JPH0651116A - 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 excellent angle of field characteristic. CONSTITUTION:A film gripping means 10 is constituted of a pair of endless guide rails 1 which consist of an upper linear guide part 11 and a lower linear guide part 12 as well as two curved guide parts 13, 14 connecting the ends thereof to each other and are arranged in parallel and plural jig 2 groups which are mounted on these guide rails by providing prescribed intervals, travel on these guide rails and grip both transverse ends of the film (p). The transversely uniaxially stretched polysulfone film is supplied to such film gripping means. Both transverse ends of the film are successively gripped in the curved guide part 13 of the guide rails and while the film is slacked in the upper linear guide part 11, the film is thermally shrunk in its longitudinal direction, by which the length in the longitudinal direction is controlled to >=1/a'<1/2> times the length before the thermal shrinkage (where, a' is the theoretical stretching expansion rate taking the shear at the time of the transverse uniaxial stretching treatment into consideration).

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. 8 (A). On the other hand, it becomes smaller in the thickness direction because it is compressed as shown in FIG. 8 (B).
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 pulled 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 refractive index takes a stretching direction perpendicular to the thickness direction both same stress, the refractive index of the stretching perpendicular direction as shown in FIG. 9 (B) (n _y) and thickness direction refractive index (n _z) is 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. 10 (A). Therefore, the thickness direction shrinks by 1 / a times, and the refractive index ( _ny ) in the direction perpendicular to the stretching direction as shown in FIG.
And the refractive index ( _nz ) in the thickness direction are different from each other, 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, an upper straight guide portion extending in a substantially horizontal direction, a lower straight guide portion provided on the lower side of the upper straight guide portion, and two curved guide portions connecting end portions of these straight guide portions are arranged in parallel in parallel. A pair of endless guide rails, and a plurality of jig groups mounted on the guide rails at a predetermined interval and traveling on the guide rails and holding both lateral ends of the polysulfone film. Constitutes the gripping means,
A polysulfone-based film that has been subjected to a laterally uniaxially stretching treatment is supplied to the film gripping means, and the polysulfone-based film is provided in a curved guide portion of a guide rail in which the distance between the jigs on the leading end side is wider than the distance between the base ends. While sequentially gripping both ends in the lateral direction of the film, the polysulfone-based film is loosened in the linear guide part of the guide rail in which the distance between the jigs on the distal side between the jigs is reduced to the distance between the proximal ends. The length of the polysulfone-based film in the longitudinal direction after being subjected to the shrinkage treatment is set to 1 of the length before the heat shrinkage.
/ A ' ^1/2 times or more (however, a'is a theoretical draw ratio of the above-mentioned transverse uniaxial stretching treatment).

The invention according to claim 2 is based on the method for producing a retardation film according to claim 1, wherein the jig is
A lower clip attached to a guide chain attached to a guide rail, and an upper clip attached to the lower clip so as to be able to come into contact with and separate from the lower clip, and the main part thereof is characterized, while The invention according to claim 3 is premised on the method for producing a retardation film according to claim 1 as in the invention according to claim 2, wherein the jig is mounted on a lower surface side of a guide chain mounted on a guide rail. Moreover, the plate is provided with a plurality of film gripping needles on its upper surface side, and the main part thereof is constituted.

On the other hand, the invention according to claim 4 relates to claim 1,
Based on the method of manufacturing a retardation film according to 2 or 3,
Retardation when a sodium D ray having a wavelength of 589.8 nm was incident on the manufactured retardation film from a direction parallel to the normal, was Re _0, and retardation when incident on the retardation film was 40 ° to the normal. Where Re ₄₀ is satisfied, the following formula (1) is satisfied.

