JP2005283878A - Manufacturing method of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film such as a 1 / 2λ plate or a 1 / 4λ plate used for the purpose of improving the display quality of various liquid crystal display devices such as TN (twisted nematic), STN (super twisted nematic) and VA (vertical alignment). Is provided at low cost by melt extrusion film formation.
SOLUTION: A thermoplastic resin film 5 extruded by a melt extrusion film forming method is cooled by a cooling roll 2 having a glass transition temperature (Tg) of the thermoplastic resin in the range of ± 30 ° C., and a predetermined tension, in particular, The optical film 5 is produced by pulling the film 3 with a tension at which the elongation rate of the film is within 10%, and setting the retardation value of the film to 50 nm to 300 nm.
[Selection] Figure 1

Description

  The present invention relates to a method for producing an optical film. More specifically, the present invention relates to a method for producing an optical film having a retardation value (hereinafter, R value) of 50 nm to 300 nm from which a 1 / 2λ plate, a 1 / 4λ plate, or the like is obtained by a melt extrusion film forming method.

  Conventionally, for various liquid crystal display devices such as TN (twisted nematic), STN (super twisted nematic) and VA (vertical alignment), an optical film such as a 1 / 2λ plate or a 1 / 4λ plate for the purpose of improving display quality. Is used. This optical film manufacturing method includes a method of reheating a thermoplastic resin film formed by a solution casting method or a melt extrusion method in a separate process and stretching it uniaxially, triacetyl cellulose (TAC), etc. There is a method of applying a liquid crystal polymer on the transparent film.

  However, productivity is low in the solution casting method, and when it is stretched in a separate process, the process is increased and the yield is reduced. In the method of applying the liquid crystal polymer, an expensive liquid crystal polymer is used. An expensive optical film could not be provided.

  In the present invention, a method for manufacturing an optical film having an R value of 50 nm to 300 nm at a low cost by controlling the film forming conditions in the melt extrusion film forming method by tackling the cost reduction of an optical film that is difficult to solve with the prior art. provide.

  As a result of conducting a technical study as to whether the present inventor can provide an optical film at a low cost, by adjusting the cooling roll temperature and the film take-up tension in the process of producing a thermoplastic resin film by the melt extrusion film-forming method. The present inventors have found a method for producing an optical film having a preferable R value in one step, and have reached the present invention.

  That is, the present invention cools a thermoplastic resin film extruded by a melt extrusion film forming method with a cooling roll having a temperature in the range of glass transition temperature (Tg) ± 30 ° C. of the thermoplastic resin, and a predetermined tension, particularly This is a method for producing an optical film, in which the film is drawn with a tension at which the elongation rate of the film is within 10%, and the retardation value of the film is 50 nm to 300 nm.

  As the thermoplastic resin used in the present invention, thermoplastic resins such as polycarbonate resins, polystyrene resins, polymethacrylate resins, polysulfone resins, polynorbornene resins, and cycloolefin resins can be used.

  Polynorbornene-based resins and cycloolefin-based resins have excellent optical properties such as high transparency and low photoelastic coefficient, but have the disadvantage of being extremely fragile due to their high mechanical rigidity. Even if the film is formed by the film method, there are difficulties in handling such as cracking at the time of winding or cracking when it is put into the next stretching step. Accordingly, these polynorbornene resins and cycloolefin resins are particularly suitable resins for the method of the present invention for obtaining an optical film as a final product all at once from the melt extrusion film forming method.

  For the thermoplastic resin used in the method of the present invention, a general-purpose plasticizer such as phosphate ester or phthalate ester can be appropriately used so as to be suitable for the melt extrusion film forming method. These plasticizers are generally used in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the thermoplastic resin.

  The reason why the chill roll temperature is set in the range of Tg ± 30 ° C. of the thermoplastic resin in the method of the present invention is to give an R value of 50 nm to 300 nm, preferably only by the take-up tension of the film. When the chill roll temperature is higher than Tg + 30 ° C. of the thermoplastic resin, the film is stretched in a molten state, so that the R value does not appear. On the other hand, when the temperature of the cooling roll is lower than Tg-30 ° C. of the thermoplastic resin, the film is completely cooled and solidified and does not elongate at all. The cooling roll temperature is preferably in the range of Tg ± 25 ° C. of the thermoplastic resin, more preferably in the range of Tg ± 20 ° C., or a temperature below Tg, that is, Tg-30 ° C. to Tg of the thermoplastic resin, preferably Tg− 30 ° C. to Tg−10 ° C.

  The take-up tension of the film in the method of the present invention can be arbitrarily selected to give an R value of 50 to 300 nm, but preferably the elongation percentage of the film is within 10%, particularly within 5%, more particularly within 3%. It is tension. Such an elongation rate within 10% is useful for obtaining a film having uniform optical characteristics because it prevents the film from causing unevenness in stretching and the R value from fluctuating. Here, the take-up tension for obtaining these elongation rates varies depending on the type of thermoplastic resin, the thickness and width of the film, the temperature of the cooling roll, etc., so it is appropriate to observe the elongation rate and R value of the film at the production site. The tension can be controlled.

