CN106257314B

CN106257314B - Method for manufacturing polarizing plate with protective film

Info

Publication number: CN106257314B
Application number: CN201610438379.3A
Authority: CN
Inventors: 古谷勉; 猪口雄平
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2015-06-19
Filing date: 2016-06-17
Publication date: 2021-04-09
Anticipated expiration: 2036-06-17
Also published as: CN106257314A; KR102502463B1; KR20160150025A

Abstract

A method for manufacturing a polarizing plate with a protective film, comprising a step of passing one surface of the polarizing plate between a pair of laminating rollers in a state of overlapping the protective film and the one surface of the polarizing plate to perform pressing, wherein the protective film has a thickness T₁(. mu.m) and a tensile elastic modulus in MD of E₁(MPa) film tension in MD before passing through a pair of laminating rollers is F₁(N/m) a thickness of the polarizing plate of T₂(μm) and a tensile modulus of elasticity in MD of E₂(MPa) film tension in MD before passing through a pair of laminating rollers is F₂(N/m), the step of extruding satisfies the following formula F₁/(E₁×T₁)＞F₂/(E₂×T₂) Under the conditions of (1).

Description

Method for manufacturing polarizing plate with protective film

Technical Field

The present invention relates to a method for manufacturing a polarizing plate with a protective film, in which a protective film is laminated on a surface of the polarizing plate.

Background

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

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

Disclosure of Invention

The polarizing plate is sensitive to the environment in which it is placed, and is easily deformed into a bow shape according to the environmental conditions. In this specification, this deformation is also referred to as "curling". The curling is classified into "forward curling" and "reverse curling". In the polarizing plate, there are a 1 st main surface on the side to be bonded to an image display element such as a liquid crystal element and a 2 nd main surface on the opposite side to the first main surface, and "forward curl" refers to a curl of a projection on the 1 st main surface side and "reverse curl" refers to a curl of a projection on the 2 nd main surface side. When the polarizing plate is reversely curled and bonded to an image display element via an adhesive layer, the following defects are likely to occur: a bonding error occurs, and air bubbles are mixed in the interface between the adhesive layer and the image display element.

The present invention is thus an optical element including a polarizing plate structure, and provides a method for manufacturing an optical element in which the reverse curl is sufficiently suppressed.

The present inventors are based on 1) a polarizing plate generally attached with a detachable protective film (also referred to as a surface protective film) that protects its surface. ) The polarizing plate with a protective film according to (1) is distributed in the market, and even if it is attached to an image display element, it is often attached in the form of a polarizing plate with a protective film; and 2) in order to solve the above problems, the present invention has been made by further intensive studies with a view to sufficiently suppressing reverse curl of a polarizing plate with a protective film. That is, the present invention provides a method for producing a polarizing plate with a protective film described below.

[1] A method for manufacturing a polarizing plate with a protective film, comprising a step of passing one surface of the polarizing plate and the protective film through a pair of laminating rollers in a superposed manner to press the polarizing plate,

the thickness of the protective film is T₁(. mu.m) and a tensile elastic modulus in MD of E₁(MPa) and the film tension in MD before passing through the pair of bonding rollers is F₁(N/m) a thickness of the polarizing plate of T₂(μm) and a tensile modulus of elasticity in MD of E₂(MPa) and the film tension in MD before passing through the pair of bonding rollers is F₂(N/m), the extrusion step is performed under the condition that the following formula (I) is satisfied.

[ number 1]

[2] The production method according to [1], wherein the step of extruding is performed under a condition satisfying the following formula (II).

Number 2

[3] The production method according to [1] or [2], wherein, when the polarizing plate is formed into a sheet, a side thereof overlapping the protective film is convex and curls.

[4] The manufacturing method according to any one of [1] to [3], wherein the polarizing plate comprises a polarizing film, a 1 st thermoplastic resin film laminated on one surface thereof, and a 2 nd thermoplastic resin film laminated on the other surface thereof.

[5] The production method according to [4], wherein the 1 st thermoplastic resin film has a higher equilibrium water content than the 2 nd thermoplastic resin film at a temperature of 23 ℃ and a relative humidity of 55%.

[6] The production method according to [5], wherein the difference in the equilibrium water content between the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film is 0.5 wt% or more.

[7] The production method according to any one of [4] to [6], wherein the protective film is disposed on the 1 st thermoplastic resin film side.

[8] The production method according to any one of [4] to [7], wherein the equilibrium water content of the 1 st thermoplastic resin film at a temperature of 23 ℃ and a relative humidity of 55% is 1.5 wt% or more.

[9] The production 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, a polarizing plate with a protective film in which reverse curling is sufficiently suppressed can be manufactured. The polarizing plate with a protective film can be bonded to an image display element satisfactorily while suppressing the above-mentioned defects.

Drawings

Fig. 1 is a schematic side view of a method for manufacturing a polarizing plate with a protective film according to an embodiment of the present invention.

Fig. 2 is a schematic view illustrating MD curl, wherein (a) is a side view and (b) is a plan view.

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

FIG. 4 is a schematic cross-sectional view of another example of a polarizer layer structure.

FIG. 5 is a schematic cross-sectional view of another example of a polarizer layer structure.

Description of the symbols

1 protective film, 2a, 2b, 2c polarizing plate, 3 polarizing plates with protective films, 5 laminating rollers, 10 polarizing films, 20 st 1 thermoplastic resin film, 30 nd 2 thermoplastic resin film, 40 adhesive layer, and 50 release film.

Detailed Description

(1) Step of carrying out extrusion

Referring to fig. 1, the method for manufacturing a polarizing plate with a protective film according to the present invention includes a step of passing one surface of a polarizing plate 2 through a pair of laminating

rollers

5 and 5 while overlapping with a protective film 1, thereby pressing a laminate of the protective film 1 and the polarizing plate 2 from above and below, and manufacturing a polarizing plate 3 with a protective film through the step. In general, the protective film 1 and the polarizing plate 2 supplied to the pressing step are continuously fed by a feeding roller, not shown, and are continuously conveyed to be introduced between the pair of laminating

rollers

5 and 5. The protective film 1 and the polarizing plate 2 are transported in the longitudinal direction of the film, and are generally transported in parallel.

