KR101591900B1 - A method of preparing Optical film - Google Patents

Abstract

More specifically, the present invention relates to a method for producing an optical film, which comprises forming a casting film by casting a dope raw material on a support or a drum rotated by a casting roll at both ends, And a step of transferring the film to a tenter and then drying the film, wherein the casting film is conveyed such that a surface not in contact with the support or the drum is brought into contact with the peeling roll, Between the casting roll and the peeling roll at the end of the peeling roll of the support or the drum immediately before the casting film touches the peeling roll from the support or the drum, the surface of the casting film, which does not contact the support, ) Having no stripes in the width direction of the optical film completed by the method for producing an optical film, A method for producing the optical film excellent.

Optical film, width direction, blowing, peeling roll

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

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

In recent years, in a liquid crystal display (LCD), a demand for a high luminance, a wide viewing angle, and a high contrast is increasing, and accordingly, the role of the optical film becomes more important. As the production method of the optical film, there are various methods, among which the melt extrusion method and the flexible film method are widely known.

A cellulose acylate (hereinafter referred to as TAC) film which is often used as such an optical film is used as a film support of a photosensitive material for photographic purposes in view of rigidity and flame resistance. The TAC film is a kind of cellulose ester and is produced from TAC having an average degree of acetylation of 58.0 to 62.5%. Since the TAC film is also excellent in optical isotropy, it is used, for example, as a protective film of a polarizing plate of a liquid crystal display device which has been spreading widely in recent years.

Therefore, a triacetyl-cellulose film (TAC) film, which is generally used as a raw material of an optical film used in a polarizing plate of a liquid crystal display, is prepared by dissolving cellulose triacetate as a raw material in a solvent and casting it on an endless belt , Followed by drying and peeling, followed by final drying in a dryer through a tenter.

However, when the casting film is peeled off from the belt, evaporation in the film causes the solvent concentration of the air around the belt surface and the air surface of the casting film to become high, and the casting film becomes low in temperature due to the latent heat of evaporation of such solvent. This results in condensation of the solvent on the air side of the casting membrane, which is more pronounced in the high speed process. The film in which the solvent is condensed on the surface has a problem of forming a pattern in the width direction of the film due to a phenomenon such as being pressed by a peeling roll after passing through the peeling roll after peeling.

In Korean Patent No. 643102, there has been proposed a method of adjusting the distribution of the solvent in the casting film by setting the surface temperature of the support and the surface temperature of the peeling roll. However, this does not disclose a specific temperature control method, and it is difficult to solve the solvent condensation due to the evaporation of the solvent and the latent heat of evaporation due to the latent heat of evaporation in the casting film after peeling, There is still a problem in that the width directional streaks are still generated.

On the other hand, in manufacturing an optical film, an endless belt is used as a support, or the amount of the residual solvent in the dope is controlled to be constant by a drum, and then peeled and sent to a post-end process. At this time, in order to stabilize the peeling, a roll called peeling roll is installed near the peeling point. At this time, in order to prevent the surface damage due to the contact of the roll, the peeling roll is generally disposed so as to be in contact with the air surface (the surface not contacting the support) having a low concentration of the residual solvent on the cross section of the film.

However, although evaporation (referred to as drying) of the residual solvent in the dope occurs continuously in the main process of a casting machine (caster), a tenter machine, and a dryer , Even during transfer of the process. In particular, since the amount of the residual solvent in the film is much more than that in the other process steps, the residual solvent is evaporated much during transfer, and the solvent is present in the air in a high concentration immediately after the separation. The presence of solvent in the air accelerates during high-speed operation.

1 is a schematic view of a portion where a casting film is peeled off from a support during a general casting film type optical film production process. Referring to FIG. 1, a cast film 1 formed by casting a dope prepared by dissolving triacetate cellulose and other additives in a solvent in a solvent through a die 11 is cast on a support 10, The solvent evaporated from the peeled casting film is distributed at a high concentration in the space from the peeling point to the peeling roll at the time of peeling from the casting roll 15 of the peeling roll 30.

