WO2022049687A1

WO2022049687A1 - Laminate for image display device and image display device

Info

Publication number: WO2022049687A1
Application number: PCT/JP2020/033339
Authority: WO
Inventors: Yuta Konno; Tomohiro Miyazaki; Ruediger Sauer; Wilfried Loevenich; Tetsuya Suzuki
Original assignee: Soken Chemical & Engineering Co., Ltd.; Heraeus Deutschland GmbH & Co. KG; Heraeus Kabushiki Kaisha
Priority date: 2020-09-02
Filing date: 2020-09-02
Publication date: 2022-03-10
Also published as: CN116056882A; KR20230054705A; TW202229010A; JP2023539890A

Abstract

The laminate for an image display device of the present invention at least comprises: an adhesive layer formed of an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C), an image display element located on one of two surfaces of the adhesive layer, and a polarizing film located on the other surface of the adhesive layer, wherein with respect to a test material comprising the adhesive layer having the polarizing film on one surface and a protective material, which has a release layer and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer, with the adhesive layer and the release layer being located so as to be adjacent to each other, when the protective material is peeled off from the test material in an environment of a temperature of 23C and a relative humidity of 50%, a surface resistivity of the adhesive layer is 1 x 10¹²Ω/□ or less, a haze value of the test material from which the protective material has been peeled off is 2% or less, and the following formula (1) is satisfied.　y/x < 10 ・・・ (1) (wherein x represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, and y represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.)

Description

LAMINATE FOR IMAGE DISPLAY DEVICE AND IMAGE DISPLAY DEVICE

　The present invention relates to a laminate for an image display device and the image display device, and particularly relates to a laminate for an image display device having an adhesive layer having a low surface resistivity and a low haze, and an image display device using the same.

　Adhesives have been conventionally used for bonding optical members in image display devices such as liquid crystal displays and organic EL displays. The adhesive used for bonding optical members is required to be transparent to the light that constitutes a display image emitted from image display elements.

　Here, examples of the optical member to be bonded with an adhesive when configuring an image display device include an optical film such as a polarizing film, a transparent conductive film, and a wide view film. Among them, the polarizing film is produced by adsorbing a dichroic dye on a polymer film such as polyvinyl alcohol, and stretching and orienting it. A protective film comprising triacetyl cellulose (TAC) or polycycloolefin (COP) etc., is provided on the surface of the polymer film after stretched and oriented.

　Patent Document 1 describes a liquid crystal display device with a touch panel in which a resistive film type touch panel is integrated on the front surface side of a liquid crystal display panel. Specifically, an image display device is described in which a transparent conductive film made of indium tin oxide (ITO) or the like is formed on a polarizing plate of a liquid crystal display panel configured to sandwich a polarizing film (polarizing layer) between a pair of protective layers made of triacetyl cellulose (TAC) and used as a flexible electrode of a touch panel.

　[PTL 1] Japanese Unexamined Patent Application, Publication No. H07-084705

Problems to be Solved by the Invention

　In recent years, in order to prevent abnormalities in image display in an image display device, it has been required to prevent static electricity from easily accumulating in various members constituting an optical member. In particular, it has been required to increase the conductivity of an adhesive layer in order to prevent static electricity from accumulating in the adhesive layer used for bonding optical members.

　A possible method for increasing the conductivity of an adhesive layer is a method that involves incorporating a conductive material such as a conductive polymer into the adhesive. However, in the method that involves incorporating the conductive material into the adhesive, the haze of the adhesive layer is increased and the light transmittance is reduced, instead of increasing the conductivity of the adhesive layer. Therefore, it has been required to further improve the light transmittance in the image display device while lowering the surface resistivity of the adhesive layer to further improve the antistatic performance.

　Further, in recent years, image display devices have been used in various applications and environments. For example, image display devices are not only used in room temperature environments, but also in severe environments such as high temperature and high humidity environments. Examples of such high temperature and high humidity environments include environments in tropical areas and vehicle interiors and the interiors of machines provided outdoor. Therefore, there has been a demand for a laminate to be used for an image display device that can be used even in such a severe environment.

　The present invention has been made in view of the above circumstances, and the purpose of the present invention is to provide a laminate for an image display device and the image display device, which can have both a low resistance value and a low haze and can be used even in a high temperature and high humidity environment.

Means for Solving the Problems

　As a result of intensive studies to solve the above problems, the present inventors have discovered that when an adhesive layer is formed using an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a cross-linking agent (C), the surface resistivity and the haze value are low, and a decrease in the surface resistivity is less likely to occur even in a high temperature and high humidity environment, and thus the above-mentioned object can be achieved.

　(1) A first invention of the present invention is a laminate for an image display device at least comprising: an adhesive layer formed of an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C), an image display element located on one of two surfaces of the adhesive layer, and a polarizing film located on the other surface of the adhesive layer, wherein with respect to a test material comprising the adhesive layer having the polarizing film on one surface and a protective material, which has a release layer and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer, with the adhesive layer and the release layer being located so as to be adjacent to each other, when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, a surface resistivity of the adhesive layer is 1 x 10¹²Ω/□ or less, a haze value of the test material from which the protective material has been peeled off is 2% or less, and the following formula (1) is satisfied,
　y/x < 10 ・・・ (1)
(wherein x represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, and y represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.)

　(2) A second invention of the present invention is the laminate for an image display device according to the first invention, wherein the adhesive composition further comprises a silane coupling agent (D).

　(3) A third invention of the present invention is the laminate for an image display device according to the first or the second invention, wherein the adhesive composition further comprises a dispersant (E) that is an amphiphilic compound, and wherein the dispersant (E) is a nonionic compound having an ether or ester of a trihydric or higher polyhydric alcohol or an oxyalkylene chain.

　(4) A fourth invention of the present invention is the laminate for an image display device according to any one of the first to third inventions, wherein a haze value of the test material is 2% or less when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.

　(5) The fifth invention of the present invention is the laminate for an image display device according to any one of the first to fourth inventions, wherein the polarizing film has a film protective layer on one or both surfaces, and wherein the film protective layer comprises cycloolefin polymer (COP), polyethylene terephthalate (PET) or polymethyl methacrylate (PMMA).

　(6) A sixth invention of the present invention is an image display device having the laminate for an image display device according to any one of the first to fifth inventions.

Effects of the Invention

　According to the present invention, a laminate for an image display device and the image display device, which have both a low resistance value and a low haze and can be used even in a high temperature and high humidity environment, can be provided.

Fig. 1 is a cross-sectional view showing a structure of a laminate for an image display device according to the present invention. Fig. 2 is a cross-sectional view showing a structure of a test material used for evaluation of an adhesive layer in a laminate for an image display device according to the present invention.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

　Embodiments of the present invention will be described as follows, but are shown only illustratively. It goes without saying that various modifications can be made without departing from the technical idea of the present invention.

<<Laminate for image display device>>
　The laminate for an image display device of the present invention at least comprises: an adhesive layer formed of an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C), an image display element located on one of two surfaces of the adhesive layer, and a polarizing film located on the other surface of the adhesive layer, wherein with respect to a test material comprising the adhesive layer having the polarizing film on one surface and a protective material, which has a release layer and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer, with the adhesive layer and the release layer being located so as to be adjacent to each other, when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, a surface resistivity of the adhesive layer is 1 x 10¹²Ω/□ or less, a haze value of the test material from which the protective material has been peeled off is 2% or less, and the following formula (1) is satisfied.
　y/x < 10 ・・・ (1)
(wherein x represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, and y represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.)

　In the laminate for an image display device of the present invention, the use of the adhesive layer formed of the adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C) reduces the surface resistivity and the haze value in the adhesive layer, and makes a decrease in the surface resistivity of the adhesive layer difficult to take place even under high temperature and high humidity conditions. Accordingly, a laminate for an image display device and the image display device, which have both a low resistance value and a low haze and can be used even in a high temperature and high humidity environment, can be obtained.

　Here, as shown in Fig. 1, a laminate 10 for an image display device of the present invention at least comprises an adhesive layer 11, an image display element 12 located on one surface of both surfaces of the adhesive layer 11, and a polarizing film 13 located on the other surface of the adhesive layer 11.

<Adhesive layer>
　The adhesive layer 11 is formed of an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C). As a result, the thus formed layer has high conductivity and high mechanical strength after crosslinking of the adhesive polymer (A), so that the image display element and the polarizing film can be firmly fixed. In particular, in the laminate 10 for an image display device of the present invention, the adhesive layer 11 has high moisture resistance, so that the polarizing film and the image display element can be hardly peeled off even in a high temperature and high humidity environment.

