JP2014072019A - Light guide board and surface illuminant device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide board which can reduce a luminance irregularity of emitted light.SOLUTION: Tabular light guide boards 10 and 110 emitting light from a light emitting surface while making light from a light source 29 enter and leading it in a light guide direction comprise a diffraction structure layer 13 possessing diffraction structure patterns 13a-13f on the light emitting surface by being formed with unevenness. At least one of the diffraction structure patterns have a structure where an edge is elongated in the light guide direction and the unevenness is arranged alternately in a direction different from the light guide direction.

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 light guide plate 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.

International Publication WO2012 / 008212

  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 view of the above problems, an object of the present invention is to provide a light guide plate capable of reducing luminance unevenness of emitted light. Moreover, a surface light source device provided with the said light-guide plate is provided.

  The present invention will be described below. In addition, in order to make an understanding of this invention easy, the referential mark of an accompanying drawing is appended, but this invention is not limited only to the form of illustration by it.

  The invention according to claim 1 is the light guide plates 10 and 110 that allow light from the light source 29 to enter and guide the light in the light guide direction and emit light from the light exit surface, and the light exit surface has irregularities formed thereon. The diffractive structure layer 12 including the diffractive structure patterns 13a to 13f is provided, and at least one of the diffractive structure patterns has a ridge line extending in the light guide direction, and irregularities are alternately arranged in a direction different from the light guide direction. It is a light-guide plate which has the structure made.

  According to the second aspect of the present invention, in the light guide plates 10 and 110 according to the first aspect, the region including the plurality of diffraction structure patterns 13a to 13f is defined as the unit diffraction structure 13, and the diffraction structure layer 12 includes the plurality of unit structures. The diffractive structure 13 is formed by being arranged side by side in a light guide direction and a direction different from the light guide direction. The unit diffractive structure has a ridge line extending in the light guide direction and uneven in a direction different from the light guide direction. Include two or more diffractive structure patterns having different forms.

  According to a third aspect of the present invention, in the light guide plate 110 according to the first or second aspect, a ridge line extends in the light guide direction at the light source side end of the light guide direction of the diffractive structure layer 12, and the light guide A region having only a diffractive structure pattern in which irregularities are alternately arranged in a direction different from the direction is provided.

  Invention of Claim 4 is arrange | positioned facing the light-incidence surface formed in the light guide plate 10 and 110 in any one of Claims 1-3, and the one end side of the light guide direction of a light guide plate. A surface light source device 1 including a light source 29 and a deflecting optical sheet 30 arranged so as to face the diffractive structure layer 12 of the light guide plate and arranged with a plurality of unit prisms 32a that are convex with respect to the diffractive structure layer. It is.

  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.

FIG. 3 is an exploded perspective view illustrating a configuration of the surface light source device 1. 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. 3 is a plan view from the light exit surface side of the light guide plate 10. FIG. It is a figure explaining the unit diffraction structure 13 which concerns on a 1st example. It is a figure explaining the unit diffraction structure 13 which concerns on a 2nd example. It is a figure explaining the unit diffraction structure 13 which concerns on a 3rd example. It is a figure explaining the unit diffraction structure 13 which concerns on a 4th example. It is a flowchart for demonstrating the evaluation method of the diffusion characteristic of a light-diffusion film. It is a top view which shows an example of the diffraction grating element model used as evaluation object of a diffusion characteristic. It is a graph which shows an example of angle distribution of the intensity | strength of incident light beam. 11 is a graph showing the calculation result of the angular distribution of the intensity of the emitted light beam when the incident light beam having the orientation shown in FIG. 11 is incident on the diffraction grating element model shown in FIG. It is a flowchart which shows the design method of a light-diffusion film. 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. It is a top view from the light emission surface side of the surface light source device 110. FIG. 4 is an exploded perspective view showing a structure of a liquid crystal display device 200. FIG.

