JP2010282023A - Optical sheet for direct liquid crystal display, and backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet for a direct liquid crystal display to which a high-degree sticking-preventing function and optical function are added, the sheet being produced with proper productivity, while restraining its cost. <P>SOLUTION: The optical sheet for a direct liquid crystal display includes a transparent base material layer and an optical layer which is laminated on the surface side of the base material layer. In this case, a biaxially stretched polyester film containing filler is used as the base material layer, and the average particle size of the filler is at least 70 nm and at most 200 nm. The filler content is, preferably, at least 0.01 mass% and at most 1 mass%. Furthermore, inorganic microparticles, such as silica or organic microparticles of an acryl-based resin, can be used as the filler. Preferably, the stretching magnification in the longitudinal direction of the biaxially stretched polyester film is set to at least 2.5 and at most 4.5, and its stretching magnification in the width direction is at least 3 and at most 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet for a direct liquid crystal display device and a backlight unit for the direct liquid crystal display device including the optical sheet.

  In the liquid crystal display device, a backlight method in which a liquid crystal layer is illuminated from the back surface is widely used, and a backlight unit such as an edge light type or a direct type is provided on the lower surface side of the liquid crystal layer. In particular, as a backlight unit for a large screen display device, a direct backlight unit is preferably used from the viewpoint of maintaining luminance uniformity over the entire surface. As shown in FIG. 6A, the direct type backlight unit 50 basically includes a backlight 52 having a plurality of lamps 51 as a light source, and various types of lamps disposed on the surface side of the backlight 52. And an optical sheet. Examples of such an optical sheet include a light diffusion sheet 53 disposed on the surface side of the backlight 52 and a prism sheet 54 disposed on the surface side of the light diffusion sheet 53.

  The function of the direct type backlight unit 50 will be described. First, light emitted from the backlight 52 enters the light diffusion sheet 53, is diffused by the light diffusion sheet 53, and is emitted from the surface of the light diffusion sheet 53. Thereafter, the light beam emitted from the light diffusion sheet 53 enters the prism sheet 54 and is emitted as a light beam having a distribution having a peak in a substantially normal direction by the prism portion 54 a formed on the surface of the prism sheet 54.

  Thus, the light beam emitted from the backlight 52 is diffused by the light diffusion sheet 53, refracted by the prism sheet 54 so as to have a peak in a substantially normal direction, and further a liquid crystal layer (not shown) on the surface side. No) Illuminates the entire surface. Although not shown, the surface of the prism sheet 54 is used for the purpose of relaxing the light condensing characteristics of the prism sheet 54, protecting the prism portion 54a, or preventing sticking between the prism sheet 54 and a liquid crystal panel such as a polarizing plate. An optical sheet is further arranged on the side.

  As the light diffusion sheet 53 provided in the backlight unit 50, generally, as shown in FIG. 6B, light in which a light diffusion agent 59 is dispersed in a transparent base material layer 55 and a binder 58. A bead-coated type light diffusion sheet having a diffusion layer 56 and an anti-sticking layer 57 in which beads 61 are dispersed in a binder 60 (see, for example, JP-A-7-5305 and JP-A-2000-89007) is used. Has been. Further, instead of coating beads, an embossed type light diffusion sheet (for example, Japanese Patent Application Laid-Open No. 2006-47608, which is disclosed in Japanese Patent Application Laid-Open No. 2006-47608, in which the uneven shape is transferred to the surface of a transparent base layer using a mold having an uneven shape. No. 2006-335028) is also used. These types of light diffusing sheets exhibit a light diffusing function due to the fine uneven shape on the surface.

  Such a light diffusion sheet 53 is generally formed by extruding a molten thermoplastic resin from a T-die, and subsequently stretching the extruded body in the film longitudinal direction and the film width direction to form a base film. A step of laminating a composition for anti-sticking layer in which beads are dispersed in a binder on the back surface of the base film, and a composition for light diffusion layer in which a light diffusing agent is dispersed in the binder It is manufactured by performing the process of laminating | stacking on the surface of a base film. In this method, a composition for anti-sticking layer and a composition for light diffusion layer are prepared in advance, and these compositions are sequentially laminated on the base film in a production line different from the production line for base film formation. (Referred to as an off-line laminating method because the production line for forming the base film including the stretching step and the production line for laminating are separate). However, the manufacturing method of the light diffusing sheet that requires such a plurality of production lines increases the manufacturing cost and makes the manufacturing process complicated, resulting in inconveniences in terms of productivity and work efficiency.

Japanese Patent Laid-Open No. 7-5305 JP 2000-89007 A JP 2006-47608 A JP 2006-335028 A

  The present invention has been made in view of these disadvantages, and can be manufactured with high productivity while suppressing cost, and is used for a direct type liquid crystal display device provided with high anti-sticking properties and optical functions. An object is to provide an optical sheet and a backlight unit including the optical sheet.

The invention made to solve the above problems is
An optical sheet for a direct liquid crystal display device comprising a transparent substrate layer and an optical layer laminated on the surface side of the substrate layer,
As the base material layer, a biaxially stretched polyester film containing a filler is used,
An optical sheet for a direct liquid crystal display device, wherein the filler has an average particle size of 70 nm to 200 nm.

  According to the optical sheet for a direct type liquid crystal display device, the filler particles and the polyester resin present in the periphery thereof are used as a base material by using a biaxially stretched polyester film containing a filler as a base material layer of the optical sheet. It protrudes on the surface of the layer, and this protruding portion exhibits an advanced anti-sticking function with respect to the other layer laminated on the back surface side of the base material layer. Therefore, this optical sheet for a direct type liquid crystal display device has an anti-sticking function without laminating a separate anti-sticking layer, so that it is not necessary to perform a conventional off-line laminating process, thereby reducing manufacturing costs. In addition, the manufacturing process can be made more efficient. In particular, for an optical sheet having a large area used for a large screen of a direct type liquid crystal display device, a significant reduction in manufacturing cost and simplification of the manufacturing process can be achieved.

  By using a filler having an average particle diameter of 70 nm or more and 200 nm or less as a filler contained in the base material layer of the optical sheet for direct liquid crystal display device, it is possible to obtain an excellent transparency together with an advanced anti-sticking function. it can. That is, by including a filler having an average particle diameter of 70 nm or more in the base material layer, it is possible to form a protruding portion having a predetermined height on the surface of the base material layer without providing a sticking prevention layer. The anti-sticking function for other layers laminated on the back side of the base material layer can be effectively expressed. On the other hand, by including a filler having an average particle diameter of 200 nm or less in the base material layer, an optical sheet having excellent transparency can be provided while exhibiting such a sticking prevention function. In addition, by using a filler having an average particle diameter of 200 nm or less as described above, it is possible to prevent a decrease in mechanical strength such as tensile strength of the optical sheet.

  The content of the filler in the base material layer is preferably 0.01% by mass or more and 1% by mass or less. By using the filler with such a content, a high level of anti-sticking function can be exhibited, and at the same time, excellent mechanical strength such as transparency and tensile strength can be obtained. That is, by making the content of the filler in the base material layer 0.01% by mass or more, a large number of protruding portions can be formed on the surface of the base material layer, so that the anti-sticking function is sufficiently developed. be able to. On the other hand, by making the content of the filler in the base material layer 1% by mass or less, while maintaining an excellent anti-sticking function, the transparency is maintained at an excellent level, and the mechanical strength of the optical sheet is reduced. It becomes possible to suppress effectively.

  The filler may be selected from the group consisting of silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, acrylic resin, melamine resin, silicone resin and crosslinked polystyrene. By using these inorganic fine particles or organic fine particles as the filler contained in the base material layer, the protruding portion formed on the surface of the base material layer can be given a certain degree of strength. An anti-sticking function for other layers laminated on the back side can be effectively expressed. Moreover, the high transparency of a base material layer is maintainable by using these filler components which have said average particle diameter. Furthermore, it is possible to enhance the heat resistance and water resistance of the base material layer by using an inorganic component of silica, alumina, titanium dioxide, calcium carbonate, kaolin or barium sulfate as the filler component contained in the base material layer. It becomes.

  The stretch ratio in the longitudinal direction of the biaxially stretched polyester film used as the base material layer is preferably 2.5 to 4.5 times, and the stretch ratio in the width direction is preferably 3 to 5 times. By setting the stretch ratio in the longitudinal direction of the biaxially stretched polyester film to 2.5 times or more and the stretch ratio in the width direction to 3 times or more, the filler resin and the polyester resin component present in the periphery thereof are Project sufficiently on the surface. And when this protrusion part contacts the surface of the other layer laminated | stacked on the back surface side of an optical sheet, sticking with a base material layer and another layer is prevented effectively. Moreover, by setting the stretch ratio in the longitudinal direction of the biaxially stretched polyester film to 4.5 times or less and the stretch ratio in the width direction to 5 times or less, an advanced anti-sticking function can be obtained and at the same time, excessive film It is possible to suppress thinning and maintain mechanical strength.

