JP5228314B2 - Diffusion sheet and backlight unit using the same - Google Patents

Description

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

  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 structure 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 milky white plate having extremely strong light diffusibility is installed on the upper side of the fluorescent tube to make the screen uniform (Patent Document 1). The milky white plate is a light diffusion plate made of an acrylic resin, a polycarbonate resin, or the like in which fine particles are dispersed. This milk white plate eliminates tube unevenness and makes the screen uniform, but because it diffuses strongly, the total light transmittance is low and the light utilization efficiency deteriorates, and it is too strong to diffuse light in an unnecessary direction. As a result, the required front brightness is insufficient. Therefore, a diffusion sheet showing a light collecting effect in the front direction is installed on the milky white plate while diffusing light isotropically (Patent Document 2). This diffusion sheet is a sheet in which a diffusion layer containing fine particles such as organic cross-linking particles is formed on a base sheet, and is an optical film that exhibits directivity in the front direction to some extent, unlike a milky white plate. In addition to these, there are a reflective film that reflects the light emitted backward from the fluorescent tube, a prism sheet for improving the light collecting property, a brightness improving sheet that exhibits a polarization separation function and improves the light utilization efficiency, and the like. Incorporated.
JP 2004-29091 A JP 2001-324607 A

  In direct-type backlights, it is necessary to eliminate tube unevenness originating from the fluorescent tube at the back of the screen and to achieve both screen uniformity and high brightness. However, the milky white plate used to eliminate tube unevenness has low total light transmittance and poor light utilization efficiency. In addition, an extremely inefficient configuration is adopted in which the light scattered too much by the milky white plate is condensed again using a diffusion sheet. Furthermore, the milky white plate has a thickness of 2 to 3 mm, which hinders thinning and weight reduction.

  Therefore, in view of the background of such conventional technology, the present invention is intended to provide a diffusion sheet excellent in the isotropic diffusion effect of light.

  That is, according to the present invention, the diffusion sheet can exhibit an efficient diffusion effect, thereby exhibiting screen uniformity and high luminance characteristics, and achieving a reduction in thickness of the backlight unit. It plays.

The present invention employs the following means in order to solve such problems. That is, in the diffusion sheet of the present invention, the ratio (Gmax / Gmin) between the maximum value Gmax and the minimum value Gmin of the 60 ° glossiness is formed on at least one surface of the internal diffusion sheet configured to contain diffusion elements inside the matrix resin. ) Is less than 1.1, and the glossiness minimum value Gmin is 1 to 50, a surface layer not containing a diffusing element is laminated, and the surface of the other surface of the internal diffusion sheet has a 60 ° gloss the ratio of the maximum value Gmax and the minimum value Gmin of time (Gmax / Gmin) is Ri der less than 1.1, and a feature that the resin layer is a biaxially oriented sheet on both sides of the internal diffusion sheet are laminated To do.

Furthermore, the diffusion sheet of the present invention preferably comprises the following features (1) to (9).
( 1 ) The said resin layer is comprised from the thermoplastic resin which has a polyester-type resin as a main component.
( 2 ) The matrix resin is composed of a thermoplastic resin whose main component is a polyester resin.
( 3 ) The total light transmittance of the diffusion sheet is 50 to 95%.
( 4 ) The total film thickness of the diffusion sheet is 25 to 500 μm.
( 5 ) On the surface where the minimum value Gmin of 60 degree glossiness satisfies 1 to 50, the minimum value Gmin85 of 85 degree glossiness is smaller than the minimum value of 60 degree glossiness.
( 6 ) The minimum value Gmin85 of 85 degree glossiness is 2 or less.
( 7 ) An uneven shape is formed on the surface satisfying the minimum value Gmin of 60 degree glossiness of 1 to 50, and the cross-sectional aspect ratio of the cross section of the uneven shape is 0.25 or more.

  The backlight unit using the diffusion sheet of the present invention includes at least a plurality of linear light sources in a substantially parallel arrangement and / or a light source having a plurality of linear portions in a substantially parallel arrangement and / or a substantially parallel light source. The diffusion sheet is installed on the upper side of a light source in which brightness and darkness are observed in a linear shape of the array.

  ADVANTAGE OF THE INVENTION According to this invention, the diffusion sheet which exhibits the isotropic diffusion effect of light efficiently can be provided, By incorporating this in the backlight unit of a liquid crystal display device, high screen uniformity and a high luminance characteristic are obtained. It is possible to achieve both compatibility and achieve further reduction in thickness.

  The present invention, as a result of intensive studies on the above-mentioned problem, that is, a diffusion sheet excellent in the isotropic diffusion effect of light, is composed of an internal diffusion sheet that includes a diffusion element inside the matrix resin, and the surface of the diffusion sheet. As a result of satisfying a specific glossiness condition, the inventors have found that such problems can be solved all at once. That is, on the surface of the diffusion sheet, the ratio (Gmax / Gmin) of the maximum value Gmax and the minimum value Gmin of 60 degree glossiness is less than 1.1, and at least the minimum gloss value Gmin on one side surface is 1 to 1. As a result of engraving and deforming to a specific surface shape of 50, a diffusion sheet that successfully accomplishes the above-mentioned problems has been completed.

