JP2001228310A - Diffusion sheet, light source unit, polarized light source unit and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion sheet suitable for use in a liquid crystal display with a reflective polarizing element, capable of reducing weight and thickness and producible at a low cost, a light source unit applying the principle of the diffusion sheet, a polarized light source unit and a liquid crystal display. SOLUTION: The diffusion sheet has 70-160 nm intrasurface phase contrast value. The light source unit 45 comprises a reflecting sheet 63, a light guide plate 62 with a light source 61 at an end and the diffusion sheet 70 arranged in this order and the intrasurface phase contrast value of diffusion 70 or that of the laminate 80 of the light guide plate and the diffusion sheet is 70-160 nm. A reflective linearly polarizing element 53 is disposed on the sheet 70 side of the light source unit 45 in such a way that the axis of light transmission of the element 53 meets the axis of a delayed phase of the laminate 80 at 40-50 deg.C angle to obtain the polarized light source unit 40. A liquid crystal cell 20 and a front dichroic polarizing element 35 are disposed on the element 53 side of the unit 40 to obtain the liquid crystal display 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and a polarized light source, a light source and a diffusion sheet suitable for use in the liquid crystal display.

[0002]

2. Description of the Related Art Liquid crystal display devices are used in various fields because of their small size and light weight. A general liquid crystal display device will be described with reference to FIG.
1 controls the polarization state of light passing therethrough by electrically changing the alignment state of liquid crystal molecules in the liquid crystal cell 20. The liquid crystal cell 20 usually includes two opposing transparent electrodes, that is, a transparent electrode 21 on the rear side and a transparent electrode 22 on the front side, and a liquid crystal layer 23 sandwiched between the transparent electrodes 21 and 22. , Front-side optical elements 30 such as a front-side dichroic polarizing element 35 and a front-side retardation element 36 for detecting the polarization state of light transmitted through the liquid crystal cell 20 are arranged. A polarized light source device 42 for extracting only light and emitting the light toward the liquid crystal cell 20 is arranged. This polarized light source device 42
Is a dichroic polarizing element 5 disposed on the back of the liquid crystal cell 20.
5, an optical element 51 such as a phase difference element 56, a light guide plate 62 disposed on the back side thereof and having a light source 61 disposed downward or laterally, a reflecting plate 63 disposed further behind the light guide plate 62, and a liquid crystal cell 20. Sheet 7 arranged between the light guide plate 62 and the light guide plate 62
1 and 1. In the polarized light source device 42, the dichroic polarizing element 55 functions as a filter that transmits only the necessary polarized light by absorbing the unnecessary polarized light, and thus is ideal for natural light in a non-polarized state. Even in the state, 50% of the light is absorbed, and the light is not used effectively.

Therefore, a reflection type polarizing element is arranged closer to the light source than the dichroic polarizing element 55, and the polarized light in the vibration direction, which is absorbed by the dichroic polarizing element 55, is reflected in advance, and is reflected to the light source side. By returning and recycling, the light is effectively used,
A method for improving the screen brightness of a liquid crystal display device with the same power consumption is proposed in Japanese Patent Application Laid-Open No. 63-168626. This publication discloses a quarter to effectively recycle light reflected by a reflective polarizer comprising a grid polarizer.
It is disclosed that a wave plate is used. Specifically, an example in which a diffusion plate is arranged on the back surface of a reflective linear polarizing element, and a quarter-wave plate and a mirror are arranged in this order on the back surface It is shown. In order to exhibit the mechanism for rotating the polarization plane of the reflected light by the reflective linear polarization element by 90 ° described in this publication, the in-plane retardation value of the diffusion plate needs to be zero, A light guide plate having a phase difference cannot be used. Therefore, as the diffusion plate, it is necessary to use an inorganic material such as a glass plate that does not exhibit a phase difference, or if the material is a polymer material, a treatment such as annealing after forming by a casting method is required. However, there is a problem in terms of thickness, weight, production cost, and the like, because the use of such materials is limited.

[0004]

Under such circumstances, the present invention improves the light use efficiency of a polarized light source device by using a reflective polarizing element, thereby improving the screen brightness of a liquid crystal display device. A light-emitting device, a polarized light source device, and a liquid crystal display device that provide a diffusion sheet that is thin, lightweight, inexpensive, and can further contribute to improving the screen brightness of a liquid crystal display device. It is intended to provide.

The inventor of the present invention has proposed an in-plane retardation of a diffusion sheet used in a polarized light source device in which the use efficiency of light is increased by using a reflective linear polarizing element or a liquid crystal display device in which the screen brightness is enhanced. Limiting the value to a certain range,
Alternatively, by limiting the in-plane retardation value of the laminate of the diffusion sheet and the light guide plate to a certain range, the thickness and weight of the diffusion sheet can be reduced, and the diffusion sheet can be produced at low cost. It has been found that it can contribute to further efficiency of light utilization and further improvement of luminance of the liquid crystal display device,
The present invention has been reached.

