JPWO2019188857A1 - Method for manufacturing long stretched film and long polarizing film - Google Patents

Abstract

The method for producing a long stretched film includes a first step of stretching a long pre-stretched film in a direction of 15 ° or more and 50 ° or less with respect to a width direction to obtain a long first stretched film. The second step of stretching the long first stretched film in the width direction to obtain a long second stretched film is included in this order, and the long second stretched film is relative to the width direction. It has a slow axis with an angle of 10 ° or more and 30 ° or less.

Description

The present invention relates to a method for producing a long stretched film and a long polarizing film.

An optical member such as a retardation film is used in the liquid crystal display device to improve the performance. When the retardation film is used for antireflection of mobile devices and organic EL televisions, and for optical compensation of liquid crystal display devices, its slow phase axis is neither parallel nor perpendicular to the transmission axis of the polarizer. It is required to be at an angle (diagonal direction).

In a long retardation film, if the slow axis is in an oblique direction, a long polarizing element whose transmission axis is perpendicular to or parallel to the flow direction is laminated by a roll-to-roll method to form a long film. A polarizing film can be produced. Therefore, a method of producing a long retardation film having a slow axis in an oblique direction has been proposed by a method including a step of stretching a long pre-stretched film in an oblique direction (Patent Documents 1 to 3). ..

Japanese Unexamined Patent Publication No. 2012-101466 International Publication No. 2015/072518 (Corresponding Gazette: US Patent Application Publication No. 2016/318233) Japanese Patent No. 5257505

If the stretching ratio of the pre-stretched film is increased in order to sufficiently develop the phase difference in the stretched film, the bonding force in the thickness direction of the obtained stretched film may be reduced. As a result, when the stretched film is attached to an element such as a polarizer and a peeling force is applied to the stretched film, the stretched film may be peeled off from the element.
Therefore, a method for producing a long stretched film having excellent peel strength while sufficiently expressing the phase difference; a long stretched film including a long stretched film having excellent peel strength while sufficiently expressing the phase difference. A method for producing a scale polarizing film; is required.

As a result of diligent studies to solve the above problems, the present inventors have excellent peel strength while sufficiently expressing a phase difference by a manufacturing method in which the pre-stretched film is stretched stepwise in a predetermined direction. We have found that a long stretched film can be obtained, and completed the present invention. That is, the present invention provides the following.

[1] A method for producing a long stretched film.
The first step of stretching a long unstretched film in a direction of 15 ° or more and 50 ° or less with respect to the width direction to obtain a long first stretched film.
The second step of stretching the long first stretched film in the width direction to obtain a long second stretched film is included in this order.
The long second stretched film has a slow axis having an angle of 10 ° or more and 30 ° or less with respect to the width direction.
A method for producing a long stretched film.
[2] The average NZ coefficient of the long second stretched film is 1.2 or more and 1.5 or less.
Assuming that the stretching ratio in the first step is A1 and the stretching ratio in the second step is A2, A1 is 1.2 times or more and 1.6 times or less, and (A1 × A2) is larger than 1.2 times. The method for producing a long stretched film according to [1], which is 2.0 times or less.
[3] The method for producing a long stretched film according to [1] or [2], wherein the average in-plane retardation Re2 of the long second stretched film is 200 nm or more and 300 nm or less.
[4] The method for producing a long stretched film according to any one of [1] to [3], wherein the stretched film contains a polymer containing an alicyclic structure.
[5] A method for manufacturing a long polarizing film.
A third step of laminating a long polarizer on a long stretched film obtained by the method for producing a long stretched film according to any one of [1] to [4] is included.
A method for manufacturing a long polarizing film.

According to the present invention, a method for producing a long stretched film having excellent peel strength while sufficiently expressing a phase difference; a long stretch having excellent peel strength while sufficiently expressing a phase difference. A method of producing a long polarizing film, including a film; is provided.

FIG. 1 is a plan view schematically showing a tenter device for carrying out the manufacturing method according to the embodiment of the present invention. FIG. 2 is a plan view schematically showing a transverse stretching device for carrying out the manufacturing method according to the embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be arbitrarily modified and implemented without departing from the scope of claims of the present invention and the equivalent scope thereof.

In the following description, the "long" film means a film having a length of at least 5 times or more with respect to the width, preferably having a length of 10 times or more, and specifically. A film that has a length that allows it to be rolled up and stored or transported. The upper limit of the ratio of the length to the width is not particularly limited, but may be, for example, 100,000 times or less.

