JPWO2008078510A1 - Light diffusing substrate and surface light source using the same - Google Patents

Abstract

Providing a light diffusing substrate that can efficiently eliminate uneven brightness and achieve both high uniformity on the screen and high luminance characteristics, and a surface light source that can be used as a direct-type backlight with high luminance and high uniformity. In order to do so, a base material having a concavo-convex shape consisting of repetition of a top part and a bottom part on at least one side, the base material is made of a material having a refractive index in the range of 1.45 to 1.65, and the top part and When the repeating direction of the bottom is x and the thickness direction of the base material is z, the angle θ of the concavo-convex shape in the xz plane is in the range of 55 ° to 85 ° or in the range of 95 to 125 °, And it is set as the light-diffusion base material from which the inclination of the tangent between adjacent bottom parts reduces in the x increase direction.

Description

  The present invention relates to a light diffusing substrate capable of exhibiting high luminance characteristics and a surface light source comprising the same, although the luminance unevenness is small and the uniformity on the screen can be increased.

  In recent years, many displays using liquid crystal elements have been used as display devices for personal computers, televisions, mobile phones and the like. Since these liquid crystal displays are not themselves light emitters, they can be used not only to irradiate light but also to irradiate the entire screen uniformly. A so-called surface light source structure is employed. At this time, if there is unevenness in the light emitted from the backlight, the image quality of the display deteriorates, so that it is required to irradiate the entire screen uniformly.

  Of these, direct type backlights are preferably used for televisions and the like. The direct type backlight is a surface light source of a type in which a light source is arranged in a hollow casing and light is emitted from the light source to emit light from one main plane of the casing (for example, Patent Document 1). ). That is, a light source such as a large number of fluorescent tubes is arranged immediately below the light exit surface.

  For this reason, the direct type backlight among the various backlights has a problem that a large luminance difference is likely to occur between a position directly above the light source on the screen and a position not so, and is easily recognized as luminance unevenness. For this reason, a translucent milky white plate (so-called light diffusing plate) in which light diffusing particles are dispersed in acrylic resin or the like, which has a very strong light diffusibility, is generally installed on the light exit surface. A diffusion sheet, a prism sheet, and the like are appropriately disposed thereon.

  On the other hand, the demand for higher luminance of the surface light source is increasing, and there are methods for increasing the number of lamps and increasing the output, for example. However, these methods cause significant cost increase and are inefficient.

In addition, in response to the above demand for higher brightness, proposals have been made regarding a film having an uneven shape on the surface. Specifically, a lens having a cylindrical lens portion in a stripe shape (see Patent Document 2), a lens having a rugby ball shape (see Patent Document 3), and the like have been proposed.
Japanese Patent Laid-Open No. 5-119311 JP 2002-62528 A JP 2002-107510 A

  However, it is difficult to make the luminance sufficiently high in the backlight provided with the conventional milky white plate because the light diffusibility is too strong. Further, in a direct type backlight equipped with a so-called lenticular sheet having a semi-cylindrical cylindrical lens portion, a part of light emitted in an oblique direction from a fluorescent tube such as a cold cathode ray tube is totally reflected, so that FIG. As shown in FIG. 4, since the light is emitted strongly in an oblique direction opposite to the incident direction, a sufficiently high front luminance cannot be obtained. That is, the situation is that none of the backlights has sufficiently high luminance and uniformity.

  In light of the background of the prior art, the present invention provides a light diffusing substrate capable of effectively eliminating luminance unevenness and increasing uniformity on the screen while achieving high luminance characteristics, and high luminance using the same It is also intended to provide a surface light source that has high uniformity.

The present invention employs any one of the following means in order to solve such a problem.
(1) A base material having an uneven shape consisting of repetition of a top part and a bottom part on at least one side, the base material being made of a material having a refractive index in a range of 1.45 to 1.65, and the top part and the bottom part Where x is the repeating direction and z is the thickness direction of the substrate, the angle θ of the concavo-convex shape in the xz plane is in the range of 55 ° to 85 ° or in the range of 95 to 125 °, and A light diffusing substrate in which the slope of a tangent line between adjacent bottoms decreases in the x increasing direction.
(2) The light diffusing substrate according to (1), wherein no substantially flat portion is present between adjacent top portions.
(3) The light diffusing substrate according to (1) or (2), wherein the skirt angle θ is in the range of 65 ° to 85 ° or in the range of 95 to 115 °.
(4) In any one of the above (1) to (3), the maximum value in the z direction of the concavo-convex shape is larger than the shape formed of a part of a perfect circle having the same skirt angle θ as the concavo-convex shape. The light-diffusion base material of description.
(5) The light-diffusion base material in any one of said (1)-(4) whose aspect-ratio of the said uneven | corrugated shape exists in the range of 1-3.
(6) The light diffusing substrate according to any one of (1) to (5), which contains a light diffusing element inside the substrate.
(7) A surface light source comprising the light diffusing substrate according to any one of (1) to (6) and a light emitting means.