[0006]

That is, the diffusion sheet according to the present invention has an in-plane retardation value of 70 nm or more and 160 nm or less. Advantageously, the diffusion sheet has a transparent polymer material as a base material. The diffusion sheet having such a transparent polymer material as a base material preferably has a haze ratio of 30% or more and 95% or less.

The light source device according to the present invention comprises, from one aspect, a reflection sheet, a light guide plate having a light source disposed at an end thereof,
The above-mentioned diffusion sheet having an in-plane retardation value of not less than 70 nm and not more than 160 nm is arranged in this order. Further, the light source device specified from another point of view, a reflection sheet, a light guide plate having a light source disposed at an end,
A diffusion sheet is arranged in this order, and the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet is 70 nm or more and 160 nm or more.
It is characterized by the following.

Further, in the polarized light source device according to the present invention, an angle of 40 ° or more and 50 ° or less with respect to the slow axis of the laminate of the light guide plate and the diffusion sheet is provided on the diffusion sheet side of any one of the light source devices. The reflective linearly polarizing element is arranged so that the optical axes intersect. In this polarized light source device, a dichroic polarizing element is arranged on the side opposite to the diffusion sheet of the reflective linear polarizing element such that the light transmission axis thereof coincides with the light transmission axis of the reflective linear polarizing element. You can also.

According to the present invention, there is also provided a liquid crystal display device using such a polarized light source device. This liquid crystal display device has a liquid crystal cell and a front dichroic element on the polarizing element side of the polarized light source device. The polarizing elements are arranged in this order.

[0010]

FIG. 1 is a cross-sectional view schematically showing one example of a liquid crystal display device according to the present invention. First, an overall configuration of the liquid crystal display device will be schematically described with reference to FIG.
The liquid crystal display device 10 basically includes a polarized light source device 40
, A liquid crystal cell 20, and a front optical element 30 including a front dichroic polarizing element 35. In this example, the front dichroic polarizing element 35 is laminated on the front retardation element (retardation film) 36, and the retardation element 36 side is arranged on the front side of the liquid crystal cell 20. .

The polarized light source device 40 basically includes a reflection sheet 63 and a light guide plate 6 having a light source 61 disposed at an end.
2 and a light source device 45 in which a diffusion sheet 70 is arranged in this order, and an optical element 50 including a reflective linear polarizing element 53 arranged on the diffusion sheet 70 side.
In this example, the dichroic polarizing element 55 is disposed on the front side of the reflective polarizing element 53, that is, on the side opposite to the surface where the diffusion sheet 70 is located, and the phase difference element 56 is further disposed on the front side thereof. The optical element 50 is constituted. Light guide plate 62
Is usually provided with white dot printing 64 or the like in order to efficiently scatter and reflect the light from the light source 61.

The present invention relates to a liquid crystal display device 10 having such a reflective linear polarizing element 53, or a polarized light source device 40 as a component thereof. The present invention also relates to the light source device 45 or the diffusion sheet 70 which is a component of the polarized light source device 40. In the present invention, the in-plane retardation value of the diffusion sheet 70 or the in-plane retardation value of the laminate 80 of the diffusion sheet 70 and the light guide plate 62 is important.

The diffusion sheet 70 is generally a sheet-like member that diffuses and transmits light rays. In one aspect of the present invention, the diffusion sheet 70 has an in-plane retardation value of 70 nm.
It is defined in the range of not less than 160 nm. In another aspect of the present invention, the in-plane retardation value of the laminate 80 of the light guide plate 62 and the diffusion sheet 70 is defined to be in the range of 70 nm or more and 160 nm or less. Further, the in-plane retardation value is 70 nm.
It is more effective to use the diffusion sheet 70 having a thickness of 160 nm or less and adjust the laminate 80 of the diffusion sheet 70 and the light guide plate 62 so as to exhibit an in-plane retardation value of 70 nm or more and 160 nm or less.

Here, the diffusion sheet 70 or the light guide plate 6
The in-plane retardation value of the laminate 80 of the second and diffusion sheets 70 is
It is preferable that the wavelength be closer to １ ／ of the wavelength at which the brightness improving effect is exhibited by the reflective linear polarizing element 53. For example, if the wavelength range in which the brightness enhancement effect is exhibited is in the visible wavelength range, it is 1/4 of the green wavelength (about 550 nm) with the highest visibility.
Preferably, it has an in-plane retardation value close to 138 nm. That is, the in-plane retardation value of the diffusion sheet 70 or the laminate 80 is preferably 100 nm or more and 150 nm or less, more preferably 110 nm or more, especially 120 nm or more, and 140 nm or less. on the other hand,
The dispersion of the in-plane retardation value of the diffusion sheet 70 is preferably 40 nm or less, more preferably 20 nm or less, particularly preferably 10 nm or less, in order to prevent luminance unevenness.

