JP2013195939A - Method of manufacturing retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an obliquely drawn retardation film with an in-plane optical axis inclined with respect to a lengthwise direction of the film, in which the optical axis can be accurately adjusted and variation in other optical characteristics such as a phase difference and an NZ coefficient can be suppressed in the case of adjustment of the optical axis.SOLUTION: In the method of manufacturing an obliquely drawn retardation film, a pair of clip groups for holding both peripheral edge parts of a band-like raw film are run to obliquely draw the raw film, whereby a retardation film is formed. Adjustment of the optical axis of the formed retardation film is performed by changing positions of the pair of clip groups for holding the raw film, in a breadthwise direction of the raw film to change an initial interval and taking the changed initial interval as a new reference to determine intervals between the pair of clip groups in the breadthwise direction per section of a path through which the raw film passes after being held by the pair of clip groups and until being released.

Description

  The present invention relates to a method for producing a retardation film.

  In recent years, as an image display device such as a liquid crystal display device (LCD) has been increased in screen size, its use environment has been expanded. Based on these situations, there is a strong demand for improving the visibility of LCDs. However, only the improvement of the liquid crystal cell main body does not sufficiently satisfy the requirement for improving the visibility. Improvement in the visibility of an image display device greatly contributes to improvement in the performance of an optical film provided in the device, such as a retardation film.

  One type of retardation film is a quarter wave plate (λ / 4 plate). The λ / 4 plate is used as a circularly polarizing plate in combination with a polarizing film, for example. The λ / 4 plate and the polarizing film in the circularly polarizing plate must be laminated so that the angle between the slow axis in the plane of the λ / 4 plate and the transmission axis of the polarizing film is about 45 °. is there. If the belt-like λ / 4 plate and the belt-like polarizing film can be continuously laminated, for example, roll-to-roll, productivity of the circularly polarizing plate can be improved. In order to perform such continuous lamination, it is necessary that the slow axis in the plane of the λ / 4 plate is inclined by about 45 ° with respect to the longitudinal direction.

  For the retardation film, an amorphous thermoplastic resin is mainly used. The thermoplastic resin generally exhibits birefringence by stretching except for a resin having a composition selected for the purpose of not exhibiting birefringence.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2008-242426) discloses a retardation film that is obtained by biaxially stretching an original film made of an acrylic resin and has both heat resistance and flexibility. This retardation film has a high light transmittance and a low photoelastic modulus based on the characteristics of the acrylic resin constituting the film. This retardation film is excellent in balance of various properties including not only optical properties but also mechanical properties, and is suitable for use in an image display device. However, the retardation film disclosed in Patent Document 1 is formed by biaxially stretching a strip-shaped original film in the longitudinal direction and the width direction. In order to form a circularly polarizing plate using the retardation film, a strip-like retardation film obtained by stretching is cut in a direction oblique to the longitudinal direction by 45 °, and the obtained individual film pieces are individually separated. It must be attached to the polarizing plate. While the absorption axis of the polarizing film is usually oriented in the longitudinal direction of the film, the slow axis in the retardation film plane is the stretching direction or the direction perpendicular to the direction, that is, the longitudinal direction or the width direction of the film. Because it is facing. For this reason, a circularly polarizing plate cannot be produced by roll-to-roll lamination using this retardation film. In addition, acrylic resins, especially acrylic resins containing an acrylic polymer having a ring structure in the main chain, tend to be hard and brittle when used as a film among thermoplastic resins commonly used in optical films. There is. This tendency leads to the generation of cracks, chips and cracks when the film piece is cut out. Also from the viewpoint of suppressing these occurrences, a belt-like retardation film having a slow axis inclined with respect to the longitudinal direction is desired.

  Methods for obtaining a belt-like retardation film having a slow axis inclined with respect to the longitudinal direction are disclosed in the following documents. Patent Document 2 (Japanese Patent No. 4557188) discloses a method using a tenter transverse stretching machine including a bent tenter rail. In this method, for example, an angle of 40 to 50 ° is set between the direction in which the original film is fed to the stretching machine and the direction in which the stretched film is wound, thereby having a slow axis that is inclined with respect to the longitudinal direction. A belt-like retardation film is produced (see FIG. 1 of the publication). Patent Document 3 (Japanese Unexamined Patent Publication No. 2009-143208) discloses a stretching method using a tenter transverse stretching machine, in which the stretching speed at one end and the stretching speed at the other end in the width direction of the original film are And a method of winding a stretched film at a speed faster than both of the stretching speeds. Patent Document 4 (Japanese Patent Laid-Open No. 2008-23775) discloses a plurality of variable pitch clips connected to the right rail and a plurality of variable pitch clips connected to the left rail. A method using a simultaneous biaxial stretching machine that travels on a rail while holding both long edge portions is disclosed. Specifically, in this method, the position at which the clip pitch starts to expand differs between the left clip and the right clip with respect to the traveling direction of the original film, or the enlargement ratios of the left and right clip pitches are mutually different. Is different. Thereby, the strip | belt-shaped phase difference film which has a slow axis inclined with respect to the longitudinal direction is manufactured.

  In Patent Document 5 (WO 2010/017639), an original film is introduced into a heating and stretching apparatus by running a pair of clips holding the long edge of the original film, and the original film is stretched in the stretching zone of the apparatus. In the stretching zone, a running delay of one clip group with respect to the other clip group is generated, and the original film is stretched obliquely with respect to the longitudinal direction of the film based on the generated delay. A method of obtaining a retardation film in which the slow axis in the film plane is inclined with respect to the longitudinal direction of the film is disclosed. According to the method described in Patent Document 5, it is described in the document that a retardation film having an NZ coefficient close to 1 and weak in biaxial stretching is obtained as compared with the case of using the method of Patent Document 4. .

JP 2008-242426 A Japanese Patent No. 4557188 JP2009-143208A JP 2008-23775 Gazette International Publication No. 2010/017639

  In order to improve the optical characteristics of an optical member such as a circularly polarizing plate with a retardation film having a slow axis inclined in the longitudinal direction and to produce the member efficiently, the in-plane of the film of the retardation film It is necessary to adjust the slow axis (hereinafter, the slow axis is also referred to as the optical axis) in the desired direction (for example, a direction of 45 ° with respect to the longitudinal direction) as accurately as possible. At the same time, it is desirable that other optical characteristics exhibited by the retardation film, such as the retardation and the NZ coefficient, do not change as much as possible when adjusting the optical axis. In the retardation film disclosed in Patent Document 1, the optical axis is oriented in the longitudinal direction or the width direction of the film based on the stretching method, and thus there is no need to consider such adjustment of the optical axis ( There is no room.) When adjusting the optical characteristics of the retardation film disclosed in Patent Document 1, for example, the retardation, only the optical characteristics need be considered.

  The present invention is a method for producing a retardation film in which the optical axis in the film plane is inclined with respect to the longitudinal direction of the film, and the optical axis (direction of the optical axis) can be adjusted with high precision. It is an object of the present invention to provide a method capable of suppressing changes in optical characteristics, such as phase difference and NZ coefficient.

  In the method for producing a retardation film of the present invention, the pair of clips each composed of a plurality of clips are used to grip both of the long side edges of the strip-shaped original film, and to grip the original film. The original film is stretched by running the clip group, and after stretching the original film, the original film is released from the pair of clip groups to obtain a belt-like retardation film. In this method, the original film is stretched between a difference in running speed between the one clip group and the other clip group and / or from when the original film is held by the pair of clip groups to when it is released. Based on the difference in travel distance between the one clip group and the other clip group, the original film is stretched obliquely with respect to the longitudinal direction of the film. The retardation film having an axis inclined with respect to the longitudinal direction of the film is formed. And in the passage route of the original film from the time when it is held by the pair of clip groups to the time when it is released, between the pair of clip groups when holding the original film for each section provided in the route The distance between the pair of clip groups with respect to the width direction of the original film as a reference (initial distance) is determined, and the adjustment of the optical axis indicated by the retardation film is (1). ) Changing the initial interval by changing the position in the width direction where the pair of clips hold the original film, and (2) using the changed initial interval as the new reference, the pair of pairs An interval in the width direction between the pair of clip groups for each section in the passage route of the original film from being gripped by the clip groups to being released is determined. That is carried out by.

  According to the present invention, the optical axis in the film plane is a method for producing a retardation film tilted with respect to the longitudinal direction of the film, and the optical axis can be adjusted with high precision, and other optical characteristics in that case, For example, a method capable of suppressing changes in the phase difference and the NZ coefficient can be provided.

It is a schematic diagram which shows an example of the running state of a pair of clip group in one Embodiment of the manufacturing method of this invention. It is a schematic diagram which shows another example of the running state of a pair of clip group in one Embodiment of the manufacturing method of this invention. In the example shown in FIG. 1, it is a schematic diagram which shows the change of the running state of a pair of clip group before and behind the change of an initial space | interval. In the example shown in FIG. 2, it is a schematic diagram which shows the change of the driving state of a pair of clip group before and behind the change of an initial space | interval. It is a schematic diagram for demonstrating an initial space | interval.

  In the present specification, “resin” is a broader concept than “polymer”. The resin may contain one or more polymers, and if necessary, additives other than the polymer, such as ultraviolet absorbers, antioxidants, fillers, compatibilizers, stabilizers, etc. Can be included.

  Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the specific embodiments shown below.

  In the manufacturing method of the present invention, the long side edge portions of the strip-shaped original film are each gripped by a pair of clips composed of a plurality of clips (Step 1), and the original film is gripped in Step 1 above. The original film is stretched by running a pair of clip groups (step 2), and after stretching the original film in step 2, the original film is released from the pair of clip groups to obtain a strip-shaped stretched film (retardation film). (Step 3). Hereinafter, the process in which the original film is gripped by the pair of clip groups in Step 1 is referred to as “clip-in”, and the process in which the original film is released from the pair of clip groups is referred to as “clip-out”.

  Further, in the production method of the present invention, the stretching of the original film in step 2 is carried out by the difference in traveling speed between one clip group and the other clip group and / or one clip group between the clip-in and the clip-out. Based on the travel distance difference from the clip group, the original film is stretched obliquely (obliquely stretched) with respect to the longitudinal direction of the film. And by the said extending | stretching, the retardation film (diagonal extending | stretching retardation film) in which the optical axis (slow axis) in the film plane inclined with respect to the longitudinal direction of the said film is formed. Step 2 can be performed twice or more between Step 1 and Step 3 as necessary.

