JP2008241743A - Light diffusion sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet which shows no shape of a light source and shows high luminance when disposed at a light source unit and further to provide its manufacturing method. <P>SOLUTION: The light diffusion sheet 1 has surface layer regions 11,13 and a middle layer region 12 between the surface layer regions 11,13. The surface layer regions 11,13 contain a sea phase 111 constituted of a first resin and an island phase 112 constituted of a second resin. The middle layer region 12 contains a sea phase 113 constituted of the first resin and an island phase 114 constituted of the second resin. At cross sections of the surface layer regions 11,13, a length ratio between an alignment direction of the island phase 112 and a direction orthogonally intersecting the alignment direction (a thickness direction and a width direction) is 6 to 30 and an aspect ratio of the island phase at a cross section of the middle layer region 12 is 0.7 to 3.3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light diffusing sheet and a manufacturing method thereof, and more particularly to a light diffusing sheet used in a light source unit such as a backlight of a liquid crystal display device and a manufacturing method thereof.

In a transmissive or transflective liquid crystal display device, a backlight is provided as a light source unit that illuminates a liquid crystal panel. This backlight is configured to allow light emitted from a linear light source such as a cold cathode tube to enter a liquid crystal panel via a light guide plate or a light diffusion sheet (Patent Document 1).
JP 2006-39503 A

  However, when a conventional light diffusion sheet is used for the backlight, when the brightness of the liquid crystal panel is increased, a lamp image of a cold cathode tube as a light source appears and the display quality deteriorates. On the other hand, if the lamp image is not generated, there is a problem that the display screen becomes dark without obtaining sufficient luminance.

  The present invention has been made in view of the above points, and provides a light diffusion sheet that does not show the shape of a light source (lamp image) when it is disposed in a light source unit, and exhibits high brightness, and a method for manufacturing the same. With the goal.

  The light diffusion sheet of the present invention includes a sea phase composed of a first resin and an island phase composed of a second resin that is incompatible with the first resin, and has a surface layer region and a middle layer region. In the sheet, the island phase is oriented in a specific direction in the surface layer region, and the aspect ratio between the orientation direction of the island phase and the direction orthogonal to the orientation direction in the cross section is 6 to 30, The middle layer region is not substantially oriented, and the aspect ratio of the island phase in the cross section is 0.7 to 3.3.

  According to this configuration, the island phase is oriented in a specific direction in the surface layer region, and the aspect ratio between the orientation direction of the island phase and the direction perpendicular to the orientation direction in the cross section is 6 to 30, Since the middle layer region is not substantially oriented and the aspect ratio of the island phase in the cross section is 0.7 to 3.3, the shape of the light source (lamp image) appears when placed in the light source unit. In addition, high luminance can be exhibited.

  In the light diffusion sheet of the present invention, it is preferable that the content weight ratio between the first resin and the second resin is 30/70 to 70/30.

  In the light diffusion sheet of the present invention, it is preferable that the ratio of the thickness of the middle layer region to the thickness of the light diffusion sheet is 20% to 80%.

  In the light diffusion sheet of the present invention, the haze value is preferably 90 or more.

  In the light diffusion sheet of the present invention, the total light transmittance is preferably 80% or less.

  In the light diffusing sheet of the present invention, it is preferable that the component that passes straight through the light diffusing sheet out of the total transmitted light is 5% or less.

  In the light diffusion sheet of the present invention, the thickness is preferably 0.05 mm to 0.5 mm.

  In the light diffusion sheet of the present invention, it is preferable that the first resin is a polyolefin-based resin and the second resin is a polycarbonate resin. In this case, the polyolefin resin is preferably a polypropylene resin.

  The liquid crystal display device of the present invention includes a liquid crystal panel in which a liquid crystal layer is sandwiched between a pair of glass substrates, and the light diffusion sheet according to any one of claims 1 to 10, wherein light from a light source is emitted from the liquid crystal display device. A light source unit that transmits the light diffusing sheet and enters the liquid crystal panel.

