JP5402463B2 - Optical sheet and surface light source device - Google Patents

Description

  The present invention relates to an optical sheet having a prism portion that changes the traveling direction of light and a surface light source device including the optical sheet.

  In liquid crystal display devices and the like, surface light source devices for illuminating liquid crystal display devices and the like from the back are also made thinner and lighter in response to demands for low power consumption, thinning and lightening, Low power consumption is achieved with a light source that effectively uses light from the light source. As a surface light source device used for such a liquid crystal display device or the like, an edge light type and a direct type surface light source device are known. These surface light source devices usually receive light from one end surface (edge light type) or back surface (directly under type) of a plate-shaped light guide made of transparent acrylic resin or the like, and one surface of the light guide The light is emitted from the light exit surface to the back surface of the liquid crystal panel or the like. In such a surface light source device, the light utilization efficiency is improved by providing a reflection plate or a reflection film that reflects light on the surface opposite to the light exit surface of the light guide. Further, a sheet-like or layer-like light diffusing element is disposed between the liquid crystal panel and the image of the light source is hidden or made inconspicuous.

  In the surface light source device described above, an optical sheet having a prism portion formed by arranging a plurality of unit prisms is disposed on the light exit surface of the light guide. The optical sheet has a substantially triangular cross section or a substantially semicircular cross section, and a large number of unit prisms each having a ridge line (also referred to as a ridge line part) at the top thereof are arranged in a direction perpendicular to the ridge line part. Those having a prism portion have been proposed.

  Particularly in recent years, there has been a strong demand for thinning and weight reduction of liquid crystal display devices and the like, for example, a light diffusion element (light diffusion sheet or light diffusion layer) between an optical sheet and a liquid crystal panel is often omitted. However, if the light diffusing element is omitted, the prism portion of the optical sheet is in direct contact with the liquid crystal panel surface. It is known that when the ridge line portion of the prism portion and the liquid crystal panel surface are in direct contact (optical contact), optical unevenness as if the liquid is soaked, so-called wet out (also referred to as “wet out”) is generated. It has been.

  In order to prevent the occurrence of such a wet-out, the technology for changing the ridge line height of the unit prism gently in the ridge line direction (Patent Documents 1 and 2), and the ridge line height of the unit prism in the direction orthogonal to the ridge line direction. A technique (Patent Document 3) has been proposed.

JP-A-8-304608 JP-T-2002-504698 Japanese National Patent Publication No. 11-501149

  However, even when the height of the ridgeline was changed, wetout still occurred. For example, an optical film for a liquid crystal display device needs to be subjected to an acceleration test defined in the JIS standard. In particular, wetout may occur in an acceleration test under a high temperature environment or a high temperature / high humidity environment. Such a problem is a technical matter that needs to be addressed, and its solution has been required.

  In addition, a light diffusing element between the optical sheet and the liquid crystal panel is omitted, and a predetermined gap is provided between the prism portion of the optical sheet and the liquid crystal panel surface so that the prism portion of the optical sheet and the liquid crystal panel surface are not in direct contact with each other. It is practiced to install them apart so as to have a clearance. However, even in this case, when the acceleration test as described above is performed, wet-out may occur.

  The present invention has been made to solve the above-mentioned problems, and its object is to reduce the wet-out when an optical sheet on which a prism portion composed of a plurality of unit prisms is formed is overlapped with another member. An object of the present invention is to provide an optical sheet that can be used. Another object of the present invention is to provide a surface light source device having such an optical sheet.

  In the process of earnestly researching the above problems, the present inventor (i) occurrence of wet-out in a high-temperature environment or high-temperature / high-humidity environment during an acceleration test when the ridge height is changed, and (Ii) In the case where a gap is provided between the prism portion and the liquid crystal panel surface, the occurrence of wet-out in a high-temperature environment or a high-temperature / high-humidity environment during an acceleration test causes thermal expansion of the optical sheet. It was thought that this was caused by the fact that the ridge line at the tip of the unit prism was in strong contact with the liquid crystal panel surface. As a result of detailed examination of the resin characteristics of the prism portion in the temperature environment at the time of the acceleration test, it was found that the wet-out can be reduced as much as possible by configuring the prism part to have a certain characteristic. Was completed.

  That is, the optical sheet according to the present invention includes a sheet-like main body portion and a prism portion in which a plurality of unit prisms are arranged side by side on one surface of the main body portion and each linearly extends in a direction intersecting the arrangement direction. The prism portion is made of a non-halogen resin in which a thermomechanical analysis curve measured in a temperature range equal to or lower than the glass transition temperature Tg is a monotonically increasing curve in a narrow sense.

  According to the present invention, the prism portion is composed of the non-halogen resin in which the thermomechanical analysis curve measured in the temperature range equal to or lower than the glass transition temperature Tg is a narrow monotonically increasing curve. Therefore, irregular and non-uniform distortion is hardly generated, and the optical sheet is hardly deformed. When such an optical sheet and a flat surface such as a liquid crystal panel are arranged to face each other and the acceleration test is performed, the optical fiber prism tip and the flat surface do not cause strong optical contact, so that the wetout can be reduced as much as possible. . The “narrowly increasing monotone increasing curve” means that when the thermal expansion coefficient is regarded as a function of temperature, the thermal expansion coefficient mathematically changes as a monotonically increasing function with respect to a temperature change. That is, when a curve representing the temperature change of the coefficient of thermal expansion is drawn with the coefficient of thermal expansion as the vertical axis and the temperature as the horizontal axis, it stays in the curve in the temperature region below the glass transition temperature of the resin constituting the prism portion. It means a curve in which the thermomechanical analysis curve increases monotonously in a narrow sense without any part, decreasing part, peak (maximum value), or valley (minimum value).

  In the optical sheet according to the present invention, the non-halogen resin constituting the prism part includes an acrylate having a fluorene skeleton.

  According to the present invention, since the non-halogen resin constituting the prism portion is an acrylate having a fluorene skeleton, the prism portion can be formed without lowering the refractive index, meeting the demand for dehalogenation in the organic compound industry. There is an advantage. Furthermore, since this resin is difficult to cure and shrink due to the presence of a bulky fluorene skeleton, there is an advantage that a prism portion with less distortion can be formed by utilizing the characteristics. Further, the bulkiness and cure shrinkage (fine) can be adjusted by the structural formula of the terminal of the non-halogen resin.

  In the optical sheet according to the present invention, the thermomechanical analysis curve measured for the main body portion is a monotonically increasing curve in a narrow sense in a temperature range equal to or lower than the glass transition temperature Tg of the prism portion.

  According to the present invention, the thermomechanical analysis curve measured for the sheet-like main body portion also becomes a monotonically increasing curve in a narrow sense in the temperature range below the glass transition temperature Tg of the prism portion, so that distortion deformation hardly occurs in the entire optical sheet. . When the optical sheet and a flat surface such as a liquid crystal panel are placed facing each other with the prism portion facing the liquid crystal panel and subjected to an acceleration test, the prism tip of the optical sheet and the flat surface have strong optical adhesion. Since it does not occur, the wet-out can be reduced as much as possible.

