TW201632923A - Optical film manufacturing method - Google Patents

Abstract

The present invention relates to a method of manufacturing an optical film using a tenter stretching device provided with multiple clips as holding means. This method involves holding both edges of an elongate resin film by means of clips at a conveyance-direction clip interval L1 (a holding step), to allowing the resin film to slacken in the width direction by decreasing the width-direction clip interval from W1 to W2 while conveying said resin film in the length direction (a slackening step), and stretching the resin film in the lengthwise direction by increasing the conveyance-direction clip interval to L2 while conveying, in the lengthwise direction, the resin film that has been slackened in the width direction (a stretching step).

Description

Optical film manufacturing method

The present invention relates to a method of producing an optical film.

Heretofore, there has been known a technique of forming an optical film by stretching and transporting a long film by a tenter jig and expanding the interval in which the tenter jig is conveyed, thereby extending the film (for example, , claim 7) of Patent Document 1. For such an extension technique, there is a case where wrinkles or breaks occur at the side edges of the film at the initial stage of the stretching, and as a result, there is a case where the side edge portion of the film is not caught by the jig and cannot be caught when the jig is clamped. The problem (hereinafter, referred to as "clamp failure") causes a decrease in productivity.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2008-26881

The present invention has been made to solve the above problems, and a main object thereof is to provide a method for producing an optical film, which comprises the step of extending a long resin film in a conveying direction by using a tenter stretching device, and the manufacturing method A method of suppressing the failure of a jig caused by wrinkles or breakage.

The present invention provides a method of manufacturing an optical film using a tenter stretching device having a plurality of jigs as gripping means. The method includes the following steps: The jig interval L1 in the transport direction grips both side edges of the elongated resin film (grip step); while the resin film is transported in the longitudinal direction, the jig spacing in the width direction is reduced from W1 to W2, and the The resin film is relaxed in the width direction (relaxation step); and the resin film which is relaxed in the width direction is transported in the longitudinal direction, and the jig interval in the transport direction is expanded to L2, and the resin film is extended in the longitudinal direction (extension step) .

In one embodiment, the total stretching magnification A (A = L2 / L1) in the longitudinal direction is 2.0 or more.

In one embodiment, the reduction ratio B (B=W2/W1) of the jig spacing in the width direction is 0.60 to 0.99.

In one embodiment, the slack step includes expanding the jig interval in the transport direction to L1 ′ while reducing the jig interval in the width direction, and extending the resin film in the longitudinal direction and extending in the longitudinal direction. The decrease ratio B (B=W2/W1) of a(a=L1'/L1) and the jig spacing in the width direction satisfies the relationship of B<1/√a.

In one embodiment, the thickness of the produced optical film is 110 μm or less.

In one embodiment, the optical film produced is a polarizing film.

In the production method of the present invention, the resin film is relaxed in the width direction before extending in the longitudinal direction. Thereby, a region in which the resin film has been loosened in the width direction is formed in a region extending in the longitudinal direction, and wrinkles or breakage occurring in a region extending in the longitudinal direction can be suppressed from reaching the tenter inlet. As a result, it is possible to suppress the occurrence of a jig failure, and it is possible to manufacture an optical film without deteriorating productivity.

10‧‧‧ Track

10L‧‧‧ring track on the left

10R‧‧‧Round track on the right

20‧‧‧ fixture

30a, 30b‧‧‧ drive sprocket

40a, 40b‧‧‧ electric motor

50‧‧‧Laminated body (resin film)

100‧‧‧Extension

A‧‧‧ grasping area

B‧‧‧TD relaxation area

C‧‧‧MD extended area

D‧‧‧Remove area

L1, L1', L2‧‧‧ clamp direction of the transport direction

W1, W2‧‧‧ clamp spacing in the width direction

Fig. 1 is a schematic plan view for explaining an overall configuration of an example of an extension device which can be used in the production method of the present invention.

Fig. 2 is a schematic view for explaining an embodiment of the present invention.

Fig. 3 is a schematic view showing another embodiment of the present invention.

