JP2014072022A - Light guide board and surface illuminant device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide board which can improve uniformity of emitted light.SOLUTION: A light guide board emitting light from a light emitting surface while making light from a light source enter and leading it in a light guide direction comprises a diffraction structure layer possessing diffraction structure patterns on the light emitting surface by being formed with unevenness. The diffraction structure pattern has a structure where an edge is formed with uneven shapes extending in one and/or two dimensions and emits a diffused light by at least primary light.

Description

  The present invention relates to a light guide plate provided in a surface light source device used for a liquid crystal display or the like, and a surface light source device using the light guide plate.

  A liquid crystal display device such as a liquid crystal television is provided with a surface light source device that illuminates a liquid crystal panel from the back side. The surface light source devices are roughly classified into a direct type in which a light source is arranged on the back side of the optical member and an edge light type in which a light source is arranged on the side of the optical member. The edge light type surface light source device has an advantage that the thickness of the surface light source device can be reduced as compared with the direct type surface light source device.

  The edge light type surface light source device is provided with a light guide plate that guides light from the side toward the center. That is, light from the light source enters the light guide plate from a light incident surface that is one end surface of the light guide plate. The light that has entered the light guide plate is repeatedly reflected in the light guide plate and travels in the direction of the surface facing the light incident surface (light guide direction). The light traveling through the light guide plate is gradually emitted from the light exit surface as it travels through the light guide plate due to the optical action of the light guide plate. As a result, the amount of light emitted from the light exit surface of the light guide plate is made uniform along the light guide direction.

  For example, Patent Document 1 discloses a light guide plate including a layer in which a plurality of prisms having a triangular cross section having a predetermined size are arranged on a light exit surface. Such an element enables efficient use of light by controlling the direction of light emitted from the surface light source device.

  Patent Document 2 describes a method for forming a computer generated hologram.

International Publication WO2012 / 008212 Japanese Patent No. 4620220

  As shown in Patent Document 1, the edge light type surface light source device often has a plurality of light sources arranged at predetermined intervals so as to face the light incident surface of the light guide plate. However, such an arrangement of light sources sometimes causes luminance unevenness between a portion along the optical axis of each light source and a portion along the optical axis.

  In addition, Patent Document 2 describes matters relating to the formation of holograms, but does not discuss light guide plates.

  Then, this invention makes it a subject to provide the light-guide plate which can improve the uniformity of the light emitted in view of said problem. Moreover, a surface light source device provided with the said light-guide plate is provided.

  The present invention will be described below.

  The invention according to claim 1 is a light guide plate that emits light from a light exit surface while allowing light from a light source to enter and guide the light in a light guide direction, and a diffraction structure formed by forming irregularities on the light exit surface The light guide plate includes a diffractive structure layer provided with a pattern, and the diffractive structure pattern has a structure in which a ridge line is formed in an uneven shape extending in one dimension and / or two dimensions and emits diffused light by at least primary light. is there.

  According to a second aspect of the present invention, in the light guide plate according to the first aspect, the diffractive structure pattern has a ridge line extending in the light guide direction, and irregularities are alternately arranged in a direction different from the light guide direction and incident. In this structure, light is diffused so as to project a straight line parallel to the direction in which the irregularities are arranged.

  According to a third aspect of the present invention, in the light guide plate according to the first or second aspect, the concavo-convex shape of the diffractive structure pattern is formed by combining a plurality of concave and convex shapes that are not uniform. .

  Invention of Claim 4 is the light source plate arrange | positioned facing the light-incidence surface formed in the one end side of the light guide direction of the light guide plate in any one of Claims 1-3, and the light guide plate, A surface light source device comprising: a deflecting optical sheet that is arranged to face the diffractive structure layer of the light guide plate and in which a plurality of unit prisms that are convex with respect to the diffractive structure layer are arranged.

  According to the present invention, it is possible to reduce luminance unevenness of emitted light, and to provide a surface light source with higher luminance uniformity.

2 is an exploded perspective view showing the configuration of the surface light source device 1. FIG. It is a part of cross section of the surface light source device 1. It is a part of other cross section of the surface light source device 1. FIG. It is a figure explaining the light-diffusion characteristic of the diffraction structure layer 12 in a 1st example. It is another figure explaining the light-diffusion characteristic of the diffraction structure layer 12 in a 1st example. It is a figure explaining the light-diffusion characteristic of the diffraction structure layer 12 in a 2nd example. It is a figure explaining the light-diffusion characteristic of the other diffraction structure layer 12 in a 2nd example. It is a figure explaining the light-diffusion characteristic of the diffraction structure layer 12 in a 3rd example. It is a figure explaining the light-diffusion characteristic of the diffraction structure layer 12 in a 4th example. It is the top view which looked at the light-guide plate 10 for demonstrating the diffraction structure layer 12 'from the light-emitting surface side. It is a figure explaining the characteristic of diffraction structure layer 12 '. It is a figure explaining the form of the diffraction structure pattern 13a. It is the top view which looked at the light-guide plate 10 for demonstrating the diffraction structure layer 12 '' from the light-emitting surface side. It is a flowchart which forms the diffraction structure pattern by a computer generated hologram. This is a mold roll for forming a light guide plate. It is a shaping sheet for light guide plate formation. It is a figure explaining the shaping | molding method of the light-guide plate by the extrusion method. 4 is a diagram for explaining a unit prism 32a of the deflection optical sheet 30. FIG. 4 is an exploded perspective view showing a structure of a liquid crystal display device 200. FIG.

