JP5961959B2 - Optical sheet, surface light source device, and liquid crystal display device - Google Patents

Description

  The present invention relates to an optical sheet used as a prism sheet or the like of a backlight for a liquid crystal display device, a surface light source device including the optical sheet, and a liquid crystal display device.

In recent years, an optical sheet having a function of condensing, converging, diffusing, polarizing, reflecting, or the like by refraction, diffraction, interference, or dispersion of light has been used in a display such as a liquid crystal display device.
Examples of such optical sheets include prism sheets used for backlights of liquid crystal display devices, lenticular lens sheets used for stereoscopic photographs and projection screens, Fresnel lens sheets and color sheets used for condenser lenses for overhead projectors, and the like. The diffraction grating used for a filter etc. can be mentioned.

  The optical sheet usually has a substrate and a fine concavo-convex shape having a predetermined refractive index and a plurality of unit concavo-convex structures such as unit prisms or unit lenses arranged on the surface. Such an optical sheet expresses a desired function by modulating light by geometric optical action such as refraction or reflection or wave optical action such as diffraction in the uneven shape. Accordingly, the resin material and the shape of the unit concavo-convex structure constituting the concavo-convex shape are determined.

  Among the above optical members, for example, a prism sheet (optical sheet) used as a backlight of a liquid crystal display device or the like generally has another optical sheet and a diffusion plate on the prism portion (uneven shape) of the prism sheet. Or a diffusion film is laminated | stacked and used. When such a laminated body is manufactured or transported, the prism portion of the prism sheet may be worn due to impact or vibration.

Further, the prism sheet is disposed on the light exit surface on the liquid crystal cell (a module in which a liquid crystal compound is sealed with glass or the like) side of either the edge light type surface light source device or the direct type surface light source device. . When the prism portion included in the optical sheet and a light guide plate, a (light) diffusion film, or a liquid crystal cell, which are adjacent to the light source plate included in the surface light source device are in contact with each other, the heat and pressure applied in the process etc. There is a problem of so-called “mountain collapse” that the top part is crushed and a problem that the prism part and the light guide plate come into contact with each other and the top part of the unit prism is chipped.
In addition, the edge light type surface light source device is usually configured to allow light source light to enter from one end face of a transparent plate-shaped light guide such as acrylic resin and to emit light from a light exit surface on the liquid crystal cell side. Device. On the other hand, a direct type surface light source device is a device in which a liquid crystal cell and a reflection plate are arranged in a manner sandwiching a light source, and is usually configured to reflect light from the light source to the liquid crystal cell side by the reflection plate. It is.

  Such a problem of deformation and chipping at the top of the unit prism causes a display unevenness such as a white spot (white pattern) on the display surface of the display device, which causes a decrease in display performance. In particular, when the concavo-convex shape has a sharp convex portion such as a prism, the above-described concavo-convex shape wear, chipping, or crushing is remarkable. In the case of other concavo-convex shaped optical sheets, there is a similar tendency.

  In order to improve the above problems, conventionally, materials used for the prism portion have been used which have high hardness and the shape of the formed unit prism is not easily deformed. For example, the condensing material for LCD back light source in which the unit prism made of UV-curing (meth) acrylate resin is formed on the transparent base material described in Patent Document 1 is caused by the friction of the prism portion during the work to be incorporated in the LCD. The problem is to prevent scratches, and a hard prism portion having scratch resistance with a haze of 60% or less before and after sandfall wear by a specific test method has been realized by devising resin formulation.

  However, such a hard prism part has a certain degree of strength against the above-mentioned uneven wear, chipping or crushing, but if it receives an external pressure exceeding the limit, it will still be worn, chipped or crushing. End up.

  Furthermore, in recent years, in order to improve mass productivity, an optical sheet has been manufactured by winding a prism sheet around a roll by a rotary 2P method using a cylindrical mold while continuously running a belt-shaped base sheet. When the optical sheet having a prism with increased hardness is wound up and stored in a rolled state, the prism tops are crushed by pressing the front and back sides of the prism sheet.

The lens part (prism part) described in Patent Document 2 has specific physical properties, so that even when a unit prism attached to the surface of the prism part is deformed due to an external factor, this is restored to its original shape. The restoration property which can be made is provided, and it is possible to maintain a desired shape.
However, the resilience of the prism portion is not sufficient to solve the problem of deformation due to external force applied to the prism portion. In addition, since the restoration property is imparted, the prism portion is easily chipped, and the restoration property and the scratch resistance are not compatible.

Japanese National Patent Publication No. 11-500072 JP 2009-37204 A

  The present invention has been made in order to solve the above-described problems, and has an optical sheet having an excellent restorability and a concavo-convex shape that is difficult to be damaged, and a surface light source device and a liquid crystal display including the optical sheet. An object is to provide an apparatus.

As described above, the concavo-convex shape of the optical sheet has a scratch resistance and a resilience that can be temporarily deformed when stress is applied and can be restored to its original shape by an elastic restoring force when released from the stress. However, since there is a trade-off relationship in which the hardness and the restoration rate are strengthened and the other is weakened, there is a limit to balance only with the indicators of the hardness and the restoration rate.
As a result of intensive studies by the present inventors, it has been found that a cured product of a (meth) acrylic resin having a specific curing state can achieve scratch resistance and resilience at a high level.

An optical sheet according to the present invention is provided with a transparent base material and an optical function manifesting part having a concavo-convex shape provided with a plurality of unit concavo-convex structures on the surface opposite to the transparent base material. An optical sheet comprising:
The optical function developing part contains an acrylic resin and / or methacrylic resin, and contains a caprolactone-modified urethane (meth) acrylate represented by the general formula (I) described later as a segment in the acrylic resin and / or methacrylic resin. It consists of a cured product of an active energy ray curable resin composition,
When the surface of the optical function developing portion is observed with an atomic force microscope, it has a raised structure having an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm.

  The optical sheet according to the present invention has a raised structure having an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm when the surface of the optical function developing portion is observed with an atomic force microscope (AFM). By having the cured state, the uneven shape has excellent recoverability, so that the unit uneven structure is not easily crushed and hardly damaged.

  The acrylic resin and / or methacrylic resin preferably includes a segment having a polymer structure composed of repeating units of caprolactone-modified urethane (meth) acrylate.

