JP2012215623A - Method for manufacturing retardation film, retardation film, composite polarizing plate, and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a retardation film that simply enables the Nz coefficient to be made closer to 0.5.SOLUTION: The method for manufacturing a retardation film includes a stretching step for stretching an amorphous thermoplastic resin film at least in a first direction and a contracting step for contracting the stretched film in the stretched first direction to obtain a retardation film having the Nz coefficient of 0.05 or more and 0.95 or less.

Description

  The present invention relates to a method for producing a retardation film and a retardation film used for improving the contrast and viewing angle of a liquid crystal display device, for example. The present invention also relates to a composite polarizing plate and a polarizing plate using the retardation film.

  Liquid crystal displays (LCDs) are widely used in applications such as personal computer displays and liquid crystal televisions.

  As the liquid crystal display device, there is a TN (twisted nematic) mode liquid crystal display device. This TN mode liquid crystal display device has a problem that the viewing angle is narrow and the response speed is slow.

  Therefore, a VA (Vertical Alignment) mode liquid crystal display device using a birefringence mode is proposed instead of an optical rotation mode such as a TN mode liquid crystal display device. As a VA mode liquid crystal display device, an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device has been proposed.

  In the MVA mode liquid crystal display device, domain regulating means such as a projection having an inclined surface is provided on the inner surface of the substrate constituting the liquid crystal cell. By this domain regulating means, the alignment direction of the liquid crystal molecules is divided into two or more directions, and the amount of light passing through the liquid crystal cell is made uniform. Thereby, the difference in display luminance due to the expected angle is suppressed, and the viewing angle dependency is improved to some extent.

  However, even in the above MVA mode liquid crystal display device, there is a problem that the contrast is lowered when the liquid crystal display surface is viewed at an angle of 45 ° with respect to the normal line of the liquid crystal display surface. Therefore, in the MVA mode liquid crystal display device, a retardation film is generally used in order to further improve the viewing angle dependency.

  In addition to the VA mode liquid crystal display device, an IPS (In-Plane Switching) mode liquid crystal display device is now widely used. The IPS mode liquid crystal display device is superior in viewing angle performance as compared with the TN mode liquid crystal display device and the VA mode liquid crystal display device. Therefore, the IPS mode liquid crystal display device is used for monitors of personal computers and television applications.

  In the IPS mode liquid crystal display device, as compared with the VA mode liquid crystal display device, a coloring phenomenon and a color shift of light leaked obliquely during black display occur slightly. For this reason, retardation films are also used in IPS mode liquid crystal display devices in order to improve the viewing angle dependency.

  In order to fully exhibit the function of the retardation film, it is necessary to match with the birefringence of the liquid crystal panel, and it is necessary to appropriately design a uniform retardation value in the plane of the retardation film. Thereby, the viewing angle performance of various liquid crystal display devices of VA mode, MVA mode, and IPS mode can be further improved.

  In order to suppress light leakage particularly when the polarizing plate is oblique, it is desirable that the Nz coefficient of the retardation film be close to 0.5.

  As an example of the method for producing the retardation film, for example, in Patent Document 1 below, the resin is extruded, the lot rod of the resin is cut into a plate shape, and then stretched, so that the Nz coefficient of the retardation film is 0. A method of approaching .5 is disclosed.

  In the following Patent Document 2, a laminate in which a shrinkable film is bonded to a resin film is heated, and the resin film is shrunk by a shrinking force of the shrinkable film, whereby the Nz coefficient of the retardation film is set to 0.5. A method of approaching is disclosed.

  Patent Document 3 below discloses a method in which the Nz coefficient of a retardation film is brought close to 0.5 by co-extrusion and stretching of a resin having a positive intrinsic birefringence value and a negative resin.

  Patent Document 4 below discloses a method of bringing the Nz coefficient close to 0.5 by forming a homeotropic liquid crystal layer on the surface of a stretched film.

JP-A-2-160204 JP-A-5-157911 JP-A-2005-77450 JP 2007-17637 A

  In the method for producing a retardation film described in Patent Document 1, since batch production is performed, productivity is considerably poor and it is difficult to obtain a large-area retardation film.

  The method for producing a retardation film described in Patent Document 2 has a problem that the production process is complicated, the productivity is very low, and a shrinkable film is required, so that the production cost of the retardation film is high.

  In the method for producing a retardation film described in Patent Document 3, two or more kinds of resins are required, so that the production process of the retardation film is complicated and the production cost is increased. Moreover, since it becomes a multilayer retardation film, there exists a problem that film thickness reduction is difficult or curl arises in a retardation film by the difference in the linear expansion coefficient between resin.

  In the method for producing a retardation film described in Patent Document 4, homeotropic liquid crystal is very expensive, so that the production cost of the retardation film is increased. Further, it is difficult to uniformly coat the homeotropic liquid crystal and to align the homeotropic liquid crystal uniformly. As a result, variations in phase difference and variations in Nz coefficient are likely to occur.

  An object of the present invention is to provide a method for producing a retardation film and a retardation film capable of easily bringing the Nz coefficient close to 0.5, and a composite polarizing plate and a polarizing plate using the retardation film. is there.