  Diagonal stretching of the original film in step 2 can be performed, for example, as follows.

  In one embodiment, while the strip-shaped original film is uniaxially stretched in the width direction, the peripheral edges on the left and right (left and right when the strip-shaped original film is viewed in the longitudinal direction, hereinafter the same) are set at different speeds. Then, it is stretched in the longitudinal direction of the original film.

  This embodiment can be implemented using, for example, a horizontal uniaxial stretching machine such as a tenter lateral stretching machine. Specifically, it can be implemented by driving the left and right clip groups in the stretching machine independently of each other. More specifically, the right and left clip groups improved so as to be independently driven while introducing the strip-shaped original film into the horizontal uniaxial stretching machine in the same manner as before and performing the horizontal uniaxial stretching at different traveling speeds. Drive. The traveling speed difference is a difference in tensile force between the left and right peripheral edge portions of the original film. Thereby, the diagonal stretch of the original film is realized. In this embodiment, the optical properties (optical axis, phase difference, NZ coefficient, etc.) exhibited by the obtained retardation film can be changed by the traveling speed difference between the left and right clip groups and / or the stretching ratio of the lateral uniaxial stretching. .

  This embodiment can also be implemented using a pantograph-type and linear motor-type simultaneous biaxial stretching machine. As in the case of using a tenter transverse stretching machine, while the uniaxial stretching of the strip-shaped original film in the width direction, the traveling speed of the clip group is made different on the left and right, that is, the traveling of the clip group holding the original film The feed speed at the peripheral edge of the original film caused by the above is made different on the left and right. Thereby, the draw ratio in the longitudinal direction of the original film is different between right and left, and the original film is obliquely drawn.

  In another embodiment, the strip-shaped original film is stretched obliquely using a tenter transverse stretching machine having a bent tenter rail. Specifically, when the left and right clip groups travel on the bent inner and outer rails at the same traveling speed, the inner rail clip group advances before the outer rail clip group. At this time, the travel distance from clip-in to clip-out differs between the clip group traveling on the inner rail and the clip group traveling on the outer rail. Thereby, the diagonal stretch of the original film is realized. In this embodiment, the optical characteristics of the obtained retardation film can be changed depending on the degree of bending of the inner and outer rails.

  Another embodiment is oblique stretching of the original film by the method described in Patent Document 5 (International Publication No. 2010/017639). An example of the method will be described with reference to FIG.

  FIG. 1 schematically shows the running state of the left and right clip groups in an example of the method described in Patent Document 5. Reference numeral 1 denotes a heating and stretching apparatus 1 that can implement the example, for example, a simultaneous biaxial stretching machine that includes a pair of clip groups configured by a plurality of clips that can be accelerated and decelerated independently. In the device 1, the clips belonging to the left clip group and the right clip group reach the clip-out part (COL, COR) from the clip-in part (CIL, CIR) through L1-L10, R1-R9, and the left clip rail. The vehicle travels back to the clip-in portion (CIL, CIR) again through the LR and the right clip rail RR. Although the illustration of the original film is omitted in FIG. 1, the left and right long edge portions of the strip-like original film are gripped by the left clip group and the right clip group, respectively, in the clip-in portions (CIL, CIR). The original film is guided to the heating and stretching apparatus 1 by the traveling of the left and right clip groups that hold the film, and also passes through the preheating zone Z1, the front-stage stretching zone Z2, the rear-stage stretching zone Z3, and the heat treatment zone Z4 in this apparatus 1 in this order. To do.

  In this embodiment, when the clip group grips the strip-shaped original film, that is, in the clip-in portion (CIL, CIR), the traveling speeds of both the left and right clip groups are equal to each other. When the traveling speeds of the left and right clip groups are not equal at the time of clip-in, the original film is pulled to the clip side having a large traveling speed, so that the movement stability of the original film to the heating stretching apparatus 1 and the heating stretching apparatus 1 The movement stability of the original film is reduced. For this reason, a retardation film having desired optical characteristics may not be obtained. In the worst case, the original film may break, and a belt-like retardation film may not be produced.

  In reality, the stress generated when the original film is stretched in the oblique direction adds a pulling back force to the relatively preceding clip, and adds a forward force to the relatively delayed clip. For this reason, it is difficult to always control the traveling speed of the left clip group and the traveling speed of the right clip group at the time of clip-in to be completely the same. Considering this, in this embodiment, the ratio v1 / v2 between the traveling speed v1 of the left clip group and the traveling speed v2 of the right clip group at the time of clip-in is maintained at 0.98 or more and 1.02 or less. The ratio v1 / v2 is preferably 0.99 or more and 1.01 or less, more preferably 0.995 or more and 1.005 or less. In the oblique stretching of the original film including the other embodiments described above or later, the traveling speed ratio v1 / v2 of the left and right clip groups at the time of clip-in is set to 0.98 or more and 1.02 or less. It is preferable.

  Similarly, the present invention is not limited to this embodiment, and in the oblique stretching of the original film including the other embodiments described above or later, the running speed ratio v1 / v2 of the left and right clip groups at the time of clip-out is 0.98 or more. It is preferable to set it to 1.02 or less.

  In the preheating zone Z1, the original film supplied to the heating and stretching apparatus 1 is heated to a temperature at which it can be stretched in the stretching zones (the first stretching zone Z2 and the second stretching zone Z3) that pass later.

  In the preceding drawing zone Z2, the traveling speed v1 of the left clip group that has traveled from the preheating zone Z1 decreases in order. Thereby, in the front | former stage extension zone Z2, the driving | running | working delay of the left side clip group generate | occur | produces with respect to the right side clip group. Then, based on the generated running delay, the original film is stretched obliquely with respect to the longitudinal direction of the film. Unlike stretching by vector sum of longitudinal stretching (stretching in the film longitudinal direction) and transverse stretching (stretching in the film width direction), this stretching has strong uniaxial stretching properties. Thereby, it is a belt-like phase difference film stretched diagonally, and its NZ coefficient is close to 1 as compared with the phase difference film formed in the other embodiments described above, and the biaxial stretchability is weak (uniaxial stretchability is strong). ) A retardation film is obtained.

  In the rear stretching zone Z3, the traveling speed of the left clip group that has traveled from the preceding stretching zone Z2 sequentially increases, and the traveling speed v1 of the left clip group and the traveling speed v2 of the right clip group are equal to each other at the exit of the zone. Become. Specifically, the ratio v1 / v2 between the traveling speed v1 of the left clip group and the traveling speed v2 of the right clip group is 0.98 or more and 1.02 or less, preferably 0.99 or more and 1.01 or less. Preferably it becomes 0.995 or more and 1.005 or less. Also in the rear stretching zone Z3, a traveling speed difference occurs between the left and right clip groups until the traveling speeds become equal to each other, and the original film is stretched obliquely based on this speed difference.

  Although not described in Patent Document 5, it is also possible to increase the traveling speed of one clip group in the pre-stage stretching zone Z2 to give a traveling speed difference between both clip groups based on the traveling speed difference. The original film can be stretched obliquely. In this case, it is preferable to reduce the traveling speed of the one clip group in the rear-stage stretching zone Z3 and make the traveling speeds of the left and right clip groups equal to each other at the exit of the zone. In either case of reducing or increasing the traveling speed of one clip group in the front drawing zone Z2, the left and right clips generated in the front drawing zone Z2 between the front drawing zone Z2 and the rear drawing zone Z3. There may be further provided a stretching zone for maintaining the traveling speed difference between the groups.

  In the heat treatment zone Z4, the original film stretched in the stretching zone is held at a specific temperature (heat treatment temperature) equal to or lower than the stretching temperature in the stretching zone. This stabilizes the molecular orientation of the polymer contained in the film, reduces the distortion of the film, and stabilizes the properties exhibited by the finally obtained retardation film, such as optical properties and mechanical properties. Is achieved. The original film that has passed through the heat treatment zone Z4 is released from both the left and right clip groups in the clip-out portions (COL, COR).

  Another example of the method described in Patent Document 5 is shown in FIG. In the method shown in FIG. 2, in the former drawing zone Z2 and the latter drawing zone Z3, that is, when the original film is drawn, the distance between the left and right clip groups with respect to the width direction of the original film is increased. Such a combination of stretching in the width direction (lateral stretching) by increasing the distance between the pair of clip groups with respect to the width direction of the original film, the degree of freedom of control of the optical properties exhibited by the obtained retardation film Becomes higher. The traveling state of the left and right clip groups in the example shown in FIG. 2 is the same as the traveling state of the left and right clip groups in the example shown in FIG. Moreover, the zones of the preheating zone Z1, the front-stage stretching zone Z2, the rear-stage stretching zone Z3, and the heat treatment zone Z4 are the same as the example shown in FIG. 1 except that the transverse stretching is used together. The transverse stretching is not limited to this embodiment, and can be used in combination with the oblique stretching of the original film including the other embodiments described above.

  Each of the embodiments described above is an example of a method for performing oblique stretching of the original film in step 2. The method of diagonally stretching the original film in step 2 includes the difference in running speed between one clip group and the other clip group and / or one clip group and the other clip group between clip-in and clip-out of the original film. A retardation film in which the original film is stretched obliquely with respect to the longitudinal direction of the film and the optical axis in the film plane is inclined with respect to the longitudinal direction of the film. As long as it is a method to form, it is not limited.

  In the production method of the present invention, oblique stretching of the original film is combined with the following points.

  In the manufacturing method of the present invention, in the passage route of the original film (from the clip-in to the clip-out) after being held by the pair of clip groups and released, the original film is removed for each section provided in the route. The distance between a pair of clip groups at the time of gripping (in the case of clip-in) (the distance in the width direction of the original film; in this specification, this distance is referred to as “initial distance”). An interval X with respect to the width direction of the original film is determined.

