KR20040000333A - Light guide plate, surface light source apparatus and image display device - Google Patents

Abstract

PURPOSE: To easily adjust the ratio of a light diffusion pattern to the other rough surface part even if the thickness of a light guide plate is reduced, and to obtain uniform surface illumination. CONSTITUTION: Since a rough surface pattern 14 formed at least on the back surface 12 side of the light guide plate 2 and functioning as an irregular light-diffusion pattern is formed of a number of fine projections 14a projecting from the reference surface of the guide plate 2 by reducing minus projections 14b recessed inside from the reference surface(back surface 12) of the guide plate 2, the travel of light propagating toward the tip side 21 of the guide plate 2 from the incident surface 4 side of the guide plate 2 is less hindered by the minus projections 14b of the pattern 14 even if the thickness of the guide plate 2 is reduced, so that the formation ratio of the pattern 14 to the rough surface part 15 can easily be adjusted.

Description

Light guide plate, surface light source device and image display device {LIGHT GUIDE PLATE, SURFACE LIGHT SOURCE APPARATUS AND IMAGE DISPLAY DEVICE}

The present invention relates to a light guide plate for inputting light from an end to emit light from an emission surface, a surface light source device using the same, and an image display device using the surface light source device. These are used, for example, in notebook personal computers, liquid crystal monitors, portable telephones, portable electronic terminal devices, electronic notebooks, car navigation devices, digital cameras, VTR devices and the like.

BACKGROUND OF THE INVENTION A light guide plate having an emission surface, a rear surface positioned opposite to the emission surface, for emitting light introduced from an end portion from the emission surface, and a surface light source device in which the light guide plate and the primary light source are combined. This type of surface light source device is employed as an illuminating means in image display devices of various apparatuses in addition to personal computers.

(First conventional example)

7 and 8 show an example of such a surface light source device 30. The surface light source device 30 includes a light guide plate 31, a fluorescent lamp (primary light source) 34, a reflection sheet 36 and a prism sheet (light control sheet) 37. The light guide plate has an emission surface 32 and a back surface 33 opposite thereto, and a light diffusion pattern 35 is formed on the back surface 33. The light diffusion pattern 35 is composed of a plurality of roughening element portions 35c whose formation density is changed in accordance with the distance from the fluorescent lamp 34 or the like. By this light diffusion pattern 35, the light propagating through the light guide plate 31 can be diffused and reflected, and the illumination light emitted from the emission surface 32 can be uniformized. Moreover, such a well-known technique is shown by Unexamined-Japanese-Patent No. 10-104432, Unexamined-Japanese-Patent No. 2967926, Unexamined-Japanese-Patent No. 2580451, for example.

However, in such a structure, since the part in which the light-diffusion pattern 35 is not formed in the back surface 33 is a smooth surface, there exists a possibility that the reflective sheet 36 may adhere to the part of the smooth surface. When such adhesion occurs, since there is no air layer between the back surface 33 and the reflective sheet 36 at the close contact portion, it is not possible to easily obtain a desired diffuse reflection function locally. As a result, the reflection sheet 36 causes the problem of being seen from the exit surface 32 side.

In addition, when the reflective sheet 36 rubs against the smooth portion of the back surface 33 for some reason, the smooth portion is scratched by the surface of the reflective sheet 36, causing abnormal light emission due to diffuse reflection of light or the like.

Moreover, even when the light-diffusion pattern 35 is formed in the emission surface 32 and the prism sheet 37 is arrange | positioned at the said emission surface 32, the same "adhesion" or "friction" is the prism sheet 37 And a smooth portion of the exit surface 32 (a portion where the light diffusion pattern 35 is not formed). In this case, the luminance variation of the stripe pattern occurs in the light emitted through the prism sheet 37 to reduce the illumination quality.

(2nd conventional example)

Therefore, the present applicant proposes to roughen the portion where the light diffusion pattern 35 is not formed when the light diffusion pattern 35 is formed on the back surface 33 or the emission surface 32 of the light guide plate 31. (See Japanese Laid-Open Patent Publication No. Hei 11-352312 and Japanese Laid-Open Patent Publication No. 2001-83507). By applying this technique, the reflection sheet 36 and the prism sheet 37 can be prevented from coming into close contact with the back surface 33 or the exit surface 32 of the light guide plate 31, so that the light diffusion function is effectively exhibited and high quality is achieved. Illumination light is obtained.