The material of the diffusion sheet 70 is not particularly limited.
Although various known materials can be used, a material using a transparent organic polymer material as a base material is one of preferred embodiments because the thickness and weight of the diffusion sheet are reduced, and handling is easy. The material of the transparent polymer is not particularly limited, for example, synthetic polymers such as polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, norbornene resin, polyurethane, polyacrylate, polymethyl methacrylate, and cellulose diacetate. And natural polymers such as cellulose triacetate. These transparent polymer materials are preferably colorless. In addition, these polymer materials can contain additives such as an ultraviolet absorber, an antioxidant, and a plasticizer, if necessary.

In order to produce a diffusion sheet from these transparent polymer materials, a method of incorporating a diffusing agent into the transparent polymer sheet, and providing a layer containing a diffusing agent on one or both sides of the surface of the transparent polymer sheet. Various known methods such as a method and a method of roughening one or both sides of the surface of the transparent polymer sheet can be used alone or in combination of two or more. When adopting a method of including a diffusing agent in the transparent polymer sheet, the diffusing agent is previously kneaded in the transparent polymer material serving as the base material,
It may be formed into a sheet by a casting method or an extrusion method. When adopting a method of providing a layer containing a diffusing agent on one or both sides of the transparent polymer sheet surface, first, the transparent polymer material is formed into a sheet by a casting method or an extrusion method, and then the diffusing agent Is dispersed in a resin liquid, and the dispersion is applied onto a transparent polymer sheet, and the resin liquid is dried or cured to produce the resin liquid. When adopting the method of roughening the surface of the transparent polymer sheet, first, the transparent polymer is formed into a sheet by a casting method or an extrusion method, and then, a stamping method using an embossing roll or a sandblasting method. It can be manufactured by roughening the surface. Regardless of which method is used, it is preferable to form the sheet by a casting method in order to reduce the variation in the in-plane retardation value.

Here, the diffusing agent is not particularly limited as long as it is colorless or white particles, and either organic particles or inorganic particles can be used. Examples of the organic particles include particles made of a polymer compound such as a polyolefin resin such as polystyrene, polyethylene and polypropylene, and an acrylic resin, and may be a crosslinked polymer. In addition, ethylene, propylene, styrene, methyl methacrylate, benzoguanamine, formaldehyde,
A copolymer obtained by copolymerizing two or more monomers selected from melamine, butadiene, and the like can also be used. As the inorganic particles, for example, silica, silicone,
Examples include particles such as titanium oxide, and glass beads may be used.

[0018] The resin liquid used in the method of coating a dispersion of a diffusing agent in a resin liquid on a transparent polymer sheet may be a solvent-evaporable or water-evaporable resin liquid, or a thermosetting or photocurable resin liquid. Mold resin liquid can be used. Solvent-evaporating or water-evaporating resin liquids include polyacrylates, polymethacrylates, polyvinyl chloride, polyvinyl acetate, cellulose, polymers such as synthetic rubber, methanol, ethanol, propanol, alcohols such as isopropanol, Cellulosolves such as methyl cellosolve and ethyl cellosolve, aromatic solvents such as toluene and xylene, organic solvents such as ethyl acetate and methylene chloride, or those dissolved or dispersed in water can be used. When these volatile resin liquids are applied on a transparent polymer sheet, a film is formed by drying. As the thermosetting resin liquid, a resin liquid obtained by mixing a liquid composed of a compound having an epoxy group and a compound condensing with an epoxy group such as an amine can be used. Examples of the photocurable resin liquid include a resin liquid obtained by adding a known photoradical polymerization initiator to a compound having an acrylate group, a methacrylate group, an aryl group, or the like, or a known photocationic polymerization for a compound having a vinyl ether group or an epoxy group. A resin solution to which an initiator has been added can be used. In these resin liquids, if necessary,
Additives such as ultraviolet absorbers and antioxidants can be added.