  For example, in the example shown in FIG. 1, transverse stretching by increasing the interval between the left and right clip groups is not used together, from the clip-in part (CIL, CIR) to the clip-out part (COL, COR), The interval X does not change from the initial interval. That is, in the example shown in FIG. 1, the interval X is determined to be equal to the reference with respect to the initial interval in all sections in the original film passage path from clip-in to clip-out. On the other hand, in the example shown in FIG. 2, in the stretching zones Z2 and Z3, lateral stretching that increases the distance between the left and right clip groups is used in combination. As shown in FIG. 2, in the passage path of the original film from the clip-in part (CIL, CIR) to the clip-out part (COL, COR), the clip-in part (CIL, CIR) to the entrance of the preceding drawing zone Z2 In the section, the interval X is determined to be equal to the reference with the initial interval as a reference. In the section from the inlet of the former drawing zone Z2 to the outlet of the latter drawing zone Z3, with the initial interval as a reference, it is equal to the reference at the inlet, and equal to a value obtained by multiplying the reference at the outlet by the draw ratio of the transverse drawing, The interval X is determined between the inlet and the outlet so as to continuously change from a value equal to the reference to a value equal to a value obtained by multiplying the reference by the draw ratio of transverse stretching. In the section from the outlet of the subsequent drawing zone Z3 to the clip-out portion (COL, COR), the initial interval is used as a reference, and the interval is equal to the value obtained by multiplying the reference by the draw ratio of the transverse drawing in the drawing zones Z2, Z3. X is defined. Similarly, also in the other embodiments described above, the interval X can be determined based on the initial interval.

  And in the manufacturing method of this invention, adjustment of the optical axis in the film surface which the retardation film formed by diagonal stretch shows (1) The position with respect to the width direction of an original film where a pair of clip group hold | grips an original film By changing the initial interval, (2) using the changed initial interval as a new reference, the original film (from clip-in to clip-out) until it is released after being gripped by a pair of clips. This is done by determining the interval X for each section in the passage route. This is a method for producing an obliquely stretched phase difference film, and the optical axis of the obtained phase difference film can be accurately adjusted in a desired direction, and other optical characteristics such as phase difference and NZ coefficient can be adjusted. Change can be suppressed. It is difficult to accurately adjust the optical axis in the desired direction by simply changing the draw ratio, and other optical characteristics such as the phase difference value and the NZ coefficient are also greatly changed.

  An example of the above (1) and (2) performed for adjusting the optical axis is shown in FIG. The example shown in FIG. 3 is an example in which the initial interval is changed in the example shown in FIG. The initial interval A is before the change, and the initial interval B is the initial interval after the change. Note that in FIG. 3 and FIG. 4 shown below, the amount of change in the initial interval is exaggerated as compared to the interval between the pair of clip groups in the width direction of the original film. Also, “L1 to L10” and “R1 to R9” are not shown.

  In the example shown in FIG. 3, in the state before the change of the initial interval, the interval X is determined to be equal to the reference with the initial interval A as the reference in all sections in the original film passage path from clip-in to clip-out. It has been. In the state after the change of the initial interval, the initial interval B is set as a new reference so that it becomes equal to the reference in the entire passage path of the original film from the clip-in to the clip-out as in the case before the change of the initial interval. The interval X is determined.

  FIG. 4 shows another example of the above (1) and (2) performed for adjusting the optical axis. The example shown in FIG. 4 is an example in which the initial interval is changed in the example shown in FIG. The initial interval C is the initial interval before the change, and the initial interval D is the initial interval after the change.

  In the example shown in FIG. 4, in the state before the change of the initial interval, the interval X is determined based on the initial interval C for each section in the original film passage path from clip-in to clip-out. The details of the determined interval X are as described above. In the state after the change of the initial interval, the interval X is determined in the same manner as before the change of the initial interval, with the initial interval D as a new reference. Specifically, in the section from the clip-in portion (CIL, CIR) to the entrance of the front-stage stretching zone Z2, it is equal to the changed standard; from the entrance of the front-stage stretching zone Z2 to the exit of the rear-stage stretching zone Z3 In the section, it is equal to the standard after the change at the start point, equal to the value obtained by multiplying the standard after the change at the exit by the draw ratio of the transverse stretching, and the standard after the change between the inlet and the outlet. So as to continuously change from a value equal to the value obtained by multiplying the changed standard to the value obtained by multiplying the draw ratio of the transverse stretch; in the section from the exit of the subsequent stretch zone Z3 to the clip-out portion (COL, COR) The interval X is determined so as to be equal to a value obtained by multiplying the changed standard by the stretching ratio of the transverse stretching in the stretching zones Z2 and Z3.

  In the example shown in FIGS. 3 and 4, the original film is stretched obliquely based on the traveling speed difference between one clip group and the other clip group, but the traveling speed difference is maintained before and after adjusting the optical axis. Has been. The traveling speed of the left and right clip groups in each section has not changed. Further, in the example shown in FIG. 4, lateral stretching is further used together, but the stretching ratio of the lateral stretching is maintained before and after adjusting the optical axis.

  In the production method of the present invention, the optical axis of the formed retardation film is adjusted based on changing the initial interval, and at this time, the above traveling speed difference and traveling distance difference for oblique stretching are maintained. Is preferred. In this case, the optical axis can be adjusted more accurately, and changes in other optical characteristics can be further suppressed at that time.

  In the production method of the present invention, the original film is stretched by stretching the original film obliquely with respect to the longitudinal direction of the film on the basis of the traveling speed difference between one clip group and the other clip group, The travel speed difference may be held when adjusting the shaft. The examples shown in FIGS. 3 and 4 correspond to this aspect. The travel speed of the clip group may be slightly adjusted for the purpose of adjusting the tension of the original film, but the travel speed difference based on the adjustment to the extent that is normally performed maintains the travel speed difference. Included in the range.

  The initial interval is an interval between the pair of clip groups in the width direction of the original film when the pair of clip groups grips the original film. The space | interval X is a space | interval with respect to the width direction of the original film between a pair of clip groups. These intervals correspond to widths that are not gripped by a pair of clips in the original film. This width, which is the initial interval, will be described with reference to FIG. FIG. 5 shows the movement of a pair of clip groups during clip-in. In the example shown in FIG. 5, one clip group 11 and the other clip group 12 run while facing each other in the width direction of the original film 13, and hold the original film 13. When the original film 13 is held by the clip groups 11 and 12, the innermost part 14 (the center side in the width direction) of the original film 13 held by the clip group 11 and the clip group 12 hold the original film 13. The distance d from the innermost portion 15 is the initial interval. When one clip group 11 and the other clip group 12 do not face each other with respect to the width direction of the original film 13, the straight line extending in the longitudinal direction of the original film 13 and the portion 15 are in contact with each other. What is necessary is just to let distance with the straight line which touches be an initial space | interval. The interval X can be determined in the same manner as the initial interval since it is the same as the initial interval that the width is not gripped by the pair of clips in the original film.

  The method for changing the initial interval is not limited. For example, what is necessary is just to change by changing the grip margin at the time of gripping an original film with a pair of clip group. The grip margin refers to the distance between the portion 14 and the end portion of the original film 13 closest to the width direction in one clip group 11 in FIG. 5, and the portion 15 and the original film 13 in the other clip group 12. The distance between the portion and the closest end in the width direction. The width obtained by removing the gripping margins of both clip groups from the width of the original film corresponds to the initial interval at the time of clip-in and the subsequent interval X. When changing the gripping margin, the end of the original film may be slit or replaced with an original film having a different width as necessary. In addition, by making the change amount of the gripping distance the same in both clip groups, the initial interval can be changed without changing the center of the original film portion stretched by the clip groups with respect to the longitudinal direction of the film.

  When changing to an original film having a different width, the initial interval can be changed while keeping the grip.

  The degree to which the initial interval is changed is, for example, 85 to 115% of the initial interval before the change, and 90 to 110% of the initial interval before the change is preferable in order to adjust the optical axis with higher accuracy.

  In the manufacturing method of the present invention, the initial interval is changed twice or more (above (1)) and the interval X is set based on the changed initial interval until the desired optical axis is realized in the formed retardation film ( The above (2)) may be performed.

  The interval X can be set from the clip-in side to the clip-out in both clip groups at the same time or sequentially from the clip-in side (upstream side of the original film). You may carry out in order from the clip-out side (downstream side of the original film). In order to prevent the original film from being broken, it is preferable to set in order from the upstream side when the initial interval is widened, and from the downstream side when the initial interval is narrowed. The setting of the interval X with the changed initial interval as a reference may be performed continuously or stepwise.

  Since it is usually possible to calculate in advance how to determine the interval X based on the initial interval after the change with respect to the change in the initial interval, the initial interval is changed (above (1)) and after the change. The setting of the interval X based on the initial interval ((2) above) may be performed simultaneously. It is also possible to automatically perform the above (1) and (2), and a person skilled in the art can construct a system for performing it automatically.

  In the manufacturing method of the present invention, a pair of clip groups separately from the above (1) and (2), for example, for the purpose of adjusting the tension of the original film in the preheating zone Z1 and the heat treatment zone Z4 shown in FIGS. The interval with respect to the width direction of the original film can be adjusted.

  The adjustment of the optical axis in the production method of the present invention can be carried out without interrupting the formation of the retardation film. That is, in the manufacturing method of the present invention, the optical axis may be adjusted while continuing the oblique stretching with respect to the original film by running the pair of clip groups. This method is particularly useful when continuously performing the process from melt extrusion of an original film to formation of a retardation film.

  In the production method of the present invention, an obliquely stretched retardation film can be continuously formed by performing the stretching on the original film continuously supplied from the original film forming apparatus. At this time, the optical axis may be adjusted without stopping the supply of the original film from the original film forming apparatus. The original film forming apparatus is, for example, a melt extrusion molding machine or a casting apparatus.

  In the production method of the present invention, an obliquely stretched retardation film can be formed by stretching the original film supplied from the roll. At this time, the optical axis may be adjusted without replacing the roll.

  In the manufacturing method of this invention, you may adjust an optical axis based on the measurement result of the optical axis with respect to the formed retardation film. More specifically, the optical axis measurement of the film is performed on the formed retardation film, the change amount of the initial interval is determined based on the measurement result, and the initial interval is changed and changed according to the determined change amount. The interval X may be determined based on the later initial interval. The measurement of the optical axis for the formed retardation film can be performed by cutting out a measurement sample from the obtained retardation film and performing batch on the sample, or continuously on the retardation film forming line. it can. These optical axis measurements, determination of the amount of change of the initial interval, change of the initial interval, and setting of the interval X can also be automatically performed, and a system for performing this automatically can be constructed by those skilled in the art. it can.

