JP7654956B2 - Manufacturing method of polarizing plate - Google Patents

Description

The present invention relates to a polarizing plate and a liquid crystal display device.

One of the optical elements that make up a liquid crystal display device is a polarizer. In order to protect the polarizer from ultraviolet rays, moisture, and the like, a protective film made of resin may be provided on at least one surface of the polarizer (Patent Documents 1 and 2).

JP 2020-091494 A JP 2009-205135 A

A laminate of a polarizing plate, which includes a polarizer and a protective film, and a plate-like optical element such as a liquid crystal panel, may warp when heated for a long period of time. Furthermore, moisture present in the air may cause the polarizer to deteriorate, resulting in a decrease in the quality of the polarizing plate. Changes such as warping of the laminate and a decrease in the quality of the polarizing plate can cause a decrease in image quality, for example, in a liquid crystal display device that uses the polarizing plate.

Therefore, there is a demand for a polarizing plate that is resistant to moist heat and in which the amount of warping after long-term heating is reduced in a laminate of the polarizing plate and a plate-shaped optical element; and a liquid crystal display device that includes the same.

Means for Solving the Problems The present inventors have conducted extensive research to find that the problems can be solved by a polarizing plate including a polarizer and a specific protective film, and have thus completed the present invention.
That is, the present invention provides the following.

[1] A polarizer including a protective film (A), a polarizer, and a protective film (B) in this order,
The protective film (A) contains a cyclic olefin polymer,
The protective film (A) satisfies the following conditions (a) and (b):
0≦R _ab ≦0.15% and 0≦R _tr ≦0.15% (a)
|R _tr -R _ab |≦0.08% (b)
(In the above conditions (a) and (b),
R _ab represents a dimensional change rate (%) of the protective film (A) in an in-plane direction of the protective film (A) and a direction parallel to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours,
R _tr represents a dimensional change rate (%) of the protective film (A) in an in-plane direction of the protective film (A) and a direction perpendicular to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours.
The protective film (B) has a moisture permeability of 20 g/m ² ·24 hr or less, measured in accordance with JIS Z0208 under conditions of 25° C. and 90% RH.
[2] The polarizing plate according to [1], wherein the cyclic olefin polymer contained in the protective film (A) has a glass transition temperature TgA of 130° C. or higher.
[3] The polarizing plate according to [1] or [2], wherein the protective film (A) has a moisture permeability of 10 g/ ^m2 ·24 hr or less, measured in accordance with JIS Z0208 at 25° C. and 90% RH.
[4] The polarizing plate according to any one of [1] to [3], wherein the protective film (A) has a thickness of 20 μm or more and 50 μm or less.
[5] The polarizing plate according to any one of [1] to [4], wherein the protective film (A) has an in-plane retardation ReA of 10 nm or less at a measurement wavelength of 590 nm.
[6] The polarizing plate according to any one of [1] to [5], wherein the protective film (B) has an in-plane retardation ReB of 40 nm or more and 80 nm or less at a measurement wavelength of 590 nm.
[7] A liquid crystal display device comprising the polarizing plate according to any one of [1] to [6] and a liquid crystal panel,
the protective film (B) is disposed between the liquid crystal panel and the polarizer.

The present invention provides a polarizing plate having resistance to moist heat, in which the amount of warping after long-term heating is reduced in a laminate of the polarizing plate and a plate-shaped optical element; and a liquid crystal display device including the same.

FIG. 1 is a cross-sectional view that illustrates a polarizing plate according to one embodiment of the present invention. FIG. 2 is an exploded perspective view illustrating a polarizing plate according to one embodiment of the present invention. FIG. 3 is a cross-sectional view that illustrates a liquid crystal display device according to one embodiment of the present invention.

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

In the following description, the in-plane retardation Re of a film or layer is a value expressed as Re = (nx - ny) x d, unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film or layer (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the in-plane direction of the film or layer that is perpendicular to the direction of nx. d represents the thickness of the film or layer. The measurement wavelength is 590 nm, unless otherwise specified.

In the following description, unless otherwise specified, the directions of elements as "parallel," "vertical," and "orthogonal" may include an error within a range that does not impair the effect of the present invention, for example, within a range of ±3°, ±2°, or ±1°.

The machine direction (MD) of a film or layer coincides with the longitudinal direction of the film or layer, which is usually long.
The width direction (TD) of a film or layer is usually a direction perpendicular to the conveying direction, and coincides with the short side direction of the film or layer, which is usually long.

In the following description, a "long" film refers to a film that is 5 times or more longer than its width, preferably 10 times or more longer, and specifically refers to a film that is long enough to be wound into a roll for storage or transportation. There is no particular upper limit to the length of the film, and it can be, for example, 100,000 times or less than its width.

[1. Polarizing Plate]
A polarizing plate according to one embodiment of the present invention includes a protective film (A), a polarizer, and a protective film (B) in this order.
Fig. 1 is a cross-sectional view illustrating a polarizing plate according to an embodiment of the present invention, and Fig. 2 is an exploded perspective view illustrating a polarizing plate according to an embodiment of the present invention.
The polarizing plate 100 includes a protective film 110 as a protective film (A), a polarizer 120, and a protective film 130 as a protective film (B) in this order. In this embodiment, the protective film 110 and the polarizer 120 are in direct contact with each other, and the protective film 130 and the polarizer 120 are in direct contact with each other. In another embodiment, the protective film 110 and the polarizer 120 may be laminated with an adhesive layer interposed therebetween. In still another embodiment, the protective film 130 and the polarizer 120 may be laminated with an adhesive layer interposed therebetween.
The polarizing plate 100 may be in a long shape or in the form of a sheet.

The polarizer 120 is a linear polarizer, and as shown in FIG. 2, in this embodiment, the absorption axis Aa of the polarizer 120 is parallel to the longitudinal direction of the polarizing plate 100. The transmission axis At of the polarizer 120 is perpendicular to the absorption axis Aa and perpendicular to the longitudinal direction of the polarizing plate 100 when viewed from the thickness direction of the polarizing plate 100.

Direction Da is an in-plane direction of protective film 110 as protective film (A) and is parallel to the absorption axis Aa of polarizer 120. Direction Dt is an in-plane direction of protective film 110 as protective film (A) and is perpendicular to the absorption axis Aa of polarizer 120 when viewed from the thickness direction of polarizing plate 100. Therefore, when viewed from the thickness direction of polarizing plate 100, direction Da in the plane of protective film 110 is parallel to the longitudinal direction of polarizing plate 100, and direction Dt in the plane of protective film 110 is perpendicular to the longitudinal direction of polarizing plate 100.

[1.1. Protective film (A)]
(Dimensional change rate during heating test)
The protective film (A) is usually a film whose dimensional change rate after a heating test satisfies the following conditions (a) and (b). The heating test is performed under the condition that the protective film (A) is placed alone in an environment at 85° C. for 500 hours. Hereinafter, the heating test under these conditions is also simply referred to as the heating test.

0≦R _ab ≦0.15% and 0≦R _tr ≦0.15% (a)
|R _tr -R _ab |≦0.08% (b)

Here, R _ab represents the dimensional change rate (%) of the protective film (A) in the in-plane direction of the protective film (A) parallel to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours, and R _tr represents the dimensional change rate (%) of the protective film (A) in the in-plane direction of the protective film (A) perpendicular to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours.

