CN107924016B

CN107924016B - Single-side protective polarizing film, polarizing film with adhesive layer, and image display device

Info

Publication number: CN107924016B
Application number: CN201680049359.5A
Authority: CN
Inventors: 徐菁璠; 上野友德; 三田聪司; 茂手木佑辅; 岸敦史
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2015-08-27
Filing date: 2016-08-05
Publication date: 2021-05-07
Anticipated expiration: 2036-08-05
Also published as: JP6675776B2; TWI822650B; KR20180044884A; JP2017044882A; CN107924016A; TW201727264A; WO2017033705A1

Abstract

The one-sided protective polarizing film of the present invention having a protective film only on one side of a polarizer has a transparent resin layer on at least one side of the polarizer, the protective film is provided with or without a transparent resin layer provided on at least one side of the polarizer, and the transparent resin layer contains at least one selected from inorganic salts of alkali metals and inorganic salts of alkaline earth metals. The single-sided protective polarizing film has crack resistance, and can suppress the reduction of optical characteristics and the bluing of color tone in a heating and humidifying test to a low level.

Description

Single-side protective polarizing film, polarizing film with adhesive layer, and image display device

Technical Field

The present invention relates to a single-sided protective polarizing film having a protective film only on one side of a polarizer. The present invention also relates to a polarizing film with an adhesive layer, which uses the above-mentioned one-side protective polarizing film. The above-mentioned single-side protective polarizing film or pressure-sensitive adhesive layer-attached polarizing film may be used alone or in the form of an optical film in which the above-mentioned polarizing film is laminated to form an image display device such as a Liquid Crystal Display (LCD) or an organic EL display device.

Background

In a liquid crystal display device, it is essential to dispose polarizing films on both sides of a glass substrate forming a surface of a liquid crystal panel in view of an image forming method. As the polarizing film, a polarizing film obtained by laminating a protective film on one surface or both surfaces of a polarizer made of a dichroic material such as a polyvinyl alcohol film and iodine with a polyvinyl alcohol adhesive or the like is generally used.

In addition, the polarizing film has a problem that cracks are easily generated in the entire absorption axis direction of the polarizer due to a change in shrinkage stress of the polarizer in a severe environment of thermal shock (for example, a test is performed at a high temperature of 95 ℃ for 250 hours). That is, the polarizing film has insufficient crack resistance to thermal shock under the above severe environment. In particular, in the case of a one-side protective polarizing film in which a protective film is provided only on one surface of a polarizer from the viewpoint of thinning, there is a problem that an excessive stress is generated inside the polarizer due to a difference between a shrinkage stress of the polarizer on the side on which the protective film is provided and a shrinkage stress of the polarizer on the side opposite to the protective film, and various cracks from a fine crack of several hundreds of μm to a through crack penetrating the entire surface are easily generated in the absorption axis direction of the polarizer.

In order to suppress the occurrence of such cracks, for example, a polarizing film with an adhesive layer has been proposed in which a protective layer having a tensile elastic modulus of 100MPa or more is provided on a single-side protective polarizing film, and an adhesive layer is further provided on the protective layer (patent document 1). Further, a polarizing film with an adhesive layer has been proposed which has a protective layer formed of a cured product of a curable resin composition on one surface of a polarizer having a thickness of 25 μm or less, a protective film on the other surface of the polarizer, and an adhesive layer on the outer side of the protective layer (patent document 2). The polarizing films with an adhesive layer described in

patent documents

1 and 2 are effective in suppressing the occurrence of cracks. In addition, from the viewpoint of reducing the thickness and weight of a polarizer while suppressing the occurrence of cracks, it has been proposed to provide a protective layer made of a water-soluble film-forming composition (polyvinyl alcohol resin composition) on at least one surface of a polarizer (patent document 3).

Documents of the prior art

Patent document

Patent document 1: japanese patent application laid-open No. 2010-009027

Patent document 2: japanese patent laid-open publication No. 2013-160775

Patent document 3: japanese patent laid-open publication No. 2005-043858

Disclosure of Invention

Problems to be solved by the invention

According to the above patent documents 1 to 3, the protective layer can suppress shrinkage of the front polarizer in the absorption axis direction to some extent, and the generation of the crack can be suppressed. In forming the protective layer, a material containing a polyvinyl alcohol resin is preferable from the viewpoints of, for example, adhesion to a polarizer, coating stability, productivity, and the like. In particular, patent document 3 describes: the polyvinyl alcohol resin is preferably blended with a water-soluble epoxy resin, a dialdehyde such as glyoxal, isocyanate, a metal ion such as an iron ion, a cobalt ion, a nickel ion, a copper ion, a zinc ion, an aluminum ion, or a zirconium ion, a curable component, or a crosslinking agent.

However, the protective layer containing a polyvinyl alcohol resin has a problem that the rate of deterioration of optical properties in a heating and humidifying test is large. In addition, the one-side protective polarizing film having the protective layer has a problem of bluing (bluish color tone) in a heating and humidifying test, as compared with the case of not having the protective layer. Since bluing of the polarizing film is easily observed by the human eye, the polarizing film is expected to have stable color tone.

In addition, when the crack is suppressed by the protective layer, the larger the thickness of the protective layer is, the better, but the larger the thickness of the protective layer is, the larger the optical characteristic degradation rate in the heating and humidifying test becomes, and the tendency of bluing becomes large. In addition, the polarizer is also thinned. When the polarizer used for the polarizing film is thinned, the change in the shrinkage stress of the polarizer is small. However, since the polarizer itself is thinned, the polarizer is broken even with a force weaker than that in the conventional art, and therefore, the crack resistance is insufficient when a thin polarizer is used.

The present invention has an object to provide a one-side protective polarizing film having a protective film only on one side of a polarizer and a transparent resin layer on at least one side of the polarizer, which has crack resistance and can suppress a decrease in optical characteristics and blue-turning in a heating and humidifying test to a small level.

Another object of the present invention is to provide a polarizing film with an adhesive layer, which uses the above polarizing film. Further, the present invention relates to an image display device having the above polarizing film or polarizing film with an adhesive layer.

Means for solving the problems

As a result of intensive studies, the present inventors have found that the above problems can be solved by the following one-side protective polarizing film and the like, and have completed the present invention.

That is, the present invention relates to a one-sided protective polarizing film having a protective film only on one side of a polarizer, wherein,

a transparent resin layer is provided on at least one surface of the polarizer,

the protective film is provided with or without a transparent resin layer on at least one surface of the polarizer,

the transparent resin layer contains at least one selected from inorganic salts of alkali metals and inorganic salts of alkaline earth metals.

In the one-side protective polarizing film, the inorganic salt is preferably an iodide. Further, it is preferable that the iodide is potassium iodide.

In the one-side protective polarizing film, a ratio (b/a) of a content (a: ionic strength) of the iodine component contained in the polarizer to a content (b: ionic strength) of the inorganic salt component contained in the transparent resin layer is preferably 0.08 or more.

In the one-side protective polarizing film, the transparent resin layer is preferably formed of a material containing a water-soluble resin. The water-soluble resin is preferably a polyvinyl alcohol resin.

In the one-side protective polarizing film, the thickness of the transparent resin layer is preferably 0.2 μm or more. The thickness of the transparent resin layer is preferably 6 μm or less.

In the one-side protective polarizing film, it is preferable that the polarizer has a thickness of 15 μm or less.

In the one-side protective polarizing film, the polarizer preferably has optical properties represented by a single transmittance T and a polarization degree P in a range represented by the following formula:

P＞－(10^{0.929T－42.4}-1) x 100 (wherein T < 42.3), and

p is more than or equal to 99.9 (wherein, T is more than or equal to 42.3).

