JP5757401B2 - Anisotropic light diffusion film, surface light source device and display device - Google Patents

Description

  The present invention relates to a light diffusing film having a diffusing function for diffusing light, and more particularly, to an anisotropic light diffusing film having an anisotropic diffusing function for diffusing light with directivity (anisotropically). . Moreover, this invention relates to the surface light source device and display apparatus containing this anisotropic light-diffusion film.

  Conventionally, a light diffusing film having a function of diffusing light has been used. In particular, not only isotropic light diffusion films that diffuse light isotropically (uniformly) but also anisotropic light diffusion films that diffuse light in a specific direction are used in various fields.

  For example, in Patent Document 1, an anisotropic light diffusion film is used for the purpose of adjusting the viewing angle of a display device. Further, in a surface light source device that emits light in a planar shape, as represented by a cold cathode tube or the like, the light emission characteristics of a light emitter that forms a light source may have directivity. It is necessary to adjust the optical characteristics along the line. Also, as disclosed in Patent Document 2, in such a surface light source device, an anisotropic light diffusion film has been used mainly for the purpose of mainly adjusting optical characteristics along a specific direction. . Patent Document 2 discloses the use of an anisotropic light diffusion film as a backlight that illuminates a liquid crystal display panel from the back side as an example of a surface light source device.

JP-A-4-314522 JP 2008-129546 A

  Many of the conventional anisotropic light diffusing films are uniaxially stretched with a light diffusing film containing light diffusing particles so that the direction of the light diffusing particles having the longitudinal direction is aligned, as represented by Patent Document 1. It has been made by. However, if an attempt is made to produce a light diffusive film by this method, voids, cracks and the like are generated between the light diffusible particles and the surrounding resin during stretching. In addition, the stretched light diffusion film has a high retardation, which may not be preferable for use of a surface light source device as a backlight.

  In Patent Document 2, an anisotropic light diffusing film is prepared by coating a resin composition containing the light diffusing particles on a substrate so that the light diffusing particles having a longitudinal direction are oriented in a certain direction. Has been made. According to the method disclosed in Patent Document 2, problems caused by uniaxial stretching of the light diffusing film can be solved, but in practice, the direction of the light diffusing particles is controlled during coating. As a result, it is practically difficult to control the anisotropic diffusion function of the light diffusion film to a desired level by employing the method disclosed in Patent Document 2.

  The present invention has been made in consideration of such points, and an object thereof is to provide an anisotropic light diffusion film having an anisotropic light diffusion function.

The anisotropic light diffusion film according to the present invention is:
A sheet-like first portion including a plurality of elongated protrusions arranged with directionality;
A binder portion provided on the surface of the first portion where the protruding portion is formed, and a second portion including light diffusing particles having a longitudinal direction dispersed in the binder portion,
The light diffusing particles of the second portion are arranged with regularity in a certain direction related to the directionality of the protruding portion of the first portion.

  In the anisotropic light diffusing film according to the present invention, the first portion includes a sheet-like main body and the plurality of protrusions arranged side by side on the main body, and the plurality of protrusions are The protrusions may be arranged side by side on the main body, and each protrusion may extend in a direction that intersects the array direction of the plurality of protrusions.

  In the anisotropic light diffusing film according to the present invention, the entirety of the light diffusing particles may be located in a groove formed between two adjacent protrusions of the plurality of protrusions.

  In the anisotropic light diffusing film according to the present invention, the width of the groove formed between two adjacent protruding portions of the plurality of protruding portions is the maximum width in a cross section perpendicular to the longitudinal direction of the light diffusing particles. The depth of the groove that is larger than Pw and formed between two adjacent protrusions of the plurality of protrusions is larger than the maximum width in the cross section perpendicular to the longitudinal direction of the light diffusing particles. , May be bigger.

In the anisotropic light diffusing film according to the present invention, the length of the light diffusing particles along the longitudinal direction is Pl, and the width of a groove formed between two adjacent protruding portions of the plurality of protruding portions. When Gw is set as Gw, the following relationship may be satisfied.
Gw <(Pl) / (2 ^1/2 )

In the anisotropic light diffusing film according to the present invention, the length of the light diffusing particles along the longitudinal direction is Pl, and the depth of a groove formed between two adjacent protrusions of the plurality of protrusions. When the thickness is Gd, the following relationship may be satisfied.
Gd <(Pl) / (2 ^1/2 )

  In the anisotropic light diffusing film according to the present invention, only a part of the light diffusing particles may be located in a groove formed between two adjacent protruding portions of the plurality of protruding portions.

  In the anisotropic light diffusing film according to the present invention, the width of the groove formed between two adjacent protruding portions of the plurality of protruding portions is the maximum width in a cross section perpendicular to the longitudinal direction of the light diffusing particles. It may be smaller than Pw.

  In the anisotropic light diffusing film according to the present invention, the depth of the groove formed between two adjacent protrusions of the plurality of protrusions is the maximum in the cross section perpendicular to the longitudinal direction of the light diffusing particles. It may be smaller than Pw.

In the anisotropic light diffusing film according to the present invention, a radius of a circle having the same area as the maximum cross-sectional area of the light diffusing particles in a cross section perpendicular to the longitudinal direction of the light diffusing particles is Pr, and the plurality of protrusions When the width of the groove formed between two adjacent protrusions is Gw, the following relationship may be satisfied.
((Pr) × 2) / (2 ^1/2 ) ≦ Gw

In the anisotropic light diffusing film according to the present invention, a radius of a circle having the same area as the maximum cross-sectional area of the light diffusing particles in a cross section perpendicular to the longitudinal direction of the light diffusing particles is Pr, and the plurality of protrusions When the depth of a groove formed between two adjacent protrusions is Gd, the following relationship may be satisfied.
Pr − ((Pr) / (2 ^1/2 )) ≦ Gd

  In the anisotropic light diffusing film according to the present invention, at least a part of one surface of the anisotropic light diffusing film is constituted by the second portion, and the other surface of the anisotropic light diffusing film is constituted by the first portion. It may be.

  In the anisotropic light diffusing film according to the present invention, one surface of the anisotropic light diffusing film is constituted by the tip surface of the protruding portion and the second part of the first portion, and the first portion of the anisotropic light diffusing film is formed. The other surface may be configured.

  The anisotropic light-diffusion film by this invention WHEREIN: The recessed part may be formed in the position comprised by the said 2nd part of said one surface.

  The anisotropic light-diffusion film by this invention WHEREIN: The convex part may be formed in the position comprised by the said protrusion part of the said 1st part among said one surfaces.

  In the anisotropic light diffusing film according to the present invention, a protrusion due to the light diffusing particles may be formed on the one surface.

  The anisotropic light diffusion film according to the present invention may further include a functional layer having at least one of an antireflection function, an antiglare function, and an abrasion resistance function.

  The anisotropic light diffusion film according to the present invention may further include unit optical elements arranged side by side.

  The surface light source device according to the present invention includes any of the anisotropic light diffusion films according to the present invention described above.

  A first display device according to the present invention includes any of the surface light source devices according to the present invention described above.

