JP6579752B2 - Manufacturing method of optical film - Google Patents

Description

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

  2. Description of the Related Art Conventionally, a technique is known in which a long film is gripped and conveyed by a tenter clip, and an optical film is produced by stretching the film by widening the interval in the conveying direction of the tenter clip (for example, Patent Documents). 1 claim 7). In such a stretching technique, wrinkles and folds may occur in the side edge of the film in the initial stage of stretching, and as a result, the problem that the side edge of the film does not reach the clip and cannot be gripped during clip chucking (hereinafter, (Referred to as “clip mistake”), which may lead to a decrease in productivity.

JP 2008-26881 A

  The present invention has been made to solve the above-mentioned problems, and its main object is a method for producing an optical film including stretching a long resin film in the transport direction using a tenter stretching device. Another object of the present invention is to provide a method capable of suppressing clip mistakes due to the occurrence of wrinkles and creases.

The present invention provides a method for producing an optical film using a tenter stretching apparatus including a plurality of clips as gripping means. In this method, both side edges of a long resin film are gripped by the clip at a clip interval L1 in the transport direction (gripping step), and the clip interval in the width direction is set to W1 while transporting the resin film in the longitudinal direction. To W2 to relax the resin film in the width direction (relaxation process), and increase the clip interval in the transport direction to L2 while transporting the resin film relaxed in the width direction in the longitudinal direction. And stretching the resin film in the longitudinal direction (stretching step).
In one embodiment, the total draw ratio A (A = L2 / L1) in the longitudinal direction is 2.0 or more.
In one embodiment, the reduction ratio B (B = W2 / W1) of the clip interval in the width direction is 0.60 to 0.99.
In one embodiment, the relaxation step includes reducing the clip interval in the width direction, expanding the clip interval in the transport direction to L1 ′, and stretching the resin film in the longitudinal direction. The stretching ratio a (a = L1 ′ / L1) and the reduction ratio B (B = W2 / W1) of the clip interval in the width direction satisfy the relationship B <1 / √a.
In one embodiment, the thickness of the manufactured optical film is 110 μm or less.
In one embodiment, the manufactured optical film is a polarizing film.

  In the production method of the present invention, the resin film is relaxed in the width direction prior to stretching in the longitudinal direction. Thereby, the relaxation area | region where the resin film loosened in the width direction in the area | region before extending | stretching to a longitudinal direction can be formed, and it can suppress that the wrinkles and folding which generate | occur | produced in the extending | stretching area | region to a longitudinal direction reach a tenter entrance. As a result, the occurrence of clip mistakes can be suppressed, and an optical film can be produced without reducing productivity.

It is a schematic plan view explaining the whole structure of an example of the extending | stretching apparatus which can be used for the manufacturing method of this invention. It is the schematic explaining one embodiment of this invention. It is the schematic explaining another embodiment of this invention.

A. Method for Producing Optical Film In the method for producing an optical film of the present invention, a tenter stretching device having a plurality of clips is used as a film gripping means. In the manufacturing method of the present invention, both side edges of a long resin film are gripped by the clip at a clip interval L1 in the transport direction (gripping step), and the clip in the width direction is transported while transporting the resin film in the longitudinal direction. Decreasing the interval from W1 to W2 to relax the resin film in the width direction (relaxation process), and transporting the resin film relaxed in the width direction in the longitudinal direction, the clip interval in the conveyance direction to L2 Enlarging and stretching the resin film in the longitudinal direction (stretching step). In a tenter stretching device that grips a film with a clip, in the process from when the end of the resin film is gripped with a clip in a state where no tension is applied before stretching, the tension is applied to the resin film by heating or stretching. It is considered that stress is applied to the resin film due to the in-plane variation in temperature and the accuracy of each clip conveyance, and as a result, the resin film is greatly wrinkled and broken in the initial stretching region, leading to clip mistakes. On the other hand, in the present invention, the resin film is relaxed in the width direction prior to stretching in the longitudinal direction. Thereby, in the region before stretching in the longitudinal direction, a relaxation region in which the resin film is loosened in the width direction is formed, and in the tenter entrance region for gripping the resin film, it is avoided that excessive tension is generated in the resin film. Therefore, the occurrence of clip mistakes can be suppressed.

