JP5755429B2 - Optical sheet and backlight unit using the same - Google Patents

Description

  The present invention relates to an optical sheet having a high anti-sticking function and a scratch-preventing function, and a backlight unit using the same.

  Liquid crystal display devices are widely used as display devices for screens of televisions, personal computers, and the like, and are broadly classified into direct-view types for directly viewing the display screen and projection types for viewing an image projected on the screen. Direct-view liquid crystal display devices include a transmissive type that transmits light from the backlight, a reflective type that does not have a backlight and uses reflected light such as natural light and room light, and a reflective type in bright places and a transmissive type in dark places. There is a transflective type. On the other hand, the projection type liquid crystal display device includes a front type that projects an image on a front screen and a rear type that captures the screen in a display cabinet and projects the image. Nowadays, a direct-view type liquid crystal display device among them is generally used as a mainstream.

  In the transmissive liquid crystal display device, a backlight system that illuminates a liquid crystal layer from the back is widespread, and backlight units such as an edge light type (side light type) and a direct type are provided on the lower surface side of the liquid crystal layer. As shown in FIG. 2, the edge light type backlight unit 20 generally includes a lamp 21 as a light source, and a rectangular plate-shaped light guide plate 22 disposed so that an end portion thereof is along the lamp 21. A plurality of optical sheets 23 stacked on the surface side of the light guide plate 22 are provided. As the lamp 21 as the light source, an LED (light emitting diode), a cold cathode tube, or the like is used, but an LED is generally used from the viewpoint of miniaturization and energy saving. The optical sheet 23 has optical functions such as diffusion and refraction with respect to transmitted light. (1) A prism that is disposed on the surface side of the light guide plate 22 and has a refraction function toward the normal direction side. Sheet 24, (2) a light diffusion sheet 25 disposed on the surface side of the prism sheet 24 and mainly having a light diffusion function is used.

  Although not shown, in consideration of the light guide characteristics of the light guide plate 22 and the optical function of the optical sheet provided in the optical sheet 23, more optical sheets 23 such as a light diffusion sheet and a prism sheet are provided. There is also a backlight unit.

  The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 22 from the lamp 21 is reflected by a reflective dot or a reflection sheet (not shown) on the back surface of the light guide plate 22 and each side surface. Emitted from the surface. The light beam emitted from the light guide plate 22 enters the prism sheet 24, is refracted toward the normal direction by the prism portions of the plurality of protrusions formed on the surface, and is emitted from the surface. Thereafter, the light beam emitted from the surface of the prism sheet 24 enters the light diffusion sheet 25, is diffused and emitted from the surface, and further illuminates the entire liquid crystal layer (not shown) above.

  As shown in FIG. 2B, the light diffusion sheet 25 disposed on the surface of the prism sheet 24 is generally composed of a transparent synthetic resin base material layer 26 and the base material layer 26. An optical layer 27 laminated on the front surface and an anti-sticking layer 28 laminated on the back surface of the base material layer 26 are provided. The optical layer 27 generally has a structure in which resin beads 30 are dispersed in a binder 29, and is configured to exhibit a light diffusion function or the like with respect to transmitted light. The anti-sticking layer 28 has a structure in which a small amount of beads 32 are dispersed and dispersed in the binder 31, and the lower part of the beads 32 protrudes from the back surface of the binder 31. The anti-sticking layer 28 is formed when the back surface of the light diffusing sheet 25 is in close contact with the surface of another optical sheet or the like (prism sheet 24), that is, when sticking occurs to generate interference fringes, or wound and stored in a roll in the manufacturing process. This prevents the inconvenience that blocking (adhesion) occurs. Since the apex of the prism portion is not an acute angle but forms a slight flat surface or curved surface, the surface side of the prism sheet 24 and the back surface side of the light diffusion sheet 25 are in contact with each other in a band shape. Sticking will occur on this surface.

  As the beads 32 dispersed in the anti-sticking layer 28 of the light diffusion sheet 25, acrylic beads or the like are generally used. Since the beads 32 are relatively hard, the beads 32 projecting from the back surface of the light diffusion sheet 25 The surface (prism portion apex portion) of the prism sheet 24 or the like laminated on the back side may be damaged. Further, the beads 32 dispersed in the anti-sticking layer 28 drop off when coming into contact with the apex of the prism portion of the prism sheet 24, and the drop-off portion of the beads 32 also causes damage. This damage to the optical sheet causes uneven brightness in the liquid crystal display device.

  Therefore, in order to prevent damage to the prism sheet or the like laminated on the back surface side, other optical sheets, or the light guide plate, an optical sheet (see Japanese Patent Application Laid-Open No. 2004-85626 etc.) provided with a scratch prevention layer on the back surface, An antiblocking curable resin composition (see Japanese Patent Application Laid-Open No. 2007-182519 etc.) has been developed that forms fine irregularities on the surface by applying and curing as a coating liquid.

  However, even in the optical sheet provided with the scratch-preventing layer, there is a fine bead for preventing sticking, so that it is not possible to sufficiently prevent damage to other optical sheets. Also, when unevenness is formed on the surface by the antiblocking curable resin composition, the surface unevenness is too fine and the anti-sticking performance is not sufficient, and the antiblocking property is improved to improve the brightness of the optical sheet. When the coating film of the curable resin composition is thinned, the unevenness formed becomes finer, and there is a disadvantage that the anti-sticking performance is further insufficient.

JP 2004-85626 A JP 2007-182519 A

  The present invention has been made in view of these disadvantages, and is an optical sheet capable of preventing scratches on the surface of other optical sheets and the like while preventing sticking with other optical sheets and the like laminated on the back side. It is an object of the present invention to provide a high-quality backlight unit by using this optical sheet to prevent luminance unevenness, interference fringes, and the like due to scratches.

The invention made to solve the above problems is
A transparent substrate layer, an optical layer laminated on one surface side of the substrate layer, and an anti-sticking layer laminated on the other surface side of the substrate layer. An optical sheet having a fine uneven shape,
The anti-sticking layer is composed of a plurality of kinds of phase-separated resins, and has a double sea island structure in which a domain phase is dispersed in a matrix phase and a granular phase is dispersed in the domain phase. It is an optical sheet.

  The optical sheet has a double sea island structure in which the anti-sticking layer is composed of a plurality of types of resins that are phase-separated, the domain phase is dispersed in the matrix phase, and the granular phase is dispersed in the domain phase. . According to the optical sheet, when the anti-sticking layer has such a double sea-island structure, fine irregularities on the anti-sticking layer surface are effectively formed. As a result, the anti-sticking layer exhibits high anti-sticking performance and can suitably prevent sticking with other sheets laminated on the anti-sticking layer side. In addition, the optical sheet can prevent scratches due to irregularities on the surface of the sticking prevention layer. Furthermore, according to the optical sheet, the surface of the anti-sticking layer has such a double sea-island structure, so that the unevenness sufficient to exhibit anti-sticking performance even if the anti-sticking layer is thin. It becomes easy to form. Thus, since the optical sheet can reduce the thickness of the anti-sticking layer, it is possible to prevent a decrease in luminance due to the provision of the anti-sticking layer. Moreover, it can be set as an optical sheet provided with the sticking prevention layer which has the desired suitable thickness and surface roughness by it.

  The main material in the matrix phase of the anti-sticking layer may be a urethane (meth) acrylate resin, the main material of the domain phase is a (meth) acrylic resin, and the main material of the granular phase is a (meth) acrylic resin. Since the main material of each of the phase-separated resin phases constituting the anti-sticking layer is the above resin, the unevenness of the anti-sticking layer surface is more effectively formed, so that the optical sheet has anti-sticking performance. Further improve. At the same time, since all of the resins forming the anti-sticking layer are (meth) acrylic resins, the optical sheet can ensure high luminance.

  It is preferable that convex portions are formed in a scattered manner on the surface of the anti-sticking layer due to the dispersed granular phase. Due to the dispersed granular phase, convex portions are formed on the surface of the anti-sticking layer in a scattered manner, whereby the anti-sticking performance of the optical sheet is very effectively exhibited. At the same time, since the convex portions on the surface of the anti-sticking layer are formed of resin, it is possible to prevent damage to other optical sheets and the like due to the concave-convex shape.

