JP2020086236A - Polarizing plate with surface protective film - Google Patents

Abstract

To provide a polarizing plate with a surface protective film that is prevented from breaking when it is reworked.SOLUTION: A polarizing plate with a surface protective film includes an adhesive layer, a polarizer, a protective layer, and a surface protective film in this order. The protective layer contains polyethylene terephthalate (PET), and the protective layer has a breaking strength ratio of 1.9-2.4.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polarizing plate with a surface protective film.

A method has been proposed in which a polyvinyl alcohol (PVA)-based resin layer is formed on a resin substrate, and the laminate is dyed and stretched to obtain a polarizer (for example, Patent Document 1). According to such a method, a polarizer having a small thickness can be obtained, and therefore, it is attracting attention because it can contribute to a reduction in the thickness of an image display device, for example.

The above-mentioned polarizer is obtained in the form of a laminate of a polarizer/resin base material, and typically, a protective film (protective layer) is attached to the surface of the polarizer, and then the resin base material is peeled and removed. .. However, the process of peeling and removing the resin base material is one of the factors that reduce the manufacturing efficiency. Therefore, there has been proposed a polarizing plate which is used as a protective layer without attaching a protective film to the laminate and without peeling and removing the resin base material from the polarizing plate.

By the way, the polarizing plate can be attached to an optical panel or the like via an adhesive layer or the like. In this case, if foreign matters such as contaminants and air bubbles are mixed in at the time of bonding, that portion will be a visual obstacle, so that the polarizing plate is peeled and removed from the optical panel or the like as a bonding error, and the optical panel is reused. Such work is called rework. The polarizing plate using the resin base material as it is as a protective layer has a problem that the polarizing plate is broken during rework.

JP 2012-073580 A JP, 2017-149923, A

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a polarizing plate in which breakage during rework is suppressed.

The polarizing plate with a surface protective film of the present invention comprises an adhesive layer, a polarizer, a protective layer and a surface protective film in this order, the protective layer contains polyethylene terephthalate, and the breaking strength ratio of the protective layer is 1.9. Is about 2.4.
In one embodiment, an antiblocking layer is further provided between the protective layer and the surface protective film, and the surface roughness Ra of the antiblocking layer is 5.0 nm to 15.0 nm.

According to the present invention, in the polarizing plate with a surface protective film, by optimizing the breaking strength ratio of the protective layer, it is possible to provide a polarizing plate with a surface protective film in which breakage during rework is suppressed.

It is a schematic sectional drawing of the polarizing plate with a surface protection film by one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Polarizing Plate with Surface Protective Film FIG. 1 is a schematic sectional view of a polarizing plate with a surface protective film according to one embodiment of the present invention. The polarizing plate 100 with a surface protective film of the illustrated example has an adhesive layer 10, a polarizer 20, a protective layer 30, and a surface protective film 50. Although not shown, an undercoat layer may be typically formed between the polarizer 20 and the protective layer 30. The protective layer comprises polyethylene terephthalate (PET). As described below, the polarizer applies a polyvinyl alcohol (PVA)-based resin solution to a resin base material and dries it to form a PVA-based resin layer, and stretches a laminate of the PVA-based resin layer and the resin base material. The PVA-based resin layer becomes a polarizer by dyeing or the like. When the undercoat layer is formed, the undercoat layer is formed on one side of the resin base material, and the PVA-based resin layer is formed on the surface of the undercoat layer. In the embodiment of the present invention, the resin base material is used as it is as the protective layer.

In the embodiment of the present invention, the breaking strength ratio of the protective layer is 1.0 to 2.4, and more preferably 1.3 to 1.9. The ratio of breaking strength ratio, the film (in this case, the protective layer) is the maximum stress when broken, the breaking strength (BS _M) and the direction of the breaking strength perpendicular to the conveying direction of the conveying direction (BS _T) is a _(BS M / _{BS T).} When the protective layer has the breaking strength ratio as described above, a polarizing plate in which breaking during rework is suppressed can be obtained.

In the embodiment of the present invention, the polarizing plate 100 with a surface protective film may have a blocking prevention layer 40 as needed, as in the illustrated example. The surface roughness Ra of the anti-blocking layer is preferably 5.0 nm to 15.0 nm, more preferably 7.0 nm to 10.0 nm. The surface roughness Ra can be determined according to JIS B 0601.

