JP2009069347A - Optical sheet and backlight unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which can maintain high optical usage efficiency and, at the same time, is excellent in anisotropic diffusion effect of light, and to provide a backlight unit capable of dissolving the tube irregularity originated from a fluorescence tube and exhibiting the screen uniformity and high luminance characteristic. <P>SOLUTION: The optical sheet has a stripe lens layer on at least one side surface of a base, wherein a unit lens constituting the stripe lens layer has a cross-sectional shape in the direction perpendicular to stripes, of a circular arc and, when width of the circular arc is p and height thereof is h, the ratio h/(p/2) falls within the range of 0.4 to 0.8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Liquid crystal display devices are used in various applications such as notebook computers and mobile phone devices, televisions, monitors, car navigation systems, and the like. The liquid crystal display device incorporates a backlight unit that serves as a light source, and displays light by controlling light rays from the backlight unit through a liquid crystal cell. The characteristic required for this backlight unit is not only as a light source that emits 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 system called a sidelight type backlight. This is a method mainly used for, for example, a notebook personal computer or the like that is required to be thin and small, but is characterized by using a light guide plate as a basic configuration. 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 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 of the light, and the 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, but the basic configuration is characterized by a structure in which fluorescent tubes are arranged directly behind the screen without using a light guide plate. By arranging a plurality of linear or partially linear fluorescent tubes in parallel at the back of the screen, it is possible to cope with a large screen and to secure sufficient brightness. 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. However, according to this light diffusing plate, tube unevenness can be eliminated and the screen can be made uniform. However, since the light is diffused strongly, the total light transmittance is lowered and the light utilization efficiency is deteriorated. Moreover, since it diffuses too strongly, the light is scattered in an unnecessary direction, and as a result, the required front brightness is insufficient. Therefore, it has also been proposed to install a diffusion sheet on the light diffusing plate, which shows the effect of condensing light in the front direction while diffusing light isotropically (Patent Document 2). This diffusion sheet is a sheet called a bead sheet in which a diffusion layer containing fine particles such as organic crosslinked particles is formed on a base sheet. Unlike a light diffusion plate, the diffusion sheet is oriented to condense light to the front direction to some extent. It is an optical film showing the properties. 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. Usually, as a direct type backlight, a light diffusing plate having extremely strong light diffusibility is installed as described above, and this plate-like member eliminates tube unevenness and increases the uniformity of the screen. In the case of a light diffusing plate that emphasizes the degree of light, the total light transmittance is low and the light utilization efficiency is poor, so high brightness cannot be achieved. There is a contradictory phenomenon that the uniformity cannot be increased due to the reduced diffusivity. 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.

  Therefore, in view of the background of the prior art, the present invention is to provide an optical sheet excellent in the anisotropic diffusion effect of light while maintaining high light utilization efficiency. That is, the present invention provides an effective diffusion effect without reducing the light utilization efficiency by such an optical sheet, thereby effectively eliminating the tube unevenness derived from the fluorescent tube, screen uniformity and high luminance characteristics. The effect that can be expressed is produced.

The present invention employs any one of the following means in order to solve such a problem.
(1) An optical sheet having a stripe lens layer on at least one surface of a substrate, wherein the unit lens constituting the stripe lens layer has a circular cross section in a direction perpendicular to the stripe, An arc is an optical sheet in which the ratio h / (p / 2) satisfies 0.4 to 0.8 when the width is p and the height is h.
(2) The optical sheet according to (1), wherein an angle of a skirt of the arc is 45 ° to 90 °.
(3) Draw a circle in contact with either of the two tangents at the hems (A and B) on both sides of the arc, and define the shape formed by the shorter arc AB and line segment AB as a pseudo unit lens. The optical sheet according to (1) or (2), wherein when viewed, the height H of the pseudo unit lens satisfies H> h.
(4) The optical sheet according to any one of (1) to (3), wherein one surface of the substrate has a stripe lens layer and the other surface is roughened.
(5) The unit lens has a diffusion angle of a light emission intensity distribution emitted from the other surface of the sheet when a light beam is incident at an incident angle of 60 ° from the one surface of the sheet in a plane perpendicular to the stripe. The optical sheet according to any one of (1) to (4), wherein the angle satisfies 30 ° to 50 °.
(6) In the plane perpendicular to the stripe, the unit lens has a diffusion angle of a light emission intensity distribution emitted from the other surface of the sheet when a light beam is incident from one surface of the sheet at an incident angle of 60 °. Is an optical sheet according to any one of (1) to (5), which is larger than a diffusion angle when a light beam is incident at an incident angle of 0 °.
(7) A backlight unit using the optical sheet according to any one of (1) to (6).
(8) 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 are observed in a straight line in a substantially parallel arrangement. The optical sheet according to any one of (1) to (6) above the light source composed of seeds, the direction parallel to the linear portion of the light source and the stripe of the stripe lens are parallel. The backlight unit according to claim 7 installed as described above.

  ADVANTAGE OF THE INVENTION According to this invention, the optical sheet which exhibits the anisotropic diffusion effect of light efficiently, without reducing light utilization efficiency can be provided, and this can be provided as the backlight unit of a liquid crystal display device, especially a direct type backlight Incorporation into a high-quality screen can achieve both high screen uniformity and high luminance characteristics.

  The present invention, as a result of intensive studies on the above-mentioned problem, that is, an optical sheet excellent in the light diffusion efficiency as well as the light utilization efficiency, forms a specific shape of a stripe lens layer on one side of the sheet. When the diffusion behavior was controlled, it was clarified that this problem can be solved at once.

  The optical sheet of the present invention is an optical sheet having a stripe lens layer on at least one surface of a substrate, and the unit lens constituting the stripe lens layer has an arc in a cross-sectional shape in a direction perpendicular to the stripe The arc is characterized in that the ratio h / (p / 2) satisfies 0.4 to 0.8 when the width is p and the height is h.

  The optical sheet of the present invention is configured to exhibit anisotropic diffusibility by forming a stripe lens layer on at least one 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 Is preferably diffused strongly in a direction perpendicular to the longitudinal direction of the light source. That is, a strong light diffusivity in one direction, that is, an optical sheet exhibiting anisotropic diffusivity is suitable.In the present invention, this anisotropic diffusivity is realized by a surface stripe lens layer. is there.

