CN106199808B - Method for manufacturing polarizing plate - Google Patents

Abstract

The invention provides a method for manufacturing a polarizing plate, which comprises the following steps: a step of heat-treating the 1 st thermoplastic resin film; a step of humidifying the 1 st thermoplastic resin film; and a step of laminating a 1 st thermoplastic resin film on one surface of the polarizing film and a 2 nd thermoplastic resin film on the other surface of the polarizing film, wherein the 2 nd thermoplastic resin film has a lower equilibrium moisture content at a temperature of 23 ℃ and a relative humidity of 55% than the 1 st thermoplastic resin film.

Description

Method for manufacturing polarizing plate

Technical Field

The present invention relates to a method for manufacturing a polarizing plate comprising a polarizing film and a thermoplastic resin film laminated thereon.

Background

In recent years, mobile phone terminals such as smartphones have been rapidly increased in size and weight in terms of design and portability. In order to realize long-term driving with a limited thickness, the polarizing plate used is required to have high brightness, thin thickness and light weight.

Conventionally, a polarizing plate in which a protective film made of triacetyl cellulose (TAC) is bonded to a polarizing film made of a polyvinyl alcohol resin with an adhesive has been generally used. In recent years, however, protective films made of resins other than TAC have been used in view of reduction in thickness, durability, cost, productivity, and the like (for example, japanese patent laid-open No. 2004-.

Disclosure of Invention

The polarizing plate is sensitive to the environment in which it is placed, and is easily deformed into a bow shape according to the environmental conditions. In this specification, this deformation is also referred to as "curling". The polarizing plate tends to be more likely to curl as it becomes a thin film. The curl is classified into "positive curl" and "reverse curl". In the polarizing plate, there are a 1 st main surface on the side to which an image display element such as a liquid crystal element is attached and a 2 nd main surface on the opposite side, and "forward curl" refers to the curl of the 1 st main surface side projection and "reverse curl" refers to the curl of the 2 nd main surface side projection. When the polarizing plate is reversely curled and is adhered to an image display element via an adhesive layer, the following problems are likely to occur: adhesion errors occur, and air bubbles are mixed in the interface between the adhesive layer and the image display element. In order to suppress these problems and to perform attachment of the polarizing plate to the image display element with good productivity, the polarizing plate is most preferably flat, and when the generated curl is a positive curl, there is no particular problem in the above-described problems and productivity.

In addition, jp 2006-030480 a describes that, in order to suppress the occurrence of striped irregularities in the polarizing plate, the water content of the protective film is adjusted to a predetermined range before the polarizing film and the protective film are laminated.

The present invention aims to provide a method for manufacturing a polarizing plate which has no reverse curl or has suppressed reverse curl.

The present invention provides a method for manufacturing the following polarizing plate.

A method for manufacturing a polarizing plate, comprising the steps of:

a step of subjecting the 1 st thermoplastic resin film to a heat treatment,

a step of subjecting the 1 st thermoplastic resin film to a humidification treatment, and

and a step of laminating the 1 st thermoplastic resin film on one surface of the polarizing film and a 2 nd thermoplastic resin film on the other surface of the polarizing film, wherein the 2 nd thermoplastic resin film has a lower equilibrium moisture content at a temperature of 23 ℃ and a relative humidity of 55% than the 1 st thermoplastic resin film.

[2] The production method according to [1], wherein the 2 nd thermoplastic resin film is not subjected to the humidification treatment.

[3] The production method according to [1] or [2], wherein the 1 st thermoplastic resin film contains a cellulose-based resin film.

[4] The production method according to any one of [1] to [3], wherein the 2 nd thermoplastic resin film contains a cyclic polyolefin resin film.

[5] The production method according to any one of [1] to [4], wherein the temperature at the time of the heating treatment is equal to or higher than the temperature at the time of the humidifying treatment.

[6] The production method according to [5], wherein the temperature during the heating treatment is higher than the temperature during the humidifying treatment by 30 ℃ or more.

[7] The production method according to any one of [1] to [6], wherein in the step of performing the heat treatment, the 1 st thermoplastic resin film is heat-treated in an environment in which a temperature is 50 ℃ or higher and a relative humidity is 50% or lower.

[8] The production method according to any one of [1] to [7], wherein in the step of performing the humidification treatment, the 1 st thermoplastic resin film is humidified in an environment having a temperature of 40 ℃ or higher and a relative humidity of 60% or higher.

[9] The production method according to any one of [1] to [8], wherein at least one of the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film is laminated on the polarizing film via an adhesive layer.

[10] The production method according to any one of [1] to [9], wherein the thickness of the 1 st thermoplastic resin film is 40 μm or less, and the thickness of the 2 nd thermoplastic resin film is 40 μm or less.

[11] The production method according to any one of [1] to [10], wherein the thickness of the polarizing film is 15 μm or less.

[12] The production method according to any one of [1] to [11], wherein in the step of performing the humidification treatment, the 1 st thermoplastic resin film is humidified so that a water content thereof is higher than an equilibrium water content of the 1 st thermoplastic resin film at a temperature of 23 ℃ and a relative humidity of 55%.

According to the present invention, a polarizing plate having no reverse curl or having a suppressed reverse curl can be produced.

Drawings

FIG. 1 is a flowchart showing an example of a method for manufacturing a polarizing plate according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of the layer structure of a polarizing plate obtained by the production method of the present invention.

FIG. 3 is a schematic side view showing an example of the method for producing a polarizing plate and the apparatus for producing the same according to the present invention.

Fig. 4 is a schematic cross-sectional view showing an example of the layer structure of the single-sided protective polarizing plate.

Fig. 5 is a schematic cross-sectional view showing an example of the layer structure of a single-sided protective polarizing plate with a temporary protective film.

Fig. 6 is a schematic cross-sectional view showing an example of the layer structure of the one-side protective polarizing plate with an adhesive layer.

Description of the reference numerals

1 double-sided protective polarizing plate, 2 single-sided protective polarizing plate, 3 single-sided protective polarizing plate with temporary protective film, 4 single-sided protective polarizing plate with adhesive layer, 5 polarizing film, 10 st 1 thermoplastic resin film, 20 nd 2 thermoplastic resin film, 15 st 1 adhesive layer, 25 nd 2 adhesive layer, 30 adhesive layer, 40 laminating roller, 50 st 1 adhesive, 55 nd 2 adhesive, 60 guide roller, 70 heating furnace, 80 humidifying furnace, 90 st 1 injection device, 91 nd 2 injection device.

Detailed Description

Referring to fig. 1, the method for manufacturing a polarizing plate according to the present invention includes the following steps in the following order:

(1) a heat treatment step S100 of heat-treating the 1 st thermoplastic resin film,

(2) a humidifying step S200 of humidifying the 1 st thermoplastic resin film, and

(3) and a laminating step S300 of laminating a 1 st thermoplastic resin film on one surface of the polarizing film and a 2 nd thermoplastic resin film on the other surface of the polarizing film. The 2 nd thermoplastic resin film has a lower equilibrium water content than the 1 st thermoplastic resin film. The equilibrium moisture content referred to herein is the equilibrium moisture content of the film after storage for 24 hours at a temperature of 23 ℃ and a relative humidity of 55% as measured by a dry weight method.

A1 st thermoplastic resin film subjected to a humidification treatment following a heating treatment is laminated on one surface of the polarizing film, and a 2 nd thermoplastic resin film is laminated on the other surface. According to the manufacturing method of the present invention, reverse curl of the obtained polarizing plate can be reduced or prevented. The reverse curl is a deformation in which the 2 nd main surface opposite to the side to which the image display element such as a liquid crystal element is attached is convex and the polarizing plate is curved in a bow shape as described above, and usually the deformation is generated in a single body of the polarizing plate. When a long polarizing plate is produced using a long raw material film (the 1 st and 2 nd thermoplastic resin films, polarizing film), the reverse curl is typically generated in a single polarizing plate cut out from the long polarizing plate.

Fig. 2 shows an example of the layer structure of the polarizing plate obtained by the manufacturing method of the present invention. The polarizing plate shown in fig. 2 is a double-sided protective polarizing plate 1, and the double-sided protective polarizing plate 1 includes a polarizing film 5, a 1 st thermoplastic resin film 10 attached to one surface thereof via a 1 st adhesive layer 15, and a 2 nd thermoplastic resin film 20 attached to the other surface thereof via a 2 nd adhesive layer 25. In the double-sided protective polarizing plate 1, the 1 st and 2 nd thermoplastic resin films 10 and 20 are optical films serving to protect the polarizing film 5, that is, protective films, and may be bonded to the surface of the polarizing film 5 using an adhesive. The other layer structure of the polarizing plate obtained by the production method of the present invention will be described later.

Hereinafter, each step will be described with reference to fig. 3. FIG. 3 is a schematic side view showing an example of the method for producing a polarizing plate and the apparatus for producing the same according to the present invention. The arrows in fig. 3 indicate the direction of conveyance of the film. In general, as shown in fig. 3, a polarizing plate can be continuously manufactured by performing processes in respective steps while continuously taking out and conveying a long raw material film. However, the production method of the present invention is not limited to continuous production using such a long raw material film, and may be a method using a single sheet of film.

(1) Heat treatment step S100

This step is a step of heat-treating the 1 st thermoplastic resin film 10. One feature of the present invention is that by performing heat treatment before humidifying the 1 st thermoplastic resin film 10, reverse curling of the polarizing plate (typically, curling in which the main surface of the 1 st thermoplastic resin film 10 is convex) can be effectively suppressed or prevented, and in addition, reverse curling of the polarizing plate can be more effectively suppressed or prevented than in the case of performing only humidifying treatment.

