JP2023154628A - Method of manufacturing protective filmed polarizing plate - Google Patents

Abstract

To provide a method of manufacturing a protective filmed polarizing plate that is less susceptible to reverse curling when cut into leaflets.SOLUTION: A method of manufacturing a protective filmed polarizing plate is disclosed, comprising a pasting step of feeding a polarizing plate with a protective film placed on one surface thereof through a pair of pasting rollers to compress the same. The pasting step satisfies a condition of the following expressions (1): 2°C≤T1-T2≤15°C ...(1), where T1 [°C] represents an ambient temperature and T2 [°C] represents a temperature of the supplied polarizing plate.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a polarizing plate with a protection film.

In recent years, image display devices such as liquid crystal display devices and organic EL display devices, and mobile terminals such as smartphones, are rapidly becoming larger and slimmer in terms of design and portability. In order to achieve long-time operation with a limited thickness, the polarizing plates used are also required to have higher brightness and be thinner and lighter.

Conventionally, a polarizing plate in which a protective film made of triacetyl cellulose (TAC) is bonded to a polarizer made of polyvinyl alcohol-based resin with an adhesive is generally used. However, in recent years, protective films made of resins other than TAC have come to be used from the viewpoints of thinning, durability, cost, productivity, etc. (for example, Patent Document 1).

Japanese Patent Application Publication No. 2004-245925

A sheet of polarizing plate that can be obtained by cutting out a long polarizing plate tends to be deformed into an arched shape. This deformation is also referred to herein as "curl."
Polarizing plates are generally distributed on the market as polarizing plates with a protection film attached with a removable protection film (also referred to as a surface protection film) for protecting the surface of the polarizing plate. A polarizing plate with a protection film also has the same tendency to curl easily when formed into a sheet. In the case of a polarizing plate with a protection film, in addition to curling, there is also the problem that air bubbles are likely to be mixed in when the protection film and the polarizing plate are bonded together.

There are two types of curl in a sheet of polarizing plate with a protection film: "normal curl" and "reverse curl." In a sheet of a polarizing plate with a protection film, a "positive curl" is a curl in which the surface on the polarizing plate side is convex, and a "reverse curl" is a curl in which the surface on the protection film side is convex.
If reverse curl occurs, a bonding error may occur when bonding the polarizing plate side of the sheet of the polarizing plate with a protective film to an image display device such as a liquid crystal cell or an organic EL device via an adhesive layer. Otherwise, problems such as air bubbles being mixed in at the interface between the adhesive layer and the image display element are likely to occur.

An object of the present invention is to provide a manufacturing method capable of manufacturing a polarizing plate with a protective film that suppresses reverse curl when formed into a sheet.

The present invention provides the following method for manufacturing a polarizing plate with a protective film.
[1] A method for producing a polarizing plate with a protective film, which includes a laminating step of stacking a protective film on one side of the polarizing plate and pressing it by passing it between a pair of laminating rolls,
In the bonding step, when the ambient temperature is T1 [° C.] and the temperature of the polarizing plate supplied is T2 [° C.], the manufacturing method satisfies the relationship of the following formula (1).
2℃≦T1-T2≦15℃ (1)
[2] The manufacturing method according to [1], which satisfies the relationship of formula (2) below, where the temperature of the protective film supplied in the bonding step is T3 [° C.].
2℃≦T3-T2≦15℃ (2)
[3] The polarizing plate includes a first thermoplastic resin film, a polarizer, and a second thermoplastic resin film in this order,
The thickness of the first thermoplastic resin film is more than 40 μm,
The thickness of the second thermoplastic resin film is 40 μm or less,
The manufacturing method according to [1] or [2], wherein in the bonding step, the protection film is stacked on the surface side of the first thermoplastic resin film of the polarizing plate.
[4] The manufacturing method according to any one of [1] to [3], wherein in the bonding step, the tension of the protect film before passing through the pair of bonding rolls is 10 kgf or more and 50 kgf or less.
[5] The manufacturing method according to any one of [1] to [4], wherein in the bonding step, the tension of the polarizing plate before passing through the pair of bonding rolls is 20 kgf or more and 100 kgf or less.
[6] The production according to any one of [1] to [5], wherein in the laminating step, the polarizing plate is laminated so that the absorption axis of the polarizing plate and the MD direction of the protective film are parallel to each other. Method.
[7] The manufacturing method according to any one of [1] to [6], wherein the polarizing plate has a thickness of 100 μm or less.
[8] The manufacturing method according to any one of [1] to [7], wherein in the bonding step, the polarizing plate and the protective film are elongated.
[9] The manufacturing method according to [8], further comprising a cutting step of cutting out a sheet from the polarizing plate with a protection film after the bonding step.

According to the present invention, it is possible to provide a method for manufacturing a polarizing plate with a protection film in which reverse curling is suppressed when the polarizing plate is formed into a sheet.

It is a side view showing an outline of a manufacturing method of a polarizing plate with a protection film concerning this embodiment. FIG. 2 is a schematic cross-sectional view showing an example of a layer structure of a polarizing plate. FIG. 3 is a schematic cross-sectional view showing another example of the layer structure of a polarizing plate. It is a schematic sectional view showing an example of the layer structure of a sheet of a polarizing plate with a protection film. FIG. 2 is a schematic diagram illustrating a method of creating a sample for measuring the amount of TD curl and measurement points of the amount of TD curl.

