TWI878719B - Easy-to-bond film, polarizing plate, polarizing plate with adhesive, and image display device - Google Patents

Abstract

The present invention provides a polarizing plate that has suppressed the decrease of monomer transmittance in a high temperature environment, and an easy-to-bond film used therefor. The easy-to-bond film (1) has an easy-to-bond layer (15) on the surface of a transparent film substrate (11). The easy-to-bond layer contains a binder resin and a water-soluble free radical scavenger. The polarizing plate (50) has the following structure: the easy-to-bond film (1) is bonded to at least one side of a polyvinyl alcohol-based polarizer (5) through an adhesive layer (6).

Description

Easy-to-bond film, polarizing plate, polarizing plate with adhesive, and image display device

The present invention relates to an easy-adhesive film having an easy-adhesive layer on the surface of a transparent film substrate. Furthermore, the present invention relates to: a polarizing plate having an easy-adhesive film attached to the surface of a polarizer, an adhesive-attached polarizing plate having an adhesive layer on at least one side of the polarizing plate, and an image display device having the polarizing plate.

Liquid crystal display devices or organic EL display devices are widely used in various image display devices such as mobile devices, car navigation devices, personal computer displays, and televisions. From the display principle of liquid crystal display devices, polarizing plates are arranged on the viewing side surface of the liquid crystal unit. In transmissive liquid crystal display devices, polarizing plates are arranged on both sides of the liquid crystal unit. In organic EL display devices, in order to suppress external light from being reflected by the metal electrode (cathode) and being viewed like a mirror, a circular polarizing plate (typically, a layered body of a polarizing plate and a 1/4 wavelength plate) is sometimes arranged on the viewing side surface.

Polarizing plates usually have a transparent film (polarizer protection film) on one or both sides of the polarizer for the purpose of protecting the polarizer. As polarizers, polyvinyl alcohol (PVA) films that adsorb iodine and orient the molecules by stretching are widely used.

Cellulose-based films such as cellulose acetate are widely used as polarizer protective films attached to the surface of polarizers because of their excellent adhesion to PVA-based polarizers. Films made of resin materials such as acrylic, polyester, polycarbonate, and cyclic polyolefin are also beginning to be used as polarizer protective films. Films made of these resin materials have lower moisture permeability than cellulose-based films, so polarizing plates with low moisture permeability resin films attached to the surface of polarizers have little change in optical properties even when exposed to high humidity environments for a long time, and tend to have excellent durability.

As described above, in a liquid crystal display device or an organic EL display device, a polarizing plate is provided on the viewing side surface of the image display unit. In recent years, a structure in which a transparent front plate such as a transparent resin plate or a glass plate (also called a "cover window") is provided on the viewing side is widely used to prevent damage caused by impact from the outer surface. Regarding the structure in which the viewing side of the polarizing plate is bonded to the front transparent plate through an adhesive layer, Patent Documents 1 and 2 point out that in a high temperature environment, the central part of the polarizing plate surface will turn red, resulting in a decrease in transmittance.

Regarding the decrease in transmittance of the polarizing plate, it is generally believed that one of the reasons is that the PVA constituting the polarizer is polyene-formed due to dehydration reaction in a high temperature environment; Patent document 1 proposes to control the water absorption or moisture permeability of the polarizer protective film bonded to the polarizer to reduce the water retained in the polarizer to inhibit the polyene-formation of PVA. Patent document 2 proposes to control the moisture permeability and moisture content of the adhesive layer used to bond the polarizing plate and the front transparent plate to allow the water to dissipate from the end surface of the adhesive layer to inhibit the polyene-formation of PVA.

Patent document 3 states that: by making the PVA-based polarizer, the adhesive for bonding the PVA-based polarizer and the polarizer protective film, or the adhesive for bonding the polarizing plate, the image display unit, and the front transparent component contain a specific hindered amine compound, the decrease in the transmittance of the polarizer caused by the polyeneization of PVA can be suppressed.

Current technical literature

Patent Literature

Patent document 1: Japanese Patent Publication No. 2014-102353

Patent document 2: Japanese Patent Publication No. 2017-75998

Patent document 3: International Publication No. 2020/100869

As image display devices become larger or brighter, polarizers that constitute image display devices are required to have less change in optical properties even in more severe environments (e.g., higher temperature conditions). The method of controlling the amount of water retained in the polarizer as described in Patent Documents 1 and 2 has limited effect on inhibiting polyeneization of PVA-based polarizers.

As for the method proposed in Patent Document 3 of adding hindered amine compounds to polarizers, adhesives or adhesives, there is still room for improvement in interlayer adhesion and the like.

In view of the above situation, the inventors of the present invention conducted research and found that by using an easy-adhesion film containing a radical scavenger in the easy-adhesion layer as a polarizer protective film attached to the surface of the polarizer, a polarizing plate with excellent inter-layer adhesion and suppressed polarizer degradation can be obtained.

One aspect of the present invention is an easy-to-bond film having an easy-to-bond layer on the surface of a transparent film substrate, and the easy-to-bond layer includes a binder resin and a water-soluble free radical scavenger. The free radical scavenger contained in the easy-to-bond layer is, for example, a hindered amine compound, preferably a compound having a nitrooxy group (N-oxy free radical compound). The free radical scavenger may also be a compound that can generate a nitrooxy group by activation.

The content of the free radical scavenger in the easy bonding layer is, for example, about 0.01 to 10% by weight. The easy bonding layer may also contain microparticles.

The easy-adhesive film can be suitably used as a polarizer protective film of a polarizing plate. Another aspect of the present invention is a polarizing plate, wherein the easy-adhesive film is bonded to a polyvinyl alcohol-based polarizer through an adhesive layer. The polarizer and the easy-adhesive film can be bonded through a photo-free radical polymerizable adhesive.

The polarizing plate can be used in practice in the form of an adhesive-attached polarizing plate having an adhesive layer on at least one side. By configuring a polarizing plate on the surface of an image display unit such as a liquid crystal display unit or an organic EL unit, an image display device can be formed.

A polarizing plate having an easy-adhesive film having an easy-adhesive layer containing a radical scavenger as a polarizing element protective film attached to at least one side of a polyvinyl alcohol-based polarizing element. The polarizing plate has little change in single body transmittance and excellent durability even when the image display device is exposed to a high temperature environment.

1: Easy to bond film

11: Film substrate

15: Easy to bond layer

2: Transparent film

5: Polarizer

6,7: Next is the agent layer

50: Polarizing plate

20,30: Adhesive layer

90: Polarizing plate with adhesive

60: Image display unit

70: Front transparent component

100: Image display device

Figure 1 is a cross-sectional view showing an example of the structure of an easy-to-bond film.

Figure 2 is a cross-sectional view showing an example of the structure of a polarizing plate.

Figure 3 is a cross-sectional view showing an example of the structure of a polarizing plate with an adhesive.

Figure 4 is a cross-sectional view showing an example of the structure of an image display device.

FIG1 is a schematic cross-sectional view showing an example of the structure of an easy-to-bond film of an embodiment of the present invention. The easy-to-bond film 1 is provided with an easy-to-bond layer 15 on at least one side of a film substrate 11. Easy-to-bond layers may also be provided on both sides of the film substrate. The easy-to-bond film is used by bonding with other films or glass substrates.

The use form of the easy-to-bond film can be exemplified by the polarizer protection film. FIG. 2 is a cross-sectional view showing an example of the structure of a polarizing plate having an easy-to-bond film 1 as a polarizer protection film. The polarizing plate 50 has an easy-to-bond film 1 bonded to one side (first main side) of the polarizer 5 through an adhesive layer 6. In the polarizing plate 50 shown in FIG. 2, the easy-to-bond film 1 has an easy-to-bond layer 15 on the bonding surface of the film substrate 11 with the polarizer 5. An easy-to-bond layer can also be provided on one side not bonded to the polarizer 5. In the polarizing plate 50 shown in FIG. 2, a transparent protective film 2 is bonded to the other side (second main side) of the polarizer 5 through an adhesive layer 7.

[Easy-adhesive film]

The easy-to-bond film 1 is provided with an easy-to-bond layer 15 on at least one side of the film substrate 11.

<Film substrate>

As the film substrate 11, a transparent film is preferred. The total light transmittance of the transparent film substrate is preferably 80% or more, preferably 85% or more, and more preferably 90% or more. As the resin material constituting the film substrate 11, acrylic resin, polyester resin, polycarbonate resin, polyolefin resin, cyclic polyolefin resin, polystyrene resin, polyamide resin, polyimide resin, etc. can be listed. When the easy-to-bond film is used as an optically isotropic polarizer protective film, the resin material of the film substrate 11 is preferably an acrylic resin or a cyclic polyolefin resin, especially an acrylic resin, because of its small birefringence.

烯。作為環狀聚烯烴系樹脂的市售品，可舉日本ZEON製之ZEONOR及ZEONEX、JSR製之ARTON、三井化學製之APEL、TOPAS ADVANCED POLYMERS製之TOPAS等。環狀聚烯烴系薄膜宜含有50重量%以上之環狀烯烴系樹脂。 As cyclic polyolefin resins, for example,

Examples of commercially available cyclic polyolefin resins include ZEONOR and ZEONEX manufactured by ZEON of Japan, ARTON manufactured by JSR, APEL manufactured by Mitsui Chemicals, and TOPAS manufactured by TOPAS ADVANCED POLYMERS. The cyclic polyolefin film preferably contains 50% by weight or more of the cyclic olefin resin.

