TWI694272B - Method for producing polarizing plate with protection film - Google Patents

Abstract

The present invention provides a method for producing polarizing plate with protection film containing a step of laminating a protection film on single surface of a polarizing plate and pressing it by passing through a pair of laminating roll. While setting the thickness of the protective film as T₁[μm], setting the stretching elastic module on MD as E₁[MPa], setting the film tension on MD prior to pass through the pair of laminating roll as F₁[N/m], setting the thickness of polarizing plate as T₂[μm], setting the stretching elastic module on MD direction as E₂[MPa], and setting the film tension on MD prior to pass through the pair of laminating roll as F₂[N/m], the pressing step is conducted in conditions satisfying the following function: F₁/(E₁×T₁) > F₂/(E₂×T₂).

Description

Method for manufacturing polarizing plate with protective film

The present invention relates to a method for manufacturing a polarizing plate with a protective film formed by laminating a protective film on the surface of a polarizing plate.

In recent years, from the perspective of design or portability, portable terminals such as smart phones have rapidly progressed in size and thinness. In order to achieve long-term driving with a limited thickness, the polarizing plate used is also expected to achieve higher brightness, thinner and lighter weight.

Conventionally, a polarizing plate has generally used a protective film containing triethyl cellulose (TAC) bonded to a polarizing film containing a polyvinyl alcohol-based resin with an adhesive. However, in recent years, from the viewpoint of thinning, durability, cost, productivity, etc., protective films composed of resins other than TAC have also been used (for example, Japanese Patent Laid-Open No. 2004-245925).

The polarizing plate is sensitive to the environment it is in, and it is easy to deform due to different environmental conditions. In this manual, this deformation is also called "curl". There are two types of curls: "forward curl" and "reverse curl". As far as the polarizing plate is concerned, there is an image display that is attached to the liquid crystal cell, etc. The first main surface on the side of the element and the second main surface on the opposite side, "positive curl" makes the first main surface side convex, and "reverse curl" makes the second main surface side Raised curl. When the polarizing plate is reversely curled, when it is bonded to the image display device through the adhesive layer, it is easy to cause a bonding error, or air bubbles are mixed into the interface between the adhesive layer and the image display device.

Therefore, the present invention is to provide a method for manufacturing an optical member including a polarizing plate structure, which is an optical member that sufficiently suppresses anti-curling.

The inventors have further elaborated according to the following concepts 1) and 2), and completed the present invention: 1) A polarizing plate is usually attached with a peelable protective film useful for protecting its surface (also It is called the surface protective film) and the polarizing plate with a protective film circulates on the market. When it is attached to an image display element, it is often bonded in the form of a polarizing plate with a protective film; and 2) Therefore In order to solve the above-mentioned problems, the polarizing plate with a protective film should only sufficiently suppress reverse curl. That is, the present invention provides a method for manufacturing a polarizing plate with a protective film as shown below.

[1] A method for manufacturing a polarizing plate with a protective film, comprising: a step of superimposing a protective film on one side of a polarizing plate and pressing it by passing between a pair of laminating rollers; The thickness of the film is T ₁ [μm], the tensile elastic modulus of MD is E ₁ [MPa], and the film tension of the MD before passing through the pair of bonding rollers is F ₁ [N/m] , The thickness of the polarizing plate is T ₂ [μm], the tensile modulus in the MD direction is E ₂ [MPa], and the film tension of the MD before passing through the pair of bonding rollers is F ₂ [N/m], the above pressing step is performed under the condition of satisfying the following formula (I):

[2] The manufacturing method according to [1], wherein the pressing step is performed under the condition that the following formula (II) is satisfied:

[3] The manufacturing method according to [1] or [2], wherein when the polarizing plate is formed as a monolithic body, curling may occur on the side where the protective film is superimposed.

[4] The manufacturing method according to any one of [1] to [3], wherein the polarizing plate contains a polarizing film, a first thermoplastic resin film laminated on one side thereof, and a second layer laminated on the other side Thermoplastic resin film.

[5] The production method according to [4], wherein the equilibrium moisture content of the first thermoplastic resin film at a temperature of 23° C. and a relative humidity of 55% is higher than that of the second thermoplastic resin film.

[6] The production method according to [5], wherein the difference between the equilibrium moisture content of the first thermoplastic resin film and the second thermoplastic resin film is 0.5% by weight or more.

[7] The production method according to any one of [4] to [6], wherein the protective film is disposed on the side of the first thermoplastic resin film.

[8] The production method according to any one of [4] to [7], wherein the equilibrium moisture content of the first thermoplastic resin film is 1.5% by weight or more.

[9] The manufacturing method according to any one of [1] to [8], wherein the thickness of the polarizing plate is 100 μm or less.

According to the present invention, it is possible to manufacture a polarizing plate with a protective film that sufficiently suppresses reverse curling. According to this polarizing plate with a protective film, the above-mentioned defects can be suppressed, and lamination to the image display element can be carried out with good productivity.

1‧‧‧Protection film

2. 2a, 2b, 2c ‧‧‧ polarizer

3‧‧‧ Polarizer with protective film

5‧‧‧ Laminating roller

10‧‧‧ Polarizing film

20‧‧‧The first thermoplastic resin film

30‧‧‧The second thermoplastic resin film

40‧‧‧adhesive layer

50‧‧‧ Separation membrane

FIG. 1 is a side view schematically showing an example of a method for manufacturing a polarizing plate with a protective film of the present invention.

FIG. 2 is a schematic diagram illustrating MD curling, (a) is a side view, and (b) is a top view.

FIG. 3 is a schematic cross-sectional view showing an example of the layer configuration of the polarizing plate.

FIG. 4 is a schematic cross-sectional view showing another example of the layer configuration of the polarizing plate.

Fig. 5 is a schematic cross-sectional view showing another example of the layer configuration of the polarizing plate.

(1) Press steps

Referring to FIG. 1, the method for manufacturing a polarizing plate with a protective film of the present invention includes: overlapping the protective film 1 on one side of the polarizing plate 2 and passing between a pair of bonding rollers 5 and 5 The step of pressing the laminate of the protective film 1 and the polarizing plate 2; and, by this step, the polarizing plate 3 with a protective film is manufactured. In general, the protective film 1 and the polarizing plate 2 used in the pressing step are continuously drawn from a drawing roller (not shown) and continuously transported, and introduced into a pair of bonding rollers 5 and 5. The transport directions of the protective film 1 and the polarizing plate 2 are the longitudinal direction of the film, and generally, the transport directions of the two are parallel.

Regarding the above pressing step, when the thickness of the protective film 1 is set to T ₁ [μm] and the tensile modulus of elasticity of MD is set to E ₁ [MPa], the MD of the MD before passing through the pair of bonding rollers 5 and 5 The film tension is set to F ₁ [N/m], the thickness of the polarizing plate 2 is set to T ₂ [μm], and the tensile modulus of elasticity in the MD direction is set to E ₂ [MPa], and will pass a pair of bonding When the film tension of the MD before the rollers 5 and 5 is set to F ₂ [N/m], the above pressing step is performed under the condition satisfying the following formula (I):

In this specification, the term MD means the mechanical flow direction of the membrane, that is, the length direction of the membrane. The direction orthogonal to MD, that is, the film width direction, is also referred to as TD in this specification.

A protective film and a polarizing plate 2 of the MD tensile modulus E _1, E _2, based on the tensile modulus of elasticity at a relative humidity of 55% 23 ℃ environment is described later follow content items to the embodiment described Determination. MD 1 and the polarizing plate protective film 2 of the membrane tension F _1, F _2, line by a pair of lamination rolls before the film tension 5,5, mean a pair of lamination rollers located on the upstream side thereof and 5,5 and The tension of the film running between the driving rollers (pair of rollers) closest to the laminating rollers 5 and 5.

