JP7462408B2 - Adhesive composition, adhesive film, and connection structure - Google Patents

Description

The present invention relates to an adhesive composition, an adhesive film, and a connection structure.

Adhesive compositions and film-like products (adhesive films) such as anisotropic conductive paste (ACP) and anisotropic conductive film (ACF) are widely used as a means for bonding electronic components to circuit boards and the like. For example, anisotropic conductive films are used when bonding and electrically connecting various terminals, including when connecting terminals of a flexible printed circuit board (FPC) and terminals of a glass substrate of an FPD panel (so-called FOG).

In order to achieve low-temperature, rapid curing in such adhesive compositions, it has been proposed to use, as the polymerizable compound, an alicyclic epoxy compound that has a higher cationic polymerization reactivity than the general-purpose glycidyl ether compounds, and to use, as a polymerization initiator that is not inhibited by oxygen and exhibits dark reactivity, a sulfonium salt-based thermal acid generator that generates protons when heated (Patent Documents 1 to 3).

Japanese Patent Application Laid-Open No. 9-176112 JP 2008-308596 A International Publication No. 2012/018123

The storage and transportation period from production to actual use of adhesive compositions is becoming longer due to factors such as the internationalization of commercial transactions. Adhesive compositions that use a combination of an alicyclic epoxy compound and a sulfonium salt-based thermal acid generator exhibit excellent adhesion when used immediately after production, but it can be difficult to manage the product life due to storage conditions.

As polymerization initiators for alicyclic epoxy compounds, in addition to sulfonium salt-based thermal acid generators, quaternary ammonium salt-based thermal acid generators are also known. The present inventors have found that when a quaternary ammonium salt-based thermal acid generator is used instead of a sulfonium salt-based thermal acid generator, the desired adhesiveness may not be guaranteed even when used immediately after production under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used. Although adhesiveness can be improved by shifting the adhesive conditions to higher temperatures and longer times, this goes against the recent trend of shifting to lower temperatures and shorter times from the standpoint of reducing thermal stress on electronic components and increasing production efficiency.

The objective of the present invention is to provide an adhesive composition that can suppress the deterioration of adhesiveness even after storage at room temperature or in a refrigerated environment, and that achieves excellent adhesiveness under the same adhesive conditions as before.

As a result of intensive research into the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by an adhesive composition having the following composition, and thus completed the present invention.

（式中、Ｒ^１はエポキシＣ_３～Ｃ_１０シクロアルキル基を有する１価の有機基を表し、Ｒ^２は水素原子、炭化水素基、又はアルコキシ基を表す。）
［７］ ４官能脂環式エポキシ化合物が、式（１）で表される構造単位を１分子中に４個有する、［６］に記載の接着剤組成物。
［８］ さらにチオール化合物を含む、［１］～［７］の何れか１つに記載の接着剤組成物。
［９］ チオール化合物が、１分子中にメルカプト基と同数のカルボニルオキシ基を含む、［８］に記載の接着剤組成物。
［１０］ チオール化合物の官能数が、２以上である、［８］又は［９］に記載の接着剤組成物。
［１１］ チオール化合物が、式（２）で表される構造単位を含む、［８］～［１０］の何れか１つに記載の接着剤組成物。

［１２］ 第４級アンモニウム塩系熱酸発生剤に対するチオール化合物の質量比［チオール化合物／第４級アンモニウム塩系熱酸発生剤］が、０．１以上である、［８］～［１１］の何れか１つに記載の接着剤組成物。
［１３］ 成膜用成分が、フェノキシ樹脂を含む、［１］～［１２］の何れか１つに記載の接着剤組成物。
［１４］ さらに導電性粒子を含む、［１］～［１３］の何れか１つに記載の接着剤組成物。
［１５］ ［１］～［１４］の何れか１つに記載の接着剤組成物からなる接着フィルム。［１６］ 第１の電子部品と第２の電子部品とが［１］～［１４］の何れか１つに記載の接着剤組成物又は［１５］に記載の接着フィルムにより接続されている接続構造体。
［１７］ 第１の電子部品と第２の電子部品とを、［１］～［１４］の何れか１つに記載の接着剤組成物又は［１５］に記載の接着フィルムを介在させて、圧着する工程を含む、接続構造体の製造方法。 That is, the present invention includes the following.
[1] An adhesive composition comprising a binder composition containing a cationic polymerizable component and a film-forming component, and a cationic polymerization initiator,
the cationic polymerization initiator is a quaternary ammonium salt-based thermal acid generator;
An adhesive composition, wherein the cationically polymerizable component comprises a difunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound.
[2] The adhesive composition according to [1], wherein the mass ratio of the tetrafunctional alicyclic epoxy compound to the difunctional alicyclic epoxy compound [tetrafunctional alicyclic epoxy compound/difunctional alicyclic epoxy compound] (hereinafter referred to as the "tetrafunctional/difunctional mass ratio") is less than 1.0.
[3] The adhesive composition according to [1] or [2], wherein the tetrafunctional/difunctional mass ratio is 0.1 or more and 0.85 or less.
[4] The adhesive composition according to any one of [1] to [3], wherein the difunctional alicyclic epoxy compound has an epoxy C ₃ -C ₁₀ cycloalkyl group.
[5] The adhesive composition according to any one of [1] to [4], wherein the tetrafunctional alicyclic epoxy compound has an epoxy C ₃ -C ₁₀ cycloalkyl group.
[6] The adhesive composition according to any one of [1] to [5], wherein the tetrafunctional alicyclic epoxy compound contains a structural unit represented by formula (1).

