CN107076912B

CN107076912B - Method for producing polarizing laminate film or polarizing plate

Info

Publication number: CN107076912B
Application number: CN201580053198.2A
Authority: CN
Inventors: 河村真一
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2014-10-01
Filing date: 2015-09-25
Publication date: 2020-08-11
Anticipated expiration: 2035-09-25
Also published as: CN107076912A; JPWO2016052331A1; WO2016052331A1; TW201618921A; KR20170065531A

Abstract

The method for producing a polarizing laminate film of the present invention comprises: a coating step (S10) in which an aqueous solution of a polyvinyl alcohol resin is coated on a base film to obtain a coated film; a drying step (S20) for drying the coating film to obtain a laminated film having a polyvinyl alcohol resin layer formed on the base film; a stretching step (S30) for obtaining a stretched laminated film by uniaxially stretching the laminated film; and a dyeing step (S40) for dyeing the polyvinyl alcohol resin layer to form a polarizer layer and obtain a polarizing laminated film, wherein in the stretching step (S40), the uniaxial stretching is started in a state that the water percentage of the laminated film is more than or equal to 0.3 mass%.

Description

Method for producing polarizing laminate film or polarizing plate

Technical Field

The present invention relates to a method for producing a polarizing laminate film or a polarizing plate.

Background

Polarizing plates are widely used as a supply element of polarized light in a display device such as a liquid crystal display device. As such a polarizing plate, a polarizing plate in which a protective film made of triacetyl cellulose is bonded to a polarizing film (polarizer layer) made of a polyvinyl alcohol resin has been conventionally used, and in recent years, thinning and weight reduction have been demanded in accordance with the spread of liquid crystal display devices to mobile devices such as notebook personal computers and cellular phones.

Conventionally, a polarizing plate has been manufactured by stretching a film made of a polyvinyl alcohol resin alone or simultaneously with the stretching, producing a polarizing film by dyeing or crosslinking, and laminating the polarizing film on a protective film or the like. On the other hand, methods are known in which: after a polyvinyl alcohol resin layer to be a polarizer layer is provided on the surface of a base film, the polyvinyl alcohol resin layer is stretched together with the base film, and the polyvinyl alcohol resin layer is formed into a polarizer layer through dyeing and crosslinking steps and a subsequent drying step, whereby the total thickness of the base film and the polarizer layer can be reduced to the maximum, and the thickness of the polarizer layer (polarizing film) can be made thinner than before (for example, see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2009-93074

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to provide a method for manufacturing a polarizing laminated film having a thin polarizer layer, which can be manufactured by the following manufacturing method, in a manufacturing method capable of manufacturing a polarizing laminated film having a thin polarizer layer, the method including: after the polyvinyl alcohol resin layer is provided on the surface of the base film, the polyvinyl alcohol resin layer is stretched together with the base film, and the polyvinyl alcohol resin layer is formed into a polarizer layer through dyeing, crosslinking, and drying processes thereafter, whereby a polarizing laminate film having a thin polarizer layer can be produced.

Means for solving the problems

The present invention includes the following aspects.

[1] A method for producing a polarizing laminate film, comprising: a coating step of coating an aqueous solution of a polyvinyl alcohol resin on a base film to obtain a coating film; a drying step of drying the coating film to obtain a laminated film in which a polyvinyl alcohol resin layer is formed on a base film; a stretching step of obtaining a stretched laminated film by uniaxially stretching the laminated film; and a dyeing step of dyeing the polyvinyl alcohol resin layer to form a polarizer layer and obtain a polarizing laminate film, wherein in the stretching step, the uniaxial stretching is started in a state where the moisture percentage of the laminate film is 0.3 mass% or more.

[2] The method for producing a polarizing laminated film according to [1], wherein the drying step is performed so that the average moisture content of the coated film is changed to 5 to 65 mass%/minute.

[3] The method for producing a polarizing laminated film according to [1] or [2], wherein a humidity control step of controlling the moisture content of the laminated film to 0.3 mass% or more is included after the drying step, and the laminated film subjected to humidity control in the humidity control step is subjected to the stretching step while maintaining the moisture content thereof.

[4] A method for producing a polarizing laminate film, comprising: a first coating step (1) of coating an aqueous solution of a polyvinyl alcohol resin on one surface of a base film to obtain a coated film; a first drying step (1) of drying the coating film to obtain a laminated film having a polyvinyl alcohol resin layer formed on one surface of a base film; a second coating step of coating the other surface of the base film with an aqueous solution of a polyvinyl alcohol resin to obtain a double-coated film; a 2 nd drying step of drying the both-side coated film to obtain a both-side laminated film in which a polyvinyl alcohol resin layer is formed on both sides of a base film; a stretching step of obtaining a stretched laminated film by uniaxially stretching the double-sided laminated film; and a dyeing step of dyeing the polyvinyl alcohol resin layer to form a polarizer layer and obtain a polarizing laminate film, wherein in the stretching step, the uniaxial stretching is started in a state where the moisture percentage of the double-sided laminate film is 0.5 mass% or more.

[5] The method of producing a polarizing laminate film according to [4], wherein the 1 st drying step is performed so that a moisture content of the laminate film after drying is 0.3 mass% or more.

[6] The method for producing a polarizing laminate film according to [4] or [5], wherein the first drying step 1 and the second drying step 2 are performed so that a change in the average moisture content of the coated film and a change in the average moisture content of the both coated films are 5 to 65 mass%/minute, respectively.

[7] The method for producing a polarizing laminate film according to any one of [4] to [6], wherein a humidity control step of controlling the moisture content of the two-sided laminate film to 0.5 mass% or more is included after the 2 nd drying step, and the two-sided laminate film subjected to humidity control in the humidity control step is subjected to the stretching step while maintaining the moisture content thereof.

[8] A method of manufacturing a polarizing plate, comprising: a step of producing a polarizing laminate film by the production method according to any one of [1] to [7 ]; a bonding step of bonding a protective film to a surface of the polarizing laminate film on a side opposite to the base film to obtain a multilayer film; and a peeling step of peeling the base film from the multilayer film to obtain a polarizing plate including the polarizer layer and the protective film.

Effects of the invention

In the present invention, by controlling the value of the water content of the laminate film subjected to the stretching step, a polarizing laminate film having a polarizer layer with excellent optical properties can be obtained.

Drawings

Fig. 1 is a flowchart illustrating a method for manufacturing a polarizing laminate film and a polarizing plate according to embodiment 1.

Fig. 2 is a flowchart showing a method for manufacturing the polarizing laminate film and the polarizing plate according to embodiment 2.

Detailed Description

In the present specification, a laminate having a polyvinyl alcohol resin layer (a layer containing a polyvinyl alcohol resin) on a base film is referred to as a "laminate film", and a laminate having a polyvinyl alcohol resin layer on both surfaces of a base film is referred to as a "double-sided laminate film".

The polyvinyl alcohol resin layer having a polarizer function is referred to as a "polarizer layer", the laminate having the polarizer layer on the base film is referred to as a "polarizing laminate film", and the laminate having at least one surface of the polarizer layer provided with a protective film is referred to as a "polarizing plate". Hereinafter, the respective constituent elements of the polarizing laminate film and the polarizing plate will be described first, and then the description of the manufacturing methods thereof will be made.

< polarizing laminate film and polarizing plate >

[ base film ]

As the resin used for the base film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, stretchability, etc. can be used, and an appropriate resin can be selected depending on the glass transition temperature (Tg) or melting point (Tm) thereof. Specific examples of the thermoplastic resin include: polyolefin-based resins, polyester-based resins, cyclic polyolefin-based resins (norbornene-based resins), (meth) acrylic resins, cellulose ester-based resins, polycarbonate-based resins, polyvinyl alcohol-based resins, vinyl acetate-based resins, polyarylate-based resins, polystyrene-based resins, polyether sulfone-based resins, polysulfone-based resins, polyamide-based resins, polyimide-based resins, and mixtures and copolymers thereof.

The base film may be a film formed of only 1 type of the above-mentioned resin, or a film obtained by mixing 2 or more types of the above-mentioned resins. The substrate film may be a single-layer film or a multilayer film.

Examples of the polyolefin-based resin include: polyethylene, polypropylene, and the like are preferable because stable and high-ratio stretching is easy. In addition, a propylene-ethylene copolymer obtained by copolymerizing ethylene and propylene, or the like can also be used. Monomers other than ethylene may be used for the copolymerization, and as another type of monomer copolymerizable with propylene, for example, α -olefins are mentioned. The alpha-olefin is preferably an alpha-olefin having 4 or more carbon atoms, and more preferably an alpha-olefin having 4 to 10 carbon atoms. Specific examples of the α -olefin having 4 to 10 carbon atoms include linear monoolefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and 1-decene; branched monoolefins such as 3-methyl-1-butene, 3-methyl-1-pentene and 4-methyl-1-pentene; vinylcyclohexane, and the like. The copolymer of propylene and other monomer copolymerizable therewith may be a random copolymer or a block copolymer. The content of the constituent unit derived from the other monomer in the copolymer can be determined by Infrared (IR) spectrometry according to the method described on page 616 of the manual for polymer analysis (1995, published by the ji yi house bookstore).

