JP2016053135A - Adhesive composition and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition capable of forming an adhesive layer achieving both of strong adhesiveness and reworkability, and an adhesive sheet having the adhesive layer achieving both of strong adhesiveness and reworkability.SOLUTION: There is provided an adhesive composition containing (meth)acrylic copolymer containing a constitutional unit derived from a monomer having a hydroxyl group, (meth)acrylic oligomer having weight average molecular weight of 4000 to 100000, containing a constitutional unit derived from a monomer having a hydroxyl group of 30 mass% to 50 mass% and having glass transition temperature of -50°C or more and a crosslinking agent.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet.

A liquid crystal display device is generally composed of a plurality of optical members such as a liquid crystal cell, a polarizing plate, a retardation plate, and a brightness enhancement film in which a liquid crystal component oriented in a predetermined direction is sandwiched between two support substrates. ing.
A touch panel is used for an input device of a portable electronic device such as a mobile phone or a portable information terminal. The touch panel is generally composed of a plurality of optical members such as a glass substrate, a transparent conductive film, and a design film.
These optical members are laminated via a pressure-sensitive adhesive layer formed of a pressure-sensitive adhesive composition.

When manufacturing a liquid crystal display device, a touch panel, etc., when a problem such as misalignment occurs during the bonding of the optical member, the optical member is peeled off or removed from the adherend, and a new optical member is pasted again ( Rework) occurs.
For this reason, the pressure-sensitive adhesive layer is required to have a characteristic that a part of the pressure-sensitive adhesive layer does not remain on the adherend during re-sticking work (hereinafter sometimes referred to as “reworkability”).

  In response to this requirement, when applied to an optical member such as a polarizing plate, as a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having excellent durability and reworkability, a high molecular weight acrylic copolymer and An adhesive composition containing a low molecular weight acrylic copolymer and a silane coupling agent has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  Further, the optical member of the portable electronic device may be peeled off by receiving an impact such as dropping. For this reason, the adhesive layer is required to have a strong adhesive force.

JP 2013-10837 A JP 2012-41453 A

Generally, when the adhesive strength of the pressure-sensitive adhesive layer is strong, the pressure-sensitive adhesive layer tends to remain on the adherend and tends to have poor reworkability. On the other hand, if the pressure-sensitive adhesive layer hardly remains on the adherend and has good reworkability, the adhesive force tends to be weak. Thus, the strength of adhesive force and the reworkability are contradictory performances.
For example, the pressure-sensitive adhesive compositions described in Patent Literature 1 and Patent Literature 2 maintain reworkability by keeping the adhesive strength of the pressure-sensitive adhesive layer weak. For this reason, the adhesive strength of the pressure-sensitive adhesive layer is weak, and when used as an optical member of a portable electronic device, the optical member may be peeled off due to an impact such as dropping.
Thus, conventionally, a pressure-sensitive adhesive composition that can secure a reworkability by weakening the pressure-sensitive adhesive strength of the pressure-sensitive adhesive layer and can form a pressure-sensitive adhesive layer that has both a strong pressure-sensitive adhesive strength and reworkability is known. It is not done.
Therefore, there is a demand for a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that has both strong adhesive strength and reworkability.

  This invention is made | formed in view of the above, and makes it a subject to achieve the following objectives. An object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having both strong pressure-sensitive adhesive strength and reworkability, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having both strong pressure-sensitive adhesive strength and reworkability. It is.

Specific means for achieving the above object are as follows.
<1> A (meth) acrylic copolymer containing a structural unit derived from a monomer having a hydroxyl group, a weight average molecular weight of 4,000 to 100,000, and 30 structural units derived from a monomer having a hydroxyl group A pressure-sensitive adhesive composition containing (meth) acrylic oligomer having a glass transition temperature of −50 ° C. or higher and a crosslinking agent.

<2> The pressure-sensitive adhesive composition according to <1>, wherein the content of the (meth) acrylic oligomer is 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer. object.
<3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the (meth) acrylic copolymer contains 10% by mass to 40% by mass of a structural unit derived from a monomer having a hydroxyl group.
<4> The content of the crosslinking agent according to any one of <1> to <3>, in which the content of the crosslinking agent is 0.5 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic copolymer. Adhesive composition.
<5> The pressure-sensitive adhesive composition according to any one of <1> to <4>, wherein the (meth) acrylic copolymer has a glass transition temperature of −50 ° C. to −15 ° C.

<6> A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of <1> to <5>.

  According to the present invention, it is possible to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having both strong pressure-sensitive adhesive strength and reworkability, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having both strong pressure-sensitive adhesive strength and reworkability. .

  Hereinafter, the pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet of the present invention will be described in detail.

In the present specification, the notation “to” represents a range in which the numerical range including this includes both the lower limit value and the upper limit value.
Further, in this specification, the expression “(meth) acryl” is used in the meaning including both “acryl” and “methacryl”. The expression “(meth) acrylate” is used to include both “acrylate” and “methacrylate”.
Further, in the present specification, the “(meth) acrylic copolymer” means that 50% by mass or more, preferably 90% by mass or more of all structural units constituting the copolymer is a (meth) acrylic monomer. The copolymer which is a structural unit derived from is meant.
Further, the “(meth) acrylic oligomer” is a homopolymer or copolymer having a weight average molecular weight of 4000 to 100,000, and is 50% by mass or more, preferably 90% of all structural units constituting the polymer. The polymer whose mass% or more is a structural unit derived from a (meth) acrylic monomer is meant.

<Adhesive composition>
The pressure-sensitive adhesive composition of the present invention has at least one (meth) acrylic copolymer having a structural unit derived from a monomer having a hydroxyl group and a structural unit derived from a monomer having a hydroxyl group ( It contains at least one kind of (meth) acrylic oligomer and at least one kind of crosslinking agent.
The (meth) acrylic oligomer has a weight average molecular weight (Mw) of 4,000 to 100,000, contains 30% by mass to 50% by mass of a structural unit derived from a structural unit having a hydroxyl group, and has a glass transition temperature (Tg) of −50. ℃ or more.
Moreover, the adhesive composition of this invention may also contain another component as needed.

  The use of the pressure-sensitive adhesive composition of the present invention is, for example, a pressure-sensitive adhesive sheet used for bonding optical members. Examples of the optical member include a polarizing plate, a retardation plate, an antireflection film, a viewing angle widening film, a brightness enhancement film, a transparent conductive film (ITO (Indium Tin Oxide) film, etc.), a liquid crystal cell, a glass substrate, and a protective film. It is.

