JP2005106931A - Optically functional sheet and surface light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optically functional sheet capable of obtaining a wide viewing angle while maintaining a high front brightness, and to provide a surface light source using the optically functional sheet. <P>SOLUTION: The optically functional sheet is constituted by alternately arranging a light diffusion phase and a transparent phase in the sheet surface direction and, further, the light diffusion phase has at least two kinds of thickness in the sheet thickness direction. The surface light source uses the optically functional sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical functional sheet suitably used in a surface light source, particularly a backlight application in a liquid crystal display.

  In recent years, various displays have been used in various applications such as portable devices, personal computers, monitors, and televisions. Among them, liquid crystal displays are widely used from small products for portable devices to recently large-sized products such as monitors and televisions. Since the liquid crystal display itself is not a light emitter, it can be displayed by making light incident from the back side by a backlight.

  On the other hand, the backlight is required not only to irradiate light but also to light the entire screen uniformly and brightly. Therefore, in order to light the backlight uniformly, an optical functional sheet such as a diffusion film or a prism sheet is usually attached. That is, in the backlight, a diffusion film that equalizes the light emission distribution is placed on the light guide plate, and a prism sheet that collects light in the front direction is used in order to improve the front brightness. It has been broken.

  The prism sheet is a sheet having a structure in which a large number of prisms having a substantially triangular cross section are arranged. By using this sheet on the diffusion film, the light equalized by the diffusion film is transmitted by the prism sheet. Since the light can be efficiently condensed (directed) in the front direction of the screen, the front luminance can be improved (for example, see Patent Document 1).

  Further, when particularly high luminance is required, two prism sheets are used in such a manner that the prism rows are perpendicular to each other. By using in this way, the brightness is further improved by first condensing the light spreading in one of the top, bottom, left and right of the screen in the first direction and then condensing the light spreading in the other one in the front direction. .

In addition, similar to the prism sheet, an optical functional sheet that exhibits a light condensing function in the front direction of the screen and enhances luminance has also been proposed. Examples of the optical functional sheet include an optical sheet in which projections having scattering properties are arranged at intervals (for example, refer to Patent Document 2), and an optical functional film in which transparent and diffusing phases are alternately arranged inside the film. (For example, refer to Patent Document 3). In the case of the prism sheet, high brightness has been achieved by improving the light utilization efficiency using the light refraction action and the light recycling action utilizing the surface shape, whereas these two types of optical functional sheets. Is a light beam control sheet utilizing diffusion / reflection by a light scattering wall provided inside the sheet surface perpendicularly. In particular, in the case of the latter optical functional film, the surface shape is a type that does not use at all, there is no reduction in the effect due to the loss of the surface shape, and further processing such as formation and bonding of other functional layers is possible.
US Pat. No. 5,161,041 (page 4, line 62 to page 5, line 47) Japanese Patent Application Laid-Open No. 2002-214411 (1 page, 2 lines to 9 lines) JP-A-2002-277613 (1 page, 2 lines to 5 lines)

  However, since the prism row on the surface of the prism sheet has a very fine and sharp apex structure, the surface is easy to be damaged during its manufacture and handling, and the defect becomes a volatile point and the image quality deteriorates. There is a point.

  Furthermore, although the luminance in the front direction is improved by incorporating the prism sheet into the backlight, the luminance is rapidly lowered depending on the viewing angle. This is not particularly a problem in applications that are viewed only from the front direction, but such a steep viewing angle dependency of luminance is fatal for applications that are viewed from a certain wide range in the vertical and horizontal directions. An optical functional sheet with low viewing angle dependency is desired while maintaining the front brightness.

  Further, the optical functional sheets used in these backlights are required to have further performance / efficiency improvement, thinness / weight reduction, etc. In order to achieve these, for example, by surface coating / bonding, etc. Means such as function integration are effective. However, such a surface processing is impossible in the case of a film that exhibits its performance by utilizing surface irregularities, such as a prism sheet.

