CN115464864A

CN115464864A - Method for manufacturing optical film

Info

Publication number: CN115464864A
Application number: CN202211235892.4A
Authority: CN
Inventors: 秦和也; 平田聪; 近藤诚司
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2015-01-14
Filing date: 2015-11-24
Publication date: 2022-12-13
Also published as: KR102323034B1; TW201632923A; KR20210135352A; JP2016129963A; CN105980133A; KR20170104367A; JP6579752B2; WO2016114004A1

Abstract

The present invention relates to a method for manufacturing an optical film using a tenter stretching apparatus provided with a plurality of clips as a gripping mechanism. The method comprises the following steps: grasping both side edge portions of the long resin film at a jig interval L1 in the conveyance direction by the jig (grasping step); reducing the width-direction jig interval from W1 to W2 while conveying the resin film in the longitudinal direction, thereby relaxing the resin film in the width direction (a relaxing step); and stretching the resin film in the longitudinal direction by conveying the resin film loosened in the width direction in the longitudinal direction while expanding the interval between the jigs in the conveying direction to L2 (stretching step).

Description

Method for manufacturing optical film

This application is a divisional application of applications having application dates 11/24/2015, application numbers 201580004486.9, filed by nipping-japanese electrical corporation under the name of "method for producing optical film", international application numbers PCT/JP2015/082871, and international publication numbers WO 2016/114004.

Technical Field

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

Background

Previously, the following techniques are known: a technique of producing an optical film by holding and conveying a long film by tenter clips and stretching the film by increasing intervals in the conveying direction of the tenter clips (for example, claim 7 of patent document 1). In such stretching techniques, wrinkles or breaks may occur in the side edge portions of the film at the beginning of stretching, and as a result, the following may occur: the problem occurs in that the side edge of the film does not contact the jig and cannot be gripped when the jig is used (hereinafter, referred to as "jig failure"), and the productivity is lowered.

[ Prior art documents ]

[ patent document ]

Patent document 1: japanese patent laid-open No. 2008-26881

Disclosure of Invention

[ problems to be solved by the invention ]

The present invention has been made to solve the above problems, and a main object thereof is to provide a method for producing an optical film, which includes a step of stretching a long resin film in a carrying direction using a tenter stretching device, and which can suppress a clip failure caused by generation of wrinkles or cracks.

[ means for solving the problems ]

The invention provides a method for manufacturing an optical film by using a tenter stretching device provided with a plurality of clips as a holding mechanism. The method comprises the following steps: gripping both side edge portions of the long resin film at a gripper interval L1 in the conveying direction by the gripper (gripping step); reducing the width-direction jig interval from W1 to W2 while conveying the resin film in the longitudinal direction, and relaxing the resin film in the width direction (a relaxing step); and stretching the resin film in the longitudinal direction by increasing the distance between the jigs in the conveying direction to L2 while conveying the resin film loosened in the width direction in the longitudinal direction (stretching step).

In one embodiment, the total draw ratio a in the longitudinal direction (a = L2/L1) is 2.0 or more.

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

In one embodiment, the relaxation step includes the following steps: the resin film is stretched in the longitudinal direction by increasing the jig interval in the conveying direction to L1 'while reducing the jig interval in the width direction, and the stretching ratio a in the longitudinal direction (a = L1'/L1) and the reduction ratio B in the jig interval in the width direction (B = W2/W1) satisfy

The relationship (2) of (c).

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

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

[ Effect of the invention ]

In the production method of the present invention, the resin film is relaxed in the width direction before stretching in the longitudinal direction. Thus, a slack region where the resin film has slackened in the width direction is formed in the region before the stretching in the longitudinal direction, and wrinkles or breaks occurring in the region stretched in the longitudinal direction can be suppressed from reaching the tenter entrance. As a result, the occurrence of jig failure can be suppressed, and the optical film can be produced without lowering the productivity.

Drawings

Fig. 1 is a schematic plan view illustrating an overall configuration of an example of a stretching apparatus usable in the production method of the present invention.

