JP2009058963A - Method of manufacturing retardation plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of efficiently and stably manufacturing a retardation plate excellent in heat resistance. <P>SOLUTION: In the method of manufacturing the retardation plate, a heat shrinkable film is adhered to one surface or both surfaces of a thermoplastic resin film so that the maximum heat shrinking direction becomes a crossed angle of within 90±5° with respect to the width direction or the length direction of the thermoplastic resin film, whereby the thermoplastic resin film is shrunk under the action of heat-shrinking force of 0.03 kg/mm<SP>2</SP>or more by the heat shrinkable film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a retardation plate suitable for improving viewing angle characteristics by optical compensation of a liquid crystal cell.

Conventional retardation plates that can be used for the purpose of improving viewing angle characteristics by compensating for changes in optical characteristics such as contrast due to changes in viewing angle due to liquid crystal birefringence are negative birefringence characteristics such as polystyrene. In other words, a biaxially stretched film made of a thermoplastic resin exhibiting a negative birefringence characteristic exhibiting a property of increasing the refractive index in a direction orthogonal to the stretching direction has been known. However, the obtained retardation plate has poor heat resistance, and there is a problem that it is difficult to obtain a plate exhibiting heat resistance that can be used for forming a liquid crystal display device or the like.
JP-A-9-318815

  An object of the present invention is to develop a method capable of stably and efficiently producing a retardation plate having excellent heat resistance.

In the present invention, a heat-shrinkable film is bonded to one side or both sides of a thermoplastic resin film so that the maximum heat-shrink direction is an intersection angle within 90 ± 5 degrees with respect to the width direction or length direction of the thermoplastic resin film. Then, the present invention provides a method for producing a retardation plate, wherein the thermoplastic resin film is shrunk under the action of a heat shrinkage force of 0.03 kg / mm ² or more by the heat shrinkable film.

  According to the present invention, the phase difference is excellent in heat resistance, can highly compensate for changes in display characteristics due to viewing angles based on the birefringence of the liquid crystal cell, and can form a liquid crystal display device having excellent visibility such as contrast in a wide viewing angle range. The plate can be obtained stably and efficiently, and can be continuously produced.

In the method for producing a retardation plate according to the present invention, a heat-shrinkable film is provided on one side or both sides of a thermoplastic resin film, and the maximum heat-shrink direction is within 90 ± 5 degrees with respect to the width direction or length direction of the thermoplastic resin film. The thermoplastic resin film is bonded so as to have an intersection angle, and the thermoplastic resin film is contracted under the action of a heat contraction force of 0.03 kg / mm ² or more by the heat-shrinkable film.

  A preferable retardation plate according to the above method satisfies the formula: (nx + ny) / 2 <nz, where nx, ny is the main refractive index in the plane, and nz is the main refractive index in the thickness direction, and vertical or horizontal. The azimuth angle of the slow axis or the fast axis relative to one of the directions is within 0 ± 5 degrees or within 90 ± 5 degrees.

  As a film to be processed, a film made of one or more appropriate thermoplastic resins can be used. What consists of a thermoplastic resin which shows the positive birefringence characteristic from which the refractive index of an extending | stretching direction becomes high is preferably used from the point which obtains the phase difference plate excellent in heat resistance.

  Incidentally, examples of the thermoplastic resin exhibiting the above-mentioned positive birefringence characteristics include polycarbonate, polyvinyl alcohol, cellulose resin, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene resin, polysulfone, and polyether. Examples thereof include polyolefins such as sulfone and polypropylene.

  In particular, a thermoplastic resin that can form a film that is amorphous, excellent in heat resistance, and excellent in transparency, particularly capable of forming a film having a light transmittance of 75% or more, particularly 80% or more, particularly 85% or more can be preferably used. The thermoplastic resin film may be formed by an appropriate method such as a casting method such as a casting method or an extrusion method. A solution casting method such as a casting method is more preferable in that a film with less thickness unevenness, orientation strain unevenness and the like is obtained.

  The thickness of the thermoplastic resin film can be appropriately determined depending on the target retardation or the like, but is generally 5 to 500 μm, especially 10 to 400 μm, and particularly 20 to 300 μm. The phase difference can be obtained as the product (Δn × L) of the refractive index difference (Δn) and the optical path length (L).

  The thermoplastic resin film may be formed into a predetermined size for the purpose of manufacturing a single retardation plate by batch processing or the like, or a long film for the purpose of continuous manufacturing of a retardation plate by continuous processing It may be what. A long film can be preferably used from the viewpoint of production efficiency of the retardation plate. The thermoplastic resin film to be treated may be non-oriented or may be an oriented film that has been subjected to appropriate orientation treatment such as uniaxial stretching in advance.

