JP6894494B2 - Manufacturing method of polarizing plate with double-sided protective film - Google Patents

Description

The present invention relates to a method for manufacturing a polarizing plate with a double-sided protective film in which protective films are bonded to both sides of an iodine-based polarizing element. The present invention relates to a method for producing a polarizing plate with a double-sided protective film.

Polarizing plates are widely used in display devices such as liquid crystal display devices, and in recent years, in various mobile devices such as smartphones. Generally, the polarizing plate has a structure in which a protective film is attached to one side or both sides of the polarizing element using an adhesive.

The polarizer itself has low moist heat resistance, and its polarization characteristics tend to deteriorate in a moist heat environment. Conventionally, a triacetyl cellulose film has been used as a protective film for protecting a polarizer. However, since a triacetyl cellulose film has a high moisture permeability, a polarizing plate using this as a protective film is particularly iodine-based as a polarizer. When a polarizer is used, there is a problem that the moisture and heat resistance is still insufficient.

Therefore, in order to improve the moisture and heat resistance of the polarizing plate, it has been proposed to attach a protective film having low moisture permeability such as a norbornene-based resin film to an iodine-based polarizing element instead of the triacetyl cellulose film. [For example, paragraph [0005] of JP-A-2004-245925 (Patent Document 1)].

Japanese Unexamined Patent Publication No. 2004-245925

If a protective film having low moisture permeability is attached to both sides of the iodine-based polarizing element, the intrusion of moisture from the outside is reduced, so that the moisture and heat resistance of the polarizing plate can be improved. However, on the other hand, the conventional polarizing plate with a double-sided protective film using such a protective film with low moisture permeability on both sides is crossed when a heat resistance test is carried out in which it is exposed to a higher temperature environment than a general moisture and heat resistance test. According to the present inventor, light leakage under Nicol (a phenomenon in which light in the red region leaks from the polarizing plate and the polarizing plate looks red. Also called reddening) occurs or the polarization characteristics deteriorate. It became clear by the examination. This problem of poor heat resistance becomes more remarkable as the thickness of the iodine-based polarizer is smaller.

Therefore, the present invention is a method for producing a polarizing plate in which a protective film having low moisture permeability is bonded to both sides of an iodine-based polarizing element, and which has both moisture and heat resistance and heat resistance. An object of the present invention is to provide a polarizing plate with a double-sided protective film having both moisture and heat resistance and heat resistance.

The present invention provides the following method for manufacturing a polarizing plate with a double-sided protective film, and a polarizing plate with a double-sided protective film.

[1] A step of peeling and removing the base film from a multilayer film containing a base film, an iodine-based polarizer and a first protective film in this order to obtain a polarizing plate with a single-sided protective film.
A step of attaching a second protective film to the outer surface of the iodine-based polarizing element in the polarizing plate with a single-sided protective film to obtain a polarizing plate with a double-sided protective film.
Including
The first protective film and the second protective film is a thermoplastic film of less moisture permeability 150 g / m ^2/24 hr or,
A method for producing a polarizing plate with a double-sided protective film, wherein the water content of the iodine-based polarizing element when the second protective film is attached is less than 8% by weight.

[2] The production method according to [1], wherein the second protective film is attached to the outer surface of the iodine-based polarizer using an active energy ray-curable adhesive.

[3] The production method according to [1] or [2], wherein the iodine-based polarizer has a thickness of 10 μm or less.

[4] A polarizing plate with a double-sided protective film is formed by laminating a second protective film on the outer surface of an iodine-based polarizing element in a polarizing plate with a single-sided protective film containing an iodine-based polarizing element and a first protective film laminated on one side thereof. Including the process of obtaining
The first protective film and the second protective film is a thermoplastic film of less moisture permeability 150 g / m ^2/24 hr or,
A method for producing a polarizing plate with a double-sided protective film, wherein the water content of the iodine-based polarizing element when the second protective film is attached is less than 8% by weight.

[5] The production method according to [4], wherein the second protective film is attached to the outer surface of the iodine-based polarizer using an active energy ray-curable adhesive.

[6] The production method according to [4] or [5], wherein the iodine-based polarizer has a thickness of 10 μm or less.

[7] Includes an iodine-based polarizer and a protective film laminated on both sides thereof.
Any protective film to be laminated on both sides, a thermoplastic resin film of less moisture permeability 150g / m ² / 24hr,
A polarizing plate with a double-sided protective film in which the moisture content of the iodine-based polarizing element is less than 8% by weight.

[8] The polarizing plate with a double-sided protective film according to [7], wherein the iodine-based polarizing element has a thickness of 10 μm or less.

According to the present invention, a method for producing a polarizing plate in which a protective film having low moisture permeability is bonded to both sides of an iodine-based polarizing element, and which has both moisture and heat resistance and heat resistance. A polarizing plate in which a protective film having low moisture permeability is bonded to both sides of an iodine-based polarizing element, and a polarizing plate with a double-sided protective film having both moisture and heat resistance and heat resistance can be provided.

It is a flowchart which shows a preferable example of the manufacturing method of the polarizing plate with a double-sided protective film which concerns on this invention. It is a schematic cross-sectional view which shows an example of the layer structure of the polarizing plate with a single-sided protective film. It is a flowchart which shows a preferable example of the polarizing plate preparation process with a single-sided protective film. It is a schematic cross-sectional view which shows an example of the layer structure of the laminated film obtained in the resin layer forming step. It is a schematic cross-sectional view which shows an example of the layer structure of the stretch film obtained in the stretching step. It is a schematic cross-sectional view which shows an example of the layer structure of the polarizing laminated film obtained in the dyeing process. It is schematic cross-sectional view which shows an example of the layer structure of the multilayer film obtained in the bonding process. It is a schematic cross-sectional view which shows an example of the layer structure of the polarizing plate with a double-sided protective film which concerns on this invention.

<Manufacturing method of polarizing plate with double-sided protective film>
As shown in FIG. 1, the method for producing a polarizing plate with a double-sided protective film according to the present invention can include the following steps.

(1) A step S10 for preparing a polarizing plate with a single-sided protective film including an iodine-based polarizing element and a first protective film laminated on one side thereof (hereinafter, also referred to as "polarizing plate preparation step S10 with a single-sided protective film"), and (2) A step S20 of attaching a second protective film to the outer surface of an iodine-based polarizing element in a polarizing plate with a single-sided protective film to obtain a polarizing plate with a double-sided protective film (hereinafter, "a polarizing plate manufacturing step S20 with a double-sided protective film"). Also called).

As described above, in the present invention, the first protective film and the second protective film are sequentially bonded to the iodine-based polarizer. At that time, in order to improve the moisture and heat resistance of the obtained polarizing plate with a double-sided protective film, a first protective film to be bonded to one surface of an iodine-based polarizing element and a second protective film to be bonded to the other surface. as a moisture permeability using a thermoplastic resin film of low moisture permeability is not more than 150g / m ² / 24hr.