The diffusion sheet of the present invention is an internal diffusion sheet configured to contain a diffusion element inside the matrix resin, and the ratio (Gmax / Gmin) of the maximum value Gmax and the minimum value Gmin of 60 degree gloss is less than 1.1. And the surface layer which does not contain a diffusing element and the minimum value Gmin of the glossiness is 1 to 50 is laminated, and the ratio between the maximum value Gmax and the minimum value Gmin of the 60 ° glossiness on the other surface (Gmax / Gmin) Is formed by laminating surface layers having a thickness of less than 1.1.

  The 60-degree glossiness referred to in the present invention is a value defined by reflection of light incident on the sheet surface, and can be measured based on the method defined in JIS Z8741. That is, the 60 degree glossiness is a value expressed as a percentage of the ratio of the specularly reflected light to the incident light when light is incident on the measurement surface at an incident angle of 60 degrees. In the present invention, 60 degree glossiness is first measured at an arbitrary measurement position, and the sheet is rotated 360 degrees in steps of 10 degrees around the measurement position and measured in each direction. Among the obtained measurement values (60 degree glossiness), the maximum value is defined as Gmax and the minimum value is defined as Gmin.

When the ratio (Gmax / Gmin) between the maximum value Gmax and the minimum value Gmin of the 60 ° glossiness obtained in this way is less than 1.1, the light rays incident on the surface are substantially the same regardless of the incident direction. In addition, the fact that the minimum value Gmin on the surface of the surface layer is 1 to 50 is satisfied at the same time, so that the incident light beam exhibits substantially the same light diffusion characteristic regardless of the incident direction, that is, etc. This shows the diffusivity of the direction.

  In the present invention, by using such a diffusion sheet exhibiting isotropic diffusivity, when incorporated in a backlight unit of a liquid crystal display device, a substantially constant brightness can be ensured regardless of the direction. Even in combination, it is easy to maintain in-plane uniformity. That is, it is important and essential that the ratio (Gmax / Gmin) satisfy less than 1.1.

  In the present invention, the absolute value of the glossiness means adjustment of the light emission characteristic of the diffusion sheet, that is, the light distribution characteristic. When the diffusion sheet of the present invention is incorporated in a backlight unit, it is preferable that a surface with a specified glossiness be provided on the light exit surface side, thereby enabling adjustment of light distribution characteristics. The adjustment of the light distribution characteristic is to convert the light beam diffused by the internal diffusion sheet into a desired state.

  For example, when it is isotropically diffused by the internal diffusion sheet, it is almost completely isotropically diffused due to the diffusion by the internal structure, and the rate of emission in the front direction is reduced. Therefore, by providing a surface defined by a glossiness of 1 to 50 on the light exit surface side, a condensing effect in the front direction is exhibited and front luminance is improved. In addition, the backlight unit is used by being overlapped with other optical sheets such as a bead sheet and a prism sheet, but when combined with the diffusion sheet of the present invention having a surface satisfying this gloss range, the light use efficiency is increased. Efficient diffusion and light collection effects are exhibited. Moreover, when it diffuses anisotropically with an internal diffusion sheet, the said effect expresses with the conversion to isotropic diffusion by the surface.

  Here, when the glossiness minimum value Gmin exceeds 50, the surface diffusion effect is insufficient, and it is unfavorably influenced by the diffusibility of the internal diffusion sheet. When the glossiness measured at 60 ° is less than 1, Since it is a special shape corresponding to 60 ° and an isotropic diffusion effect cannot be obtained, it is not preferable. A more preferable range of the glossiness minimum value Gmin is 5 to 40, more preferably 5 to 30.

In the diffusion sheet of the present invention, the surface where the ratio (Gmax / Gmin) of the maximum value Gmax to the minimum value Gmin of 60 degree gloss is less than 1.1, and at least the minimum value Gmin on the surface of the surface layer is 1 to 50 However, any shape can be preferably used as long as it satisfies the above conditions.

  FIG. 1 shows an example of a surface pattern (FIG. 1A) and a cross-sectional shape (FIG. 1B), which is an example in which hemispherical protrusions are formed on the surface.

  As shown in FIG. 2, the pattern formed on the surface is one in which the individual protrusions are regularly arranged in a two-dimensional direction (FIGS. 2A and 2B), or one in which the protrusions are randomly arranged ( Fig. 2 (c)), and protrusions of different sizes or shapes are mixed and regularly or randomly arranged (Fig. 2 (d)). A state where there is almost no or little isotropic is preferable in order that the ratio (Gmax / Gmin) satisfies less than 1.1. In addition, a shape in which the ratio of the length to width in the plane of each protrusion (aspect ratio) is extremely greater than 1, for example, in the case of FIG. It is not preferable that the ratio (Gmax / Gmin) satisfies less than 1.1.

  That is, in the diffusion sheet of the present invention, as a preferable sheet in-plane pattern for making the ratio (Gmax / Gmin) of the maximum value Gmax and the minimum value Gmin of the 60 ° glossiness less than 1.1, the surface of each protrusion The inner arrangement is a regular or random arrangement having no anisotropy, and the in-plane shape of each protrusion is a shape satisfying a ratio of length and width (aspect ratio) of 1 to 1.1. . For example, the pattern shown in FIG. 2 is one of the most preferable shapes. However, for example, even if there is a partially anisotropic arrangement or there is a protrusion with an in-plane aspect ratio exceeding 1.1, the characteristics are exhibited if the above conditions are satisfied for the entire diffusion sheet. Therefore, it is not excluded.

