JP5343492B2 - Optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet including an optical function layer having a hardly-scratchable, high-restorability, fine-rugged structure. <P>SOLUTION: The optical sheet includes the optical function layer disposed on at least one side thereof, constituted by two-dimensionally arraying units having the fine-rugged structure so as to converge or direct the transmitted light incident from the surface side opposite to the surface side having the fine-rugged structure. The optical function layer is constituted of a cured substance of an active energy curable resin composition, and the dynamic viscoelasticity tan&delta; of the optical function layer at 25&deg;C is 0.4 to 0.8, and the dynamic friction coefficient of the layer is &le;0.3, the fracture point elongation of the layer is 20% to 70%. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an optical sheet used as a prism sheet or the like used in a backlight for a liquid crystal display device.

  In recent years, with the rapid development of display technologies such as liquid crystal display devices, there is an increasing demand for sheet-like or film-like optical members used therefor that have new functions or higher quality. Examples of such sheet-like or film-like optical members include, for example, Fresnel lens sheets and lenticular sheets used for projection screens such as projection televisions, prism sheets and microlens sheets used as backlights for liquid crystal display devices, Examples include a moth-eye film that has been attracting attention as an antireflection film for thin televisions in recent years. In such a sheet-like or film-like optical member, an optical functional layer having a fine uneven structure on the surface is usually laminated on a substrate. Further, the optical member exhibits a desired function by refracting light in a fine uneven structure on the surface of the optical functional layer.

  Among the optical members, for example, a prism sheet (optical sheet) used as a backlight of a liquid crystal display device, etc., on the fine uneven structure of the optical functional layer of the optical sheet, further another optical sheet, A diffusion plate or a diffusion film is laminated and used (for example, Patent Document 1). When manufacturing such a laminated body, the fine concavo-convex structure which the optical functional layer of the said optical sheet has may be worn by an impact or a vibration.

  Further, the optical sheet is disposed on the light exit surface on the display panel side in both the edge light type surface light source device and the direct type surface light source device. In addition, the edge light type surface light source device usually enters light source light from one end face of a plate-like light guide such as a transparent acrylic resin, and the liquid crystal panel from a light exit surface that is one surface of the light guide. The direct-type surface light source device is a device in which a liquid crystal panel and a reflecting plate are arranged in a manner sandwiching the light source, and usually from the light source. Is reflected on the back surface of a liquid crystal panel or the like by a reflector.

  When the optical functional layer provided in the optical sheet is in contact with the light guide plate of the surface light source device, there is a problem of “mountain collapse” that the top of the fine concavo-convex structure is crushed by heat applied in the process, etc. Furthermore, there is a problem that the optical functional layer and the light guide plate are in contact with each other, and the top of the fine uneven structure is chipped.

  The problem of deformation or chipping at the top of such a fine concavo-convex structure causes display unevenness such as a white spot (white pattern) on the display surface of the display device, which degrades the display performance. .

JP 2004-312663 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical sheet including an optical functional layer that has a fine concavo-convex structure that is not easily scratched and has a high restoration property.

As a result of intensive studies, the present inventors have found that the above problems can be solved by providing an optical functional layer having specific physical properties, and have completed the present invention.
That is, the optical sheet according to the present invention has an optical function layer that converges or aligns transmitted light incident from the side opposite to the fine concavo-convex structure, in which units of the fine concavo-convex structure are two-dimensionally arranged on at least one side. An optical sheet provided,
The optical functional layer includes urethane acrylate containing a skeleton composed of isophorone diisocyanate and / or hexamethylene diisocyanate, EO-modified bisphenol A diacrylate represented by the following chemical formula (1), and EO-modified represented by the following chemical formula (2). One or more types selected from phenoxyethyl acrylate and a photopolymerization initiator, and as optional monomer components, biferrooxyethyl acrylate, phenoxybenzyl acrylate, polypropylene diacrylate, pentaerythritol triacrylate, isocyanuric acid triacrylate, And at least one selected from urethane acrylates different from urethane acrylates containing a skeleton composed of isophorone diisocyanate and / or hexamethylene diisocyanate. May have, a cured product of an active energy ray curable resin composition, and,
The optical functional layer has a dynamic viscoelastic property tan δ at 25 ° C. of 0.4 to 0.8, a dynamic friction coefficient of 0.3 or less, and a dynamic viscoelastic property tan δ at 25 ° C. of 0.4 to 0.4. An optical sheet having 0.8 and an elongation at break of 20% to 70%.

