JP3416302B2 - Backlight device for liquid crystal display and liquid crystal display device using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device used for a liquid crystal display element and the like and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Backlight devices are widely used for improving the visibility of non-luminous liquid crystal display devices, and are essential for high-definition displays such as television monitors and personal computers. In recent years, as colorization of liquid crystal display devices has progressed and the light transmittance of the liquid crystal display device has decreased, it is necessary to maintain the surface brightness of the liquid crystal display device at a level with good visibility, and a backlight with high brightness is required. Tend to be used. The backlight includes a linear light source such as a fluorescent discharge tube, a light guide plate that transmits the light to the display surface, and a light diffusion plate that makes the brightness uniform (edge light type), and a plurality of fluorescent discharge tubes. There is one that irradiates the liquid crystal display device through the light diffusion plate (direct type).

Since the colorization of the liquid crystal display device is realized by making white light incident on the color filter, the backlight needs to be white. On the other hand, since display in a twist nematic (TN) mode or a super twist nematic (hereinafter, sometimes referred to as STN) mode is general, light from a light source is linearly polarized through a polarizing plate and is incident on a liquid crystal display device. Need to let. Therefore, there is a problem that the amount of light from the light source is reduced to half or less by passing through the polarizing plate.

In order to increase the amount of light, a reflector is installed on the back surface of the light guide plate to reflect the light from the light source on the surface. Further, a light condensing plate such as a Fresnel lens or a microarray lens is installed in place of the light diffusing plate (hereinafter referred to as a diffusing plate) to increase the front brightness of the display device. Although it is possible to further increase the brightness of the backlight, problems such as an increase in power consumption and accompanying heat generation from the backlight, and a reduction in drive time when a battery is used and deterioration of display quality are pointed out. Has been done.

[0005]

As described above, in the conventional liquid crystal display device, since the amount of light emitted from the light source has not been sufficiently utilized, it has been required to improve the utilization efficiency of light from the light source. An object of the present invention is to provide a backlight device for a liquid crystal display, which has improved utilization efficiency of the amount of light emitted from a light source, and a high-brightness liquid crystal display device using the same.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors in order to solve the above problems, 400 to 700n
cholesteric liquid crystal layer showing selective reflection in the range of m and 1 /
The present invention has been found out that the utilization efficiency of the amount of light emitted from a light source can be improved by combining it with a four-wave plate, and that by combining these with a liquid crystal panel, a high-brightness liquid crystal display device can be obtained. It came to completion.

That is, the present invention comprises the following inventions. (1) Reflector plate, light guide plate having light source on side surfaces, 400 to 7
A backlight device for a liquid crystal display, characterized in that a circularly polarizing plate made of a cholesteric liquid crystal layer exhibiting selective reflection in a range of 00 nm, a quarter-wave plate, and a diffusing plate or a light collecting plate are arranged in this order. (2) Reflecting plate, light guide plate having light source on side surface, 400 to 7
A circularly polarizing plate made of a cholesteric liquid crystal layer showing selective reflection in the range of 00 nm, a diffusion plate or a light collecting plate, and 1 /
A backlight device for a liquid crystal display, characterized in that four wavelength plates are arranged in this order.

(3) A reflector, a circularly polarizing plate made of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm, and a light source are provided on the side surface, and the circularly polarizing plate is arranged between the light source and the light guide plate. A backlight device for a liquid crystal display, comprising: a light guide plate, a quarter-wave plate, and a diffuser plate or a light collector plate, which are arranged in this order. (4) A reflective plate, a light source, a circularly polarizing plate composed of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm, 1
A back light device for a liquid crystal display, characterized in that a / 4 wavelength plate and a diffusion plate or a light collecting plate are arranged in this order. (5) A reflective plate, a light source, a circularly polarizing plate made of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm, a diffusing plate or a light collecting plate, and a quarter wave plate are arranged in this order. Backlight device for liquid crystal display.

(6) A liquid crystal cell in which an oriented liquid crystal layer is sandwiched between substrates having electrodes, and further sandwiched between two outer polarizing plates; and the liquid crystal display according to any one of (1) to (5). LCD device for use in a liquid crystal display, wherein an angle between a vibration plane of linearly polarized light emitted from the backlight device and a transmission axis of a polarizing plate in contact with the backlight device is substantially zero. apparatus. (7) The oriented liquid crystal layer is sandwiched between substrates having electrodes,
A liquid crystal cell in which a polarizing plate is arranged on one outer side of a substrate holding a liquid crystal phase, and a liquid crystal according to any one of (1) to (5) arranged on the other outer side of a substrate holding a liquid crystal layer. A liquid crystal display device using a display backlight device.