  In the optical sheet according to the present invention, a light transmission diffusion layer is provided between the main body portion and the prism portion.

  According to this invention, since the light transmission diffusion layer is provided between the main body portion and the prism portion, the image of the light source can be hidden or the interference fringes can be made inconspicuous within a range that does not hinder the reduction in thickness and weight. Can do.

  The optical sheet which concerns on this invention WHEREIN: The distance from the said main-body part is discontinuous about the ridgeline of the said unit prism.

  According to the present invention, a conventional means for preventing the occurrence of wet-out, for example, a technique for gradually changing the ridge line height of the unit prism in the ridge line direction, or a direction perpendicular to the ridge line direction of the unit prism. It can be applied to the case where the distance (ridge line height) from the main part of the ridge line of the unit prism is discontinuous, as in the technology for changing to the so-called wet. Out can be further reduced as much as possible.

  In order to solve the above problems, a surface light source device according to the present invention includes the optical sheet according to the present invention and a light source for making light incident on the optical sheet.

  According to this invention, the prism portion of the optical sheet is composed of a non-halogen resin in which the thermomechanical analysis curve measured in the temperature range below the glass transition temperature Tg becomes a monotonically increasing curve in a narrow sense. Therefore, irregular distortion is hardly generated in the prism portion, and the optical sheet is hardly deformed. When the surface light source device equipped with such an optical sheet and a liquid crystal panel or the like are placed facing each other and subjected to an acceleration test, the prism tip of the optical sheet and the flat surface of the liquid crystal panel do not cause strong optical contact, so wet out Can be reduced as much as possible.

  In the surface light source device according to the present invention, the optical sheet is arranged such that a surface on the prism portion side is a light emitting surface.

  According to the present invention, since the surface on the prism portion side is arranged as the light emitting surface, it is possible to suppress the optical tip of the prism of the optical sheet from being in strong optical contact with a flat surface such as a liquid crystal panel arranged opposite to the light emitting surface. it can. In addition, even when the surface on the prism portion side is not a light emitting surface, it is preferable because the prism tip of the optical sheet can be prevented from being strongly optically adhered to the flat surface of the light guide plate.

  In the surface light source device according to the present invention, the optical sheet includes a first optical sheet that receives light from the light source, and a second optical sheet that is disposed so as to overlap the first optical sheet. The sheet and the second optical sheet are arranged such that the ridge lines of the unit prisms each have intersect in plan view.

  According to the present invention, when an acceleration test is performed with a surface light source device configured by stacking two optical sheets and a liquid crystal panel or the like facing each other, the prism tip of the optical sheet and the flat surface of the liquid crystal panel or the like are Since strong optical adhesion does not occur, wet-out can be reduced as much as possible.

  Since the optical sheet according to the present invention is composed of a non-halogen resin in which the thermomechanical analysis curve measured in the temperature range below the glass transition temperature Tg included in the temperature range in the accelerated test becomes a monotonically increasing curve in a narrow sense. In the temperature range, irregular distortion is unlikely to occur in the prism portion, and deformation of the optical sheet is unlikely to occur. When such an optical sheet according to the present invention is placed opposite to a flat surface such as a liquid crystal panel and an acceleration test is performed, the optical tip prism and the flat surface do not cause strong optical contact, thereby reducing wetout as much as possible. It is possible to achieve an effect that could not be achieved in the past.

  In the surface light source device according to the present invention, the prism portion of the optical sheet, which is a constituent member, is composed of a non-halogen resin in which the thermomechanical analysis curve measured in the temperature range below the glass transition temperature Tg becomes a monotonically increasing curve in a narrow sense. Therefore, irregular distortion hardly occurs in the prism portion in the temperature range, and deformation of the optical sheet hardly occurs. When the surface light source device according to the present invention is placed facing a liquid crystal panel or the like and subjected to an acceleration test, the optical tip prism tip and the flat surface of the liquid crystal panel or the like do not cause strong optical contact, so that the wetout is minimized. There is an effect that could not be achieved in the past.

It is a typical block diagram which shows an example of the optical sheet which concerns on this invention. It is a typical schematic diagram of the thermomechanical analysis curve (TMA curve) of the prism part which comprises an optical sheet. It is a schematic diagram which shows an example of the discontinuous height form of the ridgeline of a unit prism. It is a schematic diagram which shows the other example of the discontinuous height form of the ridgeline of a unit prism. It is a typical lineblock diagram showing an example of an optical sheet which has a light transmission diffusion layer. It is a block diagram which shows the example of the surface light source device which concerns on this invention. It is a block diagram which shows the other example of the surface light source device which concerns on this invention. It is a block diagram which shows the further another example of the surface light source device which concerns on this invention. It is a block diagram which shows the further another example of the surface light source device which concerns on this invention. It is a block diagram which shows an example of the display apparatus provided with the surface light source device. 6 is a graph showing thermomechanical analysis curves obtained from optical sheets of Examples 1 and 2 and Comparative Example 1. It is a typical form figure of the wetout produced when the prism part which comprises an optical sheet, and the plane part of a display member are opposingly arranged.

  Hereinafter, an optical sheet and a surface light source device according to the present invention will be described with reference to the drawings. The present invention can be variously modified as long as it has the technical features, and is not limited to the following description and drawings.

[Optical sheet]
An optical sheet 1 according to the present invention is an optical sheet used as a member constituting a surface light source device. As shown in FIG. 1, a sheet-like main body portion 11 and one surface S1 of the main body portion 11 are provided. And a prism portion 12 in which a plurality (units) of unit prisms 13 are arranged side by side. The prism portion 12 is configured in such a manner that each unit prism 13 extends linearly in a direction X (in other words, a direction in which the ridge line extends) intersecting the arrangement direction Y (in other words, a direction in which the ridge line extends). Yes. The unit prism 13 has a triangular cross section or a substantially triangular cross section, and has a ridge line 14 at the apex thereof, and a large number of unit prisms 13 are arranged in a direction Y intersecting the ridge line 14. Hereinafter, each configuration will be described in detail.

(Main body)
As shown in FIG. 1, the main body portion 11 acts as a base material for the prism portion 12 and acts so as to transmit most of the light from the light source to the prism portion 12 side. The main body 11 may be a light-transmitting base material, and in particular, a base material having a transmittance of 85% or more is preferably used. In addition, the transmittance here is a value measured by a light transmittance meter (model: HM-150) manufactured by Murakami Color Research Laboratory Co., Ltd. Although the thickness of the main-body part 11 is not specifically limited, Usually, it exists in the range of 50-500 micrometers.

  Examples of the constituent material of the main body 11 include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, acrylic resins such as polymethyl methacrylate, thermoplastic resins such as polycarbonate resin, polystyrene resin, and polymethylpentene resin. Can be mentioned.

  The main body 11 is preferably manufactured by single-layer extrusion or by co-extrusion together with the light transmission diffusion layer 17 when a light transmission diffusion layer 17 described later is provided as necessary. The main body 11 may be produced by other methods. The body part 11 produced by extrusion or the body part 11 produced by other methods is usually subjected to a stretching treatment. This stretching process may be a biaxial stretching process or a uniaxial stretching process, but usually a biaxial stretching process is preferably applied.