  In addition, as shown in FIG. 3, the sectional shape of each protrusion is hemispherical (FIG. 3A), bell-shaped (FIG. 3B), triangular pyramid (FIG. 3C), polygonal pyramid. A cylindrical shape (FIG. 3 (d)), an indefinite shape (FIG. 3 (e)), a circular shape (FIG. 3 (f)), or the like is preferably used. In the case of the circular shape in FIG. 3 (f), specifically, it is a case where spherical particles are arranged on the film surface or the like, but it is possible to arrange only the particles or fill the voids formed between the particles with resin. May be. FIG. 3 shows a state where adjacent protrusions are formed as a continuous pattern except for FIG. It is also a preferable aspect that the individual protrusions are arranged at intervals, but if the flat portion between adjacent protrusions increases, the light incident on the diffusion sheet passes through as it is, and this region is excessively large. And sufficient diffusivity may not be obtained. Therefore, an arrangement in which the individual protrusions are adjacent to each other or an arrangement in which the protrusions are continuously connected by a smooth curve as typified by FIG. 3B is preferable. These shapes can be appropriately selected depending on the light distribution characteristics of the required diffusion sheet. However, in order to improve the luminance, those having a larger aspect ratio of the individual protrusion cross-sectional shapes are preferable as will be described later. .

  The arrangement pitch and height are not particularly defined as long as they satisfy the glossiness condition, but preferred ranges are shown below. When the arrangement pitch is defined as the distance between the tops of adjacent patterns, 0.5 to 300 μm is preferable, and 1 to 200 μm is more preferable. Here, when adjacent patterns are arranged at intervals, the arrangement pitch is set to the base length of each protrusion. Moreover, about protrusion height, it prescribes | regulates as the distance of the thickness direction from the straight line which connects a recessed part lowest point, and a top part, 0.5-200 micrometers is preferable, More preferably, it is 1-150 micrometers.

  Here, in the diffusion sheet of the present invention, in order to obtain a surface having a minimum value Gmin of 60 degree glossiness of 1 to 50, each protrusion cross-sectional shape is determined by the protrusion height and the arrangement pitch (or base length). The ratio (projection height / arrangement pitch, hereinafter referred to as cross-sectional aspect ratio) is preferably 0.25 or more, and more preferably 0.5 or more. The surface shape having a cross-sectional aspect ratio of 0.25 or more is a shape extending in the thickness direction of the film, and by giving such a shape, the light incident on the diffusion sheet is condensed and the front luminance is increased. It becomes diffusive while raising. When the cross-sectional aspect ratio is less than 0.25, a diffusion effect can be obtained, but sufficient light condensing performance cannot be exhibited, and the luminance improvement effect is small.

  The arrangement pitch, height, shape, etc. are preferably used in any case where they change in a plane, regularly or randomly. In order to reduce coloring due to light diffraction and interference, randomization is preferable.

  In the diffusion sheet of the present invention, the minimum value Gmin85 of 85 degree glossiness is preferably smaller than the minimum value Gmin of 60 degree glossiness on the surface where the minimum value Gmin of 60 degree glossiness satisfies 1 to 50. . Here, the measurement of the 85 degree glossiness and the method of obtaining the minimum value Gmin85 are obtained by measuring in the same manner as the 60 degree glossiness except that the measurement angle at the time of glossiness measurement is changed to 85 degrees.

  Here, since the 85 degree glossiness has a larger incident angle than the 60 degree glossiness, the 85 degree glossiness is easily influenced by the height of the surface irregularities, and a pattern extending higher in the film thickness direction is formed. When the ratio is high, the glossiness is smaller than when the ratio is 60 degrees. That is, by making the minimum value Gmin85 of 85 degree glossiness smaller than the minimum value Gmin of 60 degree glossiness, a preferable shape for achieving high brightness and high diffusibility can be obtained.

  Moreover, it is preferable that the minimum value Gmin85 of 85 degree | times glossiness is 2 or less in the surface where the minimum value Gmin of 60 degree | times glossiness satisfies 1-50 in the diffusion sheet of this invention. By setting this value to 2 or less, it can be seen that a steep shape is formed on the surface of the diffusion sheet, which is a more preferable mode for achieving an improvement in luminance.

  In addition, it is an essential requirement that the diffusion sheet of the present invention is composed of an internal diffusion sheet containing a diffusion element inside the matrix resin.

  Examples of the diffusion element used in the internal diffusion sheet 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 diffusion element, 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 diffusing element used in the diffusion sheet of the present invention is preferably an average primary particle size of 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 smaller than 0.5 μm, a sufficient light diffusing action as a diffusing element cannot be obtained in the visible light region of 380 to 780 nm, and when it exceeds 50 μm, an effective light diffusing action is obtained. For this reason, the thickness of the internal diffusion sheet becomes too thick and it is not preferable because it cannot be thinned.

  Further, the shape of the diffusing element is not particularly limited, and any of spherical (including true spherical), spheroid, rod, needle, flat, and amorphous can be preferably used. In the present invention, as for the particle diameter in a shape other than a true sphere, the length of the narrowest portion only needs to satisfy the above range.

  Further, the amount of diffusion element added to the internal diffusion sheet varies depending on the refractive index, particle size, shape, and the like of the diffusion element, and thus is appropriately set according to the required performance. It is preferable to add in the range of -50 mass%, More preferably, it is 0.01-30 mass%, Most preferably, it is 0.1-30 mass%.

