JPH07218706A - Light diffuser - Google Patents

Abstract

(57) [Summary] [Object] To provide a light diffusing plate capable of preventing moire interference fringes and ensuring uniform surface brightness while having regular concave portions. [Structure] A large number of recesses having substantially the same shape are provided on at least one surface of a transparent resin plate, and the recesses have a pyramid shape in which an opening has a parallelogram shape and generatrices are substantially equal to each other. The light diffusing plate is characterized in that the included angles of the two adjacent sides are 15 to 165 degrees and the adjacent parallelograms share one side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusion plate used for a display plate, a lighting cover and the like.

[0002]

2. Description of the Related Art A light diffusing plate diffuses light from a point light source or a linear light source or adjusts an outgoing light angle to obtain a uniform surface illumination with a high surface brightness. It is used for a transmissive screen, a cover of a lighting device, and the like.

An example of using the light diffusing plate in the liquid crystal display plate will be described with reference to FIG. Since the liquid crystal display plate does not emit light by itself, it is necessary to illuminate the display with some kind of external light. There are roughly two types of methods of taking in external light: a reflection type that uses reflected light of room illumination and a backlight type that transmits the illumination light from behind the liquid crystal display panel.

In recent years, the backlight type has become mainstream because of its good visibility. FIG. 1 is a schematic cross-sectional view of a main part of a backlight type liquid crystal display panel. In FIG. 1, one cold cathode tube (6), which is a light source, is arranged beside the liquid crystal display panel. In addition to this, there are those in which two lights are arranged on both sides of the liquid crystal display plate, or those in which cold cathode tubes are arranged on the back surface of the liquid crystal display plate, but in the case of two lights arrangement, power consumption becomes large. In the case of the rear surface arrangement, the liquid crystal display panel becomes thicker, so recently, the lateral one lamp arrangement is mainly used.

The light (8) emitted from the cold cathode fluorescent lamp (6) is guided to a transparent plate called a light guide plate (4). Light guide plate (4)
Is usually made of a transparent resin and has a thickness of several mm to several cm. Since the light guided to the light guide plate (4) is incident on the surface of the light guide plate at a relatively shallow angle, it reaches the interface between the light guide plate (4) and air at an angle larger than the so-called critical angle, and is totally reflected inside the light guide plate. repeat. If the dots (7) and the reflection plate (5) provided by screen printing that diffusely reflect are provided on the back surface of the light guide plate (4), the light that has been repeatedly totally reflected is diffusely reflected here, and the light guide plate surface. Emits to.

The light emitted from the surface of the light guide plate then reaches the light diffusion film (3). The light diffusing film has a role of providing uniform brightness over the entire surface of the liquid crystal display plate and a role of hiding the dots (7) of the light guide plate (4). Here, if the light diffusion plate (2) has a sufficient light diffusion ability and can conceal the dots (7), the light diffusion film (3) becomes unnecessary.

In this way, the light emitted from the light guide plate (4) enters the light diffusion plate (2) through the light diffusion film (3) or directly from the light guide plate (4). At this time, the incident light has directivity in a specific direction, that is, a direction opposite to the light source, reflecting that the light source is on the side of the liquid crystal display plate. The light diffusion plate (2) plays a role of changing light having such directivity by refracting in the front direction. In addition, as described above, the dots (7) on the back surface of the light guide plate due to light diffusion.
It also plays the role of cover-up.

Conventionally, this type of light diffusing plate (2) has been formed on the surface of an extruded film or sheet of a thermoplastic resin having optical transparency by sand blasting, honing treatment, embossing roll processing, press molding or the like. It is manufactured by forming fine, regular or random irregularities. Further, in these thermoplastic resins, for example,
Metal oxides such as titanium dioxide, silicon dioxide and aluminum oxide, minerals such as mica, and light diffusing substances such as metal powders such as aluminum powder, tin powder, gold powder and silver powder, which are uniformly mixed and dispersed, are also used. ing.

In recent years, in order to improve the surface brightness of liquid crystal display panels,
The mainstream is a light diffusion plate having a regular unevenness that is highly effective in adjusting the angle of emitted light and can achieve higher brightness. The regular unevenness is, for example, a continuous prism shape or a continuous wave-shaped unevenness. By arranging the continuous direction of the unevenness in parallel with the longitudinal direction of the cold cathode tube (6), the emission light angle is adjusted. Is possible.

In this way, the light emitted from the light diffusing plate (2) is incident on the liquid crystal unit (1) as light having a uniform directivity on the entire liquid crystal display plate and image information is added. After being processed, it is further emitted to the outside and visually recognized.

