JP2014013393A - Diffusion sheet and back light unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion sheet excellent in anisotropic diffusion effect of light.SOLUTION: In a diffusion sheet, a plurality of projections having a long axis and a short axis are formed on one side of a sheet, the longitudinal directions of the projections are almost in the same direction, and when a light beam is made incident on the other side of the sheet at an incident angle of 0°, the emission intensity distribution 1 of a light beam emitted from the one side of the sheet satisfies the conditions (1) and (2) given below. (1) In the emission intensity distribution 1 within a plane perpendicular to the longitudinal direction of each projection, the emission angle at which 50% intensity is obtained with respect to an emission intensity at an emission angle of 0°is in the range of 15 to 25°.(2) In the emission intensity distribution 1 within a plane perpendicular to a sheet surface and parallel to the longitudinal direction of each projection, an emission angle at which 50% intensity is obtained with respect to an emission intensity at an emission angle of 0°is in the range of 0.5 to 5°.

Description

  The present invention relates to a diffusion sheet suitable for various display devices, particularly a backlight unit of a liquid crystal display device, and a backlight unit using the diffusion sheet.

  Liquid crystal display devices are used in various applications such as notebook computers and mobile phone devices, televisions, monitors, and car navigation systems. The liquid crystal display device incorporates a backlight unit serving as a light source, and is configured to display light by controlling light rays from the backlight unit through a liquid crystal cell. The characteristics required for the backlight unit are not only as a light source for emitting light, but also to make the entire screen shine brightly and uniformly.

  The configuration of the backlight unit can be roughly divided into two.

  One is a method called a sidelight type backlight. This is a method mainly used for, for example, a notebook personal computer that is required to be thin and small. As a basic configuration, a light guide plate is used. In the case of a sidelight type backlight, a fluorescent tube is installed on the side surface of the light guide plate, light is incident on the light guide plate from the side surface, and the light is propagated throughout the surface while totally reflecting inside the light guide plate. A part of the light is removed from the total reflection condition by diffusing dots or the like applied to the back surface, and light is collected from the front surface of the light guide plate, thereby functioning as a backlight, that is, a surface light source. In the case of a sidelight type backlight, in addition to these configurations, a reflection film that functions to reflect and reuse light leaking from the back surface of the light guide plate, and a diffusion sheet that equalizes the light emitted from the front surface of the light guide plate Many types of optical films are used, such as a prism sheet for improving the front luminance.

Another method is a method called a direct type backlight. This is a system that is preferably used for television applications that require large size and high brightness. The basic structure is characterized by a structure in which fluorescent tubes are arranged directly behind the screen without using a light guide plate. It is possible to deal with a large screen by arranging a plurality of linear or partially linear fluorescent tubes in the back of the screen in parallel, and sufficient brightness can be secured. However, uneven brightness (brightness unevenness) occurs in the screen due to the fluorescent tube installed at the back of the screen, which is also a feature. That is, the portion directly above the fluorescent tubes arranged in a row is bright and the space between adjacent fluorescent tubes is dark (tube unevenness). For this reason, in the direct type backlight, in order to eliminate this tube unevenness, a light diffusing plate (milky white plate) having extremely strong light diffusibility is installed on the upper side of the fluorescent tube to make the screen uniform (patent) Reference 1). The light diffusing plate is a light diffusing plate made of an acrylic resin or a polycarbonate resin in which fine particles are dispersed. This light diffusing plate eliminates tube unevenness and makes the screen uniform. However, since the light is diffused strongly, the total light transmittance is low and the light utilization efficiency is deteriorated. Moreover, since it diffuses too strongly, light is scattered in an unnecessary direction. As a result, the required front brightness is insufficient. Therefore, a diffusion sheet that exhibits a light collecting effect in the front direction while light isotropically diffused is installed on the light diffusion plate (Patent Document 2). This diffusion sheet is a sheet called a bead sheet in which a diffusion layer containing fine particles such as organic cross-linked particles is formed on a base material sheet. Unlike a light diffusion plate, this diffusion film is an optical film that exhibits a certain degree of directivity in the front direction. It is. In addition to these, a reflective film that reflects light emitted backward from the fluorescent tube, and a prism sheet and the like are incorporated to further improve the light collecting property as necessary.
JP 2004-29091 A JP 2001-324607 A

  In direct-type backlights, it is necessary to eliminate luminance unevenness derived from the fluorescent tube at the back of the screen and to achieve both uniform screen and high luminance. Normally, as described above, a light diffusing plate having extremely strong light diffusibility is installed as a direct type backlight, and the unevenness of the tube is eliminated by this plate-like member, and the uniformity of the screen is increased. However, in the case of a light diffusing plate that emphasizes uniformity, the total light transmittance is low and the light utilization efficiency is poor, so that high brightness cannot be achieved. In the case of a light diffusing plate that places importance on luminance, the total light transmittance is high and the light diffusibility is lowered, so that the uniformity cannot be increased. In other words, a contradictory phenomenon occurs. Of course, it is obvious that the degree of uniformity is further inferior only with the bead sheet, the prism sheet, and the brightness enhancement sheet that are conventionally used.

  Accordingly, in view of the background of such conventional technology, the present invention provides a diffusion sheet that is excellent in the anisotropic diffusion effect of light. That is, according to the present invention, an efficient diffusion effect is exhibited by such a diffusion sheet, whereby tube unevenness derived from the fluorescent tube can be efficiently eliminated, and screen uniformity and high luminance characteristics can be expressed.

The present invention employs the following means in order to solve such problems. That is, in the diffusion sheet of the present invention, a plurality of convex shapes having a major axis and a minor axis are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are substantially aligned in one direction. The diffusion sheet satisfies the following conditions (1) and (2) with the emission intensity distribution 1 of the light emitted from one surface of the sheet when the light is incident on the surface at an incident angle of 0 °.
(1) With respect to the emission intensity distribution 1 in the plane perpendicular to the longitudinal direction of the convex shape, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 15 to 25 °.
(2) With respect to the emission intensity distribution 1 in a plane perpendicular to the sheet surface and parallel to the longitudinal direction of the convex shape, the emission angle at which the intensity is 50% with respect to the emission intensity at the emission angle of 0 ° is 0.5 to 5 It is in the range of °.

  In the diffusion sheet of the present invention, a plurality of striped convex shapes are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are aligned substantially in one direction, and the longitudinal direction of the convex shape is Each shape in the vertical cross section is a diffusion sheet in which a semicircular shape is removed from at least a region having a skirt angle of 80 ° or more and 90 ° or less, and the other surface of the sheet is roughened.

  Furthermore, in the diffusion sheet of the present invention, a plurality of striped convex shapes are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are aligned substantially in one direction, and the longitudinal direction of the convex shape is Each shape in the vertical cross section is a diffusion sheet having a shape obtained by deleting at least a region having a hem angle of 80 ° to 90 ° from a semi-elliptical shape whose major axis direction is perpendicular to the sheet surface.

  Further, the backlight unit using the diffusion sheet of the present invention has a plurality of linear light sources in a substantially parallel arrangement, a light source having a plurality of linear portions in a substantially parallel arrangement, and a light and darkness in a linear shape in a substantially parallel arrangement. On the upper side of the light source composed of at least one selected from the group consisting of the observed light sources, the diffusion sheet of the present invention is arranged so that the direction parallel to the linear portion of the light source is parallel to the convex longitudinal direction. It is an installed backlight unit.

  ADVANTAGE OF THE INVENTION According to this invention, the diffusion sheet which exhibits the anisotropic diffusion effect of light efficiently can be provided, and when this is integrated in the backlight unit of a liquid crystal display device, especially a direct type backlight, high screen uniformity Compatibility and high luminance characteristics can be achieved.

It is a figure which shows typically the surface shape of the diffusion sheet of this invention. It is a figure which shows typically the preferable base material structure of the diffusion sheet of this invention. It is a figure which shows typically the surface shape of the diffusion sheet of this invention in which the striped convex shape was formed. It is a figure which shows the cross section of stripe-shaped convex shape. It is a figure which shows the metal mold | die for forming striped convex shape.

