WO2010038549A1

WO2010038549A1 - Optical sheet and surface light source for liquid crystal display device

Info

Publication number: WO2010038549A1
Application number: PCT/JP2009/064148
Authority: WO
Inventors: 直樹辻内; 基之鈴木
Original assignee: 東レ株式会社
Priority date: 2008-09-30
Filing date: 2009-08-11
Publication date: 2010-04-08
Also published as: TW201020592A; KR20110061592A; CN102203640A; JPWO2010038549A1; TWI481908B; CN102203640B

Abstract

An optical sheet containing a three-layer laminate resin sheet which is composed of a core layer and outer layers which are arranged on both sides of the core layer without having adhesive layers therebetween. The core layer is composed of an amorphous resin, and at least one of the outer layers is provided with a plurality of projections in the surface. The resins constituting the outer layers are mainly composed of resins having the same composition, and each has a glass transition temperature not less than 80˚C and lower than the glass transition temperature of the resin constituting the core layer by 10˚C or more.

Description

Optical sheet and surface light source for liquid crystal display device

The present invention relates to an optical sheet such as a so-called prism sheet and a backlight unit using the same.

Liquid crystal display devices are used in a variety of applications, including notebook computers and mobile phone devices, as well as televisions, monitors, and car navigation systems. The liquid crystal display device incorporates a backlight unit serving as a light source, and is configured to display by controlling light beams 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 structure of the backlight unit can be roughly divided into two. There are a system called a direct type backlight and a system called a sidelight type backlight.

Sidelight type backlight is a system mainly used for mobile phones, notebook computers, etc. that require thinning and miniaturization. As a basic configuration, a light guide plate is used. In addition to the light guide plate, typical examples include a reflective film that functions to reflect and reuse light leaking from the back surface of the light guide plate, a diffusion sheet that equalizes the light emitted from the front surface of the light guide plate, and a prism sheet that improves front brightness. Various kinds of optical films are used, such as a light-condensing sheet and a brightness enhancement sheet that improves the brightness on a liquid crystal panel. Among them, the prism sheet generally used is one prepared by applying a photocurable resin on a transparent substrate to form a prism pattern (Patent Document 1), and heating a mold on a sheet made of a thermoplastic resin. One produced by forming a prism pattern by pressing (Patent Document 2) or produced using a norbornene-based resin as a base material to improve heat resistance (Patent Document 3).

Japanese Patent No. 2670518 Japanese Patent Laid-Open No. 9-21908 JP-A-9-323354

However, the prism sheet produced using the photocurable resin of Patent Document 1 is curled due to shrinkage of the photocurable resin layer forming the prism layer in a durability test under heating or humidification conditions. For this reason, problems in display quality, such as color unevenness, occur when assembled in a backlight unit.

When the liquid crystal display device is intended for small-sized mobile phones and the like, it is essential to make various optical sheets thin, including a prism sheet. In the case of the prism sheet produced using the photo-curing resin, there is a drawback that the curl during the durability test is more noticeably generated as the thickness of the support is reduced in order to reduce the thickness.

In addition, the prism sheet produced using the thermoplastic resin of Patent Document 2 is curled during the durability test as compared with the photocurable resin, but is bent over the front surface of the sheet, that is, the flatness is deteriorated. Can be seen. In particular, in the test under humidified conditions, the flatness is remarkably deteriorated, and the shape formed on the surface is also deformed. *

Furthermore, although the optical sheet produced using the norbornene-based resin of Patent Document 3 is improved in terms of curl and flatness during a durability test, the glass transition temperature (hereinafter referred to as Tg) of the resin is too high. However, when the shape with a sharp top like a prism sheet is formed, it is difficult to mold into the shape of the mold. In addition, there is a disadvantage in that productivity is poor because it takes a very long time to raise the mold to a high temperature during molding of the uneven shape and a time to cool the mold after pressing the mold against the resin.

Therefore, in view of the background of the prior art, the present invention is an optical sheet having excellent formability and productivity, having a thin surface, and having less unevenness on the surface and less curling of the sheet even under a durability test, and having good flatness. Is to provide.

The present invention employs the following means in order to solve such problems. That is, the optical sheet of the present invention includes a three-layer laminate composed of a core layer and an outer layer laminated on both surfaces of the core layer without an adhesive layer, and the resin constituting the core layer is amorphous. A plurality of convex shapes formed on the surface of at least one of the outer layers, the main component of the resin constituting each outer layer is a resin having the same composition, and the glass transition of the resin constituting each outer layer The temperature is 80 ° C. or higher, and 10 ° C. or lower than the glass transition temperature of the resin constituting the core layer.
In addition, the backlight unit of the present invention is mounted with the optical sheet of the present invention.

According to the present invention, it is possible to provide an optical sheet that is excellent in formability and productivity, is thin, has little unevenness formed on the surface even under an endurance test, has little curling of the sheet, and has good flatness. it can. And the display quality of the backlight unit carrying this optical sheet can be improved.

The structure of the optical sheet of this invention is illustrated typically. (A) to (d) schematically illustrate steps of forming a convex shape on the outer layer of the optical sheet of the present invention. (A) to (e) are perspective views schematically showing the convex shape of the outer layer of the optical sheet of the present invention, (a) to (c) are stripe shapes, (d) is a dome shape, (E) is a pyramid shape. (A) to (f) are all sectional views of the convex shape of the outer layer of the optical sheet of the present invention. (A) and (b) schematically illustrate the configuration of the optical sheet of the present invention in which a release layer is formed, and (c) and (d) are optical sheets obtained by forming a convex shape on the outer layer. The structure of is typically illustrated. It is the schematic of the manufacturing apparatus of the optical sheet in Example 9 and Comparative Example 7.

d: Convex height of the convex shaped cross section h: Thickness from the bottom of the convex shaped cross section to the core layer H: Thickness of the outer layer of the optical sheet p: Convex shape pitch of the convex shaped cross section

The optical sheet of the present invention includes a three-layer laminate composed of a core layer and an outer layer laminated on both surfaces of the core layer without an adhesive layer, and the resin constituting the core layer is an amorphous resin. A plurality of convex shapes are formed on the surface of at least one outer layer, the main component of the resin constituting each outer layer is a resin having the same composition, and the glass transition temperature (hereinafter referred to as Tg) of the resin constituting each outer layer. ) Is 80 ° C. or higher and 10 ° C. or lower than the glass transition temperature of the resin constituting the core layer (FIG. 1). In addition to the three-layer laminate of “outer layer / core layer / outer layer”, layers for imparting surface releasability and adjusting optical properties may be laminated. In that case, the thickness of each layer Is preferably 1/5 or less of the thickness of the outer layer. A preferable total number of layers is 3 to 10 layers including 3 layers of a 3-layer laminate. For at least three layers, one outer layer is provided on one surface of the core layer for imparting mechanical and thermal strength to form a plurality of convex shapes, and this outer layer is formed on the other surface. This is because a layer mainly composed of a resin having the same composition as the main component of the resin is provided to suppress curling. Thus, by making the main components of the resins constituting both outer layers have the same composition, the thermal contraction rate of each outer layer becomes substantially the same, and curling of the optical sheet due to heating and humidification can be suppressed. Here, the “main component” of the resin constituting the outer layer is a resin having a composition occupying 50% by weight or more of the resin constituting the outer layer, preferably 70% by weight or more, more preferably 95% by weight. That's it.

