JPH1184129A - Sheet-like polarizing element and liquid crystal display element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polarized light sepn. and conversion type polarizing element for converting natural light to linearly polarized light with high efficiency and to provide a liquid crystal display device which has high luminance or is reduced in electric power consumption by using the same. SOLUTION: A sheet-like prism array arranged with triangular prisms of a right-angled triangular shape like are array comprises modulating parts consisting of periodic structure reflection increasing films consisting of low- and high-refractive index thin films on the slopes of the triangular prisms and the thin films of liquid crystal molecules having 1/4 spiral structures formed on the perpendicular surfaces of the prisms and existing in a molecular orientation state. Incident light is polarized and separated by the reflection increasing films and the reflected light thereof is further polarized and converted by these modulation parts and is totally reflected by the adjacent prism slopes. The reflected light is emitted outside the element nearly perpendicularly. On the other hand, the refracted light has p and s polarized light components at nearly the same ratio and is emitted outside the prisms. The reflected light and the refracted light are passed through the polarizing plate to obtain only the p polarized light, by which >=50% of the p polarized light is obtd. from the incident natural light. Namely, >=50% of transmittance is obtd., and the improvement up to about 90% is made possible by designing the reflection increasing films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-like polarizing element having a function of generating only one-way polarized light component from unpolarized light. 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 Conventionally, a sheet-like polarizing plate used for a liquid crystal panel display has a dichroic dye adsorbed in a polymer film as a base material and is arranged in a uniaxial direction. As the dichroic dye, iodine or an azo dye is used. Of the light incident on the sheet-like polarizing plate, light having a polarization component in the direction of the absorption axis is absorbed and blocked, and a polarization component orthogonal to the light is transmitted. Therefore, the transmittance of incident light is 50% in principle. In fact, the transmittance of widely commercially available polarizers is 40-45%. 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 utilization efficiency is disclosed in Japanese Patent Application Laid-Open No. Hei 8-248224, in which light having two polarization components is transmitted and reflected at a material boundary having a different refractive index. After rotating the plane of polarization by a phase shifter or a Faraday element that changes the phase of one polarized light component, the direction is changed so that the two polarized light components travel in the same direction. Is increasing.

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.

[0005]

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. Display element is provided.

[0006]

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 a high-refractive-index material are laminated on a slope of the triangular prism. A prism array sheet on which a reflection-enhancing film is formed, and a modulation section composed of a thin film in which liquid crystal molecules in a molecular alignment state having a 1/4 helical structure are fixed on one surface sandwiching a right angle is formed. It is characterized by.

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

Further, the multilayer reflection enhancing film formed on the inclined surface of the triangular prism of the sheet-like polarizing element is composed of two types of thin films having different refractive indexes, and thin films of a high refractive index material and a low refractive index material are alternately laminated. It is characterized by.

Further, the liquid crystal molecules in a 1/4 helix molecular orientation state constituting the modulating portion formed on one surface sandwiching the right angle of the triangular prism of the sheet-shaped polarizing element are formed as acrylate as a polymerization functional group. A methacrylate group, a vinyl ether group or an epoxy group.

In addition, the liquid crystal molecules in a molecular orientation state of a 1/4 helical structure constituting the modulation section formed on one surface sandwiching the right angle of the triangular prism of the sheet-like polarizing element are arranged in a chiral nematic phase. It is characterized by being in a state.

Further, the liquid crystal molecules in a 1/4 helix molecular orientation state which constitute the modulation section formed on one surface sandwiching the right angle of the triangular prism of the sheet-shaped polarizing element are arranged in a chiral smectic phase. It is characterized by being in a state.

Further, the modulation portion formed on one surface sandwiching the right angle of the triangular prism of the sheet-like polarizing element is formed of a mixture of liquid crystal molecules having a 1/4 helix molecular orientation state and other organic compounds. It is characterized by becoming.

Further, the liquid crystal molecules in a liquid crystal phase in a 1/4 helical structure, which constitutes the modulator formed on one surface of the sheet-shaped polarizing element sandwiching the right angle of the triangular prism, are formed on the inclined surface. Are fixed in orientation by photopolymerization.

Further, the liquid crystal molecules in the 1/4 helical structure, which constitutes the modulator formed on the inclined surface on one surface sandwiching the right angle of the triangular prism of the sheet-like polarizing element, are controlled. At least one alignment film of inorganic or organic molecules is used.

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

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

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the structure of a polarization separation / conversion element according to the present invention. Reference numeral 1 denotes a prism sheet in which triangular prisms each having a right-angled triangle with an apex angle of 40-50 ° are arranged in an array. is there. 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. Sheet prism array 1
In the molecular orientation state, a periodic structure reflection enhancement film 2 composed of a thin film having a low refractive index and a high refractive index is formed on a slope of a triangular prism and a quarter-helical structure formed on a plane parallel to the incident light of a right-angle prism. The modulation section 3 is formed of a thin film in which certain liquid crystal molecules are fixed in alignment.