　As the adhesive composition forming the adhesive layer 11, a composition comprising the adhesive polymer (A), the conductive polymer (B) comprising a conjugated polymer and a polyanion, and the crosslinking agent (C) can be used. The details of the adhesive composition forming the adhesive layer 11 will be described later.

　The adhesive layer 11 is as shown in Fig. 2. With respect to the test material 20 comprising the adhesive layer 11 having the polarizing film 13 on one surface and a protective material 21, which has a release layer 21a and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer 11, with the adhesive layer 11 and the release layer 21a being located so as to be adjacent to each other, when the protective material 21 is peeled off from the test material 20 in an environment of a temperature of 23°C and a relative humidity of 50%, the surface resistivity is 1 x 10¹²Ω/□ or less, preferably 1 x 10¹¹Ω/□ or less, and more preferably 1 x 10¹⁰Ω/□ or less. As a result, high antistatic properties are imparted to the adhesive layer 11, so that it is possible to prevent abnormalities from occurring in images displayed on the image display device.

　Further, with respect to the test material 20 comprising the adhesive layer 11 having the polarizing film 13 on one surface and the protective material 21, which has a release layer 21a and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer 11, with the adhesive layer 11 and the release layer 21a being located so as to be adjacent to each other, when the protective material 21 is peeled off from the test material 20 in an environment of a temperature of 23°C and a relative humidity of 50%, a haze value (i.e., a haze value of the polarizing film 13 with the adhesive layer 11 is adhered thereto) of the test material 20 is 2% or less and is preferably 1% or less. Accordingly, the transparency of the adhesive layer 11 is enhanced, and therefore the adhesive layer 11 can be preferably used also for the application of an image display device using an organic EL element or a liquid crystal display element. Note that the haze value (haze degree) in the adhesive layer 11 is found from (Td/Tt) × 100(%) when the total light transmittance is assumed as Tt and the diffusion transmittance is assumed as Td.

　With respect to the test material 20 comprising the adhesive layer 11 having the polarizing film 13 on one surface and the protective material 21, which has a release layer 21a and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer 11, with the adhesive layer 11 and the release layer 21a being located so as to be adjacent to each other, a haze value of the test material 20 (i.e., a haze value of the polarizing film 13 with the adhesive layer 11 adhered thereto) is preferably 3% or less and more preferably 2% or less when the protective material 21 is peeled off from the test material 20 in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour. As a result, even in an environment of a high temperature up to 60°C and a high humidity of up to 90% relative humidity, particularly the adhesive layer 11 can maintain high transparency, so that even in a severe environment such as a high temperature and high humidity environment, it is possible to prevent the images displayed on the image display device from fogging.

　Moreover, the adhesive layer 11 preferably has a high light transmittance. In particular, the total light transmittance of the polarizing film 13 having the adhesive layer 11 adhered thereto is preferably 30% or more, more preferably 50% or more, further preferably 70% or more, and further preferably 90% or more. As described above, increasing the total light transmittance of the polarizing film 13 having the adhesive layer 11 adhered thereto, the light transmittance of the entire laminate 1 for an image display device can also be increased, so that the laminate 1 for an image display device can be preferably used for the applications of image display devices.

　The adhesive layer 11 satisfies the following formula (1).
　y/x < 10 ・・・ (1)
(wherein x represents a surface resistivity of the adhesive layer 11 when the protective material 21 is peeled off from the test material 20 in an environment of a temperature of 23°C and a relative humidity of 50%, and y represents a surface resistivity of the adhesive layer 11 when the protective material 21 is peeled off from the test material 20 in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material 20 has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.) When the adhesive layer 11 satisfies the relationship of the above formula (1), not only in a normal temperature environment with a temperature of 23°C and a relative humidity of 50%, but also in an environment with a high temperature up to 60°C and a high humidity up to 90% relative humidity, the fluctuation of the surface resistivity of the adhesive layer 11 will be small. Therefore, even in a severe environment such as a high temperature and high humidity environment, it is possible to prevent abnormalities from occurring in the images displayed on the image display device. In particular, the value of y/x represented by the above formula (1) is preferably less than 8, and more preferably less than 5.

　The film thickness of the adhesive layer 11 is set according to the kind of the adhesive composition described below, and has a film thickness of, for example, 0.1μm or more, more preferably 1μm or more, and further preferably 5μm or more. On the other hand, the adhesive layer 11 has a film thickness of, for example, 100μm or less, more preferably 80μm or less, and further preferably 50μm or less.

<Image display element>
　The image display element 12 is an element located on one surface of both surfaces of the adhesive layer 11. Here, the image display element 12 includes an element that emits light from a surface in contact with the adhesive layer 11 to display an image, and examples thereof include an organic EL element and a liquid crystal display element. In the laminate 10 for an image display device of the present invention, light emitted from the image display element 12 is configured to pass through the adhesive layer 11 and the polarizing film 13.

　Here, the material of the surface of the image display element 12 which is in contact with the adhesive layer 11 is a material having adhesiveness to the adhesive layer 11, and an example thereof is a glass plate. With the use of the glass plate, the polarizing film can be firmly fixed via the adhesive layer 11.

<Polarizing film>
　The polarizing film 13 is an optical member located on the other surface of the adhesive layer 11. Specifically, when the image display element 12 is provided adjacent to one surface of both surfaces of the adhesive layer 11, the polarizing film 13 is provided adjacent to the other surface of the adhesive layer 11. As a result, the image display element 12 and the polarizing film 13 are fixed by the adhesive layer 11.

　The polarizing film 13 preferably has a film protective layer on one or both surfaces. In particular, as shown in Fig. 2, in the polarizing film 13, the film

protective layers

15a and 15b are more preferably formed on both surfaces of the polarizer 14. This makes it possible to appropriately protect the polarizer 14, which is particularly easily damaged, of the polarizing film 13.

　Of these, the polarizer 14 is not particularly limited, and various kinds can be used. Examples of the polarizer 14 include a polarizer produced by adsorbing a dichroic material such as iodine or a dichroic dye to a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, and an ethylene/vinyl acetate copolymer partially saponified film, followed by uniaxial stretching thereof, and polyene oriented films such as dehydrated products of polyvinyl alcohol and dehydrochlorinated products of polyvinyl chloride. Among these, the polarizer 14 made of a polyvinyl alcohol film and a dichroic material such as iodine is preferable.

　The thickness of the polarizer 14 is not particularly limited, but is preferably 50μm or less from the viewpoint of not increasing the haze value when the adhesive layer 11 is formed on the polarizing film 13.

　The degree of polarization of the polarizer 14 is also not particularly limited, but it is preferably 90% or more from the viewpoint of not increasing the haze value as well as displaying the image to be displayed by the image display element 12 with high definition.

　On the other hand, the film

protective layers

15a and 15b are made of, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like. Specific examples of such a thermoplastic resin include cyclic polyolefin resins (norbornene-based resins) such as cycloolefin polymer (COP), polyester resins such as polyethylene terephthalate (PET), (meth)acrylic resins such as polymethylmethacrylate (PMMA), cellulose resins such as triacetyl cellulose (TAC), polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Among them, a constituent material of the film protective layer 15b adjacent to the adhesive layer 11 is, from the viewpoint of adhesiveness to the adhesive layer 11, preferably comprises cycloolefin polymer (COP), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA) or triacetate cellulose (TAC). In particular, a constituent material of the film protective layer 15b is, from the viewpoint of increasing the durability of the laminate 10 for an image display device by increasing the durability of the adhesive layer 11 against the acid contained in the conductive polymer (B), and the viewpoint of making it difficult for the conductivity of the adhesive layer 11 to decrease in a high temperature and high humidity environment, preferably comprises cycloolefin polymer (COP), polyethylene terephthalate (PET), polymethylmethacrylate (PMMA) or triacetate cellulose (TAC).

　The polarizing film 13 used in the present invention preferably has excellent gas barrier properties, and particularly water vapor barrier properties. More specifically, the polarizing film 13 of the present invention preferably has a water vapor transmission rate of 1500.0g/m²・24h or less, more preferably 1000.0g/m²・24h or less, and 500.0g/m²・24h or less, and even further preferably 300.0g/m²・24h or less. This makes it difficult for water vapor to reach the adhesive layer 11, so that peeling off of the polarizing film 13 and the image display element 12 from the adhesive layer 11 in a high temperature and high humidity environment can be made more difficult to occur. As used herein, the water vapor transmission rate is a moisture permeability degree (water vapor transmission rate) measured in accordance with JIS Z0208 in an environment of a temperature of 40°C and a relative humidity of 90%.

