JP2971319B2 - Method for producing optically isotropic film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optically isotropic film by a casting method. More specifically, the present invention relates to a method for obtaining an optically isotropic film by drying a film containing a solvent after being peeled off from a casting drum or a casting belt.

[0002]

2. Description of the Related Art Optically isotropic films are used as substrates for plastic liquid crystal cells and retardation compensators. Such an optically isotropic film is manufactured by a casting film forming method.

[0003] When an optically isotropic film is produced by this casting method, the film peeled off from a casting drum or a casting belt contains a high concentration of solvent. Therefore, in order to evaporate a high-concentration solvent contained in the film, the film separated from the casting drum or the casting belt is dried in a drying step.

[0004] Conventionally, in this drying step, a suspended dryer in which the film path length can be made extremely long, a non-contact float dryer in which the film travels in the width direction free, or an interval in the width direction can be freely set. For example, a tenter-type dryer that moves a film while holding it with a pin or a clip that can be adjusted to a predetermined value is used.

[0005]

The optically isotropic film is required to be isotropic not only in the film plane but also in a direction perpendicular to the film plane. In other words, regarding the refractive index in the three-dimensional direction of the optically isotropic film, the refractive index in the running direction in the film plane is nx, the refractive index in the direction perpendicular to nx in the film plane is ny, and the refractive index perpendicular to the film plane is ny. Assuming that the refractive index in the direction is nz, the refractive index differences Δn1 = | nx−ny | and Δn2 = | nx−nz
Is preferably Δn1 ≦ 10 ⁻⁴ and Δn2 ≦ 10 ⁻³ , respectively, and more preferably Δn1 ≦ 6 × 10 ⁻⁵ and Δn2 ≦ 6 × 10 ⁻⁴ .

However, in the conventional casting film forming method, when a film containing a high-concentration solvent of about 10 to 35% separated from a casting drum or a casting belt is dried, optical isotropy is impaired. There was a problem to be done.

For example, in a suspension (or float) dryer, the film is free in the horizontal direction (width direction), so that no tension is applied in this direction, but the film is normal in the vertical direction (running direction). The line tension and the shrinkage stress accompanying the evaporation of the solvent required for proper transport act, and the film is oriented in the longitudinal direction in the film plane, thereby increasing the difference in the refractive index.

Further, in a tenter type dryer using pins (or clips) for fixing the film in the width direction, since both ends of the film are gripped, a strong shrinkage stress due to solvent evaporation acts in the width direction. In addition, since line tension is applied in the longitudinal direction, orientation occurs in the film plane, and the difference in refractive index increases.

As described above, it is difficult to obtain a film having a small difference in refractive index by the conventional drying method. In order to obtain a film having a small difference in refractive index, for example, there is a method in which heat treatment is performed offline to relax the orientation, but there is a problem that productivity is extremely low.

An object of the present invention is to solve the above problem and to obtain an optically isotropic film having a small difference in refractive index.

[0011]

The method for producing an optically isotropic film according to the present invention is characterized in that, when an optically isotropic film is produced by a casting film forming method, the film is separated from a casting drum or a casting belt. First, the film containing the solvent is dried using a tenter drier in four continuous drying steps in which the ambient temperature is controlled.

At this time, the apparent glass transition temperature Tg1 (° C.) of the film in the first drying step and the apparent glass transition temperature Tg2 of the film in the second drying step
(° C.), the apparent glass transition temperature Tg3 (° C.) of the film in the third drying step, and the apparent glass transition temperature Tg 4 (° C.) of the film in the fourth drying step, and the ambient temperature Tc1 ( ℃) Tg1 ≦
Tc1 ≦ Tg1 + 60, the ambient temperature Tc2 (° C.) in the second drying step is set to Tg2 ≦ Tc2 ≦ Tg2 + 60,
The atmosphere temperature Tc3 (° C.) in the drying step is set as Tg3 ≦ T
c3 ≦ Tg3 + 60, and the atmosphere temperature Tc4 (° C.) in the fourth drying step is controlled to Tg4-70 ≦ Tc4 ≦ Tg4-20.

