Method for manufacturing polarizing plate sheet with protection film

Abstract

The present invention provides a method for manufacturing a polarizing plate monolithic body with a protective film. The method includes a step for obtaining a polarizing plate with a protective film by bonding a protective film including a region satisfying the following formula to one surface of a polarizing plate, and a step for cutting out a monolithic body of a polarizing plate with a protective film from the region. The TD elasticity modulus-MD elasticity modulus is greater than or equal to 300MPa. In the formula, the so-called TD elastic modulus is the tensile elastic modulus in the TD direction at a temperature of 23 DEG C and a relative humidity of 55% RH, and the so-called MD elastic modulus is the tensile elastic modulus in the MD direction at a temperature of 23 DEG C and a relative humidity of 55% RH.

Description

[0001] This application is a divisional application of the application with the application number 201811473024.3, the filing date of December 4, 2018, and the invention title of "Manufacturing Method of Polarizing Plate Monolithic Body with Protective Film". Technical Field

[0002] The present invention relates to a manufacturing method of a polarizing plate monolithic body with a protective film. In addition, the present invention also relates to a polarizing plate monolithic body with a protective film and a long strip-shaped polarizing plate with a protective film. Background Art

[0003] In recent years, image display devices such as liquid crystal display devices and organic EL display devices, such as mobile terminals like smart phones, are rapidly advancing in terms of large screen size and thinness from the aspects of design and portability. In order to achieve long-term driving with a limited thickness, high brightness, thinness, and light weight are also required for the polarizing plates used.

[0004] As a polarizing plate, a polarizing plate obtained by bonding a protective film formed of triacetyl cellulose (TAC) to a polarizing film formed of a polyvinyl alcohol-based resin has generally been used in the past. However, in recent years, protective films formed of resins other than TAC have also gradually been used from the viewpoints of thinning, durability, cost, productivity, etc. [For example, Japanese Patent Laid-Open No. 2004-245925 (Patent Document 1)]. Summary of the Invention

[0005] Problems to be Solved by the Invention

[0006] Along with the requirement for thinning of the polarizing plate, thinning of the polarizing film and the protective film is being promoted. A monolithic body of a polarizing plate obtained by cutting out from a thin and non-stiff polarizing plate, especially from a long strip-shaped polarizing plate, is likely to be deformed into a bow shape. In this specification, this deformation is also referred to as "curl".

[0007] A polarizing plate generally circulates in the market as a polarizing plate with a protective film (also referred to as a surface protective film) attached to protect its surface. Even in a polarizing plate with a protective film, if it is thinned, there is also a tendency to easily generate curl when made into a monolithic body.

[0008] In the curl of a monolithic body of a polarizing plate with a protective film, there are two types: "positive curl" and "negative curl". In a monolithic body of a polarizing plate with a protective film composed of a laminate of a polarizing plate and a protective film, "positive curl" refers to a curl that makes the surface on the polarizing plate side convex, and "negative curl" refers to a curl that makes the surface on the protective film side convex.

[0009] Once reverse curling occurs, when the polarizer single body with a protective film is attached to an image display element such as a liquid crystal cell or an organic EL element with the polarizer side interposed with an adhesive layer, it is likely to cause problems such as misalignment during attachment or air bubbles mixing into the interface between the adhesive layer and the image display element.

[0010] The polarizer with a protective film is sometimes made into a multi-layered structure with more layers by further laminating one or more additional optical functional layers with an adhesive layer or an adhesive layer interposed on the polarizer side. In this case, the addition of more layers to the polarizer with a protective film acts in the direction of causing reverse curling of the multi-layered structure.

[0011] Therefore, when considering making the above multi-layered structure, it is desirable that the polarizer single body with a protective film has a sufficiently large positive curl. This is because if the multi-layered structure has reverse curling, the above-mentioned problems are likely to occur when it is attached to the image display element.

[0012] On the other hand, when the polarizer with a protective film is directly attached to the image display element without making it into the above multi-layered structure, the large positive curl it has does not prevent the attachment to the image display element.

[0013] An object of the present invention is to provide a method for manufacturing a polarizer single body with a protective film that can have a relatively large positive curl.

[0014] Another object of the present invention is to provide a polarizer single body with a protective film that can have a relatively large positive curl.

[0015] Another object of the present invention is to provide a long strip-shaped polarizer with a protective film that can provide a polarizer single body with a protective film having a relatively large positive curl.

[0016] The present invention provides a method for manufacturing a polarizer single body with a protective film, a polarizer single body with a protective film, and a long strip-shaped polarizer with a protective film as shown below.

[0017] [1]A method for manufacturing a polarizer single body with a protective film, the manufacturing method comprising: a step of attaching a protective film including a region satisfying the following formula (I) to one surface of a polarizer to obtain a polarizer with a protective film, and

[0018] a step of cutting out a single body of the polarizer with a protective film from the region.

[0019] TD elastic modulus - MD elastic modulus ≥ 300 MPa (I)

[0020] [In the formula, the TD elastic modulus refers to the tensile elastic modulus in the TD direction at a temperature of 23°C and a relative humidity of 55% RH, and the MD elastic modulus refers to the tensile elastic modulus in the MD direction at a temperature of 23°C and a relative humidity of 55% RH.]

[0021] [2] According to the manufacturing method described in [1], wherein the polarizing plate and the protective film are sandwiched between a pair of rollers and bonded.

[0022] [3] According to the manufacturing method described in [2], wherein the polarizing plate is in a long strip shape and the protective film is in a long strip shape.

[0023] [4] According to the manufacturing method described in [3], wherein the pre-bonding tension of the polarizing plate is 200 N / m or less,

[0024] and the pre-bonding tension of the protective film is 300 N / m or more.

[0025] [5] According to the manufacturing method described in any one of [1] to [4], wherein the polarizing plate is bonded in such a manner that the absorption axis of the polarizing plate is parallel to the MD direction of the protective film.

[0026] [6] According to the manufacturing method described in any one of [1] to [5], wherein the thickness of the polarizing plate is 70 μm or less.

[0027] [7] A single polarizing plate with a protective film, which comprises a polarizing plate and a protective film laminated on one side thereof,

[0028] and the protective film satisfies the following formula (II).

[0029] First elastic modulus - second elastic modulus ≥ 300 MPa (II)

[0030] [In the formula, the so-called first elastic modulus refers to the tensile elastic modulus in the direction orthogonal to the absorption axis of the polarizing plate at a temperature of 23°C and a relative humidity of 55% RH, and the so-called second elastic modulus refers to the tensile elastic modulus in the direction parallel to the absorption axis of the polarizing plate at a temperature of 23°C and a relative humidity of 55% RH.]

[0031] [8] According to the single polarizing plate with a protective film described in [7], wherein the amount of curl in the direction parallel to the absorption axis of the polarizing plate, which causes the surface on the polarizing plate side to bulge, is 40 mm or more.

[0032] [9] According to the single polarizing plate with a protective film described in [7] or [8], wherein the thickness of the polarizing plate is 70 μm or less.

[0033]

[10] A strip-shaped polarizing plate with a protective film, which comprises a strip-shaped polarizing plate and a strip-shaped protective film laminated on one side thereof.

[0034] The protective film includes a region satisfying the following formula (III).

[0035] First elastic modulus - second elastic modulus ≥ 300 MPa (III)

[0036] [In the formula, the so-called first elastic modulus is the tensile elastic modulus in the direction orthogonal to the absorption axis of the strip-shaped polarizing plate at a temperature of 23°C and a relative humidity of 55% RH, and the so-called second elastic modulus is the tensile elastic modulus in the direction parallel to the absorption axis of the strip-shaped polarizing plate at a temperature of 23°C and a relative humidity of 55% RH. ]

[0037]

[11] The strip-shaped polarizing plate with a protective film according to

[10] , wherein the region extends throughout the entire width direction of the protective film.

[0038] According to the present invention, a method capable of manufacturing a single sheet of a polarizing plate with a protective film having a large positive curl can be provided.

[0039] According to the present invention, a single sheet of a polarizing plate with a protective film capable of having a large positive curl can be provided.

[0040] According to the present invention, a strip-shaped polarizing plate with a protective film can be provided, which can provide a single sheet of a polarizing plate with a protective film having a large positive curl. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flowchart showing a method for manufacturing a single sheet of a polarizing plate with a protective film.

[0042] Figure 2 It is a schematic cross-sectional view showing an example of the layer structure of a polarizing plate.