  The F5 value in the longitudinal direction and the width direction of the biaxially stretched polyester film used as the base material layer is preferably 80 MPa or more and 120 MPa or less. By setting the F5 value in the longitudinal direction and the width direction of the biaxially stretched polyester film within the range of the predetermined value, the deformation due to the tension when processing the film is suppressed, and at the same time, the generation of corrugated wrinkles The surface of the base material layer other than the protruding portion due to the filler particles and the polyester resin existing around the filler particle can be maintained in a smooth state, and the sticking prevention function exhibited by the protruding portion is optimized. It becomes possible to do. The “F5 value” in the present application means a stress in that direction when a tensile strain of 5% is applied to the target film at 25 ° C.

  The static friction coefficient of the biaxially stretched polyester film used as the base material layer is preferably 0.3 or more and 0.6 or less, and the dynamic friction coefficient is preferably 0.3 or more and 0.5 or less. By setting the static friction coefficient of the biaxially stretched polyester film to 0.3 or more and the dynamic friction coefficient to 0.3 or more, the base material layer and the like caused by the protruding portion formed on the surface of the base material layer by filler particles, etc. The friction with the layer becomes sufficiently large, thereby effectively exerting the anti-sticking function of the other layer with respect to the base material layer. In addition, by making the static friction coefficient of the biaxially stretched polyester film 0.6 or less and the dynamic friction coefficient 0.5 or less, while exhibiting an advanced anti-sticking function, the surface of the base material layer other than the protruding portion, The surface of the other layer laminated | stacked there fully contact | adheres, and the stable laminated structure is obtained.

  The arithmetic average roughness (Ra) of the biaxially stretched polyester film used as the substrate layer is preferably 0.04 μm or more and 0.25 μm or less. By setting the arithmetic average roughness (Ra) of the biaxially stretched polyester film to 0.04 μm or more, the filler resin and the polyester resin component existing around the filler particles are sufficiently projected on the surface of the base material layer, and excellent sticking prevention Function is played. In addition, by setting the arithmetic average roughness (Ra) of the biaxially stretched polyester film to 0.25 μm or less, the adhesiveness between the base material layer and other layers laminated thereon is exhibited while exhibiting an advanced anti-sticking function. Can be maintained moderately.

  Moreover, the maximum roughness (Ry) of the biaxially stretched polyester film used as the base material layer is 0.4 μm or more and 0.8 μm or less, and the ten-point average roughness (Rz) is 0.3 μm or more and 0.6 μm or less. Is preferred. By setting the maximum roughness (Ry) or ten-point average roughness (Rz) of the biaxially stretched polyester film to a value within the above range, an excellent anti-sticking function can be obtained, and the base material layer and other layers The adhesiveness of can be maintained moderately.

  The optical layer of the optical sheet for a direct type liquid crystal display device may have a light diffusing agent and its binder. According to an optical sheet provided with an optical layer containing such a light diffusing agent and its binder, optical functions such as condensing, refraction in the normal direction, and diffusion can be improved. The optical layer may have a fine uneven shape having refractive properties. The optical sheet including the optical layer having such a fine uneven shape can improve the light diffusibility and facilitate the control of the light diffusibility. Moreover, since it is not necessary to separately form an optical layer, the optical sheet can be made thinner.

  Accordingly, in a backlight unit for a direct type liquid crystal display device in which light emitted from a lamp is dispersed and guided to the surface side, a biaxially stretched polyester film containing a filler having a predetermined average particle diameter when the optical sheet is provided By using, sticking between the back surface of the base material layer and the other layer is effectively suppressed while maintaining transparency, and the manufacturing cost can be reduced and the manufacturing process can be made more efficient. Moreover, when this optical sheet includes an optical layer containing a light diffusing agent and its binder, excellent optical functions such as light collection, refraction in the normal direction side, and diffusion are exhibited.

  As described above, according to the optical sheet for a direct type liquid crystal display device of the present invention, the filler particles and the polyester resin present around the filler particles protrude on the surface of the base material layer, and this protruding portion is the back surface of the optical sheet. In order to demonstrate a high level of anti-sticking function for other layers stacked on the side, there is no need to perform a conventional offline anti-sticking layer stacking process, reducing manufacturing costs and manufacturing processes. Efficiency can be improved. In addition, by using a filler having an average particle diameter of 70 nm or more and 200 nm or less as the filler contained in the base material layer, an excellent transparency can be obtained at the same time as an advanced anti-sticking function, and a mechanical strength of The decrease can be prevented.

1 is a schematic cross-sectional view of an optical sheet for a direct type liquid crystal display device according to an embodiment of the present invention. It is a flowchart which shows the manufacturing method of the optical sheet for direct type liquid crystal display devices of FIG. It is a schematic diagram which shows the product of each step of the manufacturing method of FIG. It is a schematic diagram which shows the apparatus for enforcing the manufacturing method of FIG. FIG. 2 is a schematic cross-sectional view of an optical sheet for a direct type liquid crystal display device according to an embodiment different from FIG. 1. (A) is a typical perspective view which shows a general direct type | mold backlight unit, (b) is typical sectional drawing which shows the conventional common light-diffusion sheet.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
The optical sheet 1 for a direct liquid crystal display device shown in FIG. 1 mainly includes a transparent base layer 2 and an optical layer 3 laminated on the surface side of the base layer.

  The transparent base material layer 2 is a biaxially stretched polyester film composed of a polyester resin 4 containing a filler 5 having an average particle diameter of 70 nm or more and 200 nm or less. On the surface of the base material layer 2, a large number of filler 5 particles and a protruding portion of the surrounding polyester resin 4 are formed.

  Since the polyester resin 4 constituting the base material layer 2 needs to transmit light, transparency is required. The polyester resin 4 is not particularly limited as long as it has transparency. For example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. Acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3- Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid , Adipic acid, 2-me At least one dicarboxylic acid such as luadipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecadicarboxylic acid, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1, 2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2- A homopolymer or copolymer obtained by polycondensation with at least one diol such as bis (4-hydroxyphenyl) propane or bis (4-hydroxyphenyl) sulfone, or a homopolymer or copolymer of these 2 A blend of more than seeds It can gel. Among these, polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate having excellent transparency and high strength are preferable, and polyethylene terephthalate is particularly preferable. Polyethylene terephthalate is prepared by, for example, charging dimethyl terephthalate and ethylene glycol into a reactor, performing an ester exchange reaction while gradually raising the internal temperature, then transferring the reaction product to the polymerization reactor, and performing a polymerization reaction under high temperature vacuum Can be generated.

  The filler 5 contained in the base material layer 2 is not particularly limited as long as the average particle diameter is 70 nm or more and 200 nm or less, and known inorganic fine particles and organic fine particles can be used. Preferable examples of the filler 5 include silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, acrylic resin, melamine resin, silicone resin, and crosslinked polystyrene. By using these specific fillers 5, the projecting portions formed on the surface of the base material layer 2 can have a strength necessary for exhibiting a sufficient anti-sticking function. Sticking of the other layer to the layer 2 can be effectively suppressed. Moreover, the high transparency required as an optical sheet is maintainable by using these fillers 5 which have a predetermined | prescribed average particle diameter. Further, by using inorganic fine particles of silica, alumina, titanium dioxide, calcium carbonate, kaolin or barium sulfate as the filler 5, the heat resistance, water resistance, impact strength, tensile strength, etc. of the base material layer can be enhanced. It becomes possible.

  The average particle diameter of the filler 5 is 70 nm or more and 200 nm or less. The polyester resin 4 containing the filler 5 having a particle diameter in such a range is biaxially stretched to form the base material layer 2, whereby the particles of the filler 5 are grouped together with the polyester resin 4 present around the polyester resin 4. A number of protruding portions are formed protruding on the surface of the material layer 2. Such a large number of protruding portions effectively exhibit a function of preventing sticking to other layers laminated on the back surface side of the base material layer 2. That is, by setting the average particle diameter of the filler 5 contained in the base material layer 2 to 70 nm or more, a protruding portion having an appropriate height is formed, and sticking with other layers is effectively prevented, Anti-sticking function is enhanced. In addition, by making the average particle size of the filler 5 contained in the base material layer 2 200 nm or less, an excellent transparency of the base material layer 2 is formed while forming a protruding portion having a sufficient size to exhibit a sticking prevention function. At the same time, the deterioration of the matrix function due to the polyester resin 4 can be prevented, and the mechanical strength such as the tensile strength of the entire optical sheet can be maintained at a high level. Furthermore, the damage to the other layer laminated | stacked with respect to the back surface side of the base material layer 2 is suppressed by making the average particle diameter of the filler 5 contained in the base material layer 2 below into said upper limit. The average particle diameter of the filler 5 can be more preferably 100 nm or more and 150 nm or less.