In the outer layer in the present invention, the Tg of the resin constituting the outer layer is 80 ° C. or higher. In the present invention, Tg is a midpoint glass transition temperature value obtained by the following procedure by differential scanning calorimetry (hereinafter referred to as DSC) measurement according to JIS K 7121-1987. That is, using a robot DSC “RDSC220” manufactured by Seiko Denshi Kogyo Co., Ltd. as a DSC and a disk station “SSC / 5200” manufactured by Seiko Electronics Co., Ltd. The mixture is heated to 300 ° C. at a rate of temperature rise / minute and melted for 5 minutes, and then quenched with liquid nitrogen. Tg obtained by the measurement in this process is employed.

In the case of an optical sheet used for a liquid crystal display device, a test under heating only and heating / humidifying conditions is usually performed as a durability test. A temperature range of 60 to 80 ° C. and a humidity range of 80 to 95% are often employed. In particular, when an optical film having a thickness of less than 60 μm is tested under these conditions, curling becomes significant. The curl is particularly large in a prism sheet obtained by forming a prism made of an acrylic UV curable resin on a conventional polyester resin. Therefore, in addition to being capable of surface shaping as the outer layer, it is also necessary that deformation does not occur in the temperature and humidity ranges in the durability test. That is, the Tg of the resin constituting the outer layer needs to be 80 ° C. or higher, which is a temperature higher than the test temperature. When Tg is less than 80 ° C., the shape formed on the sheet surface during the durability test is deformed and / or the planarity of the sheet itself is deteriorated. When an optical sheet whose flatness is likely to deteriorate is incorporated in a backlight unit, it is observed as uneven optical characteristics as the flatness deteriorates. The Tg of the resin constituting the outer layer is preferably 80 to 120 ° C. If the Tg exceeds 120 ° C, the Tg is too high, making it difficult to improve the accuracy during surface shaping. If a shape with a sharp top like a prism sheet is shaped, it will be molded into the shape as the mold. In some cases, it may be a low-precision molded product with a rounded top. In addition, the time required for raising the mold to a high temperature during surface shaping, and the time required for cooling the mold after pressing the mold against the resin are very long, resulting in poor productivity.

The resin constituting the outer layer in the present invention is not particularly limited as long as the above Tg condition is satisfied. For example, polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, cyclohexanedimethanol copolymer polyester Resin, polyester resin such as isophthalic acid copolymer polyester resin, spiroglycol copolymer polyester resin, fluorene copolymer polyester resin, polyolefin resin such as polyethylene, polypropylene, polymethylpentene, cyclic polyolefin copolymer resin, polymethyl methacrylate, etc. Acrylic resin, polycarbonate, polystyrene, polyamide, polyether, polyesteramide, polyetherester, polyvinyl chloride, and Copolymers to these as a component, or a thermoplastic resin such as a mixture of these resins. Among these, cyclic polyolefins and polyester resins are more preferably used in terms of mechanical strength, heat resistance, dimensional stability, and surface formability. Furthermore, cyclic polyolefins are particularly preferred because of excellent transparency, yellowing and moisture permeability and very small dimensional change.

Here, the cyclic polyolefin resin has a polymerizable cyclic olefin having an ethylenic double bond in the ring as a monomer unit. Examples of cyclic olefins include norbornene monomers (monocyclic and polycyclic).
The cyclic polyolefin resin preferably used in the present invention refers to a homopolymer of the above cyclic olefin, a copolymer of two or more cyclic olefins, or a copolymer of a cyclic olefin and a chain olefin.

As such a cyclic polyolefin-based resin, for example, a structure represented by the following formula (1) can be used.

In the above formula (1), A represents a cyclic olefin monomer, and B represents a chain copolymerizable monomer. M in the formula represents a positive integer, and n represents 0 or a positive integer.

As the cyclic olefin monomer represented by A in the above formula (1), a structural unit represented by the following formula (2) or (3) can be used.

In the above formula (2), a and b represent 0 or a positive integer. R ₁ to R ₄ are a hydrogen atom, a hydrocarbon group, a halogen atom, a halogen-substituted hydrocarbon group, — (CH ₂ ) x COOR ₉ (x represents 0 or a positive integer; R ₉ represents a hydrogen atom, Represents a hydrocarbon group, a halogen atom, or a halogen-substituted hydrocarbon group.

In the above formula (3), c and d represent 0 or a positive integer. R ₅ to R ₈ are a hydrogen atom, a hydrocarbon group, a halogen atom, a halogen-substituted hydrocarbon group, — (CH ₂ ) x COOR ₁₀ (x represents 0 or a positive integer. R ₁₀ represents a hydrogen atom, Represents a hydrocarbon group, a halogen atom, or a halogen-substituted hydrocarbon group.

The cyclic olefin monomer represented by A can be used by copolymerizing not only one type but also two or more types of cyclic olefin monomers.

Examples of the chain copolymerizable monomer represented by B in the above formula (1) include α-olefins such as ethylene, propylene, butene and pentene, (meth) acrylic acid, and (meth) acrylic acid esters. , Acrylonitrile, maleic anhydride and the like can be used. Of these, α-olefins are preferably used.

The cyclic polyolefin resin in the present invention may be composed of one kind of cyclic polyolefin resin, or two or more kinds of cyclic polyolefin resins may be blended and used. A method of blending two or more kinds of resins is a preferred embodiment because it allows control of thermal properties such as glass transition temperature of the optical sheet and mechanical properties such as high elongation.

