JP2013171056A - Optical sheet, surface light source device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet excellent in scratch resistance, in which even when a rugged coating film surface forming a rough surface on an opposite side of an optical element surface such as a prism of the optical sheet comes into contact with another surface, the contact surface is prevented from damages, and to provide a surface light source device and a liquid crystal display device using the optical sheet.SOLUTION: An optical sheet 10 includes unit optical elements 2 arranged on one surface 1p of a body part 1 and a rugged coating film 3 forming a rough surface with minute projections 4 including urethane resin beads as fine particles 5 on the other surface 1q. A hardness scale He of the optical element surface Pe and a hardness scale Hm of the rugged coating surface Pm are controlled to satisfy (hardness scale Hm)≥(hardness scale He), in terms of pencil hardness scales specified by JISK5600-5-4 (1999) (under the conditions of 1000 g load and 1 mm/s speed). In a surface light source device 30, a hardness scale Hp of a smooth light-exiting surface Pp of a light guide plate 32, which is to be in contact with the optical sheet, is controlled to satisfy (hardness scale Hp+2)≥(hardness scale Hm)≥(hardness scale Hp+1), wherein +1 represents a higher hardness scale by single unit in terms of the pencil hardness scale. The surface light source device is used for a liquid crystal display device.

Description

The present invention relates to an optical sheet that changes the traveling direction of light, a surface light source device using the same, and a liquid crystal display device using the surface light source device.
In particular, the present invention relates to an optical sheet excellent in scratch resistance, in which even if an optical sheet having a rough surface formed by a concavo-convex coating film on the opposite side of the optical element surface such as a columnar prism contacts the other surface, the contact surface is hardly damaged. The present invention also relates to a surface light source device using the same and a liquid crystal display device using the surface light source device.

In a transmissive liquid crystal display device, there is known an optical sheet that is arranged on a light exit surface of a back light source and collects the emitted light to improve luminance.
For example, in Patent Document 1, the back surface on the opposite side of the prism surface on which triangular prism unit prisms and the like are arranged as unit optical elements has a large number of minute projections for forming gaps whose height is not less than the wavelength of the light source light and not more than 100 μm. A faced optical sheet is disclosed. By making such a rough surface instead of a simple back surface, when the light guide plate is disposed adjacent to the back surface of the optical sheet, optical contact with the light guide plate is prevented, and brightness due to the optical contact is reduced. In-plane non-uniformity and interference fringes can be effectively prevented.

  In addition, a rough surface having many such fine protrusions on the surface can be obtained by a hot embossing method, a molding method using an ultraviolet ray or electron beam curable resin solution and a molding die (2P method: photopolymer method), and fine particles in a resin solution. It can be formed by a coating method or the like in which irregularities due to fine particles appear on the surface of the coating film of the paint contained in the coating to make it rough. Among them, the coating film method has an advantage that a thermoplastic resin or a thermosetting resin can be used for the resin, and fine particles can use resin beads or the like, which can be easily and inexpensively formed as compared with other methods.

However, although the optical adhesion can be prevented by the rough surface, the other side surface of the optical sheet and the other side of the optical sheet are arranged adjacent to the back surface of the optical sheet by the fine protrusions of the rough surface or fine particles dropped from the inside of the coating film. The surface of the optical member may be damaged.
It is a state after the optical sheet is assembled in an optical device such as a surface light source device configured to be superposed adjacent to another optical member such as a light guide plate, or a liquid crystal display device using the surface light source device. Thus, vibration may be applied when stored and transported as a semi-finished product or a product, and the contact surface is damaged due to the influence of the vibration.

  Therefore, in Patent Document 2, monodisperse spherical beads having a half-value width of 1 μm or less as a fine particle to be contained in the coating film in order to prevent such other adjacently disposed optical members from being damaged. We are proposing a technology that uses.

By the way, conventionally, the surface light source device generally has a configuration in which two light guide plates, a diffusion sheet, and an optical sheet are arranged from the light source side. For this reason, the other optical member which an optical sheet contacts becomes a diffusion sheet, and contact with this diffusion sheet has been regarded as important. Further, since two optical sheets are generally stacked, the rough surface on the light incident surface side of the optical sheet is in contact with the prism on the light output surface side of the other optical sheet. It was.
Recently, however, the performance of the light guide plate has been improved, and the in-plane luminance distribution of the diffusion sheet can be made uniform by the light guide plate itself. Further, a surface light source device that does not have a diffusion sheet for cost reduction There is a move to move to. For this reason, as another optical member in contact with the optical sheet, there is a tendency to place importance on the light guide plate, and damage due to the optical sheet is regarded as a problem in the contact state between the optical sheet and the light guide plate. There has been much to be done.

  On the other hand, the unit optical element such as the prism of the optical sheet can receive an external force in a relatively large area and does not include an object that easily falls off, such as fine particles. It is possible to design to prevent damage due to external force by using a resin having resilience.

Japanese Patent No. 3518554 Japanese Patent No. 3913870 JP 2009-37204 A

  However, even if the scratches on other optical members are improved by using monodisperse fine particles as proposed in Patent Document 2, the scratches due to the uneven coating surface of the optical sheet are relatively narrow. In addition to the concentration of stress on the area, it also contains fine particles that easily fall off, so that it is still difficult to prevent scratches even if the coating film is provided with restorability, and improvements have been desired.

That is, an object of the present invention is to provide an optical sheet having a rough surface with a concavo-convex coating film to prevent optical adhesion on the opposite side of the optical element surface by a prism or the like. Even if the front and back are in contact with each other, or the optical sheet is incorporated into a surface light source device or the like, even if the optical sheet comes into contact with another surface on the uneven coating surface, the contact surface is hardly scratched. It is to provide an optical sheet having excellent properties.
Another object of the present invention is to provide a surface light source device and a liquid crystal display device by using such an optical sheet so that the optical sheet and the light guide plate are hardly damaged.

The present invention provides an optical sheet, a surface light source device, and a liquid crystal display device having the following configurations.
(1) An optical sheet having a concavo-convex coating film in which unit optical elements are arranged on one surface of a sheet-like main body, and the other surface of the main body has a rough surface due to minute protrusions. ,
The microprojections include urethane resin beads as fine particles,
About the hardness He of the optical element surface formed by the arrayed unit optical elements, and the hardness Hm of the concavo-convex coating film surface forming the rough surface of the concavo-convex coating film,
An optical sheet having a pencil hardness measured according to JIS K5600-5-4 (1999) (load 1000 g, speed 1 mm / s) and having a hardness Hm equal to or higher than hardness He (hardness Hm ≧ hardness He).
(2) The optical sheet according to (1), wherein the relationship between the hardness He and the hardness Hm is such that the hardness He + 2 ≧ hardness Hm ≧ hardness He + 1, where 1 unit hardness on the pencil hardness scale is +1.

(3) A surface light source comprising at least a light source, a light guide plate that receives light from the light source and emits light from a smooth light exit surface, and an optical sheet disposed to face the light exit surface of the light guide plate A device,
The optical sheet is formed by arranging unit optical elements on one surface of a sheet-like main body, and has a concavo-convex coating whose surface is roughened by microprotrusions on the other surface of the main body.
The microprojections include urethane resin beads as fine particles,
About the hardness Hp of the light exit surface of the light guide plate and the hardness Hm of the concavo-convex coating film surface forming the rough surface of the concavo-convex coating film,
With pencil hardness measured according to JIS K5600-5-4 (1999) (load 1000 g, speed 1 mm / s),
When the relationship between the hardness Hp and the hardness Hm is +1 when the hardness of one unit on the pencil hardness scale is +1, the hardness Hp + 2 ≧ the hardness Hm ≧ the hardness Hp + 1,
The uneven coating film surface is disposed to face the light exit surface of the light guide plate,
Surface light source device.
(4) A liquid crystal display device comprising at least the surface light source device of the above (3) and a transmissive liquid crystal display panel placed on the light output surface of the surface light source device.