<Image display device>
　The laminate 1 for an image display device of the present invention can be preferably used for an image display device. Specifically, an image display device having the above-described laminate 1 for an image display device is preferably configured. Here, examples of the image display device can include a device that displays an image using light emitted by the image display element 12, and more specifically, a liquid crystal display, an organic EL display, and the like.

　Further, the image display device may have other optical members in addition to the laminate for an image display device. Examples of such an optical member include a member having a shape such as a plate, a sheet or a film, and further examples thereof include a backlight, a diffusion layer, an anti-glare layer, an antireflection film, a prism array, a lens array sheet, a light diffusion sheet, a phase contrast plate, an elliptically polarizing plate, an antireflection film, a brightness enhancement film, a light diffusion film, a glass shatterproof film and a surface protection film.

<<Adhesive Composition>>
　The adhesive layer 11 of the laminate 10 for an image display device of the present invention is formed of an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C). The adhesive composition preferably further comprises a silane coupling agent (D) and a dispersant (E) which is an amphipathic compound.

　As used herein, the term "solution" is a concept including also a dispersion liquid, and indicates a state of being dissolved or dispersed in a solvent or a dispersion medium.

<Adhesive polymer (A)>
　The adhesive polymer (A) used in the adhesive composition of the present invention is a polymer having adhesiveness at least at the use temperature, and preferably has adhesiveness at room temperature. The adhesive polymer is preferably formed by repeating a (meth)acrylic unit structure, and may also be a copolymer. The adhesive physical properties of the adhesive composition can be suitably adjusted using such an adhesive polymer. Here, as used herein, (meth) acryl means acryl or methacryl.

　Here, as the (meth)acrylic polymer, a polymer formed by polymerization of a monomer having a polymerizable unsaturated bond containing a (meth)acrylic ester as a main component can be used. Specifically, the repeating unit ((meth)acrylic acid ester component unit) derived from the (meth)acrylic acid ester is contained in an amount of 50% by mass or higher, preferably 70% by mass or higher, more preferably 90% by mass or higher in terms of monomer. Specific examples of the (meth)acrylic polymers can include a copolymer of n-butyl acrylate/2-ethylhexyl acrylate/2-hydroxyethyl acrylate, a copolymer of n-butyl acrylate/2-ethylhexyl acrylate/2-hydroxyethyl acrylate/acrylic acid, a copolymer of 2-ethylhexyl acrylate/2-hydroxyethyl acrylate, a copolymer of 2-ethylhexyl acrylate/2-hydroxyethyl acrylate/acrylic acid, a copolymer of 2-methoxyethyl acrylate/2-hydroxyethyl acrylate/acrylic acid, and a copolymer of 2-methoxyethyl acrylate/2-hydroxyethyl acrylate/acrylamide.

　As (meth)acrylic acid esters that derive repeating units of (meth)acrylic polymers, esters between alcohols having an alkyl group having 1 to 20 carbon atoms and (meth)acrylic acid, esters between alicyclic alcohols having 3 to 14 carbon atoms and (meth)acrylic acid, or esters between aromatic alcohols having 6 to 14 carbon atoms and (meth)acrylic acid can be used.

　Here, examples of esters between alcohols having an alkyl group having 1 to 20 carbon atoms and (meth)acrylic acid include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate. An alkyl group having 3 or more carbon atoms may have a linear structure or a branched structure.

　Of (meth)acrylic acid alkyl esters, an ester between an alcohol having an alkyl group having 4 or more carbon atoms and (meth)acrylic acid is preferably used. In addition, of these repeating units constituting an adhesive polymer, the proportion of the (meth)acrylic acid alkyl ester unit having an alkyl group having 4 or more carbon atoms is preferably 50% by mass or higher, and more preferably 65% by mass or higher, and further more preferably 80% by mass or higher.

　On the other hand, examples of esters between alicyclic alcohols having 3 to 14 carbon atoms and (meth)acrylic acid can include cyclohexyl (meth)acrylate and isobornyl(meth)acrylate, and examples of esters between aromatic alcohols having 6 to 14 carbon atoms and (meth)acrylic acid can include (meth)acrylic acid aryl esters such as phenyl (meth)acrylate, benzyl (meth)acrylate and phenoxyethyl (meth)acrylate. Such (meth)acrylic acid ester can be used alone or in combination.

　The (meth)acrylic polymer may have repeating units derived from monomers copolymerizable with (meth)acrylic acid esters, other than the above (meth)acrylic acid ester component units. Examples of such monomers can include: alkoxyalkyl (meth)acrylates such as (meth)acrylic acid, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; salts such as alkali metal (meth)acrylate; di(meth)acrylic acid esters of (poly)alkylene glycol such as di(meth)acrylic acid ester of ethylene glycol, di(meth)acrylic acid ester of diethylene glycol, di(meth)acrylic acid ester of triethylene glycol, di(meth)acrylic acid ester of polyethylene glycol, di(meth)acrylic acid ester of propylene glycol, di(meth)acrylic acid ester of dipropylene glycol and di(meth)acrylic acid ester of tripropylene glycol; poly(meth)acrylic acid esters such as trimethylol propane tri(meth)acrylic acid ester; hydroxy group-containing vinyl compounds such as (meth)acrylonitrile, vinyl acetate, 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl(meth)acrylate,4-hydroxybutyl (meth)acrylate, monoesters between (meth)acrylic acid and polypropylene glycol or polyethylene glycol, and adducts between lactones and 2-hydroxyethyl (meth)acrylate; unsaturated carboxylic acid such as itaconic acid, crotonic acid, maleic acid and fumaric acid (excluding (meth)acrylic acid); salts of these and (partially) esterified compounds and acid anhydrides of these; amide group-containing vinyl monomers such as (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxyethyl (meth)acrylamide and N-butoxymethyl (meth)acrylamide; and macromonomers having a radical polymerizable vinyl group at a terminal of a monomer to which a vinyl group is polymerized. These monomers may be copolymerized alone or in combination with a (meth)acrylic acid ester.

　The weight average molecular weight of the (meth)acrylic polymer is 50,000 or more and 2,000,000 or less, and more preferably 200,000 or more and 1,800,000 or less from the viewpoint of imparting adhesiveness at room temperature. When the weight average molecular weight is less than 50,000, the heat resistance performance of the obtained adhesive layer may be significantly reduced, and when the weight average molecular weight exceeds 2,000,000, uniform casting may be difficult. Here, the weight average molecular weight of the adhesive polymer including the (meth)acrylic polymer can be determined by, for example, gel permeation chromatography (GPC).

　The glass transition temperature (Tg) of the (meth)acrylic polymer is preferably 0°C or lower, more preferably -20°C or lower, further preferably -40°C or lower, and most preferably -50°C or lower similarly from the viewpoint of imparting adhesiveness at room temperature. On the other hand, the lower limit of the glass transition temperature (Tg) of the (meth)acrylic polymer is not particularly limited, but may be -85°C.

　The glass transition temperature (Tg) of the (meth)acrylic polymer can be calculated based on Fox's equation from the glass transition temperatures (Tg₁ to Tg_m) of homopolymers made of monomer units constituting the polymer and the content ratio thereof (W₁ to W_m), for example.
　Fox's equation: 1/Tg = (W₁/Tg₁) +(W₂/Tg₂) + ・・・ +(W_m/Tg_m)
　W₁ + W₂ + ・・・ + Wm = 1
As the glass transition temperatures (Tg₁ to Tg_m) of homopolymers made of respective polymers in the Fox's equation, values described in Polymer Handbook Fourth Edition (Wiley-Interscience Company, 2003) can be used, for example.

　Further, the (meth)acrylic polymer may contain a hydroxyl group, the hydroxyl value of the polymer is 150mgKOH/g or less, preferably 75mgKOH/g or less, and further preferably 40mgKOH/g or less, from the viewpoint of mixing properties with the conductive polymer in the present invention. Here, the hydroxyl value of the polymer can be measured, for example, by the neutralization titration method specified in JIS K0070-1992.

　In the adhesive composition in the present invention, the adhesive polymer may be used alone or in a combination of two or more kinds thereof.

　Further, the adhesive polymer may be used for preparation of the adhesive composition in a state of being dissolved or dispersed in a solvent or a dispersion medium (F) described below for facilitating the preparation of the adhesive composition.

<Conductive polymer (B)>
　The conductive polymer (B) contained in the adhesive composition of the present invention comprises a conjugated polymer (B1) and a polyanion (B2). The conductive polymer (B) may also comprise an oxidant (B3). More specifically, the conductive polymer (B) is obtained by oxidatively polymerizing a monomer to form a conjugated polymer (B1) in the presence of at least a polyanion (B2). As an example, a polymer complex of the conjugated polymer (B1) and the polyanion (B2) can be mentioned.