In the present invention, the in-plane retardation value of the diffusion sheet 70 is set to be 70 nm or more and 160 nm or less, or a laminate 80 of the light guide plate 62 and the diffusion sheet 70 is formed.
In order to control the in-plane retardation value of the diffusion sheet in this way, for example, if an organic polymer material is used, a stretching method or an annealing method may be used. A method such as a method can be adopted. That is, the in-plane retardation value can be increased by stretching, and the in-plane retardation value can be reduced by annealing. Further, the diffusion sheet according to the present invention has a haze ratio of 30% to 9%.
It is preferably at most 5%. Further, it is preferable that the diffusion sheet has a higher total light transmittance. That is, the total light transmittance is preferably 70% or more, and more preferably 8% or more.
More preferably, it is 0% or more, especially 85% or more.

Although the thickness of the diffusion sheet is not particularly limited,
In order to make the polarized light source device or the liquid crystal display device thin, it is preferable that the diffusion sheet is also thin. However, if the thickness is too thin, workability deteriorates.
It preferably has a thickness of about μm. Therefore, the thickness of the diffusion sheet is preferably about 10 μm or more and 1,000 μm or less, more preferably 50 μm or more and 500 μm or less.
m or less, especially 200 μm or less.

The diffusion sheet according to the present invention is preferably formed of a single-layer transparent polymer film, but may be formed of a multi-layer transparent polymer film in order to adjust the in-plane retardation value. Good. In the case of multi-layering, it is sufficient to simply laminate, but in order to reduce light loss due to reflection generated at the interface between the polymer film and air, a method of thermocompression bonding or a method of bonding with a pressure-sensitive adhesive is used. It is preferred to use.

The light guide plate according to the present invention functions to take in light emitted from a light source into the inside and function as a planar illuminant. Such a light guide plate may be made of plastic or glass, and may have a rear surface that has been subjected to unevenness processing, white dot printing processing, hologram processing, or the like. Here, the material of the plastic is not particularly limited, but polycarbonate, norbornene resin, polymethyl methacrylate and the like are preferably used. As a method of processing these polymer materials into a light guide plate, a method of forming a plastic sheet by an extrusion method, a solvent casting method or a liquid injection polymerization method, performing a back surface treatment after cutting to a desired size, or an injection method In this case, a method in which a molten polymer is poured into a mold and molded is employed.

It is preferable that the in-plane phase difference of the light guide plate is low in order to prevent warpage and distortion in a use environment. Further, in the case of a laminate with a diffusion sheet, the sum of in-plane retardation values of the laminate is preferably 70 nm or more and 160 nm or less, more preferably 100 nm or more, particularly 120 nm or more.
More preferably, it is 150 nm or less, especially 140 nm or less. In addition, the light guide plate formed using the sheet formed by the liquid injection polymerization method can prevent deformation because the in-plane retardation value of the light guide plate alone is almost 0 nm. This is a particularly preferable mode because a value can be set.

In the present invention, the type of the reflection sheet used to form the light source device in combination with the diffusion sheet and the light guide plate is not particularly limited, and may be used in ordinary polarized light source devices and liquid crystal display devices. What is necessary is just to select from what is done. That is, a white plastic sheet having a cavity formed therein, a plastic sheet having a surface coated with a white pigment such as titanium oxide or zinc white, a multilayer plastic sheet formed by laminating at least two types of plastic films having different refractive indexes, aluminum, A sheet made of a metal such as silver or a sheet formed by forming a coating of a metal such as aluminum or silver on a plastic sheet can be used. These sheets may be either mirror-finished or roughened. The material of the plastic sheet constituting the reflection plate is not particularly limited. For example, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, norbornene resin, polyurethane, polyacrylate, polymethyl methacrylate and the like can be used.

The type of light source disposed at the end of the light guide plate is not particularly limited, and may be appropriately selected from those used in ordinary polarized light source devices and liquid crystal display devices. Specifically, cold-cathode tubes, light-emitting diodes, inorganic or organic EL
An (electroluminescent) lamp or the like can be used.

As shown in FIG. 1, the light source device 45 according to the present invention comprises a reflection sheet 63, a light guide plate 62 having a light source 61 disposed at an end thereof, and a diffusion sheet 70 arranged in this order. is there. Here, the diffusion sheet 70 may be composed of one sheet, or may be composed of two or more sheets.
From one viewpoint, the diffusion sheet 70 has an in-plane retardation value of 70 nm or more and 160 nm or less. From another viewpoint, the in-plane retardation value of the laminate 80 of the light guide plate 62 and the diffusion sheet 70 is set to be 70 nm or more and 160 nm or less. For example, even if the in-plane retardation value of the diffusion sheet 70 itself is less than 70 nm, the laminate 8 with the light guide plate 62
If 0 has an in-plane retardation value of 70 nm or more and 160 nm or less, a certain effect can be exhibited, and if the in-plane retardation value of the diffusion sheet 70 itself is 70 nm or more and 160 nm or less, it and the light guide plate. Even if the in-plane retardation value of the laminated body 80 with 62 exceeds 160 nm, the same effect is still exhibited. When the in-plane phase difference value of the diffusion sheet 70 is large, an angle is provided between the slow axis of the light guide plate 62 and the slow axis of the diffusion sheet 70 in order to cancel the value.
For example, it is also possible to arrange both of them so that their slow axes are orthogonal to each other. Of course, an embodiment in which both the in-plane retardation value of the diffusion sheet 70 and the in-plane retardation value of the laminate 80 of the light guide plate 62 and the diffusion sheet 70 are 70 nm or more and 160 nm or less is more preferable. The in-plane retardation value of the laminate 80 is 10
0 nm or more, especially 120 nm or more,
More preferably, it is 0 nm or less, especially 140 nm or less. Further, in order to prevent deformation and uneven brightness under the use environment, the variation of the in-plane retardation value of the laminate 80 is 40%.
nm or less, more preferably 20 nm or less, particularly preferably 10 nm or less.