The acrylic resin and / or methacrylic resin is bisphenol A diglycidyl (meth) acrylate, biphenylyloxyethyl (meth) acrylate, EO-modified biphenylyloxyethyl (meth) acrylate, bisphenol as a part of the acrylic resin and / or methacrylic resin. At least one segment selected from the group consisting of A epoxy (meth) acrylate and polyethylene glycol di (meth) acrylate may be further included.

The number of the raised structures in the optical sheet according to the present invention is preferably 5 to 100/400 μm ² . In such a number range, the balance between the restoration property of the unit concavo-convex structure and the scratch resistance becomes suitable.

  The optical sheet which concerns on this invention WHEREIN: It is preferable that the said optical function expression part contains a prism and / or a micro lens as a unit uneven | corrugated structure.

  The surface light source device according to the present invention includes the optical sheet on the light emission surface side of the surface light source.

  The liquid crystal display device according to the present invention includes the optical sheet on one side of the liquid crystal cell.

The optical sheet according to the present invention has a raised structure having an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm when the surface of the optical function developing portion is observed with an atomic force microscope (AFM). When in a cured state, the uneven shape has excellent restorability and is hardly damaged.
In the surface light source device including the optical sheet, even when the optical function developing portion of the optical sheet comes into contact with a member such as a light guide plate, the top portion of the unit concavo-convex structure lacks, and crushing and deformation hardly occur.
Since the liquid crystal display device including the optical sheet is not easily clogged, crushed and deformed at the top of the unit uneven structure of the optical sheet, display unevenness such as a white spot (white pattern) is hardly generated and the appearance is excellent.

FIG. 1 is a schematic perspective view showing an example of an optical sheet according to the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the layer structure of the optical sheet according to the present invention. FIG. 3 is a schematic cross-sectional view showing another example of the layer configuration of the optical sheet according to the present invention. FIG. 4 is a schematic cross-sectional view of the surface of the optical function manifesting part having a raised structure. FIG. 5 is a schematic perspective view showing an example of a surface light source device including the optical sheet according to the present invention. FIG. 6 is a schematic perspective view showing an example of a liquid crystal display device including the surface light source device according to the present invention. FIG. 7 is a schematic view schematically showing a method for evaluating resilience and scratch resistance in an example of the present invention. FIG. 8 is a schematic view schematically showing an example of evaluation criteria for resilience and scratch resistance in Examples of the present invention. FIG. 9 is a graph plotting the number of raised structures, the reaction rate, the restoration rate, and the hardness with respect to the integrated dose in the example of the present invention. FIG. 10 is a graph plotting the number of raised structures, the reaction rate, the restoration rate, and the hardness with respect to the integrated dose in the comparative example of the present invention.

  Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the spirit thereof.

In the present invention, (meth) acrylic resin represents acrylic resin and / or methacrylic resin, and (meth) acrylate represents acrylate and / or methacrylate.
In the present invention, the resin is a concept including a polymer in addition to a monomer and an oligomer.
In the definition of film and sheet in JIS-K6900, a sheet is a thin and generally flat product whose thickness is small relative to the length and width. A film has a thickness compared to the length and width. A thin, flat product that is extremely small and has an arbitrarily limited maximum thickness, usually supplied in the form of a roll. Therefore, it can be said that a film having a particularly thin thickness among the sheets is a film, but the boundary between the sheet and the film is not clear and is difficult to distinguish clearly. Therefore, in the present invention, the meaning of both a thick sheet and a thin sheet is meant. Is defined as “sheet”.
In the present invention, the molecular weight means a weight average molecular weight which is a polystyrene equivalent value measured by gel permeation chromatography (GPC) in a THF solvent when having a molecular weight distribution, and when having no molecular weight distribution, It means the molecular weight of the compound itself.
In this invention, solid content means the part remove | excluding the solvent from the composition.

(Optical sheet)
An optical sheet according to the present invention is provided with a transparent base material and an optical function manifesting part having a concavo-convex shape provided with a plurality of unit concavo-convex structures on the surface opposite to the transparent base material. An optical sheet comprising:
The said optical function expression part consists of hardened | cured material of the active energy ray curable resin composition containing an acrylic resin and / or a methacryl resin,
When the surface of the optical function developing portion is observed with an atomic force microscope, it has a raised structure having an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm.

The optical sheet according to the present invention has a raised structure having an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm when the surface of the optical function developing portion is observed with an atomic force microscope (AFM). When it is in a cured state, the uneven shape is a cured state capable of achieving both excellent resilience and scratch resistance. Therefore, according to the present invention, even when stress is applied when the optical sheet is unwound after the optical sheet is rolled up when the optical sheet is incorporated into the apparatus or when the 2P method is manufactured, the uneven shape is not easily damaged. It is possible to provide an optical sheet that is capable of maintaining the shape and excellent in scratch resistance.
When the surface of the optical function developing part is observed with an atomic force microscope (AFM), when it does not exhibit a raised structure with an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm, / When the scratch resistance is insufficient, or the balance between the two is not achieved, and when the optical sheet is unwound and unwound after the optical sheet is rolled up when manufacturing by the 2P method When stress is applied, the occurrence of deformation, chipping or crushing cannot be sufficiently suppressed. When such an optical sheet is used as a product, the yield deteriorates.

The optical sheet is a prism sheet or a lens sheet that expresses a desired function such as condensing, diffusing, refraction, or reflection by modulating light by geometric optical action such as refraction or reflection in an uneven shape from its action mechanism. Then, the light is modulated by a wave optical action such as diffraction in the concavo-convex shape, and is roughly classified into a diffraction grating or a hologram that expresses a desired function such as diffraction or spectroscopy.
The layer structure of the optical sheet according to the present invention will be described with reference to the drawings. Hereinafter, a prism sheet will be described as an example. In FIG. 1 and subsequent drawings, for convenience of explanation, the vertical and horizontal dimension ratios and the dimension ratios between the layers are exaggerated as appropriate instead of the actual dimensions.

  FIG. 1 is a schematic perspective view illustrating an example of an optical sheet according to the present invention, and FIG. 2 is a schematic cross-sectional view illustrating an example of a layer configuration of the optical sheet according to the present invention. The optical sheet 1 is provided with an optical function manifesting part 20 made of a cured product of an active energy ray-curable resin composition containing an acrylic resin and / or a methacrylic resin on a transparent substrate 10. A prism shape having a prism structure as a plurality of unit concavo-convex structures 30 in FIGS. 1 and 2 is provided on the surface opposite to the transparent substrate.

