KR20210135352A - Optical film manufacturing method - Google Patents

Abstract

The present invention relates to a method for manufacturing an optical film using a tenter stretching apparatus having a plurality of clips as gripping means. The method is to hold the both edges of the long resin film at the clip interval L1 in the conveying direction with the clip (holding step), and while conveying the resin film in the longitudinal direction, the clip interval in the width direction from W1 to W2 reducing and loosening the resin film in the width direction (relaxation step), while conveying the resin film relaxed in the width direction in the longitudinal direction, the clip interval in the conveying direction is enlarged to L2, and the resin film is moved in the longitudinal direction stretching (stretching step) is included.

Description

The manufacturing method of an optical film {OPTICAL FILM MANUFACTURING METHOD}

This invention relates to the manufacturing method of an optical film.

DESCRIPTION OF RELATED ART Conventionally, the technique of extending|stretching the film and manufacturing an optical film by holding and conveying a long film with a tenter clip, and widening the space|interval of the conveyance direction of the tenter clip is known (for example, the claim of patent document 1) 7). In such a stretching technique, wrinkles or folds may occur at the side edge of the film in the initial stage of stretching, and as a result, the side edge of the film does not reach the clip during clip chucking and cannot be gripped. A problem (hereinafter, referred to as "clip miss") may occur and lead to a decrease in productivity.

Japanese Patent Laid-Open No. 2008-26881

The present invention has been made in order to solve the above problems, and its main object is a method for manufacturing an optical film comprising stretching a long resin film in a conveying direction using a tenter stretching apparatus, It is to provide a method which can suppress a clip miss.

The present invention provides a method for producing an optical film using a tenter stretching apparatus having a plurality of clips as gripping means. The method is to hold the both edges of the long resin film at the clip interval L1 in the conveying direction with the clip (holding step), and while conveying the resin film in the longitudinal direction, the clip interval in the width direction from W1 to W2 reducing, to relax the resin film in the width direction (relaxation step), and while conveying the resin film relaxed in the width direction in the longitudinal direction, the clip interval in the conveying direction is enlarged to L2, and the resin film is moved in the longitudinal direction stretching (stretching step).

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

In one embodiment, the reduction magnification B (B=W2/W1) of the clip space|interval of the width direction is 0.60-0.99.

In one embodiment, the said relaxation process includes extending|stretching the said resin film in the longitudinal direction by extending the clip spacing in a conveyance direction to L1' while reducing the clip spacing in the width direction, The draw ratio a (a = L1'/L1) and the reduction ratio B (B = W2/W1) of the clip spacing in the width direction satisfy the relationship of B < 1/√a.

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

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

In the manufacturing method of this invention, a resin film is relaxed in the width direction prior to extending|stretching to a longitudinal direction. Thereby, in the area|region before extending|stretching in the longitudinal direction, the relaxed area|region in which the resin film relaxed in the width direction is formed, and it can suppress that the wrinkles and folds which generate|occur|produced in the stretched area|region in the longitudinal direction reach the tenter entrance. As a result, the occurrence of clip miss can be suppressed, and it can become possible to manufacture an optical film without lowering productivity.

BRIEF DESCRIPTION OF THE DRAWINGS 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.
2 is a schematic diagram illustrating one embodiment of the present invention.
3 is a schematic diagram illustrating another embodiment of the present invention.

A. Manufacturing method of optical film

In the manufacturing method of the optical film of this invention, the tenter extending|stretching apparatus provided with a some clip is used as holding means of a film. In the manufacturing method of the present invention, the both edges of the long resin film are held by the clip at the clip interval L1 in the conveying direction (holding step), and the clip interval in the width direction is W1 while conveying the resin film in the longitudinal direction. to W2 to relax the resin film in the width direction (relaxation step), and while conveying the resin film relaxed in the width direction in the longitudinal direction to extend the clip interval in the conveying direction to L2, the resin film stretching in the longitudinal direction (stretching step). In a tenter stretching apparatus for holding a film with a clip, in the process from holding the end of the resin film with a clip in a state in which tension is not applied before stretching, until tension is applied to the resin film by heating or stretching. In this case, it is considered that stress is applied to the resin film depending on the in-plane variation of heating and the accuracy of each clip conveyance, and as a result, large wrinkles or folds occur in the resin film in the initial region of stretching, leading to clip misses. On the other hand, in this invention, a resin film is relaxed in the width direction prior to extending|stretching to a longitudinal direction. Thereby, in the region before stretching in the longitudinal direction, a relaxed region in which the resin film is relaxed in the width direction is formed, and excessive tension in the resin film can be avoided in the tenter inlet region for holding the resin film. Generation|occurrence|production of a clip miss can be suppressed.