  Examples of the matrix resin used for the internal diffusion sheet constituting the diffusion sheet of the present invention include, for example, polyethylene terephthalate, polyethylene-2, 6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, cyclohexanedimethanol copolymerized polyester resin, and isophthalic acid. Polyester resins such as copolyester resins, spiroglycol copolyester resins, and fluorene copolyester resins, polyolefin resins such as polyethylene, polyprepylene, polymethylpentene, and alicyclic olefin copolymer resins, and acrylics such as polymethyl methacrylate Resin, polycarbonate, polystyrene, polyamide, polyether, polyesteramide, polyetherester, polyvinylchloride, and Min to the copolymer, or include thermoplastic resins such as a mixture of these resins, are preferably used without any particular limitation.

  In addition to the thermoplastic resin, a photocurable resin and a thermosetting resin can also be preferably used.

  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.

As the matrix resin of the internal diffusion sheet, any combination of these thermoplastic resins, photocurable resins, and thermosetting resins may be used.
In addition to the diffusion element and the matrix resin, it is also a preferable aspect that various additives are added to the internal diffusion sheet. As the additive, for example, a dispersant, a compatibilizing agent, a pigment, a dye, a fluorescent brightening agent, an antioxidant, a heat resistance agent, a light resistance agent, a weather resistance agent and the like are preferably used, but the effect as a diffusion sheet is not hindered. Within the range, additives other than these are also preferably used.

Diffusion sheet of the present invention is I seat der containing at least internal diffusion sheet, since composed of two or more layers of the laminate including the inside diffusion sheet. Hereinafter, a preferable sheet configuration will be described.

  FIG. 4 shows a case where a shape satisfying the condition that the ratio (Gmax / Gmin) is less than 1.1 and Gmin is 1 to 50 is formed on one side. In any case, the surface shape is an example.

FIG. 4A illustrates the case where the diffusion sheet as a reference example is a single film made only of an internal diffusion sheet.

  4 (b) to 4 (f), a support layer containing an internal diffusion sheet, and a surface layer in which the ratio (Gmax / Gmin) of the maximum value Gmax to the minimum value Gmin of 60 ° gloss is less than 1.1. The structure of the preferable laminated body which consists of is illustrated. 4B and 4C show a diffusion sheet in which a surface layer satisfying the glossiness condition is laminated on one side of the internal diffusion sheet. As shown in FIG. 4B, each pattern may be formed as an isolated discontinuous layer in the cross section, or as shown in FIG. 4C so as to cover the entire inner diffusion sheet surface. May be. In order to prevent detachment of the diffusing element from the internal diffusion sheet and to improve the adhesion of the pattern, it is preferable to cover it as shown in FIG.

  Moreover, as shown in FIG.4 (d), the structure which laminated | stacked the resin layer on both sides of the internal diffusion sheet is also a preferable aspect. Lamination on both sides is preferable because it improves the mechanical strength of the internal diffusion sheet and prevents detachment of the diffusion element from the internal diffusion sheet. When laminating on both sides, it is preferable to laminate with the same film thickness in order to balance the thermal or mechanical properties of the front and back surfaces.

For the resin layer to be laminated, the same thermoplastic resin, photocurable resin, and thermosetting resin as the matrix resin of the internal diffusion sheet are preferably used, and the additives that are preferably used are also the same. The diffusion element is one viewpoint et containing no de-sense preventing from the surface.

  In the diffusion sheet of the present invention, a configuration in which biaxially stretched sheets are laminated is also preferable. As shown in FIG. 4 (e), laminating biaxially stretched sheets is preferable because mechanical strength and heat resistance are improved. Furthermore, it is preferable to laminate a biaxially stretched sheet on both sides of the internal diffusion sheet. Lamination on both sides improves the mechanical strength and heat resistance in a well-balanced manner, and lamination is preferably used on both sides, particularly when the diffusion sheet is thinned (FIG. 4 (f)). The resin used for the biaxially stretched sheet is not particularly limited, but is a polyester such as polyethylene terephthalate, polyethylene-2, 6-naphthalate, a copolymer with other components based on these, or a mixture thereof. System resins are preferably used from the viewpoints of mechanical strength, heat resistance, dimensional stability, and the like.

  Among these, the most preferable sheet configuration is preferably an internal diffusion sheet in which biaxially stretched sheets are laminated on both sides and a laminate composed of a surface layer that satisfies the glossiness condition because all of the above-mentioned merits can be covered. When a polyester-based resin is selected as the biaxially stretched sheet, it is preferable that the matrix resin of the internal diffusion sheet has a polyester-based resin as a main component in consideration of stackability and adhesiveness.

  Further, it is also a preferable aspect that a surface satisfying the above-mentioned glossiness condition is also formed on the lower surface shown as a flat surface in FIG. In addition, various other shapes can be imparted, and the mat layer, antistatic layer, antireflection layer and the like for preventing adhesion are preferably used without particular limitation.

