JP2002072201A - Backlight device for liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight device for a liquid crystal display having an improved utilization efficiency of light quantity from a light source and excellent mass productivity. SOLUTION: The backlight device for liquid crystal display is provided with a reflection plate (RP), the light source (LS), a cholesteric liquid crystal layer (Ch) and a quarter-wave plate (λ/4) arranged in this order and is characterized by having the quarter-wave plate (λ/4) containing a material with a positive intrinsic birefringence value and a material with a negative intrinsic birefringence value. Preferably, the quarter-wave plate (λ/4) is provided with a first layer containing the material with the positive intrinsic birefringence value and a second layer containing the material with the negative intrinsic birefringence value and average orientation directions of molecular chains in the first layer and in the second layer are equal to each other in the backlight device for the liquid crystal display.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for a liquid crystal display, and more particularly to a backlight device that can be suitably used for a transmission type liquid crystal display.

[0002]

2. Description of the Related Art For liquid crystal displays, TN (Tw
isted Nematic), IPS (In-Plane Switching), FL
C (Ferroelectric Liquid Crystal), OCB (Optica)
lly Compensatory Bend), STN (Supper Twisted Ne)
matic), (Vertically Aligned), HAN (Hybrid Al
Various display modes have been proposed, such as igned Nematic). In any of the above-mentioned liquid crystal displays, basically, a liquid crystal cell and a polarizing element are essential components, and the linearly polarized light passing through the polarizing element is subjected to (in the liquid crystal cell, when the voltage is applied and when no voltage is applied). Will result in different orientation states)
An image is displayed by the rod-like liquid crystal molecules optically functioning. The polarizing element has a function of transmitting a linearly polarized light component coincident with the direction of the polarization axis (transmission axis) and absorbing a linearly polarized light component in a direction orthogonal to the direction of the polarization axis. Therefore, only half of the light amount from the light source can be used for image display.

As a countermeasure, a method of increasing the light amount used for image display by increasing the light amount of the light source can be considered. However, increasing the light amount of the light source not only increases the power consumption but also increases the power consumption. Inevitably, adverse effects due to heat generation from the light source are unavoidable, and there is a limit to the increase in the light amount of the light source. Therefore, there has been proposed a backlight device for a liquid crystal display capable of improving the utilization efficiency of the amount of light from a light source (Japanese Patent Application Laid-Open No. H08-208,878).
146416, 8271731, 10-3
19235 and JP-A-10-513578. The proposed backlight device for a liquid crystal display is composed of a reflector, a light source, a cholesteric liquid crystal layer and a quarter-wave plate, and uses the selective reflection indicated by the cholesteric liquid crystal layer to reduce the entire amount of light from the light source. It can be used for image display. By the way, the quarter-wave plate used here is required to have a broadband characteristic in which the retardation is １ ／ of the wavelength in the entire visible light wavelength region. However, a single material
A quarter-wave plate having the above-mentioned broadband characteristics and the durability that can be used for a liquid crystal display has not yet been developed, and various measures have been taken to satisfy the above characteristics.

[0004]

As such a quarter-wave plate, for example, JP-A-5-27118, JP-A-5-100114, JP-A-10-68816, JP-A-10-90521, etc. Which are proposed in the above publications. The quarter wavelength plates proposed in the above four publications are formed by laminating two polymer films having different optical anisotropy. Usually, the polymer films are produced by laminating the stretched polymer films at a predetermined angle without aligning the stretching axes. Specifically, for each of the polymer films to be laminated, a pressure-sensitive adhesive is applied to the surface of the stretched polymer film to form a pressure-sensitive adhesive surface, a release film is attached to the pressure-sensitive adhesive surface, and then a predetermined angle with respect to the stretching axis. The chips are cut out, and then the cut out chips are pasted together. However, in this method, two chip-shaped polymer films to be laminated need to be produced independently of each other. Further, the production process of each film is complicated, and various materials (adhesive material, release material) are required for each process. Mold film, etc.), which inevitably increases the production cost. In addition, the cutting waste generated when cutting out the chip cannot be completely removed from the chip, causing a problem when bonding the chip, or when cutting the chip and bonding the chip. In addition, there is a problem that the shaft is misaligned and the performance of the product is liable to be poor.

As a quarter-wave plate exhibiting other broadband characteristics, there is a plate proposed in WO 00/26705. Although the proposed quarter-wave plate achieves quarter-wave characteristics in a single film, the birefringence is low, and in order to obtain sufficient quarter-wave characteristics, the draw ratio is large. In addition, it is necessary to increase the thickness of the film. When the film is thickened, the drying load increases during the solution casting in the production process, and the film production speed cannot be improved, and the production cost increases. 1 /
The problem with the four-wavelength plate eventually leads to a problem of lowering the performance of the backlight device for a liquid crystal display having the same or increasing the manufacturing cost.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide a backlight device for a liquid crystal display, which has improved utilization efficiency of a light amount from a light source and is excellent in mass productivity. .