  The above-described operation and gain of the present invention will be clarified from embodiments for carrying out the invention described below. Hereinafter, the present invention will be described based on 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 is a part of a cross-sectional view in the thickness direction (vertical direction in FIG. 1) of the surface light source device 1 taken along the line II-II in FIG. 1 (light guide direction), and FIG. FIG. 1 shows 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 III-III (light source arrangement direction). 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 exit surface side of the base portion 11, and diffuses light at least in the light source arrangement direction when the guided light is emitted to the deflecting optical sheet 30, thereby reducing luminance unevenness. A layer comprising a diffractive structure pattern configured to have a function to improve. FIG. 4 shows a plan view of the light guide plate 10 viewed from the light exit surface direction. Therefore, the diffraction structure layer 12 appears in FIG. FIG. 4 also shows the direction.

  As can be seen from FIG. 4, in the diffraction structure layer 12, a plurality of unit diffraction structures 13, which are one unit having a predetermined form, are arranged along the surface of the base 11 in the light guide direction and the light source arrangement direction. The form of one unit diffraction structure 13 is represented by a square in FIG. 4, but is not limited to this, and may be a rectangle or other polygonal shape, and can be set as appropriate. Further, since the diffraction structure layer 12 includes a function of diffusing light in the light source arrangement direction, the size of the unit diffraction structure 13 in the light source arrangement direction (see, for example, the size indicated by A in FIG. 5). Is preferably smaller than one pitch of the plurality of light sources 29 arranged.

  The specific structure in the unit diffraction structure 13 includes a structure capable of diffusing emitted light in the light source arrangement direction, and a structure for performing other functions can be added, and is not limited. . 5 to 8 illustrate examples of the structure of the unit diffraction structure 13.

FIG. 5 shows the unit diffraction structure 13 according to the first example, in which one type of diffraction structure pattern 13 a is included in the unit diffraction structure 13. FIG. 5A is a plan view of one unit diffraction structure 13 and is a view from the same viewpoint as FIG. FIG. 5B is a Vb-Vb cross-sectional view of FIG. That is, FIG. 5B is a cross-sectional view of the unit diffraction structure 13 along the light source arrangement direction.
As can be seen from FIG. 5A and FIG. 5B, the diffractive structure pattern 13a has convex portions having a rectangular cross-sectional shape arranged in parallel in the light source arrangement direction at a predetermined pitch, and is formed by concave portions formed between the convex portions. It has a concavo-convex diffractive structure. As a result, the phase modulation amount of the light transmitted through the convex portion differs from the phase modulation amount of the light transmitted through the concave portion, and as a result, the light is diffracted in a predetermined pattern as the diffraction structure pattern 13a. 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. This pitch p ₁ of the unevenness in _particular, the pitch direction size of the peaks and valleys a _1, b _1, and the height of the protrusions (depth of the concave portion of) the order of magnitude of h ₁ is largely different Can be distinguished. For example, the size of p ₁ can be 0.5 μm to 20 μm, the sizes of a ₁ and b ₁ can be 0.2 μm to ₁₀ μm, and the size of h ₁ can be about ₁ μm to ₁₀ μm. 13a, the diffractive structure pattern in which the ridges of the concavo-convex extend in the light guide direction and the concavo-convex is alternately arranged in the light source arrangement direction that is orthogonal to the ridge line is primary light, and in some cases, secondary light or later In addition to the higher-order light, the light can be diffused in the light source array direction, thereby improving luminance unevenness in the light source array direction.

FIG. 6 is an example of the unit diffraction structure 13 according to the second example, and one unit diffraction structure 13 includes three types of diffraction structure patterns 13a, 13b, and 13c arranged in the light source array direction. This is an example. FIG. 6A is a diagram corresponding to FIG. 5A in plan view of the unit diffraction structure 13. FIG. 6B is a cross-sectional view taken along line VIb-VIb in FIG. That is, FIG. 6B is a cross-sectional view of the unit diffraction structure 13 along the light source arrangement direction.
Each of the three types of diffractive structure patterns 13a, 13b, and 13c has a ridge line extending in the light guide direction, and irregularities are alternately arranged in the light source arrangement direction that is orthogonal to the ridge line. Furthermore, in the diffraction structure patterns 13a, 13b, and 13c, the pitches p ₁ , p ₂ , and p ₃ and the pitch direction sizes a ₁ , b ₁ , a ₂ , b ₂ , a ₃ , and b _{3 of the} convex portions and the concave portions are respectively Are formed differently. That is, p ₂ > p ₁ > p ₃ , a ₂ > a ₁ > a ₃ , and b ₂ > b ₁ > b ₃ .
According to such a unit diffraction structure 13, light can be diffused more smoothly in the light source array direction. The diffraction structure patterns 13a, 13b, and 13c have different diffusion angles in the light source array direction plane based on the difference in shape. Therefore, in the unit diffraction structure 13 according to the second example, light is diffused as if they were averaged (combined) as a whole, and light can be diffused more uniformly in the light source arrangement direction.

