JP2018091980A - Polarizing film and method for producing polarizing laminated film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing film which curbs contraction force while having a high optical characteristic and to provide a manufacturing method of a polarized laminate film.SOLUTION: In a polarizing film, iodine is aligned on a polyvinyl alcohol resin layer. The polarizing film has: a boron content of 2.5 wt.% or more and 4.1 wt.% or less; a visibility correction single transmission factor (Ty) of more than 40.5%; and a ratio expressed by horizontal absorbency/vertical absorbency at a wavelength of 475 nm is less than 0.022.SELECTED DRAWING: Figure 1

Description

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

  The polarizing plate is widely used in display devices such as liquid crystal display devices. As for a polarizing plate, what was comprised by bonding a protective film on the single side | surface or both surfaces of the polarizer layer which consists of polyvinyl alcohol-type resin is common. With the development of image display devices in mobile devices and thin televisions, there is an increasing demand for thinner polarizing plates.

  As a method for producing a polarizing plate having a thin polarizer layer, after stretching a laminated film in which a polyvinyl alcohol resin layer is formed by coating a coating liquid containing a polyvinyl alcohol resin on a base film A method for producing a polarizing laminated film in which a polarizer layer is formed on a base film by performing a dyeing treatment for adsorbing a dichroic dye on a polyvinyl alcohol-based resin layer is known (for example, Patent Document 1). ).

  According to the above method, since the polyvinyl alcohol-based resin layer is formed by coating, it is easier to reduce the thickness of the polyvinyl alcohol-based resin layer than to reduce the thickness of a single-layer (single) film made of polyvinyl alcohol-based resin. Therefore, it is easy to reduce the thickness of the polarizer layer.

  Patent Document 1 describes that the film is stretched at a high magnification in order to obtain excellent optical characteristics.

  On the other hand, although it was not manufactured by the method of coating the coating liquid containing the polyvinyl alcohol-based resin on the base film as described above, Patent Document 2 discloses boric acid in order to suppress the occurrence of blue leak. A polarizer with an increased degree of crosslinking is described.

Japanese Patent No. 5667016 Japanese Patent No. 5985813

  In order to improve the degree of polarization of the polarizer layer and the polarizer, as described above, it is conceivable to increase the draw ratio, increase the degree of cross-linking of boric acid, increase the neck-in rate, and the like. However, in these methods, the contraction force when the polarizer layer or the polarizer is heated tends to increase, and the polarizer layer or the polarizer is easily broken.

  An object of this invention is to provide the manufacturing method of a polarizing film and a polarizing laminated film with small shrinkage force, while having a high optical characteristic.

The present invention provides a polarizing film, a polarizing plate, a polarizing laminate film, and a method for producing the polarizing plate shown below.
[1] A polarizing film in which iodine is oriented in a polyvinyl alcohol-based resin layer,
The boron content is 2.5 wt% or more and 4.1 wt% or less,
Visibility corrected single transmittance (Ty) is over 40.5%,
A polarizing film having a ratio expressed by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm of less than 0.022.
[2] The polarizing film according to [1], wherein a shrinkage force per width of 2 mm and a thickness of 5 μm when held at 80 ° C. for 4 hours is less than 1.77 N / 5 μm.
[3] The polarizing film according to [1] or [2], wherein the thickness is 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 resin layer forming step of obtaining a laminated film by forming a polyvinyl alcohol-based resin layer on at least one surface of the base film;
A stretching step of stretching the laminated film to obtain a stretched film;
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;
A crosslinking step of obtaining a 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;
A boron removal step of obtaining a polarizing laminated film by reducing the boron content contained in the crosslinked layer of the crosslinked laminated film to form a polarizer layer, in this order,
The boron removal step includes a boron removal solution contact step in which the crosslinked layer and the boron removal solution are in contact, and the boron removal solution has a boric acid concentration lower than the boric acid concentration of the crosslinking solution,
In the deboronating liquid contact step, a polarizing laminated film that controls the magnitude of tension applied to the crosslinked laminated film to be smaller than the magnitude of tension applied to the laminated film with dyed layer in the crosslinking process. Manufacturing method.
[6] A step of producing a polarizing laminated film by the production method according to [5],
A step of bonding a protective film to the surface of the polarizer layer opposite to the base film;
Peeling and removing the base film;
In this order.

  According to the present invention, it is possible to provide a polarizing film and a polarizing plate that have high optical properties but have reduced shrinkage. Moreover, according to this invention, the manufacturing method of the light-polarizing laminated film which is excellent in an optical characteristic and has a small shrinkage force, and the manufacturing method of a polarizing plate can be provided.

It is a flowchart which shows the manufacturing method of the light-polarizing laminated film which concerns on this invention, and the manufacturing method of a polarizing plate. It is a schematic sectional drawing which shows an example of the laminated constitution of the laminated | multilayer film obtained at a resin layer formation process. It is a schematic sectional drawing which shows an example of the laminated constitution of the stretched film obtained at a extending process. It is a schematic sectional drawing which shows an example of the layer structure of the light-polarizing laminated film obtained at a deboronation process. It is a schematic sectional drawing which shows an example of the laminated constitution of the polarizing plate with a protective film obtained by a 1st protective film bonding process. It is a schematic sectional drawing which shows an example of the layer structure of the polarizing plate with a single-sided protective film obtained by a peeling process. It is a schematic sectional drawing which shows an example of the laminated constitution of the polarizing plate with a double-sided protective film obtained by a 2nd protective film bonding process.

<Polarizing film>
The polarizing film is one in which iodine is oriented in the polyvinyl alcohol-based resin layer, and can be obtained, for example, as a polarizer layer of a polarizing laminated film described later. The polarizing film has a boron content of 2.5 wt% or more and 4.1 wt% or less, a visibility corrected single transmittance (Ty) of more than 40.5%, and a parallel absorbance / orthogonal absorbance at a wavelength of 475 nm. The represented ratio can be less than 0.022. The polarizing film is a stretched film obtained by stretching a polyvinyl alcohol-based resin layer, and this stretching is preferably uniaxial stretching.

  Boron in the polarizing film is derived from boric acid in a crosslinking liquid used for crosslinking a polyvinyl alcohol-based resin layer described later. If the boron content of the polarizing film is large, that is, 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 contraction force when the polarizing film is heated tends to increase. is there. 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 during heating of the polarizing film can be reduced, but sufficient water resistance and excellent optical properties tend to be difficult to obtain. is there.

  The boron content of the polarizing film can be 2.5 wt% or more and 4.1 wt% or less. Thereby, the shrinkage force produced at the time of heating of a polarizing film can be suppressed. The boron content of the polarizing film is preferably 2.6% by weight to 4.0% by weight, and more preferably 2.7% by weight to 3.5% by weight. The boron content of the polarizing film is measured according to the description in the examples described later.

When the polarizing film is held at 80 ° C. for 4 hours, the contraction force per width of 2 mm in the absorption axis direction (stretching direction) of the polarizing film and the thickness of the polarizing film of 5 μm is preferably less than 1.77 N / 5 μm, more preferably Is 1.70 N / 5 μm or less, more preferably 1.60 N / 5 μm or less, and may be 1.40 N / 5 μm or less. The lower limit value of the contractile force is not particularly limited, but ideally 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 it is preferable that the polarizing film does not expand, it is preferably −0.01 N / 5 μm or more. The shrinkage force of the polarizing film is a value obtained by measuring the shrinkage force of the polarizing film (measured shrinkage force) and the value obtained by measuring the thickness of the polarizing film in accordance with the description in Examples below. Is a value calculated by converting per thickness of 5 μm.
Shrinkage force [N / 5 μm] = (Measured shrinkage force of polarizing film [N]) / (Polarization film thickness (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, the optical properties such as the degree of polarization can be improved, but the contraction force of the polarizing film is increased. On the other hand, when the degree of crosslinking of the polyvinyl alcohol-based resin layer is lowered to reduce the boron content in the polarizing film, it is difficult to obtain excellent optical characteristics.