(1) According to the optical sheet of the present invention, even if the uneven coating film provided for preventing optical adhesion comes into contact with other surfaces, scratch resistance is obtained that makes the contact surface difficult to be damaged, and consequently the quality deteriorates. Can be prevented.
(2) Further, according to the surface light source device and the liquid crystal display device according to the present invention, the scratch resistance of the optical sheet included in the device is improved, so that the device is incorporated even when subjected to vibration during storage or transportation. In addition, the uneven surface of the optical sheet and the light guide plate surface in contact with the uneven surface of the optical sheet can be prevented from being scratched, and quality deterioration can be prevented.

The perspective view (a) explaining one Embodiment of the optical sheet and surface light source device by this invention, and the partial expanded sectional view (b) explaining the microprotrusion containing microparticles | fine-particles. Sectional drawing explaining one Embodiment (edge light type backlight) of the surface light source device by this invention, and one Embodiment of the liquid crystal display device by this invention. Sectional drawing which shows the method of measuring and evaluating the softness | flexibility of microparticles | fine-particles. The graph which shows the pencil hardness of the contact surface of the optical sheet and light-guide plate in the surface light source device by this invention, and the relationship of scratch resistance. The graph which shows the relationship between the pencil hardness of the contact surface of the optical sheet and light-guide plate in a conventional surface light source device, and scratch resistance. The graph which shows the pencil hardness of the uneven | corrugated coating film surface of the optical sheet by this invention, and the optical element surface, and the relationship of scratch resistance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are conceptual diagrams, and the scale relationships, aspect ratios, and the like of components may be exaggerated.

[A] Overview:
First, an embodiment of an optical sheet according to the present invention and a surface light source device according to the present invention is shown in the perspective view of FIG. The optical sheet 10 shown in the figure has a large number of unit columnar prisms having a triangular cross section as unit optical elements 2 on one surface 1p of the sheet-like main body 1 (the upper surface in the drawing) parallel to each other in the ridgeline direction. The other surface 1q of the main body portion 1 has a concavo-convex coating film 3 having a rough surface. As shown in the partial enlarged cross-sectional view shown in FIG. 1B, the uneven coating film 3 has a large number of microprojections 4 on the surface, and the microprojections 4 include urethane resin beads as fine particles 5 therein. It is out.

  The concavo-convex coating film 3 is formed by coating with a paint containing urethane resin beads as fine particles 5 in a binder resin, and the surface is formed by forming microprojections 4 on the surface due to the presence of the fine particles 5 made of urethane resin beads. It is a rough surface. In the optical sheet 10, the surface having the unit optical element 2 is the optical element surface Pe, and the surface having the uneven coating film 3 is the uneven coating surface Pm.

  In FIG. 1A, the X, Y, and Z axes of the orthogonal coordinate system are parallel to the arrangement direction of the unit optical elements 2 (unit columnar prisms in the present embodiment), and the Y axis is the unit optical element 2. The Z-axis is parallel to the thickness direction of the main body 1 and the thickness direction of the uneven coating film 3 in parallel to the ridge line direction of the (unit columnar prism).

  And about the hardness He of the optical element surface Pe formed of the unit optical element 2 arranged, and the hardness Hm of the rough concavo-convex coating film Pm formed by the concavo-convex coating film 3, JIS K5600-5-4 (1999). The pencil hardness measured under the conditions of a load of 1000 g and a speed of 1 mm / s in accordance with (year), hardness Hm ≧ hardness He, that is, hardness Hm is equal to or higher than hardness He.

More specifically, in the present embodiment, the relationship satisfies the hardness He + 2 ≧ hardness Hm ≧ hardness He + 1.
This is because the optical element surface Pe can be prevented from being damaged when the uneven coating surface Pm is too hard, and the uneven coating surface Pm can be prevented from being damaged when the uneven coating surface Pm is too soft.

  In view of the above-described hardness relationship, as a basic performance of the optical sheet 10 itself, the optical sheet 10 is wound around a roll or stacked in a single sheet state before the optical sheet 10 is incorporated into the surface light source device 30. Thus, the optical sheet 10 itself can be prevented from being damaged by vibration when the front and back surfaces of the optical sheet 10 are in contact with each other and stored and transported.

  On the other hand, the surface light source device 30 shown in FIG. 1A includes a light source 31, a light guide plate 32 that receives light from the light source 31 and emits light from a smooth light exit surface Pp, and a light exit surface Pp of the light guide plate 32. The optical sheet 10 is disposed so as to face each other. The optical sheet 10 is disposed such that the uneven coating film surface Pm faces the light output surface Pp of the light guide plate 32. Specifically, the optical contact between the uneven coating surface Pm and the light exit surface Pp is prevented, but the minute protrusions 4 of the uneven coating surface 3 are in contact with the light output surface Pp of the light guide plate 32. .

The hardness Hp of the light exit surface Pp of the light guide plate 32 and the hardness Hm of the uneven coating film surface Pm that is the light incident surface of the optical sheet 10 have a relationship satisfying the relationship of hardness Hp + 2 ≧ hardness Hm ≧ hardness Hp + 1. .
By having the above hardness relationship, optical contact between the light exit surface Pp of the light guide plate 32 and the uneven coating film surface Pm of the optical sheet 10 is prevented, and both of these surfaces are in contact with each other, and the surface light source device is It can be prevented from being damaged by vibration during storage and transportation.

[B] Definition of terms:
Next, definitions of major terms used in the present invention will be explained here.

“One surface 1p” is a surface on the side where the unit optical elements 2 of the main body 1 are arranged. Further, the “one surface 1p” side of the optical sheet 10 is referred to as an “optical element side”. The “one surface 1p” is a virtual surface that does not actually exist as the outermost surface or the interface when the unit optical elements 2 are filled and arranged without gaps to form an optical element group. In addition, “one surface 1p” means that when the unit optical elements 2 are arranged with a gap therebetween to form an optical element group, the optical element group has the gap and the one surface 1p is partially formed by the gap. It becomes a real surface exposed to.
The “optical element surface Pe” is a surface of only the arranged unit optical elements 2 when the unit optical elements 2 are arranged without gaps on one surface 1p and the one surface 1p is completely filled. Further, when the unit optical elements 2 are arranged with a gap on one surface 1p, in addition to the surface with the arranged unit optical elements 2, the surface further includes one surface 1p in the gap. .
When the optical sheet 10 is used with the “optical element side” as the “light emission side”, the “optical element side” observes an image displayed on the image display panel when the optical sheet 10 is applied to the image display panel. “Observer side”.
The “main cut surface” is parallel to the normal nd (see FIG. 1A) standing on the “one surface 1p” of the main body 1 when the unit optical element 2 has a columnar shape such as a unit columnar prism. This means a cross section parallel to the arrangement direction of the unit optical elements 2. In other words, the cross section is parallel to the normal line nd and orthogonal to the ridge line of the unit optical element 2 (unit columnar prism). In FIG. 1A, the Z axis is parallel to the normal nd.
“Smooth” means smooth in an optical sense. That is, it means the degree to which a certain percentage of visible light is refracted while satisfying Snell's law on the surface constituting the optical sheet 10. Therefore, for example, if the ten-point average roughness Rz (JISB0601: 1994 version) of the other surface 1q of the main body 1 is less than the shortest visible light wavelength (0.38 μm), it is sufficiently smooth.
The “rough surface” means an uneven surface that does not satisfy the “smooth” condition. That is, if the 10-point average roughness Rz value of a certain surface is 0.38 μm or more, it can be said to be a rough surface. However, in order to sufficiently achieve the optical effects of the rough surface such as the optical adhesion prevention effect and the light diffusion effect over the entire visible light wavelength band, the surface 10-point average roughness Rz value is the longest visible. It is preferable that the light exceeds 0.78 μm. Usually, the ten-point average roughness Rz value of the surface of the rough surface is about 1 to 10 μm.
Terms that specify shape and geometric conditions, such as “triangle”, “circular”, “elliptical”, “parallel”, “orthogonal”, “polyline”, etc., are not bound to a strict meaning. These terms are interpreted to include errors, tolerances, or equivalent ranges to the extent that similar optical functions can be expected, including limitations in manufacturing technology and errors during molding.