  The second display device according to the present invention includes any one of the anisotropic light diffusion films according to the present invention described above.

  According to the present invention, the direction of the light diffusing particles can be stably controlled by the protruding portion of the first portion, and thus it is possible to stably impart the anisotropic light diffusing function to the light diffusing film. Become.

FIG. 1 is a perspective view showing an anisotropic light diffusing film for explaining a primary embodiment according to the present invention. FIG. 2 is a plan view showing the anisotropic light diffusing film shown in FIG. 1 from the normal direction to the film surface of the anisotropic light diffusing film. FIG. 3 shows the anisotropic light diffusing film shown in FIG. 1 in a cross section taken along the line III-III in FIG. 2, that is, in a cross section along the normal direction to the film surface of the anisotropic light diffusing film. It is sectional drawing. FIG. 4 is a diagram showing an example of a display device and a surface light source device in which the anisotropic light diffusion film shown in FIG. 1 is incorporated. FIG. 5 is a cross-sectional view corresponding to FIG. 3 and showing a modification of the anisotropic light diffusion film. FIG. 6 is a cross-sectional view corresponding to FIG. 3 and showing another modification of the anisotropic light diffusion film. FIG. 7 is a view corresponding to FIG. 2 and a plan view showing still another modification of the anisotropic light diffusion film. 8 is a cross-sectional view corresponding to FIG. 3 and showing another modification of the anisotropic light diffusion film shown in FIG. 7 in a cross section taken along the line VIII-VIII of FIG. FIG. 9 is a cross-sectional view corresponding to FIG. 3 and showing still another modification of the anisotropic light diffusion film. FIG. 10 is a cross-sectional view corresponding to FIG. 3 and showing still another modification of the anisotropic light diffusion film.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product.

  1 to 4 are diagrams for explaining an embodiment according to the present invention. 1 to 3 are a perspective view, a plan view, and a cross-sectional view, respectively, showing the anisotropic light diffusion film 10 according to the present embodiment.

  The anisotropic light diffusion film 10 shown in FIGS. 1 to 3 includes a sheet-like first portion 20 and a second portion 30 provided on the first portion 20. The second part 30 includes a binder part 32 provided on the first part 20 and light diffusing particles 34 dispersed in the binder part 32. First, the first portion 20 will be described, and then the second portion 30 will be described.

  In the present specification, the terms “sheet”, “film”, and “plate” are not distinguished from each other only based on the difference in names. For example, “film” is a concept including a member that can be called a sheet or a plate. Therefore, “light diffusion film (anisotropic light diffusion film)” is “light diffusion sheet (anisotropic light diffusion sheet)” or “ It cannot be distinguished only by the difference in name from a member called “light diffusing plate (anisotropic light diffusing plate)”.

  Further, the “film surface (sheet surface, plate surface)” means a surface that coincides with the planar direction of the target film-like member when the target sheet-like member is viewed as a whole and globally. Point to.

  Furthermore, terms specifying the shape and geometric conditions used in the present specification, for example, terms such as “parallel” and “orthogonal” can be expected to have the same optical function without being bound to a strict meaning. Interpretation will be made including a margin of error.

  As shown in FIGS. 1 to 3, the first portion 20 includes a sheet-like main body 22 and a large number of protrusions 24 provided on the main body 22. The main body portion 22 functions as a portion that supports the protruding portion 24. The main body 22 is formed as a sheet-like member having one flat surface 22a on which the protruding portion 24 is disposed and the other flat surface 22b opposite to the one surface 22a. One surface 22a and the other surface 22b are formed as flat surfaces parallel to each other.

  As well shown in FIGS. 1 to 3, the protrusion 24 is formed in an elongated shape and has a longitudinal direction. The elongated protrusion 24 is disposed on one surface 22a of the sheet-like main body 22 with directivity. In other words, the protrusions 24 having the longitudinal direction are arranged with regularity regarding the direction or the direction. As a result, one direction od in which the longitudinal direction of each protrusion 24 arranged on one surface 22a of the main body 22 is parallel to the sheet surface of the main body 22 (a direction serving as a reference for the angle formed by the longitudinal direction) The angle formed with respect to FIG. 1) is 0 ° or more and less than 45 °.

  In one embodiment shown in FIGS. 1 to 3, a large number of projecting portions 24 are arranged in an arrangement direction (left and right direction in FIG. 2) parallel to the sheet surface of the main body portion 22. They are arranged on one surface 22a. Each protrusion 24 extends linearly on one surface 22a of the main body 22 in a direction intersecting with the arrangement direction. In particular, in the illustrated example, the protrusions 24 extend linearly so as to be parallel to each other along a direction orthogonal to the arrangement direction. Furthermore, each protrusion 24 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction. Moreover, in this Embodiment, the some protrusion part 24 is comprised mutually the same.

  In the present embodiment, the cross section shown in FIG. 3, that is, in both directions of the normal direction nd to the arrangement direction of the protrusions 24 and the one surface 22a of the main body 22 (the sheet surface of the sheet-like main body 22). In a parallel cross section (hereinafter, also simply referred to as “main cut surface of anisotropic light diffusing film”), each projecting portion 24 has a quadrangular shape with one side positioned on one surface 22a of main body portion 22, more specifically. Has a rectangular shape.

  Such a first portion 20 is formed using a transparent material as a raw material. Specifically, the first portion 20 can be produced by extrusion molding using a transparent resin mainly composed of one or more of acrylic, styrene, polycarbonate, acrylonitrile and the like as a raw material. Alternatively, the first portion 20 is formed on the transparent substrate made of polyethylene terephthalate or the like, and the protruding portion 24 is shaped using an epoxy acrylate or urethane acrylate-based transparent reactive resin (ionizing radiation curable resin or the like). Thus, the first portion 20 can also be produced.

  Next, the second portion 30 will be described. The second portion 30 includes a binder portion 32 provided on one surface of the first portion 20 on which the protruding portion 24 is formed, and light diffusing particles 34 dispersed in the binder portion 32. .

  As shown well in FIG. 2, in the present embodiment, the second portion 30 is disposed so as to fill a groove 26 formed between two adjacent protrusions 24 among the plurality of protrusions 24. Has been. As a result, as shown in FIG. 2, one surface 10 a of the anisotropic light diffusion film 10 is configured as a flat surface formed by the tip surface 24 a of the protrusion 24 and the second portion 30. In addition, the other surface 10b of the anisotropic light diffusion film 10 is comprised from the other surface 22b of the main-body part 22 of the 1st part 20, Therefore, as mentioned above, it is comprised as a flat surface.

  The binder part 32 is a part for holding the light diffusing particles 34 on the first part 20 and may be formed of a transparent material. In the anisotropic light diffusing film 10, the light reflecting function is expressed due to the difference in refractive index between the binder portion 32 and the light diffusing particles 34, and reflection or refraction at the interface between the two. The binder portion 32 and the first portion 20 may have the same or different refractive indexes. However, by making the refractive index of the binder part 32 different from the refractive index of the first part 20, specifically, a range of 0.0001 to 0.5, more preferably 0.001 to 0.3. By making the difference within the following range, the light diffusion function, especially the anisotropic light diffusion function can be expressed also at the interface between the binder portion 34 of the first portion 20 and the second portion 30, and a larger light diffusion is realized. I can do it.