The present invention also relates to a polarizing film with an adhesive layer, which comprises the above-mentioned one-side protective polarizing film and the adhesive layer.

The present invention also relates to an image display device comprising the above-mentioned single-side protective polarizing film or the above-mentioned polarizing film with an adhesive layer.

ADVANTAGEOUS EFFECTS OF INVENTION

The one-sided protective polarizing film of the present invention is provided with a transparent resin layer on a polarizer, and thus can suppress the occurrence of cracks by the transparent resin layer.

On the other hand, in the one-side protective polarizing film provided with a transparent resin layer, the transparent resin layer is provided directly on the polarizer. Therefore, it was found that in the heating and humidifying test, the iodine component (iodine, iodide, and a complex thereof) and the potassium component (derived from iodide) in the polarizer were transferred to the transparent resin layer. It was also found that the iodine component and the potassium component transferred to the transparent resin layer cause a decrease in the optical properties of the one-side protective polarizing film and bluing.

In the one-side protective polarizing film of the present invention, an inorganic salt of an alkali metal and/or an inorganic salt of an alkaline earth metal is contained in the transparent resin layer. The inorganic salt is an iodide contained in the polarizer or a similar compound thereof. It is considered that the iodine component and the potassium component in the polarizer and the inorganic salt in the transparent resin layer are in a certain equilibrium relationship. Therefore, it is considered that the migration of the iodine component and the potassium component in the polarizer to the transparent resin layer is suppressed. Similarly, it is considered that the inorganic salt in the transparent resin layer is not transferred to the polarizer. As a result, it is considered that the single-sided protective polarizing film of the present invention can suppress the reduction of optical characteristics and the blue-turning in the heating and humidifying test to a low level even if the transparent resin layer is provided.

The single-sided protective polarizing film of the present invention is suitable for use in a case where a thin polarizer (for example, a thickness of 15 μm or less) is used. In the case of a thin polarizer, although the change in the shrinkage stress of the polarizer is small, the crack resistance is insufficient because the polarizer itself is made thin. According to the polarizing film of the present invention, even when a thin polarizer is used, since the polarizing film has a transparent resin layer, it is possible to improve crack resistance.

Drawings

Fig. 1 is an example of a schematic cross-sectional view of a polarizing film of the present invention.

Fig. 2 is an example of a schematic cross-sectional view of the polarizing film of the present invention.

Fig. 3 is an example of a schematic cross-sectional view of the polarizing film of the present invention.

Description of the symbols

1 polarizer

2 a transparent resin layer

3 protective film

10 single-sided protective polarizing film

Detailed Description

Hereinafter, the single-sided protective polarizing film 10 of the present invention will be described with reference to fig. 1 to 3. The one-side protective polarizing film 10 has a protective film 3 only on one surface of the polarizer 1, and has a transparent resin layer 2 on at least one surface of the polarizer 1. The transparent resin layer 2 is (directly) provided on the polarizer 1. In fig. 1, a transparent resin layer 2 is provided only on one side of a polarizer 1, and a protective film 3 is provided on the polarizer 1 on the side where the transparent resin layer 2 is not provided. In fig. 2, a polarizer 1 has transparent resin layers 2 on both sides thereof, and a protective film 3 is provided on one side of the transparent resin layer 2. In fig. 3, the polarizer 1 has a transparent resin layer 2 only on one side, and a protective film 3 is provided on one side of the transparent resin layer 2.

Although not shown, the protective film 3 may be used by stacking 2 or more sheets. Further, although not shown, the polarizer 1 or the transparent resin layer 2 and the protective film 3 are laminated with an adhesive layer, an undercoat layer (primer layer), and the like interposed therebetween. Further, although not shown, an easy-adhesion layer may be provided on the protective film 3, or the easy-adhesion layer and the adhesive layer may be laminated after performing activation treatment.

Further, although not shown, an adhesive layer may be provided on the one-side protective polarizing film 10 of the present invention. Further, a separator may be provided on the adhesive layer. In addition, a surface protective film may be provided on the one-side protective polarizing film 10 of the present invention.

< polarizer >

The polarizer is not particularly limited, and various polarizers can be used. Examples of polarizers include: a film obtained by adsorbing a dichroic substance such as iodine or a dichroic dye to a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene-vinyl acetate copolymer partially saponified film and uniaxially stretching the film, a polyene-based alignment film such as a dehydrated polyvinyl alcohol or a desalted polyvinyl chloride film, or the like. Among these, a polarizer made of a dichroic material such as a polyvinyl alcohol film and iodine is preferable. The thickness of these polarizers is not particularly limited, but is usually 2 to 25 μm.

The polarizer obtained by uniaxially stretching a polyvinyl alcohol film dyed with iodine can be produced, for example, by dyeing polyvinyl alcohol by immersing it in an aqueous iodine solution and stretching it to 3 to 7 times the original length. If necessary, boric acid, zinc sulfate, zinc chloride, etc. may be contained, and the container may be immersed in an aqueous solution of potassium iodide, etc. Further, the polyvinyl alcohol film may be immersed in water and washed with water before dyeing, if necessary. By washing the polyvinyl alcohol film with water, dirt and an anti-blocking agent on the surface of the polyvinyl alcohol film can be washed off, and the polyvinyl alcohol film can be swollen to prevent unevenness such as uneven dyeing. The stretching may be performed after the dyeing with iodine, or may be performed while dyeing, or may be performed after the stretching with iodine. Stretching may be carried out in an aqueous solution of boric acid, potassium iodide, or the like, or in a water bath.

As the polarizer, a thin polarizer having a thickness of 15 μm or less can be used. From the viewpoint of reduction in thickness and resistance to cracking due to thermal shock, the thickness of the polarizer is preferably 12 μm, more preferably 10 μm or less, still more preferably 8 μm or less, yet more preferably 7 μm or less, and yet still more preferably 6 μm or less. On the other hand, the thickness of the polarizer is preferably 2 μm or more, and more preferably 3 μm or more. Such a thin polarizer has excellent durability against thermal shock because of small thickness unevenness, excellent visibility, and small dimensional change.

Typical examples of the thin polarizer having a thickness of 15 μm or less include thin polarizing films (polarizers) described in japanese patent No. 4751486, japanese patent No. 4751481, japanese patent No. 4815544, japanese patent No. 5048120, japanese patent No. 5587517, international publication No. 2014/077599, and international publication No. 2014/077636, and thin polarizing films (polarizers) obtained by the production methods described in these documents.

Preferably, the polarizer is configured such that optical characteristics represented by a single transmittance T and a polarization degree P satisfy the following conditions:

P＞－(10^{0.929T－42.4}-1) x 100 (wherein T < 42.3), and

p is more than or equal to 99.9 (wherein, T is more than or equal to 42.3).

Mainly, a polarizing film configured to satisfy the above conditions has performance required as a display for a liquid crystal television using a large-sized display element. Specifically, the contrast ratio is 1000:1 or more and the maximum luminance is 500cd/m²The above. For another application, for example, the adhesive sheet can be bonded to the visible side of an organic EL display device.

As the thin polarizing film, in a production method including a step of stretching in a state of a laminate and a step of dyeing, from the viewpoint of being capable of stretching to a high magnification to improve polarizing performance, a thin polarizing film obtained by a production method including a step of stretching in an aqueous boric acid solution as described in japanese patent No. 4751486, japanese patent No. 4751481, and japanese patent No. 4815544 is preferable, and a thin polarizing film obtained by a production method including a step of stretching in an auxiliary gas atmosphere before stretching in an aqueous boric acid solution as described in japanese patent No. 4751481 and japanese patent No. 4815544 is particularly preferable. These thin polarizing films can be obtained by a process of stretching a polyvinyl alcohol resin (hereinafter, also referred to as PVA-based resin) layer and a stretching resin base material in a laminated state, and a process of dyeing. With this method, even if the PVA-based resin layer is thin, it can be stretched without causing troubles such as breakage due to stretching, because it is supported by the resin base material for stretching.