(Prism part)
As shown in FIG. 1, the prism portion 12 is a prism group in which unit prisms 13 are arranged side by side on one surface S <b> 1 of the main body portion 11. Each of the unit prisms 12 extends linearly in a direction X (a direction in which the ridgeline extends, that is, a direction in which the unit prism 12 extends linearly) intersecting the arrangement direction Y. In other words, a large number of unit prisms 13 are arranged in a direction Y (a direction perpendicular to the ridge line) intersecting the ridge line 14 so that the ridge lines are parallel. Each unit prism 13 has a triangular cross section or a substantially triangular cross section, and has a ridge line 14 at the top. A valley 15 is formed between adjacent unit prisms 13. The period of the unit prism 13 is normally selected in the range of 12.5 μm to 200 μm in order to satisfy the performance required for the surface light source device for the translucent display.

  The prism portion 12 is made of a resin whose thermomechanical analysis curve measured in a temperature range equal to or lower than the glass transition temperature Tg of the resin constituting the prism portion 12 becomes a monotonically increasing curve in a narrow sense.

  Here, the “glass transition temperature Tg” means that the constituent resin of the prism portion 12 is measured by a calorie change by DSC (differential scanning calorimetry) or tan δ = G ″ (loss elastic modulus) / G ′ (storage by a rheometer). It is a value obtained by measurement of elastic modulus. In the present invention, non-halogen resins such as acrylate having a fluorene skeleton are used, and the glass transition temperature of these resins is usually in the range of about 50 ° C to 300 ° C. “Measured in a temperature range below the glass transition temperature Tg” means a temperature range below the glass transition temperature Tg and actually measured. In the present invention, the maximum measurement is in the range of 0 ° C to 120 ° C. “Thermomechanical analysis curve” (also referred to as TMA (Thermo Mechanical Analyzer) curve) refers to the temperature dependence of dimensional change due to thermal expansion or contraction of resin obtained by measurement with a thermomechanical analyzer (TMA). As shown in FIG. 2, the horizontal axis represents temperature and the vertical axis represents thermal expansion coefficient.

  The “narrowly increasing monotone increasing curve” means that when the thermal expansion coefficient is regarded as a function of temperature, the thermal expansion coefficient mathematically changes as a monotonically increasing function with respect to a temperature change. That is, mathematically, the derivative F ′ (T) of the thermal expansion change F (T) with respect to the temperature T is positive (F ′ (T)> 0) in the entire region. That is, as shown in FIG. 2, when a curve representing the temperature change of the coefficient of thermal expansion is drawn with the coefficient of thermal expansion as the vertical axis and the temperature as the horizontal axis, in the temperature region below the glass transition temperature of the resin constituting the prism portion, It means a curve in which the thermomechanical analysis curve increases monotonously in a narrow sense without any part of the curve, a decreasing part, a peak (maximum value), or a valley (minimum value). It should be noted that even if there is a part that does not increase monotonically for a moment, such as an inflection point, it is included in the monotonic increase in the narrow sense in this application, but the stopping region is not over a moment but over a certain temperature range. In some cases, and when the thermal expansion coefficient includes a region where the coefficient of thermal expansion is a decreasing function, it is not a monotonous increase in a narrow sense.

  More specifically, as shown in FIG. 2, in the entire region (temperature range) in question, it is a curve a that constantly increases as a function of temperature and does not decrease or stop. . On the other hand, the curve b has a temperature range (60 ° C. to 80 ° C. in the example of FIG. 2) in which the coefficient of thermal expansion decreases as the temperature rises, or a maximum value or a minimum value (also called an extreme value). .) Is different from curve b. The narrowly defined monotone increasing curve a in the present invention is further different from the broadly defined monotonic increasing curve c having an inflection point retention region (in the example of FIG. 2, around 70 ° C.).

  The rate of change of the coefficient of thermal expansion with respect to the temperature rise may be constant at a temperature equal to or lower than the glass transition temperature Tg, but may be slightly increased or decreased. Specifically, the degree of increase ΔE2 / ΔT of the coefficient of thermal expansion per unit temperature in the characteristic temperature range (for example, 60 ° C. to 80 ° C.) that changes most greatly in the measured temperature range (for example, 0 ° C. to 100 ° C.). (Arbitrary temperature) is compared with the degree of increase ΔE1 / ΔT (arbitrary temperature) in the other monotonically increasing temperature range (for example, 20 ° C. to 40 ° C. or 80 ° C. to 100 ° C.), (ΔE2 / ΔT) / (ΔE1 / ΔT) = ΔE2 / ΔE1 = 1-3. Preferably it is the range of 1-2. ΔE2 / ΔE1 = 1 when monotonically increasing at a uniform change rate in any temperature range. The “arbitrary temperature” means a temperature within a certain range within the temperature range below the glass transition temperature Tg, and may be, for example, 1 ° C., 5 ° C., 10 ° C., or 20 ° C. .

  In the range of ΔE2 / ΔE1 = 1 to 3, the deformation of the prism portion 12 is small, and irregular distortion is unlikely to occur in the prism portion 12. As a result, the optical sheet 1 is hardly deformed, and when such an optical sheet 1 is placed facing a flat surface such as a liquid crystal panel and an acceleration test is performed, the optical tip 1 has a strong optical contact between the prism tip and the flat surface. Since it does not occur, the wet-out can be reduced as much as possible.

  On the other hand, if the value of ΔE2 / ΔE1 exceeds 3, the degree of expansion of the prism part 12 per unit temperature differs depending on the temperature, and if a temperature distribution occurs in the prism part, the degree of dimensional change in the prism part also increases. Unevenly distributed. Further, the deformation of the prism portion 12 is increased, and as a result, irregular distortion occurs in the prism portion 12 and the optical sheet 1 is likely to be deformed. When such an optical sheet 1 is placed opposite to a flat surface such as a liquid crystal panel and an acceleration test is performed, the prism tip of the optical sheet 1 and the flat surface partially cause strong optical adhesion, and wetout is likely to occur.

The constituent resin of the prism portion 12 is a non-halogen resin that exhibits the narrow monotonically increasing curve described above. As such a non-halogen resin, various resins can be used in combination, but it is preferable to include an acrylate resin having a fluorene skeleton. The non-halogen resin containing an acrylate resin having this fluorene skeleton (9H-fluorene (C ₁₃ H ₁₀ ) skeleton) does not have a non-strictly monotonically increasing portion such as an inflection point and is dehalogenated in the organic compound industry. There is an advantage that the prism portion 12 can be formed without lowering the refractive index. Furthermore, since such an acrylate resin is difficult to cure and shrink due to the presence of a bulky fluorene skeleton, there is an advantage that the prism portion 12 with less distortion can be formed by utilizing the characteristics.

  An acrylate resin having a fluorene skeleton can be used alone, but usually, in order to appropriately adjust monotonous increase characteristics or other physical properties, it is not a single resin, for example, an acrylate having no fluorene skeleton. It is preferable to mix and use the resin in an appropriate blending ratio.