  As shown in FIGS. 1 and 2, the light diffusing particles 34 are formed in an elongated shape and have a longitudinal direction ld. As shown in FIG. 3, the elongated light diffusing particles 34 are related to the directionality of the protrusion 24 of the first portion 20 and have a directionality, that is, a predetermined direction. It is arranged with regularity to od. In other words, the elongated light diffusing particles 34 are arranged with regularity with respect to the direction or orientation in relation to the directionality of the protrusion 24 of the first portion 20. More specifically, the light diffusing particle 34 of the second portion 30 has an angle θa that the longitudinal direction ld forms with respect to one direction parallel to the sheet surface of the main body 22 and is 0 ° or more and less than 45 °. It is distributed in the second part 20 so as to be. In the example shown in FIG. 2, the predetermined portion od in which the light diffusing particles 34 having the longitudinal direction ld are arranged with regularity is such that the protrusion 24 of the first portion 20 has directivity. (The direction in which the longitudinal direction of the protruding portion 24 is aligned with regularity).

  Note that the longitudinal direction of the light diffusing particles 34 can be specified as a linear direction having the longest length.

  The light diffusing particles 34 and the binder portion 32 are formed by reflecting the light diffusing particles 34 on the surface of the light diffusing particles 34 or having a refractive index different from that of the binder portion 32. The light diffusing function due to reflection and refraction at the interface is exhibited. This light diffusion function mainly diffuses light in a direction orthogonal to the longitudinal direction ld of the light diffusing particles 34. Therefore, the second portion 30 (the anisotropic light diffusing film 10) in which the light diffusing particles 34 are arranged with regularity so that the longitudinal direction ld of the light diffusing particles 34 is along a predetermined one direction od, Light is diffused in a direction orthogonal to a predetermined direction od. That is, the anisotropic light diffusion film 10 according to the present embodiment exhibits an anisotropic light diffusion function that mainly directs light in a direction orthogonal to a predetermined one direction od.

  In the case where the light diffusing function is expressed by reflection or refraction at the interface between the light diffusing particle 34 and the binder part 32 due to the difference in refractive index between the light diffusing particle 34 and the binder part 32, the light diffusing particle The refractive index difference between 34 and the binder part 32 is preferably in the range of 0.001 or more and 3 or less, and more preferably in the range of 0.01 or more and 1 or less.

  As described above, in the present embodiment, the second portion 30 is formed in the groove 26 formed between two adjacent protrusions 24 among the plurality of protrusions 24. Therefore, as shown in FIGS. 1 to 3, in the present embodiment, the entire light diffusing particle 34 is located in the groove 26 formed between the two adjacent protrusions 24. In other words, the light diffusing particles 34 are arranged on the first portion 20 so that the entire light diffusing particles 34 enter the groove 26 formed between the two adjacent projecting portions 24.

  In the present embodiment, in order to allow such light diffusing particles 34 to be arranged, the light diffusing particles 34 are formed between two adjacent protrusions 24 among the plurality of protrusions 24 as shown in FIG. The width Gw of the groove 26 (or the width Gw as an average value of this width), that is, the length Gw along the sheet surface of the first portion 20 of the groove 26 is orthogonal to the longitudinal direction ld of the light diffusing particles 34. It is larger than the maximum width Pw (or the average width Pw) of the cross section. At the same time, the depth Gd of the groove 26 formed between two adjacent protrusions 24 of the plurality of protrusions 24 (or the depth Gd as an average value of the depths), that is, The length Gd along the normal direction to the sheet surface of the first portion 20 is the maximum width Pw in the cross section perpendicular to the longitudinal direction ld of the light diffusing particles 34 (or the width Pw as an average value of the widths). ) Is larger than

  By the way, in this Embodiment which consists of the above structure, the light diffusible particle | grains 34 located in the groove | channel 26 defined by the two adjacent protrusion parts 24 and the main-body part 22 are parallel to the longitudinal direction of the protrusion part 24. FIG. In order to be arranged with regularity in one direction od, that is, the longitudinal direction ld of each light diffusing particle 34 in the groove 26 is the longitudinal direction of the protrusion 24 (the longitudinal direction of the groove 26). In practice, it is preferable to determine each dimension as follows in order to distribute and arrange the angles so as to form an angle of less than 45 ° with respect to one direction od parallel to (direction).

  First, the length Pl (or the length Pl as an average value of the lengths) along the longitudinal direction ld of the light diffusing particles 34 is equal to the two adjacent protrusions 24 of the plurality of protrusions 24. It is preferable that the width Gw of the groove 26 formed therebetween (or a width Gw as an average value of the widths) is larger. In this case, the direction of the light diffusing particles 34 disposed in the groove 26 can be structurally restricted by the protrusion 24 that forms the groove 26. In other words, the light diffusing particles 34 are prevented from freely rotating in the grooves 26 by the protrusions 24, and it is possible to restrict the directions that the light diffusing particles 34 can take in the grooves 26 to a specific range. Become.

Further, the length Pl of the light diffusing particles 34 along the longitudinal direction ld (or a length Pl as an average value of the lengths) and two adjacent protrusions 24 out of the plurality of protrusions 24. Is preferably designed so that the width Gw (or the width Gw as an average value of the widths) of the groove 26 formed between the two satisfies the following relationship (1a). It is more preferable to design so as to satisfy 1b).
Gw <(Pl) / (2 ^1/2 ) (1a)
Gw <(Pl) / 2... Formula (1b)
When such an expression (1a) is satisfied, in the plan view shown in FIG. 2, that is, in the observation from the normal direction to the film surface of the anisotropic light diffusion film 10, The light diffusing particles 34 are arranged such that the longitudinal direction ld forms an angle of 45 ° or more with respect to the longitudinal direction of the protruding portion 24 (longitudinal direction of the groove 26), that is, the predetermined one direction od. It can be regulated (blocked). Further, when the formula (1b) is satisfied, the light diffusing particle 34 is so formed that the longitudinal direction ld of the light diffusing particle 34 forms an angle of 30 ° or more with respect to the predetermined one direction od in plan view. Can be regulated (blocked), whereby the anisotropic light diffusion function of the anisotropic light diffusion film 10 can exhibit stronger directivity.

