JP7268967B2 - Adhesive layer for flexible image display device, laminate for flexible image display device, and flexible image display device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive layer for flexible image display devices. The present invention also relates to a laminate for a flexible image display device to which, for example, an optical film containing at least a polarizing film is applied together with the pressure-sensitive adhesive layer for a flexible image display device. The present invention also relates to a flexible image display device in which the laminate for a flexible image display device is arranged.

As a touch sensor integrated organic EL display device, as shown in FIG. ing. The optical layered body 20 includes a polarizing film 1 having protective films 2-1 and 2-2 bonded to both surfaces thereof, and a retardation film 3. The polarizing film 1 is provided on the viewing side of the retardation film 3. FIG. Further, the touch panel 30 has a structure in which the base films 5-1 and 5-2 and the transparent conductive layers 6-1 and 6-2 are laminated, and the transparent conductive films 4-1 and 4-2 It has an arranged structure (see Patent Document 1, for example).

In addition, the realization of a foldable organic EL display device that is more excellent in portability is expected. For example, it has been proposed to improve flexibility and the like by controlling the storage elastic modulus G' of adhesive layers applied to organic EL display devices and the like (see, for example, Patent Documents 2 to 4).

JP 2014-157745 A JP 2016-108555 A JP 2017-095657 A JP 2017-095659 A

A conventional organic EL display device as disclosed in Patent Document 1 is not designed with bending in mind. If a plastic film is used for the organic EL display panel substrate, flexibility can be imparted to the organic EL display panel. Further, even when a plastic film is used for the touch panel and incorporated into the organic EL display panel, flexibility can be imparted to the organic EL display panel. However, there is a problem that conventional optical films including polarizing films and the like laminated on the organic EL display panel hinder flexibility of the organic EL display device.

In addition, the conventional organic EL display device is repeatedly bent at room temperature, so that the layers such as the optical film and the adhesive layer that make up the organic EL display device and each layer are slightly distorted, resulting in peeling and cracking (fracture). ) occurs. Furthermore, in addition to the problem at room temperature, when the adhesive layer is folded in a high-temperature environment, cohesive failure occurs in the adhesive layer, and peeling tends to become noticeable.

In Patent Document 2, the storage elastic modulus G′ at −20° C. is 1×10 ⁵ Pa or less and the storage elastic modulus G′ at 85° C. is 1×10 ⁴ Pa or more from the viewpoint of flex resistance and heat resistance. It has been proposed to use an adhesive layer. Moreover, Patent Document 3 proposes to use a pressure-sensitive adhesive layer having a storage elastic modulus G′ at 23° C. of 3.0×10 ⁵ Pa or less from the viewpoint of adhesive strength and flex resistance at low temperatures. Further, in Patent Document 4, from the viewpoint of flex resistance at low temperatures, the storage elastic modulus G' at -20°C is 1.3 × 10 ⁵ Pa or more and 1 × 10 ⁶ Pa or less , further 3.0 × 10 It is proposed to use an adhesive layer of ⁵ Pa or less. However, even a pressure-sensitive adhesive layer satisfying the storage elastic modulus G' within the above range has not been able to satisfy bending resistance from low temperature to high temperature.

Accordingly, an object of the present invention is to provide a pressure-sensitive adhesive layer for a flexible image display device that can satisfy bending resistance from low temperature to high temperature.

Further, the present invention provides a laminate for a flexible image display device to which an optical film containing at least a polarizing film is applied together with the pressure-sensitive adhesive layer for a flexible image display device. It is an object of the present invention to provide an arranged flexible image display device.

The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have found the following pressure-sensitive adhesive layer for a flexible image display device, etc., and completed the present invention.

That is, in the present invention, the storage elastic modulus G' at -20°C is 3.5 × 10 ⁴ to 1.7 × 10 ⁵ Pa,
A storage modulus G′ at 23° C. of 1.0×10 ⁴ to 5.0×10 ⁴ Pa, and
The present invention relates to a pressure-sensitive adhesive layer for a flexible image display device, wherein the difference between the storage elastic modulus G' at 23°C and the storage elastic modulus G' at 85°C is 5.2×10 ³ Pa or more.

In the adhesive layer for a flexible image display device, the average value of the storage elastic modulus G' at -20°C and the storage elastic modulus G' at 23°C is 4.5×10 ⁴ to 1.5×10 ⁵ Pa. is preferably

The adhesive layer for a flexible image display device preferably has a gel fraction of 70% by weight or more.

The pressure-sensitive adhesive layer for a flexible image display device can be formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer containing an alkyl (meth)acrylate as a monomer unit.

In the pressure-sensitive adhesive layer for a flexible image display device, the alkyl (meth) acrylate preferably contains an alkyl (meth)) acrylate having an alkyl group with 10 or more carbon atoms.

In the pressure-sensitive adhesive layer for a flexible image display device, the (meth)acrylic polymer preferably contains, as monomer units, an N-vinyl group-containing lactam monomer in addition to the alkyl (meth)acrylate.

The present invention also relates to a laminate for a flexible image display device, comprising the pressure-sensitive adhesive layer and an optical film including at least a polarizing film.

Further, the present invention includes the laminate for a flexible image display device and an organic EL display panel, and the laminate for a flexible image display device is arranged on the viewing side of the organic EL display panel. flexible image display device characterized by:

In the flexible image display device, it is preferable that a window is arranged on the viewing side with respect to the laminate for a flexible image display device.

A pressure-sensitive adhesive layer that is attached to a substrate requires stress that follows minute deformation of the adjacent substrate. In particular, when bending in a high-temperature environment, the cohesive strength of the adhesive layer decreases at high temperatures, and when repeatedly bending, repeated strain is applied to the adhesive layer, causing cohesive failure of the adhesive layer and peeling. it is conceivable that. Since the pressure-sensitive adhesive layer of the present invention has a predetermined storage elastic modulus at a predetermined temperature, the pressure-sensitive adhesive layer is strained even when exposed to any environment of low temperature, normal temperature, or high temperature. Stress can be distributed, and strain applied to the substrate can be reduced. That is, the pressure-sensitive adhesive layer is easily deformed by minute strain, and the strain applied to the other layers (each layer) can be reduced. As a result, the pressure-sensitive adhesive layer of the present invention does not cause cracking, peeling, or breakage of the base material even when repeatedly bent, and can satisfy bending resistance. It is possible to prevent the occurrence of leakage, and it can be suitably applied to the use of a flexible image display device. In particular, when the optical layered body is bent, each layer is likely to be slightly distorted, and there is a high possibility that the base material will crack or the adhesive layer will peel off. be done.

1 is a cross-sectional view showing a conventional organic EL display device; FIG. 1 is a cross-sectional view showing a flexible image display device according to an embodiment of the present invention; FIG. FIG. 4 is a cross-sectional view showing a flexible image display device according to another embodiment of the present invention; FIG. 4 is a cross-sectional view showing a flexible image display device according to another embodiment of the present invention; It is a figure which shows a bending test ((A) bending angle 0 degree, (B) bending angle 180 degree). FIG. 3 is a cross-sectional view showing an evaluation sample used in Examples. It is a figure which shows the manufacturing method of the retardation used in an Example.

The pressure-sensitive adhesive layer for a flexible image display device of the present invention has a storage elastic modulus G' of 3.5×10 ⁴ to 1.7×10 ⁵ Pa at −20° C. and a storage elastic modulus G′ at 23° C. is 1.0×10 ⁴ to 5.0×10 ⁴ Pa, and the difference between the storage elastic modulus G′ at 23° C. and the storage elastic modulus G′ at 85° C. is 5.2×10 ³ Pa That's it.

As described above, the pressure-sensitive adhesive layer of the present invention has a storage elastic modulus G′ at −20° C. controlled in the range of 3.5×10 ⁴ to 1.7×10 ⁵ Pa, so that it can be It satisfies the bending resistance of The storage elastic modulus G' at -20°C is preferably 5 × 10 ⁴ to 1.6 × 10 5 Pa, more preferably 7.0 × 10 ⁴ to 1.6 × 10 ⁵ Pa, from the viewpoint of bending resistance in a low temperature environment. 5×10 ⁵ Pa is preferred.

In addition, the pressure-sensitive adhesive layer of the present invention controls the storage elastic modulus G' at 23°C within the range of 1.0 × 10 ⁴ to 5.0 × 10 ⁴ Pa, and also controls the storage elastic modulus G' at 23°C. ' and the storage elastic modulus G' at 85° C. is controlled to be 5.2×10 ³ Pa or more, thereby satisfying flex resistance under normal temperature and high temperature environments. The range of the storage elastic modulus G' at 23°C is preferably designed to be lower than the storage elastic modulus G' at -20°C, which is preferable in order to satisfy the flex resistance under normal temperature environment. Further, the storage elastic modulus G' at 85°C is designed to be lower than the storage elastic modulus G' at 23°C by a predetermined amount, thereby satisfying flex resistance in a high-temperature environment. That is, together with the control of the storage elastic modulus G' at -20°C, it is possible to satisfy flex resistance in a wide temperature range from low temperature to high temperature where reliability must be ensured.

The storage elastic modulus G′ at 23° C. is preferably 1.3×10 ⁴ to 4.0×10 4 Pa, more preferably 1.5×10 4 to 3.0× ^{10 4} Pa, from the viewpoint of flex resistance at room temperature. 5×10 ⁴ Pa is preferred. In addition, the difference between the storage elastic modulus G′ at 23° C. and the storage elastic modulus G′ at 85° C. is 5.3×10 3 Pa or more, or even 5.3×10 ³ Pa or more, from the viewpoint of flex resistance in a high-temperature environment. It is preferable to control the pressure to 5×10 ³ Pa or more. If the difference in the storage elastic modulus G ^′ becomes too large ^, the fluidity of the pressure-sensitive adhesive increases. It is preferable to control so that

In addition, the storage elastic modulus G′ at 85° C. is preferably 8.0×10 ³ to 3.4×10 ⁴ Pa, more preferably 1.0× It is preferably 10 ⁴ to 3.0×10 ⁴ Pa.

The pressure-sensitive adhesive layer of the present invention has an average value of the storage elastic modulus G' at -20°C and the storage elastic modulus G' at 23°C from the viewpoint of satisfying flex resistance in both low-temperature and normal-temperature environments. is preferably 4.0×10 ⁴ to 1.5×10 ⁵ Pa. More preferably, the average value is 4.5×10 ⁴ to 1.0×10 ⁵ Pa.

Furthermore, the pressure-sensitive adhesive layer of the present invention has a storage elastic modulus G′ at −20° C. and a storage elastic modulus at 23° C. from the viewpoint of satisfying flex resistance in any environment of low temperature, normal temperature and high temperature. The average value of G' and storage modulus G' at 85°C is preferably 5.0 x 10 ⁴ to 4.0 x 10 ⁵ Pa. More preferably, the average value is 8.0×10 ⁴ to 3.0×10 ⁵ Pa.