The resin film used in the manufacturing method of this invention may be a laminated body which has a thermoplastic resin base material and the resin layer formed on one side of this thermoplastic resin base material, and the single-layer body which consists of a single film may be sufficient as it. The optical film to be manufactured may be any suitable optical film as long as it can be manufactured by the manufacturing method including the holding process, the relaxation process, and the stretching process. The thickness of the optical film is preferably 110 µm or less, preferably 80 µm or less, more preferably 70 µm or less, still more preferably 60 µm or less. On the other hand, the thickness of an optical film becomes like this. Preferably it is 10 micrometers or more, More preferably, it is 20 micrometers or more.

As a specific example of the optical film to be manufactured, a polarizing film, an optical compensation film, etc. can be illustrated preferably.

As the tenter stretching apparatus used in the manufacturing method of the present invention, for example, a pair of rails having a tapered portion in which the distance between rails continuously decreases and a straight portion having a constant distance between the rails, and a clip interval on each rail A stretching device having a plurality of clips capable of traveling while changing may be used. According to such a stretching apparatus, by changing the clip spacing in the conveying direction (distance between clips on the same rail) and the clip spacing in the width direction (distance between clips on different rails) in a state where both edges of the resin film are gripped with clips, , stretching in the longitudinal direction (MD stretching) and relaxation in the width direction (TD relaxation) of the resin film are made possible.

BRIEF DESCRIPTION OF THE DRAWINGS 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. A stretching apparatus that can be used in the manufacturing method of the present invention will be described with reference to FIG. 1 . The stretching apparatus 100 has the endless rails 10L and the endless rails 10R on both left and right sides symmetrically in planar view. In addition, in this specification, when it sees from the entrance side of a resin film, the left endless rail is called left endless rail 10L, and the right endless rail is called right endless rail 10R. On the left and right endless rails 10L, 10R, a large number of clips 20 for holding the resin film are respectively arranged. The clip 20 is guided to each rail and circulates on a loop. The clip 20 on the left endless rail 10L cyclically moves in the counterclockwise direction, and the clip 20 on the right endless rail 10R cyclically moves in the clockwise direction. In the stretching apparatus, the holding zone (A), the TD relaxation zone (B), the MD stretching zone (C), and the release zone (D) are formed in this order from the carrying-in side of the resin film toward the carrying-out side. In addition, each of these zones means a zone in which the resin film is substantially gripped, TD relaxed (or TD relaxed and MD stretched), MD stretched, and released, and does not mean mechanically and structurally independent compartments. Moreover, it should be noted that the ratio of the length of each zone in the stretching apparatus of Fig. 1 differs from the ratio of the actual length.

In the gripping zone A, the left and right endless rails 10R, 10L are linear portions with a constant distance between the rails. Typically, the left and right endless rails 10R, 10L are comprised so that they may mutually become substantially parallel with the distance between rails corresponding to the initial stage width of the resin film used as a process object. In the TD relaxation zone B, the right and left endless rails 10R and 10L are tapered portions in which the distance between the rails continuously decreases. Typically, the left and right endless rails 10R, 10L gradually decrease from the gripping zone (A) side toward the MD stretching zone (C) side until the distance between the rails corresponds to the width after relaxation of the resin film. is composed of In the MD stretching zone (C) and the release zone (D), the left and right endless rails 10R, 10L are straight-line portions with a constant distance between the rails, and typically, a rail corresponding to the width after relaxation of the resin film. It is configured so as to be approximately parallel to each other by a daily 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 circulate. For example, the sprocket 30a, 30b for a drive of the left endless rail 10L is rotationally driven in the counterclockwise direction by the electric motors 40a, 40b, and the sprocket for a drive of the right endless rail 10R. 30a, 30b is rotationally driven in a clockwise direction by electric motor 40a, 40b. As a result, the running force is provided to the clip bearing member (not shown) of the drive roller (not shown) engaged with these drive sprockets 30a, 30b. Thereby, the clip 20 on the left cyclically moves in a counterclockwise direction, and the clip 20 on the right cyclically moves in a clockwise direction. By driving the left electric motor and the right electric motor independently, respectively, the clip 20 of the left and the clip 20 of the right can be circulated independently, respectively.