Next, the present invention will be described in detail. The circularly polarizing plate composed of a cholesteric liquid crystal layer used in the present invention includes a polymer liquid crystal, a liquid crystal oligomer polymer, a mixture of a transparent polymer with a low molecular weight liquid crystal, or a transparent polymer with a polymer liquid crystal or a liquid crystal oligomer. A film-shaped or plate-shaped material obtained by mixing the above can be used. The liquid crystal material used is required to exhibit a cholesteric phase, and a material having a cholesteric phase pitch that causes selective reflection in the visible light region is used. Two or more kinds of cholesteric liquid crystal materials having different pitches may be used to generate selective reflection in the visible light range. For this purpose, liquid crystal materials may be mixed and used, or two or more liquid crystal layers may be laminated. You may use it. The light source used in the present invention is not particularly limited, but a linear light source or a flat light source is preferably used, and a cold cathode tube or a hot cathode tube which is a fluorescent discharge tube is generally used. Further, it is preferable to attach a reflective cover around these light sources in order to increase the utilization efficiency of light from the light sources.

As the reflective cover, a metal sheet or metal foil of aluminum, silver, stainless steel or the like having a high reflectance can be used alone, or a molded body having these on the surface can be used. As the structural material of the molded body,
A metal material or a polymer such as polyethylene terephthalate can be used. The shape of the reflection cover can be appropriately designed and used so that the light from the light source can be reflected and introduced into the light guide plate.

A transparent polymer plate or polymer sheet can be used as the light guide plate used in the present invention. Polymethacrylate as polymer, Porika Bonnet over preparative, polyethylene terephthalate, and the like. Examples of the shape of the light guide plate include a plate whose upper and lower surfaces are parallel to each other, a sheet or a film, and a shape where the upper and lower surfaces are not parallel to each other and are tapered. The size of the light guide plate can be appropriately designed to a size suitable for the area of the liquid crystal cell used.

As the reflector used in the present invention, aluminum, which is a metal having a high reflectance like the reflection cover,
A metal sheet or metal foil of silver, stainless steel or the like can be used alone, or a molded body having these on the surface can be used. As the structural material of the molded body, a metal material or a polymer such as polyethylene terephthalate can be used.
Further, if necessary, it may be patterned and used in order to improve the reflection efficiency to the light guide plate. The diffuser plate used in the present invention, polymethacrylates, Porika Bonnet chromatography <br/> preparative, BaSO the resin plate such as polyethylene terephthalate
₄ , a polymer sheet or film in which powder such as TiO ₂ or air bubbles are dispersed to impart light diffusivity can be used. Further, instead of the diffusion plate, a condensing plate having a Fresnel lens, a micro array lens, a minute pyramid-shaped protrusion or the like on the surface may be used. The quarter-wave plate used in the present invention is
A polymer film obtained by uniaxially stretching a polymer film having birefringence anisotropy and having a retardation of 100 nm to 175 nm can be used. In order to act as a quarter-wave plate in the visible light range, it is also possible to use two retardation plates having different refractive index wavelength dispersions and bonded together with their optical axes displaced as a quarter-wave plate. .

An example of the liquid crystal display backlight device of the present invention is shown in FIGS. In the sidelight type, as shown in FIGS. 1 to 3, light emitted from a light source (for example, a fluorescent discharge tube) 1 arranged on a side surface of a light guide plate enters a light guide plate 3. In this case, in order to increase the efficiency of light collection on the light guide plate 3, it is preferable to install the reflection cover 2 at the rear part of the light source 1. In order to radiate light from the light guide plate 3 to the front surface, a reflection plate 4 is provided at the bottom of the light guide plate 3. Further, in order to effectively use the light reaching one end of the light guide plate 3, it is preferable to provide the reflection cover 6 also on the side opposite to the light source 1. The light emitted from the light guide plate 3 is diffused by the diffusion plate 5 and introduced into a liquid crystal cell (not shown). In the liquid crystal display backlight unit of the present invention shown in FIG. 1, a circularly polarizing plate 7 quarter-wave plate 8 is disposed between the light guide plate and the diffusion plate. Further, in the liquid crystal display backlight device shown in FIG. 2, the circular polarization plate 7 is installed between the light guide plate 3 and the diffusion plate 5, and the quarter wavelength plate 8 is installed above the diffusion plate 5. Further, as shown in FIG.
It can also be installed between the light guide plate 3 and the light guide plate 3. In this case, 1
The / 4 wavelength plate 8 is preferably installed between the light guide plate 3 and the diffusion plate 5. As shown in FIG. 1, the circularly polarizing plate 7 and 1/4
The wave plate 8 is preferably in contact with and installed between the light guide plate 3 and the diffusion plate 5.

Next, a direct type backlight for liquid crystal display
In the device , as shown in FIGS. 4 and 5, a circularly polarizing plate 7 is provided above the light source 1 having a reflection sheet at the bottom. The quarter-wave plate 8 may be installed between the circularly polarizing plate 7 and the diffusion plate 5 as shown in FIG. 4 or on the diffusion plate 5 as shown in FIG. Thus, it is preferable to install the circularly polarizing plate 7 in contact with it. A light condensing plate may be used instead of the diffusion plate in the above description.

