JPH02221924A - Light transmission plate made of methacrylic resin and its production - Google Patents

Abstract

PURPOSE:To nearly equal the quantity of the light to be emitted from the respective parts of a light emitting surface and to greatly improve an angle of visual field by dispersing and mixing inorg. fillers to the particle sizes smaller and the concns. higher the more distant from an illumination lamp in a methacrylic resin plate. CONSTITUTION:A gasket 12 is inserted between a pair of glass plates, etc., 11 to form a cell 15 for polymn. The compsn. A 14 formed by dissolving a polymn. initiator into a methacrylic resin syrup prepd. by dissolving the methacrylic resin into a monomer mixture composed of >=50wt.% methyl methacrylate, methyl acrylate, etc., copolymerizable therewith and styrene, etc., is poured therein to >=3/4. The compsn. B 13 prepd. by uniformly mixing the inorg. fillers, such as quartz powder, having 2 to 100mum average particle size, 1.4 to 1.6 refractive index and >=2.0 sp. gr. with the methacrylic resin syrup is injected in a laminar state into the remainder and thereafter, the cell 15 is erected upright and is polymerized. The concn. gradient of the fillers and the syrup can be adjusted by changing the conditions thereof.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a light guide plate for a surface light source, which has good light output efficiency and is particularly suitable for light sources of various displays and backlight devices for liquid crystal display cells. The present invention relates to a light guide plate with improved light diffusion properties.

[Conventional technology]

Conventional LCDs have a light-reflecting layer on the back and use external light from the front to display information, but when used in place of conventional CRTs, they lack brightness. , devices with a surface light source installed on the back of a liquid crystal display began to be used.

Conventionally, the light source for such LCD displays is a back panel in which an incandescent lamp, fluorescent lamp, or other illumination lamp is placed at a certain distance from the back of the LCD display, and a light diffusion plate is placed in the middle to make the light uniform. Light equipment was used.

However, such devices have a large overall thickness and lose the advantage of being thin, which is one of the characteristics of liquid crystal displays. Therefore, light guide plates are used mainly for portable, portable, and wall-mounted applications, such as molds. A variety of thin surface light sources have been proposed.

Among these, a promising method is known in which an illumination lamp such as a fluorescent lamp is provided on the side surface of a light guide plate made of acrylic resin or the like, and light is emitted from one side of the light guide plate. In order to improve the narrow viewing angle of this method, the light emitting surface of the light guide plate is roughened, and a light diffusing agent such as glass beads is used to diffuse the emitted light to the left and right of the screen. However, since light diffusing agents also have a certain degree of light absorption, when liquid crystal displays become large, there is a problem in that the brightness is insufficient on the side opposite the illumination lamp.

As a method to solve this problem,
No. 62, JP-A No. 59-81683, Publication No. 58-46
No. 447 etc. have been proposed.

These methods propose lowering the concentration of the diffusing agent on the illumination lamp side and increasing the concentration on the opposite side, so that the amount of light emitted from each part of the light emitting surface becomes equal. It is difficult to manufacture plates with the desired concentration distribution of the agent, and this has not been put to practical use.

[Problem to be solved by the invention]

The present invention was conceived in view of the above-mentioned problems,
The object of the present invention is to provide a highly practical light guide plate for a liquid crystal display that is thin, has uniform brightness on the light emitting surface, and has excellent light diffusion properties to the left and right sides of the screen, and a method for manufacturing the same.

(Means for Solving the Problems) That is, the present invention provides: (1) an average particle diameter of 2 to 100 μmφ, a refractive index of 1,
4 to 1.6, and has a refractive index different from the refractive index of the methacrylic resin, and has a specific gravity of 2.0 or more,
The filler with a large particle size is dispersed near the illumination lamp disposed on the end surface of the light guide plate, and the filler with a small particle size is dispersed in a place far from the illumination lamp, so that the amount of light emitted is substantially distributed over the entire output surface. A methacrylic resin light guide plate characterized by uniformity.