[0007]

Means for solving the above problems are as follows. That is, <1> reflector, light source, cholesteric liquid crystal layer and 1 /
A backlight device for a liquid crystal display in which four-wave plates are arranged in this order, wherein the quarter-wave plate contains a material having a positive intrinsic birefringence value and a material having a negative intrinsic birefringence value. Backlight device for a liquid crystal display. <2> The wavelength of the quarter wavelength plate is 450 nm and 550 n.
(retardation / wavelength) at m and 650 nm
2. The backlight device for a liquid crystal display according to claim 1, wherein each of the values is 0.2 or more and 0.3 or less. <3> The quarter-wave plate has a first layer containing a material having a positive intrinsic birefringence value and a second layer containing a material having a negative intrinsic birefringence value. The backlight device for a liquid crystal display according to <1> or <2>, wherein the average orientation directions of the molecular chains in the first layer and the second layer are equal.

<4> The material having a positive intrinsic birefringence value and the material having a negative intrinsic birefringence are each a resin, and the first layer and the second layer are each a stretched film of the resin. 3. The backlight device for a liquid crystal display according to item 1. <5> The backlight device for a liquid crystal display according to any one of <1> to <4>, wherein the material having a positive intrinsic birefringence value is a norbornene-based polymer. <6> The backlight device for a liquid crystal display according to any one of <1> to <5>, wherein the material having a negative intrinsic birefringence value is at least one selected from polystyrene and a styrene-based polymer. <7> The backlight device for a liquid crystal display according to <6>, wherein the styrene-based polymer is a copolymer of styrene and maleic anhydride.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic sectional view for explaining the function of a backlight device for a liquid crystal display according to the present invention. FIG. 1 is a schematic diagram for explaining the function of the backlight device for a liquid crystal display of the present invention, and the shape and configuration of each member are schematically represented. The backlight device for a liquid crystal display of the present invention is configured such that a reflector (RP), a light source (LS), a cholesteric liquid crystal layer (Ch), and a quarter-wave plate (λ / 4) are arranged in this order. Counterclockwise circularly polarized light component (2) emitted from the light source (LS) to the cholesteric liquid crystal layer (Ch)
a) can pass through the cholesteric liquid crystal layer (Ch), and the left-handed circularly polarized light component (3a) that has passed is 1 /
The light is converted into linearly polarized light (4a) by a four-wavelength plate (λ / 4). That is, the light is converted into linearly polarized light in the order of 2a → 3a → 4a. On the other hand, the clockwise circularly polarized light component (lb) emitted from the light source (LS) to the reflector (RP) is reflected by the reflector (R).
P) is reflected as a counterclockwise circularly polarized light component (la). The reflected light passes through the light source (LS), passes through the cholesteric liquid crystal layer (Ch) as described above, and is converted into linearly polarized light (4a). That is, lb → la → 2a →
The light is converted into linearly polarized light in the order of 3a → 4a.

The clockwise circularly polarized light component (2c) emitted from the light source (LS) to the cholesteric liquid crystal layer (Ch) is reflected by the cholesteric liquid crystal layer (Ch) to become a clockwise circularly polarized light component (2b). The reflected light passes through the light source (LS), is reflected by the reflector (RP) in the same manner as described above, passes again through the light source (LS), and is cholesteric liquid crystal layer (Ch).
And is converted into linearly polarized light (4a). That is,
The light is converted into linearly polarized light in the order of 2c → 2b → lb → la → 2a → 3a → 4a. On the other hand, the counterclockwise circularly polarized light component (ld) emitted from the light source (LS) to the reflecting plate (RP) is reflected as a clockwise circularly polarized light component (lc) by the opposite plate (RP). The reflected light passes through the light source (LS), is reflected by the cholesteric wave crystal layer (Ch), passes through the light source (LS) again, is reflected by the reflector (RP), and is reflected by the light source (LS). LS) three times, passes through the cholesteric liquid crystal layer (Ch), and is converted into linearly polarized light (4a). That is, ld → lc → 2c → 2b → lb → la →
The light is converted into linearly polarized light in the order of 2a → 3a → 4a. As described above, all of the light from the light source (LS) is linearly polarized (4
It is converted to a) and used for displaying an image on a liquid crystal display.

Hereinafter, each member constituting the backlight device for a liquid crystal display of the present invention will be described. [1/4 wavelength plate] In the present invention, the 1/4 wavelength plate is composed of a material having a positive intrinsic birefringence value (hereinafter sometimes simply referred to as a "positive material") and a material having a negative intrinsic birefringence (hereinafter sometimes simply referred to as "positive material"). , Which may be simply referred to as "negative material"), and other components appropriately selected as necessary. The quarter-wave plate has a single-layer configuration in which the material having the positive intrinsic birefringence value and the material having the negative intrinsic birefringence are contained in the same layer, and the intrinsic birefringence value is positive. Both the laminated form in which the material and the material having the negative intrinsic birefringence value are contained in different layers are included. Materials with positive intrinsic birefringence and negative materials have their slow axes orthogonal to each other when the molecular orientation directions are equalized by stretching or the like. Is a retardation as a complex. By variously combining the positive material and the negative material and / or adjusting the production conditions such as stretching conditions, the wavelength dispersion of the developed retardation is controlled, and the incident light in the entire visible light region is controlled. For Re
It is possible to provide a phase difference characteristic where / λ is approximately 1/4. In addition, since the quarter-wave plate can be manufactured without a complicated process such as cutting out and bonding chips, which was conventionally required, the mass productivity of a backlight device for a liquid crystal display having the same can be improved. Can be contributed to.

