KR100328106B1 - lightguide - Google Patents

Abstract

As the light guide 3 for guiding light from one or more side cross-sections, a substantially ladder-shaped convex pattern in which a convex top edge is partially in a cross section orthogonal to the axis of the linear light source has a luminance of the emitted light from the exit surface. The parts near the linear light source are low density, the parts far away are high density, and a plurality of spots, solid lines or dashed lines are arranged on the inner surface opposite to the light exit surface so that the distribution becomes roughly uniform. Here, the convex pattern has an approximately ladder shape in which two angles corresponding to both ends of the convex top edge in the cross section orthogonal to the axis of the linear light source have a substantially ladder shape, and constitutes the convex top edge in the convex pattern. When the surface roughness of the surface and the surface roughness of the surface on which the convex pattern is not formed among the convex pattern forming surfaces are each 0.2 μm or less, and the cross-sectional width of the convex pattern is represented by (W) and the height (H), respectively. It is preferable that the ratio of H / W is 0.1≤H / W≤0.6, and that the cross-sectional width (W; mu m) of the convex pattern is 20≤W≤200, respectively.

Description

Light guide {lightguide}

BACKGROUND ART A surface light source device having a so-called edge light type light guide, which is incident from a side end surface of a transparent plate and emits light from one surface (light exit surface), is illuminated by a word processor, a personal computer, It is used as a back lighting device of a liquid crystal display device installed in a thin television or the like. As such a surface light source device, generally, a tubular light source is disposed on one side cross-section of a light guide, two orthogonal side cross-sections, or two side cross-sections facing each other, so that the incident side cross-section and the light exit surface are arranged. It is comprised so that a light reflection body may cover the surface which the light guide body except for this left, and the inside of a tubular light source.

In order to uniformly and efficiently emit the primary light incident from the side end face of the light guide from the entire light exit surface of the light guide, when scattering and reflecting the light guided to the light guide in the direction perpendicular to the traveling direction, It is necessary to make the scattering reflecting ability low and to increase the diffuse reflecting ability of the part farthest from the light source, and to distribute most of the incident primary light from the emitting surface. Principles for providing scattering reflecting ability and processing methods thereof have been proposed in various ways as follows, and some of them have been put into practical use.

① mainly made up of rough surface

Roughening the entire light exit surface of the light guide or the entire opposite surface (see Japanese Patent Application Laid-Open No. 3-118593, Japanese Patent Application Laid-open No. Hei 6-118248, etc.) or varying the roughness of the light guide 63-168604, etc.), or a spot or linear roughening pattern formed by changing the area density thereof (see Japanese Patent Laid-Open No. 4-162002, etc.). The roughening method is performed by sandblasting or chemical etching of a mold, and the roughening pattern formation method is performed by the combination of photoetching and sandblasting (refer to Unexamined-Japanese-Patent No. 4-52286).

② Applying a scattering reflector

Scattered reflecting material containing white paint or fine particles in the form of dots or linear patterns on the inner surface facing the light exit surface (Japanese Patent Laid-Open No. 57-12838, Japanese Patent Laid-Open No. 1- 245220, etc.), the manufacturing process consists of two steps, a molding process of a mirrorless plate without a pattern and a pattern printing process.

③ mainly dealing with bulk diffusion

Making the light guide bulk resin itself a light diffusing scatterer by mixing light diffusing fine particles, mixing or copolymerizing incompatible polymers (Japanese Patent Application Laid-Open No. 1-172801, Japanese Patent Laid-Open No. 2-221924, Japanese Patent Laid-Open No. 5) 249319, Japanese Patent Laid-Open No. 6-186560, etc.) are disclosed.

④ by uneven pattern

It is largely divided into the following three types. The manufacturing method is to process the light guide itself or the molding die by machine cutting, laser processing, mold etching or the like.

1) concave pattern

Some concave patterns are arranged on the exit surface or on the opposite surface with respect to the plane. For example, one-dimensional linear triangular grooves (see Japanese Patent Laid-Open No. 2-165504, Japanese Patent Laid-Open No. 6-3526), and rectangular grooves (Japanese Patent Laid-Open No. 6-123810, Japanese Patent Laid-Open No. 6-265731). See Japanese Patent Application Laid-Open No. 5), a semicircular groove (see Japanese Patent Application Laid-Open No. 5-79537), and a broken triangular groove (see Japanese Patent Application Laid-Open No. 5-196936, Japanese Patent Laid-Open Publication No. 5-216030, etc.). Cone or pyramidal sculpture of two-dimensional shape (see Japanese Patent Application Laid-Open No. 4-278922), hemispherical sculpture (see Japanese Patent Application Laid-open No. Hei 6-289393, etc.) There is this. Moreover, what roughened the inner surface of the pattern recessed part (refer Unexamined-Japanese-Patent No. 4-355408, Unexamined-Japanese-Patent No. 5-94802, etc.) is also proposed.