By controlling the average value of the storage elastic modulus G' within the above range, the difference in elastic modulus for each temperature condition is reduced, which is preferable for exhibiting flex resistance in a wide temperature range.

The gel fraction of the adhesive layer of the present invention is preferably 70% by weight & more, more preferably 70 to 95% by weight, more preferably 80 to 90% by weight, even more preferably 82 to 90% by weight, Even more preferably 85 to 90% by weight. When the gel fraction of the pressure-sensitive adhesive layer is within the above range, the cohesive force of the pressure-sensitive adhesive layer can be increased, and the appearance (adhesive marks, etc.), workability, durability, and flexibility are improved. It becomes easy to achieve both flexibility under normal temperature and high temperature environments, which is a preferred embodiment.

The glass transition temperature (Tg) of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but the upper limit is preferably 5°C or less. Considering flexibility in a low-temperature environment or in a high-speed region, it is more preferably -20°C or less, and still more preferably -25°C or less. If the Tg of the pressure-sensitive adhesive layer is in such a range, the pressure-sensitive adhesive layer is less likely to harden even in a low-temperature environment or during bending at a high speed range exceeding 1 sec/bend, resulting in excellent stress relaxation. It is possible to realize a bendable or foldable flexible image display device laminate and a flexible image display device in which the flexible image display device laminate is arranged. The glass transition temperature (Tg) is a theoretical value derived from the Fox equation.

The total light transmittance (according to JIS K7136) in the visible light wavelength region of the adhesive layer used in the laminate for a flexible image display device of the present invention is preferably 85% or more, more preferably 90% or more.

The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer of the present invention, the composition thereof, and the like are described below.

Examples of adhesives forming the adhesive layer of the present invention include acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, and urethane adhesives. , fluorine-based adhesives, epoxy-based adhesives, polyether-based adhesives, and the like. The pressure-sensitive adhesives constituting the pressure-sensitive adhesive layer may be used alone or in combination of two or more. However, from the viewpoint of transparency, workability, durability, adhesion, bending resistance, etc., it is preferable to use an acrylic pressure-sensitive adhesive (composition) containing a (meth)acrylic polymer alone.

<(Meth) acrylic polymer>
When an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive composition, a (meth) acrylic containing an alkyl (meth) acrylate having a linear or branched alkyl group having 1 to 30 carbon atoms as a monomer unit It preferably contains a polymer. By using the alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 30 carbon atoms, a pressure-sensitive adhesive layer having excellent flexibility can be obtained. In the present invention, (meth)acrylic polymer means acrylic polymer and/or methacrylic polymer, and (meth)acrylate means acrylate and/or methacrylate.

Specific examples of the alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 30 carbon atoms constituting the main skeleton of the (meth)acrylic polymer include methyl (meth)acrylate, ethyl ( meth) acrylate, n-butyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, n-pentyl (meth) acrylate, isopentyl (meth) acrylate, n- Hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate (lauryl (meth)acrylate), n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, etc. is given.

Among the alkyl (meth) acrylates, alkyl (meth) acrylates having a linear or branched alkyl group having 6 to 30 carbon atoms (hereinafter referred to as “long may be referred to as "an alkyl (meth)acrylate having a chain alkyl group") is preferred. The alkyl(meth)acrylate having a long-chain alkyl group preferably contains an alkyl(meth))acrylate having an alkyl group having 10 or more carbon atoms. In particular, n-dodecyl (meth)acrylate (lauryl (meth)acrylate) is more preferable as the alkyl (meth)acrylate having a long-chain alkyl group. By using the alkyl (meth)acrylate having the long-chain alkyl group, the entanglement of the polymer is reduced, making it easier to deform with respect to minute strain, which is a favorable aspect for flexibility. In addition, from the viewpoint of flexibility and adhesion at low temperatures, it is preferable to use an alkyl (meth)acrylate whose homopolymer glass transition temperature (Tg) is -70 to -20 ° C., and has 6 to 9 carbon atoms. Among them, it is more preferable to use 2-ethylhexyl acrylate. As said alkyl (meth)acrylate, 1 type(s) or 2 or more types can be used. As the long-chain alkyl (meth)acrylate, a mixture of an alkyl (meth)acrylate having an alkyl group having 10 to 30 carbon atoms and an alkyl (meth)acrylate having an alkyl group having 6 to 9 carbon atoms is used. is preferred. In addition, the mixture has a mixing weight ratio of (alkyl (meth)acrylate having an alkyl group having 10 to 30 carbon atoms):(alkyl (meth)acrylate having an alkyl group having 6 to 9 carbon atoms) = 40: A ratio of 60 to 90:10 is preferred. A mixture of an alkyl (meth)acrylate having an alkyl group having 10 to 30 carbon atoms and an alkyl (meth)acrylate having an alkyl group having 6 to 9 carbon atoms is n-dodecyl (meth)acrylate and 2-ethylhexyl acrylate. It is preferable to use together.

The alkyl (meth)acrylate having a linear or branched alkyl group of 1 to 30 carbon atoms is the main component in all the monomers constituting the (meth)acrylic polymer. Here, the main component is 50 to 100% by weight of alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 30 carbon atoms in all the monomers constituting the (meth)acrylic polymer. is preferably 80 to 100% by weight, more preferably 90 to 99.9% by weight, and particularly preferably 94 to 99.9% by weight.

The monomer component constituting the (meth)acrylic polymer includes, in addition to the alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 30 carbon atoms, a copolymerizable monomer (copolymer polymerizable monomer). In addition, a copolymerizable monomer may be used individually or in combination of 2 or more types.

The copolymerizable monomer is not particularly limited, but is preferably a copolymerizable monomer having a reactive functional group of a polymerizable unsaturated double bond. A hydroxyl group-containing monomer is preferable as the copolymerizable monomer having a reactive functional group. By using the hydroxyl group-containing monomer, a pressure-sensitive adhesive layer having excellent adhesion and flexibility can be obtained. The hydroxyl group-containing monomer is a compound containing a hydroxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or vinyl group.

Specific examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxy Hydroxyalkyl (meth)acrylates such as octyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate. Among the hydroxyl group-containing monomers, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferable from the viewpoint of durability and adhesion. In addition, as said hydroxyl-group containing monomer, 1 type(s) or 2 or more types can be used.

Examples of the copolymerizable monomer having a reactive functional group include carboxyl group-containing monomers, amino group-containing monomers, and amide group-containing monomers having a reactive functional group. These monomers are preferable from the viewpoint of adhesion under humidification and high-temperature environments.

By using the carboxyl group-containing monomer, it is possible to obtain a pressure-sensitive adhesive layer having excellent adhesion under humidified and high-temperature environments. The carboxyl group-containing monomer is a compound containing a carboxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group and a vinyl group.

Specific examples of the carboxyl group-containing monomer include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

By using the amino group-containing monomer, it is possible to obtain a pressure-sensitive adhesive layer having excellent adhesion under humidified and high-temperature environments. The amino group-containing monomer is a compound containing an amino group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or vinyl group.

Specific examples of the amino group-containing monomer include N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate.

By using the amide group-containing monomer, a pressure-sensitive adhesive layer with excellent adhesion can be obtained. The amide group-containing monomer is a compound containing an amide group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or vinyl group.

Specific examples of the amide group-containing monomer include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N -butyl (meth)acrylamide, N-hexyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methylol-N-propane (meth)acrylamide, aminomethyl (meth)acrylamide, aminoethyl (meth)acrylamide, mercapto acrylamide-based monomers such as methyl (meth)acrylamide and mercaptoethyl (meth)acrylamide; N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, N-acryloyl heterocyclic monomers such as N-(meth)acryloylpyrrolidine; Examples thereof include N-vinyl group-containing lactam monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam.

Among copolymerizable monomers such as carboxyl group-containing monomers, amino group-containing monomers, and amide group-containing monomers, amide group-containing monomers are preferred, and N-vinyl group-containing lactam monomers are particularly preferred. An N-vinyl group-containing lactam-based monomer is preferable from the viewpoint of improving adhesion to an adherend, particularly improving adhesion during heating.

As the copolymerizable monomer having a reactive functional group, it is preferable to use a hydroxyl group-containing monomer and an amide group-containing monomer (in particular, an N-vinyl group-containing lactam monomer) in combination.

In the monomer units constituting the (meth)acrylic polymer, the blending ratio of the copolymerizable monomer having a reactive functional group as exemplified above is 20% by weight or less in all the monomers constituting the (meth)acrylic polymer. is preferred, 15% by weight or less is more preferred, and 10% by weight or less is even more preferred.

When the hydroxyl group-containing monomer is contained, the blending ratio is preferably 0.01 to 8% by weight, more preferably 0.01 to 5% by weight, and even more preferably 0.05 to 3% by weight.

When copolymerizable monomers such as the carboxyl group-containing monomer, amino group-containing monomer, and amide group-containing monomer are contained, the blending ratio is preferably 0.01 to 15% by weight, preferably 0.1 to 12% by weight. % is more preferred, and 0.1 to 10% by weight is even more preferred. In particular, the N-vinyl group-containing lactam monomer is preferably used in an amount of 3 to 12% by weight, more preferably 4 to 10% by weight. If the ratio of the N-vinyl group-containing lactam-based monomer is too large, the glass transition temperature rises, and the storage elastic modulus G' increases at normal temperature (23°C), which may cause peeling or cracking in the bending test. Therefore, it is preferable to use the N-vinyl group-containing lactam monomer within the above range.

As the copolymerizable monomer, in addition to the copolymerizable monomer having a reactive functional group as exemplified above, other copolymerizable monomers can be used as long as the effects of the present invention are not impaired.

Further, the other copolymerizable monomers include, for example, (meth)acrylate alkoxyalkyl esters [eg, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytri(meth)acrylate, Ethylene glycol, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.]; epoxy group-containing monomers [ sulfonic acid group-containing monomers [e.g., sodium vinyl sulfonate]; phosphoric acid group-containing monomers; ) Acrylic acid ester [e.g., cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc.]; (meth)acrylic acid ester having an aromatic hydrocarbon group [e.g., (meth)acrylic phenyl acid, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc.]; vinyl esters [e.g., vinyl acetate, vinyl propionate, etc.]; aromatic vinyl compounds [e.g., styrene, vinyltoluene, etc.]; olefins or dienes [eg, ethylene, propylene, butadiene, isoprene, isobutylene, etc.]; vinyl ethers [eg, vinyl alkyl ether, etc.]; vinyl chloride, and the like.

The blending ratio of the other copolymerizable monomers is not particularly limited, but is preferably 30% by weight or less, more preferably 10% by weight or less, of the total monomers constituting the (meth)acrylic polymer, and further preferably does not contain preferable. If it exceeds 30% by weight, the reaction points between the pressure-sensitive adhesive layer and other layers (film, base material) are reduced, and adhesion tends to decrease, especially when other than alkyl (meth)acrylate is used.