  The resin film used in the production method of the present invention may be a laminate having a thermoplastic resin base material and a resin layer formed on one side of the thermoplastic resin base material. It may be a layered body. The optical film to be manufactured can be any suitable optical film as long as it can be manufactured by a manufacturing method including the gripping step, the relaxation step, and the stretching step. The thickness of the optical film is preferably 110 μm or less, preferably 80 μm or less, more preferably 70 μm or less, and further preferably 60 μm or less. On the other hand, the thickness of the optical film is preferably 10 μm or more, more preferably 20 μm or more.

  Specific examples of the produced optical film are preferably a polarizing film and an optical compensation film.

  As the tenter stretching device used in the manufacturing method of the present invention, for example, a pair of rails having a tapered portion in which the distance between the rails continuously decreases and a straight portion in which the distance between the rails is constant, and a clip on each rail are clipped A stretching device including a plurality of clips that can run while changing the interval may be used. According to such a stretching device, the clip interval in the transport direction (distance between clips on the same rail) and the clip interval in the width direction (between clips on different rails) with both side edges of the resin film held by clips. By changing the distance), the resin film can be stretched in the longitudinal direction (MD stretching) and relaxed in the width direction (TD relaxation).

  FIG. 1 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the production method of the present invention. A stretching apparatus that can be used in the production method of the present invention will be described with reference to FIG. The extending | stretching apparatus 100 has the endless rail 10L and the endless rail 10R in the left-right both sides symmetrically by planar view. In this specification, the left endless rail as viewed from the entrance side of the resin film is referred to as the left endless rail 10L, and the right endless rail is referred to as the right endless rail 10R. A large number of clips 20 for gripping the resin film are arranged on the left and right endless rails 10L and 10R, respectively. The clip 20 is guided by each rail and moves in a loop. The clip 20 on the left endless rail 10L rotates in a counterclockwise direction, and the clip 20 on the right endless rail 10R rotates in a clockwise direction. In the stretching apparatus, a gripping zone A, a TD relaxation zone B, an MD stretching zone C, and a release zone D are sequentially provided from the resin film carry-in side to the carry-out side. Each of these zones means a zone where the resin film is substantially gripped, TD relaxed (or TD relaxed and MD stretched), MD stretched and released, and means a mechanically and structurally independent zone. Not what you want. It should also be noted that the ratio of the lengths of the respective zones in the stretching apparatus of FIG. 1 is different from the actual ratio of lengths.

  In the gripping zone A, the left and right endless rails 10R and 10L are straight portions having a constant distance between the rails. Typically, the left and right endless rails 10R, 10L are configured to be substantially parallel to each other at a distance between the rails corresponding to the initial width of the resin film to be processed. In the TD relaxation zone B, the left and right endless rails 10R and 10L are tapered portions where the distance between the rails continuously decreases. Typically, the left and right endless rails 10R and 10L are configured to gradually decrease until the distance between the rails corresponds to the width after relaxation of the resin film as it goes from the gripping zone A side to the MD stretching zone C side. ing. In the MD stretching zone C and the release zone D, the left and right endless rails 10R and 10L are linear portions with a constant distance between the rails. Typically, the rails correspond to the width after the relaxation of the resin film. It is comprised so that it may mutually become substantially parallel at the distance.

  The clip (left clip) 20 on the left endless rail 10L and the clip (right clip) 20 on the right endless rail 10R can each independently move around. For example, the driving sprockets 30a and 30b of the left endless rail 10L are driven to rotate counterclockwise by the electric motors 40a and 40b, and the driving sprockets 30a and 30b of the right endless rail 10R are rotated by the electric motors 40a and 40b. It is driven to rotate around. As a result, traveling force is applied to a clip carrying member (not shown) of a drive roller (not shown) engaged with the drive sprockets 30a and 30b. As a result, the left clip 20 moves in a counterclockwise direction, and the right clip 20 moves in a clockwise direction. By driving the left electric motor and the right electric motor independently, the left clip 20 and the right clip 20 can be moved independently.