  The content of the filler 5 in the base material layer 2 is not particularly limited as long as the transparency of the base material layer 2 is ensured and a desired anti-sticking effect is exhibited, but is preferably 0.01% by mass. The content is 1% by mass or less, more preferably 0.05% by mass or more and 0.8% by mass or less, and most preferably 0.08% by mass or more and 0.4% by mass or less. By setting the content of the filler 5 in the base material layer 2 to 0.01% by mass or more, a large number of particles of the filler 5 and protruding portions of the surrounding polyester resin 4 are formed on the surface of the base material layer 2. Therefore, a sufficient anti-sticking function can be exhibited. In addition, by making the content of the filler 5 in the base material layer 2 1% by mass or less, a high level of anti-sticking function, maintenance of transparency required as an optical sheet, and high mechanical strength can be achieved in a well-balanced manner. It becomes possible to do.

  The stretching ratio in the longitudinal direction of the biaxially stretched polyester film used as the base material layer 2 is preferably 2.5 to 4.5 times, and the stretching ratio in the width direction is preferably 3 to 5 times. . By setting the stretch ratio in the longitudinal direction of the biaxially stretched polyester film to 2.5 times or more and the stretch ratio in the width direction to 3 times or more, the filler 5 and the polyester-based resin 4 present therearound are stretched. It protrudes at a sufficient size at a number of locations on the surface of the base material layer 2. By contacting the surface of the other layer laminated on the back side of the optical sheet with the large number of protruding portions, excessive adhesion between the base material layer and the other layer is prevented, and an anti-sticking effect is achieved. Furthermore, by setting the stretch ratio in the longitudinal direction of the biaxially stretched polyester film to 4.5 times or less and the stretch ratio in the width direction to 5 times or less, the film is made thinner while exhibiting an advanced anti-sticking function. Therefore, it is possible to prevent the formation of an excessive protruding portion due to, and the decrease in mechanical strength accompanying this.

  The F5 value in the longitudinal direction and the width direction of the biaxially stretched polyester film used as the base material layer 2 is preferably 80 MPa or more and 120 MPa or less, more preferably 90 MPa or more and 110 MPa or less. The F5 value in the longitudinal direction and the width direction is determined using a tensile tester in accordance with the method specified in JIS-Z1702 with respect to the sample cut out from the center part of the base material layer 2 (biaxially stretched polyester film). When the sample is stretched in the longitudinal direction or the width direction at a tensile speed of 300 mm / min at room temperature of 23 ° C. and 65% RH, the stress applied to the sample with respect to an elongation of 5% is measured and divided by the cross-sectional area of the sample. It is obtained as a value. When the F5 value in the longitudinal direction of the biaxially stretched polyester film is smaller than 80 MPa, the biaxially stretched polyester film is likely to be deformed when tension is applied in the running direction during mold release processing. In addition, when the F5 value in the width direction of the biaxially stretched polyester film is smaller than 80 MPa, the stiffness of the film is reduced and corrugated wrinkles that are continuous in the running direction are likely to occur. These inconveniences can be prevented by setting the F5 value in the longitudinal direction and width direction of the biaxially stretched polyester film to 80 MPa or more. In addition, by preventing deformation and wrinkles of the film in this way, the surface of the base material layer 2 other than the protruding portion due to the filler 5 and the polyester-based resin 4 existing around the filler 5 is kept in a smooth state, and the protruding portion It is possible to optimize the anti-sticking function produced by On the other hand, when the F5 value in the longitudinal direction and the width direction of the biaxially stretched polyester film is 120 MPa or less or 110 MPa or less, the flexibility, workability, and durability of the film can be appropriately maintained.

  The static friction coefficient of the biaxially stretched polyester film used as the base material layer 2 is preferably 0.3 or more and 0.6 or less, and the dynamic friction coefficient is preferably 0.3 or more and 0.5 or less. The static friction coefficient and the dynamic friction coefficient of the biaxially stretched polyester film are measured according to the method defined in JIS-K7125. By setting the static friction coefficient of the biaxially stretched polyester film to 0.3 or more and the dynamic friction coefficient to 0.3 or more, the filler 5 formed on the surface of the base material layer 2 and the polyester-based resin 4 existing around the filler 5 are formed. Due to the large number of protruding portions, the friction between the base material layer and the other layers laminated thereon becomes sufficiently large. As a result, the sticking of the other layer with respect to the base material layer is effectively exhibited. Further, by making the static friction coefficient of the biaxially stretched polyester film 0.6 or less and the dynamic friction coefficient 0.5 or less, the sticking prevention effect by the protruding portions is sufficiently exhibited, and at the same time, the base other than those protruding portions. The surface of the material layer and the surface of the other layer laminated thereon are reliably in contact with each other, and a stable laminated structure is obtained. Furthermore, by setting the dynamic friction coefficient of the biaxially stretched polyester film to 0.5 or less, it is possible to prevent the generation of wrinkles and scratches during film processing and to suppress the appearance of non-uniform optical characteristics. .

  The arithmetic average roughness (Ra) of the biaxially stretched polyester film used as the base material layer 2 is preferably 0.04 μm or more and 0.25 μm or less, and more preferably 0.05 μm or more and 0.15 μm or less. . By setting the arithmetic average roughness (Ra) of the biaxially stretched polyester film to 0.04 μm or more, the filler 5 and the polyester-based resin 4 existing therearound protrude at a sufficient height on the surface of the base material layer 2. And the sticking with respect to the other layer laminated | stacked on the back surface side of the base material layer 2 can be prevented effectively. Further, by making the arithmetic average roughness (Ra) of the biaxially stretched polyester film 0.25 μm or less, the sticking prevention effect by the protruding portions such as the filler 5 is sufficiently exhibited, and the base materials other than those protruding portions It becomes possible to maintain the adhesion between the surface of the layer and the surface of the other layer laminated thereon at an appropriate level.

  Furthermore, it is preferable that the maximum roughness (Ry) of the biaxially stretched polyester film used as the base material layer 2 is 0.4 μm or more and 0.8 μm or less. The ten-point average roughness (Rz) of the biaxially stretched polyester film used as the base material layer 2 is preferably 0.3 μm or more and 0.6 μm or less. By setting the maximum roughness (Ry) and ten-point average roughness (Rz) of the biaxially stretched polyester film to values within the above ranges, the filler 5 and the polyester-based resin 4 present around the base 5 are formed. It protrudes at a sufficient height on the surface of the substrate to provide a high anti-sticking effect, and at the same time, the adhesion between the base material layer and the other layer is maintained at an appropriate level.

  The thickness (average thickness) of the base material layer 2 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 35 μm or more and 250 μm or less, and particularly preferably 50 μm or more and 188 μm or less. When the thickness of the base material layer 2 is less than the above range, problems such as curl are likely to occur when the resin composition for forming the optical layer 3 is applied, and handling becomes difficult. To do. On the contrary, if the thickness of the base material layer 2 exceeds the above range, the luminance of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which is contrary to the demand for thinning of the liquid crystal display device. It will also be.

  The optical layer 3 laminated on the surface side of the base material layer includes a plurality of light diffusing agents 6 disposed substantially uniformly on the surface of the base material layer 2 and a binder 7 of the plurality of light diffusing agents 6. ing. The plurality of light diffusing agents 6 are coated with a binder 7. In this way, a plurality of light diffusing agents 6 contained in the optical layer 3 uniformly diffuses the light beam transmitted through the optical layer 2 from the back side to the front side, and optical functions such as condensing and refraction in the normal direction. Can be improved. Moreover, fine irregularities are formed substantially uniformly on the surface of the optical layer 3 by the plurality of light diffusing agents 6. Thus, the light can be better diffused by the lens-like refracting action of fine irregularities formed on the surface of the optical sheet 1. In addition, although the average thickness of the optical layer 3 is not specifically limited, For example, it is about 1 micrometer or more and 30 micrometers or less.