The average thickness of the anti-sticking layer is 0.5 μm or more and 4 μm or less,
The arithmetic average roughness (Ra) of the anti-sticking layer surface may be 0.03 μm or more and 0.3 μm or less, and the average length (RSm) of the roughness curve element may be 40 μm or more and 400 μm or less. When the arithmetic average roughness (Ra) of the anti-sticking layer surface and the average length (RSm) of the roughness curve elements are relatively small values within the above range, the other sheets laminated on the anti-sticking layer side It is possible to suitably prevent the sticking from being prevented, and to prevent damage caused by the fine irregularities on the surface of the anti-sticking layer. Moreover, since the optical sheet has an average thickness of the anti-sticking layer of 0.5 μm or more and 4 μm or less, it is possible to prevent a decrease in luminance due to the provision of the anti-sticking layer.

  Therefore, in the backlight unit for a liquid crystal display device that disperses the light emitted from the lamp and guides it to the surface side, when the optical sheet is provided, the optical sheet has a high scratch resistance, so that other optical sheets or the like Occurrence of brightness unevenness due to scratches and interference fringes can be prevented, the quality of the liquid crystal display screen can be improved, and handling during manufacture, transportation, storage and the like is facilitated.

  Here, the “optical layer” means a layer having a predetermined optical function with respect to transmitted light. Specifically, (a) a light diffusing layer having a light diffusing agent in a binder, and (b) embossing. A light diffusion layer having fine irregularities formed substantially uniformly on the surface by processing, (c) a prism layer having a triangular prismatic prism portion in a stripe shape, and the concept including a case where it is formed with a base material layer. It is. In addition, “arithmetic average roughness (Ra)” and “ten-point average roughness (Rz)” are according to JIS B0601-1994, “average length of roughness curve element (RSm)” and “root mean square roughness”. “(Rq)” is a value with a cutoff λc of 2.5 mm and an evaluation length of 12.5 mm in accordance with JIS B0601-2001. “Pencil hardness” is a pencil scratch value according to JIS K5400 test method 8.4.

  As described above, the optical sheet of the present invention has sufficient irregularities on the surface of the anti-sticking layer, and even when the thickness of the anti-sticking layer is reduced, sufficient irregularities can be ensured. While ensuring a high anti-sticking function for a sheet or the like, it is possible to prevent the surface of the other sheet or the like from being damaged. In addition, the backlight unit of the present invention can prevent the occurrence of luminance unevenness and interference fringes due to scratches on the optical sheet, the light guide plate, and the like, and can be easily handled during manufacture, transportation, storage, and the like.

It is a typical sectional view showing the optical sheet concerning one embodiment of the present invention. (A) is a typical perspective view which shows a general edge light type | mold backlight unit, (b) is typical sectional drawing which shows a general light-diffusion sheet.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

  1 includes a base material layer 2, an optical layer 3 laminated on one surface side of the base material layer 2, and an anti-sticking layer laminated on the other surface side of the base material layer 2. 4 is provided.

  Since the base material layer 2 needs to transmit light, it is made of transparent, particularly colorless and transparent glass or synthetic resin. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. . Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending performance is particularly preferable.

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

  The anti-sticking layer 4 has a fine uneven shape 7 on the entire surface. For this reason, when this optical sheet 1 is disposed so as to overlap with the surface of another optical sheet such as a prism sheet or a light guide plate, the convex portions of the fine concavo-convex shape 7 come into contact with the surface of the other optical sheet, etc. The entire back surface of the sheet does not come into contact with other optical sheets or the like. As a result, sticking between the optical sheet 1 and other optical sheets or the like is prevented, and uneven brightness on the screen of the liquid crystal display device is suppressed.

  In the optical sheet 1 of the present invention, the surface of the anti-sticking layer 4 is composed of a plurality of types of resins that are phase-separated, the domain phase is dispersed in the matrix phase, and the granular phase is dispersed in the domain phase. It has a sea-island structure. When the anti-sticking layer has such a double sea-island structure, fine irregularities on the anti-sticking layer surface are effectively formed. Thereby, high anti-sticking performance can be exhibited, and sticking with other sheets laminated on the anti-sticking layer side can be suitably prevented. At the same time, it is possible to prevent damage caused by unevenness on the surface of the anti-sticking layer. In addition, since the anti-sticking layer has such a double sea-island structure, it becomes easy to form unevenness enough to prevent sticking even if the anti-sticking layer is thin. Thereby, since the thickness of the anti-sticking layer can be reduced, it is possible to prevent a decrease in luminance due to the provision of the anti-sticking layer. Moreover, it can be set as the optical sheet which has a sticking prevention layer which has the desired suitable thickness and surface roughness by it.

  The reason why the surface of the anti-sticking layer has a double sea-island structure can effectively form fine irregularities, and even when the thickness of the anti-sticking layer is thin, it is not always clear why However, for example, it is conceivable that finer irregularities are formed by synergistically combining polymerization shrinkage and particle formation that occur in each of the three resin phases.

  The anti-sticking layer has a double sea island structure in which the domain phase is dispersed in the matrix phase and the granular phase is dispersed in the domain phase, for example, using an electron microscope. be able to.

  Although it does not specifically limit as resin which forms each phase in the said sticking prevention layer, For example, acrylic resin, urethane (meth) acrylate resin, epoxy (meth) acrylate resin, ester (meth) acrylate resin, olefin resin, polystyrene resin, Examples include styrene copolymers, norbornene resins, polycarbonate resins, polyether resins, polyethersulfone resins, polyester resins, polyurethane resins, polysiloxane resins, polysilane resins, polyamide resins, polyimide resins, melamine resins, and fluorine resins. Examples of the (meth) acrylic resin include a homopolymer or copolymer of a (meth) acrylic monomer, a copolymer of a (meth) acrylic monomer and another monomer having an ethylenically unsaturated double bond, and the like. Examples of the olefin resin include polyethylene, polypropylene, ethylene / propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, ethylene-vinyl alcohol copolymer, ethylene-vinyl chloride copolymer, and the like. Examples of the polyether resin include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, unsaturated polyester resin, and alkyd resin. The resin may be a copolymer having two or more structural units of these resins, or may be a copolymer composed of the structural units of these resins and other monomer units.

  Among these, the main component of the matrix phase is preferably a urethane (meth) acrylate resin, an epoxy (meth) acrylate resin, or an ester (meth) acrylate resin. By using an acrylic resin containing such a polar group as the main material in the matrix phase, the double sea-island structure is effectively expressed, and the unevenness of the sticking prevention layer surface is increased. As a result, the anti-sticking performance of the optical sheet is increased. Even when the anti-sticking layer is thin, sufficient unevenness is formed on the surface of the anti-sticking layer, so that the anti-sticking performance of the optical sheet is ensured. Among these, a urethane (meth) acrylate resin is particularly preferable in that a double sea-island structure is more effectively expressed and the resulting optical sheet has higher anti-sticking performance.

  As the main material of the domain phase, a (meth) acrylic resin is preferable. Moreover, as a main material of a granular phase, a (meth) acrylic resin is preferable. By using an acrylic resin as the main material of the domain phase and the granular phase, an optical sheet with high luminance can be obtained.

  In the anti-sticking layer, it is particularly preferable that the main material in the matrix phase is urethane (meth) acrylate resin, the main material in domain phase is (meth) acrylate, and the main material in granular phase is (meth) acrylic resin. By adopting such a combination as the resin for forming the anti-sticking layer, the above-mentioned double sea island structure is particularly effectively expressed. As a result, uneven formation on the surface of the anti-sticking layer is particularly promoted, and the anti-sticking performance of the optical sheet can be enhanced. Moreover, it can be set as an optical sheet with high brightness | luminance.

  It is particularly preferable that the protrusions are formed as scattered points on the surface of the anti-sticking layer due to the dispersed granular phase. In the optical sheet, such a convex portion is formed on the surface of the anti-sticking layer, so that high anti-sticking performance is exhibited, and sticking with other sheets laminated on the anti-sticking layer side is suitably prevented. be able to. Moreover, the said convex part is formed with resin, and its hardness is comparatively low. As a result, the optical sheet can prevent damage due to unevenness on the surface of the anti-sticking layer.