  In the production method of the present invention, the optical axis of the obliquely stretched retardation film can be adjusted with high accuracy, and changes in other optical characteristics such as retardation and NZ coefficient can be suppressed. In some cases, it is possible to form a retardation film showing the same retardation value and NZ coefficient before and after adjusting the optical axis. In this specification, “same” of the phase difference value and the NZ coefficient includes a case where there is a certain difference. When there is a difference within ± 3 nm in the in-plane phase difference Re for light having a wavelength of 590 nm, such a change in the in-plane phase difference Re can, for example, change the optical axis and the NZ coefficient only by adjusting the stretching temperature. The phase difference is assumed to be the same because it can be realized without any problem. Similarly, it is assumed that the NZ coefficient is the same when there is a difference within ± 0.03 in the NZ coefficient.

  For the NZ coefficient, the refractive index in the slow axis direction in the plane of the retardation film is nx, the refractive index in the fast axis direction in the plane of the film is ny, and the refractive index in the thickness direction of the film is nz. Sometimes the value given by the equation (nx-nz) / (nx-ny). When the in-plane retardation Re and the thickness direction retardation Rth indicated by the retardation film are used, the NZ coefficient is given by the expression | Rth | / | Re | +0.5. The closer the value of the NZ coefficient is to 1, the lower the biaxial stretchability of the retardation film (stronger the uniaxial stretchability).

  The belt-like retardation film obtained by the production method of the present invention can be subsequently supplied to an arbitrary step. For example, the film may be wound around a roll to obtain a retardation film roll, or may be supplied to a subsequent process such as formation of a coating layer or lamination with another film.

  For example, the belt-like retardation film obtained by the production method of the present invention can be continuously laminated with the retardation film and the belt-like polarizing film (more specifically, roll-to-roll can be laminated). Therefore, it is suitable for manufacturing an efficient polarizing plate (for example, a circularly polarizing plate or an elliptically polarizing plate). In the production of a polarizing plate using roll-to-roll lamination, a step of cutting a film piece obliquely in a specific direction from a strip-like retardation film and a step of laminating the cut film piece while adjusting its optical axis can be omitted. . This omission improves the area use efficiency of the retardation film at the time of manufacturing the polarizing plate, and when the retardation film is composed of an acrylic resin, the adverse effect derived from the hardness and brittleness specific to the acrylic resin film. Make it smaller. When the acrylic resin contains an acrylic polymer having a ring structure in the main chain, the latter effect is particularly great.

  The production method of the present invention may include arbitrary steps other than those described above as long as the effects of the present invention are obtained. This step is, for example, a heat treatment (annealing) step performed to stabilize the optical properties and mechanical properties of the formed retardation film.

  The original film is typically an unstretched film. However, as long as the effect of the present invention is obtained, a film that has already been stretched can be used as the original film.

  The thermoplastic resin (A) constituting the original film preferably contains a polymer (B) having a ring structure in the main chain. That is, the original film is preferably made of a thermoplastic resin (thermoplastic resin composition) (A) containing a polymer (B) having a ring structure in the main chain. Thereby, the glass transition temperature (Tg) of the obtained retardation film improves. A retardation film having a high Tg is suitable for use in an image display device such as an LCD having a structure in which heating elements such as a power source, a light source, and a circuit board are integrated in a narrow space. In addition to this, depending on the type of ring structure, the retardation exhibited by the obtained retardation film increases.

  The content of the polymer (B) in the resin (A) is preferably 50% by weight or more, more preferably 60% by weight or more, and further preferably 70% by weight or more.

  The polymer (B) is preferably at least one selected from an acrylic polymer, a cycloolefin polymer, and a cellulose derivative. The acrylic polymer is a polymer having (meth) acrylic acid ester units in an amount of 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more of the total structural units. However, when the acrylic polymer includes a ring structure that is a derivative of a (meth) acrylate unit, the content of the ring structure is also included in the content of the (meth) acrylate unit. The cycloolefin polymer is a polymer having cycloolefin units in an amount of 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more of all the structural units. The cellulose derivative has a repeating unit such as a triacetyl cellulose (TAC) unit, a cellulose acetate propionate unit, a cellulose acetate butyrate unit, a cellulose acetate phthalate unit, etc. in an amount of 50 mol% or more, preferably 60 mol% or more of all the structural units. More preferably, it is a polymer having 70 mol% or more. The cycloolefin polymer and the cellulose derivative have a ring structure in the main chain.

  The polymer (B) is preferably an acrylic polymer. The acrylic polymer has high transparency and excellent mechanical properties such as surface strength. For this reason, by using an acrylic polymer, a retardation film suitable for use in an image display device such as an LCD can be obtained.

  The original film may be a single layer film or a laminated film of a plurality of thermoplastic resin layers. The original film preferably has a layer composed of a thermoplastic resin containing an acrylic polymer having a ring structure in the main chain. The original film can be composed of one layer made of a thermoplastic resin containing an acrylic polymer having a ring structure in the main chain. The original film may be a laminate of the layer and a thermoplastic resin layer containing a polymer other than an acrylic polymer such as cycloolefin.

  The acrylic polymer having a ring structure in the main chain includes a structural unit derived from a (meth) acrylic acid ester monomer and a ring structure. The total content of the structural units derived from the (meth) acrylic acid ester monomer and the ring structure in the acrylic polymer is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight. %, Particularly preferably 95% by weight or more, most preferably 99% by weight or more. The content of the ring structure is preferably 5% by weight or more, more preferably 10% by weight or more, and further preferably 15% by weight or more. When the content of the ring structure exceeds 40% by weight, it becomes difficult to form a polymer having such a content of the ring structure (a gel is easily formed when the cyclization reaction proceeds), or the polymer In some cases, the moldability and handling properties of the thermoplastic resin containing the resin deteriorate, and the productivity of the original film may decrease.

  (Meth) acrylic acid ester units are, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t- (meth) acrylic acid t- Butyl, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, (meth) acryl Dicyclopentanyl acid, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, (meth) acrylic acid 2, 3,4,5,6-pentahydroxyhexyl, 2,3,4,5-tetrahydro (meth) acrylic acid Shipenchiru is a structural unit derived from a monomer such as. The acrylic polymer can have two or more of these structural units. The acrylic polymer preferably has methyl methacrylate (MMA) units. In this case, the thermal stability of the retardation film is improved.

  The acrylic polymer may have a structural unit other than the (meth) acrylic ester unit. The structural unit is, for example, a structural unit having a hydroxyl group and / or a carboxylic acid group. Depending on the type of the structural unit having a hydroxyl group and / or a carboxylic acid group, the structural unit changes to a ring structure located in the main chain of the polymer by a cyclization reaction after polymerization. In the acrylic polymer, these unreacted structural units that have not changed to a ring structure may remain. The structural unit having a hydroxyl group is, for example, a structural unit derived from each monomer of methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, and methyl 2- (hydroxyethyl) acrylate. . The structural unit having a carboxylic acid group is, for example, a structural unit derived from each monomer of acrylic acid, methacrylic acid, crotonic acid, 2- (hydroxymethyl) acrylic acid, and 2- (hydroxyethyl) acrylic acid. The acrylic polymer can have two or more of these structural units.

  Further structural units other than the (meth) acrylic acid ester unit that the acrylic polymer may have include, for example, styrene, vinyltoluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylo Monomers of nitrile, methallyl alcohol, allyl alcohol, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinyl pyrrolidone, N-vinyl carbazole A structural unit derived from the body. The acrylic polymer can have two or more of these structural units.

  The type of the ring structure is not particularly limited, and is, for example, at least one selected from a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, a maleimide structure, and a maleic anhydride structure. Especially, at least 1 sort (s) chosen from a lactone ring structure, a glutarimide structure, and a maleimide structure from a heat resistant viewpoint at the time of shaping | molding is preferable.

  The lactone ring structure that the acrylic polymer may have in the main chain is not particularly limited. For example, it may be a 4- to 8-membered ring, but it is excellent in the stability of the ring structure. It is preferably a membered ring, more preferably a 6-membered ring. The lactone ring structure which is a 6-membered ring is, for example, the structure disclosed in Japanese Patent Application Laid-Open No. 2004-168882, but the high polymerization yield of the precursor and the high lactone ring due to the cyclization reaction of the precursor. The structure represented by the following formula (1) is preferable because an acrylic polymer having a content rate can be obtained and a polymer having a MMA unit as a constituent unit can be used as a precursor.

式（１）において、Ｒ¹、Ｒ²およびＲ³は、互いに独立して、水素原子または炭素数１から２０の有機残基である。有機残基は酸素原子を含んでいてもよい。

In the formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The organic residue in formula (1) is, for example, an alkyl group having 1 to 20 carbon atoms such as a methyl group, an ethyl group or a propyl group; an unsaturated group having 1 to 20 carbon atoms such as an ethenyl group or a propenyl group. An aliphatic hydrocarbon group; an aromatic hydrocarbon group having 1 to 20 carbon atoms such as a phenyl group and a naphthyl group; In the alkyl group, unsaturated aliphatic hydrocarbon group and aromatic hydrocarbon group, one or more hydrogen atoms are substituted by at least one group selected from a hydroxyl group, a carboxyl group, an ether group and an ester group. Also good.

  When the acrylic polymer has a lactone ring structure in the main chain, the content of the lactone ring structure in the polymer is not particularly limited. A content rate is 5-90 weight%, for example, Preferably it is 10-80 weight%, More preferably, it is 10-70 weight%, More preferably, it is 20-60 weight%. When the content of the ring structure in the acrylic polymer is excessively small, the properties obtained due to the presence of the ring structure, such as heat resistance, solvent resistance, surface hardness, and optical properties are insufficient in the obtained retardation film. It may become. When the content of the ring structure is excessively large, the moldability and handling properties of the acrylic polymer and the thermoplastic resin containing the polymer are lowered, and the productivity of the original film and the retardation film is lowered.

