JP3676454B2 - Production method of retardation plate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a retardation plate constituted by using a uniaxially stretched thermoplastic resin film, and more particularly to a method of manufacturing a retardation plate suitable for compensating for a phase difference in a liquid crystal display device. .
[0002]
[Prior art]
Conventionally, TN (twisted nematic) liquid crystal display devices and STN (super twisted nematic) liquid crystal display devices have been widely used in various OA devices and display devices.
[0003]
The liquid crystal display device has a problem that a display image is colored due to a phase difference generated in the liquid crystal. For example, an STN liquid crystal display device having excellent characteristics as compared with a TN liquid crystal display device has a fatal problem that a display image is colored blue or yellow. Therefore, attempts have been made to solve the above-mentioned coloring problem by bonding a retardation plate made of a thermoplastic resin film to the surface of the liquid crystal display cell to compensate for the retardation.
[0004]
By the way, the retardation plate made of the thermoplastic resin film functions to eliminate the retardation generated in the liquid crystal by utilizing the birefringence of the stretched thermoplastic resin film. As the retardation plate as described above, those made of various materials have been proposed. For example, cellulose resin (Japanese Patent Laid-Open No. 63-167363), vinyl chloride resin (Japanese Patent Publication No. 45-34477, Japanese Patent Laid-Open Publication No. 56-125702), polycarbonate resin (Japanese Patent Publication No. 41-12190). JP, 56-130703), acrylonitrile resin (JP 56-130702), styrene resin (JP 56-125703), olefin resin (JP 60-24502). The thing using the film which consists of synthetic resins, such as gazette), is proposed. Conventionally, a phase difference plate has been constituted by uniaxially stretching each thermoplastic resin film as described above. In this case, as a stretching method, a method of longitudinal uniaxial stretching (Japanese Patent Laid-Open No. 2-191904) or a method of lateral uniaxial stretching (Japanese Patent Laid-Open No. 2-42406) has been reported.
[0005]
The retardation compensation performance of the retardation plate is represented by a so-called retardation value. The retardation value is represented by Δn × d, where Δn is the anisotropy (that is, birefringence) of the refractive index of the resin film and d is the thickness of the film.
[0006]
On the other hand, in a liquid crystal display device, it is strongly required that color unevenness and contrast unevenness hardly occur over the entire surface of the display. In order to provide a liquid crystal display device capable of such uniform display, the retardation value is required to be uniform over the entire surface of the retardation plate.
[0007]
In order to satisfy the above requirements, there is no sinusoidal thickness variation with a pitch of 50 mm or less and an amplitude of thickness of 0.5 μm or more when a change in thickness is measured continuously in the length direction. It consists of a thermoplastic polymer film and a film formed by uniaxially or biaxially stretching the film in a direction perpendicular to the extrusion direction, the retardation value is 1200 nm or less, and the fluctuation width of the retardation value is 10 % Or less is proposed (JP-A-2-256003).
[0008]
In addition, a substantially non-oriented film is uniaxially stretched at a uniform temperature selected from a temperature range of glass transition temperature Tg to Tg + 30 ° C., and variation in retardation value is within 1.0% of standard deviation. A retardation plate is proposed (Japanese Patent Laid-Open No. 2-89007).
[0009]
Further, when the thermoplastic resin film is uniaxially stretched, the retardation film is contracted in a direction perpendicular to the stretch axis, and a method for producing a retardation plate with an improved viewing angle is disclosed in JP-A-2-191904. Has been.
[0010]
[Problems to be solved by the invention]
However, even if the above-described conventional method for producing a retardation plate is used, it has not yet been possible to obtain a retardation plate that is sufficiently satisfactory for practical use. That is, the retardation value is hardly uniformized to a level that can be satisfactorily satisfied practically, and when the phase difference plate is incorporated in the liquid crystal display device, there are uneven color pitches that can be visually discerned. .
[0011]
This is because when a retardation plate is incorporated in a liquid crystal display device and evaluated, the difference in retardation value between two adjacent points is easily discriminated. Therefore, the retardation value is uniform in the retardation plate. Will be more strongly demanded.
[0012]
An object of the present invention is to manufacture a retardation plate that has a uniform retardation value with high accuracy in view of the above-mentioned problems of the prior art, and can perform uniform and high-quality display over almost the entire area. It is to provide a method .
[0013]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above-mentioned problems, the present inventor has contracted in the width direction after laterally uniaxially stretching a thermoplastic resin film during the production of a retardation film obtained by uniaxially stretching a thermoplastic resin film. Uniaxially stretching in the film plane after the longitudinal uniaxial stretching, or uniaxially stretching in the longitudinal direction, and the final orientation state is uniaxial orientation in the film plane. The difference in retardation value between the two points is very small, 0.5% or less with respect to the average retardation value of the entire film. By using the retardation plate thus obtained, a liquid crystal display When applied to an apparatus, it has been found that uniform and high-quality display can be performed over substantially the entire display portion of the display device, and the present invention has been made.
