KR102587187B1 - Method for producing polarizing plate - Google Patents

Abstract

A step of heat-treating the first thermoplastic resin film, a step of humidifying the first thermoplastic resin film, laminating the first thermoplastic resin film on one side of the polarizing film, and laminating the first thermoplastic resin film on the other side of the polarizing film. A method of manufacturing a polarizing plate is provided, including the step of laminating a second thermoplastic resin film having a lower equilibrium moisture content at a temperature of 23° C. and a relative humidity of 55% than that of the thermoplastic resin film in this order.

Description

Manufacturing method of polarizing plate {METHOD FOR PRODUCING POLARIZING PLATE}

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

Recently, mobile terminals such as smart phones are rapidly becoming larger and slimmer in terms of design and portability. In order to realize long-term operation with a limited thickness, there is a demand for high brightness, thinness, and weight reduction for the polarizing plate used.

Conventionally, as a polarizing plate, a polarizing film made of a polyvinyl alcohol-based resin is generally used by bonding a protective film made of triacetylcellulose (TAC) with an adhesive. However, in recent years, from the viewpoint of thinning, durability, cost, productivity, etc., protective films made of resins other than TAC have also been used (e.g., Japanese Patent Laid-Open No. 2004-245925).

The polarizer is sensitive to the environment in which it is placed, and depending on the environmental conditions, it is prone to bending into an arc shape. In this specification, this deformation is also called “curl.” The thinner a polarizer becomes, the more likely it is to curl. There are two types of curls: “normal curls” and “reverse curls.” In a polarizing plate, there is a first main surface on the side bonded to an image display element such as a liquid crystal cell and a second main surface on the opposite side. A “normal curl” is a curl that makes the first main surface side convex, and a “reverse curl” is a curl that makes the first main surface side convex. 」 means a curl that makes the second main surface side convex. If reverse curl occurs in the polarizing plate, when it is bonded to an image display element through an adhesive layer, it is easy to cause a bonding error or a defect such as air bubbles being mixed into the interface between the adhesive layer and the image display element. In order to suppress these defects and perform bonding of the polarizing plate and the image display element with high productivity, it is most preferable that the polarizing plate is flat. However, there is no particular problem in terms of the above defects and productivity if the curls formed are regular.

Additionally, Japanese Patent Laid-Open No. 2006-030480 describes adjusting the moisture content of the protective film within a predetermined range prior to laminating the polarizing film and the protective film in order to suppress stripe-shaped irregularities occurring on the polarizing plate.

The purpose of the present invention is to provide a method for producing a polarizing plate that does not have reverse curl or has reverse curl suppressed.

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

[1] A process of heat treating the first thermoplastic resin film,

A process of humidifying the first thermoplastic resin film;

The first thermoplastic resin film is laminated on one side of the polarizing film, and a second thermoplastic film having a lower equilibrium moisture content at a temperature of 23° C. and a relative humidity of 55% is applied on the other side of the polarizing film. Process of laminating resin films

A method of manufacturing a polarizing plate comprising in this order.

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

[3] The manufacturing method according to [1] or [2], wherein the first thermoplastic resin film includes a cellulose-based resin film.

[4] The manufacturing method according to any one of [1] to [3], wherein the second thermoplastic resin film includes a cyclic polyolefin-based resin film.

[5] The manufacturing method according to any one of [1] to [4], wherein the temperature during the heat treatment is equal to or higher than the temperature during the humidification treatment.

[6] The manufacturing method according to [5], wherein the temperature during the heat treatment is at least 30°C higher than the temperature during the humidification treatment.

[7] The manufacturing method according to any one of [1] to [6], wherein in the heat treatment step, the first thermoplastic resin film is heat treated in an environment of a temperature of 50° C. or higher and a relative humidity of 50% or lower.

[8] The manufacturing method according to any one of [1] to [7], wherein in the humidification process, the first thermoplastic resin film is humidified in an environment of a temperature of 40° C. or higher and a relative humidity of 60% or higher.

[9] The manufacturing method according to any one of [1] to [8], wherein at least one of the first thermoplastic resin film and the second thermoplastic resin film is laminated on the polarizing film through an adhesive layer.

[10] The manufacturing method according to any one of [1] to [9], wherein the thickness of the first thermoplastic resin film is 40 μm or less, and the thickness of the second thermoplastic resin film is 40 μm or less.

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

[12] In the humidification process, the first thermoplastic resin film is humidified so that the moisture content is higher than the equilibrium moisture content of the first thermoplastic resin film at a temperature of 23° C. and a relative humidity of 55%, [1 The manufacturing method according to any one of ] to [11].

According to the present invention, a polarizing plate that does not have reverse curl or has reverse curl suppressed can be manufactured.

1 is a flowchart showing an example of a method for manufacturing a polarizing plate according to the present invention.
Figure 2 is a schematic cross-sectional view showing an example of the layer structure of a polarizing plate obtainable according to the manufacturing method according to the present invention.
Figure 3 is a side view schematically showing an example of a method for manufacturing a polarizing plate according to the present invention and a manufacturing apparatus used therefor.
Figure 4 is a schematic cross-sectional view showing an example of the layer structure of a single-sided protection polarizing plate.
Figure 5 is a schematic cross-sectional view showing an example of the layer structure of a single-sided protection polarizing plate with a temporary protection film.
Figure 6 is a schematic cross-sectional view showing an example of the layer structure of a single-sided protective polarizing plate provided with an adhesive layer.

Referring to Figure 1, the method for manufacturing a polarizing plate according to the present invention includes the following processes:

(1) Heat treatment process (S100) of heat treating the first thermoplastic resin film,

(2) Humidification treatment process (S200) for humidifying the first thermoplastic resin film, and

(3) Lamination process (S300) of laminating a first thermoplastic resin film on one side of the polarizing film and laminating a second thermoplastic resin film on the other side of the polarizing film.

Included in this order: As the second thermoplastic resin film, one with a lower equilibrium moisture content than the first thermoplastic resin film is used. The equilibrium moisture content referred to here is the equilibrium moisture content of a film stored for 24 hours in an environment of a temperature of 23°C and a relative humidity of 55%, measured by the dry weight method.

According to the manufacturing method of the present invention, in which a first thermoplastic resin film subjected to heat treatment followed by humidification treatment is laminated on one side of a polarizing film, and a second thermoplastic resin film is laminated on the other side, reverse curl of the obtained polarizing plate is reduced or prevented. can do. As described above, reverse curl refers to a deformation in which the polarizer is bent into an arc shape by making the second main surface on the opposite side to the side bonded to the image display element such as a liquid crystal cell convex. This deformation usually causes the sheet material of the polarizer to bend. It happens because In the case of manufacturing a long polarizing plate using long raw material films (first and second thermoplastic resin films and polarizing films), reverse curl refers to a reverse curl that typically occurs in a polarizing plate sheet obtained by cutting from a long polarizing plate.

An example of the layer structure of a polarizing plate obtained according to the manufacturing method according to the present invention is shown in FIG. 2. The polarizing plate shown in FIG. 2 includes a polarizing film 5, a first thermoplastic resin film 10 bonded to one side through a first adhesive layer 15, and a second adhesive layer 25 to the other side. It is a double-sided protective polarizing plate (1) including a second thermoplastic resin film (20) bonded through. In the double-sided protective polarizing plate 1, the first and second thermoplastic resin films 10 and 20 may be optical films, that is, protective films, that protect the polarizing film 5, and may be formed using an adhesive to form a polarizing film ( 5) Can be adhered to the surface. Other layer structures of the polarizing plate obtained according to the manufacturing method according to the present invention will be described later.

Hereinafter, each process will be described with reference to FIG. 3. Figure 3 is a side view schematically showing an example of a method for manufacturing a polarizing plate according to the present invention and a manufacturing apparatus used therefor. The arrow in FIG. 3 indicates the transport direction of the film. Generally, as shown in FIG. 3, a polarizing plate can be continuously manufactured as a long product by performing processing in each process while continuously unwinding and conveying a long raw material film. However, the manufacturing method of the present invention is not limited to continuous production using such a long raw material film, and a method using a sheet film may be used.

(1) Heat treatment process (S100)

This process is a process of heat treating the first thermoplastic resin film 10. One feature of the present invention is that heat treatment is performed before humidification treatment is performed on the first thermoplastic resin film 10, thereby causing reverse curl of the polarizer (typically, the first thermoplastic resin film 10 ) can be effectively suppressed or prevented, and reverse curl of the polarizing plate can be more effectively suppressed or prevented compared to the case where only humidification treatment is performed.

The first thermoplastic resin film 10 is a film made of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin. Thermoplastic resins constituting the first thermoplastic resin film 10 include, for example, polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); Cellulose-based resins such as triacetylcellulose and diacetylcellulose; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate-based resin; (meth)acrylic resins such as methyl methacrylate resins; polystyrene-based resin; polyvinyl chloride-based resin; Acrylonitrile, butadiene, and styrene-based resin; Acrylonitrile/styrene resin; polyvinyl acetate-based resin; polyvinylidene chloride-based resin; polyamide-based resin; polyacetal resin; Modified polyphenylene ether-based resin; polysulfone-based resin; polyethersulfone-based resin; polyarylate-based resin; polyamideimide-based resin; It may be a polyimide-based resin, etc.

