JPH0643321A - Production of phase difference film - Google Patents

Abstract

PURPOSE:To provide the process for production of a transversely uniaxially stretched polysulfone film having a retardation value Re uniform over the entire surface and an excellent visual field angle characteristic. CONSTITUTION:A film gripping means 100 is constituted of a pair of guide rails disposed in parallel and plural clip 2 groups which are mounted on these respective guide rails, glide freely in a longitudinal direction and grip the ends of the film. Both transverse ends of the polysulfone film (uniaxially stretched film p) subjected to a transverse uniaxial stretching treatment are gripped by providing proper intervals between the respective grips and thereafter, the film is subjected to a thermal shrinkage treatment to control the length in the longitudinal direction of the uniaxially stretched film p to >=/1/a'<1/2> times the length prior to the thermal shrinkage (where a' is the theoretical stretching times taking the shifting at the time of the transverse uniaxial stretching into consideration). The resulted film has the refractive index in the direction perpendicular to the stretching approximate to the refractive index in the thickness direction and has the retardation value Re by an incident angle uniform over the entire surface and, therefore, the visual field angle characteristic thereof is improved.

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 a retardation film by laterally uniaxially stretching a polysulfone film, and in particular, a retardation film having a uniform letter distribution on the entire surface and excellent viewing angle characteristics. The present invention relates to the improvement of the manufacturing method required.

[0002]

2. Description of the Related Art A retardation film uses the birefringence of a uniaxially stretched polymer film (which is caused by the difference in the refractive index between the stretching direction and the direction orthogonal to it depending on the molecular orientation accompanying stretching). The liquid crystal of the liquid crystal display device eliminates the phase difference generated between the polarized lights (referred to as phase difference compensation). The retardation compensation performance is represented by the retardation value Re, that is, the product of the film thickness d and the difference Δn between the refractive index in the stretching direction and the refractive index in the direction orthogonal thereto.

Such a retardation film is described in, for example, JP-A-2-42406, and is uniaxially stretched so that the neck-in ratio (shrinkage ratio in the direction orthogonal to the stretching direction) is 10% or less. Manufactured.

However, the retardation value Re of the retardation film manufactured in this way changes as the incident angle of incident light increases, so that color unevenness occurs on the display screen of the liquid crystal display device or the display screen is viewed from the front. A so-called color inversion phenomenon, in which black and white are inverted, occurs depending on the case and the side view.

On the other hand, in Japanese Unexamined Patent Publication No. 2-191904, when a retardation film is manufactured by the "longitudinal uniaxial stretching method", the length in the direction orthogonal to the stretching direction is 1 of the length ratio before stretching. It is described that the viewing angle characteristics are improved by controlling / a ^1/2 to 1 / a ^1/3 .

[0006]

When a polymer film is stretched to produce a retardation film, it is necessary to pay particular attention to the following three points among some important qualities.

(1) The retardation is the same on the entire surface of the film.

(2) Good viewing angle characteristics.

(3) There is no appearance defect.

On the other hand, as a method for producing a retardation film using a polymer film, there is a "longitudinal uniaxial stretching method" in which stretching is performed in the longitudinal direction of the film by utilizing the difference in rotation speed between rolls sandwiching the film. Two types of "horizontal uniaxial stretching method" of mechanically stretching in the lateral direction of the film are known. When the polysulfone-based film is stretched, the "longitudinal uniaxial stretching method" may not satisfy the quality of (3) because the film may be wound around a roll or the roll and the film may be rubbed and scratched.

Therefore, as a stretching treatment method for the polysulfone-based film so that there is no appearance defect, a "transverse uniaxial stretching method" is used.
Is usually applied. Also. The retardation (1) can be made uniform by optimizing the stretching conditions and the like.

However, the viewing angle characteristic (2) cannot be improved by stretching conditions. here,
“Good viewing angle characteristics” refers to a state in which there is no difference between the characteristics when viewed from the film normal direction and the characteristics when viewed from an oblique direction, but this viewing angle characteristics is closely related to the refractive index anisotropy in the resin. I have a relationship. Here, "refractive index anisotropy" refers to a state in which the refractive index is different in the three directions of the stretching direction of the film, the direction orthogonal to this (the direction perpendicular to the stretching), and the thickness direction of the film.

