KR20170102796A - Polarizing film production method - Google Patents

Abstract

According to the present invention, there is provided a process for producing a long-axis polarizing film. This manufacturing method includes stretching the elongated-phase resin film in the longitudinal direction and shrinking in the transverse direction by using a tenter stretching apparatus having a plurality of clips as gripping means of a long-length resin film forming a polarizing film . The stretching in the longitudinal direction includes enlarging the clip interval in the conveying direction of the elongated-phase resin film, and the contraction in the width direction includes reducing the clip interval in the width direction.

Description

POLARIZING FILM PRODUCTION METHOD [0002]

The present invention relates to a method for producing a polarizing film. More particularly, the present invention relates to a method for producing a longitudinal polarizing film using a tenter stretching apparatus.

In a liquid crystal display device which is a representative image display device, a polarizing film is arranged on both sides of a liquid crystal cell due to the image forming method. As a method of producing a polarizing film, free-end uniaxial stretching that stretches between rolls having different peripheral velocities is widely employed. In the free uniaxial stretching, there is a problem that the width of the film obtained by necking becomes narrow. In order to solve such a problem, there has been proposed a method (short-gap roll-to-roll stretching) in which the roll interval is reduced (see, for example, Patent Document 1). Short-gap roll-to-roll stretching can prevent necking by contacting rolls, and on the other hand, it is difficult to control the film width as shown in Fig. 9, for example. As a result, There is a problem that the axial precision fluctuates in the longitudinal direction of the film.

Japanese Laid-Open Patent Publication No. 2014-74786

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and its main object is to provide a method capable of producing a longitudinal polarizing film excellent in axial precision at the width direction end portion and consequently excellent in the in- have.

According to an embodiment of the present invention, a method of manufacturing a polarizing film of an elongated phase is provided. This manufacturing method uses a tenter stretching apparatus having a plurality of clips as gripping means of a long-length resin film forming the polarizing film to stretch the elongated resin film in the longitudinal direction and shrink it in the width direction . The stretching in the longitudinal direction includes enlarging the clip interval in the conveying direction of the elongated resin film, and the contraction in the width direction includes reducing the clip interval in the width direction.

In one embodiment, the elongated resin film forming the polarizing film is a single layer polyvinyl alcohol-based resin film. In the above manufacturing method, the resin film is stretched in the longitudinal direction and retracted in the width direction , And dyeing to prepare a polarizing film.

In one embodiment, the elongated resin film forming the polarizing film is a laminate having a resin base material and a polyvinyl alcohol-based resin layer formed on one side of the resin base material, Shrinking in the stretching direction and the width direction, and dyeing to prepare 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 clip size of the clip is 12 mm to 40 mm.

In one embodiment, the clip interval in the carrying direction before stretching in the longitudinal direction is 100 mm or less.

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

According to another aspect of the present invention, a polarizing film of an elongated phase is provided. This polarizing film is obtained by the above-described manufacturing method.

According to the manufacturing method of the present invention, by longitudinally stretching and shrinking in the width direction using the tenter stretching apparatus, the axial precision of the width direction end portion is excellent, and consequently, the elongated-phase polarized light A film can be obtained. Further, since this polarizing film can reduce the amount of cut by the slit processing of the end portion to be very small, the yield is excellent and the manufacturing cost can be reduced. The tenter stretching apparatus is often used for stretching in the transverse direction (width direction), and in this case, it is known that the accuracy in the axial direction of the end portion in the width direction of the obtained film is insufficient. This is considered to be due to the fact that stress is applied in a direction between the portion clipped by the tenter and the portion (the portion not clipped) between the clips in the stretched film. That is, in the clip portion, stress is applied in the width direction (transverse direction) of the film, and in the portion between the clips, stress in the oblique direction is applied toward both clips. Therefore, the accuracy in the axial direction 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 by, for example, slit processing in its width direction end portion. Since the polarizing film is strongly required to have excellent axial precision (that is, there is no deviation in the absorption axis and the transmission axis direction in the film as a whole) in the film as a whole, it is necessary to use a tenter stretching device The idea of stretching in the longitudinal direction to obtain a polarizing film is not in the art, but rather contrary to the technical common sense. On the other hand, the inventors of the present invention have found that, as a result of practicing stretching in the longitudinal direction using a tenter stretching device, the axial accuracy of the end portion in the width direction of the obtained film is good. This is because the direction in which the stress is applied in the portion between the portion clipped by the tenter and the clip in the stretched film is the same direction (longitudinal direction) because the stretching is performed by increasing the clip interval in the longitudinal direction do. Further, according to this method, since the shrinkage ratio in the width direction can be accurately controlled by being clipped by the tenter, unstable shrinkage (uncontrolled shrinkage) such as short gap roll-to-roll stretching does not occur (needless to say, And there is no case where necking occurs as in normal roll-to-roll stretching). It was also confirmed that the accuracy in the axial direction of the end portion in the width direction of the film obtained from the short- As a result, even if the gripped portion by the tenter is removed, a polarizing film having a wide width and excellent axial accuracy at the end portions in the width direction can be obtained. As described above, in the manufacturing method of the present invention, the polarizing film having excellent axial accuracy at the end portions in the width direction can be obtained by the fact that the stretching in the longitudinal direction using the tenter stretching apparatus, which is not ordinarily performed, It is an unexpected superior effect from the technical common sense concerning stretching using a tenter stretching apparatus.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic plan view illustrating an overall configuration of an example of a drawing apparatus that can be used in the manufacturing method of the present invention. FIG.
Fig. 2 is a schematic plan view of the main part of the drawing apparatus of Fig. 1;
Fig. 3 is a schematic plan view of the main part of the drawing apparatus of Fig. 1;
4 is a schematic view for explaining an example of the MD stretching and TD shrinking process.
5 is a schematic view for explaining another example of the MD stretching and TD shrinking process.
6 is a schematic view for explaining another example of the MD stretching / TD shrinking step.
7 is a schematic view for explaining another example of the MD stretching and TD shrinking process.
8 is a schematic view for explaining another example of the MD stretching / TD shrinking step.
9 is a schematic diagram for explaining the problem of short-gap roll-to-roll stretching.