  The total thickness of the diffusion sheet of the present invention is preferably 25 to 500 μm. When the film thickness is less than 25 μm, the sheet handling property is lowered, which is not preferable. A sheet having a film thickness exceeding 500 μm is preferably 500 μm or less from the viewpoint of reducing the thickness of the entire backlight unit, although a sheet preferable in terms of diffusibility can be obtained. Moreover, it is preferable that the surface layer lamination | stacking ratio at the time of laminating | stacking a biaxially stretched sheet on both sides which is the most preferable structure is 5% or more of one side. 5% or more is preferable because the rigidity and heat resistance of the entire sheet are improved.

  The diffusion sheet of the present invention preferably has a total light transmittance of 50 to 95%. When the total light transmittance satisfies this range, it is preferable because the light utilization efficiency can be increased and the brightness of the screen can be increased when incorporated in a backlight unit of a liquid crystal display device.

  The diffusion sheet of the present invention preferably has a haze of 50 to 95% as a whole. Haze is one of the indicators for evaluating the light diffusibility of the diffusion sheet. In order to achieve good screen uniformity when the diffusion sheet of the present invention is used, the haze value should satisfy the above range. preferable. Moreover, although the haze in an internal diffusion sheet single-piece | unit can be adjusted according to the diffusibility calculated | required as the whole diffusion sheet, it is used in 20 to 95% of range, for example.

  Although the method for producing the diffusion sheet of the present invention will be described, the present invention is not limited to these methods, and other methods are also preferably used. Below, the formation method of an internal diffusion sheet and the surface formation method to obtain the required glossiness will be described.

  As for the method of forming the internal diffusion sheet, for example, (1) a method in which a matrix resin in which diffusion elements are dispersed is melt-extruded and formed into a sheet, and (2) a coating material containing diffusion elements, matrix resin, and solvent is used as a base material. (3) A method in which a liquid matrix resin in which a diffusing element is dispersed is cast on a substrate, and then the matrix resin is cured by active energy rays or heat. , Etc.

  Among these, the method (1) is preferable because it is possible to produce a laminate at a stretch by laminating and extruding, and further to produce a biaxially stretched sheet layer all at once by applying a stretching process after extrusion. Is the method.

  Further, as for the surface forming method for obtaining the desired glossiness, (a) a mold transfer method using a mold, (b) a method of directly processing the surface, (c) a method of coating a coating material containing particles, (D) A method of bonding woven fabrics and the like can be mentioned.

  (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 of processing a sheet having a photocurable resin laminated on the surface into a desired shape using a technique such as lithography or a light interference exposure method.

  Moreover, (c) As a method of coating the coating agent containing particle | grains, it forms by coating the coating agent containing an organic or inorganic spherical particle, binder resin, a solvent, etc. by various methods, and removing a solvent. The method etc. are mentioned.

  Further, (d) as a method of laminating the woven fabric, there may be mentioned a method of laminating a woven fabric with controlled warp and weft diameter, density, shape, etc. on the substrate.

  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.

  The backlight unit using the diffusion sheet of the present invention includes at least a plurality of linear light sources in a substantially parallel arrangement and / or a light source having a plurality of linear portions in a substantially parallel arrangement and / or a substantially parallel light source. The diffusion sheet of the present invention is installed on the upper side of the light source where light and darkness is observed in a linear array.

FIG. 5 shows a configuration example of the direct type backlight unit.
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. Also, normally, by installing a reflective sheet under these light sources, it is possible to improve the brightness by reflecting the rays escaping to the back side to the screen side. However, the light source covers the entire bottom surface of the unit. It is not necessary in some cases. Moreover, in the backlight unit of this invention, it is also a preferable aspect that the diffusion sheet of this invention is further installed on the said diffusion sheet.

  Further, it is preferable to use a combination of optical sheets such as a bead sheet, a prism sheet, and a brightness enhancement sheet on the upper side of the diffusion sheet of the present invention. A liquid crystal cell is installed above these optical sheets.

  In the diffusion sheet of the present invention, the surface satisfying the minimum value Gmin of 60 degree glossiness of 1 to 50 may face either the fluorescent tube side or the liquid crystal cell side, but in order to improve the luminance It is preferable to face the liquid crystal cell side.

  Below, the measuring method and evaluation method of each Example and a comparative example are demonstrated. In the following measurements, the surface of each sample on which the mold processing is applied is the front surface, and the opposite surface is the back surface. Moreover, about the comparative example 1, since the metal mold | die process is not given to any surface, let the surface where the coating material 1 is applied be the surface, and let the surface on the opposite side be a back surface.

(Measurement and evaluation method)
A. Glossiness Using a digital variable angle gloss meter UGV-5B manufactured by Suga Test Instruments Co., Ltd., on both sides of a sample cut into a 50 mm square, an incident angle of 60 degrees, a light receiving angle of 60 degrees (60 degree glossiness), and an incident angle It was measured according to JIS Z8741 at 85 degrees and a light receiving angle of 85 degrees (85 degree glossiness). The measurement is first performed at an arbitrary measurement position, the sheet is rotated 360 degrees in steps of 10 degrees around the measurement position, the measurement is performed in each direction, the maximum value of the obtained measurement value is Gmax, and the minimum value is Gmin. It was.

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 50 mm square and set so that light was incident from the back side of the sample.