In order to improve the viewing angle characteristics, it is easy to make the refractive indices in the three directions perpendicular to the stretching direction equal to the refractive index in the thickness direction. This is for the following reason. That is, the in-plane retardation (characteristic when viewed from the normal direction to the film) is obtained from the difference in refractive index between the stretching direction and the direction perpendicular to the stretching. When viewed from an oblique direction, a component in the thickness direction is added to this. When the refractive index in the thickness direction is remarkably different from those in the other two directions, the retardation is significantly larger or smaller than that in the plane. The change in retardation when viewed from this oblique direction is a poor viewing angle. For example, when such a retardation film is mounted on a liquid crystal display, a phenomenon occurs in which colors are inverted between the front and the diagonal. Therefore, in order to suppress the change in retardation seen from the oblique direction as much as possible, it is preferable to make the refractive index in the direction perpendicular to the stretching direction equal to the refractive index in the thickness direction so that the apparent refractive index in the thickness direction is not affected.

By the way, this refractive index is linearly proportional to the internal stress of the resin. The polysulfone film originally has an intrinsic refractive index of 1.633, but when this resin is pulled from the inside to the outside, the refractive index increases, and when compressed from the outside to the inside, the refractive index decreases.

When the change in the refractive index is applied to stretching, the isotropic refractive index becomes large because it is pulled in the stretching direction as shown in FIG. 4 (A). On the other hand, it becomes smaller in the thickness direction because it is compressed as shown in FIG.
In addition, there is little change because it is regulated without changing in the direction perpendicular to the stretching.

On the other hand, in the "transverse uniaxial stretching method", it is difficult for force to act in the direction orthogonal to the stretching direction (direction orthogonal to the stretching) (because the roll interval for transporting the film is regulated to be constant). ), The change in the direction perpendicular to the stretching is small (actually, the compressive force remains so that it is slightly small).

Considering the unit volume of the film during the stretching treatment, when the film is stretched a times in the stretching direction (in this case, the x-axis direction) as shown in FIG. Direction and z-axis direction) is usually 1 / a ^1/2 times (that is, the volume of the film before and after stretching is constant). In this case, since the same stress is applied to the refractive index in both the direction perpendicular to the stretching direction and the thickness direction, the refractive index ( _ny ) in the direction perpendicular to the stretching direction and the refractive index ( _nz ) in the thickness direction are as shown in FIG. 5B. Will be equal.

In this state, the viewing angle characteristic is good.

However, in the "transverse uniaxial stretching method", since the longitudinal direction of the film is regulated as described above, it does not shrink in the longitudinal direction (y-axis direction) as shown in FIG. 6 (A). Therefore, the thickness direction contracts 1 / a times, and
As shown in (B), the refractive index ( _ny ) in the direction perpendicular to the stretching is different from the refractive index ( _nz ) in the thickness direction, and there is a problem that the viewing angle characteristics are deteriorated.

The present invention has been made by paying attention to such a problem, and its problem is that the retardation is uniform over the entire surface and the viewing angle characteristic is obtained in the transverse uniaxial stretching method using a polysulfone film. Another object of the present invention is to provide a method for producing a retardation film having excellent properties.

[0021]

That is, the invention according to claim 1 provides a method for producing a retardation film by heat-shrinking the polysulfone-based film in the longitudinal direction after the polysulfone-based film is transversely uniaxially stretched. As a premise, a film is gripped by a pair of guide rails arranged in parallel, and a plurality of jig groups that are mounted on the guide rails and that freely slide in the length direction and grip both lateral ends of the polysulfone-based film. Means for forming the film holding means, and sequentially holding both lateral ends of the polysulfone-based film that has been subjected to the uniaxially-stretched film in the lateral direction with the jigs of the film-holding means provided with appropriate intervals, and then heat-shrinking the polysulfone-based film. The length of the film in the machine direction is 1 / of the length before heat shrinkage.
a'1 ^{/ 2} times or more (however, a'is a theoretical draw ratio of the transverse uniaxial drawing treatment), and the invention according to claim 2 provides the invention according to claim 1. Based on the method for manufacturing the retardation film, the jig has a grip portion that grips both lateral ends of the polysulfone-based film inside the guide rails arranged in parallel, and the guide rail outside the guide rail. It is characterized by comprising a rotating portion that freely slides on the top.