(2) The average particle diameter is 2 to 100 μmφ, the refractive index is 1,
4 to 1.6, and has a refractive index different from the refractive index of the methacrylic resin, and has a specific gravity of 2.0 or more,
The filler having a large particle size is dispersed at a low concentration near the illumination lamp arranged with respect to the end surface of the light guide plate, and the filler having a small particle size is dispersed at a low or high concentration at a place far from the illumination lamp. A light guide plate made of methacrylic resin, characterized in that the amount of light emitted is substantially uniform over the entire light emitting surface.

(3) After pouring a composition in which a polymerization initiator is dissolved into methacrylic resin syrup containing methacrylic resin dissolved therein, at least one half of the total volume of the polymerization cell is poured, and then the methacrylic resin is poured into the remaining part of the polymerization cell. The dissolved methacrylic resin syrup has an average particle diameter of 2 to 100 μmφ and a refractive index of 1.4.
1.6, and has a refractive index different from the refractive index of the methacrylic resin, and a composition in which an inorganic filler and a polymerization initiator having a specific gravity of 2.0 or more are uniformly mixed is formed into a layer 3. The method for producing a light guide plate made of methacrylic resin according to claim 1, wherein the polymerization is carried out with the polymerization cell in an upright state.

(4) The method for manufacturing a methacrylic resin light guide plate according to item 3 above, characterized in that a polyvinyl alcohol film having a pear-shaped surface is applied to the surface of a glass plate or a metal plate constituting the polymerization cell.

(5) The method for producing a light guide plate made of methacrylic resin as described in Items 3 and 4 above, characterized in that a methacrylic resin syrup mixed with a polyfunctional monomer is used.

(6) A light guide plate made of methacrylic resin, characterized in that the lower surface of the light guide plate made of methacrylic resin according to item 1.2 is coated with a high reflectance substance.

I will provide a.

In the present invention, as the methacrylic resin forming the methacrylic resin light guide plate, any resin commonly used in this field can be used. A typical example is one containing 50% by weight or more of methyl methacrylate, preferably 80% by weight or more, such as a copolymer of 95% by weight of methyl methacrylate and 5% by weight of ethyl acrylate. Can be mentioned.

In the methacrylic resin syrup used in the production method of the present invention, the methacrylic resin is one containing methyl methacrylate in an amount of 50% by weight or more, preferably 80% by weight or more, similar to the methacrylic resin described above. % by weight or more, and acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, etc., which can be copolymerized with this, ethyl methacrylate, n-propyl methacrylate, n- methacrylate A methacrylic resin syrup is prepared by dissolving it in a monomer mixture of methacrylic esters such as butyl and 2-ethylhexyl methacrylate, and styrene, acrylonitrile, vinyl acetate, and the like.

In the present invention, the polymerization initiator is an azo- or peroxide-containing compound having a decomposition temperature of 30 to 90°C to obtain a half-life of 10 hours, such as 2,2-azobisisobutyronitrile, benzoyl peroxide. , lauroyl peroxide, etc., more preferably 2,2-azobis(4-methoxy2,4-dimethylvaleronitrile),
A low temperature active polymerization initiator such as cimilistyl peroxydicarbonate is used.

The inorganic filler that can be used in the present invention has a refractive index of 1.4.
~1.6, and has a refractive index different from that of the methacrylic resin, and has a specific gravity of 2.0 or more, preferably 2.3
That's all. Examples include quartz powder, glass peas, calcium carbonate, barium sulfate, fluorite, and the like.

Further, the shape of the particles is preferably close to spherical.

If the refractive index of the filler is equal to the refractive index of the methacrylic resin, the diffusion efficiency will be poor, and conversely, if the difference in refractive index is too large, hiding properties will occur, so the above range is preferable.

Further, the specific gravity of the filler is related to the sedimentation rate, and unless there is a certain degree of difference from the specific gravity of the methacrylic resin syrup, the sedimentation rate of the filler will be slow, so the above range is preferable.

In addition, if the average particle diameter of the inorganic filler is less than 2 μmφ, it will take too long for sedimentation, and if it exceeds 100 μmφ, the sedimentation time will be too fast, making it difficult to control the concentration distribution of the filler. The average particle diameter of the filler is preferably in the range of 2 to 100 μmφ, more preferably in the range of 5 to 50 μmφ.