By bonding the protective film 1 to the polarizing plate 2 under the condition satisfying the above formula (I), the shape of the polarizing plate 2 can be corrected (curl correction) so that the main surface on which the protective film 1 is superimposed is in a concave direction (That is, positive curling direction). Therefore, for example, when the polarizing plate 2 used in the pressing step is made as a single piece, when reverse curl occurs (the main surface side on which the protective film 1 is superimposed is convexly curled), according to the present invention, this The reverse curl is corrected in the forward curl direction, and as a result, the reverse curl can be sufficiently suppressed when the monolithic body is formed, and the polarizing plate 3 with a protective film that is flat without curl or has positive curl can be obtained. When the obtained polarizing plate 3 with a protective film is made into a monolithic body, it is preferably flat without curl or positive curl.

According to the discussion of the present invention, the left and right sides of the above formula (I) are respectively indicators that show the strain states of the protective film 1 and the polarizing plate 2 when they are attached to each other. The reason why the polarizing plate 2 can be corrected in the positive curling direction by bonding the protective film 1 to the polarizing plate 2 under the condition satisfying the above formula (I) is considered to be due to the strain to be removed after the bonding The reason why the force becomes larger in the protective film 1 is.

The relationship of the above formula (I) can be selected from "the thickness of the protective film 1 and/or the polarizing plate 2", "the tensile modulus of elasticity of MD", and "before passing a pair of bonding rollers 5, 5" One or two of the "MD film tension" To achieve this. The adjusted element preferably includes the film tension of the protective film 1 and/or the polarizing plate 2.

The curling is explained here. The so-called curling means that the optical member (optical film) such as the polarizing plate 2 or the polarizing plate 3 with a protective film is warped into an arch shape, and this deformation is usually generated in a single body of the optical member. Curling has a tendency that the optical member is more likely to be produced as a film.

Curling depends on which of two opposing main surfaces of the optical member is convex and curled, and can be classified into two types: "forward curl" and "reverse curl". When the main surface attached to the side of an image display element such as a liquid crystal cell is used as the first main surface, and the main surface on the opposite side is used as the second main surface, "positive curl" refers to the first main surface side A convex curl, "reverse curl" means a curl that makes the second main surface side convex. The polarizing plate 2 used in the manufacturing method of the present invention is typically formed as a single-piece body, and it typically generates reverse curl (a convex curl on the main surface side where the protective film 1 is superimposed).

In addition, curling can be classified into two types of "MD curling" and "TD curling" depending on which end (edge) of the optical member as a single body is generated. Referring to Figure 2, with the convex side facing down, when placing the single piece of the curled optical member on a flat pedestal, "MD curl" refers to the end of the MD (typically both ends) ) Curled up, "TD curl" refers to curled up end of TD (typically both ends). The manufacturing method of the present invention is particularly advantageous for correcting MD curl.

Optical components such as polarizer 2 or polarizer 3 with protective film The possible curling (normal curling, reverse curling, MD curling, TD curling, or the amount of curling) is performed on the monolithic body cut from the resulting optical member. This monolithic body is a square monolithic body with a pair of opposite sides parallel to the MD and the remaining pair of opposite sides parallel to the TD. The MD length is 300 mm and the TD length is 200 mm.

According to the present invention, when it is formed as a monolithic body, the reverse curl can be sufficiently suppressed, and it is preferable that the polarizing plate 3 with a protective film that is flat without curl or has positive curl is provided. According to the polarizing plate 3 with a protective film, when it is bonded to the image display element through the adhesive layer, it can effectively suppress the occurrence of bonding errors, or air bubbles are mixed into the interface between the adhesive layer and the image display element It is possible to carry out the bonding of the polarizing plate 3 with a protective film and the image display element with good productivity in a bad situation. When the curl produced by the polarizing plate 3 with a protective film is positive curl, even if the amount of curl is relatively large, there is no particular problem from the viewpoint of the above-mentioned disadvantages and productivity. The polarizing plate 3 with a protective film obtained by the present invention can have reverse curl to the extent that the above-mentioned defects can be suppressed (preferably, the above-mentioned defects are not generated).

The correction amount in the positive curling direction of the present invention depends on the difference between the left and right sides of the above formula (I) as an indicator of strain. The larger the difference, the greater the correction amount. The polarizing plate 2 used in the pressing step is made into a monolithic body, although it varies according to the degree of curling, but in order to make the obtained polarizing plate with protective film 3 flat without anti-curling Or with positive curl, it is preferable to perform the aforementioned pressing step under the condition of satisfying the following formula (II):

When the polarizing plate 2 provided for the pressing step has a large reverse curl, in order to make the resulting polarizing plate 3 with a protective film flat or with positive curl, it is sometimes necessary to make the left side of the above formula (II) larger than 55 (for example, 60 or more, 70 or more, 80 or more, 100 or more, 130 or more, 160 or more, or 180 or more). The left side of the above formula (II) is, for example, 1000 or less.

The left and right sides of the above formula (I) are usually 1×10 ^-5 to 1000×10 ^-5 , and may be 5×10 ^-5 to 500×10 ^-5 .

When the protective film 1 is superposed on one side of the polarizing plate 2 and passes between the pair of bonding rollers 5 and 5, the adhesive layer of the protective film 1 is superposed so as to contact the single side of the polarizing plate 2 . Before the lamination of the protective film 1 and the polarizing plate 2, the bonding surface of at least one of the adhesive layer of the protective film 1 and the polarizing plate 2 may be subjected to plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (fire) Surface activation treatment such as treatment and saponification treatment.

In the step of pressing by the pair of bonding rollers 5 and 5, the pressure (rolling) applied to the laminate of the protective film 1 and the polarizing plate 2 is, for example, 0.01 to 0.5 MPa, and may be 0.05 to 0.3 MPa. Rolling usually does not greatly affect the curling of the obtained polarizing plate 3 with a protective film. For the bonding rollers 5 and 5, a conventionally known surface such as metal (including alloys such as SUS) or rubber products can be used.

(2) Protective film

The protective film 1 is usually composed of a base film and an adhesive layer stacked thereon. The protective film 1 is a film used to protect the surface of the polarizing plate 2. Usually, for example, after the polarizing plate 3 with a protective film is attached to an image display element, etc., the entire film is peeled off together with the adhesive layer. The base film can be made of thermoplastic resins (such as polyethylene resins, polypropylene resins, cyclic polyolefin resins and other polyolefin resins; polyethylene terephthalate, polyethylene naphthalate and other polyesters Resin; polycarbonate resin; (meth)acrylic resin, etc.). The adhesive layer may be composed of (meth)acrylic adhesive, epoxy adhesive, urethane adhesive, polysiloxane adhesive, and the like. In addition, it may be composed of a resin layer having self-adhesive properties such as polypropylene resin and polyethylene resin. The tensile modulus of elasticity E _{1 in the} MD direction can be adjusted mainly through the selection of the material of the base film.

In this specification, the "(meth)acrylic resin" means at least one selected from the group consisting of acrylic resins and methacrylic resins. Other terms with "(methyl)" are also the same.

The thickness T _{1 of the} protective film 1 may be, for example, 5 to 200 μm, preferably 10 to 150 μm, particularly preferably 20 to 120 μm, more preferably 25 to 100 μm (for example, 90 μm or less, and further 75 μm or less). When the thickness T _{1 is} less than 5 μm, the protection of the polarizing plate 2 may be insufficient, and it is also disadvantageous in terms of handling. When the thickness T ₁ exceeds 200 μm, it is disadvantageous in terms of cost and reworkability of the protective film 1. In addition, when the thickness T ₁ exceeds 200 μm, it becomes difficult to satisfy the relational expressions of the above formula (I) and/or formula (II).

(3) Polarizing plate

The polarizing plate 2 is a polarizing element containing at least a polarizing film, and usually contains a thermoplastic resin film such as a protective film laminated on at least one side of the polarizing film. The protective film 1 is an optical film that plays a protective role of the polarizing film.

(3-1) Configuration example of polarizing plate

The polarizing plate 2 may contain a layer or film other than the polarizing film and the protective film, for example, an optical layer or optical film having other optical functions other than the polarizing film. Examples of the optical layer or optical film having other optical functions include a retardation film (or retardation layer), a brightness enhancement film, and the like. Various optical films containing a protective film can be laminated on the polarizing film through an adhesive layer or an adhesive layer. In addition, the polarizing plate 2 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.