In the present invention, an amorphous resin is used as the resin constituting the core layer. As a resin for an optical sheet used for a liquid crystal display or the like, an amorphous resin having excellent transparency is generally used. In addition, when forming an amorphous resin film by melt extrusion, rapid cooling for reducing crystallinity is not required as in crystalline resin, so it can be cooled slowly, and a sheet with excellent thickness accuracy can be obtained. Film formation is possible. As the main component of the resin constituting the core layer, a cyclic polyolefin resin, a polycarbonate resin, a polystyrene resin, an acrylic resin, and an amorphous polyester resin are preferable. In particular, since the cyclic polyolefin resin is excellent in transparency, yellowing and moisture permeability and has a very small dimensional change, it is suitable as an optical sheet material that achieves the effects of the present invention. Here, the “main component” of the resin constituting the core layer is a resin having a composition occupying 50% by weight or more of the resin constituting the core layer.

Further, when a surface shape is formed by processing a sheet made of an amorphous resin, deformation of the shape is observed when heated to a temperature of Tg or higher. The core layer preferably has a higher Tg than the outer layer in order to impart flatness. The cyclic polyolefin satisfies the Tg condition and is suitable as a main component of the resin constituting the core layer also in this respect.

In the present invention, the Tg of the resin constituting the outer layer is 10 ° C. or more lower than the Tg of the resin constituting the core layer. When the difference in Tg is less than 10 ° C., when the convex shape is formed on the outer layer using a flat plate pressing method, when the core layer is heated and the mold is peeled off, the entire optical sheet is molded. The flatness becomes worse due to deformation following the above. The Tg of the resin constituting the outer layer is preferably 10 to 100 ° C. lower than the Tg of the resin constituting the core layer. When the difference in Tg exceeds 100 ° C., when the sheet is formed by using the coextrusion method, the resin having the lower Tg is carbonized, and the quality of the sheet may be deteriorated.

Examples of the method for producing a three-layer laminate in the optical sheet of the present invention include the following methods for producing a laminate without using an adhesive.
(I) A method in which the resin constituting the support layer and the resin constituting the outer layer are separately charged into two extruders, melted and coextruded onto a cast drum cooled from the die, and processed into a sheet (coextrusion) Law).
(Ii) A method in which a resin constituting an outer layer is put into an extruder, melt extruded and laminated while being extruded from a die on a sheet of a support layer made of a single film (melt lamination method).
(Iii) A method in which a sheet of a support layer and a sheet of an outer layer produced by a single film are separately produced and thermocompression bonded with a heated roll group or the like (thermal lamination method).
(Iv) In addition, a method in which the outer layer sheet is dissolved in a solvent, and the solution is applied onto the support layer sheet and dried (coating method).

If the adhesive is used, the number of work steps increases and the cost increases, which is not preferable. Among these, the coextrusion method of coextrusion and processing into a sheet shape is a preferable method in that a laminate can be produced with high accuracy in a single step.

An example of a method for forming a plurality of convex shapes on the outer layer of the optical sheet of the present invention will be described with reference to FIG. Both the optical sheet of the present invention before forming a convex shape on the outer layer and a mold having a shape obtained by inverting the pattern to be transferred have a glass transition temperature Tg of the resin constituting the outer layer of Tg + 60 ° C. or lower. Heat within the temperature range (FIG. 2A). Next, the outer layer of the optical sheet and the uneven surface of the mold are brought close to each other (FIG. 2B), pressed as it is at a predetermined pressure, and held for a predetermined time (FIG. 2C). Next, the temperature is lowered while maintaining the pressed state. Finally, the press pressure is released and the optical sheet is released from the mold (FIG. 2D).

Moreover, as a pattern forming method of the outer layer, in addition to a method of pressing a flat plate as shown in FIG. 2 (flat plate pressing method), a roll-shaped mold having a pattern formed on the surface is used to form a roll-shaped sheet. The roll-to-roll continuous molding may be performed to obtain a roll-shaped molded body. The flat plate pressing method is excellent in that a finer and higher aspect ratio pattern can be formed. The roll-to-roll continuous forming is superior to the flat plate pressing method in terms of productivity. Furthermore, in the case of roll-to-roll continuous molding, since the core layer is present in the optical sheet of the present invention, there is a stiffness of the sheet itself compared to a single film made of resin constituting the outer layer. It is preferable because it is excellent.

A preferred pattern of the convex shape of the outer layer of the optical sheet of the present invention is shown in FIG.
3A to 3E are perspective views schematically showing a convex shape. As the arrangement structure within the surface of the convex shape formed on the surface of the outer layer, a stripe pattern as shown in FIGS. 3A to 3C (a convex shape in which a plurality of convex shapes each extend in one direction) And the longitudinal directions of the plurality of convex shapes are substantially parallel to each other (the difference between the longitudinal directions is 5 ° or less, preferably 1 ° or less, respectively)), FIG. A preferable example is a pattern in which a shape such as a dome shape or a pyramid shape as shown in FIG.

The stripe pattern illustrated in FIGS. 3A to 3C will be described. FIG. 4 shows a cross-sectional shape in a direction perpendicular to the longitudinal direction of the convex shape. The convex cross-sectional shape of each stripe is an isosceles triangle, equilateral triangle, right-angled isosceles triangle, a triangular shape obtained by deforming them (FIG. 4A), a semicircle, a semi-ellipse, or an arc shape obtained by deforming them. (FIG. 4B), waveform shapes such as regular sine curves and random curves (FIG. 4D), and the like are preferable examples.

Further, as shown in FIGS. 4 (a) and 4 (b), each cross-sectional shape may be a repeated pattern having the same shape, or as shown in FIG. 4 (d), a regular or random array pattern having different sized shapes. Alternatively, as shown in FIG. 4E, regular or random patterns having different shapes are also preferable embodiments. Thus, regular or random arrays of different sizes or shapes, and shapes such as the random curve in FIG. 4 (c) can cause light interference fringes and glare that can be caused by the shape formed on the sheet surface. It is preferable because it also has an inhibitory effect.

Further, as shown in FIG. 4F, a shape in which flat portions are formed between adjacent patterns in the cross section of each stripe is also used. However, since the light incident on the flat portion is likely to pass through without undergoing angle conversion, as shown in FIGS. 4A to 4E, flat portions are formed between adjacent patterns. A shape that is not done is more preferred.

Further, the cross-sectional shape of each stripe may be a uniform stripe having the same shape and size when observed in the longitudinal direction of the stripe, or may be the same shape but different in size (that is, the height fluctuates). The stripe may be a stripe, or any stripe whose shape changes is preferably used.

Furthermore, when the stripes are observed from the normal direction of the sheet, the individual stripes may be completely linear or preferably used when the stripes are not linear, such as wavy. Therefore, the distance (pitch) between the individual stripes is preferably either regular or random.