As such a light diffusing plate (2), for example, Japanese Patent Laid-Open No. 61-57902 discloses a method of adjusting the light beam direction using a light diffusing plate having continuous prism-shaped irregularities. Japanese Patent Laid-Open No. 61-15104 discloses a similar method.

The light diffusing plate usually has a continuous prism shape with a pitch of about several tens of μm to several hundreds of μm, or a continuous wave-like irregularity, while the liquid crystal unit (1) usually has several hundred μm.
Form a matrix pattern. In this manner, when continuous wave-shaped irregularities or patterns having similar sizes are overlapped with each other, interference occurs and so-called moire interference fringes occur. When such moire interference fringes are generated, the visibility of the screen of the liquid crystal display plate is significantly reduced.

In order to prevent this, for example, a method of roughening the pitch of the irregularities of the light diffusion plate can be mentioned. In this case, the brightness of the screen reflects the irregularities of the light diffusion plate (2), Bright and dark lines are generated on the liquid crystal screen, and visibility is deteriorated.

On the other hand, as another method for preventing moire interference fringes, the continuous prism shape of the light diffusing plate (2) or the continuous direction of continuous wave-like irregularities is applied to the cold cathode tube (6) and the matrix of the liquid crystal unit (1). For example, there is a method in which the pattern is not placed parallel to the pattern but is tilted by 45 degrees. However, with this method, it is difficult to obtain uniform brightness over the entire screen of the liquid crystal display panel.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to prevent moire interference fringes and have uniform surface brightness while having regular unevenness. It is to provide a light diffusing plate capable of ensuring the above.

[0015]

The transparent resin plate used in the present invention includes, for example, thermoplastic resins such as poly (meth) acrylate resin, polycarbonate resin, polyvinyl chloride resin, polyethylene terephthalate resin; thermosetting. Resin: a transparent resin plate of a photocurable resin can be used.

A large number of fine recesses of the light diffusing plate of the present invention are provided in substantially the same shape, and the openings of the recesses are parallelograms (9) as shown in FIG. Next to each other 2
The included angle formed by the side is 15 to 165 degrees, and more preferably 30 to 150 degrees, because moire interference fringes are generated regardless of whether the angle is increased or decreased.

The light diffusing plate of the present invention is provided with a large number of fine recesses that share one side of the parallelogram.

The recessed portion extends from the opening toward the bottom.
A cross section perpendicular to the depth direction is gradually reduced to one point (10) and has a pyramid shape in which the lengths of the busbars having the parallelograms as conductors are substantially equal.

As the pyramid shape, as shown in FIGS. 3 and 4, the cross section of the concave portion parallel to one side of the parallelogram and passing through the bottom portion and perpendicular to the transparent resin plate (12) has a triangular waveform ( 11), it may have a wave shape such as a triangular waveform, a sine waveform, or the like, a part of which is a curve.

If the angle formed by the wavy maximum gradient and the minimum gradient is larger or smaller than 90 degrees, the efficiency of adjusting the direction of the light beam is lowered and the surface brightness of the obtained light diffusing plate is lowered. It is preferably 45 to 135 degrees.

The above triangular waveform is preferably 0.2 or more because the efficiency of adjusting the light ray direction decreases and the surface brightness of the light diffusing plate decreases when the slope rate (S) represented by the formula (1) decreases. , And more preferably 0.5 or more.

S = A / L

[Wherein L is the length along the waveform of one cycle of the triangular waveform. A represents the length of the straight line portion. ]

When the depth of the concave portion and one side of the parallelogram forming the opening portion become smaller, it becomes difficult to maintain the accuracy of the shape, and the processing cost becomes extremely high. When used as a plate, light and darkness corresponding to the shape of the recesses are clearly visible on the screen, and the screen becomes difficult to see, so 10 to 500 μm is preferable.

As the method for producing the light diffusing plate of the present invention, any known method can be adopted as long as it can form the recesses in the transparent resin plate, and examples thereof include poly (meth) acrylate resin, polycarbonate resin and poly (meth) acrylate resin. A method of softening a vinyl chloride resin or polyethylene terephthalate resin plate by heating and press-molding the concave portion using a mold having an engraving corresponding to the concave portion, a method of forming with an embossing roll, the concave portion The method is to fill the mold with engraving corresponding to the above with a thermosetting resin or a photo-curing resin and cure by heat or light to form, and to produce the photo-curing resin in a pattern with an optical mask. Examples of the method include a method of irradiating with light, a development treatment, a formation, and a production method, and those skilled in the art can select an effective method.

As the thickness of the light diffusion plate of the present invention increases,
If the display plate using the light diffusion plate becomes thicker and thinner, it becomes difficult to give the shape of the recesses, and therefore 50 to 100 μm is preferably used.

The light diffusing plate of the present invention can be installed and used in a liquid crystal display plate as shown in FIG.