In the following description, the in-plane retardation Re of the film is a value represented by (nx-ny) × d unless otherwise specified. Further, the thickness direction retardation Rth of the film is a value represented by {(nx + ny) /2-nz} × d unless otherwise specified. Further, the NZ coefficient is a value represented by (nx-nz) / (nx-ny) unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) and in the direction in which the maximum refractive index is given. ny represents the refractive index in the in-plane direction of the film and orthogonal to the nx direction. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. The measurement wavelength shall be 590 nm unless otherwise specified.

The NZ coefficient can be obtained from the in-plane retardation Re and the thickness direction retardation Rth of the film according to the following formula.
NZ coefficient = (Rth / Re) +0.5

In the following description, the directions of the elements "parallel", "vertical" and "orthogonal" include errors within a range that does not impair the effect of the present invention, for example, within a range of ± 5 °, unless otherwise specified. You may be.

In the following description, the longitudinal direction of the long film is usually parallel to the flow direction of the film in the production line. The oblique direction is an in-plane direction of the film, not a width direction or a longitudinal direction.

[1. Method for manufacturing long stretched film]
In the method for producing a long stretched film according to an embodiment of the present invention, the long unstretched film is stretched in a direction of 15 ° or more and 50 ° or less with respect to the width direction, and the long first stretching is performed. The first step of obtaining a film and the second step of stretching the long first stretched film in the width direction to obtain a long second stretched film are included in this order.

(Film before stretching)
Usually, a resin film is used as the pre-stretched film. As the material of the resin film, a thermoplastic resin is usually used.

Examples of thermoplastic resins include polyolefin resins such as polyethylene resins and polypropylene resins; polymer resins having an alicyclic structure such as norbornene resins; cellulose resins such as triacetyl cellulose resins; polyimide resins and polyamide imide resins. Polyamide resin, polyetherimide resin, polyether ether ketone resin, polyether ketone resin, polyketone sulfide resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin, polyphenylene oxide resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene na Phtalate resin, polyacetal resin, polycarbonate resin, polyarylate resin, (meth) acrylic resin, polyvinyl alcohol resin, (meth) acrylic acid ester-vinyl aromatic compound copolymer resin, isobutene / N-methylmaleimide copolymer resin, Examples thereof include styrene / acrylic nitrile copolymer resin.
The thermoplastic resin can usually contain a polymer and further any component. One type of polymer may be used alone, or two or more types may be used in combination at any ratio.

As the resin for forming the pre-stretched film, a resin containing a polymer containing an alicyclic structure is preferable. Hereinafter, the polymer containing an alicyclic structure may be appropriately referred to as an "alicyclic structure-containing polymer".

The alicyclic structure-containing polymer is a polymer containing an alicyclic structure in a repeating unit. Examples of the alicyclic structure-containing polymer include a polymer obtained by a polymerization reaction using a cyclic olefin as a monomer; and a hydride thereof. Further, as the alicyclic structure-containing polymer, either a polymer having an alicyclic structure in the main chain or a polymer having an alicyclic structure in the side chain can be used. Above all, the alicyclic structure-containing polymer preferably contains an alicyclic structure in the main chain. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and the cycloalkane structure is preferable from the viewpoint of thermal stability and the like.

The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, more preferably 6 or more, preferably 30 or less, more preferably 20 or less. Especially preferably, the number is 15 or less. When the number of carbon atoms contained in one alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

The proportion of the repeating unit having an alicyclic structure in the alicyclic structure-containing polymer is preferably 30% by weight or more, more preferably 50% by weight or more, still more preferably 70% by weight or more, and particularly preferably 90% by weight. It may be 100% by weight or less. Heat resistance can be improved by increasing the proportion of repeating units having an alicyclic structure as described above.
Further, in the alicyclic structure-containing polymer, the remainder other than the repeating unit having the alicyclic structure is not particularly limited and can be appropriately selected according to the purpose of use.

The alicyclic structure-containing polymer is, for example, (1) norbornene-based polymer, (2) monocyclic cyclic olefin polymer, (3) cyclic conjugated diene polymer, and (4) vinyl alicyclic hydrocarbon polymer. , And these hydrides and the like. Among these, norbornene-based polymers and hydrides thereof are more preferable from the viewpoint of transparency and moldability.

Examples of the norbornene-based polymer include a ring-opening polymer of a norbornene-based monomer, a ring-opening copolymer of a norbornene-based monomer and another monomer capable of ring-opening copolymerization, and hydrides thereof; Examples thereof include a copolymer and an addition copolymer of a norbornene-based monomer and another monomer copolymerizable. Among these, a ring-opening polymer hydride of a norbornene-based monomer is particularly preferable from the viewpoint of transparency.
The alicyclic structure-containing polymer is selected from, for example, the polymers disclosed in JP-A-2002-321302.