  Therefore, in the polarizing film, the ratio represented by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm is set to less than 0.022. Thereby, while reducing the boron content to such an extent that the contraction force of the polarizing film can be suppressed, the visibility corrected single transmittance (Ty) is over 40.5%, and the visibility corrected single transmittance (Ty) is 41. When it is 0.5%, it is possible to realize an excellent optical characteristic in which the visibility correction polarization degree (Py) exceeds 99.994. The lower limit of the visibility corrected single transmittance (Ty) is preferably 41.0% or more, more preferably 41.5% or more, and the upper limit is 50% or less, preferably 47% or less. is there. The lower limit of the visibility correction polarization degree (Py) when the visibility correction single transmittance (Ty) is 41.5% is preferably 99.995 or more, and more preferably 99.996 or more.

The reason why the optical properties of the polarizing film can be improved by defining the ratio represented by the parallel absorbance / orthogonal absorbance at a wavelength of 475 nm of the polarizing film can be explained as follows. In the polyvinyl alcohol resin layer dyed with iodine, iodine is adsorbed and oriented in the polyvinyl alcohol resin layer. Iodine this adsorption orientation I ₃ ^- to form a complex of poly iodine ions such as ^- and I _5. Among these complexes, complexes of polyiodine ions having an absorption band at 475 nm (I ₃ ^- complex), since the easily disturbed orientation as compared to a complex of other polyiodine ion, cause of lowering the degree of polarization of the polarizing film Cheap.

  Among the complexes of polyiodine ions having an absorption band at a wavelength of 475 nm, there are a relatively highly oriented complex and a relatively poorly oriented complex. In order to improve the degree of polarization of the polarizing film, it is preferable to increase the content of a complex having a relatively high orientation among polyiodine ion complexes having an absorption band at a wavelength of 475 nm in the polyvinyl alcohol-based resin layer. .

  Among polyiodine ion complexes having an absorption band at a wavelength of 475 nm, the content of a relatively highly oriented complex can be evaluated by a ratio represented by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm. Here, the parallel absorbance at a wavelength of 475 nm is a value obtained by converting the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the sample (polarizing film) into absorbance. The orthogonal absorbance at 475 nm is obtained by converting the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the sample (polarizing film) into absorbance.

  The smaller the ratio expressed by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm, the smaller the parallel absorbance and the greater the orthogonal absorbance. This means that the smaller the ratio, the relatively oriented the polyiodide ion complex having an absorption band at a wavelength of 475 nm, which is oriented in the direction perpendicular to the transmission axis of the polarizing film (absorption axis direction of the polarizing film). This means that the content of a complex having a high value is increased. Therefore, the degree of polarization of the polarizing film can be improved by reducing the ratio.

  Thus, by making the ratio represented by the parallel absorbance / orthogonal absorbance at a wavelength of 475 nm of the polarizing film less than 0.022, the amount of the complex with low orientation is reduced, and the polarization degree of the polarizing film is improved. be able to. The upper limit value of the ratio is more preferably less than 0.0218, still more preferably less than 0.0217, and the lower limit value is 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 value of the thickness of the polarizing film is preferably 1 μm or more, and more preferably 2 μm or more. Such a polarizing film can improve the optical characteristics and suppress the shrinkage force while realizing thinning.

  What is mentioned later can be used about the polyvinyl alcohol-type resin and the polyvinyl alcohol-type resin layer which comprise the polyvinyl alcohol-type resin layer of a polarizing film. Moreover, a polarizing film can be manufactured according to the manufacturing method of the light-polarizing laminated film mentioned later, for example.

<Polarizing plate>
The polarizing film can be a polarizing plate by providing a protective film on at least one surface thereof. The polarizing plate may be a polarizing plate with a single-sided protective film provided with a protective film on one side of the polarizing film, or a polarizing plate with a double-sided protective film provided with protective films on both sides of the polarizing film. The two protective films of the polarizing plate with a double-sided protective film may be the same type of protective film or different types of protective films.

  What is mentioned later can be used about the material which comprises a protective film, For example, it can manufacture according to the manufacturing method of the polarizing plate mentioned later.

(Use of polarizing plate)
A polarizing plate with a single-sided protective film and a polarizing plate with a double-sided protective film can be used as a composite polarizing plate by pasting peripheral members together. As a peripheral member, a protective film for preventing scratches bonded on a protective film; on a protective film (for example, a polarizing plate with a double-sided protective film) or on a polarizer layer (for example, a polarizing plate with a single-sided protective film) Adhesive layer for laminating a polarizing plate to a display cell or other optical member; a separate film laminated on the outer surface of the adhesive layer; on a protective film (for example, with a double-sided protective film) In the case of a polarizing plate) or an optical compensation film such as a retardation film laminated on a polarizer layer (for example, in the case of a polarizing plate with a single-sided protective film) or other optical functional films.

  The pressure-sensitive adhesive layer, which is an example of the peripheral member, can be laminated on the outer surface of any protective film in a polarizing plate with a double-sided protective film. Can be stacked. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually based on a (meth) acrylic resin, styrene resin, silicone resin or the like, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. It consists of an adhesive composition. Furthermore, it can also be set as the adhesive layer which contains microparticles | fine-particles and shows light-scattering property. The thickness of an adhesive layer is 1-40 micrometers normally, Preferably it is 3-25 micrometers.

  In addition, as an optical functional film as another example of the peripheral member, a reflective polarizing film that transmits a certain kind of polarized light and reflects polarized light that shows the opposite property; anti-glare having an uneven shape on the surface A film with a function; a film with a surface antireflection function; a reflection film having a reflection function on the surface; a transflective film having both a reflection function and a transmission function; and a viewing angle compensation film.

<Method for producing polarizing laminated film>
With reference to FIG. 1, the polarizing laminated film which is a manufacturing intermediate of a polarizing plate has the following processes:
Resin layer forming step S10 for obtaining a laminated film by forming a polyvinyl alcohol-based resin layer on at least one surface of the base film,
Stretching step S20 for stretching the laminated film to obtain a stretched film,
Dyeing step S30 for obtaining a dyed laminated film by dyeing the polyvinyl alcohol-based resin layer of the stretched film with iodine to form a dyed layer,
A crosslinking step S40 for obtaining a crosslinked laminated film by crosslinking the dyed layer of the dyed laminated film with a crosslinking liquid containing boric acid to form a crosslinked layer;
Deboronization step S50 for obtaining a polarizing laminated film by reducing the boron content contained in the crosslinked layer of the crosslinked laminated film to form a polarizer layer;
In this order.

  In addition, the light-polarizing laminated film in this invention means a thing provided with the base material film and the polarizer layer laminated | stacked on the at least one surface, and the protective film is not bonded. . In order to distinguish the polarizing laminated film formed by laminating the first protective film on the polarizer layer in the first protective film laminating step S60 to be described later, It is also referred to as a “conductive laminate film”.

(1) Resin layer forming step S10
With reference to FIG. 2, this step is a step of forming the laminated film 100 by forming the polyvinyl alcohol-based resin layer 6 on at least one surface of the base film 30. 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 deboronation step S50. The polyvinyl alcohol-based resin layer 6 can be formed by applying a coating liquid containing a polyvinyl alcohol-based resin to one or both surfaces of the base film 30 and drying the coating layer. The method of forming the polyvinyl alcohol-based resin layer 6 by such coating is advantageous in that a thin polarizer layer 5 can be easily obtained. The resin layer forming step S10 is typically performed by continuously unwinding the base film 30 from a film roll that is a wound product of the long base film 30 and transporting the base film 30. it can. The film conveyance can be performed using a guide roll or the like.

