JP4511876B2 - Method for producing retardation film - Google Patents

Description

The present invention relates to a method for producing a retardation film having a high retardation value used for a liquid crystal display device and having excellent uniformity in a film plane.

  In recent years, liquid crystal display devices have been widely used in place of CRTs of cathode ray tubes. In this type of liquid crystal display device, a retardation film and a polarizing plate are bonded to a liquid crystal cell in which an electrode enclosing liquid crystal molecules is incorporated. A liquid crystal display device performs display using the birefringence of liquid crystal, but a retardation film is used to prevent a coloring phenomenon of a display viewed through a polarizing plate. This type of retardation film is required to have various optical characteristics such as viewing angle characteristics depending on the application. For this reason, the in-plane retardation value (hereinafter referred to as “Re”) is generally in the range of 50 to 800 nm. Is required.

  The retardation film is generally produced by uniaxially stretching a thermoplastic resin film. If the film temperature or stretching speed during uniaxial stretching is unstable or inappropriate, a retardation film having a desired retardation (retardation) value cannot be obtained, or the molecular main chain of the thermoplastic resin is Various stretching methods have been studied because they do not align in a certain direction and the optical axis varies, resulting in display unevenness when used in a liquid crystal display device.

  Examples of the uniaxial stretching method include a lateral uniaxial stretching method in which a tenter is widened and stretched in a transverse direction, a longitudinal uniaxial stretching method in which a speed difference in the length direction of a tenter clip is utilized, and a roll-to-roll longitudinal direction in which a circumferential speed difference of a roll is utilized. A uniaxial stretching method is known. In particular, the transverse uniaxial stretching method using a tenter has advantages in that it is easier to control than the longitudinal uniaxial stretching method described above, variation in stretching is small, and a high retardation value can be obtained.

  However, in the transverse uniaxial stretching method using a tenter, a unique phenomenon is observed in which the stretching of the central portion of the film is preceded or delayed without being synchronized with the end portion. Therefore, a so-called bowing phenomenon occurs in which the molecular main chain orientation with respect to the film width direction takes a bow-like distribution, and the molecular main chain of the film is not well oriented in the direction of the stretching axis, causing an optical axis shift, and in the width direction. It is difficult to obtain a uniform optical axis. In a liquid crystal display device using such a retardation film, defects such as display unevenness occur, and the original function of the retardation film is impaired.

  In order to solve the above problems, Patent Document 1 discloses that when a thermoplastic resin film is horizontally uniaxially stretched in the width direction by a tenter, the transverse uniaxial stretching process is multistaged, and the rail opening angle of the tenter is set to 5 degrees. By making it within the range, a method for manufacturing an optical compensation film is proposed in which the bowing phenomenon is controlled, the variation in the optical axis angle distribution is reduced, and the uniformity in the film plane is excellent.

  However, the so-called slow stretching trajectory within the above-mentioned proposed rail opening angle within 5 degrees cannot set the stretching deformation per unit time high, so that a high stretching strain rate is imparted and a high internal stress remains in the film structure. This is contrary to the principle of phase difference. Therefore, a high in-plane retardation value cannot be obtained, and variations in the optical axis angle distribution are not sufficiently small.

Further, in the above proposed method, the rail opening angle is set to 5 degrees or less, so that a long stretch drawing process is required to obtain an optical compensation film having a high draw ratio, resulting in a tenter having a long heating zone. A drawing machine is required and the equipment becomes excessive, which is not practical.
JP 2002-148437 A

The present invention solves the above-mentioned problems, and the object of the invention is to provide a retardation value having a high in-plane retardation value and having a uniform optical axis substantially parallel to the width direction of the film. It is providing the manufacturing method of the practical phase difference film for obtaining a film.

  As a result of intensive studies to achieve the above object, the present inventor has produced a conventional retardation film in which a substantially non-oriented amorphous resin film is uniaxially stretched in the width direction by a tenter and then heat treated immediately. In the method, it is found that the above-mentioned object is achieved by specially providing a specific deformation region in which the stretched film is reduced in width or width in the width direction in the conventional stretching process, and the present invention is completed. It came to.

