JP2013158928A - Method of manufacturing stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a stretched film capable of effectively manufacturing the stretched film excellent in optical characteristics.SOLUTION: A method for manufacturing a stretched film includes a step of applying heating treatment to the film after stretching with the usage of a heating treatment part capable of forming a temperature gradient, wherein the step is performed after a temperature of the heating treatment part is set so that a line segment connecting the predetermined two points in a film surface after stretching which is thermally treated and a stress application direction in the film surface have the predetermined relationship.

Description

  The present invention relates to a method for producing a stretched film, and more particularly, to a method for producing a stretched film that can uniformly heat-treat a stretched film and can easily produce a stretched film having excellent optical properties with high productivity. Is.

  When the film is stretched using a heat stretching apparatus, the stretched film stretched in the stretching zone is maintained at a specific temperature (heat treatment temperature) equal to or lower than the stretching temperature in the heat treatment zone of the apparatus.

  This heat treatment 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, for example, optical properties and mechanical properties. Is achieved.

  FIG. 4 is a top view showing a state in which the film is laterally stretched (stretched in the width direction of the film) using a conventionally known heat stretching apparatus in which the moving direction of the film is kept substantially parallel before and after stretching. .

  In FIG. 4, 300 is a heating and stretching apparatus, 111 is a right rail, 112 is a left rail, 113 is a right clip group, 114 is a left clip group, 116 is a nozzle, Z1 is a preheating zone, Z2A is a front stretching zone, and Z2B is a rear stage. The stretching zone, Z3, is a heat treatment zone. The film is fed in the direction indicated by the arrow.

  In the heat treatment zone Z3, a nozzle 116 is arranged in the width direction of the film (direction perpendicular to the long side direction of the film), and the film stretched in the front stretching zone Z2A and the rear stretching zone Z2B is sent to the heat treatment zone Z3. It is done. And it is hold | maintained at the specific temperature below extending | stretching temperature by being exposed to the hot air blown from the nozzle 116 set to the specific temperature below extending | stretching temperature.

  In the heating and stretching apparatus 300, nozzles similar to the nozzles 116 are installed in all zones, but FIG. 4 shows only the nozzles 116 installed in the heat treatment zone Z3.

  In FIG. 4, the lateral stretching using the heat stretching apparatus 300 is performed by increasing the distance between the pair of clip groups 113 and 114 that hold both long edge portions of the original film.

  At this time, in the heat treatment zone Z3, in the film plane, stress accompanying lateral stretching is applied from the center of the line segment represented by the dotted line connecting the right clip and the corresponding left clip to the right and left sides.

  That is, the direction in which the stress is applied in the film plane (actually, the stress in the flow direction accompanying the bowing phenomenon is also added, but here it is the direction of the largest stress. Hereinafter, in the plane of the film after stretching. The direction in which the greatest stress is applied is also simply referred to as “stress application direction”) and is substantially parallel to the line segment represented by the dotted line connecting the right clip and the corresponding left clip. Since the line segment is substantially parallel to the width direction of the film, the stress application direction is also substantially parallel to the arrangement direction of the nozzles 116.

  Therefore, in the heat treatment zone Z3, uniform heat treatment can be performed along the stress application direction, optical characteristics in the width direction of the film, in particular, uniformity of retardation in the width direction of the film (phase difference accuracy) and optical axis. The uniformity of the orientation (optical axis accuracy) is kept good.

  On the other hand, FIG. 5 shows the film in the longitudinal direction of the film (also referred to as the long side direction or the flow direction) using a conventionally known simultaneous biaxial stretching apparatus 400 in which the moving direction of the film is kept substantially parallel before and after stretching. 5 is a top view showing a state in which the film is stretched obliquely (hereinafter, such stretching may be referred to as “oblique stretching”). The same members as those shown in FIG. 4 are given the same members as those shown in FIG.

  In the oblique stretching, (1) when moving the clip from the preheating zone Z1 to the front stretching zone Z2A, the rear stretching zone Z2B, and the heat treatment zone Z3, the traveling speed of the left and right clips is the same in the preheating zone Z1.

  Next, (2) within the zone of the stretching zone (in this figure, two zones Z2A and Z2B are provided), by changing the difference between the traveling speeds of the left and right clips, that is, changing the interval of the clips in the flow direction. (The figure shows a state in which the clip interval on one side is once shortened and then restored), and the original film is stretched further obliquely with respect to the long side direction of the film. (3) In the heat treatment zone Z3, the difference between the traveling speeds of the left and right clips becomes constant again.

  In this case, since the film is stretched obliquely upward to the right, as shown in FIG. 5, in the heat treatment zone Z3, the stress application direction in the film plane is parallel to the line drawn from the left clip 114a to the right clip 113a. It becomes.

  However, as shown in FIG. 5, in the left heat treatment zone Z3, the nozzles 116 arranged in the width direction of the film and the stress application direction are not parallel to each other.

  Further, for example, as shown in FIG. 5, in a line segment connecting the left clip and the right clip, a portion that goes out of the heat treatment zone Z3 and is cooled, and a portion that still remains in the heat treatment zone Z3 Will also be mixed.

  In this way, when performing oblique stretching, if the uniform heat treatment along the direction of stress application in the film plane after the heat treatment is not performed, the uniformity of the retardation of the obtained stretched film is lost. The problem arises that the optical properties in the width direction of the stretched film deteriorate.

  In order to solve this problem, Patent Document 1 and Patent Document 2 disclose oblique stretching using a tenter stretching machine having a bent tenter rail in which the moving direction of the film differs before and after stretching.

Japanese Patent Laying-Open No. 2005-319660 (released on November 17, 2005) JP 2010-266723 A (released on November 25, 2010)

  However, in the techniques disclosed in Patent Documents 1 and 2, when it is necessary to change the stretching conditions (stretch ratio, etc.) in the heat stretching apparatus, a very complicated operation is required every time the stretching conditions are changed. .

  In other words, when it is desired to perform lateral stretching after performing oblique stretching, or when producing two or more retardation films having different optical axes, it is necessary to change the stretching conditions. Operations such as changing the installation location of the winder for winding the retardation film and adjusting the parallelism (centering) of the roll for supplying the original film are required. Therefore, there exists a problem that productivity of retardation film will fall.

  The present invention has been made in view of the above problems, and its purpose is to improve the productivity of a stretched film without requiring complicated work such as changing the installation location of the winder even when the stretching conditions are changed. An object of the present invention is to provide a method for producing a stretched film that can maintain a stretched film having excellent optical properties.

  As a result of intensive studies to achieve the above object, the present inventor is a point in the plane of the stretched film that is heat-treated by a heat treatment part capable of forming a temperature gradient, and is located on the most upstream side of the film. A point close to the first clip positioned, a point in the plane of the stretched film, a point close to the second clip paired with the first clip, and the first The temperature of the heat treatment part is such that a line segment connecting a point close to one clip and a point exhibiting substantially the same temperature is substantially parallel to the direction in which stress is applied in the plane of the stretched film. Setting was made and an attempt was made to heat-treat the stretched film.

  Thus, regardless of the stretching direction of the film, the film can be uniformly heat-treated, and it is possible to produce a stretched film that maintains the productivity of the stretched film and has excellent optical properties without requiring complicated operations. The inventor has found this knowledge and has completed the present invention. That is, the present invention includes the following configurations.