A. Manufacturing Method of Polarizing Film

A method of producing a long polarizing film according to an embodiment of the present invention is a method of stretching a longitudinally stretched resin film using a tenter stretching apparatus having a plurality of clips as gripping means for a longitudinally stretched resin film forming a polarizing film And shrinking in the width direction. The stretching in the longitudinal direction includes enlarging the clip interval in the conveying direction of the elongated-phase resin film, and the contraction in the width direction includes reducing the clip interval in the width direction. The elongated resin film forming the polarizing film may be a single resin film or a laminate of two or more layers. Hereinafter, as an example, an embodiment in which a polarizing film is produced by using a laminate of a resin substrate and a polyvinyl alcohol (PVA) resin layer is described, but the manufacturing method of the present invention is not limited to this embodiment. For example, it is apparent to those skilled in the art that the present invention is equally applicable to a method of manufacturing a polarizing film using a single-layer PVA-based resin film.

A-1. Preparation of laminate

The laminate is produced by forming a PVA resin layer on a resin substrate. The resin substrate may have any suitable structure as long as it can support the PVA resin layer (polarizing film obtained) from one side.

As the material for forming the resin substrate, for example, an ester resin such as a polyethylene terephthalate resin, a cycloolefin resin, an olefin resin such as polypropylene, a polyamide resin, a polycarbonate resin, Resins and the like. Among them, a cycloolefin resin (for example, a norbornene resin) and an amorphous polyethylene terephthalate resin are preferable. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid as the dicarboxylic acid and a copolymer further containing cyclohexanedimethanol as the glycol.

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 such a treatment, the adhesion between the resin substrate and the PVA-based resin layer can be improved. Further, the surface modification treatment and / or the easy adhesion layer may be carried out before or after the stretching of the resin base material, which is carried out if necessary.

As a method of forming the PVA resin layer, any appropriate method can be adopted. Preferably, the PVA resin layer is formed by applying a coating liquid containing a PVA-based resin onto the resin substrate subjected to the stretching treatment and drying it.

As the PVA resin, any suitable resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA resin is usually from 85 mol% to 100 mol%, preferably from 95.0 mol% to 99.95 mol%, and more preferably from 99.0 mol% to 99.93 mol%. The saponification degree can be obtained according to JIS K 6726-1994. By using such a saponification degree PVA resin, a polarizing film having excellent durability can be obtained. When the degree of saponification is too high, the coating liquid tends to gel, which may make it difficult to form a uniform coating film.

The average degree of polymerization of the PVA resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be obtained according to JIS K 6726-1994.

The coating liquid is typically a solution prepared by dissolving the PVA resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, ethylenediamine, diethylenetriamine and the like Amines. These may be used alone or in combination of two or more. Among them, water is preferable. The concentration of the PVA resin in the solution is preferably 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film adhered to the resin base material can be formed.

An additive may be added to the coating liquid. Examples of the additive include plasticizers, surfactants, and the like. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. The surfactant includes, for example, nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the resulting PVA-based resin layer.

As a coating method of the coating liquid, any appropriate method can be adopted. Examples of the coating method include 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, and a knife coating method (comma coating method).

The drying temperature is preferably not higher than the glass transition temperature (Tg) of the resin base, more preferably not higher than Tg-20 占 폚. By drying at such a temperature, it is possible to prevent the resin base material from being deformed before forming the PVA-based resin layer, and to prevent the orientation property of the obtained PVA-based resin layer from deteriorating. In this way, the resin base material can be well deformed together with the PVA resin layer, so that the laminate to be described later can be stretched and shrunk satisfactorily. As a result, it is possible to obtain a polarizing film having favorable optical properties and good orientation property to the PVA resin layer. Here, the term " orientation " means the orientation of the molecular chains of the PVA resin layer.

A-2. Stretching and shrinkage process

Next, while the laminate is transported in the longitudinal direction, the laminate is stretched in the longitudinal direction and shrunk in the width direction. Further, the longitudinal direction in the stretching direction becomes the absorption axis direction of the polarizing film substantially obtained.