Among the above, as the propylene-based resin constituting the propylene-based resin film, a homopolymer of propylene, a propylene-ethylene random copolymer, a propylene-1-butene random copolymer and a propylene-ethylene-1-butene random copolymer are preferably used.

The stereoregularity of the propylene resin constituting the propylene resin film is preferably substantially isotactic or syndiotactic. A propylene resin film containing a propylene resin having substantially isotactic or syndiotactic stereoregularity is excellent in handling properties and mechanical strength in a high-temperature environment.

The polyester resin is a polymer having an ester bond, and is mainly a polycondensate of a polycarboxylic acid and a polyol. The polycarboxylic acids used are mainly dicarboxylic acids, i.e. 2-membered carboxylic acids or their lower alkyl esters, such as terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl naphthalenedicarboxylate, etc. The polyol used is also mainly a diol, i.e., a 2-membered alcohol, and examples thereof include: propylene glycol, butylene glycol, neopentyl glycol, cyclohexanedimethanol, and the like. Specific examples of the resin include: polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, polypropylene naphthalate, polycyclohexanedimethylene terephthalate, polycyclohexanedimethylene naphthalate and the like. A mixed resin or copolymer of these resins may be used as appropriate.

As the cyclic polyolefin resin, a norbornene resin is preferably used. The cyclic polyolefin resin is a general term for resins obtained by polymerizing cyclic olefins as polymerization units, and examples thereof include: resins described in, for example, Japanese patent application laid-open Nos. H1-240517, H3-14882 and H3-122137. Specific examples thereof include: ring-opened (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins with α -olefins such as ethylene and propylene (typically random copolymers), graft polymers obtained by modifying these with unsaturated carboxylic acids or derivatives thereof, and hydrogenated products thereof. Specific examples of the cyclic olefin include: norbornenes.

Various products are commercially available as cyclic polyolefin resins. Specific examples thereof include: TOPAS (registered trademark) (manufactured by TOPAS Advanced developers GmbH), ARTON (registered trademark) (manufactured by JSR corporation), ZEONOR (registered trademark) (manufactured by nippon corporation), ZEONEX (registered trademark) (manufactured by nippon corporation), and APEL (registered trademark) (manufactured by mitsui chemical corporation).

As the (meth) acrylic resin, any appropriate (meth) acrylic resin can be used. Examples thereof include: polymethacrylates such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymers, methyl methacrylate- (meth) acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymers, methyl methacrylate-styrene copolymers (such as MS resins), and polymers having alicyclic hydrocarbon groups (for example, methyl methacrylate- (meth) acrylic acid cyclohexyl ester copolymers, methyl methacrylate- (meth) acrylic acid norbornyl ester copolymers, and the like). There may be preferably enumerated: methacrylic acid C such as polymethyl methacrylate₁-C₆The alkyl ester is a polymer of the main component. The (meth) acrylic resin is more preferably a methyl methacrylate resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight).

The cellulose ester resin is an ester of cellulose and a fatty acid. Specific examples of such cellulose ester resins include: cellulose triacetate, cellulose diacetate, cellulose tripropionate, cellulose dipropionate, and the like. In addition, there can be enumerated: and those in which a part of the hydroxyl group is modified with other substituent groups. Among them, cellulose triacetate is particularly preferable. Cellulose triacetate is commercially available in various products, and is advantageous in terms of availability and cost. Examples of commercially available products of cellulose triacetate include: FUJITAC (registered trademark) TD80 (manufactured by fujiac film (trademark)), FUJITAC (registered trademark) TD80UF (manufactured by fujiac (trademark)), FUJITAC (registered trademark) TD80UZ (manufactured by fujiac (trademark)), FUJITAC (registered trademark) TD40UZ (manufactured by fujiac film (trademark)), KC8UX2M (manufactured by KONICAMINOLTA (trademark)), and KC4UY (manufactured by KONICA MINOLTA (trademark)).

Polycarbonate resins are engineering plastics formed of a polymer in which monomer units are bonded via a carbonate group, and have high impact resistance, heat resistance, and flame retardancy. In addition, since polycarbonate has high transparency, it is also suitable for optical applications. Resins called modified polycarbonates, which are obtained by modifying the polymer skeleton in order to reduce the photoelastic coefficient in optical applications, copolymerized polycarbonates having improved wavelength dependence, and the like are also commercially available and can be suitably used. Such polycarbonate resins are widely commercially available, and examples thereof include: panlite (registered trademark) (imperial chemical corporation), Iupilon (registered trademark) (mitsubishi engineering plastics (mitsubishi), SD POLYCA (registered trademark) (sumitomo dow), CALIBER (registered trademark) (dow chemical corporation), and the like.

In addition to the thermoplastic resin, any appropriate additive may be added to the base film. Examples of such additives include: ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, colorants, and the like. The content of the thermoplastic resin exemplified above in the base film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, even more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. This is because, when the content of the thermoplastic resin in the base film is less than 50% by weight, high transparency and the like inherent in the thermoplastic resin may not be sufficiently exhibited.

The thickness of the base film before stretching may be appropriately determined, and from the viewpoint of workability such as strength and handling properties, and from the viewpoint of adjusting the moisture content of the laminate film in which the polyvinyl alcohol resin layer is formed on the base film in the present invention, the thickness of the base film is preferably 50 to 200 μm, and more preferably 70 to 130 μm. The base film preferably has a melting point or glass transition temperature higher than a temperature range of a drying step or a stretching step described later. By using such a base film, it is possible to prevent the base from becoming excessively soft in the drying step and the stretching step, and to avoid deterioration of the in-plane film thickness distribution of the polyvinyl alcohol resin layer.

In order to improve the adhesion to the polyvinyl alcohol resin layer, corona treatment, plasma treatment, flame treatment, or the like may be performed on the surface of the base film on the side where at least the polyvinyl alcohol resin layer is formed. In addition, in order to improve the adhesion, a thin layer such as a primer layer or an adhesive layer may be formed on the surface of the base film on the side where the polyvinyl alcohol resin layer is formed.

(undercoat layer)

When the undercoat layer is formed on the surface of the base film on the side where the polarizer layer is formed, the undercoat layer is not particularly limited as long as it is a material that exerts a strong adhesive force to some extent to both the base film and the polyvinyl alcohol resin layer. For example, a thermoplastic resin excellent in transparency, thermal stability, stretchability, and the like can be used. Specifically, there may be mentioned: acrylic resins and polyvinyl alcohol resins, but the acrylic resins and polyvinyl alcohol resins are not limited to these resins. Among them, a polyvinyl alcohol resin having good adhesion is preferably used.

Examples of the polyvinyl alcohol resin used as the undercoat layer include: polyvinyl alcohol resins and derivatives thereof. As derivatives of the polyvinyl alcohol resin, in addition to polyvinyl formal, polyvinyl acetal, and the like, there can be mentioned: polyvinyl alcohol resins are modified with olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, alkyl esters of unsaturated carboxylic acids, acrylamide and the like. Among the above polyvinyl alcohol resin materials, a polyvinyl alcohol resin is preferably used.

In order to increase the strength of the primer layer, a crosslinking agent may be added to the thermoplastic resin. As the crosslinking agent to be added to the thermoplastic resin, known crosslinking agents such as organic and inorganic crosslinking agents can be used. The crosslinking agent more suitable for the thermoplastic resin to be used may be appropriately selected. For example, in addition to low molecular weight crosslinking agents such as epoxy crosslinking agents, isocyanate crosslinking agents, dialdehyde crosslinking agents, and metal chelate crosslinking agents, polymer crosslinking agents such as methylolated melamine resins and polyamide epoxy resins can be used. When a polyvinyl alcohol resin is used as the thermoplastic resin, it is particularly preferable to use a polyamide epoxy resin, methylolated melamine, dialdehyde, a metal chelate crosslinking agent, or the like as the crosslinking agent.

The thickness of the undercoat layer is preferably 0.05 to 1 μm, and more preferably 0.1 to 0.4 μm. When the thickness is smaller than 0.05. mu.m, the adhesive force between the base film and the polyvinyl alcohol resin layer is reduced; when the thickness is larger than 1 μm, the polarizing plate becomes thicker, which is not preferable.

[ polarizer layer ]

Specifically, the polarizer layer is a layer in which a dichroic dye is adsorbed and oriented on a stretched polyvinyl alcohol resin layer.

As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin layer, a polyvinyl acetate resin saponified may be used. Examples of the polyvinyl acetate resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another copolymerizable monomer. Examples of other monomers copolymerizable with vinyl acetate include: unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, acrylamides having an ammonium group, and the like.

