JP2008065297A - Light diffusion sheet, manufacturing method thereof and its use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet capable of reducing scintillation up to a sufficiently satisfiable level when the light diffusion sheet is used as a light diffusion screen. <P>SOLUTION: The light diffusion sheet is constituted by layering a light diffusion layer 1 which contains transparent fine particles in a transparent base material on a main layer 2, wherein a difference (¾Nd-Nb¾) between a refractive index Nd of the transparent fine particles and a refractive index Nb of the transparent base material is 0.02 or less, a volume average particle size of the transparent fine particles is 2 to 13 μm, a ratio (Rz/Sm) of ten points average roughness Rz based on JIS-B0601:1994 to average space Sm is 0.02 to 0.10 on the surface of the light diffusion layer, the density of protrusions is 500 to 10,000 pieces/mm<SP>2</SP>and the haze based on JIS-K7136 is 30 to 80%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light diffusive sheet suitably used for, for example, a Fresnel lens sheet constituting a light diffusive screen useful as a display member of a rear projection type projection television, a manufacturing method thereof, and a use thereof.

  A light diffusive screen having a Fresnel lens sheet and a lenticular lens sheet is used as a display member of a rear projection type projection television. As the Fresnel lens sheet and the lenticular lens sheet constituting the light diffusive screen, the light diffusibility is used. A sheet having a Fresnel lens or a lenticular lens formed on its surface is used. However, the conventional light diffusing screen has a problem that uneven brightness of emitted light, that is, so-called scintillation occurs.

  So far, as a method for reducing the scintillation of the light diffusing screen, 1) a method of adding transparent fine particles having a light diffusing effect into the light diffusing sheet (see, for example, Patent Document 1), and 2) light diffusion. There has been proposed a method (see, for example, Patent Document 2) for providing a fine uneven shape on the surface of a conductive sheet.

  Furthermore, a method is also known in which a light diffusing layer containing transparent fine particles having a light diffusing effect is provided on the surface of the light diffusing sheet to give a fine uneven shape to the sheet surface. In this method, the portion of the light diffusing sheet that diffuses light is the interface between the irregularities on the surface outside the light diffusing layer and the air, and the interface between the transparent fine particles inside the light diffusing layer and the substrate that forms the sheet. Both. For example, if the light incident side surface of the Fresnel lens sheet has such a light diffusion layer, the distance between the light diffusion layer of the Fresnel lens sheet and the light diffusion layer of the lenticular lens sheet can be maximized. It is believed that an effect can be expected to reduce scintillation. In the light diffusing sheet having such a light diffusing layer on the surface, the scintillation tends to be reduced as the transparent fine particles having a smaller difference in refractive index from the base material and a smaller average particle diameter are used. It is known that there is.

JP 2000-221601 A JP 2000-180968 A

However, as described above, the provision of a light diffusing layer to which transparent fine particles having a light diffusing effect are added on the surface of the light diffusing sheet satisfies the scintillation while having a haze suitable for a light diffusing screen. It is difficult to reduce the level to a possible level, and in some cases, scintillation that would impede practical use may occur.
Specifically, as described above, it was considered that the transparent fine particles to be added to the light diffusion layer are preferably fine particles having a refractive index difference as small as possible with the base material. When transparent fine particles having a difference close to 0 are added to the transparent base material, light hardly diffuses inside the base material, and the light diffusion effect by the transparent fine particles protruding on the surface of the layer occupies most. That is, the state of the transparent fine particles on the surface of the light diffusion layer, that is, the surface state of the light diffusion layer greatly affects the scintillation. However, depending on the conditions such as molding, it may be difficult to form an optimal surface state with less scintillation. Moreover, in order to project many transparent fine particles on the surface of the layer, it is necessary to add a large amount of transparent fine particles to the transparent substrate, but this is disadvantageous in terms of cost. Therefore, normally, transparent fine particles having a slight difference in refractive index from the substrate have been preferably used. However, even when transparent fine particles having a slight difference in refractive index from the substrate are used, the degree of scintillation depends on the surface state of the light diffusion layer, and light diffusion outside the light diffusion layer (surface irregularities) If the scintillation reduction effect is not sufficiently obtained depending on the balance between the light diffusion at the interface between air and air) and the light diffusion inside the light diffusion layer (light diffusion at the interface between the transparent fine particles and the substrate) Had occurred.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a light diffusive sheet that can reduce scintillation to a level that can be satisfactorily satisfied when a light diffusive screen is used, and a manufacturing method that can easily obtain the light diffusable sheet. And a Fresnel lens sheet using the light diffusing sheet.