  Moreover, in the case of the optical functional sheet which expresses the condensing function given as an example in Patent Document 2 or 3, the surface is smoothed and the condensing function in the two-dimensional direction of the screen up, down, left and right is expressed. Although it is possible, no reference has been made to producing a structure having a small viewing angle dependency while maintaining a high luminance in the front direction.

  Therefore, the purpose of the present invention is to achieve a light condensing function according to the internal form without using the light condensing function due to the surface shape, achieving a wide viewing angle while ensuring high front luminance, In particular, an object of the present invention is to provide an optical functional sheet capable of greatly improving the front luminance when used for a liquid crystal backlight.

  The optical functional sheet of the present invention is an optical functional sheet in which a light diffusing phase and a transparent phase are alternately arranged in the sheet surface direction, and the light diffusing phase has at least two kinds in the cross section in the sheet surface vertical direction. It has a thickness in the sheet thickness direction.

Moreover, the optical functional sheet of the present invention preferably further includes the following requirements.
(A) Of the light diffusion phases, L1 / L2 is 0.3 or more and less than 1 when the minimum sheet thickness direction thickness is L1 and the maximum sheet thickness direction thickness is L2.
(B) The light diffusing phase is arranged in a single plane substantially parallel to the sheet surface in the cross section perpendicular to the sheet surface.
(C) A surface light source incorporating the optical functional sheet, wherein when the light from the light source enters the light diffusion phase, the light diffusion phase is arranged in a single plane substantially parallel to the sheet surface A surface light source that is arranged so that it enters from.

  According to the present invention, since a wide viewing angle can be achieved while maintaining high front luminance, it is useful for applications such as a backlight in a liquid crystal display member. Moreover, since the condensing function is exhibited depending on the internal form, the surface can be flattened, and it is possible to perform surface processing or to be bonded to another functional sheet.

  Furthermore, since the optical functional sheet of the present invention can be integrated with other functional sheets (for example, diffusion sheets) having a smooth surface, a high-brightness thin integrated sheet having both the light collecting function and the other functions described above. It is possible to apply.

  The optical functional sheet of the present invention is an optical functional sheet in which the light diffusion phase and the transparent phase are alternately arranged in the sheet surface direction, and in the sheet surface vertical cross section in which the two phases are alternately arranged, the sheet thickness The light diffusing phases having different directional thicknesses are arranged. Here, the transparent phase refers to a phase that does not substantially diffuse light.

  1 (a) to 1 (g) show a state in which the light diffusion phase and the transparent phase are alternately arranged in the sheet surface direction in the optical functional sheet of the present invention, and each light diffusion phase has at least two kinds. It is sheet | seat sectional drawing for demonstrating the state which has a sheet | seat film thickness direction thickness. In FIG. 1, the sheet thickness direction thickness of the light diffusion phase is L, and the distance between the midpoints of two adjacent light diffusion phases (hereinafter referred to as the arrangement pitch of the light diffusion phases) is p. FIG. 1A shows an arrangement state in which the positions of the light diffusion phases in the sheet thickness direction are completely random, and FIG. 1B shows an arrangement state in which two types of light diffusion phases having different thicknesses in the sheet thickness direction are arranged alternately. 1 (c) shows an arrangement state in which light diffusion phases having different thicknesses in the sheet thickness direction are regularly arranged, and FIGS. 1 (d) and (e) show one end portion of the light diffusion phase in the sheet thickness direction. FIG. 1F shows an arrangement state in which the positions in the film thickness direction are aligned, FIG. 1F shows an arrangement state where the arrangement pitches of the light diffusion phases are different, and FIG. 1G shows the thickness in the sheet surface direction of the light diffusion phase for each light diffusion phase. The different arrangement states are illustrated in FIG. 1A to 1E show the case where the arrangement pitch of the light diffusion phases is constant, and FIGS. 1F and 1G show the case where the arrangement pitch is random. The arrangement state of the light diffusion phases shown in FIG. 1 is an example, and is not limited to these. For example, those having these characteristics are also preferably used. Here, the light diffusing phase and the transparent phase are alternately arranged in the sheet surface direction as long as the light diffusing phase and the transparent phase are alternately arranged on at least one surface in the sheet surface vertical direction cross section. There may be a transparent phase at the top or bottom.