As the resin containing the alicyclic structure-containing polymer, various products are commercially available, and among them, those having desired characteristics can be appropriately selected and used. Examples of such commercially available products are the product names "ZEONOR" (manufactured by Zeon Corporation), "Arton" (manufactured by JSR Corporation), "Apel" (manufactured by Mitsui Chemicals, Inc.), and "TOPAS" (manufactured by Polyplastics Co., Ltd.). (Manufactured) product group can be mentioned.

By forming the pre-stretched film with a resin containing an alicyclic structure-containing polymer, a stretched film containing an alicyclic structure-containing polymer can be obtained.

The glass transition temperature Tg of the resin forming the pre-stretched film is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher, preferably 190 ° C. or lower, more preferably 180 ° C. or lower, particularly. It is preferably 170 ° C. or lower. By setting the glass transition temperature to the lower limit of the above range or more, the durability of the stretched film in a high temperature environment can be enhanced. Further, by setting the value to the upper limit or less, the stretching treatment can be easily performed.

The thickness of the pre-stretched film can be determined according to the draw ratio, the desired thickness of the stretched film, and the like, and is preferably 20 μm or more, more preferably 30 μm or more, preferably 120 μm or less, and more preferably 100 μm or less. ..

In the present embodiment, an unstretched film that has not been stretched is used as the pre-stretched film. However, as the pre-stretched film, a stretched film may be used.

The unstretched film can be obtained by a method such as a cast molding method, an extrusion molding method, or an inflation molding method. Of these, the extrusion molding method is preferable because it has a small amount of residual volatile components and is excellent in dimensional stability.

(First step)
In the method for producing a long stretched film of the present embodiment, the long pre-stretched film is stretched in a direction of 15 ° or more and 50 ° or less with respect to the width direction to obtain a long first stretched film. Perform one step.

In the first step, stretching is usually performed using a tenter device while continuously transporting the pre-stretched film in the longitudinal direction.

The tenter device includes, for example, a pair of guide rails and a plurality of grippers traveling along the pair of guide rails, and the pair of guide rails is a pre-stretched film conveyed by the plurality of grippers. An apparatus can be used that is formed so as to bend the traveling direction and is provided with an extension zone in which the distance between the pair of guide rails becomes wider toward the downstream.

FIG. 1 is a plan view schematically showing a tenter device 100 for carrying out the manufacturing method according to the embodiment of the present invention.
As shown in FIG. 1, the tenter device 100 stretches the unstretched film 20 unwound from the feeding roll 10 in a direction of 15 ° or more and 50 ° or less with respect to the width direction in a heating environment by an oven (not shown). It is a device of.

The tenter device 100 includes a plurality of grippers 110R and 110L, and a pair of guide rails 120R and 120L. The grippers 110R and 110L are provided so as to be able to grip the ends 21 and 22 of the pre-stretched film 20 in the width direction, respectively. Further, the guide rails 120R and 120L are provided on both sides of the film transport path to guide the grippers 110R and 110L.

The grippers 110R and 110L are provided so as to be able to travel along the guide rails 120R and 120L. Further, the grippers 110R and 110L are provided so as to be able to travel at a constant speed while maintaining a constant interval with the front and rear grippers 110R and 110L, respectively. Further, the grippers 110R and 110L grip the end portions 21 and 22 in the width direction of the pre-stretched film 20 sequentially supplied to the tenter device 100 at the inlet portion 130 of the tenter device 100, respectively, and the outlet portion of the tenter device 100. It has a configuration that can be opened at 140.

The guide rails 120R and 120L have asymmetrical shapes according to conditions such as the stretching direction and the stretching ratio of the first stretched film 30 to be manufactured. The tenter device 100 according to the present embodiment is provided with an extension zone 150 in which the distance between the guide rails 120R and 120L becomes wider toward the downstream. In the extension zone 150, the shapes of the guide rails 120R and 120L are set so that the moving distance of one gripper 110R is longer than the moving distance of the other gripper 110L. Therefore, the shapes of the guide rails 120R and 120L in the tenter device 100 are such that the grippers 110R and 110L guided by the guide rails 120R and 120L bend the traveling direction of the pre-stretching film 20 to the left before stretching. The shape is set so that the film 20 can be conveyed. Here, in the present embodiment, the traveling direction of the long film means the moving direction of the midpoint in the width direction of the film unless otherwise specified. Further, in the present embodiment, "right" and "left" indicate directions when the film transported horizontally is observed from upstream to downstream in the transport direction, unless otherwise specified.

Further, the guide rails 120R and 120L have an endless continuous track so that the grippers 110R and 110L can orbit a predetermined track. Therefore, the tenter device 100 has a configuration in which the grippers 110R and 110L, which have opened the pre-stretched film 20 at the outlet portion 140 of the tenter device 100, can be sequentially returned to the inlet portion 130.