The thickness of the protective film 1 is T₁[ μm ] and a tensile elastic modulus in MD of E₁[ MPa ], and the film tension in MD before passing through the pair of

bonding rolls

5, 5 is F₁[ N/m ] thickness of polarizing plate 2 is T₂[ μm ] and a tensile elastic modulus in the MD direction of E₂[ MPa ], and the film tension in MD before passing through the pair of

bonding rolls

5, 5 is F₂[ N/m ], the step of extruding satisfies the following formula (I):

[ number 3]

Under the conditions of (1). In the present specification, MD means a machine conveying direction of the film, i.e., a longitudinal direction of the film. The direction perpendicular to the MD, i.e., the film width direction, is also referred to as TD in this specification.

Tensile modulus of elasticity E in MD of protective film 1 and polarizing plate 2₁、E₂The tensile modulus at 23 ℃ under an atmosphere of 55% relative humidity was measured as described in the following examples. Film tension F in MD of protective film 1 and polarizing plate 2₁、F₂The film tension before passing through the pair of

bonding rollers

5, 5 means the film tension running between the pair of

bonding rollers

5, 5 and the driving roller (pair of nip rollers) located on the upstream side of the pair of

bonding rollers

5, 5 and closest to the

bonding rollers

5, 5.

By attaching 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-corrected) in a direction in which the principal surface on which the protective film 1 is superimposed becomes concave (i.e., in the positive curl direction). Therefore, for example, when a reverse curl (a curl protruding from the main surface on which the protective film 1 is superimposed) occurs when the polarizing plate 2 supplied to the pressing step is a sheet-like body, the reverse curl can be corrected in the forward curl direction according to the present invention, and as a result, a flat polarizing plate 3 with a protective film having no curl or having a forward curl in which the reverse curl is sufficiently suppressed can be obtained as a sheet-like body. When the polarizing plate 3 with a protective film is obtained as a sheet, it is preferable that the sheet be flat without curling or have a forward curl.

According to the study of the present inventors: the left and right sides of the formula (I) are indices indicating the state of deformation of the protective film 1 and the polarizing plate 2 when they are bonded to each other. The reason why the polarizing plate 2 can be corrected in the forward 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 that the force to cancel out the dynamic deformation after bonding becomes large in the protective film 1.

The relationship of the formula (I) can be achieved by adjusting one or two or more of the requirements selected from the thickness of the protective film 1 and/or the polarizing plate 2, the tensile elastic modulus in the MD, and the film tension in the MD before passing through the pair of

bonding rollers

5 and 5. The adjusting requirement preferably includes the film tension of the protective film 1 and/or the polarizing plate 2.

Here, the curl will be explained. Curl refers to warp deformation of an optical element (optical film) such as the polarizing plate 2 or the polarizing plate 3 with a protective film, and such deformation is usually generated in a sheet-like body of the optical element. The more the optical element is a thin film, the more curl is likely to occur.

The curl can be classified into two types, i.e., a "forward curl" and a "reverse curl", depending on which side of the two opposing main surfaces of the optical element is curled. When the main surface bonded to the image display element side of the liquid crystal cell or the like is the 1 st main surface and the main surface on the opposite side thereof is the 2 nd main surface, the "forward curl" is a curl of the 1 st main surface side projection and the "reverse curl" is a curl of the 2 nd main surface side projection. When the polarizing plate 2 supplied to the manufacturing method according to the present invention is a sheet-like body, reverse curl (curl of the main surface side projection on which the protective film 1 is superimposed) typically occurs.

Further, the curl can be classified into two types, that is, "MD curl" and "TD curl" according to which end (side) of the optical element as a sheet-like body the curl is generated. Referring to fig. 2, when the sheet-like body of the curled optical element is placed on the flat table with the convex side facing downward, "MD curl" refers to curl in which MD ends (typically, both ends) are raised, and "TD curl" refers to curl in which TD ends (typically, both ends) are raised. The manufacturing method according to the present invention is particularly advantageous for correcting MD curl.

Evaluation of curl that the optical element such as the polarizing plate 2 and the polarizing plate 3 with a protective film can have (forward curl, reverse curl, MD curl, identification of the kind of TD curl, and the amount of curl) was carried out on a sheet-like body cut out from the obtained optical element. The sheet is a square sheet having a pair of opposing sides parallel to the MD and the remaining pair of opposing sides parallel to the TD, and has a MD length of 300mm and a TD length of 200 mm.

According to the present invention, it is possible to obtain a flat polarizing plate 3 with a protective film, which is preferably free from curling, in which reverse curling when the polarizing plate is formed into a sheet-like body is sufficiently suppressed, or which has forward curling. According to the polarizing plate 3 with a protective film, it is possible to effectively suppress a bonding error occurring when the polarizing plate 3 with a protective film is bonded to an image display element via an adhesive layer and a defect that air bubbles are mixed in an interface between the adhesive layer and the image display element, and to perform bonding between the polarizing plate 3 with a protective film and the image display element with good productivity. In addition, when the curl generated in the polarizing plate 3 with a protective film is a positive curl portion, the above-described defects and productivity are not particularly problematic even if the curl amount is relatively large. The polarizing plate with a protective film 3 obtained according to the present invention may have reverse curl within a range in which the above-described defects (preferably, the above-described defects are not present) can be suppressed.

The correction amount in the forward curling direction according to the present invention depends on the difference between the left and right sides of the above formula (I), and the larger the difference, the larger the correction amount tends to be. In the case where the polarizing plate 2 supplied to the pressing step is a sheet-like body, although the degree of curling depends on the degree of curling, in order to obtain a polarizing plate with a protective film 3 having no reverse curl and being flat or having a forward curl, it is preferable that the pressing step satisfies the following formula (II):

[ number 4]

Under the conditions of (1). When the polarizing plate 2 supplied to the pressing step has a large reverse curl, the left side of the formula (II) must be 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) in order to obtain a polarizing plate 3 with a protective film that is flat or has a forward curl. The left side of the above formula (II) may be, for example, 1000 or less.

The left and right sides of the above formula (I) are usually 1X 10, respectively^-5～1000×10^-5May be 5X 10^-5～500×10^-5。

The protective film 1 is stacked on one surface of the polarizing plate 2, and when passing between the pair of

laminating rollers

5 and 5, the adhesive layer of the protective film 1 is stacked so as to be in contact with the one surface of the polarizing plate 2. Before the protective film 1 and the polarizing plate 2 are laminated, at least one of the adhesive layer of the protective film 1 and the bonding surface of the polarizing plate 2 may be subjected to a surface activation treatment such as a plasma treatment, a corona treatment, an ultraviolet irradiation treatment, a flame (flame) treatment, or a saponification treatment.