C. Screen uniformity and luminance characteristics Evaluation 11.5 (170mm x 235mm: diagonal 290mm) inch direct type backlight (housing, reflection film, fluorescent tube part) is lit at 12V, and after 1 hour, fluorescent tube The diffusion sheet (175 mm × 240 mm) of the present invention is stacked on the upper side, and a diffusion sheet (Kimoto Co., Ltd., 188GM3: transmittance 75%, haze 89%), prism sheet (Sumitomo 3M, BEFII90) / 50) was installed, and brightness and brightness unevenness in the front direction were measured using a brightness unevenness analyzer Eye-Scale3 manufactured by I-System Co., Ltd. Here, the prism sheet was installed so that the prism row was parallel to the longitudinal direction of the fluorescent tube. The measurement position was performed on a line passing through the center of the backlight and perpendicular to the longitudinal direction of the fluorescent tube. Moreover, the diffusion sheet was installed so that the surface might be on the opposite side of the fluorescent tube, and measurement was performed from the surface.

The luminance was evaluated as an average value at the measurement position. The screen uniformity was calculated from the ratio between the maximum value and the minimum value obtained at the measurement position using the following formula.
・ Luminance unevenness (%) = 100 × (maximum value−minimum value) ÷ minimum value For luminance unevenness, 1.5% or less is AA, 3% or less is A, 5% or less is B, and 5% is exceeded. C indicates that the unevenness is too large at the C level and is not suitable as a backlight.

The details of the evaluation backlight configuration are as follows.
(Fluorescent tube)
Diameter: 2mm
Number: 8 Adjacent spacing: 2cm
Distance from reflector (lower side): 8mm
Distance from diffusion sheet (upper side) 25mm
(Reflective sheet)
Lumirror (registered trademark) 188E60L manufactured by Toray Industries, Inc.

  All of the above measurements were performed at room temperature of 23 ° C.

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

Example 1
In the main extruder, 12 mass% of PET, 58 mass% of polyester resin copolymerized with 17 mol% of isophthalic acid component in PET, 30 mass% of polyester resin copolymerized with 33 mol% of cyclohexanedimethanol in PET, diffusion A chip mixed with 9% by mass of polymethylpentene is supplied as an element (B layer), and PET is supplied to a sub-extruder (A layer), and three-layer lamination melt extrusion is performed at 280 ° C. (A / B 3 layers of / A, lamination ratio 1/8/1), cast onto a mirror drum cooled to 25 ° C. while electrostatically applied to produce an extruded sheet. This sheet was preheated with a group of rolls heated to 90 ° C., and stretched 3.5 times in the longitudinal direction at 95 ° C. Thereafter, the sheet edge was held by a clip and introduced into a tenter heated to 95 ° C., preheated for 5 seconds, and then continuously stretched 3.5 times in the width direction in an atmosphere at 110 ° C. Further, heat treatment was continuously performed in an atmosphere at 235 ° C. for 20 seconds to produce an internal diffusion sheet having a film thickness of 125 μm.
Next, the following coating agent was coated on one side of the obtained sheet, heat-treated at 80 ° C. for 15 minutes, and the solvent was dried to form a surface layer (film thickness 40 μm).
(Coating 1)
Polyester resin OKP-4 (Osaka Gas Chemical Co., Ltd.) 20 parts by mass Methyl ethyl ketone 40 parts by mass Cyclohexanone 40 parts by mass

Next, the following mold 1 and substrate 1 were heated at 155 ° C. for 2 minutes, and the mold and the coating surface of the substrate 1 were pressure-bonded for 2 minutes at 2 MPa while maintaining 155 ° C. Subsequently, after cooling to 70 ° C., the mold was released to obtain a diffusion sheet having the following surface shape pattern on the coating surface.
(Mold 1)
In-plane pattern: Fig. 2 (a)
Individual shape: hemispherical depression (radius 20 μm)
Pitch between adjacent patterns: 45 μm.
The obtained diffusion sheet had a good pattern in which the mold shape was reversed.
When the 60 ° glossiness was measured on the surface to which the mold shape was transferred, the maximum value Gmax21.5 and the minimum value Gmin20.4 in the plane were found (ratio Gmax / Gmin = 1.05).
When this diffusion sheet was incorporated into a backlight for evaluation and luminance and luminance unevenness were evaluated, the luminance unevenness was small and good screen uniformity and high luminance were achieved, and the unit was thinned. The luminance characteristic evaluation results are shown in Table 1.