0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1) According to the inventions according to claims 1 to 4, the transverse direction of the polysulfone-based film subjected to the transverse uniaxial stretching treatment even when the transverse uniaxial stretching method is applied. Since both ends of the film in the direction of the film can be heat-shrinked in the direction perpendicular to the stretching direction, the refractive indexes in the direction perpendicular to the stretching direction and 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, there are some polymers which cannot maintain the stretched state because of the low shearing force. 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 lateral uniaxial stretching described above, as shown in FIG. 10 (A), the direction perpendicular to the stretching is 1 and the thickness direction is 1 / a times, and if the elastic recovery is simple, respectively. It becomes 1 / a ^1/2 and becomes stable, but the above "slip"
It is larger than 1 / a ^1/2 after the actual recovery due to the influence of. 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.

Hereinafter, this point will be described more specifically, and 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 with the stretched state maintained (that is, with the four sides of the stretched film fixed), the refractive index decreases 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 keeping 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 4 are based on 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 by the above-mentioned preliminary experiment, and after heating. 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.

[0042] 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 other hand, when the amount of loosening is significantly smaller than (1-1 / a ' ^1/2 ) (for example, when the neck-in amount is close to 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 the amount of heat shrinkage in the range of not less than 1 / a ' ^1/2 times and not more than 1 / a' ^1/2 times, the shrinkage does not occur in the stretching direction ( Since the jig group is mounted on each of the pair of guide rails arranged in parallel, the distance between the jigs mounted on each guide rail does not change), and the slack amount of the film is controlled to be constant only in the direction perpendicular to the stretching direction. This is achieved by adopting a method of applying heat shrinkage treatment using a film gripping means.

That is, as shown in FIG. 1, the upper linear guide portion 11 extending horizontally, the lower linear guide portion 12 provided on the lower side thereof, and the end portions of these linear guide portions 11, 12 are connected to each other. A pair of endless guide rails 1 (one of which is not shown) formed of two curved guide portions 13 and 14 and arranged in parallel in parallel, and each guide rail 1 is mounted at a predetermined interval and is mounted on each guide rail 1. A film gripping means 10 is constituted by a plurality of jigs 2 that run on the upper side and grip both ends of the polysulfone-based film p in the lateral direction, and the polysulfone-based film p laterally uniaxially stretched with respect to the film gripping means 10 is formed. It is supplied through the transport roll 3 and shown in FIG.
As shown in FIG. 2, in the curved guide portion 13 of the guide rail 1 in which the distance between the distal ends of the jigs 2 is wider than the distance between the proximal ends thereof, the lateral ends of the polysulfone film p are sequentially gripped. At the same time, the polysulfone-based film p is evenly slackened in the upper linear guide portion 11 of the guide rail 1 in which the distance between the distal ends of the jigs 2 is reduced to the distance between the proximal ends thereof. The uniaxiality of the retardation plate is enhanced by heat-treating the polysulfone-based film p to heat-shrink in the longitudinal direction. That is, in the invention according to claim 1, the distances between the jigs 2 on the tip side are the same when the curved guide portion 13 travels in a curve (section r) and when the straight guide portion 11 travels in a straight line (section L). It utilizes different things.

In FIG. 1, the polysulfone-based film p is supplied from the lower side and is sequentially gripped by the jig 2 in the curved guide portion 13 thereof, and then the polysulfone-based film p is heated in the upper straight guide portion 11 while being loosened. Although contracted, the polysulfone-based film p is supplied from the upper side and sequentially held by the jig 2 in the curved guide portion 13 thereof, and then the polysulfone-based film p is thermally contracted in the lower straight guide portion 12 while being loosened. You may employ the method of making it.

In the invention according to claim 2, the jig 2 is provided with a lower clip 21 attached to a guide chain (not shown) attached to a guide rail as shown in FIGS. 3 (A) and 3 (B). The upper clip 22 attached to the lower clip 21 so as to be able to come into contact with and separate from the lower clip 21 constitutes a main part thereof. The meshing portion between the upper clip 22 and the lower clip 21 may have any other shape such as a corrugated shape, a trapezoidal shape, a rectangular shape, or a flat surface. Further, if the polysulfone-based film p does not come off during the heat shrinking treatment, it is not necessary to fix the film p at all parts of the engagement.