  Next, the significance of the arrangement of light diffusion phases having at least two types of thicknesses in the sheet thickness direction will be described.

  The optical functional sheet of the present invention exhibits a light collecting function and exhibits a high brightness enhancement effect because the light diffusion phases are arranged at intervals in the sheet surface direction. Of the light incident from the back, the light close to the normal direction of the sheet surface (light parallel to the sheet surface normal direction and light having a small angle therefrom) passes through the transparent phase as it is, but the incident angle Light that is large and close to the sheet surface direction (light having a large angle from the normal direction of the sheet surface) hits the light diffusion phase and is diffused and reflected. In this way, light having a large incident angle is diffused and reflected by the light diffusion phase, and as a result, is directed in the normal direction. That is, the light emission direction is limited by the wall called the light diffusion phase.

  Here, in order to increase the front luminance, it is preferable to narrow the interval between adjacent light diffusion phases. This is because by narrowing the interval, the probability that incident light hits the light diffusion phase increases, and the angle of the emitted light is further limited. However, as the interval is reduced, the viewing angle is also reduced.

  Therefore, as in the present invention, when the light diffusion phases having at least two types of thicknesses in the sheet thickness direction are arranged in the sheet cross section, the thickness in the thickness direction is changed even if the interval is narrowed. Therefore, the viewing angle is not sacrificed. That is, a wide viewing angle can be obtained while maintaining high front luminance.

  Moreover, although FIG. 1 shows a case where both surfaces of the sheet are flat, there may be irregularities according to the thickness of the light diffusion phase in the sheet film thickness direction. For example, FIG. 2 shows a preferred example, but FIG. 2A shows a case where the thickness of the adjacent light diffusion phase is combined with the thinner one and the surface of the transparent phase is flat. ) Shows a case where the surface of the transparent phase is convex, and FIG. 2C shows a case where the surface of the transparent phase is concave. Still further, the transparent phase may be an air phase.

  3A to 3E are cross-sectional views illustrating the shape of the light diffusion phase 1 in the sheet cross section of the optical functional sheet of the present invention. The light diffusing phase 1 has a rectangular shape (FIG. 3A), a trapezoid shape (FIG. 3B), a triangular shape (FIG. 3C), or a modified one (FIGS. 3D and 3E). )) And a mixture of these, and the like are preferable, but shapes other than these can also be used. Further, in FIG. 3, the film thickness direction axes of the light diffusion phase are arranged so as to be substantially parallel to the sheet surface normal direction, but are arranged at an angle inclined from the normal direction or arranged at random angles. Such a state is also preferably used.

  Moreover, when the optical functional sheet of this invention is seen from a sheet surface normal direction, as a shape seen on a sheet surface, the shape of FIG. 4 etc. are mentioned, for example. When classified according to the shape of the transparent phase 2, for example, a circle (FIG. 4 (a)), a triangle (FIG. 4 (b)), a quadrangle (FIG. 4 (c)), a hexagon (FIG. 4 (d)). , And a stripe shape (FIG. 4E). The shape of FIG. 4 is an example, and is not limited thereto. In addition to this, a deformed shape such as a substantially triangular shape, a substantially square shape, a substantially hexagonal shape, an ellipse shape, or a mixture of these shapes. Etc. are preferably used.

  In the optical functional sheet of the present invention, L1 / L2 is preferably 0.3 or more and less than 1 when the minimum value of the thickness in the film thickness direction of the light diffusion phase is L1 and the maximum value is L2. It is preferable to be 0.3 or more and 0.9 or less. In order to make such a structure, for example, a mold in which a groove is formed in the shape of the desired light diffusion phase is prepared, and a transparent phase is formed by pressing into a transparent phase material and then curing. The optical functional sheet in which the light diffusing phase and the transparent phase are alternately arranged in the sheet surface direction is formed by removing the mold, filling the transparent phase in which the groove is formed with a resin that forms the light diffusing phase, and curing the resin. A method is mentioned. At this time, an optical functional sheet in which L1 / L2 is freely adjusted can be obtained by changing the length of the groove of the mold. When L1 / L2 is smaller than 0.3, the brightness enhancement effect by the light diffusion phase showing the minimum value is not sufficiently exhibited, which is not preferable.