Clip size becomes like this. Preferably they are 12 mm - 40 mm, More preferably, they are 15 mm - 35 mm. When the clip size is less than 12 mm, the stretching tension cannot be maintained, so that it may break, or a driving problem may occur due to insufficient strength of the clip conveyance portion. When a clip size exceeds 40 mm, the area|region which is not extended|stretched in the clip vicinity may become large, the nonuniformity of an edge part may generate|occur|produce, or a crack may generate|occur|produce on the surface of a resin film by a non-holding part extending|stretching locally. In addition, the clip size means the width|variety of a gripping area|region.

In addition, the clip 20 on the left and the clip 20 on the right are each variable pitch type. That is, the clips 20 and 20 on the left and right can each independently change the clip spacing (clip pitch) in the conveyance direction with movement. The variable-pitch type clip can be realized by any suitable structure, such as a pantograph mechanism (for example, the structure described in Unexamined-Japanese-Patent No. 2008-23775).

When the stretching apparatus as illustrated in Fig. 1 is used, the manufacturing method of the present invention is to hold the both edges of the resin film in the holding zone (A) with a clip at a clip interval L1 in the conveying direction (holding step) ), passing the resin film through the tapered portion to reduce the clip spacing in the width direction from W1 to W2, thereby relaxing the resin film in the width direction (relaxation step), passing the resin film through the straight portion and reducing the clip spacing in the conveying direction extending to L2 and stretching the resin film in the longitudinal direction (MD stretching step). If necessary, releasing the clip holding the resin film (release step) may be further included. 2 and 3 are schematic views each illustrating an example of the manufacturing 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 step (holding zone (A)), both sides of the resin film 50 introduced into the stretching apparatus are gripped by the left and right clips 20 at a constant gripping interval (clip interval) L1, and left and right The said resin film 50 is conveyed to the TD relaxation zone B by movement of each clip 20 guided to the endless rail of . The gripping intervals (clip intervals) of both edge portions in the gripping zone A are typically equal to each other. L1 may be, for example, 30 mm to 200 mm. In addition, a clip interval is the distance between the centers of adjacent clips.

As the resin film held by the clip, any suitable film may be selected according to the use of the optical film to be manufactured, and the like. When the optical film to be manufactured is a polarizing film, as an example, the laminated body which has a thermoplastic resin base material and the PVA-type resin layer formed on one side of this thermoplastic resin base material is hold|gripped as a resin film. Hereinafter, the characteristic characteristics, conditions, etc. are demonstrated about the said laminated body, and the process after a relaxation process is demonstrated after that. For the process after the relaxation process, the same operation, conditions, etc. can be applied irrespective of whether it is a laminate or a conventional resin film (single film).

The said laminated body is manufactured by forming a PVA-type resin layer on a long thermoplastic resin base material. A thermoplastic resin base material becomes arbitrary suitable structures, as long as it can support a PVA system resin layer (polarizing film obtained) from one side.

Examples of the material for forming the thermoplastic resin substrate include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins, and olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and the like. A synthetic resin etc. are mentioned. Among these, cycloolefin-type resin (for example, norbornene-type resin) and amorphous polyethylene-terephthalate-type resin are preferable. Specific examples of the amorphous polyethylene terephthalate-based resin include a copolymer further containing isophthalic acid as dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol as glycol.

The stretching temperature of the thermoplastic resin substrate can 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 equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, preferably Tg+10°C or higher, and more preferably Tg+15°C to Tg+30°C. When 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 forming material of the thermoplastic resin substrate, the stretching temperature is the glass transition temperature of the thermoplastic resin substrate (for example, 60 ° C.) ∼100°C)).

The thermoplastic resin substrate may be previously subjected to a surface modification treatment (eg, corona treatment or the like), or an easily bonding layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA-type resin layer can be improved. In addition, a surface modification process and/or formation of an easily bonding layer may be performed before the said extending|stretching, and may be performed after the said extending|stretching.