The present inventors have been able to form a pressure-sensitive adhesive layer having both strong adhesive force and reworkability by adopting the above-described configuration of the pressure-sensitive adhesive composition of the present invention.
The reason why the effect of the present invention is obtained is not clear, but the present inventors presume as follows.
The pressure-sensitive adhesive composition of the present invention contains both a (meth) acrylic copolymer and a (meth) acrylic oligomer. The (meth) acrylic copolymer can impart wettability and strong adhesive force to the adherend to the pressure-sensitive adhesive layer, and the (meth) acrylic oligomer is considered to impart reworkability to the pressure-sensitive adhesive layer. .
In the pressure-sensitive adhesive composition of the present invention, for example, when a coating layer is formed by coating, immediately after the coating layer is formed, the (meth) acrylic copolymer and the (meth) acrylic oligomer in the coating layer are present uniformly. However, since the (meth) acrylic oligomer has a low molecular weight, it moves near the surface of the coating layer and is unevenly distributed. Therefore, the ratio of the (meth) acrylic copolymer increases inside the coating layer, while the ratio of the (meth) acrylic oligomer increases on the surface of the coating layer.
And in the state where the (meth) acrylic oligomer is unevenly distributed on the surface of the coating layer, the (meth) acrylic copolymer and the (meth) acrylic oligomer react with the crosslinking agent to form a crosslinked structure, An adhesive layer is formed.
For this reason, it is considered that the inside of the pressure-sensitive adhesive layer has a larger proportion of the (meth) acrylic copolymer than the surface, and does not become too hard even when cross-linked, and gives the pressure-sensitive adhesive layer the necessary elasticity.
On the surface of the pressure-sensitive adhesive layer, (meth) acrylic oligomer sites are scattered in the (meth) acrylic copolymer sites. The scattered (meth) acrylic oligomer sites contain a large amount of hydroxyl groups, and thus have a high crosslinking density and an excellent cohesive force. Therefore, it is considered that reworkability is imparted to the pressure-sensitive adhesive layer.

  In addition to the above, since the (meth) acrylic copolymer contains a predetermined amount of a structural unit derived from a monomer having a hydroxyl group, the pressure-sensitive adhesive layer does not whiten even in a high-temperature and high-humidity environment ( There is also an advantage that it is excellent in moisture and heat whitening resistance.

≪ (Meth) acrylic copolymer≫
The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention contains at least one structural unit having a hydroxyl group.
The (meth) acrylic copolymer is crosslinked with a (meth) acrylic oligomer by a cross-linking agent described later by including a structural unit derived from a monomer having a hydroxyl group. Thereby, the cohesive force partially improves on the surface of the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer hardly remains on the adherend during rework.

The content rate of the structural unit derived from the monomer which has a hydroxyl group in a (meth) acrylic-type copolymer is 10 mass%-40 mass with respect to the total mass of the structural unit in a (meth) acrylic-type copolymer. % Is preferable, 15% by mass to 30% by mass is more preferable, and 18% by mass to 25% by mass is still more preferable.
When the content of the structural unit derived from the monomer having a hydroxyl group is within the above range, the adhesive force and the wet heat whitening resistance of the pressure-sensitive adhesive layer are excellent.

  The monomer having a hydroxyl group that can be used in producing the (meth) acrylic copolymer is selected from monomers having at least one hydroxyl group in one molecule. The number of hydroxyl groups in one molecule of the monomer having a hydroxyl group is not particularly limited, but is preferably 1 to 2.

  Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxy. Hexyl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-hydroxybutyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2 , 2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate, hydroxyalkyl (meth) acrylates such as glycerin mono (meth) acrylate, and polypropylene glycol mono (meta) (Poly) alkylene glycol mono (meth) acrylates such as acrylate, polyethylene glycol mono (meth) acrylate, poly (ethylene glycol-propylene glycol) mono (meth) acrylate, and N such as N-methylolacrylamide and N-hydroxyethylacrylamide Examples thereof include hydroxyalkyl (meth) acrylamides, hydroxyalkyl vinyl ethers such as 2-hydroxyethyl vinyl ether, and alcohol derivatives having an ethylenic double bond such as allyl alcohol and methallyl alcohol. Among these, the hydroxyl group-containing monomer is preferably hydroxyalkyl (meth) acrylate, more preferably hydroxyalkyl acrylate, and further preferably 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

  The alkyl group of the hydroxyalkyl (meth) acrylate may be linear or branched. 2-8 are preferable, as for carbon number of an alkyl group, 2-6 are more preferable, and 2-4 are still more preferable. The position of the hydroxyl group in the hydroxyalkyl (meth) acrylate is not particularly limited.

The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention is derived from a monomer having a hydroxyl group in the following manner from the viewpoint of improving the pressure-sensitive adhesive strength and moisture and heat whitening resistance of the pressure-sensitive adhesive layer. It is preferable that the structural unit is included.
The (meth) acrylic copolymer has a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 6 carbon atoms in the alkyl group, based on the total mass of the structural unit in the (meth) acrylic copolymer. 10% by mass to 40% by mass.
In a more preferred embodiment, the (meth) acrylic copolymer contains a structural unit derived from a hydroxyalkyl (meth) acrylate having an alkyl group having 2 to 6 carbon atoms in the (meth) acrylic copolymer. 10 mass%-40 mass% is included with respect to the total mass of a structural unit.
In a more preferred embodiment, the (meth) acrylic copolymer contains a structural unit derived from a hydroxyalkyl (meth) acrylate having an alkyl group having 2 to 4 carbon atoms in the (meth) acrylic copolymer. 10 mass%-40 mass% is included with respect to the total mass of a structural unit.
In a particularly preferred embodiment, the (meth) acrylic copolymer contains a structural unit derived from a hydroxyalkyl acrylate having 2 to 4 carbon atoms in the alkyl group as a structural unit in the (meth) acrylic copolymer. 15 to 30% by mass with respect to the total mass.
In the most preferred embodiment, the (meth) acrylic copolymer contains a structural unit derived from a hydroxyalkyl acrylate having 2 to 4 carbon atoms in the alkyl group as a structural unit in the (meth) acrylic copolymer. 18 to 25% by mass with respect to the total mass.

  The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention is at least one structural unit derived from a (meth) acrylic acid alkyl ester, in addition to the structural unit derived from a monomer having a hydroxyl group. It is preferable to contain.

  The content rate of the structural unit derived from the (meth) acrylic acid alkyl ester monomer in the (meth) acrylic copolymer is 60 mass relative to the total mass of the structural units in the (meth) acrylic copolymer. % To 90% by mass is preferable, and 70% to 85% by mass is more preferable. When the content of the structural unit derived from the (meth) acrylic acid alkyl ester monomer is within the above range, the wettability of the pressure-sensitive adhesive layer to the adherend becomes good and the adhesive strength is more excellent.

Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, t- Carbons of alkyl groups such as butyl (meth) acrylate, i-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, and isooctyl (meth) acrylate (Meth) acrylic acid alkyl ester having 1 to 8 number, isodecyl (meth) acrylate, lauryl (meth) acrylate, n-tridecyl (meth) acrylate, n-tetradecyl (meth) acrylate, and n-stearyl (meth) Al, such as acrylate Examples thereof include (meth) acrylic acid alkyl esters having 9 to 20 carbon atoms in the kill group. Among these, n-butyl (meth) acrylate, methyl (meth) acrylate, and lauryl (meth) acrylate are preferable.
In the present specification, the (meth) acrylic acid alkyl ester does not include those having a hydroxyl group and those having a cyclic group and an acidic group described later.