On the other hand, the invention according to claim 3 is premised on the method for producing a retardation film according to claim 1 or 2, and sodium having a wavelength of 589.8 nm from the direction parallel to the normal line to the produced retardation film. When the retardation when D line is incident is Re ₀ and the retardation when incident from the direction of 40 degrees to the normal is Re ₄₀ ,
It is characterized by satisfying the following formula (1).

0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1) According to the inventions according to claims 1 to 3, the lateral direction of the polysulfone-based film subjected to the lateral uniaxial stretching is applied even when the lateral uniaxial stretching method is applied. Since the film can be shrunk in the direction perpendicular to the stretching direction by gripping both ends in the direction, the refractive index in the direction perpendicular to the stretching direction and the refractive index in the thickness direction can be made uniform. That is, the length of the film in the direction perpendicular to the stretching becomes 1 / a ' ^1/2 times or more the length in the direction perpendicular to the stretching before being heat-shrinked, and the refractive index in the direction perpendicular to the stretching approaches that in the thickness direction. The difference in retardation Re due to the difference in incident angle is made small.

By the way, generally, the polymer chains constituting the stretched film are entangled with the adjacent polymer chains, and the orientation state is maintained by the shearing force generated by the entanglement. Then, in the once stretched film, the stretched state is maintained by the shearing force even when the film is heated to a temperature below the glass transition point.

However, depending on the type of polymer, the shearing force is low, so that the stretched state cannot be maintained. The slip between the resins is called "slipping" for convenience, but the amount of slippage of the polysulfone resin is larger than that of other optical resins.

In the contracted state after the transverse uniaxial stretching described above, the direction perpendicular to the stretching is 1 and the thickness direction is 1 / a times (see FIG. 6A).
It becomes a ^1/2 and stabilizes, but it is larger than 1 / a ^1/2 after the actual recovery due to the above-mentioned “slip”. It is an important point for controlling the refractive index of the polysulfone-based film to perform the recovery control in consideration of the stress relaxation.

The expected recovery amount larger than 1 / a ^1/2 is 1
It can be set as / a ' ^1/2 . That is, a film stretched a-times is apparently a ′ by canceling out the above “slip”.
The film is treated as if it were a film stretched twice (a '<a).

Then, the direction perpendicular to the stretching and the thickness direction are 1 /
A good viewing angle can be obtained by controlling to ^{a'1 / 2} .

This a '(a': theoretical stretching ratio in consideration of deviation) can be obtained from actual measurement.

This point will be described in more detail below. For example, when a polysulfone film having an intrinsic refractive index of 1.633 is laterally uniaxially stretched 1.5 times, the refractive index in the stretching direction increases to 1.6357.

Then, when the film is heated while maintaining this stretched state (that is, while the four sides of the stretched film are fixed), the refractive index is lowered to 1.6347.

Assuming that the increase in length due to stretching and the increase in refractive index are proportional to each other, the following formula (2) is obtained with a lateral uniaxial stretching ratio a, a refractive index n, and a proportional constant k. To establish.

N = k × (a-1) +1.633 (2) However, (a-1) in the formula means a value obtained by dividing the increase in length by stretching by the length before stretching. ing.

When a = 1.5, n = 1.63
Since it is 57, k = 0.0054, and the above (2) can be rewritten as the following equation (3).

N = 0.0054 (a-1) +1.633 (3) Then, since the refractive index of the film after heating while maintaining the stretched state is 1.6347, the same refractive index as this When the stretch ratio (theoretical stretch ratio) of the stretched film having the above is a ′, the following formula (4) is established.

1.6347 = 0.0054 (a'-1) +1.633 (4) When this was calculated, a '= 1.315, and the film after heating was apparently stretched 1.5 times. However, it has substantially the same orientation as that of the film stretched 1.315 times, and can be treated equivalently to the laterally uniaxially stretched polysulfone film stretched at this theoretical stretching ratio a ′. it can.