  According to a wide aspect of the present invention, a stretching step of stretching an amorphous thermoplastic resin film in at least a first direction, and the stretched film is contracted in the stretched first direction, and Nz And a shrinking step for obtaining a retardation film having a coefficient of 0.05 or more and 0.95 or less.

  In a specific aspect of the method for producing a retardation film according to the present invention, in the stretching step, the amorphous thermoplastic resin film is stretched in the MD direction, and in the shrinking step, the stretched film is By contracting in the MD direction, a retardation film in which the slow axis direction is the MD direction is obtained.

  In another specific aspect of the method for producing a retardation film according to the present invention, a retardation film having a front retardation R0 of 50 nm or more is obtained.

  In still another specific aspect of the method for producing a retardation film according to the present invention, in the stretching step, a ratio of a distance between stretching of the film to a width of the film (stretching distance / film width) is 1 or more. In the shrinking step, the ratio of the distance between shrinkage to the width of the film (distance between shrinkage / film width) is set to 1 or less.

  In still another specific aspect of the method for producing a retardation film according to the present invention, in the stretching step, the stretching ratio of the film is 1.05 times or more. In the shrinking step, the shrinkage rate of the film is 99. 9% or less.

  In another specific aspect of the method for producing a retardation film according to the present invention, in the stretching step, the first roll and the first roll are separated from each other by a distance from the first roll. The amorphous thermoplastic resin film is stretched by changing the conveying speed of the second roll.

  In still another specific aspect of the method for producing a retardation film according to the present invention, in the shrinking step, the third roll and the fourth roll separated from the third roll by the first roll. 3. The conveyance speed by a 4th roll is varied and the said stretched film is shrunk | reduced.

  In another specific aspect of the method for producing a retardation film according to the present invention, in the shrinking step, the stretched film is shrunk alone without laminating another film on the stretched film.

  In still another specific aspect of the method for producing a retardation film according to the present invention, a melt extrusion step of melt-extruding an amorphous thermoplastic resin into a film shape, and cooling the melt-extruded amorphous thermoplastic resin And a cooling step for obtaining the amorphous thermoplastic resin film.

  Further, according to a wide aspect of the present invention, there is provided a single-layer retardation film formed of an amorphous thermoplastic resin, the slow axis direction is the MD direction, the Nz coefficient is 0.05 or more, 0 A retardation film that is .95 or less is provided.

  In a specific aspect of the retardation film according to the present invention, the amorphous thermoplastic resin film is stretched in the MD direction, and then the stretched film is contracted in the MD direction.

  In another specific aspect of the retardation film according to the present invention, the front retardation R0 is 50 nm or more.

  The composite polarizing plate which concerns on this invention is equipped with the retardation film obtained by the manufacturing method of the said retardation film, and the polarizing plate laminated | stacked on one surface of this retardation film.

  The polarizing plate which concerns on this invention is equipped with the phase difference film obtained by the manufacturing method of the said phase difference film, and the polarizer arrange | positioned at the one surface side of this phase difference film.

  Since the method for producing a retardation film according to the present invention stretches an amorphous thermoplastic resin film in at least the first direction, and then the stretched film shrinks in the stretched first direction. A retardation film having an Nz coefficient of 0.05 or more and 0.95 or less can be obtained by simply bringing the Nz coefficient close to 0.5.

FIG. 1 is a schematic configuration diagram showing an example of an apparatus for forming an amorphous thermoplastic resin into a film by a melt extrusion molding method. FIG. 2 is a schematic configuration diagram for explaining a method of stretching a film. FIG. 3 is a schematic schematic configuration diagram for explaining a method of shrinking a film.

  Details of the present invention will be described below.

  The method for producing a retardation film according to the present invention includes a stretching step of stretching an amorphous thermoplastic resin film in at least a first direction, and shrinking the stretched film in the stretched first direction. And a shrinking step for obtaining a retardation film having an Nz coefficient of 0.05 or more and 0.95 or less. The amorphous thermoplastic resin film is a film formed of an amorphous thermoplastic resin. In the shrinking step, the stretched film is selectively shrunk in the stretched first direction.

  In the method for producing a retardation film according to the present invention, a retardation film having an Nz coefficient of 0.05 or more and 0.95 or less can be easily obtained.

  Further, in the method for producing a retardation film according to the present invention, in the stretching step, the amorphous thermoplastic resin film is stretched in the MD direction, and in the shrinking step, the stretched film is stretched in the MD direction. It is preferable to contract to obtain a retardation film in which the slow axis direction is the MD direction. The MD direction is the film flow direction and is the vertical direction.

  Further, the retardation film according to the present invention includes a melt extrusion process in which an amorphous thermoplastic resin is melt-extruded into a film, and the amorphous thermoplastic resin that has been melt-extruded is cooled and the amorphous thermoplastic resin is cooled. It is preferable to further include a cooling step for obtaining a resin film. By using such a melt extrusion method, a retardation film having an Nz coefficient of 0.05 or more and 0.95 or less can be obtained more easily.

  The retardation film according to the present invention is a single layer retardation film formed of an amorphous thermoplastic resin, the slow axis direction of the retardation film is the MD direction, and the Nz coefficient of the retardation film is 0. .05 or more and 0.95 or less.