Fig. 2 is a schematic diagram illustrating an embodiment of the present invention.

Fig. 3 is a schematic diagram illustrating another embodiment of the present invention.

Detailed Description

A. Method for manufacturing optical film

In the method for producing an optical film of the present invention, a tenter stretching device having a plurality of clips as film holding means is used. The manufacturing method of the present invention includes the steps of: grasping both side edge portions of the long resin film at a jig interval L1 in the conveyance direction by the jig (grasping step); while conveying the resin film in the longitudinal direction, reducing the distance between the jigs in the width direction from W1 to W2 to relax the resin film in the width direction (a relaxing step); and stretching the resin film in the longitudinal direction by expanding the distance between the jigs in the conveying direction to L2 while conveying the resin film loosened in the width direction in the longitudinal direction (stretching step). In a tenter stretching apparatus in which a film is held by clips, stress is applied to the resin film due to in-plane unevenness of heating or transfer accuracy of each clip in the process from holding the end of the resin film by the clips in a state in which tension before stretching is not applied until applying tension to the resin film by heating or stretching, and as a result, large wrinkles or breaks occur in the resin film in a stretching initial region, which may cause clip failure. In contrast, in the present invention, the resin film is relaxed in the width direction before being stretched in the longitudinal direction. Thus, a slack region in which the resin film is slack in the width direction is formed in the region before stretching in the longitudinal direction, and excessive tension can be prevented from being generated in the resin film at the tenter inlet region where the resin film is held, thereby suppressing occurrence of clip failure.

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

As specific examples of the optical film to be produced, a polarizing film, an optical compensation film, and the like can be preferably exemplified.

As the tenter stretching device used in the manufacturing method of the present invention, for example, a stretching device including: the jig has a pair of rails having a tapered portion and a straight portion, the distance between the rails being continuously reduced, and a plurality of jigs capable of moving on the rails while changing the interval between the jigs. According to such a stretching apparatus, the resin film can be stretched in the longitudinal direction (MD stretching) and relaxed in the width direction (TD relaxing) by changing the nip interval in the conveying direction (the distance between the nips on the same track) and the nip interval in the width direction (the distance between the nips on different tracks) with the both side edge portions of the resin film held by the nips.

Fig. 1 is a schematic plan view illustrating an overall configuration of an example of a stretching apparatus usable in the production method of the present invention. A stretching apparatus usable in the production method of the present invention will be described with reference to fig. 1. The stretching device 100 includes the endless track 10L and the endless track 10R in bilateral symmetry on both left and right sides in a plan view. In the present specification, the left circular orbit is referred to as a left circular orbit 10L and the right circular orbit is referred to as a right circular orbit 10R, respectively, when viewed from the entrance side of the resin film. A plurality of clamps 20 for resin film gripping are disposed on the left and right

endless tracks

10L and 10R, respectively. The jig 20 is guided by the rails to circularly move. The gripper 20 on the left endless track 10L is cyclically moved in the counterclockwise direction, and the gripper 20 on the right endless track 10R is cyclically moved in the clockwise direction. In the stretching device, a grip region a, a TD slack region B, an MD stretching region C, and a release region D are provided in this order from the carry-in side to the carry-out side of the resin film. These regions mean regions where the resin film is substantially gripped, TD relaxed (or TD relaxed and MD stretched), MD stretched and released, and do not mean mechanically and structurally independent regions. Note that the ratio of the lengths of the respective regions in the stretching apparatus of fig. 1 is different from the actual ratio of the lengths.

In the grip region a, the left and right

endless rails

10R and 10L are regarded as linear portions having a constant inter-rail distance. Representatively, the left and right

endless tracks

10R, 10L are constructed in the following manner: the resin films to be processed are substantially parallel to each other at an inter-track distance corresponding to the initial width of the resin film. In the TD slack region B, the left and right

circular tracks

10R, 10L are regarded as tapered portions in which the inter-track distance continuously decreases. Representatively, the left and right

endless tracks

10R, 10L are regarded as being constituted as follows: as the sheet advances from the grip region a to the MD stretching region C, the inter-track distance gradually decreases to a width corresponding to the relaxed width of the resin film. In the MD stretching region C and the releasing region D, the left and right

endless tracks

10R and 10L are typically configured as follows, as linear portions having a constant inter-track distance: the resin films are substantially parallel to each other at a track pitch distance corresponding to the relaxed width of the resin films.