[0043] Figure 3 It is a schematic cross-sectional view showing another example of the layer structure of a polarizing plate.

[0044] Figure 4 It is a side view showing an example of a bonding step S101 of bonding a polarizing plate and a protective film.

[0045] Figure 5 It is a schematic cross-sectional view showing an example of the layer structure of a single sheet of a polarizing plate with a protective film.

[0046] Figure 6 It is a schematic diagram for explaining a method for manufacturing a sample for measuring the MD curl amount and measurement points of the MD curl amount.

[0047] Figure 7 It is a graph showing the relationship between the widthwise position of the protective films 1 to 3 respectively used in Experimental Examples 1 to 3 and the difference in elastic modulus.

[0048] Figure 8 It is a graph showing the relationship between the widthwise position of a single-piece polarizing plate with a protective film cut out from a long polarizing plate with a protective film in Experimental Examples 1 to 3 and the MD curl amount of the cut-out single-piece polarizing plate with a protective film. Detailed implementation mode

[0049] <Manufacturing method of a single-piece polarizing plate with a protective film>

[0050] Refer to Figure 1 , the manufacturing method of the single-piece polarizing plate with a protective film of the present invention includes the following steps:

[0051] A bonding step S101 of bonding a protective film to one side of a polarizing plate to obtain a polarizing plate with a protective film, and

[0052] A cutting step S102 of cutting out a single-piece of the polarizing plate with a protective film. Hereinafter, each step will be described in detail.

[0053] In this specification, the so-called "single piece" refers to a smaller-sized film cut out from a larger-sized film (for example, a long (strip-shaped) film).

[0054] (1) Bonding step S101

[0055] (1-1) Polarizing plate provided to the bonding step S101

[0056] (1-1-1) Composition of the polarizing plate

[0057] A polarizing plate is a polarizing element containing at least a polarizer, and usually also contains a thermoplastic resin film bonded to one or both sides thereof.

[0058] The thermoplastic resin film can be a protective film for protecting the polarizer, other optical films having optical functions different from those of the polarizer, etc. Examples of other optical films are a retardation film, a brightness enhancement film, etc.

[0059] The thermoplastic resin film can have a resin layer (for example, an optical layer) laminated on its surface. Examples of the resin layer are a hard coat, an antiglare layer, an antireflection layer, an antistatic interference layer, an antifouling layer, etc.

[0060] The thermoplastic resin film can be bonded to the polarizer with an adhesive layer or an adhesive layer interposed therebetween.

[0061] The thickness of the polarizing plate is usually 150 μm or less, preferably 100 μm or less, more preferably 80 μm or less, and further preferably 70 μm or less, from the viewpoints of thinning the polarizing plate and facilitating the production of a single polarizing plate with a protective film having a sufficiently large positive curl.

[0062] The thickness of the polarizing plate is usually 20 μm or more or 30 μm or more.

[0063] Refer to Figure 2 and Figure 3 Examples of the layer structure of the polarizing plate will be described, but the layer structure is not limited to these examples.

[0064] Figure 2 The polarizing plate 2a shown includes a polarizer 10; a first thermoplastic resin film 20 attached to one surface of the polarizer 10; and a second thermoplastic resin film 30 attached to the other surface of the polarizer 10. The first and second thermoplastic resin films 20 and 30 are, for example, protective films.

[0065] It is possible to Figure 3 omit one of the first and second thermoplastic resin films 20 and 30 as in the polarizing plate 2b shown. The second thermoplastic resin film 30 is omitted in the polarizing plate 2b. Such a polarizing plate having a thermoplastic resin film only on one surface of the polarizer 10 is advantageous for thinning the polarizing plate.

[0066] Although not shown in Figure 2 and Figure 3 it is preferable to use an adhesive to attach the polarizer 10 to the first and second thermoplastic resin films 20 and 30.

[0067] The polarizing plate supplied to the bonding step S101 is preferably in a long strip shape.

[0068] The length of the long strip-shaped polarizing plate supplied to the bonding step S101 is, for example, 100 to 20000 m, preferably 1000 to 10000 m. In addition, the width of the long strip-shaped polarizing plate supplied to the bonding step S101 is, for example, 0.5 to 3 m, preferably 1 to 2.5 m.

[0069] (1-1-2) Polarizer

[0070] The polarizer 10 that constitutes the polarizing plate is an absorptive polarizer that has the property of absorbing linearly polarized light having a vibration plane parallel to its absorption axis and transmitting linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). An example of the polarizer 10 is a polarizer in which a uniaxially stretched polyvinyl alcohol-based resin film adsorbs a dichroic dye and is oriented. Such a polarizer 10 can be manufactured, for example, by a method including a step of uniaxially stretching a polyvinyl alcohol-based resin film; a step of adsorbing a dichroic dye by dyeing the polyvinyl alcohol-based resin film with a dichroic dye; a step of treating the polyvinyl alcohol-based resin film adsorbed with the dichroic dye 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.

[0071] As the polyvinyl alcohol-based resin, a resin obtained by saponifying a polyvinyl acetate-based resin can be used. As the polyvinyl acetate-based resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers capable of copolymerizing can also be cited. Examples of other monomers capable of copolymerizing with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

[0072] In this specification, the so-called “(meth)acrylic” means at least one selected from acrylic and methacrylic. The same applies to “(meth)acryloyl”, “(meth)acrylate”, etc.

[0073] The saponification degree of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin can also be modified. For example, polyvinyl formal or polyvinyl acetal modified with an aldehyde can also be used. The average degree of polymerization of the polyvinyl alcohol-based resin is usually 1000 to 10000, preferably 1500 to 5000.

[0074] The saponification degree and the average degree of polymerization of the polyvinyl alcohol-based resin can be determined according to JIS K 6726.

[0075] The film obtained by forming such a polyvinyl alcohol-based resin is used as the raw material film of the polarizer 10. The method of forming the polyvinyl alcohol-based resin film is not particularly limited, and a known method can be adopted. The thickness of the polyvinyl alcohol-based resin film is not particularly limited. For example, it is about 10 to 150 μm, preferably 50 μm or less, and more preferably 35 μm or less.

[0076] The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before the dyeing of the dichroic dye, simultaneously with the dyeing, or after the dyeing. In the case of performing uniaxial stretching after the dyeing, the uniaxial stretching can be performed before or during the crosslinking treatment. In addition, uniaxial stretching can also be performed in multiple stages of these.

[0077] In the case of uniaxial stretching, it can be carried out in a uniaxial manner between rolls with different circumferential speeds, or it can be carried out in a uniaxial manner using a hot roll. In addition, the uniaxial stretching can be dry stretching carried out in the atmosphere, or wet stretching carried out in a state where the polyvinyl alcohol-based resin film is swollen with a solvent or water. The stretching ratio is usually about 3 to 8 times.

[0078] As a method of dyeing the polyvinyl alcohol-based resin film with a dichroic pigment, for example, a method of immersing the film in an aqueous solution containing the dichroic pigment can be adopted. As the dichroic pigment, iodine or a dichroic organic dye is used. It should be noted that the polyvinyl alcohol-based resin film is preferably subjected to an immersion treatment in water before the dyeing treatment.

[0079] As the crosslinking treatment after dyeing using the dichroic pigment, a method of immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid is usually adopted. In the case of using iodine as the dichroic pigment, the aqueous solution containing boric acid preferably contains potassium iodide.

[0080] The thickness of the polarizer 10 is usually about 2 to 40 μm. From the viewpoint of thinning the polarizing plate, the thickness of the polarizer 10 is preferably 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less.

[0081] On the other hand, from the viewpoint of easily manufacturing a single polarizing plate with a protective film having a sufficiently large positive curl, it is preferable that the thickness of the polarizer 10 is large. Specifically, it is preferably 10 μm or more, more preferably 15 μm or more, and still more preferably 20 μm or more.

[0082] (1-1-3) First and second thermoplastic resin films

[0083] The first and second thermoplastic resin films 20 and 30 are each independently films made of a thermoplastic resin having light transmittance, preferably made of an optically transparent thermoplastic resin. The thermoplastic resin constituting the first and second thermoplastic resin films 20 and 30 can be, for example, a polyolefin resin such as a linear polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a norbornene resin); a cellulose resin such as triacetyl cellulose or diacetyl cellulose; a polyester resin such as polyethylene terephthalate or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as a methyl methacrylate resin; a polystyrene resin; a polyvinyl chloride resin; an acrylonitrile / butadiene / styrene resin; an acrylonitrile / styrene resin; a polyvinyl acetate resin; a polyvinylidene chloride resin; a polyamide resin; a polyacetal resin; a modified polyphenylene ether resin; a polysulfone resin; a polyethersulfone resin; a polyarylate resin; a polyamideimide resin; a polyimide resin, etc.