A. Method for manufacturing optical film

In the method for producing an optical film of the present invention, a tenter stretching device having a plurality of jigs as a gripping mechanism for a film is used. The manufacturing method of the present invention includes the step of gripping both side edges of the elongated resin film at the jig interval L1 in the transport direction by the jig (the gripping step); and transporting the resin film in the longitudinal direction The gap between the jigs in the width direction is reduced from W1 to W2, and the resin film is relaxed in the width direction (relaxation step); and the resin film which has been loosened in the width direction is transported in the longitudinal direction while the jig interval in the transport direction is enlarged. To L2, the resin film is extended in the longitudinal direction (extension step). In the tenter stretching device using the jig gripping film, in the state in which the end of the resin film is gripped by the jig in a state where the tension before the stretching is not applied, until the tension is applied to the resin film by heating or stretching, When the surface of the heating is uneven or the precision of each jig is conveyed, stress is applied to the resin film. As a result, it is considered that a large wrinkle or breakage occurs in the resin film in the initial stage of the extension, and the jig is broken. On the other hand, in the present invention, the resin film is relaxed in the width direction before extending in the longitudinal direction. Thereby, the region in which the resin film has been relaxed in the width direction is formed in the region extending in the longitudinal direction, and excessive tension is generated in the resin film in the tenter entrance region of the resin film, thereby suppressing the malfunction of the jig. produce.

The resin film which can be used in the production method of the present invention may be a laminate having a thermoplastic resin substrate and a resin layer formed on one side of the thermoplastic resin substrate, or a single layer body including a single film. The optical film to be produced may be any suitable optical film as long as it can be produced by a production method including the above-described holding step, relaxation step, and stretching step. The thickness of the optical film is preferably 110 μm or less, preferably 80 μm or less, more preferably 70 μm or less, still more preferably 60 μm or less. On the other hand, the thickness of the optical film is preferably 10 μm or more, and more preferably 20 μm or more.

As a specific example of the optical film to be manufactured, a polarizing film, an optical compensation film, or the like can be preferably exemplified.

As the tenter stretching device used in the manufacturing method of the present invention, for example, an extending device including: a pair of rails having a straight portion in which the distance between the tapered portions is continuously decreased and the straight portion between the rails is constant, And a plurality of jigs that can be moved on each track while changing the interval of the jig. According to such an extension device, the jig spacing (the distance between the jigs on the same track) and the jig spacing in the width direction are changed by the gripping of the both side edges of the resin film by the jig (on different tracks) The distance between the jigs can be extended in the longitudinal direction (MD extension) and in the width direction (TD relaxation).

Fig. 1 is a schematic plan view showing an overall configuration of an example of an extension device which can be used in the production method of the present invention. Referring to Figure 1, an extension device that can be used in the manufacturing method of the present invention will be described. The extension device 100 has an annular rail 10L and an annular rail 10R symmetrically on the right and left sides in plan view. Further, in the present specification, the annular track on the left side is referred to as the left end circular track 10L, and the right side annular track is referred to as the right side annular track 10R as viewed from the inlet side of the laminated body. A plurality of jigs 20 for holding the resin film are disposed on the left and right circular orbits 10L and 10R, respectively. The jig 20 is guided by the respective rails to move in a circular manner. The jig 20 on the left circular track 10L is circulated in the counterclockwise direction, and the jig 20 on the right circular track 10R is circulated in the clockwise direction. In the extension device, the grip area A, the TD slack area B, the MD extension area C, and the release area D are sequentially provided from the loading side of the resin film toward the carry-out side. Further, the respective regions mean a region in which the resin film is substantially grasped, TD relaxed (or TD relaxed and MD extended), MD extended and released, and does not mean a mechanically and structurally independent interval. Further, it should be noted that the ratio of the lengths of the regions in the extension device of Fig. 1 is different from the ratio of the actual length.

In the grip area A, the left and right circular orbits 10R, 10L are regarded as straight portions having a constant distance between the tracks. Typically, the left and right circular orbits 10R and 10L are configured in such a manner as to correspond to the distance between the orbits of the initial width of the resin film to be processed. They are roughly parallel to each other. In the TD relaxation region B, the left and right circular orbits 10R, 10L are regarded as tapered portions in which the distance between the tracks is continuously reduced. By way of example, the left and right circular orbits 10R, 10L are configured as follows: as the self-grip area A side advances toward the MD extension area C side, the distance between the tracks gradually decreases until the relaxation of the resin film is performed. The width of the back. In the MD extension region C and the release region D, the left and right circular orbits 10R and 10L are regarded as straight portions having a constant distance between the tracks, and are typically configured to correspond to the slack of the resin film. The distance between the tracks of the width is substantially parallel to each other.