  The method for producing a light diffusing sheet of the present invention includes a step of forming a sheet body composed of a first resin and a second resin that is incompatible with the first resin, and a biaxial stretching process for the sheet body. And a step of causing interface separation between the first resin and the second resin to generate pores between the first resin and the second resin, and a sheet main body after biaxial stretching. And a step of filling the pores with the first resin by performing heat treatment at a temperature higher than the melting point of the first resin and lower than the melting point of the second resin.

  The light diffusion sheet of the present invention includes a sea phase composed of a first resin and an island phase composed of a second resin that is incompatible with the first resin, and has a surface layer region and a middle layer region. In the sheet, the island phase is oriented in a specific direction in the surface layer region, and the aspect ratio between the orientation direction of the island phase and the direction orthogonal to the orientation direction in the cross section is 6 to 30, Since the middle layer region is not substantially oriented and the aspect ratio of the island phase in the cross section is 0.7 to 3.3, the shape of the light source does not appear and is high when arranged in the light source unit. Brightness can be shown.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a view showing a light diffusion sheet according to an embodiment of the present invention. 2 is a view of the light diffusion sheet shown in FIG. 1 as viewed from the A direction.

  The light diffusion sheet 1 shown in FIG. 1 has surface layer regions 11 and 13 and a middle layer region 12 between the surface layer regions 11 and 13. As shown in FIG. 2, the surface layer regions 11 and 13 include a sea phase 111 made of the first resin and an island phase 112 made of the second resin, and the middle layer region 12 made of the first resin. And the island phase 114 made of the second resin. Further, the surface layer regions 11 and 13 and the middle layer region 12 have pores 115 in a small proportion or not at all.

  The thickness of the light diffusion sheet 1 is preferably 0.05 mm to 0.5 mm in consideration of light transmittance, ease of winding in the process, strength of the sheet itself, and the like. In addition, the ratio of the thickness of the middle layer region 12 to the thickness of the light diffusing sheet 1 is preferably 20% to 80% in consideration of the light diffusing characteristics, the obtained luminance, and the like.

  In FIGS. 1 and 2, the surface layer regions 11 and 13 and the middle layer region 12 are clearly partitioned, but there is an interface between the surface layer regions 11 and 13 and the middle layer region 12. In addition, between the surface layer regions 11 and 13 and the middle layer region 12, there is a region in which the structure constituting the surface layer regions 11 and 13 and the structure constituting the middle layer region 12 are mixed.

  The island phases 112 in the surface layer regions 11 and 13 are oriented in a specific direction. This specific direction is the longitudinal stretching direction of the stretching process described later. Therefore, the island phase 112 in the surface layer regions 11 and 13 extends such that the longitudinal direction thereof is along the longitudinal stretching direction. Further, the ratio of the length (aspect ratio) between the orientation direction of the island phase 112 and the direction (thickness direction) orthogonal to the orientation direction in the cross section of the surface layer regions 11 and 13 is 6-30. In this specification, that the island phase 112 is oriented in a specific direction includes not only the case where all the island phases 112 are oriented in a specific direction, The case where it is oriented along a direction other than a specific direction is also included.

  Unlike the surface layer regions 11 and 13, the middle layer region 12 includes island phases 114 that are not substantially oriented in a specific direction. The ratio of the length (aspect ratio) between the orientation direction of the island phase 114 in the cross section of the middle layer region 12 and the direction (thickness direction) perpendicular to the orientation direction is 0.7 to 3.3. . Here, most of the island phases 114 in the middle layer region 12 do not have to be oriented in a specific direction, and the island phases 112 of the surface layer regions 11 and 13 may be partially included. In addition, the pores 115 in the surface layer regions 11 and 13 and the middle layer region 12 are formed in the stretching process described later and are filled with the sea phases 111 and 113 by the subsequent heat treatment, but can be completely filled with the sea phases 111 and 113 May remain. Even in such a case, the pores 115 may remain in the surface layer regions 11 and 13 and the middle layer region 12 as long as the light diffusion characteristics can be exhibited.