  The clip size is preferably 12 mm to 40 mm, more preferably 15 mm to 35 mm. When the clip size is less than 12 mm, the stretching tension may not be maintained and the clip may be broken, or a drive failure may occur due to insufficient strength of the clip transport unit. When the clip size exceeds 40 mm, a region that is not stretched in the vicinity of the clip becomes large, unevenness of the end portion occurs, or cracks may occur on the surface of the resin film due to local stretching of the non-gripping portion. . The clip size means the width of the gripping area.

  Further, 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 transport direction with movement. The variable pitch clip can be realized by any appropriate configuration such as a pantograph mechanism (for example, a configuration described in JP 2008-23775 A).

  When the stretching apparatus as illustrated in FIG. 1 is used, the manufacturing method of the present invention is such that the both side edges of the resin film are gripped by clips at the clip interval L1 in the transport direction in the gripping zone A (gripping step), Is passed through the taper part, and the clip interval in the width direction is decreased from W1 to W2, thereby relaxing the resin film in the width direction (relaxation process), and the clip in the transport direction while passing the resin film through the linear part. Extending the distance to L2 and stretching the resin film in the longitudinal direction (MD stretching step) may be included. You may further include releasing the clip which hold | grips a resin film as needed (release process). FIG. 2 and FIG. 3 are schematic views for explaining an example of the production method of the present invention including these steps. Hereinafter, each process will be described in more detail with reference to these drawings.

  First, in the gripping process (grip zone A), the left and right clips 20 grip both side edges of the resin film 50 taken into the stretching apparatus at a constant gripping interval (clip interval) L1 and guide them to the left and right endless rails. The resin film 50 is conveyed to the TD relaxation zone B by the movement of each clip 20 that has been performed. The grip interval (clip interval) between both side edges in the grip zone A is typically equal to each other. L1 can be, for example, 30 mm to 200 mm. The clip interval is the distance between the centers of adjacent clips.

  Any appropriate film can be selected as the resin film held by the clip depending on the use of the optical film to be manufactured. When the optical film to be manufactured is a polarizing film, as an example, a laminate having a thermoplastic resin substrate and a PVA resin layer formed on one side of the thermoplastic resin substrate is gripped as a resin film. Hereinafter, the characteristics / conditions unique to the laminate will be described, and then the processes after the relaxation process will be described. About the process after a relaxation process, the same operation, conditions, etc. can be applied irrespective of whether it is a laminated body or a normal resin film (single film).

  The laminate is produced by forming a PVA resin layer on a long thermoplastic resin substrate. The thermoplastic resin substrate has 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 thermoplastic resin substrate include ester resins such as polyethylene terephthalate resin, cycloolefin resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Can be mentioned. Among these, cycloolefin resins (for example, norbornene resins) and amorphous polyethylene terephthalate resins are preferable. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid as a dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol as a glycol.

  The stretching temperature of the thermoplastic resin substrate can be set to any appropriate value depending on the forming material of the thermoplastic resin substrate, the stretching method, and the like. The stretching temperature is typically not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably not less than Tg + 10 ° C., more preferably not less than Tg + 15 ° C. to Tg + 30 ° C. When a dry stretching method or a wet stretching method is employed as the stretching method, and an amorphous polyethylene terephthalate resin is used as a material for forming the thermoplastic resin substrate, the stretching temperature is set to the glass transition temperature of the thermoplastic resin substrate (for example, 60 ° C. to 100 ° C.).

  A surface modification treatment (for example, corona treatment) may be performed on the thermoplastic resin substrate in advance, or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such a treatment, the adhesion between the thermoplastic resin substrate and the PVA resin layer can be improved. The surface modification treatment and / or the formation of the easy adhesion layer may be performed before the stretching or after the stretching.