  The light diffusion base material of the present invention can have both high luminance and uniformity by changing the uneven shape imparted to the surface from a simple semi-cylindrical shape. That is, a base material having at least one concave and convex shape consisting of repetition of a top part and a bottom part, and the base material is made of a material having a refractive index within a range of 1.45 to 1.65. When the repeating direction is x and the thickness direction of the substrate is z, the angle θ of the concavo-convex shape in the xz plane is in the range of 55 ° to 85 ° or in the range of 95 to 125 °, and adjacent By reducing the slope of the tangent line between the bottoms in the x-increasing direction, the proportion of light that exits obliquely from the fluorescent tube in the oblique direction opposite to the incident direction is reduced. Thus, the front brightness can be improved. Therefore, it is suitable for a surface light source used in a display device such as a personal computer, a television or a mobile phone, particularly a flat display device such as a liquid crystal display device. As the surface light source, there are a direct type surface light source and a sidelight type surface light source, and the light diffusing substrate of the present invention can be used by attaching to the exit surface in any of the surface light sources.

It is a schematic diagram which shows one Embodiment of the uneven | corrugated shape provided in the surface of the light-diffusion base material of this invention. It is a schematic diagram which shows one Embodiment of the uneven | corrugated shape provided in the surface of the light-diffusion base material of this invention. It is a schematic diagram which shows one Embodiment of the light-diffusion base material of this invention. It is a schematic diagram which shows one Embodiment of the light-diffusion base material of this invention.

Explanation of symbols

1: Schematic diagram of surface shape of lenticular lens 2: Trajectory of light ray obliquely incident on hem of lenticular lens 3: Trajectory of light ray totally reflected out of obliquely incident light 4: Light ray totally reflected , Locus 5 of light beam emitted in the direction opposite to the incident direction due to refraction: surface uneven shape 5 ′ of light diffusing substrate showing one embodiment of the present invention: perfect circle having the same skirt angle θ as uneven shape 5 Part 10 of the concavo-convex shape 11: a position on the concavo-convex shape and a position 12 away from the bottom 10 in the distance x direction of 1/1000 of the concavo-convex shape repetition period p 12: x from the concavo-convex shape bottom 10 Straight line 100 drawn in the direction: light diffusing substrate 101: top part 102 of concave / convex shape: bottom part of concave / convex shape θ: bottom part 10 of concave / convex shape, and a repetition cycle of concave / convex shape from the bottom 10 at the position on the concave / convex shape 1/1 of p Angle formed by a straight line connecting a position 11 away from the distance x direction of 00 and a straight line 12 drawn in the x direction from the concave-convex bottom 10: distance from top to bottom in the x direction h: z direction The distance h ′ from the top to the bottom in FIG. 5: the maximum value p in the z direction of a shape consisting of a part 5 ′ of a perfect circle having the same skirt angle θ as the concavo-convex shape 5; Through x to the next bottom)
t: Total thickness defined in the present invention

  The present invention has been achieved as a result of intensive studies on the above-mentioned problem, that is, the light diffusion base material that can increase the luminance and achieve both the uniformity on the screen and the high luminance characteristics, as shown in FIG. A substrate 100 having an uneven shape consisting of repetition of the top part 101 and the bottom part 102 on at least one side, made of a material having a refractive index in the range of 1.45 to 1.65, and the repeating direction of the top part and the bottom part is x When the thickness direction of the substrate is z, the angle θ of the concavo-convex shape in the xz plane is in the range of 55 ° to 85 ° or in the range of 95 to 125 °, and between the adjacent bottom portions Light that is strongly emitted in an oblique direction opposite to the incident direction out of the light emitted obliquely from the fluorescent tube by using the base material having an uneven shape in which the inclination of the tangential line decreases in the x increasing direction. Percentage of Small Toe, and the light emitted in an oblique direction from the fluorescent tube and allow bending to the front direction has been found that the above problems can be solved at a stroke.

  As shown in detail in FIG. 2, the hem angle θ is a concavo-convex bottom 10, a position x on the concavo-convex shape, and a distance x 1/1000 of the concavo-convex shape repetition period p from the bottom 10. It is an angle formed by a straight line connecting the position 11 separated in the direction and a straight line 12 drawn in the x direction from the bottom 10 of the uneven shape.

  More preferably, the skirt angle θ is in the range of 65 ° to 85 ° or in the range of 100 to 115 °.

  The refractive index of such a substrate needs to be 1.45 to 1.65. More preferably, it is 1.5-1.6. The refractive index of the base material here means the refractive index of the base material in the case of a light diffusing base material consisting of a single layer, and in the case of a light diffusing base material consisting of a plurality of layers, a layer provided with an uneven shape. This means the refractive index. By making the refractive index of the base material within these ranges and the angle of the skirt within the above range, among the light incident obliquely from the fluorescent tube, the light that is strongly emitted in the oblique direction opposite to the incident direction It is possible to reduce the ratio of light and to bend light incident in an oblique direction from the fluorescent tube in the front direction, and to improve luminance without increasing luminance unevenness.

  Examples of the substrate that satisfies such requirements include polyester, polycarbonate, polymethyl methacrylate, polystyrene, and the like. The polyester referred to here includes polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polypropylene terephthalate, polyester having 1,4-cyclohexanedimethanol as a copolymerization component, and copolymers thereof. As the acid component and diol component to be copolymerized, aromatic dicarboxylic acid, sulfonic acid metal base-containing dicarboxylic acid, alkylene glycol having 3 to 25 carbon atoms, polyalkylene glycol, and the like can be used, but it is particularly limited to these. It is not a thing.

  Such a concavo-convex shape requires that the slope of the tangent line between adjacent bottoms gradually decreases in the x increasing direction. By satisfying such requirements, the shape becomes a curve, and it becomes possible to have a tangent angle for bending light incident at various angles in the front direction, and luminance unevenness can be reduced. Examples of the curved shape include, but are not necessarily limited to, a semicircle, a semi-ellipse, a parabola, a hyperbola, a trigonometric function, or a predetermined portion constituting such a curve.

