KR20050016008A - Diffusion plate for LCD back-light - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffuser plate for a liquid crystal display backlight having improved concealment and transmittance, wherein at least two diffusion layers having different light diffusivity gradients are coextruded or multi-layer extruded to weaken the diffusion at the inlet of the incident light. By increasing the diffusion to improve the concealment and transmittance at the same time to provide a diffuser plate useful not only for the lighting cover requiring a uniform brightness, but also for the advertising panel, especially the direct backlight backlight liquid crystal display requiring a thin thickness.

Description

Diffusion plate for LCD back-light with improved concealment and transmittance

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to diffuser plates, which are used in lighting covers, advertising panels, in particular in direct-lit backlight liquid crystal displays, and at the same time have improved concealment and transmittance.

Conventionally, the backlight in the liquid crystal display uses an edge light method and a direct type method.

In the edge light method, a fluorescent lamp is placed at the edge of the light guide plate, and the bottom of the light guide plate is manufactured in an inclined structure to attach a reflection plate. If necessary, a pattern may be formed on the bottom of the light guide plate through printing. This approach is inevitable for low brightness and is mainly applied to small size displays.

In the direct type method, a plurality of lamps are installed on a reflecting plate without using a light guide plate, and a diffuser plate is disposed thereon at a certain distance. An important point in this approach is that the lamp must be completely concealed so that the brightness is uniform. To this end, it is generally possible to lower the transmittance of the diffusion plate. In this case, a decrease in luminance is inevitable. Another method is to increase the distance between the lamp and the diffusion plate, but in this case, the display is difficult to thin. A more improved method may be a method using a light guide plate and a diffusion plate of a geometric shape as disclosed in Korean Patent Laid-Open Publication No. 2002-71358, but this method is complicated in structure, multi-process, cost, weight, etc. Causes problems.

Accordingly, an object of the present invention is to provide a diffuser plate capable of enabling a thin backlight device having improved performance by maintaining high uniformity while maintaining high uniformity with high concealability.

Diffusion plate of the present invention for achieving the above object is produced by co-extrusion or multi-layer extrusion of at least two or more diffusion layers containing a binder resin with or without diffusion particles, which is a diffuser plate to which the light of the lamp is incident It is characterized by satisfying the structure that the light diffusion rate of each diffusion layer is gradually increased from the lower end of the diffusion plate to the upper end of the diffusion plate.

The present invention will be described in more detail as follows.

Generally, the diffusion plate is obtained by extruding a diffusion layer composed of a binder resin and diffusion particles. The present invention relates to a diffusion plate manufactured by co-extrusion or multilayer extrusion of a plurality of diffusion layers. However, in the diffusion plate according to the present invention, the first diffusion layer into which the light of the lamp is incident may not include diffusion particles.

Diffusion plates for liquid crystal display backlights according to the present invention, particularly useful for direct backlight type liquid crystal displays, are obtained by coextrusion or multilayer extrusion of at least two or more diffusion layers having different diffusion rate gradients.

Co-extrusion or multi-layer extrusion to increase the diffusion rate as the light of the lamp goes from the lower end to the upper end by using a plurality of diffusion layers, at the lower end to prevent the re-escape of the light to prevent the leakage of light, gradually to the upper end The light diffusion can be maximized. A schematic diagram thereof is shown in FIG. 1.

This can be done in a number of ways, in the co-extrusion or multi-layer extrusion of multiple diffusion layers, the density distribution of the diffusion particles in the diffusion layer to have different thicknesses and transmittances (where density distribution is expressed as the number / volume of diffusion particles). Paper is defined as the number density), a method of controlling the discharge speed, a method of forming the diffusion particles having different refractive indexes from the binder resin, and the like.

For example, in the case where the density distribution of the diffuser particles is used, the number of diffuser particles may be adjusted so that the density distribution is smaller at the lower end where the light of the lamp is incident and the density distribution is higher toward the upper end.

The diffusion layer of the lower end portion in which light of the lamp is incident may include diffusion particles having a small difference in refractive index from the binder resin, and may include diffusion particles having a large difference in refractive index with the binder resin toward the upper end. Usually the refractive index of the diffuser particles can be adjusted by adjusting the content of the monomers used in the production of the diffuser particles. For example, in the case of polystyrene-methyl methacrylate copolymer beads, the refractive index may be lowered when the content of the styrene monomer is decreased at the time of manufacture.

