JP3527639B2 - Method for producing retardation film - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a retardation film, and more particularly to a method for producing a retardation film for compensating for the retardation of a liquid crystal display device or the like.

[0002]

2. Description of the Related Art Conventionally, twisted nematic (TN)
LCD and Super Twisted Nematic (ST
N) Liquid crystal display devices are used as display devices for various OA equipment. However, the above-mentioned liquid crystal display device has a drawback that the display screen is colored in blue or yellow due to the phase difference generated in the liquid crystal cell. Therefore, a method of eliminating these colorings using a retardation film is adopted.

Usually, the retardation film is obtained by longitudinally uniaxially stretching or laterally uniaxially stretching a thermoplastic resin film, as disclosed in, for example, JP-A-2-191904 and JP-A-2-42406. . The color compensation for eliminating the coloration has an optimum value in the retardation in a very narrow range of the uniaxially stretched thermoplastic resin film. Regarding the above-mentioned color compensation, the retardation property represented by the retardation value is anisotropy of the refractive index of the thermoplastic resin film, that is, when the birefringence is Δn and the thickness of the thermoplastic resin film is d, Since it is represented by Δn × d, a uniform retardation value is shown over the entire surface of the uniaxially stretched thermoplastic resin film in order to eliminate unevenness in color and contrast over the entire surface of the liquid crystal display device. Is required.

Conventionally, in order to obtain a retardation film having a uniform retardation value, a thermoplastic resin film produced by a solution casting method and having excellent thickness accuracy and surface uniformity has been used as a stretched raw fabric. Furthermore, JP-A-8-
Japanese Patent No. 122526 discloses a method of using a stretched raw fabric having a solvent content of 0.5 to 7% by weight based on the solid content.

However, in the method disclosed in JP-A-8-122526, when the thickness of the thermoplastic resin film used as the stretched raw material varies greatly, a large retardation value proportional to this variation in thickness is obtained. However, the liquid crystal display device using these retardation films had color unevenness to the extent that they could be easily visually identified.
Further, since the thermoplastic resin film is produced by the solution casting method, the productivity is low.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and its object is to:
Even if there is a large variation in thickness of the thermoplastic resin film before stretching, in the production process of the retardation film including the stretching process, the retardation film having a uniform retardation value over the entire surface is stable and high. It is intended to provide a method for producing a retardation film that can be produced with productivity.

[0007]

The method for producing a retardation film according to the first aspect of the present invention uses a retardation film producing apparatus provided with a heating zone, a cooling zone and a stretching zone in the above order. In the zone, the thermoplastic resin film has a glass transition temperature (Tg) to (Tg +
60 ° C.) to a constant temperature, and then, in the cooling zone, the thermoplastic resin film is cooled by cooling means such that a temperature difference occurs between minute portions according to the thickness of the thermoplastic resin film, and stretched. In the zone, the thermoplastic resin film is further stretched while being cooled, and the temperature of the thermoplastic resin film at the end of stretching is (Tg-30 ° C).
To (Tg + 20 ° C.).

In the heating zone, the cooling zone and the stretching zone in the retardation film manufacturing apparatus used in the present invention, the thermoplastic resin film transferred therein is continuously heated, cooled and further cooled. However, it means that each process of stretching is present, and it is unavoidable that there are some intermediate temperature regions at the boundaries of these zones. Means for reducing these intermediate temperature regions as much as possible is not particularly limited, for example, between the above-mentioned zones, a narrow slit-shaped passage through which the thermoplastic resin film is transferred, Other than the provision, a method of shielding heat with a heat insulating partition, a method of shielding heat with an air curtain, a method of combining these, and the like can be mentioned.

The thermoplastic resin film used in the present invention is not particularly limited as long as it is a thermoplastic resin film which exhibits birefringence when stretched.
For example, cellulose resin, vinyl chloride resin, polycarbonate resin, polystyrene resin, acrylonitrile resin, olefin resin, polymethyl methacrylate resin, polysulfone resin, polyarylate resin, polyether sulfone resin, A film made of a thermoplastic resin such as a polynorbornene-based resin can be used.