B. Adhesive Layer The adhesive layer 10 is typically composed of an acrylic adhesive. The pressure-sensitive adhesive layer 10 is formed on one surface of a polarizer 20 described below, and is provided for the purpose of sticking an optical panel or the like and a polarizing plate.

The thickness of the pressure-sensitive adhesive layer is preferably 1 μm to 150 μm, more preferably 2 μm to 125 μm, further preferably 3 μm to 110 μm, particularly preferably 5 μm to 95 μm, and most preferably 10 μm to 80 μm. ..

C. Polarizer The polarizer 20 is typically composed of a resin film containing a dichroic material.

Any appropriate resin film that can be used as a polarizer can be adopted as the resin film. The resin film is typically a polyvinyl alcohol-based resin (hereinafter referred to as “PVA-based resin”) film.

Any appropriate resin may be used as the PVA-based resin forming the PVA-based resin film. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. .. The saponification degree can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizer having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

Examples of the dichroic substance contained in the resin film include iodine and organic dyes. These may be used alone or in combination of two or more. Preferably, iodine is used.

The thickness of the polarizer is preferably 15 μm or less, more preferably 1 μm to 12 μm, further preferably 3 μm to 10 μm, and particularly preferably 3 μm to 8 μm. When the thickness of the polarizer is in such a range, curling at the time of heating can be favorably suppressed, and good appearance durability at the time of heating can be obtained. Further, when the thickness of the polarizer is in such a range, it can contribute to the thinning of the polarizing plate with a surface protective film (as a result, the polarizing plate and the image display device).

The polarizer 20 can be typically formed by the method described in the section G below.

D. Protective Layer The protective layer 30 contains PET as described above. That is, as the protective layer 30, the resin base material in the method described in the item G described later is used as it is.

The breaking strength ratio of the protective layer is 1.0 to 2.4, and more preferably 1.3 to 1.9. By having such a breaking strength ratio, a polarizing plate in which breaking during rework is suppressed can be obtained.

In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate resin is preferably used as a material for forming the resin base material (protective layer). Among them, an amorphous (hard to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate-based resin include a copolymer further containing isophthalic acid and/or cyclohexanedicarboxylic acid as a dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol or diethylene glycol as a glycol.

In a preferred embodiment, the resin base material is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a resin base material has extremely excellent stretchability and can suppress crystallization during stretching. It is considered that this is because the main chain is largely bent by introducing the isophthalic acid unit. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a resin base material having extremely excellent stretchability can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all repeating units. By setting such a content ratio, the crystallinity can be favorably increased in the drying shrinkage treatment described below.

The glass transition temperature (Tg) of the resin base material is preferably 170° C. or lower, more preferably 120° C. or lower. In one embodiment, the glass transition temperature of the resin substrate is preferably 60°C or higher. In another embodiment, the glass transition temperature may be lower than 60° C. when the resin base material is not deformed when the coating liquid containing the PVA-based resin is applied and dried. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

The water absorption of the resin substrate is preferably 0.2% or more, more preferably 0.3% or more. On the other hand, the water absorption rate of the resin base material is preferably 3.0% or less, more preferably 1.0% or less. The water absorption rate is a value determined according to JIS K 7209.

The thickness of the protective layer is preferably 10 μm to 120 μm.

E. Blocking Prevention Layer The blocking prevention layer 40 contains, for example, a conductive material and a binder resin. With such a configuration, excellent blocking resistance can be realized and manufacturing efficiency can be improved. Further, it can be excellent in antistatic property. Details of the conductive material and the binder resin are described in JP-A-2005-125233, the description of which is incorporated herein by reference.

The anti-blocking layer is provided by applying and drying a resin composition containing the conductive material and the binder resin on the protective layer. The resin composition is preferably aqueous. Details of the resin composition are described in JP-A-2005-125233, the description of which is incorporated herein by reference.

The surface roughness Ra of the anti-blocking layer is 5.0 nm to 15.0 nm, and more preferably 7.0 nm to 10.0 nm. By having such a surface roughness Ra, a polarizing plate with a surface protective film in which breakage during rework is suppressed can be obtained.

The thickness of the anti-blocking layer is preferably 50 nm to 300 nm, more preferably 60 nm to 150 nm.

F. Surface Protection Film The surface protection film 50 includes a base material layer 51 and an adhesive layer 52. The surface protective film 50 is releasably attached to the polarizing plate (the blocking layer 40 in the illustrated example) via the adhesive layer 52.