  The sheet thickness direction thickness L of the light diffusion phase (the length in the direction perpendicular to the sheet surface) and the ratio L / p with the distance p between the midpoints of two adjacent light diffusion phases are in the range of 0.5-10. Preferably there is. If L / p is less than 0.5, the incident light is not diffused and reflected by the light diffusing phase, and more light passes through the transparent phase as it is, which is not preferable. When L / p is larger than 10, it is not preferable because the viewing angle becomes narrow. Here, although the sheet thickness direction thickness L of each light-diffusion phase differs, it is preferable that this range is satisfy | filled in each site | part.

  The sheet thickness direction thickness L of the light diffusion phase is preferably 10 to 200 μm, and in this range, the light diffusion phase is preferably arranged with a thickness L that meets the above conditions. Moreover, it is preferable that the sheet surface direction thickness of a light-diffusion phase is 5-100 micrometers. The thickness in the sheet surface direction does not need to be constant within the sheet surface, and the thickness may change regularly or randomly.

  Moreover, 10-500 micrometers is preferable and, as for the film thickness of the optical functional sheet of this invention, 10-200 micrometers is more preferable. Here, the film thickness when the surface is uneven means the film thickness measured at the thickest part.

  The light diffusion phase arrangement pitch p of the optical functional sheet of the present invention is the distance between the midpoints of the two light diffusion phases, and is constant, regularly changed in the sheet surface, or completely random in any state. Good. Here, in the case of changing regularly and completely random, it becomes easier to control the front luminance and the viewing angle by combining with the change in the sheet thickness direction thickness L of the light diffusion phase.

  In addition, the arrangement pitch p of the light diffusion phase is preferably 10 to 500 μm, more preferably 10 to 200 μm, and most preferably 10 to 100 μm.

  Further, when the optical functional sheet of the present invention is viewed from the normal direction of the sheet surface, when the ratio of the area occupied by the transparent phase in the entire sheet surface area is defined as the aperture ratio, the aperture ratio is preferably 50% or more. . When the aperture ratio is less than 50%, the light utilization efficiency is lowered, and a sufficient luminance improvement effect cannot be exhibited.

  The optical functional sheet of the present invention is an optical functional sheet in which light diffusing phases having different thicknesses in the sheet thickness direction are arranged in a cross section in the sheet surface vertical direction, and whichever end of the light diffusing phase in the sheet thickness direction It is preferable that one of the positions is arranged so as to be substantially parallel to the sheet surface (FIGS. 1D to 1G).

  Furthermore, the sheet thickness direction thickness in the sheet surface vertical direction cross section of the light diffusion phase is different in the sheet surface direction, and either position of the end portion of the light diffusion phase in the sheet film thickness direction is substantially parallel to the sheet surface. An optical functional sheet arranged in such a manner that when the optical functional sheet is incorporated into a surface light source, the surface arranged so that the position of the light diffusion phase end is substantially parallel to the sheet surface The light incident surface from the light source is preferably used.

  By aligning either one of the ends of the light diffusion phase in the sheet thickness direction so as to be substantially parallel to the sheet surface, when light is incident from the array surface, each light having a large incident angle is not leaked. It can be applied to the light scattering phase. For this reason, the diffusion and reflection effects due to the light diffusion phase are sufficiently exhibited, and the luminance enhancement effect is further enhanced. Therefore, when the optical functional sheet of the present invention is incorporated in a surface light source, it is preferable that the arrangement surface is a light incident surface from the light source.

  In the optical functional sheet of the present invention, examples of the material used for the transparent phase 2 include polyester resins such as polyethylene terephthalate, polyethylene-2, 6-naphthalate, polypropylene terephthalate, and polybutylene terephthalate, polycarbonate, polystyrene, polyethylene, Polyolefin resins such as polypropylene and polymethylpentene, polyamides, polyethers, polyesteramides, polyetheresters, polyvinyl chloride, acrylic resins such as poly (meth) acrylic acid esters, alicyclic polyolefins, and these as main components A transparent resin made of a copolymer or a mixture of these resins can be suitably used, but is not particularly limited.

