JPH09304613A - Color filter, its production and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color filter capable of industrially manufacturing with ease, a manufacturing method thereof, and a projection type liquid crystal display device using the colot filter. SOLUTION: The color filter is a film formed by blending a polymer with cholesteric liquid crystal, the cholesteric liquid crystal and the polymer have separated phases, average grain size of a domain of the cholesteric liquid crystal is within a range of 20 to 600nm and wavelength of selective reflection light of the cholesteric liquid crystal observed from a normal direction of the film is between 400 and 800nm. Further, in this method, a mixture of the polymer and the cholesteric liquid crystal is shaped into a film and then the film is stretched to produce the color filter. Otherwise, a mixture of the polymer and the cholesteric liquid crystal having polymerizable functional groups is shaped to a film, the film is stretched and then the polymerizable functional groups are polymerized to produce the color filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color filter used for a liquid crystal display device (hereinafter sometimes referred to as LCD), a non-linear optical element, etc., a method for manufacturing the same, and a projection type liquid crystal display using the color filter. The present invention relates to a device or a polarizing film and a liquid crystal display device using the polarizing film.

[0002]

2. Description of the Related Art Liquid crystal displays have excellent characteristics such as low voltage driving and light weight, and are widely used as display terminals for personal computers, word processors and the like. Currently, mainstream color liquid crystal displays use three color R, G, B micro color filters in order to obtain a color display. The color filter is
It is composed of pigments and other pigments, and the light absorption by the pigments is used to perform spectroscopy. For this reason, there has been a problem that the light utilization efficiency is poor and the screen brightness becomes dark. It is known that twist-aligned cholesteric liquid crystal reflects light having a wavelength equal to the helical pitch, and it has been proposed to use the cholesteric liquid crystal layer as a color filter. When the cholesteric liquid crystal is directly coated on the substrate, high film thickness accuracy is required to obtain a color filter having a large area and uniform optical characteristics, which limits the industrial production.

[0003]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a color filter which can be easily manufactured industrially, a method for manufacturing the same, a projection type liquid crystal display device using the color filter,
It is intended to provide a polarizing film using the color filter and a liquid crystal display device using the polarizing film.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventor has found that the polymers (hereinafter, these polymers are sometimes referred to as matrix polymers or simply matrices). The present invention has been completed by finding that a color filter is easily obtained by orienting the cholesteric liquid crystal by mixing the cholesteric liquid crystal into a film, phase-separating the cholesteric liquid crystal from the matrix, and stretching the film. Came to.

That is, the present invention is [1] a film obtained by mixing a polymer and a cholesteric liquid crystal, wherein the cholesteric liquid crystal is phase-separated from the polymer, and the average particle size of domains of the cholesteric liquid crystal is 20 to The present invention relates to a color filter having a selective reflection wavelength of 400 to 800 nm in the cholesteric liquid crystal observed in the film normal direction in the range of 600 nm. Also, the present invention
[2] The method for producing a color filter according to [1], which comprises forming a mixture of a polymer and a cholesteric liquid crystal into a film and then stretching the film. The present invention further provides [3] the color according to [1], wherein a mixture of a polymer and a cholesteric liquid crystal having a polymerizable compound group is formed into a film, the film is stretched, and then the polymerizable compound group is polymerized. The present invention relates to a method for manufacturing a filter. The present invention also relates to [4] a projection type liquid crystal display device using the color filter described in [1] above. The present invention also relates to a polarizing film comprising [5] the color filter described in [1] above and a retardation film having a retardation corresponding to ¼ of the selective reflection wavelength of the color filter. is there. Furthermore, the present invention relates to [6] a liquid crystal display device using the polarizing film described in [5] above.

[0006]

Next, the present invention will be described in detail.
In the color filter of the present invention, the cholesteric liquid crystal is phase-separated from the polymer matrix, and the portion of the cholesteric liquid crystal (hereinafter sometimes simply referred to as liquid crystal) forms a domain. The average particle size of the domains of the cholesteric liquid crystal is 20 to 600 nm,
~ 400 nm is preferred. The average particle size of the domains of the cholesteric liquid crystal is measured by observing a color filter with a transmission electron microscope (hereinafter, also referred to as TEM), and individual particle sizes are directly measured to obtain the number average of the obtained particle sizes. It is determined by finding the value.

Visible light may be scattered at the interface of the domain. In the color filter of the present invention, it is preferable that internal scattering due to scattering at these interfaces is small. This is because the scattered light generally changes its polarization state, and thus the optical characteristics may deteriorate in the case of a color filter having a large internal scattering.