  It is essential for the acrylate resin having a fluorene skeleton to exhibit the narrow monotonically increasing curve described above. Moreover, even if it is an acrylate resin which does not have a fluorene skeleton, it is essential to show the above-mentioned monotonically increasing curve. That is, the present invention can be configured with various blending compositions as long as the above-described condition is that it is a non-halogen resin exhibiting a monotonically increasing curve. Among such constituent materials, acrylate resins having no fluorene skeleton that are used alone or appropriately mixed and used in combination with the acrylate resin having the fluorene skeleton include, for example, poly (meth) methyl acrylate, poly (meth) (Meth) acrylic acid ester homopolymers such as butyl acrylate, or (meth) acrylic acid ester copolymers such as methyl (meth) acrylate-butyl (meth) acrylate copolymer (here And “(meth) acrylic acid” means acrylic acid or methacrylic acid). Also, (meth) acrylate oligomers such as polyfunctional urethane (meth) acrylates and (meth) acrylates such as polyester (meth) acrylates, unsaturated polyester oligomers, epoxy, which are cross-linked and cured by ionizing radiation such as ultraviolet rays or electron beams Oligomers or prepolymers such as resin oligomers, monofunctional monomers such as methyl (meth) acrylate and ethyl (meth) acrylate, hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa ( One or two or more compounds selected from (meth) acrylate polyfunctional monomers such as (meth) acrylate can also be mentioned.

  In addition, (meth) acrylate compounds such as phenoxyethyl (meth) acrylate, (meth) acryl morpholine, isobornyl (meth) acrylate, benzyl (meth) acrylate, bisphenol A epoxy (meth) acrylate, and sulfur-containing (meth) acrylate are used. You can also.

  In addition, when using an ultraviolet-ray or visible light etc. as ionizing radiation, a photoinitiator is added. As the photoinitiator, known photoinitiators such as benzophenone, benzoin, thioxanthone, and phosphine oxide are used.

  Among these, an ionizing radiation curable resin composition composed of an epoxy (meth) acrylate oligomer, a urethane (meth) acrylate oligomer, the monofunctional monomer, the polyfunctional monomer, the photoinitiator, and the like is preferably used. The blending ratio of the constituent materials of the ionizing radiation curable resin composition is not particularly limited, but preferably, polyfunctional epoxy (meth) acrylate oligomer: 5 to 50 parts by weight, polyfunctional urethane (meth) acrylate oligomer: 5 to 50 Parts by weight, monofunctional monomer: 1-60 parts by weight, polyfunctional monomer: 5-30 parts by weight, photoinitiator: 0.01-10 parts by weight. The number of functional groups per molecule of the polyfunctional monomer or polyfunctional oligomer is about 2 to 8.

  In addition, you may mix | blend another arbitrary component as a resin composition in the range which does not change the summary of this invention. Moreover, what is generally used as an initiator for optical sheets can also be used as a photoinitiator (photopolymerization initiator). In addition to the above components, the resin composition may contain silicone, antioxidant, polymerization inhibitor, mold release agent, antistatic agent, ultraviolet absorber, light stabilizer, antifoaming agent, solvent, as necessary. Non-reactive acrylic resins, non-reactive urethane resins, non-reactive polyester resins, pigments, dyes, light diffusing agents, and the like can be used in combination.

  Although the refractive index of the prism part 12 is not specifically limited, Usually, the range of about 1.550-1.620 is preferable. The resin composition is adjusted to have such a refractive index.

  The prism portion 12 uses the above-described non-halogen resin composition, for example, (1) a known hot press method (Japanese Patent Laid-Open No. 56-157310), (2) a roll on an ultraviolet curable thermoplastic resin film. A method of embossing the shape of the unit prism 13 with an embossing plate and then curing the film by irradiating with ultraviolet rays (Japanese Patent Laid-Open No. 61-156273), (3) A rotating roll engraved with the shape of the unit prism 13 After applying the active energy ray-curable resin liquid on the intaglio and filling the recess, the active liquid rays such as ultraviolet rays or electron beams are irradiated through the resin liquid while the film-like main body 11 is coated on the roll intaglio. A method of curing, and then releasing them from the roll intaglio to form the shape of the unit prism 13 of the roll intaglio on the film-like main body 11 (Japanese Patent Laid-Open No. Hei 3- No. 23,883, U.S. Pat. No. 4,576,850, etc.) and the like.

  As for the main body part 11, similarly to the prism part 12, the measured thermomechanical analysis curve is preferably a monotonically increasing curve in a narrow sense in a temperature range equal to or lower than the glass transition temperature Tg of the prism part 12. If the TMA curve of the main body part 11 is a monotonically increasing curve in a temperature range equal to or lower than the glass transition temperature Tg of the prism part 12, the entire optical sheet including the main body part 11 and the prism part 12 is unlikely to be deformed. When an acceleration test is performed with the optical sheet 1 and a flat surface such as a liquid crystal panel facing each other, the optical tip 1 and the flat surface do not cause strong optical contact, thereby reducing wetout as much as possible. be able to. The temperature range here is desirably the same as the temperature range of the prism portion 12 described above, and is preferably a monotonically increasing curve in the narrow sense similar to the prism portion 12 in that temperature range.

(Structure form of prism part)
From the viewpoint of further suppressing the wet-out, it is preferable that the unit prism 13 constituting the prism portion 12 has a discontinuous distance of the ridge line 14 from the main body portion 11. As such a form, for example, the form described in Japanese Patent Application No. 2009-44048 (unpublished at the time of filing this application) already filed by the present applicant or the forms described in Patent Documents 1 to 3 can be arbitrarily applied. .

  FIG. 3 is an example of the optical sheet 1 in which the ridge line height H of each unit prism 13 (height from the surface S <b> 1 of the main body 11) varies along the longitudinal direction X of each unit prism 13. For example, the ridge line 14 that changes in the range of the maximum height H to the minimum height H ′ in the longitudinal direction X of the unit prism 13 may be a continuous gentle curved unevenness or a polygonal unevenness. May be. In addition, it is preferable that the change between the ridgeline heights H and H ′ is, for example, 1 μm or more and 10 μm or less.

  4 shows that the ridge line height H (height from the surface S1 of the main body 11) of each unit prism 13 changes along the direction Y (arrangement method) intersecting the longitudinal direction X of each unit prism 13. This is an example of the optical sheet 1. FIG. 4A shows an example in which unit prisms 14 having a ridge line height H and unit prisms 14 'having a ridge line height H' are alternately arranged. FIG. 4B shows an example in which unit prisms 14 having a ridge line height H and unit prisms 14 ′ having a ridge line height H ′ are arranged in an arbitrary order. This is an example in which an arrangement pattern in which three unit prisms having a ridge line height H ′ are arranged is repeated. In FIG. 4C, a unit prism 14 having a high ridgeline height H, a unit prism 14 ′ having a lower ridgeline height H, and a unit prism 14 ″ having a lower ridgeline height H ″ coexist. It is an example. 4A to 4C, the differences between the ridge line heights H, H ′, and H ″ are not particularly limited, and may be, for example, about 0.4 μm to 10 μm. The heights H, H ′, H ″ from the (ridge lines 14, 14 ′, 14 ″) to the surface S1 of the main body 11 are in the range of about 20 to 100 μm, and the height in the longitudinal direction of the unit prism is It may change as shown in FIG.