In addition, in this specification, "(meth)acrylic resin" refers to at least one type selected from the group consisting of acrylic resin and methacrylic resin. The same applies to other terms to which “(meta)” is added.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resin and polypropylene resin, as well as copolymers of two or more types of chain olefins. More specific examples include polypropylene-based resins (polypropylene resins that are homopolymers of propylene, or copolymers mainly composed of propylene), polyethylene-based resins (polyethylene resins that are homopolymers of ethylene, or copolymers primarily composed of ethylene). Includes.

Cyclic polyolefin-based resin is a general term for resins polymerized with cyclic olefin as a polymerization unit. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically random copolymers), and unsaturated polymers thereof. These include graft polymers modified with carboxylic acids or their derivatives and their hydrides. Among them, norbornene-based resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers as cyclic olefins are preferably used.

Cellulose resin refers to a resin in which some or all of the hydrogen atoms in the hydroxyl group of cellulose obtained from raw cellulose such as cotton linter or wood pulp (hardwood pulp, softwood pulp) are substituted with acetyl group, propionyl group and/or butyryl group. , refers to cellulose organic acid ester or cellulose mixed organic acid ester. For example, those made of acetic acid ester of cellulose, propionic acid ester, butyric acid ester, and mixed esters thereof. Among them, triacetylcellulose, diacetylcellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferable.

Polyester resin is a resin other than the above cellulose resin that has an ester bond, and is generally composed of a polycondensate of polyhydric carboxylic acid or its derivative and polyhydric alcohol. As the polyhydric carboxylic acid or its derivative, a divalent dicarboxylic acid or a derivative thereof can be used, and examples include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. As the polyhydric alcohol, a diol can be used, and examples include ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol. Examples of suitable polyester-based resins include polyethylene terephthalate.

Polycarbonate-based resin is an engineering plastic made of a polymer in which monomer units are bonded through carbonato groups, and is a resin that has high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called modified polycarbonate, which has a polymer skeleton modified to lower the photoelastic coefficient, or a copolymerized polycarbonate with improved wavelength dependence.

(meth)acrylic resin is a polymer containing structural units derived from (meth)acrylic monomers. The polymer is typically a polymer containing methacrylic acid ester. Preferably, it is a polymer containing a proportion of structural units derived from methacrylic acid ester of 50% by weight or more based on the total structural units. The (meth)acrylic resin may be a homopolymer of methacrylic acid ester, or may be a copolymer containing structural units derived from other polymerizable monomers. In this case, the proportion of structural units derived from other polymerizable monomers is preferably 50% by weight or less based on the total structural units.

As a methacrylic acid ester that can constitute a (meth)acrylic resin, alkyl methacrylic acid ester is preferable. Examples of alkyl methacrylate include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, Examples include alkyl methacrylic acid esters where the alkyl group has 1 to 8 carbon atoms, such as 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and 2-hydroxyethyl methacrylate. The carbon number of the alkyl group contained in the methacrylic acid alkyl ester is preferably 1 to 4. In the (meth)acrylic resin, methacrylic acid ester may be used individually or in combination of two or more types.

Other polymerizable monomers that can form a (meth)acrylic resin include acrylic acid esters and other compounds having a polymerizable carbon-carbon double bond in the molecule. As for other polymerizable monomers, only one type may be used individually or two or more types may be used in combination. As the acrylic acid ester, alkyl acrylic acid ester is preferable. As alkyl acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate. Examples include alkyl acrylic acid esters with an alkyl group having 1 to 8 carbon atoms. The carbon number of the alkyl group contained in the acrylic acid alkyl ester is preferably 1 to 4. In the (meth)acrylic resin, only one type of acrylic acid ester may be used individually or two or more types may be used in combination.

Other compounds having a polymerizable carbon-carbon double bond in the molecule include vinyl-based compounds such as ethylene, propylene, and styrene, and vinyl cyan compounds such as acrylonitrile. Other compounds having a polymerizable carbon-carbon double bond in the molecule may be used individually or in combination of two or more types.

The first thermoplastic resin film 10 may be a protective film for protecting the polarizing film 5, which is laminated and bonded to one side of the polarizing film 5, or may temporarily protect the surface of the polarizing film 5. It may be a temporary protective film to protect it. The first thermoplastic resin film 10, which is a temporary protection film, is peeled and removed at a desired time after constructing the polarizing plate. Additionally, the first thermoplastic resin film 10 may be a protective film that also has optical functions such as a retardation film or a brightness enhancement film. For example, a retardation film with an arbitrary retardation value can be obtained by stretching (uniaxially stretching, biaxially stretching, etc.) a thermoplastic resin film made of the above material, or forming a liquid crystal layer or the like on the film. The first thermoplastic resin film 10 may have a surface treatment layer (coating layer) such as a hard coat layer, an anti-glare layer, an anti-reflection layer, an anti-static layer, and an anti-fouling layer laminated on the surface.

The thickness of the first thermoplastic resin film 10 is usually 1 μm to 100 μm, but from the viewpoint of strength, handling, etc., it is preferably 5 μm to 60 μm, and more preferably 5 μm to 50 μm. If the thickness is within this range, the polarizing film 5 can be mechanically protected and 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 first thermoplastic resin film 10, the easier it is for the polarizing plate to curl. However, according to the present invention, even if the thickness of the first thermoplastic resin film 10 is as thin as 40 μm or less, for example, 30 μm or less. Reverse curl of the resulting polarizing plate can be effectively suppressed or prevented.

The first thermoplastic resin film 10 is a film with a higher equilibrium moisture content than the second thermoplastic resin film 20 used in the lamination process (S300) described later. In this specification, the equilibrium moisture content is the moisture content of a film stored for 24 hours in an environment of a temperature of 23°C and a relative humidity of 55% measured by the dry weight method, and is specifically obtained according to the following formula:

Equilibrium moisture content (% by weight) = {(film weight after storage - film weight after drying) / film weight after storage} × 100

Drying refers to the process of drying the film at 105°C for 2 hours. According to the method of the present invention, heat treatment and subsequent humidification treatment are performed on a first thermoplastic resin film (10) having at least a higher equilibrium moisture content, and a polarizing plate is manufactured using this first thermoplastic resin film (10). , reverse curl of the resulting polarizing plate can be suppressed or prevented.

The first thermoplastic resin film 10 and the second thermoplastic resin film 20 have a difference of 0.5% by weight or more in the equilibrium moisture content measured by the above method, that is, the equilibrium moisture content of the first thermoplastic resin film 10 is that of the second thermoplastic resin. It is preferable that it is 0.5% by weight or more larger than the resin film 20. As a result, the moisture content of the first thermoplastic resin film 10 can be more effectively increased in the humidification treatment process (S200) described later, which is more advantageous in suppressing or preventing reverse curl. The difference in the equilibrium moisture content is more preferably 1% by weight or more, and even more preferably 1.5% by weight or more.

The first thermoplastic resin film 10 preferably has an equilibrium moisture content of 1.5% by weight or more, and more preferably 2% by weight or more. As a result, the moisture content of the first thermoplastic resin film 10 can be more effectively increased in the humidification treatment process (S200) described later, which is more advantageous in suppressing or preventing reverse curl. The equilibrium moisture content of the first thermoplastic resin film 10 is usually 5% by weight or less.

Combinations of thermoplastic resin films with a difference in equilibrium moisture content of 0.5% by weight or more include, for example, a combination of a cellulose-based resin film (TAC film, etc.) and a cyclic polyolefin-based resin film, a cellulose-based resin film (TAC film, etc.) and a (meth)acrylic resin. Combination of films, combination of cellulose-based resin film (TAC film, etc.) and polyester-based resin film, combination of cellulose-based resin film (TAC film, etc.) and linear polyolefin-based resin film, (meth)acrylic resin film and cyclic polyolefin-based film Examples include a combination of resins, a combination of a (meth)acrylic resin film and a polyester resin film, etc. The difference in equilibrium moisture content between the first thermoplastic resin film 10 and the second thermoplastic resin film 20 is usually 5% by weight or less.

The equilibrium moisture content of a thermoplastic resin film can be adjusted depending on not only the material (type of thermoplastic resin constituting the film), but also the thickness of the film, the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface, and the material.

Additionally, the first thermoplastic resin film 10 is preferably a film with a higher moisture permeability than the second thermoplastic resin film 20. In this specification, moisture permeability refers to moisture permeability at a temperature of 40°C and a relative humidity of 90% measured according to the cup method specified in JIS Z 0208. According to the method of the present invention, which performs heat treatment and subsequent humidification treatment on a first thermoplastic resin film (10) having at least a higher moisture permeability, and manufactures a polarizing plate using this first thermoplastic resin film (10), the obtained This becomes more advantageous in suppressing or preventing reverse curl of the polarizer.

