JPH10100227A - Method for molding thermoplastic resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sheet with an accurately molded uneven shape on the surface and with a thin delustered tone with a central line mean roughness of about 3,000 on the back face. SOLUTION: In a method for molding a thermoplastic resin sheet, when a sheet with an uneven shape on the surface and a flat face on the back face is continuously molded by extruding a thermoplastic resin melt into a sheet from a T-die 2 and placing the melt between a metal roll 6 with an uneven shape on the peripheral face and a rubber roll 5 and cooling and solidifying it, at the outlet part of the T-die 2, a part which is a contact face of the metal roll after extrusion among the molten resin R is controlled at a higher temp. than that of a part which is a contact face of the rubber roll.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thermoplastic resin sheet, and more particularly, to a method for continuously forming a thin sheet of precision molding having an uneven shape on one side.

[0002] Such precision molded thin thermoplastic resin sheets are used for optical applications such as glazing materials and lens sheets for controlling the direction of light emission.

[0003]

2. Description of the Related Art Conventionally, a precision molded sheet made of a thermoplastic resin for optical use has been formed by sandwiching a smooth molded sheet made of an amorphous thermoplastic resin between flat molds having irregularities on the surface. Press method to form irregularities on the sheet surface,
The molten resin is extruded into a sheet shape from a T-die, pressed between a metal roll and a rubber roll having an uneven surface and solidified by cooling, and is manufactured by a so-called embossing method for forming a thin sheet having an uneven surface. I was

The rubber roll used in the embossing method is formed by bonding or casting a rubber layer made of silicone rubber, neoprene rubber or the like on the peripheral surface of a roll iron core, and polishing the peripheral surface with a buff. The surface roughness of this rubber roll is determined by the center line average roughness (J
Ra) specified in IS B0601 was about 5,000 ° or more.

Generally, in the embossing method, the heating temperature of the resin is set to a temperature as high as possible without causing thermal decomposition or the like, increasing the fluidity of the resin, and maintaining the operation stability of the molding process. By setting the heating temperature of the resin to a high temperature as described above, especially when a fine uneven shape is required such as a precision shaping sheet for optical use, T
By pressing and cooling and solidifying the molten resin extruded in the form of a sheet from the die, irregularities on the sheet surface of the metal roll are faithfully and sharply formed according to the irregularities of the metal roll.
Also, the unevenness imparted to the sheet is relaxed by the elasticity of the resin so as not to collapse.

However, under such molding conditions for transferring the irregularities precisely, the irregularities of the metal roll are faithfully and sharply formed on the sheet surface, and the surface roughness of the rubber roll peripheral surface is also formed on the sheet rear surface. Will be transferred faithfully as it is. As a result, the surface roughness of the obtained sheet for optical application became a strong matte tone of Ra3,500 ° or more, which was a factor of disturbing the optical characteristics obtained by precision molding of the uneven shape of the sheet surface.

As a rubber roll for improving the roughness of the sheet surface, Japanese Patent Application Laid-Open No. Hei 8-132515 discloses a technique in which a silicone rubber molded on a roll iron core by casting is used. However, the back surface of the sheet obtained by using this rubber roll is extremely smooth with Ra 1,000 ° or less, and when a plurality of the obtained sheets are used in a stacked state, they adhere to each other and hinder practical use. There are drawbacks such as that the surface is glaring and the eyes of the user are easily fatigued.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object the purpose of having a finely-molded uneven shape on the surface and a thin matte surface with a Ra of about 3,000 °. It is an object of the present invention to provide a thermoplastic resin sheet molding method capable of obtaining a sheet having a tone.

[0009]

According to the method of forming a thermoplastic resin sheet of the present invention, a thermoplastic resin melt is extruded into a sheet shape from a T-die, and is formed between a metal roll and a rubber roll having an irregular shape on the peripheral surface. By sandwiching and cooling and solidifying, the continuous molding of a sheet having an uneven surface and a smooth surface on the back side requires the extrusion of the molten resin at the exit of the T-die to the metal roll contact surface after extrusion. This is characterized in that the temperature of the portion to be formed is controlled to be higher than that of the portion to be the rubber roll contact surface.

