CN107399095B - Method for producing laminated film and method for producing polarizing plate - Google Patents

Abstract

The invention provides a method for manufacturing a laminated film and a method for manufacturing a polarizing plate, wherein the generation of winding offset during the winding of the laminated film is reduced. The method for manufacturing a laminated film includes: a resin layer forming step of forming a resin layer by applying a coating liquid containing a PVA-based resin to at least one surface of a base film and then drying the coating liquid; a stretching step of stretching the obtained laminate to obtain a stretched film in which a stretched base film and a resin film formed on at least one surface of the stretched base film are laminated; a first bonding step of bonding a protective film to the surface of the resin film to obtain a laminated film; and a winding step of winding the laminate film by a winding roller, wherein at the start of the winding step, the tension per unit width applied to the laminate film is 30N/m or more, that is, the absolute value of the charge amount of the laminate film wound on the winding roller is 32kV or less.

Description

Method for producing laminated film and method for producing polarizing plate

Technical Field

The present invention relates to a method for producing a laminated film and a method for producing a polarizing plate.

Background

Conventionally, polarizing plates have been widely used as a supply element of polarized light in a display device such as a liquid crystal display device and as a detection element of polarized light. As a polarizing plate, a polarizing plate having a structure in which a protective film is attached to one surface or both surfaces of a polarizing film (polarizer) using an adhesive is known.

In recent years, as liquid crystal display devices have been made higher in performance and thinner, the polarizing plate has been required to be thinner. For example, a polarizing plate having a thickness of 10 μm or less is produced by forming a resin layer made of a polyvinyl alcohol resin (hereinafter, the "polyvinyl alcohol" may be referred to as "PVA") as a forming material on a thermoplastic resin substrate, and then stretching and dyeing the resulting laminate (for example, patent document 1).

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2011-002816

Problems to be solved by the invention

In the above-described production of a polarizing plate, when the stretching step and the dyeing step are not continuous steps, the stretched film may be wound into a roll, and then the roll may be conveyed to the next step, and the film may be wound out again and dyed. Before the film is wound, a step of bonding a protective film (also referred to as a release film, a surface protection film, or the like) to the surface of the resin layer is often performed for the purpose of protecting the resin layer in the film.

However, when a film in which a seed film is laminated on the surface of a PVA-based resin layer is wound, positional deviation (winding deviation) of the end portion in the width direction of the film may occur. When a polarizing plate is produced from a film in which winding displacement has occurred, the flatness of the polarizing plate may be deteriorated, and scratches, wrinkles, and the like may be generated. Conventionally, the cause of the occurrence of the winding displacement has not been sufficiently identified, and a method for reducing the occurrence of the winding displacement has not been identified.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object of an aspect of the present invention is to provide a method for producing a laminated film, which reduces the occurrence of winding displacement when the laminated film is wound. Another object is to provide a method for producing a polarizing plate using the laminated film obtained by the above-described production method.

Means for solving the problems

The present inventors have made extensive studies to solve the above problems, and as a result, have found that the larger the absolute value of the charge amount of the laminate film, the more winding displacement occurs at the time of winding. Accordingly, the present inventors have found that winding displacement during winding can be reduced by defining an upper limit value of an absolute value of a charge amount of a laminate film, and have completed the present invention.

One aspect of the present invention provides a method for producing a laminated film, including: a resin layer forming step of forming a resin layer using a polyvinyl alcohol resin as a forming material on at least one surface of a strip-shaped base film by applying a coating liquid containing the polyvinyl alcohol resin to at least one surface of the base film while conveying the base film in a longitudinal direction, and then drying the coating liquid; a stretching step of stretching the laminate obtained in the resin layer forming step while conveying the laminate in a longitudinal direction to obtain a stretched base film and a stretched film in which a resin film formed on at least one surface of the stretched base film is laminated, wherein the stretched base film is a film obtained by stretching a base film; a first bonding step of bonding a protective film to a surface of a resin film to obtain a laminated film in which an extended base film, the resin film, and the protective film are laminated in this order; and a winding step in which the laminate film is wound by a winding roller, wherein at the start of the winding step, the tension per unit width applied to the laminate film is 30N/m or more, and the absolute value of the charge amount of the laminate film wound around the winding roller is 32kV or less.

In one aspect of the present invention, it is preferable that the protective film contains a polyolefin-based resin as a forming material.

In one aspect of the present invention, in the stretching step, the laminate is preferably uniaxially stretched in the longitudinal direction by a circumferential speed difference between the first nip roller and the second nip roller by passing the laminate through the first nip roller and the second nip roller in order.

In one aspect of the present invention, it is preferable that the tension per unit width applied to the laminated film at the start of the winding process is 90N/m or less.

One aspect of the present invention provides a method for manufacturing a polarizing plate, including: a step of obtaining a laminated film by the above-described method for producing a laminated film; a first peeling step of taking out the laminated film and peeling the seed film from the laminated film; a dyeing step of dyeing the stretched film obtained in the first peeling step with a dichroic substance to obtain a polarizing laminate film in which a stretched base film and a polarizing plate layer formed on at least one surface of the stretched base film are laminated; and a second bonding step of bonding a protective film to at least the surface of the polarizer layer of the polarizing laminate film.

In one aspect of the present invention, it is preferable that the second bonding step is followed by a second peeling step of peeling the stretched base material film.

Effects of the invention

According to one aspect of the present invention, there is provided a method for producing a laminated film, in which occurrence of winding displacement at the time of winding the laminated film is reduced. Also provided is a method for producing a polarizing plate using the laminated film obtained by the above-described production method.

Drawings

Fig. 1 is a flowchart illustrating a method for manufacturing a laminated film according to the present embodiment.

Fig. 2 is a process diagram showing the first bonding step S3 and the winding step S4.

Fig. 3 is a flowchart showing a method for manufacturing a polarizing plate according to the present embodiment.

Description of reference numerals:

11 … stretched film, 13 … laminated film, 21 … protective film, 101, 113 … nip roll, 115 … take-up roll.

Detailed Description

< method for producing laminated film >

An embodiment of the method for producing a laminated film of the present invention will be described below with reference to fig. 1. In all the drawings below, the dimensions, ratios, and the like of the respective components are appropriately different in order to facilitate the viewing of the drawings.

Fig. 1 is a flowchart illustrating a method for manufacturing a laminated film according to the present embodiment. As shown in fig. 1, the method for producing a laminate film of the present embodiment includes a resin layer forming step S1, an extending step S2, a first bonding step S3, and a winding step S4.

[ resin layer Forming Process S1]

In the resin layer forming step S1, a resin layer made of a polyvinyl alcohol resin (hereinafter, polyvinyl alcohol may be referred to as "PVA") is formed on at least one surface of the base film.

Specifically, first, a coating liquid containing a PVA-based resin is applied to at least one surface of a belt-shaped base film while the base film is conveyed in the longitudinal direction. After coating, a coating layer containing a PVA-based resin is formed on at least one surface of the base film. Next, the coating layer is dried to form a resin layer.