  Arbitrary appropriate methods can be employ | adopted for the formation method of the said PVA-type resin layer. Preferably, a PVA-based resin layer is formed by applying a coating solution containing a PVA-based resin on a thermoplastic resin substrate that has been subjected to a stretching treatment, and drying.

  Any appropriate resin can be used as the PVA-based resin. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The saponification degree can be determined according to JIS K 6726-1994. By using a PVA resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the saponification degree is too high, the coating solution is likely to gel, and it may be difficult to form a uniform coating film.

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

  The coating solution is typically a solution obtained by dissolving the PVA resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Among these, water is preferable. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the thermoplastic resin substrate can be formed.

  You may mix | blend an additive with a coating liquid. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the resulting PVA resin layer.

  Any appropriate method can be adopted as a coating method of the coating solution. Examples thereof 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, a knife coating method (comma coating method, etc.).

  It is preferable that the said drying temperature is below the glass transition temperature (Tg) of a thermoplastic resin base material, More preferably, it is below Tg-20 degreeC. By drying at such a temperature, the thermoplastic resin base material is prevented from being deformed before the PVA resin layer is formed, and the orientation of the resulting PVA resin layer is prevented from deteriorating. Can do. Thus, the thermoplastic resin substrate can be deformed well together with the PVA-based resin layer, and the later-described laminate can be satisfactorily relaxed and stretched. As a result, good orientation can be imparted to the PVA-based resin layer, and a polarizing film having excellent optical properties can be obtained. Here, “orientation” means the orientation of molecular chains of the PVA resin layer.

  Next, in the relaxation step (TD relaxation zone B), the resin film 50 held by the left and right clips 20 is relaxed in the width direction while being conveyed in the longitudinal direction. In the TD relaxation zone B, the left and right endless rails 10R and 10L are tapered portions in which the distance between the rails continuously decreases. Therefore, by passing the zone, the widthwise clip interval decreases from W1 to W2. As a result, the resin film 50 is relaxed in the width direction. The amount of relaxation can be controlled by adjusting the amount of change in the distance between the rails. Specifically, the smaller the ratio of the distance between the rails at the exit of the TD relaxation zone B (end on the MD extension zone C) to the distance between the rails at the entrance of the TD relaxation zone B (the grip zone A side end), A large amount of relaxation is obtained. In the present specification, “relaxing the resin film in the width direction” means forming a region relaxed in the width direction (in other words, no tension is applied) on the resin film. In the embodiment, the resin film may be contracted in the width direction.

  In the embodiment illustrated in FIG. 2, only relaxation in the width direction of the resin film 50 is performed in the relaxation step. In this case, the resin film 50 is allowed to pass through the TD relaxation zone B while maintaining the clip interval (L1) in the transport direction. On the other hand, in the embodiment illustrated in FIG. 3, in the relaxation step, the resin film 50 is relaxed in the width direction and stretched in the longitudinal direction. In this case, while moving the resin film 50 through the TD relaxation zone B, the moving speed of the clip 20 in the transport direction is gradually increased to increase the clip interval in the transport direction from L1 to L1 '. The final draw ratio can be increased by performing MD stretching in multiple stages in the relaxation process and the stretching process. Moreover, since the excessive relaxation can be avoided by simultaneously performing the relaxation in the width direction and the stretching in the longitudinal direction, it is possible to obtain an effect that the generation of wrinkles due to the relaxation can be suppressed.

  The reduction ratio B (B = W2 / W1) of the clip interval in the width direction can be set to any appropriate value according to the MD stretch ratio or the like. The reduction ratio B is preferably 0.60 to 0.99, more preferably 0.65 to 0.90, and still more preferably 0.70 to 0.80. With such a reduction ratio, a relaxation region can be suitably formed in the width direction of the resin film. In the production of a polarizing film, more excellent optical characteristics can be obtained. In addition, the clip space | interval of the width direction can respond | correspond to the width | variety of the resin film of the part currently hold | gripped with the clip on either side.