The gripper (left gripper) 20 on the left endless track 10L and the gripper (right gripper) 20 on the right endless track 10R can be independently moved around. For example, the driving

sprockets

30a and 30b of the left endless track 10L are rotationally driven counterclockwise by the

electric motors

40a and 40b, and the driving

sprockets

30a and 30b of the right endless track 10R are rotationally driven clockwise by the

electric motors

40a and 40 b. As a result, a traveling force is applied to a jig carrier member (not shown) of a drive roller (not shown) engaged with the

drive sprockets

30a and 30 b. Thereby, the left gripper 20 is moved in a counterclockwise direction, and the right gripper 20 is moved in a clockwise direction. The left side electric motor and the right side electric motor are driven independently, whereby the left side jig 20 and the right side jig 20 can be independently moved.

The size of the jig is preferably 12mm to 40mm, more preferably 15mm to 35mm. If the jig size is less than 12mm, the tensile force cannot be maintained and the jig may be broken, or the strength of the jig conveying section may be insufficient, which may cause driving failure. If the jig size exceeds 40mm, the unstretched region existing in the vicinity of the jig becomes large, and unevenness occurs at the end portion, or the non-grip portion is partially stretched, and thus, a crack may occur on the surface of the resin film. The jig size means the width of the grip region.

Further, the left jig 20 and the right jig 20 are of a variable pitch type. That is, the left and

right jigs

20, 20 are independent of each other, and the jig interval (jig pitch) in the conveying direction can be changed as they move. The variable-pitch jig can be realized by any appropriate configuration such as a pantograph mechanism (for example, the configuration described in japanese patent laid-open No. 2008-23775).

In the case of using the stretching apparatus as illustrated in fig. 1, the manufacturing method of the present invention may include the steps of: gripping both side edges of the resin film at a gripper interval L1 in the conveyance direction by grippers in a gripping area A (gripping step); the resin film is relaxed in the width direction by passing the resin film through the tapered portion and decreasing the distance between the jigs in the width direction from W1 to W2 (relaxation step); the resin film is stretched in the longitudinal direction by extending the distance between the jigs in the conveying direction to L2 while passing through the linear portion (MD stretching step). The method may further comprise the following steps as required: the jig holding the resin film is released (releasing step). Fig. 2 and 3 are schematic diagrams illustrating an example of the production method of the present invention including these steps. Hereinafter, each step will be described in more detail with reference to these drawings.

First, in the holding step (holding area a), both side edge portions of the resin film 50 loaded into the stretching apparatus are held at a constant holding interval (jig interval) L1 by the left and right jigs 20, and the resin film 50 is conveyed to the TD slack area B by the movement of each jig 20 guided by the left and right endless tracks. The grip intervals (jig intervals) of both side edge portions in the grip region a are representatively regarded as mutually equal intervals. L1 may be, for example, 30mm to 200mm. The jig interval is a distance between centers of adjacent jigs.

As the resin film held by the jig, any appropriate film can be selected depending on the application of the optical film to be produced. In the case where the optical film to be produced is a polarizing film, as an example, a laminate having a thermoplastic resin substrate and a PVA-based resin layer formed on one side of the thermoplastic resin substrate is held as a resin film. Hereinafter, the laminate will be described with respect to its specific features, conditions, and the like, and thereafter, the steps after the relaxation step will be described. The same operation, conditions, and the like can be applied to the steps after the relaxation step, regardless of the laminate or the normal resin film (single film).