< resin substrate >

As the resin substrate (stretching resin substrate), a resin substrate suitable for producing the thin polarizing film can be used. As a material for forming the resin base material, various thermoplastic resins can be used. Examples of the thermoplastic resin include: ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide LEO resins (レオ resin), polycarbonate resins, and copolymer resins thereof. Among these, ester resins are preferred from the viewpoint of ease of production and cost reduction. The ester thermoplastic resin base material may be an amorphous ester thermoplastic resin base material or a crystalline ester thermoplastic resin base material.

The stretching step is preferably performed such that, for example, the total stretching ratio of the PVA-based resin layer is in the range of 3 to 10 times as the total stretching ratio. The total stretching ratio is preferably 4 to 8 times, and more preferably 5 to 7 times. Preferably, the total stretching ratio is 5 or more. The stretching step may be performed in the dyeing step or in another step. When stretching is involved in a step other than the stretching step, the total stretching magnification is a cumulative stretching magnification including stretching in these steps.

The dyeing step may be performed by adsorbing and aligning a dichroic dye or iodine on the PVA-based resin layer. The dyeing step may be performed together with the stretching step. The dyeing step is usually performed by immersing the substrate in the iodine solution for an arbitrary time. As the aqueous iodine solution used as the iodine solution, an aqueous solution containing iodine ions by iodine and iodide as a dissolution aid, or the like can be used. As the iodide, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like are preferable. As the iodide, potassium iodide is preferable. The iodide used in the present invention may be used in other steps in the same manner as described above.

The iodine concentration in the iodine solution is about 0.01 to 10 wt%, preferably 0.02 to 5 wt%, and more preferably 0.02 to 0.5 wt%. The iodide concentration is preferably about 0.1 to 10 wt%, more preferably 0.2 to 8 wt%. In iodine dyeing, the temperature of the iodine solution is usually about 20 to 50 ℃, preferably 25 to 40 ℃. The dipping time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

In addition to the above-described steps, for example, an insolubilization step, a crosslinking step, a drying (adjustment of moisture content) step, and the like may be performed.

In the insolubilization step and the crosslinking step, a boron compound is used as a crosslinking agent. The order of these steps is not particularly limited. The crosslinking step may be performed together with the dyeing step and the stretching step. The insolubilization step and the crosslinking step may be performed plural times. Examples of the boron compound include boric acid and borax. The boron compound is usually used in the form of an aqueous solution or a water-organic solvent mixed solution. An aqueous solution of boric acid is generally used. The boric acid concentration of the aqueous boric acid solution is about 1 to 10 wt%, preferably 2 to 7 wt%. When heat resistance is imparted by the crosslinking degree, the boric acid concentration is preferably set as described above. The boric acid aqueous solution may contain an iodide such as potassium iodide. When the aqueous boric acid solution contains an iodide, the iodide concentration is preferably about 0.1 to 10% by weight, more preferably 0.5 to 8% by weight.

As described above, the polarizer is obtained by subjecting a PVA-based resin or the like to a dyeing step or the like. As a result, the polarizer contains an iodide such as potassium iodide for hue adjustment and iodine for controlling polarization characteristics. The content of the iodine component (iodine, iodide, and a complex thereof) and the potassium component (derived from iodide) in the polarizer is usually 1 to 10% by weight, preferably 5 to 8% by weight.

< protective film >

The material constituting the protective film is preferably excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, and the like. Examples thereof include: polyester polymers such AS polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such AS cellulose diacetate and cellulose triacetate, acrylic polymers such AS polymethyl methacrylate, styrene polymers such AS polystyrene and acrylonitrile-styrene copolymer (AS resin), and polycarbonate polymers. Examples of the polymer forming the protective film include: examples of the polymer include polyolefin polymers such as polyethylene, polypropylene, cyclic polyolefins having a norbornene structure, and ethylene-propylene copolymers, amide polymers such as vinyl chloride polymers, nylon and aromatic polyamides, imide polymers, sulfone polymers, polyethersulfone polymers, polyetheretherketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, aromatic ester polymers, polyoxymethylene polymers, epoxy polymers, and blends of the above polymers. These protective films are generally bonded to the polarizer via an adhesive layer. In addition, the protective film may be formed by: the polarizing plate is formed by applying a thermosetting resin or an ultraviolet-curable resin such as a (meth) acrylic resin, a urethane resin, an acrylic urethane resin, an epoxy resin, or a silicone resin to a polarizer and curing the resin.

The protective film may contain 1 or more kinds of any appropriate additives. Examples of additives include: ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, colorants, and the like. The content of the thermoplastic resin in the protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, even more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. When the content of the thermoplastic resin in the protective film is 50 wt% or less, there is a possibility that high transparency inherent in the thermoplastic resin cannot be sufficiently exhibited.

As the protective film, a retardation film can be used. Examples of the retardation film include a retardation film having a front retardation of 40nm or more and/or a thickness direction retardation of 80nm or more. The front phase difference is usually controlled within a range of 40 to 200nm, and the thickness direction phase difference is usually controlled within a range of 80 to 300 nm. When the retardation film is used as the protective film, the retardation film also functions as a polarizer protective film, and therefore, the thickness can be reduced.

Examples of the retardation film include a birefringent film obtained by uniaxially stretching or biaxially stretching a thermoplastic resin film. The temperature and stretch ratio of the stretching can be appropriately set depending on the retardation value, the material and thickness of the film.

The thickness of the protective film may be appropriately determined, but is preferably 3 to 200 μm, more preferably 3 to 100 μm, from the viewpoints of strength, workability such as workability, and thin layer property. Particularly, the thickness of the protective film (when a film is formed in advance) is preferably 10 to 60 μm, and more preferably 10 to 45 μm from the viewpoint of transportability. On the other hand, the thickness of the protective film (in the case of being formed by coating and curing) is preferably 3 to 25 μm, and more preferably 3 to 20 μm, from the viewpoint of transportability. The protective film may be used in a plurality of sheets or a plurality of layers.

The protective film may have a functional layer such as a hard coat layer, an antireflection layer, an adhesion prevention layer, a diffusion layer, and an antiglare layer on its surface not to be bonded to the polarizer. The functional layers such as the hard coat layer, the antireflection layer, the adhesion prevention layer, the diffusion layer, and the antiglare layer may be provided as the protective film itself, or may be provided separately from the protective film.

< sandwiching layer >

The protective film and the polarizer may be laminated with an interlayer such as an adhesive layer, and an undercoat layer (primer layer) interposed therebetween. In this case, it is preferable to stack both layers without an air gap by using an interlayer.

The adhesive layer may be formed using an adhesive. The type of the adhesive is not particularly limited, and various adhesives can be used. The adhesive layer is not particularly limited as long as it is an optically transparent layer, and various types of adhesives such as water-based, solvent-based, hot-melt, and active energy ray-curable adhesives can be used as the adhesive, but a water-based adhesive or an active energy ray-curable adhesive is preferable.

Examples of the aqueous adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, and aqueous polyesters. The aqueous adhesive is generally used in the form of an aqueous adhesive, and usually contains 0.5 to 60% by weight of solid content.