  The operations and features described above will be described based on the embodiments shown in the drawings. However, the present invention is not limited to these embodiments.

FIG. 1 is a diagram illustrating one embodiment, and is an exploded perspective view of a surface light source device 1 including a light guide plate 10. 2 shows a part of the sectional view in the thickness direction of the surface light source device 1 along the line (light guide direction) indicated by II-II in FIG. 1, and FIG. 3 shows by III-III in FIG. A part of a sectional view in the thickness direction (vertical direction in FIG. 1) of the surface light source device 1 along the line (light source arrangement direction) is shown. In addition, in this figure and the figure shown below, the thickness, shape, etc. of a member may be shown exaggerated for easy understanding, and a part of repeated reference numerals may be omitted.
As can be seen from FIGS. 1 to 3, the surface light source device 1 is configured as an edge light type surface light source device, and includes a light guide plate 10, a light source 29, a deflecting optical sheet 30, and a reflection sheet 40.

The light guide plate 10 has a base 11 and a diffractive structure layer 12. The light guide plate 10 is a plate-like member as a whole formed of a light-transmitting material, and the diffractive structure layer 12 is disposed on one plate surface side and functions as a light exit surface. The other plate surface side is the back surface.
Further, an end surface forming the plate thickness of the light guide plate 10 between the light exit surface and the back surface is a light incident surface facing the light source 29, a counter surface disposed on the side opposite to the light incident surface, and a light incident surface. Two side surfaces are formed so as to pass between and the opposite surface.

The base 11 is a part having translucency that serves as a base of the diffractive structure layer 12 and has a plate shape having a predetermined thickness. As can be seen from FIGS. 1 and 2, a plurality of prisms 11 a having a triangular prism shape are provided on the back side of the base 11 (the plate surface opposite to the side on which the diffraction structure layer 12 is disposed). The prism 11a is a plurality of columnar portions extending in a direction (light source arrangement direction) orthogonal to the light guide direction, and these are arranged in a line at a predetermined interval in the light guide direction.
The prism 11a of the present embodiment has a triangular prism shape, but is not limited to this, and may be a polygonal prism shape with four or more squares.

  The diffractive structure layer 12 is a layer formed on the light output surface side of the base portion 11, and a computer generated hologram having a concavo-convex shape in which a ridge line extends two-dimensionally and / or a concavo-convex shape in which a ridge line extends one-dimensionally. The uneven | corrugated shape based on this is formed in the surface. This computer generated hologram diffuses light and emits highly uniform light. Alternatively, a desired viewing angle distribution can be obtained.

  The diffractive structure layer 12 according to one example will be described below. The diffraction structure layer 12 has a hologram shape 12a formed on the surface thereof. The hologram shape 12a is a shape that can be emitted so as to diffuse incident light from the base 11 side into a predetermined range. Specifically, the light is diffused so as to improve the uniformity of the emitted light as the light guide plate 10. Therefore, the form is not particularly limited as long as it has a desired diffusibility. Hereinafter, the hologram shape 12a will be described with a plurality of examples using a computer generated hologram.

  First, the light diffusion characteristics of the hologram shape 12a according to the first example will be described. FIG. 4 is a diagram for explaining the light diffusion characteristics of the hologram shape 12a according to the first example. 4A to 4C are diagrams showing the relationship between the diffusion angle of the diffractive structure layer 12 and the luminance. 4A shows the relationship between the diffusion angle and the luminance in the light guide direction plane, FIG. 4B shows the relationship between the diffusion angle and the luminance in the light source arrangement direction plane, and FIG. 4C shows the light guide direction. Is the relationship between the diffusion angle and the luminance in the plane of 45 ° obliquely. According to the hologram shape 12a of the first example, when the light incident from the base 11 side is diffracted and diffused, in the normal direction of the light guide plate 10 (the direction indicated by I in FIG. 1, the front direction). It can be seen that light is emitted with high luminance. In addition, in the light guide direction plane and the light source arrangement direction plane, the brightness is obtained at a diffusion angle of ± 30 ° to ± 40 °. On the other hand, in a plane oblique to 45 ° with respect to the light guide direction, such luminance is not present except in the light guide plate normal direction. Therefore, according to the first example, the light is diffused at ± 30 ° to ± 40 ° in the front direction, the light guide direction direction plane, and ± 30 ° to ± 40 ° in the light source arrangement direction plane, Uniformity can be achieved.

  In order to obtain such light diffusion characteristics, the brightness near the front surface uses 0th-order diffraction light, ± 30 ° to ± 40 ° in the light guide direction plane, and ± 30 ° in the light source array direction plane. A brightness of ˜ ± 40 ° can utilize the diffracted primary light. Accordingly, when obtaining the shape of the computer generated hologram, it is sufficient to configure so that the primary light is diffracted to a desired angle. FIG. 5 is a graph showing the light diffusion characteristics related to the primary light. The horizontal axis represents the in-plane diffusion angle in the light guide direction, and the vertical axis represents the in-plane diffusion angle in the light source arrangement direction. A hatched portion in FIG. 5 is an angle range in which luminance should be obtained by the primary light. Therefore, the light diffusion characteristics described above can also be expressed as shown in FIG. Then, based on the diagram shown in FIG. 5, an original diagram for finally obtaining a hologram shape by Fourier transform is obtained, and by applying Fourier transform or the like to this, the above-mentioned light diffusion characteristics are finally obtained. Can be obtained. How to obtain a specific hologram shape 12a using FIG. 5 will be described later.