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

Examples of the material for forming the thermoplastic resin substrate include: ester-based resins such as polyethylene terephthalate-based resins, olefin-based resins such as cycloolefin-based resins and polypropylenes, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. Of these, preferred are cycloolefin resins (for example, norbornene resins) and amorphous polyethylene terephthalate resins. Specific examples of the amorphous polyethylene terephthalate resin include: further, a copolymer containing isophthalic acid as a dicarboxylic acid, or a copolymer containing cyclohexanedimethanol as a diol.

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

The thermoplastic resin substrate may be subjected to a surface modification treatment (e.g., corona treatment) in advance, or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing the above treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved. Further, the surface modification treatment and/or the formation of the easy adhesion layer may be performed before the stretching or may be performed after the stretching.

Any appropriate method can be used for forming the PVA-based resin layer. Preferably, the PVA-based resin layer is formed by applying a coating solution containing a PVA-based resin to the thermoplastic resin substrate subjected to the stretching treatment and drying the coating solution.

As the PVA-based resin, any suitable resin can be used. Examples thereof include: polyvinyl alcohol, ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be determined in accordance with JIS K6726-1994. By using the PVA-based resin having the above saponification degree, a polarizing film having excellent durability can be obtained. When the saponification degree is too high, the coating liquid may be easily gelled, and it may be difficult to form a uniform coating film.

The average polymerization degree of the PVA-based resin may be appropriately selected depending on the purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be determined in accordance with JIS K6726-1994.

Typically, the coating liquid is a solution obtained by dissolving the PVA-based 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 preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. When the resin concentration is the above range, a uniform coating film can be formed in close contact with the thermoplastic resin substrate.

Additives may also be added to the coating liquid. Examples of additives include: plasticizers, surfactants, and the like. Examples of the plasticizer include: polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include: a non-ionic surfactant. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the PVA-based resin layer obtained.

As a method of applying the coating liquid, any appropriate method can be adopted. Examples thereof include: roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, blade coating (comma type blade coating, etc.), and the like.

The drying temperature is preferably not higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, and more preferably not higher than Tg-20 ℃. By drying at the above temperature, the thermoplastic resin substrate is prevented from being deformed before the PVA-based resin layer is formed, and the obtained PVA-based resin layer can be prevented from being deteriorated in orientation. In this way, the thermoplastic resin substrate can be deformed favorably together with the PVA-based resin layer, and the relaxation and stretching of the laminate described below can be favorably performed. As a result, a good orientation property can be imparted to the PVA-based resin layer, and a polarizing film having excellent optical characteristics can be obtained. Here, "orientation" means orientation of a molecular chain of the PVA-based resin layer.

Then, in the relaxation step (TD relaxation region B), the resin film 50 held by the left and right jigs 20 is relaxed in the width direction while being conveyed in the longitudinal direction. In the TD relaxation region B, the left and right

circular tracks

10R and 10L are regarded as tapered portions in which the inter-track distance continuously decreases, and therefore, by decreasing the jig interval in the width direction from W1 to W2 through this region, the resin film 50 is relaxed in the width direction. The amount of slack can be controlled by adjusting the amount of change in the inter-track distance. Specifically, the smaller the ratio of the inter-track distance at the exit (MD stretching region C-side end) of the TD slack region B to the inter-track distance at the entrance (gripping region a-side end) of the TD slack region B, the larger the slack amount can be obtained. In the present specification, the phrase "relaxing the resin film in the width direction" means that the resin film is formed in a region where the resin film is relaxed in the width direction (in other words, is not subjected to tension), and in one embodiment, the resin film can be shrunk in the width direction.

In the embodiment illustrated in fig. 2, in the relaxation step, only the resin film 50 is relaxed in the width direction. In this case, the resin film 50 is passed through the TD slack region B while maintaining the jig interval (L1) in the conveyance direction. On the other hand, in the embodiment illustrated in fig. 3, in the relaxation step, relaxation of the resin film 50 in the width direction and stretching in the longitudinal direction are performed. In this case, while the resin film 50 is passed through the TD slack region B, the moving speed of the jig 20 in the conveying direction is gradually increased to expand the jig interval in the conveying direction from L1 to L1'. By performing MD stretching in multiple stages in the relaxation step and the stretching step, the final stretching magnification can be increased. Further, by simultaneously performing the slackening in the width direction and the stretching in the longitudinal direction, excessive slackening can be avoided, and therefore, an effect such as suppression of generation of wrinkles due to slackening can be obtained.

