TWI795379B - Polarizing film and method for producing polarizing laminzted film - Google Patents

Abstract

The present invention provides a polarizing film having high optical characteristics while suppressing contraction force, and a method for producing a polarizing laminated film. In the polarizing film, iodine is oriented in a polyvinyl alcohol-based resin layer. The polarizing film has a boron content of 2.5 wt% or more and 4.1 wt% or less; a visibility correction monoaxial transmittance (Ty) of more than 40.5%; the ratio represented by a parallel absorbance/orthogonal absorbance at a wavelength of 475 nm is less than 0.022.

Description

Polarizing film and method for producing polarizing laminated film

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

Polarizing plates are widely used in display devices such as liquid crystal display devices and the like. A polarizing plate is generally composed of a polarizer layer made of polyvinyl alcohol-based resin and a protective film attached to one or both sides. With the development of mobile devices such as image display devices and thin TVs, there is an increasing demand for thinner polarizing plates.

As a method of producing a polarizing plate having a thin-film polarizer layer, it is known to apply a coating solution containing a polyvinyl alcohol-based resin on a base film to form a laminated film of a polyvinyl alcohol-based resin layer, and to stretch the laminated film. Thereafter, a dyeing treatment in which a dichroic dye is adsorbed on a polyvinyl alcohol-based resin layer is performed to produce a polarizing laminated film in which a polarizer layer is formed on a base film (for example, Patent Document 1).

According to the above-mentioned method, since the polyvinyl alcohol-based resin layer is formed by coating, the polyvinyl alcohol-based resin layer is easily thinned compared to thinning of a single-layer (monomeric) film composed of the polyvinyl alcohol-based resin, Therefore, thinning of the polarizer layer becomes easy.

Patent Document 1 describes high-magnification stretching in order to obtain good optical characteristics.

On the other hand, it is not a manufacturer of the above-mentioned method of coating a coating liquid containing a polyvinyl alcohol-based resin on a base film, and Patent Document 2 describes a polarizer that increases the degree of boric acid crosslinking in order to suppress the occurrence of bleeding. piece.

[Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent No. 5667016

[Patent Document 2] Japanese Patent No. 5985813

In order to increase the polarization degree of the polarizer layer and the polarizer, as mentioned above, in addition to increasing the elongation ratio and increasing the degree of boric acid crosslinking, it is also considered to increase the necking ratio. However, in these methods, the shrinkage force tends to increase when the polarizer layer or the polarizer is heated, and cracks of the polarizer layer or the polarizer tend to occur easily.

An object of the present invention is to provide a polarizing film and a method for producing a polarizing laminated film having high optical properties and a small shrinkage force.

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

[1] A polarizing film, which is a polarizing film in which iodine is aligned to a polyvinyl alcohol-based resin layer; the boron content is not less than 2.5% by weight and not more than 4.1% by weight; the transmittance (Ty) of a single element after correction of sensitivity exceeds 40.5%; the wavelength is 475nm The ratio represented by the parallel absorbance/perpendicular absorbance is less than 0.022.

[2] The polarizing film according to [1], wherein the width in the direction of the absorption axis is 2 mm and the shrinkage force per 5 μm thickness is less than 1.77 N/5 μm when kept at 80° C. for 4 hours.

[3] The polarizing film according to [1] or [2], which has a thickness of 10 μm or less.

[4] A polarizing plate having a protective film on at least one surface of the polarizing film according to any one of [1] to [3].

[5] A method for producing a polarizing laminated film comprising, in order: forming a polyvinyl alcohol-based resin layer on at least one surface of a base film to obtain a resin layer forming a laminated film; stretching the laminated film to obtain The stretching step of stretched film; the dyeing step of obtaining a dyed laminated film by dyeing the aforementioned polyvinyl alcohol-based resin layer of the aforementioned stretched film with iodine to form a dyed layer; the dyed layer of the aforementioned dyed laminated film containing boric acid The crosslinking solution is crosslinked to form a crosslinked layer to obtain a crosslinked laminated film; The boron-removing step of the laminated film; wherein the aforementioned boron-removing step has a boron-removing liquid contact step in which the aforementioned cross-linked layer is in contact with the boron-removing liquid, and the aforementioned boron-removing liquid has a boric acid concentration lower than that of the aforementioned cross-linking liquid; In the step of contacting the boron removal solution, the magnitude of the tension applied to the cross-linked laminated film is controlled so as to be smaller than the magnitude of the tension applied to the laminated film with the dyed layer in the aforementioned cross-linking step.

[6] A method for manufacturing a polarizing plate, comprising, in order: a step of manufacturing a polarizing laminate film by the manufacturing method described in [5]; attaching a protective film to the surface of the polarizer layer opposite to the base film. a step of film; and a step of peeling and removing the aforementioned substrate film.

According to the present invention, it is possible to provide a polarizing film and a polarizing plate having high optical properties and suppressing shrinkage force. Furthermore, according to the present invention, it is possible to provide a method for producing a polarizing laminate film having a polarizer layer having excellent optical properties and a small shrinkage force, and a method for producing a polarizing plate.

1‧‧‧Polarizing plate with protective film on one side

2‧‧‧Polarizing plate with protective film on both sides

5‧‧‧polarizer layer

6‧‧‧Polyvinyl alcohol resin layer

6’‧‧‧Polyvinyl alcohol resin layer

10‧‧‧The first protective film

15‧‧‧The first adhesive layer

20‧‧‧Second protective film

25‧‧‧Second Adhesive Layer

30‧‧‧Substrate film

30’‧‧‧Substrate film

100‧‧‧Laminated film

200‧‧‧stretch film

300‧‧‧Polarizing laminated film

400‧‧‧multilayer film

Fig. 1 shows a flowchart of a method of manufacturing a polarizing laminated film and a method of manufacturing a polarizing plate of the present invention.

Fig. 2 is a schematic cross-sectional view showing an example of the layer configuration of the laminated film obtained in the resin layer forming step.

Fig. 3 is a schematic cross-sectional view showing an example of the layer constitution of the stretched film obtained in the stretching step.

Fig. 4 is a schematic cross-sectional view showing an example of the layer constitution of the polarizing multilayer film obtained in the boron removal step.

Fig. 5 is a schematic cross-sectional view showing an example of the layer configuration of a polarizing plate with a protective film obtained in the first protective film bonding step.

Fig. 6 is a schematic cross-sectional view showing an example of the layer configuration of a polarizing plate with a protective film on one side obtained in the peeling step.

Fig. 7 is a schematic cross-sectional view showing an example of the layer configuration of a polarizing plate with protective films on both sides obtained in the second protective film bonding step.

<Polarizing film>

The polarizing film is one in which iodine is aligned to the polyvinyl alcohol-based resin layer, for example, a polarizer layer as a polarizing laminated film described later can be obtained. The polarizing film has a boron content of 2.5% to 4.1% by weight, a sensitivity-corrected single transmittance (Ty) exceeding 40.5%, and a ratio expressed by parallel absorbance/perpendicular absorbance at a wavelength of 475 nm of less than 0.022. The polarizing film is a stretched film in which a polyvinyl alcohol-based resin layer is stretched, and the stretching is preferably uniaxial stretching.

Boron in the polarizing film is derived from boric acid in a crosslinking solution for crosslinking a polyvinyl alcohol-based resin layer described later. When the boron content of the polarizing film is large, that is, when the degree of crosslinking of the polyvinyl alcohol-based resin layer is high, the optical properties such as the degree of polarization can be improved, but the shrinkage force when the polarizing film is heated tends to increase.

On the other hand, when the boron content of the polarizing film is small, that is, when the degree of crosslinking is low, the shrinkage force of the polarizing film when heated can be reduced, but sufficient water resistance and good optical properties tend to be difficult to obtain.

The boron content of the polarizing film may be not less than 2.5% by weight and not more than 4.1% by weight. Thereby, the contraction force which a polarizing film generate|occur|produces at the time of heating can be suppressed. The boron content of the polarizing film is more preferably from 2.6% by weight to 4.0% by weight, more preferably from 2.7% by weight to 3.5% by weight. The boron content of the polarizing film was measured in accordance with the description in Examples described later.