Further, the length Pl of the light diffusing particles 34 along the longitudinal direction ld (or the length Pl as an average value of the lengths) and the two adjacent protrusions 24 among the plurality of protrusions 24. It is preferable that the depth Gd of the grooves 26 formed between them (or the depth Gd as an average value of the depths) is designed so as to satisfy the following relationship (2a). It is more preferable to design so as to satisfy the formula (2b).
Gd <(Pl) / (2 ^1/2 ) Formula (2a)
Gd <(Pl) / 2... Formula (2b)
When such an expression (2a) is satisfied, in the observation from the direction of the arrow A in FIG. 2, that is, a direction that is parallel to the film surface of the anisotropic light diffusion film 10 and orthogonal to the predetermined one direction od. In the observation from above, the longitudinal direction ld of the light diffusing particles 34 forms an angle of 45 ° or more with respect to the longitudinal direction of the projecting portion 24 (longitudinal direction of the groove 26), that is, the predetermined one direction od. It is possible to restrict (block) the arrangement of the light diffusing particles 34. When the expression (2b) is satisfied, the longitudinal direction ld of the light diffusing particles 34 forms an angle of 30 ° or more with respect to the predetermined one direction od in the observation from the direction of the arrow A in FIG. As described above, the arrangement of the light diffusing particles 34 can be restricted (blocked), whereby the anisotropic light diffusing function of the anisotropic light diffusing film 10 can exhibit a stronger directivity.

  Such a second portion 30 can be formed as follows, for example, on the surface of the first portion 20 on which the protruding portion 24 is formed, as described above. First, a resin composition is prepared by kneading light diffusing particles 34 having the longitudinal direction ld with a resin material that forms the binder portion 24. As a resin material that forms the binder portion 24, an epoxy acrylate or urethane acrylate-based transparent reactive resin (such as an ionizing radiation curable resin) can be used. Next, the prepared resin composition is applied onto the surface of the first portion 20 on the side where the protruding portions 24 are formed, and is filled in the grooves 26 formed between the protruding portions 24. At this time, if necessary, the groove 26 may be filled with the resin composition by wiping (scraping of excess ink outside the groove) using a squeegee, doctor blade, roller, or the like.

  Thereafter, the resin composition is cured (solidified) in the groove 26 to form the second portion 30 including the binder portion 32 and the light diffusing particles 34 dispersed in the binder portion 32, and as a result. Thus, the anisotropic light diffusion film 10 including the first portion 20 and the second portion 30 is obtained. When the dimension of the groove 26 of the first portion 20 and the dimension of the light diffusing particle 34 are set so as to satisfy the above-described formulas (1a), (1b), (2a), and (2b), In the anisotropic light diffusing film 10 obtained as described above, the orientation of the light diffusing particles 34 in the grooves 26 is structurally restricted, and as a result, the light diffusing particles 34 are directed to the projecting portions 24 of the first portion 20. It can be arranged with regularity in a predetermined one-way od related to.

  As an example of the shape of the light diffusing particle 34 having the longitudinal direction ld, various shapes such as a spheroid, a granular shape (rice granular shape), a needle shape, a scale shape, and a fine plate shape can be adopted. Further, as a specific example, the average aspect ratio (the length Pl of the light diffusing particles 34 along the longitudinal direction ld with respect to the maximum width Pw of the light diffusing particles 34 along the direction orthogonal to the longitudinal direction ld). The average ratio) is 1.5 or more and 50 or less, and the average particle diameter of the light diffusing particles 34 (the particle diameter calculated by the volume equivalent method, that is, the arithmetic average value of the volume equivalent diameter) is 0.5 μm. Particles in the range of 100 μm or less can be used as the light diffusing particles 34 having the longitudinal direction ld. As such light diffusing particles 34, light diffusing particles made of organic fibers, for example, light diffusing particles made of heat-resistant organic fibers such as aramid fibers, wholly aromatic polyester fibers, and polyimide fibers can be used. Furthermore, as the light diffusing particles 34, light diffusing particles made of inorganic fibers, for example, light diffusing particles made of fibrous fillers such as glass fibers, silica fibers, alumina fibers, zirconia fibers, etc. can be used. Further, as the light diffusing particles 34, light diffusing particles made of a thin plate filler (mica) can be used. Further, as the light diffusing particle 34, a light diffusing particle made of an amorphous filler, for example, a light diffusing particle made of an inorganic white pigment such as silica, calcium carbonate, magnesium hydroxide, clay, talc, titanium dioxide or the like is used. You can also

  In the anisotropic light diffusing film 10 as described above, the thickness Bt of the main body portion 22 of the first portion 20 can be in the range of 10 μm or more and 1 mm or less as each dimension not mentioned so far. The width Bw of the protruding portion 24 can be 0.1 μm or more and 1 mm or less.

  The anisotropic light diffusing film 10 having the above-described configuration can exhibit the following effects.

  First, the light diffusing particles 34 and the binder part are formed by the light diffusing particles 34 having reflectivity on the surface of the light diffusing particles 34 or having a refractive index different from that of the binder part 32. Thus, a light diffusing function due to reflection and refraction at the interface with 32 is developed. The light that undergoes an optical action at the interface between the light diffusing particles 34 and the binder portion 32 greatly changes the traveling direction in a plane orthogonal to the longitudinal direction ld of the light diffusing particles 34. That is, this light diffusion function mainly diffuses light in a direction orthogonal to the longitudinal direction ld of the light diffusing particles 34.

On the other hand, the light diffusing particles 34 in the anisotropic light diffusing film 10 are arranged with regularity so that the longitudinal direction ld of each light diffusing particle 34 is along a predetermined one direction od. Accordingly, the light diffusion at the interface between the light diffusing particles 34 and the binder part 32 is diffused in a direction that is perpendicular to a predetermined one direction od. That is, the anisotropic light diffusion film 10 according to the present embodiment relatively exhibits a narrow diffusion angle in a predetermined one direction od direction and a wide diffusion angle in a direction orthogonal to the predetermined one direction od. An anisotropic light diffusion function is exhibited. That is, the predetermined one direction od which can be said to be the average orientation direction in the longitudinal direction of each light diffusing particle 34 and the normal nd direction of one surface 22a (in FIG. 3, the vertical direction (not shown) ) than the diffusion angle theta _L of at the emitted light in a plane S _L comprising, means that increases towards the diffusion angle theta _T of at outgoing light plane S _T perpendicular to the direction od. When displayed as an inequality,
θ _L (diffusion angle in the od direction) <θ _T (diffusion angle in the direction orthogonal to the od direction)
Means that Incidentally, here, the term each spreading angle comprises between the direction of the surface S _L and in light intensity in each plane S _T (or brightness) is maximum, the light intensity (or brightness) of maximum light intensity It is defined as a so-called half-value angle that is half or more of (or luminance).

  Further, as described above, when there is a refractive index difference between the first portion 20 and the binder portion 32 of the second portion 30, the interface between the first portion 20 and the second portion 30, more specifically, The light diffusion function due to reflection and refraction at the interface is also expressed by the interface between the protrusion 24 or the main body 22 and the binder 32. And according to this Embodiment, the protrusion part 24 of the 1st part 20 is arrange | positioned with directionality in the direction parallel to the predetermined one direction od where the light diffusable particle 34 is directed. Yes. More specifically, the longitudinal direction of the protrusion 24 of the first portion 20 is parallel to the direction in which the light diffusing particles 34 are directed. Therefore, the light diffusion at the interface between the first portion 20 and the second portion 30 is also biased in the direction orthogonal to the predetermined one direction od to diffuse the light. That is, the optical action at the interface between the first portion 20 and the second portion 30 also causes a relatively narrow diffusion angle in the predetermined one direction od direction and a direction orthogonal to the predetermined one direction od. An anisotropic light diffusion function that exhibits a wide diffusion angle is exhibited.