The optical sheet of the present invention includes an optical functional layer having the specific physical properties described above. The optical functional layer has appropriate softness and viscosity because the dynamic viscoelastic property tan δ at 25 ° C. is 0.4 to 0.8 and the dynamic friction coefficient is 0.3 or less. This makes it possible to prevent the fine uneven structure from being damaged. Further, the optical functional layer has an appropriate softness and elasticity because the dynamic viscoelastic property tan δ at 25 ° C. is 0.4 to 0.8 and the elongation at break is 20% to 70%. Even when an external force is applied to the optical functional layer and the fine concavo-convex structure of the optical functional layer is deformed, it is possible to restore the original shape.
Therefore, according to the present invention, it is possible to obtain an optical sheet in which the shape of the fine concavo-convex structure of the optical functional layer is hardly impaired and a desired shape can be maintained.
In the optical sheet according to the present invention, the active energy ray-curable resin composition comprises at least an isocyanate curable compound, an epoxy-phenol curable compound and / or an epoxy-acrylate curable compound, and photopolymerization initiation. It is preferable to contain an agent from the viewpoint of increasing the refractive index of the cured product.
In the optical sheet according to the present invention, the optical functional layer may include a prism as a unit of a fine relief structure. Further, the optical sheet according to the present invention can include a microlens as a unit of the fine concavo-convex structure. Furthermore, the optical sheet according to the present invention can include a prism and a microlens as a unit of the fine relief structure.

According to the optical sheet of the present invention, since the optical functional layer having specific physical properties is provided, the fine concavo-convex structure of the optical functional layer is hardly damaged and can be highly restored.
Therefore, according to the present invention, it is possible to obtain an optical sheet in which the shape of the fine concavo-convex structure is hardly impaired and a desired shape can be maintained.

The present invention is described in detail below.
<Optical sheet>
The optical sheet according to the present invention is provided with an optical functional layer that converges or aligns transmitted light incident from the side opposite to the fine concavo-convex structure, in which units of the fine concavo-convex structure are two-dimensionally arranged on at least one surface side. An optical sheet,
The optical functional layer is made of a cured product of an active energy ray-curable resin composition, and
The optical functional layer has a dynamic viscoelastic property tan δ at 25 ° C. of 0.4 to 0.8, a dynamic friction coefficient of 0.3 or less, and a dynamic viscoelastic property tan δ at 25 ° C. of 0.4 to 0.4. 0.8 and the elongation at break is 20% to 70%.

〔Layer structure〕
FIG. 1 is a cross-sectional view illustrating a basic form of the optical sheet of the present invention. In the cross-sectional view shown in FIG. 1, for ease of explanation, the scale in the thickness direction (vertical direction in the figure) is greatly enlarged and exaggerated than the scale in the width direction (horizontal direction in the figure). is there. In the optical sheet 1, a transparent base material 10 and an optical functional layer 12 having a large number of fine concavo-convex structures 11 are laminated on one surface S <b> 1 of the transparent base material 10.

Hereinafter, the optical sheet of the present invention will be described in order from a transparent substrate.
(1) Transparent base material The transparent base material 10 is a main constituent member of the optical sheet 1 and acts as a base material of the optical function layer 12 described in detail later, and also a large amount of light from the light source is used in the optical function layer. It acts so as to penetrate to the 12 side. The transparent base material 10 may be a light-transmitting base material made of a resin material, and in particular, a base material having a transmittance of 85% or more is preferably used. In addition, the transmittance here is a value measured by a light transmittance meter (model: HM-150) manufactured by Murakami Color Research Laboratory Co., Ltd. Although the thickness of the transparent base material 10 is not specifically limited, Usually, it exists in the range of 50-500 micrometers which can be rolled.

  Examples of the transparent substrate 10 include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, acrylic resins such as polymethyl methacrylate, thermoplastic resins such as polycarbonate resin, polystyrene resin, and polymethylpentene resin, polyester ( Resin obtained by curing an ionizing radiation curable resin comprising an oligomer such as (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, and / or a (meth) acrylate monomer with electromagnetic radiation such as ultraviolet rays or electron beams The transparent base material comprised by these, etc. can be mentioned preferably.

