JPH11202321A - Sheet-like polarizing element and liquid crystal display element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sheet-like polarizing element which converts natural light to linearly polarized light with high efficiency and has excellent workability and to provide a liquid crystal display device which has high luminance or saves electric power consumption. SOLUTION: The sheet-like polarizing element arrayed with triangular prisms of a right-angled triangular shape in an array form comprises polarized light sepn. films 2 which consist of thin films of low and high refractive indices on the slopes of the triangular prisms, polarized light modulation parts 4 which are formed on the perpendicular faces of the prisms and consist of the thins films of liquid crystals in a molecule aligned state having a 1/4 spiral structure and alignment layers which align and fix the liquid crystal molecules in the molecule aligned state having the 1/4 spiral structure. The alignment layers 3 are deposited by diagonal vapor deposition of inorg. dielectric at a vapor deposition angle of 45 to 80 deg. with the normal of the vapor deposition surfaces, by which the sheet-like polarizing element having the excellent micromachinability of the polarized light modulation parts 4 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-shaped polarizing element having a function of generating only a polarized light component in one direction from non-polarized light and having excellent fine workability. The sheet-like polarizing element of the present invention can be used for any application requiring a polarized light beam, and is particularly advantageous for use in a polarizing plate arranged on the backlight side of a liquid crystal display element.

[0002]

2. Description of the Related Art Hitherto, a polarizing plate used for a liquid crystal panel display has an iodine association or a dichroic dye adsorbed in a polymer film as a base material and is stretched in a uniaxial direction. Of the light incident on the polarizing plate, light having a polarization component in the absorption axis direction is absorbed and blocked, and a polarization component orthogonal to the light is transmitted. Therefore, in principle, the transmittance of incident light is
50%. Actually, the transmittance of a commercially available polarizing plate is 40 to 45%. That is, at present, about half of the light amount of the backlight is lost by the polarizing plate. Therefore, in order to increase the brightness of the display screen, it is necessary to increase the output of the backlight light source, which goes against power saving.

One technique for promoting light use efficiency is disclosed in Japanese Patent Application Laid-Open No. Hei 8-248224, in which light having two polarization components is separated from transmitted light by a material boundary having a different refractive index. By turning the plane of polarization with a phase shifter or Faraday element that changes the phase of one polarization component into reflected light, and then changing the direction so that the two polarization components travel in the same direction, the light of the light source Improves usage efficiency.

However, in this technique, the rotation of the polarization plane is dispersed depending on the wavelength of the light source due to the wavelength dependence of the phase shifter or the Faraday element that converts the polarization plane, and it is not expected to improve the light use efficiency with respect to a wide band wavelength.

Further, in order to utilize the optical characteristics of the liquid crystal, it is necessary to control the liquid crystal arrangement. As a liquid crystal alignment method, there is a rubbing method (for example, see the leading edge of liquid crystal displays, Sigma Publishing, pages 83 to 84), but the alignment function is mechanically rubbed with a cloth or the like to form an alignment film. Therefore, application to a micromachined surface was impossible.

[0006]

In the present invention, the transmittance of this type of polarizing plate is low, and it is necessary to increase the power of the backlight in order to improve the brightness of a liquid crystal display device using the polarizing plate.
The purpose of the liquid crystal is to improve the brightness or reduce the power of the backlight by greatly increasing the transparency of the polarizing plate over a wide band. It is to provide a display element.

[0007]

According to the present invention, there is provided a sheet-like polarizing element in which triangular prisms having a right-angled triangular shape are arranged in an array, and a low-refractive-index and high-refractive-index material is laminated on the slope of the triangular prism. A sheet which is a prism array sheet on which a separation film is formed and further a polarization modulation section formed of a thin film in which liquid crystal molecules in a molecular alignment state having a ４ helical structure are fixed on one surface sandwiching a right angle. The polarizer has an alignment film formed by obliquely depositing an inorganic dielectric as an alignment film for fixing liquid crystal molecules in a molecular alignment state having a ら helical structure. .

Further, in the alignment film formed by obliquely vapor-depositing the inorganic dielectric constituting the sheet-like polarizing element, the oblique vaporization angle is 45 to 80 ° with respect to the normal to the surface on which the vapor-deposit is adhered.
It is characterized by being obliquely deposited at an inclined angle.

Further, it is preferable that one apex angle of the right triangle of the sheet-shaped polarizing element is 40 to 50 °.