As described above, when the casting film is peeled from the support, the peeling roll is in contact with the surface (air surface) which is not in contact with the support. Therefore, ) Passes through the peeling roll, and a narrow and long unevenness occurs in the width direction of the casting film due to the action of the high concentration solvent in the air and the peeling roll.

Fig. 2 is a side schematic view (a) and a plan schematic view (b) of a process in which stripe patterns in the width direction are generated on a surface of the cast film not contacting with the support. Fig. 2 shows a form in which stripes in the width direction are formed on a surface of the casting film on which the support does not contact.

As a result of research to solve this problem, it was found that immediately after peeling, fresh air, which does not contain a solvent, was blown on the air side of the film between the casting roll and the peeling roll, It was found that it was effective to prevent

Accordingly, an object of the present invention is to provide a method for producing an optical film without stripes in a width direction in an optical film produced by a casting film method.

In order to attain the above object, the present invention provides a casting method for casting a casting film by casting a dope raw material on a support rotating at both end casting rolls, separating the formed casting film by a peeling roll, Wherein the casting film is conveyed and peeled so that the side not in contact with the support comes into contact with the peeling roll and is peeled off immediately before the casting film contacts the peeling roll from the support, (Fresh air) is blown on a surface of the casting film not contacting with the support, between the casting roll and the peeling roll at the peeling roll direction end of the support.

In addition, the present invention provides a method for producing an optical film wherein the casting film is peeled from the support and the residual solvent amount of the casting film is 10 to 50% immediately before blowing.

The present invention provides a method for producing an optical film in which the blowing air has a temperature of 0 to 120 캜 as air dehumidified at a relative humidity of 0 to 50%. Here, the residual solvent can be calculated as follows.

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

Further, the present invention provides a process for producing an optical film wherein the optical film is a cellulose triacetate film.

Hereinafter, the present invention will be described in detail. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted so as to avoid obscuring 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 of, or approximation to, the numerical values of 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 a method for producing a cellulose triacetate film, but the kind of the optical film is not limited thereto.

In addition, blowing in the present invention means supplying air containing no solvent.

The present invention is characterized in that a casting film is formed by casting a dope raw material on a support rotated by both end casting rolls, the casting film is peeled off by a peeling roll which first contacts the support from the support, Wherein the casting film is conveyed and peeled so that the side not in contact with the support is in contact with the peeling roll and the peeling roll direction of the support immediately before the casting film contacts the peeling roll from the support, Provided is a method for producing an optical film in which air is blown on a surface of a casting film not in contact with a support between a casting roll and a peeling roll at the end.

3 is a schematic view of a process of an optical film production apparatus according to one preferred embodiment of the present invention. 3, the apparatus for producing an optical film of the present invention comprises a die 11 containing a solvent containing cellulose triacetate, a support 10 including casting rolls 13 and 15, evaporation blowers 17 and 19 A blowing roll 100 may be provided between the casting roll 13 and the peeling roll 30 on a surface not in contact with the support body, do.

The method for producing an optical film of the present invention comprises the steps of: (a) preparing a dope, which is a solution formed by dissolving a raw material of an optical film in a solvent, into a die; b) casting the prepared dope into a die to form a casting film; c) peeling the formed casting film from the support and transferring the casting film to the peeling roll; d) preparing a cast film transferred to the peeling roll through a stretching and heat setting in a tenter as a film; e) final drying of the prepared film in a dryer; and winding the prepared film. Particularly, in the step of peeling the formed casting film from the support and transferring it to the peeling roll, it is possible to eliminate or minimize the widthwise stripe of the film produced by blowing between the casting roll and the peeling roll included in the support.

a) In the present invention, first, a dope, which is a solution formed by dissolving a raw material of an optical film in a solvent, is prepared and then charged into the die 11. Examples of the solvent for dissolving cellulose acetate include aromatic hydrocarbons such as benzene and toluene, halogenated hydrocarbons such as dichloromethane and chlorobenzene, ethers such as methyl acetate and ethyl acetate, Esters such as methanol, ethanol, n-propanol, n-butanol and diethylene glycol, ketones such as acetone and methyl ethyl ketone, and organic solvents such as tetrahydrofuran, And ethers such as methyl cellosolve. In the present invention, it means a polymer solution or dispersion obtained by dissolving or dispersing the polymer in a dodecyl solvent.