The 1 st thermoplastic resin film 10 is a film made of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin. Examples of the thermoplastic resin used to form the first thermoplastic resin film 10 include polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); cellulose resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; a polycarbonate-based resin; (meth) acrylate resins such as methyl methacrylate resins; a polystyrene-based resin; a polyvinyl chloride resin; acrylonitrile-butadiene-styrene resins; acrylonitrile-styrene resins; polyvinyl acetate resin; a polyvinylidene chloride resin; a polyamide resin; a polyacetal resin; modified polyphenylene ether resin; a polysulfone-based resin; a polyether sulfone-based resin; a polyarylate-based resin; a polyamide imide resin; polyimide resins, and the like.

In the present specification, "(meth) acrylate-based resin" means at least 1 selected from the group consisting of acrylate-based resins and methacrylate-based resins. Other terms with "(methyl)" are also the same.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resins and polypropylene resins, and copolymers of 2 or more kinds of chain olefins. More specific examples include polypropylene resins (polypropylene resins, which are homopolymers of propylene, or copolymers mainly composed of propylene), and polyethylene resins (polyethylene resins, which are homopolymers of ethylene, or copolymers mainly composed of ethylene).

The cyclic polyolefin resin is a general name of a resin obtained by polymerizing a cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin resin include ring-opened (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins with linear olefins such as ethylene and propylene (typically random copolymers), graft polymers obtained by modifying these with unsaturated carboxylic acids or derivatives thereof, and hydrogenated products thereof. Among these, norbornene-based resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers are preferably used as the cyclic olefin.

The cellulose-based resin is a cellulose organic acid ester or a cellulose mixed organic acid ester obtained by substituting a part or all of hydrogen atoms in hydroxyl groups of cellulose obtained from raw material cellulose such as cotton linter and wood pulp (hardwood pulp and softwood pulp) with acetyl groups, propionyl groups and/or butyryl groups. For example, cellulose resins such as acetate, propionate, butyrate and mixed esters thereof. Among them, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferable.

The polyester resin is a resin other than the above-mentioned cellulose resin having an ester bond, and is usually a resin formed of a polycondensate of a polycarboxylic acid or a derivative thereof and a polyhydric alcohol. As the polycarboxylic 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, dimethyl naphthalate, and the like. As the polyhydric alcohol, a dihydric diol can be used, and examples thereof include ethylene glycol, propylene glycol, butanediol, neopentyl glycol, cyclohexanedimethanol, and the like. Examples of preferred polyester-based resins include polyethylene terephthalate.

Polycarbonate resins are engineering plastics composed of polymers in which monomer units are bonded via carbonate groups, and have high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called modified polycarbonate in which the polymer skeleton is modified in order to reduce the photoelastic coefficient, or a copolymerized polycarbonate in which the wavelength dependence is improved.

The (meth) acrylate-based resin is a polymer containing a structural unit derived from a (meth) acrylate-based monomer. The polymer is typically a methacrylate-containing polymer. The polymer preferably contains a structural unit derived from a methacrylate ester in a proportion of 50% by weight or more based on the total structural units. The (meth) acrylate resin may be a homopolymer of methacrylate or a copolymer containing a structural unit derived from another polymerizable monomer. In this case, the proportion of the structural unit derived from another polymerizable monomer is preferably 50% by weight or less based on the total structural units.

As the methacrylic acid ester that can constitute the (meth) acrylate-based resin, an alkyl methacrylate is preferable. Examples of the alkyl methacrylate include alkyl methacrylates having an alkyl group of 1 to 8 carbon atoms such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and 2-hydroxyethyl methacrylate. The number of carbon atoms of the alkyl group contained in the alkyl methacrylate is preferably 1 to 4. In the (meth) acrylate-based resin, only 1 kind of methacrylate may be used alone, or 2 or more kinds may be used in combination.

Examples of the other polymerizable monomers that can constitute the (meth) acrylate resin include acrylates and other compounds having a polymerizable carbon-carbon double bond in the molecule. The other polymerizable monomers may be used alone in 1 kind or in combination of 2 or more kinds. As the acrylate, alkyl acrylate is preferable. Examples of the alkyl acrylate include alkyl acrylates having an alkyl group of 1 to 8 carbon atoms such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate. The alkyl group contained in the alkyl acrylate preferably has 1 to 4 carbon atoms. In the (meth) acrylate-based resin, only 1 kind of acrylate may be used alone, or 2 or more kinds may be used in combination.

Examples of the other compounds having a polymerizable carbon-carbon double bond in the molecule include vinyl compounds such as ethylene, propylene and styrene, and vinyl cyanide compounds such as acrylonitrile. The other compounds having a polymerizable carbon-carbon double bond in the molecule may be used alone in 1 kind or in combination of 2 or more kinds.

The 1 st thermoplastic resin film 10 may be a protective film laminated and adhered to one surface of the polarizing film 5 to protect the polarizing film 5, or may be a temporary protective film temporarily protecting the surface of the polarizing film 5. The 1 st thermoplastic resin film 10 as the temporary protective film may be peeled off and removed as desired after the polarizing plate is constructed. The 1 st thermoplastic resin film 10 may be a protective film having an optical function as well as a retardation film or a brightness improving film. For example, a retardation film to which an arbitrary retardation value is given can be obtained by stretching (uniaxial stretching, biaxial stretching, or the like) a thermoplastic resin film formed of the above-mentioned material, or forming a liquid crystal layer on the film. The 1 st thermoplastic resin film 10 may further have a surface treatment layer (surface coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer laminated on the surface thereof.

The thickness of the 1 st thermoplastic resin film 10 is usually 1 to 100 μm, preferably 5 to 60 μm, and more preferably 5 to 50 μm from the viewpoint of strength and handling property. If the thickness is within this range, the polarizing film 5 can be mechanically protected, and the shrinkage of the polarizing film 5 when the polarizing plate is exposed to a moist heat environment can be suppressed. The smaller the thickness of the 1 st thermoplastic resin film 10 is, the more likely curling of the polarizing plate is to occur, and according to the present invention, even if the thickness of the 1 st thermoplastic resin film 10 is as thin as, for example, 40 μm or less, and further as thin as 30 μm or less, reverse curling of the resulting polarizing plate can be effectively suppressed or prevented.

The 1 st thermoplastic resin film 10 has a higher equilibrium moisture content than the 2 nd thermoplastic resin film 20 used in the laminating step S300 described later. In the present specification, the equilibrium water content is a water content of a film after being stored for 24 hours in an environment of 23 ℃ and 55% relative humidity measured by a dry weight method, and specifically, is obtained according to the following formula:

equilibrium water content (wt%) { (weight of film after storage-weight of film after drying treatment)/weight of film after storage } × 100.

Drying refers to a process of drying the film at 105 ℃ for 2 hours. A polarizing plate is manufactured by using a 1 st thermoplastic resin film 10 having at least a higher equilibrium water content by heating the 1 st thermoplastic resin film 10 and then humidifying the heated film. According to the method of the present invention, reverse curl of the obtained polarizing plate can be suppressed or prevented.

The difference between the equilibrium moisture contents of the 1 st thermoplastic resin film 10 and the 2 nd thermoplastic resin film 20 measured by the above-described method is preferably 0.5 wt% or more, that is, the equilibrium moisture content of the 1 st thermoplastic resin film 10 is preferably 0.5 wt% or more larger than that of the 2 nd thermoplastic resin film 20. Accordingly, in the humidification process S200 described later, the moisture content of the 1 st thermoplastic resin film 10 can be more effectively increased, and the suppression or prevention of reverse curling is more advantageous. The difference in the equilibrium water content is more preferably 1 wt% or more, and still more preferably 1.5 wt% or more.

The 1 st thermoplastic resin film 10 preferably has an equilibrium moisture content of 1.5 wt% or more, more preferably 2 wt% or more. This makes it possible to more effectively increase the water content of the 1 st thermoplastic resin film 10 in the humidification step S200 described later, and is more advantageous in suppressing or preventing reverse curling. The equilibrium moisture content of the 1 st thermoplastic resin film 10 is usually 5% by weight or less.

Examples of the combination of thermoplastic resin films having a difference in equilibrium water content of 0.5 wt% or more include a combination of a cellulose-based resin film (TAC film or the like) and a cyclic polyolefin-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a (meth) acrylate-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a polyester-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a chain polyolefin-based resin film, a combination of a (meth) acrylate-based resin film and a cyclic polyolefin-based resin, a combination of a (meth) acrylate-based resin film and a polyester-based resin film, and the like. The difference in the equilibrium moisture content between the 1 st thermoplastic resin film 10 and the 2 nd thermoplastic resin film 20 is usually 5 wt% or less.

The equilibrium water content of the thermoplastic resin film can be adjusted depending on the material (type of thermoplastic resin constituting the film) and also on the thickness of the film, the presence or absence of a surface treatment layer (surface coating layer) that can be attached to the surface of the film, the material, and the like.

The 1 st thermoplastic resin film 10 is preferably a film having a higher moisture permeability than the 2 nd thermoplastic resin film 20. In the present specification, the moisture permeability is a moisture permeability at a temperature of 40 ℃ and a relative humidity of 90%, measured by a moisture permeable cup method defined in JIS Z0208. A polarizing plate is produced from a 1 st thermoplastic resin film 10 by subjecting at least the 1 st thermoplastic resin film 10 having a higher moisture permeability to heat treatment and successively subjecting the film to humidification treatment. According to the method of the present invention, it is more advantageous in suppressing or preventing reverse curling of the obtained polarizing plate.

