JP2010044355A - Optical sheet, backlight unit for display and the display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet for a display, which is obtained by integrating a plurality of optical elements, which are composed respectively of materials, having different coefficients of linear thermal expansion, with one another by pressure-sensitive adhesion or adhesion, and the warpage of which due to thermal expansion is decreased and prevents deterioration in the display quality. <P>SOLUTION: The optical sheet is provided with: a light diffusion layer one surface of which is used as a light-incident surface and the surface opposite to the light-incident surface is used as a light-emitting surface; and an optically-functional member which is stuck to the light-emitting surface and controls at least one of the emitting direction, range, color and luminance distribution of the light which enters the light diffusion layer from the light-incident surface and is emitted from the light-emitting surface. The optical sheet satisfies the expression (1): 0.08≤M/h2≤0.15 (where h2 is the thickness of the light diffusion layer; M is the bending moment to be exerted so that the optical sheet is warped by heat), and the thickness of the optically-functional member is h1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an illumination optical path in a backlight system that irradiates a display element whose display pattern is defined according to transmission / non-transmission or transparent / scattering states in pixel units, represented by a liquid crystal panel, from the back side. The present invention relates to an optical sheet used for control, and a backlight unit for display and a display using the same.

In recent years, liquid crystal display devices using TFT liquid crystal panels and STN liquid crystal panels have been commercialized mainly for color notebook PCs (personal computers) in the OA field.

Such a liquid crystal display device employs a so-called backlight system in which a light source is disposed on the back side of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source.

The backlight units used in this type of backlight system can be broadly divided into multiple light sources such as cold cathode fluorescent lamps (CCFT) within a flat light guide plate made of acrylic resin with excellent light transmission. There are a “light guide plate light guide method” (so-called edge light method) and a “direct type method” that does not use a light guide plate.

As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 15 is generally known. As shown in FIG. 15, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and a substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic is used on the back side thereof. A light guide plate 79 is provided, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate 79. On the lower surface of the light guide plate 79, a scattering reflection pattern portion for scattering and reflecting the light introduced into the light guide plate 79 so as to be uniform in the direction of the liquid crystal panel 72 is provided by printing or the like (see FIG. A reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion. A light source lamp 76 is attached to a side end portion of the light guide plate 79. In order to make the light from the light source lamp 76 enter the light guide plate 79 efficiently, a high-reflectance lamp reflector 81 is provided so as to cover the back side of the light source lamp 76. The scattering reflection pattern portion is formed by printing a mixture of white titanium dioxide (TiO2) powder in a transparent adhesive or the like, printing it in a predetermined pattern, for example, a dot pattern, and drying it. This is a device for imparting directivity to the emitted light and guiding it to the light exit surface side to increase the luminance.

Recently, as shown in FIG. 16, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 in order to increase the light utilization efficiency and increase the luminance. 74, 75 are proposed. The prism films 74 and 75 are configured to collect light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

However, in the apparatus illustrated in FIG. 15, since the control of the viewing angle depends only on the diffusibility of the diffusion film 78, the control is difficult, and the central part in the front direction of the display is bright and becomes darker toward the peripheral part. The phenomenon is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.

Further, in the apparatus using the prism film illustrated in FIG. 16, two prism films are necessary, so that not only the light amount is greatly reduced due to absorption of the film but also the cost is increased due to an increase in the number of members. It was.

On the other hand, the direct type is used for a display device such as a large liquid crystal TV in which it is difficult to use a light guide plate.

As a direct-type liquid crystal display device, a device illustrated in FIG. 17 is generally known. As shown in FIG. 17, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper part, and a light source 51 made of a fluorescent tube or the like is provided on the lower surface side thereof. The light emitted from the light source 51 is diffused by the diffusion film 82 and condensed on the effective display area of the liquid crystal panel 72 with high efficiency. In order to efficiently use the light from the light source 51 as illumination light, a reflector 52 is disposed on the back surface of the light source 51.

In the direct type liquid crystal display device, it is required that light from a linear light source is scattered and the light source cannot be seen through. Therefore, light scattering particles are blended in the diffusion film. Along with the rapid increase in direct type in recent years, various developments have been made on diffusion films. Many of the developments aim at high transmission and high diffusion, and control the kind, particle size, and amount of light scattering particles. Is.

However, even in the apparatus illustrated in FIG. 17, the control of the viewing angle depends only on the diffusibility of the diffusion film 82, which is difficult to control, and the central portion in the front direction of the display is bright and becomes darker toward the peripheral portion. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.

In order to increase the brightness, a brightness enhancement film 86 (Brightness Enhancement Film: BEF, a registered trademark of 3M USA) is disposed on the diffusion film 85 as shown in FIG. 18, and the diffusion is performed thereon as shown in FIG. A method of arranging the film 82 is employed.