　The concentration of the conductive polymer (B) in the adhesive composition of the present invention is preferably 0.01 part by mass or higher, more preferably 0.05 part by mass or higher and more preferably 0.1 part by mass or higher relative to 100 parts by mass of the adhesive polymer (A). By setting the concentration of the conductive polymer (B) to 0.01 part by mass or higher, the surface resistivity of the adhesive layer can be lowered when the adhesive layer is formed from the adhesive composition, and therefore the generation of static electricity upon peeling off of the adhesive layer can be suppressed. On the other hand, the concentration of the conductive polymer (B) is preferably 20.0 parts by mass or lower, more preferably 10.0 parts by mass or lower, and even more preferably 5.0 parts by mass or lower relative to 100 parts by mass of the adhesive polymer (A). By setting the concentration of the conductive polymer (B) to 20.0 parts by mass or lower, the mixing stability of the adhesive composition can be improved and the formation of aggregated precipitates in the adhesive composition can be reduced, and, the light transmittance in the adhesive layer can be increased and the haze value can be reduced.

(Conjugated polymer (B1))
　As the conjugated polymer (B1) contained in the conductive polymer (B), a π electron conjugated system polymer is preferable, and it is more preferable to contain polythiophene present as an electrically conductive polymer.

　The polythiophene preferably includes a repeating unit of general formula (I).

(R₄ and R₅ in general formula (I), independently from each other, respectively represent H, an optionally substituted C₁-C₁₈ alkyl radical or an optionally substituted C₁-C₁₈ alkoxy radical, and R₄ and R₅ together represent an optionally substituted C₁-C₈ alkylene radical (in the optionally substituted C₁-C₈ alkylene radical, one or more C atoms may be substituted by one or more identical or different hetero atoms selected from O or S, preferably a C₁-C₈ dioxyalkylene radical), an optionally substituted C₁-C₈ oxythialkylene radical or an optionally substituted C₁-C₈ dithialkylene radical, or an optionally substituted C₁-C₈ alkylidene radical (in the optionally substituted C₁-C₈ alkylidene radical, at least one C atom may be optionally substituted by a hetero atom selected from O and S)).

　More preferably, the polythiophene is a polythiophene containing repeating units of the general formula (I-a) and/or (I-b).

Here, in the general formula (I-a) and the general formula (I-b), A represents an optionally substituted C₁-C₅ alkylene radical and preferably an optionally substituted C₂-C₃ alkylene radical; Y represents O or S; R₆ represents a linear or branched, optionally substituted C₁-C₁₈ alkyl radical, preferably a linear or branched, optionally substituted C₁-C₁₄ alkyl radical, an optionally substituted C₅-C₁₂ cycloalkyl radical, an optionally substituted C₆-C₁₄ aryl radical, an optionally substituted C₇-C₁₈ aralkyl radical, an optionally substituted C₇-C₁₈ alkaryl radical, an optionally substituted C₁-C₄ hydroxyalkyl radical or a hydroxyl radical; y represents an integer of from 0 to 8, preferably 0, 1 or 2, particularly preferably 0 or 1; when a plurality of radicals R₆ are bonded to A, these may be identical or different.

　Here, the general formula (I-a) is to be understood to mean that the substituent R₆ may be bonded y times to the alkylene radical A.

　More preferably, the polythiophene including repeating units of the general formula (I) is a polythiophene including repeating units of the general formula (I-aa) and/or of the general formula (I-ab).

Here, R₆ and y in the general formula (I-aa) and the general formula (I-ab) are as described in the above general formula (I-a) and general formula (I-b).

　Most preferably, the polythiophene including repeating units of the general formula (I) is a polythiophene including a polythiophene of the general formula (I-aaa) and/or the general formula (I-aba).

　As used herein, the prefix "poly" is understood to mean that a plurality of identical or different repeating units are included in the polythiophene. This polythiophene includes a total of n repeating units of general formula (I), wherein n can be an integer from 2 to 2,000, preferably from 2 to 100. The repeating units of the general formula (I) in the polythiophene may all be the same or different. Polythiophenes including the same repeating units of the general formula (I) are preferable.

　Preferably, each conjugated polymer (B1) has H at the end groups.

　The conjugated polymer (B1) is particularly preferably poly (3,4-ethylenedioxythiophene), poly (3,4-ethyleneoxythiathiophene) or poly (thieno[3,4-b] thiophene); that is, a homopolythiophene including the repeating unit of formula (I-aaa), (I-aba) or (I-b) in which Y = S, and among them, most preferably a homopolymer (poly(3,4-ethylenedioxythiophene)) including the repeating unit of (I-aaa).

　Further, the conjugated polymer (B1) is cationic, and “cationic” relates only to the electric charges existing on the polythiophene main chain. Depending on the substituents of the radicals R₄ and R₅, the polythiophenes may have positive and negative charges in their structural units. In this case, positive charges may be present on the polythiophene main chain and the negative charges may be present on the radical R which is substituted by sulfonates or a carboxylate group. In that case, the positive charge of this polythiophene main chain may be partially or completely saturated by an anionic group which may be present on the radical R. Collectively, the polythiophenes in these cases may be cationic, uncharged, or even anionic. Nevertheless, for the purposes of the present invention, they are all considered cationic polythiophenes. This is because the positive charge on this polythiophene main chain is important. The positive charge is not shown in the equation. This is because the positive charge is conjugated and delocalized. The number of positive charges, however, is at least 1 and at most n, where n is the total number of all repeating units (identical or different) within this polythiophene.

　As a thiophene monomer that serves as a base of the conjugated polymer (B1), optionally substituted 3,4-alkylenedioxythiophenes can be used, and, as an example, can be represented by the general formula (II).

Here, A, R₆ and y in general formula (II) have the meanings described in the formula (I-a). When a plurality of radicals R₆ are bonded to A, these may be identical or different.

　As more preferred thiophene monomers, optionally substituted 3,4-ethylenedioxythiophenes can be used, most preferably, unsubstituted 3,4-ethylenedioxythiophene can be used.

(Polyanion (B2))
　Examples of the polyanion (B2) contained as a dopant in the conductive polymer include those having a structure such as a homopolymer, a random copolymer and a block copolymer, and among them, those having a block copolymer structure are preferably used. As the polyanion (B2), those having a plurality of anions in one molecule can be used, and examples thereof include homopolymers such as styrene sulfonic acid, vinyl sulfonic acid, and (meth) acrylic acid ester having sulfonic acid in the molecule, or, at least partially sulfonated polymers, such as copolymers thereof. Above all, at least partially sulfonated block copolymers are preferably used. Further, it is preferable to use one having a hydrogenated or unhydrogenated diene structure, and for example, a sulfonated synthetic rubber can be used. The sulfonated synthetic rubber is an at least partially sulfonated block copolymer having styrene and diene units. By using the polyanion (B2) having such a block copolymer structure, the conductive polymer can be easily dissolved or dispersed in an organic solvent. Therefore, it is possible to reduce the surface resistivity of the adhesive layer while maintaining the transparency of the adhesive layer, and reduce the generation of static electricity when the adhesive layer formed from the adhesive composition is peeled off.

　As used herein, the term “sulphonated” is preferably understood to mean that in the styrene units and/or diene units concerned, preferably in the optionally hydrogenated butadiene or isoprene units, an -SO₃X group is bonded to at least one C atom of these units via a sulfur atom (X is preferably selected from the group consisting of H⁺, NH₄ ⁺, Na⁺, K⁺ and Li⁺.) It is particularly preferable that the -SO₃X groups are almost exclusively bonded to the styrene units and accordingly sulphonated styrene units are present.

　Also, as used herein, the term "hydrogenated, partially and optionally alkyl-substituted styrene-diene block copolymer" or "hydrogenated styrene-isoprene block copolymer" is understood to respectively mean a block copolymer wherein double bonds of diene units are hydrogenated or subjected to hydrogenation, while aromatic ring systems of styrene units are not hydrogenated or not subjected to hydrogenation. Furthermore, the term "styrene-diene block copolymer" is understood to mean a polymer comprising at least styrene and diene monomer units, and thus the presence of further comonomers is not excluded.

　Furthermore, as used herein, the term "alkyl-substituted styrene-diene block copolymers" is understood to mean block copolymers in which the styrene unit is alkyl-substituted, whereby in particular a methyl group, an ethyl group, an isopropyl group or a tert-butyl group is considered as an alkyl substituent.