The method of manufacturing a circularly polarizing plate comprising a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm used in the present invention is not particularly limited, but after the cholesteric liquid crystal material is formed into a film, heat treatment is carried out. From the viewpoint of obtaining a circularly polarizing plate having good characteristics, a method in which the helical axis of orientation is made substantially parallel to the film normal direction and then the polymerizable group is polymerized is preferable. For this purpose, it is preferable to perform a horizontal alignment treatment on a smooth base material and then form a cholesteric liquid crystal layer. The base material used is preferably a transparent or translucent base material, and specific examples thereof include an inorganic substrate and a polymer film.

As the inorganic substrate, a transparent or semi-transparent glass plate, the outside of a glass plate used for a liquid crystal cell, or an inorganic compound such as oxides or fluorides of Si, Al, Mg, Zr, or ceramics is used. A substrate is exemplified.

[0018] As the polymer film, polycarbonate, polysulfone, polyarylate, polyether scan Le <br/> Hong, 2 cellulose acetate, cellulose triacetate, polystyrene, ethylene vinyl alcohol copolymer, polyethylene terephthalate, polyethylene naphthalate, etc. Are more preferable, and more preferable examples are polycarbonate, polysulfone, and polyethylene terephthalate.

When the base material is a polymer film, the glass transition temperature of the base material to be used during the heat treatment of the side chain type polymer liquid crystal, or the flow of the base material in the base material to which the additive is added. It is preferable to select a substrate according to the heat treatment temperature in order to avoid problems in the manufacturing method such as deformation of the substrate at temperatures above the temperature.

As the horizontal alignment treatment method, known methods such as a rubbing method and an oblique vapor deposition method can be used, but the rubbing method is more preferable from the viewpoint of industrialization. When the rubbing method is used, the base material before the liquid crystal oligomer is formed is directly rubbed, or the alignment film is formed on the base material and then rubbed.

As the alignment film, known films can be used as long as the liquid crystal molecules are horizontally aligned. For example, a film of polyimide, polyamide, polyvinyl alcohol or the like is exemplified. Examples of the method for applying the alignment film include a roll coating method, a gravure coating method, a bar coating method, a spin coating method, a spray coating method, a printing method, and a dipping method. Regarding the film thickness of the alignment film, generally, if the film thickness is 0.01 μm or more, the alignment performance is exhibited, but if the alignment film is too thick, workability deteriorates.
5.0 μm is preferable, and more preferably 0.02 to
It is 3.0 μm.

Then, depending on the type of the applied alignment film,
After post-treatment such as drying and curing, the alignment film is rubbed, or when the substrate is directly rubbed, the substrate is rubbed directly. The rubbing method is not particularly limited, and a known method can be used. For example, when using a rubbing roller, the material of the rubbing roller,
There is no particular limitation on the amount of rubbing roller pushed into the alignment film, the moving speed of the roller with respect to the base material, the number of times of rubbing, etc., and the optimum conditions are selected according to the type of alignment film, substrate, liquid crystal oligomer, etc. do it.

As the oblique evaporation method, an oblique evaporation film of an inorganic material is used.
The method used is illustrated, and columnar growth occurs during vapor deposition as an inorganic substance.
Is preferably used, and the film is formed by a usual method. The inorganic
As the product, SiO, SiO₂, SiO_x(In the formula, 1 <
x <2), MgO, MgO_y(Where 0 <y <1), M
gF₂, Pt, ZnO, MoO₃, WO₃, Ta
₂O _Five, SnO₂, CeO₂, LiNbO₃, LiTa
O₃, ZrO₂, Bi₂O₃, TiZrO_Four, HfO₂
Are exemplified.

Next, a cholesteric liquid crystal layer or a layer dispersed in a polymer matrix is formed on the base material subjected to the horizontal alignment treatment. Examples of the film forming method include a method of applying the liquid crystal composition in a solution state and a method of applying in a isotropic phase state, and the method of applying in a solution state is preferable from the viewpoint of the film quality of the obtained film. Examples of the coating method include an ordinary roll coating method, gravure coating method, bar coating method, spin coating method, spray coating method, printing method, and depping method. The thickness of the obtained film is preferably 0.1 to 100 μm. When the thickness is less than 0.1 μm, the expression of optical properties becomes small, and when it exceeds 100 μm, it is not economically preferable.