  As described above, conventional means for preventing the occurrence of wet-out, for example, the technique of gently changing the ridge line height H of the unit prism 13 in the ridge line direction X, and the ridge line height H of the unit prism 13 in the ridge line direction. Like the technique of changing in the orthogonal direction Y, so to speak, it can be preferably applied even when the distance (ridge line height H) of the ridge line 14 of the unit prism 13 from the main body 12 is discontinuous, and the acceleration test is performed. It is possible to further reduce the wet-out that has occurred in the case of performing.

(Light transmission diffusion layer)
The optical sheet 1 can be given a function of transmitting and diffusing light. As the provision of the light transmission diffusion function, a light transmission diffusion layer can be provided on at least one surface (S1 or S2) of the main body 11 or a so-called mat treatment can be performed. The light transmission diffusion layer only needs to have a function of transmitting and diffusing light. Examples thereof include a general light transmission diffusion layer in which light diffusing fine particles are dispersed in a light transmitting resin. Such a light transmission diffusion layer may be provided on the other surface S2 of the main body portion 11, or between the one surface S1 of the main body portion 11 and the prism portion 12 (for example, the light transmission diffusion layer 17 of FIG. 5). Position), or may be provided at both of them.

  As the translucent resin material constituting the light transmissive diffusion layer, a resin material similar to that of the main body 11 described above, for example, a transparent material such as acrylic, polystyrene, polyester, or vinyl polymer is used. Further, the light diffusing fine particles are uniformly dispersed in the light transmission diffusion layer. As the light diffusing fine particles, light diffusing fine particles generally used for optical sheets are used. For example, polymethyl methacrylate (acrylic) beads, polybutyl methacrylate beads, polycarbonate beads, polyurethane beads , Calcium carbonate beads, silica beads and the like are used. The light transmission diffusion layer can be produced by various methods. For example, a paint in which light diffusing fine particles are dispersed in a translucent binder resin may be formed by spray coating, roll coating, or the like, or a resin material in which light diffusing fine particles are dispersed is prepared. The resin material may be coextruded together with the extrusion material of the main body 11 to form the resin material. The thickness of the light transmission diffusion layer is usually in the range of 1 to 20 μm.

  In addition to the general light transmission diffusion layer as described above, in the present invention, the following light transmission diffusion layer 17 can be provided between the main body portion 11 and the prism portion 12. With this light transmission diffusion layer 17, the image of the light source can be hidden or made inconspicuous within a range that does not hinder the reduction in thickness and weight.

On the surface of the light transmission diffusion layer 17 on the prism portion side, as shown in FIG. 5B, there are minute irregularities 18 having an average roughness ΔZ ₂ and an average interval ΔS _{2 that} are not less than the maximum wavelength λmax of the light source light spectrum. Is formed. Further, the light transmission diffusion layer 17 has a refractive index different from that of the prism portion 12, and the light transmission diffusion layer 17 and the prism portion 12 are not optically integrated, and irregularities are formed at the interface between both layers. It is preferable that it is made to do so. In this case, (i) a light transmissive diffusion layer 17 made of the same material is formed between the main body portion 11 and the prism portion 12, and the entire light transmissive diffusion layer 17 is made of the same material. And (ii) a single layer of transparent fine particles dispersed in a resin binder between the main body portion 11 and the prism portion 12. The light transmission diffusion layer 17 may be formed, and the transparent fine particles in the light transmission diffusion layer 17 may be projected to form the unevenness 18 on the surface. (iii) Alternatively, it is also possible to form minute irregularities directly on the surface S1 of the main body 11 on the prism portion 12 side, and to make the light transmission diffusion layer 17 near the surface of the main body 11.

  In the case of (i), as the material of the light transmissive diffusive layer 12, the prism portion is selected from resins such as acrylic resin, polycarbonate resin, polystyrene, polyester resin, epoxy resin, polyurethane resin, and perokine structure polytungstic acid. A refractive index different from 12 is selected. The difference in refractive index between the prism portion 12 and the light transmission diffusion layer 17 is 0.1 or more, more preferably, in order to form an optical interface (discontinuous surface) that sufficiently exhibits a diffusion function in both layers. It is good to set it as 0.2 or more. When the acrylate resin having a fluorene skeleton having a refractive index of 1.49 is used as the prism portion 12, polycarbonate, polystyrene, epoxy, or the like having a refractive index of 1.60 is preferably used as the light transmission diffusion layer 17. It is done. As a method for forming the irregularities 18, the light transmission diffusion layer 17 is once coated or bonded on the main body 11 and then embossed by a known hot press embossing method, or disclosed in JP-A-6-324205 [ [0010] is preferably used. Further, when the difference in refractive index between the light transmission diffusion layer 17 and the prism portion 12 cannot be made large, a transparent material of a high refractive index or a low refractive index is transparent between the light transmission diffusion layer 17 and the prism portion 12. A layer may be formed. Examples of such a high refractive index substance include titanium dioxide (refractive index 2.5), cerium dioxide (refractive index 2.3), and low refractive index substances include magnesium fluoride (refractive index 1. 38), quartz stone (refractive index 1.35) and the like. These layers can be formed on the light transmission diffusion layer 17 or the prism portion 12 by vacuum deposition, sputtering, or the like. For example, when the prism portion 12 is made of an acrylate resin having a fluorene skeleton, the light transmission diffusion layer 17 is made of an acrylate resin or a polyester resin that has the above refractive index difference.

In the case of (ii), fine particles of a transparent material having a refractive index different from that of the prism portion 12 is dispersed in the resin binder. As the shape of the fine particles, spheres, spheroids, polygons, scaly foil pieces and the like can be used. Particle size of TsubuMichiko is the average roughness [Delta] Z ₂ of the surface of the fine irregularities 18 are comparable, the lower limit (in the case of normal white light source, about 0.8 [mu] m) the maximum wavelength of the source light spectrum extent preferable. The upper limit is about 100 μm, more preferably 60 μm. Fine particle materials include resins such as acrylic resin, polycarbonate resin, polystyrene, epoxy resin, and polyester resin, glass, calcium carbonate, silica (SiO ₂ ), Arnami (Al ₂ O ₃ ), quartz stone (AlF ₃ / 3NaF). Solid particles such as magnesium fluoride (MgF ₂ ) and mica, or hollow particles such as resin, glass, and shirasu can be used. The fine particles are selected from those having a refractive index different from that of the prism portion 12. Also in this case, it is preferable to use a particle having a refractive index different from that of the prism portion 12 by 0.1 or more, more preferably 0.2 or more, as in the case of (i). . In the case of (ii), the refractive index of the dispersion medium (resin binder) in the light transmissive diffusive layer 12 may be the same as that of the prism portion 12, but in order to perform light diffusive transmission more efficiently. As the dispersion medium, it is preferable to use a dispersion medium different from the prism portion 12 like the fine particles.