Therefore, when the length in the direction perpendicular to the stretching (longitudinal direction of the transversely uniaxially stretched polysulfone film) is controlled to be 1 / a ' ^1/2 times or more the length before heat shrinkage, the direction perpendicular to the stretching direction And the refractive index in the thickness direction are equal, the retardation value Re is constant regardless of the incident angle, and the viewing angle characteristics are excellent.

The inventions according to claims 1 to 3 are made on the basis of such technical reasons.

In these inventions, the theoretical stretching ratio a'specified by the refractive index after heating while maintaining the stretched state is the refractive index n and the stretching ratio a before heating and the heating ratio after heating by the above-mentioned preliminary experiment. The refractive index n'of is measured and can be calculated from the following equations (5) and (6).

That is, n = k × (a−1) + n ₀ (5) n ′ = k × (a′−1) + n ₀ (6) where n ₀ is the intrinsic refractive index before stretching and k is proportional It is a constant.

[0041] Then, equation (5) and a from (6) '= 1 + ( a-1) × (n'-n 0) / (n-n 0) (7) Note that this theory stretched by repeating the experiment According to the result of obtaining the magnification, in general, 1 / a ^1/2 <1.05 / a ^1/2
<1 / a ' ^1/2 relation holds.

The magnitude relationship between 1 / a ^1/3 and 1 / a ' ^1/2 differs depending on the stretching conditions. Japanese Patent Laid-Open No. 2-191904
The control within the range of 1 / a ^1/3 or less as described in Japanese Patent Publication can be dealt with only under a limited stretching condition as long as a laterally uniaxially stretched polysulfone film is used.

Next, it is assumed that the shrinkage amount of the polysulfone film to be heat-shrinkable is (1-1 / a ' ^1/2 ), but an accurate shrinkage amount is not given due to a defect. For example, as described in JP-A-2-191904,
If the heat shrinkage treatment is performed by slackening in the range of −1 / a ^1/2 to 1 / a ^{1/3 in} the direction perpendicular to the stretching, the slackening amount is 1
If it is larger than -1.05 / a ^1/2 (more precisely, 1-1 / a ' ^1/2 ), the film cannot be completely shrunk due to slippage, and wavy wrinkles remain on the surface to be used as an optical film. Can not.

On the contrary, when the amount of loosening is significantly smaller than (1-1 / a ' ^1/2 ) (for example, when the neck-in amount is almost 0), heat shrinkage treatment is added. However, since it does not shrink in the direction perpendicular to the stretching, the refractive index does not change. Therefore, it is difficult to bring the refractive index in the direction perpendicular to the stretching close to the refractive index in the thickness direction, and improvement in viewing angle characteristics cannot be expected. In addition, since it causes careless displacement, the difference in refractive index in the film plane becomes small, and it becomes difficult to obtain a predetermined retardation.

Therefore, it is larger than 1.05 / a ^1/2 and 1 /
It is indispensable to control so that ^a'1 / ² or more and not significantly larger than 1 / a'1 / ² .

In the above-mentioned Japanese Patent Laid-Open No. 2-42406, the neck-in rate is 10% or less, preferably 0.
However, if the neck-in is restrained and the stretching is performed, the direction orthogonal to the stretching direction cannot be 1 / a ′ ^1/2 times as described above, so that the stretching is performed at a right angle to the stretching direction. Refractive indices in the thickness direction are not equal. Therefore, improvement in viewing angle characteristics cannot be expected. In particular, in the film of a '> 1.24, when the neck-in ratio is 10% or less, the refractive index in the direction perpendicular to the stretching and the refractive index in the thickness direction are absolutely not equal, and a retardation film having a good viewing angle characteristic cannot be obtained.

In the present invention, in order to realize a heat shrinkage amount in the range of 1 / a ' ^1/2 times or more and not significantly larger than 1 / a' ^1/2 times, the shrinkage does not occur in the stretching direction ( Since the jig group is mounted on each pair of guide rails arranged in parallel, the distance between the jigs mounted on each guide rail does not change.) This is achieved by adopting a method of gripping both lateral ends of the film with a group of sliding jigs.