-Material having a positive intrinsic birefringence value- In the present invention, "a material having a positive intrinsic birefringence value" refers to an optically positive uniaxial when a molecule is oriented in a uniaxial order. Refers to a material having properties showing the properties. For example, in the case where the positive material is a resin, when light is incident on a layer formed by molecules having a uniaxial orientation, the refractive index of light in the orientation direction is in a direction orthogonal to the orientation direction. A resin whose refractive index is higher than light. Examples of the positive material include various materials such as resin, rod-shaped liquid crystal, and rod-shaped liquid crystal polymer. These may be used alone or in combination of two or more. In the present invention,
Among these, a resin (hereinafter, a “resin having a positive intrinsic birefringence value” is sometimes simply referred to as a “positive resin”) is preferable.

Examples of the resin include olefin polymers (eg, polyethylene, polypropylene, norbornene polymers, cycloolefin polymers, etc.), polyester polymers (eg, polyethylene terephthalate, polybutylene terephthalate, etc.), and polyarylene sulfide polymers (eg, For example, polyphenylene sulfide), polyvinyl alcohol-based polymer, polycarbonate-based polymer, polyarylate-based polymer, cellulose ester-based polymer (some of which have a negative intrinsic birefringence value), polyethersulfone-based polymer, polysulfone-based polymer, Examples include polyallylsulfone-based polymers, polyvinyl chloride-based polymers, and multi-component (binary, ternary, etc.) copolymers thereof. These may be used alone or in combination of two or more. In the present invention, among these, an olefin-based polymer is preferable, and among the olefin-based polymers, a norbornene-based polymer is particularly preferable from the viewpoints of light transmittance characteristics, heat resistance, dimensional stability, photoelastic characteristics and the like. As the olefin-based polymer,
"Arton" made by Japan Synthetic Rubber, "Zeonex" and "Zeonor" made by Zeon Japan, "A" made by Mitsui Petrochemical
PO ”and the like are preferably used.

The norbornene-based polymer has a norbornene skeleton as a repeating unit. Specific examples thereof include JP-A-62-252406 and JP-A-6-252406.
JP-A-2-252407, JP-A-2-133413, JP-A-63-145324, JP-A-63-2
JP-A-64626, JP-A-1-240517, JP-B-57-8815, JP-A-5-39403, JP-A-5-43663, JP-A-5-4383
4, JP-A-5-70655, JP-A-5-5-2
JP-A-79554, JP-A-6-206985, JP-A-7-62028, JP-A-8-176411, JP-A-9-241484 and the like can be suitably used, but It is not limited. These may be used alone or
Two or more kinds may be used in combination.

In the present invention, among the norbornene-based polymers, those having a repeating unit represented by any of the following structural formulas (I) to (IV) are preferable.

[0016]

Embedded image

In the above structural formulas (I) to (IV), A, B, C
And D each independently represent a hydrogen atom or a monovalent organic group.

Further, among the norbornene-based polymers, at least one compound represented by the following structural formula (V) or (VI) and an unsaturated cyclic compound copolymerizable therewith are obtained by metathesis polymerization. A hydrogenated polymer obtained by hydrogenating the obtained polymer is also preferable.

[0019]

Embedded image

In the above structural formula, A, B, C and D each independently represent a hydrogen atom or a monovalent organic group.

The norbornene-based polymer has a weight average molecular weight of about 5,000 to 1,000,000, preferably 8,000 to 200,000.

-Material having a negative intrinsic birefringence value- In the present invention, "a material having a negative intrinsic birefringence value" refers to an optically negative uniaxial value when molecules are oriented in a uniaxial order. Refers to a material having properties showing the properties. For example, when the negative material is a resin, when light enters a layer in which molecules are formed in a uniaxial orientation, light having a refractive index of light in the orientation direction orthogonal to the orientation direction. Refers to a resin having a refractive index smaller than the refractive index. Examples of the negative material include various materials such as a resin, a discotic liquid crystal, and a discotic liquid crystal polymer. These may be used alone or in combination of two or more.
In the present invention, among these, resins are preferable (hereinafter, "resin having a negative intrinsic birefringence value" may be simply referred to as "negative resin").

Examples of the resin include polystyrene, styrene-based polymers (copolymers of styrene and / or a styrene derivative and other monomers), polyacrylonitrile-based polymers, polymethyl methacrylate-based polymers, and cellulose ester-based polymers (the above-mentioned specific copolymers). Some have positive refraction values), or their multiples (binary, ternary, etc.)
Copolymers and the like. These may be used alone or in combination of two or more. As the styrene-based polymer, a copolymer of styrene and / or a styrene derivative and at least one selected from acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene is preferable. In the present invention, among these, at least one selected from polystyrene, a styrene-based polymer, a polyacrylonitrile-based polymer and a polymethyl methacrylate-based polymer is preferable, and among these, from the viewpoint of high birefringence expression. , A polystyrene and a styrene-based polymer are more preferable, and a copolymer of styrene and / or a styrene derivative and maleic anhydride is particularly preferable in terms of high heat resistance. The resin has a glass transition point of 110 ° C.
The above (more preferably 120 ° C. or higher) is preferable in terms of heat resistance.