However, in recent years, there has been a high demand for better thinning and lightening of surface light source devices and large size of display screens (effective lighting area), which has resulted in unsatisfactory cases in the first conventional example. This point will be briefly described with reference to FIGS. 9 to 11.

Fig. 9 is a sectional view of a surface light source device showing a second conventional example, and Fig. 10 is a view seen from the back side of the light guide plate with the reflection sheet of the surface light source device removed. Fig. 11 is a diagram showing a diffuse reflection state of light of the light guide plate according to the second conventional example. As shown in these figures, the roughness of the uneven group (uneven group consisting of the projection 35a and the negative projection 35b) forming the light diffusion pattern 35 of the light guide plate 31 employed in the second conventional example is It is larger than the roughness which the other rough surface part 38 has.

Therefore, the concave portion (negative projection 35b) of the light diffusion pattern 35 is largely encroached into the light guide plate 31. Such an encroaching portion (minus projection 35b) can be formed even near the incident surface 40 of the light guide plate 31. Therefore, the thinner the light guide plate 31 increases the rate at which light is diffused in the negative projection 35b of the light diffusion pattern 35, and the amount of light emitted from the exit surface 32 near the incident surface 40 increases. do.

As a result, the ratio of the amount of light reaching the tip side (opposite side of the incident surface 40; 41) of the light guide plate 31 is insufficient, resulting in lack of brightness at the tip side 41. From such a situation, the thinner the light guide plate 31 and the larger the size of the exit surface (effective area), the ratio between the light diffusion pattern 35 and the other rough surface portion 38 (ratio of the occupied area) Becomes difficult to adjust. In other words, if the light diffusing ability of the light diffusing pattern 35 (light diffusing ability per area or unit area of the light diffusing pattern 35) is too weak, a sufficient light diffusing effect cannot be obtained. The luminance is uneven under the influence of obstacles.

Therefore, even if the thickness of the light guide plate is made thin, the basic object of the present invention is to make it easy to adjust the ratio of the light diffusion pattern and the other rough part, thereby enabling uniform surface illumination. In addition, the present invention is to provide a high-performance light guide plate, a surface light source device and an image display device using the same.

1 is an exploded perspective view of an image display device according to an embodiment of the present invention.

2 is a cross-sectional view taken along the line A-A in FIG.

3 is a view taken from the rear side of the light guide plate with the reflection sheet of the surface light source device shown in FIG. 2 (indicated by an arrow from the direction B in FIG. 2).

4 is a cross-sectional view schematically showing an injection molding die.

FIG. 5 is a view from the direction B in FIG. 4; FIG.

FIG. 6 is a partially enlarged cross-sectional view showing a processing state of the cavity inner surface of the injection molding die shown in FIG. 4; FIG.

7 is a sectional view of a surface light source device showing a first conventional example.

FIG. 8 is a view of the back surface of the light guide plate with the reflection sheet of the surface light source device shown in FIG. 7 removed; FIG.

9 is a sectional view of a surface light source device showing a second conventional example.

FIG. 10 is a view of the back surface of the light guide plate with the reflection sheet of the surface light source device shown in FIG. 9 removed; FIG.

Fig. 11 is a view showing a diffuse reflection state of light of the light guide plate according to the second conventional example.

Explanation of symbols on the main parts of the drawings

1: Image display device

2: light guide plate

4: incident surface (side)

5: fluorescent lamp (primary light source)

6: exit surface

11: liquid crystal display panel (member for display)

12: back side

13 surface light source device

14: rough surface pattern (light diffusion pattern)

14a: plus smile projection

14b: minus bump

15: roughing part

16: injection molding mold

17: cavity

18: inside

20: rough surface pattern for transfer

20a: protrusion

22: transfer surface

The present invention is first applied to a light guide plate having a light emitting surface and a rear surface located on the opposite side of the light emitting surface, wherein light introduced from an end is emitted from the light emitting surface. The light guide plate can be manufactured by injection molding using an injection molding die having a cavity. In one embodiment of the present invention, the following conditions (a) and (b) are given to the inner surface of the cavity.

(a) As the inner surface of the cavity, among the areas corresponding to the exit surface and the rear surface, at least a region corresponding to the rear surface is formed with a roughening pattern for transfer of roughness for forming a light diffusion pattern, and then Cut and remove at least a portion of the roughness pattern in use.

(b) All or most of the transfer roughening pattern other than the roughing pattern is a recessed roughening portion having a smaller recess than the roughening pattern.