The difference between the moisture permeability at 40 ℃ and the relative humidity of 90% as measured by the moisture permeable cup method defined in JIS Z0208 between the 1 st thermoplastic resin film 10 and the 2 nd thermoplastic resin film 20 is preferably 30 g/(m)²24hr) or more, that is, the moisture permeability of the 1 st thermoplastic resin film 10 is preferably 30 g/(m) larger than that of the 2 nd thermoplastic resin film 20²24hr) above. This makes it possible to more effectively increase the water content of the 1 st thermoplastic resin film 10 in the humidification step S200 described later, and is more advantageous in suppressing or preventing reverse curling. The difference in moisture permeability is more preferably 50 g/(m)²24hr) or more, and more preferably 100 g/(m)²24hr) above.

No. 1 thermoplastic resin film10 the preferred moisture permeability is 300 g/(m)²24hr) or more, more preferably 400 g/(m)²24hr) above. This can more effectively increase the water content of the 1 st thermoplastic resin film 10 in the humidification process S200 described later, and is more advantageous for preventing or suppressing reverse curling. Further, the moisture permeability was 300 g/(m)²24hr) or more, it is advantageous in that when the 1 st thermoplastic resin film 10 and the polarizing film 5 are bonded using the aqueous adhesive, the layer formed by the aqueous adhesive can be dried more effectively, and productivity can be improved. The moisture permeability of the 1 st thermoplastic resin film 10 is usually 5000 g/(m)²24hr) or less.

The difference in moisture permeability was 30 g/(m)²24hr) or more, for example, a combination of a cellulose-based resin film (TAC film or the like) and a cyclic polyolefin-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a (meth) acrylate-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a polyester-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a chain polyolefin-based resin film, a combination of a (meth) acrylate-based resin film and a cyclic polyolefin-based resin, a combination of a (meth) acrylate-based resin film and a polyester-based resin film, or the like can be cited. The difference in moisture permeability between the 1 st thermoplastic resin film 10 and the 2 nd thermoplastic resin film 20 is usually 5000 g/(m)²24hr) or less.

The moisture permeability of the thermoplastic resin film may be adjusted depending on the material (type of thermoplastic resin constituting the film), the thickness of the film, the presence or absence of a surface treatment layer (surface coating layer) that can be attached to the surface of the film, the material, and the like.

The method of the heat treatment of the 1 st thermoplastic resin film 10 in this step is not particularly limited as long as the 1 st thermoplastic resin film 10 can be heated to a desired temperature. As shown in fig. 3, the heat treatment may be a treatment of introducing the 1 st thermoplastic resin film 10 into, for example, a heating furnace 70 and heating the same. The heating furnace 70 is preferably a heating furnace capable of controlling the temperature inside the furnace. The heating furnace 70 is a hot blast furnace capable of raising the temperature inside the furnace by, for example, supplying hot air.

The heat treatment of the 1 st thermoplastic resin film 10 may be a treatment of adhering the film to 1 or 2 or more heating bodies having a convex curved surface, or a treatment of heating the film by a heater. Examples of the heating body include a roller (e.g., a hot roller such as a guide roller whose surface is made of metal) having a heat source (e.g., a heat medium such as warm water or an infrared heater) therein and capable of increasing the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a plate heater. FIG. 3 shows an example in which the 1 st thermoplastic resin film 10 is introduced into a heating furnace 70 and heated while being conveyed along a guide roller 60 in the furnace.

Wherein, the 1 st thermoplastic resin film 10 is introduced into a heating furnace 70 whose temperature in the furnace is adjusted to a desired temperature, and the film is heated while being conveyed by 1 or 2 or more guide rollers 60 in the furnace; and a method of heating the film while conveying the film and adhering the film to 1 or 2 or more heating bodies having a convex curved surface, are preferable in that the surface of the 1 st thermoplastic resin film 10 can be smoothed before the laminating step S300 described later. That is, the raw material film such as the 1 st thermoplastic resin film 10 has minute surface irregularities at the time of production or has minute surface irregularities generated in the storage step after production, and the surface of the 1 st thermoplastic resin film 10 is smoothed by the above-described method in this step, whereby the appearance quality of the polarizing plate can be improved and the adhesiveness to the polarizing film 5 can be improved.

Temperature T at the time of heat treatment_1-1(e.g., the temperature in the heating furnace 70, the surface temperature of the hot roll, etc.), and the temperature T of the 1 st thermoplastic resin film 10 reached by the heating treatment_1-2Preferably, the temperature T at the time of humidification in the humidification processing step S200 to be described later_2-1(for example, the temperature in the humidifying furnace 80) or more, and more preferably, the temperature T is higher than the temperature T in the humidifying treatment_2-1High. Furthermore, the temperature T_1-1And T_1-2Preferably, the temperature T of the 1 st thermoplastic resin film 10 reached by the humidification treatment_2-2The aboveMore preferably above the temperature T_2-2. This can more effectively suppress or prevent the reverse curl of the obtained polarizing plate. That is, by satisfying the above temperature relationship, it is possible to prevent the occurrence of dew condensation on the surface of the 1 st thermoplastic resin film 10 when the humidifying treatment step S200 is conducted, and to surely perform the humidifying treatment on the entire film under a desired temperature and humidity condition. This improves the effect of suppressing/preventing reverse curl. T is_1-1、T_1-2Preferred ratio T_2-1、T_2-2The temperature is higher by 10 ℃ or more, more preferably higher by 20 ℃ or more, and still more preferably higher by 30 ℃ or more. T is_1-1And T_2-1Or with T_2-2A difference of (a) and T_1-2And T_2-1Or T_2-2The difference of (A) is usually 70 ℃ or less.

The temperature T in the heat treatment_1-1And the temperature T of the 1 st thermoplastic resin film 10 attained by the heat treatment_1-2Preferably the same, or substantially the same, temperature. Further, the temperature T at the time of humidification_2-1And the temperature T of the 1 st thermoplastic resin film 10 reached by the humidification treatment_2-2Preferably the same, or substantially the same, temperature.

If condensation occurs on the surface of the 1 st thermoplastic resin film 10 in the humidification step S200, the temperature of the film cannot be raised to a desired value in the condensation portion due to the latent heat of vaporization of water, and as a result, humidification cannot be performed under desired temperature and humidity conditions, and therefore, the effect of preventing or suppressing reverse curling is reduced or the reverse curling cannot be suppressed. In addition, when the 1 st thermoplastic resin film 10 at room temperature (23 ℃) is introduced into the humidifying treatment step S200 without performing the heat treatment step S100 and is subjected to humidifying treatment under a temperature and humidity condition where dew condensation does not occur, the humidifying treatment becomes insufficient, and reverse curling of the polarizing plate cannot be suppressed.

When dew condensation occurs on the surface of the 1 st thermoplastic resin film 10, dew condensation marks (dew condensation occurs, and drying marks remain after drying) remain on the surface of the polarizing plate, and the appearance quality of the polarizing plate is deteriorated. The method of the present invention for producing a polarizing plate using the 1 st thermoplastic resin film subjected to the heat treatment and then the humidification treatment can also reduce the occurrence of the dew condensation mark.

Temperature T at the time of heat treatment_1-1And the temperature T of the 1 st thermoplastic resin film 10 reached by the heat treatment_1-2Usually 50 to 150 ℃, preferably 60 to 130 ℃, and more preferably 70 to 120 ℃. If the temperature T is_1-1、T_1-2Below 50 ℃, it is difficult to satisfy the temperature relationship (T)_1-1、T_1-2≧T_2-1、T_2-2) Alternatively, even if the relationship is satisfied, the humidification processing cannot be performed under the appropriate temperature and humidity conditions in the humidification processing step S200, and as a result, the effect of suppressing/preventing reverse curl tends to decrease. In addition, if the temperature T is_1-1、T_1-2When the temperature is less than 50 ℃, the surface of the 1 st thermoplastic resin film 10 tends to be insufficiently smoothed. On the other hand, if the temperature T is_1-1、T_1-2When the temperature exceeds 150 ℃, the 1 st thermoplastic resin film 10 may be thermally deteriorated and the 1 st thermoplastic resin film 10 may not be efficiently humidified in the humidifying step S200. The temperature T is set to a temperature T from the viewpoint of effectively humidifying the 1 st thermoplastic resin film 10 in the humidifying step S200_1-1、T_1-2More preferably 110 ℃ or lower, and particularly preferably 100 ℃ or lower.

The heat treatment in this step may be performed in an environment with a relative humidity of 50% or less, preferably 45% or less. In other words, the term "heat treatment" as used herein refers to a heat treatment performed in an environment having a relative humidity of 50% or less, and is distinguished from the term "humidification treatment" in the humidification treatment step S200 in which humidification is preferably performed while heating is performed in an environment having a higher relative humidity (for example, a relative humidity of 60% or more). The relative humidity of the heat treatment environment is more preferably 30% or less, still more preferably 20% or less, and particularly preferably 10% or less (for example, 5% or less).

