on the surface side of this light-diffusion sheet,
These two prism sheets are arranged so that the ridges cross each other,
The refractive index of these two prism sheets is 1.50 or more, The optical unit characterized by the above-mentioned. The optical unit according to claim 9 or 10, wherein the refractive index of the prism sheet is 1.55 or more and 1.70 or less. Light source,
A light guide plate on which light rays from the light source are incident and which exit the incident light rays;
The optical unit of Claim 9 or 10 laminated | stacked on the light guide plate, The backlight unit characterized by the above-mentioned. A backlight unit according to claim 12,
And a liquid crystal display element disposed on the prism sheet of the backlight unit.

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