  The light diffusing agent 6 is a particle having a property of diffusing light, and is roughly classified into an inorganic filler and an organic filler. As the inorganic filler, for example, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or a mixture thereof can be used. As the organic filler material, for example, acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, and the like can be used. Among them, an acrylic resin having high transparency is preferable, and polymethyl methacrylate (PMMA) is particularly preferable.

  The shape of the light diffusing agent 6 is not particularly limited, and examples thereof include a spherical shape, a spindle shape, a needle shape, a rod shape, a cubic shape, a plate shape, a scale shape, and a fiber shape, and are particularly excellent in light diffusibility. Spherical beads are preferred.

  The lower limit of the average particle size of the light diffusing agent 6 is preferably 1 μm, particularly 2 μm, and more preferably 5 μm. On the other hand, the upper limit of the average particle diameter of the light diffusing agent 6 is preferably 50 μm, particularly 20 μm, and more preferably 15 μm. When the average particle diameter of the light diffusing agent 6 is less than the above range, the unevenness of the surface of the optical layer 3 formed by the light diffusing agent 6 becomes small, and the light diffusibility necessary for the light diffusing sheet may not be satisfied. Conversely, if the average particle size of the light diffusing agent 6 exceeds the above range, the thickness of the optical sheet 1 increases and uniform diffusion becomes difficult.

  The lower limit of the amount of the light diffusing agent 6 (the amount in terms of solid content relative to 100 parts of the base polymer in the polymer composition that is the forming material of the binder 7) is preferably 10 parts, particularly 20 parts, and more preferably 50 parts. The upper limit of this amount is preferably 500 parts, particularly 300 parts, and more preferably 200 parts. If the blending amount of the light diffusing agent 6 is less than the above range, the light diffusing property becomes insufficient. On the other hand, if the blending amount of the light diffusing agent 6 exceeds the above range, the light diffusing agent 6 is fixed. It is because the effect to do falls. In the case of the so-called upward light diffusion sheet disposed on the surface side of the prism sheet, high light diffusibility is not required, so the amount of the light diffusing agent 6 is 10 parts or more and 40 parts or less, particularly 10 parts. The amount is preferably 30 parts or less.

  The binder 7 is formed by crosslinking and curing a polymer composition containing a base polymer. The light diffusing agent 6 is arranged and fixed on the surface of the base material layer 2 by the binder 7 at a substantially equal density. In addition to the base polymer, the polymer composition for forming the binder 7 includes, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, an ultraviolet absorber, an antioxidant, a viscosity modifier, and the like. A quality agent, a lubricant, a light stabilizer and the like may be appropriately blended.

  The base polymer is not particularly limited, and examples thereof include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamideimides, epoxy resins, ultraviolet curable resins, and the like. Can be used singly or in combination of two or more. In particular, the base polymer is preferably a polyol that has high processability and can easily form the optical layer 3 by means such as coating. Further, the base polymer itself used for the binder 7 is preferably transparent from the viewpoint of enhancing light transmittance, and particularly preferably colorless and transparent.

  Examples of the polyol include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, a polyester polyol obtained under the condition of excess hydroxyl group, and the like alone or in combination of two or more. Can be used as a mixture.

  Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, homoallyl alcohol, Keihi Hydroxyl group-containing unsaturated monomers such as alcohol and crotonyl alcohol, (b) for example ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4-bis (hydroxymethyl) cyclohexane, phenylglycidyl Dihydric alcohols or epoxy compounds such as ether, glycidyl decanoate, Plaxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.) and, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, Tonsan, and the like hydroxyl group-containing unsaturated monomers obtained by reaction of an unsaturated carboxylic acid such as itaconic acid. One or more selected from these hydroxyl group-containing unsaturated monomers can be polymerized to produce a polyol.

  The above polyols are ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methacrylic acid. N-butyl acid, tert-butyl methacrylate, ethyl hexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyl toluene, 1-methylstyrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, stearic acid Vinyl, allyl acetate, diallyl adipate, diallyl itaconate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylolacrylamide, N-but One or more ethylenically unsaturated monomers selected from dimethyl acrylamide, diacetone acrylamide, ethylene, propylene, isoprene and the like, and hydroxyl group-containing unsaturated selected from the above (a) and (b) It can also be produced by polymerizing a monomer.

  The number average molecular weight of a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer is from 1,000 to 500,000, preferably from 5,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.

  The polyester polyol obtained under the condition of excess hydroxyl group is (c), for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl. Glycol, hexamethylene glycol, decamethylene glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, hexanetriol, glycerin, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis (hydroxymethyl) Polyhydric alcohols such as cyclohexane, hydroquinone bis (hydroxyethyl ether), tris (hydroxyethyl) isosinurate, xylylene glycol, and (d) for example malee , Fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimetic acid, terephthalic acid, phthalic acid, isophthalic acid and other polybasic acids, and propanediol, hexanediol, polyethylene glycol, trimethylolpropane, etc. It can be produced by reacting under the condition that the number of hydroxyl groups in the monohydric alcohol is larger than the number of carboxyl groups of the polybasic acid.

  The number average molecular weight of the polyester polyol obtained under such an excessive hydroxyl group condition is 500 or more and 300,000 or less, and preferably 2000 or more and 100,000 or less. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.

  The polyol used as the base polymer of the polymer composition is obtained by polymerizing a monomer component containing the polyester polyol and the hydroxyl group-containing unsaturated monomer, and is a (meth) acryl unit or the like. An acrylic polyol having The binder 7 having such a polyester polyol or acrylic polyol as a base polymer has high weather resistance and can suppress yellowing of the optical layer 3 and the like. In addition, any one of this polyester polyol and acrylic polyol may be used, and both may be used.

  The number of hydroxyl groups in the polyester polyol and acrylic polyol is not particularly limited as long as it is 2 or more per molecule, but if the hydroxyl value in the solid content is 10 or less, the number of crosslinking points decreases, and the solvent resistance , Film properties such as water resistance, heat resistance and surface hardness tend to decrease.

  The polymer composition that forms the binder 7 may contain a fine inorganic filler. Thus, by including a fine inorganic filler in the binder 7, the heat resistance of the optical layer 3 and thus the optical sheet 1 is improved. The inorganic material constituting the fine inorganic filler is not particularly limited, but an inorganic oxide is preferable. This inorganic oxide is defined as various oxygen-containing metal compounds in which a metal element mainly forms a three-dimensional network through bonds with oxygen atoms. As the metal element constituting the inorganic oxide, for example, an element selected from Groups 2 to 6 of the Periodic Table of Elements is preferable, and an element selected from Groups 3 to 5 of the Periodic Table of Elements is more preferable. In particular, an element selected from Si, Al, Ti, and Zr is preferable, and colloidal silica in which the metal element is Si is most preferable as a fine inorganic filler in terms of heat resistance improvement effect and uniform dispersibility. The shape of the fine inorganic filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scale shape, and a crushed shape, and is not particularly limited.

  The lower limit of the average particle size of the fine inorganic filler is preferably 5 nm, and particularly preferably 10 nm. On the other hand, the upper limit of the average particle size of the fine inorganic filler is preferably 50 nm, particularly preferably 25 nm. This is because if the average particle size of the fine inorganic filler is less than the above range, the surface energy of the fine inorganic filler becomes high and aggregation or the like is likely to occur. Conversely, if the average particle size exceeds the above range, This is because it becomes cloudy under the influence of a short wavelength and the transparency of the optical sheet 1 cannot be maintained completely.

  The lower limit of the amount of the fine inorganic filler based on 100 parts of the base polymer (the amount of only the inorganic component) is preferably 5 parts, particularly preferably 50 parts in terms of solid content. On the other hand, the upper limit of the amount of the fine inorganic filler is preferably 500 parts, more preferably 200 parts, and particularly preferably 100 parts. This is because if the blending amount of the fine inorganic filler is less than the above range, the heat resistance of the optical sheet 1 may not be sufficiently expressed, and conversely if the blending amount exceeds the above range. This is because blending into the polymer composition becomes difficult and the light transmittance of the optical layer 3 may be lowered.

  As the fine inorganic filler, one having an organic polymer fixed on its surface may be used. Thus, by using the organic polymer-fixed fine inorganic filler, the dispersibility in the binder 7 and the affinity with the binder 7 can be improved. The organic polymer is not particularly limited with respect to its molecular weight, shape, composition, presence or absence of a functional group, and any organic polymer can be used. Moreover, about the shape of an organic polymer, the thing of arbitrary shapes, such as a linear form, a branched form, and a crosslinked structure, can be used.