In the step of pressing with the pair of bonding rollers 5, the pressure (nip pressure) applied to the laminate of the protective film 1 and the polarizing plate 2 is, for example, 0.01 to 0.5MPa, and may be 0.05 to 0.3 MPa. The nip pressure does not greatly affect the curl of the obtained polarizing plate 3 with a protective film. As the

bonding rollers

5 and 5, conventionally known rollers having a metal (including alloys such as SUS) or rubber surface can be used.

(2) Protective film

The protective film 1 is generally composed of a base film and an adhesive layer laminated thereon. The protective film 1 is a film for protecting the surface of the polarizing plate 2, and in general, for example, the polarizing plate 3 with the protective film is attached to an image display element or the like, and then the protective film 1 is peeled off and removed together with the pressure-sensitive adhesive layer included therein. The substrate film may be made of thermoplastic resins such as: polyolefin resins such as polyethylene resins, polypropylene resins, and cyclic polyolefin resins; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; a polycarbonate-based resin; (meth) acrylic resins, and the like. The adhesive layer may be formed of a (meth) acrylic adhesive, an epoxy adhesive, a urethane adhesive, a silicone adhesive, or the like. Further, the resin layer may be formed of a self-adhesive resin layer such as a polypropylene resin or a polyethylene resin. The tensile modulus E in the MD direction can be adjusted mainly by selecting the material of the base film₁。

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

Thickness T of protective film 1₁For example, the particle diameter may be 5 to 200. mu.m, preferably 10 to 150. mu.m, more preferably 20 to 120. mu.m, and still more preferably 25 to 100. mu.m (for example, 90 μm or less, and further 75 μm or less). Thickness T₁If the thickness is less than 5 μm, the protection of the polarizing plate 2 becomes insufficient, and the handling property is also unfavorable. Thickness T₁Cost and security of more than 200 μmThe reworkability of the protective film 1 is disadvantageous. Furthermore, the thickness T₁When the particle diameter exceeds 200. mu.m, it tends to be difficult to satisfy the relational expression of the above formula (I) and/or formula (II).

(3) Polarizing plate

The polarizing plate 2 is a polarizing element including at least a polarizing film, and usually further includes a thermoplastic resin film such as a protective film laminated on at least one surface of the polarizing film. The protective film is an optical film that plays a role of protecting the polarizing film.

(3-1) example of polarizing plate construction

The polarizing plate 2 may include a polarizing film and a layer or film other than a protective film, for example, an optical layer or optical film having an optical function other than a polarizing film. Examples of the other optical layer or optical film having an optical function include a retardation film (or retardation layer), a brightness enhancement film, and the like. Various optical films including a protective film may be laminated and bonded to a polarizing film via an adhesive layer or an adhesive layer. The polarizing plate 2 may have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer.

Thickness T of polarizing plate 2₂Usually 200 μm or less, and from the viewpoint of making the film thinner, 125 μm or less is preferred, 100 μm or less is more preferred, and 75 μm or less is even more preferred. Thickness T₂The smaller the size, the more easily curl develops in the sheet-like body of the polarizing plate 2, even if the thickness T of the polarizing plate 2 is made according to the present invention₂The polarizing plate 2 becomes thin and a reverse curl is generated when it becomes a sheet-like body, and such a reverse curl can be effectively corrected in the forward curl direction. In view of the reduction in thickness and optical properties, it is difficult to adjust the mechanical properties of the polarizing film and the protective film so that the curl of the polarizing plate 2 when it is a sheet is flat or positive, but the protective film is usually peeled off after the polarizing plate 3 with the protective film is attached to an image display element or the like, and therefore adjustment of the mechanical properties aimed at the correction of the curl becomes possible.

Examples of the layer structure of the polarizing plate 2 will be described with reference to fig. 3 to 5, but the layer structure is not limited to these examples. The polarizing plate 2a shown in fig. 3 includes: a polarizing film 10; a 1 st thermoplastic resin film 20 laminated on one surface of the polarizing film 10; a 2 nd thermoplastic resin film 30 laminated on the other surface of the polarizing film 10; an adhesive layer 40 laminated on an outer surface of the 2 nd thermoplastic resin film 30; and a release film 50 laminated on an outer surface of the adhesive layer 40. The release film 50 is a releasable film for protecting the surface (outer surface) of the adhesive layer 40. The 1 st and 2 nd

thermoplastic resin films

20 and 30 are, for example, pellicle films.

As in the polarizing plate 2b shown in fig. 4, one of the 1 st and 2 nd

thermoplastic resin films

20 and 30 may be omitted. In the polarizing plate 2b, the 2 nd thermoplastic resin film 30 is omitted, and the adhesive layer 40 is directly attached to the outer surface (the surface opposite to the surface on which the 1 st thermoplastic resin film 20 is laminated) of the polarizing film 10. In this way, a polarizing plate having a thermoplastic resin film only on one surface of the polarizing film 10 is advantageous for making the polarizing plate thin. In the polarizing plate 2 in which the thermoplastic resin film is laminated only on one side of the polarizing film 10, curling is likely to occur in a sheet-like body, but according to the present invention, the thermoplastic resin film is laminated only on one side of the polarizing film 10, and even if reverse curling occurs in the polarizing plate 2 in the form of a sheet, such reverse curling can be effectively corrected in the direction of forward curling.

As shown in the polarizing plate 2c shown in fig. 5, the adhesive layer 40 and the separation film 50 may be omitted. The polarizing plate 2 may have a protective film different from the protective film 1 supplied to the above-described pressing step on one surface thereof in advance. In this case, the obtained polarizing plate 3 with a protective film is a polarizing plate having protective films on both sides.

Although not shown in fig. 3 to 5, the polarizing film 10 and the 1 st and 2 nd

thermoplastic resin films

20 and 30 may be preferably bonded using an adhesive.

(3-2) polarizing film

The polarizing film 10 may be a dichroic pigment oriented and adsorbed on a uniaxially stretched polyvinyl alcohol-based resin film. As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, a saponified product of a polyvinyl acetate resin can be used. As the polyvinyl acetate resin, in addition to polyvinyl acetate as a vinyl acetate homopolymer, a copolymer of vinyl acetate and other monomers copolymerizable therewith can be exemplified. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group.

The saponification degree of the polyvinyl alcohol resin may be in the range of 80.0 to 100.0 mol%, preferably 90.0 to 100.0 mol%, and more preferably 98.0 to 100.0 mol%. When the saponification degree is less than 80.0 mol%, the water resistance and the moist heat resistance of the obtained polarizing plate 2 may be lowered.