The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention is derived from a monomer having a hydroxyl group in the following manner from the viewpoint of improving the heat-and-moisture whitening resistance of the pressure-sensitive adhesive layer. In addition to the units, it is preferable to include structural units derived from (meth) acrylic acid alkyl esters.
The (meth) acrylic copolymer is composed of a structural unit derived from a monomer having a hydroxyl group, a structural unit derived from a (meth) acrylic acid alkyl ester having 1 to 8 carbon atoms in the alkyl group, and an alkyl group. And a structural unit derived from a (meth) acrylic acid alkyl ester having 9 to 20 carbon atoms.
In a more preferred embodiment, the (meth) acrylic copolymer is derived from a structural unit derived from a monomer having a hydroxyl group and a (meth) acrylic acid alkyl ester having 1 to 6 carbon atoms in the alkyl group. A structural unit derived from a structural unit and a (meth) acrylic acid alkyl ester having 9 to 16 carbon atoms in the alkyl group.
In a more preferred embodiment, the (meth) acrylic copolymer is derived from a structural unit derived from a monomer having a hydroxyl group and a (meth) acrylic acid alkyl ester having 1 to 4 carbon atoms in the alkyl group. And a structural unit derived from a (meth) acrylic acid alkyl ester having 9 to 12 carbon atoms in the alkyl group.
In a particularly preferred embodiment, the (meth) acrylic copolymer includes a structural unit having a hydroxyl group, a structural unit derived from at least one selected from n-butyl (meth) acrylate and methyl (meth) acrylate, And a structural unit derived from lauryl (meth) acrylate.

The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention is derived from a monomer having a hydroxyl group in the following manner from the viewpoint of improving the pressure-sensitive adhesive strength and moisture and heat whitening resistance of the pressure-sensitive adhesive layer. And a structural unit derived from a (meth) acrylic acid alkyl ester monomer.
The (meth) acrylic copolymer is a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 6 carbon atoms in the alkyl group, and a (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group. And a structural unit derived from a monomer.
In a more preferred embodiment, the (meth) acrylic copolymer has a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 4 carbon atoms in the alkyl group, and 1 to 8 carbon atoms in the alkyl group. A structural unit derived from a (meth) acrylic acid alkyl ester and a structural unit derived from a (meth) acrylic acid alkyl ester having 9 to 20 carbon atoms in the alkyl group.
In a more preferred embodiment, the (meth) acrylic copolymer has a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 4 carbon atoms in the alkyl group, and 1 to 6 carbon atoms in the alkyl group. A structural unit derived from a (meth) acrylic acid alkyl ester, and a structural unit derived from a (meth) acrylic acid alkyl ester having 9 to 16 carbon atoms in the alkyl group.
In a particularly preferred embodiment, the (meth) acrylic copolymer includes a structural unit derived from a hydroxyalkyl acrylate having 2 to 4 carbon atoms in the alkyl group and an alkyl acrylate having 1 to 4 carbon atoms in the alkyl group. And a structural unit derived from an ester and a structural unit derived from an alkyl acrylate ester having 9 to 12 carbon atoms in the alkyl group.
In the most preferred embodiment, the (meth) acrylic copolymer comprises a structural unit derived from at least one selected from 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate, n-butyl (meth) acrylate, methyl A structural unit derived from at least one selected from (meth) acrylates and a structural unit derived from lauryl (meth) acrylate are included.

  The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention can contain a structural unit derived from a monomer having a cyclic group, if necessary.

  Examples of the cyclic group in the monomer having a cyclic group include an aromatic ring group and a non-aromatic cyclic group such as an aromatic hydrocarbon group, an aromatic heterocyclic group, and a cyclic aliphatic hydrocarbon group. Among these, the cyclic group in the monomer having a cyclic group is preferably an aromatic hydrocarbon group, and more preferably an aromatic hydrocarbon group having 6 to 10 carbon atoms. 1-2 is preferable and, as for the content number of the cyclic group in the monomer which has a cyclic group, 1 is more preferable.

Examples of the monomer having a cyclic group include (meth) acrylate having a cyclic group, (meth) acrylamide having a cyclic group, and a styrene derivative.
Among these, the monomer having a cyclic group is preferably a (meth) acrylate having a cyclic group, more preferably a (meth) acrylate having an aromatic ring group, and the aromatic ring group being an alkylene group, an oxyalkylene group or a polyoxyalkylene. A (meth) acrylate having an ester bond via a group is more preferable, and a (meth) acrylate having an aromatic ring group ester-bonded via an oxyalkylene group is particularly preferable.

  Examples of the monomer having a cyclic group include phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypropyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, ethylene oxide-modified cresol (meta ) Acrylates, ethylene oxide modified nonylphenol (meth) acrylates, β-naphthyloxyethyl (meth) acrylates, biphenyl (meth) acrylates and other (meth) acrylates, cyclohexyl (meth) acrylates, isobornyl (meth) acrylates , (Meth) acrylates having a non-aromatic cyclic group such as cyclopentanyl (meth) acrylate and cyclopentenyl (meth) acrylate, styrene, α -Styrene derivatives having an aromatic ring group such as methyl styrene, t-butyl styrene, p-chloro styrene, chloromethyl styrene and vinyl toluene. Among these, a monomer having a cyclic group has an aromatic ring group such as phenoxyethyl (meth) acrylate, phenoxypropyl (meth) acrylate, and β-naphthyloxyethyl (meth) acrylate bonded via an oxyalkylene group. A (meth) acrylate is preferred.

  The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention can contain a structural unit derived from a monomer having an acidic group, if necessary.

As for the content rate of the structural unit derived from the monomer which has an acidic group, 3 mass% or less is preferable with respect to the total mass of the structural unit in a (meth) acrylic-type copolymer.
When the content of the structural unit derived from the monomer having an acidic group is within the above range, the pressure-sensitive adhesive layer derived from the pressure-sensitive adhesive composition of the present invention comes into contact with a metal-containing member such as a transparent electrode of the touch panel. In this case, corrosion of a member containing metal can be suppressed. For this reason, the adhesive composition of this invention can be used conveniently for bonding of what has a member containing metals, such as a touch panel.
From the above viewpoint, the content of the structural unit derived from the monomer having an acidic group is more preferably 1% by mass or less based on the total mass of the structural unit in the (meth) acrylic copolymer, 0.1 mass% or less is still more preferable, and it is especially preferable not to contain.

  Examples of the acidic group in the monomer having an acidic group include a carboxy group, a sulfonic acid group, and a phosphoric acid group. Among these, the acidic group in the monomer having an acidic group is preferably a carboxy group from the viewpoint of controlling the reaction rate between the (meth) acrylic copolymer and the crosslinking agent.

  Monomers having a carboxy group include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, cinnamic acid and other unsaturated carboxylic acids, itaconic acid monomethyl, itaconic acid monobutyl, and 2-acryloyl. Unsaturated dicarboxylic acid monoesters such as oxyethylphthalic acid, unsaturated tricarboxylic acid monoesters such as 2-methacryloyloxyethyl trimellitic acid, 2-methacryloyloxyethyl pyromellitic acid, carboxyethyl acrylate (β-carboxyethyl acrylate) ), Carboxyalkyl acrylates such as carboxypentyl acrylate, acrylic acid dimers, acrylic acid trimers, unsaturated dicarboxylic acid anhydrides such as itaconic anhydride, maleic anhydride, and fumaric anhydride.

  Examples of the monomer having a sulfonic acid group include styrene sulfonic acid, allyl sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, (meth) acrylamide propane sulfonic acid, sulfopropyl (meth) acrylate, (Meth) acryloyloxynaphthalenesulfonic acid and the like.

  Examples of the monomer having a phosphoric acid group include 2-hydroxyethyl acryloyl phosphate.

  The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention can contain a constitutional unit derived from a monomer other than the monomers described above, if necessary.

  The content of structural units derived from monomers other than the aforementioned monomers is preferably 30% by mass or less, and 25% by mass with respect to the total mass of the structural units in the (meth) acrylic copolymer. The following is more preferable, and 20% by mass or less is further preferable.