As the base film, a film conventionally used as a protective film of a polarizing plate can be used, and as a material for forming the base film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture cuttability, isotropy, stretchability, and the like is used.

Examples of such thermoplastic resins include polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins (norbornene resins), polyester resins, (meth) acrylic resins, cellulose ester resins such as cellulose triacetate and cellulose diacetate, polycarbonate resins, polyvinyl alcohol resins, polyvinyl acetate resins, polyarylate resins, polystyrene resins, polyether sulfone resins, polysulfone resins, polyamide resins, polyimide resins, and mixtures thereof. Further, a copolymer obtained by copolymerizing monomers of the above resin may be used as a material for forming the base film. Among them, polyolefin resins such as polypropylene and polyester resins such as amorphous polyethylene terephthalate are preferable.

The base film is formed of one or two or more thermoplastic resins. The substrate film may have a single-layer structure composed of one thermoplastic resin layer or a multilayer structure in which a plurality of thermoplastic resin layers are stacked. The base film is preferably formed of a resin that can be stretched at a stretching temperature suitable for stretching the resin layer in a stretching step performed after the resin layer forming step.

The base film may contain additives such as an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a mold release agent, an anti-coloring agent, a flame retardant, a nucleating agent, an antistatic agent, a pigment, and a coloring agent, as long as the effects of the present invention are not impaired.

The thickness of the base film is preferably 1 to 500 μm, more preferably 1 to 300 μm, still more preferably 5 to 200 μm, and particularly preferably 5 to 150 μm from the viewpoint of strength and handling property.

As the PVA-based resin, a resin obtained by saponifying a polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and another monomer copolymerizable with vinyl acetate.

Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

The PVA-based resin is preferably completely saponified. The saponification degree of the PVA resin is preferably 80.0 mol% or more and 99.5 mol% or less, more preferably 90.0 mol% or more and 99.5 mol% or less, and still more preferably 94.0 mol% or more and 99.0 mol% or less. When the saponification degree of the PVA-based resin is less than 80.0 mol%, water resistance and moist heat resistance may be reduced when the PVA-based resin is formed into a polarizing plate. In addition, if the saponification degree of the PVA-based resin is greater than 99.5 mol%, the dyeing speed may be reduced in the polarizing plate production process, the productivity may be reduced, and a polarizing plate having sufficient polarizing performance may not be obtained.

The saponification degree (unit: mol%) of the PVA-based resin is a value represented by a unit ratio (unit: mol%) of the ratio of the change of the acetoxy group contained in the polyvinyl acetate-based resin, which is a raw material of the PVA-based resin, to the hydroxyl group through the saponification step, and is a numerical value defined by the following formula (S1). This value can be determined by a method prescribed in JIS K6726 (1994).

Degree of saponification (number of hydroxyl groups)/(number of hydroxyl groups + number of acetoxy groups) × 100 … (S1)

The higher the degree of saponification of the PVA resin, the higher the proportion of hydroxyl groups, that is, the lower the proportion of acetate groups inhibiting crystallization.

The PVA resin may be a partially modified PVA. For example, a PVA-based resin is modified with an olefin such as ethylene or propylene, an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or crotonic acid, an alkyl ester of an unsaturated carboxylic acid, acrylamide or the like to obtain a resin, and the like. The proportion of modification is preferably less than 30 mol%, more preferably less than 10 mol%. When the modification is performed in an amount exceeding 30 mol%, the dichroic material is less likely to be adsorbed, and the polarizing performance of the polarizing plate may be lowered.

The average polymerization degree of the PVA-based resin is not particularly limited, but is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average polymerization degree of the PVA-based resin can be determined by a method prescribed in JIS K6726 (1994) in the same manner as the saponification degree.

Examples of the PVA-based resin having such characteristics include PVA124 (degree of saponification: 98.0 to 99.0 mol%), PVA117 (degree of saponification: 98.0 to 99.0 mol%), PVA624 (degree of saponification: 95.0 to 96.0 mol%) and PVA617 (degree of saponification: 94.5 to 95.5 mol%) manufactured by Korea; examples thereof include AH-26 (saponification degree: 97.0 to 98.8 mol%), AH-22 (saponification degree: 97.5 to 98.5 mol%), NH-18 (saponification degree: 98.0 to 99.0 mol%), and N-300 (saponification degree: 98.0 to 99.0 mol%); examples of the "resin" include JC-33 (degree of saponification: 99.0 mol% or more), JM-33 (degree of saponification: 93.5 to 95.5 mol%), JM-26 (degree of saponification: 95.5 to 97.5 mol%), JP-45 (degree of saponification: 86.5 to 89.5 mol%), JF-17 (degree of saponification: 98.0 to 99.0 mol%), JF-17L (degree of saponification: 98.0 to 99.0 mol%), and JF-20 (degree of saponification: 98.0 to 99.0 mol%).

The coating liquid containing a PVA-based resin is obtained by swelling powder, pulverized product, cut product, or the like of the PVA-based resin with a solvent, and then heating and stirring the swollen PVA-based resin. As the solvent, for example, water is preferable. The concentration of the PVA-based resin in the coating liquid is preferably 5 mass% or more and 15 mass% or less, and more preferably 5 mass% or more and 10 mass% or less.

The coating liquid containing the PVA-based resin is applied by a conventionally known coating method. Examples of the conventionally known coating method include a roll coating method such as a wire bar coating method, a reverse coating method, and a gravure coating method, a die coating method, a comma coating method, a die lip coating method, a screen coating method, an injection coating method, a dipping method, and a spraying method. The coating liquid may be applied to only one surface of the substrate film, or may be applied to both surfaces.

The obtained coating layer is dried by a conventionally known apparatus. Examples of a conventionally known device include a device including a plurality of drying rollers having rotation axes parallel to each other. The drying of the coating layer may be performed under reduced pressure as necessary. Further, as a method for drying the coating layer by heating, for example, drying by a hot roll, warm air drying, or the like can be given.

The thickness of the resin layer obtained in the resin layer forming step S1 may be appropriately determined depending on the desired thickness of the laminated film and the draw ratio in the subsequent drawing step, but is preferably 3 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less, for example.

In order to improve the adhesion between the base film and the resin layer, at least the surface of the base film on the side where the resin layer is to be formed may be subjected to a surface treatment. Examples of such surface treatment include corona treatment, plasma treatment, flame (flame) treatment, and the like. In addition, a coating layer may be formed on the base film via an undercoat layer or the like for the same purpose.

As a material for forming the undercoat layer, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture cuttability, isotropy, stretchability, and the like is used. Examples of such thermoplastic resins include (meth) acrylic resins and polyvinyl alcohol resins.

The material for forming the undercoat layer is preferably a PVA-based resin, and more preferably a PVA resin, because it can exhibit good adhesion to both the substrate film and the resin layer.