[0084] As the linear polyolefin resin, in addition to homopolymers of linear olefins such as polyethylene resin and polypropylene resin, copolymers formed from two or more linear olefins can also be cited. More specific examples include polypropylene resins (polypropylene resin as a homopolymer of propylene, copolymers mainly composed of propylene) and polyethylene resins (polyethylene resin as a homopolymer of ethylene, copolymers mainly composed of ethylene).

[0085] The cyclic polyolefin resin is a general term for resins polymerized with cyclic olefins as polymerization units. If specific examples of the cyclic polyolefin resin are cited, they are ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and linear olefins such as ethylene and propylene (the representative case is a random copolymer), graft polymers obtained by modifying them with unsaturated carboxylic acids or their derivatives, and their hydrides, etc. Among them, norbornene resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers as cyclic olefins are preferably used.

[0086] The so-called cellulose resin refers to a cellulose organic acid ester or a cellulose mixed organic acid ester in which part or all of the hydrogen atoms of the hydroxyl groups of cellulose obtained from raw material cellulose such as cotton linter and wood pulp (hardwood pulp, softwood pulp) are replaced by acetyl, propionyl, and / or butyryl groups. For example, resins formed from acetate, propionate, butyrate, and mixed esters thereof of cellulose can be cited. Among them, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferred.

[0087] A polyester resin is a resin other than the above-mentioned cellulose resin having an ester bond, and is generally a resin formed by a condensate of a polybasic acid or its derivative and a polyol. A dibasic acid or its derivative can be used as the polybasic acid or its derivative, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethyl naphthalate, etc. A dihydric alcohol can be used as the polyol, and examples thereof include ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, cyclohexanedimethanol, etc. Examples of suitable polyester resins include polyethylene terephthalate.

[0088] A polycarbonate resin is an engineering plastic formed by a polymer obtained by bonding monomer units via carbonate groups, and is a resin having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate resin can also be a resin called a modified polycarbonate in which the polymer skeleton is modified to reduce the photoelastic coefficient, a copolymer polycarbonate in which the wavelength dependence is improved, etc.

[0089] A (meth)acrylic resin is a polymer containing a structural unit derived from a (meth)acrylic monomer. In a typical case, the polymer is a polymer containing a methacrylate. Preferably, the proportion of the structural unit derived from a methacrylate is 50% by weight or more based on all the structural units. The (meth)acrylic resin can be a homopolymer of a methacrylate or a copolymer containing a structural unit derived from another polymerizable monomer. In this case, the proportion of the structural unit derived from another polymerizable monomer is preferably 50% by weight or less based on all the structural units.

[0090] As the methacrylate that can constitute the (meth)acrylic resin, a methacrylic acid alkyl ester is preferred. Examples of the methacrylic acid alkyl ester include methacrylic acid alkyl esters having 1 to 8 carbon atoms in the alkyl group such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, 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, only one kind of methacrylate can be used alone, or two or more kinds can be used in combination.

[0091] As the other polymerizable monomers that can form the (meth)acrylic resin, acrylate esters and other compounds having a polymerizable carbon-carbon double bond in the molecule can be mentioned. The other polymerizable monomers can be used alone or in combination of two or more. As the acrylate ester, an alkyl acrylate is preferred. As the alkyl acrylate, alkyl acrylates having 1 to 8 carbon atoms in the alkyl group such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, 2-hydroxyethyl acrylate, etc. can be mentioned. The number of carbon atoms in the alkyl group contained in the alkyl acrylate is preferably 1 to 4. In the (meth)acrylic resin, the acrylate ester can be used alone or in combination of two or more.

[0092] As other compounds having a polymerizable carbon-carbon double bond in the molecule, vinyl compounds such as ethylene, propylene, styrene, and vinyl cyanide compounds such as acrylonitrile can be mentioned. The other compounds having a polymerizable carbon-carbon double bond in the molecule can be used alone or in combination of two or more.

[0093] The first and second thermoplastic resin films 20 and 30 can be protective films for protecting the polarizing plate 10 laminated on one side of the polarizing plate 10. The first or second thermoplastic resin film 20 or 30 can also be a protective film having an optical function such as a retardation film or a brightness enhancement film.

[0094] For example, by stretching (uniaxial stretching, biaxial stretching, etc.) the thermoplastic resin film formed of the above materials, or forming a liquid crystal layer on the film, etc., a retardation film having an arbitrary retardation value can be produced. The first and / or second thermoplastic resin films 20 and 30 can also have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic interference layer, an antifouling layer, etc. laminated on their surfaces.

[0095] The thickness of the first and second thermoplastic resin films 20 and 30 is usually 1 to 100 μm, however, from the viewpoints of strength, handleability, etc., it is preferably 5 to 60 μm, more preferably 5 to 50 μm.

[0096] From the viewpoint of easily manufacturing a single polarizing plate with a protective film having a sufficiently large positive curl, it is preferred that the thickness of the first thermoplastic resin film 20 and the second thermoplastic resin film 30 is small, specifically preferably 40 μm or less, more preferably 30 μm or less.

[0097] In Figure 2When a thermoplastic resin film is provided on both sides of the polarizing film 10 as in the polarizing plate 2a shown, these thermoplastic resin films may be composed of the same type of thermoplastic resin or different types of thermoplastic resins. In addition, the thicknesses may be the same or different. Further, they may have the same retardation characteristics or different retardation characteristics. When the compositions of the thermoplastic resin films adhered to both sides are different, curling is particularly likely to occur in the single polarizing plate with a protective film. Therefore, the present invention is particularly advantageous in such a case.

[0098] (1-1-4) Adhesive

[0099] As described above, the first and second thermoplastic resin films 20 and 30 can be adhered to the polarizing film 10 with an adhesive layer interposed therebetween, for example. As the adhesive for forming the adhesive layer, an aqueous adhesive, an energy ray curable adhesive, or a thermosetting adhesive can be used, and an aqueous adhesive and an energy ray curable adhesive are preferred.

[0100] Examples of the aqueous adhesive include an adhesive formed from an aqueous solution of a polyvinyl alcohol-based resin, an aqueous two-component urethane-based emulsion adhesive, etc. Among them, an aqueous adhesive formed from an aqueous solution of a polyvinyl alcohol-based resin can be suitably used. As the polyvinyl alcohol-based resin, in addition to a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate which is a homopolymer of vinyl acetate, a polyvinyl alcohol-based copolymer obtained by saponifying a copolymer of vinyl acetate and other monomers copolymerizable therewith, or a modified polyvinyl alcohol-based polymer obtained by partially modifying their hydroxyl groups can also be used. The aqueous adhesive may contain a crosslinking agent such as an aldehyde compound (e.g., glyoxal), an epoxy compound, a melamine-based compound, a hydroxymethyl compound, an isocyanate compound, an amine compound, a polyvalent metal salt, etc.

[0101] When using an aqueous adhesive, it is preferable to perform a drying process for removing the water contained in the aqueous adhesive after adhering the polarizing film 10 to the first and second thermoplastic resin films 20 and 30. After the drying process, a curing process for curing at a temperature of 20 to 45°C can be provided, for example.

[0102] The so-called energy ray curable adhesive is an adhesive containing a curable compound that cures by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, X-rays, etc., and an ultraviolet curable adhesive is preferred.

[0103] The curable compound can be a cationically polymerizable curable compound or a free-radically polymerizable curable compound. Examples of the cationically polymerizable curable compound include epoxy compounds (compounds having one or more epoxy groups in the molecule), oxetane compounds (compounds having one or more oxetane rings in the molecule), or combinations thereof. Examples of the free-radically polymerizable curable compound include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule), other vinyl compounds having a free-radically polymerizable double bond, or combinations thereof. A cationically polymerizable curable compound and a free-radically polymerizable curable compound can also be used in combination. The energy ray-curable adhesive usually further contains a cationic polymerization initiator and / or a free-radical polymerization initiator for initiating the curing reaction of the curable compound.