  The material used as the light diffusion phase 1 is not particularly limited, but is preferably made of a material in which fine particles having a refractive index different from that of the matrix component are dispersed in a transparent matrix component. As the transparent matrix component, for example, as with the resin that can be used for the transparent phase 2, polyester resins such as polyethylene terephthalate, polyethylene-2, 6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, polycarbonate, polystyrene, polyethylene, Polyolefin resins such as polypropylene and polymethylpentene, polyamides, polyethers, polyesteramides, polyetheresters, polyvinyl chloride, acrylic resins such as poly (meth) acrylates, alicyclic polyolefins, and main components thereof A transparent resin made of a copolymer or a mixture of these resins is not particularly limited.

  The fine particles dispersed in the light diffusion phase 1 are not particularly limited as long as the refractive index is different from that of the matrix component. For example, acrylic resin, organic silicone resin, polystyrene resin, urea resin, formaldehyde condensate, fluororesin, polyolefin Resins such as resins and polyester resins and resin particles, inorganic particles such as glass, silica, barium sulfate, titanium oxide, magnesium sulfate, magnesium carbonate, and calcium carbonate, or bubbles are preferably used.

  The optical functional sheet of the present invention may be a single-layer sheet, but has a laminated structure in which the sheet is formed on a base sheet in terms of mechanical strength, heat resistance, ease of handling and the like of the sheet itself. It is also a preferred embodiment. In the case of a laminated structure formed on a substrate sheet, as the substrate sheet, for example, a polyester resin represented by polyethylene terephthalate, polyethylene-2,6-naphthalate, or the like is preferably used. The base sheet may be transparent, the entire sheet may be a diffusion sheet having light diffusivity, or a sheet having other functions. By using a sheet having other functions as the base sheet, the functions can be integrated, and the sheet can be made thinner and lighter. For example, when the optical functional sheet of the present invention and a light diffusive sheet are laminated, a composite sheet in which the functions of a conventionally used light diffusive sheet and a prism sheet are integrated is obtained.

  The example of the method of manufacturing the optical functional sheet of this invention is shown below. The method listed here is an example, and the present invention is not limited to this.

  (1) When manufacturing an optical functional sheet in which either one of the end portions in the sheet thickness direction of the light diffusion phase is arranged substantially parallel to the sheet surface, the following method is used. Can be used. A transparent phase is formed by pressing a mold (FIG. 5 (a)) in which a groove that represents the shape of the desired light diffusing phase is pressed into a material of the transparent phase (FIG. 5 (b)). Next, the optical functional sheet is removed by removing the mold (FIG. 5C), filling the grooved transparent phase with a material for forming a light diffusion phase (FIG. 5D), and curing. can get.

  (2) The following method can be used when manufacturing an optical functional sheet in which the positions of the light diffusion phase in the sheet thickness direction are completely randomly arranged. A light diffusion phase is formed by pressing a mold (FIG. 6 (a)) having a groove in the shape of the desired light diffusion phase into the light diffusion phase material and curing it (FIG. 6 (b)). . Next, another mold (FIG. 6C) is pushed in to remove excess light diffusion phase material (FIG. 6D). One mold is removed (FIG. 6 (e)), and the material for forming the transparent phase is filled (FIG. 6 (f)), and the other mold is removed (FIG. 6 (g)), and the transparent phase is removed again. An optical functional sheet can be obtained by filling the material to be formed (FIG. 6 (h)).

  Various additives can be used for the optical functional sheet of the present invention. Examples of such additives include film-forming aids, ultraviolet absorbers, light stabilizers, heat stabilizers, pigments, dyes, plasticizers, viscosity modifiers, antioxidants, and the like.

