JP2000319414A - Method for producing optical transparent film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a transparent film for optical use having a low wavelength dispersion characteristic of a refractive index and a low photoelastic coefficient and having very few optical defects. SOLUTION: In the method for producing an optical transparent film by a solution casting method of an alicyclic olefin resin, a coating film is dried by infrared heating, the method for producing an optical transparent film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a transparent optical film. More specifically, the present invention relates to a method for producing an optical transparent film by a solution casting method using an alicyclic olefin resin.

[0002]

2. Description of the Related Art Optically transparent films have been used as retardation compensation films or polarizing plate protective films in liquid crystal displays and the like.

[0003] In recent years, with the trend toward matching with the characteristics of liquid crystal used in a reflection type liquid crystal display device, which is a new display method, and the trend toward a larger screen of the liquid crystal display device, low wavelength dispersion characteristics of refractive index and low photoelastic coefficient have been developed. There is an increasing need for optical transparent films having the following.

[0004]

However, polycarbonate resins, which have been widely used as retardation compensation films, have a large wavelength dispersion of the refractive index, and have an optical characteristic with a liquid crystal used in a reflection type liquid crystal display device. Therefore, it is difficult to improve the display quality of the optical transparent film.

Further, triacetyl cellulose used as a polarizing plate protective film has low dimensional stability with respect to temperature and humidity and generates a large phase difference with respect to stress. In a humid environment, due to the deformation of triacetylcellulose itself on the surface of the polarizing plate and the development of shrinkage stress of the polarizer, stress concentrates on the edges and a phase difference is generated. There was a problem of getting up.

In view of the above, the present inventor has conducted intensive studies to develop an optically transparent film having a low wavelength dispersion characteristic of refractive index and a low photoelastic coefficient and having few optical defects. In the drying step of the coating film by the solution casting method of the olefin resin, when dried using infrared heating,
The present inventors have found that an optically transparent film having a low wavelength dispersion characteristic of a refractive index and a low photoelastic coefficient and having very few optical defects can be obtained, and completed the present invention.

An object of the present invention is to provide a method for producing a transparent optical film having a low wavelength dispersion characteristic of refractive index and a low photoelastic coefficient and having very few optical defects.

[0008]

That is, the present invention provides a method for producing an optically transparent film by a solution casting method of an alicyclic olefin resin, wherein the coating film is dried by infrared heating. It is intended to provide a method for producing a transparent film.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail.

The alicyclic olefin resin used in the present invention means an olefin resin having a cycloaliphatic hydrocarbon in a main chain or a side chain. An optical transparent film having a low wavelength dispersion characteristic and a low photoelastic coefficient can be obtained.

As the cycloaliphatic hydrocarbon, for example,
There is a compound represented by the structural formula shown in "Chemical formula 1".

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As the alicyclic olefin resin, commercially available products can be used. For example, ZEONEX (registered trademark) and ZEONOR (registered trademark) of Nippon Zeon Co., Ltd. having a repeating unit represented by the following “Chemical Formula 2”, and “Chemical Formula 3” below J having a repeating unit of
Arton (registered trademark) of SR Corporation.

[0013]

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In the present invention, the alicyclic olefin resin is formed into a film by a solution casting method. The solution casting method is not particularly limited, and an alicyclic olefin resin solution dissolved in a solvent is applied on a support, for example, a metal endless belt or a smooth resin film.

The solvent used for dissolving the alicyclic olefin resin is basically not problematic as long as it is capable of dissolving the alicyclic olefin resin. In the case of a solvent having an extremely low boiling point, such as methylene chloride, the solvent volatilizes vigorously before entering the drying furnace, and in some cases, dew condensation occurs, and the film surface may be roughened. Conversely, if the boiling point is higher than the Tg of the resin, foaming is less likely to occur, but drying is insufficient, and the deformation start temperature of the formed film is lowered, resulting in a film having no heat resistance. From the above, the boiling point of the solvent used is 70 ° C.
The range of not less than 180 ° C. is good, preferably 90 ° C.
Solvents having a boiling point in the range of not lower than 150 ° C. and higher are preferred.

The coater for applying the alicyclic olefin resin solution is used according to the properties of the solution to be applied, such as the thickness of the coating and the viscosity of the coating solution. For example, a commonly used coater such as a comma coater, a roll coater, and a die coater can be used.

