JP2006309029A - Method for manufacturing phase difference compensation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively manufacturing a phase difference compensation film which hardly causes bowing and has satisfactory accuracy of optical axis angle, in sequential biaxial stretching of subjecting a thermoplastic resin film to longitudinal stretching and, thereafter, to lateral stretching. <P>SOLUTION: When the thermoplastic resin film is laterally deformed in the lateral stretching step, stretching temperature of the lateral stretching is made higher than the stretching temperature of the longitudinal stretching and wind speed of the lateral stretching in a preheating zone and in a stretching zone is set to be 8 m/sec to 30 m/sec. According to such a method, the phase difference compensation film which hardly causes bowing and has satisfactory accuracy of optical axis angle can be manufactured inexpensively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a retardation compensation film used for improving a viewing angle and a contrast of a liquid crystal display device.

  In recent years, with the increase in screen size of liquid crystal display devices, the required quality of retardation compensation films used for improving the viewing angle and contrast of liquid crystal display devices has been rapidly increasing. In particular, the optical axis angle accuracy and the phase difference variation are required to be good over a large film area. In addition, in order for the liquid crystal display devices to become widespread in the world, innovative cost reduction of components used in the liquid crystal display devices, that is, innovations in structure, materials, manufacturing methods, supply, etc., and productivity through standardization Need to be improved.

  In order for the retardation compensation film to appropriately improve the viewing angle and contrast of the liquid crystal display device, highly controlled birefringence in the film plane and in the film thickness direction is required. As a method for applying the birefringence of the film with high control, sequential biaxial stretching composed of longitudinal and lateral sequential stretching is generally used.

  However, when the retardation compensation film is produced by the sequential biaxial stretching method, when the lateral stretching is performed, the so-called bowing, which is different in the traveling speed at the end portion and the central portion of the film, causes the molecules in the width direction. Non-uniform orientation occurs. Due to this bowing phenomenon, it has been difficult to obtain a retardation compensation film capable of precisely compensating the liquid crystal alignment.

  In order to solve this problem, for example, a low-angle widening method has been proposed, which is disclosed in Patent Document 1 and uses a tenter for lateral stretching, and the opening angle of the tenter rail is within 10 degrees. Yes. However, this method has insufficient measures for bowing, and the range in which the accuracy in the optical axis direction is within ± 1 degree is about 60 to 65% of the film width after transverse stretching.

In addition, for example, a method of improving the optical axis accuracy by providing a relaxation step after the transverse stretching step disclosed in Patent Document 2, or a tenter rail opening angle disclosed in Patent Document 3, for example. A method has been proposed in which the angle is within a range of 8 to 20 degrees and the state is kept at a distance of twice or more the film width before widening. According to these methods, the range in which the accuracy in the optical axis direction is within ± 1 degree is 80% or more of the film width after transverse stretching, and a good retardation compensation film can be obtained. However, these methods are expensive norbornene It is necessary to use a resin, and although the quality of the obtained retardation compensation film is sufficient, there is a problem that the film becomes expensive in terms of cost.
JP 2002-148438 A JP 2002-196135 A JP 2004-144492 A

  The present invention has been made in view of the above-described problems of the prior art, and in sequential biaxial stretching in which transverse stretching is performed after longitudinal stretching of a thermoplastic resin film, there is little bowing, and the retardation of the optical axis angle is good. It is an object of the present invention to provide a method for producing a compensation film at a low cost.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research and have made the stretching temperature during transverse stretching higher than the stretching temperature during longitudinal stretching when the thermoplastic resin film is deformed in the width direction in the transverse stretching step. In addition, by setting the wind speed of the preheating zone and the stretching zone of the transverse stretching to 8 m / sec to 30 m / sec, it is possible to manufacture a retardation compensation film with low bowing and good optical axis angle at low cost. As a result, the present invention has been achieved.

  Specifically, according to the present invention, there is provided a method for producing a retardation compensation film by sequential biaxial stretching in which an amorphous thermoplastic resin film is longitudinally stretched and then laterally stretched, and the stretching temperature at the time of lateral stretching is set. There is provided a method for producing a retardation compensation film, characterized in that the temperature is higher than the stretching temperature at the time of longitudinal stretching, and the wind speed of the preheating zone and the stretching zone for transverse stretching is 8 m / sec to 30 m / sec.

  In the method for producing an optical film according to the present invention, a resin composition containing an imide resin is preferably used as the amorphous thermoplastic resin.