  Here, the ratio of the luminance magnitude of the primary light (luminance at a viewing angle of ± 30 ° to 40 °) to the luminance magnitude of the zero-order light (luminance at a viewing angle of 0 °) is not particularly limited. However, it is preferable that the brightness of the primary light is 0.1 times or more than the brightness of the 0th-order light.

  In the first example, the luminance at the light guide direction in-plane diffusion angle ± 30 ° to ± 40 ° and the light source arrangement direction in-plane diffusion angle ± 30 ° to ± 40 ° are set to be the same. Although it is configured (see FIG. 4A and FIG. 4B), either of them may be enlarged to obtain a desired light diffusion performance.

Next, the light diffusion characteristics of the hologram shape 12a according to the second example will be described. FIG. 6 and FIG. 7 show diagrams corresponding to FIG. 5 among the diagrams for explaining the hologram shape 12a according to the second example. 6 and 7, the example illustrated in FIG. 6 is an example in which the luminance increases in a plurality of angle ranges in the light guide direction in-plane diffusion angle and the light source array direction in-plane diffusion angle. More specifically, in addition to high brightness at the front due to zero-order light, ± 30 ° to ± 40 ° and ± 60 ° to ± 70 ° within the light guide direction plane and the light source array direction plane due to primary light. The brightness increases in the range of.
On the other hand, the example shown in FIG. 7 is an example in which the luminance increases in a wider angle range than the first example in the light guide direction in-plane diffusion angle and the light source array direction in-plane diffusion angle. More specifically, in addition to the high brightness in the front due to the 0th order light, the brightness becomes high in the range of ± 30 ° to ± 70 ° in the light guide direction plane and the light source array direction plane due to the primary light.
As described above, in the second example, a hologram shape for diffusing light in a wider range is formed in the light guide direction inner surface and the light source array direction surface, so that highly uniform diffused light and a desired viewing angle distribution can be obtained. Is possible.

  Next, the light diffusion characteristics of the hologram shape 12a according to the third example will be described. FIG. 8 shows a diagram corresponding to FIG. 5 among the diagrams explaining the hologram shape 12a according to the third example. In the example shown in FIG. 8, in addition to the diffusion angle described in the first example, the luminance is also increased in the range of −10 ° to + 10 °. That is, the hologram shape 12a is formed so that light is continuously diffused from the front to ± 45 ° in the light guide direction plane and from the front to ± 45 ° in the light source arrangement direction.

Next, the light diffusion characteristics of the hologram shape 10a according to the fourth example will be described. FIG. 9 shows an explanatory diagram. The upper part of FIG. 9 shows the in-plane luminance distribution in the light guide direction in this example. Here, the luminance distribution having the maximum luminance at the viewing angle of 0 ° is due to the 0th order light, and the luminance distribution having the maximum luminance at the angle other than the viewing angle of 0 ° is due to the primary light. The lower part of FIG. 9 is a diagram for obtaining a hologram shape 12a for realizing such a luminance distribution, and corresponds to FIG. As can be seen from FIG. 9, in this example, the viewing angle at which the primary light has the maximum luminance is diffused outside the half-value angle of the zero-order light (the position of the viewing angle at which the luminance is halved with respect to the maximum luminance). It is comprised so that it may become a corner.
According to the hologram shape having such light diffusion characteristics, the continuity between the zero-order light and the first-order light can be improved. Therefore, by arranging a hologram having a desired viewing angle distribution, light can be continuously diffused from the front to the light guide direction plane and from the front to the light source array direction plane.
Although only the in-plane diffusion angle in the light guide direction has been described in FIG. 9 and the above description, the same applies to the in-plane diffusion angle in the light source arrangement direction.

  Each example described above is an exemplification, and in addition to the above, it is possible to form a hologram shape for obtaining desired light diffusion characteristics. In this embodiment, only the 0th-order light and the 1st-order light in diffraction are considered, but higher-order light higher than the 2nd-order light may be considered.

  The above-described computer generated holograms are obtained by arranging a plurality of minute unit computer holograms having the respective optical functions described above and combining them, or unit computer holograms arranged in a compound eye shape. For example, a unit computer hologram is formed in a square and a plurality of the unit computer holograms having a square shape are densely arranged in a vertical and horizontal lattice pattern, or a so-called zigzag pattern in which the vertical or horizontal lines are shifted by half a pitch every other row. Can be mentioned. In addition, it is also conceivable that the unit computer generated holograms are not densely arranged with no gap but are sparsely arranged with a predetermined gap or arranged based on a predetermined pattern. Of course, the shape of the unit computer hologram is not limited to a square, and may be formed in any shape including a rectangle and other polygons. Further, the shape and arrangement of unit computer holograms included in one computer hologram are not necessarily constant, and may be changed depending on the location.