  Examples of other monomers include basic groups such as acrylamide, methacrylamide, diacetone acrylamide, Nn-butoxymethylacrylamide, Ni-butoxymethylacrylamide, N, N-dimethylacrylamide, and N-methylacrylamide. Monomers of saturated fatty acid vinyl esters such as vinyl group monomers, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, vinyl formate, vinyl acetate, vinyl propionate and “vinyl versatate” (trade name) Examples include the body.

The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention has a weight average molecular weight (Mw) of preferably 300,000 to 2,000,000, more preferably 300,000 to 1,000,000, and more preferably 300,000 to 1,000,000. More preferably.
When the Mw of the (meth) acrylic copolymer is 300000 or more, the (meth) acrylic oligomer tends to be unevenly distributed on the surface of the pressure-sensitive adhesive layer, which is preferable. Further, the cohesive force of the (meth) acrylic copolymer itself is increased, and the cohesive force of the pressure-sensitive adhesive layer is also increased. Therefore, the pressure-sensitive adhesive layer hardly remains on the adherend and is excellent in reworkability, which is preferable. It is preferable that the Mw of the (meth) acrylic copolymer is 2000000 or less because the wettability of the pressure-sensitive adhesive layer becomes good and the adhesive strength becomes strong.
Moreover, the dispersity (Mw / Mn) of the (meth) acrylic copolymer is not particularly limited, and can be 2 to 20, for example. From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive layer, the degree of dispersion (Mw / Mn) of the (meth) acrylic copolymer is preferably from 3 to 15, and more preferably from 4.5 to 12.

  In addition, in this specification, a weight average molecular weight (Mw) and a number average molecular weight (Mn) are the values measured according to following (1)-(3).

(1) A sample solution is applied onto a release film (release sheet) and dried at 100 ° C. for 2 minutes to obtain a film-like sample.
(2) The film-like sample obtained in (1) is dissolved in tetrahydrofuran (THF) so that the solid content is 0.2% by mass.
(3) Under the following conditions, Mw and Mn of the sample are measured as standard polystyrene conversion values using gel permeation chromatography (GPC).
<Condition>
・ GPC: HLC-8220 GPC [manufactured by Tosoh Corporation]
・ Column: TSK-GEL GMHXL (4 used)
-Mobile phase solvent: Tetrahydrofuran-Standard sample: Standard polystyrene-Flow rate: 0.6 ml / min
-Column temperature: 40 ° C

  The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention is characterized by improving the properties of the pressure-sensitive adhesive such as tack, cohesive strength, wettability, and pressure-sensitive adhesive layer, and pressure-sensitive adhesiveness and rework. The glass transition temperature (Tg) is preferably −50 ° C. to −15 ° C., and more preferably −45 ° C. to −20 ° C., from the viewpoint of easily achieving compatibility.

In this specification, the glass transition temperature (Tg) is a molar average glass transition temperature determined by the following calculation. _{Tg 1,} Tg 2 of the following formulas, ... and Tg _n is the monomer 1, monomer 2, in ..... and the monomer n glass transition temperatures of homopolymers Yes, converted to absolute temperature (K). m ₁ , m ₂ ,..., and _mn are the mole fractions of the respective monomers.
In addition, although absolute temperature (K) is used for calculation of glass transition temperature, when describing glass transition temperature in this specification, Celsius degree (degreeC) may be used.

[Calculation formula of glass transition temperature (Tg)]

  The “glass transition temperature of the homopolymer” used herein is a differential scanning calorimeter (DSC) (manufactured by Seiko Instruments Inc., EXSTAR 6000), in a nitrogen stream, 10 mg of a measurement sample, a heating rate of 10 ° C./min. The inflection point of the obtained DSC curve is taken as the glass transition temperature of the homopolymer.

  “Glass transition temperature of homopolymer” of typical monomers is: methyl acrylate 5 ° C., methyl methacrylate 103 ° C., ethyl acrylate-27 ° C., n-butyl acrylate-57 ° C., 2-ethylhexyl acrylate-76 ° C. Acrylic acid 163 ° C, methacrylic acid 185 ° C, t-butyl acrylate 41 ° C, isobutyl methacrylate 48 ° C, 2-hydroxyethyl acrylate -15 ° C, lauryl acrylate -15 ° C.

  The (meth) acrylic copolymer contained in the pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic monomer having a hydroxyl group, and a monomer composition containing other monomers as necessary. It can be produced by polymerizing the product. The polymerization method of the monomer composition is not particularly limited and can be appropriately selected from commonly used polymerization methods. Examples of the polymerization method include solution polymerization, emulsion polymerization, suspension polymerization and the like. Among these, the polymerization method is preferably solution polymerization because a (meth) acrylic copolymer can be easily produced.

In solution polymerization, a predetermined organic solvent, a monomer, a polymerization initiator, a catalyst used as required, and a chain transfer agent are generally charged in a polymerization tank, and stirred in a nitrogen stream or under reflux of the organic solvent. The reaction is performed by heating for several hours. The polymerization initiator is not particularly limited, and for example, an azo compound can be used.
In addition, Mw and Mn of the (meth) acrylic copolymer can be adjusted to a desired molecular weight by adjusting the reaction temperature, the reaction time, the amount of the organic solvent, and the type and amount of the catalyst.

≪ (Meth) acrylic oligomer≫
The (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention has a weight average molecular weight (Mw) of 4,000 to 100,000, and 30% by mass to 50% by mass of a structural unit derived from a monomer having a hydroxyl group. And the glass transition temperature (Tg) is −50 ° C. or higher.
Moreover, the (meth) acrylic-type oligomer contained in the adhesive composition of this invention contains at least 1 sort (s) of the structural unit derived from monomers other than the monomer which has a hydroxyl group.

When the content of the structural unit derived from the monomer having a hydroxyl group in the (meth) acrylic oligomer is less than 30% by mass, the (meth) acrylic oligomer can sufficiently react with the crosslinking agent described later. The reworkability of the pressure-sensitive adhesive layer is inferior. When the content rate of the structural unit derived from the monomer which has a hydroxyl group exceeds 50 mass%, a part will gelatinize at the time of preparation of a (meth) acrylic-type oligomer, and the rework property and adhesive force of an adhesive layer will be inferior.
From the above viewpoint, the content of the structural unit derived from the monomer having a hydroxyl group in the (meth) acrylic oligomer is preferably 35% by mass to 45% by mass, and more preferably 37% by mass to 43% by mass. preferable.

  The monomer having a hydroxyl group that can be used when producing a (meth) acrylic oligomer is the same as the monomer having a hydroxyl group that can be used when producing a (meth) acrylic copolymer. Can be mentioned. Moreover, a monomer preferable as a monomer having a hydroxyl group that can be used when producing a (meth) acrylic oligomer also has a hydroxyl group that can be used when producing a (meth) acrylic copolymer. The thing similar to a preferable monomer as a monomer can be mentioned.