The polyvinyl alcohol resin constituting the polarizer layer (polyvinyl alcohol resin layer) is preferably a completely saponified product. The saponification degree is preferably in the range of 80.0 mol% to 100.0 mol%, more preferably in the range of 90.0 mol% to 99.5 mol%, and most preferably in the range of 94.0 mol% to 99.0 mol%. When the saponification degree is less than 80.0 mol%, there is a problem that the water resistance and the moist heat resistance are remarkably deteriorated after the polarizing plate is produced. In addition, when a polyvinyl alcohol resin having a saponification degree of more than 99.5 mol% is used, the dyeing speed is significantly reduced, and a polarizing laminated film having sufficient polarizing performance may not be obtained, and the following problems may occur: in the production, dyeing time is usually several times as long.

The saponification degree referred to herein is a ratio of an acetoxy group contained in a polyvinyl acetate resin as a raw material of a polyvinyl alcohol resin to a hydroxyl group in a saponification step, and is a numerical value defined by the following formula. It can be determined by a method prescribed in JIS K6726 (1994).

Degree of saponification (% by mole) — (number of hydroxyl group) ÷ (number of hydroxyl group + number of acetate group) × 100

The higher the degree of saponification, the higher the proportion of hydroxyl groups, i.e., the lower the proportion of acetate groups inhibiting crystallization.

The polyvinyl alcohol resin used in the present invention may be partially modified polyvinyl alcohol. Examples thereof include: olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, alkyl esters of unsaturated carboxylic acids, and modified polyvinyl alcohol resins such as acrylamide. The proportion of modification is preferably less than 30 mol%, more preferably less than 10 mol%. When the modification is carried out at more than 30 mol%, the dichroic dye is less likely to be adsorbed, and the polarization performance may be deteriorated.

The average polymerization degree of the polyvinyl alcohol resin is not particularly limited, and is preferably 100 to 10000, more preferably 1500 to 8000, and most preferably 2000 to 5000. The average polymerization degree as referred to herein is also a value determined by a method defined in accordance with JIS K6726 (1994).

Examples of the polyvinyl alcohol resin having such properties include: for example, PVA124 (degree of saponification: 98.0 to 99.0 mol%) manufactured by Coli, 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%); 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%) manufactured by Nippon synthetic chemical industry Co., Ltd.; for example, JAPAN VAM & POVAL CO., 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%), JF-20 (degree of saponification: 98.0 to 99.0 mol%), and the like of LTD. can be applied to the present invention.

The polyvinyl alcohol resin is applied to a substrate film in the form of an aqueous solution and dried to form a polyvinyl alcohol resin layer.

The polyvinyl alcohol resin layer is stretched together with the base film to be oriented, and the oriented dichroic dye is adsorbed to form the polarizer layer. The stretch ratio is preferably more than 5 times, and more preferably more than 5 times and 17 times or less.

The thickness of the polarizer layer (the thickness of the stretched polyvinyl alcohol resin layer) is 10 μm or less, preferably 7 μm or less. By setting the thickness of the polarizer layer to 10 μm or less, a thin polarizing plate can be formed.

Examples of the dichroic dye used in the polarizer layer include: iodine, organic dyes, and the like. As the organic dye, for example, red BR, red LR, red R, pink LB, Rubin (Rubin) BL, purplish red (Bordeaux) GS, Sky Blue LG, lemon yellow, Blue BR, Blue 2R, Navy (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, bright purple BK, sulta (Supra) Blue G, sulta Blue GL, sulta Orange GL, Direct Sky Blue (Direct Sky), Direct Fast Orange (Direct Fast Orange) S, Fast Black (Fast Black) and the like can be used. One of these dichroic substances may be used, or two or more of them may be used in combination.

[ protective film ]

The protective film may not have an optical function but only be a protective film, or may be a protective film having an optical function such as a retardation film or a brightness enhancement film.

The material of the protective film is not particularly limited, and examples thereof include films that have been widely used in the art, such as a cyclic polyolefin resin film, a cellulose acetate resin film containing a resin such as triacetyl cellulose or diacetyl cellulose, a polyester resin film containing a resin such as polyethylene terephthalate, polyethylene naphthalate or polybutylene terephthalate, a polycarbonate resin film, an acrylic resin film, and a polypropylene resin film.

Suitable commercially available products can be applied as the cyclic polyolefin resin, for example, TOPAS (registered trademark) (manufactured by TOPAS advanced Polymers GmbH), ARTON (registered trademark) (manufactured by JSR), ZEONOR (registered trademark) (manufactured by japan risonique), ZEONEX (registered trademark) (manufactured by japan risonique), and APEL (registered trademark) (manufactured by mitsui chemical). When such a cyclic polyolefin resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method can be appropriately used. Commercially available films made of cyclic polyolefin resins previously formed into films, such as Escena (registered trademark) (manufactured by waterlogging chemical industry, ltd.), SCA40 (manufactured by waterlogging chemical industry, ltd.), ZEONOR (registered trademark) films (manufactured by nippon (ltd)), can be used.

The cyclic polyolefin resin film may be a film uniaxially or biaxially stretched. By stretching, an arbitrary phase difference value can be imparted to the cyclic polyolefin resin film. Generally, stretching is continuously performed while winding a film roll, and stretching is performed in a direction of travel of the roll, a direction perpendicular to the direction of travel, or both directions by a heating furnace. The temperature of the heating furnace is usually in the range from about the glass transition temperature of the cyclic polyolefin resin to +100 ℃. The stretching magnification is usually 1.1 to 6 times, preferably 1.1 to 3.5 times in one direction.

The cyclic polyolefin resin film generally has poor surface activity, and therefore, the surface to be bonded to the polarizing film is preferably subjected to a surface treatment such as a plasma treatment, a corona treatment, an ultraviolet irradiation treatment, a flame (flame) treatment, or a saponification treatment. Among these, plasma treatment and corona treatment which can be relatively easily performed are preferable.

Suitable commercially available cellulose acetate resin films include FUJITAC (registered trademark) TD80 (manufactured by FUJITAC corporation), FUJITAC (registered trademark) TD80UF (manufactured by FUJITAC corporation), FUJITAC (registered trademark) TD80UZ (manufactured by FUJITAC corporation), FUJITAC (registered trademark) TD40UZ (manufactured by fuji film corporation), KC8UX2M (manufactured by KONICAMINOLTA corporation), and KC4UY (manufactured by KONICA MINOLTA corporation).

In order to improve the viewing angle characteristics, a liquid crystal layer or the like may be formed on the surface of the cellulose acetate resin film. In addition, the cellulose acetate resin film may be stretched in order to impart a retardation. In order to improve the adhesiveness to a polarizing film, a saponification treatment is generally performed on a cellulose acetate resin film. The saponification treatment may be carried out by immersing the substrate in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide.

An optical layer such as a hard coat layer, an antiglare layer, or an antireflection layer may be formed on the surface of the protective film. The method for forming these optical layers on the surface of the protective film is not particularly limited, and a known method can be used.

In accordance with the demand for thinning, the thickness of the protective film is preferably as thin as possible, preferably 90 μm or less, and more preferably 50 μm or less. Conversely, when too thin, the strength is lowered and the workability is deteriorated, so that it is preferably 5 μm or more.

< methods for producing polarizing laminate film and polarizing plate >

[ embodiment 1]

Fig. 1 is a flowchart illustrating a method for manufacturing a polarizing laminate film and a polarizing plate according to embodiment 1. The method for producing a polarizing laminate film of embodiment 1 includes the steps of:

a coating step (S10) in which an aqueous solution of a polyvinyl alcohol resin is applied to one surface of a base film to obtain a coated film;

a drying step (S20) for drying the coating film to obtain a laminated film having a polyvinyl alcohol resin layer formed on a base film;

a stretching step (S30) for obtaining a stretched laminated film by uniaxially stretching the laminated film; and

and a dyeing step (S40) in which the polyvinyl alcohol resin layer is dyed to form a polarizer layer and a polarizing laminate film is obtained.

In order to manufacture the polarizing plate, the polarizing plate further comprises:

a bonding step (S50) in which a transparent protective film is bonded to the surface of the polarizing laminate film on the side opposite to the base film, thereby obtaining a multilayer film; and

and a peeling step (S60) of peeling the base film from the multilayer film to obtain a polarizing plate including the polarizer layer and the transparent protective film.

< production Processes >

The respective steps of S10 to S60 in fig. 1 will be described in detail below.

[ coating Process (S10) ]

In this step, an aqueous solution of a polyvinyl alcohol resin is applied to one surface of a base film to obtain a coated film.

Suitable materials for the base film are those described in the description of the constituent elements of the above-mentioned polarizing laminate film. The substrate film is preferably a substrate film that can be stretched in a temperature range suitable for stretching the polyvinyl alcohol resin.

