KR102475070B1 - Stretched film manufacturing method and polarizing film manufacturing method - Google Patents

Abstract

Provided is a method for producing a stretched film made of a polyvinyl alcohol-based resin capable of realizing a high draw ratio in TD (film width direction) and having excellent axial orientation in TD, and a method for producing a polarizing film exhibiting good optical performance using the same do. A stretching step of obtaining a stretched film by stretching the polyvinyl alcohol-based resin film, wherein the stretching step is performed by transversely stretching the polyvinyl alcohol-based resin film at a MD shrinkage ratio of the polyvinyl alcohol-based resin film in comparison at the same TD stretching ratio. A first stretching treatment step of simultaneously performing TD stretching and MD shrinkage so that the MD shrinkage ratio is larger than the MD shrinkage ratio in the case of performing, and a second stretching treatment step of simultaneously performing TD stretching and MD shrinkage so that the MD shrinkage ratio is lowered by 0.17 or more. It is the manufacturing method of the stretched film included in this order, and the manufacturing method of the polarizing film using the obtained stretched film.

Description

Stretched film manufacturing method and polarizing film manufacturing method

The present invention relates to a method for producing a stretched film made of polyvinyl alcohol-based resin and a method for producing a polarizing film.

BACKGROUND OF THE INVENTION Polarizing plates are widely used in image display devices typified by liquid crystal display devices. As a polarizing plate, the thing of the structure which bonded the protective film to the single side|surface or both sides of the polarizing film obtained by performing the extending|stretching process and the dyeing process by a dichroic dye with respect to a polyvinyl alcohol-type resin film is common.

As for the extending|stretching of the polyvinyl alcohol-type resin film performed when manufacturing a polarizing film, longitudinal stretching is conventionally common. Longitudinal stretching means stretching of the film in the "machine flow direction" (ie, the film longitudinal direction), and this direction is also referred to as MD in this specification. The direction orthogonal to MD, that is, the film width direction is also referred to as TD in this specification.

According to longitudinal stretching, it is relatively easy to stably manufacture a polarizing film having excellent optical performance (eg, polarization performance). However, in order to sufficiently improve the optical performance, it is necessary to neck-in the polyvinyl alcohol-based resin film greatly in the width direction by longitudinal stretching, and a neck-in rate of 50% or more is typically required. Therefore, the manufacturing method of the polarizing film by longitudinal stretching has the essential subject that it is difficult to manufacture a polarizing film of a wide width. If a very wide film is used as the original polyvinyl alcohol-based resin film, it is possible to obtain a polarizing film with a relatively wide width, but it is difficult to make the original film wide in terms of manufacturing facilities.

On the other hand, an attempt to manufacture a polarizing film using transverse stretching (stretching in TD) has also been proposed, examples of which include Japanese Patent No. 4701555 (Patent Document 1) and Japanese Patent No. 5362059 (Patent Document 2). , Japanese Patent No. 4971066 (Patent Document 3) and the like.

Japanese Patent No. 4701555 Japanese Patent No. 5362059 Japanese Patent No. 4971066

An object of the present invention is to provide a method for producing a stretched film made of a polyvinyl alcohol-based resin capable of realizing a high stretch ratio in the TD (film width direction) and having excellent TD axial orientation. Another object of the present invention is to provide a method for producing a polarizing film using the stretched film, wherein the TD is the direction of the slow axis (absorption axis) and exhibits good optical performance.

The present invention provides a method for producing a stretched film shown below, a stretched film, and a method for producing a polarizing film.

[1] A stretching step of obtaining a stretched film having a TD stretch ratio of A _f [times] and an MD shrink ratio of B _f [times] by stretching the polyvinyl alcohol-based resin film,

The stretching process,

In comparison at the same TD stretching ratio, the first stretching treatment step of simultaneously performing TD stretching and MD shrinkage such that the MD shrinkage ratio is greater than the MD shrinkage ratio in the case of transversely stretching the polyvinyl alcohol-based resin film at the free end. class,

A second stretching treatment step in which stretching to TD and shrinkage to MD are simultaneously performed so that the MD shrinkage ratio decreases by 0.17 or more.

A method for producing a stretched film comprising in this order.

[2] The manufacturing method according to [1], wherein the TD draw ratio of the polyvinyl alcohol-based resin film at the start of the second stretching treatment step is 4.3 times or more.

[3] By performing the second stretching treatment step, the TD stretch ratio of the polyvinyl alcohol-based resin film reaches A _f [times] and the MD shrinkage ratio reaches B _f [times] [1] or [2] ] The manufacturing method described in.

[4] The polyvinyl alcohol-based resin film is an unstretched film,

The manufacturing method according to any one of [1] to [3], wherein the first stretching treatment step is first performed in the stretching step.

[5] The manufacturing method according to any one of [1] to [4], wherein the MD shrinkage ratio B _f of the stretched film is 0.2 to 0.8 times.

[6] The manufacturing method according to any one of [1] to [5], wherein the TD stretch ratio A _f of the stretched film is 5 times or more.

[7] The manufacturing method according to any one of [1] to [6], wherein the stretched film laminated on the base film is obtained by stretching the laminated film having the polyvinyl alcohol-based resin film on the base film.

[8] The manufacturing method according to any one of [1] to [7], wherein the stretched film has a thickness of 30 µm or less.

[9] A stretched film of 100 m or more in length made of polyvinyl alcohol-based resin,

When the refractive index in the film width direction within the film plane at a wavelength of 590 nm is n _x , and the refractive index in the direction orthogonal to the film width direction within the film plane is n _y , the following formula:

Birefringence ΔP=n _x -n _y

A stretched film having a birefringence ΔP expressed by 0.031 or more.

[10] a step of obtaining a stretched film by the production method according to any one of [1] to [8];

Step of dyeing the stretched film with a dichroic dye

Method for producing a polarizing film comprising a.

According to the present invention, a stretched film having a high TD draw ratio and high axial orientation can be produced. Further, according to the present invention, it is possible to manufacture a polarizing film exhibiting good optical performance with TD as the direction of the slow axis (absorption axis).

1 is a flowchart showing a preferred example of a method for producing a stretched film according to the present invention.
Fig. 2 is a schematic cross-sectional view showing an example of the layer structure of the laminated film obtained in the PVA-based resin film forming step.
Fig. 3 is a schematic cross-sectional view showing an example of the layer configuration of a stretched laminated film obtained in the stretching step.
4 is a graph showing an example of a stretching pattern in a stretching process according to the present invention.
Fig. 5 is a plan view schematically showing an example of the internal configuration of a tenter type stretching device.
6 is a flowchart showing a preferred example of a method for manufacturing a polarizing film and a polarizing plate according to the present invention.
Fig. 7 is a schematic cross-sectional view showing an example of the layer structure of a light-polarizing laminated film obtained in a dyeing step.
Fig. 8 is a schematic sectional view showing an example of the layer structure of the light-polarizing laminated film with a protective film obtained in the first bonding step.
Fig. 9 is a schematic cross-sectional view showing an example of the layer structure of a polarizing plate with a single-sided protective film obtained in a peeling step.
Fig. 10 is a schematic cross-sectional view showing an example of the layer configuration of a polarizing plate with double-sided protective films obtained in a second bonding step.
11 is a graph showing stretching patterns in the stretching process in Examples and Comparative Examples.