The jig (the jig on the left side) 20 on the circular track 10L on the left side and the jig (the jig on the right side) 20 on the right end track 10R can be independently oscillated. For example, the driving sprocket wheels 30a, 30b of the left circular orbiting track 10L are rotationally driven in the counterclockwise direction by the electric motors 40a, 40b, and the driving sprocket 30a, 30b of the right circular orbiting track 10R is driven by the electric motors 40a, 40b. Rotate the drive clockwise. As a result, the urging force is supplied to the jig carrier member (not shown) that is engaged with the drive rollers (not shown) of the drive sprocket wheels 30a and 30b. Thereby, the jig 20 on the left side moves in the counterclockwise direction, and the jig 20 on the right side moves in the clockwise direction. By independently driving the electric motor on the left side and the electric motor on the right side, the jig 20 on the left side and the jig 20 on the right side can be independently oscillated.

The size of the jig is preferably from 12 mm to 40 mm, more preferably from 15 mm to 35 mm. When the size of the jig is less than 12 mm, there is a case where the stretching tension cannot be maintained and the driving force is abnormal due to insufficient strength of the jig conveying portion. When the size of the jig exceeds 40 mm, the area which is not extended in the vicinity of the jig becomes large, and the unevenness of the end portion occurs, or the non-grip portion is partially extended to cause cracking on the surface of the resin film. Furthermore, the term "clamp size" means the width of the grip area.

Further, the jig 20 on the left side and the jig 20 on the right side are each of a variable pitch type. In other words, the left and right jigs 20 and 20 are independent and can be moved, and the jig interval (clamp pitch) in the transport direction changes. Variable pitch type fixtures can be used by a zoomer mechanism (for example, Japan) It is realized by any appropriate configuration such as the configuration described in Japanese Patent Laid-Open Publication No. 2008-23775.

In the case of using the stretching device as illustrated in FIG. 1, the manufacturing method of the present invention may include the steps of: in the gripping area A, gripping the both sides of the resin film by the jig at the jig interval L1 of the conveying direction by the jig a portion (clamping step); the resin film is passed through the tapered portion to reduce the gap between the jigs in the width direction from W1 to W2, thereby relaxing the resin film in the width direction (relaxation step); while the resin film passes through the straight portion The jig interval in the transport direction is expanded to L2, and the resin film is extended in the longitudinal direction (MD extension step). Further, if necessary, the method further includes the step of releasing the jig holding the resin film (release step). 2 and 3 are schematic views for explaining an example of the manufacturing method of the present invention including the steps. Hereinafter, each step will be described in more detail with reference to the drawings.

First, in the gripping step (grip area A), the both sides of the resin film 50 loaded into the stretching device are gripped by the left and right jigs 20 at a certain grip interval (clamp interval) L1, The resin film 50 is transported to the TD relaxation region B by the movement of each of the jigs 20 guided by the left and right circular orbits. The grip intervals (clamp intervals) of the both side edges in the grip area A are representatively considered to be equal intervals. L1 can be, for example, 30 mm to 200 mm. Furthermore, the so-called jig spacing is the distance between the centers of adjacent jigs.

As the resin film held by the jig, any appropriate film can be selected depending on the use of the optical film to be produced or the like. In the case where the optical film to be produced is a polarizing film, as an example, a laminate having a thermoplastic resin substrate and a PVA-based resin layer formed on one side of the thermoplastic resin substrate is used as a resin film. Hereinafter, the unique features, conditions, and the like will be described with respect to the laminated body, and then the steps after the relaxation step will be described. For the steps after the relaxation step, the same operation, conditions, and the like can be applied regardless of whether it is a laminate or a usual resin film (single film).

The above laminated system is produced by forming a PVA-based resin layer on a long-length thermoplastic resin substrate. The thermoplastic resin substrate can be obtained by supporting the PVA-based resin layer from one side The polarizing film can be configured as any appropriate.

Examples of the material for forming the thermoplastic resin substrate include an ester resin such as a polyethylene terephthalate resin, a cycloolefin resin, an olefin resin such as polypropylene, a polyamide resin, and a polycarbonate resin. Resin, such copolymer resins, and the like. Among these, a cycloolefin type resin is preferable (for example, An olefinic resin) or an amorphous polyethylene terephthalate resin. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer containing isophthalic acid as a dicarboxylic acid or a copolymer containing cyclohexane dimethanol as a diol. .

The extension temperature of the thermoplastic resin substrate can be set to an appropriate value depending on the material for forming the thermoplastic resin substrate, the stretching method, and the like. The stretching temperature is typically at least the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably Tg + 10 ° C or higher, and more preferably Tg + 15 ° C to Tg + 30 ° C. When the dry stretching method or the wet stretching method is used as the stretching method, and the amorphous polyethylene terephthalate resin is used as the material for forming the thermoplastic resin substrate, the elongation temperature can be made lower than that of the thermoplastic resin. The glass transition temperature of the substrate (for example, 60 ° C to 100 ° C).