The active energy ray-curable adhesive is an adhesive that is cured by an active energy ray such as an electron beam or ultraviolet ray (radical-curable type or cation-curable type), and can be used in the form of, for example, an electron beam-curable type or an ultraviolet-curable type. As the active energy ray-curable adhesive, for example, a photo radical-curable adhesive can be used. When a photo radical curing active energy ray-curable adhesive is used as an ultraviolet curing adhesive, the adhesive contains a radical polymerizable compound and a photopolymerization initiator.

The application method of the adhesive can be appropriately selected depending on the viscosity of the adhesive and the target thickness. Examples of the coating method include: reverse coaters, gravure coaters (direct, reverse, or offset), bar reverse coaters, roll coaters, die coaters, wire wound bar coaters, and the like. Further, the coating may be performed by a dipping method or the like.

When an aqueous adhesive or the like is used for the application of the adhesive, the adhesive layer to be finally formed is preferably made to have a thickness of 30 to 300 nm. The thickness of the adhesive layer is more preferably 60 to 250 nm. On the other hand, when an active energy ray-curable adhesive is used, the thickness of the adhesive layer is preferably set to 0.1 to 200 μm. More preferably 0.5 to 50 μm, and still more preferably 0.5 to 10 μm.

In the lamination of the polarizer and the protective film, an easy-adhesion layer may be provided between the protective film and the adhesive layer. The easy-adhesion layer can be formed using various resins having, for example, a polyester skeleton, a polyether skeleton, a polycarbonate skeleton, a polyurethane skeleton, silicones, a polyamide skeleton, a polyimide skeleton, a polyvinyl alcohol skeleton, and the like. These polymer resins may be used alone in 1 kind, or in combination of 2 or more kinds. In addition, other additives may be added to the formation of the easy adhesion layer. Specifically, a thickener, an ultraviolet absorber, an antioxidant, a stabilizer such as a heat stabilizer, and the like can be further used.

In general, the easy-adhesion layer is provided in advance on the protective film, and the easy-adhesion layer side of the protective film and the polarizer are laminated via the adhesive layer. The easy adhesion layer can be formed by applying a material for forming the easy adhesion layer to the protective film by a known technique and drying the applied material. The material for forming the easy-adhesion layer is usually adjusted to a solution diluted to an appropriate concentration in consideration of the thickness after drying, the smoothness of application, and the like. The thickness of the easy adhesion layer after drying is preferably 0.01 to 5 μm, more preferably 0.02 to 2 μm, and still more preferably 0.05 to 1 μm. In this case, the total thickness of the easy adhesion layer is preferably within the above range.

The adhesive layer is formed of an adhesive. As the binder, various binders can be used, and examples thereof include: rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl pyrrolidone-based adhesives, polyacrylamide-based adhesives, cellulose-based adhesives, and the like. The adhesive base polymer can be selected according to the kind of the above adhesive. Among the above-mentioned pressure-sensitive adhesives, acrylic pressure-sensitive adhesives are preferably used because they are excellent in optical transparency, exhibit adhesive properties such as suitable wettability, cohesiveness and adhesiveness, and are excellent in weather resistance, heat resistance and the like.

The undercoat layer (undercoat layer) is formed to improve the adhesion between the polarizer and the protective film. The material constituting the undercoat layer is not particularly limited as long as it exerts a certain degree of strong adhesion to both the base film and the polyvinyl alcohol resin layer. For example, a thermoplastic resin or the like excellent in transparency, thermal stability, stretchability, and the like can be used. Examples of the thermoplastic resin include: acrylic resin, polyolefin resin, polyester resin, polyvinyl alcohol resin, or a mixture thereof.

< transparent resin layer >

The transparent resin layer is formed of various forming materials. The transparent resin layer can be formed by applying the above-described forming material to the polarizer, for example. The transparent resin layer is provided on at least one surface of the polarizer. The thickness of the transparent resin layer is 0.2 μm or more, and the occurrence of cracks can be suppressed by the transparent resin layer having such a thickness. The thickness of the transparent resin layer is preferably 0.4 μm or more, more preferably 0.5 μm or more, and still more preferably 0.7 μm or more. On the other hand, if the transparent resin layer becomes too thick, the optical reliability and water resistance are lowered, and therefore the thickness of the transparent resin layer is preferably 6 μm or less, more preferably 5 μm or less, and further preferably 3 μm or less.

Examples of the material for forming the transparent resin layer include: polyester-series resins, polyether-series resins, polycarbonate-series resins, polyurethane-series resins, silicone-series resins, polyamide-series resins, polyimide-series resins, polyvinyl alcohol-series resins, acrylic-series resins, and the like. These resin materials may be used alone in 1 kind, or may be used in combination in 2 or more kinds. The resin may be in any form of aqueous form or solvent form.

The resin forming the transparent resin layer is preferably a water-soluble resin. The water-soluble resin can be used in the form of an aqueous solution and has good affinity with a polarizer-forming material. Typical examples of the water-soluble resin component include: polyvinyl alcohol resin, polyacrylic acid, polyacrylamide, methylolated melamine resin, methylolated urea-formaldehyde resin, resol type phenol resin, polyethylene oxide, carboxymethyl cellulose, and the like. These may be used alone or in combination of two or more. As the resin component, polyvinyl alcohol-based resins, polyacrylic acid, and methylolated melamine are preferably used. Polyvinyl alcohol resins are particularly preferred. Hereinafter, a case where a polyvinyl alcohol resin is used will be described.

Examples of the polyvinyl alcohol resin include polyvinyl alcohol. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The polyvinyl alcohol resin may be a saponified copolymer of vinyl acetate and a copolymerizable monomer. When the copolymerizable monomer is ethylene, an ethylene-vinyl alcohol copolymer is obtained. Further, as the copolymerizable monomer, there may be mentioned: unsaturated carboxylic acids such as maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, and (meth) acrylic acid, and esters thereof; α -olefins such as ethylene and propylene, (meth) allylsulfonic acid (sodium), (monoalkyl maleate) sodium sulfonate, alkyl maleate disulfonic acid sodium, N-methylolacrylamide, alkali salts of acrylamide alkylsulfonic acid, N-vinylpyrrolidone, and N-vinylpyrrolidone derivatives. These polyvinyl alcohol resins may be used alone in 1 kind, or may be used in combination in 2 or more kinds. From the viewpoint of satisfying the moist heat resistance and water resistance, polyvinyl alcohol obtained by saponifying polyvinyl acetate is preferable.

The polyvinyl alcohol resin having a saponification degree of, for example, 96 mol% or more can be used. From the viewpoint of satisfying the moist heat resistance and the water resistance, the saponification degree is preferably 99 mol% or more, more preferably 99.3 mol% or more, and still more preferably 99.7 mol% or more. The saponification degree indicates the proportion of units which are actually saponified into vinyl alcohol units among the units which can be converted into vinyl alcohol units by saponification, and the residue is a vinyl ester unit. The degree of saponification can be determined in accordance with JIS K6726-1994.

The polyvinyl alcohol resin having an average degree of polymerization of, for example, 500 or more can be used, but from the viewpoint of satisfying the moist heat resistance and water resistance, the average degree of polymerization is preferably 1000 or more, more preferably 1500 or more, and still more preferably 2000 or more. The average polymerization degree of the polyvinyl alcohol resin was measured in accordance with JIS-K6726.

As the polyvinyl alcohol resin, a modified polyvinyl alcohol resin having a hydrophilic functional group in a side chain of the polyvinyl alcohol or a copolymer thereof can be used. Examples of the hydrophilic functional group include an acetoacetyl group and a carbonyl group. Further, a modified polyvinyl alcohol obtained by acetalizing, urethanizing, etherifying, grafting, phosphorylating, or the like, a polyvinyl alcohol resin may be used.