BEF is a film in which unit prisms having a triangular cross section are periodically arranged in one direction on a transparent member. This prism has a larger size (pitch) than the wavelength of light. BEF collects light from “off-axis” and directs this light “on-axis” to the viewer, either “redirect” or “recycle”. To do. “On-axis” is a direction that coincides with the visual direction of the observer, and is generally on the normal direction side with respect to the display screen. BEF increases on-axis brightness by reducing off-axis brightness in this way.

When the repetitive array structure of prisms is arranged in only one direction, only the direction change or recycling in the parallel direction is possible. In order to control the luminance of the display light in the horizontal and vertical directions, two sheets are combined and used so that the parallel directions of the prism groups are substantially orthogonal to each other.

The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption.

A display employing a luminance control member having a repetitive array structure of prisms represented by BEF is disclosed in many patent documents as exemplified in Patent Documents 1 to 3.

In the optical sheet using the BEF as a brightness control member as described above, the light from the light source is refracted and emitted at a controlled angle, thereby controlling the light intensity in the visual direction of the observer. can do.

However, at the same time, there is an unexpected light beam that is wasted in the lateral direction without proceeding in the visual direction of the observer. As shown by a broken line B in FIG. 20, the light intensity distribution emitted from the optical sheet using BEF has the highest light intensity when the observer's visual direction, that is, the angle with respect to the visual direction is 0 ° (corresponding to the on-axis direction). However, a small light intensity peak also occurs around ± 90 ° from the front. That is, there is a problem that light (side lobes) emitted from the lateral direction is increased. A luminance distribution having such a light intensity peak is not desirable. As shown by the solid line A in FIG. 20, a smooth luminance distribution with no light intensity peak around ± 90 ° is preferable. On the other hand, when only the on-axis luminance is excessively improved, the peak width of the luminance distribution curve is remarkably narrowed, resulting in an extreme luminance change. In order to realize a smooth profile, it is necessary to install another diffusion film 82 on the prism sheet, and there is a problem that the number of members increases.

As described above, the optical sheet of the backlight unit is required not only to improve the light use efficiency, but also to perform various functions such as removing unevenness of the light source, erasing the lamp image, and securing the viewing area of the display. In general, a plurality of optical sheets are overlapped. However, if the number of optical sheets is large, there are problems such as complicated operations for assembling the display and being affected by dust between the optical sheets.

In addition, liquid crystal display devices are strongly required as market needs to be lightweight, low power consumption, high brightness, and thin, and the backlight unit mounted on the liquid crystal display device is also light weight, low power consumption. Therefore, it is required to have high brightness. In particular, in color liquid crystal display devices that have been remarkably developed recently, the transmittance of the liquid crystal panel is much lower than that of a monochrome-compatible liquid crystal panel, so improving the brightness of the backlight unit can reduce the consumption of the device itself. It is essential to get power.

However, as described above, it is difficult to say that the conventional liquid crystal display device sufficiently satisfies the user's demand for low price, thinness, high brightness, high display quality, and low power consumption. Therefore, development of an optical sheet that can realize such a demand, and a display backlight unit and a display using the optical sheet is desired.

Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

In the display backlight unit, the optical sheet generates heat due to the heat radiation of the backlight, and the warp due to the thermal expansion of the optical sheet occurs in the housing, which may deteriorate the display quality of the display.

In particular, in an optical sheet in which a plurality of layers made of materials having different linear thermal expansion coefficients are integrated by adhesion or adhesion, the linear thermal expansion differs for each layer. There is a possibility that warping will occur remarkably in the housing, which is disadvantageous in obtaining a clear display image.

An object of the present invention is to provide a backlight unit for a display which is generated by thermal expansion due to the influence of the backlight in an optical sheet in which a plurality of layers made of materials having different linear thermal expansion coefficients are integrated by adhesion or adhesion. An object of the present invention is to provide an optical sheet, a backlight unit for display, and a display that can reduce warpage in a casing and can effectively suppress a reduction in display quality.

の関係を満たすことを特徴とする光学シートが提供される。 According to one aspect of the present invention, a light diffusing layer having one surface as a light incident surface and a surface opposite to the light incident surface as a light emitting surface is bonded to the light emitting surface, An optical functional member that controls at least one of an emission direction, a range, a color, and a luminance distribution of light incident on the light diffusion layer and emitted from the light emission surface, and the thickness of the light diffusion layer is h2, When the thickness of the optical functional member is h1 and the bending moment acting so as to cause warpage by heat is M, M and h2 are expressed by the following formula (1).

An optical sheet characterized by satisfying the above relationship is provided.