1 Diffusion sheet of the present invention
2 Line-shaped convex shape on one surface (A surface) of diffusion sheet 3 Base material 4 Rough surface layer on the other surface (B surface) of diffusion sheet 5 Bottom angle of stripe-shaped convex cross section 6 Striped shape Mold for forming convex shape 7 Unit cross section of mold 8 Bottom angle of unit cross section

  As a result of intensive studies on the above-mentioned problem, that is, a diffusion sheet excellent in the anisotropic diffusion effect of light, the present invention has a plurality of projections having a major axis and a minor axis on one side (hereinafter referred to as A plane) of the sheet. The inventors have found that when the shape is formed, the longitudinal directions of the plurality of convex shapes are aligned in approximately one direction, and the light diffusion behavior of the diffusion sheet is controlled, this problem can be solved all at once.

In the diffusion sheet of the present invention, a plurality of convex shapes having a major axis and a minor axis are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are substantially aligned in one direction, and the other surface of the sheet The emission intensity distribution 1 of the light beam emitted from one surface of the sheet when the light beam is incident on the sheet at an incident angle of 0 ° satisfies the following conditions (1) and (2).
(1) With respect to the emission intensity distribution 1 in the plane perpendicular to the longitudinal direction of the convex shape, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 15 to 25 °.
(2) With respect to the emission intensity distribution 1 in a plane perpendicular to the sheet surface and parallel to the longitudinal direction of the convex shape, the emission angle at which the intensity is 50% with respect to the emission intensity at the emission angle of 0 ° is 0.5 to 5 It is in the range of °.

  The diffusion sheet of the present invention has a configuration in which a plurality of convex shapes (hereinafter, referred to as a line-shaped uneven pattern) having a major axis and a minor axis, the longitudinal direction of which is substantially aligned in one direction, are formed on the A surface. Here, “aligned substantially in one direction” means that the angle formed by the longitudinal directions of the individual convex shapes is ± 15 ° or less with respect to the direction in which the longitudinal directions of the individual convex shapes are averaged in the film plane. It means a state. The anisotropic diffusivity is expressed by the line-shaped uneven pattern on the A surface. In direct type backlights in which linear light sources are arranged in parallel in the plane, in order to eliminate unevenness in luminance according to the shape of the light source and efficiently increase the screen uniformity, a member installed on the upper side of the backlight Can be achieved by diffusing strongly in a direction perpendicular to the longitudinal direction of the light source, instead of diffusing strongly isotropically. This means that a diffusion sheet exhibiting strong light diffusivity in one direction, that is, anisotropic diffusion, is suitable. In the present invention, this anisotropic diffusion is realized by a line-shaped uneven pattern on the surface. .

  Therefore, when the diffusion sheet of the present invention is incorporated in a backlight unit having a configuration described later, a linear light source image is diffused by the effect of anisotropic diffusion, and uneven brightness is eliminated, and light utilization efficiency is improved by a rough surface. The effect of improving brightness is obtained, and a backlight unit with high uniformity and high brightness can be obtained.

  The pattern formed on the A surface of the diffusion sheet of the present invention has a plurality of convex shapes (line-shaped concave / convex patterns) having a major axis and a minor axis, and the direction of the major axis, that is, the longitudinal direction is substantially aligned in one direction. It is characterized by that. In FIG. 1, the surface shape of the A surface of the diffusion sheet of this invention is illustrated. 1A and 3A show the sheet in-plane pattern, and FIGS. 1B and 3B show the sheet cross-sectional pattern in a cross section perpendicular to the longitudinal direction of the convex shape.

  The sheet in-plane pattern of the A surface of the diffusion sheet of the present invention is a shape (line shape) in which each convex shape extends in one direction, as illustrated in FIGS. 1 (a) and 3 (a). It is characterized by that. Furthermore, it is the surface spread | laid so that the longitudinal direction of each line-shaped convex shape might align in substantially one direction. The diffusion sheet of the present invention is formed by aligning the longitudinal direction of the line-shaped convex shape in substantially one direction, so that the anisotropic diffusion property is strong in the direction perpendicular to the longitudinal direction and weakly diffuses in the parallel direction. Will be expressed. In addition, it is preferable that this line-shaped convex shape is laid without gaps on the sheet surface, that is, without a flat portion, thereby reducing the component that exits in the same direction without diffusing among the rays incident on the diffusion sheet. This is preferable because the diffusibility is improved.

  The sheet cross-sectional pattern (surface observed in the cross section perpendicular to the longitudinal direction of the convex shape) of the A surface of the diffusion sheet of the present invention is a curved pattern in which curved lines such as arcs are connected, and is smooth like a sinusoidal curve, for example. Preferable examples include patterns connected to each other, patterns such as lenticular lenses connected to semi-circular and semi-elliptical (or its inverted shape) curves, and combinations thereof.

  Regarding the regularity of the sheet in-plane pattern and the sheet cross-sectional pattern of the A surface of the diffusion sheet of the present invention, either regular or irregular patterns are preferably used. However, in the following points, the same shape and the same size are used. A random pattern in which shapes having irregularly different shapes and sizes are arranged may be preferable to a regular pattern in which the shapes are repeated. If the pattern is random, it prevents light interference fringes and moire patterns from optical sheets other than the sheet and liquid crystal cell patterns and moire patterns when mounted on the backlight unit, making defects less noticeable and improving uniformity. There is. With such a random pattern, as shown in FIG. 1 (a), the lengths of the convex major axis and the minor axis extending in one direction are irregular in the sheet in-plane pattern. Is good. Further, as illustrated in FIG. 1B, even in the sheet cross-sectional pattern, it is preferable that the shapes are not the same, but irregular shapes are linked and the arrangement pitch is random.

  In the in-sheet pattern of the A surface of the diffusion sheet of the present invention, the longer the length in the major axis direction of each convex shape forming the line pattern, the better the longer the length in the minor axis direction. When the length in the major axis direction is long, anisotropic diffusibility can be improved. The ratio of the length in the major axis direction to the length in the minor axis direction (length in the major axis direction / length in the minor axis direction) of each convex shape is preferably 10 or more, and the shape with the most improved anisotropic diffusibility is As shown in FIG. 3A, the stripe has a linear stripe shape with a very long major axis.

  An example of a preferable size of the sheet cross-sectional pattern on the A surface of the diffusion sheet of the present invention is as follows. In the case of an irregular pattern as shown in FIGS. The length in the direction) is in the range of 2-15 μm and the height is in the range of 0.5-10 μm. Here, the pitch refers to the length between adjacent top portions of the pattern, and the height refers to the length in the thickness direction from the straight line connecting the adjacent concave portions of the pattern to the top portion. By forming an irregular curve shape in this range, it becomes possible to satisfy the range of the emission intensity distribution described later. Moreover, this range shows an example, and even outside this range, any material that satisfies the later-described emission intensity distribution can be preferably used.

  In the case of a regular pattern as shown in FIGS. 3 (a) and 3 (b), a shape obtained by deleting at least the hem angle of 80 ° to 90 ° from the semicircular shape, or the long axis direction is the sheet. This is a shape obtained by deleting at least the area of the hem angle of 80 ° or more and 90 ° or less from the semi-elliptical shape perpendicular to the surface. This will be described with reference to FIG. FIG. 4A shows a semicircular shape or semi-elliptical shape that is the basis of the shape. The shape obtained by deleting the skirt angle (5 in FIG. 4B) from 80 ° to 90 ° (the hatched portion in FIG. 4B) from the original shape is the regular pattern of the present invention. It is the shape used for the diffusion sheet which has.