The polarized light source device 40 according to the present invention has an optical element 50 including a reflective linear polarizing element 53 disposed on the front surface of the light source device 45 described above, that is, on the diffusion sheet 70 side. The reflection type linearly polarized light element here transmits linearly polarized light in a specific vibration direction and reflects linearly polarized light orthogonal to it. As such a reflective linear polarizing element, for example, a reflective linear polarizing element utilizing the difference in the reflectance of the polarized light component depending on the Brewster angle (for example, the one described in JP-A-6-508449), Reflective linear polarizing element (for example, disclosed in Japanese Patent Application Laid-Open No. 2-308106) on which a transparent metal linear pattern is applied, and at least two types of polymer films are laminated, and the difference in reflectance due to refractive index anisotropy is obtained. A reflective linear polarizing element utilizing anisotropy (for example, one described in Japanese Patent Publication No. 9-506837), which has a sea-island structure formed of at least two kinds of polymers in a polymer film, and has a refractive index A reflective linear polarizing element utilizing the anisotropy of the reflectance due to the anisotropy (for example, see US Pat. No. 5,82
No. 5,543), a reflective linear polarizing element in which particles are dispersed in a polymer film and utilizing the anisotropy of the reflectance due to the refractive index anisotropy (for example, Japanese Patent Application Laid-Open No. 11-509014). Japanese Patent Application Laid-Open No. 9-29720), a reflective linear polarizing element in which inorganic particles are dispersed in a polymer film and the anisotropy of reflectance based on the difference in scattering power depending on the size is used.
No. 4) can be used.

The thickness of these reflective linear polarizing elements is not particularly limited, but when applied to a liquid crystal display device or the like,
The thickness of the polarizing element is preferably thin, specifically, 1 mm or less, more preferably 0.2 mm or less. Therefore, at least two types of polymer films are laminated and a reflective polarizing element utilizing the anisotropy of the reflectance due to the refractive index anisotropy, or the polymer film has a sea-island structure and has a refractive index anisotropy The reflective polarizing element utilizing the anisotropy of the reflectance due to
It is particularly preferable to reduce the thickness of the polarized light source device according to the present invention.

In the polarized light source device 40 of the present invention, the light transmission axis of the reflective linear polarization element 53 is at least 40 ° with respect to the slow axis of the laminate 80 of the light guide plate 62 and the diffusion sheet 70.
They are arranged to intersect at an angle of 0 ° or less. Here, the light transmission axis of the reflective linear polarization element 53 is defined as that when polarized light in a specific vibration direction is incident on the polarized element 53 from a perpendicular direction, the polarization element is rotated to maximize the transmittance of the polarized light. The direction of the polarizing element. The slow axis of the laminate 80 is
The direction in which the refractive index is the largest in the plane of the laminate 80. Light transmission axis of reflective linear polarizing element 53 and laminate 80
Is more preferably 42 ° or more and 48 ° or less, and most preferably 45 °.

In the polarized light source device 40, the optical element 50
May be constituted only by the reflective linear polarizing element 53,
With the reflective linear polarization element 53 alone, the degree of polarization is low and it is difficult to obtain a desired polarization performance, or the contrast may be reduced by shining the external light to raise the negative image. Therefore, in such a case, the dichroic polarizing element 55 is provided in front of the reflective linear polarizing element 53.
And the reflective linear polarizing element 53 and the dichroic polarizing element 55 can constitute the optical element 50. At this time, the reflective linear polarization element 53 and the dichroic polarization element 55 are arranged such that the light transmission axes of both elements substantially coincide with each other. When the dichroic polarizing element 55 is used as described above, a phase difference element 56 is further disposed on the front side of the dichroic polarizing element
The optical element 50 can be constituted by the fifth element 5 and the phase difference element 56. The reflective linear polarizing element 53 and the dichroic polarizing element 55 may be simply laminated, but from the viewpoint of reducing light loss due to interfacial reflection, it is preferable that both are adhered to each other. For this purpose, a method of bonding the reflective linear polarizing element 53 and the dichroic polarizing element 55 using a pressure-sensitive adhesive can be adopted. The same applies to the case where the phase difference elements 56 are stacked.