(Example 2)
In the main extruder, 12 mass% of PET, 58 mass% of polyester resin copolymerized with 17 mol% of isophthalic acid component in PET, 30 mass% of polyester resin copolymerized with 33 mol% of cyclohexanedimethanol in PET, diffusion A chip mixed with 7% by mass of polymethylpentene was supplied as an element (B layer), and PET was supplied to the sub-extruder (A layer), and three-layer lamination melt extrusion was performed at 280 ° C. (A / B 3 layers of / A, lamination ratio 1/8/1), cast onto a mirror drum cooled to 25 ° C. while electrostatically applied to produce an extruded sheet. This sheet was preheated with a group of rolls heated to 90 ° C., and stretched 3.5 times in the longitudinal direction at 95 ° C. Thereafter, the sheet edge was held by a clip and introduced into a tenter heated to 95 ° C., preheated for 5 seconds, and then continuously stretched 3.5 times in the width direction in an atmosphere at 110 ° C. Further, a heat treatment was continuously performed for 20 seconds in an atmosphere at 235 ° C. to produce an internal diffusion sheet having a thickness of 150 μm.
Next, the following coating agent 2 was coated on one side of the obtained sheet to form a surface layer having a thickness of 30 μm, whereby a substrate 2 was obtained.
(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 following mold 2 is pressed against the surface of the base material 2 coated with the coating agent ^{2 and} irradiated with 1 J / m ² from the back side of the base material 2 with an ultrahigh pressure mercury lamp to cure the coating material, and the mold is released. Thus, a diffusion sheet having a pattern having the following surface shape on the coating surface was obtained.
(Mold 2)
In-plane pattern: Fig. 2 (a)
Individual shape: hemispherical depression (radius 15 μm)
Pitch between adjacent patterns: 40 μm.
The obtained diffusion sheet had a good pattern in which the mold shape was reversed.
When the 60-degree glossiness was measured on the surface to which the mold shape was transferred, the maximum value Gmax 35.6 and the minimum value Gmin35.1 in the plane were found (ratio Gmax / Gmin = 1.01).
When this diffusion sheet was incorporated into a backlight for evaluation and luminance and luminance unevenness were evaluated, the luminance unevenness was small and good screen uniformity and high luminance were achieved, and the unit was thinned. The luminance characteristic evaluation results are shown in Table 1.
(Example 3)
In Example 1, a diffusion sheet was obtained in the same manner as in Example 1 except that the following mold 3 was used instead of the mold 1.
(Mold 3)
In-plane pattern: Fig. 2 (a)
Individual shape: oval depression (minor axis 15 μm: surface direction, major axis 20 μm: thickness direction)
Pitch between adjacent patterns: 33 μm.
The obtained diffusion sheet had a good pattern in which the mold shape was reversed.
When the 60 ° glossiness was measured on the surface to which the mold shape was transferred, the maximum value Gmax10.3 and the minimum value Gmin9.7 in the surface were found (ratio Gmax / Gmin = 1.06).

  When this diffusion sheet was incorporated into a backlight for evaluation and luminance and luminance unevenness were evaluated, the luminance unevenness was small and good screen uniformity and high luminance were achieved, and the unit was thinned. The luminance characteristic evaluation results are shown in Table 1.

( Reference example )
In an extruder, 12% by mass of PET, 58% by mass of a polyester resin obtained by copolymerizing 17 mol% of an isophthalic acid component with PET, 30% by mass of a polyester resin obtained by copolymerizing 33 mol% of cyclohexanedimethanol with PET, a diffusion element A chip mixed with 9% by mass of polymethylpentene is supplied, melt extruded at 280 ° C. (single layer sheet), cast on a mirror drum cooled to 25 ° C. while electrostatically applied, and a film thickness of 500 μm. An internal diffusion sheet was prepared.

Next, the mold 3 and the substrate were heated at 110 ° C. for 2 minutes, and the mold 3 and the substrate were pressure-bonded for 1 minute at a pressure of 2 MPa while maintaining 110 ° C. Subsequently, after cooling to 60 ° C., the mold was released to obtain a diffusion sheet having a pattern in which the mold shape was reversed. Here, the whole base material was deformed and compressed by thermocompression bonding, and the film thickness was 230 μm.
When this diffusion sheet was incorporated into a backlight for evaluation and luminance and luminance unevenness were evaluated, the luminance unevenness was small and good screen uniformity and high luminance were achieved, and the unit was thinned. The luminance characteristic evaluation results are shown in Table 1.
(Example 4 )
In the main extruder, 21 mass% of PET, 52 mass% of polyester resin copolymerized with 17 mol% of isophthalic acid component in PET, 27 mass% of polyester resin copolymerized with 33 mol% of cyclohexanedimethanol in PET, diffused A chip mixed with 9% by mass of polymethylpentene is supplied as an element (B sheet), and PET is supplied to a sub-extruder (A sheet), and three sheet lamination melt extrusion is performed at 280 ° C. (A / B) / A three sheets (lamination ratio 15/70/15), cast onto a mirror drum cooled to 25 ° C. while electrostatically applied to produce an extruded sheet. This sheet was preheated with a group of rolls heated to 90 ° C., and stretched 3.5 times in the longitudinal direction at 95 ° C. Thereafter, the sheet edge was held by a clip and introduced into a tenter heated to 95 ° C., preheated for 5 seconds, and then continuously stretched 3.5 times in the width direction in an atmosphere at 110 ° C. Further, a heat treatment was continuously performed for 20 seconds in an atmosphere at 235 ° C. to produce a sheet having an internal diffusion sheet with a film thickness of 188 μm.
Next, the coating agent 1 was coated on one side of the obtained sheet, heat-treated at 80 ° C. for 15 minutes, and the solvent was dried to form a surface layer (film thickness 30 μm) to obtain a substrate.
Subsequently, the following mold 5 and the substrate were heated at 160 ° C. for 2 minutes, and the mold 5 and the coating surface of the substrate were pressure-bonded for 2 minutes at a pressure of 2 MPa while maintaining 160 ° C. Subsequently, after cooling to 70 ° C., the mold was released to obtain a diffusion sheet having a pattern in which the following shape was reversed on the coating surface.
(Mold 5)
In-plane pattern: Fig. 2 (a)
Individual shape: Upper 1/5 of a hemisphere with a radius of 25 μm
(Height 5 μm, base 30 μm)
Pitch between adjacent patterns: 40 μm.
This diffusion sheet was incorporated into a backlight for evaluation, and luminance and luminance unevenness were evaluated. The luminance characteristic evaluation results are shown in Table 1.
(Examples 5 to 6 )
In Example 4 , a diffusion sheet was prepared in the same manner except that the following mold 6 (Example 5 ) and mold 7 (Example 6 ) were used, and the diffusion sheet was incorporated into an evaluation backlight to obtain luminance and luminance unevenness. evaluated. The luminance characteristic evaluation results are shown in Table 1.
(Mold 6)
In-plane pattern: Fig. 2 (a)
Individual shape: Upper part 2/5 of a semicircle with a radius of 25 μm
(Height 10 μm, base 40 μm)
Pitch between adjacent patterns: 45 μm
(Mold 7)
In-plane pattern: Fig. 2 (a)
Individual shape: Upper 3/5 of a hemisphere with a radius of 25 μm
(Height 15 μm, base 46 μm)
Pitch between adjacent patterns: 50 μm.