The degree of saponification is an acetoxy group (acetoxy group: -OCOCH) contained in a polyvinyl acetate resin as a raw material of a polyvinyl alcohol resin, expressed in unit ratio (mol%)₃) The proportion hydroxylated by the saponification step is defined by the following formula:

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 in accordance with JIS K6726 (1994). The higher the degree of saponification, the higher the proportion of hydroxyl groups and thus the lower the proportion of acetate groups inhibiting crystallization.

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

The dichroic pigment contained (oriented and adsorbed) in the polarizing film 10 may be iodine or a dichroic organic dye. Specific examples of dichroic organic dyes include red BR, red LR, red R, pink LB, ruby red (Rubine) BL, purplish red (Bordeaux) GS, sky blue LG, lemon yellow, blue BR, blue 2R, dark blue RY, green LG, violet LB, violet B, black H, black B, black GSP, yellow 3G, yellow R, orange LR, orange 3R, scarlet (scarlet) GL, scarlet KGL, Congo red (concred), bright purple BK, super blue (Supra blue) G, super blue GL, super orange (Supra orange) GL, direct sky blue, direct fast orange S, fast black. The dichroic pigment may be used alone or in combination of two or more. The dichroic pigment is preferably iodine.

The polarizing film 10 is produced through the following steps: a step of uniaxially stretching a polyvinyl alcohol resin film; a step of adsorbing a dichroic pigment by dyeing a polyvinyl alcohol resin film with the dichroic pigment; a step of subjecting the dichroic dye-adsorbed polyvinyl alcohol resin film to a crosslinking treatment; and a step of washing the resultant product after the crosslinking treatment.

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

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

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

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

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

On the other hand, when a dichroic organic dye is used as the dichroic dye, a dyeing method of immersing a polyvinyl alcohol-based resin film in an aqueous dyeing solution containing a water-soluble dichroic organic dye is generally employed. The dichroic organic dye is contained in the aqueous dyeing solution in an amount of usually 1X 10 parts by weight per 100 parts by weight of water^-4About 10 parts by weight, preferably about 1X 10^-3About 1 part by weight. The aqueous dyeing solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dyeing solution is usually about 20 to 80 ℃.

The crosslinking treatment after dyeing with the dichroic pigment can be performed by immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing a crosslinking agent. As a suitable example of the crosslinking agent, boric acid may be used, and other crosslinking agents such as boron compounds such as borax, glyoxal, and glutaraldehyde may also be used. The crosslinking agent may be used alone or in combination of two or more.

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 dye, the aqueous solution containing the crosslinking agent preferably contains potassium iodide. The amount of potassium iodide in the aqueous solution containing the crosslinking agent is usually 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 ℃ or higher, preferably 50 to 85 ℃.

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

After washing with water, drying treatment is performed to obtain the polarizing film 10. The drying treatment can be performed by drying with a hot air dryer, drying in contact with a heating roller, or drying with a far infrared heater. The temperature of the drying treatment is usually about 30 to 100 ℃, preferably 50 to 90 ℃.

The polarizing film 10 is generally about 2 to 40 μm thick. In view of the thinning of the polarizing plate 2, the thickness of the polarizing film 10 is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less. The smaller the thickness of the polarizing film 10, the more likely the curling occurs in the sheet-like body of the polarizing plate 2, but according to the present invention, the smaller the thickness of the polarizing film 10, even if the reverse curling occurs when the polarizing plate 2 is a sheet-like body, such reverse curling can be effectively corrected in the forward curling direction.

(3-3) No. 1 and No. 2 thermoplastic resin films

The 1 st and 2 nd

thermoplastic resin films

20 and 30 may be films each independently made of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin. The thermoplastic resin constituting the 1 st and 2 nd

thermoplastic resin films

20 and 30 may be, for example, a polyolefin resin such as a chain polyolefin resin (e.g., a polypropylene resin) or a cyclic polyolefin resin (e.g., a norbornene resin); cellulose resins such as triacetylcellulose and diacetylcellulose; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; a polycarbonate-based resin; (meth) acrylic resins such as methyl methacrylate resins; a polystyrene-based resin; a polyvinyl chloride resin; acrylonitrile-butadiene-styrene resins; acrylonitrile-styrene resins; a polyvinyl acetate resin; a polyvinylidene chloride resin; a polyamide resin; a polyacetal resin; modified polyphenylene ether resin; a polysulfone-based resin; a polyether sulfone-based resin; a polyarylate-based resin; a polyamide imide resin; polyimide resins, and the like.

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

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

The cellulose-based resin is a cellulose organic acid ester or a cellulose mixed organic acid ester in which some or all of the hydrogen atoms in the hydroxyl groups of cellulose obtained from raw material cellulose such as cotton linter and wood pulp (hardwood pulp and softwood pulp) are substituted with acetyl groups, propionyl groups and/or butyryl groups. Examples thereof include esters of cellulose such as acetate, propionate, butyrate and mixed esters thereof. Among them, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, and cellulose acetate butyrate are preferable.

The polyester resin is a resin other than the above-mentioned cellulose resin having an ester bond, and is generally a resin formed of a polycondensate of a polycarboxylic acid or a derivative thereof and a polyhydric alcohol. As the polycarboxylic acid or a derivative thereof, a dicarboxylic acid having a valence of 2 or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl naphthalenedicarboxylate and the like. As the polyhydric alcohol, a divalent alcohol having a valence of 2, such as ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, cyclohexanediol, and the like, can be used. Examples of suitable polyester resins include polyethylene terephthalate.

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

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

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

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

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

The 1 st and 2 nd

thermoplastic resin films

20 and 30 may be protective films laminated and attached to one surface of the polarizing film 10 to protect the polarizing film 10. The 1 st or 2 nd

thermoplastic resin films

20 and 30 may be a pellicle film having optical functions such as a retardation film and a brightness enhancement film. For example, a retardation film to which an arbitrary retardation value is given can be obtained by stretching (uniaxial stretching, biaxial stretching, or the like) a thermoplastic resin film made of the above-mentioned material to form a liquid crystal layer or the like on the film. The 1 st and/or 2 nd

thermoplastic resin films

20, 30 may have surface treatment layers (coating layers) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, an antifouling layer, and the like laminated on the surfaces thereof.

The thickness of the 1 st and 2 nd

thermoplastic resin films

20 and 30 is usually 1 to 100. mu.m, preferably 5 to 60 μm, more preferably 5 to 50 μm, from the viewpoint of strength and handling property. When the 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 moist heat environment can be suppressed. The smaller the thickness of the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 is, the more likely curling is to occur in the sheet-like body of the polarizing plate 2, but according to the present invention, when the thickness of the 1 st thermoplastic resin film 20 or the 2 nd thermoplastic resin film 30 is, for example, 40 μm or less, and further, may be as thin as 30 μm or less, even if reverse curling occurs when the polarizing plate 2 is a sheet-like body, such reverse curling can be effectively corrected in the forward curling direction.