The thermoplastic resin substrate may be subjected to surface modification treatment (for example, corona treatment or the like) in advance, or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing the above treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved. Furthermore, the surface modification treatment and/or the formation of the easy-to-adhere layer may be performed before the above extension, or may be performed after the above extension.

The method for forming the PVA-based resin layer described above may be any appropriate method. It is preferable to apply a coating liquid containing a PVA-based resin to a thermoplastic resin substrate subjected to the elongation treatment and to dry it, thereby forming a PVA-based resin layer.

As the PVA-based resin, any appropriate resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be saponified by copolymerizing an ethylene-vinyl acetate copolymer obtain. The saponification degree of the PVA-based resin is usually from 85 mol% to 100 mol%, preferably from 95.0 mol% to 99.95 mol%, and further preferably from 99.0 mol% to 99.93 mol%. The degree of saponification can be determined in accordance with JIS K 6726-1994. By using the PVA-based resin having a saponification degree as described above, a polarizing film excellent in durability can be obtained. When the degree of saponification is too high, the coating liquid is liable to gel, and it becomes difficult to form a uniform coating film.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually from 1,000 to 10,000, preferably from 1200 to 4,500, and more preferably from 1,500 to 4,300. Further, the average degree of polymerization can be determined in accordance with JIS K 6726-1994.

The coating liquid is typically a solution obtained by dissolving the PVA-based resin in a solvent. Examples of the solvent include polyols such as water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and trimethylolpropane. Amines such as ethylenediamine and diethylenetriamine. These may be used singly or in combination of two or more. Among these, water is preferred. The concentration of the PVA resin in the solution is preferably from 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. When it is the said resin density, it can form the uniform coating film adhered in the thermoplastic resin base material.

It is also possible to formulate an additive to the coating liquid. Examples of the additive include a plasticizer, a surfactant, and the like. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As a surfactant, a nonionic surfactant is mentioned, for example. These can be used for the purpose of further improving the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

As the coating method of the coating liquid, any appropriate method can be employed. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (using a double-angle roller) Roll coating method, etc.).

The drying temperature is preferably not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, and more preferably Tg to 20 °C or less. By drying at the above temperature, deformation of the thermoplastic resin substrate before formation of the PVA-based resin layer can be prevented, and the obtained PVA system can be prevented. The alignment of the resin layer is deteriorated. As described above, the thermoplastic resin substrate can be favorably deformed together with the PVA-based resin layer, and the slack and elongation of the laminate described below can be favorably performed. As a result, a good alignment property can be imparted to the PVA-based resin layer, and a polarizing film having excellent optical characteristics can be obtained. Here, the "alignment property" means the alignment of the molecular chains of the PVA-based resin layer.

Then, in the relaxation step (TD relaxation region B), the resin film 50 held by the left and right jigs 20 is loosened in the width direction while being conveyed in the longitudinal direction. In the TD relaxation region B, the left and right circular orbits 10R, 10L are regarded as tapered portions in which the distance between the tracks is continuously reduced, and therefore, by passing the region, the jig interval in the width direction is reduced from W1 to W2, thereby performing The resin film 50 is slack in the width direction. The amount of slack can be controlled by adjusting the amount of change in the distance between the tracks. Specifically, the ratio of the inter-track distance at the exit of the TD relaxation region B (the end portion on the side of the MD extension region C) to the distance between the rails at the entrance of the TD relaxation region B (the end portion on the grip region A side) becomes small. The more the amount of slack can be obtained. In the present specification, the term "relaxing the resin film in the width direction" means that the resin film is formed in a region which is relaxed in the width direction (in other words, is not subjected to tension), and in one embodiment, the resin film can be used. Shrink in the width direction.

In the embodiment illustrated in Fig. 2, only the relaxation of the resin film 50 in the width direction is performed in the relaxation step. In this case, the resin film 50 is allowed to pass through the TD relaxation region B while maintaining the jig interval (L1) in the conveyance direction. On the other hand, in the embodiment illustrated in Fig. 3, in the relaxation step, the resin film 50 is relaxed in the width direction and extended in the longitudinal direction. In this case, while the resin film 50 passes through the TD relaxation region B, the moving speed of the jig 20 in the conveyance direction is gradually increased, and the jig interval in the conveyance direction is expanded from L1 to L1'. The final stretching ratio can be made high by performing the MD stretching in multiple stages in the relaxation step and the stretching step. Moreover, since the slack in the width direction and the extension in the longitudinal direction are simultaneously performed, excessive slack can be avoided, and therefore an effect of suppressing generation of wrinkles due to slack can be obtained.