In addition, the monomer component constituting the (meth)acrylic polymer is, in addition to the monofunctional monomer having one reactive functional group of the polymerizable unsaturated double bond as exemplified above, a multifunctional monomer having a plurality of the reactive functional groups. Functional monomers can be used.

When a polyfunctional monomer is included, a cross-linking effect can be obtained by polymerization, and it is possible to easily adjust the gel fraction and improve the cohesive force. For this reason, cutting becomes easy, and workability tends to be improved. Furthermore, peeling due to cohesive failure of the pressure-sensitive adhesive layer can be prevented during bending (especially in a high-temperature environment). Examples of polyfunctional monomers include, but are not limited to, hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate. ) acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylol polyfunctional acrylates such as propane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate; Among them, 1,6-hexanediol diacrylate and dipentaerythritol hexa(meth)acrylate are preferable as polyfunctional acrylates. In addition, a polyfunctional monomer may be used individually or in combination of 2 or more types.

The blending ratio of the polyfunctional monomer is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and 3 parts by weight or less with respect to 100 parts by weight of the total amount of monofunctional monomers constituting the (meth)acrylic polymer. More preferred. When the blending ratio of the polyfunctional monomer increases, the number of cross-linking points increases and the pressure-sensitive adhesive (layer) loses its flexibility, which tends to result in poor stress relaxation.

The pressure-sensitive adhesive layer is formed of a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition may be a pressure-sensitive adhesive composition having any form, for example, emulsion type, solvent type (solution type) , active energy ray curing type, heat melting type (hot melt type), and the like. Among them, as the pressure-sensitive adhesive composition, a solvent-type pressure-sensitive adhesive composition and an active energy ray-curable pressure-sensitive adhesive composition are preferable.

As the solvent-based pressure-sensitive adhesive composition, a pressure-sensitive adhesive composition containing the (meth)acrylic polymer as an essential component is preferably used. In addition, the active energy ray-curable pressure-sensitive adhesive composition is preferably a pressure-sensitive adhesive composition containing a mixture (monomer mixture) of monomer components constituting the (meth)acrylic polymer or a partial polymer thereof as an essential component. mentioned. The term "partially polymerized product" means a composition in which one or more of the monomer components contained in the monomer mixture are partially polymerized. In addition, the "monomer mixture" includes the case where only one type of monomer component is used.

In particular, the pressure-sensitive adhesive composition is a mixture of monomer components constituting a (meth)acrylic polymer ( It is preferably an active energy ray-curable pressure-sensitive adhesive composition containing a monomer mixture) or a partial polymer thereof as an essential component.

The (meth)acrylic polymer is obtained by polymerizing the monomer components. More specifically, it can be obtained by polymerizing the monomer component, the monomer mixture, or a partially polymerized product thereof by a known and commonly used method. Examples of the polymerization method include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by heat or active energy ray irradiation (thermal polymerization, active energy ray polymerization). Among them, solution polymerization and active energy ray polymerization are preferred in terms of transparency, water resistance, cost, and the like. In addition, it is preferable that the polymerization is carried out while avoiding contact with oxygen in order to suppress polymerization inhibition due to oxygen. For example, it is preferable to carry out the polymerization in a nitrogen atmosphere, or to carry out the polymerization while blocking oxygen with a release film (separator). The (meth)acrylic polymer to be obtained may be a random copolymer, a block copolymer, a graft copolymer, or the like.

Examples of the active energy ray irradiated during the active energy ray polymerization (photopolymerization) include ionizing radiation such as α rays, β rays, γ rays, neutron beams and electron beams, and ultraviolet rays, particularly ultraviolet rays. is preferred. Moreover, the irradiation energy, irradiation time, irradiation method, and the like of the active energy ray are not particularly limited as long as the photopolymerization initiator can be activated to cause the reaction of the monomer components.

Various general solvents can be used for the solution polymerization. Examples of such solvents include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; Alicyclic hydrocarbons such as cyclohexane; and organic solvents such as ketones such as methyl ethyl ketone and methyl isobutyl ketone. In addition, the said solvent may be used individually or in combination of 2 or more types.

In the polymerization, a polymerization initiator such as a photopolymerization initiator (photoinitiator) or a thermal polymerization initiator may be used depending on the type of polymerization reaction. In addition, a polymerization initiator may be used individually or in combination of 2 or more types.

The photopolymerization initiator is not particularly limited. Examples include active oxime photopolymerization initiators, benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, and thioxanthone photopolymerization initiators.

Examples of the benzoin ether photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, anisole methyl ether and the like. Examples of the acetophenone-based photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenylketone, 4-phenoxydichloroacetophenone, 4-(t-butyl ) and dichloroacetophenone. Examples of the α-ketol photopolymerization initiator include 2-methyl-2-hydroxypropiophenone, 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one, and the like. be done. Examples of the aromatic sulfonyl chloride photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the photoactive oxime photopolymerization initiator include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of the benzoin-based photopolymerization initiator include benzoin. Examples of the benzyl-based photopolymerization initiator include benzyl. Examples of the benzophenone-based photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of the ketal photopolymerization initiator include benzyl dimethyl ketal. Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

The amount of the photopolymerization initiator used is not particularly limited, but is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.5 part by weight, based on 100 parts by weight of the total amount of the monomer components.

Examples of polymerization initiators used in the solution polymerization include azo polymerization initiators, peroxide polymerization initiators (eg, dibenzoyl peroxide, tert-butyl permaleate, etc.), redox polymerization initiators, and the like. is mentioned. Among them, the azo polymerization initiator disclosed in JP-A-2002-69411 is preferable. Examples of the azo polymerization initiator include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis-2-methylbutyronitrile, 2,2′-azobis(2-methylpropionic acid ) dimethyl, 4,4′-azobis-4-cyanovaleric acid and the like.

The amount of the azo polymerization initiator used is not particularly limited, but is preferably 0.05 to 0.5 parts by weight, more preferably 0.1 to 0.3 parts by weight, based on 100 parts by weight of the total amount of the monomer components. is.

The polyfunctional monomer (polyfunctional acrylate) used as the copolymer monomer can also be used in a solvent-type or active energy ray-curable pressure-sensitive adhesive composition. When a polyfunctional monomer (polyfunctional acrylate) and the photopolymerization initiator are mixed and used, active energy ray curing is performed after thermal drying.

In the present invention, the (meth)acrylic polymer used in the solvent-based pressure-sensitive adhesive composition generally has a weight-average molecular weight (Mw) in the range of 1,000,000 to 2,500,000. Considering durability, especially heat resistance and flexibility, it is preferably 1.2 million to 2 million, more preferably 1.4 million to 1.8 million. If the weight-average molecular weight is less than 1,000,000, when the polymer chains are cross-linked to ensure durability, the number of cross-linking points increases compared to those with a weight-average molecular weight of 1,000,000 or more, resulting in an adhesive (layer ), the strain on the outer side (convex side) and the inner side (concave side) of bending that occurs between each layer (each film) during bending cannot be relaxed, and each layer is likely to break. In addition, when the weight average molecular weight is larger than 2,500,000, a large amount of diluent solvent is required to adjust the viscosity for coating, which is not preferable because it increases the cost, and the obtained (meth)acrylic Since the entanglement between the polymer chains of the polymer becomes complicated, the flexibility is deteriorated, and each layer (film) is likely to break when bent. The weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and calculated by polystyrene conversion.

<(Meth) acrylic oligomer>
The pressure-sensitive adhesive composition may contain a (meth)acrylic oligomer. The (meth)acrylic oligomer preferably uses a polymer having a weight average molecular weight (Mw) smaller than that of the (meth)acrylic polymer. ) The (meth)acrylic oligomer intervenes between the acrylic polymers to reduce the entanglement of the (meth)acrylic polymers, making it easier to deform with respect to a minute strain, and is a preferred embodiment for flexibility. Become.

Examples of monomers constituting the (meth)acrylic oligomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylates, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, Such as octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate Alkyl (meth)acrylates; esters of (meth)acrylic acid and alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate; phenyl (meth)acrylate, benzyl Aryl (meth)acrylates such as (meth)acrylates; (meth)acrylates obtained from terpene compound derivative alcohols; and the like. Such (meth)acrylates can be used alone or in combination of two or more.

Examples of the (meth)acrylic oligomer include alkyl (meth)acrylates having a branched alkyl group structure such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; cyclohexyl (meth)acrylate; ) Esters of (meth)acrylic acid and alicyclic alcohols such as acrylate dicyclopentanyl (meth)acrylate; Cyclic structures such as aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate It is preferable that the acrylic monomer having a relatively bulky structure represented by (meth)acrylate having is included as a monomer unit. By imparting such a bulky structure to the (meth)acrylic oligomer, the adhesiveness of the pressure-sensitive adhesive layer can be further improved. In particular, in terms of bulkiness, those having a cyclic structure are highly effective, and those containing a plurality of rings are even more effective. In addition, when ultraviolet rays are used in the synthesis of (meth)acrylic oligomers or in the preparation of the pressure-sensitive adhesive layer, those with saturated bonds are preferable because they are less likely to cause polymerization inhibition. An alkyl (meth)acrylate having a branched structure or an ester with an alicyclic alcohol can be suitably used as a monomer constituting the (meth)acrylic oligomer.

From this point of view, suitable (meth)acrylic oligomers include, for example, a copolymer of butyl acrylate (BA), methyl acrylate (MA) and acrylic acid (AA), cyclohexyl methacrylate (CHMA) and isobutyl methacrylate ( IBMA), cyclohexyl methacrylate (CHMA) and isobornyl methacrylate (IBXMA) copolymers, cyclohexyl methacrylate (CHMA) and acryloylmorpholine (ACMO) copolymers, cyclohexyl methacrylate (CHMA) and diethylacrylamide ( DEAA), copolymer of 1-adamantyl acrylate (ADA) and methyl methacrylate (MMA), copolymer of dicyclopentanyl methacrylate (DCPMA) and isobornyl methacrylate (IBXMA), dicyclopentanyl Methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), copolymer of cyclopentanyl methacrylate (DCPMA) and methyl methacrylate (MMA), dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA) homopolymers.

The (meth)acrylic oligomer may be polymerized in the same manner as in the (meth)acrylic polymer by solution polymerization, emulsion polymerization, bulk polymerization, emulsion polymerization, polymerization by heat or active energy ray irradiation (thermal polymerization, active energy linear polymerization) and the like. Among them, solution polymerization and active energy ray polymerization are preferred in terms of transparency, water resistance, cost, and the like. Moreover, the (meth)acrylic oligomer to be obtained may be any of random copolymers, block copolymers, graft copolymers, and the like.

The (meth)acrylic oligomer can be used in the solvent-based pressure-sensitive adhesive composition and the active energy ray-curable pressure-sensitive adhesive composition in the same manner as the (meth)acrylic polymer. For example, as the active energy ray-curable pressure-sensitive adhesive composition, a mixture of monomer components constituting the (meth)acrylic polymer (monomer mixture) or a partial polymer thereof, and further the (meth)acrylic oligomer. Can be mixed and used. When the (meth)acrylic oligomer is dissolved in a solvent, the pressure-sensitive adhesive layer can be obtained by heat-drying the pressure-sensitive adhesive composition to remove the solvent and then completing active energy ray curing.