  Next, another form of the diffractive structure layer 12 'will be described. This is because a diffractive structure is formed by a so-called one-dimensional computer generated hologram so that when the guided light is emitted to the deflecting optical sheet 30, it is diffused only in the plane of the light source arrangement direction to emit linear projection light. A configured diffractive structure pattern is provided. FIG. 10 shows a plan view of the light guide plate 10 viewed from the light exit surface direction. Accordingly, the diffractive structure layer 12 'appears in FIG. FIG. 10 also shows the direction.

  As can be seen from FIG. 10, in the diffractive structure layer 12 ′, a plurality of unit diffractive structures 13, which are one unit extending in the light guide direction, are arranged side by side in the light source arrangement direction of the surface of the base 11. Since the diffraction structure layer 12 includes a function of diffusing light in the light source arrangement direction, the size of the unit diffraction structures 13 in the light source arrangement direction (the size indicated by A in FIG. 10) is arranged. It is preferable that the pitch is smaller than one pitch of the plurality of light sources 29.

  As schematically shown in FIG. 11, the diffraction structure pattern in the unit diffraction structure 13 can project light in a straight line parallel to the light source arrangement direction when the incident light L51, L52, and L53 is emitted. It is set as the structure which can radiate | emit and diffuse. And this is comprised so that it may continue in a light guide direction like B1, B2, and B3.

  FIG. 12 is a cross section in the thickness direction of the unit diffraction structure 13 along the line VI-VI shown in FIG. 10, and is an example schematically showing the diffraction structure pattern 13 a included in the unit diffraction structure 13. However, the sectional shape itself shown in FIG. 12 is conceptual and does not represent a precise shape.

As can be seen from FIG. 12, the diffractive structure pattern 13a is formed between a plurality of convex portions which are rectangular in cross-sectional shape and nonuniform in various sizes and are arranged in parallel in the light source arrangement direction with a gap. The concavo-convex diffractive structure is formed by the concave portion. And such a cross-sectional shape is maintained and the ridgeline is extended in the light guide direction.
As a result, the phase modulation amount of the light transmitted through the convex portion and the phase modulation amount of the light transmitted through the concave portion are different, and as a result, the light in the diffraction structure pattern 13a is in the direction in which the unevenness as described above is arranged. Diffraction in a pattern that is projected in a straight line that is parallel. Accordingly, the unevenness constituting the diffractive structure pattern 13a is an unevenness that diffuses light by using a diffraction phenomenon, and is different from an unevenness that deflects light by utilizing light refraction. Specifically, the size of the convex portion and the concave portion in the light source arrangement direction (for example, a ₁ , b ₁ ) and the height of the convex portion (the depth of the concave portion, for example, the size of h ₁ ) are large. It can be distinguished by being different. For example, the size of a ₁ and b ₁ can be about 0.2 μm to ₁₀ μm, and the size of h ₁ can be about ₁ μm to 10 μm.

  Such a diffraction structure pattern 13a is a structure by a computer generated hologram. Therefore, as will be described later, the diffractive structure pattern 13a has a shape guided by a computer generated hologram based on a desired light diffusion pattern. According to the computer generated hologram, a diffractive structure pattern for realizing a desired light diffusion pattern can be directly derived. The computer generated hologram in the present invention includes a diffractive optical element (DOE) using a diffraction effect.

Next, still another example will be described. In the other example, a diffractive structure layer 12 ″ is formed on the base 11. FIG. 13 is a diagram for explaining the diffractive structure layer 12 ″ and shows a diagram corresponding to FIG. In the diffractive structure layer 12 '', as can be seen from FIG. 13, the one-dimensional computer generated hologram as the diffractive structure pattern 13a is formed in the light source side region which is a predetermined region on the light source side in the light guide direction. In this area, a two-dimensional computer generated hologram 12a is formed.
This is because, in the light source side region close to the light guide direction, the radial spread of light from the light source is not sufficient, and the brightness unevenness of brightness in the light source arrangement direction is larger than the others. By applying such a structure, the diffusion of light in the light source array direction is increased, and luminance unevenness in the light source array direction is reduced.

Although the size of the light source side region is not particularly limited, it is a region up to a position where incident diffused light from adjacent light sources overlap from a qualitative viewpoint. Specifically, although it depends on the light diffusion characteristics of the light source, a range of 0 mm or more and 20 mm or less can be set in the light guide direction from the light incident surface.
It is also possible to change the structure between a portion where the LED exists and a portion where the LED does not exist, set parameters (pitch, depth, etc.) of the diffraction structure pattern, change the diffraction efficiency, and modulate the diffusion angle.

  In the light guide plate 10 configured as described above, the diffractive structure layer 12 may be directly formed on one surface of the base 11, or the diffractive structure layer 12 may be attached to one surface of the base 11. Good. An example of a specific manufacturing method will be described later. The material constituting the base 11 and the diffractive structure layer 12 is preferably highly transparent. For example, thermoplastic resins such as acrylic resins, polycarbonate resins, and styrene resins, epoxy resins, thermosetting urethane resins, and thermosetting polyesters. There may be mentioned thermoplastic resins such as resins. Other (meth) acrylates such as polyester (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, polyether (meth) acrylate, polyol (meth) acrylate, melamine (meth) acrylate, and triazine (meth) acrylate Radical-polymerizable prepolymers such as 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa An ionizing radiation curable resin comprising a composition comprising one or more selected from radically polymerizable unsaturated monomers such as (meth) acrylates may also be mentioned. Here, “(meth) acrylate” means acrylate or methacrylate.