The thickness T _{2 of the} polarizing plate 2 is usually 200 μm or less, and from the viewpoint of thinning, it is preferably 125 μm or less, particularly preferably 100 μm or less, and more preferably 75 μm or less. Although the smaller the thickness T ₂ is, the more easily the polarizing plate 2 is curled in its monolithic body, according to the present invention, even if the thickness T ₂ of the polarizing plate 2 is thin and the polarizing plate 2 is made into a monolithic body Curlers can also effectively correct this reverse curl in the direction of positive curl. From the viewpoint of thinning and optical characteristics, although it is difficult to adjust the mechanical properties of the polarizing film and the protective film in order to make the curl when the polarizing plate 2 is made into a single body flat or positive curl, the protective film is usually in The polarizing plate 3 with a protective film is peeled off after being attached to, for example, an image display element. Therefore, it is possible to adjust mechanical characteristics for the purpose of curl correction.

An example of the layer configuration of the polarizing plate 2 will be described with reference to FIGS. 3 to 5, but the layer configuration is not limited to these examples. The polarizing plate 2a shown in FIG. 3 includes: a polarizing film 10; a first thermoplastic resin film 20 attached to one side of the polarizing film 10; and a second thermoplastic resin film 30 attached to the other side of the polarizing film 10; The adhesive layer 40 laminated on the outer surface of the second thermoplastic resin film 30; and the separation film 50 laminated on the outer surface of the adhesive layer 40. The separation film 50 is a peelable film for protecting the surface (outer surface) of the adhesive layer 40. The first and second thermoplastic resin films 20 and 30 are, for example, protective films.

As for the polarizing plate 2b shown in FIG. 4, one of the first and second thermoplastic resin films 20, 30 may be omitted. In the polarizing plate 2b, the second thermoplastic resin film 30 is omitted, and the adhesive layer 40 is directly bonded to the outer surface of the polarizing film 10 (the surface on the opposite side to the surface on which the first thermoplastic resin film 20 is laminated). Such a polarizing plate having a thermoplastic resin film on only one side of the polarizing film 10 is advantageous for the thinning of the polarizing plate. Although the polarizing plate 2 may easily curl in its monolithic body when there is a thermoplastic resin film on only one area of the polarizing film 10, according to the present invention, even if the thermoplastic resin film is laminated on only one area of the polarizing film 10 If the resin film has reverse curl when the polarizing plate 2 is made as a single body, it can also effectively correct the reverse curl in the positive curl direction.

In addition, as in the polarizing plate 2c shown in FIG. 5, the adhesive layer 40 and the separation film 50 can be omitted. The polarizing plate 2 may have a protective film different from the protective film 1 provided for the pressing step on one side in advance. At this time, the obtained polarizing plate 3 with a protective film is biased with a protective film on both sides Light board.

Although FIGS. 3 to 5 are not shown in the drawings, the polarizing film 10 and the first and second thermoplastic resin films 20 and 30 can be bonded together preferably by using an adhesive.

(3-2) Polarizing film

The polarizing film 10 may be formed by aligning a dichroic dye with a uniaxially stretched polyvinyl alcohol-based resin film. As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, a saponified polyvinyl acetate resin can be used. As for the polyvinyl acetate-based resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, copolymers such as vinyl acetate and other monomers copolymerizable therewith can also be exemplified. Other monomers copolymerizable 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 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, and particularly preferably in the range of 98.0 to 100.0 mol%. When the degree of saponification is less than 80.0 mol%, the water resistance and heat and humidity resistance of the obtained polarizing plate 2 may decrease.

The degree of saponification means the unit ratio (mol%) to represent the acetate group (ethoxyl group) contained in the polyvinyl acetate resin as the raw material of the polyvinyl alcohol resin through the saponification step. -The ratio of OCOCH ₃ ) to hydroxyl group, and is defined by the following formula.

Saponification degree (mol%) = 100 × (number of hydroxyl groups) / (number of hydroxyl groups + acetate group) (Number) Saponification degree can be obtained according to JIS K 6726 (1994). The higher the degree of saponification, the higher the ratio of hydroxyl groups, and therefore the lower the ratio of acetic acid groups that hinder crystallization.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10,000, particularly preferably 1500 to 8000, and more preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol-based resin can also be determined in accordance with JIS K 6726 (1994). When the average degree of polymerization is less than 100, it is difficult to obtain better polarizing performance, and when it exceeds 10,000, the solubility to solvents deteriorates, and it may be difficult to form a polyvinyl alcohol-based resin film.

The dichroic pigment contained (adsorption alignment) in the polarizing film 10 may be iodine or a dichromatic 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, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Sky Red GL, Sky Red KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL , Direct Sky Blue, Direct Fast Orange S, Fast Black, etc. The dichroic pigments can be used alone or in combination of two or more. The dichromatic pigment is preferably iodine.

The polarizing film 10 can be manufactured through the following steps: a step of uniaxially stretching the polyvinyl alcohol-based resin film; a step of dyeing the polyvinyl alcohol-based resin film with a dichromatic pigment to adsorb the dichromatic pigment; The step of performing cross-linking treatment on the polyvinyl alcohol-based resin film with dichromatic pigment; and the step of washing with water after the cross-linking treatment.

The polyvinyl alcohol-based resin film is obtained by forming the polyvinyl alcohol-based resin into a film. The film formation method is not particularly limited, and generally known methods such as a melt extrusion method and a solvent casting method can be used. The film thickness of the polyvinyl alcohol-based resin film is, for example, about 10 to 150 μm, preferably 50 μm or less, and particularly preferably 35 μm or less.

The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before, simultaneously with, or after the dyeing of the dichroic pigment. When uniaxial stretching is performed after dyeing, the uniaxial stretching can be performed before or during the cross-linking treatment. In addition, it is also possible to perform uniaxial stretching in these plural stages.

In uniaxial stretching, uniaxial stretching can be performed between rolls with different peripheral speeds, or uniaxial stretching using hot rollers. In addition, the uniaxial stretching may be dry stretching performed in the atmosphere or wet stretching performed in the solution of the polyvinyl alcohol-based resin film. The stretching ratio is usually about 3 to 8 times.

For the method of dyeing the 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 may be used. The polyvinyl alcohol-based resin film is preferably treated by immersion in water (swelling treatment) before dyeing.

When iodine is used as the dichroic pigment, a method of immersing the polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide for dyeing is generally used. The content of iodine in the dyeing aqueous solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. In addition, 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 to 40°C.

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

The cross-linking treatment after dyeing with a dichroic pigment is usually performed by immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing a cross-linking agent. A preferred example of the cross-linking agent is boric acid, but boron compounds such as borax, glyoxal, glutaraldehyde and other cross-linking agents can also be used. Only 1 type may be used for a crosslinking agent, or 2 or more types may be used together.

The amount of the crosslinking agent in the aqueous solution containing the crosslinking agent is usually 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic pigment, the aqueous solution containing the crosslinking agent preferably contains potassium iodide. The amount of potassium iodide in the aqueous solution containing the cross-linking agent is generally 0.1 to 15 parts by weight, preferably 5 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, preferably 50 to 85°C.

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

After washing with water, a drying treatment is applied to obtain a polarizing film 10. The drying treatment may be drying by a hot air dryer, drying by contact with a hot roller, drying by a far-infrared heater, or the like. The temperature of the drying process is usually about 30 to 100°C, preferably 50 to 90°C.

The thickness of the polarizing film 10 is usually about 2 to 40 μm. From the viewpoint of thinning the polarizing plate 2, the thickness of the polarizing film 10 is preferably 20 μm or less, particularly preferably 15 μm or less, and more preferably 10 μm or less. Although the smaller the thickness of the polarizing film 10, the more easily the polarizing plate 2 is curled in its monolithic body, but according to the present invention, even if the thickness of the polarizing film 10 is small and a reflection occurs when the polarizing plate 2 is made into a monolithic body Curlers can also effectively correct this reverse curl in the direction of positive curl.