-Preferred Combination of Positive Material and Negative Material- In the present invention, a material having a positive intrinsic birefringence value and a material having a negative intrinsic birefringence are combined using the following condition as an index. Is preferred. Wavelength 450 nm and wavelength 5
Assuming that the absolute values of the retardation (Re) value at 50 nm are Re (450) and Re (550), respectively, the (Re (450) / Re (55)
0)) and (Re (450) / Re) of the negative material.
Combinations in which the value of (550)) is not equal (ie, one is smaller or larger than the other) are mentioned as preferred. More specifically, the difference between the two values is 0.0
A combination of 3 or more is preferable, and a combination of 0.05 or more is more preferable.

Further, (Re (450) /
The value of Re (550) is (Re (45) of the negative material.
0) / Re (550)), the value of Re (550) of the positive material is larger than the value of Re of the negative material.
(550) and the value of (Re (450) / Re (550)) of the positive material is equal to the value of (Re (450) / Re (550)) of the negative material. Less than, the value of Re (550) of the positive material is greater than the value of Re (550) of the negative material;
Is preferable.

Next, a preferred combination when the positive material and the negative material are each a resin will be described. When a resin having a large wavelength dispersion of the intrinsic refraction value (Δn) is used as the negative material, it is preferable to use a resin having a small wavelength dispersion of Δn as the positive material. When a resin having a small wavelength dispersion of the intrinsic refraction value (Δn) is used as the negative material, it is preferable to use a resin having a large wavelength dispersion of Δn as the positive material. For example, when a norbornene-based polymer is used as the positive material, a material having a large wavelength dispersion of its intrinsic birefringence is preferable as the negative material.
When the intrinsic birefringence value (Δn) of m and the wavelength of 550 nm is Δn (450) and Δn (550), respectively,
It is preferable to be selected from resins satisfying the following relational expression. | Δn (450) / Δn (550) | ≧ 1.02 Further, it is more preferable to select from resins satisfying the following relational expression. | Δn (450) / Δn (550) | ≧ 1.05 It is preferable that the value of | Δn (450) / Δn (550) | is large, but in the case of resin, it is generally 2.0 or less.

More specifically, when the negative material is polymethyl methacrylate or the like having a small value of (Re (450) / Re (550)), the positive material to be combined therewith is polyethylene. Preferred are a terephthalate polymer, a polyphenylene sulfide polymer, a polycarbonate polymer, a polyarylate polymer, a polyether sulfone polymer, a polysulfone polymer, a polyallylsulfone polymer, and a polyvinyl chloride polymer. When the negative material is a polystyrene or a styrene-based polymer having a large value of (Re (450) / Re (550)), the positive material to be combined therewith includes an olefin-based polymer and a cycloolefin. Based polymers (eg, polyethylene, polypropylene, norbornene-based polymers, etc.), cellulose ester-based polymers, and the like are preferable. Among them, a combination of a polystyrene and / or styrene-based polymer as a negative material and a norbornene-based polymer among olefin-based polymers as a positive material is particularly preferable.

-Other Components- The other components are not particularly limited as long as they do not impair the effects of the present invention, and can be appropriately selected according to the purpose. For example, a compatibilizer is preferably exemplified. The compatibilizer can be suitably used in a quarter-wave plate having a layer containing a mixture of the positive material and the negative material, for example, when the mixture causes phase separation, By using the compatibilizer, it is possible to improve the mixing state between the material having the positive intrinsic birefringence value and the material having the negative intrinsic birefringence value.

Examples of the quarter-wave plate having a single-layer structure include a film or a sheet comprising a polymer blend of a resin having a positive intrinsic birefringence and a resin having a negative intrinsic birefringence. As the laminated type quarter-wave plate, for example, a quarter-wave plate 10 having a configuration shown in FIG. 1/4 wavelength plate 10
Has a configuration in which a layer 12 made of a resin having a positive intrinsic birefringence value and a layer 14 made of a resin having a negative intrinsic birefringence value are laminated. Layers 12 and 14 consist of a stretched film.
The molecules of the positive resin contained in the layer and the molecules of the negative resin contained in the layer 14 are oriented in a predetermined direction by the stretching treatment, and the orientation directions are the same. Therefore,
The layers 12, 14 have birefringence and are stacked with their slow axes orthogonal to each other. Quarter-wave plate 10 of laminated structure
Is preferable because the material can be selected without considering the compatibility between the positive resin and the negative resin.