The first thermoplastic resin film 10 and the second thermoplastic resin film 20 have a difference in moisture permeability of 30 g/(㎡·24 at a temperature of 40°C and a relative humidity of 90%, measured according to the cup method specified in JIS Z 0208. hr) or more, that is, the moisture permeability of the first thermoplastic resin film 10 is preferably greater than that of the second thermoplastic resin film 20 by at least 30 g/(m2·24 hr). As a result, the moisture content of the first thermoplastic resin film 10 can be more effectively increased in the humidification treatment process (S200) described later, which is more advantageous in suppressing or preventing reverse curl. The difference in moisture permeability is more preferably 50 g/(m2·24 hr) or more, and even more preferably 100 g/(m2·24 hr) or more.

The first thermoplastic resin film 10 preferably has a moisture permeability of 300 g/(m2·24 hr) or more, and more preferably 400 g/(m2·24 hr) or more. As a result, the moisture content of the first thermoplastic resin film 10 can be more effectively increased in the humidification treatment process (S200) described later, which is more advantageous in suppressing or preventing reverse curl. In addition, the moisture permeability of 300 g/(m2·24 hr) or more means that in the case of bonding the first thermoplastic resin film 10 and the polarizing film 5 using a water-based adhesive, the layer made of the water-based adhesive can be efficiently formed. It is advantageous in that it can be dried and thus increases productivity. The moisture permeability of the first thermoplastic resin film 10 is usually 5000 g/(m2·24 hr) or less.

Combinations of thermoplastic resin films having a difference in moisture permeability of 30 g/(m2·24 hr) or more include, for example, a combination of a cellulose-based resin film (TAC film, etc.) and a cyclic polyolefin-based resin film, and a cellulose-based resin film (TAC film, etc.) Combination of (meth)acrylic resin film, combination of cellulose resin film (TAC film, etc.) and polyester resin film, combination of cellulose resin film (TAC film, etc.) and chain polyolefin resin film, (meth)acrylic resin Examples include a combination of a film and a cyclic polyolefin-based resin, a combination of a (meth)acrylic-based resin film and a polyester-based resin film, and the like. The difference in moisture permeability between the first thermoplastic resin film 10 and the second thermoplastic resin film 20 is usually 5000 g/(m2·24 hr) or less.

The moisture permeability of a thermoplastic resin film can be adjusted depending on not only its material (type of thermoplastic resin constituting the film), but also the thickness of the film, the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface, and the material.

The means for heat treatment of the first thermoplastic resin film 10 in this process is not particularly limited as long as the first thermoplastic resin film 10 can be heated to a desired temperature. As shown in FIG. 3, the heat treatment may be a process of heating the first thermoplastic resin film 10 by introducing it into the heating furnace 70, for example. The heating furnace 70 is preferably capable of controlling the temperature within the furnace. The heating furnace 70 is a hot air oven that can increase the temperature within the furnace by supplying hot air, for example.

In addition, the heat treatment of the first thermoplastic resin film 10 may be a process of bringing the film into close contact with one or two or more heating elements having a convex curved surface, or a process of heating the film using a heater. The heating body includes a roll that has a heat source (e.g., a heating medium such as hot water or an infrared heater) inside and can increase the surface temperature (e.g., a heat roll such as a guide roll whose surface is made of metal). . Examples of the heater include an infrared heater, a halogen heater, and a panel heater. FIG. 3 shows an example in which the first thermoplastic resin film 10 is introduced into the heating furnace 70 and heat treatment is performed while conveying the film along the guide roll 60 in the furnace.

Among them, the first thermoplastic resin film 10 is introduced into a heating furnace 70 in which the temperature in the furnace is adjusted to a desired temperature, and the film is heated while being conveyed along one or two guide rolls 60 in the furnace. In the method of heating the film by conveying it while being brought into close contact with one or two or more heating elements having a convex curve, the surface of the first thermoplastic resin film 10 can be smoothed before the lamination process (S300) described later. It is desirable in that it exists. That is, the raw material film such as the first thermoplastic resin film 10 may have minute surface irregularities during manufacture, or may cause minute irregularities on the surface during the storage process after manufacture, and in this process, the above method By smoothing the surface of the first thermoplastic resin film 10 using , the external quality of the polarizing plate can be improved and adhesion with the polarizing film 5 can be improved.

Temperature during heat treatment (T _1-1 ) (e.g., temperature inside the furnace 70, surface temperature of the heat roll, etc.) and temperature of the first thermoplastic resin film 10 reached by heat treatment (T _1-2 ) is preferably greater than or equal to the temperature (T _2-1 ) (e.g., the temperature inside the furnace of the humidification furnace 80) during the humidification treatment in the humidification treatment process (S200) described later, and the temperature during the humidification treatment It is more preferable that it is higher than (T _2-1 ). In addition, the temperatures (T _1-1 and T _1-2 ) are preferably equal to or higher than the temperature (T _2-2 ) of the first thermoplastic resin film 10 reached by humidification treatment, and the temperature (T _2-2 ) Higher is more preferable. Thereby, reverse curl of the resulting polarizing plate can be more effectively suppressed or prevented. That is, by satisfying the above-described temperature relationship, it is possible to prevent condensation from forming on the surface of the first thermoplastic resin film 10 when introducing the humidification treatment process (S200), so that humidification treatment under the desired temperature and humidity conditions can be performed on the entire film. It can be carried out reliably over a period of time. This increases the effect of suppressing and preventing reverse curls. T _1-1 and T _1-2 are preferably at least 10°C higher than T _2-1 and T _2-2 , more preferably at least 20°C higher, and even more preferably at least 30°C higher. The difference between T _1-1 and T _2-1 or T _2-2 and the difference between T _1-2 and T _2-1 or T _2-2 are usually 70°C or less.

In addition, the temperature (T _1-1 ) during the heat treatment and the temperature (T _1-2 ) of the first thermoplastic resin film 10 reached by the heat treatment are preferably the same or substantially the same temperature. . In addition, the temperature (T _2-1 ) during the humidification treatment and the temperature (T _2-2 ) of the first thermoplastic resin film 10 reached by the humidification treatment are preferably the same or substantially the same temperature. .

When condensation occurs on the surface of the first thermoplastic resin film 10 in the humidification treatment process (S200), the temperature of the film does not rise to the desired value in the condensation portion due to the latent heat of evaporation of water, and as a result, the desired temperature and humidity Since humidification treatment under the conditions cannot be performed, the effect of suppressing and preventing reverse curl is reduced or reverse curl cannot be suppressed. In addition, without performing the heat treatment process (S100), for example, the first thermoplastic resin film 10 at room temperature (23° C.) is introduced into the humidification treatment process (S200), and the humidification treatment is performed under temperature and humidity conditions where condensation does not occur. In the case of performing this, the humidification treatment becomes insufficient and reverse curl of the polarizing plate cannot be suppressed.

Additionally, if condensation occurs on the surface of the first thermoplastic resin film 10, traces of condensation (dry traces remaining after condensation occurs and dries) remain on the surface of the polarizing plate, deteriorating the appearance quality of the polarizing plate. According to the method of the present invention for manufacturing a polarizing plate using a first thermoplastic resin film subjected to heat treatment followed by humidification treatment, the occurrence of these condensation traces can also be reduced.

The temperature (T _1-1 ) during the heat treatment and the temperature (T _1-2 ) of the first thermoplastic resin film 10 reached by the heat treatment are usually 50°C to 150°C, preferably 60°C to 60°C. It is 130°C, more preferably 70°C to 120°C. If the temperature (T _1-1 , T _1-2 ) is less than 50°C, it becomes difficult to satisfy the above-mentioned temperature relationship (T _1-1 , T _1-2 ≥T _2-1 , T _{2- 2} ). , or even if it is possible to satisfy the above relationship, the humidification treatment cannot be performed under appropriate temperature and humidity conditions in the humidification treatment process (S200), and as a result, the effect of suppressing and preventing reverse curl tends to decrease. Moreover, if the temperature (T _1-1 , T _1-2 ) is less than 50°C, smoothing of the surface of the first thermoplastic resin film 10 tends to become insufficient. On the other hand, if the temperature (T _1-1 , T _1-2 ) exceeds 150°C, there is a risk that thermal deterioration may occur in the first thermoplastic resin film 10, and in the humidification treatment process (S200), the first thermoplastic resin film 10 There are cases where (10) cannot be humidified effectively. From the viewpoint of effectively humidifying the first thermoplastic resin film 10 in the humidification treatment step (S200), the temperature (T _1-1 , T _1-2 ) is more preferably 110° C. or lower, and particularly preferably is below 100℃.

The heat treatment in this process is carried out in an environment with a relative humidity of 50% or less, preferably 45% or less. In other words, heat treatment performed in an environment with a relative humidity of 50% or less is referred to as “heat treatment” in this specification, and in this regard, in an environment with a relative humidity higher than this (e.g., a relative humidity of 60% or more), preferably It is distinguished from the “humidification treatment” in the humidification treatment process (S200), which humidifies while heating. The relative humidity of the heat treatment environment is more preferably 30% or less, further preferably 20% or less, and particularly preferably 10% or less (for example, 5% or less).