As shown in the

polarizing plates

2a, 2c shown in fig. 3 and 5: when the polarizing film 10 has the 1 st thermoplastic resin film 20 on one surface and the 2 nd thermoplastic resin film 30 on the other surface, the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 may be formed of the same kind of thermoplastic resin or different kinds of thermoplastic resins, and when the polarizing film is formed of different kinds of thermoplastic resins, the sheet-like body of the polarizing plate 2 is particularly likely to be curled when the equilibrium moisture content and moisture permeability of the thermoplastic resin films laminated on both surfaces are different from each other.

For example, as the 1 st thermoplastic resin film 20, a film having a higher equilibrium water content than the 2 nd thermoplastic resin film 30 can be used. The larger the difference in the equilibrium moisture content between the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 bonded to both sides of the polarizing film 10, the more likely the curling occurs in the sheet-like body of the polarizing plate 2, but according to the present invention, when the difference in the equilibrium moisture content is 0.5 wt% or more, further 1 wt% or more, and further 1.5 wt% or more, even if the reverse curling occurs when the polarizing plate 2 is a sheet-like body, such reverse curling can be effectively corrected in the forward curling direction.

In the present specification, the equilibrium water content of the film is measured by a dry weight method, and specifically, it is determined by the following formula:

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

Here, the weight of the film before the drying treatment is the weight after the film is stored at 23 ℃ and 55% relative humidity for 24 hours, and the drying refers to a treatment of drying the film at 105 ℃ for 2 hours. Examples of the combination of the thermoplastic resin films having a difference in equilibrium water content of 0.5 wt% or more include: a combination of a cellulose-based resin film (TAC film or the like) and a cyclic polyolefin-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a (meth) acrylic resin film, a combination of a cellulose-based resin film (TAC film or the like) and a polyester-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a chain polyolefin-based resin film, a combination of a (meth) acrylic resin film and a cyclic polyolefin-based resin, a combination of a (meth) acrylic resin film and a polyester-based resin film, and the like. The difference in the equilibrium moisture content between the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 is usually 5 wt% or less, preferably 2.5 wt% or less.

The equilibrium water content of the 1 st thermoplastic resin film 20 is, for example, 1.5 wt% or more, and may be 2 wt% or more. The equilibrium water content of the 1 st thermoplastic resin film 20 is usually 5% by weight or less.

When a film having a higher equilibrium moisture content than the 2 nd thermoplastic resin film 30 is used as the 1 st thermoplastic resin film 20, the equilibrium moisture content of the 2 nd 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 2 nd thermoplastic resin film 30 from which the equilibrium moisture content can be obtained include cyclic polyolefin resins, (meth) acrylic resins, polyester resins, and chain polyolefin resins.

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

When a film having a higher equilibrium moisture content than the 2 nd thermoplastic resin film 30 is used as the 1 st thermoplastic resin film 20, the protective film 1 is usually disposed on the 1 st thermoplastic resin film 20 side of the polarizing plate 2 in the above-described pressing step, from the viewpoint of facilitating the correction of the reverse curl generated in the polarizing plate 2 toward the forward curl direction.

Further, as the 1 st thermoplastic resin film 20, for example, a film having a higher moisture permeability than the 2 nd thermoplastic resin film 30 can be used. The greater the difference in moisture permeability between the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 bonded on both sides of the polarizing film 10, the more likely curling occurs in the sheet-like body of the polarizing plate 2, and according to the present invention, the difference in moisture permeability is 30 g/(m)²24hr) or more, and further 50 g/(m)²24hr) or more, and further 100 g/(m)²24hr) or more, even if reverse curl occurs in the polarizing plate 2 as a sheet-like body, the reverse curl can be effectively corrected in the forward curl direction.

In the present specification, the moisture permeability of the film is a moisture permeability at a temperature of 40 ℃ and a relative humidity of 90% measured according to the moisture permeability kapton method specified in JIS Z0208. The difference of the moisture permeability is 30 g/(m)²24hr) or moreExamples of combinations of plastic resin films include: a combination of a cellulose-based resin film (TAC film or the like) and a cyclic polyolefin-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a (meth) acrylic resin film, a combination of a cellulose-based resin film (TAC film or the like) and a polyester-based resin film, a combination of a cellulose-based resin film (TAC film or the like) and a chain polyolefin-based resin film, a combination of a (meth) acrylic resin film and a cyclic polyolefin-based resin, a combination of a (meth) acrylic resin film and a polyester-based resin film, and the like. The difference in moisture permeability between the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 is usually 5000 g/(m)²24hr) or less.

The moisture permeability of the 1 st thermoplastic resin film 20 is, for example, 300 g/(m)²24hr) or more, and may be 400 g/(m)²24hr) above. The moisture permeability is 300 g/(m) in order to efficiently dry the layer made of the water-based adhesive and improve productivity when the 1 st thermoplastic resin film 20 and the polarizing film 10 are bonded using the water-based adhesive²24hr) above is beneficial. The moisture permeability of the 1 st thermoplastic resin film 20 is usually 5000 g/(m)²24hr) or less.

When a film having a higher moisture permeability than the 2 nd thermoplastic resin film 30 is used as the 1 st thermoplastic resin film 20, the moisture permeability of the 2 nd thermoplastic resin film 30 is usually 1 to 350 g/(m)²24hr), preferably 5 to 200 g/(m)²24 hr). Examples of the thermoplastic resin constituting the 2 nd thermoplastic resin film 30 capable of obtaining such moisture permeability include cyclic polyolefin resins, (meth) acrylic resins, polyester resins, and chain polyolefin resins.

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

When a film having a higher moisture permeability than the 2 nd thermoplastic resin film 30 is used as the 1 st thermoplastic resin film 20, the protective film 1 is usually disposed on the 1 st thermoplastic resin film 20 side of the polarizing plate 2 in the above-described pressing step, from the viewpoint of facilitating the correction of the reverse curl generated in the polarizing plate 2 toward the forward curl direction.

As described above, the polarizing film 10 and the 1 st and 2 nd

thermoplastic resin films

20 and 30 may be bonded using an adhesive. Before laminating and bonding the 1 st and 2 nd

thermoplastic resin films

20 and 30 to the polarizing film 10, a surface activation treatment such as a plasma treatment, a corona treatment, an ultraviolet irradiation treatment, a flame (flame) treatment, or a saponification treatment may be performed on the polarizing film 10 and/or the bonding surface of the 1 st and 2 nd

thermoplastic resin films

20 and 30. By this surface activation treatment, the adhesiveness between the polarizing film 10 and the 1 st and 2 nd

thermoplastic resin films

20 and 30 can be improved.

