CN107614645B

CN107614645B - Adhesive composition, adhesive sheet and display

Info

Publication number: CN107614645B
Application number: CN201580080267.9A
Authority: CN
Inventors: 小泽祐树; 荒井隆行; 高桥洋一
Original assignee: Lintec Corp
Current assignee: Lintec Corp
Priority date: 2015-06-30
Filing date: 2015-06-30
Publication date: 2020-06-12
Anticipated expiration: 2035-06-30
Also published as: KR20180022685A; TW201702342A; TWI746441B; JP6343717B2; WO2017002218A1; KR102350144B1; CN107614645A; JPWO2017002218A1

Abstract

The present invention provides an adhesive composition for bonding a first display structural member and a second display structural member having a step difference at least on a surface on a bonded side, wherein the first display structural member and/or the second display structural member has an electrode at least on the surface on the bonded side, the adhesive composition comprising a (meth) acrylate polymer (A) and a silane coupling agent (B) having a mercapto group. The adhesive obtained from the adhesive composition can effectively prevent and suppress migration on the electrode.

Description

Adhesive composition, adhesive sheet and display

Technical Field

The present invention relates to an adhesive composition, an adhesive, and an adhesive sheet that can be used for a display such as a touch panel, and a display using the same.

Background

In recent years, a touch panel has been frequently used as a display in various mobile electronic devices such as a smart phone and a tablet terminal device. As a touch panel system, there are a resistive film system, a capacitive system, and the like, and in the mobile electronic device described above, the capacitive system is mainly used.

Recently, the touch panel is required to be increased in size, and as an electrode material for such a touch panel, a mesh-shaped metal electrode, for example, a copper electrode or a silver electrode, has been studied. However, when a conventional adhesive is used in contact with a metal electrode, particularly a copper electrode or a silver electrode, ion migration (electrochemical migration) may occur (hereinafter, simply referred to as "migration"). Specifically, the positive electrode is dissolved and disconnected, or the negative electrode is short-circuited by dendrite formation due to precipitation of the positive electrode component.

This migration is particularly likely to occur when a voltage is applied to the electrodes under high temperature and high humidity. If such a transition occurs, the touch panel cannot be normally driven. In particular, in recent years in which miniaturization and narrowing of the pitch (pitch) of electrodes have been advanced, disconnection and short-circuiting of the electrodes due to migration are likely to occur.

Thus, patent document 1 discloses an adhesive composition for a touch panel containing a benzotriazole compound as a rust inhibitor.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-177611

Disclosure of Invention

Technical problem to be solved by the invention

However, benzotriazole compounds as rust inhibitors cannot sufficiently prevent and inhibit migration even if they have an anticorrosive effect on metal wiring.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive composition, an adhesive sheet, and a display, which can effectively prevent and suppress migration.

Means for solving the problems

In order to achieve the above object, the present invention provides an adhesive composition for forming an adhesive for bonding a first display structural member and a second display structural member having a step difference at least on a surface of a bonded side, wherein the first display structural member and/or the second display structural member has an electrode at least on the surface of the bonded side, and the adhesive composition contains a (meth) acrylate polymer (a) and a silane coupling agent (B) having a mercapto group.

The adhesive obtained from the adhesive composition according to the invention (invention 1) above can effectively prevent and suppress migration on the electrodes of the first display structural member and/or the second display structural member with which the adhesive is in contact, particularly by the action of the silane coupling agent (B) having a mercapto group.

In the above invention (invention 1), the silane coupling agent (B) having a mercapto group is preferably an oligomer-type silane coupling agent containing a mercapto group (invention 2).

In the above inventions (inventions 1 and 2), the organosilicon compound constituting the mercapto group-containing silane coupling agent (B) preferably has a mercapto equivalent of 100 g/mol or more and 1000 g/mol or less (invention 3).

In the above inventions (inventions 1 to 3), the content of the silane coupling agent (B) having a mercapto group in the adhesive composition is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the (meth) acrylate polymer (a) (invention 4).

In the above inventions (inventions 1 to 4), it is preferable that the (meth) acrylate polymer (a) contains 3 to 35 mass% of a hydroxyl group-containing monomer as a monomer unit constituting the polymer (invention 5).

In the above inventions (inventions 1 to 5), it is preferable that the adhesive composition further contains a crosslinking agent (C) (invention 6).

The second aspect of the invention provides an adhesive obtained by crosslinking the adhesive composition (invention 1 to 6) (invention 7).

The third aspect of the present invention provides an adhesive sheet having an adhesive layer (invention 8) formed from the adhesive (invention 7).

In the above invention (invention 8), it is preferable that: the adhesive sheet comprises two release sheets, and the adhesive layer is sandwiched between the release sheets so as to be in contact with release surfaces of the two release sheets (invention 9).

Fourth, the present invention provides a display device including: a first display structural member having a step at least on a surface of the bonded side; a second display structural member; and an adhesive layer for bonding the first display structural member and the second display structural member to each other, wherein the first display structural member and/or the second display structural member has an electrode at least on a surface on a side to be bonded, and the adhesive layer is an adhesive layer (invention 10) of the adhesive sheet (inventions 8 and 9).

Effects of the invention

According to the adhesive composition, the adhesive sheet and the display, migration can be effectively prevented and suppressed.

Drawings

Fig. 1 is a sectional view of an adhesive sheet according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view showing one configuration example of the touch panel.

Fig. 3 is a reference image of evaluation criteria in the evaluation of the migration prevention effect of test example 3.

Detailed Description

Hereinafter, embodiments of the present invention will be described.

[ adhesive composition ]

The adhesive composition according to the present embodiment (hereinafter, may be referred to as "adhesive composition P") is an adhesive composition for bonding a first display structural member and a second display structural member having a step difference at least on a surface to be bonded (the first display structural member and/or the second display structural member having an electrode at least on the surface to be bonded), and contains a (meth) acrylate polymer (a) and a silane coupling agent (B) having a mercapto group, and preferably further contains a crosslinking agent (C). In the present specification, "(meth) acrylate" refers to both acrylate and methacrylate. Other similar terms are also the same. Further, the term "copolymer" is also included in the term "polymer". The display and the display structural member will be described later.

When the adhesive composition P according to the present embodiment contains the silane coupling agent (B) having a mercapto group, the adhesive obtained from the adhesive composition P can prevent and suppress electrode dissolution at the positive electrode and dendrite formation at the negative electrode when the adhesive comes into contact with the electrode. That is, migration on the electrode can be effectively prevented and suppressed (this effect is sometimes referred to as "migration prevention effect"). Thus, even when the adhesive is in contact with an electrode having a miniaturized and narrow pitch, for example, disconnection and short circuit of the electrode can be prevented. In particular, when the electrode is an electrode of a touch panel, driving failure of the touch panel due to disconnection or short circuit of the electrode can be prevented.