  That is, the first invention is a method for producing a retardation film in which a substantially non-oriented amorphous resin film is uniaxially stretched in the width direction by a tenter, and is from the start of widening to the completion of widening in the stretching step. Are provided with a low widening or low relaxation region, the deformation speed V1 (% / min) in the film width direction in the region is −10 ≦ V1 ≦ + 10, and the film transit time T (seconds) in the region is 2 < T <10, and the relationship between the stretching strain rate V2 (% / min) in the film width direction before the region and the stretching strain rate V3 (% / min) in the film width direction after the region is 300 ≦ V2 <V3. It is a manufacturing method of retardation film characterized by satisfying.

Hereinafter, “low widening or low relaxation region” is abbreviated as “low distortion region”.
The amorphous resin constituting the amorphous resin film in the present invention is excellent in transparency, heat resistance, moisture resistance and matching with liquid crystal, low in intrinsic birefringence, low in photoelastic coefficient, etc. There is no particular limitation as long as it is a thermoplastic resin that has suitable characteristics as a member and has substantially no crystallinity. For example, cyclic olefin resin and maleimide resin are mentioned. Among the cyclic olefin resins, a norbornene resin is particularly preferably used, and among the maleimide resins, an olefin-maleimide copolymer is particularly preferably used.

  The norbornene-based resin is a resin that has been conventionally used for films for optical applications. For example, (i) a ring-opening (co) polymer of a norbornene-based monomer or a hydrogenated product of this ring-opening (co) polymer (B) an addition copolymer of a norbornene monomer and an olefin monomer, and (c) an addition copolymer of norbornene monomers. These norbornene resins may be used alone or in combination of two or more.

  The norbornene-based monomer used for the production of the norbornene-based resin is not particularly limited as long as it has a norbornene ring. For example, a bicyclic ring such as norbornene or norbornadiene; Tetracycles such as cyclododecene; pentacycles such as cyclopentadiene trimer; heptacycles such as tetracyclopentadiene; alkyl such as methyl, ethyl, propyl and butyl, alkenyl such as vinyl, and ethylidene Substitutes such as aryls such as alkylidene, phenyl, tolyl, naphthyl, etc .; furthermore, these ester groups, ether groups, cyano groups, halogen atoms, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carboxylic acid groups, amino groups, non-hydroxyl groups, silyls Group, epoxy group, acrylic group, methacryl group, etc. Groups containing elements other than carbon and hydrogen, substitution products having a so-called polar group.

  Among these norbornene-based monomers, those which are easily available, excellent in reactivity, and excellent in heat resistance of the obtained retardation film are preferable. Therefore, polycyclic norbornene-based monomers having three or more rings are preferable. A cyclic, tetracyclic, or pentacyclic norbornene-based monomer is more preferable. In addition, a norbornene-type monomer may be used independently and 2 or more types may be used together.

  Examples of the olefin monomer to be copolymerized include ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-pentene, 1 -Hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like. In particular, an olefin monomer having 2 to 10 carbon atoms having high copolymerization property is preferable, and ethylene is more preferable. When other olefin monomers are copolymerized with norbornene monomers, the presence of ethylene is preferable because the copolymerizability is increased.

  And, the number average molecular weight of the norbornene-based resin is not particularly limited, but when it becomes smaller, the mechanical strength of the obtained retardation film is lowered, and conversely, when it becomes larger, the retardation of the retardation film is exhibited. Therefore, it is preferably 5000 to 50000, more preferably 8000 to 30000, as measured by gel permeation chromatography (GPC) using a tetrahydrofuran solvent or a cyclohexane solvent.

  This type of norbornene-based resin is commercially available, for example, under the trade name “Zeonor” series from Zeon Corporation, the “Arton” series from JSR Corporation, and the “Apel” series from Mitsui Chemicals.

  Similarly, the maleimide resin is also a resin conventionally used for optical films, for example, at least one binary or more containing a repeating unit having an N-substituted or unsubstituted maleimide structure. In particular, an olefin-maleimide copolymer is preferable. These maleimide resins may be used alone or in combination of two or more.

  Examples of maleimide monomers having a maleimide structure include maleimide, N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn-butylmaleimide, Ni-butylmaleimide, N -S-butylmaleimide, Nt-butylmaleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide N-cyclobutylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, N-cycloheptylmaleimide, N-cyclooctylmaleimide and the like. Among these, N-methylmaleimide is preferable. These maleimide monomers may be used alone or in combination of two or more.