The dimensional change rate (%) after the heating test is calculated as follows.
If the dimension of the protective film (A) in a predetermined direction before being placed in an 85° C. environment is L0, and the dimension of the protective film in the predetermined direction after being placed in an 85° C. environment for 500 hours is L500, the dimensional change rate R (%) of the protective film (A) in the predetermined direction is calculated according to the following formula. When the protective film (A) shrinks due to the heating test, the dimensional change rate R will be a positive value.
R (%)=(L0-L500)/L0×100

In this embodiment, the dimensional change rate after a heating test in direction Da within the plane of the protective film 110 as the protective film (A) corresponds to the dimensional change rate R _ab , and the dimensional change rate after a heating test in direction Dt within the plane of the protective film 110 corresponds to the dimensional change rate R _tr .

By satisfying the above conditions (a) and (b) for the dimensional change rate, warping of a plate-like object such as a liquid crystal panel can be reduced when the polarizing plate is laminated with the plate-like object.

In condition (a), the value of R _ab is preferably 0.10% or less, usually 0.00% or more, and may be 0.00%. The value of R _tr is preferably 0.10% or less, usually 0.00% or more, and may be 0.00%.

In condition (b), the value of |R _tr - _{R ab} | is preferably 0.05% or less, usually 0.00% or more, and may be 0.00% or more.

The protective film (A) satisfying the above conditions (a) and (b) can be produced, for example, by adjusting the conditions for producing the protective film (A) from a resin containing a cyclic olefin polymer.
For example, the conditions for forming a resin containing a cyclic olefin polymer into a film by melt extrusion may be adjusted as follows to obtain a protective film (A) that satisfies the conditions (a) and (b).

The temperature of the cooling drum is preferably (Tg-30°C) or more, more preferably (Tg-25°C) or more, and is preferably (Tg-10°C) or less, more preferably (Tg-15°C) or less. Here, Tg is the glass transition temperature of the cyclic olefin polymer contained in the resin. When the resin forming the film contains multiple types of cyclic olefin polymers, Tg is the glass transition temperature of the cyclic olefin polymer contained in the largest proportion among the multiple types of cyclic olefin polymers.
This reduces the distortion remaining in the produced film and reduces the rate of dimensional change when the protective film (A) is heated, thereby enabling the protective film (A) to satisfy conditions (a) and (b).

It is preferable that the ratio of the die lip opening to the thickness of the film to be produced (drawdown ratio) is small. By making the drawdown ratio smaller, the residual distortion in the film to be produced can be reduced, and the dimensional change rate when the protective film (A) is heated can be reduced, and thus the protective film (A) can satisfy conditions (a) and (b).

It is preferable that the tension for taking up the film is small. By making the tension for taking up the film smaller, the residual distortion in the produced film can be reduced, and the dimensional change rate when the protective film (A) is heated can be reduced, and thus the protective film (A) can satisfy the conditions (a) and (b).

(Configuration of protective film (A))
The protective film (A) may have a single-layer structure or a multi-layer structure.
The surface of the protective film (A) may be subjected to a surface treatment such as a corona treatment.

The protective film (A) usually contains a cyclic olefin polymer. Usually, the protective film (A) is formed from a resin containing a cyclic olefin polymer. Here, the cyclic olefin polymer means a polymer containing a structural unit obtained by polymerizing a cyclic olefin or a derivative thereof, and a hydrogenated product thereof. Hereinafter, the structural unit obtained by polymerizing a cyclic olefin or a derivative thereof is also referred to as a cyclic olefin unit. Examples of derivatives of cyclic olefins include those having a substituent on the ring.

The protective film (A) may contain one type of cyclic olefin polymer alone or a combination of two or more types.

The cyclic olefin may be monocyclic or polycyclic.
The number of carbon atoms constituting the cyclic olefin-based unit is preferably 4 or more, more preferably 5 or more, and is preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. By setting the number of carbon atoms constituting the cyclic olefin-based unit within this range, the mechanical strength, heat resistance, and moldability of the resin containing the cyclic olefin-based polymer are highly balanced.

In the cyclic olefin polymer, the proportion of the cyclic olefin units can be appropriately selected depending on the intended use. The proportion of the cyclic olefin units in the cyclic olefin polymer is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more, and can be 100% by weight or less. When the proportion of the cyclic olefin units in the cyclic olefin polymer is within this range, the transparency and heat resistance of the resin containing the cyclic olefin polymer are good.

Examples of cyclic olefin polymers include norbornene polymers, monocyclic cyclic olefin polymers, cyclic conjugated diene polymers, and hydrogenated versions of these. Among these, norbornene polymers are preferred because of their good transparency and moldability.

Examples of norbornene-based polymers include ring-opening polymers of monomers having a norbornene structure and their hydrogenated products; addition polymers of monomers having a norbornene structure and their hydrogenated products. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer that can be copolymerized therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer that can be copolymerized therewith.

Among these, hydrogenated ring-opening polymers of monomers having a norbornene structure, addition copolymers of monomers having a norbornene structure and α-olefins, and hydrogenated addition copolymers of monomers having a norbornene structure and α-olefins are preferred, and hydrogenated ring-opening copolymers of two or more monomers having norbornene structures, addition copolymers of monomers having a norbornene structure and α-olefins, and hydrogenated addition copolymers of monomers having a norbornene structure and α-olefins are more preferred.

Examples of monomers having a norbornene structure include bicyclo[2.2.1]hept-2-ene (common name: norbornene), tricyclo[4.3.0.1 ^2,5 ]deca-3,7-diene (common name: dicyclopentadiene), 7,8-benzotricyclo[4.3.0.1 ^2,5 ]deca-3-ene (common name: methanotetrahydrofluorene), tetracyclo[4.4.0.1 ^2,5 .1 ^7,10 ]dodeca-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent on the ring). Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. These substituents may be the same or different, and a plurality of them may be bonded to the ring. The monomer having a norbornene structure may be used alone or in combination of two or more kinds at any ratio.

Examples of the polar group include a heteroatom or an atomic group having a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfonic acid group.

Examples of monomers capable of ring-opening copolymerization with a monomer having a norbornene structure include monocyclic olefins and derivatives thereof, such as cyclohexene, cycloheptene, and cyclooctene; cyclic conjugated dienes and derivatives thereof, such as cyclohexadiene and cycloheptadiene; and the like. One type of monomer capable of ring-opening copolymerization with a monomer having a norbornene structure may be used alone, or two or more types may be used in combination in any ratio.

A ring-opening polymer of a monomer having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomer in the presence of a ring-opening polymerization catalyst.

In the addition copolymer of a monomer having a norbornene structure and an α-olefin, examples of the α-olefin include α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, and 1-butene, and derivatives thereof. Among these, ethylene is preferred. The α-olefins may be used alone or in combination of two or more in any ratio.

Addition polymers of monomers having a norbornene structure can be produced, for example, by polymerizing or copolymerizing the monomers in the presence of an addition polymerization catalyst.

The hydrogenated products of the ring-opening polymer and the addition polymer described above can be produced, for example, by hydrogenating the carbon-carbon unsaturated bonds, preferably to 90% or more, in a solution of the ring-opening polymer and the addition polymer in the presence of a hydrogenation catalyst containing a transition metal such as nickel or palladium.

The glass transition temperature TgA of the cyclic olefin polymer contained in the protective film (A) is preferably 130°C or higher, more preferably 150°C or higher, from the viewpoint of further reducing the rate of dimensional change due to heat, and is preferably 180°C or lower, from the viewpoint of facilitating film forming processing.

The weight average molecular weight Mw of the cyclic olefin polymer contained in the protective film (A) is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and is preferably 100,000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight average molecular weight is in such a range, the mechanical strength and formability of the protective film (A) are highly balanced.