The time for the heat treatment in this step is, for example, about 2 to 300 seconds, preferably about 5 to 120 seconds. If the time of the heat treatment is too short, it becomes difficult to control the temperature T of the 1 st thermoplastic resin film 10_1-2The above-mentioned temperature is reached. A long heat treatment time may thermally degrade the 1 st thermoplastic resin film 10, and a long film transfer path is required, which may result in an excessive increase in size of the polarizing plate manufacturing apparatus. The time of the heat treatment is a residence time of the film in the heating furnace 70, a time of adhering to a heating body, a time of heating the film using a heater, or the like.

(2) Humidification processing step S200

This step is a step of subjecting the 1 st thermoplastic resin film 10 after the heat treatment to a humidification treatment. The humidifying treatment is a treatment for increasing the water content of the 1 st thermoplastic resin. As described above, by performing the humidification treatment subsequent to the heating treatment, the reverse curl of the polarizing plate can be effectively suppressed or prevented, and in addition, the reverse curl of the polarizing plate can be more effectively suppressed or prevented than the case where only the humidification treatment is performed.

The 1 st thermoplastic resin film 10 may be subjected to a humidification process by introducing the 1 st thermoplastic resin film 10 into a humidification furnace 80 as shown in fig. 3, or may be subjected to a process in an environment in which the relative humidity is adjusted. The humidifying furnace 80 is preferably a humidifying furnace capable of controlling the relative humidity inside the furnace, and more preferably a humidifying furnace capable of controlling the temperature inside the furnace. The humidifying furnace 80 is an oven capable of increasing the temperature in the furnace by, for example, supplying hot air and controlling the relative humidity in the furnace by adjusting the moisture in the furnace.

In order to maintain the temperature of the heat-treated 1 st thermoplastic resin film 10 even when it is introduced into the humidification step, or not to significantly reduce it, the interval between the heat treatment and the humidification is preferably as short as possible. FIG. 3 shows an example in which the 1 st thermoplastic resin film 10 taken out from the heating furnace 70 is immediately introduced into a humidifying furnace 80, and the film is humidified while being conveyed along a guide roller 60 in the furnace. In order to adjust the temperature in the humidification process using the humidification furnace 80, the heater described above or the heating body (for example, a hot roll) described above may be used instead of the hot air.

The relative humidity is adjusted in an environment in which the relative humidity is adjusted, for example, the relative humidity in the humidifying furnace 80 is adjusted to be at least more than 50%, preferably 60% or more, and more preferably 70% or more. This enables the 1 st thermoplastic resin film 10 to be humidified effectively. The relative humidity of the environment in which the relative humidity is adjusted is usually 99% or less, and more preferably 95% or less. If the relative humidity is too high, dew condensation may occur depending on the temperature of the 1 st thermoplastic resin film 10.

Temperature T during humidification_2-1(temperature of the environment in which the relative humidity is adjusted), and the temperature T of the 1 st thermoplastic resin film 10 reached by the humidification treatment_2-2Usually 35 ℃ or higher, preferably 40 ℃ or higher, and more preferably 45 ℃ or higher. Temperature T_2-1、T_2-2Humidification can be efficiently performed at 35 ℃ or higher. On the other hand, if the temperature T is_2-1、T_2-2If the temperature is too high, it becomes difficult to satisfy the temperature relationship (T)_1-1、T_1-2≧T_2-1、T_2-2) Thus temperature T_2-1、T_2-2Preferably 90 ℃ or lower and within a range satisfying the above temperature relationship, and more preferably 80 ℃ or lower and within a range satisfying the above temperature relationship.

The time for the humidification treatment in this step is, for example, about 5 to 500 seconds, preferably about 20 to 300 seconds. If the time of the humidification treatment is too short, the 1 st thermoplastic resin film 10 is insufficiently humidified (the water content is increased). In addition, an excessively long humidification processing time requires a long film transfer path, which may lead to an excessive increase in the size of the polarizing plate manufacturing apparatus. The time of the humidification processing means a residence time of the thin film in the humidification furnace 80.

The preferred water content of the 1 st thermoplastic resin film 10 after the humidification step S200 depends on the equilibrium water content of the film (more typically, the material of the film). The moisture content of the 1 st thermoplastic resin film 10 is preferably adjusted to be higher than the equilibrium moisture content in a normal environment (temperature of about 23 ℃ and relative humidity of about 55%) in which the polarizing plate is stored after production by humidification. For example, when the 1 st thermoplastic resin film 10 is a triacetyl cellulose film, the moisture content after the humidification treatment is preferably 1 to 5% by weight, more preferably 2 to 4.5% by weight (e.g., 2 to 4% by weight). The water content can be measured by a dry weight method in the same manner as the equilibrium water content, and specifically, is obtained according to the following formula:

water content (% by weight) { (weight of film before drying treatment — weight of film after drying treatment)/weight of film before drying treatment } × 100. Drying refers to a process of drying the film at 105 ℃ for 2 hours.

In the humidifying step S200, the 1 st thermoplastic resin film 10 is humidified to have a water content higher than the equilibrium water content at a temperature of 23 ℃ and a relative humidity of 55%, whereby reverse curling of the polarizing plate can be effectively suppressed or prevented. When the moisture content of the 1 st thermoplastic resin film 10 after the humidification step S200 is equal to or lower than the equilibrium moisture content of the 1 st thermoplastic resin film 10 at a temperature of 23 ℃ and a relative humidity of 55%, the suppression of reverse curling is insufficient.

The difference between the water content of the 1 st thermoplastic resin film 10 after the humidification step S200 and the equilibrium water content of the 1 st thermoplastic resin film 10 at a temperature of 23 ℃ and a relative humidity of 55% is preferably 0.1% by weight or more. In addition, from the viewpoint of suppressing excessive positive curling, the difference is preferably 3 wt% or less (for example, 2 wt% or less).

It is desirable that the 1 st thermoplastic resin film 10 can maintain or substantially maintain the moisture content after the humidification process even in the laminating process S300 after the humidification process S200.

(3) Laminating step S300

Referring to fig. 3, this step is a step of laminating a 1 st thermoplastic resin film 10 on one surface of a polarizing film 5 and a 2 nd thermoplastic resin film 20 on the other surface of the polarizing film 5.

(3-1) polarizing film

The polarizing film 5 may be a polarizing film obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film. As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, a resin obtained by saponifying a 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 the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group.

The saponification degree of the polyvinyl alcohol resin may be in the range of 80.0 to 100.0 mol%, preferably 90.0 to 100.0 mol%, and more preferably 98.0 to 100.0 mol%. If the saponification degree is less than 80.0 mol%, the water resistance and the moist heat resistance of the obtained polarizing plate are lowered.

The saponification degree is the degree of saponification of the polyvinyl alcohol resin, i.e., the degree of saponification of the polyvinyl acetate group (acetoxy group: -OCOCH) contained in the polyvinyl acetate resin as the raw material of the polyvinyl alcohol resin₃) The value represented by the unit ratio (mol%) of the ratio of hydroxyl groups changed by the saponification step is defined by the following formula:

the degree of saponification (mol%) was 100 × (number of hydroxyl groups)/(number of hydroxyl groups + number of acetic acid groups). The degree of saponification can be determined in accordance with JIS K6726 (1994). The higher the degree of saponification, the higher the proportion of hydroxyl groups, and therefore the lower the proportion of acetate groups inhibiting crystallization.

The polyvinyl alcohol resin preferably has an average polymerization degree of 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average polymerization degree of the polyvinyl alcohol resin can be determined in accordance with JIS K6726 (1994). When the average polymerization degree is less than 100, satisfactory polarizing performance is difficult to obtain, and when it exceeds 10000, solubility in a solvent is deteriorated, and formation of a polyvinyl alcohol resin film is difficult.

The dichroic dye contained (adsorbed and oriented) in the polarizing film 5 may be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include red BR, red LR, red R, pink LB, ruby red (Rubine) BL, purplish red (Bordeaux) GS, sky blue LG, lemon yellow, blue BR, blue 2R, dark blue RY, green LG, violet LB, violet B, black H, black B, black GSP, yellow 3G, yellow R, orange LR, orange 3R, scarlet (scarlet) GL, scarlet KGL, Congo red (concred), bright purple BK, super blue (Supra blue) G, super blue GL, super blue (Supra orange) GL, direct sky blue, direct fast orange S, fast black. The dichroic pigment may be used alone in 1 kind, or may be used in combination in 2 or more kinds. The dichroic pigment is preferably iodine.

The polarizing film 5 can be produced by the following steps: a step of uniaxially stretching a polyvinyl alcohol resin film; a step of staining the polyvinyl alcohol resin film with a dichroic pigment to thereby adsorb the dichroic pigment; a step of crosslinking the polyvinyl alcohol resin film having the dichroic dye adsorbed thereon; and a step of washing with water after the crosslinking treatment.

The polyvinyl alcohol resin film is obtained by forming the polyvinyl alcohol resin film. The film forming method is not particularly limited, and a known method such as a melt extrusion method or a solvent extraction method can be used. The thickness of the polyvinyl alcohol resin film is, for example, about 10 to 150. mu.m, preferably 50 μm or less, and more preferably 35 μm or less.

The uniaxial stretching of the polyvinyl alcohol resin film may be performed before, simultaneously with, or after the dyeing of the dichroic dye. When the uniaxial stretching is performed after dyeing, the uniaxial stretching may be performed either before or during the crosslinking treatment. In addition, uniaxial stretching may be performed at these multiple stages.