[C] Optical sheet:
Hereinafter, each component is further demonstrated from an optical sheet.

[Main body]
As the main body 1, a polyester resin such as polyethylene terephthalate or polyethylene naphthalate, a transparent resin material such as an acrylic resin, a polycarbonate resin, or a polyolefin resin, or a transparent inorganic material such as glass or ceramics can be used.
The main body 1 is “sheet-like”, and “sheet” here also includes the concept of “film” and “plate”, and these terms are different from each other based only on the difference in designation. It is not distinguished. That is, they are not distinguished by thickness or rigidity. For example, the thickness of the main body 1 is 25 μm to 5 mm or the like.
However, in terms of excellent productivity, the optical sheet is preferably flexible enough to be wound on a roll. In this respect, it is preferable that the optical sheet is not called a rigid so-called plate or substrate. Considering this point, the thickness of the main body 1 is preferably about 25 μm to 500 μm.
In addition, the other surface 1q of the main body 1 is a surface on which the uneven coating film 3 is formed, and is usually a smooth surface. However, the other surface 1q as the uneven coating film forming surface may not be a smooth surface.
Moreover, both the 1st surface 1p and the other surface 1q of the main-body part 1 are normally planes, and when the main-body part 1 is a plate, it will become flat form.

(Formation of main body and unit optical element)
In addition, the part of the optical sheet 10 which consists of the main-body part 1 and the unit optical element 2 can be formed from a conventionally well-known method and a transparent material. For example, an optical element group formed by arranging unit optical elements 2 and the main body 1 are integrally molded with the same material by a molding method such as a melt extrusion method, an injection molding method, or an embossing method by hot pressing. Can be formed. Alternatively, the resin body is brought into contact with the previously formed or molded main body 1 and the resin liquid is sandwiched between the mold and the main body 1 and solidified by a chemical reaction such as a curing reaction or cooling. Thus, different layers can be formed by a molding method in which an optical element group such as a prism shape is formed on the surface. When the resin liquid is cured with ionizing radiation using an ionizing radiation curable resin that is cured with ionizing radiation such as ultraviolet rays or electron beams, it is called a so-called 2P method (photopolymer method). At this time, when a transparent substrate such as a resin sheet is used as the main body 1, an optical element group including a resin layer is formed on the transparent substrate. That is, a resin layer having a slight thickness is formed between the adjacent optical elements 2 even at the valleys. In such a case, the main body 1 is composed of a resin layer in a portion other than the valley and the valley corresponding to the thickness of the resin layer in the valley, and a transparent substrate, A part of the thickness of the formed resin layer is included.

(Unit optical element)
The unit optical element 2 is typically a unit columnar prism, but besides this, a microlens (a microlens in which a large number of microlenses are arranged is called a fly-eye lens or an eyelet lens). Various conventionally known unit optical elements can be appropriately employed.
Hereinafter, the unit columnar prism will be further described.

(Unit columnar prism)
The unit columnar prism is typically a unit prism having a triangular shape with a main cut surface having a base on the main body 1 side. As such unit columnar prisms, various conventionally known prisms can be appropriately employed. The main cutting plane shape is not only a straight line shape such as a triangle, quadrangle, pentagon, hexagon, etc., but also a shape with a curve in part, a shape only with a curve (for example, a circle, an ellipse, a fence line, A part of a curve such as a hyperbola or a sine curve may also be included.
When the main cut surface is a part of a curve such as a circle or an ellipse, it can also be called a unit columnar lens, and the unit columnar prism in the present invention may include a unit columnar lens.

In addition, the unit columnar prisms may be arranged such that each of the unit columnar prisms arranged is different in shape or size in addition to the same shape and size, or may be irregularly different. Further, the arrangement of the unit columnar prisms may be different from each other in the arrangement period other than the regular arrangement in the same arrangement period, or may be irregularly different.
Further, as the unit columnar prism, the height of the ridge line described in Japanese Patent No. 3119471, Japanese Translation of PCT International Publication No. 2002-504698, etc. is changed into a polygonal line shape, and the shape is not constant. It is a kind of a preferable shape in that various problems caused by optical adhesion such as can be prevented. In order to manufacture a prism group in which unit columnar prisms in which the height of the ridgeline is changed to a polygonal line are manufactured, for example, cylindrical (cylindrical) molding conventionally used for manufacturing this type of prism group is used. When the mold is manufactured with a cutting tool, it can be easily manufactured by cutting while changing the cutting depth of the cutting tool into a polygonal line.

(Specific examples of dimensions and distribution)
Here, if the specific example of the dimension of a unit columnar prism and the optical element group (prism group) which consists of it is shown, the width | variety of the bottom face (dimension in a prism arrangement direction) of a unit columnar prism will be 10-500 micrometers, and the top part which forms a ridgeline When the main cutting plane shape is an isosceles triangle, the apex angle forming the ridge line is 80 to 110 °, preferably 90 °.

  Similarly to the unit columnar prism, each of the arranged microlenses may have one or more different shapes and dimensions other than the same shape and size, and may be irregularly different. good. Further, the arrangement of the microlenses may be other than the regular arrangement with the same arrangement period, the arrangement period may be different, and the arrangement may be irregularly different. A typical microlens is a part of a sphere or ellipsoid whose bottom shape is a circle or an ellipse, but other shapes (for example, a cone or a pyramid) may be used.

  As described above, the unit optical element 2 typically includes a unit columnar prism and a microlens, but the unit optical element 2 provided in the optical sheet 10 includes a unit columnar prism (can include a unit columnar lens). Only a microlens, or a unit columnar prism and a microlens.

[Uneven film]
The concavo-convex coating 3 is a transparent layer having a concavo-convex coating surface Pm on the surface thereof roughened by the fine protrusions 4, and the microprotrusions 4 contain urethane resin beads as fine particles 5 therein.
The concavo-convex coating film 3 includes a binder resin and urethane resin beads as the fine particles 5 as essential components, and further, if necessary, is applied using a resin composition (coating liquid, paint) containing various additives, solvents, and the like. Can be formed. When the resin composition contains a solvent, the surface of the concavo-convex coating film 3, that is, the concavo-convex coating film, is formed due to the decrease in the film thickness due to the contraction of the coating film volume during solidification, so that the protruding portion of the urethane resin beads protrudes. The surface Pm is formed as a rough surface. Alternatively, a resin that hardens the binder resin by a cross-linking reaction, an addition polymerization reaction, or the like may be used so that the urethane resin beads protrude from the surface of the concavo-convex coating film by volume contraction during the curing.
Note that, in the protruding microprotrusions 4, the surface of the urethane resin beads can be either coated with a binder resin or not coated with a binder resin. However, a form in which the surface of the urethane resin beads is coated with a binder resin is preferable in terms of preventing the urethane resin beads from falling off and preventing other optical members such as the optical sheet 10 and the light guide plate 32 from being damaged by the urethane resin beads. .

(Binder resin)
As the binder resin, the urethane resin beads are firmly fixed in the binder resin matrix, and the adhesion between the main body 1 and the urethane resin beads is strong from the viewpoint of preventing the uneven coating 3 itself from being peeled off from the main body 1. A transparent resin may be used as appropriate.
As such a binder resin, a transparent resin such as a thermoplastic resin or a curable resin such as a thermosetting resin or an ionizing radiation curable resin can be used. For example, the thermoplastic resin is an acrylic resin, a polyester resin, a polyurethane resin, a vinyl chloride-vinyl acetate copolymer, and the thermosetting resin is a thermosetting acrylic resin, a thermosetting polyester resin, Examples thereof include thermosetting polyurethane resins, and ionizing radiation curable resins are acrylic resins, epoxy resins, polyester resins, and the like that are cured by ultraviolet rays or electron beams. In the case of a curable resin, a curing agent, a polymerization disclosure agent, and the like can be included as part of the resin component.
Among the various binder resins mentioned above, the ionizing radiation curable resin, in particular, is quick in curing and excellent in productivity, and also can increase the coating strength of the formed uneven coating film 3 and have excellent scratch resistance. Is preferable.