  Next, an example of a method for manufacturing the light guide plate 10 will be described. The light guide plate 10 obtains each diffractive structure pattern shape, obtains the form of the diffractive structure layer, and forms a light guide plate by producing a mold based on the obtained form of the diffractive structure layer. Manufactured including. Each step will be described below.

  In the step of obtaining the form of the diffractive structure layer, a method for obtaining a diffractive structure pattern shape by a computer generated hologram will be described. Since the computer generated hologram itself is known, a known method (for example, Japanese Patent No. 4620220 (Patent Document 2)) can be applied to a method for obtaining the computer generated hologram shape. Here, an example will be described.

  In general, a computer generated hologram is obtained as follows. That is, assuming a certain diffractive structure (hologram), when the reproduction distance from it is sufficiently large compared to the size of the hologram and illuminating light parallel to the normal of the hologram surface, the diffracted light obtained on the reproduced image surface is It is expressed by Fourier transform of amplitude distribution and phase distribution on the hologram surface (Fraunhofer diffraction). Therefore, in order to give a predetermined diffracted light to the reproduction image plane, a computer generated hologram arranged on the hologram plane is repeatedly repeated with Fourier transform and inverse Fourier transform while applying a constraint condition between the hologram plane and the reproduction image plane. The method to obtain | require is known (Gerchberg-Saxton iterative calculation method).

Therefore, it is considered to obtain a computer generated hologram that diffracts light only to a predetermined observation area when light parallel to the normal line of the hologram surface is illuminated from behind by using the Gerchberg-Saxton iterative calculation method. Here, for easy understanding, the amplitude distribution on the hologram surface is _represented by A _HOLO , the phase distribution on the hologram surface is represented by φ _HOLO , the amplitude distribution on the reproduction image surface is represented by A _IMG , and the phase distribution on the reproduction image surface is represented by φ _IMG . . FIG. 14 shows the flow.

In the surface region (x0 ≦ x ≦ x1, y0 ≦ y ≦ y1) in which the computer generated hologram is formed in step S1, 1 is given to A _HOLD as an initial value, and a random value is given to φ _HOLD .
In step S2, a predetermined Fourier transform is applied to the initialized value to obtain A _IMG and φ _IMG .
In step S3, if it is determined that A _IMG is substantially constant within a predetermined area and is substantially 0 outside the predetermined area, A _HOLD and φ _HOLD initialized in step S1 are the desired computer holograms. It becomes.

On the other hand, if it is determined in step S3 that such a condition is not satisfied, a constraint condition is assigned in step S4. Specifically, A _IMG is set to 1, for example, in the predetermined area, and is set to 0 in the other areas, and φ _IMG is maintained as it is.
Next, a predetermined inverse Fourier transform is performed under the condition after the binding condition is given in step S5.
The value on the hologram surface obtained by the inverse Fourier transform is given a constraining condition in step S6, A _HOLD is set to 1, and φ _HOLD is multivalued (approximate the original function to a digital step-like function (quantum )). However, in the case where φ _HOLD may have continuous values, this multi-value conversion is not necessarily required.

  And it returns to process S2 and Fourier-transform is given to the value. Thereafter, the same processing as described above is performed, and the process can be repeated until the condition of step S3 is satisfied (until convergence) to obtain a final desired computer generated hologram (diffraction structure pattern).

  Thus, each diffraction structure pattern 13a is obtained, and unit diffraction structures 13 are obtained by combining single or plural kinds of diffraction structure patterns as described above, and these are arranged in the light guide direction and the light source arrangement direction. Thus, the form of the diffractive structure layer 12 can be obtained.

  Next, a process of producing a mold based on the form of the obtained diffractive structure layer and thereby forming the light guide plate 10 will be described.

In this example, a method of obtaining the light guide plate 10 by producing a light guide plate strip 10 ′ (see FIG. 17) having a continuous form of the light guide plate 10 by an extrusion method and punching it out at a predetermined size therefrom. explain. Specifically, it is as follows.
In this example, prior to manufacturing the light guide plate strip 10 ′ by the extrusion method, a mold roll 50 capable of shaping the prism 11a and a shaping sheet 60 capable of shaping the diffraction structure layer 12 are prepared. To do. FIG. 15A shows a conceptual perspective view of the mold roll 50. FIG. 15B shows a cross-sectional shape orthogonal to the longitudinal direction of the groove 51 formed on the surface of the mold roll 50. On the other hand, the form of the shaping sheet 60 was shown with the conceptual perspective view to Fig.16 (a). FIG. 16B shows a cross-sectional shape orthogonal to the longitudinal direction of the groove 61 formed on the surface of the shaped sheet 60. This example will be described using the diffraction structure layer 12 according to the first example shown in FIG.