Then, the cholesteric liquid crystal layer or
Heat treatment of polymer layer containing steric liquid crystal
Is preferred. Heat treatment temperature is T_t, The crystal phase of the liquid crystal composition
Or the transition temperature from the glass phase to the liquid crystal phase is T_g, Base material and
T is the temperature at which the tunica membrane deforms _kWhen you write
The processing temperature is T_g+ 30 ° C ≦ T_t≤T_k-30 ° C
Preferably T_g+ 40 ° C ≦ T_t≤T_kIn the range of -40 ° C
Heat treatment is more preferable, considering ease of production
And 60 to 200 ° C. is preferable. Heat treatment
If the time is too short, orientation will not be realized, and if it is too long, it will be industrial.
Is not preferable, so 0.2 minutes or more and 20 hours or less is preferable.
More preferably, it is more preferably 1 minute or more and 1 hour or less. More than
By heat treatment, the liquid crystal composition becomes parallel to the film normal direction.
It comes to have an orientation having a large spiral axis. In heat treatment
There is no particular limitation on the heating rate and cooling rate.

The circularly polarizing plate comprising a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm used in the present invention is 400 nm or more and less than 500 nm, 50
0 nm or more and less than 600 nm, 600 nm or more and 700 nm
It is possible to use one in which at least three cholesteric liquid crystal layers exhibiting selective reflection in each of the ranges below are laminated. Further, as the circularly polarizing plate, one having a layer in which a cholesteric liquid crystal material is dispersed in a polymer can be used. In this case, 400 nm or more and 500 nm
Or less, 500 nm or more and less than 600 nm, and at least three kinds of cholesteric liquid crystal materials exhibiting selective reflection in the respective ranges of 600 nm or more and less than 700 nm may be dispersed in the polymer, or at least selective reflection in the range of 400 nm to 500 nm is achieved. One type of cholesteric liquid crystal material may be dispersed in the polymer. Further, after the cholesteric liquid crystal material is dispersed in the polymer, an electric field may be applied to adjust the pitch of the cholesteric liquid crystal material. As a method of dispersing the cholesteric liquid crystal material in the polymer matrix, a method of mixing the liquid crystal material and the polymer compound by an appropriate method and then forming a film to phase-separate the liquid crystal material and the polymer compound, or an encapsulated liquid crystal Examples include a method of dispersing a material in a matrix.

When a cholesteric layer is produced by phase separation of a liquid crystal material and a polymer compound, the polymer compound used as a matrix is not particularly limited, but suitable polymer compounds include polyethylene, polypropylene,
Polyolefins such as polybutylene, poly aromatic vinyl compounds such as polystyrene; polyacrylic acid esters such as polymethyl acrylate; polyvinyl acetate; polyvinyl chloride; polyvinylidene chloride polymethacrylic acid esters such as polymethyl methacrylate; poly Acrylonitrile; polyvinyl ethers such as polymethyl vinyl ether; polyvinyl ketones; polyalkylene oxides such as polypropylene oxide and polyethylene oxide; polycarbonates; polyesters such as polyethylene terephthalate and polybutylene terephthalate; epoxy resins and the like. These high molecular compounds may be copolymers, and may be used alone or in combination.

The method of mixing the liquid crystal material and the polymer compound is not particularly limited as long as it does not impair the characteristics of the liquid crystal material or the polymer compound. Examples thereof include a method of melting and mixing a liquid crystal material and a polymer compound in a bulk state, a method of mixing by roll kneading, a method of dissolving both of them in a solvent and mixing.

The cholesteric layer used in the present invention is
After the film formation, the liquid crystal material and the polymer compound need to have a phase-separated structure. As a method of inducing a phase-separated structure, a method of forming a mixture of a liquid crystal material and a polymer compound and then performing phase separation by lowering the temperature, casting a solution of the liquid crystal material and the polymer compound on a substrate, and then removing a solvent Examples thereof include a method of causing phase separation by evaporation. These phase separation structures can be controlled by changing the mixing ratio of the liquid crystal material and the polymer compound, the temperature decrease rate after film formation, the solvent evaporation rate, and the like. In addition, a layer separation structure can be induced by mixing a cholesteric liquid crystal material and a polymerizable monomer and polymerizing the monomer after film formation. Furthermore, by the method of dispersing the encapsulated liquid crystal material in the matrix,
As an example of forming the cholesteric layer, a method of casting a suspension obtained by mixing and stirring a liquid crystal material in a polyvinyl alcohol aqueous solution and evaporating the solvent can be mentioned.

[0030] As the polymer liquid crystal or liquid crystal oligomers showing a cholesteric phase used in the present invention, polyester, it was introduced optically active component in the bending chain connecting the chain polymeric liquid crystal mesogen such Porika Bonnet over preparative system Or a poly (acrylic acid ester), poly (methacrylic acid ester), polysiloxane, or the like, which has a cholesterine derivative and / or an asymmetric carbon atom as a side chain through a skeleton main chain through a bent chain such as a methylene chain. Among the side chain type polymer liquid crystals and side chain type liquid crystal oligomers to which mesogen is bound, thermotropic liquid crystal materials are suitable. Among the thermotropic liquid crystal materials, those that exhibit a cholesteric liquid crystal phase after melting and then transition to an isotropic phase are more cholesteric than those that exhibit a cholesteric liquid crystal phase at a glass transition temperature or higher and then transition to an isotropic phase. Preferred for phase immobilization.