In the optical sheet of the present invention, when the longitudinal elastic constant of the light diffusion layer is E2 and the longitudinal elastic constant of the optical function member is E1, it is preferable that E1 and E2 satisfy the relationship of the following formula (2).

In the optical sheet of the present invention, when the linear expansion coefficient of the light diffusion layer is α2 and the linear expansion coefficient of the optical function member is α1, it is preferable that α1 and α2 satisfy the relationship of the following expression (3).

In the optical sheet of the present invention, the light diffusion layer and the optical functional member are bonded with an adhesive or an adhesive.

According to another aspect of the present invention, there is provided a display backlight unit comprising a direct light source and the optical sheet, and provided on the back surface of an image display element that defines a display image. .

According to another aspect of the present invention, a display comprising an edge light type light source and a surface light source having a light guide plate, and the optical sheet, and provided on a back surface of an image display element that defines a display image. A backlight unit is provided.

According to still another aspect of the present invention, there is provided a display comprising an image display element and the display backlight unit.

In the optical sheet of the present invention, when the thickness of the light diffusing layer is h2, the thickness of the optical functional member is h1, and the bending moment acting so as to cause warp by heat is M, M and h2 are expressed by the following formulas. By satisfying 1, it is possible to reliably reduce the warpage of the optical sheet and to reliably prevent the display quality from deteriorating.

In addition, the optical sheet of the present invention reliably reduces the warpage of the optical sheet by ensuring that the longitudinal elastic constant E2 of the light diffusion layer and the longitudinal elastic constant E1 of the optical functional member satisfy the relationship of the following formula 2. It is possible to prevent the display quality from deteriorating.

The block diagram which shows the display (liquid crystal display device) which has a backlight unit provided with the optical sheet which concerns on embodiment of this invention. Sectional drawing of the optical sheet which concerns on embodiment of this invention. The block diagram which shows the display which has a side-edge type backlight unit which concerns on other embodiment of this invention. The block diagram which shows the display using the EL light source which concerns on other embodiment of this invention. The block diagram which shows the display using the LED light source which concerns on other embodiment of this invention. Explanatory drawing which shows the parameter used for calculation of a bending moment. Explanatory drawing which shows the bending moment and curvature which act on a light-diffusion layer and an optical function member. Sectional drawing of the optical sheet containing a light-diffusion layer and an optical function member. The figure which shows the relationship between longitudinal elastic constant ratio E1 / E2 and curvature v. The figure which shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the bending moment M. The figure which shows the relationship between longitudinal elastic constant ratio E1 / E2 and curvature v. The figure which shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the bending moment M. The figure which shows the relationship between longitudinal elastic constant ratio E1 / E2 and curvature v. The figure which shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the bending moment M. The block diagram of the liquid crystal display device by a prior art. The block diagram of the liquid crystal display device by a prior art. The block diagram of the liquid crystal display device by a prior art. The perspective view of BEF by a prior art. The block diagram of the lens sheet for liquid crystal displays by a prior art. Explanatory drawing which shows the light intensity distribution radiate | emitted from the lens sheet using BEF.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram illustrating a display (liquid crystal display device) having a backlight unit including an optical sheet according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the optical sheet.

The liquid crystal display device shown in FIG. 1 has a configuration in which a backlight unit 44 including an optical sheet 39 and a plurality of direct light sources 41 is provided on the back surface of a liquid crystal panel 32. The liquid crystal panel 32 includes a liquid crystal panel 35 sandwiched between polarizing plates 31 and 33. The plurality of light sources 41 have a cylinder shape and are accommodated in the lamp house 43. A light reflecting plate 45 is disposed on the back side of the plurality of light sources 41. An optical sheet 39 is provided between the light source 41 and the liquid crystal panel 32.

As shown in FIGS. 1 and 2, the optical sheet 39 is obtained by integrating the light diffusing layer 1 and the optical function member 4 through the fixing element 3 in the thickness direction. A gap 2 is formed between the light diffusion layer 1 and the optical function member 4. Light from the light source 41 passes through the optical sheet 39 and is supplied to the liquid crystal panel 32.

The display of FIG. 1 is a liquid crystal display device, but is not limited to this as long as it includes the optical sheet 39, and may be a projection screen device, a plasma display, an EL display, or the like.

The light source 41 is a linear light source such as a fluorescent lamp, and a cold cathode tube is usually used for a liquid crystal display.

The light diffusion layer 1 of the optical sheet 39 includes a transparent resin 1R and particles 1P dispersed in the transparent resin.

As the transparent resin used for the light diffusion layer 1, for example, polycarbonate resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methylstyrene resin, fluorene resin, PET, polypropylene, acrylonitrile styrene copolymer and the like can be used.