酯共聚物等)。 Examples of acrylic resins include poly(meth)acrylates such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, methyl (meth)acrylate-styrene copolymers (MS resins, etc.), polymers having alicyclic hydrocarbon groups (e.g., methyl methacrylate-cyclohexyl methacrylate copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, etc.), and poly(meth)acrylates such as poly(meth)acrylates.

ester copolymers, etc.).

In this specification, "(meth)acrylic acid" refers to acrylic acid and/or methacrylic acid. Acrylic resins include those with acrylic acid or its derivatives as monomer components and those with methacrylic acid or its derivatives as monomer components.

As the acrylic resin, an acrylic resin having a glutaric anhydride structure described in Japanese Patent Laid-Open Nos. 2006-283013, 2006-335902, 2006-274118, etc., and/or an acrylic resin having a lactone ring structure described in Japanese Patent Laid-Open Nos. 2000-230016, 2001-151814, 2002-120326, 2002-254544, 2005-146084, etc. can be used. Acrylic resins with glutaric anhydride structures and acrylic resins with lactone ring structures have high heat resistance, high transparency, and high mechanical strength, and are therefore suitable for manufacturing polarizing plates with high polarization and excellent durability.

When the film substrate 11 is an acrylic film, the content of acrylic resin in the film substrate is preferably 50% by weight or more, preferably 60-98% by weight, and more preferably 70-97% by weight. The acrylic film may also contain thermoplastic resins other than acrylic resins. For example, by mixing other thermoplastic resins to eliminate the birefringence of acrylic resin, an acrylic film with excellent optical isotropy can be obtained. In addition, for the purpose of improving the mechanical strength of the film, thermoplastic resins other than acrylic resins may also be mixed.

As thermoplastic resins other than acrylic resins, there can be listed: olefin polymers, halogenated vinyl polymers, polystyrene, copolymers of styrene and acrylic monomers, polyesters, polyamides, polyacetals, polycarbonates, polyphenylene oxides, polyphenylene sulfide, polyetheretherketones, polysulfones, polyethersulfones, polyoxybenzenes, polyamideimides, rubber polymers, etc.

The film substrate 11 may also contain additives such as antioxidants, stabilizers, reinforcing materials, ultraviolet absorbers, flame retardants, antistatic agents, colorants, fillers, plasticizers, lubricants, and fillers. The resin material and additives may also be mixed to form a thermoplastic resin composition such as pellets in advance, and then formed into a film.

The thickness of the film substrate 11 is about 5 to 200 μm. From the perspective of mechanical strength, transparency, and operability, the thickness of the film substrate 11 is preferably 10 to 100 μm, and more preferably 15 to 60 μm.

The glass transition temperature Tg of the film substrate 11 is preferably above 100°C, more preferably above 110°C. When the film substrate 11 is an acrylic film, as mentioned above, by using an acrylic resin having a glutaric anhydride structure or an acrylic resin having a lactone ring structure as the acrylic resin, the Tg of the acrylic film can be increased and the heat resistance can be improved. The upper limit of the Tg of the film substrate 11 is not particularly limited, but from the perspective of formability, it is preferably below 170°C.

As a method for manufacturing the film substrate 11, solution casting, melt extrusion, calendering, compression molding, etc. can be listed. The film substrate 11 can be an unstretched film or a stretched film. When the film substrate 11 is an acrylic film, from the perspective of improving mechanical strength, the acrylic film is preferably a stretched film stretched in at least one direction, and is particularly preferably a biaxially stretched film. By mixing other thermoplastic resins to eliminate the birefringence of the acrylic resin, an acrylic film with low hysteresis and excellent optical isotropy can be obtained even when stretched.

<Easy to bond layer>

The easy-adhesion layer 15 provided on the surface of the film substrate 11 includes a binder resin and a radical scavenger. By providing the easy-adhesion layer 15, the adhesion to a film such as a polarizer or a glass substrate can be improved. By making the easy-adhesion layer 15 include a radical scavenger, in a polarizing plate having the easy-adhesion film 1 and the polarizer 5 bonded together, the degradation of the polarizer 5 can be suppressed.

The easy-adhesion layer 15 may further include microparticles. By including microparticles in the easy-adhesion layer 15, fine concavo-convexities are formed on the surface of the easy-adhesion layer 15, thereby improving the slipperiness of the film. Therefore, it helps to reduce the damage of the easy-adhesion film 1 during roller conveyance and inhibits adhesion when it is rolled into a roll.

(Adhesive resin)

唑啉基等交聯性官能基的丙烯酸系樹脂等具有反應性基之樹脂(聚合物)。作為易接著層15的黏結劑樹脂，特別宜為聚胺甲酸酯樹脂。包含聚胺甲酸酯樹脂黏結劑的易接著層15其與薄膜基材11的密著性高。又，易接著層15包含聚胺甲酸酯樹脂黏結劑的易接著薄膜1其在透過接著劑層來積層偏光件等薄膜時，有顯示高接著性的傾向。 As the adhesive resin of the easy-adhesion layer 15, polyurethane resin, epoxy resin, isocyanate resin, polyester resin, polymers containing amino groups in the molecule, and

Resins (polymers) having reactive groups such as acrylic resins having cross-linking functional groups such as oxazoline groups. Polyurethane resins are particularly preferred as the binder resin of the easy-bonding layer 15. The easy-bonding layer 15 containing a polyurethane resin binder has high adhesion to the film substrate 11. In addition, the easy-bonding film 1 in which the easy-bonding layer 15 contains a polyurethane resin binder tends to show high adhesion when a film such as a polarizer is laminated through the adhesive layer.

Urethane resin is typically a reaction product of polyol and polyisocyanate. As the polyol component, high molecular weight polyols such as polyacrylic polyol, polyester polyol, and polyether polyol can be preferably used. As the polyisocyanate, aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate can be used. From the perspective of transparency, aliphatic diisocyanate or alicyclic diisocyanate is preferred.

The urethane resin constituting the easy-bonding layer 15 preferably has a carboxyl group. By providing the urethane resin with a carboxyl group, a cross-linked structure can be introduced, and the bonding durability of the easy-bonding film 1 and the polarizer, etc. tends to be improved. The urethane resin having a carboxyl group can be obtained, for example, by reacting a chain extender having a free carboxyl group in addition to a polyol and a polyisocyanate. Examples of the chain extender having a free carboxyl group include dihydroxycarboxylic acids and dihydroxysuccinic acid. Examples of the dihydroxycarboxylic acid include dialkanol alkanoic acids such as dihydroxymethyl alkanoic acid (e.g., dihydroxymethyl acetic acid, dihydroxymethyl butyric acid, dihydroxymethyl propionic acid, dihydroxymethyl butyric acid, and dihydroxymethyl valeric acid).

The method for producing urethane resin is not particularly limited, and may be any one of a one-shot method in which monomer components react at once and a multi-step method in which they react in stages. When a chain extender having a free carboxyl group is used to introduce a carboxyl group into the urethane resin, a multi-step method is preferred. When producing the urethane resin, a urethane reaction catalyst may be used as needed.

The number average molecular weight of urethane resin should be 5,000~600,000, preferably 10,000~400,000. The acid value of urethane resin should be 10~50, preferably 20~45.

As the urethane resin, commercial products can also be used. Examples of commercially available water-based urethane resins include: "Superflex" series (150, 150HS, 210, 460, 470, 870, etc.) and "Elastron" series (H-3, etc.) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "TAKELAC" series (W-6010, W-6020, W-605, W-6061, WS-4000, WS-5100, WSA-5920, etc.) and "OLESTER" series (UD-350, etc.) manufactured by Mitsui Chemicals, "HYDRAN" series (AP-20, AP-40F, RCP-A-220, WLS-210, etc.) manufactured by DIC, and "PERMARIN" series (UA-368, etc.) manufactured by Sanyo Chemical Industries, Ltd., etc.

唑啉基、環氧基、碳二亞胺基等的交聯劑。該等之中，宜為具有

唑啉基的交聯劑。

唑啉基由於在常溫下與羧基的反應性小，因此與胺甲酸酯樹脂混合時的適用期長，而可靈活應對步驟的前置時間(lead time)。 The urethane resin may have a crosslinking structure. By introducing a crosslinking structure into the urethane resin, the bonding durability between the film 1 and the polarizer etc. tends to be improved. As a crosslinking agent, a crosslinking agent that can react with the crosslinking functional group of the urethane resin can be used without particular limitation. When the urethane resin has a carboxyl group, a crosslinking functional group containing an amino group,

Among them, preferably having

Azoline-based crosslinking agent.

Since the oxazoline group has low reactivity with the carboxyl group at room temperature, it has a long pot life when mixed with the urethane resin, and can flexibly cope with the lead time of the step.