The reduction ratio B (B = W2/W1) of the grip interval in the width direction may be set to any appropriate value depending on the MD stretching ratio and 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. If the magnification is reduced in this manner, a relaxed region can be suitably formed in the width direction of the resin film. In addition, more excellent optical characteristics can be obtained in the production of the polarizing film. Further, the interval between the clamps in the width direction may correspond to the width of the resin film at the portion gripped by the left and right clamps.

In an embodiment in which the relaxation step includes MD stretching (embodiment illustrated in fig. 3), it is preferred that: the width-direction jig interval is reduced so as to have a larger shrinkage rate in the width direction than in the case where the free end is uniaxially stretched in the longitudinal direction. Specifically, it is preferable that the draw ratio a in the longitudinal direction (a = L1'/L1) and the reduction ratio B of the jig interval in the width direction satisfy

The relationship (2) of (c). In the case where the above-mentioned relationship is satisfied,the slack region can be suitably formed in the width direction of the resin film regardless of the stretching in the longitudinal direction. The stretch ratio a in the longitudinal direction may be preferably 1.0 to 5.5 times, and more preferably 1.1 to 4.0 times.

The temperature of the resin film in the relaxation step (relaxation temperature) may be set to any appropriate value depending on the material for forming the resin film and the like. The relaxation temperature of the laminate in the case of producing a polarizing film is typically not lower than the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably not lower than the glass transition temperature (Tg) +10 ℃, and more preferably not lower than Tg +15 ℃. On the other hand, the relaxation temperature of the laminate is preferably 170 ℃ or lower.

Then, in the stretching step (MD stretching region C), the resin film 50 held by the left and right jigs 20 is stretched in the longitudinal direction while being conveyed in the longitudinal direction. The stretching of the resin film 50 is performed by: the moving speed of the jig 20 in the conveying direction is gradually increased, and the jig interval in the conveying direction is increased to L2. By adjusting the nip interval (L1 or L1') in the conveyance direction at the entrance of the MD stretching region C and the nip interval (L2) in the conveyance direction at the exit of the MD stretching region C, the stretching ratio (L2/L1 in the case where the relaxing step does not include MD stretching, and L2/L1 in the case where the relaxing step includes MD stretching) can be controlled. Further, the shrinkage in the width direction may be performed simultaneously in the stretching step. When the shrinkage in the width direction is performed simultaneously in the stretching step, the MD stretched region C may be provided with a tapered portion in which the distance between the left and right

endless tracks

10R and 10L continuously decreases. 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 step (the product of the stretch ratio in the stretching step and the stretch ratio in the relaxing step, L2/L1) is preferably 2.0 times or more, and more preferably 2.0 times to 6.5 times the original length of the resin film.

The stretching temperature may be set to any appropriate value depending on the material for forming the resin film, etc. The stretching temperature in the case of producing a polarizing film is typically not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably not less than the glass transition temperature (Tg) +10 ℃ of the thermoplastic resin substrate, and more preferably not less than Tg +15 ℃. On the other hand, the stretching temperature is preferably 170 ℃ or lower. By stretching at the above temperature, rapid progress of crystallization of the PVA-based resin can be suppressed, and abnormalities caused by the crystallization (for example, inhibition of orientation of the PVA-based resin layer by stretching) can be suppressed.

Finally, in the release step (release region D), the jig 20 holding the resin film 50 is released. In the release step, representatively, both the inter-jig distance and the jig interval are considered to be constant. If necessary, the resin film 50 is cooled to a desired temperature (preferably, glass transition temperature (Tg) or less) and then the jig is released.