In addition, the inorganic dielectric constituting the alignment film for fixing the liquid crystal molecules in a molecular alignment state having a ら helical structure of the sheet-like polarizing element is made of an inorganic oxide, an inorganic fluoride, or an inorganic oxide. And at least one of a compound of a compound and an inorganic fluoride.

Further, it is preferable that a polarizing plate is provided on the surface of the sheet-like polarizing element from which the transmitted light and the reflected light whose polarization planes coincide are emitted, so that the polarization plane of the emitted light coincides with the polarization axis of the polarizing plate.

In the liquid crystal display device, a sheet-like polarizing element is preferably used as a polarizing element on a light source side in a polarizing plate sandwiching a liquid crystal cell.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural view of a sheet-like polarizing element according to the present invention, and 1 is a prism sheet in which triangular prisms having a right angle of 40 to 50 ° are arranged in an array. This prism sheet can be manufactured by plastic molding technology. Alternatively, it can be easily manufactured by arranging long prisms made of glass in an array. The sheet-shaped prism array 1 includes a polarization separation film 2 formed of a thin film having a low refractive index and a high refractive index on a slope of a triangular prism, and a molecule having a ４ spiral structure formed on a plane parallel to incident light of a right-angle prism. Polarization modulator 4 composed of a thin film in which liquid crystal molecules in an aligned state are fixed.
In addition, the alignment film 3 is formed by forming an inorganic dielectric for fixing the alignment of the liquid crystal molecules by oblique deposition.

The polarizing beam splitting film 2 composed of a thin film having a low refractive index and a high refractive index includes a material having a low refractive index such as zinc sulfide, cerium oxide and titanium oxide, and a material having a low refractive index such as magnesium fluoride. , Neodymium fluoride and the like are used. Vacuum evaporation or sputtering is used as a film formation method. The thickness and the number of layers of the high and low refractive index thin films alternately laminated are important in designing the performance of the polarization splitting film.

A polarization modulator 4 comprising a thin film in which liquid crystal molecules in a molecular alignment state having a １ ／ helical structure are fixed in alignment.
Is an optical modulator having a function of rotating the incident polarization plane by 90 degrees, and desirably has a polymerizable functional group in order to fix the molecular alignment state of the liquid crystal phase of the constituting liquid crystal molecules,
Acrylate group, methacrylate group,
It preferably has at least one of a vinyl ether group and an epoxy group. The liquid crystal molecules are 1
Cholesteric liquid crystals are preferred for expressing a / 4 helical structure, and chiral nematic liquid crystals, chiral smectic liquid crystals, mixtures of nematic liquid crystals and chiral agents,
Mixtures of smectic liquid crystals and chiral agents are more preferred.

The oblique vapor deposition method is preferred as a method for forming the alignment film 3 for obtaining the modulation section 4 composed of a thin film in which liquid crystal molecules in a molecular alignment state having a 1/4 helical structure are fixed in alignment.
As the vapor deposition method, a film formation method having directivity in the direction of attachment and growth of the vapor deposition particles to the substrate is preferable, and a resistance heating vapor deposition method or an electron beam vapor deposition method is particularly preferable.

The obliquely deposited film made of an inorganic dielectric used as the alignment film 3 for controlling the molecular alignment state of the liquid crystal molecules preferably has a function of expressing uniaxial alignment of the liquid crystal molecules near the alignment layer. Particularly preferred are those obtained by obliquely depositing an inorganic oxide such as tantalum oxide, tungsten oxide, silicon oxide, and titanium oxide, and those obtained by obliquely depositing an inorganic fluoride such as magnesium fluoride and neodymium fluoride.

The angle of deposition of the obliquely deposited film made of an inorganic dielectric used as the alignment film 3 for controlling the molecular alignment state of the liquid crystal molecules is 45 to 80 ° with respect to the normal to the surface on which the deposited material is adhered.
It is preferable that the film is obliquely vapor-deposited at an inclined angle, and it is more preferably 55 to 70 ° depending on the inorganic dielectric used. When the oblique deposition angle is 45 ° or less, poor alignment of liquid crystal molecules occurs and the function as an alignment film is not exhibited.
On the other hand, when the oblique deposition angle is less than 80 °, the tilt angle of the liquid crystal with respect to the substrate becomes large and uniform alignment is obtained, but the function as a polarization modulation unit is deteriorated, which is not preferable.