(Fine particles: Urethane resin beads)
In the present invention, in order to generate the fine protrusions 4 on the uneven coating surface Pm of the uneven coating film 3, urethane resin beads are used as the fine particles 5 included in the fine protrusions 4. Urethane resin beads are fine particles having transparency so as not to impair the light transmission, which is the basic performance as an optical sheet. As the fine particles 5 for generating the fine protrusions 4, spherical particles having a spherical shape are preferable. Note that the term “spherical” refers to particles having a spherical shape or a nearly spherical shape. By making the particle shape spherical, the shape of the top of the microprotrusions 4 generated on the surface of the uneven coating film 3 by the fine particles and the periphery thereof can be generated in a rounded shape instead of a square shape. In addition, when the fine protrusions 4 do not expose the fine particles and the spherical fine particles are covered with the binder resin, the fine particles are difficult to drop off, and the binder resin itself comes into contact. As a result, the microprojections 4 can be made slippery in shape, so that the optical member that contacts the optical sheet or the optical sheet itself (also the microprojections 4 such as the tips of the microprojections 4) is scratched by friction or the like. This makes it difficult to prevent chipping of the contact portion.
As such spherical fine particles 5, that is, spherical particles, various kinds of inorganic beads such as glass beads and silica beads are known in addition to resin beads such as acrylic resin beads, polycarbonate resin beads and urethane resin beads. Of these, urethane resin beads exhibit excellent performance, and in the present invention, these urethane resin beads are used as the fine particles 5.

  The urethane resin beads may be non-crosslinked, but are preferably crosslinked urethane resin beads like other organic resin beads. This is because when the uneven coating film 3 is formed by a resin composition containing a solvent other than the binder resin, it is dissolved by the solvent and does not disappear.

Urethane resin beads tend to be more flexible than organic resin beads such as acrylic resin beads and polycarbonate resin beads, or inorganic beads such as glass beads and silica beads. It is speculated that it may contribute to the improvement.
For example, when comparing compressive strength as an index of flexibility, acrylic resin beads show 25.0 MPa, whereas urethane resin beads show 1.72 MPa. Urethane resin beads Is about one tenth of that of acrylic resin beads.

  The compressive strength is 0.9d because the diameter d of the spherical fine particles 5 is reduced by 10% by pressurization as schematically shown in FIG. 3 because the fine particles 5 to be measured are spherical. It is a value calculated from the force when The measurement is calculated from a 10% compressive load and a diameter d when a force is applied from the top of one particle 5 placed on a measurement table and the diameter d is reduced by 10%. Since it is the compressive strength at the time of 10% deformation, it is also called 10% compressive strength. It can be said that the smaller the 10% compressive strength, the softer and more flexible.

  The particle diameter of the urethane resin beads which are spherical particles is, for example, about 1 to 10 μm in terms of (primary of individual particles not averaged). Further, if the particle size distribution is wide, the distribution of the respective protrusion heights of the microprotrusions 4 (the altitudes of the individual microprotrusions 4 from the surface of the uneven coating film 3 where the microprotrusions 4 do not exist) becomes wide. Accordingly, the urethane resin beads having a large particle diameter generate microprojections 4 having a high protrusion height and positively act on the formation of voids. However, since the contact frequency with the optical member is large and the external force due to the contact is also large, The uneven coating film surface Pm is easily damaged. For this reason, it is preferable that the particle size distribution is narrow. Accordingly, it is more preferable that the particle size distribution is narrow, that is, monodisperse or has a particle size distribution close to monodispersion. For example, as disclosed in the above-mentioned Patent Document 2, it is preferable that the particle size distribution has a half width of 1 μm or less in the particle size distribution curve. By using monodisperse urethane resin beads having a half width of 1 μm or less as the fine particles 5 in this way, the uniformity of the projection height of the microprojections 4 generated by the urethane resin beads is improved, and the relative height of the projections is increased. It is possible to reduce the degree of load concentration on the minute protrusions 4 that are extremely high. The half-value width is the particle diameter (value distribution) width at a portion corresponding to a height that is ½ of the peak height of the particle diameter distribution curve. For this reason, the scratch resistance can be improved also from the urethane resin bead side.

  The particle size distribution and the average particle size may be based on the number, but generally, the volume basis (or weight) is used. In the present invention, the volume-based volume average particle size is also used in the same manner. The price range is the same. Such a volume-based particle size distribution or average particle size can be measured by a dynamic light scattering method using a laser beam. Moreover, the particle diameter of each spherical particle may be measured by microscopic observation and calculated from this.

Further, when the maximum diameter (individual particles) of urethane resin beads, which are spherical particles, exceeds 10 μm, the light path changing action increases. For this reason, when the optical sheet 10 is used as a brightness enhancement sheet, the light condensing action that functions on the optical element surface Pe of the optical sheet 10 is reduced, and the optical function thereof starts to be impaired. Therefore, it is preferable to avoid particles exceeding 10 μm as much as possible.
However, it is not intended to exclude a mode of giving a function of appropriately diffusing by adopting a particle having a large particle diameter. On the other hand, when the minimum diameter (individual particles) of the urethane resin beads is less than 1 μm, a high level of technology is required to disperse the urethane resin beads in the coating composition that forms the uneven coating film 3, and the rough surface It is not preferable from the viewpoints that it is difficult to ensure the height of the uneven projections (evaluated by the ten-point average roughness Rz) of 0.78 μm or more, and the material itself is expensive.
In addition, content of a urethane resin bead shall be 2-15 mass% with respect to binder resin, for example. By adjusting the content of the urethane resin beads, the surface density of the fine protrusions 4 can be adjusted.

  The uneven coating film 3 may be positively imparted with a light diffusion function for diffusing light. For example, the light diffusing function can be imparted by causing the urethane resin beads contained in the uneven coating film 3 to function as a light diffusing agent. In order to make the urethane resin beads function as a light diffusing agent, it is preferable to use a material having a large refractive index difference between the urethane resin beads and the binder resin. In this case, the difference in refractive index between the urethane resin beads and the binder resin is 0.1 or more, preferably 0.15 or more.

(Additive)
The uneven coating film 3 may contain various known additives such as a lubricant, a dispersant, a stabilizer, a plasticizer, an ultraviolet absorber, and an antistatic agent. These are used by adding to the resin composition for forming the uneven coating film 3.

For example, the lubricant improves the slipperiness of the roughened surface of the concavo-convex coating film 3, makes it difficult to damage the optical sheet itself, and can improve the scratch resistance.
Lubricants include hydrocarbon lubricants such as liquid paraffin, paraffin wax, synthetic polyethylene wax, fatty acid lubricants such as lauric acid, higher alcohol lubricants such as stearyl alcohol, stearic acid amide, oleic acid amide, erucic acid amide, etc. Aliphatic amide lubricants, methylene bis stearamide, alkylene fatty acid amide lubricants of ethylene bis stearamide, metal soap lubricants made of metal stearate such as zinc stearate, calcium stearate, magnesium stearate, stearic acid monoglyceride And fatty acid ester lubricants such as stearyl stearate and hydrogenated oil, and silicone lubricants such as silicone oil and modified silicone oil.
In addition to the above, modified silicone oils include polyether modified silicone oil, amino modified silicone oil, epoxy modified silicone oil, olefin modified silicone oil, fluorine modified silicone oil, alcohol modified silicone oil, higher fatty acid modified silicone oil, etc. Can be mentioned.