  In an embodiment in which the relaxation step includes MD stretching (the embodiment illustrated in FIG. 3), the width direction is set so that the contraction rate is larger than the contraction rate in the width direction when the free end is uniaxially stretched in the longitudinal direction. It is preferable to reduce the clip interval. Specifically, it is preferable that the draw ratio a (a = L1 ′ / L1) in the longitudinal direction and the reduction ratio B of the clip interval in the width direction satisfy the relationship of B <1 / √a. When satisfy | filling such a relationship, a relaxation area | region can be formed suitably in the width direction of a resin film irrespective of extending | stretching to a longitudinal direction. The draw ratio “a” in the longitudinal direction is preferably 1.0 to 5.5 times, more preferably 1.1 to 4.0 times.

  The temperature of the resin film (relaxation temperature) in the relaxation step can be set to any appropriate value depending on the material for forming the resin film. The relaxation temperature of the laminate in the production of the polarizing film is typically not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10 ° C. As mentioned above, More preferably, it is Tg + 15 degreeC or more. On the other hand, the relaxation temperature of the laminate is preferably 170 ° C. or lower.

  Next, in the stretching step (MD stretching zone C), the resin film 50 held by the left and right clips 20 is stretched in the longitudinal direction while being transported in the longitudinal direction. The stretching of the resin film 50 is performed by gradually increasing the moving speed of the clip 20 in the transport direction and expanding the clip interval in the transport direction to L2. By adjusting the clip interval (L1 or L1 ′) in the transport direction at the entrance of the MD stretch zone C and the clip interval (L2) in the transport direction at the exit of the MD stretch zone C, the stretch ratio (relaxation process is performed by MD stretching). When not included, L2 / L1 can be controlled, and when included, L2 / L1 ′) can be controlled. In the stretching step, shrinkage in the width direction may be performed simultaneously. When shrinking in the width direction is simultaneously performed in the stretching process, a taper portion in which the distance between the rails of the left and right endless rails 10R and 10L is continuously reduced may be provided in the MD stretching zone C. The shrinkage rate in the width direction can be controlled by adjusting the amount of decrease in the distance between the left and right rails.

  The total stretch ratio of the resin film after the stretching process (the product of the stretch ratio in the stretching process and the stretch ratio in the relaxation process, L2 / L1) is preferably 2.0 times or more with respect to the original length of the resin film. Preferably they are 2.0 times-6.5 times.

  The stretching temperature can be set to any appropriate value depending on the resin film forming material and the like. In the case of producing a polarizing film, the stretching temperature is typically at least the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably at least the glass transition temperature (Tg) of the thermoplastic resin substrate, and more than 10 ° C. Preferably it is Tg + 15 degreeC or more. On the other hand, the stretching temperature is preferably 170 ° C. or lower. By stretching at such a temperature, it is possible to suppress rapid progress of crystallization of the PVA-based resin, and to suppress problems due to the crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching). it can.

  Finally, in the release step (release zone D), the clip 20 that holds the resin film 50 is released. In the releasing step, typically, the distance between clips and the clip interval are both constant. If necessary, the clip is released after cooling the resin film 50 to a desired temperature (preferably below the glass transition temperature (Tg)).

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

  The dyeing step is typically a step of dyeing the PVA resin layer with a dichroic substance. Preferably, it is performed by adsorbing a dichroic substance to the PVA resin layer. As the adsorption method, for example, a method of immersing a PVA resin layer (laminate) in a dye solution containing a dichroic substance, a method of applying a dye solution to the PVA resin layer, and a dye solution on a PVA resin layer The method of spraying etc. are mentioned. Preferably, the laminate is immersed in a staining solution containing a dichroic substance. It is because a dichroic substance can adsorb | suck favorably. Both surfaces of the laminate may be immersed in the dyeing solution, or only one surface may be immersed. In addition, you may extend | stretch simultaneously in the dyeing process and / or the bridge | crosslinking process mentioned later.