  Further, in the method for producing an optical film according to the present invention, the imide resin includes a unit represented by the following general formula (1), a unit represented by the following general formula (2), and / or (3 It is preferable that it is an imide resin having a unit represented by:

(Wherein, R ¹ and R ² each independently represents a hydrogen or an alkyl group having 1 to 8 carbon atoms, R ³ is an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(However, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(Wherein, R ⁷ is a hydrogen or an alkyl group having 1 to 8 carbon atoms, R ⁸ represents a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

  Since the constitution of the method for producing the retardation compensation film of the present invention is as described above, in sequential biaxial stretching in which the thermoplastic resin film is stretched longitudinally and then laterally stretched, there is little bowing and the optical axis angle is good. A method for producing a compensation film at low cost can be provided and is useful.

[Composition of film]
First, the film used in the method for producing an optical film according to the present invention will be described. In the present invention, the film is made of at least an amorphous thermoplastic resin. The amorphous thermoplastic resin includes polymethyl methacrylate resin, polycarbonate resin, polystyrene resin, cycloolefin resin, cellulose resin, vinyl chloride resin, polysulfone resin, and polyether sulfone resin. , A single resin such as a maleimide / olefin resin and a glutarimide resin, or a resin composition obtained by mixing these resins.

  As the amorphous thermoplastic resin, an imide resin having a unit represented by the following general formula (1) is preferable, and a unit represented by the following general formula (1) and the following general formula (2) are represented. An imide resin copolymerized with a unit, an imide resin copolymerized with a unit represented by the following general formula (1) and a unit represented by the following general formula (3), or represented by the following general formula (1) An imide resin obtained by copolymerizing a unit represented by the following general formula (2) and a unit represented by the following general formula (3) is more preferable.

(Wherein, R ¹ and R ² each independently represents a hydrogen or an alkyl group having 1 to 8 carbon atoms, R ³ is an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(However, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(Wherein, R ⁷ is a hydrogen or an alkyl group having 1 to 8 carbon atoms, R ⁸ represents a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

  The imide resin is usually a resin having a unit represented by the general formula (1). The resin composed of the unit represented by the general formula (1) has positive intrinsic birefringence. On the other hand, the resin composed of the unit represented by the general formula (2) has an intrinsic birefringence near zero, and the resin composed of the unit represented by the formula (3) has a negative intrinsic birefringence. . Therefore, if an imide resin in which the unit represented by the general formula (1) and the unit represented by the general formula (2) and / or (3) are copolymerized at an appropriate ratio is used, it is suitable for optical applications. A zero birefringent film or a film close thereto can be realized.

  Examples of the resin having a unit represented by the general formula (1) include glutarimide resin. Examples of the resin having the unit represented by the general formula (1) and the unit represented by the general formula (2) include imidized polymethyl methacrylate resin (imidized PMMA resin). It is done. Moreover, as resin which has a unit represented by the said General formula (1) and a unit represented by the said General formula (3), an imidized styrene resin etc. are mentioned, for example. Examples of the resin having a unit represented by the general formula (1), a unit represented by the general formula (2), and a unit represented by the general formula (3) include, for example, imidized methacrylstyrene. Resin (imidized MS resin) etc. are mentioned. In addition, the synthesis | combining method of these resin is not specifically limited, It can synthesize | combine using a conventionally well-known method.

  Further, the amorphous thermoplastic resin may be a resin composition. In the present invention, the specific composition of the resin composition that can be used as an amorphous thermoplastic resin is not particularly limited, and the various thermoplastic resins described above (preferably the imide resin described above) and the present invention. Other components known in the technical field may be contained in a known ratio. As other components, other resin components may be used, and stabilizers and lubricants generally used in the following extrusion process, and / or ultraviolet absorbers may be used.

[Film forming method]
As a method of forming the film, any conventionally known method can be used, and examples thereof include a solution casting method and a melt extrusion method. Any of these methods can be employed, but from the viewpoint of the global environment, work environment, and production cost, a melt extrusion method that does not use a solvent is preferable.

  In the method for producing a film according to the present invention, it is only necessary to include a sequential biaxial stretching process in which at least longitudinal stretching is performed and then lateral stretching is performed, and other processes are not particularly limited, but as a preferred embodiment Furthermore, the manufacturing method including each process of a preliminary drying process, an extrusion process, and a cooling process can be mentioned.

  The pre-drying step is a step of pre-drying the thermoplastic resin to be used before film formation. The preliminary drying is performed by, for example, using a hot air dryer or the like in the form of pellets or the like. By the above preliminary drying, foaming of the extruded resin can be prevented. By adopting this step, particularly when an optical film is produced, it is possible to avoid a deterioration in the quality of the optical film due to foaming, which is preferable. Specific conditions for the preliminary drying are not particularly limited, and conditions known in the technical field of the present invention can be employed. In addition, it is preferable that the temperature at the time of preliminary drying is high enough to vaporize water sufficiently and low enough that the raw material pellets do not block.