Inorganic salt

The transparent resin layer of the present invention contains at least 1 selected from inorganic salts of alkali metals and inorganic salts of alkaline earth metals. Examples of the alkali metal include lithium, sodium, and potassium, and examples of the alkaline earth metal include calcium, strontium, and barium. On the other hand, examples of the inorganic salt include a halide (fluoride, chloride, bromide, iodide, etc.), a sulfide, a carbonate, a sulfate, a borate, a phosphate, and a titanate.

Specific examples of the inorganic salt of an alkali metal of the present invention include: lithium carbonate, lithium chloride, lithium sulfide, lithium iodide; sodium iodide, sodium chloride, sodium fluoride, sodium bromide, trisodium phosphate; sodium borate, sodium carbonate; potassium iodide, potassium chloride, and the like.

Specific examples of the inorganic salt of an alkaline earth metal include calcium phosphate, calcium chloride, calcium iodide, calcium carbonate, calcium nitrate; strontium iodide, strontium carbonate, strontium titanate, strontium sulfate, strontium chloride; barium sulfate, barium carbonate, barium titanate, barium fluoride, and the like.

The inorganic salt is preferably an inorganic salt of an alkali metal, and among them, a potassium salt is preferable. On the other hand, as for the kind of the inorganic salt, iodide is preferable. From the above viewpoint, potassium iodide is particularly preferable as the inorganic salt. When an iodide, particularly potassium iodide, is used as an inorganic salt to be incorporated in the transparent resin, it is preferable that the iodide is the same as a material contained in a polarizer used in the process of producing the polarizer, in that the potassium iodide component in the polarizer is prevented from being transferred to the transparent resin layer.

The inorganic salt is clearly different from the curable component such as a metal ion or the like or the crosslinking agent in patent document 3, which is added to the polyvinyl alcohol resin to form the protective layer of the polarizer. The inorganic salt does not crosslink the polyvinyl alcohol resin even when it is blended in a transparent resin layer using the polyvinyl alcohol resin. Further, even if an organic salt of an alkali metal and/or an organic salt of an alkaline earth metal is used instead of the inorganic salt, the iodine component in the polarizer cannot be sufficiently suppressed from transferring to the transparent resin layer, and thus the decrease in optical characteristics and bluing in the heating and humidifying test cannot be suppressed to a low level.

The proportion of the inorganic salt in the transparent resin layer is preferably in the range of 1 to 25 parts by weight per 100 parts by weight of a material (for example, polyvinyl alcohol resin) forming the transparent resin layer. The content of the inorganic salt is preferably 2 to 15 parts by weight, and more preferably 5 to 15 parts by weight. By increasing the content of the inorganic salt, bluing can be suppressed. Further, the transmittance on the short wavelength side and the long wavelength side becomes small, and deterioration of the polarizer can be suppressed. However, if the content of the inorganic salt is too large, it is not preferable in terms of lowering the crack resistance because it causes a trouble in forming the transparent resin layer. On the other hand, if the content of the inorganic salt is small, it is not preferable to suppress the decrease in optical characteristics and the blue formation in the heating and humidifying test to a low level.

The inorganic salt has the function of inhibiting the iodine and potassium iodide in the polarizer from transferring into the transparent resin. Therefore, the content of the inorganic salt is preferably determined in consideration of the content of the iodine component in the polarizer. For example, it is preferable that the ratio (b/a) of the content (a: ionic strength) of the iodine component contained in the polarizer to the content (b: ionic strength) of the inorganic salt component contained in the transparent resin layer is controlled to be 0.08 or more. From the viewpoint of suppressing the bluing of the polarizer, the ratio (b/a) is preferably 0.08 or more, and more preferably 0.4 or more. On the other hand, from the viewpoint of crack resistance, the ratio (b/a) is preferably 2 or less, and more preferably 1.2 or less. The content (a) of the iodine component and the content (b) of the inorganic salt contained in the transparent resin layer used for calculating the ratio (b/a) are the ionic strengths obtained by the measurement methods described in the examples.

The transparent resin layer may be formed of a material containing no curable component. For example, the resin composition may be formed of a material containing the polyvinyl alcohol resin (PVA-based resin) as a main component.

The forming material containing the polyvinyl alcohol resin as a main component may contain a curable component (crosslinking agent) and the like. The proportion of the polyvinyl alcohol resin in the transparent resin layer or the forming material (solid content) is preferably 80 wt% or more, more preferably 90 wt% or more, and still more preferably 95 wt% or more. However, it is preferable that the forming material does not contain a curable component (crosslinking agent).

From the viewpoint of improving water resistance, the curable component (crosslinking agent) may be used in a proportion of preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 5 parts by weight or less, based on 100 parts by weight of the polyvinyl alcohol resin.

The forming material may be prepared as a solution in which the polyvinyl alcohol 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 solvents may be used alone or in combination of two or more. Among them, water is preferably used as an aqueous solution using water as a solvent. The concentration of the polyvinyl alcohol resin in the forming material (e.g., aqueous solution) is not particularly limited, but is 0.1 to 15 wt%, preferably 0.5 to 10 wt%, in consideration of coating properties, storage stability, and the like.

In the above-mentioned forming material (for example, an aqueous solution), 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. Further, a coupling agent such as a silane coupling agent or a titanium coupling agent, a stabilizer such as various tackifiers, an ultraviolet absorber, an antioxidant, a heat stabilizer, and a hydrolysis stabilizer, and the like may be added.

The transparent resin layer may be formed by applying the forming material to a polarizer and drying the coating. The coating of the forming material is performed so that the thickness after drying becomes 0.2 μm or more. There is no particular limitation on the coating operation, and any suitable method may be employed. For example, various methods such as roll coating, spin coating, wire-wound bar coating, dip coating, die coating, shower coating, spray coating, and blade coating (doctor blade coating, etc.) can be used.

The transparent resin layer can be formed by applying the forming material to the other surface (surface having no transparent protective film) of the polarizer and drying the coating. The coating of the forming material is performed so that the thickness after drying becomes 0.2 μm or more. There is no particular limitation on the coating operation, and any suitable method may be employed. For example, various methods such as roll coating, spin coating, wire-wound bar coating, dip coating, die coating, shower coating, spray coating, and blade coating (doctor blade coating, etc.) can be used. The drying temperature is preferably 60 to 120 ℃ in general, and more preferably 70 to 100 ℃. The drying time is preferably 10 to 300 seconds, and more preferably 20 to 120 seconds.

< adhesive layer >

The polarizing film with an adhesive layer can be used by providing an adhesive layer on the above-mentioned one-side protective polarizing film. The pressure-sensitive adhesive layer may be provided on one side of the transparent resin layer, the protective film or the polarizer depending on the form of the one-side protective polarizing film. A separator may be disposed on the adhesive layer of the polarizing film with the adhesive layer.

The pressure-sensitive adhesive layer may be formed using a suitable pressure-sensitive adhesive, and the type thereof is not particularly limited. Examples of the binder include: rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl pyrrolidone-based adhesives, polyacrylamide-based adhesives, cellulose-based adhesives, and the like.

Among these pressure-sensitive adhesives, those excellent in optical transparency, exhibiting suitable adhesive properties such as wettability, cohesiveness and adhesiveness, and excellent in weather resistance, heat resistance and the like can be preferably used. As the adhesive exhibiting such characteristics, an acrylic adhesive can be preferably used.

As a method for forming the pressure-sensitive adhesive layer, the following method can be used: a method of applying the pressure-sensitive adhesive to a separator or the like subjected to a peeling treatment, drying the pressure-sensitive adhesive to remove a polymerization solvent or the like to form a pressure-sensitive adhesive layer, and then transferring the pressure-sensitive adhesive layer to a one-side protective polarizing film, a method of applying the pressure-sensitive adhesive to a one-side protective polarizing film, drying the pressure-sensitive adhesive to remove a polymerization solvent or the like to form a pressure-sensitive adhesive layer on a polarizer, or the like. In the case of applying the adhesive, one or more solvents other than the polymerization solvent may be added newly as appropriate.