Also, the upper clip 22 and the lower clip 2
Each jig consisting of 1 is connected at equal intervals on a guide chain (not shown), and the guide chains are connected at their ends to form a ring. In addition, 5 in FIG. 3 (A) shows a turn roll.

The jigs 2 for gripping both lateral ends of the film p are mounted on different guide rails and face each other. The timing to start gripping the film p of the jig 2 facing it and the timing to release it are the same. The chucking of the film p is performed in the curved guide portion 13 (section r) of FIG. 1 as shown in FIG. Further, the upper straight guide portion 11 (section L) is in a state as shown in FIG. 3 (B).

The looseness of the film p in FIG. 3B (the looseness between the clips as the jig 2) is the clip length h, the thickness d of the lower clip 21, and the turning radius of the clip group. It can be calculated from R and the film chucking timing. In the heat shrinking treatment step, the amount of slack shrinks to a flat state, so that the amount of shrinkage s can be controlled to control the amount of shrinkage Q.

Calculation of the slack amount s and the contraction amount M is easy. For example, one clip length h is 40 mm, clip interval i is 10 mm, and thickness d of lower clip 21 is 20 m.
m, the radius of gyration R is 150 mm, and the chucking start timing of the film p is such that the end point of the upper surface of the lower clip 21 (the surface in contact with the film) is farthest from the previous clip and If it is just before the clip is guided to the upper linear guide portion 11, the slack amount s generated between the clips under these conditions is calculated as s = 2 × 20 × sin (20/150) (8) can do.

Under the above conditions, the slack amount s is 50 mm (1
5.3mm per clip) and shrinkage rate is 9.8%
Can be controlled.

Generally, the chucking start timing of the film p is set so that the end point of the upper surface (the surface that contacts the film) of the lower clip 21 is the farthest from the previous clip and the previous clip is Until just before being guided to the upper linear guide portion 11, the amount of slack s = 2 x d x sin (h / 2 x R) (9) The amount of contraction Q = [1- (h + i) / (h + i + s)] x It can be represented by 100 (10).

However, d is the thickness of the lower clip, h is the clip length, R is the radius of rotation of the clip group, and i is the clip interval.

Here, in order to change the contraction amount Q, at least one item among the respective conditions may be changed, but it is easiest to change the turning radius R of the clip group among them. As a method of changing the radius of gyration R, for example, a method in which a sprocket having the center of rotation q is a transmission gear, a method in which the entire clip group is movable, and the like can be mentioned. Other methods may be used as long as the radius of rotation can be smoothly changed. As an example, if the rotation radius R is changed to 170 mm by the transmission gear system, the contraction rate becomes 8.5%.

The clips hold both ends of the film p in the stretching direction at equal intervals while facing each other. Since the guide rails are fixed, the facing clip interval does not change. Therefore, in the stretching direction, the film p does not shrink in the stretching direction even if shrinkage stress is generated in the film p by heating.

Next, in the invention according to claim 3, the jig 2 is attached at its lower surface side to a guide chain (not shown) which is attached to the guide rail as shown in FIGS. 4 (A) and 4 (B). And a plurality of film gripping needles 25 on the upper surface side thereof
The plate 26 is provided with. In addition, both lateral ends of the polysulfone film p are pierced and fixed by the film gripping needle 25. This needle 2
5 is a film p while the clip, which is a jig, is being driven.
The shape is not particularly limited as long as it has a function of penetrating and holding. Further, each plate 26 is connected to a guide chain (not shown) at equal intervals, and the guide chains are connected to each other at their ends to form a ring. The fixing of the film p by the jig 2 is performed in the curve guide portion 13 (section r) of FIG.
It is performed as shown in FIG.
In (section L), the state is as shown in FIG.