　Here, the term “sulfonated styrene units” is preferably understood to mean units (III).

　Further, the term "sulphonated butadiene unit" is preferably understood to mean, for example, the unit (IV).

　Instead of the acids shown in units (III) and (IV), the sulphonate group may also be bonded in the form of a salt, for example in the form of an ammonium salt or an alkali salt, in particular in the form of an Na⁺, K⁺ or Li⁺ salt.

　Preferably, the hydrogenated or unhydrogenated, optionally partially alkyl-substituted styrene-diene copolymers contained as the sulfonated synthetic rubber in the conductive polymer are preferably obtainable by sulphonating a styrene-diene copolymer (this may optionally be hydrogenated).

　The hydrogenated or non-hydrogenated, partially optionally alkyl-substituted styrene-diene copolymers are essentially styrene-diene block copolymers. The term "block" in the context of the present invention is preferably understood to be a polymer unit consisting of at least 2, preferably at least 4, even more preferably at least 6, even more preferably at least 8 and most preferably at least 10 identical monomer units which are continuous with one another.

　Therefore, the hydrogenated or unhydrogenated block copolymers may be copolymers in which only the styrene units are present in blocks, copolymers in which only the diene units (or the hydrogenated forms of the diene units) are present in blocks, or copolymers in which both the diene units (or the hydrogenated forms of the diene units) and the styrene units are present in blocks. For example, hydrogenated or unhydrogenated block copolymers in which styrene blocks are present in addition to monomeric styrene units and diene units (or the hydrogenated forms of the diene units), hydrogenated or unhydrogenated block copolymers in which diene blocks (or blocks of the hydrogenated forms of the diene units) are present in addition to monomeric styrene units and diene units (or the hydrogenated forms of the diene units), hydrogenated or unhydrogenated block copolymers in which styrene blocks and diene blocks (or blocks of the hydrogenated forms of the diene units) are present in addition to monomeric diene units (or the hydrogenated forms of the diene units), hydrogenated or unhydrogenated block copolymers in which styrene blocks and diene blocks (or blocks of the hydrogenated forms of the diene units) are present in addition to monomeric styrene units, or hydrogenated or unhydrogenated block copolymers in which styrene blocks and diene blocks (or blocks of the hydrogenated forms of the diene units) are present in addition to monomeric diene units (or the hydrogenated forms of the diene units) and monomeric styrene units are also conceivable.

　According to a particular embodiment, the sulphonated synthetic rubber includes hydrogenated or unhydrogenated, preferably hydrogenated styrene-isoprene block copolymers having a structure A-B-A, in which the block A corresponds to a sulphonated polystyrene block and the block B corresponds to a hydrogenated or unhydrogenated, preferably however hydrogenated polyisoprene block (a fully hydrogenated polyisoprene block corresponds chemically to a block of alternating copolymerized ethylene-propylene units). The lengths of the blocks A and B are each preferably at least 5 monomer units, particularly preferably at least 10 units and most preferably at least 20 units.

　According to another particular embodiment, the sulphonated synthetic rubber includes hydrogenated or unhydrogenated, preferably hydrogenated styrene-isoprene block copolymers having a structure of A-B-C-B-A, in which the block A corresponds to a polystyrene block partially substituted with at least a tert-butyl group, the block B corresponds to a hydrogenated or unhydrogenated, preferably however hydrogenated polyisoprene block (a fully hydrogenated polyisoprene block corresponds chemically to a block of alternating copolymerized ethylene-propylene units), and the block C corresponds to a sulphonated polystyrene block. The lengths of the blocks A, B and C are each preferably at least 5 monomer units, particularly preferably at least 10 units and most preferably at least 20 units. Such copolymers are available, for example, from Kraton Polymers, Inc., Houston, USA, under the product name NEXAR(R).

　There is basically no limitation with respect to the mass ratio of styrene units to diene units in the hydrogenated or unhydrogenated styrene-diene block copolymer used for sulfonation. For example, the block copolymer can be based on 5 to 95% by mass, particularly preferably 15 to 80% by mass, most preferably 25 to 65% by mass of polymerized styrene and 95 to 5% by mass, preferably 80 to 15% by mass, and most preferably 65 to 25% by mass of polymerized optionally hydrogenated dienes, wherein the total amount of optionally hydrogenated dienes and styrene is preferably 100% by mass. However, when additional monomer units are present in the block copolymer in addition to the styrene units and optionally hydrogenated diene units, the total amount does not have to add up to 100% by mass.

　The sulfonated synthetic rubber further preferably has a weight average molecular weight (Ms) ranging from 1000 to 10,000,000g/mol, particularly preferably 10,000 to 1,000,000 g/mol, most preferably 100,000 to 1,000,000g/mol. This molecular weight is determined by gel permeation chromatography using a polymer having a well-defined molecular weight, particularly polystyrene in the case of a water-immiscible solvent or dispersion medium, or polystyrene sulphonic acid in the case of a water-miscible solvent or dispersion medium.

　A mass ratio of the conjugated polymer (B1) to the polyanion (B2) (conjugated polymer : polyanion) in the conductive polymer (B) is preferably in the range of from 1 : 0.1 to 1 : 100, more preferably in the range of from 1 : 0.2 to 1 : 20 and further preferably in the range of from 1 : 0.5 to 1 : 10.

(Oxidant (B3))
　The conductive polymer (B) may contain an oxidant (B3) and its reaction product. This is because the polymerization reaction of the thiophene monomer in the presence of the sulfonated synthetic rubber is oxidatively performed using the oxidant (B3).

　As the oxidant (B3), for example, an organic peroxide such as tert-butyl peroxide, benzoyl peroxide, diisobutyryl peroxide, di-n-propyl peroxydicarbonate, didecanoyl peroxide, dibenzoyl peroxide, tert-butyl perbenzoate, and di-tert-amyl peroxide can be used. For example, an organic azo compound such as 2,2'-azodiisobutyronitrile or an inorganic oxidant such as ammonium persulfate can be used.

　Further, as the oxidant (B3), an inexpensive and easy-to-handle oxidant may be used for practical reasons. Examples thereof include iron (III) salts such as Fe₂(SO₄)₃, FeCl₃, and Fe(ClO₄)₃, and iron (III) salts of organic acids and iron (III) salts of inorganic acids containing organic radicals. Examples of the iron (III) salts of inorganic acid containing organic radicals include iron (III) salts of sulfuric acid hemiesters of C₁-C₂₀ alkanols, and the Fe(III) salts of lauryl sulfate. The following may be mentioned as examples of iron (III) salts of organic acids: Fe(III) salts of C₁-C₂₀ alkylsulphonic acids, such as methanesulphonic acid and dodecanesulphonic acid; Fe (III) salts of aliphatic C₁-C₂₀carboxylic acids, such as 2-ethylhexylcarboxylic acid; Fe (III) salts of aliphatic perfluorocarboxylic acids such as trifluoroacetic acid and perfluorooctanoic acid; Fe (III) salts of aliphatic dicarboxylic acids such as oxalic acid; and, in particular, Fe (III) salts of aromatic sulphonic acids which may be substituted with C₁-C₂₀ alkyl groups, such as benzenesulphonic acid, p-toluenesulphonic acid and dodecylbenzenesulphonic acid. Iron (III) salts of organic acids have the great advantage of application such that they are partially or completely soluble in organic solvents, especially in water-immiscible organic solvents.

<Crosslinking agent (C)>
　The adhesive composition according to the present invention comprises a crosslinking agent (C). As a result, at least the adhesive polymer (A) is crosslinked to form an adhesive layer having excellent high heat resistance and wet heat resistance, and at the same time, the image display element and the polarizing film located on both sides thereof can be firmly fixed.

　As the crosslinking agent (C), for example, an isocyanate compound, an epoxy compound, or a metal chelate compound that can react with the crosslinking group contained in the adhesive polymer (A) can be used. As the crosslinking agent (C), one kind may be used alone, or two or more kinds may be used in combination.

　Among these, as the isocyanate compound, for example, an isocyanate compound having 2 or more isocyanate groups in one molecule is usually used, and preferably 2 to 8 isocyanate groups are used. When the number of isocyanate groups is within the above range, it is preferable in terms of increasing the efficiency of the crosslinking reaction with the adhesive polymer (A) and maintaining the flexibility of the adhesive layer.

　Examples of the diisocyanate compound having 2 isocyanate groups in one molecule include aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate. Among them, examples of aliphatic diisocyanates include aliphatic diisocyanates having 4 to 30 carbon atoms such as ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Examples of the alicyclic diisocyanate include alicyclic diisocyanates having 7 to 30 carbon atoms such as isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethyl xylene diisocyanate. Further, examples of aromatic diisocyanates include aromatic diisocyanates having 8 to 30 carbon atoms such as phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate and diphenylpropane diisocyanate.