The weight average molecular weight (Mw) of the (meth)acrylic oligomer used in the solvent-based pressure-sensitive adhesive composition is preferably 1000 or more, more preferably 2000 or more, still more preferably 3000 or more, and particularly preferably 4000 or more. . The weight average molecular weight (Mw) of the (meth)acrylic oligomer is preferably 30,000 or less, more preferably 15,000 or less, even more preferably 10,000 or less, and particularly preferably 7,000 or less. By adjusting the weight average molecular weight (Mw) of the (meth)acrylic oligomer within the range, for example, when used in combination with the (meth)acrylic polymer, (meth)acrylic polymer between the (meth)acrylic polymer ) acrylic oligomer intervenes to reduce the entanglement of (meth)acrylic polymers, making it easier for the adhesive layer to deform due to minute strain, reducing the strain applied to other layers, and preventing cracking and sticking of each layer. It is possible to suppress peeling between the agent layer and other layers, which is a preferable embodiment. In addition, the weight average molecular weight (Mw) of the (meth)acrylic oligomer is measured by GPC (gel permeation chromatography) in the same manner as the (meth)acrylic polymer, and the value calculated by polystyrene conversion is say.

When the (meth)acrylic oligomer is used in the pressure-sensitive adhesive composition, the amount thereof is not particularly limited, but it is preferably 70 parts by weight or less with respect to 100 parts by weight of the (meth)acrylic polymer. It is more preferably 1 to 70 parts by weight, still more preferably 2 to 50 parts by weight, still more preferably 3 to 40 parts by weight. By adjusting the blending amount of the (meth)acrylic oligomer within the above range, the (meth)acrylic oligomer is appropriately interposed between the (meth)acrylic polymers, and the entanglement of the (meth)acrylic polymers is prevented. The pressure-sensitive adhesive layer can be easily deformed against minute strain, strain applied to other layers can be reduced, and cracking of each layer and peeling between the pressure-sensitive adhesive layer and other layers can be suppressed, which is preferable. form.

<Measurement of weight average molecular weight (Mw) of (meth)acrylic polymer and acrylic oligomer>
The weight average molecular weights (Mw) of the obtained (meth)acrylic polymers and acrylic oligomers were measured by GPC (gel permeation chromatography).
・ Analyzer: HLC-8120GPC manufactured by Tosoh Corporation
・Column: G7000H _XL +GMH _XL +GMH _XL manufactured by Tosoh Corporation
・Column size: 7.8 mmφ×30 cm each, 90 cm in total
・Column temperature: 40°C
・Flow rate: 0.8 ml/min
・Injection volume: 100 μl
・ Eluent: Tetrahydrofuran ・ Detector: Differential refractometer (RI)
・Standard sample: polystyrene

<Crosslinking agent>
The pressure-sensitive adhesive composition of the present invention can contain a cross-linking agent. As the cross-linking agent, an organic cross-linking agent or a polyfunctional metal chelate can be used in both solvent-type and active energy ray-curable pressure-sensitive adhesive compositions. Examples of organic cross-linking agents include isocyanate-based cross-linking agents, peroxide-based cross-linking agents, epoxy-based cross-linking agents, and imine-based cross-linking agents. Polyfunctional metal chelates are those in which polyvalent metals are covalently or coordinately bonded to organic compounds. Polyvalent metal atoms include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, and Ti. mentioned. An oxygen atom etc. are mentioned as an atom in the organic compound which carries out a covalent bond or a coordinate bond, and an alkylester, an alcohol compound, a carboxylic acid compound, an ether compound, a ketone compound etc. are mentioned as an organic compound. In particular, in the case of a solvent-type pressure-sensitive adhesive composition, a peroxide cross-linking agent or an isocyanate cross-linking agent is preferable, and it is particularly preferable to use a peroxide cross-linking agent. Peroxide-based cross-linking agents, for example, generate radicals by abstracting hydrogen from the side chains of (meth)acrylic polymers, and promote cross-linking between side chains of (meth)acrylic polymers. Compared to cross-linking using a cross-linking agent (for example, a polyfunctional isocyanate-based cross-linking agent), the cross-linking state is relatively loose, and the cohesive force is increased while maintaining the ease of deformation against minute strain. This is a preferred embodiment in terms of achieving both flexibility (suppression of cracking and peeling) under normal temperature and high temperature environments. In addition, an isocyanate-based cross-linking agent (especially a trifunctional isocyanate-based cross-linking agent) is preferable in terms of durability, and a peroxide-based cross-linking agent and an isocyanate-based cross-linking agent (especially a bifunctional isocyanate-based cross-linking agent). is preferable from the point of flexibility. Both the peroxide-based cross-linking agent and the bifunctional isocyanate-based cross-linking agent form flexible two-dimensional cross-linking, while the tri-functional isocyanate-based cross-linking agent forms stronger three-dimensional cross-linking. Two-dimensional cross-linking, which is a more flexible cross-linking, is advantageous when flexing. However, with only two-dimensional cross-linking, the durability is poor and peeling easily occurs. or a bifunctional isocyanate-based cross-linking agent is preferably used in combination. As for the active energy ray-curable pressure-sensitive adhesive composition, it is preferable to obtain a cross-linking effect by polymerization using the above-mentioned polyfunctional monomer from the viewpoint of productivity and thick film coating. Alternatively, it can be used in combination with the polyfunctional monomer. For example, a mixture of monomer components constituting the (meth)acrylic polymer (monomer mixture) or a partial polymer thereof is mixed with a crosslinking agent, and the pressure-sensitive adhesive composition is crosslinked by heat drying before and after the active energy ray curing. The reaction of the agent can be completed.

The amount of the crosslinking agent used is, for example, preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, and 0.3 to 3 parts by weight with respect to 100 parts by weight of the (meth)acrylic polymer. Parts by weight are more preferred. If it is within the above range, it is excellent in flex resistance and is a preferred embodiment. In order to increase the cohesive force without changing the micro deformation stress, it is preferable to increase the amount of the cross-linking agent.

When the peroxide-based cross-linking agent is used alone, it is preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight, relative to 100 parts by weight of the (meth)acrylic polymer. Within the above range, cohesive force can be sufficiently increased while easiness of deformation against minute strain is maintained, and durability and flex resistance can be improved, which is a preferable embodiment.

In addition, when a peroxide-based cross-linking agent and an isocyanate-based cross-linking agent are used together, the lower limit of the weight ratio of the peroxide-based cross-linking agent to the isocyanate-based cross-linking agent (peroxide-based cross-linking agent/isocyanate-based cross-linking agent) is preferably 1.2 or more, more preferably 1.5 or more, and still more preferably 3 or more. The upper limit of the weight ratio is preferably 500 or less, more preferably 300 or less, and even more preferably 200 or less. Within the above range, the cohesive force can be sufficiently increased while maintaining the easiness of deformation against minute strain, which is a preferred embodiment.

<Other additives>
Further, the pressure-sensitive adhesive composition in the present invention may contain other known additives, such as various silane coupling agents, polyether compounds of polyalkylene glycols such as polypropylene glycol, colorants, pigments, and the like. powder, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic Agents (alkali metal salts, ionic liquids, ionic solids, etc., which are ionic compounds), inorganic or organic fillers, metal powders, particulates, foils, etc. can be added as appropriate according to the intended use. Also, a redox system with a reducing agent added may be employed within a controllable range.

The method for preparing the pressure-sensitive adhesive composition is not particularly limited, but a known method can be used. For example, as described above, the solvent-based acrylic pressure-sensitive adhesive composition comprises a (meth)acrylic polymer, It is prepared by mixing components (for example, the (meth)acrylic oligomer, cross-linking agent, silane coupling agent, solvent, additives, etc.) that are added as necessary. Further, as described above, the active energy ray-curable acrylic pressure-sensitive adhesive composition includes a monomer mixture or a partial polymer thereof, components added as necessary (e.g., the photopolymerization initiator, the polyfunctional monomer, the (meth)acrylic oligomer, cross-linking agent, silane coupling agent, solvent, additive, etc.).

The pressure-sensitive adhesive composition preferably has a viscosity suitable for handling and coating. Therefore, the active energy ray-curable acrylic pressure-sensitive adhesive composition preferably contains a partially polymerized monomer mixture. The polymerization rate of the partially polymerized product is not particularly limited, but is preferably 5 to 20% by weight, more preferably 5 to 15% by weight.

Further, the polymerization rate of the partially polymerized product is determined as follows.
A part of the partially polymerized product is sampled and used as a sample. The sample is accurately weighed to determine its weight, which is defined as "the weight of the partially polymerized product before drying". Next, the sample is dried at 130° C. for 2 hours, and the sample after drying is accurately weighed to determine its weight, which is defined as “the weight of the partially polymerized product after drying”. Then, from the "weight of the partial polymer before drying" and the "weight of the partial polymer after drying", the weight of the sample that was reduced by drying at 130 ° C. for 2 hours was obtained, and the "weight loss" (volatile content, unreacted monomer weight).
From the obtained "weight of the partially polymerized product before drying" and "weight loss", the polymerization rate (% by weight) of the partially polymerized product of the monomer component is obtained from the following formula.
Polymerization rate (% by weight) of partial polymer of monomer component=[1-(weight loss)/(weight of partial polymer before drying)]×100

<Formation of adhesive layer>
As a method for forming the pressure-sensitive adhesive layer, for example, the solvent-based pressure-sensitive adhesive composition is applied to a separator (release film) or the like that has been subjected to release treatment, and the polymerization solvent or the like is removed by drying to form the pressure-sensitive adhesive layer. , a method of applying the solvent-based adhesive composition to a polarizing film, etc., and drying and removing the polymerization solvent, etc. to form an adhesive layer on the polarizing film, etc., and a peeling treatment of the active energy ray-curable adhesive composition. For example, a method of forming by applying an active energy ray onto a separator, etc., which has been prepared, and the like can be mentioned. Heat drying may be performed in addition to the active energy ray irradiation, if necessary. Moreover, in applying the pressure-sensitive adhesive composition, one or more solvents other than the polymerization solvent may be newly added as appropriate.

A silicone release liner is preferably used as the release-treated separator. When the pressure-sensitive adhesive composition of the present invention is applied onto such a liner and dried to form a pressure-sensitive adhesive layer, any appropriate method may be employed as a method for drying the pressure-sensitive adhesive depending on the purpose. . Preferably, a method of heating and drying the coating film is used. The heat drying temperature, for example, when preparing an acrylic pressure-sensitive adhesive using a (meth)acrylic polymer, is preferably 40 to 200°C, more preferably 50 to 180°C, and particularly preferably 70 to 170°C. A pressure-sensitive adhesive having excellent adhesive properties can be obtained by setting the heating temperature within the above range.