In the light diffusing layer 1, as particles dispersed in the transparent resin, particles made of an inorganic oxide or particles made of a resin can be used. Examples of the particles made of an inorganic oxide include particles made of silica or alumina. Examples of the resin particles include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine-formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene). -Fluoropolymer particles such as hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), and silicone resin particles.

In order to obtain sufficient light diffusion characteristics, it is preferable that the refractive index of the transparent resin constituting the light diffusion layer 1 and the refractive index of the particles are different. Specifically, it is desirable that the difference between the refractive index of the transparent resin and the refractive index of the particles is 0.02 or more.

In order to manufacture the plate-like light diffusion layer 1, a method is used in which particles are dispersed in a transparent resin and extruded. The thickness of the light diffusion layer 1 is preferably 1 to 5 mm. When the thickness of the light diffusing layer 1 is less than 1 mm, the light diffusing layer 1 loses stiffness and is easily bent. If the thickness of the light diffusion layer 1 exceeds 5 mm, the transmittance of light from the light source 41 is deteriorated.

As described above, the fixing element 3 is provided between the exit surface of the light diffusion layer 1 and the entrance surface of the optical function member 4. The fixing element 3 is formed so as to cover the exit surface of the light diffusing layer 1 and a part of the incident surface of the optical functional member 4, whereby the gap 2 is held between the light diffusing layer 1 and the optical functional member 4. The gap 2 is made of a gas such as air or nitrogen. Light transmitted through the gap 2 can be collected and guided to the optical function member 4.

The fixing element 3 includes a plurality of ribs that transmit light scattered by the light diffusion layer 1, an adhesive layer or an adhesive layer, and a plurality of light that reflects light scattered by the light diffusion layer 1 toward the light diffusion layer 1 side. Examples thereof include a rib having a reflective surface or containing a reflective material, or an adhesive layer or a pressure-sensitive adhesive layer containing the reflective material. However, the fixing element 3 is not limited to those formed by these methods, and may be formed by a welding method, a method using a fixing tool, a method of performing room temperature bonding by irradiating excimer laser light, or the like.

The case where an adhesive layer or an adhesive layer is used for the fixing element 3 will be described. The position where the adhesive layer or the pressure-sensitive adhesive layer is applied is, for example, outside the display region of the light diffusion layer 1 and the optical function member 4 (region other than that used for image display when the optical function member 4 is incorporated in the display). To do. However, the position where the adhesive layer or the pressure-sensitive adhesive layer is applied may be within the display area as long as there is no influence on the image display quality such that the fixing element 3 is visually recognized from the display.

Examples of the material for the adhesive layer or the pressure-sensitive adhesive layer include acrylic, urethane-based, rubber-based, and silicone-based adhesives or pressure-sensitive adhesives. Since the fixing element 3 in the backlight unit becomes high temperature, it is desirable that the adhesive layer or the pressure-sensitive adhesive layer used therefor has a storage elastic modulus G ′ at 100 ° C. of 1.0E + 04 Pa or more. If the storage elastic modulus G ′ is lower than this value, the light diffusion layer 1 and the optical functional member 4 may be displaced during use, which is not desirable. In order to stably maintain the gap 2 between the light diffusion layer 1 and the optical functional member 4, transparent fine particles such as beads may be mixed in the adhesive layer or the pressure-sensitive adhesive layer. The adhesive layer or the pressure-sensitive adhesive layer may be a double-sided tape or a single layer.

When an adhesive layer or a pressure-sensitive adhesive layer is attached in the display area, it is preferable that light absorption associated with the use of the adhesive layer or the pressure-sensitive adhesive layer is within 1%. If the light absorption exceeds 1%, the integrated light quantity emitted from the optical sheet 39 is reduced, and this is not preferable because the on-axis luminance is lowered regardless of the shape of the optical function member 4.

In order to attach the adhesive layer or the pressure-sensitive adhesive layer, various coating devices such as a comma coater, a printing device, a dispenser, a spray, or the like may be used, or coating may be performed manually using a brush or the like.

The optical functional member 4 will be described in more detail with reference to FIG. The optical functional member 4 includes a plate-like light-transmitting substrate 4A and a lens array unit 4B that is provided on the surface opposite to the surface facing the light diffusion layer 1 of the light-transmitting substrate 4A and controls the direction of light. Have. That is, the lens array portion 4B constitutes the exit surface of the optical function member 4. In the lens array portion 4B, for example, a large number of convex cylindrical unit lenses are formed in parallel.

When the same material is used for the light transmissive substrate 4A and the lens array portion 4B, for example, the thermoplastic resin is melted and extruded, and the optical function is achieved by pressing through a mold roll cut into the shape of the optical function member 4. The member 4 is produced.