2) convex pattern

The convex pattern is arrange | positioned based on a plane at the exit surface or the opposite surface. For example, one-dimensional linear triangular convex (see Japanese Patent Application Laid-Open No. 5-313163, Japanese Patent Laid-Open Publication No. 6-75123), rectangular convex (see Japanese Patent Application Laid-Open No. 5-79537), semicircular convex (Japanese Patent) See Publication 6-281928. Moreover, as a two-dimensional shape, there exist hemispherical convex (refer Unexamined-Japanese-Patent No. 5-79537, Unexamined-Japanese-Patent No. 6-281929, etc.). There are also those in which these convex portions are roughened (see Japanese Patent Application Laid-open No. Hei 5-94802, Japanese Patent Laid-Open No. 6-186562, etc.).

3) uneven pattern

There exists a plane which has one-dimensional saw-shaped pattern or two-dimensional grid | lattice-shaped pattern, without having a plane on an exit surface or the opposite surface. For example, one-dimensional saw shapes (see Japanese Patent Application Laid-Open No. 64-11203, Japanese Patent Application Laid-Open No. 6-250024, etc.), Two-dimensional lattice shapes (Japanese Patent Application Laid-Open No. 62-278505, Japanese Patent Laid-Open No. 3-) 189679, etc.), and also roughened the whole (see Japanese Patent Laid-Open No. 6-342159 and Japanese Patent Laid-Open No. 6-123885).

In addition to the demands for high brightness and high uniformity in the past, in recent years, the demand for large screen, thin, light weight, and low power consumption is gradually increasing. From the flat light guide, which has been practically used as a main body, to a thinner, lighter, tapered light guide, the technique of ② is unnecessary, and the required pattern printing process is unnecessary, and the injection molding method can simultaneously form scattering reflection patterns. This cost is said to be preferable.

From this point of view, the above methods 1 to 4 each have the following problems.

The same rough surface of ① can be mass-produced by an injection molding method using a mold, but in order to achieve uniform luminance as a surface light source, a complicated curved comb-like shape such as thickening the primary light source incident part sufficiently and thinning the far side of the light source. Since the mold has to be complicated, there is a difficulty in that the mold is complicated, the degree of freedom in the shape of the light guide is limited, and in principle, there is a limit in thinning the light guide in a large area. Moreover, although there are proposals to change the roughness, it is difficult to realize. On the other hand, the method of distributing the rough surface into spots or linear patterns is a relatively excellent method of freeing the shape of the light guide and achieving a uniform brightness in the pattern design. The risks are high due to instability during mold making, such as unevenness in pattern formation precision and roughening treatment such as blasting in subsequent processes.

The printing method by ② is the most practical method in the conventional flat type light guide, but the first problem is that there is no cost advantage compared to the method of simultaneously forming the pattern by the injection molding method because the pattern printing is a different process. . Further, due to the limitation of printing accuracy (see Japanese Patent Laid-Open No. 4-289822), the dot pitch of the scattering reflection pattern cannot be made smaller than about 1 mm (see Japanese Patent Laid-Open No. 5-100118). In addition, the problem of the printing accuracy causes a low reproducibility of the minimum point and the minimum line when printing patterns, resulting in a decrease in productivity and cost increase (see Japanese Patent Laid-Open No. 3-9304 and Japanese Patent Laid-Open No. 4-278922). ). In addition, in terms of performance, since the pattern is rough, a local contrast difference occurs in a portion with and without a pattern, and a luminance unevenness is caused. Therefore, a diffusion plate or a diffusion sheet having a high diffusion efficiency is provided on the light guide surface. It is common practice to equalize local luminance unevenness due to pattern roughness. However, a diffusion plate or a diffusion sheet having a high diffusion efficiency has a low total light transmittance, which causes loss of brightness (see Japanese Patent Laid-Open No. 5-100118 and Japanese Patent Laid-Open No. 6-265732).