The molecular weight distribution (Mw/Mn) of the cyclic olefin polymer contained in the protective film (A) is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, and is preferably 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. Here, Mn represents the number average molecular weight. By making the molecular weight distribution equal to or greater than the lower limit of the above range, the productivity of the polymer can be increased and the manufacturing cost can be reduced. In addition, by making it equal to or less than the upper limit, the amount of low molecular weight components can be reduced. As a result, the stability of the protective film (A) can be improved.

The weight average molecular weight (Mw) and number average molecular weight (Mn) can be measured using gel permeation chromatography (GPC). Solvents used in GPC include cyclohexane, toluene, and tetrahydrofuran. When GPC is used, the weight average molecular weight is measured, for example, as a relative molecular weight in terms of polyisoprene or polystyrene.

In addition to the cyclic olefin polymer, the protective film (A) may contain optional components such as a polymer other than the cyclic olefin polymer; an antiblocking agent; an ultraviolet absorber; and a light stabilizer.

As described above, the protective film (A) may have a multilayer structure. Therefore, the protective film (A) may have a multilayer structure including different layers, such as a slippery layer including a cyclic olefin polymer and an antiblocking material, and an ultraviolet absorbing layer including a cyclic olefin polymer and an ultraviolet absorbing agent.

The protective film (A) may include a lubrication layer.
In addition to the cyclic olefin polymer, the slip layer usually contains an antiblocking agent, such as inorganic particles, such as silica particles, or organic particles, such as organic polymer particles.
As the organic particles, from the viewpoint of facilitating adjustment of the refractive index of the lubrication layer, crosslinked particles of an acrylic-styrene copolymer are preferred. A specific example of a preferred organic particle is "Techpolymer (registered trademark)" manufactured by Sekisui Plastics Co., Ltd.

The average particle size of the antiblocking material may be adjusted as appropriate to impart the desired slip properties to the protective film (A), and is preferably in the range of 0.05 μm to 0.5 μm.

The content of the antiblocking material in the slip layer is not particularly limited.
The content of the antiblocking material in the protective film (A) may be, for example, in the range of 0.01% by weight to 2% by weight.

The easy-slip layer is usually disposed on the outermost side of the protective film (A). The easy-slip layer has an arithmetic mean roughness Ra of preferably 10 nm or more, more preferably 20 nm or more. This can improve the anti-blocking properties when the protective film (A) is stored in the form of a roll. The easy-slip layer also has an arithmetic mean roughness Ra of preferably 60 nm or less, more preferably 50 nm or less. This can reduce the external haze of the protective film (A) and improve the visibility of an image display device equipped with a polarizing plate including the protective film (A).

The slipperiness of the slippery layer can be evaluated by determining the static friction coefficient of the slippery layer using a friction tester in accordance with JIS K7125 with a load of 1 kg. The static friction coefficient of the slippery layer is preferably 0.4 or more, preferably 0.8 or less, and more preferably 0.7 or less.

The protective film (A) may include an ultraviolet absorbing layer. When the protective film (A) includes an ultraviolet absorbing layer, the protective film (A) can reduce ultraviolet light incident on the polarizer, thereby suppressing deterioration in the quality of the polarizing plate.
The ultraviolet absorbing layer usually contains an ultraviolet absorber in addition to the cyclic olefin polymer. Examples of the ultraviolet absorber are not particularly limited, and include benzotriazole-based ultraviolet absorbers and triazine-based ultraviolet absorbers. Examples of commercially available ultraviolet absorbers include the "Adeka STAB series" manufactured by ADEKA Corporation (e.g., Adeka STAB LA-31RG).

The content of the ultraviolet absorbing agent in the ultraviolet absorbing layer is not particularly limited.
The content of the ultraviolet absorbing agent in the protective film (A) may be, for example, in the range of 0.01% by weight to 10% by weight.

The protective film (A) may contain a light stabilizer in addition to the cyclic olefin polymer. When the protective film (A) contains a light stabilizer, discoloration of the protective film (A) caused by light such as ultraviolet light can be reduced. Examples of light stabilizers include the "Tinuvin (registered trademark) series" manufactured by BASF (e.g., Tinuvin 144), and Tinuvin 144 is preferred because it can effectively reduce discoloration of the cyclic olefin polymer.

The content of the light stabilizer in the protective film (A) may be, for example, in the range of 0.01% by weight to 5% by weight.

The thickness of the protective film (A) is preferably 20 μm or more, more preferably 30 μm or more. This improves the handleability of the protective film (A). The thickness of the protective film (A) is preferably 50 μm or less, more preferably 45 μm or less. This can improve the visibility of an image display device equipped with a polarizing plate including the protective film (A). In addition, when a polarizing plate including the protective film (A) is laminated with a plate-like object such as a liquid crystal panel, warping of the plate-like object can be effectively reduced.

The moisture permeability of the protective film (A) is preferably low. Specifically, the moisture permeability of the protective film (A) measured according to JIS Z0208 at 25°C and 90% RH is preferably 10 g/ ^m2 ·24 hr or less, more preferably 4 g/ ^m2 ·24 hr or less, usually 0 g/ ^m2 ·24 hr or more, and may be 0 g/ ^m2 ·24 hr.
When the protective film (A) has low moisture permeability, deterioration in the quality of the polarizer (for example, a decrease in the degree of polarization) caused by moisture absorption can be effectively reduced.

It is preferable that the protective film (A) has a small in-plane retardation. Specifically, the in-plane retardation ReA of the protective film (A) at a measurement wavelength of 590 nm is preferably 10 nm or less, more preferably 8 nm or less, and is usually 0 nm or more, and may be 0 nm.

[1.2. Polarizer]
The polarizer according to this embodiment may be any polarizer, and is usually a linear polarizer.
An example of the polarizer is a linear polarizer that can be produced by a production method including a step of adsorbing a dichroic dye to a polyvinyl alcohol-based resin film.
Such a linear polarizer can be produced by a method including the steps of uniaxially stretching a polyvinyl alcohol-based resin film, dyeing the polyvinyl alcohol-based resin film with a dichroic dye to adsorb the dichroic dye, treating the polyvinyl alcohol-based resin film having the dichroic dye adsorbed thereon with an aqueous boric acid solution, and washing the polyvinyl alcohol-based resin film having the dichroic dye adsorbed thereon after the treatment with the aqueous boric acid solution.

The polyvinyl alcohol resin may be a resin obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin may be a homopolymer of vinyl acetate or a copolymer of vinyl acetate and another monomer copolymerizable therewith.
Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

The degree of saponification of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more, and usually 100 mol% or less, and may be 100 mol%.

The polyvinyl alcohol resin may be modified, for example, a modified polyvinyl alcohol resin such as polyvinyl formal resin or polyvinyl acetal resin modified with aldehydes.

The degree of polymerization of polyvinyl alcohol resins is usually about 1,000 to 10,000, and preferably about 1,500 to 5,000.

The process of uniaxially stretching the polyvinyl alcohol-based resin film may be carried out before the dyeing process with a dichroic dye, simultaneously with the dyeing process, or after the dyeing process, or before the treatment process with an aqueous boric acid solution, or simultaneously with the treatment process with an aqueous boric acid solution. The uniaxial stretching process may also be carried out in multiple of these stages.

In the step of uniaxially stretching the polyvinyl alcohol-based resin film, any stretching method can be used. For example, a method of uniaxially stretching while conveying with two or more rolls having different peripheral speeds, and a method of uniaxially stretching using a heated roll can be mentioned. Furthermore, the uniaxial stretching may be dry stretching or wet stretching. In dry stretching, stretching is usually performed in the atmosphere. In wet stretching, stretching is usually performed in a state where the polyvinyl alcohol-based resin film is swollen using a solvent.
The stretching ratio in the uniaxial stretching can usually be about 3 to 8 times.