In the first drying step, the film is run without gripping both ends in the film width direction. In the second drying step, the film is run while gripping both ends in the film width direction by the gripping tool, and the third drying step is performed. In the step, after cutting and removing at least the region of the grip portion at both ends in the film width direction, the film is run in a state where both ends in the film width direction are not gripped, and even in the fourth drying step, the film is held without gripping both ends in the film width direction. Let it run.

Further, the residence time tm1 (min) of the film in the first drying step is 1 ≦ tm1 ≦ 5, and the residence time tm2 (min) of the film in the second drying step is 1 ≦ tm2 ≦
5. The residence time tm3 of the film in the third drying step
(Min) is 0.5 ≦ tm3 ≦ 2.5, and the residence time tm4 (min) of the film in the fourth drying step is 0.5 ≦ tm4 ≦
The film after passing through the fourth drying step is further dried in the fifth drying step. In the fifth drying step, drying is performed by a suspension type or a float type dryer. Then, with respect to the apparent glass transition temperature Tg5 (° C.) of the film in the fifth drying step, the atmosphere temperature Tc5 (° C.) in the fifth drying step is set to T.
g5-20 ≦ Tc5 ≦ Tg5 + 50, and the residence time tm5 (min) of the film in the fifth drying step is 10 ≦
tm5 ≦ 60, and the tension in the film running direction in the fifth drying step is set to 0.5 to 2.5 kg / cm 2. The above is the feature of the present invention.

The present inventors have conducted intensive studies on the mechanism of increasing the difference in refractive index in the conventional drying method, and have obtained the following findings. In other words, when a pin (or clip) tenter-type dryer is used to dry the film from the inlet to the outlet of the dryer while holding the film at both ends, the film is transported in the initial stage of the drying process. In, a sudden shrinkage accompanying the evaporation of the solvent occurs. At this time, since both ends of the film are gripped, free shrinkage does not occur in the width direction and strong shrinkage stress is applied to the film. Then, the contraction stress in the width direction is added to the line tension in the vertical direction (flow direction), and tension is applied simultaneously in the vertical and horizontal directions. Therefore, orientation occurs in the film plane, and the difference in the refractive index increases.

In a subsequent step, when the drying temperature is relatively low (around the glass transition temperature of the film at that time), the orientation relaxation is small. For this reason, the distortion generated in the initial stage of the pin (or clip) tenter dryer cannot be eliminated. Therefore, the refractive index difference remains large.

On the other hand, when the drying temperature is relatively high (higher than the glass transition temperature of the film at that time), sagging occurs due to the elongation of the film. At this time, since both ends of the film are gripped, orientation relaxation near the both ends of the film is unlikely to occur, but near the center, the influence of the tension due to sagging is small, so that the orientation is relaxed, and the difference in refractive index is reduced. Therefore, the pattern in the width direction of the refractive index difference of the film is a so-called pan-bottom pattern in which both ends are high and the center is low.

Further, in consideration of shrinkage and elongation occurring in the pin (or clip) tenter type dryer, the drying process was divided into a plurality of regions and the rail width was adjusted for each region to perform drying. Resin solvent changes every moment in the pin (or clip) tenter type dryer, and at the same time the behavior of the film changes. It is difficult to change the rail width for each area, and the width changes sharply for each area. Is required, the pin (or clip) of the film comes off, and a process trouble occurs.

Further, when the film is not gripped over the entire area of the pin (or clip) tenter type dryer, that is, when the film is conveyed in a free state in the width direction of the film from the entrance to the exit of the pin (or clip) tenter type dryer, It was found that orientation occurred in the film plane due to its own weight and line tension, and the difference in refractive index slightly increased, but the distribution in the width direction was eliminated.

On the other hand, when a film containing a high-concentration solvent immediately after being peeled off from a casting drum or a casting belt is dried by a suspension type (or float type) drier, as described above, the vertical length in the film plane is increased. Although orientation occurs in the direction to increase the refractive index difference, it was found that when a film having a relatively low solvent concentration was dried, the orientation could be relaxed depending on the conditions of the drying temperature and the line tension.