Among these, side chain type polymer liquid crystals and side chain type liquid crystal oligomers (hereinafter, these two liquid crystal materials are generically referred to as side chain type polymer liquid crystal materials) are used from the viewpoint of orientation and film forming property. preferable. As these side chain type polymer liquid crystal materials,
Examples thereof include side chain type polymer liquid crystals or side chain type liquid crystal oligomers having the repeating units represented by the general formulas (I) and (II).

[0032]

[Chemical 1]

[Chemical 2] [In the formula, A is a group represented by the following formula (III) or (IV), and in formula (III), -Si-O- is the main chain of formula (I) or (II), -C-CH ₂ in IV) - is the main chain of the formula (I) or (II), COO group is positioned in the side chain is not a R ₁ or R ₂ side chains. When A is formula (III) in formula (I) and A is formula (III) in formula (II), R ₁
And R ₂ are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms or a phenyl group. When A is formula (IV) in formula (I) and A is formula (IV) in formula (II), R ₁ and R ₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms. .

[0033]

[Chemical 3]

[Chemical 4] k and k ′ each independently represent an integer of 2 to 10, m and m ′ are each independently 0 or 1, and Ar ₁ , Ar
₂ and Ar ₃ are each independently 1,4-phenylene group, 1,4-cyclohexylene group, pyridine-2,5-
A diyl group, a pyrimidine-2,5-diyl group, L ′
It is _{-CH 2 -O -, - O-} CH 2 -, - COO -, - O
_{CO -, - CH 2 -CH 2} -, - CH = N -, - N = C
H- or

[0034]

[Chemical 5] Is a divalent group represented by, p ′ is 0 or 1,
R represents an optically active group, R'is hydrogen or a carbon number of 1 to 5
Is an alkyl group. ]

The side chain type polymer liquid crystal material comprising the repeating units (I) and (II) is a side chain type polymer liquid crystal or a side chain type liquid crystal oligomer having a cholesteric phase in a liquid crystal state. Examples of the skeletal chain of the side chain type polymer liquid crystal material include poly-1-alkylacrylic acid ester and polysiloxane, and linear or cyclic ones can be used. From the viewpoint of stability, a cyclic structure is preferable. The poly-1-alkyl acrylic acid ester is preferably a polymethacrylic acid ester or a polyacrylic acid ester, more preferably a polymethacrylic acid ester. Among these, polysiloxane-based side-chain polymer liquid crystal materials are particularly preferable. The group that imparts liquid crystallinity (hereinafter, sometimes referred to as mesogen group) has a bent chain (hereinafter,
Sometimes called a spacer. Those linked to the main chain via () are generally usable.

The side chain type polymer liquid crystal material is required to be in a liquid crystal state at a use temperature, that is, from room temperature to about 60 ° C. The transition temperature from the liquid crystal phase to the isotropic phase (hereinafter sometimes referred to as the transition temperature of the liquid crystal phase / isotropic phase) becomes 200 ° C. or less due to drying or orientation treatment during lamination with the substrate. As described above, it is preferable to select the length of the spacer, the kind of the mesogenic group, and the degree of polymerization so that the temperature is preferably 170 ° C. or lower, and more preferably 150 ° C. or lower.

The side chain type polymer liquid crystal material used in the present invention is
It is necessary to control the helical pitch of the cholesteric phase so that the selective reflection of visible light occurs and the wavelength range of the selective reflection does not change with temperature. is important. When the number of repeating units is large, the viscosity is high, and the liquid crystal transition temperature is high, so that high temperature and long time are required for the alignment, and when the number of repeating units is small, the alignment is relaxed at room temperature, which is not preferable. As the degree of polymerization of the high-molecular liquid crystal, the total number of repeating units is 20 to
50,000 is preferable, and 100 to 2 is more preferable.
It is 000. In the case of a side chain type liquid crystal oligomer,
When the numbers of the repeating unit (I) and the repeating unit (II) are n and n ', respectively, they are each independently an integer of 1 to 20,
It is selected so that the sum of n and n'is 4 to 21. Further, the side chain type liquid crystal polymer material is aligned to form repeating units (I
The orientation can be fixed by polymerizing the terminal of I). The ratio of the repeating units is in the range of 1: 5 to 5: 1, and the ratio of the repeating units (I) to the repeating units (II) is in the range of 1: 5 to 5: 1 from the viewpoint of the alignment property of the polymer liquid crystal and the fixed alignment after polymerization. It is preferably 1: 3 to 3: 1. Control of these ratios can be carried out when synthesizing these polymer liquid crystals as described later.