  The area where the hem angle is large is an area that plays a role of directing light incident on the diffusion sheet at a high incident angle (light incident on the sheet surface from a more horizontal direction) to the front. This is an important area for improvement. However, while the front luminance is improved, the component emitted to the high emission angle region (region close to the horizontal direction with respect to the sheet surface) increases. Thereby, although the front is bright, an area that appears bright in the horizontal direction with respect to the sheet surface is generated, and luminance unevenness of the backlight unit appears. This tendency is particularly strong in the region where the hem angle is 80 ° or more and 90 ° or less. Therefore, by removing this region, a backlight unit with high uniformity can be obtained while maintaining high front luminance. Preferably, the above characteristics can be obtained in a well-balanced manner by setting the hem angle to 70 ° or more and less than 80 °.

  As the original semi-elliptical shape (FIG. 4A), when the lengths a and b are set as shown in FIG. 4A, the aspect ratio b / a is larger than 1 and 1.5 or less. It is preferable to use this shape. Here, the length a indicates half the distance between the hem ends (radius in the sheet surface direction), and the length b indicates the distance from the straight line connecting the hem ends to the top of the shape (perpendicular to the sheet surface). Direction radius). When the original shape is a semicircular shape, the aspect ratio is 1. Here, when the aspect ratio b / a is less than 1, the front luminance improvement effect is small, and when the aspect ratio b / a is larger than 1.5, the front luminance improvement effect is large, but the uniformity is high. The degree may decrease.

  In the diffusion sheet of the present invention, it is preferable that a surface (hereinafter referred to as B surface) opposite to the A surface of the sheet is roughened. In the diffusion sheet of the present invention, as described above, a line-shaped uneven pattern is formed on the A surface of the sheet, and the anisotropic diffusion property is expressed by this pattern. In order to increase the uniformity of the backlight, it is preferable to install the A side so that it is on the light emitting side. A method in which a line-shaped uneven pattern is formed on the exit surface is a preferable installation method because the anisotropic diffusion effect is high. Therefore, the B surface is preferably a light incident surface.

  Therefore, in the diffusion sheet of the present invention, by roughing the B surface of the sheet, when mounted on the backlight unit, the light reflection of the B surface which is the light incident surface is suppressed, in addition to the light rays directly incident from the light source, It is possible to improve the utilization efficiency of light rays that are reflected and reused inside the backlight, and to increase the brightness of the backlight. Moreover, when using it overlapping with another member, contact | adherence with a lower member can be prevented. Furthermore, since the slipperiness is improved by the rough surface treatment, handling in various processes such as cutting of the sheet according to the backlight shape and incorporation into the backlight as well as the improvement of the handling property at the time of manufacturing the diffusion sheet are performed. Can be facilitated, contributing to speeding up of each process and a reduction in defect rate.

The rough surface applied to the B-side of the diffusion sheet of the present invention is prepared by coating a coating material in which particles are dispersed in a binder resin, prepared by transferring the shape of a mold, sandblasting method, etc. A preferable example is a material whose surface is mechanically cut and processed.
Any of these methods is preferably used, but among these, the method of coating a coating material in which particles are dispersed in a binder resin selects the type / combination of particles, particle size, addition amount, resin type, resin film thickness, etc. This is a preferable method because the state and degree of the rough surface can be easily changed.

  Preferred particles used in this method include, for example, inorganic fine particles such as silica, or organic (crosslinked) fine particles such as acrylic resin, organic silicone resin, and polystyrene resin, and the particle diameter is 80 nm to 50 μm. It is preferable to use those in the range. One type of particle may be used alone, or two or more types may be used in combination. Examples of the binder resin include thermoplastic resins such as acrylic resins, polyester resins, polyolefin resins, and polyurethane resins, thermosetting resins, and photocurable resins.

  As a preferable combination of the particle and the binder resin, it is preferable that both are made of the same material or have substantially the same refractive index so that unnecessary light scattering does not occur at the interface between the particle and the binder resin. Furthermore, it is preferable that the film thickness of the binder resin after coating is thinner than the particle diameter in order to easily impart slipperiness. By making it thinner than the particle diameter, the particles protrude from the resin layer after coating and function as protrusions, so that slipperiness can be easily imparted.

  Further, as an example of the roughness of the B surface of the diffusion sheet of the present invention, for example, using glossiness, when measuring the 60 ° glossiness, for example, the length of the line-shaped uneven pattern formed on the A surface A rough surface having a glossiness within the range of 70 to 90 in the direction perpendicular to the direction and 90 to 120 in the parallel direction is suitable. Here, the 60 ° glossiness is a value defined by reflection of light incident on the sheet surface, and is a value measured based on the method defined in JIS Z8741.

  As the layer structure of the diffusion sheet of the present invention, (a) a single layer structure in which a line-shaped uneven pattern is formed on one surface of a substrate and a rough surface treatment is applied to the other surface of the substrate (FIG. 2 ( a)) (b) A two-layer structure in which a line-shaped uneven pattern is formed on one surface of a substrate, and a layer subjected to a roughening treatment is laminated on the other surface of the substrate (FIG. 2B) (C) A two-layer structure in which a layer having a line-shaped uneven pattern formed on one surface of a substrate is laminated, and a roughening treatment is performed on the other surface of the substrate (FIG. 2 (c)). d) A three-layer structure in which a layer having a line-shaped uneven pattern formed on one surface of a substrate is laminated, and a layer subjected to roughening treatment is laminated on the other surface of the substrate (FIG. 2D Any of)) is preferably used.

  The base material constituting the diffusion sheet of the present invention is either a substantially transparent base material, a single layer body containing particles inside, or a base material comprising a laminate having at least a layer containing particles inside Are also preferably used. The substantially transparent substrate here means that when used in a liquid crystal display device, in the visible light region of 380 to 800 nm, an absorption peak at a specific wavelength is not observed, and light is not substantially scattered. State (range of about 20% or less in haze value).

  When a transparent base material is used as the base material of the diffusion sheet of the present invention, the light use efficiency is high because it does not contain a component that backscatters the light rays inside, and as a result, it contributes to the improvement of luminance. Therefore, it is effective to use a transparent substrate when priority is given to the luminance of the backlight. In addition, when a diffusible base material (for example, a diffusion plate) is inserted between the diffusion sheet of the present invention and the light source as the backlight structure, the uniformity can be ensured by the combination with the diffusion plate. The substrate of the diffusion sheet of the present invention may not have diffusibility, and it is preferable to give priority to luminance and use a transparent substrate as a diffusion sheet.

  As the material of the transparent substrate, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, cyclohexanedimethanol copolymer polyester resin, isophthalic acid copolymer polyester resin, spiroglycol copolymer polyester resin, Polyester resins such as fluorene copolymerized polyester resins, polyolefin resins such as polyethylene, polypropylene, polymethylpentene, and alicyclic olefin copolymer resins, acrylic resins such as polymethyl methacrylate, polycarbonate, polystyrene, polyamide, polyether, polyester Thermoplastics such as amides, polyetheresters, polyvinyl chloride, and copolymers containing these components, or mixtures of these resins Butter, and the like. Among these, in terms of mechanical strength, heat resistance, dimensional stability, biaxially stretched polyethylene terephthalate, polyethylene-2,6-naphthalate, or a copolymer with other components based on these, A polyester resin such as a mixture is more preferably used.

  In addition, when using a diffusible substrate comprising a monolayer containing particles inside or a laminate having at least a layer containing particles inside as the substrate, the uniformity of the backlight is further increased. For example, it is possible to secure sufficient uniformity without inserting a diffusible base material such as a diffusion plate between the diffusion sheet of the present invention and the light source as a configuration of the backlight. Therefore, priority is given to the uniformity. It is effective in the case.