Based on the above findings, the present inventors have found that a film separated from a casting drum or a casting belt does not have a refractive index difference in the width direction by using the pin (or clip) tenter dryer of the present invention. It has been found that an optically isotropic film having a small difference in refractive index can be obtained by drying by a method and subsequently drying by a hanging type (or float type) drier, and has reached the present invention. That is, even if the order in which the film immediately after being peeled off from the casting drum or the casting belt is processed by the pin (or clip) tenter type dryer and the suspension type (or float type) dryer is reversed, either one of them is used alone. It was found that the optically isotropic film having a small difference in the refractive index of the present invention could not be obtained even if the treatment was carried out.

Therefore, in the first drying step of the method for producing an optically isotropic film of the present invention, the film is run without gripping both ends in the film width direction. At that time, the first
Apparent glass transition temperature T of film in drying process
The ambient temperature Tc1 (° C) in the first drying step is set to Tg1 ≦ Tc1 ≦ Tg1 + 60 with respect to g1 (° C).
And the residence time tm1 of the film in the first drying step.
(Minute) is set to 1 ≦ tm1 ≦ 5. Thereby, shrinkage accompanying the evaporation of the solvent is caused freely in the width direction of the film. As a result, the in-plane orientation of the film is minimized.

Subsequently, in the second drying step, the film is run while gripping both ends in the film width direction with a gripper such as a pin or a clip. At this time, the apparent glass transition temperature Tg2 of the film in the second drying step
(° C.) with respect to the ambient temperature Tc in the second drying step.
2 (° C.) is set to Tg2 ≦ Tc2 ≦ Tg2 + 60. And the residence time tm2 (min) of the film in the second drying step.
Is set to 1 ≦ tm2 ≦ 5. Thereby, while the drying of the film is continued, the influence of sagging and line tension due to the weight of the film is reduced, and running stability is ensured. However, at this stage, since the film travels with both ends gripped, the widthwise pattern of the refractive index difference becomes a pan bottom shape.

In the subsequent third drying step, at least the region of the grip portion at both ends in the film width direction is cut and deleted, and then the film is run without holding both ends in the film width direction. At that time, with respect to the apparent glass transition temperature Tg3 (° C.) of the film in the third drying step,
The ambient temperature Tc3 (° C.) in the third drying step is Tg3
≤ Tc3 ≤ Tg3 + 60. The residence time tm3 (min) of the film in the third drying step is 0.5 ≦ tm
3 ≦ 2.5. Thereby, the pan-bottom pattern of the refractive index difference in the width direction of the film can be eliminated. Further, the orientation is relaxed in the entire width direction, and the refractive index difference can be reduced.

It is more preferable that the area of the film to be cut and removed in the third drying step is in the range of the gripping portions at both ends in the film width direction and 5 to 15 mm inside the gripping portion. Thus, the pan bottom pattern of the refractive index difference in the width direction of the film can be eliminated with higher productivity.

Further, in the fourth drying step, the film is continuously run without gripping both ends in the film width direction. At this time, with respect to the apparent glass transition temperature Tg4 (° C.) of the film in the fourth drying step, the ambient temperature Tc4 (° C.) in the fourth drying step is Tg4−70 ≦ Tc.
4 ≦ Tg4−20. The residence time tm4 (min) of the film in the fourth drying step is 0.5 ≦ tm3 ≦
Set to 2.5. As a result, the film is quenched, and the removed film is fixed with a small difference in refractive index over the entire width direction.

Next, drying in a fifth drying step is performed by a suspension type (or float type) dryer. At this time, the apparent glass transition temperature Tg5 of the film in the fifth drying step
(° C.) with respect to the ambient temperature Tc in the fifth drying step.
5 (° C.) as Tg5-20 ≦ Tc5 ≦ Tg5 + 50,
And the residence time tm5 of the film in the fifth drying step.
(Min) is set to 10 ≦ tm5 ≦ 60, and the tension in the film running direction in the fifth drying step is set to 0.5 to 2.5 kg.
/ Square cm. In the fifth drying step, orientation relaxation occurs throughout the width direction, and the difference in refractive index decreases.