<Method for producing stretched film>

The stretched film according to the present invention is a film obtained by performing a stretching step of stretching a polyvinyl alcohol-based resin film (hereinafter, polyvinyl alcohol-based resin is also referred to as "PVA-based resin"). The stretched film according to the present invention may be a film supported by a base film (laminated on the base film), or may be a film that is not supported by a base film and exists alone. In the case of the former, a stretched film supported by the base film can be obtained by subjecting a laminated film comprising a base film and a PVA-based resin film (PVA-based resin layer) formed thereon to the stretching step (first embodiment). ). In the case of the latter, an individual stretched film can be obtained by subjecting an individual PVA-based resin film to the stretching step (2nd embodiment).

Hereinafter, the first embodiment for producing a stretched film supported by a base film will be mainly described. Referring to FIG. 1, the manufacturing method of the stretched film according to the first embodiment includes the following steps:

A PVA-based resin film forming step (S10) of forming a laminated film by coating a coating liquid containing a PVA-based resin on at least one side of a base film and then drying it to form a PVA-based resin film; and

Stretching step of stretching the laminated film to obtain a stretched laminated film comprising a base film and a stretched film (S20)

A method including in this order may be used.

Hereinafter, each process is demonstrated. Moreover, in the PVA-type resin film formation process (S10), you may form a PVA-type resin film on both surfaces of a base film, but below, the case where it mainly forms on one side is demonstrated.

(1) PVA-based resin film forming step (S10)

Referring to FIG. 2 , this step is a step of obtaining a laminated film 100 by forming a PVA-based resin film 6 on at least one surface of a base film 30 . The PVA-based resin layer 6 can be formed by coating a coating solution containing a PVA-based resin on one or both surfaces of the base film 30 and drying the coated layer. The method of forming the PVA-type resin film 6 by such coating is advantageous in that it is easy to obtain the thin-film PVA-type resin film 6 and also a thin-film polarizing film.

The base film 30 can be composed of a thermoplastic resin, and among these, it is preferable to be composed of a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, stretchability, and the like. Specific examples of such a thermoplastic resin include, for example, polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins (norbornene resins and the like); polyester-based resin; (meth)acrylic resin; cellulose ester-based resins such as cellulose triacetate and cellulose diacetate; polycarbonate-based resin; polyvinyl alcohol-based resin; polyvinyl acetate-based resin; polyarylate-based resins; polystyrene-based resin; polyethersulfone-based resins; polysulfone-based resins; polyamide-based resin; polyimide-based resin; and mixtures and copolymers thereof.

The base film 30 may have a single-layer structure composed of one resin layer composed of one or two or more types of thermoplastic resins, or may have a multilayer structure in which a plurality of resin layers composed of one or two or more types of thermoplastic resins are laminated. The base film 30 is preferably composed of a resin capable of being stretched at a stretching temperature suitable for stretching a PVA-based resin film in a stretching step (S20) described later.

The base film 30 may contain additives. Specific examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments and colorants.

The thickness of the base film 30 is usually 1 to 500 μm, preferably 1 to 300 μm, more preferably 5 to 200 μm, still more preferably 5 to 150 μm, from the viewpoint of strength, handleability, etc. .

It is preferable that the coating liquid coated on the base film 30 is an aqueous solution of PVA-based resin containing PVA-based resin and water. This aqueous solution may contain additives, such as solvents other than water, a plasticizer, and surfactant, as needed. Examples of solvents other than water include organic solvents compatible with water such as alcohols represented by methanol, ethanol, propanol, and polyhydric alcohols (eg, glycerin).

As PVA type resin, what saponified polyvinyl acetate type resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable with this. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group. In addition, in this specification, "(meth)acryl" means at least one selected from the group which consists of acryl and methacryl. The same applies to "(meth)acryloyl" and the like.

The degree of saponification of the PVA-based resin may be in the range of 80.0 to 100.0 mol%, but is preferably in the range of 90.0 to 99.5 mol%, and more preferably in the range of 94.0 to 99.0 mol%. If the saponification degree is less than 80.0 mol%, the water resistance of the polarizing film obtained from the stretched film tends to decrease. When a PVA-based resin having a saponification degree of more than 99.5 mol% is used, the dyeing speed in the dyeing step of the method for producing a polarizing film described later decreases, productivity decreases, and it is sometimes difficult to obtain a polarizing film having sufficient polarizing performance. .

The degree of saponification is the ratio of the acetic acid group (acetoxy group: -OCOCH ₃ ) contained in the polyvinyl acetate-based resin, which is a raw material of the PVA-based resin, to the hydroxyl group by the saponification step, expressed as a unit ratio (mol%), ceremony:

Saponification degree (mol%) = 100 × (number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetic acid groups)

is defined as The degree of saponification can be obtained in accordance with JIS K 6726 (1994). The higher the degree of saponification, the higher the ratio of hydroxyl groups, and thus the lower the ratio of acetic acid groups that inhibit crystallization.

The modified polyvinyl alcohol partially modified may be sufficient as the PVA-based resin. For example, olefins such as ethylene and propylene for PVA-based resin; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; What was modified|denatured with the alkyl ester of an unsaturated carboxylic acid, (meth)acrylamide, etc. is mentioned. The ratio of modification is preferably less than 30 mol%, and more preferably less than 10%. In the case of modification exceeding 30 mol%, the adsorption of the dichroic dye to the stretched film becomes difficult, and it tends to be difficult to obtain a polarizing film having sufficient polarization performance.

The average degree of polymerization of the PVA-based resin is preferably 100 to 10000, more preferably 1500 to 8000, still more preferably 2000 to 5000. The average degree of polymerization of the PVA-based resin can also be obtained in accordance with JIS K 6726 (1994).

A method of applying the coating solution to the base film 30 may include a wire bar coating method; roll coating methods such as reverse coating and gravure coating; die coat method; comma coat method; lip coat method; spin coating method; screen coating method; fountain coating method; dipping method; It can select suitably from methods, such as a spray method. The coating layer may be formed on only one side of the base film 30 or may be formed on both sides.

The drying temperature and drying time of the coating layer are set according to the type of solvent contained in the coating solution. The drying temperature is, for example, 50 to 200°C, preferably 60 to 150°C. When the solvent contains water, the drying temperature is preferably 80°C or higher.

The thickness of the PVA-based resin film 6 in the laminated film 100 is preferably 3 to 100 μm, more preferably 5 to 50 μm, still more preferably 5 to 30 μm. If the PVA-based resin film 6 having a thickness within this range passes through a stretching step (S20) and a dyeing step described later, the dyeability of the dichroic dye is good and the polarization performance is excellent, and it is sufficiently thin (e.g., 10 μm in thickness). The following) polarizing film can be obtained.

Prior to coating of the coating solution, in order to improve the adhesion between the base film 30 and the PVA-based resin film 6, corona treatment, plasma treatment, You may flame (flame) treatment, etc. For the same reason, a coating layer may be formed on the base film 30 via a primer layer or the like.

A primer layer can be formed by coating the coating liquid for primer layer formation on the surface of the base film 30, and then drying it. This coating solution contains a component that exerts a certain degree of strong adhesion to both the base film 30 and the PVA-based resin film 6, and usually contains a resin component and a solvent that impart such adhesion. As the resin component, a thermoplastic resin having excellent transparency, thermal stability, stretchability, etc. is preferably used, and examples thereof include (meth)acrylic resins and polyvinyl alcohol-based resins. Among them, a polyvinyl alcohol-based resin that imparts good adhesion is preferably used. More preferably, it is a polyvinyl alcohol resin. As the solvent, a general organic solvent or aqueous solvent capable of dissolving the resin component is usually used, but it is preferable to form the primer layer with a coating solution using water as the solvent.