Hereinafter, the present invention will be described using examples.
(Evaluation methods)
A. Front luminance measurement The backlight of a 5.8-inch liquid crystal display mounted on a commercially available car navigation display was taken out. This backlight was a sidelight type backlight having a cold cathode tube bent in a “U” shape so as to surround three sides of the light guide plate.
A surface light source for evaluation was assembled using a cold cathode tube, a light guide plate, and a reflection sheet in a relative positional relationship as shown in FIG. 7, and the cold cathode tube was turned on at an operating voltage of 13.0 V. The front brightness of the backlight was measured in a dark room using -7 (Topcon Co., Ltd.).
With the relative positional relationship as shown in FIG. 7, the front luminance of the backlight when measured without placing the optical functional sheet according to the present invention was 3986 cd / m ² at an operating voltage of 13.0 V.

B. Viewing angle measurement The surface light source for evaluation used in the front luminance measurement was installed in the variable angle photometer Goniophotometer GP-10 (manufactured by Optec Corporation). Next, as shown in FIG. 8, the screen vertical direction and horizontal direction were set, and the light intensity in increments of 5 ° was measured in the dark room in the range of −90 ° to + 90 ° in the horizontal direction and vertical direction of the screen. The light intensity at each measurement angle was In (n is an angle), and the intensity ratio I45 ° / I0 ° between I0 ° and I45 ° was compared.

  Here, when the light intensity in the vertical and horizontal directions of the screen was measured without placing the optical functional sheet according to the present invention on the surface light source for evaluation, it was as shown in FIG.

C. Measurement of sheet thickness direction thickness L of light diffusing phase, distance p between midpoints of two adjacent light diffusing phases, ratio L / p S500, 500 times with S-2100A (manufactured by Hitachi, Ltd.) From the image obtained by magnifying observation, the sheet thickness direction thickness L of the light diffusion phase, the distance p between the midpoints of two adjacent light diffusion phases, and the ratio L / p were determined.

(Example 1)
A transparent phase composition described below is prepared by repeatedly and regularly arranging molds having a wall width of 30 μm, an interval between adjacent walls (pitch) of 90 μm (constant), and a height of 80 μm, 60 μm, and 40 μm in this order. After pushing in and drying at 80 ° C. for 30 minutes, the mold was removed. In the obtained transparent mold, grooves according to the dimensions of the mold were formed. Moreover, when the film thickness after drying was measured, the film thickness of the flat part in which the groove | channel was not formed was 160 micrometers.
(Transparent phase composition)
“ELITEL” UE3600 (manufactured by Unitika Ltd.) 100 parts by weight cyclohexanone 15 parts by weight methyl ethyl ketone 30 parts by weight Next, the following composition for light diffusion phase was poured into the formed groove and dried at 80 ° C. for 30 minutes.
(Composition for light diffusion phase)
Titanium oxide (anatase type average particle size 0.4 μm) 15 parts by weight “Elitel” UE3600 (manufactured by Unitika Ltd.) 100 parts by weight cyclohexanone 20 parts by weight methyl ethyl ketone 40 parts by weight The resulting sheet has a film thickness of 160 μm and a light diffusion phase A structure in which three types of width 30 μm, pitch 90 μm, sheet thickness direction thickness 80 μm, 60 μm, 40 μm are repeatedly arranged in this order, and one end of the light diffusion phase is arranged parallel to the sheet surface Met.

This optical functional sheet was incorporated into a backlight and front luminance was measured. In the installation method to the backlight, the surface on which one end of the light diffusion phase is aligned was used as the light incident surface.
As a result, the luminance improvement rate of 37.6% (hereinafter, the rate of change in luminance when the optical functional sheet according to the present invention is measured on the light guide plate compared to the case where the luminance of the light guide plate is directly measured). , Called luminance improvement rate). Next, the viewing angle was measured (FIG. 10). As a result, I45 ° / I0 ° was 0.983 in the horizontal direction of the screen and 0.298 in the vertical direction of the screen.