  FIG. 3 is a schematic cross-sectional view showing another example of the layer configuration of the optical sheet according to the present invention. An optical function developing unit 20 is provided on one surface side of the transparent substrate 10, and a light diffusion layer 40 is provided on the surface of the transparent substrate 10 opposite to the surface on which the optical function developing unit 20 is provided. .

  Hereinafter, the transparent base material and the optical function developing part, which are indispensable constituent elements of the optical sheet according to the present invention, and the light diffusion layer that can be appropriately provided as necessary will be described.

(Transparent substrate)
The transparent base material 10 is a base material of the optical sheet 1 and is not particularly limited, and a transparent base material used in a conventionally known optical sheet can be used. The material and thickness of the transparent substrate may be appropriately selected in consideration of required requirements such as desired transparency and mechanical strength. The transparent substrate may be a resin substrate or a glass substrate.
Examples of the resin material for the transparent film include (meth) acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylimide resin, polyester resin, cycloolefin polymer (COP) resin, and cycloolefin copolymer (COC) resin. it can.

The transparent base material may have a long shape or a single wafer shape having a predetermined size. However, when an optical sheet is produced by the 2P method, a long transparent substrate is used. Use. The thickness of the transparent substrate is usually preferably 50 to 500 μm, but is not limited thereto.
As the light transmittance of the transparent base material, 100% is ideal for installation on the front surface of the display, and the transmittance is preferably 85% or more.
The transparent base material may be subjected to a conventionally known mat treatment (formation of light diffusive minute irregularities), an antistatic treatment or an antireflection treatment on the surface thereof as necessary. Further, a matte treatment, an antistatic treatment, an antireflection treatment or the like may be performed between the transparent resin and the base material, or these may be used in any combination.

(Optical function expression part)
The optical function developing unit 20 is made of a cured product of an active energy ray-curable resin composition containing at least an acrylic resin and / or a methacrylic resin, and includes a plurality of unit concavo-convex structures 30 on the surface opposite to the transparent substrate 10. It has an uneven shape. When the surface of the optical function developing part is observed with an atomic force microscope (AFM), it has a raised structure with an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm. Thus, when the optical function manifesting part is in a cured state exhibiting the above raised structure, the uneven shape of the optical function manifesting part is a cured state capable of achieving both excellent resilience and scratch resistance. Even when stress is applied when the optical sheet of the present invention is incorporated into an apparatus or when the optical sheet of the present invention is unwound after being unwound in the 2P method, the optical function is manifested only by temporary deformation. The uneven shape of the part is hard to be damaged, and when it is released from stress, the uneven shape is recovered, the desired shape can be maintained, and the scratch resistance is excellent.

The raised structure in the present invention will be described with reference to FIG. FIG. 4 is a schematic cross-sectional view of the surface of the optical function manifesting part 20 having the raised structure 2. In the present invention, the raised structure observed by the AFM means a very flat dome-shaped or trapezoidal flat raised raised from the surface of the optical function developing unit 20. The size of the raised structure is an average diameter of 0.1 to 2 μm, preferably 0.1 to 1 μm, more preferably 0.1 to 0.8 μm, and an average height of 1 nm to 100 nm, preferably 1 nm to 30 nm. If the above upper limit is exceeded, there is a possibility that the desired light reflection will be hindered. If the above upper limit is not reached, sufficient restorability to exhibit scratch resistance cannot be obtained.
As can be seen from the above size, the raised structure of the present invention is very fine, has a low height value compared to the diameter, and looks almost flat when viewed macroscopically. In addition, when viewed from a plane, it can be intuitively seen as a particulate structure.
As an atomic force microscope (AFM) used for the observation, Nanoscope (trade name) manufactured by Bruker AXS can be exemplified. The average diameter can be obtained by directly reading each particle diameter from the line profile and taking the average. The average height can be obtained by reading the value obtained by subtracting the maximum value of the height from the minimum value of the height from the line profile of the particle diameter for each particle and taking the average.

  Such a raised structure has a domain structure (polymer alloy structure) generated because the curing reaction of the active energy ray-curable resin composition containing an acrylic resin and / or a methacrylic resin constituting the optical function developing portion is not uniform. ). In the optical function manifesting part of the present invention, it can be easily imagined that there is a domain not only on the surface but also inside, and a part of the domain of the ellipsoid or sphere shape in the optical function manifesting part is the optical function manifesting part. It is inferred that what appeared on the surface is a raised structure observed by AFM in the present invention. Further, the optical function developing part of the present invention, that is, the cured product of the active energy ray-curable resin composition is in a state where relatively hard domains are scattered in a relatively soft matrix, and the scratch resistance in the present invention is It is presumed that a suitable balance of the restorability is expressed. The raised structure is very fine and does not contribute to optical properties such as diffusivity.

The number of raised structures means the number of raised structures per unit area (20 μm × 20 μm in the surface area of the unevenness) where the unevenness is developed, and the number of raised structures is 5 to 100/400 μm ^2. Is more preferable, and 5 to 50/400 μm ² is more preferable. If the lower limit is not reached, neither hardness nor restorability is sufficiently exhibited, and if the upper limit is exceeded, the hardness becomes too high and the restorability becomes poor. The number of particles tends to be proportional to the integrated dose of active energy rays, and the number of particles increases as the integrated dose increases.
The integrated dose is a value (mJ / cm ² ) obtained by multiplying the illuminance by the irradiation time.

In the optical sheet according to the present invention, the hardness (N / mm ² ) at the depth of 1 μm at the top of the unit concavo-convex structure 30 is 1 to 100, preferably 1.5 to 5. Hardness is indented using a micro hardness tester manufactured by Fisher Instruments (trade name: PICODETOR HM500, indenter is a diamond pyramid type, facing angle 90 °) in accordance with ISO14577-1. This is a value obtained by measuring the indentation depth while changing the load, and dividing the load (N) at the maximum indentation by the contact area (mm ² ) between the indenter and the sample.
When the hardness is lower than the lower limit, the concavo-convex shape is weak against external pressure. When the hardness is higher than the upper limit, the rugged shape has toughness against the external pressure but the restorability is poor.
In addition, the measurement of the hardness does not hold because the resin composition is not sufficiently cured in the range of the integrated dose of less than 100 mJ / cm ² , and the uneven shape is unstable.