As a result, an optically isotropic film having a small difference in refractive index, that is, Δn 1 ≦ 6 × 10 ⁻⁵ and Δn 2 ≦ 6 × 10 ⁻⁴ with a residual solvent concentration of 0.5 wt% or less can be obtained.
Further, in the manufacturing method of the present invention, the orientation is relaxed in a state where a slight tension acts in the running direction. As a result, the slow axis angle distribution in the width direction can be made within ± 5 °.

Incidentally, the apparent glass transition temperature of the film in the present invention is defined as follows. First,
The glass transition temperature of a film containing a solvent varies depending on the residual solvent concentration. As an example, when the solvent is methylene chloride, the glass transition temperature of the polycarbonate film is 15 when the residual solvent concentration is 0 wt%.
9 ° C., 103 ° C. when the residual solvent concentration is 5 wt%, 66 ° C. when the residual solvent concentration is 10 wt%, and 15 wt% residual solvent concentration
% Is 49 ° C. Further, even during each drying step of the present invention, the glass transition temperature of the film changes every moment according to the change in the residual solvent concentration.

Therefore, in the present invention, drying is carried out on a trial basis in advance while changing the conditions. At that time, the residual solvent concentration of the film in each drying step is actually measured, a glass transition temperature corresponding to the measured concentration is determined, and the temperature is determined as an apparent glass transition temperature of the film in the drying step.

Here, as the position where the concentration of the residual solvent in the film is actually measured in each drying step, various methods such as a physical intermediate position in each drying step or an inlet portion and an outlet portion in each step are used. be able to. Among these, the glass transition temperature of the film at the entrance portion of each step and the glass transition temperature of the film at the exit portion thereof are both determined, and the intermediate temperature is determined as the apparent glass transition temperature of the film in the process. More preferred. This allows the film to follow the change in the state of the film, and is also excellent in productivity.

In the first drying step and the second drying step in the present invention, the residence time of the film is relatively long, and the speed of the state change of the film is high. Therefore, the first
The drying step and the second drying step are equally divided into the first half and the second half, respectively. The apparent glass transition temperature Tg1a (° C.) of the film in the first half of the first drying step, and the apparent glass transition temperature Tg1b of the film in the second half of the first drying step (° C),
Compared with the apparent glass transition temperature Tg2a (° C.) of the film in the first half of the second drying step and the apparent glass transition temperature Tg2b (° C.) of the film in the second half of the second drying step, the ambient temperature Tc1a in the first half of the first drying step is different.
(° C.) is Tg1a ≦ Tc1a ≦ Tg1a + 60, and the ambient temperature Tc1b (° C.) in the latter half of the first drying step is Tg1.
b ≦ Tc1b ≦ Tg1b + 60, the ambient temperature Tc2a (° C.) in the first half of the second drying step is set to Tg2a ≦ Tc2a ≦
Tg2a + 60, the ambient temperature Tc2b (° C.) in the second half of the second drying step is set to Tg2b ≦ Tc2b ≦ Tg2b + 60.
It is more preferable to control to.

The fifth drying step is divided into two equal parts, the first half and the second half, and the apparent glass transition temperature Tg5a (° C.) of the film in the first half of the fifth drying step and the apparent glass transition temperature of the film in the second half of the first drying step. Tg5b
(° C.), the ambient temperature Tc5a (° C.) in the first half of the fifth drying step is set to Tg5a−20 ≦ Tc5a ≦ Tg5a.
+50, ambient temperature Tc5b in the second half of the fifth drying step
(° C.) can be set to Tg5b−20 ≦ Tc5b ≦ Tg5b + 50.

Further, if necessary, the first, second and fifth drying steps may be divided into three or more divisions. Third and fourth
The drying step can be divided into two or more parts.