FIG. 2 is a structural sectional view of the polarizing element of the present invention.
The function of the present invention will be described below.

When unpolarized light (natural light) 6 enters the inclined surface of the first prism 11, it is reflected and refracted by the prism inclined surface on which the polarization separation film 2 is formed, and is separated into reflected light 7 and refracted light 8. You. The polarization state and light intensity of the reflected light 7 and the refracted light 8 are determined by the configuration of the polarization separation film 2, that is, the values of the high and low refractive indexes, the film thickness, and the number of layers.
Here, the polarization separation film 2 is designed so that the s-polarized light component of the reflected light 7 increases and the p-polarized light component of the refracted light 8 increases. In the reflected light 7, the s and p polarization components are reversed by the action of the polarization modulator 4 composed of a thin film in which liquid crystal molecules in a molecular alignment state having a ら helical structure are aligned and fixed. As a result, the p polarization component increases. , As transmitted light 9, is incident on the adjacent second prism 12, and is totally reflected by the inclined surface to become polarized light 9 ′. At this time, the polarization state does not change.

Further, the light passes through the polarizing plate 5 arranged so that the p-polarized light passes therethrough, and becomes the emission light 10. This emitted light 1
0 is linearly polarized light having only p-polarized light as a polarization component. On the other hand, the refracted light 8 is elliptically polarized light composed of a p-polarized light component and an s-polarized light component, and the s-polarized light intensity is sufficiently lower than the s-polarized light intensity of the reflected light 7 due to the action of the polarization separation film 2. The refracted light 8 passes through the polarizing plate 5 as in the case of the reflected light, and is emitted as linearly polarized light 13 having only a p-polarized component. Reflected light 7
Can be used as a linearly polarized light source by combining the linearly polarized light 10 whose polarization has been converted and the linearly polarized light 13 due to the refracted light 8. That is, the incident natural light 5 is polarized and separated by the slope having the polarization splitting film 2 and further converted into linearly polarized light by polarization plane modulation of the reflected light. Its conversion efficiency is at least 50%, typically about 80%.

That is, by the sheet-like polarizing element of the present invention, non-polarized light is emitted as transmitted light having a large amount of p-polarized light components.
By converting reflected light having a large amount of polarized light into p-polarized light and then emitting the light, non-polarized light can be converted into unidirectional polarized light with high light utilization efficiency without loss of light energy. In addition, since the polarization modulator is composed of a thin film in which liquid crystal molecules in a 1/4 helical structure are aligned, the polarization plane conversion with a small dispersion of polarization plane rotation in a wide wavelength band becomes possible. Improvement of light use efficiency can be obtained in a wide band.

[0023]

Next, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples.

[Example 1] A long prism made of glass having a cross section of a right-angled isosceles triangle having two right-angled sides of 4 mm and having a length of 5 cm was prepared, and zinc sulfide (H 0.05 μm and magnesium fluoride (abbreviated as L) which is a low-refractive-index thin-film material.
Nine layers of 09 μm were laminated in the order of HLHLHLHLH. The film was formed by a vacuum evaporation method having two evaporation sources. Next, a tantalum pentoxide thin film was obliquely vapor-deposited on only one side of the right angle at an angle of 60 ° with respect to the normal line of the vapor-deposited surface to form an alignment film. The film was formed by electron beam evaporation. Next, the chiral agent (CNL611L: manufactured by Asahi Denka Co., Ltd.) and the monoacrylate liquid crystal (UCL-001: manufactured by Roddick) were adjusted to d / p = 1/4, and the photocuring initiator (IRG651: manufactured by Ciba Geigy) was added. 1/4 on the vertical plane of the prism array
Liquid crystal molecules in a molecular alignment state having a helical structure were prepared on an alignment thin film. Thereafter, the alignment state of the liquid crystal molecules was fixed by irradiation with UV light. The five long prisms thus prepared were arranged in an array on a glass plate.
A polarizing plate was attached to the lower surface of the glass plate so that the p-polarization plane emitted from the prism array coincided with the polarization axis, and a sheet-like polarizing element of the present invention was prepared and irradiated with natural light. The light power of linearly polarized light emitted from the sheet-shaped polarizing element of the present invention was 83% of the incident natural light.