  The retardation film according to the present invention can be obtained, for example, by stretching the amorphous thermoplastic resin film in the MD direction and then shrinking the stretched film in the MD direction. The retardation film according to the present invention is preferably obtained by stretching the amorphous thermoplastic resin film in the MD direction and then shrinking the stretched film in the MD direction.

(Amorphous thermoplastic resin)
The amorphous thermoplastic resin film is a film formed of an amorphous thermoplastic resin. The retardation film is formed using an amorphous thermoplastic resin.

  The transparency of the amorphous thermoplastic resin constituting the retardation film is preferably high. Examples of the amorphous thermoplastic resin having high transparency include polycarbonate, polysulfone, polyethersulfone, polystyrene, cyclic olefin, polyvinyl alcohol, cellulose acetate, polyvinyl chloride, and poly (meta). ) Polymers such as acrylic, polyarylate and polyamide are listed. Examples of the poly (meth) acrylic polymer include polymethyl (meth) acrylate. As for an amorphous thermoplastic resin, only 1 type may be used and 2 or more types may be used together.

  The amorphous thermoplastic resin is preferably a cyclic olefin polymer, and more preferably a norbornene resin. Norbornene resin has a small photoelastic coefficient and excellent retardation stability against external stress.

  Examples of the norbornene resin include ring-opening (co) polymers of norbornene monomers, addition copolymers of norbornene monomers and olefin monomers, addition (co) polymers of norbornene monomers with each other, and derivatives thereof. Etc. As for norbornene-type resin, only 1 type may be used and 2 or more types may be used together.

  In a (co) polymer with ring opening, an unsaturated bond may inevitably remain. Furthermore, even in an addition (co) polymer, an unsaturated bond may remain depending on the type of monomer. From the viewpoint of emphasizing durability such as suppression of oxidative degradation due to thermal history or suppression of discoloration due to ultraviolet rays, the norbornene resin is saturated by hydrogenation in order to reduce the amount of unsaturated double bonds. It is preferable.

  In the range that does not hinder the function of the retardation film, in order to prevent the deterioration of the amorphous thermoplastic resin during film formation and to improve the heat resistance and ultraviolet resistance of the retardation film, the amorphous thermoplastic resin is added to the above-mentioned amorphous thermoplastic resin. Various additives may be added. Examples of the additive include antioxidants, heat deterioration inhibitors, ultraviolet absorbers, lubricants, and antistatic agents. As for the said additive, only 1 type may be used and 2 or more types may be used together.

  Examples of the antioxidant include phenolic antioxidants and phosphorus antioxidants. Examples of the thermal degradation inhibitor include lactone thermal degradation inhibitors. Examples of the ultraviolet absorber include benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, and acrylonitrile ultraviolet absorbers. Examples of the lubricant include aliphatic alcohol ester lubricants, polyhydric alcohol partial ester lubricants, and partial ether lubricants. Examples of the antistatic agent include amine-based antistatic agents.

(Details of retardation film production method and retardation film)
As a method for obtaining the pre-stretch film (raw film), which is the amorphous thermoplastic resin film, using the amorphous thermoplastic resin, a conventionally used method can be used. The film before stretching is a substantially unstretched film.

  As a method for obtaining a film before stretching, specifically, after casting a solution in which an amorphous thermoplastic resin is dissolved onto an appropriate support, the solvent is removed by drying, and the film is further peeled off from the support. Examples include a solution casting method for obtaining a film, a melt extrusion method for supplying an amorphous thermoplastic resin to an extruder, melting and kneading, and extruding the film from a mold attached to the tip of the extruder to obtain a film. It is done. The melt extrusion method is preferred because of its low cost and low environmental burden. The film before stretching is preferably formed by a melt extrusion method, and is preferably a melt-extruded film.

  FIG. 1 shows a schematic configuration diagram illustrating an example of an apparatus for forming a film of an amorphous thermoplastic resin by a melt extrusion molding method.

  When the amorphous thermoplastic resin is formed into a film using the melt extrusion apparatus 11 shown in FIG. 1, first, the molten amorphous thermoplastic resin is extruded from the extruder 12, and the mold 13 is then extruded. To supply.

  The amorphous thermoplastic resin supplied to the mold 13 is extruded from the opening of the mold 13 and discharged to form a film of the amorphous thermoplastic resin. The discharged film A is brought into contact with the cooling roll 14 and cooled. In order to press the film A against the cooling roll 14, a touch roll 15 is provided.

  The film A cooled by the cooling roll 14 is further cooled by the cooling rolls 16 and 17, solidified, wound up, and a roll-shaped raw film is obtained. The roll-shaped raw film is a long amorphous thermoplastic resin film.

  The distance from the opening of the mold 13 to the contact point where the film A contacts the cooling roll 14, that is, the air gap is preferably short. When the air gap is short, thickness variation due to disturbance can be reduced. That is, a film having an appropriate thickness profile can be stably produced. The air gap is preferably 70 mm or less.

  When the film A comes into contact with the cooling roll 14, it is desirable that air does not enter between the cooling roll 14 and the film A and that the cooling rate is uniform over the entire surface of the film A. Therefore, it is desirable to press the film A toward the cooling roll 14 by pressing means such as the touch roll 15 in the vicinity of the downstream side of the contact point between the film A and the cooling roll 14.