When the rough pattern is arranged regularly, moiré pattern occurs between the prism sheet and the liquid crystal panel arranged for the purpose of increasing the luminance in the direction perpendicular to the light guide exit surface due to such local luminance unevenness. . In order to prevent this, the pattern spacing is irregularly arranged (see Japanese Patent Application Laid-Open No. 5-313017, Japanese Patent Application Laid-open No. 6-242442), or the ridge direction of the prism sheet is inclined with respect to the pattern arrangement direction (Japan). Although Japanese Patent Laid-Open No. 5-257144 and Japanese Patent Laid-Open No. 6-230228 are proposed), design and assembly become difficult.

3) can be mass-produced by the injection molding method and the like, and in principle, it is expected that there is no local luminance unevenness due to the pattern, but it is considered difficult to achieve uniform luminance only in the bulk scattering direction. Moreover, it is not easy to distribute light diffusion performance to the light guide bulk itself, and mass production is difficult. In addition, in order to realize uniform luminance with a resin material in which a homogeneous diffusing agent is distributed, it is necessary to change the thickness of the tapered shape or the like, or to form an uneven pattern, so that it is necessary to use other means of achieving uniformity in brightness. It may become complicated, or the restriction to the shape of the light guide may be a big problem.

④ is an excellent method for mass production on the premise of press method or injection molding method. As means for achieving the uneven pattern, mechanical cutting, laser processing, chemical etching and the like are disclosed. However, in any of the processing methods, the pattern area precision, the dimensional accuracy, and the roughness of the pattern forming surface, the larger the area of the fine pattern, the greater the difficulty in processing stability, reproducibility, and cost, and the greater the risk. What has been put to practical use so far is a small light guide having a size of several inches, and the pitch of the pattern is also about 1 mm, which cannot be avoided from the problem of the roughness of the pattern in?. In addition, even when a relatively large uneven surface is formed and the uneven surface is roughened again, unevenness of roughening treatment is added to the problem of uneven surface formation accuracy, resulting in instability in mold making, and therefore, in terms of cost for mold production. A problem arises.

SUMMARY OF THE INVENTION An object of the present invention is to provide a uniform, thin, large-area light guide without causing local luminance unevenness or luminance unevenness of the entire light emitting surface by efficiently emitting primary light incident on the light guide from the exit surface. have.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a light guide for a surface light source used in a liquid crystal display device and the like, and the light guide of the present invention can be effectively used as a back lighting device of a liquid crystal display device such as a word processor, a personal computer and a thin television.

1 is a configuration example of a lighting apparatus using the light guide of the edge light method according to the present invention.

2 is a partially enlarged explanatory view of an edge light guide according to the present invention.

3 is a classification diagram of scattered reflected light whose cross section is a ladder-shaped convex pattern.

4 is an explanatory diagram of a ray trace simulation in which a cross section is a ladder-shaped convex pattern.

5 is a diagram showing a calculation result of a ray tracing simulation having a rectangular convex pattern in cross section.

FIG. 6 is a view showing a calculation result of a ray tracing simulation having a ladder-shaped convex pattern in cross section. FIG.

7 is a view showing a calculation result of the ray tracing simulation in which the cross section is a ladder-shaped convex pattern.

FIG. 8 is a diagram showing a calculation result of a ray tracing simulation having a ladder-shaped convex pattern in cross section. FIG.

9 is a view showing a calculation result of the ray tracing simulation in which the cross section is a ladder-shaped convex pattern.

FIG. 10 is a view showing a calculation result of a ray tracing simulation having a ladder-shaped convex pattern in cross section. FIG.

Fig. 11 is a view showing the calculation result of the ray tracing simulation in which the cross section is a ladder-shaped convex pattern.

It is a figure explanatory drawing of the convex pattern of ladder shape with round cross section.

It is explanatory drawing of the metal mold | die manufacturing method of the cross-sectional convex pattern using photolithography.

Fig. 14 is an explanatory view of ray tracing of a light guide having a ladder-shaped concave pattern in cross section.

15 is a diagram showing an example of the pattern design of the light guide according to the present invention.

In order to achieve the above object, the light guide of the present invention has the following features.