Example 2 A sheet having a right-angled isosceles triangle having two right-angled sides of 2 mm and having prisms arranged in an area of 10 cm × 10 cm in an array was formed by a die molding method. Polymethyl methacrylate (PMMA) was used as the molding resin. Next, a mask is arranged, and a tantalum pentoxide film is deposited obliquely at an angle of 60 ° with respect to the normal to the prism array vertical surface so that an alignment film can be formed only on the vertical surface of the prism array. did. Next, a chiral agent (CNL611L: manufactured by Asahi Denka Co., Ltd.) and a monoacrylate liquid crystal (UCL-002: manufactured by Roddick) were d / p = 1.
/ 4, and liquid crystal molecules in a molecular alignment state having a 1/4 helix structure on the prism array vertical surface were prepared on the alignment thin film using a photocuring initiator (IRG651: manufactured by Ciba Geigy). Thereafter, the alignment state of the liquid crystal molecules was fixed by irradiation with UV light. A modulated portion was formed by removing the cured thin film of the liquid crystal molecules in a molecular alignment state having a ら helical structure only on the slope of the prism array by a resist method and a dry etching method. Furthermore, a multilayer film could be formed only on the slope by vapor deposition from the vertical direction on the prism sheet on which the modulation portion was manufactured. At this time, the thin film material and the film thickness were the same as in the first embodiment, and the layer configuration was seven layers of HLHLHLH. The prism array sheet completed by the above process was irradiated with natural light, and the efficiency of polarization separation / conversion was measured. As a result, the efficiency was 81%. Furthermore, the sheet-like polarizing element of the present invention was replaced with a polarizing plate on the backlight side of the liquid crystal panel, and the effects were compared. As a result, it was confirmed that the image brightness when the sheet-like polarizing element of the present invention was inserted was clearly high.

[0026]

According to the present invention, natural light can be converted into linearly polarized light with very high efficiency. By using the sheet-like polarizing element of the present invention, the brightness of the liquid crystal display screen was improved by about 30% as compared with the case where a conventional polarizing plate was used. That is, by using the sheet-shaped polarizing element of the present invention, power saving of a backlight for a liquid crystal display device and high luminance of a liquid crystal display screen can be obtained.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view of a sheet-like polarizing element of the present invention.

FIG. 2 is a structural sectional view of a sheet-shaped polarizing element of the present invention.

[Explanation of symbols]

 1: Prism sheet 2: Polarization separating film 3: Alignment film 4: Polarization modulator 5: Polarizer 6: Natural light 7: Reflected light 8: Refracted light 9: Transmitted light 9 ': Polarized light 10: Emitted light 11: First Prism 12: second prism 13: outgoing light

Claims (6)

[Claims] 1. A right-angled triangular triangular prism is arranged in an array, a polarization separating film in which a low-refractive-index and a high-refractive-index material is laminated on a slope of the triangular prism, and one surface sandwiching the right angle. A sheet-shaped polarizing element, which is a prism array sheet on which a polarization modulating portion formed of a thin film in which liquid crystal molecules in a molecular alignment state having a ら helical structure are fixed and aligned, has a １ ／ helical structure. A sheet-shaped polarizing element comprising an alignment film formed by obliquely depositing an inorganic dielectric as an alignment film for fixing liquid crystal molecules in a molecular alignment state. 2. An oblique evaporation of an orientation film formed by obliquely depositing an inorganic dielectric with an oblique deposition angle of 45 to 80 ° with respect to a normal to a surface on which a deposit is deposited. The sheet-like polarizing element according to claim 1, wherein: 3. An apex angle of one of the right triangles is 40 to 50 °.
The sheet-like polarizing element according to claim 1, wherein 4. An inorganic dielectric constituting an alignment film for aligning and fixing liquid crystal molecules in a molecular alignment state having a 1/4 helix structure is an inorganic oxide or an inorganic fluoride or an inorganic oxide and an inorganic fluoride. The sheet-like polarizing element according to claim 1, wherein the sheet-like polarizing element is constituted by at least one of the composites. 5. The sheet-like polarized light according to claim 1, wherein a polarizing plate is provided on a surface from which the transmitted light and the reflected light whose polarization planes coincide with each other are emitted such that the polarization plane of the emitted light coincides with the polarization axis of the polarizing plate. element. 6. A liquid crystal display device using the sheet-like polarizing element according to claim 1 as a polarizing element on a light source side in a polarizing plate sandwiching a liquid crystal cell.