The thickness of the surface protective film is preferably 5 μm to 500 μm, more preferably 10 μm to 450 μm, further preferably 15 μm to 400 μm, and particularly preferably 20 μm to 300 μm.

The high-speed peeling force of the surface protective film is preferably 0.1N to 2.0N. In the present specification, the high-speed peeling force means, in a polarizing plate with a surface protective film, when peeling at a peeling angle of 180° and a peeling speed of 30 m/min at 23° C.×50% RH with respect to the polarizing plate of the surface protective film. The required power.

The base material layer 51 may be only one layer or two or more layers. The base material layer may be stretched.

As the material of the base material layer 51, any appropriate material can be adopted depending on the application. Examples include plastics, paper, metal films, and non-woven fabrics. Preferred is plastic. That is, the base material layer is preferably a plastic film. The base material layer 51 may be made of one kind of material, or may be made of two or more kinds of materials. For example, it may be composed of two or more kinds of plastics. Details of the plastic are described in JP-A-2017-149923, and the description of the publication is incorporated herein by reference.

The thickness of the base material layer 51 is preferably 4 μm to 450 μm, more preferably 8 μm to 400 μm, still more preferably 12 μm to 350 μm, and particularly preferably 16 μm to 250 μm.

As the pressure-sensitive adhesive contained in the pressure-sensitive adhesive layer 52, any suitable pressure-sensitive adhesive can be adopted as long as the effects of the present invention are not impaired. From the viewpoint that the effect of the present invention can be further expressed, preferably, at least one selected from an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive and a silicone-based pressure-sensitive adhesive, and in that the effect of the present invention can be further expressed, More preferably, it is an acrylic adhesive. The acrylic pressure-sensitive adhesive preferably contains a (meth)acrylic polymer having a hydroxy group and a carboxyl group. The details of the acrylic pressure-sensitive adhesive are described in JP-A-2014-111703, and the description in that publication is incorporated herein by reference.

The thickness of the pressure-sensitive adhesive layer 52 is preferably 1 μm to 150 μm, more preferably 2 μm to 140 μm, further preferably 3 μm to 130 μm, and particularly preferably 4 μm to 120 μm.

G. Method for producing polarizing plate with surface protective film The polarizing plate with surface protective film of the present invention can be produced by any appropriate method. An example will be described below.

G-1. Manufacturing Method of Polarizing Plate The manufacturing method of the polarizing plate in the above-mentioned polarizing plate with a surface protective film typically includes forming a PVA-based resin layer on one side of a resin base material, and the resin base material and the PVA-based resin layer. Stretching and dyeing a laminate with a resin layer to make the polyvinyl alcohol-based resin layer a polarizer. When the undercoat layer is formed, the undercoat layer is formed on one side of the resin base material, and the PVA-based resin layer is formed on the surface of the undercoat layer.

G-2. Formation of PVA-based resin layer Any appropriate method can be adopted as a method of forming the PVA-based resin layer. Preferably, a PVA-based resin layer is formed by applying a coating liquid containing a PVA-based resin on a resin base material and drying it. When the undercoat layer is formed, the undercoat layer forming composition is applied to one side of the resin substrate to form the undercoat layer, and the PVA-based resin layer is formed on the surface of the undercoat layer. By forming the undercoat layer, the adhesion between the resin base material and the PVA resin layer can be improved.

As described above, PET is used as the material for forming the resin base material.

The thickness of the resin substrate before stretching is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form the PVA-based resin layer. When it exceeds 300 μm, for example, in the underwater stretching, it may take a long time for the resin base material to absorb water, and an excessive load may be required for the stretching.

The undercoat layer forming composition preferably contains a PVA-based component and a polyolefin-based component. With such a composition, it is possible to obtain a laminate having excellent adhesion and excellent appearance. Any appropriate PVA-based resin can be used as the PVA-based component. Specific examples include PVA and modified PVA. Examples of the modified PVA include PVA modified with an acetoacetyl group, a carboxylic acid group, an acrylic group and/or a urethane group. Among these, acetoacetyl-modified PVA is preferably used.

Any appropriate method can be adopted as a method of applying the composition for forming the undercoat layer. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (a comma coating method, etc.) and the like can be mentioned.