The (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention contains a structural unit derived from a monomer having a hydroxyl group in the following manner from the viewpoint of the adhesive strength and reworkability of the pressure-sensitive adhesive layer. Is preferred.
The (meth) acrylic oligomer is a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 6 carbon atoms in the alkyl group as a structural unit derived from a monomer having a hydroxyl group. It is preferable to contain 30 mass%-50 mass% with respect to the total mass of the structural unit of an oligomer.
As a more preferred embodiment, the (meth) acrylic oligomer is a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 4 carbon atoms in the alkyl group as a structural unit derived from a monomer having a hydroxyl group. Is contained in an amount of 30% by mass to 50% by mass with respect to the total mass of the structural units of the (meth) acrylic oligomer.
In a more preferred embodiment, the (meth) acrylic oligomer is a structural unit derived from a hydroxyalkyl (meth) acrylate having 2 to 4 carbon atoms in the alkyl group as a structural unit derived from a monomer having a hydroxyl group. Is 35 mass%-45 mass% with respect to the total mass of the structural unit of a (meth) acrylic-type oligomer.
As a particularly preferred embodiment, the (meth) acrylic oligomer is a structural unit derived from a hydroxyalkyl acrylate having 2 to 4 carbon atoms in the alkyl group as a structural unit derived from a monomer having a hydroxyl group. It contains 37 mass%-43 mass% with respect to the total mass of the structural unit of a meth) acrylic-type oligomer.

  Moreover, it is preferable that a (meth) acrylic-type oligomer contains at least 1 sort (s) of the structural unit derived from the (meth) acrylic-acid alkylester as a structural unit derived from monomers other than the monomer which has a hydroxyl group.

  As for the content rate of the structural unit derived from the (meth) acrylic-acid alkylester in a (meth) acrylic-type oligomer, 50 mass%-70 mass% are preferable with respect to the total mass of the structural unit of a (meth) acrylic-type oligomer, 55 mass%-65 mass% are more preferable. When the content of the structural unit derived from the (meth) acrylic acid alkyl ester is within the above range, the pressure-sensitive adhesive layer is excellent in the balance between the adhesive force and the reworkability.

The (meth) acrylic acid alkyl ester that can be used when producing the (meth) acrylic oligomer is the same as the (meth) acrylic acid alkyl ester that can be used when producing the (meth) acrylic copolymer. Can be mentioned.
As the (meth) acrylic acid alkyl ester that can be used when producing the (meth) acrylic oligomer, n-butyl (meth) acrylate and methyl (meth) acrylate are preferable.

  The (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention can contain a structural unit derived from a monomer having a cyclic group, if necessary.

The monomer having a cyclic group that can be used when producing a (meth) acrylic oligomer is the same as the monomer having a cyclic group that can be used when producing a (meth) acrylic copolymer. Can be mentioned.
In addition, examples of preferable cyclic group and preferable monomer having a cyclic group include the same as those preferable for the (meth) acrylic copolymer.

  The (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention can contain a structural unit derived from a monomer having an acidic group, if necessary.

As for the content rate of the structural unit derived from the monomer which has an acidic group, 4 mass% or less is preferable with respect to the total mass of the structural unit in a (meth) acrylic-type oligomer.
When the content of the structural unit derived from the monomer having an acidic group is within the above range, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition of the present invention is in contact with a member containing a metal such as a transparent electrode of a touch panel. When doing, corrosion of the member containing a metal can be suppressed. For this reason, the adhesive composition of this invention can be used conveniently for bonding of what has a member containing metals, such as a touch panel.
From the above viewpoint, the content of the structural unit derived from the monomer having an acidic group is more preferably 1% by mass or less based on the total mass of the structural unit in the (meth) acrylic oligomer. 1 mass% or less is still more preferable, and it is especially preferable not to contain.

The monomer having an acidic group that can be used when producing a (meth) acrylic oligomer is the same as the monomer having an acidic group that can be used when producing a (meth) acrylic copolymer. Can be mentioned.
In addition, examples of the preferable acidic group and the preferable monomer as the monomer having an acidic group include the same as those preferable for the (meth) acrylic copolymer.

  The (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention can contain a structural unit derived from a monomer other than the above-described monomers as necessary.

  The content of structural units derived from monomers other than the aforementioned monomers is preferably 30% by mass or less, and preferably 25% by mass or less, based on the total mass of the structural units in the (meth) acrylic oligomer. More preferred is 20% by mass or less.

  In addition, other monomers that can be used when producing (meth) acrylic oligomers are the same as other monomers that can be used when producing (meth) acrylic copolymers. Can be mentioned.

Mw of the (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention is 4,000 to 100,000, preferably 6,000 to 50,000, and more preferably 6,000 to 10,000.
When the Mw of the (meth) acrylic oligomer is less than the lower limit value, the reworkability of the pressure-sensitive adhesive layer is inferior. When the upper limit is exceeded, the compatibility between the (meth) acrylic copolymer and the (meth) acrylic oligomer is poor, so the (meth) acrylic copolymer and the (meth) acrylic oligomer are cross-linked. It is difficult to rework the adhesive layer.

Moreover, the dispersity (Mw / Mn) of the (meth) acrylic oligomer is not particularly limited, and can be, for example, 1.1 to 10. From the viewpoint of improving the reworkability of the pressure-sensitive adhesive layer, the dispersity (Mw / Mn) of the (meth) acrylic oligomer is preferably 1.3 to 5, and more preferably 1.5 to 3.
Mw and Mn are values measured by the method described above.

The glass transition temperature (Tg) of the (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention is −50 ° C. or higher. When the Tg of the (meth) acrylic oligomer is less than −50 ° C., the adhesive strength and reworkability of the adhesive layer are inferior.
Further, from the above viewpoint, the glass transition temperature of the (meth) acrylic oligomer is preferably −40 ° C. or higher, and more preferably −30 ° C. or higher.
Tg is a value obtained by the above-described method.

It is preferable that content of the (meth) acrylic-type oligomer in the adhesive composition of this invention is 0.1 mass part-10 mass parts with respect to 100 mass parts of (meth) acrylic-type copolymers.
When the content of the (meth) acrylic oligomer is 0.1 to 10 parts by mass, the adhesive strength, reworkability, and durability of the pressure-sensitive adhesive layer are further improved.
Further, from the above viewpoint, the content of the (meth) acrylic oligomer is more preferably 0.8 parts by mass to 5 parts by mass.

  The (meth) acrylic oligomer can be produced by polymerizing a monomer composition containing a monomer having a hydroxyl group and another monomer. The polymerization method of the monomer composition is not particularly limited and can be appropriately selected from commonly used polymerization methods. Examples of the polymerization method include solution polymerization, emulsion polymerization, suspension polymerization and the like. Among these, the polymerization method is preferably solution polymerization because a (meth) acrylic oligomer can be easily produced.

In solution polymerization, a predetermined organic solvent, a monomer, a polymerization initiator, and a chain transfer agent and a catalyst used as necessary are generally charged in a polymerization tank, and stirred in a nitrogen stream or under reflux of the organic solvent. The reaction is performed by heating for several hours. The polymerization initiator is not particularly limited, and for example, an azo compound can be used.
The Mw and Mn of the (meth) acrylic oligomer can be adjusted to a desired molecular weight by adjusting the reaction temperature, reaction time, amount of organic solvent, and type and amount of catalyst.