When the polarizing film is kept at 80°C for 4 hours, the width of the polarizing film in the direction of the absorption axis (extension direction) is 2mm, and the shrinkage force of the polarizing film per 5μm thickness is ideally less than 1.77N/5μm, and less than 1.70N/ 5 μm is more desirable, more preferably 1.60 N/5 μm or less, and may be 1.40 N/5 μm or less. The lower limit of the contraction force is not particularly limited, but is preferably 0 N/5 μm, usually 0.1 N/5 μm or more, and may be 0.2 N/5 μm or more. On the other hand, since the polarizing film is ideal not to expand, it is ideal to be -0.01N/5μm or more. The contraction force of the polarizing film is the value obtained by measuring the contraction force of the polarizing film (measured contraction force) and the value obtained by measuring the thickness of the polarizing film according to the description of the examples described later, and the value calculated per 5 μm thickness by conversion according to the following formula .

Contraction force [N/5μm]=(measured contraction force of polarizing film [N])/(thickness of polarizing film (measured value)[μm])×5

As described above, when the degree of crosslinking of the polyvinyl alcohol-based resin layer is increased to increase the boron content of the polarizing film, optical properties such as polarization degree can be improved, but the shrinkage force of the polarizing film becomes large. On the other hand, lowering the degree of cross-linking of the polyvinyl alcohol-based resin layer reduces the boron content in the polarizing film, making it difficult to obtain favorable optical properties.

Therefore, in a polarizing film, the ratio represented by the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm is less than 0.022. In this way, the boron content rate becomes smaller to the extent that the shrinkage force of the polarizing film can be suppressed, and at the same time, the single transmittance (Ty) of the light sensitivity correction exceeds 40.5%. When the light sensitivity correction single transmittance (Ty) is 41.5% , can achieve good optical characteristics with a sensitivity-corrected degree of polarization (Py) exceeding 99.994. The lower limit of the sensitivity-corrected single transmittance (Ty) is preferably 41.0% or more, more preferably 41.5% or more, and the upper limit is 50% or less, more preferably 47% or less. The lower limit value of the sensitivity-corrected polarization degree (Py) when the sensitivity-corrected single transmittance (Ty) is 41.5% is preferably 99.995 or more, more preferably 99.996 or more.

The reason why the optical characteristics of the polarizing film can be improved by specifying the ratio represented by the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm of the polarizing film can be explained as follows. In the polyvinyl alcohol-based resin layer dyed with iodine, iodine is adsorbed and aligned to the polyvinyl alcohol-based resin layer. The iodine adsorbed and aligned forms complexes of polyiodide ions such as I ₃ ^- , I ₅ ^- and the like. Among these complexes, the polyiodide ion complex (I ₃ ^-complex ) having an absorption band at 475nm, compared with other polyiodide ion complexes, is easily disturbed due to alignment, and is easy to become The reason why the degree of polarization of the polarizing film decreases.

Furthermore, in complexes of polyiodide ions having an absorption band at a wavelength of 475 nm, complexes with high relative alignment and complexes with low relative alignment also exist. In order to increase the degree of polarization of the polarizing film, in the polyvinyl alcohol-based resin layer, among polyiodide ion complexes having an absorption band at 475 nm, it is desirable to increase the content of the relatively high-alignment complex.

The content of the polyiodide ion complex having an absorption band at 475 nm can be evaluated by the ratio represented by the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm. Here, the parallel absorbance at a wavelength of 475 nm is the transmittance when the direction of polarized light emitted from the Grand Thomson Prism is parallel to the transmission axis of the sample (polarizing film), and is converted into an absorbance value. In addition, the vertical absorbance at a wavelength of 475 nm is the transmittance when the direction of polarized light emitted from the Grand Thomson Prism is perpendicular to the transmission axis of the sample (polarizing film), and is converted into an absorbance value.

The smaller the ratio represented by the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm, the smaller the parallel absorbance and the larger the perpendicular absorbance. This means that the smaller the above-mentioned ratio, the complex of polyiodide ions having an absorption band at 475 nm is aligned in a direction perpendicular to the transmission axis of the polarizing film (direction of the absorption axis of the polarizing film) and has a high relative alignment. The content rate becomes larger. Therefore, the degree of polarization of the polarizing film can be increased by reducing the above ratio.

In this way, when the ratio of the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm of the polarizing film is less than 0.022, the amount of complexes with low alignment is reduced, and the degree of polarization of the polarizing film can be increased. The upper limit of the ratio is more preferably less than 0.0218, more preferably less than 0.0217, and the lower limit is more preferably 0.010 or more, more preferably 0.015 or more.

The thickness of the polarizing film is preferably 10 μm or less, more preferably 7 μm or less. When the thickness of the polarizing film is 10 μm or less, it is possible to reduce the thickness of the polarizing plate described later. The lower limit of the thickness of the polarizing film is preferably 1 μm or more, more preferably 2 μm or more. Such a polarizing film can also be thinned, the optical characteristics can be improved, and the shrinkage force can be suppressed.

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin layer of the polarizing film, those described later for the polyvinyl alcohol-based resin layer can be used. In addition, the polarizing film can be produced, for example, according to the production method of the polarizing laminated film described later.

<Polarizing plate>

The polarizing film may be provided with a protective film on at least one surface thereof to form a polarizing plate. The polarizing plate may be a polarizing plate with a protective film on one side of the polarizing film, or a polarizing plate with protective films on both sides of the polarizing film. The two protective films of the polarizing plate with protective films on both sides may be the same type of protective film or may be different types of protective films.

As for the material constituting the protective film, those described later can be used, and it can be manufactured, for example, according to the manufacturing method of a polarizing plate described later.

(Application of polarizing plate)

A polarizing plate with a protective film on one side, a polarizing plate with a protective film on both sides, can be used as such a composite polarizing plate by bonding peripheral components together to form a composite polarizing plate. As a peripheral member, such as a protective film attached to the protective film to prevent scratches; laminated on the protective film (such as the case of a polarizer with a protective film on both sides) or on the polarizer layer (such as a protective film on one side) In the case of polarizing plates), the adhesive layer used to attach the polarizing plate to the display unit and other optical components; the separator film laminated on the outer surface of the adhesive layer; laminated on the protective film (such as polarizing plates with protective films on both sides case) or on the polarizer layer (for example, in the case of a polarizer with a protective film on one side), an optical compensation film such as a retardation film, and other optical functional films.

The adhesive layer as an example of the peripheral member can be laminated on the outer surface of either protective film in the case of a polarizing plate with protective films on both sides, or on the peeling surface in the case of a polarizing plate with a protective film on one side. The adhesive forming the adhesive layer usually uses (meth)acrylic resin, styrene resin, polysiloxane resin, etc. It is composed of the adhesive composition of the cross-linking agent. Further containing fine particles, it can become an adhesive layer exhibiting light scattering properties. The thickness of the adhesive layer is usually 1 to 40 μm, preferably 3 to 25 μm.

Furthermore, an optical functional film as an example of a peripheral member includes, for example, a reflective polarizing film that transmits a certain polarized light and reflects light that exhibits polarized light of the opposite nature; Reflective film; reflective film with reflective function on the surface; semi-transparent reflective film with reflective function and transmission function; viewing angle compensation film, etc.

<Manufacturing method of polarizing laminated film>

Referring to Fig. 1, the polarizing laminated film, which is an intermediate in the production of polarizing plates, is produced by sequentially including the following steps: forming a polyvinyl alcohol-based resin layer on at least one surface of the base film to obtain a resin layer of the laminated film forming step S10; stretching step S20 of stretching the laminated film to obtain a stretched film; dyeing step S30 of obtaining a dyed laminated film by dyeing the polyvinyl alcohol-based resin layer of the stretched film with iodine to form a dyed layer; The crosslinking step S40 of obtaining the crosslinked laminated film by crosslinking the dyed layer of the dyed laminated film with a crosslinking solution containing boric acid to form a crosslinked layer; by reducing the Boron Content Forming a polarizer layer to obtain a boron removal step S50 of a polarizing laminated film.

Furthermore, the so-called polarizing laminated film of the present invention refers to a film having a substrate film and a polarizer layer laminated on at least one surface thereof, and without a protective film attached thereto. In the first protective film bonding step S60 described later, the polarizing laminated film formed by bonding the first protective film to the polarizer layer is hereinafter also referred to as "polarizer with protective film" in order to distinguish it from the polarizing laminated film. Laminated film".