In the present invention, the stretching in the longitudinal direction (hereinafter also referred to as MD stretching) and the shrinking in the width direction (hereinafter also referred to as TD shrinkage) of the laminate are carried out by a tenter stretching method comprising a plurality of clips Equipment. More specifically, the laminate is stretched in the longitudinal direction by grasping both side edges of the laminate at a clip interval (L1) in the carrying direction and enlarging the clip interval from L1 to L2, So that the laminate is shrunk in the width direction. The order of MD stretching and TD shrinking can be suitably set according to the purpose. For example, the MD stretching may be performed first, the TD shrinkage may be performed first, or the MD stretching and the TD shrinkage may be simultaneously performed.

Examples of the tenter stretching device include a pair of rails having a straight portion having a constant rail distance and a taper portion having a continuously decreasing distance between rails and a plurality of clips May be used. According to such a stretching apparatus, by changing the clip intervals (the distance between the clips on the same rail) in the carrying direction and the clip intervals in the width direction (the distances between clips on different rails) while holding both side edges of the laminate with clips , It is possible to stretch and shrink the laminate.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic plan view for explaining the overall configuration of an example of a drawing apparatus that can be used in the manufacturing method of the present invention; FIG. Referring to Fig. 1, a drawing apparatus usable in the manufacturing method of the present invention will be described. The elongating device 100 has left and right symmetrical endless rails 10L and endless rails 10R on both left and right sides when viewed in plan. In this specification, the left endless rail as viewed from the entrance side of the laminate is referred to as the left endless rail 10L, and the right endless rail as the right endless endrail 10R. On the left and right endless rails 10L and 10R, a plurality of clips 20 for holding a laminate are disposed. The clip 20 is guided to each rail and travels in a loop. The clip 20 on the left endless rail 10L is moved in the counterclockwise direction while the clip 20 on the right endless rail 10R is moved in the clockwise direction. In the drawing device of the illustrated example, a ripple zone A, a MD stretching zone B, a TD shrinkage zone C and a release zone D are formed in order from the carry-in side to the carry-out side of the laminate . Further, each of these zones means a zone in which the laminate substantially grasps, MD stretches, TD shrinks (or TD shrinks and MD stretches) and releases, and does not mean mechanically and structurally independent zones. It should be noted that the ratio of the length of each zone in the stretching apparatus of Fig. 1 is different from the ratio of the actual length.

In the grip zone A and the MD stretching zone B, the left and right endless rails 10R and 10L are linear portions having a constant distance between rails. Typically, the left and right endless rails 10R, 10L are configured to be substantially parallel to each other at a rail-to-rail distance corresponding to an initial width of a laminate to be processed. In the TD shrinkage zone C, the left and right endless rails 10R and 10L are tapered portions in which the distance between rails is continuously reduced. Typically, the left and right endless rails 10R and 10L are gradually reduced from the MD stretching zone B side toward the release zone D side until the rail-to-rail distance corresponds to the width after shrinkage of the laminate . In the release zone D, the left and right endless rails 10R, 10L are linear portions having a constant rail-to-rail distance, and are typically configured such that they are substantially parallel to each other at a rail- .

The clips (left clip) 20 on the left stepless rail 10L and the clips (right clip) 20 on the right stepless rail 10R can independently travel through each other. For example, the driving sprockets 30a and 30b of the left endless rail 10L are rotationally driven in the counterclockwise direction by the electric motors 40a and 40b, and the driving sprockets 30a and 30b of the right- (30a, 30b) are rotationally driven in the clockwise direction by the electric motors (40a, 40b). As a result, a driving force is applied to a clip supporting member (not shown) of a driving roller (not shown) engaged with the driving sprockets 30a and 30b. As a result, the left clip 20 moves in the counterclockwise direction while the right clip 20 moves in the clockwise direction. The left clip 20 and the right clip 20 can be independently traversed by independently driving the left electric motor and the right electric motor.

The clip size is preferably 12 mm to 40 mm, and more preferably 15 mm to 35 mm. When the clip size is less than 12 mm, the stretching tension can not be maintained and may be broken, or a driving problem may occur due to a lack of strength of the clip conveying portion. If the clip size exceeds 40 mm, a region that is not stretched in the vicinity of the clip becomes large to cause irregularity of the end portion, or cracks may be generated on the surface of the resin film by locally stretching the non-peeling portion. The clip size means the width of the grip area.

The left clip 20 and the right clip 20 are each of a variable pitch type. That is, the left and right clips 20 and 20 can independently change the clip interval (clip pitch) in the conveying direction MD with the movement. The variable pitch type clip can be realized by any suitable configuration such as the configuration described in Japanese Laid-Open Patent Publication No. 2008-23775.

Fig. 2 and Fig. 3 are schematic plan views of the main part of the drawing apparatus of Fig. 1, respectively. Fig. 2 is a schematic plan view of a portion of the rail transited from the MD stretching zone B to the TD shrinkage zone C in the stretching apparatus of Fig. 1. Fig. Fig. 3 is a schematic plan view of a portion of the rail transited from the TD shrinkage zone C to the release zone D in the stretching apparatus of Fig. 1. Fig. As shown in Figs. 2 and 3, both ends of the tapered portion become bent portions 11 and 12 bent at a predetermined angle [theta] 1, thereby making it possible to connect the linear portion with a constant distance between rails . The bending angle can be appropriately set according to the desired shrinkage rate and productivity. The bending angle [theta] 1 may be, for example, 1 [deg.] To 20 [deg.].