In the case of uniaxial stretching, the stretching may be uniaxial between rolls having different peripheral speeds, or uniaxial stretching may be performed by hot roll stretching. The uniaxial stretching may be dry stretching in which stretching is performed in the air, or wet stretching in which the polyvinyl alcohol resin film is stretched in a solution. The draw ratio is usually about 3 to 8 times.

As a method for dyeing the polyvinyl alcohol resin film with the dichroic dye, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution (dyeing solution) containing the dichroic dye can be used. The polyvinyl alcohol resin film is preferably subjected to an immersion treatment (swelling treatment) in water before the dyeing treatment.

When iodine is used as the dichroic dye, a method of immersing a polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide to dye the film is generally employed. The iodine content of the aqueous dyeing solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. Further, the content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing aqueous solution is usually about 20-40 ℃.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing a polyvinyl alcohol resin film in an aqueous dyeing solution containing a water-soluble dichroic organic dye to dye the film is generally employed. The content of the dichroic organic dye in the dyeing aqueous solution is usually 1X 10^-410 parts by weight per 100 parts by weight of water, preferably 1X 10^-3About 1 part by weight. The aqueous dyeing solution may further contain an inorganic salt such as sodium sulfate as a dyeing auxiliary. The temperature of the dyeing aqueous solution is usually about 20-80 ℃.

The crosslinking treatment after dyeing with the dichroic pigment can be performed by immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing a crosslinking agent. A preferable example of the crosslinking agent is boric acid, and other crosslinking agents such as a boron compound such as borax, glyoxal, and glutaraldehyde may be used. The crosslinking agent may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The amount of the crosslinking agent in the crosslinking agent-containing aqueous solution is usually 2 to 15 parts by weight per 100 parts by weight of water, and preferably 5 to 12 parts by weight. When iodine is used as the dichroic pigment, the aqueous solution containing a crosslinking agent preferably contains potassium iodide. The amount of potassium iodide in the aqueous solution containing a crosslinking agent is usually 0.1 to 15 parts by weight per 100 parts by weight of water, preferably 5 to 12 parts by weight. The temperature of the aqueous solution containing the crosslinking agent is usually 50 ℃ or higher, preferably 50 to 85 ℃.

The crosslinked polyvinyl alcohol resin film is usually washed with water. The water washing treatment is performed by, for example, immersing the crosslinked polyvinyl alcohol resin film in water. The temperature of water during the water washing treatment is usually about 1-40 ℃.

After washing with water, the polarizing film 5 was dried. The drying treatment may be drying by a hot air dryer, drying by contact with a hot roll, drying by a far infrared heater, or the like. The temperature of the drying treatment is usually about 30 to 100 ℃, preferably 50 to 90 ℃.

The thickness of the polarizing film 5 is usually about 2 to 40 μm. From the viewpoint of making the polarizing plate thinner, the thickness of the polarizing film 5 is preferably 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less. The smaller the thickness of the polarizing film 5 is, the more curling of the polarizing plate is likely to occur, and according to the present invention, even if the thickness of the polarizing film 5 is as thin as, for example, 15 μm or less, and further as thin as 10 μm or less, the reverse curling of the obtained polarizing plate can be effectively suppressed or prevented.

By the drying treatment, the moisture content of the polarizing film 5 can be reduced to a practical level. The water content is usually 5 to 20% by weight, preferably 8 to 15% by weight. If the moisture content is less than 5% by weight, the flexibility of the polarizing film 5 is lost, and the polarizing film 5 may be damaged or broken after drying. When the water content exceeds 20% by weight, the thermal stability of the polarizing film 5 may be poor. The water content is measured by the dry weight method, and the measurement method is as described above.

(3-2) No. 2 thermoplastic resin film

The 2 nd thermoplastic resin film 20 is composed of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin, similarly to the 1 st thermoplastic resin film 10. As a specific example of the thermoplastic resin capable of constituting the 2 nd thermoplastic resin film 20, the example described for the 1 st thermoplastic resin film 10 can be cited. However, the thermoplastic resin constituting the 2 nd thermoplastic resin film 20 may be selected so that the equilibrium moisture content of the film at a temperature of 23 ℃ and a relative humidity of 55% is lower than that of the 1 st thermoplastic resin film 10.

The 2 nd thermoplastic resin film 20 may be a protective film having an optical function as well as a temporary protective film, a retardation film, or a brightness enhancement film, similarly to the 1 st thermoplastic resin film 10. The 2 nd thermoplastic resin film 20 may further have a surface treatment layer (surface coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer laminated on the surface thereof. The thickness of the 2 nd thermoplastic resin film 20 is usually 1 to 100 μm, and is preferably 5 to 60 μm, and more preferably 5 to 50 μm from the viewpoint of strength, handling property, and the like. The smaller the thickness of the 2 nd thermoplastic resin film 20 is, the more likely the polarizing plate becomes to curl, but according to the present invention, even if the thickness of the 2 nd thermoplastic resin film 20 is as thin as, for example, 40 μm or less, and further as thin as 30 μm or less, the reverse curl of the obtained polarizing plate can be effectively suppressed or prevented.

As described above, the equilibrium moisture content (and moisture permeability) of the thermoplastic resin film can be adjusted depending on the material (type of thermoplastic resin constituting the film), the thickness of the film, the presence or absence of a surface treatment layer (surface coating layer) that can be attached to the surface of the film, the material, and the like. Therefore, the 1 st thermoplastic resin film 10 and the 2 nd thermoplastic resin film 20 are films having different equilibrium water content from each other, and may be made of the same thermoplastic resin.

The equilibrium moisture content of the 2 nd thermoplastic resin film 20 is usually 0.05 to 1.5% by weight, preferably 0.05 to 1% by weight. The 2 nd thermoplastic resin film 20 has a moisture permeability of usually 1 to 350 g/(m)²24hr), preferably 5 to 200 g/(m)²24 hr). Examples of the thermoplastic resin constituting the 2 nd thermoplastic resin film 20 which can achieve the above-mentioned balance of moisture content and moisture permeability are a cyclic polyolefin-based resin, (meth) acrylate-based resin, polyester-based resin, chain polyolefin-based resin, and the like.

The 2 nd thermoplastic resin film 20 may be subjected to the same humidification treatment or combination of heating treatment and humidification treatment as the 1 st thermoplastic resin film 10 before the laminating step S300, but from the viewpoint of suppressing or preventing reverse curling of the polarizing plate, it is preferable that the 2 nd thermoplastic resin film 20 is not subjected to the humidification treatment or combination of heating treatment and humidification treatment. However, by subjecting the 2 nd thermoplastic resin film 20 to the same heat treatment as the 1 st thermoplastic resin film 10, the surface of the 2 nd thermoplastic resin film 20 can be smoothed.

(3-3) laminating step

Referring to fig. 3, the lamination of the polarizing film 5 in this step with the 1 st and 2 nd thermoplastic resin films 10 and 20 can be continuously performed while continuously conveying long products of the respective raw material films, for example. The raw material films may be conveyed so that the longitudinal direction thereof is the conveying direction. The film transport path may be provided with a guide roller (free roller) 60 for supporting the traveling film, and a driving roller such as a nip roller as needed. In general, the direction of conveyance of the polarizing film 5 (film longitudinal direction) is parallel to the direction of conveyance of the 1 st and 2 nd thermoplastic resin films 10 and 20 (film longitudinal direction).

When the 1 st and 2 nd thermoplastic resin films 10 and 20 are both protective films or protective films having an optical function, the 1 st and 2 nd thermoplastic resin films 10 and 20 are generally laminated and adhered to the polarizing film 5 via the 1 st and 2 nd adhesive layers 15 and 25, respectively. Specifically, as shown in fig. 3, the 1 st thermoplastic resin film 10, the polarizing film 5, and the 2 nd thermoplastic resin film 20 are stacked in parallel with the longitudinal direction (the transport direction) thereof and passed between a pair of bonding rollers 40, and the stacked films are pressed up and down to laminate and bond the films, and at this time, before passing between the bonding rollers 40, the 1 st adhesive 50 and the 2 nd adhesive 55 are injected between the polarizing film 5 and the 1 st thermoplastic resin film 10 and between the polarizing film 5 and the 2 nd thermoplastic resin film 20 by using the 1 st injection device 90 and the 2 nd injection device 91, respectively, to form adhesive layers therebetween.

After lamination, the adhesive layer is dried and/or cured, thereby obtaining the double-sided protective polarizing plate 1 shown in fig. 2. The 1 st adhesive layer 15 is formed of a 1 st adhesive 50, and the 2 nd adhesive layer 25 is formed of a 2 nd adhesive 55.

The method of forming the adhesive layer between the films is not limited to the injection by the injection devices 90 and 91, and for example, coating methods such as a doctor blade method (ドクターブレード method), a wire-bar coating method (wire-bar coating method), a die coating method, a doctor blade method (カンマコーター method), a gravure coating method, a dip coating method, and a casting method may be appropriately selected depending on the viscosity of the adhesive, and the adhesive may be applied to the bonding surface of at least one of the films to be stacked.

Before laminating and adhering the 1 st and 2 nd thermoplastic resin films 10 and 20 to the polarizing film 5, the adhering surface of the polarizing film 5 and/or the 1 st and 2 nd thermoplastic resin films 10 and 20 may be subjected to surface activation treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, or saponification treatment. By this surface activation treatment, the adhesiveness between the polarizing film 5 and the 1 st and 2 nd thermoplastic resin films 10 and 20 can be improved.