(In the formula, R ¹ represents a monovalent organic group having an epoxy C ₃ -C ₁₀ cycloalkyl group, and R ² represents a hydrogen atom, a hydrocarbon group, or an alkoxy group.)
[7] The adhesive composition according to [6], wherein the tetrafunctional alicyclic epoxy compound has four structural units represented by formula (1) in one molecule.
[8] The adhesive composition according to any one of [1] to [7], further comprising a thiol compound.
[9] The adhesive composition according to [8], wherein the thiol compound contains the same number of carbonyloxy groups as the number of mercapto groups in one molecule.
[10] The adhesive composition according to [8] or [9], wherein the functionality of the thiol compound is 2 or more.
[11] The adhesive composition according to any one of [8] to [10], wherein the thiol compound contains a structural unit represented by formula (2).

[12] The adhesive composition according to any one of [8] to [11], wherein a mass ratio of the thiol compound to the quaternary ammonium salt thermal acid generator [thiol compound/quaternary ammonium salt thermal acid generator] is 0.1 or more.
[13] The adhesive composition according to any one of [1] to [12], wherein the film-forming component includes a phenoxy resin.
[14] The adhesive composition according to any one of [1] to [13], further comprising conductive particles.
[15] An adhesive film comprising the adhesive composition according to any one of [1] to [14]. [16] A connection structure in which a first electronic component and a second electronic component are connected by the adhesive composition according to any one of [1] to [14] or the adhesive film according to [15].
[17] A method for producing a connection structure, comprising a step of pressure-bonding a first electronic component and a second electronic component with the adhesive composition according to any one of [1] to [14] or the adhesive film according to [15] interposed therebetween.

The present invention provides an adhesive composition that can suppress the deterioration of adhesiveness even after storage at room temperature or in a refrigerated environment, and achieves excellent adhesiveness under the same adhesive conditions as before.

<Terminology>
In this specification, the term "C _n -C _m " (n and m are positive integers satisfying n<m) means that the organic group described immediately following this term has n to m carbon atoms. For example, "C ₁ -C ₁₂ alkyl group" refers to an alkyl group having 1 to 12 carbon atoms.

In this specification, "alicyclic epoxy compound" means an epoxy compound having an alicyclic ring in the molecule. In an alicyclic epoxy compound, the oxirane ring may be formed by two carbon atoms and one oxygen atom that constitute the alicyclic ring, or may be formed as a glycidyl group separate from the alicyclic ring.

The present invention will be described in detail below based on a preferred embodiment. The present invention is not limited to the following description, and each component can be modified as appropriate without departing from the gist of the present invention.

[Adhesive composition]
The adhesive composition of the present invention includes a binder composition containing a cationic polymerizable component and a film-forming component, and a cationic polymerization initiator,
the cationic polymerization initiator is a quaternary ammonium salt-based thermal acid generator;
The cationic polymerizable component is characterized by containing a difunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound.

<Cationic Polymerization Initiator>
The adhesive composition of the present invention is characterized by containing a quaternary ammonium salt-based thermal acid generator as a cationic polymerization initiator.

As mentioned above, the sulfonium salt-based thermal acid generator contributes to low-temperature rapid curing in combination with an alicyclic epoxy compound, and provides excellent adhesion immediately after the production of the adhesive composition; however, when the adhesive composition is stored at room temperature and in a refrigerated environment for a certain period of time, the adhesiveness may be significantly reduced. In contrast, the adhesive composition of the present invention using a quaternary ammonium salt-based thermal acid generator can suppress the decrease in adhesiveness even when stored at room temperature and in a refrigerated environment for a certain period of time. Moreover, by using a quaternary ammonium salt-based thermal acid generator in combination with a specific cationic polymerizable component described below, it is possible to achieve excellent adhesiveness under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used.

As a quaternary ammonium salt-based thermal acid generator, a salt of a quaternary ammonium cation and an acid anion or a borate anion can be suitably used.

An example of the quaternary ammonium cation is a cation represented by the formula: NR ^a R ^b R ^c R ^{d +} , where R ^a , R ^b , R ^c and R ^d are linear, branched or cyclic C ₁ to C ₁₂ alkyl or aryl groups, each of which may have a hydroxyl group, a halogen atom, an alkoxy group, an amino group, an ester group or the like.

The acid anion may be either an inorganic acid anion or an organic acid anion, and examples thereof include hexafluoroantimonate anion, hexafluorophosphate anion, trifluoromethanesulfonate anion, perfluorobutanesulfonate anion, dinonylnaphthalenesulfonate anion, dinonylnaphthalenesulfonate anion, p-toluenesulfonate anion, and dodecylbenzenesulfonate anion.

Examples of borate anions include alkylborate anions and arylborate anions, which may further contain a halogen atom. Among these, arylborate anions containing a fluorine atom (F-; fluoro group) are preferred, and tetrakis(pentafluorophenyl)borate anions are particularly preferred.

Quaternary ammonium salt-based thermal acid generators may be used alone or in combination of two or more.

Specific examples of quaternary ammonium salt-based thermal acid generators include CXC-1612, CXC-1733, CXC-1738, TAG-2678, CXC-1614, TAG-2689, TAG-2690, TAG-2700, CXC-1802-60, and CXC-1821 manufactured by King Industries, Inc. These are available from Kusumoto Chemicals Co., Ltd.

The content of the quaternary ammonium salt-based thermal acid generator in the adhesive composition is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and even more preferably 7% by mass or more, when the total of the non-volatile components of the cationically polymerizable components is taken as 100% by mass. The upper limit of the content is not particularly limited, but is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

<Binder Composition>
The adhesive composition of the present invention comprises a binder composition that contains a cationically polymerizable component and a film-forming component.