  Examples of the olefin monomer to be copolymerized include, for example, isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, 2-methyl-1-hexene, 1-methyl-1-heptene, 1- Examples include isooctene, 2-methyl-1-octene, 2-ethyl-1-pentene, 2-ethyl-2-butene, 2-methyl-2-pentene, and 2-methyl-2-hexene.

  The olefin-maleimide copolymer can be obtained by a known method (for example, see JP-A No. 5-117484). For example, it can be obtained by a radical copolymerization reaction between an olefin monomer and an N-substituted or unsubstituted maleimide monomer. Alternatively, it can be obtained by graft copolymerizing the other monomer with a polymer of one monomer. Further, a copolymer of olefin and maleic anhydride is used by using an alkylamine such as methylamine, ethylamine n-propylamine, i-propylamine, n-butylamine, s-butylamine, t-butylamine, cyclohexylamine, It can be obtained by post-imidization.

  The content of the maleimide component in the olefin-maleimide copolymer is not particularly limited, but is preferably 30 to 80 mol%, more preferably 40 to 60 mol%, still more preferably 45 to 55 mol%. is there. Outside this range, the heat resistance and mechanical strength of the resulting retardation film are impaired. The weight average molecular weight of the copolymer is not particularly limited, but is preferably in the range of 1,000 to 500,000 considering the moldability and stretchability of the film and the quality of the obtained retardation film.

  The olefin-maleimide copolymer may be any of a random copolymer, a block copolymer, a graft copolymer, and an alternating copolymer, but is preferably an alternating copolymer. In particular, an alternating copolymer of isobutene and N-substituted maleimide such as maleimide or N-methylmaleimide is preferred. Such an olefin-maleimide copolymer is commercially available, for example, from Tosoh Corporation under the trade name “TI-160α”.

  In addition, in the above-mentioned amorphous resin, in order to improve the weather resistance, heat resistance, smoothness, antistatic property, etc. within a range not deteriorating the function as a retardation film, benzophenone series, benzotriazole series, salicylic acid UV absorbers such as ester, cyanoacrylate, and acrylonitrile; antioxidants such as phenol and phosphorus; thermal degradation inhibitors such as lactone and phenol; fatty alcohol esters and polyhydric alcohol moieties An ester-based or partial ether-based lubricant; an amine-based antistatic agent or the like may be added.

  In the present invention, the method for obtaining a substantially non-oriented amorphous resin film is not particularly limited. For example, an amorphous resin is supplied to an extruder, melt-kneaded, melt-extruded into a film form from a mold attached to the tip of the extruder, and so-called melt extrusion is performed to form a long amorphous resin film Can be used. In addition, a solution in which an amorphous resin is dissolved in an organic solvent is cast on a drum, an endless belt, etc., and then the organic solvent is evaporated and dried to form a long amorphous resin film. A known method such as the elongation method can be used. The film obtained by such a method is substantially non-oriented.

  The thickness of the amorphous resin film is not particularly limited, but when it becomes thin, it becomes difficult to express a retardation, and conversely, when the retardation film obtained when it becomes thick is used for a liquid crystal display device, a liquid crystal panel Is generally 30 to 200 μm, more preferably 40 to 150 μm. When the thickness of the resin film is 80 μm or more, it is difficult to sufficiently evaporate and remove the organic solvent by the solution casting method. Therefore, it is preferable to manufacture the resin film by a melt extrusion method.

  In the present invention, the substantially non-oriented amorphous resin film obtained by the above-described method is uniaxially stretched in the width direction (hereinafter referred to as “lateral uniaxial stretching”). For this lateral uniaxial stretching, a conventionally known lateral uniaxial tenter stretching method is employed. For example, both end portions of the amorphous resin film are held with a tenter clip, and the film heated to a suitable stretching temperature is gradually widened on both sides. A method in which the tenter clip is run on the side rails installed in this manner to gradually widen and stretch the film in the width direction can be mentioned.

  Specifically, the transverse uniaxial tenter stretching method includes a preheating step in which the amorphous resin film is heated and softened, and stretching in which the preheated film is heated to an appropriate stretching temperature and widened in the width direction to perform lateral uniaxial stretching. It is preferable to comprise a process, a thermal relaxation process for reducing the bowing of the stretched film and aligning the orientation direction, and a cooling process for fixing the orientation of the film.