[0104] When laminating the polarizing plate 10 to the first and second thermoplastic resin films 20 and 30, in order to improve the adhesiveness, a surface activation treatment can be performed on the lamination surface of at least any one of them. Examples of the surface activation treatment include dry treatments such as corona treatment, plasma treatment, discharge treatment (such as glow discharge treatment), flame treatment, ozone treatment, UV ozone treatment, and ionizing active ray treatment (such as ultraviolet treatment and electron beam treatment); wet treatments such as ultrasonic treatment, saponification treatment, and anchor coating treatment using solvents such as water and acetone. These surface activation treatments can be performed alone or in combination of two or more.

[0105] In the case of laminating thermoplastic resin films on both sides of the polarizing plate 10, the adhesive used for laminating these thermoplastic resin films can be the same adhesive or different adhesives.

[0106] (1-2) The protective film supplied to the lamination step S101

[0107] (1-2-1) Constitution of the protective film

[0108] The protective film is a film for protecting the surface of the polarizing plate. Usually, after laminating a single polarizing plate with a protective film on, for example, an image display element, etc., in the case of having an adhesive layer, it is peeled off together with the adhesive layer. Therefore, the protective film 1 is detachably laminated on the above surface of the polarizing plate 2.

[0109] The protective film can be composed of, for example, a base film and an adhesive layer laminated thereon.

[0110] The base film can be composed of polyolefin resins such as thermoplastic resins, for example, polyethylene resins, polypropylene resins, cyclic olefin resins, etc.; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, etc.; polycarbonate resins; (meth)acrylic resins, etc. The base film can be a single-layer structure or a multi-layer structure.

[0111] The adhesive layer can be composed of (meth)acrylic adhesives, epoxy adhesives, urethane adhesives, silicone adhesives, etc.

[0112] In addition, the protective film can also be a resin film with self-adhesive properties such as polypropylene resins and polyethylene resins. In this case, the protective film does not have an adhesive layer.

[0113] The thickness of the protective film can be, for example, 5 to 150 μm, preferably 10 to 100 μm, more preferably 20 to 75 μm, and further preferably 25 to 70 μm (for example, 60 μm or less, and further preferably 55 μm or less). 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 disposability. If the thickness of the protective film is greater than 150 μm, it is disadvantageous in terms of thinning the single polarizing plate with the protective film and the reprocessability of the protective film.

[0114] The protective film provided to the laminating step S101 is preferably in a long strip shape.

[0115] The length of the long strip-shaped protective film provided to the laminating step S101 is, for example, 100 to 20000 m, preferably 1000 to 10000 m. In addition, the width of the long strip-shaped protective film provided to the laminating step S101 is, for example, 0.5 to 3 m, preferably 1 to 2.5 m.

[0116] (1-2-2) Elastic modulus of the protective film

[0117] The protective film provided to the laminating step S101 includes a region that satisfies the following formula (I):

[0118] TD elastic modulus - MD elastic modulus ≥ 300 MPa (I)

[0119] In formula (I), the so-called TD elastic modulus is the tensile elastic modulus (MPa) in the TD direction at a temperature of 23°C and a relative humidity of 55%RH, and the so-called MD elastic modulus is the tensile elastic modulus (MPa) in the MD direction at a temperature of 23°C and a relative humidity of 55%RH.

[0120] The so-called MD direction refers to the mechanical flow direction of the film, that is, the length direction of the film, and the so-called TD direction refers to the direction orthogonal to the MD direction.

[0121] By attaching a protective film including the above-described region to a polarizing plate and cutting out a single piece from this region in the cutting step S102, that is, by making the cut-out single piece have a protective film satisfying formula (I), a single piece of polarizing plate with a protective film having a sufficiently large positive curl can be obtained.

[0122] The so-called "cutting out a single piece from this region" described above means that the entire protective film of the cut-out single piece is included in this region.

[0123] Here, the curl of a single piece of polarizing plate with a protective film can be classified into two types, namely "MD curl" and "TD curl", in addition to the above classifications of "positive curl" and "negative curl". The so-called "MD curl" is a curl caused by stress (such as a contraction force or an expansion force), and the direction of this stress is parallel to the MD direction of the long-strip-shaped polarizing plate with a protective film from which the single piece of polarizing plate with a protective film is cut out.

[0124] Specifically for MD curl, when a measurement sample (single piece) is cut out from a long-strip-shaped polarizing plate with a protective film according to the description of an embodiment to be described later and the measurement sample is placed on a horizontal table with the concave side facing up, the size of the curl can be measured as the curl in which two corners on one diagonal with a small angle to the MD direction of the long-strip-shaped polarizing plate with a protective film among the two diagonals of the measurement sample are lifted. When the absorption axis direction of the polarizing plate in the long-strip-shaped polarizing plate with a protective film is parallel to the MD direction of the protective film, the MD curl can be measured as the curl in which two corners on one diagonal with a small angle to the absorption axis direction of the polarizing plate of the measurement sample among the two diagonals of the measurement sample are lifted (the curl in the absorption axis direction).

[0125] The so-called "TD curl" is a curl caused by stress (such as a contraction force or an expansion force), and the direction of this stress is parallel to the TD direction of the long-strip-shaped polarizing plate with a protective film from which the single piece of polarizing plate with a protective film is cut out.

[0126] In the present invention, attention is focused on MD curl. The so-called positive curl of the "single piece of polarizing plate with a protective film having a sufficiently large positive curl" that can be manufactured by the present invention refers to the positive curl that is MD curl. Hereinafter, this curl will also be referred to as "MD positive curl".

[0127] The so-called "satisfying formula (I)" in the above "the protective film provided to the attaching step S101 includes a region satisfying formula (I)" and "the cut-out single piece has a protective film satisfying formula (I)" means that throughout the entire protective film, that is, no matter where a measurement sample is collected on this protective film, the TD elastic modulus and the MD elastic modulus measured according to the description of an embodiment to be described later satisfy formula (I).

[0128] According to the research of the present inventors, it is obvious that if multiple points are measured along the TD direction of the generally available protective film on the left side of formula (I), there are protective films in which the values on the left side vary greatly depending on the product lot and the like. On the other hand, it has also been found that when multiple points are measured along the MD direction of the generally available protective film on the left side of formula (I), there is no significant variation in the values on the left side within the same roll.

[0129] Therefore, a protective film that satisfies formula (I) throughout the TD direction can generally be said to satisfy formula (I) throughout the entire protective film (that is, regardless of which position of the protective film the measurement sample is collected from).

[0130] From the viewpoint of improving the yield of the single polarizing plate with a protective film, the above-mentioned region of the protective film preferably has as large an occupied area as possible, more preferably this region extends throughout at least the entire TD direction (width direction) of the protective film provided to the bonding step S101, and still more preferably throughout the entire protective film.

[0131] From the viewpoint of increasing the MD positive curling of the obtained single polarizing plate with a protective film, the left side of formula (I) is preferably 400 MPa or more, more preferably 500 MPa or more. The left side of formula (I) is usually 2000 MPa or less, and typically 1500 MPa or less.

[0132] As the protective film provided to the bonding step S101, as long as the left side of formula (I) is measured for the obtained protective film, a protective film including a region that satisfies formula (I) can be used.

[0133] (1 - 3) Bonding of the polarizing plate and the protective film

[0134] Refer to Figure 4 , the bonding of the polarizing plate 2 and the protective film 1 can be carried out, for example, using a pair of rollers (bonding rollers) 5, 5. From the viewpoint of manufacturing efficiency, this method is particularly advantageous when the polarizing plate 2 and the protective film 1 are in a long strip shape.

[0135] Specifically, the long strip-shaped polarizing plate 2 is continuously transported, and at the same time, the long strip-shaped protective film 1 is continuously transported. The protective film 1 is overlapped on one side of the polarizing plate 2 and passed through between a pair of bonding rollers 5, 5 and clamped, whereby a polarizing plate 3 with a protective film in which the two films are bonded can be manufactured.

[0136] The MD direction (transport direction) of the polarizing plate 2 and the MD direction (transport direction) of the protective film 1 are usually parallel. By "parallel" is meant that the angle formed by the MD direction of the polarizing plate 2 and the MD direction of the protective film 1 is 0 degrees ± 5 degrees, preferably 0 degrees ± 2 degrees.

[0137] From the viewpoint of increasing the MD positive curl of the obtained single polarizing plate with a protective film, it is preferable to bond the two films in such a way that the absorption axis of the polarizing plate 2 is parallel to the MD direction of the protective film 1. By "parallel", it means that the angle formed by the absorption axis of the polarizing plate 2 and the MD direction of the protective film 1 is 0 degrees ± 5 degrees, preferably 0 degrees ± 2 degrees.