As a method for forming the undercoat layer, for example, a method in which a mixed solution of the resin and the solvent is applied to the surface of the base film and then dried is given. The solvent is not particularly limited as long as it can dissolve the resin, and water is preferred. The method of applying the primer layer is the same as the method of applying the coating liquid containing the PVA-based resin. The drying temperature for forming the undercoat layer is preferably 50 to 200 ℃, and more preferably 60 to 150 ℃. When water is contained as the solvent, the drying temperature is preferably 80 ℃ or higher.

The undercoat layer may contain a crosslinking agent for the purpose of increasing the strength thereof. Specific examples of the crosslinking agent include epoxy-based, isocyanate-based, dialdehyde-based, metal-based, or polymer-based crosslinking agents. Examples of the metal-based crosslinking agent include metal salts, metal oxides, metal hydroxides, and organic metal compounds. When a polyvinyl alcohol resin is used as a material for forming the undercoat layer, a polyamide epoxy resin, a methylolated melamine resin, a dialdehyde crosslinking agent, a metal chelate compound crosslinking agent, or the like is preferably 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 of the primer layer is less than 0.05 μm, the adhesion between the substrate film and the resin layer may not be sufficiently obtained.

[ elongation step S2]

In the stretching step S2, the laminate obtained in the resin layer forming step S1 is stretched while being conveyed in the longitudinal direction, to obtain a stretched film. The stretched film is formed by laminating a stretched base film obtained by stretching a base film and a resin film formed on at least one surface of the stretched base film.

The stretching ratio in the stretching step S2 may be appropriately selected depending on the desired polarizing performance when formed into a polarizing plate, and is preferably greater than 5 times and 17 times or less, and more preferably greater than 5 times and 8 times or less, with respect to the original length of the laminate. When the draw ratio exceeds 5 times, the orientation of the PVA-based resin is sufficient, and therefore, sufficient polarizing performance can be obtained when the PVA-based resin is formed into a polarizing plate. On the other hand, if the draw ratio is 17 or less, the stretched film is less likely to be broken, and workability and handleability in the subsequent steps can be sufficiently ensured.

If the draw ratio is within the above range, the drawing step S2 may be performed in multiple stages. In this case, all the multistage stretching may be performed continuously before the subsequent dyeing step, or the stretching after the second stage may be performed simultaneously with the dyeing step. In such an embodiment, for example, the first stage of drawing may be performed in a dry manner so that the draw ratio is more than 1.1 times and 3.0 times or less, and the second stage of drawing may be performed in water (for example, a dyeing bath or a crosslinking bath described later) so that the draw ratio is 2 times or more and 5 times or less.

The extending direction in the extending step S2 may be the longitudinal direction of the laminate (the transport direction of the laminate), the width direction, or an oblique direction. The stretching step S2 is preferably longitudinal uniaxial stretching in which the laminate is uniaxially stretched in the longitudinal direction. Specifically, the laminate is preferably passed through the first nip roller and the second nip roller in this order, and is uniaxially stretched in the longitudinal direction by the circumferential speed difference between the first nip roller and the second nip roller.

In the stretching step S2, either wet stretching or dry stretching may be used, but the dry stretching is preferred because the stretching temperature can be selected from a wide range.

The stretching temperature is preferably set to a temperature at which fluidity is exhibited to such an extent that the laminate can be stretched, and is preferably 80 ℃ to 170 ℃, and more preferably 90 ℃ to 160 ℃.

The thickness of the resin film in the stretched film is preferably 1 μm or more and 10 μm or less, and more preferably 2 μm or more and 7 μm or less. When the thickness of the resin film is in the above range, the polarizing plate can be easily dyed with a dichroic material during the production thereof, and the polarizing plate can be formed with excellent polarizing performance.

The length of the resulting stretched film in the longitudinal direction is preferably 1000m or more, and may be 2000m or more. The longer the length of the oriented film in the longitudinal direction, the more likely the winding displacement occurs in the subsequent winding step S4, but according to the present embodiment, even if the length of the oriented film in the longitudinal direction is 2000m or more, the occurrence of the winding displacement can be effectively reduced.

[ first bonding step S3]

Fig. 2 is a process diagram showing the first bonding step S3 and the winding step S4. As shown in fig. 2, in the first bonding step S3, the seed film 21 is bonded to the surface of the resin film in the stretched film 11 conveyed by the nip roller 101, to obtain the laminated film 13. The laminated film is formed by sequentially laminating an extended base film, a resin film, and a seed film.

By forming the laminate film 13 by bonding the seed film 21, the resin film can be protected in the subsequent winding step S4. Further, by bonding the protective film 21, the laminate film 13 can be wound and unwound beautifully and smoothly.

The pellicle film 21 is not particularly limited as long as it has adhesiveness to the stretched film 11 and can be wound in the subsequent winding step S4. The pellicle film 21 is formed by laminating an adhesive-releasable resin layer or an adhesive resin layer on a film made of a thermoplastic resin as a material, as required.

The thermoplastic resin includes, for example, a polyolefin resin or a polyester resin, and preferably includes a polyolefin resin. The polyolefin resin may have a chain structure or a ring structure. Examples of the polyolefin resin include polyimide resins, polyethylene, polypropylene, and ethylene-propylene copolymers.

Examples of the adhesion-releasable resin layer include acrylic adhesives, natural rubber adhesives, styrene-butadiene copolymer resin adhesives, polyisobutylene adhesives, vinyl ether resin adhesives, and silicone resin adhesives.

Examples of the adhesive resin layer include ethylene-vinyl acetate copolymer resins.

When a film formed of a thermoplastic resin has adhesion-releasability or adhesive properties, the resin layer may not be provided.

As the pellicle film 21, a commercially available pellicle film can be used, and examples thereof include Toretec7332 (manufactured by dongli film processing corporation), and a pellicle tape #625T (manufactured by hydropneumatic chemical corporation).

The adhesion force of the pellicle film 21 to the stretched film 11 is preferably 0.02N/25mm or more and 0.08N/25mm or less. If the adhesion force of the seed film 21 is 0.02N/25mm or more, the seed film 21 is less likely to float (also referred to as tunnel formation) or peel. When the adhesion of the pellicle film 21 is 0.08N/25mm or less, the pellicle film 21 is easily peeled off.

Here, the adhesion force of the pellicle 21 to the stretched film 11 can be determined as follows. A test piece was produced by cutting the laminated film 13 in which the seed film 21 was bonded to the stretched film 11, such that the laminated film 13 had a width of 25mm or a multiple thereof and a length of about 150mm with the conveyance direction (MD) being the long side, and the stretched film 11 side of the test piece was bonded to a glass plate with an adhesive and fixed. Next, the lengthwise end portion (side having a width of 25mm or a multiple thereof) of the pellicle 21 was sandwiched by a tensile tester in accordance with JIS K6854-2: 1999, the 180 DEG peeling test was conducted at a nip moving speed of 300 mm/min. Then, the average peeling force over the peeling length except for the first 25mm nip moving distance was determined from the obtained force-nip moving distance curve. This value is the adhesion force to the stretched film 11 per width of the pellicle film 21 in the test piece.