  Thus, the anisotropic light diffusion film 10 according to the present embodiment can exhibit an anisotropic light diffusion function that mainly directs light in a direction orthogonal to a predetermined one direction od. In particular, in the present embodiment, the possible orientation of the light diffusing particles 34 having the longitudinal direction ld is constrained structurally by the protrusion 24 of the first portion 20. For this reason, the directionality regarding the arrangement of the light diffusing particles 34 having the longitudinal direction ld is stably ensured by the protrusions 24 of the first portion 20, and as a result, the anisotropic light diffusing film 10 is An anisotropic light diffusion function can be expressed stably. Further, the orientation of the light diffusing particles 34 having the longitudinal direction ld can be controlled by the configuration of the protrusions 24 of the first portion 20 and the configuration of the light diffusing particles 34 of the second portion 30, and Thus, the degree of the anisotropic light diffusion function that the anisotropic light diffusion film 10 can express can be adjusted with a high degree of freedom.

  Such an anisotropic light diffusion film 10 can be used by being incorporated in the display device A shown in FIG. 4 as an example. The display device A shown in FIG. 4 is configured as a liquid crystal display device, and includes a liquid crystal display panel C and a surface light source device B as a backlight that illuminates the liquid crystal display panel C from the back side. Yes. The horizontal viewing angle characteristics and the vertical viewing angle characteristics required for the display device 10 are usually different. For example, a display device as a television receiver is required to have a wide horizontal viewing angle, but there is usually no need to widen the vertical viewing angle. Conversely, display devices incorporated in mobile devices are required to narrow the horizontal viewing angle (horizontal viewing angle) from the viewpoint of peeping prevention, while the vertical viewing angle (vertical viewing angle) is reduced. It is required to set wider than the horizontal viewing angle. The anisotropic light diffusing film 10 can be effectively used for such a demand for the viewing angle characteristics of the display device A.

  Here, the horizontal direction means the horizontal direction of the image observer, that is, the horizontal direction. In the case of a television receiver, it usually coincides with a narrow horizontal direction orthogonal to the direction in which gravity works. The vertical direction means a direction orthogonal to the horizontal direction, and does not necessarily coincide with the gravitational direction (vertical direction). In the case of a television receiver, normally, the vertical direction is generally the vertical direction or a direction close thereto.

  Specifically, as shown in FIG. 4, the anisotropic light diffusion film 10 </ b> A is disposed on the light exit surface of the liquid crystal display panel C in a predetermined direction. For example, for a display device as a television receiver, anisotropic light is applied so that a predetermined one direction od in which the light diffusing particles 34 having the longitudinal direction ld exhibit directionality is parallel to the vertical direction. A diffusion film 10A is disposed. In this case, the anisotropic light diffusion film 10A diffuses the image light from the liquid crystal display panel C in a horizontal direction, and effectively uses the limited image light by suppressing the diffusion in the vertical direction. However, a wide horizontal viewing angle can be ensured. Further, in the display device A incorporated in a mobile device, the predetermined one direction od in which the light diffusing particles 34 having the longitudinal direction ld exhibit directionality is parallel to the horizontal direction (lateral direction). An anisotropic light diffusion film 10A is disposed. In this case, the anisotropic light diffusing film 10A diffuses the image light from the liquid crystal display panel C in the vertical direction (longitudinal direction) and diffuses it (with a wide diffusion angle), and suppresses diffusion in the horizontal direction (diffusion angle). The display device A can be given excellent visibility by promoting diffusion in the vertical direction while providing the display device A with a function of preventing peeping from the left and right direction (horizontal direction). it can.

  As another example, the anisotropic light diffusion film 10 can be used by being incorporated into a surface light source device B that emits light in a planar shape. As an example of this, FIG. 4 discloses an example in which an anisotropic light diffusion film 10B is applied to a surface light source device B as a backlight that can be used in a liquid crystal display panel. The surface light source device B shown in FIG. 4 includes a light source B1 having a plurality of light emitters B1a, and a large number of optical sheets for changing the traveling direction of light from the light emitter Bla. It is designed so that the liquid crystal display panel C can be illuminated with optical characteristics. In the example of the surface light source device B shown in FIG. 4, a diffusion plate B2, a condensing sheet (prism sheet) B3, and an anisotropic light diffusion film 10B are provided in this order from the light emitter B1a side of the light source B1. A reflector B4 is provided on the back side of the light source B1.

  In the example of FIG. 4, each light emitter B1a is formed of an elongated cold cathode tube extending in the first direction, and the plurality of light emitters B1a are arranged in the second direction so that their longitudinal directions are parallel to each other. It is arranged. The condensing sheet B3 is configured as a prism sheet including a large number of unit prisms B3a each extending in the first direction and arranged in the second direction. The condensing sheet C has a function (condensing function) for reducing the light traveling direction to the front direction and improving the luminance in the front direction. In addition, the condensing sheet B3 has a function of reducing brightness unevenness (luminance unevenness, tube unevenness) along the second direction, which occurs according to the arrangement of the light emitters B1a.

  In such a surface light source device B shown in FIG. 4, brightness unevenness along the second direction generated according to the arrangement of the light emitters B <b> 1 a by the condensing sheet B <b> 3 and the diffusion plate B <b> 2, a so-called light source image ( (Light image) may not be sufficiently resolved. In this case, the anisotropic light diffusing film 10B is arranged so that the predetermined one direction od in which the light diffusing particles 34 having the longitudinal direction ld become directional is parallel to the first direction, and the difference is made. The isotropic light diffusion film 10B may be biased in the second direction to diffuse light. According to this aspect, the unevenness of brightness along the second direction can be made inconspicuous effectively. On the other hand, excessively diffusing light along the first direction is effectively prevented, so that it is possible to avoid a light amount loss due to unnecessary diffusion (reflection).

  Further, in the case where the unevenness of brightness along the second direction generated according to the arrangement of the light emitters B1a can be sufficiently eliminated by the light collecting sheet B3, the light diffusing particles having the longitudinal direction ld The anisotropic light diffusing film 10B is arranged so that a predetermined one direction od in which 34 exhibits directionality is parallel to the second direction, and the anisotropic light diffusing film 10B is biased in the first direction to emit light. You may make it diffuse. According to this aspect, since the traveling direction of the component along the second direction of the light collected in the front direction by the light collecting function of the light collecting sheet B3 is not greatly disturbed by the anisotropic light diffusion film 10B, High front direction luminance can be ensured. In addition, the light collecting sheet B3 can sufficiently eliminate the unevenness of brightness along the second direction that occurs in accordance with the arrangement of the light emitters B1a, and the anisotropic light diffusion film 10B can be aligned in the first direction. When light is diffused in a biased manner, the diffusing plate B2 can be deleted. In this case, the manufacturing cost of the surface light source device B can be directly reduced, and the surface light source device B can be made thinner and lighter.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above-described embodiment are used, and redundant descriptions are omitted.