The heat treatment time in this step is, for example, about 2 seconds to 300 seconds, and is preferably about 5 seconds to 120 seconds. If the heat treatment time is too short, it becomes difficult to reach the temperature (T _1-2 ) of the first thermoplastic resin film 10 to the above-mentioned temperature. A heat treatment time that is too long may cause thermal deterioration of the first thermoplastic resin film 10, and also requires a long film transport path, which may lead to excessive enlargement of the polarizing plate manufacturing equipment. The heat treatment time refers to the residence time of the film in the heating furnace 70, the time to bring it into close contact with the heating body, or the time to heat the film using a heater.

(2) Humidification treatment process (S200)

This process is a process of performing humidification treatment on the first thermoplastic resin film 10 after heat treatment. Humidification treatment refers to treatment that increases the moisture content of the first thermoplastic resin. As described above, by performing heat treatment followed by humidification treatment, reverse curl of the polarizing plate can be effectively suppressed or prevented, and reverse curling of the polarizing plate can be suppressed or prevented more effectively compared to the case where only humidification treatment is performed.

As shown in FIG. 3, the humidification treatment of the first thermoplastic resin film 10 is performed in an environment in which the relative humidity is adjusted, such as a process of humidifying the first thermoplastic resin film 10 by introducing it into the humidification furnace 80. It can be a treatment to put. The humidifying furnace 80 is preferably capable of controlling the relative humidity within the furnace, and more preferably is capable of controlling the temperature within the furnace. The humidifying furnace 80 is an oven that can increase the temperature in the furnace by supplying hot air, for example, and can control the relative humidity in the furnace by adjusting the moisture in the furnace.

The interval between the heat treatment and the humidification treatment is preferably as short as possible so that the temperature of the heat-treated first thermoplastic resin film 10 is maintained or does not decrease significantly even when the humidification treatment process is introduced. Figure 3 shows an example in which the first thermoplastic resin film 10 from the heating furnace 70 is immediately introduced into the humidification furnace 80 and the film is humidified while being conveyed along the guide roll 60 in the furnace. there is. To adjust the temperature in the humidification process using the humidification furnace 80, the above-described heater may be used instead of hot air, or the above-described heating element (eg, a heat roll) may be used.

The environment in which the relative humidity is adjusted, for example, the inside of the humidification furnace 80, is adjusted to a relative humidity of at least 50% or more, preferably 60% or more, and more preferably 70% or more. Thereby, the humidification treatment of the first thermoplastic resin film 10 can be effectively performed. The relative humidity of the environment in which the relative humidity is adjusted is usually 99% or less, and preferably 95% or less. If the relative humidity is too high, condensation may occur depending on the temperature of the first thermoplastic resin film 10.

The temperature (T _2-1 ) during the humidification treatment (temperature of the environment where the relative humidity is adjusted) and the temperature (T _2-2 ) of the first thermoplastic resin film 10 reached by the humidification treatment are usually 35°C. or higher, preferably 40°C or higher, and more preferably 45°C or higher. When the temperature (T _2-1 , T _2-2 ) is 35°C or higher, humidification treatment can be performed efficiently. On the other hand, if the temperature (T _2-1 , T _2-2 ) is too high, it becomes difficult to satisfy the above-mentioned temperature relationship (T _1-1 , T _1-2 ≥T _2-1 , T _2-2 ) Therefore, the temperature (T _2-1 , T _2-2 ) is preferably 90°C or lower, within a range that satisfies the above-mentioned temperature relationship, and more preferably 80°C or lower, satisfying the above-mentioned temperature relationship. It is within the scope.

The time of humidification treatment in this process is, for example, about 5 seconds to 500 seconds, and is preferably about 20 seconds to 300 seconds. If the humidification treatment time is too short, humidification (increase in moisture content) of the first thermoplastic resin film 10 becomes insufficient. Additionally, too long a humidification treatment time may result in excessive enlargement of polarizing plate manufacturing equipment because a long film transport path is required. The time of humidification treatment refers to the residence time of the film in the humidification furnace 80, etc.

The desirable moisture content of the first thermoplastic resin film 10 after the humidification treatment process (S200) depends on the equilibrium moisture content of the film (more typically, the material of the film). By humidification treatment, the first thermoplastic resin film 10 is preferably adjusted to a moisture content higher than the equilibrium moisture content in the normal environment in which the polarizing plate is stored after manufacturing (temperature about 23°C, relative humidity about 55%). do. For example, when the first thermoplastic resin film 10 is a triacetylcellulose film, the moisture content after humidification is preferably 1% by weight to 5% by weight, more preferably 2% by weight to 4.5% by weight (e.g., 2% by weight). % to 4% by weight). The moisture content is measured according to the dry weight method like the equilibrium moisture content, and is specifically obtained according to the following formula:

Moisture content (% by weight) = {(film weight before drying process - film weight after drying process) / film weight before drying process} × 100

Drying refers to the process of drying the film at 105°C for 2 hours.

In the humidification treatment process (S200), the first thermoplastic resin film 10 is humidified so that the moisture content is higher than the equilibrium moisture content at a temperature of 23° C. and a relative humidity of 55%, thereby effectively suppressing or preventing reverse curl of the polarizing plate. there is. If the moisture content of the first thermoplastic resin film 10 after the humidification treatment process (S200) is equal to or lower than the equilibrium moisture content of the first thermoplastic resin film 10 at a temperature of 23° C. and a relative humidity of 55%, reverse curl suppression becomes insufficient.

The difference between the moisture content of the first thermoplastic resin film 10 after the humidification treatment process (S200) and the equilibrium moisture content of the first thermoplastic resin film 10 at a temperature of 23° C. and a relative humidity of 55% is preferably 0.1% by weight or more. am. Also, from the viewpoint of suppressing excessive junking, the difference is preferably 3% by weight or less (for example, 2% by weight or less).

It is preferable that the first thermoplastic resin film 10 maintains or approximately maintains the moisture content after the humidification treatment even in the lamination process (S300) after the humidification treatment process (S200).

(3) Lamination process (S300)

Referring to Figure 3, this process laminates the first thermoplastic resin film 10 on one side of the polarizing film 5, and the second thermoplastic resin film 20 on the other side of the polarizing film 5. It is a process of laminating.

(3-1) Polarizing film

The polarizing film 5 may be one in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film. As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film, saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith. Other monomers that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

The saponification degree of the polyvinyl alcohol-based resin may be in the range of 80.0 mol% to 100.0 mol%, but is preferably in the range of 90.0 mol% to 100.0 mol%, and more preferably in the range of 98.0 mol% to 100.0 mol%. am. If the degree of saponification is less than 80.0 mol%, the water resistance and heat-and-moisture resistance of the polarizing plate obtained may decrease.

The degree of saponification refers to the rate at which the acetic acid group (acetoxy group: -OCOCH ₃ ) contained in polyvinyl acetate resin, which is the raw material of polyvinyl alcohol resin, is changed to hydroxyl group through the saponification process, expressed in unit ratio (mol%). , is defined by the following equation:

Degree of saponification (mol%) = 100 × (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups)

The degree of saponification can be determined based on JIS K 6726 (1994). The higher the degree of saponification, the higher the proportion of hydroxyl groups, and therefore the lower the proportion of acetic acid groups that inhibit crystallization.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and still more preferably 2,000 to 5,000. The average degree of polymerization of polyvinyl alcohol-based resin can also be determined based on JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain desirable polarization performance, and if it exceeds 10,000, solubility in solvents deteriorates, making it difficult to form a polyvinyl alcohol-based resin film.

The dichroic dye contained (adsorption oriented) in the polarizing film 5 may be iodine or a dichroic organic dye. Specific examples of dichroic organic dyes include red BR, red LR, red R, pink LB, rubin BL, Bordeaux GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy RY, green LG, violet LB, and violet. B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Includes Blue, Direct First Orange S, and First Black. One type of dichroic dye may be used individually, or two or more types may be used together. The dichroic dye is preferably iodine.

The polarizing film 5 includes a step of uniaxially stretching a polyvinyl alcohol-based resin film; A process of adsorbing a dichroic dye by dyeing a polyvinyl alcohol-based resin film with a dichroic dye; A process of crosslinking a polyvinyl alcohol-based resin film to which a dichroic dye is adsorbed; It can be manufactured through a process of washing with water after crosslinking treatment.

The polyvinyl alcohol-based resin film is a film produced from the above-mentioned polyvinyl alcohol-based resin. The film production method is not particularly limited, and known methods such as melt extrusion and solvent casting can be adopted. The thickness of the polyvinyl alcohol-based resin film is, for example, about 10 μm to 150 μm, preferably 50 μm or less, and more preferably 35 μm or less.

Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before, simultaneously with, or after dyeing with a dichroic dye. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before or during crosslinking treatment. Additionally, uniaxial stretching may be performed in these plural steps.