A feature of the present invention resides in a method for drying an alicyclic olefin resin coating film applied to a support. That is, in the drying step of the coating film in the solution casting method, the coating film is dried by uniformly heating the coating film by infrared heating. In the present invention, infrared heating means near-infrared heating or far-infrared heating, and unlike a hot air heating method, direct heating eliminates the need for heating an intermediate heating medium, has a high heating effect, and penetrates inside the coating film. As a result, drying can be promoted not only on the surface of the coating film but also inside the coating film. The temperature control of the infrared heating cannot be controlled by the blowing temperature or the ambient temperature as in the hot air drying, and is performed by the surface temperature of the infrared radiator. In addition, since there is radiation unevenness of the infrared radiator, it is preferable to reduce the size of one unit of the radiator and reduce the radiation unevenness by individually controlling the temperature.

As the infrared supply device which is an infrared radiator, for example, an electric far infrared heater, a gas far infrared heater, a steam far infrared heater, a lamp infrared heater and the like can be used.

The drying of the coating by infrared heating preferably involves two or more drying steps. In one step, the coating is dried at a temperature not higher than the boiling point of the solvent by infrared heating. It is preferable that the residual solvent amount be 10% by weight or less. In the second and subsequent stages, drying is performed by hot air heating, infrared heating, or a combination of both. The temperature in the second and subsequent stages is preferably higher than the boiling point of the solvent, and it is preferable to finally dry the film to a residual volatile content of 4% by weight or less. Regarding the drying temperature in the second and subsequent stages, an optimum drying temperature can be appropriately selected based on the condition of the equipment and the amount of residual solvent in the film due to the drying in the first stage.

When the coating film of the alicyclic olefin resin used in the present invention is dried by a usual hot air drying method, the temperature rises from the surface of the coating film, and the internal temperature of the coating film gradually rises. At this time, a dry thin film is formed on the surface of the coating film. However, in the case of a coating film made of a conventional resin solution which is conventionally used, the solvent gas passes through the film and is dried to form a film. However, in the case of an alicyclic olefin resin, the present inventors have found that when a thin film of the surface layer is formed, the solvent gas generated from the inside is difficult to pass through the dried film, so that the film swells and a foaming phenomenon occurs. Was done.

That is, when an alicyclic olefin resin is formed into a film by a solution casting method of a hot-air drying method, foaming is easily generated in a drying furnace, and if foaming occurs, it is not suitable as a film for optical use. In addition, if hot air drying is performed at a reduced temperature so that foaming does not occur, the amount of solvent remaining in the film increases, and the heat distortion temperature decreases, making it incompatible with applications in terms of heat resistance. . As a method of performing hot air drying while suppressing foaming, it is conceivable to lengthen the drying time at a low temperature, sufficiently reduce the remaining volatilization amount, and then increase the drying temperature. And is unrealistic in terms of production efficiency. It is also possible to increase the wind speed in order to shorten the drying time while suppressing foaming, but the surface of the coating film is roughened and optical distortion occurs. As a result, an image viewed through the formed film is distorted, and the film is defective and unsuitable for optical use. Furthermore, when applied as a retardation compensation film to a film that has been subjected to hot-air drying at a low temperature to suppress foaming, even if the retardation to be developed is small, the characteristics of the resin originally do not easily exhibit the retardation. In addition, when the amount of the residual solvent is large, the relaxation of the stress is accelerated, the phase difference is hardly generated, and the required phase difference cannot be generated.

On the other hand, in the solution casting method of the present invention for drying a coating film made of an alicyclic olefin resin solution by infrared heating, while delaying the formation of a surface layer,
By heating the surface layer and the inside of the coating film as uniformly as possible, the amount of foaming and residual solvent can be reduced, and an excellent optical transparent film free from optical defects can be produced.

The alicyclic olefin resin film formed by the above method is used as an optical transparent film.
For example, it is used for applications such as a protective film for a polarizing plate and a retardation compensation film. The optical transparent film manufactured by the method of the present invention has excellent optical properties such that the photoelastic coefficient is extremely small, the phase difference generated when stress is applied is small, and the wavelength dispersion of the refractive index is also extremely small. .

[0024]

Next, the present invention will be described more specifically with reference to examples. The present invention is not limited only to the following examples.

With respect to the optical transparent films produced in the following Examples and Comparative Examples, the foamed state of the film after drying,
The optical distortion and the residual amount of the solvent were compared, and the results are shown in Table 1. The foaming state is 5 cm by visual observation.
The presence or absence of foaming at the corner was counted. As for the optical distortion, the presence or absence of distortion of an image which is seen through the film obliquely was evaluated. The measurement of the residual amount of the solvent is performed by measuring the film after drying with a width of 2
Approximately 5.0 g of a sample finely cut into a size of about mm × length 10 mm is accurately weighed, dried in a gear oven set at 140 ° C. for 24 hours, and weighed again,
The amount of the dried solvent was calculated from the difference, and the remaining amount of the original film was obtained. The remaining volatile amount X [%] was calculated from the weight Y ₀ [g] of the film before drying and the weight Y ₁ [g] after drying according to the following “Equation 1”.