FIG. 7 shows an example of the unit diffraction structure 13 according to the third example, in which two types of diffraction structure patterns 13a and 13d arranged in the light source array direction are included in one unit diffraction structure 13. It is. FIG. 7 is a diagram corresponding to FIG. 5A in plan view of the unit diffraction structure 13.
In the unit diffraction structure 13 according to the third example, a diffraction structure pattern 13d is provided in addition to the diffraction structure pattern 13a described above. The diffractive structure pattern 13d is a pattern in which concave and convex ridge lines extend in the light source arrangement direction and irregularities are alternately arranged in the light guide direction. Thereby, light is diffused also in the light guide direction plane.

FIG. 8 shows an example of the unit diffraction structure 13 according to the fourth example, in which four types of diffraction structure patterns 13 a, 13 d, 13 e, and 13 f are included in one unit diffraction structure 13. FIG. 8 is a diagram corresponding to FIG. 5A in plan view of the unit diffraction structure 13 according to the fourth example.
In the unit diffraction structure 13 according to the fourth example, in addition to the unit diffraction structure 13 according to the third example, diffraction structure patterns 13e and 13f arranged in the light guide direction are provided. In the diffractive structure patterns 13e and 13f, the ridges of the projections and depressions extend obliquely with respect to the light source arrangement direction and the light guide direction, and the projections and depressions are alternately arranged in a direction orthogonal to the extending direction. The diffractive structure pattern 13e and the diffractive structure pattern 13f are structures having different extending directions, and are configured such that the extending directions are orthogonal to each other.
According to such a unit diffraction structure 13, light can be diffused in different planes, and the directions in which light can be diffused can be increased.

As in the example described above, the unit diffractive structure 13 including at least one pattern having a ridge line extending in the light guide direction and having unevenness along the light source array direction diffuses light in the light source array direction. It is possible to improve the uniformity of the light and improve the luminance unevenness.
In addition, by combining this with a diffraction structure of another pattern, light can be diffused in other directions.

  Here, all of the unit diffractive structures 13 included in the diffractive structure layer 12 include a diffractive structure pattern including at least one pattern in which a ridge line extends in the light guide direction and unevenness is provided in the light source arrangement direction. It is preferable, but not necessarily all. At this time, the ridge line extends in the light guide direction provided in the light source side half of the light guide direction of the light guide plate, and the amount of the pattern provided with unevenness along the light source arrangement direction is the amount of the pattern provided in the opposite half More than the amount is preferred. This is because the luminance unevenness caused by the light source is larger near the light source side.

  Here, in the cross-sectional shape of each of the above examples, the corners of the protrusions and the corners of the recesses may be arcuate or tapered. This facilitates manufacturing.

  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.

  The step of obtaining the form of the diffractive structure layer is not particularly limited as long as each diffractive structure pattern shape having the functions described above can be obtained. For example, the following method can be employed.

Here, a method for evaluating the diffusion characteristics of a diffraction structure layer when a plurality of diffraction structure patterns are included will be described first.
When the light guide plate is designed and fabricated, the diffusion characteristics of the obtained light guide plate are usually evaluated before actually applying to various devices. For example, a well-known light diffusing film with a light diffusing agent added therein is easy to manufacture. You should evaluate. On the other hand, in order to manufacture a light diffusing film using a computer-generated hologram as disclosed in WO2005-0708383 and JP2001-356673A, it is generally necessary to manufacture a mold having a super-precision structure. . For this reason, in a conventional light diffusion film using a computer-generated hologram, the diffusion characteristics are often evaluated by simulation before preparing an expensive mold. However, the calculation is very complicated and takes a long time.