<Production method of polarizing plate with protection film>
FIG. 1 is a side view schematically showing a method for manufacturing a polarizing plate with a protection film according to the present embodiment. The manufacturing method of this embodiment includes a bonding step of stacking the protective film 1 on one side of the polarizing plate 2 and pressing it by passing it between a pair of bonding rolls 5, 5.

In the method for manufacturing a polarizing plate with a protection film according to the present embodiment, in the bonding step, the polarizing plate and the protection film are elongated, and after the bonding step, the polarizing plate with a protection film is separated into sheets. The method may further include a cutting step of cutting out the body.
As used herein, the term "sheet" refers to a smaller-sized film cut out from a larger-sized film (for example, a long (band-shaped) film).

In the bonding step, if the ambient temperature is T1 [°C] and the temperature of the polarizing plate supplied is T2 [°C], the relationship T1>T2 is satisfied, and the relationship of formula (1) below is satisfied, preferably The following formula (1a) is satisfied.
2℃≦T1-T2≦15℃ (1)
3℃≦T1-T2≦12℃ (1a)

By satisfying the relationship of the above formula (1), it is possible to suppress reverse curling in a sheet of a polarizing plate with a protection film. Suppression of reverse curls as used herein refers to any of the following: reducing the amount of reverse curls, preventing the occurrence of reverse curls, causing positive curls, and increasing the amount of positive curls. Good too. This is because an increase in the amount of positive curl means that the force that causes reverse curl is relatively smaller than the force that causes normal curl. Although it is not clear why reverse curl can be suppressed by satisfying the relationship of formula (1) above, in the lamination process, the temperature of the polarizing plate gradually increases from temperature T1 to temperature T2. It is presumed that the expansion caused by this, and the expansion after the protection film is bonded, is due to the difference in the amount of expansion of the protection film, which acts in a direction to suppress reverse curling. Further, by setting T1-T2≦15°C, it is easy to prevent dew condensation from forming on the polarizing plate and the like.

Note that a protect film usually has a smaller expansion coefficient than a polarizing plate, so even if its temperature rises in the same way as a polarizing plate, the amount of expansion will be smaller than that of the polarizing plate, and the expansion coefficient will be smaller than that of the polarizing plate. If the amount of temperature increase is small, the amount of expansion will be small compared to the amount of expansion of the polarizing plate.

From the above viewpoint, it is preferable that the protection film has a smaller expansion coefficient than that of the polarizing plate. Further, when the temperature of the protect film supplied to the bonding step is T3 [°C], preferably the relationship T3>T2 is satisfied, more preferably the relationship of the following formula (2) is satisfied, and even more preferably the following formula ( The relationship 2a) is satisfied.
2℃≦T3-T2≦15℃ (2)
3℃≦T3-T2≦12℃ (2a)

Here, the curl of a sheet of polarizing plate with a protection film can be classified into two types, "MD curl" and "TD curl", in addition to the above-mentioned "normal curl" and "reverse curl". can. "MD curl" is caused by stress (shrinkage force, expansion force, etc.) in a direction parallel to the MD direction of a long polarizing plate with a protective film from which a sheet of the polarizing plate with a protective film is cut out. It's curly.

"TD curl" is a curl that occurs due to stress (shrinkage force, expansion force, etc.) in a direction parallel to the TD direction of a long polarizing plate with a protective film that is cut out from a sheet of polarizing plate with a protective film. It is. Specifically, TD curl is performed by cutting a measurement sample (sheet) from a polarizing plate with a long protective film according to the description in the Examples section below, and placing the measurement sample with the concave side facing up. When the measurement sample is placed on a horizontal table, the two corners on the diagonal that has a smaller angle with the TD direction of the long polarizing plate with a protective film will be lifted up. Its size can be measured as a curl (typically a curl in the direction of the transmission axis).

"MD curl" is a curl that occurs due to stress (shrinkage force, expansion force, etc.) in a direction parallel to the MD direction of a long polarizing plate with a protective film from which a sheet of polarizing plate with a protective film is cut out. It is. In a long polarizing plate with a protective film, when the absorption axis direction of the polarizing plate and the MD direction of the protective film are parallel, the MD curl is determined by the direction of the polarizing plate of the measurement sample among the two diagonals of the measurement sample. It can be measured as a curl (curl in the absorption axis direction) in which the two diagonal corners with the smaller angle with the absorption axis direction are lifted.

The present invention focuses on TD curl. The ability to suppress reverse curl that can be produced by the present invention means that reverse curl of TD curl in a sheet body can be suppressed. In the present invention, since it is possible to suppress the reverse curl of the TD curl of a sheet, when laminating a sheet of a polarizing plate with a protection film to an image display element via an adhesive layer, This makes it possible to suppress problems such as pasting errors and air bubbles being mixed in at the interface between the adhesive layer and the image display element. It is preferable that both the TD curl and the MD curl are positive curls in the sheet of the polarizing plate with a protection film that can be produced according to the present invention.