The composition for forming an undercoat layer is preferably applied so that the thickness of the obtained undercoat layer is 500 nm to 3000 nm, and more preferably 800 nm to 2000 nm. If the undercoat layer is too thin, sufficient adhesion may not be obtained. On the other hand, when the thickness of the undercoat layer is too thick, problems such as cissing may occur and unevenness may occur in the obtained coating film when the PVA-based resin coating layer described later is formed, and the laminate having excellent appearance may be obtained. It can be difficult to get a body.

After applying the composition for forming the undercoat layer, the coating film can be dried. The drying temperature is, for example, 50° C. or higher. Details of the composition for forming an undercoat layer and the method for forming the undercoat layer are described in JP-A-2017-114052, and the description of the publication is incorporated herein by reference.

The coating liquid is typically a solution in which the PVA resin is dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the resin base material.

You may mix an additive with a coating liquid. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer. Further, examples of the additive include an easily adhesive component. By using the easy-adhesion component, the adhesion between the resin base material and the PVA-based resin layer can be improved. As a result, for example, a defect such as peeling of the PVA-based resin layer from the resin base material can be suppressed, and dyeing and underwater stretching described below can be favorably performed. As the easy-adhesion component, for example, modified PVA such as acetoacetyl-modified PVA is used.

Any appropriate method can be adopted as a method for applying the application liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (a comma coating method, etc.) and the like can be mentioned.

The coating/drying temperature of the coating liquid is preferably 50° C. or higher.

Prior to forming the PVA-based resin layer, the resin base material may be subjected to surface treatment (for example, corona treatment), or the easy adhesion layer may be formed on the resin base material. By performing such a treatment, the adhesion between the resin base material and the PVA-based resin layer can be improved.

The thickness of the PVA-based resin layer (before stretching) is preferably 3 μm to 20 μm.

G-3. Stretching Any appropriate method can be adopted as a stretching method for the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching by passing a laminate between rolls having different peripheral speeds). Free end drawing is preferred.

The stretching direction of the laminate can be set appropriately. In one embodiment, the long laminate is stretched in the longitudinal direction. In this case, typically, a method is adopted in which the laminate is stretched between rolls having different peripheral speeds. In another embodiment, the elongated laminate is stretched in the width direction. In this case, a stretching method using a tenter stretching machine is typically employed.

The stretching method is not particularly limited, and may be an in-air stretching method or an underwater stretching method. The underwater stretching method is preferred. According to the underwater stretching method, it is possible to stretch at a temperature lower than the glass transition temperature (typically about 80° C.) of the resin base material or the PVA-based resin layer, and suppress the crystallization of the PVA-based resin layer. However, it can be stretched at a high ratio. As a result, a polarizer having excellent optical characteristics can be manufactured.

Stretching of the laminate may be performed in one stage or in multiple stages. When performing in multiple stages, for example, the above free-end stretching and fixed-end stretching may be combined, or the above-mentioned underwater stretching method and aerial stretching method may be combined. Moreover, when performing in multiple steps, the draw ratio (maximum draw ratio) of the laminated body described later is the product of the draw ratio of each step.

The stretching temperature of the laminate can be set to any appropriate value depending on the resin base material, the stretching method, and the like. When the in-air stretching method is adopted, the stretching temperature is preferably the glass transition temperature (Tg) of the resin substrate or more, more preferably the glass transition temperature (Tg) of the resin substrate+10° C. or more, particularly preferably Tg+15° C. That is all. On the other hand, the stretching temperature of the laminate is preferably 170° C. or lower. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems due to the crystallization (for example, hinder the orientation of the PVA-based resin layer due to stretching). it can.

When the underwater stretching method is adopted, the liquid temperature of the stretching bath is 60°C or higher, preferably 65°C to 85°C, more preferably 65°C to 75°C. With such a temperature, the PVA-based resin layer can be stretched at a high magnification while suppressing the dissolution. Specifically, as described above, the glass transition temperature (Tg) of the resin base material is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 60° C., it may not be possible to stretch well even if the plasticization of the resin substrate by water is taken into consideration. On the other hand, the higher the temperature of the drawing bath, the higher the solubility of the PVA-based resin layer, and there is a risk that excellent optical characteristics will not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