The reduction ratio B (B=W2/W1) of the jig interval in the width direction can be set to an appropriate value depending on the MD extension ratio or the like. The reduction magnification B is preferably from 0.60 to 0.99, more preferably from 0.65 to 0.90, still more preferably from 0.70 to 0.80. If the reduction ratio is such, a relaxed region can be preferably formed in the width direction of the resin film. Further, in the production of a polarizing film, more excellent optical characteristics can be obtained. Further, the jig spacing in the width direction may correspond to the width of the resin film of the portion held by the left and right jigs.

In the embodiment in which the relaxation step includes the MD extension (the embodiment illustrated in FIG. 3), the shrinkage ratio in the width direction is reduced as compared with the case where the free end is uniaxially stretched in the longitudinal direction. Clamp spacing in the width direction. Specifically, it is preferable that the magnification ratio a in the longitudinal direction (a=L1'/L1) and the reduction ratio B in the width direction satisfy the relationship of B<1/√a. When the above relationship is satisfied, it is preferable to form a slack region in the width direction of the resin film regardless of the extension in the longitudinal direction. The stretching ratio a in the longitudinal direction may preferably be 1.0 to 5.5 times, more preferably 1.1 to 4.0 times.

The temperature (relaxation temperature) of the resin film in the relaxation step is set to an appropriate value depending on the material for forming the resin film or the like. The relaxation temperature of the laminate in the case of producing a polarizing film is typically a glass transition temperature (Tg) or more of the thermoplastic resin substrate, preferably a glass transition temperature (Tg) of the thermoplastic resin substrate + 10 Above °C, it is more preferably Tg+15 °C or more. On the other hand, the relaxation temperature of the laminate is preferably 170 ° C or lower.

Then, in the extending step (MD extension region C), the resin film 50 held by the right and left jigs 20 is extended in the longitudinal direction while being conveyed in the longitudinal direction. The extension of the resin film 50 is performed by gradually increasing the moving speed of the jig 20 in the conveying direction and increasing the jig interval in the conveying direction to L2. The stretch ratio can be controlled by adjusting the jig interval (L1 or L1') of the transport direction at the entrance of the MD extension region C and the jig interval (L2) of the transport direction at the exit of the MD extension region C (not included in the relaxation step) In the case of MD extension, it is L2/L1, and in the case where the relaxation step includes MD extension, it is L2/L1'). Furthermore, also The shrinkage in the width direction can be simultaneously performed in the stretching step. In the case where the contraction in the width direction is simultaneously performed in the extending step, the tapered portion in which the distance between the tracks of the left and right circular orbits 10R and 10L is continuously reduced may be provided in the MD extending region C. The contraction rate in the width direction can be controlled by adjusting the amount of decrease in the distance between the left and right rails.

The total stretching ratio of the resin film after the stretching step (the product of the stretching ratio in the stretching step and the stretching ratio in the relaxation step, L2/L1) is preferably 2.0 times or more, more preferably the original length of the resin film. It is 2.0 times to 6.5 times.

The stretching temperature is set to an appropriate value depending on the material for forming the resin film or the like. The elongation temperature in the case of producing a polarizing film is typically a glass transition temperature (Tg) or more of the thermoplastic resin substrate, and preferably a glass transition temperature (Tg) of the thermoplastic resin substrate + 10 ° C or more. Further preferably, it is Tg + 15 ° C or more. On the other hand, the stretching temperature is preferably 170 ° C or lower. By extending at the above temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin, and to suppress the abnormality caused by the crystallization (for example, to hinder the alignment of the PVA-based resin layer which is extended).

Finally, in the releasing step (release region D), the jig 20 that grips the resin film 50 is released. In the release step, representatively, it is considered that the distance between the jigs and the interval between the jigs are constant. If necessary, the resin film 50 is cooled to a desired temperature (preferably below the glass transition temperature (Tg)), and then the jig is released.

The method for producing an optical film of the present invention may include other steps in addition to the above. Examples of other steps in the case of producing a polarizing film as an optical film include an insolubilization step, a dyeing step, a crosslinking step, an extension step different from the above extension, a washing step, and a drying (adjustment of moisture content) step. Other steps can be performed at any appropriate time.