In order to reduce the scintillation of a light diffusive sheet having a light diffusing layer containing a transparent fine particle in a transparent substrate, the present inventors have conducted extensive research to solve the above problems. More precise control of the balance between light diffusion outside the layer (light diffusion at the interface between the surface irregularities and air) and light diffusion inside the light diffusion layer (light diffusion at the interface between the transparent fine particles and the substrate) It was important to do this, and it was necessary to have parameters that could accurately grasp the light diffusion outside and inside the light diffusion layer. The light diffusion inside the light diffusion layer can be grasped by the difference (| Nd−Nb |) between the refractive index (Nd) of the transparent fine particles and the refractive index (Nb) of the transparent substrate. External light diffusion includes the volume average particle diameter of the transparent fine particles, the ratio (Rz / Sm) of the ten-point average roughness (Rz) of the light diffusion layer surface to the average interval (Sm) of the irregularities, and the protrusions on the surface of the light diffusion layer. It is found that the density can be grasped, and further, when each of these parameters is in a specific range, it is found that the scintillation can be most reduced while having a specific range of haze suitable for the light diffusing screen. It was.
In addition, in light of the fact that a light diffusive sheet that satisfies the above-mentioned characteristics could not be easily obtained by the conventional manufacturing method, as a result of examining a method for easily obtaining this, after co-extrusion in the co-extrusion molding method It has been found that when cooling with a plurality of cooling rolls, the front and back surfaces of the extruded laminated sheet are controlled and the interval between specific cooling rolls is controlled.
The present invention has been completed based on these findings.

That is, the light diffusive sheet of the present invention is a light diffusive sheet in which a light diffusing layer containing transparent fine particles in a transparent base material is laminated on a main layer, and the refraction of the transparent fine particles The difference (| Nd−Nb |) between the refractive index (Nd) and the refractive index (Nb) of the transparent substrate is 0.02 or less, and the volume average particle size of the transparent fine particles is 2 to 13 μm. On the surface of the light diffusion layer, the ratio (Rz / Sm) of the ten-point average roughness (Rz) based on JIS-B0601: 1994 to the average interval of irregularities (Sm) is 0.02 to 0.10, the protrusion density Is 500 to 10,000 pieces / mm ² , and haze based on JIS-K7136 is 30 to 80%.

  The method for producing a light diffusing sheet according to the present invention comprises a step of coextruding a light diffusing layer forming material and a main layer forming material comprising transparent fine particles and a transparent substrate from a die, and then a plurality of laminated sheets extruded. In the method for producing the light diffusive sheet of the present invention, the laminated sheet immediately after being extruded is a first cooling roll and a second cooling adjacent to the first cooling roll. After passing between the rolls while the main layer side is in contact with the second cooling roll, it is cooled on the second cooling roll in the same state, and then the interval between the second cooling roll and the second cooling roll is It passes between the 3rd cooling roll arrange | positioned so that it may become larger than the thickness of a lamination sheet, It is made to send to a 3rd cooling roll, It is characterized by the above-mentioned.

  The Fresnel lens sheet of the present invention is a Fresnel lens sheet that constitutes a light diffusive screen for projection televisions in combination with a lenticular lens sheet, and is characterized by using the light diffusive sheet of the present invention. .

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that the light diffusable sheet which can reduce a scintillation to the level fully satisfied when it is set as a light diffusable screen can be provided by an easy method. Such a light diffusive sheet of the present invention is extremely effective for a Fresnel lens sheet constituting a light diffusive screen in order to effectively suppress scintillation.

The light diffusing sheet of the present invention is a sheet in which a light diffusing layer 1 is laminated on a main layer 2 as shown in FIGS. 1 (a) and 1 (b).
The light diffusion layer 1 in the present invention is a layer in which transparent fine particles are contained in a transparent substrate.