(1) Lamination process (1-1) Polarizing plate used in the lamination process (1-1-1) Structure of polarizing plate A polarizing plate is a polarizing element containing at least a polarizer, and usually one side or It further includes a thermoplastic resin film laminated on both sides.
The thermoplastic resin film can be a protective film that protects the polarizer, another optical film that has an optical function different from that of the polarizer, or the like. Examples of other optical films include retardation films, brightness enhancement films, and the like.
The thermoplastic resin film may include a resin layer (for example, an optical layer) laminated on its surface. Examples of the resin layer include a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, an antifouling layer, and the like.
The thermoplastic resin film can be bonded to the polarizer via an adhesive layer or a pressure-sensitive adhesive layer.

The thickness of the polarizing plate is usually 150 μm or less, and from the viewpoint of making the polarizing plate thinner, it is preferably 100 μm or less, more preferably 80 μm or less, and still more preferably 70 μm or less.
The thickness of the polarizing plate is usually 20 μm or more or 30 μm or more.

Examples of the layer structure of the polarizing plate will be described with reference to FIGS. 2 and 3, but the layer structure is not limited to these examples.
The polarizing plate 2a shown in FIG. 2 includes a polarizer 10; a first thermoplastic resin film 20 bonded to one surface of the polarizer 10; A resin film 30 is provided. The first and second thermoplastic resin films 20 and 30 are, for example, protective films.

Like the polarizing plate 2b shown in FIG. 3, one of the first and second thermoplastic resin films 20 and 30 may be omitted. In the polarizing plate 2b, the second thermoplastic resin film 30 is omitted. Such a polarizing plate having a thermoplastic resin film on only one surface of the polarizer 10 is advantageous in making the polarizing plate thin.

Although not shown in FIGS. 2 and 3, the polarizer 10 and the first and second thermoplastic resin films 20 and 30 can be bonded together preferably using an adhesive.

It is preferable that the polarizing plate used in the bonding process has a long shape.
The length of the long polarizing plate to be subjected to the bonding step is, for example, 100 to 20,000 m, preferably 1,000 to 10,000 m. Further, the width of the long polarizing plate to be subjected to the bonding step S101 is, for example, 0.5 to 3 m, preferably 1 to 2.5 m.

(1-1-2) Polarizer The polarizer 10 constituting the polarizing plate absorbs linearly polarized light with a vibration plane parallel to its absorption axis, and has a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). It is an absorption type polarizer that has the property of transmitting linearly polarized light. An example of the polarizer 10 is a polarizer in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film. Such a polarizer 10 can be produced, for example, by a step of uniaxially stretching a polyvinyl alcohol resin film; a step of dyeing a polyvinyl alcohol resin film with a dichroic dye to adsorb the dichroic dye; It can be produced by a method including a step of treating the adsorbed polyvinyl alcohol resin film with a crosslinking solution such as an aqueous boric acid solution; and a step of washing with water after the treatment with the crosslinking solution.

As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers that can be copolymerized. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

In this specification, "(meth)acrylic" means at least one selected from acrylic and methacryl. The same applies to "(meth)acryloyl", "(meth)acrylate", etc.

The degree of saponification of polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The average degree of polymerization of the polyvinyl alcohol resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.
The degree of saponification and average degree of polymerization of polyvinyl alcohol resin can be determined in accordance with JIS K 6726.

A film made of such a polyvinyl alcohol resin is used as the original film of the polarizer 10. The method of forming a polyvinyl alcohol resin into a film is not particularly limited, and any known method may be employed. The thickness of the polyvinyl alcohol resin film is not particularly limited, but is, for example, about 10 to 150 μm, preferably 50 μm or less, more preferably 35 μm or less.

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

In the uniaxial stretching, it may be uniaxially stretched between rolls having different circumferential speeds, or it may be uniaxially stretched using hot rolls. Further, the uniaxial stretching may be dry stretching in which the film is stretched in the atmosphere, or wet stretching in which the polyvinyl alcohol resin film is stretched in a swollen state using a solvent or water. The stretching ratio is usually 3 to 8 times.

As a method for dyeing a polyvinyl alcohol resin film with a dichroic dye, for example, a method of immersing the film in an aqueous solution containing a dichroic dye is employed. Iodine and dichroic organic dyes are used as the dichroic dye. In addition, it is preferable that the polyvinyl alcohol resin film is subjected to a immersion treatment in water before the dyeing treatment.

As the crosslinking treatment after dyeing with a dichroic dye, a method of immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid is usually adopted. When using iodine as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide.

The thickness of the polarizer 10 is usually about 2 to 40 μm. From the viewpoint of making the polarizing plate thinner, the thickness of the polarizer 10 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.
On the other hand, from the viewpoint of making it easier to manufacture a sheet polarizing plate with a protective film that has a sufficiently large positive curl, the thickness of the polarizer 10 is preferably large, and specifically, preferably 10 μm or more, more preferably 15 μm. The thickness is more preferably 20 μm or more.

(1-1-3) First and second thermoplastic resin films The first and second thermoplastic resin films 20 and 30 are each independently made of a translucent thermoplastic resin, preferably optically transparent. It is a film made of thermoplastic resin. The thermoplastic resin constituting the first and second thermoplastic resin films 20 and 30 is, for example, a polyolefin resin such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin (norbornene resin, etc.) ; Cellulose resins such as triacetylcellulose and diacetylcellulose; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate resins; (meth)acrylic resins such as methyl methacrylate resins; Polystyrene resins; Polyvinyl chloride resin; Acrylonitrile/butadiene/styrene resin; Acrylonitrile/styrene resin; Polyvinyl acetate resin; Polyvinylidene chloride resin; Polyamide resin; Polyacetal resin; Modified polyphenylene ether resin; Polysulfone resin; Examples include polyether sulfone resin; polyarylate resin; polyamideimide resin; polyimide resin.