Here, examples of the electrode include: metal electrodes (including mesh-shaped and grid-shaped metal electrodes) formed of copper, silver, or the like, transparent conductive films (including patterned transparent conductive films) formed of tin-doped indium oxide (ITO), or the like, and the like. Among the electrodes, a metal electrode containing an unoxidized metal as a main component, specifically, a metal electrode made of copper or silver is preferable. Although the non-oxidized metal has a higher ionization tendency than a metal oxide such as ITO, the adhesive obtained from the adhesive composition P according to the present embodiment can effectively prevent disconnection and short circuit of the electrode even in such a case.

Further, the adhesive layer formed from the adhesive obtained from the adhesive composition P containing the silane coupling agent (B) having a mercapto group is a layer having high adhesion to a display structural member and excellent step-following properties because a component derived from the silane coupling agent (B) having a mercapto group is present at the interface with the display structural member as an adherend. Specifically, even when the adhesive layer is attached to a display structural member having a step and exposed to a high-temperature and high-humidity condition for a predetermined time (for example, 72 hours at 85 ℃ and 85% RH), the generation of bubbles, floating, peeling, and the like in the vicinity of the step can be suppressed (excellent step followability under high-temperature and high-humidity conditions). This suppresses the reflection loss of light near the step difference, and can maintain the image quality of the display device well.

(1) (meth) acrylate ester Polymer (A)

The (meth) acrylate polymer (A) can exhibit good adhesion by containing an alkyl (meth) acrylate having 1 to 20 carbon atoms in the alkyl group as a monomer unit constituting the polymer. From this viewpoint, the (meth) acrylic acid ester polymer (a) preferably contains, as a monomer unit constituting the polymer, an alkyl (meth) acrylate having 1 to 20 carbon atoms which contains an alkyl group in an amount of 50 mass% or more, particularly preferably 60 mass% or more, and more preferably 70 mass% or more. When the alkyl (meth) acrylate is contained in an amount of 50% by mass or more, the (meth) acrylate polymer (a) can exhibit appropriate tackiness. The (meth) acrylic acid ester polymer (a) preferably contains 97% by mass or less, particularly preferably 90% by mass or less, and further preferably 85% by mass or less of the alkyl (meth) acrylate as a monomer unit constituting the polymer, in terms of the above-mentioned limit. By containing 97% by mass or less of the above-mentioned alkyl (meth) acrylate, other monomer components can be introduced into the (meth) acrylate polymer (a) in an appropriate amount.

Examples of the alkyl (meth) acrylate in which the alkyl group has 1 to 20 carbon atoms include: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, and the like, and among them, alkyl (meth) acrylates having 4 to 8 carbon atoms containing an alkyl group are preferable from the viewpoint of further improving the adhesiveness. These may be used alone or in combination of two or more. The alkyl group in the alkyl (meth) acrylate in which the alkyl group has 1 to 20 carbon atoms is a linear, branched or cyclic alkyl group.

Further, as the alkyl (meth) acrylate in which the alkyl group has 1 to 20 carbon atoms, it is preferable to use a hard monomer having a glass transition temperature (Tg) of more than 0 ℃ (preferably 70 ℃ or higher) as a homopolymer and a soft monomer having a glass transition temperature (Tg) of 0 ℃ or lower as a homopolymer in combination. This is because the soft monomer can maintain adhesiveness and flexibility, and the hard monomer can increase cohesive force, thereby further improving step following properties on the display panel (touch panel).

The mass ratio of the hard monomer to the soft monomer is preferably 5:95 to 40:60, and particularly preferably 20:80 to 30: 70.

Examples of the hard monomer include: methyl acrylate (Tg10 ℃ C.), methyl methacrylate (Tg105 ℃ C.), isobornyl acrylate (Tg94 ℃ C.), isobornyl methacrylate (Tg180 ℃ C.), adamantyl acrylate (Tg115 ℃ C.), adamantyl methacrylate (Tg141 ℃ C.), etc. These may be used alone or in combination of two or more.

Among the above hard monomers, methyl acrylate, methyl methacrylate and isobornyl acrylate are preferable from the viewpoint of preventing adverse effects on other properties such as tackiness and transparency and further exhibiting the performance of the hard monomers. In view of the tackiness, methyl acrylate and methyl methacrylate are more preferable, and methyl methacrylate is particularly preferable.

The soft monomer preferably includes: an alkyl acrylate having a linear or branched alkyl group having 2 to 12 carbon atoms. For example, 2-ethylhexyl acrylate (Tg-70 ℃ C.), n-butyl acrylate (Tg-54 ℃ C.) and the like are preferable. These may be used alone or in combination of two or more.

The (meth) acrylate polymer (a) preferably contains a reactive functional group-containing monomer as a monomer unit constituting the polymer. The reactive functional group derived from the reactive functional group-containing monomer reacts with the crosslinking agent (C) described later to form a crosslinked structure (three-dimensional network structure), and an adhesive having a desired cohesive force can be obtained.

As the reactive functional group-containing monomer contained in the (meth) acrylate polymer (a) as a monomer unit constituting the polymer, preferable are: a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxyl group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), and the like. Among these, a hydroxyl group-containing monomer which is excellent in reactivity with the crosslinking agent (C) and resistance to wet-heat whitening and has little adverse effect on the electrode is particularly preferable.

Examples of the hydroxyl group-containing monomer include: hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. Among them, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferable from the viewpoint of reactivity of the hydroxyl group in the obtained (meth) acrylate polymer (a) with the crosslinking agent (C) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

Examples of the carboxyl group-containing monomer include: ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferable because of reactivity of the carboxyl group in the obtained (meth) acrylate polymer (a) with the crosslinking agent (C) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

Examples of the amino group-containing monomer include: aminoethyl (meth) acrylate, n-butylaminoethyl (meth) acrylate, and the like. These may be used alone or in combination of two or more.

The lower limit of the content of the (meth) acrylate polymer (a) is preferably 3% by mass or more, particularly preferably 10% by mass or more, and further preferably 15% by mass or more of a hydroxyl group-containing monomer as a monomer unit constituting the polymer. In addition, the (meth) acrylate polymer (a) preferably contains 35% by mass or less, particularly preferably contains 30% by mass or less, and further preferably contains 25% by mass or less of a hydroxyl group-containing monomer as a monomer unit constituting the polymer, in terms of the above-mentioned limit value. When the (meth) acrylate polymer (a) contains the hydroxyl group-containing monomer as a monomer unit in the above-mentioned amount, a predetermined amount of hydroxyl groups remain in the obtained adhesive. When a hydroxyl group is a hydrophilic group and such a hydrophilic group is present in a predetermined amount in the adhesive, the adhesive has good compatibility with moisture impregnated into the adhesive under high-temperature and high-humidity conditions even when the adhesive is left under high-temperature and high-humidity conditions, and as a result, whitening of the adhesive when the adhesive is returned to normal temperature and normal humidity (excellent resistance to moist-heat whitening) can be suppressed.