In the side chain type polymer liquid crystal, the liquid crystal transition temperature and the orientation are also influenced by the spacer connecting the main chain and the mesogenic group. A short spacer does not have good orientation of the mesogen group, and a long spacer tends to cause relaxation after orientation of the mesogen group. Therefore, the spacer is preferably an alkylene group having 2 to 10 carbon atoms or an alkyleneoxy group. Particularly, an alkylene group having 2 to 6 carbon atoms or an alkyleneoxy group is preferable from the viewpoint of high orientation. In addition, an alkyleneoxy group is more preferable because of ease of synthesis. Specifically, as a preferable group,-(CH ₂ )
_{2 -, - (CH 2)} 3 -, - (CH 2) 4 -, - (CH
_{2) 5 -, - (CH} 2) 6 -, - (CH 2) 3 -O-,
_{- (CH 2) 4 -O -} , - (CH 2) 5 -O -, - (C
H _{2) 6} -O- is exemplified.

Since the R group in the repeating unit (I) contributes to the development of the cholesteric phase of the liquid crystal oligomer,
It is essential that the group is an optically active group, and from the viewpoint of stabilizing the cholesteric phase, a group having the following structure is preferable.

[Chemical 6] Or

[Chemical 7] (In the formula, R ₃ represents -H or the following formula,

[Chemical 8] R ₄ represents —H or a methyl group, and R ₅ represents —H or R ₆
R ₆ is a linear or branched carbon number of 1 to 20
1 to 3 alkyl groups or straight or branched carbon atoms
20 represents an alkanoyl group, and when branched, may have an asymmetric carbon. )

As a method for synthesizing a side chain type polymer liquid crystal material, Japanese Patent Publication No. 63-41400 and Japanese Patent Publication No. 63-47 are available.
The methods described in Japanese Patent No. 759 and Japanese Patent Laid-Open No. 2-149544 can be adopted. Examples thereof include a method of adding a mesogenic group of the side chain to a polysiloxane chain and a method of polymerizing an acrylic acid ester or a methacrylic acid ester having a mesogenic group via a flexible spacer group. The terminal group in the repeating unit (II) is a group that fixes the alignment of the liquid crystal oligomer by polymerization. -OCO as the polymerizing group
_{-C (R ') = CH 2} ( wherein, R' is. Represents a hydrogen or an alkyl group having 1 to 5 carbon atoms), and acrylate groups, methacrylate groups. The method of polymerizing these groups is not particularly limited, but photopolymerization or thermal polymerization with a radical initiator is exemplified, and photopolymerization is preferable from the viewpoint of ease of operation and efficiency of fixing orientation. Known photopolymerization initiators can be used.

When a mesogenic group is added to the polysiloxane chain, it has the same structure as the mesogenic group of the side chain of the repeating unit (I) or (II), and the alkyleneoxy group serving as a spacer is not terminated. Ω- with a saturated double bond
It is obtained by reacting a reaction raw material having an alkenyloxy group with polysiloxane under a platinum catalyst. During the reaction, the bond ratio of the two kinds of mesogen groups can be controlled by the reaction raw material charging ratio corresponding to the non-polymerizable mesogen group and the polymerizable mesogen group. Similarly, in the case where the main chain is an acrylic ester type or an α-alkyl-acrylic ester type, when two kinds of monomers having corresponding mesogenic groups are copolymerized, the polymerization ratio is controlled by controlling the charging ratio of the monomers. The ratio of mesogenic groups to non-polymerizable mesogenic groups can be controlled. The side chain type polymer liquid crystal material thus obtained is preferably one having a cholesteric phase.

As the cholesteric liquid crystal material, a material in which a side chain type polymer liquid crystal material is mixed with another polymer liquid crystal, a liquid crystal oligomer or a low molecular weight compound to adjust the pitch may be used. In this case, in the production of the cholesteric liquid crystal layer, in order to polymerize the side chain type polymer liquid crystal material after alignment,
Compatibility after polymerization is important. Therefore, the low molecular weight compound used preferably has a polymerizable group.

As the other polymer liquid crystals, liquid crystal oligomers and polymerizable low molecular weight compounds added to the side chain type polymer liquid crystal material, those exhibiting a liquid crystal phase are preferable in order to uniformly mix, and particularly nematic. Those exhibiting a phase or a cholesteric phase are preferable.

The addition amount of the low molecular weight compound mixed with the side chain type polymer liquid crystal material is 0 to 50 wt% of the side chain type polymer liquid crystal material.
Is preferable, and more preferably 0 to 40 wt%. Furthermore, if the addition amount of the low molecular weight compound exceeds 50%, the film formability and the stability of orientation may be impaired.

[0045]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The phase transition temperature of the liquid crystal oligomer was determined by texture observation with a differential scanning calorimeter (DSC) and a polarizing microscope.