  The combination of the first resin and the second resin is substantially incompatible. Thus, the structure of the sea phase 111 and the island phase 112 can be formed by using a combination of substantially incompatible resins. Further, the melting point of the first resin constituting the sea phase 111 is set to be lower than the melting point of the second resin constituting the island phase 112. The melting point here refers to the crystalline melting point or the minimum melt processing temperature when the resin is crystalline, and the glass transition point or the minimum melt processing temperature when the resin is amorphous.

  The first resin is preferably a polyolefin resin. Among these, a polypropylene resin is preferable. Here, the polypropylene resin refers to a homopolymer of propylene or a copolymer with a monomer such as ethylene that can be copolymerized with propylene. Further, the second resin is preferably a polycarbonate resin. Here, the polycarbonate resin refers to an aromatic polycarbonate, a linear polycarbonate, or a branched polycarbonate that is used alone or in combination. The content weight ratio between the first resin and the second resin is preferably 30/70 to 70/30 in consideration of ease of taking the sea-island structure.

  The light diffusion sheet according to the present invention preferably has a haze value of 90 or more in consideration of light transmittance and the like. The light diffusion sheet according to the present invention preferably has a total light transmittance of 80% or less. Furthermore, it is preferable that the light diffusing sheet according to the present invention contains 5% or less of a component that travels straight through the light diffusing sheet out of the total transmitted light. Due to these characteristics, when the light diffusion sheet is used for a light source unit and the display panel is illuminated with the light source unit, the brightness of the display panel can be increased and at the same time, the diffusibility can be obtained in a balanced manner.

Next, the manufacturing method of the light-diffusion sheet which has the said structure is demonstrated.
In the method for producing a light diffusion sheet according to the present invention, a step of forming a sheet body composed of a first resin and a second resin that is incompatible with the first resin, and biaxial stretching with respect to the sheet body Performing a treatment to cause interfacial separation between the first resin and the second resin to generate pores between the first resin and the second resin, and a sheet body after biaxial stretching In contrast, the method includes a step of performing a heat treatment at a temperature equal to or higher than the melting point of the first resin and lower than the melting point of the second resin to fill the pores with the first resin.

  The manufacture of the light diffusion sheet according to the present invention is performed by, for example, a manufacturing apparatus shown in FIG. This manufacturing apparatus includes a reflection sheet manufacturing line X and a diffusion sheet manufacturing line Y. The reflection sheet production line X includes an extruder 31 that mixes and extrudes a resin, a film forming machine 32 that is disposed in a subsequent stage of the extruder 31 and that forms the material mixed in the extruder 31 into a sheet body, and a film forming process. Longitudinal stretching machine 33 that is disposed downstream of machine 32 and performs longitudinal stretching on the sheet body, and lateral stretching machine that is disposed downstream of longitudinal stretching machine 33 and that performs lateral stretching on the longitudinally stretched sheet body. 34 and a winder 35 that is disposed downstream of the transverse stretching machine 34 and winds up the sheet body that has been subjected to the biaxial stretching process. Further, the diffusion sheet production line Y includes a heat treatment device 36 that performs heat treatment on the sheet main body after the biaxial stretching treatment in a state where the sheet main body is fixed so that there is no dimensional change in the surface direction, and a subsequent stage of the heat treatment apparatus 36. And a winder 37 that winds up the sheet body after the heat treatment.

  In the extruder 31, the dried first resin and second resin are melted and mixed, and the obtained mixed material is extruded and sent to the film forming machine 32 side. In the extruder 31, when the resin passes through a gap between the cylinder and the screw or a gap between the screws, a shearing force due to the rotation of the screw causes a normal size of about several μm from the pellet of about several μm. It is subdivided into large sized dispersed phases. At this time, by appropriately setting the shape of the screw of the extruder, the cylinder temperature, the number of rotations of the screw, etc., the average value and distribution of the size into which the resin is divided can be adjusted.

  In the extruder 31, for example, the melted and mixed raw resin is extruded into a sheet form from a die attached to the tip. It is presumed that different morphologies are formed in the surface layer portion and the middle layer portion depending on the viscosity of the resin, the mixing ratio, the kneading state, the shear stress received by the resin from the die wall, and the degree of the shear rate.