(1) Resin layer forming step S10

Referring to FIG. 2 , this step is a step of forming a polyvinyl alcohol-based resin layer 6 on at least one surface of a base film 30 to obtain a laminated film 100 . The polyvinyl alcohol-based resin layer 6 is a layer that becomes the polarizer layer 5 through the stretching step S20 , the dyeing step S30 , the crosslinking step S40 and the boron removal step S50 . The polyvinyl alcohol-based resin layer 6 can be formed by applying a coating solution containing a polyvinyl alcohol-based resin to one or both surfaces of the base film 30 and drying the coated layer. The method of forming the polyvinyl alcohol-based resin layer 6 by such coating is advantageous in that it is easy to obtain the polarizer layer 5 of a thin film. Generally, the resin layer forming step S10 can continuously unwind the base film 30 from the film roll of the roll of the long base film 30 conventionally, and can be carried out continuously while conveying. The transport system of the film can be performed using a guide roll or the like.

(substrate film)

The base film 30 may be made of a thermoplastic resin, among which those made of a thermoplastic resin good in transparency, mechanical strength, thermal stability, elongation, etc. are preferable. Specific examples of such thermoplastic resins include, for example, polyolefin-based resins such as chain polyolefin-based resins and cyclic polyolefin-based resins (norbornene-based resins, etc.); polyester-based 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 Polyether-based resins; polyether-based resins; polyamide-based resins; polyamide-based resins; polyimide-based resins; and their mixtures, copolymers, etc.

The base film 30 may be a single-layer structure composed of one resin layer composed of one or more thermoplastic resins, or may be a multi-layered resin layer composed of one or two or more thermoplastic resins. Multi-layer construction. The base film 30 is preferably composed of a resin that can be stretched at a preferable stretching temperature for stretching the polyvinyl alcohol-based resin layer 6 when the laminated film 100 is stretched in the stretching step S20 described later.

The chain polyolefin-based resin includes, for example, a copolymer composed of two or more chain olefins other than a homopolymer of chain olefins such as polypropylene resin. The base film 30 made of a chain polyolefin resin is preferable in that it is easy to stretch stably at a high ratio. Among them, the base film 30 is made of polypropylene resin (polypropylene resin of a homopolymer of propylene, or a copolymer mainly composed of propylene), polyethylene resin (polyethylene resin of a homopolymer of ethylene, or a copolymer of ethylene It is more preferable to consist of a copolymer as the main body).

A copolymer mainly composed of propylene, which is an example of the thermoplastic resin constituting the base film 30 , is a copolymer of propylene and other monomers copolymerizable therewith.

As other monomers copolymerizable with propylene, for example, ethylene, α-olefin. As the α-olefin, an α-olefin having 4 or more carbon atoms is preferably used, more preferably an α-olefin having 4 to 10 carbon atoms. Specific examples of α-olefins having 4 to 10 carbon atoms include linear monoolefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 1-decene Classes; branched monoolefins such as 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene; vinylcyclohexane, etc. The copolymer of propylene and other monomers that can be copolymerized with it can be a random copolymer or a block copolymer.

The content of the above-mentioned other monomers in the copolymer is, for example, 0.1 to 20% by weight, preferably 0.5 to 10% by weight. The content of other monomers in the copolymer was determined by performing infrared (IR) spectrum measurement according to the method described on page 616 of "Polymer Analysis Handbook" (published by Kinokuniya Shoten in 1995).

Among the above, it is preferable to use a propylene homopolymer, a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, or a propylene-ethylene-1-butene random copolymer as the polypropylene-based resin. .

The stereoregularity of polypropylene-based resins is essentially isotactic or syndiotactic, which is ideal. The base film 30 made of polypropylene-based resin substantially having isotactic or syndiotactic stereoregularity has good handling properties and good mechanical strength under high temperature environment.

Cyclic polyolefin-based resins are a general term for resins polymerized with cyclic olefins as polymerized units, such as those described in JP-A-1-240517, JP-3-14882, JP-3-122137, etc. resin. When citing specific examples of cyclic polyolefin-based resins, there are ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, and copolymers of cyclic olefins and chain olefins such as ethylene and propylene. (Representatively random copolymers) and these graft copolymers modified with unsaturated carboxylic acids and their derivatives, and their hydrogenated products. Among them, as the cyclic olefin, it is preferable to use a norbornene-based resin such as a norbornene-based monomer such as norbornene and a polycyclic norbornene-based monomer.

Polyester-based resins are resins with ester bonds, and are generally polycondensates of polycarboxylic acids or their derivatives and polyhydric alcohols. As the polycarboxylic acid or its derivative, divalent dicarboxylic acid or its derivative, for example, terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalene dicarboxylate can be used. As the polyhydric alcohol, divalent diols such as ethylene glycol, propylene glycol, butanediol, neopentyl glycol, and cyclohexanedimethanol can be used.

As a representative example of the polyester-based resin, polyethylene terephthalate, which is a polycondensate of terephthalic acid and ethylene glycol, is exemplified. Polyethylene terephthalate is a crystalline resin, and it is easy to perform stretching and other treatments in the state before crystallization treatment. If necessary, crystallization treatment may be performed by heat treatment during stretching or after stretching. Furthermore, copolyesters whose crystallinity is reduced (or become amorphous) by copolymerization with other types of monomers through the skeleton of polyethylene terephthalate are also suitable for use. Examples of such resins include those copolymerized with cyclohexanedimethanol and isophthalic acid. These resins are suitable for use due to their good extensibility.

When specific examples of polyester-based resins other than polyethylene terephthalate and its copolymers are given, for example, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, Polytrimethylene terephthalate, Polytrimethylene naphthalate, Poly(cyclohexanedimethylene terephthalate), Poly(cyclohexanedimethylene naphthalate).

(Meth)acrylic resin is a resin mainly composed of a compound having a (meth)acryl group as a monomer. Specific examples of (meth)acrylic resins include, for example, poly(meth)acrylate such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-( Meth) acrylate copolymer; methyl methacrylate-acrylate-(meth)acrylic acid copolymer; (meth)methyl acrylate-styrene copolymer (MS resin, etc.); methyl methacrylate with Copolymers of alicyclic hydrocarbon-based compounds (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). It is more desirable to use poly(meth)acrylate C _1-6 alkyl ester as the main component polymer such as poly(meth)acrylate, and it is more desirable to use methyl methacrylate as the main component (50 to 100 wt. %, preferably 70 to 100% by weight) of methyl methacrylate resin.

Cellulose ester-based resins are esters of cellulose and fatty acids. Specific examples of cellulose ester-based resins include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Furthermore, these copolymers and those in which a part of the hydroxyl groups are modified with other substituents can be used. Among these, cellulose triacetate (triacetyl cellulose) is particularly desirable. Cellulose triacetate is commercially available in many products and is advantageous in terms of ease of acquisition and cost.

Polycarbonate-based resins are engineering plastics composed of polymers bonded to monomer units through carbonate groups. They are resins with high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin constituting the base film 30 may be a resin called a modified polycarbonate that modifies a polymer skeleton in order to lower the photoelastic coefficient, or a copolymerized polycarbonate that improves wavelength dependence.

Among the above, it is preferable to use polypropylene-based resins from the viewpoint of elongation, heat resistance, and the like.

In addition to the above-mentioned thermoplastic resin, the base film 30 may contain arbitrary appropriate additives. Examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, and colorants. The content of the thermoplastic resin in the base film 30 is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, still more preferably 60 to 98% by weight, particularly preferably 70 to 97% by weight.

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

(Formation of polyvinyl alcohol-based resin layer)

The coating liquid applied to the base film 30 is preferably a polyvinyl alcohol-based resin solution obtained by dissolving polyvinyl alcohol-based resin powder in a good solvent (eg, water). As the polyvinyl alcohol-based resin, saponified polyvinyl acetate-based resin can be used. Polyvinyl acetate-based resins include, for example, copolymers of vinyl acetate and other monomers copolymerizable therewith, other than polyvinyl acetate which is a homopolymer of vinyl acetate.

Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, acrylamides having ammonium groups, and the like.

The degree of saponification of the polyvinyl alcohol-based resin may be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 99.5 mol%, more preferably in the range of 94.0 to 99.0 mol%. When the degree of saponification is less than 80.0 mol %, the water resistance and heat and humidity resistance of the polarizing plate may be low. When a polyvinyl alcohol-based resin with a degree of saponification exceeding 99.5 mol% is used, the iodine dyeing speed of the dichroic dye becomes slow, and productivity is low, and a polarizing plate having sufficient polarizing performance cannot be obtained.