Also, regarding the method of installing the optical functional sheet on the backlight, the surface with one end of the light diffusing phase is aligned in the direction opposite to the light incident surface (light exit surface) and incorporated into the backlight to increase the front luminance. It was measured.
The result was an improvement effect of 35.1%. Regarding the viewing angle, the screen horizontal direction I45 ° / I0 ° was 0.944, and the screen vertical direction I45 ° / I0 ° was 0.282.

(Example 2)
In Example 1, two types of molds to be used were regularly arranged in this order: a wall width of 30 μm, an interval between adjacent walls (pitch) of 90 μm (constant), a height of 100 μm, and 25 μm. Except for the above, an optical functional sheet was prepared and measured in the same manner as in Example 1.
The obtained sheet has a film thickness of 160 μm, a light diffusion phase width of 30 μm, a pitch of 90 μm, a sheet thickness direction thickness of 100 μm, and a thickness of 25 μm are repeatedly arranged in this order, and one end of the light diffusion phase is The structure was arranged so as to be parallel to the sheet surface.

This optical functional sheet was incorporated into a backlight and front luminance was measured. In the installation method to the backlight, the surface on which one end of the light diffusion phase is aligned was used as the light incident surface.
The front luminance was an improvement effect of 35.5%, and the luminance decreased as compared with Example 1. The viewing angle was 0.868 in the screen left-right direction I45 ° / I0 ° and 0.213 in the screen vertical direction I45 ° / I0 °, which was narrower than that in Example 1.

(Example 3)
A mold 1 in which three types of walls having a wall width of 30 μm, an interval between adjacent walls (pitch) of 90 μm (constant), a height of 20 μm, 5 μm, and 10 μm are regularly arranged in this order is used for the following light diffusion phase The mold 2 was pressed into the composition, and the hole 2 was 30 μm wide, the interval (pitch) between adjacent holes was 90 μm (constant), the depth was 80 μm, 45 μm, and 90 μm, and the mold 2 was regularly arranged in this order. After pressing from the opposite side of the mold 1 and drying at 80 ° C. for 30 minutes, the mold 1 was removed.
(Composition for light diffusion phase)
Titanium oxide (anatase type average particle size 0.4 μm) 15 parts by weight “Elitel” UE3600 (manufactured by Unitika Co., Ltd.) 100 parts by weight cyclohexanone 20 parts by weight methyl ethyl ketone 40 parts by weight And dried for 30 minutes, and the mold 2 was removed. Then, the same composition for transparent phase was poured and dried at 80 ° C. for 30 minutes.
(Transparent phase composition)
“ELITEL” UE3600 (manufactured by Unitika Ltd.) 100 parts by weight cyclohexanone 15 parts by weight methyl ethyl ketone 30 parts by weight The obtained sheet (FIG. 11) has a film thickness of 160 μm, a light diffusion phase width of 30 μm, a pitch of 90 μm, and a sheet thickness direction. The thickness of 60 μm, 40 μm, and 80 μm was a structure that was repeatedly arranged in this order without aligning either end.

  This optical functional sheet was incorporated into a backlight and front luminance was measured. As for the installation method to the backlight, the surface A in FIG. As a result, the luminance improvement rate was 33.8%. Next, the viewing angle was measured. As a result, I45 ° / I0 ° was 0.916 in the horizontal direction of the screen and 0.260 in the vertical direction of the screen.

  Moreover, when the B surface of FIG. 11 was made into the light-incidence surface and it integrated in the backlight and the front luminance was measured, the result obtained the luminance improvement rate of 34.3%. Next, the viewing angle was measured. As a result, I45 ° / I0 ° was 0.921 in the horizontal direction of the screen and 0.263 in the vertical direction of the screen.

  From these results, it was possible to achieve both high brightness and high viewing angle by arranging the light diffusion phase on a single plane substantially parallel to the sheet surface.

(Comparative Example 1)
In Example 1, an optical functional sheet was prepared and measured in the same manner as in Example 1 except that the height of the mold wall used was 40 μm and constant.
The obtained sheet has a thickness of 160 μm, a light diffusion phase width of 30 μm, a pitch of 90 μm, and a thickness of 40 μm in the sheet thickness direction, and one end of the light diffusion phase is parallel to the sheet surface. It was an arrayed structure.