The stretching device illustrated in Fig. 1 is configured to perform MD stretching and TD shrinking in this order, and it is also possible to perform MD stretching at the time of TD shrinkage. Concretely, in the MD stretching and TD shrinking step, the both side edges of the laminate are held by a clip at a clip interval (L1) in the carrying direction (holding step), while the laminate is passed through the straight portion, (MD stretching step), stretching from L1 to L2, stretching in the longitudinal direction (MD stretching step), and shrinking the laminate in the width direction (TD shrinking step) by passing through the tapered part. And releasing the clip for gripping the laminate (releasing step), if necessary. Figs. 4 and 5 are schematic views showing an example of a shrinkage / stretch process including these processes, respectively. Hereinafter, each step in the shrinkage and stretching process will be described in more detail with reference to these drawings.

First, in the gripping process (grip zone A), the right and left clips 20 grip both side edges of the laminate 50 introduced into the stretching device at a fixed gripping interval (clip interval) The laminate 50 is conveyed to the MD stretching zone B by the movement of each clip 20 guided by the endless rail of the MD. The gripping intervals (clip intervals) of the side edges in the grip zone A are typically equal to each other. The clip interval is the distance between the centers of neighboring clips.

Subsequently, in the MD stretching process (MD stretching zone B), the laminate 50 gripped by the left and right clips 20 is transported (MD stretching) in the longitudinal direction. The MD stretching of the layered product 50 is carried out by gradually increasing the moving speed of the clip 20 in the carrying direction and enlarging the clip interval in the carrying direction from L1 to L2. (Gripping interval L1 in the gripping step) in the conveying direction at the entrance of the MD stretching zone B and the clip interval L2 in the conveying direction at the exit of the MD stretching zone B are adjusted , It is possible to control the drawing magnification (L2 / L1).

The stretching magnification (L2 / L1) in the MD stretching process is, for example, 1.5 to 6.5 times, preferably 1.8 to 5.0 times, more preferably 1.8 to 3.0 times. If the draw ratio is less than 1.5 times, desired optical characteristics may not be obtained. On the other hand, when the draw ratio exceeds 6.5 times, the laminate sometimes breaks.

Here, if the clip interval L1 is excessively large, a stress that contracts in the width direction is generated in a portion of the stacked body 50 not held by the clip 20, and as a result, the optical characteristics (for example, It is presumed that non-uniformity occurs in the polarization characteristics. Therefore, typically, the clip interval L1 is set to be equal to or smaller than the interval at which the occurrence of such unevenness is suppressed.

Specifically, the clip interval L1 is preferably 100 mm or less, more preferably 60 mm or less, and further preferably 40 mm or less. By making L1 smaller than 100 mm, it is possible to suppress the occurrence of unevenness, and as a result, it is possible to reduce the width of cutting and removing by slit processing. The lower limit of L1 is not particularly limited as long as the clip interval L2 described later can be achieved after stretching, and may be 25 mm or more, for example.

On the other hand, if the clip interval L1 is set to a predetermined interval or less as described above, the clip interval L2 after the MD stretching becomes smaller according to the stretching magnification, and the clips 20 in the tapered portion It may not be possible to achieve desired shrinkage due to interference of contact or the like (as a result, desired optical characteristics can not be obtained). Typically, the clip interval L2 is equal to or larger than the interval at which the clips 20 do not interfere with each other when the laminated body 50 passes the TD shrinkage zone C (particularly, the bent section) do. By setting L2 to such a value, L1 can be reduced without being limited by the interval at which the clips do not interfere with each other at the bent portion. The phrase " clips do not interfere with each other " means that the clip and its supporting member and the gap adjusting mechanism do not contact with each other, and the bending portion can be moved as set by the clip.

The clip interval L2 can be appropriately set in accordance with the bending angle, the size and shape of the clip, and the like. The clip interval L2 is preferably 25 mm to 300 mm, and more preferably 35 mm to 150 mm. When the clip interval L2 is within the above range, interference between the clips 20 in the tapered portion (particularly, the bent portion) can be avoided in the TD shrinking process and a sufficient bending angle can be realized, Shrinkage can be realized.

The stretching (MD stretching) temperature of the laminate can be set to any appropriate value depending on the forming material of the resin base material and the like. The drawing temperature is typically at least the glass transition temperature (Tg) of the resin base, preferably at least the glass transition temperature (Tg) of the resin base is at least 10 deg. C, more preferably at least Tg + 15 deg. On the other hand, the stretching temperature of the laminate is preferably 170 占 폚 or less. By stretching at such a temperature, the crystallization of the PVA resin can be inhibited from proceeding rapidly, and the problems caused by the crystallization (for example, the orientation of the PVA resin layer due to stretching can be prevented) can be suppressed.

Subsequently, in the TD shrinkage process (TD shrink zone C), the laminate 50 gripped by the left and right clips 20 is shrunk (TD shrink) in the width direction while being transported in the longitudinal direction. In the TD shrinkage zone C, since the left and right endless rails 10R, 10L are tapered parts in which the rail-to-rail distance is continuously reduced, the shrinkage in the width direction of the laminated body 50 . The TD shrinkage can be controlled by adjusting the amount of change in the distance between rails. Concretely, at the exit of the TD shrinkage zone C (the end on the release zone D side) with respect to the rail-to-rail distance at the entrance (the MD stretching zone B side end) of the TD shrinkage zone C The smaller the ratio of the rail-to-rail distance, the larger the shrinkage ratio is obtained.

