JP3410608B2 - Manufacturing method of light guide - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a light guide for a backlight used in a liquid crystal display device or the like, and a light guide having a surface provided with unevenness for scattering or reflecting light. The present invention relates to a method that can be efficiently manufactured.

[0002]

2. Description of the Related Art A light guide used for a backlight of a surface light source device used for a liquid crystal display device or the like generally has an emission surface and a surface facing the emission surface. At least one of these surfaces has an element that changes the angle of light transmitted through the light guide body or the angle of light reflected by the light guide body (hereinafter, this is referred to as a "deflection element". The deflecting element can also be referred to as "scattering / reflecting means" in that it scatters light or reflects light.).
The light that has entered the light guide body from the end surface is changed in its direction at the emission surface or the surface facing it and then emitted from the emission surface, or is totally reflected by these surfaces and propagates in the light guide body. Here, the distribution density of the deflection elements or the angle deflected by the deflection elements is often determined so that the brightness of the emitted light is uniform over the entire surface of the light guide.

As the above-mentioned deflecting element, a light guide surface coated with a substance that scatters or reflects light, and a light guide surface provided with an uneven shape for scattering or reflecting light, The light guide contains a light diffusing agent. For the light guide of this type, a resin (paint or the like) containing a light diffusing agent or a resin having a refractive index different from the material of the base material of the light guide may be applied to the surface of the light guide. It is common. With respect to this type of light guide, there are a light guide whose surface is roughened and a light guide whose surface is provided with regular irregularities. The planar shape of the concavities and convexities provided on the surface of the light guide may be a line shape, a dot shape, or the like, and the cross-sectional shape thereof may be a rectangular shape, a trapezoidal shape, a triangular shape, a part of a circle, or the like. Regarding the type of light guide of (3), a light diffusing agent composed of resin or glass micro beads having a refractive index different from that of the material of the base of the light guide is often dispersed in the base of the light guide. . Hereinafter, in the present specification, a set of deflecting elements whose distribution density is changed according to a predetermined relational expression is referred to as a “deflecting pattern” for the purpose of making the distribution of luminance on the exit surface of the light guide uniform.

By the way, the light guide of this type is generally manufactured by a screen printing method. This type of light guide is generally manufactured by an etching method, a sandblast method, a machining method, or the like. Further, a large number of resin light guides are often duplicated by injection molding or the like using a stamper provided with a deflection element by a mechanical processing method. Further, the light guide body of the type is generally manufactured by mixing glass beads or the like in a resin material forming a base material of the light guide body and molding the resin using the resin.

[0005]

Regarding the method of manufacturing a light guide body of the type described above, the reproducibility of a fine shape is low due to the characteristics of the manufacturing method called screen printing, and a fine pattern having a width or pitch of 100 microns or less is used. It is virtually impossible to provide a deflecting element (see Japanese Patent Laid-Open No. 3-68923). Therefore, when a deflection element having a distribution density according to a predetermined relational expression is to be provided, the lower limit of the pitch of the deflection element is limited to 100 μm or more as described above, and the upper limit of the pitch of the deflection element is limited. Size 1
It may be over mm. At this time, in the portion where the pitch of the deflection elements is large, the deflection pattern itself is recognized as a bright and dark pattern, and uniform illumination light cannot be obtained. Further, the pitch of the deflecting element and the pitch of the prism sheet or the pixel pitch of the liquid crystal display device may interfere with each other to cause moire, and the image quality of the liquid crystal display device may be deteriorated (Japanese Patent Laid-Open No. 5-257144). Or refer to Japanese Patent Laid-Open No. 5-313017). That is, if an attempt is made to form the deflection pattern of the light guide by the screen printing method, the desired optical performance may not be obtained.

Further, in the method of manufacturing a light guide body of the type (1), it is generally difficult to machine a fine deflection element with high precision by a mechanical processing method, and desired optical performance may not be obtained. is there. Since it is used for manufacturing light guides by injection molding, etc., when machining a deflection pattern on a stamper by machine cutting, due to the limit of positioning accuracy of the processing tool and wear of the processing tool, many of the accurate shapes as designed It is difficult to provide fine deflection elements so as to have a distribution density according to a predetermined relational expression. In particular, if the light guide has a large area, it is very difficult to process it. If the processing accuracy is low, the deflection characteristics as designed may not be obtained, and the high luminance that is first required for backlight performance may not be obtained. Further, since the minimum dimensional value that can be processed is large, the size of one deflection element must be several hundreds of microns or more. However, if the size of one deflecting element is several hundreds of microns or more, there arises a disadvantage that the deflection pattern looks like uneven brightness as in the case of the above-mentioned type of light guide.