≪Crosslinking agent≫
The crosslinking agent contained in the pressure-sensitive adhesive composition of the present invention is not particularly limited as long as it reacts with the (meth) acrylic oligomer and (meth) acrylic copolymer to form a crosslinked structure. Examples of the crosslinking agent include isocyanate compounds, epoxy compounds, aziridine compounds, melamine formaldehyde condensates, metal salts, and metal chelate compounds.
From the viewpoint of achieving both strong adhesive strength and reworkability of the pressure-sensitive adhesive layer, and the stability of the pressure-sensitive adhesive composition after mixing the crosslinking agent with the (meth) acrylic oligomer and (meth) acrylic copolymer From the viewpoint, the crosslinking agent is preferably at least one selected from an isocyanate compound and an epoxy compound, and more preferably an isocyanate compound.

As for content of the crosslinking agent in the adhesive composition of this invention, 0.001 mass part-1.0 mass part are preferable with respect to 100 mass parts of (meth) acrylic-type copolymers.
As for content when using an isocyanate type compound as a crosslinking agent, 0.01 mass part-0.5 mass part or less are more preferable with respect to 100 mass parts of (meth) acrylic-type copolymers, 0.05 mass part -0.3 mass part is still more preferable.
As for content when using an epoxy-type compound as a crosslinking agent, 0.001 mass part-1.0 mass part are more preferable with respect to 100 mass parts of (meth) acrylic-type copolymers, 0.01 mass part- 0.5 parts by mass is more preferable.
When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present invention is within the above range, the pressure-sensitive adhesive layer is excellent in the balance between the adhesive force and the reworkability.

  Moreover, a crosslinking agent can be used in combination of 2 or more types, for example, you may combine an isocyanate type compound and an epoxy-type compound. In that case, content of an isocyanate type compound and an epoxy type compound can be suitably selected in the range of the said content, respectively. In the case of using a combination of an isocyanate compound and an epoxy compound, the content ratio is an active ingredient mass ratio, preferably isocyanate compound: epoxy compound = 1: 1 to 300: 1, and 10: 1 to 100. : 1 is more preferable.

Examples of the isocyanate compounds include aromatic polyisocyanates such as xylylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated products of the aromatic polyisocyanate compound, and the like. And aliphatic or alicyclic polyisocyanates.
In addition, dimers or trimers of the isocyanate compounds, adducts of the isocyanate compounds and polyol compounds such as trimethylolpropane, and biurets of the isocyanate compounds may be used as the isocyanate compounds. Can do. Among these isocyanate compounds, those derived from hexamethylene diisocyanate or xylylene diisocyanate such as hexamethylene diisocyanate dimer or trimer, or hexamethylene diisocyanate or adduct of xylylene diisocyanate are preferable.

  As the isocyanate compound, commercially available products may be used. For example, “Coronate L”, “Coronate HX”, “Coronate HL-S”, “Coronate 2234” (manufactured by Nippon Polyurethane Industry Co., Ltd.) "Death module N3400" (manufactured by Sumitomo Bayer Urethane Co., Ltd.), "Duranate E-405-80T", "Duranate TSE-100" (manufactured by Asahi Kasei Corporation), "Takenate D-110N", "Takenate D -120N "," Takenate M-631N "," MT-Oresta-NP1200 "(manufactured by Mitsui Chemicals, Inc.) and the like can be suitably used.

  Examples of the epoxy compound include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and neopentyl glycol diglycidyl ether. 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, resorcin diglycidyl ether, 2,2- Dibromoneopentyl glycol diglycidyl ester Ter, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris (glycidyl) isocyanurate, tris (glycidoxyethyl) isocyanurate, 1 , 3-bis (N, N-glycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine and the like.

Among the epoxy compounds, polyepoxy compounds containing three or more epoxy groups are preferable, and among them, tris (glycidyl) isocyanurate, tris (glycidoxyethyl) isocyanurate, 1,3-bis (N, N-glycidylamino) More preferred are polyepoxy compounds such as methyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, 1,3-bis (N, N-glycidylaminomethyl) cyclohexane, N, N , N ′, N′-tetraglycidyl-m-xylylenediamine is more preferred.
Moreover, you may use the commercial item marketed as a polyepoxy compound, for example, "TETRAD-C", "TETRAD-X", etc. by Mitsubishi Gas Chemical Co., Ltd. can be used suitably.

≪Other ingredients≫
Other components that the pressure-sensitive adhesive composition of the present invention may contain include various additives, solvents, silane coupling agents, ultraviolet absorbers, tackifiers, plasticizers, softeners, dyes, pigments, inorganic fillers, and the like. Is mentioned.
Other components are blended in the pressure-sensitive adhesive composition in an amount that does not impair the effects of the present invention.
The amount of the silane coupling agent is preferably 0.2 parts by mass or less, more preferably 0.1 parts by mass or less, from the viewpoint of suppressing the adhesive force of the adhesive layer from changing with time. Is more preferable.

<Adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention described above. The pressure-sensitive adhesive layer includes a crosslinked structure formed between the (meth) acrylic copolymer and (meth) acrylic oligomer contained in the pressure-sensitive adhesive composition of the present invention described above and a crosslinking agent. The pressure-sensitive adhesive layer is excellent in adhesive strength and reworkability.

The pressure-sensitive adhesive sheet of the present invention may be a type having no base material (non-base material type) or a type having a base material (base material type).
Examples of the substrate include a resin film (for example, a polyester film such as polyethylene terephthalate (PET)). The substrate is preferably transparent. Although the thickness of a base material is not specifically limited, 5 micrometers-100 micrometers are preferable from a durable viewpoint.
The pressure-sensitive adhesive sheet of the present invention is preferably a non-base material type from the viewpoint of transparency.

As for the adhesive layer of the adhesive sheet of this invention, the exposed surface may be protected by the peeling film.
The release film is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer. For example, a resin film (for example, PET or the like) that has been subjected to easy release treatment on at least one side using a release treatment agent. Polyester film). Examples of the release treatment agent include fluorine compounds, silicone compounds, and long-chain alkyl compounds.
The release film protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is practically used, and is peeled off during use.

  The thickness of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention is preferably 20 μm to 300 μm, more preferably 25 μm to 250 μm, and more preferably 50 μm to 50 μm, from the viewpoint of easily following the level difference of the adherend and the productivity of the pressure sensitive adhesive sheet. 250 μm is more preferable.

35 mass%-90 mass% are preferable, as for the gel fraction of the adhesive layer of the adhesive sheet of this invention, 35 mass%-80 mass% are more preferable, and 35 mass%-75 mass% are still more preferable. When the gel fraction of the pressure-sensitive adhesive layer is within the above range, the pressure-sensitive adhesive layer has excellent balance of adhesive force and reworkability.
In addition, the gel fraction of an adhesive layer is a ratio of a solvent insoluble content measured using ethyl acetate as an extraction solvent. Details of the measurement method are as follows.

-Gel fraction measurement method-
1. About 0.25 g of a film-like pressure-sensitive adhesive layer is applied to a 250-mesh wire mesh (100 mm × 100 mm) whose mass has been accurately measured with a precision balance, and wrapped so that the gel content does not leak. Thereafter, the mass is accurately measured with a precision balance to prepare a sample.
2. The obtained sample is immersed in 80 ml of ethyl acetate for 3 days.
3. A sample is removed, washed with a small amount of ethyl acetate and dried at 120 ° C. for 24 hours. Thereafter, the mass is accurately measured with a precision balance.
4). The gel fraction is calculated by the following formula.
Gel fraction (mass%) = (Z−X) / (Y−X) × 100
However, X is the mass (g) of the wire mesh, Y is the mass (g) before immersing the wire mesh with the adhesive layer attached, and Z is the mass (g) after immersing and drying the wire mesh with the adhesive layer attached. .