The looseness of the film p in FIG. 4B (the looseness s between the clips which is the jig 2 and the looseness s1 + s2 + s3 + s4 within the needle 25 of the clip) is
Clip length h, clip interval i, film gripping needle 2
It can be calculated from the length j of 5, the thickness d of the plate 26, the turning radius R of the clip group, and the like. In the heat-shrinking process, the amount of slack shrinks to a flat state. Therefore, by controlling the amount of slack, the amount of shrinkage Q can be controlled.

The calculation of the contraction amount Q and the slack amount S'is easy. For example, one clip length h is 40 mm, clip interval i is 10 mm, number n of needles 25 is 10/1 clip, length j of needles 25 is 30 mm, thickness d of plate 26.
Is 10 mm, the radius of gyration R is 150 mm, and
Assuming that the needles 25 are arranged at equal intervals from the clip end, the slack amount S'is 17.07 mm per 50 mm (1 clip), and the contraction rate is 25.8%.

Here, in order to change the contraction amount Q, at least one item among the respective conditions may be changed, but it is easiest to change the turning radius R of the clip group among them. As a method of changing the radius of gyration R, for example, a method in which a sprocket having the center of rotation q is a transmission gear, a method in which the entire clip group is movable, and the like can be mentioned. Other methods may be used as long as the radius of rotation can be smoothly changed. As an example, if the rotation radius R is changed to 170 mm by the transmission gear system, the shrinkage ratio becomes 24.3%.

In this case, the relationship between each condition under the above conditions and the shrinkage amount Q is expressed by the following equation (11).

[0066]

[Equation 1] Further, each condition and the contraction amount Q are expressed by the following formula (12) under all the mounting conditions.

[0067]

[Equation 2] The f function represents the film length including the slack in the clips, and the g function represents the film length including the slack in the needle 25. The symbols in parentheses are as described above.

Regarding the transverse uniaxial stretching conditions of the inventions according to claims 1 to 4, the stretching temperature, the draw ratio, the stretching speed, the heat setting (heat treatment in the latter stage of stretching) temperature, This is done by appropriately changing the conditions such as heat setting time.

The heat treatment in these inventions includes the step of gripping both ends of the film in the length direction and the heating (contraction).
The heating step and the heating time in the heating step can be appropriately set.

As described above, the setting conditions are appropriately changed depending on the case where a desired retardation value is obtained, and the contraction stress of the polysulfone-based film applied changes accordingly. That is, the amount of contraction slightly changes. In the invention according to claims 1 to 4, since the shrinkage amount is determined by, for example, smoothly changing the radius of the rotating gear in accordance with the optimum shrinkage condition of the film, the shrinkage amount of the film is always subjected to an arbitrary heat treatment. It is possible to approach the theoretical shrinkage value corresponding to the conditions.

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

[0072]

According to the inventions according to claims 1 to 3, the upper linear guide portion extending substantially horizontally, the lower linear guide portion provided below the upper linear guide portion, and the end portions of these linear guide portions are connected to each other. Two
A pair of endless guide rails, each of which is composed of two curved guide portions and arranged in parallel in parallel, and mounted on each guide rail at a predetermined interval and traveling on each guide rail, and both lateral ends of the polysulfone film. The film gripping means is composed of a plurality of jig groups for gripping the film, and the polysulfone-based film that has been subjected to the lateral uniaxial stretching is supplied to the film gripping means. A guide in which the lateral end portions of the polysulfone film are sequentially gripped in the curved guide portion of the guide rail that extends from the distance between the end side members, and the distance between the front end side members between the jigs is reduced to the base end side member distance. After slackening the polysulfone-based film in the linear guide portion of the rail, heat-shrinking treatment is applied to the polysulfone-based film in the longitudinal direction. Length before heat shrink 1 / a '
^Since it is controlled to be ^1/2 times or more (however, a'is the theoretical draw ratio of the transverse uniaxial drawing process), it has a good appearance and the refractive index in the direction perpendicular to the drawing and the refractive index in the thickness direction are almost the same. A retardation film can be manufactured.