[0014]
That is, the method for producing a phase difference plate of the present invention is a method for producing a phase difference plate obtained by uniaxially stretching a thermoplastic resin film, while the thermoplastic resin film is horizontally uniaxially stretched and then contracted in the width direction. After longitudinally uniaxially stretching or longitudinally uniaxially stretching, laterally uniaxially stretching while shrinking in the longitudinal direction to make the final orientation state uniaxially oriented in the film plane, thereby allowing any arbitrary distance of 1 cm in the film plane The difference in retardation value between two points is 0.5% or less with respect to the average retardation value of the entire film.
[0015]
Details of the present invention will be described below.
As the thermoplastic resin film used in the present invention, a film made of an appropriate resin that exhibits birefringence upon stretching can be used. For example, a cellulose resin, a vinyl chloride resin, a polycarbonate resin, an acrylonitrile resin, an olefin Examples of the resin include polystyrene resin, polystyrene resin, polymethyl methacrylate resin, polysulfone resin, polyarylate resin, and polyether sulfone resin. Moreover, as a manufacturing method of the said thermoplastic resin film, arbitrary methods, such as a solvent cast method, a calendar method, or a melt extrusion method, are employable.
[0016]
In the present invention, the thermoplastic resin film is stretched by the following two-stage stretching. That is, (1) a method of stretching uniaxially in the horizontal direction and then longitudinally uniaxially stretching while shrinking in the width direction, or (2) a method of stretching in the uniaxial direction while stretching in the longitudinal direction and then shrinking in the longitudinal direction.
[0017]
In the above stretching method (1) or (2), stretching is performed in two stages in directions orthogonal to each other. In the second stage stretching, stretching is performed while contracting in the direction stretched in the first stage. Is called. Therefore, the orientation state in the finally obtained thermoplastic resin film is uniaxial orientation in the film plane .
[0018]
In the present invention, the first-stage stretching is performed in order to make the orientation in the first-stage stretching direction uniform by uniformizing the stress in the stretching direction. As a result, in the second stage stretching, not only the stress in the second stage stretching direction is equalized, but also the stress in the first stage stretching direction is uniformed. Directional contraction also proceeds uniformly. As a result, it is possible to obtain a retardation plate in which the retardation value difference between any two points 1 cm apart is 0.5% or less and the retardation value in the film plane is uniform with high accuracy. Become.
[0019]
In addition, it is preferable that the draw ratio in the said extending | stretching is 1.05 times or more and 2.0 times or less about the draw ratio of the 1st step. If it is less than 1.05 times, the effect of homogenizing the orientation in the stretching direction may be small, and if it exceeds 2.0 times, the amount of shrinkage during the second-stage stretching becomes too large. The value may be non-uniform. The draw ratio in the second stage is appropriately determined according to the drawing temperature and the necessary retardation value.
[0020]
Moreover, it is preferable that the temperature at the time of extending | stretching shall be in the range of glass transition point (Tg) -10 degreeC or more and Tg + 30 degreeC or less. When the stretching temperature is lower than Tg−10 ° C., the thermoplastic resin film does not have sufficient flexibility, so that it is easily broken during stretching. On the other hand, when the stretching temperature exceeds Tg + 30 ° C., the increase in stretching stress accompanying deformation becomes small, so that only the portion that has once been stretched is preferentially stretched, and uneven stretching tends to occur.
[0021]
In the present invention, the stress in the stretching direction is made uniform by the first stage stretching, and not only the stress in the second stage stretching direction is made uniform in the second stage stretching, Shrinkage in the stretching direction in the first stage also proceeds uniformly, and the orientation state in the finally obtained thermoplastic resin film is uniaxial orientation in the film plane . Therefore, as described above, the retardation value difference between any two points 1 cm apart is 0.5% or less, and the retardation value in the film surface can be made uniform with high accuracy.
[0022]
【Example】
Hereinafter, the present invention will be clarified by giving specific examples of the present invention.
Example 1
A polysulfone resin (Tg = 190 ° C.) obtained by cocondensation of 4,4-dichlorophenylsulfone and a sodium salt of bisphenol A and having a styrene equivalent weight average molecular weight of 7 × 10 ⁴ is dissolved in methylene chloride. A 20% by weight methylene chloride solution of polysulfone resin was obtained.
[0023]
The above solution is cast on a chrome-plated steel belt, dried in a hot air oven, the solvent is removed, and then peeled off from the steel belt to produce an unstretched polysulfone raw material having a width of 800 mm and an average thickness of 75 μm. did.
[0024]
The polysulfone unstretched original fabric is uniaxially stretched at a stretching temperature of 190 ° C. and a draw ratio of 1.2 times using a tenter stretching machine, and then both ends of the raw fabric are slit, and a film having a width of 850 mm and an average thickness of 65 μm Got.
[0025]
Subsequently, the film was stretched uniaxially with a roll stretching machine. The roll stretching machine used was configured to stretch between two pairs of nip rolls having different peripheral speeds, and the length between the nip rolls was 2.5 m. The film was stretched uniaxially in the longitudinal direction while shrinking in the width direction at a stretching temperature of 190 ° C. and a stretching ratio of 1.4 times by the roll stretching machine to obtain a film having a width of 610 mm and an average thickness of 65 μm.