As another laminated type quarter wave plate,
A quarter wavelength plate 10 'shown in FIG. The 波長 wavelength plate 10 ′ includes a layer 14 made of a resin having a negative intrinsic birefringence value between two layers 12 made of a resin having a positive intrinsic birefringence value.
It is a structure which has. As described above, a structure having a symmetrical cross section is more preferable because the physical characteristics of the 波長 wavelength plate are improved. An embodiment in which a layer made of a resin having a positive intrinsic birefringence value is sandwiched between two layers made of a resin having a negative intrinsic birefringence value is also preferable. Further, in the three-layer structure, it is preferable that the layers made of a resin having the same sign of the intrinsic birefringence value are also laminated in the same molecular orientation direction. Are preferably the same material.

In the laminated type quarter-wave plate, the adhesiveness of both layers is determined between the layer made of a resin having a positive intrinsic birefringence value and the layer made of a resin having a negative intrinsic birefringence value. A layer to be improved (hereinafter, may be referred to as an “adhesive layer”) may be provided. For example, a five-layer structure of a layer made of a positive resin / an adhesive layer / a layer made of a negative resin / an adhesive layer / a layer made of a positive resin can be used. For the adhesive layer, a material having an intrinsic birefringence value that is compatible with both the positive resin and the negative resin can be used. For example, when a norbornene-based polymer is used as the resin having a positive intrinsic birefringence value and polystyrene (or a styrene-based polymer) is used as the negative resin, the adhesive layer is made of an olefin-based polymer and a polystyrene (or a styrene-based polymer). polymer)
A layer having a glass transition point of 5 compared to the glass transition points of the positive resin and the negative resin.
It is preferably a layer made of a polymer having a low temperature of not more than 10 ° C (more preferably not more than 10 ° C). However, it is not limited to this. The product of the birefringence and the thickness of the adhesive layer is preferably small.

The quarter-wave plate has a wavelength of 450 nm to 6 nm.
Wide range up to 50 nm, at least 450n wavelength
m, at 550 nm and 650 nm, the value of (retardation (Re) / wavelength (λ)) is each 0.2 or more and 0.3 or less, in other words, the value of retardation (Re) at a wavelength of 550 nm is , 110 nm ~
165 nm, and preferably has a positive correlation with the wavelength length. More preferably, at least wavelength 450n
m, at 550 nm and 650 nm, (Re / λ)
Is 0.23 or more and 0.27 or less, and more preferably 0.24 or more and 0.26 or less.

The 波長 wavelength plate has a photoelastic modulus of 20
It is preferably at most blue star, more preferably at most 10 blue star, even more preferably at most 5 blue star. When the photoelastic modulus is within the above range, a partial difference in retardation occurs even when a partially biased stress is applied, such as when bonding with another member (for example, a polarizing plate). Is preferred because it can suppress

The quarter-wave plate can be manufactured by various methods. When a quarter-wave plate having a single-layer structure is manufactured, first, a positive material and a negative material are appropriately selected according to the above-described index, and the compounding ratio is determined. Add) and mix. Then, this formulation,
A coating solution is prepared by dissolving the coating solution in an arbitrary organic solvent, and the coating solution is applied onto a support (or a temporary support) and dried to form a film (solution casting method). Alternatively, the compound can be pelletized, melt-extruded, and formed into a film to produce (extrusion molding method). In the case of manufacturing a quarter-wave plate having a laminated structure, for example, a coating solution in which the positive resin and the negative resin are respectively dissolved in a solvent is prepared, and the coating solution is used as a support (or a temporary support). On the body) sequentially (or simultaneously superimposed application), and then dried to form a film. Further, it can also be produced by utilizing co-extrusion.
Above all, it is preferable to manufacture by a method using co-extrusion described later, because the manufacturing process can be further simplified and the manufacturing cost can be reduced.

When manufacturing a laminated type quarter-wave plate,
A method comprising co-extruding the positive resin and the negative resin to form a laminate including a first layer made of the positive resin and a second layer made of the negative resin. It is preferable to produce it because it can be produced more easily. When the laminate shows the desired retardation as the broadband quarter-wave plate described above, the laminate can be used as it is as a quarter-wave plate. When the laminate does not exhibit a desired retardation, a step of stretching the laminate and adjusting the retardation can be further performed.

In the step of forming the laminate, for example,
Each of the positive resin and the negative resin is stored in an extruder, heated and pressurized so as to be in a fluidized state, and each is continuously extruded from a die to form a laminate. Subsequently, the laminate may be continuously inserted through the nip portion of the nip roll and pressed. When a quarter-wave plate having a structure of three or more layers is produced, in the step of forming the laminate, the positive or negative resin constituting the third layer is stored in an extruder, A laminate having a three-layer structure is formed by extrusion.
In the case where a quarter-wave plate having a layer for improving the adhesion between the two layers is provided between a layer composed of a positive resin and a layer composed of a negative resin, the above-described lamination is performed. In the step of forming the body, a resin for improving the adhesiveness is separately stored in an extruder, and the adhesiveness is improved between the layer made of the positive resin and the layer made of the negative resin by co-extrusion. A laminated body having a configuration in which layers for causing the layers are arranged is formed.
Also, a plurality of flow paths are provided between the place where the resin in the extruder is stored and the extrusion die, for example, a positive resin / a resin for an adhesive layer / a negative resin / a resin for an adhesive layer / a positive resin. A laminate having a five-layer structure composed of three kinds of resins having the above structure can be formed.