  The transparent substrate 10 is preferably produced by extrusion or coextrusion together with the light diffusion layer 13 described later. In addition, the transparent base material 10 may be produced by other methods. The transparent substrate 10 produced by extrusion or the transparent substrate 10 produced by other methods is usually stretched. This stretching process may be a biaxial stretching process or a uniaxial stretching process, but usually a biaxial stretching process is preferably applied.

(2) Optical Function Layer The optical function layer 12 is provided on one surface S1 of the transparent substrate 10, and has a large number of fine concavo-convex structures 11 as shown in FIG. The unit structure of the fine concavo-convex structure 11 is not particularly limited as long as it is a structure capable of expressing an optical function, and examples thereof include a triangular prism structure, a hemispherical structure, and a moth-eye structure. Here, the “moth-eye structure” refers to a structure in which the reflectance of the surface is reduced as a result of dense projections having a structure having a wavelength equal to or less than the wavelength of incident electromagnetic waves (for example, visible light) on the surface of the substance. Since this is a structure found in certain types of eyelids, it is called a moth-eye structure in the sense of “eyelid eyes” and is known to be used as an antireflection film for screens, displays, etc. (See, for example, JP-T-2001-517319).

  Further, the height from the concave portion (planar portion) to the convex portion (top) of the fine concavo-convex structure 11 is not particularly limited, but the fine concavo-convex structure 11 is a prism sheet, microlens, or lens sheet. In this case, the height is preferably about 10 to 50 μm, more preferably about 10 to 30 μm. When the fine concavo-convex structure 11 is a moth eye, the height is preferably about 100 to 400 nm, and more preferably about 100 to 300 nm.

The optical functional layer 12 of the present invention has a dynamic viscoelastic property tan δ of 0.4 to 0.8, preferably 0.4 to 0.7, and a dynamic friction coefficient of 0.3 or less, preferably at 25 ° C. Is 0.25 or less. When the dynamic viscoelastic property tan δ and the dynamic friction coefficient at 25 ° C. are within the above ranges, the optical functional layer 12 has appropriate softness and viscosity, and the fine concavo-convex structure 11 included in the optical functional layer 12. Can be made difficult to hurt.
The optical functional layer 12 of the present invention has a dynamic viscoelastic property tan δ of 0.4 to 0.8, preferably 0.4 to 0.7, and an elongation at break of 20 at 25 ° C. % To 70%, preferably 20% to 60%. When the dynamic viscoelastic property tan δ and the elongation at break at 25 ° C. are within the above ranges, the optical functional layer 12 has appropriate softness and stretchability, and external force is applied to the optical functional layer 12. Thus, even when the fine concavo-convex structure of the optical functional layer 12 is deformed, it is possible to have a recoverability capable of restoring the original shape.
Therefore, according to the present invention, it is possible to obtain an optical sheet in which the shape of the fine concavo-convex structure of the optical functional layer is hardly impaired and a desired shape can be maintained.
Here, the dynamic viscoelastic property tan δ is obtained when the dynamic viscoelasticity measuring device is heated from 0 ° C. to 120 ° C. at 3 ° C./min while applying a vibration of 1 Hz to the cured product. Furthermore, it can obtain | require by measuring the detected viscoelastic modulus. Examples of the measuring device include a rheometer (trade name: Rheogel E4000, manufactured by UBM).
The dynamic friction coefficient can be determined by applying a load of 200 g in a direction perpendicular to the cured product at a test speed of 5 mm / s using a friction wear tester. Examples of the measuring device include a friction wear tester (trade name: HEIDON, manufactured by Shinto Kagaku Co., Ltd.).
The elongation at break can be determined by using a tensile tester and pulling the test piece under the conditions of 25 ° C. and a tensile speed of 20 m / min and measuring the elongation at break. In addition, the elongation at the time of fracture | rupture at the time of extending | stretching to 2 times the natural length shall be 100%. An example of the measuring device is a universal testing machine (trade name: Tensilon, manufactured by A & D).