In the color filter of the present invention, the domain of the cholesteric liquid crystal has a spheroidal shape or 3
The orientation of the cholesteric liquid crystal can be controlled by using ellipsoids having different axes. The shapes of these domains can be controlled by the stretching operation described below.

Next, the matrix polymer will be described. In the present invention, a matrix having a small polymer retardation is preferably used as the color filter matrix. The retardation by the polymer is measured by using the Senarmont method on a polymer film produced under the same conditions as the color filter except that the liquid crystal is not contained (5
(Measured with light having a wavelength of 46 nm). The retardation of the polymer is preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 30 nm or less.

The retardation of the matrix is represented by the product Δnd of the birefringence Δn of the matrix polymer and the thickness d of the film. If the film is made thin to reduce the retardation, it becomes difficult to handle the film, which is not preferable, and the film thickness has a preferable lower limit. It is preferable to reduce the birefringence of the matrix in order to reduce the retardation.
Generally, the birefringence Δn due to the orientation of the polymer is calculated by using the intrinsic birefringence Δn ₀ of the polymer and the orientation function f,
It is represented as

## EQU1 ## Δn = Δn ₀ × f As a method of reducing the birefringence of a polymer, a polymer having a small intrinsic birefringence is used, or a polymer having a positive intrinsic birefringence is mixed with a polymer having a negative A method of reducing the apparent intrinsic birefringence and a method of reducing the orientation function are exemplified.

As the polymer having a small intrinsic birefringence, polymethacrylic acid derivatives such as polymethylmethacrylate, poly-n-butylmethacrylate, poly-t-butylmethacrylate, polyglycolmethacrylate, polyacrylic acid, polymethylacrylate, polyethyl, etc. Polyacrylic acid derivatives such as acrylate, polyvinyl acetate, polyvinyl butyrate, polyoxymethylphenylsilylene, etc., norbornene-ethylene copolymer (Mitsui Petrochemical Co., Ltd .: trade name APEL, etc.), norbornene-containing resin (Nippon Synthetic) Rubber Co., Ltd .: Product name ART
ON, etc.), amorphous polyolefin (manufactured by Nippon Zeon Co., Ltd .: trade name ZEONEX, etc.), polyester resin for optical use (manufactured by Kanebo Co., Ltd.), acryl-butadiene-styrene copolymer (manufactured by Toray Industries, Ltd .: trade name Toyolac) Transparent grade). Among them, polymethyl methacrylate, poly-n-butyl methacrylate, poly-t-butyl methacrylate, norbornene-ethylene copolymer, polyester resin for optical use, amorphous polyolefin, and acryl-butadiene-styrene copolymer are preferable.

Next, when a polymer having a positive intrinsic birefringence and a polymer having a negative intrinsic birefringence are mixed and used as a matrix of a color filter, a polymer having a positive intrinsic birefringence is obtained. Examples include polyvinyl chloride, polyvinylidene fluoride, vinylidene fluoride / trifluoroethylene copolymer, polyethylene oxide, polyphenylene oxide, polycarbonate, and the like, and as a polymer having negative intrinsic birefringence, polymethylmethacrylate, Examples include polystyrene.

A polymer having positive or negative intrinsic birefringence, and a mixing ratio (weight ratio) of a combination of compatible polymers and a reduction in apparent intrinsic birefringence is 20: polyphenylene oxide and polystyrene. 80-3
0:70, 30:70 to 40:60 for polyethylene oxide and polymethyl methacrylate, 5:95 to 15:85 for vinylidene fluoride / ethylene trifluoride copolymer and polymethyl methacrylate, polyvinylidene fluoride and polymethyl methacrylate Then 15:85 to 25: 7
5. 1 for polyvinyl chloride and polymethyl methacrylate
5:85 to 25:75. Among these, a combination of polyphenylene oxide and polystyrene, which are easily soluble in a solvent, and a combination of polyethylene oxide and polymethyl methacrylate are preferable.

As a method of reducing the orientation function, there is a method of stretching while heating the mixed film above the glass transition temperature and below the melting temperature. Suitable polymers for the method include polycarbonate, polysulfone, polyarylate, polyether sulfone, and 2.
Cellulose acetate, cellulose triacetate, polystyrene, ethylene vinyl alcohol copolymer, polyethylene terephthalate, polyethylene naphthalate, etc. are exemplified,
Preferred examples include polycarbonate, polysulfone, cellulose acetate, polyethylene terephthalate, and polystyrene.