Then, the transfer rough surface pattern and the transfer rough surface portion are transferred to the back surface of the light guide plate by using an injection molding die that satisfies such conditions.

In another aspect, the present invention provides a light guide plate having a light emitting surface and a rear surface positioned opposite to the light emitting surface, wherein light guided from the end is emitted from the light emitting surface as follows (c), ( d) and (e).

(c) A rough surface pattern for diffusing and reflecting light is formed on at least the rear surface of the exit surface and the rear surface.

(d) At least a part of the plurality of roughening element parts constituting the roughening pattern is formed such that the ratio of positive minute protrusions projecting from the reference plane becomes larger than the number of negative protrusions concave from the reference plane.

(e) Roughening all or most of the region not occupied by the roughening pattern by protruding from the reference plane a plurality of protrusions having a lower protrusion height than the roughening pattern, as a region on the surface on which the roughening pattern is formed. .

The light guide plate improved by the aspect mentioned above is combined with the primary light source which supplies light to the edge part of the said light guide plate, and provides the surface light source device which concerns on this invention. Further, the surface light source device is combined with a display member illuminated by the output light of the surface light source device to provide an image display device according to the present invention.

Embodiment

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings. 1 to 3 are diagrams showing an image display device according to one embodiment of the present invention. In these figures, the image display apparatus is indicated by reference numeral 1, and the light guide plate is indicated by reference numeral 2. In FIG. 1 is an exploded perspective view of the image display apparatus 1, and FIG. 2 is a cross-sectional view along the line A-A in FIG. 3 is the figure seen from the back side of the light-guide plate 2, Comprising: The reflection sheet 3 was removed, and it is a figure shown by the arrow seen from the B direction in FIG.

(Schematic Configuration of Image Display Device)

In the image display apparatus 1, a rod-shaped fluorescent lamp (primary light source) 5 is disposed along an incident surface (one side surface) 4 located at one end of the light guide plate 2. Along the emission surface (upper surface in FIG. 1) 6 of the light guide plate 2, the diffusion sheet 7, the first prism sheet 8, and the second prism sheet 10 are arranged in this order as a light control member. . And the liquid crystal display panel 11 is arrange | positioned on the upper surface side in FIG. 1 of the 2nd prism sheet 10 as a display member.

The rear surface (lower surface in FIG. 1) 12 of the light guide plate 2 is a surface opposite to the emission surface 6, and arranges the reflective sheet 3 accordingly. In addition, the fluorescent lamp 5, the light guide plate 2, the diffusion sheet 7, the first prism sheet, the second prism sheet 8, 10, and the reflective sheet 3 have the liquid crystal display panel 11 in a planar shape. The surface light source device 13 to illuminate is comprised.

(Light guide plate)

The light guide plate 2 consists of materials excellent in light transmittance, such as PMMA (methyl polymethacrylate), PC (polycarbonate), and cycloolefin resin material. The cross-sectional shape of the light guide plate 2 is a substantially wedge shape in which the plate thickness becomes thin as it moves away from the incident surface 4 (see FIG. 2). In addition, the plane shape of the exit surface is substantially rectangular (see Fig. 3). The back surface 12 of the light guide plate 2 can be divided into a region where the rough surface pattern 14 is formed as a light diffusion pattern, and a remaining region. The remaining regions (regions in the rear surface 12 not occupied by the roughening pattern 14) also roughen all of them. The roughening pattern 14 consists of the some roughening element part 14c, and is formed so that the area of the roughening element part 14c may increase as it moves away from the incident surface 4. This is because the light diffusion efficiency is increased as the distance from the incident surface 4 increases.

The area | region in which the roughening pattern 14 was not formed in the back surface 12 forms the roughening part 15 of roughness smaller than the roughening pattern 14 altogether. These rough surface patterns 14 and the rough surface part 15 are formed with many micro protrusions 14a and 15a formed so that they may protrude from the "reference surface" which represents the back surface 12. As shown in FIG. In addition, a "reference plane" is a plane in the case of removing the roughening pattern 14 etc. virtually.

The protrusion height of the minute protrusions 14a of the roughening pattern 14 is higher than the protrusion height of the minute protrusions 15a of the roughening part 15. As a result, the rough surface pattern 14 exhibits a stronger light diffusion function than the rough surface portion 15.