[0138] Pass the laminate of the polarizing plate 2 and the protective film 1 between a pair of bonding rollers 5, 5, and thereby press the laminate from above and below, so as to bond the two films closely.

[0139] When the polarizing plate 2 has a transparent hard coat (a hard coat with a smooth surface) on its outermost surface and the protective film 1 is bonded to the transparent hard coat, it is easy to improve the bonding strength between the polarizing plate 2 and the protective film 1, and thus there is a tendency to easily obtain a single polarizing plate with a protective film having a sufficiently large MD positive curl. Therefore, the polarizing plate 2 preferably has a transparent hard coat (a hard coat with a smooth surface) on its outermost surface.

[0140] When the protective film 1 is composed of a base film and an adhesive layer laminated thereon, when the protective film 1 is overlapped on one surface of the polarizing plate 2 and then passed between a pair of bonding rollers 5, 5, the adhesive layer of the protective film 1 is overlapped in contact with the above-mentioned one surface of the polarizing plate 2. Before laminating the protective film 1 and the polarizing plate 2, a surface activation treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, or saponification treatment can be performed on at least any one of the bonding surfaces of the protective film 1 and the polarizing plate 2.

[0141] In the process of bonding using a pair of bonding rollers 5, 5, the pressure (clamping pressure) applied to the laminate of the protective film 1 and the polarizing plate 2 is, for example, 0.01 to 0.5 MPa, and can also be 0.05 to 0.3 MPa. As the bonding rollers 5, 5, conventionally known bonding rollers such as rollers with a metal surface (including alloys such as SUS) or rubber rollers can be used.

[0142] In the process of bonding the polarizing plate 2 and the protective film 1, it is preferable to perform bonding while applying tension to the polarizing plate 2 and the protective film 1, and more preferably, the pre-bonding tension of the polarizing plate 2 is less than the pre-bonding tension of the protective film 1. Such tension control is advantageous from the viewpoint of increasing the MD positive curl of the obtained single polarizing plate with a protective film. The pre-bonding tension refers to the tension applied in the MD direction of the film before bonding the two films (the laminate of the two films passes between a pair of bonding rollers 5, 5), and can be measured according to the description in an embodiment described later.

[0143] From the viewpoint of increasing the MD positive curl of the obtained single polarizing plate with a protective film, the pre-bonding tension in the MD direction of the polarizing plate 2 is preferably 250 N / m or less, and more preferably 200 N / m or less.

[0144] From the same perspective, the pre-tension in the MD direction of the protective film 1 is preferably 260 N / m or more, more preferably 300 N / m or more.

[0145] (2) Cutting process S102

[0146] This process is a process of cutting out from the above-mentioned region satisfying formula (I) in the polarizing plate 3 with a protective film obtained in the laminating process S101 to obtain a single polarizing plate with a protective film.

[0147] Cutting (trimming) can be performed using a conventionally known cutting device such as a cutting machine for cutting.

[0148] As described above, the so-called "cutting out a single piece from the region" means that the entire protective film of the cut-out single piece is included in the region.

[0149] The size, shape, and cutting angle of the single polarizing plate with a protective film to be cut out are not particularly limited.

[0150] The single polarizing plate with a protective film is preferably square-shaped, more preferably square-shaped with a long side and a short side. This square shape is preferably rectangular.

[0151] When the shape of the single polarizing plate with a protective film is rectangular, 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.

[0152] Generally speaking, if the size of the single polarizing plate with a protective film becomes larger, there will be a tendency that it is difficult to generate MD positive curling. Therefore, when the size of the single polarizing plate with a protective film is large, in order to impart a sufficient amount of MD positive curling, it is sometimes preferable to further increase the left side of formula (I).

[0153] Although not particularly limited, when the shape of the single polarizing plate with a protective film is rectangular, the single polarizing plate with a protective film can be cut out from the polarizing plate 3 with a protective film in such a way that when observing the single polarizing plate with a protective film from the protective film side, the absorption axis direction of the polarizing plate (the MD direction of the polarizing plate) forms an angle of 45 degrees with respect to its long side and short side.

[0154] Alternatively, when the shape of the single polarizing plate with a protective film is rectangular, the single polarizing plate with a protective film can also be cut out from the polarizing plate 3 with a protective film in such a way that when observing the single polarizing plate with a protective film from the protective film side, the absorption axis direction of the polarizing plate (the MD direction of the polarizing plate) is parallel to its long side, or forms an angle of 90 degrees with respect to its long side.

[0155] <Polarizing plate single body with protective film>

[0156] The polarizing plate single body with a protective film of the present invention includes a polarizing plate and a protective film laminated on one surface thereof, and the protective film satisfies the following formula (II):

[0157] First elastic modulus - second elastic modulus ≥ 300 MPa (II)

[0158] In formula (II), the so-called first elastic modulus is the tensile elastic modulus (MPa) in the direction orthogonal to the absorption axis of the polarizing plate at a temperature of 23°C and a relative humidity of 55% RH, and the so-called second elastic modulus is the tensile elastic modulus (MPa) in the direction parallel to the absorption axis of the polarizing plate at a temperature of 23°C and a relative humidity of 55% RH.

[0159] By providing a protective film that satisfies formula (II), the polarizing plate single body with a protective film can have a sufficiently large MD positive curl.

[0160] According to the polarizing plate single body with a protective film having a sufficiently large MD positive curl, even when one or more additional optical functional layers or the like are laminated on the polarizing plate side to form the above-mentioned multilayer structure, the state without reverse curl (flat state) or the state with positive curl can be maintained. Therefore, when the polarizing plate single body with a protective film or the multilayer structure is adhered to an image display element with an adhesive layer interposed therebetween, the occurrence of adhesion errors or the poor condition of air bubbles mixing into the interface between the adhesive layer and the image display element can be suppressed.

[0161] The polarizing plate single body with a protective film of the present invention can be manufactured by the manufacturing method of the polarizing plate single body with a protective film described above.

[0162] Regarding the direction orthogonal to the absorption axis of the polarizing plate, when manufacturing a polarizing plate single body with a protective film by the manufacturing method of the polarizing plate single body with a protective film described above, it is synonymous with the TD direction of the protective film and the polarizing plate.

[0163] The so-called "satisfying formula (II)" means that throughout the entire protective film, that is, no matter where the measurement sample is collected on the protective film, the first elastic modulus and the second elastic modulus measured according to the description in one of the following examples satisfy formula (II).

[0164] For the same reasons as those described in the section <Manufacturing method of polarizing plate single body with protective film>, in the polarizing plate single body with a protective film, the protective film that satisfies formula (II) throughout the entire direction orthogonal to the absorption axis of the polarizing plate can generally be said to satisfy formula (II) throughout the entire protective film (that is, no matter where the measurement sample is collected from the protective film).

[0165] From the viewpoint of increasing the MD positive curl of the single polarizing plate with a protective film, the left side of the formula (II) is preferably 400 MPa or more, more preferably 500 MPa or more. The left side of the formula (II) is usually 2000 MPa or less, and typically 1500 MPa or less.

[0166] The size and shape of the single polarizing plate with a protective film are not particularly limited. For specific sizes and shapes, reference is made to the description in <Manufacturing method of the single polarizing plate with a protective film>. When the size of the single polarizing plate with a protective film is large, in order to impart a sufficient amount of MD positive curl, it is sometimes preferable to further increase the left side of the formula (II).

[0167] The single polarizing plate with a protective film (the same applies to the single polarizing plate with a protective film obtained by the manufacturing method of the single polarizing plate with a protective film of the present invention) preferably exhibits MD positive curl. In order to also exhibit MD positive curl as the above-mentioned multilayer structure or exhibit a flat state without curl, it is more preferable that the MD positive curl amount measured according to the description in the following Examples is 40 mm or more. The MD positive curl amount can also be 45 mm or more. The MD positive curl amount is preferably 100 mm or less.

[0168] Although not particularly limited, when the shape of the single polarizing plate with a protective film is rectangular, when observing the single polarizing plate with a protective film from the protective film side, the absorption axis direction of the polarizing plate can form an angle of 45 degrees with respect to its long side and short side.

[0169] Alternatively, when the shape of the single polarizing plate with a protective film is rectangular, when observing the single polarizing plate with a protective film from the protective film side, the absorption axis direction of the polarizing plate can be parallel to its long side or form an angle of 90 degrees with respect to its long side.