In order to increase the strength of the primer layer, a crosslinking agent may be added to the coating solution for forming the primer layer. Specific examples of the crosslinking agent include epoxy-based, isocyanate-based, dialdehyde-based, metal-based (eg, metal salts, metal oxides, metal hydroxides, organometallic compounds), and polymer-based crosslinking agents. In the case of using a polyvinyl alcohol-based resin as the resin component forming the primer layer, polyamide epoxy resins, methylolized melamine resins, dialdehyde-based crosslinking agents, metal chelate compound-based crosslinking agents, and the like are suitably used.

The thickness of the primer layer is preferably about 0.05 to 1 μm, and more preferably 0.1 to 0.4 μm. If the thickness is less than 0.05 μm, the effect of improving the adhesion between the base film 30 and the PVA-based resin film 6 is small.

A method of coating the coating liquid for forming the primer layer on the base film 30 may be the same as the coating liquid for forming the PVA-based resin film. The drying temperature of the coating layer made of the coating solution for forming the primer layer is, for example, 50 to 200°C, preferably 60 to 150°C. When the solvent contains water, the drying temperature is preferably 80°C or higher.

(2) Stretching process (S20)

Referring to FIG. 3, in this step, the laminated film 100 including the base film 30 and the PVA-based resin film 6 is stretched, and the stretched base film 31 and the stretched film made of the PVA-based resin ( 7) is a step of obtaining the stretched laminated film 200 including.

The stretching process (S20) is the following process:

In comparison at the same TD stretching ratio, the first stretching treatment step (S20- 1), and

A second stretching treatment step (S20-2) of simultaneously performing TD stretching and MD shrinkage so that the MD shrinkage ratio decreases by 0.17 or more

include in this order.

According to the stretching treatment method including the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2) in this order, the polyvinyl alcohol-based resin has a high TD draw ratio and excellent TD axial orientation. The stretched film 7 made of can be stably manufactured. A polarizing film produced using this stretched film 7 as a raw material film is a polarizing film having TD as the slow axis (absorption axis) direction, and can exhibit good optical performance (polarization performance, etc.).

Fig. 4 is a graph showing an example of a stretching pattern in the stretching step (S20) according to the present invention, and shows two types of stretching patterns X and Y as specific examples. The horizontal axis of the graph is the TD draw ratio A (TD draw ratio, unit: times). When the TD draw ratio A of the PVA-based resin film 6 provided in the stretching step (S20) is set to 1, a value exceeding 1 can be employed for the TD draw ratio A in the stretching step (S20). The TD stretching ratio A is:

TD stretching ratio A [times] = (TD length of the stretched PVA-based resin film 6)/(TD length of the PVA-based resin film 6 subjected to the stretching step)

is indicated by The "TD length" is synonymous with the width of the PVA-based resin film 6. The "stretched PVA-based resin film 6" does not necessarily refer only to the PVA-based resin film 6 (ie, the stretched film 7) at the end of the stretching step (S20), but during the stretching step (S20). The stretched PVA-based resin film 6 is also indicated.

The vertical axis of the graph shown in FIG. 4 is MD shrinkage ratio B (MD shrinkage ratio, unit: times). When the MD shrinkage factor B of the PVA-based resin film 6 provided in the stretching step (S20) is set to 1, a value less than 1 can be employed for the MD shrinkage factor B in the stretching step (S20). The MD shrinkage factor B is:

MD shrinkage ratio B [times] = (MD length of the PVA-based resin film 6 that has shrunk) / (MD length of the PVA-based resin film 6 subjected to the stretching step)

is indicated by "MD length" is synonymous with the length of the PVA system resin film 6. The "shrinked PVA-based resin film 6" does not necessarily refer only to the PVA-based resin film 6 (ie, the stretched film 7) at the end of the stretching step (S20), but during the stretching step (S20). The shrinked PVA-based resin film 6 is also indicated.

As illustrated in the stretching patterns X and Y of FIG. 4, the stretching step (S20) in the present invention includes a first stretching treatment step (S20-1) and a second stretching treatment step (S20-2) in this order. do. The stretching treatment performed in the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2) is stretching to TD (horizontal stretching) as is clear from the fact that the graph line has an inclination. It is a simultaneous biaxial stretching process in which shrinkage in MD and MD (longitudinal shrinkage) are simultaneously performed. In the stretched pattern X, between the first stretching processing step (S20-1) and the second stretching processing step (S20-2), a third stretching processing step of performing only transverse stretching is interposed. Like the stretching pattern X, the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2) may be discontinuous. In the stretching pattern Y, such a third stretching processing step is not intervened, and a second stretching processing step (S20-2) is performed following the first stretching processing step (S20-1).

In the first stretching treatment step (S20-1), in comparison at the same TD stretching ratio A, simultaneous biaxial stretching treatment is performed so that the MD shrinkage ratio B is larger than the MD shrinkage ratio in the case of transversely stretching the PVA-based resin film at the free end. do In the first stretching treatment step (S20-1), it is preferable to satisfy the above conditions throughout the entire process. "In the case of transversely stretching the PVA-based resin film at the free end" means the stretching pattern Z in Fig. 4, and is a stretching pattern in the case of performing transverse stretching (TD stretching) while freely shrinking in MD. Stretching pattern Z serving as this standard can be actually measured using the same film as the PVA-based resin film 6 (laminated film 100 when supported by a base film) provided in the stretching step (S20). .

Prior to the second stretching treatment step (S20-2), by performing the first stretching treatment step (S20-1) satisfying the above conditions, a high draw ratio in TD is possible without accompanying problems such as film breakage, Moreover, it becomes easy to obtain the stretched film 7 excellent in axial orientation in TD. In addition, it is possible to suppress appearance defects such as wrinkles in the stretched film 7 obtained by appropriately shrinking the film 7 along with transverse stretching in the initial stage of the stretching step (S20) so as to satisfy the above conditions.

The TD draw ratio A at the end of the first stretching treatment step (S20-1) preferably exceeds the elastic region of the PVA-based resin film 6 (laminated film 100 when supported by a base film) , preferably 1.5 to 4.8 times, more preferably 1.8 to 4.5 times. In addition, in the MD shrinkage ratio B at the end of the first stretching treatment step (S20-1), in the case of free end transverse stretching, most of the shrinkage occurs in this region, but in the second stretching treatment step (S20-2), In view of the fact that it is preferable to shrink the MD by a degree or more, it is preferably 0.6 to 0.97 times, and more preferably 0.65 to 0.85 times.

On the other hand, the second stretching treatment step (S20-2) is a step of performing simultaneous biaxial stretching treatment while contracting MD to a certain extent or more, and specifically, is a step of performing simultaneous biaxial stretching treatment so that MD shrinkage ratio B decreases by 0.17 or more. . The amount of decrease in the MD shrinkage ratio B referred to herein is the difference between the MD shrinkage ratio [times] at the start of the second stretching treatment step (S20-2) and the MD shrinkage ratio [B] at the end of the process. The amount of decrease in MD shrinkage ratio B in the second stretching treatment step (S20-2) is preferably 0.2 or more, and more preferably 0.25 or more.