  The lower limit of the average thickness of the sticking prevention layer 4 is preferably 0.5 μm, more preferably 1 μm, and particularly preferably 1.5 μm. On the other hand, the upper limit of the average thickness of the anti-sticking layer 4 is preferably 4 μm, more preferably 3.5 μm, and particularly preferably 3 μm. When the average thickness of the anti-sticking layer 4 is smaller than the above lower limit, it is difficult to form a sufficiently uneven shape when forming the fine uneven shape 7 by applying and curing a resin and a monomer or an oligomer described later. Become. On the other hand, if the average thickness of the anti-sticking layer 4 exceeds the above upper limit, the amount of light absorbed by the anti-sticking layer 4 increases, and the light transmittance decreases.

  The lower limit of the arithmetic average roughness (Ra) of the anti-sticking layer 4 surface is preferably 0.03 μm, more preferably 0.05 μm, and particularly preferably 0.08 μm. On the other hand, the upper limit of the arithmetic average roughness (Ra) is preferably 0.3 μm, more preferably 0.25 μm, and particularly preferably 0.2 μm. If the arithmetic average roughness (Ra) of the surface of the anti-sticking layer 4 is smaller than the above lower limit, the fine concavo-convex shape 7 becomes small. Therefore, the portions other than the convex portions come into contact with the surface of other optical sheets and the like, and the anti-sticking function is provided. There is a risk that it will not be demonstrated. Conversely, when the arithmetic average roughness (Ra) of the surface of the anti-sticking layer 4 exceeds the above upper limit, the uneven shape becomes rough, and there is a possibility that the surface of other optical sheets or the like disposed on the back surface may be damaged.

  The lower limit of the average length (RSm) of the roughness curve element on the surface of the anti-sticking layer 4 is preferably 40 μm, more preferably 80 μm, and particularly preferably 120 μm. On the other hand, the upper limit of the average length (RSm) of the roughness curve element is preferably 400 μm, more preferably 280 μm, and particularly preferably 240 μm. When the average length (RSm) of the roughness curve element on the surface of the anti-sticking layer 4 takes a relatively small value within the above range, the fine uneven shape 7 is formed in an island shape and uniformly on the entire surface. Even when the arithmetic average roughness (Ra) is a relatively small value within the above range, it is possible to prevent the occurrence of interference fringes due to close contact (sticking) with the light guide plate surface or the like.

  In particular, when the arithmetic average roughness (Ra) is relatively small, the average length (RSm) of the roughness curve elements is in the above range, and the fine irregularities 7 are formed in an island shape and uniformly on the entire surface. Thus, even when the anti-sticking layer 4 is in contact with the apex of the belt-like prism portion on the surface of the prism sheet, it is possible to create a contact portion and a non-contact portion in the belt-like portion. Therefore, according to the optical sheet 1, it is possible to effectively exhibit a sticking prevention function with respect to the prism sheet surface (surface on the prism portion side).

  If the average length (RSm) of the roughness curved surface element is smaller than the lower limit, the surface of another optical sheet or the like that comes into contact may be damaged due to the size of each convex portion being reduced. Further, when the prism sheet surface (the surface on the prism portion side) is in contact with the anti-sticking layer 4, there is a possibility that a contact portion and a non-contact portion do not occur at the apex of the belt-like prism portion in contact with the anti-sticking layer 4. . Conversely, when the average length (RSm) of the roughness curved surface element exceeds the upper limit, a fine uneven shape is not sufficiently formed, and in contact with the surface of another optical sheet or the like on a surface other than the convex portion, Interference fringes may occur.

  The lower limit of the ten-point average roughness (Rz) of the anti-sticking layer 4 surface is preferably 0.2 μm, particularly preferably 0.3 μm, and further preferably 0.4 μm. On the other hand, the upper limit of the ten-point average roughness (Rz) is preferably 1.4 μm, particularly preferably 1 μm, and further preferably 0.8 μm. When the ten-point average roughness (Rz) of the surface of the anti-sticking layer 4 is smaller than the lower limit, in the fine irregularities 7 on the surface of the anti-sticking layer 4, the portion other than the convex portion comes into contact with the surface of another optical sheet or the like. This may cause sticking. On the contrary, if this ten-point average roughness (Rz) is larger than the above upper limit, the uneven shape becomes too rough, and there is a risk of scratching the surface of other optical sheets or the like laminated on the back side.

  The lower limit of the ratio (Rz / Ra) of the ten-point average roughness (Rz) to the arithmetic average roughness (Ra) of the anti-sticking layer 4 is preferably 3, more preferably 4, and even more preferably 5. On the other hand, the upper limit of this ratio is preferably 10, more preferably 9, and still more preferably 8. By setting the ratio (Rz / Ra) of the ten-point average roughness (Rz) to the arithmetic average roughness (Ra) of the anti-sticking layer 4 to a value as small as the above range, the optical sheet 1 has a relatively high height. A uniform uneven shape is provided uniformly. Therefore, the optical sheet 1 can prevent the other sheets from being damaged due to the force concentrated on the protruding portion among the protruding portions of the fine concavo-convex shape 7 of the anti-sticking layer 4. Further, it is possible to prevent the surface of another optical sheet or the like from being damaged due to the protruding convex portion dropping out. If the ratio (Rz / Ra) of the ten-point average roughness (Rz) to the arithmetic average roughness (Ra) of the anti-sticking layer 4 is smaller than the lower limit, it is difficult to sufficiently form the fine irregularities 7. Conversely, if this ratio (Rz / Ra) exceeds the above upper limit, the difference in height of the convex portion in the fine concavo-convex shape 7 becomes significant, and force concentrates on that portion, so that other optical sheets and the like There is a risk of scratching the surface.

  The lower limit of the root mean square roughness (Rq) of the anti-sticking layer 4 surface is preferably 0.04 μm, particularly preferably 0.07 μm, and further preferably 0.1 μm. On the other hand, the upper limit of the root mean square roughness (Rq) is preferably 0.4 μm, particularly preferably 0.3, and more preferably 0.2. According to the optical sheet 1, when the root mean square roughness (Rq) of the surface of the anti-sticking layer 4 has a value smaller than the above range, the inclination of the fine concavo-convex shape 7 is gently formed and laminated. Scratches of other optical sheets can be prevented. If the root mean square roughness (Rq) of the anti-sticking layer 4 surface is smaller than the lower limit, the anti-sticking function may be deteriorated because the fine uneven shape 7 is not sufficiently formed. Conversely, when the root mean square roughness (Rq) exceeds the above upper limit, a steeply inclined portion is generated in the fine concavo-convex shape 7, which may cause damage to the surface of the light guide plate or the like in the vicinity of this steep inclination.

  As a minimum of average height (h) of each convex part on the sticking prevention layer 4 surface, 0.5 micrometer is preferred, 0.7 micrometer is especially preferred, and 1 micrometer is still more preferred. Moreover, as an upper limit of this average height (h), 3 micrometers is preferable, 2.5 micrometers is more preferable, and 2 micrometers is still more preferable. According to the optical sheet, by reducing the average height (h) of each convex portion on the surface of the anti-sticking layer 4 as described above, it is possible to reduce scratches on the surface of other optical sheets. In addition, the depth of the scratch when the scratch occurs can be reduced. When the average height (h) of each convex portion is smaller than the lower limit, a sufficient anti-sticking function cannot be exhibited. On the other hand, when the average height (h) exceeds the upper limit, the surface of another optical sheet may be damaged, and the generated scratch may be deep. The average height (h) is calculated by the average height of the top 16 convex portions having the highest height among the plurality of convex portions observed by observing a predetermined area with a laser microscope.

The lower limit of the average protrusion diameter (r ₁ ) of each convex portion on the surface of the sticking prevention layer 4 is preferably 2 μm, particularly preferably 2.5 μm, and particularly preferably 3 μm. On the other hand, the upper limit of the average protrusion diameter (r ₁ ) is preferably 5 μm, particularly preferably 4.5 μm, and still more preferably 4 μm. According to the optical sheet, as described above, the average protrusion diameter (r ₁ ) of each convex portion on the surface of the sticking prevention layer 4 is relatively small as described above, thereby reducing scratches on the surfaces of other optical sheets and the like. In addition, the width of the generated scratch can be narrowed. If the average protrusion diameter (r ₁ ) of each convex portion is smaller than the lower limit, a sufficient anti-sticking function cannot be exhibited. On the other hand, when the average protrusion diameter (r ₁ ) exceeds the above upper limit, the surface of the other optical sheet is damaged, and the scratch width of the generated scratch becomes wide. The average protrusion diameter (r ₁ ) is calculated by the average protrusion diameter of the top 16 convex portions having the highest height among the plurality of convex portions observed by observing a predetermined area with a laser microscope. The protrusion diameter (r ₁ ) is a diameter of a cross section cut at a height (0.9 h) of 90% of the height (h) of the convex portion, and the average of each protrusion diameter is the ferret diameter ( (Interval when the projected image is sandwiched between parallel lines in a certain direction).