唑啉基之丙烯酸系聚合物作為交聯劑時，有易接著薄膜1與偏光件等薄膜的接著性提高的傾向。 The crosslinking agent may be a low molecular weight compound or a polymer. In view of its high solubility in water-based compositions and excellent compatibility with urethane resins, acrylic polymers are preferred as crosslinking agents.

When an oxazoline-based acrylic polymer is used as a crosslinking agent, the adhesion between the film 1 and a film such as a polarizer tends to be improved.

The amount of crosslinking agent used is preferably 1 to 30 parts by weight, preferably 3 to 20 parts by weight, relative to 100 parts by weight of urethane resin.

(Free radical scavenger)

The radical scavenger contained in the easy-bonding layer 15 has the function of inhibiting the degradation of the polarizer in a high temperature environment (mainly the decrease in monomer transmittance). We believe that in a high temperature environment, as the water retained in the polarizer moves, the radical scavenger will migrate from the easy-bonding layer to the polarizer, which helps to inhibit the degradation of the polarizer.

From the perspective of promoting migration from the easy-bonding layer 15 to the polarizer 5, etc. in the presence of water, the free radical scavenger is preferably water-soluble. The solubility of the free radical scavenger in water at 25°C (the mass (g) of the free radical scavenger soluble in 100g of water) is preferably 1 or more, more preferably 2 or more, and even more preferably 5 or more.

系化合物等具有自由基捕捉功能的化合物。其中，由抑制偏光件劣化之效果高的方面出發，宜為受阻胺系化合物。 Examples of water-soluble free radical scavengers include hindered phenol compounds, hindered amine compounds, phosphorus compounds, sulfur compounds, benzotriazole compounds, diphenyl ketone compounds, hydroxylamine compounds, salicylate compounds, tris(2-hydroxy-2-amino-2-yl)-4-nitropropene compounds, and the like.

Among them, hindered amine compounds are preferred because of their high effect of suppressing polarizer degradation.

Hindered amine compounds are compounds in which the carbon atom adjacent to the nitrogen atom of a diamine or tertiary amine is substituted with an alkyl group. Examples of hindered amine compounds that function as free radical scavengers include compounds having a structure represented by the general formula (1).

[Chemical formula 1]

In the general formula (1), the left side of the dotted line is an arbitrary organic group. In the general formula (1), ^R1 is an oxygen radical, a hydrogen atom, a hydroxyl group, an acryloyl group, a methacryloyl group, or an alkyl group having 1 to 30 carbon atoms, an alkoxy group, a hydroxyalkyl group, a hydroxyalkoxy group, or an acyl group.

In the general formula (1), R ² to R ⁵ are each independently an alkyl group having 1 to 10 carbon atoms, and the alkyl group preferably has 1 to 6 carbon atoms, and preferably has 1 to 3 carbon atoms. From the viewpoint of the stability of the compound and the free radical scavenging effect, it is preferred that all of R ² to R ⁵ are methyl groups.

In the general formula (1), n is 0 or 1. From the viewpoint of structural stability, n is preferably 0. The compound wherein n=0 in the general formula (1) is a derivative of 2,2,6,6-tetraalkylpiperidine. The compound wherein n=0 in the general formula (1) and R ² to R ⁵ are all methyl groups is a derivative of 2,2,6,6-tetramethylpiperidine.

In the general formula (1), the nitroxy group of the compound (N-oxyl radical compound) in which R ¹ bonded to the nitrogen atom is an oxygen free radical has the function of generating a stable nitroxy free radical (R ₂ NO‧) and capturing free radicals. The nitroxy free radical has a reaction cycle of returning to the nitroxy free radical by absorbing peroxy acid after capturing free radicals, so it continues to have a free radical capturing function even if a small amount is added.

When ^R1 is other than an oxygen radical, a nitroxy group (nitroxy radical) is generated by activation such as ultraviolet irradiation. Therefore, the compound represented by the general formula (1) has a free radical scavenging effect similar to the N-oxyl radical compound in which ^R1 is an oxygen radical even when ^R1 is other than an oxygen radical. That is, the free radical scavenger is preferably a compound having a nitroxy group or a compound that can generate a nitroxy group by activation.

From the viewpoint of being able to exert a radical scavenging action without being activated by ultraviolet irradiation or the like, the radical scavenger is preferably a compound having a nitrooxy group, and R ¹ in the above general formula (1) is preferably an oxygen radical.

Examples of compounds having the structure represented by general formula (1) include compounds represented by the following general formulas (2) to (5).

In general formulae (2) to (5), R ¹ to R ⁵ and n are the same as those in general formula (1). In general formulae (2) and (3), R ⁶ to R ⁸ are each independently a hydrogen atom, an alkyl group or acyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. In general formulae (4) and (5), R ⁹ to R ¹² are each independently a hydrogen atom, a hydroxyl group, an alkyl group, an acyl group, an amino group or an alkoxy group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

From the viewpoint of water solubility and availability of the compound, R ⁶ to R ⁸ in the general formula (2) and the general formula (3) are preferably hydrogen atoms or alkyl groups with 1 to 10 carbon atoms, and are particularly preferably hydrogen atoms. From the viewpoint of water solubility and availability of the compound, R ⁹ to R ¹¹ in the general formula (4) are preferably hydrogen atoms or alkyl groups with 1 to 10 carbon atoms, and R ¹² in the general formula (5) is preferably a hydroxyl group, an amino group, or an alkoxy group.

As mentioned above, N-oxy radical compounds have a radical scavenging effect. Examples of N-oxy radical compounds that function as radical scavengers include compounds described in Japanese Patent Publication No. 2003-64022, Japanese Patent Publication No. 11-222462, Japanese Patent Publication No. 2002-284737, and International Publication No. 2016/047655.

Furthermore, even in addition to the compound represented by the general formula (1), N-nitroxide compounds can also function as free radical scavengers. Examples of N-nitroxide compounds include compounds represented by the following formulas (6) to (8).

In the general formula (6), R is a hydrogen atom, an alkyl or acyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

From the perspective of water solubility or inhibition of polarizer degradation, the molecular weight of the radical scavenger is preferably 1000 or less, preferably 500 or less, and more preferably 300 or less. The radical scavenger contained in the easy-bonding layer may be only one type or may be two or more types.

The content of the free radical scavenger in the easy bonding layer is preferably 0.01 wt% or more, more preferably 0.05 wt% or more, more preferably 0.1 wt% or more, and particularly preferably 0.15 wt% or more, and can also be 0.2 wt% or more, 0.3 wt% or more, 0.5 wt% or more, or 1.0 wt% or more. The more the free radical scavenger content in the easy bonding layer 15 is, the more the free radical scavenger migrates to the polarizer 5, and the polarizer deterioration tends to be more suppressed. In addition, when the free radical scavenger is included in the easy bonding layer, it is not easy to have poor orientation during extension, or hinder hardening, hinder bonding, etc., so a larger amount can be added compared to the case where the free radical scavenger is included in the polarizer or the bonding agent layer, the adhesive layer, etc.

On the other hand, when the easy-bonding layer 15 contains a radical scavenger, even if a small amount is added, the radical scavenger is still easy to migrate to the polarizer 5, thereby suppressing the degradation of the polarizer. In particular, when the easy-bonding layer 15 contains a hindered amine compound having a nitrooxy group as a radical scavenger, even at a low concentration of less than 1% by weight, it still exhibits an excellent polarizer degradation suppression effect.

When the amount of free radical scavenger contained in the easy bonding layer 15 is too much, the transparency may be reduced. In addition, the amount of free radical scavenger that migrates to other layers during the manufacturing steps of the polarizing plate or the image display device may be large, which may become the cause of bonding inhibition. Therefore, the content of free radical scavenger in the easy bonding layer is preferably 10% by weight or less, preferably 7% by weight or less, more preferably 5% by weight or less, and can also be 4% by weight or less, 3% by weight or less, or 2% by weight or less.

(Microparticles)

As mentioned above, the easy-adhesion layer 15 may also contain microparticles. By making the easy-adhesion layer 15 contain microparticles, fine concave-convex shapes are formed on the surface of the easy-adhesion layer, thereby improving the slipperiness of the easy-adhesion film 1 and inhibiting adhesion.

From the perspective of forming unevenness that helps improve slip, the particle size (average primary particle size) of the microparticles is preferably 10 nm or more, preferably 15 nm or more, and more preferably 20 nm or more. The average primary particle size of the microparticles is preferably smaller than the thickness of the easy-adhesion layer. By making the particle size of the microparticles smaller than the thickness of the easy-adhesion layer, the microparticles can be prevented from falling off the easy-adhesion layer. The particle size of the microparticles is preferably 250 nm or less, preferably 200 nm or less. In addition, by making the average primary particle size of the microparticles smaller than the wavelength of visible light, visible light scattering at the interface between the binder resin and the microparticles can be suppressed. From the perspective of improving transparency, the particle size of the microparticles is preferably 100 nm or less, preferably 80 nm or less, more preferably 60 nm or less, and particularly preferably 50 nm or less.