  On the other hand, unlike the computer-generated hologram having irregular interference fringes, the light guide plate described above expresses a light diffusion function using a diffractive structure layer. For this reason, the diffusion characteristic of each unit optical structure can be calculated accurately in a short time compared with the diffusion characteristic of the computer-generated hologram. In addition, in the evaluation method described below, by using the area ratio of a plurality of diffraction structure patterns, the diffusion characteristics of a light guide plate including a plurality of unit diffraction structures having different diffraction structure patterns are accurately calculated in a short time. can do. Hereinafter, a method for evaluating the diffusion characteristics of the diffractive structure layer will be described with reference to FIGS.

As shown in FIG. 9, the method for evaluating the diffusion characteristics of the diffractive structure layer described here is:
A model setting step for setting a diffraction grating element model having a corresponding configuration for each of the diffraction structure patterns included in the diffraction structure layer;
A first calculation step of calculating diffraction efficiency for each of a plurality of selected diffraction grating element models;
・ Considering the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the diffraction structure layer A second calculation step for calculating an angular distribution of the intensity of the emitted light;
Is included.

  In the model setting step, a plurality of diffraction structure patterns included in the diffraction structure layer to be evaluated are specified as a diffraction grating element model. Assuming that the diffractive structure pattern of the target diffractive structure layer is defined by the concavo-convex surface forming the refractive index interface, as described above, the pitch of the concavo-convex surface between the selected diffraction grating element models. p, the ratio (a / p) of the width a of the convex portion forming the concave and convex surface to the pitch p of the concave and convex surface, the arrangement direction of the convex portion forming the concave and convex surface, the height h of the convex portion forming the concave and convex surface, and the cross section of the concave and convex surface One or more of the shape, the area ratio with respect to another diffraction grating element model, and the refractive index difference on both sides of the uneven surface are made different. When the diffractive structure layer is composed of a large number of unit diffractive structures that are configured identically, it is only necessary to focus on a plurality of diffractive structure patterns included in one unit diffractive structure.

  As a specific example, the diffraction structure pattern 13a and the diffraction structure pattern 13d included in the diffraction structure layer shown in FIG. 7 are used as the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. evaluated. In this evaluation, for the convenience of understanding, the first diffraction grating element model 55a and the second diffraction grating element model 55b are set as follows. The first diffraction grating element model 55a and the second diffraction grating element model 55b are composed of a first layer on the light incident side and a second layer on the light emission side, and a refractive index interface between the first layer and the second layer. It was decided that a concavo-convex surface was formed. The refractive index of the material forming the first layer was 1.588, and the refractive index of the material forming the second layer was 1.410. The first diffraction grating element model 55a and the second diffraction grating element model 55b are different in that the arrangement directions of the grating patterns are different, and the configurations of the other uneven surfaces are the same. In other words, the first diffraction grating element model 55a is specified to be the same as the second diffraction grating element model 55b when turned 90 °. The area ratio of the first diffraction grating element model 55a and the second diffraction grating element model 55b was set to 1: 1.

  Next, in the first calculation step, the diffraction efficiency is calculated for each of the plurality of selected diffraction grating element models. For each diffraction grating element model, calculation is performed for zero-order diffraction efficiency, first-order diffraction efficiency, and, if necessary, second-order or higher diffraction efficiency. For example, the diffraction efficiency of each order can be calculated for each diffraction grating element model by using rigorous coupled wave theory or time domain difference method (FDTD Finite Difference Time Domain method). When using the rigorous coupled wave theory or the time domain difference method, specify the incident angle of incident light, the wavelength of incident light, and the configuration of the diffraction grating element model (cross-sectional shape and refractive index difference on the uneven surface). The following diffraction efficiency can be calculated. Therefore, when it is assumed that light in a plurality of wavelength regions is incident on the diffraction structure layer to be evaluated, in each of the light in the plurality of wavelength regions in the first calculation step and the second calculation step described below. What is necessary is just to perform calculation. In addition, when it is assumed that light enters the diffraction structure layer to be evaluated with an angle width, diffraction efficiency is calculated for a plurality of incident angles.