The optical functional layer 12 of the present invention is formed of an active energy ray-curable resin composition in which a conventionally known compound is blended so that the cured product exhibits the specific physical properties. Examples of such active energy ray curable resin compositions include various curable compounds such as isocyanate curable compounds, epoxy-phenol curable compounds, epoxy-acrylate curable compounds, and fluorene acrylates. And a resin composition containing a photopolymerization initiator.
Among them, an active energy ray-curable resin composition containing at least an isocyanate-based curable compound, an epoxy-phenol-based curable compound and / or an epoxy-acrylate-based curable compound, and a photopolymerization initiator is a refractive index of a cured product. It is preferable from the point which raises.
As an isocyanate type curable compound, the urethane acrylate containing the frame | skeleton which consists of isophorone diisocyanate (IPDI) and / or hexamethylene diisocyanate (HDI) can be mentioned, for example. Moreover, as an epoxy-phenol type curable compound, EO modified | denatured bisphenol A diacrylate represented by following Chemical formula (1) can be mentioned, for example. Examples of the epoxy-acrylate curable compound include EO-modified phenoxyethyl acrylate represented by the following chemical formula (2).

The content of the isocyanate-based curable compound is preferably 10 to 60% by weight, more preferably 20 to 50% by weight, based on the total solid content.
Moreover, it is preferable that content of said epoxy-phenol type curable compound and / or epoxy-acrylate type curable compound is 10 to 50 weight% with respect to the total solid, More preferably, it is 20-40. % By weight.
In addition, in this invention, solid content means things other than a solvent among the components contained in an active energy ray curable resin composition.

  The active energy ray-curable resin composition used in the present invention can contain a compound (monomer component) containing a (meth) acryloyl group or vinyl group other than the curable compound as an optional component. Examples of such a compound include monofunctional monomers such as biferrooxyethyl acrylate and phenoxybenzyl acrylate, and polyfunctional monomers such as polypropylene diacrylate, pentaerythritol triacrylate, isocyanuric acid triacrylate, and urethane acrylate.

  Examples of the photopolymerization initiator used in the present invention include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2,2-dimethoxy-1,2-diphenylethane- 1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-methyl-1- [4- (methylthio) phenyl]- 2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1,2-hydroxy-2-methyl-1-phenyl-propane-1-ketone 2,4,6-trimethylbenzoyldiphenylphosphine oxide, phenylbis (2,4,6-trimethylbenzoyl) -phosphine Kisaido, and the like. These can be used alone or in combination of two or more.

(Other ingredients)
In addition to the above components, the active energy ray-curable resin composition used in the present invention includes silicone, antioxidant, polymerization inhibitor, mold release agent, antistatic agent, UV stabilizer, antifoam as necessary. Agents, solvents, non-reactive acrylic resins, non-reactive urethane resins, non-reactive polyester resins, pigments, dyes, diffusing agents, and the like can be used in combination.

  The active energy ray-curable resin composition preferably has a refractive index of 1.53 or more after being cured. When the refractive index of the cured product is 1.55 or more, for example, when the optical sheet of the present invention is used as a prism sheet of a backlight for a liquid crystal display device, the viewing angle and the luminance of the liquid crystal display device can be compatible. This is because it becomes easy to control the shape of the fine uneven structure (unit prism) of the prism sheet.

  The optical functional layer 12 uses the above-mentioned active energy ray-curable resin composition. For example, (1) a known hot press method (Japanese Patent Laid-Open No. 56-157310), (2) an ultraviolet curable thermoplastic resin. A method of embossing the shape of the unit fine concavo-convex structure 11 on a film with a roll emboss plate and then curing the film by irradiating with ultraviolet rays (Japanese Patent Laid-Open No. 61-156273), (3) Shape of the unit fine concavo-convex structure 11 After applying the active energy ray-curable resin liquid onto the rotating roll intaglio engraved with and filling the recess, ultraviolet rays or electrons are applied while the film-like transparent substrate 10 is coated on the roll intaglio via the resin liquid. An active energy ray such as a wire is irradiated and cured, and then they are released from the roll intaglio, and the shape of the unit fine relief structure 11 of the roll intaglio is changed to a film-like transparent substrate 1. A method of forming the above (JP-A-3-223883, U.S. Pat. No. 4,576,850, etc.) and the like.

(3) Other layers The optical sheet 1 can be provided with a light diffusion function. For example, as shown in FIG. 1, the light diffusion function can be provided by providing a light diffusion layer 13 on at least one surface of the transparent substrate 10 or performing a so-called mat treatment. Since many proposals have been made to provide such a light diffusing function, only the following explanation will be given here and will not be explained in detail.

  The light diffusion layer 13 illustrated in FIG. 1 is an arbitrary layer that is preferably provided, and may have any function of diffusing light, and is formed on a general light diffusion sheet. For example, a layer in which light diffusing fine particles are dispersed in a translucent resin can be applied. The light diffusing layer 13 may be provided on the other surface S2 of the transparent substrate 10 or between the one surface S1 of the transparent substrate 10 and the optical function layer 12 (not shown). It may be provided in both of them.