  Examples of the dichroic substance include iodine and organic dyes. These may be used alone or in combination of two or more. The dichroic material is preferably iodine. When iodine is used as the dichroic substance, the staining 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 with respect to 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 the aqueous iodine solution. 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, and iodide. Examples include titanium. Among these, potassium iodide and sodium iodide are preferable. The compounding amount of the iodide salt is preferably 0.3 to 15 parts by weight with respect to 100 parts by weight of water.

  The liquid temperature during staining of the staining liquid is preferably 20 ° C to 40 ° C. When the PVA resin layer is immersed in the staining solution, the immersion time is preferably 5 seconds to 300 seconds. Under such conditions, the dichroic substance can be sufficiently adsorbed to the PVA resin layer.

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

B. Polarizing Film The polarizing film produced by the above production method is substantially a PVA resin film in which a dichroic substance is adsorbed and oriented. The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm.

  Arbitrary appropriate methods can be employ | adopted for the usage method of a polarizing film. Specifically, it may be used in a state of being integrated with the thermoplastic resin base material, or it is used by transferring from the thermoplastic resin base material to another member (peeling the thermoplastic resin base material). May be.

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

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

[Example 1]
<Production of laminate>
As a thermoplastic resin substrate, an amorphous PET substrate (100 μm thickness) was prepared, an aqueous PVA solution was applied to the amorphous PET substrate, and dried at a temperature of 50 ° C. to 60 ° C. As a result, a PVA layer having a thickness of 14 μm was formed on the amorphous PET substrate to produce a laminate.

<TD relaxation and MD stretching>
The obtained laminate was relaxed in the width direction using a stretching apparatus as shown in FIG. 1, and then stretched in the longitudinal direction. Specifically, in the gripping zone A, the side edges of the laminate are gripped and conveyed in the longitudinal direction at a clip interval L1: 40 mm, and in the TD relaxation zone B, the widthwise clip interval is set to 800 mm (W1 ) To 680 mm (W2), and the laminate was contracted in the width direction (clip interval L1 ′ at the outlet of the TD relaxation zone B: 40 mm). Next, in the MD stretching zone C, the laminate was stretched in the longitudinal direction three times in the longitudinal direction at 120 ° C. (clip interval L2 at the outlet of the MD stretching zone C: 120 mm, clip interval W3 in the width direction: 680 mm). Thereafter, in the release zone D, the clip holding the laminate was released.
In the TD relaxation, the draw ratio a (a = L1 ′ / L1) in the longitudinal direction is 1, the reduction ratio B (B = W2 / W1) of the clip interval in the width direction is 0.85, and B <1 / √a relationship was satisfied.
Chucking mistakes did not occur in TD relaxation and MD stretching.

<Dyeing process>
Next, the laminate was immersed in an aqueous iodine solution at 25 ° C. (iodine concentration: 0.5 wt%, potassium iodide concentration: 10 wt%) for 30 seconds.

<Crosslinking treatment>
The laminated body after dyeing 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 stretched 1.6 times in the MD direction ( Total draw ratio: 5 times).

<Cleaning process>
After the crosslinking treatment, the laminate was immersed in a 25 ° C. aqueous potassium iodide solution (potassium iodide concentration: 5% by weight) for 5 seconds.
Thus, a polarizing film having a thickness of 3.5 μm was produced on the thermoplastic resin substrate.