The lower limit of the average diameter (r ₂ ) of each convex portion on the surface of the sticking prevention layer 4 is preferably 40 μm, particularly preferably 60 μm, and even more preferably 70 μm. On the other hand, the upper limit of the average diameter (r ₂ ) is preferably 200 μm, particularly preferably 150 μm, and particularly preferably 120 μm. According to the optical sheet, when the average diameter (r ₂ ) of each convex portion on the surface of the sticking prevention layer 4 is relatively increased as described above, the surface of the other optical sheet is damaged. , Can reduce the depth of scratches. When the average diameter (r ₂ ) of each convex portion is smaller than the lower limit, a sufficient anti-sticking function cannot be exhibited. On the other hand, when the average diameter (r ₂ ) exceeds the upper limit, damage to other optical sheet surfaces is likely to occur, and the depth of the damage becomes deep. The average diameter (r ₂ ) is calculated from the average diameter of the top 16 convex portions having the highest height among the plurality of convex portions observed by observing the predetermined area with a laser microscope. Each diameter means a diameter of a cross section cut at a height (0.05 h) of 5% of the height (h) of the convex portion, and the average of the diameters is the ferret diameter (parallel lines in a certain direction). (Interval when the projected image is sandwiched between).

The lower limit of the height ratio (h / r ₂ ) of each convex portion on the surface of the sticking prevention layer 4 is preferably 1/400, particularly preferably 1/200, still more preferably 1/150, and even more preferably 1/120. Particularly preferred. Moreover, as an upper limit of this height ratio (h / r ₂ ), 1/10 is preferable, 1/30 is particularly preferable, 1/60 is further more preferable, and 1/80 is still more preferable. According to the optical sheet, by reducing the height ratio (h / r ₂ ) between the convex portions on the surface of the sticking prevention layer 4 as described above, the occurrence of scratches on the surfaces of other optical sheets is suppressed. At the same time, it is possible to reduce the size of the scratch itself when it is damaged. If the height ratio (h / r ₂ ) is smaller than the lower limit, it may not be possible to exhibit a sufficient anti-sticking function. On the other hand, when the height ratio (h / r ₂ ) exceeds the above upper limit, the surface of another optical sheet is likely to be damaged, and the size of the scratch itself is increased.

Further, the convex portions on the surface of the anti-sticking layer 4 have a relatively small average height (h), a relatively small average protrusion diameter (r ₁ ), a relatively large average diameter (r ₂ ), and a small height. By providing the ratio (h / r ₂ ), the frictional force on the surface in contact with this layer can be improved. According to the optical sheet 1 provided with such an anti-sticking layer 4, the friction between the anti-sticking layer 4 and other optical sheets or prism sheets in contact with this layer is increased, thereby preventing slipping. By suppressing the minute displacement that occurs between the sheets, it is possible to suppress damage to the surface of other optical sheets or prism sheets.

The lower limit of the density of the convex portion of the anti-sticking layer 4 surface, preferably 40 / mm ^2, particularly preferably 60 / mm ^2, more particularly preferably from 80 / mm ^2. Moreover, as an upper limit of the density of this convex part, 500 piece / mm < ² > is preferable, 400 piece / mm < ² > is especially preferable, 300 piece / mm < ² > is still more especially preferable. If the density of the convex portions on the surface of the anti-sticking layer 4 is smaller than the lower limit, it may not be possible to exhibit a sufficient anti-sticking function. Conversely, if the density of the convex portions is higher than the upper limit, the surface of other optical sheets or the like is likely to be damaged. The density of the convex portions is calculated by measuring the number of convex portions in the field of view observed by magnifying 1000 times with a laser microscope and using the visual field area.

The average height (h), the average protrusion diameter (r ₁ ), the average diameter (r ₂ ), and the convex portion when calculating the existence density are protrusions having a height of 0.2 μm or more on the surface of the sticking prevention layer 4. Say.

  As a lower limit of the pencil hardness on the surface of the sticking prevention layer 4, when the base material layer 2 is glass, H is preferable and 2H is particularly preferable. On the other hand, the upper limit of the pencil hardness is preferably 5H, particularly preferably 4H. When the base material layer 2 is a synthetic resin such as polyethylene terephthalate, B is preferable as the lower limit of the pencil hardness on the surface of the sticking prevention layer 4 and HB is particularly preferable. On the other hand, the upper limit of the pencil hardness in this case is preferably 3H, particularly preferably 2H. According to the optical sheet 1, the surface of the anti-sticking layer 4 has the above shape, and the pencil hardness is in the above range. Sticking can be prevented. If the pencil hardness on the surface of the sticking prevention layer 4 is smaller than the lower limit, the unevenness is so fine that the tip or the like becomes brittle, and as a result, the surface of the light guide plate or the like may be damaged. Conversely, if the pencil hardness exceeds the above upper limit, the surface of the light guide plate or the like may be damaged by the fine uneven shape itself having a high hardness.

<Curable composition for forming anti-sticking layer>
Each of the anti-sticking layers 4 can be formed by applying and curing a curable composition containing at least one of three components selected from the group consisting of polymers, oligomers and monomers. . According to the curable composition, when the curable composition is applied and cured, a matrix phase, a domain phase, and a granular phase are formed from the three components included, and the anti-sticking layer having the double sea-island structure described above. Is formed. The formation of such a double sea island structure may occur due to the difference in physical properties of each component when the curable composition is applied to the base material layer, and is formed during the subsequent curing. This may occur due to a difference in physical properties of the obtained resin.

  Examples of the polymer include (meth) acrylic polymer, polyolefin, polyether resin, polyethersulfone, polystyrene, styrene copolymer, norbornene resin, polycarbonate, polyester, polyurethane, polysiloxane, polysilane, polyamide, polyimide, and melamine resin. Or a fluororesin etc. are mentioned. Examples of the (meth) acrylic polymer include a homopolymer or copolymer of a (meth) acrylic monomer, a copolymer of a (meth) acrylic monomer and another monomer having an ethylenically unsaturated double bond, and the like. . Examples of the polyolefin include polyethylene, polypropylene, ethylene / propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, ethylene-vinyl alcohol copolymer, ethylene-vinyl chloride copolymer, and the like. Examples of the polyether resin include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of the polyester include polyethylene terephthalate, polybutylene terephthalate, unsaturated polyester, and alkyd resin. The polymer may be a copolymer having two or more structural units of these polymers, or may be a copolymer comprising the structural units of these polymers and other monomer units. Among these, from the viewpoint of promoting the formation of irregularities and improving the anti-sticking performance of the optical sheet, a homopolymer or copolymer of (meth) acrylic monomer is preferable, and a copolymer of (meth) acrylic monomer is further included. preferable. As the polymer, one type or a plurality of types can be used.

  The lower limit of the weight average molecular weight of the polymer is preferably 2,000, and more preferably 5,000. On the other hand, the upper limit of the weight average molecular weight of the polymer is preferably 100,000, more preferably 50,000. When the weight average molecular weight of the polymer is smaller than the above lower limit, the unevenness of the anti-sticking layer formed becomes small, and the anti-sticking performance may be lowered. On the contrary, if the weight average molecular weight of the polymer exceeds the above upper limit, the unevenness of the anti-sticking layer becomes high, and there is a possibility that the optical sheet or the like in contact with the anti-sticking layer may be damaged.

  Examples of the oligomer include those having a low molecular weight of the polymer. As the oligomer, those having 3 to 10 repeating units and a weight average molecular weight of 8,000 or less are preferable. The oligomer may be a copolymer having two or more of these oligomer structural units, or may be a copolymer composed of these oligomer structural units and other monomer units. As the oligomer, one type or a plurality of types can be used.