When different materials are used for the light transmissive substrate 4A and the lens array portion 4B, a UV curable resin is applied to the lens shape on the light transmissive substrate 4A made of a resin such as PET, and the applied UV is applied. An optical functional member is fabricated by irradiating the curable resin with UV to form the lens array portion 4B.

FIG. 2 shows that fine particles 7 for diffusing light are mixed in both the light transmissive substrate 4A and the lens array portion 4B. However, when using the fine particles 7 for diffusing light, the fine particles 7 may be mixed with at least one of the light transmissive substrate 4A and the lens array portion 4B.

For example, polycarbonate, polystyrene, methylstyrene resin, and cycloolefin polymer are used for the light diffusion layer 1, and the linear expansion coefficients of these polymers are 6.7 × 10 −5 (/ ° C.) and 7 × 10 −5 ( /.Degree. C.), 7.times.10.sup.-5 (/.degree. C.) and 6-7.times.10.sup.-5 (/.degree. C.). On the other hand, when, for example, PET is used for the optical function member 4, its linear expansion coefficient is 2.7 × 10 −5 (/ ° C.). In this case, the difference between the linear expansion coefficient of the light diffusion layer 1 and the linear expansion coefficient of the optical function member 4 is large. Since the light diffusion layer 1 and the optical function member 4 are fixed, when the optical sheet 39 receives heat, it is deformed by the bimetal effect.

In the optical sheet of the present invention, when the thickness of the light diffusing layer is h2, the thickness of the optical functional member is h1, and the bending moment acting so as to cause warp by heat is M, M and h2 are expressed by the following formula (1). It is set to satisfy the relationship.

In the present invention, when the longitudinal elastic constant of the light diffusion layer is E2 and the longitudinal elastic constant of the optical function member is E1, E1 and E2 are set so as to satisfy the relationship of the following two expressions.

The above equation in the present invention was derived by simulation based on the calculation of bending moment M and strain (hereinafter referred to as warpage) v based on material mechanics. Here, the bending moment M represents a force that acts to cause the object to warp.

Specifically, the bending moment M and the warp v are calculated through the following procedure.
(A) When heat is applied to the optical sheet 39, the bending moment M due to the thermal stress generated by the difference in linear expansion coefficient between the light diffusion layer 1 and the optical function member 4 is calculated.

(B) When warping occurs due to the bending moment M, the neutral axis that is the center of bending that becomes the boundary between the stretched portion and the contracted portion in the cross section is obtained.

(C) A cross-sectional second moment representing the ease of deformation when the optical sheet is made of one kind of substance is calculated.

(D) The differential equation of the deflection equation is solved, and the warp value is obtained using the values obtained in (b) and (c) above.

(E) Define parameter conditions effective in warping suppression when each parameter is changed.

As shown in FIG. 6, the light diffusion layer 1 has a longitudinal elastic modulus E2, a linear expansion coefficient α2, a cross-sectional area A2, and a thickness h2, and the optical function member 4 has a longitudinal elastic modulus E1, a linear expansion coefficient α1, a cross-sectional area A1, The thickness is h1, the depth is b, and the width is l. The influence on the warping of the fixing element 3 is small and is not considered here.

With reference to FIG. 7, calculation of the bending moment due to thermal stress will be described. Here, the linear expansion coefficient is α1 <α2, and the direction of the bending moment is calculated as the direction warping the light exit side. As shown in FIG. 7, since two materials having different linear expansion coefficients are joined as the light diffusing layer 1 and the optical function member 4, a force P having the same size and the opposite direction acts on both materials. The following strains are generated in the light diffusion layer 1 and the optical function member 4, respectively.

(A) Strain due to heat (b) Strain due to force P (c) Strain due to warp By the way, (c) is common to both, and the strain at the joint is equal. Therefore, the sum of the strains of (a) and (b) may be equal, and when the temperature changes by t ° C., the following equation (f1) holds.

Further, since A1 = bh1 and A2 = bh2, the force P is expressed by the following equation (f2) by substituting it into the equation (f1).

Therefore, the bending moment M is obtained by the following equation (f3).

The optical sheet 39 is considered as a model of a combined beam that bends as one beam when it receives a bending moment M.

FIG. 8 shows a cross-sectional view of the beam. When bending as one beam, there is a neutral axis L that becomes the boundary between the stretched portion and the contracted portion. When the distance from the upper side of the beam cross section to the neutral axis L is y, it is necessary to apply a weight of each material property Ei to the cross section, which is expressed by the following equation (f4).

From the beam deflection equation, the relationship between the deflection v and the moment M can be obtained from the following equation (f5).