  As the translucent resin material constituting the light diffusion layer 13, a resin material similar to that of the above-described transparent substrate 10, for example, a transparent material such as acrylic, polystyrene, polyester, or vinyl polymer is used. Further, light diffusing fine particles are uniformly dispersed in the light diffusion layer 13. As the light diffusing fine particles, light diffusing fine particles generally used for optical sheets are used. For example, polymethyl methacrylate (acrylic) beads, polybutyl methacrylate beads, polycarbonate beads, polyurethane beads , Calcium carbonate beads, silica beads and the like are used.

  The light diffusion layer 13 can be produced by various methods. For example, a paint in which light diffusing fine particles are dispersed in a translucent binder resin may be formed by spray coating, roll coating, or the like, or a resin material in which light diffusing fine particles are dispersed is prepared. The resin material may be coextruded together with the extrusion material of the transparent substrate 10 to form. In addition, the thickness of the light diffusion layer 13 is usually in the range of 1 to 20 μm.

  Further, although not shown in the figure, the mat treatment is performed by providing a light diffusion function by giving a predetermined surface roughness to the surface S2 instead of providing the light diffusion layer 13 on the other surface S2 of the transparent substrate 10, for example. Is. Examples of such means include a method of mechanically roughening the surface, and forming an uneven layer containing particles.

(4) Use of optical sheet The optical sheet of the present invention is, for example, a prism sheet or microlens used in a backlight of a liquid crystal display device or the like, a Fresnel lens sheet or lenticular sheet used in a projection screen such as a projection television, or a thin television. The moth-eye film used for the antireflection film can be mentioned. The optical sheet of the present invention can be suitably used in any of these, and among them, it can be suitably used as a prism sheet and a microlens for a backlight for a liquid crystal display device.

<Surface light source device>
FIG. 2 is a perspective view showing an example of a surface light source device including the optical sheet of the present invention. The surface light source device 20 of FIG. 2 is a so-called edge light type surface light source device, and a light guide 22 that emits light introduced from at least one side end surface 22A from a light emission surface 22B as one surface; A light source 24 that allows light to enter from at least one side end surface 22A of the light guide 22 and a light emission surface 22B of the light guide 22 are provided via an adhesive layer 21, for example, from the light emission surface 22B. It has the optical sheet 1 according to the present invention that transmits outgoing light.

  The light guide 22 is a plate-like body made of a translucent material, and is configured to emit light introduced from the left side end surface 22A in FIG. 2 from the upper light emission surface 22B. The light guide 22 is made of a light-transmitting material similar to the material of the optical sheet 1, but is usually made of acrylic or polycarbonate resin. The thickness of the light guide 22 is usually about 1 to 10 mm, and the thickness may be constant over the entire range, or as shown in FIG. 2, it is the thickest at the position of the side end face 22A on the light source 24 side. The taper shape may be gradually thinned in the opposite direction. In order to emit light from a wide surface (light emission surface 22B), the light guide 22 preferably has a light scattering function added to the inside or the surface thereof.

  The light source 24 causes light to enter the inside from at least one side end face 22 </ b> A of the light guide 22, and is disposed along the side end face 22 </ b> A of the light guide 22. The light source 24 is not limited to a linear light source as shown in FIG. 2, and a point light source such as an incandescent bulb or LED (light emitting diode) may be arranged in a line along the side end face 22A. . A plurality of small flat fluorescent lamps may be arranged along the side end face 22A.

  On the light emission surface 22 </ b> B of the light guide 22, the above-described optical sheet 1 according to the present invention is provided via, for example, an adhesive layer 21. The optical sheet 1 is provided so that the opposite surface of the optical functional layer 12 becomes the light emission surface 22B of the light guide 22.

  The light reflection plate 26 is provided on a surface opposite to the light emission surface 22B of the light guide 22 and is provided on a side end surface other than the left side end surface 22A, and reflects and guides light emitted from these surfaces. This is for returning to the light body 22. As the light reflecting plate 26, a thin metal plate deposited with aluminum or the like, or white foamed PET (polyethylene terephthalate) is used.