  Of the above-mentioned various lubricants, modified silicone oils are preferable, and polyether-modified silicone oils are particularly preferable lubricants. The polyether-modified silicone oil is a compound in which the siloxane skeleton of the silicone oil is modified with the polyether skeleton, and a block in which the polyether skeleton is bonded to one or more of one end, both ends, and side chains of the siloxane skeleton. It is a copolymer. As a preferred compound example of such a polyether-modified silicone oil, for example, polyether-modified dimethylpolysiloxane can be mentioned. The polyether-modified dimethylpolysiloxane is a compound in which the siloxane skeleton is dimethylpolysiloxane and the polyether skeleton is bonded thereto.

〔hardness〕
In the present invention, in the optical sheet 10 alone, the hardness He of the optical element surface Pe which is the surface on the unit optical element 2 side of the optical sheet 10 and the uneven coating surface which is the surface forming the rough surface on the uneven coating film 3 side. With respect to the hardness Hm of Pm, a specific hardness relationship is established by pencil hardness.
This is because, as a basic performance of the optical sheet 10, the optical sheet 10 is wound around a roll or stacked in a single sheet state before the optical sheet 10 is incorporated into an optical device. This is to prevent the optical sheet 10 itself from being damaged by vibration when stored and transported with the front and back surfaces in contact.
In addition, as will be described later in the section of the surface light source device 30, in the surface light source device 30 incorporating the optical sheet 10, the hardness Hm of the uneven coating surface Pm of the uneven coating film 3 and the uneven coating surface Pm are About the hardness Hp of the light emission surface Pp of the light-guide plate 32 which touches, it is set as a specific hardness relationship by pencil hardness.

(Pencil hardness)
Here, the pencil hardness related to the hardness He and the hardness Hm means the pencil hardness measured under conditions of a load of 1000 g and a speed of 1 mm / s in accordance with JIS K5600-5-4 (1999 edition). Then, the hardness of the optical element surface Pe on the opposite surface is set to be not less than the hardness He (Hm ≧ He) according to the pencil hardness.
The reason why the hardness Hm is equal to or higher than the hardness He is that the concave / convex coating surface Pm is easily damaged unless the hardness Hm of the concave / convex coating surface Pm is equal to or higher than the hardness He of the optical element surface Pe. Further, the optical element surface Pe needs to be prevented from being damaged by being deformed when an external force is applied and softened so as to return to the original state when released from the external force, and is usually designed as such. On the other hand, the uneven coating surface Pm, on the other hand, needs to withstand and maintain its shape without being deformed appropriately in order to prevent optical adhesion even when an external force is applied. Compared with the optical element surface, the stress is concentrated and it is necessary to withstand this. Therefore, it is preferable that the hardness Hm is not less than the hardness He.
By adopting such a hardness relationship, even if contact occurs between the front and back surfaces of the optical sheet (between the optical element surface Pe and the uneven coating film surface Pm), the optical element surface Pe and the uneven coating film of the optical sheet It is possible to prevent scratches such that the surface Pm is cut.

  More preferably, the relationship between the hardness He and the hardness Hm is such that hardness He + 2 ≧ hardness Hm ≧ hardness He + 1, where 1 unit hardness on the pencil hardness scale is +1. That is, the hardness Hm of the concavo-convex coating surface Pm is at least +1 unit harder than the hardness He of the optical element surface Pe on the pencil hardness scale. However, at most, the hardness Hm of the uneven coating surface Pm may be hardened up to +2 units on the pencil hardness scale with respect to the hardness He of the optical element surface Pe, but exceeds 2 units. Don't be stiff. From a simple perspective, it can be considered that the harder the pencil hardness, the harder it is to be scratched.

  In addition, the scale of pencil hardness is 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, etc. in order from the softer to the harder. In this pencil hardness scale, for example, “+1 unit” with respect to “HB” means “F”, which is one higher hardness unit, and “+2 unit” means two higher hardness units. Means “H”. Therefore, for example, if He is F, hardness He + 2 ≧ hardness Hm ≧ hardness He + 1 means 2H ≧ hardness Hm ≧ H.

  By adopting such a hardness relationship, it is possible to more reliably prevent the optical element surface Pe and the concavo-convex coating film surface Pm of the optical sheet from being scraped even if contact between the optical sheets occurs.

Furthermore, the hardness Hm is preferably equal to or higher than HB. Even if the hardness Hm and the hardness He are defined as described above, the uneven coating surface Pm that prevents optical adhesion prevents the optical adhesion even when an external force is applied. For this reason, it is necessary to endure without corresponding deformation and maintain the shape, and the microprotrusions 4 are concentrated in stress as compared with the optical element surface Pe and need to withstand this. For this reason, a certain degree of hardness is required.
The hardness Hm is preferably 5H or less. This is because if the hardness Hm of the concavo-convex coating surface Pm is too hard, the mating contact surface with which the concavo-convex coating surface Pm comes into contact may be damaged.

[Others]
The optical sheet 10 of the present invention may include other layers other than the above-described layers within a range not departing from the gist of the present invention.
For example, an antistatic layer may be further provided. The antistatic layer can reduce the adhesion of foreign matters such as dust, and can prevent the attached foreign matter from being damaged. In addition, an antistatic layer may be added to any one or more of the main body 1, the unit optical element 2, and the concavo-convex coating film 3 without providing an antistatic layer separately to impart an antistatic function.
Further, an antireflection layer composed of a low refractive index layer having a relatively lower refractive index than that of the layer immediately below the surface may be provided on the surface of the optical sheet 10 as the light incident surface. The reflection loss of incident light on the optical sheet 10 can be reduced. For example, an antireflection layer is provided on the concavo-convex coating 3 when the concavo-convex coating Pm is used as a light incident surface.

In addition, although the optical sheet 10 of the present invention is composed of the uneven coating film 3 in which the uneven coating film surface Pm has a rough surface, in the state of the main body 1 and the uneven coating film 3 where the unit optical element 2 does not exist As the total light transmittance, an optical member having high transparency of 90% or more can be obtained. In the same state, the haze can be 10% or less. In the same state, the transmission definition can be 50% or more in the optical combs of 0.125 mm and 0.5 mm.
The total light transmittance can be measured according to JIS K-7361, and the haze can be measured according to JIS K-7136. For example, it can be measured with a haze / transmittance meter HM-15 (manufactured by Murakami Color Research Laboratory). The transmitted sharpness is measured with five types of optical combs (0.125 mm, 0.25 mm, 0.5 mm, 1 mm, and 2 mm) using transmitted light in accordance with the image sharpness defined in JIS K-7105. The image sharpness at the comb is displayed in%, and the larger the value, the better the image sharpness. In addition, a measurement can be measured with a image clarity measuring device (Suga Test Instruments Co., Ltd., ICM-1DP) etc., for example.

  In the optical sheet 10 of the present invention, the contact surface with which the concavo-convex coating surface Pm contacts is a diffusion sheet or other optical member other than its own optical element surface Pe or the light exit surface Pp of the light guide plate 32. There may be.

[D] Surface light source device:
As shown in FIGS. 1 (a) and 2, the surface light source device according to the present invention includes at least a light source 31, a light guide plate 32 that receives light from the light source and emits light from a smooth light exit surface Pp, The surface light source device includes the optical sheet 10 disposed to face the light exit surface Pp of the light guide plate 32.
Moreover, the optical sheet 10 is formed by arranging the unit optical elements 2 on one surface 1p of the sheet-like main body 1 and the surface of the main body 1 is roughened by the minute protrusions 4 on the other surface 1q. The concavo-convex coating 3 is present, the microprojections 4 include urethane resin beads as the fine particles 5, and the concavo-convex coating surface forming the hardness Hp of the light exit surface Pp of the light guide plate 32 and the rough surface of the concavo-convex coating 3. About the hardness Hm of Pm
With pencil hardness measured according to JIS K5600-5-4 (1999) (load 1000 g, speed 1 mm / s),
The relationship between the hardness Hp and the hardness Hm is as follows: hardness Hp + 2 ≧ hardness Hm ≧ hardness Hp + 1, where 1 unit hardness on the pencil hardness scale is +1.
And this optical sheet 10 is arrange | positioned so that the uneven | corrugated coating film surface Pm may oppose the light emission surface Pp of the said light-guide plate 32. FIG.
Therefore, the orientation of the optical sheet 10 is such that the optical element surface Pe is on the light output surface side above the drawing, and the uneven coating film surface Pm is on the light guide plate 32 side, and is in contact with the light output surface Pp of the light guide plate 32.