Stretching of the pre-stretching film 20 using the tenter device 100 is performed as follows.
The pre-stretched film 20 is fed out from the feeding roll 10, and the pre-stretched film 20 is continuously supplied to the tenter device 100.
The tenter device 100 sequentially grips both end portions 21 and 22 of the pre-stretched film 20 at its inlet portion 130 by the grippers 110R and 110L. The pre-stretched film 20 gripped at both ends 21 and 22 is conveyed as the grippers 110R and 110L travel. As described above, in the present embodiment, the shapes of the guide rails 120R and 120L are set so that the traveling direction of the pre-stretched film 20 is bent to the left. Therefore, the distance of the track that one gripper 110R travels while gripping the pre-stretched film 20 is longer than the distance of the track that the other gripper 110L travels while gripping the pre-stretched film 20. Therefore, the set of grippers 110R and 110L that were opposed to the traveling direction of the pre-stretched film 20 at the inlet portion 130 of the tenter device 100 are the left grippers at the outlet portion 140 of the tenter device 100. Since 110L precedes the right gripper 110R, the pre-stretching film 20 is stretched in an oblique direction to obtain a long first stretched film 30. The obtained first stretched film 30 is released from the grippers 110R and 110L at the outlet portion 140 of the tenter device 100, is wound up, and is collected as a roll 40.

The stretching direction in the first step is 15 ° or more and 50 ° or less with respect to the width direction.
The stretching direction in the first step is preferably 20 ° or more, more preferably 25 ° or more, preferably 48 ° or less, and more preferably 45 ° or less with respect to the width direction. By setting the stretching direction in the first step within the above range, a stretched film having a slow phase axis in an oblique direction with respect to the width direction can be obtained.

The draw ratio A1 in the first step is preferably 1.2 times or more, more preferably 1.25 times or more, still more preferably 1.3 times or more, preferably 1.6 times or less, and more preferably 1. It is 5 times or less, more preferably 1.4 times or less. By setting the draw ratio A1 in the first step to the lower limit of the above range or more, the in-plane retardation of the stretched film can be increased. Further, by setting the value to the upper limit or less, the peel strength of the stretched film can be increased.

The stretching direction and stretching ratio in the first step can be adjusted according to the stretching conditions in the first step described above. For example, the stretching direction of the first stretched film 30 can be adjusted by adjusting the feeding direction φ formed by the feeding direction D20 of the unstretched film 20 from the feeding roll 10 and the winding direction D30 of the first stretched film 30. .. Here, the feeding direction D20 of the pre-stretched film 20 indicates the traveling direction of the pre-stretching film 20 fed from the feeding roll 10. Further, the winding direction D30 of the first stretched film 30 indicates the traveling direction of the first stretched film 30 wound as the roll 40.
Further, by adjusting the widths of the guide rail 120R and the guide rail 120L, the draw ratio of the first stretched film 30 in the first step can be adjusted.

The stretching temperature T1 in the first step is preferably (Tg) ° C. or higher, more preferably (Tg + 2) ° C. or higher, particularly preferably (Tg + 5) ° C. or higher, preferably (Tg + 40) ° C. or lower, and more preferably (Tg + 35). ) ° C. or lower, particularly preferably (Tg + 30) ° C. or lower. Here, Tg refers to the glass transition temperature of the resin forming the pre-stretched film. Further, in the present embodiment, the stretching temperature T1 in the first step means the temperature in the stretching zone 150 of the tenter device 100. By setting the stretching temperature T1 in the first step to the above range, the molecules contained in the pre-stretching film 20 can be reliably oriented, so that the first stretched film 30 having desired optical characteristics can be easily obtained. Can be done.

The average in-plane retardation Re1 of the first stretched film 30 is preferably 180 nm or more, more preferably 200 nm or more, preferably 260 nm or less, and more preferably 240 nm or less. By setting the average in-plane retardation Re1 of the first stretched film 30 within the above range, a second stretched film having a desired average in-plane retardation Re2 can be easily obtained.
The average in-plane retardation of the film can be obtained by measuring the in-plane retardation at a plurality of points arranged in the width direction of the film at intervals of 50 mm and calculating the average value of the in-plane retardation at these points. ..

The direction of the slow axis of the first stretched film 30 is preferably set according to the direction of the slow axis of the second stretched film. Normally, the angle (orientation angle) formed by the slow axis of the second stretched film obtained in the second step with respect to the width direction is larger than the angle formed by the slow axis of the first stretched film with respect to the width direction. Also becomes smaller. Therefore, it is preferable that the angle formed by the slow axis of the first stretched film 30 with respect to the width direction is larger than the angle formed by the slow axis of the second stretched film with respect to the width direction. For example, the first stretched film 30 is delayed in the range of preferably 20 ° or more, more preferably 25 ° or more, and preferably 60 ° or less, more preferably 55 ° or less on average with respect to the width direction thereof. It has a phase axis. Thereby, a second stretched film having an orientation angle of 10 ° or more and 30 ° or less can be easily obtained. The direction of the slow axis of the first stretched film 30 can be adjusted by adjusting the stretching direction in the first step.