The degree of whitening suppression is preferably 1.0% or less, particularly preferably 0.9% or less, and more preferably 0.8% or less, of the haze value (measured according to JIS K7136: 2000) of the adhesive layer when the adhesive layer is returned to normal temperature and normal humidity after being subjected to high temperature and high humidity conditions. In addition, the adhesive layer preferably has a haze value as described above also in a normal state. When the haze value is 1.0% or less, the transparency is extremely high, and the coating composition is suitably used for optical applications.

However, if the hydrophilic group is present in a predetermined amount in the adhesive as described above, the adhesive easily absorbs water, and the adhesive easily migrates to the electrode in contact with the adhesive. However, the adhesive composition P according to the present embodiment contains the silane coupling agent (B) having a mercapto group, and thus migration of the adhesive composition P to an electrode in contact with the electrode can be effectively prevented and suppressed.

The (meth) acrylate polymer (a) preferably does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer, but is allowed to contain a predetermined amount. This is because, although there is a general concern about migration of the target member because the carboxyl group is an acid component, the adhesive according to the present embodiment can exhibit a migration prevention effect even if the carboxyl group is present, by being obtained from the adhesive composition P containing the silane coupling agent (B) having a mercapto group. Specifically, the (meth) acrylate polymer (a) is allowed to contain a carboxyl group-containing monomer as a monomer unit in an amount of 5% by mass or less, preferably 2% by mass or less.

The (meth) acrylate polymer (a) may contain other monomers as a monomer unit constituting the polymer, if necessary. As the other monomer, a monomer having no reactive functional group is preferable in order not to hinder the action of the reactive functional group-containing monomer. Examples of the other monomer include: alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate; (meth) acrylic esters having a non-crosslinkable tertiary amino group such as N, N-dimethylaminoethyl (meth) acrylate, N-dimethylaminopropyl (meth) acrylate, and (meth) acryloylmorpholine; (meth) acrylamide, dimethylacrylamide, vinyl acetate, styrene, and the like. These may be used alone or in combination of two or more.

The polymerization form of the (meth) acrylate polymer (a) may be a random copolymer or a block copolymer.

The lower limit of the weight average molecular weight of the (meth) acrylate polymer (a) is preferably 20 ten thousand or more, particularly preferably 30 ten thousand or more, and more preferably 40 ten thousand or more. When the lower limit of the weight average molecular weight of the (meth) acrylate polymer (a) is not less than the above, the adhesive is excellent in step following property under high temperature and high humidity conditions. The weight average molecular weight in the present specification is a value in terms of standard polystyrene measured by a Gel Permeation Chromatography (GPC) method.

The upper limit of the weight average molecular weight of the (meth) acrylate polymer (a) is preferably 100 ten thousand or less, particularly preferably 90 ten thousand or less, and more preferably 70 ten thousand or less. When the upper limit of the weight average molecular weight of the (meth) acrylate polymer (a) is not more than the above, the step following property at the time of adhesive application is excellent.

In the adhesive composition P, one kind of the (meth) acrylate polymer (a) may be used alone, or two or more kinds may be used in combination.

(2) Silane coupling agent (B) having mercapto group

The silane coupling agent (B) having a mercapto group is composed of an organosilicon compound having at least 1 mercapto group and at least 1 alkoxysilyl group in the molecule. Considering the use of the adhesive obtained, the silane coupling agent (B) having a mercapto group is preferably a silane coupling agent having light transmittance, for example, substantially transparent.

Specific examples of the silane coupling agent (B) having a mercapto group include: low molecular type silane coupling agents containing mercapto groups such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane and the like; and mercapto group-containing oligomer-type silane coupling agents such as cocondensates of mercapto group-containing silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. Among these, a mercapto group-containing oligomer-type silane coupling agent having a further excellent migration prevention effect and good workability is preferable, a cocondensate of a mercapto group-containing silane compound and an alkyl group-containing silane compound is particularly preferable, and a cocondensate of 3-mercaptopropyltrimethoxysilane and methyltriethoxysilane is even more preferable. These may be used alone or in combination of two or more.

The lower limit of the mercapto equivalent of the organosilicon compound constituting the mercapto group-containing silane coupling agent (B) is preferably 100 g/mole or more, particularly preferably 120 g/mole or more, and more preferably 150 g/mole or more. By setting the lower limit value as described above, the difference in polarity from the (meth) acrylate polymer (a) can be set within an appropriate range, and the dispersibility of the silane coupling agent (B) in the adhesive can be made appropriate.

The upper limit of the mercapto equivalent of the organosilicon compound constituting the mercapto group-containing silane coupling agent (B) is preferably 1000 g/mole or less, particularly preferably 800 g/mole or less, and more preferably 500 g/mole or less. By setting the upper limit value as described above, deterioration of optical characteristics due to phase separation from the (meth) acrylate polymer (a) can be prevented.

The content of the silane coupling agent (B) having a mercapto group in the adhesive composition P is preferably 0.01 parts by mass or more, particularly preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more, in terms of the lower limit value, relative to 100 parts by mass of the (meth) acrylate polymer (a). The upper limit is preferably 5 parts by mass or less, particularly preferably 1.5 parts by mass or less, and further preferably 1.0 part by mass or less. When the content of the silane coupling agent (B) having a mercapto group is in the above range, the migration prevention effect becomes more excellent.

The lower limit of the number of moles of mercapto groups (the amount of mercapto groups) in the silane coupling agent (B) per 100g of the (meth) acrylate polymer (a) is preferably 0.01mmol or more, particularly preferably 0.1mmol or more, and more preferably 0.2mmol or more. The upper limit of the number of moles is preferably 30mmol or less, particularly preferably 5mmol or less, and further preferably 1.5mmol or less. When the number of moles of the mercapto group of the silane coupling agent (B) relative to the number of moles of the (meth) acrylate polymer (a) is in the above range, the migration prevention effect can be further improved.

(3) Crosslinking agent (C)

The adhesive composition P preferably contains a crosslinking agent (C). The adhesive composition P contains the crosslinking agent (C) and forms a three-dimensional network structure by crosslinking the (meth) acrylate polymer (a), whereby the cohesive force of the obtained adhesive can be improved and the step following property under high-temperature and high-humidity conditions can be further improved.

The crosslinking agent (C) may be reacted with the reactive group of the (meth) acrylate polymer (a), and examples thereof include: isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, ammonium salt crosslinking agents, and the like. When the (meth) acrylate polymer (a) contains a hydroxyl group-containing monomer as a monomer unit constituting the polymer, an isocyanate-based crosslinking agent excellent in reactivity with the hydroxyl group is preferably used. The crosslinking agent (C) may be used singly or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include: aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and biuret or isocyanurate thereof, and further, adducts thereof with a low-molecular active hydrogen-containing compound such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane or castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanates are preferable from the viewpoint of reactivity with hydroxyl groups, and trimethylolpropane-modified tolylene diisocyanate is particularly preferable.