  For example, in the above-described embodiment, the example in which the protruding portion 24 of the first portion 20 has a rectangular shape on the main cut surface of the anisotropic light diffusing film 10 is shown, but is not limited thereto, and is shown in FIG. It may be a trapezoidal shape, a polygonal shape other than a quadrangle such as a triangle, pentagon, hexagon, etc., a shape corresponding to a part of an ellipse or a shape corresponding to a part of a circle, Also good.

  As in the example shown in FIG. 5, when the width Bw of the protrusion 24 is not constant, the width Gw of the groove 26 formed by the two adjacent protrusions 24 also changes. In this case, the maximum value Gwmax of the width Gw of the groove 26 is smaller than the length Pl along the longitudinal direction ld of the light diffusing particles 34 and is the maximum width in a cross section perpendicular to the longitudinal direction ld of the light diffusing particles 34. It is preferable that it is larger than Pw. In this case, the possible orientation of the light diffusing particles 34 can be effectively restricted to a specific range, and as a result, regularity can be imparted to the arrangement of the light diffusing particles 34.

  Further, in order to impart regularity to the arrangement of the light diffusing particles 34, the minimum value Gwmin of the width Gw of the groove 26 is between the above-described length Pl along the longitudinal direction ld of the light diffusing particles 34. It is effective to satisfy the formulas (1a) and (1b), and the maximum value Gwmax of the width Gw of the groove 26 is as described above with respect to the length Pl along the longitudinal direction ld of the light diffusing particles 34. It is more effective to satisfy the expressions (1a) and (1b).

In consideration of the ease of manufacturing the first portion, and / or the light diffusing particles 34 forming the second portion 30 are arranged in the groove 26, and the arrangement of the light diffusing particles 34 is given regularity. In consideration of this, as shown in FIG. 5, the width Bw of the protrusion 24 is preferably increased from the distal end toward the proximal end, that is, as it approaches the main body portion 22. That is, it is preferable that the width Gw of the groove 26 becomes smaller as it approaches the main body 22. In this case, as shown in FIG. 5, the groove width Gw takes a minimum value Gwmin at a position where it is connected to the main body 22, and takes a maximum value Gwmax at a position farthest from the main body 22.

  In the above-described embodiment, the example in which the one surface 10a of the anisotropic light diffusion film 10 is configured as a flat surface formed by the protruding portion 24 and the second portion 30 of the first portion 20 has been shown. It is not limited to this. For example, as shown in FIG. 5, the surface of the second portion 30 and the tip surface 24a of the projecting portion 24 are arranged at different height positions so that one surface 10a of the anisotropic light diffusion film 10 is uneven. You may make it comprise as a surface. In the example shown in FIG. 5, a convex portion is formed at a position constituted by the protruding portion 24 of the first portion 20 in one surface 10 a of the anisotropic light diffusing film 10, and one surface of the anisotropic light diffusing film 10 is formed. A recess is formed at a position constituted by the second portion 30 of 10a. According to such an example, the protrusion 24 and the second portion 30 of the first portion 20 are directed in a predetermined one direction od in which the light diffusing particles 34 having the longitudinal direction ld become directional. (For example, when extending in parallel with a predetermined direction od), the convex portion and the concave portion formed on the one surface 10a of the anisotropic light diffusion film 10 also cause the anisotropic light diffusion film 10 to The anisotropic light diffusion function can be enhanced.

  Furthermore, in the above-described embodiment, the example in which the tip surface 24a of the projecting portion 24 is formed as a flat surface parallel to the film surface of the anisotropic light diffusion film 10 has been described, but the present invention is not limited thereto. The tip of the protrusion 24 may be formed as a curved surface as indicated by a two-dot chain line in FIG. 5 or may be formed as a vertex instead of a surface. According to such a modified example, when the protrusion 24 has the same directionality in the predetermined one direction od in which the light diffusing particles 34 having the longitudinal direction ld become directional ( For example, the anisotropic light diffusing function of the anisotropic light diffusing film 10 can be strengthened also at the tip of the protruding portion 24 when extending in parallel with a predetermined one direction od).

  Further, in the above-described embodiment, the second portion 30 is provided only in the groove 26 formed between two adjacent protruding portions 24 among the multiple protruding portions 24 of the first portion 20. However, the present invention is not limited to this. The second portion 30 may be formed so as to extend and spread on the surface of the first portion 20 on the side where the protruding portion 24 is formed, that is, to cover at least a portion of the protruding portion 24. 6-8, the binder part 32 of the 2nd part 30 is arrange | positioned so that the surface of the side in which the protrusion part 24 of the 1st part 20 is formed may be covered. 6 to 8, the second portion 30 completely covers the surface of the first portion 20 on the side where the protruding portion 24 is formed, and the binder of the second portion 30 is not limited to the examples shown in FIGS. The part 32 may form the one surface 10a of the anisotropic light diffusion film 10 as a flat surface. Also in these examples, the direction of the elongated light diffusing particles 34 in the second portion 30 can be controlled on the first portion 20 by the elongated protrusion 24 of the first portion 20.

  Further, when the second portion 30 is disposed so as to cover a portion other than the groove 26 of the first portion 20, the light diffusing particles are formed on one surface 10 a of the anisotropic light diffusing film 10 as shown in FIG. 6. The convex part resulting from 34 may be made to be formed. More specifically, the light diffusing particles 34 may be exposed or the outline of the light diffusing particles 34 may be raised to form convex portions. Such a configuration can be realized, for example, by adjusting the amount of the resin material forming the binder part 32 of the second portion 30. According to such an example, the anisotropic light diffusing function of the anisotropic light diffusing film 10 is also strengthened by the convex portions due to the light diffusing particles 34 on the one-step surface 10 a of the anisotropic light diffusing film 10. be able to.

  Further, as shown in FIG. 8, a convex portion due to the protruding portion 24 may be formed on one surface 10 a of the anisotropic light diffusion film 10. More specifically, the protrusion 24 may be exposed or the outline of the protrusion 24 may be raised to form a protrusion. Such a configuration can be realized, for example, by adjusting the height of the protruding portion 24 of the first portion 20 or the amount of the resin material forming the binder portion 32 of the second portion 30. According to such an example, the protrusion 24 has a directionality in a predetermined one direction od in which the light diffusing particles 34 having the longitudinal direction ld exhibit a directionality (for example, a predetermined amount). In the first direction od), the anisotropic light diffusing function of the anisotropic light diffusing film 10 is also enhanced by the protrusions caused by the protrusions 24 on the one surface 10a of the anisotropic light diffusing film 10. Can be.