Any suitable method can be employ|adopted for the formation method of the said PVA system resin layer. Preferably, the PVA-type resin layer is formed by apply|coating and drying the coating liquid containing PVA-type resin on the thermoplastic resin base material to which the extending|stretching process was given.

Any suitable resin can be used as said PVA-type resin. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of PVA-type resin is 85 mol% - 100 mol% normally, Preferably they are 95.0 mol% - 99.95 mol%, More preferably, they are 99.0 mol% - 99.93 mol%. Saponification degree can be calculated|required according to JISK6726-1994. By using PVA-type resin of such a saponification degree, the polarizing film excellent in durability can be obtained. When the degree of saponification is too high, the coating liquid tends to gel, and there is a fear that it becomes difficult to form a uniform coating film.

The average degree of polymerization of PVA-type resin can be suitably selected according to the objective. The average degree of polymerization is usually from 1000 to 10000, preferably from 1200 to 4500, more preferably from 1500 to 4300. In addition, an average degree of polymerization can be calculated|required according to JISK6726-1994.

The said coating liquid is typically the solution which melt|dissolved the said PVA-type resin in the solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, ethylenediamine, diethylenetriamine, and the like. and amines. These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. If it is such a resin concentration, the uniform coating film closely_contact|adhered to a thermoplastic resin base material can be formed.

You may mix|blend an additive with a coating liquid. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. As a plasticizer, polyhydric alcohols, such as ethylene glycol and glycerol, are mentioned, for example. As surfactant, a nonionic surfactant is mentioned, for example. These can be used in order to further improve the uniformity, dyeability, and stretchability of the PVA-type resin layer obtained.

Any suitable method can be employ|adopted as a coating method of a coating liquid. For example, the roll coat method, the spin coat method, the wire bar coat method, the dip coat method, the die coat method, the curtain coat method, the spray coat method, the knife coat method (comma coat method, etc.) etc. are mentioned.

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 Tg-20 degreeC or less. By drying at such a temperature, it can prevent that a thermoplastic resin base material deform|transforms before forming a PVA-type resin layer, and it can prevent that the orientation of the PVA-type resin layer obtained deteriorates. In this way, the thermoplastic resin substrate can be favorably deformed together with the PVA-based resin layer, so that relaxation and elongation of the laminate, which will be described later, can be satisfactorily performed. As a result, favorable orientation can be provided to a PVA-type resin layer, and the polarizing film which has the outstanding optical characteristic can be obtained. Here, "orientation" means the orientation of the molecular chain of a PVA-type resin layer.

Next, in a relaxation process (TD relaxation zone (B)), it is made to relax in the width direction, conveying the resin film 50 hold|gripped by the clip 20 on either side in a longitudinal direction. In the TD relaxation zone (B), since the left and right endless rails 10R, 10L are tapered portions in which the distance between the rails continuously decreases, the clip spacing in the width direction decreases from W1 to W2 by passing the zone, Thereby, relaxation to the width direction of the resin film 50 is performed. The amount of relaxation can be controlled by adjusting the amount of change in the distance between rails. Specifically, at the outlet of the TD relaxation zone B (end on the MD stretching zone C side) relative to the distance between the rails at the inlet of the TD relaxation zone B (end on the grip zone A side) As the ratio of the distance between the rails is made small, a large amount of relaxation is obtained. In addition, in this 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) in the resin film, and in one embodiment In this case, the resin film may be contracted in the width direction.

In embodiment illustrated in FIG. 2, in a relaxation process, only the relaxation|loosening to the width direction of the resin film 50 is implemented. In this case, the resin film 50 is made to pass through the TD relaxation zone B, maintaining the clip space|interval L1 of a conveyance direction. On the other hand, in embodiment illustrated in FIG. 3, in a relaxation process, the relaxation to the width direction of the resin film 50 and extending|stretching to a longitudinal direction are implemented. In this case, while the resin film 50 is passed through the TD relaxation zone B, the moving speed of the clip 20 in the conveying direction is gradually increased, and the clip interval in the conveying direction is enlarged from L1 to L1'. The final draw ratio can be made high by performing MD extending|stretching in multiple steps in a relaxation process and an extending|stretching process. In addition, since excessive relaxation can be avoided by simultaneously performing the stretching in the width direction and the stretching in the longitudinal direction, the effect that generation of wrinkles and the like resulting from the relaxation can be suppressed can be obtained.

