TW201631338A - Polarizing film production method - Google Patents

Abstract

A method is provided of producing an elongate polarizing film is provided. Using a tenter stretching device which is provided with multiple clips as holding means for holding an elongate resin film that will form a polarizing film, this production method involves stretching the elongate resin film in the length direction and contracting the same in the width direction. The length-direction stretching involves expanding the conveyance-direction interval between clips on the elongate resin film, and the width-direction contraction involves reducing the width-direction interval between clips.

Description

Method for manufacturing polarizing film

The present invention relates to a method of producing a polarizing film. More specifically, the present invention relates to a method of manufacturing a long strip-shaped polarizing film using a tenter stretching device.

In a liquid crystal display device as a representative image display device, a polarizing film is disposed on both sides of a liquid crystal cell due to an image forming method. As a method of producing a polarizing film, a free end uniaxial stretching which extends between rolls having different peripheral speeds is widely used. In the uniaxial stretching at the free end, there is a problem that the width of the obtained film is narrowed due to necking. In order to solve the above problem, there has been proposed a method of extending the roll gap and extending it (short gap roll extension) (for example, Patent Document 1). According to the extension between the short gap rollers, the necking is suppressed by contact with the roller, but on the other hand, for example, there is a problem that it is difficult to control the width of the film as shown in Fig. 9, and as a result, the axis of the end portion in the width direction of the film The accuracy varies in the direction of the length of the film.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2014-74786

The present invention has been made to solve the above problems, and a main object of the present invention is to provide a method for producing a long-length polarizing film which is excellent in axial precision at the end portion in the width direction and which has excellent in-plane uniformity in optical characteristics.

According to an embodiment of the present invention, a method of producing a long polarizing film is provided. The manufacturing method includes the step of extending the elongated resin film in the longitudinal direction by using a tenter stretching device having a plurality of jigs as a gripping mechanism for forming a long resin film of the polarizing film. Shrink in the width direction. The extension in the longitudinal direction includes a step of expanding the interval of the jig in the transport direction of the elongated resin film, and the contracting in the width direction includes a step of reducing the interval between the jigs in the width direction.

In one embodiment, the long resin film forming the polarizing film is a single-layer polyvinyl alcohol resin film, and the production method includes stretching the resin film in the longitudinal direction and shrinking in the width direction, and dyeing the resin film. The step of making a polarizing film.

In one embodiment, the elongated resin film forming the polarizing film is a laminate of a resin substrate and a polyvinyl alcohol-based resin layer formed on one side of the resin substrate, and the manufacturing method includes the laminate. The step of stretching in the longitudinal direction and shrinking in the width direction, and dyeing to form a polarizing film on the resin substrate.

In one embodiment, the shrinkage ratio in the width direction is 0.8 or less.

In one embodiment, the jig has a jig size of 12 mm to 40 mm.

In one embodiment, the jig interval in the transport direction before the extension in the longitudinal direction is 100 mm or less.

In one embodiment, the stretching ratio in the longitudinal direction is 1.5 times to 6.5 times.

According to another aspect of the present invention, a long strip-shaped polarizing film is provided. The polarizing film is obtained by the above-described production method.

According to the production method of the present invention, the stretching in the longitudinal direction and the contraction in the width direction can be performed by using the tenter stretching device, whereby the axial precision of the end portion in the width direction is excellent, and as a result, the in-plane uniformity of the optical characteristics is excellent. Polarized film. Further, such a polarizing film can reduce the amount of cut by the slit processing at the end portion, so that the yield is excellent and can be reduced. Less manufacturing costs. The tenter stretching device is often used for the extension in the lateral direction (width direction), and it is known that the axial accuracy of the end portion in the width direction of the obtained film is insufficient. It is considered that the reason is that the portion of the film to be stretched which is held by the tenter and the portion between the jigs (the portion which is not clamped) are subjected to different stress directions. That is, in the nip portion, the film is subjected to stress in the width direction (lateral direction), and the jigs facing the both sides are subjected to the oblique stress in the portion between the jigs. Therefore, the axial accuracy of the end portion in the width direction of the obtained film becomes insufficient. As a result, the obtained film must be cut and removed in the width direction end portion by, for example, slit processing. In the polarizing film, it is strongly required that the entire film has excellent axial precision (that is, the film as a whole has no deviation in the direction of the absorption axis and the transmission axis), and therefore it is necessary to remove the width direction end portion and use the tenter extension device to extend in the longitudinal direction to obtain polarized light. The idea of membrane does not exist in the industry, but it is a violation of technical common sense. On the other hand, the inventors of the present invention actually performed the extension of the tenter stretching device in the longitudinal direction, and as a result, it was found that the axial accuracy of the end portion in the width direction of the obtained film was good. It is presumed that the reason is that the direction of the stress applied to the portion between the portion sandwiched by the tenter and the jig in the film to be stretched is the same direction (longitudinal direction) as the length of the jig is widened. Further, according to the above method, the shrinkage ratio in the width direction can be accurately controlled by the nip by the tenter, so that unstable shrinkage (uncontrolled shrinkage) does not occur as the gap between the short gap rollers is extended (of course It is also not possible to cause necking as in the case of the usual stretching between rolls. It is also confirmed that the axial precision of the end portion in the width direction of the obtained film is short and the gap between the rolls is well extended. As a result, even if the portion gripped by the tenter is removed, a polarizing film having a wide width and excellent axial accuracy at the end portion in the width direction can be obtained. As described above, in the production method of the present invention, the case where the polarizing film having the axial precision of the end portion in the width direction is obtained is actually obtained for the first time, and the initial observation is made without using the extension of the tenter stretching device. It has an excellent effect that cannot be expected from the previous technical knowledge regarding the use of the extension of the tenter extension device.

