JPH0263060B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a coated plastic sheet particularly suitable for use as a backing plate for liquid crystal displays.

[Conventional technology]

A backing plate for a liquid crystal display is used to make displayed characters easier to see by stacking a polarizing plate, a liquid crystal plate, and a backing plate in this order. The performance required for the material of the backing plate is that when viewed through a polarizing plate, a clear image with appropriate brightness and good contrast can be obtained.

Conventionally, backing plates for liquid crystal displays have been made of foamed plastic sheets or transparent acrylic plates with aluminum foil attached to one side.

[Problem to be solved by the invention]

However, since the former is mainly manufactured by the melting method, there may be changes in quality that are thought to be caused by heating, such as the formation of foamed and non-foamed areas, resulting in visible unevenness. Many defects such as scattered gel-like parts were observed. Moreover, in the case of the latter, there is a problem that when visually viewed through a polarizing plate, the contrast becomes unclear and characters etc. are difficult to see. On the other hand, it is conceivable to use a plastic sheet with a coating layer containing pearlescent pigments as the backing plate, but a coating layer consisting only of pearlescent pigments has low opacity, that is, high light transmittance and no In order to increase transparency, that is, to suppress light transmittance, it is necessary to use a large amount of expensive pearlescent pigment. In order to increase this opacity, it is possible to use a mixture of pearlescent pigment and white pigment, but this has the disadvantage that sufficient light diffused reflection cannot be obtained, and in both cases, the backing plate of the liquid crystal display As such, it was not satisfactory.

Furthermore, a type that allows light to enter from the back side is being developed recently (back light type).
In the case of a liquid crystal display, the disadvantages of the backing plate of the above-mentioned known liquid crystal display cannot be ignored. Also,
For the backing plate of back light type liquid crystal display,
Not only light reflectance but also moderate light transmittance (30~50
%), we create fine holes in the backing plate to measure this light transmittance.
Special hole drilling is required, leading to higher costs.

Therefore, it has been desired to develop a backing plate for a liquid crystal display that not only functions as a light reflecting plate but also has the function of transmitting light from a backlight.

[Means to solve the problem]

In view of the above-mentioned difficulties of the prior art, the present invention aims to provide a plastic sheet for a backing plate of a liquid crystal display that has both appropriate light diffuse reflection and light transmittance required to clarify liquid crystal display expression. It was made for this purpose, and its composition is either a plastic sheet containing a white pigment and formed to have suppressed light transmittance, or a transparent or translucent plastic sheet with a white pigment on the top surface. A coating layer containing a pearlescent pigment as the main pigment and having suppressed light transmittance and diffused light reflection is provided on a plastic sheet provided with a coating layer having suppressed light transmittance. It is characterized by:

[Effect]

That is, the inventors of the present invention have repeatedly conducted experiments in which various types of coating layers are provided on plastic sheets in various ways. If the layer responsible for suppressed optical transparency is formed as separate layers,
The present invention was completed based on the knowledge that the disadvantages of the conventional products can be overcome, and that the regular multiple reflection characteristics of pearl pigments provide a bright field of view and clear images with high contrast even when viewed through a polarizing plate. It was.

〔Example〕

Next, the coated plastic sheet for liquid crystal display backing plate of the present invention will be described in detail as follows.

First, the plastic sheet which is the base of the plastic sheet of the present invention may be a single sheet of polyethylene, polypropylene, polystyrene, polyliquefied vinyl, polyester, polyacrylic acid ether, polysulfone polycarbonate, etc. that contains a white pigment or is transparent or translucent. Alternatively, sheets made of copolymers can be used, and these are
It may be of single layer and/or multilayer.

In addition, as white pigments, titanium dioxide, zinc oxide, lead oxide, calcium carbonate, etc. can be used, and as pearlescent pigments, those having a structure in which mica is coated with titanium dioxide (hereinafter abbreviated as mica titanium) can be used. ), fish scale pearls, etc. are used. These particles are plate-shaped and arranged within the coating film to form a layered structure, so that incident light regularly undergoes multiple reflections.

There are various methods for providing a coating layer containing the pigment on the plastic sheet as the base, but for example, a coating method using a knife coater or a gravure roll coater is used. If a coating layer containing gravure ink (white pigment) is provided on the polyester film, use a thinner for it, or if a coating layer containing mica titanium (pearl luster pigment) is provided, use isopropyl alcohol and water as the base material. Coating liquid resins and solvents similar to those used in ordinary coating methods can be used depending on the plastic film, pigment, etc.

In addition, in order to obtain good pearlescent luster, it has become clear through various experiments that using acrylic acid-based or methacrylic acid-based resin in the layer containing pearlescent pigments leads to good results. Depending on the form of the acrylic acid-based or methacrylic acid-based resin in the resin, the interaction between the resin and the pigment in the coating layer becomes favorable, affecting the refractive index, and improving the diffuse reflection to the extent that the difference can be visually confirmed. It is thought that this is because of this.

