JP2012045914A - Production method of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an optical film which is hard to generate a lateral stripe extending in a film width direction and also has a good optical performance, even if molding speed is increased to enhance productivity.SOLUTION: In the production method of the optical film, a thermoplastic resin film 6, which is melt-extruded, is pressed by a metallic-mold roll 2 and a metallic endless belt 3, so that a fine structure is formed on the surface of the thermoplastic resin film 6, wherein when the glass transition temperature of the thermoplastic resin film is denoted by Tg, the coefficient of kinetic friction between the metallic endless belt 3 and the thermoplastic resin film 6 is ≤0.3 at the transition temperature Tg of +40°C and also the surface roughness Ra of the metallic endless belt 3 is ≤0.2 μm.

Description

  The present invention relates to a method for producing an optical film used for optical applications or display fields, and more specifically, by pressing a melt-extruded thermoplastic resin film with a mold roll and a metal endless belt, The present invention relates to a method for producing an optical film that forms a microstructure on the surface of a thermoplastic resin film.

  In a display device such as a liquid crystal display device, an optical film such as a sheet for increasing luminance and a sheet for diffusing light is used. In this type of optical film, fine irregularities are formed on the surface of the optical film. In recent years, in order to improve the optical characteristics, the miniaturization of the concavo-convex pattern has further advanced.

  An example of a method for producing the optical film as described above is disclosed in Patent Document 1 below. In the method for producing an optical film described in Patent Document 1, a thermoplastic resin is melt-extruded from a T die. The melt-extruded thermoplastic resin film is guided between a mold roll having a concavo-convex pattern formed on the outer surface and a metal endless belt. And a fine uneven | corrugated pattern is formed in the surface of a thermoplastic resin film by pressing a thermoplastic resin film with a metal mold | die roll and a metal endless belt. In the method for producing an optical film described in Patent Document 1, an optical film having excellent flatness and extending in a direction intersecting with a long thermoplastic resin film, that is, in which a horizontal stripe extending in the width direction is hardly generated can be obtained. It is described.

JP 2007-245700 A

  In recent years, there has been a strong demand for increasing productivity in the production of optical films. In the method for producing an optical film described in Patent Document 1, in order to increase productivity, the rotational speed of the mold roll may be increased. However, in the manufacturing method described in Patent Document 1, when the rotational speed of the mold roll, that is, the line speed is increased, horizontal streaks may occur in the obtained optical film. Therefore, an optical film with good appearance cannot be obtained with high productivity.

  An object of the present invention is a method of manufacturing an optical film in which a thermoplastic resin film is formed by melt extrusion and pressed by a mold roll and a metal endless belt, and the productivity is increased by increasing the rotation speed of the mold roll. Even if it is a case where it raises, it is providing the manufacturing method of an optical film which is hard to produce the horizontal stripe extended in a film width direction.

  The optical film manufacturing method according to the present invention is a method for manufacturing an optical film that forms a microstructure on the surface of a thermoplastic resin film by pressing a melt-extruded thermoplastic resin film with a mold roll and a metal endless belt. Is the method.

  In the present invention, when the glass transition temperature of the thermoplastic resin is Tg, the coefficient of dynamic friction between the metal endless belt and the thermoplastic resin film at a temperature of Tg + 40 ° C. is 0.3 or less, and the metal endless belt The surface roughness Ra of the surface is 0.2 μm or less.

  In the method for producing an optical film according to the present invention, it is preferable that a coating layer containing a fluororesin is provided on the surface of the metal endless belt that is in contact with the thermoplastic resin film. As a result, the thermoplastic resin film and the metal endless belt are continuously more slippery, and the occurrence of lateral stripes can be more reliably suppressed.

  In the method for producing an optical film according to the present invention, the coefficient of dynamic friction between the metal endless belt and the thermoplastic resin film is 0.3 or less, and the surface roughness Ra of the surface of the metal endless belt is 0.2 μm or less. Therefore, even when the rotational speed of the mold roll is increased to increase the productivity, the slipping property between the metal endless belt and the thermoplastic resin film is improved. Therefore, the thermoplastic resin film is continuously shifted to the metal endless belt. Therefore, even when productivity is increased, it is possible to effectively suppress the occurrence of horizontal stripes extending in the width direction of the optical film. Therefore, it is possible to provide an optical film that is inexpensive and has good appearance.