  Furthermore, it is preferable that this shape is line symmetric with respect to the top. The light diffusing substrate of the present invention is suitably used for, for example, a liquid crystal display, and in that case, it is preferable because the appearance when viewed from the left and right is not changed by satisfying such requirements.

  In the present invention, it is preferable that there is no substantial flat portion as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-142622 between adjacent top portions. The substantially flat portion refers to a portion where light emitted from the fluorescent tube is transmitted straight through, for example, a width that is unavoidable when a concave / convex shape is imparted to the base material by die processing (the above x direction). (Length in) does not include a flat portion of 1 μm or less. By eliminating the substantially flat portion, it is possible to prevent the light emitted from the fluorescent tube from being transmitted in a straight line and to prevent uneven brightness.

  In the present invention, the maximum value (h) in the z direction of the concavo-convex shape is a shape formed of a part 5 ′ of a perfect circle having the same skirt angle θ as the concavo-convex shape 5 as shown in FIG. It is preferably larger than the maximum value (h ′) in the z direction. Satisfying such a requirement means that a region having a large tangent slope in the concavo-convex shape 5 is increased. Therefore, the effect of bending light incident obliquely on the light diffusing substrate in the front direction can be strengthened, and even when applied to a backlight with a small number of fluorescent tubes or a thin backlight, the brightness unevenness The effect of eliminating can be strengthened.

  The concavo-convex shape preferably has an aspect ratio in the range of 1 to 3. As shown in FIG. 2, the aspect ratio here is the ratio of the distance w from the top to the bottom in the x direction and the distance h from the top to the bottom in the z direction, and is h / w. By setting the aspect ratio to 1 or more, light incident in an oblique direction from the fluorescent tube can be more reliably directed to the front direction, and luminance unevenness can be more reliably prevented. On the other hand, by setting the aspect ratio to 3 or less, it is possible to secure luminance when the screen is viewed obliquely. A more preferable range of the aspect ratio is 1.3 to 2.8.

  Moreover, it is preferable that an uneven | corrugated shape has a discontinuous point in the top part. In addition, having a discontinuous point at the top means that the top is a non-differentiable point. By having a discontinuous point at the top, incident light can be refracted even immediately above the fluorescent tube, and luminance unevenness can be reduced.

  Furthermore, the repetition period (p) of the concavo-convex shape is preferably 1 μm to 1000 μm. By setting the repetition period p to 1 μm or more, light diffraction can be ignored, coloring due to light diffraction, and deterioration of the image quality of the screen when the backlight is mounted can be prevented. On the other hand, by setting it to 1000 μm or less, it is possible to prevent the surface shape from being visible and to prevent the image quality of the screen from being deteriorated when the backlight is mounted. The repetition period (p) is more preferably 10 μm to 200 μm. By setting the repetition period of the concavo-convex shape within such a range, it becomes easy to impart the concavo-convex shape, and productivity can be improved. Note that the repetition period (p) is a length in the x direction from the bottom 102 of a certain uneven shape to the next bottom 102 through the top 101 as shown in FIG.

  In this invention, it is preferable that the total thickness (t) of a light-diffusion base material is 10 micrometers-1000 micrometers. More preferably, it is 20-500 micrometers, More preferably, it is 50-250 micrometers. By making it in this range, the advantages of cost and handleability become significant. A light diffusing substrate having a thickness (t) of 1000 μm or more is unsuitable because the amount of raw material used increases and the cost increases. Further, when the thickness (t) is 10 μm or less, the handling property is poor, and a dedicated facility may be required when assembling the backlight, resulting in high cost. In the present invention, the total thickness (t) of the light diffusing substrate means that when the concavo-convex shape is provided only on one side, the concavo-convex shape is provided from the top of the concavo-convex provided on one surface as shown in FIG. This refers to the distance to the other surface that does not, and when both surfaces have an uneven shape, the distance from the top of the unevenness provided on one surface to the top of the unevenness on the opposite surface.

  Moreover, it is preferable that the light-diffusion base material of this invention has a light-diffusion element inside. Here, the light diffusing element means inorganic fine particles such as glass, silica, barium sulfate, titanium oxide, magnesium sulfate, calcium carbonate, or acrylic resin, organic silicone resin, polystyrene, polyolefin, polyester, urea resin, formaldehyde condensate, Although it is organic fine particles, such as a fluororesin, it is not limited to these in particular. Moreover, these can be used 1 type or in mixture of 2 or more types.

  The average particle size of the light diffusing element is usually preferably 1 to 50 μm. More preferably, it is 1-30 micrometers, More preferably, it is 1-20 micrometers. By making the particle diameter larger than 1 μm, a screen with higher brightness can be obtained, and by making it smaller than 50 μm, good light diffusibility can be obtained without reducing the strength of the substrate. Here, the average particle diameter is the average particle diameter of the primary particles, and for each particle, the average value of the longest particle diameter and the particle diameter in the direction perpendicular thereto is determined, and this operation is performed on the particles. The calculation is performed for 50 pieces, and the arithmetic average of these values is used.