Furthermore, in the embodiment shown in FIG. 2, the hardness Hm of the uneven coating film surface Pm and the hardness Hp of the light exit surface Pp of the light guide plate 32 are both HB or more.
This is because the hardness Hm of the uneven coating surface Pm is preferably HB or more as described above.
On the other hand, if the hardness Hp of the light exit surface Pp of the light guide plate 32 is too soft, the light exit surface Pp may be damaged.

[Optical sheet]
As the optical sheet 10 constituting the surface light source device 30, the optical sheet 10 described above can be used. Therefore, further explanation is omitted.

〔Light guide plate〕
As the light guide plate 32 constituting the surface light source device 30, a light guide plate 32 using a transparent resin such as an acrylic resin or a polycarbonate resin can be used. The light guide plate 32 has a light exit surface Pp that is a smooth surface. The light guide plate 32 may form a coating film in order to make the hardness Hp of the light exit surface Pp appropriate. On the surface of the light guide plate 32 that faces the light exit surface Pp, a light diffusing portion is appropriately provided by printing, prism, or the like.

〔light source〕
There is no restriction | limiting in particular as the light source 31 which comprises the surface light source device 30, A well-known thing can be used. For example, as the light source 31, in addition to a fluorescent lamp such as a linear cold cathode tube, a spot LED (light emitting diode), a planar EL (electroluminescent element), or the like can be used.

[Other components]
Other than the optical sheet 10, the light source 31 and the light guide plate 32, other optical members arranged as necessary, and their arrangement relationship, etc., are various optical members and arrangements of conventionally known surface light source devices. Can be employed as appropriate.

  In this way, the optical sheet 10 is prevented from optical contact with the light guide plate 32 by the concavo-convex coating film 3, and has the effect of effectively preventing in-plane luminance unevenness, interference fringes, and the like due to the optical contact. can get. Furthermore, since the scratch resistance of the concavo-convex coating surface is improved, an effect of preventing the contact surfaces of the optical sheet 10 and the light guide plate 32 that are in contact with each other can be obtained.

[Deformation as a surface light source device]
In the embodiment of FIG. 2, the optical sheet 10 is an example in which one sheet is arranged. However, in the present invention, a plurality of sheets such as two sheets may be arranged.
Although the surface light source device of FIG. 2 is an edge light type embodiment, a direct surface light source device may be used in the present invention.
The light source 31 is usually provided with a reflecting member such as a reflecting plate in order to direct light from the light source 31 toward the light guide plate 32 or the optical sheet 10. The reflecting member is made of a highly reflective material such as metal. In addition, optical members such as a light diffusing plate, a polarization separation film, and a retardation plate may be further arranged as necessary.

[E] Liquid crystal display device:
A liquid crystal display device according to the present invention is a display device including at least the surface light source device as a backlight and a transmissive displayable liquid crystal panel disposed on a light output surface of the surface light source device. The optical sheet 10 according to the present invention is provided in the surface light source device. As the constituent members other than the surface light source device and the liquid crystal panel, for example, optical members, panel driving circuits, and the like, conventionally known constituent members of the liquid crystal display device can be appropriately employed.
For example, in the liquid crystal display device 40 illustrated in FIG. 2, the above-described surface light source device 30 is used as a backlight, and a transmissive liquid crystal panel 41 is disposed adjacently on the light exit surface. Accordingly, as shown in the figure, the light emitting surface of the surface light source device 30 is the optical element surface Pe of the optical sheet 10, so that the optical element surface Pe is liquid crystal as another optical member that contacts the optical sheet 10. The panel 41 is in contact with the back surface. Note that a polarizing plate is usually laminated on the back surface of the liquid crystal panel 41 in contact. Then, the image on the liquid crystal panel 41 is observed by the observer V above the drawing by the light from the surface light source device 30.
As a liquid crystal display device having such a configuration, even when the optical sheet 10 and the liquid crystal panel are disposed adjacent to each other, the scratch resistance of the optical element surface Pe is improved, and thus the optical sheet itself can be prevented from being damaged. It has become.

  In the liquid crystal display device 40 illustrated in FIG. 2, the surface light source device 30 included in the liquid crystal display device 40 is an edge light type, but may be a direct type as described above.

  Hereinafter, the present invention will be further described with reference to examples and comparative examples.

[Preparation of paint for forming uneven film]
In order to form uneven coating films having various pencil hardnesses, paints having the following respective compositions were prepared.

(Composition A1: for pencil hardness 2B)
Prepolymer (caprolactone-modified urethane acrylate) 10 parts by weight Prepolymer (tolylene diisocyanate urethane acrylate) 8 parts by weight Bisphenol A diacrylate (EO4 mole modified) (bifunctional monomer) 68 parts by weight Isocyanuric acid triacrylate (EO3 mole modified) (Trifunctional monomer) 10 parts by mass Fine particles (cross-linked urethane resin beads; average particle size 6 μm) 1 part by mass (Negami Kogyo Co., Ltd., Art Pearl (registered trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

(Composition A2: for pencil hardness B)
Prepolymer (caprolactone-modified urethane acrylate) 10 parts by weight Prepolymer (tolylene diisocyanate urethane acrylate) 8 parts by weight Bisphenol A diacrylate (EO4 mole modification) (bifunctional monomer) 48 parts by weight Isocyanuric acid triacrylate (EO3 mole modification) (Trifunctional monomer) 30 parts by mass Fine particles (cross-linked urethane resin beads; average particle size 6 μm) 1 part by mass (Negami Kogyo Co., Ltd., Art Pearl (registered trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

(Composition A3: for pencil hardness HB)
Fluorine atom-containing urethane acrylate UV curable resin 99 parts by mass Fine particles (cross-linked urethane resin beads; average particle size 6 μm) 1 part by mass (Negami Kogyo Co., Ltd., Art Pearl (registered trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

(Composition A4: for pencil hardness F)
Fluorine atom-containing urethane acrylate UV curable resin 49.5 parts by mass Pentaerythritol triacrylate 49.5 parts by mass Fine particles (cross-linked urethane resin beads; average particle diameter 6 μm) 1 part by mass (Negami Kogyo Co., Ltd., Art Pearl (registered) Trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

(Composition A5: for pencil hardness H)
Pentaerythritol triacrylate 99 parts by mass Fine particles (cross-linked urethane resin beads; average particle size 6 μm) 1 part by mass (Negami Kogyo Co., Ltd., Art Pearl (registered trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

(Composition A6: for pencil hardness 2H)
Pentaerythritol triacrylate 49.5 parts by mass Dipentaerythritol hexaacrylate 49.5 parts by mass Fine particles (cross-linked urethane resin beads; average particle diameter 6 μm) 1 part by mass (Negami Kogyo Co., Ltd., Art Pearl (registered trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

(Composition A7: for pencil hardness 3H)
99 parts by weight of dipentaerythritol hexaacrylate Fine particles (cross-linked urethane resin beads; average particle size 6 μm) 1 part by weight (Negami Kogyo Co., Ltd., Art Pearl (registered trademark))
Photoinitiator (1-hydroxycyclohexyl phenyl ketone) 1 part by mass
(Irgacure (registered trademark) 184)
Solvent (Methyl isobutyl ketone: cyclohexanone = 1: 1 mass ratio) Appropriate amount

[Example A1] [He = B, Hm = HB]
The optical sheet 10 which employ | adopted the unit columnar prism as the unit optical element 2 like FIG.