Further, regarding the method of manufacturing a light guide body of the type (1), even if a deflecting element is provided so as to have a distribution density according to a predetermined relational expression, the light diffusing agent is highly reproducibly contained in the substrate. There is a problem that it is very difficult to disperse.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a light guide body which has a uniform distribution of emitted light and is suitable for use in a large-area backlight. An object of the present invention is to provide a method of efficiently manufacturing with processing accuracy.

[0009]

A method of manufacturing a light guide according to the present invention, which solves the above-mentioned problems, has a flat base material of 5 to 50 μm.
Fine uneven cross section by a method including a step of forming a photoresist layer having a thickness of, a step of exposing the photoresist, a step of developing the exposed photoresist, a step of making the surface of the photoresist conductive, and an electroforming step. It is characterized in that a light guide is obtained by producing a stamper having a shaped surface and molding using the stamper. Also books
The method for manufacturing a light guide according to the present invention has a viscosity of 200 on a flat substrate.
With photoresist in the range of ~ 1200 cps
By spin coating, the thickness of the film is 5 to 30 μm.
Step of forming photoresist layer, exposing photoresist
The step of developing, the step of developing the exposed photoresist,
Process for making the surface of photoresist conductive and electroforming process
A stamper having a surface with a fine uneven cross-sectional shape
By making and molding using the stamper.
The feature is to obtain a light guide. Furthermore, the guidance of the present invention
The method of manufacturing an optical body is as follows.
20 to 50 μm by heating and attaching a gyst
Of photoresist layer with different thickness
Stroke exposure process, developing exposed photoresist
And the step of making the surface of the photoresist conductive.
The method including the electroforming process has a surface with a fine uneven cross-sectional shape.
One stamper is manufactured and molded using the stamper.
It is characterized in that a light guide is obtained by doing so.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a light guide according to the present invention will be described with reference to FIG.
Will be described in more detail. As the base material (10) in FIG. 3 (a), a glass plate or a metal plate whose surface is polished to improve its flatness is generally used. A photoresist layer (9) is formed on the surface of the base material as shown in FIG.
To form. As a method for forming the photoresist layer, spin coating, dip coating, roll coating, electrodeposition,
There is a method of attaching a film-like photoresist while heating, but any method may be used as long as it can form a film having a uniform thickness over the entire surface.

The height of the deflection element is determined by the thickness of the photoresist layer. In order to realize high brightness, the deflection pattern is recognized as a bright and dark pattern, and to prevent moire from occurring, it is important to obtain the deflection element height as designed. However, while the height of the pits in an optical disk such as an LD or a CD is about 0.1 μm, the height of the deflection element is generally extremely large, and a photoresist layer having a thickness suitable for forming the deflection element is obtained. Is difficult. To provide the deflection element, the viscosity should be 200-120.
It is preferable to spin coat using a photoresist in the range of 0 cps to form a photoresist layer having a thickness of 5 to 30 μm. It is also preferable to form a photoresist layer having a thickness of 20 to 50 μm by sticking a film-shaped photoresist (so-called dry film resist) while heating. There are positive type and negative type photoresists, but the type is not limited in the present invention. When exposing a photoresist using a photomask, if a positive photoresist and a negative photoresist are used,
Using one photomask, two types of stampers having deflecting elements with opposite concavities and convexities can be manufactured. As a positive type photoresist, P manufactured by Tokyo Ohka Kogyo Co., Ltd.
MER P-AR900, PMER P-AR300 series and the like can be used, and as a negative type photoresist, BMER C-10 manufactured by Tokyo Ohka Kogyo Co., Ltd.
00 or the like can be used. Examples of the dry film resist include VANX A-900 series and A manufactured by Fuji Hunt Electronics Technology Co., Ltd.
-800 series, A-600 series and U-12
0 and ORDYL α-430 manufactured by Tokyo Ohka Kogyo Co., Ltd.
T and ORDYL α-450T can be used.

By the way, the brightness distribution of the light guide can be adjusted by changing the film thickness of the photoresist applied on the substrate. That is, when the uniformity of the luminance distribution of the light guide manufactured experimentally by the method of the present invention (which is the value obtained by dividing the minimum luminance by the maximum luminance) is not sufficiently high, the photoresist to be applied is By changing the film thickness, the height of the deflection element can be easily changed, and a light guide body having a uniform brightness distribution with a higher degree of uniformity can be obtained without redesigning the deflection element. Therefore, the light guide size can be efficiently optimized at the trial stage of the light guide, and the light guide size can be easily finely adjusted at the mass production stage.