  Therefore, when the optical 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 to eliminate uneven brightness, and a highly uniform and high brightness backlight. Unit is obtained.

  As shown in FIG. 1, the stripe lens layer of the optical sheet of the present invention has a plurality of unit lenses 2 that extend in one direction so that the longitudinal direction is substantially unidirectional in the plane of the optical sheet 1. An ordered layer.

  In the present invention, the unit lens has a cross-sectional shape in a direction perpendicular to the stripe of the optical sheet having an arc as shown in FIG. 2, where the ratio is h / (where the width is p and the height is h. p / 2) has a circular arc satisfying 0.4 to 0.8. By making the unit lens shape an arc satisfying the ratio h / (p / 2) of 0.4 to 0.8, the uniformity of the screen is enhanced in the front direction and the oblique direction, that is, in a wide viewing angle. As a result, a sharp luminance distribution can be obtained while suppressing a rapid decrease in luminance in the high emission angle region. The ratio h / (p / 2) is preferably 0.5 to 0.7. Here, when the ratio h / (p / 2) is less than 0.4, the anisotropic diffusibility of the stripe lens layer becomes insufficient and the uniformity is lowered, which is not preferable. Further, when the ratio h / (p / 2) exceeds 0.8, the light rays incident on the sheet are collected too much in the front direction, and when mounted on the backlight unit, the brightness is rapidly increased in the high emission angle region. This is not preferable because it may cause a decrease or the degree of uniformity when the backlight is viewed from an oblique direction.

The unit lens preferably has a cross-sectional shape in a direction perpendicular to the stripe of the optical sheet having an arc that is symmetrical with respect to a normal passing through the apex of the unit lens (normal to the sheet surface). Since the cross-sectional shape of the unit lens has a symmetrical arc, when the optical sheet of the present invention is mounted on a backlight unit, the unit lens is symmetrically arranged around the front surface in a plane perpendicular to the stripe of the stripe lens layer. This is preferable because a uniform backlight unit can be obtained which has optical characteristics and does not depend on the viewing direction.
In the optical sheet of the present invention, it is preferable that the angle of the skirt of the arc in the cross section of the unit lens constituting the stripe lens layer is 45 ° to 90 °. The hem angle is an acute angle formed by a straight line connecting the left and right hems of the unit lens and a tangent line of the hem. Next, how to find the tangent of the hem is shown. Here, in the cross section in the direction perpendicular to the stripe of the unit lens, the arrangement direction of the unit lens (the direction connecting the left and right hems of the unit lens) is the X axis, and the direction orthogonal to the X axis (the convex direction of the unit lens) is the Y axis. XY coordinates, and place one hem at the origin of the XY coordinates and the other hem at the coordinates (± 1000x, 0) (where the left skirt is the origin, the right skirt is the coordinate (+ 1000x, 0), where the right skirt is the origin, the left skirt is coordinates (-1000x, 0)). At this time, when the coordinates of the unit lens curve corresponding to the coordinates (± x, 0) are (± x, y), the straight line passing through the origin (0, 0) and the coordinates (± x, y) The tangent line. FIG. 3 shows the hem angle 4. When the hem angle is 45 ° to 90 °, the uniformity of the screen can be increased in the front direction and the oblique direction, that is, in a wide viewing angle range. Also, the hem refracts incident light and directs it in the front direction to increase the brightness. By setting the hem angle to 45 ° to 90 °, it is possible to increase the brightness in the front direction. It becomes. If the hem angle is less than 45 °, anisotropic diffusion is insufficient and it is difficult to increase the uniformity, and the effect of improving the luminance in the front direction is reduced, which is not preferable. Further, if the hem angle exceeds 90 °, it is difficult to refract in the front direction and the luminance may be lowered.

  Also, as shown in FIG. 4, in the cross section of the unit lens 2 constituting the stripe lens layer 20, a circle that is in contact with any of the two tangents at the hems (A and B) on both sides is drawn, When the shape formed by the shorter arc AB and line segment AB is regarded as a pseudo unit lens, the height H of the pseudo unit lens preferably satisfies H> h.

  That is, it means that the aspect ratio (h / (p / 2)) of the unit lens 2 in the present invention is smaller than the aspect ratio (H / (p / 2)) of the pseudo unit lens. A preferable unit lens is a lens having an aspect ratio lower than that of a perfect circular arc corresponding to the skirt angle while having a high angle at the skirt portion. Here, the unit lens of the present invention may be either one whose curvature changes continuously or discontinuously from the apex to the skirt, or one in which arcs having the same curvature are connected.

  In the present invention, if the shape satisfies the above-described condition, the effect of the present invention can be obtained even if H = h. However, by setting H> h, a light beam having a large incident angle entering the sheet can be reduced. The high angle region of the portion can be used to direct the front direction, and the emission amount can be increased to increase the brightness. In addition, the arc shape has a continuous or discontinuous change compared to a perfect circular arc whose light refraction angle changes uniformly, so that it is possible to improve the scattering characteristics and make the light uniform. .

  In the present invention, the shape of the unit lens constituting the stripe lens layer can be preferably used as long as it satisfies the above-described conditions. A preferable size of the unit lens is a size satisfying the range of the ratio h / (p / 2) with a width p of 10 to 200 μm and a height p of the height h.

  In addition, the unit lenses constituting the stripe lens layer 20 are preferably arranged in parallel without leaving a gap in the sheet surface. Here, the state where there is a gap indicates that adjacent unit lenses 2 are arranged via the flat portion 5 as shown in FIG. In the present invention, it is preferable to dispose the adjacent unit lenses 2 without leaving a gap, since the component that is emitted without being diffused among the light rays incident on the optical sheet is reduced and the uniformity is improved. As shown in FIG. 5B, when adjacent unit lenses 2 are arranged via a curved surface (in this case, a curved surface convex in the direction opposite to the convexity of the unit lens), they are arranged without leaving a gap. This is preferably used because the same effect as that obtained can be obtained. However, the arrangement without gaps is preferred because the degree of uniformity is further increased. When arraying via a curved surface, the position of the bottom of the unit lens 2 is an inflection point between the unit lens and the curved surface.