(Base film)
The base film 30 can be composed of a thermoplastic resin, and among them, it is preferably composed of a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, stretchability, and the like. Specific examples of such thermoplastic resins include, for example, polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins (norbornene resins, etc.); polyester resins; (meth) acrylic resins; cellulose triacetate, Cellulose ester resins such as cellulose diacetate; Polycarbonate resins; Polyvinyl alcohol resins; Polyvinyl acetate resins; Polyarylate resins; Polystyrene resins; Polyethersulfone resins; Polysulfone resins; Polyamide resins; System resins; and mixtures and copolymers thereof.

  The base film 30 may have a single-layer structure made of one resin layer made of one kind or two or more kinds of thermoplastic resins, or a plurality of resin layers made of one kind or two or more kinds of thermoplastic resins. A laminated multilayer structure may be used. The base film 30 is preferably made of a resin that can be stretched at a stretching temperature suitable for stretching the polyvinyl alcohol-based resin layer 6 when the laminated film 100 is stretched in the stretching step S20 described later.

  Examples of the chain polyolefin-based resin include a homopolymer of a chain olefin such as a polyethylene resin and a polypropylene resin, and a copolymer composed of two or more chain olefins. The base film 30 made of a chain polyolefin-based resin is preferable in that it is easily stretched stably at a high magnification. Among them, the base film 30 is composed mainly of a polypropylene resin (a polypropylene resin that is a propylene homopolymer or a copolymer mainly composed of propylene), a polyethylene resin (a polyethylene resin that is an ethylene homopolymer or ethylene). It is more preferable that it consists of a copolymer.

  The copolymer mainly composed of propylene, which is one example suitably used as the thermoplastic resin constituting the base film 30, is a copolymer of propylene and another monomer copolymerizable therewith.

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

  Content of the said other monomer is 0.1-20 weight% in a copolymer, for example, Preferably it is 0.5-10 weight%. The content of other monomers in the copolymer can be determined by measuring infrared (IR) spectrum according to the method described on page 616 of "Polymer Analysis Handbook" (1995, published by Kinokuniya Shoten). Can be sought.

  Among these, as the polypropylene resin, a propylene homopolymer, a propylene-ethylene random copolymer, a propylene-1-butene random copolymer or a propylene-ethylene-1-butene random copolymer is preferably used.

  It is preferable that the stereoregularity of the polypropylene resin is substantially isotactic or syndiotactic. The base film 30 made of a polypropylene-based resin having substantially isotactic or syndiotactic stereoregularity has relatively good handleability and excellent mechanical strength in a high temperature environment.

  The cyclic polyolefin resin is a general term for resins that are polymerized using a cyclic olefin as a polymerization unit, and is described in, for example, JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, and the like. Resin. Specific examples of cyclic polyolefin resins include ring-opening (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically Are random copolymers), graft polymers obtained by modifying them with unsaturated carboxylic acids or their derivatives, and hydrides thereof. Among these, norbornene resins using norbornene monomers such as norbornene and polycyclic norbornene monomers as cyclic olefins are preferably used.

  The polyester resin is a resin having an ester bond, and is generally made of a polycondensate of a polyvalent carboxylic acid or a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a divalent dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. As the polyhydric alcohol, a divalent diol can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol.

  A typical example of the polyester resin is polyethylene terephthalate which is a polycondensate of terephthalic acid and ethylene glycol. Polyethylene terephthalate is a crystalline resin, but the one in a state before crystallization treatment is more easily subjected to treatment such as stretching. If necessary, it can be crystallized during stretching or by heat treatment after stretching. Further, a copolymerized polyester having a crystallinity lowered (or made amorphous) by further copolymerizing another monomer with a polyethylene terephthalate skeleton is also preferably used. Examples of such resins include those obtained by copolymerizing cyclohexanedimethanol and isophthalic acid. Since these resins are also excellent in stretchability, they can be suitably used.

  Specific examples of polyester resins other than polyethylene terephthalate and copolymers thereof include, for example, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexanedimethyl terephthalate. Polycyclohexanedimethyl naphthalate.

The (meth) acrylic resin is a resin containing a compound having a (meth) acryloyl group as a main constituent monomer. Specific examples of (meth) acrylic resins include, for example, poly (meth) acrylic acid esters such as polymethyl methacrylate; methyl methacrylate- (meth) acrylic acid copolymer; methyl methacrylate- (meth) acrylic acid Ester copolymer; methyl methacrylate-acrylic ester- (meth) acrylic acid copolymer; (meth) methyl acrylate-styrene copolymer (MS resin etc.); methyl methacrylate and alicyclic hydrocarbon group And a copolymer (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer). Preferably, a polymer based on a poly (meth) acrylic acid C _1-6 alkyl ester such as poly (meth) acrylic acid methyl is used, and more preferably methyl methacrylate is the main component (50-100). % Methyl methacrylate resin is used.

  The cellulose ester resin is an ester of cellulose and a fatty acid. Specific examples of the cellulose ester resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Further, these copolymers and those in which a part of the hydroxyl group is modified with other substituents are also included. Among these, cellulose triacetate (triacetyl cellulose) is particularly preferable. Many products of cellulose triacetate are commercially available, which is advantageous in terms of availability and cost.

  The polycarbonate-based resin is an engineering plastic made of a polymer in which monomer units are bonded via a carbonate group, and is a resin having 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 in which the polymer skeleton is modified in order to lower the photoelastic coefficient, or a copolymerized polycarbonate with improved wavelength dependency.

  Among these, polypropylene resins are preferably used from the viewpoints of stretchability and heat resistance.

  The base film 30 can contain any appropriate additive in addition to the above thermoplastic resin. Examples of the additive include an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a mold release agent, a coloring inhibitor, a flame retardant, a nucleating agent, an antistatic agent, a pigment, and a coloring agent. 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, and 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 viewpoints of strength and handleability.

(Formation of polyvinyl alcohol resin layer)
The coating liquid applied to the base film 30 is preferably a polyvinyl alcohol resin solution obtained by dissolving a polyvinyl alcohol resin powder in a good solvent (for example, water). As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The degree of saponification of the polyvinyl alcohol-based resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 99.5 mol%, more preferably 94.0. It is in the range of ˜99.0 mol%. When the saponification degree is less than 80.0 mol%, the water resistance and heat-and-moisture resistance of the polarizing plate may be lowered. When a polyvinyl alcohol-based resin having a saponification degree exceeding 99.5 mol% is used, the dyeing rate of iodine, which is a dichroic dye, is slowed down, and productivity is lowered and a polarizing plate having sufficient polarization performance is obtained. It may not be possible.

The degree of saponification is the unit ratio (mol%) of the proportion of acetate groups (acetoxy groups: —OCOCH ₃ ) contained in polyvinyl acetate resin, which is a raw material for polyvinyl alcohol resins, changed to hydroxyl groups by the saponification step. The following formula:
Saponification degree (mol%) = 100 × (number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetate groups)
Defined by The degree of saponification can be determined according to JIS K 6726-1994. The higher the degree of saponification, the higher the proportion of hydroxyl groups, and hence the lower the proportion of acetate groups that inhibit crystallization.

  The polyvinyl alcohol-based resin may be a modified polyvinyl alcohol partially modified. For example, polyvinyl alcohol resins 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 can be used. The proportion of modification is preferably less than 30 mol%, and more preferably less than 10%. When modification exceeding 30 mol% is performed, iodine which is a dichroic dye is difficult to adsorb, and it is difficult to obtain a polarizing plate having sufficient polarization performance.

  The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10,000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol resin can also be determined according to JIS K 6726-1994. If the average degree of polymerization is less than 100, it is difficult to obtain preferable polarizing performance, and if it exceeds 10,000, the solubility in a solvent deteriorates, and it is difficult to form a polyvinyl alcohol-based resin layer in the method for producing a polarizing laminated film described later. Become.

  The coating liquid may contain additives such as a plasticizer and a surfactant as necessary. As the plasticizer, polyol or a condensate thereof can be used, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The blending amount of the additive is preferably 20% by weight or less of the polyvinyl alcohol resin.