  In the preheating step, the amorphous resin film is heated and softened to near the temperature at which it can be stretched. The amorphous resin film is expanded and deformed by heating and the film width is widened, so that the amorphous resin film may relax due to its own weight during the preheating process, and may contact a furnace member such as a hot air nozzle. Such a traveling trouble can be avoided by slightly widening the clip rail width with respect to the film width.

  In the preheating step, the amorphous resin film is heated to near the temperature at which it can be stretched. Therefore, it may be heated to near the stretching temperature set in the following stretching step.

  If the stretching temperature of the amorphous resin film in the stretching process is too low, the film may be cut or disengaged from the tenter clip at the time of widening stretching. High retardation value cannot be obtained. Accordingly, the stretching temperature is preferably Tg to Tg + 20 ° C. of the amorphous resin, more preferably Tg + 2 ° C. to Tg + 10 ° C. of the amorphous resin. Here, Tg represents the glass transition temperature of the amorphous resin. The stretching temperature in the stretching step may be the same temperature as long as it is within the above temperature range, or the stretching zone may be divided to have a different temperature by inserting a low widening or low relaxation step described later. In this case, it is particularly preferable to set the first half of stretching higher than the second half of stretching in order to obtain a high phase difference.

  In addition, when the stretching strain rate in the stretching process becomes small, the retardation value decreases due to thermal relaxation, and the effect of suppressing the bowing phenomenon decreases. Therefore, the stretching strain rate (V2 and V3) is preferably 300% / min or more. However, if it is too fast, the film will be cut or detached from the tenter clip, so 400-1000% / min is more preferred. Further, by stretching at a high stretching strain rate, it becomes possible to increase the rail opening angle of the tenter and shorten the length of the stretching zone.

Thus, in the present invention, one or more low widening or low relaxation regions are provided between the start of widening and the completion of widening in the stretching step, and the film deformation speed V1 (% / min) in this region is set as follows: It is necessary to satisfy −10 ≦ V1 ≦ + 10. Such low widening or low relaxation is performed by slightly narrowing or slightly widening the clip width to a desired deformation speed at a predetermined position in the conventional stretching zone. Here, the deformation speed V1 (% / min) = deformation rate D (%) / deformation time (min). However, the deformation rate D (%) = (W ₂ −W ₁ ) / W ₁ × 100 is calculated. W ₁ is the film width between tenter clips at the entrance of the low widening or low relaxation region, and W ₂ is the minimum film width (for low relaxation) or the maximum film width (for low widening) in the low widening or low relaxation region. Represents.

  By setting the deformation speed as described above, the bowing generated in a convex shape with respect to the traveling direction in the preceding drawing process is corrected by heat treatment in the low widening or low relaxation region continuously arranged in the drawing process. After that, it is further stretched in a subsequent stretching step. By repeating the stretching and heat treatment in the stretching process in this way, the bowing is repeatedly changed in small increments before it grows sufficiently, and as a result, the distribution of the molecular main chain orientation angle is controlled to be flat along the width direction. be able to. In other words, the bowing generated in the stretching process is sequentially corrected by alternately arranging the stretching regions and the deformation regions.

  In the case where the widening stretching is completed in a single step as in the prior art, the bowing continues to grow during the widening stretching and the absolute amount thereof increases. In order to suppress such bowing, the heat treatment temperature in the subsequent heat treatment step must be increased, but the high retardation value obtained by stretching is greatly impaired.

  Moreover, in this invention, in addition to the effect | action with respect to the above bowing control, the uniaxially stretched film obtained by complete | finishing all the extending processes has high thickness uniformity in the width direction. That is, by heat-treating in the middle of the stretching process, the rigidity of the central part preferentially stretched in the previous stage is improved by the annealing effect in the low-widening or low-relaxation region, so that the end is prioritized in the subsequent stretching process. Therefore, uniform stretching in the film width direction is possible. Thus, the provision of the above-described low widening or low relaxation region has a great effect on uniforming the thickness in the width direction after the end of stretching.