Further, in order to improve the heat resistance of the obtained polarizing plate with a double-sided protective film, the water content of the iodine-based polarizing element when the second protective film is attached to the iodine-based polarizing element is set to less than 8% by weight. In the present invention, in order to improve the heat resistance to moisture and heat, protective films having low moisture permeability are attached to both sides of the iodine-based polarizing element to form a polarizing plate.
a) When a protective film with low moisture permeability is applied to both sides, the moisture in the iodine-based polarizer is not easily released to the outside, and the moisture accumulates in the iodine-based polarizer.
b) Iodine-based polarized light when the second protective film is attached as described above because reddening and deterioration of polarization characteristics in the heat resistance test are caused by the moisture remaining in the iodine-based polarizer. It is effective to control the water content of the offspring. The water content of the iodine-based polarizer is measured according to the method described in the section of Examples.

The water content of the iodine-based polarizing element is determined at any stage during the process of manufacturing the polarizing plate with the double-sided protective film and before the second protective film is attached to the iodine-based polarizing element (3) iodine-based. This can be achieved by providing a step S30 (hereinafter, also referred to as “moisture content reducing step S30”) in which the film containing the polarizer is subjected to the moisture content reducing treatment (see FIG. 1).

Hereinafter, each step will be described with reference to FIGS. 2 to 8.

(1) Polarizing plate preparation step S10 with single-sided protective film
This step is a step of preparing (preparing) a polarizing plate 100 with a single-sided protective film, for example, as shown in FIG. 2, which includes an iodine-based polarizing element 5 and a first protective film 10 laminated on one side thereof. As shown in FIG. 2, the first protective film 10 is usually bonded (adhesively fixed) to one side of the iodine-based polarizer 5 via the first adhesive layer 15.

[Iodine-based polarizer]
The iodine-based polarizing element 5 is a polarizing element in which iodine is adsorbed and oriented as a dichroic dye. Specifically, iodine is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin layer (or film). There can be. The thickness of the iodine-based polarizing element 5 can be, for example, 30 μm or less, further 20 μm or less, but particularly for mobile devices, it is preferably 10 μm or less from the viewpoint of thinning the polarizing plate with a double-sided protective film. It is more preferably 8 μm or less. The thickness of the iodine-based polarizer 5 is usually 2 μm or more.

As the thickness of the iodine-based polarizer 5 becomes smaller, the concentration of iodine becomes higher, and the concentration of the iodine complex existing near the interface with the protective film laminated on both sides also becomes higher, so that the influence of moisture invading from the outside also increases. Easy to receive. Therefore, the smaller the thickness of the iodine-based polarizer 5, the lower the moisture and heat resistance tends to be. Further, when the thickness of the iodine-based polarizer 5 becomes smaller and the iodine concentration becomes higher, it is more likely to be affected by the moisture remaining in the iodine-based polarizer, and the heat resistance is likely to be lowered. As described above, the smaller the thickness of the iodine-based polarizer 5, the lower the moist heat resistance and the heat resistance tend to be. Therefore, the present invention is particularly advantageous when the thickness of the iodine-based polarizing element 5 is small.

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

As used herein, the term "(meth) acrylic" means at least one selected from acrylic and methacryl. The same applies to the case of "(meth) acryloyl".

The film formed from the polyvinyl alcohol-based resin constitutes the iodine-based polarizing element 5. The method for forming the film of the polyvinyl alcohol-based resin is not particularly limited, and the film can be formed by a known method. However, it is easy to obtain an iodine-based polarizer 5 having a small thickness, and the iodine-based polarizing film of the thin film in the process is easily obtained. Since the child 5 is also excellent in handleability, a method of coating a solution of a polyvinyl alcohol-based resin as described later on a base film to form a film is preferable.

The degree of saponification of the polyvinyl alcohol-based resin can be in the range of 80.0 to 100.0 mol%, but is 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 moisture heat resistance of the obtained polarizing plate with a double-sided protective film are lowered. When a polyvinyl alcohol-based resin having a saponification degree of more than 99.5 mol% is used, the iodine dyeing rate becomes slow, the productivity is lowered, and the iodine-based polarizer 5 having sufficient polarization performance cannot be obtained. There is.

The degree of saponification is the unit ratio (mol%) of the rate at which the _{acetic acid group (acetoxy group: -OCOCH 3} ) contained in the polyvinyl acetate resin, which is the raw material of the polyvinyl alcohol resin, is changed to a hydroxyl group by the saponification process. It is expressed by the following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetic acid groups)
Defined in. The degree of saponification can be determined in accordance with JIS K 6726-1994. The higher the saponification degree, the higher the proportion of hydroxyl groups, and therefore the lower the proportion of acetic acid groups that inhibit crystallization.

The polyvinyl alcohol-based resin may be a partially modified polyvinyl alcohol. For example, polyvinyl alcohol-based 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, (meth) acrylamide and the like can be mentioned. The rate of denaturation is preferably less than 30 mol%, more preferably less than 10%. When the modification is performed in an amount of more than 30 mol%, it becomes difficult to adsorb iodine, and it tends to be difficult to obtain an iodine-based polarizer 5 having sufficient polarization performance.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol-based resin can also be determined in accordance with JIS K 6726-1994.

[1st protective film]
The first protective film 10 has a light-transmitting property (preferably optically clear) a thermoplastic resin, and the moisture permeability is less film 150g / m ² / 24hr. The moisture permeability is a temperature of 40 ° C. and a relative humidity of 90 measured in accordance with JIS Z 0208-1976 "Dampproof packaging material moisture permeability test method (cup method)" including the moisture permeability of the second protective film described later. Moisture permeability in%. Moisture permeability is preferably 100g / m ² / 24hr or less.

As a means for the moisture permeability of the first protective film 10 below 150g / m ² / 24hr, or used as moisture permeability is lower in the thermoplastic resin constituting the film, or by increasing the thickness of the film, onto the film It is possible to provide a barrier layer having low moisture permeability.

The thermoplastic resin constituting the first protective film 10 is not particularly limited as long as the moisture permeability can be achieved, but since the moisture permeability is low and the thickness of the first protective film 10 can be reduced, a chain polyolefin resin (polypropylene type) Resins, etc.), polyolefin resins such as cyclic polyolefin resins (norbornen resins, etc.); polyester resins such as polyethylene terephthalate resins; polycarbonate resins; (meth) acrylic resins; polystyrene resins; or these Mixtures, copolymers and the like are preferably used.

The first protective film 10 can also be a protective film having an optical function such as a retardation film and a brightness improving film. For example, a retardation film to which an arbitrary retardation value is imparted by stretching a film made of the thermoplastic resin (uniaxial stretching, biaxial stretching, etc.) or forming a liquid crystal layer or the like on the film. Can be.

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

Cyclic polyolefin resin is a general term for resins that are polymerized using cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin resin include an open (co) polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymer of a cyclic olefin and a chain olefin such as ethylene and propylene (typically). Is a random copolymer), a graft polymer obtained by modifying these with an unsaturated carboxylic acid or a derivative thereof, and a hydride thereof. Of these, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer is preferably used as the cyclic olefin.

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

Specific examples of the polyester-based resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexanedimethylterephthalate, and polycyclohexanedimethylnaphthalate.

The polycarbonate-based resin is composed of a polymer in which monomer units are bonded via a carbonate group. The polycarbonate-based resin may be a resin called modified polycarbonate having a modified polymer skeleton, a copolymerized polycarbonate, or the like.