  The pressing means is not limited to the touch roll 15. As the pressing means, an air knife or electrostatic pinning may be used. A touch roll having a surface formed of an elastic material is preferably used because the film A is excellent in stability and the film A can be uniformly pressed against the cooling roll 14.

  The temperature of the cooling roll 14 can be changed as appropriate depending on the type of amorphous thermoplastic resin constituting the film A. When the glass transition temperature Tg (° C.) of the amorphous thermoplastic resin is used, the temperature of the cooling roll 14 is preferably in the range of (Tg−10) ° C. to (Tg−100) ° C.

  In order to ensure the smoothness and transparency of the film A, the surface roughness of the surface of the cooling roll 14 is preferably an Ry value defined in JIS B 0601 of 0.5 μm or less. More preferably, it is 3 μm or less.

  The cooling roll 14 can be composed of various materials. The surface of the cooling roll 14 is preferably made of metal, and more preferably made of carbon steel or stainless steel. When the cooling roll 14 having a metal surface is used, the temperature of the cooling roll 14 can be quickly maintained at a constant temperature, and the film A can be efficiently cooled.

  In order to increase the thickness accuracy in the length direction of the film A, it is desirable that the eccentric runout of the cooling roll 14 is small. The eccentric runout of the cooling roll 14 is desirably 30 μm or less, and more desirably 10 μm or less.

  Since the fluidity of the amorphous thermoplastic resin changes when the temperature of the mold 13 varies, it is desirable that the temperature of the mold 13 is stable. The temperature of the portion of the mold 13 that contacts the molten resin constituting the film A is preferably within a set temperature ± 0.5 ° C., and more preferably within a set temperature ± 0.2 ° C.

  In general, the temperature of the cooling roll 14 greatly affects the solidification point of the amorphous thermoplastic resin. Therefore, it is desirable that the cooling roll 14 has a temperature adjusting means in the shaft core portion so that the cooling roll 14 can be adjusted to various temperatures. As a preferred temperature adjusting means, a sheathed heater is incorporated in the shaft core portion, an electric heating type temperature adjusting means for heating the cooling roll 14 so as to set an appropriate temperature, a temperature due to electromagnetic induction action by an induction heating coil. Examples of the adjusting means include a temperature adjusting means such as a heating medium circulating heating method in which a heat medium for temperature control is circulated through a flow path provided in the shaft core portion to heat the cooling roll to a set temperature. Of these, the heat medium circulation heating method is preferable. As the heat medium used in the heat medium circulation system, a gas or a liquid such as water or oil may be used. As the heat medium, it is desirable to use a liquid such as water or oil having a large heat capacity. Preferable examples of the heat medium flow path include those having a two-row spiral structure or a four-row spiral structure inside.

  Next, details of a method for producing a retardation film by performing a stretching step and a shrinking step using the above-described long amorphous thermoplastic resin film will be described.

  In order to produce a retardation film using the above-described long amorphous thermoplastic resin film, the amorphous thermoplastic resin film is made of the amorphous thermoplastic resin constituting the amorphous thermoplastic resin film. Drawing is performed at a temperature in the vicinity of the glass transition temperature Tg. Thereby, the polymer molecules are oriented in a predetermined direction.

  In the method for producing a retardation film according to the present invention, an amorphous thermoplastic resin film is stretched in at least a first direction. The first direction is the stretching direction. The film is preferably stretched in the MD direction, preferably stretched in the machine direction, and stretched in the flow direction of the film.

  As a method of stretching the film, a longitudinal stretching method in which stretching is performed in the length direction of the film (also referred to as longitudinal direction), a lateral stretching method in which stretching is performed in the width direction of the film (hereinafter also referred to as lateral direction), and longitudinal Examples thereof include a sequential biaxial stretching method in which transverse stretching is performed after stretching, a sequential biaxial stretching method in which longitudinal stretching is performed after transverse stretching, and a simultaneous biaxial stretching method in which stretching is performed simultaneously in the longitudinal direction and the transverse direction. The stretching method for obtaining the retardation film according to the present invention is not particularly limited. Depending on the phase difference value to be imparted, the stretching method is properly used.

  As the longitudinal stretching method, for example, an inter-roll neck-in stretching method and a proximity roll stretching method can be applied. Since there is an advantage that the retardation is easily controlled and defects such as scratches and wrinkles are hardly generated on the film, the inter-roll neck-in stretching method is desirable. The inter-roll neck-in stretching method is to hold the film being transported by two pairs of nip rolls located across a stretching zone that is sufficiently longer than the film width, and against the peripheral speed of the upstream nip roll. This is a method of obtaining a desired draw ratio by increasing the peripheral speed of the nip roll on the downstream side. At this time, both ends in the width direction of the film are free ends that are not constrained, and exhibit a neck-in phenomenon in the width direction along with stretching in the longitudinal direction.

  As the transverse stretching method, for example, using a tenter stretching machine, both ends in the width direction of the film are gripped by arbitrary gripping means such as a tenter clip, and run while gradually shifting the gripping means away from each other. A method is mentioned.