  A heat-shrinkable film that adheres to one or both surfaces of a thermoplastic resin film transmits a shrinkage force due to the heating to the thermoplastic resin film, and the thermoplastic resin film is subjected to the shrinkage force in the width direction (TD) or long. The purpose is to control the phase difference characteristic, particularly the refractive index in the thickness direction, by shrinking in the longitudinal direction (MD) or both directions.

  Therefore, as the heat-shrinkable film, an appropriate film that exhibits shrinkage by heat treatment can be used, and there is no particular limitation. In general, a stretched film of a thermoplastic resin such as uniaxial or biaxial that starts thermal shrinkage at a temperature lower than the processing temperature of the thermoplastic resin film is used from the standpoint of transmission of shrinkage force. In that case, the thermal shrinkage force can be made different by changing the stretching conditions such as the kind of the thermoplastic resin and the stretching ratio.

  Incidentally, examples of the thermoplastic resin forming the heat-shrinkable film include polyvinyl chloride, polyethylene, polypropylene, polyester, polystyrene, and polyamide. In the above, from the viewpoint of the accuracy of the shrinkage treatment of the thermoplastic resin film, a heat-shrinkable film exhibiting heat-shrinkability in the vicinity of the glass transition temperature of the thermoplastic resin film, especially within the range of ± 20 ° C. is preferable. Used.

  An adhesive may be used for bonding the heat-shrinkable film and the thermoplastic resin film. In particular, the heat transfer property of heat-shrinkable film during heat shrinkage, and the shrinkage of the heat-shrinkable film after shrinkage from the processed thermoplastic resin film after shrinkage treatment, that is, the obtained retardation plate An adhesive is preferably used from the viewpoint of properties.

  As said adhesive, appropriate things, such as an acrylic type, a silicone type, a polyester type, a polyurethane type, a polyether type, and a rubber type, can be used, for example, There is no limitation in particular. What forms the adhesion layer in which the adhesive force hardly increases as much as possible by the heat shrink treatment of the heat shrinkable film is preferably used.

  The pressure-sensitive adhesive layer can be attached to one or both of the adhesive surfaces when the thermoplastic resin film and the heat-shrinkable film are bonded, but when the formed retardation plate and the heat-shrinkable film are separated, the heat-shrinkable layer is attached. Since it is preferable from the viewpoint of production efficiency and the like that the adhesive film can be separated with the adhesive layer accompanied, the heat-shrinkable film is preferably used as the adhesive layer previously attached.

  Attaching the adhesive layer to the heat-shrinkable film can be done by applying a pressure-sensitive adhesive to the heat-shrinkable film and drying it, but the shrinkage characteristics of the heat-shrinkable film change due to the drying process. A method of transferring the pressure-sensitive adhesive layer provided on the separator to the heat-shrinkable film is preferable from the viewpoint of preventing the above.

  In the above case, the separator can be used as a protective cover for preventing the adhesive layer from being contaminated until the separator is adhered as it is and the heat-shrinkable film is put to practical use. The heat-shrinkable film surface to which the adhesive layer is attached can be subjected to an appropriate surface treatment such as corona treatment for the purpose of improving the adhesion with the adhesive layer.

In the present invention, one or two heat-shrinkable films are provided on one or both sides of the thermoplastic resin film so that a heat shrinkage force of 0.03 kg / mm ² or more acts when the thermoplastic resin film is shrunk. The appropriate number of the above is adhered. If the action of the heat shrinkage force is less than 0.03 kg / mm ^{2, the} force for shrinking the thermoplastic resin film (in-plane direction) is poor, and it has the desired retardation characteristics by controlling the refractive index in the thickness direction. A retardation plate cannot be obtained stably.

Stable adhesion state of the preferred aforementioned heat-shrinkable film from the point of application of the retardation characteristics of interest, 0.04 kg / mm ² or more, so that especially 0.05 kg / mm ² or more heat shrinking force acts It is a thing. On the other hand, there is no particular limitation on the upper limit of the heating shrinkage force. In general, it is 5 kg / mm ² or less, especially 1 kg / mm ² or less, particularly 0.5 kg / mm ² or less in terms of operability during processing.