  As said monomer, as long as it is a compound which has a polymerizable functional group, it can be used. Examples of the polymerizable functional group include an unsaturated double bond and an epoxy group, and an unsaturated double bond is preferable, and a (meth) acryloyl group is particularly preferable in terms of easy polymerization. Moreover, as a monomer, a polyfunctional monomer is preferable at the point which the unevenness | corrugation of the sticking prevention layer surface becomes large. Examples of the polyfunctional monomer include (meth) acrylate esters such as polyhydric alcohols, and specifically include 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and ethylene glycol. Bifunctional (meth) acrylates such as di (meth) acrylate; Trifunctional (meth) acrylates such as trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate and glycerol tri (meth) acrylate; pentaerythritol tetra ( Tetrafunctional (meth) acrylates such as (meth) acrylate and ditrimethylolpropane tetra (meth) acrylate; pentafunctional (meth) acrylates such as dipentaerythritol penta (meth) acrylate; dipentaerythritol hexa Examples thereof include hexafunctional (meth) acrylates such as (meth) acrylate and sorbitol hexa (meth) acrylate. The monomer includes functional groups other than polymerizable functional groups such as urethane groups, isocyanurate groups, urea groups, carbonate groups, amide groups, ester groups, carboxyl groups, ether groups, imino groups, amino groups, hydroxyl groups, and the like. You may have in the molecule. The monomer may have atoms such as halogen such as fluorine and chlorine, silicon, sulfur and phosphorus.

  The three components contained in the curable composition preferably have functional groups that react with each other. When each component has such a functional group, the strength of the resulting anti-sticking layer is increased, and durability can be improved. Examples of such combinations of reactive functional groups include ethylenically unsaturated groups and ethylenically unsaturated groups, functional groups having active hydrogen (hydroxyl group, amino group, thiol group, carboxyl group, etc.), epoxy groups, active groups Examples include functional groups having hydrogen and isocyanate groups, functional groups having active hydrogen and functional groups having active hydrogen, silanol groups and silanol groups, silanol groups and epoxy groups, active methylene groups and acryloyl groups, oxazoline groups and carboxyl groups. It is done. Among them, the combination of the ethylenically unsaturated group and the ethylenically unsaturated group is preferable as the functional group that reacts with each other because the generated bond is strong and the formation of irregularities on the surface of the anti-sticking layer is promoted. Moreover, it is preferable that all three components contained in the curable composition have an ethylenically unsaturated group. This further improves the strength of the anti-sticking layer and further promotes the formation of irregularities on the surface of the anti-sticking layer. Although it does not specifically limit as an ethylenically unsaturated group, A (meth) acryloyl group is especially preferable at the point which is easy to superpose | polymerize.

  From the viewpoint of promoting the formation of the double sea-island structure and increasing the irregularities on the surface of the anti-sticking layer, the curable composition contains at least one polymer component and at least one monomer or oligomer component. Is preferred. By adopting such a combination as each component of the curable composition, a granular phase is effectively formed from the polymer component to be blended, and convex portions are scattered on the surface of the anti-sticking layer by this granular phase. Therefore, the optical sheet can exhibit high anti-sticking performance. Moreover, since the convex part of the said sticking prevention layer surface is formed with resin, the damage with respect to the other optical sheet etc. resulting from an uneven | corrugated shape can be prevented.

  Of the three components, one component is a polymer, the other one component is a monomer or oligomer, and the remaining one component is particularly preferably a monomer or oligomer having a polar group. Since the curable composition includes a monomer or oligomer having a polar group as one component, phase separation between the matrix phase and the domain phase is promoted, and unevenness is further effectively formed. This further improves the anti-sticking performance. When the curable composition has such components, the dispersed phase formed by curing the monomer or oligomer is dispersed in the matrix formed by curing the monomer or oligomer having a polar group. In this dispersed layer, a double sea island structure is formed in which a granular phase formed by curing of the polymer is present. Thereby, the unevenness | corrugation formed becomes large and the sticking prevention performance of the optical sheet obtained becomes high.

  The polar group is not particularly limited as long as it is an organic group that is polarized by atoms having high electronegativity such as oxygen, nitrogen, sulfur, and halogen. For example, a urethane group, an isocyanurate group, a urea group, a carbonate group, Examples thereof include an amide group, an ester group, a carboxyl group, an acid anhydride group, an ether group, an epoxy group, an imino group, and an amino group. Among these, a urethane group or an isocyanurate group is preferable in that the double sea island structure is easily formed, the unevenness on the surface of the anti-sticking layer is increased, and the anti-sticking performance of the optical sheet is enhanced. Specific examples of the monomer or oligomer having a polar group include urethane (meth) acrylate, epoxy (meth) acrylate, and polyester (meth) acrylate. Among them, urethane (meth) acrylate is particularly preferable because the double sea island structure is easily formed, the unevenness of the surface of the anti-sticking layer is increased, and the anti-sticking performance of the optical sheet is enhanced.

  Urethane (meth) acrylate is a monomer or oligomer having functional groups of both urethane groups (—N—CO—O—) and (meth) acryloyl groups in one molecule. The urethane (meth) acrylate can be obtained, for example, by reacting a polyfunctional isocyanate, a (meth) acryloyl group, a compound having an active hydrogen such as a hydroxyl group or an amino group, and a polyol as necessary. As polyfunctional isocyanates, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate , Cyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isopropylidenebis (4-cyclohexylisocyanate), hexamethylene diisocyanate and the like. In addition, modified products such as burettes of these polyfunctional isocyanates and polyfunctional isocyanate trimers containing isocyanurate groups can also be used.

  Examples of the compound having a (meth) acryloyl group and active hydrogen include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate; ethylene glycol mono (meth) acrylate, propylene glycol mono (meth) acrylate, diethylene glycol mono ( Polyalkylene glycol mono (meth) acrylates such as (meth) acrylate, dipropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, and polypropylene glycol mono (meth) acrylate; caprolactone-modified hydroxy (meth) acrylate and the like . Examples of the polyol used as needed include ethylene glycol, propylene glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,8-octanediol, 1,9-nonanediol, , 10-decanediol, polyalkylene glycol such as 1,4-cyclohexanediol, and the like.

  Specific examples of urethane (meth) acrylates include, for example, a reaction product of diphenylmethane diisocyanate and ethylene glycol mono (meth) acrylate, a reaction product of isophorone diisocyanate and 2-hydroxyethyl (meth) acrylate, and an isocyanurate of hexamethylene diisocyanate. Reaction product of modified product with polyethylene glycol mono (meth) acrylate, reaction product of isocyanurate modified product of hexamethylene diisocyanate and polycaprolactone modified hydroxyethyl (meth) acrylate, isocyanuric acid ethylene oxide modified di (meth) acrylate, isophorone Reaction materials such as diisocyanate or a multimer thereof and pentaerythritol polyfunctional (meth) acrylate are exemplified.

  When the formation of the double sea-island structure is promoted, the three-component solubility parameter (SP value) contained in the curable composition, the glass transition temperature (Tg) of the resin, the surface tension, and the molecular weight are constant. And the like.

  From the viewpoint of promoting the formation of the double sea-island structure, it is preferable that the difference in solubility parameter (SP value) between the three components contained in the curable composition is 0.3 or more. More preferably, it is 4 or more. The SP value can be obtained by, for example, the Fedors method. The method is described in POLYMERENG INEERING AND SCIENCE, FEBRUARY, 1974, vol. 14, Issue 2, p. 147-154.

  From the viewpoint of promoting the formation of the double sea-island structure, when the polymer component is contained in the curable composition, the glass transition temperature (Tg) of the polymer component is preferably 0 ° C. or higher. When the Tg of the polymer component is 0 ° C. or higher, the double sea-island structure is effectively formed from the curable composition, so that the anti-sticking performance of the obtained optical sheet is improved. Moreover, when two or more polymer components are contained among the three components of the curable composition, the difference in glass transition temperature (Tg) between these polymer components is preferably 10 ° C. or more. More preferably, all of them are 20 ° C. or higher.