An appropriate drying time can be adopted as appropriate. The drying time is, for example, when preparing an acrylic pressure-sensitive adhesive using a (meth)acrylic polymer, preferably 5 seconds to 20 minutes, more preferably 5 seconds to 10 minutes, particularly preferably 10 seconds to 5 minutes. minutes.

Various methods are used as a method for applying the pressure-sensitive adhesive composition. Specifically, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coater, etc. A method such as an extrusion coating method can be used.

The thickness of the pressure-sensitive adhesive layer of the present invention is preferably 1-200 μm, more preferably 5-150 μm, still more preferably 10-100 μm. The pressure-sensitive adhesive layer may be a single layer or may have a laminated structure. If it is within the above range, it is a preferred embodiment in terms of adhesion (holding resistance) without hindering bending. Moreover, when it has multiple adhesive layers, it is preferable that all the adhesive layers exist in the said range.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of an optical film, a laminate for a flexible image display device, and a flexible image display device according to the present invention will be described in detail with reference to the drawings and the like.

Although the present invention will be described in detail below, the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention.

[Laminate for flexible image display device]
The laminate for a flexible image display device of the present invention is characterized by including an adhesive layer and an optical film.

[Optical film]
The laminate for a flexible image display device of the present invention is characterized by comprising an optical film containing at least a polarizing film. and retardation films. In the present invention, the optical film includes the polarizing film, a protective film of a transparent resin material provided on the first surface of the polarizing film, and a second surface different from the first surface of the polarizing film. and a retardation film provided in the optical layered body. The optical film does not include a pressure-sensitive adhesive layer such as a first pressure-sensitive adhesive layer to be described later.

The thickness of the optical film is preferably 92 μm or less, more preferably 60 μm or less, still more preferably 10 to 50 μm. If it is within the above range, it becomes a preferred embodiment without inhibiting bending.

As long as the characteristics of the present invention are not impaired, the polarizing film may have a protective film attached to at least one side with an adhesive (layer) (not shown in the drawings). An adhesive can be used for bonding the polarizing film and the protective film. Examples of adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl-based latex-based adhesives, water-based polyesters, and the like. The adhesive is usually used as an aqueous adhesive, and usually contains 0.5 to 60% by weight of solids. In addition to the above, examples of the adhesive between the polarizing film and the protective film include an ultraviolet curing adhesive, an electron beam curing adhesive, and the like. The electron beam-curing adhesive for polarizing film exhibits suitable adhesion to the various protective films described above. Also, the adhesive used in the present invention may contain a metallic compound filler. In the present invention, a polarizing film (polarizing plate) is sometimes referred to as a polarizing film (polarizing plate) that is formed by laminating a polarizing film and a protective film with an adhesive (layer).

<Polarizing film>
The polarizing film (also referred to as a polarizer) contained in the optical film of the present invention is a polyvinyl alcohol (PVA) with iodine oriented, which is stretched by a stretching process such as an air stretching (dry stretching) or a boric acid water stretching process. system resin can be used.

As a method for producing a polarizing film, a typical method includes a step of dyeing and stretching a single layer of PVA-based resin, as described in JP-A-2004-341515 (single-layer stretching method ). In addition, JP-A-51-069644, JP-A-2000-338329, JP-A-2001-343521, WO 2010/100917, JP-A-2012-073563, JP-A-2011-2816 and a step of stretching the PVA-based resin layer and the resin substrate for stretching in the state of a laminate, and a step of dyeing, as described in . With this manufacturing method, even if the PVA-based resin layer is thin, it can be stretched without problems such as breakage due to stretching because it is supported by the stretching resin substrate.

The manufacturing method including the step of stretching and the step of dyeing in the state of the laminate, as described in the above-mentioned JP-A-51-069644, JP-A-2000-338329, JP-A-2001-343521. There is an air stretching (dry stretching) method. Then, in terms of being able to stretch at a high magnification and improving the polarizing performance, the step of stretching in an aqueous boric acid solution as described in WO 2010/100917 and JP 2012-073563 A is included. A production method containing the film is preferable, and a production method including a step of performing in-air auxiliary stretching before stretching in an aqueous boric acid solution (two-stage stretching method) as in JP-A-2012-073563 is particularly preferable. Further, as described in JP-A-2011-2816, after stretching the PVA-based resin layer and the stretching resin base material in the state of a laminate, the PVA-based resin layer is excessively dyed and then decolored. (Overstaining destaining method) is also preferred. The polarizing film contained in the optical film of the present invention is made of the polyvinyl alcohol-based resin in which iodine is oriented as described above, and is stretched in a two-step stretching process consisting of auxiliary stretching in air and stretching in boric acid solution. can do. In addition, the polarizing film is made of a polyvinyl alcohol-based resin in which iodine is oriented as described above. It can be a manufactured polarizing film.

The thickness of the polarizing film is 20 μm or less, preferably 12 μm or less, more preferably 9 μm or less, still more preferably 1 to 8 μm, particularly preferably 3 to 6 μm. If it is within the above range, it becomes a preferred embodiment without inhibiting bending.

<Retardation film>
The optical film used in the present invention can contain a retardation film, and the retardation film (also referred to as retardation film) is obtained by stretching a polymer film or aligning and fixing a liquid crystal material. can be used. In this specification, the retardation film means one having birefringence in the plane and/or in the thickness direction.

As the retardation film, an antireflection retardation film (see JP 2012-133303 [0221], [0222], [0228]), a viewing angle compensation retardation film (JP 2012-133303 [0225 ], see [0226]), an oblique orientation retardation film for viewing angle compensation (see JP-A-2012-133303 [0227]), and the like.

As the retardation film, as long as it substantially has the above functions, for example, the retardation value, the arrangement angle, the three-dimensional birefringence, the single layer or the multilayer, etc. are not particularly limited. can be used.

The thickness of the retardation film is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 1 to 9 μm, particularly preferably 3 to 8 μm. If it is within the above range, it becomes a preferred embodiment without inhibiting bending.

<Protective film>
The optical film used in the present invention can include a protective film formed of a transparent resin material, and the protective film (also referred to as a transparent protective film) is made of cycloolefin resin such as norbornene resin, polyethylene, Olefin-based resins such as polypropylene, polyester-based resins, (meth)acrylic-based resins, and the like can be used.

The thickness of the protective film is preferably 5 to 60 μm, more preferably 10 to 40 μm, still more preferably 10 to 30 μm. can be done. If it is within the above range, it becomes a preferred embodiment without inhibiting bending.

[Adhesive layer]
A laminate for a flexible image display device of the present invention is a laminate for a flexible image display device including an adhesive layer, wherein the adhesive layer has the predetermined storage elastic modulus.

In addition, the pressure-sensitive adhesive layer may be a single layer, but in addition to the optical film, for lamination of a transparent conductive film, an organic EL display panel, a window, a decorative printing film, a retardation layer, a protective film, etc. may have two or more layers (e.g., a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer, etc.). etc.). When it has a plurality of pressure-sensitive adhesive layers, it preferably has 2 to 5 layers. When the number of layers is more than 5, the thickness of the entire laminate becomes thick, and the strain difference between the outermost layer and the innermost layer at the bent portion of the laminate becomes large, and peeling and breakage are likely to occur, which is not preferable.

[First adhesive layer]
Among the pressure-sensitive adhesive layers used in the laminate for a flexible image display device of the present invention, the first pressure-sensitive adhesive layer is arranged on the side opposite to the surface in contact with the polarizing film with respect to the protective film. is preferred (see FIG. 2).

[Other adhesive layers]
Among the pressure-sensitive adhesive layers used in the laminate for a flexible image display device of the present invention, the second pressure-sensitive adhesive layer may be arranged on the side opposite to the surface in contact with the polarizing film with respect to the retardation film. (See Figure 2).

Among the adhesive layers used in the laminate for a flexible image display device of the present invention, the third adhesive layer is in contact with the second adhesive layer with respect to the transparent conductive layer constituting the touch sensor. On the opposite side of the face, a third adhesive layer can be placed (see Figure 2).

Among the adhesive layers used in the laminate for a flexible image display device of the present invention, the third adhesive layer is in contact with the first adhesive layer with respect to the transparent conductive layer constituting the touch sensor. It can be placed on the opposite side of the face (see Figure 3).

In addition to the first pressure-sensitive adhesive layer, when using a second pressure-sensitive adhesive layer and further another pressure-sensitive adhesive layer (for example, a third pressure-sensitive adhesive layer, etc.), these pressure-sensitive adhesive layers are There are no particular restrictions on the composition (the same adhesive composition), whether it has the same properties or different properties, but from the viewpoint of workability, economy, and flexibility, all adhesives It is preferred that the layers are adhesive layers having substantially the same composition and the same properties.

[Transparent conductive layer]
The member having a transparent conductive layer is not particularly limited, and known ones can be used. A member having cells can be mentioned.

The transparent base material may be any material as long as it has transparency, and examples thereof include base materials such as resin films (eg, sheet-like, film-like, plate-like base materials, etc.). The thickness of the transparent substrate is not particularly limited, but is preferably about 10 to 200 μm, more preferably about 15 to 150 μm.

The material of the resin film is not particularly limited, but includes various transparent plastic materials. For example, the materials include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and (meth)acrylic resins. , polyvinyl chloride-based resins, polyvinylidene chloride-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, polyarylate-based resins, polyphenylene sulfide-based resins, and the like. Among these, particularly preferred are polyester-based resins, polyimide-based resins and polyethersulfone-based resins.

In addition, the surface of the transparent base material is preliminarily subjected to etching treatment such as sputtering, corona discharge, flame, ultraviolet irradiation, electron beam irradiation, chemical conversion, oxidation, or the like, or undercoating treatment. You may make it improve the adhesiveness with respect to a transparent base material. In addition, before the transparent conductive layer is provided, dust removal and cleaning may be performed by solvent cleaning, ultrasonic cleaning, or the like, if necessary.

The constituent material of the transparent conductive layer is not particularly limited, and is selected from the group consisting of indium, tin, zinc, gallium, antimony, titanium, silicon, zirconium, magnesium, aluminum, gold, silver, copper, palladium, tungsten, and molybdenum. At least one kind of metal or metal oxide, or an organic conductive polymer such as polythiophene is used. The metal oxide may further contain the metal atoms shown in the above groups, if necessary. For example, indium oxide (ITO) containing tin oxide and tin oxide containing antimony are preferably used, and ITO is particularly preferably used. ITO preferably contains 80 to 99% by weight of indium oxide and 1 to 20% by weight of tin oxide.

In addition, examples of the ITO include crystalline ITO and non-crystalline (amorphous) ITO. Crystalline ITO can be obtained by applying a high temperature during sputtering or by further heating amorphous ITO.

The thickness of the transparent conductive layer of the invention is preferably 0.005 to 10 μm, more preferably 0.01 to 3 μm, still more preferably 0.01 to 1 μm. If the thickness of the transparent conductive layer is less than 0.005 μm, the change in electrical resistance of the transparent conductive layer tends to increase. On the other hand, if the thickness exceeds 10 μm, the productivity of the transparent conductive layer tends to decrease, the cost increases, and the optical properties tend to decrease.