  In the above, when the heat-shrinkable film is bonded to the thermoplastic resin film, the maximum heat shrinkage direction by the heat-shrinkable film is within 90 ± 5 degrees with respect to the width direction or length direction of the thermoplastic resin film. Glued to become Thereby, the phase difference plate which maintained the original orientation angle favorably in the thermoplastic resin film used suppressing the fluctuation | variation of the orientation angle by shrinkage | contraction can be obtained.

  The orientation angle is defined as the azimuth angle of the slow axis or the fast axis based on one of the longitudinal direction and the lateral direction of the thermoplastic resin film or the retardation film. Particularly in the case of a thermoplastic resin film, it is defined as the azimuth angle of the slow axis with reference to the width (lateral) direction. Therefore, the suppression of the change in the orientation angle due to the shrinkage described above means that a retardation plate having excellent orientation angle uniformity and little variation is obtained. Incidentally, in the case of a phase difference plate having a large variation in the orientation angle, when it is applied to a liquid crystal cell in combination with the phase difference plate, a problem such as a liquid crystal display device with poor contrast occurs.

  In addition, when adhering the heat-shrinkable film on both sides of the thermoplastic resin film or adhering a multilayer on one side, the heat-shrinkable film on the front and back surfaces and the upper and lower layers may be the same, Those having different heat shrinkage characteristics such as heat shrinkage ratio may be used.

  The heat-shrinkage treatment of the heat-shrinkable film adhered to the thermoplastic resin film can be performed via an appropriate stretching machine such as a roll stretching machine, a tenter, or a biaxial stretching machine. As described above, the treatment temperature is preferably in the vicinity of the glass transition temperature of the thermoplastic resin film, in particular within the range of ± 20 ° C., particularly above the glass transition temperature, from the viewpoint of controllability of the treatment operation.

  Further, the shrinkage treatment given to the thermoplastic resin film under the action of the shrinkage force of the heat-shrinkable film by heating may be either the width direction or the length direction of the thermoplastic resin film as described above, Both may be sufficient and can be determined as appropriate according to the retardation plate to be formed.

  The above-described shrinkage treatment direction in the width direction or the length direction can be controlled through the difference in shrinkage ratio between the width direction and the length direction in the heat-shrinkable film. That is, for example, by using a heat-shrinkable film having a larger shrinkage rate in the width direction (length direction) than in the length direction (width direction), a thermoplastic resin film in a direction corresponding to the width direction (length direction). Can be shrunk.

  In the above description, when the shrinkage treatment is applied to one of the width direction and the length direction, a stretching treatment can be applied to the other direction. Further, the shrinkage treatment applied to the thermoplastic resin film under the action of the shrinkage force of the heat-shrinkable film can be performed in two or three or more steps.

  When the necessary shrinkage treatment for the thermoplastic resin film is completed, the heat-shrinkable film after the shrinkage treatment is peeled off from the formed retardation plate and separated. The obtained retardation plate can be used practically as it is, or it can be used practically as a phase-adjustment characteristic is adjusted by adding a stretching process or the like.

  The production method according to the present invention can be preferably applied to the formation of various retardation films having retardation characteristics according to various applications. In particular, since the refractive index in the thickness direction can be controlled, the viewing angle and contrast of various display devices such as TFT type and MIM type using liquid crystal cells exhibiting birefringence such as TN type and STN type are increased. The present invention can be advantageously applied to the formation of a retardation plate suitable for compensation of retardation due to birefringence for the purpose of improving the above.

  The retardation plate that can be preferably used for the above-described retardation compensation satisfies the formula: (nx + ny) / 2 <nz, where in-plane main refractive index is nx, ny and thickness direction main refractive index is nz. In addition, the orientation angle (the azimuth angle of the slow axis or the fast axis with respect to one of the vertical and horizontal directions) is within 0 ± 5 degrees or within 90 ± 5 degrees.

  Further, the variation in retardation and orientation axis (the orientation angle) due to birefringence is as small as possible, and in particular, the variation in retardation in transmitted light perpendicular to the film surface (in the front direction) is 10 nm or less, especially 8 nm. Hereinafter, a retardation plate having an alignment axis variation of 8 degrees or less, particularly 5 degrees or less, and particularly 3 degrees or less, particularly 5 nm or less, can be preferably used for phase difference compensation.

Example 1
On both sides of the long polyester film having a thickness of 65μm by the belt casting method, via an acrylic adhesive layer was attached to it stretched polyester film of the heat shrinking force is 0.11 kg / mm ² is one by one maximum heating shrinkage direction After bonding so that the crossing angle is 88 degrees with respect to the length direction of the long polyester film (the counterclockwise direction is the positive direction, the same shall apply hereinafter), it is contracted by 9% in the width direction at 160 ° C. via a tenter. The stretched polyester film was peeled off to obtain a 71 μm thick retardation plate continuously.