Next, the deflection pattern is exposed on the photoresist on the substrate. At this time, as shown in FIG. 3B, a photomask (11) is overlaid on the photoresist layer and the whole is exposed by parallel rays at once, or a pattern is directly formed on the photoresist using a light beam or the like. There is a way to draw. The former is for preparing a photomask in which a deflection pattern is drawn in advance, which is advantageous when a plurality of stampers having the same pattern is manufactured, and the latter is suitable for manufacturing only one stamper having the same pattern. The deflection pattern may have any shape such as dots and lines.
When a photomask is used, the width of the pattern on the photomask may not match the width of the deflecting element of the photoresist after development, depending on the conditions in the steps from exposure to development. In this case, the width of the photomask pattern may be determined in a direction in which the change in the width of the deflecting element after development is taken into consideration. Further, ultraviolet rays are generally used as light when exposing using a photomask, and it is desirable to use an equipment that emits rays that are as parallel as possible. Further, in the case of direct drawing, it is general to use a laser beam or an electron beam.

In the above-mentioned exposure method, the deflection element generally has a rectangular cross section (FIG. 4A) or trapezoid (FIG. 4B) having a constant height. In the case of the mask exposure method, the boundary portion between the exposed portion and the unexposed portion is widened by exposing the resist surface at a minute distance from the resist surface without adhering the photomask, and the side surface of the deflection element having a trapezoidal cross section is formed. The inclination angle and the roundness of the corners of the deflection element can be changed (FIG. 4 (c)). By irradiating the light beam at the time of exposure obliquely from above the right or left side of the base material, it is possible to obtain a deflecting element having a left-right asymmetric cross-sectional shape in which the angles of the side surfaces with respect to the bottom surface of the deflecting element are different. In addition, after exposing once with a light amount of 1/2 of a predetermined exposure amount, the substrate is rotated by 180 ° together with the photomask to obtain a half of the predetermined exposure amount.
It is possible to obtain the deflection element having two kinds of cross-sectional shapes by exposing again with the light amount of.

On the other hand, in the method of exposing by directly drawing with a light beam or the like, the focus of the light beam spot condensed on the photoresist surface is shifted by a minute amount (that is, the focus is blurred). The tilt angle of the side surface and the roundness of the corners of the deflecting element in the deflecting element having the trapezoidal cross-sectional shape can be changed according to the configuration (FIG. 4).
(C)). By selecting conditions such as using non-parallel light rays for exposure, a sinusoidal cross-sectional shape (Fig. 4
(E)) can also be obtained. By adjusting the exposure conditions in this way, it becomes possible to adjust the deflection performance of the deflection element, and it is also possible to improve the transferability during molding. The above-mentioned adjustment of the cross-sectional shape can also be realized by changing the conditions such as the concentration of the developing solution, the developing temperature and the developing time in the developing process. In addition, a heat treatment process is added between the development process and the surface conduction process to deform the cross-sectional shape of the photoresist remaining after the development process, thereby forming a cross-sectional shape such as a part of a circle (FIG. 4D). ) Can be obtained.

If the photoresist used in the present invention is a positive type, the exposed portion (12) of the photoresist layer is removed in the developing step and the unexposed portion (13) as shown in FIG. 3 (c). ) Remains, a deflection pattern appears. On the other hand, in the case of a negative photoresist, the unexposed portion is removed, and the exposed portion remains. As a developing method, a dipping method, a paddle method, a shower method, or the like, which is performed using a predetermined developing solution, is generally used.

After development, a metal film is provided on the surface of the resist by vapor deposition, sputtering, electroless plating or the like to make it conductive (FIG. 3 (d)), and the stamper (16) is formed by electroforming.
Is obtained (FIG. 3 (e), FIG. 3 (f)). In some cases, after the electroforming, the surface of the stamper is subjected to a peeling treatment, and then the electroforming treatment is performed again to obtain a duplicate stamper having a deflection pattern in which unevenness is reversed from that of the first stamper. Furthermore, by electroforming using this duplicate stamper, it is possible to obtain a plurality of duplicate stampers having the same uneven deflection pattern as the first stamper.

If the back surface of the stamper produced by electroforming is rough, it is polished and flattened, and the outer shape is processed to a required size to obtain a stamper for molding. Injection molding, press molding, 2P (Ph
It is possible to obtain a large amount of light guides on which the concavo-convex pattern is precisely transferred by performing oto-polymer molding or the like.