The total light transmittance of the transparent conductive layer of the invention is preferably 80% or more, more preferably 85% or more, and still more preferably 90% or more.

The density of the transparent conductive layer of the present invention is preferably 1.0-10.5 g/cm ³ , more preferably 1.3-3.0 g/cm ³ .

The surface resistance value of the transparent conductive layer of the present invention is preferably 0.1 to 1000 Ω/square, more preferably 0.5 to 500 Ω/square, still more preferably 1 to 250 Ω/square.

The method for forming the transparent conductive layer is not particularly limited, and conventionally known methods can be employed. Specifically, for example, a vacuum deposition method, a sputtering method, and an ion plating method can be exemplified. Also, an appropriate method can be employed depending on the required film thickness.

Moreover, an undercoat layer, an oligomer prevention layer, etc. can be provided between the transparent conductive layer and the transparent substrate, if necessary.

The transparent conductive layer constitutes a touch sensor and is required to be foldable.

In the laminate for a flexible image display device of the present invention, the transparent conductive layer constituting the touch sensor is arranged on the side opposite to the surface in contact with the retardation film with respect to the second adhesive layer. (See Figure 2).

In the laminate for a flexible image display device of the present invention, the transparent conductive layer constituting the touch sensor may be arranged on the side opposite to the surface in contact with the protective film with respect to the first adhesive layer. (See Figure 3).

Further, in the laminate for a flexible image display device of the present invention, the transparent conductive layer constituting the touch sensor can be arranged between the protective film and the window film (OCA) (see FIG. 3).

The transparent conductive layer can be suitably applied to a liquid crystal display device with a built-in touch sensor such as an in-cell type or an on-cell type as a flexible image display device, and in particular, an organic EL display panel with a built-in touch sensor. may be (embedded)

[Conductive layer (antistatic layer)]
Moreover, the laminate for a flexible image display device of the present invention may have a conductive layer (conductive layer, antistatic layer). Since the laminate for a flexible image display device has a bending function and has a very thin thickness, it is highly reactive to weak static electricity generated in the manufacturing process, etc., and is easily damaged. By providing a conductive layer on the substrate, the load due to static electricity in the manufacturing process or the like is greatly reduced, which is a preferable embodiment.

In addition, one of the major features of the flexible image display device including the laminate is that it has a bending function, but when it is continuously bent, static electricity is generated due to shrinkage between the films (base materials) at the bent portion. Sometimes. Therefore, when the laminate is provided with conductivity, the generated static electricity can be quickly removed, and the damage caused by the static electricity to the image display device can be reduced, which is a preferable aspect.

The conductive layer may be an undercoat layer having a conductive function, an adhesive containing a conductive component, or a surface treatment layer containing a conductive component. For example, a method of forming a conductive layer between the polarizing film and the pressure-sensitive adhesive layer using an antistatic agent composition containing a conductive polymer such as polythiophene and a binder can be employed. Furthermore, a pressure-sensitive adhesive containing an ionic compound that is an antistatic agent can also be used. Moreover, the conductive layer preferably has one or more layers, and may contain two or more layers.

[Flexible image display device]
A flexible image display device of the present invention includes the above laminate for a flexible image display device and an organic EL display panel. configured as possible. Optionally, a window can be positioned on the viewing side of the flexible image display laminate (see FIGS. 2-4).

FIG. 2 is a cross-sectional view showing one embodiment of a flexible image display device according to the present invention. This flexible image display device 100 includes a flexible image display device laminate 11 and an organic EL display panel 10 configured to be foldable. The flexible image display device laminate 11 is disposed on the viewing side of the organic EL display panel 10, and the flexible image display device 100 is configured to be foldable. Optionally, a transparent window 40 can be arranged on the viewing side of the flexible image display device laminate 11 via the first pressure-sensitive adhesive layer 12-1.

The flexible image display device laminate 11 includes an optical laminate 20, and adhesive layers constituting a second adhesive layer 12-2 and a third adhesive layer 12-3.

The optical laminate 20 includes a polarizing film 1 , a protective film 2 made of a transparent resin material, and a retardation film 3 . A protective film 2 made of a transparent resin material is bonded to the first surface of the polarizing film 1 on the viewing side. The retardation film 3 is bonded to the second surface of the polarizing film 1 that is different from the first surface. The polarizing film 1 and the retardation film 3, for example, generate circularly polarized light in order to prevent light entering the inside from the visible side of the polarizing film 1 from being internally reflected and emitted to the visible side. It is intended to compensate for

In the present embodiment, the protective film is provided on both sides of the conventional polarizing film, whereas the protective film is provided only on one side, and the polarizing film itself is also used in the conventional organic EL display device. The thickness of the optical layered body 20 can be reduced by using a very thin polarizing film (20 μm or less) compared to the existing polarizing film. In addition, since the polarizing film 1 is much thinner than the polarizing film used in the conventional organic EL display device, stress due to expansion and contraction caused by temperature or humidity conditions is extremely small. Therefore, the possibility that the stress caused by the contraction of the polarizing film causes deformation such as warpage in the adjacent organic EL display panel 10 is greatly reduced, and deterioration of display quality and destruction of the panel sealing material due to deformation are greatly reduced. can be suppressed to In addition, the use of a thin polarizing film does not hinder bending, which is a favorable aspect.

When the optical layered body 20 is folded with the protective film 2 side facing inward, the thickness of the optical layered body 20 (for example, 92 μm or less) is reduced, and the first optical layered body 20 having the characteristics of 100% modulus and 500% modulus as described above is used. By arranging the adhesive layer 12-1 on the side opposite to the retardation film 3 with respect to the protective film 2, it is possible to reduce the stress applied to the optical layered body 20, whereby the optical layered body 20 is bent. Moreover, cracking of each layer and peeling of the pressure-sensitive adhesive layer can be suppressed at the bent portion, and finally the flexible image display device laminate 11 can be bent. Also, therefore, appropriate ranges of 100% modulus and 500% modulus may be set according to the environmental temperature in which the flexible image display device is used.

Optionally, on the side of the retardation film 3 opposite to the protective film 2, a bendable transparent conductive layer 6 forming a touch sensor can be further arranged. The transparent conductive layer 6 is configured to be directly bonded to the retardation film 3 by a manufacturing method such as that disclosed in JP-A-2014-219667, thereby reducing the thickness of the optical laminate 20. It is possible to further reduce the stress applied to the optical layered body 20 when the is bent.

Optionally, an adhesive layer constituting the third adhesive layer 12-3 can be further arranged on the side of the transparent conductive layer 6 opposite to the retardation film 3. FIG. In this embodiment, the second adhesive layer 12-2 is directly bonded to the transparent conductive layer 6. As shown in FIG. By providing the second adhesive layer 12-2, the stress applied to the optical layered body 20 when the optical layered body 20 is folded can be further reduced.

The flexible image display device shown in FIG. 3 is substantially the same as that shown in FIG. 2, but in the flexible image display device of FIG. While the bendable transparent conductive layer 6 constituting the is arranged, in the flexible image display device of FIG. 2, a bendable transparent conductive layer 6 constituting a touch sensor is arranged. Further, in the flexible image display device of FIG. 2, the third adhesive layer 12-3 is arranged on the side opposite to the retardation film 3 with respect to the transparent conductive layer 2, whereas in FIG. The flexible image display device is different in that the second adhesive layer 12 - 2 is arranged on the side opposite to the protective film 2 with respect to the retardation film 3 .

Optionally, when the window 40 is arranged on the viewing side of the flexible image display device laminate 11, the third adhesive layer 12-3 can be arranged.

The flexible image display device of the present invention can be suitably used as an image display device such as a flexible liquid crystal display device, an organic EL (electroluminescence) display device, and an electronic paper. In addition, it can be used regardless of the type of touch panel, such as a resistive film type or an electrostatic capacitance type.

Further, as the flexible image display device of the present invention, as shown in FIG. 4, it is also used as an in-cell type flexible image display device in which the transparent conductive layer 6 constituting the touch sensor is built in the organic EL display panel 10-1. It is possible to

Several examples related to the present invention are described below, but the present invention is not intended to be limited to those shown in such specific examples.

Example 1
<Preparation of prepolymer>
A monomer mixture containing 59 parts by weight of lauryl acrylate (LA), 40 parts by weight of 2-ethylhexyl acrylate (2EHA), and 1 part by weight of 4-hydroxybutyl acrylate (4HBA) and 2,2-dimethoxy-1 as a photoinitiator , 2-diphenylethan-1-one (trade name “Irgacure 651”, manufactured by BASF Japan Ltd.), and 1-hydroxy-cyclohexyl-phenyl-ketone (trade name “Irgacure 184”, manufactured by BASF Japan Ltd.) 0.05 part by weight of each is put into a four-necked flask and irradiated with ultraviolet rays until the viscosity (BH viscometer No. 5 rotor, 10 rpm, temperature 30 ° C.) reaches about 15 Pa s in a nitrogen atmosphere. A partially polymerized monomer syrup (partially polymerized monomer component) was obtained by photopolymerization.

<Preparation of acrylic adhesive composition>
To 100 parts by weight of the obtained partially polymerized monomer syrup, 5 parts by weight of N-vinylpyrrolidone and 1,6-hexanediol diacrylate (trade name "A-HD-N", manufactured by Shin-Nakamura Chemical Co., Ltd.) were added as additional monomers. , HDDA, polyfunctional monomer) 0.15 parts by weight, photopolymerization initiator 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name “Irgacure 651”, manufactured by BASF Japan Ltd., added Initiator) 0.1 parts by weight and 0.3 parts by weight of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) are uniformly mixed to obtain an acrylic pressure-sensitive adhesive composition. Obtained.

<Formation of adhesive layer>
The above acrylic pressure-sensitive adhesive composition is applied onto the release-treated surface of a release film (trade name “MRF #38”, manufactured by Mitsubishi Plastics, Inc.) so that the thickness after forming the pressure-sensitive adhesive layer is 70 μm. Then, a release film (trade name “MRN#38”, manufactured by Mitsubishi Plastics, Inc.) was laminated on the surface of the adhesive composition layer. Thereafter, ultraviolet irradiation was performed under the conditions of an illumination intensity of 4 mW/cm ² and a light amount of 1200 mJ/cm ² to photocure the adhesive composition layer to form an adhesive layer. Thus, a pressure-sensitive adhesive layer having both sides protected by a release film was obtained.

Examples 2-3, Comparative Examples 1-5
In the preparation of the prepolymer of Example 1, the monomer mixture (type, composition) of the prepolymer was changed as shown in Table 2, and in the preparation of the acrylic pressure-sensitive adhesive composition, the additional monomer (type, amount) was changed. A prepolymer and an acrylic pressure-sensitive adhesive composition were prepared in the same manner as in Example 1 except for the changes shown in Table 2, and then a pressure-sensitive adhesive layer was formed.
In Comparative Examples 2 and 3, as shown in Table 2, the blending amount of 1,6-hexanedioldiacrylate was changed to 0.3 parts by weight. The amount of dimethoxy-1,2-diphenylethan-1-one (trade name “Irgacure 651”, manufactured by BASF Japan Ltd., additional initiator) was changed to 0.6 parts by weight.