[0170] An example of the layer constitution of the single polarizing plate with a protective film is shown in Figure 5 as follows. As Figure 5 shown, when the protective film 1 is composed of a base film 40 and an adhesive layer 50 laminated thereon, they are overlapped in such a manner that the adhesive layer 50 of the protective film 1 contacts the above-mentioned one surface of the polarizing plate 2.

[0171] For more specific descriptions of the polarizing plate 2 and the protective film 1, reference is made to the description in <Manufacturing method of the single polarizing plate with a protective film>.

[0172] <Long strip-shaped polarizing plate with a protective film>

[0173] The strip-shaped polarizing plate with a protective film of the present invention includes a strip-shaped polarizing plate and a strip-shaped protective film laminated on one side thereof, and the protective film includes a region satisfying the following formula (III):

[0174] First elastic modulus - second elastic modulus ≥ 300 MPa (III)

[0175] In formula (III), the so-called first elastic modulus is the tensile elastic modulus (MPa) in the direction orthogonal to the absorption axis of the strip-shaped polarizing plate at a temperature of 23°C and a relative humidity of 55% RH, and the so-called second elastic modulus is the tensile elastic modulus (MPa) in the direction parallel to the absorption axis of the strip-shaped polarizing plate at a temperature of 23°C and a relative humidity of 55% RH.

[0176] According to the strip-shaped polarizing plate with a protective film including the above region, a single piece is cut out from this region, and the single piece cut out thus has a protective film satisfying formula (III), so that a single piece of the polarizing plate with a protective film having a sufficiently large positive curl can be obtained.

[0177] The so-called "cutting out a single piece from this region" mentioned above means that the entire protective film of the single piece cut out is included in this region.

[0178] The strip-shaped polarizing plate with a protective film of the present invention can be manufactured by implementing the bonding step S101 of the manufacturing method of the single piece of the polarizing plate with a protective film described above.

[0179] For the direction orthogonal to the absorption axis of the polarizing plate, in the case of manufacturing a strip-shaped polarizing plate with a protective film by implementing the bonding step S101 of the manufacturing method of the single piece of the polarizing plate with a protective film described above, it is synonymous with the TD direction of the protective film and the polarizing plate.

[0180] The so-called "satisfying formula (III)" means that throughout the entire protective film, that is, no matter at which position of the protective film a measurement sample is collected, the first elastic modulus and the second elastic modulus measured according to the description in one of the following examples satisfy formula (III).

[0181] For the same reasons as those described in the item <Manufacturing Method of a Single Piece of a Polarizing Plate with a Protective Film>, in the strip-shaped polarizing plate with a protective film, a protective film that satisfies formula (III) throughout the entire direction orthogonal to the absorption axis of the polarizing plate can generally be said to satisfy formula (III) throughout the entire protective film (that is, no matter from which position of the protective film a measurement sample is collected).

[0182] From the viewpoint of improving the yield of a single polarizing plate with a protective film, the above-mentioned region of the protective film preferably has as large an occupied area as possible, more preferably, this region extends over at least the entire width direction of the protective film provided to the bonding step S101, and still more preferably, it extends over the entire protective film.

[0183] From the viewpoint of improving the MD positive curl of a single polarizing plate with a protective film cut out from a long strip-shaped polarizing plate with a protective film, the left side of the formula (III) is preferably 400 MPa or more, more preferably 500 MPa or more. The left side of the formula (III) is usually 2000 MPa or less, and typically 1500 MPa or less.

[0184] The size, shape, and cutting angle of the single polarizing plate with a protective film are not particularly limited. For specific size, shape, and cutting angle, refer to the description in the item <Manufacturing method of a single polarizing plate with a protective film>. When the size of the single polarizing plate with a protective film cut out from a long strip-shaped polarizing plate with a protective film is large, in order to impart a sufficient amount of MD positive curl, it is sometimes preferable to further increase the left side of the formula (III).

[0185] The length of the long strip-shaped polarizing plate with a protective film is, for example, 100 to 20000 m, preferably 1000 to 10000 m. In addition, the width of the long strip-shaped polarizing plate with a protective film is, for example, 0.5 to 3 m, preferably 1 to 2.5 m.

[0186] For a more specific description of the layer structure of the long strip-shaped polarizing plate with a protective film, the polarizing plate and the protective film constituting the long strip-shaped polarizing plate with a protective film, refer to the descriptions in the items <Manufacturing method of a single polarizing plate with a protective film> and <Single polarizing plate with a protective film>.

[0187] <Multi-layer structure>

[0188] One or more optical functional layers or a separator (release film) etc. can be laminated on one side of the polarizing plate side of the polarizing plate with a protective film or the long strip-shaped polarizing plate with a protective film, with an adhesive layer or an adhesive layer interposed therebetween.

[0189] The optical functional layer can be a retardation layer etc., and the optical functional layer can be laminated on one side of the polarizing plate side with an adhesive layer or an adhesive layer interposed therebetween.

[0190] [Examples]

[0191] Hereinafter, experimental examples are given to further specifically illustrate the present invention, however, the present invention is not limited by these examples.

[0192] In the following experimental examples, the thicknesses of the polarizing plate and the film, the difference in elastic modulus of the protective film, the pre-tension before lamination in the MD direction of the polarizing plate and the protective film, and the MD curl amount of the single polarizing plate with the protective film were measured according to the following methods.

[0193] (1) Thicknesses of the polarizing plate and the film

[0194] Measured using the digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0195] (2) Difference in elastic modulus of the protective film

[0196] Using a super cutter, rectangular small pieces with a long side of 100 mm and a short side of 25 mm were cut out from the long-strip polarizing plate with the protective film. The cutting was performed such that the long side of the small piece was parallel to the MD direction of the long-strip polarizing plate with the protective film, and the short side of the small piece was parallel to the TD direction of the long-strip polarizing plate with the protective film. The polarizing plate was peeled off from the small piece, and the obtained small piece of the protective film monomer was used as a sample for measuring the MD elastic modulus.

[0197] Additionally, in the same manner, rectangular small pieces with a long side of 100 mm and a short side of 25 mm were cut out from the long-strip polarizing plate with the protective film. Among them, the cutting was performed such that the long side of the small piece was parallel to the TD direction of the long-strip polarizing plate with the protective film, and the short side of the small piece was parallel to the MD direction of the long-strip polarizing plate with the protective film. The polarizing plate was peeled off from the small piece, and the obtained small piece of the protective film monomer was used as a sample for measuring the TD elastic modulus.

[0198] Then, using the upper and lower clamps of a tensile testing machine [Autograph AG-Xplus testing machine manufactured by Shimadzu Corporation], the two ends in the long side direction of the above-mentioned measurement sample were clamped such that the distance between the clamps was 5 cm, and in an environment of 23°C and a relative humidity of 55%, the measurement sample was stretched along the length direction of the measurement sample at a stretching speed of 1 mm / minute. Based on the slope of the straight line between 3 and 6 MPa in the obtained stress-strain curve, the tensile elastic modulus [MPa] at 23°C and a relative humidity of 55% was calculated. At this time, as the thickness used for calculating the stress, only the thickness value of the biaxially stretched polyethylene terephthalate (substrate film) was used.

[0199] The tensile elastic modulus calculated from the measurement of the sample for measuring the MD elastic modulus is the MD elastic modulus, and the tensile elastic modulus calculated from the measurement of the sample for measuring the TD elastic modulus is the TD elastic modulus.

[0200] In the following experimental examples, a polarizing plate with a protective film was produced by laminating the two films in such a way that the absorption axis (MD direction) of the polarizing plate was parallel to the MD direction of the protective film. Therefore, the TD elastic modulus in the above formula (I) is synonymous with the first elastic modulus in the above formulas (II) and (III), and the MD elastic modulus in the above formula (I) is synonymous with the second elastic modulus in the above formulas (II) and (III).

[0201] Hereinafter, the TD elastic modulus (first elastic modulus) will be simply referred to as the "TD elastic modulus", and the MD elastic modulus (second elastic modulus) will be simply referred to as the "MD elastic modulus".

[0202] Based on the obtained TD elastic modulus and MD elastic modulus, the TD elastic modulus - MD elastic modulus (first elastic modulus - second elastic modulus) was calculated.

[0203] Hereinafter, the TD elastic modulus - MD elastic modulus (first elastic modulus - second elastic modulus) will be simply referred to as the "elastic modulus difference".