The microparticles of the easy-bonding layer 15 may be either inorganic microparticles or organic microparticles. Inorganic microparticles are preferred because of their excellent dispersibility and uniformity of particle size. Examples of inorganic microparticles include inorganic oxides such as titanium oxide, aluminum oxide, and zirconium oxide; calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Among these, inorganic oxides are preferred. Examples of organic microparticles include silicone resins, fluorine resins, and acrylic resins. In order to suppress light scattering caused by microparticles, the refractive index difference between the binder resin (usually with a refractive index of about 1.5) and the microparticles should be small. From the perspective of small refractive index difference with the binder resin and excellent dispersibility, the microparticles of the easy-to-bond layer 15 are preferably silica particles.

When the easy-adhesion layer 15 is formed from a water-based composition, it is preferable to use microparticles with high water dispersibility. An aqueous dispersion of the microparticles may also be mixed into the composition. In order to improve the dispersibility of the microparticles, alkaline components such as amines or ammonia may also be added to make the easy-adhesion composition weakly alkaline.

As water-dispersible silica particles, colloidal silica is preferably used. As colloidal silica, commercially available products such as Quartron.PL series manufactured by Fuso Chemical Industries, Ltd., SnowTex series manufactured by Nissan Chemical Industries, Ltd., AERODISP series and AEROSIL series manufactured by NIPPON AEROSIL Co., Ltd., and SEAHOSTAR KE series manufactured by Nippon Catalyst Co., Ltd. can be used.

From the viewpoint of improving the slip of the easy-adhesion film 1 by forming projections and depressions on the surface of the easy-adhesion layer 15, the content of microparticles in the easy-adhesion layer 15 is preferably 3% by weight or more, more preferably 5% by weight or more. In particular, when the thickness of the easy-adhesion layer 15 is small, it is preferable to increase the amount of microparticles per unit area (number density) by increasing the content of microparticles, and uniformly form projections and depressions on the surface of the easy-adhesion layer 15. The content of microparticles in the easy-adhesion layer 15 is preferably 8% by weight or more, more preferably 10% by weight or more, and even more preferably 12% by weight or more. When the content of microparticles in the easy-adhesion layer 15 is too large, there is a possibility that the optical properties are reduced due to increased light scattering at the interface between the binder resin and the microparticles. In addition, as the content of microparticles increases, the relative content of the binder resin decreases, so the adhesion of the easy-adhesion layer may decrease. Therefore, the content of microparticles in the easy-adhesion layer 15 is preferably 50% by weight or less, preferably 40% by weight or less, and more preferably 30% by weight or less.

<Formation of easy-to-bond layer>

The method for forming the easy-adhesion layer 15 on the surface of the film substrate 11 is not particularly limited. It is preferable to coat an easy-adhesion composition (coating liquid) containing a binder resin and a radical scavenger, as well as fine particles as needed, on the film substrate 11 and heat it to form the easy-adhesion layer 15.

(Easy-to-bond composition)

The easily bondable composition is preferably an aqueous composition using water as a solvent. The concentration of the solid component (non-volatile component) in the easily bondable composition is preferably 1-30% by weight, more preferably 2-20% by weight, and even more preferably 3-15% by weight.

The water-based adhesive composition includes water as a solvent (and dispersion medium), a binder resin or its precursor, and microparticles. In order to improve the dispersibility of the microparticles, the adhesive composition may further include alkaline components such as ammonia or amines.

In addition to the binder resin (or its precursor), free radical scavenger and microparticles, the easy-to-bond composition may also contain a crosslinking agent. The easy-to-bond composition may also contain catalysts such as crosslinking promoters, antioxidants, ultraviolet absorbers, leveling agents, anti-adhesive agents, antistatic agents, dispersion stabilizers, defoamers, thickeners, dispersants, surfactants, lubricants and other additives.

(Forming an easy-to-adhesive layer on a film substrate)

Before applying the easy-to-bond composition on the film substrate 11, the film substrate may be subjected to surface treatment. By performing surface treatment, the wetting tension of the film substrate can be adjusted to improve the adhesion with the easy-to-bond layer 15. Examples of surface treatment include corona treatment, plasma treatment, ozone blowing, ultraviolet irradiation, flame treatment, and chemical treatment. Among these, corona treatment or plasma treatment is preferred.

As the coating method of the adhesive composition, rod coating, roller coating, gravure coating, rod coating, narrow hole coating, curtain coating, spray coating, etc. can be listed. The adhesive layer 15 is formed by heating the coated adhesive composition to remove the solvent. The precursor of the binder resin can also be reacted and hardened by heating. For example, when the adhesive composition contains a crosslinking agent, the crosslinking reaction can be promoted by heating.

The heating temperature during the formation of the easy-bonding layer is, for example, about 50 to 200°C. From the perspective of promoting the curing reaction of the resin component in the easy-bonding composition, the heating temperature is preferably above 100°C, more preferably above 120°C, more preferably above 130°C, and particularly preferably above 135°C. When the easy-bonding composition contains alkaline components such as amines or ammonia, the heating temperature is preferably higher than the boiling point of the alkaline component from the perspective of efficiently volatilizing and removing the alkaline component to reduce the residual alkali content.

The easy-adhesion layer can also be formed in the manufacturing step of the film substrate. In addition, the easy-adhesion layer can also be formed by heating the film substrate during its formation. For example, when the film substrate is a stretched film, the easy-adhesion composition can be applied to the surface of the film before stretching or after longitudinal stretching, and the solvent can be dried or the resin can be cured by heating during transverse stretching or synchronous biaxial stretching by a tenter.

When the film substrate is stretched after the easy-to-bond composition is applied, the stretching ratio is preferably 5 times or less, preferably 4 times or less, more preferably 3 times or less, and particularly preferably 2.5 times or less from the perspective of suppressing the occurrence of cracks in the easy-to-bond layer. There is no particular lower limit for the stretching ratio, but from the perspective of improving the film strength, the stretching ratio is preferably 1.3 times or more, preferably 1.5 times or more. When the film substrate is an acrylic film, from the perspective of improving the film strength, it is preferable to stretch in the transport direction (MD) and the width direction (TD) at the above stretching ratios.

When biaxial stretching of the film substrate is performed, the biaxial stretching can be step-by-step biaxial stretching or synchronous biaxial stretching. In addition, oblique stretching can also be performed. When performing step-by-step biaxial stretching, as described above, the film can be stretched in one direction (MD) by roller stretching, and then an easy-to-bond composition can be coated on the film, and the easy-to-bond composition can be heated when stretching by a tenter.

The thickness of the easy-to-bond layer 15 can be adjusted by adjusting the solid component concentration and coating thickness of the easy-to-bond composition. When the film substrate is stretched after the easy-to-bond composition is coated, the thickness of the easy-to-bond layer 15 can also be adjusted by the stretching ratio.

The thickness of the easy-bonding layer is not particularly limited and is usually about 10nm~2μm. From the perspective of improving the adhesion to polarizers and the like and increasing the amount of free radical scavengers contained in the easy-bonding layer to inhibit the degradation of the polarizer, the thickness of the easy-bonding layer is preferably 50nm or more, preferably 80nm or more, more preferably 100nm or more, and can also be 110nm or more, 120nm or more, 130nm or more, 140nm or more, or 150nm or more. From the perspective of inhibiting uneven bonding when bonding with polarizers and the like, or inhibiting streak-like unevenness when the polarizing plate is exposed to a humidified environment, the thickness of the easy-bonding layer is preferably 500nm or less, preferably 300nm or less, more preferably 280nm or less, and can also be 250nm or less or 230nm or less.

[Polarizing plate]

The polarizing plate is a plate that has a transparent protective film (polarizing element protective film) on at least one side of the polarizing element. The polarizing plate can be a plate that has a polarizing element protective film on only one side of the polarizing element, or a plate that has a polarizing element protective film on both sides of the polarizing element 5 as shown in FIG. 2 .

By laminating the above-mentioned easy-to-bond film on one side of the polarizer, a polarizing plate is formed in which the easy-to-bond film as a polarizer protective film is provided only on one side of the polarizer. In addition, FIG. 2 shows a polarizing plate 50 in which an easy-to-bond film 1 is laminating on one side of the polarizer as a polarizer protective film and a transparent film 2 is laminating on the other side, but as mentioned above, the polarizing plate may also be a polarizer protective film laminating only on one side of the polarizer (so-called "single-sided protected polarizing plate"). The side of the single-sided protected polarizing plate where the polarizer protective film is not provided may be connected to the polarizer 5 to provide an adhesive layer, etc.

Regarding the polarizing plate having polarizing element protective films on both sides of the polarizing element, the above-mentioned easy-to-adhesive film may be attached to at least one side of the polarizing element. The polarizing plate may also be one having the above-mentioned easy-to-adhesive film attached to both sides of the polarizing element. The polarizing element 5 and the easy-to-adhesive film 1 are attached via an adhesive layer 6.

<Polarizer>

As the polarizer 5, a polyvinyl alcohol (PVA) polarizer can be used, in which a dichroic substance such as iodine or a dichroic dye is adsorbed on a polyvinyl alcohol film such as polyvinyl alcohol or partially formalized polyvinyl alcohol, and oriented in one direction. For example, a PVA polarizer can be obtained by dyeing a polyvinyl alcohol film with iodine and stretching it.