The (meth) acrylic resin is a resin containing a compound having a (meth) acryloyl group as a main constituent monomer. Specific examples of the (meth) acrylic resin include poly (meth) acrylic acid esters such as polymethyl methacrylate; methyl methacrylate- (meth) acrylic acid copolymers; methyl methacrylate- (meth) acrylic acid. Ester copolymer; methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymer; (meth) methyl acrylate-styrene copolymer (MS resin, etc.); methyl methacrylate and alicyclic hydrocarbon group It contains a copolymer with the compound (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate- (meth) norbornyl copolymer, etc.). _{Preferably, a polymer containing poly (meth) acrylic acid C 1-6} alkyl ester as a main component, such as methyl poly (meth) acrylate, is used, and more preferably, methyl methacrylate as a main component (50 to 100) is used. A methyl methacrylate-based resin having a weight of% by weight, preferably 70 to 100% by weight) is used.

On the surface of the first protective film 10 opposite to the iodine-based polarizing element 5, 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 provided. It can also be formed. The method for forming the surface treatment layer is not particularly limited, and a known method can be used.

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. it can.

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

[First adhesive layer]
The first adhesive layer 15 is a layer for adhering and fixing the first protective film 10 to one surface of the iodine-based polarizer 5. The adhesive forming the first adhesive layer 15 is an active energy ray-curable adhesive containing a curable compound that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays (preferably. Can be an ultraviolet curable adhesive) or an aqueous adhesive in which an adhesive component such as a polyvinyl alcohol-based resin is dissolved or dispersed in water.

The curable compound can be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of the cationically polymerizable curable compound include an epoxy compound (a compound having one or more epoxy groups in the molecule) and an oxetane compound (one or two or more oxetane rings in the molecule). Compounds), or a combination thereof. Examples of the radically polymerizable curable compound include a (meth) acrylic compound (a compound having one or more (meth) acryloyloxy groups in the molecule) and a radically polymerizable double bond. Other vinyl compounds or combinations thereof can be mentioned. A cationically polymerizable curable compound and a radically polymerizable curable compound may be used in combination. The active energy ray-curable adhesive usually further contains a cationic polymerization initiator and / or a radical polymerization initiator for initiating the curing reaction of the curable compound.

The polarizing plate 100 with a single-sided protective film may be prepared in advance or may be manufactured by any method. Examples of the manufacturing method include the following.

i) A method of attaching the first protective film 10 to one side of an iodine-based polarizing element 5 made of a single (single) film produced by a known method, and
ii) A manufacturing method including the following steps as shown in FIG.

Resin layer forming step S10-1 to obtain a laminated film by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of the base film and then drying to form a polyvinyl alcohol-based resin layer.
Stretching step S10-2, in which the laminated film is stretched to obtain a stretched film,
Dyeing step S10-3, in which the polyvinyl alcohol-based resin layer of the stretched film is dyed with iodine to form an iodine-based polarizer to obtain a polarizing laminated film.
A bonding step S10-4 in which the first protective film 10 is bonded onto an iodine-based polarizer of a polarizing laminated film to obtain a multilayer film, and a polarizing plate with a single-sided protective film by peeling and removing the base film from the multilayer film. Peeling step S10-5 to obtain 100.

[Resin layer forming step S10-1]
With reference to FIG. 4, this step is a step of forming a polyvinyl alcohol-based resin layer 6 on at least one surface of the base film 30 to obtain a laminated film 200. The polyvinyl alcohol-based resin layer 6 is a layer that becomes an iodine-based polarizer 5 through the stretching step S10-2 and the dyeing step S10-3. 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 sides of the base film 30 and drying it. The method of forming the polyvinyl alcohol-based resin layer by such coating is advantageous in that it is easy to obtain the iodine-based polarizer 5 of the thin film.

The base film 30 can be made of a thermoplastic resin, and more preferably it is made of a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, stretchability, and the like. Specific examples of such thermoplastic resins include polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins (norbornen resins, etc.); polyester resins; (meth) acrylic resins; cellulose triacetates, Cellulosic ester-based resins such as cellulose diacetate; Polycarbonate-based resin; Polypolyalcohol-based resin; Polyvinyl acetate-based resin; Polyarylate-based resin; Polystyrene-based resin; Polyether sulfone-based resin; Polysulfone-based resin; Polyamide-based resin; Polyethylene Based resins; and mixtures and copolymers thereof.

The base film 30 may have a single-layer structure composed of one resin layer made of one or more kinds of thermoplastic resins, or a plurality of resin layers made of one kind or two or more kinds of thermoplastic resins. It may have a laminated multi-layer structure. The base film 30 is preferably composed of a resin that can be stretched at a stretching temperature suitable for stretching the polyvinyl alcohol-based resin layer 6 in the stretching step S10-2 described later.

The base film 30 can contain additives. Specific examples of additives include UV absorbers, antioxidants, lubricants, plasticizers, mold release agents, color retardants, flame retardants, nucleating agents, antistatic agents, pigments, and colorants.

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

The coating liquid to be applied to the base film 30 is preferably a polyvinyl alcohol-based resin solution obtained by dissolving a polyvinyl alcohol-based resin powder in a good solvent (for example, water). Details of the polyvinyl alcohol-based resin are as described above. The coating liquid may contain additives such as a plasticizer and a surfactant, if necessary.

The method of applying the above coating liquid to the base film 30 is a wire bar coating method; a roll coating method such as reverse coating or gravure coating; a die coating method; a comma coating method; a lip coating method; a spin coating method; a screen coating. Method; Fountain coating method; Dipping method; Spray method and the like can be 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 formed on both sides, curling of the film that may occur during the production of the polarizing laminated film 400 (see FIG. 6) can be suppressed, and two polarizing plates can be obtained from one polarizing laminated film 400. It is also advantageous in terms of efficiency.

The thickness of the polyvinyl alcohol-based resin layer 6 in the laminated film 200 is preferably 3 to 30 μm, more preferably 5 to 20 μm. The polyvinyl alcohol-based resin layer 6 having a thickness within this range has good iodine dyeability, excellent polarization performance, and is sufficiently thin through the stretching step S10-2 and the dyeing step S10-3, which will be described later. For example, an iodine-based polarizer 5 having a thickness of 10 μm or less can be obtained.

Prior to coating the coating liquid, in order to improve the adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6, at least on the surface of the base film 30 on the side where the polyvinyl alcohol-based resin layer 6 is formed. , Corona treatment, plasma treatment, frame (flame) treatment and the like may be performed. Further, 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 coating liquid for forming a primer layer to the surface of the base film 30 and then drying it. This coating liquid contains a component that exerts a certain degree of strong adhesion to both the base film 30 and the polyvinyl alcohol-based resin layer 6, and usually contains a resin component and a solvent that impart such adhesion. .. As the resin component, a thermoplastic resin having excellent transparency, thermal stability, stretchability and the like is preferably used, and examples thereof include (meth) acrylic resin and polyvinyl alcohol resin. Of these, polyvinyl alcohol-based resins that provide 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 above resin component is usually used, but it is preferable to form a primer layer from a coating liquid using water as a solvent.