The average orientation angle of the film can be obtained by measuring the orientation angles at a plurality of points arranged in the width direction of the film at intervals of 50 mm and calculating the average value of the orientation angles at these points.

(Second step)
In the method for producing a long stretched film of the present embodiment, after the first step, a second step of stretching the first stretched film in the width direction to obtain a long second stretched film is performed.
Here, "stretching in the width direction" means stretching so that the angle formed by the width direction and the stretching direction is within the range of 0 ° ± 5 °.
Stretching in the width direction in the second step is usually performed by using a transverse stretching device while continuously transporting the first stretched film in the longitudinal direction.

FIG. 2 is a plan view schematically showing a transverse stretching device for carrying out the manufacturing method according to the embodiment of the present invention.
As shown in FIG. 2, the transverse stretching device 400 is a device that stretches the first stretched film 30 unwound from the roll 40 in the width direction orthogonal to the flow direction in a heating environment using an oven (not shown).

The transverse stretching device 400 includes a plurality of grippers 410R and 410L, and a pair of guide rails 420R and 420L. The grippers 410R and 410L are provided so as to be able to grip the widthwise ends 31 and 32 of the first stretched film 30, respectively. Further, the guide rails 420R and 420L are provided on both sides of the film transport path to guide the grippers 410R and 410L.

The grippers 410R and 410L are provided so as to be able to travel along the guide rails 420R and 420L. Further, the grippers 410R and 410L are provided so as to be able to travel at a constant speed while maintaining a constant interval with the front and rear grippers 410R and 410L, respectively. Further, the grippers 410R and 410L grip the widthwise ends 31 and 32 of the first stretched film 30 sequentially supplied to the transverse stretching device 400 at the inlet portion 430 of the transverse stretching device 400, respectively, and the transverse stretching device 400. It has a configuration that can be opened at the outlet portion 440 of 400.

The guide rails 420R and 420L are provided with an extension zone 450 in which the distance between the guide rails 420R and the guide rails 420L increases toward the downstream side. The shapes of the guide rail 420R and the guide rail 420L in the stretch zone 450 are symmetrical with respect to the line LN40 passing through the midpoint in the width direction of the first stretched film 30 to be conveyed, and the guide rail 420R in the stretch zone 450. The distance between the rail and the guide rail 420L can be adjusted according to the draw ratio in the second step.

Further, the guide rails 420R and 420L have an endless continuous track so that the grippers 410R and 410L can orbit a predetermined track. Therefore, the transverse stretching device 400 has a configuration in which the grippers 410R and 410L in which the first stretched film 30 is opened at the outlet portion 440 of the transverse stretching device 400 can be sequentially returned to the inlet portion 430.

Stretching of the first stretched film 30 using the transverse stretching device 400 is performed as follows.
The first stretched film 30 is unwound from the roll 40, and the first stretched film 30 is continuously supplied to the transverse stretching device 400.
The transverse stretching device 400 sequentially grips the widthwise ends 31 and 32 of the first stretched film 30 at its inlet 430 by the grippers 410R and 410L. The first stretched film 30 gripped by the ends 31 and 32 is conveyed as the grippers 410R and 410L travel.

As described above, the guide rails 420R and 420L on which the grippers 410R and 410L travel are symmetrical with respect to the line LN40 passing through the midpoint in the width direction of the first stretched film 30 to be conveyed in the stretching zone 450. Since the spacing is increased toward the downstream side, the first stretched film 30 gripped by the grippers 410R and 410L is stretched in the stretching zone 450 in the width direction of the first stretched film 30 and is long. The second stretched film 50 of the above is obtained. The obtained second stretched film 50 is released from the grippers 410R and 410L at the outlet portion 440 of the transverse stretching device 400, is wound up, and is collected as a roll 60.

The draw ratio A2 in the second step is preferably set so that the product (A1 × A2) with the draw ratio A1 in the first step becomes a predetermined value.
(A1 × A2) is preferably larger than 1.2 times, more preferably 1.25 times or more, preferably 2.0 times or less, more preferably 1.85 times or less, still more preferably 1.65 times. It is less than double.
By setting (A1 × A2) to the range of the lower limit value, sufficient in-plane retardation can be expressed in the second stretched film 50. Further, by setting the value to the upper limit or less, the peel strength of the stretched film can be increased.