  Specific resins constituting the organic polymer include, for example, (meth) acrylic resins, polystyrene, polyvinyl acetate, polyolefins such as polyethylene and polypropylene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, and the like. Examples thereof include a resin partially modified with a functional group such as a copolymer, an amino group, an epoxy group, a hydroxyl group, or a carboxyl group. Among them, those having an organic polymer containing a (meth) acryl unit such as a (meth) acrylic resin, a (meth) acrylic-styrene resin, and a (meth) acrylic-polyester resin have a film forming ability. Is preferred. On the other hand, a resin having compatibility with the base polymer of the polymer composition is preferred, and therefore, the resin having the same composition as the base polymer contained in the polymer composition is most preferred.

  The fine inorganic filler may contain an organic polymer in the fine particles. As a result, moderate softness and toughness can be imparted to the inorganic material that is the core of the fine inorganic filler.

  As the organic polymer, one containing an alkoxyl group may be used, and the content is preferably 0.01 mmol or more and 50 mmol or less per 1 g of the fine inorganic filler to which the organic polymer is fixed. Such an alkoxy group can improve the affinity with the matrix resin constituting the binder 7 and the dispersibility in the binder 7.

  The alkoxyl group represents an RO group bonded to a metal element that forms a fine particle skeleton. R is an alkyl group which may be substituted, and the RO groups in the fine particles may be the same or different. Specific examples of R include methyl, ethyl, n-propyl, isopropyl, n-butyl and the like. It is preferable to use the same metal alkoxyl group as the metal constituting the fine inorganic filler, and when the fine inorganic filler is colloidal silica, it is preferred to use an alkoxyl group having silicon as a metal.

  The content of the organic polymer in the fine inorganic filler to which the organic polymer is fixed is not particularly limited, but is preferably 0.5% by mass or more and 50% by mass or less based on the fine inorganic filler.

  A polyfunctional isocyanate compound, melamine compound and amino having at least two functional groups capable of reacting with a hydroxyl group in the polymer composition constituting the binder 7 using the organic polymer having a hydroxyl group as the organic polymer fixed to the fine inorganic filler. It is good to contain the at least 1 sort (s) chosen from plast resin. Thereby, the fine inorganic filler and the matrix resin of the binder 7 are bonded with a cross-linked structure, and the storage stability, stain resistance, flexibility, weather resistance, storage stability, etc. are improved, and the resulting film is further obtained. It becomes glossy.

  As the base polymer, a polyol having a cycloalkyl group is preferable. Thus, by introducing a cycloalkyl group into the polyol as the base polymer constituting the binder 7, the hydrophobicity of the binder 7 such as water repellency and water resistance becomes high, and the optical properties under high temperature and high humidity conditions are increased. The bending resistance and dimensional stability of the sheet 1 are improved. Further, the basic properties of the coating film such as weather resistance, hardness, feeling of holding, and solvent resistance of the optical layer 3 are improved. Furthermore, the affinity with the fine inorganic filler having the organic polymer fixed on the surface and the uniform dispersibility of the fine inorganic filler are further improved.

  The cycloalkyl group is not particularly limited, and examples thereof include a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, a cycloundecyl group, a cyclododecyl group, a cyclotridecyl group, Examples thereof include a cyclotetradecyl group, a cyclopentadecyl group, a cyclohexadecyl group, a cycloheptadecyl group, and a cyclooctadecyl group.

  The polyol having a cycloalkyl group can be obtained by copolymerizing a polymerizable unsaturated monomer having a cycloalkyl group. The polymerizable unsaturated monomer having a cycloalkyl group is a polymerizable unsaturated monomer having at least one cycloalkyl group in the molecule. The polymerizable unsaturated monomer is not particularly limited, and examples thereof include cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, and cyclododecyl (meth) acrylate.

  Moreover, it is good to contain isocyanate as a hardening | curing agent in a polymer composition. Thus, by containing an isocyanate hardening | curing agent in a polymer composition, it becomes a much stronger bridge | crosslinking structure and the film physical property of the optical layer 3 further improves. As this isocyanate, the same substance as the polyfunctional isocyanate compound is used. Of these, aliphatic isocyanates that prevent yellowing of the coating are preferred.

  In particular, when a polyol is used as the base polymer, one or more of hexamethylene diisocyanate, isofurone diisocyanate and xylene diisocyanate may be mixed and used as a curing agent to be blended in the polymer composition. When these curing agents are used, the curing reaction rate of the polymer composition is increased. Therefore, even if a cationic agent that contributes to the dispersion stability of the fine inorganic filler is used as the antistatic agent, the cationic antistatic agent is used. Can sufficiently compensate for a decrease in the curing reaction rate. Moreover, the improvement in the curing reaction rate of such a polymer composition contributes to the uniform dispersibility of the fine inorganic filler in the binder. As a result, the optical sheet 1 can remarkably suppress bending and yellowing due to heat, ultraviolet rays and the like.

  Furthermore, an antistatic agent may be kneaded in the polymer composition. By forming the binder 7 from the polymer composition in which the antistatic agent is kneaded in this way, the antistatic effect is exhibited on the optical sheet 1, and it becomes difficult to attract dust or to overlap with the prism sheet or the like. Inconvenience caused by static electricity charging can be prevented. Further, when the surface is coated with an antistatic agent, the surface becomes sticky or contaminated. However, such an adverse effect is reduced by kneading into the polymer composition. The antistatic agent is not particularly limited. For example, anionic antistatic agents such as alkyl sulfates and alkyl phosphates, cationic antistatic agents such as quaternary ammonium salts and imidazoline compounds, polyethylene glycol type Nonionic antistatic agents such as polyoxyethylene sorbitan monostearic acid ester and ethanolamides, and high molecular antistatic agents such as polyacrylic acid are used. Among these, a cationic antistatic agent having a relatively large antistatic effect is preferable, and an antistatic effect is exhibited by addition of a small amount.

  An easy-adhesion layer (primer layer) may be provided between the base material layer 2 and the optical layer 3 (not shown). Although the average thickness in the case of providing an easily bonding layer is not specifically limited, For example, it can be set as about 1 micrometer or more and 30 micrometers or less. By providing such an easy-adhesion layer, it is possible to ensure the bonding between the base layer 2 and the optical layer 3 through the easy-adhesion layer, and to obtain a more stable laminated structure. As the resin constituting the easy-adhesion layer, an acrylic resin, a polyurethane resin, a polyester resin, a rubber resin, or the like is preferably used.

  As an example of acrylic resin which comprises an easily bonding layer, resin which has acrylic acid, methacrylic acid, and these derivatives as a component is mentioned. Specifically, acrylic acid, methacrylic acid, methyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylamide, acrylonitrile, hydroxyl acrylate, etc., and monomers copolymerizable therewith (for example, styrene, divinylbenzene, etc.) And a copolymer.

  The polyurethane-based resin constituting the easy-adhesion layer is a resin having a urethane bond in the main chain, and is usually obtained by reaction of polyisocyanate and polyol. Examples of polyisocyanates include TDI, MDI, NDI, TODI, HDI, IPDI and the like. Examples of the polyol include ethylene glycol, propylene glycol, glycerin, hexanetriol and the like. In addition, a resin having an increased molecular weight can be used by reacting a chain extender with a polyurethane polymer obtained from a polyisocyanate and a polyol.

  The polyester-based resin constituting the easy-adhesion layer is a resin having an ester bond in the main chain, and is usually obtained by a reaction between a polycarboxylic acid and a polyol. Examples of the polycarboxylic acid include fumaric acid, itaconic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid and the like. As an example of a polyol, what was illustrated regarding the said polyurethane-type resin is mentioned.

  A typical example of the rubber-based resin constituting the easy-adhesion layer is a diene-based synthetic rubber. Examples of the diene synthetic rubber include polybutadiene, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-butadiene-divinylbenzene copolymer, butadiene-acrylonitrile copolymer, polychloroprene, and the like. .

  As shown in FIG. 2, the optical sheet 1 for a direct liquid crystal display device of FIG. 1 can be manufactured by a base film forming step (STP1), a stretching step (STP2), and an optical layer forming step (STP3). .

  The base film forming step (STP1) in the method of manufacturing the optical sheet 1 in FIG. 2 is a polyester-based resin 4 containing filler 5 substantially uniformly as shown in FIG. 3 by a known extrusion method using a T die. It is the process of forming the base film extrusion body 9 which is a long strip | belt-shaped body comprised from these. As a known extrusion molding method using a T-die, for example, a polishing roll method and a chill roll method can be cited.