[Formula 1] X = [(Y ₀ −Y ₁ ) / Y ₀ ] × 100

[Example 1] ZEON of Nippon Zeon Co., Ltd.
EX was dissolved in toluene so that the polymer concentration was 42% by weight. This was applied on a PET film using an applicator such that the film thickness after drying was 60 μm. This was dried in two stages using an electric far-infrared ceramic heater. The drying condition was such that the temperature of the heater surface was set at 60 ° C. in one step for 5 minutes, and the temperature of the heater surface was set at 120 ° C. for two steps, and drying was performed for 5 minutes. At that time, the ceramic heater was arranged at an interval of 500 mm from the coating surface. At the end of one stage, the residual volatility was 9.7% by weight, and at the end of two stages, 3.5% by weight. The dried film was transparent and free from optical distortion, and no foaming was observed.

Example 2 ZEONE of ZEON CORPORATION
X was dissolved in toluene so that the polymer concentration became 42% by weight. This was applied on a PET film using an applicator such that the film thickness after drying was 60 μm. This was dried in two stages using an electric far-infrared ceramic heater. The drying condition was such that the heater surface temperature was set to 60 ° C. in one stage for 5 minutes, and the heater surface temperature was set to 120 ° C. for two stages, and drying was performed for 10 minutes. At that time, the ceramic heater was arranged at an interval of 500 mm from the coating surface. The residual volatility at the end of one stage was 9.6% by weight and 2.2% at the end of two stages. The dried film was transparent and free from optical distortion, and no foaming was observed.

[Comparative Example 1] ZEONE of ZEON CORPORATION
X was dissolved in toluene so that the polymer concentration became 42% by weight. This was applied on a PET film using an applicator such that the film thickness after drying was 60 μm. This was dried in two stages using a gear oven. First at 60 ° C for 5 minutes, then at 120 ° C for 5 minutes.
Drying was performed for minutes. The residual volatility at the end of the first stage was 11.0% by weight and 5.2% by weight at the end of the second stage. The dried film had seven foams of 100 μm or more in the area of 5 cm × 5 cm. Although the film was transparent, a distortion occurred in an image which was seen through the film from an oblique direction, and the film had optical distortion.

Comparative Example 2 ZEONE of ZEON CORPORATION
X was dissolved in toluene so that the polymer concentration became 42% by weight. This was applied on a PET film using an applicator such that the film thickness after drying was 60 μm. This was dried in two stages using a gear oven. First at 60 ° C for 5 minutes, then at 120 ° C for 1 minute
Drying was performed for 0 minutes. After the completion of one stage, the remaining capacity is 10.8
% At the end of the two stages. The dried film had four foams having a size of 100 μm or more in a range of 5 cm × 5 cm. An image transmitted through the film from an oblique direction was distorted, and the film had optical distortion.

Comparative Example 3 ZEONE of ZEON CORPORATION
X was dissolved in toluene so that the polymer concentration became 42% by weight. This was applied on a PET film using an applicator such that the film thickness after drying was 60 μm. This was put in a gear oven at 55 ° C for 3
Drying was performed for 0 minutes. The film is transparent, 100μ
m or more was not observed. However, an image seen through the film from an oblique direction is distorted, and the film has optical distortion.

[0031]

[Table 1] ---------------------------------------------- ------------------------- Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 ---------- -------------------------------------------------- ----------- Foaming number 0 0 7 5 0 Optical distortion No No Yes Yes Yes Yes Residue amount (% by weight) 3.5 2.2 5.2 4.0 9.2 --- -------------------------------------------------- ------------------

From the results shown in Table 1, it can be seen that the optical transparent film produced by the production method of the present invention is an excellent film having no foaming, a small amount of solvent residues, and no optical distortion.

[0033]

According to the present invention, it is possible to provide a method for producing a transparent optical film having a low wavelength dispersion characteristic of refractive index and a low photoelastic coefficient and having very few optical defects.

Continued on the front page F-term (Reference) 2H049 BA06 BB22 BB42 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FB02 FC01 FC22 FC23 GA16 LA12 4F071 AA14 AC02 AE19 AF30 AH19 BA02 BB02 BC01 4F073 AA14 BA06 BA34 BB001 CA53 GA01171

Claims (1)

[Claims] 1. A method for producing a transparent optical film by a solution casting method of an alicyclic olefin resin, comprising drying a coating film by infrared heating.