When the underwater stretching method is adopted, it is preferable that the laminate is immersed in a boric acid aqueous solution and stretched (boric acid underwater stretching). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be provided with rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can generate a tetrahydroxyborate anion in an aqueous solution to crosslink with a PVA-based resin by hydrogen bond. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer, to perform good stretching, and to manufacture a polarizer having excellent optical characteristics.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in water which is a solvent. In the present invention, the concentration of boric acid is 3.5% by weight or less, preferably 2.0% by weight to 3.5% by weight, and more preferably 2.5% by weight to 3.5% by weight. .. When the boric acid concentration is in such a range, the resulting polarizer can have both excellent optical characteristics and excellent durability and water resistance. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

When a dichroic substance (typically, iodine) is previously adsorbed on the PVA-based resin layer by dyeing described below, iodide is preferably added to the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Etc. Among these, potassium iodide is preferable. The iodine concentration in the polarizer can be adjusted by adjusting the potassium iodide concentration. The concentration of potassium iodide in the stretching bath is preferably 0.05 parts by weight to 15 parts by weight, and more preferably 0.5 parts by weight to 8 parts by weight with respect to 100 parts by weight of water.

The stretching ratio (maximum stretching ratio) of the laminate is preferably 5.0 times or more the original length of the laminate. Such a high draw ratio can be achieved, for example, by adopting an underwater drawing method (boric acid underwater drawing). In the present specification, the "maximum stretch ratio" refers to the stretch ratio immediately before the laminate is broken, and the stretch ratio at which the laminate is broken is confirmed separately, and is a value 0.2 lower than that value. ..

In one embodiment, after stretching the laminate at high temperature (for example, 95° C. or higher) in the air, the stretching in boric acid in water and the dyeing described below are performed. Such in-air stretching can be positioned as a preliminary or auxiliary stretching for the boric acid in-water stretching, and is hereinafter referred to as "in-air supplementary stretching".

It may be possible to stretch the laminate at a higher magnification by combining the in-air auxiliary stretching. As a result, a polarizer having more excellent optical characteristics (for example, the degree of polarization) can be manufactured. For example, when a polyethylene terephthalate-based resin is used as the resin substrate, it is preferable to combine the in-air auxiliary stretching and the boric acid in-water stretching to suppress the orientation of the resin substrate, rather than stretching only in boric acid in water. It can be stretched. As the orientation of the resin base material is improved, the drawing tension increases, which makes stable drawing difficult or breaks. Therefore, by stretching while suppressing the orientation of the resin substrate, the laminate can be stretched at a higher magnification.

Further, by combining in-air auxiliary stretching, the orientation of the PVA-based resin can be improved, and thereby the orientation of the PVA-based resin can be improved even after the drawing in boric acid in water. Specifically, by preliminarily improving the orientation of the PVA-based resin by auxiliary stretching in the air, the PVA-based resin is easily cross-linked with boric acid during stretching in boric acid in water, and boric acid serves as a node. It is presumed that the orientation of the PVA-based resin will be high even after the drawing in boric acid in water by stretching in this state. As a result, a polarizer having excellent optical characteristics (for example, the degree of polarization) can be manufactured.

The draw ratio in the in-air auxiliary drawing is preferably 3.5 times or less. The stretching temperature of the in-air auxiliary stretching is preferably equal to or higher than the glass transition temperature of the PVA-based resin. The stretching temperature is preferably 95°C to 150°C. In addition, the maximum draw ratio in the case of combining the in-air auxiliary drawing and the above boric acid in-water drawing is preferably 5.0 times or more, more preferably 5.5 times or more, and further preferably, with respect to the original length of the laminate. Is 6.0 times or more.

G-4. Dyeing The PVA-based resin layer is typically dyed by adsorbing iodine to the PVA-based resin layer. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and a method of applying the dyeing solution to the PVA-based resin layer. Examples include a method of spraying. A preferred method is to immerse the PVA-based resin layer (laminate) in the dyeing solution. This is because iodine can be favorably adsorbed.

The dyeing solution is preferably an aqueous iodine solution. The content of iodine is preferably 0.1 to 0.5 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. As mentioned above, potassium iodide is preferable as the iodide. The iodine concentration in the polarizer can be adjusted by adjusting the potassium iodide concentration. The content of potassium iodide in the dyeing bath is preferably 0.02 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of water. The liquid temperature at the time of dyeing the dyeing liquid is preferably 20°C to 50°C in order to suppress dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes in order to secure the transmittance of the PVA-based resin layer. Further, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or simple substance transmittance of the finally obtained polarizer falls within a predetermined range. In one embodiment, the immersion time is set so that the obtained polarizer has a polarization degree of 99.98% or more. In another embodiment, the immersion time is set so that the single transmittance of the obtained polarizer is 43.0% or less. In any of the embodiments, the iodine concentration, the potassium iodide concentration and the immersion time in the dyeing solution can be adjusted so that the iodine concentration and the potassium concentration in the obtained polarizer will be in the desired ranges.