The dyeing step is representatively a step of dyeing the PVA-based resin layer with a dichroic substance. It is preferred to carry out the adsorption of the dichroic substance by the PVA-based resin layer. As the adsorption method, for example, a PVA-based resin layer (layered body) is immersed A method of staining in a dyeing liquid containing a dichroic substance; a method of applying a dyeing liquid to a PVA-based resin layer; a method of spraying a dyeing liquid onto a PVA-based resin layer; Preferably, the layered body is immersed in a dyeing liquid containing a dichroic substance. The reason for this is that the dichroic substance can be adsorbed well. Both sides of the laminate may be immersed in the dyeing liquid, or only the laminated body may be immersed in the dyeing liquid on one side. Further, in the dyeing step and/or the crosslinking step described below, the stretching may be carried out simultaneously.

Examples of the dichroic substance include iodine and an organic dye. These may be used singly or in combination of two or more. The dichroic material is preferably iodine. In the case where iodine is used as the dichroic substance, the above dyeing liquid is preferably an aqueous iodine solution. The amount of iodine to be added is preferably 0.1 part by weight to 1.0 part by weight based on 100 parts by weight of water. In order to improve the solubility of iodine in water, it is preferred to formulate an iodide salt in an aqueous iodine solution. Examples of the iodide salt include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, and titanium iodide. Wait. Among these, potassium iodide and sodium iodide are preferred. The amount of the iodide salt to be added is preferably from 0.3 part by weight to 15 parts by weight per 100 parts by weight of the water.

The liquid temperature at the time of dyeing the dyeing liquid is preferably from 20 ° C to 40 ° C. When the PVA-based resin layer is immersed in the dyeing liquid, the immersion time is preferably from 5 seconds to 300 seconds. Under the above conditions, the PVA-based resin layer can sufficiently adsorb the dichroic substance.

The insolubilization step and the crosslinking step are typically carried out by immersing the PVA-based resin layer in an aqueous boric acid solution. The washing step is typically carried out by immersing the PVA-based resin layer in an aqueous solution of potassium iodide. The drying temperature in the above drying step is preferably from 30 ° C to 100 ° C.

B. Polarizing film

The polarizing film produced by the above production method is substantially a PVA-based resin film which adsorbs an alignment dichroic substance. The polarizing film preferably exhibits absorption dichroism at any of wavelengths of 380 nm to 780 nm.

The method of using the polarizing film can be any suitable method. Specifically, it may be used in a state of being integrated with the thermoplastic resin substrate, or may be used by transferring the thermoplastic resin substrate to another member (peeling the thermoplastic resin substrate).

The polarizing film produced by the above production method has a small shrinkage stress and is excellent in dimensional stability even in a high temperature environment. Further, the degree of polarization at a monomer transmittance of 42% is preferably 99.99% or more. As described above, it is excellent in optical characteristics.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the invention is not limited by the examples.

[Example 1]

<Production of laminated body>

An amorphous PET substrate (100 μm thick) was prepared as a thermoplastic resin substrate, and a PVA aqueous solution was applied to the amorphous PET substrate, and dried at a temperature of 50 ° C to 60 ° C. Thereby, a 14 μm thick PVA layer was formed on an amorphous PET substrate to form a laminate.

<TD relaxation and MD extension>

The obtained laminate was loosened in the width direction and then extended in the longitudinal direction using an extension device as shown in FIG. Specifically, in the grip area A, the both side edges of the laminated body are gripped at the jig spacing L1: 40 mm and transported in the longitudinal direction, and in the TD slack area B, the jigs in the width direction are separated at 100 ° C. The 800 mm (W1) was reduced to 680 mm (W2) and the laminated body was shrunk in the width direction (the jig interval L1' at the exit of the TD relaxation region B: 40 mm). Then, in the MD extension region C, the laminate body was extended to three times in the longitudinal direction at 120 ° C (the jig interval L2 at the exit of the MD extension region C: 120 mm, and the jig interval W3: 680 mm in the width direction). Thereafter, in the release region D, the jig for grasping the laminated body is released.

In the TD relaxation, the extension ratio a (a=L1'/L1) in the longitudinal direction is 1, and the width direction The reduction ratio B (B=W2/W1) of the jig interval is 0.85, and the relationship of B<1/√a is satisfied.

In the TD relaxation and MD extension, no clamping failure occurred.