In the coating step (S10), a polyvinyl alcohol resin solution obtained by dissolving a polyvinyl alcohol resin powder in a good solvent is preferably coated on the surface of the base film to obtain a coating film. By forming the polyvinyl alcohol resin layer through the coating step, the polyvinyl alcohol resin can be made thinner. As a method for applying the polyvinyl alcohol resin solution to the base film, a known method such as a wire bar coating method, a roll coating method such as reverse coating or gravure coating, a die coating method, a comma coating method, a lip coating method, a spin coating method, a screen printing method, a spray coating method, a dip coating method, or a spray coating method can be appropriately selected. Comma coating (doctor blade coating), die coating, and lip coating are preferable.

The thickness of the polyvinyl alcohol resin layer of the stretched laminated film after stretching in the stretching step (S30) is preferably 10 μm or less. Therefore, the thickness of the resin layer formed through the coating step (S10) and the drying step (S20) is preferably 3 to 50 μm, and more preferably 5 to 40 μm. When the thickness of the resin layer is 3 μm or less, the resin layer becomes too thin after stretching, and dyeing property is remarkably deteriorated, which is not preferable. On the other hand, if the thickness of the resin layer exceeds 50 μm, the thickness of the finally obtained polarizer layer may exceed 10 μm, which is not preferable.

In order to improve the adhesion between the base film and the polyvinyl alcohol resin layer, an undercoat layer may be provided between the base film and the polyvinyl alcohol resin layer. From the viewpoint of adhesion, the primer layer is preferably formed from a composition containing a polyvinyl alcohol resin, a crosslinking agent, and the like. Materials suitable for the undercoat layer and the like are as described in the description of the constituent elements of the polarizing laminate film.

[ drying Process (S20) ]

The coating film obtained in the coating step (S10) is dried, and the solvent of the aqueous solution of the polyvinyl alcohol resin is evaporated, thereby obtaining a laminated film in which a polyvinyl alcohol resin layer is formed on the base film.

The drying step is preferably performed so that the average moisture content of the coated film changes from 5 to 65 mass%/minute, more preferably so that the average moisture content of the coated film changes from 7.5 to 50 mass%/minute, and still more preferably so that the average moisture content of the coated film changes from 7.5 to 30 mass%/minute. The average moisture percentage change in the drying step described herein is a value obtained by dividing the difference between the moisture percentage (%) of the coated film at the start of drying and the moisture percentage (%) of the laminated film at the end of drying by time. Note that, a method of calculating the moisture content of the coating film or the laminated film will be described later. When the average moisture content changes more than 65 mass%/minute, the drying temperature needs to be increased, and therefore, there is a possibility that problems such as dissolution of the base film and discoloration of the polyvinyl alcohol resin occur, which is not preferable. When the average moisture content changes by less than 5 mass%/minute, productivity is not preferable because of deterioration.

The drying temperature in the drying step is, for example, 50 to 200 ℃, preferably 60 to 150 ℃. The drying method includes various methods such as a method of blowing hot air, a method of contacting with a hot roll, and a method of heating with an IR heater, and can be suitably used. In the drying step, the drying temperature refers to an ambient temperature in the drying furnace in the case of a method of blowing hot air or a drying device provided with a drying furnace such as an IR heater, or to a surface temperature of the heat roll in the case of a contact-type drying device such as a heat roll. A laminated film having a polyvinyl alcohol resin layer formed thereon is produced through the above steps. The drying time is, for example, 2 to 20 minutes.

[ stretching Process (S30) ]

In this step, the laminated film obtained in the drying step (S20) is stretched. In the stretching step (S30), uniaxial stretching is started in a state where the moisture percentage of the laminate film having the polyvinyl alcohol resin layer formed on one surface of the base film is 0.3 mass% or more. By setting the water content at the start of uniaxial stretching to 0.3 mass% or more, a polarizing laminate film or a polarizing plate having a polarizer layer with excellent optical properties can be produced. The adjustment of the moisture content can be performed by, for example, adjusting the degree of drying in the drying step (S20) or by adjusting the moisture content in the humidity control step described later.

The degree of drying in the drying step (S20) varies depending on the drying temperature and drying time, as well as the thickness (or weight per unit area) of the polyvinyl alcohol resin coating layer formed on the base film, the moisture concentration of the atmosphere in the drying step, the water vapor pressure, humidity, and the like, and therefore, it is possible to adjust the conditions to a predetermined moisture content (0.3 mass% or more and 3 mass% or less, preferably 0.35 mass% or more and 1.8 mass% or less) by performing a simple preliminary experiment. In some cases, air adjusted to a prescribed water vapor pressure may also be introduced into the drying oven. The laminate film dried to a predetermined moisture content in this manner is preferably subjected to the stretching step (S30) while maintaining the moisture content, or may be subjected to the stretching step (S30) after being adjusted to a predetermined moisture content in the humidity control step described later.

(calculation of Water content of laminated film)

In this specification, the moisture percentage of the laminated film (or the coated film) is a value calculated as follows. First, a sample was taken from the laminated film (or the coated film), the mass (a) of the measurement sample was obtained, and the measurement sample was put into an oven at 105 ℃ for 1 hour. Then, the mass (B) of the measurement sample taken out of the oven was determined. The water content of the laminated film (or coated film) was calculated by the following formula (1).

The moisture content of the laminate film (or coating film) was (a-B)/a × 100 (%)

(calculation of Water content of polyvinyl alcohol resin layer)

In the present specification, the moisture percentage of the polyvinyl alcohol resin layer is a value calculated as follows. First, a sample was taken from the laminated film, the mass (a) of the measurement sample was obtained, and the measurement sample was put into an oven at 105 ℃ for 1 hour. Then, the mass (B) of the measurement sample taken out of the oven was determined. Further, the polyvinyl alcohol resin layer was removed from the measurement sample, and the mass (C) of the base film itself was determined. The moisture content of the polyvinyl alcohol resin layer was calculated by the following formula (2).

The moisture content of the polyvinyl alcohol resin layer was (a-B)/(a-C) × 100 (%)

The moisture content of the polyvinyl alcohol resin layer is preferably 2.5 mass% or more. When the value of the moisture percentage of the polyvinyl alcohol resin layer is within the above range, cracks generated in the stretched polyvinyl alcohol resin layer can be suppressed, and therefore, the value is preferable.

In the stretching step (S30), the uniaxial stretching is preferably performed at a stretching ratio of more than 5 times and 17 times or less. It is further preferable to perform uniaxial stretching at a stretching ratio of more than 5 times and 8 times or less. When the stretching ratio is 5 or less, the polyvinyl alcohol resin layer may be insufficiently oriented, and as a result, the degree of polarization of the polarizer layer may not be sufficiently improved. On the other hand, if the stretch ratio exceeds 17 times, the laminate film is likely to break during stretching, and the thickness of the stretched laminate film after stretching becomes thinner than necessary, which may lower the processability and handleability in the subsequent step. The stretching process in the stretching step (S30) is not limited to one-stage stretching, and may be performed in a plurality of stages. When the stretching treatment is performed in a plurality of stages, the stretching treatment is performed such that the total stretching ratio of all the stretching treatments exceeds 5 times.

In the stretching step (S30) in the present embodiment, a longitudinal stretching process of stretching the laminate film in the longitudinal direction, a transverse stretching process of stretching the laminate film in the transverse direction, and the like may be performed. Examples of the longitudinal stretching method include an inter-roll stretching method and a compression stretching method, and examples of the transverse stretching method include a tenter method.

In the present invention, the stretching treatment is preferably performed by a dry stretching method. This is because, by dry-stretching the polyvinyl alcohol resin layer together with the base film before the dyeing step, the polyvinyl alcohol resin film (polyvinyl alcohol resin layer) thinner than conventional films can be stretched at a high magnification without breaking, and the resulting polarizer layer, and hence the polarizer, can be made thinner.

(humidity control Process)

After the drying step (S20), a humidity control step may be provided in which the moisture content of the laminated film is adjusted to 0.3 mass% or more and 3 mass% or less, preferably 0.35 mass% or more and 1.8 mass% or less. In this case, the laminated film subjected to humidity control in the humidity control step is subjected to a stretching step (S30) while maintaining a water content of 0.3 mass% or more and 3 mass% or less. The humidity control in the humidity control step can be performed by the following method: for example, a method of placing the laminated film in a room adjusted to an appropriate humidity and temperature, a method of passing the laminated film through a humidity-controlling furnace adjusted to an appropriate humidity and temperature, or the like. In the humidity control step, depending on the state of the laminated film up to that point, the moisture content can be increased (humidified) or decreased (dried), and the moisture content itself can be made uniform in the polyvinyl alcohol resin layer without being changed.

[ dyeing Process (S40) ]

In this step, the polyvinyl alcohol resin layer of the laminated film is dyed with a dichroic dye. As the dichroic dye, iodine or an organic dye can be used as described above.

The dyeing step is performed by, for example, immersing the entire stretched laminated film in a solution (dyeing solution) containing the dichroic dye. As the dyeing solution, a solution in which the above-described dichroic dye is dissolved in a solvent can be used. As the solvent of the dyeing solution, water may be generally used, and an organic solvent compatible with water may be further added. The concentration of the dichroic dye is preferably 0.01 to 10 wt%, more preferably 0.02 to 7 wt%, and particularly preferably 0.025 to 5 wt%.