That is, co-extrusion or multi-layer extrusion of the multi-layer diffusion layer using the density distribution difference of the diffusion particles, or co-extrusion or multi-layer extrusion of the multi-layer diffusion layer using the refractive index gradient of the diffusion particles, as a result has a multi-layer diffusion layer using the diffusion rate gradient The diffusion plate can be obtained.

For example, in the case of manufacturing a diffusion plate by co-extrusion or multilayer extrusion of two diffusion layers, the diffusion layer at the lower end portion where the light of the lamp is incident has a transmittance of 70 to 93% (light diffusion rate of 98 to 6%) and a thickness of 0.5 to 1.5 mm and the upper part has a transmittance of 30 to 80% (light diffusion rate of 99 to 96%) and a thickness of 0.5 to 1.5 mm, resulting in a transmittance of 20 to 75% having a thickness of 1 to 3 mm. ~ 98%) diffusion plate can be obtained. The thickness of each diffusion layer can be adjusted by adjusting the discharge rate during extrusion.

The diffusion plate of the present invention obtained as described above has a high concealability compared to a single-layer diffusion plate of the same transmittance to maintain a uniform high brightness, so that the desired brightness can be obtained even if the distance between the lamp and the diffusion plate is not far away. This can be done for the required direct type backlight.

In the present invention, the number of co-extrusion or multi-layer extruded diffusion layers can be adjusted to a large or small number and the thickness of each layer can also be adjusted.

In preparing the diffusion plate according to the present invention, the type of binder resin and diffusion particles for forming a diffusion layer is generally as follows.

As the binder resin, unsaturated polyester, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, Hydroxypropyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer or Acrylic type, urethane type, epoxy type melamine type, such as a copolymer or a terpolymer is mentioned.

As the diffusing particles, various organic and inorganic particles are used to increase the light transmittance and the diffusing rate while having a difference in refractive index from that of the ordinary binder resin. Typical particles used are methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxy Propyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer or copolymer Or a multi-layered multi-component system made by forming olefinic particles such as ternary copolymers, olefinic particles such as polyethylene, polystyrene, polypropylene, copolymers of acrylic and olefins, and particles of homopolymer, and then covering the layers with other monomers. Organic particles such as particles. In addition, inorganic particles such as silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and magnesium fluoride are used. Usually, the light diffusivity of organic particles is superior to inorganic particles.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example  1: Due to the difference in density distribution of the diffusion particles Diffusion layer Diffusion rate  Adjustment example

In this example, a diffusion plate was manufactured by coextrusion of a diffusion layer having a transmittance of 90% (light diffusion rate of 30%) and a thickness of 1.5 mm and a diffusion layer having a transmittance of 70% (light diffusion rate of 98%) and a thickness of 0.5 mm.

Here, the transmittance and light diffusivity are measured for sheets obtained through single extrusion at their respective thicknesses, measured by the standard method of ASTM D 1003, and the measuring instrument is NDH 2000 of Denshoku, Japan.

In this embodiment, the transmittance of the diffusion layer was adjusted by adjusting the density distribution of the diffusion particles, the thickness of the diffusion layer was adjusted by controlling the discharge rate of the extruder.

In this case, polymethyl methacrylate (refractive index 1.49%) of Mitsubishi Rayon brand name VH-001 was used as the binder resin, and crosslinked polystyrene beads (Diasphere of Kolon) were used as the diffusion particles. Details are shown in Table 1 below.

The resulting thickness of the diffuser plate was 2 mm and the transmittance was 63%.

The diffuser plate thus obtained was cut to a 17-inch standard, and eight cold cathode fluorescent lamps were placed at a distance of 13 mm on a device arranged at regular intervals, and the luminance was measured immediately above the lamp and the center of the lamp. Got.

Diffused particles product name manufacturer Refractive index (%) Content (% by weight) Density distribution Incident light diffusion layer Diasphere SPB-X10 Kolon 1.57 0.3 6.5 ㅧ 10 ⁶ Outgoing light diffusion layer Diasphere SPB-X10 Kolon 1.57 10 2.2 ㅧ 10 ⁸

Example  2: diffusion of particles On the refractive index  by Diffusion layer Diffusion rate  Adjustment example

In this example, a diffusion plate was manufactured by co-extrusion of a diffusion layer having a transmittance of 90% (light diffusion rate of 30%) and a thickness of 1.5 mm and a diffusion layer having a transmittance of 70% (light diffusion rate of 98%) and a thickness of 0.5 mm. It was.