[0204] (3) Pretension in the MD direction of the polarizing plate and the protective film

[0205] Using a tension detection roller provided between the laminating roller and a pair of pinch rollers closest to the laminating roller, the film tensions [N / m] of the polarizing plate and the protective film traveling between a pair of laminating rollers for laminating the polarizing plate and the protective film and a pair of pinch rollers located upstream thereof and closest to the laminating roller were measured as the pretension in the MD direction.

[0206] (4) MD curl amount of a single polarizing plate with a protective film

[0207] As Figure 6 shown, from the obtained long strip-shaped polarizing plate 60 with a protective film, a rectangular (long side 140 mm × short side 70 mm) small piece (single piece) was cut out using a super cutter in such a way that the absorption axis 61 of the polarizing plate was 45 degrees with respect to the long side and the short side when viewed from the protective film side, and this was used as a sample 70 for measuring the MD curl amount. The sample 70 for measurement was cut out in an environment of 23°C and a relative humidity of 55% shortly after laminating the polarizing plate and the protective film.

[0208] The sample 70 for measurement was placed on a reference surface (a horizontal table) with the concave side facing up. In this state, the heights of the two corners 80 on one of the two diagonals of the sample 70 for measurement, which has a smaller angle with the absorption axis direction of the polarizing plate, were measured with respect to the reference surface, and the MD curl amount [mm] was obtained as the average of the heights of these two corners 80.

[0209] The state where the protective film side is recessed is a state with positive curling, and the state where the polarizing plate side is recessed is a state with reverse curling. In the following Experimental Examples 1 to 3, any measurement sample (a single polarizing plate with a protective film) has positive curling.

[0210] <Experimental Examples 1 - 3>

[0211] (A)Production of Polarizer

[0212] While continuously transporting a long-sized polyvinyl alcohol film [average degree of polymerization: about 2400, saponification degree: 99.9 mol% or more, thickness: 30 μm], it is uniaxially stretched about 4 times by a dry method. Then, while keeping the tension state unchanged, it is immersed in pure water at 40°C for 1 minute, and then immersed in an aqueous solution with a weight ratio of iodine / potassium iodide / water of 0.1 / 5 / 100 at 28°C for 60 seconds. Thereafter, it is immersed in an aqueous solution with a weight ratio of potassium iodide / boric acid / water of 10.5 / 7.5 / 100 at 68°C for 300 seconds. Next, it is washed with pure water at 5°C for 5 seconds and then dried at 70°C for 180 seconds to obtain a long strip-shaped polarizer in which iodine is adsorbed and oriented on the uniaxially stretched polyvinyl alcohol film. The thickness of the polarizer is 13 μm.

[0213] (B)Production of Polarizing Plate

[0214] The long strip-shaped polarizer obtained in the above (A) is continuously transported, and at the same time, a long strip-shaped first thermoplastic resin film [trade name "COP25ST - HC" manufactured by Nippon Paper Industries Co., Ltd., a film with a transparent hard coating formed on a cyclic olefin-based resin film, thickness: 29 μm] and a long strip-shaped second thermoplastic resin film [trade name "ZRG20SL" manufactured by Fujifilm Corporation, a triacetyl cellulose (TAC) film, thickness: 20 μm] are continuously transported. While injecting an aqueous adhesive between the polarizer and the first thermoplastic resin film, and between the polarizer and the second thermoplastic resin film, it is passed through a pair of laminating rollers to obtain a laminated film composed of the first thermoplastic resin film / aqueous adhesive layer / polarizer / aqueous adhesive layer / second thermoplastic resin film.

[0215] Next, the obtained laminated film is transported through a hot air dryer and subjected to a heat treatment at 80°C for 300 seconds to dry the aqueous adhesive layer and obtain a long strip-shaped polarizing plate.

[0216] As the aqueous adhesive described above, an aqueous solution was used which was obtained by mixing a crosslinking agent [sodium glyoxylate manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] in a proportion of 1 part by weight with respect to 10 parts by weight of polyvinyl alcohol powder in an aqueous polyvinyl alcohol solution having a concentration of 3% by weight obtained by dissolving polyvinyl alcohol powder [trade name "GOHSEFIMER" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization: 1100] in hot water at 95°C. The thickness of the obtained polarizing plate was 62 μm.

[0217] (C) Production of a long polarizing plate with a protective film

[0218] The long polarizing plate obtained in the above (B) was continuously transported, and at the same time, a long protective film with the separator peeled off [trade name "AY-4212" manufactured by Fujimori Kogyo Co., Ltd. in which a (meth)acrylic adhesive layer (thickness: 15 μm) was laminated on biaxially stretched polyethylene terephthalate (thickness: 38 μm)] was continuously transported. They were overlapped and passed through a pair of laminating rollers, whereby the laminate of the protective film and the polarizing plate was pressed from above and below, and a long polarizing plate with a protective film was continuously manufactured.

[0219] The protective film was laminated on the first thermoplastic resin film (transparent hard coating film) surface of the polarizing plate with the adhesive layer interposed therebetween.

[0220] It should be noted that the pressure (clamping pressure) applied to the laminate of the protective film and the polarizing plate by the laminating rollers was 0.1 MPa. At this time, the pre-tension before lamination in the MD direction of the polarizing plate was 151 N / m, and the pre-tension before lamination in the MD direction of the protective film was 327 N / m.

[0221] The manufacturing methods of the long polarizing plates with protective films in Experimental Examples 1 to 3 were the same except that the protective films used were different (the products were the same, but the batches were different). Hereinafter, the protective films used in Experimental Examples 1 to 3 will also be referred to as Protective Films 1 to 3, respectively.

[0222] From the obtained long polarizing plate with a protective film, the TD elastic modulus, the MD elastic modulus, and the elastic modulus difference were determined according to the above method.

[0223] The protective films 1 to 3 each have a width (length in the TD direction) of 1300 mm. When measuring the elastic modulus of each protective film, at an arbitrary position in the MD direction, measurement samples were cut out at a total of 7 positions along the width direction, which were 100 mm, 280 mm, 470 mm, 650 mm, 830 mm, 1020 mm, and 1200 mm from one end of the width direction. For these 7 measurement samples, the TD elastic modulus, MD elastic modulus, and elastic modulus difference were respectively obtained. Their results are shown in the "1" column of Table 1. At a position 20 mm away from the above-mentioned arbitrary MD direction position along the MD direction, 7 measurement samples were cut out in the same manner as above. For these 7 measurement samples, the TD elastic modulus, MD elastic modulus, and elastic modulus difference were respectively obtained. Their results are shown in the "2" column of Table 1. At a position 50 mm away from the above-mentioned arbitrary MD direction position along the MD direction, 7 measurement samples were cut out in the same manner as above. For these 7 measurement samples, the TD elastic modulus, MD elastic modulus, and elastic modulus difference were respectively obtained. Their results are shown in the "3" column of Table 1.

[0224] In addition, a graph showing the relationship between the width direction position of the protective films 1 to 3 and the elastic modulus difference (the elastic modulus recorded in the "1" column of Table 1) is shown in Figure 7 .

[0225] Regarding the position where the measurement samples are cut out, for example, the so-called "cutting out the measurement sample at a position 100 mm from one end of the width direction" means cutting out the measurement sample in such a way that the position 100 mm from one end of the width direction coincides with the center position in the width direction of the measurement sample. The same applies to other positions relative to one end of the width direction.

[0226] [Table 1]

[0227]

[0228] As shown in Table 1 and Figure 7 , it can be seen that the long strip-shaped protective films 1 and 2 contain regions that satisfy formulas (I) and (III) throughout the whole, that is, throughout the entire TD direction (the direction orthogonal to the absorption axis of the long strip-shaped polarizing plate) and throughout the entire MD direction (the absorption axis direction of the long strip-shaped polarizing plate), and this region extends throughout the entire width direction of the protective film.

[0229] In contrast, although the strip-shaped protective film 3 includes regions that satisfy formulas (I) and (III) throughout the entire TD direction (the direction orthogonal to the absorption axis of the strip-shaped polarizer) and throughout the entire MD direction (the absorption axis direction of the strip-shaped polarizer), these regions do not extend throughout the entire width direction of the protective film. That is, the strip-shaped protective film 3 satisfies formulas (I) and (III) only in the region from one end to about 700 mm with respect to one end in the width direction.