By performing the second stretching treatment step (S20-2) that satisfies the above conditions after the first stretching treatment step (S20-1), a high draw ratio in TD becomes possible without accompanying problems such as film breakage, and , it becomes easy to obtain a stretched film 7 excellent in axial orientation in TD. If the amount of decrease in MD shrinkage factor B in the second stretching treatment step (S20-2) is too large, the resulting stretched film 7 tends to have appearance defects such as wrinkles, so the amount of decrease in MD shrinkage factor B is , is preferably 0.45 or less, more preferably 0.4 or less, still more preferably 0.35 or less.

The TD draw ratio A at the start of the second stretching treatment step (S20-2) is performed in a region exceeding the lower yield point of the PVA-based resin film 6 (laminated film 100 when supported by a base film). In terms of preference, it is preferably 4.0 times or more, and more preferably 4.3 times or more. The TD draw ratio A at the start of the second stretching treatment step (S20-2) is usually less than 5 times. In addition, the MD shrinkage ratio B at the start of the second stretching treatment step (S20-2) is preferably 0.6 to 0.97 times, more preferably 0.65 to 0.85 times, since it is preferable to sufficiently shrink in the above step. .

In the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2), TD stretching and MD shrinkage are usually performed at a constant rate from the start of the process to the end, respectively (MD shrinkage ratio). The ratio of the amount of change/the amount of change in TD stretching ratio is constant), and may be accompanied by slight speed fluctuations. As described above, the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2) may be continued, and in this case, the TD stretching at the end of the first stretching treatment step (S20-1) Magnification A and MD shrinkage ratio B are the same as the TD draw ratio A and MD shrinkage ratio B at the start of the second stretching treatment step (S20-2), respectively. In addition, when the ratio of MD shrinkage ratio change amount/TD draw ratio change amount is constant from the start to the end of the stretching step (S20), the first stretching treatment step (S20-1) or the second stretching treatment step (S20-2) ), and it is assumed that the condition of including the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2) in this order is not satisfied.

As described above, even if a third (and further fourth, fifth, ...) stretching treatment step is interposed between the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2). good night. In this case, the third stretching treatment step may be simultaneous biaxial stretching treatment or other stretching treatment such as transverse stretching or longitudinal shrinkage, but at least the ratio of MD shrinkage ratio change amount/TD draw ratio change amount is It is different from that of a process (S20-1) and a 2nd stretching treatment process (S20-2).

The stretching step (S20) may include other stretching treatment steps such as transverse stretching and longitudinal shrinkage before the first stretching treatment step (S20-1). However, from the viewpoint of sufficiently generating MD shrinkage during TD stretching to improve the orientation of the stretched film 7, it is preferable to first perform the first stretching treatment step (S20-1) in the stretching treatment step (S20). . In this case, the film provided in the first stretching treatment step (S20-1) is an unstretched PVA-based resin film 6 (laminated film 100 when supported by a base film).

The stretching step (S20) may include other stretching treatment steps such as transverse stretching and longitudinal shrinkage after the second stretching treatment step (S20-2). However, since the stress of transverse stretching increases after the lower yield point is exceeded, it is preferable to perform the second stretching treatment step (S20-2) last in the stretching treatment step (S20). In this case, the PVA-based resin film 6 is stretched until the TD draw ratio A and the MD shrink ratio B reach desired values (A _f and B _f below) by the execution of this second stretching treatment step (S20-2). By simultaneous biaxial stretching, a stretched film 7 having a final TD draw ratio A _f and a final MD shrink ratio B _f can be obtained.

The final TD draw ratio A _f in the stretched film 7 obtained by a series of stretching treatments in the stretching step (S20) is preferably 5 times or more, and more preferably 5.3 times or more. According to the stretching method according to the present invention, a TD stretching ratio of 5 or more times _Af can be achieved without causing problems such as breakage of the film or generation of wrinkles. The final TD draw ratio A _f is usually 10 times or less, preferably 7 times or less. TD stretching of more than 10 times, although depending on the thickness of the stretched film, is likely to involve film breakage.

The final MD shrinkage ratio B _f in the stretched film 7 is preferably 0.2 to 0.8 times, and more preferably 0.35 to 0.7 times. When the MD shrinkage ratio B _f is within this range, a high draw ratio in TD becomes easy, and the axial orientation in TD becomes good.

In the simultaneous biaxial stretching treatment performed in the first stretching treatment step (S20-1) and the second stretching treatment step (S20-2), which simultaneously performs stretching in TD (transverse stretching) and contraction in MD (vertical shrinkage), a well-known A tenter type stretching device can be used. 5 is a plan view schematically showing an example of the internal configuration of a tenter type stretching device. As shown in FIG. 5, the tenter type stretching device grips both ends in the width direction of a running film (PVA-based resin film 6) with a plurality of clips 50 arranged in the running direction (machine flow direction), , The film is stretched in the width direction by widening the clip interval in the width direction while moving the clip 50 together with the film in the stretching zone, and shrinking the film in the running direction by narrowing the clip interval in the running direction. More specifically, TD stretching can be performed by increasing the clip spacing D ₂ in the width direction immediately after exiting the drawing zone from the clip spacing D ₁ in the width direction in front of the drawing zone. Further, by making the clip distance G ₂ in the travel direction immediately after leaving the stretching zone smaller than the clip distance G ₁ in the travel direction in front of the stretching zone, MD contraction can be performed. The stretching pattern of the simultaneous biaxial stretching process can be controlled by adjusting the clip spacing.

The stretching temperature in the stretching step (S20) including the simultaneous biaxial stretching treatment step is to provide the PVA-based resin film 6 supported by the base film 30, that is, the laminated film 100, to the stretching step (S20). In this case, the PVA-based resin film 6 and the entire base film 30 are set to a temperature equal to or higher than the temperature exhibiting fluidity to the extent that the whole can be stretched, preferably the phase transition temperature (melting point or glass transition temperature) of the base film 30 - It is in the range of 30°C to +30°C, more preferably in the range of -30°C to +5°C, still more preferably in the range of -25°C to +0°C. When the base film 30 is composed of a plurality of resin layers, the phase transition temperature means the highest phase transition temperature among the phase transition temperatures exhibited by the plurality of resin layers.

When the stretching temperature is lower than -30°C of the phase transition temperature, it is difficult to achieve a high-magnification stretching of 5 times or more, or the flowability of the base film 30 tends to be too low, making the stretching process difficult. When the stretching temperature exceeds +30°C of the phase transition temperature, the fluidity of the base film 30 is too large, and stretching tends to be difficult. When the laminated film 100 is subjected to the stretching step (S20), the stretching temperature is within the above range, more preferably 120°C or higher, from the viewpoint that a high stretching ratio of 5 times or more is easier to achieve. Moreover, the extending|stretching temperature is 230 degreeC or less normally.

Examples of the method for heating the film in the stretching treatment include a zone heating method (for example, a method of heating in a stretching zone such as a heating furnace adjusted to a predetermined temperature by blowing hot air); There is a heater heating method (a method of heating by radiant heat by installing an infrared heater, a halogen heater, a panel heater, or the like above and below the film), and the like.

Prior to the stretching step (S20), a preheat treatment step of preheating the film provided in the extending step (S20) may be provided. As the preheating method, the same method as the heating method in the stretching treatment can be used. The preheating temperature is preferably in the range of -50°C to ±0°C of the stretching temperature, and more preferably in the range of -40°C to -10°C of the stretching temperature.

Further, after the stretching treatment in the stretching step (S20), a heat setting treatment step may be provided. The heat setting treatment is a treatment in which heat treatment is performed at a temperature equal to or higher than the crystallization temperature of PVA while maintaining a tension state in a state where the end portion of the stretched film 7 is held tightly by a clip. Crystallization of the stretched film 7 is promoted by this heat setting treatment. The temperature of the heat setting treatment is preferably in the range of -0°C to -80°C of the stretching temperature, and more preferably in the range of -0°C to -50°C of the stretching temperature.