10‧‧‧ Track

10L‧‧‧ring track on the left

10R‧‧‧Round track on the right

11, 12‧‧‧ bending

20‧‧‧ fixture

30a, 30b‧‧‧ drive sprocket

40a, 40b‧‧‧ electric motor

50‧‧‧Laminated body (resin film)

100‧‧‧Extension

A‧‧‧ grasping area

B, B'‧‧‧MD extended area

BC‧‧‧MD extended ‧TD contraction area

C, C'‧‧‧TD contraction area

D‧‧‧Remove area

L1, L1', L2, L3‧‧‧ clamp spacing in the transport direction

Width of the laminate at the entrance to the W1‧‧‧TD contraction zone

The width of the laminate at the exit of the W2‧‧‧TD contraction zone

1 is an overall configuration of an example of an extension device that can be used in the manufacturing method of the present invention. A schematic plan view for explanation.

Fig. 2 is a schematic plan view showing a main part of the extension device of Fig. 1.

Fig. 3 is a schematic plan view showing the main part of the extension device of Fig. 1.

Fig. 4 is a schematic view for explaining an example of the MD extension ‧ TD contraction step.

Fig. 5 is a schematic view for explaining another example of the MD extension ‧ TD contraction step.

Fig. 6 is a schematic view for explaining still another example of the MD extension ‧ TD contraction step.

Fig. 7 is a schematic view for explaining still another example of the MD extension ‧ TD contraction step.

Fig. 8 is a schematic view for explaining still another example of the MD extension ‧ TD contraction step.

Fig. 9 is a schematic view for explaining a problem of the extension between the short gap rollers.

A. Method for manufacturing polarizing film

The method for producing a long-length polarizing film according to an embodiment of the present invention includes the step of using a tenter stretching device having a plurality of jigs as a gripping mechanism for forming a long resin film as a polarizing film, and stripping the strip The resin film extends in the longitudinal direction and contracts in the width direction. The extension in the longitudinal direction includes a step of expanding the jig interval in the transport direction of the elongated resin film, and the shrinkage in the width direction includes a step of reducing the jig interval in the width direction. The long resin film forming the polarizing film may be a single layer resin film or a laminate of two or more layers. In the following, an embodiment in which a polarizing film is produced using a laminate of a resin substrate and a polyvinyl alcohol (PVA) resin layer will be described as an example. However, the production method of the present invention is not limited to the embodiment. For example, it is clear that the present invention can be similarly applied to a method for producing a polarizing film using a single-layer PVA-based resin film.

A-1. Production of laminated body

The laminated system is produced by forming a PVA-based resin layer on a resin substrate. The resin substrate may have any appropriate configuration as long as it can support the PVA-based resin layer (the obtained polarizing film) from one side.

Examples of the material for forming the 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. 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 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 resin substrate. By performing the above treatment, the adhesion between the resin substrate and the PVA-based resin layer can be improved. Further, the surface modification treatment and/or the formation of the easy-adhesion layer may be performed before the extension of the resin substrate as needed, or may be performed after the 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 resin substrate subjected to the stretching treatment, and to dry it to form 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 obtained by saponifying an ethylene-vinyl acetate copolymer. 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 water, dimethyl hydrazine, and dimethylformamidine. Amines such as amines, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane, and the like, and 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 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 a coating method of a coating liquid, any appropriate method can be employ|adopted. 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 at most the glass transition temperature (Tg) of the resin substrate, and more preferably at most Tg-20 °C. By drying at the above temperature, deformation of the resin substrate before formation of the PVA-based resin layer can be prevented, and the alignment of the obtained PVA-based resin layer can be prevented from being deteriorated. As described above, the resin substrate can be favorably deformed together with the PVA-based resin layer, and the laminate and the following laminate can be favorably extended and shrunk. 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.

A-2. Extension and contraction steps

Then, the laminated body is conveyed in the longitudinal direction, and is extended in the longitudinal direction and contracted in the width direction. Further, the longitudinal direction of the extending direction is substantially the absorption axis direction of the obtained polarizing film.