In the present invention, the thermoplastic resin film is first heated in the heating zone so that the thermoplastic resin film has a constant temperature of Tg to (Tg + 60 ° C.). The temperature of the thermoplastic resin film in the present invention refers to the surface of the thermoplastic resin film (hereinafter the same). By maintaining the temperature of the thermoplastic resin film at the outlet of the heating zone at the constant temperature of Tg to (Tg + 60 ° C.), the variation in the viscosity of the thermoplastic resin film is reduced, and the thermoplastic resin stretched while being cooled as described below. Variations in the thickness of the resin film are reduced.

When the temperature of the thermoplastic resin film at the outlet of the heating zone is lower than Tg, the shear stress generated in the thermoplastic resin film during stretching in the stretching zone described later becomes larger than the strength of the thermoplastic resin film. Brittle fracture may occur, and the thermoplastic resin film may be broken during stretching. If it is higher than (Tg + 60 ° C), the viscosity of the thermoplastic resin film becomes low and the conveyed thermoplastic resin film hangs, causing trouble. There is a possibility that it may occur or the stretching effect may not be obtained in the stretching zone described below.

The heating means in the heating zone is not particularly limited. For example, hot air, combined use of hot air and cold air, electromagnetic wave heaters such as microwaves and far infrared rays, temperature controlled heating rolls, heat pipe rolls. , A temperature-controlled heating metal belt and the like.

Then, the thermoplastic resin film held at a constant temperature of Tg to (Tg + 60 ° C.) is cooled by a cooling means such that a temperature difference occurs between minute portions according to the thickness. The thermoplastic resin film, due to the difference in heat capacity between minute portions according to the thickness of the thickness,
The thick part is relatively hard to cool, and the thin part is relatively easy to cool.Therefore, the cooling causes temperature difference between minute parts according to the thickness of the thermoplastic resin film. A difference can be made.

The cooling means for the thermoplastic resin film is
If it is cooled too rapidly, it may reach a temperature below the appropriate temperature for stretching until the next stretching step.If it is cooled too slowly, the temperature difference between minute parts depending on the thickness of the film may be different. Therefore, a cooling rate and a cooling temperature that do not bring about such a state are selected, and cooling is performed by a cooling unit that causes a temperature difference between minute portions according to the thickness.

The cooling means in the cooling zone is not particularly limited. For example, hot air, a combination of hot air and cold air, electromagnetic wave heaters such as microwaves and far infrared rays,
Examples thereof include a temperature-controlled heating roll, a heat pipe roll, and a temperature-controlled heating metal belt.

In the stretching zone of the third step, the thermoplastic resin film is further cooled while the stretching is started, and the temperature of the thermoplastic resin film at the end of the stretching is (Tg
-30 ° C) to (Tg + 20 ° C).

In the stretching zone, the thermoplastic resin film is further cooled. The purpose of the cooling is to cool the thermoplastic resin film in the cooling zone to a relatively thick portion and a relatively thin portion. It is to maintain the temperature difference generated between the above and the above and try to start the stretching in this state. The cooling means is not particularly limited as long as it can achieve the above purpose, but is preferably 1
A method of cooling to a temperature 10 to 30 ° C. lower than the temperature of the thermoplastic resin film in the cooling zone in about 20 seconds is adopted.

The cooling means in the stretching zone is not particularly limited, but for example, hot air used in the previous step, combined use of hot air and cold air, electromagnetic wave heaters such as microwaves and far infrared rays, and temperature controlled. Similarly, a heating roll, a heat pipe roll, a temperature-controlled heating metal belt and the like can be mentioned.

The thermoplastic resin film stretched while being cooled in two stages in this way has cooling conditions in the stretching zone such that the temperature of the film at the end of stretching is (Tg-30 ° C) to (Tg + 20 ° C). Is set.

The temperature of the film at the end of stretching is (Tg-3
If it is lower than 0 ° C), the thermoplastic resin film in the stretching process may have a partial stress concentration, which may cause uneven stretching, and if it is higher than (Tg + 20 ° C), it is stretched by annealing. The effect is diminished, and the desired retardation value may not be obtained, so it is limited to the above range.