The thickness of the stretched film 7 obtained through the stretching step (S20) may be, for example, 30 μm or less, and further 20 μm or less, but from the viewpoint of reducing the thickness of the polarizing film and further the polarizing plate, it is preferably 15 μm or less, more preferably It is preferably 10 μm or less, more preferably 7 μm or less. The thickness of the stretched film 7 is usually 2 μm or more.

As described above, the method (first embodiment) of manufacturing the stretched film 7 supported by the base film 31 using the PVA-based resin film 6 supported by the base film 30 is described in the present invention. Although the manufacturing method of the stretched film according to the above has been described, even for the PVA-based resin film that is not supported by the base film 30 and exists alone, by carrying out a predetermined stretching step as described above, breakage of the film, occurrence of wrinkles, etc. A stretched film 7 having a high TD draw ratio and high axial orientation can be obtained without any problems (second embodiment). When the PVA-based resin film 6 present alone is subjected to the stretching step (S20), the stretching temperature in the stretching step (S20) including the simultaneous biaxial stretching treatment step is preferably 150°C or higher. Moreover, the extending|stretching temperature is 230 degreeC or less normally. Also in the second embodiment, a preheat treatment step and/or a heat setting treatment step can be provided.

In the PVA-based resin film forming step (S10) (when using a base film) and the stretching step (S20), the long base film 30 (when using a base film) or the long PVA-based resin film 6 ( When not using a base film), it can be carried out continuously while conveying continuously. In this case, the stretched film 7 obtained is also long, and it usually winds up with a winding device, and becomes the roll body of the stretched film 7. Alternatively, the elongated stretched film 7 manufactured continuously may be subjected to the polarizing film forming step (dyeing step) without winding up. The length of the stretched film, which is a long product, is usually 100 m or more, and preferably 1000 m or more. Moreover, the length of a stretched film is 10000 m or less normally.

Since the stretched film 7 according to the present invention is obtained through the stretching step (S20), it has high uniaxial orientation in TD. When the refractive index in the film width direction within the film plane at a wavelength of 590 nm is n _x , and the refractive index in the direction orthogonal to the film width direction within the film plane is n _y , the stretched film 7 according to the present invention has the following formula:

Birefringence ΔP=n _x -n _y

The birefringence ΔP represented by is 0.031 or more, may be 0.032 or more, and is usually 0.04 or less. In the case where the stretched film 7 is obtained as supported by the base film 31, the birefringence ΔP of the stretched film 7 is obtained by peeling and removing the base film 31. It is measured by

<Method for producing polarizing film and polarizing plate>

The manufacturing method of the polarizing film concerning this invention manufactures a polarizing film by using the stretched film obtained by the said manufacturing method of the stretched film concerning this invention as a raw material film. According to this manufacturing method, it is possible to obtain a polarizing film exhibiting good optical performance with TD as the direction of the slow axis (absorption axis).

The stretched film as the raw material film may be the stretched film 7 supported by the base film 31 (that is, the stretched laminated film 200), or may be a single stretched film 7 not supported by the base film 30. .

Taking a method of manufacturing a polarizing film supported by a base film from the stretched laminated film 200 as an example, this manufacturing method refers to FIG. 6, the following steps:

It may be a method including a dyeing step (S30) of obtaining a polarizing laminated film by dyeing the stretched film of the stretched laminated film with a dichroic dye to form a polarizing film (polarizer layer). The polarizing laminated film is a laminated film having a base film and a polarizing film laminated thereon (ie, a polarizing film supported by the base film).

Referring to FIG. 6, the polarizing laminated film is prepared in the following process:

1st bonding process (S40) which bonds a 1st protective film on the polarizing film of a polarizing laminated film, and obtains a polarizing laminated film with a protective film

When provided to, a light-polarizing laminated film with a protective film can be obtained.

Referring to Fig. 6, the polarizing laminated film with a protective film is prepared in the following steps:

Peeling step of obtaining a polarizing plate with a single-sided protective film by peeling and removing the base film from the polarizing laminated film with a protective film (S50)

, a polarizing plate with a single-sided protective film can be obtained, which is further processed in the following steps:

2nd bonding process of bonding a 2nd protective film to the polarizing film surface of a polarizing plate with a single-sided protective film (S60)

If provided to, a polarizing plate with a double-sided protective film can be obtained.

In addition, in this specification, a film laminate containing a polarizing film and not containing a base film is referred to as a "polarizing plate".

(1) Dyeing process (S30)

Referring to FIG. 7 , this step is a step of dyeing the stretched film 7 of the stretched laminated film 200 with a dichroic dye and adsorbing orienting this to form a polarizing film (polarizer layer) 5 . Through this process, the polarizing laminated film 300 in which the polarizing film 5 is laminated on one side or both sides of the base film 31 can be obtained.

As a dichroic dye, iodine or a dichroic organic dye is specifically mentioned. Specific examples of dichroic organic dyes include, for example, Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo-Red, Brilliant Violet BK, SupraBlue G, SupraBlue GL, Supra Orange GL, Includes Direct Sky Blue, Direct First Orange S, and First Black. A dichroic dye may be used individually by 1 type, and may use 2 or more types together.

The dyeing step (S30) can be usually performed by immersing the stretched laminated film 200 in a liquid (dyeing bath) containing a dichroic dye. As the dyeing bath, a solution in which the dichroic dye is dissolved in a solvent can be used. Although water is generally used as a solvent for the dyeing solution, an organic solvent compatible with water may be further added. It is preferable that it is 0.01 to 10 weight%, and, as for the concentration of the dichroic dye in a dyeing bath, it is more preferable that it is 0.02 to 7 weight%.

In the case of using iodine as the dichroic dye, it is preferable to further add iodide to the dyeing bath containing iodine from the viewpoint of improving the dyeing efficiency. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of iodide in the dyeing bath is preferably 0.01 to 20% by weight. Among iodides, it is preferable to add potassium iodide. When potassium iodide is added, the ratio of iodine to potassium iodide is by weight, preferably 1:5 to 1:100, more preferably 1:6 to 1:80. The temperature of the dyeing bath is preferably 10 to 60°C, more preferably 20 to 40°C.

The dyeing step (S30) may include a crosslinking treatment step performed subsequent to the dyeing treatment. The crosslinking treatment can be performed by immersing the dyed stretched film in a liquid containing a crosslinking agent (crosslinking bath). Examples of the crosslinking agent include boric acid, boron compounds such as borax, glyoxal, and glutaraldehyde. A crosslinking agent may use only 1 type, and may use 2 or more types together. As the crosslinking bath, a solution in which a crosslinking agent is dissolved in a solvent can be used. Although water can be used as a solvent, you may further contain an organic solvent compatible with water. The concentration of the crosslinking agent in the crosslinking bath is preferably 1 to 20% by weight, more preferably 6 to 15% by weight.

The crosslinking bath may further contain iodide. By adding iodide, the in-plane polarization characteristic of the polarizing film 5 can be made more uniform. Specific examples of iodide are the same as above. The concentration of iodide in the crosslinking bath is preferably 0.05 to 15% by weight, more preferably 0.4 to 8% by weight. The temperature of the crosslinking bath is preferably 10 to 90°C.