In the present invention, the longitudinal extension of the laminated body is performed by using a tenter stretching device having a plurality of jigs as a gripping mechanism of the laminated body (hereinafter, also referred to as MD extension). Stretching and shrinkage in the width direction (hereinafter, also referred to as TD shrinkage). Specifically, the both side edges of the laminated body are gripped by the jig spacing L1 in the conveying direction, and the laminated body is extended in the longitudinal direction by expanding the jig interval from L1 to L2, and the jig spacing in the width direction is reduced. The laminate is shrunk in the width direction. The order of MD extension and TD contraction can be appropriately set depending on the purpose. For example, MD extension can be performed first, or TD shrinkage can be performed first, and MD extension and TD shrinkage can be performed simultaneously.

As the above-described tenter extension device, for example, an extension device including: a pair of rails having a tapered portion in which a straight line between the rails is constant and a distance between the rails is continuously reduced, and which can be moved while changing the interval of the jig A plurality of clamps on each track. 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 in a state in which the both side edges of the laminated body are grasped by the jig (on different tracks) The distance between the clamps can be extended and contracted.

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. 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 laminated body 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 of the illustrated example, the gripping area A, the MD extending area B, the TD contracting area C, and the releasing area D are sequentially provided from the loading side of the laminated body toward the carrying-out side. Furthermore, the regions mean substantially the areas of gripping, MD stretching, TD shrinkage (or TD shrinkage and MD extension) and release of the laminate, and do not mean mechanically or structurally. On the 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 and the MD extension area B, 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 such that the distance between the tracks corresponding to the initial width of the laminated body to be processed is substantially parallel to each other. In the TD contraction region C, the left and right circular orbits 10R, 10L are regarded as tapered portions in which the distance between the tracks is continuously reduced. Typically, the left and right circular orbits 10R and 10L are configured as follows: as the direction from the MD extension region B side toward the release region D side is gradually decreased, the distance between the rails is gradually decreased until it corresponds to the contraction of the laminate. The width is up. In 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 have an inter-track distance corresponding to the contracted width of the laminate. They are roughly 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. If the fixture size exceeds 40 In the case of mm, the unextended region near the jig becomes large to cause unevenness of the end portion, or the crack is generated on the surface of the resin film by partially extending the non-grip portion. 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. That is, the left and right jigs 20 and 20 are independent, and the jig interval (clamp pitch) in the conveyance direction (MD) can be changed with the movement. The variable pitch type jig can be realized by any appropriate configuration such as the configuration described in Japanese Laid-Open Patent Publication No. 2008-23775.

2 and 3 are schematic plan views of main parts of the extension device of Fig. 1, respectively. 2 is a schematic plan view of a portion of the extension device of FIG. 1 in which the portion extending from the MD extension region B to the TD contraction region C is moved. Fig. 3 is a schematic plan view of a portion of the extension device of Fig. 1 in which a portion from the TD contraction region C to the release region D is moved. As shown in FIGS. 2 and 3, both ends of the tapered portion are regarded as curved portions 11 and 12 which are bent at a specific angle (θ1), whereby they can be connected to a straight portion having a constant distance between the rails. The bending angle can be appropriately set depending on the required shrinkage ratio and productivity. The bending angle θ1 can be, for example, 1° to 20°.

The extension device illustrated in FIG. 1 is configured by sequentially performing MD extension and TD contraction, and can also perform MD extension when the TD is contracted. Specifically, the MD extension ‧ TD shrinking step may include the steps of: gripping both side edges of the laminated body by the jig at the jig spacing L1 of the conveying direction by the jig (the gripping step); while passing the laminated body through the straight portion The jig interval in the transport direction is extended from L1 to L2, and extends in the longitudinal direction (MD extension step); the laminated body is shrunk in the width direction by the tapered portion (TD contraction step). Further, if necessary, the method further includes the step of releasing the jig holding the laminated body (release step). 4 and 5 are schematic diagrams each showing an example of a contraction and extension step including the steps. Hereinafter, each step in the contraction and extension steps will be described in more detail with reference to the drawings.

First, in the gripping step (grip area A), the left and right jigs 20 are used to grip the both side edges of the laminated body 50 that are loaded into the extension device at a certain grip interval (clamp interval). The laminated body is moved by the respective clamps 20 guided by the left and right circular orbits 50 is transported to the MD extension area B. The grip intervals (clamp intervals) of the both side edges in the grip area A are representatively considered to be equal intervals. Furthermore, the so-called jig spacing is the distance between the centers of adjacent jigs.

Then, in the MD extending step (MD extension region B), the laminated body 50 held by the right and left jigs 20 is conveyed, and the laminated body 50 is extended in the longitudinal direction (MD extension). The MD extension of the laminated body 50 is performed by gradually increasing the moving speed of the jig 20 in the conveying direction, and expanding the jig interval of the conveying direction from L1 to L2. The stretch ratio (L2/) can be controlled by adjusting the jig interval (the grip interval in the gripping step) L1 of the transport direction at the entrance of the MD extension region B and the jig interval L2 of the transport direction at the exit of the MD extension region B. L1).