  The film forming machine 32 is constituted by a cooling roller, and the resin extruded from the die of the extruder 31 is cooled and solidified by the cooling roller and formed into a sheet body. The formed sheet body is sent to the longitudinal stretching machine 33 and subjected to stretching processing in the longitudinal direction. In the longitudinal stretching machine 33, by stretching the peripheral speed of the heating roll, stretching in the longitudinal direction is realized by friction between the roll and the sheet. Specifically, after preheating the sheet body, the sheet body is stretched. The sheet body subjected to the longitudinal stretching process is continuously sent to the lateral stretching machine 34 and subjected to the stretching process in the lateral direction (a direction substantially orthogonal to the longitudinal direction). In the transverse stretching machine 34, after the sheet body is preheated, the sheet body is stretched. In this way, by performing a biaxial stretching process on the sheet body, it is possible to form a sheet having surface layer regions and intermediate layer regions having different morphologies and having pores due to interfacial peeling.

  In the step shown in FIG. 3, the case where the sheet body is subjected to the stretching process in the longitudinal direction after the stretching process in the longitudinal direction is described, but the present invention is not limited to this, and the sheet body is subjected to the lateral direction. A method of performing a stretching process in the longitudinal direction after the stretching process, a method of simultaneously performing a stretching process in the longitudinal direction and a stretching process in the transverse direction, and a stretching process in the longitudinal direction and / or the transverse direction after the biaxial stretching process. The method of performing again etc. can be employ | adopted. The stretching ratio of the biaxial stretching process is 1.5 times or more in each of the machine direction (MD) and the transverse direction (TD), and the area stretching ratio is from 3 times to 50 times. Preferably, MD and TD are each 2 times or more, and the area magnification is 4 times or more and 30 times or less. In the stretching treatment, it is preferable to perform stretching at as low a temperature as possible in order to generate pores due to interfacial peeling.

  Although the sheet body after biaxial stretching treatment depends on the stretching method, if the sheet body is thermally contracted in the vicinity of the stretching temperature after stretching, the sheet body is largely thermally contracted in either the longitudinal direction or the transverse direction or in both the longitudinal direction and the transverse direction. For this reason, in this invention, it is preferable that the thermal contraction rate in 150 degreeC / 30 minutes is 15% or less in any of a vertical direction and a horizontal direction. This heat shrinkage rate is preferably 12% or less, particularly preferably 10% or less. For this reason, it is preferable to perform relaxation heat treatment on the sheet body after the biaxial stretching treatment. In this relaxation heat treatment, in order to suppress thermal contraction of the sheet main body, for example, the heat treatment is performed while restraining the end of the sheet main body.

  In the apparatus shown in FIG. 3, the sheet body is conveyed by a roller to an extruder 31, a film forming machine 32, a longitudinal stretching machine 33, a lateral stretching machine 34, and a winder 35, and is wound up. The sheet main body is conveyed to the take-up machine 37 by a roller and wound up. However, in the present invention, the sheet main body may be continuously conveyed by a roller over all the processes, You may comprise so that it may send to the following process, after winding up a sheet | seat main body.

  Here, as described above, since the sheet main body has the property of being thermally contracted, the heat treatment for melting the first resin is performed without stretching while restraining the end of the sheet main body. Therefore, in this heat treatment, the end of the sheet main body is constrained and the dimension in the surface direction is maintained, so that the thickness is reduced by heat shrinkage. Moreover, you may perform heat processing in a non-stretched state using a extending | stretching processing apparatus.

  Conditions such as the temperature and time of the heat treatment can be appropriately set according to the types of the first resin and the second resin, under the restriction that the temperature is higher than the melting point of the first resin and lower than the melting point of the second resin. . For example, when the first resin is a polypropylene resin and the second resin is a polycarbonate resin, the heat treatment is preferably performed at about 160 ° C. to 200 ° C. for 10 minutes to 30 minutes.