  As the simultaneous biaxial method, for example, using a tenter stretching machine, the both ends in the width direction of the film are gripped by arbitrary gripping means such as a tenter clip, and the gripping means are gradually displaced in a direction away from each other, and At the same time, there is a method in which the gripping means is moved away from the film in the longitudinal direction while being gradually displaced.

  In the method for producing a retardation film according to the present invention, the conveying speeds of the first and second rolls are made different between the first roll and the second roll spaced apart from the first roll. It is preferable to stretch the amorphous thermoplastic resin film. The first roll is located on the upstream side in the film flow direction, and the second roll is located on the downstream side in the film flow direction.

  Here, the method for producing a retardation film by the longitudinal stretching method will be described in detail. FIG. 2 is a schematic configuration diagram illustrating an example of a stretching apparatus that longitudinally stretches an amorphous thermoplastic resin film by an inter-roll neck-in stretching method.

  As shown in FIG. 2, when a long film before stretching A1 unwound from a roll-shaped raw film is stretched in the longitudinal direction, an infeed nip roll 1 (first roll) and an outfeed nip roll 2 (second roll) is held while sandwiching the unstretched film A1 and conveyed. By making the peripheral speed of the outfeed nip roll 2 faster than the infeed nip roll 1, the film A1 before stretching is stretched, and the film A2 after stretching is obtained. At this time, by heating in the stretching furnace 6, the temperature of the film during stretching can be increased, and the film can be stretched without breaking.

  The temperature of the film at the time of stretching, that is, the temperature of the film at the time of stretching the amorphous thermoplastic resin film in the longitudinal direction is appropriately adjusted according to the amount of compensation retardation to be imparted to the obtained retardation film. It is preferable to stretch the film at a temperature in the vicinity of the glass transition temperature Tg of the amorphous thermoplastic resin constituting the film. Thereby, the molecules of the amorphous thermoplastic resin can be oriented in a predetermined direction. In the present specification, the glass transition temperature Tg is measured by a differential scanning calorimeter.

  When the glass transition temperature of the amorphous thermoplastic resin is Tg (° C.), the film temperature T1 during stretching is preferably (Tg-20) ° C. or higher, more preferably (Tg-10) ° C. or higher. Preferably it is (Tg + 50) degrees C or less, More preferably, it is (Tg + 40) degrees C or less. When the temperature T1 is equal to or higher than the lower limit, the film is more difficult to break during stretching. When the temperature T1 is not more than the above upper limit, retardation of the retardation film is further improved.

  The draw ratio of the film is preferably 1.05 times or more, more preferably 1.1 times or more, and preferably 5.0 times or less. In the case of the stretching apparatus shown in FIG. 2, the stretching ratio is adjusted by the peripheral speed difference between the infeed nip roll 1 and the outfeed nip roll 2. When the draw ratio is not less than the above lower limit, it is easy to obtain a desired retardation value to be applied, the film transport tension is hardly lowered, and the possibility that the film meanders is lowered. When the draw ratio is not more than the above upper limit, the film is hardly broken.

  The ratio of the distance between stretching of the film to the width of the film (stretching distance / film width) is preferably 1 or more. The ratio (stretching distance / film width) is more preferably 1.3 or more. The upper limit of the ratio (distance between stretching / film width) is not particularly limited.

  The stretched film A2 stretched in the above-described manner may be cooled and solidified at a temperature equal to or lower than the glass transition temperature Tg (° C.) of the unstretched film A1 after leaving the stretching furnace 6, or as it is. (C) The above shrinking process may be continuously performed while maintaining the above.

  Next, a retardation film can be obtained by shrinking the stretched film A2 (film before shrinkage).

  In the method for producing a retardation film according to the present invention, the stretched film is contracted in the stretched first direction. That is, in the method for producing a retardation film according to the present invention, the stretched film is selectively contracted in a specific direction. The first direction is a contraction direction. The stretched film is preferably contracted in the MD direction, preferably contracted in the longitudinal direction, and preferably contracted in the film flow direction.

  In the method for producing a retardation film according to the present invention, the conveyance speeds of the third and fourth rolls are made different between the third roll and the fourth roll spaced apart from the third roll. The stretched film is preferably shrunk. The third roll is located on the upstream side in the film flow direction, and the fourth roll is located on the downstream side in the film flow direction.

  As shown in FIG. 3, when the stretched film A2 is shrunk in the longitudinal direction, the stretched film A2 is sandwiched between the infeed nip roll 3 (third roll) and the outfeed nip roll 4 (fourth roll). Hold and transport with. By making the peripheral speed of the outfeed nip roll 4 slower than the infeed nip roll 3, the film A2 after stretching is contracted to obtain a film A3 after contraction. Under the present circumstances, by heating in the shrink furnace 7, the temperature of the film at the time of shrinkage | contraction can be made high, and it can be made to shrink | contract without fracture | rupture.

  The shrinkage ratio of the film is preferably 99.9% or less, and more preferably 95% or less. On the other hand, if the shrinkage rate is too small, the film transport tension decreases, and the film may meander. The length in the MD direction of the film A3 after shrinkage is preferably equal to or longer than the length in the MD direction of the film A1 before stretching, and therefore the shrinkage ratio is preferably (1 / applied stretching ratio × 100)% or more. .