  Moreover, it is preferable that the refractive index of these light diffusing elements is different from that of the main constituent components of the light diffusing substrate whose refractive index is in the range of 1.45 to 1.65. When the main constituent components of the light diffusing element and the light diffusing substrate are the same, the light diffusion phenomenon due to refraction and reflection at the interface between the main constituent component and the light diffusing element does not occur, and it is difficult to obtain a desired light diffusing effect. Furthermore, in order to obtain effective light diffusibility, the difference in refractive index between the main constituent components of the light diffusing substrate and the light diffusing element is preferably 0.01 or more. When the difference in refractive index is less than 0.01, the light diffusion effect is small, and in order to obtain a good diffusion effect, it is necessary to add a large amount of particles or increase the thickness of the base material. There may be an effect that it must be thicker than the film thickness.

  Further, the cross-sectional shape of the light diffusing element is not particularly limited, such as a circle, an ellipse, a triangle, a polygon such as a quadrangle, or an aggregate of a part of these, but in the present invention, it has a shape close to a circle. Preferably there is. In addition, the cross-sectional shape of the diffusion element referred to here is a cross-sectional shape observed when the base material is cut perpendicularly to the base material surface.

  Further, the ratio of the light diffusing element to be blended in the light diffusing substrate is appropriately selected depending on the desired degree of light diffusibility, but in general, the volume fraction is preferably 0.01% to 50%, Preferably it is 0.1%-35%, Most preferably, it is 1-25%.

  Next, a method for producing the light diffusing substrate of the present invention will be described. The light diffusing substrate of the present invention can be obtained, for example, by imparting the above uneven shape to the surface of a known thermoplastic resin film, sheet, plate (hereinafter referred to as a base substrate). It is done.

  Here, the method for imparting the uneven shape as described above is not particularly limited, and examples thereof include a thermal imprint method and an optical imprint method.

  Thermal imprinting is a technique that heats a mold and resin with a fine surface shape, presses the mold against the resin, cools, and then releases, thereby transferring the shape applied to the mold surface to the resin. is there. Here, the resin used for thermal imprinting may be a thermoplastic resin or a thermosetting resin, but is preferably a highly transparent resin.

  Examples of the thermoplastic resin include polyester terephthalate, polyethylene-2.6-naphthalate, polypropylene phthalate, polybutylene terephthalate, cyclohexanedimethanol copolymer polyester resin, isophthalic acid copolymer polyester resin, and spiroglycol copolymer polyester. Examples thereof include resins and fluorene copolymer polyester resins. Examples of the olefin resin include alicyclic olefin copolymer resins, and examples of the acrylic resin include polymethyl methacrylate. Further, as other resins, polycarbonate, polystyrene, polyamide, polyether, polyesteramide, polyetherester, polyvinyl chloride, and the like can be given. Furthermore, it is a copolymer which uses these as a component, and the mixture of these resin can also be used.

  Among them, in terms of mechanical strength, heat resistance, and dimensional stability, a biaxially stretched polyethylene terephthalate, polyethylene-2.6-naphthalate, a copolymer with other components based on these, a mixture, etc. A polyester resin is more preferably used.

  Examples of the thermosetting resin include acrylic resin, epoxy resin, unsaturated polyester resin, phenol resin, urea / melamine resin, polyurethane resin, silicone resin, and the like. A mixture of the above can be used.

  On the other hand, with the photoimprint method, a photocurable resin is applied on a film, a sheet-like material, or a plate-like material, and a die having a fine uneven shape is pressed against the photocurable resin portion. This is a method of transferring a fine uneven shape of a mold onto a film or the like by irradiating ultraviolet light from the opposite direction to the surface pressed to cure the photocurable resin and releasing the mold.

  Examples of the photocurable resin include a compound having at least one radical polymerizability in the molecule or a compound having cationic polymerizability. The compound having radical polymerizability is a compound that undergoes a polymer or a crosslinking reaction by irradiation with active energy rays in the presence of a polymerization initiator that generates radicals by active energy rays. For example, the structural unit includes at least one ethylenically unsaturated bond, and includes other functional vinyl monomers in addition to a monofunctional vinyl monomer. Moreover, these oligomers, polymers, and mixtures may be used. Examples of the compound having at least one cationic polymerizability in the molecule include one or more compounds selected from a compound having an oxirane ring, a compound having an oxetane ring, and a vinyl ether compound.

  As the base substrate, in the case of a film, for example, a polyethylene terephthalate that has been vacuum-dried at 180 ° C. for 4 hours is supplied to a film forming apparatus consisting of a main extruder, melt-extruded, and this sheet is a mirror-cooled drum having a surface temperature of 20 ° C. Cast above to obtain an unstretched sheet. Then, this sheet can be obtained by stretching 3 times in the longitudinal direction at 85 ° C. and continuously stretching 3 times in the width direction in an atmosphere at 100 ° C. In addition, when the base substrate is a sheet or plate, the thickness may be different from that of the film, which may not be obtained by the same manufacturing method, but may be manufactured by a known method.

  The light diffusing substrate of the present invention as described above is useful because it can be suitably used for the light exit surface of a backlight (surface light source), and can exhibit good performance particularly in a direct type backlight.

  The direct type backlight has, for example, a light emitting means such as a fluorescent tube in a hollow casing, and a light diffusion base material disposed above the light emitting means, and the light emitted from the light emitting means is transmitted to the casing. Is a surface light source that emits light from one main plane, that is, the surface on which the light diffusion base material is disposed. In addition, a so-called reflecting plate exhibiting excellent reflection characteristics may be mounted on the bottom and side portions of the hollow casing in the direct type backlight. The reflective plate may be a single reflective film, or may be a housing or a laminate of the reflective film on an aluminum plate different from the housing. Further, it may be grooved according to the arrangement of the light sources. The number of light emitting means such as fluorescent tubes and the screen size are not particularly limited.