When the color filter or polarizing plate of the present invention is used in a projection type liquid crystal display device, there is a risk that the color filter may be deformed by heat from a light source for projection. In order to avoid deformation, a polymer having a high glass transition temperature or heat deformation temperature is preferably used as the matrix polymer. Among the above-mentioned polymers, examples of polymers having a high glass transition temperature or heat distortion temperature include polycarbonate, polysulfone, polyarylate, optical polyester, amorphous polyolefin, norbornene-containing resin, and the like.

Additives may be added to these matrix polymers for the purpose of imparting mechanical strength or improving the adhesiveness when they are laminated to an LCD panel. The kind and amount of the additive are not particularly limited as long as they do not impair the object of the present invention.

The structure and molecular weight of the cholesteric liquid crystal used in the present invention are not particularly limited, and the polymer matrix used in combination is phase-separated, and the domain size of the cholesteric liquid crystal when phase-separated satisfies the above conditions. Those satisfying the above conditions can be preferably used. As the cholesteric liquid crystal in the present invention, those having a polymerizable compound group are also suitably used. The polymerizable compound group is not particularly limited, but a photopolymerizable compound group is preferable because photopolymerization is preferably used rather than thermal polymerization as described later. As the cholesteric liquid crystal in the present invention, a liquid crystal exhibiting a cholesteric phase alone may be used, or a nematic liquid crystal mixed with a chiral dopant to express a cholesteric phase may be used. The type of chiral dopant and the mixing ratio with the nematic liquid crystal are not particularly limited. As the phase sequence of the cholesteric liquid crystal, those exhibiting a cholesteric liquid crystal phase at room temperature or higher and exhibiting a cholesteric phase or a glass phase at around room temperature are preferably used.

In the present invention, since the selective reflection of light vertically incident on the color filter is in the wavelength range of 400 to 800 nm, the spiral pitch of the cholesteric liquid crystal is 250.
It is preferably in the range of ˜500 nm. The method for adjusting the spiral pitch of the liquid crystal is not particularly limited, and a known method can be used. For example, a method of adjusting the amount of the chiral dopant and a method of adjusting the temperature of the liquid crystal having a polymerizable compound group depending on the temperature during the polymerization are exemplified. When a liquid crystal having a photopolymerizable compound group is used as the polymerizable compound group, it is possible to pattern the color filter by utilizing the fact that the helical pitch changes by changing the temperature during photocrosslinking. Therefore, it is possible to create a micro color filter.

Regarding the mixing ratio of the cholesteric liquid crystal and the matrix polymer, if the mixing ratio of the liquid crystal is too large, the mechanical strength of the color filter decreases and it becomes difficult to handle, and if the ratio of the liquid crystal is too small, the liquid crystal hardly separates from the matrix. Is not preferable. Concentration of cholesteric liquid crystal [weight of cholesteric liquid crystal / (weight sum of cholesteric liquid crystal and matrix polymer)]
Is preferably 0.1 to 20% by weight, more preferably 1
１５15% by weight.

Next, a method for manufacturing the color filter of the present invention will be described. As a method for mixing the cholesteric liquid crystal and the matrix polymer, it is preferable to mix them in a solution state in order to uniformly mix them. Specifically, a method may be mentioned in which a polymer is suspended or dissolved in a solvent, and a cholesteric liquid crystal is suspended or dissolved therein and mixed.
The polymer used in the present invention preferably has a high solubility in a solvent.

The film formation method comprising a cholesteric liquid crystal and a matrix includes a solvent casting method of dissolving a cholesteric liquid crystal or matrix polymer in a solvent and casting, an extrusion molding method of kneading in a solid state into an extruded film from a die, a solid state. Examples of the method include a calendering method in which the film is kneaded in a state and then formed into a film with a calendar roll, a press molding method in which a film is formed using a press or the like. The thickness of the film after film formation is not particularly limited, but if it is too thin, it will adversely affect the mechanical strength and the degree of polarization. Since the evaporation rate of the solvent becomes slow and the productivity deteriorates, it is necessary to make it thin to some extent. The thickness of the film after film formation is preferably 20 to 500 μm, more preferably 70 to 300 μm.