　Examples of the isocyanate compound having 3 or more isocyanate groups in one molecule include aromatic polyisocyanate, aliphatic polyisocyanate, and alicyclic polyisocyanate.

　Examples of the isocyanate compound include a multimer (for example, a dimer or trimer, a biuret body, an isocyanurate body), a derivative (for example, addition reaction products of a polyhydric alcohol and two or more molecules of the diisocyanate compound) and polymerized products of the above isocyanate compound having 2 or 3 or more isocyanate groups. Examples of the polyhydric alcohol in the derivative, specifically, examples of the low molecular weight polyhydric alcohol include trihydric or higher alcohols such as trimethylolpropane, glycerin, and pentaerythritol, and examples of the high molecular weight polyhydric alcohol include polyether polyol, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols.

　Examples of such isocyanate compounds include diphenylmethane diisocyanate trimer, polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate or tolylene diisocyanate biuret or isocyanurate, a reaction product (for example, a three-molecule adduct of tolylene diisocyanate or xylylene diisocyanate) of trimethylolpropane and tolylene diisocyanate or xylylene diisocyanate, a reaction product (for example, a three molecule adduct of hexamethylene diisocyanate) of trimethylolpropane and hexamethylene diisocyanate, polyether polyisocyanate and polyester polyisocyanate. As such an isocyanate compound, an adduct of tolylene diisocyanate of trimethylolpropane can be obtained from Tosoh Corporation under the product name Coronate L.

　The adhesive composition of the present invention comprises the crosslinking agent (C) in an amount of 0.01 to 10 parts by mass relative to 100 parts by mass of the adhesive polymer (A). The lower limit is preferably 0.05 part by mass or higher, more preferably 0.1 part by mass or higher. The upper limit is preferably 5 parts by mass or lower, more preferably 3 parts by mass or lower. If the content of the cross-linking agent (C) is too low, proper cross-linking cannot be achieved, and if the content is too high, the adhesiveness will be hardly exhibited.

<Silane coupling agent (D)>
　The adhesive composition in the present invention preferably further comprises a silane coupling agent (D). The silane coupling agent (D) is a component which, when combined with the adhesive polymer (A), makes it difficult for the polarizing film and the image display element to peel off in a high temperature and high humidity environment. In particular, even when the surface of the image display element is made of an inorganic compound such as a glass substrate, it is a component that brings about the action of firmly adhering the adhesive layer to the adherend.

　Examples of the silane coupling agent (D) include: polymerizable unsaturated group-containing silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; epoxy groups containing silane coupling agents such as 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; and halogen-containing silane coupling agents such as 3-chloropropyltrimethoxysilane. In particular, an epoxy group-containing silane coupling agent is preferable from the viewpoint of stress relaxation property and the like.

　The content of the silane coupling agent (D) in the adhesive composition of the present invention is usually 1 part by mass or lower, preferably 0.01 to 0.8 part by mass, and more preferably 0.05 to 0.5 part by mass relative to 100 parts by mass of the adhesive polymer (A). By setting the content of the silane coupling agent (D) within this range, peeling of the polarizing plate in a high temperature and high humidity environment is less likely to occur, and the bleeding of the silane coupling agent (D) in a high temperature environment can be made to hardly take place.

<Dispersant (E)>
　The adhesive composition in the present invention preferably further comprises a dispersant (E) which is an amphipathic compound. Such an amphipathic compound is contained as the dispersant (E), so that a lower surface resistivity can be stably brought to the adhesive layer, the haze value of the adhesive layer can be reduced, and the light transmittance can thus be increased.

　Examples of the amphiphilic compound that is the dispersant (E) include compounds having high affinity to both aqueous solvents (solvents or dispersion media) and nonaqueous solvents and preferable examples thereof are nonionic compounds having a hydrophilic group and a hydrophobic group in a molecule.

　Among these, the nonionic amphipathic compound is preferably an ether or ester of a trihydric or higher polyhydric alcohol, or a nonionic compound having an oxyalkylene chain. Among these, trihydric or higher polyhydric alcohol esters are more preferable, and compounds that are trihydric or higher polyhydric alcohol fatty acid esters having no polyoxyalkylene structure are even more preferable. In particular, the use of an ester of a trihydric or higher polyhydric alcohol can reduce the influence of the kind of the base material on the surface resistivity and the antistatic property.

　Among these, trihydric or higher polyhydric alcohol ethers and esters are compounds having a total of three or more hydroxyl groups, ether bonds and ester bonds in the molecule. Examples of the nonionic compound having an oxyalkylene chain include compounds having oxyethylene or oxypropylene as a repeating structural unit, and the number of repeating units in the oxyalkylene chain is preferably 2 or more, and more preferably 5 or more. These compounds exhibit hydrophilicity in the hydroxyl group, ether bond and ester bond.

　Specific examples of nonionic amphiphilic compounds include: polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether; polyoxyalkylene derivatives such as polyoxyethylene alkylene alkyl ether; polyoxyalkylene alkenyl ether and polyoxyethylene alkyl phenyl ether; sorbitan aliphatic acid esters such as sorbitan octadecanoic acid ester, sorbitan lauric acid ester, sorbitan oleic acid ester, sorbitan stearic acid ester and sorbitan palmitic acid ester; sucrose fatty acid esters such as sucrose oleic acid ester; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monolaurate, and polyoxyethylene sorbitan monooleate; polyoxyethylene sorbitol fatty acid ester; glycerin fatty acid ester; polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate and polyethylene glycol distearate; polyoxyethylene cured castor oil, polyoxyethylene alkyl amine, and alkyl alkanol amide; and block copolymers having polyethylene glycol, polypropylene glycol or the like as a unit structure.

　The content of the dispersant (E) is preferably adjusted to, for example, 0.1 part by mass or higher, more preferably 0.3 part by mass or higher, relative to 100 parts by mass of the adhesive polymer (A). The content of the dispersant (E) is preferably adjusted to, for example, 10.0 parts by mass or lower, more preferably 5.0 parts by mass or lower, and further preferably 3.0 parts by mass, and further preferably 1.0 part by mass or lower relative to 100 parts by mass of the adhesive polymer (A).

<Solvent or dispersion medium>
　The adhesive composition may contain a non-aqueous solvent or dispersion medium. The use of such a non-aqueous solvent or non-aqueous dispersion medium can accelerate the dissolution and dispersion of the adhesive polymer (A) and the conductive polymer (B) in the adhesive composition, so as to be able to reduce the formation of aggregated precipitates in the adhesive composition.

　As the solvent and the dispersion medium, the solvent or the dispersion medium used when the adhesive polymer (A) or the conductive polymer (B) is prepared may be used as it is. Examples of the solvents and dispersion media include: linear, branched or cyclic aliphatic hydrocarbons such as pentane, hexane, heptane, octane, petroleum ether, cyclohexane, methyl cyclohexane or cycloheptane; aromatic hydrocarbons such as benzene, toluene or xylene; mono- or bivalent alcohols such as methanol, ethanol, iso-propanol, ethylene glycol, propylene glycol, butanediol, diethylene glycol, or triethylene glycol; ethers such as diethyl ether, diisopropyl ether, methyl tert-butyl ether or anisole; halogenated hydrocarbons such as dichloromethane, chloroform, tetrachloromethane, trichloroethane and trichloroethene; halogenated aromatic hydrocarbons such as chlorobenzene; aliphatic nitriles such as acetonitrile; aliphatic sulphoxides and sulphones such as dimethyl sulphoxide or sulpholane; aliphatic carboxylic acid amides such as methyl acetamide, dimethyl acetamide or dimethyl formamide; ketones such as acetone, methyl ethyl ketone or methyl t-butyl ketone; and esters such as methyl acetate, ethyl acetate or butyl acetate; or mixtures thereof. Among these, as the solvent or dispersion medium, one kind or 2 or more kinds selected from ethyl acetate, butyl acetate, tolunene, methyl ethyl ketone, propylene glycol, and anisole are preferably used.

<Other Components>
　The adhesive composition can further contain an antioxidant, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, an antistatic agent, a rework agent, etc. within a range that does not impair the effects of the present invention. Further, various components such as a conductivity enhancing agent may be contained for the purpose of increasing the conductivity of the conductive polymer.