The periodic structure reflection increasing film 2 composed of a low-refractive-index and high-refractive-index thin film includes a low-refractive-index material such as zinc sulfide, cerium oxide and titanium oxide, and a low-refractive-index material such as fluorinated. Magnesium iodide is used. Vacuum evaporation or sputtering is used as a film formation method. The thickness of each of the high and low refractive index thin films alternately laminated,
The number of layers is important in designing the performance of the periodic structure reflection enhancement film.

The modulator 3 made of a thin film in which liquid crystal molecules in a molecular alignment state having a せ ん helical structure are fixed in alignment is an optical modulator having a function of rotating the incident polarization plane by 90 degrees. It is desirable to have a polymerizable functional group in order to fix the molecular alignment state of the liquid crystal phase of the liquid crystal phase, and to have at least one of an acrylate group, a methacrylate group, a vinyl ether group, and an epoxy group as the polymerizable functional group. preferable. The liquid crystal molecules are 1 /
A cholesteric liquid crystal is preferable to exhibit a four-helix structure, and a chiral nematic liquid crystal, a chiral smectic liquid crystal, a mixture of a nematic liquid crystal and a chiral agent, and a mixture of a smectic liquid crystal and a chiral agent are more preferable.

Further, in order to obtain a modulation section 3 composed of a thin film in which liquid crystal molecules in a molecular alignment state having a ら helical structure are fixed in alignment, an alignment layer for controlling the molecular alignment state of the liquid crystal molecules includes an alignment layer. An inorganic or organic molecule alignment film may be used as long as it exhibits uniaxial orientation of liquid crystal molecules in the vicinity of the layer.However, if an organic molecule is used, a polyimide film is photoaligned, and a photoisomerized molecule is photoaligned. Preferred are those obtained by forming a film of dichroic organic molecules by a dry process such as oblique deposition, those obtained by obliquely depositing an inorganic oxide, and those obtained by obliquely depositing an inorganic fluoride.

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

When unpolarized light (natural light) 5 is incident on the inclined surface of the first prism 10, it is reflected and refracted by the prism inclined surface on which the periodic structure reflection increasing film 2 is formed, and becomes reflected light 6 and refracted light 7. Separated. The polarization state and light intensity of the reflected light 6 and the refracted light 7 are determined by the periodic structure reflection increasing film 2.
, That is, the values of the high and low refractive indexes, the film thickness and the number of layers. Here, the periodic structure reflection increasing film 2 is adjusted so that the s-polarized light component of the reflected light 6 is increased and the p of the refracted light 7 is increased.
The polarization component is designed to be large. Reflected light 6 is 1/4
The s- and p-polarized light components are reversed by the action of the modulating portion 3 composed of a thin film in which liquid crystal molecules in a molecular alignment state having a helical structure are fixed in alignment. The light enters the second prism 11 and is totally reflected by the inclined surface to become polarized light 8 '. At this time, the polarization state does not change.

Further, the light passes through the polarizing plate 4 arranged so that the p-polarized light passes therethrough, and becomes the emission light 9. The emitted light 9 is linearly polarized light having only p-polarized light as a polarized light component. On the other hand, the refracted light 7 is elliptically polarized light having substantially equal amounts of the p-polarized component and the s-polarized component, but the light intensity thereof is sufficiently lower than the reflected light 6 due to the action of the periodic structure reflection increasing film 2. The refracted light 7 passes through the polarizing plate 4 as in the case of the reflected light, and is emitted as linearly polarized light 12 having only a p-polarized component. The linearly-polarized light 9 and the linearly-polarized light 12 whose reflected light 6 has been subjected to polarization conversion are added together, and can be used as a linearly-polarized light source. That is, the incident natural light 5 is polarization-separated on the slope having the periodic structure reflection increasing 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, the sheet-like polarizing element of the present invention allows non-polarized light to be 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 plane modulation section is formed by a thin film in which liquid crystal molecules in a 1/4 helix molecular orientation state are fixed, the polarization plane conversion with a small dispersion of polarization plane rotation in a wide wavelength band is possible. That is, the light use efficiency can be improved in a wide band.

[0025]

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 angles of 4 mm and a length of 5 cm was prepared, and zinc sulfide (abbreviated as H) which is a high-refractive-index thin film material was provided on the slope. ) Nine layers of 0.05 μm and 0.09 μm of magnesium fluoride (abbreviated as L) as a low refractive index thin film material were laminated in the order of HLHLHLHLH. The film was formed by a vacuum evaporation method having two evaporation sources. Next, an alignment film was formed by obliquely depositing a tantalum pentoxide thin film on one side sandwiching the right angle. 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-002: manufactured by Roddick) were adjusted to d / p = 1/4, and the photocuring initiator (IRG65) was adjusted.
1: Ciba Geigy) to form liquid crystal molecules in a molecular alignment state having a 1/4 helix structure on the vertical surface of the prism array on the 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 adhered to the lower surface of the glass plate to produce a polarization separation / conversion type polarizing element of the present invention, and irradiated with natural light. The optical power of the linearly polarized light emitted from the polarization separation / conversion type polarization element was 83% of the incident natural light.