The dyeing process can be performed at any appropriate timing. When the underwater stretching is performed, it is preferably performed before the underwater stretching.

G-5. Other Treatments The PVA-based resin layer (laminate) may be appropriately subjected to a treatment for a polarizer other than stretching and dyeing. Examples of the treatment for producing a polarizer include insolubilization treatment, crosslinking treatment, washing treatment, drying treatment, and heat treatment. The number and order of these processes are not particularly limited.

The insolubilization treatment is typically performed by immersing the PVA-based resin layer (laminate) in a boric acid aqueous solution. By applying the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 50°C. Preferably, the insolubilization treatment is performed before the underwater stretching or the dyeing treatment.

The cross-linking treatment is typically performed by immersing the PVA-based resin layer (laminate) in a boric acid aqueous solution. Water resistance can be imparted to the PVA-based resin layer by performing the crosslinking treatment. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Further, when the crosslinking treatment is performed after the dyeing treatment, it is preferable to further add iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. As mentioned above, potassium iodide is preferable as the iodide. The iodine concentration in the polarizer can be adjusted by adjusting the potassium iodide concentration. The content of potassium iodide in the crosslinking bath is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 60°C. Preferably, the crosslinking treatment is performed before the underwater stretching. In a preferred embodiment, in-air stretching, dyeing treatment and crosslinking treatment are performed in this order.

The cleaning treatment is typically performed by immersing the PVA-based resin layer (laminate) in an aqueous potassium iodide solution. The drying temperature in the above drying treatment is preferably 30°C to 100°C.

A heat treatment may be further performed after the drying treatment. Examples of the heat treatment include non-contact (holding with a tenter) heating, continuous heating with a roll, and oven heating. Preferably, non-contact (tenter gripping) heating can be adopted. In the tenter gripping heating, heating is performed while gripping the end portion of the film to be stretched (here, the resin base material) with a clip. By such heat treatment, shrinkage of the resin base material in the TD (lateral) direction is suppressed. That is, it is considered that the resin base material is in a pseudo biaxially stretched state and the biaxiality of the resin base material is increased. By increasing the biaxiality of the resin substrate, a desired breaking strength ratio of the resin substrate (protective layer) can be obtained, and as a result, a polarizing plate with a surface protective film in which breaking during rework is suppressed is obtained. Can be done. Furthermore, the heat treatment may promote crystallization of the PET-based resin base material.

As described above, the polarizer is formed on the resin base material. The resin base material can be used as it is as the protective layer. Therefore, a polarizing plate having a constitution of resin base material (protective layer)/polarizer can be obtained.

G-6. Lamination of Surface Protective Film The surface protective film is attached to the protective layer surface of the polarizing plate obtained above via the pressure-sensitive adhesive layer 52. Furthermore, the pressure-sensitive adhesive layer 10 is formed on the surface of the polarizer, and a separator is releasably attached to the surface of the pressure-sensitive adhesive as needed. In this way, a polarizing plate with a surface protective film can be obtained.

H. Image Display Device The polarizing plate with a surface protective film according to the embodiment of the present invention can be applied to an image display device. Typically, the polarizing plate with a surface protection film is arranged on the viewing side of the image display device with the surface protection film on the viewing side, and in practical use, the surface protection film is peeled off. Typical examples of the image display device include a liquid crystal display device, an organic electroluminescence (EL) display device, and a quantum dot display device. A liquid crystal display device is preferable, and an IPS mode liquid crystal display device is more preferable. This is because the hue improvement in the diagonal direction is more remarkable.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The measuring method of each characteristic is as follows.