The adhesive may be an aqueous adhesive, an active energy ray-curable adhesive or a thermosetting adhesive, and is preferably an aqueous adhesive or an active energy ray-curable adhesive. When thermoplastic resin films are laminated on both sides of the polarizing film 10, the adhesives on both sides may be the same type of adhesive or different types of adhesives. Although curling is likely to occur in the sheet-like body of the polarizing plate 2 when different types of adhesives are used, according to the present invention, even if reverse curling occurs when the polarizing plate 2 is made into a sheet-like body using different types of adhesives, the reverse curling can be effectively corrected in the forward curling direction.

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

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

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

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

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

In the case of using the aqueous adhesive, after the polarizing film 10 and the 1 st and/or 2 nd

thermoplastic resin films

20 and 30 are bonded, a drying step for removing water contained in the aqueous adhesive is preferably performed. After the drying step, a curing step of curing at a temperature of, for example, 20 to 45 ℃ may be provided.

The active energy ray-curable adhesive is an adhesive that is cured by irradiation with an active energy ray such as an ultraviolet ray, a visible light, an electron beam, or an X-ray. When an active energy ray-curable adhesive is used, the adhesive layer of the polarizing plate 2 is a cured layer of the adhesive.

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

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

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

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

When an active energy ray-curable adhesive is used for lamination bonding of the polarizing film 10 and the 1 st and/or 2 nd

thermoplastic resin films

20 and 30, after lamination bonding, a drying step is performed as necessary, and then a curing step of curing the active energy ray-curable adhesive by irradiation with active energy rays is performed. The light source of the active energy ray is not particularly limited, and ultraviolet rays having an emission distribution at a wavelength of 400nm or less are preferable, and specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, or the like can be used.

The irradiation intensity of the active energy ray to the adhesive layer formed of the active energy ray-curable adhesive can be appropriately determined depending on the composition of the adhesive, and is preferably set so that the irradiation intensity in a wavelength region effective for activation of the polymerization initiator is 0.1 to 6000mW/cm². The irradiation intensity is 0.1mW/cm²When the above reaction time is 6000mW/cm, the reaction time is not too long²In the following case, yellowing of the adhesive layer and deterioration of the polarizing film 10 due to heat radiated from the light source and heat generation during curing of the adhesive are less likely to occur.

The irradiation time of the active energy ray may be appropriately determined depending on the composition of the adhesive, and is preferably setThe integrated light quantity represented by the product of the irradiation intensity and the irradiation time is set to 10-10000 mJ/cm². The integrated light quantity is 10mJ/cm²In the above case, the active ingredient derived from the polymerization initiator can be sufficiently generated, the curing reaction can be more surely carried out, and 10000mJ/cm²In the following case, the irradiation time does not become excessively long, and the good productivity of the polarizing plate 2 can be maintained.

(3-4) adhesive layer and Release film

The polarizing plate 2 shown in fig. 3 and 4 may include an adhesive layer 40. The pressure-sensitive adhesive layer 40 may be directly laminated on the surface of the 1 st or 2 nd

thermoplastic resin film

20 or 30 or the polarizing film 10, and may be used for bonding the polarizing plate 3 with a protective film to an image display element (for example, a liquid crystal element).

The pressure-sensitive adhesive layer 40 for bonding the polarizing plate 3 with a protective film to an image display element (for example, a liquid crystal element) is disposed on the main surface (1 st main surface) of the polarizing plate on the side where the image display element such as a liquid crystal element is bonded. For example, when the polarizing plate 2 includes the 1 st and 2 nd

thermoplastic resin films

20 and 30 and a film having a higher equilibrium water content and/or moisture permeability than the 2 nd thermoplastic resin film 30 is used as the 1 st thermoplastic resin film 20, the adhesive layer 40 is disposed on the 2 nd thermoplastic resin film 30 side.

The pressure-sensitive adhesive layer 40 may be composed of a pressure-sensitive adhesive composition containing a resin such as a (meth) acrylic, rubber, urethane, ester, silicone, or polyvinyl ether resin as a main component (base polymer). Among them, a pressure-sensitive adhesive composition containing a (meth) acrylic resin having excellent transparency, weather resistance, heat resistance and the like as a base polymer is preferable. The adhesive composition may be an active energy ray-curable type or a heat-curable type.

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

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

The active energy ray-curable adhesive composition means: the pressure-sensitive adhesive composition has a property of being cured by irradiation with an active energy ray such as an ultraviolet ray or an electron ray, and has a property of being capable of adhering an adherend such as a film with an adhesive property even before irradiation with an active energy ray, being cured by irradiation with an active energy ray, and being capable of adjusting the adhesive strength. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable adhesive composition. The active energy ray-curable adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the crosslinking agent. Further, a photopolymerization initiator, a photosensitizer and the like may be contained as necessary.

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

The adhesive layer 40 can be formed by applying an organic solvent diluted solution of the adhesive composition onto the adhesive layer-forming surface of the polarizing plate 2 (i.e., the polarizing film 10, the 1 st or 2 nd thermoplastic resin film 20, 30) and drying the same. Alternatively, the organic solvent diluted solution of the pressure-sensitive adhesive composition may be applied to a release film (for example, release film 50), dried to form a pressure-sensitive adhesive layer, and then transferred to the pressure-sensitive adhesive layer-forming surface of polarizing plate 2. In either case, a release film is preferably applied to the outer surface of the adhesive layer 40 to protect the adhesive layer 40 until use. When an active energy ray-curable pressure-sensitive adhesive composition is used, a cured product having a desired degree of curing can be formed by irradiating the formed pressure-sensitive adhesive layer with an active energy ray. The thickness of the adhesive layer 40 is usually 1 to 40 μm, but is preferably 3 to 25 μm from the viewpoint of making the polarizing plate 2 thin.

The release film 50 is a film that protects the surface of the pressure-sensitive adhesive layer 40 and is attached to the image display element (for example, a liquid crystal element). The release film 50 is generally made of a thermoplastic resin film whose one surface is subjected to a release treatment, and the release-treated surface is bonded to the pressure-sensitive adhesive layer 40. The thermoplastic resin constituting the release film 50 may be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, a polyester resin such as polyethylene terephthalate or polyethylene naphthalate, or the like. The thickness of the release film 50 is, for example, 10 to 100 μm.