That is, a pair of guide rails are arranged in parallel, and a jig group such as a clip is installed on each guide rail. In this case, the jig rails of the jig groups mounted on the separate guide rails are arranged in parallel, so that the distance between these jigs is kept constant. Also, each jig is
A grip portion that grips both lateral ends of the polysulfone-based film inside the guide rails arranged in parallel,
A rotating portion that freely slides (runs) on the guide rail is provided outside the guide rail, and the rotating portion is in contact with the guide rail.

The above-mentioned rotating portion is strongly pressed against the guide rail due to the shrinking stress in the film stretching direction (that is, the lateral direction of the film) during the heat shrinking treatment. Even if such a force acts, the rotating portion slides on the guide rail. It is optional as long as it can (roll). For example, application of a heat resistant bearing can be considered.

The shape of the gripping part for gripping both lateral ends of the film may be any as long as it has a function of holding both ends of the film and does not give cracks or wrinkles to the film. Instead, any one can be applied.

The jig group mounted on different guide rails holds both lateral ends of the laterally uniaxially stretched polysulfone film at equal intervals. Since the guide rails are arranged in parallel, the distance between the jigs facing each other does not change. Therefore, even if the film is heated in the stretching direction (that is, the lateral direction of the film) and contraction stress occurs in the film. The film cannot shrink in the stretch direction.

On the other hand, no constraining force acts in the direction perpendicular to the stretching direction, and the rotating portion of the jig rotates and freely slides on the guide rail to change the position, so that contraction stress occurs in the direction perpendicular to the stretching direction. Then, the film can freely shrink in the direction perpendicular to the stretching in accordance with the magnitude of this stress.

Further, since the film begins to shrink after heating and the jig group moves incidentally in accordance with the stress, the film is attached to the film holding means composed of the guide rail and the jig group. No particular attention is required as long as the film has no wrinkles immediately after mounting.

Regarding the transverse uniaxial stretching conditions in the present invention, various factors such as the stretching temperature, the magnification, the stretching speed, the heat setting (heat treatment in the latter stage of stretching) temperature, the heat setting time, etc. may be selected depending on the case where a desired retardation value is obtained. This is done by appropriately changing the conditions.

Further, the heat treatment in the present invention comprises a step of gripping both ends of the film in the lengthwise direction and a heating (shrinking) step, and conditions such as heating temperature and heating time in the heating step can be set appropriately. is there.

As described above, the setting conditions are appropriately changed depending on the case where the desired retardation value is obtained, and the contraction stress of the polysulfone-based film applied is also changed with this change. That is, the amount of contraction slightly changes. The jig group that freely slides in the length direction of the guide rail determines the shrinkage amount in a chain according to the shrinkage stress of the film, so the shrinkage amount of the film always corresponds to any heat treatment condition etc. It becomes possible to approach the theoretical contraction value.

Although the surface of the rotating portion of the guide rail and the jig group mounted on the guide rail is adjusted smoothly, a slight rolling friction is generated.
Therefore, in the heat shrink treatment, the length of the polysulfone film in the longitudinal direction is 1 / a ' ^1/2 of the length before heat shrink.
It is difficult to reach double, and actually the contraction ends in a state slightly larger than 1 / a ' ^1/2 . This state is ideal because, as described above, the shrinkage amount in the direction perpendicular to the stretching is realized in the range of not less than 1 / a ' ^1/2 times and not more than 1 / a' ^1/2 times.

A lateral uniaxial tenter stretching method is preferable as a method for performing the lateral uniaxial stretching treatment of the polysulfone film.

[0059]

According to the first and second aspects of the present invention, a pair of guide rails arranged in parallel with each other, mounted on each of the guide rails and freely sliding in the longitudinal direction, and both end portions in the lateral direction of the polysulfone film. The film gripping means is composed of a plurality of jigs for gripping, and the lateral ends of the polysulfone-based film that has been subjected to the lateral uniaxial stretching treatment are sequentially gripped with the jigs of the film gripping means being provided with appropriate intervals. After that, heat-shrinking treatment is applied to make the longitudinal length of the polysulfone-based film 1 / a ' ^1/2 of the length before heat-shrinking.
The retardation film has a good appearance and has substantially the same refractive index in the direction perpendicular to the stretching direction and the refractive index in the thickness direction, since the retardation film is controlled to be more than twice (where a'is the theoretical stretching ratio of the transverse uniaxial stretching process). Can be manufactured.