The temperature of the film immediately after the stretching is preferably within 1 second, more preferably within 0.5 seconds, and further preferably within 0.25 seconds.
The molecular orientation of the thermoplastic resin film is frozen by rapid cooling to −20 ° C.). Thus, by rapidly cooling the thermoplastic resin film immediately after the stretching and suppressing excessive relaxation of the stretching stress due to annealing, it is possible to stably obtain a desired retardation value with little variation.

The means for quenching the thermoplastic resin film immediately after the stretching is not particularly limited, and for example, it may be selected from the cooling means in the stretching zone described above. A cooling roll provided may be additionally used.

The stretching means in the stretching zone is not particularly limited, and examples thereof include a longitudinal uniaxial stretching method using a roll, a horizontal uniaxial stretching method using a tenter, and a biaxial stretching method combining these. The stretching ratio in the stretching means is determined according to the intended use of the retardation film to be obtained and is not particularly limited. For example, in the case of a retardation film for liquid crystal display device, preferably 1. It is about 1 to 2 times.

According to a second aspect of the present invention, there is provided a method for producing a retardation film according to the first aspect, wherein the cooling means in the cooling zone is 1
-10 seconds from the temperature of the thermoplastic resin film in 20 seconds
It is cooled to a temperature lower by -30 ° C, and the cooling means in the stretching zone further has a temperature of 10 to 20 seconds from the temperature of the thermoplastic resin film in the cooling zone in 1 to 20 seconds.
The stretching is started while cooling to a temperature lower by 30 ° C.

FIG. 1 shows the cooling means 1 to 20 of the present invention.
10 to 30 from the temperature of the thermoplastic resin film in a second
2 shows a cooling rate for cooling to a temperature lower than that of the thermoplastic resin by comparison with a cooling method shown in FIG. 2 in which cooling is performed at a rapid cooling rate of 35 ° C./second and at a slower cooling rate of 0.3 ° C./second. A temperature curve is shown with the vertical axis representing the temperature difference between the relatively thick portion and the thin portion of the film and the horizontal axis representing the time.

The heated thermoplastic resin film is
When cooled at a slow cooling rate of less than 0.5 ° C./second, as is clear from FIG. 2, there is almost no temperature difference between the relatively thick portion and the thin portion of the thermoplastic resin film.
Further, when it is cooled at an extremely rapid cooling rate of more than 30 ° C./sec, the temperature of each part of the thermoplastic resin film is cooled uniformly in a short time as shown in FIG. 2, and as a result, the thermoplastic resin film is cooled. There is no temperature difference between the relatively thick part and the relatively thin part of the film. The thickness of the stretched raw material, which has a relatively large variation in thickness and has almost no temperature difference between the thick and thin portions of the thermoplastic resin film as described above, can be rapidly cooled with a slow cooling rate. However, the retardation film having a retardation value having a relatively large variation proportional to the variation in the thickness described above is obtained in the next step of stretching while being cooled, even if the cooling rate is different.

The cooling rate in the stretching zone is 1 to 20 for the same reason as in the cooling zone described above.
In a second, stretching is started while being cooled to a temperature 10 to 30 ° C. lower than the temperature of the thermoplastic resin film in the cooling zone. In the thermoplastic resin film stretched while being cooled in two stages in this way, the cooling conditions in the stretching zone are set so that the temperature of the film at the end of stretching is (Tg-30 ° C) to (Tg + 20 ° C). .

The method for producing a retardation film of the invention described in claim 3 is the same as the stretched thermoplastic resin film (Tg) in the method for producing a retardation film described in claim 1 or 2.
It is characterized by being rapidly cooled to a temperature of -20 ° C or lower.

In the thermoplastic resin film in the stretching zone, the horizontal axis represents the time from the stretching step to the annealing step, the vertical axis represents the stress applied to the thermoplastic resin film, and the minute portion corresponding to the thickness is shown. The thermoplastic resin film stress profile is shown in a schematic graph separately for "thick" and "thin". Generally, immediately after stretching, the "thin" portion has a larger stress than the "thick" portion. However, in the annealing process, the stress relaxation rate increases and the difference in stress tends to be smaller than immediately after stretching.