  The base film forming step (STP1) is performed by an extrusion molding apparatus that occupies a part of the schematic diagram shown in FIG. This extrusion molding apparatus mainly includes an extruder and a T die 20, a pair of pressing rolls 21, a winder, and the like. As the extruder, a single screw extruder or a twin screw extruder can be used. As the T die 20, for example, a well-known one such as a fish tail die, a manifold die, a coat hanger die, or the like can be used. A pair of pressing rolls 21 are arranged adjacent to each other in parallel, and the extruder and the T die 20 can extrude a mixture 8 of the polyester resin 4 and filler 5 in a molten state into the nip of the pair of pressing rolls 21. It is configured. The pair of pressing rolls 21 is provided with a temperature control means, and is configured to be able to control the surface temperature to a temperature optimum for extrusion molding. As the pressing roll 21, it is preferable to use a metal elastic roll composed of a metal roll and a flexible roll whose surface is covered with an elastic body. Using the extrusion molding apparatus having such a structure, first, a mixture 8 of the polyester resin 4 and the filler 5 in a molten state is supplied to the T die 20, and the mixture 8 is extruded by the extruder and the T die 20. The base film extrudate 9 is formed by pressing. The melting temperature of the polyester resin 4 extruded from the T die 20 is appropriately selected in consideration of the melting point of the polyester resin used.

  The filler 5 is dispersed almost uniformly in the polyester resin 4 constituting the base film extrusion 9, but the surface of the base film extrusion 9 has almost no polyester resin 4 or filler 5 protruding. Forming a substantially flat surface. The thickness of the base film extrudate 9 is not particularly limited, but is appropriately set depending on the structure of the T-die used and the ratio of stretching performed later, and can be about 40 μm or more and 2000 μm or less.

  As shown in FIG. 3, the stretching step (STP2) in the method for manufacturing the optical sheet 1 in FIG. 2 is performed by using the base film extrudate 9 formed in the base film forming step as described above in the film longitudinal direction and the film width direction. Is a step of forming a base material layer 2 which is a stretched film, that is, a biaxially stretched polyester film.

  This stretching step (STP2) can be performed at an appropriate temperature between the softening temperature and the melting temperature of the polyester resin 4 constituting the base film extrudate 9. The stretching ratio in the stretching step can be adjusted depending on the thickness of the desired base material layer 2 (biaxially stretched polyester film), but the stretching ratio in the longitudinal direction is 2.5 to 4.5 times, and the width The stretching ratio in the direction is preferably 3 to 5 times. The thickness of the stretched base material layer 2 is thinner than the thickness of the base film extrudate 9 by the reciprocal of this stretch ratio (product). The preferable thickness of the base material layer 2 is as described above. By setting the stretch ratio in the longitudinal direction of the biaxially stretched polyester film to 2.5 times or more and the stretch ratio in the width direction to 3 times or more, the filler 5 contained inside the base film extrudate 9 is It protrudes in many places on the surface of the base material layer with the polyester-based resin 4 present in the periphery. And many sticking parts formed with the filler 5 etc. are in contact with the surface of the other layer laminated | stacked on the back surface side of an optical sheet in a scattered manner, and the sticking with a base material layer and another layer is effective Is prevented. Further, by setting the stretch ratio in the longitudinal direction of the biaxially stretched polyester film to 4.5 times or less and the stretch ratio in the width direction to 5 times or less, the protruding portion of the filler 5 and the polyester resin 4 present in the periphery thereof is set. As a result, an advanced anti-sticking function can be obtained, and excessive protrusion of the filler 5 and the like, and deterioration of mechanical strength due to excessive thinning of the film can be prevented.

  The stretching step (STP2) is performed by a biaxial stretching apparatus 22 having a known structure that occupies a part of the schematic diagram shown in FIG. This biaxial stretching apparatus 22 mainly includes a heating stretching section, a heat treatment section, and the like. As the biaxial stretching method, a known method such as a tubular film biaxial stretching method or a flat film biaxial stretching method can be employed. Further, the biaxial stretching method may be a sequential biaxial stretching method in which stretching in the film longitudinal direction and stretching in the film width direction are separately performed, or simultaneously performing stretching in the film longitudinal direction and stretching in the film width direction simultaneously. A biaxial stretching method may be used. According to sequential biaxial stretching, a stretched film with good flatness and dimensional stability and less thickness unevenness can be obtained. On the other hand, according to simultaneous biaxial stretching, a stretched film with good in-plane balance can be obtained.

  As a method of sequential biaxial stretching, for example, the base film extrudate 9 is guided to a heated roll group, stretched in the longitudinal direction of the film, and then guided to a heated tenter while holding both ends of the film with clips. The film can be stretched in the film width direction. As a method of simultaneous biaxial stretching, for example, the both ends of the base film extruded body 9 are guided to a heated tenter while being gripped by clips, and stretched in the film width direction, and at the same time, the clip traveling speed is accelerated. Thus, the film can be stretched in the longitudinal direction. In general, heat treatment is performed to further impart planar stability and dimensional stability to these stretched products.

  As shown in FIG. 3, the optical layer forming step (STP3) in the method for producing the optical sheet 1 in FIG. 2 is performed on the surface of the base material layer 2 that is a biaxially stretched polyester film formed in the stretching step. An optical layer 3 is formed by laminating a composition 10 for an optical layer containing a plurality of light diffusing agents 6 and a binder 7 of the light diffusing agent 6 by using a well-known roll coating technique and then drying. In this step, the optical sheet 1 is completed.

  The roll coating in the laminating step (STP3) is performed by a roll coater having a known structure that occupies a part of the schematic diagram shown in FIG. This roll coater mainly includes a coater pan 23, a pickup roll 24a, an adjustment roll 24b, a coating roll 24c, and a backup roll 24d. A direct roll coater in which the rotation direction of the coating roll and the traveling direction of the coating object are the same or a reverse roll coater in which the rotation direction of the coating roll and the traveling direction of the coating object are reversed can be used. The coater pan 23 is filled with an optical layer composition 10 including a plurality of light diffusing agents 6 and a binder 7 of the light diffusing agent 6, and the optical layer composition is formed from the coater pan 23 by the rotation of the pickup roll 24 a. Object 10 is pumped up. Thus, the optical layer composition 10 containing the light diffusing agent 6 and the binder 7 adheres to the outer peripheral surface of the pickup roll 24a and is delivered to the coating roll 24c. Meanwhile, the adjustment roll 24b adjusts the amount of the optical layer composition 10 attached to the outer peripheral surface of the pickup roll 24a. The base material layer that is supported between the application roll 24c and the backup roll 24d by rotating the application roll 24c with the optical layer composition 10 in the same direction as the feeding direction of the base material layer 2 or in the opposite direction. The optical layer composition 10 is laminated on 2 and then dried to form the optical sheet 1 that is a laminate of the base layer 2 and the optical layer 3.

  In the optical layer forming step (STP3), the optical layer composition 10 is laminated in place of the above-described method using a roll coater, such as a bar coater, a blade coater, a spin coater, a gravure coater, a flow coater, spray, screen printing, etc. You may employ | adopt the well-known coating method using.

  After the stretching step (STP2), prior to the optical layer forming step (STP3), a step of forming the above easy-adhesion layer (primer layer) on the surface of the base material layer 2 may be provided. As the method and apparatus for forming the easy-adhesion layer, the same methods as those for forming the optical layer 2 can be used. In the coating liquid for forming the easy-adhesion layer, for example, a curing agent in an amount of about 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the resin component (for example, polyisocyanate resin, carbodiimide resin, etc.) May be blended.

  A cutting step is performed between the stretching step (STP2) and the optical layer forming step (STP3) or after the optical layer forming step (STP3) to cut the obtained base material layer 2 or optical sheet 1 into a predetermined size. Good. By performing the cutting step after the optical layer forming step (STP3), a desired optical sheet can be efficiently manufactured, and curling due to winding of the optical sheet, occurrence of peeling of the optical layer, etc. can be suppressed. it can.

  As described so far, according to the optical sheet for a direct type liquid crystal display device of the present embodiment, filler particles protrude onto the surface of the base material layer together with the polyester-based resin present in the periphery, and a large number of protruding portions The sticking prevention function with respect to the other layer laminated | stacked on the back surface side of a base material layer is show | played effectively. Further, according to this optical sheet, it is possible to achieve a high level of anti-sticking function, maintenance of transparency required for the optical sheet, and high mechanical strength in a balanced manner. Furthermore, since it is not necessary to perform a separate process for forming an anti-sticking layer on the optical sheet, it is possible to reduce the manufacturing cost and increase the efficiency of the manufacturing process for the optical sheet used for a direct liquid crystal display device with a particularly large display area. Can be achieved. In addition, the manufacturing process can be simplified and speeded up by manufacturing the optical sheet for a direct type liquid crystal display device on one continuous production line as shown in FIGS.