  (1) A stretched film manufacturing method including a heat treatment step of heat treating a stretched film using a heat treatment section capable of forming a temperature gradient, wherein the stretched film is composed of a plurality of clips. Both long side edges are respectively held by a pair of clips, and the heat treatment step is in the plane of the stretched film to be heat treated, and is the first clip located on the most upstream side of the film. A point close to the second clip that is in the plane of the stretched film to be heat-treated and is paired with the first clip, and the first clip Of the heat treatment part so that the line connecting the point adjacent to the point and the point exhibiting substantially the same temperature is substantially parallel to the direction in which the greatest stress is applied in the plane of the stretched film. Warm Method for producing a stretched film which is performed after performing the setting.

  (2) The said heat processing part is a manufacturing method of the stretched film as described in (1) provided with at least 4 temperature control apparatus.

  (3) The heat treatment section includes four temperature control devices, the set temperature of one set of temperature control devices is substantially the same, and the set temperature is substantially the same as the other set of temperature control devices. (1) or the manufacturing method of the stretched film as described in (2) higher than preset temperature.

  (4) The method for producing a stretched film according to any one of (1) to (3), wherein the stretched film is stretched in the longitudinal direction of the film and / or in the transverse direction of the film.

  (5) The method for producing a stretched film according to any one of (1) to (4), wherein the stretched film is stretched obliquely with respect to the long side direction of the film.

  (6) The said heat processing is a manufacturing method of the stretched film in any one of (1)-(5) performed by hold | maintaining the film after extending | stretching below stretching temperature.

  A method for producing a stretched film according to the present invention is a method for producing a stretched film including a heat treatment step of heat treating the stretched film using a heat treatment part capable of forming a temperature gradient, Both long edge portions are respectively held by a pair of clip groups constituted by a plurality of clips, and the heat treatment step is in the plane of the stretched film to be heat treated, and is the most upstream of the film. A point close to the first clip located on the side and a point close to the second clip that is in the plane of the stretched film to be heat treated and is paired with the first clip, The line segment connecting the point close to the first clip and the point showing substantially the same temperature is substantially the same as the direction in which the greatest stress is applied in the plane of the stretched film. So that the row is a structure that is performed after performing the temperature setting of the heat treatment unit.

  Therefore, the film can be uniformly heat-treated regardless of the stretching direction of the film, and it is easy to produce a stretched film that maintains the productivity of the stretched film and has excellent optical properties without requiring complicated operations. There is an effect that can be done.

It is the top view which showed a mode that the film was extended | stretched diagonally using the tenter horizontal extending | stretching machine which installed the temperature range variable nozzle provided with four temperature control apparatuses in the heat processing zone. It is the top view which showed a mode that the film was extended | stretched diagonally using the simultaneous biaxial stretching machine which installed the temperature range variable nozzle provided with four temperature control apparatuses in the heat processing zone. The heat treatment section includes four temperature control devices, the set temperature of one set of temperature control devices is substantially the same, and the set temperature is substantially the same as the set temperature of the other set of temperature control devices. It is a schematic diagram which shows the temperature area | region formed in a heat processing part when it is high. It is the top view which showed a mode that the film was laterally stretched using the conventionally well-known heating stretching apparatus by which the moving direction of a film is maintained substantially parallel before and after extending | stretching. It is the top view which showed a mode that the film was diagonally stretched using the conventionally well-known heating stretching apparatus by which the moving direction of a film is maintained substantially parallel before and after extending | stretching. In the stretched film that is heat-treated by the temperature region variable nozzle (heat treatment part), the point that is close to the first clip, the point that is close to the second clip, and close to the first clip The example which acquired the point which shows the temperature which is substantially the same temperature as a point, and obtained the line segment which connects these points is shown. It is a schematic diagram which shows the stress application direction in the film after extending | stretching which the bowing phenomenon produced.

  Hereinafter, embodiments of the present invention will be described in detail. All of the academic and patent literature described in this specification are hereby incorporated by reference. Unless otherwise specified in this specification, “A to B” representing a numerical range means “A or more (including A and greater than A) and B or less (including B and less than B)”. “%” Means “% by weight” and “parts” means “parts by weight”.

<1. Manufacturing method of stretched film>
A method for producing a stretched film according to the present invention is a method for producing a stretched film including a heat treatment step of heat treating the stretched film using a heat treatment part capable of forming a temperature gradient, Both long edge portions are respectively held by a pair of clip groups constituted by a plurality of clips, and the heat treatment step is in the plane of the stretched film to be heat treated, and is the most upstream of the film. A point close to the first clip located on the side and a point close to the second clip that is in the plane of the stretched film to be heat treated and is paired with the first clip, The line segment connecting the point close to the first clip and the point showing substantially the same temperature is substantially the same as the direction in which the greatest stress is applied in the plane of the stretched film. So that a row as long as it is performed after performing the temperature setting of the thermal processing, and other specific steps, conditions and the like are not particularly limited.

  The stretching method for producing the “film after stretching” is not particularly limited, and conventionally known stretching methods such as uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching can be used.

  In the present specification, the “film after stretching” refers to a film that has been stretched and is subjected to heat treatment, and may refer to a portion of a film that has been stretched or stretched. It may be all parts of a finished film.

  In the former case, for example, a portion of the film provided for a heating and stretching apparatus including a preheating zone, a stretching zone, and a heat treatment zone that has been stretched and introduced into the heat treatment zone is applicable. From the viewpoint of continuous efficient production, the former is preferable to the latter.

  Examples of the heat stretching apparatus used in the production method of the stretched film include, for example, an apparatus that stretches only the longitudinal direction of the film, an apparatus that stretches only the transverse direction of the film, and an apparatus that simultaneously stretches the longitudinal and lateral directions of the film. Any of these devices can be used. That is, in this method, the film is preferably stretched in the longitudinal direction of the film and / or in the lateral direction of the film.

  In particular, in the production method of the stretched film, it is preferable that the stretching of the film is performed obliquely with respect to the longitudinal direction of the film. For example, (i) “bending method” (for example, the technique disclosed in Patent Documents 1 and 2) for bending a film conveyance lane, and (ii) left and right clips of a simultaneous biaxial stretching apparatus. , A “trajectory difference / lateral speed difference method” for driving the trajectory and speed differently, and (iii) “simultaneous biaxial stretching method in which the film is stretched simultaneously in the longitudinal and transverse directions and stretched in an oblique direction. ".

  As described above, (i) requires operations such as changing the installation location of the winder that winds up the retardation film obtained each time the stretching conditions are changed, and decreases the productivity of the stretched film. In the method for producing a stretched film, it is preferable to keep the moving direction of the original film in the heat stretching apparatus substantially parallel before and after the stretching zone.

  In other words, the traveling direction of the clip when gripping the original film is preferably substantially parallel to the traveling direction of the clip when releasing the stretched film. Therefore, the production method of the stretched film can be particularly suitably used for (ii) “trajectory difference / lateral speed difference method” and (iii) “simultaneous biaxial stretching method”.

  The traveling direction of the clip takes into account the case where lateral stretching is further applied to the original film, and the traveling direction of the clip that grips or releases one long edge and the clip that grips or releases the other long edge. This means the direction of the vector sum with the traveling direction.

  Examples of (ii) “trajectory difference / lateral speed difference method” include those described in JP-A-2009-143208, for example. Examples of (iii) “simultaneous biaxial stretching method” include those described in JP-A-2008-023775 and JP-A-2009-255344.

  In the manufacturing method of this stretched film, the method of supplying a strip | belt-shaped original film to a heating stretching apparatus is not limited. For example, what is necessary is just to supply to a heat | fever stretching apparatus, paying out the said film in order from the roll of an original film.

  The stretching temperature is preferably Tg-20 ° C to Tg + 60 ° C, more preferably Tg-10 ° C to Tg + 30 ° C, based on the glass transition temperature (Tg) of the thermoplastic resin constituting the original film.