The minute irregularities 18 transmit and diffuse the light incident on the main body 11, thereby uniforming the angular distribution of the output light luminance within the diffusion angle of the light output from the main body 11 to the prism side (isotropic). In addition, the distribution of the output light within the light exit surface is made uniform (uniform). The average roughness ΔZ ₂ and average interval ΔS ₂ of the fine irregularities 18 are averaged and evaluated, but are suitable according to the ISO standard average interval such as the ten-point average roughness (Rz) defined in JIS-B-0601. Can be evaluated. ΔZ ₂ and ΔS ₂ are preferably set to be not less than the maximum wavelength λmax of the light source light spectrum. If it is less than λmax, the haze and coherence reduction (phase disturbance) effect due to the light diffusion effect due to the unevenness is lost. In addition, the upper limit value is not particularly present in terms of the light diffusion effect, but if it is too large, the uniformity of the in-plane distribution of the output light is deteriorated (coarse), and bright spots or unevenness become conspicuous in the output light. Usually, it is desirable to use at a maximum of about 200 μm or less. The uneven shape of the minute unevenness 18 may be a random isotropic shape such as a grain or a satin, or a minute light that uniformly diffuses light within a predetermined angle, such as an eyelet lens, a two-dimensional array of pyramid lenses, etc. A lens array can also be used. The average interval ΔS ₂ between the convex portions (or the concave portions) of the minute irregularities 18 is preferably about the same as the average roughness ΔZ ₂ from the viewpoint of light transmission diffusivity and output light uniformity. The reason for the upper limit and the lower limit for this interval is the same as the average roughness. Between the concave portions (or convex portions) are averaged and evaluated. As an indicator, for example, JISB
It can be suitably evaluated by the average interval defined by 0601. In addition, the evaluation of the light transmission diffusion layer based on the steps of the micro unevenness is performed by using haze (JISK 7015) and total light transmittance (JIS K).
7105), haze is preferably 5 to 80%, and total light transmittance is preferably 80% or more. When the haze is less than 5%, the spatial coherence of the transmitted light is reduced, and the effect of eliminating the equal thickness interference fringes is lost. On the other hand, when the haze exceeds 80%, the diffusion angle of the transmitted light becomes too wide, and the luminance within a predetermined angle of the output light is remarkably lowered.

  Although not shown, for example, instead of providing the light transmission diffusion layer 17 on the other surface S2 of the main body 11, the mat processing is performed by giving the surface S2 a predetermined surface roughness and providing a light diffusion function. Is. Examples of the means include a method of mechanically roughening the surface by sandblasting or the like, or a method of forming an uneven layer containing particles.

  An antistatic layer may be provided between the main body portion 11 and the prism portion 12. With this antistatic layer, it is possible to make the prism portion 12 exhibit antistatic performance, and there is an effect of reducing adhesion of foreign matters such as dust. By providing between the main body part 11 and the prism part 12, it is possible to prevent adhesion deterioration between the protective film and the prism part due to bleeding out of the antistatic agent over time. Further, the light transmission diffusion layer 17 may also serve as an antistatic layer.

  The antistatic layer is appropriately composed of a layer obtained by adding an antistatic agent to a resin binder. As an antistatic agent, various cationic antistatic agents having cationic groups such as conductive fine particles made of indium, zinc, tin, antimony, quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups. Agents, sulfonates, sulfate ester bases, phosphate ester bases, phosphonate bases and other anionic antistatic agents, amino acid-based and aminosulfate-based amphoteric antistatic agents, amino alcohol-based, glycerol-based, polyethylene glycol, etc. And various surfactant-based antistatic agents such as nonionic antistatic agents, and polymer antistatic agents obtained by increasing the molecular weight of antistatic agents. Further, a monomer or oligomer having a tertiary amino group or a quaternary ammonium group and capable of being polymerized by ionizing radiation, such as N, N-dialkylaminoalkyl (meth) acrylate monomers, their quaternary compounds, etc. A polymerizable antistatic agent can also be used. In addition, polyoxyethylene alkylamine, polyhydric alcohol derivatives and the like can also be used. In any case, commercially available antistatic agents can be used.

  The optical sheet 1 according to the present invention can be used as a single sheet as shown in FIG. 1 and the like, but in order to control the light diffusion angle in two directions (vertical direction and horizontal direction), it is shown in FIG. As described above, the two optical sheets 1 </ b> A and 1 </ b> B having the prism portion 12 may be laminated so that the ridge lines 14 cross each other. The crossing angle is usually about 15 ° to 90 ° (orthogonal). In this case, it is most preferable that the prism surfaces are oriented in the same direction because both have high light transmission, but the prism portions are opposed to each other, or the prism portions are directed back to back. May be. In the present invention, since the optical sheet 1 as described above is used, even when the top portion of one unit prism 13 is pressed against the other optical sheet by overlapping in this manner, the contact portion is generated. The white spot generated based on the portion can be made inconspicuous, or the occurrence of the white spot can be prevented.

  According to the optical sheet 1 described above, since the thermomechanical analysis curve measured in the temperature range below the glass transition temperature Tg included in the temperature range in the accelerated test is composed of a non-halogen resin that becomes a monotonically increasing curve. In the temperature range, irregular distortion is unlikely to occur in the prism portion 12, and deformation of the optical sheet 1 is unlikely to occur. When the optical sheet 1 (1A, 1B) according to the present invention is placed facing a flat surface such as a liquid crystal panel and an acceleration test is performed, the prism tip of the optical sheet 1 and the flat surface do not cause strong optical adhesion. The wet out can be reduced as much as possible.

[Surface light source device]
A surface light source device 30 shown in FIG. 6 is a so-called edge light type surface light source device, and a light guide 32 that emits light introduced from at least one side end surface 32A from a light emission surface 32B as one surface. A light source 34 for allowing light to enter from at least one side end surface 32A of the light guide 32 and a light emission surface 32B of the light guide 32 are provided, for example, via a gap layer 31, and the light emission surface 32B. And the optical sheet 1 according to the present invention, which transmits the light emitted from the light source. 6A shows a two-sided surface light source device in which the light source 34 is on both end faces, and FIG. 6B shows a single-sided surface light source device in which the light source 34 is one. Show.

  The light guide 32 is a plate-like body made of a translucent material, and is introduced from the side end faces 32A and 32A on both sides in FIG. 6A and from the left side end face 32A in FIG. 6B. The light is emitted from the upper light emitting surface 32B. The light guide 32 is made of a light-transmitting material similar to the material of the optical sheet 1 and is usually made of acrylic or polycarbonate resin. The thickness of the light guide 32 is usually about 1 to 10 mm, and the thickness may be constant over the entire range as shown in FIG. 6 (A), or the light source as shown in FIG. 6 (B). The taper shape may be the thickest at the position of the side end surface 32A on the 34th side and gradually thin in the opposite direction. In order to emit light from a wide surface (light emission surface 32B), it is preferable that a light scattering function is added to the inside or the surface of the light guide 32.