  Such a light diffusion sheet includes a sea phase composed of a first resin and an island phase composed of a second resin that is incompatible with the first resin, and has a surface layer region and a middle layer region. The island phase is oriented in a specific direction in the surface layer region, and the island phase in the middle layer region is not oriented in the specific direction. In such a configuration, the island phase in the middle layer region is not oriented in a specific direction but is spherical, so that the lens effect is mainly exerted from its shape, and mainly contributes to light collection, that is, luminance improvement. it is conceivable that. On the other hand, since the island phase in the surface layer region is oriented in a specific direction and has a rod shape, it is considered that the lamp image is removed by diffusing light from the light source from the shape. This light diffusing sheet achieves a balance between the improvement of brightness and the removal of the lamp image, that is, the contradictory phenomenon of light condensing and diffusing properties. As a result, the lamp image of the light source is displayed without reducing the brightness. The light from the light source can be diffused without any problem.

  The light diffusion sheet having the above configuration is disposed in the light source unit of the liquid crystal display device. FIG. 4 is a view showing a liquid crystal display device using the light diffusion sheet according to the embodiment of the present invention. The liquid crystal display device shown in FIG. 4 mainly includes a liquid crystal panel 21 and a light source unit 22 that makes light incident on the liquid crystal panel 21. The liquid crystal panel 21 includes a pair of glass substrates 211 and 212 and a liquid crystal layer 213 sandwiched between the glass substrates 211 and 212. The light source unit 22 includes a light source 221 such as a cold cathode tube, and a light diffusion sheet 222 according to the present invention disposed between the light source 221 and the liquid crystal panel 21. In such a liquid crystal display device, the light from the light source 221 passes through the light diffusion sheet 222 and enters the liquid crystal panel 21.

  Since this liquid crystal display device uses the light diffusion sheet according to the present invention, it is possible to perform screen display without revealing the lamp image of the light source in a state having sufficient luminance. In the liquid crystal panel 21, description of various optical elements such as a polarizing plate protective film, a retardation film, a diffusion plate, an alignment film, a transparent electrode, and a color filter that are usually used is omitted.

Next, examples performed for clarifying the effects of the present invention will be described.
Example 1
8 kg per hour of 55 parts by weight of polypropylene resin having a melt flow rate of 1.4 (Novatech, Nippon Polypro) and 45 parts by weight of polycarbonate resin having a melt flow rate of 5.3 (Iupilon, manufactured by Mitsubishi Engineering Plastics) Was fed to the extruder at a speed of, melted and mixed, charged into a twin-screw extruder rotating in the same direction at 100 rpm, and the raw sheet was wound at a winding speed of 0.2 m / min and a die temperature of 230 ° C. This original fabric sheet was 1.5 mm thick.

  Next, the obtained raw fabric sheet is passed through a roll gap heated to 160 ° C. to form a sheet body, and the circumferential speed of the roll is adjusted so that the sheet body is stretched three times in the extrusion direction. Stretching was performed. Next, using a chuck type tenter heated to 155 ° C., the sheet width is adjusted in the transverse direction by adjusting the chuck width so that the sheet is stretched four times in the direction perpendicular to the extrusion direction (lateral direction). did. Thereby, the biaxial stretching process was performed with respect to the sheet | seat main body.

  Next, using a chuck type tenter heated to 180 ° C. with respect to the biaxially stretched sheet body, the inlet and outlet chuck widths are the same, in a state where the sheet body is not stretched and in-plane shrinkage, A light diffusion sheet (Example 1) was obtained by heat treatment for 20 minutes. When this light diffusion sheet was examined with a scanning electron microscope (S-4700, manufactured by Hitachi, Ltd.), it had a three-layer structure including a surface layer region and a middle layer region. The micrographs are shown in FIG. 5 (surface layer region) and FIG. 6 (middle layer region), respectively. As can be seen from FIG. 5, the island phases are oriented in a specific direction.