  As the transparent base material constituting the light diffusion layer 1, a highly transparent thermoplastic resin generally used for optical applications is used. Specifically, acrylic resins such as methyl methacrylate polymer, methyl methacrylate-methyl acrylate copolymer, methyl methacrylate-styrene copolymer, methyl methacrylate-styrene-butadiene copolymer, and polycarbonate Examples thereof include resins and transparent polystyrene resins. These resins may be reinforced with rubber, and depending on the purpose, a light diffusing agent, an antioxidant, a plasticizer, a release agent, a colorant, an antistatic agent, an ultraviolet absorber, One or more of various additives such as a flame retardant may be added.

  Examples of the transparent fine particles contained in the light diffusion layer 1 include thermoplastic resins such as methyl methacrylate polymer, methyl methacrylate-methyl acrylate copolymer, methyl methacrylate-styrene copolymer, and styrene polymer. In addition to crosslinked particles made of talc, glass beads, silicone particles and the like are used.

  In the present invention, the transparent fine particles contained in the light diffusion layer 1 have a volume average particle size of 2 to 13 μm, preferably 2 to 11 μm, more preferably 2 to 9 μm, and still more preferably 4 to 6 μm. It is good to be. When the volume average particle size of the transparent fine particles contained in the light diffusing layer 1 is less than 2 μm, the effect of coloring will appear on the sheet due to light diffraction, while when it exceeds 13 μm, the desired haze is obtained. Therefore, the projection density does not reach the range described later.

  The content (concentration) of the transparent fine particles in the light diffusion layer 1 is preferably 1 to 40% by mass, and more preferably 3 to 30% by mass. If the concentration of the transparent fine particles in the light diffusion layer 1 is less than 1% by mass, the haze may not be 30% or more. On the other hand, if it exceeds 40% by mass, the haze may not be 80% or less. In addition, the density | concentration of the transparent fine particle in this invention has shown the ratio (mass ratio) of the transparent fine particle with respect to the total amount of a transparent base material and transparent fine particle in percentage.

  The layer thickness of the light diffusing layer 1 is not particularly limited, but is usually 10 to 500 μm, preferably 40 to 400 μm. If the layer thickness of the light diffusion layer 1 is less than 10 μm, the content of the transparent fine particles may be excessive in order to increase the haze to 30% or more. On the other hand, if it exceeds 500 μm, the haze is 80% or less. In order to achieve this, the concentration of the transparent fine particles is lowered, and the projection density may be reduced.

  In the present invention, the difference (| Nd−Nb |) between the refractive index (Nd) of the transparent fine particles constituting the light diffusion layer 1 and the refractive index (Nb) of the transparent substrate is 0.02 or less. When both are selected in such a combination that the difference in refractive index between the transparent fine particles and the transparent substrate falls within the above range, the closer the refractive index difference (| Nd−Nb |) is to 0, the more the light diffusion layer 1 No internal diffusion occurs, and the diffusion due to the unevenness formed by the projections of the transparent fine particles on the surface becomes strong. In particular, when the refractive index difference (| Nd−Nb |) is 0 (both refractive indexes (Nd) and When (Nb) is the same), light is diffused only by the surface irregularities. In the present invention, when the unevenness of the surface of the light diffusion layer 1 greatly affects the light diffusion, the volume average particle diameter of the transparent fine particles and the ten-point average roughness (Rz) of the surface of the light diffusion layer 1 are as follows. By setting the ratio (Rz / Sm) between the average spacing of the projections and the unevenness (Rz / Sm) and the protrusion density on the surface of the light diffusion layer 1 to a specific range, good haze is exhibited and sufficient light diffusion is ensured. It is possible to effectively suppress scintillation.

  The surface of the light diffusion layer 1 in the present invention has a ratio (Rz / Sm) between the ten-point average roughness (Rz), which is a roughness parameter in accordance with JIS-B0601: 1994, and the average interval of unevenness (Sm). It is 0.02 to 0.10, preferably 0.02 to 0.07. Here, the ten-point average roughness (Rz) is a roughness parameter in the vertical direction of the actual surface, whereas the average interval (Sm) of the unevenness is a roughness parameter in the horizontal direction of the actual surface. The ratio of Rz to Sm (Rz / Sm) is effective for expressing the surface irregularity shape and the average peak angle, and within this range, the refractive index (Nd) of the transparent fine particles and the transparent group When the difference (| Nd−Nb |) from the refractive index (Nb) of the material is in the above range, it is possible to exhibit good haze and secure sufficient light diffusion and effectively suppress scintillation. is there. If Sm is about the same size, the greater the Rz / Sm, the more light is scattered and the haze becomes higher. On the other hand, if Rz / Sm is approximately the same, the haze is approximately the same, but generally scintillation decreases as Rz and Sm decrease.