  The light source 34 causes light to enter from the side end surfaces 32A, 32A on either side of the light guide 32 or the side end surface 32A on one side, and is disposed along the side end surface 32A of the light guide 32. The light source 34 is not limited to a linear light source such as a fluorescent tube (fluorescent lamp) as shown in FIG. 6, but a point light source such as an incandescent bulb or LED (light emitting diode) is provided along the side end face 32A. It may be arranged in a line. A plurality of small flat fluorescent lamps may be arranged along the side end face 32A.

  The optical sheet 1 according to the present invention described above may be provided on the light emission surface 32B of the light guide 32 via, for example, a light diffusion sheet. The optical sheet 1 is provided so that the opposite surface of the prism portion 12 becomes the light emission surface 32 </ b> B of the light guide 32. The details of the optical sheet 1 have already been described and are omitted here.

  As shown in FIG. 6A, the reflector 36 is provided on the surface of the light guide 32 opposite to the light emitting surface 32B. In the embodiment shown in FIG. 6B, the reflector 36 is provided on the side opposite to the light emitting surface 32B of the light guide 32 and on the side end surface other than the left side end surface 32A. The reflector 36 is for reflecting light back into the light guide 32. As the reflector 36, a thin metal plate deposited with aluminum or the like, or white foamed PET (polyethylene terephthalate) is used.

  A surface light source device 40 shown in FIG. 7 is a direct-type surface light source device, and includes the optical sheet 1 according to the present invention, a light source 34 that emits light from the opposite surface of the optical sheet 1 on the prism portion 12 side, A concave reflector 44 that is disposed on the opposite side of the optical sheet as viewed from the light source 34 and reflects light from the light source 34 in the direction of the optical sheet 1 is provided. The details of the optical sheet 1 have already been described and are omitted here.

  The light from the light source 34 is transmitted through the optical sheet 1 toward the light emission surface 42 on the optical sheet 1 side, and is transmitted through the optical sheet 1 toward the light emission surface 42 after being reflected by the reflector 44. is there. The reflector 44 is formed by depositing aluminum or the like on a thin metal plate, white foamed PET (polyethylene terephthalate), or the like, similarly to the surface light source device 30 shown in FIG. The shape of the reflector 44 is not particularly limited as long as the light from the light source 34 can be uniformly reflected as a parallel light beam, and a shape such as a rectangular parallelepiped shape, a concave arc shape, a parabolic columnar shape, a hyperbolic columnar shape, an elliptical columnar shape, or the like is selected. .

  The surface light source device 39 shown in FIG. 8 is an edge light type surface light source device similar to that in FIG. In the surface light source device 39, two optical sheets 1A and 1B having a prism portion 12 are provided in a stacked manner. Specifically, as shown in FIG. 8, the two optical sheets 1 are provided so as to cross each other so that the ridge lines 14 intersect each other. The crossing angle is usually about 15 ° to 90 ° (orthogonal). In this case, the direction of the prism surface is the same in both directions (upward or downward as shown in FIG. 8), which is the best because of the high light transmission. Or you may comprise so that a prism part side may face back to back. In the example of FIG. 8, since the optical sheet according to the present invention is used, even if the ridgeline 14 of one of the superimposed prism portions 12 is pressed against the flat surface of the other optical sheet, a contact portion is generated. The wet-out that occurs based on the contact portion can be prevented.

  9A, the surface light source device 30 ′ may be a surface light source device 30 ′ in which the prism portion 12 is provided on the light emission surface 32B side of the light guide 32. As shown in FIG. 9B, the surface light source device 40 ′ in which the prism portion 12 is provided on the light emitting surface 42 side on the optical sheet 1 side may be used.

  In the surface light source device shown in FIGS. 6 to 9, the linear light source 34 or the light source 34 arranged in a line in one direction is used. With respect to the direction in which the ridge line 14 of the unit prism 13 of the optical sheet 1 extends, it may be arranged so as to be parallel as shown in FIGS. Examples of the non-parallel case include a case where the light source 34 and the unit prism 13 are arranged so that the direction in which the ridge line 14 of the unit prism 13 extends is orthogonal, or a case where the light source 34 and the ridge line 14 are arranged obliquely at an arbitrary angle. .

  As described above, in the surface light source device of the present invention, the prism portion 12 of the optical sheet 1 that is a constituent member of the surface light source device becomes a monotonously increasing curve in a narrow sense in the thermomechanical analysis curve measured in the temperature range below the glass transition temperature Tg. Since it is made of a non-halogen resin, irregular distortion is unlikely to occur in the prism portion 12 within that temperature range, and deformation of the optical sheet 1 is unlikely to occur. When the surface light source device according to the present invention is placed opposite to a liquid crystal panel or the like and an acceleration test is performed, the prism tip of the optical sheet 1 and the flat surface of the liquid crystal panel or the like do not cause strong optical adhesion, There is an effect that could not be achieved in the past, that can be reduced as much as possible.

[Display device]
FIG. 10 is a schematic perspective view showing a liquid crystal display device which is a typical example of a translucent display device provided with the surface light source device of the present invention. A liquid crystal display device 50 shown in FIG. 10 includes a liquid crystal panel 52 which is a flat light-transmitting display, and the edge light of the present invention which is disposed on the back surface of the liquid crystal panel 52 and irradiates the liquid crystal panel 52 with light from the back surface. And a surface light source device 30 (see FIG. 6A). The liquid crystal display device 50 is a transmissive liquid crystal display device including a backlight surface light source device 30, and is configured to illuminate each pixel forming a liquid crystal screen from the back side with light emitted from the surface light source device 30. Yes. In addition, as a surface light source device, you may apply the surface light source device of the aspect shown in FIGS.

  Next, the present invention will be described in more detail with reference to examples and comparative examples.

[Example 1]
A polyethylene terephthalate (hereinafter referred to as “PET”) resin having a refractive index of 1.56 is used as an extrusion resin for forming the main body, and it is extruded by being put into an extrusion apparatus so that the thickness after extrusion becomes 180 μm. Then, the main-body part 11 was produced by extending | stretching (biaxial stretching) with the extending | stretching apparatus in the elongate direction and the width direction of the obtained sheet | seat. Next, the prism portion 12 was formed on the surface of the main body portion 11. Prepare a prism part shaping mold in which unit prism shaping grooves of a right isosceles triangle with a depth of 12 μm are arranged in parallel on the surface of a metal cylinder with a spacing of 24 μm, and apply the prism part composition a having the following composition to the shaping mold. After that, the composition was crosslinked and cured by irradiating with ultraviolet rays with a mercury lamp, and simultaneously adhered to the main body 11. Then, it peeled off from the shaping mold and produced the optical sheet 1 which concerns on Example 1 of the aspect shown in FIG.