<Display device>
FIG. 3 is a schematic perspective view showing an example of a liquid crystal display device provided with the edge light type surface light source device shown in FIG. A liquid crystal display device 30 shown in FIG. 3 includes a liquid crystal panel 32 that is a flat, translucent display, and an edge light type surface light source that is disposed on the back surface of the liquid crystal panel 32 and that irradiates the liquid crystal panel 32 from the back surface. Device 20. The liquid crystal display device 30 is a so-called backlight type liquid crystal display device, and is configured to illuminate each pixel forming a liquid crystal screen from the back side with light emitted from the surface light source device 20.

  Since the liquid crystal display device 30 includes the surface light source device 20 including the optical sheet according to the present invention as a constituent member, the display surface does not cause display unevenness such as a white spot (white pattern) and is stable and good. Display performance can be provided.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

  Hereinafter, the present invention will be described more specifically with reference to examples. These descriptions do not limit the present invention. In the examples, parts represent parts by weight unless otherwise specified.

Example 1
After dropping the active energy ray-curable resin composition shown below onto a lens mold formed with a unit prism shape, a polyethylene terephthalate substrate (PET, trade name: A4300, thickness: 125 μm, manufactured by Toyobo Co., Ltd.) Then, the entire surface of the PET was pressure-bonded to the resin composition with a laminator.
[Active energy ray-curable resin composition]
-Caprolactone-modified urethane acrylate having a hexamethylene diisocyanate skeleton: 45 parts by weight-EO-modified bisphenol A diacrylate (M-211B: trade name, manufactured by Toagosei Co., Ltd.): 5 parts by weight-EO-modified phenoxy acrylate (M-101A: product) Name, manufactured by Toa Gosei Co., Ltd.): 25 parts by weight Phenoxybenzyl acrylate: 25 parts by weight Photopolymerization initiator (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight Next, 780 mJ / cm ² Then, the resin composition was irradiated with ultraviolet rays, the optical functional layer having a large number of unit prisms was cured and integrated with the polyethylene terephthalate substrate. Then, the optical sheet | seat of this invention was obtained by peeling the said lens type | mold.
Here, the unit prism has a triangular shape. More specifically, the shape is an isosceles triangle having a height of 25 μm, a pitch of 50 μm, and the apex angle of the unit prism being 90 °, and a plurality of unit prisms are adjacent to each other so that the ridge lines are balanced with each other.

(Example 2)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
Polyester-modified urethane acrylate having a saturated cyclic structure: 80 parts by weight EO-modified phenoxy acrylate (M-102: trade name, manufactured by Toagosei Co., Ltd.): 10 parts by weight EO-modified phenoxyethyl acrylate: 10 parts by weight Agent (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight

(Example 3)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
EO-modified bisphenol A diacrylate (M-211B: trade name, manufactured by Toagosei Co., Ltd.): 10 parts by weight Caprolactone-modified urethane acrylate having a hexamethylene diisocyanate skeleton: 75 parts by weight Polypropylene diacrylate (M-225: trade name) , Manufactured by Toa Gosei Co., Ltd.): 15 parts by weight Photoinitiator (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight

(Comparative Example 1)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
Polyester-modified urethane acrylate having a saturated cyclic structure copolymerized with phenylmaleimide: 80 parts by weight EO-modified bisphenol A diacrylate (M-211B: trade name, manufactured by Toagosei Co., Ltd.): 10 parts by weight EO-modified phenoxyethyl Acrylate: 10 parts by weight-Photopolymerization initiator (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight

(Comparative Example 2)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
-Full orange acrylate (Ogsol EA-5503: trade name, manufactured by Osaka Gas Chemical Co., Ltd.): 15 parts by weight-Phenoxyethyl acrylate: 25 parts by weight-EO-modified phenoxyethyl acrylate: 10 parts by weight-Orthophenoxyethyl acrylate: 10 Part by weight-EO-modified bisphenol A diacrylate (M-211B: trade name, manufactured by Toa Gosei Co., Ltd.): 40 parts by weight-Photopolymerization initiator (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight

(Comparative Example 3)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
Polyester-modified urethane acrylate having a saturated cyclic structure: 60 parts by weight EO-modified bisphenol A diacrylate (M-211B: trade name, manufactured by Toagosei Co., Ltd.): 10 parts by weight EO-modified phenoxyethyl acrylate: 10 parts by weight Tri Propylene glycol diacrylate (M-220: trade name, manufactured by Toa Gosei Co., Ltd.): 20 parts by weight Photopolymerization initiator (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight

(Comparative Example 4)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
MMA-styrene-dodecyl methacrylate copolymer: 45 parts by weight Urethane ester having a hexamethylene diisocyanate skeleton: 44.5 parts by weight Organic silicone: 0.5 parts by weight EO-modified phenoxyethyl acrylate: 5 parts by weight Photopolymerization initiator (Irgacure 184: trade name, manufactured by Ciba Japan Co., Ltd.): 5 parts by weight

(Comparative Example 5)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
-Bisphenol A epoxy acrylate: 25 parts by weight-Phenoxyethyl acrylate: 20 parts by weight-Isobornyl acrylate (manufactured by Daicel Cytec Co., Ltd.): 5 parts by weight-Acrylic morpholine (manufactured by Kojin Co., Ltd.): 5 parts by weight-Bisphenol A diacrylate: 10 parts by weight Bisphenol A dimethacrylate: 25 parts by weight Isonuric acid EO-modified diacrylate (M-215: trade name, manufactured by Toagosei Co., Ltd.): 10 parts by weight Photoinitiator (Irgacure 184: commodity Name, Ciba Japan Co., Ltd.): 3 parts by weight

(Comparative Example 6)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
-Fluorene acrylate: 45 parts by weight-Phenoxyethyl acrylate: 35 parts by weight-Isonuric acid EO-modified triacrylate (M-315: trade name, manufactured by Toagosei Co., Ltd.): 20 parts by weight-Photopolymerization initiator (Irgacure 184: trade name) Ciba Japan Co., Ltd.): 5 parts by weight

(Comparative Example 7)
In Example 1, an optical sheet was obtained in the same manner as in Example 1 except that the active energy ray-curable resin composition having the following composition was used.
[Active energy ray-curable resin composition]
-Caprolactone-modified urethane acrylate having a hexamethylene diisocyanate skeleton: 80 parts by weight-Bilphenol A epoxy diacrylate: 5 parts by weight-Phenoxybenzyl acrylate: 15 parts by weight-Photopolymerization initiator (Irgacure 184: trade name, Ciba Japan ( Co., Ltd.): 5 parts by weight

(Evaluation results)
The following points were evaluated with respect to each of the above Examples and Comparative Examples. The results are listed in Table 1.
(1) Dynamic viscoelastic properties The optical sheet obtained above was cut into a length of 20 mm and a width of 5 mm to obtain a test piece. Using a rheometer (trade name: Rheogel E4000, manufactured by UBM), the test piece was heated to 0 ° C. to 120 ° C. under a temperature rising rate of 3 ° C./min while applying a vibration of 1 Hz. The viscoelasticity detected was measured.
(2) Coefficient of dynamic friction Using a friction wear tester (trade name: HEIDON, manufactured by Shinto Kagaku Co., Ltd.), in the direction perpendicular to the prism ridgeline of the optical sheet obtained above, at a test speed of 5 mm / s. A load of 200 g was applied and the dynamic friction coefficient was measured.
(3) Elongation at break The optical sheet obtained above was cut into a length of 150 mm and a width of 20 mm as a test piece. Using a universal testing machine (trade name: Tensilon, manufactured by A & D Co., Ltd.), the test piece was pulled under the conditions of 25 ° C. and a tensile speed of 20 m / min, and the elongation at break was measured. In addition, the elongation at the time of fracture | rupture at the time of extending | stretching to 2 times the natural length was made into 100%.
(4) Scratch property Using an academic wear tester (trade name: AB-301, manufactured by Tester Co., Ltd.), the optical sheet obtained above is pulled in a direction perpendicular to the prism ridge line of the optical sheet. The surface of the optical sheet after being pulled under conditions of a speed of 300 mm / min and a moving distance of 100 mm was observed with a microscope.
[Evaluation]
・ 5: No flaws were observed by microscopic observation. ・ 4: One flaw was seen by microscopic observation. ・ 3: Two or three flaws were seen by microscopic observation. : After the surface of the test piece was scraped over the entire surface of the specimen by microscopic observation (5) Restorability Optics obtained above using a Gakushin abrasion tester (trade name: AB-301, manufactured by Tester Co., Ltd.) The surface of the optical sheet after the sheet was pulled in the direction perpendicular to the prism ridgeline of the optical sheet under the conditions of a pulling speed of 300 mm / min and a moving distance of 100 mm was observed with a microscope.
[Evaluation]
-5: No deformation of the shape was confirmed by microscopic observation-4: Deformation was visible with a microscope but was not visible-3: The original shape was restored within 10 minutes at 25 ° C (room temperature)-2 : It was not restored to its original shape within 10 minutes at 25 ° C (room temperature), but when it was heated to 35 ° C, it was restored to its original shape within 5 minutes.-1: Heated at 35 ° C and within 5 minutes Was not restored to its original shape, but when heated at 80 ° C for 1 minute, it was restored to its original shape.