As described above, when a test piece having a width of 25mm is used, the value is directly the adhesion force (unit: N/25mm) to the stretched film 11. On the other hand, when a test piece having a width of a multiple of 25mm is used, the obtained average peeling force may be converted into a close adhesion force per 25mm width. For example, when a test piece having a width of 100mm (4 times of 25mm) is used, the average peel force obtained is multiplied by 1/4 to obtain the adhesion force (N/25mm) of the seed film 21 to the stretched film 11.

The lamination of the seed film 21 can be performed by a conventionally known lamination method. As an example of a conventionally known bonding method, there is a method in which the stretched film 11 and the seed film 21 are overlapped and bonded by pressing with a nip roller 113 as shown in fig. 2. As a material of the nip roller 113, metal, rubber, or the like can be used.

When resin layers are formed on both surfaces of the base film, the seed film 21 may be bonded to one surface of the resin layer.

The thickness of the seed film 21 is preferably 1 μm or more and 100 μm or less, more preferably 1 μm or more and 80 μm or less, and further preferably 1 μm or more and 50 μm or less, from the viewpoint of strength, handling property, and the like.

In the first bonding step S3, the end portions of the seed film 21 or the extension film 11 may be cut as necessary. The cutting of the end portion of the pellicle 21 or the stretch film 11 is not particularly limited, and may be performed by a slitting method using a slitter, for example. The slitting method is preferable because the edge of the long film can be continuously cut off.

As an example of the slitting method, there is a method in which two circular blades called shearing blades are used to rotate in accordance with the conveyance of the film (the pellicle film 21 or the stretched film 11), and the upper blade applies a contact pressure to the lower blade to perform slitting. As other examples of the slitting method, there are a method using a razor blade called a leather blade, a method of pressing a blade called a ruling blade against a quenching roller or the like and slitting the blade, and the like. As methods using leather blades, there are known a hollow cutting method in which slitting is performed in the air without providing a backing guide, a grooved roller method in which a blade is put into a grooved roller as a backing guide to stabilize the meandering of slitting, and the like. Among these methods, a slitting method using a cutting blade capable of easily changing the slitting position of the film is preferably employed.

The portion removed by slitting is discharged from the manufacturing line. The removed portion can be discharged by using a known device such as a scrap winder. For example, the film may be wound by a scrap winder or the like immediately after the film is cut and discharged, or may be wound by a scrap winder or the like and discharged after the subsequent winding step S4.

[ coiling step S4]

In the winding step S4, the tape-like laminate film 13 obtained in the first laminating step S3 is wound around the winding roll 115 in a roll shape while being conveyed in the longitudinal direction. In the winding step S4, the winding may be performed such that the seed film 21 side is the inside, or the winding may be performed such that the seed film 21 side is the outside.

The laminated film 13 obtained in the first bonding step S3 is easily charged. Due to the electrification of the laminated film 13, there are cases where: the laminated films 13 adjacent to each other in the laminated film 13 wound in a roll shape are electrically repelled from each other, and a positional shift (winding shift) of the end portion in the width direction of the laminated film 13 occurs immediately after winding or during storage for a certain period of time. The greater the absolute value of the charge amount of the laminated film 13, the greater the winding displacement when the laminated film 13 is wound into a roll.

Here, the winding displacement of the laminated film 13 is a maximum distance by which an end portion in the width direction of the laminated film 13 is displaced in a direction substantially perpendicular to the winding direction at any end surface of the laminated film 13 wound in a roll. Such winding displacement can be measured using a square, a straight ruler, or the like.

When the laminated film 13 in which the winding displacement occurs is applied to a polarizing plate, the flatness of the polarizing plate may be deteriorated, and scratches, wrinkles, and the like may be generated. The winding deviation of the laminate film 13 in the winding step S4 is preferably 5mm or less, and more preferably 1mm or less. If the winding displacement of the laminated film 13 is 5mm or less, the winding displacement can be corrected when the laminated film 13 is wound in a subsequent step.

The present inventors have conducted extensive studies and, as a result, have found that: if the absolute value of the charge amount of the laminate film 13 in the winding step S4 is 32kV or less, the winding deviation of the laminate film 13 can be controlled within the above range. Here, it is preferable to measure the amount of charge with respect to the laminated film 13 to be wound around the winding roller 115. Here, it is experimentally clarified that the charge amount of the laminate film 13 does not change between a portion immediately after winding on the winding roller 115 and a portion located on the peripheral portion of the winding roller 115, and the charge amount may be measured with respect to the laminate film 13 on the peripheral portion of the winding roller 115 from the viewpoint of workability. From the viewpoint of reducing the winding displacement of the laminated film 13, the absolute value of the charge amount of the laminated film 13 is preferably 25kV or less.

The space in which the winding step S4 is performed is preferably controlled to have a temperature of 13 to 33 ℃ and a relative humidity of 25 to 85%, more preferably controlled to have a temperature of 18 to 28 ℃ and a relative humidity of 40 to 70%. The higher the humidity of the space in which the winding step S4 is performed, the smaller the charge amount of the laminated film 13 can be. Further, the relative humidity is preferably 85% or less from the viewpoint of suppressing the generation of rust in the apparatus used in the winding step S4.

In the present embodiment, the laminated film 13 is subjected to charge removal between the first bonding step S3 and the winding step S4. From the viewpoint of reducing the charge amount of the laminate film 13 during winding, it is preferable to remove the charge from the oriented film 11 between the stretching step S2 and the first laminating step S3 in addition to the period. The laminate film 13 can be electrically removed by using a conventionally known electrostatic removing device. Examples of conventionally known static electricity removing devices include a static electricity removing rod, a static electricity removing wire, and an ion blowing type static electricity removing device, and the ion blowing type static electricity removing device is preferable. These static electricity removing devices may be used alone or in combination of a plurality of devices.

The winding of the laminated film 13 is preferably performed while applying tension to the laminated film 13. By increasing the tension applied to the film at the time of winding, winding displacement can be further suppressed. However, it is known that if the tension applied to the film during winding is too large, a rib or the like may be generated in the laminated film 13. The number of the ribs or the like is preferably as small as possible because the ribs or the like may cause a poor appearance in a subsequent step. On the other hand, by reducing the tension applied to the film at the time of winding, the generation of a rib or the like can be suppressed. However, it is also known that if the tension applied to the film during winding is too small, air is mixed into the film to increase the possibility of winding displacement.

The present inventors have conducted extensive studies and, as a result, have found that: if the tension per unit width applied to the laminate film 13 at the start of winding the laminate film 13 is 30N/m or more, the occurrence of winding displacement can be reduced by suppressing the mixing of air. It is further known that: if the tension applied to the laminate film 13 is 90N/m or less, the occurrence of winding displacement is more significantly reduced, and the laminate film 13 is less likely to have streaks.