  The stripe lens layer of the optical sheet of the present invention is a layer having unit lenses that satisfy the above range. As an arrangement state, (1) when unit lenses having the same shape and size are regularly arranged (FIG. 6 ( a)), (2) When unit lenses that are not of the same shape but satisfy the above range are regularly arranged (for example, alternately arranged) (FIG. 6B), (3) It is not the same shape but satisfies the above range In the case where the unit lenses are randomly arranged (FIG. 6C), a preferable example is given. From the viewpoint of eliminating interference fringes (moire, etc.) seen when the optical sheet alone or another member is superimposed, the random arrangement of (3) is the most preferable configuration, and then the order of the arrangement of (2) Become. The stripe lens layer of the optical sheet of the present invention may include a unit lens that does not satisfy the above range. For example, as shown in FIG. 6D, there is a stripe lens layer 20 in which unit lenses 2 that satisfy the above range and unit lenses 6 that do not satisfy the above range but have a strong light collecting action are alternately arranged. In this case, in addition to the effect obtained by having a unit lens that satisfies the above range, it is possible to obtain a strong light condensing effect by the unit lens that does not satisfy the above range, and it is possible to further increase the brightness. is there. Although an example of the alternating arrangement is given here, the alternating arrangement is a preferable arrangement state for eliminating the bias in the optical characteristics within the sheet surface and improving the uniformity. In addition, as shown in FIG. 6 (e), instead of the alternating arrangement of FIG. 6 (d), a stripe lens in which a set of unit lenses satisfying the above range and a set of unit lenses not satisfying the above range are arranged in a block shape. Layer 20 is also preferably used. In this case, the unit lenses satisfying the above range are concentrated and arranged only in the portion where the function of the unit lens satisfying the above range is desired to be expressed. For example, in a backlight with noticeable luminance unevenness, the effect may be exerted by forming a stripe lens layer composed of unit lenses that satisfy the above range only in a portion where unevenness is desired to be eliminated. In the case of the block arrangement shown in FIG. 6E, a flat portion where no unit lens is formed may be used for a portion other than the set of unit lenses satisfying the above range.

  In the present invention, it is also preferable that a stripe lens layer is formed on one surface of the substrate and a roughening treatment is performed on the other surface.

  In the optical sheet of the present invention, a stripe lens layer is formed on at least one surface, and the anisotropic diffusion property is expressed by the stripe lens layer. It is preferable to install the lens layer so that the surface on which the lens layer is formed is on the light emitting side, since the anisotropic diffusion effect is enhanced, so that the uniformity of the backlight is increased.

  In the case of an optical sheet in which a stripe lens layer is formed only on one surface, the other surface is a light incident surface, but when this surface is roughened, when it is mounted on a backlight unit, it reflects light. In addition to light rays that are 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 luminance 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 roughening treatment, not only the handling property at the time of manufacturing the diffusion sheet is improved, but also in various processes such as cutting of the sheet according to the backlight shape and incorporation into the backlight. Handling becomes easy and it can contribute to speeding up of each process and a reduction in defect rate.

  Examples of the roughening treatment applied to the optical sheet of the present invention include a method of coating a base material with a coating material in which particles are dispersed in a binder resin, a method of transferring the shape of a mold to a base material, a sandblasting method, etc. A preferred example is a method of mechanically cutting and processing the substrate surface. Any of these methods is preferably used, but among these, the method of coating the base material with a coating material in which particles are dispersed in a binder resin is the type / combination of particles, particle size, addition amount, resin type, resin film thickness. This is a preferable method because the state and degree of the rough surface can be easily changed by selecting the above.

  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. FIG. 7A shows an example of a rough surface preferably formed by the roughening treatment.

  Moreover, unlike the above-mentioned roughening process, the roughening process for providing strong light diffusibility is also a preferable aspect. Specifically, as shown in FIGS. 7B and 7C, a light diffusion layer having a strong light diffusibility is formed on one surface. FIG. 7B shows a case where a combination of a binder resin and particles having a large refractive index difference is used, and a particle-dispersed resin layer of the combination is formed on a substrate. FIG. 7C shows a mode in which particles are spread on a base material to form a light diffusion layer. As the particles and binder resin used for these, the same materials as those of the particles and matrix resin that are preferably used for the diffusible substrate described later can be used. By forming such a light diffusing layer exhibiting strong light diffusivity on one side, the uniformity when mounted on the backlight unit can be further increased, which is preferably used.

  The substrate constituting the optical sheet of the present invention includes a substantially transparent substrate, a single layer containing particles inside, or a substrate comprising a laminate having at least a layer containing bubbles inside. Both are 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 optical sheet of the present invention, the light utilization efficiency is high because it does not contain a component that scatters 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 optical sheet of the present invention and the light source as a configuration of the backlight, uniformity can be ensured by a 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 single layer body containing particles inside or a laminate having at least a layer containing bubbles inside (hereinafter referred to as a diffusible base material) as the base material, The degree of uniformity can be further increased. For example, the degree of uniformity can be sufficiently secured without inserting a diffusible substrate such as a diffusion plate between the optical sheet of the present invention and the light source as a backlight structure. This is effective when priority is given to uniformity.

  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 (cross-linked) 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 just a preferred example of the diffusing element used for the diffusive substrate, and are not limited to these, as long as they are components having a refractive index different from that of the matrix resin at least in the visible light region (380 to 780 nm). Can be used.

  The average primary particle size of the particles of the diffusible substrate 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 in the base material with the direction of strong diffusion on the surface with diffusion anisotropy, the light diffusion performance as a diffusive base material is further improved, and the uniformity and luminance characteristics are improved. It is preferable because it contributes to improvement.

  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 diffusive 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.

  FIG. 8 illustrates a preferred layer configuration of the optical sheet of the present invention. 8A to 8C show the case where a transparent substrate is used, and FIGS. 8D to 8E show the case where a diffusible substrate is used. Here, the case where the stripe lens layer is formed on one surface is shown, but similarly, the present invention can be applied to the case where the stripe lens layer is formed on both surfaces and the other surface is roughened.