  When the stretching temperature is less than Tg-20 ° C, the original film is easily broken during stretching. When the stretching temperature exceeds Tg + 60 ° C., the looseness of the original film in the stretching zone of the heat stretching apparatus becomes large, and the contact between the film and the heat stretching apparatus and the breaking of the original film easily occur. The stretching temperature is, for example, the temperature setting temperature of the stretching zone in the heat stretching apparatus or the temperature of the atmosphere through which the original film passes in the stretching zone.

  The stretching speed in the stretching zone is, for example, 10 to 20000% / min, and preferably 100 to 10000% / min.

  When the stretching speed is less than 10% / min, the time required to complete the stretching becomes long, and the production cost of the retardation film increases. Further, the length required for the stretching zone becomes long, and such a heat stretching apparatus is not practical. When the stretching speed is higher than 20000% / min, the original film is easily broken.

  In the manufacturing method of this stretched film, the heat processing part which can form a temperature gradient is used. The said heat processing part can be provided in the heat processing zone of a conventionally well-known heating drawing machine, for example. In the present specification, the heat treatment part and the heat treatment zone may be collectively referred to as a “heat treatment part”.

  The heat treatment part includes a temperature control device for forming a temperature gradient in the heat treatment part. Since it is easy to create a temperature gradient in which the temperature changes in a gradation (continuously) from the high temperature portion to the low temperature portion, it is preferable to use a heating device having at least four temperature control devices as the heat treatment portion. .

  Examples of the heating device include a nozzle provided with four or more ducts, a temperature control device provided at each duct outlet, and a panel heater provided with four or more heaters in the surface.

  As the temperature control device, a conventionally known heater, hot air device, or the like can be used. Further, from the viewpoint of forming a temperature gradient, each temperature control device needs to be able to set the temperature independently.

  The temperature setting of the heat treatment section can be performed by appropriately setting the temperature of the temperature control device provided in the heat treatment section. Moreover, the said temperature gradient can be formed by changing suitably the preset temperature of each temperature control apparatus with which a heat processing part is provided.

  The above-mentioned “forms a temperature gradient in the heat treatment part” means that a temperature distribution is given to the heat generated from the heat treatment part by providing a difference in set temperatures of a plurality of temperature control devices. The temperature gradient is preferably such that the temperature changes in a gradation (continuously) from a high temperature portion to a low temperature portion (or from a low temperature portion to a high temperature portion). This is because it is easy to obtain two points showing substantially the same temperature from the formed temperature gradient.

  In the heat treatment process, “heat-treating the stretched film” means that the heat generated by the heat treatment part is applied to the stretched film, and the heat is a temperature gradient formed. Is preferred. The heat treatment can be performed, for example, by introducing a stretched film from a stretching zone of a heat stretching apparatus into the heat treatment zone and radiating heat from the heat treatment portion to the stretched film.

  The film temperature in the heat treatment step is preferably not more than the stretching temperature. By maintaining the stretched film below the stretching temperature, the molecular orientation of the polymer contained in the film is stable, the distortion of the film is reduced, and the properties exhibited by the finally obtained retardation film, For example, stabilization of optical characteristics and mechanical characteristics can be achieved. Therefore, it is preferable that the set temperature of each temperature control device provided in the heat treatment section is equal to or lower than the stretching temperature.

  That is, the heat treatment is preferably performed by maintaining the stretched film at a temperature equal to or lower than the stretching temperature in an atmosphere in which a temperature gradient is formed. That is, the stretched film is heat-treated by passing through an atmosphere having a temperature gradient generated by the heat treatment part, and the maximum temperature of the atmosphere is preferably equal to or lower than the stretching temperature.

  The heat treatment is more preferably performed by keeping the stretched film below the stretching temperature. Thereby, since the film shrinks and the shrinkage stress generated in the film can be appropriately maintained, the molecular orientation in the stretched film is stabilized, and the optical properties can be further stabilized. Therefore, it is more preferable that the set temperature of each temperature control device provided in the heat treatment section is lower than the stretching temperature.

  FIG. 1 includes a heating furnace in which a preheating zone, a stretching zone, and a heat treatment zone are set in order from the upstream side to the downstream side in the flow direction of the original film indicated by arrows, and four temperature control devices A, It is the top view which showed a mode that the film was extended | stretched diagonally using the tenter horizontal extending | stretching machine 100 which installed the temperature range variable nozzle (heat processing part) 115 provided with B, C, and D. The stretching machine was also used in Example 1 described later.

  In FIG. 1, the original film is gripped by the right clip group 113 and the left clip group 114 on the right rail 111 and the left rail 112 although not shown. The temperature region variable nozzle (heat treatment part) 115 is positioned vertically above the original film. In the figure, the same members as those in FIG. Z2 is a stretching zone.

  In this specification, the stretched film that is subjected to the heat treatment step and subjected to the heat treatment has both long side edges gripped by a pair of clips composed of a plurality of clips. The pair of clip groups corresponds to a clip group such as the right clip 113a and the left clip 114a shown in FIG.

  The relative positional relationship between the pair of clip groups varies depending on the stretching conditions, and is determined by appropriately setting the stretching conditions by a conventionally known method.

  The surface of the heat treatment part facing the surface of the stretched film to be heat-treated preferably has an area equal to or larger than the surface of the stretched film to be heat treated. This is because uniform heat treatment is performed.

  The number of heat treatment parts is not limited to one. For example, when heat treating a large film, the number of heating furnaces used as the heat treatment zone is increased to provide a plurality of heat treatment zones, each of which is provided with a heat treatment portion, and a plurality of heat treatment portions form a single temperature gradient. It is also possible to perform a heat treatment.

  In the present specification, the “point in the plane of the stretched film to be heat-treated” refers to a point included in a plane that receives heat radiation from the heat treatment portion among the faces of the stretched film.

  In addition, “a point in the plane of the stretched film to be heat-treated and close to the first clip located on the most upstream side of the film” (hereinafter referred to as “the point close to the first clip”). Is a clip that holds the stretched film to be heat-treated among the above points, and is close to the clip (first clip) located on the most upstream side in the film flow direction. Say point.

  As such a point, for example, a point in the film plane that is close to the clip 113a shown in FIG.

  Furthermore, “a point that is in the plane of the stretched film and is close to the second clip that is paired with the first clip” (hereinafter referred to as “a point that is close to the second clip”); Means a point close to the clip (second clip) that holds the long side edge opposite to the long side edge held by the first clip.

  As such a point, for example, a point in the film plane that is close to the clip 114a shown in FIG. 1 and inside the gripping portion of the clip 114a can be cited.

  Specifically, first, as the position in the flow direction, both “the point close to the first clip” and “the point close to the second clip” may be in the heat treatment zone. That is, the most upstream point is a point immediately after entering the heat treatment zone and a point close to the corresponding second clip, and the most downstream point is a point close to the second clip. "Is the point immediately before leaving the heat treatment zone and the point close to the corresponding first clip.

  In addition, as the position in the width direction, the “point close to the first clip” is the width direction end when winding up as a product roll after stretching (that is, the width after slitting if cut (slit) after stretching) Any position that falls within the range of 100 mm from 0 mm (that is, the end in the width direction of the product film) toward the inner side in the width direction with respect to the position that becomes the end in the direction) "Is a point included in the range from 0 mm to 100 mm inward in the width direction with reference to the end opposite to the" point close to the first clip ".

For example, as shown in FIG. 6, the “point close to the first clip” is drawn in the width direction from the center of the portion of the long edge of the film held by the clip 113 a to the inside of the film. Mention may be made of the end a of a perpendicular with a length of 100 mm.
However, the “point close to the first clip” is not limited to this. Since the long edge held by the clip is easily damaged, it is usually excised (slit). The above “100 mm” is an example set by the size of the cut-off portion.