The winding of the laminate film 13 may be performed at a constant winding tension, but it is preferable that the tension applied to the laminate film 13 is maximum immediately after the start of winding and gradually decreases as the diameter of the laminate film 13 wound in a roll shape thereafter becomes larger. At this time, the ratio of the tension immediately before the end of winding to the tension immediately after the start of winding (hereinafter referred to as a decreasing rate) can be determined according to the diameter of the laminate film 13.

The winding speed of the laminated film 13 is preferably 5m/min or more, more preferably 15m/min or more, further preferably 25m/min or more, and usually 70m/min or less, more preferably 50 m/min. When the winding speed exceeds 70m/min, the air is greatly mixed, and winding deviation is likely to occur.

< method for producing polarizing plate >

Hereinafter, an embodiment of the method for manufacturing a polarizing plate of the present invention will be described with reference to fig. 3. The polarizing plate of the present embodiment is produced using the laminated film obtained by the above-described production method.

Fig. 3 is a flowchart showing a method for manufacturing a polarizing plate according to the present embodiment. As shown in fig. 3, the method for manufacturing a polarizing plate according to the present embodiment includes a first peeling step S5, a dyeing step S6, a second bonding step S7, and a second peeling step S8.

[ first peeling step S5]

In the first peeling step S5, the obtained laminated film is wound out, and the seed film is peeled from the laminated film to obtain an extended film again. The method for peeling the protective film is not particularly limited. The pellicle film peeled from the laminate film is preferably wound up on a take-up reel. At this time, the protective film may be peeled off by hand and wound around the winding shaft, or may be sucked by a suction roller and conveyed to the winding shaft and wound. In addition, the peeling of the pellicle film is preferably performed while removing electricity around the peeled portion as necessary.

[ dyeing step S6]

In the dyeing step S6, the stretched film obtained in the first peeling step S5 is dyed with a dichroic substance to obtain a polarizing laminate film in which a stretched base film and a polarizing plate layer formed on at least one surface of the stretched base film are laminated.

The dyeing step S6 includes dyeing, crosslinking, washing, and drying. First, in the dyeing treatment, a band-shaped stretched film is dyed with a dichroic substance while being conveyed in the longitudinal direction, and the dichroic substance is adsorbed and aligned. Next, in the crosslinking treatment, the resin film dyed with the dichroic material is crosslinked with a crosslinking agent. In the cleaning treatment, the crosslinked resin film is cleaned with a crosslinking agent. Then, the resin film after cleaning is dried to obtain a polarizing laminate film.

In the dyeing treatment, the stretched film is dyed by immersing it in a liquid containing a dichroic substance (hereinafter referred to as a dyeing bath). As the dyeing bath, a solution in which a dichroic substance is dissolved in a solvent may be used. As the solvent of the dyeing bath, for example, water is preferable. An organic solvent compatible with water may be further added to the dyeing bath. Specific examples of the organic solvent include methanol, ethanol, propanol, and glycerol.

Examples of the dichroic material used in the present embodiment include iodine and dichroic organic dyes known as pigments for polarizing films. Examples of the dichroic organic dye include red BR, red LR, red R, pink LB, gem red BL, purplish red GS, sky blue LG, lemon yellow, blue BR, blue 2R, deep blue RY, green LG, violet LB, violet B, black H, black B, black GSP, yellow 3G, yellow R, orange LR, orange 3R, deep red GL, deep red KGL, congo red, bright violet BK, Supra blue G, Supra blue GL, Supra orange GL, direct sky blue, direct fast orange S, fast black. The dichroic substance may be used alone or in combination of two or more.

The concentration of the dichroic substance in the dyeing bath is preferably 0.01 mass% or more and 10 mass% or less, and more preferably 0.02 mass% or more and 7 mass% or less.

In the case where iodine is used as the dichroic substance, it is preferable to further add an iodide to the dyeing bath containing iodine for the purpose of improving 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, and potassium iodide is preferably added. In addition, the dye bath may also contain a crosslinking agent.

The concentration of iodide in the dyeing bath is preferably 0.01 mass% or more and 20 mass% or less. When potassium iodide is added to the dyeing bath containing iodine, the ratio of iodine to potassium iodide is preferably 1: 5 to 1: 100, more preferably 1: 6 to 1: 80, in terms of mass ratio.

The temperature of the dyeing bath is preferably 10 ℃ or more and 60 ℃ or less, and more preferably 20 ℃ or more and 40 ℃ or less.

In the dyeing step S6, the stretched film including the dyed resin film is subjected to a crosslinking treatment in which the stretched film is immersed in a liquid containing a crosslinking agent (hereinafter referred to as a crosslinking bath) subsequent to the dyeing treatment.

The crosslinking agent used in the present embodiment is preferably a boron compound, glyoxal, or glutaraldehyde, and more preferably a boron compound. Examples of the boron compound include boric acid and borax. The crosslinking agent may be used alone or in combination of two or more.

As the crosslinking bath of the present embodiment, a solution in which a crosslinking agent is dissolved in a solvent can be used. As the solvent, for example, water is preferable. The crosslinking bath may further contain an organic solvent compatible with water. Specific examples of the organic solvent are the same as those of the organic solvent described above. The concentration of the crosslinking agent in the crosslinking bath is preferably 1% by mass or more and 20% by mass or less, and more preferably 6% by mass or more and 15% by mass or less.

The crosslinking bath of the present embodiment may further include an iodide. By adding an iodide to the crosslinking bath, the in-plane polarization performance of the obtained polarizing plate can be made uniform.

Specific examples of the iodide are the same as those of the iodide described above.

The concentration of the iodide in the crosslinking bath is preferably 0.05% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less.

The temperature of the crosslinking bath is preferably 10 ℃ to 90 ℃.

In the dyeing step S6, after the crosslinking treatment, a washing treatment is performed in which the stretched film provided with the crosslinked resin film is immersed in pure water such as ion-exchanged water or distilled water (hereinafter referred to as a washing bath). This can reduce the amount of chemicals remaining in the crosslinked resin film, for example, excess dichroic substances or unreacted crosslinking agents. The cleaning bath may further contain an organic solvent compatible with water. Specific examples of the organic solvent are the same as those of the organic solvent described above.

The cleaning temperature is preferably 3 ℃ or more and 50 ℃ or less, and more preferably 4 ℃ or more and 20 ℃ or less.

The cleaning treatment in the present embodiment may be a cleaning treatment with an aqueous solution containing iodide, or a combination of a cleaning treatment with an aqueous solution containing iodide and a cleaning treatment with pure water. Specific examples of the iodide are the same as those of the iodide described above. By including an iodide in the cleaning bath, the color tone of the obtained polarizing plate can be adjusted. The cleaning bath may contain a crosslinking agent, and the amount of the crosslinking agent added is preferably 1 part by mass or less based on 100 parts by mass of water in order to prevent defects caused by precipitation of the crosslinking agent on the membrane surface.

The concentration of iodide in the cleaning bath is preferably 1 mass% or more and 15 mass% or less.