The stretching ratio (L2/L1) in the MD stretching step is, for example, 1.5 times to 6.5 times, preferably 1.8 times to 5.0 times, more preferably 1.8 times to 3.0 times. If the stretching ratio is less than 1.5 times, there is a case where the desired optical characteristics are not obtained. On the other hand, when the stretching ratio exceeds 6.5 times, there is a case where the laminated body is broken.

Here, if the jig interval L1 is excessively large, it is presumed that the portion of the laminated body 50 that is not gripped by the jig 20 generates a stress that shrinks in the width direction, and as a result, the optical characteristics of the obtained polarizing film (for example, polarization characteristics) ) produces unevenness. Therefore, representatively, the jig interval L1 is set to be equal to or less than the interval at which the above-described unevenness is generated.

Specifically, the jig interval L1 is preferably 100 mm or less, more preferably 60 mm or less, and still more preferably 40 mm or less. By setting L1 to 100 mm or less, the occurrence of unevenness can be suppressed, and as a result, the width which is cut and removed by the slit processing can be made small. The lower limit of L1 is not limited as long as it can achieve the following jig interval L2 after stretching, and may be, for example, 25 mm or more.

On the other hand, if the jig interval L1 is set to be equal to or less than the specific interval as described above, there is a case where the jig interval L2 after the MD extension is also small depending on the stretching ratio, and the taper portion (especially the curved portion) Part) produces fixtures 20 that are in contact with each other, etc. The desired shrinkage ratio is achieved (as a result, the desired optical properties are not obtained). Therefore, representatively, the jig interval L2 is equal to or larger than the interval at which the jigs 20 do not interfere with each other when the laminated body 50 is regarded as the TD contraction region C (particularly, the curved portion) of the tapered portion. By setting it as L2 mentioned above, L1 is not limited to the size which does not interfere with each other in the bending part clamp. In addition, "the jigs do not interfere with each other" means that the jig and its supporting member or the spacing adjusting mechanism do not contact each other, and the jig can be moved in the curved portion as set.

The jig interval L2 is appropriately set depending on the bending angle, the size of the jig, the shape, and the like. The jig spacing L2 is preferably 25 mm to 300 mm, more preferably 35 mm to 150 mm. If the jig interval L2 is within the above range, in the TD shrinking step, the jigs 20 in the tapered portion (especially the bent portion) can be prevented from interfering with each other to achieve a sufficient bending angle, and more uniform shrinkage can be achieved.

The elongation (MD extension) temperature of the laminate is set to any appropriate value depending on the material for forming the resin substrate or the like. The stretching temperature is typically at least the glass transition temperature (Tg) of the resin substrate, and preferably the glass transition temperature (Tg) of the resin substrate is +10 ° C or higher, and more preferably Tg + 15 ° C or higher. On the other hand, the extension temperature of the laminate 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 suppress the abnormality caused by the crystallization (for example, the alignment of the PVA-based resin layer by stretching).

Then, in the TD shrinking step (TD shrinkage region C), the laminated body 50 held by the right and left jigs 20 is conveyed in the longitudinal direction, and the laminated body 50 is shrunk in the width direction (TD contraction). In the TD contraction region C, the left and right circular orbits 10R and 10L are regarded as tapered portions in which the distance between the tracks is continuously reduced. Therefore, the laminated body 50 is contracted in the width direction by passing through the region. The TD shrinkage rate can be controlled by adjusting the amount of change in the distance between the tracks. Specifically, the ratio of the distance between the tracks at the exit of the TD contraction region C (the end portion on the side where the region D is removed) to the distance between the rails at the entrance of the TD contraction region C (the end portion on the side of the MD extension region B) is changed. Small, the greater the shrinkage rate.

The TD shrinkage ratio ((the width of the laminate at the exit of the TD shrinkage region C: W2) / (the width of the laminate at the entrance of the TD shrinkage region C: W1)) can be set to any appropriate value. The TD shrinkage ratio is preferably from 0.85 to 0.4, more preferably from 0.8 to 0.6. When the TD shrinkage ratio exceeds 0.85, there is a case where a sufficient shrinkage effect is not obtained and the shaft accuracy is insufficient. If the TD shrinkage ratio is less than 0.4, there is a case where the resin film is slack and the elongation is uneven.

In the embodiment illustrated in Fig. 4, in the TD contraction step, only the laminate 50 is shrunk in the width direction. In this case, the laminated body 50 is passed through the TD contraction region C while maintaining the jig interval (L2) in the conveyance direction. On the other hand, in the embodiment illustrated in Fig. 5, in the TD shrinking step, the laminated body 50 is contracted in the width direction and extended in the longitudinal direction. In this case, the laminated body 50 passes through the TD contraction region C while expanding the jig interval in the transport direction from L2 to L3. In the MD stretching step and the TD shrinking step, the final stretching ratio can be made high by performing MD stretching in multiple stages. Further, by simultaneously performing TD shrinkage and MD stretching, an effect of suppressing occurrence of bending or wrinkles can be obtained.