[0026]
A phase difference plate sample having a width of 500 mm and a length of 1000 mm was cut out from the center of the film obtained as described above. When the retardation value at 590 nm of the obtained sample was measured at intervals of 1 cm in both the width direction and the length direction, the average value was 436 nm. Further, the difference in retardation value between two points separated by 1 cm was a maximum of 1.0 nm (0.23% of the above average value) when the number of measurements = 146.
[0027]
Example 2
A polycarbonate resin (Tg = 155 ° C.) was melt-extruded from a T die to produce an unstretched original fabric having a width of 500 mm and an average thickness of 70 μm.
[0028]
The raw fabric was longitudinally uniaxially stretched at a stretching temperature of 160 ° C. and a stretch ratio of 1.1 times using a roll stretching machine to obtain a film having a width of 475 mm and an average thickness of 67 μm.
Next, using the stretching apparatus shown in FIGS. 1 and 2, the film was uniaxially stretched in the transverse direction while shrinking in the longitudinal direction. In the apparatus shown in FIGS. 1 and 2, the film p is configured to be conveyed by the conveyance roll 3, and a plurality of jigs 2 are arranged along the guide rail 1. Each jig 2 is provided with a film gripping means 10 for gripping the end of the film. Reference numeral 4 denotes an oven, which is provided for heating the film p. In addition, 11 shows an upper side linear guide part, 12 shows a lower side linear guide part, 13 and 14 show a curve guide part, respectively, and the film p is the film grip provided in the said jig | tool 2 so that FIG. The edge is gripped by the means, and the film p is gripped on both sides of the film p. The distance between the jigs 2 is increased, and the film p is stretched laterally uniaxially while being transported.
[0029]
In the present embodiment, the film gripping means 10 sequentially grips the lateral ends of the film p in the guide guides 13 of the guide rails, and the upper linear guide 11 in the temperature of 160 ° C. The film was stretched 1.3 times in the transverse direction while shrinking in the longitudinal direction, thereby obtaining a film having a width of 600 mm and an average thickness of 60 μm.
[0030]
A phase difference plate sample having a width of 500 mm and a length of 1000 mm was cut out from the center of the obtained film. The retardation value at 590 nm of this sample was measured at intervals of 1 cm in both the width direction and the length direction. As a result, the average retardation value was 539 nm, and the difference in retardation value between two points 1 cm apart was 1.3 nm at maximum (0.24% of the average value) when the number of measurements = 146. .
[0031]
Comparative Example 1
Polysulfone unstretched raw material having a width of 800 mm and an average thickness of 75 μm obtained in the same manner as in Example 1 was stretched uniaxially at a stretching temperature of 190 ° C. and a stretching ratio of 1.4 times using a roll stretching machine, A film having a width of 670 mm and an average thickness of 65 μm was obtained.
[0032]
A retardation plate sample having a width of 500 mm and a length of 1000 mm was cut out from the center of the film obtained as described above, and the retardation value was measured in the same manner as in Example 1. As a result, the average retardation value of the entire film was 452 nm, and the difference in retardation value between two points 1 cm apart was a maximum of 3.5 nm (0.77% of the average value).
[0033]
【The invention's effect】
As described above, in the method for producing a retardation plate of the present invention, the thermoplastic resin film is stretched in two stages as described above. In the second stage stretching, the thermoplastic resin film is contracted in the direction stretched in the first stage. Since stretching is performed, the orientation state in the finally obtained thermoplastic resin film is uniaxial orientation in the film plane. Therefore, the difference in retardation value between any two points 1 cm apart in the film plane is obtained. , And 0.5% or less of the average retardation value.
Therefore, the retardation plate obtained by the method for producing a retardation plate of the present invention has a uniform retardation value over almost the entire area of the film. It can exhibit excellent phase difference compensation performance without occurring. Therefore, it is possible to provide a liquid crystal display device that can perform uniform and excellent display over substantially the entire area of the screen without coloring the peripheral portion of the screen.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram for explaining a stretching apparatus used in transverse uniaxial stretching in Example 2. FIG.
FIG. 2 is a partially cutaway enlarged plan view for explaining a process of stretching the film uniaxially in the stretching apparatus shown in FIG.
[Explanation of symbols]
p ... film 1 ... guide rail 2 ... jig 3 ... transport roll 4 ... oven 10 ... film gripping means 11 ... upper straight guide part 12 ... lower straight guide part 13, 14 ... curve guide part

Claims (1)

A method for producing a retardation film obtained by uniaxially stretching a thermoplastic resin film,
After laterally uniaxially stretching the thermoplastic resin film, longitudinally uniaxially stretching while shrinking in the width direction, or longitudinally uniaxially stretching and then laterally uniaxially stretching while shrinking in the longitudinal direction, the final orientation state is in the film plane By uniaxial orientation of
A method for producing a phase difference plate, characterized in that the difference in retardation value between any two points 1 cm apart in the film plane is 0.5% or less with respect to the average retardation value of the entire film. .

Images