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

Cyclic polyolefin resin is a general term for resins that are polymerized using cyclic olefins as polymerization units. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, and copolymers of cyclic olefins with chain olefins such as ethylene and propylene (typically is a random copolymer), a graft polymer obtained by modifying these with an unsaturated carboxylic acid or a derivative thereof, and a hydride thereof. Among them, a norbornene resin using a norbornene monomer such as norbornene or a polycyclic norbornene monomer as the cyclic olefin is preferably used.

Cellulose resin is obtained from raw material cellulose such as cotton linter or wood pulp (hardwood pulp, softwood pulp), and some or all of the hydrogen atoms in the hydroxyl groups of cellulose are substituted with acetyl, propionyl, and/or butyryl groups. Also refers to cellulose organic acid ester or cellulose mixed organic acid ester. Examples include cellulose acetate, propionate, butyrate, and mixed esters thereof. Among these, triacetylcellulose, diacetylcellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferred.

The polyester resin is a resin other than the above-mentioned cellulose resin that has an ester bond, and is generally a polycondensate of a polyhydric carboxylic acid or a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or its derivative, a divalent dicarboxylic acid or its derivative can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl naphthalene dicarboxylate, and the like. As the polyhydric alcohol, divalent diols can be used, such as ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol, and the like. Examples of suitable polyester resins include polyethylene terephthalate.

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

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

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

Examples of other compounds having a polymerizable carbon-carbon double bond in the molecule include vinyl compounds such as ethylene, propylene, and styrene, and vinyl cyan compounds such as acrylonitrile. As for the other compounds having a polymerizable carbon-carbon double bond in the molecule, one type may be used alone or two or more types may be used in combination.

The first and second thermoplastic resin films 20 and 30 can be protective films laminated on one surface of the polarizer 10 to protect the polarizer 10. The first or second thermoplastic resin film 20, 30 can also be a protective film that also has an optical function, such as a retardation film or a brightness enhancement film.
For example, by stretching (uniaxial stretching or biaxial stretching, etc.) a thermoplastic resin film made of the above material, or by forming a liquid crystal layer, etc. on the film, an arbitrary retardation value can be imparted. It can be a film. The first and/or second thermoplastic resin films 20, 30 have surface treatment layers (coatings) laminated on their surfaces, such as a hard coat layer, an anti-glare layer, an anti-reflection layer, an antistatic layer, and an antifouling layer. layer).

The thickness of the first and second thermoplastic resin films 20, 30 is usually 1 to 100 μm, but from the viewpoint of strength and handleability, it is preferably 5 to 60 μm, and more preferably 5 to 50 μm.

In the case where thermoplastic resin films are provided on both sides of the polarizer 10 like the polarizing plate 2a shown in FIG. 2, these thermoplastic resin films may be composed of the same type of thermoplastic resin or different types of thermoplastic resins. It may be made of thermoplastic resin. Moreover, the thicknesses may be the same or different. Furthermore, they may have the same phase difference characteristics or may have different phase difference characteristics.

In the case of a layered structure including a first thermoplastic resin film 20 and a second thermoplastic resin film 30 like the polarizing plate 2a shown in FIG. 2, when a sheet is formed, the thicker thermoplastic resin film Curls with convex sides tend to occur. Therefore, when a protect film is bonded to the first thermoplastic resin film 20 side, and the first thermoplastic resin film is thicker than the second thermoplastic resin film, reverse curl is likely to occur. In the present invention, even in such a case, reverse curl can be suppressed. As an example, in the present invention, a protection film is laminated on the first thermoplastic resin film 20 side, and the thickness of the first thermoplastic resin film 20 is more than 40 μm, and the second thermoplastic resin film Even when the thickness of 30 is 40 μm or less, reverse curling can be suppressed.

(1-1-4) Adhesive As described above, the first and second thermoplastic resin films 20 and 30 can be bonded to the polarizer 10 via, for example, an adhesive layer. As the adhesive forming the adhesive layer, a water-based adhesive, an active energy ray-curable adhesive, or a thermosetting adhesive can be used, and preferably a water-based adhesive or an active energy ray-curable adhesive.

Examples of the water-based adhesive include adhesives made of polyvinyl alcohol resin aqueous solutions, water-based two-component urethane emulsion adhesives, and the like. Among them, a water-based adhesive made of an aqueous solution of a polyvinyl alcohol resin is preferably used. Polyvinyl alcohol-based resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as vinyl alcohol homopolymers obtained by saponifying vinyl acetate and other monomers that can be copolymerized with vinyl acetate. A polyvinyl alcohol copolymer obtained by saponifying a polymer, a modified polyvinyl alcohol copolymer obtained by partially modifying the hydroxyl groups thereof, or the like can be used. The water-based adhesive can contain a crosslinking agent such as an aldehyde compound (such as glyoxal), an epoxy compound, a melamine compound, a methylol compound, an isocyanate compound, an amine compound, or a polyvalent metal salt.

When using a water-based adhesive, after bonding the polarizer 10 and the first and second thermoplastic resin films 20, 30, a drying process is performed to remove water contained in the water-based adhesive. It is preferable. After the drying step, a curing step of curing at a temperature of, for example, 20 to 45° C. may be provided.