(Cationically Polymerizable Component)
The adhesive composition of the present invention is characterized by using a bifunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound in combination as a cationic polymerizable component. By using such a specific cationic polymerizable component in combination with a quaternary ammonium salt-based thermal acid generator, the adhesive composition of the present invention can not only suppress a decrease in adhesiveness even when stored for a certain period of time under room temperature or refrigerated conditions, but also achieve excellent adhesiveness under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used.

-Difunctional alicyclic epoxy compound-
The difunctional alicyclic epoxy compound is not particularly limited as long as it is an alicyclic epoxy compound having two epoxy groups in one molecule, and may be appropriately selected from, for example, a difunctional cycloalkene oxide type epoxy compound and a diglycidyl ether compound of an alicyclic dihydric alcohol.

A difunctional cycloalkene oxide type epoxy compound is a compound having two epoxy cycloalkyl groups in one molecule. The number of carbon atoms in the epoxy cycloalkyl group is preferably 3 to 10. Therefore, in a preferred embodiment, the difunctional alicyclic epoxy compound has an epoxy C ₃ -C ₁₀ cycloalkyl group. The number of carbon atoms in the epoxy cycloalkyl group is more preferably 4 to 10, even more preferably 6 to 10, even more preferably 6 to 8, and particularly preferably 6. The two epoxy cycloalkyl groups in the difunctional alicyclic epoxy compound may be the same or different from each other. Among them, it is preferred that the difunctional alicyclic epoxy compound has two epoxy cyclohexyl groups.

Difunctional cycloalkene oxide type epoxy compounds can be produced, for example, by directly epoxidizing a compound having two cycloalkene skeletons, or by polymerizing a monofunctional cycloalkene oxide type epoxy compound having a polymerizable functional group (e.g., (meth)acrylic group, allyl group, silanol group, etc.) to make it difunctional.

In the bifunctional cycloalkene oxide type epoxy compound, the structure other than the epoxy cycloalkyl group is not particularly limited, and may be any structure as long as it does not inhibit reactivity. From the viewpoint of realizing an adhesive composition exhibiting excellent adhesion, it is preferable that the structure has an epoxy equivalent of preferably 500 or less, more preferably 400 or less, even more preferably 350 or less, even more preferably 300 or less, particularly preferably 250 or less, and especially preferably 200 or less. The lower limit of the epoxy equivalent of the bifunctional cycloalkene oxide type epoxy compound is not particularly limited, but is preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, and even more preferably 95 or more.

Specific examples of bifunctional cycloalkene oxide type epoxy compounds include 3,4-epoxycyclohexenylmethyl-3',4'-epoxycyclohexenecarboxylate, diepoxybicyclohexyl, etc.

A diglycidyl ether compound of an alicyclic dihydric alcohol is a compound having an alicyclic ring and two glycidyl groups in one molecule. The alicyclic ring may have any structure as long as it does not inhibit reactivity, and may be a single ring or a condensed ring, and one or more alicyclic rings may be contained in one molecule. From the viewpoint of realizing an adhesive composition that exhibits excellent adhesion, it is preferable that the structure has an epoxy equivalent in the same range as that described above for the cycloalkene oxide type epoxy compound.

Diglycidyl ether compounds of alicyclic dihydric alcohols can be produced, for example, by hydrogenating the aromatic ring of an aromatic dihydric alcohol diglycidyl ether (e.g., a bisphenol-type diglycidyl ether such as bisphenol A diglycidyl ether) to form an alicyclic ring, or by glycidyl etherifying an aliphatic dihydric alcohol (e.g., a hydrogenated bisphenol such as hydrogenated bisphenol A). A specific example of a diglycidyl ether compound of an alicyclic dihydric alcohol is hexahydrobisphenol A diglycidyl ether.

The bifunctional alicyclic epoxy compounds may be used alone or in combination of two or more.

-Tetrafunctional alicyclic epoxy compound-
The tetrafunctional alicyclic epoxy compound is not particularly limited as long as it is an alicyclic epoxy compound having four epoxy groups in one molecule, and may be appropriately selected from, for example, a tetrafunctional cycloalkene oxide type epoxy compound and a tetraglycidyl ether compound of an alicyclic tetrahydric alcohol.

In order to realize an adhesive composition with particularly excellent adhesion when combined with a difunctional alicyclic epoxy compound, it is preferable that the tetrafunctional alicyclic epoxy compound contains a tetrafunctional cycloalkene oxide type epoxy compound.

The tetrafunctional cycloalkene oxide type epoxy compound is a compound having four epoxy cycloalkyl groups in one molecule. The number of carbon atoms in the epoxy cycloalkyl group is preferably 3 to 10. Therefore, in a preferred embodiment, the tetrafunctional alicyclic epoxy compound has an epoxy C ₃ -C ₁₀ cycloalkyl group. The number of carbon atoms in the epoxy cycloalkyl group is more preferably 4 to 10, even more preferably 6 to 10, even more preferably 6 to 8, and particularly preferably 6. The four epoxy cycloalkyl groups in the tetrafunctional alicyclic epoxy compound may be the same or different from each other. Among them, it is preferred that the tetrafunctional alicyclic epoxy compound has four epoxy cyclohexyl groups.

Tetrafunctional cycloalkene oxide type epoxy compounds can be produced, for example, by directly epoxidizing a compound having four cycloalkene skeletons, or by polymerizing a monofunctional cycloalkene oxide type epoxy compound having a polymerizable functional group (e.g., (meth)acrylic group, allyl group, silanol group, etc.) to make it tetrafunctional.