  An optical sheet 11 for a direct liquid crystal display device in FIG. 5 is an optical sheet according to an embodiment different from that in FIG. 1, and a fine uneven shape 12 having a refractive property is formed on the surface thereof. In the optical sheet 11, a portion having a fine uneven shape 12 functions as an optical layer. The components and configuration of the base material layer 2 of the optical sheet 11 are the same as those of the optical sheet 1 of the above embodiment.

  The fine concavo-convex shape 12 is not particularly limited as long as it exhibits a light diffusibility equivalent to that of the optical layer 3 in the above embodiment. For example, the height of each convex portion (both adjacent concave portions) Of the height from the higher bottom position) can be 0.05 μm or more and 1 μm or less.

  Although it does not specifically limit as a manufacturing method of the optical sheet 11, For example, the following methods are employable. That is, prior to the above-described stretching step (sequential biaxial stretching or simultaneous biaxial stretching in the film longitudinal direction and film width direction), (a) a polyester resin and filler into a sheet mold having an inverted shape of the surface of the optical sheet (B) An injection molding process for injecting and injecting a molten mixture of polyester resin and filler into a mold having an inverted shape of the surface of the optical sheet. And (c) a method of reheating the sheet-like polyester resin and filler mixture and pressing the same between the mold and the metal plate to transfer the shape. (D) The above-mentioned shape is transferred by passing a molten mixture of polyester resin and filler through a nip between a roll mold having a reverse shape of the surface of the optical sheet on the peripheral surface and another roll. How to carry out the process can be exemplified.

  According to the optical sheet for a direct type liquid crystal display device of the present embodiment, similar to the optical sheet of the above-described embodiment, the base material layer and the other layer are formed by the filler particles and the protruding portion of the polyester resin existing around the filler particles. The anti-sticking function can be effectively achieved, and high transparency and mechanical strength can be maintained. Furthermore, since it is not necessary to perform a separate step of forming an anti-sticking layer on the optical sheet, manufacturing costs can be reduced, manufacturing steps can be made more efficient, and the like. In addition, the optical sheet including the optical layer having such a fine concavo-convex shape can improve light diffusibility and facilitate control.

  The optical sheet for a direct type liquid crystal display device of the present invention is not limited to these embodiments. For example, an optical layer having a fine uneven shape may be separately formed on the surface of the base material layer. As a material for the optical layer having a fine unevenness formed separately as described above, a synthetic resin having light transmittance can be used. Examples of such synthetic resins include polyester resins such as polyethylene terephthalate and polyethylene naphthalate; cellulose resins such as diacetyl cellulose and triacetyl cellulose; polycarbonate resins; acrylic resins such as polymethyl methacrylate; polystyrene and acrylonitrile.・ Styrene resins such as styrene copolymers; polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin resins such as ethylene / propylene copolymers; vinyl chloride resins; amide resins such as nylon and aromatic polyamide Imide resin; sulfone resin; polyether sulfone resin; polyether ether ketone resin; polyphenylene sulfide resin; vinyl alcohol resin; System resin, vinyl butyral resins; arylate resin; polyoxymethylene-based resin, epoxy-based resins.

  Further, as the optical layer laminated on the surface of the base material layer, in addition to the above, for example, (i) a microlens sheet having a microlens array composed of a plurality of hemispherical microlenses on the surface, and (ii) on the surface A prism sheet having a plurality of triangular prismatic prism portions in a stripe shape, (iii) a lenticular lens sheet having a plurality of semi-cylindrical cylindrical lens portions in a stripe shape on the surface, and (iv) only the curvature of the lens arranged on the surface. A Fresnel lens sheet or the like can also be used. These optical layers can also be laminated on the base material layer according to a known coating method.

  The manufacturing method of the optical sheet for a direct type liquid crystal display device is not limited to the method using one continuous production line. In consideration of the flexibility of the production process, the sharing of manufacturing equipment and manpower resources, etc., the base film forming process, the stretching process, and the optical layer forming process can be carried out as separate production lines.

  The optical sheet for a direct liquid crystal display device of the present invention is not only used as a lower diffusion sheet installed in the vicinity of the backlight in a backlight unit for a liquid crystal display device such as a television monitor, but also as other prism sheet or the like. It can also be used as an upper diffusion sheet installed above the optical sheet. That is, since the optical sheet for a direct liquid crystal display device of the present invention has an excellent anti-sticking function, it is suitably used as a lower diffusion sheet installed on a smooth surface close to the backlight. And since such a sticking prevention function does not prevent application to applications other than the lower diffusion sheet, the optical sheet for a direct liquid crystal display device can be used not only as a lower diffusion sheet but also as an upper diffusion sheet. By using it, it is possible to improve the manufacturing efficiency of the entire backlight unit and reduce the manufacturing cost while maintaining excellent transparency and mechanical strength.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

The measuring method of the physical property value in the following examples is as follows.
(1) Anti-sticking property Each polyester film was allowed to stand for 24 hours under environmental test conditions (70 ° C. × RH 95%) with water intervened and completely overlapped with an acrylic plate. After standing, peeling of the polyester film and the acrylic plate was attempted, and the ease of peeling was judged based on the following criteria.
Peeled very easily ... ◎ (very good)
Easily peeled off ... (good)
There was a little resistance, but it peeled off… △ (somewhat bad)
Resistance was large and did not peel off easily x (defect)

(2) Static friction coefficient and dynamic friction coefficient About each polyester film, the static friction coefficient and the dynamic friction coefficient were measured according to ASTM-D1894-08 standard using a slip tester.

(3) Arithmetic mean roughness (Ra)
About each polyester film, arithmetic mean roughness (Ra) was calculated | required based on JISB0601-2001.

(4) Maximum roughness (Ry)
About each polyester film, maximum roughness (Ry) was calculated | required based on JISB0601-2001.

(5) Ten point average roughness (Rz)
About each polyester film, ten-point average roughness (Rz) was calculated | required based on JISB0601-2001.

(6) Total light transmittance About the optical sheet which laminated | stacked the optical layer, according to JISK7105-1981, the total light transmittance was measured with the haze meter by Suga Test Instruments Co., Ltd.

[Example 1]
A molten mixture of polyethylene terephthalate (hereinafter referred to as “PET”) 99.9% by mass and colloidal silica 0.1% by mass with an average particle size of 120 nm is supplied to a T-die and extruded to form a PET film extrudate, The PET film extrudate was successively stretched at a magnification of 3 times in the film longitudinal direction and 4 times in the film width direction to obtain a base material layer (biaxially stretched polyester film) having an average thickness of 188 μm. With respect to this biaxially stretched polyester film, the anti-sticking property, static friction coefficient, dynamic friction coefficient, arithmetic average roughness (Ra), maximum roughness (Ry) and ten-point average roughness (Rz) were measured according to the above methods. Furthermore, on the surface of this biaxially stretched polyester film, 100 parts by mass of a polyurethane resin (“Byron 3900” from Toyobo Co., Ltd.) and a modified polyisocyanate resin (“Coronate L” from Nippon Polyurethane Industry Co., Ltd.) An easy-adhesion layer (primer layer) having a thickness of 10 μm was formed by applying a blending solution containing 5 parts by mass and drying. Next, 100 parts by mass of a binder resin compound (“Toiron Boseki” “Byron 200”) having polyester polyol as a base polymer, 50 parts by mass of colloidal silica having an average particle size of 20 nm, a curing agent (Nippon Polyurethane Co., Ltd.) In a polymer composition containing 5 parts by mass of “Coronate HX” and 5 parts by mass of a light stabilizer (“PUVA-1033” from Otsuka Chemical Co., Ltd.) 50 parts of “MBX-15” from Seikoku Kogyo Co., Ltd. were mixed to prepare a coating solution. The coating liquid was applied to the surface of the easy-adhesion layer and cured to form an optical layer having a thickness of 20 μm, thereby obtaining an optical sheet. With respect to this optical sheet, the total light transmittance was measured according to the above method. Table 1 shows the measurement results of these physical properties.