  Here, in the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. 10, the pitch of the uneven surface is 0.9 μm and the height h of the convex portion forming the uneven surface is 1.3 μm. In the set example, the results of calculating the diffraction efficiency of each order are as shown in Table 1. The diffraction efficiency in Table 1 is a calculation result when incident light is incident on the first diffraction grating element model 55a and the second diffraction grating element model 55b from the front direction.

  Finally, in the second calculation step, the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and each diffraction grating element in the diffraction structure layer The angle distribution of the intensity of the emitted light is calculated in consideration of the area ratio of the model. The angular distribution of the intensity of the emitted light can be calculated using the following formula.

here,
m: diffraction grating number n: diffraction order λ: wavelength (x, y): direction cosine of incident light (X, Y): direction cosine of outgoing light (d _x , d _y ): grating vector σ _m : m th Diffraction grating area ratio O (X, Y, λ): angle distribution of emitted light intensity η _{m, n} (x, y, λ): nth-order diffraction efficiency D _{m, n} ( X, Y, x, y, λ): n-th order diffracted light distribution I (x, y, λ) of the m-th diffraction grating: angular distribution of the intensity of incident light. In the expression of D _{m, n} (X, Y, x, y, λ) indicating the n-th order diffracted light distribution of the m-th diffraction grating, the delta function δ is used, and (d _x , d in the delta function is used. _y ) is a lattice vector. Accordingly, the expression D _{m, n} (X, Y, x, y, λ) represents that the incident light is diffracted by the diffraction grating element model and the propagation direction is changed. O (X, Y, λ) is basically obtained by the ray tracing method. That is, first, the incident light beam is represented by a number of light beams, and the diffraction phenomenon of each light beam in the diffraction grating element model is calculated. Thereafter, the diffracted light is collected to obtain an angular distribution of the intensity of the emitted light beam. In a conventional light diffusion film using a computer-generated hologram, it is impossible to obtain O (X, Y, λ) by such a method.

  FIG. 11 shows a graph representing an example of the angular distribution of the intensity of the incident light beam. In the graph of FIG. 11, the solid line indicates the angular distribution of the intensity of the incident light beam in the plane along both the front direction and the first direction d1, and the broken line indicates both the front direction and the second direction d2. The angular distribution of the intensity | strength of the incident light beam in the in-plane is shown. When the incident light flux having the orientation shown in FIG. 11 is incident on the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. 10, the first diffraction grating element model 55a and the second diffraction grating element model 55a. The angular distribution of the intensity of the emitted light beam that has passed through the diffraction grating element model 55b is shown as a graph in FIG.

  The graph of FIG. 12 shows the angular distribution of the intensity of the emitted light beam in the plane along both the front direction and the first direction d1. In this evaluation of the angular distribution of the intensity, that is, in the evaluation obtained as a result of FIG. 12, it is assumed that 400 nm light, 500 nm light, 600 nm light and 700 nm light are included in the incident light flux with the same light amount. The conditions were adopted. Further, in the evaluation with which the result of FIG. 12 was obtained, the pitch of the concave and convex surfaces of the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. The height h was set to 1.3 μm, and the width a of the convex portion forming the irregular surface was set to 0.45 μm. Further, the incident light beam is linearly polarized light that vibrates along the first direction d1.

  Further, the pitch p of the concavo-convex surfaces of the first diffraction grating element model 55a and the second diffraction grating element model 55b in FIG. 10 and the convex portions forming the concavo-convex surfaces of the first diffraction grating element model 55a and the second diffraction grating element model 55b. The height h was set to various values, and the diffusion characteristics of the first diffraction grating element model 55a and the second diffraction grating element model 55b were evaluated and calculated. The pitch p of the uneven surface was changed by 0.2 μm from 0.9 μm to 2.1 μm. About the height h of the convex part which makes an uneven surface, it set to 1.3 micrometers, 1.5 micrometers, and 1.7 micrometers.