<Summary of results>
From the results shown in Table 1, the dynamic viscoelastic property tan δ at 25 ° C. of the optical functional layer is 0.4 to 0.8, the dynamic friction coefficient is 0.3 or less, and the dynamic viscoelasticity at 25 ° C. In Examples 1 to 3 in which the characteristic tan δ is 0.4 to 0.8 and the elongation at break is 20% to 70%, the fine concavo-convex structure of the optical functional layer is not damaged and is not deformed. . On the other hand, in Comparative Examples 1, 2, 5, and 6 in which the dynamic friction coefficient exceeded 0.3, the surface of the optical functional layer was difficult to slip, so that the fine uneven structure of the optical functional layer was scratched. In particular, in Comparative Examples 5 and 6 in which the dynamic viscoelastic property tan δ at 25 ° C. is less than 0.4, the optical functional layer is hard and difficult to slip. It was. Further, in Comparative Examples 3 to 6 having an elongation at break of less than 20%, the optical functional layer was low in elasticity, and thus the fine uneven structure of the optical functional layer was deformed. In particular, in Comparative Examples 5 and 6 in which the dynamic viscoelastic property tan δ at 25 ° C. is less than 0.4, the optical functional layer is hard and has low stretchability, so that the deformation of the fine uneven structure of the optical functional layer is noticeable. It was. In Comparative Example 7 in which the elongation at break exceeds 70% and the dynamic viscoelastic property tan δ at 25 ° C. exceeds 0.8, the optical functional layer is soft and highly stretchable. Although the structure was not deformed, the surface of the fine concavo-convex structure was scratched.

It is the schematic which shows an example of the optical sheet of this invention. It is a perspective view which shows an example of a surface light source device provided with the optical sheet of this invention. It is a schematic perspective view which shows an example of a liquid crystal display device provided with the surface light source device shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical sheet 10 Transparent base material 11 Fine uneven structure 12 Optical functional layer 13 Light diffusion layer 20 Surface light source device 21 Adhesive layer 22 Light guide 22A Side end surface 22B Light emission surface 24 Light source 26 Light reflector 30 Liquid crystal display device 32 Liquid crystal panel S1 One surface of transparent substrate S2 Other surface of transparent substrate

Claims (4)

An optical sheet comprising an optical functional layer for converging or orienting transmitted light incident from the side opposite to the fine concavo-convex structure, wherein the units of the fine concavo-convex structure are two-dimensionally arranged on at least one surface side,
The optical functional layer includes urethane acrylate containing a skeleton composed of isophorone diisocyanate and / or hexamethylene diisocyanate, EO-modified bisphenol A diacrylate represented by the following chemical formula (1), and EO-modified represented by the following chemical formula (2). One or more types selected from phenoxyethyl acrylate and a photopolymerization initiator, and as optional monomer components, biferrooxyethyl acrylate, phenoxybenzyl acrylate, polypropylene diacrylate, pentaerythritol triacrylate, isocyanuric acid triacrylate, And at least one selected from urethane acrylates different from urethane acrylates containing a skeleton composed of isophorone diisocyanate and / or hexamethylene diisocyanate. May have, a cured product of an active energy ray curable resin composition, and,
The optical functional layer has a dynamic viscoelastic property tan δ at 25 ° C. of 0.4 to 0.8, a dynamic friction coefficient of 0.3 or less, and a dynamic viscoelastic property tan δ at 25 ° C. of 0.4 to 0.4. An optical sheet having 0.8 and an elongation at break of 20% to 70%.

The optical sheet according to claim 1 , wherein the optical functional layer includes a prism as a unit of a fine concavo-convex structure. The optical sheet according to claim 1 , wherein the optical functional layer includes a microlens as a unit of a fine concavo-convex structure. The optical sheet according to claim 1 , wherein the optical functional layer includes a prism and a microlens as a unit of a fine concavo-convex structure.

Images