In the tetrafunctional cycloalkene oxide type epoxy compound, the structure other than the epoxy cycloalkyl group is not particularly limited, and may be any structure as long as it does not inhibit reactivity. From the viewpoint of realizing an adhesive composition exhibiting excellent adhesion, it is preferable that the structure has an epoxy equivalent of preferably 500 or less, more preferably 400 or less, even more preferably 350 or less, even more preferably 300 or less, and particularly preferably 250 or less. The lower limit of the epoxy equivalent of the tetrafunctional cycloalkene oxide type epoxy compound is not particularly limited, but is preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, and even more preferably 95 or more.

In a preferred embodiment, the tetrafunctional alicyclic epoxy compound contains a structural unit represented by formula (1).

（式中、Ｒ^１はエポキシＣ_３～Ｃ_１０シクロアルキル基を有する１価の有機基を表し、Ｒ^２は水素原子、炭化水素基、又はアルコキシ基を表す。）

(In the formula, R ¹ represents a monovalent organic group having an epoxy C ₃ -C ₁₀ cycloalkyl group, and R ² represents a hydrogen atom, a hydrocarbon group, or an alkoxy group.)

The organic group having an epoxy C ₃ -C ₁₀ cycloalkyl group represented by R ¹ is not particularly limited as long as it has an epoxy C ₃ -C ₁₀ cycloalkyl group. The number of epoxy C ₃ -C ₁₀ cycloalkyl groups contained in the organic group is not particularly limited, but is preferably 1 to 4, more preferably 1 or 2, and even more preferably 1.

In one embodiment, R ¹ is a monovalent group represented by the formula E-(L) _m -, where E represents an epoxy C ₃ -C ₁₀ cycloalkyl group, L represents an alkylene group, a cycloalkylene group, an oxyalkylene group, or an oxycycloalkylene group, and m represents 0 or 1.

The epoxy C ₃ -C ₁₀ cycloalkyl group represented by E is more preferably an epoxy C ₄ -C ₁₀ cycloalkyl group, an epoxy C ₆ -C ₁₀ cycloalkyl group, or an epoxy C ₆ -C ₈ cycloalkyl group, and even more preferably an epoxy C ₆ cycloalkyl group, i.e., an epoxy cyclohexyl group.

The number of carbon atoms in the alkylene group or oxyalkylene group represented by L is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4.

The number of carbon atoms in the cycloalkylene group or oxycycloalkylene group represented by L is preferably 3 to 10, and more preferably 3 to 6.

From the viewpoint of achieving an adhesive composition with particularly excellent adhesion in combination with a difunctional alicyclic epoxy compound, L is preferably an alkylene group, more preferably a C ₁ -C ₆ alkylene group.

When combined with a bifunctional alicyclic epoxy compound, m is preferably 1, from the viewpoint of achieving an adhesive composition with particularly excellent adhesion.

In formula (1), examples of the hydrocarbon group represented by ^R2 include an alkyl group, a cycloalkyl group, and a monovalent group formed by combining two or more of these. The number of carbon atoms in the alkyl group is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. The number of carbon atoms in the cycloalkyl group is preferably 3 to 10, more preferably 3 to 6, and even more preferably 4 to 6.

In formula (1), the alkoxy group represented by ^R2 preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 to 3 carbon atoms.

From the viewpoint of realizing an adhesive composition having particularly excellent adhesiveness in combination with a difunctional alicyclic epoxy compound, ^R2 is preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably a methyl group, an ethyl group, a propyl group, or a butyl group.

The tetrafunctional alicyclic epoxy compound preferably has 2 to 4, more preferably 3 or 4, and particularly preferably 4 structural units represented by the above formula (1) in one molecule.

When the tetrafunctional alicyclic epoxy compound has a structural unit represented by the above formula (1), it may have a chain siloxane structure or a cyclic siloxane structure. In combination with a bifunctional alicyclic epoxy compound, it is preferable for it to have a cyclic siloxane structure, from the viewpoint of realizing an adhesive composition with particularly excellent adhesive properties.

In a particularly preferred embodiment, the tetrafunctional alicyclic epoxy compound includes a compound represented by formula (1-1).

The tetrafunctional alicyclic epoxy compounds may be used alone or in combination of two or more.

In the adhesive composition of the present invention, the total content of the bifunctional alicyclic epoxy compound and the tetrafunctional alicyclic epoxy compound is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, and even more preferably 20% by mass or more, when the non-volatile components in the adhesive composition are taken as 100% by mass. The upper limit of the content is not particularly limited, but is preferably 60% by mass or less, more preferably 55% by mass or less or 50% by mass or less.