When iodine is used as the dichroic dye, it is preferable to further add an iodide in order to further improve 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, titanium iodide, and the like. The addition ratio of the iodide is preferably 0.01 to 20 wt% based on the dyeing solution. Among the iodides, potassium iodide is preferably added. When potassium iodide is added, the ratio of iodine to potassium iodide is preferably in the range of 1: 5 to 1: 100, more preferably in the range of 1: 6 to 1: 80, and particularly preferably in the range of 1: 7 to 1: 70 in terms of weight ratio.

The immersion time of the stretched laminate film in the dyeing solution is not particularly limited, but is preferably in the range of usually 15 seconds to 15 minutes, and more preferably 1 minute to 3 minutes. The temperature of the dyeing solution is preferably 10 to 60 ℃, and more preferably 20 to 40 ℃.

In the dyeing step, the crosslinking treatment may be performed after dyeing. The crosslinking treatment is performed, for example, by immersing the stretched laminate film in a solution containing a crosslinking agent (crosslinking solution). As the crosslinking agent, conventionally known ones can be used. Examples thereof include: boric acid, boron compounds such as borax, glyoxal, glutaraldehyde, etc. One of these may be used, or two or more of these may be used in combination.

As the crosslinking solution, a solution in which a crosslinking agent is dissolved in a solvent can be used. The solvent may be, for example, water, or may further contain an organic solvent compatible with water. The concentration of the crosslinking agent in the crosslinking solution is not limited to this, but is preferably in the range of 1 to 20% by weight, more preferably 6 to 15% by weight.

Iodide may be added to the crosslinking solution. The addition of the iodide can make the in-plane polarization properties of the polyvinyl alcohol resin layer more uniform. 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, titanium iodide. The content of the iodide is 0.05 to 15 wt%, more preferably 0.5 to 8 wt%.

The time for immersion of the stretched laminate in the crosslinking solution is generally preferably from 15 seconds to 20 minutes, more preferably from 30 seconds to 15 minutes. The temperature of the crosslinking solution is preferably in the range of 10 to 80 ℃.

In the dyeing step (S40), the polyvinyl alcohol resin layer is made to function as a polarizer layer, and a polarizing laminate film is obtained.

[ washing Process ]

Then, a washing step of washing the polarizing laminate film is preferably performed. As the washing step, water washing treatment may be performed. The water washing treatment can be usually performed by immersing the stretched film in pure water such as ion-exchanged water or distilled water. The washing temperature is usually 3 to 50 ℃, preferably 4 to 20 ℃. The immersion time is usually 2 to 300 seconds, preferably 3 to 240 seconds.

In the washing step, a washing treatment with an iodide solution and a washing treatment with water may be combined, or a solution appropriately containing a liquid alcohol such as methanol, ethanol, isopropanol, butanol, or propanol may be used. After the washing step, a water removal step using a nip roller, an air knife, or the like may be provided.

After the washing step, the polarizing laminate film is preferably dried. The drying preferably includes a drying step at a temperature of 60 ℃ or higher, and more preferably includes a drying step at a temperature of 70 ℃ or higher. Of course, a plurality of stages of drying steps at different temperatures may be included. In this case, any one of the drying steps of the plurality of stages may be 60 ℃ or higher.

In addition to the temperature, in order to enhance the drying performance, a method of circulating hot air such as an air volume and an air direction may be optimized, or an IR heater for local heating may be provided. By these aids, the drying efficiency is further improved, contributing to an improvement in productivity.

The upper limit of the drying temperature is preferably a temperature below the boiling point of water, preferably below 100 ℃. Further, it is preferably 95 ℃ or lower, and most preferably 90 ℃ or lower.

[ bonding Process (S50) ]

In this step, a protective film is bonded to the surface of the polarizing laminated film subjected to the above step opposite to the base film side, thereby obtaining a multilayer film. Examples of the method for bonding the polarizer layer and the protective film include: and a method of bonding the polarizer layer and the protective film via the adhesive layer and the adhesive layer. Materials suitable for the protective film are as described in the above description of the constituent elements of the polarizing plate.

(adhesive layer)

The adhesive constituting the adhesive layer generally contains a composition containing an acrylic resin, a styrene resin, a silicone resin, or the like as a base polymer and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound added thereto. Further, fine particles may be mixed in the binder to form a binder layer exhibiting light scattering properties.

The thickness of the adhesive layer is preferably 1 to 40 μm, and it is preferable to coat the adhesive layer thinly within a range not impairing the characteristics of processability and durability, and more preferably 3 to 25 μm. When the thickness is 3 to 25 μm, the film has good processability and is preferably thick in suppressing dimensional change of the polarizing film. When the adhesive layer is less than 1 μm, the adhesiveness is lowered, and when it exceeds 40 μm, troubles such as adhesive overflow are likely to occur.

The method for forming the pressure-sensitive adhesive layer on the protective film or the polarizing plate is not particularly limited, and a solution containing each component represented by the above-mentioned base polymer may be applied to the protective film surface or the polarizing plate surface, dried to form the pressure-sensitive adhesive layer, and then bonded to the spacer or another type of film, or the pressure-sensitive adhesive layer may be formed on the spacer and then bonded and laminated to the protective film surface or the polarizing plate surface. In the case of forming an adhesive layer on the surface of the protective film or the polarizing plate, one or both of the protective film or the surface of the polarizing plate and the adhesive layer may be subjected to an adhesion treatment such as corona treatment, if necessary.

(adhesive layer)

Examples of the adhesive constituting the adhesive layer include: an aqueous adhesive such as a polyvinyl alcohol resin aqueous solution or an aqueous two-pack type urethane latex adhesive is used. Among them, a polyvinyl alcohol resin aqueous solution can be preferably used. The polyvinyl alcohol resin used as the adhesive includes, in addition to a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate as a homopolymer of vinyl acetate, a vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and another monomer copolymerizable therewith, and a modified polyvinyl alcohol polymer obtained by partially modifying hydroxyl groups thereof. The water-based adhesive may contain a polyaldehyde, a water-soluble epoxy compound, a melamine compound, a zirconium oxide compound, a zinc compound, and the like as additives. When such an aqueous adhesive is used, the adhesive layer obtained therefrom is usually much thinner than 1 μm, and even when the cross section is observed with a normal optical microscope, the adhesive layer is not observed in fact.

The method of bonding the film using the water-based adhesive is not particularly limited, and examples thereof include: a method of uniformly coating or casting an adhesive on the surface of a film, laminating another film on the coated surface with a roller or the like, and drying the film. Generally, the adhesive is coated at a temperature of 15 to 40 ℃ after preparation thereof, and the bonding temperature is generally in the range of 15 to 30 ℃.

In the case of using an aqueous adhesive, a film is attached and then dried in order to remove water contained in the aqueous adhesive. The temperature of the drying furnace is preferably 30 to 90 ℃. When the temperature is less than 30 ℃, the adhesive surface tends to be easily peeled off. When the temperature is 90 ℃ or higher, the optical performance of the polarizing plate or the like may be deteriorated by heat. The drying time may be set to 10 to 1000 seconds.

After drying, the product can be further cured for about 12 to 600 hours at room temperature or a slightly higher temperature than the room temperature, for example, about 20 to 45 ℃. The temperature during curing is generally set to be lower than the temperature used during drying.

Further, a photocurable adhesive may be used as the nonaqueous adhesive. Examples of the photocurable adhesive include: a mixture of a photocurable epoxy resin and a photocationic polymerization initiator, and the like.

As a method for laminating a film with a photocurable adhesive, conventionally known methods can be used, and examples thereof include: a method of coating an adhesive on the adhesive surface of the film by a casting method, a bar coating method, a gravure coating method, a comma coating method, a doctor blade method, a die coating method, a dip coating method, a spray method, or the like, and stacking 2 films. The casting method is a method of spreading 2 films as an object to be coated while running down an adhesive on the surface thereof in a substantially vertical direction, a substantially horizontal direction, or an oblique direction therebetween.

After the adhesive is applied to the surface of the film, 2 films are bonded by being nipped by a nip roll or the like. Further, a method of pressing the laminate with a roller or the like to spread it uniformly may be applied. In this case, metal, rubber, or the like can be used as a material of the roller. Further, it is also preferable to adopt a method of spreading the laminate by passing the laminate between rolls and applying pressure. In this case, the rollers may be made of the same material or different materials. The thickness of the adhesive layer after the bonding using the nip roll or the like is preferably 5 μm or less and 0.01 μm or more before drying or curing.

In order to improve the adhesiveness, the adhesive surface of the film may be subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, saponification treatment, or the like as appropriate. Examples of the saponification treatment include: and immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide.

In the case of using a photocurable resin as the adhesive, the photocurable adhesive is cured by irradiation with active energy rays after the lamination of the films. The light source of the active energy ray is not particularly limited, and active energy rays having an emission distribution at a wavelength of 400nm or less are preferable, and specifically, 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, a microwave-excited mercury lamp, a metal halide lamp, or the like can be preferably used.