  The coating liquid is applied to the base film 30 by 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; The method can be appropriately selected from a method such as a fountain coating method, a dipping method, and a spray method.

  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 solution. A drying temperature is 50-200 degreeC, for example, Preferably it is 60-150 degreeC. When the solvent contains water, the drying temperature is preferably 80 ° C. or higher.

  The polyvinyl alcohol-based resin layer 6 may be formed only on one surface of the base film 30 or may be formed on both surfaces. When it is formed on both sides, curling of the film that may occur during the production of the polarizing laminated film can be suppressed, and two polarizing plates can be obtained from one polarizing laminated film. It is advantageous.

  The thickness of the polyvinyl alcohol-based resin layer 6 in the laminated film 100 is preferably 3 to 30 μm, more preferably 5 to 20 μm. If it is the polyvinyl alcohol-type resin layer 6 which has the thickness in this range, the dyeing | staining property of the iodine which is a dichroic dye will be favorable through the extending | stretching process S20 and dyeing | staining process S30 which are mentioned later, and it is excellent in polarizing performance, and fully A thin polarizer layer 5 (for example, a thickness of 10 μm or less) can be obtained.

  Prior to the application of the coating liquid, in order to improve the adhesion between the base film 30 and the polyvinyl alcohol resin layer 6, at least the surface of the base film 30 on the side where the polyvinyl alcohol resin layer 6 is formed is provided. Corona treatment, plasma treatment, flame (flame) treatment or the like may be performed. For the same reason, the polyvinyl alcohol-based resin layer 6 may be formed on the base film 30 via a primer layer or the like.

  The primer layer can be formed by applying a primer layer forming coating solution to the surface of the substrate film 30 and then drying it. This coating solution includes a component that exhibits a certain degree of strong adhesion to both the base film 30 and the polyvinyl alcohol-based resin layer 6, and usually includes a resin component that provides such adhesion and a solvent. . As the resin component, a thermoplastic resin excellent in transparency, thermal stability, stretchability and the like is preferably used, and examples thereof include (meth) acrylic resins and polyvinyl alcohol resins. Among these, polyvinyl alcohol resins that give good adhesion are preferably used. More preferably, it is a polyvinyl alcohol resin. As the solvent, a general organic solvent or an aqueous solvent capable of dissolving the resin component is usually used, but it is preferable to form the primer layer from a coating solution containing water as a solvent.

  In order to increase the strength of the primer layer, a crosslinking agent may be added to the primer layer forming coating solution. Specific examples of the crosslinking agent include epoxy-based, isocyanate-based, dialdehyde-based, metal-based (for example, metal salts, metal oxides, metal hydroxides, organometallic compounds), and polymer-based crosslinking agents. When a polyvinyl alcohol resin is used as the resin component for forming the primer layer, a polyamide epoxy resin, a methylolated melamine resin, a dialdehyde crosslinking agent, a metal chelate compound crosslinking agent, or the like is preferably used.

  The thickness of the primer layer is preferably about 0.05 to 1 μm, more preferably 0.1 to 0.4 μm. When it becomes thinner than 0.05 μm, the effect of improving the adhesion between the base film 30 and the polyvinyl alcohol resin layer 6 may be reduced.

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

(2) Stretching step S20
With reference to FIG. 3, this process is a process of extending the laminated film 100 to obtain a stretched film 200 composed of the stretched base film 30 ′ and the polyvinyl alcohol-based resin layer 6 ′. Stretching is usually uniaxial stretching. In the stretching step S20, typically, the laminated film 100 is continuously unwound from a film roll that is a wound product of the long laminated film 100 while the long laminated film 100 is conveyed. It can be carried out continuously while being conveyed. The film conveyance can be performed using a guide roll or the like.

  The stretching ratio of the laminated film 100 can be appropriately selected depending on the desired polarization characteristics, but is preferably more than 5 times and not more than 17 times, more preferably more than 5 times the original length of the laminated film 100. 8 times or less. When the draw ratio is 5 times or less, the polyvinyl alcohol-based resin layer 6 ′ is not sufficiently oriented, and the degree of polarization of the polarizer layer 5 may not be sufficiently high. On the other hand, when the draw ratio exceeds 17 times, the film is easily broken during stretching, and the thickness of the stretched film 200 becomes unnecessarily thin, and the workability and handleability in subsequent steps may be reduced. The stretching process is not limited to stretching in one stage, and can be performed in multiple stages.

  The stretching treatment may be longitudinal stretching that extends in the film longitudinal direction (film transport direction), and may be lateral stretching or oblique stretching that extends in the film width direction. Examples of the longitudinal stretching method include inter-roll stretching using a roll, compression stretching, stretching using a chuck (clip), and the like, and examples of the lateral stretching method include a tenter method. As the stretching treatment, either a wet stretching method or a dry stretching method can be adopted. However, it is preferable to use the dry stretching method because the stretching temperature can be selected from a wide range.

  The stretching temperature is set to be equal to or higher than the temperature at which the polyvinyl alcohol-based resin layer 6 and the entire base film 30 can be stretched, and preferably the phase transition temperature (melting point or glass transition temperature) of the base film 30. It is in the range of −30 ° C. to + 30 ° C., more preferably in the range of −30 ° C. to + 5 ° C., and still more preferably in the range of −25 ° C. to + 0 ° C. When the base film 30 consists of a plurality of resin layers, the phase transition temperature means the highest phase transition temperature among the phase transition temperatures exhibited by the plurality of resin layers.

  If the stretching temperature is lower than the phase transition temperature of −30 ° C., high-strength stretching exceeding 5 times is difficult to achieve, or the fluidity of the base film 30 is too low and the stretching treatment tends to be difficult. When the stretching temperature exceeds + 30 ° C. of the phase transition temperature, the fluidity of the base film 30 is too large and stretching tends to be difficult. Since it is easier to achieve a high draw ratio of more than 5 times, the drawing temperature is within the above range, and more preferably 120 ° C. or higher.

  As a heating method of the laminated film 100 in the stretching process, a zone heating method (for example, a method in which hot air is blown and heated in a stretching zone such as a heating furnace adjusted to a predetermined temperature); There is a method of heating the roll itself; a heater heating method (a method in which infrared heaters, halogen heaters, panel heaters, etc. are installed above and below the laminated film 100 and heated by radiant heat). In the inter-roll stretching method, the zone heating method is preferable from the viewpoint of the uniformity of the stretching temperature.

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

  Moreover, you may provide a heat setting process process after the extending | stretching process in extending process S20. The heat setting treatment is a treatment in which heat treatment is performed at a temperature equal to or higher than the crystallization temperature of the polyvinyl alcohol resin while maintaining the tensioned state with the end portion of the stretched film 200 held by the clip. The crystallization of the polyvinyl alcohol-based resin layer 6 'is promoted by this heat setting treatment. The temperature of the heat setting treatment is preferably in the range of −0 ° C. to −80 ° C. of the stretching temperature, and more preferably in the range of −0 ° C. to −50 ° C. of the stretching temperature.

(3) Dyeing step S30
In this step, the polyvinyl alcohol resin layer 6 ′ of the stretched film 200 is dyed with iodine, which is a dichroic dye, and adsorbed and oriented to form a dyed layer, and the dyeing comprising the base film 30 ′ and the dyed layer. This is a step of obtaining a laminated film. The dyeing step S30 typically unwinds the stretched film 200 continuously while conveying the long stretched film 200 or from a film roll that is a wound product of the long stretched film 200. It can be carried out continuously while being conveyed. The film conveyance 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 liquid (dye bath) containing iodine. As the dyeing bath, a solution in which iodine is dissolved in a solvent can be used. As a solvent for the dyeing solution, water is generally used, but an organic solvent compatible with water may be further added. The concentration of iodine in the dyeing bath is preferably 0.01 to 10 parts by weight and more preferably 0.02 to 7 parts by weight with respect to 100 parts by weight of the solvent. The immersion time in the dye bath is preferably adjusted according to the iodine concentration in the dye bath so as to obtain a desired visibility corrected single transmittance (Ty).