In order to increase the strength of the primer layer, a cross-linking agent may be added to the coating liquid for forming the primer layer. Specific examples of the cross-linking agent include epoxy-based, isocyanate-based, dialdehyde-based, metal-based (for example, metal salts, metal oxides, metal hydroxides, organic metal compounds), and polymer-based cross-linking agents. When a polyvinyl alcohol-based resin is used as the resin component forming the primer layer, a polyamide epoxy resin, a methylolated melamine resin, a dialdehyde-based cross-linking agent, a metal chelate compound-based cross-linking 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. If it is thinner than 0.05 μm, the effect of improving the adhesion between the base film 30 and the polyvinyl alcohol-based resin layer 6 is small, and if it is thicker than 1 μm, it is disadvantageous in reducing the thickness of the polarizing plate with the double-sided protective film.

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

[Stretching step S10-2]
With reference to FIG. 5, this step is a step of stretching the laminated film 200 to obtain a stretched film 300 composed of the stretched base film 30'and the polyvinyl alcohol-based resin layer 6'. The stretching treatment is usually uniaxial stretching.

The draw ratio of the laminated film 200 can be appropriately selected according to the desired polarization characteristics, but is preferably more than 5 times and 17 times or less, more preferably more than 5 times the original length of the laminated film 200. It is 8 times or less. If the draw ratio is 5 times or less, the polyvinyl alcohol-based resin layer 6'is not sufficiently oriented, so that the degree of polarization of the iodine-based polarizer 5 may not be sufficiently high. On the other hand, if the draw ratio exceeds 17 times, the film is likely to break during stretching, and the thickness of the stretched film 300 becomes thinner than necessary, which may reduce workability and handleability in a subsequent process.

The stretching treatment is not limited to one-stage stretching, and can be performed in multiple stages. In this case, all of the multi-step stretching treatment may be continuously performed before the dyeing step S10-3, and the second and subsequent stretching treatments may be combined with the dyeing treatment and / or the cross-linking treatment in the dyeing step S10-3. It may be done at the same time. When the stretching treatment is performed in multiple stages in this way, it is preferable to perform the stretching treatment so that the total stretching ratio of all the stages of the stretching treatment is more than 5 times.

The stretching treatment may be longitudinal stretching that stretches in the film longitudinal direction (film transport direction), or may be lateral stretching or diagonal stretching that stretches in the film width direction. Examples of the longitudinal stretching method include inter-roll stretching using rolls, compression stretching, stretching using a chuck (clip), and the like, and examples of the transverse stretching method include a tenter method. As the stretching treatment, either a wet stretching method or a dry stretching method can be adopted.

The stretching temperature is set to be equal to or higher than a temperature at which the polyvinyl alcohol-based resin layer 6 and the entire base film 30 exhibit fluidity to the extent that they 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 even more preferably in the range of −25 ° C. to + 0 ° C. When the base film 30 is composed of a plurality of resin layers, the phase transition temperature means the highest phase transition temperature among the phase transition temperatures exhibited by the plurality of resin layers.

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

The heating method of the laminated film 200 in the stretching treatment is a zone heating method (for example, a method of heating in a stretching zone such as a heating furnace in which hot air is blown and adjusted to a predetermined temperature); in the case of stretching using a roll. , A method of heating the roll itself; a heater heating method (a method of installing an infrared heater, a halogen heater, a panel heater, etc. above and below the laminated film 200 and heating with radiant heat) and the like. In the inter-roll stretching method, the zone heating method is preferable from the viewpoint of uniformity of stretching temperature.

Prior to the stretching step S10-2, a preheat treatment step for preheating the laminated film 200 may be provided. As the preheating method, the same method as the heating method in the stretching treatment can be used. The preheating temperature is preferably in the range of −50 ° C. to ± 0 ° C. of the stretching temperature, and more preferably in the range of −40 ° C. to −10 ° C. of the stretching temperature.

Further, a heat fixing treatment step may be provided after the stretching treatment in the stretching step S10-2. The heat fixing treatment is a treatment in which heat treatment is performed at a crystallization temperature or higher while maintaining a tense state while the end portion of the stretched film 300 is gripped by a clip. This heat fixing treatment promotes the crystallization of the polyvinyl alcohol-based resin layer 6'. 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.

[Dyeing step S10-3]
With reference to FIG. 6, this step is a step of dyeing the polyvinyl alcohol-based resin layer 6'of the stretched film 300 with iodine and adsorbing and orienting the polyvinyl alcohol-based resin layer 6'to form an iodine-based polarizing element 5. Through this step, a polarizing laminated film 400 in which the iodine-based polarizer 5 is laminated on one side or both sides of the base film 30'is obtained.

The dyeing step can be performed by immersing the stretched film 300 in a solution containing iodine (dyeing solution). As the dyeing solution, a solution in which iodine is dissolved in a solvent can be used. Water is generally used as the solvent, but an organic solvent compatible with water may be further added. The concentration of iodine in the dyeing solution is preferably 0.01 to 10% by weight, more preferably 0.02 to 7% by weight.

It is preferable to further add iodide to the dyeing solution 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. Can be mentioned. The concentration of iodide in the dyeing solution is preferably 0.01 to 20% by weight. Among the iodides, it is preferable to add potassium iodide. When potassium iodide is added, the ratio of iodine to potassium iodide is preferably 1: 5 to 1: 100, more preferably 1: 6 to 1:80 by weight. The temperature of the dyeing solution is preferably 10 to 60 ° C, more preferably 20 to 40 ° C.

Although it is possible to perform the dyeing step S10-3 before the stretching step S10-2 or to perform these steps at the same time, it is possible to satisfactorily orient the iodine to be adsorbed on the polyvinyl alcohol-based resin layer. It is preferable to carry out the dyeing step S10-3 after applying at least some stretching treatment to the laminated film 200 so that the laminated film 200 can be stretched.

The dyeing step S10-3 can include a cross-linking treatment step carried out following the dyeing treatment. The cross-linking treatment can be performed by immersing the dyed film in a solution (cross-linking solution) in which a cross-linking agent is dissolved in a solvent. Examples of the cross-linking agent include boric acid, boron compounds such as borax, glyoxal, and glutaraldehyde. Only one type of cross-linking agent may be used, or two or more types may be used in combination. Water can be used as the solvent for the cross-linking solution, but an organic solvent compatible with water may be further contained. The concentration of the cross-linking agent in the cross-linking solution is preferably 1 to 20% by weight, more preferably 6 to 15% by weight.

The cross-linked solution can further contain iodide. By adding iodide, the in-plane polarization performance of the iodine-based polarizer 5 can be made more uniform. Specific examples of iodide are the same as above. The concentration of iodide in the crosslinked solution is preferably 0.05 to 15% by weight, more preferably 0.5 to 8% by weight. The temperature of the cross-linked solution is preferably 10 to 90 ° C.

The cross-linking treatment can also be performed at the same time as the dyeing treatment by blending a cross-linking agent in the dyeing solution. Further, the treatment of immersing in the cross-linking solution may be performed twice or more by using two or more kinds of cross-linking solutions having different compositions.