The TD shrinkage ratio (the width of the laminate at the outlet of the TD shrinkage zone: W2) / (the width of the laminate at the inlet of the TD shrinkage zone: W)) can be set to any appropriate value Can be set. The TD shrinkage is preferably 0.85 to 0.4, more preferably 0.8 to 0.6. If the TD shrinkage ratio exceeds 0.85, sufficient shrinking effect can not be obtained and the shaft precision may become insufficient. If the TD shrinkage ratio is less than 0.4, the resin film may slacken due to uneven stretching.

In the embodiment shown in Fig. 4, in the TD shrinking process, only the shrinkage in the width direction of the layered product 50 is performed. In this case, the laminated body 50 is passed through the TD shrinkage zone C while the clip interval L2 in the carrying direction is maintained. On the other hand, in the embodiment illustrated in Fig. 5, in the TD shrinking process, the laminate 50 shrinks in the width direction and is stretched in the longitudinal direction. In this case, the stacking body 50 is allowed to pass through the TD shrinkage zone C while expanding the clip interval in the carrying direction from L2 to L3. In the MD stretching process and the TD shrinking process, the MD stretching in multiple stages can be performed to increase the final stretch magnification. In addition, by simultaneously performing TD shrinkage and MD stretching, it is possible to obtain an effect of suppressing occurrence of warpage and wrinkles.

The draw ratio of the laminate after the TD shrinking process (also referred to as the final draw ratio, which is the product of the draw ratio in the MD draw process and the draw ratio in the TD shrink process) The final drawing magnification is L3 / L1, and the final drawing magnification when the TD shrinking process does not include MD drawing is L2 / L1) is 3.0 times or more, for example, 4.0 times or more, It is more than double. By stretching at such a high magnification, a polarizing film having excellent optical characteristics can be obtained. The final drawing magnification here is a final drawing magnification in the manufacturing method when the manufacturing method of the present invention does not include a separate drawing step to be described later and the manufacturing method of the present invention includes a separate drawing step Is the final draw ratio of the drawing process using the tenter stretching apparatus.

The temperature environment in the TD shrinking process may be the same as the stretching temperature in the MD stretching process.

Finally, in the release step (release zone D), the clip 20 holding the stacked body 50 is released. In the liberation process, the clip-to-clip distance and clip interval are typically constant. After the laminate 50 is cooled to a desired temperature as required, the clip is released.

The MD stretching and the TD shrinkage are carried out in this order using the stretching apparatus exemplified in Fig. 1, but as described above, the TD shrinkage may be performed before the MD stretching, and the MD stretching and the TD shrinkage may be simultaneously performed . As shown in Figs. 6 and 7, in the case of performing TD shrinkage before MD stretching, the elongation at break (A) and the TD shrinkage zone C '), a MD stretching zone B', and a release zone D may be formed in this order. In the embodiment illustrated in Fig. 6, the distance between rails (the width of the laminate) is changed from W1 to W2 (width) while maintaining the clip interval L1 in the transport direction in the TD shrinkage process (TD shrink zone C ' Then, in the MD stretching process (MD stretching zone B '), the clip interval in the carrying direction is increased from L1 to L2 while maintaining the rail-to-rail distance at W2. In the embodiment illustrated in Fig. 7, in the TD shrinkage process (TD shrink zone C '), MD stretching can be performed at the same time. In this case, the distance between the rails (the width of the laminate) is changed from W1 to W2 while the clip interval in the carrying direction is increased from L1 to L1 ', and then, in the MD stretching process (MD stretching zone B') , The clip interval in the carrying direction is increased from L1 'to L2 while maintaining the distance between rails at W2. When MD stretching and TD shrinking are simultaneously carried out, for example, as shown in Fig. 8, the rails in the MD stretching zone may be tapered in such a manner that the distance between rails decreases continuously. That is, in the stretching apparatus, the MD stretching / TD shrinkage zone BC is formed between the grip zone A and the release zone D, and in the MD stretching / TD shrinkage zone BC, The width of the sieve is reduced from W1 to W2 and the clip interval in the carrying direction is increased from L1 to L2. Details of the operations and / or conditions in these embodiments are as described with reference to Figs. 1 to 5. Fig.

A-3. Other processes

The polarizing film manufacturing method of the present embodiment may include other processes besides the above. Examples of the other steps include an insolubilizing step, a dyeing step, a crosslinking step, a stretching step other than the stretching step, a washing step, and a drying step (controlling the moisture content). Other processes can be carried out at any appropriate timing.

The dyeing step is typically a step of dyeing the PVA resin layer with a dichroic material. Preferably by adsorbing a dichroic substance on the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA resin layer (laminate) in a dyeing solution containing a dichroic substance, a method of applying a dyeing solution to a PVA resin layer, a method of dyeing a PVA resin layer And a method of spraying the liquid. Preferably, the laminate is immersed in a dyeing solution containing a dichroic substance. This is because the dichroic material can be adsorbed well. Further, both sides of the laminate may be immersed in the dyeing solution, or only one side may be immersed.