The reduction ratio B (B=W2/W1) of the clip spacing in the width direction can be set to any appropriate value according to the MD draw ratio or the like. The reduction ratio B is preferably 0.60 to 0.99, more preferably 0.65 to 0.90, still more preferably 0.70 to 0.80. With such a reduction magnification, a relaxed region can be preferably formed in the width direction of the resin film. Moreover, in manufacture of a polarizing film, the more excellent optical characteristic can be acquired. In addition, the clip space|interval of the width direction can respond|correspond to the width|variety of the resin film of the part hold|gripped by the clip on either side.

In the embodiment in which the relaxation step includes MD stretching (the embodiment illustrated in FIG. 3 ), the clip in the width direction has a larger shrinkage rate than the shrinkage rate in the width direction when uniaxially stretched in the longitudinal direction at the free end. It is desirable to reduce the spacing. Specifically, it is preferable that the draw ratio a in the longitudinal direction (a=L1'/L1) and the reduction ratio B of the clip spacing in the width direction satisfy the relationship of B<1/√a. When such a relationship is satisfied, the relaxed region can be preferably formed in the width direction of the resin film regardless of the stretching in the longitudinal direction. The draw ratio a in the longitudinal direction may be preferably 1.0 times to 5.5 times, more preferably 1.1 times to 4.0 times.

The temperature (relaxation temperature) of the resin film in a relaxation process can be set to arbitrary appropriate values according to the forming material of a resin film, etc. The relaxation temperature of the laminate in the case of manufacturing a polarizing film is typically the glass transition temperature (Tg) or more of the thermoplastic resin substrate, preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or more, further Preferably it is Tg+15 degreeC or more. On the other hand, the relaxation temperature of the laminate is preferably 170°C or less.

Next, in an extending process (MD extending zone (C)), it extends|stretches in a longitudinal direction, conveying the resin film 50 hold|gripped by the clip 20 on either side to a longitudinal direction. Extending|stretching of the resin film 50 is performed by increasing the moving speed to the conveyance direction of the clip 20 gradually, and expanding the clip space|interval of a conveyance direction to L2. By adjusting the clip distance (L1 or L1') in the conveying direction at the entrance of the MD stretching zone (C) and the clip interval (L2) in the conveying direction at the exit of the MD stretching zone (C), the draw ratio (relaxation) L2/L1 when the process does not include MD stretching and L2/L1') can be controlled if it does. In addition, in an extending process, you may perform contraction|shrinkage to the width direction simultaneously. What is necessary is just to form the taper part in which the distance between rails of endless rails 10R, 10L on either side decreases continuously in MD extending zone C, when performing contraction|shrinkage to the width direction simultaneously in an extending process. By adjusting the decrease amount of the distance between the left and right rails, the shrinkage rate in the width direction can be controlled.

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

Extending|stretching temperature can be set to arbitrary appropriate values according to the forming material of a resin film, etc. In the case of manufacturing a polarizing film, the extending|stretching temperature is typically the glass transition temperature (Tg) or more of a thermoplastic resin base material, Preferably it is glass transition temperature (Tg) of a thermoplastic resin base material + 10 degreeC or more, More preferably, It is more than Tg+15 degreeC. On the other hand, the stretching temperature is preferably 170°C or less. By extending|stretching at such a temperature, it can suppress that crystallization of PVA-type resin advances rapidly, and the problem (for example, the orientation of the PVA-type resin layer by extending|stretching is hindered) by the said crystallization can be suppressed.

Finally, in the release step (release zone (D)), the clip 20 holding the resin film 50 is released. In a release process, typically, both the distance between clips and a clip space|interval become constant. If necessary, the clip is released after the resin film 50 is cooled to a desired temperature (preferably below the glass transition temperature (Tg)).

The manufacturing method of the optical film of this invention can include the process other than the above. Other processes in the case of manufacturing a polarizing film as an optical film include, for example, an insolubilization process, a dyeing process, a crosslinking process, a stretching process different from the above-mentioned stretching, a washing process, a drying (controlling moisture content) process, etc. can be heard Other steps can be performed at any appropriate timing.