An active energy ray-curable adhesive is an adhesive containing a curable compound that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays, and is preferably an ultraviolet curable adhesive. be.

The curable compound can be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of cationic polymerizable curable compounds include epoxy compounds (compounds having one or more epoxy groups in the molecule) and oxetane compounds (compounds having one or more oxetane rings in the molecule). ) or a combination thereof. Examples of radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule) and radically polymerizable double bonds. Other vinyl compounds or combinations thereof can be mentioned. A cationically polymerizable curable compound and a radically polymerizable curable compound may be used together. The active energy ray-curable adhesive usually further contains a cationic polymerization initiator and/or a radical polymerization initiator for initiating the curing reaction of the curable compound.

When bonding the polarizer 10 and the first and second thermoplastic resin films 20, 30, surface activation treatment may be performed on at least one of these bonding surfaces in order to improve adhesiveness. good. Surface activation treatments include dry treatments such as corona treatment, plasma treatment, discharge treatment (glow discharge treatment, etc.), flame treatment, ozone treatment, UV ozone treatment, ionizing active ray treatment (ultraviolet treatment, electron beam treatment, etc.) Examples include wet treatments such as ultrasonic treatment using a solvent such as water or acetone, saponification treatment, and anchor coating treatment. These surface activation treatments may be performed alone or in combination of two or more.

When thermoplastic resin films are bonded to both sides of the polarizer 10, the adhesives for bonding these thermoplastic resin films may be the same type of adhesive or different types of adhesives. It's okay.

(1-2) Protect film used in the lamination process A protect film is a film for protecting the surface of a polarizing plate, and usually, for example, a sheet of a polarizing plate with a protect film is pasted on an image display element, etc. After being combined, if an adhesive layer is included, the adhesive layer is peeled off and removed. Therefore, the protection film 1 is releasably bonded to the above-mentioned surface of the polarizing plate 2.

The protect film can be composed of, for example, a base film and an adhesive layer laminated thereon.
The base film is made of thermoplastic resin, such as polyolefin resin such as polyethylene resin, polypropylene resin, or cyclic polyolefin resin; polyester resin such as polyethylene terephthalate or polyethylene naphthalate; polycarbonate resin; (meth)acrylic resin It can be made of resin or the like. The base film may have a single layer structure or a multilayer structure.
The adhesive layer can be composed of a (meth)acrylic adhesive, an epoxy adhesive, a urethane adhesive, a silicone adhesive, or the like.
Further, the protection film may be a self-adhesive resin film such as a polypropylene resin or a polyethylene resin. In this case, the protection film does not have an adhesive layer.

The thickness of the protect film can be, for example, 5 to 150 μm, preferably 10 to 100 μm, more preferably 20 to 75 μm, and even more preferably 25 to 70 μm (for example, 60 μm or less, further 55 μm or less). be. When the thickness of the protective film is less than 5 μm, the protection of the polarizing plate may be insufficient, and it is also disadvantageous in terms of handleability. When the thickness of the protect film exceeds 150 μm, it is disadvantageous in terms of thinning of the polarizing plate sheet with the protect film and reworkability of the protect film.

It is preferable that the protection film to be subjected to the bonding process has a long shape.
The length of the long protective film to be subjected to the lamination step is, for example, 100 to 20,000 m, preferably 1,000 to 10,000 m. Further, the width of the long protective film to be subjected to the bonding step S101 is, for example, 0.5 to 3 m, preferably 1 to 2.5 m.

(1-3) Lamination of polarizing plate and protection film Referring to FIG. 1, lamination of polarizing plate 2 and protection film 1 is performed using, for example, a pair of rolls (lamination rolls) 5, 5. be able to. From the viewpoint of manufacturing efficiency, this method is particularly advantageous when the polarizing plate 2 and the protection film 1 are long.

Specifically, the elongated polarizing plate 2 is continuously conveyed, and the elongated protective film 1 is continuously conveyed, and the protective film 1 is stacked on one side of the polarizing plate 2, and then a pair of laminating rolls are formed. By sandwiching the film between 5 and 5, a polarizing plate 3 with a protect film in which both films are bonded can be manufactured.
The MD direction (transportation direction) of the polarizing plate 2 and the MD direction (transportation direction) of the protection film 1 are usually parallel. Parallel means that the angle between the MD direction of the polarizing plate 2 and the MD direction of the protection film 1 is 0 degrees ± 5 degrees, preferably 0 degrees ± 2 degrees.
From the viewpoint of suppressing the amount of change in MD curl of the sheet of the obtained polarizing plate with a protective film, both films are laminated so that the absorption axis of the polarizing plate 2 and the MD direction of the protective film 1 are parallel to each other. is preferred. Parallel means that the angle between the absorption axis of the polarizing plate 2 and the MD direction of the protection film 1 is 0 degrees ± 5 degrees, preferably 0 degrees ± 2 degrees.
By passing the laminate of the polarizing plate 2 and the protection film 1 between the pair of bonding rolls 5, 5, the laminate is pressed from above and below, so that both films are brought into close contact with each other.
The polarizing plate 2 may have a clear hard coat layer (a hard coat layer with a smooth surface) on its outermost surface.

