JPS61169824A - Polarizing plate for transmission type liquid crystal display device - Google Patents

Abstract

PURPOSE:To display a bright and easily visible image screen with large contrast by conducting the light from a light source on the rear side to a liquid crystal cell through a polarizing plate provided with a phosphor layer on one side so that the light is selectively transmitted and shut off. CONSTITUTION:A liquid crystal element 35 is constituted by sandwiching a TN type liquid crystal cell 21 sealed with a liquid crystal 32 between transparent electrodes 25, 29 and substrates 23, 31 by the polarizing plate 11 provided with the phosphor layer 15 on one side and an observation side polarizing plate 33. The light emitted from the layer 15 is made incident on a polarizing plate body 13 when a UV light source 37 is lighted up. The bright polarizing light is thereby obtd. The light is shut off when a voltage is impressed to the electrodes 25, 29. The bright and easily visible large image screen with the large contrast is thus displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate used in a transmission type liquid crystal display device.

A transmissive liquid crystal display device has a light source on the back side of a liquid crystal cell containing a liquid crystal substance, and selectively transmits or blocks light from the back light source by applying a signal voltage to the electrodes. It is designed to display one character, two figures, etc. Fluorescent lamps and tungsten lamps are used as backlight sources.

A diffuser plate is used to distribute the light evenly.

As a liquid crystal element that blocks and transmits light using a signal voltage,
Twisted nematic (TN) type liquid crystal display elements and guest-host type (GH) type liquid crystal display elements are used. For example, when performing a positive display using the TN method or the GH method, the color of the polarizing plate will appear as a background in the non-lit areas (areas where no signal is applied), but since the polarizing plate is colored to a certain extent, there will be a contrast. Furthermore, in the case of the GH method, the dichroic ratio of the dye is not yet sufficient, resulting in poor color fading and a certain amount of dye color remaining, which colors the non-lit areas and further reduces the contrast. On the other hand, in the case of the TN system, since observation is performed through yet another polarizing plate provided on the viewing side of the liquid crystal cell, there is a problem in that the light is cut and the image becomes dark and difficult to see. As described above, conventional transmissive liquid crystal elements have the problem of insufficient contrast, resulting in dark display.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a polarizing plate for a transmission type liquid crystal display device that can provide a bright and easy-to-see display with high contrast.

The polarizing plate for a transmissive liquid crystal display device of the present invention is useful for a transmissive liquid crystal display device that guides light from a back light source to a liquid crystal cell through the polarizing plate and selectively transmits and blocks this light. It is characterized by having a phosphor layer formed on one surface thereof that emits fluorescence when irradiated with electromagnetic waves.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of a polarizing plate 11 of the present invention, in which a phosphor layer 15 is formed on one surface of a polarizing plate main body 13. As the polarizing plate main body 13, any conventional polarizing plate can be used. The polarizing plate main body 13 has the function of transmitting only light components that vibrate strongly in a specific direction perpendicular to the direction of propagation of light and absorbing other components, and is made of - axially stretched polyvinyl alcohol film impregnated with iodine, or , dichroic dye-triacetate film type, etc. can be used.

The phosphor layer is formed by uniformly dispersing the phosphor in a resin binder and coating it on the polarizing plate main body. The phosphor used has a desired luminescent color depending on the color of the light transmitting part of the liquid crystal display element, that is, the background part in the case of positive display. For example, when forming a white-emitting phosphor layer, equal amounts of red, blue, and green phosphors may be mixed. Examples of the phosphor include MgO as the red phosphor.

MgF, Gem, :Mn compound, Y, 03:Eu, Zn as green phosphor, Sin, :Mn.

LaPO4: Ce, Tb, as a blue phosphor (SrCa
Ba), (PO,), CQ: En, S r, P, o,
: S n etc. The binder is preferably one that has low absorption of ultraviolet light, and acrylic resin, nitrocellulose, triacetate, and other fiber-based resins are used.

When this polarizing plate is irradiated with external radiation from the oven from the side of the phosphor layer, polarized light emitted uniformly over the entire surface can be obtained.

FIG. 1 is a cross-sectional view of a TN mode transmission type liquid crystal element using the polarizing plate of the present invention, in which twisted nematic (T N ) type liquid crystal cell 21 is arranged to constitute a liquid crystal element 35. A liquid crystal composition 3 is placed between the upper substrate 23 and the lower substrate 31 provided with transparent electrodes 25 and 29, respectively, so that the upper and lower substrates 23 and 31 are twisted by 90 degrees.
2 is included. 27 represents a sealant.

The observation side polarizing plate 33 and the polarizing plate 11 of the present invention are arranged so that their absorption axes are perpendicular to each other.

When a voltage is applied to the transparent electrodes 25 and 29, the liquid crystal element 35
is designed to block light.

The first polarizing plate 33 is a normal polarizing plate;

In the polarizing plate 11 of the present invention, as already explained, the phosphor layer 15 is formed on the polarizing plate main body 13 made of a normal polarizing plate. The polarizing plate 11 of the present invention is arranged with the phosphor layer 15 facing outward, and furthermore, an ultraviolet light source 37 is provided on the lower surface thereof.

When the ultraviolet light source 37 is turned on, the phosphor layer 15 formed on the polarizing plate main body 13 emits light, which enters the main body 13 to obtain polarized light. Since this polarized light is emitted from a phosphor, it is very bright, and since the phosphor layer 15 acts as a surface light source, uniform polarized light can be obtained over the entire surface, making it suitable for large screen display.

When a liquid crystal element is driven by applying a signal voltage, light passes through the non-voltage areas and the color of the emitted light is visible, while in the voltage-applied areas the light is blocked and appears black.

Since this light is bright due to the color generated by the phosphor, it is possible to display a bright image without sufficiently compensating for the light cutting and coloring by the polarizing plate.In particular, when the phosphor layer is formed to emit white light, it is possible to display a bright image. This makes it possible to display images with high contrast.

By making the absorption axes of the two polarizing plates parallel, negative display in which the voltage application section is displayed in white is also possible.

In the above explanation, the case where it is applied to a TN type display element has been explained, but any device that can control the transmission/blocking of light from the back side may be used.For example, a guest-host type liquid crystal element or a dual-frequency drive type liquid crystal element Also used as Furthermore, the liquid crystal element can be used as a light switching element and used as a polarized light source for a color display device that displays color using a color filter.

Effects of the Invention According to the polarizing plate of the present invention, uniform and bright polarized light can be obtained due to the light emission of the phosphor. By using this polarizing plate,
It is possible to make the light-transmitting part of a transmissive display device such as a TN-type display element or a GH-type display element sufficiently bright, and compensate for the limitations of light absorption and coloring by polarizing plates and the dichroic ratio of dichroic dyes. This makes it possible to display a bright image with high contrast.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention. FIG. 2 is a sectional view showing an example of the configuration of a TN type display device using the polarizing plate of the present invention. 11...Polarizing plate 13...Polarizing plate body 15.
...Phosphor layer 21...Liquid crystal cell 23...Top group
Plate 25.29... Transparent electrode 31... Lower substrate 33... Observation side polarizing plate 37... Ultraviolet light source

Claims (1)

[Claims] 1. A polarizing plate used in a transmissive liquid crystal display device that guides light from a backside light source to a liquid crystal cell via a polarizing plate and selectively transmits or blocks this light. A polarizing plate for a transmission type liquid crystal display device, characterized in that a phosphor layer that emits light is formed.