Additives such as a plasticizer such as phthalic acid ester and phosphoric acid ester, an ultraviolet absorber, an antioxidant and a matting agent may be added to the above dope. It is not limited.

The die 11 can be adjusted to cast the dope uniformly onto the support as a casting die.

b) forming the casting film 1 by casting the dope introduced into the die into the support 10; The support 10 is positioned such that the ends of the support are supported by the casting rolls 13 and 15 at the lower portion of the die and the belt can be moved endlessly by the rotation of the casting rolls 13 and 15, The casting film 1 is formed as the dope injected from the die is cast on the support. A drum-shaped support may be used instead of the belt.

As described above, a blowing evaporator (17, 18, 19) for evaporating the solvent in the casting film cast on the support is disposed near the surface of the support (10) so that the solvent can be dried to form a casting film have.

The present invention provides a method for producing an optical film in which the casting film is peeled off from a support and the residual solvent amount of the casting film is 10 to 50% immediately before supplying fresh air containing no solvent. The amount of the residual solvent in the present invention can be calculated as follows.

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

If the amount of the residual solvent is less than 10%, it is difficult to separate the casting film. If the amount of the residual solvent is more than 50%, it is difficult to transfer the film to the next step.

c) subsequently c) peeling the formed casting film from the support and transferring the casting film to the peeling roll; It is possible to supply air between the casting roll 15 and the peeling roll 30 included in the support in order to prevent the widthwise pattern of the film in the present invention. But it is preferable that the blowing air is the air dehumidified at a relative humidity of 0 to 50% and the temperature is 0 to 120 ° C. If the humidity and the temperature are out of the above range, the blowing effect is lowered, and the effect of preventing the width direction pattern of the film may be lowered.

Particularly, the blowing of the present invention is an important factor to be supplied to the surface of the casting film that is not in contact with the support or the surface in contact with the peeling roll, and when the casting film is blown onto the surface contacting with the support, the amount of residual solvent in the casting film is decreased Although it seems that there is a slight improvement effect by reducing the amount of the solvent evaporating in the space immediately after the peeling, since it does not provide a direct effect on the part where the defect occurs, as the operation continues, A pattern in the width direction remains when the film is produced.

Fig. 4 is a schematic view showing a state in which the casting film is blown onto the surface contacting with the support. Referring to FIG. 4, since the solvent concentration is still high in the surface space, that is, the non-blown space, in which the support is not contacted by the casting film, There is a high possibility of condensation on the non-contact side, and therefore stripes in the width direction are formed when the film is produced.

5 is a schematic view of a blowing device according to a preferred embodiment of the present invention. Referring to FIG. 5, the casting film 1 is blown 100 between the casting roll 15 and the peeling roll 30 of the support 10 on the side not in contact with the support.

Such a blowing air minimizes the condensation of the residual solvent on the casting film surface contacting the peeling roll by supplying fresh air when the casting film is separated from the support and the solvent in the casting film is distributed in a high concentration in the space immediately after peeling So that deformation of the casting film can be minimized, thereby preventing stripe patterns in the width direction.

Thereafter, d) the step of preparing the peeled casting film as a film through stretching and heat setting in a tenter. The casting film peeled off by the peeling roll is transferred to a tenter, and both ends of the casting film are fixed with a clip. In this state, the casting film is made into a film by stretching the film in the machine direction, the width direction or both directions, if necessary, through stretching and heat fixing. In the present invention, the film refers to a state after stretching fixed by applying a tensile force to the casting film.

e) final drying of the prepared film in a dryer; and winding the prepared film. The dryer (50) can be finally dried by the drying wind. After the final drying and cooling, the optical film of the present invention can be completed.