An example of a method for dyeing a polyvinyl alcohol-based resin film with a dichroic dye is to immerse the polyvinyl alcohol-based resin film in an aqueous solution containing the dichroic dye. Examples of dichroic dyes include iodine and dichroic dyes. It is preferable to subject the polyvinyl alcohol-based resin film to an immersion treatment in which it is immersed in water before the dyeing treatment.

When iodine is used as the dichroic dye, dyeing is usually performed by immersing the polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is usually about 20 to 40°C.
The immersion time in the aqueous solution (dyeing time) is usually about 20 to 1,800 seconds.

When a dichroic dye is used as the dichroic pigment, dyeing is usually performed by immersing a polyvinyl alcohol resin film in an aqueous solution containing a water-soluble dichroic dye. The content of the dichroic dye in this aqueous solution is usually about 1×10 ⁻⁴ to 10 parts by weight, preferably about 1×10 ⁻³ to 1 part by weight, per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous solution used for dyeing is usually about 20 to 80° C.
The immersion time in the aqueous solution (dyeing time) is usually about 10 to 1,800 seconds.

The process of treating the polyvinyl alcohol-based resin film on which the dichroic dye is adsorbed with an aqueous solution of boric acid can usually be carried out by immersing the polyvinyl alcohol-based resin film on which the dichroic dye is adsorbed in an aqueous solution containing boric acid.

The amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight, per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50°C or higher, preferably 50 to 85°C, and more preferably 60 to 80°C.

After the step of treating with the aqueous boric acid solution, the polyvinyl alcohol-based resin film is usually washed with water. The washing can be performed, for example, by immersing the boric acid-treated polyvinyl alcohol-based resin film in water. The temperature of the water used in the washing is usually about 5 to 40°C. The immersion time in water is usually about 1 to 120 seconds.

After the water washing process, a drying process is usually performed to obtain a polarizer. The drying process may be performed by any method, for example, using a device such as a hot air dryer or a far-infrared heater. The temperature of the drying process is usually about 30 to 100°C, preferably 50 to 80°C. The time of the drying process is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

The moisture content of the polarizer is usually reduced to a practical level by the drying process. The moisture content of the polarizer after the drying process is usually 5 to 20% by weight, and preferably 8 to 15% by weight. When the moisture content is equal to or greater than the lower limit, the flexibility of the polarizer is usually good, and damage or breakage of the polarizer after drying can be suppressed. When the moisture content is equal to or less than the upper limit, the thermal stability of the polarizer can usually be improved.

The thickness of the polarizer can be, for example, 5 μm to 35 μm.

[1.3. Protective film (B)]
(Moisture permeability of protective film (B))
The moisture permeability of the protective film (B), measured in accordance with JIS Z0208 under conditions of 25°C and 90% RH, is usually 20 g/ ^m2 ·24 hr or less, preferably 10 g/ ^m2 ·24 hr or less, more preferably 5 g/ ^m2 ·24 hr or less, and is usually 0 g/ ^m2 ·24 hr or more, and may be 0 g/ ^m2 ·24 hr.
When the moisture permeability of the protective film (B) is equal to or less than the upper limit, moisture permeation from the side of the protective film (B) is reduced, and moisture penetrating from the main surface of the protective film (A) is prevented from reaching the polarizer, thereby preventing deterioration in the quality of the polarizing plate (e.g., change in the degree of polarization).

(Configuration of protective film (B))
The protective film (B) may have a single-layer structure or a multi-layer structure.
The surface of the protective film (B) may be subjected to a surface treatment such as a corona treatment.

An example of a material for forming the protective film (B) is a resin containing a polymer. Examples of polymers that can be included in the material for forming the protective film (B) include cyclic olefin polymers: polyesters such as polyethylene terephthalate; acrylic polymers such as polymethyl methacrylate; and polycarbonates. These polymers may be homopolymers or copolymers. In addition, the protective film (B) may contain one type of polymer alone or a combination of two or more types.

In addition to the polymer, the protective film (B) may contain optional components such as an antiblocking agent, an ultraviolet absorber, and a light stabilizer.

As described above, the protective film (B) may have a multilayer structure. Therefore, the protective film (B) may have a multilayer structure including different layers, such as a slippery layer including a polymer and an antiblocking material, and an ultraviolet absorbing layer including a polymer and an ultraviolet absorbing agent.

The protective film (B) may include a slippery layer. The slippery layer is usually disposed on the outermost side of the protective film (B). The arithmetic mean roughness Ra of the slippery layer that can be included in the protective film (B) can be in the same range as the preferred range exemplified in the description of the protective film (A).
Preferred examples of the antiblocking material that can be included in the easy-slip layer of the protective film (B) include the same examples as the antiblocking material that can be included in the protective film (A). The preferred average particle size of the antiblocking material and the preferred content ratio of the antiblocking material can be the same range as the range exemplified in the description of the protective film (A). This can provide the same effect as the effect of the easy-slip layer that can be included in the protective film (A).

The static friction coefficient of the slippery layer that may be included in protective film (B) may be in the same range as that exemplified in the description of protective film (A).

The protective film (B) may include an ultraviolet absorbing layer. The ultraviolet absorbing layer usually includes an ultraviolet absorber in addition to the polymer. Preferred examples of ultraviolet absorbers that can be included in the ultraviolet absorbing layer of the protective film (B) include the same examples as the ultraviolet absorbers that can be included in the ultraviolet absorbing layer of the protective film (A). The content ratio of the ultraviolet absorber in the protective film (A) can be in the same range as the range exemplified in the explanation of the protective film (A). This can provide the same effect as the effect of the ultraviolet absorbing layer that can be included in the protective film (A).

In addition to the polymer, the protective film (B) may contain a light stabilizer. When the protective film (B) contains a light stabilizer, discoloration of the protective film (B) caused by light such as ultraviolet light can be reduced. Examples of light stabilizers include the same examples as the light stabilizers that can be contained in the protective film (A). The content ratio of the light stabilizer can be in the same range as the range exemplified in the explanation of the protective film (A).

The thickness of the protective film (B) is preferably 20 μm or more, more preferably 30 μm or more. This improves the handleability of the protective film (B). The thickness of the protective film (B) is preferably 70 μm or less, more preferably 60 μm or less. This can improve the visibility of an image display device equipped with a polarizing plate including the protective film (B). In addition, when a polarizing plate including the protective film (B) is laminated with a plate-like object such as a liquid crystal panel, warping of the plate-like object can be effectively reduced.

The retardation value of the protective film (B) can be any value depending on the characteristics of the optical element used in combination with the polarizing plate (for example, the display mode of the liquid crystal panel when used in combination with a liquid crystal panel).

For example, in one embodiment, the in-plane retardation ReB of the protective film (B) at a measurement wavelength of 590 nm is preferably 10 nm or less, more preferably 8 nm or less, and is usually 0 nm or more, and may be 0 nm.

For example, in another embodiment, the in-plane retardation ReB of the protective film (B) at a measurement wavelength of 590 nm is preferably 40 nm or more, more preferably 50 nm or more, and is preferably 80 nm or less, more preferably 70 nm or less.