  “A point that is close to the second clip and that is substantially the same temperature as the point that is close to the first clip” is, for example, the long edge that the second clip is holding. On the straight line connecting the points separated from the inner side of the film in the width direction at equal intervals (for example, 100 mm intervals) in parallel with the long edge, at equal intervals (for example, 100 mm intervals) in the flow direction from the boundary with the stretching zone It can be obtained by measuring the temperature of each point and selecting a point that is substantially the same as the temperature of the point close to the first clip.

  FIG. 6 shows a point a close to the first clip and a point close to the second clip in the stretched film heat-treated by the temperature region variable nozzle (heat treatment part) 115 by such a method. In addition, an example is shown in which a point near the first clip and a point b indicating substantially the same temperature are acquired, and a line segment connecting the point a and the point b is obtained.

  In the case of performing oblique stretching, the direction of the stress applied in the plane of the stretched film is determined by the slower clip among the paired clips entering the heat treatment zone. A line segment connecting a point close to the first clip and a point close to the second clip and showing a temperature substantially the same as the point close to the first clip. Is set in the optical axis direction of the film (a film having positive birefringence) by setting the temperature of the heat treatment part so as to be substantially parallel to the direction of the stress applied in the plane of the stretched film. Then, the temperature of the slow axis and the fast axis in the case of a film having negative birefringence are substantially uniform.

  Therefore, uniform heat treatment can be performed, and the obtained stretched film becomes a film excellent in optical characteristics such as phase difference accuracy and optical accuracy.

  The line segment can be obtained, for example, by approximating at least two set temperatures of a temperature control device provided in the heat treatment unit. For example, when the heat treatment section includes four temperature control devices, the set temperature of one set of temperature control devices is substantially the same, and the set temperature is substantially the same as that of the other set of temperature control devices. By making it higher than the set temperature, it can be obtained more easily.

  In FIG. 3, the heat treatment section includes four temperature control devices, the set temperatures of the set of temperature control devices A and C are substantially the same, and the set temperature is the other set of temperature control devices. It is a schematic diagram which shows the temperature area | region formed in a heat processing part, when it is higher than the substantially same preset temperature of B and D.

  When the set temperature of the temperature controller is set in this way, for example, a high temperature region and a low temperature region as shown in FIG. 3 are generated in the heat treatment section, and a temperature gradient is formed from the high temperature region toward the low temperature region. Since heat having this temperature gradient is applied to the stretched film by the heat treatment section, a temperature gradient corresponding to the temperature gradient is also formed on the film. As a result, it is possible to obtain a point that is close to the second clip and that exhibits substantially the same temperature as a point that is close to the first clip.

  In this specification, “substantially the same temperature” means that the temperature difference is in the range of ± 5 ° C., preferably in the range of ± 3 ° C., and in the range of ± 1 ° C. More preferably, the temperature difference is most preferably zero.

  For example, in Example 1, the set temperature of the temperature control devices A and B is 135 ° C., the set temperature of the temperature control devices C and D is 124 ° C., and the set temperature of the pair of temperature control devices A and B is the same. In addition, the set temperature is higher than the same set temperature of the other set of temperature control devices C and D.

  At this time, a temperature gradient from about 135 ° C. to about 124 ° C. is formed in the temperature region variable nozzle (heat treatment section) 115 of FIG. 1, and heat having the temperature gradient is irradiated to the stretched film.

  As a result, it is possible to obtain a point that is close to the second clip 114a and that has substantially the same temperature as a point that is close to the first clip 113a.

  In FIG. 1, the left clip group is obliquely stretched obliquely upward to the left by increasing the traveling speed of the left clip group than that of the right clip group. Therefore, the direction (stress application direction) in which the greatest stress is applied in the plane of the stretched film heat-treated by the temperature region variable nozzle (heat treatment section) 115 is substantially the same as the stretching direction of the stretched film. It is.

  In FIG. 1, in the plane of the stretched film existing in the heat treatment zone Z3, the stress application direction is a direction indicated by a dotted line from the right clip 113a toward the left clip 114a.

  The above-mentioned “stretching direction of the stretched film” refers to a stretching direction applied to the stretched film and is a direction determined after the stretching is completed. In FIG. 1, in the stretching zone Z2, oblique stretching is performed by increasing the speed of the left clip group 114 relative to the right clip group. For example, the direction of the dotted line from the right clip 113a to the left clip 114a is the stretching direction. . The stretching direction can also be represented by an angle from the long side direction (longitudinal direction) of the film.

  The stretching direction can be set in a desired direction in a heat stretching machine used for stretching the film. In addition, when the stretched film is heat-treated by the heat treatment section, the film shrinks. Therefore, the direction indicated by the largest stress applied to the stretched film may not completely match the stretching direction. Although there is a substantial match.

  Therefore, in the present specification and the drawings attached to the present specification, the stretching direction is regarded as the stress application direction. Thus, the stress application direction can be determined by determining the stretching direction.

  The direction of stress application in the stretched film is, in other words, the direction of the optical axis of the product (however, in the case of a film made of resin having positive birefringence, the direction of the slow axis, in the case of film made of resin having negative birefringence) Is the fast axis direction). For this reason, the stress application direction can be confirmed by a known optical axis measurement method.

  However, when the film is stretched, depending on the stretching conditions (particularly the temperature conditions), stress in the flow direction of the film is also added along with the bowing phenomenon. At this time, the optical axis is obtained in a state of being bowed on the upstream side of the film from the stretching direction of the stretched film (represented by the line segment connecting the clip 113a and the clip 114a in FIG. 1).

  FIG. 7 is a schematic diagram showing the direction of stress application in the stretched film in which the bowing phenomenon has occurred. In FIG. 7, the temperature region variable nozzle (heat treatment part) 115 and the preheating zone Z1 are not shown. In FIG. 7, the optical axis in the stretched film in which the bowing phenomenon occurs is obtained by connecting the values obtained by measuring the optical axis at a pitch of, for example, 50 mm in the width direction with a line from the center of the film existing in the heat treatment zone Z3. can get. The line is a line c shown in FIG.

  The point on the line c is substantially the same as the point a ′ close to the first clip 114a and the point close to the second clip 113a and close to the first clip 113a. The direction (the direction from a ′ to b ′) indicated by the line segment d connecting the point b ′ indicating the temperature of is the direction in which the greatest stress is applied when the bowing phenomenon occurs (stress application direction). Become.

  In FIG. 1, a gradation-like temperature gradient from approximately 135 ° C. to approximately 124 ° C. is formed in the temperature region variable nozzle (heat treatment section) 115 from the lower left to the upper right.

  A line segment connecting a point that is close to the first clip 113a and a point that is close to the second clip 114a and that is substantially the same temperature as the point close to the first clip. Is controlled in parallel with the stress application direction obtained as a line segment connecting the first clip 113a and the second clip 114a, the temperature control devices A, B, C, Set the temperature of D.

  The temperature setting is a point that is close to the first clip 113a and a point that is close to the second clip 114a and a point that is substantially the same temperature as the point close to the first clip. The set temperature may be changed as appropriate until the line segment is parallel to the stress application direction.

  When irradiating heat from the temperature control devices A, B, C, and D of the temperature region variable nozzle (heat treatment section) 115 to the point close to the first clip 113a and the point close to the second clip 114a, A temperature gradient is formed inside the temperature region variable nozzle (heat treatment part) 115 by the heat irradiated from the adjusting devices A, B, C, and D.