In the optical sheet according to the present invention, the restoration rate (%) at the top of the unit concavo-convex structure 30 is 20 to 100%. Restoration rate is based on ISO14577-1, using a microhardness tester (trade name: PICODETOR HM500, indenter made of diamond, pyramid type, facing angle 90 °) manufactured by Fisher Instruments Co., Ltd. Measure the indentation depth by changing the indentation load, measure the indentation depth after unloading when the maximum indentation depth is reached, and determine the difference between the maximum indentation depth and the indentation depth after unloading (elastic deformation ) Divided by the maximum indentation depth (overall deformation).
When the optical sheet according to the present invention has a restoration rate in the above range, it is temporarily deformed when a stress due to contact with other members or winding of the sheet is applied, and when released from the stress, the optical sheet is restored by an elastic restoring force. The permanent shape (deformation) does not occur. When the restoration rate is lower than the above lower limit, the unevenness of the uneven shape with respect to the external pressure is poor, and the uneven shape is easily damaged or remains deformed.
The restoration rate of the concavo-convex shape of the present invention tends to gradually decrease as the cumulative dose increases in the range of the cumulative dose of 100 mJ / cm ² or more. If the lower limit is not reached, since the resin composition is not sufficiently cured, the uneven shape is unstable and the measurement of the restoration rate is not established.

Next, the concavo-convex shape including a plurality of unit concavo-convex structures of the optical function manifesting part according to the present invention will be described. In the present invention, the concavo-convex shape including the unit concavo-convex structure may be appropriately selected or set according to the required performance, but is specifically selected by a device on which an optical sheet is mounted, such as a prism, a lenticular lens, a Fresnel lens, etc. Lens, diffraction grating and the like.
For example, as a concrete shape (structure) of the concave-convex shape of the optical function developing portion as a prism sheet, a prismatic unit prism (unit concave-convex structure) such as a triangular prism (see FIG. 2), a quadrangular prism, a pentagonal prism, etc. Examples include a plurality of prisms arranged in a direction perpendicular to the ridge line direction (extending direction) (prism linear array). In the case of the prismatic unit prism as described above, the thickness T of the optical function manifesting part may or may not be uniform in the ridge line direction. For example, it may be different in the ridge line direction such that it is higher as it is closer to the peripheral portion and lower as it is closer to the central portion.

In addition, as an example of the specific shape of the concave-convex shape of the optical function developing portion as the prism sheet, a unit concave-convex structure such as a cone, a truncated cone, a pyramid such as a triangle, a square, a pentagon, or a hexagon, or a truncated pyramid is used as a transparent base. Examples include a two-dimensional array on the material surface.
The cross-sectional shape of the unit prism in the normal direction of the plane of the transparent substrate (hereinafter simply referred to as “thickness direction”) may be an isosceles triangle as shown in FIG. good.
The value of the apex angle of the triangular unit prism in the cross section in the thickness direction may be 90 ° as shown in FIG. 2, or may be any other angle, and can be adjusted within a range of 40 to 120 °. .

  The top of the unit prism may have a pointed shape as shown in FIGS. 1 and 2, or a circle having a radius of curvature of 1 to 10 μm (that is, a blunt apex) may be provided in the vicinity of the top of the cross section in the thickness direction (not shown). If the top of the unit prism in the cross section in the thickness direction has such a blunt apex, stress concentrated mechanically and geometrically on the top can be dispersed, and deformation, chipping or crushing of the top can be reduced or suppressed.

  As an example of the specific shape of the concave-convex shape of the optical function manifesting part as a lens sheet, a curved columnar unit lens (unit concave-convex structure) such as a semi-cylindrical or semi-elliptical column is orthogonal to the ridge line direction (extending direction) A large number of lens units arranged in a direction (lenticular lens), or a unit of curved unit lenses (unit uneven structure) such as a semi-spherical or spheroid half-shape, two-dimensionally arranged on the surface of a transparent substrate (moss eye lens) And an annular or linear Fresnel lens.

  Thickness T of the optical function developing portion (length from the convex top of the concavo-convex shape to the surface on the transparent substrate side as shown in FIG. 2 (maximum thickness when the thickness varies in the ridge direction) ) May be appropriately adjusted according to the required performance, and is usually 20 to 1000 μm.

(Active energy ray-curable resin composition)
The active energy ray-curable resin composition (hereinafter sometimes simply referred to as “composition”) includes an acrylic resin and / or a methacrylic resin, and is cured by irradiation with active energy rays to form an optical function manifesting part. . The active energy ray-curable resin composition of the present invention contains at least 50% by mass of an acrylic resin and / or a methacrylic resin with respect to the total solid mass of the composition.
In the present invention, the term “active energy ray” refers to an active energy ray, which is a generic term for not only visible light rays but also electromagnetic waves having wavelengths in the invisible region such as ultraviolet rays and X-rays, but also particle rays such as electron rays and α rays. Radiation having an energy quantum sufficient to cause a crosslinking reaction or a polymerization reaction to a molecule having a curable group is included. As the active energy ray, ultraviolet rays are preferable.

As the acrylic resin and / or methacrylic resin, those having a conventionally known (meth) acryloyl group and (meth) acryloyloxy group for forming an optical sheet can be used. It may contain a segment of a polymerized structure consisting of units. The segment includes an oligomer, a prepolymer, and a polymer. In addition, the segment may be an independent compound in the resin composition before being cured, or may be a structure that forms part of the polymer or crosslinked product. In the following, the segment will be described mainly using independent compounds as representative examples, but structures derived from the exemplified compounds and introduced into the polymer or crosslinked product also fall under the segment.
The segment has a monofunctional, ie, a polymer structure segment composed of a repeating unit of a (meth) acrylic compound having one active energy ray-curable group, and two functional groups, ie, two active energy ray-curable groups. A segment having a polymer structure composed of repeating units of a (meth) acrylic compound can be included.

In this invention, it is preferable to include the segment of the polymerization structure which consists of a repeating unit of caprolactone modified urethane (meth) acrylate. The repeating unit of this caprolactone-modified urethane (meth) acrylate contributes to the formation of a raised structure due to a heterogeneous polymerization reaction in the present invention, and also contributes to the development of resilience as a soft segment. It is guessed.
Examples of the repeating unit of caprolactone-modified urethane (meth) acrylate include general formula (I).