The so-called degree of saponification refers to the ratio of the acetic acid group (acetyloxy group: -OCOCH ₃ ) contained in the polyvinyl acetate resin, which is the raw material of the polyvinyl alcohol resin, into a hydroxyl group through the saponification step, expressed in unit ratio (molar %) is defined by the following formula: degree of saponification (mole %)=100×(number of hydroxyl groups)÷(number of hydroxyl groups+number of acetic acid groups). The degree of saponification can be obtained in accordance with JIS K 6726-1994. The higher the degree of saponification, the higher the proportion of hydroxyl groups, and thus the lower the proportion of acetic acid groups that inhibit crystallization.

The polyvinyl alcohol-based resin may be partially modified modified polyvinyl alcohol. For example, polyvinyl alcohol-based 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, and acrylamide. The ratio of modification is ideally less than 30 mol%, more ideally less than 10%. When the modification exceeds 30 mol%, iodine of the dichroic dye becomes difficult to adsorb, and a polarizing plate having sufficient polarizing performance tends not to be obtained.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably from 100 to 10,000, more preferably from 1,500 to 8,000, and still more preferably from 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol-based resin can also be obtained in accordance with JIS K 6726-1994. When the average degree of polymerization is less than 100, it is difficult to obtain good polarizing performance, and when it exceeds 10000, the solubility to solvents deteriorates, and it becomes difficult to form a polyvinyl alcohol-based resin layer in the production method of a polarizing laminated film described later.

The coating liquid may contain additives such as plasticizers and surfactants as necessary. As the plasticizer, a polyhydric alcohol or a condensate thereof, such as glycerol, diglycerol, triglycerol, ethylene glycol, propylene glycol, polyethylene glycol, etc., can be used. The compounding amount of the additive is suitably 20% by weight or less of the polyvinyl alcohol-based resin.

The method for applying the above-mentioned coating liquid to the substrate film 30 can be a wire bar coating method; a roll coating method such as a reverse coating method, a gravure coating method, etc.; a slit coating method; Cloth method; lip coating method; spin coating method; screen coating method; jet coating method; dip coating method; spray coating method and the like are appropriately selected.

The drying temperature and drying time of the coating layer (polyvinyl alcohol-based resin layer before drying) are set according to the type of solvent contained in the coating liquid. The drying temperature is, for example, 50 to 200°C, preferably 60 to 150°C. When the solvent contains water, the drying temperature is preferably 80°C or higher.

The polyvinyl alcohol-based resin layer 6 may be formed on only one surface of the base film 30, or may be formed on both surfaces. When it is formed on both sides, it can suppress the curling of the polarizing laminated film during production, and at the same time, two polarizing plates can be obtained from one polarizing laminated film, which is also advantageous in terms of production efficiency of polarizing plates.

The thickness of the polyvinyl alcohol-based resin layer 6 of the laminated film 100 is preferably 3 to 30 μm, more preferably 5 to 20 μm. As long as the polyvinyl alcohol-based resin layer 6 has a thickness within this range, after the stretching step S20 and the dyeing step S30 described later, the iodine dyeability of the dichroic dye is good, the polarizing performance is good, and it can be sufficiently thin (such as A polarizer layer 5 with a thickness of 10 μm or less).

Before the coating of the coating liquid, in order to improve the adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6, at least the surface of the base film 30 on the side where the polyvinyl alcohol-based resin layer 6 is formed, can be electroplated. Halo treatment, plasma treatment, flame treatment, etc. In addition, for the same reason, the polyvinyl alcohol-based resin layer 6 may be formed on the base film 30 through a primer layer or the like.

The undercoat layer can be formed by applying the coating liquid for undercoat layer formation to the surface of the base film 30 and then drying it. The coating liquid contains a component capable of exerting a certain level of adhesive force between the base film 30 and the polyvinyl alcohol-based resin layer 6, and usually includes a resin component and a solvent that impart such an adhesive force. As the resin component, it is preferable to use a thermoplastic resin excellent in transparency, thermal stability, extensibility, etc., such as (meth)acrylic resin, polyvinyl alcohol-based resin, and the like. Among them, it is preferable to use a polyvinyl alcohol-based resin that imparts good adhesion. More preferably, it is a polyvinyl alcohol resin. As a solvent, a general organic solvent or an aqueous solvent that can dissolve the above-mentioned resin components is usually used, and it is preferable to form an undercoat layer from a coating solution in which water is used as a solvent.

In order to increase the strength of the undercoat layer, a crosslinking agent may be added to the coating liquid for undercoat layer formation. Specific examples of the crosslinking agent include epoxy-based, isocyanate-based, dialdehyde-based, metal-based (such as metal salts, metal oxides, metal hydroxides, organometallic compounds), and polymer-based cross-linking agents. When polyvinyl alcohol-based resin is used as the resin component for forming the undercoat layer, polyamide epoxy resin, methylolated melamine resin, dialdehyde-based crosslinking agent, metal chelating compound-based crosslinking agent, and the like are suitably used.

The thickness of the primer layer is preferably about 0.05 to 1 μm, more preferably 0.1 to 0.4 μm. If it is thinner than 0.05 μm, the effect of improving the adhesive force between the base film 30 and the polyvinyl alcohol-based resin layer 6 becomes small.

The method of applying the coating liquid for undercoat layer formation to the base film 30 may be the same as the coating liquid for polyvinyl-alcohol-type resin layer formation. The drying temperature of the coating layer composed of the coating liquid for forming an undercoat layer is, for example, 50 to 200°C, preferably 60 to 150°C. When the solvent contains water, the drying temperature is preferably 80°C or higher.

(2) Extending step S20

Referring to FIG. 3, this step is a step of stretching the laminated film 100 to obtain the stretched film 200 composed of the stretched base film 30' and the polyvinyl alcohol-based resin layer 6'. The extension is usually uniaxial. The stretching step S20 is conventionally conveying the long laminated film 100, or continuously unwinding the laminated film 100 from the film roll of the long laminated film 100, which can be carried out continuously while conveying. A guide roll etc. can be used for the conveyance system of a film.

The elongation ratio of the laminated film 100 can be appropriately selected according to the desired polarizing characteristics, and it is preferably more than 5 times and not more than 17 times the original length of the laminated film 100, more preferably more than 5 times and not more than 8 times. . When the stretching ratio is less than 5 times, the degree of polarization of the polarizer layer 5 may not be sufficiently high because the polyvinyl alcohol-based resin layer 6' cannot be sufficiently aligned. On the other hand, when the stretching ratio exceeds 17 times, film breakage is likely to occur during stretching, and the thickness of the stretched film 200 becomes thinner than necessary, which may lower the workability and handling properties in subsequent steps. The elongation treatment is not limited to one-stage elongation, and may be performed in multiple stages.

The stretching treatment may be not only longitudinal stretching that stretches the film in the longitudinal direction (film transport direction), but also transverse stretching or oblique stretching that stretches the film in the width direction. The longitudinal stretching method includes, for example, inter-roll stretching using roll stretching, compression stretching, and chuck (clip) stretching, and the like, and the transverse stretching method includes, for example, a tenter method. For the stretching treatment, either a wet stretching method or a dry stretching method can be used, and the dry stretching method is preferable because the stretching temperature can be selected from a wide range.

The stretching temperature is set to be above the temperature at which both the polyvinyl alcohol-based resin layer 6 and the base film 30 exhibit extensible fluidity, preferably the phase transition temperature (melting point or glass transition temperature) of the base film 30 - The range of 30°C to +30°C, more preferably the range of -30°C to +5°C, more preferably the range of -25°C to +0°C. When the base film 30 is comprised by several resin layers, the said phase transition temperature means the highest phase transition temperature among the phase transition temperatures shown by this several resin layer.

If the stretching temperature is lower than -30° C. which is the phase transition temperature, it may be difficult to achieve high-magnification stretching exceeding 5 times, or the fluidity of the base film 30 may be too low, and the stretching process may become difficult. When the stretching temperature exceeds +30° C. of the phase transition temperature, the fluidity of the base film 30 becomes too high, and stretching tends to become difficult. Since it is easier to achieve high-magnification extension exceeding 5 times, the extension temperature is within the above range, more preferably 120° C. or higher.