The content of the crosslinking agent (C) in the adhesive composition P is preferably 0.001 parts by mass or more, particularly preferably 0.01 parts by mass or more, and more preferably 0.02 parts by mass or more, in terms of the lower limit, relative to 100 parts by mass of the (meth) acrylate polymer (a). The above limit is preferably 10 parts by mass or less, particularly preferably 5 parts by mass or less, and further preferably 1 part by mass or less.

When the content of the crosslinking agent (C) is in the above range, the cohesive force of the obtained adhesive is good, and the step following property of the adhesive, particularly the step following property under high temperature and high humidity conditions, is further improved.

(4) Various additives

Various additives generally used in acrylic adhesives, for example, antistatic agents, tackifiers, antioxidants, ultraviolet absorbers, light stabilizers, softeners, fillers, refractive index adjusters, and the like may be added to the adhesive composition P as needed. In addition, other silane coupling agents may be added in addition to the above silane coupling agent (B) having a mercapto group. However, the rust inhibitor, particularly the benzotriazole-based rust inhibitor, preferably does not have to be added because it has an effect of inhibiting crosslinking of the adhesive composition P.

The adhesive composition P represents a mixture of various components remaining in the adhesive layer as they are or in a reacted state, and components removed in a drying step or the like, and for example, a polymerization solvent and a dilution solvent described below are not included in the adhesive composition P.

(5) Preparation of adhesive composition

The adhesive composition P can be prepared by: the (meth) acrylate polymer (A) is prepared, and the resulting (meth) acrylate polymer (A) is mixed with the silane coupling agent (B) having a mercapto group, while adding the crosslinking agent (C) and additives as needed.

The (meth) acrylate polymer (a) can be prepared by polymerizing a mixture of monomer units constituting the polymer by a general radical polymerization method. The polymerization of the (meth) acrylate polymer (a) may be carried out by a solution polymerization method or the like using a polymerization initiator as needed. Examples of the polymerization solvent include: ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like, and two or more thereof may be used simultaneously.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used simultaneously. Examples of the azo compound include 2,2 ' -azobisisobutyronitrile, 2 ' -azobis (2-methylbutyronitrile), 1 ' -azobis (cyclohexane 1-carbonitrile), 2 ' -azobis (2, 4-dimethylvaleronitrile), 2 ' -azobis (2, 4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2 ' -azobis (2-methylpropionate), 4 ' -azobis (4-cyanovaleric acid), 2 ' -azobis (2-hydroxymethylpropionitrile), and 2,2 ' -azobis [2- (2-imidazolin-2-yl) propane ].

Examples of the organic peroxide include: benzoyl peroxide, tert-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, bis (2-ethoxyethyl) peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, 3,5, 5-trimethylhexanoyl peroxide, dipropionyl peroxide, diacetyl peroxide, and the like.

In the polymerization step, the weight average molecular weight of the obtained polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

After the (meth) acrylate polymer (a) is obtained, a silane coupling agent (B) having a mercapto group and, if necessary, a crosslinking agent (C), an additive and a diluting solvent are added to a solution of the (meth) acrylate polymer (a) and sufficiently mixed to obtain an adhesive composition P (coating solution) diluted with a solvent.

Examples of the diluting solvent include aliphatic hydrocarbons such as hexane, heptane and cyclohexane; aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and dichloroethane; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve solvents such as ethyl cellosolve.

The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as the coating solution can be applied, and may be appropriately selected according to the situation. For example, the adhesive composition P is diluted so that the concentration thereof is 10 to 40 mass%. In addition, when obtaining the coating solution, the addition of the diluting solvent or the like is not essential, and the diluting solvent may not be added as long as the adhesive composition P has a viscosity capable of being coated or the like. In this case, the adhesive composition P is a coating solution in which the polymerization solvent of the (meth) acrylate polymer (a) is directly used as a dilution solvent.

[ Adhesives ]

The adhesive according to the present embodiment is obtained by crosslinking the adhesive composition P. The crosslinking of the adhesive composition P can be carried out by heat treatment. Further, the drying treatment when evaporating the diluent solvent or the like of the applied adhesive composition P may also be used as the heating treatment.

When the heat treatment is performed, the heating temperature is preferably 50 to 150 ℃, and particularly preferably 70 to 120 ℃. The heating time is preferably 30 seconds to 10 minutes, and particularly preferably 50 seconds to 2 minutes. After the heat treatment, a curing period of about 1 to 2 weeks may be set at normal temperature (e.g., 23 ℃ C., 50% RH) as required. When the curing period is required, an adhesive layer is formed after the curing period; when the aging period is not required, an adhesive layer is formed after the heat treatment is completed.

The lower limit of the gel fraction of the pressure-sensitive adhesive according to the present embodiment is preferably 30% or more, particularly preferably 40% or more, and more preferably 50% or more. When the lower limit of the gel fraction of the adhesive is not less than the above, the adhesive has high cohesive force and excellent step following property under high-temperature and high-humidity conditions. The upper limit of the gel fraction is preferably 90% or less, particularly preferably 85% or less, and more preferably 80% or less. When the upper limit of the gel fraction of the adhesive is the above-mentioned or less, the adhesive does not become too hard, and the step following property at the time of sticking is excellent. Here, the method of measuring the gel fraction of the adhesive is shown in the test examples described later.

[ adhesive sheet ]

As shown in fig. 1, the adhesive sheet 1 according to the present embodiment includes: two

release sheets

12a, 12 b; and an adhesive layer 11 sandwiched between the two

release sheets

12a, 12b so as to be in contact with the release surfaces of the two

release sheets

12a, 12 b. However, the

release sheets

12a and 12b are not essential components of the adhesive sheet 1, and are peeled and removed when the adhesive sheet 1 is used. The release surface of the release sheet in the present specification means a surface having releasability in the release sheet, and includes any of a surface subjected to a release treatment and a surface showing releasability even if the release treatment is not performed.

(1) Adhesive layer

The adhesive layer 11 is composed of the adhesive described above. The lower limit of the thickness (value measured according to JI S K7130) of the adhesive layer 11 is preferably 10 μm or more, particularly preferably 25 μm or more, and more preferably 50 μm or more. When the lower limit of the thickness of the adhesive agent layer 11 is set to the above value, excellent adhesive force can be sufficiently exhibited. The upper limit of the thickness of the adhesive layer 11 is preferably 300 μm or less, particularly preferably 250 μm or less, and more preferably 100 μm or less. When the upper limit of the thickness of the adhesive agent layer 11 is set to the above value or less, the processability becomes good. The adhesive layer 11 may be formed as a single layer or may be formed by stacking a plurality of layers.