Here, the transmittance and light diffusivity are measured for sheets obtained through single extrusion at their respective thicknesses, measured by the standard method of ASTM D 1003, and the measuring instrument is NDH 2000 of Denshoku, Japan.

In this embodiment, the transmittance of the diffusion layer was adjusted by varying the difference in the refractive index between the diffusion particles and the binder resin, the thickness of the diffusion layer was adjusted by controlling the discharge rate of the extruder.

As the binder resin, polymethyl methacrylate (refractive index 1.49%) of Mitsubishi Rayon brand name VH-001 was used as the binder resin, and polystyrene-methyl methacrylate copolymer beads (Diasphere) were used as the diffusion particles in each layer. MSP-X10) and polystyrene beads (Diasphere SPB-X10) were used. The refractive index of the diffusion particles may be adjusted according to the content of the monomers used in the production of the diffusion particles. For example, if the styrene content of the monomer is low, the refractive index is lowered to obtain a high transmittance. Details are shown in Table 2 below.

The thickness of the obtained diffuser plate was 2 mm, and the transmittance | permeability was 63%.

The diffuser plate thus obtained was cut to a 17-inch standard, and eight cold cathode fluorescent lamps were placed at a distance of 13 mm on a device arranged at regular intervals, and the luminance was measured immediately above the lamp and the center of the lamp. Got.

Contents Diffused particles product name manufacturer Refractive index Refractive Index Difference with Binder Resin Content (% by weight) Incident light diffusion layer Diasphere MSP-X10 Kolon 1.51 0.02 3 Outgoing light diffusion layer Diasphere SPB-X10 Kolon 1.57 0.09 10

Comparative example  One

In this example, the diffusion layer using the same binder resin and diffusion particles as in the above embodiment was extruded to obtain a diffusion plate having a thickness of 2 mm and a transmittance of 63% (99% light diffusion).

The transmittance and light diffusivity were measured by the standard method of ASTM D 1003 and the measuring instrument is NDH 2000, Tenshoku, Japan.

As the binder resin, polymethyl methacrylate (refractive index 1.49%) of Mitsubishi Rayon brand name VH-001 was used as the binder resin, and polystyrene beads (Diasphere SPB-X10) were used as the diffusion particles. Details are shown in Table 3 below.

As a result of adjusting the distance between the lamp and the diffuser plate so that the luminance ratio averaged 1.02 in the same manner as in Example 1, the luminance of the diffuser plate thus obtained was 18 mm.

Contents Diffused particles product name manufacturer Refractive index (%) Content (% by weight) Single layer diffuser Diasphere SPB-X10 Kolon 1.57 3

From the results of the above examples and comparative examples, in order to obtain the same luminance ratio, the distance between the lamp and the diffusion plate is about 13 mm in the case of the embodiment, whereas in the case of the diffusion plate extruded a single diffusion layer as in the comparative example, it is 18 mm. It can be seen that the thickness of the backlight can be reduced by about 5 mm by using the diffusion plate of the present invention.

As described above in detail, according to the present invention, a diffusion plate manufactured by co-extrusion or multilayer extrusion of a multi-layered diffusion layer so as to have a different diffusion rate gradient has a higher permeability and haze than a diffusion plate manufactured by extruding a single diffusion layer having the same permeability. The thickness of the backlight device can be reduced without loss.

1 is a schematic diagram showing a diffusion state of light in a diffusion plate having a diffusion layer having a multilayer structure according to the present invention.

Claims (3)

A diffuser plate for a liquid crystal display backlight manufactured by co-extrusion or multilayer extrusion of at least two or more diffusion layers containing binder resin with or without diffusing particles, the upper end of the diffuser plate at the lower end of the diffuser plate to which light of the lamp is incident. Diffusion plate for a liquid crystal display backlight, characterized in that to satisfy the structure that the light diffusion rate of each diffusion layer gradually increases. The diffusion layer of claim 1, wherein the two or more diffusion layers have density gradients of different diffusion particles, which satisfies a structure in which the density distribution of the diffusion particles gradually increases from the lower end of the diffusion plate to which the light of the lamp is incident to the upper end of the diffusion plate. And wherein the density distribution is defined as the number of diffuser particles per volume. 3. The structure of claim 1, wherein the two or more diffusion layers satisfy a structure including diffusion particles having a difference in refractive index difference from the binder resin gradually increased from the lower end of the diffusion plate to which the light of the lamp is incident to the upper end of the diffusion plate. Diffusion plate for liquid crystal display backlight, characterized in that.