  The mold roll 50 is a roll mold that can shape the shape of the prism 11a as described above. Accordingly, the mold roll 50 has a groove 51 having a shape corresponding to the convex shape of the prism 11a as shown in FIG. As can be seen from FIG. 15A, the groove 51 extends in a direction along the rotation axis of a roll-shaped mold, and a plurality of grooves 51 are arranged in the circumferential direction. The arrangement pitch of the plurality of grooves 51 corresponds to the arrangement pitch of the prisms 11 a of the light guide plate 10.

  The shaped sheet 60 is a belt-like sheet that can shape the shape of the diffractive structure layer 12 as described above. Accordingly, in the shaped sheet 60, as shown in FIG. 16B, a plurality of grooves 61 corresponding to the shape of the diffractive structure layer 12 are formed on the sheet surface on one side. As can be seen from FIG. 16A, the groove 61 extends in a direction along the longitudinal direction of the strip-shaped sheet (the feeding direction of the shaped sheet), and a plurality of grooves 61 are arranged in the width direction of the sheet. The arrangement pitch of the plurality of grooves 61 corresponds to the diffractive structure pattern obtained above. For example, the following method can be used to form the shaped sheet.

First, a resist layer having dry etching resistance is formed in a thin film shape on a chromium thin film of a photomask blank plate in which a surface low-reflection chromium thin film is laminated on a substrate such as synthetic quartz. As an example of the resist for dry etching, ZEP7000 manufactured by Nippon Zeon Co., Ltd. can be used. The resist is laminated by spin coating using a spinner or the like.
The resist layer is subjected to pattern exposure. The pattern exposure can be performed by a plate-like pattern, laser beam scanning with a laser drawing apparatus, or electron beam scanning with an electron beam drawing apparatus.
This exposure forms a readily soluble part in which the resist resin is cured and an unexposed part. Therefore, the resist pattern is formed by removing the easily soluble part by solvent development by spray development performed by spraying a developer. Form.

  Using the formed resist pattern, the portion of the chromium thin film not covered with the resist is removed by dry etching, and the underlying quartz substrate is exposed in the removed portion. Next, dry etching is similarly performed on the exposed quartz substrate, and the quartz substrate is etched. The quartz substrate in which the concave portion generated by the progress of etching, the chromium thin film, and the resist thin film are sequentially coated from the bottom. A convex portion made of the original portion is formed. Thereafter, the resist thin film is removed by dissolution or the like, and a quartz substrate having a concave portion formed by etching the quartz substrate and a convex portion composed of a portion where a chromium thin film is laminated on the top is obtained.

With only the above method, only a binary part of the convex part and the concave part (high and low two steps, and a depth of another level surface occurs in addition to the surface of the original quartz substrate) is obtained. However, by repeating the photo-etching process consisting of resist formation → pattern exposure → resist development → dry etching of chromium thin film → dry etching of quartz substrate → resist removal for those obtained above Photoetching can be further performed on the concave portions and the convex portions generated by the first photoetching. By repeating this a plurality of times, it is possible to accurately obtain a plurality of irregularities having a height difference. In this way, after obtaining the predetermined number of steps, the chromium thin film is removed by wet etching to obtain a computer generated hologram type in which irregularities with a predetermined number of steps are formed on the surface of the quartz substrate.
Based on this concavo-convex mold, a concavo-convex shape can be formed on the surface of a resin or the like coated on the film surface to obtain a shaped sheet.

  When a one-dimensional pattern as shown in FIG. 10 is obtained, a cutting tool in which the whole or a part of the concavo-convex shape is processed is prepared, and a roll plate is created by lathe processing on a plated roll. Using this plate, an uneven shape can be formed on the surface of a resin or the like coated on the film surface to obtain a shaped sheet.

  The mold roll 50 prepared as described above, the shaping sheet 60, and the like are arranged as follows, and the belt shape for the light guide plate including the concavo-convex shape provided in the light guide plate 10 by supplying materials and extruding is provided. A sheet 10 ′ is obtained. FIG. 17 shows a conceptual explanatory diagram. That is, the shaped sheet 60 is sequentially fed between the mold roll 50 and the feed roll 70 arranged with a predetermined gap with respect to the mold roll 50, and the shaped sheet 60 and the mold are further fed. A molten thermoplastic resin flows into the roll 50 from the nozzle 74. Here, the feeding direction of the shaped sheet 60 is the longitudinal direction of the shaped sheet 60 having a strip shape. Moreover, it is preferable that the form of the thermoplastic resin to flow in is a strip | belt shape which has a magnitude | size (width | variety) comparable as the width direction magnitude | size of the mold roll 50 and the shaping sheet | seat 60. FIG. Thereby, uniform material supply in the width direction is possible.

The supplied thermoplastic resin flows between the mold roll 50 and the shaping sheet 60 with a predetermined pressure. Thereby, the thermoplastic resin is filled in the mold roll 50 and the grooves 51 and 61 of the shaping sheet 60, respectively, and the thermoplastic resin has a shape along the grooves 51 and 61. Finally, the thermoplastic resin is cured and the shape is fixed, so that the light guide plate strip 10 'is obtained. More specifically, the strip-shaped sheet 10 ′ for the light guide plate coming out between the mold roll 50 and the shaping sheet 60 moves following the outer periphery on the mold roll 50 side along with the shaping sheet 60, and the nip roll 71 and the release roll 72 to release the mold. And the strip | belt-shaped sheet | seat 10 'for light guide plates and the shaping sheet 60 are isolate | separated with the separation roll 73. FIG. The strip-shaped sheet 10 ′ for the light guide plate is wound up into a sheet roll.
And the light guide plate 10 is obtained by punching out to a predetermined size while rewinding the sheet roll.