By a method such as etching or sandblasting, the flat surface of the base material to which the photoresist is applied is roughened so as to have a concavo-convex structure smaller than the deflection element, and the base material having this rough surface is coated with the photoresist. Then, by applying the same treatment as described above, the fine roughness of the substrate is transferred to the light guide, and the top or bottom of the deflecting element is manufactured to have a satin-finished light guide. You can

Depending on the conventional machining, even with the precision processing technique using the diamond bite, the precise and minute deflection element required for the light guide cannot be obtained, and the light utilization efficiency is sufficiently improved. Could not be improved. However, as described above, by applying the photolithography technique used for forming fine uneven patterns with high accuracy in the manufacturing process of optical discs, semiconductors, etc., a light guide body having high and uniform brightness can be obtained. It is possible to form a fine concavo-convex pattern required for obtaining. Further, according to the present invention, the height of the irregularities in the deflection element of the light guide can be controlled by the film thickness of the photoresist, and the height of each deflection element can be made constant.

[0021]

EXAMPLES Examples of a liquid crystal display device using a light guide manufactured by the method of the present invention will be specifically described below.

A light guide used for a backlight of a surface light source device used in a liquid crystal display device or the like has a flat light emitting surface and a surface having a deflecting element facing the flat light emitting surface. The light is reflected and deflected by the deflecting element, and the density is generally distributed over the entire surface of the light guide body by providing a gradient according to a predetermined relational expression to the density of the deflecting elements. is there. FIG. 1 shows a side view of a typical single-lamp edge-light type backlight and a liquid crystal display device. A linear lamp is used as the light source (2), and the lamp is placed at the focal position of the reflecting mirror (3) having a semicircular shape or a parabolic shape. The light guide (1) is generally a transparent plate-like object having a rectangular cross section. Recently, a tapered cross-sectional shape is often adopted to reduce the weight. A diffusion sheet (6) is disposed on the upper side (emission surface side) of the light guide for the purpose of evenly distributing the light, and a prism sheet (for deflecting the light so that the light is substantially vertical) 7) is arranged. Incidentally, recently, in order to improve the luminance in the vertical direction, it has become common to arrange two prism sheets so as to be orthogonal to each other. A deflection element (5) is provided on the lower surface of the light guide body so that the light incident from the end surface is emitted from the upper surface. A gradient is given to the distribution density of the deflecting elements in order to make the emission amount uniform from the side closer to the light source to the side farther from the light source. Generally, the density of the deflection elements on the side closer to the light source is reduced, and the density of the deflection elements on the side farther from the light source is increased. Further, the density is partially changed, and the correction is performed to make the brightness of the entire surface uniform. A deflection sheet (4) is arranged below the light guide body to reflect the light emitted to the lower side back to the light guide body side. The above structure serves as a backlight and is placed behind the liquid crystal display panel (8). FIG. 2 shows an example in which the distribution density of the deflection elements is given a gradient (FIG. 2 (a)). Top of surface (side away from light source)
2 has a high density distribution as shown in FIG. 2B, and has a low density distribution at the lower end (light source side) as shown in FIG. 2C.

The method of manufacturing the light guide according to the present invention will be described in detail below. A case of using a glass base material, a positive photoresist and a photomask will be described. On a circular glass substrate with a diameter of 350 mm and a thickness of 5 mm, a positive photoresist for thick film (with a viscosity of 90
It is 0 cps. Was spin-coated to a thickness of 20 μm. After prebaking, overlay a photomask with a diagonal size of 10.4 inches and a deflection pattern with a gradient in the distribution density of the deflection elements on top of this, and specify it by the photoresist maker with a mask exposure device. It was exposed to the desired light intensity. For a photomask, a glass plate is coated with an emulsion in which silver chloride particles are dispersed, and CA
The pattern image produced in D was applied by the general method of reducing and printing by applying the principle of photography. A predetermined developer suitable for this positive photoresist was used, and development was performed by the dip method to obtain a master with a pattern of deflection elements. In this master, the photoresist remaining after development had a substantially rectangular or trapezoidal cross section. Tens of nm on the surface of this master
A nickel film was provided by a sputtering method so as to have a thickness of about 3 μm to form a conductive film. Next, the thickness of the nickel film is 3
After nickel electroforming to a thickness of 00 μm, the photoresist remaining on the surface was removed, the back surface was polished, and the outer shape was processed to obtain a stamper. Injection molding was carried out using this stamper to obtain a light guide body having a deflection element composed of fine irregularities on one surface. The dimensions are such that the diagonal of the effective area of the deflection pattern portion is 10.4 inches, the thickness of the end portion on the light incident side is 3.0 mm, and the thickness of the end portion on the opposite side is 1. It is 1 mm. When evaluating the performance of the light guide, a white scattering sheet, 3.0 m
An m diameter cold cathode tube, a diffusion sheet and a prism sheet were used. The measuring instrument is a luminance meter (type: B
M-7) was used under the conditions of a measurement distance of 500 mm and a measurement angle of 1 degree. The luminance distribution in the light guide obtained by this manufacturing method (indicated by A in the figure) and the luminance distribution in the conventional light guide in which dots of white scatterers are provided by the screen printing method (B in the figure)
5) is shown in FIG. It is clear from FIG. 5 that the present invention provides a light guide with high brightness.