The thus obtained coated plastic sheet for the backing plate of the liquid crystal display of the present invention is as follows:
The sheet substrate containing white pigment or the coating layer containing white pigment is mainly responsible for opacity, and the coating layer containing pearlescent pigment is mainly responsible for diffuse reflection. Since the layers formed containing separate pigments are responsible for this, it is not only easy to form an extremely good balance between light transmittance and light diffused reflection, but also to improve opacity. Since there is no need to use pearlescent pigments, the price can be kept low compared to its performance. In particular, the appropriately adjusted balance between light transmittance and light diffuse reflection is well suited to the backing plate of the new backlight type liquid crystal display.

Furthermore, since the coated plastic sheet of the present invention does not use any high-temperature heating means, there are no unevenness or gel-like areas caused by heat, and light transmission is almost uniform over the entire surface. In particular, when produced by a coating method, for example, when a polyester film with good heat resistance is used as a substrate, a plastic sheet for a backing plate of a liquid crystal display of the present invention with high heat resistance can be obtained. The present invention makes it possible to obtain a plastic sheet for a backing plate of a liquid crystal display that takes advantage of the characteristics of a plastic film as a substrate, such as that it can be provided at a low cost using an inexpensive polypropylene film as a substrate.

In view of the structure of the present invention and the effects brought about by it, even if the coating layer containing the white pigment and the coating layer containing the pearlescent pigment are on the same side with respect to the plastic sheet that is the base material, they may be on different sides. It is clear that there is no problem even if it is on the side.

Next, specific examples of the present invention will be described.

Example 1 A coating solution having the following composition 1 was applied to a 38μ thick polyester film using a knife coater, and then air-dried.
A coating layer containing a white pigment with a thickness of 3 μm was provided, and a coating solution having the following composition 2 was applied thereon and air-dried to form a coating layer containing a pearlescent pigment with a thickness of 7 μm.

An example of the obtained plastic sheet of the present invention exhibited a sparkling pearlescent luster, and the light transmittance (according to JISK6717 method) was 50%.

Composition 1 Gravure ink (white pigment) 100 parts Thinner for gravure ink 50 parts Composition 2 Mica titanium (pearl luster pigment) 20 parts Isopropyl alcohol 20 parts Water 30 parts Acrylic acid resin liquid 100 parts Example 2 38μ thick white A coating solution having the following composition 3 was applied to an opalescent polyester film opalescent with a pigment using a gravure roll coater, and then air-dried to form a coating layer containing a pearlescent pigment with a thickness of 6 μm.

Composition 3 Mica titanium (pearl luster pigment) 20 parts methyl ethyl ketone 200 parts toluene 200 parts methyl methacrylate butadiene styrene resin
30 parts The obtained plastic sheet of the present invention exhibited a sparkling pearlescent luster and had a light transmittance of 40%.

〔Effect of the invention〕

As described above, the plastic sheet for a liquid crystal display backing plate of the present invention has a layer mainly responsible for light transmittance and a layer mainly responsible for light diffuse reflection, so that the balance between light transmittance and light diffuse reflection is improved. In addition, since the sheet as a whole has suppressed light transmittance, it can be suitably used not only as a backing plate for ordinary liquid crystal displays but also for backlight type liquid crystal displays. Therefore,
By using the above-described sheet of the present invention, it becomes easier to distinguish between brightness and darkness between the characters and the background, and the legibility of the characters can be greatly improved.

Claims (1)

[Scope of Claims] 1. A plastic sheet containing a white pigment and having suppressed light transmittance, or a transparent or translucent plastic sheet containing a white pigment on the upper surface and having suppressed light transmittance. It is characterized by comprising a coating layer containing a pearlescent pigment as the main pigment, which has a suppressed light transmittance and a diffused light reflection property, on a plastic sheet provided with a coating layer having a light transmittance. Coated plastic sheet for LCD backing plate. 2. The coating layer, which has a pearlescent pigment as the main pigment and has suppressed light transmittance and diffused light reflection,
The coated plastic sheet for a liquid crystal display backing plate according to claim 1, wherein the coated plastic sheet is laminated on a coating layer containing a white pigment. 3. A coating layer containing pearlescent pigment as the main pigment, which has suppressed light transmittance and has light diffuse reflection properties,
A coated plastic sheet for a liquid crystal display backing plate according to claim 1, wherein the coated plastic sheet is provided on the opposite side of the plastic sheet to the coating layer containing a white pigment. 4. The coating layer containing a pearlescent pigment and having suppressed light transmittance and diffused light reflection is made of an acrylic acid-based or methacrylic acid-based resin. A coated plastic sheet for a liquid crystal display backing plate according to any of Item 3.