  Examples of particles dispersed in the diffusible substrate include inorganic fine particles such as barium sulfate, titanium oxide, magnesium sulfate, magnesium carbonate, calcium carbonate, and silica, or acrylic resin, organic silicone resin, polystyrene resin, urea resin, and formaldehyde condensation. Products, organic (crosslinked) fine particles such as fluororesins, or polyolefin resins represented by polymethylpentene, polypropylene, polyethylene, alicyclic olefins dispersed in islands, polyethylene terephthalate, polyethylene-2,6-naphthalate, etc. Examples thereof include thermoplastic resins (including various copolymers), hollow particles, bubbles, and the like made of polyester resins typified by, acrylic resins typified by polymethyl methacrylate, and the like. As the particles, one kind may be used alone, or two or more kinds may be used in combination. These are examples that are preferable as the diffusion elements used in the diffusion sheet of the present invention, and are not limited to these as long as the components have a refractive index different from that of the matrix resin at least in the visible light region (380 to 780 nm). It can be preferably used.

  The particle size of the diffusible substrate particles is preferably 0.5 to 50 μm, more preferably 0.5 to 30 μm, and most preferably 0.5 to 20 μm. When the average primary particle size is 0.5 μm or more, a light diffusing action as a diffusing element is sufficiently obtained in the visible light region of 380 to 780 nm. Moreover, it is preferable for the average primary particle diameter to be 50 μm or less because the film thickness of the base material for obtaining an effective light diffusion effect does not become too thick and can be made thin.

  The shape of the particles is not particularly limited, and any of spherical (including true spherical), spheroid, rod, needle, flat, amorphous, etc. can be preferably used. In the present invention, the particle diameter in a shape other than the true sphere may be such that the length of the narrowest portion satisfies the above range of 0.5 to 50 μm. Here, in the case where the shape of the particles is a shape extending in a uniaxial direction such as a spheroid, a rod shape, or a needle shape, it is also a preferable aspect that these major axis directions are arranged in a certain direction within the sheet surface. With such an arrangement, light is strongly diffused in a direction perpendicular to the major axis direction, and the base material alone exhibits anisotropic diffusion. Therefore, by matching the direction of strong diffusion on the base material with the direction of strong diffusion on the surface with diffusion anisotropy, the light diffusion performance as a diffusion sheet is further improved, and the uniformity and luminance characteristics are improved. Is also preferable.

  Further, since the appropriate amount of particles added varies depending on the refractive index, particle size, shape, etc. of the particles, it is appropriately set according to the required performance, but is about 0.01 to 50% by weight with respect to the diffusible substrate. It is preferably added in a range, more preferably 0.01 to 30% by weight, and most preferably 0.1 to 30% by weight.

  Examples of the matrix resin used for the diffusible substrate include polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, cyclohexanedimethanol copolymer polyester resin, isophthalic acid copolymer polyester resin, and spiroglycol. Polyester resins such as copolyester resins and fluorene copolyester resins, polyolefin resins such as polyethylene, polypropylene, polymethylpentene, and alicyclic olefin copolymer resins, acrylic resins such as polymethyl methacrylate, polycarbonate, polystyrene, polyamide , Polyethers, polyester amides, polyether esters, polyvinyl chloride, and copolymers comprising these, or these They include thermoplastic resins such as a mixture of fat, preferably used without being particularly limited.

  In addition to the thermoplastic resin, a photocurable resin and a thermosetting resin can also be preferably used as the matrix resin for the transparent substrate and the diffusible substrate.

  As an example of a photocurable resin, the compound which has at least 1 radical polymerizability in a molecule | numerator, or a compound which has cationic polymerizability is mentioned. The compound having radical polymerizability is a compound that is polymerized or cross-linked by irradiation with active energy rays in the presence of a polymerization initiator that generates radicals by active energy rays. For example, ethylenically unsaturated in the structural unit. It contains at least one bond, contains a polyfunctional vinyl monomer in addition to a monofunctional vinyl monomer, and may be an oligomer, polymer or mixture thereof. Examples of the compound having at least one cationic polymerizability in the molecule include a compound having an oxirane ring, a compound having an oxetane ring, a compound selected from one or more compounds selected from vinyl ether compounds, and the like. .

  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. Mixtures can be used.

A polymerization initiator is used for the photocurable resin and the thermosetting resin. In the case of a photocurable resin, a photopolymerization initiator that generates radical species or cationic species by irradiation with active energy rays is matched to the photosensitive wavelength and polymerization type, and in the case of a thermal polymerization initiator, it is adjusted to the process temperature. It is preferable to use a thermal polymerization initiator.
When the diffusion sheet of the present invention has a single film configuration in which a line-shaped uneven pattern / base material / rough surface is integrated, a line-shaped uneven pattern is formed on one surface of the base material, The surface is roughened.

  In the case of a two-layer or three-layer structure in which a layer having a line-shaped uneven pattern is laminated on a substrate, the material constituting the layer forming the line-shaped uneven pattern is a matrix of the diffusible substrate. It is preferable to be composed of a thermoplastic resin similar to the resin, or a resin selected from the photocurable resin and the thermosetting resin. In order to control the diffusibility of the line-shaped uneven pattern, it is also a preferable aspect to include particles inside.

In the case of a two-layer or three-layer structure in which a roughened layer is laminated on a substrate, it is preferable to use the materials described above as the roughened layer.
It is also a preferred embodiment that various additives are added to each layer of the diffusion sheet of the present invention. As the additive, for example, an antistatic agent, a light-resistant agent, a dispersant, a compatibilizing agent, a pigment, a dye, and the like are preferably used, but other additives may be used as long as the effect as a diffusion sheet is not hindered. Preferably used.

  The total thickness of the diffusion sheet of the present invention is preferably 25 to 500 μm. It is preferable for the film thickness to be 25 μm or more since the handling properties of the sheet are improved. A sheet having a film thickness exceeding 500 μm is preferably 500 μm or less from the viewpoint of thinning the entire backlight unit, although a sheet preferable in terms of diffusibility can be obtained.

By taking the configuration as described above, the diffusion sheet of the present invention has an emission intensity distribution 1 of the light beam emitted from the A surface of the sheet when the light beam is incident on the B surface of the sheet at an incident angle of 0 °. Conditions (1) and (2) are satisfied.
(1) With respect to the emission intensity distribution 1 in the plane perpendicular to the longitudinal direction of the convex shape of the A surface, the emission angle at which the intensity is 50% with respect to the emission intensity at the emission angle of 0 ° is in the range of 15 to 25 °. There is.
(2) With respect to the emission intensity distribution 1 in a plane perpendicular to the sheet surface and parallel to the longitudinal direction of the convex shape of the A surface, the emission angle at which the intensity is 50% with respect to the emission intensity of 0 ° is 0. It should be in the range of 5-5 °.

  In the present invention, the incident angle is an acute angle formed by the normal direction of the sheet surface and the optical axis of the incident light beam, and the output angle is formed by the normal direction of the sheet surface and the optical axis of the output light beam. It is an acute angle.

  Hereinafter, the light beam behavior of the diffusion sheet of the present invention is defined by the result of measurement using a goniophotometer GP-200 manufactured by Murakami Color Research Laboratory. The light source of the device uses a halogen lamp 12V50W, puts a light quantity adjustment filter with an average transmittance of 1%, and has a light beam aperture setting 3 (φ about 11 mm) and a light receiving aperture setting 6 (φ about 13 mm), with a reflection and transmission tilt. Place a diffusion sheet on the standard sample stage and measure.

  In the diffusion sheet of the present invention, when a light beam is incident on the B surface of the sheet at an incident angle of 0 °, the emission intensity distribution 1 of the light beam emitted from the A surface of the sheet is perpendicular to the longitudinal direction of the convex shape of the A surface. In such a plane, when the emission angle that is 50% of the emission intensity at the emission angle of 0 ° satisfies the range of 15 to 25 °, the characteristics in which the luminance and the uniformity are balanced can be exhibited. it can. More preferably, the emission angle satisfies a range of 18 to 25 °, and further preferably the emission angle satisfies 19.5 to 24 °. As will be described later, when the diffusion sheet of the present invention is mounted on a backlight unit, a direction with strong diffusivity (by setting the direction parallel to the linear portion of the light source and the longitudinal direction of the line-shaped uneven pattern ( The image of the light source is diffused by the action of the direction perpendicular to the longitudinal direction to improve the uniformity, so if the diffusibility in this direction is insufficient, the light source image can be seen through, resulting in poor uniformity. . In other words, if the emission angle at which the intensity is 50% is less than 15 °, the diffusibility is insufficient and luminance unevenness appears remarkably, which is not preferable. Further, when the angle at which the intensity of 50% exceeds 25 °, the diffusibility is sufficient and preferable in terms of uniformity. However, since the light in the front direction decreases due to excessive diffusion of light, the luminance and uniformity are reduced. It is hard to say that this is a preferable range in terms of balance of degrees.