Manufacturing by such an extrusion process has higher continuity than injection molding and press molding, and can efficiently manufacture a thin light guide plate.
Although the example which forms the unevenness | corrugation of front and back by the die roll 50 and the shaping sheet 60 was given at this example substantially in this example, it is not limited to this, In the aspect which makes one side precede and the other after that There may be.

  Returning to FIGS. 1 to 3, the light source 29 will be described. The light source 29 is disposed to face the light incident surface of the end surface of the base 11 of the light guide plate 10. Accordingly, the light source 29 is disposed on one end side of the light guide plate 10 in the light guide direction. The type of the light source is not particularly limited, but may be configured in various forms such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), or an incandescent lamp. In the present embodiment, the light source 29 has a plurality of LEDs arranged in the light source arrangement direction, and a control device (not shown) outputs each LED, that is, turns on and off each LED, and / or brightness when each LED is turned on. It can be adjusted independently from the output of other LEDs.

  Next, the deflection optical sheet 30 will be described. As can be seen from FIGS. 1 and 2, the deflecting optical sheet 30 is provided on the surface of the main body 31 formed in a sheet shape and the surface of the main body 31 that faces the light guide plate 10, that is, the light incident side surface. Unit prism portion 32.

  As will be described later, the deflection optical sheet 30 changes (deflects) the traveling direction of light incident from the light incident side and emits the light from the light output side, thereby intensively improving the luminance in the front direction (normal direction). It has a function (light collecting function). This condensing function is mainly exhibited by the unit prism portion 32 of the deflecting optical sheet 30.

  As shown in FIGS. 1 to 3, the main body 31 is a flat sheet-like member having a function of supporting the unit prism portion 32. And the surface on the opposite side to the side which faces the light-guide plate 10 among the surfaces of the main-body part 31 becomes a light emission side surface. In the present embodiment, the light outgoing side surface of the main body 31 is formed as a flat (flat) and smooth surface. However, the light emission side surface is not limited to being a smooth surface, and may be a surface with a minute unevenness (so-called mat surface), and it is possible to apply a surface form as required. is there.

  The unit prism portion 32 is arranged such that a plurality of unit prisms 32 a are arranged along the light incident side surface of the main body portion 31 as well shown in FIGS. 1 to 3. More specifically, the unit prism 32a is a columnar member formed so as to extend while maintaining the triangular cross-sectional shape shown in FIG. 2 in a direction orthogonal to the arranged direction. The extending direction is a direction that is orthogonal to the direction in which the unit prisms 32 a are arranged, and is a direction that is shifted by 90 degrees with respect to the light guide direction of the light guide plate 10 described above.

  Next, the sectional shape of the unit prism 32a in the parallel direction will be described. 18 is an enlarged view of a part of the deflection optical sheet 30 in FIG. Here, nd represents the normal direction of the sheet surface of the main body 31.

  As can be seen from FIG. 14, in this embodiment, the unit prism 32 a has a cross section of an isosceles triangle projecting from the surface of the main body 31 on the light guide plate 10 side. That is, the width of the unit prism 32 a in the direction parallel to the sheet surface of the main body 31 decreases as the distance from the main body 31 increases along the normal direction nd of the main body 31.

  In the present embodiment, the outer contour of the unit prism 32a is line symmetric with respect to an axis parallel to the normal direction nd of the main body 31, and the cross section is an isosceles triangle. Thereby, the luminance on the light exit surface of the deflecting optical sheet 30 has a symmetrical angular distribution of luminance about the front direction on the surface parallel to the parallel direction of the unit prisms 32a.

Here, the dimensions of the unit prism 32a are not particularly limited, but appropriate light collection characteristics can be obtained by setting the apex angle θ ₁ (see FIG. 18) to 60 ° to 70 ° and the base width W to about 50 μm. Can often be obtained.

  The deflecting optical sheet 30 having the above-described configuration can be manufactured by extrusion molding or by molding the unit prism 32a on the main body 31. Various materials can be used as the material forming the deflection optical sheet 30. However, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost, such as acrylic, styrene, polycarbonate, Transparent resins mainly composed of one or more of polyethylene terephthalate, acrylonitrile and the like, and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins and the like) can be suitably used.

  In the present embodiment, the unit prism having a triangular cross section as described above has been described. However, the present invention is not limited to this, and a trapezoid having a short upper base at the apex of the triangle may be used. The shape of the hypotenuse may be a polygonal line or a curve.

  Returning to FIGS. 1 to 3, the reflection sheet 40 of the surface light source device 1 will be described. The reflection sheet 40 is a member that reflects light emitted from the back surface of the light guide plate 10 and makes light enter the light guide plate 10 again. The reflection sheet 40 is a sheet that is capable of so-called specular reflection, such as a sheet made of a material having a high reflectivity such as a metal, or a sheet that includes a thin film (for example, a metal thin film) made of a material having a high reflectivity as a surface layer. It can be preferably applied. As a result, the light convergence can be improved, and the energy utilization efficiency can be improved.