In the manufacturing process of the polarizer 5, water washing, swelling, crosslinking and other treatments can also be performed as needed. Stretching can be performed before or after iodine dyeing, or while dyeing. Stretching can be done in the air (dry stretching), or in water or in an aqueous solution containing boric acid, potassium iodide, etc. (wet stretching), or a combination of these can be used. The film thickness of the polarizer 5 is not particularly limited, and is usually about 1~50μm.

As the polarizer 5, a thin PVA-based polarizer with a thickness of 10 μm or less may be used. As the thin polarizer, for example, there are thin polarizers described in Japanese Patent Laid-Open No. 51-069644, Japanese Patent Laid-Open No. 2000-338329, WO2010/100917, Japanese Patent No. 4691205, Japanese Patent No. 4751481, etc. These thin polarizers can be obtained by a method including a step of extending a PVA-based resin layer and an extending resin substrate in a laminated state and an iodine dyeing step. If this manufacturing method is used, even if the PVA resin layer is thin, it can be stretched without any undesirable problems such as breakage caused by stretching because it is supported by the stretching resin substrate.

The polarizer may also contain a free radical scavenger such as a hindered amine compound. By making the polarizer contain a free radical scavenger, there is a tendency to suppress the degradation of the polarizer in the use environment of the image display device. Among them, in order to include a free radical scavenger in the polarizer, it is necessary to add a free radical scavenger to the solution used to form the PVA film (or PVA coating) and stretch it after film formation, or it is necessary to include a free radical scavenger in the solution used for iodine dyeing or the washing liquid after dyeing. Therefore, there is a situation where the free radical scavenger hinders the iodine dyeing of PVA or the iodine orientation during stretching, or when the free radical scavenger is adsorbed on PVA, it is accompanied by iodine desorption, which may become the cause of reduced polarization or coloring of transmitted light.

Therefore, the content of the radical scavenger in the polarizer is preferably less than 1% by weight, more preferably less than 0.1% by weight, more preferably less than 0.05% by weight, and may be less than 0.01% by weight, less than 0.005% by weight, or less than 0.001% by weight. The polarizer may also be free of radical scavengers. In addition, here, the polarizer before being bonded to the easy-bonding film 1 containing the radical scavenger with the easy-bonding layer 15 is described. As mentioned above, in the polarizing plate bonded with the easy-bonding film 1 and the polarizer 5, since the radical scavenger will migrate from the easy-bonding layer 15 to the polarizer 5, the polarizer may also contain a radical scavenger in an amount greater than the above range.

<Adhesive>

If the adhesive layer 6 used to bond the polarizer 5 and the easy-bond film 1 is optically transparent, there is no particular restriction on its material, and examples thereof include epoxy resins, silicone resins, acrylic resins, polyurethane, polyamide, polyether, polyvinyl alcohol, etc. The thickness of the adhesive layer 6 is, for example, about 0.01 to 20 μm, and can be appropriately set according to the type of adherend or the material of the adhesive. When using a curing adhesive that exhibits adhesion through a cross-linking reaction after coating, the thickness of the adhesive layer 6 is preferably 0.01 to 5 μm, preferably 0.03 to 3 μm.

As adhesives, various types of adhesives can be used, such as water-based adhesives, solvent-based adhesives, hot melt adhesives, and active energy ray-curing adhesives. Among these, water-based adhesives or active energy ray-curing adhesives are preferred because they can reduce the thickness of the adhesive layer.

As polymer components of water-based adhesives, vinyl polymers, gelatin, vinyl latex, polyurethane, polyester, epoxy, etc. can be exemplified. Among them, vinyl polymers are preferred, and polyvinyl alcohol resins are particularly preferred, due to their excellent adhesion to films and polarizers. Among polyvinyl alcohol resins, polyvinyl alcohol containing acetyl groups is preferred.

From the perspective of adhesion, the average degree of polymerization of polyvinyl alcohol resins should be around 100-5000, preferably 1000-4000. The average saponification degree of polyvinyl alcohol resins should be above 85 mol%, preferably above 90 mol%.

In addition to the polymer such as polyvinyl alcohol resin, the aqueous adhesive composition (solution) may also contain a crosslinking agent. As the crosslinking agent, a compound having at least two functional groups reactive with the polymer constituting the adhesive in one molecule may be used. As the crosslinking agent for polyvinyl alcohol resin, there are: alkylenediamines; isocyanates; epoxides; aldehydes; amino-formaldehydes such as hydroxymethyl urea and hydroxymethyl melamine. Among them, amino-formaldehyde is preferred. As the amino-formaldehyde resin, a compound having a hydroxymethyl group is preferred, and hydroxymethyl melamine is particularly preferred. The amount of the crosslinking agent in the adhesive composition is preferably about 10 to 60 parts by weight, preferably 20 to 50 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol resin.

Active energy ray curing adhesives are adhesives that can undergo free radical polymerization, cationic polymerization, or anionic polymerization by irradiation with active energy rays such as electron beams or ultraviolet rays. Among them, photoradical polymerizable adhesives that initiate free radical polymerization by ultraviolet ray irradiation are preferred because they can be cured at low energy.

烷二醇二丙烯酸酯、EO改質二甘油四丙烯酸酯等多官能單體作為交聯成分。 As monomers of the radical polymerizable adhesive, compounds having a (meth)acryloyl group or compounds having a vinyl group can be cited. Among them, compounds having a (meth)acryloyl group are preferred. As compounds having a (meth)acryloyl group, (meth)acrylic acid alkyl esters such as (meth)acrylic acid C _1-20 chain alkyl esters, (meth)acrylic acid cyclic alkyl esters, and (meth)acrylic acid polycyclic alkyl esters can be cited; (meth)acrylic acid esters containing a hydroxyl group; (meth)acrylic acid esters containing an epoxy group such as (meth)acrylic acid glycidoxylate, etc. The free radical polymerizable adhesive may also include nitrogen-containing monomers such as hydroxyethyl (meth) acrylamide, N-hydroxymethyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, (meth) acrylamide, (meth) acrylamide, and (meth) acrylyl isoflurane. The free radical polymerizable adhesive may also include tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclotrihydroxymethylpropane methyl acrylate, dipropylene glycol diacrylate, and 1,9-nonanediol diacrylate.

Multifunctional monomers such as alkylene glycol diacrylate and EO-modified diglycerol tetraacrylate are used as crosslinking components.

Photocurable adhesives such as photoradical polymerizable adhesives preferably contain a photopolymerization initiator. The photopolymerization initiator can be appropriately selected according to the type of reaction. For example, in the radical polymerizable adhesive, a photoradical generator that generates free radicals by light irradiation is preferably mixed as a photopolymerization initiator. The content of the photoradical generator is generally about 0.1 to 10 parts by weight, preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of the monomer. In addition, when the radical polymerizable adhesive is used in the form of an electron beam curing type, a photopolymerization initiator is not particularly required. In the radical polymerizable adhesive, a photosensitizer represented by a carbonyl compound or the like can also be added as needed. The photosensitizer is used to increase the curing speed or sensitivity by an electron beam. The amount of photosensitizer used is usually about 0.001 to 10 parts by weight relative to 100 parts by weight of the monomer, preferably 0.01 to 3 parts by weight.

The bonding agent may also contain appropriate additives as needed. Examples of additives include coupling agents such as silane coupling agents and titanium coupling agents, bonding promoters such as ethylene oxide, ultraviolet absorbers, anti-degradation agents, dyes, processing aids, ion scavengers, antioxidants, thickeners, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, etc.

The adhesive may also contain a radical scavenger such as a hindered amine compound. By including a radical scavenger in the adhesive, the radical scavenger in the adhesive will migrate to the polarizer in the use environment of the image display device, so there is a tendency to suppress the degradation of the polarizer. Among them, when the adhesive contains a radical scavenger, the radical scavenger will inhibit the curing reaction of the adhesive, which may become a cause of reduced bonding strength. In particular, for radical polymerization adhesives, the radicals required for the curing reaction will be captured by the radical scavenger, so the influence of polymerization inhibition is large.

Therefore, the content of free radical scavenger in the adhesive is preferably less than 1% by weight, more preferably less than 0.1% by weight, and more preferably less than 0.05% by weight, and may also be less than 0.01% by weight, less than 0.005% by weight, or less than 0.001% by weight. The adhesive may also be one that does not contain free radical scavenger. In addition, here, the adhesive before bonding with the adherend such as polarizer or easy-bond film (i.e., before curing) is described. In the cured adhesive layer, free radical scavenger that has migrated from the easy-bond layer, etc., may also be included in an amount greater than the above range.

<Production of polarizing plate>

By bonding the easy-bonding film 1 to one surface (first main surface) of the polarizer 5 through the adhesive layer 6, a polarizing plate can be manufactured. The easy-bonding film 1 can be bonded to the polarizer 5 through the adhesive layer on the surface where the easy-bonding layer is formed, or can be bonded to the polarizer 5 through the adhesive layer on the surface where the easy-bonding layer is not formed.