  FIG. 8A shows a single film configuration in which a transparent substrate and a stripe lens layer are integrated. 8B and 8C show a two-layer structure in which the stripe lens layer 20 is laminated on the transparent substrate 11. FIG. Among these, when the biaxially stretched polyester resin film is used as the transparent substrate with the two-layer configuration, the stripe lens layer can be shaped with high accuracy, and excellent mechanical properties and heat resistance can be imparted to the optical sheet. Therefore, this is a preferable configuration.

  FIG. 8D shows a single film configuration in which the diffusion base material and the stripe lens layer are integrated. FIG. 8E shows a two-layer configuration in which the stripe lens layer 20 is laminated on the diffusion base material 12, and FIG. 8F shows a lamination in which the diffusible base material 12 is sandwiched between the transparent base materials 11 from both sides. 4 shows a four-layer structure in which a stripe lens layer 20 is formed on a substrate made of a body. Also here, as a configuration capable of accurately shaping the stripe lens layer and imparting excellent mechanical properties and heat resistance to the optical sheet, a preferred example is a four-layer configuration using a biaxially stretched polyester resin film as the transparent substrate. Can be mentioned.

  It is also a preferred embodiment that various additives are added to each layer of the optical 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 optical sheet of the present invention preferably has a total film thickness of 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. In terms of diffusibility, the film thickness preferably exceeds 500 μm, but is preferably 500 μm or less from the viewpoint of reducing the thickness of the entire backlight unit. In addition, the film thickness here indicates the thickness of the entire optical sheet including all of the stripe lens layer, the base material, and the rough surface, and adopts the thickest (highest) portion in the measured range, The film thickness.

  In the optical sheet of the present invention, when a light beam is incident at an incident angle of 60 ° in a plane perpendicular to the stripe of the stripe lens layer, the diffusion angle of the light intensity distribution of the light beam emitted from the other surface of the sheet is 30. It is preferable to satisfy the angle of 50 ° to 50 °. Here, the diffusion angle refers to the angle D2-D1 when the emission angle indicating 50% of the peak intensity in the emission intensity distribution curve is D1, D2 (D2> D1) (FIG. 10). . 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. When the stripe lens layer is formed only on one surface of the substrate, light is incident from the surface on which the stripe lens layer is not formed, and the diffusion angle is measured.

  Hereinafter, the light behavior of the optical 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 amount adjustment filter with an average transmittance of 1%, and has a light beam aperture setting 3 (φ11 mm) and a light receiving aperture setting 6 (φ13 mm). Set the optical sheet and measure.

  When the diffusion angle of the optical sheet of the present invention satisfies 30 ° to 50 °, it exhibits excellent diffusibility with respect to light incident at a high angle, thereby increasing the effect of improving screen uniformity, This is preferable because the luminance in the direction is also improved. The diffusion angle is more preferably 40 ° to 50 °. Here, when the diffusion angle is less than 30 °, the diffusibility is not sufficient and the uniformity is inferior, and when it exceeds 50 °, the uniformity is improved, but the brightness is increased by spreading the light beam too much. Since it may decrease, it is not preferable.

  The optical sheet of the present invention emits light from the other surface of the sheet when light is incident at an incident angle of 60 ° from one surface of the sheet in a plane perpendicular to the stripe of the stripe lens layer. The diffusion angle of the intensity distribution is preferably larger than the diffusion angle when a light beam is incident at an incident angle of 0 °. By doing in this way, since the optical sheet with a high screen uniformity is obtained, maintaining the brightness | luminance of a front direction high, it is preferable. When the diffusion angle at the incident angle of 0 ° is larger than the diffusion angle at the incident angle of 60 °, the uniformity is high, but the luminance in the front direction may be lowered, which is not preferable. Moreover, as a preferable range of the diffusion angle when a light beam is incident at an incident angle of 0 °, it is 20 ° to 40 °, and more preferably 30 ° to 40 °.

  The optical sheet of the present invention preferably has a total light transmittance of 50% or more. The total light transmittance is an index related to the light use efficiency of the optical sheet. When the total light transmittance is extremely low, the use efficiency is inferior and it is difficult to increase the luminance. In the configuration of the optical sheet of the present invention, it is preferable that the total light transmittance is 50% or more because high luminance can be exhibited when mounted on a backlight unit. The total light transmittance is preferably 60% or more, and most preferably 70% or more. In the case of an optical sheet in which the stripe lens layer is formed only on one side, it is sufficient that the total light transmittance measured by entering light from the other side where the layer is not formed satisfies the above range. In the case of an optical sheet in which stripe lens layers are formed on both sides, a direction satisfying the above range may be present regardless of the incident direction of light rays.

  Next, although the method to manufacture the optical sheet of this invention is demonstrated, it is not limited to these methods, Other methods are also preferably used.

  First, the manufacturing method of a base material is demonstrated.

  Examples of the method for producing the substrate include a method of extruding or injection-molding a resin into a sheet, and a method of producing a stretched film by uniaxially or biaxially stretching a resin and then heat-treating the resin into a sheet. When the substrate has a laminated structure, a method of bonding a plurality of sheets formed into a sheet shape via an adhesive, a method of thermocompression bonding, a method of obtaining a laminated product at once by co-extrusion, etc. Is mentioned. Among these, the method of producing a stretched film by biaxially stretching and heat-treating after extrusion is a preferable method because of excellent surface flatness, mechanical properties, heat resistance, and productivity.

  Next, a stripe lens layer is formed on at least one surface of the substrate obtained as described above.

  Examples of the method for forming the stripe lens layer include (a) a mold transfer method using a mold, (b) a method of directly processing the substrate surface, and the like. (A) The mold transfer method will be described in more detail. (A1) A mold or / and a method in which a mold is pressed and pressed in a heated state, and (a2) a surface of the substrate. A method in which a light or thermosetting resin is laminated on the surface, the mold is pressed against the surface, the resin is cured by irradiation with active energy rays or heating, and (a3) the concave portion of the mold is filled in advance. And a method of transferring the resin on the substrate.

  Further, (b) the method of directly processing the substrate surface includes (b1) a method of mechanically cutting into a desired shape using a cutting jig, (b2) a method of cutting by a sandblast method, and (b3) a method of cutting by a laser. (B4) A method of laminating a photocurable resin on the surface of the base material, and processing the surface of the base material into a desired shape using a technique such as lithography or optical interference exposure.