According to the third aspect of the invention, Re ₀ is defined as the retardation when sodium D line having a wavelength of 589.8 nm is incident on the manufactured retardation film from a direction parallel to its normal line. When the retardation when incident from a direction of 40 degrees with respect to the normal line is Re ₄₀ , the produced retardation film has 0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1) (1 ) Is satisfied, the refractive index in the direction perpendicular to the stretching and the refractive index in the thickness direction are approximated, and the change in retardation value depending on the incident angle is reduced, so that the viewing angle characteristic can be improved.

[0061]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[Embodiment 1] First, as shown in FIGS. 2 and 3, a pair of guide rails 1 each having a horizontal portion 10 and a vertical portion 11 and a strip-shaped opening 12 in the vertical portion 11 and having a substantially L-shaped cross section. , 1'are arranged in parallel and these guide rails 1, 1 '
On the other hand, a plurality of clips 2 shown in FIG. Also, the above clip 2
Includes a lower clip 23 having a base end side slidably fitted in the opening 12 of the guide rail 1, a heat resistant bearing 21 attached to the base end portion thereof, and a step portion 22 at its tip, and a base clip 23 thereof. An upper clip 25 having an end side rotatably attached to the upper surface of the lower clip 23 and having a step portion 24 fitted to the step portion 22 on the tip side thereof constitutes a main portion thereof, and A spring 2 is provided between the upper surface of the clip 25 and the horizontal portion 10 of the guide rail 1.
6 is interposed so that both lengthwise ends of the film p can be held between the stepped portion 22 of the lower clip 23 and the stepped portion 24 of the upper clip 25, and the guide rails 1, 1 ' Adjusted to allow free gliding along the length.

Next, width (stretching direction) 430.0 mm, length (stretching perpendicular direction) 500.0 mm, thickness 100.0 μm.
m polysulfone film (Tg = 190 ° C.) with a tenter stretching machine, stretching temperature 190 ° C., stretching ratio 1.5 times,
Heat set temperature 170 ℃, heat set time 30 sec
Was uniaxially stretched in the horizontal direction. The theoretical draw ratio a ′ was 1.386 times as determined by measurement.

The theoretical reduction rate = (1-1 / a '
Assuming ^1/2 ) × 100 (%), the theoretical reduction ratio in this case was 15.05%.

Then, the two ends of the transversely uniaxially stretched film p in the length direction are sequentially gripped while the respective clips 2 of the film gripping means 100 are appropriately spaced as shown in FIG. 1 (A), and then 190 The size in the longitudinal direction was reduced by applying heat shrinkage treatment at 2 ° C. for 2 minutes. In this case, since each clip 2 is adjusted so that it can slide freely along the length direction of the guide rails 1 and 1 ′, the film p shrinks in the longitudinal direction (direction perpendicular to the stretching) during the heat shrinking treatment. When a stress is generated, the film p can freely shrink according to the stress (see FIG. 1B).

Then, the dimension of the heat-shrinked film p in the length direction (direction perpendicular to the stretching) is measured to be 425.6.
mm, and the reduction rate from 425.6 / 500.0 = 0.8512 was 14.88%, which was slightly smaller than the theoretical reduction rate. This is exactly within the range of 1 / a ' ^1/2 or more and not significantly larger than 1 / a' ^1/2 .

Next, the R value and (Re ₄₀ / Re ₀ ) of the obtained retardation film were evaluated.

The R value is the phase difference value when the measured wavelength and the phase difference value are equal.

Further, (Re ₄₀ / Re ₀ ) is the retardation value R when the film is rotated by 40 degrees about the stretching axis and the axis (in the plane of the film) orthogonal to the stretching axis.
e ₄₀ (590 nm) and the retardation value Re ₀ at 0 ° were measured and the ratio was taken.

As a result of the evaluation, the R value was 580.9 nm, and (R
e ₄₀ / Re ₀ ) = 1.089, 0.911, and had the characteristics of 0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1).