The dichroic polarizing element 55 used here is a material that transmits linearly polarized light in a specific vibration direction and absorbs linearly polarized light perpendicular to the polarized light. As such a dichroic polarizing element, for example, a known iodine-based polarizing film or dye-based polarizing film can be used. The iodine-based polarizing film is a film in which iodine is adsorbed to a stretched polyvinyl alcohol film, and the dye-based polarizing film is
This is a film in which a dichroic dye is adsorbed on a stretched polyvinyl alcohol film. These polarizing films are
In order to improve the durability, it is preferable that one or both surfaces are covered with a plastic film. Examples of the material of the plastic coated for such protection include cellulose diacetate, cellulose triacetate, polyethylene terephthalate, norbornene resin, and the like. Although the thickness of the dichroic polarizing element 55 is not particularly limited, when the polarized light source device of the present invention is applied to a liquid crystal display element or the like, the thinner is preferably, specifically 1 mm or less, more preferably 0.2 mm or less. It is preferred that When the retardation element 56 is provided, a retardation film or the like which is a stretched film of a generally known polymer material can be used.

The liquid crystal display device 10 according to the present invention comprises a front surface of the polarized light source device 40 described above, that is, an optical element 50.
The liquid crystal cell 20 and the front-side optical element 30 including the front-side dichroic polarizing element 35 are arranged in this order on the side. Here, as the front-side dichroic polarizing element 35, an iodine-based polarizing film or a dye-based polarizing film similar to that described above as the back-side dichroic polarizing element 55 can be used. The front-side optical element 30 may be a laminated product of the front-side dichroic polarizing element 35 and the front-side retardation element 36. When the front-side retardation element 36 is disposed, the same retardation film as described above as the rear-side retardation element 56 can be used. Adhesion between the polarized light source device 40 and the liquid crystal cell 20 and / or between the liquid crystal cell 20 and the front optical element 30 using a pressure-sensitive adhesive is effective in reducing light loss due to reflection at the interface. preferable. The kind of the pressure-sensitive adhesive is not particularly limited, and various kinds of known pressure-sensitive adhesives can be used. Among them, it is preferable to use an acrylate-based pressure-sensitive adhesive.

Liquid crystal cell 20 constituting liquid crystal display device 10
As shown in FIG. 2, a liquid crystal 23 is injected into a cell in which a rear transparent electrode 21 and a front transparent electrode 22 are arranged so as to face each other. By changing the alignment state, the state of polarized light transmitted through the cell is changed. Examples of such a liquid crystal cell include a known TN (twisted nematic) liquid crystal cell, a TFT (thin film transistor) driven TN liquid crystal cell,
In-plane nematic liquid crystal cells, VA (vertical alignment) nematic liquid crystal cells, STN (super twisted nematic) liquid crystal cells, and the like can be used.

[0034]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described with reference to examples, but the present invention is not limited to these examples. In addition, the evaluation method in an Example is as follows.

(1) Total light transmittance and haze ratio A sample was cut into 5 cm squares, and the haze computer “HGM-
2DP "(manufactured by Suga Test Instruments Co., Ltd.).

(2) Phase difference value A sample was cut into 4 cm squares, and an automatic birefringence meter “KOBRA-21AD” was used.
H "(manufactured by Oji Scientific Instruments).

(3) Brightness improvement rate First, as shown in a schematic cross-sectional view of FIG. 3, a light source 61 composed of a cold cathode tube is disposed at an end, and a back side of a light guide plate 62 having a white dot print 64 on the back. Then, a reflection plate 63 made of foamed PET (polyethylene terephthalate) was arranged to produce a light source device 46. The light guide plate 62 is made by cutting a polymethyl methacrylate sheet having a thickness of 8 mm formed by an extrusion method. The in-plane retardation value at the center of the sheet is 8 nm, and the slow axis is the sheet axis. The direction (width direction) was orthogonal to the flow direction. An iodine-based polarizing film “SR1862A” sold by Sumitomo Chemical Co., Ltd. is disposed thereon as the dichroic polarizing element 55, and its light transmission axis forms an angle of 45 ° with the long side of the light guide plate 62. A glass plate 82 having a thickness of 1.1 mm was laminated on the dichroic polarizing element 55 via a pressure-sensitive adhesive, to produce a polarized light source device 43 for control.
Then, a photometric unit 86 connected to a light receiving unit of the spectrophotometer by an optical fiber 87 was disposed vertically on the glass plate 82 of the polarized light source device 43. The emission line spectra corresponding to blue, green and red of the cold cathode fluorescent lamp 61 used as the light source of the polarized light source device 42 are 435 nm, 545 nm and 6 nm, respectively.
Since the wavelength was 12 nm, the received light intensity at these wavelengths was measured and used as the reference received light intensity A at each wavelength.