FIG. 1 is a schematic configuration diagram for explaining a method for producing an optical film according to an embodiment of the present invention.

  Details of the present invention will be described below.

  The optical film manufacturing method according to the present invention is a method for manufacturing an optical film that forms a microstructure on the surface of a thermoplastic resin film by pressing a melt-extruded thermoplastic resin film with a mold roll and a metal endless belt. Is the method. FIG. 1 is a schematic configuration diagram for explaining an embodiment of the method for producing an optical film of the present invention.

  As shown in FIG. 1, a molten thermoplastic resin film 6 is extruded from a die 1. The thermoplastic resin film 6 is guided between the mold roll 2 and the metal endless belt 3. The mold roll 2 has a fixed pivot point and is rotated in the direction of the arrow shown. On the outer surface of the mold roll 2, a concavo-convex pattern that is reversed with respect to the concavo-convex pattern to be formed on the surface of the thermoplastic resin film is formed.

  On the other hand, the metal endless belt 3 is stretched between the rolls 4 and 5. By rotating one of the roll 4 and the roll 5 in the illustrated arrow direction, the metal endless belt 3 is moved in the illustrated arrow direction.

  The thermoplastic resin film 6 is pressed by the mold roll 2 and the metal endless belt 3. Thereby, the concavo-convex pattern is transferred to the surface of the thermoplastic resin film 6 in contact with the mold roll 2. Accordingly, a fine uneven pattern is formed on the surface of the thermoplastic resin film 6.

  On the other hand, annealing rolls 7 and 8 are disposed at the subsequent stage of the mold roll 2. The thermoplastic resin film 6 to which the fine concavo-convex pattern has been transferred is annealed by the annealing rolls 7 and 8 and conveyed in the direction of the arrow shown in the drawing.

The optical film manufacturing apparatus shown in FIG. 1 is an example of an apparatus used in the optical film manufacturing method of the present invention. In the present invention, the manufacturing apparatus used has the structure shown in FIG. It is not limited.

  By the way, in the manufacturing method of the optical film described in Patent Document 1 described above, when the line speed is increased by increasing the rotational speed of the mold roll 2, there is a problem that horizontal streaks occur in the thermoplastic resin film 6. I understood. As a result of studying this problem, the inventor of the present application has found that when the rotational speed of the mold roll 2 is increased, intermittent deviation occurs between the thermoplastic resin film and the metal endless belt, thereby causing horizontal stripes. I found out.

  The optical film production method of the present invention is characterized in that the coefficient of dynamic friction between the metal endless belt 3 and the thermoplastic resin film 6 at a temperature of Tg + 40 ° C. is 0, where Tg is the glass transition temperature of the thermoplastic resin. 3 or less and the surface roughness Ra of the surface of the metal endless belt 3 is 0.2 μm or less. Therefore, even when the rotational speed of the mold roll 2 is increased when the thermoplastic resin film is pressed and embossed between the metal endless belt 3 and the mold roll 2, The endless belt 3 and the thermoplastic resin film 6 are continuously displaced. Therefore, since the above-mentioned intermittent deviation is unlikely to occur, the occurrence of lateral stripes can be reliably suppressed.

  In order to suppress the occurrence of lateral streaks by causing the above-described continuous shift, as described above, the dynamic friction coefficient between the metal endless belt 3 and the thermoplastic resin film 6 at a temperature of Tg + 40 ° C. It is necessary to be 0.3 or less. More preferably, it is 0.2 or less. If the dynamic friction coefficient exceeds 0.3, lateral streaks are likely to occur.

  On the other hand, the surface roughness Ra of the portion of the metal endless belt that is in contact with the thermoplastic resin film needs to be 0.2 μm or less, and preferably has a mirror surface state of 0.1 μm or less. When the surface of the portion of the metal endless belt 3 that comes into contact with the thermoplastic resin film 6 becomes rough, the contact area between the metal endless belt 3 and the thermoplastic resin film 6 is reduced, and slipperiness is improved. Therefore, the occurrence of horizontal stripes can be suppressed. However, when the surface roughness Ra exceeds 0.2 μm, the light transmittance is lowered and the optical performance as an optical film cannot be obtained. Therefore, in the present invention, the surface roughness Ra of the surface of the metal endless belt 3 that contacts the thermoplastic resin film 6 needs to be 0.2 μm or less.