The said dyeing process is a process of dyeing|staining a PVA-type resin layer with a dichroic substance typically. Preferably, it carries out by making a dichroic substance adsorb|suck to a PVA-type resin layer. As the said adsorption method, the method of immersing a PVA-type resin layer (laminated body) in the dyeing liquid containing a dichroic substance, the method of apply|coating the dyeing liquid to a PVA-type resin layer, dyeing to a PVA-type resin layer, for example. The method of spraying a liquid, etc. are mentioned. Preferably, it is a method of immersing a laminated body in the dyeing solution containing a dichroic substance. This is because dichroic substances can be adsorbed favorably. Both surfaces of the laminate may be immersed in the dyeing solution, or only one surface may be immersed. In addition, in the dyeing|staining process and/or the bridge|crosslinking process mentioned later, you may perform extending|stretching simultaneously.

Examples of the dichroic substance include iodine and organic dyes. These can be used individually or in combination of 2 or more types. The dichroic substance is preferably iodine. In the case of using iodine 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 with respect to 100 parts by weight of water. In order to improve the solubility of iodine in water, it is preferable to mix|blend an iodide salt with iodine aqueous 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. Among these, potassium iodide and sodium iodide are preferable. To [ the compounding quantity of an iodide salt / 100 weight part of water ], Preferably they are 0.3 weight part - 15 weight part.

The liquid temperature at the time of dyeing|staining of a dyeing liquid becomes like this. Preferably it is 20 degreeC - 40 degreeC. When immersing a PVA-type resin layer in a dyeing solution, immersion time becomes like this. Preferably they are 5 second - 300 second. Under such conditions, the dichroic substance can be sufficiently adsorbed to the PVA-based resin layer.

The said insolubilization process and a bridge|crosslinking process are typically implemented by immersing a PVA-type resin layer in boric-acid aqueous solution. The washing step is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. The drying temperature in the said drying process becomes like this. Preferably it is 30 degreeC - 100 degreeC.

B. Polarizing film

The polarizing film manufactured by the said manufacturing method is substantially the PVA-type resin film which carried out the adsorption|suction orientation of the dichroic substance. The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm.

Any suitable method may be employed as the method of using the polarizing film. Specifically, it may be used in a state integrated with the thermoplastic resin substrate, or may be used by transferring it from the thermoplastic resin substrate to another member (by peeling the thermoplastic resin substrate).

The polarizing film manufactured by the manufacturing method may have a small shrinkage stress and excellent dimensional stability even in a high-temperature environment. Moreover, the polarization degree in 42% of single transmittance becomes like this. Preferably it is 99.99 % or more. As such, optical properties may be excellent.

Example

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

[Example 1]

<Production of laminated body>

As a thermoplastic resin base material, an amorphous PET base material (100 micrometers thickness) was prepared, PVA aqueous solution was apply|coated to the said amorphous PET base material, and it dried at the temperature of 50 degreeC - 60 degreeC. Thus, a PVA layer having a thickness of 14 μm was formed on the amorphous PET substrate to prepare a laminate.

<TD relaxation and MD stretching>

The obtained laminate was relaxed in the width direction using a stretching device as shown in Fig. 1 , and then stretched in the longitudinal direction. Specifically, in the holding zone (A), the both edges of the laminate are gripped at a clip interval L1: 40 mm and conveyed in the longitudinal direction, and in the TD relaxation zone (B), the clip interval in the width direction at 100°C was reduced from 800 mm (W1) to 680 mm (W2) to shrink the laminate in the width direction (clip gap L1' at the exit of the TD relaxation zone B: 40 mm). Next, in the MD stretching zone (C), the laminate was stretched three times in the longitudinal direction at 120°C (clip spacing L2 at the exit of the MD stretching zone (C): 120 mm, clip spacing W3 in the width direction) : 680 mm). Then, in the release zone D, the clip which holds the laminated body was released.

In the TD relaxation, the stretching ratio in the longitudinal direction a (a = L1'/L1) is 1, and the decrease ratio B (B = W2/W1) of the clip spacing in the width direction is 0.85, and B < 1/√a relationship was satisfied.