Further, the crosslinking treatment may be performed simultaneously with the dyeing treatment by blending a crosslinking agent into the dyeing bath. Further, using two or more types of crosslinking baths having different compositions, the treatment of immersing in a crosslinking bath may be performed twice or more.

It is preferable to perform a washing process and a drying process after the dyeing process (S30). A washing process usually includes a water washing process. The water washing treatment can be performed by immersing the film after dyeing treatment or crosslinking treatment in pure water such as ion-exchanged water or distilled water. The water washing temperature is usually 3 to 50°C, preferably 4 to 20°C. The washing process may be a combination of a water washing process and a washing process using an iodide solution. As the drying step performed after the washing step, any suitable method such as natural drying, blow drying, heat drying, or the like can be employed. For example, in the case of heat drying, the drying temperature is usually 20 to 95°C.

The thickness of the polarizing film 5 included in the polarizing laminated film 300 may be, for example, 30 μm or less, or even 20 μm or less, but from the viewpoint of thinning the polarizing plate, it is preferably 15 μm or less, more preferably 10 μm. or less, more preferably 7 μm or less. The thickness of the polarizing film 5 is 2 micrometers or more normally. In addition, the visibility correction single transmittance Ty of the polarizing film 5 may be a value normally required in an image display device such as a liquid crystal display device to which the polarizing film or a polarizing plate containing the polarizing film is applied, and specifically, 40 to 47%. It is preferable that it is within the range of Ty is more preferably in the range of 41 to 45%, and in this case, the balance between Ty and Py becomes better. When Ty is too high, Py deteriorates and the display quality of the image display device deteriorates. When Ty is excessively low, the luminance of the image display device is lowered and the display quality is lowered, or it is necessary to increase input power in order to sufficiently increase the luminance. It is preferable that it is 99.9 % or more, and, as for the visibility correction|amendment polarization degree Py of the polarizing film 5, it is more preferable that it is 99.95 % or more. When Ty and Py of the polarizing film 5 exist as a single substance (when it exists alone), itself is measured as a measurement sample. On the other hand, when the polarizing film 5 exists as the polarizing laminated film 300 supported by the base film 31, the base film 31 is removed from the polarizing laminated film 300, and the polarizing laminated film Isolate the polarizing film 5 included in (300), use this as a measurement sample, or use the polarizing laminated film 300 itself as a measurement sample, measure Ty and Py, and measure them as polarizing film 5 of Ty and Py.

(2) 1st joining process (S40)

Referring to FIG. 8 , this step is performed on the polarizing film 5 of the polarizing laminated film 300, that is, on the surface of the polarizing film 5 opposite to the base film 31 side, the first adhesive layer 15 It is a process of obtaining the polarizing laminated film 400 with a protective film by bonding the 1st protective film 10 through ).

Moreover, when the polarizing laminated film 300 has the polarizing film 5 on both surfaces of the base film 31, the 1st protective film 10 is normally bonded on the polarizing film 5 of both surfaces, respectively. In this case, these first protective films 10 may be the same type of protective film or a different type of protective film.

The adhesive forming the first adhesive layer 15 is an active energy ray curable adhesive (preferably an ultraviolet ray curable adhesive) containing a curable compound that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays, It may be a water-based adhesive in which an adhesive component such as a polyvinyl alcohol-based resin is dissolved or dispersed in water.

As the active energy ray-curable adhesive, an active energy ray-curable adhesive composition containing a cationically polymerizable curable compound and/or a radically polymerizable curable compound can be preferably used from the viewpoint of exhibiting good adhesiveness. The active energy ray-curable adhesive may further include a cationic polymerization initiator and/or a radical polymerization initiator for initiating a curing reaction of the curable compound.

As the cationically polymerizable curable compound, for example, an epoxy-based compound (a compound having one or two or more epoxy groups in a molecule), an oxetane-based compound (a compound having one or two or more oxetane rings in a molecule), or Combinations of these are exemplified. Examples of the radically polymerizable curable compound include (meth)acrylic compounds (compounds having one or two or more (meth)acryloyloxy groups in the molecule), other vinyl compounds having radically polymerizable double bonds, or Combinations of these are exemplified. A cationic polymerizable curable compound and a radical polymerizable curable compound may be used together.

Active energy ray-curable adhesives, if necessary, cationic polymerization accelerator, ion trapping agent, antioxidant, chain transfer agent, tackifier, thermoplastic resin, filler, flow regulator, plasticizer, antifoaming agent, antistatic agent, leveling agent, solvent, etc. May contain additives.

When the first protective film 10 is bonded using an active energy ray-curable adhesive, the first protective film 10 is formed on the polarizing film 5 through the active energy ray-curable adhesive, which becomes the first adhesive layer 15. After lamination, the adhesive layer is cured by irradiating active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. Among them, ultraviolet rays are suitable, and as a light source in this case, a low-pressure mercury-vapor lamp, a medium-pressure mercury-vapor lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excited mercury lamp, a metal halide lamp, or the like can be used. In the case of using a water-based adhesive, the first protective film 10 may be laminated on the polarizing film 5 through the water-based adhesive and then heat-dried.

In bonding the first protective film 10 to the polarizing film 5, the bonding surface of the first protective film 10 and/or the polarizing film 5 is to improve adhesion with the polarizing film 5. For this purpose, surface treatment (adhesion-facilitating treatment) such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, or saponification treatment can be performed, and among them, plasma treatment, corona treatment, or saponification treatment is preferably performed. .

The first protective film 10 is made of a light-transmitting (preferably optically transparent) thermoplastic resin, for example, a polyolefin such as chain polyolefin-based resin (polypropylene-based resin or the like) or cyclic polyolefin-based resin (norbornene-based resin or the like). system resin; cellulose ester-based resins such as cellulose triacetate and cellulose diacetate; polyester-based resin; polycarbonate-based resin; (meth)acrylic resin; polystyrene-based resin; Alternatively, it may be a film made of a mixture or copolymer thereof.

The first protective film 10 may be a protective film having both optical functions such as a retardation film or a brightness enhancing film. For example, a retardation film having an arbitrary retardation value can be obtained by stretching the film made of the thermoplastic resin (eg, uniaxial stretching or biaxial stretching) or forming a liquid crystal layer or the like on the film.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resins and polypropylene resins, as well as copolymers composed of two or more types of chain olefins.

Cyclic polyolefin resin is a general term for resins polymerized using cyclic olefins as polymerized units. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically random copolymers), and these graft polymers modified with unsaturated carboxylic acids or derivatives thereof, hydrides thereof, and the like. Among them, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer as the cyclic olefin is preferably used.

Cellulose ester-type resin is an ester of a cellulose and a fatty acid. Specific examples of the cellulose ester-based resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Copolymers of these or those in which a part of hydroxyl groups are modified with other substituents can also be used. Among these, cellulose triacetate (triacetyl cellulose: TAC) is particularly preferred.

Polyester-based resins are resins other than the above cellulose ester-based resins that have ester bonds, and are generally composed of polycondensates of polyhydric carboxylic acids or derivatives thereof and polyhydric alcohols. Dicarboxylic acids or derivatives thereof may be used as polyhydric carboxylic acids or derivatives thereof, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalene dicarboxylic acid. As the polyhydric alcohol, diols can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol.

Specific examples of the polyester-based resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexane dimethyl terephthalate, and polycyclohexane. Contains dimethylnaphthalate.