  Further, in the diffusion sheet of the present invention, when a light beam is incident on the B surface of the sheet at an incident angle of 0 °, the emission intensity distribution 1 of the light beam emitted from the A surface of the sheet is perpendicular to the sheet surface and the A surface. In a plane parallel to the longitudinal direction of the line-shaped concavo-convex pattern, an emission angle that is 50% of the emission intensity at an emission angle of 0 ° satisfies the range of 0.5 to 5 °, thereby moving to an unnecessary direction. Therefore, it is possible to achieve a high-brightness backlight. More preferably, the emission angle satisfies 0.5 to 3 °, and further preferably the emission angle satisfies 0.5 to 1.5 °. When the diffusion sheet of the present invention is mounted on the backlight unit, this direction corresponds to a direction parallel to the straight line portion of the light source, so that strong diffusibility is not necessary. That is, by satisfying the above range and giving a fine diffusion effect while suppressing diffusion in an unnecessary direction as much as possible, it is possible to contribute to improvement in luminance while preventing unevenness such as interference fringes. When the emission angle is less than 0.5 °, the regularity of the line-shaped uneven pattern on the A surface is high, and unevenness such as interference fringes appears. On the other hand, when the emission angle exceeds 5 °, the anisotropic diffusibility of the sheet due to the A-surface line uneven pattern is insufficient and an efficient diffusion effect cannot be obtained.

  Thus, when the diffusion sheet of the present invention exhibits anisotropic diffusion satisfying the emission intensity distribution, a backlight with high brightness and high uniformity can be obtained when the diffusion sheet is mounted on a backlight unit. .

In the diffusion sheet of the present invention, it is preferable that the diffusivity defined by the following formula satisfies the range of 25 to 40 for the emission intensity distribution 1 in the plane perpendicular to the longitudinal direction of the convex shape of the A surface. In the following equation, I (θ) represents the emission intensity of a light beam emitted at an angle θ °.
Diffusivity = 100 × 0.5 × (I (70) + I (20)) / I (5)
Here, the degree of diffusion is an index indicating the degree of light diffusibility of the diffusion sheet, and a larger value indicates that the light beam is diffused more widely.

  The diffusion sheet of the present invention preferably has a diffusivity of 25 to 40, more preferably 25 to 35, in the direction perpendicular to the longitudinal direction of the convex shape of the A surface, that is, the direction in which it is strongly diffused. When the diffusivity is 25 or more, the spread of light diffused by the diffusion sheet is sufficient, and the uniformity of the backlight can be increased, which is preferable. A diffusivity of 40 or less is preferable because the diffusibility is too strong and does not diffuse too much, and when mounted on a backlight, the uniformity is increased and the decrease in front luminance is suppressed. In other words, it is preferable to set the diffusivity in the range of 25 to 40, since the luminance can be increased while maintaining high uniformity when mounted on the backlight.

In addition, the diffusion sheet of the present invention is such that when light rays are incident on the B surface of the sheet at an incident angle α (10 ° ≦ α ≦ 80 °) in a plane perpendicular to the longitudinal direction of the convex shape of the A surface, It is preferable that the emission intensity distribution 2 emitted from the A surface satisfies the following condition (3).
(3) With respect to the emission intensity distribution 2 in the plane perpendicular to the longitudinal direction of the convex shape, the emission angle β at which the emission intensity is maximum for each incident angle α is α / 3 <β <2α / 3. To meet.

  Here, the output angle β means that incident light (incident angle α) is angle-converted and output with the strongest intensity at the output angle β. That is, as the above formula shows, it is preferable that the diffusion sheet of the present invention has a characteristic that the light is emitted as an emission angle β that is more front-facing with respect to the incident angle α.

  In this way, by converting the angle to the emission angle β that faces more front, light rays that are incident at a high angle also face more front, which contributes to improvement in luminance, which is a preferable characteristic. When the emission angle β is less than 2α / 3, a brightness improvement effect appears due to the angle conversion action. Further, when the angle β is larger than α / 3, the emitted light is not collected too much in the normal direction of the sheet surface, and the viewing angle is not narrowed.

  In addition, the diffusion sheet of the present invention preferably has a total light transmittance of 70% or more measured by entering light from the B surface of the sheet. The total light transmittance is an index related to the light use efficiency of the diffusion sheet. When the total light transmittance is extremely low, the use efficiency is inferior and it is difficult to increase the luminance. In the structure of the diffusion sheet of the present invention, it is preferable that the total light transmittance is 70% or more because high luminance can be expressed when mounted on the backlight unit.

  Next, although the method to manufacture the diffusion sheet of this invention is demonstrated, it is not limited to these methods, Other methods are also preferably used. Below, the line-shaped uneven | corrugated pattern of the A surface of a sheet | seat and the rough surface processing method of the B surface of a sheet | seat are demonstrated.

  As a method of forming a line-shaped uneven pattern on the A surface of the sheet, (a) a mold transfer method using a mold, (b) a method of directly processing the surface, (c) particles having anisotropy in shape And (d) a method of bonding woven fabrics, and the like.

  (A) The mold transfer method will be described in further detail. (A1) A mold or / and a sheet whose surface exhibits thermoplasticity is heated and pressed to press and form, (a2) Light or thermosetting on the surface. A method in which a mold is pressed against a sheet laminated with a functional resin and the resin is cured by irradiation with active energy rays or heating, and (a3) a resin previously filled in the recesses of the mold is used as a base material For example, a method of transferring to the top.

  Further, (b) as a direct machining method, (b1) a method of mechanically cutting into a desired shape using a cutting jig, (b2) a method of cutting by a sandblast method, (b3) a method of cutting by a laser, (b4) Examples thereof include a method in which a sheet having a photocurable resin laminated on the surface thereof is processed into a desired shape using a technique such as lithography or a light interference exposure method.

  In addition, (c) as a method of coating a coating material containing particles having anisotropy in shape, particles having an anisotropic shape such as a rod shape, needle shape, fiber shape, spheroid, or a coating containing these particles may be used. Examples thereof include a method of forming a sheet in which particles are oriented in a certain direction by coating the agent while applying shearing force.

  In addition, as a method of bonding a fabric having anisotropy to the shape (d), a method of bonding a fabric having anisotropy on a base material by controlling the diameter, density, shape, and the like of warp and weft. Etc.

  Among these, from the viewpoint of productivity, (a) a mold transfer method is a more preferable manufacturing method, but these processes can be combined, and a desired diffusion sheet is obtained by selecting an appropriate process. be able to.

  Further, as the roughening treatment method for the B surface of the sheet, the above-described (a) mold transfer method using a mold, (b) a method of directly processing the surface, and (e) forming a particle-dispersed resin layer And the like. (E) is the same process as (c), but here it is not necessary to positively use particles having anisotropy in shape, for example, isotropic spheres (or part of the spheres). This can be achieved by coating the contained coating. Here, the coating material contains at least one resin selected from a thermoplastic resin, a photocurable resin, and a thermosetting resin as a binder resin, and is diluted with a solvent as necessary. An additive can be added to form a coating film having desired physical properties.

  Among these, the method (e) is a preferable method from the viewpoint of productivity because it has a possibility of being formed in-line at the same time as the film formation of the substrate.