(3-3) First and second thermoplastic resin films

The first and second thermoplastic resin films 20 and 30 are each independently composed of a translucent thermoplastic resin (preferably an optically transparent thermoplastic resin). The thermoplastic resin constituting the first and second thermoplastic resin films 20 and 30 may be, for example, a chain polyolefin resin (polypropylene resin, etc.) or a cyclic polyolefin resin (norbornene resin, etc.). Olefin resins; cellulose ester resins such as cellulose triacetate and cellulose diacetate; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resins; (Meth)acrylic resins such as methyl acrylate resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile-butadiene-styrene resins; acrylonitrile-styrene resins; polyvinyl acetate Ester resin; Polyvinylidene chloride resin; Polyamide resin; Polyketal resin; Modified polyphenylene ether resin; Polyphenol resin; Polyether resin; Polyarylate resin; Polyamide imide resin; Polyimide resin, etc.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resins and polypropylene resins, and copolymers composed of two or more chain olefins. More specific examples include polypropylene resins (polypropylene resins that are homopolymers of propylene, or copolymers based on propylene), polyethylene resins (polyethylene resins that are homopolymers of ethylene, or It is a copolymer mainly composed of ethylene).

Cyclic polyolefin 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, and copolymers of cyclic olefins and chain olefins such as ethylene and propylene. (Representatives are random copolymers), graft polymers modified with unsaturated carboxylic acids or their derivatives, and these hydrides. Among them, it can be preferably used as a norbornene-based resin using norbornene-based monomers such as norbornene or a polycyclic norbornene-based monomer as a cyclic olefin.

Cellulose-based resin means that part or all of the hydrogen atoms in the hydroxyl groups of cellulose obtained from raw cellulose such as cotton linter or wood pulp (broad-leaved wood pulp, coniferous wood pulp) and the like are passed through acetyl, propyl and And/or cellulose organic acid ester or cellulose mixed organic acid ester substituted with butyl acetyl group. For example, those composed of cellulose acetate, propionate, butyrate, and mixed esters thereof can be cited. Among them, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, and cellulose acetate butyrate are preferred.

Polyester resin refers to resins other than the above-mentioned cellulose resins having an ester bond, and is generally composed of polycarboxylic acid or its derivatives and Consists of polycondensate of alcohol. As the polycarboxylic acid or its derivative, a divalent dicarboxylic acid or its derivative can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalene dicarboxylate. Wait. As the polyhydric alcohol, a divalent diol can be used, and examples thereof include ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, and cyclohexane dimethanol. Examples of preferred polyester resins include polyethylene terephthalate.

Polycarbonate-based resin refers to an engineering plastic containing a polymer bonded by a monomer unit through a carbonate group, and is a resin having high impact resistance, heat resistance, flame resistance, and transparency. The polycarbonate-based resin may also be a resin called modified polycarbonate for modifying the polymer skeleton in order to reduce the photoelastic coefficient, or a copolymerized polycarbonate with improved wavelength dependence.

(Meth)acrylic resin means a polymer containing structural units derived from (meth)acrylic monomers. The polymer is typically a polymer containing methacrylate. Preferably, the ratio of methacrylate-derived structural units contains 50% by weight or more of the polymer relative to the entire structural units. The (meth)acrylic resin may be a homopolymer of methacrylate or a copolymer containing structural units derived from other polymerizable monomers. In this case, it is preferable that the ratio of structural units derived from other polymerizable monomers is 50% by weight or less relative to the entire structural units.

The methacrylate that can constitute the (meth)acrylic resin film is preferably an alkyl methacrylate. Examples of alkyl methacrylates include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, Isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tertiary butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, methacrylic acid 2 -Alkyl methacrylates having an alkyl group having 1 to 8 carbon atoms, such as hydroxyethyl esters. The carbon number of the alkyl group contained in the alkyl methacrylate is preferably 1 to 4. Among (meth)acrylic resins, methacrylate may be used alone or in combination of two or more.

The other polymerizable monomers that can constitute the (meth)acrylic resin film include acrylates and other compounds having a polymerizable carbon-carbon double bond in the molecule. Other polymerizable monomers may be used alone or in combination of two or more. The acrylate is preferably an alkyl acrylate. Examples of alkyl acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, acrylic ring Alkyl acrylates, such as hexyl esters and 2-hydroxyethyl acrylate, with an alkyl group having 1 to 8 carbon atoms. The alkyl group contained in the alkyl acrylate preferably has 1 to 4 carbon atoms. Among (meth)acrylic resins, acrylates may be used alone or in combination of two or more.

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

The first and second thermoplastic resin films 20 and 30 may also be protective films laminated on one surface of the polarizing film 10 and protecting the polarizing film 10. The first and second thermoplastic resin films 20 and 30 may also be protective films having optical functions such as retardation films and brightness enhancement films. For example, you can include The thermoplastic resin film of the aforementioned material is stretched (uniaxially stretched, biaxially stretched, etc.), or a liquid crystal layer is formed on the film, etc., thereby making a retardation film given an arbitrary retardation value. The first and/or second thermoplastic resin films 20 and 30 may also have surface treatment layers (coating layers) such as a hard coat layer, an anti-glare layer, an anti-reflection layer, an anti-static layer, and an anti-fouling layer stacked on the surface.

The thickness of the first and second thermoplastic resin films 20 and 30 is usually 1 to 100 μm, and from the viewpoint of strength and handleability, it is preferably 5 to 60 μm, and particularly preferably 5 to 50 μm. If the film thickness is within this range, the polarizing film 10 can be mechanically protected, and the shrinkage of the polarizing film 10 when the polarizing plate 2 is exposed to a hot and humid environment can be suppressed. Although the smaller the thickness of the first thermoplastic resin film 20 or the second thermoplastic resin film 30, the more easily the polarizing plate 2 is curled in its monolithic body, but according to the present invention, even the first thermoplastic resin film 20 or the second thermoplastic resin film 30 If the thickness of the resin film 30 is, for example, thinner than 40 μm or thinner and thinner than 30 μm, and the reverse curl is generated when the polarizing plate 2 is formed into a single body, the reverse curl can be effectively corrected in the positive curl direction.

When the polarizing plates 2a and 2c shown in FIGS. 3 and 5 are provided with the first thermoplastic resin film 20 on one side of the polarizing film 10 and the second thermoplastic resin film 30 on the other side, the first thermoplastic resin film 20 and The second thermoplastic resin film 30 may be composed of the same kind of thermoplastic resin, or may be composed of different kinds of thermoplastic resin, but in the case of being composed of different kinds of thermoplastic resin, etc., it is attached to the equilibrium moisture of the thermoplastic resin film on both sides When the rate or the moisture permeability are different from each other, the monolithic body of the polarizing plate 2 is particularly prone to curl, so the present invention is particularly advantageous at this time.

For example, the first thermoplastic resin film 20 series can be balanced The film having a higher moisture content than the second thermoplastic resin film 30. Although the greater the difference between the equilibrium moisture rates of the first thermoplastic resin film 20 and the second thermoplastic resin film 30 attached to the double sides of the polarizing film 10, the polarizing plate 2 is more likely to curl in its monolithic body, but according to this The invention is effective even if the difference in equilibrium moisture content is 0.5% by weight or more, further 1% by weight or more, and further 1.5% by weight or more, and the anti-curling occurs when the polarizing plate 2 is made as a monolithic body. Correct this reverse curl in the direction of positive curl.