Next, as shown in FIGS. 3D and 3E, a pattern in which shapes such as a dome shape and a pyramid shape are spread will be described. Preferable shapes can be roughly divided into a hemispherical shape such as a dome shape and a polygonal pyramid shape such as a pyramid shape.

In the case of a hemispherical shape, a hemisphere, a shape obtained by expanding and contracting the hemisphere in the height direction (semi-spheroid), and the like may be used, and the shape may be anisotropic in the sheet plane. In the case of anisotropy, anisotropy can be optically induced by aligning the major axis directions of the individual shapes. For the arrangement in the hemispherical sheet surface, either a regular arrangement (such as closest packing) or a random arrangement is preferably used.

Further, in the case of a polygonal pyramid shape, a triangular pyramid, a quadrangular pyramid, a hexagonal pyramid, an octagonal pyramid, etc. are given as examples. Also in this case, as the arrangement in the sheet surface, either a regular arrangement or a random arrangement is preferably used.

These shapes may be a repetitive pattern of a single shape within the sheet surface, or may be a composite shape in which a plurality of shape types are arranged.

For example, when a stripe pattern as shown in FIGS. 3A to 3C is formed on the surface, anisotropy may occur depending on the direction of the stripe, particularly with respect to the curl of the sheet. The effect by making the optical sheet structure of the present invention is great. That is, the present invention is effective when a prism sheet used for exhibiting a luminance improvement effect is produced as an optical sheet for a liquid crystal display device.

The prism sheet is a prism sheet in which a plurality of triangular prisms each having a convex (cross-sectional) shape are triangular. When the optical sheet of the present invention is a prism sheet, the apex angle of the triangle in the cross section is preferably 70 to 110 °, more preferably 80 to 100 °, and still more preferably 90 °. When the apex angle is less than 70 ° and exceeds 110 °, the front luminance improvement effect when incorporated in the backlight unit may be insufficient. Moreover, although it selects with the structure of a backlight, since the triangle of the said cross section is an isosceles triangle and it is excellent in the front brightness improvement effect in any structure, it is preferable.

The prism sheet that is preferably used as the optical sheet of the present invention preferably uses either a repeated arrangement in which the individual triangles of the cross section have the same shape or a different shape array. Further, the height in the film thickness direction of the prism formed on the sheet surface may be constant or oscillated as viewed in the longitudinal direction of the triangular prism of the prism. Further, in the sheet surface, the line at the top of the prism may be linear or may change into a wave shape.

The lamination ratio of the outer layer and the core layer of the optical sheet of the present invention is not particularly limited, but preferably the thickness of the outer layer (one side): the thickness of the core layer = 1: 0.05 to 1:20, more preferably the thickness of the outer layer. (Single side): Thickness of the core layer = 1: 1 to 1:10. By setting the lamination ratio of the outer layer and the core layer within this range, even a thin film has a sufficiently thick surface layer, and the curl of the entire optical sheet is reduced while maintaining the mechanical strength, which is preferable. The thickness ratio between the outer layers provided on both sides of the core layer is preferably 1: 1 to 1: 2 in order to reduce the curl of the entire optical sheet.

In the optical sheet of the present invention, in order to perform high-quality and high-yield pattern formation, the convex bottom (minimum value) from the lowest bottom of the convex shape to the core layer and the outer layer The relationship between the minimum outer layer thickness h, which is the distance to the interface of the core layer, and the convex height d, which is the distance between the top and bottom of the convex shape, is in the range of d / 10 ≦ h ≦ 10d. preferable. When the value of h is less than d / 10, it may be difficult to fill the details of the mold when the mold is pressed against the surface layer. On the other hand, if it exceeds 10d, the characteristics of the pattern formed on the surface layer cannot be fully exhibited, which may cause a decrease in luminance. In order to obtain such a shape, it is preferable that the thickness of the outer layer before the convex shape is formed be equal to or greater than the convex height d of the cross section of the convex shape to be formed.

Further, the largest convex height dmax of the convex-shaped cross section provided in the outer layer may be appropriately determined according to the required optical characteristics, but is preferably 1 to 10 μm, and more preferably 5 to 10 μm. By setting it as this range, curl of the entire optical sheet can be reduced while maintaining mechanical strength.

The number of convex-shaped optical sheet widths may be appropriately determined according to the required optical characteristics, but is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more for a 1 mm width. . When the density of the concavo-convex shape is 5 or more per 1 mm width, the optical function is good.

The total thickness of the optical sheet of the present invention is preferably 60 μm or less, more preferably 10 to 50 μm, still more preferably 30 to 50 μm. A thinner optical sheet is preferable because the backlight module itself can be made thinner, and as a result, the design of the liquid crystal display device is improved. However, when the thickness of the optical sheet is less than 10 μm, it may be difficult to handle when incorporated in the backlight module. Here, the “total thickness” means that the optical sheet is formed by laminating another layer (for example, a release layer described later) on a three-layer laminate composed of an outer layer / core layer / outer layer. Is the thickness including all of the other layers and the three-layer laminate. Further, when a convex shape is formed on the surface of the optical sheet, the thickness is measured from the apex of the convex shape.

When forming the convex shape on the outer layer in the optical sheet of the present invention, it is preferable to provide a release layer in advance on the surface of the outer layer in contact with the mold. As shown in FIG. 5A, a release layer may be provided on the surface of one of the outer layers, or a release layer may be provided on the surfaces of both outer layers as shown in FIG. . An optical sheet can be obtained by forming a pattern on the sheets shown in FIGS.

By providing a release layer on the outer layer, the durability (repetitive use) of the release coat formed on the mold surface can be improved, and a mold that partially lost the release effect was used. Even in this case, it is possible to release the mold uniformly without any problem. Further, even if the mold is not subjected to a mold release process at all, it is preferable that a mold release layer is formed on the sheet side in advance so that the mold can be released and the mold mold release process cost can be reduced. . In addition, it is possible to prevent deformation of the molding pattern due to resin adhesion when releasing the optical sheet from the mold, and it is possible to release at a higher temperature, thereby shortening the cycle time. This is also preferable in terms of points. Further, it is preferable because the slip resistance on the surface of the optical sheet is further improved and the scratch resistance is improved, and defects caused in the manufacturing process can be reduced.

The resin constituting the release layer is not particularly limited, but is preferably composed mainly of a silicone resin, a fluorine resin, a fatty acid resin, a polyester resin, an olefin resin, and a melamine resin. Among these, silicone resins, fluorine resins, and fatty acid resins are more preferable. In addition to the above-mentioned resin, for example, an acrylic resin, a urethane resin, an epoxy resin, a urea resin, a phenol resin, and the like may be blended in the release layer, and various additives such as an antistatic agent, Surfactants, antioxidants, heat stabilizers, weathering stabilizers, ultraviolet absorbers, pigments, dyes, organic or inorganic fine particles, fillers, nucleating agents, crosslinking agents and the like may be blended. The thickness of the release layer is not particularly limited, but is preferably 0.01 to 3 μm. When the thickness of the release layer is less than 0.01 μm, the above-mentioned release property improving effect may be lowered.