(In the formula, R ₁ is H or CH ₃ , m is 2-6, and n is 2-6.)

In the general formula (I), R ₁ is a hydrogen atom or a methyl group, m is 2 to 6, and n is 2 to 6.

  Content of the segment represented by general formula (I) is 5-30 mass% with respect to the total solid content mass of the said composition from a viewpoint which fully expresses the said specific restoring property and scratch resistance. It is preferable.

  As the segment represented by the general formula (I), those having a single structure and a weight average molecular weight may be used, or those having different structures and weight average molecular weights may be used in combination.

In addition to the polymer structure segment composed of repeating units of the above caprolactone-modified urethane (meth) acrylate, the monofunctional segment includes a chain aliphatic group containing a hetero atom such as a halogen atom, a sulfur atom, an oxygen atom or a nitrogen atom. Or a segment of a cyclic alicyclic or aromatic (meth) acrylic compound, for example, vinyl monomer, (meth) acrylic acid ester monomer, (meth) acrylamide derivative, urethane (meth) acrylate, phenyl Examples thereof include group-containing (meth) acrylates.
Among these, bisphenol A diglycidyl (meth) acrylate, biphenylyloxyethyl (meth) acrylate, EO-modified biphenylyloxyethyl (meth) acrylate, and bisphenol A epoxy (meth) acrylate are preferable.
The said monofunctional segment may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the monofunctional segment other than the segment of the polymer structure composed of the repeating unit of the caprolactone-modified urethane (meth) acrylate is preferably 20 to 65% by mass with respect to the total solid content of the composition. .

The polyfunctional segment is a chain aliphatic or cyclic alicyclic or aromatic (meth) acrylic segment containing a hetero atom such as a halogen atom, a sulfur atom, an oxygen atom or a nitrogen atom. Examples thereof include polyethylene glycol di (meth) acrylate, bisphenol A polyethoxydiol di (meth) acrylate, and pentaerythritol tri (meth) acrylate.
The said polyfunctional segment may be used individually by 1 type, and may be used in combination of 2 or more type.

  It is preferable that content of the said polyfunctional segment is 10-30 mass% with respect to the total solid content mass of the said composition.

  In addition, cyanate resin etc. can be used, for example, tolylene diisocyanate etc. can be used.

  It is preferable that content of the said other resin is 1-5 mass% with respect to the total solid content mass of the said composition.

  Examples of the photoinitiator (photopolymerization initiator) used in the resin composition of the present invention include bisacylphosphinoxide, 1-hydroxycyclohexyl phenyl ketone, and 2-hydroxy-2-methyl-1-phenylpropane-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, Nirubisu (2,4,6-trimethylbenzoyl) - phosphine oxide, and the like. These can be used alone or in combination of two or more.

  It is preferable that content of a photoinitiator is 1-5 mass% with respect to the total solid content mass of the said composition.

  In addition to the above components, the active energy ray-curable resin composition includes a stabilizer, a release agent, silicone, an antioxidant, a polymerization inhibitor, a thickener, an antistatic agent, an ultraviolet stabilizer, as necessary. Anti-foaming agents, solvents, non-reactive urethane resins such as non-reactive urethane polymers, non-reactive acrylic resins, non-reactive polyester resins, pigments, dyes or diffusing agents can also be used in combination.

(Light diffusion layer)
In the optical sheet according to the present invention, as shown in FIG. 3, a light diffusion layer 40 may be provided to provide a light diffusion function as necessary.
The light diffusion layer is an arbitrary layer that is preferably provided, and may have any function of diffusing light, and a layer formed on a general light diffusion sheet can be used.
For example, a layer in which light diffusing fine particles are dispersed in a translucent resin can be applied. As shown in FIG. 3, the light diffusion layer may be provided on the surface of the transparent substrate 10 opposite to the optical function developing unit 20, or although not shown, provided between the transparent substrate and the optical function developing unit. It may be done.

As translucent resin which comprises a light-diffusion layer, resin similar to the said transparent base material can be mentioned.
Further, as the light diffusing fine particles, light diffusing fine particles generally used for a light diffusing sheet are used. For example, polymethyl methacrylate (acrylic) beads, polybutyl methacrylate beads, polycarbonate beads, Examples include polyurethane beads, calcium carbonate beads, and silica beads.
In addition, the thickness of a light-diffusion layer is 1-20 micrometers normally.

(Optical sheet manufacturing method)
The method for producing an optical sheet of the present invention is particularly limited except that the active energy ray-curable resin composition containing the acrylic resin and / or methacrylic resin described above is used, and the irradiation conditions described later are adopted when the resin composition is cured. Instead, a conventionally known method can be employed.
For example, an active energy ray-curable resin composition containing the acrylic resin and / or methacrylic resin described above is prepared, the composition is filled in a mold having a desired unit uneven shape, a transparent substrate is stacked thereon, a laminator, etc. The transparent substrate is pressure-bonded to the composition using, and the composition is cured with ultraviolet rays or the like to form a unit uneven shape. Next, an optical sheet including an optical function developing part having a desired uneven shape on a transparent substrate is obtained by peeling or removing the unit uneven shape mold.
In order to improve mass productivity, it is preferable to manufacture an optical sheet by winding a prism sheet around a roll by a rotary 2P method.

In either method, the active energy ray to cure the active energy ray curable resin composition ultraviolet preferably as described above, as the irradiation conditions, the accumulated irradiation dose is 100mJ ^/ cm ² ~10000mJ ^/ cm 2 it is preferable, further it is preferable from the viewpoint obtained an optical sheet having a ridged structure of the present invention is ^{200mJ / cm 2 ~2000mJ / cm 2} . If the lower limit of the integrated irradiation dose is not reached, the resin composition is not sufficiently cured, and if the upper limit is exceeded, the curing becomes excessive and the hardness is increased, but the restorability is reduced.
As the irradiation device, an ultra-high pressure mercury lamp (manufactured by HOYA-SCHOTT; trade name: UV LIGHT SOURCE EX250; light source: 250 W) or the like can be used.

(Use of optical sheet)
The optical sheet according to the present invention can be used for, for example, a prism sheet used in a backlight of a liquid crystal display device or the like, a Fresnel lens sheet or a lenticular sheet used in a projection screen such as a projection television. The optical sheet according to the present invention can be suitably used in any of these, but among them, it can be suitably used as a prism sheet for a backlight for liquid crystal display devices.