In other words, a light guide for guiding light from one or more side cross-sections, wherein a generally ladder-shaped convex pattern having a convex top edge partially in a cross section orthogonal to the axis of the linear light source has a luminance of the emitted light from the exit surface. The portion near the linear light source is low density so that the distribution is substantially uniform, and the distant portion is high density and is arranged on the inner surface opposite to the light exit surface in spot, solid, or dashed lines. Here, the convex pattern has a substantially ladder-like shape in which two angles corresponding to both ends of the convex top edge in a cross section orthogonal to the axis of the linear light source have a ladder shape, and constitute the convex top edge in the convex pattern. The surface roughness of the surface to be formed and the surface roughness of the surface where the convex pattern is not formed on the convex pattern forming surface are each 0.2 μm or less, and the cross-sectional width of the convex pattern is (W) and the height is (H), respectively. When it shows, it is preferable that ratio of H / W is 0.1 <= H / W <= 0.6, and the cross-sectional width (W; micrometer) of a convex pattern is 20 <= W <= 200, respectively.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

Fig. 1 is an embodiment of the present invention, in which Fig. 1 (a) is a cross-sectional view of a cross section orthogonal to the axis of a linear primary light source, in which the inner surface on the opposite side of the light exit surface 3c of the light guide 3 is scattered. The ladder-shaped convex pattern 3a, which has the reflective surfaces 3a and 3b, and whose convex top edge partly has a straight portion, is formed at a low density at a portion close to the primary light source 1 and at a high density at a distant place. It is. The arrangement of the light source is not limited to the first equation, it may be possible to use the two equations arranged to face each other, or the light may be guided from two orthogonal cross sections using an L-shaped light source. Moreover, the reflecting plate or the reflecting sheet 4 is arrange | positioned through the air layer 7 on the scattering reflection surfaces 3a and 3b. Fig. 1 (b) is a plan view of the scattering reflecting surface of the light guide 3, showing an example in which the pattern 3a is spot, straight or dashed. The spot is not limited to a circle and may be a polygon. As a chain line, what connected the round solid line at both ends, and what connected the rectangular solid line may be sufficient. The plurality of pattern shapes seen in the planar direction are not limited to the same shape, and may be a combination of spots, chain lines, or straight lines, and the size or width of the plurality of patterns may be changed. As the transparent material of the light guide, in addition to acryl, a transparent material such as polystyrene, polycarbonate, ABS resin, or a light scattering semitransparent material obtained by dispersing an inorganic light scattering agent or a heteropolymer having a different refractive index or the like is also used.

FIG. 2 is a partially enlarged view of the cross section of the light guide of the present invention shown in FIG. 1, in which light rays from the primary light source are totally reflected on the smooth surface 3b of the scattering reflection surface opposite to the exit surface 3c of the light guide; The whole body (전반). The light rays incident on the convex pattern 3a of the scattering reflecting surface are reflected and refracted along the pattern, partly emitted directly from the pattern, and partly at the exit surface 3c via reflection by the reflecting plate 4. It is emitted.

① Pattern shape

3 classifies the behavior of the refraction refractive index in the unit pattern of light incident on the convex pattern. As shown in Fig. 3 (a), the light beam L0 having a cross section generally incident on the ladder pattern 3a is totally reflected by the top edge BC and, in some cases, also by the quadrilateral CD, and the edge AD as it is. Return to the inside of the light guide body, and total emission is made again within the total reflection critical angle at the exit surface 3c, so that the light is not emitted. Thus, the pattern with the large ratio of the light beam L1 which does not contribute to emission among the total light beams L0 which entered the pattern can be said to be a pattern with low scattering emission efficiency. However, since this light beam becomes total light again, it does not involve loss as described later.

In FIG. 3B, the pattern incident light L0 is totally reflected by the top side BC and the quadrilateral CD to return to the light guide 3 via the side AD, but the critical angle is set from the exit surface 3c. It becomes the light beam L2 emitted beyond. With such a pattern, the light rays emitted only through total reflection have the least loss and have high light utilization efficiency.

In Fig. 3 (c), the incident light L0 is totally reflected at the top side BC or directly, refracted from the quadrilateral CD and exits the air layer 7 once, but is directed upward, so that the reflection scattering surface is smooth. It is reincident to the surface 3b. Since the smooth surface 3b and the emitting surface 3c are substantially parallel, the light beam L3 is emitted from the emitting surface 3c. Although the light beam L3 is a light beam having a low loss similarly to the light beam L2, the reflection loss at two interfaces is transmitted through the side CD and the scattered emission smooth surface 3b, which are two interfaces having different refractive indices unnecessarily. Occurs, accompanied by a decrease in light utilization efficiency. For example, when the light guide is an interface between acrylic resin (refractive index 1.49) and air (refractive index 1.00), there is a reflection loss of about 4 at at least one interface and about 8 at two interfaces, in particular to (3b) interface. Since the incidence is not perpendicular, the reflection loss is further increased. Not all of the eight or more reflected lights are lost, and some of them are reused as the light beams directed in the reverse direction in the light guide, and some are reflected by the inner reflecting plate or reflecting sheet 4 so as to be emitted and used from the exit surface. However, such light rays are stray light that loses the direction, and most of them are lost and cannot be used.