<staining treatment>

Then, the laminate was immersed in an aqueous iodine solution (iodine concentration: 0.5% by weight, potassium iodide concentration: 10% by weight) at 25 ° C for 30 seconds.

<Crosslinking treatment>

The dyed layered body was immersed in a boric acid aqueous solution (boric acid concentration: 5% by weight, potassium iodide concentration: 5% by weight) at 60 ° C for 60 seconds, and at the same time, extended to 1.6 times in the MD direction (total stretching ratio: 5) Double).

<Washing treatment>

After the crosslinking treatment, the laminate was immersed in a potassium iodide aqueous solution (potassium iodide concentration: 5% by weight) at 25 ° C for 5 seconds.

In the above manner, a polarizing film having a thickness of 3.5 μm was formed on a thermoplastic resin substrate.

[Embodiment 2]

A polarizing film having a thickness of 3.5 μm was formed on the resin substrate in the same manner as in Example 1 except that the TD relaxation and the MD extension were carried out in the following manner.

<TD relaxation and MD extension>

The obtained laminate was loosened in the width direction and then extended in the longitudinal direction by using an extension device as shown in FIG. Specifically, in the grip area A, the both side edges of the laminated body are gripped at the jig spacing L1: 40 mm and transported in the longitudinal direction, and in the TD slack area B, the jigs in the width direction are separated at 100 ° C. 800 mm (W1) is reduced to 680 mm (W2) to shrink the laminate in the width direction. At the same time, in the TD relaxation region B, the jig interval is increased to L1': 45 mm and extends in the length direction. Then, in the MD extension region C, the laminate body is extended to three times in the longitudinal direction at 120 ° C (the jig spacing L2 at the exit of the MD extension region C is 120 mm, and the jig interval W3: 680 in the width direction) Mm). Thereafter, in the release region D, the jig for grasping the laminated body is released. In other words, TD relaxation and MD extension were performed in the same manner as in Example 1 except that the MD extension was simultaneously performed in the TD relaxation region B.

In the TD relaxation, the stretching magnification a (a=L1'/L1) in the longitudinal direction is 1.125, so 1/√a is 0.943, and the reduction ratio B (B=W2/W1) of the jig interval in the width direction is 0.85, and Satisfy the relationship of B<1/√a.

In the TD relaxation and MD extension, no clamping failure occurred.

[Example 3]

A polarizing film having a thickness of 3.5 μm was formed on the resin substrate in the same manner as in Example 1 except that the TD relaxation and the MD extension were carried out in the following manner.

<TD relaxation and MD extension>

The obtained laminate was loosened in the width direction and then extended in the longitudinal direction by using an extension device as shown in FIG. Specifically, in the grip area A, the both side edges of the laminated body are gripped at the jig spacing L1: 40 mm and transported in the longitudinal direction, and in the TD slack area B, the jigs in the width direction are separated at 100 ° C. 800 mm (W1) is reduced to 680 mm (W2) to shrink the laminate in the width direction. At the same time, in the TD relaxation region B, the jig interval is increased to L1': 45 mm and extends in the length direction. Then, in the MD extension region C, the laminate body was extended to three times in the longitudinal direction at 120 ° C (the jig interval L2 at the exit of the MD extension region C: 120 mm). At the same time, in the extended region C, the jig spacing in the width direction is reduced from 680 mm (W2) to 560 mm (W3), and the laminated body is shrunk in the width direction. Thereafter, in the release region D, the jig for grasping the laminated body is released. In other words, the TD relaxation and the MD extension were performed in the same manner as in the first embodiment except that the MD extension was simultaneously performed in the TD relaxation region B and the MD direction was simultaneously contracted in the MD extension region C.

In the TD relaxation, the stretching magnification a (a = L1 ' / L1) in the longitudinal direction is 1.125, so 1 / √ a is 0.943, and the reduction ratio B (B = W2 / W1) of the jig interval in the width direction is 0.85, and satisfy the relationship of B<1/√a.

In the TD relaxation and MD extension, no clamping failure occurred.

[Example 4]

A polarizing film having a thickness of 3.5 μm was formed on the resin substrate in the same manner as in Example 1 except that the TD relaxation and the MD extension were carried out in the following manner.