The stretching temperature T2 in the second step may be the same as the stretching temperature T1 in the first step. Specifically, it is preferably (Tg) ° C. or higher, more preferably (Tg + 2) ° C. or higher, particularly preferably (Tg + 5) ° C. or higher, preferably (Tg + 40) ° C. or lower, more preferably (Tg + 35) ° C. or lower, Particularly preferably, it is (Tg + 30) ° C. or lower. Here, Tg refers to the glass transition temperature of the resin forming the pre-stretched film. Further, in the present embodiment, the stretching temperature T2 in the second step means the temperature in the stretching zone 450 of the transverse stretching device 400.

The stretching temperature T2 may be different from the stretching temperature T1. When the stretching temperature T2 is different from the stretching temperature T1, it is preferable that the stretching temperature T2 is lower than the stretching temperature T1. The stretching temperature T2 is preferably (T1-15) ° C. or higher, more preferably (T1-10) ° C. or higher, preferably (T1-2) ° C. or lower, and more preferably (T1-5) ° C. or lower. ..

The average in-plane retardation Re2 of the second stretched film 50 is preferably 200 nm or more, more preferably 210 nm or more, still more preferably 220 nm or more, preferably 300 nm or less, more preferably 290 nm or less, still more preferably 280 nm or less. Is.
The average in-plane retardation Re2 of the second stretched film 50 can be adjusted by adjusting the product (A1 × A2) of the stretch ratio A1 in the first step and the stretch ratio A2 in the second step. For example, by increasing (A1 × A2), the average in-plane retardation Re2 can be increased.

Since the second stretched film 50 is stretched in the oblique direction in the first step, it has a slow axis in the oblique direction. Specifically, the second stretched film 50 has a slow axis having an angle of 10 ° or more and 30 ° or less with respect to the width direction.

The second stretched film 50 has an average NZ coefficient of preferably 1.2 or more, more preferably 1.21 or more, still more preferably 1.22 or more, preferably 1.5 or less, and more preferably 1.48. Below, it is more preferably 1.46 or less.
The average NZ coefficient can be adjusted by adjusting the draw ratio A1 in the first step and the draw ratio A2 in the second step. For example, the average NZ coefficient can be reduced by increasing the draw ratio A2.

The average NZ coefficient of the film can be obtained by measuring the NZ coefficient at a plurality of points at intervals of 50 mm arranged in the width direction of the film and calculating the average value of the NZ coefficient at these points.

In the method for producing a stretched film including stretching in an oblique direction, it may be difficult to obtain a desired retardation. In this case, if the stretching ratio is increased in order to obtain the desired retardation, the stretched film tends to undergo cohesive failure, and the peel strength between the stretched film and the bonded product of another film may be insufficient. On the other hand, as in the present embodiment, by stretching the pre-stretched film in two steps in a predetermined direction by the first step and the second step, a long stretch having a large average in-plane retardation and a high peel strength You can get the film. The reason why a stretched film having a large average in-plane retardation and a large peel strength can be obtained by the production method of the present embodiment is the degree of in-plane orientation of the polymer contained in the film in the production method of the present embodiment. It is considered that this is because the bonding force of the polymer in the thickness direction is balanced, but the present invention is not limited.

(Modification example)
The present invention is not limited to the above-described embodiment, and may be further modified.
For example, the above-mentioned manufacturing method may further have an arbitrary step in addition to the first step and the second step. Examples of such a step include a step of providing a protective layer on the surface of the stretched film and a step of subjecting the stretched film to a surface treatment such as a corona treatment.

Further, for example, as the pre-stretched film, a film obtained by stretching an unstretched film in an arbitrary direction may be used. As described above, as a method of stretching the pre-stretched film before it is subjected to the first step, for example, a roll method, a float-type longitudinal stretching method, a transverse stretching method using a tenter device, or the like can be used.

Further, in the above-described embodiment, the first stretched film 30 is wound into a roll 40, and the first stretched film 30 is unwound from the roll 40 and supplied to the second step. The film 30 may be supplied to the second step without being wound up.

[2. Polarizing film manufacturing method]
A long polarizing film can be manufactured by using the long stretched film obtained by the manufacturing method of the present invention.
The method for producing a polarizing film according to an embodiment of the present invention is a third step of laminating a long polarizer on a long stretched film obtained by the method for producing a long stretched film according to the above embodiment. including.

Regarding the method for producing a long stretched film according to an embodiment of the present invention, the above item [1. Method for producing a long stretched film] is the same as the method described.

According to the method for producing a long polarizing film of the present embodiment, the stretched film included in the polarizing film has a high peel strength, so that a polarizing film having excellent mechanical strength can be obtained.