In Fig. 3 (d), the incident light L0 is directly refracted from the quadrilateral CD and exits the air layer 7, but the refractive angle becomes downward and is incident on the reflective sheet 4. The reflecting sheet is a specular reflecting sheet made of a diffuse reflecting sheet or metal deposition, and most of the reflecting sheet is emitted as a light beam L4 from the light guide emitting surface as long as the reflected light rays touch the scattering reflecting mirror surface 3b. In the case where the reflective sheet is a diffuse reflecting sheet, however, the reflecting sheet is reflected not only in the vertical direction but also in the horizontal direction. Therefore, the loss caused by re-entry into the light guide is impossible and is caused by the diffuse reflecting sheet itself. Return loss occurs. Moreover, also when a reflecting sheet is a metal mirror reflector, the reflectance is generally about 70-90, and there exists an absorption loss in a reflector. Therefore, such a light ray L4 has the largest loss in light ray utilization efficiency.

As described above, by considering the ratio at which the light beam L0 incident on the unit convex pattern of the cross section is scattered to (L1, L2, L3, L4), the scattering reflection performance and the light utilization efficiency of the unit pattern are examined. Can be evaluated. The larger the ratio of the scattered rays (L2 + L3 + L4) to the pattern of the total incident rays L0 to the pattern is, the higher the scattering reflection efficiency is, and the larger the ratio of the scattered rays (L2, L3, L4) is, the smaller the loss is. It is a pattern with high utilization efficiency.

The inventors of the present invention provide the ladder-shaped pattern width W, the pattern height H, and the pattern slope angle with respect to the ladder-shaped convex pattern ABCD of the acrylic light guide (acrylic refractive index 1.49, air refractive index 1.00) as shown in FIG. δ) was changed and the ratio at which scattered light becomes (L1 to L4) was calculated as the incident angle (θ) = 0 ° from the incident side AD at the critical angle (θ) = θc (= 47.8 °). . The incidence position is each equal point divided by the incident side AD by 100, the incidence angle is divided into 100 equal parts by (θ) = 0 to θc, and 10,000 total intensity beams are generated as the incident light L0, and the side (AB ), Sides (BC), and specular reflection and refraction at sides (CD) were calculated, aggregated with scattered rays L1 to L4, and the ratio with respect to the entire light beam L0 was calculated.

The result of having computed the ratio with respect to all incident light L0, such as (L2, L3, L4) with respect to H / W, changing the pattern slope angle (delta) is shown to FIGS. 5-11. When the sum of the respective ratios (L1 + L2 + L3) is the pattern scattering reflection efficiency (hereinafter referred to as η), and when the inclination angle δ≥5 ° of the ladder type (Figs. 7 to 11), all of H / W = 0.1 to η = Η = 1.0 at 0.57 and H / W = 0.60. H / W &lt; 0.1, i.e., if the pattern width becomes 10 times or more with respect to the pattern height, η &lt; 0.57, so that the diffuse reflection efficiency is low as the unit pattern. On the contrary, at H / W> 0.6, since the scattering reflection efficiency (η) is saturated, even if the height of the pattern is extremely high with respect to the pattern width, the difficulty in engraving or forming the mold increases, indicating no effect. have.

When rectangular (FIG. 5, (delta) = 0 degree) or a ladder-shaped inclination angle is small (FIG. 6, (delta) = 2 degrees), even if H / W≥0.6, efficiency is bad as scattering reflection efficiency (eta) <1. This is because when the pattern incidence angle θ is large, there are light rays totally reflected at the rectangular sides AB, BC and CD, and become total light again at the same angle as the incident angle to the pattern. Therefore, a ladder pattern having an inclination angle δ ≧ 5 ° is preferable in view of the scattering reflection efficiency η.

It is preferable that the ratios of L2 and L3 to the incident light L0 are large with respect to the light beam utilization efficiency. From this point of view, L2 in the range of 0.1? H / W? 0.6 indicates that δ = 10 to 30 °, and L2 + L3, the larger the value, the higher the light utilization efficiency and the smaller the loss. In the case of a rectangle (δ = 0 °), L2 = 0, and L3 is smaller than a ladder. It is clear that the ladder pattern is also excellent in terms of light efficiency.