  In order to improve the dyeing efficiency, it is preferable to further add an iodide to the dyeing bath containing iodine. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Is mentioned. The iodide concentration in the dyeing bath is preferably 0.01 to 20 parts by weight with respect to 100 parts by weight of the solvent. Of the iodides, it is preferable to add potassium iodide. When potassium iodide is added, the ratio of iodine to potassium iodide is, by weight, preferably 1: 5 to 1: 100, more preferably 1: 6 to 1:80. The temperature of the dyeing bath is preferably 10 to 60 ° C, more preferably 20 to 40 ° C.

  In addition, you may perform an additional extending | stretching process further with respect to the stretched film 200 during dyeing process S30. Embodiments in this case are as follows: 1) In the stretching step S20, after the stretching process is performed at a lower ratio than the target, the stretching process is performed so that the total stretching ratio becomes the target ratio during the dyeing process in the dyeing process S30. In the case of performing the crosslinking treatment after the dyeing treatment, as described later, 2) In the drawing step S20, after the drawing treatment at a lower magnification than the target in the drawing step S20, during the dyeing treatment in the dyeing step S30 Examples include a mode in which the stretching process is performed to such an extent that the total stretching ratio does not reach the target ratio, and then the stretching process is performed during the crosslinking process so that the final total stretching ratio becomes the target ratio.

(4) Crosslinking step S40
This step is a step of crosslinking the dyed layer of the dyed laminated film to form a crosslinked layer to obtain a crosslinked laminated film comprising the base film 30 ′ and the crosslinked layer. The crosslinking step can be performed by immersing the dyed laminated film in a crosslinking liquid containing a crosslinking agent containing at least boric acid. In the crosslinking step S40, typically, the dyed laminated film is continuously unwound from a film roll that is a wound product of the long dyed laminated film while conveying the long dyed laminated film. It can be carried out continuously while being conveyed. The film conveyance can be performed using a guide roll or the like.

  The crosslinking liquid may contain only boric acid as a crosslinking agent, but may contain other crosslinking agents such as boron compounds such as borax, glyoxal, and glutaraldehyde in addition to boric acid. Good. Other crosslinking agents may be used alone or in combination of two or more. As the crosslinking liquid, a solution in which boric acid is dissolved in a solvent can be used. As the solvent, water can be used, but an organic solvent compatible with water may be further included. The content of boric acid in the crosslinking liquid is preferably 1 to 20 parts by weight, more preferably 5 to 15 parts by weight with respect to 100 parts by weight of the solvent, and the content of other crosslinking agents other than boric acid. Is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the solvent.

  The crosslinking liquid can further contain iodide. By adding iodide, the polarization characteristics in the plane of the dyed layer can be made more uniform. Specific examples of iodide are the same as described above. The content of iodide in the cross-linking solution is preferably less than 10 parts by weight, more preferably 8 parts by weight or less, and may be 0 parts by weight (including iodide) with respect to 100 parts by weight of the solvent. You do n’t have to). The lower limit value of the temperature of the crosslinking liquid is preferably 40 ° C. or higher, and the upper limit value is preferably 82 ° C. or lower. When the temperature of the cross-linking liquid exceeds 82 ° C., the polyvinyl alcohol resin in the dyed layer is partially dissolved, and unevenness is likely to occur after dyeing.

  The crosslinking treatment can be performed simultaneously with the dyeing treatment by blending a crosslinking agent into the dyeing bath. Moreover, you may perform the process immersed in a crosslinking agent containing liquid twice or more using the 2 or more types of crosslinking agent containing liquid from which a composition differs. By sufficiently carrying out the crosslinking treatment, the boron content in the dyed layer is increased, and the orientation of the complex of polyiodine ions can be improved. You may perform an extending | stretching process during a crosslinking process. The specific mode for carrying out the stretching treatment during the crosslinking treatment is as described above.

  In the crosslinking step S40, the tension applied to the dyed laminated film is preferably 1 N / cm or more, more preferably 2 N / cm or more, and further preferably 5 N / cm or more per unit length in the width direction. . The upper limit value 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 preferable to continue to apply tension in the stretching direction of the dyed laminated film so as not to relax the orientation of the polyvinyl alcohol resin forming the dyed layer.

  For example, when the dyed laminated film is transported between two nip rolls and immersed in a crosslinking liquid in a crosslinking tank to perform continuous crosslinking treatment, the rotation speed of the nip roll on the carry-in side and the nip roll on the carry-out side The tension applied to the dyed laminated film can be adjusted by adjusting the rotation speed.

(5) Boron removal step S50
Referring to FIG. 4, in this step, a polarizing film composed of the base film 30 ′ and the polarizer layer 5 is formed by reducing the boron content contained in the crosslinked layer of the crosslinked laminated film to form the polarizer layer 5. This is a step of obtaining the conductive laminated film 300. Typically, the deboronization step S50 is to continuously unwind the cross-linked laminated film from a film roll that is a wound product of the long cross-linked laminated film while conveying the long cross-linked laminated film. Can be carried out continuously while being conveyed. The film conveyance can be performed using a guide roll or the like.

  The boron removal step S50 may include a boron removal solution contact step in which a boron removal solution having a boric acid concentration lower than the concentration of boric acid in the crosslinking solution used in the crosslinking step S40 is brought into contact with the crosslinked layer of the crosslinked laminated film. it can. The boron removal liquid contact step can be performed by immersing the crosslinked laminated film in the boron removal liquid, washing the crosslinked layer of the crosslinked laminated film with a shower of the boron removal liquid, and the like. As the deboronating solution, a solution obtained by dissolving boric acid in a solvent or a solution not containing boric acid can be used. Water can be used as the liquid not containing the solvent and boric acid, but it may further contain an organic solvent compatible with water. The content of boric acid in the deboronating solution is preferably less than 10 parts by weight, more preferably 8 parts by weight or less, and may be 0.1 parts by weight or more with respect to the total weight of the solvent.

  Excess boric acid contained in the cross-linked layer or a complex of polyiodine ions with low orientation can be removed by performing a treatment in which the deboronating solution and the cross-linked layer are brought into contact with each other. Thereby, since the boron content rate contained in the polarizer layer 5 falls, the shrinkage force when heating the polarizer layer 5 (polarizing film) can be made small. Moreover, the polarization degree and the transmittance | permeability of the polarizer layer 5 of the light-polarizing laminated film 300 can be improved.

  The deboronating solution may contain iodide. Specific examples of iodide are the same as described above. The content of iodide in the deboronated solution is preferably 15 parts by weight or less, more preferably 8 parts by weight or less, and preferably 5 parts by weight or more based on the total weight of the solvent. By adjusting the content of iodide contained in the deboronating solution, the hue of the resulting polarizing laminate film can be adjusted. The temperature of the deboronating liquid is preferably 70 ° C. or lower, more preferably 65 ° C. or lower. The temperature of the crosslinking liquid is preferably higher than the temperature of the deboronation liquid.

  By using two or more types of deboronated liquids having different compositions, the deboronated liquid contacting step may be performed twice or more. When performing a boron removal liquid contact process in multiple times, the processing method in a boron removal liquid contact process may be the same, and may differ.

  In the cross-linking step and the deboration step, when a plurality of steps are performed with a solution containing boric acid, the boric acid concentration of the solution containing boric acid is lower than that in the previous step and the tension applied to the film All the subsequent steps controlled so as to be small are boron removal steps. For example, the boric acid concentration may be gradually lowered as the process proceeds to the subsequent step, or may be kept constant after the boric acid concentration is once lowered, or a combination thereof. Further, the tension applied to the film may be gradually decreased as the process proceeds to the subsequent step, or may be kept constant after the tension is once reduced, or a combination thereof. When a liquid having a boric acid concentration equal to or higher than the boric acid concentration in the preceding step is used in the subsequent step, the subsequent step is a crosslinking step.