  The extrusion process is a process in which a thermoplastic resin is supplied to an extruder and extruded into a sheet shape to form a film. The type of the extruder and the extrusion conditions are not particularly limited, and conditions known in the technical field of the present invention can be employed. For example, an extruder having a configuration in which a thermoplastic resin heated and melted in an extruder is supplied to a T die through a gear pump or a filter can be preferably used. By using the gear pump, the uniformity of the resin extrusion amount can be improved, and the thickness unevenness can be reduced. Further, by using a filter, it is possible to remove foreign substances in the resin and obtain a film having an excellent appearance without defects. By adopting such a configuration, the quality of the obtained optical film can be further improved.

  The cooling process is a process in which the extruded sheet-like molten resin is sandwiched between two cooling drums and cooled. By adopting the cooling step, the optical film can be formed efficiently and with high quality. Here, of the two cooling drums, one is a rigid metal drum having a smooth surface, and the other is a flexible drum having an elastically deformable metal elastic outer cylinder having a smooth surface. Particularly preferred. By sandwiching the extruded sheet-like molten resin between the rigid drum and the flexible drum and cooling to form a film, fine irregularities on the surface and die lines are corrected, and the surface has smooth and uneven thickness. A film having a thickness of 5 μm or less can be obtained.

  The specific material, shape, size, and the like of the rigid drum and the flexible drum are not particularly limited as long as the extruded sheet-like molten resin can be sufficiently cooled. In the present specification, the “cooling drum” includes so-called “touch roll” and “cooling roll”.

  In this cooling process, even if one of the drums can be elastically deformed, the surfaces of the drums are usually made of metal, so that the drum surfaces come into contact with each other and the outer surface of the drum is easily damaged. It is easy to break itself. Accordingly, the thickness of the film to be molded is preferably 10 μm or more, more preferably 50 μm or more, further preferably 80 μm or more, and particularly preferably 100 μm or more.

  Further, in this cooling step, if the film is thick, the cooling of the film is likely to be non-uniform, and the optical characteristics are likely to be non-uniform. Accordingly, the thickness of the film is preferably 200 μm or less, and more preferably 170 μm or less.

  As a preferred embodiment of the present invention, the production method including the preliminary drying step, the extrusion step, the cooling step, and the stretching step described later is exemplified, but the present invention is of course not limited to this, and as necessary. Some steps may be omitted, or other steps known in the technical field of the present invention may be added. Examples of other steps include a surface treatment step described later, but are not particularly limited.

[Stretching method of film]
In the present invention, a stretched film is obtained by subjecting the film obtained as described above to a stretching step. That is, a stretched film can be obtained by subjecting an unstretched film obtained by the method described in the above [Film Forming Method] or the like to sequential biaxial stretching that is longitudinally stretched and then laterally stretched (however, It is also possible to apply to a stretched film instead of an unstretched film.) By performing these stretching operations, birefringence in the film plane and in the film thickness direction can be appropriately imparted. In addition, after shape | molding a raw material film, a film may be once stored or moved as needed, and a film may be extended after that.

  For the longitudinal stretching, any conventionally known stretching method may be adopted, and generally zone stretching or roll longitudinal stretching is common. The zone stretching method is longitudinal uniaxial stretching having a heating zone between two nip rolls, and the roll longitudinal stretching method rotates the roll on the outlet side from the roll speed on the inlet side between the stretching rolls set to a predetermined temperature. This is a method of stretching by increasing the number. The stretching temperature varies depending on the thermoplastic resin to be used, but in general, a range of glass transition temperature to glass transition temperature + 10 ° C. of the thermoplastic resin is preferable.

  The transverse stretching is generally tenter stretching. That is, the film is held horizontally by holding the end in the width direction of the film with the tenter clip, and moving the tenter clip holding the end in the width direction of the film along the tenter rail installed so that the gap gradually increases. It is usual to stretch.

  In the present invention, the stretching temperature during transverse stretching must be higher than the stretching temperature during longitudinal stretching. When the stretching temperature in the transverse stretching is lower than the stretching temperature in the longitudinal stretching, the molecular orientation direction becomes nonuniform and the optical axis angle accuracy is deteriorated. Accordingly, the stretching temperature in the transverse stretching is limited to a temperature higher than the stretching temperature in the longitudinal stretching, and is preferably the stretching temperature in the longitudinal stretching + 5 ° C. or more.

  The wind speed of the preheating zone and the stretching zone of the transverse stretching needs to be in the range of 8 m / sec to 30 m / sec. When the wind speed is slow, the temperature distribution in the width direction of the film becomes large, so that the optical axis angle accuracy deteriorates. When the wind speed is too high, the film is blown by the hot air and comes into contact with the hot air blowing nozzle, causing problems such as the film breaking. Therefore, the wind speed of the pre-heating zone and the stretching zone in the transverse stretching is limited to the range of 8 m / sec to 30 m / sec, and preferably in the range of 10 m / sec to 25 m / sec.