The smaller the ratio of L2 at δ <10 ° (FIGS. 5 to 7) is that the angle of the ladder quadrilateral (CD) is close to a rectangle, so that the light is totally reflected twice in the ladder top (BC) and the quadrilateral (CD). This is because it does not cause this angular change but becomes total light again. Further, at δ> 30 ° (FIG. 11), the ratio of the length of the top side BC in the ladder pattern width W is decreased, so that L2 becomes less incident on the pattern and first touches the top side BC. It is reduced. Therefore, the ladder slope angle? = 10 to 30 ° is preferable as the light utilization efficiency is high and the loss is small.

As mentioned above, it turns out that a ladder pattern is excellent also in both a scattering reflection efficiency ((eta)) and a light beam utilization efficiency.

② Cross-sectional shape and formability

In fact, in the case of manufacturing the light guide, the finer the pattern, the greater the difficulty in manufacturing, such as mold manufacturing, pattern transfer, and mold release between the mold and the molded article in molding. Therefore, the ladder pattern is more preferable than the rectangular pattern if the angle of both ends of the sadiri-shaped top edge is round. For example, it is very difficult to process a slope of a pattern having a rectangular cross section of 10 μm width vertically (δ = 0 °) and precisely by cutting the angles at both ends of the top edge 2, for example, even if a mold is possible. And mold release property is very bad. The larger the ladder angle, the larger the angle δ, the easier the mold processing and the better the moldability. The rounder the angle, the better the mold transfer property and the releasability. 12 is an explanatory view of a ladder (a) and a ladder (b to d) having rounded angles in the light guide of the present invention. As described above, as the unit scattering pattern, it is important to have a substantially ladder shape consisting of the top side BC, the quadrilateral AB, and the quadrilateral CD, and the straight portion of the top side BC exists (W0> 0). ), The larger the ladder angle (δ) is, the more round the ladder is, the more preferable the convex pattern is in view of transferability and mold release property during molding.

③ Fine pattern

The ladder shape and the fine convex pattern of this invention can be shape | molded by the metal mold | die produced using the photolithographic method like FIG.

First, (a) a resist is apply | coated to board | substrates, such as glass, by spincoat etc. so that it may become a predetermined | prescribed film thickness. Thereafter, (b) the desired pattern is directly drawn by using an electron beam drawing apparatus or a laser drawing apparatus, or the pattern is exposed to the resist film by performing ultraviolet exposure or the like by superposing a photomask on the resist film. (c) The resist film in which the pattern is exposed is developed, and the resist pattern is formed on the substrate so as to have a ladder-shaped convex shape as shown in Fig. 12A. The height of the pattern at this time is determined by the film thickness of the spin coat. Here, when (d), for example, heat treatment is performed, the resist having a ladder cross section is semi-melted to deform into a rounded ladder-shaped convex shape (see Figs. 12 (b) to (d)). The degree of rounding can be controlled by temperature and time. Then, (e) this surface is subjected to conductive treatment, and then a molding die (f) having a pattern formed by nickel electroforming or the like is obtained. By using this mold, injection molding or press molding is performed using a transparent material such as acryl to produce a light guide member having a precise and fine convex scattering reflection pattern.

The drawing accuracy of the pattern has a precision of about 0.1 μm according to the electron beam writing, and the accuracy of 1 to 2 μm also by the laser beam writing. Therefore, a mold having a fine pattern of about 10 μm of any planar shape is easily and highly accurate. Can be written. Although the width W of the pattern can be arbitrarily set to several micrometers or more, it is preferable that the width W is large enough so that the interference color (see Japanese Patent Laid-Open No. 6-160636) due to the fine structure is small and small enough so that the luminance unevenness is not noticeable. About 10-300 micrometers is preferable, and the magnitude | size of 20-200 micrometers is more preferable. The height of the resist pattern, that is, the height H of the ladder pattern can be easily controlled by the thickness of the resist, for example, several micrometers to 30 micrometers are possible. In addition, the ladder slope angle δ is suppressed in the range of δ = 5 to 40 ° by changing the exposure conditions or changing the developing conditions by sandwiching a spacer between the photomask and the substrate on which the resist is applied. You can.

Although the manufacturing method in carrying out the present invention is not limited, the cross-section of the cross section, which has not been easily obtained in the conventional pattern processing methods such as mechanical cutting, laser processing, chemical etching, and the like by the photolithography technique described above, is ladder-shaped. A large number of precise and fine patterns having an arbitrary planar shape can be formed at high precision with good reproducibility and easily at low cost.