  As a blending ratio of the three components contained in the curable composition, the mass ratio of the granular phase forming component based on the total amount of the granular phase forming component, the domain phase forming component, and the matrix phase forming component is 0.1% by mass. It is preferable that the mass ratio of the domain phase forming component is 10% by mass or more and 50% by mass or less, and the mass ratio of the matrix phase forming component is 40% by mass or more and 89.9% by mass or less. Moreover, the mass ratio of the granular phase forming component is 0.1 mass% or more and 5 mass% or less, the mass ratio of the domain phase forming component is 12 mass% or more and 50 mass% or less, and the mass ratio of the matrix phase forming component is 49.9. More preferably, it is more than mass% and less than 87.9 mass%. The mass ratio of the granular phase forming component is 0.1% by mass to 3% by mass, the mass ratio of the domain phase forming component is 20% by mass to 50% by mass, and the mass ratio of the matrix phase forming component is 49.9% by mass. The content is more preferably 79.9% by mass or less. The optical sheet obtained by forming the unevenness of the anti-sticking layer surface more effectively when the blending ratio of the three components contained in the curable composition forming each phase of the anti-sticking layer is within the above range. This further improves the anti-sticking performance. Moreover, when one component is a monomer or oligomer among the above three components and the other one component is a monomer or oligomer having a polar group, the blending ratio (mass ratio) of these components is the monomer or oligomer. The mass ratio of the monomer or oligomer component having a polar group with respect to the mass of the component is preferably 1 or more, more preferably 1.2 or more, and particularly preferably 1.3 or more. Of the curable composition, the two components, which are monomers or oligomers, have such a compounding ratio, so that phase separation occurs more effectively and unevenness on the surface of the anti-sticking layer increases. This further improves the anti-sticking performance.

  The curable composition may further contain a solvent from the viewpoint of facilitating coating. Examples of the solvent include aromatic hydrocarbons such as toluene and xylene; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, isopropanol, and butanol; diethyl ether, isopropyl ether, tetrahydrofuran , Ethers such as dioxane, anisole, phenetole, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether; esters such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol diacetate; dimethylformamide, diethylformamide, Amides such as N-methylpyrrolidone; methyl cellosol , Ethyl cellosolve, cellosolve butyl cellosolve and the like; dichloromethane, halogenated hydrocarbons such as chloroform and the like. Among these, aromatic hydrocarbons, ketones, esters, alcohols, and ethers are preferable from the viewpoint of solubility, and ketones are particularly preferable. One kind or a plurality of kinds of these solvents can be used.

  When the component has an unsaturated double bond, the curable composition may contain a polymerization initiator for curing. As such a polymerization initiator, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-hydroxy-cyclohexyl-phenyl ketone, 2-methyl-1- (4-methylthiophenyl) -2- Morpholinopropan-1-one, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, etc. Photopolymerization initiators of azo groups such as azobisisobutyronitrile and peroxide type thermal polymerization initiators such as benzoyl peroxide. The curable composition may contain a curing agent, a catalyst, a photosensitizer, and the like.

  The optical layer 3 has a binder 5 and a light diffusing agent 6 dispersed in the binder 5. By dispersing the light diffusing agent 6 in the optical layer 3 in this way, it is possible to uniformly diffuse the light beam that passes through the optical layer 3 from the back side to the front side. Moreover, the fine unevenness | corrugation is formed in the surface of the optical layer 3 substantially uniformly by the light-diffusion agent 6, and each recessed part and convex part of this fine unevenness | corrugation are formed in the lens form. The optical sheet 1 exhibits an excellent light diffusing function due to the lens action of the fine unevenness, and the refracting function that refracts the transmitted light toward the normal direction due to the light diffusing function and the transmitted light as the normal line. It also has a light condensing function that condenses macroscopically in the direction.

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

  The binder 5 is formed by curing (crosslinking or the like) a polymer composition containing a base polymer. By this binder 5, the light diffusing agent 6 is disposed and fixed at substantially equal density over the entire surface of the base material layer 2. In addition, the polymer composition for forming the binder 5 includes other fine inorganic fillers, curing agents, plasticizers, dispersants, various leveling agents, antistatic agents, ultraviolet absorbers, antioxidants, viscosity modifiers, and the like. A quality agent, a lubricant, a light stabilizer and the like may be appropriately blended.

  Next, a method for manufacturing the optical sheet 1 will be described. As a method for producing the optical sheet 1, generally, (a) a step of producing a coating solution for an optical layer by mixing a light diffusing agent 6 with a polymer composition constituting the binder 5, and (b) ) A step of laminating the optical layer 3 by coating the surface of the substrate layer 2 with the coating solution for the optical layer, (c) a step of producing the curable composition for forming the anti-sticking layer, d) The anti-sticking layer forming composition is applied to the back surface of the base material layer 2 to form the anti-sticking layer 4 and cured to form a fine uneven shape on the surface.

  Since the optical sheet 1 has the above-described fine uneven shape on the entire surface of the anti-sticking layer, the gently and evenly formed convex portion is disposed on the other surface side with a light guide plate or the like. Sticking can be prevented, and scratches on the surface of the light guide plate or the like can be prevented. Furthermore, even if the optical sheets 1 are wound or overlapped, the optical sheets 1 themselves are prevented from being damaged or blocked even if the optical sheets 1 are rubbed with each other.

  Accordingly, the backlight for the liquid crystal display device includes the lamp 21, the light guide plate 22, the light diffusion sheet 25, and the prism sheet 24 as shown in FIG. 2A, and disperses the light emitted from the lamp 21 and guides it to the surface side. In the unit 20, when the optical sheet 1 is used as the light diffusion sheet 24, scratches on the surface of the prism sheet 24 are reduced due to good scratch resistance of the optical sheet 1, and as a result, luminance unevenness occurs due to the scratches. Is reduced and quality is increased.

  The optical sheet of the present invention is not limited to the above embodiment. For example, a prism sheet (refractive optical sheet), a microlens sheet, a polarizing sheet, a reflective polarizing sheet, a reflective sheet, a retardation sheet, and a field expansion sheet. It is also possible to provide the anti-sticking layer on one surface of the optical sheet of another form such as the above. By the anti-sticking layer laminated on one surface (the surface opposite to the optical layer), it is possible to impart scratch resistance and anti-sticking properties to various forms of optical sheets.

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

(Synthesis Example 1 [Synthesis of unsaturated double bond-containing acrylic copolymer (A-1)])
100 parts by mass of propylene glycol monomethyl ether was charged into a 2 L reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a cooler, and a dropping funnel, followed by nitrogen substitution, and then heated to 110 ° C. Next, 50 parts by mass of isobornyl methacrylate, 1 part by mass of methyl methacrylate and 3 parts by mass of methacrylic acid, 0.5 parts by mass of t-butylperoxy-2-ethylhexanoate as a polymerization initiator, and A mixture of 20 parts by mass of propylene glycol monomethyl ether was simultaneously added dropwise over 3 hours. After completion of the dropwise addition, the reaction was further carried out at 110 ° C. for 1 hour. Thereafter, a mixture consisting of 0.1 parts by mass of t-butylperoxy-2-ethylhexanoate and 5 parts by mass of propylene glycol monomethyl ether was added dropwise and reacted at 110 ° C. for 30 minutes.

  To this reaction mixture was added a mixture of 0.5 parts by mass of tetrabutylammonium bromide, 0.03 parts by mass of hydroquinone and 2 parts by mass of propylene glycol monomethyl ether, and then 4-hydroxybutyl acrylate glycidyl ether while bubbling air. A mixture consisting of 7 parts by mass and 2 parts by mass of propylene glycol monomethyl ether was added dropwise over 1 hour, followed by further reaction for 5 hours. In this way, an unsaturated double bond-containing acrylic copolymer (A-1) was obtained. The number average molecular weight of the unsaturated double bond-containing acrylic copolymer (A-1) was 6000, the weight average molecular weight was 20000, the SP value was 9.6, and the Tg was 95 ° C.

(Synthesis Example 2 [Synthesis of acrylic copolymer (A-2)])
100 parts by mass of propylene glycol monomethyl ether was charged into a 2 L reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a cooler, and a dropping funnel, followed by nitrogen substitution, and then heated to 110 ° C. Next, a mixture comprising 50 parts by mass of isobornyl methacrylate, 1 part by mass of methyl methacrylate and 3 parts by mass of methacrylic acid, 3 parts by mass of t-butylperoxy-2-ethylhexanoate as a polymerization initiator and propylene glycol A mixture of 20 parts by mass of monomethyl ether was simultaneously added dropwise over 3 hours. After completion of the dropwise addition, the reaction was further carried out at 110 ° C. for 30 minutes. In this way, an acrylic copolymer (A-2) was obtained. The acrylic copolymer (A-2) had a number average molecular weight of 3000, a weight average molecular weight of 5,500, an SP value of 10.1, and a Tg of 117 ° C.