The intensity of light irradiation to the photocurable adhesive can be determined according to the photocurable adhesiveThe composition is not particularly limited, and the irradiation intensity in the wavelength region effective for activating the polymerization initiator is preferably 0.1 to 6000mW/cm². The irradiation intensity is 0.1mW/cm²When the above reaction time is above 6000mW/cm, the reaction time is not too long²In the following cases, yellowing of the epoxy resin and deterioration of the polarizing film due to heat emitted from the light source and heat generated during curing of the photocurable adhesive rarely occur. The light irradiation time of the photocurable adhesive can be applied according to the photocurable adhesive to be cured, and is not particularly limited, and it is preferable that the cumulative light amount represented by the product of the irradiation intensity and the irradiation time is 10 to 10000mJ/cm²The mode of (2). The cumulative light amount of the photocurable adhesive was 10mJ/cm²In the above case, the curing reaction can be more reliably carried out by generating a sufficient amount of active species derived from the polymerization initiator to 10000mJ/cm²In the following case, the irradiation time is not excessively long, and good productivity can be maintained. The thickness of the adhesive layer after the irradiation with the active energy ray is usually about 0.001 to 5 μm, preferably 0.01 μm or more and 2 μm or less, and more preferably 0.01 μm or more and 1 μm or less.

When the photocurable adhesive of the film including the polarizer layer and the protective film is cured by irradiation with an active energy ray, it is preferable to cure the photocurable adhesive under conditions that do not reduce various functions of the polarizing plate, such as the degree of polarization, transmittance, and color tone of the polarizer layer, and the transparency of the protective film.

In the bonding step (S50) of bonding the polarizer layer and the protective film, when a solution containing a solvent is used to form the adhesive layer or the pressure-sensitive adhesive layer, the multilayer film is dried. The drying is mainly performed for the purpose of drying the adhesive layer or the pressure-sensitive adhesive layer, and the drying conditions are substantially the same as those after the aforementioned washing step. In particular, when a polyvinyl alcohol resin aqueous solution or the like is used to form the adhesive layer, it is preferable to perform drying at a temperature of 60 ℃ or higher.

[ peeling step (S60) ]

After the bonding step (S50), a peeling step (S60) of peeling the base material film from the multilayer film to obtain a polarizing plate having a polarizer layer and a protective film is performed. The method for peeling the base film from the multilayer film is not particularly limited, and the same method as the peeling film peeling step performed in a general polarizing plate with an adhesive can be employed. After the bonding step (S50), the peeling may be performed immediately, or may be performed after being wound in a roll form and then provided with a separate peeling step.

[ other optical layers ]

The polarizing plate obtained in the present invention can be used as a polarizing plate in which other optical layers are laminated in actual use. In addition, the protective film may have functions of these optical layers.

Examples of other optical layers include: a reflective polarizing film which transmits a polarized light of a certain polarization and reflects a polarized light showing a property opposite to the polarized light, a film with an antiglare function having a surface having a concavo-convex shape, a film with a surface antireflection function, a reflective film having a surface reflection function, a semi-transmissive reflective film having both a reflection function and a transmission function, and a viewing angle compensation film.

As a commercially available product corresponding to a reflective polarizing film that transmits a certain polarized light and reflects a polarized light showing a property opposite thereto, for example: DBEF (available from Sumitomo 3M, 3M Co., Ltd.) and APF (available from Sumitomo 3M, 3M Co., Ltd.). As the viewing angle compensation film, there can be mentioned: an optical compensation film in which a crystalline compound is coated and oriented on the surface of a base material, a retardation film formed of a polycarbonate resin, and a retardation film containing a cyclic polyolefin resin. Commercially available products corresponding to optical compensation films in which a crystalline compound is coated on the surface of a substrate and oriented include: WV film (manufactured by Fuji photo film Co., Ltd.), NH film (manufactured by JX Ridai Stone energy Co., Ltd.), NV film (manufactured by JX Ridai Stone energy Co., Ltd.), and the like. Further, commercially available products corresponding to a retardation film containing a cyclic polyolefin resin include: ARTON (registered trademark) membrane (manufactured by JSR corporation), ESCENA (registered trademark) (manufactured by SEWAGE CHEMICAL CO., LTD.), ZEONOR (registered trademark) membrane (manufactured by Nippon Ralskii corporation), and the like.

[2 nd embodiment ]

Fig. 2 is a flowchart showing a method for manufacturing the polarizing laminate film and the polarizing plate according to embodiment 2. The method for producing a polarizing laminate film according to embodiment 2 includes the steps of:

a first coating step (S11) of coating an aqueous solution of a polyvinyl alcohol resin on one surface of a base film to obtain a coated film;

a first drying step (S21) of drying the coating film to obtain a laminated film having a polyvinyl alcohol resin layer formed on one surface of a base film;

a second coating step (S12) of coating an aqueous solution of a polyvinyl alcohol resin on the other surface of the base film to obtain a double-coated film;

a 2 nd drying step (S22) of drying the both-side coated film to obtain a both-side laminated film in which a polyvinyl alcohol resin layer is formed on both sides of a base film;

a stretching step (S31) for obtaining a stretched laminated film by uniaxially stretching the double-sided laminated film; and

To manufacture the polarizing plate, the method further comprises the following steps in sequence:

a bonding step (S50) in which a transparent protective film is bonded to the surface of the polarizing laminate film on the side opposite to the base film to obtain a multilayer film; and

In this embodiment, by forming the polyvinyl alcohol resin layers on both surfaces of the base film, two polarizer layers can be formed at the same time.

< production Processes >

The following describes each step of embodiment 2 in fig. 2 in comparison with the corresponding step of embodiment 1 in fig. 1. Features not specifically described are performed in the same manner as in the corresponding step of embodiment 1. In addition, the same steps are denoted by the same reference numerals, and description thereof is omitted.

[1 st coating step (S11) ]

The first coating step (S11) is the same as the coating step (S10) in fig. 1.

[1 st drying step (S21) ]

The 1 st drying step (S21) is preferably performed so that the moisture percentage of the dried laminate film is 0.3 mass% or more and 3 mass% or less, preferably 0.35 mass% or more and 1.8 mass% or less. By setting the water content to this value, the water content at the start of uniaxial stretching can be easily adjusted to a desired value in the stretching step (S31) described later. The preferable numerical range of the change in the average moisture content of the coating film in the 1 st drying step (S21), preferable drying conditions, and the like are as described in the drying step (S20) in embodiment 1.

[ second coating step (S12) ]

The second coating step (S12) is a step of applying an aqueous solution of a polyvinyl alcohol resin to the surface of the base film opposite to the surface to which the aqueous solution of a polyvinyl alcohol resin was applied in the first coating step (S11) to obtain a double-coated film. The conditions for applying the aqueous solution of the polyvinyl alcohol resin in the second application step (S12) are as described in the application step (S10) of embodiment 1.

[2 nd drying step (S22) ]

The 2 nd drying step (S22) is the same as the drying step (S20) in embodiment 1. The preferable numerical range, preferable drying conditions, and the like of the average moisture percentage change of the coating film in the second drying step (S22) are also as described in the drying step (S20) in embodiment 1.

[ stretching Process (S31) ]

In this step, the double-sided laminate film obtained in the 2 nd drying step (S22) is stretched. In the stretching step (S31), uniaxial stretching is started in a state where the moisture percentage of the double-sided laminate film is 0.5 mass% or more. By setting the water content at the start of uniaxial stretching to 0.5 mass% or more, a polarizing laminate film or a polarizing plate having a polarizer layer with excellent optical properties can be produced. The adjustment of the moisture content can be performed by adjusting the degree of drying in the 1 st drying step (S21) and the 2 nd drying step (S22), or by adjusting in the humidity control step described later, for example.

The degree of drying in the 1 st drying step (S21) and the 2 nd drying step (S22) varies depending on the temperature and time in the above-described respective steps, and also varies depending on the thickness (or weight per unit area) of the polyvinyl alcohol resin coating layer formed on the base film, the moisture concentration of the atmosphere in the drying step, the water vapor pressure, the humidity, and the like, and therefore, conditions can be adjusted by performing a simple preliminary experiment so as to achieve a predetermined moisture content (0.5 mass% or more and 4 mass% or less, preferably 0.6 mass% or more and 2.5 mass% or less) after passing through the 2 nd drying step (S22). In some cases, air adjusted to a prescribed water vapor pressure may also be introduced into the drying oven. The laminated film dried to a predetermined moisture content in the 2 nd drying step (S22) in this way is preferably supplied to the stretching step (S31) while maintaining the moisture content, or may be supplied to the stretching step (S31) after being adjusted to a predetermined moisture content in the humidity control step described later.