Here, the average particle diameter refers to the particle diameter corresponding to 50% of the cumulative volume in an integral curve in which the horizontal axis is the particle diameter and the vertical axis is the cumulative volume of particles up to a certain particle diameter. It can be determined using a device such as a counter (Coulter Electronics, Inc., USA).

The inorganic filler has a particle size distribution, and may be within the range of commercially available fillers commonly used in this technical field.

As a typical example, for example, in the case of glass beads with an average particle diameter of 30 μmφ, it contains particles of 1 μmφ or less to 60 μmφ, and the particles of 10 μmφ or less have a cumulative volume of 5.
%, particles with a diameter of 20 μm or less account for a cumulative volume of 15%, 30 μm
Particles with a diameter of φ or less account for 50% of the cumulative volume, and particles with a diameter of 40 um or less account for 80% of the cumulative volume.

In order to achieve the purpose of the present invention, the concentration of the inorganic filler needs to be changed depending on the type of inorganic filler, particle size, thickness and size of the light guide plate, etc. However, if it is used for boat fishing, it is 5
% by weight or less is sufficient.

Next, in the method for manufacturing a methacrylic resin light guide plate, a composition in which a polymerization initiator is dissolved is injected into methacrylic resin syrup in which a methacrylic resin is dissolved, at least one-half of the total volume of the polymerization cell. As can be seen from FIG. 2, the methacrylic resin light guide plate obtained by the present invention has the following characteristics:
This is because only the portion injected with the methacrylic resin syrup or a portion slightly larger than that can be obtained, so it becomes uneconomical to reduce the amount by half or less, and preferably three-fourths or more.

Next, as an example of the present invention, a light guide plate having a concentration gradient as well as a particle size will be described in more detail with reference to the accompanying drawings.

As the particle size becomes smaller, the light diffusion efficiency improves, so it is not necessarily necessary to have a concentration gradient, but a light guide plate without a concentration gradient can also be considered in the same manner as described below.

FIG. 1 shows a cross section of an example of a backlight device using a light guide plate made of methacrylic resin according to the present invention.

In FIG. 1, 1 is a light guide plate made of methacrylic resin, and 3 is an illumination lamp such as a fluorescent lamp. Methacrylic resin light guide plate 1
, inorganic filler particles 2 are dispersed and mixed in a methacrylic resin plate 8, and the average particle diameter is 2 to 10.
0 μmφ and has a refractive index different from the refractive index of methacrylic resin, and the filler with large particle size has a low concentration near the illumination lamp 3, and the filler with small particle size has a high concentration in the far place. It is distributed with a continuous concentration gradient.

Further, on the lower surface 6 of the light emitting surface 5, a reflective layer 4 made of a film of a highly reflective material such as aluminum is provided, and the light emitting surface 5 and the lower surface 6
can be made into a pear background.

The function of the methacrylic resin light guide plate according to the present invention will be explained with reference to FIG.

The light guide plate 1 made of methacrylic resin has a methacrylic resin plate 8 containing an inorganic filler 2 with a large particle size at a low concentration near the illumination lamp 3, and a small concentration of inorganic filler 2 with a small particle size in a place far from the illumination lamp 3. Since the inorganic filler 2 is dispersed and mixed at a high concentration, the light diffusion rate is low near the illumination lamp 3, which has a large amount of light, and the light output rate from the light output surface 5 (=light output amount/light is small) On the other hand, as the distance from the illumination lamp 3 increases and the light intensity decreases, the light diffusion rate increases, so the light output rate from the light output surface 5 increases, and the light output from each part of the light output surface 5 (
- light amount x light output rate) 7 becomes equal.

Further, by providing the reflective layer 4 on the lower surface 6 of the light emitting surface 5, the illumination effect can be enhanced, and the light emitting surface 5 and the lower surface 6
By using a pear-free background, it is possible to further increase the light diffusion efficiency.

FIG. 2 schematically shows, in cross section, an example of a method for manufacturing a light guide plate made of methacrylic resin according to the present invention.