Examples of the dichroic material include iodine and organic dyes. These may be used alone or in combination of two or more. The dichroic substance is preferably iodine. When iodine is used as the dichroic substance, the dyeing solution is preferably an iodine aqueous solution. The blending amount of iodine 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 preferable to add an iodide salt to an aqueous solution of iodine. Examples of the iodide salt include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like. Among them, potassium iodide and sodium iodide are preferable. The compounding amount of the iodide salt is preferably 0.3 part by weight to 15 parts by weight based on 100 parts by weight of water.

The liquid temperature at the time of staining of the staining solution is preferably from 20 캜 to 40 캜. When the PVA resin layer is immersed in the dyeing solution, the immersing time is preferably 5 to 300 seconds. Under such conditions, the dichroic substance can be sufficiently adsorbed to the PVA-based resin layer.

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

As another stretching process, for example, roll stretching can be mentioned. By performing a separate drawing process, the final draw ratio can be further increased. For example, the final stretching magnification can be increased to 5 times or more by further stretching the laminate which has been stretched to about 3 times by using a tenter stretching apparatus in a separate stretching process. As a result, a polarizing film having even better optical characteristics can be obtained. The separate stretching step may be performed simultaneously with the dyeing step, the insolubilization step and / or the crosslinking step, or may be carried out separately. If carried out separately, the separate drawing process can be carried out at any appropriate timing.

B. Polarizing film

The polarizing film produced by the above production method is substantially a PVA-based resin film in which a dichroic substance is adsorbed and oriented. The polarizing film preferably exhibits absorption dichroism at a wavelength of 380 nm to 780 nm. The transmittance Ts of the polarizing film is preferably 39% or more, more preferably 39.5% or more, still more preferably 40% or more, particularly preferably 40.5% or more. In addition, the theoretical upper limit of the unit transmittance is 50%, and the practical upper limit is 46%. The unitary transmittance Ts is a Y value obtained by measuring the visual sensitivity by a 2-degree field of view (C light source) of JIS Z 8701 and measuring it using, for example, a microscopic spectroscopic system (manufactured by Lambda Vision, LVmicro) can do. The degree of polarization of the polarizing film is preferably 99.9% or more, more preferably 99.93% or more, and still more preferably 99.95% or more.

In the polarizing film produced by the above-described manufacturing method, the deviation of the absorption axis in the longitudinal direction at the end portion in the width direction (for example, 250 mm from the end) is very small. For example, in a polarizing film produced by a manufacturing method including only stretching using a tenter stretching device, the deviation of the absorption axis at a position of 250 mm from the end in the width direction is smaller than the deviation of the absorption axis in the set absorption axis direction Longitudinal direction) is preferably within a range of +/- 0.30 deg., More preferably within a range of +/- 0.25 deg. The deviation of the absorption axis in the longitudinal direction at the center in the width direction of the polarizing film is within a range of, for example, ± 0.20 °. As described above, the polarizing film obtained by the manufacturing method of the present invention has excellent axial precision at the end portions in the width direction, and can achieve the axial precision equivalent to the central portion. As a result, since the polarizing film is excellent in the in-plane uniformity of the optical characteristics, the polarizing film as the final product after the cutting has a small variation in quality for each product, and excellent display characteristics can be realized when used in an image display apparatus have. Further, for example, the polarizing film obtained by roll stretching has a large deviation of the absorption axis in the longitudinal direction at a position of 250 mm from the end in the width direction (for example, a deviation of about 0.75 °) , The slit is about 250 mm from the end. On the other hand, since the polarizing film obtained by the production method of the present invention can be practically used up to the end portion in the width direction, the yield is high and it is advantageous in cost. Even when the production method of the present invention includes a separate stretching step, the deviation of the optical axis of the PVA-based resin layer in the laminate obtained by stretching using the tenter stretching device becomes very small, and consequently, The deviation of the absorption axis of the polarizing film becomes very small.

As for the method of using the polarizing film, any suitable method can be employed. Concretely, it may be used as a single-layer PVA-based resin film, or may be used as a laminate of a resin substrate and a PVA-based resin film, or a laminate of a PVA-based resin film or a PVA- I.e., a polarizing plate).

C. polarizer

The polarizing plate has a protective film disposed on at least one side of the polarizing film and the polarizing film. Examples of the material for forming the protective film include cellulose resins such as diacetylcellulose and triacetylcellulose, olefinic resins such as (meth) acrylic resins, cycloolefin resins and polypropylene, polyethylene terephthalate resins and the like Ester-based resins, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof.

The thickness of the protective film is preferably 20 m to 100 m. Typically, the protective film is laminated on the polarizing film with an adhesive layer (specifically, an adhesive layer and a pressure-sensitive adhesive layer) sandwiched therebetween. The adhesive layer is typically formed of a PVA-based adhesive or an activation energy ray-curable adhesive. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive. When a laminate of a resin substrate / PVA resin film (polarizing film) is used, preferably, the resin substrate can be peeled off after laminating the protective film on the surface opposite to the resin substrate of the polarizing film. If necessary, a separate protective film may be laminated on the release face. By peeling the resin base material, the curl can be more reliably suppressed.