The method for forming the release layer is not particularly limited, but various coating methods such as in-line coating method, reverse coating method, gravure coating method, rod coating method, bar coating method, die coating method or spray coating method should be used. Can do. In particular, the in-line coating method can be coated at the same time as the film formation of the base material, and thus is preferable from the viewpoint of productivity and coating uniformity.

The basic configuration of the direct type backlight unit will be described. A plurality of linear fluorescent tubes are arranged in parallel at the back of the screen, a light reflecting film below the light source (in the opposite direction to the screen), a diffuser plate, a diffusion sheet, a prism sheet, and brightness above the light source (screen side) An optical member such as an improvement sheet is installed. As the arrangement of the optical member on the upper side of the light source, it is preferable to use a diffusion plate directly above the light source and a brightness enhancement sheet on the uppermost side. Between the two members, a diffusion sheet or / and a prism sheet can be used. In addition, it is preferably used in any configuration.

Also, the basic configuration of the sidelight type backlight unit will be described. In the case of this backlight unit, a light guide plate for propagating light rays and spreading it in a planar shape is used, and a light source such as a straight line (for example, a fluorescent tube) or a dot (for example, LED) is provided on the side surface of the light guide plate, A light reflecting film is installed below the light guide plate (in the opposite direction to the screen), and optical members such as a diffusion sheet, a prism sheet, and a brightness enhancement sheet are installed above the light guide plate (screen side).

As the arrangement of the optical member on the upper side of the light source of the sidelight type backlight unit, it is preferable to use a brightness enhancement sheet at the uppermost position, and a diffusion sheet or / and a prism sheet are used between the light guide plate and the brightness enhancement sheet. It is preferable to use it by arbitrary structures according to.

The optical sheet of the present invention can exhibit the effects of light diffusibility and light condensing, like the diffusion sheet and the prism sheet, by giving the shapes exemplified so far. Therefore, in the direct type backlight unit, it can be installed at the same position as the diffusion sheet and the prism sheet.

(Measurement and evaluation method)
The following measurements were performed under conditions of a room temperature of 23 ° C. and a humidity of 65% unless otherwise specified.

A. Tg measurement In accordance with JIS K 7121-1987, Seiko Denshi Kogyo's robot DSC “RDSC220” is used for differential scanning calorimetry (DSC), and its disk station “SSC / 5200” is used for data analysis. An aluminum pan is filled with 5 mg of composition or film sample. This sample is heated from room temperature to 300 ° C. at a temperature rising rate of 20 ° C./min and melted for 5 minutes. Next, it was quenched with liquid nitrogen, and the glass transition temperature (midpoint glass transition temperature) was measured in this process.

B. Cross section observation The optical sheet passes through the top of the convex shape, and is cut along a plane perpendicular to the surface of the outer layer on which the convex shape is formed and across the plurality of convex shapes. Palladium was deposited. The cross section was observed by taking a photograph using a scanning electron microscope S-2100A manufactured by Hitachi, Ltd., and the dimensions of the sheet cross section and the convex shape formed on the surface were measured. If the convex shape collapses during cutting, the entire optical sheet is preliminarily immersed in liquid nitrogen and frozen or cut, or embedded in another resin and then cut. Prevent collapse.

C. Sheet thickness In cross-sectional observation, the magnification is adjusted to 200 times so that the entire sheet is within the field of view, a photograph is taken, the length of the photograph is measured, and the dimension between both surfaces of the sheet is measured. At this time, when a convex shape is formed on the surface, the dimension that maximizes the distance between both surfaces is measured. This is performed for 10 points randomly selected from within the sheet, and the average value is obtained as the sheet thickness.

D. Outer layer thickness H
In cross-sectional observation, the photograph is taken with the magnification adjusted to 200 times so that the entire outer layer is included in the field of view, and the photograph is measured to measure the dimension between both surfaces of the sheet. At this time, when a convex shape is formed on the surface, the dimension that maximizes the distance between both surfaces is measured. This is performed for 10 points randomly selected from within the sheet, and the average value is obtained as the outer layer thickness.

In addition, when the interface between the outer layer and the core layer is unclear in the cross-sectional observation, instead of using the scanning electron microscope so that this is observed, the observation with the laser microscope, the observation with the optical microscope, or the thin film with the transmission electron microscope Section observation can be employed depending on the material properties.

Also, when a release layer or a slippery layer is formed along the convex shape on the surface of the outer layer, it is also measured as a part of the outer layer.

E. Convex height d of convex shaped cross section
In cross-sectional observation, photographs were taken with the magnification adjusted to 200 times so that the top (maximum value) of 10 to 20 convex shapes was included in the field of view, and 10 consecutively selected points were selected. In the convex shape, the difference between the minimum height and the maximum height of the cut surface of the convex shape is measured. This is performed for 10 or more points arbitrarily extracted in the sheet and averaged to obtain a convex height d which is the distance between the top and bottom of the convex shape.

That is, when the shape of the cut surface is a single convex repetitive pattern as shown in FIGS. 4A, 4B, and 4F, the difference between the maximum height and the minimum height of the convex shape is measured.

In the case where the shape of the cut surface is a repeating pattern in which different shapes are combined as shown in FIGS. 4D and 4E, the difference between the maximum height and the minimum height in the repeating unit is measured.

In addition, when the shape of the cut surface changes randomly as shown in FIG. 4 (c) and the size of each convex shape, an arbitrary continuous 10-point convex shape is selected on the cut surface. Measure the difference between the height and the minimum height.

Also, for the pattern in which shapes such as a dome shape and a pyramid shape shown in FIGS. 3D and 3E are spread, the convex height d can be determined by applying the above-described determination criteria according to the cross-sectional shape.

F. Minimum outer layer thickness h
In cross-sectional observation, take a picture by adjusting the magnification to 200 times so that the field of view includes 5 to 20 convex bottoms (minimum value) and the interface between the outer layer and the core layer at the same time. Measure the minimum distance between the bottom and the interface in the 10 consecutive convex shapes selected. This is performed on 10 or more points arbitrarily extracted in the sheet and averaged to obtain the minimum outer layer thickness h.