The light diffusion layer 1 in the present invention has a protrusion density on the surface of 500 to 10,000 / mm ² , preferably 1000 to 10,000 / mm ² . When the protrusion density is within the above range, light is finely scattered on the surface of the light diffusion layer 1, so that the difference between the refractive index (Nd) of the transparent fine particles and the refractive index (Nb) of the transparent substrate (| Nd When -Nb |) is in the above range, good haze is exhibited and sufficient light diffusion is ensured, so that scintillation can be effectively suppressed. When the protrusion density is less than 500 pieces / mm ² , the scintillation is not sufficiently reduced. On the other hand, a protrusion density exceeding 10,000 pieces / mm ² is difficult to achieve with transparent fine particles having a volume average particle diameter of 2 to 13 μm. . In order to make the protrusion density within the above range, it is effective to adjust the concentration of the transparent fine particles added to the light diffusion layer 1. For example, to increase the number of protrusions, the transparent fine particles added to the light diffusion layer 1 What is necessary is just to raise a density | concentration. However, normally, depending on the difference (| Nd−Nb |) between the refractive index (Nd) of the transparent fine particles and the refractive index (Nb) of the transparent base material, the haze becomes too high when the concentration of the transparent fine particles is increased. In some cases, sufficient screen brightness cannot be obtained. Further, when the concentration of the transparent fine particles is increased, a problem may occur depending on the size of the particles. If the volume average particle size of the transparent fine particles is too large, the projection density reaches the above range when the desired haze is obtained. On the other hand, if it is too small, coloring of the sheet may occur due to light diffraction. In the light diffusing sheet of the present invention, the refractive index difference (| Nd−Nb |) between the transparent fine particles and the transparent base material, the volume average particle diameter and the haze of the transparent fine particles are set in a specific range together with the protrusion density. Therefore, all these problems can be avoided.

  The material which comprises the main layer 2 in this invention is not restrict | limited in particular, For example, the thing similar to resin mentioned above as a transparent base material which comprises the light-diffusion layer 1 can be used. Further, the main layer 2 in the present invention may not contain any transparent fine particles as shown in FIG. 1 (a), or contains transparent fine particles as shown in FIG. 1 (b). It may be. However, when the main layer 2 contains transparent fine particles, the content thereof is preferably 20% or less of the concentration of the transparent fine particles in the light diffusion layer 1. There is no restriction | limiting in particular as transparent fine particle contained in the main layer 2, For example, the thing similar to what was mentioned above as a transparent base material in the light-diffusion layer 1 can be used.

  The layer thickness of the main layer 2 is not particularly limited, but is usually preferably 0.5 to 5 mm. If the thickness of the main layer 2 is less than 0.5 mm, the strength of the light diffusing sheet may be insufficient. On the other hand, if it exceeds 5 mm, this is combined with a lenticular lens sheet as a Fresnel lens sheet to diffuse light. When the screen is made to be a reflective screen, the distance between the Fresnel lens sheet and the lenticular lens sheet is increased, and the resolution may be lowered.

  The light diffusing sheet of the present invention has a haze according to JIS-K7136 of 30 to 80%. Within this range, the intensity of the light source of the projection TV to be applied, the size of the screen, and the transmission degree of the image light of the combined lenticular lens The optimal value may be appropriately set according to the above.

  The method for producing a light diffusing sheet according to the present invention comprises a step of coextruding a light diffusing layer forming material and a main layer forming material comprising transparent fine particles and a transparent substrate from a die, and then a plurality of laminated sheets extruded. This is a method for easily producing the light diffusable sheet of the present invention in which the light diffusion layer is provided on the main layer by cooling with a cooling roll.