④ Surface precision

It is important that the smooth surface 3b of the light guide is specular to totally reflect light and guide light away from the light source without loss due to scattering. Also from this point of view, it is preferable that the surface roughness of the smooth surface 3b of the molded article is 0.2 占 퐉 or less by making the resist substrate a glass substrate with high mirror surface precision. In addition, in terms of reflection scattering efficiency, light utilization efficiency, or reproducibility of the pattern, at least the smoothness and reproducibility of the top (BC) surface of the ladder pattern are important, but the film surface of the resist film should have a surface roughness of 0.2 m or less. It can be easily achieved and also has high reproducibility. Further, by heat-treating the resist pattern, not only the ladder top edge BC but also the quadrilateral (AB) surface and the quadrilateral (CD) shaving surface roughness can be easily realized with a smoothness of 0.2 µm or less.

⑤ Advantages of the Convex Pattern

Scattered reflection characteristics of the unit ladder-shaped block pattern are as described above, the openings of the convex pattern provided on the scattering reflecting surface 3b, that is, the sides (ADCD) of the ladder (ABCD) of Fig. 4 (a). It is necessary to consider only the light rays incident on the light, and even if the patterns are closely arranged, the influence of the adjacent patterns is small, and the pattern density design for uniform luminance is easy. However, the case of the concave pattern is complicated. Fig. 14 is an explanatory view of ray tracing by a ladder-shaped concave pattern, in which (a) shows a case where the pattern is arranged at a low density, and (b) shows a high density. When attaching to a ladder pattern (ABCD), which is one pattern, respectively, only the side AB is effective for scattering reflection, and the side AB corresponds to the opening of the convex pattern, that is, the side AD. In the case of the low density of (a), the light ray which can be incident near the point A of the side AB is in the angle range of α1, and the one in the angle range of α2 is incident near the point B. Each incident point of the middle part of the side AB is also the same. It is clear that the sum of all the light beams that can be incident on the side AB is the opening of the concave pattern ABCD, and becomes smaller because the opening of (b) is adjacent to the pattern compared to (a). In other words, when the pattern density is low, the scattering reflection performance of the unit pattern is high efficiency, and when the pattern density is high, the scattering reflection performance of the unit pattern is low, and the scattering reflection performance of the unit pattern changes in accordance with the pattern arrangement density. In the concave pattern, such a complexity is involved, so that the design of the pattern density for making the luminance uniform is very difficult.

In general, when a diffusion sheet or a scattering reflection sheet having minute unevenness is brought into contact with a light guide smooth surface having air as an interface, the guided light is scattered outside the light guide system at the contact point and leaks. This situation is greatly changed not only by the uneven surface state of the diffusion sheet or the reflective sheet but also by pressing. The general backlight has such a configuration, and the uniform luminance as the surface light source becomes unstable. The smooth surface 3b on the pattern forming surface is important to the light guide light, and it is preferable that there is no such instability. From this point of view, however, the smooth surface 3b does not come into contact with the diffusion sheet or the reflecting sheet if it is a convex pattern. none. A convex pattern is preferable for the above reasons.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Examples 1-3

The cross-sectional width (W) of the unit pattern is 20, 60, and 200 μm, and the H / W is 0.6, 0.3, and 0.1, respectively, and the pattern height (H) is suitable for the scattering reflection performance of the ladder type which is generally 12, 18, and 20 μm. The pattern density distribution was designed, and the glass photomask of the pattern as illustrated in FIG. 15 (a) was manufactured (pitch P is as shown in FIG. 15 (b). , 2 and 3). A positive type photoresist was spin-coated to a glass substrate with a film thickness as designed, and the photomask was superimposed and subjected to ultraviolet exposure at a predetermined light amount. After developing using a developer, a substantially ladder-shaped convex resist pattern was formed on the glass substrate whose cross sections were 12, 18 and 20 mu m in height, and the slope angle δ was about 20 degrees. Thereafter, the resist pattern surface was subjected to electroconductive treatment by nickel sputtering having a thickness of several tens of nanometers, and a nickel electrocasting method was performed to a thickness of 300 占 퐉 to prepare a mold. This mold was used for injection molding, and the cross section having a size of 10.4 inches, the light incident end of the long side at 3.0 mm, and the thickness of the opposite end at 1.1 mm was tapered. An acrylic light guide formed with many patterns was obtained. The results are the same as in Examples 1, 2, and 3 of Table 1, respectively, and the transferability of the pattern and the releasability with the mold were particularly difficult, with W = 20 µm having a large H / W, but molding was possible. A 2.6 mm diameter cold cathode tube was used as the primary light source in the cross section of the thick long side of the light guide member, and a reflective sheet was placed on the inner surface of the scattering reflection pattern, and visually observed from above. Local luminance unevenness due to the roughness of the pattern was not observed but uniform. In addition, one diffuser sheet and a prism sheet were disposed on the emission surface, and the luminance distribution was measured. As shown in Table 1, the luminance uniformity was good, the average luminance was high, and the light guide was bright and uniform.