Separately, as shown in a schematic sectional view of FIG. 4, a diffusion sheet 70 is provided between the light guide plate 62 and the dichroic polarizing element 55.
The dichroic polarizing element 55 is arranged such that its slow axis is in the same direction as the slow axis of the light guide plate 62.
On the opposite surface, as a reflective linear polarizing element 53, a reflective polarizing film “DBEF” composed of a laminate of two types of polymer films sold by Sumitomo 3M Limited.
Were laminated via a pressure-sensitive adhesive such that the light transmission axis thereof coincided with the light transmission axis of the dichroic polarizing element 55, and the other components were the same as those in FIG. 3 to produce a polarized light source device 41. . In the vertical direction on the glass plate 82 of the polarized light source device 41, a light measuring unit 86 connected to a light receiving unit of a spectrophotometer by an optical fiber 87 is arranged as in FIG. 435 nm, 545 which are the emission line spectra corresponding to
The received light intensity B at nm and 612 nm was measured. The luminance improvement effect was evaluated by the ratio B / A of the received light intensity B at this time to the reference received light intensity A measured by the apparatus in FIG.

COMPARATIVE EXAMPLE 1 As a diffusion sheet 70, a diffusion film "Light Up 125TD3" having a light diffusion layer coated on one side of a polycarbonate film base material sold by Kimoto Co., Ltd.
(Film thickness 136 μm, total light transmittance 90%, haze 30
%, An in-plane retardation value of 34 nm) was used to evaluate the effect of improving brightness. The received light intensity ratio at each wavelength is shown in Table 1 together with the in-plane retardation value of the diffusion sheet and the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet.

Example 1 As a diffusion sheet 70, a polycarbonate film (thickness: 143 μm, total light transmittance: 92%, haze rate: 2%) formed by solvent casting on “Light-up 125TD3” used in Comparative Example 1 was used. , An in-plane retardation value of 41 nm) that are stacked such that the slow axes of both are in the same direction.
The brightness improvement effect was evaluated. The received light intensity ratio at each wavelength is shown in Table 1 together with the in-plane retardation value of the diffusion sheet and the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet.

Example 2 Two polycarbonate films the same as those used in Example 1 were bonded together using a pressure-sensitive adhesive such that their slow axes were in the same direction. The film was laminated on “Light Up 125TD3” used in Comparative Example 1 so that the slow axes of both films were in the same direction, and the laminated sheet was used as the diffusion sheet 70 to evaluate the effect of improving brightness. The received light intensity ratio at each wavelength is shown in Table 1 together with the in-plane retardation value of the diffusion sheet and the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet.

Example 3 Three pieces of the same polycarbonate film as used in Example 1 were bonded together using a pressure-sensitive adhesive such that the slow axes thereof were in the same direction. The film was laminated on “Light Up 125TD3” used in Comparative Example 1 so that the slow axes of both films were in the same direction, and the laminated sheet was used as the diffusion sheet 70 to evaluate the effect of improving brightness. The received light intensity ratio at each wavelength is shown in Table 1 together with the in-plane retardation value of the diffusion sheet and the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet.

Comparative Example 2 Four pieces of the same polycarbonate film as used in Example 1 were bonded using a pressure-sensitive adhesive such that the slow axes thereof were in the same direction. The film was laminated on “Light Up 125TD3” used in Comparative Example 1 so that the slow axes of both films were in the same direction, and the laminated sheet was used as the diffusion sheet 70 to evaluate the effect of improving brightness. The received light intensity ratio at each wavelength is shown in Table 1 together with the in-plane retardation value of the diffusion sheet and the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet.