The ratio of the front direction luminance, the front direction luminance ratio, the half-value angle, and the chromatic dispersion coefficient in the angular distribution of the emitted light intensity in the plane along both the front direction and the first direction d1, obtained for each condition, Table 2, Table 3 and Table 4 show. The chromatic dispersion coefficient refers to the maximum value, minimum value, and average value related to the intensity of the emitted light of each wavelength along the normal direction of the diffractive structure layer, and the difference X ( It is a ratio value (x / y) to the average value y of (see FIG. 12). The greater the value of the chromatic dispersion coefficient, the more dispersed the color. As shown in Tables 2 to 4, it was confirmed that the diffusion characteristics of the diffractive structure layer can be greatly changed by changing the pitch p of the uneven surface and the height h of the convex portion forming the uneven surface.
Here, the angle of the incident light on the diffractive structure layer is not limited to the incident light from the normal direction to the diffractive structure layer, and even in the case of oblique incidence having a predetermined angle from the normal direction. Can be calculated.

  Diffraction structure layers having other diffraction structure patterns can be similarly formed. According to the method for evaluating the diffusion characteristics of the diffractive structure layer as described above, the diffractive structure pattern included in the diffractive structure layer has a periodic grating pattern and the areas of two or more unit diffractive structures having different grating patterns. Because the ratio is used, it is not necessary to consider the shape of the pattern edge as in the case of a conventional light diffusing film using a computer-generated hologram, and it is also necessary to consider the calculation area of the pattern Absent. Thereby, there are few errors, the accuracy of the evaluation result is greatly improved, and the calculation time is shortened. In particular, in the case of a diffractive structure layer composed of a number of unit diffractive structures that are configured identically, only a small part of the diffractive structure layer needs to be calculated, and a conventional light diffusion using a computer-generated hologram that requires a large area to be calculated. Compared with film, the calculation time can be greatly reduced.

  Next, a method for designing the diffractive structure layer will be described. As described above, the diffusion characteristics of the diffractive structure layer can be evaluated with high accuracy in a short time compared to the diffusion characteristics of a conventional light diffusion film using a computer-generated hologram. By utilizing this point, a diffractive structure layer that can exhibit a desired diffusion function can be designed with high accuracy in a short time using a computer. Hereinafter, a method for designing the diffractive structure layer will be described.

As shown in FIG. 13, the design method of the diffractive structure layer described here is:
A model setting step of selecting a diffraction grating element model given a specific configuration for each of a plurality of diffraction structure patterns included in the diffraction structure layer;
A first calculation step of calculating diffraction efficiency for each of a plurality of selected diffraction grating element models;
・ Considering the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the diffraction structure layer A second calculation step for calculating an angular distribution of the intensity of the emitted light;
Confirming whether or not a preset condition is satisfied based on the calculated angular distribution of the intensity of the emitted light, and a confirmation step;
Is included.

  First, in the model design process, a plurality of diffraction grating element models having different grating patterns are selected. As an example, when each diffraction grating element model set in the model setting process is modeled as an uneven surface, the uneven surface pitch p and the uneven surface pitch p between the multiple uneven surface element models The ratio (a / p) of the width a of the convex portion forming the surface, the arrangement direction of the convex portion forming the concave and convex surface, the height h of the convex portion forming the concave and convex surface, the cross-sectional shape of the concave and convex surface, and other diffraction grating element models A plurality of diffraction grating element models can be selected so that one or more of the area ratio and the refractive index difference on both sides of the uneven surface are different.

  In the model setting step, it is preferable that a plurality of diffraction grating element models are selected in consideration that a preset condition is satisfied. At this time, based on the results obtained in advance, for example, the information that is the basis of the evaluation is investigated and acquired in advance, and this information is compared with the desired orientation of the emitted light, and a plurality of information is obtained. It is preferable to select a diffraction grating element model.

  The first calculation step and the second calculation step performed next are performed in the same manner as the first calculation step and the second calculation step in the method for evaluating the diffusion characteristics of the diffraction structure layer described above. Through the second calculation step, information on the diffusion characteristics of the temporarily designed diffraction structure layer can be obtained.

  In the confirmation process, the diffractive structure layer provisionally designed in the model setting process based on the information on the obtained diffusion characteristics exhibits an effective light diffusion function for the incident light flux with the assumed orientation. It is examined whether or not a predetermined condition regarding the angular distribution of the intensity of the light beam is satisfied. The predetermined condition confirmed here is a condition determined according to the intended use of the diffraction structure layer to be designed.