  Moreover, when a bridge | crosslinking process includes two or more processes processed with the liquid containing a boric acid, compared with any process of these several processes, a boric acid concentration is low and the tension | tensile_strength provided to a film becomes small. All steps after the controlled cross-linking step are deboronation steps, and the deboronation step is preferably lower in boric acid concentration and lower in tension applied to the film than the last step of the cross-linking step. Be controlled.

  After carrying out the boron removal step S50, it is preferable to perform a drying treatment of the polarizing laminated film. In the case of performing this drying treatment, it is preferable to prevent the surface of the polarizer layer from being defective by using a deboronation solution not containing boric acid in the treatment of immersing in the deboronation solution performed immediately before the drying treatment. . Arbitrary appropriate methods, such as natural drying, ventilation drying, and heat drying, can be employ | adopted for a drying process. For example, in the case of heat drying, the drying temperature can be usually 20 to 95 ° C., and the drying time can be usually 1 to 15 minutes.

  It is preferable to control the magnitude of the tension applied to the cross-linked laminated film in the deboronating liquid contact process of the deboronating process S50 so as to be smaller than the magnitude of the tension applied to the dyed laminated film in the cross-linking process S40. This effectively removes excess boric acid and low-orientation polyiodide ion complexes contained in the cross-linked layer, so that the contraction force when the polarizer layer is heated is suppressed, and the optical characteristics Can be produced efficiently. The tension applied to the crosslinked laminated film in the deboronization step S50 is preferably less than 16 N / cm, more preferably 14 N / cm or less per unit length in the width direction. The lower limit value of the tension may be more than 0 N / cm, preferably 1 N / cm. In the deboronation step S50, it is preferable that the crosslinked laminated film is not substantially stretched. The fact that the film is not substantially stretched means that the stretch ratio is 1.05 times or less.

  When carrying out the deboronation treatment while transporting the cross-linked laminated film between two nip rolls in the same manner as the dyed laminated film described above, the rotational speed of the carry-in nip roll and the carry-out nip roll are adjusted. The tension applied to the crosslinked laminated film can be adjusted.

  The crosslinked layer of the crosslinked laminated film can be thinned by being obtained by the above-described method. In the thinned cross-linked layer, when the deboronation process is performed with the above-described tension in the deboronization step S50, excess boric acid contained in the cross-linked layer and polyiodide ion complexes with low orientation may be easily removed. I can expect. Therefore, the polarizer layer formed by the above-described manufacturing method can improve the optical characteristics and suppress an increase in contraction force while realizing thinning.

<Production method of polarizing plate>
With reference to FIG. 1, the manufacturing method of the polarizing plate according to the present invention includes the following steps:
1st protective film bonding process S60 which bonds a 1st protective film to the surface on the opposite side to the base film in the polarizer layer of the polarizing laminated film manufactured by the above-mentioned method,
Peeling process S70 for peeling and removing the base film,
Are included in this order.

  Through the first protective film bonding step S60 and the peeling step S70, the single-sided protective film-attached polarizing plate 1 in which the first protective film 10 is bonded to one surface of the polarizer layer 5 is obtained (FIG. 6). Moreover, as shown in FIG. 1, after peeling process S70, the surface (henceforth a peeling surface) which appears by peeling removal of the base film 30 'in the polarizing plate 500 with a single-side protective film is called the 2nd. The 2nd protective film bonding process S80 which bonds 2 protective film 20 may be provided, and the polarizing plate 2 with a double-sided protective film may be obtained (FIG. 7).

(6) 1st protective film bonding process S60
Referring to FIG. 5, in this step, the first protective film 10 is bonded to the surface opposite to the surface on the base film 30 ′ side (that is, on the polarizer layer 5) in the polarizing laminated film 300 to form a multilayer. In this step, the film 400 is obtained. The 1st protective film 10 respond | corresponds to the protective film which the polarizing plate mentioned above has. The first protective film laminating step S60 is typically a polarizing laminate from a film roll that is a rolled product of the long polarizing laminated film 300 while conveying the long polarizing laminated film 300. The film 300 can be continuously unwound and continuously conveyed. The film conveyance can be performed using a guide roll or the like.

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

  The first protective film 10 can be bonded onto the polarizer layer 5 via the first adhesive layer 15. The adhesive forming the first adhesive layer 15 is an active energy ray-curable adhesive (preferably containing a curable compound that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays). UV curable adhesives) and aqueous adhesives in which adhesive components such as polyvinyl alcohol resins are dissolved or dispersed in water.

  When bonding the 1st protective film 10 using an active energy ray hardening adhesive, the 1st protective film 10 is put on the polarizer layer 5 through the active energy ray hardening adhesive used as the 1st adhesive layer 15. After being laminated, the adhesive layer is cured by irradiating active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. Among them, ultraviolet rays are preferable, and as a light source in this case, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excitation mercury lamp, a metal halide lamp, or the like can be used. When using a water-based adhesive, the first protective film 10 may be laminated on the polarizer layer 5 via a water-based adhesive and then dried by heating.

  In bonding the first protective film 10 to the polarizer layer 5, plasma is applied to the bonding surface of the first protective film 10 and / or the polarizer layer 5 in order to improve the adhesion with the polarizer layer 5. Surface treatment (easy adhesion treatment) such as treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment can be performed, and among them, plasma treatment, corona treatment or saponification treatment is preferable. .

(First protective film)
The material constituting the first protective film is preferably a light-transmitting (preferably optically transparent) thermoplastic resin. Examples of such a resin include a chain polyolefin resin (polypropylene resin). Etc.), polyolefin resins such as cyclic polyolefin resins (norbornene resins, etc.); cellulose ester resins such as cellulose triacetate and cellulose diacetate; polyester resins; polycarbonate resins; (meth) acrylic resins; polystyrene Resin, or a mixture or copolymer thereof. Specific examples of these thermoplastic resins include those described for the thermoplastic resin constituting the base film 30 described above.

  The first protective film can also be a protective film having an optical function such as a retardation film and a brightness enhancement film. For example, a retardation film provided with an arbitrary retardation value by stretching a film made of the thermoplastic resin (uniaxial stretching or biaxial stretching) or by forming a liquid crystal layer or the like on the film. It can be.

  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 is formed on the surface of the first protective film 10 opposite to the polarizer layer 5. You can also The surface treatment layer may be formed in advance on the first protective film 10 prior to the first protective film bonding step S60, or after the first protective film bonding step S60 or after the peeling step described later. You may form after S70 implementation. The first protective film 10 contains one or more additives such as a lubricant, a plasticizer, a dispersant, a heat stabilizer, an ultraviolet absorber, an infrared absorber, an antistatic agent, and an antioxidant. Can do.

  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, and particularly preferably 30 μm or less from the viewpoint of thinning the polarizing plate. The thickness of the 1st protective film 10 is 5 micrometers or more normally from a viewpoint of intensity | strength and a handleability.

(7) Peeling step S70
With reference to FIG. 6, this process is a process of peeling and removing base film 30 'from multilayer film 400, and obtaining a polarizing plate (polarizing plate 1 with a single-sided protective film). 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 both the polarizer layers 5, the peeling process S 70 causes 1 Two polarizing plates 1 with a single-sided protective film can be obtained from one polarizing laminated film 300. In the peeling step S70, typically, the multilayer film 400 is continuously unwound from a film roll that is a wound product of the long multilayer film 400 while the long multilayer film 400 is conveyed. It can be carried out continuously while being conveyed. The film conveyance can be performed using a guide roll or the like.

  The method for peeling and removing the base film 30 ′ is not particularly limited, and can be peeled by the same method as the peeling step S <b> 70 of the separator (peeling film) performed with an ordinary polarizing plate with an adhesive. The base film 30 ′ may be peeled off immediately after the first protective film bonding step S60, or is wound up into a roll once after the first protective film bonding step S60 and wound in the subsequent steps. You may peel off while taking out.