It is preferable to perform a washing step and a drying step after the dyeing step S10-3 and before the bonding step S10-4 described later. The cleaning step usually includes a water cleaning step. The water washing treatment can be performed by immersing the film after the dyeing treatment or the cross-linking treatment in pure water such as ion-exchanged water or distilled water. The water washing temperature is usually 3 to 50 ° C, preferably 4 to 20 ° C. The cleaning step may be a combination of a water cleaning step and a cleaning step with an iodide solution. As the drying step performed after the washing step, any suitable method such as natural drying, blast drying, and heat drying can be adopted. For example, in the case of heat drying, the drying temperature is usually 20 to 95 ° C.

[Lasting step S10-4]
In this step, referring to FIG. 7, in this step, the first adhesive layer 15 is formed on the iodine-based polarizing element 5 of the polarizing laminated film 400, that is, on the surface of the iodine-based polarizing element 5 opposite to the base film 30'. This is a step of obtaining the multilayer film 500 by laminating the first protective film 10 through the film. The adhesive forming the first adhesive layer 15 is as described above.

When the polarizing laminated film 400 has iodine-based polarizers 5 on both sides of the base film 30', the first protective film 10 is usually bonded onto the iodine-based polarizers 5 on both sides. In this case, these first protective films 10 may be the same type of protective film or different types of protective films.

When the first protective film 10 is bonded using an active energy ray-curable adhesive, the first protective film 10 is attached to the iodine-based polarizer 5 via the active energy ray-curable adhesive that becomes the first adhesive layer 15. After laminating on top, the adhesive layer is cured by irradiating with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. Among them, ultraviolet rays are preferable, and as the light source in this case, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, or the like can be used. When a water-based adhesive is used, the first protective film 10 may be laminated on the iodine-based polarizer 5 via the water-based adhesive, and then heat-dried.

In order to improve the adhesiveness of the first protective film 10 and / or the iodine-based polarizing element 5 to the bonding surface of the first protective film 10 when the first protective film 10 is attached to the iodine-based polarizer 5. Surface treatment (easy adhesion treatment) such as plasma treatment, corona treatment, ultraviolet irradiation treatment, frame (flame) treatment, and iodination treatment can be performed. Among them, plasma treatment, corona treatment, or iodination treatment is performed. Is preferable.

[Peeling step S10-5]
This step is a step of peeling and removing the base film 30'from the multilayer film 500. Through this step, a polarizing plate 100 with a single-sided protective film similar to that shown in FIG. 2 is obtained. When the polarizing laminated film 400 has iodine-based polarizing elements 5 on both sides of the base film 30'and the first protective film 10 is attached to both of these iodine-based polarizing elements 5, the peeling step S50 is performed. From one polarizing laminated film 400, two polarizing plates with a single-sided protective film 100 can be obtained.

The method for peeling and removing the base film 30'is not particularly limited, and the base film 30'can be peeled by the same method as the peeling step of the separator (peeling film) performed by a normal polarizing plate with an adhesive. The base film 30'may be peeled off as it is after the bonding step S10-4, or after the bonding step S10-4, it is once wound into a roll and then peeled off while being unwound in the subsequent process. You may.

(2) Polarizing plate manufacturing step S20 with double-sided protective film
In this step, a polarizing plate with a double-sided protective film can be obtained by laminating the second protective film 20 on the outer surface of the iodine-based polarizing element 5 in the polarizing plate 100 with a single-sided protective film. FIG. 8 shows an example of the layer structure of the polarizing plate with the double-sided protective film. Like the polarizing plate 600 with a double-sided protective film shown in FIG. 8, the second protective film 20 is usually bonded (adhesively fixed) to the iodine-based polarizing element 5 via the second adhesive layer 25. The outer surface of the iodine-based polarizing element 5 means the surface of the iodine-based polarizing element 5 opposite to the first protective film 10, and the polarizing plate 100 with a single-sided protective film undergoes a step of peeling and removing the base film 30'. Means the surface of the iodine-based polarizing element 5 exposed by peeling and removing the base film 30'.

Also the second protective film 20, similarly to the first protective film 10, having a light transmitting property (a preferably optically clear) a thermoplastic resin, and moisture permeability by the following film 150 g / m ^2/24 hr or is there. It may be a protective film having an optical function such as a retardation film and a brightness improving film. Regarding the surface treatment layer and the thickness, material, and the like of the second protective film 20, the above description of the first protective film 10 is cited. The first protective film 10 and the second protective film 20 may be protective films made of the same type of resin or different types of resin.

The adhesive forming the second adhesive layer 25 can be an active energy ray-curable adhesive or a water-based adhesive like the first adhesive layer 15, but preferably such as an ultraviolet curable adhesive. It is an active energy ray-curable adhesive. When a water-based adhesive is used, water is supplied to the iodine-based polarizer 5, so that the moisture content of the iodine-based polarizer 5 when the second protective film 20 is attached may not be less than 8% by weight. is there. The adhesive forming the second adhesive layer 25 may have the same composition as the adhesive forming the first adhesive layer 15, or may have a different composition.

(3) Moisture content reduction step S30
The method for producing a polarizing plate with a double-sided protective film according to the present invention is as described above in order to make the water content of the iodine-based polarizing element 5 less than 8% by weight when the second protective film 20 is attached. In the step of manufacturing the polarizing plate with the double-sided protective film, the moisture content reduction step S30 carried out at any one or more steps before the step of manufacturing the polarizing plate with the double-sided protective film S20 is included. The water content reduction step S30 is a step of applying a process of reducing the water content of the iodine-based polarizing element 5 to the film containing the iodine-based polarizer 5.

An example of the timing for carrying out the water content reduction step S30 is as follows.

1) A method in which the first protective film 10 is attached to one side of an iodine-based polarizing element 5 made of a single (single) film to obtain a polarizing plate 100 with a single-sided protective film, and then the second protective film 20 is attached. If there is, before bonding the first protective film 10, after bonding (including immediately before the polarizing plate manufacturing step S20 with a double-sided protective film), or both of them. However, if the water content is lowered in the state of a single (single) film, the iodine-based polarizing element 5 is likely to be torn or broken, so that it is preferably after the first protective film 10 is attached.

2) In the method of bonding the second protective film 20 after obtaining the polarizing plate 100 with the single-sided protective film according to the method shown in FIG. 3, after the dyeing step S10-3 and after the bonding step S10-4. , After the peeling step S10-5 (including immediately before the polarizing plate manufacturing step S20 with a double-sided protective film), or two or more steps thereof. Since it is easy to reduce the water content, the water content reduction step S30 is preferably performed at a stage where the surface of the iodine-based polarizer 5 is exposed, for example, before the bonding step S10-4 or after the peeling step S10-5. ..

For example, regardless of the above 1) or 2), as in the case where the moisture content reduction step S30 is carried out before the bonding step S10-4 in the above 2), the moisture content reduction step S30 and the polarizing plate with a double-sided protective film are produced. When there is a relatively long interval with the step S20, take measures to suppress moisture absorption so that the moisture content during the interval does not exceed 8% by weight when the second protective film 20 is attached. Alternatively, the moisture content reduction step S30 may be performed again during this interval.