In TD relaxation and MD stretching, chucking errors did not occur.

<Dyeing treatment>

Then, the laminated body was immersed for 30 second in 25 degreeC iodine aqueous solution (iodine density|concentration: 0.5 weight%, potassium iodide density|concentration: 10 weight%).

<Crosslinking treatment>

While immersing the laminated body after dyeing in 60 degreeC boric-acid aqueous solution (boric acid concentration: 5 weight%, potassium iodide concentration: 5 weight%) for 60 second, it extended|stretched 1.6 times in MD direction (total draw ratio: 5 times).

<Washing treatment>

After the crosslinking treatment, the layered product was immersed in a 25°C aqueous potassium iodide solution (potassium iodide concentration: 5 wt%) for 5 seconds.

In this way, a polarizing film having a thickness of 3.5 µm was prepared on the thermoplastic resin substrate.

[Example 2]

A polarizing film having a thickness of 3.5 µm was manufactured on a thermoplastic 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 device as shown in Fig. 1 , and then stretched in the longitudinal direction. Specifically, in the holding zone (A), the both edges of the laminate are gripped at a clip interval L1: 40 mm and conveyed in the longitudinal direction, and in the TD relaxation zone (B), the clip interval in the width direction at 100°C was reduced from 800 mm (W1) to 680 mm (W2) to shrink the laminate in the width direction. Simultaneously, in the TD relaxation zone (B), the clip space|interval was increased to L1':45 mm, and it extended|stretched in the longitudinal direction. Next, in the MD stretching zone (C), the laminate was stretched three times in the longitudinal direction at 120°C (clip spacing L2 at the exit of the MD stretching zone (C): 120 mm, clip spacing W3 in the width direction) : 680 mm). Then, in the release zone D, the clip which holds the laminated body 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).

The draw ratio a (a = L1'/L1) in the longitudinal direction in the TD relaxation is 1.125, so 1/√a is 0.943, and the reduction ratio B (B = W2/W1) of the clip spacing in the width direction is As 0.85, the relationship of B<1/√a was satisfied.

In TD relaxation and MD stretching, chucking errors did not occur.

[Example 3]

A polarizing film having a thickness of 3.5 µm was manufactured on a thermoplastic 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 device as shown in Fig. 1 , and then stretched in the longitudinal direction. Specifically, in the holding zone (A), the both edges of the laminate are gripped at a clip interval L1: 40 mm and conveyed in the longitudinal direction, and in the TD relaxation zone (B), the clip interval in the width direction at 100°C was reduced from 800 mm (W1) to 680 mm (W2) to shrink the laminate in the width direction. Simultaneously, in the TD relaxation zone (B), the clip space|interval was increased to L1':45 mm, and it extended|stretched in the longitudinal direction. Next, in the MD stretching zone (C), the laminate was stretched three times in the longitudinal direction at 120°C (clip spacing L2 at the exit of the MD stretching zone (C): 120 mm). Simultaneously, in the MD stretching zone (C), the clip spacing in the width direction was reduced from 680 mm (W2) to 560 mm (W3) to shrink the laminate in the width direction. Then, in the release zone D, the clip which holds the laminated body was released. That is, in the TD relaxation zone (B), MD stretching was performed simultaneously, and in the MD stretching zone (C), TD relaxation and MD stretching were carried out in the same manner as in Example 1, except that contraction in the width direction was simultaneously performed. did.

The draw ratio a (a = L1'/L1) in the longitudinal direction in the TD relaxation is 1.125, so 1/√a is 0.943, and the reduction ratio B (B = W2/W1) of the clip spacing in the width direction is As 0.85, the relationship of B<1/√a was satisfied.

In TD relaxation and MD stretching, chucking errors did not occur.