　In addition, it is preferable that the water content of the adhesive composition is low. More specifically, the concentration of water in the adhesive composition is preferably less than 0.5% by mass, more preferably less than 0.1% by mass, and further preferably less than 0.01% by mass. By reducing the water content of the adhesive composition, the formation of aggregated precipitates in the adhesive composition can be reduced, and the surface resistivity of the adhesive layer can be reduced.

<Formation of Adhesive Layer>
　The adhesive layer 11 can be formed by applying the above-mentioned adhesive composition to the image display element 12, the polarizing film 13, and the protective material 21, which have been pretreated as necessary.

　Here, the image display element 12 and the polarizing film 13 to which the adhesive composition is applied may be those having flat surfaces.

　The protective material (separator) 21 is detachably provided on the surface of the image display element 12 or the polarizing film 13, and is used for temporarily protecting the adhesive layer 11 in the test material 20 described above, as well as for protecting the image display element 12 and the polarizing film 13 from heating due to drying and aging when obtaining the adhesive layer 11 from the adhesive composition. As the protective material 21, a material having a weaker adhesive force to the adhesive layer 11 than that of the image display element 12 or the polarizing film 13 that adheres to the adhesive layer 11 at the same time as the protective material 21 can be used. More specifically, when the film protective layer 15b of the polarizing film 13 comprises cycloolefin polymer (COP), polyethylene terephthalate (PET), polymethylmethacrylate (PMMA) or triacetate cellulose (TAC), a polyethylene terephthalate (PET) film that has been subjected to a peeling treatment or a polyethylene film can be used as the protective material 21, for example.

　Known means can be employed as means for applying the adhesive composition to the image display element 12, the polarizing film 13, and the protective material 21. For example, the application can be performed by wire bar coating, spin coating, dipping (immersion), pouring, dripping, injecting, spraying, doctor blade coating, painting, printing means or the like. Among these, as the printing means, inkjet printing, screen printing, relief printing, offset printing or pad printing can be employed.

　The pre-drying film thickness of the adhesive composition to be applied to the image display element 12, the polarizing film 13, and the protective material 21 is set depending on the concentration of the non-volatile components in the adhesive composition and the thickness of the adhesive layer after drying. For example, the adhesive composition can be applied to the optical member with a thickness of preferably 0.1μm or more, more preferably 0.5μm or more. Further preferably, it can be applied with a thickness of 500μm or less, and more preferably 300μm or less to the image display element 12, the polarizing film 13 and the protective material 21.

　Next, the solvent and the dispersion medium are at least partially removed from the applied adhesive composition, and then the cross-linking reaction of the obtained coating film can be advanced to obtain the adhesive layer 11. Of these, the removal of the solvent or dispersion medium can be carried out usually by drying at 50 to 150°C, preferably 60 to 100°C, usually for 1 to 10 minutes, and preferably 2 to 7 minutes. The cross-linking reaction with the cross-linking agent (C) on the coating film is preferably performed by leaving the film for usually 1 day or longer, preferably 3 to 10 days to stand in an environment of a temperature usually ranging from 5 to 60°C, and preferably 15 to 40°C and a relative humidity usually ranging from 30 to 70%, and preferably 40 to 70% for aging.

　Here, when the image display element 12 and the polarizing film 13 are bonded together by using a coating film formed by applying the adhesive composition to the protective material 21, one of the image display element 12 and the polarizing film 13 is adhered onto the side of the adhesive layer 11 where the protective material 21 is absent, the protective material 21 is peeled off after the crosslinking reaction is advanced by aging, and then the other one of the image display element 12 and the polarizing film 13 may be adhered to the side from which the protective material has been peeled off.

Examples

　In what follows, although the present invention will be described in more detail with reference to Examples, the present invention is by no means limited to these descriptions.

<Preparation of Solution of Adhesive Polymer (A)>
　As an adhesive polymer (A), a copolymer of n-butyl acrylate and 2-hydroxyethyl acrylate (weight average molecular weight of 500,000, glass transition temperature of -48°C, hydroxyl value of 5mgKOH/g) was prepared by the following procedure. First, to a flask equipped with a stirrer, a nitrogen gas introduction tube, a thermometer, and a reflux condenser, n-butyl acrylate (291g), 2-hydroxyethyl acrylate (9.0g), and ethyl acetate (580g) were charged, followed by heating the content of the flask to 66°C while introducing nitrogen gas into the flask. Then, azobisisobutyronitrile (AIBN) (0.15g), which is an initiator sufficiently replaced by nitrogen gas, was added to the flask with stirring, and the temperature of the content in the flask was maintained to 65 to 66°C for 3 hours. Then, the content was heated at 75°C and refluxed for 5 hours, and then ethyl acetate (120g) was added finally, thereby obtaining an adhesive polymer (A) solution. This adhesive polymer (A) solution contains an acrylic polymer having a monomer weight ratio of n-butyl acrylate/2-hydroxyethyl acrylate/acrylic acid = 97/3, and ethyl acetate as a solvent.

　With respect to the obtained adhesive polymer solution, a weight average molecular weight (Mw) was determined according to gel permeation chromatography (GPC), following the GPC measurement conditions below.
<GPC determination conditions>
・ Measurement instrument: HLC-8120GPC (Tosoh Corporation)
・ GPC column structure: the following five consecutive columns (all the columns are manufactured by Tosoh Corporation)
(1) TSK-GEL HXL-H (guard column)
(2) TSK-GEL G7000HXL
(3) TSK-GEL GMHXL
(4) TSK-GEL GMHXL
(5) TSK-GEL G2500HXL
・ Sample concentration: the sample was diluted with tetrahydrofuran so that the concentration was 1.0mg/cm³.
・ Mobile phase solvent: tetrahydrofuran
・ Flow rate: 1cm³/min
・ Column temperature: 40°C

<Preparation of Conductive Polymer (B)>
　Into a 1-liter three-necked flask, a solution of a sulfonated block copolymer which is a polyanion (B2) (manufactured by Kraton, trade name: Nexar MD9260, non-volatile content 11%) (75.0g) and benzoyl peroxide (9.4g) as the oxidant (B3), p-toluenesulfonic acid (2.8g), and anisole as a solvent (262.0g) were added and mixed. The mixture was stirred under a nitrogen atmosphere for 30 minutes. Next, after the temperature was increased to 60°C, 3,4-ethylenedioxythiophene (4.95g), which is a monomer of the conjugated polymer (B1), was added, and then additional anisole (40.0g) was added dropwise for 40 minutes. Then, the resultant was stirred at a temperature of 60°C for 3 hours. After returning to room temperature, the obtained dispersion liquid was allowed to stand overnight and the supernatant was removed by decantation to obtain a uniform dispersion liquid. Butyl acetate (20.0g) was added to the obtained dispersion liquid (20.0g), and the mixture was dispersed using ultrasonic waves to obtain a conductive polymer dispersion liquid (B) containing polymer complex of Nexar MD9260 and 3,4-ethylenedioxythiophene. At this time, the content of water in the dispersion liquid of the conductive polymer was 800ppm with respect to the total mass of the dispersion medium. The content of nonvolatile components in the dispersion liquid of the conductive polymer was 1.2% by mass, and the conductivity of the nonvolatile components was 5.8S/cm.

<Preparation of cross-linking agent (C)>
　As the cross-linking agent (C), a polyisocyanate curing agent (manufactured by Tosoh Corporation, trade name: Coronate L) was used.

　As the silane coupling agent (D), 3-glycidoxypropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KBE-403) was used.

　An amphipathic compound was used as the dispersant (E), and more specifically, sorbitan monooctadecanoate (manufactured by Croda, trade name Span 60) was used.

<Preparation of Adhesive Composition>
　The adhesive polymer (A), the conductive polymer (B), the cross-linking agent (C), the silane coupling agent (D) and the dispersant (E) of the kinds listed in Table 1 were charged into a mixer so that the mass ratio was as shown in Table 1, and then the mixture was stirred and mixed, thereby obtaining an adhesive composition to be used in each of Examples and Comparative Examples.

　Meanwhile, as the polarizing film, in Examples 1 to 6 and Comparative Examples 2 and 3, a polarizing film having a film protective layer comprising a cycloolefin polymer (COP) formed on the surface of the polarizer was used. This polarizing film has a film protective layer thickness of 40μm, a polarizer thickness of 40μm, a water vapor transmission rate of 20g/(m²・24h), and a dimensional change rate before and after maintaining the film in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours is 2%.

　As the polarizing film of Example 7, a polarizing film having a film protective layer comprising polymethylmethacrylate (PMMA) formed on the surface of the polarizer was used. This polarizing film has a film protective layer thickness of 40μm, a polarizer thickness of 40μm, and a water vapor transmission rate of 60g/(m²・24h).