The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention preferably has high transparency. Specifically, for example, the total light transmittance in the visible light wavelength region (JIS K 7361 (1997)) is 85% or more. It is preferably 90% or more.
The haze (JIS K 7136 (2000)) of the pressure-sensitive adhesive layer is preferably less than 2.0%, more preferably less than 1.0%, and still more preferably 0.5% or less.

  The pressure-sensitive adhesive sheet of the present invention can be prepared, for example, by a method of forming a pressure-sensitive adhesive layer by applying a pressure-sensitive adhesive composition of the present invention containing a crosslinking agent to a release film and the like and drying to cause a crosslinking reaction. it can.

  A substrate-type pressure-sensitive adhesive sheet is produced, for example, by applying a pressure-sensitive adhesive composition on both sides of a base material, stacking a release film on each of the two coating layers so that the release-treated surfaces are in contact with each other, and causing a crosslinking reaction can do. In addition, it can be produced by a method in which a pressure-sensitive adhesive layer is formed on the release-treated surface of the release film and the pressure-sensitive adhesive layer with the release film is adhered to both surfaces of the substrate.

  Non-base type pressure-sensitive adhesive sheet, for example, by applying a pressure-sensitive adhesive composition to the release-treated surface of the release film, and stacking another release film on this coating layer so that the release-treated surface is in contact, causing a crosslinking reaction Can be produced by a method of forming a pressure-sensitive adhesive layer.

  Examples of the method for applying the pressure-sensitive adhesive composition to the release film or substrate include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, etc. It is done.

  The adhesive sheet of this invention can be used suitably for bonding of the optical member in a touch panel, a display panel, etc. That is, the pressure-sensitive adhesive sheet of the present invention includes, for example, a polarizing plate, a phase difference plate, an antireflection film, a viewing angle widening film, a brightness enhancement film, a transparent conductive film (ITO (Indium Tin Oxide) film), a liquid crystal cell, glass It can use suitably for pasting of optical members, such as a substrate and a protection film.

<Touch panel>
A touch panel using the pressure-sensitive adhesive or pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer includes a crosslinked structure formed by a crosslinking reaction of the pressure-sensitive adhesive of the present invention described above.
Therefore, since the adhesive strength of the adhesive layer is excellent, it is difficult to peel off even when subjected to an impact such as dropping.

  The touch panel having the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention includes, for example, a glass plate, a transparent conductive film such as an ITO layer sputtered on the glass plate, and the pressure-sensitive adhesive composition of the present invention. It can be set as the structure which laminated | stacked the adhesive layer formed from and the cover film used as a protective material.

  The preferred range of the gel fraction, total light transmittance and haze of the pressure-sensitive adhesive layer in the touch panel having the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is the same as that of the pressure-sensitive adhesive sheet of the present invention described above.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

<Production of (meth) acrylic oligomer>
(Production Example 1)
A reaction apparatus equipped with a stirrer, a reflux condenser, a sequential dropping apparatus, and a thermometer was added with 28 parts by mass of ethyl acetate and 21 parts by mass of butyl acetate and heated, and maintained at the reflux temperature for 10 minutes. Subsequently, under reflux temperature conditions, 70 parts by mass of n-butyl acrylate (BA) (70% by mass with respect to the total mass of the structural units in the acrylic oligomer), 30 parts by mass of 2-hydroxyethyl acrylate (2HEA) (also 30 parts by mass) %), 10 parts by mass of ethyl acetate, 10 parts by mass of butyl acetate and 10 parts by mass of dimethyl 2,2-azobis (2-methylpropionate) [trade name: V-601, manufactured by Wako Pure Chemical Industries, Ltd.] The monomer mixture was successively dropped over 180 minutes, and after completion of the dropping, a polymerization reaction was further performed for 230 minutes. After completion of the reaction, the (meth) acrylic oligomer 1 having a solid content of 61% by mass, a weight average molecular weight (Mw) of 7000, a dispersity (Mw / Mn) of 2.0, and a glass transition temperature (Tg) of −45 ° C. Solution was obtained.
The weight average molecular weight (Mw), number average molecular weight (Mn), and glass transition temperature (Tg) were measured or calculated by the method described above.

(Production Example 2 to Production Example 8)
In the said manufacture example 1, except having changed BA and 2HEA into the monomer shown in the following Table 1, and its quantity, it is the same as that of manufacture example 1, (meth) acrylic oligomer 2- (meth) acrylic type A solution of oligomer 8 was prepared. All the solutions have a solid content of 61% by mass. In Table 1, MA represents methyl acrylate and 2EHA represents 2-ethylhexyl acrylate.

<Production of (meth) acrylic copolymer>
(Production Example A)
350 parts by mass of ethyl acetate was charged into a reactor equipped with a stirrer, a reflux condenser, a sequential dropping device, and a thermometer. Next, in another container, 225 parts by mass of lauryl acrylate (LA) (15% by mass with respect to the total mass of structural units in the acrylic copolymer), 570 parts by mass of n-butyl acrylate (BA) (also 38 masses) %), 405 parts by weight of methyl acrylate (MA) (also 27% by weight), and 300 parts by weight (also 20% by weight) of 2-hydroxyethyl acrylate (2HEA). 300 parts by mass (20% by mass of the monomer mixture) was charged into the reactor, heated, and refluxed at the reflux temperature for 10 minutes.
Subsequently, the remaining 1200 parts by mass of the monomer mixture (80% by mass of the monomer mixture), 32 parts by mass of ethyl acetate, and 2,2′-azobis (2,4-dimethylvaleronitrile) under reflux temperature conditions 0.12 parts by mass were successively added dropwise over 120 minutes, and the polymerization reaction was further carried out for 30 minutes.
Thereafter, a mixed liquid of 15 parts by mass of ethyl acetate and 0.13 parts by mass of t-butyl peroxypivalate was successively dropped over 40 minutes, and a polymerization reaction was further performed for 150 minutes.
After completion of the reaction, the mixture was diluted with ethyl acetate to a solid content of 42% by mass, the weight average molecular weight (Mw) was 500,000, the dispersity (Mw / Mn) was 5.8, and the glass transition temperature (Tg) was −25 ° C. ( A solution of (meth) acrylic copolymer A was obtained.
The weight average molecular weight (Mw), number average molecular weight (Mn), and glass transition temperature (Tg) were measured or calculated by the method described above.

(Production Example B to Production Example G)
(Meth) acrylic copolymer B in the same manner as in Production Example A, except that LA, BA, MA, and 2HEA were changed to the monomers and amounts shown in Table 2 below in Production Example A. A solution of a (meth) acrylic copolymer G was produced. All solutions have a solid content of 42% by mass. In Table 2, 2EHA represents 2-ethylhexyl acrylate.

(Example 1)
-Preparation of adhesive solution-
An adhesive solution was prepared according to the following procedure.
100 parts by mass of the solution of the (meth) acrylic copolymer A as a solid content, 1 part by mass of the solution of the (meth) acrylic oligomer 1 as a solid content, and a crosslinking agent (trade name: Takenate D-110N) , Manufactured by Mitsui Chemicals, Inc .; isocyanate compound) was mixed with 0.2 part by mass to prepare a pressure-sensitive adhesive solution 1.