The heating method of the stretched laminated film 100 includes a regional heating method (for example, a method of heating in the stretching area of a heating furnace adjusted to a specified temperature by blowing hot air); a method of heating the roll itself when stretching with a roll; Heating method (a method of installing infrared heaters, halogen lamp heaters, plate heaters, etc. on the upper and lower sides of the laminated film 100 and heating with radiant heat), etc. The stretching method between rolls is preferably a zone heating method from the viewpoint of the uniformity of the stretching temperature.

Before the stretching step S20, a preheating step of preheating the laminated film 100 may also be provided. As the preheating method, the same method as the heating method of the stretching treatment can be used. The preheating temperature is preferably in the range of -50°C to ±0°C of the extension temperature, and more preferably in the range of -40°C to -10°C of the extension temperature.

Moreover, after the stretching process in the stretching step S20, a heat fixing process step may be provided. The heat setting treatment is a process of heat-treating at a temperature equal to or higher than the crystallization temperature of the polyvinyl alcohol-based resin while holding the end of the stretched film 200 with a jig and maintaining a tensioned state. Crystallization of the polyvinyl alcohol-based resin layer 6' is accelerated by this heat-fixing treatment. The temperature of the heat fixing treatment is preferably in the range of -0°C to -80°C of the stretching temperature, and more preferably in the range of -0°C to -50°C of the stretching temperature.

(3) Dyeing step S30

In this step, the polyvinyl alcohol-based resin layer 6' of the stretched film 200 is dyed with iodine of a dichroic dye to make it absorb and align to form a dyed layer, and obtain a dyed laminated film composed of the base film 30' and the dyed layer. the steps. The dyeing step S30, in general, is to convey the elongated stretched film 200, or roll out the stretched film 200 continuously from the film roll of the elongated stretched film 200, which can be carried out continuously while it is conveyed. . The transport system of the film can be performed using a guide roll or the like.

The dyeing step S30 can be performed by immersing the stretched film 200 in a solution (dyeing bath) containing iodine. As a dyeing bath, a solution of iodine dissolved in a solvent can be used. As the solvent of the dyeing solution, water is generally used, and an organic solvent compatible with water can also be added. The concentration of iodine in the dyeing bath is preferably 0.01 to 10 parts by weight, more preferably 0.02 to 7 parts by weight, relative to 100 parts by weight of the solvent. It is ideal to adjust the immersion time of the dyeing bath to correspond to the concentration of iodine in the dyeing bath so that the desired sensitivity-corrected monomer transmittance (Ty) can be obtained.

The dyeing bath containing iodine is ideal to further add iodide because the dyeing efficiency can be improved. Examples of 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 concentration of iodide in the dyeing bath is preferably 0.01 to 20 parts by weight with respect to 100 parts by weight of the solvent. Among the iodides, it is more desirable to add potassium iodide. 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 in terms of weight ratio. The temperature of the dyeing bath is preferably 10 to 60°C, more preferably 20 to 40°C.

In addition, in the dyeing step S30 , an additional stretching process may be performed on the stretched film 200 . As an implementation aspect of this case, for example, 1) after stretching at a magnification lower than the target in the above-mentioned stretching step S20, stretching is performed in the dyeing process in the dyeing step S30 so that the total stretching magnification becomes the target magnification. When carrying out the cross-linking treatment after the dyeing treatment as described later, 2) in the above-mentioned elongation step S20, after performing the elongation treatment at a magnification lower than the target, in the dyeing treatment of the dyeing step S30, the total elongation magnification does not reach the target magnification level stretching treatment, and then, in the cross-linking treatment, a stretching treatment in which the final total stretching ratio becomes a target ratio is performed, and the like.

(4) Cross-linking step S40

This step is a step of cross-linking the dyed layer of the dyed laminated film to form a cross-linked layer to obtain a cross-linked laminated film composed of the base film 30' and the cross-linked layer. The cross-linking step can be performed by immersing the dyed laminated film in a cross-linking liquid containing a cross-linking agent containing at least boric acid. The cross-linking step S40, in general, is to convey the long strip of dyed laminated film, or continuously roll out the dyed laminated film from the film roll of the long strip of dyed laminated film, which can be conveyed continuously conduct. The conveyance of the film can be performed using guide rollers or the like.

The cross-linking liquid may contain only boric acid as a cross-linking agent, and other cross-linking agents such as boron compounds such as borax, glyoxal, and glutaraldehyde may be contained in addition to boric acid. As for other crosslinking agents, one kind may be used alone, or two or more kinds may be used in combination.

As the crosslinking solution, a solution obtained by dissolving boric acid in a solvent can be used. As the solvent, water may be used, and an organic solvent compatible with water may be further included. The content of boric acid in the crosslinking solution is preferably 1 to 20 parts by weight, more preferably 5 to 15 parts by weight, for 100 parts by weight of the solvent, and the content of other crosslinking agents other than boric acid is 100 parts by weight for the solvent. In other words, it is more preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight.

The cross-linking solution may further contain iodide. The in-plane polarization characteristics of the dyed layer can be made more uniform by the addition of iodide. Specific examples of iodide are the same as above. The content of iodide in the crosslinking liquid is preferably less than 10 parts by weight, more preferably 8 parts by weight or less, or 0 parts by weight (the iodide may not be included) with respect to 100 parts by weight of the solvent. The lower limit of the temperature of the crosslinking solution is preferably 40°C or higher, and the upper limit is preferably 82°C or lower. When the temperature of the cross-linking solution exceeds 82°C, part of the polyvinyl alcohol-based resin in the dyed layer is eluted, and unevenness is likely to occur after dyeing.

The cross-linking treatment can be carried out simultaneously with the dyeing treatment by preparing a cross-linking agent in the dyeing bath. Furthermore, two or more cross-linking agent-containing solutions having different compositions may be used, and the treatment of immersing in the cross-linking agent-containing solution may be performed two or more times. By sufficiently performing the cross-linking treatment, the boron content in the dyed layer increases, and the alignment of the polyiodide ion complex can be improved. Stretching treatment may also be performed during the crosslinking treatment. The specific aspects of carrying out the stretching treatment in the crosslinking treatment are as described above.

The tension applied to the dyed laminated film in the crosslinking step S40 is preferably 1 N/cm or more, more preferably 2 N/cm or more, and still more preferably 5 N/cm or more per unit length in the width direction. The upper limit of the tension is not particularly limited, but is preferably 30 N/cm or less, more preferably 20 N/cm or less. In the crosslinking step S40, it is desirable to continuously apply tension in the extending direction of the dyed laminated film so that the alignment of the polyvinyl alcohol-based resin used as the dyed layer is not eased.

For example, when the dyed laminated film is conveyed by two rolls while being immersed in the cross-linking solution in the cross-linking tank, and the cross-linking process is continuously performed, by adjusting the rotation speed of the rolls on the feeding side and the rotation speed of the rolls on the sending side The speed can adjust the tension attached to the dyed laminated film.

(5) boron removal step S50

With reference to Fig. 4, this step is to form the polarizer layer 5 by reducing the boron content contained in the crosslinked layer of the crosslinked laminated film, and obtain the polarizing properties formed by the base film 30' and the polarizer layer 5. The step of laminating film 300. The boron removal step S50, in general, is to convey the long strip of cross-linked laminated film, or continuously roll out the cross-linked laminated film from the film roll of the long strip of cross-linked laminated film, which can be sent simultaneously and continuously. The conveyance of the film can be performed using guide rollers or the like.

The boron-removing step S50 may include a boron-removing solution having a boric acid concentration lower than that of the crosslinking solution used in the crosslinking step S40, and a step of contacting the boron-removing solution with the crosslinked layer of the crosslinked laminated film. The step of contacting the boron-removing solution can be carried out by immersing the cross-linked laminated film in the boron-removing solution, and rinsing the cross-linked layer of the cross-linked laminated film with the boron-removing solution. As the boron removal solution, a solution in which boric acid is dissolved in a solvent or a solution without boric acid can be used. As the solution free of solvent and boric acid, water may be used, and an organic solvent compatible with water may be further included. The content of boric acid in the boron-removing solution is preferably less than 10 parts by weight, more preferably less than 8 parts by weight, and may be more than 0.1 parts by weight relative to the total weight of the solvent.

By performing the treatment of bringing the boron-removing solution into contact with the cross-linked layer, excess boric acid contained in the cross-linked layer and complexes of polyiodide ions with low orientation can be removed. Thereby, since the boron content rate contained in the polarizer layer 5 is reduced, the contraction force of the polarizer layer 5 (polarizing film) during heating can be reduced. Furthermore, the degree of polarization and the transmittance of the polarizer layer 5 of the polarizing laminated film 300 can be increased.