As the separator subjected to the peeling treatment, a silicone release liner can be preferably used. In the step of forming the pressure-sensitive adhesive layer by applying the pressure-sensitive adhesive of the present invention to such a liner and drying the applied pressure-sensitive adhesive, a suitable method can be appropriately employed as a method for drying the pressure-sensitive adhesive according to the purpose. The method of drying the coating film by heating is preferably used. The heating and drying temperature is preferably 40 to 200 ℃, more preferably 50 to 180 ℃, and particularly preferably 70 to 170 ℃. By setting the heating temperature in the above range, an adhesive having excellent adhesive characteristics can be obtained.

The drying time may be suitably employed as appropriate. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 10 minutes, and particularly preferably 10 seconds to 5 minutes.

As a method for forming the adhesive layer, various methods can be employed. Specific examples thereof include: roll coating, roll and lick coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, blade coating, air knife coating, curtain coating, lip coating, extrusion coating using a die coater, and the like.

The thickness of the adhesive layer is not particularly limited, and is, for example, about 1 to 100 μm. Preferably 2 to 50 μm, more preferably 2 to 40 μm, and further preferably 5 to 35 μm.

When the adhesive layer is exposed, the adhesive layer may be protected with a sheet (separator) subjected to a peeling treatment until it is actually used.

Examples of the constituent material of the separator include: plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films, porous materials such as paper, cloth, and nonwoven fabrics, and suitable sheets such as nets, foamed sheets, metal foils, and laminates thereof, and the like.

The plastic film is not particularly limited as long as it can protect the pressure-sensitive adhesive layer, and examples thereof include: polyethylene films, polypropylene films, polybutylene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polybutylene terephthalate films, polyurethane films, ethylene-vinyl acetate copolymer films, and the like.

The thickness of the separator is usually 5 to 200 μm, preferably about 5 to 100 μm. The separator may be subjected to mold release and antifouling treatment, or antistatic treatment such as coating type, mixing type, and vapor deposition type, using a mold release agent of silicone type, fluorine type, long chain alkyl group, or fatty acid amide type, silica powder, or the like, as necessary. In particular, the releasability from the pressure-sensitive adhesive layer can be further improved by appropriately performing a release treatment such as a silicone treatment, a long-chain alkyl treatment, or a fluorine treatment.

< surface protective film >

A surface protective film may be disposed on the one-side protective polarizing film. The surface protective film generally has a base film and an adhesive layer, and the polarizer is protected by the adhesive layer.

The base film of the surface protective film may be selected from materials having isotropy or near isotropy from the viewpoints of inspection property, manageability, and the like. Examples of the film material include: transparent polymers such as polyester resins such as polyethylene terephthalate films, cellulose resins, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and acrylic resins. Of these, polyester-based resins are preferred. The substrate film may be a laminate of 1 or 2 or more kinds of film materials, or a stretched product of the above film. The thickness of the base film is usually 500 μm or less, preferably 10 to 200 μm.

As the pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer of the surface protective film, a pressure-sensitive adhesive containing a polymer such as a (meth) acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine polymer, or a rubber as a base polymer can be appropriately selected and used. From the viewpoint of transparency, weather resistance, heat resistance and the like, an acrylic adhesive containing an acrylic polymer as a base polymer is preferred. The thickness of the adhesive layer (dry film thickness) may be determined according to the desired adhesive force. Usually about 1 to 100 μm, preferably 5 to 50 μm.

In the surface protective film, a release treated layer may be provided on the surface of the base film opposite to the surface on which the pressure-sensitive adhesive layer is provided, using a low-adhesion material subjected to a silicone treatment, a long-chain alkyl treatment, a fluorine treatment, or the like.

< other optical layers >

The single-sided protective polarizing film of the present invention can be used in practice as an optical film laminated with other optical layers. The optical layer is not particularly limited, and optical layers that are used for forming liquid crystal display devices and the like may be used, for example, 1 or 2 or more layers of reflective plates, semi-transmissive plates, retardation plates (including 1/2 wave plates, 1/4 wave plates, and the like), viewing angle compensation films, and the like. In particular, a reflective polarizing film or a semi-transmissive polarizing film obtained by further laminating a reflective plate or a semi-transmissive reflective plate on the single-side protective polarizing film of the present invention, an elliptical polarizing film or a circular polarizing film obtained by further laminating a phase difference plate on the single-side protective polarizing film, a wide-angle polarizing film obtained by further laminating a viewing angle compensation film on the single-side protective polarizing film, or a single-side protective polarizing film obtained by further laminating a brightness enhancement film on the single-side protective polarizing film is preferable.

The optical film obtained by laminating the optical layers on the one-side protective polarizing film may be formed by sequentially laminating the optical layers in the manufacturing process of a liquid crystal display device or the like, but when the optical film is laminated in advance, there are advantages in that the optical film is excellent in stability of quality, assembling work, and the like, and the manufacturing process of a liquid crystal display device or the like can be improved. The laminate may be bonded by a suitable bonding means such as an adhesive layer. When the single-sided protective polarizing film and the other optical film are bonded to each other, the optical axes thereof may be arranged at an appropriate angle depending on the desired retardation characteristics and the like.

The single-sided protective polarizing film or optical film of the present invention can be preferably used for formation of various devices such as a liquid crystal display device. The liquid crystal display device can be formed in a conventional manner. That is, the liquid crystal display device can be generally formed by appropriately assembling a liquid crystal cell, a single-sided protective polarizing film or an optical film, and components such as an illumination system used as needed, and introducing them into a driver circuit or the like. As the liquid crystal cell, any type of liquid crystal cell such as IPS type, VA type, or the like can also be used.

A liquid crystal display device in which a single-sided protective polarizing film or an optical film is disposed on one side or both sides of a liquid crystal cell, a liquid crystal display device using a backlight or a reflector in an illumination system, or the like can be formed. At this time, the one-side protective polarizing film or the optical film of the present invention may be disposed on one side or both sides of the liquid crystal cell. In the case where a single-sided protective polarizing film or optical film is provided on both sides, they may be the same material or different materials. Further, in forming a liquid crystal display device, appropriate members such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight may be disposed in appropriate positions in 1 layer or 2 layers or more.

Examples

The present invention will be described below with reference to examples, but the present invention is not limited to the examples shown below. In each example, parts and% are on a weight basis. The following conditions of standing at room temperature, which are not particularly specified, are all 23 ℃ and 65% RH.

< making of polarizer >

One surface of a substrate of an amorphous isophthalic acid-copolymerized polyethylene terephthalate (IPA-copolymerized PET) film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of 75 ℃ was subjected to corona treatment, and an aqueous solution containing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl-modification rate 4.6%, saponification degree 99.0 mol% or more, manufactured by japan synthetic chemical industries, ltd., trade name "GOHSEFIMER Z200") in a ratio of 9:1 was applied to the corona-treated surface at 25 ℃ and dried to form a PVA-based resin layer having a thickness of 11 μm, thereby producing a laminate.

The obtained laminate was subjected to free-end uniaxial stretching (auxiliary stretching treatment in a gas atmosphere) of 2.0 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 120 ℃.

Next, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution prepared by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30 ℃ for 30 seconds (insolubilization treatment).