As shown in FIG2 , the polarizer 5 is bonded to the surface of the easy-bonding layer 15 of the easy-bonding film 1 through the adhesive layer 6, thereby achieving excellent adhesion between the polarizer and the polarizer protection film (easy-bonding film 1). In addition, when the surface of the easy-bonding layer 15 of the easy-bonding film 1 faces the polarizer 5, since the distance between the easy-bonding layer 15 and the polarizer 5 is close, the free radical scavenger contained in the easy-bonding layer 15 can easily migrate into the polarizer 5 through the adhesive layer 6 in the presence of moisture in the use environment of the image display device, thereby achieving a better polarizer degradation inhibition effect.

In laminating the polarizer 5 and the easy-to-bond film 1, it is preferable to apply the adhesive composition to either or both of the polarizer 5 and the easy-to-bond film 1, and then laminate the polarizer 5 and the easy-to-bond film 1 by a roller laminating machine, and harden the adhesive. As a method for applying the adhesive composition to the polarizer 5 and/or the easy-to-bond film 1, a roller method, a spray method, an immersion method, etc. can be listed. Before applying the adhesive composition to the surface of the polarizer 5 and/or the easy-to-bond film 1, a surface treatment such as a corona treatment, a plasma treatment, or a saponification treatment can also be performed.

After the polarizer 5 and the easy-bonding film 1 are bonded, the adhesive layer 6 is formed by curing the adhesive according to the type of adhesive. When a water-based adhesive is used, the adhesive is cured by heating and drying. When an active energy ray curing adhesive is used, the adhesive is cured by irradiation with active energy rays such as electron beams or ultraviolet rays. As mentioned above, by making the adhesive substantially free of free radical scavengers, it is difficult to hinder the curing of the adhesive, and a polarizing plate with high bonding strength between the polarizer 5 and the easy-bonding film 1 can be obtained.

<Transparent protective film>

A transparent protective film 2 can also be bonded to the second main surface of the polarizer 5 through an adhesive layer 7. As the transparent protective film 2, any appropriate transparent film can be used. The thickness of the transparent protective film 2 is about 5 to 200 μm. From the perspective of mechanical strength, transparency, and operability, the thickness of the transparent protective film 2 is preferably 10 to 100 μm, preferably 15 to 60 μm. The thickness of the easy-to-bond film 1 and the transparent protective film 2 can be the same or different.

烯等環狀聚烯烴；聚碳酸酯等。 As materials for forming the transparent protective film 2, there can be listed: polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); cellulose polymers such as cellulose diacetate and cellulose triacetate; styrene polymers such as polystyrene and acrylonitrile-styrene copolymer; polystyrene-based polymers such as polystyrene-based polymers ...

Cyclic polyolefins such as olefins; polycarbonates, etc.

The transparent protective film 2 may also be provided with an easy-bonding layer (not shown) on the bonding surface with the polarizer 5. The transparent protective film 2 may also be provided with an easy-bonding layer that is the same as the easy-bonding layer 15 of the easy-bonding film 1. The transparent protective film 2 may also be an optical functional film such as a phase difference film or a viewing angle compensation film.

As the adhesive layer 7 for bonding the polarizer 5 and the transparent protective film 2, various adhesives such as water-based adhesives, solvent-based adhesives, hot melt adhesives, and active energy ray-curing adhesives can be used. The same adhesive composition can also be used for the adhesive layer 6 and the adhesive layer 7.

The polarizing plate may also be one that has optical layers such as a phase difference film, a viewing angle compensation film, and a brightness enhancement film in addition to the transparent protective film 2 that serves as a polarizer protective film.

[Polarizing plate with adhesive]

An adhesive layer 20 for bonding to an image display unit 60 such as a liquid crystal unit or an organic EL unit, or an adhesive layer 30 for bonding to a front transparent component 70 may also be provided on one or both sides of the polarizing plate 50.

FIG3 is a cross-sectional view showing an example of the structure of a polarizing plate 90 with adhesive layers 20 and 30 provided on both sides of the polarizing plate 50. A peeling pad (not shown) may be temporarily adhered to the surface of the adhesive layers 20 and 30 to prevent contamination of the adhesive layers. As the peeling pad, a peeling pad obtained by coating the surface of a plastic film with a peeling agent such as a silicone-based release agent, a long-chain alkyl-based release agent, or a fluorine-based release agent is preferably used.

If a polarizing plate with an adhesive layer pre-attached on the polarizing plate is used, when forming an image display device, there is no need to set a step of attaching another adhesive layer on the polarizing plate 50 in order to bond with the image display unit 60 or the front transparent component. Therefore, the manufacturing steps of the image display device can be simplified.

As the adhesive forming the adhesive layer 20, 30, an adhesive having an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-based polymer or a rubber-based polymer as a base polymer can be appropriately selected and used. In particular, an acrylic adhesive is preferred because of its excellent optical transparency, moderate wettability and cohesiveness, and excellent weather resistance and heat resistance.

If the acid contained in the adhesive layer migrates to the polarizer, it will act as an acid catalyst for polyene formation due to dehydration of polyvinyl alcohol, and may become the reason for the decrease in the monomer transmittance of the polarizer. Therefore, the adhesive layers 20 and 30 provided on the polarizer 50 should have a low content of organic acid monomers (free organic acids) such as (meth) acrylic acid. The content of acid monomers in the adhesive layers 20 and 30 should be less than 100 ppm, preferably less than 70 ppm, and more preferably less than 50 ppm. The acid monomer content of the adhesive layer can be obtained by immersing the adhesive in pure water and heating it at 100°C for 45 minutes, and then quantifying the acid monomers extracted into the water by ion chromatography.

In thermosetting or light-curing polymers, there will inevitably be unreacted residual monomers. Therefore, in order to reduce the acid monomer content in the adhesive layer, it is advisable to reduce the amount of organic acid monomer components such as (meth) acrylic acid in the monomer components constituting the base polymer. The base polymer of the adhesive should substantially not contain organic acid monomers (carboxyl-containing monomers) as monomer units. Relative to the total amount of monomer components constituting the base polymer, the content of carboxyl-containing monomer components should be less than 0.5% by weight, more preferably less than 0.1% by weight, and more preferably less than 0.05% by weight.

The thickness of the adhesive layer 20, 30 is not particularly limited. From the perspective of adhesion or operability, it is usually about 5~500μm, and can also be about 10~300μm. The thickness of the adhesive layer 20 arranged on one side of the polarizing plate 50 and the thickness of the adhesive layer 30 arranged on the other side of the polarizing plate 50 can be the same or different.

The adhesive layer may also contain a free radical scavenger such as a hindered amine compound. By making the adhesive contain a free radical scavenger, in the use environment of the image display device, the free radical scavenger in the adhesive will migrate to the polarizer, so there is a tendency to suppress the degradation of the polarizer. However, in the image display device, the adhesive layers 20 and 30 are separated and arranged away from the polarizer 5, so the amount of free radical scavenger that migrates from the adhesive layers 20 and 30 to the polarizer 5 is small, and the effect of suppressing the degradation of the polarizer is limited. In order to improve the effect of inhibiting polarizer degradation, it is necessary to increase the amount of free radical scavenger contained in the adhesive. However, when the amount of free radical scavenger is too much, the adhesive's adhesion (anchoring force to the adherend) tends to decrease due to changes in the adhesive composition (reduction of components that contribute to adhesion) or the seepage of free radical scavenger. In addition, when the adhesive is a photocurable composition, the free radical scavenger may become a cause of hindering curing.

Therefore, the content of the radical scavenger in the adhesive layer is preferably less than 10% by weight, more preferably less than 5% by weight, and more preferably less than 1% by weight, and may also be less than 0.5% by weight, less than 0.1% by weight, less than 0.05% by weight, less than 0.01% by weight, less than 0.005% by weight, or less than 0.001% by weight. The adhesive layer may also be free of radical scavengers. In addition, the adhesive layer before bonding with the adherend such as the polarizing plate is described here. The adhesive layer after bonding with the polarizing plate may also contain radical scavengers that have migrated from the easy bonding layer, etc., in an amount greater than the above range.

[Image display device]

By attaching a polarizing plate 50 to the surface of an image display unit 60 such as a liquid crystal unit or an organic EL unit, an image display device can be formed. The formation of a liquid crystal display device is formed by appropriately assembling a liquid crystal unit and a polarizing plate, and components such as a lighting system as required, and incorporating a driving circuit, etc. In an organic EL display device, a circular polarizing plate composed of a polarizing plate and a phase difference film (typically a 1/4 wavelength plate) is attached to the surface of an organic EL unit, which can reduce the re-emission of reflected light from external light caused by metal electrodes, etc., thereby improving visibility.

FIG4 is a schematic cross-sectional view showing one form of an image display device. In the image display device 100 of FIG4 , a polarizing plate 50 is bonded to the visual side of the image display unit 60 through an adhesive layer 20, and a front transparent component 70 is bonded to the visual side of the polarizing plate 50 through an adhesive layer 30.

In addition, although not shown, in a liquid crystal display device having a liquid crystal unit, a light source side polarizing plate is attached to the surface of the image display unit 60 opposite to the visual side through an appropriate adhesive layer or bonding agent layer, and then a light source such as a backlight is configured.