  A hole serving as a heat outlet is opened with a punching metal or the like on the surface of the box-shaped temperature range variable nozzle (heat treatment portion) 115 facing the stretched film to be heat treated, and the first clip 113a. And the temperature of the heat applied to the point close to the first clip 113a and the point close to the second clip 114a from the hole corresponding to the point close to the second clip 114a. Measured with a thermocouple provided adjacent to the hole.

  As a result, a line connecting a point that is close to the first clip 113a and a point that is close to the second clip 114a and that is substantially the same temperature as the point close to the first clip. The minute can be easily made substantially parallel to various stress application directions.

  That is, even when the stress application direction is changed, by changing the temperature setting of the temperature control device provided in the heat treatment unit, the point close to the first clip and the point close to the second clip And the line segment which connected the point which adjoins the said 1st clip, and the point which shows substantially the same temperature can be made substantially parallel to a stress addition direction easily.

  The degree of proximity of the point close to the first clip 113a and the point close to the second clip 114a to the first clip and the second clip is the line segment connecting these points. What is necessary is just to be close to the 1st clip 113a and the 2nd clip 114a, respectively, to such an extent that it can be parallel to the stress application direction.

  As described above, the stretched film is heat-treated from the upstream side to the downstream side of the film by the temperature gradient formed by the above-described line segment substantially parallel to the stress application direction. In other words, the heat treatment is performed in a state where the stress application direction and the temperature gradient direction (the direction from the high temperature region to the low temperature region) are substantially orthogonal to each other.

  In this specification, “substantially parallel” and “substantially orthogonal” may include a parallel state or a state shifted by 10 ° from an orthogonal state. If it is this range, it can heat-process, without impairing the optical characteristic of the stretched film obtained.

  As described above, a point that is close to the first clip, a point that is close to the second clip, and a point that is substantially the same temperature as the point that is close to the first clip. The stretched film has a positive phase difference by performing heat treatment so that the connected line segments are substantially parallel to the direction in which the largest stress is applied in the plane of the stretched film (stress application direction). In this case, the direction of the optical axis is substantially orthogonal to the direction of the line segment, and when the phase difference is negative, the direction of the optical axis is substantially parallel to the direction of the line segment.

  As a result, the temperature in the direction of the optical axis of the film (slow axis for a film having positive birefringence, and fast axis for a film having negative birefringence) is almost uniform, so uniform heat treatment should be performed. The stretched film obtained can be a film excellent in optical properties such as retardation accuracy and optical accuracy.

  In addition, although the case where the temperature control apparatus with which a heat processing part is provided was demonstrated so far so far, the number of temperature control apparatuses is not restricted to this.

  Although not shown, for example, (1) In addition to the temperature control apparatuses A to D in FIG. 1, temperature control apparatuses are also installed at the four corners of the heat treatment zone Z3, and the entire heat treatment zone Z3 is used as a heat treatment section, (2) Instead of providing the heat treatment section 115, a mode in which temperature control devices are installed only at the four corners of the heat treatment zone Z3, (3) a mode in which more than four temperature control devices are arranged in the array at regular intervals in the heat treatment unit 115, etc. Is possible.

  Especially, since the aspect of said (1) can form a temperature gradient in the heat processing zone Z3 whole, it is more preferable.

  According to the method for producing the stretched film, as described above, the temperature gradient formed by the line segment substantially parallel to the stress application direction from the upstream side to the downstream side of the film by forming the temperature gradient in the heat treatment section. Can be heat-treated. Therefore, the above method can be suitably used particularly for a stretched film that is obliquely stretched.

  However, the present invention is not limited to this, and the present invention can also be applied to a stretched film stretched in the longitudinal direction of the film and / or in the transverse direction of the film.

  Since the manufacturing method of this stretched film uses the heat processing part which can form a temperature gradient, the preset temperature of the temperature control apparatus with which a heat processing part is provided can be changed suitably. For example, when all set temperatures of the temperature control device provided in the heat treatment unit capable of forming a temperature gradient are the same, the temperature gradient is not formed.

  However, even in this case, a point close to the first clip, a point close to the second clip, and a point showing substantially the same temperature as the point close to the first clip It is possible to make the connected line segment and the stress application direction of the stretched film in the plane to be heat-treated by the heat treatment part substantially parallel.

  Therefore, using the same heat treatment part, not only the obliquely stretched film but also the stretched film stretched in the longitudinal direction of the film and / or in the lateral direction of the film can be subjected to heat treatment.

  That is, the production method of the stretched film is stretched not only in the obliquely stretched film but also in the longitudinal direction of the film and / or in the lateral direction of the film without changing the heat stretching apparatus according to the type of stretching. It can be said that this is a highly versatile method that can also be applied to stretched films.

  The strip-like retardation film obtained in the method for producing the stretched film 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.

  When a belt-like retardation film is produced by the method for producing a stretched film, for example, the retardation film and the belt-like polarizing film can be continuously laminated (as a more specific example, the film can be laminated by roll-to-roll). Therefore, an elliptically polarizing plate can be manufactured efficiently. The production method of the stretched film may include any step other than those described above as long as the effect of the present invention is obtained.

<2. Original film>
The original film used in the production method of the present invention is usually composed of a thermoplastic resin composition. The thermoplastic resin composition (A) constituting the original film preferably contains a polymer (B) having a ring structure in the main chain.

  That is, the original film used in the production method of the present invention is preferably composed of a 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. Further, depending on the type of the ring structure, it has an effect of increasing the retardation in the obtained retardation film.

  The content of the polymer (B) in the resin composition (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 (meth) acrylic polymers, cycloolefin polymers, and cellulose derivatives. The (meth) 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 based on all structural units.

  However, when the (meth) acrylic polymer includes a ring structure that is a derivative of a (meth) acrylic acid ester unit, the content of the ring structure is also included in the content of the (meth) acrylic acid ester 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. 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 a (meth) acrylic polymer. The (meth) acrylic polymer has high transparency and excellent mechanical properties such as surface strength. For this reason, by using a (meth) acrylic polymer, a retardation film suitable for use in an image display device such as an LCD can be obtained.

The ring structure that the (meth) acrylic polymer may have in the main chain is, for example, a ring structure having an ester group, an imide group, or an acid anhydride group. The ring structure has the ring structure in the main chain (
It preferably has an action of imparting positive intrinsic birefringence to the (meth) acrylic polymer.

More specifically, the ring structure is a lactone ring structure, a glutarimide structure, or a glutaric anhydride structure. Since the (meth) acrylic polymer having such a ring structure in the main chain has a large positive intrinsic birefringence, it is suitable for use in a retardation film.

  The ring structure is preferably a lactone ring structure and / or a glutarimide structure, and more preferably a lactone ring structure. When the (meth) acrylic polymer has such a ring structure (particularly, a lactone ring structure) in the main chain, the wavelength dispersion of retardation caused by orientation is particularly small. Further, depending on the combination with the polymer having negative intrinsic birefringence, the degree of freedom in controlling the wavelength dispersion in the obtained retardation film is improved.

  The lactone ring structure is not particularly limited, and for example, is a structure represented by the following formula (1).

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

The organic residue 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 aliphatic hydrocarbon group having 1 to 20 carbon atoms such as an ethenyl group or a propenyl group; a phenyl group; An aromatic hydrocarbon group having 1 to 20 carbon atoms such as a naphthyl group; one or more hydrogen atoms in the alkyl group, the unsaturated aliphatic hydrocarbon group, or the aromatic hydrocarbon group are a hydroxyl group, a carboxyl group, or an ether A group substituted by at least one group selected from a group and an ester group.