In this specification, the equilibrium moisture content of the membrane is measured by the dry weight method, specifically, it is determined according to the following formula: equilibrium moisture ratio (weight %) = {(membrane weight before drying treatment-drying treatment Weight of film after drying)/Weight of film before drying}×100 Here, the weight of the film before drying refers to the weight after storing the film for 24 hours in an environment with a temperature of 23° C. and a relative humidity of 55%. Drying refers to Drying at 105°C for 2 hours. Combinations of thermoplastic resin films with a difference in equilibrium moisture content of 0.5% by weight or more include, for example, combinations of cellulose-based resin films (TAC films, etc.) and cyclic polyolefin-based resin films, and cellulose-based resin films (TAC Film, etc.) and (meth)acrylic resin film, cellulose resin film (TAC film, etc.) and polyester resin film, cellulose resin film (TAC film, etc.) and chain polyolefin Combination of resin film, combination of (meth)acrylic resin film and cyclic polyolefin resin film, combination of (meth)acrylic resin film and polyester resin film, etc. The difference in the equilibrium moisture content between the first thermoplastic resin film 20 and the second thermoplastic resin film 30 is usually 5% by weight or less, preferably 2.5% by weight or less.

The equilibrium moisture content of the first thermoplastic resin film 20 is, for example, 1.5% by weight or more, and may be 2% by weight or more. The equilibrium moisture content of the first thermoplastic resin film 20 is usually 5% by weight or less.

When a film having a balanced moisture content higher than that of the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, the balanced moisture content of the second thermoplastic resin film 30 is usually 0.1 to 1.5% by weight, preferably 0.1 to 1% by weight . Examples of the thermoplastic resin constituting the second thermoplastic resin film 30 that can achieve this equilibrium moisture content include cyclic polyolefin resins, (meth)acrylic resins, polyester resins, chain polyolefin resins, and the like.

The equilibrium moisture content of the thermoplastic resin film can be adjusted not only by its material (the type of thermoplastic resin film that constitutes the film), but also by the thickness of the film and the surface treatment layer (coating layer) that can be attached to the surface of the film ) To adjust the presence or material.

When a film having a balanced moisture content higher than the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, from the viewpoint of correcting the reverse curl easily generated by the polarizing plate 2 toward the positive curl direction, the pressure is usually In the step, the protective film 1 is arranged on the first thermoplastic resin film 20 side of the polarizing plate 2.

In addition, for example, as the first thermoplastic resin film 20, a film having a moisture permeability higher than that of the second thermoplastic resin film 30 can be used. Although the greater the difference in the moisture permeability between the first thermoplastic resin film 20 and the second thermoplastic resin film 30 attached to the both sides of the polarizing film 10, the polarizer 2 is more likely to curl in its monolithic body, but according to the present invention , even if the moisture permeability of this difference of 30g / (m ² .24hr) or more, and further 50g / (m ² .24hr) above, further to 100g / (m ^2. 24hr) or more and the polarizing plate 2, Ltd. If a reverse curl occurs when it becomes a monolithic body, this reverse curl can also be effectively corrected in the forward curl direction.

In this specification, the moisture permeability of the film refers to the moisture permeability at a temperature of 40° C. and a relative humidity of 90% measured by the cup method specified in JIS Z 0208. The combination of thermoplastic resin films having a difference in moisture permeability of 30 g/(m ² .24 hr) or more includes, 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. Combination of resin film (TAC film, etc.) and (meth)acrylic resin film, combination of cellulose resin film (TAC film, etc.) and polyester resin film, cellulose resin film (TAC film, etc.) and chain Combination of polyolefin-based resin film, combination of (meth)acrylic resin film and cyclic polyolefin-based resin film, combination of (meth)acrylic resin film and polyester-based resin film, etc. 20 and the difference between the moisture permeability of the first thermoplastic resin film of the second thermoplastic resin film 30 is generally of 5000g / (m ² .24hr) or less.

The moisture permeability of the first thermoplastic resin film 20 is, for example, 300 g/(m ² .24 hr) or more, and may be 400 g/(m ² .24 hr) or more. When the moisture permeability is 300 g/(m ² .24hr) or more, when the first thermoplastic resin film 20 and the polarizing film 10 are bonded using an aqueous adhesive, the layer containing the aqueous adhesive can be efficiently dried and improved From the viewpoint of productivity, it is also advantageous. The moisture permeability of the first thermoplastic resin film 20 is usually 5000 g/(m ² .24 hr) or less.

When a film having a moisture permeability higher than that of the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, the moisture permeability of the second thermoplastic resin film 30 is usually 1 to 350 g/(m ² .24hr), preferably 5 to 200g / (m ² .24hr). Examples of the thermoplastic resin constituting the second thermoplastic resin film 30 that can achieve this moisture permeability include cyclic polyolefin resin, (meth)acrylic resin, polyester resin, chain polyolefin resin, and the like.

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

When a film having a moisture permeability higher than that of the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, from the viewpoint of correcting the reverse curl easily generated by the polarizing plate 2 toward the positive curl direction, usually in the above pressing step In this case, the protective film 1 is arranged on the first thermoplastic resin film 20 side of the polarizing plate 2.

As described above, the polarizing film 10 and the first and second thermoplastic resin films 20 and 30 can be bonded using an adhesive. Before laminating the first and second thermoplastic resin films 20 and 30 to the polarizing film 10, plasma treatment may be performed on the bonding surface of the polarizing film 10 and/or the first and second thermoplastic resin films 20 and 30 , Corona treatment, ultraviolet irradiation treatment, flame (fire) treatment, saponification treatment and other surface activation treatment. By this surface activation treatment, the adhesion between the polarizing film 10 and the first and second thermoplastic resin films 20 and 30 can be improved.

As the adhesive, an aqueous adhesive, an activation energy ray-curable adhesive or a thermosetting adhesive can be used, and preferably an aqueous adhesive or an activation energy ray-curable adhesive. When the thermoplastic resin film is laminated on both sides of the polarizing film 10, the adhesives on both sides may be the same type of adhesives or different types of adhesives. Although when using different kinds of adhesives, the polarizing plate 2 may easily curl in its monolithic body, but according to the present invention, even If different types of adhesives are used and reverse curl is generated when the polarizing plate 2 is made into a single piece, the reverse curl can be effectively corrected in the positive curl direction.

The water-based adhesive system dissolves or disperses the adhesive component in water. The water-based adhesive that can be preferably used is, for example, an adhesive composition using a polyvinyl alcohol-based resin or urethane resin as a main component.

When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin may be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol or fully saponified polyvinyl alcohol. Modified polyvinyl alcohol such as carboxyl-modified polyvinyl alcohol, acetyl-acetyl-modified polyvinyl alcohol, hydroxymethyl-modified polyvinyl alcohol, and amine-modified polyvinyl alcohol Department of resin. Polyvinyl alcohol-based resins, in addition to vinyl alcohol homopolymers obtained by saponification of polyvinyl acetate which is a homopolymer of vinyl acetate, can also be used other copolymerizable vinyl acetate A polyvinyl alcohol copolymer obtained by saponification of a copolymer of monomers.

A water-based adhesive that uses a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of a polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol-based resin in the adhesive is generally 1 to 10 parts by weight, preferably 1 to 5 parts by weight relative to 100 parts by weight of water.

The adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin is preferably added with a polyaldehyde, a melamine-based compound, a zirconia compound, a zinc compound, a glyoxal, a glyoxal derivative, Water-soluble epoxy resin and other hardening components or cross-linking agent. Water soluble The epoxy resin, for example, can be preferably used: for polyamidoamines obtained by the reaction of polyalkylene polyamines such as diethylenetriamine and triethylenetetramine with dicarboxylic acids such as adipic acid, epichlorohydrin Polyamide polyamine epoxy resin obtained by reacting alcohol with it. Examples of commercially available products of this polyamine polyamine epoxy resin include "Sumirez Resin 650" (manufactured by Taoka Chemical Industry Co., Ltd.), "Sumirez Resin 675" (manufactured by Taoka Chemical Industry Co., Ltd.), and "WS-525" "(Made by Japan PMC Co., Ltd.) etc. The addition amount of these hardenable components or crosslinking agents (the total amount when both the hardenable components and crosslinking agents are added) is usually 1 to 100 parts by weight, preferably 1 to 100 parts by weight relative to 100 parts by weight of the polyvinyl alcohol-based resin It is 1 to 50 parts by weight. When the addition amount of the curable component or the crosslinking agent is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving the adhesiveness tends to decrease. In addition, when the addition amount is relative to the polyvinyl alcohol When 100 parts by weight of the system resin exceeds 100 parts by weight, the adhesive layer tends to become brittle.