  As described above, the multilayer film 400 obtained in the first protective film bonding step S60 is a film in which the polarizer layer 5 and the first protective film 10 are laminated on both surfaces of the base film 30 ′, that is, the first film. 1 protective film 10 / polarizer layer 5 / base film 30 ′ / polarizer layer 5 / first protective film 10 (the first adhesive layer 15 is omitted) and can be a film having a layer structure. . In this case, two single-sided protective film-attached polarizing plates 1 are obtained from one multilayer film 400 through a two-stage peeling process. In the first peeling step, the film having the layer configuration of “first protective film 10 / polarizer layer 5 / base film 30 ′” is peeled from the multilayer film 400 having the above-described configuration, and a polarizing plate with a single-side protective film Get one. In the second peeling process, the base film 30 ′ is peeled from the peeled film having the layer structure of “first protective film 10 / polarizer layer 5 / base film 30 ′”, and further a single-side protective film A polarizing plate 1 is obtained.

(8) 2nd protective film bonding process S80
With reference to FIG. 7, this process is an arbitrary process which pastes the 2nd protective film 20 on the polarizer layer 5 in the polarizing plate 1 with a single-sided protective film, and obtains the polarizing plate 2 with a double-sided protective film. The second protective film laminating step S80 is typically a film roll which is a rolled product of the long polarizing plate 1 with a single-side protective film while conveying the long polarizing plate 1 with single-side protective film. The single-sided protective film-attached polarizing plate 1 can be continuously unwound and continuously conveyed. The film conveyance can be performed using a guide roll or the like.

  The second protective film 20 can be bonded onto the polarizer layer 5 via the second adhesive layer 25. About the structure and material of the 2nd protective film 20 and the 2nd adhesive layer 25, and the bonding method of the 2nd protective film 20, the 1st protective film 10, the 1st adhesive layer 15, and the 1st protective film 10, respectively. The description about the pasting method is quoted. 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 1st adhesive bond layer 15 and the 2nd adhesive bond layer 25 may be formed from the mutually same kind of adhesive agent, and may be formed from a different kind of adhesive agent.

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

[Visibility corrected single transmittance (Ty) and visibility corrected polarization degree (Py)]
About each polarizing laminated film, the parallel transmittance | permeability and orthogonal transmittance | permeability in the wavelength range of 380-780 nm are measured using the spectrophotometer with an integrating sphere ("V7100" by JASCO Corporation), and following formula:
Single transmittance (%) = (parallel transmittance + orthogonal transmittance) / 2
Polarization degree (%) = {(parallel transmittance−orthogonal transmittance) / (parallel transmittance + orthogonal transmittance)} × 100
Based on the above, the single transmittance and the degree of polarization at each wavelength were calculated. In the measurement, light was incident from the side of the polarizing laminated film that became the polarizer layer, and the base film side of the polarizing laminated film was set as the detector side. In addition, since the base film is sufficiently transparent, there is a difference between the optical properties measured with the polarizing laminate film and the optical properties when only the polarizer layer (polarizing film) of the polarizing laminate film is measured. However, the value of the optical property measured with the polarizing laminated film can be said to be a value when the optical property is measured only for the polarizer layer (polarizing film).

  Here, the “parallel transmittance” is a transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing film sample. The “orthogonal transmittance” is a transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the polarizing film sample.

About the obtained single transmittance and degree of polarization, visibility correction is performed by a two-degree field of view (C light source) of JIS Z 8701: 1999 “Color display method—XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system”. The visibility corrected single transmittance (Ty) and the visibility corrected polarization degree (Py) were obtained.

[Ratio represented by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm]
The parallel transmittance and the orthogonal transmittance at a wavelength of 475 nm measured as described above are expressed by the following formula:
Absorbance = −log ₁₀ (T / T ₀ )
Was converted into parallel absorbance and orthogonal absorbance, respectively. In the above formula, T ₀ is the light intensity of polarized light having a wavelength of 475 nm emitted from the Glan-Thompson prism incident on the polarizing laminated film, and T is the parallel transmittance or the orthogonal transmittance at the wavelength of 475 nm.

[Measurement of boron content]
After 0.2 g of a polarizer layer (polarizing film) obtained by peeling and removing the base film from the polarizing laminated film was immersed in 100 mL of hot water at a temperature of 95 ° C. for 60 minutes for complete dissolution, an aqueous mannitol solution ( 12.5 wt%) was added to prepare a sample solution for measurement. A sodium hydroxide aqueous solution (1 mol / L) is dropped until the measurement sample solution reaches the neutralization point, and the boron content (% by weight) in the polyvinyl alcohol-based resin film is calculated from the amount added by the following formula:
Boron content (% by weight) = 1.08 × amount of sodium hydroxide aqueous solution dropped (mL) / weight of polarizing film (g)
Calculated from For the cross-linked layer obtained by peeling and removing the base film from the cross-linked laminated film before the deboronation process in the same procedure, the boron content is calculated, and the change in the boron content before and after the deboronation process confirmed.

[Measurement of contraction force]
A sample having a width of 2 mm and a length of 8 mm having a long side in the absorption axis direction (stretching direction) is cut out from the polarizing laminated film, and the base film is peeled off to obtain a sample for measuring the polarizer layer (polarizing film). The thickness of the measurement sample was measured by a contact-type film thickness meter (trade name “DIGIMICRO MH-15M” manufactured by Nikon Corporation). This measurement sample was set in a thermo-mechanical analyzer (TMA) “EXSTAR-6000” (manufactured by SII NanoTechnology Co., Ltd.) for 240 minutes at 80 ° C. while keeping the dimensions constant. The contraction force (measured contraction force) in the long side direction (absorption axis direction, stretching direction) generated when held was measured. The measured actual contraction force was divided by the actually measured thickness of the measurement sample, and then multiplied by 5 μm to obtain the contraction force [N / 5 μm] per 2 mm width and 5 μm thickness (the following formula).
Shrinkage force [N / 5 μm] = (Measured shrinkage force [N] of polarizer layer (polarizing film)) / (Thickness of polarizer layer (polarizing film) (actual value) [μm]) × 5

[Example 1]
(Primer layer formation process)
Polyvinyl alcohol powder (“Z-200” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree 1100, saponification degree 99.5 mol%) was dissolved in 95 ° C. hot water to give a concentration of 3% by weight of polyvinyl alcohol. An aqueous solution was prepared. The resulting aqueous solution was mixed with a crosslinking agent (“Smiles Resin 650” manufactured by Taoka Chemical Co., Ltd.) at a ratio of 5 parts by weight to 6 parts by weight of the polyvinyl alcohol powder to form a primer layer forming coating solution. Got.

  Next, a corona treatment was performed on one surface of the substrate film (unstretched polypropylene film, melting point: 163 ° C.) having a thickness of 90 μm continuously conveyed, and then the micronagravure coater was used on the corona treatment surface. The primer layer-forming coating solution was continuously applied and dried at 80 ° C. for 10 minutes to form a primer layer having a thickness of 0.2 μm.

(Production of laminated film (resin layer forming step))
Polyvinyl alcohol powder (“PVA124” manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 98.0 to 99.0 mol%) was dissolved in hot water at 95 ° C. to give a polyvinyl alcohol having a concentration of 7.5% by weight. An aqueous alcohol solution was prepared and used as a coating solution for forming a polyvinyl alcohol-based resin layer.

  While the substrate film having the primer layer prepared in the primer layer forming step is continuously conveyed, the polyvinyl alcohol resin layer forming coating solution is continuously applied to the surface of the primer layer using a die coater. After that, by drying at a temperature of 80 to 90 ° C., a 9 μm-thick polyvinyl alcohol resin layer is formed on the primer layer to obtain a laminated film composed of a base film / primer layer / polyvinyl alcohol resin layer. It was.