The denominator part of the equation (f5) is expressed by the equation (f6) as follows.

When the equation (f5) is solved, the maximum warpage of the beam is expressed by the equation (f7).

Therefore, the relationship between the bending moment and the warpage can be obtained by using the above equations (f3) and (f4) for the equation (f7).

An actual simulation is described. Tables 1 to 3 show parameters used in this simulation.

Parameters common to the light diffusion layer 1 and the optical function member 4 are fixed. Here, the direction of the bending moment is set to warp toward the light exit side. Further, the simulation is used in a strip shape having a width b = 10 mm in accordance with a beam bending model. However, since there is a correlation in a plate shape, this result can be reflected in an actual optical sheet.

From the equation (f3), the bending moment M and the warp are related to the parameters of the thickness h2 of the light diffusion layer 1, the longitudinal elastic modulus E2, the thickness h1 of the optical function member 4, and the longitudinal elastic modulus E1. The simulation was performed for the bending moment M and the warp value when h2 and E2 were fixed and h1 and E1 were changed.

Table 1 is a parameter table used when h2 = 2.0 mm. FIG. 9 shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the warp v. FIG. 10 shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the bending moment M.

Table 2 is a parameter table used when h2 = 3.0 mm. FIG. 11 shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the warp v. FIG. 12 shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the bending moment M.

Table 3 is a parameter table used when h2 = 5.0 mm. FIG. 13 shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the warp v. FIG. 14 shows the relationship between the longitudinal elastic constant ratio E1 / E2 and the bending moment M.

As shown in FIGS. 9 to 14, as the longitudinal elastic constant ratio E1 / E2 between the light diffusion layer 1 and the optical function member 4 decreases, the warp v and the bending moment M tend to decrease. Further, as h1 is thicker, the warp / bending moment increases, and as h2 is thicker, the warp / bending moment decreases. In particular, when h1 is 1.0 mm, the warp value reaches a saturated state when the bending moment is greater than a certain value.

The bending moment M and h2 have a linear relationship, and if M / h2 ≦ 0.1, there is an effect that the warp can be surely reduced. Regarding the longitudinal elastic constant ratio E1 / E2, if E1 / E2 ≦ 0.8, there is an effect that the warp can be surely reduced.

(Example 1)
As a material for the light transmissive substrate 4A and the lens array portion 4B, a material obtained by dispersing 0.1% by weight of methacryl particles having a refractive index of 1.49 and a particle size of 2 μm in a thermoplastic polystyrene resin having a refractive index of 1.59. Charged to the extruder. The lens array portion 4B was formed by a mold roll cut into a convex cylindrical shape disposed in the vicinity of the extruder by melting the resin, extruded as a sheet, and the sheet was cooled and cured to produce the optical functional member 4. . The lens array portion 4B has a convex cylindrical shape with a pitch of 140 μm. The lens shape is not limited to the convex cylindrical shape, but may be a prism shape or the like.

This optical functional member 4 had a longitudinal elastic modulus E1 of 3300 MPa, a linear expansion coefficient α1 of 8 × 10 −5 (cm 2 / ° C.), and a thickness h1 of 0.4 mm.

Optically, the addition of particles changes the emission luminance distribution shape compared to the case where particles are not added, the side lobe is reduced, the maximum inclination angle is gentle, and the viewing angle is wide. became.

As a material for the light diffusing layer 1, 3 parts by weight of silicone beads having an average particle diameter of 6 μm and 3 parts by weight of silicone beads having an average particle diameter of 3 μm were added to 100 parts by weight of the polycarbonate resin. The laminated sheet was extruded by a lamination extruder to produce a light diffusion layer 1. At this time, the die temperature of the extruder was set to 250 ° C., the roll temperature (2 rolls) was set to 90 ° C., and the extrusion amount of the resin was adjusted to prepare the light diffusion layer 1.

This light diffusing layer 1 was manufactured in this way, having a longitudinal elastic modulus E2 of 2500 MPa, a linear expansion coefficient α2 of 6.7 × 10 −5 (cm 2 / ° C.), and a thickness h2 of 2.0 mm. The optical function member 4 and the light diffusion layer 1 were integrated using a pressure-sensitive adhesive sheet having a size of 500 × 900 mm and a thickness of 10 μm. As an integration method, an adhesive material or an adhesive may be used. That is, the fixing method and the fixing member are not limited. The obtained optical sheet has a longitudinal elastic modulus ratio E1 / E2 of 1.32.

In order to test the reliability, the integrated optical sheet was placed on a display, and after being kept at a temperature of 80 ° C. for 24 hours, the warped shape was confirmed. As a result, it was found that the amount of warpage was large.