In addition, a preferred example when using urethane resin as the main component of the adhesive includes a mixture of a polyester-based ionic polymer urethane resin and a compound having a glycidyloxy group. The polyester ionic polymer urethane resin refers to a urethane resin having a polyester skeleton, into which a small amount of ionic components (hydrophilic components) are introduced. The ionic polymer urethane resin is emulsified directly in water without using an emulsifier and becomes an emulsifier, so it can be preferably used as an aqueous adhesive.

When an aqueous adhesive is used, after the polarizing film 10 is bonded to the first and/or second thermoplastic resin films 20, 30, it is preferably implemented to remove The water is a drying step of the water contained in the adhesive. After the drying step, for example, a curing step for curing at a temperature of 20 to 45°C may be set.

The active energy ray hardening adhesive includes, for example, an adhesive hardened by irradiation of active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. When an active energy ray hardening adhesive is used, the adhesive layer included in the polarizing plate 2 is a hardened layer of the adhesive.

The active energy ray-curable adhesive may be an adhesive containing an epoxy-based compound hardened by cationic polymerization as a curable component, and preferably an ultraviolet-curable adhesive containing the epoxy-based compound as a curable component. Here, the epoxy-based compound refers to a compound having an average of one or more, preferably two or more epoxy groups in the molecule. Epoxy compounds may be used alone or in combination of two or more.

Examples of epoxy compounds that can be preferably used include hydrogenated epoxy compounds obtained by subjecting epichlorohydrin to an alicyclic polyol obtained by hydrogenating an aromatic ring of an aromatic polyol (Glycidyl ether of a polyhydric alcohol having an alicyclic ring); aliphatic epoxy compounds such as aliphatic polyhydric alcohols or polyglycidyl ethers of the alkylene oxide adduct; alicyclic epoxy compounds, which are An epoxy compound having one or more epoxy groups bonded to an alicyclic ring in the molecule.

The active energy ray-curable adhesive may contain a (meth)acrylic compound that is free-radically polymerizable in place of or together with the epoxy compound as the curable component. Examples of (meth)acrylic compounds include: (meth)acrylate monomers having at least one (meth)acryloyloxy group in the molecule; two or more types of A compound of a functional group is obtained by reaction, and a (meth)acrylate oligomer such as a (meth)acrylate oligomer having at least two (meth)acryloyloxy groups in the molecule.

When the active energy ray-curable adhesive contains an epoxy-based compound hardened by cationic polymerization as a curable component, it preferably contains a photo-cationic polymerization initiator. Examples of the photo-cationic polymerization initiator system include, for example, onium salts such as aromatic diazonium salts, aromatic iodonium salts, and aromatic osmium salts; and iron-propadiene complexes. In addition, when the activation energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth)acrylic compound, it preferably contains a photoradical polymerization initiator. Examples of the photo-radical polymerization initiator system include acetophenone-based initiators, diphenyl ketone-based initiators, benzoin ether-based initiators, thioxanthone-based initiators, xanthones, and stilbene. Ketone, camphorquinone, benzaldehyde, anthraquinone, etc.

When the activation energy ray-curable adhesive is used in the lamination of the polarizing film 10 and the first and/or second thermoplastic resin films 20, 30, after the lamination, a drying step may be performed if necessary, followed by irradiation The step of hardening the active energy ray to harden the active energy ray hardening adhesive. The light source of the activation energy ray is not particularly limited, and it is preferably ultraviolet light having a luminous distribution below 400 nm. Specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, Chemical lamp, black light lamp, microwave excited mercury lamp, metal halide lamp, etc.

The irradiation intensity of the activation energy ray for the adhesive layer containing the activation energy ray hardening adhesive can be appropriately determined according to the composition of the adhesive, preferably in the wavelength region where activation of the polymerization initiator is effective The irradiation intensity is set so that it becomes 0.1 to 6000 mW/cm ² . When the irradiation intensity is 0.1mW/cm ² or more, the reaction time will not be too long. When it is 6000mW/cm ² or less, it will be caused by the heat radiated from the light source and the heat generated by the adhesive during curing. There is little concern about yellowing of the agent layer or deterioration of the polarizing film 10.

The irradiation time of the activation energy ray is appropriately determined according to the composition of the adhesive, but it is preferably set so that the integrated light amount represented by the product of the irradiation intensity and the irradiation time becomes 10 to 10000 mJ/cm ² . When the integrated light quantity is 10mJ/cm ² or more, the active species from the polymerization initiator can be sufficiently generated, and the hardening reaction can be more reliably performed. When it is 10000mJ/cm ² or less, the irradiation time will not be too long. Maintain good productivity of the polarizing plate 2.

(3-4) Adhesive layer and separation membrane

As shown in FIGS. 3 and 4, the polarizing plate 2 may contain an adhesive layer 40. The adhesive layer 40 can be directly laminated on the surface of the first or second thermoplastic resin film 20, 30 or the polarizing film 10, and can be used to attach the polarizing plate 3 with a protective film to an image display device (such as a liquid crystal cell) .

The adhesive layer 40 for attaching the polarizing plate 3 with a protective film to an image display element (for example, a liquid crystal cell) is arranged on the main surface of the polarizing plate attached to the side of the image display element such as a liquid crystal cell ( 1st main surface) side. For example, when the polarizing plate 2 contains the first and second thermoplastic resin films 20 and 30 and uses a film with a balanced moisture content and/or moisture permeability higher than the second thermoplastic resin film 30 as the first thermoplastic resin film 20, the adhesive Layer 40 configurable On the second thermoplastic resin film 30 side.

The adhesive layer 40 may be composed of an adhesive composition mainly composed of resins such as (meth)acrylic, epoxy, urethane, ester, polysiloxane, and polyvinyl ether. Among them, an adhesive composition using a (meth)acrylic resin excellent in transparency, weather resistance, heat resistance, etc. as a base polymer is preferred. The adhesive composition may be activated energy ray hardening type or thermosetting type.

As the (meth)acrylic resin used in the adhesive composition, for example, butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, (meth) ) A polymer or copolymer in which one or more (meth)acrylates such as 2-ethylhexyl acrylate are monomers. Preferably, the polar monomer is copolymerized in the (meth)acrylic resin. Examples of polar monomers include (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, alkyl ethyl (meth)acrylate, (meth)acrylamide, and (meth)acrylic acid N,N -Monomers having a carboxyl group, a hydroxyl group, an amide group, an amine group, an epoxy group, etc., such as dimethylamine ethyl ester and glycidyl (meth)acrylate.

The adhesive composition may contain only the above-mentioned base polymer, but usually contains a crosslinking agent. The crosslinking agent can be exemplified by: metal ions with a valence of 2 or more, and a metal salt of carboxylic acid formed between it and the carboxyl group; a polyamine compound, and an amide bond formed between it and the carboxyl group; a polyepoxy compound or Polyol, and form an ester bond between it and carboxyl group; Polyisocyanate compound, and form an amide bond between it and carboxyl group. Among them, polyisocyanate compounds are preferred.

Activated energy ray hardening type adhesive composition, with It is hardened by the irradiation of active energy rays such as ultraviolet rays or electron beams. Before the irradiation of the activated energy rays, it also has adhesiveness and can adhere to the adherend such as a film. Able to adjust the nature of adhesion. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable type. The active energy ray hardening type adhesive composition may contain an active energy ray polymerizable compound in addition to the base polymer and the crosslinking agent. In addition, photopolymerization initiators, photosensitizers, etc. may be contained as necessary.

The adhesive composition may contain: particles for imparting light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, adhesion imparting agents, fillers (metal powder or other inorganic Powder, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, anti-corrosion agents, photopolymerization initiators and other additives.