  Further, the backlight unit using the diffusion sheet of the present invention includes at least a plurality of linear light sources having a substantially parallel arrangement, a light source having a plurality of linear portions having a substantially parallel arrangement, and a linear shape having a substantially parallel arrangement. On the upper side of the light source composed of at least one selected from the group consisting of light sources where brightness and darkness are observed, the diffusion sheet of the present invention is formed in a direction parallel to the linear portion of the light source and on the A surface of the diffusion sheet. It is characterized by being installed so that the longitudinal direction of the shape is parallel.

  The light source of the direct type backlight in which the diffusion sheet of the present invention exerts an effect is linear or has a linear part (such as a U-shaped tube or a W-shaped tube), or light and dark are observed in a linear shape. There is no particular limitation as long as it is, but for example, a fluorescent tube is preferably used. It is also a preferable aspect that the arrangement pitch of the light sources is unequal within the backlight unit plane. For example, when it is desired to brighten the central portion of the backlight, this can be achieved by shortening the light source array pitch at the central portion of the screen. Moreover, since it becomes dark near the frame of the casing at the edge of the screen, it can be brightened by shortening the arrangement pitch here. As described above, for the purpose of adjusting the brightness in the screen, it is preferable that the effect is exhibited by making the arrangement pitch of the light sources unequal.

  Moreover, it is usually preferable to install a reflecting member such as a light reflecting film on the lower side of these light sources (in the direction opposite to the screen). By this reflecting member, the light beam directly emitted from the light source or the light beam returned from the upper member is reflected to the screen side, so that the light use efficiency can be increased and the luminance can be improved.

  In the backlight unit of the present invention, the convex longitudinal direction formed on the A surface of the diffusion sheet of the present invention and the direction parallel to the linear portion of the light source are installed in parallel. . The direction perpendicular to the longitudinal direction of the convex shape of the A surface is the direction in which the sheet exhibits the strongest diffusivity, so that the anisotropic diffusivity of the diffusion sheet is maximized, and the luminance through which the fluorescent tube image can be seen is shown. It becomes possible to eliminate unevenness efficiently.

  Moreover, it is also a preferable aspect that the backlight unit of the present invention further uses the diffusion sheet of the present invention on the upper side of the diffusion sheet. Here, as a more preferable installation direction of the diffusion sheet stacked on the upper side, there is a direction in which the longitudinal direction of the convex shape formed on the A surface and the direction parallel to the linear portion of the light source are parallel or perpendicular. In the case where they are installed in parallel, the anisotropic diffusibility is further enhanced, and the uniformity of the backlight unit is further improved, which is a preferable configuration. In addition, in the case where the backlight unit is installed vertically, it is a preferable configuration because the uniformity can be increased in both the vertical and horizontal directions of the backlight unit and the luminance can be improved. The diffusion sheet according to the present invention exhibits a light collecting function in the direction perpendicular to the longitudinal direction of the convex shape along with the anisotropic diffusivity due to the line-shaped uneven pattern on the A surface. It is also possible to expect an improvement in brightness while increasing the uniformity.

  In addition to the light source, the diffusion sheet of the present invention, and the light reflecting film described above, various members can be preferably used as the configuration of the backlight unit of the present invention as shown below.

  In the backlight unit of the present invention, it is also preferable to install a light diffusing plate, which is a plate-like member containing particles inside, below the diffusion sheet of the present invention. As a requirement required for the backlight unit, in particular, in the case of a direct type backlight unit, it is necessary to eliminate unevenness in luminance caused by the shape and arrangement of a light source installed directly under the screen and to have uniform brightness over the entire surface. Here, the diffusion sheet of the present invention is a sheet that can enhance luminance while efficiently eliminating luminance unevenness by exhibiting anisotropic diffusivity, but by installing a light diffusion plate containing particles inside Further, it becomes possible to improve the uniformity of the screen. In the backlight unit, the arrangement pitch of the light sources and the distance between the members such as the light source and the diffusion sheet are greatly related to the screen uniformity. For example, when the arrangement pitch of the light sources is increased, or when the distance between the light sources and the members is shortened, the luminance unevenness appears more remarkably. Therefore, it is preferable to combine the diffusion sheet of the present invention with the light diffusing plate because it can easily eliminate luminance unevenness corresponding to backlight units having various structures.

  In addition, the light diffusing plate has a plurality of convex shapes having a major axis and a minor axis or a plurality of striped convex shapes formed on at least one surface of the light diffusing plate so that the longitudinal direction is substantially aligned in one direction. Is also preferable. In order to further increase the uniformity of the backlight unit, the backlight unit is preferably installed so that the direction parallel to the linear portion of the light source is parallel to the convex longitudinal direction of the light diffusion plate. Further, the shape of the cross section perpendicular to the longitudinal direction of the convex shape is not particularly limited. For example, a regular or irregular shape such as an arc shape such as a semicircle or an ellipse, a waveform shape such as a sine curve, a prism shape such as a triangle, or a rectangle. It can be preferably used regardless of the rules.

  In addition, a substantially transparent plate-like member can be used instead of a diffusive base material containing particles inside like the light diffusion plate. When using a transparent base material with smooth both surfaces, it functions as a support for optical members such as the diffusion sheet of the present invention, and the surface is formed with a plurality of convex shapes whose longitudinal directions are substantially aligned in one direction. Thus, it is possible to improve the uniformity and brightness of the backlight unit as in the case of the light diffusion plate.

  In the backlight unit of the present invention, an optical sheet selected from the group consisting of a diffusion sheet, a prism sheet, and a polarization separation sheet is preferably disposed on the upper side and / or the lower side of the diffusion sheet. These optical sheets can be appropriately selected depending on the luminance and screen uniformity required for the backlight unit.

  The structure of the backlight unit of the present invention includes, for example, a linear light source, a linear portion, or a linear light / dark portion pitch of 2p, each light source and a member (the sheet, film, A structure in which an angle θ at which tan θ = p / h satisfies 25 ° ≦ θ ≦ 60 °, where h is a distance to a plate-like member or the like, is preferably used.

  Moreover, about the installation method of the diffusion sheet of this invention, it is preferable that B surface is made into the light source side, ie, a light-incidence surface, and A surface in which the linear uneven | corrugated pattern was formed is made into a light-projection surface. Further, as described above, when the B surface is roughened, the light utilization efficiency can be improved and the luminance can be improved by using the roughened B surface as the light incident surface. This is a preferable installation method because the anisotropic diffusion effect is enhanced by forming a line-shaped uneven pattern on the exit surface. Further, in the case of a direct type backlight, since the inside has a hollow structure, when installing the diffusion sheet of the present invention, a method of extending the casing or a plate-like member as a support on the present invention. A method of installing a diffusion sheet is preferably used.

  Below, the measuring method and evaluation method of each Example and a comparative example are demonstrated. In each of the following measurements, each sample was evaluated with an average value of values obtained by performing the measurement three times.

(Measurement and evaluation method)
A. Outgoing intensity distribution, diffusivity Optical properties of the diffusion sheet were measured using a goniophotometer GP-200 manufactured by Murakami Color Research Laboratory. The diffusion sheet was set on the sample stage so that the light beam was incident from the B surface (the surface subjected to the rough surface treatment), and the emission intensity distribution emitted from the A surface was measured under the following conditions. In the following description, the incident angle is an acute angle formed by the normal direction of the incident surface and the optical axis of the incident light, and one direction is positive with respect to the normal direction and the other direction is negative. The exit angle is an acute angle formed by the normal direction of the exit surface and the optical axis of the outgoing light, plus one direction relative to the normal direction (the direction through which the extension of the optical axis of the incident light passes) However, if the incident angle is 0 °, either direction may be positive), and the other direction is negative.

(1) Incident angle 0 ° (incident from normal direction)
The intensity of the emitted light emitted from the A surface of the sheet when a light beam is incident on the B surface of the sheet at an incident angle of 0 ° (normal direction), in the plane perpendicular to the longitudinal direction of the convex shape of the A surface, and the sheet Measurements were made in 0.1 ° increments within an emission angle range of −90 ° to 90 ° in a plane perpendicular to the surface and parallel to the longitudinal direction of the convex shape of the A surface.