The stretching ratio of the laminated body after the TD shrinking step (the product of the stretching ratio in the MD stretching step and the stretching ratio in the TD shrinking step, also referred to as the final stretching ratio. The TD shrinking step includes the final stretching ratio in the case of MD stretching) In the case of L3/L1, the final stretching ratio L2/L1) when the TD shrinking step does not include the MD stretching is, for example, 3.0 times or more, preferably 4.0 times or more, relative to the original length of the laminated body. By extending at the above higher magnification, a polarizing film having excellent optical characteristics can be obtained. Furthermore, the so-called final stretching ratio herein refers to the final stretching ratio in the manufacturing method when the manufacturing method of the present invention does not include another extending step described below, and the manufacturing method of the present invention includes another extension. In the case of a step, it refers to the final extension ratio of the extension step using the tenter extension device.

The temperature environment in the TD shrinking step can be the same as the extension temperature in the MD stretching step.

Finally, in the releasing step (release area D), the clamp 20 of the laminated body 50 is grasped. except. 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 laminated body 50 is cooled to a desired temperature and the jig is released.

Although the embodiment in which the MD extension and the TD contraction are sequentially performed using the extension device illustrated in Fig. 1 has been described, as described above, the TD contraction can be performed before the MD extension, and the MD extension and the TD contraction can be simultaneously performed. When the TD is contracted before the MD is extended, for example, as shown in FIG. 6 and FIG. 7, in the extension device, the gripping area A and the TD contraction area C' are sequentially disposed from the loading side of the laminated body toward the carrying-out side. , MD extension area B', and release area D. In the embodiment illustrated in FIG. 6, in the TD contraction step (TD contraction region C'), the inter-track distance (the width of the laminated body) is changed from W1 to W2 while maintaining the jig interval L1 in the transport direction, and then In the MD extension step (MD extension region B'), the jig interval between the rails is increased from L1 to L2 while maintaining the distance between the rails at W2. In the embodiment illustrated in Fig. 7, in the TD contraction step (TD contraction region C'), MD extension can be simultaneously performed. In this case, the distance between the rails in the transport direction is increased from L1 to L1', and the distance between the rails (the width of the laminated body) is changed from W1 to W2, and then in the MD extension step (MD extension region B'). While maintaining the distance between the rails at W2, the jig interval of the transport direction is expanded from L1' to L2. When the MD extension and the TD contraction are simultaneously performed, for example, as shown in FIG. 8, the track in the MD extension region may be tapered such that the distance between the tracks continuously decreases. That is, in the extension device, the MD extension ‧ TD contraction region BC is provided between the grip region A and the release region D, and the distance between the tracks (the width of the laminate) is from W1 in the MD extension ‧ TD contraction region BC When it is reduced to W2, the jig interval of the conveyance direction is expanded from L1 to L2. Further, the details of the operations and/or conditions in the embodiments will be described with reference to FIGS. 1 to 5.

A-3. Other steps

The method for producing a polarizing film of the present embodiment may include other steps in addition to the above. As another step, for example, 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) steps are mentioned. Wait a minute. Other steps can be performed at any appropriate time.

The dyeing step is typically a step of dyeing a PVA-based resin layer with a dichroic material. It is preferred to carry out the adsorption of the dichroic substance by the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (laminate) in a dyeing liquid containing a dichroic material, a method of applying a dyeing liquid to a PVA-based resin layer, and a PVA-based resin layer. A method of spraying a dyeing solution, and the like. 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. Further, both sides of the laminated body may be immersed in the dyeing liquid, or only one side of the laminated body may be immersed in the dyeing liquid.

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 increase 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 compounding amount of the iodide salt 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.

As another extension step, for example, roll extension can be cited. By making another extension The final stretch ratio can be further increased. For example, in another extension step, the laminate having the tenter stretching device extended to about 3 times is used for further stretching, whereby the final stretching ratio can be set to 5 times or more. As a result, a polarizing film having more excellent optical characteristics can be obtained. Another extension step can be carried out simultaneously with the dyeing step, the insolubilization step and/or the crosslinking step, or can be carried out in one step. In the case where the steps are performed one step at a time, another extension step can be performed at any appropriate point in time.

B. Polarizing film

The polarizing film produced by the above-described production method is substantially a PVA-based resin film in which a dichroic substance is adsorbed and aligned. The polarizing film preferably exhibits absorption dichroism at any of wavelengths of 380 nm to 780 nm. The monomer transmittance (Ts) of the polarizing film is preferably 39% or more, more preferably 39.5% or more, still more preferably 40% or more, and particularly preferably 40.5% or more. Furthermore, the theoretical upper limit of the monomer transmittance is 50%, and the practical upper limit is 46%. Further, the monomer transmittance (Ts) is a Y value obtained by measuring a visibility of a 2 degree field of view (C light source) of JIS Z8701 and performing visibility correction, and can be performed, for example, using a microscopic spectroscopic system (manufactured by Lambda-vision, LVmicro). Determination. The degree of polarization of the polarizing film is preferably 99.9% or more, more preferably 99.93% or more, still more preferably 99.95% or more.

