KR101352334B1 - A method of preparing Optical film - Google Patents

Abstract

The present invention relates to a method for manufacturing an optical film, and specifically, a raw material of an optical film is dissolved in a solvent on a support or drum which is rotated by casting rolls at both ends, thereby casting a flexible, flexible film drying, peeling, tenter, and final drying on a belt. In the method of manufacturing a flexible film type optical film comprising the step, the casting film is transported and peeled so as not to contact the support or the drum in contact with the peeling roll, the lower portion of the space between the peeling roll from the portion where the casting film is peeled off The present invention relates to a method for producing an optical film having an excellent appearance without a widthwise streak defect produced by using a peeling roll maintained at a constant temperature.

Optical film, width direction, infrared heater

Description

Manufacturing method of optical film {A method of preparing Optical film}

The present invention relates to a method for manufacturing an optical film, and more particularly, to a method for manufacturing an optical film produced by a flexible film method.

In recent years, in the case of a liquid crystal display (LCD), the demand for high brightness, wide viewing angle, and high contrast is increasing, and the role of the optical film is becoming more and more important. Although there are various methods as a manufacturing method of an optical film, the cast film method using a cellulose acylate (Tri-Acetyl-Cellulose film; hereinafter TAC) is known widely.

The TAC cast membrane method is a method in which cellulose triacetate, a raw material, is dissolved in a solvent such as methylene chloride, is then cast on an endless belt or drum, dried to a predetermined level, peeled off, and finally dried in a dryer through a tenter.

However, when the film is peeled off the belt or drum, evaporation of the residual solvent in the casting film, especially on the belt side which is in contact with the belt or drum, occurs severely, and the latent heat of evaporation of the solvent lowers the temperature of the casting film. , The solvent content in the surrounding air of the casting membrane becomes high. Even in the peeling rolls attached to increase the peeling stability of the casting film, the roll temperature is lowered by the latent heat of solvent evaporation, and the casting film surface and the peeling roll surface are caused by the lower casting film and peeling roll temperature and ambient air having a high concentration of solvent content. Condensation of the solvent that has evaporated may occur, especially in high-speed processes where the solvent evaporates and the resulting heat loss is high. Due to the condensed solvent, the casting film has a problem of forming constant streaks in the width direction of the film due to the phenomenon that the casting film surface is pressed by the release roll while passing through the release roll.

In Korean Patent Invention No. 643102, a method of evenly distributing a solvent in a casting film by setting a support surface temperature and a surface temperature of a release roll has been proposed. However, this suggests only the temperature, shape and position of the rolls for the purpose of evening the widthwise solvent distribution in the casting film, which is due to the temperature drop of the casting film and the peeling roll due to the solvent evaporation and latent heat of evaporation occurring in the casting film after peeling. Solvent condensation and the resulting defects are not solved. Moreover, since the first roll for leveling the solvent distribution is provided on the film surface in contact with the support or vice versa, there is a problem that the widthwise streaks generated by the contact between the peeling roll and the casting film to be solved here still occur. .

An object of the present invention is to provide a method for producing an optical film without streaks in the width direction in the optical film produced by the flexible film method.

In order to achieve the above object, the present invention is a method of manufacturing a flexible film type optical film comprising the step of dissolving the raw material of the optical film in a solvent to cast, flexible film drying, peeling, tenter, final drying step on the belt, the casting film is a support Alternatively, a surface which is not in contact with the drum is transported to be in contact with the peeling roll, and is peeled off. In the space between the peeling part from the support or the drum, a heating means is provided at the bottom to heat the casting film to maintain a constant temperature. And it provides a manufacturing method of the optical film excellent in appearance without the width direction stripes using the peeling roll maintained at a constant temperature.

In the present invention, it is preferable to adjust the temperature of the casting film heated by the heating means to be 20 to 40 ° C., and it is preferable to use heating means by radiation such as an infrared heater as the heating means. The heating means may heat the release roll as well as the cast film in the release zone. It is preferable that a peeling roll is maintained at 20-40 degreeC. Peeling roll is good to maintain the temperature through the hot water circulation or electric heater installed therein.

In the present invention, the amount of the residual solvent of the casting film immediately after the casting film is peeled off the support or the drum is 10 to 50%. Here, the residual solvent amount can be calculated as follows.

Residual solvent amount = (total dope weight-solid weight) / total dope weight × 100

Hereinafter, preferred embodiments of the present invention will be described in detail. In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the subject matter of the present invention.

The terms " about ", " substantially ", etc. used to the extent that they are used herein are intended to be taken to mean an approximation to or in the numerical value of the manufacturing and material tolerances inherent in the meanings mentioned, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure.

The optical film of the present invention will be described with respect to the manufacturing method of the TAC film, but the type of optical film is not limited thereto.

The present invention forms a casting film by casting a dope-like raw material on the support or drum rotated by the casting roll of both ends, and the formed casting film is peeled by a peeling roll that is first contacted from the support or drum and then transferred to the tenter In the manufacturing method of the optical film of the casting film method comprising the step of drying, the casting film is transported and peeled so as not to contact the support or the drum in contact with the release roll, and after the casting film is peeled from the support or drum Provided is a method for producing an optical film for maintaining a casting film at a constant temperature by heating a space immediately before contacting a release roll and a surface not in contact with a support or drum at a lower end thereof.