(2) Release sheet

The

release sheets

12a and 12b are not particularly limited, and a known plastic film may be used. For example, a polyethylene film, a polypropylene film, a polybutylene film, a polybutadiene film, a polymethylpentene film, a polyvinyl chloride film, a vinyl chloride copolymer film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polybutylene terephthalate film, a polyurethane film, an ethylene vinyl acetate film, an ionomer resin film, an ethylene- (meth) acrylic acid copolymer film, an ethylene- (meth) acrylate copolymer film, a polystyrene film, a polycarbonate film, a polyimide film, a fluororesin film, or the like may be used. In addition, crosslinked films thereof may also be used. Further, a laminated film thereof may be used.

The release surfaces (particularly, the surfaces in contact with the adhesive agent layer 11) of the

release sheets

12a and 12b are preferably subjected to a release treatment. Examples of the release agent used in the release treatment include alkyd based, silicone based, fluorine based, unsaturated polyester based, polyolefin based, and wax based release agents. Of the

release sheets

12a and 12b, one release sheet is preferably a heavy release type release sheet having a large release force, and the other release sheet is preferably a light release type release sheet having a small release force.

The thickness of the

release sheets

12a and 12b is not particularly limited, but is usually about 20 to 150 μm.

(3) Production of adhesive sheet

As an example of the production of the adhesive sheet 1, a coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and after the coating layer is formed by heat treatment to crosslink the adhesive composition P, the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer. When the curing period is required, the coating layer becomes the adhesive layer 11 by the lapse of the curing period; when the curing period is not required, the coating layer directly becomes the adhesive layer 11. Thus, the adhesive sheet 1 was obtained. The heat treatment and the aging conditions were as described above.

As another production example of the adhesive sheet 1, a coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a, and heat treatment is performed to crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 12a with a coating layer. Further, the coating solution of the adhesive composition P is applied to the release surface of the other release sheet 12b, and heat treatment is performed to crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 12b with a coating layer. Next, the coated release sheet 12a and the coated release sheet 12b are bonded to each other so that the two coated layers are in contact with each other. When the curing period is required, the laminated coating layer becomes the adhesive layer 11 by the lapse of the curing period; when the aging period is not required, the laminated coating layer directly becomes the adhesive layer 11. Thus, the adhesive sheet 1 was obtained. According to this production example, even when the adhesive agent layer 11 is thick, stable production can be performed.

Examples of the method for applying the coating liquid of the adhesive composition P include bar coating, doctor coating, roll coating, blade coating, die coating, and gravure coating.

(4) Adhesive force

The lower limit of the adhesive force of the adhesive sheet 1 according to the present embodiment to soda-lime glass is preferably 5N/25mm or more, particularly preferably 8N/25mm or more, and more preferably 10N/25mm or more. When the lower limit of the adhesive force of the adhesive sheet 1 is not less than the above, the step following property under high temperature and high humidity conditions is excellent. On the other hand, the upper limit of the above-mentioned adhesive force is not particularly limited, but is preferably 50N/25mm or less, particularly preferably 30N/25mm or less, in consideration of easiness of peeling the

release sheets

12a and 12b from the adhesive layer 11 in use. Further, considering the reworkability, it is preferably 26N/25mm or less. In this case, even if a bonding error occurs, the display structural member can be easily reused.

Here, the adhesive force in the present specification means an adhesive force obtained by substantially adhering a rubber composition according to JIS Z0237: 2009, the adhesive force measured by the 180 degree peel method is a value obtained by attaching a measurement sample to an adherend under pressure of 0.5MPa and 50 ℃ for 20 minutes, then leaving the sample under normal pressure, 23 ℃ and 50% RH for 24 hours, and then measuring the adhesive force at a peel rate of 300 mm/minute, wherein the measurement sample has a width of 25mm and a length of 100 mm.

[ display ]

The display according to the present embodiment includes: a first display structural member having a step at least on a surface of the bonded side; a second display structural member; and an adhesive layer for bonding the first display structural member and the second display structural member to each other. The adhesive layer is formed of the adhesive according to the present embodiment. Here, the first display structural member and/or the second display structural member has an electrode on at least a surface of the bonded side (adhesive layer side). Preferably, the second display structural member has an electrode on at least the surface on the bonded side.

Examples of the display include: a Liquid Crystal (LCD) display, a Light Emitting Diode (LED) display, an organic electroluminescence (organic EL) display, electronic paper, or the like, and may also be a touch panel. The display may be a member constituting a part of them.

The first display structural member is preferably a glass plate, a plastic plate, or the like, or a protective panel composed of a laminate or the like including these plates. The first display structural member preferably has a step on the surface on the adhesive layer side, specifically, a step formed by a printed layer. The printed layer is generally formed in a frame shape.

The glass plate is not particularly limited, and examples thereof include chemically strengthened glass, alkali-free glass, quartz glass, soda-lime glass, barium-strontium-containing glass, aluminosilicate glass, lead glass, borosilicate glass, and barium borosilicate glass. The thickness of the glass plate is not particularly limited, but is usually 0.1 to 5mm, preferably 0.2 to 2 mm.

The plastic plate is not particularly limited, and examples thereof include an acrylic plate and a polycarbonate plate. The thickness of the plastic sheet is not particularly limited, but is usually 0.2 to 5mm, preferably 0.4 to 3 mm.

Further, various functional layers (an electrode layer, a silica layer, a hard coat layer, an antiglare layer, etc.) may be provided on one surface or both surfaces of the glass plate or the plastic plate, and an optical member may be laminated.

The material constituting the printing layer is not particularly limited, and known materials for printing can be used. The lower limit of the thickness of the printed layer, that is, the height of the step is preferably 3 μm or more, more preferably 5 μm or more, particularly preferably 7 μm or more, and most preferably 10 μm or more. By setting the lower limit value to the above value, it is possible to sufficiently ensure concealment that the circuit or the like cannot be seen from the viewer side. The upper limit is preferably 50 μm or less, more preferably 35 μm or less, particularly preferably 25 μm or less, and further preferably 20 μm or less. By setting the upper limit to the above value or less, deterioration in step following property of the adhesive layer to the print layer can be prevented.

The second display structural member is preferably an optical member, a display module (for example, a Liquid Crystal (LCD) module, a Light Emitting Diode (LED) module, an organic electroluminescence (organic EL) module, or the like), an optical member that is a part of the display module, or a laminate including the display module to be bonded to the first display structural member, and has an electrode on at least a surface on the adhesive layer side.

Examples of the optical member include: electrode films, transparent conductive films, film sensors, metal nanowire films, wire grid polarizing films (wire grid polarizing films), and the like.