In addition, the elongation rate of a film is a value calculated | required by the following formula.
Elongation rate (%) = 100 × (t ₀ −t ₁ ) / t ₀
Here, t ₀ is the thickness of the film on the cooling roll, and t ₁ is the thickness of the film after the take-up roll.

  The R value of the optical film obtained by the method of the present invention is 50 nm to 300 nm. When a film is formed without controlling the film forming conditions as in the method of the present invention in the ordinary melt extrusion film forming method, the R value is usually 50 nm or less, and a 1 / 4λ plate (about 140 nm) or 1 / 2λ plate (About 280 nm) is not obtained. In addition, it is necessary to stretch | stretch a film strongly for R value of 300 nm or more, and the process of extending | stretching by reheating the film obtained by the solution casting method and the melt extrusion film-forming method is generally taken. .

  The method for producing an optical film of the present invention is an inexpensive production of an optical film having an R value of 50 nm to 300 nm by appropriately controlling the cooling roll temperature and film take-up tension of the film forming conditions in the melt extrusion film forming method. It is to provide.

  The apparatus that can be used in the method of the present invention is basically as shown in FIG. 1, from an extruder and a winding device such as a T die 1, a cooling roll 2, a take-up roll 3, and a take-up roll 4. It is a general film manufacturing apparatus configured. Here, the film can be stretched between a cooling roll and a take-up roll. Optionally, an extruder can be appropriately used of a single-screw type or a biaxial type depending on the type of thermoplastic resin. The extrusion direction may be a horizontal direction or a vertical direction with respect to the ground.

  The cooling roll is preferably a mirror roll for an optical film, and the roll temperature is preferably an oil circulation method or heat pipe method that can control the variation in temperature within the roll surface within ± 0.5 ° C. If the in-plane temperature variation is large, the variation of the R value of the final optical film becomes large.

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the examples. Here, the retardation value (R value) was measured with an automatic birefringence meter KOBRA (trademark) manufactured by Oji Scientific Instruments.

[Example 1]
A polynorbornene resin (manufactured by JSR Corporation, Arton resin, Tg: 135 ° C.) is put into a 90 mmφ extruder, a film is melt-extruded from a T die having a width of 1000 mm at 270 ° C., and passed through a cooling roll set at 125 ° C. An optical film having a width of 900 mm, a thickness of 50 μm, and an R value of 135 nm was obtained with a tension that gave an elongation of 4%. The film was a film suitable for a 1 / 4λ plate and could be suitably used as a circularly polarizing plate for LCD antireflection.

[Example 2]
A cycloolefin resin (Nippon Zeon Co., Ltd., ZEONOR resin, Tg: 136 ° C.) is charged into a 90 mmφ extruder, a film is melt-extruded from a T-die having a width of 1000 mm at 260 ° C., and a cooling roll set at 110 ° C. After that, the film was taken up with a tension that gave 2% elongation to obtain an optical film having a width: 930 mm, a thickness: 60 μm, and an R value: 140 nm. The film was a film suitable for a 1 / 4λ plate and could be suitably used as a circularly polarizing plate for LCD antireflection.

[Example 3]
Polycarbonate resin (Pure Ace (trademark), manufactured by Teijin Ltd., Tg: 158 ° C) is put into a 90 mmφ extruder, a film is melt-extruded from a T-die having a width of 1000 mm at 270 ° C, and a cooling roll set at 140 ° C is provided. Then, the film was taken up with a tension that gave an elongation of 7% to obtain an optical film having a width of 900 mm, a thickness of 60 μm, and an R value of 275 nm. The film was a film suitable for a 1 / 2λ plate and a broadband polarization axis rotating plate, and could be suitably used for improving the display quality of LCDs and optical parts of liquid crystal projectors.

[Comparative Example 1]
In Example 1, when the chill roll temperature was set to 100 ° C., the film was completely cooled and solidified, and the R value of the obtained film was 25 nm without elongation even when the take-up tension was the maximum tension of the equipment.

[Comparative Example 2]
In Example 3, when the cooling roll temperature was 190 ° C., the film was stretched by 10% with low tension, but the R value of the obtained film was 15 nm.

It is the schematic of the extrusion film forming apparatus which can be used for the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Extruder and T die 2 ... Cooling roll 3 ... Take-up roll 4 ... Winding roll 5 ... Film

Claims (3)

  The thermoplastic resin film extruded by the melt extrusion film forming method is cooled by a cooling roll having a temperature in the range of the glass transition temperature (Tg) ± 30 ° C. of the thermoplastic resin, and the film is taken out with a predetermined tension. The manufacturing method of an optical film which makes the retardation value of 50 nm-300 nm.   The method for producing an optical film according to claim 1, wherein the predetermined tension is a tension at which an elongation rate of the film is within 10%.   The method for producing an optical film according to claim 1, wherein the thermoplastic resin film is a polynorbornene resin film or a cycloolefin resin film.

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