Example 2 Width (stretching direction) 430.0 m
m, length (direction perpendicular to stretching) 500.0 mm, thickness 10
0.0 μm polysulfone film (Tg = 190
C.) was stretched horizontally with a tenter stretching machine at a stretching temperature of 190 ° C., a stretching ratio of 1.5 times, a heat setting temperature of 170 ° C., and a heat setting time of 30 sec. The theoretical reduction ratio was 12.43% from the theoretical stretching ratio a'determined by the measurement.

Next, this laterally uniaxially stretched polysulfone-based film is used as in the film holding means 100 of the first embodiment.
After being sequentially gripped, heat shrinking treatment was performed at 192 ° C. for 5 minutes.

Then, the dimension of the heat-shrinked film in the lengthwise direction (direction perpendicular to stretching) is measured to be 439.3 m.
m was 439.3 / 500.0 = 0.8786, and the reduction rate was 12.14%, which was slightly smaller than the theoretical reduction rate.

Next, as in the first embodiment, the R value and (R
e ₄₀ / Re ₀ ) was evaluated.

As a result of the evaluation, the R value was 540.3 nm and (R
e ₄₀ / Re ₀ ) = 1.089 and 0.910, and the characteristics of 0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1) were satisfied.

[0076]

According to the inventions according to claims 1 and 2, it becomes possible to make the refractive index in the direction orthogonal to the stretching direction and the refractive index in the thickness direction of the laterally uniaxially stretched polysulfone film uniform.

Further, according to the invention of claim 3, it becomes possible to manufacture a retardation film having a good appearance and having substantially the same refractive index in the direction perpendicular to the stretching direction and in the thickness direction.

Therefore, since the variation of the retardation value depending on the incident angle in the manufactured retardation film is small, there is an effect that the viewing angle characteristic can be improved.

[Brief description of drawings]

FIG. 1A is an explanatory view showing a state in which a film-holding means holds a laterally uniaxially stretched polysulfone-based film in an example, and FIG. 1B is an explanatory view showing a film-holding state after a heat shrinking treatment.

FIG. 2 is a plan view showing a state in which a laterally uniaxially stretched polysulfone-based film is held by a film holding means.

FIG. 3 is a cross-sectional view of a clip that constitutes a part of film gripping means.

4 (A) and 4 (B) are explanatory views showing changes in the film due to the stretching treatment.

FIG. 5A is an explanatory diagram showing changes in the y-axis and z-axis directions per unit volume when the film is uniaxially stretched a times in the x-axis direction a times, and FIG. Explanatory drawing which shows the change of a refractive index.

FIG. 6A is an explanatory view showing changes in the y-axis and z-axis directions per unit volume when the film is laterally uniaxially stretched a times in the x-axis direction a times, and FIG. 6B is each direction accompanying this stretching. Explanatory diagram showing a change in the refractive index of.

[Explanation of symbols]

 p uniaxially stretched film 1 guide rail 1'guide rail 2 clip 100 film gripping means

Claims (3)

[Claims] 1. A method for producing a retardation film by laterally uniaxially stretching a polysulfone-based film and then heat-shrinking the polysulfone-based film in the longitudinal direction, wherein a pair of guide rails arranged in parallel and each guide are provided. A film gripping means is composed of a plurality of jig groups that are mounted on rails and slide freely in the length direction and grip both lateral ends of the polysulfone-based film. After the lateral uniaxially stretched polysulfone-based film is sequentially gripped at both ends in the state of being provided with heat, heat-shrinking treatment is performed to change the length of the polysulfone-based film in the longitudinal direction to 1 / a ^'1/2 times or more (however, a' is a is a theoretical draw ratio of the transverse uniaxial stretching) method for producing a retardation film and controlling the 2. A jig for holding the lateral ends of a polysulfone film inside guide rails arranged in parallel, and a rotation for free sliding on the guide rail outside the guide rail. The manufacturing method of the retardation film according to claim 1, further comprising: 3. Retardation when a sodium D ray having a wavelength of 589.8 nm is incident on the produced retardation film from a direction parallel to its normal line, and the retardation is Re _0, and it is incident from a direction of 40 degrees to the normal line. When the retardation in this case is Re ₄₀ , the following formula (1) is satisfied:
Or the method for producing the retardation film according to 2. 0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1)