(Synthesis Example 3 [Synthesis of unsaturated double bond-containing acrylic copolymer (A-3)])
100 parts by mass of propylene glycol monomethyl ether was charged into a 2 L reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a cooler, and a dropping funnel, followed by nitrogen substitution, and then heated to 110 ° C. Next, a mixture composed of 25 parts by mass of isobornyl methacrylate, 1 part by mass of methyl methacrylate, 25 parts by mass of ethylhexyl acrylate and 3 parts by mass of methacrylic acid, and t-butylperoxy-2-ethylhexanoate which is a polymerization initiator A mixture consisting of 0.5 parts by mass and 20 parts by mass of propylene glycol monomethyl ether was simultaneously added dropwise over 3 hours. After completion of the dropwise addition, the reaction was further carried out at 110 ° C. for 1 hour. Thereafter, a mixture consisting of 0.1 parts by mass of t-butylperoxy-2-ethylhexanoate and 5 parts by mass of propylene glycol monomethyl ether was added dropwise and reacted at 110 ° C. for 30 minutes.

  To this reaction mixture was added a mixture of 0.5 parts by mass of tetrabutylammonium bromide, 0.03 parts by mass of hydroquinone and 2 parts by mass of propylene glycol monomethyl ether, and then 5 parts by mass of glycidyl methacrylate and propylene while bubbling air. A mixture consisting of 2 parts by mass of glycol monomethyl ether was added dropwise over 1 hour, followed by further reaction for 5 hours. In this way, an unsaturated double bond-containing acrylic copolymer (A-3) was obtained. The number average molecular weight of the unsaturated double bond-containing acrylic copolymer (A-3) was 4,300, the weight average molecular weight was 9000, the SP value was 10.1, and the Tg was 6 ° C.

(Synthesis Example 4 [Synthesis of unsaturated double bond-containing acrylic copolymer (A-4)])
100 parts by mass of propylene glycol monomethyl ether was charged into a 2 L reaction vessel equipped with a stirrer, a thermometer, a nitrogen inlet tube, a cooler, and a dropping funnel, followed by nitrogen substitution, and then heated to 110 ° C. Next, a mixture consisting of 50 parts by mass of isobornyl methacrylate, 1 part by mass of methyl methacrylate, and 3 parts by mass of methacrylic acid, and 0.5 parts by mass of t-butylperoxy-2-ethylhexanoate as a polymerization initiator And the mixture of 20 mass parts of propylene glycol monomethyl ether was dripped simultaneously over 3 hours, respectively. After completion of the dropwise addition, the reaction was further carried out at 110 ° C. for 1 hour. Thereafter, a mixture consisting of 0.1 parts by mass of t-butylperoxy-2-ethylhexanoate and 5 parts by mass of propylene glycol monomethyl ether was added dropwise and reacted at 110 ° C. for 30 minutes.

  To this reaction mixture, a mixture consisting of 0.5 parts by mass of tetrabutylammonium bromide, 0.03 parts by mass of hydroquinone and 2 parts by mass of propylene glycol monomethyl ether was added, and 5 parts by mass of glycidyl methacrylate and propylene glycol monomethyl were bubbled while bubbling air. A mixture consisting of 2 parts by mass of ether was added dropwise over 1 hour, followed by further reaction for 5 hours. In this way, an unsaturated double bond-containing acrylic copolymer (A-4) was obtained. The number average molecular weight of the unsaturated double bond-containing acrylic copolymer (A-4) was 1700, the weight average molecular weight was 2500, the SP value was 10.4, and Tg was 121 ° C.

(Synthesis Example 5 [Synthesis of Urethane Acrylate (C-1)])
In a 2 L reaction vessel equipped with a stirrer, a thermometer and a cooler, an isocyanurate modified form of hexamethylene diisocyanate (“Takenate D-170N” manufactured by Takeda Pharmaceutical Company Limited: isocyanate group (—NCO) content: 20.9 mass) %) 50 parts by mass, polyethylene glycol monoacrylate (“Blemmer AE-150” manufactured by NOF Corporation: hydroxyl value 264 mg KOH / g, ethylene oxide equivalent repeating unit number: 3.4) 42 parts by mass, dibutyltin laurate 0.02 Part by mass and 0.02 part by mass of hydroquinone monomethyl ether were charged and reacted at 70 ° C. for 5 hours. In this way, urethane acrylate (C-1) was obtained.

(Synthesis Example 6 [Synthesis of Urethane Acrylate (C-2)])
In a 2 L reaction vessel equipped with a stirrer, a thermometer and a condenser, 50 parts by mass of toluene, 50 parts by mass of isocyanurate-modified type of hexamethylene diisocyanate (Takenate D-170N manufactured by Takeda Pharmaceutical Co., Ltd.), polycaprolactone-modified hydroxy 63 parts by mass of ethyl acrylate (“Placcel FA1” manufactured by Daicel Chemical Industries, Ltd.), 0.02 parts by mass of dibutyltin laurate and 0.02 parts by mass of hydroquinone monomethyl ether were charged and reacted at 70 ° C. for 5 hours. Thereafter, 63 parts by mass of toluene was added to obtain urethane acrylate (C-2) having a solid content of 50% by mass. The number of repeating caprolactone units per acrylate monomer residue in urethane acrylate (C-2) is 1.

(Synthesis Example 7 [Synthesis of Urethane Acrylate (C-3)])
To a 2 L reaction vessel equipped with a stirrer, a thermometer and a cooler, add 50 parts by mass of toluene and 4.2 parts by mass of stearyl alcohol (“NAA-46” manufactured by NOF Corporation, hydroxyl value: 207), up to 40 ° C. The temperature was raised to completely dissolve the stearyl alcohol. Next, 50 parts by mass of an isocyanurate modified type of hexamethylene diisocyanate (Takeda Pharmaceutical Co., Ltd. “Takenate D-170N”) was added and reacted at 70 ° C. for 30 minutes. Further, caprolactone-modified hydroxyethyl acrylate (Daicel Chemical Industries, Ltd. “Placcel FA5” 179 parts by mass, dibutyltin laurate 0.02 parts by mass and hydroquinone monomethyl ether 0.02 parts by mass were added and reacted at 70 ° C. for 3 hours. Thereafter, 118 parts by mass of toluene was added to obtain a urethane acrylate (C-3) having a solid content of 50% by mass, and the number of repeating caprolactone units per acrylate monomer residue in the urethane acrylate (C-3) was 3. is there.

[Example 1]
100 parts by mass of a binder resin blend (“Toronbo Co., Ltd.” “Byron”) having polyester polyol as a base polymer, colloidal silica having an average particle diameter of 20 nm (“PL-1” from Fuso Chemical Industry Co., Ltd.) 50 In a polymer composition containing 5 parts by mass, 5 parts by mass of a curing agent (“Coronate HX” from Nippon Polyurethane Co., Ltd.) and 5 parts by mass of a light stabilizer (“PUVA-1033” from Otsuka Chemical Co., Ltd.) 50 parts by mass of acrylic resin beads having a particle size of 15 μm (“MBX-15” from Sekisui Plastics Co., Ltd.) are mixed to prepare a coating liquid, and this coating liquid is 100 μm thick by roll coating. An optical layer was formed by applying 15 g / m ² (in terms of solid content) to the surface of a transparent polyester base layer (“A-4300” manufactured by Toyobo Co., Ltd.) and curing it.

Further, 0.6 part by mass of the unsaturated double bond-containing acrylic copolymer (A-1) of Synthesis Example 1 and 41.9 of pentaerythritol triacrylate (B-1) which is a polyfunctional unsaturated double bond-containing monomer. A solution containing 5 parts by mass of the urethane acrylate (C-1) of Synthesis Example 5 was 57.7 parts by mass, and 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropane-1-, which is a photoinitiator. Methyl ethyl ketone (MEK) and methyl isobutyl ketone (MEK) were added dropwise to a solution containing 7 parts by weight of ON ("IRGACURE907" manufactured by Ciba-Geigy) and 3 parts by weight of 1-hydroxy-cyclohexyl-phenylketone ("IRGACURE184" manufactured by Ciba-Geigy) MIBK) mixed solvent (mixing ratio: MEK / MIBK = 1: 1 mass ratio) has a non-volatile component ratio of 5 As it will become mass%, to prepare a coating solution containing the matrix-forming component, the domain phase forming component, the three components of the particulate phase forming components. This coating solution was applied to the back surface of the substrate layer by a roll coating method at 2 g / m ² (in terms of solid content) and cured by UV irradiation to form an anti-sticking layer having an average thickness of 2.8 μm. . This obtained the optical sheet of Example 1.