(3-5) other constituent elements of polarizing plate

The polarizing plate 2 may include other components than those described above. Other components can be listed as follows: specific examples of optical layers or optical films having other optical functions than the polarizing film 10 include: optical films such as retardation films and brightness enhancement films. Other optical films may be laminated and attached via an adhesive layer and an adhesive layer.

The polarizing plate 2 may include a protective film different from the protective film 1 supplied to the above-described pressing step. The protective film is disposed on one surface of the polarizing plate 2. The structure of the protective film can be cited as described above with respect to the protective film 1.

(3-6) curling of polarizing plate

As described above, according to the present invention, the polarizing plate 2 can be corrected in the forward curl direction, and thus, the polarizing plate 3 with the protective film, which is flat and preferably has no curl and has a forward curl, can be obtained in which the reverse curl is sufficiently suppressed when the polarizing plate is formed into a sheet-like body. The manufacturing method according to the present invention is particularly advantageous when a reverse curl (a curl in which the main surface side of the protective film 1 is superimposed is convex) occurs when the polarizing plate 2 is a sheet-like body (further, when the reverse curl occurs and an MD curl occurs).

As described above, one of the methods of the polarizing plate 2 that is likely to generate reverse curl when formed into a sheet is: the 1 st thermoplastic resin film 20 and the 2 nd thermoplastic resin film 30 have different equilibrium water content and/or moisture permeability from each other, but are not limited thereto, and when the polarizing plate 2 has an asymmetric layer structure based on the polarizing film 10, for example, reverse curling is likely to occur.

Examples of the structure of the polarizing plate 2 in which reverse curl is easily generated are as follows.

(a) A structure in which a thermoplastic resin film (e.g., a protective film) is bonded to only one surface of the polarizing film 10,

(b) a structure in which a protective film is bonded to one surface of the polarizing film 10 and an optical film (such as a brightness enhancement film) other than the protective film is bonded to the other surface,

(c) the thermoplastic resin films (protective films and the like) bonded to both surfaces of the polarizing film 10 have different structures (resin type, thickness, equilibrium water content, moisture permeability, presence or absence of a surface treatment layer, and the like),

(d) the adhesive layer for adhering thermoplastic resin film (protective film, etc.) on both sides of the polarizing film 10 is formed by different kinds of adhesives,

(e) a structure in which a thermoplastic resin film (e.g., a pellicle film) is bonded to both surfaces of the polarizing film 10, and another optical film is bonded to one of the thermoplastic resin films,

(f) in other cases, the total number of films and layers on one side is different from the total number of films and layers on the other side with respect to the polarizing film 10.

(4) Other procedures

The manufacturing method according to the present invention may further include a step of cutting the polarizing plate 3 with a protective film obtained in the pressing step to obtain a sheet-like body of the polarizing plate 3 with a protective film. For cutting, a commonly used cutting device such as a cutter can be used.

The shape of the sheet-like body is not particularly limited, but is generally a square shape, preferably a square shape having long sides and short sides, and more preferably a rectangular shape. In general, the sheet is cut so that a pair of opposing sides are parallel to the MD and the remaining pair of opposing sides are parallel to the TD, and each side may be cut in a direction oblique to the MD or TD. The length of the long side and the short side of the sheet is not particularly limited, but is usually 50mm or more for the long side and 30mm or more for the short side. The larger the size of the sheet-like body, the more likely curling occurs. The problem of curling when the dimensions (long side and/or short side) are too small is difficult to generate as such.

[ examples ] A method for producing a compound

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

(1) Equilibrium water content of film

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

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

(2) Moisture permeability of film

The water vapor permeability [ g/(m) at a temperature of 40 ℃ and a relative humidity of 90% was measured according to the Kpu method for water vapor permeability specified in JIS Z0208²·24hr)〕。

(3) Thickness of polarizing plate and film

Measured using a digital micrometer "MH-15M" manufactured by Nikon corporation (Ltd.) (ニコン).

(4) Tensile modulus of elasticity in MD of polarizing plate and protective film

A rectangular test piece having an MD length of 100 mm. times.TD length of 25mm was cut out. Then, the test piece was stretched in the MD direction (longitudinal direction of the test piece) at a stretching speed of 1 mm/min under an environment of 23 ℃ and a relative humidity of 55% with the interval of the upper and lower grips of the tensile tester ((AUTOGRAPH AG-1S tester, manufactured by Shimadzu corporation)) between the both ends in the longitudinal direction, and the tensile modulus [ MPa ] in the MD at 23 ℃ and a relative humidity of 55% was calculated from the slope of the initial straight line in the obtained stress-strain curve.

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

The film tension [ N/m ] of the polarizing plate and the protective film running between the pair of laminating rollers for laminating the polarizing plate and the protective film, and the pair of nip rollers on the upstream side thereof closest to the laminating rollers was measured by using a tension detection roller provided between the laminating roller and the pair of nip rollers closest to the laminating rollers.

(6) Polarizing plate with protective film and curl amount of polarizing plate

From the obtained polarizing plate with a protective film, a rectangular test piece having a length of 300mm MD. times. a length of 200mm TD was cut out and left for 24 hours at a temperature of 25 ℃ and a relative humidity of 55%. The test piece was placed on a reference surface (horizontal table) with its concave surface facing upward, i.e., with 4 ends tilted. In this state, the heights of the 4 corners of the test piece from the reference plane were measured, and the heights of the 4 corners were averaged to determine the curl [ mm ]. When the curl amount is a positive value, it means that the 1 st thermoplastic resin film side becomes concave (positive curl), and when it is a negative value, it means that the 2 nd thermoplastic resin film side becomes concave (reverse curl). In the polarizing plate with a protective film of example 2, no curling occurred on either the 1 st thermoplastic resin film side or the 2 nd thermoplastic resin film side.