After an optical laminate was produced using each member produced by the following method, an optical laminate with an adhesive layer was produced using the adhesive layers obtained in the above Examples and Comparative Examples.

[Polarizing film]
As a thermoplastic resin substrate, an amorphous polyethylene terephthalate (hereinafter also referred to as “PET”) (IPA copolymer PET) film (thickness: 100 μm) having 7 mol % of isophthalic acid units was prepared, and the surface was corona-treated ( 58 W/m ² /min) was applied. On the other hand, acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: GOSEFIMER Z200 (average degree of polymerization: 1200, degree of saponification: 98.5 mol%, degree of acetoacetylation: 5 mol%) was used. Prepare PVA (degree of polymerization 4200, degree of saponification 99.2%) added by 1% by weight, prepare a coating solution of PVA aqueous solution with 5.5% by weight of PVA resin, and film thickness after drying was coated so as to have a thickness of 12 μm, and dried by hot air drying in an atmosphere of 60° C. for 10 minutes to prepare a laminate in which a PVA-based resin layer was provided on the substrate.

This laminate was then first free-end stretched 1.8 times at 130° C. in air (in-air auxiliary stretching) to produce a stretched laminate. Next, the stretched laminate was immersed in a boric acid insolubilizing aqueous solution at a liquid temperature of 30° C. for 30 seconds to insolubilize the PVA layer in which the PVA molecules contained in the stretched laminate were oriented. The boric acid insolubilizing aqueous solution in this step had a boric acid content of 3 parts by weight per 100 parts by weight of water. A colored laminate was produced by dyeing this stretched laminate. The colored laminate is obtained by exposing the stretched laminate to a dyeing solution containing iodine and potassium iodide at a liquid temperature of 30 ° C. so that the single transmittance of the PVA layer constituting the finally produced polarizing film is 40 to 44%. The PVA layer contained in the stretched laminate is dyed with iodine by immersing it in for an arbitrary time. In this step, the dyeing solution used water as a solvent, had an iodine concentration in the range of 0.1 to 0.4% by weight, and had a potassium iodide concentration in the range of 0.7 to 2.8% by weight. The ratio of iodine and potassium iodide concentrations is 1:7. Next, the colored laminate was immersed in a boric acid cross-linking aqueous solution at 30° C. for 60 seconds to cross-link the PVA molecules of the iodine-adsorbed PVA layer. The boric acid cross-linking aqueous solution in this step had a boric acid content of 3 parts by weight per 100 parts by weight of water and a potassium iodide content of 3 parts by weight per 100 parts by weight of water.

Furthermore, the obtained colored laminate was stretched in an aqueous boric acid solution at a stretching temperature of 70° C. in the same direction as the previous stretching in the air by a factor of 3.05 (boric acid aqueous stretching), and the final An optical film laminate having a draw ratio of 5.50 was obtained. The optical film laminate was removed from the boric acid aqueous solution, and the boric acid adhering to the surface of the PVA layer was washed with an aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water. The washed optical film laminate was dried by a drying process using hot air at 60°C. The thickness of the polarizing film included in the obtained optical film laminate was 5 μm.

[Protective film]
As the protective film, methacrylic resin pellets having a glutarimide ring unit were extruded to form a film, which was then stretched. This protective film had a thickness of 20 μm and was an acrylic film with a moisture permeability of 160 g/m ² .

Next, the polarizing film and the protective film were bonded together using the adhesive shown below to obtain a polarizing film.

As the adhesive (active energy ray-curable adhesive), each component was mixed according to the formulation shown in Table 1, stirred at 50 ° C. for 1 hour, and the adhesive (active energy ray-curable adhesive A) was prepared. Numerical values in the table indicate weight % when the total amount of the composition is 100% by weight. Each component used is as follows.
HEAA: Hydroxyethyl acrylamide M-220: ARONIX M-220, tripropylene glycol diacrylate), manufactured by Toagosei ACMO: Acryloylmorpholine AAEM: 2-acetoacetoxyethyl methacrylate, manufactured by Nippon Synthetic Chemical Co., Ltd. UP-1190: ARUFON UP- 1190, Toagosei IRG907: IRGACURE907, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, DETX-S manufactured by BASF: KAYACURE DETX-S, diethylthioxanthone, Nippon Kayaku Yakusha

After laminating the protective film and the polarizing film with the adhesive interposed therebetween, the adhesive was cured by irradiation with ultraviolet rays to form an adhesive layer. A gallium-filled metal halide lamp (manufactured by Fusion UV Systems, Inc., trade name “Light HAMMER10”, bulb: V bulb, peak illuminance: 1600 mW/cm ² , integrated irradiation amount 1000/mJ/cm ² (wavelength 380-440 nm)) was used.

[Phase contrast film]
The retardation film (1/4 wavelength retardation plate) of this embodiment is composed of two layers of a retardation layer for a quarter wavelength plate and a retardation layer for a half wavelength plate in which a liquid crystal material is oriented and fixed. It was a retardation film composed of Specifically, it was manufactured as follows.

(liquid crystal material)
As a material for forming the half-wave plate retardation layer and the quarter-wave plate retardation layer, a polymerizable liquid crystal material exhibiting a nematic liquid crystal phase (manufactured by BASF, trade name Paliocolor LC242) was used. A photopolymerization initiator for the polymerizable liquid crystal material (manufactured by BASF, trade name Irgacure 907) was dissolved in toluene. Furthermore, for the purpose of improving coating properties, a liquid crystal coating solution was prepared by adding 0.1 to 0.5% of MEGAFACE series manufactured by DIC, depending on the thickness of the liquid crystal. The liquid crystal coating liquid was applied onto an alignment substrate using a bar coater, dried by heating at 90° C. for 2 minutes, and then aligned and fixed by ultraviolet curing in a nitrogen atmosphere. The substrate used was, for example, PET, to which the liquid crystal coating layer could be transferred later. Furthermore, for the purpose of improving coatability, 0.1% to 0.5% of fluorine-based polymer, which is a megafac series manufactured by DIC, is added according to the thickness of the liquid crystal layer, and MIBK (methyl isobutyl ketone), cyclohexanone, or MIBK is added. and cyclohexanone in a mixed solvent of 25% solid content to prepare a coating solution. This coating liquid was applied to the base material with a wire bar, a drying process was performed at 65° C. for 3 minutes, and the orientation was fixed by ultraviolet curing in a nitrogen atmosphere. The substrate used was, for example, PET, to which the liquid crystal coating layer could be transferred later.

(Manufacturing process)
The manufacturing process of this embodiment will be described with reference to FIG. Note that the numbers in FIG. 7 are different from the numbers in other drawings. In this manufacturing process 20 , the base material 14 is provided by a roll, and the base material 14 is supplied from the supply reel 21 . In the manufacturing process 20 , a coating liquid of the ultraviolet curable resin 10 was applied to the base material 14 using a die 22 . In this manufacturing process 20, the roll plate 30 was a cylindrical molding die having a concave-convex shape related to the quarter-wave plate alignment film of the quarter-wave retardation plate formed on the peripheral side surface. In the manufacturing process 20, the base material 14 coated with the ultraviolet curable resin is pressed against the peripheral side surface of the roll plate 30 by the pressure roller 24, and the ultraviolet curable resin is irradiated by the ultraviolet irradiation device 25 consisting of a high-pressure mercury lamp. Hardened. As a result, in the manufacturing process 20, the concave-convex shape formed on the peripheral side surface of the roll plate 30 is transferred to the substrate 14 so as to form an angle of 75° with respect to the MD direction. After that, the substrate 14 was peeled off from the roll plate 30 integrally with the cured ultraviolet curable resin 10 by the peeling roller 26 , and the liquid crystal material was applied by the die 29 . After that, the liquid crystal material was cured by irradiation with ultraviolet rays from the ultraviolet irradiation device 27, thereby forming a structure related to the quarter-wave plate retardation layer.
Subsequently, in this step 20, the base material 14 is conveyed to the die 32 by the conveying roller 31, and the coating liquid of the ultraviolet curable resin 12 is applied onto the quarter-wave plate phase difference layer of the base material 14 by the die 32. bottom. In this manufacturing process 20, the roll plate 40 was a cylindrical mold for shaping, on the peripheral side surface of which the concave-convex shape related to the orientation film for the half-wave plate of the quarter-wave retardation plate was formed. In the manufacturing process 20, the base material 14 coated with the ultraviolet curable resin is pressed against the peripheral side surface of the roll plate 40 by the pressure roller 34, and the ultraviolet curable resin is irradiated with ultraviolet rays by the ultraviolet irradiation device 35 consisting of a high-pressure mercury lamp. Hardened. Thus, in the manufacturing process 20, the uneven shape formed on the peripheral side surface of the roll plate 40 is transferred to the substrate 14 so as to be 15° with respect to the MD direction. After that, the substrate 14 was peeled off from the roll plate 40 integrally with the cured ultraviolet curable resin 12 by the peeling roller 36 , and the liquid crystal material was applied by the die 39 . Further, after that, the liquid crystal material is cured by irradiation with ultraviolet rays from the ultraviolet irradiation device 37, thereby creating a structure related to the retardation layer for the 1/4 wavelength plate, the retardation layer for the 1/4 wavelength plate, the 1/2 wavelength. A 7 μm-thick retardation film composed of two plate retardation layers was obtained.

[Optical film (optical laminate)]
The retardation film obtained as described above and the polarizing film obtained as described above are continuously bonded using the adhesive by a roll-to-roll method, and the slow axis and the absorption axis are A laminate film (optical laminate) was produced so that the angle was 45°.

<Preparation of optical laminate with pressure-sensitive adhesive layer>
The separator having the pressure-sensitive adhesive layer (second) obtained in the above Examples and Comparative Examples was transferred to the protective film side (corona-treated) of the obtained optical layered body, and the pressure-sensitive adhesive layer-attached optical layered body was obtained. was made.

[First adhesive layer]
A pressure-sensitive adhesive layer (first) was formed in the same manner as in each example except that the thickness of the pressure-sensitive adhesive layer used in each example was changed to 50 μm. A separator having the pressure-sensitive adhesive layer (first) is transferred to the surface (corona-treated) of a 75 μm-thick polyimide film (PI film, manufactured by Toray DuPont Co., Ltd., Kapton 300V, base material), A PI film with an adhesive layer was formed.

[Third adhesive layer]
A pressure-sensitive adhesive layer (third) was formed in the same manner as in each example except that the thickness of the pressure-sensitive adhesive layer used in each example was changed to 50 μm. A separator having the adhesive layer (third) formed thereon is transferred to the surface (corona-treated) of a 125 μm thick PET film (transparent substrate, manufactured by Mitsubishi Plastics Co., Ltd., trade name: Diafoil), A PET film with an adhesive layer was formed.