　As the polarizing film of Example 8, a polarizing film having a film protective layer comprising polyethylene terephthalate (PET) formed on the surface of the polarizer was used. This polarizing film has a film protective layer thickness of 40μm, a polarizer thickness of 40μm, and a water vapor transmission rate of 40 g/(m²・24h).

　Further, as the polarizing films of Examples 9 and 10, polarizing films having a film protective layer comprising triacetate cellulose (TAC) formed on the surface of the polarizer were used. This polarizing film has a film protective layer thickness of 40μm, a polarizer thickness of 40μm, and a water vapor transmission rate of 400g/(m²・24h).

　Further, as the polarizing film of Comparative Example 1, a polarizing film having a film protective layer comprising triacetate cellulose (TAC) formed on the surface of the polarizer was used. This polarizing film has a film protective layer thickness of 10μm, a polarizer thickness of 40μm, and the water vapor transmission rate of 1100g/(m²・24h).

　For each of Examples and Comparative examples, a protective material comprising a polyethylene terephthalate film (PET film) having a size of 90mm long × 160mm wide and having a thickness of 50μm and which had been subjected to peeling treatment was used. A surface subjected to the peeling treatment was coated with the adhesive composition using a doctor blade, and then dried at 90°C for 3 minutes, thereby obtaining an adhesive sheet having a coating film having a dry film thickness of 25μm. Next, a polarizing film was adhered to the surface of the adhesive sheet where the coating film was exposed, and allowed to stand for 7 days for aging under conditions of 23°C/50% RH. Thereafter, the adhesive sheet was cut into a sized of 90mm × 160mm. Hence, a test material, which comprises a 25μm-thick adhesive layer having a polarizing film on one surface and a protective material having a release layer and comprising a polyethylene terephthalate (PET) film on the other surface of the adhesive layer, was obtained. The surface resistivity and haze value of the obtained test material were measured under the following conditions.

<Characteristic evaluation of test materials>
(Measurement of Surface Resistivity)
　For the obtained test material, the surface resistivity of the adhesive layer was measured when the protective material was peeled off in an environment of a temperature of 23°C and a relative humidity of 50%, and then the measured value was defined as the surface resistivity at normal temperature (x). Here, the surface resistivity of the adhesive layer was measured using a resistivity meter (HIRESTA UX MCP-HT800, Nittoseiko Analytech Co., Ltd.) at an applied voltage of 1000V according to JIS-K-6911. The results of surface resistivity at normal temperature (x) are shown in Table 1.

　Further, when the obtained test material was maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours, and then dried at 80°C for 1 hour, and then the protective material was peeled off in an environment of a temperature of 23°C and a relative humidity of 50%, the surface resistivity of the adhesive layer was measured, and then the measured value was defined as the surface resistivity after exposure to a high temperature and high humidity environment (y). Then, the ratio (y/x ratio) of the surface resistivity after exposure to a high temperature and high humidity environment (y) to the surface resistivity at normal temperature (x) described above was found. Table 1 shows the results of the surface resistivity after exposure to a high temperature and high humidity environment (y) and the y/x ratio.

(Measurement of haze value)
　The haze value (%) of the thus obtained test material, when the protective material was peeled off in an environment of a temperature of 23°C and a relative humidity of 50%, was measured, and the measured value was defined as a haze value x at normal temperature. Further, the obtained test material was maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours, and then dried at 80°C for 1 hour. Subsequently, when the protective material was peeled off in an environment of a temperature of 23°C and a relative humidity of 50%, the haze value (%) of the test material was measured, and then the measured value was defined as the haze value y after exposure to a high temperature and high humidity environment. Here, the haze value of the test material (that is, the haze value of the polarizing film to which the adhesive layer was adhered) was measured using a haze meter (HM-150, Murakami Color Research Laboratory). Table 1 shows the results of the haze value at normal temperature (z1) and the haze value after exposure to a high temperature and high humidity environment (z2).

(Results of Characteristic Evaluation)
　Regarding the surface resistivity at normal temperature (x), as shown in Table 1, in Examples 1 to 10, the adhesive compositions contained the conductive polymer (B), and any surface resistivity at normal temperature (x) was 1 × 10¹²Ω/□ or less, more specifically 1 × 10¹⁰Ω/□ or less. On the other hand, in Comparative Example 3, when the adhesive composition contained no conductive polymer (B), the surface resistivity at normal temperature (x) exceeded 1 x 10¹²Ω/□. From this, it is assumed that in the laminates for image display devices of Examples 1 to 10, the surface resistivity at normal temperature (x) of the adhesive layer is decreased because of the conductive polymer (B) contained in the adhesive composition.

　Further, regarding the surface resistivity after exposure to a high temperature and high humidity environment (y), as shown in Table 1, in Examples 1 to 10, the adhesive composition contained the conductive polymer (B), and any surface resistivity after exposure to a high temperature and high humidity environment (y) was less than 1 × 10¹³Ω/□, more specifically, less than 1 × 10¹¹Ω/□. On the other hand, in Comparative Example 3, when the adhesive composition contained no conductive polymer (B), the surface resistivity after exposure to a high temperature and high humidity environment (y) exceeded 1 × 10¹²Ω/□. From this, it is assumed that in the laminates for image display devices of Examples 1 to 10, the surface resistivity after exposure to a high temperature and high humidity environment (y) of the adhesive layer is also decreased because of the conductive polymer (B) contained in the adhesive composition.

　Regarding the ratio (y/x ratio) of the surface resistivity after exposure to a high temperature and high humidity environment (y) to the surface resistivity at normal temperature (x), as shown in Table 1, in Examples 1 to 10, any y/x ratio was less than 10, more specifically less than 4. On the other hand, in Comparative Example 1, the y/x ratio exceeded 10. From this, it is understood that the laminates for image display devices of Examples 1 to 10 have a small change in surface resistivity between before exposure and after exposure to a high temperature and high humidity environment.

　Regarding the haze value at normal temperature (z1), as shown in Table 1, in Examples 1 to 10, each of the haze values at normal temperature (z1) was 2% or less, and more specifically 1.8% or less. On the other hand, in Comparative Example 1, the haze value at normal temperature (z1) exceeded 2%. From this, it is understood that the laminates for image display devices of Examples 1 to 10 have a small haze value and high transparency.

　Therefore, it is assumed that the laminates for image display devices of Examples 1 to 10 have a low surface resistivity of the adhesive layer at normal temperature, a small change in surface resistivity between before exposure and after exposure to a high temperature and high humidity environment, have both a low resistance value and a low haze because of the small haze value, and thus can withstand a high temperature and high humidity environment.

Claims

　A laminate for an image display device, at least comprising:
　an adhesive layer formed of an adhesive composition comprising an adhesive polymer (A), a conductive polymer (B) comprising a conjugated polymer and a polyanion, and a crosslinking agent (C),
　an image display element located on one of two surfaces of the adhesive layer, and
　a polarizing film located on the other surface of the adhesive layer,
　with respect to a test material comprising the adhesive layer having the polarizing film on one surface and a protective material, which has a release layer and which comprises polyethylene terephthalate (PET), on the other surface of the adhesive layer, with the adhesive layer and the release layer being located so as to be adjacent to each other, when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, a surface resistivity of the adhesive layer is 1 x 10¹²Ω/□ or less, a haze value of the test material from which the protective material has been peeled off is 2 or less, and the following formula (1) is satisfied,
　y/x < 10 ・・・ (1)
　wherein x represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, and
　y represents a surface resistivity of the adhesive layer when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.
　The laminate for an image display device according to claim 1, wherein the adhesive composition further comprises a silane coupling agent (D).
　The laminate for an image display device according to claim 1 or 2,
　wherein the adhesive composition further comprises a dispersant (E) that is an amphiphilic compound, and
　wherein the dispersant (E) is a nonionic compound having an ether or ester of a trihydric or higher polyhydric alcohol or an oxyalkylene chain.
　The laminate for an image display device according to any one of claims 1 to 3,
　wherein a haze value of the test material is 3% or less when the protective material is peeled off from the test material in an environment of a temperature of 23°C and a relative humidity of 50%, provided that the test material has been maintained in an environment of a temperature of 60°C and a relative humidity of 90% for 500 hours and dried at 80°C for 1 hour.
　The laminate for an image display device according to any one of claims 1 to 4,
　wherein the polarizing film has a film protective layer on one or both surfaces, and
　wherein the film protective layer comprises cycloolefin polymer (COP), polyethylene terephthalate (PET) or polymethyl methacrylate (PMMA).
　An image display device, having the laminate for an image display device according to any one of claims 1 to 5.