JPH06186422A - Multilayer polarizing plate - Google Patents

Abstract

PURPOSE:To obtain a bright display when this polarizing plate is used for a transmission type liquid crystal display element as a polarizing light source by constituting the polarizing plate of plastic films laminated via spacers and fixing materials fixing the peripheral parts of these plastic films. CONSTITUTION:This polarizing plate consists of >=5 sheets of the plastic films 1 laminated via the spacers 2 and the fixing materials 3 fixing the peripheral parts of the plastic films 1. The material of the spacers 2 is properly selected from high polymers and inorg. materials. The spacers 2 having the refractive index nearly equal to the refractive index of the plastic films 1 to be used are used. The spacers 2 are sprayed on the plastic films 4 and thereafter the plastic films 1 are laminated at the time of laminating of the plastics in order to interpose the spacers 2 between the plastic films 1. Further, the peripheral parts which are not utilized to maintain the stability of the shape are fixed by the fixing materials, such as adhesives in order to maintain the stability of the shape.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a multilayer polarizing plate.

[0002]

2. Description of the Related Art In recent years, with the progress of liquid crystal display element technology, a TFT driven reflective twisted nematic (T
N) A liquid crystal element or a multiplex driving reflective super twisted nematic (STN) element has been adopted as a display element of a thin and lightweight personal computer called a notebook computer for monochrome display.

However, as the demand for colorization has increased as this display element, the type has changed from a reflection type to a transmission type element using a backlight, and in particular, a so-called direct type backlight in which a lamp is placed on the back side of the transmission type element. Since the adoption of lights goes against the slimming down of laptop computers, the edge light type with a lamp on the side is becoming mainstream.
On the other hand, for applications such as notebook computers that are premised on battery drive, there is an urgent need to reduce the power consumption of display elements.

However, in the TN type and STN type elements, linear polarizing plates are mounted on the incident light side and the outgoing light side of the element, and the light utilization efficiency is extremely low.

[0005]

In order to solve this problem, the present inventors have proposed a display system in which a multilayer film polarizing plate is newly added in Japanese Patent Application No. 4-298021. In this system, an illuminating device having a multilayer polarizing plate on the light exit surface side of the planar light guide is used as a backlight of the liquid crystal display element, and the polarization axis of the multilayer polarizing plate and the light incident surface side of the liquid crystal display element are used. The polarization axis of the polarizing plate of 1 is made to substantially match. Here, the multilayer polarizing plate is a multilayer structure in which a translucent medium having a large refractive index and a translucent medium having a relatively small refractive index are alternately laminated as a whole.

However, conventionally, a multilayer polarizing plate has been known to be made of a plastic film having flat closed cells or a polymer mixed with glass flakes, but each has a complicated shape. Therefore, the utilization efficiency of the light was also slightly low.

An object of the present invention is to provide a multilayer film polarizing plate suitable for the above-mentioned uses and a method for producing the same.

[0008]

The present invention is intended to solve the above-mentioned problems, and it is preferable that the layers 5 are stacked with a spacer interposed therebetween.
The present invention provides a multi-layer film polarizing plate comprising one or more plastic films and a fixing material for fixing the peripheral portion of the plastic films. Further, in the above-mentioned multilayer polarizing plate, there is provided a multilayer polarizing plate characterized in that the refractive index of the plastic film and the refractive index of the spacer are substantially equal. Furthermore, in the above-mentioned multilayer polarizing plate, a spacer is bonded to a plastic film to provide a multilayer polarizing plate.

FIG. 1 is a conceptual diagram of the multilayer polarizing plate of the present invention. 1 is a plastic film, 2 is a spacer, and 3 is a fixing material.

The plastic film used in the present invention efficiently separates p-polarized light and s-polarized light due to the difference in refractive index from air, and is not used to scatter or absorb light. Therefore, it is preferably basically colorless and transparent. As for the thickness, if it is too thin, it is difficult to manufacture, and if it is too thick, it is bulky and absorbs a large amount of light.
Is preferred. If the refractive index is as large as an ordinary plastic film, it will be sufficiently practical. However, the magnitude of the birefringence is preferably as small as possible in order to efficiently separate the p-polarized light and the s-polarized light.
It is preferably 2 or less.

The material is preferably one that can be manufactured by a method suitable for mass production, such as an extrusion method or a casting method. Specific examples include polyether sulfone, triacetyl cellulose, polystyrene, polyethylene terephthalate, polybutylene terephthalate, polymethyl methacrylate, polycarbonate, transparent polyurethane, transparent silicone and the like.

The number of laminated plastic films is 5 or more. When it is 5 or less, the efficiency is low and the effect of the present invention is difficult to be obtained. Further, it is preferably 20 or less. This is because if the number of laminated layers is too large, it is bulky and uneconomical.

Since the spacer is used as a gap material between the plastic films and is not used for scattering or absorbing light,
It is preferably essentially colorless and transparent.