The method for producing an optical film of the present invention may include other steps than the above. Examples of other steps in the case of producing a polarizing film as an optical film include: insolubilization step, dyeing step, crosslinking step, stretching step different from the above stretching step, washing step, drying (adjustment of water content), and the like. The other steps may be performed at any suitable time.

The dyeing step is typically a step of dyeing the PVA-based resin layer with a dichroic substance. Preferably, the PVA-based resin layer adsorbs a dichroic substance. Examples of the adsorption method include: a method of immersing the PVA-based resin layer (laminate) in a dyeing liquid containing a dichroic substance; a method of coating a PVA-based resin layer with a dyeing liquid; and a method of spraying a dyeing solution onto the PVA-based resin layer. The method of immersing the laminate in the dyeing solution containing the dichroic substance is preferable. The reason for this is that: the dichroic substance can be adsorbed well. Both surfaces of the laminate may be immersed in the dyeing solution, or only one surface of the laminate may be immersed in the dyeing solution. Further, the stretching may be performed simultaneously in the dyeing step and/or the crosslinking step described below.

Examples of the dichroic substance include: iodine, organic dyes. These may be used alone or in combination of two or more. The dichroic substance is preferably iodine. In the case of using iodine as the dichroic material, the dyeing liquid is preferably an aqueous iodine solution. The amount of iodine to be added is preferably 0.1 to 1.0 part by weight based on 100 parts by weight of water. In order to improve the solubility of iodine in water, it is preferable to mix an iodide salt in an aqueous iodine solution. Examples of the iodide salt include: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like. Of these, potassium iodide and sodium iodide are preferable. The amount of the iodide salt is preferably 0.3 to 15 parts by weight based on 100 parts by weight of water.

The liquid temperature of the dyeing liquid during dyeing is preferably 20 to 40 ℃. When the PVA-based resin layer is immersed in the dyeing liquid, the immersion time is preferably 5 seconds to 300 seconds. Under the above conditions, the dichroic material can be sufficiently adsorbed on the PVA-based resin layer.

Typically, the insolubilization step and the crosslinking step are performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Typically, the cleaning step is performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. The drying temperature in the drying step is preferably 30 to 100 ℃.

B. Polarizing film

The polarizing film produced by the above production method is substantially a PVA-based resin film in which a dichroic material is adsorbed and oriented. The polarizing film preferably exhibits absorption dichroism at any one of wavelengths 380nm to 780 nm.

The polarizing film can be used by any suitable method. Specifically, the thermoplastic resin substrate may be used in an integrated state, or may be transferred from the thermoplastic resin substrate to another member (the thermoplastic resin substrate is peeled off).

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

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[ example 1]

< preparation of laminated body >

An amorphous PET substrate (100 μm thick) was prepared as a thermoplastic resin substrate, and an aqueous PVA solution was applied to the amorphous PET substrate and dried at a temperature of 50 to 60 ℃. Thus, a 14 μm thick PVA layer 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 length direction. Specifically, in the grip area a, the grip interval L1: the laminate was held at 40mm at both side edges and transported in the longitudinal direction, and the laminate was shrunk in the width direction by reducing the width-direction jig spacing from 800mm (W1) to 680mm (W2) at 100 ℃ in the TD slack region B (jig spacing L1' at the exit of the TD slack region B: 40 mm). Then, in the MD stretching region C, the laminate was stretched 3 times in the lengthwise direction at 120 ℃ in the air (L2: 120mm distance between the clamps at the exit of the MD stretching region C, W3:680mm distance between the clamps in the widthwise direction). Thereafter, in the release region D, the jig holding the laminate is released.

The TD relaxation has a stretching ratio a (a = L1'/L1) in the longitudinal direction of 1 and a reduction ratio B (B = W2/W1) of the clip interval in the width direction of 0.85, and satisfies

The relationship (c) in (c).

No clamping failure occurred during TD relaxation and MD stretching.

