JPH05288932A - Production of phase difference plate - Google Patents

Abstract

PURPOSE:To provide the process which can easily produce the phase difference plate having phase difference compensation performance uniform and excellent over approximately the entire area of a film and visual field angle characteristic. CONSTITUTION:A polysulfone film p is so molded that the sectional shape in its longitudinal direction has a waveform; in addition, both ends in the transverse direction of this film are fixed in the state of maintaining this waveform shape and thereafter, the film is subjected to a stretching treatment in a transverse uniaxial direction while the free shrinkage in the longitudinal direction exclusive of its fixed parts is permitted, by which the phase difference plate is produced. The film is subjected to the stretching in the state of fixing both ends in the transverse direction of the film while maintaining the waveform shape and, therefore, the partial shrinkage (neck-in) in the transverse direction of the film does not arise and the shrinkage uniform in the longitudinal direction is enabled until the waveform shape attains a flat shape. The reduction rate in the longitudinal direction is thus controlled constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate which is composed of a uniaxially stretched thermoplastic resin film and is suitably used for, for example, a liquid crystal display plate, and particularly to a retardation film having excellent viewing angle characteristics. The present invention relates to a method for manufacturing a plate.

[0002]

2. Description of the Related Art A retardation film (film) utilizes the birefringence of a stretched polymer film (generated due to the difference in refractive index between the stretching direction and the direction orthogonal thereto due to the molecular orientation due to stretching). It is intended to eliminate the phase difference generated in the liquid crystal of the liquid crystal display plate (referred to as phase difference compensation). Conventionally, as this type of phase difference plate (film), a cellulose resin (see JP-A-63-167363), Vinyl chloride resin (JP-B-45-34477, JP-A-56-)
125702), polycarbonate resin (Japanese Patent Publication No. 41190/41, JP 56-130).
No. 703), acrylonitrile resin (see JP-A-56-130702), styrene resin (see JP-A-56-125703), olefin resin (see JP-A-60-24502). Etc. are known, and longitudinal uniaxial stretching (see Japanese Patent Application Laid-Open No. 2-191904), transverse uniaxial stretching (see Japanese Patent Application Laid-Open No. 2-42406), and the like have been proposed as uniaxial stretching methods.

The retardation compensation performance of the retardation film (film) is called a retardation value, and is represented by Δn × d. Here, Δn is the anisotropy of the refractive index, and d is the thickness of the film.

By the way, when the angle formed by the incident light and the normal to the film surface increases, the retardation value changes (in the case of rotating about the stretching direction and in the case of rotating about the axis perpendicular to the stretching direction). (The increase and decrease are different depending on the). Coloring of the liquid crystal display occurs.

An optical anisotropic body such as a retardation film (film) does not have a uniform three-dimensional refractive index (nx, ny, nz) and is represented by a refractive index ellipsoid. The relationship between the refractive indexes in the respective directions is, for example, in the uniaxially stretched film p shown in FIG. 5, where x is the stretching axis, y is the axis orthogonal to the stretching direction in the film plane, and z is the normal direction of the film. , A film having a positive intrinsic refractive index has a relationship of nx> ny ≧ nz,
A film having a negative intrinsic refractive index has a relationship of nx <ny ≦ nz. In the case of a completely uniaxially stretched film, the refractive index ny in the direction y orthogonal to the stretching direction in the film plane and the refractive index nz in the normal direction z of the film are equal, and ny = nz holds.

In the following, as an example, θ from the z axis in the xz plane
(Viewing angle) Birefringence [Δn
_xz (θ)] and the retardation value [R _xz (θ)] are represented by the following formulas (see Electronic Material, February 1991, p. 40).

[0007]

[Equation 1] However, in the formula, d is the thickness of the film, and n is the average refractive index.

FIG. 6 shows the result calculated based on the above equations (1) and (2).

In the graph of FIG. 6, the horizontal axis is the viewing angle θ,
The vertical axis represents the retardation value R at the viewing angle θ in the xz plane.
_xz retardation value R _xz (0) divided by the value R _xz of (θ) the viewing angle 0 (when viewed from the normal direction z) (θ) / R
_xz (0), and the rate of change in retardation R is [1-
It is represented by the absolute value of R _xz (θ) / R _xz (0)]. Also,
In FIG. 6, a represents a completely uniaxially stretched film of nz = ny,
b shows the perfect uniaxially stretched film of nz <ny.