According to the invention of claim 4, the retardation when the sodium D line having a wavelength of 589.8 nm is incident on the produced retardation film from a direction parallel to the normal line is Re ₀ , 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.

[0074]

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

Example 1 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 draw ratio a ′ at 190 ° C. for 10 minutes was 1.41 times as determined by measurement.

The theoretical reduction ratio = (1-1 / a '
^{Assuming 1/2} ) × 100 (%), the theoretical reduction ratio in this case was 15.78%.

Next, the two lateral ends of the polysulfone film p laterally uniaxially stretched by the film gripping means 10 shown in FIGS. 1 and 5 are attached to the curved guide portion 1 of the guide rail.
3 is sequentially gripped, and the film p is evenly loosened in the upper linear guide portion 11, and then the oven 4
At 190 ° C., heat treatment was performed at 190 ° C. for 10 minutes to thermally shrink the polysulfone film p in the longitudinal direction to produce a retardation film.

As shown in FIG. 6, each jig 2 is attached to a lower clip 21 attached to a guide chain 20 attached to a guide rail, and is attached to and detachable from the lower clip 21. What constitutes the main part with the upper clip 22 is applied.

The length h of the lower clip 21 is 30.
mm, the thickness d of the lower clip 21 = 10 mm, the clip interval i = 10 mm, and the radius of gyration R = 120 mm, and the contraction rate was controlled to 15.75%.

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 is 570.3 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 draw ratio a ′ at 192 ° C. for 5 minutes was 1.42 times as determined by measurement.

The theoretical reduction rate = (1-1 / a '
^{Assuming 1/2} ) × 100 (%), the theoretical reduction ratio in this case was 16.6%.

Next, the laterally uniaxially stretched polysulfone film is used as the film gripping means 100 which is substantially the same as that in the first embodiment.
(Only the above radius of gyration R is changed to 112 mm)
After being sequentially gripped, heat shrinking treatment was performed at 192 ° C. for 5 minutes.

Then, as in the first embodiment, the R value and
The evaluation was performed on (Re ₄₀ / Re ₀ ).

As a result of the evaluation, the R value is 582.4 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.

Example 3 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 1.8 times, a heat setting temperature of 170 ° C., and a heat setting time of 30 sec. The theoretical draw ratio a'was 1.73 times as determined by measurement.

The theoretical reduction rate = (1-1 / a '
^{Assuming 1/2} ) × 100 (%), the theoretical reduction ratio in this case was 24.3%.

Next, the two lateral ends of the polysulfone film p laterally uniaxially stretched by the film gripping means 10 shown in FIGS. 1 and 5 are connected to the curved guide portion 1 of the guide rail.
3 is sequentially gripped, and the film p is evenly loosened in the upper linear guide portion 11, and then the oven 4
At 190 ° C., heat treatment was performed at 190 ° C. for 10 minutes to thermally shrink the polysulfone film p in the longitudinal direction to produce a retardation film.

However, unlike Embodiments 1 and 2 described above, each jig 2 of the film gripping means 10 has its lower surface side attached to a guide chain 20 mounted on a guide rail as shown in FIG. 7 and its upper surface. A plate 26 having a plurality of film gripping needles 25 on its side constitutes the main part of the plate 26.

The length of the plate 26 h = 40 m
m, thickness of plate 26 d = 10 mm, clip interval i
= 10 mm, the number of needles 25 n = 10/1 clip, the length of the needle 25 j = 10 mm, the radius of gyration R = 170 mm, and the contraction rate was controlled to 24.3%.

Next, the R value and (Re ₄₀ / Re ₀ ) of the obtained retardation film were evaluated in the same manner as in Example 1.

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 4 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 1.8 times, a heat setting temperature of 170 ° C., and a heat setting time of 30 sec. The theoretical draw ratio a ′ was 1.78 times as determined by measurement.

The theoretical reduction rate = (1-1 / a '
^{Assuming 1/2} ) × 100 (%), the theoretical reduction ratio in this case was 25.1%.