(Example 2)
An optical functional member 4 was produced by an extrusion method in the same manner as in Example 1 using polycarbonate resin as the material of the optical functional member. This optical functional member 4 had a longitudinal elastic modulus E1 of 2500 MPa, a linear expansion coefficient α1 of 6.6 × 10 −5 (cm 2 / ° C.), and a thickness h1 of 0.4 mm.

A polystyrene resin was used as the material of the light diffusion layer 1, and the light diffusion layer 1 was produced by an extrusion method in the same manner as in Example 1. This light diffusion layer 1 had a longitudinal elastic modulus E2 of 3300 MPa, a linear expansion coefficient of 8 × 10 −5 (cm 2 / ° C.), and a thickness of 2 mm.

The optical functional member 4 and the light diffusion layer 1 thus manufactured were integrated using a pressure-sensitive adhesive sheet having a size of 500 × 900 mm and a thickness of 10 μm. The obtained optical sheet has a longitudinal elastic modulus ratio E1 / E2 of 0.76.

In order to test the reliability, the integrated optical sheet was placed on a display, and after being kept at a temperature of 80 ° C. for 24 hours, the warped shape was confirmed. As a result, it was found that the amount of warpage was small.

(Example 3)
An optical functional member 4 was produced by an extrusion method in the same manner as in Example 1 using polypropylene resin as the material of the optical functional member. This optical functional member 4 had a longitudinal elastic modulus E1 of 1400 MPa, a linear expansion coefficient α1 of 7 × 10 −5 (cm 2 / ° C.), and a thickness h1 of 0.4 mm.

A polystyrene resin was used as the material of the light diffusion layer 1, and the light diffusion layer 1 was produced by an extrusion method in the same manner as in Example 1. This light diffusion layer 1 had a longitudinal elastic modulus E2 of 3300 MPa, a linear expansion coefficient of 8 × 10 −5 (cm 2 / ° C.), and a thickness of 2 mm.

The optical functional member 4 and the light diffusion layer 1 thus manufactured were integrated using a pressure-sensitive adhesive sheet having a size of 500 × 900 mm and a thickness of 10 μm. The longitudinal elastic modulus ratio E1 / E2 of the obtained optical sheet is 0.42.

In order to test the reliability, the integrated optical sheet was placed on a display, and after being kept at a temperature of 80 ° C. for 24 hours, the warped shape was confirmed. As a result, it was found that the amount of warpage was small.

(Example 4)
Using a high-density polyethylene resin as the material of the optical functional member, an optical functional member 4 was produced by an extrusion method in the same manner as in Example 1. This optical functional member 4 had a longitudinal elastic modulus E1 of 500 MPa, a linear expansion coefficient α1 of 11 × 10 −5 (cm2 / ° C.), and a thickness h1 of 0.4 mm.

A polystyrene resin was used as the material of the light diffusion layer 1, and the light diffusion layer 1 was produced by an extrusion method in the same manner as in Example 1. This light diffusion layer 1 had a longitudinal elastic modulus E2 of 3300 MPa, a linear expansion coefficient of 8 × 10 −5 (cm 2 / ° C.), and a thickness of 2 mm.

The optical functional member 4 and the light diffusion layer 1 thus manufactured were integrated using a pressure-sensitive adhesive sheet having a size of 500 × 900 mm and a thickness of 10 μm. The obtained optical sheet has a longitudinal elastic modulus ratio E1 / E2 of 0.15.

In order to test the reliability, the integrated optical sheet was placed on a display, and after being kept at a temperature of 80 ° C. for 24 hours, the warped shape was confirmed. As a result, it was found that the amount of warpage was large.

In Table 4, the evaluation result of the reliability test regarding the optical sheet of Examples 1-4 is shown.

であることが望ましい。｜α１−α２｜が３．０×１０−５ を超える場合、反りの抑制効果が得られない。 The results in Table 4 show the same tendency as the simulation results. When the longitudinal elastic modulus ratio E1 / E2 of Examples 1 to 3 is 0.4 or more, the warpage decreases as E1 / E2 decreases. . About Example 4, generation | occurrence | production of the curvature by a linear expansion coefficient difference was large, and the effect was not seen. When the linear expansion coefficient α1 of the optical function member 4 and the linear expansion coefficient α2 of the light diffusion layer 1 are set,

It is desirable that When | α1-α2 | exceeds 3.0 × 10 −5, the effect of suppressing warpage cannot be obtained.

According to the optical sheet of the present invention, warping is suppressed even after a reliability test and the shape is kept good, so that the thickness can be reduced. The material is not limited to the above materials, and other materials may be used as long as the conditions of the expressions (1) and (2) are satisfied. In the above description, the direction of the bending moment is on the light emitting side, but the bending moment may be in the opposite direction. In this case, it can be similarly applied only by reversing the parameter relationship between the optical function member 4 and the light diffusion layer 1.