(Polarizer)
As the polarizer used in the present embodiment, a film of an appropriate vinyl alcohol-based polymer such as polyvinyl alcohol and partially formalized polyvinyl alcohol is dyed and stretched with a dichroic substance such as iodine and a dichroic dye. , Appropriate treatment such as cross-linking treatment is performed in an appropriate order and method. Such a polarizer is capable of transmitting linearly polarized light when natural light is incident on it, and is particularly preferably one having excellent light transmittance and degree of polarization. Any member (for example, a protective film) may be laminated on the polarizer.

(Third step)
In the third step, a step of laminating a long polarizer on a long stretched film is performed.
Lamination can be performed, for example, by laminating a long polarizer and a long stretched film in a roll-to-roll manner with their longitudinal directions parallel to each other. At the time of bonding, an adhesive may be used if necessary. By manufacturing using a long film in this way, a long polarizing film can be efficiently manufactured.

Further, in the third step, a film in which an arbitrary member such as a protective film is laminated on a long polarizer may be laminated on the long stretched film.

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to the following examples, and may be arbitrarily modified and implemented without departing from the scope of claims of the present invention and the equivalent scope thereof.

The following operations were performed in the air at normal temperature and pressure unless otherwise specified.

[Evaluation methods]
(Average in-plane retardation Re of film)
For the film to be evaluated, in-plane retardation was measured at a plurality of points at intervals of 50 mm arranged in the width direction of the film using a phase difference measuring device (product name "Axoscan" manufactured by Axometric) at a wavelength of 590 nm. The average value of the in-plane retardation at these points was calculated, and this average value was taken as the average in-plane retardation Re of the film.

(Average NZ coefficient of film)
For the film to be evaluated, the NZ coefficient was measured at a plurality of points at intervals of 50 mm arranged in the width direction of the film using a phase difference measuring device (product name "Axoscan" manufactured by Axometric) at a wavelength of 590 nm. The average value of the NZ coefficient at these points was calculated, and this average value was used as the average NZ coefficient of the film.

The NZ coefficient is a value obtained by measuring the in-plane retardation Re and the thickness direction retardation Rth according to the following formula.
NZ coefficient = (Rth / Re) +0.5

(Average orientation angle of film)
Using a phase difference measuring device (product name "Axoscan" manufactured by Axometric), the orientation angles formed by the slow axis and the width direction of the film were measured at a plurality of points at intervals of 50 mm arranged in the width direction of the film. The average value of the orientation angles at these points was calculated, and this average value was used as the average orientation angle of the film.

(Film peel strength)
An unstretched film (glass transition temperature 160 ° C., thickness 100 μm, manufactured by Zeon Corporation) made of a resin containing a polymer (cycloolefin polymer) containing an alicyclic structure was prepared. One side of the stretched film to be evaluated and the unstretched film was subjected to corona treatment. An adhesive was adhered to the corona-treated surface of the stretched film and the corona-treated surface of the unstretched film, and the surfaces to which the adhesive was adhered were bonded to each other. At this time, a UV adhesive was used as the adhesive. As a result, a sample film including a stretched film and an unstretched film was obtained.
Then, the sample film was cut to a width of 15 mm, and the stretched film side was attached to the surface of the slide glass with an adhesive. At this time, a double-sided adhesive tape (manufactured by Nitto Denko KK, product number "CS9621") was used as the adhesive.
A 90-degree peeling test was carried out by sandwiching the unstretched film at the tip of the force gauge and pulling it in the normal direction of the surface of the slide glass. At this time, the force measured when the unstretched film is peeled off is the force required to peel off the stretched film and the unstretched film. Therefore, the magnitude of this force is the peeling strength of the stretched film to be evaluated. And said.

[Example 1]
(Manufacturing of long pre-stretched film)
Pellets of resin A (resin of norbornene-based polymer having a glass transition temperature of 126 ° C., manufactured by Nippon Zeon Co., Ltd.) containing a polymer containing an alicyclic structure (hydride of cycloolefin polymer) are dried at 100 ° C. for 5 hours. did. The pellets were supplied to an extruder, melted in the extruder, and extruded into a sheet from a T-die onto a casting drum via a polymer pipe and a polymer filter. The extruded resin was cooled on a casting drum and cured to obtain a long pre-stretched film 20 having a thickness of 70 μm. This unstretched film was wound up to obtain a feeding roll 10.

(First step)
As shown in FIG. 1, a long pre-stretched film 20 is fed from a feeding roll 10 and supplied to a tenter device 100 having a structure described in the above-described embodiment, and stretched in an oblique direction under the conditions shown in Table 1. , The first stretched film 30 was obtained. The obtained first stretched film 30 was wound up and recovered as a roll 40. At this time, the feeding angle φ formed by the feeding direction D20 of the unstretched film 20 from the feeding roll 10 and the winding direction D30 of the first stretched film 30 was set to 45 °. Using a part of the obtained first stretched film 30, the average in-plane retardation Re1 and the average orientation angle θ1 were measured.