In the method for producing a retardation film of the present invention, the stretched thermoplastic resin film is rapidly cooled to a temperature of (Tg-20 ° C.) or less to give a minute amount according to the thickness of the thermoplastic resin film. The stress difference immediately after the stretching between the different portions is frozen, the reduction of the stress difference due to annealing is suppressed, and the birefringence Δn difference generated in proportion to the stress is held. The birefringence Δn generated in proportion to the stress
Is inversely proportional to the stretching temperature, so that there is a thickness between the minute portions and a thermoplastic resin film having a temperature difference between the minute portions according to the thickness is Δn
The retardation value represented by xd can be made more uniform.

A method for producing a retardation film according to a fourth aspect of the present invention is the method for producing a retardation film according to the first, second or third aspect, wherein the thermoplastic resin film is a polysulfone resin film.

In the method for producing a retardation film according to the first aspect of the present invention, the thermoplastic resin film heated to a constant temperature of Tg to (Tg + 60 ° C.) of the thermoplastic resin film in the heating zone as described above is used. , Cooling in two stages in the cooling zone and the stretching zone, the stretching is started while cooling as described above, and the temperature of the thermoplastic resin film at the end of the stretching is (Tg-30 ° C) to (Tg + 20 ° C). Since there is a difference in temperature between the thicker part and the thinner part of the thermoplastic resin film at the time of stretching, Δn is relatively small in the thicker part. Δn becomes relatively large in a thin portion of, and the retardation value represented by Δn × d is leveled as a whole, and a retardation film showing uniform retardation characteristics with little variation is obtained. It is constant.

Therefore, the thermoplastic resin film used in the present invention is not limited to the thermoplastic resin film prepared by the solution casting method and having a relatively small variation in thickness, and may be a melt casting method such as a T-die method. It is possible to obtain a retardation film showing uniform retardation characteristics with little variation as described above even in the case of the thermoplastic resin film prepared in 1., brittle fracture occurs due to excessive shear stress during stretching, and during stretching Without breaking the thermoplastic resin film, on the contrary, the viscosity of the thermoplastic resin film decreases and does not cause a problem of sagging during transportation,
The retardation film can be stably produced with high productivity.

The method for producing a retardation film according to the second aspect of the present invention is as described above, in the method for producing the retardation film according to the first aspect of the invention, the cooling method in the cooling zone is 1 to 20 seconds. Then, from the film temperature above 10
It is cooled to a temperature lower by -30 ° C, and the cooling method in the stretching zone is further 1 to 20 seconds, and is 10 to 10 ° C lower than the temperature of the thermoplastic resin film in the cooling zone.
Since the stretching is started while cooling to a temperature lower by 30 ° C., in the cooling zone and the stretching zone, the relatively thick portion of the thermoplastic resin film is kept at a high temperature, and the thin portion is quickly cooled. It is cooled to a low temperature and cooled so as to cause a temperature difference between the thick portion and the thin portion, and the stretching is started while cooling in this way. In the same manner as the method for producing a retardation film of the invention according to item 1, high productivity, and
The retardation film can be stably produced.

According to the method for producing a retardation film of the invention described in claim 3, as described above, the stretched thermoplastic resin film in the method for producing a retardation film according to claim 1 or 2 (Tg-20 ° C) is used. ) By rapidly cooling to the following temperature, the stress difference immediately after the stretching between the minute portions according to the thickness of the thermoplastic resin film is frozen to suppress the reduction of the stress difference due to stress relaxation, and Since the difference in birefringence Δn generated in proportion to the stress is retained, the retardation value represented by Δn × d of the thermoplastic resin film can be made more uniform.

That is, the retardation value is such that the birefringence Δn generated in proportion to the stretching stress is inversely proportional to the stretching temperature, so that the thermoplastic resin film has a small thickness between the minute portions. However, if there is a temperature difference between the minute portions depending on the thickness, Δn of the relatively thick portion appears small, and Δn of the relatively thin portion is large. Appearance, even if there is a thin or thin portion between the minute portions of the thermoplastic resin stretched film, as a result, Δn
The retardation value represented by xd is presumed to be more uniform.