  When the light diffusing substrate of the present invention is applied to such a surface light source, the surface light source has high brightness without increasing unevenness in brightness, and can be made thin and lightweight. It is possible to improve the dimensional stability and strength. Therefore, it is suitably used particularly for a direct type backlight of a liquid crystal display. In addition, when applying the light-diffusion base material of this invention to a surface light source, it arrange | positions so that the surface of the side which has the above uneven | corrugated of the characteristic shape may be on the opposite side to a light source.

  In the surface light source, the light diffusion base material of the present invention may be disposed alone on the light emitting means, but a bead layer-containing base material or a hemispherical dome shape is provided on the surface of the light emitting means. When a diffusion plate containing a light diffusing material such as a base material or a milky white plate is arranged and the light diffusing substrate of the present invention is placed thereon, the display is viewed not only from the front but also from an angle. Also, good luminance characteristics can be obtained. The bead layer-containing base material refers to a layer in which transparent beads are coated on a transparent base material or a diffusion base material containing a diffusing material therein and fixed with a binder resin. Further, the base material having a hemispherical dome shape on the surface refers to a surface of a diffusion base material in which a transparent base material or a diffusing material is contained, and a hemispherical dome shape is provided by pressing or the like. .

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Measurement method and evaluation method of characteristics]
Each of the following measurements was performed at room temperature (20 ° C. to 30 ° C.) and atmospheric pressure, avoiding high humidity conditions (80% or more).

(1) Luminance and luminance unevenness of backlight Remove a diffusion plate (made of acrylic having a thickness of 2 mm) set on a cold cathode ray tube from a direct type backlight as disclosed in, for example, Japanese Patent Application Laid-Open No. 5-119411, Here, the light diffusing substrate of the present invention is installed so that the surface having irregularities is on the CCD camera side, and the direction perpendicular to the xz plane of the substrate and the longitudinal direction of the cold cathode ray tube are matched. After lighting the cold cathode ray tube for 60 minutes and stabilizing the light source, using EYESCALE-3 (Eye System Co., Ltd.), attach the attached CCD camera to the backlight surface at a point 90 cm from the backlight surface. It installed so that it might become the front with respect to it, and the brightness | luminance (cd / m < ² >) was measured.

Note that the luminance is the position of the two cold cathode ray tubes in the center of the backlight (two points in total), and the position of the midpoint of the two cold cathode ray tubes and two further cold cathode ray tubes adjacent thereto. Observed at (total 3 points), the average of the luminance at the position of the cold cathode ray tube was L _max , and the average of the luminance at the midpoint position of the four cold cathode ray tubes was L _min . At this time, the positions of the two cold cathode ray tubes and the two cold cathode ray tubes adjacent to the two cold cathode ray tubes were determined by measuring the luminance only with the backlight without installing the light diffusion base material.

And ( _Lmax + _Lmin ) / 2 was made into the average luminance in this invention. The average luminance is preferably high, and P is defined as 3400 cd / m ² or more, and F is defined as 3400 cd / m ^{2 or} less.

In addition, (L _max −L _min ) was used as a value indicating luminance unevenness. The smaller the brightness unevenness, the better. Where brightness unevenness is 600 cd / ^{m 2} or less P, and if it exceeds 600 cd / ^{m 2} was F.

As for the luminance characteristics, when both the average luminance and the luminance unevenness are P, when the value obtained by subtracting the luminance unevenness from the average luminance is 3000 cdm ² or less, it is B, and when it is more than 3000 cd / m ² , it is A. The results thus evaluated are shown in Table 1.

In addition, the luminance characteristics when the backlight is viewed obliquely were also measured using EYESCALE-3 (Eye System Co., Ltd.). First, the attached CCD camera was installed on a stand with a variable angle so that the distance from the backlight surface was 90 cm directly above the backlight, and the luminance was measured. Subsequently, the CCD camera is rotated so that the distance between the CCD camera and the backlight center is maintained at 90 cm, with the measurement angle at this time being 0 °, and the focal point at the measurement angle 0 ° being the rotation center. In the range from 0 to 60 °, the luminance was measured every 15 °. In any case, the case where the luminance unevenness was 600 cd / m ² or less was defined as A. The brightness unevenness from 0 ° to 30 ° was 600 cd / m ² or less, but the brightness unevenness exceeded 600 cd / m ² in the range exceeding 30 ° was designated as B, and the brightness from 0 ° to 30 °. The case where the unevenness was over 600 cd / m ² was defined as C.

(2) Measurement of concavo-convex hem angle (θ), aspect ratio and concavo-convex shape repetition period (p), and confirmation method of light diffusing element inclusion, concavo-convex shape bottom, position on concavo-convex shape and bottom The angle (θ) of the skirt of the concavo-convex shape formed by the straight line connecting the position away from the concavo-convex shape by a distance of 1/1000 of the repetition period p in the x direction and the straight line drawn in the x direction from the bottom of the concavo-convex shape Uses a microtome to freeze-cut the light diffusion substrate perpendicularly to the surface of the light diffusion substrate, deposits platinum / palladium on an ion coater on the cross-section, and performs field emission scanning by JEOL Ltd. Using a scanning electron microscope JSM-6700F, the thickness of the layer having irregularities is enlarged to a size that can be confirmed in the range of 500 to 10,000 times, and each irregular point is digitized by image processing software. To determine the value of θ by differentiating on the spreadsheet. This operation was performed 5 times, and the average value was defined as θ. However, when the difference between the maximum value and the minimum value is 50% or more of the average value of the five times as a result of the five operations, the operation is performed 50 times, and the average value is defined as θ. The value of θ was calculated to the whole number by rounding off the first decimal place. The results thus evaluated are shown in Table 1. In the table, θ ₁ is a position on the concavo-convex shape, and is a value obtained when a position away from the bottom in the positive direction in a distance x direction that is 1/1000 of the concavo-convex shape repetition period p. in, theta ₂ is in the negative direction from the bottom is a value when the sought position spaced 1/1000 distance x direction of the repetition period p of the uneven shape.