Examples of the electrode include: a metal electrode (including a mesh-shaped or grid-shaped metal electrode) formed of copper, silver, or the like, a transparent conductive film (including a patterned transparent conductive film) formed of tin-doped indium oxide (ITO), or the like. As described above, among the electrodes, a metal electrode containing an unoxidized metal as a main component, specifically, a metal electrode made of copper or silver is preferable.

Fig. 2 shows a capacitance type touch panel 2 as an example of the display according to the present embodiment. The touch panel 2 is configured by including: a display module 3; a first film sensor 5a laminated thereon via an adhesive layer 4; a second film sensor 5b laminated thereon via a first adhesive layer 11; and a covering material 6 laminated thereon via a second adhesive layer 11. Since the printed layer 7 is formed on the surface of the covering material 6 on the second adhesive layer 11 side, a step is present depending on the presence or absence of the printed layer 7. In the present embodiment, the cover member 6 corresponds to the first display component, and the second film sensor 5b corresponds to the second display component.

In the touch panel 2, at least the second adhesive layer 11 is the adhesive layer 11 of the adhesive sheet 1, and considering the migration prevention effect, both the first adhesive layer 11 and the second adhesive layer 11 are preferably the adhesive layer 11 of the adhesive sheet 1. When the first adhesive layer 11 is not the adhesive layer 11 of the adhesive sheet 1, examples of the adhesive constituting the first adhesive layer 11 include acrylic adhesives, rubber adhesives, silicone adhesives, urethane adhesives, polyester adhesives, and polyvinyl ether adhesives, and among them, acrylic adhesives are preferable.

The adhesive layer 4 may be formed of the adhesive layer 11 of the adhesive sheet 1, or may be formed of another adhesive or adhesive sheet. In the latter case, as the adhesive constituting the adhesive layer 4, an acrylic adhesive, a rubber adhesive, a silicone adhesive, a urethane adhesive, a polyester adhesive, a polyvinyl ether adhesive, and the like can be mentioned, and among them, an acrylic adhesive is preferable.

The first film sensor 5a and the second film sensor 5b in the present embodiment each include a base film 51 and an electrode 52 formed on the base film 51. The base film 51 is not particularly limited, and for example, a polyethylene terephthalate film, an acrylic film, a polycarbonate film, or the like can be used.

The electrode 52 is composed of, for example, a metal electrode made of copper, silver, or the like, and a patterned transparent conductive film made of tin-doped indium oxide (ITO) or the like.

The electrodes 52 of the first film sensor 5a and the electrodes 52 of the second film sensor 5b usually form a circuit pattern in the X-axis direction, and the other forms a circuit pattern in the Y-axis direction.

The electrode 52 of the second film sensor 5b in the present embodiment is located above the second film sensor 5b in fig. 2. On the other hand, the electrode 52 of the first film sensor 5a is located above the first film sensor 5a in fig. 2, but is not limited thereto, and may be located below the first film sensor 5 a.

An example of the method for manufacturing the touch panel 2 will be described below.

First adhesive sheet 1 and second adhesive sheet 1 are prepared as adhesive sheet 1. One release sheet 12a is peeled off from the first adhesive sheet 1, and the exposed adhesive layer 11 (first adhesive layer) is bonded to the first film sensor 5a so as to be in contact with the electrode 52 of the first film sensor 5 a. One release sheet 12a is peeled off from the second adhesive sheet 1, and the exposed adhesive layer 11 (second adhesive layer 11) is bonded to the second film sensor 5b so as to be in contact with the electrode 52 of the second film sensor 5 b.

Then, the other release sheet 12b of the first adhesive sheets is peeled off, and the exposed first adhesive layer 11 and the surface of the second film sensor 5b opposite to the side on which the second adhesive layer 11 is laminated (the exposed surface of the base film 51 of the second film sensor 5 b) are bonded so as to be in contact with each other. Thus, a laminate in which the release sheet 12b, the second adhesive layer 11, the second film sensor 5b, the first adhesive layer 11, and the first film sensor 5a are laminated in this order was obtained.

Next, the adhesive layer 4 provided on the release sheet is bonded to the surface of the laminate on the first film sensor 5a side (exposed surface of the base film 51 of the first film sensor 5 a). Next, the release sheet 12b is peeled off from the laminate, and the covering material 6 is bonded to the exposed second adhesive layer 11 so that the printed layer 7 side of the covering material 6 is in contact with the second adhesive layer 11. In this case, the second adhesive layer 11 is excellent in step following property at the time of application, and therefore, generation of a gap or floating in the vicinity of the step formed by the printed layer 7 can be suppressed. By the above bonding, a structure in which the cover material 6, the second adhesive layer 11, the second film sensor 5b, the first adhesive layer 11, the first film sensor 5a, the adhesive layer 4, and the release sheet are stacked in this order can be obtained.

Finally, the release sheet is peeled off from the structure, and the structure is attached to the display module 3 so that the exposed adhesive layer 4 comes into contact with the display module 3. Thereby, the touch panel 2 shown in fig. 2 is manufactured.

Even when the touch panel 2 is placed under high-temperature and high-humidity conditions and a voltage is applied to the electrode 52 in this state, migration of the electrode 52 can be effectively suppressed by including a component derived from the silane coupling agent (B) having a mercapto group in the adhesive layer 11 in contact with the electrode 52. This can prevent a drive failure of the touch panel 2 due to disconnection or short-circuit of the electrodes 52.

Further, since the adhesive layer 11 is excellent in step following property even under high temperature and high humidity conditions, even when the touch panel 2 is exposed to high temperature and high humidity conditions for a predetermined time (for example, 72 hours at 85 ℃ and 85% RH), the occurrence of bubbles, floating, falling, and the like in the vicinity of the step formed by the printed layer 7 can be effectively suppressed.

The embodiments described above are described for the convenience of understanding the present invention, and are not described for the purpose of limiting the present invention. Therefore, the elements disclosed in the above embodiments are intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, any of the

release sheets

12a and 12b in the adhesive sheet 1 may be omitted.

Examples

The present invention will be described in more detail with reference to examples and the like, but the scope of the present invention is not limited to these examples and the like.

[ example 1]

Preparation of (meth) acrylate copolymer

A (meth) acrylate polymer (A) was prepared by copolymerizing 60 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of methyl methacrylate, and 20 parts by mass of 2-hydroxyethyl acrylate. The molecular weight of the (meth) acrylate polymer (a) was measured by the method described later, and as a result, the weight average molecular weight (Mw) was 60 ten thousand.

2. Preparation of adhesive composition

100 parts by mass (a value converted into a solid content; the same shall apply hereinafter) of the (meth) acrylate polymer (A) obtained in the step 1, 0.05 part by mass of a co-condensate of 3-mercaptopropyltrimethoxysilane and methyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-41-1810", oligomer type, mercapto equivalent: 450 g/mol) as a silane coupling agent (B) having a mercapto group, and 0.23 part by mass of trimethylolpropane-modified toluene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., product name "Coronate L") as a crosslinking agent (C) were mixed, sufficiently stirred, and diluted with methyl ethyl ketone to obtain a coating solution of an adhesive composition having a solid content of 38 mass%.