As described above, in the color filter of the present invention, by stretching the film, the shape of the domain is changed and the alignment of the liquid crystal can be controlled. Examples of the film stretching method include a tenter stretching method, a roll-to-roll stretching method, and a roll-to-roll compression stretching method. Among these, the tenter stretching method and the inter-roll stretching method are preferable from the viewpoint of uniformity of the film surface. The heating method of the film during stretching is not particularly limited, and the heating temperature is appropriately selected depending on the softening temperature of the matrix polymer used, the transition temperature of the liquid crystal, the mixing ratio of the liquid crystal, and the like.

In the color filter of the present invention, when the cholesteric liquid crystal having a polymerizable compound group is used, the film forming and stretching methods are the same as those described above. Examples of the method for fixing the orientation of the cholesteric liquid crystal include photopolymerization, electron beam polymerization and thermal polymerization, and photopolymerization is preferable from the viewpoint of orientation stability. There is no particular limitation on the polymerization initiator used for the polymerization, and a known polymerization initiator having good compatibility with the liquid crystal and the polymer can be used. The mixing ratio of the polymerization initiator to the cholesteric liquid crystal or the matrix is not particularly limited as long as it does not impair the characteristics of the color filter of the present invention.

The projection type liquid crystal display device of the present invention is characterized by using the color filter of the present invention. Further, the polarizing film of the present invention is characterized by using the color filter of the present invention and a retardation film having a phase difference corresponding to ¼ of the selective reflection wavelength of the color filter. In the polarizing film of the present invention, as the λ / 4 wavelength retardation film used, a known retardation film can be used as long as the retardation is close to ¼ of the selected wavelength of the color filter used in combination. Furthermore, the liquid crystal display device of the present invention is characterized by using the above-mentioned polarizing film.

[0025]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The structure of the liquid crystal compound was confirmed by elemental analysis, infrared absorption spectrum and H-NMR spectrum, and the molecular weight was confirmed by gel permeation chromatography (GPC). The retardation of the color filter and matrix alone is based on a polarizing microscope (manufactured by Nikon Corporation, OPTIPHOTO2-P
OL] and using the Senarmont method. The wavelength of the measurement light is 546 nm. The retardation when the film was tilted was measured by mounting a tilting jig on the microscope. The liquid crystal display device of the present invention was evaluated by using the color filter of the present invention as a TFT-T.
It was mounted on an N-type liquid crystal display device and visually evaluated.

Example 1 A cholesteric liquid crystal (a liquid crystal oligomer having a cholesteric phase temperature range of 14 to 114 ° C.), a polymerization initiator and polymethylmethacrylate are mixed to prepare a methylene chloride solution. A film is obtained by casting this solution on a glass substrate surface-treated with a silane coupling agent. The obtained film is stretched while being heated using a tensile tester having a heating layer, and a color filter is obtained by irradiating ultraviolet rays immediately after stretching. The color filter obtained shows good selective reflection.

[0027]

According to the present invention, a color filter can be easily mass-produced, the obtained color filter can be suitably used for a projection type liquid crystal display device, and a color difference between the color filter and the color filter can be obtained. A polarizing film can be suitably obtained by using a retardation film corresponding to 1/4 of the selective reflection wavelength of the filter, and a liquid crystal display device can be suitably obtained by using the polarizing film, so that it has industrial value. large.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G09F 9/00 331 G09F 9/00 331A

Claims (7)

[Claims] 1. A film obtained by mixing a polymer and a cholesteric liquid crystal, wherein the cholesteric liquid crystal is phase-separated from the polymer, and the domain average diameter of the cholesteric liquid crystal is in the range of 20 to 600 nm. The wavelength of selective reflection of cholesteric liquid crystal observed from the normal direction is 4
A color filter characterized by being in the range of 00 to 800 nm. 2. A polymer having a retardation of 100.
The color filter according to claim 1, which has a thickness of not more than nm. 3. The method for producing a color filter according to claim 1, wherein a mixture of a polymer and a cholesteric liquid crystal is formed into a film and then the film is stretched. 4. The method according to claim 1, wherein a mixture of a polymer and a cholesteric liquid crystal having a polymerizable compound group is formed into a film, the film is stretched, and then the polymerizable compound group is polymerized. A method for producing the described color filter. 5. A projection type liquid crystal display device using the color filter according to claim 1. 6. The color filter according to claim 1 or 2 having a phase difference of 1 / the selective reflection wavelength of the color filter.
And a retardation film corresponding to No. 4, which is a polarizing film. 7. A liquid crystal display device using the polarizing film according to claim 6.