As the front transparent member 70 disposed on the visual side of the image display unit 60, a front transparent plate (cover window) or a touch panel can be used. As the front transparent plate, a transparent plate with appropriate mechanical strength and thickness can be used. As the transparent plate, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate can be used. As the touch panel, various touch panels such as a resistive film method, a capacitive method, an optical method, an ultrasonic method, etc., or a glass plate or a transparent resin plate with a touch sensor function can be used.

The image display device 100 has an image display unit 60 and a front transparent component 70 attached to both sides of the polarizing plate 50 through adhesive layers 20 and 30, so it is difficult for moisture to escape from the main surface of the polarizing plate 50, and it is easy for moisture to be retained inside the polarizing plate. It is known that when the polarizer is exposed to a high temperature environment for a long time with moisture retention, the polyeneization of the polarizer is easy to progress, thereby reducing the monomer transmittance of the polarizing plate.

As described above, by making the easy-adhesion layer 15 of the easy-adhesion film 1 attached to the polarizer 5 contain a radical scavenger, even in the image display device 100 in which the image display unit 60 and the front transparent component 70 are provided on both sides of the polarizer 50, the polyeneization of the polarizer 5 can be suppressed, so the decrease in the monomer transmittance of the polarizer caused by heating is small.

We believe that when the polarizing plate is exposed to a high temperature environment in the presence of moisture, the radical scavenger contained in the easy-bonding layer 15 is easily diffused (migrated) to other layers through the moisture, and the radical scavenger will also migrate to the polarizer 5 attached to the easy-bonding film 1, and play a role in inhibiting the polyeneization of the polyvinyl alcohol of the polarizer. In other words, we believe that in an environment that is easy to promote polyeneization, such as high temperature and the presence of moisture, the migration of the radical scavenger from the easy-bonding layer 15 to the polarizer 5 will also be promoted, so the polyeneization will be inhibited, thereby inhibiting the decrease in the monomer transmittance of the polarizing plate.

As mentioned above, when the polarizer 5 contains a radical scavenger, it may cause poor dyeing or poor orientation of iodine. When the adhesive layer 6, 7 or the adhesive layer 20, 30 contains a radical scavenger, there is a risk of hindering curing or reducing the bonding force due to seepage. In addition, since the polarizer protective films 1, 2 are arranged between the adhesive layer 20, 30 and the polarizer 5, the distance between the adhesive layer and the polarizer is long, and the amount of radical scavenger migrating from the adhesive layer to the polarizer is small, so the polyene inhibition effect is limited.

In contrast, when the easy-bonding layer 15 of the easy-bonding film 1 adjacent to the polarizer 5 contains a radical scavenger, it is less likely to hinder curing or poor bonding, and because the easy-bonding layer 15 is close to the polarizer 5, the radical scavenger is easy to migrate to the polarizer 5. Therefore, an image display device can be obtained that suppresses the decrease in the monomer transmittance of the polarizing plate in a high temperature environment and does not reduce the bonding strength between the layers.

In addition, FIG. 4 shows a polarizing plate 50 disposed on the visual side of the image display unit 60, in which an easily bonded film 1 as a polarizing element protective film is provided between the polarizer 5 and the front transparent member 70, but the configuration of the easily bonded film 1 containing a radical scavenger in the easily bonded layer 15 is not limited to this form. For example, the polarizing element protective film disposed between the polarizer 5 and the image display unit 60 may also be the above-mentioned easily bonded film. In a liquid crystal display device, the polarizing plate disposed between the image display unit and the light source may also have the above-mentioned easily bonded film as a polarizing element protective film. As mentioned above, the polarizing plate used for the image display device may also be a single-sided protected polarizing plate in which the easily bonded film as a polarizing element protective film is attached to only one side of the polarizer.

Implementation example

The following examples are provided to further illustrate the present invention, but the present invention is not limited to these examples. In the following, the concentration "%" is expressed as weight % unless otherwise specified.

[Implementation Example 1]

<Production of easy-to-bond films>

(Preparation of easy-to-attach compositions)

唑啉之聚合物水溶液(日本觸媒製「Epocros WS-700」)4.2重量份、1%之氨水2.3重量份、平均一次粒徑35nm的膠質氧化矽的20%水分散液(扶桑化學工業製「Quartron PL-3」)6重量份及純水71重量份予以混合，調製易接著組成物A，其中前述水系聚胺甲酸酯包含作為樹脂成分的聚酯胺甲酸酯及異佛酮二異氰酸酯，並進一步包含作為硬化觸媒之三乙胺及分散介質之甲基乙基酮。 16.5 parts by weight of water-based polyurethane (Superflex 210R manufactured by Daiichi Kogyo Seiyaku) with a solid content of 35% and 25% of

4.2 parts by weight of an aqueous solution of a polymer of oxazoline ("Epocros WS-700" manufactured by Nippon Catalyst), 2.3 parts by weight of 1% ammonia water, 6 parts by weight of a 20% aqueous dispersion of colloidal silica having an average primary particle size of 35 nm ("Quartron PL-3" manufactured by Fuso Chemical Industries), and 71 parts by weight of pure water were mixed to prepare an easily bondable composition A, wherein the aqueous polyurethane comprises polyester urethane and isophorone diisocyanate as resin components, and further comprises triethylamine as a curing catalyst and methyl ethyl ketone as a dispersion medium.

0.0008 parts by weight (equivalent to 0.01 parts by weight relative to 100 parts by weight of the solid content of the composition) of the free radical scavenger (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl free radical) represented by the following formula (9) is added to the easily bonded composition A to prepare an easily bonded composition containing the free radical scavenger.

[Chemical formula 4]

(Forming an easy-to-adhesive layer on acrylic film)

The easy-to-adhesive film was produced using a film production device equipped with a melt extrusion film production device, a gravure coating machine, a tenter-type synchronous double-axis stretching device, and a winding device. As the acrylic resin, pellets of imidized MS resin (glass transition temperature: 120°C) were used, which was the same as that used in the production of the "transparent protective film 1A" described in the embodiment of Japanese Patent Laid-Open No. 2017-26939. After the acrylic resin was melt-extruded from a T-die and formed into a film with a thickness of 160μm, the above-mentioned easy-adhesion composition was coated on one side of the film with a wet thickness of about 9μm using a gravure coater, and then stretched to 2 times in the longitudinal direction (MD) and the width direction (TD) using a synchronous biaxial stretching tenter in a heating furnace at a temperature of 140°C, thereby obtaining an easy-adhesion film with a 200nm thick easy-adhesion layer on one side of the 40μm thick acrylic film.

<Production of polarizing plate>

(Production of polarizing elements)

A 45μm thick polyvinyl alcohol (PVA) resin film ("PE4500" manufactured by Kuraray Co., Ltd.) was stretched uniaxially in the longitudinal direction by 5.9 times by a roller stretching machine, while the swelling bath, dyeing bath, crosslinking bath 1, crosslinking bath 2 and cleaning bath shown in Table 1 were sequentially conveyed and dried at 70°C for 5 minutes to produce a polarizer with a thickness of 18μm. The iodine concentration and potassium iodide concentration in the dyeing bath were adjusted so that the single body transmittance of the polarizer was 43.4%.

(Preparation of UV-curable adhesive)

A UV curable adhesive was prepared, which contained 40 parts by weight of N-hydroxyethylacrylamide and 60 parts by weight of acrylamide as curing components, and 3 parts by weight of 2-methyl-1-(4-methylthiophenyl)-2-aminofolin-1-one ("Irgacure 819" manufactured by BASF Corporation) as a polymerization initiator.

(Lamination of polarizer and polarizer protective film)

The easy-bonding film prepared as described above was used as a polarizer protective film on one side, and a biaxially stretched annular polyolefin film ("ZEONOR Film ZF-14" manufactured by ZEON Japan) was used as a polarizer protective film on the other side. The above-mentioned UV-curable adhesive was applied to the easy-bonding layer forming surface of the adhesive film and the surface of the ZEONOR Film with a thickness of about 1 μm, and after being bonded to the polarizer using a roller laminating machine, the adhesive was cured by irradiating with UV light with a cumulative light amount of 1000 mJ/ ^cm2 , thereby obtaining a polarizing plate having an acrylic film (easy-bonding film) on one side of the polarizer and a ZEONOR Film on the other side.

[Examples 2~5]

In the preparation of the easy-to-bond composition, the amount of the free radical scavenger added to the easy-to-bond composition A (relative to the amount of the solid component of the composition) is changed as shown in Table 2. In addition, an easy-to-bond film is prepared in the same manner as in Example 1, and the obtained easy-to-bond film is attached to a polarizer to obtain a polarizing plate.

[Comparison Example 1]

In the preparation of the easy-to-bond composition, no free radical scavenger is added, and the easy-to-bond composition A is directly used. In addition, an easy-to-bond film is prepared in the same manner as in Example 1, and the obtained easy-to-bond film is bonded to a polarizer to obtain a polarizing plate.

[Comparison Example 2]

In the preparation of the adhesive, the radical scavenger represented by the above formula (9) is added to make the concentration 10%, and the adhesive containing the radical scavenger is prepared. The polarizing plate is prepared in the same manner as in Comparative Example 1, except that the adhesive is used in the bonding of the polarizer and the easy-bonding film.