(Second step)
The first stretched film obtained in the first step was supplied to a transverse stretching apparatus under the conditions shown in Table 1 and uniaxially stretched to obtain a stretched film which is a second stretched film. Using this stretched film, the average in-plane retardation Re2, the average orientation angle θ2, the average NZ coefficient, and the peel strength were evaluated.

[Examples 2 to 4]
Production of a long first stretched film and stretched film in the same manner as in Example 1 except that the stretching direction of the first step and the stretching ratio and stretching temperature of the second step were changed as shown in Table 1. Evaluation was performed. The results are shown in Table 1.

[Example 5]
Instead of the pellet of resin A, resin B (resin of norbornene-based polymer having a glass transition temperature of 135 ° C., manufactured by Nippon Zeon Co., Ltd.) containing a polymer containing an alicyclic structure (hydride of cycloolefin polymer) A long roll of the pre-stretched film was produced using the pellets, and the length was the same as in Example 1 except that the stretching temperature of the first step and the stretching temperature of the second step were changed as shown in Table 1. The first stretched film and the stretched film were produced and evaluated. The results are shown in Table 1.

[Comparative Examples 1 and 2]
Production and evaluation of a long stretched film in the same manner as in Example 1 except that the stretching direction, stretching ratio, and stretching temperature of the first step were changed as shown in Table 2 and the second step was not performed. Was done. The results are shown in Table 2. Table 2 shows the value of A1 as the value of A1 × A2. The peel strength indicates a value measured for a long stretched film (first stretched film) obtained in the first step.

[Comparative Examples 3 and 4]
Production of a long first stretched film and stretched film in the same manner as in Example 1 except that the stretching direction and stretching ratio of the first step and the stretching ratio of the second step were changed as shown in Table 2. Evaluation was performed. The results are shown in Table 2.

[Table description]
In Tables 1 and 2 below, the stretching angle and the average orientation angles θ1 and θ2 indicate values with respect to the width direction of the film.

From the above results, it can be seen that the stretched films (second stretched films) obtained in Examples 1 to 5 express sufficient in-plane retardation and have high peel strength.
On the other hand, the stretched films (first stretched films) obtained in Comparative Examples 1 and 2 in which the second step was not performed were inferior in either in-plane retardation or peel strength, and were excellent in in-plane retardation. It can be seen that the peel strength cannot be compatible with each other.
Further, the stretched films (second stretched films) obtained in Comparative Examples 3 to 4 in which the stretching angle in the first step is larger than 50 ° with respect to the width direction are also inferior in either in-plane retardation or peel strength. It can be seen that sufficient in-plane retardation and excellent peel strength cannot be achieved at the same time.

10 Feeding roll 20 Pre-stretched film 21 and 22 Width end of pre-stretched film 30 First stretched film 31 and 32 Width end of first stretched film 40 roll 50 Second stretched film 60 roll 100 Tenter device 110R And 110L grippers 120R and 120L guide rails 130 entrance of the tenter device 140 exit of the tenter device 150 extension zone of the tenter device 400 lateral stretching devices 410R and 410L grippers 420R and 420L guide rails 430 inlet of the lateral stretching device 440 lateral Outlet part of stretching device 450 Stretching zone of transverse stretching device

Claims (5)

A method for producing a long stretched film.
The first step of stretching a long unstretched film in a direction of 15 ° or more and 50 ° or less with respect to the width direction to obtain a long first stretched film.
The second step of stretching the long first stretched film in the width direction to obtain a long second stretched film is included in this order.
The long second stretched film has a slow axis having an angle of 10 ° or more and 30 ° or less with respect to the width direction.
A method for producing a long stretched film. The average NZ coefficient of the long second stretched film is 1.2 or more and 1.5 or less.
Assuming that the stretching ratio in the first step is A1 and the stretching ratio in the second step is A2, A1 is 1.2 times or more and 1.6 times or less, and (A1 × A2) is larger than 1.2 times. The method for producing a long stretched film according to claim 1, which is 2.0 times or less. The method for producing a long stretched film according to claim 1 or 2, wherein the average in-plane retardation Re2 of the long second stretched film is 200 nm or more and 300 nm or less. The method for producing a long stretched film according to any one of claims 1 to 3, wherein the stretched film contains a polymer containing an alicyclic structure. It is a method of manufacturing a long polarizing film.
A third step of laminating a long polarizer on a long stretched film obtained by the method for producing a long stretched film according to any one of claims 1 to 4 is included.
A method for manufacturing a long polarizing film.

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