  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 an optical sheet to be obtained can be obtained by selecting an appropriate process. be able to.

  In the present invention, it is also preferable to provide a stripe lens layer on one surface of the substrate and roughen the other surface, but as the roughening treatment method, the above-described stripe lens layer is formed. (A) a mold transfer method using a mold, (b) a method of directly processing the substrate surface, and (c) a method of forming a particle-dispersed resin layer. (C) The method of forming the particle-dispersed resin layer can be achieved, for example, by coating a coating material containing an isotropic spherical body (or a substance having a part of a spherical surface). As a binder resin, it contains at least one resin selected from a thermoplastic resin, a photocurable resin, and a thermosetting resin, diluted with a solvent as necessary, and further added with various additives as desired. Those having physical properties can be used.

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

  The optical sheet of the present invention obtained as described above is suitably used for a backlight unit. Among them, it is preferably used for a direct type backlight unit, and at least 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 in darkness in a substantially parallel arrangement of linear light sources. The optical sheet of the present invention is placed on the upper side of the light source composed of at least one selected from the group consisting of the light sources where the light source is observed, and the direction parallel to the linear portion of the light source and the stripe of the stripe lens of the optical sheet It is preferable to install them in parallel.

  The light source of the direct type backlight in which the optical sheet of the present invention exhibits the most effect is linear or has a linear portion (U-shaped tube, W-shaped tube, etc.), or light and dark are observed in a linear shape. The fluorescent tube is not particularly limited, and for example, a fluorescent tube is preferably used. Moreover, it is also a preferable aspect that the arrangement pitch of the light sources is not uniform in 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. Further, although it tends to be dark in the vicinity of the frame of the casing at the edge of the screen, it can be brightened by shortening the arrangement pitch here. Thus, in order to adjust the brightness within the screen, it is also a preferable aspect to make the arrangement pitch of the light sources non-uniform.

  In general, it is preferable to install a reflecting member such as a light reflecting film on the lower side of these light sources (on the side opposite to the optical sheet arrangement side of the present invention with the light source interposed therebetween). 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, it is preferable that the stripe direction of the stripe lens of the optical sheet of the present invention and the direction parallel to the linear portion of the light source are installed in parallel. In the optical sheet, the direction perpendicular to the stripe direction of the stripe lens is the direction in which the sheet exhibits the strongest diffusivity. Therefore, by arranging the linear portion of the light source so as to be parallel to the stripe, The anisotropic diffusivity is maximized, and it is possible to efficiently eliminate luminance unevenness through which the fluorescent tube image can be seen.

  In the backlight unit, it is also preferable that the optical sheet of the present invention is further used on the upper side of the optical sheet, that is, two optical sheets of the present invention are stacked. Here, as a more preferable installation direction of the optical sheet of the present invention further superimposed on the upper side of the optical sheet arranged as described above, the stripe direction of the stripe lens and the direction parallel to the linear portion of the light source are parallel or perpendicular. The direction to become. 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 is improved. The optical sheet of the present invention exhibits an anisotropic diffusion property as well as a light collecting function in a direction perpendicular to the stripe direction by the stripe lens, so that the stripe direction of the second optical sheet is perpendicular to the linear portion of the light source. By so installing, it is possible to expect an improvement in luminance while increasing the uniformity in both the vertical and horizontal directions.

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

  In the backlight unit of the present invention, a plate-shaped member containing particles therein, that is, a light diffusing plate is also preferably installed on the lower side (light source side) of the optical sheet of the present invention. In the case of a backlight unit, in particular, a direct type backlight unit, it is required to eliminate luminance unevenness caused by the shape and arrangement of the light source installed immediately below the screen and to provide a light source with high in-plane uniformity. Therefore, in addition to the optical sheet of the present invention exhibiting anisotropic diffusivity, by installing a light diffusion plate containing particles inside, the luminance unevenness is further eliminated while the luminance is increased, and the uniformity of the screen is increased. It becomes possible. In the backlight unit, the arrangement pitch of the light sources and the distance between the members such as the light source and the optical sheet are greatly related to the screen uniformity. For example, when the arrangement pitch of the light sources is widened 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 optical sheet of the present invention with the light diffusing plate, since it is possible to easily eliminate luminance unevenness corresponding to backlight units having various structures. Examples of the material constituting the light diffusing plate include mainly matrix resin and diffusing particles dispersed inside, but these are not particularly limited and can be preferably used. The total light transmittance of the light diffusing plate can be appropriately selected from 50 to 90% according to the desired luminance and level of uniformity.

  It is also preferred that the light diffusing plate has a line-shaped uneven pattern formed on at least one surface. Here, the line-shaped concavo-convex pattern is a pattern in which the longitudinal direction is aligned in substantially one direction. In order to further increase the uniformity of the backlight unit, it is preferable to install the backlight unit so that the direction parallel to the linear portion of the light source is parallel to the line direction of the line-shaped uneven pattern of the light diffusion plate. In addition, the shape of the cross section perpendicular to the line direction of the line-shaped uneven pattern is not particularly limited. For example, arc shapes such as semicircles and ellipses, waveform shapes such as sinusoids, isosceles triangles, isosceles triangles, and these Regardless of regular or irregular shapes such as a prism shape such as a triangular shape with a round top and a rectangular shape, it can be preferably used. In the combination with the optical sheet of the present invention, the more preferable cross-sectional shape of the line-shaped uneven pattern formed on the surface of the light diffusing plate is preferably a prism shape from the viewpoint of high luminance and high uniformity. Among the prism shapes, when a triangular shape with a rounded top is used, high brightness and smooth viewing angle characteristics are manifested, and there are defects (top defects, etc.) that occur in various processes such as manufacturing, cutting, and assembly. This is a more preferable shape. As a preferable prism shape, the unit shape is an isosceles triangle having an apex angle of 70 ° to 120 °, or a substantially triangular shape in which the apex portion is rounded. For example, the unit shape has a pitch between the tops of 10 to 300 μm. The thing arranged in the dimension to satisfy | fill is mentioned.