A polycarbonate-type resin consists of a polymer to which monomer units are bonded via a carbonate group. The polycarbonate-based resin may be a resin called a modified polycarbonate obtained by modifying a polymer skeleton, a copolymerized polycarbonate, or the like.

A (meth)acrylic resin is a resin which uses a compound having a (meth)acryloyl group as a main constituent monomer. Specific examples of the (meth)acrylic resin include poly(meth)acrylic acid esters such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-(meth)acrylic acid ester copolymer; methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer; methyl (meth)acrylate-styrene copolymers (such as MS resin); and copolymers of methyl methacrylate and a compound having an alicyclic hydrocarbon group (eg, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). Preferably, a polymer containing poly(meth)acrylic acid C _1-6 alkyl ester as a main component such as poly(meth)acrylate is used, more preferably, methyl methacrylate as a main component (50 to 100% by weight, Preferably 70 to 100% by weight) of methyl methacrylate-based resin is used.

In addition, the description about each thermoplastic resin shown above is applicable also about the thermoplastic resin which comprises the base film 30.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, or an antifouling layer may be formed on the surface of the first protective film 10 opposite to the polarizing film 5 . In addition, the first protective film 10 may contain one or more additives such as a lubricant, a plasticizer, a dispersant, a heat stabilizer, an ultraviolet absorber, an infrared absorber, an antistatic agent, and an antioxidant.

The thickness of the first protective film 10 is preferably 90 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less, from the viewpoint of thinning the polarizing plate. The thickness of the first protective film 10 is usually 5 μm or more from the viewpoint of strength and handleability.

(3) Peeling process (S50)

Referring to FIG. 9 , this step is a step of obtaining a polarizing plate 1 with a single-sided protective film by peeling and removing the base film 31 from the polarizing laminated film 400 with a protective film. When the polarizing laminated film 300 has the polarizing film 5 on both sides of the base film 31 and the first protective film 10 is bonded to both polarizing films 5, this peeling step ( In S50), two polarizing plates 1 with single-sided protective films can be obtained from one polarizing laminated film 300.

The method of peeling and removing the base film 31 is not particularly limited, and can be peeled by the same method as the separator (peeling film) peeling step performed with a normal polarizing plate with an adhesive. The base film 31 may be peeled immediately after the first bonding step (S40) as it is, or may be wound up in a roll form once after the first bonding step (S40), and may be peeled while unwinding in a subsequent step.

(4) Second bonding process (S60)

Referring to FIG. 10, this step is performed on the polarizing film 5 of the polarizing plate 1 with a single-sided protective film, that is, on the surface opposite to the first protective film 10 bonded in the first bonding step (S40), It is the process of further bonding the 2nd protective film 20 via the 2nd adhesive layer 25, and obtaining the polarizing plate 2 with a double-sided protective film. Bonding of the second protective film 20 through the second adhesive layer 25 can be performed in the same manner as bonding of the first protective film 10 . Regarding the configuration and materials of the second protective film 20 and the second adhesive layer 25, descriptions of the first protective film 10 and the first adhesive layer 15 are cited, respectively.

In the above, the method for producing a polarizing film (polarizing laminated film, polarizing laminated film with a protective film) and further a polarizing plate using a stretched film (stretched laminated film) supported by a base film has been described, but it is not supported by a base film. Even in the case of using a single stretched film that is not used, a polarizing film can be manufactured similarly by performing dyeing treatment. Moreover, a polarizing plate with a single-sided protective film or a polarizing plate with a double-sided protective film can be manufactured by bonding a protective film to single side|surface or both surfaces of this polarizing film through an adhesive bond layer in the same way.

On the polarizing film 5 in the polarizing plate 1 with a single-sided protective film shown in FIG. 9, or the first protective film 10 or the second protective film on the polarizing plate 2 with a double-sided protective film shown in FIG. 10 On (20), you may laminate|stack the adhesive layer for bonding a polarizing plate to another member (for example, a liquid crystal cell in the case of application to a liquid crystal display device). The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually made of a pressure-sensitive adhesive composition obtained by adding a (meth)acrylic resin, a styrene-based resin, a silicone-based resin, or the like as a base polymer, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound thereto. Moreover, it is also possible to make a pressure-sensitive adhesive layer exhibiting light scattering properties by containing fine particles. The thickness of the pressure-sensitive adhesive layer is usually 1 to 40 μm, preferably 3 to 25 μm.

The polarizing plate 1 with a single-sided protective film and the polarizing plate 2 with a double-sided protective film further include other optical layers laminated on the first and/or second protective films 10 and 20 or the polarizing film 5. can do. Other optical layers include a reflective polarizing film that transmits some kind of polarized light and reflects polarized light exhibiting the opposite property; A film having an anti-glare function having a concavo-convex shape on the surface; Films with surface antireflection; a reflective film having a reflective function on its surface; A transflective reflective film having both a reflective function and a transmissive function; A viewing angle compensation film etc. are mentioned.

By using a stretched film uniaxially oriented in TD, a polarizing film and a polarizing plate having TD as an absorption axis direction can be provided. If such a polarizing plate is used as one of a pair of polarizing plates constituting a liquid crystal panel, the pair of polarizing plates can be directly bonded to the liquid crystal cell without distorting their MDs by 90°. That is, roll-to-panel bonding is possible in which the pair of polarizers are bonded to the liquid crystal cell so that their MDs are parallel, and the absorption axes of the pair of polarizers are orthogonal to each other. In addition, according to the long polarizing plate having TD as the direction of the absorption axis, roll-to-roll bonding becomes possible when bonding with a brightness enhancing film (reflection type polarizing plate).

Example

Hereinafter, the present invention will be described more specifically by showing examples and comparative examples, but the present invention is not limited by these examples. In the following examples, the birefringence ΔP of the stretched film, the breakability of the film during the stretching step, the external appearance quality of the stretched film, the visibility corrected single transmittance Ty and the visibility corrected polarization degree Py of the polarizing film are determined according to the following measurement methods and evaluation methods. .

[a] Measurement of birefringence ΔP of a stretched film

A stretched film obtained by peeling and removing the base film from the stretched laminated film was used as a sample, and birefringence ΔP at a wavelength of 590 nm based on the above formula was measured using a retardation measuring device “KOBRA-WR” manufactured by Ouji Instruments Co., Ltd. Measured. The results are shown in Table 1.

[b] Evaluation of breakability of the film during the stretching step

According to the following evaluation criteria, the breakage of the film at the time of extending|stretching a laminated|multilayer film was evaluated. The results are shown in Table 1.

A: There is no film breakage,

B: The number of film breaks per 10 m of laminated film is 1 time,

C: The number of film breaks per 10 m of laminated film is 2 or more.

[c] Evaluation of appearance quality of stretched film

The stretched film of the obtained stretched laminated film was visually observed, and the appearance quality was evaluated according to the following evaluation criteria. The results are shown in Table 1.

A: No wrinkles,

B: Some wrinkles are visible,

C: Many wrinkles are visible.

[d] Measurement of visibility-corrected single transmittance Ty and visibility-corrected polarization degree Py of polarizing film

Using the light-polarizing laminated film as a sample, the visibility corrected single transmittance Ty and the visibility corrected polarization degree Py were measured using a spectrophotometer ("V7100" manufactured by Nippon Bunko Co., Ltd.). In the measurement, the polarizing laminated film sample was set so that the polarizing film side was irradiated with incident light. The results are shown in Table 1.