  The aspect ratio was determined by freezing and cutting the light diffusing substrate perpendicularly to the surface of the light diffusing substrate using a microtome, and depositing platinum / palladium with an ion coater on the cross section, and manufactured by JEOL Ltd. Using a field emission scanning electron microscope JSM-6700F, the thickness of the layer with irregularities is expanded to a size that can be confirmed in the range of 500 to 10,000 times, and each coordinate point is digitized by image processing software. I asked for it. This operation was performed 5 times, and the average value was defined as the aspect ratio. However, when the difference between the maximum value and the minimum value is 20% or more of the average value of the five times as a result of the five operations, the operation was performed 50 times and the average value was used as the aspect ratio. The aspect ratio value was rounded off to the second decimal place. The results thus evaluated are shown in Table 1.

  The repetition period (p) of the concavo-convex shape means the distance from the bottom to the next bottom in one concavo-convex shape, and the light diffusing substrate is applied to the surface of the light diffusing substrate using a microtome. On the other hand, the section was frozen and cut, and platinum / palladium was vapor-deposited on its cross section with an ion coater, and unevenness was formed in the range of 500 to 10,000 times using a field emission scanning electron microscope JSM-6700F manufactured by JEOL Ltd. The thickness of the layer is enlarged to a size that allows confirmation, and one concavo-convex shape is obtained by quantifying each coordinate point with image processing software. This operation was performed 5 times, and the average value was defined as p. However, when the difference between the maximum value and the minimum value is 20% or more of the average value of the five times as a result of the five operations, the operation was performed 50 times, and the average value was defined as p. The value of p was rounded off to the first decimal place. The results thus evaluated are shown in Table 1.

  Confirmation of the presence of the light diffusing element was carried out by freezing and cutting the light diffusing substrate perpendicularly to the surface of the light diffusing substrate using a microtome, and depositing platinum / palladium on the cross section with an ion coater. Using a field emission scanning electron microscope JSM-6700F manufactured by Co., Ltd., observation was performed at a magnification of 500 to 10,000 times with the total thickness of the light diffusion base material, and the measurement position was changed five times for observation. . Thus, it is shown in Table 1 that W is the one that was found to contain a light diffusing element (not transparent) inside the film and W / O that was not recognized (transparent).

(3) Total thickness measurement (t)
The total thickness of the light diffusing substrate was measured by using a Mitutoyo dial gauge and placing the light diffusing substrate so that the probe contacted the surface having no irregularities. The measurement was performed 5 times at different locations, and the average value was taken as the total thickness. In the case where there are irregularities on both sides, the probe may be in contact with either side.

(4) Refractive index measurement of substrate uneven portion The refractive index of the material constituting the uneven portion is a sample piece obtained by cutting only the uneven portion using a microtome, the sample piece is placed on a slide glass, and the refractive index is 1 A commercially available refracting liquid that is different by 0.01 in the range of 4 to 1.7 is dropped, a cover glass is placed thereon, a preparation is prepared, and the preparation is a microscope whose light source is sodium D-line (wavelength 589 nm) The refractive index of the refracting liquid where the outline of the sample piece is most difficult to be seen was taken as the refractive index of the sample piece. This operation was performed 5 times, and the average value was taken as the refractive index, and the value was calculated to the second decimal place.

[Example 1]
Apply a photocurable resin to a transparent polyester film with a thickness of 100 μm so that the coating film thickness is 50 μm, push a mold with the following surface shape into the coating film, and irradiate light from the film direction. The desired surface shape was imparted by curing and peeling the photocurable resin. Here, a = b = 50 μm.

<Mold shape>
A shape in which the curves represented by (Expression 1) and (Expression 2) are reversed at the position of z = z _min +0.2 (z _max −z _min ) and repeatedly in the x-axis direction.

However, z _min is the minimum value of z in the curve represented by (Formula 1), and z _max is the maximum value.

As a photocurable resin, Daidick Ink Chemical Industries, Ltd. Unidic 15-829 was used. A mercury lamp was used as a light source, and irradiation was performed for 36 seconds at an intensity of 500 mJ / cm ² . Then, it heated at 80 degreeC for 30 minutes, implemented the photocuring process, and obtained the light-diffusion film which has fine uneven | corrugated shape on the surface by peeling a metal mold | die after that.

The thus obtained film, as shown in Table 1, the average luminance 3500 cd / ^{m 2,} a luminance unevenness 500 cd / ^{m 2,} and both high average luminance and low luminance irregularity showed excellent luminance characteristics. Further, the oblique luminance characteristic was B with a luminance unevenness of 1500 cd / m ² occurring at a measurement angle of 45 °, although the luminance unevenness was 600 cd / m ² or less at a measurement angle of 30 ° or less.