1. Breaking strength ratio This is the ratio (BSM/BST) of the breaking strength (BSM) in the carrying direction and the breaking strength (BST) in the direction orthogonal to the carrying direction.
Conditions: Measured according to JIS K 7127. (600 mm/min)

2. Floating Edges The state of the end faces of the polarizing plate to which the surface protective film was attached was confirmed before the evaluation of reworkability.
The distance that the surface protective film and the pressure-sensitive adhesive layer 52 float from the polarizing plate was measured.
◯: No floating Δ: 10 μm to 99 μm
X: 100 μm or more

3. Rework <Evaluation of reworkability>
The produced polarizing film with an adhesive layer was cut into 32 inches to prepare a sample. The sample was attached to a non-alkali glass plate using a laminator, and then autoclaved at 50° C. and 5 atm for 15 minutes to completely adhere the sample. Then, using a rework device, the success rate was confirmed when reworking was performed under the conditions of a peeling angle of 90° and a peeling speed of 0.6 m/min. The number of samples was two. And the following criteria evaluated.
◎: 100% rework
◯: Rework 50% or more ×: Rework 25% or less

[Example 1]
As the resin base material, an elongated isophthalic acid-copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long length, a water absorption of 0.75% and a Tg of 75° C. was used.
Next, corona treatment (treatment condition: 55 W·min/m ² ) is applied to one surface of the resin substrate, an undercoat layer having a thickness of 2 μm is formed on the corona-treated surface, and polyvinyl alcohol (having a polymerization degree of 4200) is formed on the undercoat layer. , Saponification degree 99.2 mol %), acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosephimmer Z410") 10 parts by weight, and an aqueous solution containing 13 parts by weight potassium iodide. It was applied and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, and a laminate was prepared.

The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130° C. (in-air auxiliary stretching).
Next, the laminated body was immersed in an insolubilizing bath at a liquid temperature of 40° C. (boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Then, it is immersed for 60 seconds in a dyeing bath having a liquid temperature of 30° C. (an iodine aqueous solution obtained by mixing 0.3 part by weight of iodine and 2.0 parts by weight of potassium iodide with 100 parts by weight of water). (Dyeing process).
Then, it was immersed in a crosslinking bath at a liquid temperature of 40° C. (boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds. (Crosslinking treatment).
Then, while the laminate was immersed in a boric acid aqueous solution (boric acid concentration 3.0% by weight) at a liquid temperature of 70° C., the total draw ratio was 5.5 in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so as to double the length (underwater stretching).
After that, the laminate was immersed in a cleaning bath having a liquid temperature of 20° C. (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, the laminated body was dried in an oven kept at 70° C. (drying treatment).
Further, the PET film was crystallized by heating the film at 100° C. for 30 seconds while holding both ends of the film by a tenter heating method (heat treatment).
In this way, a polarizer having a thickness of 5 μm was formed on the resin base material to obtain a polarizing plate having a structure of polarizer/resin base material (protective layer).

Further, a surface protective film was attached to the surface of the resin substrate (protective layer) of the obtained polarizing plate. Furthermore, the pressure-sensitive adhesive layer 10 was formed on the surface of the polarizer (the surface opposite to the protective layer), and the separator was releasably attached to the surface of the pressure-sensitive adhesive to obtain a polarizing plate with a surface protective film. The breaking strength ratio of the protective layer was 1.9. The obtained polarizing plate with a surface protection film was used for evaluation of edge floating and rework. The results are shown in Table 1.

[Comparative Example 1]
A polarizing plate with a surface protective film was produced in the same manner as in Example 1 except that heating was performed at 100° C. for 30 seconds by a roll heating method. The breaking strength ratio of the resulting protective layer was 2.5. The obtained polarizing plate with a surface protective film was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

As is clear from Table 1, the polarizing plates with surface protective films of the examples of the present invention have no floating at the edges and are prevented from being broken by rework.

The polarizing plate with a surface protective film of the present invention can be suitably used for an image display device such as a liquid crystal display device, an organic EL display device and a quantum dot display device.

10 Adhesive Layer 20 Polarizer 30 Protective Layer 40 Anti-blocking Layer 50 Surface Protective Film 51 Base Material Layer 52 Adhesive Layer 100 Polarizing Plate with Surface Protective Film

Claims (3)

An adhesive layer, a polarizer, a protective layer and a surface protective film are provided in this order,
The protective layer comprises polyethylene terephthalate,
The breaking strength ratio of the protective layer is 1.9 to 2.4,
Polarizing plate with surface protection film. The polarizing plate with a surface protective film according to claim 1, further comprising an antiblocking layer between the protective layer and the surface protective film, and the surface roughness Ra of the antiblocking layer is 5.0 nm to 15.0 nm. Board. An image display device comprising the polarizing plate with a surface protective film according to claim 1.

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