As the moisture absorption suppressing means, after the method of temporarily adhering a peelable moisture-proof film to the exposed surface of the iodine-based polarizer 5 or the step of forming a film containing the iodine-based polarizer 5 having an exposed surface is completed. Examples include a method of winding the film in a roll shape as soon as possible to suppress the intrusion of moisture from the outside, and a method of further packing the roll-shaped film with a moisture-proof film such as aluminum laminate. The method of winding in a roll shape is particularly advantageous when the film to be wound has a base film and the base film has low moisture permeability. Alternatively, without taking any special measures for suppressing moisture absorption as described above, in consideration of the moisture absorption rate of the iodine-based polarizing element 5, the polarizing plate with double-sided protective film manufacturing step S20 before the moisture content becomes 8% by weight or more due to moisture absorption. The process may be designed so that

Further, for example, when there is a relatively long interval between the moisture content reducing step S30 and the polarizing plate manufacturing step S20 with a double-sided protective film, the moisture content reducing step S30 takes into consideration the moisture absorption rate of the iodine-based polarizing element 5. The water content may be lowered sufficiently lower than the weight%. Even with this method, the moisture content when the second protective film 20 is bonded is less than 8% by weight without taking any special measures between the moisture content reducing step S30 and the polarizing plate manufacturing step S20 with the double-sided protective film. It is possible to.

As described above, a water-based adhesive can be used for bonding the iodine-based polarizer 5 and the first protective film 10, but when the water-based adhesive is used, water is supplied to the iodine-based polarizer 5. Therefore, it is preferable to perform the moisture content reduction step S30 between the time when the first protective film 10 is attached and the time when the second protective film 20 is attached. The water content reduction step S30 does not have to be the first water content reduction step S30.

From the viewpoint of heat resistance, the water content of the iodine-based polarizing element 5 when the second protective film 20 is attached is preferably less than 6% by weight, more preferably 5% by weight or less. The specific method for reducing the moisture content is not particularly limited, for example, a method of blowing dry air, a method of passing through a humidity control zone adjusted to low humidity, a method of passing through a hot air drying furnace, an infrared heater, and the like. Examples thereof include a method of heating using a simple heating device and a combination thereof.

<Polarizing plate with double-sided protective film>
As shown in FIG. 8, the polarizing plate with a double-sided protective film according to the present invention includes an iodine-based polarizing element 5, a first protective film 10 laminated on one surface thereof, and a first protective film laminated on the other surface. 2 Protective film 20 and the like are included. Usually, the first protective film 10 and the second protective film 20 are bonded (adhesively fixed) to the iodine-based polarizer 5 via the first adhesive layer 15 and the second adhesive layer 25, respectively.

In the polarizing plate with a double-sided protective film according to the present invention, the water content of the iodine-based polarizing element 5 is less than 8% by weight, preferably less than 6% by weight, and more preferably 5% by weight or less. Further, the first protective film 10 and the second protective film 20 both moisture permeability 150 g / m ^2/24 hr or less, preferably 100 g / m ^2/24 hr or less of the thermoplastic resin film is used. The above description is cited for the specific configurations of the iodine-based polarizer 5, the first protective film 10 and the second protective film 20.

The polarizing plate with a double-sided protective film according to the present invention can be suitably manufactured by the method described above. The polarizing plate with a double-sided protective film according to the present invention has an iodine-based polarizing element 5 having a moisture content of less than 8% by weight and a low-moisture-permeable protective film laminated on both sides. Even when the thickness of iodine is small (for example, the thickness is 10 μm or less), it has both moisture and heat resistance and heat resistance. The polarizing plate with a double-sided protective film can be suitably applied to an image display device such as a liquid crystal display device or an organic EL device. When applied to a liquid crystal display device, the polarizing plate with a double-sided protective film according to the present invention may be a polarizing plate arranged on the front surface (visual recognition) side of the liquid crystal cell, or may be arranged on the back surface (backlight) side. It may be a polarizing plate to be used.

The polarizing plate with a double-sided protective film is an adhesive layer laminated on the first protective film 10 or the second protective film 20 for bonding to another member (for example, a liquid crystal cell when applied to a liquid crystal display device). May be provided. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually based on a (meth) acrylic resin, styrene-based resin, silicone-based resin, or the like, and a cross-linking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. It consists of a pressure-sensitive adhesive composition. Further, it can be used as a pressure-sensitive adhesive layer containing fine particles and exhibiting light scattering properties. The thickness of the pressure-sensitive adhesive layer is usually 1 to 40 μm, preferably 3 to 25 μm.

Further, the polarizing plate with a double-sided protective film may further include another optical layer laminated on the first protective film 10 or the second protective film 20. Other optical layers include a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties; a film with an antiglare function that has an uneven shape on the surface; a film with a surface antireflection function. A reflective film having a reflective function on the surface; a transflective reflective film having both a reflective function and a transmissive function; a viewing angle compensating film and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.

<Example 1>
(1) Primer layer forming step Polyvinyl alcohol powder (“Z-200” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization 1100, saponification degree 99.5 mol%) was dissolved in hot water at 95 ° C. A polyvinyl alcohol aqueous solution having a concentration of 3% by weight was prepared. A cross-linking agent (“Sumirace Resin 650” manufactured by Taoka Chemical Industry Co., Ltd.) is mixed with the obtained aqueous solution at a ratio of 5 parts by weight to 6 parts by weight of polyvinyl alcohol powder, and a coating liquid for forming a primer layer is used. Got

Next, the substrate film having a thickness of 90μm made of polypropylene (melting point: 163 ° C., moisture permeability: 15g / m ² / 24hr) was subjected to corona treatment on one surface of, using a small-diameter gravure coater on the corona-treated surface above A primer layer having a thickness of 0.2 μm was formed by applying a coating solution for forming a primer layer and drying at 80 ° C. for 10 minutes.

(2) Preparation of laminated film (resin layer forming step)
Polyvinyl alcohol powder (“PVA124” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, saponification degree 98.0-99.0 mol%) is dissolved in hot water at 95 ° C., and a polyvinyl alcohol aqueous solution having a concentration of 8% by weight is dissolved. Was prepared and used as a coating liquid for forming a polyvinyl alcohol-based resin layer.

The surface of the primer layer of the base film having the primer layer prepared in (1) above is coated with the above-mentioned coating liquid for forming a polyvinyl alcohol-based resin layer using a die coater, and then dried at 80 ° C. for 20 minutes. , A polyvinyl alcohol-based resin layer was formed on the primer layer to obtain a laminated film composed of a base film / primer layer / polyvinyl alcohol-based resin layer.

(3) Preparation of stretched film (stretching step)
The laminated film produced in (2) above was subjected to 5.3 times free-end uniaxial stretching at 160 ° C. using a floating longitudinal uniaxial stretching device to obtain a stretched film. The thickness of the polyvinyl alcohol-based resin layer after stretching was 5.1 μm.

(4) Preparation of Polarizing Laminated Film (Dyeing Step)
Approximately 180 parts of the stretched film prepared in (3) above is placed in a dyeing aqueous solution containing iodine and potassium iodide at 30 ° C. (containing 0.6 parts by weight of iodine and 10 parts by weight of potassium iodide per 100 parts by weight of water). After immersing for seconds to dye the polyvinyl alcohol-based resin layer, excess dyeing aqueous solution was washed away with pure water at 10 ° C.