(humidity control Process)

After the 2 nd drying step (S22), a humidity control step may be further provided in which the moisture content of the double-sided laminated film is adjusted to 0.5 mass% or more and 4 mass% or less, preferably 0.6 mass% or more and 2.5 mass% or less. In this case, the double-sided laminate film subjected to humidity control in the humidity control step can be subjected to the stretching step (S31) while maintaining the water content of 0.5 mass% or more and 4 mass% or less, preferably 0.6 mass% or more and 2.5 mass% or less. The humidity control in this humidity control step is performed in the same manner as described in the humidity control step of embodiment 1.

Examples

[ example 1]

The process proceeds to a dyeing step (S40) to produce a double-sided polarizing laminate film, and further proceeds to a peeling step (S60) to produce a polarizing plate, as shown in the flowchart of fig. 2.

(substrate film)

A base material film having a 3-layer structure was produced by coextrusion molding using a multilayer extruder, and resin layers each composed of homopolypropylene (product name: Sumitomo Noblen FLX80E4, product name: Sumitomo Noblen Tm 163 c) as a homopolymer of propylene were disposed on both sides of a resin layer composed of a propylene/ethylene random copolymer (product name: Sumitomo Noblen W151, product name: Sumitomo flaen Tm 138 c) containing about 5 wt% of ethylene units. The total thickness of the obtained substrate film was 100 μm, and the thickness ratio of each layer (FLX80E4/W151/FLX80E4) was 3/4/3.

(priming solution)

Polyvinyl alcohol powder (trade name: Z-200, average degree of polymerization 1100, average degree of saponification 99.5 mol%, manufactured by Nippon synthetic chemical industry Co., Ltd.) was dissolved in hot water at 95 ℃ to prepare an aqueous solution having a concentration of 3 wt%. To the obtained aqueous solution, 1 part by weight of a crosslinking agent (product name: Sumirezresin650, manufactured by Takaguchi chemical Co., Ltd.) was mixed relative to 2 parts by weight of the polyvinyl alcohol powder to obtain a primer solution.

(aqueous solution of polyvinyl alcohol resin)

Polyvinyl alcohol powder (trade name: PVA124, average polymerization degree 2400, average saponification degree 98.0 to 99.0 mol%) was dissolved in hot water at 95 ℃ to prepare an aqueous polyvinyl alcohol solution having a concentration of 8 wt%.

(1 st coating step, 1 st drying step)

After one surface of the substrate film was subjected to corona treatment while continuously conveying the substrate film, the corona-treated surface was continuously coated with the above-mentioned undercoat solution using a small-diameter gravure coater, and dried at 60 ℃ for 3 minutes, thereby forming an undercoat layer having a thickness of 0.2 μm. Subsequently, the polyvinyl alcohol aqueous solution was continuously applied to the undercoat layer using a comma coater while the film was conveyed (coating step 1), and dried at 90 ℃ for 4 minutes (drying step 1), thereby forming a polyvinyl alcohol resin layer (hereinafter referred to as "PVA layer 1") having a thickness of 11.5 μm on the undercoat layer, and obtaining a single-sided laminated film.

(measurement of moisture content)

The moisture content of the single-sided laminate film produced in the above manner was measured, and found to be 0.39 mass%. From this moisture content and the moisture content of the coated film before the drying step 1, it was calculated that the drying rate in the drying step 1 was 16.4 mass%/min as the change in the average moisture content. The moisture percentage of the 1 st PVA layer monomer of the single-sided laminate film was measured, and the result was 2.76 mass%.

(2 nd coating step, 2 nd drying step)

In the single-sided laminate film produced as described above, a primer layer of 0.2 μm was formed on the surface of the substrate film opposite to the surface on which the 1 st PVA layer was formed, and a polyvinyl alcohol aqueous solution was applied to the primer layer (the 2 nd application step) and dried at 90 ℃ for 4 minutes (the 2 nd drying step), thereby forming a polyvinyl alcohol resin layer (hereinafter, "the 2 nd PVA layer") having a thickness of 10.6 μm on the primer layer, and obtaining a double-sided laminate film.

(measurement of moisture content)

The water content of the double-sided laminate film produced in the above manner was measured, and found to be 0.6 mass%. From this moisture content and the moisture content of the both-side coated film before the 2 nd drying step, it was calculated that the drying rate in the 2 nd drying step was 15.9 mass%/min as the change in the average moisture content. The water content of the PVA layer 1 alone and the water content of the PVA layer 2 alone in the double-sided laminate film were measured to be 4.66 mass% and 3.79 mass%, respectively.

(stretching Process)

While continuously conveying the double-sided laminated film obtained in the above manner, the film was stretched 5.8 times in the longitudinal direction (film conveying direction) at a stretching temperature of 160 ℃ by a method of stretching between nip rolls to obtain a stretched laminated film. In the stretched laminated film, the thickness of the 1 st PVA layer became 5.7 μm and the thickness of the 2 nd PVA layer became 5.4. mu.m.

(dyeing step)

The stretched laminated film obtained in the above manner was immersed in a dyeing solution containing iodine and potassium iodide at 30 ℃ for a retention time of 180 seconds while continuously being conveyed, to dye the 1 st PVA layer and the 2 nd PVA layer, and then the excess dyeing solution was washed away with pure water at 10 ℃. Then, this was immersed in a crosslinking solution containing boric acid and potassium iodide at 76 ℃ so that the residence time was about 600 seconds to perform crosslinking treatment. Then, the film was washed with pure water at 10 ℃ for 4 seconds and dried at 80 ℃ for 300 seconds, thereby obtaining a polarizing laminated film.

The mixing ratio of the dyeing solution and the crosslinking solution was set as follows:

< dyeing solution >

Water: 100 parts by weight

Iodine: 0.6 part by weight

Potassium iodide: 10 parts by weight

< crosslinking solution >

Water: 100 parts by weight

Boric acid: 9.5 parts by weight

Potassium iodide: 5 parts by weight.

(measurement of optical Properties)

The 1 st PVA layer (1 st polarizer layer) and the 2 nd PVA layer (2 nd polarizer layer) of the obtained polarizing laminate film were peeled off and removed from the polarizer layer not to be measured, and a laminate comprising a polarizer layer and a substrate film as a measurement object was prepared, and an acrylic pressure-sensitive adhesive layer was laminated on the polarizer layer of the laminate and bonded to glass via the acrylic pressure-sensitive adhesive layer, and this was used as an evaluation sample.

The optical properties of the samples were evaluated by measurement with an integrating sphere spectrophotometer (manufactured by Nippon spectral Co., Ltd., V7100). Incident light is made incident from the glass side, and the MD transmittance and TD transmittance in the wavelength range of 380nm to 780nm are obtained, and the individual transmittance and the degree of polarization at each wavelength are calculated based on the expressions (3) and (4), and further the visibility correction is performed by a 2-degree field of view (C light source) according to JIS Z8701, and the visibility correction individual transmittance (Ty) and the visibility correction degree of polarization (Py) are obtained.

In the above description, "MD transmittance" refers to transmittance when the direction of polarized light from the glan-thompson prism is parallel to the transmission axis of the evaluation sample, and is expressed as "MD" in the formulas (3) and (4). The "TD transmittance" is a transmittance when the direction of polarized light from the glan-thompson prism is orthogonal to the transmission axis of the evaluation sample, and is represented as "TD" in the formulas (3) and (4).

(MD + TD)/2 (3) in% transmittance alone

Degree of polarization (%) { (MD-TD)/(MD + TD) }^1/2× 100 formula (4).

(adhesive solution)

Polyvinyl alcohol powder (trade name: KL-318, average polymerization degree 1800, manufactured by Korea corporation) was dissolved in hot water at 95 ℃ to prepare a 3% by weight aqueous polyvinyl alcohol solution. To the obtained aqueous solution, 1 part by weight of a crosslinking agent (product name: Sumirezresin650, manufactured by takaki chemical industries, inc.) was mixed as an adhesive solution with respect to 2 parts by weight of the polyvinyl alcohol powder.

(bonding step)

While continuously feeding the polarizing laminate film obtained above, the adhesive solution was applied to the polarizer layers on both sides, and then a protective film (product name: KC4UY manufactured by KONICA MINOLTA corporation, transparent protective film made of triacetyl cellulose (TAC)) having a thickness of 40 μm and subjected to saponification treatment was bonded to the applied surface, and the film was passed between a pair of bonding rollers and pressure-bonded to obtain a multilayer film composed of KC4UY, 1 st polarizer layer/undercoat layer/base film/undercoat layer/2 nd polarizer layer/KC 4UY (bonding step). The multilayer film was peeled between the substrate film and the base coat to form two laminates of KC4 UY/1 st polarizer layer/base coat/substrate film and base coat/2 nd polarizer layer/KC 4UY, and further, the substrate film was peeled off and removed (peeling step). Two polarizing plates each composed of KC4 UY/polarizer layer/primer layer/adhesive layer/ZF-14 were obtained by laminating a cyclic polyolefin resin film (product name: ZF-14, manufactured by Nippon Ralskii Co., Ltd.) having a thickness of 23 μm on the primer layer of each laminate via an adhesive layer. The peeling step did not cause a failure such as breakage.