  The light diffusion layer forming material used in the production method of the present invention is appropriately selected by combining the above-described transparent fine particles and the transparent base material so as to satisfy the above-described refractive index difference (| Nd−Nb |). What is necessary is just to use what was mixed and disperse | distributed. As the main layer forming material used in the production method of the present invention, for example, the same material as the above-described transparent substrate can be used, but it is not limited thereto.

  There is no restriction | limiting in particular about the method at the time of performing coextrusion molding, What is necessary is just to carry out according to a normal coextrusion molding method. For example, a light diffusing layer forming material and a main layer forming material are melt-kneaded using a uniaxial or biaxial extruder of 2 to 3 units, respectively, and then coextruded through a feed block die or a multi-manifold die, and light diffusion is performed. It can be performed by integrating the layer and the main layer as a laminated sheet.

  The laminated sheet extruded by the coextrusion molding is cooled and solidified by a roll unit having a plurality of cooling rolls. As shown in FIG. 2, the roll unit used here includes a first cooling roll 4 and a second cooling roll 5 adjacent to the first cooling roll 4, after the laminated sheet 3 immediately after being extruded from the die 7. The second cooling roll 5 is cooled while being closely attached and wound around the second cooling roll 5, and then the second cooling roll 5 and the second cooling roll 5 are disposed in the vicinity. It is wound around the three cooling rolls 6 and cooled on the third cooling roll 6. If necessary, the roll unit may include fourth and subsequent cooling rolls (not shown) that are sequentially arranged adjacent to the third cooling roll 6 in the same manner.

  In the production method of the present invention, when the laminated sheet 3 is cooled by the roll unit, the laminated sheet 3 immediately after being extruded is sandwiched between the first cooling roll 4 and the second cooling roll 5, and the second cooling roll 5. When cooling above, as shown in FIG. 2, the main layer 3b side is in contact with the second cooling roll 5, passing between the first and second cooling rolls, and in the same state on the second cooling roll 5 It is important to cool. That is, the light diffusion layer 3 a containing transparent fine particles is on the side in contact with the first cooling roll 4 between the first cooling roll 4 and the second cooling roll 5, and is cooled on the second cooling roll 5. Will be cooled outside. Thereby, in the 2nd cooling roll 5, a light-diffusion layer will be rapidly cooled on the outer side, and more transparent fine particles may protrude on the surface due to the difference in thermal shrinkage between the transparent substrate and the transparent fine particles. As a result, it is possible to obtain a light diffusive sheet that satisfies the above-described protrusion density and the like.

  In the manufacturing method of the present invention, after that, the gap between the second cooling roll 5 and the third cooling roll 6 disposed so that the distance from the second cooling roll 5 is slightly larger than the thickness of the laminated sheet 3 is then passed. It is important to send it to the third cooling roll 6. In other words, the second cooling roll 5 and the third cooling roll 6 are not disposed in close contact as in a normal roll unit, but are disposed so that the interval is slightly larger than the thickness of the laminated sheet 3. It is important to cool with a roll unit. Thereby, it is prevented that the transparent fine particles protruding due to the linear pressure applied to the laminated sheet 3 between the second cooling roll 5 and the third cooling roll 6 are pushed back, and the surface state having moderate unevenness is maintained. As a result, it is possible to obtain a light diffusive sheet that satisfies the above-described protrusion density and the like.

Although the space | interval of the 2nd cooling roll 5 and the 3rd cooling roll 6 will not be restrict | limited if it is slightly larger than the thickness of the lamination sheet 3, specifically, 0.01-3 mm is usually larger than the thickness of the lamination sheet 3. The interval may be about as large as possible, and is more preferably about 0.1 to 0.5 mm larger than the thickness of the laminated sheet 3. If the space between the second cooling roll 5 and the third cooling roll 6 is excessively widened, the laminated sheet 3 does not move smoothly from the second cooling roll 5 to the third cooling roll 6 and is wound around the second cooling roll 5. When peeling from the second cooling roll 5, there is a possibility that a trace may be attached in the sheet width direction.
In the production method of the present invention, conditions other than those described above are not particularly limited, and may be appropriately set according to a conventionally known method.