G. Measurement of curl amount A 100 mm × 100 mm size sample was placed in a constant temperature and humidity tester (manufactured by Tabai Espec Co., Ltd., PR-3SPW) and allowed to stand at 85 ° C. and 85% RH for 240 hours. The sample immediately after taking out from the constant temperature and humidity tester was placed on a desk with the surface on which the convex shape was formed facing up. The curl amount (height from the film installation surface) of the four corners of the sample was measured, and the average value was taken as the curl amount.

H. Flatness Evaluation A sample of 100 mm × 100 mm size was put into a constant temperature and humidity tester (manufactured by Tabai Espec Co., Ltd., PR-3SPW) and allowed to stand at 85 ° C. and 85% RH for 240 hours. After taking out from the constant temperature and humidity tester, it was placed on a desk with the shaped surface facing downward, and the non-shaped surface was observed.
In the evaluation method, two linear fluorescent tubes were turned on, and the fluorescent lamp image reflected on the non-shaped surface was observed to judge whether or not the image of the linear fluorescent tube was distorted. The evaluation was performed by three people, and C was given when two or more people were distorted, B was given when one was judged to be distorted, and A was given when all were judged to be distorted.

I. Luminance evaluation 3.5-inch sidelight backlight for evaluation (housing, reflection film, light guide plate) is turned on, and after 10 minutes, a diffusion sheet (TDF187, manufactured by Toray Sehan Co., Ltd.) and a sample sheet are installed on the light guide plate. Then, the luminance in the front direction was measured using a two-dimensional luminance meter (Konica Minolta Sensing, CA-2000). The luminance was evaluated by an average value in a square range with a side of 50 mm centered on the center of the backlight.

In addition, the luminance evaluation is performed before and after the test for 240 hours (before and after the moist heat test) under the conditions of 85 ° C. and 85% RH described in G and H above. The luminance before the test is “initial luminance”, and the luminance after the test is Defined as “post-test brightness”. *

The measurement method and evaluation method of each example and comparative example will be described below.

Example 1
Cyclic polyolefin resin 1 ('TOPAS' 6013, Tg 130 ° C, manufactured by Polyplastics Co., Ltd.) is used as the resin constituting the core layer, and cyclic polyolefin resins 1 and 2 (cyclic olefin resin 'TOPAS' are used as the resin constituting the outer layer. A blend of '8007, Tg 78 ° C, manufactured by Polyplastics Co., Ltd.) at a mass ratio of 60:40 (Tg 110 ° C after blending) was prepared. These were dried at 100 ° C. for 6 hours and then melted in a separate extruder at a temperature of 240 ° C. Next, the laminated resin extruded from the molten three-layer coextrusion die was extruded into a sheet shape on a metal drum maintained at 100 ° C. A laminated sheet 1 was obtained by winding the metal drum at a speed of 25 m / min. In the laminated sheet 1, the thickness H of each outer layer was 7.5 μm, the thickness of the core layer was 23 μm, and the total was 38 μm.

Next, the following mold 1 and the laminated sheet 1 were heated at 135 ° C. for 1 minute, and the mold 1 and the laminated sheet 1 were pressure-bonded for 30 seconds at a pressure of 2 MPa while maintaining 135 ° C. Then, after cooling to 70 degreeC, the optical sheet 1 which has the pattern which reversed the shape of the following metal mold | die 1 on the laminated sheet 1 surface was obtained by releasing a metal mold | die. The total thickness of the optical sheet 1 (from the top of the shaping surface to the back surface) was 40 μm.
(Mold 1)
In-plane pattern: striped (FIG. 1 (a))
Individual shape: right-angled isosceles triangle (height d: 10 μm)
Pitch between adjacent patterns (p): 20 μm
Size: 100mm x 100mm (pattern area)
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 1.
Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 1 maintained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

(Example 2)
An optical sheet 2 was obtained in the same manner as in Example 1 except that a mold having a pitch p of 15 μm between adjacent patterns and a height of d7.5 μm was used. Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 2. Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 2 maintained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

(Example 3)
In Example 1, the extrusion amount of each extruder was adjusted to change the outer layer thickness and the core layer thickness. An optical sheet 3 was obtained in the same manner as in Example 1 except that the laminated sheet 2 having an outer layer thickness H of 9 μm, a core layer thickness of 30 μm, and a total of 48 μm was used. Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 3. Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 3 retained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

Example 4
An optical sheet 4 was obtained in the same manner as in Example 3 except that a metal mold having a pitch p of 15 μm between adjacent patterns and a height of d7.5 μm was used. Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 4. Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 4 maintained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

(Example 5)
In Example 1, the extrusion amount of each extruder was adjusted to change the outer layer thickness and the core layer thickness. An optical sheet 5 was obtained in the same manner as in Example 1 except that the laminated sheet 3 having an outer layer thickness H of 9 μm, a core layer thickness of 40 μm, and a total of 58 μm was used. Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 5. Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 5 retained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

(Example 6)
An optical sheet 6 was obtained in the same manner as in Example 5 except that a mold having a pitch p of 15 μm between adjacent patterns and a height of d7.5 μm was used. Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 6. Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 6 maintained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

(Example 7)
(Manufacture of polyethylene naphthalate pellets (PEN))
To 100 parts by weight of 2,6-naphthalenedicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol, 0.018 parts by weight of magnesium acetate tetrahydrate and 0.003 parts by weight of calcium acetate monohydrate as transesterification catalysts were added. The ester exchange reaction was carried out at 170 to 240 ° C. and 0.5 kg / cm ² , and then 0.004 parts by weight of trimethyl phosphate was added to complete the ester exchange reaction. Further, 0.23 parts by weight of antimony trioxide was added as a polymerization catalyst, and a polycondensation reaction was performed under high temperature and high vacuum to obtain polyethylene naphthalate 1 (PEN) pellets having an intrinsic viscosity of 0.60 dl / g. A laminated sheet 4 was obtained in the same manner as in Example 1 except that the cyclic polyolefin resin 1 was used for the core layer and PEN1 (Tg: 116 ° C.) was used for the outer layer. The laminated sheet 4 had a thickness H of each outer layer of 9 μm, a thickness of the core layer of 20 μm, and a total of 38 μm. Next, an optical sheet 7 was obtained in the same manner as in Example 1 except that the laminated sheet 4 was used.
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 7. Regarding the brightness characteristic evaluation results, the brightness of the backlight of the optical sheet 7 after the wet heat resistance test was slightly reduced compared to the value before the heat resistance test.