The mass ratio of the tetrafunctional alicyclic epoxy compound to the difunctional alicyclic epoxy compound (i.e., the tetrafunctional/bifunctional mass ratio) is preferably less than 1.0, more preferably 0.9 or less, from the viewpoint of realizing good adhesion under the same adhesion conditions as before in combination with a quaternary ammonium salt-based thermal acid generator. In particular, a tetrafunctional/bifunctional mass ratio of 0.85 or less is preferable because it can significantly suppress the occurrence of lifting at the connection points of the connection structure even after a reliability test in a high-temperature and high-humidity environment. The tetrafunctional/bifunctional mass ratio is more preferably 0.7 or less, even more preferably 0.6 or less, even more preferably 0.5 or less, and particularly preferably 0.4 or less. The inventors have found that an adhesive composition with exceptionally excellent adhesion can be realized when the tetrafunctional/bifunctional mass ratio is 0.4 or less. The lower limit of the tetrafunctional/bifunctional mass ratio is preferably 0.05 or more, more preferably 0.1 or more, from the viewpoint of realizing good adhesion under the same adhesion conditions as before in combination with a quaternary ammonium salt-based thermal acid generator. In particular, the inventors have found that a tetrafunctional/bifunctional mass ratio of 0.1 or more is preferable because it can significantly prevent lifting at the connection points of the connection structure even after reliability testing in a high-temperature, high-humidity environment, and can also realize an adhesive composition with exceptionally excellent adhesion. The tetrafunctional/bifunctional mass ratio is more preferably 0.11 or more, and even more preferably 0.12 or more.

-Other cationic polymerizable components-
The adhesive composition of the present invention may contain other cationic polymerizable components as long as it contains a bifunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound. Examples of other cationic polymerizable components include a trifunctional alicyclic epoxy compound, a pentafunctional or higher alicyclic epoxy compound, and an oxetane compound. When other cationic polymerizable components are contained, the content is not particularly limited, but when an oxetane compound is contained, the content of the oxetane compound is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 1% by mass or less, when the total of the bifunctional alicyclic epoxy compound and the tetrafunctional alicyclic epoxy compound is taken as 100% by mass, and may not be contained.

(Film-forming components)
The film-forming component is not particularly limited as long as it has a film-forming ability. The film-forming component may be appropriately selected according to the purpose, and may be, for example, a phenoxy resin, an epoxy resin (excluding alicyclic epoxy resins), a polyvinyl acetal resin, an unsaturated polyester resin, a saturated polyester resin, a urethane resin, a butadiene resin, a polyimide resin, a polyamide resin, or a polyolefin resin. The film-forming component may be used alone or in combination of two or more kinds.

Among these, phenoxy resin can be preferably used from the viewpoints of film-forming property, processability, and connection reliability, and polyvinyl acetal resin can also be preferably used from the viewpoint of realizing good adhesion. Thus, in one embodiment, the film-forming component includes phenoxy resin. In another embodiment, the film-forming component includes polyvinyl acetal resin. In another preferred embodiment, the film-forming component includes phenoxy resin and polyvinyl acetal resin.

From the viewpoint of film-forming properties, the polystyrene-equivalent weight average molecular weight (Mw) of the film-forming component is preferably 10,000 or more, more preferably 15,000 or more, and even more preferably 20,000 or more. The upper limit of the Mw is not particularly limited, but is preferably 80,000 or less, more preferably 70,000 or less, and may be 60,000 or less. It may be appropriately selected depending on the other ingredients and the purpose of use. If the film-forming component contains a phenoxy resin with Mw of 50,000 or less, it is preferable because it can significantly suppress the occurrence of floating at the connection points of the connection structure even after a reliability test in a high-temperature and high-humidity environment. The polystyrene-equivalent Mw of the film-forming component can be measured by gel permeation chromatography (GPC) and calculated using a calibration curve of standard polystyrene.

The content of the film-forming components in the adhesive composition is not particularly limited and may be determined appropriately depending on the purpose, but is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more, when the non-volatile components in the adhesive composition are taken as 100% by mass. The upper limit of the content is not particularly limited, but is preferably 70% by mass or less, more preferably 60% by mass or less.

<Thiol compounds>
The adhesive composition of the present invention may further comprise a thiol compound.

The present inventors have found that the adhesive composition of the present invention, which uses a combination of a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component, can specifically and dramatically improve adhesion by further including a thiol compound. In this regard, the present inventors have confirmed that in adhesive compositions using conventional sulfonium salt-based thermal acid generators, not only is there no improvement in adhesion, but the addition of a thiol compound may even result in a decrease in adhesion (Comparative Example 3).

The thiol compound is not particularly limited as long as it has a mercapto group (-SH) in one molecule, but from the viewpoint of achieving particularly excellent adhesion in the adhesive composition of the present invention, which uses a combination of a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component, a compound having the same number of carbonyloxy groups (-C(=O)-O-) as mercapto groups in the molecule is preferred.

In particular, from the viewpoint of realizing particularly excellent adhesive properties in combination with a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component, it is preferable that the thiol compound contains a structural unit represented by formula (2). The structural unit of formula (2) may be included in the main chain of the thiol compound, or may be present at the end. In particular, when the structure of formula (2) is present at the end as a 3-mercapto-butyryloxy group, it tends to result in an adhesive composition with exceptionally excellent adhesive properties.

The number of functionalities of the thiol compound is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, from the viewpoint of realizing excellent adhesive properties. In particular, a compound having preferably 2, more preferably 3, and even more preferably 4 structural units represented by the above formula (2) in the molecule is suitable from the viewpoint of realizing particularly excellent adhesive properties.

The molecular weight of the thiol compound is preferably 200 or more, more preferably 250 or more, and even more preferably 300 or more, from the viewpoint of realizing particularly excellent adhesion in combination with a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component, and the upper limit of the molecular weight is preferably 1000 or less, more preferably 800 or less, even more preferably 700 or less, and even more preferably 600 or less.

Specific examples of suitable thiol compounds include 1,4-bis(3-mercaptobutyryloxy)butane [bifunctional, molecular weight 294], 1,3,5-tris(3-mercaptobutyryloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione [trifunctional, molecular weight 568], trimethylolpropane tris(3-mercaptobutyrate) [trifunctional, molecular weight 440], and pentaerythritol tetrakis(3-mercaptobutyrate) [tetrafunctional, molecular weight 545].