As the 1 st adhesive 50 and the 2 nd adhesive 55, an aqueous adhesive, an active energy ray-curable adhesive, or a thermosetting adhesive can be used, and an aqueous adhesive or an active energy ray-curable adhesive is preferable. The 1 st adhesive 50 and the 2 nd adhesive 55 may be the same type of adhesive or different types of adhesives. When different types of adhesives are used, curling of the polarizing plate is likely to occur, but according to the present invention, reverse curling of the polarizing plate can be effectively suppressed or prevented even in such a case.

The aqueous adhesive is an adhesive obtained by dissolving or dispersing an adhesive component in water. The water-based adhesive preferably used is an adhesive composition containing a polyvinyl alcohol resin or a polyurethane resin as a main component.

When a polyvinyl alcohol resin is used as a main component of the adhesive, the polyvinyl alcohol resin may be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol or completely saponified polyvinyl alcohol, or may be a modified polyvinyl alcohol resin such as carboxyl-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, hydroxymethyl-modified polyvinyl alcohol, or amino-modified polyvinyl alcohol. The polyvinyl alcohol resin may be a polyvinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate.

The aqueous adhesive containing a polyvinyl alcohol resin as an adhesive component is usually an aqueous solution of a polyvinyl alcohol resin. The concentration of the polyvinyl alcohol resin in the adhesive is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of water.

In order to improve the adhesiveness, the adhesive composed of an aqueous solution of a polyvinyl alcohol resin preferably contains a curing component such as a polyaldehyde, a melamine compound, a zirconium oxide compound, a zinc compound, glyoxal, a glyoxal derivative, or a water-soluble epoxy resin, or a crosslinking agent. As the water-soluble epoxy resin, for example, a polyamidoamine epoxy resin obtained by reacting epichlorohydrin with polyamidoamine obtained by reacting polyalkylene polyamine such as diethylenetriamine, triethylenetetramine and the like with dicarboxylic acid such as adipic acid and the like can be preferably used. Commercially available products of polyamide polyamine epoxy resins include "Sumirez 650" (スミレーズレジン 650) (manufactured by okra chemical industry (ltd) ")," Sumirez 675 "(manufactured by okra chemical industry (ltd)"), "WS-525" (manufactured by PMC (ltd) ") and the like. The amount of the curable component and the crosslinking agent added (the total amount of the curable component and the crosslinking agent when added simultaneously) is usually 1 to 100 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the polyvinyl alcohol resin. When the amount of the above-mentioned curable component and crosslinking agent added is less than 1 part by weight based on 100 parts by weight of the polyvinyl alcohol resin, the effect of improving the adhesiveness tends to be small, and when the amount added exceeds 100 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin, the adhesive layer tends to become brittle.

In addition, as a preferable example when a polyurethane resin is used as a main component of the adhesive, a mixture of a polyester ionomer polyurethane resin and a compound having a glycidyloxy group can be mentioned. The polyester ionomer type polyurethane resin is a polyurethane resin having a polyester skeleton, and a small amount of an ionic component (hydrophilic component) is introduced therein. The ionomer type polyurethane resin is preferably used as an aqueous adhesive because it is emulsified in water as it is without using an emulsifier to form an emulsion.

The active energy ray-curable adhesive is an adhesive that is cured by irradiation with an active energy ray such as an ultraviolet ray, a visible light, an electron beam, or an X-ray. When an active energy ray-curable adhesive is used, the adhesive layer of the polarizing plate is a cured layer of the adhesive.

The active energy ray-curable adhesive may be an adhesive containing an epoxy compound that is cured by cationic polymerization as a curable component, and is preferably an ultraviolet-curable adhesive containing the epoxy compound as a curable component. The epoxy compound as used herein means a compound having an average of 1 or more, preferably 2 or more, epoxy groups in the molecule. The epoxy compound may be used alone in 1 kind, or 2 or more kinds may be used in combination.

Specific examples of the epoxy-based compound which can be preferably used include: a hydrogenated epoxy compound (glycidyl ether of a polyol having an alicyclic ring) obtained by reacting an alicyclic polyol obtained by hydrogenation on an aromatic ring of an aromatic polyol with epichlorohydrin; aliphatic epoxy compounds such as polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene adducts thereof; an alicyclic epoxy compound which is an epoxy compound having 1 or more epoxy groups bonded to an alicyclic ring in a molecule.

The active energy ray-curable adhesive may contain, as a curable component, a radically polymerizable (meth) acrylate compound in place of the epoxy compound, or may contain both the radically polymerizable (meth) acrylate compound and the epoxy compound. Examples of the (meth) acrylate-based compound include (meth) acrylate monomers having at least 1 (meth) acryloyloxy group in the molecule; a (meth) acryloyloxy group-containing compound such as a (meth) acrylate oligomer having at least 2 (meth) acryloyloxy groups in the molecule, which is obtained by reacting 2 or more functional group-containing compounds.

When the active energy ray-curable adhesive contains an epoxy compound that is cured by cationic polymerization as a curable component, it preferably contains a photo cationic polymerization initiator. Examples of the photo cation polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; iron-arene complexes, and the like. When the active energy ray-curable adhesive contains a radical polymerizable curable component such as a (meth) acrylate compound, a photoradical polymerization initiator is preferably contained. Examples of the photo radical polymerization initiator include acetophenone type initiators, benzophenone type initiators, benzoin ether type initiators, thioxanthone type initiators, xanthone, fluorenone, camphorquinone, benzaldehyde, and anthraquinone.

One of the 1 st and 2 nd thermoplastic resin films 10 and 20 may be a temporary protective film for temporarily protecting the surface of the polarizing film 5. In this case, in the laminating step S300, the temporary protective film is laminated in place of the polarizing film 5 and the temporary protective film with a volatile liquid or without any adhesive. The temporary protective film is a film that can be peeled off from the polarizing film 5, and can be peeled off and removed at a desired time (for example, the polarizing plate is stuck to a liquid crystal element) after the polarizing plate is manufactured. "peelable" means that the polarizing film 5 and the temporary protective film can be separated without damaging or injuring the polarizing film 5 and the temporary protective film.

As an example, fig. 4 shows a layer structure of a single-sided protective polarizing plate 2 obtained by performing a laminating step S300 of a 2 nd thermoplastic resin film 20 as a temporary protective film and then peeling off and removing the temporary protective film.

When the temporary protective film is used, it is preferable that a volatile liquid be present between the polarizing film 5 and the temporary protective film in the laminating step S300. This can prevent the polarizing film 5 from being broken during the process of manufacturing the polarizing plate or prevent wrinkles from being generated in the film laminate including the polarizing film 5, as compared with the case where none of them is present.

The peeling force between the polarizing film 5 and the temporary protective film is, for example, 0.01 to 0.5N/25mm, preferably 0.01 to 0.2N/25mm, and more preferably 0.01 to 0.15N/25 mm. When the peeling force is less than 0.01N/25mm, the adhesion between the polarizing film 5 and the temporary protective film is small, and therefore, partial peeling of the temporary protective film may occur, or the polarizing film 5 may be torn in the stretching direction in a storage tube in a state where the single-sided protective polarizing plate with the temporary protective film is wound up in a roll. When the peel force exceeds 0.5N/25mm, it becomes difficult to peel the temporary protective film from the polarizing film 5, and therefore, the polarizing film 5 is easily torn in the stretching direction when the temporary protective film is peeled.

The peeling force can be obtained as follows: the one-sided protective polarizing plate with the temporary protective film was cut into a width of 25mm to obtain a measurement sample, and the temporary protective film and the one-sided protective polarizing plate of the measurement sample were grasped by a precision universal tester "AUTOGRAPHAGS-50 NX" (オートグラフ AGS-50 NX) manufactured by Shimadzu corporation to measure the force at the time of peeling in the 180 ℃ direction. The peel force was measured at a peel speed of 300mm/min, at a temperature of 23. + -. 2 ℃ and at a relative humidity of 50. + -. 5%.

The existing volatile liquid is volatilized and removed after the laminating step S300. Thus, a single-sided protective polarizing plate with a temporary protective film can be obtained. Fig. 5 shows an example of the layer structure of the one-sided protective polarizing plate 3 with a temporary protective film. In the example of fig. 5, the 2 nd thermoplastic resin film 20 is a temporary protective film. The volatile liquid can be removed by evaporation by heating. By this heat treatment, the temporary protective film is directly laminated on the surface of the polarizing film 5 with a moderate adhesive force. The heating temperature is, for example, 30 to 90 ℃.

The volatile liquid is a liquid that can be volatilized by the heat treatment, and is preferably a liquid that does not adversely affect the polarizing film 5. An antistatic agent may be added as long as it does not adversely affect the properties. Examples of the volatile liquid include water, and a mixture of water and a hydrophilic liquid. The hydrophilic liquid is preferably a liquid that does not remain after heat treatment, and examples thereof include methanol, ethanol, 1-butanol, tetrahydrofuran, acetone, acetonitrile, N-dimethylformamide, dimethyl sulfoxide, formic acid, acetic acid, and the like.

(4) Other procedures

When an aqueous adhesive is used for laminating and affixing the polarizing film 5 and the 1 st and/or 2 nd thermoplastic resin films 10 and 20, it is preferable to perform a drying step for removing water contained in the aqueous adhesive after the laminating step S300. The drying temperature is, for example, 30 to 90 ℃. When the temporary protective film is laminated on the polarizing film 5 via the volatile liquid, the drying step may also be combined with the above-described heating treatment for volatilizing and removing the volatile liquid. After the drying step, a curing step of curing at a temperature of, for example, 20 to 50 ℃, preferably 30 to 45 ℃ may be provided.