(Example 8)
Polycarbonate resin 1 (Taflon, Tg 145 ° C., manufactured by Idemitsu Kosan Co., Ltd.) is used as the resin constituting the core layer, and polystyrene resin 1 (SX100, Tg 100 ° C., manufactured by PS Japan Co., Ltd.) is used as the resin constituting the outer layer. A laminated sheet 5 was obtained in the same manner as in Example 1 except that. The laminated sheet 5 had a thickness H of each outer layer of 9 μm, a thickness of the core layer of 20 μm, and a total of 38 μm. Next, an optical sheet 8 was obtained in the same manner as in Example 1 except that the laminated sheet 5 was used.
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 8. Regarding the luminance characteristic evaluation results, in the optical sheet 8, the luminance of the backlight after the moisture and heat resistance test was slightly reduced compared to the value before the heat resistance test.

Example 9
The laminated sheet 1 was sandwiched and pressed between the roll-shaped mold 1 set at 180 ° C. and the nip roll by an apparatus as shown in FIG. 6, and the sheet was peeled off by a peeling roll to obtain a wound optical sheet 9. . The line speed was 10 m / min.
(Roll mold 1)
In-plane pattern: striped (FIG. 1 (a), parallel to the rotation direction)
Individual shape: right-angled isosceles triangle (height d: 10 μm)
Pitch between adjacent patterns (p): 20 μm
Size: 100mm width, φ3inch
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 9. Regarding the result of evaluating the luminance characteristics, it was confirmed that the optical sheet 9 retained the luminance of the backlight even after the moisture and heat resistance test, and it was found that the sheet was excellent in moisture and heat resistance.

(Example 10)
Laminated polyolefin resin 1 and 2 blended at a mass ratio of 60:40 as the resin constituting the core layer, and laminated in the same manner as in Example 1 except that polystyrene resin 1 was used as the resin constituting the outer layer. Sheet 6 was obtained. The laminated sheet 6 had a thickness H of each outer layer of 9 μm, a thickness of the core layer of 20 μm, and a total of 38 μm. Next, an optical sheet 10 was obtained in the same manner as in Example 1 except that the laminated sheet 6 was used.
The curl amount, flatness, and luminance characteristics of the optical sheet 10 are shown in Table 2. Regarding the luminance characteristic evaluation results, in the optical sheet 10, the luminance of the backlight after the wet heat resistance test was slightly reduced as compared with the value before the heat resistance test.

(Comparative Example 1)
The cyclic olefin resin 2 was dried at 60 ° C. for 6 hours and then charged into an extruder, heated to 230 ° C. to be melted, and extruded from a T-die into a metal drum maintained at 50 ° C. in a sheet form. A single layer sheet 1 having a thickness of 38 μm was obtained by winding the metal drum at a speed of 25 m / min.
Next, the mold 1 and the single-layer sheet 1 were heated at 110 ° C. for 1 minute, and the mold 1 and the single-layer sheet 1 were pressure-bonded for 30 seconds at a pressure of 2 MPa while maintaining 110 ° C. Then, after cooling to 50 degreeC, the optical sheet 11 which has the pattern which reversed the shape of the following metal mold | die 1 on the single layer sheet | seat 1 surface was obtained by releasing a metal mold | die. The entire thickness of the optical sheet 11 (from the top of the shaping surface to the back surface) was 40 μm, and the flatness deteriorated during molding.
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 11. It was found that the brightness of the backlight of the optical sheet 11 was lowered after the moisture and heat resistance test with respect to the luminance characteristic evaluation results.

(Comparative Example 2)
A single-layer sheet 2 was obtained in the same manner as in Comparative Example 1 except that the cyclic polyolefin resins 1 and 2 were blended at a mass ratio of 60:40.
Next, the mold 1 and the single-layer sheet 2 were heated at 135 ° C. for 1 minute, and the mold 1 and the single-layer sheet 2 were pressure-bonded for 30 seconds at a pressure of 2 MPa while maintaining 135 ° C. Then, after cooling to 70 degreeC, the optical sheet 12 which has the pattern which reversed the shape of the following metal mold | die 1 on the single-layer sheet | seat 2 surface was obtained by releasing a metal mold | die. The total thickness of the optical sheet 12 (from the top of the shaping surface to the back surface) was 40 μm, but the flatness deteriorated during molding.
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 12. Regarding the result of evaluating the luminance characteristics, the optical sheet 12 did not show a decrease in the luminance of the backlight after the wet heat resistance test.

(Comparative Example 3)
Optical sheet 13 was obtained in the same manner as in Example 1 except that a laminated sheet 7 having an outer layer thickness H of 7.5 μm, a core layer thickness of 30.5 μm, and a total of 38 μm was obtained using a molten two-layer coextrusion die. Got. However, curling of 10 mm or more occurred at the time of producing the sheet, and it did not change after the durability test.

(Comparative Example 4)
The uneven surface of the mold 1 is filled with the following coating agent 1, and a transparent polyethylene terephthalate film (PET film) having a thickness of 30 μm is placed on the surface, and the coating is irradiated with 1 J / m ² from the PET film side with an ultrahigh pressure mercury lamp. The optical sheet 14 was obtained by curing the agent and releasing the mold. The total thickness of the optical sheet 14 (from the top of the shaping surface to the back surface) was 40 μm.
(Coating 1)
KAYARAD R-551 (manufactured by Nippon Kayaku Co., Ltd.) 60 parts by mass KAYARAD R-128H (manufactured by Nippon Kayaku Co., Ltd.) 40 parts by mass Darocur 1173 (manufactured by Ciba Japan Co., Ltd.) 4 parts by mass This optical sheet 14 Table 2 shows the curl amount, flatness, and luminance characteristics. After 240 hours at a temperature of 85 ° C. and a humidity of 85%, the optical sheet 13 was remarkably curled (curled on the shaping surface side) after a lapse of 240 hours at a temperature of 85 ° C. and a humidity of 85% (after the heat and humidity resistance test).
The optical sheet 14 was incorporated in a backlight for evaluation before and after the moisture and heat resistance test, and an attempt was made to evaluate the luminance. However, after the moisture and heat resistance test, the end portion was lifted up and could not be evaluated.