[Example 2]
A light diffusion film was obtained in the same manner as in Example 1 except that the following mold shape was used.

<Mold shape>
A shape in which the curves represented by (Expression 3) and (Expression 4) are inverted at the position of z = z _min +0.4 (z _max −z _min ) and repeatedly in the x-axis direction.

The thus obtained film, as shown in Table 1, the average luminance 3400cd / ^{m 2,} a luminance unevenness 400 cd / ^{m 2,} and both high average luminance and low luminance irregularity showed excellent luminance characteristics. Further, the oblique luminance characteristic was B with a luminance unevenness of 1500 cd / m ² occurring at a measurement angle of 45 °, although the luminance unevenness was 600 cd / m ² or less at a measurement angle of 30 ° or less.

[Example 3]
A light diffusion film was obtained in the same manner as in Example 1 except that the following mold shape was used and a = b = 50 μm and c = 0.1.

<Mold shape>
In (Expression 5) and (Expression 6), when c = 0.1 and (z ₁ −z ₂ ) ≧ 0, z = z _{2 and} according to (z ₁ −z ₂ ) <0, according to z = z ₁ A shape in which the curve in which the range of z is expressed by (Expression 7) is inverted at a position of z = z _min +0.2 (z _max −z _min ) and repeatedly in the x-axis direction. However, z _min is the minimum value of z in the curves represented by (Expression 5) and (Expression 6), and z _max is the maximum value.

The thus obtained film, as shown in Table 1, the average luminance 3500 cd / ^{m 2,} a luminance unevenness 300 cd / ^{m 2,} and both high average luminance and low luminance irregularity showed excellent luminance characteristics. Further, the oblique luminance characteristics, luminance unevenness in measurement angle 30 ° or less but was 600 cd / ^{m 2} or less, uneven brightness 1300 cd / ^{m 2} is generated in the measuring angle 45 °, was B.

[Example 4]
A light diffusion film was obtained in the same manner as in Example 1 except that a = 50 and b = 100 μm.

As shown in Table 1, the film thus obtained had an average luminance of 3700 cd / m ² and luminance unevenness of 200 cd / m ² , and both high average luminance and low luminance unevenness were achieved, and exhibited excellent luminance characteristics. Further, the oblique luminance characteristic was B, where the luminance unevenness was 600 cd / m ² or less at a measurement angle of 30 ° or less, but 1200 cd / m ² of luminance unevenness occurred at a measurement angle of 45 °.

[Example 5]
A light diffusion film was obtained in the same manner as in Example 1 except that the following mold shape was used and a = 50 and b = 100 μm.

<Mold shape>
A shape having the curves represented by (Equation 8) and (Equation 9) inverted at the position of z = z _min +0.4 (z _max −z _min ) and repeatedly in the x-axis direction.

As shown in Table 1, the film thus obtained had an average luminance of 3800 cd / m ² and a luminance unevenness of 200 cd / m ² , and had both high average luminance and low luminance unevenness, and exhibited excellent luminance characteristics.

The oblique luminance characteristic was B with a luminance unevenness of 1000 cd / m ² at a measurement angle of 45 °, although the luminance unevenness was 600 cd / m ² or less at a measurement angle of 30 ° or less.

[Example 6]
A light diffusion film was obtained in the same manner as in Example 1 except that the following mold shape was used and a = 50 and b = 125 μm.

<Mold shape>
A shape in which the curves represented by (Expression 10) and (Expression 11) are reversed at the position of z = z _min +0.56 (z _max −z _min ) and repeatedly in the x-axis direction.

As shown in Table 1, the film thus obtained had an average luminance of 3900 cd / m ² and a luminance unevenness of 200 cd / m ² , and had both high average luminance and low luminance unevenness and exhibited excellent luminance characteristics. Further, the oblique luminance characteristic was B, where the luminance unevenness was 600 cd / m ² or less at a measurement angle of 30 ° or less, but 1000 cd / m ² of luminance unevenness occurred at a measurement angle of 45 °.

[Example 7]
A light diffusion film was obtained in the same manner as in Example 1 except that a = 50 and b = 137.5.

As shown in Table 1, the film thus obtained had an average luminance of 3800 cd / m ² and a luminance unevenness of 200 cd / m ² , and had both high average luminance and low luminance unevenness, and exhibited excellent luminance characteristics. Further, the oblique luminance characteristic was B, where the luminance unevenness was 600 cd / m ² or less at a measurement angle of 30 ° or less, but 1000 cd / m ² of luminance unevenness occurred at a measurement angle of 45 °.

[Example 8]
In Example 4, a light diffusion film was obtained by the same method except that a film having a thickness of 125 μm prepared by the following method was used instead of the transparent polyester film having a thickness of 100 μm. A method for producing a film having a thickness of 125 μm will be described below.

  Raw materials having the following composition were supplied to a composite film forming apparatus having a main extruder A and a sub extruder B. That is, in main extruder A, polyethylene terephthalate (PET) vacuum-dried at 180 ° C. for 4 hours was copolymerized with 10 mol% of isophthalic acid component, and cyclohexane dimethanol (glass transition point 163 ° C., refractive index 1.46) 10 mol. A chip containing 96% by weight of polyester resin (melting point 200 ° C., glass transition point 70 ° C., refractive index 1.6) and 4% by weight of polymethylpentene (melting point 230 ° C., refractive index 1.46) is supplied. did. Further, polyethylene terephthalate (melting point 265 ° C.) was supplied to the sub-extruder B.