Next, the result of measuring the relationship between the film thickness of the photoresist and the uniformity in the above embodiment will be described. FIG. 6 shows the results of measuring the luminance distribution of the light guide (the measuring machine and the measuring method are the same as above). The luminance distributions when the film thickness of the photoresist is 12 μm, 10 μm and 17 μm are shown by A, B and C in FIG. 6, respectively. When the uniformity ratio is obtained from the measurement results, as shown by B in the figure, when the film thickness is 10 μm, the uniformity ratio is low at 74%, but when the photoresist film thickness is 12 μm, it is indicated by A in the figure. Thus, the uniformity was improved to 84%. Further, when the film thickness of the photoresist was set to 17 μm, the uniformity was deteriorated to 43%, as shown by C in the figure.

[0025]

According to the present invention, it is possible to efficiently manufacture a light guide body, which has a uniform distribution of emitted light and is suitable for a large-area backlight, with high processing accuracy.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a general configuration of an edge light type backlight.

FIG. 2 is a plan view of an example of a deflection pattern.

FIG. 3 is an explanatory view of a method for manufacturing a stamper for a light guide according to the present invention.

FIG. 4 shows an enlarged cross section of an example of a deflection element.

FIG. 5 shows a brightness measurement result A of a light guide manufactured by the method shown in the embodiment of the present invention and a brightness measurement result B of a light guide having a conventional dot-printed deflection element. It is a figure.

FIG. 6 is a diagram showing the results of luminance measurement when the photoresist film thickness was changed in the example of the present invention.

[Explanation of symbols]

1 ... Light guide 2 ... Light source (cold cathode tube) 3 ... Reflector 4 ... Scatter reflection sheet 5 Deflection element (deflection pattern) 6 ... diffusion sheet 7 ... Prism sheet 8 ... Liquid crystal display board

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-250179 (JP, A) JP-A-6-118245 (JP, A) JP-A-5-60920 (JP, A) JP-A-4- 229211 (JP, A) JP 4-52286 (JP, A) JP 3-198003 (JP, A) JP 6-88254 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00 331 B29C 33/38 F21V 8/00 601 G02F 1/13357

Claims (6)

(57) [Claims] 1. A step of forming a photoresist layer having a thickness of 5 to 50 μm on a flat substrate, a step of exposing a photoresist, a step of developing the exposed photoresist, a surface of the photoresist. A light guide body, characterized in that a light guide body is obtained by producing a stamper having a surface with a fine uneven cross-sectional shape by a method including a step of making conductive and an electroforming step, and molding the stamper using the stamper. Manufacturing method. 2. A flat base material having a viscosity of 200 to 1200 c.
Spin coating with photoresist in the ps range
Thereby forming a photoresist layer having a thickness of 5 to 30 μm , exposing the photoresist, developing the exposed photoresist, making the surface of the photoresist electrically conductive, and electroforming. By the method, a stamper having a surface with a fine uneven cross-sectional shape is produced,
A method for manufacturing a light guide, comprising obtaining the light guide by molding using the stamper. 3. A film-shaped photoresist on a flat base material.
The thickness of 20-50 μm
Forming a a photoresist layer, exposing the photoresist, a step of developing the exposed photoresist, the minute uneven cross-sectional shape by a method comprising a step and electroforming process to electric conductivity of the surface of the photoresist A method for producing a light guide, comprising producing a stamper having a surface and molding the stamper to obtain a light guide. 4. The conductor according to claim 1, wherein the photoresist layer is formed using a flat base material having a surface roughened in advance to have irregularities smaller than the fine irregularities. Manufacturing method of optical body. 5. The method of exposing a photoresist coated on a substrate by a mask exposure method, wherein the photoresist and the photoresist surface are separated by a minute distance.
5. The method for manufacturing a light guide body according to any one of items 4 to 4. 6. The light guide according to claim 1, wherein a heat treatment is applied between the developing step and the surface electroconducting step to deform the fine uneven sectional shape of the photoresist. Production method.