The lactone ring structure represented by the formula (1) is obtained by copolymerizing a monomer group including, for example, methyl methacrylate (MMA) and 2- (hydroxymethyl) methyl acrylate (MHMA), It can be formed by subjecting adjacent MMA units and MHMA units in the coalescence to dealcoholization cyclocondensation. At this time, R ¹ is H, R ² is CH ₃ , and R ³ is CH ₃ .

In the (meth) acrylic polymer having a ring structure in the main chain, the content of the ring structure is not particularly limited, but is usually 5 to 90% by weight, preferably 20 to 90% by weight, and 30 to 90% by weight.
Is more preferred, 35 to 90% by weight is more preferred, 40 to 80% by weight and 45 to 7%.
5% by weight is particularly preferred. The content of the ring structure in the (meth) acrylic polymer can be determined by the method described in JP-A No. 2001-151814.

The original film may be a single layer film or a laminated film. As needed, functional layers, such as a hard-coat layer, an easily bonding layer, and an antistatic layer, may be provided in the one or both surfaces of the original film. The original film is usually an unstretched film, but may be a stretched film.

The method for producing the original film is not particularly limited. For example, known methods such as a solution casting method (solution casting method, cast molding method), a melt casting method (melt extrusion method, extrusion molding method), and a press molding method are known. It can be manufactured by a technique. Among these, the melt film forming method is preferable from the viewpoint of low environmental load and excellent productivity.

<3. Retardation film>
The stretched film produced by the method for producing a stretched film is preferably a retardation film. The specific configuration of the retardation film is not particularly limited. For example, the film may be stretched in the longitudinal direction and / or stretched in the lateral direction.

  Especially, it is preferable that it is a phase difference film in which the slow axis in the film plane inclined 10 degrees-80 degrees with respect to the longitudinal direction of the said film. Moreover, it is preferable that it is a phase difference film which has the orientation angle with respect to the width direction of a film in the range of 45 degrees ± 10 degrees.

  In other words, it is preferable that the in-plane slow axis of the retardation film is inclined by approximately 45 ° (45 ° ± 10 °) with respect to the longitudinal direction of the film. Such a retardation film is preferable because it can be used as an elliptically polarizing plate in combination with a polarizing film, for example, as a quarter wavelength plate (λ / 4 plate).

  The thickness of the retardation film 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 is preferably 85% or more, more preferably 90% or more, and still more 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 total light transmittance is a measure of transparency, and if it is less than 85%, the transparency is lowered and it is not suitable as an optical film.

  The glass transition temperature (Tg) of the retardation film 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.

  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.

  The in-plane retardation Re for light with a wavelength of 589 nm in the retardation film obtained by the method for producing the stretched film is preferably 20 to 500 nm.

  The in-plane retardation Re can be controlled by the stretching conditions of the original film. The in-plane retardation Re can be appropriately determined according to the use of a retardation film such as a quarter-wave plate or a half-wave plate.

  The in-plane retardation Re is expressed by the formula (nx−ny), where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and d is the thickness of the film. ) × d.

  The retardation film obtained by the production method of the stretched film 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.

  The present invention is not limited to the configurations described above, and various modifications can be made within the scope described in the specification, and implementations obtained by appropriately combining technical means disclosed in different embodiments. The form is also included in the technical scope of the present invention.

  Moreover, all the literatures described in this specification are used as reference. EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited only to this Example.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples. First, the evaluation method of the resin produced in this example will be described below.

<Glass transition temperature (Tg)>
The Tg of the resin was determined in accordance with JIS K7121 regulations. 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 conversion using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement are as follows.
System: Tosoh GPC system HLC-8220
Measurement side column configuration;
Guard column: Tosoh TSKguardcolumn SuperHZ-L
-Separation column: Tosoh TSKgel SuperHZM-M 2 series connection reference side column configuration;
Reference column: Tosoh TSKgel SuperH-RC
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade)
Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Column temperature: 40 ° C
<Phase difference>
The in-plane retardation Re, the thickness direction retardation value Rth, and the optical axis direction of the retardation film at a wavelength of 589 nm were measured using RETS-100 manufactured by Otsuka Electronics Co., Ltd.

  Regarding the thickness direction retardation value Rth (nm), the average refractive index of the film measured with an Abbe refractometer, the film thickness d, the retardation value measured by tilting by 40 ° (Re (40 °)), and the three-dimensional refraction. After obtaining the values of the rates nx, ny, and nz, the values were obtained from the formula d × {(nx + ny) / 2−nz}. The refractive index in the flow direction of the film was nx, the refractive index in the width direction of the film was ny, and the refractive index in the thickness direction of the film was nz.

  The film thickness d was measured using a Digimatic micrometer (Mitutoyo). The tilt direction is measured by measuring Re (S40 °) with the slow axis as the tilt axis and Re (F40 °) with the fast axis as the tilt axis, and Re (S40 °)> Re (F40 °). In this case, the slow axis was the tilt axis, and conversely, when Re (S40 °) <Re (F40 °), the fast axis was the tilt axis.

  Moreover, the uniaxial stretchability of the retardation film was evaluated by the NZ coefficient (NZ = | Rth | / | Re (590) | +0.5). Further, the slow axis when the film was cut perpendicularly to the flow direction of the roll film, the cut edge was aligned with the reference bar of the RETS-100, and the sample was set so that the reference axis did not shake was measured. Was the direction of the optical axis (the direction of the slow axis in the film plane).

  The direction of the optical axis is 0 ° for the film flow direction and 90 ° for the width direction. When viewed from the upstream side to the downstream side, the clockwise direction is “+” and the counterclockwise direction is “−”. Expressed as an angle from the direction (long side direction of the film, vertical direction).

  Optical axis accuracy, that is, unevenness (variation) in the direction of the optical axis is measured in the direction of the optical axis at a pitch of 50 mm, with the center portion 300 mm in the width direction strip-shaped film sample cut out from the obtained film roll as the measurement region, The difference between the maximum and minimum measured values was taken. If this difference was 1 ° or less, it was considered acceptable. Moreover, the average value (center value) of the measured values was also obtained.

  Regarding the phase difference accuracy, that is, in-plane retardation unevenness (variation), the in-plane phase difference is measured at a pitch of 50 mm using the center portion of 300 mm as a measurement region, and the difference between the maximum value and the minimum value of the measured value is determined. The phase difference accuracy was assumed. If this difference was 5 nm or less, it was judged as acceptable. Moreover, the average value (center value) of the measured values was also obtained.

<Production Example 1>
40 parts by weight of methyl methacrylate (MMA), 10 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA), antioxidant in a reaction vessel equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introduction pipe 0.025 parts by weight of tris (2,4-di-t-butylphenyl) phosphite (manufactured by ADEKA, trade name: ADK STAB 2112), and 50 parts by weight of toluene as a polymerization solvent were charged with nitrogen. The temperature was raised to 105 ° C.

  When refluxing with a rise in temperature started, 0.05 parts by weight of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator, and 0.10 parts by weight of While the above t-amyl peroxyisononanoate was added dropwise over 2 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by further aging for 4 hours.

  Next, 0.05 parts of 2-ethylhexyl phosphate (product name: Phoslex A-8) manufactured by Sakai Chemical Co., Ltd. was added to the resulting polymer solution, and cyclization condensation was performed at 90 to 105 ° C under reflux for 2 hours. Reaction was performed.

  Next, the obtained polymer solution was heated to 240 ° C. through a heat exchanger, barrel temperature 240 ° C., degree of vacuum 13.3 to 400 hPa (10 to 300 mmHg), rear vent number 1 and fore vent number 4 A side feeder is provided between the third vent and the fourth vent (referred to as the first, second, third, and fourth vents from the upstream side), and a leaf disk type polymer filter (filtered at the tip) It was introduced into a vent type screw twin screw extruder (L / D = 52) with a precision of 5 μm) at a processing rate of 70 parts / hour in terms of resin amount, and devolatilization was performed.