  First, a metallic cylinder-shaped mold having an uneven surface opposite to the prism group composed of unit columnar prisms was prepared as a mold. Then, a transparent acrylic ultraviolet curable resin liquid having a resin composition for forming unit optical elements described below was applied to the mold, and a transparent biaxially stretched polyethylene terephthalate film (PET film) having a thickness of 188 μm was further formed thereon. The resin liquid was cured by ultraviolet irradiation from a high pressure mercury lamp. Then, a prism sheet member having a prism group in which unit columnar prisms as unit optical elements 2 are arranged on one surface 1p of the sheet-like main body portion 1 in parallel with each other in the ridgeline was manufactured.

[Resin composition for unit optical element formation]
Prepolymer (caprolactone-modified urethane acrylate) 11 parts by weight Prepolymer (tolylene diisocyanate urethane acrylate) 8 parts by weight Bifunctional monomer (bisphenol A diacrylate) 47 parts by weight Trifunctional monomer (glycerin epoxy triacrylate) 30 parts by weight Initiator 2.5 parts by mass (2,4,6-trimethylbenzoyldiphenylphosphine oxide)
Lubricant (phosphate ester lubricant) 1 part by mass

  The main body 1 is composed of the PET film and a part of the cured product layer corresponding to the thickness of the cured product layer of the ultraviolet curable resin liquid between the PET film and the convex portion on the mold surface. The Further, the remaining thickness portion of the cured product layer constitutes a prism group having a number of unit columnar prisms as unit optical elements 2. The unit columnar prism has a main cut surface shape of a right isosceles triangle having an apex angle of 90 °, a base of 50 μm, a constant height of 25 μm, and an arrangement period of 50 μm. Further, the unit optical element 2 composed of the unit columnar prisms completely covers one surface 1p of the main body 1 to form a prism structure in which unit optical elements are arranged with the same shape, the same size and the same period. Is the optical element surface Pe.

Next, the other surface 1q of the main body 1 that is the back surface side of the prism sheet member is coated with the coating film for forming an uneven film of the composition A3, dried by heating, and then cured by irradiating with ultraviolet rays to form an uneven surface with a thickness of 3 μm. The coating film 3 was formed, and the target optical sheet was produced.
Regarding the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was B, and the hardness Hm of the uneven coating surface Pm was HB.

[Example A2] [He = B, Hm = F]
In Example A1, an optical sheet was produced in the same manner as in Example A1, except that the coating film for forming an uneven coating film was changed to composition A4.
As for the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was B, and the hardness Hm of the uneven coating surface Pm was F.

[Example A3] [He = B, Hm = H]
In Example A1, an optical sheet was produced in the same manner as in Example A1, except that the coating film for forming an uneven coating film was changed to composition A5.
As for the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was B, and the hardness Hm of the uneven coating surface Pm was H.

[Example A4] [He = B, Hm = 2H]
In Example A1, an optical sheet was produced in the same manner as in Example A1, except that the coating film for forming an uneven coating film was changed to composition A6.
Regarding the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was B, and the hardness Hm of the uneven coating film surface Pm was 2H.

[Example A5] [He = B, Hm = 3H]
In Example A1, an optical sheet was produced in the same manner as in Example A1, except that the coating film for forming an uneven coating film was changed to composition A7.
Regarding the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was B, and the hardness Hm of the uneven coating film surface Pm was 3H.

[Comparative Example A1] [He = B, Hm = 2B]
In Example A1, an optical sheet was produced in the same manner as in Example A1, except that the coating film for forming an uneven coating film was changed to composition A1.
Regarding the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was 2B, and the hardness Hm of the uneven coating surface Pm was 2B.

[Example A6] [He = B, Hm = B]
In Example A1, an optical sheet was produced in the same manner as in Example A1, except that the coating film for forming an uneven coating film was changed to composition A2.
Regarding the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was B, and the hardness Hm of the uneven coating surface Pm was B.

[Example B1] [He = HB, Hm = HB]
In Example A1, the coating composition for forming an uneven coating film was left as composition A3, the resin composition for forming unit optical elements was changed to the following composition, and an optical sheet was produced in the same manner as in Example A1.
The resin composition for forming an optical element uses caprolactone-modified urethane acrylate and ethylene oxide-modified biphenyloxyethyl acrylate as prepolymers, and further uses neopentyl glycol methacrylate and bisphenol A diacrylate as bifunctional monomers. A glycerin epoxy triacrylate is used as a functional monomer, and a bisacylphosphine oxide-based initiator and 1-hydroxycyclohexyl phenyl ketone (Irgacure (registered trademark) 184) are added as initiators, and a phosphate ester-based lubricant is added. It is the added resin composition.
Regarding the pencil hardness of the obtained optical sheet, the hardness He of the optical element surface Pe was HB, and the hardness Hm of the uneven coating surface Pm was HB.

[Examples B2 to B5] [He = HB, Hm = HB to 3H]
In Example B1, an optical sheet was produced in the same manner as in Example B1, except that the coating for forming an uneven coating film was changed to compositions A4 to A7.

[Comparative Examples B1-B2] [He = HB, Hm = 2B-B]
An optical sheet was produced in the same manner as in Example B1, except that the uneven coating film-forming coating material was changed to compositions A1 and A2 in Example B1.

[Examples C to D series and Comparative examples C to D series] [He = F to H, Hm = 2B to 3H]
A main body part on the back side of the prism sheet member prepared in the same manner as in Example A1 by adjusting the resin composition for forming the unit optical element so that the hardness He of the optical element surface Pe becomes F and H The other surface 1q of 1 is coated with a coating film for forming an uneven coating film having compositions A1 to A7 having different hardnesses, heated and dried, and then cured by irradiation with ultraviolet rays to form an uneven coating film 3 having a thickness of 3 μm. A target optical sheet was produced in the same manner as in Example A1.

[Comparative Example E Series] [He = HB to F, Hm = 2B to 3H]
In the B series of Examples and Comparative Examples, and the C series of Examples and Comparative Examples, except that the crosslinked urethane resin beads in the concavo-convex coating film 3 were changed to crosslinked acrylic resin beads (average particle diameter of 5 μm). Thus, a target optical sheet was produced.

[Performance evaluation]
The contact surface in the state where the uneven coating surface Pm is in contact with the smooth light exit surface Pp of the light guide plate 32 by incorporating the scratch resistance of the optical sheet obtained in each of the above Examples and Comparative Examples into the surface light source device. In order to evaluate the scratch resistance, the scratch resistance was evaluated based on the degree of scratching of the contact surface in the contact state with the transparent resin plate assumed to be the light guide plate 32.
Moreover, the pencil hardness of the optical sheet and the acrylic resin plate was measured. The pencil hardness test of the optical element surface Pe was performed by moving the pencil in the prism ridge direction.
Moreover, the scratch resistance in the state in which the front and back surfaces of the optical sheet 10 itself were in contact with each other before the incorporation into the surface light source device was also evaluated.

(1) The pencil hardness is measured under the conditions of a load of 1000 g and a speed of 1 mm / s according to JIS K5600-5-4 (1999 edition).
(2) Scratch resistance is evaluated by the occurrence of scratches on the contact surface after a vibration test assuming vibration during storage and transportation.