In the dyeing step S6, the cleaning process is followed by a drying process for drying the stretched film including the cleaned resin film. The drying treatment may be carried out by a conventionally known method, and examples thereof include natural drying, forced air drying, and heat drying. In the case of, for example, heat drying, the drying temperature is preferably 20 ℃ or more and 95 ℃ or less. If the drying temperature is too low, the drying time becomes long, and the production efficiency is lowered. On the other hand, if the drying temperature is too high, the obtained polarizing plate is deteriorated, and the polarizing performance and color tone are deteriorated. The drying time is preferably 2 minutes to 20 minutes.

[ second bonding step S7]

In the second bonding step S7, a bonded film is obtained in which a protective film is bonded to at least the surface of the polarizer layer of the polarizing laminate film using an adhesive.

As a material of the protective film, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture cuttability, isotropy, and the like is preferable. Examples of the thermoplastic resin include an acetyl cellulose resin such as triacetyl cellulose, a cycloolefin resin, a cycloolefin copolymer resin, a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, an acrylic resin such as polycarbonate resin and polymethyl methacrylate, an acyclic olefin resin such as polypropylene and polyethylene, and a mixture thereof.

The thickness of the protective film is preferably 1 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and still more preferably 10 μm or more and 50 μm or less.

In the present embodiment, when protective films are provided on both surfaces of the polarizing laminate film, protective films made of the same resin material may be used on both surfaces, or protective films made of different resin materials may be used.

Examples of the adhesive include an aqueous adhesive and an active energy ray-curable adhesive. Examples of the aqueous adhesive include adhesives obtained by dissolving or dispersing a polyvinyl alcohol resin in water. Examples of the active energy ray-curable adhesive include adhesives containing a curable compound that is cured by irradiation with an active energy ray such as ultraviolet light, visible light, an electron beam, or X-ray.

The active energy ray-curable adhesive composition preferably contains one or both of a cationically polymerizable curable compound and a radically polymerizable curable compound, from the viewpoint of exhibiting good adhesiveness. The active energy ray-curable adhesive may further contain a cationic polymerization initiator or a radical polymerization initiator for initiating a curing reaction of the curable compound.

Examples of the cationically polymerizable curable compound include an epoxy compound (a compound having one or two or more epoxy groups in a molecule), an oxetane compound (a compound having one or two or more oxetane rings in a molecule), and a combination thereof.

Examples of the radically polymerizable curable compound include a (meth) acrylic compound (a compound having one or more (meth) acryloyloxy groups in a molecule), another vinyl compound having a radically polymerizable double bond, and a combination thereof.

The active energy ray-curable adhesive may contain additives such as a cationic polymerization accelerator, an ion scavenger, an antioxidant, a chain transfer agent, a thickener, a thermoplastic resin, a filler, a flow control agent, a plasticizer, an antifoaming agent, an antistatic agent, a leveling agent, and a solvent, as required.

The method for forming the adhesive film will be described below. When the protective film is attached using an active energy ray-curable adhesive, the protective film is laminated on the polarizing laminate film with the active energy ray-curable adhesive interposed therebetween. Next, the adhesive layer composed of the active energy ray-curable adhesive is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. Ultraviolet rays are preferable as the active energy rays, and as the light source in this case, a low-pressure mercury lamp, a medium-pressure mercury 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.

On the other hand, in the case of attaching the protective film using an aqueous adhesive, the protective film may be laminated on the polarizing laminate film via the aqueous adhesive and then dried by heating.

In addition, for the purpose of improving the adhesiveness with the adhesive, the polarizing laminate film or the protective film or both the polarizing laminate film and the protective film may be subjected to surface treatment. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet treatment, undercoating treatment, saponification treatment, solvent treatment by solvent coating and solvent treatment by drying.

Further, a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer may be formed on the surface of the protective film opposite to the polarizing laminate film.

[ second peeling step S8]

In the second peeling step S8, the stretched base material film is peeled from the bonded film to obtain a polarizing plate.

The stretched base material film peeled from the bonded film is preferably wound on a winding reel in the same manner as in the first peeling step S5. The method of peeling the stretched base film is not particularly limited, and for example, the same method as in the first peeling step S5 can be used. The stretched base film is preferably peeled off while removing electricity around the peeled portion as necessary.

According to the method for producing a laminated film of the above-described method, a laminated film in which the occurrence of winding displacement at the time of winding the laminated film is reduced can be obtained.

According to the method for producing a polarizing plate of the above-described method, since the laminated film is used, a polarizing plate with less occurrence of winding displacement at the time of winding the laminated film can be obtained.

< modification example >

The technical scope of the present invention is not limited to the above-described embodiments, and various modifications may be made within a scope not impairing the effects of the present invention.

For example, between the stretching step S2 and the first bonding step S3, or between the first peeling step S5 and the dyeing step S6, the resin film on the stretched base film may be insolubilized so as not to dissolve it. The insolubilization treatment may be performed by immersing the stretched film in a solution containing a crosslinking agent (hereinafter referred to as an insolubilization bath). The crosslinking agent contained in the insolubilization bath is the same as the crosslinking agent used for the crosslinking treatment in the dyeing step S6. As the solvent of the insolubilization bath, for example, water is preferable. The insoluble bath may further contain an organic solvent compatible with water. Specific examples of the organic solvent are the same as those of the organic solvent described above.

The concentration of the crosslinking agent in the above-mentioned insolubilization bath is preferably 1 mass% or more and 4 mass% or less. The temperature of the insolubilization bath is preferably 25 ℃ or higher, more preferably 30 ℃ or higher and 85 ℃ or lower, and still more preferably 30 ℃ or higher and 60 ℃ or lower. The time for immersing the laminated film in the insolubilization bath is preferably 5 seconds to 800 seconds, and more preferably 8 seconds to 500 seconds.

The dyeing process is performed after the stretching step S2, but may be performed before the stretching step S2, or may be performed simultaneously.

In the dyeing treatment, the crosslinking treatment is performed after the dyeing treatment, but may be performed simultaneously with the dyeing treatment by adding a crosslinking agent to the dyeing bath. Further, the crosslinking treatment may be performed twice or more using two or more crosslinking baths having different compositions.

In the above embodiment, an example in which the stretched base film is finally peeled is shown, and the stretched base film may be used as a protective film of a polarizing plate without being peeled.

An adhesive layer for bonding the polarizing plate to another member (for example, a liquid crystal cell in the case of application to a liquid crystal display device) may be laminated on at least the surface of the polarizer layer in the obtained polarizing plate. The adhesive forming the adhesive layer is formed of an adhesive composition obtained by adding a crosslinking agent to a base polymer. Examples of the base polymer include (meth) acrylic resins, styrene resins, and silicone resins. Examples of the crosslinking agent include isocyanate compounds, epoxy compounds, and aziridine compounds. The pressure-sensitive adhesive composition may further contain fine particles to form a pressure-sensitive adhesive layer exhibiting light scattering properties. The thickness of the pressure-sensitive adhesive layer is preferably 1 μm or more and 40 μm or less, and more preferably 3 μm or more and 25 μm or less.