[Example 2]
A polarizing film having a thickness of 3.5 μm was produced on a resin substrate in the same manner as in Example 1 except that TD relaxation and MD stretching were performed as follows.
<TD relaxation and MD stretching>
The obtained laminate was relaxed in the width direction using a stretching apparatus as shown in FIG. 1, and then stretched in the longitudinal direction. Specifically, in the gripping zone A, the side edges of the laminate are gripped and conveyed in the longitudinal direction at a clip interval L1: 40 mm, and in the TD relaxation zone B, the widthwise clip interval is set to 800 mm (W1 ) To 680 mm (W2) to shrink the laminate in the width direction. At the same time, in the TD relaxation zone B, the clip interval was increased to L1 ′: 45 mm and stretched in the longitudinal direction. Next, in the MD stretching zone C, the laminate was stretched in the longitudinal direction three times in the longitudinal direction at 120 ° C. (clip interval L2 at the outlet of the MD stretching zone C: 120 mm, clip interval W3 in the width direction: 680 mm). Thereafter, in the release zone D, the clip holding the laminate was released. That is, TD relaxation and MD stretching were performed in the same manner as in Example 1 except that MD stretching was simultaneously performed in the TD relaxation zone B.
In the TD relaxation, the draw ratio a (a = L1 ′ / L1) in the longitudinal direction is 1.125, and therefore 1 / √a is 0.943, and the reduction ratio B (B = W2) of the clip interval in the width direction. / W1) was 0.85, and the relationship of B <1 / √a was satisfied.
Chucking mistakes did not occur in TD relaxation and MD stretching.

[Example 3]
A polarizing film having a thickness of 3.5 μm was produced on a resin substrate in the same manner as in Example 1 except that TD relaxation and MD stretching were performed as follows.
<TD relaxation and MD stretching>
The obtained laminate was relaxed in the width direction using a stretching apparatus as shown in FIG. 1, and then stretched in the longitudinal direction. Specifically, in the gripping zone A, the side edges of the laminate are gripped and conveyed in the longitudinal direction at a clip interval L1: 40 mm, and in the TD relaxation zone B, the widthwise clip interval is set to 800 mm (W1 ) To 680 mm (W2) to shrink the laminate in the width direction. At the same time, in the TD relaxation zone B, the clip interval was increased to L1 ′: 45 mm and stretched in the longitudinal direction. Next, in the MD stretching zone C, the laminate was stretched in the longitudinal direction in the longitudinal direction at 120 ° C. three times (clip interval L2 at the outlet of the MD stretching zone C: 120 mm). At the same time, in the stretching zone C, the widthwise clip interval was decreased from 680 mm (W2) to 560 mm (W3) to shrink the laminate in the width direction. Thereafter, in the release zone D, the clip holding the laminate was released. That is, TD relaxation and MD stretching were performed in the same manner as in Example 1 except that MD stretching was simultaneously performed in the TD relaxation zone B and shrinkage in the width direction was simultaneously performed in the MD stretching zone C.
In the TD relaxation, the draw ratio a (a = L1 ′ / L1) in the longitudinal direction is 1.125, and therefore 1 / √a is 0.943, and the reduction ratio B (B = W2) of the clip interval in the width direction. / W1) was 0.85, and the relationship of B <1 / √a was satisfied.
Chucking mistakes did not occur in TD relaxation and MD stretching.

[Example 4]
A polarizing film having a thickness of 3.5 μm was produced on a resin substrate in the same manner as in Example 1 except that TD relaxation and MD stretching were performed as follows.
<TD relaxation and MD stretching>
The obtained laminate was relaxed in the width direction using a stretching apparatus as shown in FIG. 1, and then stretched in the longitudinal direction. Specifically, in the gripping zone A, the side edges of the laminate are gripped and conveyed in the longitudinal direction at a clip interval L1: 40 mm, and in the TD relaxation zone B, the widthwise clip interval is set to 800 mm (W1 ) To 680 mm (W2) to shrink the laminate in the width direction. At the same time, in the TD relaxation zone B, the clip interval was increased to L1 ′: 60 mm and stretched in the longitudinal direction. Next, in the MD stretching zone C, the laminate was stretched in the longitudinal direction in the longitudinal direction at 120 ° C. three times (clip interval L2 at the outlet of the MD stretching zone C: 120 mm). At the same time, in the stretching zone C, the widthwise clip interval was decreased from 680 mm (W2) to 560 mm (W3) to shrink the laminate in the width direction. Thereafter, in the release zone D, the clip holding the laminate was released. That is, TD relaxation and MD stretching were performed in the same manner as in Example 3 except that the MD stretching ratio in the TD relaxation zone B was 1.5.
In the TD relaxation, the draw ratio a (a = L1 ′ / L1) in the longitudinal direction is 1.5, and therefore 1 / √a is 0.816, and the reduction ratio B (B = W2) of the clip interval in the width direction. / W1) was 0.85 and did not satisfy the relationship of B <1 / √a.
In TD relaxation and MD stretching, some wrinkles were observed in the laminate, but no chucking error occurred and no practical problem occurred.