Practically, the polarizing plate has a pressure-sensitive adhesive layer as an outermost layer. The pressure-sensitive adhesive layer is typically the outermost layer on the side of the image display apparatus. The separator is temporarily adhered to the pressure-sensitive adhesive layer so that the separator can be peeled off, thereby protecting the pressure-sensitive adhesive layer until actual use, and enabling roll formation.

The polarizing plate may further have any appropriate optical functional layer depending on the purpose. Typical examples of the optical function layer include a retardation film (optical compensation film) and a surface treatment layer. For example, a retardation film may be disposed between the protective film and the pressure-sensitive adhesive layer (not shown). The optical properties (for example, the refractive index ellipsoid, in-plane retardation, thickness direction retardation) of the retardation film can be appropriately set in accordance with the purpose, the characteristics of the image display device, and the like. For example, when the image display apparatus is an IPS mode liquid crystal display apparatus, a retardation film having a refractive index ellipsoid of nx> ny> nz and a retardation film having a refractive 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 apparatus side may be omitted. On the contrary, the protective film may have an optical compensation function (that is, it may have an appropriate refractive index ellipsoid depending on the purpose, in-plane retardation and thickness retardation). Is a refractive index in a direction perpendicular to the slow axis in the film plane, and " nz " is a refractive index in a direction perpendicular to the slow axis in the film plane. Refractive index.

The surface treatment layer can 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. The surface treatment layer is preferably a layer having a low moisture permeability for the purpose of improving the damping durability of the polarizing film, for example. The hard coat layer is formed for the purpose of preventing scratches on the surface of the polarizing plate. The hard coat layer can be formed by, for example, a method of adding a cured film having excellent hardness, slipperiness and the like by a suitable ultraviolet curable resin such as acrylic or silicone to the surface. The hard coat layer preferably has a pencil hardness of 2H or higher. The antireflection layer is a low reflection layer formed for the purpose of preventing reflection of external light on the surface of the polarizing plate. Examples of the antireflection layer include a thin layer type which prevents reflection by using a canceling effect of reflected light due to the interference action of light disclosed in Japanese Patent Application Laid-Open No. 2005-248173, And a surface structure type that exhibits a low reflectance by imparting a fine structure. The anti-glare layer is formed for the purpose of preventing external light from being reflected on the surface of the polarizing plate to prevent visibility of the light transmitted through the polarizing plate. The anti-glare layer is formed, for example, by imparting a fine concavo-convex structure to the surface by a suitable method such as a sand blast method, a roughening method by an embossing method, or a blending method of transparent fine particles. The anti-glare layer may also serve as a diffusion layer (time magnification function or the like) for diffusing the polarized-plate transmitted light to enlarge the viewing angle or the like. Instead of forming the surface treatment layer, the surface of the outside protective film may be subjected to the same surface treatment.

Up to this point, as an example of the method for producing a polarizing film of the present invention, an embodiment in which a polarizing film is produced by using a laminate of a resin substrate and a PVA resin layer is described, but as described above, It is obvious to a person skilled in the art that the same can be applied to a method for producing a polarizing film using a single-layer PVA resin film. That is, in the present invention, the same procedure can be applied even if the laminate of resin substrate / PVA resin layer is replaced with a single resin film, and the same effect can be obtained.

Example

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]

≪ Laminate preparation process >

As the resin substrate, an amorphous PET substrate (thickness: 100 占 퐉) was prepared, and an aqueous solution of PVA was applied to the amorphous PET substrate and dried at a temperature of 50 占 폚 to 60 占 폚. Thus, a PVA layer having a thickness of 14 占 퐉 was formed on the amorphous PET substrate to prepare a laminate.

<MD stretching · TD shrinking step>

The obtained laminate was subjected to MD stretching and TD shrinkage using a stretching apparatus similar to that of Fig. Concretely, in the gripping zone A, gripping both side edges of the laminated body at a clip interval L1 of 35 mm and transporting them in the longitudinal direction. In the MD stretching and TD shrinkage zone BC, (Clip interval L3 at the exit of the MD stretching / TD shrinkage zone BC: 105 mm, width of the laminate: 650 mm) in the transverse direction and 30% in the longitudinal direction. Thereafter, in the release zone D, the clip holding the laminate was released. The clip size was 15 mm.

<Dyeing treatment>

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

<Crosslinking Treatment>

The laminate after dyeing was immersed in a boric acid aqueous solution (boric acid concentration: 5 wt%, potassium iodide concentration: 5 wt%) at 60 캜 for 60 seconds and stretched 1.7 times in the longitudinal direction in the boric acid aqueous solution (final draw ratio 5.1 ship).

<Cleaning Treatment>

After the crosslinking treatment, the laminate was immersed in an aqueous potassium iodide solution (potassium iodide concentration: 5 wt%) at 25 캜 for 5 seconds.

Thus, a polarizing film having a thickness of 4.0 mu m was formed on the resin base material.