When the active energy ray-curable adhesive is used for laminating and bonding the polarizing film 5 and the 1 st and/or 2 nd thermoplastic resin films 10 and 20, a drying step is performed as necessary after the laminating step S300, and then a curing step of curing the active energy ray-curable adhesive by irradiation with an active energy ray is performed. The light source of the active energy ray is not particularly limited, and ultraviolet rays having an emission distribution at a wavelength of 400nm or less are preferable, and specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-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.

The irradiation intensity of the active energy ray to the adhesive layer formed of the active energy ray-curable adhesive can be appropriately determined depending on the composition of the adhesive, and is preferably 0.1 to 6000mW/cm in accordance with the irradiation intensity in the wavelength region effective for activation of the polymerization initiator²The mode of (2). The irradiation intensity is 0.1mW/cm²When the above is adopted, the reaction time is too long, and is 6000mW/cm²In the following case, yellowing of the adhesive layer and deterioration of the polarizing film 5 due to heat radiated from the light source and heat generation during curing of the adhesive are less likely to occur.

The irradiation time of the active energy ray can be appropriately determined depending on the composition of the adhesive, and is preferably determined so that the integrated light quantity expressed as the product of the irradiation intensity and the irradiation time is 10 to 10000mJ/cm²The mode of (2). The integrated light quantity is 10mJ/cm²In the above case, the amount of active species derived from the polymerization initiator is 10000mJ/cm, which enables the generation of a sufficient amount of active species and the curing reaction to proceed more reliably²In the following case, the irradiation time does not become excessively long, and good productivity can be maintained.

When the laminating step S300 is performed using the temporary protective film for one of the 1 st and 2 nd thermoplastic resin films 10 and 20, the one-sided protective polarizing plate 3 with the temporary protective film shown in fig. 5, for example, can be obtained as described above, and the temporary protective film is peeled off and removed therefrom, whereby the one-sided protective polarizing plate 2 shown in fig. 4, for example, can be obtained. As described above, in fig. 4 and 5, the 2 nd thermoplastic resin film 20 is used as the temporary protective film, but the 1 st thermoplastic resin film 10 may be used as the temporary protective film. The adhesive layer 30 may be laminated on the polarizing film surface of the single-sided protective polarizing plate 2 on which the temporary protective film is laminated, to obtain the adhesive layer-attached single-sided protective polarizing plate 4 shown in fig. 6, for example. The adhesive layer 30 can be used for attaching a single-sided protective polarizing plate to a liquid crystal cell.

In the double-sided protective polarizing plate 1 shown in fig. 2, the adhesive layer 30 may be laminated on the outer surface of the 1 st thermoplastic resin film 10 or the 2 nd thermoplastic resin film 20. The adhesive layer 30 can be used for attaching the double-sided protective polarizing plate 1 to a liquid crystal cell. In the double-sided protective polarizing plate 1, the adhesive layer 30 is preferably laminated on the outer surface of the 2 nd thermoplastic resin film 20.

The adhesive layer 30 may be formed of an adhesive composition containing a resin such as a (meth) acrylate-based, rubber-based, urethane-based, ester-based, silicone-based, or polyvinyl ether-based resin as a main component (base polymer). Among these, an adhesive composition containing a (meth) acrylate resin having excellent transparency, weather resistance, heat resistance, and the like as a base polymer is preferable. The adhesive composition may be an active energy ray-curable adhesive composition or a thermosetting adhesive composition.

As the (meth) acrylate-based resin used in the adhesive composition, for example, a polymer or copolymer of 1 or 2 or more kinds of (meth) acrylic esters as monomers such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate is preferably used. The (meth) acrylate-based resin is preferably obtained by copolymerizing a polar monomer. Examples of the polar monomer include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like, such as (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth) acrylamide, N-dimethylaminoethyl (meth) acrylate, and glycidyl (meth) acrylate.

The adhesive composition may contain only the base polymer, and usually further contains a crosslinking agent. Examples of the crosslinking agent include: a metal salt of a carboxylic acid is formed between a metal ion having a valence of 2 or more and a carboxyl group; polyamine compounds which form amide bonds with carboxyl groups; is a polyepoxy compound or a polyol, which forms an ester bond with a carboxyl group; is a polyisocyanate compound, which forms an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

The active energy ray-curable adhesive composition is a composition having a property of being cured by irradiation with an active energy ray such as an ultraviolet ray or an electron ray, and has: an adhesive composition which is adhesive even before irradiation with an active energy ray, can adhere an adherend such as a film, can be cured by irradiation with an active energy ray, and can adjust the properties of adhesion. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable adhesive composition. The active energy ray-curable adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the crosslinking agent. Further, a photopolymerization initiator, a photosensitizer, and the like may be contained as necessary.

The adhesive composition may contain additives such as fine particles, beads (resin beads, glass beads, and the like), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powder, other inorganic powder, and the like), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, preservatives, and photopolymerization initiators for imparting light scattering properties.

The adhesive layer 30 can be formed by applying a diluted organic solvent solution of the adhesive composition onto the adhesive layer-formed surface of the polarizing plate (i.e., the polarizing film 5, the 1 st or 2 nd thermoplastic resin films 10 and 20) and drying the same. Alternatively, a diluent of the adhesive composition in an organic solvent may be applied to a release film (a thermoplastic resin film subjected to a release treatment), dried to form an adhesive layer, and then transferred to the adhesive layer-formed surface of the polarizing plate. In either method, a release film is preferably attached to the outer surface of the adhesive layer 30 to protect the adhesive layer 30 until use. When an active energy ray-curable adhesive composition is used, a cured product having a desired degree of curing can be formed by irradiating the formed adhesive layer with an active energy ray. The thickness of the adhesive layer 30 is usually 1 to 40 μm, but is preferably 3 to 25 μm from the viewpoint of making the polarizing plate thin.

The method may further comprise a step of laminating a protective film on the outer surface of the 1 st and/or 2 nd thermoplastic resin film 10, 20 of the double-sided protective polarizing plate 1 or the single-sided protective polarizing plate 2. The protective film is composed of a base film and an adhesive layer laminated thereon. The protective film is a film for protecting the surface of the polarizing plate, and is usually peeled off and removed together with an adhesive layer provided thereon after the polarizing plate with the protective film is attached to, for example, a liquid crystal cell. The base film may be made of a thermoplastic resin, for example, a polyolefin resin such as a polyethylene resin and a polypropylene resin; a cyclic polyolefin resin; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; a polycarbonate-based resin; and (meth) acrylate resins.

Further, a step of laminating an optical film other than the polarizing film on the outer surface of the 1 st and/or 2 nd thermoplastic resin film 10, 20 of the double-sided protective polarizing plate 1 or the single-sided protective polarizing plate 2 may be provided. Examples of other optical films include a retardation film, a brightness enhancement film, and the like. The other optical films may be laminated and attached via an adhesive layer or an adhesive layer.

According to the manufacturing method of the present invention, a single sheet of a polarizing plate (double-sided protective polarizing plate or single-sided protective polarizing plate) in which reverse curling is favorably suppressed or prevented can be obtained. As described above, the reverse curl is a curl in which the 2 nd main surface opposite to the side capable of being attached to an image display element such as a liquid crystal element is convex, and is typically a curl in which the 1 st thermoplastic resin film 10 side is convex in the double-sided protective polarizing plate 1 or the single-sided protective polarizing plate 2. Such reverse curling of the protrusion on the 1 st thermoplastic resin film 10 side can be favorably suppressed or prevented in the single sheet of the polarizing plate obtained by the present invention, and typically, the sheet is in a flat plate shape having no curling, a shape having a little positive curling, or a shape having a little reverse curling. A flat plate shape with no curl, or a shape with a little positive curl is desirable.

[ examples ] A method for producing a compound

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following examples, the equilibrium water content, moisture permeability, and thickness of the film, and the amount of curl of the polarizing plate were measured by the following methods.

(1) Equilibrium water content W of film_H

A test piece having a MD length of 150 mm. times.TD length of 100mm was cut out. The weight of the film after storage at 23 ℃ and 55% relative humidity for 24 hours was measured. Thereafter, the film was dried at 105 ℃ for 2 hours, and the weight of the film after the drying was measured. The equilibrium water content W was determined from the film weight before and after drying according to the following equation_H：

Equilibrium moisture content (wt%) { (weight of film before drying treatment-weight of film after drying treatment)/weight of film before drying treatment } × 100.

(2) Water content W of film

A test piece having a length of MD of 150 mm. times.TD of 100mm was cut out, and its weight was measured immediately. Subsequently, the film was dried at 105 ℃ for 2 hours, and the weight of the film after the drying was measured. The water content W was determined from the weight of the film before and after drying based on the following formula:

water content (% by weight) { (weight of film before drying treatment — weight of film after drying treatment)/weight of film before drying treatment } × 100.

(3) Moisture permeability of film

The measurement temperature was 40 ℃ according to the moisture-permeable cup method defined in JIS Z0208Water vapor transmission rate [ g/(m DEG C.) at relative humidity of 90%²·24hr)〕。

(4) Thickness of the film

The measurement was carried out using a digital micrometer "MH-15M" manufactured by Nikon corporation of (digital micrometer, Inc.; ニコン).