  Further, for example, a substantially transparent plate-like member can be provided in addition to the diffusive base material containing particles therein as in the light diffusion plate. When using a transparent substrate having smooth surfaces, it functions as a support for an optical member such as the optical sheet of the present invention, and forms a line-shaped uneven pattern on the surface, similar to the case of the light diffusion plate. In addition, the uniformity and brightness of the backlight unit can be improved.

  In the backlight unit, it is also a preferable aspect that an optical sheet selected from the group of a diffusion sheet, a prism sheet, and a polarization separation sheet is installed on the upper side and / or the lower side of the optical sheet of the present invention. These optical sheets can be appropriately selected depending on the luminance, screen uniformity and structure 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 2a, each light source and a member (an optical sheet, film, When the distance to a plate-like member or the like is b, a structure satisfying 25 ° ≦ θ ≦ 60 ° can be preferably used as the angle θ where tan θ = a / b. As the backlight unit, the luminance unevenness tends to occur as the angle θ increases. However, by using the optical sheet of the present invention, a backlight unit having a high screen uniformity in the angle range can be obtained. In particular, it is also preferably used in a backlight unit that satisfies 40 ° ≦ θ ≦ 60 ° in which uneven brightness tends to occur.

  Further, in the case of a direct type backlight, since the inside is a hollow structure, when installing the optical sheet of the present invention, the method of extending to the housing or the plate-shaped member as a support on the present invention The method of installing the optical sheet is preferably used.

  Below, the measuring method and evaluation method of each Example and a comparative example are demonstrated.

(Measurement and evaluation method)
A. Observation of cross section of optical sheet A cross section perpendicular to the stripe direction of the stripe lens layer is observed at 500 times using a scanning electron microscope S-2100A (manufactured by Hitachi, Ltd.). ), Height h (μm), hem angle (°), and H (μm) illustrated in FIG. Three unit lenses having the same shape were measured and the arithmetic average value was taken. Here, the hem angle was obtained by determining the tangent line of the skirt as follows and measuring the angle formed with the straight line connecting the left and right hems of the unit lens.

  Tangent line of hem: In the cross section in the direction perpendicular to the stripe of the unit lens, the arrangement direction of the unit lenses (direction connecting the left and right hems of the unit lens) is the X axis, and the direction orthogonal to the X axis (unit lens convex direction) is Y Considering the XY coordinates as axes, place one hem at the origin of the XY coordinates and the other hem at the coordinates (± 1000x, 0) (where the left skirt is the origin, the right skirt is Coordinates (+ 1000x, 0), where the right skirt is the origin, the left skirt is the coordinate (-1000x, 0)). At this time, when the coordinates of the unit lens curve corresponding to the coordinates (± x, 0) are (± x, y), a straight line passing through the origin (0, 0) and the coordinates (± x, y) Tangent.

B. Transmittance of optical sheet Using a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd., a sample was cut into a 100 mm square, the total light transmittance was measured three times, and the arithmetic average value was obtained. In the measurement, the incident direction of the light beam is the case where the stripe lens layer is formed on one side, and the other side is used as the incident surface, and when the stripe lens layer is formed on both sides, individual examples and comparisons are made. In the example, the incident surface was specified and measured.

C. Diffusion angle in optical sheet The following measurement was performed under the conditions described below using a variable angle photometer GP-200 manufactured by Murakami Color Research Laboratory, and the diffusion angle was calculated. In the measurement, the incident direction of the light beam is determined by the individual examples when the stripe lens layer is formed on one surface and the other surface is the incident surface, and when the stripe lens layer is formed on both surfaces.・ Measured by specifying the incident surface in the comparative example. In the following, the incident angle is an acute angle formed by the normal direction of the incident surface and the optical axis of the incident light beam, and the output angle is an acute angle formed by the normal direction of the output surface and the optical axis of the output light beam. That is.

  The intensity of the emitted light emitted from the exit surface of the sheet when a light beam is incident on the entrance surface of the sheet at an incident angle of 60 ° or 0 ° is the exit angle in a plane perpendicular to the stripe direction of the stripe lens layer on the exit surface. The measurement was made in the range of -90 ° to 90 ° in increments of 0.1 °.

  The peak intensity (P in FIG. 10) is read from the obtained emission intensity distribution, and the emission angle at which the intensity is 50% of the peak intensity (H in FIG. 10) is set to the low angle side (D1) and the high angle side (D2). ). From these two points, the diffusion angle (D2-D1) was calculated for each of the incident angles of 60 ° and 0 °. The value of the diffusion angle was determined by repeating the above measurement three times for each sample and averaging the obtained values.

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% Luminous aperture: Setting 3 (φ11 mm)
Receiving aperture: Setting 6 (φ13mm)
Sample stage: Standard specimen stage with tilt for reflection and transmission (no tilt is used)
Measurement mode: transmission Backlight characteristics Evaluation 15-inch direct type backlight (housing, reflection film, fluorescent tube part) is turned on at 12 V, and after 1 hour, the member including the optical sheet of the present invention on the upper side of the fluorescent tube (in the examples) The brightness and uniformity in the front direction were measured using a luminance unevenness analyzer Eye-Scale 3 manufactured by I-System Co., Ltd.

  When the stripe lens layer is formed on one surface, the optical sheet is installed in the direction of the individual surface when the other surface is directed to the light source and the stripe lens layer is formed on both surfaces. The incident surface was specified in the comparative example. In both cases, the stripe direction of the stripe lens layer was set to be parallel to the direction parallel to the linear portion of the fluorescent tube.

  The measurement was performed on a line in a direction perpendicular to the linear part of the fluorescent tube through a point shifted from the center of the backlight (intersection of diagonal lines) to the right or left by 25 mm parallel to the linear part of the fluorescent tube. . The measurement points were directly above the fluorescent tube on the line (8 measurement points) and an intermediate point between the adjacent fluorescent tubes (7 measurement points), and the measurement was performed at a total of 15 points.

The luminance was evaluated by an average value at the 15 measurement positions. The uniformity was calculated from the ratio between the maximum value and the minimum value of luminance obtained at the measurement position using the following formula.
Uniformity (%) = 100 × (maximum value−minimum value) ÷ minimum value Here, the maximum value is the average value of the top five luminance values among the measurement results at the 15 locations, and the minimum value is Of the measurement results at the 15 locations, the average value of the lower 5 points of the luminance value was used.