  The Fresnel lens sheet of the present invention is a Fresnel lens sheet that constitutes a light diffusive screen for projection televisions in combination with a lenticular lens sheet, and uses the light diffusive sheet of the present invention. The light diffusing sheet of the present invention can be used as a Fresnel lens sheet by forming a Fresnel lens on the surface thereof. The light diffusing sheet of the present invention is combined with a lenticular lens sheet as shown in FIG. 3 to form a light diffusing screen (screen set).

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to a following example.
The measurement methods of physical properties and scintillation evaluation methods in the following examples and comparative examples are as follows.
<Layer Thickness> By observing the end surface of the obtained laminated sheet (light diffusing sheet) with an optical microscope, the thickness of the entire sheet (total thickness) (mm) and the thickness of the light diffusing layer (surface layer thickness) (μm) ) Was measured.

  <Haze> The obtained laminated sheet (light diffusive sheet) is cut into 4 cm × 6 cm, and is diffusing using a haze meter (“HM-150” manufactured by Murakami Color Science Laboratory Co., Ltd.) in accordance with JIS-K7136. The sample was set so that the layer (surface layer) side was the light incident side, and haze (%) was measured.

  <10-point average roughness (Rz), average interval of unevenness (Sm)> The obtained laminated sheet (light diffusive sheet) was cut into 4 cm × 6 cm, and the surface roughness was measured on the light diffusion layer (surface layer) side. Using a machine (“SJ-201P” manufactured by Mitutoyo Corporation), the ten-point average roughness (Rz) (μm) and the average interval of unevenness (Sm) (μm) were measured. In the measurement, based on JIS-B0601: 1994, the cutoff value was 0.8 mm, the evaluation length was 4 mm, and the other measurement conditions were default values.

<Protrusion Density> The obtained laminated sheet (light diffusive sheet) was cut into 4 cm × 6 cm, and the light diffusion layer (surface layer) side was cut using a laser ultra-deep microscope (“VK-8500” manufactured by Keyence Corporation). was observed at 500 magnifications to count the projections by the transparent fine particles in the range of 300 [mu] m × 225 .mu.m, in terms of the number per 1 mm ^2, it was determined protrusion density (number / mm ^2).

  <Scintillation Evaluation> The obtained laminated sheet (light diffusive sheet) and a lenticular lens having a black stripe with a pitch of 0.25 mm were bonded together as shown in FIG. 3 to obtain a screen set. Prepare a replacement of a commercially available 62-inch rear projection TV screen with a DLP light source with a transparent acrylic plate, output a white screen, and place a screen set in the center of the screen. It stuck so that the diffusion layer 1 side might become a light source side. Then, visual sensory evaluation of scintillation was performed from a place 1 m away from the screen, and the case where the scintillation was the least was set to 1, and the case where the scintillation was the most was determined in 10 steps.

The transparent base materials and transparent fine particles used in the following examples and comparative examples are as follows.
・ Transparent substrate: Low moisture-absorbing acrylic resin (“SUMIPEX HW” manufactured by Sumitomo Chemical Co., Ltd .; Nb = 1.535)
Transparent fine particles (A): crosslinked particles made of methyl methacrylate-styrene copolymer (“XX-69K” manufactured by Sekisui Plastics Co., Ltd .; Nd = 1.525, volume average particle diameter 5.5 μm)
Transparent fine particles (B): crosslinked particles made of methyl methacrylate-styrene copolymer (“XX-71K” manufactured by Sekisui Plastics Co., Ltd .; Nd = 1.525, volume average particle size 10.5 μm)
Transparent fine particles (C): crosslinked particles made of a styrene polymer (“SBX-12” manufactured by Sekisui Plastics Co., Ltd .; Nd = 1.590, volume average particle size 11.4 μm)