Such a light guide plate 2 is processed with high precision by injection molding. That is, the rough surface pattern 14 and the rough surface part 15 are formed in the outer surface of the molded object (light guide plate) by transferring the inner surface shape of the cavity of the injection molding die to resin.

4 is a cross-sectional view schematically showing a mold used for injection molding of the light guide plate 2. 5 is the figure seen from the B direction in FIG. The inner surface 18 of the cavity 17 of the mold 16 is shown in FIG. 5 by electric discharge machining, blast treatment (the process of spraying iron shots, etc. on the cavity surface), or other known roughening treatment. The transfer roughening pattern 20 as described above is formed.

The illustrated rough surface pattern 20 is comprised from the projection part 20a which protrudes from the inner surface (plane) 18 of the cavity 17, and the recessed part 20b which concave from the plane 18 of the cavity 17. As shown in FIG. . By injection molding the light guide plate 2 using the mold 16 having the cavity 17, the portion (protrusion 20a) protruding from the inner surface 18 of the cavity 17 is a concave portion of the rear surface 12. Becomes On the other hand, the recessed part (concave part 20b) from the inner surface 18 of the cavity 17 becomes a protrusion part of the back surface 12 of the light guide plate 2.

It should be noted here that if there are negative projections (concave portions: 14b) in the rough surface pattern 14 on the incident surface 4 side among the rough surface patterns 14 formed on the rear surface 12, light is diffused by this. The ratio increases and the amount of light emitted from the exit face 6 near the entrance face 4 increases. In this case, the ratio of the amount of light reaching the tip side (the side far from the incident surface 4) 21 of the light guide plate 2 decreases (see FIG. 11).

This means that, as described above, the thinner the plate thickness of the light guide plate 2, the more difficult the ratio adjustment of the rough surface pattern 14 and the rough surface portion 15 for emitting uniform illumination light becomes.

Therefore, in this embodiment, as shown in FIG. 6, after the transfer roughening pattern 20 is formed in the cavity 17, the entire surface of the inner surface 18 of the cavity 17 is blasted, and the transfer roughening surface is provided. Most of the projections 20a of the pattern 20 are cut off to form the transfer rough surface portion 22. When the molten resin is injected into the cavity 17 of the mold 16, the light guide plate 2 having only a small number of negative protrusions can be obtained (see FIGS. 1 to 3).

According to this light guide plate 2, the light propagating inside is diffused in the rough surface pattern 14 and the rough surface part 15, and this diffused light is radiate | emitted uniformly from the exit surface 6. As shown in FIG. In addition, even if the reflective sheet 3 rubs against the rear surface 12, since the rear surface 12 is the rough surface pattern 14 and the rough surface portion 5, the light guide plate 2 does not easily be scratched. In other words, even if a flaw is formed, since the light tends to diffuse in the roughening pattern 14 and the roughening portion 15, the flaw can be avoided.

In addition, the reflection sheet 3 does not come into close contact with the light guide plate 2, and the reflection sheet 3 is prevented from appearing on the exit surface 6 side of the light guide plate 2. Therefore, according to the light guide plate 2 of this embodiment, uniform and high quality surface shape illumination is attained.

(Reflective sheet)

The reflective sheet 3 is formed of a material having excellent light reflectivity such as white PET (polyethylene terephthalate). The size and shape are almost the same as the back surface 12 of the light guide plate 2. The reflective sheet 3 diffuses and reflects the light leaked from the back surface 12 and returns to the inside of the light guide plate 2 to increase the effective use of the light.

(Diffusion Sheet)

The diffusion sheet 7 is a substantially rectangular sheet formed of a resin material having excellent light transmittance such as PET, PMMA, and PC, and the size is almost the same as that of the exit surface 6. The manufacturing method, effect | action, etc. of the diffusion sheet 7 are known conventionally. That is, the diffusion sheet 7 includes (i) mixing a light diffusing material in PET, (ii) forming a film of light diffusing material on the surface of the PET sheet, or (iii) roughening the surface of the PET sheet (uneven cotton) To manufacture). Light emitted from the light guide plate 2 diffuses when passing through the diffusion sheet 7.

(Prism sheet)

The first prism sheet and the second prism sheet 8, 10 are known light control sheets formed of materials having excellent light transmittance, such as PET, PMMA, and PC. It is formed in substantially the same rectangle as the diffusion sheet 7. Each prism sheet is provided with a plurality of prism protrusions 23 and 24 having a substantially triangular cross section. The first prism sheet 8 is disposed such that the prism protrusions 23 on the upper surface side thereof follow the substantially X direction of FIG. 1. As a result, the first prism sheet 8 emits the output light of the diffusion sheet 7 in the plane along the Y direction in FIG. 1 and in the plane substantially orthogonal to the exit surface 6 of the light guide plate 2. It functions to condense in the normal direction of the surface 6.