Further, following the fifth drying step,
A sixth drying step for rapidly cooling the film may be provided. At this time, the ambient temperature Tc6 (° C) in the sixth drying step is set to Tg6-105 ≦ with respect to the apparent glass transition temperature Tg6 (° C) of the film in the sixth drying step.
Tc6 ≦ Tg6-55, the film residence time tm6 (min) in the sixth drying step is 1 ≦ tm6 ≦ 5, and the tension in the film running direction in the sixth drying step is 0.5 to 2.5 kg / square. cm is preferable.

In the present invention, all resins that can be produced by the casting method can be applied. For example, a cellulose resin, a polycarbonate resin, a polyarylate resin, a polyolefin resin, a polystyrene resin, a vinyl chloride resin, an acrylic resin, a polysulfone resin, a polyethersulfone resin, and a mixture of two or more thereof. Alternatively, copolymerization and the like can be mentioned.

The solvents applicable to the present invention include methylene chloride, dichloroethane, trichloroethane, chlorobenzene, chloroform, tetrahydrofuran, dioxane, dioxolan, cyclohexanone, n-methylpyrrolidone, benzene, toluene, xylene, n-hexane, acetone and methyl ethyl ketone. One or two such as
A mixed solvent of at least one kind can be appropriately selected and used according to the shape of the resin and / or the apparatus.

Among these materials, in order to obtain an optically isotropic film having more preferable physical properties with good productivity, a polycarbonate resin is used as a resin of the film material, and methylene chloride or dioxolane is used as a solvent. Is more preferable. It is more preferable that the concentration of the residual solvent in the film after the film is peeled off from the casting drum or the casting belt is 10 to 20% by weight.

Examples of the present invention and comparative examples are shown below. Note that the technical scope of the present invention is not limited to these examples.

[0040]

Example 1 Methylene chloride as a residual solvent was added to 17
The polycarbonate film containing wt% was dried using the pin tenter type dryer of the present invention. The pin tenter type dryer used has a total length of 9 m and a total width of 1.5
m. The dryer was divided into first to fourth drying steps. As the polycarbonate resin, "C-1400" manufactured by Teijin Chemicals Ltd. was used.

First, in the first drying step, the film runs with both ends in the width direction not being gripped. That is, the film travels in a free state without contacting the pin rail of the pin tenter type dryer. Note that the control of the atmosphere temperature in the first drying step is performed by two steps in the first half and the second half.
This was performed separately in equal parts.

Subsequently, in the second drying step, the film is first pressed at both ends in the film width direction against the pin rail by the film press. Then, the film runs while both ends in the width direction are gripped by the pin rail. Note that the control of the atmosphere temperature in the second drying step was performed by dividing the step into two equal parts, a first half and a second half.

Thereafter, in the third drying step, the film is firstly cut by an edge cutter to the gripping portions at both ends of the film and further to a portion 10 mm inward. As a result, the film travels with the width direction being free again.

Further, also in the fourth drying step, the film continuously travels in a free state in the width direction. At the end of the fourth drying step and the end of the pin rail, both ends of the cut film are removed. By the above,
The drying process using the pin tenter type dryer is completed.

At that time, in the first half of the first drying step of the first embodiment, the ambient temperature Tc1a (° C.) was set to 90 ° C. At this time, the glass transition temperatures of the film containing the residual solvent at the entrance and the exit in the first half of the first drying step are 45 ° C. and 65 ° C., respectively, and the apparent glass transition temperature Tg1a (° C.) in the first half of the first drying step is 55 ° C.
That is, in the first half of the first drying step, the ambient temperature Tc1a
Was set to Tg1a + 35. In the first half of the first drying step, the residence time of the film is 0.8 minutes.

In the second half of the subsequent first drying step, the ambient temperature Tc1b (° C.) was set to 130 ° C. At this time,
The glass transition temperatures of the film containing the residual solvent at the inlet and outlet in the latter half of the first drying step were 65 ° C. and 75 ° C., respectively.
° C, and the apparent glass transition temperature Tg1b (° C) in the latter half of the first drying step is 70 ° C. That is, in the latter half of the first drying step, the ambient temperature Tc1b is set to Tg1b +
It was set to 60. In the latter half of the first drying step, the residence time of the film is 0.8 minutes.