Example 1 A polyvinyl alcohol alignment film was formed on a washed glass substrate by a spin coating method and heat-treated at 100 ° C. for 1 hour. Then, the alignment film was rubbed using a rubbing machine. In the same manner as the method described in JP-B-63-41400, vinyl monomers (1) and (2) shown below are reacted with pentamethylcyclopentasiloxane at a mixing ratio such that the reactants show selective reflection at 280 nm. A cyclic pentasiloxane liquid crystal oligomer (a) was obtained.

[0047]

[Chemical 9]

[Chemical 10] The glass transition temperature of the liquid crystal oligomer was 14 ° C., the transition temperature to the isotropic phase was 114 ° C., and a cholesteric phase was exhibited at 14 ° C. to 114 ° C.

Similarly, dihydrocholesteryl of the formula (1)
Incorporation of mesogenic group as cholesteryl group instead of group
The ratio so that the selective reflection of the reaction product is 680 nm.
Liquid crystal is reacted in the same manner as liquid crystal oligomer (a) except
An oligomer (b) is obtained. Obtained liquid crystal oligomer
66/34 (weight) of (a) and liquid crystal oligomer (b)
Ratio) and dissolve in toluene to 40 wt%
It Furthermore, as a photopolymerization initiator, the trade name Irgacure
-907 (manufactured by Ciba Geigy) for liquid crystal oligomers
To 2.0 wt%. The resulting solution
Spin glass on a glass substrate with a polyvinyl alcohol alignment film
After heating and heating at 80 ° C for 5 minutes, use a high pressure mercury lamp.
And the integrated light intensity is 0.2 J / cm ²UV rays to
Irradiate. Film of the obtained liquid crystal oligomer polymer film
The thickness shows selective reflection at 550 nm. Liquid crystal oligomer
74/26 (weight) of (a) and liquid crystal oligomer (b)
(Ratio) and the film was formed under the same conditions as above.
Then, a film having a selective reflection wavelength of 450 nm is obtained. Furthermore
, A liquid crystal oligomer (b) is used alone to form a film,
A film having a selective reflection wavelength of 680 nm is obtained.

A laminated layer of these three layers of cholesteric liquid crystal film is used as a circularly polarizing plate and laminated with a quarter wavelength plate having a retardation of 140 nm, and the light guide plate of the backlight and the light diffusion are arranged in the arrangement shown in FIG. It was installed between the boards. When the light transmittance was measured when a polarizing film (trade name Sumikaran SK-1842AP, manufactured by Sumitomo Chemical Co., Ltd.) was laminated on the upper part of the light diffusion plate, the light transmittance was higher than that in the case without the cholesteric liquid crystal phase. Increase. Further, when a circularly polarizing plate produced by laminating these three layers of cholesteric liquid crystal film and a quarter-wave plate having a retardation of 140 nm were laminated and attached to a word processor, it was compared with a place without a cholesteric liquid crystal layer. Thus, the surface brightness is improved.

Next, a liquid crystal display device using the backlight device of the present invention will be described. An example of the liquid crystal display device is shown in FIGS. In the figure, reference numeral 9 is the backlight device of the present invention, 10 and 11 are polarizing plates, and 12 is a liquid crystal cell. In FIGS. 6 and 7, a retardation film or the like may be disposed between the polarizing plate and the liquid crystal cell in order to further improve the optical characteristics of the liquid crystal display device. Further, in the arrangement shown in FIG. 6, it is essential that the arrangement is such that the angle between the vibration plane of the linearly polarized light emitted from the backlight device and the transmission axis of the polarizing plate 10 is substantially zero.

[0051]

In the backlight device for a liquid crystal display of the present invention, a circularly polarizing plate made of a cholesteric liquid crystal layer is incorporated into the backlight device so that a part of the light from the light source is directly transmitted as circularly polarized light and the reverse direction is applied. The circularly polarized light of is converted into circularly polarized light that can be transmitted by reflecting it with a reflection sheet or a reflective cover, and since it is added to the circularly polarized light that directly transmits from the light source, this can be converted into linearly polarized light, and the amount of light emitted from the light source is used. The efficiency can be improved, and the liquid crystal display device using the liquid crystal display device has high brightness and is of great industrial value.

[Brief description of drawings]

FIG. 1 is a diagram showing a laminated state of a backlight device for a liquid crystal display of the present invention.

FIG. 2 is a diagram showing a stacked state of the backlight device for a liquid crystal display of the present invention.

FIG. 3 is a diagram showing a laminated state of the backlight device for a liquid crystal display of the present invention.

FIG. 4 is a diagram showing a stacked state of the backlight device for a liquid crystal display of the present invention.

FIG. 5 is a diagram showing a laminated state of the backlight device for a liquid crystal display of the present invention.

FIG. 6 is a diagram showing a stacked state of the liquid crystal display device of the present invention.