  The front luminance was an improvement effect of 26.3%, and the luminance was reduced as compared with Example 1. As for the viewing angle (FIG. 10), the screen horizontal direction I45 ° / I0 ° was 0.998, and the screen vertical direction I45 ° / I0 ° was 0.311, which was wider than that in Example 1.

(Comparative Example 2)
In Example 1, an optical functional sheet was prepared and measured in the same manner as in Example 1 except that the height of the used mold wall was constant at 60 μm.
The obtained sheet has a film thickness of 160 μm, a light diffusion phase width of 30 μm, a pitch of 90 μm, and a thickness of 60 μm in the sheet film thickness direction, and one end of the light diffusion phase is parallel to the sheet surface. It was an arrayed structure.

  The front luminance was an improvement effect of 34.4%, and the luminance decreased as compared with Example 1. As for the viewing angle (FIG. 10), the screen horizontal direction I45 ° / I0 ° was 0.894, and the screen vertical direction I45 ° / I0 ° was 0.256, which was narrower than that in Example 1.

(Comparative Example 3)
In Example 1, an optical functional sheet was prepared and measured in the same manner as in Example 1 except that the height of the used mold wall was constant at 80 μm.

  The obtained sheet has a film thickness of 160 μm, a light diffusion phase width of 30 μm, a pitch of 90 μm, and a sheet thickness direction thickness of 80 μm, and one end of the light diffusion phase is parallel to the sheet surface. It was an arrayed structure.

  The front luminance was improved by 37.9%, and the luminance was improved as compared with Example 1. As for the viewing angle (FIG. 10), the screen horizontal direction I45 ° / I0 ° was 0.812, and the screen vertical direction I45 ° / I0 ° was 0.122, which was narrower than that in Example 1.

It is a sheet surface perpendicular direction sectional view of the optical functional sheet of the present invention. It is a sheet surface perpendicular direction sectional view of the optical functional sheet of the present invention. It is a sheet surface perpendicular direction sectional view of the optical functional sheet of the present invention, and is a figure showing section shape of a light diffusion phase. It is the figure which looked at the optical functional sheet of this invention from the sheet surface normal direction, and is a figure which shows the pattern which consists of a light-diffusion phase and a transparent phase in a sheet | seat surface. It is a figure which shows the example of the manufacturing method of the optical functional sheet of this invention. It is a figure which shows the example of the manufacturing method of the optical functional sheet of this invention. It is a figure which shows the backlight structure in the case of the brightness | luminance measurement using the optical functional sheet of this invention. It is a figure which shows the conditions of the viewing angle measurement using the optical functional sheet of this invention. It is a figure which shows the result of the viewing angle measurement of the backlight used for the brightness | luminance measurement of the optical functional sheet by this invention. It is a figure which shows the result of the viewing angle measurement using the optical functional sheet of this invention. It is a figure which shows the Example of the optical functional sheet of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusion phase 2 Transparent phase 3 Optical functional sheet 4 of this invention Diffusion sheet 5 Light guide plate 6 Fluorescent tube 7 Reflection sheet

Claims (5)

An optical functional sheet in which a light diffusing phase and a transparent phase are alternately arranged in the sheet surface direction, and the light diffusing phase has at least two kinds of thicknesses in the sheet thickness direction in the cross section in the sheet surface vertical direction. Optical functional sheet. 2. The optical functional sheet according to claim 1, wherein L1 / L2 is 0.3 or more and less than 1 when the minimum value in the thickness direction of the light diffusion phase sheet is L1 and the maximum value is L2. 3. The optical functional sheet according to claim 1, wherein the light diffusion phase is arranged in a single plane substantially parallel to the sheet surface in a cross section perpendicular to the sheet surface. A surface light source incorporating the optical functional sheet according to claim 1. A surface light source incorporating the optical functional sheet according to claim 3, wherein when the light from the light source enters the light diffusion phase, the light diffusion phase is arranged in one plane substantially parallel to the sheet surface. A surface light source arranged to enter from the side.

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