< example 1 >

(A) Production of polarizing film

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

(B) Manufacture of polarizing plate

While continuously conveying the polarizing film obtained in the above (a), a film having a hard coat layer formed on a TAC film "KC 2 UAW" made by konica minolta precision optics corporation (コニカミノルタオプト) was continuously conveyed in a long length form 1, and the thickness: 32.4 μm, equilibrium water content: 1.9% by weight, moisture permeability: 455 g/(m)²24hr), and a long 2 nd thermoplastic resin film [ a cyclic polyolefin resin film made of JSR (strain, "FEKB 015D 3", thickness: 15.1 μm, equilibrium water content: 0.8 wt%, moisture permeability: 115 g/(m)²24 hr)), and a water-based adhesive is injected between the polarizing film and the 1 st thermoplastic resin film and between the polarizing film and the 2 nd thermoplastic resin film, and a laminated film composed of the 1 st thermoplastic resin film/water-based adhesive layer/polarizing film/water-based adhesive layer/the 2 nd thermoplastic resin film is obtained between the laminating rollers. Next, the obtained laminated film was conveyed and subjected to heat treatment at 80 ℃ for 300 seconds by a hot air dryer, thereby drying the aqueous adhesive layer to obtain a polarizing plate. The aqueous adhesive is an aqueous solution obtained by the following method: polyvinyl alcohol powder (trade name "GOHSEFIMER" (ゴーセファイマー) manufactured by Nippon synthetic chemical industry Co., Ltd.) was dissolved in hot water at 95 ℃ to obtain a 3 wt% polyvinyl alcohol aqueous solution, and a crosslinking agent (sodium glyoxylate manufactured by Nippon synthetic chemical industry Co., Ltd.) was added to the polyvinyl alcohol aqueous solution in an amount of 1 part by weight based on 10 parts by weight of the polyvinyl alcohol powder.

Thickness T of polarizer₂58.6 μm, tensile modulus of elasticity E in MD₂6540 MPa. The roll of polarizing plate was measured according to the above methodThe amount of curl was-10 mm (reverse curl).

(C) Manufacture of polarizing plate with protective film

Continuously conveying the polarizing film obtained in the above (B) while continuously conveying a long-sized protective film [ the base film is made of polyethylene terephthalate, and has thereon a protective film of a (meth) acrylic pressure-sensitive adhesive layer, and the total thickness T₁: 57.3 μm, tensile modulus of elasticity E in MD₁: 2521 MPa), and passing them in a laminating zone in a laminating roller in a superposed manner, thereby producing a polarizing plate with a protective film by pressing the laminate of the protective film and the polarizing plate from above and below. The protective film is bonded to the 1 st thermoplastic resin film (TAC film) surface of the polarizing plate via the adhesive layer. The pressure (nip pressure) applied by the laminating roller to the laminate of the protective film and the polarizing plate was 0.1MPa, and this value was almost the same in the following examples and comparative examples.

Film tension in MD of polarizing plate and protective film, left side by 10 of the above formula (I)⁵The resulting value, right times 10⁵The values obtained, the differences, and the curl amounts of the polarizing plates with protective films are shown in table 1. "Δ" in Table 1 represents the left-hand product of the above formula (I) by 10⁵The resulting value is multiplied by 10 on the right⁵The difference in the values obtained, i.e. to the left of the above formula (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 tensions of the polarizing plate and the protective film in the MD were as shown in table 1. Left side of the above formula (I) by 10⁵The resulting value, right times 10⁵The values obtained, their differences, and the amount of curl of the polarizing plate with a protective film are shown in table 1.

< example 6 >

Using a base film composed of polyethylene terephthalate, having thereon a (meth) acrylic adhesive layer, and having a total thickness T₁69.3 μm and tensile modulus of elasticity E in MD₁A polarizing plate with a protective film was produced in the same manner as in example 1, except that the protective film was a 2743MPa long protective film, and the film tensions of the polarizing plate and the protective film in the MD were as shown in table 1. Left side of the above formula (I) by 10⁵The obtained valueRight side by 10⁵The values obtained, the differences, and the curl amounts of the polarizing plates with protective films are shown in table 1.

< example 7 >

Except that a 2 nd thermoplastic resin film [ a cyclic polyolefin resin film manufactured by nippon reesei corporation, trade name "ZF 14-023", thickness: 22.9 μm, equilibrium water content: 0.1 wt%, moisture permeability: 17 g/(m)²24 hr)), the thickness T was produced in the same manner as in example 1₂A tensile modulus E in MD of 66.8 μm₂A 6080MPa polarizing plate. The amount of curl of the polarizing plate was measured to be-6 mm (reverse curl) according to the above method.

Next, a polarizing plate with a protective film was produced in the same manner as in example 1, except that the polarizing plate obtained above and the film tension in MD of the polarizing plate and the protective film were used as shown in table 1. Left side of the above formula (I) by 10⁵The resulting value, right times 10⁵The values obtained, the differences, and the curl amounts of the polarizing plates with protective films are shown in table 1.

< comparative example 1 >

As the 1 st thermoplastic resin film, a TAC film "KC 2 UAW" manufactured by konica minolta precision optics co. [ thickness: 25.5 μm, equilibrium water content: 3.0 wt%, moisture permeability: 1207 g/(m)²24 hr)), and the thickness T was produced in the same manner as in example 1₂A tensile modulus of elasticity E in MD of 51.7 μm₂6839 MPa. The amount of curl of the polarizing plate was measured to be-13 mm (reverse curl) according to the above method.

[ TABLE 1]

Claims

1. A method for manufacturing a polarizing plate with a protective film,

which comprises a step of passing one surface of a polarizing plate and a protective film through a pair of laminating rollers in an overlapping manner to perform extrusion,

when the polarizing plate is formed into a sheet, the side of the polarizing plate overlapping the protective film is raised to generate a curl,

the polarizing plate comprises a polarizing film, a 1 st thermoplastic resin film laminated on one surface of the polarizing film, and a 2 nd thermoplastic resin film laminated on the other surface of the polarizing film,

the 1 st thermoplastic resin film has a higher equilibrium water content than the 2 nd thermoplastic resin film at a temperature of 23 ℃ and a relative humidity of 55%,

the protective film is disposed on the 1 st thermoplastic resin film side,

the thickness of the protective film is T₁μ m, tensile modulus of elasticity in MD of E₁MPa and a film tension in MD before passing through the pair of laminating rollers is F₁N/m, the thickness of the polarizing plate is T₂μ m and a tensile elastic modulus in MD of E₂MPa and a film tension in MD before passing through the pair of laminating rollers is F₂N/m, the step of extruding is performed under the condition of satisfying the following formula (I),

[ number 1]

2. The production method according to claim 1, wherein the step of extruding is performed under a condition satisfying the following formula (II),

number 2

3. The production method according to claim 1, wherein the difference in the equilibrium water content between the 1 st thermoplastic resin film and the 2 nd thermoplastic resin film is 0.5 wt% or more.

4. The production method according to any one of claims 1 to 3, wherein the 1 st thermoplastic resin film has an equilibrium water content of 1.5 wt% or more at a temperature of 23 ℃ and a relative humidity of 55%.

5. The manufacturing method according to claim 1, wherein the polarizing plate has a thickness of 100 μm or less.