Another optical layer may be laminated on at least the surface of the polarizer layer in the obtained polarizing plate.

Examples of the other optical layers include a reflective polarizing film, a film having a function of preventing surface reflection, a reflective film having a reflection function on a surface, a transflective film having both a reflection function and a transmission function, and a viewing angle compensation film. The polarizing plate of the present embodiment can be preferably applied to both the visual recognition side and the back side of the display device.

[ examples ]

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

[ example 1]

[ production of base Material film ]

A substrate film was formed by producing a long film having a three-layer structure of: resin layers composed of homopolypropylene, which is a homopolymer of propylene, were disposed on both sides of a resin layer composed of a propylene/ethylene random copolymer containing about 5 mass% of ethylene units. The base film is produced by coextrusion using a multilayer extruder.

The following materials were used as a propylene/ethylene random copolymer and homopolypropylene.

Random copolymer of propylene/ethylene: sumitomo (registered trademark) Noblene (registered trademark) W151, manufactured by sumitomo chemical co., melting point 138 ℃;

homopolymerized propylene: noblene (registered trademark) FLX80E4 manufactured by sumitomo chemical corporation, melting point 163 ℃;

the total thickness of the obtained base film was 100 μm, and the thickness ratio of each layer (FLX80E4/W151/FLX80E4) was 3/4/3.

[ formation of undercoat layer ]

PVA powder (Z-200, average degree of polymerization 1100, and degree of saponification of 99.5 mol%, manufactured by Nippon synthetic chemical Co., Ltd.) was dissolved in hot water at 95 ℃ to prepare a 3 mass% PVA aqueous solution.

The obtained PVA aqueous solution was mixed with 1 part by mass of a crosslinking agent (manufactured by tianoka chemical industry co., ltd., "Sumirez Resin (registered trademark) 650") per 2 parts by mass of the PVA powder to form a coating liquid for forming an undercoat layer.

The substrate film thus produced was subjected to corona treatment on one surface while being continuously conveyed. Next, the obtained coating liquid for forming an undercoat layer was applied to the surface of the base material film subjected to corona treatment using a micro gravure coater. An undercoat layer having a thickness of 0.2 μm was formed by drying the coated substrate film at 80 ℃ for 3 minutes.

[ production of laminate (resin layer Forming step) ]

PVA powder (PVA 124, manufactured by Korea corporation, average polymerization degree 2400, saponification degree 98.0 to 99.0 mol%) was dissolved in hot water at 95 ℃ to prepare an 8 mass% PVA aqueous solution. The obtained PVA aqueous solution was coated on the undercoat layer using a die coater while conveying the substrate film having the undercoat layer formed thereon. The coated substrate film was dried at 90 ℃ for 1 minute, 70 ℃ for 3 minutes, and 60 ℃ for 4 minutes in stages to form a resin layer having a thickness of 10 μm.

Further, the surface of the substrate film opposite to the surface on which the resin layer was formed was subjected to the same treatment as described above, thereby forming an undercoat layer having a thickness of 0.2 μm and a resin layer having a thickness of 10.0 μm in this order. In this way, a laminate having a primer layer and a resin layer on both sides of the base film, that is, a laminate having a layer structure of resin layer/primer layer/base film/primer layer/resin layer, was obtained.

[ production of stretched film (stretching step) ]

While the laminate was continuously conveyed, the free end of the laminate in the conveyance direction was uniaxially stretched, i.e., longitudinally uniaxially stretched, using nip rolls, to obtain a stretched film. The drawing temperature in the uniaxial longitudinal drawing was set to 160 ℃ and the drawing speed was set to 2.5 m/min at the inlet and 14.5 m/min at the outlet. As a result, the draw ratio of the laminate was 5.80 times. The length of the stretched film in the longitudinal direction was 2000 m.

[ production of laminated film (first bonding step) ]

A guard film made of polyethylene was bonded to the surface of the resin film formed on one side of the obtained stretched film to obtain a laminated film.

< evaluation 1 (evaluation of winding deflection) >

[ winding of laminated film (winding Process) ]

The obtained laminate film was wound up so that the surface to which the pellicle was bonded was positioned outside.

At this time, the tension at the start of winding was 60N/m. In addition, the rate of decrease was 20%. The charge amount of the laminated film immediately before the winding was measured at a position spaced apart from the surface of the laminated film by about 25mm using an electrostatic measuring instrument (manufactured by SIMCO, FMX-003). As a result, the absolute value of the charge amount of the laminated film was 0.4 kV. With respect to the laminated film which was left for one week after winding, the winding displacement was measured, and it was found that the winding displacement was within 1mm, and the appearance was good.

In addition, the charge amount of the stretched film or the laminated film is adjusted by using a plurality of ion-blowing type electrostatic removal devices during the period from the stretching step to the winding step. The space for the winding step was set to 23 ℃ and 55% relative humidity.

[ example 2]

A laminated film of example 2 was produced in the same manner as in example 1, except that the amount of removal by the ion blowing type static electricity removal device was adjusted so that the absolute value of the charge amount of the laminated film to be wound was 21 kV. The length of the stretched film in the longitudinal direction was 3500 m. The laminate film left for one week after winding was measured for winding displacement, and found to have winding displacement of 1mm or less and good appearance.

[ example 3]

A laminated film of example 3 was produced in the same manner as in example 1, except that the amount of removal by the ion blowing type static electricity removal device was adjusted so that the absolute value of the charge amount of the laminated film to be wound was set to 28 kV. Further, the length of the stretched film in the longitudinal direction was 4400 m. The laminate film left for one week after winding was measured for winding displacement, and found to have winding displacement of 5mm and good appearance.

[ example 4]

The tension applied to the laminate film at the start of winding was set to 100N/m. Meanwhile, a laminated film of example 4 was produced in the same manner as in example 1, except that the amount of removal by the ion-blowing electrostatic removal device was adjusted so that the absolute value of the charge amount of the laminated film to be wound was set to 31 kV. The length of the stretched film in the longitudinal direction was 2000 m. With respect to the laminated film which was left for one turn after the winding, the winding displacement was measured and found to be within 1mm, but a rib was generated in the central portion of the laminated film in the roll.

Comparative example 1

The tension applied to the laminate film at the start of winding was set to 80N/m. Meanwhile, a laminated film of comparative example 1 was produced in the same manner as in example 1, except that the amount of removal by the ion-blowing electrostatic removal device was adjusted so that the absolute value of the charge amount of the laminated film to be wound was 33 kV. Further, the length of the stretched film in the longitudinal direction was 4000 m. The laminate film left for one week after winding was measured for winding displacement, and found to have winding displacement of 20mm and good appearance. However, when the obtained laminated film is wound out, the laminated film meanders and wrinkles are generated.

Comparative example 2

The obtained laminate film was wound up so that the surface to which the pellicle was bonded was positioned outside.

At this time, the tension at the start of winding was 25N/m. In addition, the rate of decrease was 20%. The laminate film left for one turn after winding was measured for winding displacement, and found to have winding displacement larger than 5mm and good appearance.