[Examples 2 to 8]
Prevention of sticking in the same manner as in Example 1 except that the acrylic copolymer, the domain phase forming component, and the matrix phase forming component, which are granular phase forming components as described in Table 1, were used in respective amounts. Optical sheets according to the respective examples were obtained in the same manner as in Example 1 except that the layer forming coating solution was prepared and used. In Example 7, as a matrix phase forming component, urethane acrylate (C-2) and urethane acrylate (C-3) are mixed at a mixing ratio (C-2 / C-3) = 3/1 (mass ratio). Used together. In Example 8, methyl methacrylate (C-4) was used as a matrix phase forming component.

[Comparative Example 1]
In Example 1, the preparation of the anti-sticking layer forming coating solution was carried out in the same manner as in Example 1, except that the urethane acrylate (C-1), which is a matrix phase forming component, was not blended. Such an optical sheet was obtained.

[Comparative Example 2]
100 parts by mass of a binder resin blend (“Toronbo Co., Ltd.” “Byron”) having polyester polyol as a base polymer, colloidal silica having an average particle diameter of 20 nm (“PL-1” from Fuso Chemical Industry Co., Ltd.) 50 In a polymer composition containing 5 parts by mass, 5 parts by mass of a curing agent (“Coronate HX” from Nippon Polyurethane Co., Ltd.) and 5 parts by mass of a light stabilizer (“PUVA-1033” from Otsuka Chemical Co., Ltd.) A coating solution is prepared by mixing 10 parts by mass of acrylic resin beads having a particle size of 5 μm (“MBX-5” from Sekisui Plastics Co., Ltd.). Comparative Example in which the average thickness of the anti-sticking layer is 3.0 μm in the same manner as in Example 1 except that the anti-sticking layer is formed by applying ² g / m ² (in solid content) to the back surface of the film and curing it. 2 An optical sheet was obtained.

(Characteristic evaluation)
Using the optical sheets of Examples 1 to 8 and Comparative Examples 1 and 2 above, the resin phase separation structure on the surface of the anti-sticking layer was observed, the arithmetic average roughness (Ra) of the surface properties, and the average length of the roughness curve elements (RSm), ten-point average roughness (Rz), root-mean-square roughness (Rq), and pencil hardness were measured, and the front luminance when these optical sheets were incorporated into a backlight unit, and the optical sheet The effects on other optical sheets (adhesion, generation of interference fringes, generation of scratches) were evaluated. The results are shown in Table 1 below.

The resin phase separation structure on the surface of the anti-sticking layer was observed with an electron microscope and evaluated from the following viewpoints.
A: Formation of a double sea island structure (matrix phase-domain phase-granular phase) was observed.
B: Formation of a double sea island structure (matrix phase-domain phase-granular phase) was not observed.

  The “arithmetic average roughness (Ra)” and “ten-point average roughness (Rz) of surface properties are in accordance with JIS B0601-1994,“ average length of roughness curve element (RSm) ”and“ root mean square roughness. “(Rq)” was measured using a stylus type surface roughness measuring instrument “Surfcom 470A” manufactured by Tokyo Seimitsu Co., Ltd. according to JIS B0601-2001 with a cutoff λc of 2.5 mm and an evaluation length of 12.5 mm. . “Pencil hardness” was measured in accordance with JIS K5400 test method 8.4.

  In addition, the front brightness when the optical sheet is incorporated into the backlight unit and the quality of the liquid crystal display device screen exerted by the optical sheet are actually incorporated into the edge light type backlight unit (as an optical sheet). The prism sheet H505 manufactured by Eiwa Co., Ltd. laminated on the surface of the light guide plate and the optical sheet [light diffusion sheet] of Example or Comparative Example laminated on this surface were used.), Front luminance, prism sheet and The adhesiveness and the occurrence of interference fringes were confirmed.

The adhesiveness with the prism sheet was evaluated from the following viewpoints after being left for 48 hours at a temperature of 40 ° C. and a humidity of 90%.
◎: Not in close contact ○: In close contact in some cases Δ: Adhered to a certain degree ×: Adhered strongly

The occurrence of interference fringes was visually evaluated from the following viewpoints.
◎: Interference fringes are not generated at all ○: Interference fringes can be confirmed slightly by gazing △: Interference fringes can be confirmed without gazing
X: Interference fringes can be clearly confirmed.

The occurrence of scratches is caused by scratches on the prism portion after rubbing the optical sheet anti-sticking layer and the surface (prism portion side surface) of the prism sheet H505 manufactured by Eiwa Co., Ltd. 100 times. The presence or absence was observed with a microscope and evaluated from the following viewpoints.
A: No scratches are observed. O: Slight scratches are observed. Δ: Scratches are observed. X: Scratches are clearly observed.

  As shown in Table 1 above, the optical sheets of Examples 1 to 8 have high front luminance when incorporated in a backlight unit, and suppress the adhesion with other optical sheets and the occurrence of interference fringes. In addition, it can be seen that scratches on the surface of other optical sheets are reduced.

[Examples 9 to 16]
In Example 1, the unsaturated double bond-containing acrylic copolymer (A-1), pentaerythritol triacrylate (B-1), and urethane acrylate (C-1), which are components of the coating solution for the anti-sticking layer, are used. The blending amount is as shown in Table 2 below, except that the non-volatile component ratio of the anti-sticking layer coating solution is 60% by mass, and the average thickness of the anti-sticking layer to be formed is 2 μm. Obtained optical sheets of Examples 9 to 16 in the same manner as Example 1.

[Evaluation of characteristics]
With respect to all of the obtained optical sheets of Examples 9 to 16, formation of a double sea-island structure on the surface of the anti-sticking layer was observed by observation with the electron microscope. In addition, similarly to the above, the arithmetic average roughness (Ra) of the surface property, the average length (RSm) of the roughness curve element, the ten-point average roughness (Rz), the root mean square roughness (Rq), and the pencil hardness In addition, the front brightness when these optical sheets are incorporated in the backlight unit, and the influence of other optical sheets on the optical sheet (adhesion, occurrence of interference fringes, generation of scratches), Evaluation was performed according to the above evaluation criteria. In addition, the average height (h), average protrusion diameter (r ₁ ), average diameter (r ₂ ), and existence density of each convex portion on the surface of the anti-sticking layer were measured. A laser microscope “VK-8500” (manufactured by Keyence Corporation) was used for measurement of each convex portion. The results are shown in Table 2 below.

  From the results of Table 2, the surface property of the anti-sticking layer can be adjusted and laminated while maintaining high front luminance and scratch resistance by changing the blending ratio of the components forming the optical sheet. It was shown that the adhesion prevention property can be further improved by designing according to other optical sheets.

  As described above, the optical sheet of the present invention is useful as a component of a backlight unit of a liquid crystal display device, and can be suitably used particularly for a transmissive liquid crystal display device.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Base material layer 3 Optical layer 4 Sticking prevention layer 5 Binder 6 Light diffusing agent 7 Fine uneven | corrugated shape

Claims (3)

A transparent substrate layer, an optical layer laminated on one surface side of the substrate layer, and an anti-sticking layer laminated on the other surface side of the substrate layer. An optical sheet having a fine uneven shape,
Said anti-sticking layer, the phase-separated a plurality of kinds of resins are, domain phase dispersed in the matrix phase, particulate phase have a double island structure dispersed in a domain phase,
On the surface of the anti-sticking layer, convex portions are formed as scattered points due to the dispersed granular phase,
The average thickness of the anti-sticking layer is 0.5 μm or more and 4 μm or less,
The arithmetic average roughness (Ra) of the surface of the anti-sticking layer is 0.03 μm or more and 0.3 μm or less, the average length (RSm) of the roughness curve element is 80 μm or more and 400 μm or less, and the ten-point average roughness (Rz) is 0. An optical sheet having a thickness of 4 μm or more and 1.4 μm or less .  The main material in the matrix phase of the anti-sticking layer is a urethane (meth) acrylate resin, the main material of the domain phase is a (meth) acrylic resin, and the main material of the granular phase is a (meth) acrylic resin. Optical sheet. In a backlight unit for a liquid crystal display device that guides light emitted from a lamp to the surface side by dispersing it,
A backlight unit for a liquid crystal display device, comprising the optical sheet according to claim 1 .

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