  The shrinkage rate is expressed by the following formula (X).

  Shrinkage rate (%) = (Dimension in shrinking direction of film after shrinking) / (Dimension in shrinking direction of film before shrinking) × 100 Formula (X)

  The ratio of the distance between shrinkage to the width of the film (distance between shrinkage / film width) is preferably 1 or less. The ratio (distance between shrinkage / film width) is more preferably 0.7 or less. The lower limit of the ratio (distance between shrinkage / film width) is not particularly limited.

  The film shrunk as described above is preferably cooled and solidified at a temperature equal to or lower than the glass transition temperature Tg (° C.) of the unstretched film A1 after leaving the shrinking furnace 7.

  In the method for producing a retardation film according to the present invention, when the stretched film is contracted, it is preferable to contract the stretched film alone without laminating another film on the stretched film. . In this case, since it is not necessary to use the other film such as a shrinkable film, the manufacturing cost of the retardation film can be reduced. Furthermore, it can suppress that the foreign material adhering to the other film adheres to the retardation film. Moreover, when a shrinkable film is used, it is difficult to control the shrinking direction of the film.

  In order to improve the wettability of the film surface, the surface of the retardation film obtained as described above may be subjected to corona treatment, plasma treatment, anchor layer coating treatment, or the like. In order to protect the surface, a protective film may be attached to the surface of the retardation film. You may give a knurling process to the both ends of retardation film. In order to obtain a desired width, both ends of the retardation film may be removed by slit processing. These treatments or processing are appropriately selected according to the specifications of the retardation film.

  The phase difference film may be in the form of a roll wound in a roll shape.

  The Nz coefficient represented by the following formula (1) of the retardation film is 0.05 or more and 0.95 or less.

  Nz coefficient = (nx−nz) / (nx−ny) (1)

  In the above formula (1), nx represents the refractive index in the in-plane x direction of the retardation film, ny represents the refractive index in the in-plane y direction perpendicular to the x direction of the retardation film, and nz represents the retardation film. Represents the refractive index in the thickness direction.

  The retardation film preferably has a front retardation R0 (nm) defined by the following formula (2) of 50 nm or more. The front retardation R0 (nm) is preferably 500 nm or less. A retardation film satisfying such front retardation R0 value can be provided by the method for producing a retardation film according to the present invention.

  R0 (nm) = | nx−ny | × d (2)

  In the above formula (2), nx represents the in-plane maximum refractive index, ny represents the refractive index in the direction perpendicular to the nx direction of the retardation film, and d represents the average thickness (nm) of the retardation film. ).

  The retardation film preferably has an absolute value of thickness retardation Rth (nm) defined by the following formula (3) of 20 nm or more. The absolute value of the thickness retardation Rth (nm) is more preferably 50 nm or more, and preferably 600 nm or less.

  Rth (nm) = ((nx + ny) / 2−nz) × d (3)

  In the above formula (3), nx represents the maximum refractive index in the plane of the retardation film, ny represents the refractive index in the direction orthogonal to the nx direction in the plane of the retardation film, and nz represents the nx direction and the ny direction. Represents the refractive index in the direction perpendicular to the direction, and d represents the average thickness (nm) of the retardation film.

  When the front retardation R0 and the thickness retardation Rth are not less than the above lower limit and not more than the above upper limit, the display image can be made high quality when the retardation film is incorporated in a liquid crystal display device. If the front retardation R0 deviates from the range of 50 to 500 nm or the absolute value of the thickness retardation Rth deviates from the range of 20 to 600 nm, the birefringence when passing through the liquid crystal tends not to be sufficiently compensated. Yes, the commercial value as a retardation film decreases.

(Use of retardation film)
The retardation film according to the present invention is suitably used to fulfill each function of a retardation film in a composite polarizing plate, a polarizing plate and a liquid crystal display device after being cut into a predetermined size as necessary.

  The composite polarizing plate includes, for example, a retardation film and a polarizing plate laminated on one surface of the retardation film. It is preferable that the retardation film and the polarizing plate are integrated.

  The polarizing plate includes, for example, the retardation film and a polarizer disposed on one surface side of the retardation film. The polarizing plate is preferably the side opposite to the surface of the retardation film, the adhesive layer disposed on one surface side of the retardation film, and the surface of the adhesive layer on which the retardation film is laminated. And a polarizer laminated on the surface of the substrate. It is preferable that the retardation film and the polarizer are integrated through the adhesive layer.

  The liquid crystal display device can be obtained, for example, by laminating the composite polarizing plate or the polarizing plate on a pair of substrates constituting a liquid crystal cell and at least one outer surface of the pair of substrates. The liquid crystal display device includes a pair of substrates constituting a liquid crystal cell, and the composite polarizing plate or the polarizing plate laminated on at least one outer surface of the pair of substrates.

  The retardation film is suitably used as a component of a liquid crystal display device. The retardation film may be used alone, or may be laminated with a polarizing plate and used as a composite polarizing plate. Furthermore, the retardation film may be laminated on a polarizer via an adhesive layer and used as a polarizing plate instead of a protective film on the liquid crystal cell side of the polarizing plate.