As described above, the method for producing a retardation film of the invention of claim 4 is the method of producing a retardation film of the invention of claim 1, 2 or 3, wherein the thermoplastic resin film is a polysulfone type. Since it is made of a resin film, it is possible to stably produce a retardation film with high productivity as in the method for producing a retardation film according to the first or second aspect of the invention.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an apparatus for manufacturing a retardation film for carrying out the present invention is shown in a conceptual diagram in FIG.
In the film forming zone indicated by arrow 1, 11 is cooled by a cooling device composed of a T-die connected to the tip of the extruder, a rubber roll 12 and a metal roll 13 to form a thermoplastic resin film (before stretching) 14. In the heating zone indicated by arrow 2, the thermoplastic resin film 14 is heated by the hot air supply device 22 while being transferred between the plurality of guide rolls 21, 21, .... The surface temperature of the thermoplastic resin film 14 is measured by a temperature measuring device (not shown) and fed back to the hot air supply device 22 via a control device. The surface temperature of the thermoplastic resin film 14 at the outlet of the heating zone is uniformly heated to a set temperature of Tg to (Tg + 60 ° C.) of the thermoplastic resin film 14.

FIG. 4 shows an embodiment in which the thermoplastic resin film 14 supplied to the heating zone 2 is supplied by directly connecting the thermoplastic resin film 14 formed in the film forming zone 1. It is not limited to the above, but may be, for example, a rolled long body of a thermoplastic resin film that is preformed by a solution casting method.

In the cooling zone indicated by arrow 3, in the heating zone 2, the thermoplastic resin film 14 uniformly heated to the set temperature of Tg to (Tg + 60 ° C.) is cooled by the cool air device 31. FIG. 4 shows an example in which the cooled thermoplastic resin film 14 is cooled by the upper and lower cool air devices 31 without being supported in the cooling zone, but the embodiment is not limited to this and, for example, As in the heating zone 2, it may be cooled while being transferred between a plurality of rolls.

The surface temperature of the thermoplastic resin film 14 at the exit of the cooling zone 3 is the same as that of the thermoplastic resin film 14.
From Tg to (Tg + 60 ° C.) set temperature of 10 to 30 ° C. in 1 to 20 seconds. Whether the cooling rate is too fast or slow, as detailed above with reference to FIG. 2,
The thermoplastic resin film 14 is completely cooled and fixed so that there is no temperature difference between a relatively thick portion and a relatively thin portion, or a slow temperature at which there is almost no temperature difference. Since the temperature decreases, it is cooled at the above cooling rate.

In the stretching zone indicated by arrow 4, the thermoplastic resin film 14 cooled in the cooling zone 3 is
While being cooled by the cold air device 31, it is stretched between the pair of gripping rolls 42 and 43 and the pair of pulling rolls 44 and 45. As in the cooling zone 3, the cooling rate in the stretching zone 4 is lower than the temperature of the thermoplastic resin film 14 at the outlet of the cooling zone 3 at 10 to 30 ° C in 1 to 20 seconds, and when stretched at such a temperature, The surface temperature of the thermoplastic resin film (after stretching) 46 immediately after leaving between the tension rolls 44 and 45 is (Tg−30 ° C.) to (Tg).
+ 20 ° C).

FIG. 5 shows another example of the retardation film manufacturing apparatus for carrying out the present invention.
The cooling zone indicated by is the pulling roll 4 of the drawing zone 4.
Thermoplastic resin stretched film 4 immediately after leaving between 4 and 45
This is a zone for cooling the surface temperature of No. 6 to a temperature lower than Tg, and is for preventing the stretched thermoplastic resin film 46 from shrinking after cooling. Incidentally, arrows 1 to
Since the zones indicated by 4 are the same as those in FIG. 4, the same reference numerals are used for the respective parts. In FIG. 5, 51
Is a cold air device. When being rapidly cooled and fixed, the thermoplastic resin stretched film 46 immediately after leaving between the pulling rolls 44 and 45 of the stretching zone 4 has an equal surface by a take-up roll (not shown) so that stretching stress is retained. The thermoplastic resin stretched film 4
6 is cooled to a temperature below Tg.