(Examples 1-3)
The transparent substrate was put into a first extruder (manufactured by Tanabe Plastics Co., Ltd .; screw diameter 40 mm, uniaxial, with vent). On the other hand, in the second extruder (manufactured by Tanabe Plastics Co., Ltd .; screw diameter 20 mm, uniaxial, with vent), transparent fine particles (A) were mixed with a transparent substrate, and the fine particle concentrations (transparency shown in Table 1). A solution diluted to have a ratio of the transparent fine particles to the total amount of the base material and the transparent fine particles) was added. Next, after co-extrusion molding from the first extruder and the second extruder, it was cooled by three cooling rolls (polishing roll, vertical type) shown in FIG. 2 to obtain a laminated sheet (light diffusing sheet). . At this time, by opening the upper side of the multi-manifold die (manufactured by Tanabe Plastics Co., Ltd .; 2 types, 3 layers distribution) and closing the lower side and co-extrusion, the surface of the layer extruded from the first extruder in the laminated sheet By making it contact with the second cooling roll and setting the space between the second cooling roll and the third cooling roll slightly wider than the total thickness of the laminated sheet, no linear pressure was applied to the laminated sheet. .
The physical properties (haze, Rz / Sm, protrusion density, etc.) of the obtained light diffusive sheet are as shown in Table 1, and the scintillation evaluation results were all good as shown in Table 1.

Example 4
Instead of the transparent fine particles (A), the transparent fine particles (B) are mixed with the transparent base material, and the fine particle concentrations shown in Table 1 (the ratio of the transparent fine particles to the total amount of the transparent base material and the transparent fine particles) A light diffusable sheet was obtained in the same manner as in Examples 1 to 3, except that the diluted product was added to the second extruder.
The physical properties (haze, Rz / Sm, protrusion density, etc.) and scintillation evaluation results of the obtained light diffusive sheet were as shown in Table 1. Although the scintillation is slightly higher than that of Example 1 in which the haze is at the same level, it was not at a level causing a practical problem.

(Comparative Example 1)
Instead of the transparent fine particles (A), the transparent fine particles (C) are mixed with the transparent base material, and the fine particle concentrations shown in Table 1 (the ratio of the transparent fine particles to the total amount of the transparent base material and the transparent fine particles) A light diffusable sheet was obtained in the same manner as in Examples 1 to 3, except that the diluted product was added to the second extruder.
The physical properties (haze, Rz / Sm, protrusion density, etc.) and scintillation evaluation results of the obtained light diffusive sheet were as shown in Table 1. It was found that there was much scintillation compared to Example 1 where the haze was almost the same level.

It is sectional drawing which shows embodiment of the light diffusable sheet | seat of this invention. It is a schematic diagram which shows the roll unit used for the manufacturing method of the light diffusable sheet of this invention. It is sectional drawing which shows the screen set at the time of using the light diffusable sheet | seat of this invention for a Fresnel lens sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusing layer 2 Main layer 3 Laminated sheet 3a Light diffusing layer 3b Main layer 4 First cooling roll 5 Second cooling roll 6 Third cooling roll 7 Die 10 Light diffusing sheet 11 Lenticular lens sheet

Claims (3)

A light diffusing sheet in which a light diffusing layer containing transparent fine particles in a transparent substrate is laminated on a main layer,
The difference (| Nd−Nb |) between the refractive index (Nd) of the transparent fine particles and the refractive index (Nb) of the transparent substrate is 0.02 or less, and the volume average particle size of the transparent fine particles is In addition, the ratio (Rz / Sm) of the ten-point average roughness (Rz) and the average interval (Sm) of irregularities in accordance with JIS-B0601: 1994 is 0.02 to 2 to 13 μm. 0.10, protrusion density of 500 to 10,000 pieces / mm ^2, the haze of the compliant JIS-K7136 is 30% to 80%, light diffusing sheet, characterized in that. The light diffusing layer forming material comprising the transparent fine particles and the transparent substrate and the main layer forming material are coextruded from the die, and then the extruded laminated sheet is cooled by a plurality of cooling rolls. A method for producing the light diffusing sheet according to claim 1,
The laminated sheet immediately after being extruded passes between the first cooling roll and the second cooling roll adjacent to the first cooling roll in a state where the main layer side is in contact with the second cooling roll, and then remains in the same state. Cooling on the second cooling roll, and then passing between the second cooling roll and the third cooling roll arranged so that the distance between the second cooling roll and the second cooling roll is larger than the thickness of the laminated sheet. (3) A method for producing a light diffusing sheet, characterized by being sent to a cooling roll.   A Fresnel lens sheet comprising a light diffusive sheet according to claim 1, wherein the Fresnel lens sheet is used in combination with a lenticular lens sheet to constitute a light diffusing screen for a projection television.

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