  As an example, in the confirmation step, whether the half-value angle of the angular distribution of the intensity of emitted light in a plane along a specific direction is greater than or equal to a preset value (or exceeds a preset value) ) Whether or not the intensity of the emitted light traveling in the normal direction of the diffractive structure layer is greater than or equal to a preset angle (or exceeds a preset angle), or the diffractive structure layer It can be determined whether the intensity of the outgoing light traveling in the normal direction is less than a preset value (or less than a preset value).

  In the first calculation step and the second calculation step, when calculation is performed for light of a plurality of wavelengths, the confirmation step sets in advance based on the angular distribution of the intensity of the emitted light calculated for the light of each wavelength. It may be confirmed whether or not the conditions are satisfied. For example, it may be determined whether or not the calculated angular distribution of the intensity for light of all wavelengths satisfies a predetermined condition. Further, in the confirmation step, the chromaticity angle change may be confirmed as a predetermined condition. As a specific example, the maximum value, minimum value, and average value regarding the intensity of the emitted light of each wavelength along the normal direction of the diffractive structure layer are specified, and the ratio of the difference between the maximum value and the minimum value to the average value is determined. Whether or not the value, that is, the above-described chromatic dispersion coefficient is equal to or less than a preset value (or less than a preset value) may be determined in the confirmation step.

  As shown in FIG. 13, when it is confirmed that a preset condition is satisfied in the confirmation process, the configuration of the diffraction grating element model that is the calculation target is the configuration of the corresponding diffraction grating element. And the design of the diffractive structure layer is completed. On the other hand, when it is confirmed that the preset condition is not satisfied in the confirmation process, the process returns to the model setting process, and a specific configuration is assigned to each of the plurality of diffraction structure patterns included in the diffraction structure layer. The selected diffraction grating element model is selected again, and the first calculation step, the second calculation step, and the confirmation step are performed again. At this time, if it is confirmed that a preset condition is satisfied in the second confirmation step, the configuration of the diffraction grating element model that is the second calculation target is determined as the configuration of the diffraction grating element. The design ends. Conversely, when it is confirmed that the preset condition is not satisfied in the second confirmation process, it is confirmed that the preset condition is satisfied in the confirmation process performed thereafter. Until it is done, the model setting process, the first calculation process, the second calculation process, and the confirmation process are repeated.

  As an example, when it is confirmed that a preset condition is not satisfied in the confirmation process, when reselecting a plurality of diffraction grating element models in the subsequent model setting process, Only the area ratio is changed, that is, the configuration other than the area ratio of each diffraction grating element model may be maintained. When such a method is used, the direction of the grating pattern is different between two or more of the selected diffraction grating element models in the first model setting process. Is preferred. According to such a method, when the second calculation process is performed again, it is possible to use a part of the calculation result obtained in the first second calculation process. By using the calculation result obtained in the calculation process as it is, it is not necessary to actually perform the first calculation process again.

  When it is confirmed that the preset condition is not satisfied in the confirmation process, it is necessary to reselect a plurality of diffraction grating element models in the model setting process that is subsequently performed. The next model condition value is determined by changing the model condition value so that the evaluation value (a value indicating the degree to which the condition is satisfied) is improved, and changing the model condition value. If the value improves, a method of adopting the change and proceeding to the next can be exemplified. Examples of the former include a damped least-squares method (DLM), and examples of the latter include a genetic algorithm (GA) and simulated annealing (SA).

  As described above, it is possible to design the shape of the diffractive structure layer that exhibits effective light diffusion characteristics with respect to the assumed incident light and can control the orientation of the emitted light.

  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. 16) 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. 14A is a conceptual perspective view showing the form of the mold roll 50. FIG. 14B 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.15 (a). FIG. 15B 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. The groove | channel 51 is extended in the direction along the rotating shaft of the metal mold | die which is roll shape so that FIG.14 (a) may show, and the several groove | channel 51 is 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. Therefore, in the shaped sheet 60, as shown in FIG. 15B, a plurality of grooves 61 corresponding to the shape of the diffractive structure layer 12 are formed on one sheet surface. As can be seen from FIG. 15A, the groove 61 extends in a direction along the longitudinal direction of the belt-like 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. The shape can be obtained as follows, for example.