  Furthermore, in embodiment mentioned above, the example in which the whole light diffusable particle | grains 34 are located in the groove | channel 26 formed between the two adjacent protrusion parts 24 among the some protrusion parts 24 is shown. It was. However, as shown in FIG. 6, only a part of the light diffusing particles 34 may be positioned in the groove 26 formed between two adjacent protrusions 24 among the plurality of protrusions 24. Good. Also in such an example, for example, by adjusting the specific gravity of the light diffusing particles 34 with respect to the binder portion 32 or the specific gravity of the light diffusing particles 34 with respect to the resin composition for producing the second portion 30, or The direction of the elongated light diffusing particles 34 of the second portion 30 is adjusted on the first portion 20 by adjusting the amount of the resin material forming the binder portion 32 of the second portion 30. This can be controlled by the elongated protrusion 24.

In addition, as a result of extensive research conducted by the present inventors, in a mode in which only a part of the light diffusing particles 34 is located in the groove 26 as shown in FIG. In the case where it can be regarded as a substantially circular shape, by creating a condition such that a quarter of the arc of the circle is located in the groove 26 between the two adjacent projecting portions 24, the elongated light diffusibility is obtained. The direction of the particles 34 can be controlled particularly stably on the first portion 20 by the elongated groove 26 (projecting portion 24). That is, in an embodiment in which only a part of the light diffusing particle 34 is located in the groove 26, the light diffusing particle 34 has the same area as the maximum cross-sectional area of the light diffusing particle 34 in a cross section perpendicular to the longitudinal direction ld. The width Gw of the groove 26 formed between the radius Pr of the circle (or the radius Pr as an average value of the radii) and the two adjacent projections 24 of the plurality of projections 24 (or this width). It is preferable to design so that the width Gw) as an average value of the above satisfies the following relationship (3a).
((Pr) × 2) / (2 ^1/2 ) ≦ Gw Expression (3a)

In addition, in order for the light diffusing particles 34 to be stably positioned on the groove 26, the light diffusing particles 34 supported by the two adjacent protrusions 24 are arranged between the two protrusions 24. It is preferable that the groove 26 is not in contact with the bottom of the groove 26 or in contact with the bottom of the groove 26. That is, a radius Pr of the circle having the same area as the maximum cross-sectional area of the light diffusing particle 34 in the cross section perpendicular to the longitudinal direction ld of the light diffusing particle 34 (or a radius Pr as an average value of the radii), The depth Gd (or the depth Gd as an average value of the depths) of the groove 26 formed between two adjacent protrusions 24 out of the plurality of protrusions 24 has the following relationship (3b It is preferable to design so as to satisfy.
Pr − ((Pr) / (2 ^1/2 )) ≦ Gd Expression (3b)

  Further, in the above-described embodiment, the protruding portions 24 of the first portion 20 are arranged in parallel on the main body portion 22 and are configured identically, and each protruding portion 24 has a constant cross-sectional shape in the longitudinal direction. Although the example which has is shown, it is not restricted to this. Even if the configuration of the projecting portion 24 is different from the configuration in the above-described embodiment, the direction of the elongated light diffusing particles 34 of the second portion 30 is changed to the elongated shape of the first portion 20 on the first portion 20. The shape of the protrusion 24 can be controlled, and as a result, the light diffusing particles 34 of the second portion 20 are regulated in a predetermined direction od related to the directionality of the protrusion 24 of the first portion 20. It can be arranged with sex.

  In the example shown in FIGS. 7 and 8, the elongated protrusions 24 are not arranged in parallel to each other, but are arranged with a directivity in a predetermined one direction od. Specifically, the elongated protrusion 24 has a predetermined longitudinal direction in the longitudinal direction in the observation from the normal direction to the film surface of the anisotropic light diffusion film 10, that is, in the plan view shown in FIG. It arrange | positions so that the angle made with respect to may be 0 degree or more and less than 45 degrees. In particular, in the example shown in FIG. 7 and FIG. 8, each protrusion 24 extends not only in the longitudinal direction but also in a direction extending at an arbitrary position (in the straight line direction, the straight line direction, in the curved shape, the tangent line). In the direction of 0 to 45 degrees with respect to a predetermined direction. Further, in the example shown in FIGS. 7 and 8, the plurality of protrusions 24 are configured with different shapes, dimensions, and arrangements, and the cross-sectional shape of each protrusion 24 is the longitudinal direction of the protrusion 24. Is not constant along. 7 and 8 also, the light diffusing particles 34 of the second portion 20 have regularity in a predetermined direction od related to the directionality of the protrusions 24 of the first portion 20. Have and be placed.

  Furthermore, in the above-described embodiment, the example in which the anisotropic light diffusion film 10 is formed only from the first portion 20 and the second portion 30 has been described, but the present invention is not limited thereto. For example, when the display surface of the display device A is arranged on the light output surface of the liquid crystal display panel C as in the anisotropic light diffusion film 10A in FIG. The isotropic light diffusion film 10 may further include a functional layer 40 having some function, for example, a functional layer 40 that functions as an outermost surface layer. Here, examples of the functional layer 40 that can be disposed on the outermost surface layer include an antireflection layer for preventing reflection of light, an antiglare layer for preventing reflection, and a hard coat layer for the purpose of improving scratch resistance. obtain. In the example shown in FIG. 9, the functional layer 40 is formed on the surface formed by only the first portion 20 of the anisotropic light diffusion film 10 (the other surface 10b described above). Without being limited thereto, the functional layer 40 may be formed on the surface of the anisotropic light diffusing film 10 on which the second portion 30 is formed (the one surface 10a described above).

  When incorporated in the surface light source device B like the anisotropic light diffusing film 10b in FIG. 4, the anisotropic light diffusing film 10 further has an optical function other than the anisotropic light diffusing function as shown in FIG. You may make it have the optical element 45 which can be exhibited. In the example shown in FIG. 10, the anisotropic light diffusion film 10 includes a large number of elongated unit optical elements (unit prisms, unit lenses) 50 arranged in parallel as an example. An optical element 45 constituting a prism surface (lens surface) capable of exhibiting a condensing function is formed.

  In the example shown in FIG. 10, the unit optical element 50 is provided on the surface (one surface 10a described above) on the side where the second portion 30 of the anisotropic light diffusion film 10 is formed. The unit optical element 50 may be provided on the surface formed by only the first portion 20 of the anisotropic light diffusing film 10 (the other surface 10b described above). In the example shown in FIG. 10, the unit optical elements 50 arranged one-dimensionally are provided on the anisotropic light diffusion film 10. However, the present invention is not limited to this, and a microlens (fly-eye lens) is used. The anisotropic light diffusing film 10 may be provided with two-dimensionally arranged unit optical elements that constitute an optical element that functions as an optical element.

  In the above-described embodiment, the example in which the anisotropic light diffusion film 10 is used in combination with the liquid crystal display device A has been described, but the present invention is not limited thereto. A plasma display (PDP) device, a cathode ray tube, which can be applied to a display unit of a television receiver, various measuring devices and instruments, various office devices, various medical devices, computing devices, telephones, electrical signs, various game devices, etc. The anisotropic light diffusion film 10 can be used for various display devices such as a display (CRT) device, an electroluminescent display (EL) device, and a projection display device (projection display). Moreover, although the example which applied the anisotropic light-diffusion film 10 to the surface light source device B as a backlight which illuminates the liquid crystal display panel C from the back side was shown in embodiment mentioned above, it is not restricted to this, An example The present invention can also be applied to a surface light source device used as a lighting device.