[0044]

EXAMPLES Examples of the present invention will be described below.
The invention is not limited to these examples. (Example 1) Polysulfone resin (Acomo, trade name "UDEL P3500", glass transition point 190 ° C)
Was melt-extruded at a mold temperature of 340 ° C. with a single screw type extruder equipped with a T die shown in FIG. 4, and cooled while nipping with a pair of cooling rolls controlled to a surface temperature of 165 ° C., A polysulfone resin film having a thickness of 75 μm ± 2.0 μm was produced.

The polysulfone resin film obtained was used for 2
The heating zone consisting of an oven controlled at 35 ° C. is transferred between the guide rolls 21, 21, ...
And then introduced into a cooling zone consisting of an oven controlled at 215 ° C. and passed through the oven controlled at 215 ° C. for 3 seconds to bring the temperature of the polysulfone resin film at the outlet of the cooling zone to 220 ° C. Cooled.

The polysulfone resin film exiting the cooling zone was then guided to a stretching zone consisting of an oven controlled at 190 ° C., in a longitudinal uniaxial stretching machine including gripping rolls 42 and 43 and pulling rolls 44 and 45. It was stretched 1.3 times in the length direction. The polysulfone resin film passed between the gripping roll and the tension roll of the longitudinal uniaxial stretching machine in the stretching zone in 3 seconds, and the temperature of the polysulfone resin stretched film immediately after leaving the tension roll was 20.
It was 8 ° C. The stretched polysulfone resin film was further left to cool in an environment of 20 ° C. during constant velocity transfer, cooled to a temperature of Tg or lower, and wound on a core body as a retardation film.

Example 2 Using a device shown in FIG. 5, a polycarbonate resin (manufactured by Teijin Kasei Co., Ltd., trade name “Panlite”, glass transition point 150 ° C.) was used at a mold temperature of 25.
Melt extrusion at 0 ° C., cooling while nipping with a pair of cooling rolls controlled to a surface temperature of 130 ° C., thickness of 75 μm
A polysulfone resin film of ± 2.0 μm was produced.

The obtained polycarbonate resin film was transferred between guide rolls through a heating zone consisting of an oven controlled at 200 ° C., heated to 200 ° C., and then placed in a cooling zone consisting of an oven controlled at 175 ° C. Induction was performed and the mixture was passed through the oven for 3 seconds to cool the temperature of the polycarbonate resin film at the exit of the cooling zone to 187 ° C.

The polycarbonate resin film exiting the cooling zone was then guided to a stretching zone consisting of an oven controlled at 155 ° C. and stretched 1.3 times in the length direction with a longitudinal uniaxial stretching machine. The polycarbonate resin film passed in 3 seconds between the gripping roll of the longitudinal uniaxial stretching machine and the pulling roll in the stretching zone, and the temperature of the polycarbonate resin stretched film immediately after leaving the pulling roll was 176 ° C. . The polycarbonate resin stretched film was further rapidly cooled to a temperature of Tg or lower by cold air during the uniform velocity transfer, and wound on a core body as a retardation film. The obtained polycarbonate resin stretched film has a thickness of 67.
It was μm ± 2.5 μm.

(Embodiment 3) A thickness of 8 is obtained in the same manner as in Embodiment 2.
A polysulfone resin film having a thickness of 3 μm ± 2.0 μm was formed, stretched in the same manner as in Example 2, and further rapidly cooled with cool air to a temperature of Tg or less during the uniform velocity transfer to a thickness of 73 μm ±.
A 2.5 μm stretched polysulfone resin film was produced.

(Embodiment 4) A thickness of 8 is obtained in the same manner as in Embodiment 2.
A polysulfone resin film of 3 μm ± 2.0 μm was molded. The resulting polysulfone resin film is 240
A heating zone consisting of an oven controlled at ℃ was transferred between the guide rolls and heated to 240 ℃, then 22
The polysulfone resin film was guided to a cooling zone consisting of an oven controlled at 0 ° C., passed through the oven for 3 seconds, and the temperature of the polysulfone resin film at the exit of the cooling zone was set to 228 ° C.
Cooled to.