[Example 2]
A base material layer (biaxially stretched polyester film) and an optical sheet are formed in the same manner as in Example 1 except that the average particle size of colloidal silica used as a raw material component for forming a PET film extrudate is changed to 80 nm. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 3]
A base material layer (biaxially stretched polyester film) and an optical sheet are formed in the same manner as in Example 1 except that the average particle size of colloidal silica used as a raw material component for forming a PET film extrudate is changed to 170 nm. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 4]
Substrate layer (biaxially stretched polyester film) and optical sheet as in Example 1, except that the amount of colloidal silica used as a raw material component for forming the PET film extrudate was changed to 0.005% by mass. And the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 5]
A base material layer (biaxially stretched polyester film) and an optical sheet were prepared in the same manner as in Example 1 except that the amount of colloidal silica used as a raw material component for forming the PET film extrudate was changed to 2.0% by mass. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Comparative Example 1]
A base material layer and an optical sheet were formed in the same manner as in Example 1 except that a polyester film having an average thickness of 188 μm was obtained without stretching in the film longitudinal direction and the film width direction, and this was used as the base material layer. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Comparative Example 2]
A base material layer (biaxially stretched polyester film) and an optical sheet are formed in the same manner as in Example 1 except that the average particle diameter of colloidal silica used as a raw material component for forming a PET film extrudate is changed to 40 nm. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Comparative Example 3]
A base material layer (biaxially stretched polyester film) and an optical sheet are formed in the same manner as in Example 1 except that the average particle diameter of colloidal silica used as a raw material component for forming a PET film extrudate is changed to 300 nm. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 6]
As a raw material for forming a PET film extrudate, a molten mixture of 99.9% by mass of polyethylene terephthalate and 0.1% by mass of polymethyl methacrylate (hereinafter referred to as “PMMA”) particles having an average particle diameter of 120 nm was used. In the same manner as in Example 1, a substrate layer (biaxially stretched polyester film) and an optical sheet were formed, and the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 7]
A base material layer (biaxially stretched polyester film) and an optical sheet were formed in the same manner as in Example 6 except that the average particle diameter of the PMMA particles used as a raw material component for forming the PET film extrudate was changed to 80 nm. The above physical properties were measured. The measurement results are also shown in Table 1.

[Example 8]
A base material layer (biaxially stretched polyester film) and an optical sheet are formed in the same manner as in Example 6 except that the average particle diameter of PMMA particles used as a raw material component for forming a PET film extrudate is changed to 170 nm. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 9]
A base material layer (biaxially stretched polyester film) and an optical sheet were prepared in the same manner as in Example 6 except that the amount of PMMA particles used as a raw material component for forming the PET film extrudate was changed to 0.005% by mass. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Example 10]
Substrate layer (biaxially stretched polyester film) and optical sheet as in Example 6, except that the amount of PMMA particles used as a raw material component for forming the PET film extrudate was changed to 2.0 mass%. And the above physical properties were measured. The measurement results are also shown in Table 1.

[Comparative Example 4]
A base material layer and an optical sheet were formed in the same manner as in Example 6 except that a polyester film having an average thickness of 188 μm was obtained without stretching in the film longitudinal direction and the film width direction, and this was used as the base material layer. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

[Comparative Example 5]
A base material layer (biaxially stretched polyester film) and an optical sheet were formed in the same manner as in Example 1 except that the average particle diameter of the PMMA particles used as a raw material component for forming the PET film extrudate was changed to 40 nm. The above physical properties were measured. The measurement results are also shown in Table 1.

[Comparative Example 6]
A base material layer (biaxially stretched polyester film) and an optical sheet are formed in the same manner as in Example 1 except that the average particle diameter of PMMA particles used as a raw material component for forming a PET film extrudate is changed to 300 nm. Then, the above physical properties were measured. The measurement results are also shown in Table 1.

  As can be seen from the results in Table 1, the biaxially stretched polyester films of Examples 1 to 10 containing an inorganic filler or an organic filler having an average particle diameter in the range of 70 nm to 200 nm do not perform biaxial stretching. Compared to the polyester films of Comparative Examples 1 and 4 and the biaxially stretched polyester films of Comparative Examples 2 and 5 containing a filler having an average particle size outside the above range, the anti-sticking property was remarkably superior. It was found that In addition, the polyester films of Comparative Examples 3 and 6 showed high anti-sticking property due to the large particle size of the filler, but when observed with an electron microscope, they were fine at many locations on the surface of the acrylic plate laminated in the test. Scratches were observed.

  Further, Examples 1 and 6 using an inorganic filler or an organic filler having an average particle diameter value of 120 nm within a range of 100 nm to 150 nm are examples including fillers having an average particle diameter value outside this range. Compared with 2 and 3, or Examples 7 and 8, it was found that a better anti-sticking effect was exhibited. Further, Examples 1 and 6 using an inorganic filler or an organic filler whose amount is 0.1% by mass within a range of 0.01% by mass or more and 1% by mass or less include a filler having an amount outside this range. Compared to Examples 4 and 5, or Examples 9 and 10, it was found that a better anti-sticking effect was exhibited as described above.

  According to the optical sheet for a direct type liquid crystal display device, it is possible to effectively prevent sticking with other layers laminated on the back surface side, and to reduce the manufacturing cost and increase the efficiency of the manufacturing process. Therefore, in particular, an optical sheet having a large area used for a large screen of a direct type liquid crystal display device is industrially useful because a significant reduction in manufacturing cost and simplification of the manufacturing process can be achieved.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Base material layer 3 Optical layer 4 Polyester-type resin 5 Filler 6 Light diffusing agent 7 Binder 8 Mixture of the polyester-type resin 4 and the filler 5 9 Base film extrusion 10 Optical containing the light diffusing agent 6 and the binder 7 Layer composition 11 Optical sheet 12 Fine uneven shape 20 T die 21 A pair of pressing rolls 22 Stretching device 23 Coater pan 24a Pickup roll 24b Adjustment roll 24c Coating roll 24d Backup roll 50 Backlight unit 51 Lamp 52 Backlight 53 Light diffusion Sheet 54 Prism sheet 54a Prism portion 55 Base material layer 56 Light diffusion layer 57 Sticking prevention layer 58 Binder 59 Light diffusion agent 60 Binder 61 Beads

Claims (12)

An optical sheet for a direct liquid crystal display device comprising a transparent substrate layer and an optical layer laminated on the surface side of the substrate layer,
As the base material layer, a biaxially stretched polyester film containing a filler is used,
An optical sheet for a direct type liquid crystal display device, wherein the average particle size of the filler is 70 nm or more and 200 nm or less.   The optical sheet for a direct type liquid crystal display device according to claim 1, wherein the content of the filler is 0.01% by mass or more and 1% by mass or less.   The direct type according to claim 1 or 2, wherein the filler is selected from the group consisting of silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, acrylic resin, melamine resin, silicone resin, and crosslinked polystyrene. Optical sheet for liquid crystal display devices.   The stretch ratio in the longitudinal direction of the biaxially stretched polyester film is 2.5 times or more and 4.5 times or less, and the stretch ratio in the width direction is 3 times or more and 5 times or less. An optical sheet for a direct type liquid crystal display device as described in 1.   The optical sheet for a direct type liquid crystal display device according to any one of claims 1 to 4, wherein an F5 value in a longitudinal direction and a width direction of the biaxially stretched polyester film is 80 MPa or more and 120 MPa or less.   The direct type according to any one of claims 1 to 5, wherein the biaxially stretched polyester film has a static friction coefficient of 0.3 to 0.6 and a dynamic friction coefficient of 0.3 to 0.5. Optical sheet for liquid crystal display devices.   The optical sheet for a direct liquid crystal display device according to any one of claims 1 to 6, wherein an arithmetic average roughness (Ra) of the biaxially stretched polyester film is 0.04 µm or more and 0.25 µm or less.   The optical sheet for a direct liquid crystal display device according to any one of claims 1 to 7, wherein the maximum roughness (Ry) of the biaxially stretched polyester film is 0.4 µm or more and 0.8 µm or less.   The optical sheet for a direct type liquid crystal display device according to any one of claims 1 to 8, wherein the biaxially stretched polyester film has a ten-point average roughness (Rz) of 0.3 µm or more and 0.6 µm or less. .   The optical sheet for a direct type liquid crystal display device according to any one of claims 1 to 9, wherein the optical layer has a light diffusing agent and a binder thereof.   The optical sheet for a direct type liquid crystal display device according to any one of claims 1 to 9, wherein the optical layer has a fine uneven shape having refractive properties. In a backlight unit for a direct liquid crystal display device that guides light emitted from a lamp to the surface side by dispersing it,
A backlight unit for a direct liquid crystal display device, comprising the optical sheet for a direct liquid crystal display device according to any one of claims 1 to 11.

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