The thiol compounds may be used alone or in combination of two or more.

When a thiol compound is used, the mass ratio of the thiol compound to the quaternary ammonium salt-based thermal acid generator [thiol compound/quaternary ammonium salt-based thermal acid generator] is preferably 0.1 or more, more preferably 0.12 or more, even more preferably 0.14 or more, even more preferably 0.15 or more, particularly preferably 0.16 or more, and especially preferably 0.18 or more, from the viewpoint of realizing particularly excellent adhesion. The upper limit of the mass ratio is not particularly limited, but is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1 or less.

<Conductive particles>
The adhesive composition of the present invention may further contain conductive particles. By containing conductive particles, the adhesive composition and a film-like product thereof can be used as a conductive paste and a conductive film, or an anisotropic conductive paste and an anisotropic conductive film.

As the conductive particles, known conductive particles used in anisotropic conductive films may be used. Examples of conductive particles include particles of metals such as nickel, iron, copper, aluminum, tin, lead, chromium, cobalt, silver, and gold; particles of alloys of these metals; and coated particles in which metal is coated on the surface of particles such as metal oxides, carbon, graphite, glass, ceramics, and resins. When using metal-coated resin particles in which a metal is coated on the surface of resin particles, examples of the material for the resin particles include epoxy resin, phenolic resin, acrylic resin, acrylonitrile-styrene (AS) resin, benzoguanamine resin, divinylbenzene resin, and styrene resin. In addition, the conductive particles may be further coated with an insulating thin film on the surface of the particles or may be insulated by attaching insulating particles to the surface in order to avoid the risk of short circuits between terminals, as long as the conductive performance after connection is not impaired. These conductive particles may be used alone or in combination of two or more types.

The average particle diameter of the conductive particles is not particularly limited and may be appropriately determined depending on the purpose, but is preferably 40 μm or less, more preferably 30 μm or less, even more preferably 25 μm or less, and even more preferably 20 μm or less. The lower limit of the average particle diameter is not particularly limited, but is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. The average particle diameter of the conductive particles may be measured, for example, by observing with a scanning electron microscope (SEM), measuring the particle diameters of multiple conductive particles (n≧10), and calculating the average value. Alternatively, it may be a measured value (N=1000 or more) measured using an image-type particle size distribution measuring device (for example, FPIA-3000 (Malvern Instruments)).

When conductive particles are used, the content of the conductive particles in the adhesive composition is not particularly limited and may be determined appropriately depending on the purpose, but is preferably 1 mass% or more, more preferably 2 mass% or more, and even more preferably 3 mass% or more. From the viewpoint of obtaining the desired anisotropic conductivity, the upper limit of the content is preferably 30 mass% or less, more preferably 30 mass% or less, even more preferably 25 mass% or less, and even more preferably 20 mass% or less.

The adhesive composition of the present invention may further contain other components as necessary. Examples of such components include known additives used in the manufacture of adhesive compositions, such as organic fillers (e.g., butadiene-based rubber particles, acrylic-based rubber particles, silicone-based rubber particles), insulating inorganic fillers (e.g., silica fillers) and other fillers that do not inhibit electrical conduction, surface modifiers, flame retardants, coupling agents, colorants, etc.

The adhesive composition of the present invention can suppress the deterioration of adhesiveness even when stored for a certain period of time under room temperature or refrigerated conditions, and can achieve excellent adhesiveness under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used. Therefore, the adhesive composition of the present invention can be suitably used as a means for bonding electronic components, etc. Furthermore, when it contains conductive particles, it can be used as a conductive paste or anisotropic conductive paste.

[Adhesive film]
The adhesive composition of the present invention has good film-forming properties and can be suitably formed into a film-like product (adhesive film). The present invention also provides such an adhesive film, which is characterized in that the adhesive film is made of the adhesive composition of the present invention.

The adhesive film of the present invention may be composed of a single layer or multiple layers. When composed of multiple layers, the adhesive film of the present invention includes at least a first adhesive layer made of the adhesive composition of the present invention and a second adhesive layer made of the adhesive composition of the present invention provided on the first adhesive layer. It is preferable that one of the first adhesive layer and the second adhesive layer contains conductive particles. Therefore, in one embodiment, the adhesive film of the present invention includes at least a first adhesive layer made of the adhesive composition of the present invention and a second adhesive layer made of the adhesive composition of the present invention provided on the first adhesive layer, and one of the first adhesive layer and the second adhesive layer contains conductive particles. In addition, a layer different from the present invention may be provided in the adhesive layer of the present invention. The front and rear of the layer may be sandwiched by the adhesive layers of the present invention. In this case, the conductive particles may be included in at least one of the adhesive layers of the present invention, or may be included in a different layer. This different layer may be a layer made of an adhesive composition different from the present invention, or may be a resin layer that is not an adhesive layer (does not contribute to adhesion). It is preferable that it is insulating. There is no particular restriction on the inclusion of a different layer as long as adhesion is possible.

The adhesive film can be produced, for example, by mixing the adhesive composition of the present invention with an organic solvent if necessary, applying it to a release substrate, and then drying it to form an adhesive layer. The adhesive composition can be applied using a coating device such as a bar coater. A known coating method for adhesive films, such as a doctor blade method, can be used. When producing an adhesive film consisting of multiple layers, the above coating and drying steps can be repeated multiple times. Alternatively, the layers can be produced individually and laminated by lamination or the like.