[Example 4]

A polarizing film having a thickness of 3.5 µm was manufactured on a thermoplastic 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 device as shown in Fig. 1 , and then stretched in the longitudinal direction. Specifically, in the holding zone (A), the both edges of the laminate are gripped at a clip interval L1: 40 mm and conveyed in the longitudinal direction, and in the TD relaxation zone (B), the clip interval in the width direction at 100°C was reduced from 800 mm (W1) to 680 mm (W2) to shrink the laminate in the width direction. Simultaneously, in the TD relaxation zone (B), the clip space|interval was increased to L1':60 mm, and it extended|stretched in the longitudinal direction. Next, in the MD stretching zone (C), the laminate was stretched three times in the longitudinal direction at 120°C (clip spacing L2 at the exit of the MD stretching zone (C): 120 mm). Simultaneously, in the MD stretching zone (C), the clip spacing in the width direction was reduced from 680 mm (W2) to 560 mm (W3) to shrink the laminate in the width direction. Then, in the release zone D, the clip which holds the laminated body 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 times.

The draw ratio a (a = L1'/L1) in the longitudinal direction in the TD relaxation is 1.5, so 1/√a is 0.816, and the reduction ratio B (B = W2/W1) of the clip spacing in the width direction is 0.85, which did not satisfy the relation of B<1/√a.

In TD relaxation and MD stretching, although some wrinkles were confirmed in the laminated body, chucking error did not occur and a practical problem did not arise.

[Comparative Example 1]

A polarizing film having a thickness of 3.5 µm was manufactured on a thermoplastic resin substrate in the same manner as in Example 1 except that MD stretching and TD contraction were performed as follows.

<MD elongation and TD shrinkage>

The obtained laminate was first stretched in the longitudinal direction and then shrunk in the width direction while stretching in the longitudinal direction. Specifically, at first, the clip spacing L1: 40 mm, gripping both edges of the laminate and conveying it in the longitudinal direction, and then, at 100° C., maintaining the clip spacing in the width direction at 800 mm (W1) while the clip spacing is L1. ': It extended to 70 mm and extended|stretched in the longitudinal direction. Then, at 120°C, the clip spacing in the width direction was reduced from 800 mm (W2 = W1) to 560 mm (W3), and the laminate was stretched in the air three times in the longitudinal direction while shrinking in the width direction (at the exit of the stretching zone) Clip spacing L2: 120 mm). Then, in the release zone (D), the clip which holds the laminated body was released.

In MD stretching and TD contraction, chucking errors occurred.

[evaluation]

When Examples 1-4 and Comparative Example 1 are compared, generation|occurrence|production of a chucking error can be suppressed by loosening a resin film in the width direction prior to extending|stretching to a longitudinal direction so that it will be clear when Examples 1-4 and Comparative Example 1 are compared. As is clear when Example 3 and Example 4 are compared, the occurrence of wrinkles and the like is further suppressed by controlling the draw ratio in the longitudinal direction in the TD relaxation and the reduction ratio of the clip gap in the width direction in a predetermined relationship. , As a result, it can be seen that the occurrence of chucking errors can be further suppressed.

Industrial Applicability

The manufacturing method of this invention is used suitably for manufacture of optical films, such as a polarizing film and an optical compensation film.

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

Claims (6)

A method for producing an optical film using a tenter stretching apparatus having a plurality of clips as gripping means, the method comprising:
Gripping both edges of the long resin film at the clip interval L1 in the conveying direction with the clips (holding step);
while conveying the resin film in the longitudinal direction, reducing the clip interval in the width direction from W1 to W2 to relax the resin film in the width direction (relaxation step);
The manufacturing method of an optical film comprising extending the clip interval in a conveyance direction to L2 while conveying the said resin film relaxed in the width direction in a longitudinal direction, and extending|stretching the said resin film in a longitudinal direction (stretching process). The method of claim 1,
The manufacturing method of the optical film whose total draw ratio A (A=L2/L1) in a longitudinal direction is 2.0 or more. The method of claim 1,
The reduction magnification B (B=W2/W1) of the clip space|interval of the width direction is 0.60-0.99, The manufacturing method of the optical film. The method of claim 1,
The relaxation step includes stretching the resin film in the longitudinal direction by reducing the clip interval in the width direction and increasing the clip interval in the conveying direction to L1',
The draw ratio a in the longitudinal direction (a = L1'/L1) and the reduction ratio B (B = W2/W1) of the clip spacing in the width direction satisfy the relationship of B < 1/√a, manufacturing method of an optical film . The method of claim 1,
The thickness of the optical film to be manufactured is 110 μm or less, the manufacturing method of the optical film. The method of claim 1,
The manufacturing method of the optical film whose optical film manufactured is a polarizing film.

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