As described above, in the method of the present invention, when peeling the casting film cast on a support, the casting roll is peeled off from the casting roll and the peeling roll of the support, There is no stripe and excellent surface property.

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 triphenyl phosphate were dissolved in a dissolving oven for 5 hours with stirring, dissolved and filtered through a filter press to prepare a dope.

Example 1

The dope according to Production Example 1 was placed in the die of Fig. 3 and the dope was sent to the coating hanger die by a pressurization metering pump, and the casting roll was rotated at an operation speed of 5 m / min so as to have a dry film thickness of 80 탆. And at the same time, the casting film is formed by evaporating the solvent with a blowing evaporator controlled at 30 ° C and 0.2 m / s on the belt, and the amount of the residual solvent at the time of peeling the casting film from the belt to peel the casting film is 30% Between the casting roll and the peeling roll of the belt, fresh air not containing a solvent dehumidified at a relative humidity of 0% is applied to the surface of the casting film not contacting the belt at a temperature of 6 kg / cm ² And the casting roll was transferred to a peeling roll. The casting roll was biaxially stretched in a tenter at a stretching ratio of 100 x 103% in the machine direction x width direction and finally dried at 130 deg. C to obtain cellulose To give a triacetate film. The results are shown in Table 1.

Comparative Example 1

The procedure of Example 1 was repeated except that no air was supplied.

Comparative Example 2

The same procedure as in Example 1 was carried out, except that air was supplied to the surface of the casting film contacting with the support between the casting roll and the peeling roll of the support.

* evaluation

1. Appearance

If the surface condition of the produced film shows no wrinkles or streaks, and if there is a problem with the appearance of the film, the evaluation is made.

[Table 1]

division phenomenon Exterior Example 1 Dirt disappears and transparent film production Good Comparative Example 1 Film width direction stain occurred Width stripe occurrence Comparative Example 2 Supply initial stains disappear,
Reappear after 1 hour Width stripe occurrence

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.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a portion where a casting film is peeled from a support during an optical film production process of a general casting film type.

Fig. 2 is a side schematic view (a) and a plan schematic view (b) of a process in which stripe patterns in the width direction are generated on the surface of the cast film not contacting with the support.

3 is a schematic view of a process of an optical film production apparatus according to a preferred embodiment of the present invention.

4 is a schematic view showing a state in which a casting film is blown onto a surface contacting with a support.

5 is a schematic view of a blowing device according to a preferred embodiment of the present invention.

DESCRIPTION OF THE RELATED ART [0002]

1: casting membrane 3: solvent-rich zone

10: Support 11: Die

13, 15: casting rolls 17, 19: evaporative blower

30: peeling roll 50: dryer

70: Winding roll

100: Ventilation

Claims (4)

Casting a dope raw material on a support or drum rotated by a casting roll at both ends to form a casting film; And a step of separating the formed cast film from the support or the drum by a peeling roll and transferring the cast film to a tenter and drying the cast film, Wherein the forming of the casting film comprises controlling the amount of residual solvent in the casting film by drying the solvent using an evaporative blower near the periphery of the support or drum on which the dope raw material is cast, Wherein fresh air not containing a solvent is blown onto a surface of the casting film which is not in contact with the support or the drum, between the drum and the peeling roll adjacent to the place where the dope raw material is cast. The method according to claim 1, Wherein the casting film has a residual solvent amount of 10 to 40% in the cast film immediately before peeling off from the support or the drum and blowing. The method according to claim 1, Wherein the blowing air is dehumidified air at a relative humidity of 0 to 50% and a temperature of 0 to 120 캜. 4. The compound according to any one of claims 1 to 3, Wherein the optical film is a cellulose triacetate film.

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