The release substrate is not particularly limited as long as it is a film-like material that can support the adhesive film and can be peeled off from the adhesive film at the desired timing. Examples of materials that can be used for the release substrate include polyesters such as polyethylene terephthalate (PET), polyolefins such as polypropylene (PP), and plastic materials such as poly-4-methylpen-1 (PMP) and polytetrafluoroethylene (PTFE). The release substrate may also be a substrate having a release layer on the surface that is bonded to the adhesive film, and the release layer may contain a release agent such as a silicone resin or a polyolefin resin.

The thickness of the release substrate is not particularly limited, but is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less, and even more preferably 50 μm or less. The lower limit of the thickness of the release substrate is not particularly limited, but is preferably 8 μm or more from the viewpoint of ease of handling during the production and slitting of the adhesive film.

The thickness of the adhesive film of the present invention is not particularly limited and may be appropriately determined depending on the purpose, but is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The upper limit of the thickness of the adhesive layer is not particularly limited, but is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less, even more preferably 50 μm or less, and particularly preferably 40 μm or less. When multiple layers are laminated, the total thickness is used.

The adhesive film may be slit to the desired width. During slitting, a cover film may be provided on the exposed surface to prevent contamination of the adhesive layer by cutting debris or the like. In this case, the thickness may be appropriately selected according to the purpose. The cover film may be a known film used when slitting the adhesive film. The cover film may be provided separately from the release substrate to prevent contamination during use as a product used for connection in addition to the manufacturing process such as slitting. In this case, it is preferable that the cover film has releasability and is preferably the same thickness as or thinner than the release substrate.

The adhesive film of the present invention can suppress a decrease in adhesiveness even when stored for a certain period of time under room temperature or refrigerated conditions, and can achieve excellent adhesiveness under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used. Therefore, the adhesive film of the present invention can be suitably used as a means for adhering electronic components, etc. Furthermore, when it contains conductive particles, it can be used as an anisotropic conductive film.

[Connection structure]
The adhesive composition or adhesive film of the present invention can be used to produce a connection structure in which electronic components are bonded to each other. The present invention also provides such a connection structure, which is characterized in that a first electronic component and a second electronic component are connected by the adhesive composition or adhesive film of the present invention.

The first electronic component may be, for example, a general PWB, and may include rigid substrates, glass substrates, ceramic substrates, plastic substrates, FPCs, etc., and the second electronic component may be, for example, an FPC, an IC chip, or a semiconductor element other than an IC chip. There are no particular restrictions on the electronic component, and there are no particular restrictions on the use of the connection structure. For example, it may be used in a portable information terminal or for electrical mounting for vehicles. In the present invention, as an example, a variety of connection structures such as FOB, FOG, FOP, FOF, COG, and COP may be manufactured. In particular, it is preferably applicable to FOG and FOP.

[Method of manufacturing the connection structure]
The method for producing the connection structure of the present invention is not particularly limited as long as it is possible to produce a connection structure in which a first electronic component and a second electronic component are connected by the adhesive composition or adhesive film of the present invention. Hereinafter, an example of the method for producing the connection structure of the present invention will be described.

In one embodiment, the method for producing a connection structure of the present invention includes a step of bonding a first electronic component and a second electronic component by pressure bonding with the adhesive composition or adhesive film of the present invention interposed therebetween.

First, the first electronic component is placed on a stage, the adhesive composition or adhesive film of the present invention is applied thereon, and then the second electronic component is placed thereon. After the adhesive composition or adhesive film of the present invention is applied on the first electronic component placed on the stage, the electrodes of the first electronic component and the electrodes of the second electronic component are aligned so as to face each other, and temporary compression is performed from the second electronic component side using a compression tool. The temperature, pressure, and time during temporary compression may be appropriately determined according to the specific design, and may be, for example, 60 to 80°C, 0.5 to 2 MPa, and 0.5 to 2 seconds. By performing such temporary compression prior to performing the main compression described below, electronic components (the conductive parts of each component) can be more accurately aligned and connected, which is preferable. By performing temporary compression, it is expected that misalignment during main compression, which is pressed with a higher pressure, can be suppressed.

After the temporary pressure bonding, the main pressure bonding is performed from the second electronic component side using a pressure bonding tool. The temperature, pressure, and time during the main pressure bonding may be any known condition used when bonding electronic components using an adhesive film, and may be appropriately determined according to the specific design. As described above, by using the adhesive film of the present invention that uses a combination of a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component, good adhesion can be achieved under the previous adhesion conditions using a sulfonium salt-based thermal acid generator. For example, even if the pressure bonding is performed at a low temperature (e.g., 200°C or less, 180°C or less, 160°C or less) and for a short time (e.g., 10 seconds or less, 8 seconds or less, 6 seconds or less), the first electronic component and the second electronic component can be well bonded.

Regardless of whether temporary or permanent bonding is performed, a cushioning material (e.g., a cushioning sheet) may be provided between the second electronic component and the bonding tool. The cushioning material, including whether or not it is used, may be adjusted and determined appropriately depending on the combination of electronic components.