In the first half of the subsequent second drying step, the ambient temperature Tc2a (° C.) was set to 135 ° C. At this time,
The glass transition temperatures of the film containing the residual solvent at the inlet and outlet in the first half of the second drying step were 75 ° C. and 90 ° C., respectively.
° C, and the apparent glass transition temperature Tg2a (° C) in the first half of the second drying step is 83 ° C. That is, in the first half of the second drying step, the ambient temperature Tc2a is equal to Tg2a +
52 was set. In the first half of the second drying step, the residence time of the film is 0.8 minutes.

In the second half of the subsequent second drying step, the ambient temperature Tc2b (° C.) was set to 135 ° C. At this time,
The glass transition temperatures of the film containing the residual solvent at the inlet and outlet in the latter half of the second drying step were 90 ° C. and 10 ° C., respectively.
5 ° C., and the apparent glass transition temperature Tg2b (° C.) in the latter half of the second drying step is 98 ° C. That is, the second
In the latter half of the drying step, the ambient temperature Tc2b is set to Tg2b
Set to +37. In the latter half of the second drying step, the residence time of the film is 0.8 minutes.

In the subsequent third drying step, the ambient temperature Tc3 (° C.) was set to 135 ° C. At this time, the glass transition temperatures of the film containing the residual solvent at the entrance and the exit of the third drying step are 105 ° C. and 115 ° C., respectively, and the apparent glass transition temperature Tg in the third drying step.
3 (° C.) is 110 ° C. That is, in the third drying step, the ambient temperature Tc3 was set to Tg3 + 25. In the third drying step, the residence time of the film is 0.8
Minutes.

In the subsequent fourth drying step, the ambient temperature Tc4 (° C.) was set to 70 ° C. At this time, the glass transition temperatures of the film containing the residual solvent at the entrance and the exit of the fourth drying step were 115 ° C. and 125 ° C., respectively, and the apparent glass transition temperature Tg in the fourth drying step.
4 (° C.) is 120 ° C. That is, in the fourth drying step, the ambient temperature Tc4 was set to Tg4-50. In the fourth drying step, the residence time of the film is 0.8
Minutes.

Subsequently, drying was performed in a fifth drying step using a hanging dryer. In the fifth drying step, the ambient temperature Tc5 (° C.) was set to 145 ° C. At this time, the glass transition temperature of the film containing the residual solvent at the entrance and exit of the fifth drying step was 1
25 ° C. and 155 ° C., and the apparent glass transition temperature Tg5 (° C.) in the fifth drying step is 140 ° C. That is, in the fifth drying step, the ambient temperature Tc5 is set to Tg5
Set to +5. Further, in the fifth drying step, a tension of 1.5 kg / cm 2 was applied to the film in the running direction. In the fifth drying step, the residence time of the film was 45 minutes.

Subsequently, drying was performed in a sixth drying step using a hanging dryer. In the fifth drying step, the ambient temperature Tc6 (° C.) was set to 90 ° C. At this time, the glass transition temperature of the film containing the residual solvent at the inlet and the outlet in the sixth drying step is 155 ° C. That is, Tc6 was set such that the relationship between the apparent glass transition temperature Tg6 (° C.) and the ambient temperature Tc6 in the sixth drying step was Tc6 = Tg6-65. Further, the residence time in the sixth drying step is 2
The tension in the traveling direction was 1.5 kg / cm 2.

The optical characteristics of the thus obtained film having a thickness of 100 μm were measured with a measuring device (trade name “KOBRA-21ADH”) manufactured by KS System. First, the angle dependence of the retardation value was determined by measuring the retardation value while rotating the optical axis of the film about the rotation axis. Next, using a film thickness of 100 μm and an index of refraction ellipsoid using an average refractive index of 1.585,
The refractive indices nx, ny and nz in the three-dimensional direction are obtained, and the refractive index differences Δn1 = | nx−ny | and Δn2 = | nx−nz |
Was calculated.