  Furthermore, in the present invention, the passage time T (second) of the film in the low widening or low relaxation region needs to be 2 <T <10, and more preferably 5 ≦ T <10. Thus, by setting the passage time T, the bowing phenomenon that occurs in the stretching process can be corrected without causing a significant decrease in the retardation value due to thermal relaxation. If the passage time T is less than 2 seconds, bowing cannot be corrected effectively. Conversely, if the passage time T is longer than 10 seconds, a decrease in retardation value due to thermal relaxation cannot be ignored.

  The low widening or low relaxation region is a region for reducing the bowing of the film stretched in the previous stretching process, aligning the molecular orientation direction, and further increasing the rigidity of the film to provide the film for the subsequent stretching process. . Further, this region also has a meaning of a preheating step for the subsequent stretching. For this reason, if the temperature of the region is too high, the bowing developed in a convex shape with respect to the advancing direction is shifted to a concave shape, and as a result, the alignment cannot be made uniform, and the retardation value is further lowered. On the other hand, when the temperature is too low, cutting or detachment of the clip may occur in the subsequent stretching process, and stretching may become impossible. Therefore, the temperature of the low broadening or low relaxation region is preferably a temperature intermediate between the Tg + 2 ° C. of the amorphous resin and the stretching step before and after the low widening or low relaxation region.

  Further, in the present invention, the stretching strain rate V2 (% / min) in the film width direction before passing through the low widening or low relaxation region and the stretching in the film width direction after passing through the low widening or low relaxation region. It is necessary to deform the stretched film under such a condition that the strain rate V3 (% / min) is 300 ≦ V2 <V3. That is, it is preferable to perform lateral uniaxial stretching so that the stretching strain rate is reduced in the first half of the stretching step and the stretching strain rate is increased in the second half of the stretching step.

  In other words, in the first half of the stretching process, the resin molecule main chain in the non-oriented state is uniformly oriented in the film width direction at a low stretching strain rate, and the stretching is performed by correcting the bowing phenomenon and improving the rigidity in the low widening or low relaxation region. A high retardation value can be obtained by rapid stretching at a high stretching strain rate in the latter half of the process. Conversely, when V2> V3, the stretching strain rate is stretched non-uniformly in the first half of the stretching process, and most of the molecular main chain oriented in the first half of the stretching process is heated under low stress in the second half of the stretching process. The orientation returns due to relaxation, and a sufficient retardation value cannot be obtained.

  The final stretch ratio of the film in the stretching step is appropriately determined depending on the amount of compensation retardation required for the obtained retardation film, but if the stretch ratio is low, the orientation direction may not be uniform, and conversely is too high. The center part of the film is loosened, the retardation value of the obtained retardation film varies in the width direction, and the main orientation axis and the thickness are not uniform. Therefore, the final draw ratio is preferably 1.2 to 2.5 times, more preferably 1.5 to 2.2 times.

  The film uniaxially stretched in this way is introduced into the heat treatment step as in the conventional case, and is held at a predetermined temperature for a predetermined time while maintaining the chuck width after stretching for the purpose of fixing the orientation of the film. This heat treatment step is a step for reducing the bowing phenomenon of the stretched film and aligning the orientation.If the temperature of this heat treatment step is too high, the retardation value decreases, so the temperature of this heat treatment step is It is below the stretching temperature and is preferably Tg to Tg + 10 ° C. of the amorphous resin.

  Further, after the heat treatment step, it is introduced into the cooling step as in the conventional case. This cooling step is a step for fixing the orientation formed on the film by cooling the heat-treated film, and the cooling temperature in this cooling step is Tg-50 ° C. to Tg of the amorphous resin. -5 ° C is preferred.

  In order to use it suitably as a retardation film, it is necessary to suppress thickness variation in the width direction with respect to the average thickness. The value obtained by dividing R (maximum value-minimum value) of thickness in the range of 80% of the film width around the center in the film width direction by d (average thickness in the range of 80% of the film width) is 0.00. It is preferable that it is 05 or less. By suppressing the film thickness fluctuation within this range, it becomes possible to make the retardation value of the film uniform distribution, and when this retardation film is laminated on the liquid crystal panel, there is no display unevenness and a stable image display can be obtained. it can.