Here, the blending amounts (values in terms of solid content) of the adhesive compositions when the (meth) acrylate polymer (a) is set to 100 parts by mass (values in terms of solid content) are shown in table 1. The details of the abbreviations and the like shown in table 1 are as follows.

[ (meth) acrylic ester Polymer (A) ]

2 EHA: 2-ethylhexyl acrylate

MMA: methacrylic acid methyl ester

HEA: 2-Hydroxyethyl acrylate

[ silane coupling agent (B) having mercapto group ]

X-41-1810: cocondensate of 3-mercaptopropyltrimethoxysilane and methyltriethoxysilane (manufactured by Shin-Etsu chemical Co., Ltd., trade name "X-41-1810", oligomer type, mercapto equivalent: 450 g/mole)

KBM-803: 3-mercaptopropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., product name "KBM-803" by Ltd., low-molecular type, mercapto equivalent: 196.4 g/mol)

[ other silane coupling agents ]

KBM-403: 3-glycidoxypropyltrimethoxysilane (Shin-Etsu Silicone Co., Ltd., product name "KBM-403", low-molecular type)

KBE-9007: 3-isocyanatopropyltriethoxysilane (Shin-Etsu Silicone Co., Ltd., product name "KBE-9007", Low molecular type)

3. Production of adhesive sheet

A coating solution of the adhesive composition obtained in step 2 was applied to a release-treated surface of a heavy release type release sheet (manufactured by Lintec Corporation, trade name "SP-PET 382150", thickness: 38 μm) obtained by subjecting one surface of a polyethylene terephthalate film to a release treatment with a silicone-based release agent, and then heated at 90 ℃ for 1 minute to form a coating layer (thickness: 25 μm). Similarly, the coating solution of the adhesive composition obtained in step 2 was applied to the release-treated surface of a light release type release sheet (product name "SP-PET 382120", manufactured by L intec Corporation) having one surface of a polyethylene terephthalate film subjected to a release treatment with a silicone-based release agent, and then heated at 90 ℃ for 1 minute to form a coating layer (thickness: 25 μm).

Next, the coated layer-provided heavy release sheet obtained in the above was laminated to the coated layer-provided light release sheet obtained in the above, with the two coating layers in contact with each other, and the resultant was aged at 23 ℃ and 50% RH for 7 days, thereby producing an adhesive sheet having a structure of a heavy release sheet/adhesive layer (thickness: 50 μm)/light release sheet.

Examples 2 to 10 and comparative examples 1 to 10

Adhesive sheets were produced in the same manner as in example 1, except that the kinds and proportions of the silane coupling agents (silane coupling agent (B) having a mercapto group and other silane coupling agents) and the proportion of the crosslinking agent (C) were changed as shown in table 1. In comparative examples 7 to 10, N-bis (2-ethylhexyl) - (4 or 5) -methyl-1H-benzotriazole-1-methanamine (product name "IRGMET 39" manufactured by BASF) was used as a rust inhibitor and blended in the adhesive composition in the proportions shown in table 1.

Here, the weight average molecular weight (Mw) is a weight average molecular weight in terms of polystyrene measured by Gel Permeation Chromatography (GPC) under the following conditions (GPC measurement).

< measurement Condition >

GPC measurement apparatus: HLC-8020 manufactured by TOSOH CORPORATION

GPC column (passage in the following order): TOSOH CORPORATION, Inc

TSK guard column HXL-H

TSK gel GMHXL (× 2)

TSK gel G2000HXL

Determination of the solvent: tetrahydrofuran (THF)

Measurement temperature: 40 deg.C

[ test example 1] (measurement of gel fraction)

The adhesive sheets obtained in examples and comparative examples were cut into 80mm × 80mm sizes, the adhesive layers were wrapped in a polyester net (mesh size 200), the masses thereof were weighed by a precision balance, and the masses of the individual nets were subtracted to calculate the masses of the adhesives themselves. The mass at this time was set to M1.

Subsequently, the adhesive wrapped in the polyester net was immersed in ethyl acetate at room temperature (23 ℃ C.) for 24 hours. Thereafter, the adhesive was taken out, and air-dried at a temperature of 23 ℃ and a relative humidity of 50% for 24 hours, and further dried in an oven at 80 ℃ for 12 hours. After drying, the mass was weighed by a precision balance, and the mass of the web alone was subtracted, thereby calculating the mass of the adhesive itself. The mass at this time was set to M2. The gel fraction (%) was expressed as (M2/M1). times.100. The results are shown in Table 2.

[ test example 2] (measurement of adhesive force)

The light release sheet was peeled from the pressure-sensitive adhesive sheets obtained in examples and comparative examples, and the exposed pressure-sensitive adhesive layer was bonded to an easy-adhesive layer of a polyethylene terephthalate (PET) film (TOYOBO co., ltd., product name "PET a 4300" having a thickness of 100 μm) having an easy-adhesive layer, to obtain a laminate of a heavy release sheet/a pressure-sensitive adhesive layer/a PET film. The laminate thus obtained was cut into a width of 25mm and a length of 100mm, and used as a sample.

The heavy-release type release Sheet was peeled from the sample at 23 ℃ and 50% RH, and the exposed adhesive layer was attached to soda-lime Glass (manufactured by Nippon Sheet Glass co., ltd.), followed by pressurization at 0.5MPa and 50 ℃ for 20 minutes using an autoclave manufactured by KURIHARA CORPORATION. After that, the sheet was left at 23 ℃ and 50% RH for 24 hours, and then the adhesion (N/25mm) was measured using a tensile tester (ORIENTEC Co., LTD., manufactured by TENSILON) under conditions of a peel speed of 300 mm/min and a peel angle of 180 degrees. Conditions other than those described herein were as follows according to JIS Z0237: 2009 was measured. The results are shown in Table 2.

[ test example 3] (evaluation of migration prevention Effect)

(1) Manufacture of circuit substrate

An etching resist pattern was printed by screen printing on the surface of a copper foil of a copper-clad laminate (NIKKAN INDUSTRIES co., ltd., product name "NIKAFLEX") in which a copper foil (thickness: 18 μm) and a polyethylene terephthalate film (thickness: 50 μm) were laminated. Thereafter, unnecessary copper foil is removed by etching, thereby forming a comb-shaped electrode. The line width of each electrode was 300 μm, and the gap between the electrodes was 50 μm.