In FIG. 2(a), reference numeral 11 designates a pair of glass plates or metal plates, with a gasket 12 sandwiched between them to form a polymerization cell 15.

In the polymerization cell 15, a methacrylic resin, 50% by weight or more of methyl methacrylate, and an acrylic ester such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, etc., which can be copolymerized with the methacrylic resin, are added. , methacrylic acid esters such as ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, and 2-ethylhexyl methacrylate, and methacrylic resin syrup dissolved in a mixed monomer with styrene, acrylonitrile, vinyl acetate, etc. Composition (A) in which a polymerization initiator is dissolved
After injecting at least three quarters of the total volume of the polymerization cell 15 into the polymerization cell 15, a methacrylic resin syrup with an average particle size of 2
~100 μmφ, a refractive index of 1.4 to 1.6, and a refractive index different from that of methacrylic resin, and a specific gravity of 2.0 or more, preferably 2.3 or more, such as an inorganic filler, e.g. , quartz powder, glass peas, calcium carbonate, barium sulfate, fluorite, etc. 2 and a polymerization initiator were gently injected into the polymerization cell. Polymerize in the upright state to obtain a methacrylic resin light guide plate.

The polymerization temperature varies depending on the polymerization initiator used, but for azo- or peroxide-containing compounds such as 2,2-
Using commonly used polymerization initiators such as azobisisobutyronitrile and benzoyl peroxide,
Polymerize at a temperature of 100°C.

FIG. 2(C) shows the state when the polymerization is completed, and FIG. 2(C) schematically represents an example of the concentration gradient of the inorganic filler.

The concentration gradient of the inorganic filler can be freely changed by changing the specific gravity, average particle size, particle size distribution, shape of the inorganic filler, and the viscosity, polymerization temperature, polymerization rate, wall thickness, etc. of the methacrylic resin syrup.

In the present invention, by adjusting the above conditions, the amount of light emitted from the light emitting surface of the light guide plate (=light amount x light emitting rate) can be adjusted to be substantially uniform over the entire surface of the light emitting surface. . In this case, the uniformity of the amount of light output is that the amount of light output at each point on the light output surface is ±3 with respect to the average value of those points.
It may be within 0%, preferably within ±15%.

The amount of light emitted at each point on the light guide plate is measured by entering light from an illumination lamp such as a fluorescent lamp from the end face of the light guide plate made of methacrylic resin, and using an illuminance meter (Minolta digital illuminance meter T-) at each measurement point.
IM, etc.) was used for measurement.

FIG. 3 shows a method for manufacturing a light guide plate made of methacrylic resin with a pear-shaped surface, in which a polyvinyl alcohol film 16 having a pear-shaped surface is attached to the inside of the polymerization cell 15 explained in FIG. Accordingly, it is possible to easily obtain a methacrylic resin light guide plate having a pear-shaped surface.

In addition, by mixing a small amount of polyfunctional monomers such as ethylene glycol dimethacrylate, neopentyl glycol diacrylate, trimethylpropane trimethacrylate, etc. with methacrylic resin syrup, a crosslinked methacrylic resin light guide plate with excellent heat resistance can be easily obtained. .

Further, by coating the surface 6 of the methacrylic resin light guide plate opposite the light output surface 5 with a highly reflective substance by aluminum vapor deposition or the like, a methacrylic resin light guide plate with improved light diffusion efficiency can be obtained.

〔Example〕

Next, to explain the present invention more specifically with reference to Examples, polymethyl methacrylate 5 having an average molecular weight of 1oooooo
0 g was dissolved in a monomer mixture of 180.5 g of methyl methacrylate and 9.5 g of methyl acrylate to obtain a methacrylic resin syrup, and 2,2-azobis(4-
methoxy-2,4-dimethylvaleronitrile) 0.1
g was added and mixed uniformly while defoaming under vacuum to obtain a composition (A).