  The particle diameter distribution in the minor axis direction and the major axis direction of the longitudinal direction of the island phase in the surface layer region was examined. The results are shown in FIGS. 7 and 8, respectively. From the particle size distribution shown in FIGS. 7 and 8, the aspect ratio between the orientation direction of the island phase and the direction perpendicular to the orientation direction was about 5 to 10. Further, the particle size distribution in the longitudinal stretching direction in the middle layer region was examined. The result is shown in FIG. One (left) bar graph in FIG. 9 shows the particle size distribution in the longitudinal stretching direction, and the other bar graph shows the particle size distribution in the thickness direction. From the particle size distribution shown in FIG. 9, it was found that the vertical and horizontal particle size distributions of the island phases are almost the same, and the spherical distribution has an aspect ratio of about 1.

  Moreover, it was 99.02 when the haze value was measured by Nippon Denshoku Industries Co., Ltd. haze meter NDH2000 using D65 light source about this light-diffusion sheet. Moreover, front luminance measurement and lamp image evaluation were performed on this light diffusion sheet. The front luminance and the lamp image were evaluated by measuring with a two-dimensional color luminance meter CA-2000 manufactured by Konica Minolta by arranging a light diffusion sheet on the backlight of the liquid crystal television LC26BD1 manufactured by Sharp Corporation. The result is shown in FIG. Furthermore, when the total light transmittance of this light diffusing sheet was measured with a Nippon Denshoku Industries Haze Meter NDH2000, it was 69.31%. The manufacturing conditions and evaluation results described above are shown in Table 1 below.

(Comparative Example 1)
A raw sheet was prepared in the same manner as in Example 1 except that a polypropylene resin having a melt flow rate of 10.5 (Novatec, manufactured by Nippon Polypro Co., Ltd.) was used. The original fabric sheet was sandwiched between hot plates heated to 200 ° C., and heated and pressed at a gauge pressure of 80 kg / cm 2 to prepare a light diffusion sheet of Comparative Example 1. When this light diffusion sheet was examined with a scanning electron microscope, as shown in FIG. 10 (surface layer region) and FIG. 11 (middle layer region), the light diffusion sheet had a structure in which polycarbonate was distributed in a granular manner throughout the surface region. The aspect ratio of 6 to 30 was not satisfied. Moreover, it did not have a three-layer structure.

  Further, when the haze value of this light diffusing sheet was measured in the same manner as in Example 1, it was 98.57. Further, for the light diffusion sheet, front luminance measurement and lamp image evaluation were performed in the same manner as in Example 1. The results are also shown in FIG. Moreover, when the total light transmittance was measured about this light-diffusion sheet, it was 80.16%. The manufacturing conditions and evaluation results described above are also shown in Table 1 below.

(Comparative Example 2)
A raw sheet was prepared in the same manner as in Example 1 except that the polypropylene resin and the polycarbonate resin were the same amount of 50 parts by weight, and the feed amount per hour was 5 kg. The original fabric sheet was sandwiched between hot plates heated to 200 ° C., and heated and pressed at a gauge pressure of 80 kg / cm 2 to prepare a light diffusion sheet of Comparative Example 1. When this light diffusing sheet was examined with a scanning electron microscope, as shown in FIG. 12 (surface layer region) and FIG. 13 (middle layer region), the light diffusion sheet had a structure in which polycarbonate was distributed in a rod shape throughout, and a three-layer structure. Did not have.

  Further, the haze value of this light diffusing sheet was measured in the same manner as in Example 1, and it was 99.07. Further, for the light diffusion sheet, front luminance measurement and lamp image evaluation were performed in the same manner as in Example 1. The results are also shown in FIG. Further, the total light transmittance of this light diffusing sheet was measured and found to be 63.86%. The manufacturing conditions and evaluation results described above are also shown in Table 1 below.

  For reference, FIG. 14 also shows the front luminance and the lamp image of only the light source (CCFL). As can be seen from FIG. 14, the liquid crystal television using the light diffusing sheet of Example 1 has no portion where the brightness rapidly increases depending on the position, and there is no lamp image, and the entire surface is about 5500 Cd / m 2 or more. The brightness was shown. This is because the light diffusion sheet has a surface layer region having an island phase oriented in a specific direction and a middle layer region having an island phase not oriented in a specific direction, so that the brightness enhancement ability and the lamp image are It is thought that the light diffusing ability that does not appear is exhibited.