The boron removal solution may also contain iodide. Specific examples of iodide are the same as above. The content of the iodide in the boron-removing solution is preferably less than 15 parts by weight, more preferably less than 8 parts by weight, and more than 5 parts by weight, to the total weight of the solvent. By adjusting the content of iodide in the boron removal solution, the hue of the obtained polarizing laminated film can be adjusted. The temperature of the boron removal solution is preferably below 70°C, more preferably below 65°C. Moreover, the temperature of the cross-linking solution is ideally higher than that of the boron-removing solution.

By using two or more kinds of boron-removing liquids with different compositions, it is possible to perform two or more contact steps of boron-removing liquids. When carrying out multiple boron-removing liquid contact steps, the treatment methods of the boron-removing liquid contact steps can be the same or different.

When the cross-linking step and the boric acid removal step include multiple steps of treating with a boric acid-containing solution, compared with the previous step, the boric acid concentration of the boric acid-containing solution is controlled to be low and the tension added to the membrane becomes smaller. The step becomes the boron removal step. For example, the concentration of boric acid can be gradually decreased with the progress of subsequent steps, once the concentration of boric acid is decreased, it can be kept constant, or a combination of these can also be used. Moreover, the tension added to the film can be gradually reduced as the subsequent steps progress, and once the tension is reduced, it can be kept constant, or it can be a combination of these. In the latter step, when a solution having the same high boric acid concentration as that of the former step is used, the latter step becomes a crosslinking step.

Furthermore, when the cross-linking step includes a plurality of steps of treating with a boric acid-containing solution, compared with any one of the plurality of steps, the concentration of boric acid is controlled to be low and the tension applied to the membrane is reduced. , becomes the boron removal step, and the boron removal step is ideally controlled so that the concentration of boric acid is lower than that of the last step of the crosslinking step and the tension added to the membrane becomes smaller.

After performing the boron removal step S50, it is preferable to dry the polarizing laminated film. When performing this drying treatment, it is preferable to use a boron-free solution that does not contain boric acid for the treatment of immersion in the boron-removing solution before the drying treatment, so as to prevent defects on the surface of the polarizer layer. For the drying treatment, any appropriate method such as natural drying, air drying, and heating drying can be adopted. For example, in heat drying, the drying temperature is usually 20 to 95° C., and the drying time is usually 1 to 15 minutes.

In the boron-removing solution contact step of the boron-removing step S50, the tension added to the cross-linked laminated film is ideally controlled to be smaller than the tension added to the dyed laminated film in the cross-linked step S40. In this way, the excess boric acid contained in the cross-linked layer and the polyiodide ion complex with low alignment can be removed more effectively, so the shrinkage force of the polarizer layer during heating can be suppressed, and the optical fiber can be efficiently produced. Polarizing laminated film with excellent properties. In the boron removal step S50, the tension applied to the cross-linked laminated film is preferably less than 16 N/cm, more preferably 14 N/cm or less, per unit length in the width direction. The lower limit of the tension should just exceed 0 N/cm, and is preferably 1 N/cm. In the boron removal step S50, it is preferable that the cross-linked laminated film does not substantially extend. The term "substantially not stretched" means that the stretch ratio is 1.05 times or less.

Similar to the above-mentioned dyed laminated film, when the cross-linked laminated film is conveyed by two rollers while undergoing boron removal treatment, by adjusting the rotation speed of the rollers on the feeding side and the rotating speed of the rollers on the sending side, it is possible to adjust the amount added to the cross-linked laminated film. Tension of co-laminated membranes.

The crosslinked layer of the crosslinked laminated film can be obtained and thinned by the above method. In the thinned cross-linked layer, in the boron removal step S50, when the boron removal process is carried out with the above-mentioned tension, it can be expected that the complexes of excessive boric acid and polyiodide ions contained in the cross-linked layer can be easily removed. Therefore, the polarizer layer formed by the above manufacturing method not only achieves thinning, but also improves optical characteristics and suppresses the increase of shrinkage force.

<Manufacturing method of polarizing plate>

With reference to Fig. 1, the manufacturing method of the polarizing plate of the present invention includes the following steps in sequence: on the opposite side of the substrate film of the polarizer layer of the polarizing laminated film manufactured by the above method, stick the first The first protective film lamination step S60 of the protective film; and the peeling step S70 of peeling and removing the base film.

After the first protective film bonding step S60 and the peeling step S70, a polarizing plate 400 with a protective film on one side is obtained (FIG. 5 ) in which the first protective film 10 is bonded to one side of the polarizer layer 5 . Moreover, as shown in FIG. 1, after the peeling step S70, a second protective film bonding step S80 is provided, which is based on the peeling and removal of the base film 30' of the polarizing plate 400 with a protective film on one side. (hereinafter also referred to as "peeling surface"), the second protective film 20 is attached to obtain a polarizing plate 2 with protective films on both sides (Fig. 7).

(6) Step S60 of attaching the first protective film

Referring to Fig. 5, this step is the step of laminating the first protective film 10 on the opposite side of the polarizing laminated film 300 to the base film 30' side (that is, on the polarizer layer 5) to obtain the multilayer film 400. The first protective film 10 corresponds to the protective film included in the above-mentioned polarizing plate. The first protective film bonding step S60, generally, is to continuously roll out the polarizing laminate while conveying the elongated polarizing laminate film 300, or from the film roll of the elongated polarizing laminate film 300 The film 300 can be carried out continuously while being conveyed. The conveyance of the film can be performed using guide rollers or the like.

When the polarizing laminated film 300 has polarizer layers 5 on both surfaces of the base film 30', the first protective films 10 are usually attached to the polarizer layers 5 on both surfaces, respectively. In this case, the first protective films 10 may be of the same type or of different types.

The first protective film 10 can be attached to the polarizer layer 5 via the first adhesive layer 15 . The adhesive forming the first adhesive layer 15 may be an active energy ray-curable adhesive (preferably UV-curable adhesives), water-based adhesives in which adhesive components such as polyvinyl alcohol-based resins are dissolved or dispersed in water.

When laminating the first protective film 10 using an active energy ray-curable adhesive, the first protective film 10 is laminated on the polarizer layer 5 via the active energy ray-curable adhesive that becomes the first adhesive layer 15 , The adhesive layer is cured by irradiating active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. Among them, ultraviolet light is suitable. As the light source at this time, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, and metal halide lamps can be used. When a water-based adhesive is used, the first protective film 10 is laminated on the polarizer layer 5 through the water-based adhesive, and then heated and dried.

When the first protective film 10 is attached to the polarizer layer 5, in order to improve the adhesiveness with the polarizer layer 5 on the bonding surface of the first protective film 10 and/or the polarizer layer 5, plasma treatment, electric current, etc. can be carried out. Corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, saponification treatment and other surface treatment (adhesive treatment), among them, plasma treatment, corona treatment or saponification treatment is more ideal.

(1st protective film)

The material constituting the first protective film is preferably a thermoplastic resin having translucency (preferably optically transparent), and such resins include chain polyolefin resins (polypropylene resins, etc.), cyclic polyolefin resins, etc. Polyolefin-based resins of olefin-based resins (norcamphene-based resins, etc.); cellulose ester-based resins such as cellulose triacetate and cellulose diacetate; polyester-based resins; polycarbonate-based resins; ( Meth)acrylic resin; polystyrene resin; or a film composed of a mixture or copolymer thereof. Specific examples of such thermoplastic resins include those described above for the thermoplastic resin constituting the base film 30 .

The first protective film may be a protective film having combined optical functions such as a retardation film and a brightness enhancement film. For example, stretching (uniaxial stretching or biaxial stretching, etc.) a film made of the above-mentioned thermoplastic resin, and forming a liquid crystal layer etc. on the film can become a retardation film imparting an arbitrary retardation value.

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 also be formed on the surface of the first protective film 10 opposite to the polarizer layer 5 . The surface treatment layer may be preformed on the first protective film 10 before the first protective film bonding step S60, or may be formed after the first protective film bonding step S60 or the peeling step S70 described later. Furthermore, the first protective film 10 may contain one or more additives such as lubricants, plasticizers, dispersants, heat stabilizers, ultraviolet absorbers, infrared absorbers, antistatic agents, and antioxidants.