The metal roll used in the method of the present invention having an irregular shape on the peripheral surface may be provided with an irregular shape (for example, a large number of peaks having a right-angled isosceles triangular cross section in parallel) depending on the optical application and performance of the obtained sheet. (A concave and convex shape having a saw-tooth cross-sectional shape). The material of the metal roll is not particularly limited as long as it is a material usually used as an embossing roll. In the case of engraving the peripheral surface of a cylindrical roll by cutting, using a precision lathe or the like, an aluminum alloy material is preferably used. Examples of the method of forming the concavo-convex shape include etching, sand blasting, anilox method engraving, and bite cutting engraving, and a means depending on the purpose is appropriately employed. The peripheral surface of the metal roll provided with the uneven shape is difficult to use the obtained sheet for optical applications even if there are slight scratches, so it is assumed that the peripheral surface of the metal roll hardly contains scratches during use. Therefore, it is preferable to perform chromium plating or nickel plating, and when the base material is an aluminum alloy, to perform anodizing treatment or the like.

[0011] On the other hand, the rubber roll used in the method of the present invention is not particularly limited as long as its peripheral surface is polished with a buff or the like to finish the surface. For example, solid rubber having good adhesion to liquid rubber, for example, neoprene A layer of cross-linked rubber such as rubber or silicone rubber is fixedly formed on a roll iron core with an adhesive, and the peripheral surface of this rubber layer is polished with a buff and smoothed. The upper layer is preferably formed into a plurality of layers, and the outer surface of the outermost layer is polished with a buff and finished to be smooth. Particularly, a rubber roll obtained by bonding a neoprene rubber layer on the peripheral surface of a roll iron core, further molding a room-temperature-curable silicone rubber layer on the peripheral surface by casting, and polishing and finishing the peripheral surface is preferably used. You.

The thermoplastic resin used in the method of the present invention is not particularly limited. However, since the obtained sheet is generally used for optical applications, an amorphous colorless and transparent thermoplastic resin, for example, Polycarbonate resin, polymethacrylate resin, polyvinyl chloride resin and the like are preferably used.

[0013] The molding method according to the present invention is characterized in that, at the outlet of the T-die, the temperature of the portion of the molten resin that becomes the metal roll contact surface after extrusion is controlled to be higher than that of the rubber roll contact surface. .

At the exit of the T-die, the temperature difference between the portion of the molten resin that becomes the metal roll contact surface after extrusion and the portion that becomes the rubber roll contact surface after extrusion depends on the characteristics of the resin used, especially the fluidity in the applicable temperature range. It is set appropriately according to the temperature dependency.

Taking polycarbonate resin as an example, T
At the exit of the die, the temperature of the portion of the molten resin that becomes the metal roll contact surface after extrusion may be equal to or lower than the temperature (350 ° C.) at which thermal denaturation of the resin starts, and is preferably 2 ° C.
80-330 ° C. The temperature of the portion of the molten resin that becomes a rubber roll contact surface after extrusion is 250 ° C. or higher at which extrusion molding can be performed stably, and in order to minimize surface roughness transfer of the rubber roll peripheral surface, it is preferable. 260
280 ° C. Under these temperature conditions, the temperature of the portion of the molten resin that becomes the metal roll contact surface after extrusion is controlled to be higher than the temperature of the portion that becomes the rubber roll contact surface.

The heating control means at the outlet of the T-die is as described in the above 2
There is no particular limitation as long as the temperature of the two resin portions can be individually controlled. Because it is desirable to heat as short as possible, preferably an electric heater is provided at the exit of the T-die,
The method of controlling the temperature of the resin with this heater is simple and suitable. In addition, a method of bonding or embedding a heating medium circulation pipe such as heating oil, a jacket, or the like along the lip portion, or a method of electromagnetically heating each lip portion can be applied.

In the method of the present invention, the peripheral surface temperature of the metal roll at the time of sheet forming is determined by the irregularity formed on the peripheral surface.
In order to faithfully and precisely transfer onto the surface of the sheet-like molten resin extruded from the die, it is preferable to maintain the resin in a certain temperature range around the glass transition temperature of the resin. If the peripheral surface temperature of the metal roll is higher than this temperature range, peeling cannot be performed smoothly when the resin sheet is separated from the metal roll, and if the temperature is lower than this temperature range, the metal roll peripheral surface shape is sufficiently transferred to the sheet. Since the resin is cooled and solidified, precise transfer becomes impossible. As a method for controlling the peripheral surface temperature of the metal roll, a method in which a heat medium flow path is provided inside the roll and a heat medium for heating is circulated through the flow path is generally used.

In the method of the present invention, the temperature of the peripheral surface of the rubber roll at the time of sheet molding is preferably controlled as low as possible in order to suppress the transfer of the surface roughness to the obtained sheet. Generally, a method is used in which a heat medium flow path is provided inside the roll and a heat medium for cooling is circulated through the heat medium flow path. Alternatively, a method of directly cooling the peripheral surface may be applied.