The polysulfone resin film exiting the cooling zone was then guided to a stretching zone consisting of an oven controlled at 190 ° C. and stretched 1.3 times in the length direction with a longitudinal uniaxial stretching machine. The polysulfone resin film passed in 3 seconds between the gripping roll of the longitudinal uniaxial stretching machine and the pulling roll in the stretching zone, and the temperature of the polysulfone resin stretched film immediately after leaving the pulling roll was 2
It was 18 ° C. The stretched polycarbonate resin film was further cooled to a temperature of Tg or lower while nipping it with a pair of cooling rolls controlled to have a surface temperature of 165 ° C., and wound on a core body as a retardation film. The obtained polycarbonate resin stretched film has a thickness of 73 μm ± 2.5 μm
Met.

(Comparative Example 1) A thickness of 7 was obtained in the same manner as in Example 1.
A 5 μm ± 2.0 μm polysulfone resin film was molded. The obtained polysulfone resin film is 245
The heating zone consisting of an oven controlled at 0 ° C. is transferred between guide rolls and heated to 245 ° C., then immediately guided to a stretching zone consisting of an oven controlled at 180 ° C., in a longitudinal uniaxial stretching machine, It was stretched 1.3 times in the length direction. The polysulfone resin film passed between the gripping roll and the tension roll of the longitudinal uniaxial stretching machine in the stretching zone in 1 second, and the temperature of the polysulfone resin stretched film immediately after leaving the tension roll was 234 ° C. . The stretched polysulfone resin film was further left to cool in an environment of 20 ° C. during constant velocity transfer, cooled to a temperature of Tg or lower, and wound on a core body as a retardation film. The obtained polysulfone resin stretched film has a thickness of 67 μm.
It was m ± 2.5 μm.

(Comparative Example 2) A thickness of 7 was obtained in the same manner as in Example 1.
A 5 μm ± 2.0 μm polysulfone resin film was molded. The obtained polysulfone resin film is 230
A heating zone consisting of an oven controlled at ℃ was transferred between guide rolls and heated to 230 ℃, then 22
The temperature of the polysulfone resin film at the exit of the cooling zone was set to 225 by introducing it into a cooling zone consisting of an oven controlled at 0 ° C. and passing through the oven for 30 seconds.
Cooled to ° C.

The polysulfone resin film exiting the cooling zone was then guided to a stretching zone consisting of an oven controlled at 205 ° C. and stretched 1.3 times in the length direction with a longitudinal uniaxial stretching machine. Between the gripping roll of the longitudinal uniaxial stretching machine in the stretching zone and the pulling roll, the polysulfone resin film passed in 30 seconds, and the temperature of the polysulfone resin stretched film immediately after leaving the pulling roll was:
It was 218 ° C. The polysulfone resin stretched film is further cooled in an environment of 20 ° C. while being transported at a constant speed,
It was cooled to a temperature of g or less and wound on a core as a retardation film.

(Comparative Example 3) A thickness of 8 was obtained in the same manner as in Example 1.
A polysulfone resin film of 3 μm ± 2.0 μm was molded. The obtained polysulfone resin film is 210
A heating zone consisting of an oven controlled at 0 ° C. was transferred between guide rolls to heat it to 210 ° C., then immediately guided to a stretching zone consisting of an oven controlled at 210 ° C., as in Example 1. It was stretched 1.3 times in the length direction with a longitudinal uniaxial stretching machine. The stretched polysulfone resin film that had left the pulling roll was further allowed to cool in an environment of 20 ° C. during constant velocity transfer, cooled to a temperature of Tg or lower, and wound on the core body as a retardation film. The obtained polysulfone resin stretched film has a thickness of 73 μm ±
It was 2.5 μm.

(Comparative Example 4) A thickness of 8 was obtained in the same manner as in Example 1.
A polysulfone resin film of 3 μm ± 2.0 μm was molded. The resulting polysulfone resin film is 240
A heating zone consisting of an oven controlled at ℃ was transferred between the guide rolls and heated to 240 ℃, then 22
The polysulfone resin film was cooled to 225 ° C. by passing through a cooling zone consisting of an oven controlled at 0 ° C. and passing through the oven for 30 seconds.