  From the obtained emission intensity distribution, the emission angle on the plus side, which is 50% of the emission intensity at the emission angle of 0 °, was read in each direction.

Further, the diffusivity was calculated by reading the emission intensity at + 5 °, + 20 °, and + 70 ° from the emission intensity distribution in the plane perpendicular to the longitudinal direction of the convex shape of the A surface, and substituting it into the following equation.
Diffusivity = 100 × 0.5 × (I (70) + I (20)) / I (5)
In the above equation, I (θ) represents the emission intensity of the light beam having the emission angle θ °.

(2) Incident angle α (10 ° ≦ α ≦ 80 °)
In a plane perpendicular to the longitudinal direction of the convex shape of the A surface of the A surface of the sheet, light rays are incident on the B surface of the sheet at an incident angle α (10 ° ≦ α ≦ 80 °, in 10 ° increments). The emission distribution intensity in the plane exiting from the surface was measured. The measurement range was an emission angle of −90 ° to 90 °, measured in increments of 0.1 °, and the emission angle β at which the emission intensity was maximum for each incident angle α was read.
The conditions common to each measurement were as follows.
Light source: halogen lamp 12V50W
Light source side filter: Light intensity adjustment filter with an average transmittance of 1% Light beam stop: Setting 3 (φ 11 mm)
Receiving diaphragm: Setting 6 (φ approximately 13mm)
Sample stage: Standard specimen stage with tilt for reflection and transmission (no tilt is used)
Measurement mode: Transmission.

B. Transmittance and haze The transmittance and haze were measured using a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. The sample was cut into a 100 mm square and set and measured so that the light was incident from the B surface (the surface subjected to the rough surface treatment) of the diffusion sheet.

C. Glossiness
Using a digital variable angle gloss meter UGV-5B manufactured by Suga Test Instruments Co., Ltd., the 60 ° glossiness of the B side (surface subjected to rough surface treatment) of the sheet was measured based on JIS Z8741. On the B side of the diffusion sheet cut out to a 100 mm square, the measurement was performed in two planes, a plane parallel to the longitudinal direction of the convex shape of the A plane and a plane parallel to the longitudinal direction.

D. Backlight characteristics Evaluation 21 inch (330 mm × 410 mm: diagonal 520 mm) direct type backlight (housing, reflection film, fluorescent tube part) is lit at 12 V, and after 1 hour, the upper side of the fluorescent tube A member (described in the example) including a diffusion sheet (340 mm × 420 mm) was installed, and the luminance and uniformity in the front direction were measured using a luminance unevenness analyzer Eye-Scale3 manufactured by I-System Co., Ltd.

The installation direction of the diffusion sheet was such that the B surface was directed to the light source side, and the convex longitudinal direction of the A surface was parallel to the direction parallel to the linear portion of the fluorescent tube.
The measurement position was performed on a line shifted to the right or left by 25 mm from the center of the backlight in the direction perpendicular to the linear portion of the fluorescent tube.
The brightness was evaluated as an average value of the measurement positions. The uniformity was calculated from the ratio of the maximum value and the minimum value obtained at the measurement position using the following formula.
・ Uniformity (%) = 100 × (maximum value−minimum value) ÷ minimum value As for the uniformity, 2% or less is AA, 2% to 3% is A, 3% to 5% is B, The case of greater than 5% is defined as C, and the level of C indicates that the unevenness is too large to be suitable as a backlight.

The backlight configuration for evaluation was as follows.
(Fluorescent tube)
Diameter: 3mm
Number: 12 Adjacent spacing (pitch): 25 mm (= 2p)
Distance between tube center and reflector (lower side): 5mm
Distance between tube center and member (upper side) 10mm (= h)
θ: 51.3 ° (tan θ = p / h = 1.25)
(Reflective sheet)
Lumirror (registered trademark) 188E60L manufactured by Toray Industries, Inc.

  All of the above measurements were performed at room temperature of 23 ° C. and humidity of 65%.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

Example 1
Coating 1 was coated on one side of a 188 μm transparent polyethylene terephthalate (PET) substrate and dried at 110 ° C. for 4 minutes to form a 5 μm particle-containing coating (rough surface).

(Coating 1)
Acrylic resin A-811 (manufactured by Aiken Chemical) 30 parts by weight Acrylic particles MX330 (manufactured by Soken Chemical Co., Ltd., particle size 3 μm) 0.8 parts by weight Methyl ethyl ketone 70 parts by weight Antistatic agent 1.5 parts by weight.

  Next, the surface (A surface) opposite to the surface coated with the coating material 1 (A surface) was coated with the coating material 2 to form a coating film having a thickness of 30 μm.

(Coating agent 2)
Adeka optomer KRM-2199 (Asahi Denka Kogyo Co., Ltd.) 10 parts by mass Aron Oxetane OXT-221 (Toagosei Co., Ltd.) 1 part by mass Adeka optomer SP170 (Asahi Denka Kogyo Co., Ltd.) 0.25 Parts by mass.

The mold with a line-shaped uneven pattern pressed against the A side of the base material coated with the coating agent 2 and irradiated with 1 J / m ² from the B side of the base material with an ultra-high pressure mercury lamp, the coating agent was applied. After curing, the mold was released to obtain a diffusion sheet 1. The line-shaped uneven pattern on the A-side of the obtained diffusion sheet had an irregular shape with a pitch of 3 to 8 μm and a height of 0.6 to 6 μm.
The characteristics of the diffusion sheet 1 are shown in Table 1.

Next, from the light source side to the evaluation backlight, a light diffusion plate (transmittance 65%), this diffusion sheet, prism sheet (Sumitomo 3M, BEFII), brightness enhancement sheet (Sumitomo 3M, DBEF-D400) in this order. It was installed in piles, and brightness and uniformity were measured. The evaluation results are shown in Table 2.
This backlight unit equipped with the diffusion sheet 1 was found to exhibit high brightness and excellent screen uniformity.

(Example 2)
In Example 1, a diffusion sheet is formed by changing the mold shape, and an irregularly shaped diffusion sheet 2 in which the line-shaped uneven pattern fluctuates with a pitch of 3 to 11 μm and a height of 1 to 3 μm is produced. did. Other than that, it installed in the backlight for evaluation similarly to Example 1, and measured the brightness | luminance and the uniformity. The evaluation results are shown in Table 2.
This backlight unit equipped with the diffusion sheet 2 was found to exhibit high brightness and excellent screen uniformity.

(Example 3)
In Example 1, instead of the light diffusing plate mounted on the evaluation backlight, a semicylindrical pattern having a semicircular cross section (radius of 100 μm) is arranged at a pitch of 200 μm on the surface of the light diffusing plate (transmittance 65%). The backlight member was evaluated by placing a plate-like member having a lenticular pattern formed thereon. The plate member was installed so that the side opposite to the surface on which the lenticular pattern was formed was the fluorescent tube side. The results are shown in Table 2. As a result, the brightness and the uniformity were higher than those in Example 1.

Example 4
In Example 1, instead of the light diffusing plate mounted on the evaluation backlight, the surface of the light diffusing plate (transmittance 65%) has a right-angled isosceles triangle (vertical angle 90 °, height 25 μm). A plate-like member having a prism shape formed at a pitch of 50 μm was placed to evaluate the backlight characteristics. The plate member was installed such that the surface opposite to the surface on which the prism shape was formed was the fluorescent tube side. The results are shown in Table 2. As a result, the brightness and the uniformity were higher than those in Example 1.

(Example 5)
In Example 1, coating the coating agent 2 on the A surface to form a coating film having a thickness of 50 μm, and then pressing the mold 1 having the following shape to obtain a diffusion sheet, the same as in Example 1 Thus, a diffusion sheet 3 was obtained. The characteristics of the diffusion sheet 3 are shown in Table 1.