<Example 1>

(1) Primer layer formation process

PVA powder (“Z-200” manufactured by Nippon Synthetic Chemical Industries, Ltd., average degree of polymerization 1100, degree of saponification 99.5 mol%) was dissolved in hot water at 95° C. to prepare a PVA aqueous solution having a concentration of 3% by weight. A crosslinking agent (“Sumirez Resin 650” manufactured by Taoka Chemical Industry Co., Ltd.) was mixed with the obtained aqueous solution at a ratio of 5 parts by weight to 6 parts by weight of PVA powder to obtain a coating solution for forming a primer layer.

Next, as a base film, an unstretched polypropylene (PP) film (melting point: 163° C.) having a thickness of 90 μm is prepared, one side thereof is corona-treated, and the corona-treated side is coated with a small-diameter gravure coater. A primer layer having a thickness of 0.2 μm was formed by coating the coating solution for forming a primer layer and drying the coating solution at 80° C. for 10 minutes.

(2) Preparation of laminated film (PVA-based resin film forming step)

Polyvinyl alcohol powder ("PVA124" manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 98.0 to 99.0 mol%) was dissolved in hot water at 95 ° C. to prepare a polyvinyl alcohol aqueous solution having a concentration of 8% by weight, This was used as the coating liquid for forming a PVA-based resin film. After coating the coating solution for forming the PVA-based resin film using a die coater on the surface of the primer layer of the base film having the primer layer prepared in (1) above, by drying at 70 ° C. for 4 minutes, the PVA on the primer layer A base resin film was formed to obtain a long laminated film. The thickness of the PVA-based resin film (PVA-based resin layer) was 9 μm.

(3) Production of stretched film (stretching process)

With respect to the long laminated film produced in (2) above, while continuously unwinding, simultaneous biaxial stretching in TD (transverse stretching) and shrinkage in MD (longitudinal shrinkage) are simultaneously performed according to the stretching pattern shown in FIG. 11 . The stretching treatment including the first stretching treatment step and the second stretching treatment step, which are the stretching treatment, was continuously performed using a tenter-type stretching device to obtain a long stretched laminated film. The stretching treatment was performed at 160°C (the same applies to the following comparative examples). The stretching pattern was controlled by adjusting the clip spacing. The final TD draw ratio A _f and the final MD shrink ratio B _f in the stretched laminated film were set to 5.5 times and 0.5 times, respectively (similar to the following comparative examples). The thickness of the stretched film (PVA-based resin layer) in the stretched laminated film was about 3 µm. A stretched laminated film exceeding 100 m in length was obtained without breakage of the film in the stretching step.

(4) Preparation of polarizing laminated film (dyeing process)

The stretched laminated film prepared in (3) above is immersed in a 30 ° C. dyeing solution containing iodine and potassium iodide (including 0.4 parts by weight of iodine and 5.0 parts by weight of potassium iodide per 100 parts by weight of water) for about 70 seconds, and then immersed in PVA. After performing the dyeing treatment of the film, the excess dyeing solution was washed off with pure water at 10°C.

Then, it was immersed in a 78 ° C. first crosslinking aqueous solution containing boric acid (including 10.4 parts by weight of boric acid per 100 parts by weight of water) for 120 seconds, and then 70 ° C. 5.0 parts by weight of boric acid and 12.0 parts by weight of potassium iodide per part by weight) were immersed for 60 seconds to perform crosslinking treatment. Then, it was immersed in pure water at 10°C for about 10 seconds and finally dried at 80°C for 300 seconds to obtain a polarizing laminated film containing a polarizing film. Ty and Py of the polarizing film were 41.5% and >99.99%, respectively.

<Example 2>

A stretched laminated film was obtained in the same manner as in Example 1 except that the stretched pattern in the stretching step was changed as shown in FIG. 11 . The thickness of the stretched film (PVA-based resin layer) in the stretched laminated film was about 3 µm. Furthermore, a light-polarizing laminated film containing a polarizing film was obtained in the same manner as in Example 1 except that the obtained stretched laminated film was used. At this time, Ty of the polarizing film was set to 41.5% by adjusting the immersion time in the dyeing aqueous solution. Py of the polarizing film was >99.99%.

<Comparative Examples 1 to 4>

A stretched laminated film was obtained in the same manner as in Example 1 except that the stretched pattern in the stretching step was changed as shown in FIG. 11 . The thickness of the stretched film (PVA-based resin layer) in the stretched laminated film was all about 3 µm. Furthermore, a light-polarizing laminated film containing a polarizing film was obtained in the same manner as in Example 1 except that the obtained stretched laminated film was used. At this time, Ty of the polarizing film was set to 41.5% by adjusting the immersion time in the dyeing aqueous solution (however, Ty and Py were not measured in Comparative Example 4). In Comparative Example 3, no breakage of the film occurred in the stretching step, and a stretched laminated film exceeding 100 m in length was obtained. However, in Comparative Examples 1, 2 and 4, film breakage occurred and the length of the obtained stretched laminated film was They were about 10 m, less than 10 m, and less than 10 m, respectively.

DESCRIPTION OF SYMBOLS 1: Polarizing plate with single-sided protective film, 2: Polarizing plate with double-sided protective film, 5: Polarizing film (polarizer layer), 6: PVA-type resin film (PVA-type resin layer), 7: Stretched film, 10: 1st protective film, 15: first adhesive layer, 20: second protective film, 25: second adhesive layer, 30: base film, 31: stretched base film, 50: clip, 100: laminated film, 200: stretched laminated film, 300: Polarizing laminated film, 400: Polarizing laminated film with protective film.

Claims (10)

A stretching step of obtaining a stretched film having a TD draw ratio of A _f [times] and an MD shrink ratio of B _f [times] by stretching the polyvinyl alcohol-based resin film,
The stretching process,
In comparison at the same TD stretching ratio, the first stretching treatment step of simultaneously performing TD stretching and MD shrinkage such that the MD shrinkage ratio is greater than the MD shrinkage ratio in the case of transversely stretching the polyvinyl alcohol-based resin film at the free end. class,
A second stretching treatment step in which stretching to TD and shrinkage to MD are simultaneously performed so that the MD shrinkage ratio decreases by 0.17 or more.
in this order,
The manufacturing method of the stretched film whose TD draw ratio of the said polyvinyl alcohol-type resin film at the time of the start of the said 2nd stretching treatment process is 4.0 times or more. The manufacturing method according to claim 1, wherein the TD draw ratio of the polyvinyl alcohol-based resin film at the start of the second stretching treatment step is 4.3 times or more. The method according to claim 1 or 2, by performing the second stretching treatment step, the TD draw ratio of the polyvinyl alcohol-based resin film reaches A _f [times], and the MD shrinkage ratio reaches B _f [times]. manufacturing method. According to claim 1 or 2,
The polyvinyl alcohol-based resin film is an unstretched film,
A manufacturing method in which the first stretching treatment step is performed first in the stretching step. The manufacturing method according to claim 1 or 2, wherein the MD shrinkage ratio B _f of the stretched film is 0.2 to 0.8 times. The manufacturing method according to claim 1 or 2, wherein the TD draw ratio A _f of the stretched film is 5 times or more. The manufacturing method according to claim 1 or 2, wherein the stretched film laminated on the base film is obtained by stretching the laminated film having the polyvinyl alcohol-based resin film on the base film. The manufacturing method according to claim 1 or 2, wherein the stretched film has a thickness of 30 µm or less. delete A step of obtaining a stretched film by the manufacturing method according to claim 1 or 2;
Step of dyeing the stretched film with a dichroic dye
Method for producing a polarizing film comprising a.

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