(Stretching process)
Using the floating longitudinal uniaxial stretching device, the laminated film is subjected to 5.3 times free end uniaxial stretching (air stretching) at a maximum temperature of 150 ° C. during stretching. Got. The thickness of the stretched polyvinyl alcohol resin layer was 5 μm.

(Dyeing process)
While continuously transporting the stretched film, in a dye bath at 30 ° C. containing iodine and potassium iodide (containing 0.35 parts by weight iodine and 5.0 parts by weight potassium iodide per 100 parts by weight water) The polyvinyl alcohol-based resin layer was dyed continuously by dipping so that the residence time was about 90 seconds to obtain a dyed laminated film.

(Crosslinking process)
While continuously transporting the dyed laminated film, a 78 ° C. cross-linking liquid containing boric acid (containing 10.4 parts by weight of boric acid per 100 parts by weight of water) has a tension of 16 N / cm and a residence time of 120 seconds. The film was continuously dipped so as to be cross-linked to obtain a cross-linked laminated film.

(Deboronization process)
Next, while continuously transporting the cross-linked laminated film, a 65 ° C. deboronization solution containing boric acid and potassium iodide (2 parts by weight of boric acid and 6.0 parts by weight of potassium iodide per 100 parts by weight of water) Part), a boron removal treatment was performed by continuous immersion so that the residence time was 60 seconds at a tension of 1 N / cm. Thereafter, the film is immersed in water at 7 N ° C. for 5 seconds at a tension of 1 N / cm for further deboronation treatment, the liquid adhering to both surfaces is removed using an air blower, and dried at a temperature of 60 ° C. A polarizing laminated film having a polarizer layer with a thickness of 5 μm was obtained.

  An evaluation sample is obtained from the obtained polarizing laminated film as described in [Preparation of Evaluation Sample], and the visibility correction single transmittance (Ty), the visibility correction polarization degree (Py), the contraction force, and the evaluation The boron content of the sample was calculated, and changes in the boron content before and after the deboronation process were examined. The results are shown in Table 1. In Table 1, “decrease” in the column of changes in boron content indicates that the boron content after the deboronation step is smaller than the boron content before the deboronation step.

[Example 2]
In the deboronization step, a polarizing laminate film was obtained in the same manner as in Example 1 except that the tension was set to 5 N / cm, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 3
In the deboronization step, a polarizing laminate film was obtained in the same manner as in Example 1 except that boric acid was changed to 5 parts by weight, and evaluation was performed in the same manner as in Example 1.

Example 4
A polarizing laminated film was obtained in the same manner as in Example 1 except that 5 parts by weight of boric acid and 5 N / cm in tension were used in the deboronation step, and evaluation was performed in the same manner as in Example 1.

Example 5
A polarizing laminate film was obtained in the same manner as in Example 1 except that 5 parts by weight of boric acid and 10 N / cm in tension were used in the deboronation step, and evaluation was performed in the same manner as in Example 1.

[Comparative Example 1]
In the deboronization step, a polarizing laminated film was obtained in the same manner as in Example except that the tension was 16 N / cm, and evaluation was performed in the same manner as in Example 1.

[Comparative Example 2]
A polarizing laminate film was obtained in the same manner as in Example except that 3.5 parts by weight of boric acid and the tension was 16 N / cm in the deboronation step, and evaluation was performed in the same manner as in Example 1.

[Comparative Example 3]
In the deboronization step, a polarizing laminated film was obtained in the same manner as in Example except that 5 parts by weight of boric acid and the tension was 16 N / cm, and evaluation was performed in the same manner 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 2.5% by weight or more and 4.1% by weight or less, and visibility correction. The single transmittance (Ty) was more than 40.5%, and the ratio expressed by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm was less than 0.022. The polarizing layers (polarizing films) of Examples 1 to 5 had a visibility correction polarization degree (Py) exceeding 99.994 when the visibility correction single transmittance (Ty) was 41.5. The shrinkage force in the long side direction (absorption axis direction, stretching direction) of the polarizing layers (polarizing films) of Examples 1 to 5 was suppressed to less than 1.77 N / 5 μm.

  In Comparative Examples 1 to 3, the visibility correction polarization degree (Py) when the visibility correction single transmittance (Ty) is 41.5 was low. This is presumably because the magnitude of the tension applied to the crosslinked laminated film in the deboronation process was the same as the magnitude of the tension applied to the dyed laminated film in the crosslinking process. In Comparative Examples 1 to 3, the ratio represented by the parallel absorbance / orthogonal absorbance at a wavelength of 475 nm was large. In Examples 1 to 5 and Comparative Examples 1 to 3, the boron content decreased before and after the deboronation process, and excess boric acid contained in the cross-linked layer was removed in the deboronation process. In Examples 1 to 3, it was speculated that the removal of the polyiodine ion complex having low orientation was not sufficient in the deboronation step.

  DESCRIPTION OF SYMBOLS 1 Polarizing plate with single-sided protective film, 2 Polarizing plate with double-sided protective film, 5 Polarizer layer, 6 Polyvinyl alcohol-type resin layer, 6 'Stretched polyvinyl alcohol-type resin layer, 10 1st protective film, 15 1st adhesive agent Layer, 20 second protective film, 25 second adhesive layer, 30 substrate film, 30 ′ stretched substrate film, 100 laminate film, 200 stretched film, 300 polarizing laminate film, 400 multilayer film.

The boron removal step S50 may include a boron removal solution contact step in which a boron removal solution having a boric acid concentration lower than the concentration of boric acid in the crosslinking solution used in the crosslinking step S40 is brought into contact with the crosslinked layer of the crosslinked laminated film. it can. The boron removal liquid contact step can be performed by immersing the crosslinked laminated film in the boron removal liquid, washing the crosslinked layer of the crosslinked laminated film with a shower of the boron removal liquid, and the like. As the deboronating solution, a solution obtained by dissolving boric acid in a solvent or a solution not containing boric acid can be used. Water can be used as the liquid not containing the solvent and boric acid, but it may further contain an organic solvent compatible with water. The content of boric acid in the deboronated solution is preferably less than 10 parts by weight, more preferably 8 parts by weight or less, and may be 0.1 parts by weight or more with respect to 100 parts by weight of the solvent. .

Claims (6)

A polarizing film in which iodine is oriented in a polyvinyl alcohol resin layer,
The boron content is 2.5 wt% or more and 4.1 wt% or less,
Visibility corrected single transmittance (Ty) is over 40.5%,
A polarizing film having a ratio expressed by parallel absorbance / orthogonal absorbance at a wavelength of 475 nm of less than 0.022.   2. The polarizing film according to claim 1, wherein a contraction force per width of 2 mm and a thickness of 5 μm when held at 80 ° C. for 4 hours is less than 1.77 N / 5 μm.   The polarizing film of Claim 1 or 2 whose thickness is 10 micrometers or less.   The polarizing plate which has a protective film in the at least one surface of the polarizing film of any one of Claims 1-3. A resin layer forming step of forming a polyvinyl alcohol resin layer on at least one surface of the base film to obtain a laminated film;
A stretching step of stretching the laminated film to obtain a stretched film;
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;
A crosslinking step of obtaining a 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;
A boron removal step of obtaining a polarizing laminated film by reducing the boron content contained in the crosslinked layer of the crosslinked laminated film to form a polarizer layer, in this order,
The boron removal step includes a boron removal solution contact step in which the crosslinked layer and the boron removal solution are in contact, and the boron removal solution has a boric acid concentration lower than the boric acid concentration of the crosslinking solution,
In the deboronating liquid contact step, a polarizing laminated film that controls the magnitude of tension applied to the crosslinked laminated film to be smaller than the magnitude of tension applied to the laminated film with dyed layer in the crosslinking process. Manufacturing method. A step of producing a polarizing laminated film by the production method according to claim 5;
A step of bonding a protective film to the surface of the polarizer layer opposite to the base film;
Peeling and removing the base film;
In this order.

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