The step of adjusting the retardation by stretching the laminate can be carried out using various stretching machines. For example, longitudinal uniaxial stretching that extends in the mechanical flow direction, tenter stretching that extends in the direction perpendicular to the mechanical flow direction, and the like can be preferably used, and for thickness direction control,
It is also possible to impart biaxiality. Here, the stretching temperature is determined by the basic materials (positive resin and negative resin) constituting the layer.
Is the minimum glass transition temperature of Tg _min , (Tg _min
-20) ° C. to (Tg _min ) ° C.

By adjusting the weight ratio of the negative resin to the positive resin, the stretching temperature, the stretching ratio, and the like, a quarter-wave plate satisfying the characteristics as a wide-band quarter-wave plate can be manufactured. . For example, an example of an adjustment method when a norbornene-based polymer is used as a resin having a positive intrinsic birefringence value and polystyrene is used as a resin having a negative intrinsic birefringence value will be described.
The melting softening temperatures of the polystyrene and the norbornene-based polymer are Ts and Tn, respectively. Since Ts <Tn, when a laminate of a layer composed of a norbornene-based polymer and a layer composed of polystyrene is stretched at a temperature close to Tn, the orientation of polystyrene molecules is relaxed rapidly, and molecules of the layer composed of polystyrene are almost completely oriented. The layer made of polystyrene has no birefringence. As a result, the laminated film in which the layer composed of the norbornene-based polymer and the layer composed of the polystyrene are laminated has almost the same wavelength dispersion as the layer composed of the norbornene-based polymer. As the stretching temperature is lowered, the polystyrene molecules become oriented, and the polystyrene layer becomes birefringent. Since the retardation of the layer made of polystyrene is negative, the positive retardation of the layer made of the norbornene-based polymer decreases. The reduction rate of the retardation is large on the short wavelength side due to the wavelength dispersion of polystyrene, and the retardation is greatly reduced, and Re (450) <R
The characteristic of e (550) <Re (650) is obtained. By controlling the stretching temperature, the R
A wide-band quarter-wave plate functioning as a wide-band quarter-wave plate having e / λ of approximately 1/4 can be manufactured.
For a 1/4 wavelength plate having a single layer structure of a polymer blend type instead of a laminated type by co-extrusion, an appropriate stretching temperature is determined based on the same concept, and a broadband 1/4 wavelength plate that functions as a broadband 1/4 wavelength plate is formed. Can be made.

When a quarter-wave plate having the adhesive layer is formed between the layer made of the positive resin and the layer made of the negative resin, the resin constituting the adhesive layer is as follows:
It is preferable to use a resin having a melt softening temperature lower than the stretching temperature. Specifically, it is preferable to use a resin having a low glass transition point, and it is more preferable to use a resin having a glass transition temperature lower by 5 ° C. or more with respect to the positive resin and the negative resin, Preferably, 2
0 ° C. or higher.

[Light Source] In the backlight device for a liquid crystal display of the present invention, a light source used in an ordinary liquid crystal display can be used. A surface light source type light source is preferable. For example, a configuration in which a light source is arranged on a side surface of a light guide plate or a diffusion plate is preferable.

[Reflecting Plate] In the backlight device for a liquid crystal display of the present invention, a reflecting plate used in a usual liquid crystal display can be used. The reflecting plate has a function of converting the incident circularly polarized light component into polarized light (converting clockwise clockwise to counterclockwise or converting clockwise clockwise to clockwise) and reflecting it. Any mirror having a reflection function similar to that of a normal mirror can be widely used.

[Cholesteric Liquid Crystal Layer] In the backlight device for a liquid crystal display of the present invention, the cholesteric liquid crystal layer rotates counter to the spiral of liquid crystal molecules (clockwise in FIG. 1, but may be counterclockwise). In FIG. 1, the light transmits the left-handed circularly polarized light component and reflects the same circularly-polarized light component as the helix of the liquid crystal molecules. However, unlike normal reflection, the direction of the circularly polarized light component does not change. The cholesteric liquid crystal layer preferably shows selective reflection in a visible wavelength region of 380 nm to 780 nm. The selective reflection of the cholesteric liquid crystal layer is one of the optical properties of liquid crystal which has been known for the longest time, and is described in various documents. It is preferable to provide a plurality of cholesteric liquid crystal layers having different selective reflection center wavelengths. A cholesteric liquid crystal layer used in a backlight device for a liquid crystal display is disclosed in JP-A-8-1464.
No. 16, No. 8-271731, No. 10-319235
And Japanese Patent Application Laid-Open No. 10-513578 are also applicable to the present invention.

The backlight device for a liquid crystal display of the present invention is applicable to various liquid crystal displays. For example, TN (Twisted Nematic), IPS (In Plane Sw
itching), FLC (Ferroelectric Liquid crysta)
l), OCB (Optically Compensatory Bend), STN
(Supper Twisted Nematic), VA (Vertically Align)
ed) and HAN (Hybrid Aligned Nematic).