Next, in a dyeing bath at a liquid temperature of 30 ℃, immersion was performed while adjusting the iodine concentration and immersion time so that the polarizing plate could have a predetermined transmittance. In this example, an aqueous iodine solution prepared by adding 0.2 parts by weight of iodine and 1.0 part by weight of potassium iodide to 100 parts by weight of water was immersed for 60 seconds (dyeing treatment).

Subsequently, the substrate was immersed in a crosslinking bath (an aqueous boric acid solution prepared by mixing 3 parts by weight of potassium iodide with 100 parts by weight of water and boric acid) at a liquid temperature of 30 ℃ for 30 seconds (crosslinking treatment).

Then, the laminate was immersed in an aqueous boric acid solution (aqueous solution prepared by adding 4 parts by weight of boric acid to 100 parts by weight of water and potassium iodide) at a liquid temperature of 70 ℃ and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds so that the total stretching ratio became 5.5 times (stretching treatment in the aqueous solution).

Then, the laminate was immersed in a cleaning bath (aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water) at a liquid temperature of 30 ℃ (cleaning treatment).

In this way, an optical film laminate including a polarizer having a thickness of 5 μm was obtained.

(preparation of protective film)

Protecting the film: the easy-adhesion-treated surface of a (meth) acrylic resin film having a lactone ring structure and having a thickness of 40 μm was subjected to corona treatment and used.

(preparation of adhesive for protective film)

An ultraviolet-curable adhesive was prepared by mixing 40 parts by weight of N-hydroxyethyl acrylamide (HEAA), 60 parts by weight of acryloyl morpholine (ACMO), and 3 parts by weight of a photoinitiator IRGACURE 819 (BASF corporation).

(method of evaluating polyvinyl alcohol resin)

The polymerization degree and saponification degree of the polyvinyl alcohol resin were measured according to JIS K6726.

(active energy ray irradiation)

As the active energy ray, a visible light (metal halide lamp in which gallium is sealed) irradiation device was used: light HAMMER10 manufactured by Fusion UV Systems, valve: v valve, maximum illuminance: 1600mW/cm²Cumulative dose of radiation 1000/mJ/cm²(wavelength 380-440 nm). The illuminance of visible light was measured using the Sola-Check system manufactured by Solatell corporation.

Comparative example 1

< production of Single-sided protective polarizing film >

The ultraviolet-curable adhesive is applied to the surface of the polarizing film of the optical film laminate so that the thickness of the cured adhesive layer becomes 0.5 μm, and the protective film is bonded thereto, and then the adhesive is cured by irradiation with an active energy ray. Next, the amorphous PET substrate was peeled off, and a single-sided protective polarizing film using a thin polarizing film was produced. The optical properties of the obtained single-sided protective polarizing film were: the transmittance is 42.8 percent, and the polarization degree is 99.99 percent.

Comparative examples 2 and 3

< preparation of polyvinyl alcohol-based Forming Material >

A polyvinyl alcohol resin having a polymerization degree of 2500 and a saponification degree of 99.7 mol% was dissolved in pure water to prepare an aqueous solution having a solid content of 4% by weight.

< production of Single-sided protective polarizing film with transparent resin layer: corresponding to FIG. 1 >

The polyvinyl alcohol-based material adjusted to 25 ℃ was applied to one surface (polarizing mirror surface without a protective film) of the polarizing film (polarizing mirror) of the one-side protective polarizing film obtained in comparative example 1 using a wire-wound rod coater so that the thickness thereof after drying became 1.2 μm or 3.3 μm, and then hot air-dried at 60 ℃ for 1 minute, thereby producing a one-side protective polarizing film with a transparent resin layer. The optical properties of the obtained one-side protective polarizing film with a transparent resin layer were: the transmittance is 42.8 percent, and the polarization degree is 99.99 percent.

Comparative example 4

< preparation of polyvinyl alcohol-based Forming Material >

100 parts of a polyvinyl alcohol resin having a polymerization degree of 2500 and a saponification degree of 99.7 mol% and 1 part of sodium acetate were dissolved in pure water to prepare an aqueous solution having a solid content of 4% by weight.

The polyvinyl alcohol-based material adjusted to 25 ℃ was applied to one surface (polarizing mirror surface without a protective film) of the polarizing film (polarizing mirror) of the one-side protective polarizing film obtained in comparative example 1 using a wire-wound rod coater so that the thickness thereof after drying became 1.2 μm, and then hot-air drying was performed at 60 ℃ for 1 minute to prepare a one-side protective polarizing film with a transparent resin layer. The optical properties of the obtained one-side protective polarizing film with a transparent resin layer were: the transmittance is 42.8 percent, and the polarization degree is 99.99 percent.

Comparative examples 5 to 7 and examples 1 to 15

< preparation of polyvinyl alcohol-based Forming Material >

An aqueous polyvinyl alcohol resin solution having a solid content of 4 wt% was prepared in the same manner as in comparative example 4, except that the kind and the blending amount of the additive (organic salt or inorganic salt) in comparative example 4 were changed as shown in table 1.

The polyvinyl alcohol-based material adjusted to 25 ℃ was applied to one surface (polarizing mirror surface without a protective film) of the polarizing film (polarizer) of the one-side protective polarizing film obtained in comparative example 1 using a wire-wound rod coater, and the thickness after drying was as shown in table 1, followed by hot air drying at 60 ℃ for 1 minute to prepare a one-side protective polarizing film with a transparent resin layer. The optical properties of the obtained one-side protective polarizing film with a transparent resin layer were: the transmittance is 42.8 percent, and the polarization degree is 99.99 percent.

The one-side protective polarizing films obtained in the comparative examples and examples were evaluated as follows. The results are shown in Table 1. The obtained one-side protective polarizing film or the polarizing film with an adhesive layer prepared as described below was evaluated.

< preparation of acrylic Polymer >

A4-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube and a condenser was charged with a monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate. Further, 0.1 part of 2, 2' -azobisisobutyronitrile as a polymerization initiator was added together with ethyl acetate to 100 parts of the monomer mixture (solid content), nitrogen gas was introduced while slowly stirring the mixture to replace nitrogen, and then the polymerization reaction was carried out for 7 hours while maintaining the liquid temperature in the flask at about 60 ℃. Then, ethyl acetate was added to the obtained reaction solution to obtain a solution of an acrylic polymer having a solid content concentration of 30% and a weight average molecular weight of 140 ten thousand.

(preparation of adhesive composition)

An acrylic pressure-sensitive adhesive solution was prepared by mixing 0.1 part of trimethylolpropane xylylene diisocyanate (manufactured by Mitsui chemical Co., Ltd.: Takenate D110N), 0.3 part of dibenzoyl peroxide, and 0.075 part of gamma-glycidoxypropyltrimethoxysilane (manufactured by shin-Etsu chemical Co., Ltd.; trade name: KMB-403) with 100 parts of the solid content of the acrylic polymer solution.

(formation of adhesive layer)

Subsequently, the acrylic pressure-sensitive adhesive solution was uniformly applied to the surface of a polyethylene terephthalate film (separator) treated with a silicone-based release agent by a spray coater, and dried in an air-circulating oven at 155 ℃ for 2 minutes to form a pressure-sensitive adhesive layer having a thickness of 20 μm on the surface of the separator.

< production of polarizing film with adhesive layer >

Next, the pressure-sensitive adhesive layer formed on the release-treated surface of the release sheet (separator) was laminated on the transparent resin layer (specifically, polarizer side in comparative example 1) of the one-side protective polarizing film obtained in each example, to prepare a polarizing film with a pressure-sensitive adhesive layer.