<Axis Precision>

The deviation of the absorption axis in the longitudinal direction at a position of 250 mm from the end in the width direction of the layered product (substantially the dyed PVA resin layer, that is, the polarizing film) after the dyeing treatment was measured. Specifically, as the measuring device, the direction of the absorption axis was measured every 20 mm over 1200 mm in the longitudinal direction using the apparatus name &quot; AXOSCAN &quot;, manufactured by AXOMETRICS. The maximum deviation of the deviation from the longitudinal direction was regarded as an index of the axis accuracy. The deviation of the absorption axis was ± 0.21 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed.

[Example 2]

A polarizing film having a thickness of 4.0 탆 was formed on the resin base material in the same manner as in Example 1 except that the side edge portions of the laminate were held at a clip interval (L1) of 60 mm in the waveguide zone (A). The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.29 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed.

[Example 3]

A polarizing film having a thickness of 4.0 탆 was formed on the resin base material in the same manner as in Example 1, except that both side edges of the laminate were held at a clip interval (L1) of 90 mm in the waveguide zone (A). The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.47 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed.

[Example 4]

A polarizing film having a thickness of 4.0 탆 was formed on a resin substrate in the same manner as in Example 1 except that MD stretching and TD shrinking were performed as follows.

Using the stretching apparatus similar to that in Fig. 5, both side edges of the laminate were gripped at the clip interval (L1) of 40 mm and conveyed in the longitudinal direction in the grip zone A, and in the MD stretching zone B, (Length (L2) at the exit of the MD stretching zone (B): 56 mm) at 140 占 폚 in the longitudinal direction. Subsequently, in the TD shrinkage zone C, 30% shrinkage in the width direction and further elongation in the longitudinal direction (the clip interval L3 at the exit of the TD shrinkage zone C: 120 mm, Final draw ratio by stretching apparatus: 3 times).

The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.41 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed.

[Example 5]

A polarizing film having a thickness of 4.0 mu m was produced on the resin base material in the same manner as in Example 1 except that both side edges of the laminate were held in the clip zone A with a clip size of 30 mm and a clip interval L1 of 60 mm Respectively. The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.39 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed.

[Example 6]

A polarizing film having a thickness of 4.0 탆 was produced on the resin base material in the same manner as in Example 1 except that both side edges of the laminate were held at a clip size of 45 mm and a clip spacing (L1) of 60 mm Respectively. The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.44 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed. On the other hand, cracking occurred on the surface of the resin film due to localized stretching of the non-flammable part.

[Example 7]

In Examples 1 and 2 except that both side edges of the laminate were gripped at a clip interval (L1) of 60 mm and shrunk by 10% in the width direction in the MD stretching and TD shrinkage zone (BC) In the same manner, a polarizing film having a thickness of 4.0 탆 was formed on a resin substrate. The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.38 °. It was confirmed that the deviation of the absorption axis of the laminate was remarkably suppressed, and the deviation of the finally obtained polarizing film was also remarkably suppressed.

[Comparative Example 1]

A laminate of an amorphous PET substrate and a PVA layer was prepared in the same manner as in Example 1. Next, this laminate was stretched three times in the longitudinal direction by using two sets of nip rolls (diameter 350 mm) having a gap interval of 22 mm. After the dyeing treatment, a polarizing film having a thickness of 4.0 탆 was formed on the resin substrate in the same manner as in Example 1.

The laminate after the dyeing treatment was provided for evaluation of the deviation of the absorption axis in the same manner as in Example 1. [ The deviation of the absorption axis was ± 0.82 °. It was confirmed that the deviation of the polarizing film finally obtained also becomes larger by increasing the deviation of the absorption axis of the laminate.

[evaluation]

As described above, according to the embodiment of the present invention, by employing the stretching in the longitudinal direction using the tenter stretching device, it is possible to reduce the deviation in the axial precision of the end portions in the width direction of the obtained laminate and the polarizing film.

Industrial availability

The production method of the present invention is preferably used for producing a polarizing film.

10: Rail
20: Clip
50: laminate (resin film)
100: stretching device

Claims (8)

As a method for producing a polarizing film of a long-
Stretching the elongated-phase resin film in the machine direction and shrinking it in the transverse direction by using a tenter stretching apparatus having a plurality of clips as gripping means of a long-length resin film forming the polarizing film,
Wherein the stretching in the longitudinal direction includes enlarging the clip interval in the transport direction of the elongated resin film,
Wherein said shrinking in the width direction comprises reducing the clip spacing in the width direction. The method according to claim 1,
Wherein the elongated resin film forming the polarizing film is a single-layered polyvinyl alcohol-based resin film, and the resin film is stretched and longitudinally stretched in the longitudinal direction and dyed to produce the polarizing film. The method according to claim 1,
Wherein the elongated resin film forming the polarizing film is a laminate having a resin substrate and a polyvinyl alcohol resin layer formed on one side of the resin substrate and the laminate is stretched in the length direction and shrunk in the width direction and is dyed And producing a polarizing film on the resin base. The method according to claim 1,
And the shrinkage ratio in the width direction is 0.8 or less. The method according to claim 1,
Wherein the clip size of the clip is 12 mm to 40 mm. The method according to claim 1,
Wherein a clip interval in the transport direction before stretching in the longitudinal direction is 100 mm or less. The method according to claim 1,
Wherein the stretching ratio in the longitudinal direction is 1.5 to 6.5 times. A long polarizing polarizing film obtained by the manufacturing method according to claim 1.

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