  For uniformity, 2% or less is AA, 2% to 3% is A, 3% to 5% is B, and 5% is C, and the C level is too uneven. It is unsuitable as a light.

  Further, when viewed from an oblique direction (a range larger than 0 ° and smaller than 90 ° with respect to the normal direction of the backlight surface), all three observers cannot see the fluorescent tube image at any angle. The case was evaluated as ◯, and the case where a fluorescent tube image could be seen at any angle by one person was evaluated as x.

The backlight configuration for evaluation was as follows.
(Fluorescent tube)
Diameter: 3mm
Number: 8 Adjacent spacing (pitch): 28 mm (= 2a)
Distance between tube center and reflective film (lower side): 4mm
Distance between tube center and member (optical sheet, plate member, etc.) (upper side) 10.7mm (= b)
θ: 52.6 ° (tan θ = a / b = 1.31)
(Reflective film)
Toray Industries, Lumirror (registered trademark) 188E6SL
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
The following coating agent 1 was coated on one side of a 188 μm transparent polyethylene terephthalate film to form a coating film having a thickness of 30 μm.
(Coating 1)
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 Part by mass Pressing a mold with the shape of the stripe lens layer reversed to the surface of the base material coated with the coating 1, and curing the coating by irradiating 1 J / m ² with an ultra-high pressure mercury lamp from the back side of the base The optical sheet having the stripe lens layer on one side was obtained by releasing the mold.

  When the obtained optical sheet was observed for the unit lens cross-sectional shape of the stripe lens layer, the width p was 65 μm and the height h was 13 μm, that is, h / (p / 2) (hereinafter referred to as aspect ratio) was 0.4. The stripe lens layer has a structure in which the arcs are regularly arranged with an arrangement pitch (distance between vertices of adjacent arcs) of 65 μm without gaps. The angle of the hem of the unit lens was 44 °, which was symmetrical with respect to the vertex of the unit lens, and the curvature was constant from the vertex to the hem.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, the light beam intensity distribution was measured, and the diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 34 °, and when the incident angle was 0 °, the diffusion angle was 27 °.

  This optical sheet was incorporated into a backlight unit, and the brightness and uniformity were measured. The structure of the members is a diffusion plate (manufactured by Nitto Jushi Kogyo Co., Ltd., “Clarex” DR-65C), the optical sheet, prism sheet (manufactured by Sumitomo 3M Co., Ltd., “Vicuity” BEFII 90/50), A brightness enhancement sheet (manufactured by Sumitomo 3M Co., Ltd., “Vicuity” DBEF-D400) was used. Here, the optical sheet was installed so that the stripe lens layer faced the direction opposite to the light source, and the stripe direction of the stripe lens layer was parallel to the longitudinal direction of the fluorescent tube of the light source. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Example 2)
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc having a width p of 65 μm, a height h of 14.5 μm, and an aspect ratio h / (p / 2) of 0.45, and the stripe lens layer has the arc. However, there was no gap and the structure was regularly arranged at an arrangement pitch (distance between vertices of adjacent arcs) of 65 μm. The unit lens had a hem angle of 48 °, was symmetrical about the vertex of the cross section, and had a constant curvature from the vertex to the hem.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, and a diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 35 °, and when the incident angle was 0 °, the diffusion angle was 28 °.

  This optical sheet was incorporated into a backlight unit in the same manner as in Example 1, and the luminance and uniformity were measured. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Example 3)
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc having a width p of 65 μm, a height h of 19 μm, and an aspect ratio h / (p / 2) of 0.58, and the stripe lens layer has no gap between the arcs. , And a regular arrangement with an arrangement pitch (distance between vertices of adjacent arcs) of 65 μm. The unit lens had a hem angle of 62 °, was symmetrical about the vertex of the cross section, and had a constant curvature from the vertex to the hem.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, and a diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 38 °, and when the incident angle was 0 °, the diffusion angle was 30 °.

  This optical sheet was incorporated into a backlight unit in the same manner as in Example 1, and the luminance and uniformity were measured. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

Example 4
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc with a width p of 65 μm, a height h of 26 μm, and an aspect ratio h / (p / 2) of 0.8, and the stripe lens layer has no gap between the arcs. , And a regular arrangement with an arrangement pitch (distance between vertices of adjacent arcs) of 65 μm. In addition, the hem angle of the unit lens was 77 °, symmetric about the vertex of the cross section, and the curvature was constant from the vertex to the hem.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, and a diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 36 °, and when the incident angle was 0 °, the diffusion angle was 29 °.

  This optical sheet was incorporated into a backlight unit in the same manner as in Example 1, and the luminance and uniformity were measured. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Example 5)
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc having a width p of 48 μm, a height h of 15.5 μm, and an aspect ratio h / (p / 2) of 0.65, and the stripe lens layer has an arc. There was no gap and the structure was regularly arranged at an arrangement pitch (distance between vertices of adjacent arcs) of 48 μm. The angle of the hem of the unit lens was 73 °, and it was symmetrical with respect to the vertex of the cross section. Further, the height H of the pseudo unit lens obtained by drawing as shown in FIG. 4 was 17.7 μm, and the relationship of H> h was satisfied.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, and a diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 45 °, and when the incident angle was 0 °, the diffusion angle was 34 °.

  This optical sheet was incorporated into a backlight unit in the same manner as in Example 1, and the luminance and uniformity were measured. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Example 6)
An optical sheet is produced in the same manner as in Example 5, and instead of the diffuser plate, the top is rounded on one side surface of “Clarex” DR-85C manufactured by Nitto Resin Kogyo Co., Ltd. Evaluation was performed in the same manner as in Example 5 except that a diffuser plate shaped like a prismatic shape (45 ° hem angle on both sides, pitch 75 μm) was used.

  Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Example 7)
In the same manner as in Example 5, an optical sheet was produced, and a lenticular lens (a semicircle with a radius of 50 μm) was used as a member to be incorporated into a backlight unit, instead of the diffuser plate, on the one-side surface of Kuraray Co., Ltd. The evaluation was performed in the same manner as in Example 5 except that a diffusion plate shaped like) was used.

  Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Example 8)
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc with a width p of 48 μm, a height h of 14.4 μm, and an aspect ratio h / (p / 2) of 0.6, and the stripe lens layer has an arc. There was no gap and the structure was regularly arranged at an arrangement pitch (distance between vertices of adjacent arcs) of 48 μm. The hem angle of the unit lens was 68 °, and it was symmetrical with respect to the vertex of the cross section. Further, the height H of the pseudo unit lens obtained by drawing as shown in FIG. 4 was 16.2 μm, and the relationship of H> h was satisfied.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, and a diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 43 °, and when the incident angle was 0 °, the diffusion angle was 33 °.

  This optical sheet was incorporated into a backlight unit in the same manner as in Example 1, and the luminance and uniformity were measured. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

Example 9
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc having a width p of 48 μm, a height h of 16.8 μm, and an aspect ratio h / (p / 2) of 0.7, and the stripe lens layer has an arc. There was no gap and the structure was regularly arranged at an arrangement pitch (distance between vertices of adjacent arcs) of 48 μm. The hem angle of the unit lens was 75 °, and it was symmetrical with respect to the vertex of the cross section. Further, the height H of the pseudo unit lens obtained by drawing as shown in FIG. 4 was 18.4 μm, and the relationship of H> h was satisfied.

  Next, a light beam was incident from the surface of the optical sheet where the stripe lens layer was not formed, and a diffusion angle was calculated. When the incident angle was 60 °, the diffusion angle was 46 °, and when the incident angle was 0 °, the diffusion angle was 35 °.

  This optical sheet was incorporated into a backlight unit in the same manner as in Example 1, and the luminance and uniformity were measured. Table 1 shows the results of unit lens shape, diffusion angle, and backlight characteristics. As a result, it was found that the backlight unit using the optical sheet of the present invention showed high luminance and high uniformity.

(Comparative Example 1)
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc having a width p of 65 μm, a height h of 6.5 μm, and an aspect ratio h / (p / 2) of 0.2, and the stripe lens layer has the arc. There was no gap and the structure was regularly arranged at an arrangement pitch (distance between vertices of adjacent arcs) of 65 μm. Further, the hem of the unit lens had an angle of 23 °, was symmetrical about the vertex of the cross section, and had a constant curvature from the vertex to the hem.

  When this optical sheet was incorporated in a backlight unit and the brightness and the uniformity were measured, it was found that the optical sheet was inferior to the optical sheet of the present invention.

(Comparative Example 2)
An optical sheet was produced in the same manner as in Example 1 except that the unit lens shape of the stripe lens layer of the optical sheet was produced in the following shape. That is, the cross-sectional shape of the unit lens has an arc having a width p of 65 μm, a height h of 32.5 μm, and an aspect ratio h / (p / 2) of 1, and the stripe lens layer has no gap between the arcs. , And a regular arrangement with an arrangement pitch (distance between vertices of adjacent arcs) of 65 μm. In addition, the hem angle of the unit lens was 90 °, and it was symmetrical about the vertex of the cross section, and the curvature was constant from the vertex to the hem.

  When this optical sheet was incorporated into a backlight unit and the luminance and the uniformity were measured, it was found that the uniformity was inferior to the uniformity when viewed from an oblique direction, resulting in uneven luminance derived from the fluorescent tube image.

  The optical sheet of the present invention can be applied as an optical member that exhibits high screen uniformity and high luminance characteristics by being incorporated in various display devices, particularly a backlight unit of a liquid crystal display device.

It is a figure which shows typically the optical sheet of this invention. It is a figure which shows typically the cross section of the optical sheet of this invention. It is a figure which shows typically the cross section of the optical sheet of this invention. It is a figure which shows typically the cross section of the optical sheet of this invention. It is a figure which shows typically the cross section of the optical sheet of this invention. It is a figure which shows typically the preferable unit lens arrangement | sequence of the optical sheet of this invention. It is a figure which shows typically the preferable laminated structure of the optical sheet of this invention. It is a figure which shows typically the preferable laminated structure of the optical sheet of this invention. It is a figure which shows the calculation method of the diffusion angle of the optical sheet of this invention.

Explanation of symbols

1 Optical sheet
2 unit lens 3 base material 4 angle of hem of unit lens 5 flat portion between adjacent unit lenses 6 unit lens 8 roughened surface 9 light diffusion layer 10 particle 11 transparent base material 12 diffusive base material 20 stripe lens layer

Claims (8)

  An optical sheet having a stripe lens layer on at least one surface of a substrate, the unit lens constituting the stripe lens layer has an arc in a cross-sectional shape in a direction perpendicular to the stripe, An optical sheet in which the ratio h / (p / 2) satisfies 0.4 to 0.8 when the width is p and the height is h.   The optical sheet according to claim 1, wherein an angle of a bottom of the arc is 45 ° to 90 °.   A circle that is in contact with any of the two tangents at the hems (A and B) on both sides of the arc is drawn, and the shape formed by the shorter arc AB and line segment AB is regarded as a pseudo unit lens. The optical sheet according to claim 1 or 2, wherein the height H of the pseudo unit lens satisfies H> h.   The optical sheet according to claim 1, wherein one surface of the substrate has a stripe lens layer and the other surface is roughened.   In the unit lens, in a plane perpendicular to the stripe, when a light beam is incident from one surface of the sheet at an incident angle of 60 °, a diffusion angle of a light beam intensity distribution emitted from the other surface of the sheet is 30 °. The optical sheet according to any one of claims 1 to 4, satisfying -50 °.   The unit lens has a diffusion angle of a light emission intensity distribution emitted from the other surface of the sheet when a light beam is incident at an incident angle of 60 ° from one surface of the sheet in a plane perpendicular to the stripe. The optical sheet according to claim 1, wherein the optical sheet is larger than a diffusion angle when a light beam is incident at an angle of 0 °.   The backlight unit using the optical sheet in any one of Claims 1-6.   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 On the upper side of the light source, the optical sheet according to any one of claims 1 to 6 is installed so that the direction parallel to the linear portion of the light source and the stripe of the stripe lens are parallel. The backlight unit according to claim 7.

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