In uniaxial stretching, the material may be stretched uniaxially between rolls with different peripheral speeds, or may be stretched uniaxially using hot rolls. In addition, uniaxial stretching may be dry stretching in which stretching is performed in the air, or wet stretching in which the polyvinyl alcohol-based resin film is stretched in a solution. The stretching ratio is usually about 3 to 8 times.

As a method of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of immersing the polyvinyl alcohol-based resin film in an aqueous solution (dyeing solution) containing a dichroic dye is adopted. The polyvinyl alcohol-based resin film is preferably immersed in water (swelling treatment) before dyeing treatment.

When using iodine as a dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film by immersing it in an aqueous solution containing iodine and potassium iodide is usually adopted. The content of iodine in this aqueous dyeing solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. Additionally, 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°C to 40°C.

On the other hand, when using a dichroic organic dye as a dichroic dye, a method of dyeing the polyvinyl alcohol-based resin film by immersing it in an aqueous dyeing solution containing a water-soluble dichroic organic dye is usually adopted. The content of the dichroic organic dye in the dyeing aqueous solution is usually 1 × 10 ^-4 to 10 parts by weight, and preferably 1 × 10 ^-3 to 1 part by weight, per 100 parts by weight of water. This aqueous dyeing solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dyeing aqueous solution is usually about 20°C to 80°C.

Crosslinking treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing a crosslinking agent. A suitable example of a cross-linking agent is boric acid, but other cross-linking agents such as boron compounds such as borax, glyoxal, and glutaraldehyde may be used. Only one type of crosslinking agent may be used, or two or more types may be used in combination.

The amount of the cross-linking agent in the aqueous solution containing the cross-linking agent is usually 2 parts by weight to 15 parts by weight, preferably 5 parts by weight to 12 parts by weight, per 100 parts by weight of water. When using iodine as a dichroic dye, it is preferable that the aqueous solution containing the crosslinking agent contains potassium iodide. The amount of potassium iodide in the aqueous solution containing the crosslinking agent is usually 0.1 parts by weight to 15 parts by weight, preferably 5 parts by weight to 12 parts by weight, per 100 parts by weight of water. The temperature of the aqueous solution containing the crosslinking agent is usually 50°C or higher, and is preferably 50°C to 85°C.

The polyvinyl alcohol-based resin film after crosslinking treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in water. The temperature of the water in the water washing process is usually about 1°C to 40°C.

After washing with water, a drying process is performed, and the polarizing film 5 is obtained. Drying treatment may include drying using a hot air dryer, drying by contacting a heat roll, drying using a far-infrared heater, etc. The temperature of the drying treatment is usually about 30°C to 100°C, and 50°C to 90°C is preferable.

The thickness of the polarizing film 5 is usually about 2 μm to 40 μm. From the viewpoint of thinning the polarizing plate, 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, the easier it is for the polarizing plate to curl. However, according to the present invention, even if the thickness of the polarizing film 5 is as thin as 15 μm or less, for example, 10 μm or less, reverse curl of the resulting polarizing plate can be effectively prevented. It can be suppressed or prevented.

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

(3-2) Second thermoplastic resin film

The second thermoplastic resin film 20, like the first thermoplastic resin film 10, is made of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin. For specific examples of the thermoplastic resin that can constitute the second thermoplastic resin film 20, what was described with respect to the first thermoplastic resin film 10 is cited. However, the thermoplastic resin constituting the second thermoplastic resin film 20 is selected so that the equilibrium moisture content of the film at a temperature of 23° C. and a relative humidity of 55% is lower than that of the first thermoplastic resin film 10.

Like the first thermoplastic resin film 10, the second thermoplastic resin film 20 may be a protective film, a temporary protective film, or a protective film that also has an optical function such as a retardation film or a brightness enhancement film. The second thermoplastic resin film 20 may have a surface treatment layer (coating layer) such as a hard coat layer, an anti-glare layer, an anti-reflection layer, an anti-static layer, and an anti-fouling layer laminated on the surface. The thickness of the second thermoplastic resin film 20 is usually 1 μm to 100 μm, but from the viewpoint of strength, handleability, etc., it is preferably 5 μm to 60 μm, and more preferably 5 μm to 50 μm. The smaller the thickness of the second thermoplastic resin film 20, the easier it is for the polarizing plate to curl. However, according to the present invention, even if the thickness of the second thermoplastic resin film 20 is as thin as 40 μm or less, for example, 30 μm or less. Reverse curl of the resulting polarizing plate can be effectively suppressed or prevented.

As mentioned above, the equilibrium moisture content (and moisture permeability) of a thermoplastic resin film depends on its material (type of thermoplastic resin constituting the film), the thickness of the film, and the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface. It can be adjusted depending on the material, etc. Accordingly, although the first thermoplastic resin film 10 and the second thermoplastic resin film 20 have different equilibrium moisture content, they may be made of the same thermoplastic resin.

The equilibrium moisture content of the second thermoplastic resin film 20 is usually 0.05% by weight to 1.5% by weight, and is preferably 0.05% by weight to 1% by weight. Additionally, the moisture permeability of the second thermoplastic resin film 20 is usually 1 g/(m2·24 hr) to 350 g/(m2·24 hr), and preferably 5 g/(m2·24 hr) to 200 g. /(㎡·24 hr). Examples of thermoplastic resins constituting the second thermoplastic resin film 20 that can achieve such equilibrium moisture content and moisture permeability include cyclic polyolefin resins, (meth)acrylic resins, polyester resins, and chain polyolefin resins.

Before the lamination process (S300), the second thermoplastic resin film 20 may be subjected to the same humidification treatment as that of the first thermoplastic resin film 10, or a combination of heat treatment and humidification treatment, but reverse curl of the polarizer is suppressed. Alternatively, from the viewpoint of prevention, it is preferable not to perform humidification treatment or a combination of heat treatment and humidification treatment on the second thermoplastic resin film 20. However, by subjecting the second thermoplastic resin film 20 to the same heat treatment as the first thermoplastic resin film 10, the surface of the second thermoplastic resin film 20 can be smoothed.

(3-3) Lamination process

Referring to FIG. 3, the lamination of the first and second thermoplastic resin films 10 and 20 on the polarizing film 5 in this process is, for example, carried out continuously using long products of each raw material film. It can be done continuously while doing this. Each raw material film is conveyed so that its longitudinal direction becomes the conveyance direction. A guide roll (pre-roll) 60 that supports the running film and, if necessary, a drive roll such as a nip roll are provided in the film transport path. Normally, the transport direction (film longitudinal direction) of the polarizing film 5 and the transport direction (film longitudinal direction) of the first and second thermoplastic resin films 10 and 20 are parallel.

When both the first and second thermoplastic resin films 10 and 20 are protective films or protective films having an optical function, the first and second thermoplastic resin films 10 and 20 are usually the first and second thermoplastic resin films, respectively. 2 It is laminated and bonded to the polarizing film (5) through the adhesive layers (15, 25). Specifically, as shown in FIG. 3, a pair of the first thermoplastic resin film 10, the polarizing film 5, and the second thermoplastic resin film 20 are overlapped so that their longitudinal directions (conveyance directions) are parallel. By passing between the bonding rolls 40, 40, the laminated film can be bonded by pressing the laminated film from above and below. However, at this time, just before passing between the bonding rolls 40, 40, the first injection Using the device 90 and the second injection device 91, the agent is applied between the polarizing film 5 and the first thermoplastic resin film 10 and between the polarizing film 5 and the second thermoplastic resin film 20, respectively. An adhesive layer is interposed by injecting the first adhesive 50 and the second adhesive 55.

After lamination, the adhesive layer is dried and/or cured to obtain the double-sided protective polarizing plate 1 shown in FIG. 2. The first adhesive layer 15 is formed of the first adhesive 50, and the second adhesive layer 25 is formed of the second adhesive 55.

In addition, the method for interposing the layer made of adhesive is not limited to injection using the injection devices 90 and 91, and, for example, depending on the viscosity of the adhesive, etc., doctor blade method, wire bar coat method, die coat method, comma method, etc. A coating method such as a coater method, a gravure coating method, a dip coating method, or a casting method may be appropriately selected and the adhesive may be coated on the bonding surface of at least one film to be polymerized.

Before laminating and bonding the first and second thermoplastic resin films (10, 20) to the polarizing film (5), the bonding surface of the polarizing film (5) and/or the first and second thermoplastic resin films (10, 20) Alternatively, surface activation treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, or saponification treatment may be performed. By this surface activation treatment, the adhesion between the polarizing film 5 and the first and second thermoplastic resin films 10 and 20 can be improved.

As the first adhesive 50 and the second adhesive 55, a water-based adhesive, an active energy ray-curable adhesive, or a heat-curable adhesive can be used, and water-based adhesives and active energy ray-curable adhesives are preferred. The first adhesive 50 and the second adhesive 55 may be the same type of adhesive or may be different types of adhesives. When a different type of adhesive is 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 this case.