Here, the viewing angle is wider as the rate of change of the retardation R, that is, the absolute value of [1-R _xz (θ) / R _xz (0)] is smaller. From FIG. 6, the complete uniaxial stretching (nz = ny) has a smaller change in retardation value and a wider viewing angle, while the molecular orientation has biaxiality (nz <ny). It can be confirmed that the change in the foundation value is large and the viewing angle is very narrow.

FIG. 7 shows the calculation results when a viewing angle φ tilted from the z axis in the yz plane is used instead of θ.
In FIG. 7, c indicates a completely uniaxially stretched film of nz = ny,
d indicates a completely uniaxially stretched film of nz <ny.

Also from this result, if the molecular orientation is biaxial, the rate of change in retardation value, that is, [1
The larger the absolute value of −R _yz (φ) / R _yz (0)] and the narrower the viewing angle, and the higher the uniaxial orientation of the molecule, the higher the rate of change in retardation value, ie, [1-R _yz (φ) / R
_yz (0)] has a small absolute value and a wide viewing angle. Further, it can be seen that the viewing angle is widest in the case of perfect uniaxial stretching of nz = ny.

Therefore, from these results of FIG. 6 and FIG.
From any direction, it can be seen that the higher the uniaxial orientation of the molecule, the smaller the rate of change in retardation value and the wider the viewing angle.

By the way, in order to enhance the uniaxiality of the molecular orientation, it is necessary to minimize the stress generated in the direction perpendicular to the stretching direction (residual stress to be reduced). In other words, it is sufficient to reduce in the direction perpendicular to the stretching direction by the amount of reduction considered to occur in the stretching in the direction perpendicular to the stretching direction.

In Japanese Patent Application Laid-Open No. 2-191904, this reduction ratio is referred to as "neck-in ratio (refers to the rate of change in the length of the film in the direction orthogonal to the stretching direction before and after stretching)". That is, neck-in rate = (b−a) / b × 100; where a is the length in the direction orthogonal to the stretching direction after annealing, and b is the length in the direction orthogonal to the stretching direction of the film before stretching. ], And the neck-in ratio is set to (1-1 / square root of draw ratio) × 100 (%) to (1-1 / third root of draw ratio) × 100 (%) It is disclosed that an excellent retardation plate (film) can be manufactured. As this specific method, there is disclosed a method (longitudinal uniaxial free width stretching method) in which the distance between the stretching rolls is set to 5 times or more of the film width and the film is stretched in the longitudinal direction while allowing free shrinkage in the width direction. .

Further, in Japanese Patent Laid-Open No. 3-23405,
Applying a pantograph-type simultaneous biaxial tenter stretching machine, both ends of the film in the width direction are partially held by tenter clips and simultaneously stretched in both the longitudinal direction and the width direction.
A method for producing a retardation plate having a neck-in rate of (1-1 / square root of draw ratio) is disclosed.

[0017]

However, Japanese Patent Laid-Open No. 2-1.
In the method disclosed in Japanese Patent No. 91904, since the distance between the stretching rolls is set to 5 times or more the film width as described above, it is possible to uniformly control the heating temperature during stretching over the entire area between the rolls. There was a difficult problem.

Further, according to this method, since the film is stretched in the machine direction while allowing the film to freely shrink in the width direction between the stretched rolls arranged at intervals, the film in the vicinity of the stretch roll is processed. The shrinkage amount in the width direction of the film in the vicinity of the central portion between the stretching rolls becomes larger than the shrinkage amount in the width direction. There is a defect that the direction of the stretching axis in the central portion of the film does not match. Therefore, the width direction both ends of the film have to be discarded in large quantities as defective products because the phase difference compensation performance and the viewing angle characteristics are different between the width direction both ends and the center part of the stretched film. There was a problem that the yield was poor.

On the other hand, in the method disclosed in Japanese Patent Application Laid-Open No. 3-23405, since both widthwise end portions of the film are partially held by the tenter clips and stretched, the tenter clips are used. Partial shrinkage (neck-in) occurs in the unsupported portion, and there is a problem in the retardation compensation performance of the manufactured retardation plate and the uniformity of viewing angle characteristics.

The present invention has been made by paying attention to such a problem, and an object thereof is to provide a phase difference having uniform and excellent phase difference compensation performance and viewing angle characteristics over substantially the entire area of the film. It is to provide a method for easily manufacturing a plate.

[0021]

That is, the invention according to claim 1 forms a thermoplastic resin film so that its longitudinal cross-sectional shape is corrugated, and the thermoplastic resin film is transversely shaped. It is characterized in that both ends are fixed in a state where the corrugated shape is maintained, and that the thermoplastic resin film is stretched in the lateral uniaxial direction while allowing free contraction in the longitudinal direction excluding the fixed part. .