Further, the casting film is heated from a portion peeled from the support or drum to a space immediately before contacting the peeling roll, using a heating means such as an infrared heater at the lower end, and the peeling roll is heated to an internal heating means such as hot water circulation or an electric heater. It provides a method for producing an optical film maintained at a constant temperature by.

1 is a process schematic diagram of an optical film manufacturing apparatus according to a preferred embodiment of the present invention. Referring to FIG. 1, the optical film manufacturing apparatus of the present invention includes a dope tank containing a solvent containing TAC, a casting die 11, a support 10 including casting rolls 13 and 15, and an evaporator 17. And 18), a peeling roll 30 having an internal heating means, a tenter 50, a dryer 70, a winding roll 90, and the casting film heating means includes a casting roll 13 and a peeling roll ( 30) is below the non-contact surface.

Optical film manufacturing method of the present invention by using a flexible film method, a) preparing a dope (dope) is a solution formed by dissolving the raw material of the optical film in a solvent to the doping tank; b) casting the dope prepared in the dope tank to a support or a drum to form a casting film; c) peeling the formed casting film from the support or the drum and transferring the film to a release roll; d) manufacturing the cast film transferred to the release roll into a film through stretching and heat setting in a tenter; e) final drying the prepared film in a dryer; can be completed by winding the prepared film, including. In particular, in the step of peeling the formed casting film from the support or drum to transfer to the release roll, providing a heating means of the casting film between the casting roll and the release roll contained in the support or drum, and is maintained at a constant temperature by the internal heating means By providing a release roll, the widthwise streaks of the produced film can be eliminated or minimized.

a) First, the present invention proceeds with the step of preparing a dope which is a solution formed by dissolving the raw material of the optical film in a solvent and putting it in the dope tank. As a raw material of the optical film, cellulose acetate can be mainly used. As a solvent for dissolving the cellulose acetate, aromatic hydrocarbons such as benzene and toluene, halogenated hydrocarbons such as dichloromethane and chlorobenzene, methyl acetate, ethyl acetate, Ester, such as propyl acetate, may be used, and alcohols such as methanol, ethanol, n-propanol, n-butanol, diethylene glycol, ketones such as acetone and methyl ethyl ketone, tetrahydrofuran, and methyl cellulose may be used as the organic solvent. Ethers such as Rosolve. In the present invention, dope means a polymer solution or dispersion obtained by dissolving or dispersing the polymer in a solvent.

In addition, additives, such as plasticizers, such as a phthalic ester and a phosphate ester, a ultraviolet absorber, antioxidant, and a mat agent, can be used in the said dope, The kind of additive is not limited to this.

The dope tank can be adjusted to uniformly cast the dope onto the support or drum with a casting die 11.

b) casting the dope prepared in the dope tank to the support 10 or the drum to form a casting film (1); can proceed. The support 10 is positioned in the lower portion of the dope tank so that both ends are supported by the casting rolls 13 and 15 so that the belt can move endlessly by the rotation of the casting rolls 13 and 15, and the casting As the rolls 13 and 15 rotate, the dope injected from the dope tank is cast on the support to form the casting film 1. A drum may be used instead of the belt.

As described above, blow evaporators 17 and 18 for evaporating the solvent from the casting film cast on the support are disposed near the surface of the support 10 or the drum peripheral surface to dry the solvent to form the casting film to have the required amount of residual solvent. Can be.

The present invention provides a method for producing an optical film having a residual solvent amount of 10 to 50% of the casting film immediately after the casting film is peeled from the support or the drum. The residual solvent amount in the present invention can be calculated as follows.

Residual Solvent = (Total Doping Weight-Solid Weight) / Total Doping Weight × 100

When the amount of such residual solvent is less than 10%, it is difficult to peel off the casting film, and when it exceeds 50%, the peeled casting film is not self-supporting and it is difficult to transfer to the next process.

c) next peeling the formed casting film from the support or drum to transfer to the release roll; In the present invention, in order to prevent the width pattern of the film in the present invention, the casting film can be heated between the casting roll 15 and the peeling roll 30 included in the support or the drum, and this heating is performed between the casting roll and the peeling roll. Any means for heating the casting film is not limited, but radiation heating means such as an infrared heater is preferable because it does not break the internal air equilibrium state and there is no discharge of air requiring post-treatment.

By such heating means, the casting film is preferably 20 to 40 ° C. Since the casting film is compensated for the heat loss due to the evaporation of the solvent by the heating means, when the temperature of the casting film is lower than the temperature, the heating effect is reduced, and thus the widthwise streaks of the film may appear. On the contrary, if the temperature of the casting film is too high, bubbles in the casting film may be generated.