[Comparative Example 1]
A polarizing film having a thickness of 3.5 μm was produced on a resin substrate in the same manner as in Example 1 except that MD stretching and TD shrinkage were performed as follows.
<MD stretching and TD shrinkage>
The obtained laminate was first stretched in the longitudinal direction, and then contracted in the width direction while stretching in the longitudinal direction. Specifically, first, the both sides of the laminated body are gripped at a clip interval L1: 40 mm and conveyed in the longitudinal direction, and then the clip is maintained while maintaining the clip interval in the width direction at 800 mm (W1) at 100 ° C. The distance was increased to L1 ′: 70 mm and stretched in the longitudinal direction. Next, at 120 ° C., the clip interval in the width direction was reduced from 800 mm (W2 = W1) to 560 mm (W3), and the laminate was stretched in the air in the longitudinal direction by three times while shrinking in the width direction (at the exit of the stretching zone). Clip interval L2: 120 mm). Thereafter, in the release zone D, the clip holding the laminate was released.
Chucking errors occurred in MD stretching and TD shrinkage.

[Evaluation]
As is clear when Examples 1 to 4 and Comparative Example 1 are compared, the occurrence of chucking mistakes can be suppressed by relaxing the resin film in the width direction prior to stretching in the longitudinal direction. As is apparent from a comparison between Example 3 and Example 4, the occurrence of wrinkles and the like is caused by controlling the stretching ratio in the longitudinal direction and the reduction ratio of the clip interval in the width direction to a predetermined relationship in TD relaxation. It is further suppressed, and as a result, it can be seen that occurrence of chucking mistakes can be further suppressed.

  The production method of the present invention is suitably used for the production of optical films such as polarizing films and optical compensation films.

10 rails 20 clips 50 laminate (resin film)
100 Stretching device

Claims (5)

A method for producing an optical film using a tenter stretching apparatus including a plurality of clips as gripping means,
Gripping both side edges of the long resin film at the clip interval L1 in the transport direction with the clip (gripping step);
Decreasing the clip interval in the width direction from W1 to W2 while conveying the resin film in the longitudinal direction, and relaxing the resin film in the width direction (relaxation step),
Expanding the clip interval in the transport direction to L2 while transporting the resin film relaxed in the width direction to the longitudinal direction, and stretching the resin film in the longitudinal direction (stretching step),
In any of the gripping step, the relaxation step and the stretching step, the resin film is gripped by the same clip ,
A method in which the total draw ratio A (A = L2 / L1) in the longitudinal direction is 2.0 or more . The method according to claim 1, wherein a reduction factor B (B = W2 / W1) of the clip interval in the width direction is 0.60 to 0.99. The relaxation step includes reducing the clip interval in the width direction, expanding the clip interval in the transport direction to L1 ′, and stretching the resin film in the longitudinal direction,
A reduction magnification B of draw ratio a (a = L1 '/ L1 ) and the width direction of the clip interval in the longitudinal direction (B = W2 / W1), but satisfy the relation of B <1 / {square root} A, according to claim 1 or 2. The method according to 2 . The method in any one of Claim 1 to 3 whose thickness of the optical film manufactured is 110 micrometers or less. The optical film produced is a polarizing film, a method according to any one of claims 1 to 4.

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