The material may be appropriately selected from polymers and inorganic materials, but it is preferable to use a spacer having a refractive index substantially equal to the refractive index of the plastic film used because it suppresses reflection at the interface between them. Examples of materials include inorganic materials such as glass and silica, and polymers such as polystyrene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polymethylmethacrylate, polycarbonate, transparent polyurethane, and transparent silicone. Further, these may be crosslinked in order to maintain strength.

The shape thereof can be used as long as it can play a role of keeping voids between the plastic films, and it may be cylindrical or spherical. However, spherical particles are preferable in order to keep the voids in a small amount.

If the diameter is too small, the space between the plastic films becomes too narrow, so that coloring due to light interference occurs, and if it is too large, the plastic film becomes bulky.
It is preferably μm. The accuracy of the diameter is not as severe as that required for the spacer of the liquid crystal cell.

In order to interpose the spacer between the plastic films, the spacers may be scattered on the plastic film when laminating the plastics, and then the plastic film may be laminated. The spacers may be sprinkled on one side or both sides of the plastic. Further, the spraying may be performed by a dry method, or may be performed by a wet method by dispersing the spacer in a solvent or the like.

In order to keep the shape of the multilayer film polarizing plate stable, the multilayer polarizing plate is fixed by a fixing material such as an adhesive in the peripheral portion which is not effectively used. The fixing may be performed by adhesion or mechanical clamping.
However, it is most preferable to fix the peripheral portion of the polarizing plate with an adhesive because the whole structure becomes compact and the manufacturing is easy.

This adhesion may be performed at the same time as lamination,
When the multilayer polarizing plate has, for example, a rectangular shape, it is also possible to adopt a method in which two opposing sides are continuously bonded, then cut to a desired length, and the remaining two sides are bonded. The width of adhesion is not particularly limited, but is about 0.5 to 10 mm. As the adhesive, a thermosetting adhesive, a hot melt adhesive, a photopolymerization adhesive, or the like may be appropriately selected and used.

In order to keep the shape of the multilayer polarizing plate stable, it is preferable that the spacer is adhered to the plastic film.

In order to carry out the adhesion, for example, a dispersion in which spacers are dispersed in a solution prepared by diluting an epoxy resin and its curing agent in a suitable solvent is sprayed on a plastic film, and after the solvent is volatilized, another It is possible to adopt a method in which the plastic films are superposed and then the reaction between the epoxy resin and the curing agent thereof is promoted by heating, light irradiation or the like to cure the epoxy resin. Also, this step may be carried out simultaneously on a large number of plastic films to be laminated.

Of course, the spacer itself may be made of a material exhibiting adhesiveness by heating or light irradiation.

The present invention can be used by adding various constitutions as long as the effect is not impaired.

[0024]

EXAMPLE A multilayer polarizing plate was manufactured using the manufacturing apparatus shown in FIG. 10 rolls 11, 11, ..., 10 rolls 35 cm wide, 25 micron thick polyethersulfone films 13, 13, ..., 1
, 12 is sprayed with a dispersion liquid in which a spacer having an average diameter of 10 μm is dispersed in a solution prepared by diluting a bisphenol A epoxy resin and its amine curing agent in a Freon solvent. Then, each film is passed through the dry section A to volatilize the fluorocarbon, and then, in the pressure-bonding section B, pressure is applied by two rolls of 20 and 21, and then by the heating rolls 22 to 27 of the heat-curing section C. After heat curing, the laminate was wound on the winding roll 28.

A 30 cm × 20 cm laminate was cut out from this roll, and the bisphenol A epoxy resin and its amine curing agent were supplied from the feeder to the periphery of the laminate.
After coating to a width of about 0.5 cm, it was cured.

The multilayer polarizing plate thus obtained had high transparency and was easy to handle. This multi-layer film polarizing plate is attached to a backlight to make a transmission type TN.
It was used as lighting for the liquid crystal element. At this time, the polarization axes of the multilayer film polarizing plate and the polarization axis on the illumination side of the liquid crystal element were substantially aligned with each other. It was 1.2 times brighter than a conventional TN liquid crystal device having a similar structure in which a closed-cell polystyrene multilayer polarizing plate was attached to a backlight.

[0027]

The multilayer film polarizing plate of the present invention is extremely suitable for a polarized light source used in a transmission type liquid crystal display device. When used in a transmissive liquid crystal display device, an extremely bright display can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the structure of a multilayer polarizing plate of the present invention.

FIG. 2 is a conceptual diagram showing a method for producing a multilayer polarizing plate of the present invention.

[Explanation of symbols]

 1: Plastic film 2: Spacer 3: Fixing material 11: Roll 12: Sprayer 13: Polyethersulfone film 20, 21: Crimping roll 22, 23, 24, 25, 26, 27: Heating roll 28: Winding roll

Claims (3)

[Claims] 1. A multilayer film polarizing plate comprising five or more plastic films laminated via a spacer and a fixing material for fixing a peripheral portion of the plastic film. 2. The multilayer polarizing plate according to claim 1, wherein the plastic film and the spacer have substantially the same refractive index. 3. The multilayer polarizing plate according to claim 1, wherein a spacer is adhered to the plastic film.