On the other hand, the 2nd prism sheet 10 is arrange | positioned so that the prism protrusion 24 of the upper surface side may follow substantially Y direction in FIG. Thereby, the 2nd prism sheet 10 emits the output light of the diffusion sheet 7 in the surface along the substantially X direction of FIG. 1, and in the surface substantially orthogonal to the output surface 6 of the light guide plate 2 It functions to condense in the normal direction of the surface 6. A protective sheet (not shown) formed of a resin material excellent in light transmittance such as PET, PMMA, and PC may be disposed between the second prism sheet 10 and the liquid crystal display panel 11.

(Effects of Embodiments)

The rough behavior of the light in the image display apparatus 1 described above is as follows. Light emitted from the fluorescent lamp 5 is introduced into the light guide plate 2 from the incident surface 4 located at the end of the light guide plate 2. This light propagates inside the light guide plate 2 while repeating reflection between the emission surface 6 and the back surface 12. In the process, the light reaching the rear surface 12 is diffusely reflected by the rough surface pattern 14 or the rough surface portion 15 to the exit surface 6. In this light, the incidence angle with respect to the exit surface 6 becomes below the critical angle, and it exits from the exit surface 6 to the exterior.

Here, the density per unit area of the roughening pattern 14 is adjusted so that uniform surface light emission is possible with respect to the roughening part 15. Therefore, the luminance of the illumination light emitted from the exit surface 6 becomes almost uniform. In addition, in this embodiment, the back surface 12 is occupied by the rough surface pattern 14 and the rough surface part 15, and there exists no area | region which forms a mirror surface. For this reason, the reflective sheet 3 does not adhere to the back surface 12. In addition, the reflection sheet 3 is also prevented from rubbing against the rear surface 12 and causing scratches on the rear surface 12. As a result, occurrence of abnormal light emission is prevented.

In addition, in this embodiment, many fine (for example, 70% or more) of the roughening pattern 14 and the roughening part 15 formed in the back surface 12 protrude from the reference surface which represents the back surface 12 It is formed by the projections 14a and 15a. Therefore, the ratio in which the negative protrusion 14b is formed in the back surface 12 is very small, and even if some negative protrusions 14b remain, most of them have a small amount of encroachment into the light guide plate 2.

Thereby, even if the plate | board thickness of the light guide plate 2 is made thin, excessive emission from the exit surface 6 near the incident surface 4 does not occur. In other words, the light reaching the tip side (the end portion on the side far from the entrance face 4) 21 is not shorted. This means that the ratio adjustment of the roughening pattern 14 and the other roughening portion 15 for emitting uniform illumination light is easy.

(Modification of Embodiment)

The above-described embodiments are not intended to limit the present invention, but allow the following modifications, for example.

(1) In the above-mentioned embodiment, the rough surface pattern 14 and the rough surface part 15 are formed only in the back surface 12 of the light guide plate 2. However, the roughening pattern 14 and the roughening part 15 may also be provided in the exit surface 6. In this case, the effect | action which prevents the fall of the illumination light quality resulting from adhesion | attachment of the diffusion sheet 7 and the exit surface 6 is acquired.

(2) In the above-described embodiment, the blasting is performed on all of the transfer roughening patterns 20 of the injection molding die 16. Then, the projections 20a of all the transfer roughening patterns 20 are shaved to prevent negative projections from occurring in the roughening pattern 14 of the light guide plate 2. However, the present invention is not limited to this.

For example, in particular, the surface of the transfer roughening pattern 20 may be partially masked so as not to perform a blasting process, limited only to the transfer roughening pattern 20 corresponding to the point requiring the emission light luminance improvement. .

(3) In the inside of the light guide plate 2, fine particles made of a material having a refractive index different from that of the light guide plate 2 may be mixed.

(4) In embodiment mentioned above, the diffusion sheet 7 and the two prism sheets 8 and 10 were arrange | positioned at the emission surface 6 side. But this is just an example. For example, only the diffusion sheet 7 may be disposed, and only two prism sheets 8 and 10 may be disposed.