(Comparative Example 5)
A cyclic polyolefin resin 1 was prepared as the resin constituting the core layer, and a cyclic polyolefin resin 2 (cyclic olefin resin 'TOPAS' 8007, Tg 78 ° C., manufactured by Polyplastics Co., Ltd.) was prepared as the resin constituting the outer layer. They were dried at 60 ° C. for 6 hours and then melted in a separate extruder at a temperature of 270 ° C. Next, the laminated resin extruded from the molten three-layer coextrusion die was extruded into a sheet shape on a metal drum maintained at 100 ° C. A laminated sheet 8 was obtained by winding the metal drum at a speed of 25 m / min.
Next, the mold 1 and the laminated sheet 8 were heated at 110 ° C. for 1 minute, and the mold 1 and the laminated sheet 8 were pressure-bonded for 30 seconds at a pressure of 2 MPa while maintaining 110 ° C. Then, after cooling to 50 degreeC, the optical sheet 15 which has the pattern which reversed the shape of the metal mold | die 1 on the laminated sheet 8 surface was obtained by releasing a metal mold | die. The total thickness of the optical sheet 15 was 40 μm.
Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 15. The flatness deteriorated after 240 hours at a temperature of 85 ° C. and a humidity of 85%.
Further, regarding the luminance characteristic evaluation results, the luminance of the backlight of the optical sheet 15 was significantly reduced even after the wet heat resistance test.

(Comparative Example 6)
(Manufacture of polyethylene terephthalate pellets (PET))
Using terephthalic acid as the acid component and ethylene glycol as the glycol component, adding to the polyester pellets that can obtain antimony trioxide (polymerization catalyst) to 300 ppm in terms of antimony atoms, performing a polycondensation reaction, limiting viscosity A polyethylene terephthalate pellet 1 (PET) having 0.63 dl / g and a carboxyl end group amount of 40 equivalents / ton was obtained.
Cyclic polyolefin-based resin 1 was prepared as the resin constituting the core layer, PET1 (Tg: 67 ° C.) was prepared as the resin constituting one outer layer, and PEN1 was prepared as the resin constituting the other outer layer. Cyclic polyolefin 1 and PEN 1 were dried at 100 ° C. and PET 1 was dried at 60 ° C. for 6 hours, respectively, and then melted in a separate extruder at a temperature of 240 ° C. Next, the laminated resin extruded from the molten three-layer coextrusion die was extruded into a sheet shape on a metal drum maintained at 100 ° C. A laminated sheet 9 was obtained by winding the metal drum at a speed of 25 m / min. In the laminated sheet 9, the thickness H of each surface layer was 7.5 μm, the thickness of the core layer was 23 μm, and the total was 38 μm.
Next, the mold 1 and the laminated sheet 9 were heated at 110 ° C. for 1 minute, and the mold 1 and the PET 1 side of the laminated sheet 9 were pressure-bonded for 30 seconds while maintaining 110 ° C. at a pressure of 2 MPa. Then, after cooling to 50 degreeC, the optical sheet 16 was obtained by releasing a metal mold | die. The total thickness of the optical sheet 16 (from the top of the shaping surface to the back surface) was 40 μm.
However, a curl of 5 mm was generated at the time of producing the sheet, and after the durability test, it was curled by 10 mm or more, and the luminance could not be measured.

(Comparative Example 7)
An optical sheet 17 was obtained in the same manner as in Example 9 except that the single-layer sheet 2 was used. The total thickness of the optical sheet 17 (from the top of the shaping surface to the back surface) was 40 μm, but the flatness deteriorated during peeling from the peeling roll.
Table 2 shows the curl amount, planarity, and luminance characteristics of the optical sheet 17.
Further, regarding the result of evaluating the luminance characteristics, the optical sheet 17 did not show a decrease in the luminance of the backlight after the moisture and heat resistance test, but the luminance before the test was found to be lower than that in Example 1.

(Comparative Example 8)
Except for using a polyolefin resin 1 and 2 blended in a mass ratio of 50:50 (Tg 100 ° C. after blending) as a resin constituting the core layer, and using a polystyrene resin 1 as the resin constituting the outer layer, A laminated sheet 10 was obtained in the same manner as Example 1. The laminated sheet 10 had a thickness H of each outer layer of 9 μm, a thickness of the core layer of 20 μm, and a total of 38 μm. Next, an optical sheet 18 was obtained in the same manner as in Example 1 except that the laminated sheet 10 was used. The total thickness of the optical sheet 18 (from the top of the shaping surface to the back surface) was 40 μm, but the flatness deteriorated during molding. Table 2 shows the curl amount, flatness, and luminance characteristics of the optical sheet 18. Regarding the luminance characteristic evaluation results, in the optical sheet 18, the luminance of the backlight after the wet heat resistance test was slightly reduced compared to the value before the heat resistance test.

From Table 1, the following is clear. From Examples 1 to 8, it can be seen that, among the present invention, the use of a cyclic polyolefin-based resin for the core layer and the surface layer can further suppress a decrease in luminance even under a durability test.
Further, it can be seen from Example 1 and Comparative Examples 1 and 2 that the planarity can be improved by providing a core layer, and curling can be suppressed by having a three-layer symmetrical structure as compared with Comparative Examples 3 and 4.
Further, it can be seen from Example 1 and Comparative Example 5 that a decrease in luminance before and after the durability test can be suppressed by laminating a resin having a Tg of 80 ° C. or more on the outer layer.
It can be seen from Example 1 and Comparative Example 6 that the outer layer can suppress curling by laminating the same composition.
Further, it can be seen from Example 9 and Comparative Example 7 that a sheet having excellent flatness can be produced even in a roll-to-roll type production apparatus as shown in FIG.
Furthermore, it can be seen from Example 10 and Comparative Example 8 that a sheet having excellent planarity can be produced by setting the Tg difference between the core layer and the outer layer to 10 ° C. or more.

The laminated sheet of the present invention is applicable to various fields such as liquid crystal display members.

Claims

An optical sheet comprising a three-layer laminate resin sheet composed of a core layer and an outer layer laminated on both surfaces of the core layer without an adhesive layer, wherein the resin constituting the core layer is an amorphous resin A plurality of convex shapes are formed on the surface of at least one of the outer layers, the glass transition temperature of the resin constituting each outer layer is 80 ° C. or higher, and the main components thereof are resins having the same composition, and An optical sheet that is at least 10 ° C. lower than the glass transition temperature of the resin constituting the core layer.
The optical sheet according to claim 1, wherein a main component of the resin constituting the core layer is a cyclic polyolefin resin.
3. The optical sheet according to claim 1, wherein the main component of the resin constituting each outer layer is a cyclic polyolefin having the same composition.
The convex height of the cut surface of the convex shape cut through a plane passing through the top of the convex shape and perpendicular to the surface of the outer layer on which the convex shape is formed and crossing the plurality of convex shapes is 1 to 10 μm. The optical sheet according to claim 1, wherein the total thickness of the optical sheet is 60 μm or less.
5. The optical sheet according to claim 1, wherein the plurality of convex shapes are convex shapes extending in one direction, and the longitudinal directions of the plurality of convex shapes are parallel to each other.
A surface light source for a liquid crystal display device on which the optical sheet according to any one of claims 1 to 5 is mounted.