(5) Curl amount of polarizing plate

A300 mm × 200mm test piece was cut out from the double-sided protective polarizing plate so that the absorption axis direction (MD) thereof was 45 degrees with respect to each side, and the test piece was left to stand at 25 ℃ under an atmosphere of 55% relative humidity for 24 hours. The test piece was placed on a reference surface (horizontal table) with its concave surface facing upward, i.e., with its 4 ends raised. In this state, the heights of the 4 corners of the test piece from the reference plane were measured, and the heights of the 4 corners were averaged to determine the curl [ mm ]. When the curl amount is a positive value, it means that the 1 st thermoplastic resin film side becomes concave (positive curl), and when it is a negative value, it means that the 2 nd thermoplastic resin film side becomes concave (reverse curl). In the double-sided protective polarizing plates of examples 2 and 3, no curling occurred on either the 1 st thermoplastic resin film side or the 2 nd thermoplastic resin film side.

< example 1 >

(A) Production of polarizing film

While continuously conveying a long polyvinyl alcohol film (average polymerization degree: about 2400, saponification degree: 99.9 mol% or more, thickness: 30 μm), the film was uniaxially stretched in a dry state to about 4 times, and further immersed in pure water at 40 ℃ for 1 minute in a state of being kept in a tense state, and then immersed in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.1/5/100 at 28 ℃ for 60 seconds. Thereafter, the plate was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10.5/7.5/100 at 68 ℃ for 300 seconds. Subsequently, the film was washed with pure water at 5 ℃ for 5 seconds and then dried at 70 ℃ for 180 seconds to obtain a long polarizing film in which iodine was oriented and adsorbed on the uniaxially stretched polyvinyl alcohol film. The thickness of the polarizing film was 11 μm.

(B) Manufacture of double-side protective polarizing plate

The polarizing plate manufacturing apparatus shown in FIG. 3 was usedThe same apparatus was set up to produce a double-sided protective polarizing plate in the following order. While continuously conveying a long 1 st thermoplastic resin film (a TAC film "KC 2 UAW" made by Konica Minolta Opto Products co., Ltd (コニカミノルタオプト strain)), thickness: 25 μm, equilibrium water content W_H: 3.0 wt%, moisture permeability: 1207 g/(m)²24 hr)), a heating furnace set to a furnace temperature of 95 ℃ and a furnace relative humidity of 3%, and a humidifying furnace set to a furnace temperature of 50 ℃ and a furnace relative humidity of 70%, to perform a film humidifying treatment. The residence time of the film in the drying furnace and the humidifying furnace was 8 seconds and 12 seconds, respectively. The humidifying furnace is arranged behind the heating furnace, and the temperature of the film just before the humidifying furnace is introduced is almost the same as the temperature in the heating furnace. Both the heating furnace and the humidifying furnace increase the temperature in the furnace by supplying hot air. The moisture content W of the 1 st thermoplastic resin film after the humidification treatment was 3.1 wt%.

The polarizing film obtained in (a) above was continuously transferred, and the humidified 1 st thermoplastic resin film and the long 2 nd thermoplastic resin film [ a cyclic polyolefin resin film manufactured by JSR (japan) trade name "FEKB 015D 3", thickness: 15 μm, equilibrium water content W_H: 0.8 wt%, moisture permeability: 115 g/(m)²24hr) and used as it is without heating or humidifying the purchased product, a laminate film comprising 1 st thermoplastic resin film/aqueous adhesive layer/polarizing film/aqueous adhesive layer/2 nd thermoplastic resin film was prepared between laminating rollers while injecting an aqueous adhesive between the polarizing film and the 1 st thermoplastic resin film and between the polarizing film and the 2 nd thermoplastic resin film (step 1). The laminating step is performed within 10 seconds after the humidifying treatment of the 1 st thermoplastic resin film.

The aqueous adhesive is an aqueous solution obtained by using: polyvinyl alcohol powder [ GOHSEFIMER (ゴーセファイマー) (trade name, manufactured by Nippon synthetic chemical industry Co., Ltd.); average degree of polymerization 1100 ] was dissolved in hot water at 95 ℃ to obtain a 3 wt% polyvinyl alcohol aqueous solution, and a crosslinking agent [ sodium glyoxylate manufactured by Nippon synthetic chemical industry Co., Ltd. ]wasmixed thereto in a ratio of 1 part by weight to 10 parts by weight of the polyvinyl alcohol powder ].

Next, the obtained laminated film was conveyed, and the aqueous adhesive layer was dried by heat treatment at 80 ℃ for 300 seconds in a hot air dryer, thereby obtaining a double-sided protective polarizing plate.

< examples 2 to 3 and comparative examples 1 to 3 >

A double-sided protective polarizing plate was produced in the same manner as in example 1, except that the furnace environments of the heating furnace and the humidifying furnace and the residence time of the film were as shown in table 1. In comparative examples 2 and 3, the heat treatment of the 1 st thermoplastic resin film was not performed.

The curl amounts of the double-sided protective polarizing plates obtained in examples 1 to 3 and comparative examples 1 to 3 are shown in table 1. Table 1 shows the furnace environments of the heating furnace and the humidifying furnace and the residence time of the thin film. The outer surface 1 shows the moisture content W of the 1 st thermoplastic resin film after the humidification treatment and the equilibrium moisture content W of the 1 st thermoplastic resin film_HAnd the moisture content W after the humidification treatment and the equilibrium moisture content W_HThe difference between them. In comparative example 1, the 1 st thermoplastic resin film was passed through a humidifying furnace, but the humidifying treatment was not performed. In comparative example 1 of table 1, the numerical value described in the column "moisture content after humidification" means the moisture content of the 1 st thermoplastic resin film after passing through the humidification furnace.

In any of examples 1 to 3, comparative examples 1 and 3, no trace of condensation was observed on the surface of the 1 st thermoplastic resin film. In comparative example 2, a trace of condensation was observed on the surface of the 1 st thermoplastic resin film.

[ TABLE 1]

< examples 4 and 5 >

As the 1 st thermoplastic resin film, a hard coat film (a film in which a hard coat layer is formed on a TAC film "KC 2 UAW" made by Konica Minolta Opto products co., Ltd, thickness: 32.4 mum, equilibrium water content W_H: 1.9% by weight, moisture permeability: 455 g/(m)²24 hr)), a cyclic polyolefin resin film [ product name "ZF 14-023" manufactured by zeon corporation, thickness: 22.9 μm, equilibrium water content W_H: 0.1 wt%, moisture permeability: 17 g/(m)²24 hr)), the furnace environments of the heating furnace and the humidifying furnace, and the residence time of the film are shown in table 2, and a double-sided protective polarizing plate was produced in the same manner as in example 1. The curl amounts of the double-sided protective polarizing plates obtained in examples 4 and 5 are shown in table 2. Table 2 shows the furnace environments of the heating furnace and the humidifying furnace and the residence time of the thin film. Further, in Table 2, the moisture content W of the 1 st thermoplastic resin film after the humidification treatment and the equilibrium moisture content W of the 1 st thermoplastic resin film are shown_HAnd the moisture content W after the humidification treatment and the equilibrium moisture content W_HThe difference between them.

[ TABLE 2]

Claims (11)

1. A method for manufacturing a polarizing plate, comprising the steps of:

a step of heat-treating the 1 st thermoplastic resin film having a thickness of 40 μm or less,

a step of subjecting the 1 st thermoplastic resin film to a humidification treatment so that the difference between the moisture content of the 1 st thermoplastic resin film after the humidification treatment and the equilibrium moisture content of the 1 st thermoplastic resin film at a temperature of 23 ℃ and a relative humidity of 55% is 0.1 wt% or more and 3 wt% or less, and

and a step of laminating the 1 st thermoplastic resin film on one surface of the polarizing film and a 2 nd thermoplastic resin film having a thickness of 40 μm or less on the other surface of the polarizing film, wherein the 2 nd thermoplastic resin film has a lower equilibrium moisture content at a temperature of 23 ℃ and a relative humidity of 55% than the 1 st thermoplastic resin film.

2. The manufacturing method according to claim 1, wherein the 2 nd thermoplastic resin film is not subjected to the humidification treatment.

3. The production method according to claim 1, wherein the 1 st thermoplastic resin film comprises a cellulose-based resin film.

4. The production method according to claim 1, wherein the 2 nd thermoplastic resin film comprises a cyclic polyolefin resin film.

5. The production method according to claim 1, wherein the temperature during the heating treatment is equal to or higher than the temperature during the humidifying treatment.

6. The production method according to claim 5, wherein the temperature during the heating treatment is higher than the temperature during the humidifying treatment by 30 ℃ or more.

7. The production method according to claim 1, wherein in the step of performing the heat treatment, the 1 st thermoplastic resin film is heat-treated in an environment in which a temperature is 50 ℃ or higher and a relative humidity is 50% or lower.

8. The production method according to claim 1, wherein in the step of performing the humidification treatment, the 1 st thermoplastic resin film is humidified in an environment having a temperature of 40 ℃ or higher and a relative humidity of 60% or higher.

9. The manufacturing method according to claim 1, wherein at least one of the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film is laminated on the polarizing film via an adhesive layer.

10. The manufacturing method according to claim 1, wherein the thickness of the polarizing film is 15 μm or less.

11. The production method according to any one of claims 1 to 10, wherein in the step of subjecting to the humidification treatment, the 1 st thermoplastic resin film is subjected to humidification treatment such that a water content thereof is higher than an equilibrium water content of the 1 st thermoplastic resin film at a temperature of 23 ℃ and a relative humidity of 55%.

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