[0044]

EXAMPLES [Example 1] -Preparation of quarter wave plate- As a resin having a positive intrinsic birefringence, a cycloolefin-based norbornene resin (trade name "Zeonor 1420R"; manufactured by Zeon Corporation), intrinsic birefringence Polystyrene (trade name “HF-77”; manufactured by A & M Styrene) was used as the resin having a negative value. These resins were dried beforehand under a nitrogen purge to reduce the amount of water. The absolute values of the retardation (Re) at the wavelengths of 450 nm and 550 nm are represented by Re (45), respectively.
0) and Re (550), (Re (450) / Re (55) of the cycloolefin-based norbornene resin.
0)) is 1.005, and the value of (Re (450) / Re (550)) of the polystyrene is 1.080.
Where the two values are not the same and the difference is 0.075.

An apparatus 20 having the structure shown in FIG. 4 was used. The device is "LABO PLASTOMIL" manufactured by Toyo Seiki.
I ", and the dice 22 had a width of 250 mm. Two extruders 24 and 26 are attached to the die 22,
The resin hoppers housed in the extruder 24 and the extruder 26 join together inside the die 22.
The extruder 26 has two openings. Inside the die 22, the resin hopper 2 extruded from the two openings of the extruder 26 is centered around the resin hopper 1 extruded from the extruder 24. Has a structure that merges from both sides. The internal structure of the die 22 is shown in FIG. In addition, rolls 28, 30,
A film 32 having a three-layer structure extruded from the die 22 can be adjusted in thickness.

The polystyrene hopper was stored in the extruder 24 and the norbornene resin hopper was stored in the extruder 26, and a three-layered melt-formed film 34 composed of norbornene resin / polystyrene / norbornene resin was prepared. Regarding the thickness of the laminated film 34, the roll 2
The adjustment was attempted by the peripheral speed control of 8, 30, and 32. When the peripheral speeds of the rolls 18, 20, and 22 were determined with a target of a final thickness of 100 µm, an actual laminated film having a thickness of 102 µm was obtained. The molding conditions are shown in Table 1 below. still,
The meanings of the symbols in Table 1 below are shown below. C1 to C3: Cylinder temperature of the extruder (below C1 hopper) D: Die (lip) temperature

[0047]

[Table 1]

The obtained laminated film was subjected to a 19% stretching treatment in an atmosphere at 95 ° C. to obtain a stretched film.
The wavelength dependence of Re of the obtained 19% stretched film was measured by "KOBRA 21DH" manufactured by Oji Scientific. The obtained 19% stretched film has a wavelength of 450 nm,
At 550 nm and 650 nm, Re / λ is
The values were 0.245, 0.250 and 0.230, which proved that the device had broadband quarter-wave plate characteristics. Also,
When the photoelastic modulus of the obtained laminated film was measured using “M-150” manufactured by JASCO, it was 5 Brewster.

-Production of backlight device for liquid crystal display-A cholesteric liquid crystal film in which the cholesteric pitch continuously changes in the thickness direction and selectively reflects light having a wavelength of 400 nm to 700 nm,
A four-wavelength plate is bonded, and the back surface of the quarter-wave plate (the surface on which the cholesteric liquid crystal film is not bonded) is provided with a planar light source and a reflector of a commercially available liquid crystal display, The two substrates were bonded together on the quarter-wave plate side to produce a backlight device for a liquid crystal display. For this backlight device, when the average degree of polarization for vertically incident light was measured at a wavelength of 400 to 700 nm,
It was 91%. The light use efficiency of the light source was 1.5 times that of the case where the polarizing plate was used alone.

Example 2 As a resin having a positive intrinsic birefringence, a cycloolefin-based norbornene resin (trade name “Zeonor 1420R”; manufactured by Zeon Corporation) was used. As a resin having a negative intrinsic birefringence, a styrene-based anhydride was used. A maleic acid copolymer resin (manufactured by Nova Chemical Co., Ltd., “Dailac D332”) was used. These resins were dried beforehand under a nitrogen purge to reduce the amount of water. Note that the absolute values of the retardation (Re) at wavelengths of 450 nm and 550 nm are Re (450) and Re (5), respectively.
50), the value of (Re (450) / Re (550)) of the cycloolefin-based norbornene resin is 1.005, and the (Re (450) / Re () of the styrene-maleic anhydride copolymer resin. 550)) is 1.
069, the values are not the same and the difference is 0.06
4.

An apparatus 20 having the structure shown in FIG. 4 was used. The device is "LABO PLASTOMIL" manufactured by Toyo Seiki.
I ", and the dice 22 had a width of 250 mm. Two extruders 24 and 26 are attached to the die 22,
The resin hoppers housed in the extruder 24 and the extruder 26 join together inside the die 22.
The extruder 26 has two openings. Inside the die 22, the resin hopper 2 extruded from the two openings of the extruder 26 is centered around the resin hopper 1 extruded from the extruder 24. Has a structure that merges from both sides. The internal structure of the die 22 is shown in FIG. In addition, rolls 28, 30,
A film 32 having a three-layer structure extruded from the die 22 can be adjusted in thickness.