When the protect film 1 is composed of a base film and an adhesive layer laminated thereon, when the protect film 1 is stacked on one side of the polarizing plate 2 and passed between a pair of laminating rolls 5, 5, , the adhesive layer of the protection film 1 is stacked on one side of the polarizing plate 2 so as to be in contact with the above-mentioned one side. Prior to laminating the protective film 1 and the polarizing plate 2, the bonding surface of at least one of the protective film 1 and the polarizing plate 2 is subjected to plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification treatment. A surface activation treatment may also be performed.

In the step of laminating using a pair of laminating rolls 5, 5, the pressure (nip pressure) applied to the laminate of the protect film 1 and the polarizing plate 2 is, for example, 0.01 to 0.5 MPa, and 0.05 MPa. ~0.3 MPa. As the bonding rolls 5, 5, conventionally known ones such as those whose surfaces are made of metal (including alloys such as SUS) or rubber can be used.

In the step of laminating the polarizing plate 2 and the protection film 1, it is preferable to perform the lamination while applying tension to the polarizing plate 2 and the protection film 1. The tension before bonding can be adjusted depending on the rigidity of each film. For example, when the rigidity of the polarizing plate 2 is greater than that of the protection film 1, it is preferable to make the tension of the polarizing plate 2 before lamination larger than the tension of the protection film 1 before lamination. Such tension control is advantageous in controlling the amount of curl of the obtained sheet of polarizing plate with a protect film. The pre-lamination tension means the tension applied in the MD direction of the films before the two films are laminated (the laminate of both films passes through the pair of lamination rolls 5, 5).

From the viewpoint of reducing the amount of change in MD curl of the obtained polarizing plate sheet with a protect film, the tension before lamination in the MD direction of the protect film 1 is preferably 10 kgf or more and 50 kgf or less, and 20 kgf or more and 40 kgf or less. It is more preferable that there be.
From the same viewpoint, the tension before lamination in the MD direction of the polarizing plate 2 is preferably 20 kgf or more and 100 kgf or less, and more preferably 30 kgf or more and 70 kgf or less.

(1-4) Atmospheric temperature T1 in the bonding process
In this embodiment, the temperature of the bonding process means the ambient temperature at which the pair of bonding rolls 5, 5 are placed. This atmospheric temperature is assumed to be T1 [° C.]. T1 is usually room temperature, and may be appropriately adjusted to a temperature different from room temperature by temperature control. T1 is not limited as long as it satisfies the above formula (1), but is, for example, 20°C or more and 30°C or less, preferably 22°C or more and 28°C or less. Room temperature is, for example, 23°C.

(1-5) Temperature T2 of polarizing plate subjected to lamination process
In this embodiment, the temperature of the polarizing plate subjected to the bonding process means the temperature of the polarizing plate immediately before contacting the pair of bonding rolls 5, 5. This temperature is defined as T2 [°C]. T2 is not limited as long as it satisfies the above formula (1), but is, for example, 5°C or more and 28°C or less, preferably 7°C or more and 26°C or less, and more preferably 10°C or more and 22°C or less. . In order to set T2 within the above temperature range, the manufacturing method of this embodiment preferably includes a cooling step of cooling the polarizing plate to be subjected to the bonding step. The cooling process may be a process of cooling a polarizing plate being transported or a process of cooling a stored polarizing plate roll. The method of cooling the polarizing plate being transported is not limited, and examples include cooling it by bringing it into close contact with a cooling roll, cooling it by blowing cooling air, and transporting it under a stream of cooling air or a stream of nitrogen. For example, a method of cooling by In the case of the method of cooling by spraying cooling air, the cooling air can be sprayed from one side or both sides of the polarizing plate, for example, the method may be such that the cooling air is sprayed from the first thermoplastic resin film side.

The temperature T2 of the polarizing plate to be subjected to the bonding process is a value obtained by measuring the temperature of the polarizing plate to be subjected to the bonding process. It is preferable that the cooling step is carried out so that the temperature is the same no matter where on the polarizing plate the temperature is measured.

(1-6) Temperature T3 of the protect film subjected to the lamination process
In this embodiment, the temperature of the protect film subjected to the bonding process means the temperature of the protect film immediately before contacting the pair of bonding rolls 5, 5. This temperature is defined as T3 [°C]. T3 is not limited as long as it satisfies the above formula (2), but is, for example, 20° C. or higher and 30° C. or lower, preferably 22° C. or higher and 28° C. or lower, and more preferably room temperature. Room temperature is, for example, 23°C. T3 is preferably the same as T1. T3 may be a temperature higher than T1, and in this case, includes a heating step of heating the protection film to be subjected to the bonding step. T3 may be a temperature lower than T1, and in this case, a cooling step is included in which the protection film to be subjected to the bonding step is cooled.

(2) Cutting process This process is a process of cutting out the polarizing plate with a protection film obtained in the bonding process to obtain a sheet of a polarizing plate with a protection film.
Cutting out (cutting) can be performed using a conventionally known cutting means such as a cutting cutter.

The size, shape, and cutting angle of the cut out sheet of polarizing plate with a protection film are not particularly limited.
The sheet of the polarizing plate with a protection film is preferably rectangular, more preferably rectangular having long sides and short sides. This square shape is preferably rectangular.
When the sheet of the polarizing plate with a protection film has a rectangular shape, the length of the long side is, for example, 50 mm to 300 mm, preferably 70 mm to 150 mm. The length of the short side is, for example, 30 mm to 200 mm, preferably 40 mm to 100 mm.