  The content of the lactone ring structure in the acrylic polymer can be evaluated by a known method. Specifically, for example, dynamic TG measurement is performed on an acrylic polymer, and a weight reduction rate (measured weight reduction rate) when heated from 150 ° C. to 300 ° C. is obtained. This weight reduction rate corresponds to the amount of hydroxyl groups remaining in the acrylic polymer to be evaluated. 150 ° C. is a temperature at which an unreacted (non-cyclized) hydroxyl group remaining in the acrylic polymer starts a cyclization reaction again, and 300 ° C. is a temperature at which the acrylic polymer starts to decompose. From this measured weight loss rate and the theoretical weight loss rate assuming that all the hydroxyl groups (which can be calculated from the precursor composition) of the precursor before the cyclization reaction have undergone dealcoholization cyclization, The content of the structure can be calculated. That is, in the dynamic TG measurement of an acrylic polymer having a lactone ring structure, an actual weight loss rate (X) between 150 ° C. and 300 ° C. is measured. Separately from this, the theoretical weight loss rate (Y) is calculated from the composition of the polymer when it is assumed that all the hydroxyl groups contained in the composition are involved in the formation of the lactone ring (dealcoholization cyclization reaction). More specifically, the theoretical weight reduction rate (Y) is calculated from the molar ratio of the monomer having a structure (hydroxyl group) involved in the dealcoholization cyclization reaction in the polymer, that is, the content of the monomer. sell. By substituting these values X and Y into the formula {1- (actually measured weight reduction rate (X) / theoretical weight reduction rate (Y))} × 100 (%), the dealcoholization reaction rate A is obtained. Next, assuming that the cyclization reaction has proceeded at a rate corresponding to the determined dealcoholization reaction rate A, the content of the lactone ring is determined by the formula B × A × MR / Mm. B is the content of the monomer having a hydroxyl group in the precursor (the polymer before the lactone cyclization reaction proceeds), and MR is the formula weight of the lactone ring structure formed by the cyclization reaction. Yes, Mm is the molecular weight of the monomer having a hydroxyl group, and A is the dealcoholization reaction rate.

  The weight average molecular weight (Mw) of the acrylic polymer having a ring structure in the main chain is preferably 80,000 or more, more preferably 100,000 or more. The molecular weight dispersity is preferably 3.5 or less, more preferably 3 or less. In these cases, there are few branched structures in the acrylic polymer, the thermal stability during processing is improved, and the strength and appearance of the obtained retardation film are improved. Mw and dispersity can be determined by polystyrene conversion using GPC (gel permeation chromatograph). The degree of dispersion is the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer. Mn can also be obtained using GPC.

  The glass transition temperature Tg of the acrylic polymer having a ring structure in the main chain is, for example, 110 ° C. or higher, preferably 115 ° C. or higher, and more preferably 120 ° C. or higher. On the other hand, when the Tg exceeds 200 ° C., the moldability to the film and the stretchability of the film are deteriorated, for example, it becomes difficult to form a film by melting. The general acrylic polymer having no ring structure in the main chain has a Tg of about 100 ° C.

  The acrylic polymer having a ring structure in the main chain can be produced by a known method. An acrylic polymer whose ring structure is a glutaric anhydride structure or a glutarimide structure can be produced, for example, by the method described in WO2007 / 26659 or WO2005 / 108438. An acrylic polymer whose ring structure is a maleic anhydride structure or an N-substituted maleimide structure can be produced, for example, by the method described in JP-A-57-153008 or JP-A-2007-31537. An acrylic polymer having a lactone ring structure as a ring structure can be produced, for example, by the method described in JP-A-2006-96960, JP-A-2006-171464, or JP-A-2007-63541.

  The thermoplastic resin constituting the original film may contain other polymers than those described above. The content of the polymer in the thermoplastic resin is preferably 0 to 50% by weight, more preferably 0 to 25% by weight, and still more preferably 0 to 10% by weight. Examples of the polymer include olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; Polystyrene such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; polyester such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; poly Biodegradable polyester such as lactic acid and polybutylene succinate; polycarbonate; polyamide such as nylon 6, nylon 66, nylon 610; polyacetal; polyphenylene oxide; Polyetheretherketone; Polyethernitrile; Polysulfone; Polyethersulfone; Polyoxypentylene; Polyamideimide; Rubbery polymer such as ABS resin or ASA resin blended with polybutadiene rubber or acrylic rubber; It is. When the thermoplastic resin constituting the original film contains an acrylic polymer having a ring structure in the main chain, the other polymer is a styrene-acrylonitrile copolymer from the viewpoint of compatibility with the acrylic polymer. Is preferred. The rubbery polymer preferably has on its surface a graft portion having a composition compatible with the acrylic polymer. The average particle diameter of the rubber polymer is, for example, 400 nm or less, preferably 200 nm or less, more preferably 100 nm or less, and further preferably 70 nm or less, from the viewpoint of improving the transparency as a retardation film. It is.

  The thermoplastic resin constituting the original film can include a polymer having an α, β-unsaturated monomer unit having a heteroaromatic group as a constituent unit. In this case, depending on the composition of the thermoplastic resin, the degree of freedom in controlling the birefringence wavelength dispersibility of the obtained retardation film is increased, and for example, a retardation film exhibiting reverse wavelength dispersibility is obtained. Inverse wavelength dispersion is wavelength dispersion in which the birefringence decreases (the phase difference decreases) as the wavelength becomes shorter, at least in the visible light region. The heteroaromatic group is at least one selected from, for example, a carbazole group, a pyridine group, a thiophene group, and an imidazole group. The α, β-unsaturated monomer unit having a heteroaromatic group is, for example, at least one selected from an N-vinylcarbazole unit, a vinylpyridine unit, a vinylthiophene unit, and a vinylimidazole unit. Among these, an N-vinylcarbazole unit is preferable, and in this case, the retardation film can exhibit good reverse wavelength dispersion. For example, an elliptically polarizing plate exhibiting a high antireflection effect is realized by the retardation film exhibiting reverse wavelength dispersion.

  The polymer having an α, β-unsaturated monomer unit having a heteroaromatic group as a constituent unit may be an acrylic polymer having a ring structure in the main chain. The thermoplastic resin constituting the original film is a polymer having, as a constituent unit, an α, β-unsaturated monomer unit having a heteroaromatic group as a polymer different from an acrylic polymer having a ring structure in the main chain. Can be included.

  A retardation film exhibiting reverse wavelength dispersion is an original film composed of an acrylic polymer having a ring structure in the main chain and a polymer having an α, β-unsaturated monomer unit having a heteroaromatic group as a constituent unit. Can be realized not only when they are included in the same layer, but also when both polymers are included in separate layers (when a layered structure of layers including each polymer is included).

  The thermoplastic resin constituting the original film can contain known additives. Additives include, for example, UV absorbers; antioxidants; phase difference modifiers such as phase difference increasing agents and phase difference reducing agents; phase difference stabilizers, light resistance stabilizers, weather resistance stabilizers and heat stabilizers, etc. Stabilizers; reinforcements such as glass and carbon fibers; near infrared absorbers; flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate and antimony oxide; anionic, cationic, nonionic Antistatic agents typified by surface active agents; colorants such as inorganic pigments, organic pigments, dyes; organic fillers, inorganic fillers; resin modifiers; antiblocking agents; matting agents; Metal deactivators; plasticizers; lubricants; flame retardants; rubbery polymers such as ASA and ABS; and other materials that adjust the optical and / or mechanical properties of the retardation film. The addition amount of the additive is, for example, 0 to 10% by weight, preferably 0 to 5% by weight, more preferably 0 to 2% by weight, and further preferably 0 to 0.5% by weight. .

  A functional layer that is not a thermoplastic resin layer may be provided on the surface of the original film. The functional layer is, for example, a hard coat layer, an easy adhesion layer, an antistatic layer, an antireflection layer and an antiblocking layer.

  Functional processing such as knurling can be applied to the left and right end portions (width direction end portions) of the original film. The functional processing may be affixing a tape for the purpose of preventing breakage of the original film or imparting anti-blocking property to the original film. The tape is, for example, Sekisui Chemical's taffete tape (trade name).

  The method for producing the original film is not particularly limited. The original film can be produced by a known method such as a solution casting method (solution casting method, cast molding method), a melt casting method (melt extrusion method, extrusion molding method), or a press molding method. Of these, the production of the original film by the melt film-forming method is preferred from the viewpoint of low environmental burden and excellent productivity.

  In the solution casting method, for example, the thermoplastic resin constituting the original film and a good solvent are mixed by stirring to form a uniform mixed solution, and the resulting mixed solution is cast onto a support film or drum to form a cast film. The cast film thus formed is pre-dried to form a film having self-supporting properties, and this film is peeled off from the supporting film or drum and dried to form an original film. The thermoplastic resin constituting the original film contains a material such as an additive if necessary. This is the same in other film forming methods. Solvents used in the solution casting method include, for example, chlorinated solvents such as chloroform and dichloromethane; aromatic solvents such as toluene, xylene, benzene and mixed solvents thereof; methanol, ethanol, isopropanol, n-butanol, Alcohol solvents such as 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, ethyl acetate, diethyl ether; As a solvent, only 1 type of these may be used and 2 or more types may be used together. An apparatus for performing the solution casting method is, for example, a drum-type casting machine or a belt-type casting machine.

  In the melt film forming method, for example, each component of the thermoplastic resin constituting the original film is pre-blended using a mixer such as an omni mixer, and the resulting mixture is kneaded with a kneader and then extruded. Form the original film. An original film may be formed by melt extrusion molding a separately formed thermoplastic resin. A kneading machine is not specifically limited, For example, it is a well-known kneading machine like a single screw extruder, a twin screw extruder, and a pressure kneader.

  Extrusion molding is, for example, a T-die method or an inflation method. The extrusion molding temperature (molding temperature) is preferably 200 to 350 ° C, more preferably 250 to 300 ° C, still more preferably 255 ° C to 300 ° C, and particularly preferably 260 ° C to 300 ° C. According to the T-die method, an original film wound on a roll (original film roll) can be obtained by attaching a T-die to the tip of the extruder and winding the film obtained by extrusion from the T-die.

  The type of the extruder used for extrusion molding is not particularly limited, and any of single-screw, twin-screw, and multi-screw extruders can be used. In order to sufficiently plasticize the thermoplastic resin to obtain a good kneaded state, the L / D value of the extruder (L is the length of the cylinder of the extruder and D is the cylinder inner diameter) is preferably 10 or more and 100 or less. Yes, more preferably from 15 to 80, and even more preferably from 20 to 60. When the L / D value is less than 10, the thermoplastic resin may not be sufficiently plasticized and a good kneaded state may not be obtained. When the L / D value exceeds 100, the polymer contained in the resin may be thermally decomposed due to excessive generation of shear heat with respect to the thermoplastic resin.