Further, the optical functional member 4 and the light diffusing layer 1 were placed in the bonding, and the fixing element was bonded at a different area ratio. Using the adhesive material as the fixing element, the fixing element and the air layer were arranged in a stripe shape to adjust the area ratio. Further, the adhesion force at this time is set to 1000 gf / inch.
Table 5 shows the result of the reliability test of the optical sheet.

When the area ratio was less than 30%, the difference in the warpage of the unbonded portion could not be absorbed in the environmental test regardless of the parameter conditions of the optical function member 4 and the light diffusion layer 1, resulting in a large warpage amount as an optical sheet.
When the area ratio was 30% or more, the warp had the same tendency as in the case of 100% bonding, and the warp amount was small.

In the above description, the example in which the optical sheet according to the present invention is applied to a direct backlight unit has been described, but the present invention is not limited to this. As shown in FIG. 3, the optical sheet according to the present invention can also be applied to a side-edge type backlight unit provided with a light guide plate 47.

The optical sheet of the present invention is highly reliable and stable in behavior at both high and low temperatures. The optical sheet of the present invention is used for viewing angle control films for displays such as LCD, EL, and PDP, contrast enhancement films, light control films for solar cells, projection screens, etc., in addition to uses for improving the brightness of backlights. You can also.

The optical sheet of the present invention can be used not only in the case of using a cold cathode fluorescent lamp as a light source, but also in a display using an LED, EL, semiconductor laser or the like as a light source.

FIG. 4 shows a display using an EL light source 49. 5A and 5B show a display using the LED light source 53. FIG. The display shown in FIG. 5A uses an array of red, green, and blue LEDs, and mixes light from the array of red, green, and blue LEDs with a light guide plate or the like to uniformly emit white light. The display shown in FIG. 5B mixes light from an array of red, green, and blue LEDs using a diffusion plate or the like, and emits uniformly as white light.

DESCRIPTION OF SYMBOLS 1 ... Light-diffusion layer, 1R ... Transparent resin, 1P ... Particle | grains, 2 ... Space | gap, 3 ... Fixed element, 4 ... Optical functional member, 4A ... Light transmissive base material, 4B ... Lens array part, 5 ... Lens part, 7 ... fine particles, 31, 33, 71, 73 ... polarizing plate, 32, 72 ... liquid crystal panel, 35 ... liquid crystal layer, 39 ... optical sheet, 41, 51, 76 ... light source, 43 ... lamp house, 44 ... backlight unit, 45: Light reflection plate, 47, 79 ... Light guide plate, 49 ... EL light source, 53 ... LED light source, 78, 82 ... Diffusion film, 74, 75 ... Prism, 77 ... Reflection film, 85 ... Diffusion film, 86 ... Brightness enhancement Film (BEF).

Claims (8)

A light diffusing layer having one surface as a light incident surface and a surface opposite to the light incident surface as a light emitting surface, and the light diffusing layer are bonded to the light diffusing layer and are incident on the light diffusing layer from the light incident surface. An optical function member that controls at least one of the emission direction, range, color, and luminance distribution of light emitted from the emission surface, the thickness of the light diffusion layer is h2, the thickness of the optical function member is h1, An optical sheet characterized in that M and h2 satisfy the relationship of the following expression (1), where M is a bending moment that acts to cause warping by heat.

E1 and E2 satisfy | fill the relationship of following (2) Formula, when the longitudinal elastic constant of the said light-diffusion layer is set to E2, and the longitudinal elastic constant of the said optical function member is set to E1, The optical sheet characterized by the above-mentioned.

2. The optical sheet according to claim 1, wherein α1 and α2 satisfy the relationship of the following expression (3), where α2 is a linear expansion coefficient of the light diffusion layer and α1 is a linear expansion coefficient of the optical function member. .

The optical sheet according to claim 1, wherein the light diffusing layer and the optical functional member are bonded with an adhesive or an adhesive. The pressure-sensitive adhesive or adhesive that contacts the light diffusing layer and the optical function member occupies an area ratio of 30% to 100% with respect to the surface area of the light incident surface of the optical function member, and is bonded. The optical sheet according to claim 1. A display backlight unit comprising a direct light source and the optical sheet according to claim 1 and provided on a back surface of an image display element for defining a display image. A display backlight unit comprising an edge light type light source and a surface light source having a light guide plate, and the optical sheet according to claim 1, and is provided on a back surface of an image display element for defining a display image. A display comprising an image display element and the display backlight unit according to claim 5.

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