Then, the film of Example 1 has Δn 1 =
4 × 10^-FiveAnd Δn 2 = 5 × 10 ^-FourAnd the refractive index difference
And a good optically isotropic film having a small value. Also
The slow axis angle distribution in the width direction obtained by the above measuring machine is ± 3 °.
there were. The residual solvent concentration was 0.2% by weight.

[0055]

Comparative Example 1 Methylene chloride as a residual solvent was added to 17
The polycarbonate film containing wt% was dried in the drying step A and the drying step B by using a direct suspension type drier without using the pin tenter type drier of the present invention.

Atmosphere temperature TcA in the first drying step A
(° C.) was set to 120 ° C. At this time, the glass transition temperatures of the film at the entrance and exit of the drying step A are 45 ° C. and 150 ° C., respectively, and the apparent glass transition temperature TgA (° C.) in the drying step A is 98 ° C. That is, in the drying step A, the ambient temperature was set so that TcA = TgA + 22. Further, in the drying step A, the film is moved in the traveling direction by 1.5 kg / cm 2.
Tension. In the drying step A, the residence time of the film was 45 minutes.

Next, the ambient temperature TcB (° C.) in the drying step B
Was set to 90 ° C. At this time, both the glass transition temperature of the film at the entrance and the exit of the drying step B are 150 ° C. That is, the relationship between the apparent glass transition temperature TgB (° C.) and TcB (° C.) in the drying step B is TcB
= Atmosphere temperature was set so that = TgB-60. Further, the residence time in the drying step B was 2 minutes, and the tension in the running direction was 1.5 kg / cm 2.

The optical characteristics of the thus obtained film having a thickness of 100 μm were measured in the same manner as in Example 1, and the refractive index differences Δn1 and Δn2 were calculated. The result is Δn1 = 8
× 10 ^-4 and Δn2 = 2 × 10 ^-3 , and the difference in refractive index was large. The slow axis angle distribution in the width direction measured by the same method as in Example 1 was ± 3 °. The residual solvent concentration was 0.4% by weight.

[0059]

Comparative Example 2 Methylene chloride as a residual solvent was added to 17
Each section corresponding to the first to fourth drying steps in Example 1 except that the conditions for gripping and cutting both ends of the film were changed when the polycarbonate film containing wt% was dried with a pin tenter dryer. Was dried using a pin tenter type drier having the same atmosphere temperature and residence time as in Example 1.

That is, in the section corresponding to the first to fourth drying steps of Example 1, first, both ends in the film width direction were pressed against the pin rail by the film pressing. Then, during a section corresponding to the first to fourth drying steps, the film was run while holding both ends in the width direction by the pin rail.

At the end of the drying step,
Both ends in the width direction of the film were cut and removed. That is, the gripping portions at both ends of the film and the portion further 10 mm inside from the gripping portions were cut and removed by an edge cutter.

Subsequently, drying corresponding to the fifth to sixth drying steps was performed using the hanging dryer under the same conditions as in Example 1.

The optical characteristics of the thus obtained film having a thickness of 100 μm were measured in the same manner as in Example 1, and the refractive index differences Δn 1 and Δn 2 were calculated. The result is Δn1 =
1.5 × 10 ⁻⁴ and Δn 2 = 9.0 × 10 ⁻⁴ ,
The refractive index difference was large. The slow axis angle distribution measured by the same method as in Example 1 was ± 10 °. The residual solvent concentration was 0.2% by weight.

[0064]

According to the present invention, as described in detail above, Δn1 ≦
An optically isotropic film having a small refractive index difference of 6 × 10 ⁻⁵ and Δn2 ≦ 6 × 10 ⁻⁴ can be obtained. At the same time, the distribution of the slow axis angle in the width direction can be kept within ± 5 °.