1.4. Optional Layers
The polarizing plate may include any layer in addition to the protective film (A), polarizer, and protective film (B).
For example, the polarizing plate may include an adhesive layer between the protective film (A) and the polarizer. For example, the polarizing plate may include an adhesive layer between the protective film (B) and the polarizer.
For example, the polarizing plate may include an adhesive layer, which is a layer of an adhesive (pressure-sensitive adhesive), on the surface of the protective film (B).
For example, the polarizing plate may include a hard coat layer on the surface of the protective film (A).

(Adhesive Layer)
The polarizing plate may include, for example, an adhesive layer for bonding the polarizer and the protective film (A). The polarizing plate may also include, for example, an adhesive layer for bonding the polarizer and the protective film (B).
Any adhesive may be used as the adhesive for forming the adhesive layer. Examples of the adhesive include water-based adhesives in which the components are dispersed or dissolved in water, solvent-based adhesives in which the components are dispersed or dissolved in an organic solvent, and solventless adhesives.
From the viewpoint of reducing moisture transmission from the side surface of the polarizing plate and improving the moisture resistance of the polarizing plate, the adhesive forming the adhesive layer is preferably a solvent-based adhesive or a solventless adhesive, and from the viewpoint of improving productivity, it is preferably an ultraviolet-curing adhesive.

The thickness of the adhesive layer is preferably 1 μm or more, and preferably 5 μm or less, more preferably 3 μm or less.

The adhesive layer that may be included between the protective film (A) and the polarizer and the adhesive layer that may be included between the protective film (B) and the polarizer may be formed from the same adhesive or different adhesives. Furthermore, these adhesive layers may have the same thickness or different thicknesses.

(Adhesive Layer)
The polarizing plate may include, for example, a pressure-sensitive adhesive layer for bonding the polarizing plate to an optical element such as a liquid crystal panel, etc. The pressure-sensitive adhesive layer is provided, for example, on the surface of the protective film (B).
Any adhesive can be used as the adhesive (pressure-sensitive adhesive) forming the adhesive layer. The adhesive usually contains a base polymer. Examples of the base polymer that can be contained in the adhesive include acrylic polymers; silicone polymers; polyesters; polyurethanes; polyamides; polyvinyl ethers; vinyl acetate/vinyl chloride copolymers; modified polyolefins; epoxy polymers; fluororesin polymers; and rubber polymers such as natural rubber and synthetic rubber. The adhesive may contain one type of base polymer alone or two or more types in combination. The adhesive may contain additives such as a silane coupling agent in addition to the base polymer.

The adhesive is preferably an adhesive containing an acrylic polymer as the base polymer, and more preferably an adhesive containing an acrylate or urethane acrylate, from the viewpoints of excellent optical transparency, excellent adhesive properties such as moderate wettability, cohesiveness, and adhesion, and excellent weather resistance and heat resistance.

The pressure-sensitive adhesive layer preferably has a storage modulus of 0.01 to 0.1 MPa at 23°C, and more preferably 0.02 to 0.06 MPa.

(Hard Coat Layer)
The polarizing plate may include, for example, a hard coat layer for imparting scratch resistance to the surface of the polarizing plate. The hard coat layer is provided, for example, on the surface of the protective film (A).
As the hard coat layer, a layer having an antiglare function may be used. Also, a layer having an antireflection (AR) function or a low reflection (LR) function may be used.
When the polarizing plate includes a hard coat layer having an antiglare function, the haze of the hard coat layer is preferably 2% or less, more preferably 1% or less, and usually 0% or more. When the hard coat layer has such a low haze, the visibility of an image display device using the polarizing plate can be improved.

Examples of materials for forming the hard coat layer include compositions that contain a polymerizable monomer and can be polymerized by irradiation with active energy rays such as ultraviolet rays. As the polymerizable monomer, a monomer containing an acryloyl group is preferable from the viewpoint of increasing the pencil hardness of the hard coat layer. Commercially available products can be used as materials for forming the hard coat layer.

The pencil hardness of the hard coat layer is preferably H or higher in the pencil hardness test specified in JIS K5600-5-4.

The surface of the layer, such as the protective film (A) on which the hard coat layer is to be formed, may be subjected to a surface treatment such as anchor treatment, corona treatment, or plasma treatment.

[1.5. Manufacturing method of polarizing plate]
The polarizing plate can be produced by any method. For example, the polarizing plate can be produced by bonding the protective film (A) and the protective film (B) to a polarizer. An adhesive can be used for bonding.
The long polarizing plate can be produced by laminating a long polarizer, a long protective film (A), and a long protective film (B) by a roll-to-roll method so that the longitudinal directions of the films are parallel to each other. An adhesive can be used for lamination.

[2. Liquid crystal display]
A liquid crystal display device according to one embodiment of the present invention includes the polarizing plate and a liquid crystal panel, and a protective film (B) is disposed between the liquid crystal panel and the polarizer.

FIG. 3 is a cross-sectional view that illustrates a liquid crystal display device according to one embodiment of the present invention.
The liquid crystal display device 1000 includes a polarizing plate 200, a liquid crystal panel 10, a polarizing plate 300, and a backlight 20 in this order.
The liquid crystal panel 10 may be a liquid crystal panel of any mode, such as an in-plane switching (IPS) mode or a vertical alignment (VA) mode.

The polarizing plate 200 includes, in this order, a hard coat layer 260, a protective film 210 as a protective film (A), an adhesive layer 240a, a polarizer 220, an adhesive layer 240b, a protective film 230 as a protective film (B), and a pressure-sensitive adhesive layer 250. The polarizing plate 200 is attached to one surface of the liquid crystal panel 10 by the pressure-sensitive adhesive layer 250 included in the polarizing plate 200 such that the protective film 230 as the protective film (B) is disposed between the liquid crystal panel 10 and the polarizer 220.
The polarizing plate 300 includes, in this order, a protective film 310 as a protective film (A), an adhesive layer 340a, a polarizer 320, an adhesive layer 340b, a protective film 330 as a protective film (B), and a pressure-sensitive adhesive layer 350. The polarizing plate 300 is attached to the other surface of the liquid crystal panel 10 by the pressure-sensitive adhesive layer 350 included in the polarizing plate 300 such that the protective film 330 as a protective film (B) is disposed between the liquid crystal panel 10 and the polarizer 320. The protective film 310 as a protective film (A) of the polarizing plate 300 is in contact with the backlight 20.

The protective film 210 as protective film (A), the polarizer 220, and the protective film 230 as protective film (B) constituting the polarizing plate 200 have the same configuration as the protective film 110 as protective film (A), the polarizer 120, and the protective film 130 as protective film (B) constituting the polarizing plate 100, respectively, and therefore their explanations are omitted.
The protective film 310 as protective film (A), the polarizer 320, and the protective film 330 as protective film (B) that constitute the polarizing plate 300 have the same configuration as the protective film 110 as protective film (A), the polarizer 120, and the protective film 130 as protective film (B) that constitute the polarizing plate 100, respectively, and therefore their explanations are omitted.

The hard coat layer 260, the adhesive layers 240a and 240b, and the pressure-sensitive adhesive layer 250 constituting the polarizing plate 200 may have the same configurations as the preferred examples of the hard coat layer, the adhesive layer, and the pressure-sensitive adhesive layer described in the section [1. Polarizing plate].
The adhesive layers 340a and 340b and the pressure-sensitive adhesive layer 350 constituting the polarizing plate 300 may have the same configurations as the preferred examples of the adhesive layer and the pressure-sensitive adhesive layer described in the section [1. Polarizing plate].