  The set temperature of the cylinder of the extruder is preferably 200 ° C. or higher and 300 ° C. or lower, more preferably 250 ° C. or higher and 300 ° C. or lower. When the set temperature of the cylinder is less than 200 ° C., the melt viscosity of the resin becomes excessively high, and the productivity of the original film tends to be lowered. When the set temperature of the cylinder exceeds 300 ° C., the polymer contained in the resin may be thermally decomposed.

  The shape of the extruder is not particularly limited. The extruder preferably has one or more open vents. In this case, the cracked gas can be sucked from the open vent portion of the extruder, and the amount of volatile components remaining in the obtained original film is reduced. In order to suck the decomposition gas from the open vent portion, for example, the open vent portion may be in a reduced pressure state. 1.3-931 hPa is preferable and, as for the pressure of the open vent part in a pressure reduction state, 13.3-798 hPa is more preferable. When the pressure in the open vent is higher than 931 hPa, the volatile component and the monomer component generated by the decomposition of the polymer are likely to remain in the resin. It is industrially difficult to keep the pressure of the open vent part lower than 1.3 hPa.

  For the production of the original film, it is preferable to use a thermoplastic resin filtered through a polymer filter. Filtration using a polymer filter removes foreign substances present in the resin, reducing optical defects and appearance defects of the retardation film. Filtration is solution filtration or melt filtration.

  During melt filtration, the resin is in a molten state at a high temperature. When the components contained in the resin deteriorate when passing through the polymer filter, the gas components or colored degradation products generated by the deterioration flow out, and defects such as perforations, flow patterns, and flow lines are observed in the resulting original film. May be. These disadvantages are particularly easily observed during continuous forming of the original film. Deterioration of the resin during melt filtration can be prevented by reducing the melt viscosity of the resin and shortening the residence time of the resin in the polymer filter. From this viewpoint, the molding temperature of the resin melt-filtered by the polymer filter is, for example, 255 to 320 ° C, and preferably 260 to 300 ° C.

  The configuration of the polymer filter is not particularly limited. A polymer filter in which a large number of leaf disk filters are arranged in a housing is preferably used. The filter material of the leaf disk type filter may be either a type in which a metal fiber nonwoven fabric is sintered, a type in which metal powder is sintered, a type in which several metal meshes are laminated, or a hybrid type in which they are combined. A type in which a metal fiber nonwoven fabric is sintered is most preferable.

  The filtration accuracy of the polymer filter is not particularly limited, but is usually 15 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the filtration accuracy is 1 μm or less, since the residence time of the resin in the polymer filter becomes long, the polymer contained in the resin is likely to be thermally deteriorated. Furthermore, the productivity of the original film is also reduced. When the filtration accuracy exceeds 15 μm, it is difficult to remove foreign substances in the resin.

  The shape of the polymer filter is not particularly limited. For example, an inner flow type having a plurality of resin flow ports and a resin flow path in the center pole; an inner peripheral surface of the leaf disk filter at a plurality of vertices or faces And an external flow type having a resin flow path on the outer surface of the center pole. Among these, an external flow type with few resin staying portions is preferable.

  The residence time of the resin in the polymer filter is preferably 20 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less. The filter inlet pressure and the outlet pressure during filtration are, for example, 3 to 15 MPa and 0.3 to 10 MPa, respectively, and the pressure loss (pressure difference between the filter inlet pressure and the outlet pressure) is preferably 1 MPa to 15 MPa. When the pressure loss is 1 MPa or less, the flow path through which the resin passes through the filter tends to be biased, and the quality of the obtained film tends to deteriorate. When the pressure loss exceeds 15 MPa, the polymer filter is easily damaged.

  What is necessary is just to set suitably the temperature of resin introduce | transduced into a polymer filter according to the melt viscosity, for example, it is 250-300 degreeC, Preferably it is 255-300 degreeC, More preferably, it is 260-300 degreeC.

  The specific procedure for obtaining an original film with few foreign matters and colored substances by melt filtration using a polymer filter is not particularly limited. For example, (1) a process in which a resin is formed and filtered in a clean environment, followed by molding in a clean environment; (2) a resin having foreign matters or colored substances is filtered in a clean environment and then continuously And (3) a process in which a resin having a foreign substance or a colored substance is subjected to filtration treatment in a clean environment and simultaneously molded. The filtration treatment can be performed a plurality of times for each step.

  When the resin is melt-filtered with the polymer filter, it is preferable to stabilize the pressure of the resin in the filter by installing a gear pump between the extruder and the polymer filter.

  In the production method of the present invention, depending on a specific oblique stretching method, for example, a retardation film having a low biaxial stretching property and an NZ coefficient of 0.95 or more and 1.30 or less can be formed. At this time, it is possible to form a retardation film having an NZ coefficient of 0.95 or more and 1.2 or less, and further 0.95 or more and 1.15 or less, depending on the configuration of the original film and the stretching conditions. When the NZ coefficient is 1.0, the retardation film is an ideal free end uniaxially stretched film.

  The configuration of the retardation film obtained by the production method of the present invention is basically the same as the configuration of the original film except that it is stretched in an oblique direction. However, in the retardation film, there may be a layer that is not in the original film before stretching, for example, a layer added by a process after stretching, or a layer modified during or after stretching.

  The retardation film obtained by the production method of the present invention has, for example, a layer composed of a thermoplastic resin containing an acrylic polymer having a ring structure in the main chain.

  The in-plane retardation Re indicated by the retardation film obtained by the production method of the present invention is, for example, 20 nm or more and 500 nm or less, and preferably 30 nm or more and 320 nm or less, with respect to light having a wavelength of 590 nm. The value of the in-plane retardation Re indicated by the retardation film can be controlled by, for example, the stretching conditions of the original film. The in-plane retardation Re can be appropriately set according to the specific application of the retardation film such as a quarter wavelength plate or a half wavelength plate. The in-plane retardation Re is expressed by a formula in which the refractive index in the slow axis direction in the retardation film plane is nx, the refractive index in the fast axis direction in the retardation film plane is ny, and the thickness of the retardation film is d. It is a value given by (nx−ny) × d. The retardation Rth in the thickness direction is a value given by the expression {(nx + ny) / 2−nz} × d, where nz is the refractive index in the thickness direction of the retardation film.

  The retardation film obtained by the production method of the present invention exhibits reverse wavelength dispersion depending on its configuration. In this case, for example, when the retardation film is used in an image display device, the visibility and contrast characteristics of the device are improved. This improvement in characteristics brings about a reduction in bluishness in black display, for example. Conventionally, polycarbonate and cycloolefin polymers have been mainly used for retardation films, but retardation films composed of these general polymers have larger retardation as the wavelength of light becomes shorter. The wavelength dispersibility (forward wavelength dispersibility).

  The index of reverse wavelength dispersion is as follows. The in-plane retardation of the retardation film for light with a wavelength of 447 nm is Re (447), the in-plane retardation of the retardation film for light with a wavelength of 590 nm is Re (590), and the in-plane retardation for light with a wavelength of 750 nm is Re. (750), for example, Re (447), Re (590) and Re (750) are represented by the formula Re (447) / Re (590) ≦ 0.98 and the formula Re (750) / Re (590 ) ≧ 1.01 is satisfied. Preferably, Re (447) / Re (590) of 0.50 or more and 0.98 or less and Re (750) / Re (590) of 1.01 or more and 1.50 or less, more preferably 0.60. Re (447) / Re (590) of 0.95 or less and Re (750) / Re (590) of 1.02 or more and 1.40 or less, more preferably 0.70 or more and 0.93 or less. Re (447) / Re (590) and Re (750) / Re (590) of 1.03 to 1.30.

  The thickness of the retardation film obtained by the production method of the present invention is, for example, 10 μm to 500 μm, preferably 20 μm to 300 μm, and more preferably 30 μm to 150 μm.

  The total light transmittance of the retardation film obtained by the production method of the present invention is preferably 85% or more, more preferably 90% or more, and further preferably 91% or more. The total light transmittance is a measure of the transparency of the retardation film. A retardation film having a total light transmittance of less than 85% is not suitable as an optical film.

  The Tg of the retardation film obtained by the production method of the present invention is preferably 110 ° C. or higher, more preferably 115 ° C. or higher, and further preferably 120 ° C. or higher. The upper limit of Tg is not limited, but is preferably 200 ° C. or less, more preferably 180 ° C. or less in consideration of the productivity and handling properties of the retardation film.

  The retardation film obtained by the production method of the present invention can be processed into an arbitrary size and shape.

  The composition of the resin constituting the retardation film is basically the same as the composition of the resin constituting the original film.

  Various functional coating layers may be formed on the surface of the retardation film as necessary. Functional coating layers include, for example, antistatic layers, adhesive layers, adhesive layers, easy adhesion layers, antiglare (non-glare) layers, antifouling layers such as photocatalyst layers, antireflection layers, hard coat layers, and UV shielding layers. A layer, a heat ray shielding layer, an electromagnetic wave shielding layer, and a gas barrier layer. Formation of a functional coating layer may be performed with respect to the original film before extending | stretching, and may be performed with respect to the retardation film obtained by extending | stretching.

  For example, an elliptically polarizing plate is obtained by laminating the retardation film and the polarizing film obtained by the production method of the present invention. The elliptically polarizing plate is preferably used, for example, as an antireflection film for an LCD or EL light emitting display device. For example, the polarizing film has a structure in which a polarizer protective film is laminated on at least one main surface of the polarizer. When laminating | stacking a retardation film with a polarizing film so that a polarizer protective film may be contact | connected, it is preferable to form an easily bonding layer in advance on the surface of the said retardation film.

  The retardation film obtained by the production method of the present invention can be suitably used as various optical members. The optical member is, for example, an optical protective film, specifically, a polarizing film used for a protective film for substrates of various optical disks (VD, CD, DVD, MD, LD, etc.), and a polarizing plate included in an image display device such as an LCD. It is a child protection film. You may use for a viewing angle compensation film, a light-diffusion film, a reflection film, an antireflection film, an anti-glare film, a brightness enhancement film, a conductive film for touch panels, etc.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples.

  First, a method for evaluating the properties of the thermoplastic resin (thermoplastic resin composition) produced in the production example, the retardation film produced in the film production example, and the retardation film produced in the examples and comparative examples will be described.