  As a method for producing a liquid crystal display device using the retardation film alone, a polarizing plate is disposed on each outer surface of a pair of substrates constituting the liquid crystal cell, The retardation film is disposed between at least one substrate and a polarizing plate facing the substrate, and a backlight is disposed on the polarizing plate disposed on the substrate side opposite to the liquid crystal display surface in the liquid crystal cell. For example, there is a method in which a known lighting system of a type or side light type is provided and a driving circuit is incorporated. The retardation film is preferably disposed on the outer surface of the substrate on the liquid crystal display surface side.

  The retardation film is a film that is sufficiently effective for improving the viewing angle of VA mode, MVA mode, and IPS mode liquid crystal display devices. In the liquid crystal display device using the retardation film, optical quality deterioration such as color unevenness hardly occurs.

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

(Production Example 1 of non-oriented film)
A saturated norbornene resin (manufactured by Zeon Corporation, trade name “Zeonor 1420”) was prepared as an amorphous thermoplastic resin. This amorphous thermoplastic resin was supplied to a single screw extruder, melted and kneaded, and melt extruded from a T die attached to the tip of the single screw extruder to obtain a long non-oriented film (A-1). . The obtained non-oriented film (A-1) had an average thickness of 100 μm, a width of 1500 mm, a glass transition temperature Tg of 135.5 ° C., and an average refractive index of 1.530. The resin constituting the non-oriented film (A-1) was a resin having a positive intrinsic birefringence value.

(Production example 2 of non-oriented film)
As an amorphous thermoplastic resin, a polycarbonate having a bisphenol A skeleton (manufactured by Teijin Chemicals Ltd., trade name “Panlite”) was prepared. A long non-oriented film (B-1) was obtained by a solution casting method using a dope solution in which this amorphous thermoplastic resin was dissolved in methylene chloride to a solid content concentration of 20% by weight. The obtained non-oriented film (B-1) had an average thickness of 100 μm, a width of 1000 mm, a glass transition temperature Tg of 151.1 ° C., and an average refractive index of 1.585. The resin constituting the non-oriented film (B-1) was a resin having a positive intrinsic birefringence value.

(Production Example 3 of non-oriented film)
Polymethylmethacrylate resin as an amorphous thermoplastic resin (methyl methacrylate component content 55 mol%, styrene component content 30 mol%, maleic acid component content 15 mol%, Tg: 120 ° C., weight average molecular weight: 120,000) 90 parts by weight, and acrylonitrile-styrene-butadiene copolymer (butadiene component content 50 mol%, styrene component content 25 mol%, acrylonitrile component content 18 mol%, methyl methacrylate component content 7 mol%, weight average) (Molecular weight: 48000) A mixture prepared by mixing 10 parts by weight was prepared. This mixture was supplied to a single screw extruder, melted and kneaded, and melt extruded from a T die attached to the tip of the single screw extruder to obtain a long non-oriented film (C-1). The obtained non-oriented film (C-1) had an average thickness of 150 μm, a width of 1500 mm, a glass transition temperature Tg of 120.0 ° C., and an average refractive index of 1.510. The resin constituting the non-oriented film (C-1) was a resin having a negative intrinsic birefringence value.

(Examples 1-5 and Reference Examples 1-2)
The unoriented film obtained by the above production examples 1 to 3 is continuously unwound, supplied to a neck-in stretching machine between rolls, and in the stretching zone where the unoriented film is heated, the peripheral speed difference of the roll is determined. It was used and stretched in the length direction (longitudinal direction, flow direction and MD direction). Further, the film was continuously cooled to 80 ° C. in the cooling zone and fixed in orientation, and then wound around a vinyl chloride resin core at a winding tension of 100 N at a room temperature of 23 ° C. to obtain a stretched film.

  The measurement results of the type of non-oriented film, the temperature of the stretching zone, the stretching ratio, the distance between stretching / film width, and the width of the obtained stretched film are as shown in Table 1 below. In addition, the distance between extending | stretching points out the distance between rolls.

  Next, the obtained stretched film is continuously unwound and supplied to a shrinkage device between rolls, and the stretched film is heated in the shrinkage zone, and the length direction (longitudinal direction, Shrinkage was performed in the flow direction and MD direction. Further, the film was continuously cooled to 80 ° C. in the cooling zone and fixed in orientation, and then wound around a vinyl chloride resin core at a winding tension of 100 N at a room temperature of 23 ° C. to obtain a retardation film.

  Table 1 below shows the measurement results of the shrinkage zone temperature, shrinkage rate, distance between shrinkage / film width, and front retardation R0 and Nz coefficient of the obtained retardation film. In addition, the distance between contraction refers to the distance between rolls.

(Comparative Examples 1-3)
The unoriented film obtained by the above production examples 1 to 3 is continuously unwound, supplied to a neck-in stretching machine between rolls, and in the stretching zone where the unoriented film is heated, the peripheral speed difference of the roll is determined. It was used and stretched in the length direction (longitudinal direction, flow direction and MD direction). Further, the film was continuously cooled to 80 ° C. in the cooling zone and fixed in orientation, and then wound around a vinyl chloride resin core at a winding tension of 100 N at a room temperature of 23 ° C. to obtain a stretched film.