With respect to examples 1 to 4 and comparative examples 1 and 2, the tension (N/m) at the start of winding, the absolute value (kV) of the charge amount of the laminate film, the winding offset, and the appearance defect of the laminate film in the roll shape are summarized in table 1. Regarding the winding offsets of examples 1 to 4 and comparative examples 1 and 2, the case where the winding offset is within 5mm is regarded as "ok", and the case where the winding offset exceeds 5mm is regarded as "no".

In examples 1 to 4 and comparative examples 1 and 2, the laminated films having the winding displacement of "ok" were qualified. Here, when the appearance of the laminated film was good, the overall evaluation was indicated as "excellent", and when the laminated film had recognized the streak or the like, the overall evaluation was indicated as "o".

On the other hand, the laminated film having winding deviation "impossible" was rejected, and the overall evaluation was indicated by "x".

[ Table 1]

As shown in Table 1, in examples 1 to 4, since the tension at the start of winding was 30N/m or more and the absolute value of the charge amount of the laminate film was 32kV or less, the winding deviation of the laminate film could be controlled within 5 mm. On the other hand, in comparative example 1, the tension at the start of winding was 30N/m or more, but the absolute value of the charge amount of the laminate film was larger than 32kV, and therefore the winding offset of the laminate film was larger than 5 mm. In comparative example 2, it is understood that the winding deviation of the laminate film is larger than 5mm because the tension at the start of winding is smaller than 30N/m.

In example 4, it was found that, although no winding displacement occurred, the tension at the start of winding was greater than 90N/m, and therefore, the surface of the rolled laminate film had streaks.

< evaluation 2 (evaluation of appearance of polarizing plate) >

[ production of polarizing laminate film (first peeling step and dyeing step) ]

The pellicle film was peeled off while the laminated films obtained in examples 1 to 4 and comparative examples 1 and 2 were wound off. Subsequently, the obtained stretched film was immersed in a warm water bath at 60 ℃ for 60 seconds while continuously conveying the film, and then immersed in a dyeing bath at 30 ℃ containing iodine and potassium iodide for about 150 seconds to dye the resin film. Subsequently, the dyed resin film was washed with pure water at 10 ℃ to reduce excess iodine and potassium iodide. Further, the dyed resin film was immersed in a crosslinking bath containing boric acid and potassium iodide at 76 ℃ for 600 seconds and crosslinked. Further, the crosslinked resin film was washed with pure water at 10 ℃ for 4 seconds and then dried at 80 ℃ for 300 seconds, thereby producing a polarizing laminate film.

Production of polarizing plate (second bonding step and second peeling step)

PVA powder (manufactured by Korea corporation, "KL-318", average polymerization degree 1800) was dissolved in hot water at 95 ℃ to prepare a 3 mass% PVA aqueous solution. The obtained aqueous PVA solution was mixed with a crosslinking agent (manufactured by takaki chemical industries, inc. "Sumirez Resin (registered trademark) 650") at a ratio of 1 part by mass to 2 parts by mass of PVA to form an adhesive.

The obtained adhesive was applied to the polarizer layers on both sides of the polarizing laminate film while continuously conveying the polarizing laminate film. Next, as a protective film, triacetyl cellulose (TAC) (manufactured by konica minolta corporation, "KC 4 UY") having an adhesive surface saponified and a thickness of 40 μm was bonded to the polarizing plate coated with the adhesive, and the polarizing plate was passed between a pair of bonding rollers and pressed. In this way, a laminate film having a layer structure of TAC/polarizer layer/undercoat layer/extended substrate film/undercoat layer/polarizer layer/TAC was obtained.

The obtained laminated film was peeled off at the interface between the extended substrate film and the undercoat layer and divided, to obtain a film composed of TAC/polarizer layer/undercoat layer/extended substrate film and a polarizing plate composed of undercoat layer/polarizer layer/TAC. The stretched substrate film was peeled from the film composed of TAC/polarizer layer/undercoat layer/stretched substrate film to further obtain a polarizing plate.

In examples 1 to 4 and comparative examples 1 and 2, defects such as film breakage did not occur when the stretched base material film was peeled.

In comparative examples 1 and 2, wrinkles were generated when the laminated film was wound out. Such a wrinkled portion is known to become a stain, resulting in poor appearance.

From the above results, it was confirmed that the present invention is useful.

Claims (6)

1. A method for manufacturing a laminated film, comprising:

a resin layer forming step of forming a resin layer using a polyvinyl alcohol resin as a forming material on at least one surface of a strip-shaped base film by applying a coating liquid containing the polyvinyl alcohol resin to the base film while conveying the base film in a longitudinal direction and then drying the coating liquid;

a stretching step of stretching the laminate obtained in the resin layer forming step while conveying the laminate in a longitudinal direction to obtain a stretched base film and a stretched film in which a resin film formed on at least one surface of the stretched base film is laminated, wherein the stretched base film is a film obtained by stretching the base film;

a first bonding step of bonding a seed film to a surface of the resin film to obtain a laminated film in which the extended base film, the resin film, and the seed film are laminated in this order; and

a winding step of winding the laminated film by a winding roller,

the base film is formed from a polyolefin resin, a polyester resin, a cellulose ester resin, a polycarbonate resin, a polyvinyl alcohol resin, a polyvinyl acetate resin, a polyarylate resin, a polystyrene resin, a polyethersulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, or a mixture thereof,

the protective film comprises a polyolefin-based resin or a polyester-based resin,

the length of the stretched film in the longitudinal direction is 2000m or more,

a tension per unit width applied to the laminated film at the start of the winding step is 30N/m or more,

that is, the absolute value of the charge amount of the laminated film wound around the winding roller is 32kV or less.

2. The method for manufacturing a laminated film according to claim 1,

the protective film contains a polyolefin resin as a forming material.

3. The method for producing a laminated film according to claim 1 or 2, wherein,

in the stretching step, the laminate is sequentially passed through a first nip roller and a second nip roller, and is uniaxially stretched in the longitudinal direction by a circumferential speed difference between the first nip roller and the second nip roller.

4. The method for manufacturing a laminated film according to any one of claims 1 to 3,

the tension per unit width applied to the laminated film at the start of the winding process is 90N/m or less.

5. A method for manufacturing a polarizing plate, comprising:

a step of obtaining a laminated film by the method for producing a laminated film according to any one of claims 1 to 4;

a first peeling step of taking out the laminated film and peeling the seed film from the laminated film;

a dyeing step of dyeing the stretched film obtained in the first peeling step with a dichroic substance to obtain a polarizing laminate film in which a stretched base film and a polarizing plate layer formed on at least one surface of the stretched base film are laminated; and

and a second bonding step of bonding a protective film to at least a surface of the polarizer layer of the polarizing laminate film.

6. The method of manufacturing a polarizing plate according to claim 5,

the method for manufacturing a polarizing plate includes a second peeling step of peeling the extended base material film after the second bonding step.

Images