  In addition, although the some modification with respect to embodiment mentioned above was demonstrated above, naturally, it is also possible to apply combining several modifications suitably.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.

  The light diffusion films according to Examples 1 to 3 and the light diffusion films according to Comparative Examples 1 and 2 were actually prepared, and it was investigated whether or not the anisotropic light diffusion function could be exhibited.

<Light diffusion film>
As described in the above-described embodiment, each light diffusion film first prepares a sheet-like first portion, and then forms a second portion including light diffusing particles and a binder portion. The resin composition was applied on the first part, and then the binder part in the resin composition was solidified. That is, each light diffusing film is composed of a sheet-like first portion, and a binder portion provided on the first portion and a second portion having light diffusing particles dispersed in the binder portion. I made it. The refractive index of the first part and the binder part of the second part were made the same. On the other hand, in the second portion, the binder portion and the light diffusing particles have a refractive index difference of 0.1.

  In the light diffusing films according to Examples 1 to 3, the first portion made of the polycarbonate resin has a thickness of the main collar portion of 50 μm, and extends linearly arranged on one surface so as to be parallel to each other. A number of protrusions (protrusions provided in the arrangement shown in FIG. 1) were included. And in the light-diffusion film which concerns on Examples 1-3, the 2nd part was formed on the surface in which the protrusion part of the 1st part is formed. However, between the light diffusion films according to Examples 1 to 3, the groove depth Gd and the groove width Gw were changed by changing the dimensions of the protrusions. In the light diffusing films according to Examples 1 to 3, elongated particles having a longitudinal direction were used as the light diffusing particles. Further, among the light diffusing films according to Examples 1 to 3, the shape and size of the elongated light diffusing particles, and the amount added to the binder part are the same, and all the binder parts are the same acrylic resin. It was. In the light diffusing films according to Examples 1 to 3, the light diffusing particles of the second part are arranged with regularity in the longitudinal direction of the protrusions of the first part.

  The light-diffusion film which concerns on the comparative example 1 was made to differ from the light-diffusion film which concerns on Examples 1-3 in the point which used the sheet-like protrusion part in which the protrusion part was not provided. On the other hand, the resin composition for producing the 2nd part used the same thing as the light-diffusion film which concerns on Examples 1-3. Therefore, the light diffusing particles contained in the light diffusing film according to Comparative Example 1 were the same as the light diffusing particles contained in the light diffusing films according to Examples 1 to 3.

  The light diffusion film according to Comparative Example 2 had the same first portion as the first portion of the light diffusion film according to Example 1. However, the light diffusing particles contained in the resin composition for producing the second part were not elongated (needle-like) but spherical. In this respect, the light diffusion film according to Comparative Example 2 was different from the light diffusion film according to Example 1.

  For each light diffusion film, the average value of the width Gw of the grooves formed between two adjacent protrusions, the average value of the depth Gd of the grooves formed between the two adjacent protrusions, light diffusibility Table 1 shows the shape of the particles, the average value of the maximum width Pw in the cross section orthogonal to the longitudinal direction of the light diffusing particles, and the average value of the length Pl along the longitudinal direction ld of the light diffusing particles. It is shown in the columns of “groove width”, “groove depth”, “particle shape”, “particle width” and “particle length”.

<Evaluation>
Each light diffusion film was illuminated, and the optical characteristics of the light transmitted through the light diffusion film were investigated. Specifically, each light diffusion film is arranged on the light emitting surface of a surface light source device incorporated in a commercially available liquid crystal display device (liquid crystal television receiver), and the side of the light diffusion film that does not face the surface light source device The angular distribution of luminance in various planes along the normal direction to the film plane was investigated on the plane of the film. And the half value angle was calculated | required about each of the angle distribution of the brightness | luminance obtained about each light-diffusion film. By comparing the maximum half-value angle for each light diffusion film with the half-value angle measured on the measurement surface orthogonal to the measurement surface where the maximum half-value angle was measured, the light diffusion function of each light diffusion film The presence or absence of anisotropy was investigated. Specifically, when the maximum half-value angle for the light diffusion film is 110% or more with respect to the half-value angle measured on the measurement surface orthogonal to the measurement surface on which the maximum half-value angle is measured. It was evaluated that there was anisotropy. The evaluation results are shown in the “Anisotropy” column of Table 1.

10 Anisotropic light diffusion film 10a One surface (one surface)
10b The other surface (the other surface)
20 1st part 20a One side 20b The other side 22 Main part 24 Protrusion part 24a Tip end face 26 Groove 30 Second part 32 Binder part (binder resin part)
34 Light Diffusing Particle 40 Functional Layer 45 Optical Element 50 Unit Optical Element A Display Device B Surface Light Source Device C Liquid Crystal Display Panel

Claims (8)

An anisotropic diffusion film for anisotropically diffusing transmitted light,
A sheet-like first portion including a plurality of elongated protrusions arranged with directionality;
A binder portion provided on the surface of the first portion where the protruding portion is formed, and a second portion including light diffusing particles having a longitudinal direction dispersed in the binder portion,
The width of the groove formed between two adjacent protrusions of the plurality of protrusions is larger than the maximum width Pw in the cross section perpendicular to the longitudinal direction of the light diffusing particles,
The depth of the groove formed between two adjacent protrusions of the plurality of protrusions is larger than the maximum width in a cross section perpendicular to the longitudinal direction of the light diffusing particles,
The length of the light diffusing particles along the longitudinal direction is Pl, the width of a groove formed between two adjacent protrusions of the plurality of protrusions is Gw, and the plurality of protrusions When the depth of the groove formed between two adjacent protrusions is Gd, the following two relationships are satisfied:
Gw <(Pl) / (2 ^1/2 )
Gd <(Pl) / (2 ^1/2 )
In the groove formed between two adjacent protrusions of the plurality of protrusions, the entire light diffusing particles are located,
The anisotropic light diffusing film, wherein the light diffusing particles of the second portion are arranged with regularity in a certain direction related to the directionality of the protruding portion of the first portion. The first portion includes a sheet-like main body portion and the plurality of protrusions arranged side by side on the main body portion,
2. The anisotropic light diffusing film according to claim 1, wherein the plurality of protrusions are arranged side by side on the main body, and each protrusion extends in a direction intersecting with an arrangement direction of the plurality of protrusions.   The anisotropic light diffusion film according to claim 1, wherein the light diffusing particles have a refractive index different from that of the binder part.   The anisotropic light diffusion film according to any one of claims 1 to 3, wherein the first portion has a refractive index different from that of the binder portion of the second portion.   The anisotropic light-diffusion film as described in any one of Claims 1-4 with which the said binder part of the said 1st part and the said 2nd part is transparent.   A surface light source device provided with the anisotropic light-diffusion film as described in any one of Claims 1-5.   A display device comprising the surface light source device according to claim 6.   A display apparatus provided with the anisotropic light-diffusion film as described in any one of Claims 1-5.

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