Next, this laterally uniaxially stretched polysulfone film is used as the film gripping means 100 which is substantially the same as in the first embodiment.
(Only the above radius of gyration R is changed to 160 mm)
After being sequentially gripped, heat shrinking treatment was performed at 192 ° C. for 5 minutes.

Then, as in the first embodiment, the R value and
The evaluation was performed on (Re ₄₀ / Re ₀ ).

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.

[0101]

According to the inventions according to claims 1 to 3, 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 polysulfone-based film uniaxially stretched.

Further, according to the invention of claim 4, 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. 1 is an explanatory view showing steps of a manufacturing method according to claim 1.

FIG. 2 is a partially enlarged explanatory view of FIG.

3 (A) and 3 (B) are operation explanatory views of a film gripping means to which the jig according to claim 2 is applied.

4A and 4B are explanatory views of the action of the film gripping means to which the jig according to claim 3 is applied.

FIG. 5 is a partial plan view of film gripping means.

FIG. 6 is a schematic cross-sectional view of the structure of a jig according to claim 2.

FIG. 7 is a schematic cross-sectional view of a jig according to claim 3.

8A and 8B are explanatory views showing changes in a film due to a stretching treatment.

FIG. 9 (A) 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. 10 (A) is an explanatory view showing changes in the y-axis and z-axis directions per unit volume when a film is laterally uniaxially stretched a times in the x-axis direction by a times, and FIG. 10 (B) is each direction accompanying this stretching Explanatory diagram showing a change in the refractive index of.

[Explanation of symbols]

 p film 1 guide rail 2 jig 3 transport roller 4 oven 10 film gripping means 11 upper linear guide portion 12 lower linear guide portion 13 curved guide portion 14 curved guide portion

Claims (4)

[Claims] 1. A method for producing a retardation film by subjecting a polysulfone-based film to transverse uniaxial stretching treatment and then heat-shrinking the polysulfone-based film in the longitudinal direction to produce a retardation film, wherein an upper linear guide portion extending in a substantially horizontal direction and a lower side thereof are provided. A pair of endless guide rails arranged in parallel in parallel with each other, each of which includes a lower straight guide portion and two curved guide portions connecting end portions of these straight guide portions to each other, and a predetermined interval between the guide rails. Is attached and runs on each guide rail, and a film gripping means is constituted by a plurality of jig groups for gripping both lateral ends of the polysulfone-based film, and the film is uniaxially stretched laterally with respect to the film gripping means. A curved guide part of a guide rail that supplies treated polysulfone-based film, and the distance between the jigs on the front side of each jig is wider than the distance between the bases. At the same time, the both lateral ends of the polysulfone-based film are sequentially gripped, and the polysulfone-based film is slackened at the linear guide portion of the guide rail in which the distance between the distal ends of the jigs is reduced to the distance between the proximal ends thereof. After that, heat-shrinking treatment is applied so that the length of the polysulfone-based film in the longitudinal direction is 1 / a ' ^1/2 times or more of the length before heat-shrinking (where a'is the theoretical stretching of the lateral uniaxial stretching treatment). The method for producing a retardation film is characterized by controlling the magnification. 2. A main part of the jig is composed of a lower clip attached to a guide chain attached to a guide rail and an upper clip attachable to and detachable from the lower clip. The method for producing a retardation film according to claim 1, wherein 3. The jig is characterized in that a lower surface side is attached to a guide chain mounted on a guide rail and a main portion is constituted by a plate having a plurality of film gripping needles on the upper surface side. The method for producing a retardation film according to claim 1. 4. The retardation when the sodium D line having a wavelength of 589.8 nm is incident on the produced retardation film from a direction parallel to the normal line thereof is Re _0, and the retardation 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, the method for producing a retardation film according to claim 1, 2 or 3. 0.90 ≤ Re ₄₀ / Re ₀ ≤ 1.10 (1)