A water-based adhesive is one in which adhesive components are dissolved in water or dispersed in water. A water-based adhesive that is preferably used is, for example, an adhesive composition using polyvinyl alcohol-based resin or urethane resin as the main component.

When using a polyvinyl alcohol-based resin as the main component of the adhesive, the polyvinyl alcohol-based resin may be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, or carboxyl group-modified polyvinyl alcohol, It may be a modified polyvinyl alcohol-based resin such as acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, or amino group-modified polyvinyl alcohol. Polyvinyl alcohol-based resin is a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as a polyvinyl alcohol-based copolymer obtained by saponifying a copolymer of vinyl acetate and other monomers copolymerizable with it. It's okay too.

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

Adhesives made of aqueous solutions of polyvinyl alcohol-based resins contain curable ingredients or crosslinking agents such as polyvalent aldehydes, melamine-based compounds, zirconia compounds, zinc compounds, glyoxal, glyoxal derivatives, and water-soluble epoxy resins in order to improve adhesion. It is desirable to do so. Water-soluble epoxy resins include, for example, polyalkylene polyamines such as diethylenetriamine and triethylenetetramine, and polyamideamines obtained by reacting dicarboxylic acids such as adipic acid with epichlorohydrin. Amidepolyamine epoxy resin can be suitably used. Commercially available products of such polyamide polyamine epoxy resin include “Sumirez Resin 650” (manufactured by Taoka Chemical Chemical Co., Ltd.), “Sumirez Resin 675” (manufactured by Taoka Chemical Chemical Co., Ltd.), and “WS-525” (manufactured by Taoka Chemical Chemical Co., Ltd.) (manufactured by Nippon PMC Co., Ltd.), etc. can be mentioned. The addition amount of these curable components and cross-linking agents (total amount when added together as a curable component and cross-linking agent) is usually 1 part by weight to 100 parts by weight, preferably 1 part by weight to 100 parts by weight of the polyvinyl alcohol-based resin. It is 50 parts by weight. When the amount of the curable component or crosslinking agent added is less than 1 part by weight based on 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving adhesion tends to be reduced, and the added amount is less than 1 part by weight based on 100 parts by weight of the polyvinyl alcohol-based resin. When the amount exceeds 100 parts by weight, the adhesive layer tends to become weak.

Additionally, a suitable example when using urethane resin as the main component of the adhesive includes a mixture of a polyester-based ionomer type urethane resin and a compound having a glycidyloxy group. A polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton, into which a small amount of ionic component (hydrophilic component) is introduced. This ionomer-type urethane resin is suitable as an aqueous adhesive because it emulsifies directly in water to form an emulsion without using an emulsifier.

An active energy ray-curable adhesive is an adhesive that hardens by irradiation of active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. When using an active energy ray-curable adhesive, the adhesive layer that the polarizing plate has is a cured product layer of the adhesive.

The active energy ray-curable adhesive may be an adhesive that contains an epoxy-based compound that hardens by cationic polymerization as a curable component, and is preferably an ultraviolet-curable adhesive that contains this epoxy-based compound as a curable component. The epoxy-based compound referred to herein means a compound having an average of one or more epoxy groups, preferably two or more, in the molecule. As for the epoxy-based compound, only one type may be used or two or more types may be used in combination.

Specific examples of epoxy-based compounds that can be suitably used include hydrogenated epoxy-based compounds obtained by reacting epichlorohydrin with an alicyclic polyol obtained by hydrogenating the aromatic ring of an aromatic polyol (glyceryl of a polyol having an alicyclic ring) cidyl ether); Aliphatic epoxy-based compounds such as polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts; It includes an alicyclic epoxy-based compound, which is an epoxy-based compound having one or more epoxy groups bonded to an alicyclic ring in the molecule.

The active energy ray-curable adhesive may contain a radically polymerizable (meth)acrylic compound as a curable component instead of or together with the epoxy compound. Examples of the (meth)acrylic compound include (meth)acrylate monomers having at least one (meth)acryloyloxy group in the molecule; It is obtained by reacting two or more types of functional group-containing compounds, and includes (meth)acryloyloxy group-containing compounds such as (meth)acrylate oligomers having at least two (meth)acryloyloxy groups in the molecule.

When the active energy ray-curable adhesive contains an epoxy-based compound that hardens by cationic polymerization as a curable component, it is preferable to contain a photo-cationic polymerization initiator. Examples of photocationic polymerization initiators include aromatic diazonium salts; Onium salts such as aromatic iodonium salts and aromatic sulfonium salts; An iron-allene complex, etc. can be mentioned. Additionally, when the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth)acrylic compound, it is preferable to contain a radical photopolymerization initiator. Examples of radical photopolymerization initiators include acetophenone-based initiators, benzophenone-based initiators, benzoin ether-based initiators, thioxanthone-based initiators, xanthone, fluorenone, camphorquinone, benzaldehyde, and anthraquinone.

One of the first and second thermoplastic resin films 10 and 20 may be a temporary protection film for temporarily protecting the surface of the polarizing film 5. In this case, in the lamination process (S300), an adhesive is not interposed between the polarizing film 5 and the temporary protection film, but instead, the temporary protection film is laminated with a volatile liquid or nothing interposed. The temporary protection film is a film that can be peeled from the polarizing film 5, and is peeled and removed at a desired time (for example, when bonding the polarizing plate to a liquid crystal cell) after production of the polarizing plate. “Releasable” means that the polarizing film 5 and the temporary protective film can be separated without damaging or damaging the polarizing film 5 and the temporary protective film.

As an example, the layer structure of the single-sided protective polarizing plate 2 obtained by using the second thermoplastic resin film 20 as a temporary protection film, performing a lamination process (S300), and then peeling and removing the temporary protection film is shown in FIG. 4.

When using a temporary protective film, it is preferable to interpose a volatile liquid between the polarizing film 5 and the temporary protective film in the lamination process (S300). As a result, compared to the case where nothing is interposed, defects such as the polarizing film 5 breaking during the process of manufacturing the polarizing plate or wrinkles forming in the film laminate containing the polarizing film 5 can be suppressed.

The peeling force between the polarizing film 5 and the temporary protection film is, for example, 0.01 N/25 mm to 0.5 N/25 mm, preferably 0.01 N/25 mm to 0.2 N/25 mm, more preferably 0.01 N. /25 mm∼0.15 N/25 mm. If the peeling force is less than 0.01 N/25 mm, the adhesion between the polarizing film 5 and the temporary protective film is small, and partial peeling of the temporary protective film may occur, or the single-sided protective polarizing plate with the temporary protective film is rolled. During storage, the polarizing film 5 may crack along the stretching direction. In addition, when the peeling force exceeds 0.5 N/25 mm, it becomes difficult to peel the temporary protective film from the polarizing film 5, so that the polarizing film 5 cracks along the stretching direction when peeling the temporary protective film. It gets easier.

The peeling force was measured by cutting a single-sided protective polarizing plate with a temporary protective film to a width of 25 mm, obtaining a measurement sample, and using a precision universal tester “Autograph AGS-50NX” manufactured by Shimadzu Seisakusho Co., Ltd. It is obtained by holding the sample's temporary protection film and one-sided protection polarizing plate and measuring the force when peeling in the 180° direction. The peeling force is measured in an environment with a peeling speed of 300 mm/min, a temperature of 23 ± 2°C, and a relative humidity of 50 ± 5%.

The interposed volatile liquid is volatilized and removed after the lamination process (S300). Thereby, a single-sided protection polarizing plate with a temporary protection film is obtained. Figure 5 shows an example of the layer structure of the single-sided protection polarizing plate 3 with a temporary protection film. In the example of Fig. 5, the second thermoplastic resin film 20 is a temporary protection film. Volatile liquids can be volatilized and removed by heating. By this heat treatment, the temporary protective film is laminated directly on the surface of the polarizing film 5 with appropriate adhesion. The heating temperature is, for example, 30°C to 90°C.

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 cause adverse effects. Examples of volatile liquids include water or a mixture of water and a hydrophilic liquid. It is preferable that the hydrophilic liquid does not remain after heat treatment, and for example, methanol, ethanol, 1-butanol, tetrahydrofuran, acetone, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, formic acid, acetic acid, etc. I can hear it.

(4) Other processes

When using a water-based adhesive for lamination bonding of the polarizing film 5 and the first and/or second thermoplastic resin films 10 and 20, drying to remove water contained in the water-based adhesive is performed after the lamination process (S300). It is desirable to carry out the process. The drying temperature is, for example, 30°C to 90°C. When laminating a temporary protective film on the polarizing film 5 via a volatile liquid, this drying process may also serve as the above-described heat treatment for volatilizing and removing the volatile liquid. After the drying process, a curing process may be provided, for example, curing at a temperature of 20°C to 50°C, preferably 30°C to 45°C.