<Vibration test>
An optical sheet having dimensions of 100 mm in length and 90 mm in width is placed on a transparent first acrylic resin plate having dimensions of 110 mm in length, 100 mm in width, and 3 mm in thickness as if viewed from the light guide plate. At this time, the optical sheet is installed so that the uneven coating film surface Pm faces the surface of the first acrylic resin plate. A spacer 250 μm thicker than the thickness of the optical sheet is fixed to the first acrylic resin plate in a frame shape around the four sides of the optical sheet. The optical sheet is movable in the horizontal direction parallel to the optical sheet surface between the spacers on the four sides, and the maximum movement amount is 5 mm in the direction parallel to each side.
Next, on the first acrylic resin plate, a transparent second acrylic resin plate having dimensions of 110 mm in length, 100 mm in width, and 3 mm in thickness is stacked via the spacer, and both acrylic resin plates are placed from the outside. The periphery of the four sides is fixed with an adhesive tape, and the optical sheet is surrounded by the first and second acrylic resin plates on the top and bottom and surrounded by the spacers on the left and right.
Then, after confirming that the optical sheet is movable between the first and second acrylic resin plates and that no foreign matter is visually mixed between the first and second acrylic resin plates. The vibration test is performed in a state where the vibration test machine is mounted on the vibration table and fixed.
In the vibration test, two acrylic resin plates surrounded by the optical sheet were fixed on a horizontal vibration table of a vibration tester (manufactured by IDEX Co., Ltd., BF-50UL). 3 axis simultaneous vibration is added. The vibration is an acceleration of 7.3 G and a frequency of 67 Hz for 20 minutes.

<Hardness of the first acrylic resin plate>
The first acrylic resin plate is subjected to a vibration test by changing the pencil hardness. For those having a pencil hardness of H, F, and HB, a commercially available product is used. For B, a paint having a composition in which only fine particles are removed from the above-described composition A3 for forming an uneven coating film on the surface of a commercially available product of HB. What formed the coating film was used.

<Vibration test for evaluating the scratch resistance of a single optical sheet>
As basic performance as a step before incorporating the optical sheet 10 into the surface light source device, scratch resistance when the optical sheet is subjected to vibration with the front and back surfaces in contact with each other is evaluated as follows.
In the vibration test, 10 optical sheets are placed on the first acrylic resin plate, each optical element surface of each optical sheet faces downward, and each unit optical element, that is, unit. The alignment direction of the columnar prisms is aligned in the same direction and stacked, and a second acrylic resin plate is stacked thereon, and the four sides are fixed with an adhesive tape. The vibration test is performed in a state in which this is placed on a vibration table of a vibration tester and a weight with a load of 10 g is further placed thereon and fixed. The vibration conditions for the vibration test are the same as above.

<Scratch evaluation>
For the optical sheet and the first acrylic resin plate after the vibration is applied, the surface condition is evaluated by visual observation with a microscope having a magnification of 500 times, and the superiority or inferiority is evaluated by the presence or absence of the occurrence of scratches.
a) As for the concavo-convex coating film surface Pm, a square region having an area of 9 mm ² was observed, and when there were no scratches (0 pieces), it was judged good (OK), and when there were more than one place, it was judged bad (NG).
b) As for the light exit surface Pp of the light guide plate, a square region having an area of 9 mm ² of the first acrylic resin plate is observed. If there is no scratch (0), it is good (OK), and if it is more than one place, it is bad. It was determined as (NG).
c) As for the optical element surface Pe, an area extending over a length of 3 mm of the ridge line portion of the unit columnar prism is observed. When there is no scratch (0), it is good (OK), and when it is one or more, it is bad (NG). It was determined.
d) As a comprehensive evaluation, from the evaluation of each scratch on the surfaces in contact with each other, the following was performed. 4 and 6 show the results of the comprehensive evaluation.
・ Both contact surfaces are good (circle),
・ Only concavo-convex film surface Pm is NG, slightly good (upward triangular triangle mark),
・ Only the first acrylic resin plate is NG, a little better (downward triangle ▽ mark),
・ If the contact surfaces were both NG, the defect was marked as x.

[Performance comparison]
When urethane resin beads are used as the fine particles 5 and evaluation is made in a contact state with the first acrylic resin plate that looks like a light guide plate, FIG. 4 shows the case where acrylic resin beads are used as the fine particles 5 instead of the urethane resin beads. Is shown in FIG. In the figure, the horizontal axis corresponds to the hardness Hp of the light exit surface Pp of the light guide plate, and the vertical axis corresponds to the hardness Hm of the uneven coating surface Pm.

  As shown in FIG. 4, it can be seen that the scratch resistance is good in the region where the hardness Hm and the hardness Hp satisfy the specific conditions described above. In the drawing, a region Ea is a region where hardness Hp + 2 ≧ hardness Hm ≧ hardness Hp + 1.

  Next, as shown in FIG. 5, when the fine particles 5 are not urethane resin beads but acrylic resin beads in the contact state with the first acrylic resin plate, even within the range of good hardness relationship in FIG. The scratch resistance is not as good as that of urethane resin beads. In the case of acrylic resin beads, the conditions under which good results are obtained are very narrow. In the results shown in FIG. 5, the hardness Hm = F and the hardness Hp = HB are slightly different from the hardness Hm = H and the hardness Hp = H. This is only when the contact surface is good, and only one light exit surface Pp is good.

  In addition, the scratch resistance due to the contact between the front and back surfaces of the optical sheet 10 itself before being incorporated into the surface light source device was as shown in FIG. In the drawing, a region Eb is a region where hardness Hm ≧ hardness He, and a region Ec is a region where hardness He + 2 ≧ hardness Hm ≧ hardness He + 1. It can be seen that the scratch resistance is good in the region where the hardness Hm and the hardness He satisfy the specific conditions described above.

DESCRIPTION OF SYMBOLS 1 Main-body part 1p One surface 1q The other surface 2 Unit optical element 3 Uneven coating film 4 Microprotrusion 5 Fine particle 10 Optical sheet 30 Surface light source device 31 Light source 32 Light guide plate 40 Liquid crystal display device 41 Liquid crystal panel He Pencil hardness of an optical element surface Hm Pencil hardness of uneven surface Hp Pencil hardness of light exit surface of light guide plate nd Normal Pe Optical element surface Pm Convex surface Pp Light exit surface V of light guide plate

Claims (4)

An optical sheet having a concavo-convex coating film in which unit optical elements are arranged on one surface of a sheet-like main body, and the other surface of the main body has a rough surface due to microprotrusions,
The microprojections include urethane resin beads as fine particles,
About the hardness He of the optical element surface formed by the arrayed unit optical elements, and the hardness Hm of the concavo-convex coating film surface forming the rough surface of the concavo-convex coating film,
An optical sheet having a pencil hardness measured according to JIS K5600-5-4 (1999) (load 1000 g, speed 1 mm / s) and having a hardness Hm equal to or higher than hardness He (hardness Hm ≧ hardness He).   2. The optical sheet according to claim 1, wherein the relationship between the hardness He and the hardness Hm further satisfies the following formula: hardness He + 2 ≧ hardness Hm ≧ hardness He + 1, where 1 unit hardness on the pencil hardness scale is +1. A surface light source device comprising at least a light source, a light guide plate that receives light from the light source and emits light from a smooth light exit surface, and an optical sheet disposed to face the light exit surface of the light guide plate. And
The optical sheet is formed by arranging unit optical elements on one surface of a sheet-like main body, and has a concavo-convex coating whose surface is roughened by microprotrusions on the other surface of the main body.
The microprojections include urethane resin beads as fine particles,
About the hardness Hp of the light exit surface of the light guide plate and the hardness Hm of the concavo-convex coating film surface forming the rough surface of the concavo-convex coating film,
With pencil hardness measured according to JIS K5600-5-4 (1999) (load 1000 g, speed 1 mm / s),
When the relationship between the hardness Hp and the hardness Hm is +1 when the hardness of one unit on the pencil hardness scale is +1, the hardness Hp + 2 ≧ the hardness Hm ≧ the hardness Hp + 1,
The uneven coating film surface is disposed to face the light exit surface of the light guide plate,
Surface light source device. A liquid crystal display device comprising at least the surface light source device according to claim 3 and a transmissive liquid crystal display panel placed on a light output surface of the surface light source device.

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