In the polarizing film produced by the above-described production method, the deviation of the absorption axis in the longitudinal direction of the end portion in the width direction (for example, a position of 250 mm from the edge) is extremely small. For example, regarding a polarizing film which is produced by a manufacturing method including only an extension using a tenter stretching device, the deviation of the absorption axis at a position of 250 mm from the edge in the width direction with respect to the set absorption axis direction (representing In terms of the length direction, it is preferably within a range of ±0.30°, more preferably within a range of ±0.25°. Moreover, the deviation of the absorption axis in the longitudinal direction of the central portion in the width direction of the polarizing film is, for example, within a range of ±0.20°. As described above, in the polarizing film obtained by the production method of the present invention, the axial accuracy of the end portion in the width direction is extremely excellent, and the axial accuracy equivalent to the central portion can be achieved. As a result, the optical characteristics of the polarizing film are excellent in in-plane uniformity, and therefore, each of the polarizing films as the final product after trimming is used. The quality deviation of the product is small, and excellent display characteristics can be achieved when used in an image display device. Further, the polarizing film obtained by, for example, stretching the roller has a large deviation in the longitudinal direction of the absorption axis at a position of 250 mm from the edge in the width direction (for example, the deviation is about ±0.75°), and thus is large. In most cases, the crack is about 250mm from the edge. On the other hand, the polarizing film obtained by the manufacturing method of the present invention is also practically applicable in the width direction end portion, so that the yield is high and the cost is also advantageous. Further, even in the case where the manufacturing method of the present invention includes another stretching step, since the deviation of the optical axis of the PVA-based resin layer in the laminated body obtained by using the stretching of the tenter stretching device becomes very small, As a result, the deviation of the absorption axis of the polarizing film obtained is also extremely small.

The method of using the polarizing film may be any appropriate method. Specifically, the PVA-based resin film which can be used as a single layer can also be used as a laminate of a resin substrate and a PVA-based resin film, or can be used as at least one side of a PVA-based resin film or a PVA-based resin film. A laminate having a protective film (ie, a polarizing plate).

C. Polarizer

The polarizing plate has a polarizing film and a protective film disposed on at least one side of the polarizing film. Examples of the material for forming the protective film include cellulose resins such as diethyl ketone cellulose and triethylene fluorene cellulose, olefin resins such as (meth)acrylic resin, cycloolefin resin, and polypropylene, and poly-pairs. An ester resin such as an ethylene phthalate resin, a polyamide resin, a polycarbonate resin, or a copolymer resin thereof.

The thickness of the protective film is preferably from 20 μm to 100 μm. The protective film is typically laminated on the polarizing film via an adhesive layer (specifically, an adhesive layer or an adhesive layer). The subsequent layer is typically formed of a PVA-based adhesive or an active energy ray-curable adhesive. The adhesive layer is typically formed of an acrylic adhesive. In the case of using a laminate of a resin substrate/PVA-based resin film (polarizing film), it is preferred that the resin substrate be peeled off after the protective film is laminated on the surface of the polarizing film opposite to the resin substrate. Another protective film may be peeled off from the area layer as needed. By peeling off the resin substrate, it is more sure Curl.

In terms of practicality, the polarizing plate has an adhesive layer as the outermost layer. The adhesive layer is representatively the outermost layer on the image display device side. The separator is temporarily peeled off on the adhesive layer, the adhesive layer is protected before actual use, and roll formation is possible.

The polarizing plate can also have any suitable optical functional layer for the purpose. Typical examples of the optical functional layer include a retardation film (optical compensation film) and a surface treatment layer. For example, a retardation film (not shown) may be disposed between the protective film and the adhesive layer. The optical characteristics of the retardation film (for example, the refractive index ellipsoid, the in-plane retardation, and the thickness direction retardation) can be appropriately set depending on the purpose, characteristics of the image display device, and the like. For example, when the image display device is an IPS mode liquid crystal display device, a retardation film having an index ellipsoid of nx>ny>nz and a retardation film having an index ellipsoid of nz>nx>ny may be disposed. The retardation film may also serve as a protective film. In this case, the protective film disposed on the image display device side can be omitted. Conversely, the protective film may also have an optical compensation function (that is, it may have an appropriate refractive index ellipsoid, in-plane phase difference, and thickness direction phase difference) depending on the purpose. Further, the refractive index of the direction in which the refractive index of the "nx" film is maximized (that is, the direction of the slow axis) is "ny", and the refractive index of the direction perpendicular to the slow axis is "ny". Nz" is the refractive index in the thickness direction.