[0019]

According to the molding method of the present invention, a specific portion of the molten resin is controlled at a high temperature at the exit of the T-die.
The temperature of the metal roll contact surface of the sheet-like molten resin extruded from the T-die can be higher than the rubber roll contact surface, and the temperature of the rubber roll contact surface does not need to be raised more than necessary. It is possible to increase the transfer rate of the surface irregularities and to suppress the transfer of the surface roughness of the rubber roll as much as possible. In this way, the surface has a concavo-convex shape precisely molded, and the back surface has a surface roughness of Ra3,000.
A thin matte-tone optical application sheet can be obtained.

[0020]

Embodiments of the present invention will be specifically described below.

Example 1 As shown in FIG. 1, a polycarbonate resin heated and melted at 270.degree. C. in an extruder 1 is supplied to a T-die 2 heated to 270.degree. Extruded. At the outlet of the T-die 2, bar-shaped heaters 3 and 4 are provided along a pair of lips, respectively, to control the heating of the metal roll side heater 4 to 300 ° C. and the heating of the rubber roll side heater 3 to 270 ° C. . The sheet-like molten resin R extruded from the exit of the T-die was then pressed between opposed metal rolls 6 and rubber rolls 5.

The peripheral surface of the metal roll 6 has a base of 100 μm,
A large number of 50 μm-height isosceles triangular ridges having a right-angled cross section are provided in parallel, engraved over the entire circumference into a saw-toothed uneven shape, and hard chrome plated thereon. 5 is 2m thick on the peripheral surface of the roll iron core
m neoprene rubber layer was adhered, and a room temperature-curable silicone rubber layer was formed on the peripheral surface thereof by casting so as to have a thickness of 1 mm, and the peripheral surface was polished with a # 1000 buff. Things.

The metal roll 6 circulates 140 ° C. heat medium oil through a heat medium flow path provided inside, and the rubber roll 5 circulates 15 ° C. cooling water through a heat medium flow path provided inside. Was. The formed sheet peeled from the metal roll 6 was removed from the distortion through a plurality of annealing rolls 7 and passed between a pair of take-up rolls 8. Thus, a thin precision molded sheet P having a thickness of 200 μm was obtained as a product.

Comparative Example 1 A sheet was obtained in the same manner as in Example 1 except that the metal roll side heater 4 was heated to 270 ° C.

Comparative Example 2 A sheet was obtained in the same manner as in Example 1 except that the rubber roll side heater 3 was heated to 300 ° C.

Performance Evaluation For the precision molded sheets obtained in Example 1 and Comparative Examples 1 and 2, the ratio of the depth of the valleys of the irregularities on the sheet surface to the height of the peaks of the irregularities on the peripheral surface of the metal roll ( The surface roughness Ra of the back surface of the sheet in contact with the rubber roll, the appearance, and the two sheets on the surface light source device for a liquid crystal display device were each formed with a sawtooth groove of 90 ° on the sheet surface. The luminance in the normal direction, that is, the front luminance (according to JIS C7614) when superimposed so as to have an intersection angle was evaluated. Table 1 summarizes the evaluation results.

[0027]

[Table 1]

As is clear from Table 1, the sheet of Example 1 showed good results in any of the items.

[0029]

According to the method of forming a thermoplastic resin sheet of the present invention, the contact surface of the molten resin extruded from the T-die into the metal roll can be heated to a higher temperature than the rubber roll contact surface. Since the temperature on the surface side does not need to be raised more than necessary, it is possible to increase the transfer rate of the uneven shape on the peripheral surface of the metal roll and to suppress the transfer of the surface roughness of the rubber roll as much as possible. Thus, the surface has an irregular shape precisely molded, and the back surface has a surface roughness of Ra.
A thin matte-tone sheet for optical use of about 3,000 ° can be obtained.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention.

[Explanation of symbols]

 1: Extruder 2: T-die 3: Metal roll side heater 4: Rubber roll side heater 5: Rubber roll 6: Metal roll 7: Annealing roll 8: Take-up roll R: Molten resin P: Precision molded sheet

Claims (1)

[Claims] 1. A thermoplastic resin melt is extruded into a sheet shape from a T-die, pressed between a metal roll and a rubber roll having an irregular shape on the peripheral surface, and cooled and solidified to form an irregular shape on the surface. In addition, in continuously forming a sheet having a smooth back surface, at the exit of the T-die, the temperature of a portion of the molten resin that becomes a metal roll contact surface after extrusion is controlled to a higher temperature than a portion that becomes a rubber roll contact surface. A method for forming a thermoplastic resin sheet.