In the method for producing a retardation film in the present invention, it is preferable to control the in-plane retardation value Re to be 150 nm or more in a range of 80% of the film width centered on the center in the film width direction. Retardation value Re in the plane, _| n x _-n y | defined in × d, wherein, n _x is the maximum refractive index in the film plane, n _y in the direction showing the maximum refractive index in a film plane The refractive index in the orthogonal direction, d represents the thickness (nm) of the film. If the retardation value is smaller than 150 nm, the liquid crystal display device in which the retardation film is laminated on the liquid crystal panel cannot fully compensate the birefringence when passing through the liquid crystal, and the commercial value as the retardation film is lowered.

According to the method for producing a retardation film in the present invention, in the range of 80% of the film width centering on the center in the film width direction, the molecular main chain orientation angle θ with respect to the film width direction is parallel to the width direction of 1 ° or less. In addition, it can be controlled to have a uniform optical axis. Since the molecular main chain orientation angle is in the above range, the molecular main chain is uniformly oriented and the optical axis is stabilized. Therefore, according to the liquid crystal display device in which such a retardation film is laminated on a liquid crystal panel, display is performed. There is no unevenness and a stable display can be obtained.

  In addition, the retardation film obtained by this invention can obtain a biaxial retardation film by extending | stretching further in a length direction. For stretching in the length direction, a conventionally known roll-to-roll longitudinal stretching method based on a peripheral speed difference of a roll or a tenter longitudinal stretching method based on a speed difference of a tenter clip can be used. At this time, when the value of the retardation Re after the uniaxial stretching is small, the retardation Rth in the thickness direction of the obtained biaxial retardation film is hardly expressed when stretched in the length direction, and the stretching Since the value of retardation Re is reduced by the heating at the time, the value of retardation Re after uniaxial stretching is preferably 200 nm or more.

  The method for producing a retardation film of the present invention is as described above, and a low widening or low relaxation region is provided between the start of widening and the completion of widening in the stretching step, and the deformation speed V1 in the film width direction in the same region ( % / Min) is −10 ≦ V1 ≦ + 10, the passage time T (seconds) of the film in the same region is 2 <T <10, and the stretching strain rate V2 in the film width direction before the same region (% / min) ) And the film width direction stretch strain rate V3 (% / min) after the same region is 300 ≦ V2 <V3, and thus has a high retardation, a phase difference parallel to the width direction and a uniform optical axis. The film can be easily obtained with a practical apparatus. Therefore, when the obtained retardation film is used in a liquid crystal display device, the birefringence of the liquid crystal substance is compensated, display unevenness is eliminated, and the image display of the liquid crystal panel is stabilized.

  Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to these examples.

(Examples 1-5, Comparative Examples 1-4)
A norbornene-based resin (manufactured by Nippon Zeon Co., Ltd .: trade name “Zeonor 1420”, glass transition temperature Tg = 142 ° C.) was supplied to a single screw extruder, melt kneaded at 230 ° C., and attached to the tip of the single screw extruder. While being melt-extruded into a film form at 230 ° C. from a T-die and being brought into contact with a chill-plated cooling roll on the surface, the roll was wound around a vinyl chloride resin core at a take-up speed of 20 m / min. A substantially non-oriented norbornene resin film (raw film) having an average thickness of 100 μm was formed.

  The above norbornene-based resin film is continuously unwound, supplied to a horizontal uniaxial tenter stretching machine at a speed of 10 m / min, and both ends thereof are gripped with a tenter clip, and finally processed in the width direction through the steps described below. Thus, the film was stretched 2.0 times to obtain a retardation film. That is, the horizontal uniaxial tenter stretching machine includes a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone in succession, and the temperature can be set individually. The stretching zone is further divided into three zones. From the entrance to the exit, the widening stretching region, the low widening or low relaxation region, and the widening stretching region are arranged in this order. In the previous widening and stretching step, the film is stretched to 1.5 times the width of the supply film in the width direction, heat treated in the low widening or low relaxation region, and then in the width direction in the widening and stretching process on the outlet side, 2.0 times the width of the supply film. It was extended to.

  In the horizontal uniaxial tenter stretching machine, the preheating zone is set to 150 ° C., the film is heated to 150 ° C., heated to 145 ° C. in the stretching zone set to 145 ° C., and immediately stretched to 140 ° C. in the heat treatment zone. And then cooled to 100 ° C. in the cooling zone.