< durability: rate of change of degree of polarization (optical reliability test) >

The obtained adhesive-attached one-side protective polarizing film was cut into a size of 25mm × 50mm (absorption axis direction is 50 mm). The adhesive-attached single-sided protective polarizing film (sample) was placed in a constant temperature and humidity machine at 85 ℃/85% RH for 150 hours. The degrees of polarization of the one-side protective polarizing films before and after the input were measured using a spectral transmittance measuring instrument with an integrating sphere (Dot-3 c of color technology research institute in village), and the following were obtained:

the change rate (%) of the polarization degree is 1- (polarization degree after charging/polarization degree before charging)).

The degree of polarization P is determined by applying the transmittance (parallel transmittance: Tp) when 2 sheets of the same polarizing films are stacked such that their transmission axes are parallel to each other and the transmittance (orthogonal transmittance: Tc) when the polarizing films are stacked such that their transmission axes are orthogonal to each other to the following equation. The polarization degree P (%) P { (Tp-Tc)/(Tp + Tc) }^1/2×100

Each transmittance is a transmittance represented by a Y value obtained by correcting visibility with a 2-degree field of view (C light source) according to JIS Z8701, assuming that the fully polarized light obtained by polarizing with a glan-taylor prism is 100%.

Table 1 shows the change rate of the polarization degree, and the change rate was determined based on the following criteria.

O: the rate of change of the degree of polarization is less than 0.4%.

And (delta): the rate of change in the degree of polarization is 0.4% or more and less than 0.5%.

X: the rate of change in the degree of polarization is 0.5% or more.

< durability: orthogonal hue (optical reliability test) >

The obtained adhesive-attached one-side protective polarizing film was cut into a size of 25mm × 50mm (absorption axis direction is 50 mm). The adhesive-attached single-sided protective polarizing film (sample) was placed in a constant temperature and humidity machine at 85 ℃/85% RH for 150 hours. The orthogonal a value (red direction) and the orthogonal b value (blue direction) of the adhesive-equipped one-side protective polarizing film before and after the input were measured using a spectral transmittance measuring instrument with an integrating sphere (Dot-3 c of color technology research institute in village).

The orthogonal b value (blue direction) is shown in table 1, and was determined based on the following criteria.

O: the orthogonal b value is greater than-2.4.

And (delta): the orthogonal b value is larger than-3 and less than-2.4.

X: the orthogonal b value is-3 or less.

< relative ratio of content of inorganic salt in transparent resin layer to content of iodine in polarizer >

The inorganic salt content of the transparent resin layer and the iodine content in the polarizer were measured by TOF-SIMS (TRIFT V manufactured by Ulvac-Phi) equipped with a gas cluster ion gun.

The conditions for the measurement are shown below.

Etching ions: ar gas cluster ion

Primary ion irradiated: bi₃ ²⁺

Primary ion acceleration voltage: 30kV

And (3) measuring the polarity: negative ion

While etching the transparent resin layer side of the single-side protective polarizing film with argon clusters to the polarizer side, the iodine component I from the polarizer was extracted by observing the depth section^－(m/z 127) "(ionic strength a), and inorganic salt component" ex: KI "derived from the transparent resin layer₂ ^－(m/z 293) "(ion intensity b), and the ratio (b/a) thereof was calculated.

In addition, the inorganic salt component derived from the transparent resin layer is a case where potassium iodide is used as the inorganic component. m/z is a "mass-to-charge ratio" (an amount corresponding to a value obtained by dividing an atomic weight/molecular weight by a charge), and KI as a secondary ion was detected for the inorganic salt component₂ ^－(m/z 293)。

The ionic strength b is derived from the inorganic salt content as follows.

Case of sodium chloride: cl^－(m/z 35)

Sodium sulfate and zinc sulfate conditions: SO (SO)₃ ^－(m/z 80)

Case of calcium chloride: cl^－(m/z 35)

< crack resistance >

The polarizing film with the adhesive layer thus obtained was cut into a size of 400mm in length × 708mm in width (absorption axis direction: 400mm) and a size of 708mm in length × 400mm in width (absorption axis direction: 708mm), and both surfaces of alkali-free glass of 402mm × 710mm × thickness 1.3mm were bonded in the cross nicol direction to prepare a sample. After the sample was put into an oven at 95 ℃ for 250 hours, it was taken out and it was visually confirmed whether or not cracks were generated in the polarizing film with an adhesive layer. This test was performed on 10 specimens for 1 specimen, and the number of specimens having cracks was counted and judged based on the following criteria.

O: 0 piece.

And (delta): 1 to 3 pieces.

X: more than 4 pieces.

From table 1 it can be confirmed that: in the examples, the composition has crack resistance and optical reliability, and can suppress bluing of color tone to a low level. In particular, when potassium iodide is used as the inorganic salt (inorganic salt of alkali metal, inorganic salt of alkaline earth metal) contained in the transparent resin layer, the effect of suppressing blue formation is more excellent than that of other inorganic salts in the same amount. It is considered that potassium iodide is the same as the potassium component and the iodine component contained in the polarizer, and therefore, the bleeding is most easily suppressed. On the other hand, comparative example 1 does not have a transparent resin layer, and therefore, the crack resistance cannot be satisfied. In comparative examples 2 and 3, since neither organic salt nor inorganic salt was added to the transparent resin layer, the optical reliability was insufficient, and blue of hue could not be suppressed to a low level. It is understood that in comparative examples 4 and 5, the transparent resin layer contains an organic salt, but the optical reliability is insufficient. As shown in comparative examples 6 and 7, when an inorganic salt (an inorganic salt of an alkali metal or an inorganic salt other than an alkaline earth metal) such as a zinc salt is used as the inorganic salt, bluing cannot be sufficiently suppressed. Further, since metal ions of inorganic salts such as zinc salts have a function of crosslinking the polyvinyl alcohol resin of the transparent resin layer, the flexibility tends to be impaired and the crack resistance tends to be lowered.

Claims

1. A single-sided protective polarizing film having a protective film only on one side of a polarizer,

a transparent resin layer is provided on at least one surface of the polarizer,

the transparent resin layer contains at least one selected from inorganic salts of alkali metals and inorganic salts of alkaline earth metals,

the ratio b/a of the content b of the inorganic salt component contained in the transparent resin layer to the content a of the iodine component contained in the polarizer is 0.08-2.0, and both the contents a and b have ionic strength.

2. The single-sided protective polarizing film of claim 1, wherein the inorganic salt is an iodide.

3. The single-sided protective polarizing film of claim 2, wherein the iodide is potassium iodide.

4. The single-sided protective polarizing film according to any one of claims 1 to 3, wherein the transparent resin layer is formed of a forming material containing a water-soluble resin.

5. The one-side protective polarizing film according to claim 4, wherein the water-soluble resin is a polyvinyl alcohol-based resin.

6. The single-sided protective polarizing film according to any one of claims 1 to 3, wherein the thickness of the transparent resin layer is 0.2 μm or more.

7. The single-sided protective polarizing film according to any one of claims 1 to 3, wherein the thickness of the transparent resin layer is 6 μm or less.

8. The single-sided protective polarizing film according to any one of claims 1 to 3, wherein the polarizer has a thickness of 15 μm or less.

9. The single-sided protective polarizing film according to any one of claims 1 to 3, wherein the polarizer is configured such that optical properties represented by a monomer transmittance T and a degree of polarization P satisfy the following conditions:

P＞－(10^{0.929T－42.4}-1) x 100, wherein T < 42.3, or

P is more than or equal to 99.9, wherein T is more than or equal to 42.3.

10. A polarizing film with an adhesive layer, comprising the one-side protective polarizing film according to any one of claims 1 to 9 and an adhesive layer.

11. An image display device having the one-side protective polarizing film of any one of claims 1 to 9 or the adhesive layer-attached polarizing film of claim 10.