A hopper of the styrene / maleic anhydride copolymer resin is stored in an extruder 24, and a hopper of the norbornene resin is stored in an extruder 26. Was produced. Regarding the thickness of the laminated film 34, the rolls 28, 30,
Adjustment was attempted by controlling the peripheral speed of 32. Final thickness is 150
When the peripheral speeds of the rolls 18, 20, and 22 were determined with a target of μm, an actual laminated film having a thickness of 102 μm was obtained.

The obtained laminated film was subjected to a 65% stretching treatment in an atmosphere at 120 ° C. to obtain a three-layer stretched film. The thickness of the obtained stretched film was 36 μm / 39 μm / 38 μm for the layer of norbornene resin / the layer of styrene-maleic anhydride copolymer resin / the layer of norbornene resin. With respect to the obtained stretched film, the wavelength dependence of Re was measured by “KOBRA 21DH” manufactured by Oji Scientific. The obtained 65% stretched film has a wavelength of 450 n.
At m, 550 nm, and 650 nm, Re / λ was 0.245, 0.250, and 0.235, respectively, indicating that the film had broadband quarter-wave plate characteristics. In addition, the photoelastic modulus of the obtained laminated film was measured using "M-150" manufactured by JASCO, and was 4 Brewster.

-Production of backlight device for liquid crystal display-The cholesteric pitch changes in the thickness direction and the wavelength is 400
A cholesteric liquid crystal film having selective reflection with respect to light of nm to 700 nm is bonded to the prepared broadband quarter-wave plate, and the back surface of the quarter-wave plate (the cholesteric liquid crystal film is not bonded) A surface light source and a reflection plate of a commercially available liquid crystal display were adhered to the (surface) with the surface light source being the １ ／ wavelength plate side to produce a backlight device for a liquid crystal display. The average degree of polarization of this backlight device with respect to vertically incident light at a wavelength of 400 to 700 nm was 93%. The light use efficiency of the light source was 1.6 times that of the case where the polarizing plate was used alone.

Example 2 was the same as Example 2 except that a commercially available iodine-based polarizing plate (polarization degree: 99.99%) was laminated on the １ ／ wavelength plate so that the polarization axis coincided therewith. Similarly, a backlight device was manufactured. With respect to this backlight device, when the average degree of polarization for vertically incident light was measured at a wavelength of 400 to 700 nm, it was 99.9.
9%. The light use efficiency of the light source was 1.5 times that of the case where the polarizing plate was used alone.

[0056]

As described above, according to the present invention, it is possible to provide a backlight device for a liquid crystal display, which has an improved utilization efficiency of the amount of light from a light source and is excellent in mass productivity.

[Brief description of the drawings]

FIG. 1 is a drawing used to explain the function of a backlight device for a liquid crystal display of the present invention.

FIG. 2 is an example of a schematic cross-sectional view of a quarter-wave plate that can be used in the present invention.

FIG. 3 is an example of a schematic cross-sectional view of a quarter-wave plate that can be used in the present invention.

FIG. 4 is a schematic diagram of an extrusion apparatus used in Examples.

FIG. 5 is a cross-sectional view of a die of an extruder used in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 10 'Quarter-wave plate 12 Layer made of resin whose intrinsic birefringence value is positive 14 Layer made of resin whose intrinsic birefringence value is negative 20 Extruder 22 Dice 24, 26 Extruder 28, 30, 32 Roll 34 laminated film

Claims (7)

[Claims] 1. A backlight device for a liquid crystal display in which a reflector, a light source, a cholesteric liquid crystal layer and a 波長 wavelength plate are arranged in this order, wherein the 波長 wavelength plate has a positive intrinsic birefringence value. A backlight device for a liquid crystal display, comprising a certain material and a negative material. 2. The wavelength of said quarter-wave plate of 450 nm, 5
(Retardation / 50 nm and 650 nm)
2. The backlight device for a liquid crystal display according to claim 1, wherein the values of (wavelength) are each not less than 0.2 and not more than 0.3. 3. The method according to claim 1, wherein the quarter-wave plate includes a first layer containing a material having a positive intrinsic birefringence value, and a second layer containing a material having a negative intrinsic birefringence value. 3. The backlight device for a liquid crystal display according to claim 1, wherein the first layer and the second layer have the same average molecular chain orientation direction. 4. 4. The material according to claim 3, wherein the material having a positive intrinsic birefringence value and the material having a negative intrinsic birefringence are each a resin, and the first layer and the second layer are each a stretched film of the resin. The backlight device for a liquid crystal display according to the above. 5. The backlight device for a liquid crystal display according to claim 1, wherein the material having a positive intrinsic birefringence value is a norbornene-based polymer. 6. The backlight device for a liquid crystal display according to claim 1, wherein the material having a negative intrinsic birefringence value is at least one selected from polystyrene and a styrene-based polymer. 7. The backlight device for a liquid crystal display according to claim 6, wherein the styrene-based polymer is a copolymer of styrene and maleic anhydride.