Here, the angle γ (hereinafter referred to as “arrangement angle”) formed by one side of the parallelogram forming the opening of the recess and the matrix pattern of the liquid crystal unit is set to be 15 to 165 degrees. Is preferred.

The arrangement angle is less than 15 degrees or 165
If it exceeds the limit, moire interference fringes are generated between the matrix pattern of the liquid crystal unit and the light diffusion plate, and the visibility of the liquid crystal display plate deteriorates.

When the light diffusing plate is used for the liquid crystal display plate, at least one of the parallelograms forming the opening of the recess is formed.
If the side is deviated from parallel or perpendicular to the longitudinal direction of the cold cathode tube installed on the side surface of the liquid crystal display plate, the unevenness of the surface brightness becomes large. Therefore, one side of the parallelogram is
It is preferably arranged in parallel or vertically.

[0031]

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

(Example 1) Diameter 100 mmφ, effective width 3
00 mm, 200 mesh on the surface (pitch 127μ)
A light-diffusing plate having a large number of fine recesses on the surface of an engraving roll having a regular pyramid shape (height 40 μ, apex angle 105 °) is pressed against a polyethylene terephthalate film having a thickness of 100 μm. Got

The above-mentioned molding conditions were a roll temperature of 150 ° C., a pressure of 50 Kg / cm ² , and a conveying speed of 3 m / min.

In the obtained light diffusing plate, an angle formed by one side of the parallelogram forming the opening of the recess with the longitudinal direction of the cold cathode tube is 45 degrees, and the arrangement angle with the matrix pattern of the liquid crystal unit is set. It was set on the liquid crystal display panel so as to be 45 degrees.

Comparative Example 1 200-mesh continuous prism shape (pitch 127 μm; height 40 μ; apex angle 105)
The engraving roll having a number of degrees) was prepared, and a light diffusing plate having a large number of fine recesses on the surface was obtained in the same manner as in Example 1 except that this was used. The obtained light diffusing plate was subjected to liquid crystal display so that one side of the parallelogram forming the opening of the recess was parallel to the longitudinal direction of the cold cathode tube and the angle formed with the matrix pattern of the liquid crystal unit was 90 degrees. Placed on a plate.

Comparative Example 2 The light diffusion plate obtained above was
Installed on the liquid crystal display plate so that one side of the parallelogram forming the opening of the recess is 45 degrees with respect to the longitudinal direction of the cold cathode tube and is 45 degrees with the matrix pattern of the liquid crystal unit. did.

Using the liquid crystal display panel on which the light diffusing plate obtained in Example 1 and Comparative Examples 1 and 2 was arranged, the surface luminance, the uniformity of surface luminance, and the generation of moire interference fringes were tested, and the results are shown. 1
It was shown to.

(Measurement of Surface Luminance, Generation of Moire Interference Fringes and Uniformity of Surface Luminance) Surface luminosity is measured on a light guide plate of a backlight module for liquid crystal display panel in which one cold cathode tube is installed. A diffuser is installed and a luminance meter (Minolta LS
-100) is installed at a distance of 30 cm from the surface of the light diffusion plate,
It was measured.

The moire interference fringe and brightness uniformity tests were visually judged.

[0040]

[Table 1]

[0041]

EFFECTS OF THE INVENTION The light diffusing plate of the present invention is provided with the above-mentioned concave portions on the surface thereof at a constant angle with respect to the matrix pattern of the liquid crystal unit, so that the surface luminance is not lowered and the moire interference is prevented. It can be used for liquid crystal displays, illumination covers, etc. because it can prevent the generation of stripes and can maintain high surface brightness and uniformity of surface brightness.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an essential part of a backlight type liquid crystal display panel.

FIG. 2 is a schematic top view showing a part of the surface of the light diffusing plate of the present invention on which the concave portion is provided.

FIG. 3 is a schematic cross-sectional view taken along the line AA ′ of the light diffusing plate of the present invention.

FIG. 4 is a schematic sectional view taken along the line BB ′ of the light diffusing plate of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal unit 2 Light diffusing plate 3 Light diffusing film 4 Light guide plate 5 Reflecting plate 6 Cold cathode tube 7 Dots 8 Rays 9 Opening of recess 10 Dotted bottom of recess 11 A-A 'Triangular waveform of recess 11' Triangular corrugation of the recess of BB 'section 12 Recess

Claims (1)

[Claims] 1. A transparent resin plate is provided with a large number of recesses having substantially the same shape on at least one surface, and the recesses have a pyramid shape in which an opening has a parallelogram shape and generatrices are substantially equal to each other.
A light diffusing plate characterized in that an included angle of two adjacent sides of the parallelogram is 15 to 165 degrees, and the adjacent parallelograms share one side.