(2) Evaluation of migration prevention Effect

The light release sheet was peeled from the pressure-sensitive adhesive sheets obtained in examples and comparative examples, and the exposed pressure-sensitive adhesive layer was bonded to an easy-adhesive layer of a polyethylene terephthalate (PET) film (TOYOBO co., ltd., product name "PET a 4300" having a thickness of 100 μm) having an easy-adhesive layer, to obtain a laminate of a heavy release sheet/a pressure-sensitive adhesive layer/a PET film. Next, the heavy-release type release sheet was peeled from the laminate, and the exposed adhesive layer was attached to the comb-shaped electrode to obtain a sample.

The sample was allowed to stand under the hot and humid conditions of 85 ℃ and 85% RH, and a voltage of 5V was applied between the electrodes in this state to perform a migration test. After 8 hours, 24 hours, and 48 hours from the start of the test, the comb-shaped electrode was observed with an optical microscope (magnification: 10 times), and the migration prevention effect was evaluated based on the evaluation criteria shown below. The results are shown in Table 2.

◎ dissolution of the electrode (positive electrode) and dendrite formation on the electrode (negative electrode) were not observed at all.

○ dissolution was observed only at the end of the electrode (positive electrode) and formation of dendrites on the electrode (negative electrode) was not observed.

X: dissolution of the electrode (positive electrode) and formation of dendrites on the electrode (negative electrode) were observed.

Fig. 3 shows a reference image of the evaluation criterion.

[ test example 4] (evaluation of step tracking ability)

(a) Preparation of evaluation sample

An ultraviolet curable ink (Teikoku Printing Inks mfg. co., ltd., product name "POS-911 ink") was screen-printed in a frame shape (outer shape: 90mm in length × 50mm in width, 5mm) on the surface of a glass plate (NSG Precision co., ltd., product name "Corning glass eagleexg", 90mm in length × 50mm in width × 0.5mm in thickness) so as to be applied to any one of 5 μm, 10 μm, and 15 μm in thickness. Then, ultraviolet rays (80W/cm) were irradiated²2 metal halide lamps having a lamp height of 15cm and a conveyor speed of 10 to 15 m/min), the printed ultraviolet curable ink was cured, and a printed ultraviolet curable ink having a step (height of step: any one of 5 μm, 10 μm and 15 μm).

The light-release type release sheet was peeled from the adhesive sheets obtained in examples and comparative examples, and the exposed adhesive layer was bonded to an easy-adhesion layer of a polyethylene terephthalate film (PET a4300, thickness: 100 μm, manufactured by toyobo co., ltd.) having an easy-adhesion layer. Subsequently, the heavy-release sheet is peeled off to expose the surface of the adhesive layer. Then, the laminate was laminated on glass plates having different steps so that the adhesive layer covered the entire frame-shaped printing surface using a laminator (product name "LPD 3214" manufactured by fujiapla inc.) to obtain a sample for evaluation.

(b) Evaluation of evaluation sample

The obtained evaluation sample was autoclaved at 50 ℃ and 0.5MPa for 30 minutes and then left at normal pressure, 23 ℃ and 50% RH for 24 hours. Next, the sample was stored for 72 hours under a durable condition of 85 ℃ and 85% RH. After that, the adhesive layer (particularly, the vicinity of the level difference formed by the printed layer) was visually observed, and the level difference following property was evaluated according to the following criteria. The results are shown in Table 2.

◎ no bubbles and no floating.

○ fewer than 10 bubbles were observed near the level difference.

X: air bubbles are present and/or float.

[ test example 5] (evaluation of resistance to Wet Heat whitening)

The adhesive layers of the adhesive sheets obtained in examples or comparative examples were sandwiched between two sheets of alkali-free glass having a thickness of 1.1mm, and the laminate was used as a sample. The obtained sample was stored at 85 ℃ and 85% RH for 120 hours. After that, the temperature was returned to the normal temperature and humidity of 23 ℃ and 50% RH, and whether whitening was present or not was visually observed according to the following criteria, and the wet heat whitening resistance was evaluated, and the haze value of the adhesive layer was measured. The haze value was measured by using a haze meter (NIPPON DENSHOKU IND usties co., ltd., product name "NDH 2000") within 30 minutes after the sample was returned to normal temperature and humidity in accordance with JIS K7136: 2000 were measured. The results are shown in Table 2.

○ whitening was not observed even when the temperature was returned to normal temperature and humidity, or some whitening occurred but disappeared within 30 minutes.

X: whitening occurs overall. Alternatively, after some whitening occurs, the film cannot be restored to its original state even when stored at normal temperature and humidity.

[ Table 1]

[ Table 2]

As is clear from Table 2, the pressure-sensitive adhesive sheets obtained in the examples were excellent in migration prevention effect, step following property and wet heat whitening resistance.

Industrial applicability

The adhesive composition, the adhesive and the adhesive sheet of the present invention can be suitably used for a capacitance type touch panel using a copper electrode or a silver electrode, for example. The display according to the present invention is suitable as a capacitance type touch panel using a copper electrode or a silver electrode, for example.

Description of the reference numerals

1 … adhesive sheet

11 … adhesive layer

12a, 12b … release sheet

2 … touch panel

3 … display module

4 … adhesive layer

5a … first film sensor

5b … second film sensor

51 … substrate film

52 … electrode

6 … covering material

7 … printing layer

Claims

1. An adhesive for bonding a first display structural member and a second display structural member having a step difference at least on a surface on a side to be bonded, which is obtained by crosslinking an adhesive composition,

the first display structural member and/or the second display structural member have an electrode at least on the surface of the attached side,

the adhesive composition comprises (meth) acrylate polymer (A) and silane coupling agent (B) having mercapto group,

the (meth) acrylate polymer (A) contains 15 to 35 mass% of a hydroxyl group-containing monomer as a monomer unit constituting the polymer,

the adhesive has a gel fraction of 30% to 90%.

2. Adhesive according to claim 1,

the silane coupling agent (B) having a mercapto group is an oligomer type silane coupling agent containing a mercapto group.

3. Adhesive according to claim 1,

the organosilicon compound constituting the silane coupling agent (B) having a mercapto group has a mercapto equivalent of 100 g/mol or more and 1000 g/mol or less.

4. Adhesive according to claim 1,

the content of the silane coupling agent (B) having a mercapto group in the adhesive composition is 0.01 to 5 parts by mass with respect to 100 parts by mass of the (meth) acrylate polymer (a).

5. Adhesive according to claim 1,

the adhesive composition further contains a crosslinking agent (C).

6. An adhesive sheet comprising an adhesive layer formed from the adhesive according to any one of claims 1 to 5.

7. The adhesive sheet according to claim 6,

the adhesive sheet is provided with two sheets of release sheets,

the adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the release sheets.

8. A display device is provided with: a first display structural member having a step at least on a surface of the bonded side; a second display structural member; and an adhesive layer for bonding the first display structural member and the second display structural member to each other,

the adhesive layer is the adhesive layer of the adhesive sheet according to claim 6.