The polysulfone resin film exiting the cooling zone was then guided to a stretching zone consisting of an oven controlled at 190 ° C., and stretched 1.3 times in the length direction with a longitudinal uniaxial stretching machine. The polysulfone resin stretched film that has left the pulling roll of the longitudinal uniaxial stretching machine has a further 170
The film was guided to a slow cooling zone consisting of an oven controlled at 0 ° C., cooled to 170 ° C. in 1 minute of constant velocity transfer, and wound on a core as a retardation film. The obtained polysulfone resin stretched film has a thickness of 73 μm ± 2.5 μm.
It was m.

The retardation values of the retardation films obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were measured, and the average value and the variation were determined in the following manner. The measurement results are shown in Table 1.

[Sample] Except for both sides of the retardation film having a width of 1000 mm, the central portion having a width of 500 mm has a length of 100 mm.
It was cut out at 0 mm and used as a sample.

[Measurement of Retardation Value] A retardation value of 630 nm was measured at 1 cm intervals in the width direction and the length direction of the sample. As the measured values, the average value, the maximum value of the variation, the difference between the maximum value and the minimum value of the measured values, and the maximum value of the variation were calculated as the maximum value of the difference between the measured values of two adjacent points.

[0062]

[Table 1]

[0063]

The method for producing a retardation film of the present invention comprises:
Since it is configured as described above, it is not limited to the thermoplastic resin film prepared by the solution casting method and having a relatively small thickness variation, and the thermoplastic resin prepared by the melt casting method such as the T-die method is used. Even a resin film can obtain a retardation film showing uniform retardation characteristics with little variation, brittle fracture occurs due to excessive shear stress during stretching, and the thermoplastic resin film ruptures during stretching, or the reverse. In addition, the retardation film can be stably obtained with high productivity without the viscosity of the thermoplastic resin film lowering and causing a trouble during transportation.

[Brief description of drawings]

FIG. 1 is an image view of a temperature difference generated in a thick portion and a thin portion in a cooling zone and a stretching zone of a method for producing a retardation film of the present invention.

FIG. 2 is an image diagram of a temperature difference generated in a thick and thin portion in a cooling zone and a stretching zone of a cooling method, which is compared with the method for producing a retardation film of the present invention.

FIG. 3 is an image diagram of a stress difference caused by a difference in thickness of a thermoplastic resin film in a stretching process.

FIG. 4 is a conceptual diagram showing an example of an apparatus for producing a retardation film used in the present invention.

FIG. 5 is a conceptual diagram showing another example of a retardation film manufacturing apparatus used in the present invention.

[Explanation of symbols]

1 Film forming zone 11 T die 12, 13 Cooling roll (rubber roll and metal roll) 14 Thermoplastic resin film 2 heating zones 21 guide roll 22 Heating device 3, 5 cooling zone 31, 41, 51 Cooling device 4 stretching zone 42,43 Grasping roll (drawing machine) 44, 45 Tension roll (drawing machine) 46 Stretched film of thermoplastic resin

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Claims (4)

(57) [Claims] 1. A retardation film manufacturing apparatus provided with a heating zone, a cooling zone and a stretching zone in the above order,
First, in the heating zone, the thermoplastic resin film is
The glass transition temperature (Tg) to (Tg + 60 ° C.) is heated to a constant temperature, and then, in the cooling zone, the thermoplastic resin film has a temperature difference between minute portions according to the thickness. The thermoplastic resin film is cooled by such a cooling means as it occurs, and in the stretching zone, the thermoplastic resin film is further cooled while being stretched.
A method for producing a retardation film, which comprises stretching at 20 ° C.). 2. The cooling means in the cooling zone is 1
-10 seconds from the temperature of the thermoplastic resin film in 20 seconds
It is cooled to a temperature lower by -30 ° C, and the cooling means in the stretching zone further has a temperature of 10 to 20 seconds from the temperature of the thermoplastic resin film in the cooling zone in 1 to 20 seconds.
The method for producing a retardation film according to claim 1, wherein the stretching is started while cooling to a temperature lower by 30 ° C. 3. The stretched thermoplastic resin film is rapidly cooled to a temperature of (Tg−20 ° C.) or lower.
A method for producing the retardation film described. 4. The method for producing a retardation film according to claim 1, 2 or 3, wherein the thermoplastic resin film is a polysulfone resin film.