The absorption axis (not shown) of the polarizer 220 and the absorption axis (not shown) of the polarizer 320 included in the liquid crystal display device 1000 are perpendicular to each other when viewed in the thickness direction of the liquid crystal display device 1000. In this embodiment, the liquid crystal panel 10 included in the liquid crystal display device 1000 is rectangular, the absorption axis of the polarizer 220 is parallel to the long side of the liquid crystal panel 10, and the absorption axis of the polarizer 320 is parallel to the short side of the liquid crystal panel.

By providing the liquid crystal display device 1000 with the polarizing plate 200, warping of the liquid crystal panel 10 can be reduced, and degradation of image display performance due to deterioration of the quality of the polarizer 220 can be reduced.
By providing the liquid crystal display device 1000 with the polarizing plate 300, warping of the liquid crystal panel 10 can be reduced, and degradation of image display performance due to deterioration in the quality of the polarizer 320 can be reduced.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and may be modified as desired without departing from the scope of the claims of the present invention and the scope of equivalents thereto.

In the following explanation, the percentages and parts are by weight unless otherwise specified. Furthermore, the operations described below were carried out at room temperature and pressure unless otherwise specified.

[Evaluation method]
(Dimensional Change Rate of Protective Film (A))
The protective film (A) was cut into a square having a size of 150×150 mm to obtain a sample. The square was cut so that a pair of opposing sides of the square were parallel to the longitudinal direction of the protective film (A).

Next, marks were made at four positions on the cut square, each 25 mm away from the adjacent sides. The four marks correspond to the four vertices of a square measuring 100 mm x 100 mm. The length of the side of the square (i.e., the distance between the vertices) L0 is 100 mm.

The marked sample was heated in an oven for 500 hours under dry conditions at 85° C. The oven used was a PR3KPH oven manufactured by Espec Corporation.
The samples heated under the above conditions were removed from the oven and allowed to cool at room temperature.

After cooling, the length of each side of the rectangle with the four marks on the sample as vertices was measured using a Nikon Profileprojector V-12B. From the measured side lengths, the average value L500 of the lengths of a pair of opposing sides was calculated.
The dimensional change rate R (%) was calculated from L0 and L500 according to the following formula.
R (%)=(L0-L500)/L0×100

The dimensional change rate R(MD)(%) of the protective film (A) in the in-plane direction of the protective film (A) and parallel to the longitudinal direction was determined using the average value L500 of the lengths of a pair of sides parallel to the longitudinal direction of the protective film (A). The dimensional change rate R(TD)(%) of the protective film (A) in the in-plane direction of the protective film (A) and perpendicular to the longitudinal direction of the protective film (A) was determined using the average value L500 of the lengths of a pair of sides perpendicular to the longitudinal direction of the protective film (A).
In addition, the absolute value of the difference between the dimensional change rate R(TD) (%) and the dimensional change rate R(MD) (%) (|R(TD)-R(MD)|) was calculated.

(Moisture permeability)
The moisture permeability of the protective film (A) and the protective film (B) was measured according to JIS Z0208 (cup method). The moisture absorbent enclosed in the moisture permeability cup was anhydrous calcium chloride. The test conditions were 25°C and 95% RH. The moisture permeability cup was repeatedly weighed every 24 hours, and the moisture permeability was calculated based on the weight increase of the moisture permeability cup.

(In-plane retardation Re of film)
The retardation in the in-plane direction (in-plane retardation Re) of the protective film (A) and the protective film (B) was measured using "AXOSCAN" manufactured by AXOMETRICS.

(Thickness of each layer of the polarizing plate)
The thicknesses of the protective film (A), the protective film (B), and the polarizer were measured using a thickness gauge manufactured by Mitutoyo Corp. The thicknesses of the other layers were measured by directly slicing the polarizing plate into slices having a thickness of 0.05 μm using a microtome (manufactured by Daiwa Koki Co., Ltd., "RV-240") and observing the cross section under a microscope.

(Glass transition temperature Tg)
The glass transition temperature of the resin was measured by differential scanning calorimetry using a Hitachi DSC7020. The measurement was performed in a nitrogen atmosphere at a temperature rise rate of 20° C./min and a holding time of 30 min.

(Warpage of laminate)
In order to evaluate the effect of reducing warpage of a laminate obtained by attaching a polarizing plate to a liquid crystal panel, a laminate obtained by attaching polarizing plates to both sides of a glass plate was heated and the warpage of the laminate was measured.
A rectangular glass plate having a thickness of 0.4 mm, a long side length of 200 mm, and a short side length of 110 mm was prepared. The polarizing plate obtained in the Example or Comparative Example was cut into a rectangle of the same size as the glass plate to obtain two polarizing plate samples. The polarizing plate was cut so that the absorption axis of the polarizer contained in the polarizing plate was parallel to the longitudinal direction or the short direction. In this way, polarizing plate sample 1 in which the absorption axis of the polarizer is parallel to the longitudinal direction and polarizing plate sample 2 in which the absorption axis of the polarizer is parallel to the short direction were obtained.

Polarizing plate sample 1 was attached to one side of a glass plate, and polarizing plate sample 2 was attached to the other side of the glass plate using a pressure-sensitive adhesive ("LUCIACS CS98610US" manufactured by Nitto Denko Corporation) to obtain a laminate for warpage evaluation. The thickness of the adhesive layer (adhesive layer) was set to 25 μm.

The resulting laminate was heated in an oven at a dry temperature of 85°C for 500 hours. The oven used was a PR3KPH oven manufactured by Espec Corporation.

The laminate heated under the above conditions was removed from the oven and cooled at room temperature. The cooled laminate was placed on a table with the attached polarizing plate sample 1 facing up. The distance from the table to each of the four corners of the laminate was measured with a metal ruler. The arithmetic average value of the distances measured for the four corners was taken as the warpage of the laminate.
In the heated laminates according to the following Examples and Comparative Examples, the polarizing plate sample 1 side was warped in a concave manner.

(Change in degree of polarization)
The polarizing plate was attached to one side of a glass plate to prepare a sample for measuring the degree of polarization. The degree of polarization of the sample was measured and designated as P0 (%).
Next, the sample was placed in an oven at 60° C. and 90% RH for 500 hours to perform a moist heat resistance test. The oven used was a PR3KPH oven manufactured by Espec Corp. After the moist heat resistance test for 500 hours, the polarization degree of the sample was measured and determined as P500(%).
The degree of polarization was measured using an ultraviolet-visible-near infrared spectrophotometer ("V7200" manufactured by JASCO Corporation) and a polarizing film measuring device ("VAP7070" manufactured by JASCO Corporation). The difference (P0-P500) (%) between the degree of polarization before and after the moist heat resistance test was calculated, and the change in the degree of polarization was evaluated according to the following criteria.

Good: The difference in the degree of polarization is 0% or more and 0.01% or less.
Poor: The difference in the degree of polarization is more than 0.01% and 0.05% or less.
Poor: The difference in the degree of polarization is greater than 0.05%.

[Example 1]
(Production of protective film (A))
Resin A was produced by blending crosslinked particles of an acrylic-styrene copolymer ("Techpolymer" manufactured by Sekisui Chemical Co., Ltd., average particle size 0.38 μm) with a cycloolefin polymer ("ZEONOR1600" manufactured by Zeon Corporation, glass transition temperature Tg: 160° C.) as a cyclic olefin polymer (hydrogenated norbornene polymer) in an amount of 5 wt % relative to the total weight of the resin.
Resin B was produced by blending a benzotriazole-based ultraviolet absorber ("ADEKA STAB LA-31RG" manufactured by ADEKA Corporation) in an amount of 5 wt % relative to the total weight of the resin with a cycloolefin polymer ("ZEONOR1600" manufactured by Zeon Corporation, glass transition temperature Tg: 160° C.) as a cyclic olefin polymer (hydrogenated norbornene polymer).