  Preferably, it is desirable to provide a coating layer on the surface of the metal endless belt 3 that is in contact with the thermoplastic resin film 6 in order to enhance slipperiness. As such a coating layer, generally, a silicone release agent used as a release agent, or an inorganic release agent such as a fluororesin or a ceramic material can be used.

  Preferably, a coating layer containing a fluororesin is provided as the coating layer. In a fluororesin, particularly polytetrafluoroethylene, the crystal layer and the amorphous layer have a plate-like shape and are easily sheared in the amorphous layer. Therefore, the friction coefficient can be effectively reduced. Therefore, when the fluororesin-containing coating layer is provided, the slipping property between the metal endless belt 3 and the thermoplastic resin film 6 can be further enhanced. Accordingly, it is possible to more reliably suppress the occurrence of lateral stripes.

  In the present invention, the mold roll 2 can be constituted by an appropriate metal roll as long as it has a concavo-convex pattern obtained by inverting the intended concavo-convex pattern on the surface. Examples of such metals include stainless steel, nickel, copper, nickel phosphorus, and the like.

  The metal endless belt can be formed of an appropriate metal such as stainless steel or nickel.

  In the present invention, the thermoplastic resin film used for obtaining the optical film is not particularly limited as long as it is a transparent thermoplastic resin film. That is, an appropriate thermoplastic resin used as a transparent thermoplastic resin for optics can be used. Moreover, materials other than the said transparent thermoplastic resin may be added to the thermoplastic resin film. However, in order to obtain optically excellent performance, it is desirable that the transparent thermoplastic resin occupies 80% by weight or more in the thermoplastic resin composition obtained by adding other materials to the thermoplastic resin.

  Examples of the transparent thermoplastic resin include polycarbonate, acrylic resin, polystyrene, polyvinyl chloride, chain polyolefin such as polypropylene or polymethylpentene, cyclic polyolefin such as cycloolein polymer and norbornene, polyethylene terephthalate, polybutylene terephthalate or polyethylene naphthalene. Examples thereof include polyester such as phthalate, polyamide, polyarylate, and polyimide.

  Of these, polycarbonate is preferred because of its excellent transparency and excellent heat resistance and weather resistance.

  Hereinafter, the present invention will be specifically described with reference to examples of the present invention. However, the present invention is not limited to the following examples.

Example 1
Polycarbonate resin (manufactured by Teijin Chemicals Ltd., trade name: Panlite L-1225LL, transparent, Tg = 143 ° C.) is melt-extruded from a die into a film shape, and an uneven pattern is formed on the surface by inverting the unevenness of the prism sheet. The condensing film was produced at a temperature of 260 ° C. between the mold roll and the metal endless belt on which the coating layer containing a fluororesin made of polytetrafluoroethylene was formed on the outer surface, and the pressure was reduced. . The rotational speed of the mold roll, that is, the line speed was 30 m / min. The prism shape of the condensing film was a shape in which the cross-sectional shape was a triangular prism shape composed of isosceles triangles having an apex angle of 90 degrees, and a plurality of triangular prism shapes were arranged in parallel at a center distance, that is, a pitch of 100 μm. Moreover, the thickness of the condensing film obtained as described above was 200 μm.

(Example 2)
A light-collecting film was produced in the same manner as in Example 1 except that the resin used was changed from polycarbonate to cyclol hen polymer (polyplastics, trade name: TOPAS 6013LS-04, Tg = 138 ° C.). did.

(Example 3)
A condensing film was prepared in the same manner as in Example 1 except that the resin used was changed from polycarbonate to norbornene resin (manufactured by JSR, trade name: ARTON D4531, Tg = 131 ° C.).

(Comparative Example 1)
Instead of the metal endless belt used in Example 1, a metal endless belt constructed in the same manner as in Example 1 except that it does not have a coating layer was used. Otherwise, the same as in Example 1 Thus, a condensing film was produced.

(Comparative Example 2)
Instead of the metal endless belt used in Example 2, a metal endless belt constructed in the same manner as in Example 2 except that it does not have a coating layer was used, and otherwise the same as in Example 2 Thus, a condensing film was produced.

(Comparative Example 3)
Instead of the metal endless belt used in Example 3, a metal endless belt constructed in the same manner as in Example 3 except that it does not have a coating layer was used. Otherwise, the same as in Example 3 Thus, a condensing film was produced.

(Comparative Example 4)
A condensing film was produced in the same manner as in Example 1 except that a metal endless belt whose outer surface was matted was used.