  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, and the lamination of the resist can be performed 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 the binary structure of the convex part and the concave part (high and low two steps, the depth is generated 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 → chromium thin film dry etching → quartz substrate dry etching → 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 a predetermined number of steps, the chromium thin film is removed by wet etching to obtain a mold shape in which irregularities having 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.

  In addition, in order to obtain unevenness only by a one-dimensionally extending pattern as shown in FIG. 5, a cutting tool in which the entire unevenness shape or a part of the unevenness shape is processed is prepared, and a roll plate is obtained by lathe processing on a plated roll. Create 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. 16 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. FIG. 17 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. 17, in this embodiment, the unit prism 32a has a cross section of an isosceles triangle protruding 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. 17) 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, the operation of the light guide plate 10 having the above-described configuration and the surface light source device 1 having the same will be described with reference to an example of an optical path.

  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 has the unit diffractive structure 13 as described above, and includes a diffractive structure pattern 13a in which ridge lines extend in the light guide direction and irregularities are alternately arranged in the light source arrangement direction. The diffractive structure layer 12 is provided. Thereby, the light emitted from the light guide plate 10 via the diffractive structure layer 12 includes a component that diffuses in the light source arrangement direction when emitted from the light guide plate 10, for example, as indicated by the lights L 31 and L 32 in FIG. It becomes like this. Thereby, the uniformity of light is improved in the light source arrangement direction, and unevenness in luminance can be reduced.

The optical path will be described continuously 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 L141 in FIG. 17, 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.

  Next, another embodiment will be described. The other embodiment is different in that a light guide plate 110 is used instead of the light guide plate 10 of the above embodiment, and the other configurations are the same. Further, in the light guide plate 110, only the form of the diffractive structure layer 112 is different from that of the diffractive structure layer 12, and other parts are the same. Therefore, here, the diffraction structure layer 112 will be described. FIG. 18 is a diagram illustrating the diffractive structure layer 112 and a diagram corresponding to FIG. 4. In the diffractive structure layer 112, as can be seen from FIG. 18, the unit diffractive structures 113 are arranged in the light source side region which is a predetermined region on the light source side in the light guide direction. In the region other than the light source side region, the unit diffraction structures 113 are arranged in the same manner as the above-described diffraction structure layer.

The unit diffractive structure 113 includes only diffractive structure patterns included in the ridge line extending in the light guide direction and the unevenness being alternately arranged in the light source arrangement direction, for example, as shown in FIGS. 5 and 6. It has a shape like the example.
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 brightness unevenness in the light source arrangement direction is larger than the others, so in this part, the unit diffraction structure 113 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 the portion where the LED exists and the portion where the LED does not exist, set the shape (pitch, depth, etc.) of the diffraction structure pattern, and modulate the diffraction efficiency fluctuation and the degree of diffusion angle. .

  As shown in FIG. 19, the liquid crystal display device 10 and 110 described above 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 10,110 Light guide plate 10 'Light guide plate strip | belt sheet | seat 11 Base part 12,112 Diffraction structure layer 13,113 Unit diffraction structure 13a-13f Diffraction structure pattern 29 Light source 30 Deflection optical sheet 40 Reflection sheet 50 Mold roll 51 61 Grooves 55a to 55b Diffraction grating element model 60 Molding sheet 70 Feed roll 71 Nip roll 72 Release roll 73 Separation roll 74 Nozzle 200 Liquid crystal display device

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,
At least one of the diffractive structure patterns is a light guide plate having a structure in which ridge lines extend in the light guide direction and irregularities are alternately arranged in a direction different from the light guide direction. A region including a plurality of the diffraction structure patterns is a unit diffraction structure, and the diffraction structure layer is formed by arranging the plurality of unit diffraction structures side by side in a direction different from the light guide direction and the light guide direction. And
2. The unit diffractive structure includes two or more types of diffractive structure patterns having ridges extending in the light guide direction and irregularities alternately arranged in a direction different from the light guide direction. The light guide plate described in 1.   A light source side end of the light guide direction of the diffraction structure layer includes only the diffraction structure pattern in which a ridge line extends in the light guide direction and irregularities are alternately arranged in a direction different from the light guide direction. The light guide plate according to claim 1, wherein a region is provided. 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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