The thickness of the first protective film 10 is preferably 90 μm or less, more preferably 50 μm or less, still more preferably 35 μm or less, particularly preferably 30 μm or less, from the viewpoint of thinning the polarizing plate. The thickness of the first protective film 10 is usually 5 μm or more from the viewpoint of strength and handleability.

(7) Stripping step S70

Referring to FIG. 6, this step is a step of peeling and removing the base film 30' from the multilayer film 400 to obtain a polarizing plate (polarizing plate with a protective film on one side). When the polarizing laminated film 300 has the polarizer layer 5 on both surfaces of the base film 30', and the first protective film 10 is bonded to the polarizer layers 5 of the two, by this peeling step S70, from one sheet The polarizing laminated film 300 can be used to obtain two polarizing plates 1 with a protective film on one side. Peeling step S70, in general, is to convey the long multilayer film 400, or roll out the multilayer film 400 continuously from the film roll of the roll of the long multilayer film 400, which can be carried out continuously while it is conveyed. . The conveyance of the film can be performed using guide rollers or the like.

The method of peeling and removing the base film 30' is not particularly limited, and it can be peeled by the same method as the peeling step S70 of the separator (peeling film) usually performed on a polarizing plate with an adhesive. The base film 30' can be peeled off directly after the first protective film laminating step S60, or it can be rolled into a roll once after the first protective film laminating step S60, and rolled out in subsequent steps. Peel off one side.

As mentioned above, the multilayer film 400 obtained in the step S60 of attaching the first protective film is laminated with the polarizer layer 5 and the first protective film 10 on both sides of the base film 30', that is, it can have the first protective film 10/polarizer A film composed of layers of sheet layer 5/substrate film 30'/polarizer layer 5/first protective film 10 (the description of the first adhesive layer 15 is omitted). In this case, two polarizing plates 1 with a protective film on one side are obtained from one multilayer film 400 through two peeling steps. In the peeling step of the first stage, from the multilayer film 400 of the above structure, the film having the layer composition of "first protective film 10/polarizer layer 5/substrate film 30'" is peeled off to obtain polarized light with a protective film on one side. plate 1. In the peeling step of the second stage, the substrate film 30' is peeled off from the film having the peeled "first protective film 10/polarizer layer 5/substrate film 30'" layer, and then a single-sided protective film is obtained. Film polarizer 1.

(8) Second protective film bonding step S80

Referring to Fig. 7, this step is an arbitrary step of attaching the second protective film 20 on the polarizer layer 5 of the polarizer 1 with a protective film on one side to obtain a polarizer 2 with protective films on both sides. The second protective film sticking step S80, in general, is to convey the long polarizing plate 1 with a protective film on one side, or the film roll from the roll of the long polarizing plate 1 with a protective film on one side , Continuously roll out the polarizing plate 1 with a protective film on one side, which can be carried out continuously while conveying it. The conveyance of the film can be performed using guide rollers or the like.

The second protective film 20 can be attached to the polarizer layer 5 via the second adhesive layer 25 . Regarding the composition and material of the second protective film 20 and the second adhesive layer 25, and the bonding method of the second protective film 20, references are made to the articles on the first protective film 10, the first adhesive layer 15, and the first protective film 10, respectively. Records of lamination methods. The first protective film 10 and the second protective film 20 may be the same type of protective film or different types of protective films. The first adhesive layer 15 and the second adhesive layer 25 may be formed of the same type of adhesive or may be formed of different types of adhesives.

[Example]

Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these examples.

[Sensitivity Corrected Single Transmittance (Ty) and Sensitivity Corrected Polarization Degree (Py)]

For each polarizing laminated film, use a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation) to measure the parallel transmittance and vertical transmittance in the wavelength range from 380 to 780 nm, according to the following formula: Monomer Transmittance (%)=(parallel transmittance + vertical transmittance)/2

Degree of polarization (%)={(parallel transmittance-vertical transmittance)/(parallel transmittance+vertical transmittance)}×100

Calculate the single transmittance and polarization degree of each wavelength. In the measurement, light is incident from the polarizer layer side of the polarizing laminated film, and the base film side of the polarizing laminated film is the detector side. Furthermore, because the base film is sufficiently transparent, there is no difference between the optical characteristics measured by the polarizing laminated film and the optical characteristics when only the polarizer layer (polarizing film) of the polarizing laminated film is measured. The value of the optical characteristic of , can be regarded as the value when the optical characteristic is measured only for the polarizer layer (polarizing film).

Here, the "parallel transmittance" refers to the transmittance when the direction of the polarized light emitted from the Glan-Thomson's is parallel to the transmission axis of the polarizing film sample. In addition, the term "vertical transmittance" refers to the transmittance when the direction of the polarized light emitted from the Glan-Thomson Plasma is perpendicular to the transmission axis of the polarizing film sample.

For the obtained single transmittance and polarization degree, the viewing angle is 2 degrees (C light source) by JIS Z 8701: 1999 "Expression method of color - XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system" Sensitivity correction, get the sensitivity correction monomer transmittance (Ty) and the sensitivity correction polarization degree (Py).

[The ratio expressed by the parallel absorbance/perpendicular absorbance at a wavelength of 475nm]

The parallel transmittance and vertical transmittance measured at a wavelength of 475 nm as described above are converted into parallel absorbance and vertical absorbance respectively according to the following formula: absorbance=-log ₁₀ (T/T ₀ ). In the above formula, T ₀ is the light intensity of polarized light with a wavelength of 475nm emitted from the Glan-Thomson ellipse entering the polarizing multilayer film, and T is the parallel transmittance or vertical transmittance at a wavelength of 475nm.

[Measurement of boron content]

0.2 g of the polarizer layer (polarizing film) obtained by peeling and removing the substrate film from the polarizing laminated film was immersed in 100 mL of hot water at a temperature of 95°C for 60 minutes, and after it was completely dissolved, 30 g of mannitol aqueous solution (12.5% by weight) was added to obtain the measurement. with sample solution. A sodium hydroxide aqueous solution (1 mol/liter) was added dropwise to the measurement sample solution until it reached the neutralization point. From this dropping amount, according to the following formula: boron content rate (weight %)=1.08×sodium hydroxide aqueous solution dropping amount (mL)/weight of polarizing film (g)

The boron content (% by weight) in the polyvinyl alcohol-based resin film was calculated. In the same procedure, the boron content was calculated for the crosslinked layer obtained by peeling and removing the base film from the crosslinked laminated film before the boron removal step, and the change in the boron content before and after the boron removal step was confirmed.

[Measurement of contraction force]

From the polarizing laminated film, a sample with a width of 2 mm and a length of 8 mm in the direction of the absorption axis (extension direction) is cut out, and the substrate film is peeled off to obtain a sample for measurement of the polarizer layer (polarizing film). The thickness was measured using a contact-type film thickness meter (trade name "DIGIMICRO MH-15M" manufactured by Nikon Co., Ltd.). This measurement sample was set in a thermomechanical analyzer (Thermo-Mechanical Analyzer: TMA) "EXSTAR-6000" (manufactured by SII Nanotechnology Co., Ltd.), and the long side that occurred when the size was kept at 80°C for 240 minutes was measured. The contraction force (measured contraction force) in the direction (absorption axis direction, extension direction). Divide the measured shrinkage force by the measured thickness of the measurement sample, and multiply by 5 μm to obtain the shrinkage force [N/5 μm] per 5 μm thickness with a width of 2 mm (the following formula).

Contraction force [N/5μm]=(measured shrinkage force of polarizer layer (polarizer film) [N])/(thickness of polarizer layer (polarizer film) (measured value)[μm])×5

[Example 1]

(undercoat layer forming step)

Polyvinyl alcohol powder ("Z-200" manufactured by Nippon Gosei Chemical Industry Co., Ltd., average degree of polymerization 1100, average degree of saponification 99.5 mole%) was dissolved in hot water at 95°C to prepare polyvinyl alcohol with a concentration of 3% by weight aqueous solution. The resulting aqueous solution was mixed with a crosslinking agent (Sumirez Resin 650 manufactured by Taoka Chemical Industry Co., Ltd.) at a ratio of 5 parts by weight to 6 parts by weight of polyvinyl alcohol powder to obtain a coating solution for forming an undercoat layer.

Next, a substrate film (unstretched polypropylene film, melting point: 163° C.) with a thickness of 90 μm was continuously conveyed, and after corona treatment was performed on one side thereof, a micro-gravure coater was used on the corona-treated side, The above-mentioned coating liquid for forming an undercoat layer was continuously applied, and dried at 80° C. for 10 minutes to form an undercoat layer having a thickness of 0.2 μm.