Next, it was immersed in a 78 ° C. first crosslinked aqueous solution containing boric acid (containing 10.4 parts by weight of boric acid per 100 parts by weight of water) for 120 seconds, and then at 70 ° C. containing boric acid and potassium iodide. The cross-linking treatment was carried out by immersing in a 2-crosslinked aqueous solution (including 5.7 parts by weight of boric acid and 12 parts by weight of potassium iodide per 100 parts by weight of water) for 60 seconds. Then, it was washed with pure water of 10 degreeC for 10 seconds. Finally, it was dried at 50 ° C. for 60 seconds and then at 80 ° C. for 60 seconds (moisture content reduction step) to obtain a polarizing laminated film composed of a base film / iodine-based polarizer. The water content of the iodine-based polarizer in the polarizing laminated film at the end of drying was 0.4% by weight. The thickness of the iodine-based polarizer was 5.6 μm.

The surface of the iodine-based polarizing element on the opposite side of the base film has removability and moisture permeability so that the moisture content in the air can be absorbed and the moisture content of the iodine-based polarizer can be suppressed from increasing. the low moisture resistance film (polyolefin resin film of moisture permeability 30g / m ² / 24hr), was stuck after drying quickly. As a result, the iodine-based polarizer is sandwiched between the base film having a low moisture permeability and the moisture-proof film, so that a low moisture content can be maintained.

(5) Fabrication of multilayer film (bonding process)
Immediately (within 1 minute) while peeling the moisture-proof film from the polarizing laminated film with the moisture-proof film produced in (4) above, the first protective film was attached to the peeled surface. The first protective film, the moisture permeability is 16g / m ² / 24hr, using thermoplastic resin film 23μm thick made of cyclic polyolefin resin (Nippon Zeon's "ZF-14"). To attach the first protective film, use a small-diameter gravure coater so that the thickness after curing is about 1.0 μm with an ultraviolet curable adhesive (“KR-75T” manufactured by ADEKA Corporation) on one side. After coating, this is bonded to the peeled surface using a bonding roll, and then, using a high-pressure mercury lamp, ultraviolet rays are irradiated ^{from the base film side with an integrated light amount of 200 mJ / cm 2 to bond them.} This was done by curing the agent layer.

(6) Fabrication of polarizing plate with double-sided protective film (peeling step and polarizing plate fabrication step with double-sided protective film)
Immediately after peeling the base film from the multilayer film produced in (5) above, a second protective film is attached to the peeled surface to form a first protective film / adhesive layer / iodine-based polarizer / adhesive. A polarizing plate with a double-sided protective film made of a layer / second protective film was obtained. The second protective film, the moisture permeability is 16g / m ² / 24hr, using thermoplastic resin film 23μm thick made of cyclic polyolefin resin (Nippon Zeon's "ZF-14"). To attach the second protective film, use a small-diameter gravure coater so that the thickness after curing is about 1.0 μm with an ultraviolet curable adhesive (“KR-75T” manufactured by ADEKA Corporation) on one side. After coating, this is bonded to the peeled surface using a bonding roll, and then ultraviolet rays are irradiated from the second protective film side with an integrated light amount of ^{200 mJ / cm 2 using a high-pressure mercury lamp.} This was done by curing the adhesive layer. The water content of the iodine-based polarizer when the second protective film was attached was 0.5% by weight.

<Example 2>
A polarizing plate with a double-sided protective film was produced in the same manner as in Example 1 except that the conditions of the final drying treatment (moisture content reduction step) of the dyeing step were 50 ° C. for 60 seconds and then 65 ° C. for 60 seconds. .. The water content of the iodine-based polarizer when the second protective film was attached was 4.6% by weight.

<Example 3>
A polarizing plate with a double-sided protective film was produced in the same manner as in Example 2. The moisture content of the iodine-based polarizing element when the second protective film is attached is 4.4% by weight, the luminous efficiency correction polarization degree Py of the polarizing plate with the double-sided protective film is 99.995%, and the luminous efficiency correction single unit transmittance. The rate Ty was 40.9%.

<Example 4>
As the first protective film and second protective film, the moisture permeability is 63 g / m ^2/24 hr or, using a thermoplastic resin film having a thickness of 80μm made of an acrylic resin, an ultraviolet curable adhesive ((Ltd.) ADEKA manufactured A polarizing plate with a double-sided protective film was produced in the same manner as in Example 2 except that “KR-15P”) was used. The moisture content of the iodine-based polarizing element when the second protective film is attached is 4.2% by weight, the luminous efficiency correction polarization degree Py of the polarizing plate with the double-sided protective film is 99.994%, and the luminous efficiency correction single unit transmittance. The rate Ty was 41.4%.

<Example 5>
As the first protective film, a moisture permeability of 63 g / m ^2/24 hr or, a thermoplastic resin film having a thickness of 80μm made of an acrylic resin, a second protective film, the moisture permeability is 16g / m ² / 24hr, A thermoplastic resin film having a thickness of 23 μm (“ZF-14” manufactured by Nippon Zeon Co., Ltd.) made of a cyclic polyolefin resin was used. The first protective film uses an ultraviolet curable adhesive (“KR-15P” manufactured by ADEKA Corporation), and the second protective film uses an ultraviolet curable adhesive “KR-75T” manufactured by ADEKA Corporation. A polarizing plate with a double-sided protective film was produced in the same manner as in Example 2 except that it was used. The moisture content of the iodine-based polarizing element when the second protective film is attached is 4.8% by weight, the luminous efficiency correction polarization degree Py of the polarizing plate with the double-sided protective film is 99.994%, and the luminous efficiency correction single unit transmittance. The rate Ty was 41.4%.

<Comparative example 1>
A polarizing plate with a double-sided protective film was produced in the same manner as in Example 1 except that the conditions of the final drying treatment (moisture content reduction step) of the dyeing step were 40 ° C. for 60 seconds and then 50 ° C. for 60 seconds. .. The water content of the iodine-based polarizer when the second protective film was attached was 10.7% by weight.

<Comparative example 2>
A polarizing plate with a double-sided protective film was produced in the same manner as in Example 1 except that the conditions of the final drying treatment (moisture content reducing step) of the dyeing step were set at 40 ° C. for 120 seconds. The water content of the iodine-based polarizer when the second protective film was attached was 12.5% by weight.

<Comparative example 3>
After the final drying process (moisture content reduction step) of the dyeing process, the iodine-based polarizing element is stored for about 2 days in an environment of 25 ° C. and 55% RH without affixing a moisture-proof film, and the moisture content of the iodine-based polarizer is near the equilibrium moisture content. Then, a polarizing plate with a double-sided protective film was produced in the same manner as in Example 2 except that the first and second protective films were bonded together. The water content of the iodine-based polarizer when the second protective film was attached was 15.3% by weight.

The moisture permeability of the film and the water content of the iodine-based polarizer in each Example and Comparative Example were measured by the following methods.

(1) Moisture Permeability The moisture permeability was measured at a temperature of 40 ° C. and a relative humidity of 90% in accordance with JIS Z 0208-1976 "Humidity Permeability Test Method for Moisture-Proof Packaging Material (Cup Method)".