In the invention according to claim 1, the thermoplastic resin film shaped in a corrugated shape is stretched in a state in which both lateral (widthwise) ends thereof are fixed while maintaining the corrugated shape. Since the film does not partially shrink (neck-in) in the lateral direction during the stretching treatment, the above-mentioned drawbacks of the manufacturing method disclosed in JP-A-3-23405 are eliminated.

In addition, the thermoplastic resin film formed in a corrugated shape is stretched in the lateral uniaxial direction while allowing both ends in the lateral direction to be fixed, while allowing free contraction in the longitudinal direction excluding this fixing portion. Since the uniform contraction in the vertical direction is possible until the corrugated shape becomes a flat shape, the contraction rate in the vertical direction can be controlled to be constant.
The adverse effect of the manufacturing method disclosed in Japanese Patent Publication No. 04 can be eliminated.

The above operation will be described in detail by taking the case where the corrugations are set in a triangular shape as shown in FIG. 3 as an example. The length of the film after shrinkage (along the axis of the corrugations) (Represented by a straight line distance) is α, and the length of the film along the waveform is β, the reduction ratio in the longitudinal direction is (β-α) /
β × 100%, the reduction ratio in the lateral direction is 0%, and these reduction ratios are constant regardless of the part. Therefore, the stretching axis is also maintained in a constant direction regardless of the part.

Then, as a concrete shape of this waveform,
For example, shapes such as a triangular shape in cross section and a trapezoidal shape in cross section can be cited, but the shape is not limited to these. Further, the pitch and the height of the wave are also arbitrary, and can be appropriately set in correspondence with a desired reduction ratio. Further, a shaping method and a method of fixing both lateral ends of the film are also arbitrary, and any method may be used as long as it does not damage or tear the film.

Further, in such a technical means, the stretching of the thermoplastic resin film in the lateral uniaxial direction can be performed by a device obtained by modifying the lateral uniaxial tenter stretching machine. Also,
Various conditions such as the stretching temperature, the stretching ratio, the stretching speed, the heat setting (heat treatment after stretching), the heat setting time and the like can be appropriately set according to the desired retardation characteristics, and are described in JP-A-2-191904. The control is extremely easy as compared with the manufacturing method disclosed in US Pat.

Next, as the thermoplastic resin film applied in this technical means, for example, cellulose resin, vinyl chloride resin, polycarbonate resin, acrylonitrile resin, olefin resin, polystyrene resin, polymethacryl Examples of the film include methyl acid resin, polysulfone resin, polyarylate resin, and polyether sulfone resin.

The film may be produced by any of the solvent casting method, calendering method and extrusion method.

[0029]

According to the first aspect of the present invention, the thermoplastic resin film is shaped so that its longitudinal cross-section has a wavy shape, and both lateral ends of the thermoplastic resin film have the wavy shape. The thermoplastic resin film is stretched in the lateral uniaxial direction while allowing free contraction in the longitudinal direction excluding the fixing portion.

That is, since the thermoplastic resin film shaped in a corrugated shape is stretched while the lateral ends of the film are fixed while maintaining the corrugated shape, the film is partially stretched in the lateral direction during the stretching treatment. Contraction (neck-in)
Does not occur, and it is stretched in the horizontal uniaxial direction while allowing free contraction in the vertical direction excluding the fixed part, and uniform contraction in the vertical direction is possible until the corrugated shape becomes a flat shape. The reduction ratio in the direction can be controlled to be constant.

Therefore, it becomes possible to align the direction of the stretching axis (main stretching axis) in a fixed direction over the entire film stretched in the lateral uniaxial direction.

[0032]

EXAMPLES Examples of the present invention will be described in detail below.

Example 1 Width 430 mm, Thickness 100 μ
m, the glass transition point (Tg) of the polysulfone film p of 190 ° C. was shaped into the waveform shown in FIG. 1 (reduction ratio 14%),
The both ends in the transverse direction are fixed while maintaining the corrugated shape, and a tenter stretching machine is used to stretch at a stretching temperature of 190.
C., a draw ratio of 1.5 times, a heat setting temperature of 170.degree. C., and a heat setting time of 30 sec were subjected to transverse uniaxial stretching treatment.

The uniaxially stretched film thus obtained was evaluated for viewing angle characteristics, R value and edge defect rate.