<Preparation of laminate for flexible image display device>
As shown in FIG. 6, the first to third pressure-sensitive adhesive layers (together with each transparent base material) obtained as described above were coated on a PET film having a thickness of 25 μm to be a transparent base material 8-1, and then coated on a second adhesive layer. The adhesive layer 12-2 is attached, the third adhesive layer 12-3 is attached to the retardation film 3, and the second adhesive layer 12-2 is attached to the transparent substrate 8- 1 (PET film) and a first pressure-sensitive adhesive layer 12-1 were bonded to each other to prepare a laminate 11 for a flexible image display device.

[evaluation]
The adhesive layers and laminates for flexible image display devices obtained in Examples and Comparative Examples were evaluated as follows. Table 2 shows the results.

<Storage elastic modulus G′ of pressure-sensitive adhesive layer>
A separator was peeled off from the pressure-sensitive adhesive layer obtained in each example and comparative example, and a plurality of pressure-sensitive adhesive layers were laminated to prepare a test sample having a thickness of about 2 mm. This test sample was punched into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to dynamic viscoelasticity measurement under the following conditions using Rheometric Scientific's "Advanced Rheometric Expansion System (ARES)". From the results, the storage modulus G' of the pressure-sensitive adhesive layer at -20°C, 23°C and 85°C was read.
(Measurement condition)
Deformation mode: Torsion Measurement temperature: -70°C to 150°C
Heating rate: 5°C/min

<Measurement of gel fraction of adhesive layer>
Sample 1 was obtained by scraping about 0.2 g from the pressure-sensitive adhesive layer formed on the release-treated surface of the separator film one week after the production. Sample 1 was wrapped in a Teflon (registered trademark) film having a diameter of 0.2 μm (trade name “NTF1122”, manufactured by Nitto Denko Corporation) and tied with a kite string. The weight of sample 2 was measured before being subjected to the following test, and this was defined as weight A. The weight A is the total weight of the sample 1 (adhesive layer), the Teflon (registered trademark) film, and the kite string. The weight B is the total weight of the Teflon (registered trademark) film and the kite string. Next, the sample 2 was placed in a 50 ml container filled with ethyl acetate and allowed to stand at 23° C. for 1 week. After that, sample 2 was taken out from the container and dried in a dryer at 130° C. for 2 hours to remove ethyl acetate, and the weight of sample 2 was measured. After being subjected to the test, the weight of Sample 2 was measured and designated as Weight C. Then, the gel fraction (% by weight) was calculated from the following formula.
Gel fraction (% by weight) = (C - B) / (A - B) x 100

The gel fraction of the pressure-sensitive adhesive layer is preferably 55 to 90% by weight, more preferably 57 to 90% by weight, even more preferably 60 to 88% by weight, even more preferably 62 to 88% by weight, particularly Preferably 65-86% by weight, most preferably 70-86% by weight. When the gel fraction of the pressure-sensitive adhesive layer is within the above range, the appearance (paste marks, etc.), workability, durability, and flexibility are good, and in particular, flexibility is compatible under normal temperature environment and high temperature environment. This is a preferred mode.

<Measurement of thickness>
The thicknesses of the polarizing film, the retardation film, the protective film, the optical layered body, the pressure-sensitive adhesive layer, and the like were measured using a dial gauge (manufactured by Mitutoyo).

<Folding resistance (continuous bending) test method>
5(A) and 5(B) show schematic diagrams of a bending test based on a U-shaped stretching tester (Yuasa System Co., Ltd.).
The tester has a mechanism that repeats 180° U-shaped bending with no load on the sheet-like body work in a constant temperature chamber. can change.
In the test, the 2.5 cm × 10 cm flexible image display laminate obtained in each example and comparative example was set in a tester so that it could be folded in the long side direction, and -20 ° C., 25 ° C. × 50% Evaluation was performed at RH and 85° C. under the conditions of a bending angle of 180°, a bending radius of 3 mm, and a bending speed of 1 second/bend.
As a measurement (evaluation) sample, the configuration shown in FIG. 6 is adopted, the transparent base material 8-2 (PET film) is on the concave side (inner side), and the base material 9 (PI film) is on the convex side (outer side). ) and bent in the long side direction near the center for evaluation. Folding endurance was evaluated by the number of times until cracking or interlayer peeling occurred at the bent portion of the laminate for a flexible image display device. Here, the test was terminated when the number of times of bending reached 200,000.
<Presence or absence of peeling/cracking>
◎: No defects at 200,000 times or more (practically no problem)
○: Defective at less than 100,000 to 200,000 times (no practical problem)
△: Defective at less than 50,000 to 100,000 times (practically no problem)
×: Less than 50,000 times, defective (practical problem)

<Measurement of modulus stress>
A pressure-sensitive adhesive layer having a thickness of 50 μm and having release films (trade name “MRF#38”, manufactured by Mitsubishi Plastics, Inc.) on both sides was prepared using the same pressure-sensitive adhesive composition as in Examples and Comparative Examples. The pressure-sensitive adhesive layer was cut into a size of 30 mm in width and 100 mm in length, and then the release films on both sides were peeled off. Using a Tensilon type tensile tester, this sample was measured under the conditions of 10 mm between chucks and a tensile speed of 300 mm / min. mm ² ) was obtained. Here, 100% elongation means that the distance between chucks is 20 mm, 500% elongation means that the distance between chucks is 60 mm, and 700% elongation means that the distance between chucks is 80 mm.

<Adhesion>
The PI film, optical laminate, and PET film used above were adhered and fixed onto a glass plate via a general-purpose double-sided tape (manufactured by Nitto Denko, No. 500) to prepare an adherend.
A pressure-sensitive adhesive layer having a thickness of 50 μm and having release films (trade name “MRF#38”, manufactured by Mitsubishi Plastics, Inc.) on both sides was prepared using the same pressure-sensitive adhesive composition as in Examples and Comparative Examples. The adhesive layer was cut into a size of 25 mm in width and 100 mm in length, one release film was peeled off, and after bonding to a 25 μm thick PET film (manufactured by Toray, Lumirror S10), the other separator was peeled off. As a sample, the surface of the adhesive layer was exposed. The sample was attached to the previously prepared adherend. They were crimped at a linear pressure of 78.5 N/cm and a speed of 0.3 m/min. After leaving this in an environment of 23 ° C. and 50% RH for 30 minutes, using a universal tensile tester under the same environment, a sample from the adherend under the conditions of a peel speed of 0.3 m / min and a peel angle of 180 ° was peeled off, and the peeling force at this time was evaluated as adhesion (N/25 mm).

Abbreviations in Table 2 are as follows.
LA: lauryl acrylate 2EHA: 2-ethylhexyl acrylate 4HBA: 4-hydroxybutyl acrylate NVP: N-vinylpyrrolidone A-HD-N: 1,6-hexanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name : A-HD-N)

From the evaluation results in Table 2, the storage elastic modulus G′ of the pressure-sensitive adhesive layer at −20° C. is 3.5×10 ⁴ to 1.7×10 ⁵ Pa in all the examples.
A storage modulus G′ at 23° C. of 1.0×10 ⁴ to 5.0×10 ⁴ Pa, and
The difference between the storage elastic modulus G′ at 23° C. and the storage elastic modulus G′ at 85° C. is 5.2×10 ³ Pa or more. It was confirmed that even when exposed to 25°C x 50% RH and 85°C (low temperature, normal temperature, or high temperature environment), cracking (breaking) and peeling are at a level that poses no practical problem. . That is, in the laminate for a flexible image cover device of each example, by using an adhesive layer having a storage elastic modulus G' within a predetermined range, cracking (folding) and peeling due to repeated bending are prevented. It was confirmed that a laminate for a flexible image display device having excellent flex resistance and adhesion can be obtained.

On the other hand, since Comparative Examples 1 to 4 are not included in the predetermined range of storage elastic modulus G', the folding endurance (continuous bending) test showed -20 ° C., 25 ° C. x 50% RH, and 85 ° C. ( When exposed to low temperature, normal temperature or high temperature environment), cracking (breaking) and peeling are at a practically problematic level, and it has been confirmed that either flex resistance or adhesion is inferior.

1 polarizing film 2 protective film 2-1 protective film 2-2 protective film 3 retardation layer 4-1 transparent conductive film 4-2 transparent conductive film 5-1 base film 5-2 base film 6 transparent conductive layer 6- 1 transparent conductive layer 6-2 transparent conductive layer 7 spacer 8 transparent substrate 8-1 transparent substrate (PET film)
8-2 Transparent substrate (PET film)
9 Base material (PI film)
10 Organic EL display panel 10-1 Organic EL display panel (with touch sensor)
11 Laminate for flexible image display device (Laminate for organic EL display device)
12 Adhesive layer 12-1 First adhesive layer 12-2 Second adhesive layer 12-3 Third adhesive layer 13 Decorative printing film 14 Double-sided adhesive tape 20 Optical laminate 30 Touch panel 40 Window 100 Flexible Image display device (organic EL display device)
P bending point UV UV irradiation L liquid crystal material

Claims (7)

Formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer containing, as monomer units, an alkyl (meth)acrylate, an N-vinyl group-containing lactam monomer, and a hydroxyl group-containing monomer,
The hydroxyl group-containing monomer is 0.05 to 3% by weight in all monomers constituting the (meth)acrylic polymer,
The storage modulus G′ at −20° C. is 3.5×10 ⁴ to 1.7×10 ⁵ Pa,
A storage modulus G′ at 23° C. of 1.0×10 ⁴ to 5.0×10 ⁴ Pa, and
A pressure-sensitive adhesive layer for a flexible image display device, wherein the difference between the storage elastic modulus G' at 23°C and the storage elastic modulus G' at 85°C is 5.2×10 ³ Pa or more. The storage elastic modulus G′ at −20° C. and the storage elastic modulus G′ at 23° C. have an average value of 4.5×10 ⁴ to 1.5×10 ⁵ Pa according to claim 1. A pressure-sensitive adhesive layer for a flexible image display device. 3. The pressure-sensitive adhesive layer for a flexible image display device according to claim 1, wherein the gel fraction is 70% by weight or more. The pressure-sensitive adhesive for a flexible image display device according to any one of claims 1 to 3, wherein the alkyl (meth)acrylate contains an alkyl (meth))acrylate having an alkyl group having 10 or more carbon atoms. layer. A laminate for a flexible image display device, comprising the pressure-sensitive adhesive layer according to any one of claims 1 to 4 and an optical film containing at least a polarizing film. A flexible image display device laminate according to claim 5 , and an organic EL display panel, wherein the flexible image display device laminate is disposed on a viewing side with respect to the organic EL display panel. A flexible image display device. 7. The flexible image display device according to claim 6 , wherein a window is arranged on the viewing side with respect to the laminate for a flexible image display device.

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