<TD relaxation and MD extension>

The obtained laminate was loosened in the width direction and then extended in the longitudinal direction by using an extension device as shown in FIG. Specifically, in the grip area A, the both side edges of the laminated body are gripped at the jig spacing L1: 40 mm and transported in the longitudinal direction, and in the TD slack area B, the jigs in the width direction are separated at 100 ° C. 800 mm (W1) is reduced to 680 mm (W2) to shrink the laminate in the width direction. At the same time, in the TD relaxation region B, the jig interval is increased to L1': 60 mm and extends in the length direction. Then, in the MD extension region C, the laminate body was extended to three times in the longitudinal direction at 120 ° C (the jig interval L2 at the exit of the MD extension region C: 120 mm). At the same time, in the extended region C, the jig spacing in the width direction is reduced from 680 mm (W2) to 560 mm (W3), and the laminated body is shrunk in the width direction. Thereafter, in the release region D, the jig for grasping the laminated body is released. In other words, TD relaxation and MD extension were performed in the same manner as in Example 3 except that the MD stretching magnification in the TD relaxation region B was 1.5.

In the TD relaxation, the stretching magnification a (a=L1'/L1) in the longitudinal direction is 1.5, so 1/√a is 0.816, and the reduction ratio B (B=W2/W1) of the jig interval in the width direction is 0.85, and The relationship of B<1/√a is not satisfied.

In the TD relaxation and the MD extension, a number of wrinkles were observed in the laminate, but no clamping failure occurred, and no practical problem occurred.

[Comparative Example 1]

A polarizing film having a thickness of 3.5 μm was formed on the resin substrate in the same manner as in Example 1 except that MD stretching and TD shrinkage were carried out in the following manner.

<MD extension and TD shrinkage>

First, the obtained laminated body is extended in the longitudinal direction, and then stretched in the longitudinal direction and contracted in the width direction. Specifically, initially, the both side edges of the laminated body are gripped at the jig spacing L1: 40 mm and transported in the longitudinal direction, and then the jig spacing is maintained at 800 ° C (W1) while maintaining the jig interval in the width direction at 100 ° C. Up to L1': 70mm and extending in the length direction. Then, the width of the jig is reduced from 800 mm (W2 = W1) to 560 mm (W3) at 120 ° C to shrink the laminate in the width direction and extend to 3 times in the longitudinal direction (the exit of the extended region) The clamp interval is L2: 120 mm). Thereafter, in the release region D, the jig for grasping the laminated body is released.

In the MD extension and TD shrinkage, no clamping failure occurred.

[Evaluation]

When the examples 1 to 4 were compared with the comparative example 1, it was confirmed that the occurrence of the nip failure can be suppressed by loosening the resin film in the width direction before extending in the longitudinal direction. When the third embodiment is compared with the fourth embodiment, it is clear that the reduction ratio in the longitudinal direction and the reduction ratio in the width direction of the TD slack are controlled to a specific relationship, thereby further suppressing wrinkles and the like. As a result, it can be seen that the occurrence of the nip failure can be further suppressed.

[Industrial availability]

The production method of the present invention can be preferably used for the production of an optical film such as a polarizing film or an optical compensation film.

20‧‧‧ fixture

50‧‧‧Layered body

A‧‧‧ grasping area

B‧‧‧TD relaxation area

C‧‧‧MD extended area

D‧‧‧Remove area

L1, L2‧‧‧ clamp spacing in the transport direction

W1, W2‧‧‧ clamp spacing in the width direction

Claims (6)

A method for producing an optical film, which comprises producing a film by using a tenter stretching device having a plurality of jigs as gripping means, and comprising the steps of: holding the length of the jig interval L1 in the conveying direction by the jig Both side edges of the strip-shaped resin film (grip step); while the resin film is conveyed in the longitudinal direction, the gap between the width direction is reduced from W1 to W2, and the resin film is relaxed in the width direction (relaxation step) And the resin film which has been loosened in the width direction is conveyed in the longitudinal direction, and the jig interval in the conveyance direction is expanded to L2, and the resin film is extended in the longitudinal direction (extension step). The method of claim 1, wherein the total stretching magnification A (A = L2 / L1) in the longitudinal direction is 2.0 or more. The method of claim 1, wherein the reduction ratio B (B=W2/W1) of the jig interval in the width direction is 0.60 to 0.99. The method of claim 1, wherein the relaxing step comprises: reducing a jig interval in the width direction, and expanding the jig interval of the conveying direction to L1', and extending the resin film in the longitudinal direction and extending the magnification in the longitudinal direction a (a=L1'/L1) The reduction ratio B (B=W2/W1) of the jig spacing in the width direction satisfies the relationship of B<1/√a. The method of claim 1, wherein the optical film produced has a thickness of 110 μm or less. The method of claim 1, wherein the optical film produced is a polarizing film.