  At that time, a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator was added at a rate of 1.05 parts / hour from the back of the first vent, and 1.05 parts / hour of ion-exchanged water. Were charged from the back of the second and third vents, respectively.

  As a mixed solution of an antioxidant / cyclization catalyst deactivator, 5 parts of an antioxidant (Ciba Japan, Irganox 1010) and 55 parts of zinc octylate (manufactured by Nippon Chemical Industry, (Nikka octix zinc 3.6%) in 45 parts of toluene was used.

  From the side feeder, pellets of a styrene-acrylonitrile copolymer (the ratio of styrene / acrylonitrile is 73% by mass / 27% by mass, weight average molecular weight 220,000) were added at a charging rate of 30 parts / hour.

  By the devolatilization operation, pellets of a thermoplastic resin composition (1A) containing an acrylic polymer having a lactone ring structure in the main chain and a styrene-acrylonitrile copolymer and having negative intrinsic birefringence were obtained. In addition, the weight average molecular weight of the obtained resin composition was 146000, the glass transition temperature was 122 degreeC, and the melt flow rate was 13.6 g / 10min.

  Next, the obtained resin (1A) pellets were melt-extruded at 270 ° C. using a single-screw extruder equipped with a polymer filter (filtration accuracy 5 μm) and a T-die at the tip, and a 200 μm-thick original film (1F) was wound. I took it.

<Example 1>
In Example 1, as shown in FIG. 1, a heating furnace in which a preheating zone Z1, a stretching zone Z2, and a heat treatment zone Z3 are set in order from the upstream side to the downstream side in the flow direction of the original film indicated by arrows in the drawing. The tenter transverse stretching machine 100 provided was used.

  In the heat treatment zone Z3 of the tenter transverse stretching machine 100, a temperature region variable nozzle (heat treatment part) 115 provided with temperature control devices A, B, C, D was installed. And after extending | stretching the unstretched film (1F) produced by manufacture example 1 on the conditions shown in Table 1 using the said tenter horizontal extending | stretching machine 100, it introduce | transduced into heat processing zone Z3 and heat-processed.

  The lengths of the preheating zone Z1, the stretching zone Z2, and the heat treatment zone Z3 in the longitudinal direction (moving direction of the original film) were all 2 m.

  In the preheating zone Z1 and the heat treatment zone Z2, stretching in the width direction was not performed, but fine adjustment of expansion / contraction for the purpose of eliminating the slackness of the original film by heating and adjusting the shrinkage stress generated in the film during cooling was performed. This fine adjustment was also performed in the following examples and comparative examples.

  In Example 1-1, lateral stretching was performed at a magnification of 1.5 times without providing a difference in moving speed between the left and right clips. In this specification, the left clip refers to the left clip when viewed from the upstream side in the film flow direction, and the right clip refers to the right clip as viewed from the upstream side to the downstream side.

  In Example 1-2, while giving a speed difference of 7% to the moving speed of the left and right clips, diagonal stretching was performed by performing lateral stretching at a magnification of 1.3 times. The speed difference was given by setting so that the left rail travels faster when viewed from the upstream side.

  In Table 1, “Temperature condition of heat treatment zone” indicates the setting of hot air introduced into the heat treatment section from the temperature control devices A, B, C, D provided in the temperature region variable nozzle (heat treatment section) 115 as shown in FIG. Indicates temperature. The temperature conditions of the preheating zone and the stretching zone indicate the set temperatures inside the preheating zone Z1 and the stretching zone Z2, respectively.

  Table 2 shows the optical properties of the stretched film obtained under the conditions shown in Table 1.

  As shown in Table 2, the obtained stretched film was very excellent in both phase difference accuracy and optical axis accuracy. That is, according to the method of the present invention, an accurate retardation film can be obtained both when lateral stretching is performed (Example 1-1) and when oblique stretching is performed (Example 1-2). I understand.

  In Example 1-2, the temperature range based on the temperature condition of the heat treatment zone shown in Table 1, that is, the set temperature of hot air introduced into the temperature range variable nozzle (heat treatment section) 115 from the temperature control devices A, B, C, and D. A temperature gradient is formed in the variable nozzle (heat treatment part) 115.

  The temperature gradient is the direction in which the greatest stress is applied in the plane of the heat treated stretched film, the point close to the first clip 113a, the point close to the second clip 114a, and The temperature setting is selected and formed so that the line connecting the point close to the first clip 113a and the line showing the substantially same temperature is substantially parallel.

  As a result, in the stretched film that has been heat-treated, when the retardation of the film is positive, the direction of the optical axis is substantially orthogonal to the direction of the line segment, and when the phase difference is negative, the direction of the optical axis is the line segment. It becomes substantially parallel to the direction. Therefore, it is considered that an accurate retardation film can be obtained.

  In Example 1-1, the set temperature of the temperature control device is changed from that in Example 1-2, and the temperature gradient used in Example 1-2 is not formed. Stretching is performed.

  In other words, from the results of Example 1, the method for producing the stretched film is a complicated operation such as changing the installation location of the winder every time the stretching conditions are changed, only by adjusting the temperature setting of the heat treatment section. It can be seen that the present invention can be applied to both oblique stretching and lateral stretching without performing the process, and the accuracy of the optical characteristics in the width direction of the film can be improved.

<Comparative Example 1>
In Comparative Example 1, unlike the tenter transverse stretching machine used in Example 1, stretching was performed under the temperature conditions shown in Table 3 using a tenter transverse stretching machine (not shown) that does not include a heat treatment section. Otherwise, the unstretched film (1F) produced in Production Example 1 was stretched by the same method as in Example 1. Table 4 shows the optical properties of the obtained stretched film.

  The tenter transverse stretching machine used here is a film width such as the nozzle 116 shown in the heat treatment zone Z3 of FIG. 4 in place of the temperature region variable nozzle (heat treatment part) 115 shown in FIG. 1 in the heat treatment zone. A stretching machine having nozzles arranged in a direction.

  As shown in Table 4, with respect to the lateral stretching (Comparative Example 1-1), both the phase difference accuracy and the optical axis accuracy were good. If this is transverse stretching, the hot air blowing direction and the direction of the largest stress applied to the stretched film substantially coincide (substantially parallel) without adjusting the temperature gradient in the heat treatment zone. )

  On the other hand, when oblique stretching (Comparative Example 1-2) was performed, both the phase difference accuracy and the optical axis accuracy were poor. This is because in the above-mentioned tenter transverse stretching machine, in the heat treatment zone, the blowing direction of hot air and the direction of stress applied to the stretched film are not parallel, and thus the film cannot be uniformly heat treated. It is believed that there is.

<Example 2>
FIG. 2 is a top view showing a state in which a film is stretched obliquely using a simultaneous biaxial stretching machine in which temperature range variable nozzles having four temperature control devices are installed in the heat treatment zone.

  In Example 2, as shown in FIG. 2, the preheating zone Z1 (length 1.6 m) and the pre-stage stretching zone Z2A (length 2 m) are sequentially arranged from the upstream side to the downstream side in the flow direction of the original film indicated by the arrows. In the heat treatment zone Z3 of the simultaneous biaxial stretching machine 200 provided with a heating furnace in which a subsequent drawing zone Z2B (length 2 m) and a heat treatment zone Z3 (length 2 m) are set, temperature control devices A, B, C, and D The temperature region variable nozzle (heat treatment part) 115 provided was installed. In addition, the same member number as FIG. 1 is attached | subjected to the same member as the tenter transverse stretching machine 100 shown in FIG.