The surface treatment layer may be disposed on the outer side of the outer protective film (not shown). Typical examples of the surface treatment layer include a hard coat layer, an antireflection layer, and an antiglare layer. As for the surface treatment layer, for example, in order to improve the humidifying durability of the polarizing film, a layer having a low moisture permeability is preferable. The hard coat layer is provided for the purpose of preventing damage to the surface of the polarizing plate. The hard coat layer can be formed, for example, by adding a hardened film excellent in hardness or sliding property formed by an appropriate ultraviolet curable resin such as acrylic or polyoxygen to the surface. As the hard coat layer, the pencil hardness is preferably 2H or more. The antireflection layer is a low reflection layer provided to prevent external light from being reflected on the surface of the polarizing plate. As the anti-reflection layer, for example, a thin-type anti-reflection layer that prevents reflection by utilizing the canceling effect of reflected light based on the interference of light as disclosed in Japanese Laid-Open Patent Publication No. 2005-248173; 2011- A surface structure type antireflection layer which exhibits a low reflectance by imparting a fine structure to a surface as disclosed in Japanese Laid-Open Publication No. 2759. The anti-glare layer is provided for the purpose of preventing external light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. The anti-glare layer is formed, for example, by imparting a fine uneven structure to the surface by a sandblasting method, a roughening method using an embossing method, or a method of blending transparent fine particles. The anti-glare layer may be a diffusion layer (viewing angle expansion function or the like) that expands the viewing angle or the like by diffusing the polarizing plate to transmit light. Instead of providing a surface treatment layer, the same surface treatment may be applied to the surface of the outer protective film.

Heretofore, as an example of a method for producing a polarizing film of the present invention, an embodiment in which a polarizing film is produced using a laminate of a resin substrate and a PVA-based resin layer has been described. However, as described above, the manufacturer has clarified, for example, The invention can also be applied to a method of producing a polarizing film using a single-layer PVA-based resin film. In other words, in the present invention, even if the laminated body of the resin substrate/PVA-based resin layer is replaced with a single-layer resin film, the same procedure can be applied, and the same effect can be obtained.

[Examples]

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

[Example 1]

<Laminating process step>

An amorphous PET substrate (100 μm thick) was prepared as a resin substrate, and a PVA aqueous solution was applied onto 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 prepare a laminate.

<MD extension ‧ TD shrinking step>

The obtained laminate was subjected to MD extension and TD shrinkage using an extension device similar to that of FIG. Specifically, in the grip area A, both side edges of the laminated body are gripped at a jig interval L1: 35 mm and transported in the longitudinal direction, in the MD extension ‧ TD contraction area BC, While shrinking by 30% in the width direction at 140 ° C, it extends to 3 times in the longitudinal direction (the jig interval L3 at the exit of the MD extension ‧ TD contraction region BC is 105 mm, and the width of the laminate is 650 mm). Thereafter, in the release region D, the jig that grips the laminated body is released. Furthermore, the fixture size is 15 mm.

<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 further extended by 1.7 times in the longitudinal direction in the aqueous boric acid solution (final stretching ratio 5.1). 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 4.0 μm was formed on the resin substrate.

<axis accuracy>

The deviation of the absorption axis in the longitudinal direction at a position of 250 mm from the end portion in the width direction of the laminated body (substantially the dyed PVA-based resin layer, that is, the polarizing film) after the dyeing treatment was measured. Specifically, the device name "AXOSCAN" manufactured by AXOMETRICS Co., Ltd. was used as a measuring device, and the direction of the absorption axis was measured every 20 mm in the longitudinal direction in the range of 1200 mm. The maximum value deviated from the length direction is set as the deviation, and is set as an index of the axis accuracy. The deviation of the absorption axis is ±0.21°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed.

[Embodiment 2]

In the gripping area A, the two sides of the laminated body are gripped by the clamp interval L1: 60 mm. A polarizing film having a thickness of 4.0 μm was formed on the resin substrate in the same manner as in Example 1 except for the above. The laminate after the dyeing treatment was subjected to evaluation of the deviation of the absorption axis in the same manner as in Example 1. The deviation of the absorption axis is ±0.29°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed.

[Example 3]

A polarizing film having a thickness of 4.0 μm was formed on the resin substrate in the same manner as in Example 1 except that the both sides of the laminated body were gripped at a jig interval L1: 90 mm in the grip area A. . The laminate after the dyeing treatment was subjected to evaluation of the deviation of the absorption axis in the same manner as in Example 1. The deviation of the absorption axis is ±0.47°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed.

[Example 4]

A polarizing film having a thickness of 4.0 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.

Using a stretching device similar to that of FIG. 5, in the gripping area A, both side edges of the laminated body are gripped at a jig spacing L1: 40 mm and transported in the longitudinal direction, and in the MD extended region B, at a length of 140 ° C The direction is extended to 1.4 times (the jig spacing L2 at the exit of the MD extension region B is L2: 56 mm). Then, in the TD shrinkage region C, the shrinkage is 30% in the width direction, and further extends in the longitudinal direction (the jig interval L3 at the exit of the TD shrinkage region C: 120 mm, and the final stretch ratio obtained by the tenter extension device: 3 times).