FIG. 7 is a diagram showing a stacked state of the liquid crystal display device of the present invention.

[Explanation of symbols]

1: Light source. 2: Reflective cover. 3: Light guide plate. 4: Reflector. 5: Diffuser or light collector. 6: Reflective cover. 7: circularly polarizing plate. 8: 1/4 wave plate. 9: Backlight device of the present invention. 10, 11: Polarizing plates. 12: Liquid crystal cell.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-6-250169 (JP, A) JP-A-6-230223 (JP, A) JP-A-6-160840 (JP, A) JP-A-5- 100114 (JP, A) JP-A-1-133003 (JP, A) JP-A-6-281814 (JP, A) JP-A-6-324333 (JP, A) JP-B-49-44666 (JP, B1) European Patent Application Publication 606939 (EP, A 1) (58) Fields searched (Int.Cl. ⁷ , DB name) G02F 1/13357 G02F 1/13363 G02F 1/1335 G02F 1/1333 F21V 8/00

Claims (12)

(57) [Claims] 1. A light guide plate having a reflector and a light source on its side surface, 4.
A backlight device for a liquid crystal display, characterized in that a circularly polarizing plate made of a cholesteric liquid crystal layer exhibiting selective reflection in a range of 00 to 700 nm, a quarter wave plate, and a diffusing plate or a light collecting plate are arranged in this order. . 2. A light guide plate having a reflector and a light source on its side surface, 4
A backlight device for a liquid crystal display, characterized in that a circularly polarizing plate made of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 00 to 700 nm, a diffusing plate or a light collecting plate, and a quarter wave plate are arranged in this order. . 3. A reflective plate, a circularly polarizing plate composed of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm, a light source and a reflective cover arranged at the rear of the light source, and the circularly polarizing plate is provided. A backlight device for a liquid crystal display, characterized in that a light guide plate arranged between a light source and a light guide plate, a quarter-wave plate, and a diffusion plate or a light collection plate are arranged in this order. 4. A reflecting plate, a light source, a circularly polarizing plate made of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm, a quarter wavelength plate, and a diffusing plate or a light collecting plate,
A backlight device for a liquid crystal display, which is arranged in this order. 5. A reflecting plate, a light source, a circularly polarizing plate composed of a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm, a diffusing plate or a light collecting plate, and a quarter-wave plate,
A backlight device for a liquid crystal display, which is arranged in this order. 6. The quarter-wave plate is formed by laminating two or more optically anisotropic bodies having different wavelength dispersions with their optical axes displaced from each other. Backlight device for LCD. 7. A circularly polarizing plate comprising a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm is 400
7. At least three cholesteric liquid crystal layers exhibiting selective reflection in respective ranges of not less than 500 nm and less than 500 nm, not less than 500 nm and less than 600 nm, and not less than 600 nm and less than 700 nm are laminated. Backlight device for LCD. 8. A circularly polarizing plate comprising a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm is 400
a layer in which at least one cholesteric liquid crystal material exhibiting selective reflection in the range of 500 nm to less than 500 nm is dispersed in a polymer, and at least one cholesteric liquid crystal material exhibiting selective reflection in the range of 500 nm to less than 600 nm is dispersed in a polymer 7. A liquid crystal according to claim 1, wherein a layer and a layer in which at least one kind of cholesteric liquid crystal material exhibiting selective reflection in a range of 600 nm or more and less than 700 nm is dispersed in a polymer are laminated. Backlight device for display. 9. A circularly polarizing plate comprising a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm is 400
nm or more and less than 500 nm, 500 nm or more and less than 600 nm, and at least three types of cholesteric liquid crystal materials exhibiting selective reflection in the ranges of 600 nm or more and less than 700 nm, respectively. A backlight device for a liquid crystal display according to any one of claims. 10. A circularly polarizing plate comprising a cholesteric liquid crystal layer exhibiting selective reflection in the range of 400 to 700 nm is 40
The backlight device for liquid crystal display according to claim 1, comprising a layer in which at least one kind of cholesteric liquid crystal material exhibiting selective reflection in a range of 0 to 500 nm is dispersed in a polymer. 11. A liquid crystal cell in which an oriented liquid crystal layer is sandwiched between substrates having electrodes, and further sandwiched between two outer polarizing plates, and a backlight for a liquid crystal display according to claim 1. A liquid crystal display device, characterized in that an angle formed between a vibrating surface of linearly polarized light emitted from the backlight device and a transmission axis of a polarizing plate in contact with the backlight device is about 0. 12. A liquid crystal cell in which an oriented liquid crystal layer is sandwiched between substrates having electrodes, and a polarizing plate is disposed outside one of the substrates sandwiching a liquid crystal phase, and the other outside of the substrates sandwiching the liquid crystal layer. A liquid crystal display device using the backlight device for a liquid crystal display according to any one of claims 1 to 10, which is disposed in the liquid crystal display device.