[Comparison Examples 3 and 4]

A polarizing plate was prepared in the same manner as in Comparative Example 2, except that the amount of free radical scavenger added to the adhesive (concentration in the adhesive) was changed to that shown in Table 2.

[Evaluation of polarizing plates]

<Next strength>

The polarizing plate was cut into a size of 200mm in the direction parallel to the extension direction of the polarizer (absorption axis direction) and 15mm in the orthogonal direction (transmission axis direction). A cut was made between the easy-to-bond film and the polarizer with a cutter, and then the ZEONOR Film side of the polarizing plate was attached to the glass plate. A peeling test was performed using a tensile compression tester (MINEBEA "TG-1kN") at a peeling angle of 90° and a peeling speed of 1000mm/min to measure the adhesion between the polarizer and the easy-to-bond film.

<Changes in single body transmittance during heating test>

(Preparation of acrylic adhesive)

In a solution of an acrylic polymer with a weight average molecular weight of 1.8 million formed by copolymerization of butyl acrylate and 4-hydroxybutyl acrylate at a weight ratio of 99:1, 0.02 weight parts of an isocyanate crosslinking agent ("Takenate D110N" manufactured by Tosoh) and 0.2 weight parts of a silane coupling agent ("X-41-1056" manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed with 100 weight parts of the polymer to prepare an acrylic adhesive composition.

(Preparation of adhesive layer)

The above-mentioned acrylic adhesive composition was applied to the release layer forming surface of a peeling pad (a polyester film having a silicone release layer on the surface; "MRF38" manufactured by Mitsubishi Chemical) in such a way that the thickness of the adhesive layer after drying became 20μm, and dried at 90°C for 1 minute to form an adhesive layer on the peeling pad.

(Production of simulation image display device for evaluation)

The polarizing plate was cut into a square with a side length of 40 mm, and the ZEONOR Film side was bonded to a glass plate through the above adhesive layer. The other side of the polarizing plate (the side that is easy to bond to the film) was bonded to another glass plate through a 200 μm thick acid-free acrylic adhesive sheet (Nitto Denko, "LUCIACS CS9868"), and a simulated image display device was produced with both sides of the polarizing plate bonded to glass plates through adhesive layers.

(Evaluation of the change in single-body transmittance △Ts due to heating)

The simulated image display device was placed in a hot air oven at 105°C for 48 hours to perform a heating test. The decrease in the single transmittance _ΔTs before and after the heating test was calculated by the following formula based on the single transmittance Ts 0 before the heating test and the single transmittance Ts ₁ after the heating test. In addition, the single transmittance is the Y value corrected for the visual sensitivity using the 2-degree field (C light source) of JIS Z 8701-1982, and is measured using a spectrophotometer (Murakami Color Technology Laboratory, "DOT-3").

△Ts(%)= _Ts0 (%)- _Ts1 (%)

[Evaluation Results]

The easy-bonding layer of the easy-bonding film in the polarizing plate of Examples 1 to 5 and Comparative Examples 1 to 4 and the content of the free radical scavenger in the adhesive, the bonding strength between the polarizer and the easy-bonding film, and the reduction in the monomer transmittance △Ts before and after the heating test are shown in Table 2.

For Comparative Example 1, in which the easy-bonding layer does not contain a radical scavenger, the decrease in monomer transmittance due to the heating test is 19%. In contrast, for Example 1, which uses an easy-bonding film having an easy-bonding layer containing 0.01% of a radical scavenger, the △Ts is 5%, which suppresses the decrease in monomer transmittance of the polarizing plate caused by heating. For Examples 2 to 5, the △Ts is smaller than that of Example 1, and it is observed that the more radical scavenger contained in the easy-bonding layer, the more the decrease in monomer transmittance is suppressed. We believe that this is because the radical scavenger contained in the easy-bonding layer migrates to the polarizer under a heating environment, and has the effect of suppressing the polyeneization of polyvinyl alcohol.

In Comparative Examples 2 to 4, where the adhesive layer includes a radical scavenger, it is observed that ΔTs tends to decrease as the amount of radical scavenger added increases, similar to Examples 1 to 5. However, in Comparative Examples 2 to 4, it is observed that the bonding strength between the polarizer and the easy-to-bond film tends to decrease as the amount of radical scavenger added increases, indicating that it is difficult to have both excellent heat durability and bonding strength. Regarding Comparative Examples 2 to 4, we believe that the reason for the decrease in bonding strength is that the radical scavenger contained in the adhesive hinders the curing reaction of the adhesive.

[Comparative Examples 5-7: Examples in which a radical scavenger is added to an adhesive] In Comparative Examples 5-7, the polarizing plate prepared in Comparative Example 1 was used, and the radical scavenger represented by the above formula (9) was added to the acrylic adhesive to obtain the concentration shown in Table 3. Thus, a simulated image display device containing a radical scavenger in the adhesive layer for bonding the ZEONOR Film side of the polarizing plate to the glass plate was prepared, and the reduction in the single unit transmittance △Ts of the simulated image display device before and after the heating test was measured.

<Determination of anchoring strength>

The adhesive layer containing the radical scavenger is attached to the ZEONOR Film side of the polarizing plate to make a polarizing plate with adhesive and cut into 50mm wide and 200mm long. The side of the polarizing plate with easy-to-bond film is attached to a glass plate with double-sided tape. An ITO film cut into 25mm wide and 200mm long is attached to the adhesive layer of the polarizing plate with adhesive and left at room temperature for 20 minutes as a test sample. Using a tensile compression tester ("TCM-1kNB" manufactured by MINEBEA), a peeling test was performed at a peeling angle of 180° and a peeling speed of 1000 mm/min to determine the peeling force at the interface between the polarizing plate (ZEONOR Film) and the adhesive layer, which was used as the anchoring force of the adhesive.

The anchoring force between the polarizing plate of Examples 1, 5 and Comparative Example 1 and the adhesive layer without free radical scavenger was measured in the same manner as above.

[Evaluation Results]

The free radical scavenger content of the easy-bonding layer and the adhesive layer of the easy-bonding film in the polarizing plate of Examples 1 and 5 and Comparative Examples 1, 7 and 8, the anchoring strength of the adhesive layer to the polarizing plate, and the reduction in the monomer transmittance △Ts before and after the heating test are shown in Table 3.

For example, in Comparative Example 5, in which the adhesive layer contains 0.01% of free radical scavenger, ΔTs is smaller than that of Comparative Example 1, but the effect of suppressing the decrease in the monomer transmittance is limited compared to Examples 1 to 5. One of the reasons for the limited effect of reducing ΔTs is that a polarizer protective film is disposed between the adhesive layer and the polarizer, and the two are separated, so the amount of free radical scavenger migrating from the adhesive layer to the polarizer is small.

In Comparative Example 6, in which the adhesive layer contains 0.2% of free radical scavenger, ΔTs is smaller than that in Comparative Example 5, but the effect of suppressing the decrease in monomer transmittance is not sufficient. In Comparative Example 6, a decrease in the anchoring force of the adhesive was observed. In Comparative Example 7, in which the adhesive layer contains 20% of free radical scavenger, ΔTs is smaller than that of Comparative Examples 5 and 6. However, since the amount of free radical scavenger added to the adhesive layer is excessive, the anchoring force of the adhesive is greatly reduced.

From the results of the above-mentioned embodiments and comparative examples, it can be seen that by making the easy-bonding layer of the easy-bonding film attached to the polarizer contain a radical scavenger, the decrease in the monomer transmittance of the polarizing plate in a high temperature environment can be suppressed, and the impact on the polarization characteristics or the adhesion between components is small.

1: Easy to bond film

11: Film substrate

15: Easy to bond layer

2: Transparent film

5: Polarizer

6,7: Next is the agent layer

50: Polarizing plate

Claims (7)

A polarizing plate comprises: a polyvinyl alcohol-based polarizer having a first main surface and a second main surface, and a polarizer protective film bonded to the first main surface of the polarizer; the polarizer protective film is an easy-to-bond film having an easy-to-bond layer on the surface of a transparent film substrate; the easy-to-bond layer comprises a binder resin and a water-soluble free radical scavenger; the easy-to-bond layer of the easy-to-bond film and the first main surface of the polarizer are bonded via the adhesive layer, and the adhesive layer is composed of a cured product of a curing type adhesive that exhibits adhesiveness through a crosslinking reaction. As in claim 1, the polarizing plate, wherein the aforementioned free radical scavenger is a hindered amine compound. As in the polarizing plate of claim 1 or 2, the free radical scavenger is a compound having a nitrooxy group, or a compound that can generate a nitrooxy group. As in claim 1 or 2, the polarizing plate, wherein the aforementioned easy-to-bond layer contains 0.01 to 10 weight % of the aforementioned free radical scavenger. As in claim 1 or 2, the polarizing plate, wherein the aforementioned easy-to-bond layer further comprises microparticles. A polarizing plate with adhesive, wherein an adhesive layer is provided on at least one side of the polarizing plate of any one of claims 1 to 5. An image display device having an image display unit and a polarizing plate as described in any one of claims 1 to 5.