(Prism part composition a)
Bisphenol A epoxy acrylate 5 parts by weight, bisphenol A epoxy diacrylate 9 parts by weight, full orange acrylate 33 parts by weight, phenoxyethyl acrylate 8 parts by weight, isonulic acid EO-modified triacrylate 16 parts by weight, orthophenylphenoxyethyl Acrylate: 29 parts by weight, and photopolymerization initiator Irgacure 184 [Substance name: 1-hydroxy-cyclohexyl-phenyl-ketone]: 3 parts by weight. The EO modification is an abbreviation for ethylene oxide modification.

[Example 2]
In Example 1, the optical sheet 1 according to Example 2 was produced in the same manner as in Example 1 except that the prism part 12 was formed with the following prism part composition b instead of the prism part composition a.

(Prism part composition b)
Bisphenol A epoxy acrylate 20 parts by weight, phenoxyethyl acrylate 20 parts by weight, isobornyl acrylate 5 parts by weight, acryloylmorpholine 5 parts by weight, bisphenol A diacrylate 10 parts by weight, bisphenol AA dimethacrylate 25 parts by weight, Isocyanuric acid EO-modified triacrylate ... 10 parts by weight and photopolymerization initiator [substance name; 1-hydroxy-cyclohexyl-phenyl-ketone] ... 3 parts by weight

[Example 3]
In Example 1, for each groove of the unit prism shaping groove, the depth in the longitudinal (prism ridgeline) direction X is changed in a random period distributed in an amplitude range of 1 μm to 5 μm and in a range of 74 mm to 850 mm, The depth of each unit prism shaping groove is changed so that the depths in the parallel direction (prism arrangement cycle direction) Y are not the same at the same X coordinate between adjacent grooves in the Y coordinate direction. The prism part 12 was formed using a prism part forming shaping mold in which the phase of the prism part was shifted and the groove depth (prism ridge line height) was modulated. Otherwise, an optical sheet according to Example 3 was produced in the same manner as Example 1.

[Example 4]
In Example 2, the depth in the longitudinal direction X is not modulated for each groove of the unit prism shaping groove (the depth is constant for a specific groove), and the unit prism shaping grooves are arranged in parallel. The prism portion 12 is formed by using a prism portion forming shaping die in which the depth of the groove is sequentially changed in the direction Y direction so that four grooves having a depth of 15 μm and 15 grooves having a depth of 11 μm are alternately arranged. Formed. Otherwise, the optical sheet according to Example 4 was produced in the same manner as Example 2.

[Comparative Example 1]
In Example 3, an optical sheet 1 according to Comparative Example 1 was produced in the same manner as in Example 3 except that the prism part 12 was formed with the following prism part composition c instead of the prism part composition a.

(Prism part composition c)
Full orange acrylate 45 parts by weight, phenoxyethyl acrylate 35 parts by weight, isonuric acid EO-modified triacrylate 20 parts by weight, and photopolymerization initiator [substance name: 1-hydroxy-cyclohexyl-phenyl-ketone] 3 parts by weight

[Measurement of linear expansion coefficient]
The prism part 12 is cut out from the optical sheet 1 obtained in Examples 1 to 4 and Comparative Example 1, and the prism part 12 is further cut into a 14 mm × 5 mm strip, and the thermomechanical analyzer TMA-60 (Shimadzu Corporation) is cut. (Manufactured by Seisakusho). The measurement was performed at a heating rate of 5 ° C./min, a load of 5 g, and a measurement temperature range of 0 ° C. to 100 ° C., and Tg and TMA curve forms were evaluated. Moreover, ΔE1 of the expansion coefficient in the 20 ° C. range of 20 ° C. to 40 ° C. and ΔE2 of the expansion coefficient in the 20 ° C. range of 60 ° C. to 80 ° C. were evaluated. FIG. 11 shows thermomechanical analysis curves obtained from the optical sheets of Examples 1 and 2 and Comparative Example 1. Table 1 shows the glass transition temperature Tg obtained from the optical sheets of Examples 1 to 4 and Comparative Example 1, the form of the thermomechanical analysis curve (TMA curve), ΔE2 / ΔE1, and the presence or absence of occurrence of wetout. It was.

[Wet-out evaluation]
The optical sheet 1 obtained in Examples 1 to 4 and Comparative Example 1 and the liquid crystal panel are arranged to face each other with the prism portion facing the liquid crystal panel, and left in an oven at 60 ° C./95% RH for 24 hours. After taking out, visual evaluation of the presence or absence of wet-out was performed. As shown in FIG. 10, the optical sheet 1 and the liquid crystal panel are arranged so that the prism portion 12 of the optical sheet 1 and the liquid crystal panel face each other with an interval of 188 μm in design. The results are shown in Table 1. FIG. 12 is a schematic diagram (drawing substitute photograph) of the wetouts 19 and 19 generated on the surface of the liquid crystal panel 52.

DESCRIPTION OF SYMBOLS 1,1A, 1B Optical sheet 11 Main body part 12 Prism part 13 Unit prism 14, 14 ', 14 "Ridge line 15 Valley 17 Light transmission diffused layer 18 Concavity and convexity 19 Wetout 30, 30', 39, 40, 40 'Surface light source device DESCRIPTION OF SYMBOLS 31 Gap layer 32 Light guide body 32A Side end surface 32B, 42 Light emission surface 34 Light source 36, 44 Reflector 50 Liquid crystal display device 52 Liquid crystal panel S1 One surface of the main body S2 Other surface of the main body X The unit prism is linear Direction extending in the direction of the ridgeline
Y Unit prism array direction (direction intersecting ridgeline)
Z Thickness direction of optical sheet H, H ', H "Height of ridgeline from main body surface S1

Claims (8)

A sheet-like main body portion, and a prism portion in which a plurality of unit prisms are arranged side by side on one surface of the main body portion, and each linearly extends in a direction intersecting the arrangement direction,
The prism portion is composed of a non-halogen resin in which a thermomechanical analysis curve measured in a temperature range equal to or lower than a glass transition temperature Tg becomes a monotonically increasing curve in a narrow sense ,
The thermal expansion coefficient of the non-halogen resin is 1.014 or less at a temperature range of 0 to 100 ° C.,
An optical sheet characterized by that.   The optical sheet according to claim 1, wherein the non-halogen resin constituting the prism portion includes an acrylate having a fluorene skeleton.   The optical sheet according to claim 1 or 2, wherein the thermomechanical analysis curve measured for the main body portion is a monotonically increasing curve in a narrow sense in a temperature range equal to or lower than the glass transition temperature Tg of the prism portion.   The optical sheet according to claim 1, further comprising a light transmission diffusion layer between the main body portion and the prism portion. 5. The optical sheet according to claim 1, wherein a distance from the main body portion of the ridge line of the unit prism varies along a longitudinal direction of each unit prism .   A surface light source device comprising: the optical sheet according to claim 1; and a light source for allowing light to enter the optical sheet.   The surface light source device according to claim 6, wherein the surface of the optical sheet is disposed as a light emitting surface. The optical sheet is composed of a first optical sheet that receives light from the light source and a second optical sheet that is disposed to overlap the first optical sheet,
8. The surface light source device according to claim 6, wherein the first optical sheet and the second optical sheet are arranged such that ridge lines of unit prisms included respectively intersect in a plan view.

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