< dyeing treatment >

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

< crosslinking treatment >

The dyed laminate was immersed in an aqueous boric acid solution (boric acid concentration: 5 wt%, potassium iodide concentration: 5 wt%) at 60 ℃ for 60 seconds, and simultaneously stretched 1.6 times in the MD direction (total stretching ratio: 5 times).

< cleaning treatment >

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

In the above manner, 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 in the following manner.

< TD relaxation and MD stretching >

The obtained laminate was relaxed in the width direction using a stretching apparatus shown in fig. 1, and then stretched in the length direction. Specifically, in the grip region a, the grip interval L1: the laminate was held at 40mm at both side edges and conveyed in the longitudinal direction, and the laminate was shrunk in the width direction by reducing the width-direction jig spacing from 800mm (W1) to 680mm (W2) at 100 ℃ in the TD slack region B. Simultaneously in TD relaxation region B, the clip spacing is increased to L1':45mm and stretched in the longitudinal direction. Then, in the MD stretching region C, the laminate was stretched 3 times in the lengthwise direction at 120 ℃ (the nip interval L2 at the exit of the MD stretching region C: 120mm, and the nip interval W3 in the widthwise direction: 680 mm). Thereafter, in the release region D, the jig holding the laminate is released. That is, TD relaxation and MD stretching were performed in the same manner as in example 1 except that MD stretching was performed simultaneously in the TD relaxation region B.

The stretching magnification a (a = L1'/L1) in the longitudinal direction in TD relaxation is 1.125, and therefore

0.943, and a reduction ratio B of the jig interval in the width direction (B = W2/W1) of 0.85, and satisfies

The relationship (2) of (c).

No clamping failure occurred during TD relaxation and MD stretching.

[ example 3]

< TD relaxation and MD stretching >

The obtained laminate was relaxed in the width direction using a stretching apparatus shown in fig. 1, and then stretched in the length direction. Specifically, in the grip area a, the grip interval L1: the laminate was held at 40mm at both side edges and transported in the longitudinal direction, and the laminate was shrunk in the width direction by reducing the width-direction jig spacing from 800mm (W1) to 680mm (W2) at 100 ℃ in the TD slack region B. Simultaneously in TD relaxation region B, the clip spacing is increased to L1':45mm and stretched in the longitudinal direction. Subsequently, in the MD stretching region C, the laminate was stretched 3 times in the lengthwise direction at 120 ℃ in the air (the grip interval L2 at the exit of the MD stretching region C: 120 mm). At the same time, in the stretching region C, the laminate was shrunk in the width direction by decreasing the width-direction jig interval from 680mm (W2) to 560mm (W3). Thereafter, in the release region D, the jig holding the laminate is released. That is, TD relaxation and MD stretching were performed in the same manner as in example 1 except that MD stretching was performed simultaneously in the TD relaxation region B and shrinkage in the width direction was performed simultaneously in the MD stretching region C.

The relationship (2) of (c).

No clamping failure occurred during TD relaxation and MD stretching.

[ example 4]

< TD relaxation and MD stretching >

The obtained laminate was relaxed in the width direction using a stretching apparatus shown in fig. 1, and then stretched in the length direction. Specifically, in the grip area a, the grip interval L1: the laminate was held at 40mm at both side edges and conveyed in the longitudinal direction, and the laminate was shrunk in the width direction by reducing the width-direction jig spacing from 800mm (W1) to 680mm (W2) at 100 ℃ in the TD slack region B. Simultaneously in TD relaxation region B, the clip spacing is increased to L1':60mm in the longitudinal direction. Subsequently, in the MD stretching region C, the laminate was stretched 3 times in the lengthwise direction at 120 ℃ in the air (the grip interval L2 at the exit of the MD stretching region C: 120 mm). At the same time, in the stretching region C, the laminate was shrunk in the width direction by decreasing the distance between the jigs in the width direction from 680mm (W2) to 560mm (W3). Thereafter, in the release region D, the jig holding the laminate is released. That is, TD relaxation and MD stretching were performed in the same manner as in example 3, except that the MD stretching magnification in the TD relaxation region B was set to 1.5 times.