  On the other hand, the liquid crystal television using the light diffusing sheet of Comparative Example 1 had a luminance of about 5500 Cd / m 2 or less over the entire surface, although there was no portion where the luminance suddenly increased depending on the position. This is presumably because the light diffusion sheet is composed only of a region having an island phase that is not oriented in a specific direction, so that the luminance enhancement ability is not exhibited. Further, the liquid crystal television using the light diffusion sheet of Comparative Example 2 has a relatively high luminance, but has a position where the luminance rapidly increases depending on the position. Since this position corresponds to the arrangement position of the light source, it can be considered that a lamp image appears. This is presumably because the light diffusing sheet is composed only of regions having island phases oriented in a specific direction, so that the light diffusing ability to the extent that a lamp image does not appear is not exhibited.

(Example 2)
A light diffusion sheet (Example 2) was produced in the same manner as in Example 1 except that the heat treatment temperature was 185 ° C. When this light diffusion sheet was examined with a scanning electron microscope, it had a three-layer structure including a surface layer region and a middle layer region. Further, the haze value of this light diffusing sheet was measured in the same manner as in Example 1, and it was 99.02. Further, when this light diffusion sheet was subjected to front luminance measurement and lamp image evaluation, substantially the same results as in Example 1 were obtained. Further, when the total light transmittance of this light diffusing sheet was measured, it was 74.46%. The manufacturing conditions and evaluation results described above are also shown in Table 1 below.

(Example 3)
A light diffusion sheet (Example 3) was produced in the same manner as in Example 1 except that the heat treatment temperature was set to 190 ° C. When this light diffusion sheet was examined with a scanning electron microscope, it had a three-layer structure including a surface layer region and a middle layer region. Further, the haze value of this light diffusing sheet was measured in the same manner as in Example 1, and it was 99.99. Further, when this light diffusion sheet was subjected to front luminance measurement and lamp image evaluation, substantially the same results as in Example 1 were obtained. Further, when the total light transmittance of this light diffusing sheet was measured, it was 74.39%. The manufacturing conditions and evaluation results described above are also shown in Table 1 below.

Example 4
A light diffusion sheet (Example 4) was produced in the same manner as in Example 3 except that the stretching ratio in the transverse direction was 3 times. When this light diffusion sheet was examined with a scanning electron microscope, it had a three-layer structure including a surface layer region and a middle layer region. Further, the haze value of this light diffusing sheet was measured in the same manner as in Example 1, and it was 99.07. Further, when this light diffusion sheet was subjected to front luminance measurement and lamp image evaluation, substantially the same results as in Example 1 were obtained. Further, the total light transmittance of this light diffusing sheet was measured and found to be 67.44%. The manufacturing conditions and evaluation results described above are also shown in Table 1 below.

  As described above, according to the light diffusing sheet of the present invention, when arranged in the light source unit, the shape of the light source does not appear, and high brightness can be exhibited. Moreover, according to the manufacturing method of this invention, since a series of processes can be performed in a sheet state, it is excellent in continuous productivity. Further, since it can be handled in a sheet state, subsequent processes such as punching and cutting are easy, roll shipment is possible, and handling is easy.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, the dimensions, materials, and the like in the above-described embodiment are illustrative, and can be changed as appropriate. In the above embodiment, the case where the present invention is applied to a light source unit of a liquid crystal television has been described. However, the present invention can be similarly applied to a case where it is used for a light source unit of a device other than a liquid crystal television. In addition, various modifications can be made without departing from the scope of the present invention.

  The present invention can be applied to a light source unit of a display device such as a liquid crystal display device.