  Then, using the simultaneous biaxial stretching machine 200, the unstretched film (1F) produced in Production Example 1 was stretched under the temperature conditions shown in Table 5 and the stretching conditions shown in Table 6.

  In Table 5, “Temperature condition of heat treatment zone” indicates a set temperature of hot air introduced into the heat treatment section from the temperature control devices A, B, C, and D provided in the heat treatment section as shown in FIG. Further, the temperature conditions of the preheating zone and the stretching zone indicate the set temperatures inside the preheating zone Z1, the front stretching zone Z2A, and the rear stretching zone Z2B, respectively.

  The column “Total” in Table 6 shows a value obtained by multiplying the magnification in the former drawing zone by the magnification in the latter drawing zone in each of the left clip magnification, the right clip magnification, and the transverse draw magnification.

  The “clip magnification” is a value indicating how many times the clip traveling speed is the traveling speed in the immediately preceding zone. For example, “1.50 times” in the front stretching zone of the left clip magnification in Table 6 is a speed of 1.50 times the traveling speed in the preheating zone Z1, which is the immediately preceding zone, in the front stretching zone Z2A. Indicates traveling.

  Under the stretching conditions of Example 2-2 shown in Table 6, the traveling speed of the right clip decreases in the previous stretching zone Z2A until it becomes 0.67 times (1 / 1.50 times) before entering the zone. (The interval between adjacent clips is 0.67 times), and in the rear-stage stretching zone Z2B, it is 1.50 times that when moving from the front-stage stretching zone Z2A (the distance between adjacent clips is also 1. 50 times).

  The product (total value) of these numerical values is 1.00 times. That is, the right clip is decelerated in the former drawing zone Z2A and then recovered to the original traveling speed in the latter drawing zone Z2B (the interval between adjacent clips has been restored).

  On the other hand, the traveling speed of the left clip is not actively changed through the front drawing zone Z2A and the rear drawing zone Z2B. That is, the interval between adjacent clips in the left clip is substantially constant throughout the front drawing zone Z2A and the rear drawing zone Z2B.

  Table 7 shows the optical properties of the stretched films obtained under the conditions shown in Tables 5 and 6.

  As shown in Table 7, the obtained stretched film was very excellent in both phase difference accuracy and optical axis accuracy. That is, according to the method of the present invention, it is possible to obtain a retardation film with high accuracy both in the case of performing transverse stretching (Example 2-1) and in the case of performing oblique stretching (Example 2-2). I understand that I can do it.

  Similar to Example 1, in Example 2-2, the temperature gradient formed in the heat treatment part is the direction in which the greatest stress is applied in the plane of the heat treated stretched film, and the first clip 113a. The adjacent points and the line segments connecting the points that are close to the second clip 114a and have the same temperature as the close points to the first clip 113a are substantially parallel to each other. Since it was formed based on such temperature setting, it is considered that a highly accurate retardation film could be obtained for the obliquely stretched film.

  In addition, as in Example 1, the method for producing the stretched film requires only complicated adjustments such as changing the installation location of the winder every time the stretching conditions are changed, only by adjusting the temperature setting of the heat treatment section. It can be seen that the present invention can be applied to both oblique stretching and lateral stretching without performing the process, and the accuracy of the optical characteristics in the width direction of the film can be improved.

<Comparative example 2>
In Comparative Example 2, unlike the simultaneous biaxial stretching machine 200 used in Example 2, a simultaneous biaxial stretching machine (not shown) that does not include the temperature region variable nozzle (heat treatment section) 115 is used. Drawing was performed under the temperature conditions shown. Otherwise, the unstretched film (1F) produced in Production Example 1 was stretched by the same method as in Example 2. Table 9 shows the optical properties of the obtained stretched film.

  In addition, the simultaneous biaxial stretching machine used here is not the temperature region variable nozzle (heat treatment part) 115 shown in FIG. 2 in the heat treatment zone, but the film 116 like the nozzle 116 shown in the heat treatment zone Z3 of FIG. It is a drawing machine having nozzles arranged in the width direction.

  As shown in Table 9, regarding the lateral stretching (Comparative Example 2-1), both the phase difference accuracy and the optical axis accuracy were good. In the case of lateral stretching, the hot air blowing direction and the stress application direction in the plane of the stretched film to be heat-treated substantially coincide with each other without adjusting the temperature gradient in the heat treatment zone (approximately parallel). )

  On the other hand, when oblique stretching (Comparative Example 2-2) was performed, both the phase difference accuracy and the optical axis accuracy were poor. This is because, in the simultaneous biaxial stretching machine, since the blowing direction of hot air and the direction of stress applied to the stretched film are not parallel in the heat treatment zone, the film cannot be uniformly heat treated. It is thought that.

  In Example 2 using the simultaneous biaxial stretching machine having the temperature region variable nozzle (heat treatment part) 115, the temperature gradient of the region through which the stretched film passes in the heat treatment part is represented by temperature control devices A and B (set temperature). The temperature gradient decreases from the peripheral region of 130 ° C. toward the peripheral region of the temperature control devices C and D (set temperature 70 ° C.).

  And the said temperature gradient is substantially corresponded with the stress application direction in the surface of the film which passes a heat processing part. Therefore, since the entire film passing through the heat treatment part can be uniformly heat treated, it is considered that excellent optical characteristics as shown in Table 7 are exhibited.

  According to the present invention, since the optical axis of the stretched film can be uniformly heat-treated, a stretched film having excellent optical properties can be obtained. Therefore, the present invention can be suitably used for applications such as image display devices such as LCDs and organic EL displays.

DESCRIPTION OF SYMBOLS 100 ... Tenter lateral stretching machine 113 ... Right side clip group 113a ... First clip 114 ... Left side clip group 114a ... Second clip 115 ... Temperature region variable nozzle (heat treatment part)
200 ... Simultaneous biaxial stretching machine A, B, C, D ... Temperature controller Z1 ... Preheating zone Z2 ... Drawing zone Z2A ... Pre-stage stretching zone Z2B ... Post-stage stretching zone Z3 ... Heat treatment zone

Claims (6)

A method for producing a stretched film comprising a heat treatment step of heat treating a stretched film using a heat treatment part capable of forming a temperature gradient,
The stretched film is gripped on both long edges by a pair of clips each composed of a plurality of clips,
The heat treatment step is in the plane of the stretched film to be heat treated, in the vicinity of the first clip located on the most upstream side of the film, and in the plane of the stretched film to be heat treated. A line segment connecting a point that is close to the second clip that is paired with the first clip and that is substantially the same temperature as a point that is close to the first clip. Is performed after setting the temperature of the heat treatment part so as to be substantially parallel to the direction in which the largest stress is applied in the plane of the stretched film.   The method for producing a stretched film according to claim 1, wherein the heat treatment section includes at least four temperature control devices.   The heat treatment section includes four temperature control devices, the set temperature of one set of temperature control devices is substantially the same, and the set temperature is substantially the same set temperature of the other set of temperature control devices. It is higher than this, The manufacturing method of the stretched film of Claim 1 or 2 characterized by the above-mentioned.   The method for producing a stretched film according to any one of claims 1 to 3, wherein the stretched film is stretched in the longitudinal direction of the film and / or in the transverse direction of the film. .   The method for producing a stretched film according to any one of claims 1 to 4, wherein the stretched film is stretched obliquely with respect to the longitudinal direction of the film. The method for producing a stretched film according to any one of claims 1 to 5, wherein the heat treatment is performed by keeping the stretched film at a stretching temperature or lower.

Images