Although not particularly limited, when the shape of the sheet of polarizing plate with protection film is rectangular, when the sheet of polarizing plate with protection film is viewed from the protection film side, the long and short sides of the sheet of polarizing plate with protection film are On the other hand, a sheet of a polarizing plate with a protection film can be cut out from the polarizing plate with a protection film 3 so that the absorption axis direction of the polarizing plate (MD direction of the polarizing plate) forms an angle of 45 degrees.
Alternatively, when the shape of the sheet of polarizing plate with a protection film is rectangular, when the sheet of polarizing plate with a protection film is viewed from the protection film side, the absorption axis direction of the polarizing plate (polarization A sheet of a polarizing plate with a protect film may be cut out from the polarizing plate with a protect film 3 so that the MD direction of the plate is parallel or at an angle of 90 degrees.

FIG. 4 is a cross-sectional view showing an example of the layer structure of a sheet of a polarizing plate with a protection film. As shown in FIG. 4, when the protection film 1 is composed of a base film 40 and an adhesive layer 50 laminated thereon, the adhesive layer 50 of the protection film 1 is in contact with one side of the polarizing plate 2. It can be stacked like this.

<Multilayer structure>
On the polarizing plate side of the polarizing plate with a protective film or the long polarizing plate with a protective film, one or more other optical functional layers, a separate film (release film), etc. are further applied via an adhesive layer or an adhesive layer. It may be laminated.
The optical functional layer may be a retardation layer or the like, and the optical functional layer can be laminated on the surface on the polarizing plate side via a pressure-sensitive adhesive layer or an adhesive layer.

Hereinafter, the present invention will be explained in more detail with reference to experimental examples, but the present invention is not limited to these examples.

<Examples 1 and 2, Comparative Examples 1 and 2>
(A) Preparation of polarizer A long polyvinyl alcohol film [thickness 40 μm, width 2,980 mm, VF-PE#4000, degree of saponification 99.9 mol% or more, manufactured by Kuraray Co., Ltd.] is continuously conveyed. uniaxially stretched to about 4 times in a dry process, and then immersed in pure water at 40°C for 1 minute while maintaining the tension, and the weight ratio of iodine/potassium iodide/water was 0.1/5/ 100 at 28° C. for 60 seconds. Thereafter, it was immersed for 300 seconds in a 68° C. aqueous solution having a weight ratio of potassium iodide/boric acid/water of 10.5/7.5/100. Subsequently, the film was washed with pure water at 5° C. for 5 seconds and then dried at 70° C. for 180 seconds to obtain a long polarizer in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. The thickness of the polarizer was 15 μm.

(B) Preparation of polarizing plate A long first thermoplastic resin film A [Clear HC-TAC, manufactured by Toppan TOMOEGAWA Optical Film Co., Ltd., A hard coat layer with a thickness of 7 μm and a TAC film with a thickness of 40 μm, trade name: 40FJCHCN-TC] were prepared.
As a second thermoplastic resin film laminated on the opposite side to the first thermoplastic resin film, a second thermoplastic resin film A [manufactured by Konica Minolta, Inc., TAC film, thickness 20 μm, product name: KC2CT1W] is used. , a second thermoplastic resin film B [manufactured by Konica Minolta, Inc., TAC film, thickness 40 μm, trade name: KC4CT1W] was prepared.
While continuously conveying the elongated polarizer obtained in the above (A), the elongated first thermoplastic resin film A and the elongated second thermoplastic resin film A or B are transported. It was continuously conveyed and passed between a pair of bonding rolls while injecting a water-based adhesive between the polarizer and the first thermoplastic resin film and between the polarizer and the second thermoplastic resin film. . Subsequently, the obtained laminated film was transported and heated through a hot air dryer at 80° C. for 300 seconds to dry the water-based adhesive layer, thereby obtaining a long polarizing plate. In this way, a polarizing plate consisting of first thermoplastic resin film/aqueous adhesive layer/polarizer/aqueous adhesive layer/second thermoplastic resin film was obtained. The thicknesses of the polarizing plates were 102 μm and 82 μm, respectively.
For the above water-based adhesive, 50 g of a modified PVA resin containing an acetoacetyl group (Gosenetas Z-410 manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, and then allowed to cool to room temperature. It was cooled to obtain a PVA solution. A PVA adhesive was prepared by mixing a PVA solution, maleic acid, and glyoxal so that the PVA resin was 3.0% by mass, the maleic acid was 0.01% by mass, and the glyoxal was 0.15% by mass. .