(2) Moisture content of iodine-based polarizers The relationship between the water content measured by a near-infrared moisture content meter (“IRMA1100S” manufactured by Chino Co., Ltd.) and the moisture content obtained by the dry gravimetric method is expressed by a linear equation. The calibration line to be represented is obtained in advance from both moisture rates obtained for a plurality of iodine-based polarizer samples having different moisture rates, and the moisture content measured by a near-infrared moisture content meter is measured by the dry weight method using the above calibration line. This was used as the water content of the iodine-based polarizer. The water content according to the dry gravimetric method is calculated by the following formula, where W0 is the weight of the sample before drying and W1 is the weight when the sample is dried at 105 ° C. for 1 hour.
Moisture content (% by weight) = 100 x (W0-W1) / W0
Defined in.

[Evaluation of heat resistance and heat resistance of polarizing plate with double-sided protective film]
(1) Evaluation of Moisture Heat Resistance The polarizing plates with double-sided protective films produced in Examples 1 and 2 and Comparative Examples 1 to 3 are allowed to stand in an environment of 65 ° C. and 90% RH for 500 hours. The corrected polarization degree Py and the Py before the test were measured using an absorptiometer (“V7100” manufactured by JASCO Corporation), and the difference between the two ΔPy (Py before the test-Py after the test) showed moisture resistance. The thermal properties were evaluated. The smaller the absolute value of ΔPy, the higher the moisture resistance and heat resistance. The results are shown in Table 1. In the measurement of Py, a polarizing plate sample with a double-sided protective film was set so that the incident light was irradiated to the second protective film side. The luminous efficiency correction degree of polarization Py after the moist heat resistance test was measured after being allowed to stand in an environment of 23 ° C. and 55% RH for about 12 hours after the moist heat resistance test.

The Py before the moisture resistance test (and the heat resistance test below) was 99.995% for each of the Examples and Comparative Examples. The luminous efficiency correction single transmittance Ty measured using the same absorptiometer was 41.6% for each of the Examples and Comparative Examples.

(2) Evaluation of heat resistance The above-mentioned heat resistance test was performed on the polarizing plates with double-sided protective films produced in Examples 1 and 2 and Comparative Examples 1 to 3 by allowing them to stand in an environment of 85 ° C. dry for 500 hours. In the same manner as the evaluation of moisture resistance and heat resistance, the heat resistance was evaluated from ΔPy (Py before the test-Py after the test). The smaller the absolute value of ΔPy, the higher the heat resistance. The results are shown in Table 1.

(3) Evaluation of Moisture and Heat Resistance under Accelerated Conditions The wet and heat resistance test of the polarizing plate with a double-sided protective film produced in Examples 3 to 5 was performed by allowing the polarizing plate with a double-sided protective film to stand in an environment of 80 ° C. and 90% RH for 48 hours. ) The same method as the evaluation of moisture and heat resistance was performed. The results are shown in Table 2.

(4) Evaluation of heat resistance under accelerated conditions The heat resistance test of the polarizing plate with a double-sided protective film produced in Examples 3 to 5 was performed by allowing the polarizing plate with a double-sided protective film to stand in an environment of 105 ° C. and dry for 48 hours. It was performed in the same way as the sex evaluation. The results are shown in Table 2.

In addition, the degree of light leakage (red discoloration) was visually confirmed for the polarizing plate with the double-sided protective film after the heat resistance test. Specifically, two 10 cm × 20 cm sample pieces were cut out from the polarizing plate with a double-sided protective film after the heat resistance test, and these samples were bonded to both sides of the glass plate using an adhesive. At this time, the side of the second protective film was set to the side of the glass plate, and the sample pieces arranged on both sides were arranged so as to have a positional relationship of cross Nicol. Then, a backlight was applied from one polarizing plate side in a dark room, and a red discoloration was visually evaluated according to the following evaluation criteria. The results are shown in Tables 1 and 2.

A: It stays black and the reddish color cannot be visually recognized.
B: A clear reddish color is observed.

5 iodine-based polarizer, 6 polyvinyl alcohol-based resin layer, 6'stretched polyvinyl alcohol-based resin layer, 10 first protective film, 15 first adhesive layer, 20 second protective film, 25 second adhesive layer, 30 base film, 30'stretched base film, 100 single-sided protective film polarizing plate, 200 laminated film, 300 stretched film, 400 polarized laminated film, 500 multilayer film, 600 double-sided protective film polarizing plate.

Claims (7)

A step of peeling off the base film from a multilayer film containing a base film, an iodine-based polarizer and a first protective film in this order to obtain a polarizing plate with a single-sided protective film.
A step of attaching a second protective film to the outer surface of the iodine-based polarizing element in the polarizing plate with a single-sided protective film to obtain a polarizing plate with a double-sided protective film.
Including
The first protective film and the second protective film is a thermoplastic film of less moisture permeability 150 g / m ^2/24 hr or,
The water content of the iodine-based polarizer when the second protective film is attached is 4.8% by weight or less .
The single-sided protective film so that the moisture content does not exceed 4.8% by weight between the step of obtaining the polarizing plate with the single-sided protective film and the step of obtaining the polarizing plate with the double-sided protective film. A method for manufacturing a polarizing plate with a double-sided protective film, in which a peelable moisture-proof film is temporarily attached to the exposed surface of an iodine-based polarizing element in the polarizing plate, or the polarizing plate with a single-sided protective film is wound in a roll shape. .. The water content of the iodine-based polarizer when the second protective film is attached is 4.2% by weight or less.
The single-sided protective film so that the moisture content does not exceed 4.2% by weight between the step of obtaining the polarizing plate with the single-sided protective film and the step of obtaining the polarizing plate with the double-sided protective film. The production method according to claim 1, wherein a peelable moisture-proof film is temporarily bonded to the exposed surface of the iodine-based polarizing element in the polarizing plate, or the polarizing plate with the single-sided protective film is wound in a roll shape. The production method according to claim 1 or 2, wherein the second protective film is attached to the outer surface of the iodine-based polarizer using an active energy ray-curable adhesive. The production method according to any one of claims 1 to 3, wherein the iodine-based polarizer has a thickness of 10 μm or less. A step of attaching a second protective film to the outer surface of an iodine-based polarizing element in a polarizing plate with a single-sided protective film including an iodine-based polarizing element and a first protective film laminated on one side thereof to obtain a polarizing plate with a double-sided protective film. Including
The first protective film and the second protective film is a thermoplastic film of less moisture permeability 150 g / m ^2/24 hr or,
The water content of the iodine-based polarizer when the second protective film is attached is 4.8% by weight or less .
After obtaining the one surface protective film with the polarizing plate, and before the step of obtaining said two-sided protective film-attached polarizing plate, wherein the moisture regain of not become 4.8 wt.%, The one-side protective attached film A method for producing a polarizing plate with a double- sided protective film, wherein a peelable moisture-proof film is temporarily bonded to the exposed surface of an iodine-based polarizing element in the polarizing plate, or the polarizing plate with a single-sided protective film is wound in a roll shape. The production method according to claim 5, wherein the second protective film is attached to the outer surface of the iodine-based polarizer using an active energy ray-curable adhesive. The production method according to claim 5 or 6, wherein the iodine-based polarizer has a thickness of 10 μm or less.

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