  Next, operations of the light guide plate 10 having the above-described configuration and the surface light source device 1 including the light guide plate 10 will be described with reference to examples of optical paths.

  First, as shown in FIG. 2, the light emitted from the light source 29 enters the light guide plate 10 through the light incident surface of the light guide plate 10. FIG. 2 shows an example of an optical path of the light L21 and L22 incident on the light guide plate 10 from the light source 29 as an example. Here, in order for the light emitted from the light source 29 to enter the light guide plate 10 from the light incident surface efficiently, the light incident surface is preferably a smooth surface.

  As shown in FIG. 2, the light L21 and L22 incident on the light guide plate 10 is repeatedly guided by total reflection due to a difference in refractive index with air on the surface of the diffraction structure layer 12 of the light guide plate 10 and the back surface on the opposite side. Proceed in the light direction.

  However, a prism 11 a is provided on the back surface of the base 11 of the light guide plate 10. Therefore, as shown in FIG. 2, the light L21 and L22 traveling in the light guide plate 10 has their traveling direction changed by the oblique interface of the prism 11a, and is incident on the diffraction structure layer 12 and the back surface at an incident angle less than the total reflection critical angle. It may be incident. In this case, the light can be emitted from the diffraction structure layer 12 and the back surface of the light guide plate 10.

  The lights L21 and L22 emitted from the diffractive structure layer 12 travel to the deflecting optical sheet 30 disposed on the light output side of the light guide plate 10. On the other hand, the light emitted from the back surface is reflected by the reflection sheet 40 disposed on the back surface of the light guide plate 10, enters the light guide plate 10 again, and travels through the light guide plate 10.

  Since the prisms 11a are arranged with a predetermined interval, the light traveling through the light guide plate 10 is gradually emitted from the light exit surface. Thereby, the light quantity distribution along the light guide direction of the light emitted from the diffractive structure layer 12 of the light guide plate 10 can be made uniform.

  The diffractive structure layer 12 of the light guide plate 10 diffuses and emits light according to the above-described examples, for example, as shown by the lights L31, L32, and L33 in FIG. Thereby, the emitted light can be made highly uniform. In particular, in the case of a diffractive structure layer having a diffusing component in the light source array direction, light transmitted and diffracted by the diffractive structure and light emitted from the surface while the reflected diffracted light is repeatedly reflected and diffracted inside the light guide plate are combined in a complex manner It is possible to eliminate luminance unevenness due to the light sources being arranged at predetermined intervals.

The optical path will be described with reference to FIG. The light emitted from the light guide plate 10 then enters the deflection optical sheet 30. The unit prism 32a of the deflecting optical sheet 30 exerts a condensing action on the transmitted light by refraction and total reflection at the light incident surface of the unit prism 32a. In the deflection optical sheet 30, components in the light guide direction of the deflection optical sheet 30 are condensed. That is, as indicated by L111 in FIG. 18, the light incident on the unit prism 32a is totally reflected at the interface based on the refractive index difference between the unit prism 32a and air. At this time, since the hypotenuse of the unit prism 32a is inclined by θ _{1/2 with} respect to the sheet surface normal nd, the reflected light at the interface has an angle closer to the normal nd than the incident light.

  With respect to the light guide plate 10 described above, as shown in FIG. 19, a liquid crystal display device can be formed by providing the liquid crystal panel 201 and the optical sheet 202 on the light output side of the surface light source device 1. A known structure can be applied to the liquid crystal panel 201 and the optical sheet 202.

DESCRIPTION OF SYMBOLS 1 Surface light source device 10 Light guide plate 11 Base 12 Diffraction structure layer 13 Unit diffraction structure 13a Diffraction structure pattern 29 Light source 30 Deflection optical sheet 31 Main body part 32 Unit prism part 40 Reflection sheet 50 Mold roll 51, 61 Groove 60 Molding sheet 70 Feed roll 71 Nip roll 72 Release roll 73 Separation roll 74 Nozzle 200 Liquid crystal display device 201 Liquid crystal panel 202 Optical sheet

Claims (4)

A light guide plate that emits light from a light exit surface while allowing light from a light source to enter and guide the light in a light guide direction,
The light exit surface includes a diffractive structure layer provided with a diffractive structure pattern formed by forming irregularities,
The diffractive structure pattern is a light guide plate having a structure in which a ridge line is formed by an uneven shape extending in one dimension and / or two dimensions and emits diffused light by at least primary light.   The diffractive structure pattern has a ridge line extending in the light guide direction, irregularities are alternately arranged in a direction different from the light guide direction, and incident light is projected in a straight line parallel to the direction in which the irregularities are arranged. The light guide plate according to claim 1, wherein the light guide plate has a structure that diffuses into the light.   The light guide plate according to claim 1 or 2, wherein the concave and convex shapes of the diffraction structure pattern are formed by combining a plurality of concave shapes and convex shapes that are not uniform. The light guide plate according to any one of claims 1 to 3,
A light source disposed opposite to a light incident surface formed on one end side in the light guide direction of the light guide plate;
A surface light source device, comprising: a deflecting optical sheet that is disposed so as to face the diffractive structure layer of the light guide plate and in which a plurality of unit prisms that are convex with respect to the diffractive structure layer are arranged.

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