[0230] It should be noted that, as described above, a protective film that satisfies formulas (I) and (III) at each arbitrary MD direction position generally also satisfies formulas (I) and (III) at other MD direction positions.

[0231] (D) Fabrication of a polarizer single body with a protective film

[0232] As Figure 6 shown, from the strip-shaped polarizer with a protective film obtained in the above (C), a rectangular (long side 140 mm × short side 70 mm) small piece (single body) is cut out using a super cutter in such a way that the absorption axis of the polarizer is 45 degrees with respect to the long side and the short side when viewed from the protective film side, obtaining a polarizer single body with a protective film.

[0233] For the obtained polarizer single body with a protective film, the MD curl amount is measured according to the above method.

[0234] The strip-shaped polarizers with a protective film in Experimental Examples 1 to 3 each have a width (TD direction length) of 1330 mm. When measuring the MD curl amount of the polarizer single bodies with a protective film obtained from each strip-shaped polarizer with a protective film, at an arbitrary MD direction position, polarizer single bodies with a protective film are cut out at a total of 7 positions along the width direction at positions 100 mm, 280 mm, 470 mm, 650 mm, 830 mm, 1020 mm, and 1200 mm with respect to one end in the width direction, and the MD curl amount is measured for each of these 7 single bodies. Seven single bodies are cut out near the cutting positions of the measurement samples for measuring the difference in elastic modulus of the protective film recorded in the "1" column of Table 1. The results are shown in Table 2. In addition, a graph showing the relationship between the width direction positions of the polarizer single bodies with a protective film cut out from the strip-shaped polarizers with a protective film in Experimental Examples 1 to 3 and the MD curl amount of the cut-out polarizer single bodies with a protective film is shown in Figure 7 .

[0235] Regarding the position where a single polarizing plate with a protective film is cut out, for example, the so-called "cutting out a single polarizing plate with a protective film at a position 100 mm from one end in the width direction" means cutting out the single polarizing plate with a protective film in such a way that the position 100 mm from one end in the width direction coincides with the center position in the width direction of the single polarizing plate with a protective film. The same applies to other positions from one end in the width direction.

[0236] The single polarizing plates with a protective film cut out from the long strip-shaped polarizing plates with a protective film in Experimental Examples 1 to 3 all have positive curl. Therefore, the measured MD curl amount is the amount of positive MD curl.

[0237] [Table 2]

[0238]

[0239] Among the 7 single polarizing plates with a protective film cut out from the long strip-shaped polarizing plates with a protective film in Experimental Example 1 using Protective Film 1 and the 7 single polarizing plates with a protective film cut out from the long strip-shaped polarizing plates with a protective film in Experimental Example 2 using Protective Film 2, the protective film laminated on the polarizing plate satisfies Formula (II).

[0240] Among the 7 single polarizing plates with a protective film cut out from the long strip-shaped polarizing plates with a protective film in Experimental Example 3 using Protective Film 3, the single plates cut out at positions 100 mm, 280 mm, 470 mm, and 650 mm from one end in the width direction of the long strip-shaped polarizing plate with a protective film satisfy Formula (II) with respect to the protective film laminated on the polarizing plate. However, the single plates cut out at positions 830 mm, 1020 mm, and 1200 mm do not satisfy Formula (II).

[0241] As shown in Table 2 and Figure 8 as shown, the single polarizing plates with a protective film that satisfy Formula (II) show an MD positive curl amount of 40 mm or more. On the other hand, the MD positive curl amount of the single polarizing plates with a protective film that do not satisfy Formula (II) is 40 mm or less.

[0242] Explanation of symbols

[0243] 1 Protective film, 2, 2a, 2b Polarizing plate, 3 Polarizing plate with a protective film, 5 Laminating roller, 10 Polarizing sheet, 20 First thermoplastic resin film, 30 Second thermoplastic resin film, 40 Substrate film, 50 Adhesive layer, 60 Long strip-shaped polarizing plate with a protective film, 61 Absorption axis of the polarizing plate, 70 Sample for measuring MD curl amount, 80 Angle of the measuring sample.

Claims

1. A method for manufacturing a single sheet of a polarizing plate with a protective film, The manufacturing method includes: A step of laminating a protective film including a region satisfying the following formula (I) on one surface of the polarizing plate to obtain a polarizing plate with a protective film, and A step of cutting out a single sheet of the polarizing plate with a protective film from the region; 908 MPa ≥ TD elastic modulus - MD elastic modulus ≥ 338 MPa (I) In the formula, the so-called TD elastic modulus is the tensile elastic modulus in the TD direction at a temperature of 23°C and a relative humidity of 55% RH, and the so-called MD elastic modulus is the tensile elastic modulus in the MD direction at a temperature of 23°C and a relative humidity of 55% RH. The polarizing plate sequentially includes a first thermoplastic resin film, a polarizing film, and a second thermoplastic resin film, and the thickness of the polarizing plate is 70 μm or less. The first thermoplastic resin film includes a cyclic olefin resin. The protective film is detachably laminated on the surface of the polarizing plate. The protective film has a polyester resin film. The protective film is composed of the polyester resin film and an adhesive layer laminated thereon.

2. The manufacturing method according to claim 1, wherein The polarizing plate and the protective film are sandwiched between a pair of rollers and laminated.

3. The manufacturing method according to claim 2, wherein The polarizing plate is in a long strip shape, and the protective film is in a long strip shape.

4. The manufacturing method according to claim 3, wherein The pre-laminating tension of the polarizing plate is 200 N / m or less. The pre-laminating tension of the protective film is 300 N / m or more.

5. The manufacturing method according to any one of claims 1 to 4, wherein The polarizing plate is laminated in such a manner that the absorption axis of the polarizing plate is parallel to the MD direction of the protective film.

6. A single sheet of a polarizing plate with a protective film, It includes a polarizing plate and a protective film laminated on one surface thereof. The protective film satisfies the following formula (II): 908 MPa ≥ first elastic modulus - second elastic modulus ≥ 338 MPa (II) In the formula, the so-called first elastic modulus is the tensile elastic modulus in the direction orthogonal to the absorption axis of the polarizing plate at a temperature of 23°C and a relative humidity of 55% RH, and the so-called second elastic modulus is the tensile elastic modulus in the direction parallel to the absorption axis of the polarizing plate at a temperature of 23°C and a relative humidity of 55% RH. The polarizing plate sequentially includes a first thermoplastic resin film, a polarizing film, and a second thermoplastic resin film, and the thickness of the polarizing plate is 70 μm or less. The first thermoplastic resin film includes a cyclic olefin resin. The protective film is detachably laminated on the surface of the polarizing plate. The protective film has a polyester resin film. The protective film is composed of the polyester resin film and an adhesive layer laminated thereon.

7. The single sheet of a polarizing plate with a protective film according to claim 6, wherein The amount of curl in the direction parallel to the absorption axis of the polarizing plate with the surface on the polarizing plate side being convex is 40 mm or more. Regarding the amount of curl, a rectangular measurement sample in which the absorption axis of the polarizing plate has an angle of 45 degrees with respect to the long side and the short side is placed on the reference surface, and the heights with respect to the reference surface are measured for two corners on one diagonal of the measurement sample having a smaller angle with the absorption axis direction of the polarizing plate, and the average of the heights of these two corners at this time is obtained.

8. A strip-shaped polarizing plate with a protective film, which comprises a strip-shaped polarizing plate and a strip-shaped protective film laminated on one surface thereof, the protective film includes a region satisfying the following formula (III): 908 MPa ≥ first elastic modulus - second elastic modulus ≥ 338 MPa (III) In the formula, the so-called first elastic modulus is the tensile elastic modulus in the direction orthogonal to the absorption axis of the strip-shaped polarizing plate at a temperature of 23°C and a relative humidity of 55%RH, and the so-called second elastic modulus is the tensile elastic modulus in the direction parallel to the absorption axis of the strip-shaped polarizing plate at a temperature of 23°C and a relative humidity of 55%RH. The polarizing plate sequentially includes a first thermoplastic resin film, a polarizer, and a second thermoplastic resin film, and the thickness of the polarizing plate is 70 μm or less. The first thermoplastic resin film includes a cyclic olefin resin. The protective film is peelably adhered to the surface of the polarizing plate. The protective film has a polyester resin film. The protective film is composed of the polyester resin film and an adhesive layer laminated thereon.

9. The strip-shaped polarizing plate with a protective film according to claim 8, wherein the region extends throughout the entire width direction of the protective film.

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