(Surface light source device)
The surface light source device according to the present invention can be used in various specifications (forms) and is not particularly limited. The above-described optical sheet of the present invention is placed on the light emitting surface side of a surface light source in the form of a conventionally known so-called edge light type surface light source device, direct type surface light source device, EL (electroluminescence) type surface light source device or the like. Thus, the surface light source device of the present invention is configured. Here, an example of an edge light type surface light source device will be described in detail. The edge light type surface light source device according to the present invention is characterized in that the optical sheet is provided on the light emission surface side of the surface light source.
FIG. 5 is a schematic perspective view showing an example of a surface light source device including the optical sheet according to the present invention. In the surface light source device 50 of FIG. 5, the light diffusion layer 40, the transparent base material 10, and the optical function expression unit 20 are provided on the light emission surface 61 side of the light guide plate 60 from the light emission surface 61 side. The surface light source device 50 in FIG. 5 is an edge light type surface light source device. Light is incident on the light guide plate 60 from the light source 70 provided on at least one side end surface 62 of the light guide plate 60 to emit light. Light is emitted from the surface 61.

The light guide plate is a plate-like body made of a translucent material. The light guide plate 60 of FIG. 5 is configured to emit light introduced from the left side end surface 62 from the upper light emitting surface 61. The light guide plate may be a conventionally known light guide plate, and may be formed of a light-transmitting material similar to the optical sheet or the transparent substrate. The light guide plate is usually made of acrylic resin or polycarbonate resin.
The thickness of the light guide plate is usually 1 to 10 mm, and the thickness may be constant over the entire range. As shown in FIG. 5, when the light source 70 is provided on one end side, the side on which the light source 70 is provided. The end surface 62 side may be the thickest, and the taper shape which becomes gradually thin as the opposite side of the side end surface 62 may be sufficient. The light guide plate is preferably provided with a light scattering function inside or on the surface in order to emit light from the light emitting surface.

In the case of the edge light type surface light source device, the light source is for making light incident inside from at least one side end surface thereof, and is disposed along the side end surface of the light guide plate. The light source is not limited to the linear light source 70 as shown in FIG. 5, 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 surface. A plurality of small flat fluorescent lamps may be arranged along the side end surface.
When the apex angle of the unit concavo-convex structure is less than 80 degrees, the optical function developing unit 20 side of the optical sheet 1 is arranged in the direction facing the light guide plate 60 side, which is not illustrated, but contrary to the case of FIG.

As shown in FIG. 5, light emitted from the side opposite to the light emission surface 61 of the light guide plate 60 or the like on the surface opposite to the light emission surface of the light guide plate or a surface other than the light emission surface. A light reflecting plate 80 may be provided for returning to the inside and emitting from the light emitting surface 61.
As the light reflecting plate, a thin metal plate deposited with aluminum or the like, or white foamed PET (polyethylene terephthalate) is used.
According to the surface light source device according to the present invention, since the optical sheet according to the present invention is provided, even if the optical function developing portion of the optical sheet is in contact with a member such as a light guide plate, the top of the unit concavo-convex structure is lacking, Crushing and deformation are unlikely to occur.

(Liquid crystal display device)
The liquid crystal display device according to the present invention includes the optical sheet on one side of the liquid crystal cell. In the present invention, the liquid crystal cell refers to a module in which a liquid crystal compound is sealed between two transparent plates such as a glass plate, and may be a module including other members such as a polarizing plate or a color filter.

  6 is a schematic perspective view showing an example of a liquid crystal display device including the edge light type surface light source device shown in FIG. A liquid crystal display device 90 shown in FIG. 5 includes a liquid crystal cell 100 and a surface light source device including the optical sheet 1 on one side thereof (the back side (the side opposite to the side on which image display is observed in the liquid crystal display device)). 50.

  The liquid crystal display device may be a transmissive liquid crystal display device having a surface light source device (backlight) on the back side of the liquid crystal cell, or both reflected light display by external light and display by the backlight on the back side. It may be a transflective liquid crystal display device capable of achieving the above.

  According to the liquid crystal display device according to the present invention, since the optical sheet according to the present invention is provided, display irregularities such as white spots (white patterns) are not generated on the display surface, and stable and good display performance is obtained. be able to.

  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.

  The following compositions 1 and 2 were prepared respectively. Table 1 shows a summary of the composition of each composition.

(Preparation of Composition 1)
・ Bisphenol A diglycidyl acrylate (manufactured by NOF Corporation; trade name: BREMMER G): 40 parts by mass Ethyl acrylate (Osaka Organic Chemical Co., Ltd .; trade name: V # 193): 8 parts by mass EO-modified biphenylyloxyethyl acrylate (Osaka Organic Chemical Co., Ltd .; trade name: V # 193 '): 7 parts by mass / bisphenol A epoxy acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd .; trade name: A-B1206PE; molecular weight 500): 5 parts by mass polyethylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd .; trade name: A-400): 20 parts by mass Tolylene diisocyanate ( Nikka Trading Co., Ltd .; trade name: TDI): 5 parts by mass / photoinitiator (bisacylphosphine oxide; Ciba Specialty Chemicals; trade name: Irgacure 819): 3 parts by mass / N-dioctylmethylamine (Merck Co., Ltd .; trade name: 820790): 1 part by mass. Phosphate ester release agent (SC Organic Chemical Co., Ltd .; trade name Chelex H-18D): 0.1 part by weight

(Preparation of composition 2)
-Phenoxyethyl acrylate (Sartomer; trade name: SR339A): 18.9 parts by mass-Isobornyl acrylate (Daicel; trade name: UBOA): 8 parts by weight-Bisphenol A diacrylate (EO4 molar modification; general In formula (2), m = n = 2, and R ¹ and R ³ are all hydrogen atoms; manufactured by Kyoeisha Chemical Co., Ltd .; trade name: Light acrylate BP-4EA): 12 parts by mass

(In General Formula (2), R ¹ and R ³ are each independently a hydrogen atom or a methyl group, and n and m are positive integers satisfying n + m = 2 to 20)