Example 2
On both sides of the long polycarbonate film having a thickness of 65μm by the belt casting method, via an acrylic adhesive layer was attached to it a stretched polypropylene film of the heat shrinking force is 0.07 kg / mm ² is one by one maximum heating shrinkage direction After bonding so that the crossing angle is 93 degrees with respect to the width direction of the long polycarbonate film, it is contracted by 4% in the length direction at a roll speed ratio of 0.96 times through a roll stretching machine at 155 ° C. The stretched polypropylene film was peeled off to obtain a retardation plate having a thickness of 77 μm continuously.

Example 3
On both sides of the long polyester film having a thickness of 70μm by the belt casting method, via an acrylic adhesive layer was attached to it stretched polystyrene film of heat shrinkage force is 0.03 kg / mm ² is one by one maximum heating shrinkage direction After adhering to the crossing angle of 91 degrees with respect to the width direction of the long polyester film, it is subjected to shrinkage treatment of 4% in the length direction and 5% in the width direction at 150 ° C. through a roll stretching machine and a tenter. The stretched polystyrene film was peeled off to obtain a 75 μm thick retardation plate continuously.

Comparative Example 1
On both sides of the long polyester film having a thickness of 65μm by the belt casting method, via an acrylic adhesive layer was attached to it stretched polyester film of the heat shrinking force is 0.01 kg / mm ² is one by one maximum heating shrinkage direction After bonding so that the crossing angle is 88 degrees with respect to the length direction of the long polyester film, it is contracted in the length direction at a roll speed ratio of 0.96 times through a roll stretching machine at 155 ° C. The stretched polyester film was peeled off by treatment, and a retardation plate having a thickness of 65 μm was continuously obtained.

Comparative Example 2
A retardation plate having a thickness of 77 μm was obtained in the same manner as in Example 2 except that the stretched polypropylene film was bonded such that the maximum heat shrinkage direction was 80 ° with respect to the width direction of the long polycarbonate film.

Evaluation Test About the retardation plates obtained in Examples and Comparative Examples, nx, ny, and nz were examined with an automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-21ADH), and the formula: P = (nx + ny) / While calculating P value based on 2-nz, the orientation angle was investigated. The orientation angle of the long film to be treated was defined as the positive direction in the counterclockwise direction based on the azimuth angle with the slow axis with the length (longitudinal) direction as the reference (0 degree).

The results are shown in the following table.
nx ny nz P value Orientation angle (degrees)
Example 1 1.5853 1.5836 1.5860 −0.0016 −1.6
Example 2 1.5848 1.5831 1.5871 −0.0032 −88.1
Example 3 1.5850 1.5838 1.5862 -0.0018 0.5
Comparative Example 1 1.5854 1.5853 1.5843 0.0010 88.5
Comparative Example 2 1.5848 1.5831 1.5871 -0.0032 79.5

  In Comparative Example 1, the set shrinkage treatment was not achieved, and the desired P <0 characteristic was not obtained. Also, during the shrinking process, no tension was obtained between the rolls, and the film meandered and the running stability was poor. In Comparative Example 2, those satisfying the characteristics with an orientation angle of 0 ± 5 degrees or 90 ± 5 degrees were not obtained.

Each retardation plate obtained in the above example was placed on both sides of a TN type liquid crystal cell, and a polarizing plate was placed on it, and the display characteristics due to the contrast in the front direction and the change in viewing angle were examined. There was no change in display characteristics in the range, and the liquid crystal display device was of high display quality and excellent in visibility.


Patent applicant Nitto Denko Corporation
Agent Tsutomu Fujimoto

Claims (3)

Adhere the heat-shrinkable film to one or both sides of the thermoplastic resin film so that the maximum heat shrinkage direction is an intersection angle within 90 ± 5 degrees with respect to the width direction or length direction of the thermoplastic resin film. A method for producing a retardation plate, comprising shrinking the thermoplastic resin film under the action of a heat shrinkage force of 0.03 kg / mm ² or more by a shrinkable film.   The manufacturing method according to claim 1, wherein a retardation film is continuously obtained by using a long film made of a thermoplastic resin exhibiting positive birefringence characteristics as the thermoplastic resin film.   3. The method for producing a retardation plate according to claim 1, wherein the thermoplastic resin film is contracted in the width direction, the length direction, or both directions.