  EXAMPLES Although this invention is demonstrated further in detail based on an Example, this invention is not limited only to these Examples. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. In addition, the optical axis angle accuracy measured in the following examples and comparative examples is determined using the birefringence meter (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments Co., Ltd.) and the optical axis angle at intervals of 35 mm in the film width direction. The ratio of the optical axis angle at each measurement point within ± 1.0 degrees was shown as a percentage.

(Production Example 1)
A polymethyl methacrylate-styrene copolymer (MS) resin was imidized with monomethylamine as an imidizing agent to produce an imidized MS resin. The imidized MS resin includes a unit represented by the general formula (1), a unit represented by the general formula (2), and a unit represented by the general formula (3) described in [Film Composition] of the embodiment. Corresponds to an imide resin copolymerized. The obtained imide resin was formed into pellets with an extruder, and the obtained pellets were dried at 140 ° C. for 5 hours, and then extruded at 260 ° C. using a 40 mm single screw extruder and a 400 mm wide T-die. A film was obtained.

(Production Example 2)
A polymethyl methacrylate (PMAA) resin, which is an acrylic ester resin, was imidized with monomethylamine, which is an imidizing agent, to produce an imidized PMAA resin. This imidized PMAA resin corresponds to an imide resin obtained by copolymerizing the unit represented by the general formula (1) and the unit represented by the general formula (2) described in [Film Composition] of the embodiment. . The obtained imide resin was pelletized with an extruder, and the obtained pellet was dried at 100 ° C. for 5 hours, and then extruded at 230 ° C. using a 40 mm single-screw extruder and a 400 mm wide T-die. A film was obtained.

[Example 1]
The film of Production Example 1 was longitudinally stretched under the conditions of a stretching temperature of 160 ° C. and a stretching ratio of 2.0 times. Next, the longitudinally stretched film was guided to a tenter, and stretched transversely under the conditions of a stretching temperature of 170 ° C., a wind speed of the preheating zone and the stretching zone of 12 m / sec, and a stretching ratio of 2.1 times. Then, after trimming the ears of the film, a biaxially stretched film having a thickness of 40 μm was obtained.

  The obtained film had an optical axis angle accuracy of 85%, had little bowing, and had a good optical axis angle accuracy.

[Example 2]
A biaxially stretched film was obtained in the same manner as in Example 1, except that the film of Production Example 2 was used, the stretching temperature for longitudinal stretching was 120 ° C., and the stretching temperature for transverse stretching was 135 ° C.

  The obtained film had an optical axis angle accuracy of 82%, had little bowing, and had a good optical axis angle accuracy.

[Comparative Example 1]
A biaxially stretched film having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the stretching temperature for transverse stretching was 155 ° C.

  The obtained film had an optical axis angle accuracy of 63%, a large bowing, and an inferior optical axis angle accuracy.

[Comparative Example 2]
A biaxially stretched film having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the preheating zone for transverse stretching and the wind speed of the stretching zone were 5 m / sec.

  The obtained film had an optical axis angle accuracy of 50%, a large bowing, and an inferior optical axis angle accuracy.

[Comparative Example 3]
A biaxially stretched film having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the wind speed of the transverse stretching preheating zone and the stretching zone was 40 m / sec. An axially stretched film could not be obtained stably.

Claims (3)

  A method for producing a retardation compensation film by sequential biaxial stretching in which an amorphous thermoplastic resin film is stretched in the longitudinal direction and then stretched in the longitudinal direction, wherein the stretching temperature in the transverse stretching is higher than the stretching temperature in the longitudinal stretching, and A method for producing a retardation compensation film, wherein the pre-heating zone for transverse stretching and the wind speed of the stretching zone are 8 m / sec to 30 m / sec.   The method for producing a retardation compensation film according to claim 1, wherein an imide resin or a resin composition containing an imide resin is used as the amorphous thermoplastic resin. The imide resin is an imide resin having a unit represented by the following general formula (1) and a unit represented by the following general formula (2) and / or a unit represented by (3). The method for producing a retardation compensation film according to claim 2, wherein:

(Wherein, R ¹ and R ² each independently represents a hydrogen or an alkyl group having 1 to 8 carbon atoms, R ³ is an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(However, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(Wherein, R ⁷ is a hydrogen or an alkyl group having 1 to 8 carbon atoms, R ⁸ represents a substituent containing an aromatic ring having 5 to 15 carbon atoms.)