  From these extruders A and B, each raw material is melt-extruded at 280 ° C., and the molten raw material of the main extruder A is co-extruded in three layers so that the molten raw material of the sub-extruder B becomes both surface layers. A composite film was produced. The thickness composition ratio of the composite film was B / A / B (10/80/10). This sheet was cast on a mirror-cooled drum having a surface temperature of 20 ° C. to form an unstretched sheet. This sheet was stretched 3 times in the longitudinal direction at 85 ° C. Thereafter, the film was continuously stretched 3 times in the width direction in an atmosphere of 100 ° C., and the stretch ratio between the longitudinal direction and the width direction was set to 1. Furthermore, heat treatment was performed for 20 seconds in an atmosphere of 235 ° C., which is higher than the melting point of the main constituent polyester resin, to obtain a polyester film having a thickness of 125 μm.

The thus obtained film, as shown in Table 1, the average luminance 3600 cd / ^{m 2,} a luminance unevenness 100 cd / ^{m 2,} and both high average luminance and low luminance irregularity showed excellent luminance characteristics. Further, the oblique luminance characteristics, luminance unevenness in measurement angle 30 ° or less but was 600 cd / ^{m 2} or less, uneven brightness 800 cd / ^{m 2} is generated in the measuring angle 45 °, was B.

[Example 9]
Under the light diffusion base material of Example 6, 188GM3 manufactured by Kimoto Co., Ltd. was placed as the base material containing the bead layer.

The thus obtained surface light source, as shown in Table 1, the average luminance 4300cd / ^{m 2,} a luminance unevenness 100 cd / ^{m 2,} and both high average luminance and low luminance irregularity showed excellent luminance characteristics. In addition, the oblique luminance characteristic was A with a luminance unevenness of 400 cd / m ² even at a measurement angle of 60 °.

[Comparative Example 1]
A light diffusion film was obtained in the same manner as in Example 1 except that the following mold shape was used.

<Mold shape>
A shape having the curve represented by (Equation 12) inverted at the position of z = z _min and having it repeatedly in the x-axis direction

As shown in Table 1, the film thus obtained had an average luminance of 3100 cd / m ² and luminance unevenness of 1500 cd / m ² , resulting in a screen with poor luminance and large luminance unevenness.

[Comparative Example 2]
A light diffusion film was obtained in the same manner as in Example 1 except that the following mold shape was used.

<Mold shape>
A shape having the curves represented by (Equation 13) and (Equation 14) reversed at the position of z = z _min +0.6 (z _max −z _min ) and repeatedly in the x-axis direction.

As shown in Table 1, the film thus obtained had an average luminance of 3300 cd / m ² and luminance unevenness of 1200 cd / m ² , resulting in a screen with poor luminance and large luminance unevenness.

[Comparative Example 3]
In Example 1, a light diffusion film was obtained by the same method except that a flat portion of 2 μm was provided between the repeated shapes.

As shown in Table 1, the film thus obtained had an average luminance of 3500 cd / m ² and luminance unevenness of 1800 cd / m ² , and the luminance unevenness was large.

[Comparative Example 4]
A light diffusing film was obtained in the same manner as in Example 1 except that a mold having irregularities with an isosceles triangle having an apex angle of 30 ° and a period of 100 μm was used. That is, a light diffusing film was obtained in which the tangential slope between adjacent bottoms did not increase in the x increasing direction.

The thus obtained film, as shown in Table 1, the average luminance 3500 cd / ^{m 2,} a luminance nonuniformity 5000 cd / ^{m 2,} very uneven brightness is large, it becomes poor appearance screen.

[Comparative Example 5]
A light diffusion film was obtained in the same manner as in Comparative Example 1 except that a = 50 and b = 100.

As shown in Table 1, the film thus obtained had an average luminance of 3000 cd / m ² and luminance unevenness of 400 cd / m ² , and had a low average luminance and a dark screen.

  The light diffusing film of the present invention and a surface light source using the same are suitable and useful for a surface light source used in a display device such as a personal computer, a television or a mobile phone, particularly a flat display device such as a liquid crystal display device.

Claims (7)

A base material having a concave and convex shape consisting of repetition of a top part and a bottom part on at least one side, wherein the base material is made of a material having a refractive index in a range of 1.45 to 1.65, and the top and bottom parts are repeated. Where x is the thickness direction of the base material and z is the thickness direction of the base material, the angle θ of the concavo-convex shape in the xz plane is in the range of 55 ° to 85 ° or in the range of 95 to 125 °, and adjacent bottom portions A light diffusing substrate in which the slope of the tangent line decreases in the direction of increasing x. The light-diffusion base material of Claim 1 in which a substantially flat part does not exist between adjacent top parts. The light diffusing substrate according to claim 1 or 2, wherein the skirt angle θ is in a range of 65 ° to 85 ° or in a range of 95 to 115 °. The light diffusing substrate according to any one of claims 1 to 3, wherein a maximum value in the z direction of the concavo-convex shape is larger than a shape composed of a part of a perfect circle having the same skirt angle θ as the concavo-convex shape. . The light-diffusion base material in any one of Claims 1-4 whose aspect-ratio of the said uneven | corrugated shape exists in the range of 1-3. The light-diffusion base material in any one of Claims 1-5 which contains a light-diffusion element inside a base material. The surface light source provided with the light-diffusion base material in any one of Claims 1-6, and the light emission means.

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