The adhesive layer 40 can be applied to the adhesive layer forming surface of the polarizing plate 2 by applying an organic solvent dilution of the adhesive composition (that is, the polarizing film 10 or the first or second thermoplastic resin films 20, 30) It is formed by drying and drying. Alternatively, the organic solvent dilution of the adhesive composition is applied to a separation film (for example, separation film 50) and dried to form an adhesive layer, and this is transferred to the adhesive layer forming surface of the polarizing plate 2. Regardless of the method, it is preferable to attach the separation film to the outer surface of the adhesive layer 40 and protect the adhesive layer 40 until use. When an activation energy ray hardening type adhesive composition is used, by irradiating the activation energy ray to the formed adhesive layer, a cured product having a desired degree of hardening can be produced. The thickness of the adhesive layer 40 is usually 1 to 40 μm, from the polarizing plate From the viewpoint of thinning of 2, it is preferably 3 to 25 μm.

The separation film 50 is a film that is used to protect the surface of the image display device (such as a liquid crystal cell) before the adhesive layer 40 is bonded to the surface. The separation membrane 50 is usually composed of a thermoplastic resin film subjected to release treatment on one side, and the release treatment surface is bonded to the adhesive layer 40. The thermoplastic resin film constituting the separation membrane 50 may be, for example, polyethylene resin such as polyethylene, polypropylene resin such as polypropylene, polyester resin such as polyethylene terephthalate or polyethylene naphthalate, etc. . The thickness of the separation membrane 50 is, for example, 10 to 100 μm.

(3-5) Other components of polarizer

The polarizing plate 2 may contain other components other than the above. Other constituent elements include optical layers or optical films having other optical functions other than the polarizing film 10. Specific examples include optical films such as retardation films and brightness enhancement films. Other optical films can be laminated and laminated through an adhesive layer or an adhesive layer.

In addition, the polarizing plate 2 may contain a protective film different from the protective film 1 provided for the above-mentioned pressing step. This protective film is arranged on one surface of the polarizing plate 2. Regarding the configuration of this protective film, the description related to the protective film 1 can be cited.

(3-6) curling of polarizing plate

As described above, according to the present invention, the polarizing plate 2 can be corrected in the forward curling direction, whereby the reverse curling can be sufficiently suppressed when it is made into a monolithic body, preferably flat without curling, or With positive curl Protective film polarizer 3. According to the manufacturing method of the present invention, when the polarizing plate 2 is made into a single piece, reverse curling occurs (the main surface side where the protective film 1 is overlaid is convexly curled) (again, reverse curling occurs and is MD curling Time) is particularly advantageous.

As described above, regarding one of the forms of the polarizing plate 2 that is likely to cause reverse curl when it is made as a single body, the series cites “the first thermoplastic resin film 20 and the second thermoplastic resin film 30 have mutually different equilibrium moisture rates and/or The case of "moisture permeability" is not limited to this. It is easy to cause reverse curl when the polarizing plate 2 has an asymmetric layer structure based on the polarizing film 10.

An example of the configuration of the polarizing plate 2 that is prone to reverse curl is as follows.

(a) A structure in which a thermoplastic resin film (protective film, etc.) is bonded only on one side of the polarizing film 10; (b) A protective film is bonded on one side of the polarizing film 10, and an optical film other than the protective film is bonded on the other side ( Brightness enhancement film, etc.); (c) Composition of double-sided thermoplastic resin film (protective film, etc.) attached to the polarizing film 10 (resin type, thickness, equilibrium moisture rate, moisture permeability, presence or absence of surface treatment layer, etc.) ) Are different from each other; (d) the adhesive layer used to attach the thermoplastic resin film (protective film, etc.) to both sides of the polarizing film 10 is composed of different types of adhesives; (e ) A thermoplastic resin film (protective film, etc.) is laminated on both sides of the polarizing film 10, and another optical film is laminated on one thermoplastic resin film; (f) Others, based on the polarizing film 10, the total number of films and layers on one side is different from the total number of films and layers on the other side.

(4) Other steps

The manufacturing method of the present invention may further include the step of cutting the polarizing plate with protective film 3 obtained by the above pressing step to obtain a monolithic body of the polarizing plate with protective film 3. For cutting, a cutting device such as a shearing cutter can be used.

The shape of the monolithic body is not particularly limited, and it is generally a square shape, preferably a square shape having long sides and short sides, and particularly preferably a rectangular shape. This monolithic body is usually cut so that the opposite pair of sides is parallel to MD, and the remaining opposite pair of sides is parallel to TD, but it can also be cut so that each side becomes inclined from MD or TD Of direction. The length of the long side and the short side of the monolithic body is not particularly limited, usually the long side is more than 50mm, and the short side is more than 30mm. When the size of the monolithic body is larger, curling is more likely to occur. If the size (long side and/or short side) is too small, the problem of curling itself is not easily generated.

[Example]

The following are examples and comparative examples to illustrate the present invention more specifically, but the present invention is not limited to these examples. In the following examples, the equilibrium moisture content, moisture permeability, thickness and tensile modulus of elasticity, and film tension and curl amount are measured according to the following method.

(1) The equilibrium moisture rate of the membrane

Cut out the test piece with MD length 150mm×TD length 100mm. Measurement The weight of the film after storage for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%. Then, a drying process was performed at 105°C for 2 hours, and the weight of the film after the drying process was measured. From the weight of the film before and after drying, the equilibrium moisture content was determined according to the following formula.

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

(2) Permeability of membrane

By the cup method specified in JIS Z 0208, the moisture permeability [g/(m ² .24hr)] at a temperature of 40° C. and a relative humidity of 90% was measured.

(3) Thickness of polarizing plate and film

It was measured using Digital Micrometer "MH-15" manufactured by Nikon Corporation.

(4) MD tensile modulus of polarizer and protective film

A rectangular test piece with an MD length of 100 mm and a TD length of 25 mm was cut out. The upper and lower clamps of the tensile tester [AUTOGRAPH AG-IS testing machine manufactured by Shimadzu Corporation] were held so that the distance between the clamps was 5 cm so that the two ends of the test piece in the longitudinal direction were held at 23°C, opposite In an environment with a humidity of 55%, the test piece is stretched toward the MD (the length direction of the test piece) at a stretching speed of 1 mm/min. From the initial linear slope of the obtained stress-strain curve, 23°C and 55 relative humidity are calculated % Of time The tensile modulus of elasticity of MD [MPa].

(5) MD film tension of polarizing plate and protective film

Use the tension detection roller installed between the laminating roller and the pair of rollers closest to the laminating roller to measure: the pair of laminating rollers used to bond the polarizing plate and the protective film, and the upstream and most The film tension [N/m] of the polarizing plate and the protective film running between the pair of rollers close to the bonding roller.

(6) Amount of curling of polarizing plate and polarizing plate with protective film

From the obtained polarizing plate with a protective film, a rectangular test piece having an MD length of 300 mm and a TD length of 200 mm was cut out, and left for 24 hours under an environment of a temperature of 23° C. and a relative humidity of 55%. Place the test piece on the reference surface (platform base) so that the concave surface is facing upward, even if the four edges are raised. In this state, the height of each of the four corners of the test piece from the reference plane was measured, and the average of the heights of these four corners was determined as the curl amount [mm]. A positive curl value means that the first thermoplastic resin film side is concave (positive curl), and a negative value means that the second thermoplastic resin film side is concave (reverse curl). In addition, the polarizing plate with a protective film of Example 2 did not curl regardless of which side of the first thermoplastic resin film side or the second thermoplastic resin film side was facing upward.

<Example 1> (A) Fabrication of polarizing film

Continuously transport long strips of polyvinyl alcohol film (average degree of polymerization: about 2400, degree of saponification: 99.9 mol% or more, thickness: 30 μm), and at the same time, the uniaxial stretching is performed about 4 times in dry mode, and then immersed in pure water at 40 ℃ for 1 minute while maintaining tension, after Immerse in an aqueous solution with a weight ratio of iodine/potassium iodide/water of 0.1/5/100 at 28°C for 60 seconds. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10.5/7.5/100 at 68°C for 300 seconds. Then, 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 having iodine adsorbed and aligned on the uniaxially stretched polyvinyl alcohol film. The thickness of the polarizing film is 11.1 μm.