[Glass transition temperature (Tg)]
The glass transition temperature (Tg) of the resin was determined in accordance with the provisions of JIS K7121. Specifically, a differential scanning calorimeter (manufactured by Rigaku, DSC-8230) is used, and a sample of about 10 mg is heated from normal temperature to 200 ° C. (temperature increase rate: 20 ° C./min) in a nitrogen gas atmosphere. The DSC curve was evaluated by the starting point method. Α-alumina was used as a reference.

[Weight average molecular weight]
The weight average molecular weight of the resin was determined by gel permeation chromatography using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement are as follows.
System: Tosoh GPC system HLC-8220
Measurement column configuration:
Guard column (Tosoh, TSKguardcolumn SuperHZ-L)
Two separation columns (Tosoh, TSKgel SuperHZM-M) connected in series Reference column configuration:
Reference column (Tosoh TSKgel SuperH-RC)
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade), Flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (Tosoh, PS-oligomer kit)
Column temperature: 40 ° C

[Melt flow rate (MFR)]
The melt flow rate (MFR) of the resin was determined according to JIS K6874, with the test temperature set at 240 ° C. and the test load set at 10 kg.

[Intrinsic birefringence]
The positive / negative of the intrinsic birefringence of the resin constituting the film (original film and retardation film) was evaluated as follows. First, an 80 mm × 50 mm film piece was cut out from the produced unstretched original film, and uniaxially stretched at a stretching ratio of 2 times at Tg + 3 ° C. of the original film using an autograph (manufactured by Shimadzu Corporation) equipped with a heating chamber. Thus, a stretched film was obtained. At this time, since 20 mm at both ends in the longitudinal direction of the film piece was used as the allowance for attaching the chuck, the film piece was substantially stretched to a 40 mm × 50 mm portion. Next, the orientation angle of the obtained stretched film was calculated | required using the fully automatic birefringence meter (the Oji Scientific Instruments make, KOBRA-WR), and the positive / negative of the intrinsic birefringence of resin which comprises a film was determined by this. If the measured orientation angle is near 0 ° (that is, if the orientation direction of the resin is substantially parallel to the stretching direction), the intrinsic birefringence of the resin constituting the film is positive. If the measured orientation angle is near 90 ° (that is, if the orientation direction of the resin is substantially perpendicular to the stretching direction), the intrinsic birefringence of the resin constituting the film is negative.

[Refractive index anisotropy]
The in-plane retardation Re (590) for the light of wavelength 590 nm and the thickness direction retardation Rth for the light of wavelength 590 nm and the direction of the optical axis (the direction of the slow axis in the film plane) of the produced retardation film, Evaluation was performed using a retardation film / optical material inspection apparatus (RETS-100, manufactured by Otsuka Electronics Co., Ltd.). The thickness d of the retardation film input to the apparatus at the time of measurement was measured with a Digimatic micrometer (manufactured by Mitutoyo), and the average refractive index of the retardation film was measured with an Abbe refractometer. As Rth, a value given by the expression {(nx + ny) / 2−nz} × d was used. Uniaxial stretchability of the retardation film was evaluated by the NZ coefficient (NZ = | Rth | / | Re (590) | +0.5).

  The optical axis of the retardation film (slow axis in the film plane) is obtained by cutting out a strip-shaped evaluation film that crosses the film in the width direction from the produced strip-shaped retardation film, and defining the short side of the cut-out evaluation film. The measurement was performed in accordance with the reference bar of the apparatus so that the reference axis did not shake. The direction of the optical axis was expressed as an angle from the direction, with the longitudinal direction of the retardation film serving as the reference direction being 0 °. At this time, when the optical axis is tilted clockwise from the upstream side to the downstream side of the belt-like retardation film, the value is positive (+), and the case where the optical axis is tilted counterclockwise is negative. It was expressed by the value of (-).

  For the optical properties of the retardation film, the central portion in the width direction of the produced belt-like retardation film was evaluated.

(Production Example 1)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 10 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA), 40 parts by weight of methyl methacrylate (MMA), and toluene 50 as a polymerization solvent. 0.025 part by weight of ADK STAB 2112 (manufactured by ADEKA) was charged as a part by weight and an antioxidant. Next, the temperature was raised to 105 ° C. while introducing nitrogen gas into the reaction vessel, and when refluxing started, t-amyl peroxyisononanoate (trade name: Luperox 570, manufactured by Arkema Yoshitomi) was used as a polymerization initiator. 05 parts by weight were added. At the same time, dropwise addition of 0.10 parts by weight of the above t-amyl peroxyisononanoate was started, and solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C. while dropping over 2 hours. After completion of the dropwise addition, the reaction vessel was kept warm for 4 hours and aged.

  Next, 0.05 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemicals, trade name: Phoslex A-8) is added to the polymerization solution thus obtained as a catalyst for the cyclization reaction, The cyclization condensation reaction forming a lactone ring structure was allowed to proceed for 2 hours under reflux at 105 ° C. Next, the obtained polymerization solution was passed through a heat exchanger and heated to 240 ° C., and a bent type screw twin screw extruder (L / L) in which a leaf disk type polymer filter (filtration accuracy: 5 μm) was arranged at the tip portion. D = 52) was introduced at a treatment rate of 70 parts by weight per hour in terms of resin amount, and the polymerization solution was devolatilized. The vent type screw twin screw extruder used had 1 rear vent and 4 fore vents (referred to as the first, second, third and fourth vents from the upstream side), and the third and fourth vents. A side feeder was placed between the barrel temperature of 240 ° C. and the degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg). At the time of devolatilization, 1.05 parts of ion-exchanged water was added from behind the first vent at a charging rate of 1.05 parts by weight / hour with a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator. Charges were made from behind the second and third vents, respectively, at an input speed of parts by weight / hour. 5 parts by weight of an antioxidant (manufactured by Ciba Specialty Chemicals, Irganox 1010) and 55 parts by weight of zinc octylate as a cyclization catalyst deactivator (Japan) A solution obtained by dissolving 45% by weight of toluene, manufactured by Chemical Industry Co., Ltd. and trade name: Nikka Octics Zinc 3.6%) was used. Furthermore, pellets of a styrene-acrylonitrile copolymer (the ratio of styrene units / acrylonitrile units is 73% by weight / 27% by weight, weight average molecular weight 220,000) were charged from the side feeder at a charging rate of 30 parts by weight / hour. .

  Thereafter, the molten resin in the extruder is discharged from the tip of the extruder, pelletized by a pelletizer, and a thermoplastic resin containing an acrylic polymer having a lactone ring structure in the main chain and a styrene-acrylonitrile copolymer A pellet of the composition (1A) was obtained. The intrinsic birefringence of the resin (1A) was negative, the Tg was 122 ° C., the weight average molecular weight was 146000, and the MFR was 13.6 g / 10 minutes.

(Film formation example 1)
The resin (1A) pellets produced in Production Example 1 were melt-extruded at a molding temperature of 270 ° using a single-screw extruder equipped with a polymer filter (filtration accuracy 5 μm) and a T-die at the tip. A 150 μm unstretched film (original film) was formed. The formed strip-shaped original film was trimmed in-line at the end in the width direction so as to have a width of 570 μm and wound on a roll.

  Next, the original film is continuously unwound from the produced roll, and obliquely using a simultaneous biaxial stretching machine in which a preheating zone Z1, a front-stage stretching zone Z2, a rear-stage stretching zone Z3, and a heat treatment zone Z4 are set as shown in FIG. Stretched.

  The simultaneous biaxial stretching machine used for the oblique stretching is a pair of rails (left clip rail and right clip rail) on which a pair of clips composed of a plurality of clips travels, and from the upstream side to the downstream side of the original film. A heating furnace in which a preheating zone Z1, a front-stage stretching zone Z2, a rear-stage stretching zone Z3, and a heat treatment zone Z4 were set in order was provided. The shape of the left clip rail and the shape of the right clip rail were symmetric with respect to a straight line extending in the longitudinal direction of the original film, which was divided into two in the width direction when viewed from above the simultaneous biaxial stretching machine. In other words, in the left clip rail and the right clip rail, the midpoints of the line segments connecting the points equidistant from the entrance of the preheating zone are always on the straight line (center line). At the boundary between the zones on both the left and right rails, a rail portion was adjusted, and a joint portion was provided to enable combined use of lateral stretching in the front stretching zone and the rear stretching zone. In the front stretching zone Z2, the traveling speed of the clip group (left clip group) traveling on the left rail is decreased, and in the rear stretching zone Z3, the traveling speed of the left clip group decelerated in the preceding stretching zone Z2 is reduced to the traveling speed before deceleration. Recovered. The traveling speed of the left and right clip groups (traveling speed at the left and right clip-in portions) when gripping the belt-shaped original film was set to 2.0 m / min. The position where the clip group grips the original film was 25 mm from the end in the width direction of the film (the grip margin was 25 mm for both the left and right clip groups). That is, the initial interval of the original film was 520 nm. The length of each stretching zone (length in the flow direction of the original film) was the same.

  In Film Production Example 1, the original film was stretched obliquely according to the stretching conditions shown in Tables 1 and 2 below. As shown in Table 2, in the former drawing zone Z2 and the latter drawing zone Z3, a difference in running speed was given to the left and right clip groups, and the original film was drawn obliquely. Moreover, in the front | former stage extending | stretching zone Z2 and the back | latter stage extending | stretching zone Z3, the horizontal extending | stretching which increases the space | interval between the clip groups on either side with respect to the width direction of an original film was used together. In other sections through which the original film passes from clip-in to clip-out, the traveling speed of the left and right clip groups and the interval are maintained without change. However, in the preheating zone Z1 and heat treatment zone Z4, fine adjustments were made to the running speed of the clip group and the distance between the clip groups for the purpose of eliminating the looseness of the original film due to heating and adjusting the shrinkage stress generated in the film during cooling. did. Moreover, the fluctuation | variation to such an extent that the traveling speed of a clip group usually arises by the stress which arises in the case of diagonal extending | stretching was shown. These points are the same in the following film forming examples, examples and comparative examples unless otherwise specified.