Therefore, the optically isotropic film of the present invention can be used not only as an electrode substrate material for plastic liquid crystal cells and touch panels, a polarizing plate material, an optical filter material, a goggle material and the like, but also as an optical material of the present invention. The distribution of retardation values when stretched in the vertical and / or horizontal directions using an isotropic film is uniform, and is excellent as a retardation plate material and an elliptic (or circular) polarizing plate material.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 41/12 B29C 41/46

Claims (4)

(57) [Claims] When producing an optically isotropic film by a casting film forming method, a film containing a solvent which has been peeled off from a casting drum or a casting belt is first subjected to an atmosphere using a tenter type dryer. A step of drying the film by four successive drying steps of controlled temperature, wherein an apparent glass transition temperature Tg1 (° C.) of the film in the first drying step and an apparent glass transition temperature of the film in the second drying step Transition temperature Tg2
(° C.), the apparent glass transition temperature Tg3 (° C.) of the film in the third drying step, and the apparent glass transition temperature Tg 4 (° C.) of the film in the fourth drying step, and the ambient temperature Tc1 ( ℃) Tg1 ≦
Tc1 ≦ Tg1 + 60, the ambient temperature Tc2 (° C.) in the second drying step is set to Tg2 ≦ Tc2 ≦ Tg2 + 60,
The atmosphere temperature Tc3 (° C.) in the drying step is set as Tg3 ≦ T
c3 ≦ Tg3 + 60, the atmosphere temperature Tc4 (° C.) in the fourth drying step is controlled to Tg4-70 ≦ Tc4 ≦ Tg4-20, and in the first drying step, the film is run without gripping both ends in the film width direction, In the second drying step, the film is run while gripping both ends in the film width direction by the gripping tool. In the third drying step, at least the area of the grip portion at both ends in the film width direction is cut and deleted, and then both ends in the film width direction are removed. The film is run without being gripped, the film is run without gripping both ends in the film width direction in the fourth drying step, and the residence time tm1 (minute) of the film in the first drying step is 1 ≦ t.
m1 ≦ 5, residence time t of the film in the second drying step
m2 (min) is 1 ≦ tm2 ≦ 5, and the residence time tm3 (min) of the film in the third drying step is 0.5 ≦ tm3 ≦ 2.
5. The residence time tm4 of the film in the fourth drying step
(Minutes) is set to 0.5 ≦ tm4 ≦ 2.5, and in order to further dry the film after the fourth drying step, drying is performed by a suspension type or a float type drier.
A drying step is provided, and the ambient temperature Tc5 (° C) in the fifth drying step is set to Tg5−20 ≦ T with respect to the apparent glass transition temperature Tg5 (° C) of the film in the fifth drying step.
c5 ≦ Tg5 + 50, the residence time tm5 (min) of the film in the fifth drying step is 10 ≦ tm5 ≦ 60, and the tension in the film running direction in the fifth drying step is 0.5 to 2.5 kg / cm 2. A method for producing an optically isotropic film. 2. The optical device according to claim 1, wherein the area of the film to be cut and removed in the third drying step is a range between the gripping portions at both ends in the film width direction and 5 to 15 mm inside the gripping portion. A method for producing a isotropic film. 3. The first drying step and the second drying step are equally divided into the first half and the second half, respectively, and the apparent glass transition temperature Tg1a (° C.) of the film in the first half of the first drying step,
The apparent glass transition temperature Tg1b (° C.) of the film in the latter half of the drying step, the apparent glass transition temperature Tg2a (° C.) of the film in the first half of the second drying step, and the apparent glass transition temperature Tg of the film in the latter half of the second drying step.
2b (° C.), the ambient temperature Tc1a (° C.) in the first half of the first drying step is set to Tg1a ≦ Tc1a ≦ Tg1a +
60, ambient temperature Tc1b in the second half of the first drying step
(° C) is Tg1b ≦ Tc1b ≦ Tg1b + 60, and the ambient temperature Tc2a (° C) in the first half of the second drying step is Tg2.
a ≦ Tc2a ≦ Tg2a + 60, the ambient temperature Tc2b (° C.) in the second half of the second drying step is set to Tg2b ≦ Tc2b ≦
4. The control of Tg2b + 60.
3. The method for producing an optically isotropic film according to any one of 2. 4. The apparent glass transition temperature of the film in each drying step is an intermediate temperature between the glass transition temperature of the film at the entrance of each step and the glass transition temperature of the film at the exit thereof. The method for producing an optically isotropic film according to claim 1.