(B) Fabrication of polarizing plates

Continuously transport the polarizing film obtained in (A) above, and simultaneously and continuously transport the long first thermoplastic resin film [a film with a hard coating layer formed on the TAC film "KC2UAW" manufactured by Konica Minolta Opto Co., Ltd. , Thickness: 32.4 μm, equilibrium moisture content: 1.9% by weight, moisture permeability 455 g/(m ² .24hr)] and long second thermoplastic resin film [cyclic polyolefin resin film made by JSR Corporation] Product name "FEKB015D3", thickness: 15.1 μm, equilibrium moisture content: 0.8% by weight, moisture permeability 115 g/(m ² .24hr)], between the polarizing film and the first thermoplastic resin film, and between the polarizing film and A water-based adhesive is injected between the second thermoplastic resin films and passes between the bonding rollers to obtain a laminate composed of the first thermoplastic resin film/water-based adhesive layer/polarizing film/water-based adhesive layer/second thermoplastic resin film membrane. Then, the obtained laminated film was transported and subjected to heat treatment at 80° C. for 300 seconds in a hot air dryer, thereby drying the water-based adhesive layer to obtain a polarizing plate. The above-mentioned water-based adhesive system is used: polyethylene with a concentration of 3% by weight obtained by dissolving polyvinyl alcohol powder [trade name "Gohsefimer" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree 1100] in hot water at 95°C In the alcohol aqueous solution, an aqueous solution obtained by mixing a crosslinking agent [sodium glyoxylate manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] at a ratio of 1 part by weight with respect to 10 parts by weight of the polyvinyl alcohol powder.

The thickness T ₂ of the polarizing plate was 58.6 μm, and the tensile elastic modulus E ₂ of MD was 6540 MPa. The curling amount of the polarizing plate measured according to the above method was -10 mm (reverse curling).

(C) Manufacture of polarizing plate with protective film

Continuously transport the polarizing film obtained in (B) above, and simultaneously and continuously transport the long protective film [The base film is composed of polyethylene terephthalate and has (methyl) on it Protective film of acrylic adhesive; total thickness T ₁ : 57.3 μm, MD tensile elastic modulus E ₁ : 2521 MPa], superimpose this and pass between the bonding rollers, thereby pressing the protective film and polarized light from above and below The laminate of the board is used to make a polarizing plate with a protective film. The protective film is bonded to the surface of the first thermoplastic resin film (TAC film) of the polarizing plate through its adhesive layer. In addition, the pressure (rolling) applied to the laminate of the protective film and the polarizing plate by the bonding roller was 0.1 MPa, and this value was also substantially the same in the following examples and comparative examples.

Table 1 shows the film tension of the polarizer and the MD of the protective film, multiplying 10 ⁵ by the left side of the above formula (I), multiplying 10 ⁵ by the right side, and the difference between these, the polarizing plate with a protective film Amount of curl. In the first table, "△" represents the difference between 10 ⁵ multiplied by the left side of the above formula (I) and 10 ⁵ multiplied by the right side, that is, the left side of the above (II).

<Examples 2 to 5>

A polarizing plate with a protective film was produced in the same manner as in Example 1 except that the film tension of the polarizing plate and the MD of the protective film was as shown in Table 1. Table 1 displays the first line ¹⁰⁵ is multiplied on the left by the above formula (I), and the right side is multiplied by ^105, and the difference between these, the amount of curl of the polarizing plate attached to the protective film.

<Example 6>

The base film used is made of polyethylene terephthalate with a (meth)acrylic adhesive on it and has a total thickness T ₁ of 69.3 μm and a MD tensile elastic modulus E ₁ of 2743 MPa A strip-shaped protective film, and the film tension of the polarizing plate and the MD of the protective film are as shown in Table 1, except that the polarizing plate with a protective film was produced in the same manner as in Example 1. Table 1 displays the first line ¹⁰⁵ is multiplied on the left by the above formula (I), and the right side is multiplied by ^105, and the difference between these, the amount of curl of the polarizing plate attached to the protective film.

<Example 7>

Using the second thermoplastic resin film [ZF14-023, a trade name of cyclic polyolefin resin film manufactured by Zeon Japan Co., Ltd.], thickness: 22.9 μm, equilibrium moisture rate: 0.1% by weight, moisture permeability 17 g/(m ^{2 .24hr)],} except otherwise identical to Example 1 and a thickness T ₂ of 66.8μm, MD tensile elastic modulus of 6080MPa E ₂ is a polarizer. The curling amount of the polarizing plate was measured according to the above method, and was -6 mm (reverse curling).

Next, the polarizing plate obtained as described above was used, and the film tension of the polarizing plate and the MD of the protective film were as shown in Table 1, except that the polarizing plate with protective film was produced in the same manner as in Example 1. Table 1 displays the first line ¹⁰⁵ is multiplied on the left by the above formula (I), and the right side is multiplied by ^105, and the difference between these, the amount of curl of the polarizing plate attached to the protective film.

<Comparative Example 1>

As the first thermoplastic resin film, a TAC film "KC2UAW" [thickness: 25.5 μm, equilibrium moisture content: 3.0% by weight, moisture permeability of 1207 g/(m ² .24hr)] manufactured by Konica Minolta Opto Co., Ltd. was used. In the same manner as in Example 1, a polarizing plate having a thickness T ₂ of 51.7 μm and an MD tensile elastic modulus E ₂ of 6839 MPa was produced. The curling amount of the polarizing plate measured according to the above method was -13 mm (reverse curling).

Next, using the polarizing plate obtained above, and setting the film tension of the polarizing plate and the MD of the protective film as shown in Table 1, the polarizing plate with protective film was produced in the same manner as in Example 1 except for the above. . Table 1 displays the first line ¹⁰⁵ is multiplied on the left by the above formula (I), and the right side is multiplied by ^105, and the difference between these, the amount of curl of the polarizing plate attached to the protective film.

1‧‧‧Protection film

2‧‧‧ Polarizer

3‧‧‧ Polarizer with protective film

5‧‧‧ Laminating roller

Claims (9)

A method for manufacturing a polarizing plate with a protective film, comprising: a step of overlapping a protective film on one side of a polarizing plate and pressing it by passing between a pair of bonding rollers; wherein, when the thickness of the protective film It is set to T ₁ [μm], the tensile elastic modulus of MD is set to E ₁ [MPa], the film tension of the MD before passing through the pair of bonding rollers is set to F ₁ [N/m], and the The thickness of the polarizing plate is T ₂ [μm], the tensile modulus in the MD direction is E ₂ [MPa], and the film tension of the MD before passing through the pair of bonding rollers is F ₂ [N /m], the aforementioned pressing step is performed under the condition that the following formula (I) is satisfied:

The manufacturing method as described in item 1 of the patent application scope, wherein the pressing step is performed under the condition of satisfying the following formula (II):

According to the manufacturing method described in item 1 of the patent application range, when the polarizing plate is formed as a monolithic body, curling may occur on one side where the protective film is superimposed. The manufacturing method described in item 1 of the patent application range, wherein the polarizing plate includes a polarizing film, a first thermoplastic resin film laminated on one side thereof, and a second thermoplastic resin film laminated on the other side. The manufacturing method as described in item 4 of the patent application scope, wherein the aforementioned 1 The equilibrium moisture content of the thermoplastic resin film at a temperature of 23° C. and a relative humidity of 55% is higher than that of the aforementioned second thermoplastic resin film. The manufacturing method according to item 5 of the patent application range, wherein the difference between the equilibrium moisture content of the first thermoplastic resin film and the second thermoplastic resin film is 0.5% by weight or more. The manufacturing method according to any one of claims 4 to 6, wherein the protective film is disposed on the first thermoplastic resin film side. The manufacturing method according to any one of claims 4 to 6, wherein the equilibrium moisture content of the first thermoplastic resin film at a temperature of 23° C. and a relative humidity of 55% is 1.5% by weight or more. The manufacturing method as described in item 1 of the patent application range, wherein the thickness of the polarizing plate is 100 μm or less.

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