The stretching magnification a (a = L1'/L1) in the longitudinal direction in TD relaxation is 1.5, and therefore

0.816, and a reduction ratio B of the jig interval in the width direction (B = W2/W1) of 0.85, which is not satisfied

The relationship (c) in (c).

In TD relaxation and MD stretching, although some wrinkles appear in the laminate, no clamping failure occurred, and no practical problem occurred.

Comparative example 1

Polarizing films having a thickness of 3.5 μm were produced on resin substrates in the same manner as in example 1, except that MD stretching and TD shrinking were performed in the following manner.

< MD stretching and TD shrinking >

The obtained laminate was first stretched in the longitudinal direction and then shrunk in the width direction while being stretched in the longitudinal direction. Specifically, initially at a jig interval L1: the laminate was held at both side edge portions by 40mm and conveyed in the longitudinal direction, and then the jig spacing was increased to L1' while maintaining the jig spacing in the width direction at 800mm (W1) at 100 ℃:70mm and stretched in the longitudinal direction. Then, the laminate was shrunk in the width direction by decreasing the jig interval in the width direction from 800mm (W2 = W1) to 560mm (W3) at 120 ℃, and was stretched 3 times in the longitudinal direction (the jig interval L2:120mm at the exit of the stretched region). Thereafter, in the release region D, the jig holding the laminate is released.

In MD stretching and TD shrinkage, a clamping failure occurred.

[ evaluation ]

When examples 1 to 4 were compared with comparative example 1, it was found that the occurrence of a clamping failure can be suppressed by relaxing the resin film in the width direction before stretching in the longitudinal direction. When example 3 and example 4 were compared, it was found that by controlling the stretching magnification in the longitudinal direction and the reduction magnification of the clip interval in the width direction in TD relaxation to have a specific relationship, the occurrence of wrinkles and the like was further suppressed, and as a result, the occurrence of a pinching failure was further suppressed.

[ industrial applicability ]

The production method of the present invention can be preferably used for production of optical films such as polarizing films, optical compensation films and the like.

Description of the symbols

10. Track

20. Clamp apparatus

50. Laminate (resin film)

100. Stretching device

Claims

1. A method for manufacturing an optical film using a tenter stretching apparatus provided with a plurality of clips as gripping means,

the method for manufacturing the optical film comprises the following steps:

a holding step of holding both side edges of the long resin film by the jig so that a jig interval in the conveying direction is set to L1;

a relaxation step of relaxing the resin film in the width direction by reducing the width-direction jig interval from W1 to W2 while conveying the resin film in the length direction, thereby forming a relaxed region in which the resin film is relaxed in the width direction; and

a stretching step of stretching the resin film in the longitudinal direction by expanding the interval between the jigs in the conveying direction to L2 while conveying the resin film relaxed in the width direction in the longitudinal direction,

a total draw ratio A in the longitudinal direction of 2.0 or more, wherein A = L2/L1,

the relaxation step includes: a step of reducing the width-direction jig interval and expanding the conveyance-direction jig interval to L1' to stretch the resin film in the longitudinal direction,

the reduction ratio B between the stretching ratio a in the longitudinal direction and the clamp interval in the width direction satisfies

Wherein a = L1'/L1, B = W2/W1.

2. The method of claim 1, wherein,

the stretching ratio a in the longitudinal direction in the relaxation step is 1.1 to 1.5 times, where a = L1'/L1.

3. The method of claim 1, wherein,

the reduction ratio B of the jig interval in the width direction is 0.60 to 0.99, wherein B = W2/W1.

4. The method of claim 1, wherein,

the thickness of the optical film produced was 110 μm or less.

5. The method of claim 1, wherein,

the resin film is a laminate comprising a thermoplastic resin substrate and a polyvinyl alcohol resin layer formed on one side of the thermoplastic resin substrate.

6. The method of claim 5, wherein,

the optical film produced was a polarizing film.