  The left (right side) clip magnification of each stretching zone shown in Table 2 and the following tables is an indicator of the change in the running speed of the left (right) clip group in each stretching zone. Specifically, the ratio of the traveling speed of the left (right) clip group at the exit of each stretching zone to the traveling speed of the left (right) clip group at the entrance of each stretching zone is the clip magnification. When the clip magnification is 1, the traveling speed of the clip group in the stretching zone is constant, and when the clip magnification is less than 1, it decreases, and when it exceeds 1, it indicates that it increases. The total clip magnification is a value obtained by multiplying the clip magnification in the former drawing zone by the clip magnification in the latter drawing zone. When this value is 1, the traveling speed of the clip group at the entrance of the former drawing zone and the latter drawing It shows that the traveling speed of the clip group at the exit of the zone is equal. In the example shown in Table 2, since the total clip magnification is 1 in both the left and right clip groups, it indicates that the traveling speed at the time of clip-in was maintained except for each stretching zone. Further, regarding the right clip group, the clip magnification in each stretching zone is also 1, indicating that the traveling speed was constant from clip-in to clip-out. Note that “constant”, “equal”, and “maintained” allow the above-described fine adjustment of the traveling speed and fluctuations in the traveling speed of the clip group due to wobbling.

  In order to carry out the horizontal stretching at a constant ratio, the clip rail was set to be straight through the front stretching zone and the rear stretching zone on both the left and right sides. However, with respect to transverse stretching, in Table 2, the magnification in each stretching zone is different from each other. This is because the transverse draw ratio in each drawing zone is based on the width of the original film after the transverse drawing in the immediately preceding drawing zone. The same applies to the transverse draw ratio in the following tables.

  The obliquely stretched film was trimmed in-line at the end in the width direction so as to have a width of 650 mm, and then wound on a roll.

  The optical properties of the retardation film thus obtained are shown in Table 3 below.

Example 1
In Example 1, the initial interval was changed so that the optical axis of the retardation film produced in Film Formation Example 1 was −45 °, and from the clip-in to the clip-out based on the changed initial interval. The interval X was determined. Specifically, after continuously feeding the original film from the roll produced in Film Formation Example 1, both end portions in the width direction are trimmed inline by 15 mm each so that the width of the original film is 540 mm, Other conditions (temperature of each zone in the biaxial stretching machine, clip magnification and lateral stretching ratio of the left and right clip groups) were the same as in Film Production Example 1 to obtain an obliquely stretched retardation film. Since the left and right grip margins remained at 25 mm, the initial interval after the change was 490 mm. By changing the initial interval to 490 mm, the interval X in the section from the clip-in to the entrance of the preceding drawing zone is also changed from 520 mm to 490 mm, and the interval X after the transverse drawing (the interval in the section from the exit of the subsequent drawing zone to the clip-out) X) was also a value obtained by multiplying the distance X (490 mm) after the change by the transverse draw ratio (1.60). The interval X in the former drawing zone and the latter drawing zone was continuously changed from 490 mm to 490 × 1.60 mm.

  The optical properties of the retardation film thus obtained are shown in Table 4 below.

  As shown in Table 4, in Example 1, the optical axis can be accurately adjusted to approach the target of −45 °, and the in-plane phase difference Re (590), the thickness direction phase difference Rth, and The change in the NZ coefficient could be suppressed.

(Film formation example 2)
The resin (1A) pellets produced in Production Example 1 were melt-extruded at a molding temperature of 270 ° using a single-screw extruder equipped with a polymer filter (filtration accuracy 5 μm) and a T-die at the tip. A 150 μm unstretched film (original film) was formed. Subsequently, both end portions of the formed original film were continuously trimmed in-line to obtain an original film having a width of 520 mm. Further, the original film was obliquely stretched in the same manner as in Example 1 except that the stretching conditions shown in the following Tables 5 and 6 were used, and an obliquely stretched retardation film was obtained. The line speed immediately before the drawing machine at this time was 2.5 m / min.

  The optical properties of the retardation film thus obtained are shown in Table 7 below.

(Example 2)
In Example 2, the initial interval is changed so that the optical axis of the retardation film produced in Film Formation Example 2 is −45 °, and from the clip-in to the clip-out based on the changed initial interval. The interval X was determined. Specifically, while continuing to stretch the original film diagonally, the gripping distance of the original film by the left and right clip groups was gradually changed from 30 mm to 15 mm, respectively, and the initial interval was changed from 460 mm to 490 mm. Other conditions (temperature of each zone in the biaxial stretching machine, clip magnification and lateral stretching ratio of the left and right clip groups) were the same as in Example 2 to obtain a diagonally stretched retardation film. By changing the initial interval to 490 mm, the interval X in the section from the clip-in to the entrance of the preceding drawing zone is also changed from 460 mm to 490 mm, and the interval X after the transverse drawing (the interval in the section from the exit of the subsequent drawing zone to the clip-out) X) was also a value obtained by multiplying the distance X (490 mm) after the change by the transverse draw ratio (1.60). The interval X in the former drawing zone and the latter drawing zone was continuously changed from 490 mm to 490 × 1.60 mm.

  The optical properties of the retardation film thus obtained are shown in Table 8 below.

  As shown in Table 8, in Example 2, the optical axis can be accurately adjusted to approach the target of −45 °, and the in-plane phase difference Re (590), the thickness direction phase difference Rth, and The change in the NZ coefficient could be suppressed.

(Comparative Examples 1 and 2)
In Comparative Examples 1 and 2, the clip magnification of the left clip group in the pre-stage stretching zone Z2 was increased so that the optical axis of the retardation film produced in Film Formation Example 2 was −45 °. The clip magnification of the right clip group was kept as in film forming example 2, and the total clip magnification in the front stretching zone Z2 and the rear stretching zone Z3 was kept at 1 for the left and right clip groups. That is, compared with the example 2 of film formation, the traveling speed difference between the left and right clip groups in the front drawing zone Z2 and the rear drawing zone Z3 was reduced. Other conditions (temperature of each zone in the biaxial stretching machine and transverse stretching ratio) were the same as those in Example 2 of film formation. The initial interval and the interval X were not changed from the film forming example 2. That is, the interval X in the section from the clip-in to the entrance of the preceding drawing zone is 460 mm, and the interval X after the transverse drawing (the interval X in the section from the outlet of the succeeding drawing zone to the clip-out) is transversely drawn to the initial interval of 460 mm. It is a value obtained by multiplying by a magnification (1.60), and the interval X in the former drawing zone and the latter drawing zone was continuously changed from 460 mm to 460 × 1.60 mm. The oblique stretching conditions in Comparative Examples 1 and 2 are shown in Tables 9 to 11 below.

  The optical properties of the retardation film thus obtained are shown in Table 12 below.

  As shown in Table 12, in Comparative Examples 1 and 2, it is difficult to accurately adjust the optical axis, and in addition to the change of the optical axis, in-plane phase difference Re (590), which is another optical characteristic, The phase difference Rth and the NZ coefficient changed greatly.

  The retardation film produced by the production method of the present invention is used for the same applications as conventional retardation films, for example, a liquid crystal display (LCD), an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED). ) Can be suitably used for a polarizer protective film, a viewing angle compensation film, a light diffusion film, a reflection film, an antireflection film, an antiglare film, a brightness enhancement film, and a conductive film for a touch panel.

1 Heating and stretching apparatus Z1 Preheating zone Z2 Previous stretching zone Z3 Rear stretching zone Z4 Heat treatment zone CIL Clip-in part of the left clip group CIR Clip-in part of the right clip group COL Clip-out part of the left clip group COR Clip-out part of the right clip group LR Left clip rail RR Right clip rail 11 One clip group 12 The other clip group 13 Original film 14 (Innermost gripped by one clip group in the original film) 15 (By the other clip group in the original film) Innermost part being gripped

Claims (10)

With a pair of clips composed of a plurality of clips, each of the long side edges of the strip-shaped original film is gripped,
Stretching the original film by running the pair of clips holding the original film,
After stretching the original film, the original film is released from the pair of clip groups to obtain a belt-like retardation film, a method for producing a retardation film,
The stretching of the original film is performed by changing the running speed difference between one clip group and the other clip group and / or one of the above-described ones between the time when the original film is held by the pair of clip groups and the time when the original film is released. Based on the travel distance difference between the clip group and the other clip group, by stretching the original film obliquely with respect to the longitudinal direction of the film,
By the stretching, the retardation film in which the optical axis in the film plane is inclined with respect to the longitudinal direction of the film is formed,
In the passage route of the original film from being gripped by the pair of clip groups to being released, the section between the pair of clip groups at the time of gripping the original film for each section provided in the route. An interval with respect to the width direction between the pair of clip groups based on an interval with respect to the width direction of the original film (initial interval) is defined,
Adjustment of the optical axis indicated by the retardation film,
The pair of clip groups grips the original film, the initial interval is changed by changing the position in the width direction,
Using the changed initial interval as a new reference, the width direction between the pair of clip groups for each section in the path of passage of the original film from the time when the original film is gripped to the opening is released. Determine the interval,
A method for producing a retardation film.   The method for producing a retardation film according to claim 1, wherein the initial interval is changed by changing a grip margin when the original film is held by the pair of clips. Stretching the original film by stretching the original film obliquely with respect to the longitudinal direction of the film based on the traveling speed difference,
The method for producing a retardation film according to claim 1, wherein the traveling speed difference is maintained when the optical axis is adjusted.   The retardation film production according to any one of claims 1 to 3, wherein when the original film is stretched, the stretching in the width direction by increasing the distance between the pair of clip groups in the width direction is used together. Method.   The method for producing a retardation film according to claim 1, wherein the optical axis is adjusted while continuing the stretching of the original film by running of the pair of clip groups. The retardation film is continuously formed by performing the stretching on the original film continuously supplied from the original film forming apparatus,
The method for producing a retardation film according to claim 1, wherein the optical axis is adjusted without stopping the supply of the original film from the apparatus. Forming the retardation film by performing the stretching on the original film supplied from a roll,
The method for producing a retardation film according to claim 1, wherein the optical axis is adjusted without replacing the roll.   The method for producing a retardation film according to claim 1, wherein the optical axis is adjusted based on a measurement result of the optical axis with respect to the formed retardation film.   The method for producing a retardation film according to claim 1, wherein the retardation film showing the same retardation value and NZ coefficient is formed before and after the adjustment of the optical axis. The method for producing a retardation film according to claim 1, wherein the original film has a layer composed of a thermoplastic resin containing an acrylic polymer having a ring structure in the main chain.

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