(5) In the above-mentioned embodiment, the light guide plate 2 is substantially wedge-shaped in cross section along the A-A line in FIG. But this is just an example. For example, you may employ | adopt the light guide plate whose cross section along the A-A line in FIG. 1 is rectangular. Alternatively, a light guide plate having a thin plate thickness at the center portion and a thick plate thickness at both ends may be used in the cross section along the line A-A in FIG. In these cases, primary light sources (fluorescent lamps and the like) may be disposed at both ends, respectively.

(6) In the above-described embodiment, the shape of the inner surface 18 of the cavity 17 of the injection molding die 16 is transferred to the back surface 12 of the light guide plate 2. And the rough surface pattern 14 and the rough surface part 15 are formed in the back surface 12 by this. However, the roughening pattern 14 and the roughening portion 15 may be formed by other means.

(7) In embodiment mentioned above, the roughening pattern 14 formed in the back surface 12 was formed so that area might increase as it moves away from the fluorescent lamp 5. As shown in FIG. However, it is not limited to this, You may adjust suitably the density of the roughening pattern 14 as needed. For example, the predetermined range of the substantially center portion of the emission surface 6 may be made to emit light brighter than other portions. Alternatively, the density of the rough surface pattern 14 of the corner portion on the incident surface 4 side may be made high so as to reduce the influence of the dark portions at both ends of the fluorescent lamp 5.

(8) In embodiment mentioned above, the roughening pattern 14 formed in the back surface 12 is comprised from the some roughening element part 14c which is rectangular. But this is an example. The shape of each roughening element portion 14c may be a suitable shape such as a circle or a rhombus.

(9) In the above-mentioned embodiment, the back surface 12 of the light guide plate 2 is occupied by either the rough surface pattern 14 and the rough surface part 15 over the whole area, and there is no smooth area. However, a part of the back surface 12 may be a flat portion (smooth portion) as long as the flaw preventing action of the light guide plate 2 and the light diffusion function are not impaired. However, it is preferable that the occupancy rate of the flat portion (smooth portion) does not exceed 25%, and more preferably 10% or less.

(9) Instead of the fluorescent lamp as the primary light source, an array in which a plurality of other light sources, for example, light emitting diodes (LEDs) are arranged, may be employed.

As described above, according to the present invention, since the negative projections concave inward from the reference plane representing the rear surface of the light guide plate are reduced, even if the plate thickness of the light guide plate is made thin, it does not interfere with the internal propagation of light, Adjustment is easy. As a result, the uniformity of the luminance of the emitted light from the light guide plate can be easily realized.

Claims (6)

In the light guide plate which has an emission surface and the back surface located on the opposite side to the said emission surface, and emits the light introduced from the edge part from the said emission surface, The light guide plate is manufactured by injection molding using an injection molding mold having a cavity, The transfer rough surface pattern is formed on an inner surface of the cavity and at least a region corresponding to the rear surface among the emission surface and the region corresponding to the rear surface. At least a part of the projections are scraped and removed, and all or most of the projections other than the rough surface pattern are transfer rough surfaces having a smaller recess than the rough surface pattern. The light guide plate, characterized in that the transfer rough surface pattern and the transfer rough surface portion is transferred to the rear surface. In the light guide plate which has an emission surface and the back surface located on the opposite side to the said emission surface, and emits the light introduced from the edge part from the said emission surface, A rough surface pattern for diffusing and reflecting light is formed on at least the rear surface of the emission surface and the rear surface, At least a part of the plurality of roughening element parts constituting the roughening pattern is formed such that the ratio of the positive minute protrusions projecting from the reference plane becomes larger than the number of negative protrusions concave from the reference plane, All or most of the area on the surface on which the rough surface pattern is formed and not occupied by the rough surface pattern are roughened by protruding from the reference plane a plurality of projections having a lower projection height than the rough surface pattern. Light guide plate. In the surface light source device provided with a light guide plate and the primary light source which supplies light to the edge part of the said light guide plate, The light guide plate is a surface light source device according to claim 1. In the surface light source device provided with a light guide plate and the primary light source which supplies light to the edge part of the said light guide plate, The said light guide plate is a light guide plate of Claim 2, The surface light source device characterized by the above-mentioned. An image display apparatus comprising a surface light source device and a display member illuminated by the output light of the surface light source device, The surface light source device is an image display device according to claim 3. An image display apparatus comprising a surface light source device and a display member illuminated by the output light of the surface light source device, The surface light source device is an image display device according to claim 4.