(Evaluation of dynamic friction coefficient)
Resin films formed by melt extrusion used in Examples 1 to 3 and Comparative Examples 1 to 4, respectively, and the same metal endless belts used in Examples 1 to 3 and Comparative Examples 1 to 4 A metal plate was prepared. That is, taking Example 1 as an example, the metal endless belt has a coating layer made of a fluororesin on the surface, so that the prepared metal plate was mirror-finished in the same manner as the endless belt used in Example 1 A metal plate formed by forming a fluororesin coating layer on the metal plate in the same manner as in Example 1 was prepared. Taking Comparative Example 1 as an example, a mirror-finished metal plate having no coating layer made of the fluororesin was prepared.

  And in Examples 1-3 and Comparative Examples 1-4 so that it may become the same combination as Examples 1-3 and Comparative Examples 1-4, it is 40 degreeC rather than the glass transition temperature Tg of the used thermoplastic resin. The resin film was allowed to stand for 5 minutes on each metal plate sample at a high temperature. Thereafter, a load of 170 g is applied from the upper surface of the resin film, and the resistance force when the resin film is moved at a speed of 5 m / min in a direction parallel to the surface where the resin film and the metal plate are in contact is measured with a surface property measuring machine ( Measurement was made using HEIDON 14DR, manufactured by Shinto Kagaku Co., and the dynamic friction coefficient was calculated. That is, the dynamic friction coefficient is obtained by the dynamic friction coefficient = F / P, where F is the resistance force and P is the vertical load applied to the resin film.

(Measurement of surface roughness)
An appropriate amount of a two-component mixed silicone resin (manufactured by Struers, trade name: Reprise-F5) was dropped on the surface of the metal endless belt used in Examples 1 to 3 and Comparative Examples 1 to 4, and the surface shape was transferred. A replica was produced. Thereafter, based on this replica, the surface roughness Ra was measured using a measuring apparatus (P.16 +, manufactured by KLA Tencor).

(Evaluation of Examples and Comparative Examples)
The condensing films obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were cut into dimensions of 300 mm length × 400 mm width. The condensing film sample thus obtained is placed on a flat panel (Gunma Ushio Electric, product number: FP-404) so that the ridge line direction of the prism lens of the condensing film is the horizontal direction of the screen, that is, the horizontal direction. Placed. Thereafter, the front luminance was measured using EzContrast EI80 manufactured by ELDIM. The relative luminance was determined with the front luminance when the light collecting film was not placed on the flat panel as 100. The results are shown in Table 1 below.

(Horizontal stripe evaluation)
The condensing films obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were visually observed, and the presence or absence of horizontal stripes extending in the film width direction was evaluated. The results are shown in Table 1 below.

  As is apparent from Table 1, in Examples 1 to 3 and Comparative Example 4 in which the dynamic friction coefficient is 0.3 or less, the line speed is as high as 30 m / min, but no horizontal streak was observed. On the other hand, in Comparative Examples 1 to 3, since the line speed was as high as 30 m / min, horizontal streaks occurred.

  Moreover, in Examples 1-3 and Comparative Examples 1-3 whose surface roughness Ra is 0.2 micrometer or less, it turns out that front brightness can be made high compared with the comparative example 4. FIG. Therefore, it can be seen that by setting the dynamic friction coefficient to 0.3 or less and the surface roughness Ra to 0.2 μm or less, it is possible to suppress the occurrence of lateral stripes without deteriorating the optical characteristics.

DESCRIPTION OF SYMBOLS 1 ... Die 2 ... Mold roll 3 ... Metal endless belt 4, 5 ... Roll 6 ... Thermoplastic resin film 7, 8 ... Annealing roll

Claims (2)

By pressing a melt-extruded thermoplastic resin film with a mold roll and a metal endless belt, a method for producing an optical film that forms a microstructure on the surface of the thermoplastic resin film,
When the glass transition temperature of the thermoplastic resin is Tg, the coefficient of dynamic friction between the metal endless belt and the thermoplastic resin film at a temperature of Tg + 40 ° C. is 0.3 or less, and the surface of the metal endless belt The manufacturing method of the optical film whose surface roughness Ra is 0.2 micrometer or less. The manufacturing method of the optical film of Claim 1 with which the coating layer containing a fluororesin is provided in the surface of the said metal endless belt.

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