The laminate after the dyeing treatment was subjected to evaluation of the deviation of the absorption axis in the same manner as in Example 1. The deviation of the absorption axis is ±0.41°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed.

[Example 5]

In the grip area A, the grip size is 30mm, and the clamp interval is L1: 60mm. A polarizing film having a thickness of 4.0 μm was formed on the resin substrate in the same manner as in Example 1 except that the both side edges of the laminate were used. The laminate after the dyeing treatment was subjected to evaluation of the deviation of the absorption axis in the same manner as in Example 1. The deviation of the absorption axis is ±0.39°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed.

[Embodiment 6]

In the grip area A, the both sides of the laminated body were grasped at a jig size of 45 mm and a jig interval of L1: 60 mm, except that the thickness was 4.0 on the resin substrate in the same manner as in the first embodiment. Mm polarizing film. The laminate after the dyeing treatment was subjected to evaluation of the deviation of the absorption axis in the same manner as in Example 1. The deviation of the absorption axis is ±0.44°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed. On the other hand, since the non-grip portion is partially extended, cracking occurs on the surface of the resin film.

[Embodiment 7]

In the grip area A, the both side edges of the laminated body were gripped at a jig interval L1: 60 mm, and contracted by 10% in the width direction in the MD extension ‧ TD contraction area BC, except that the same as in the first embodiment In the manner, a polarizing film having a thickness of 4.0 μm was formed on the resin substrate. The laminate after the dyeing treatment was subjected to evaluation of the deviation of the absorption axis in the same manner as in Example 1. The deviation of the absorption axis is ±0.38°. Since the deviation of the absorption axis of the laminate was remarkably suppressed, it was confirmed that the deviation of the finally obtained polarizing film was remarkably suppressed.

[Comparative Example 1]

A laminate of the /PVA layer on the amorphous PET substrate was produced in the same manner as in Example 1. Then, using two sets of nip rolls (350 mm in diameter) arranged at a gap interval of 22 mm, the laminated body was extended to three times in the longitudinal direction. The procedure after the dyeing treatment was carried out in the same manner as in Example 1, and a polarizing film having a thickness of 4.0 μm was formed on the resin substrate.

The layered body after the dyeing treatment was supplied to the absorption axis in the same manner as in Example 1. Bad evaluation. The deviation of the absorption axis is ±0.82°. Since the deviation of the absorption axis of the laminate becomes large, it is confirmed that the deviation of the finally obtained polarizing film is also large.

[Evaluation]

As described above, according to the embodiment of the present invention, by using the extension of the tenter stretching device in the longitudinal direction, the deviation of the axial precision of the obtained laminated body and the polarizing film in the width direction end portion can be reduced.

[Industrial availability]

The production method of the present invention can be preferably used for the production of a polarizing film.

10L‧‧‧ring track on the left

10R‧‧‧Round track on the right

20‧‧‧ fixture

30a, 30b‧‧‧ drive sprocket

40a, 40b‧‧‧ electric motor

100‧‧‧Extension

A‧‧‧ grasping area

B‧‧‧MD extended area

C‧‧‧TD contraction area

D‧‧‧Remove area

Claims (8)

A method for producing a polarizing film, which is a method for producing a long-length polarizing film, and comprising the steps of: using a tenter stretching device having a plurality of jigs as a gripping mechanism for forming a long resin film of the polarizing film; The elongated resin film is stretched in the longitudinal direction and contracted in the width direction, and the extension in the longitudinal direction includes a step of expanding the gap between the jigs in the transport direction of the elongated resin film, and the shrinkage in the width direction This includes the step of reducing the jig spacing in the width direction. The manufacturing method of claim 1, wherein the elongated resin film forming the polarizing film is a single-layer polyvinyl alcohol-based resin film, and the manufacturing method comprises extending the resin film in the longitudinal direction and shrinking in the width direction. The step of dyeing to form a polarizing film is carried out. The manufacturing method of claim 1, wherein the elongated resin film forming the polarizing film is a laminate of a resin substrate and a polyvinyl alcohol-based resin layer formed on one side of the resin substrate, and the manufacturing method includes The layered body is stretched in the longitudinal direction and shrunk in the width direction, and dyed to form a polarizing film on the resin substrate. The manufacturing method of claim 1, wherein the shrinkage ratio in the width direction is 0.8 or less. The manufacturing method of claim 1, wherein the jig has a jig size of 12 mm to 40 mm. The manufacturing method of claim 1, wherein the jig interval in the transport direction before the extension in the longitudinal direction is 100 mm or less. The manufacturing method of claim 1, wherein the extension ratio in the longitudinal direction is 1.5 times to 6.5 times. A strip-shaped polarizing film obtained by the manufacturing method of claim 1.