(C) Preparation of a polarizing plate with a long protective film The long polarizing plate obtained in (B) above is continuously conveyed, and a long protective film [biaxial A (trade name: AY-638 manufactured by Fujimori Kogyo Co., Ltd.), in which a (meth)acrylic adhesive layer (thickness: 15 μm) was laminated on stretched polyethylene terephthalate (thickness: 19 μm), was continuously conveyed. By stacking these and passing them between a pair of bonding rolls, the laminate of the protection film and the polarizing plate was pressed from above and below, to continuously produce a long polarizing plate with a protective film.
The protect film was bonded to the first thermoplastic resin film (clear hard coat film) surface of the polarizing plate via the adhesive layer. In the bonding process, the absorption axis of the polarizing plate and the MD direction of the protect film were parallel.
In Examples 1 and 2, cooling air at a temperature of 17°C was blown from the first thermoplastic resin film side of the polarizing plate on the conveyance path that continuously conveyed the long polarizing plate, so that the temperature T2 of the polarizing plate was 17°C. After adjusting the temperature to ℃, it was applied to a laminating roll.
In Comparative Examples 1 and 2, the elongated polarizing plate was subjected to a bonding roll without adjusting the temperature T2 of the polarizing plate on a conveyance path that continuously conveyed it. Therefore, the temperature T2 of the polarizing plate could be considered to be 23° C., which is the temperature of room temperature.
In the Examples and Comparative Examples, the temperature of the atmosphere in which the bonding roll was placed was not controlled, so the atmosphere temperature T1 could be considered to be 23° C., which is the temperature of room temperature.
In Examples and Comparative Examples, the protective film was applied to a laminating roll without temperature control. Therefore, the temperature T3 of the protect film could be considered to be 23° C., which is the temperature of room temperature.
Note that the pressure (nip pressure) applied to the laminate of the protect film and the polarizing plate by the laminating roll was 0.1 MPa. At this time, the tension before lamination in the MD direction of the polarizing plate was 70 kgf, and the tension before lamination in the MD direction of the protect film was 40 kgf.

(D) Preparation of a sheet of a polarizing plate with a protective film As shown in Figure 5, from the polarizing plate with a long protective film obtained in (C) above, the polarizing plate is A small square (200 mm on a side) piece (sheet) was cut out using a super cutter so that the absorption axis was at 45 degrees with respect to each side, to obtain a sheet of a polarizing plate with a protection film.

<Evaluation>
(Measurement of curl amount)
As shown in FIG. 5, from the obtained polarizing plate 60 with a long protective film, a square shape ( A small piece (200 mm on each side) was cut out using a super cutter, and this was used as sample 70 for measuring the amount of TD curl. The measurement sample 70 was cut out in an environment of 23° C. and 55% relative humidity immediately after bonding the polarizing plate and the protection film.
The measurement sample 70 was placed on a reference surface (horizontal table) with the concave side facing up. In this state, among the two diagonals of the measurement sample 70, the heights from the reference plane are measured for each of the two corners 80 on the diagonal of the transmission axis direction of the polarizing plate of the measurement sample 70, and The TD curl amount [mm] was determined as the average of the heights of 80.
A state in which the protect film side is concave is a state in which the film has a normal curl, and a state in which the polarizing plate side is concave is a state in which it has a reverse curl.
Table 1 shows the TD curl amount. When the TD curl amount is a positive value, it means that the curl is a positive curl, and when it is a negative value, it means that the curl is a reverse curl.

From the results shown in Table 1, when comparing Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, which differ only in the temperature of the polarizing plate supplied, it is found that Example 1 has a reverse curl compared to Comparative Example 1. It can be seen that reverse curl is suppressed in Example 2 compared to Comparative Example 2.

1 Protective film, 2, 2a, 2b Polarizing plate, 3 Polarizing plate with protective film, 5 Lamination roll, 10 Polarizer, 20 First thermoplastic resin film, 30 Second thermoplastic resin film, 40 Base film, 50 Adhesive layer, 60 Polarizing plate with long protective film, 61 Absorption axis of polarizing plate, 70 Sample for measuring TD curl amount, 80 Corner of sample for measurement.

Claims (9)

A method for producing a polarizing plate with a protective film, comprising a laminating step of stacking a protective film on one side of the polarizing plate and pressing it by passing it between a pair of laminating rolls,
In the bonding step, when the ambient temperature is T1 [° C.] and the temperature of the polarizing plate supplied is T2 [° C.], the manufacturing method satisfies the relationship of the following formula (1).
2℃≦T1-T2≦15℃ (1) The manufacturing method according to claim 1, which satisfies the following formula (2) when the temperature of the protective film supplied in the bonding step is T3 [° C.].
2℃≦T3-T2≦15℃ (2) The polarizing plate includes a first thermoplastic resin film, a polarizer, and a second thermoplastic resin film in this order,
The thickness of the first thermoplastic resin film is more than 40 μm,
The thickness of the second thermoplastic resin film is 40 μm or less,
The manufacturing method according to claim 1 or 2, wherein in the bonding step, the protection film is stacked on the surface side of the first thermoplastic resin film of the polarizing plate. The manufacturing method according to claim 1 or 2, wherein in the bonding step, the tension of the protect film before being passed through the pair of bonding rolls is 10 kgf or more and 50 kgf or less. The manufacturing method according to claim 1 or 2, wherein in the bonding step, the tension of the polarizing plate before passing through the pair of bonding rolls is 20 kgf or more and 100 kgf or less. The manufacturing method according to claim 1 or 2, wherein in the bonding step, the polarizing plate is bonded so that the absorption axis of the polarizing plate and the MD direction of the protect film are parallel to each other. The manufacturing method according to claim 1 or 2, wherein the thickness of the polarizing plate is 100 μm or less. The manufacturing method according to claim 1 or 2, wherein in the bonding step, the polarizing plate and the protection film are elongated. The manufacturing method according to claim 8, further comprising a cutting step of cutting out a sheet from the polarizing plate with a protection film after the bonding step.

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