  At this time, by adjusting the opening angle of the tenter so that the clip rail width of the central part of the stretching zone is low widened or relaxed, a predetermined low widening or low relaxation region is provided in the stretching zone. Retardation films (Examples 1 to 5 and Comparative Examples 1 to 4) were produced. The width of the obtained retardation film was 570 mm excluding the tenter clip gripping part, and the average thickness was 48 μm.

Example 6
Examples 1-5 and Comparative Examples 1 to 5 except that the widened stretch region before the low widening or low relaxation region was set to 150 ° C and the widened stretched region after the low widening or low relaxation region was set to 143 ° C. In the same manner as in No. 4, a retardation film was produced. The width of the obtained retardation film was 570 mm excluding the tenter clip gripping part, and the average thickness was 48 μm.

  For the above Examples 1 to 6 and Comparative Examples 1 to 4, while measuring the passage time T of the low widening or low relaxation region, the stretching strain rate V1 (% / min) in the film width direction in this region, before and after the same region The stretching strain rates V2 and V3 (% / min) in the film width direction of the widened region were calculated by the following method. Further, the molecular main chain orientation angle (θ), in-plane retardation value (Re), thickness variation (R / d) and Tg of the retardation film were measured by the following methods. The results are shown in Table 1.

(Measurement method of deformation rate and stretching strain rate)
In each stretching process, the distance between the clip rails at the starting point of each stretching process is L, the distance between the clip rails at time t (minutes) and after dt (minutes), that is, at t + dt (minutes) is L _t and L _{t + dt} , respectively. Then, the stretching strain rate V is expressed by the following formula. In Table 1, the-sign of V1 represents the deformation rate of low shrinkage, and the + symbol represents the deformation rate of low widening.
V = lim _{dt → 0} [(L _{t + dt} −L _t ) / dt] × 100 / L

(Measurement method of molecular main chain orientation angle of retardation film)
Using an axis perpendicular to the length direction of the film stretched in the width direction as a reference axis, an automatic birefringence measuring device (manufactured by Oji Scientific Instruments: trade name “KOBRA-21ADH”) is used. The refractive index is measured at intervals of 10 mm, the angle (absolute value) formed between the direction indicating the maximum refractive index at each position and the reference axis is obtained, and the average value thereof is defined as the molecular main chain orientation angle θ.

(Measurement of in-plane retardation value Re of retardation film)
Using an automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments Co., Ltd .: trade name “KOBRA-21ADH”), the central 460 mm portion in the width direction of the film was measured at 10 mm intervals, and the average value was calculated as the in-plane retardation value Re and To do.

(Measurement of variation in thickness of retardation film)
Using a continuous thickness measuring device (trade name “milllon1240” manufactured by Seiko EM Co., Ltd.), the thickness of the central 460 mm portion of the film is measured at intervals of 10 mm, and the difference between the maximum value and the minimum value (R) And average thickness (d) are calculated, and thickness variation (R / d) is calculated.

(Measurement of glass transition temperature Tg of amorphous resin)
Using a differential scanning calorimeter (trade name “DSC2920 Modulated DSC” manufactured by TA Instruments), the glass transition temperature at the final temperature rise was defined as the glass transition temperature of the resin used under the following temperature program conditions. The temperature was raised from room temperature to 50 ° C. at 10 ° C./min and held at 50 ° C. for 5 minutes, from 50 ° C. to 200 ° C. at 10 ° C./min and held at 200 ° C. for 5 minutes, from 200 ° C. to −50 The temperature is lowered to 10 ° C./minute and held at −50 ° C. for 5 minutes, and the temperature is raised from −50 ° C. to 200 ° C. at 10 ° C./minute and held at 200 ° C. for 5 minutes.

Claims (2)

A method for producing a retardation film in which a substantially non-oriented amorphous resin film is uniaxially stretched in a width direction by a tenter, wherein a low widening or low relaxation region is present between the start of widening and the completion of widening in the stretching step. The deformation speed V1 (% / min) in the film width direction in the same region is −10 ≦ V1 ≦ + 10, and the film transit time T (seconds) in the same region is 2 <T <10. The stretching strain rate V2 (% / min) in the previous film width direction and the stretching strain rate V3 (% / min) in the film width direction after the same region satisfy the relationship of 300 ≦ V2 <V3. A method for producing a phase difference film. The method for producing a retardation film according to claim 1, wherein the amorphous resin film comprises a cyclic olefin resin film or a maleimide resin film .