-Preparation of test samples-
The test sample was produced according to the following procedure.
On the release-treated surface of a release film (trade name: Film Vina 100E, manufactured by Fujimori Kogyo Co., Ltd.) surface-treated with a silicone release agent, the coating amount after drying is 50 g / cm ^2. The adhesive solution 1 was applied and the coating layer was laminated.
Next, the obtained laminate was dried with a hot air circulation dryer at 100 ° C. for 120 seconds.
Subsequently, the surface on which the coating layer was exposed was bonded to a separately prepared release film (trade name: film binder 100E, manufactured by Fujimori Kogyo Co., Ltd.).
After pasting, it was cured at 23 ° C. and 50% RH for 4 days to obtain a test sample (non-base material type double-sided pressure-sensitive adhesive sheet). The gel fraction of the pressure-sensitive adhesive layer of the obtained test sample was 59.0% by mass. The gel fraction was measured by the method described above.
Various measurements shown below were performed using the obtained test samples. The results are shown in Table 3.

(1) Reworkability One release film of the produced test sample was peeled, and the surface on which the pressure-sensitive adhesive layer was exposed was bonded to optical glass (manufactured by Matsunami Glass Industrial Co., Ltd., optical soda glass). This was left for 1 hour at 80 ° C. and 0% RH (dry), then peeled off at room temperature (23 ° C.), and the residue of the adhesive layer on the optical glass was visually observed. Sex was evaluated. In addition, the less the adhesive layer remains on the adherend, the better. The evaluation criteria A and B in the following evaluation criteria are practically problematic levels, and C is a practically problematic level.

<Evaluation criteria>
A: No residual adhesive layer is observed.
B: The adhesive layer remains in 0.1% or more and less than 5% of the peeled area.
C: The adhesive layer remains in 5% or more of the peeled area.

(2) Adhesive strength One release film of the prepared test sample was peeled, and the surface on which the pressure-sensitive adhesive layer was exposed was bonded to the easy-adhesion treated surface of the 100 μm PET film subjected to the easy-adhesion treatment. The test sample bonded to this PET film is cut to a size of 25 mm × 150 mm, and then the other release film is peeled off, and the pressure-sensitive adhesive layer contacts the glass plate using a rubber roller weighing 2 kg on the surface of the glass plate. A sample for adhesion test was prepared by pressure bonding. This sample for adhesive strength test was allowed to stand for 24 hours under the conditions of 23 ° C. and 50% RH, and then the adhesive strength at 180 ° peeling (N / 25 mm) was measured at a peeling speed of 300 mm / min. The adhesive strength was evaluated according to the following evaluation criteria. The stronger the adhesive strength, the better. A and B in the following evaluation criteria are levels having no practical problem, and C is a level having a practical problem.

<Evaluation criteria>
A: Adhesive strength is 20 N / 25 mm or more.
B: Adhesive strength is 15 N / 25 mm or more and less than 20 N / 25 mm.
C: Adhesive strength is less than 15 N / 25 mm.

(3) Moisture and heat whitening resistance The prepared test sample was cut into a size of 80 mm × 60 mm, the release film was peeled off, and the exposed adhesive layer was formed into a 1.8 mm thick glass plate (manufactured by Matsunami Glass Industrial Co., Ltd., The sample was laminated on an optical soda glass and pressure-bonded using a table laminating machine to prepare a sample for moisture and heat whitening resistance test.
The haze (%) of this moisture and heat whitening test sample was measured by irradiating light from the optical glass side with a spectrocolorimeter (CM-3500d manufactured by Konica Minolta).
Next, the sample for moisture and heat whitening resistance test was placed in an environment of 85 ° C. and 90% RH for 250 hours, and immediately after taking out from this environment, haze (%) was measured in the same manner.
A difference (ΔH) in haze (%) before and after introduction into the test environment was calculated, and wet heat and heat whitening resistance was evaluated according to the following evaluation criteria. In addition, moisture-heat whitening resistance is excellent, so that (DELTA) H is small.
<Evaluation criteria>
A: ΔH is less than 1.0.
B: ΔH is 1.0 or more and less than 2.0.
C: ΔH is 2.0 or more.

(4) Durability (Evaluation of durability against high temperature and humidity environment)
The prepared test sample was cut to a size of 80 mm × 60 mm, the release film was peeled off, and the exposed adhesive layer was stacked on a 1.8 mm thick glass plate (Matsunami Glass Industrial Co., Ltd., optical soda glass), The sample was subjected to pressure bonding using a table laminating machine to obtain a sample for durability test.
Thereafter, the sample for durability test was left in a high temperature and high humidity (85 ° C., 90% RH) environment for 250 hours.
After standing, the number of bubbles generated in the sample for durability test was visually observed and evaluated according to the following evaluation criteria. The smaller the number of bubbles generated, the better the durability.

<Evaluation criteria>
A: Generation | occurrence | production of the bubble was not recognized at all.
B: Generation of bubbles was 1 or more and less than 5.
C: Generation of bubbles was 5 or more and less than 11.
D: Generation of bubbles was 11 or more.

<Examples 2 to 15 and Comparative Examples 1 to 4>
In Example 1, a pressure-sensitive adhesive solution was prepared in the same manner as in Example 1 except that the composition of the pressure-sensitive adhesive solution 1 was changed as shown in Table 3 and Table 4 below. Evaluation was performed. The evaluation results are shown in Tables 3 and 4.
In addition, the comparative example 1 does not contain the (meth) acrylic-type oligomer in an adhesive solution.

As shown in Tables 3 and 4, in the examples, the adhesive strength and reworkability of the pressure-sensitive adhesive layer are excellent.
As in Comparative Example 1, in a system that does not contain a (meth) acrylic oligomer, the reworkability of the pressure-sensitive adhesive layer is inferior.
Like the comparative example 2, the rework property of an adhesive layer is inferior that the quantity of the structural unit derived from the monomer which has a hydroxyl group contained in a (meth) acrylic-type oligomer is less than 30 mass%.
As in Comparative Example 3, when the amount of the structural unit derived from the monomer having a hydroxyl group contained in the (meth) acrylic oligomer exceeds 50% by mass, the reworkability and adhesive strength of the pressure-sensitive adhesive layer are inferior.
As in Comparative Example 4, when the Tg of the (meth) acrylic oligomer is less than −50 ° C., both the reworkability and the adhesive strength of the pressure-sensitive adhesive layer are inferior.

Claims (6)

A (meth) acrylic copolymer containing a structural unit derived from a monomer having a hydroxyl group;
A (meth) acrylic oligomer having a weight average molecular weight of 4,000 to 100,000, containing 30% by mass to 50% by mass of a structural unit derived from a monomer having a hydroxyl group, and having a glass transition temperature of −50 ° C. or higher;
A crosslinking agent;
A pressure-sensitive adhesive composition comprising:   The pressure-sensitive adhesive composition according to claim 1, wherein the content of the (meth) acrylic oligomer is 0.1 to 10 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer.   The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the (meth) acrylic copolymer contains 10 mass% to 40 mass% of a structural unit derived from a monomer having a hydroxyl group.   Content of the said crosslinking agent is 0.5 mass part or less with respect to 100 mass parts of said (meth) acrylic-type copolymers, The adhesive composition of any one of Claims 1-3. object.   The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the (meth) acrylic copolymer has a glass transition temperature of -50 ° C to -15 ° C.   The adhesive sheet which has an adhesive layer formed from the adhesive composition of any one of Claims 1-5.