(Preparation of laminated film (resin layer formation step))

Polyvinyl alcohol powder (“PVA124” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, saponification degree 98.0 to 99.0 mole%) was dissolved in hot water at 95°C to prepare a polyvinyl alcohol aqueous solution with a concentration of 7.5% by weight. This is used as a coating liquid for forming a polyvinyl alcohol-based resin layer.

The substrate film having the undercoat layer produced in the above undercoat layer forming step is continuously conveyed, and the above-mentioned coating liquid for forming a polyvinyl alcohol-based resin layer is continuously coated on the surface of the undercoat layer using a die coater. Afterwards, by drying at 80 to 90°C, a polyvinyl alcohol-based resin layer with a film thickness of 9 μm is formed on the primer layer to obtain a laminated film consisting of base film/primer layer/polyvinyl alcohol-based resin layer .

(extended steps)

The above-mentioned laminated film was conveyed continuously, using a floating longitudinal uniaxial stretching device, and the maximum temperature during stretching was 150° C., and 5.3 times free-end uniaxial stretching (in-air stretching) was performed to obtain a stretched film. The thickness of the stretched polyvinyl alcohol-based resin layer was 5 μm.

(Dyeing step)

While continuously conveying the above stretched film, it is continuously immersed in a 30°C dyeing bath containing iodine and potassium iodide (containing 0.35 parts by weight of iodine and 5.0 parts by weight of potassium iodide per 100 parts by weight of water), and the residence time is about 90 seconds. , the dyeing treatment of the polyvinyl alcohol-based resin layer is performed to obtain a dyed laminated film.

(cross-linking step)

Continuously convey the above-mentioned dyed laminated film, and continuously immerse it in a 78°C cross-linking solution containing boric acid (10.4 parts by weight of boric acid per 100 parts by weight of water), with a tension of 16N/cm and a residence time of about 120 seconds , and carry out cross-linking treatment to obtain a cross-linked laminated film.

(removal of boron step)

Then, while the above-mentioned cross-linked laminated film is continuously conveyed, it is continuously immersed in a 65°C boron-removing solution containing boric acid and potassium iodide (for every 100 parts by weight of water, 2 parts by weight of boric acid and 6.0 parts by weight of potassium iodide are included), and the tension 1N/cm, the residence time is about 60 seconds, and the boron removal treatment is carried out. Then, immerse in water at 7°C for 5 seconds with a tension of 1N/cm, perform boron removal treatment, use a blower to remove the liquid adhering to both sides, and dry it at 60°C to obtain a polarized film with a thickness of 5 μm on the substrate film. Sheet polarizing laminated film.

From the obtained polarizing laminated film, evaluation samples were obtained as described in the above "Preparation of Evaluation Samples", and the sensitivity-corrected single transmittance (Ty), sensitivity-corrected polarization degree (Py), shrinkage force, and evaluation parameters were calculated. The boron content of the sample is checked for changes in the boron content before and after the boron removal step. The results are shown in Table 1. In Table 1, "decrease" in the column of change in boron content rate means that the boron content rate after the boron removal step is smaller than the boron content rate before the boron removal step.

[Example 2]

In the boron removal step, the same operation as in Example 1 was performed except that the tension was 5 N/cm to obtain a polarizing laminated film, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Example 3]

In the boron-removing step, the same operation as in Example 1 was performed except that boric acid was 5 parts by weight to obtain a polarizing laminated film, and the same evaluation as in Example 1 was performed.

[Example 4]

In the boron removal step, except that the boric acid was 5 parts by weight and the tension was 5 N/cm, the same operation as in Example 1 was carried out to obtain a polarizing laminated film, and the same evaluation was performed as in Example 1.

[Example 5]

In the boron removal step, except that the boric acid was 5 parts by weight and the tension was 10 N/cm, the same operation as in Example 1 was carried out to obtain a polarizing laminated film, and the evaluation was performed in the same manner as in Example 1.

[Comparative Example 1]

In the boron removal step, the same operation as in Example 1 was performed except that the tension was 16 N/cm to obtain a polarizing laminated film, and the same evaluation as in Example 1 was performed.

[Comparative Example 2]

In the boron removal step, the same operation as in Example 1 was carried out except that the boric acid was 3.5 parts by weight and the tension was 16 N/cm, to obtain a polarizing laminated film, and the same evaluation as in Example 1 was performed.

[Comparative Example 3]

In the boron-removing step, the same operation as in Example 1 was performed except that the boric acid was 5 parts by weight and the tension was 16 N/cm, to obtain a polarizing laminated film, and the same evaluation was performed as in Example 1.

As shown in Table 1, the polarizing layer (polarizing film) of the polarizing laminated film obtained in Examples 1 to 5 has a boron content of not less than 2.5% by weight and not more than 4.1% by weight, and the single transmittance (Ty ) exceeds 40.5%, and the ratio represented by the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm does not reach 0.022. Furthermore, the polarizing layer (polarizing film) of Examples 1 to 5 has a sensitivity-corrected polarization degree (Py) exceeding 99.994 when the sensitivity-corrected single transmittance (Ty) is 41.5. The shrinkage force in the longitudinal direction (absorption axis direction, stretching direction) of the polarizing layer (polarizing film) of Examples 1 to 5 was controlled to be less than 1.77 N/5 μm.

In Comparative Examples 1 to 3, the sensitivity-corrected polarization degree (Py) was low when the sensitivity-corrected single transmittance (Ty) was 41.5. It is speculated that the magnitude of the tension added to the cross-linked laminated film in the boron-removing step is the same as the magnitude of the tension added to the dyed laminated film in the cross-linked step. Furthermore, in Comparative Examples 1 to 3, the ratio represented by the parallel absorbance/perpendicular absorbance at a wavelength of 475 nm was large. In Examples 1 to 5 and Comparative Examples 1 to 3, the boron content before and after the boron removal step decreases. It is speculated that in the boron removal step, the excessive boric acid contained in the cross-linked layer is removed, while in Comparative Examples 1 to 3, In the boron-removing step, the polyiodide ion complexes with low alignment were not sufficiently removed.

Claims (4)

A polarizing film, which is a polarizing film in which iodine is aligned to a polyvinyl alcohol-based resin layer; the boron content rate is not less than 2.5% by weight and not more than 3.0% by weight; the transmittance (Ty) of a single light sensitivity correction exceeds 40.5%; the wavelength is 475nm The ratio of parallel absorbance/perpendicular absorbance is less than 0.022; when kept at 80°C for 4 hours, the width in the direction of the absorption axis is 2mm, and the shrinkage force per 5μm thickness is less than 1.77N/5μm; the thickness is less than 10μm. A polarizing plate, which is provided with a protective film on at least one side of the polarizing film described in item 1 of the scope of the patent application. A method for producing a polarizing laminated film comprising, in order: forming a resin layer forming a polyvinyl alcohol-based resin layer on at least one surface of a base film to obtain a laminated film; stretching the laminated film to obtain a stretched film stretching step; a dyeing step of obtaining a dyed laminated film by dyeing the polyvinyl alcohol-based resin layer of the stretched film with iodine to form a dyed layer; crosslinking the dyed layer of the dyed laminated film with boric acid liquid cross-linking, forming a cross-linked layer to obtain a cross-linked laminated film; Up to 3.0% by weight of the polarizer layer is obtained from the base film and the patent application scope No. 1 Or the boron removal step of the polarizing laminated film formed by the polarizing film described in item 2; wherein the aforementioned boron removal step has the step of contacting the aforementioned cross-linked layer with the boron removal liquid, and the aforementioned boron removal liquid has a higher ratio than the aforementioned cross-linked boron removal step. The low boric acid concentration of the boric acid concentration of the linking solution; in the aforementioned contact step of the boron-removing solution, the amount of tension added to the aforementioned cross-linked laminated film is controlled in a manner that is smaller than the tension of the laminated film attached to the aforementioned dyed layer in the aforementioned cross-linking step. The size of the tension. A method for manufacturing a polarizing plate, comprising sequentially: using the manufacturing method described in claim 3 of the scope of the patent application, the step of manufacturing a polarizing laminated film; on the surface of the polarizer layer opposite to the substrate film, a step of attaching a protective film; and a step of peeling and removing the aforementioned base film.

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