[ example 2]

A polarizing laminated film and a polarizing plate were produced in the same manner as in example 1, except that the drying conditions in the 1 st drying step and the 2 nd drying step were changed to 90 ℃ for 3 minutes, and the thickness of the 1 st PVA layer after the 1 st drying step was 9.2 μm and the thickness of the 2 nd PVA layer after the 2 nd drying step was 9.4 μm. The peeling step did not cause a failure such as breakage.

[ example 3]

A polarizing laminated film and a polarizing plate were produced in the same manner as in example 1 except that the drying conditions in both the 1 st drying step and the 2 nd drying step were changed to 90 ℃ for 2 minutes and then 80 ℃ for 1.5 minutes for 3.5 minutes, and further, the thickness of the 1 st PVA layer after the 1 st drying step was 9.3 μm and the thickness of the 2 nd PVA layer after the 2 nd drying step was 9.2 μm. The peeling step did not cause a failure such as breakage.

[ example 4]

A polarizing laminated film and a polarizing plate were produced in the same manner as in example 1, except that the drying conditions in both the 1 st and 2 nd drying steps were changed to 75 ℃ for 2 minutes and then 80 ℃ for 2 minutes for 4 minutes, and the thickness of the 1 st PVA layer after the 1 st drying step was 9.0 μm and the thickness of the 2 nd PVA layer after the 2 nd drying step was 9.1 μm. The peeling step did not cause a failure such as breakage.

[ example 5]

The process proceeds to a dyeing step (S40) to produce a single-sided polarizing laminate film, and further proceeds to a peeling step (S60) to produce a polarizing plate, as shown in the flowchart of fig. 1. The same materials as in examples 1 to 4 were used for the base film, the undercoat solution, and the polyvinyl alcohol aqueous solution.

(1 st coating step, 1 st drying step)

One surface of the substrate film was subjected to corona treatment while continuously conveying the substrate film, and then the corona-treated surface was continuously coated with the above-mentioned undercoat solution using a small-diameter gravure coater and dried at 60 ℃ for 3 minutes to form an undercoat layer having a thickness of 0.2 μm. Subsequently, the polyvinyl alcohol aqueous solution was continuously applied to the undercoat layer using a comma coater while the film was conveyed (coating step 1), dried at 90 ℃ for 2 minutes, then dried at 80 ℃ for 1.5 minutes, and dried for 3.5 minutes in total (drying step 1), thereby forming a1 st PVA layer having a thickness of 9.2 μm on the undercoat layer to obtain a single-sided laminated film.

(stretching Process)

While continuously conveying the single-sided laminated film obtained in the above manner, the single-sided laminated film was stretched 5.8 times in the longitudinal direction (film conveying direction) at a stretching temperature of 160 ℃ by a method of stretching between nip rolls to obtain a single-sided stretched laminated film. In the stretched laminated film, the thickness of the 1 st PVA layer became 4.7. mu.m.

(dyeing step)

The single-sided stretched laminate film obtained in the above manner was dyed in the same manner as in example 1 to obtain a single-sided polarizing laminate film.

(bonding step)

While continuously conveying the obtained single-sided polarizing laminate film, the same adhesive solution as in example 1 was applied to a polarizing plate (1 st polarizing plate layer), and then a protective film (product name: KC4UY, a transparent protective film made of triacetyl cellulose (TAC)) having a thickness of 40 μm and subjected to saponification treatment was bonded to the applied surface, and the film was pressed between a pair of bonding rolls to obtain a multilayer film composed of KC4 UY/1 st polarizing plate layer/base film (bonding step).

The base film was peeled and removed from the interlayer between the base film and the undercoat layer in the multilayer film to obtain a laminate composed of KC4 UY/the 1 st polarizer layer/the undercoat layer (peeling step). A cyclic polyolefin resin film (trade name: ZF-14, manufactured by Nippon Ralskii Co., Ltd.) having a thickness of 23 μm was laminated on the primer layer of the obtained laminate via an adhesive layer, to obtain a polarizing plate composed of KC4UY, No. 1 polarizer layer, primer layer, adhesive layer and ZF-14. The peeling step did not cause a failure such as breakage.

[ example 6]

A single-sided polarizing laminate film and a polarizing plate were produced in the same manner as in example 5, except that the drying conditions in the first drying step 1 were the same as in example 4, and the thickness of the PVA layer after the first drying step 1 was set to 9.0 μm. The peeling step did not cause a failure such as breakage.

Comparative example 1

A polarizing laminate film and a polarizing plate were produced in the same manner as in example 1 except that the thickness of the 1 st PVA layer after the 1 st drying step was changed to 9.0 μm and the thickness of the 2 nd PVA layer after the 2 nd drying step was changed to 8.9 μm.

Comparative example 2

A polarizing laminate film and a polarizing plate were produced in the same manner as in example 1 except that the thickness of the 1 st PVA layer after the 1 st drying step was changed to 9.2 μm and the thickness of the 2 nd PVA layer after the 2 nd drying step was changed to 9.3 μm.

Table 1 shows the drying conditions and the measurement results in examples 1 to 6 and comparative examples 1 and 2.

[ Table 1]

As shown in table 1, in comparative examples 1 and 2, the moisture percentage of the laminate film in the state of being subjected to the stretching step was less than 0.5 mass%, and the moisture percentage after the 1 st drying step was less than 0.3 mass%. The polarizing laminate films of comparative examples 1 and 2 had a lower visibility correction polarization degree Py than the polarizing laminate films of examples 1 to 6.

An acrylic adhesive layer was provided on the KC4UY surface of the polarizing plate comprising KC4UY, polarizer layer, primer layer, adhesive layer and ZF-14 produced in examples 1 to 6, and was bonded to glass via the adhesive layer, and the test sample was subjected to the moist heat resistance test and the heat resistance test described below. As a result, Δ Py in the moist heat resistance test of each of the evaluation samples was about 0.001%, and Δ Py in the heat resistance test was about 0.005%, which was a level without any problem. The polarizing plates produced in comparative examples 1 and 2 were evaluated in the same manner, and as a result, Δ Py was larger than that of the evaluation samples of examples 1 to 6.

(1) Evaluation of Wet Heat resistance

The degree of visibility-corrected polarization Py after the moist heat resistance test in which the film was left to stand at 65 ℃ under an environment of 90% relative humidity for 500 hours and the Py before the test were measured by using an absorption spectrophotometer (V7100, manufactured by japan corporation), and the difference Δ Py between them (Py before the test — Py after the test) was determined. In the measurement of Py, an evaluation sample was set so that the glass surface was irradiated with incident light, and after the above-mentioned moist heat resistance test, the test was left to stand at 23 ℃ and 55% relative humidity for about 12 hours, and then the visibility-corrected polarization degree Py after the test was measured. The smaller the absolute value of Δ Py, the higher the moist heat resistance.

(2) Evaluation of Heat resistance

A heat resistance test was performed by leaving the test stand at 85 ℃ for 500 hours in a dry environment, and the difference Δ Py between the visibility corrected polarization degree Py before and after the test (Py before the test — Py after the test) was determined in the same manner as described in the above-mentioned wet heat resistance test. The smaller the absolute value of Δ Py, the higher the heat resistance.

Claims

1. A method for producing a polarizing laminate film, comprising:

a coating step of coating an aqueous solution of a polyvinyl alcohol resin on a base film to obtain a coating film;

a drying step of drying the coating film to obtain a laminated film in which a polyvinyl alcohol resin layer is formed on a base film;

a stretching step of obtaining a stretched laminated film by uniaxially stretching the laminated film; and

a dyeing step of dyeing the polyvinyl alcohol resin layer to form a polarizer layer and obtain a polarizing laminated film, and

the thickness of the polarizer layer in the obtained polarizing laminate film is 10 μm or less,

in the stretching step, the uniaxial stretching is started in a state where the moisture content of the laminate film is 0.80 mass% or more and 1.13 mass% or less and the moisture content of the polyvinyl alcohol resin layer is 5.52 mass% or more and 7.65 mass% or less.

2. The method of claim 1, wherein the drying step is performed such that the average moisture percentage of the coated film is changed to 5 to 65 mass%/minute.

3. The method for producing a polarizing laminate film according to claim 1 or 2, wherein a humidity control step of controlling the moisture content of the laminate film to 0.80 mass% or more and 1.13 mass% or less is included after the drying step, and the laminate film subjected to humidity control in the humidity control step is subjected to the stretching step while maintaining the moisture content thereof.

4. A method of manufacturing a polarizing plate, comprising:

a step of producing a polarizing laminated film by the production method according to any one of claims 1 to 3;

a bonding step of bonding a protective film to a surface of the polarizing laminate film on the side opposite to the base film to obtain a multilayer film; and

and a peeling step of peeling the base film from the multilayer film to obtain a polarizing plate including the polarizer layer and the protective film.