When using an active energy ray-curable adhesive for lamination bonding of the polarizing film 5 and the first and/or second thermoplastic resin films 10 and 20, a drying process is performed as necessary after the lamination process (S300), Next, a curing process is performed in which the active energy ray curable adhesive is cured by irradiating active energy rays. The light source of the active energy ray is not particularly limited, but ultraviolet rays having a luminescence distribution in a wavelength of 400 nm or less are preferable, and specifically, low pressure mercury lamp, medium pressure mercury lamp, high pressure mercury lamp, ultra-high pressure mercury lamp, chemical lamp, black light lamp, and microwave excitation. Mercury lamps, metal halide lamps, etc. can be used.

The intensity of active energy ray irradiation to the adhesive layer made of an active energy ray-curable adhesive is appropriately determined depending on the composition of the adhesive, but the irradiation intensity in the wavelength range effective for activating the polymerization initiator is 0.1 mW/cm2 to 6000 mW/cm2. It is desirable to set it as much as possible. When the irradiation intensity is 0.1 mW/cm2 or more, the reaction time does not become too long, and when it is 6000 mW/cm2 or less, yellowing of the adhesive layer or polarizing film 5 occurs due to heat radiated from the light source and heat generation during curing of the adhesive. There is little risk of deterioration.

The irradiation time of active energy rays is also appropriately determined depending on the composition of the adhesive, but is preferably set so that the accumulated light amount expressed as the product of the irradiation intensity and irradiation time is 10 mJ/cm2 to 10000 mJ/cm2. When the integrated light amount is 10 mJ/cm2 or more, a sufficient amount of activated species derived from the polymerization initiator can be generated to proceed the curing reaction more reliably. When the accumulated light amount is 10000 mJ/cm2 or less, the irradiation time is not excessively long, thereby maintaining good productivity. You can.

When the lamination process (S300) is performed using a temporary protection film on one side of the first and second thermoplastic resin films 10 and 20, as described above, for example, one side having a temporary protection film as shown in FIG. 5 A protective polarizing plate 3 is obtained, and by peeling and removing the temporary protection film therefrom, a single-sided protective polarizing plate 2 as shown in FIG. 4, for example, is obtained. As described above, in FIGS. 4 and 5, the second thermoplastic resin film 20 is used as a temporary protection film, but the first thermoplastic resin film 10 may also be a temporary protection film. A step of laminating an adhesive layer 30 on the surface of the polarizing film on which the temporary protection film was laminated in this single-sided protective polarizing plate 2 is provided, for example, a single-sided protective polarizing plate 4 having an adhesive layer as shown in FIG. 6. ) can also be obtained. This adhesive layer 30 can be used to bond a single-sided protective polarizing plate to a liquid crystal cell.

Also in the double-sided protective polarizing plate 1 shown in FIG. 2, the adhesive layer 30 can be laminated on the outer surface of the first thermoplastic resin film 10 or the second thermoplastic resin film 20. This adhesive layer 30 can be used to bond the double-sided protective polarizer 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 second thermoplastic resin film 20.

The adhesive layer 30 may be composed of an adhesive composition containing a resin such as (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether as the main component (base polymer). Among them, an adhesive composition containing a (meth)acrylic resin excellent in transparency, weather resistance, heat resistance, etc. as a base polymer is suitable. The adhesive composition may be of an active energy ray curing type or a heat curing type.

Examples of the (meth)acrylic resin used in the adhesive composition include (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Polymers or copolymers containing a species or two or more species as monomers are suitably used. It is preferable to copolymerize a polar monomer with a (meth)acrylic resin. Polar monomers include, for example, (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycyrrhizate. Monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc., such as dil (meth)acrylate, can be mentioned.

The pressure-sensitive adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. Examples of the crosslinking agent include metal ions of divalence or higher, which form a metal carboxylic acid salt between carboxyl groups; Polyamine compounds that form amide bonds between carboxyl groups; A polyepoxy compound or polyol that forms an ester bond between carboxyl groups; As a polyisocyanate compound, one that forms an amide bond between carboxyl groups is exemplified. Among them, polyisocyanate compounds are preferable.

An active energy ray-curable adhesive composition has the property of curing when irradiated with active energy rays such as ultraviolet rays or electron beams, and has adhesiveness even before irradiation of active energy rays and can be brought into close contact with an adherend such as a film. It is an adhesive composition that has the property of adjusting the adhesion force by curing. The active energy ray-curable adhesive composition is preferably of an ultraviolet ray-curable type. The active energy ray curable adhesive composition further contains an active energy ray polymerizable compound in addition to the base polymer and crosslinking agent. Additionally, if necessary, a photopolymerization initiator, a photosensitizer, etc. may be contained.

The adhesive composition includes fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, It may contain additives such as ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, and photopolymerization initiators.

The adhesive layer 30 is formed by applying an organic solvent dilution of the adhesive composition onto the adhesive layer formation surface of the polarizing plate (i.e., the polarizing film 5, the first or second thermoplastic resin film 10, 20), and drying it. It can be formed by doing so. Alternatively, the organic solvent dilution of the pressure-sensitive adhesive composition may be applied onto an independent film (thermoplastic resin film subjected to a silver transfer treatment), dried to form a pressure-sensitive adhesive layer, and then transferred to the pressure-sensitive adhesive layer formation surface of the polarizing plate. In either method, it is preferable to attach an independent film to the outer surface of the adhesive layer 30 and 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 obtained by irradiating active energy rays to the formed adhesive layer. The thickness of the adhesive layer 30 is usually 1 μm to 40 μm, but is preferably set to 3 μm to 25 μm from the viewpoint of thinning the polarizing plate.

A process of laminating a protective film on the outer surfaces of the first and/or second thermoplastic resin films 10 and 20 of the double-sided protective polarizing plate 1 and the single-sided protective polarizing plate 2 may be provided. The protective film is composed of a base film and an adhesive layer laminated thereon. A protection film is a film for protecting the surface of a polarizing plate, and usually, for example, after a polarizing plate having a protection film is bonded to a liquid crystal cell or the like, it is peeled and removed for each adhesive layer it has. The base film may be a thermoplastic resin, such as a polyolefin-based resin such as a polyethylene-based resin or a polypropylene-based resin; Cyclic polyolefin resin; Polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polycarbonate-based resin; It can be composed of (meth)acrylic resin, etc.

Additionally, a process of laminating an optical film other than a polarizing film on the outer surface of the first and/or second thermoplastic resin films 10 and 20 of the double-sided protective polarizing plate 1 and the single-sided protective polarizing plate 2 may be provided. . Examples of other optical films include retardation films and brightness enhancement films. Other optical films can be laminated and bonded through a pressure-sensitive adhesive layer or adhesive layer.

According to the manufacturing method according to the present invention, it is possible to obtain a single-layer polarizing plate (double-sided protective polarizing plate or single-sided protective polarizing plate) in which reverse curl is well suppressed or prevented. As described above, reverse curl is a curl that makes the second main surface on the opposite side to the side bonded to the image display element such as a liquid crystal cell convex, and in the double-sided protective polarizer 1 or the single-sided protective polarizer 2, typically is a curl that makes the side of the first thermoplastic resin film 10 convex. In the sheet body of the polarizing plate obtained according to the present invention, the reverse curl that makes the side of the first thermoplastic resin film 10 convex is well suppressed or prevented, and is typically a flat shape without curl or slightly curled. , it has a shape that has regular curls, or even if it has reverse curls, the amount is small. Preferably, it is a flat shape without curls, or a shape with some regular curls.

Example

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

(1) Equilibrium moisture content of the film (W _H )

A test piece with an MD length of 150 mm × TD length of 100 mm was cut. The film weight was measured after being stored for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%. After that, drying treatment was performed at 105°C for 2 hours, and the weight of the film after drying treatment was measured. From the film weight before and after drying, the equilibrium moisture content (W _H ) was determined based on the following equation:

Equilibrium moisture content (% by weight) = {(film weight before drying process - film weight after drying process) / film weight before drying process} × 100

(2) Moisture content of film (W)

A test piece measuring 150 mm in MD length x 100 mm in TD was cut and its weight was immediately measured. Next, drying treatment was performed at 105°C for 2 hours, and the weight of the film after drying treatment was measured. From the film weight before and after drying, the moisture content (W) was determined based on the following formula:

Moisture content (% by weight) = {(film weight before drying process - film weight after drying process) / film weight before drying process} × 100

(3) Water vapor permeability of the film

According to the cup method specified in JIS Z 0208, the moisture permeability [g/(㎡·24 hr)] was measured at a temperature of 40°C and a relative humidity of 90%.

(4) Thickness of film

Measurements were made using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(5) Curl amount of polarizer

From the obtained double-sided protective polarizing plate, a test piece of 300 mm x 200 mm was cut so that its absorption axis direction (MD) was 45° with respect to each side, and left for 24 hours in an environment with a temperature of 25°C and a relative humidity of 55%. This test piece was placed on a reference surface (horizontal) with its concave side facing up, that is, with the four short sides raised. In this state, the height from the reference surface was measured for each of the four corners of the test piece, and the amount of curl [mm] was determined as the average of the heights of these four corners. When the curl amount is a positive value, it means that the first thermoplastic resin film side is concave (normal curl), and when the curl amount is a negative value, it means that the second thermoplastic resin film side is concave (reverse curl). In addition, the double-sided protective polarizing plates of Examples 2 and 3 did not curl even when either the first thermoplastic resin film side or the second thermoplastic resin film side was turned upward.