Resin A and resin B were supplied to the feed block of an extruder so as to obtain a three-layer film consisting of two types of resins having a layer structure of (Layer 1 of resin A)/(Layer 2 of resin B)/(Layer 3 of resin A), and a multilayer film serving as protective film (A) was produced as a long film by a melt extrusion method.
As the extruder, a T-die molding extruder (manufactured by Labtech) equipped with a T-die was used. As the die, one with a width of 350 mm was used. The average lip opening in the width direction of the die was 400 μm. The temperature of the cooling drum was 140° C. The thicknesses of the layer 1 of resin A and the layer 3 of resin A were both 5 μm. The thickness of the layer 2 of resin B was 30 μm. The total thickness of the protective film (A) including layers 1 to 3 was 40 μm. The width of the protective film (A) was 250 mm.
The dimensional change rate, moisture permeability, and in-plane retardation ReA of the obtained protective film (A) were measured by the above-mentioned methods.

(Manufacture of Polarizer)
A polyvinyl alcohol film (Poval manufactured by Kuraray Co., Ltd.) was dyed in a solution containing potassium iodide while being transported in the longitudinal direction, treated in an aqueous solution of boric acid, and uniaxially stretched in the transport direction simultaneously with the dyeing and treatment in the aqueous solution of boric acid. The stretching ratio was 5.8 times.
The stretched film was dried to obtain a polarizer having a thickness of 25 μm. The absorption axis of the obtained polarizer was parallel to the machine direction (transport direction).

(Preparation of protective film (B))
As the protective film (B), a cycloolefin polymer film (ZEONORFILM ZB, thickness 52 μm, manufactured by ZEON CORPORATION) containing a cyclic olefin polymer (a hydrogenated product of a norbornene polymer) was prepared. The moisture permeability and in-plane retardation ReB of the protective film (B) were measured by the above-mentioned method.

(Manufacture of polarizing plate)
One side of the produced protective film (A) was subjected to a corona treatment. One side of the prepared protective film (B) was subjected to a corona treatment.
A protective film (A) was attached to one surface of the polarizer. At that time, the longitudinal direction of the polarizer (the direction of the absorption axis) was parallel to the longitudinal direction of the protective film (A). In addition, the corona-treated surface of the protective film (A) was on the polarizer side. A UV-curable adhesive ("Hardrock" manufactured by ADEKA Corporation) was used to attach the polarizer and the protective film (A).
Next, the protective film (B) was attached to the other surface of the polarizer. At that time, the longitudinal direction of the polarizer (the direction of the absorption axis) and the longitudinal direction of the protective film (B) were parallel to each other. In addition, the corona-treated surface of the protective film (B) was placed on the polarizer side. A UV-curable adhesive ("Hardrock" manufactured by ADEKA Corporation) was used to attach the polarizer and the protective film (B).
By the above operations, a film having a layer structure of protective film (A)/adhesive layer/polarizer/adhesive layer/protective film (B) was obtained, and the film was irradiated with ultraviolet light to harden the adhesive layer contained in the film, thereby obtaining a polarizing plate.
The obtained polarizing plate was used to evaluate the change in polarization degree and the warpage of the laminate by the above-mentioned methods.

[Comparative Example 1]
As the protective film (A), an acrylic resin (polymethyl methacrylate) film (OXIS, manufactured by Okura Kogyo Co., Ltd., thickness 40 μm) was used.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 2]
As the protective film (A), a polyethylene terephthalate (PET) film (Cosmoshine SRF, manufactured by Toyobo Co., Ltd., thickness 80 μm) was used.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 3]
As the protective film (B), a triacetyl cellulose (TAC) film (VA-TAC film, manufactured by Konica Minolta, Inc., thickness 40 μm) was used.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 4]
As the protective film (A), an acrylic resin (polymethyl methacrylate) film (OXIS, manufactured by Okura Kogyo Co., Ltd., thickness 40 μm) was used.
As the protective film (B), a triacetyl cellulose (TAC) film (VA-TAC film, manufactured by Konica Minolta, Inc., thickness 40 μm) was used.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 5]
As the protective film (A), a polyethylene terephthalate (PET) film (Cosmoshine SRF, manufactured by Toyobo Co., Ltd., thickness 80 μm) was used.
As the protective film (B), a triacetyl cellulose (TAC) film (VA-TAC film, manufactured by Konica Minolta, Inc., thickness 40 μm) was used.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 6]
As the protective film (A), a TAC film (manufactured by Fujifilm: 0-TAC, thickness 40 μm) was used.
As the protective film (B), a TAC film (manufactured by Fujifilm: 0-TAC, thickness 40 μm) was used.
The adhesive used for bonding the polarizer and the protective film (A) or (B) was changed to a water-based adhesive (a modified polyvinyl alcohol-based adhesive including "GOHSENOL (trademark) Z200" manufactured by Mitsubishi Chemical Corporation and "Sefelink (trademark) SPM-01" manufactured by Mitsubishi Chemical Corporation). The step of irradiating the film with ultraviolet light to cure the adhesive layer was not performed.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 7]
As the protective film (B), a TAC film (manufactured by Fujifilm: 0-TAC, thickness 40 μm) was used.
The adhesive used for bonding the polarizer and the protective film (A) or (B) was changed to a water-based adhesive (a modified polyvinyl alcohol-based adhesive including "GOHSENOL (trademark) Z200" manufactured by Mitsubishi Chemical Corporation and "Sefelink (trademark) SPM-01" manufactured by Mitsubishi Chemical Corporation). The step of irradiating the film with ultraviolet light to cure the adhesive layer was not performed.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 8]
As the protective film (A), an acrylic resin (polymethyl methacrylate) film (OXIS, manufactured by Okura Kogyo Co., Ltd., thickness 40 μm) was used.
As the protective film (B), a TAC film (manufactured by Fujifilm: 0-TAC, thickness 40 μm) was used.
The adhesive used for bonding the polarizer and the protective film (A) or (B) was changed to a water-based adhesive (a modified polyvinyl alcohol-based adhesive including "GOHSENOL (trademark) Z200" manufactured by Mitsubishi Chemical Corporation and "Sefelink (trademark) SPM-01" manufactured by Mitsubishi Chemical Corporation). The step of irradiating the film with ultraviolet light to cure the adhesive layer was not performed.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 9]
As the protective film (A), a polyethylene terephthalate (PET) film (Cosmoshine SRF, manufactured by Toyobo Co., Ltd., thickness 80 μm) was used.
As the protective film (B), a TAC film (manufactured by Fujifilm: 0-TAC, thickness 40 μm) was used.
The adhesive used for bonding the polarizer and the protective film (A) or (B) was changed to a water-based adhesive (a modified polyvinyl alcohol-based adhesive including "GOHSENOL (trademark) Z200" manufactured by Mitsubishi Chemical Corporation and "Sefelink (trademark) SPM-01" manufactured by Mitsubishi Chemical Corporation). The step of irradiating the film with ultraviolet light to cure the adhesive layer was not performed.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

[Comparative Example 10]
As the protective film (A), a film containing a cyclic olefin polymer (a hydrogenated norbornene polymer) (ZEONORFILM ZF14-023, thickness 23 μm, manufactured by Zeon Corporation) was used.
Except for the above, a polarizing plate was obtained in the same manner as in Example 1. Using the obtained polarizing plate, the change in polarization degree and the warpage of the laminate were evaluated by the above-mentioned methods.

