JP3558697B2 - Molding method for resin sheet - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for forming a resin sheet. The resin sheet molded according to the present invention is suitably used for a lenticular lens sheet for a screen of a projector TV or the like.
[0002]
[Prior art]
When a resin molded product is used as the screen of the rear projection type projector TV, it is generally manufactured by an extrusion method in many cases. However, a lenticular lens having a pitch of 0.3 mm or less is often used as a screen for a rear projection projection TV using a liquid crystal panel, and in that case, it is difficult to manufacture by a extrusion method. Therefore, a pressing method is often used. At this time, the shape of the manufactured lens often has an acute-angled shape as disclosed in, for example, JP-A-58-145933.
[0003]
[Problems to be solved by the invention]
When a screen is manufactured by a press method using a thermoplastic resin containing light diffusing fine particles, it is necessary to prepare an original plate for the press, cut the work after the press, and have a problem of many processes. is there. When the injection molding method is used as the molding method, the production and cutting processes of the original plate can be omitted, so that the cost can be reduced. However, there are the following problems in molding an acute-angled shape by the injection molding method.
[0004]
First, in the injection molding method, the resin is usually filled from one gate, but the aspect condition t / at · t / b (where a is the width of the molded sheet, b is the height of the molded sheet, t represents the thickness of the molded sheet.) When the thickness is small with respect to the width and the height, the time difference between the filling of the resin becomes large and the original sheet shape is applied to a part of the molded sheet where the resin does not easily flow around. An area with an insufficient mold (an area having a rounder shape than the original plate) is generated. In a region where the shaping is insufficient, the diffusion angle of light becomes small, resulting in uneven brightness on the screen.
[0005]
Secondly, if the gate of the mold is enlarged and the resin is easily filled, the resin flows out before the filling of the resin into the mold starts, and the molding is insufficient in a region where the molding is not sufficiently performed and solidified. As in the first problem, the brightness may be uneven on the screen.
[0006]
Third, if the filling time is shortened and the flow speed of the resin is increased in order to achieve sufficient shaping, the flow between the thermoplastic resin and the light-diffusing fine particles becomes non-uniform, and the difference in speed becomes large. An area where the fine particles aggregate may be generated, and the brightness may become uneven on the screen.
[0007]
Fourth, even when the molding is sufficiently performed, the shape may be deformed at the time of release, and a defect called a release mark may occur.
[0008]
The present invention has been made in view of the above-described problems, and has a resin sheet that can be sufficiently shaped, has no aggregation of light diffusing fine particles and does not generate a release mark, and can produce a high-quality screen. An object is to provide a method for molding.
[0009]
[Means for Solving the Problems]
The resin sheet molding method of the present invention that achieves the above object has a surface shape of a fine uneven structure having a tip angle smaller than 90 ° and a tip radius of curvature smaller than 20 μm, and an aspect condition t / a. 50% of a resin sheet satisfying <0.015, t / b <0.019 (where a represents the width of the molded sheet, b represents the height of the molded sheet, and t represents the thickness of the molded sheet). a thermoplastic resin having an average particle diameter contains light diffusing fine particles is less than 17 .mu.m, the width of the gate is formed by injection molding using a mold is at least 30% of the width of the molded sheet, light diffusing fine particles This is a method of forming a resin sheet without aggregation . The width of the gate of the mold is preferably 50% or more of the width of the molded sheet, and more preferably 80% or more.
[0010]
In the molding method, it is particularly effective that the thickness of the gate having the smallest thickness of the die used for injection molding is 1.2 mm or less in order to solve the second problem. Further, the third problem is solved when the 50% average particle diameter of the light diffusing fine particles is 13 μm or less, or the specific gravity difference between the thermoplastic resin and the light diffusing fine particles is 0.2 or less. It is particularly preferable in terms of performing. Further, when the mold is opened after the injection molding, it is particularly preferable to release the mold from the fine uneven structure surface in order to solve the fourth problem. The 50% average particle size is one of the methods of expressing the size of a particle, and when all the particles are arranged in descending order, the weight becomes 50% of the weight of all the particles. Refers to particle size.
[0011]
【Example】
Example 1
A lenticular lens sheet having a width of 212 mm, a height of 158 mm, and a thickness of 2 mm is produced by injection molding. At this time, the width of the gate of the mold is 205 mm, and the thickness of the thinnest part of the gate is 1.5 mm. The pitch of the lenticular lens is 0.24 mm. PMMA is used as a thermoplastic resin, and 2% of an MS cross-linking resin having a 50% average particle size of 17 μm as light diffusing fine particles is mixed. This was heated to 250 ° C., and injection molding was performed with a filling time of 1 second. A lenticular lens sheet having a more uniform shape than the above-mentioned molding and a good dispersion of the light diffusing fine particles was obtained.
[0012]
Example 2
Molding was performed under the same conditions as in Example 1 except that the thickness of the thinnest part of the gate was set to 1 mm. As a result, a more uniform molding was obtained than in Example 1.
[0013]
Example 3
Molding was carried out under the same conditions as in Example 2 except that the 50% average particle size of the light diffusing fine particles was changed to 11 μm. As a result, a uniformly dispersed sheet was obtained with less aggregation of the fine particles than in Examples 1 and 2. Was done.
[0014]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, sufficient shaping is possible, the aggregation of light diffusing fine particles and the generation of a release mark are obtained, and the resin sheet which can manufacture a high quality screen is obtained.

Claims (5)

It has a surface shape of a fine uneven structure in which the angle of the tip is smaller than 90 ° and the radius of curvature of the tip is smaller than 20 μm, and the aspect conditions t / a <0.015 and t / b <0.019 (where a Is the width of the molded sheet, b is the height of the molded sheet, and t is the thickness of the molded sheet.) A resin sheet satisfying 50% average particle diameter of 17 μm or less is used. A method for forming a resin sheet without aggregation of light diffusing fine particles, wherein the resin sheet is formed by injection molding using a metal mold having a gate width of 30% or more of the width of the molded sheet. The method for molding a resin sheet according to claim 1, wherein the thickness of the portion of the mold having the smallest gate thickness is 1.2 mm or less. 3. The method according to claim 1, wherein the light diffusing fine particles have a 50% average particle diameter of 13 [mu] m or less. 4. The method according to claim 3, wherein a difference in specific gravity between the thermoplastic resin and the light diffusing fine particles is 0.2 or less. 2. The method for molding a resin sheet according to claim 1, wherein the mold is released from the surface of the fine uneven structure when the mold is opened after the injection molding.