The viewing angle characteristic is 45 with respect to the stretching axis of the film and the axis (in the plane of the film) orthogonal to the stretching axis.
The absolute value of the difference between the retardation value (590 nm) when rotated by 0 degree and the retardation value when 0 degree is divided by the retardation value (590 nm) at 0 degree to be 1
The larger value multiplied by 00 was used as the substitute characteristic.

It can be said that the smaller this value is, the better the viewing angle characteristic is.

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

Next, regarding the above-mentioned defect rate, the deviation between the optical principal axis and the stretching direction (the width direction of the film) is measured with a polarization microscope, and the portion where this axis deviation exceeds 1 degree is defined as an end defective portion. The larger one of the width dimensions of the defective end portions on both sides was used as a representative value and calculated by the following formula.

Edge defect rate = (representative value of width dimension of edge defect portion / width dimension after stretching) × 100% The results are shown in Table 1.

Example 2 Transverse uniaxial stretching was performed in the same manner as in Example 1 except that the polysulfone film was shaped into the waveform shown in FIG. 2 (reduction ratio 14%).

Viewing angle characteristics of the obtained uniaxially stretched film,
Table 1 shows the R value and the end defect rate.

Comparative Example 1 A polysulfone film having a width of 430 mm (distance between initial tenter clips is 400 mm), a thickness of 100 μm and a glass transition point (Tg) of 190 ° C. was used with a tenter stretching machine at a stretching temperature of 195 ° C. and a stretching ratio of 1 The film was laterally uniaxially stretched under the conditions of 0.35 times and a heat setting temperature of 170 ° C.

Viewing angle characteristics of the obtained uniaxially stretched film,
Table 1 shows the R value and the end defect rate.

[Comparative Example 2] width 600 mm, thickness 100 μ
A polysulfone film having m and a glass transition point (Tg) of 190 ° C. was longitudinally uniaxially stretched at a stretching temperature of 200 ° C. and a stretching ratio of 1.5 times by using a longitudinal uniaxial stretching machine while allowing free shrinkage in the width direction.

The distance between stretchings at this time (see FIG. 4) is 80.
0 mm, neck-in ratio (width contracted by stretching /
The width before stretching × 100%) was 17.2%.

Viewing angle characteristics of the obtained uniaxially stretched film,
Table 1 shows the R value and the end defect rate.

[0047]

[Table 1] [Confirmation] From the results shown in Table 1 above, the thermoplastic resin film was formed into a corrugated shape, and both lateral ends of the film were fixed while maintaining the corrugated shape. It was confirmed that the viewing angle characteristics can be improved by stretching the film in the lateral uniaxial direction while allowing the free shrinkage, and the defect rate can be improved by aligning the optical principal axes of the entire film in a certain direction.

[0048]

According to the invention of claim 1, since the thermoplastic resin film formed in a corrugated shape is stretched while being fixed at both lateral ends thereof while maintaining the corrugated shape, stretching is performed. No lateral shrinkage (neck-in) occurs in the film during processing, and the film is stretched in the lateral uniaxial direction while allowing free contraction in the longitudinal direction excluding the fixed part, and the corrugated shape is flat. Since uniform shrinkage in the machine direction can be achieved until it becomes uniform, the reduction ratio in the machine direction can be controlled to be constant, and the stretching axis (stretching main axis) can be aligned in a constant direction over the entire stretched film. It will be possible.

Therefore, there is an effect that a retardation plate having uniform and excellent retardation compensation performance and viewing angle characteristics over almost the entire area of the film can be easily manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a waveform of a thermoplastic resin film according to an example.

FIG. 2 is an explanatory view showing a waveform of a thermoplastic resin film according to another example.

FIG. 3 is an explanatory view for explaining a reduction rate of the thermoplastic resin film according to the present invention.

FIG. 4 is an explanatory view showing a longitudinal uniaxial stretching method according to a comparative example.

FIG. 5 is a perspective view of a uniaxially stretched film.

FIG. 6 is a graph showing the relationship between the viewing angle θ and R _xz (θ) / R _xz (0) in the _xz plane.

FIG. 7 is a graph showing the relationship between the viewing angle φ and R _yz (φ) / R _yz (0) in the _yz plane.

[Explanation of symbols]

 p Uniaxially stretched film

Claims (1)

[Claims] 1. A thermoplastic resin film is shaped so that its vertical cross-sectional shape is corrugated, and both lateral ends of this thermoplastic resin film are fixed while maintaining its corrugated shape. A method for producing a retardation plate, which is characterized in that the thermoplastic resin film is stretched in the lateral uniaxial direction while allowing free contraction in the longitudinal direction excluding the fixing portion.