The structures of the polarizing plates obtained in the Examples and Comparative Examples are shown in Tables 1 and 2.
In Tables 1 and 2, the abbreviations have the following meanings.
"COP1": a protective film containing a cyclic olefin polymer having a layer structure of (Layer 1 of Resin A)/(Layer 2 of Resin B)/(Layer 3 of Resin A) "COP-ZF": a film containing a cyclic olefin polymer (manufactured by Zeon Corporation: Zeonorfilm ZF14-023)
"COP-ZB": Film containing a cyclic olefin polymer (ZEON Corporation: ZEONORFILM ZB)
"PMMA": Polymethyl methacrylate film (manufactured by Okura Kogyo Co., Ltd.: OXIS)
"PET": Polyethylene terephthalate film (Toyobo Co., Ltd.: Cosmoshine SRF)
"0-TAC": Triacetyl cellulose film (manufactured by Fujifilm: 0-TAC)
"VA-TAC": Triacetyl cellulose film (VA-TAC film manufactured by Konica Minolta)
"UV": UV-curable adhesive ("Hardrock" manufactured by ADEKA)
"Water-based": Water-based adhesive (modified polyvinyl alcohol-based adhesive including "GOHSENOL Z200" manufactured by Mitsubishi Chemical Corporation and "Sefelink SPM-01" manufactured by Mitsubishi Chemical Corporation)
"ReA": In-plane retardation of protective film (A) "ReB": In-plane retardation of protective film (B)

In both the examples and the comparative examples, the protective film (A) is laminated so that the longitudinal direction is parallel to the longitudinal direction of the polarizer to obtain a polarizing plate. Since the absorption axis direction of the polarizer is parallel to the longitudinal direction of the polarizer, the longitudinal direction (transport direction) of the protective film (A) is parallel to the absorption axis of the polarizer in the polarizing plate. In addition, the short side direction (width direction) of the protective film (A) is perpendicular to the absorption axis of the polarizer in the polarizing plate.
Therefore, the dimensional change rate R(TD) of the protective film (A) corresponds to the dimensional change rate R _{tr (%) of the protective film (A) in the in-plane direction of the protective film (A) perpendicular to the absorption axis of the polarizer. Also, the dimensional change rate R(MD) of the protective film (A) corresponds to the dimensional change rate R ab (} %) of the protective film (A) in the in-plane direction of the protective film parallel to the absorption axis of the polarizer. The value of |R(TD)-R(MD)| corresponds to the value of |R _tr -R _ab |.

[result]
The results are shown in Tables 3 and 4.
In Tables 3 and 4, "immeasurable" means that the polarized light transmittance of the polarizing plate was so significantly deteriorated that the degree of polarization could not be measured.

From the above results, the polarizing plate according to Example 1, in which the protective film (A) contains a cyclic olefin polymer and satisfies the above conditions (a) and (b), and the protective film (B) has a moisture permeability of 20 g/ ^m2 ·24 hr or less, shows a small change in polarization degree after the moist heat resistance test, being 0.01% or less. Moreover, the laminate of the polarizing plate and the glass plate according to Example 1 shows a small amount of warping after the heating test, being 0.4 mm or less.
On the other hand, the laminates of the polarizing plate and the glass plate according to Comparative Examples 1, 2, 4 to 6, and 8 to 10 in which the protective film (A) does not satisfy the above conditions (a) and (b) have a large amount of warping after the heating test.
Moreover, the polarizing plates according to Comparative Examples 3 to 9, in which the moisture permeability of the protective film (B) is greater than 20 g/m ² ·24 hr, show a large change in the polarization degree after the moist heat resistance test.

The above results show that the polarizing plate according to the present invention shows little change in polarization degree even after a moist heat resistance test, and that in a laminate of a polarizing plate and a plate-shaped optical element, the amount of warping after long-term heating can be reduced.

100, 200, 300: Polarizing plate 110, 210, 310: Protective film (protective film (A))
120, 220, 320: Polarizer 130, 230, 330: Protective film (protective film (B))
240a, 240b, 340a, 340b: adhesive layer 250, 350: pressure sensitive adhesive layer 260: hard coat layer 1000: liquid crystal display device 10: liquid crystal panel 20: backlight

Claims (6)

A method for producing a polarizing plate, comprising the steps of:
The polarizing plate is
The polarizer includes a protective film (A), a polarizer, and a protective film (B) in this order,
The protective film (A) contains a cyclic olefin polymer having a glass transition temperature TgA of 150° C. or higher,
The protective film (A) satisfies the following conditions (a) and (b):
0≦R _ab ≦0.15% and 0≦R _tr ≦0.15% (a)
|R _tr -R _ab |≦0.08% (b)
(In the above conditions (a) and (b),
R _ab represents a dimensional change rate (%) of the protective film (A) in an in-plane direction of the protective film (A) and a direction parallel to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours,
R _tr represents a dimensional change rate (%) of the protective film (A) in an in-plane direction of the protective film (A) and a direction perpendicular to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours.
The protective film (B) has a moisture permeability of 20 g/m2·24 hr or less, ^measured in accordance with JIS Z0208 under conditions of 25° C. and 90% RH;
The manufacturing method includes:
The method includes a step of producing the protective film (A) by molding a resin containing the cyclic olefin polymer by a melt extrusion method,
The method for producing a polarizing plate comprises performing the molding by the melt extrusion method at a cooling drum temperature of (TgA-30°C) or more and (TgA-10°C) or less . A method for producing a polarizing plate, comprising the steps of:
The polarizing plate is
The polarizer includes a protective film (A), a polarizer, and a protective film (B) in this order,
The protective film (A) contains a cyclic olefin polymer having a glass transition temperature TgA of 150° C. or higher,
The protective film (A) satisfies the following conditions (a) and (b):
0≦R _ab ≦0.15% and 0≦R _tr ≦0.15% (a)
|R _tr -R _ab |≦0.08% (b)
(In the above conditions (a) and (b),
R _ab represents a dimensional change rate (%) of the protective film (A) in an in-plane direction of the protective film (A) and a direction parallel to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours,
R _tr represents a dimensional change rate (%) of the protective film (A) in an in-plane direction of the protective film (A) and a direction perpendicular to the absorption axis of the polarizer when the protective film (A) is placed in an environment of 85° C. for 500 hours.
The protective film (B) has a moisture permeability of 20 g/m2·24 hr or less, ^measured in accordance with JIS Z0208 under conditions of 25° C. and 90% RH;
The manufacturing method includes:
The method includes a step of producing the protective film (A) by molding a resin containing the cyclic olefin polymer by a melt extrusion method,
The method for producing a polarizing plate , wherein the molding by the melt extrusion method is performed in such a manner that a ratio of a die lip opening to a thickness of the protective film (A) is 400/40 or less . The method for producing a polarizing plate according to claim 1 or 2 , wherein the protective film (A) has a moisture permeability of 10 g/m ² ·24 hr or less, measured according to JIS Z0208 at 25° C. and 90% RH. The method for producing a polarizing plate according to any one of claims 1 to 3 , wherein the protective film (A) has a thickness of 20 µm or more and 50 µm or less. The method for producing a polarizing plate according to any one of claims 1 to 4 , wherein the protective film (A) has an in-plane retardation ReA of 10 nm or less at a measurement wavelength of 590 nm. The method for producing a polarizing plate according to any one of claims 1 to 5 , wherein the protective film (B) has an in-plane retardation ReB at a measurement wavelength of 590 nm of 40 nm or more and 80 nm or less.

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