Composition (A) was prepared with an inner dimension of 220mm x 140ma+
After injecting into a cell consisting of two glass plates of x 9 mm t and a gasket, a separately prepared sample with an average molecular weight of 100
000 polymethyl methacrylate was dissolved in a mixed monomer of 47.5 g of methyl methacrylate and 2.5 g of methyl acrylate, and 1 g of glass beads with an average particle size of 17 μmφ and 2.2-azobis(4-methoxy -2,
Add 0.03 g of 4-dimethylvaleronitrile) and mix uniformly while degassing under vacuum. After gently injecting and sealing the cell, the cell was placed in a water bath with a temperature controlled temperature of 50°C. Polymerization was performed in an upright state to obtain a methacrylic resin light guide plate.

The obtained methacrylic resin light guide plate had an average particle diameter of 5 μm at the upper part (position approximately 3 cIIl below the upper gasket).
The concentration of glass beads at φ is 0.6% by weight, and the other end (
At a position approximately 3 CIl above the lower gasket, the concentration of glass beads with an average particle size of 22 μm was 0.1% by weight, and the concentration varied continuously in the longitudinal direction.

〔Effect of the invention〕

As explained above, in the methacrylic resin light guide plate of the present invention, the inorganic filler with a large particle size is contained in the methacrylic resin plate at a low concentration near the lighting lamp, and in the area far from the lighting lamp. Because inorganic fillers with small particle diameters are dispersed and mixed at a high concentration, the light diffusion rate is low near lighting lamps that produce a large amount of light, and the light output rate from the light output surface (=light output amount / light amount) is small. On the other hand, as the distance from the illumination lamp decreases, the light diffusion rate increases, so the light output rate from the light output surface increases, and the light output from each part of the light output surface (= light output x light output rate) becomes almost equal. Therefore, the viewing angle can be greatly improved.

In addition, if a reflective layer is provided on the surface under the light emitting surface, this can enhance the lighting effect, and if the light emitting surface and the bottom surface are blank, this can easily further increase the light diffusion efficiency. I can do it.

In addition, when polymerizing with the addition of a polyfunctional polymer, a crosslinked methacrylic resin light guide plate can be obtained, but this material has excellent heat resistance, so an illumination lamp can be brought close to the light guide plate. , it is possible to create a more compact system.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a backlight device using the methacrylic resin light guide plate of the present invention, and FIGS. 2 and 3 are explanatory diagrams of a method for manufacturing the methacrylic resin light guide plate according to the present invention. The explanation of the main symbols is as follows. 1... Methacrylic resin light guide plate, 2...
・Inorganic filler (filler), 3... Illumination lamp, 4... High reflectance material film, 5... Light output surface, 8... Methacrylic resin Board, 11...
・Glass plate or metal plate, 12... Gasket, 13... Composition (B), 14...
・Composition (A), 15... Polymerization cell, 16.
...A polyvinyl alcohol film with a pear-shaped surface on its surface. Patent applicant: Asahi Kasei Industries, Ltd. Figure 2 Figure 3 (b) (c)

Claims (2)

[Claims] (1) The average particle diameter is 2 to 100 μmφ, and the refractive index is 1.
4 to 1.6, and has a refractive index different from the refractive index of the methacrylic resin, and has a specific gravity of 2.0 or more,
The filler having a large particle size is dispersed near the illumination lamp disposed on the end surface of the light guide plate, and the filler having a small particle size is dispersed at a place far from the illumination lamp, so that the amount of light emitted is substantially distributed over the entire light emitting surface. A methacrylic resin light guide plate characterized by uniformity in (2) After pouring a composition in which a polymerization initiator is dissolved into methacrylic resin syrup containing methacrylic resin dissolved therein, at least one half of the total volume of the polymerization cell is poured, and then the methacrylic resin is poured into the remaining part of the polymerization cell. Dissolved into methacrylic resin syrup with an average particle diameter of 2 to 100 μmφ and a refractive index of 1.4.
~ 1.6, and has a refractive index different from the refractive index of the methacrylic resin, and a composition in which an inorganic filler and a polymerization initiator having a specific gravity of 2.0 or more are uniformly mixed is formed into a layer. The method for manufacturing a methacrylic resin light guide plate according to claim 1, characterized in that the polymerization is carried out with the polymerization cell in an upright state.