(Comparative Example 1)
In Example 1, a diffusion sheet was produced in the same manner as in Example 1 except that mold transfer was not performed.

  When the 60-degree glossiness on the sheet surface was measured, it was found that the in-plane maximum value Gmax was 117.9 and the minimum value Gmin was 116.1 (ratio Gmax / Gmin = 1.02).

  When this diffusion sheet was incorporated into a backlight for evaluation and the luminance and luminance unevenness were evaluated, the uniformity of the screen and the decrease in luminance were observed. The luminance characteristic evaluation results are shown in Table 1.

(Comparative Example 2)
A diffusion sheet was prepared in the same manner as in Example 1 except that the following mold 4 was used.
(Mold 4)
In-plane pattern: Fig. 2 (a)
Individual shape: hemispherical depression (radius 20 μm)
Pitch between adjacent patterns: 200 μm.
The obtained diffusion sheet had a good pattern in which the mold shape was reversed.

  When the glossiness at 60 ° was measured on the surface to which the mold shape was transferred, the maximum value Gmax84.0 and the minimum value Gmin83.0 in the plane were found (ratio Gmax / Gmin = 1.01).

  When this diffusion sheet was incorporated into a backlight for evaluation and the luminance and luminance unevenness were evaluated, the uniformity of the screen and the decrease in luminance were observed. The luminance characteristic evaluation results are shown in Table 1.

  The diffusion sheet of the present invention can be applied as a thin optical member that expresses 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 preferable shape of the diffusion sheet of this invention. It is a figure which shows typically the preferable surface pattern of the diffusion sheet of this invention. It is a figure which shows typically the preferable cross-sectional shape of the base material which comprises the diffusion sheet of this invention. It is a figure which shows typically the preferable cross-sectional shape of the base material which comprises the diffusion sheet of this invention. It is a figure which shows typically the structure at the time of incorporating the diffusion sheet of this invention in a backlight.

Explanation of symbols

1 Diffusion sheet of the present invention
2 Surface satisfying glossiness 3 Internal diffusion sheet 4 Resin layer 5 Biaxially stretched sheet layer 6 Fluorescent tube 7 Reflective sheet 8 Case 9 Bead sheet 10 Prism sheet 11 Brightness enhancing sheet 12 Liquid crystal cell

Claims (9)

The ratio (Gmax / Gmin) of the maximum value Gmax and the minimum value Gmin of 60 degree glossiness is less than 1.1 on at least one surface of an internal diffusion sheet configured to contain diffusion elements inside the matrix resin, and A surface layer not containing a diffusing element having a minimum glossiness value Gmin of 1 to 50 is laminated, and a maximum value Gmax and a minimum value Gmin of 60 ° glossiness on the surface of the other surface of the internal diffusion sheet. ratio (Gmax / Gmin) is Ri der less than 1.1, and a diffusion sheet in which the resin layer is a biaxially oriented sheet on both sides of the internal diffusion sheet are laminated. The diffusion sheet according to claim 1 , wherein the resin layer is made of a thermoplastic resin mainly composed of a polyester-based resin. The diffusion sheet according to claim 1 or 2 , wherein the matrix resin is composed of a thermoplastic resin mainly composed of a polyester-based resin. The diffusion sheet according to any one of claims 1 to 3 , wherein the total light transmittance of the diffusion sheet is 50 to 95%. The diffusion sheet according to any one of claims 1 to 4 , wherein the total thickness of the diffusion sheet is 25 to 500 µm. The surface the minimum value Gmin of 60 degree gloss of the diffusion sheet satisfies 1-50, minimum Gmin85 of 85 ° glossiness, in any of 60 degree gloss less claim 1 than the minimum value of 5 The diffusion sheet described. The diffusion sheet according to claim 6 , wherein a minimum value Gmin85 of 85 ° glossiness of the diffusion sheet is 2 or less. The diffusion sheet has a concavo-convex shape formed on a surface satisfying a minimum value Gmin of 60 degree glossiness of 1 to 50, and a cross-sectional aspect ratio defined in the specification of a cross section of the concavo-convex shape is 0.25 or more. The diffusion sheet according to any one of claims 1 to 7 . At least above a plurality of linear light sources in a substantially parallel arrangement and / or a light source having a plurality of linear portions in a substantially parallel arrangement and / or a light source in which light and darkness are observed in a straight line of a substantially parallel arrangement, The backlight unit which installed the diffusion sheet in any one of Claims 1-8 .

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