[0044]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Example No. Diffusion sheet light guide plate / diffusion sheet light receiving In- plane retardation value of intensity ratio In- plane retardation value of laminate 435 nm 545 nm 612 nm ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━ Comparative Example 1 34 nm 42 nm 1.59 1.73 1.75 ────────────────────────────────── Execute Example 1 75 nm 83 nm 1.63 1.76 1.78 〃 2 116 nm 124 nm 1.60 1.79 1.82 ３ 3 157 nm 165 nm 1.54 1.79 1.83 ─────────────────────── ─────────── Comparative Example 2 198 nm 206 nm 1.49 1.73 1.81 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━

As can be seen from Table 1, Examples 1 to 3 in which the in-plane retardation value of the diffusion sheet is within the range specified by the present invention.
The light receiving intensity ratio is large, especially at the wavelength of 545 nm corresponding to the highest green of visibility, the in-plane retardation value of the diffusion sheet is too small or too large compared to Comparative Examples 1 and 2. The received light intensity ratio is large. In particular, as in Example 2, the in-plane retardation value of the diffusion sheet and / or
Alternatively, the in-plane retardation value of the laminate of the light guide plate and the diffusion sheet is set to 1
When adjusted between 00 nm and 150 nm, the received light intensity ratio is larger than that of the comparative example at any wavelength corresponding to blue, green, and red. Therefore, by using this diffusion sheet, in a polarized light source device having a reflective linear polarizing element, light can be more effectively used, and the screen brightness of a liquid crystal display device using the same can be improved. be able to.

In the above example, the in-plane retardation value of the diffusion sheet was adjusted by laminating a polycarbonate film formed by a solvent casting method on a commercially available diffusion film. A diffusion treatment in which the in-plane retardation value of the diffusion sheet is adjusted using a film in which the retardation value is adjusted, or the above-described diffusing agent is contained in the stretched film, a diffusing agent layer is provided, or the surface is roughened. If the material subjected to is used as a diffusion sheet, the thickness and weight can be further reduced.

[0047]

By using the diffusion sheet of the present invention, the effect of improving the luminance by the reflective linear polarizing element can be further enhanced, so that a brighter screen can be obtained even with the same power consumption as before. For this reason, for example, the power consumption for obtaining the same screen brightness as that of the related art can be reduced, and the liquid crystal display device can be used for a long time with one charge of the battery. In addition, the capacity of the battery can be reduced, and the size and weight of the liquid crystal display device can be reduced. Further, the thickness and weight of the diffusion sheet itself can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a liquid crystal display device of the present invention.

FIG. 2 is a schematic sectional view showing an example of a conventional liquid crystal display device.

FIG. 3 is a schematic cross-sectional view of an apparatus used for measuring a reference light receiving intensity in the example.

FIG. 4 is a schematic cross-sectional view of an apparatus used for measuring a received light intensity of a sample in an example.

[Explanation of symbols]

 10, 11: Liquid crystal display device, 20: Liquid crystal cell, 21, 22: Transparent electrode, 23: Liquid crystal layer, 30: Front-side optical element, 35: Front-side dichroic polarizing element, 36 ... ... front-side retardation element, 40, 41, 42, 43 ... polarized light source device, 45, 46 ... light source device, 50, 51 ... optical element, 53 ... reflective linear polarizing element, 55 ... two colors Polarizing element, 56 ... Phase difference element, 61 ... Light source, 62 ... Light guide plate, 63 ... Reflector plate, 64 ... White dot printing, 70, 71 ... Diffusion sheet, 80 ... Light guide plate and diffusion Sheet laminated body, 82: glass plate, 86: light receiving section, 87: optical fiber.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 336 G02F 1/1335 530

Claims (8)

[Claims] 1. A diffusion sheet having an in-plane retardation value of 70 nm or more and 160 nm or less. 2. The diffusion sheet according to claim 1, wherein the diffusion sheet is made of a transparent polymer material. 3. The diffusion sheet according to claim 2, wherein the haze ratio is 30% or more and 95% or less. 4. A light source device comprising: a reflection sheet; a light guide plate having a light source disposed at an end thereof; and a diffusion sheet having an in-plane retardation value of not less than 70 nm and not more than 160 nm. . 5. A reflection sheet, a light guide plate having a light source disposed at an end thereof, and a diffusion sheet are arranged in this order, and the in-plane phase difference value of a laminate of the light guide plate and the diffusion sheet is determined. 70nm
A light source device having a wavelength of 160 nm or less. 6. The light-transmitting axis of the light source device according to claim 4 or 5, wherein the light-transmitting axis has an angle of 40 ° or more and 50 ° or less with respect to a slow axis of a laminate of the light guide plate and the diffusion sheet. A polarized light source device characterized by comprising reflective linear polarization elements arranged so as to cross each other. 7. A dichroic polarizing element is arranged on the opposite side of the reflective linear polarizing element from the diffusion sheet so that the light transmitting axis thereof coincides with the light transmitting axis of the reflective linear polarizing element. The polarized light source device according to claim 6, wherein 8. A liquid crystal display device, comprising: a liquid crystal cell and a front dichroic polarizing element arranged in this order on the polarizing element side of the polarized light source device according to claim 6.