<Example 1>

(A) Production of polarizing film

While continuously conveying a long polyvinyl alcohol film (average degree of polymerization: about 2400, degree of saponification: 99.9 mol% or more, thickness: 30 μm), it was uniaxially stretched about 4 times in a dry manner and further maintained under tension, 40 After immersing in pure water at ℃ for 1 minute, it was immersed in an aqueous solution with a weight ratio of iodine/potassium iodide/water of 0.1/5/100 at 28℃ for 60 seconds. Afterwards, it was immersed in an aqueous solution with a weight ratio of potassium iodide/boric acid/water of 10.5/7.5/100 at 68°C for 300 seconds. Subsequently, after washing with pure water at 5°C for 5 seconds, it was dried at 70°C for 180 seconds to obtain a long polarizing film in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. The thickness of the polarizing film was 11 μm.

(B) Fabrication of double-sided protective polarizer

Using the same device as the polarizing plate manufacturing device shown in FIG. 3, a double-sided protective polarizing plate was produced by the following means. A long first thermoplastic resin film [TAC film "KC2UAW" manufactured by Konica Minolta Opto Co., Ltd., thickness: 25 ㎛, equilibrium moisture content (W _H ): 3.0 wt%, moisture permeability: 1207 g/(㎡·24 hr)] While continuously conveyed, the film is humidified by introducing it into a heating furnace set at a furnace temperature of 95°C and a relative humidity within the furnace of 3%, and then into a humidification furnace set at a furnace temperature of 50°C and a relative humidity within the furnace of 70%. was carried out. The residence times of the film in the drying furnace and humidifying furnace were 8 seconds and 12 seconds, respectively. The humidifying furnace was installed immediately after the heating furnace, and the temperature of the film immediately before being introduced into the humidifying furnace was almost the same as the temperature inside the heating furnace. Both the heating furnace and the humidifying furnace increase the temperature within the furnace by supplying hot air. The moisture content (W) of the first thermoplastic resin film after humidification treatment was 3.1% by weight.

The polarizing film obtained in (A) above is continuously conveyed, and the first thermoplastic resin film and the long second thermoplastic resin film after the humidification treatment [trade name "FEKB015D3", a cyclic polyolefin resin film manufactured by JSR Co., Ltd., thickness: 15 ㎛, equilibrium moisture content (W _H ): 0.8% by weight, moisture permeability: 115 g/(㎡·24 hr), use as is without heating/humidifying the purchased product] was continuously conveyed, and the polarizing film and the first While injecting a water-based adhesive between the thermoplastic resin films and between the polarizing film and the second thermoplastic resin film, it is passed between bonding rolls to form the first thermoplastic resin film/water-based adhesive layer/polarizing film/water-based adhesive layer/second thermoplastic resin film. A laminated film was formed (first process). This lamination process was performed within 10 seconds after humidification treatment of the first thermoplastic resin film.

In the water-based adhesive, polyvinyl alcohol powder [trade name "Gosephimer" manufactured by Nippon Kosei Chemical Co., Ltd., average degree of polymerization 1100] was dissolved in hot water at 95°C, and a crosslinking agent was added to an aqueous polyvinyl alcohol solution with a concentration of 3% by weight. [Sodium glyoxylate manufactured by Nippon Kosei Chemical Co., Ltd.] was used as an aqueous solution mixed in a ratio of 1 part by weight to 10 parts by weight of polyvinyl alcohol powder.

Next, the obtained laminated film was transported, passed through a hot air dryer, and subjected to heat treatment at 80° C. for 300 seconds to dry the water-based adhesive layer, thereby obtaining a double-sided protective polarizing plate.

<Examples 2 to 3, Comparative Examples 1 to 3>

A double-sided protective polarizing plate was manufactured in the same manner as in Example 1, except that the furnace environment of the heating furnace and humidification furnace and the residence time of the film were as shown in Table 1. In Comparative Examples 2 and 3, heat treatment of the first thermoplastic resin film was not performed.

Table 1 shows the amount of curl of the double-sided protective polarizing plates obtained in Examples 1 to 3 and Comparative Examples 1 to 3. Table 1 lists the furnace environment of the heating furnace and humidification furnace and the residence time of the film. Additionally, in Table 1, the moisture content (W) of the first thermoplastic resin film after humidification treatment, the equilibrium moisture content (W _H ) of the first thermoplastic resin film, and the moisture content (W) after humidification treatment are the difference in equilibrium moisture content (W _H ). It is shown together. Additionally, in Comparative Example 1, the first thermoplastic resin film was passed through a humidification furnace, but no humidification treatment was performed. In Comparative Example 1 of Table 1, the numerical value described in the column “Moisture content after humidification treatment” means the moisture content of the first thermoplastic resin film after passing through the humidification furnace.

In any of Examples 1 to 3, Comparative Example 1, and Comparative Example 3, no traces of condensation were observed on the surface of the first thermoplastic resin film. In Comparative Example 2, traces of condensation were observed on the surface of the first thermoplastic resin film.

<Examples 4 and 5>

As the first thermoplastic resin film, a hard coat film [a film in which a hard coat layer is formed on TAC film "KC2UAW" manufactured by Konica Minolta Opto Co., Ltd., thickness: 32.4 μm, equilibrium moisture content (W _H ): 1.9 wt%, moisture permeability: 455 g/(㎡·24 hr)] was used as the second thermoplastic resin film, and a cyclic polyolefin-based resin film [trade name “ZF14-023” manufactured by Nippon Zeon Co., Ltd., thickness: 22.9 μm, equilibrium moisture content (W _H ) : 0.1% by weight, moisture permeability: 17 g/(㎡·24 hr)], the same as Example 1 except that the furnace environment of the heating furnace and humidification furnace and the residence time of the film were as shown in Table 2. Thus, a double-sided protective polarizer was manufactured. The curl amounts of the double-sided protective polarizers obtained in Examples 4 and 5 are shown in Table 2. Table 2 lists the furnace environment of the heating furnace and humidification furnace and the residence time of the film. In addition, in Table 2, the moisture content of the first thermoplastic resin film after humidification treatment (W), the equilibrium moisture content of the first thermoplastic resin film (W _H ), and the difference between the moisture content after humidification treatment (W) and the equilibrium moisture content (W _H ) indicates.

1: Double-sided protective polarizer,
2: one-sided protective polarizer,
3: One-sided protective polarizer with temporary protective film,
4: One-sided protective polarizer with an adhesive layer,
5: Polarizing film,
10: first thermoplastic resin film,
20: second thermoplastic resin film,
15: first adhesive layer,
25: second adhesive layer,
30: adhesive layer,
40: joint roll,
50: first adhesive,
55: second adhesive,
60: guide roll,
70: heating furnace,
80: humidification furnace,
90: first injection device,
91: Second injection device.

Claims (12)

A process of heat-treating a first thermoplastic resin film having a thickness of 40 μm or less;
A process of humidifying the first thermoplastic resin film;
The first thermoplastic resin film is laminated on one side of the polarizing film, and the equilibrium moisture content at a temperature of 23° C. and a relative humidity of 55% is lower than that of the first thermoplastic resin film on the other side of the polarizing film, and the thickness is lower than that of the first thermoplastic resin film. Process of laminating a second thermoplastic resin film of 40 ㎛ or less
Contains in this order,
In the humidification process, the first thermoplastic resin film is humidified so as to be higher than the equilibrium moisture content at a temperature of 23° C. and a relative humidity of 55%, which are normal environmental conditions in which the polarizing plate is stored after manufacturing. . The manufacturing method according to claim 1, wherein the second thermoplastic resin film has not been subjected to the humidification treatment. The manufacturing method of claim 1, wherein the first thermoplastic resin film includes a cellulose-based resin film. The manufacturing method of claim 1, wherein the second thermoplastic resin film includes a cyclic polyolefin-based resin film. The manufacturing method according to claim 1, wherein the temperature during the heat treatment is equal to or higher than the temperature during the humidification treatment. The manufacturing method according to claim 5, wherein the temperature during the heat treatment is 30°C or more higher than the temperature during the humidification treatment. The manufacturing method according to claim 1, wherein in the heat treatment step, the first thermoplastic resin film is heat treated in an environment of a temperature of 50° C. or higher and a relative humidity of 50% or lower. The manufacturing method according to claim 1, wherein in the humidification treatment step, the first thermoplastic resin film is humidified in an environment of a temperature of 40° C. or higher and a relative humidity of 60% or higher. The manufacturing method according to claim 1, wherein at least one of the first thermoplastic resin film and the second thermoplastic resin film is laminated on the polarizing film through an adhesive layer. delete The manufacturing method according to claim 1, wherein the polarizing film has a thickness of 15 μm or less. delete

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