Example 2 A right-angled isosceles triangle having two right-angled sides of 2 mm was used as a cross section, and the area was 10 cm × 10 cm.
A sheet in which prisms were arranged in an array was formed by a mold forming method. The molding resin was polymethyl methacrylate (PMMA), and was molded by a photocuring method. Next, a mask was arranged and a tantalum pentoxide film was obliquely deposited so that an alignment film could be formed only on the vertical surface of the prism array, thereby preparing an alignment film. Next, the chiral agent (CNL6
11L: Asahi Denka Co., Ltd. and monoacrylate liquid crystal (UCL-002:
Liquid crystal molecules having a 1/4 helix structure on the prism array vertical surface using a photo-curing initiator (IRG651: Ciba-Geigy) with d / p = 1/4. Was prepared on an oriented thin film. 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. The thin film material and thickness at this time are
This is the same as the case of the first embodiment, and the layer configuration is 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%. Further, the 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 luminance when the polarization separation / conversion polarizing element of the present invention was inserted was clearly high.

[0027]

According to the present invention, natural light can be converted into linearly polarized light with very high efficiency. By using the polarization separation / conversion type 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. It is clear that this leads to power saving of the liquid crystal display device of the backlight.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view of a polarization separation / conversion element of the present invention.

FIG. 2 is a structural sectional view of a polarization beam splitter / converter of the present invention.

[Explanation of symbols]

1 Prism sheet 2 Periodical structure reflection increasing film 3 Thin film with fixed alignment of liquid crystal molecules in 1/4 helical structure in molecular alignment state 4 Polarizer 5 Natural light 6 Reflected light 7 Refracted light 8 Transmitted light 8 'Polarized light 9 Emitted light 10 First prism 11 Second prism 12 Outgoing light

Claims (11)

[Claims] 1. A right-angled triangular triangular prism is arranged in an array, and a multi-layer reflection increasing film in which a low refractive index material and a high refractive index material are laminated is formed on the slope of the triangular prism. A sheet-shaped polarizing element, comprising: a prism array sheet on which a modulating portion formed of a thin film in which liquid crystal molecules in a molecular alignment state having a ４ helical structure are fixed on a surface. 2. A sheet-like polarizing element according to claim 1, wherein a right angle of the right triangle is 40-50 °. 3. The multi-layer reflection enhancing film formed on the inclined surface of the triangular prism according to claim 1, comprising two types of thin films having different refractive indexes, and thin films of a high refractive index material and a low refractive index material are alternately laminated. A sheet-like polarizing element characterized by the above-mentioned. 4. A liquid crystal molecule in a 1/4 helix molecular orientation state which forms the modulation section and is formed on one surface sandwiching a right angle of the triangular prism according to claim 1 as an acrylate as a polymerization functional group. A sheet-like polarizing element having at least one of a group, a methacrylate group, a vinyl ether group and an epoxy group. 5. A liquid crystal molecule in a 1/4 helix molecular orientation state, which constitutes the modulation section formed on one surface sandwiching a right angle of the triangular prism according to claim 1, and has a chiral nematic phase molecular orientation. A sheet-like polarizing element, which is in a state. 6. A liquid crystal molecule in a molecular orientation state of a quarter helical structure, which is formed on an inclined surface on one surface sandwiching a right angle of the triangular prism according to claim 1, and has a molecular orientation of a chiral smectic phase. A sheet-like polarizing element, which is in a state. 7. The liquid crystal display device according to claim 1, wherein the modulation portion formed on one of the surfaces sandwiching the right angle of the triangular prism is a mixture of liquid crystal molecules having a 1/4 helix molecular orientation state and other organic compounds. A sheet-shaped polarizing element, comprising: 8. The molecular alignment state of a liquid crystal phase of a liquid crystal molecule in a 1/4 helical structure, which constitutes the modulating portion, which is formed on one surface sandwiching a right angle of the triangular prism according to claim 1. Wherein the orientation is fixed by photopolymerization. 9. The molecular alignment state of liquid crystal molecules in a 1/4 helix molecular alignment state that forms the modulating section and is formed on one surface sandwiching a right angle of the triangular prism according to claim 1. A sheet-like polarizing element comprising at least one inorganic or organic molecule alignment film. 10. The sheet-like polarizing element according to claim 1, wherein the planes of transmitted light and reflected light whose polarization planes coincide with each other are:
A sheet-like polarizing element provided with a polarizing plate such that the polarization plane of the emitted light coincides with the polarization axis of the polarizing plate. 11. 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.