Example Comparative example One 2 3 4 5 6 One 2 pattern One 2 3 One 2 3 One 4 Resist Pattern Heat Treatment radish radish radish U U U radish radish Uneven pattern 凸 凸 凸 凸 凸 凸 凸 凹 Ladder Cross Section Width (W) (Μm) 20 60 200 20 60 200 20 20 Ladder cross section height (H) (Μm) 12 18 20 12 18 20 12 12 H / W 0.6 0.3 0.1 0.6 0.3 0.1 0.6 0.6 Ladder cross section inclination angle (δ) (°) 20 25 25 20 25 25 3 20 Formability △ ○ ○ ◎ ◎ ◎ × △ Fineness of the pattern ◎ ○ △ ◎ ○ △ ◎ ◎ Average luminance (cd / ㎡) 1,710 1,690 1,700 1,670 1,650 1,730 1,420 1,530 Uniformity and uniformity () 92 88 90 87 85 81 72 69

Examples 4-6

Using photomasks of patterns 1, 2, and 3, the same processes as in Examples 1, 2, and 3 were carried out, respectively, to form a convex resist pattern substantially in a ladder shape. These were heat-treated to deform into a convex resist pattern in a substantially ladder shape having a rounded angle. Similarly, the conductive treatment was performed to form a 10.4 inch acrylic light guide through an electroforming die. The results are shown in Table 1, and both the transferability and the release property were very good. The uniformity and average brightness of the luminance were inferior to those of Examples 1, 2 and 3, respectively.

Comparative Example 1

By using the photomask of pattern 1, W = 20 micrometers, H / W = 0.6, and H = 12 micrometers were processed and the exposure and image development conditions were changed, and the cross section of the slope angle (delta <3 degrees) becomes substantially rectangular. A convex resist pattern was obtained. When the mold was manufactured and molded in the same manner as in Example, the transferability of the pattern was poor and the mold release with the mold was very difficult. The luminance distribution was measured. As shown in Comparative Example 1 of Table 1, since the scattering reflection performance of the single pattern was low, the luminance near the light source was low, high at the end, poor in uniformity, and low in average luminance.

Comparative Example 2

Using the negative photomask 4 in which the black and white pattern of the photomask 1 was reversed, it was processed and molded in the same manner as in Example except that the film was spin-coated to have a film thickness of 12 µm. The pattern had a substantially ladder-shaped cross section and was concave, with high luminance near the light source and low at the end, poor luminance uniformity, and low average luminance. When the light guide is partially pressed, the brightness of the portion is increased, or the uniformity of the brightness is impaired depending on the fixing method, which is unstable, and thus it is not suitable as the light guide.

As described above, the light guide according to the present invention has high brightness and excellent luminance uniformity, and thus can be effectively used as a back lighting device of liquid crystal display devices such as word processors, personal computers, and thin televisions.

Claims (5)

A light guide for guiding light from one or more side cross sections, The portion close to the linear light source has a low density so that the substantially ladder-shaped convex pattern in which the convex top edge in the cross section orthogonal to the axis of the linear light source has a straight portion is roughly uniform so that the luminance distribution of the emitted light from the exit surface is approximately uniform. The edge portion of the light guide is characterized in that the distant portion is disposed in a high density in a spot, solid or broken line on the inner surface opposite to the light exit surface. The method of claim 1, The convex pattern has a ladder shape in which two angles corresponding to both ends of the convex top edge in a cross section perpendicular to the axis of the linear light source have a ladder shape. The method of claim 1, The surface roughness of the surface which comprises the straight part of the convex top edge in a convex pattern, and the surface roughness of the surface in which the convex pattern formation is not formed among the convex pattern formation surface, respectively are 0.2 micrometer or less, The edge light type light guide body characterized by the above-mentioned. . The method of claim 1, An edge light type light guide, wherein the ratio of H / W is 0.1 ≦ H / W ≦ 0.6 when the cross-sectional width of the convex pattern is represented by (W) and the height is represented by (H), respectively. The method of claim 1, The cross-sectional width (W; mu m) of the cross section of the convex pattern is 20? W?