The heating of the present invention is preferably performed on the surface not in contact with the support or drum of the casting film or on the surface in contact with the release roll, and the release roll may be heated together at this time. The present invention is to compensate for the heat loss by evaporation of the solvent and to prevent the solvent from re-condensing in the casting film whose temperature is lowered by the heat loss, so that the part touching the release roll is heated. When the opposite side is heated, the casting film is heated but does not provide a direct effect on the part where the defect occurs, so that the effect is lowered, and thus the pattern in the width direction remains when the film is manufactured for a long time. In addition, the release roll is also continuously cooled due to heat loss due to solvent evaporation, which may condense the solvent in the surrounding air, thereby maintaining a temperature above a certain temperature, preferably 20 to 40 ° C, more preferably 35 to 40 ° C. It is recommended to heat so that. Such heating is preferably performed by providing hot water circulation or an electric heater inside the peeling roll in addition to heating by the heating means of the lower end portion.

Thereafter, d) manufacturing the peeled casting film into a film through stretching and heat setting in a tenter; may be performed. The casting film peeled by the said peeling roll is transferred to a tenter, and the both ends are fixed with a clip. In this state, the casting film is made into a film by stretching and heat fixing as necessary in the machine direction or the width direction or in both directions.

e) final drying the prepared film in a dryer; winding the prepared film can be completed to complete the film.

As described above, the method of the present invention heats the surface where the support or drum of the casting film is not in contact or the surface where the release roll is in contact between the casting roll of the support or the drum and the release roll when the casting film is cast onto the support or the drum, By using a peeling roll maintained at a constant temperature, the finished optical film has no widthwise streaks and has an excellent appearance.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto.

Production Example 1

Manufacture of dope

100 parts by weight of cellulose triacetate, 400 parts by weight of dichloromethane, 80 parts by weight of ethanol, and 15 parts by weight of triphenylphosphate were dissolved with stirring for 5 hours in a dissolving kiln, and dissolved and filtered through a filter press to prepare a dope.

Example 1

The dope according to Preparation Example 1 was introduced into the dope tank of FIG. 1, and the dope was sent to the coat hanger die using a pressure metering pump, and the casting roll including the casting roll rotated at an operating speed of 5 m / min so that the final dry film thickness was 80 µm. Casting on the belt support, and at the same time to form a casting film produced by evaporating the solvent in a blower evaporator controlled at 30 ℃, 0.2m / s on the belt, and the amount of residual solvent at the time of peeling the casting film by peeling the casting film from the belt In case of 30% transfer to the peel roll, the cast film is transferred to the peel roll by heating with the infrared heater installed at the bottom of the surface not in contact with the belt of the cast film between the casting roll of the belt and the peel roll so that the surface temperature of the cast film is 35 ° C. The temperature of the peeling roll was circulated by setting the internal hot water at 35 ° C so as to maintain 35 ° C. The conveying casting roll was stretched by the tenter at the draw ratio of 100x103% of a machine direction x width direction, and finally dried at 130 degreeC, and the cellulose triacetate film was obtained. The results are shown in Table 1.

Comparative Example 1

The same procedure as in Example 1 was conducted except that the lower end heating and the hot water circulation were not performed.

Comparative Example 2

It carried out similarly to Example 1 except heating to the surface which the support body of the casting film contacted between the casting roll of a support body, and a peeling roll.

* evaluation

1. Appearance

If the surface condition of the produced film does not appear wrinkles or streaks was good, if there is a problem in the appearance of the film was evaluated to describe the matter.

[Table 1]

division phenomenon Exterior Example 1 Spots disappear and transparent film production Good Comparative Example 1 Film width direction smear occurs Width streaks occur Comparative Example 2 The initial stain disappears when heated
Reoccur after 1 hour Width streaks occur

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

1 is a process schematic diagram of an optical film manufacturing apparatus according to the present invention.

DESCRIPTION OF THE RELATED ART [0002]

1: casting membrane 10: support

11: casting die

13, 15: casting roll 17, 18: evaporative blower

30: peeling roll provided with hot water circulation device 50: tenter

70: dryer

90: winding roll

100: lower heating means before the peel roll

Claims (7)

Casting the dope phase raw material onto the rotating support or drum by the casting rolls at both ends to form a casting film, and peeling the formed casting film by the peeling roll which is first contacted from the support or drum to transfer to the tenter and then drying In the manufacturing method of the optical film of the flexible film including a, The casting membrane is transported and peeled so that the surface which is not in contact with the support or the drum is in contact with the release roll, And a heating means at a lower end of the space immediately after the casting film is peeled from the support or the drum to reach the release roll to heat the surface not in contact with the support or the drum to maintain the casting film at a constant temperature. The method of claim 1, The heating method of manufacturing an optical film using a heating means in which the temperature of the casting film is adjusted to 20 ~ 40 ℃. 3. The method of claim 2, The heating means is a method of manufacturing an optical film by a radiation method. The method of claim 1, The manufacturing method of the optical film in which the said peeling roll is maintained at 20-40 degreeC 5. The method of claim 4, The method of manufacturing an optical film, wherein the temperature maintaining means of the release roll is by internal hot water circulation or internal electric heater. The method of claim 1, The casting film is a method for producing an optical film of 10 to 50% of the residual solvent amount of the casting film immediately after peeling from the support. 7. The method according to any one of claims 1 to 6, The optical film is a cellulose triacetate film manufacturing method of an optical film.

Images