(Mold 1)
Unit cross-sectional shape: a semi-circle having a radius of 50 μm shown in FIG. 5 is the original shape (aspect ratio b / a = 1), and a shape pitch p = 96.6 μm, height obtained by removing a region exceeding the hem angle of 75 ° h = 37 μm
Pattern viewed from the surface of the mold: Regular stripe pattern.

  A plurality of striped convex shapes obtained by inverting the mold 1 are formed on the A surface of the obtained diffusion sheet 3, and the cross section perpendicular to the longitudinal direction of each convex shape is a shape with a pitch of 96.6 μm and a height of 37 μm. Met.

Next, from the light source side to the evaluation backlight, a light diffusion plate (transmittance 65%), this diffusion sheet, prism sheet (Sumitomo 3M, BEFII), brightness enhancement sheet (Sumitomo 3M, DBEF-D400) in this order. It was installed in piles, and brightness and uniformity were measured. The evaluation results are shown in Table 2.
This backlight unit equipped with the diffusion sheet 3 was found to exhibit high brightness and excellent screen uniformity.

(Example 6)
In Example 1, coating the coating agent 2 on the A surface to form a coating film having a thickness of 50 μm, and then pressing the mold 2 having the following shape to obtain a diffusion sheet, the same as in Example 1 Thus, a diffusion sheet 4 was obtained. The characteristics of this diffusion sheet 4 are shown in Table 1.

(Mold 2)
Unit cross-sectional shape: a semi-elliptical shape having a minor axis a = 50 μm and a major axis b = 62.5 μm shown in FIG. 5 as an original shape (aspect ratio b / a = 1.25), and a region exceeding the hem angle of 75 ° Deleted shape pitch p = 94.8 μm, height h = 42.6 μm
Pattern viewed from the surface of the mold: Regular stripe pattern.

  A plurality of striped convex shapes obtained by inverting the mold 2 are formed on the A surface of the obtained diffusion sheet 4, and the cross section perpendicular to the longitudinal direction of each convex shape is a pitch of 94.8 μm and a height of 42.6 μm. It was the shape of.

Next, from the light source side to the evaluation backlight, a light diffusion plate (transmittance 65%), this diffusion sheet, prism sheet (Sumitomo 3M, BEFII), brightness enhancement sheet (Sumitomo 3M, DBEF-D400) in this order. It was installed in piles, and brightness and uniformity were measured. The evaluation results are shown in Table 2.
This backlight unit equipped with the diffusion sheet 4 was found to exhibit high brightness and excellent screen uniformity.

(Example 7)
In Example 3, instead of using the diffusion sheet 1, the backlight characteristics were evaluated in the same manner as in Example 3 except that the diffusion sheet 4 (described in Example 6) was used. The results are shown in Table 2.

(Example 8)
In Example 4, backlight characteristics were evaluated in the same manner as in Example 4 except that the diffusion sheet 4 (described in Example 6) was used instead of using the diffusion sheet 1. The results are shown in Table 2.

(Comparative Example 1)
In Example 1, the backlight characteristics were evaluated in the same manner except that Kimoto diffusion sheet “Light Up” 188GM2 was used instead of the diffusion sheet of the present invention. Table 1 shows the characteristics of GM2 and the backlight evaluation results. This sheet does not exhibit anisotropic diffusivity like the diffusion sheet of the present invention, and does not satisfy the scope of the present invention in terms of diffusivity and angle conversion, and luminance unevenness derived from the light source image is eliminated. The result was poor screen uniformity.

  The diffusion sheet of the present invention can be applied as a thin optical member that develops high screen uniformity and high luminance characteristics by being incorporated into various display devices, particularly backlight units of liquid crystal display devices.

( Reference Example 5)
In Example 1, coating the coating agent 2 on the A surface to form a coating film having a thickness of 50 μm, and then pressing the mold 1 having the following shape to obtain a diffusion sheet, the same as in Example 1 Thus, a diffusion sheet 3 was obtained. The characteristics of the diffusion sheet 3 are shown in Table 1.

( Reference Example 6)
In Example 1, coating the coating agent 2 on the A surface to form a coating film having a thickness of 50 μm, and then pressing the mold 2 having the following shape to obtain a diffusion sheet, the same as in Example 1 Thus, a diffusion sheet 4 was obtained. The characteristics of this diffusion sheet 4 are shown in Table 1.

( Reference Example 7)
In Example 3, instead of using the diffusion sheet 1, the backlight characteristics were evaluated in the same manner as in Example 3 except that the diffusion sheet 4 (described in Reference Example 6) was used. The results are shown in Table 2.

( Reference Example 8)
In Example 4, instead of using the diffusion sheet 1, the backlight characteristics were evaluated in the same manner as in Example 4 except that the diffusion sheet 4 (described in Reference Example 6) was used. The results are shown in Table 2.

Claims (9)

  A plurality of stripe-shaped convex shapes are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are aligned in substantially one direction, and individual shapes in a cross section perpendicular to the longitudinal direction of the convex shapes are A diffusion sheet having a shape obtained by deleting at least a region having a hem angle of 80 ° or more and 90 ° or less from a semi-elliptical shape whose major axis direction is perpendicular to the sheet surface.   2. The diffusion sheet according to claim 1, wherein an aspect ratio of the original semi-elliptical shape is greater than 1 and 1.5 or less in a shape obtained by deleting at least a region having a skirt angle of 80 ° to 90 ° from the semi-elliptical shape. .   A plurality of stripe-shaped convex shapes are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are aligned in substantially one direction, and individual shapes in a cross section perpendicular to the longitudinal direction of the convex shapes are A diffusion sheet having a shape obtained by deleting at least a region having a hem angle of 80 ° to 90 ° from a semicircular shape.   The diffusion sheet according to claim 1, wherein the other surface of the sheet is subjected to a rough surface treatment. A plurality of convex shapes having a major axis and a minor axis are formed on one surface of the sheet, and the longitudinal directions of the plurality of convex shapes are substantially aligned in one direction,
A diffusion sheet in which the emission intensity distribution 1 of light emitted from one surface of the sheet satisfies the following conditions (1) and (2) when the light is incident on the other surface of the sheet at an incident angle of 0 °.
(1) With respect to the emission intensity distribution 1 in the plane perpendicular to the longitudinal direction of the convex shape, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 15 to 25 °.
(2) With respect to the emission intensity distribution 1 in a plane perpendicular to the sheet surface and parallel to the longitudinal direction of the convex shape, the emission angle at which the intensity is 50% with respect to the emission intensity at the emission angle of 0 ° is 0.5 to 5 It is in the range of °.   The diffusion sheet according to claim 5, wherein the other surface of the sheet is roughened. The diffusion sheet according to claim 5 or 6, wherein the diffusivity defined by the following formula is within a range of 25 to 40 for the emission intensity distribution 1 in a plane perpendicular to the longitudinal direction of the convex shape.
Diffusivity = 100 × 0.5 × {I (70) + I (20)} / I (5)
(In the above equation, I (θ) represents the intensity of light emitted at an angle θ °) Light rays emitted from one surface of the sheet when incident on the other surface of the sheet at an incident angle α (10 ° ≦ α ≦ 80 °) in a plane perpendicular to the longitudinal direction of the convex shape. The diffusion sheet according to claim 5, wherein the emission intensity distribution 2 satisfies the following condition (3).
(3) With respect to the emission intensity distribution 2 in the plane perpendicular to the longitudinal direction of the convex shape, the emission angle β at which the emission intensity is maximum for each incident angle α is α / 3 <β <2α / 3. Fulfill.   Consists of at least one selected from the group consisting of a plurality of linear light sources in a substantially parallel arrangement, a light source having a plurality of linear portions in a substantially parallel arrangement, and a light source in which light and darkness is observed in a straight line in a substantially parallel arrangement A backlight unit in which the diffusion sheet according to any one of claims 1 to 8 is installed on the upper side of the light source so that a direction parallel to a linear portion of the light source is parallel to a longitudinal direction of the convex shape .

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