It is a figure which shows the light-diffusion sheet which concerns on embodiment of this invention. It is the figure which looked at the light-diffusion sheet shown in FIG. 1 from the A direction. It is a figure which shows the manufacturing apparatus used for the manufacturing method of the light-diffusion sheet which concerns on embodiment of this invention. It is a figure which shows the liquid crystal display device using the light-diffusion sheet which concerns on embodiment of this invention. 2 is a scanning electron micrograph showing a cross section in the longitudinal stretching direction of a surface layer region of the light diffusion sheet of Example 1. FIG. 2 is a scanning electron micrograph showing a cross section in the longitudinal stretching direction of the middle layer region of the light diffusion sheet of Example 1. FIG. 2 is a diagram showing a particle size distribution (minor axis direction) in the longitudinal stretching direction of the surface layer region of Example 1. FIG. FIG. 3 is a diagram showing a particle size distribution (longitudinal direction) in the longitudinal stretching direction of the surface layer region of Example 1. It is a figure which shows the particle diameter distribution of the longitudinal stretch direction of the middle layer area | region of Example 1. FIG. 3 is a scanning electron micrograph showing a cross section in the longitudinal stretching direction of the surface layer region of the light diffusion sheet of Comparative Example 1. FIG. 4 is a scanning electron micrograph showing a cross section in the longitudinal stretching direction of the middle layer region of the light diffusion sheet of Comparative Example 1. 6 is a scanning electron micrograph showing a cross section in the longitudinal stretching direction of a surface layer region of a light diffusion sheet of Comparative Example 2. FIG. 6 is a scanning electron micrograph showing a cross section in the longitudinal stretching direction of the middle layer region of the light diffusion sheet of Comparative Example 2. FIG. It is a figure which shows the front luminance and lamp image of a liquid crystal display device at the time of arrange | positioning a light-diffusion sheet.

Explanation of symbols

1,222 Light diffusion sheet 11,13 Surface layer region 12 Middle layer region 21 Liquid crystal panel 22 Light source unit 111,113 Sea phase 112,114 Island phase 115 Pore 211,212 Glass substrate 213 Liquid crystal layer 221 Light source

Claims (11)

  A light diffusion sheet comprising a sea phase composed of a first resin and an island phase composed of a second resin that is incompatible with the first resin, and having a surface layer region and a middle layer region, wherein the surface layer region In the cross section, the island phase is oriented in a specific direction, the aspect ratio between the orientation direction of the island phase and the direction orthogonal to the orientation direction in the cross section is 6 to 30, and the middle layer region is substantially oriented. The light diffusion sheet is characterized in that the aspect ratio of the island phase in the cross section is 0.7 to 3.3.   The light diffusion sheet according to claim 1, wherein a content weight ratio between the first resin and the second resin is 30/70 to 70/30.   The light diffusion sheet according to claim 1 or 2, wherein a ratio of the thickness of the middle layer region to the thickness of the light diffusion sheet is 20% to 80%.   The light diffusion sheet according to any one of claims 1 to 3, wherein a haze value is 90 or more.   The light diffusion sheet according to any one of claims 1 to 4, wherein the total light transmittance is 80% or less.   The light diffusing sheet according to any one of claims 1 to 5, wherein a component that travels straight through the light diffusing sheet out of the total transmitted light is 5% or less.   The light diffusion sheet according to any one of claims 1 to 6, wherein the thickness is 0.05 mm to 0.5 mm.   The light diffusion sheet according to any one of claims 1 to 7, wherein the first resin is a polyolefin-based resin and the second resin is a polycarbonate resin.   The light diffusion sheet according to claim 8, wherein the polyolefin resin is a polypropylene resin.   A liquid crystal panel having a liquid crystal layer sandwiched between a pair of glass substrates, and the light diffusion sheet according to any one of claims 1 to 9, wherein light from a light source is transmitted through the light diffusion sheet and the light diffusion sheet is transmitted. A liquid crystal display device comprising: a light source unit that is incident on a liquid crystal panel.   A step of molding a sheet body composed of a first resin and a second resin that is incompatible with the first resin, and a biaxial stretching process is performed on the sheet body to form the first resin and the second resin. Interfacial delamination with the resin to generate pores between the first resin and the second resin, and the sheet body after biaxial stretching with respect to the melting point of the first resin. Performing a heat treatment at a temperature lower than the melting point of the two resins, and filling the pores with the first resin.

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