Bisphenol A dimethacrylate (EO 2 mol modified; in general formula (2), m = n = 1, R ¹ is all methyl group, and R ³ is all hydrogen atom; manufactured by Kyoeisha Chemical Co., Ltd .; trade name: Light acrylate BP-2EM): 27 parts by mass-Bisphenol A epoxy diacrylate (manufactured by Kyoeisha Chemical Co., Ltd .; trade name: FLEA-POA; 49% by mass of bisphenol A epoxy diacrylate with respect to the total mass; content of phenoxyethyl acrylate 51% by mass; weight average molecular weight 2000): 16.1 parts by mass / isocyanuric acid triacrylate (EO3 molar modification; manufactured by Toagosei Co., Ltd .; trade name: Aronix M-315): 13 parts by mass / 4-acryloylmorpholine ( Product name: 4-Acryloylmorpholine manufactured by Tokyo Chemical Industry Co., Ltd. ): 5 parts by mass, 1-hydroxycyclohexyl phenyl ketone (Ciba Japan Co., Ltd .; trade name: Irgacure 184): 3 parts by mass, phosphate ester release agent (SC Organic Chemicals Co., Ltd .; trade name) Chelex H-18D): 0.05 parts by mass

Example 1
<Measurement of raised structure>
The composition 1 prepared above was applied to a polyethylene terephthalate (PET) substrate having a thickness of 125 μm (trade name A4300 manufactured by Toyobo Co., Ltd.), and an ultra-high pressure mercury lamp (manufactured by HOYA-SCHOTT; trade name: UV LIGHT). Using SOURCE EX250; light source: 250 W), the composition 1 was irradiated with ultraviolet rays at 170 mJ / cm ² and cured, and then cut into a length of 10 mm and a width of 10 mm to prepare a test piece.
When the above specimens were observed with an atomic force microscope (manufactured by Bruker AXS; trade name: Nanoscope V), and there were raised structures, the diameter and height were measured, and the average value and the number per unit area were determined. Obtained. The measurement results are shown in Table 2.

<Measurement of hardness>
In the above test piece, in accordance with ISO14577-1, a microhardness tester manufactured by Fisher Instruments Co., Ltd. (trade name PICODETOR HM500, indenter is a diamond pyramid type, facing angle 90 °) is used. The indentation depth was measured by changing the indentation load, and the value obtained by dividing the maximum indentation load (N) by the contact area (mm ² ) between the indenter and the sample was taken as the hardness. The measurement results are shown in Table 2. The measurement was performed in a mode for controlling the indentation depth, and the condition was set such that the tip of the indenter reached the depth of 1 μm in 5 seconds.

<Measurement of restoration rate>
In the above test piece, in accordance with ISO14577-1, a microhardness tester manufactured by Fisher Instruments Co., Ltd. (trade name PICODETOR HM500, indenter is a diamond pyramid type, facing angle 90 °) is used. , Measure the indentation depth by changing the indentation load, measure the indentation depth after unloading when the maximum indentation depth is reached, and determine the difference between the maximum indentation depth and the indentation depth after unloading (elasticity The value obtained by dividing (deformation) by the maximum indentation depth (overall deformation) was taken as the restoration rate. The measurement results are shown in Table 2. The measurement was performed in a mode for controlling the indentation depth, and the condition was set so that the tip of the indenter reached the depth of 1 μm in 5 seconds, and after the maximum indentation depth was reached, unloading was performed over 5 seconds.

<Evaluation of resilience and scratch resistance>
After the composition 1 prepared above was dropped onto a prism mold having a linear arrangement of unit prisms as shown in FIG. 2, a 125 μm thick polyethylene terephthalate (PET) substrate (Toyobo Co., Ltd.) Product name A4300) was stacked, and the entire surface of the PET substrate was pressure-bonded to the composition 1 with a laminator.

Next, the composition 1 was irradiated with ultraviolet rays at 170 mJ / cm ² using an ultrahigh pressure mercury lamp (manufactured by HOYA-SCHOTT; trade name: UV LIGHT SOURCE EX250; light source: 250 W), and a prism having a large number of unit prisms. The part was cured and integrated with the PET substrate. Thereafter, the prism sheet was peeled off to obtain an optical sheet.
Here, the shape of the unit prism was an isosceles triangular triangular prism shape having a height of 25 μm, a base of 50 μm, and an apex angle of 90 ° C. in the cross section in the thickness direction. Then, the optical function developing unit has a plurality of unit prisms arranged adjacent to each other in a direction orthogonal to the ridge line at an arrangement period of 50 μm so that the ridge lines of the unit prisms are balanced with each other.

The restoration property of the concavo-convex shape and the scratch resistance of the optical function developing part of the optical sheet were evaluated by the following methods and evaluation criteria. The results are shown in Table 2.
(Evaluation method)
FIG. 7 is a schematic view schematically showing a method for evaluating resilience and scratch resistance according to the present invention. As shown in FIG. 7, an optical sheet which is a test piece on the movable platen 110 of an abrasion resistance tester. 1 was set so that the transparent substrate side was positioned on the movable platen side, and a load of 2.45 N (250 gf) was applied to the load portion 130 via the polarizing film 120 having an area of 12 cm ^{2 on} the test piece. And the state of the top part of the optical function expression part when moving the movable board | plate 110 to the arrow 140 direction of FIG. 7 for 20 second at speed 5mm / s was evaluated by visual observation and microscope observation.

In the above evaluation method, the test piece was obtained by cutting the obtained optical sheet into a length of 150 mm and a width of 40 mm.
As a measuring device, a trade name AB-301 Gakushin type friction fastness tester manufactured by Tester Sangyo Co., Ltd. was used.
As the polarizing film, a product name H25 manufactured by Dai Nippon Printing Co., Ltd. with an area of 12 cm ² was used, and the mat layer side was arranged facing the test piece.
The microscope used the brand name digital microscope VHX-200N by Keyence Corporation.
The bottom surface of the load portion is a donut shape having an outer diameter of 20 mm and an inner diameter of 10 mm, and the bottom area is 2.36 cm ² .

(Restorability evaluation)
Evaluation 5: No deformation of the shape was confirmed by microscopic observation.
-Evaluation 4: Although deformation of the shape was confirmed by microscopic observation, it was not visually confirmed on the backlight.
Evaluation 3: Although deformation of the shape was confirmed visually on the backlight, it was restored to the original shape within 10 minutes at room temperature (25 ° C.).
Evaluation 2: Deformation of the shape was confirmed visually on the backlight, and it did not recover to the original shape within 10 minutes at room temperature (25 ° C), but when heated to 35 ° C, the original shape was restored within 5 minutes. Restored shape.
Evaluation 1: Deformation of the shape was confirmed visually on the backlight, and even when heated at 35 ° C., the original shape was not restored within 5 minutes, but when heated at 80 ° C. for 1 minute, the original shape Restored.