  The measurement results of the type of non-oriented film, the temperature of the stretching zone, the stretching ratio, the distance between stretching / film width, and the width of the obtained stretched film are as shown in Table 1 below. In addition, the distance between extending | stretching points out the distance between rolls.

  Next, the obtained stretched film is continuously unwound and supplied to a shrinkage device between rolls, and the stretched film is heated in the shrinkage zone, and the length direction (longitudinal direction, Shrinkage was performed in the flow direction and MD direction. Further, the film was continuously cooled to 80 ° C. in the cooling zone and fixed in orientation, and then wound around a vinyl chloride resin core at a winding tension of 100 N at a room temperature of 23 ° C. to obtain a retardation film.

  The measurement results of the front retardation R0 and the Nz coefficient of the obtained retardation film are as shown in Table 1 below.

(Evaluation method)
The measuring method of the average thickness of the retardation film, the front retardation R0, and the Nz coefficient is as follows.

[Measurement method of average thickness of retardation film]
A strip-shaped film piece was collected in the entire width direction of the film. Film thickness measuring device (trade name “Millitron 1240” manufactured by Seiko EM Co., Ltd.) was measured at intervals of 10 mm parallel to the width direction of the film piece, the total average of the measured values was calculated, and the average thickness of the retardation film ( μm).

[Measurement method of front retardation value R0 and Nz coefficient of retardation film]
Using an automatic birefringence measuring device (manufactured by Oji Scientific Instruments, trade name “KOBRA-WR”), the wavelength of the measurement light is set to 590 nm, the retardation film is measured at intervals of 50 mm in the width direction, and the average value is calculated. The front retardation R0 of the retardation film was determined, and the Nz coefficient of the retardation film was calculated from the measurement results and the average refractive index.

    The results are shown in Table 1 below.

DESCRIPTION OF SYMBOLS 1 ... Infeed nip roll 2 ... Outfeed nip roll 3 ... Infeed nip roll 4 ... Outfeed nip roll 6 ... Stretching furnace 7 ... Shrink furnace 11 ... Melt extrusion apparatus 12 ... Extruder 13 ... Mold 14 ... Cooling roll 15 ... Touch roll 16 , 17 ... Cooling roll A ... Film A1 ... Film before stretching A2 ... Film after stretching A3 ... Film after shrinkage

Claims (14)

A stretching step of stretching the amorphous thermoplastic resin film in at least the first direction;
A shrinking step of shrinking the stretched film in the stretched first direction to obtain a retardation film having an Nz coefficient of 0.05 or more and 0.95 or less. . In the stretching step, the amorphous thermoplastic resin film is stretched in the MD direction,
The method for producing a retardation film according to claim 1, wherein in the shrinking step, the stretched film is shrunk in the MD direction to obtain a retardation film whose slow axis direction is the MD direction.   The method for producing a retardation film according to claim 1 or 2, wherein a retardation film having a front retardation R0 of 50 nm or more is obtained. In the stretching step, the ratio of the distance between stretching of the film to the width of the film (distance between stretching / film width) is 1 or more,
The method for producing a retardation film according to claim 1, wherein, in the shrinking step, a ratio of the distance between shrinkage to the width of the film (distance between shrinkage / film width) is 1 or less. . In the stretching step, the stretching ratio of the film is 1.05 times or more,
The method for producing a retardation film according to claim 1, wherein in the shrinking step, the shrinkage rate of the film is 99.9% or less.   In the stretching step, the non-crystalline heat is changed between the first roll and the second roll spaced apart from the first roll by different conveying speeds by the first and second rolls. The method for producing a retardation film according to claim 1, wherein the plastic resin film is stretched.   In the shrinking step, the stretched film is made by changing the conveying speed of the third and fourth rolls between the third roll and the fourth roll spaced apart from the third roll. The manufacturing method of the retardation film of any one of Claims 1-6 which shrink | contracts.   The method for producing a retardation film according to claim 1, wherein, in the shrinking step, the stretched film is shrunk alone without laminating another film on the stretched film. . A melt extrusion step of melt-extruding an amorphous thermoplastic resin into a film,
The production of the retardation film according to any one of claims 1 to 8, further comprising a cooling step of cooling the amorphous thermoplastic resin that has been melt-extruded to obtain the amorphous thermoplastic resin film. Method. A single-layer retardation film formed of an amorphous thermoplastic resin,
The slow axis direction is the MD direction,
A retardation film having an Nz coefficient of 0.05 or more and 0.95 or less.   The retardation film according to claim 10, which is obtained by stretching the amorphous thermoplastic resin film in the MD direction and then shrinking the stretched film in the MD direction.   The retardation film according to claim 10 or 11, wherein the front retardation R0 is 50 nm or more. A retardation film obtained by the method for producing a retardation film according to any one of claims 1 to 9,
A composite polarizing plate comprising: a polarizing plate laminated on one surface of the retardation film. A retardation film obtained by the method for producing a retardation film according to any one of claims 1 to 9,
A polarizing plate comprising: a polarizer disposed on one surface side of the retardation film.

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