(Evaluation of scratch resistance)
Evaluation 5: No scratch was confirmed by microscopic observation.
Evaluation 4: One flaw was confirmed by microscopic observation, but no flaw was visually confirmed on the backlight.
-Evaluation 3: Two to three scratches were confirmed visually on the backlight.
Evaluation 2: Many scratches (streaks) were visually confirmed on the backlight.
Evaluation 1: It was confirmed that the entire prism surface was scraped by visual observation on the backlight.
In the restoration evaluation and scratch resistance evaluation, the microscope observation was performed by appropriately adjusting the magnification of the microscope within a range of 100 to 1000 times.

FIG. 8 is another schematic diagram schematically showing a method for evaluating resilience and scratch resistance in the present invention. The resilience evaluation 3 and the scratch resistance evaluation 5 are, for example, a dent (deformation) with a width L of the polarizing film 120 at the top of the unit concavo-convex structure 30 of the optical function manifesting part 20 as shown in FIG. In the case where the uneven shape is restored to the original shape as shown in FIG. 8B and the scratches are not confirmed by microscopic observation within 10 minutes at room temperature (25 ° C.). Say.
The resilience evaluation 3 and the scratch resistance evaluation 3 are, for example, a recess (deformation) having a width L of the polarizing film 120 at the top of the unit uneven structure 30 of the optical function manifesting part 20 as shown in FIG. After the width l smaller than the width L of the polarizing film 120 is formed, the concavo-convex shape is restored to the original shape as shown in FIG. 8D within 10 minutes at room temperature (25 ° C.). In this case, two to three scratches that remain without being restored on the surface near the top of the concavo-convex structure are formed, and the scratches are visually confirmed on the backlight.

(Examples 2 to 4 and Comparative Examples 1 to 4)
Examples 2 to 4 were measured and evaluated in the same manner as in Example 1 except that the integrated dose was changed as shown in Table 2 in Example 1.
Further, Comparative Examples 1 to 4 were carried out in the same manner as in Example 1 except that the composition 1 was changed to the composition 2 in Example 1 and the integrated dose was changed as shown in Table 2. went.

(Summary of results)
FIG. 9 shows a graph plotting the number of raised structures, the reaction rate, the restoration rate, and the hardness with respect to the integrated dose in the example of the present invention. FIG. 10 is a graph plotting the number of raised structures, the reaction rate, the restoration rate, and the hardness with respect to the integrated dose in the comparative example of the present invention.
What can be said comprehensively with reference to Table 2, FIG. 9 and FIG. 10 is that the way in which the reaction proceeds is completely different between Examples and Comparative Examples. Therefore, when FIG. 9 and FIG. 10 are compared, the transition of the reaction rate is completely different between the example and the comparative example.

In the examples, raised structures were observed. Referring to FIG. 9, as the integrated dose increases, the number of raised structures increases.
Referring to FIG. 9, in the example, it has a certain degree of hardness but not high toughness, and the recovery rate is gradually decreased as the integrated irradiation amount increases, but is higher than that in the comparative example. From this, it can be said that the Examples are balanced between scratch resistance and restoration. This can also be understood from the height of the evaluation results of the resilience and scratch resistance shown in Table 2.

On the other hand, no raised structure was observed in the comparative example.
Referring to FIG. 10, in the comparative example, the hardness rapidly increases as the integrated dose increases, but the restoration rate does not increase, and the restoration rate is lower than that in the example. From this, it can be said that the comparative example has a poor balance between resilience and scratch resistance. This can be understood from the low evaluation results of the restoring property and scratch resistance shown in Table 2.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Raised structure 10 Transparent base material 20 Optical function expression part 30 Unit uneven structure 40 Light diffusion layer 50 Surface light source device 60 Light guide plate 61 Light emission surface 62 Side end surface 70 Light source 80 Light reflection plate 90 Liquid crystal display device 100 Liquid crystal Cell 100 Liquid crystal cell 110 Movable plate 120 Polarizing film 130 Load section 140 Moving method 150 Scratches

Claims (7)

An optical sheet provided with a transparent base material and an optical function manifesting part that is provided on one surface side of the transparent base material and has a concavo-convex shape having a plurality of unit concavo-convex structures on the surface opposite to the transparent base material. ,
The optical function-expressing part contains an acrylic resin and / or methacrylic resin, and is represented by the following general formula (I) as a segment in the acrylic resin and / or methacrylic resin: caprolactone-modified urethane (meth) acrylate:

(In the formula, R ₁ is H or CH ₃ , m is 2-6, and n is 2-6.)
A cured product of an active energy ray-curable resin composition containing
An optical sheet having a raised structure having an average diameter of 0.1 to 2 μm and an average height of 1 nm to 100 nm when the surface of the optical function developing part is observed with an atomic force microscope.   The active energy ray-curable resin composition contains at least 50% by mass of acrylic resin and / or methacrylic resin with respect to the total solid content mass of the active energy ray-curable resin composition, and is one of the acrylic resin and / or methacrylic resin. The caprolactone-modified urethane (meth) acrylate represented by the general formula (I) as a part is contained in an amount of 5 to 30% by mass based on the total solid content of the active energy ray-curable resin composition. The optical sheet according to 1.   The acrylic resin and / or methacrylic resin is bisphenol A diglycidyl (meth) acrylate, biphenylyloxyethyl (meth) acrylate, EO-modified biphenylyloxyethyl (meth) acrylate, bisphenol as part of the acrylic resin and / or methacrylic resin. The optical sheet according to claim 2, further comprising at least one segment selected from the group consisting of A epoxy (meth) acrylate and polyethylene glycol di (meth) acrylate. 4. The optical sheet according to claim 1, wherein the number of the raised structures is 5 to 100/400 μm ² .   The optical sheet according to any one of claims 1 to 4, wherein the optical function developing part includes a prism and / or a microlens as a unit concavo-convex structure.   A surface light source device comprising the optical sheet according to claim 1 on a light emission surface side of a surface light source.   A liquid crystal display device comprising the optical sheet according to claim 1 on one side of a liquid crystal cell.

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