The adhesive composition or adhesive film of the present invention, which uses a combination of a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component, can suppress a decrease in adhesion even when stored for a certain period of time under room temperature/refrigerated conditions. For example, when bonded under bonding conditions of 160°C, 3 MPa, and 5 seconds, a connection structure between an FPC and a glass substrate manufactured using the adhesive composition or adhesive film of the present invention can exhibit an adhesive strength of 7 N/cm or more in a 90-degree peel test, regardless of whether the adhesive composition (adhesive film) used is immediately after manufacture or the adhesive composition (adhesive film) stored for a certain period of time under room temperature/refrigerated conditions.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below. In the following description, "parts" and "%" representing amounts mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[Example 1]
--Preparation of adhesive composition--
Bisphenol F type epoxy resin (trade name: jER4007P, manufactured by Mitsubishi Chemical Corporation) 17.4 parts, phenoxy resin (trade name: YP-50, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., Mw = 60,000) 26.1 parts, polyvinyl acetal resin (trade name: KS-10, manufactured by Sekisui Chemical Co., Ltd.) 8.7 parts, bifunctional alicyclic epoxy compound (trade name: CELLOXIDE 2021P, manufactured by Daicel Corporation, a compound represented by the following formula (i)) 13.0 parts, tetrafunctional alicyclic epoxy compound (trade name: KR-470, manufactured by Shin-Etsu Chemical Co., Ltd., a compound represented by the following formula (ii) A mixture of 10.9 parts of a compound represented by the formula (I) (trade name: CXC-1612, manufactured by Kusumoto Chemical Co., Ltd.) and 2.6 parts of a quaternary ammonium salt-based thermal acid generator (trade name: CXC-1612, manufactured by Kusumoto Chemical Co., Ltd.) and 5.7 parts of conductive particles (trade name: Micropearl, manufactured by Sekisui Chemical Co., Ltd., Ni resin particles having an average particle size of 4 μm) and 13.0 parts of a butadiene-based rubber (trade name: RKB-5515, manufactured by Resinous Chemical Co., Ltd.) and 2.6 parts of a silane coupling agent (trade name: A187, manufactured by Dow Corning Toray Co., Ltd.) was added with PMA as a solvent so that the total solid content was 43.38%, and the mixture was mixed uniformly to obtain an adhesive composition.

- Preparation of adhesive film -
A PET film (thickness 50 μm) was prepared as a release substrate. The adhesive composition was uniformly applied onto this release substrate so that the thickness of the adhesive film (adhesive layer) after drying was 18 μm. Then, the adhesive composition was dried in an oven at 70° C. for 5 minutes to form an adhesive layer on the release substrate. Next, a cover film was laminated at 45° C. on the exposed surface of the adhesive layer.

[Reference Example 1] (Conventional system of bifunctional alicyclic epoxy compound + sulfonium salt-based thermal acid generator)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Example 1, except that 2.6 parts of a sulfonium salt-based thermal acid generator (product name: SI-60L, manufactured by Sanshin Chemical Industry Co., Ltd.) was used in place of 2.6 parts of a quaternary ammonium salt-based thermal acid generator (product name: CXC-1612, manufactured by Kusumoto Chemical Industries Co., Ltd.), and only a bifunctional alicyclic epoxy compound (product name: CELLOXIDE 2021P, manufactured by Daicel Corporation) was used in the amount shown in Table 1 as a cationic polymerizable component.

[Comparative Example 1] (Difunctional alicyclic epoxy compound + quaternary ammonium salt-based thermal acid generator system)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Example 1, except that only 23.9 parts of a bifunctional alicyclic epoxy compound (product name: CELLOXIDE 2021P, manufactured by Daicel Corporation) was used as the cationically polymerizable component.

[Comparative Example 2] (Conventional system of bifunctional alicyclic epoxy compound + sulfonium salt-based thermal acid generator)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Example 1, except that 2.5 parts of a sulfonium salt-based thermal acid generator (product name: SI-60L, manufactured by Sanshin Chemical Industry Co., Ltd.) was used instead of 2.6 parts of a quaternary ammonium salt-based thermal acid generator (product name: CXC-1612, manufactured by Kusumoto Chemical Industries Co., Ltd.), and only a bifunctional alicyclic epoxy compound (product name: CELLOXIDE 2021P, manufactured by Daicel Corporation) was used as the cationically polymerizable component, and the blending amounts of each component were as shown in Table 1.

[Examples 2 to 6] (Effect of tetrafunctional/bifunctional mass ratio)
Except for changing the amount ratio of the difunctional alicyclic epoxy compound and the tetrafunctional alicyclic epoxy compound as shown in Table 2, adhesive compositions were prepared and adhesive films were produced in the same manner as in Example 1.

[Examples 7 to 11] (Effect of thiol compounds)
Adhesive compositions were prepared and adhesive films were produced in the same manner as in Example 1, except that a tetrafunctional thiol compound (trade name: Karenz MT PE1, manufactured by Showa Denko K.K., a compound represented by the following formula (iii)), a trifunctional thiol compound (trade name: Karenz MT NR1, manufactured by Showa Denko K.K., a compound represented by the following formula (iv)), or a bifunctional thiol compound (trade name: Karenz MT BD1, manufactured by Showa Denko K.K., a compound represented by the following formula (v)) was further added in the amounts shown in Table 3.

[Comparative Example 3] (Effect of thiol compound on conventional system)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Reference Example 1, except that 0.4 parts of a tetrafunctional thiol compound (product name: Karenz MT PE1, manufactured by Showa Denko K.K.) was further added.

[Examples 12 to 15] (Effect of composition of film-forming components - phenoxy resin Mw -)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Example 1, except that a phenoxy resin (trade name: jER4210, manufactured by Mitsubishi Chemical Corporation, Mw = 30,000) was used in the amount shown in Table 3 in addition to/instead of the phenoxy resin (trade name: YP-50, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., Mw = 60,000).

[Example 16] (Effect of composition of film-forming components - no polyvinyl acetal resin -)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Example 1, except that a polyvinyl acetal resin (product name: KS-10, manufactured by Sekisui Chemical Co., Ltd.) was not used.

[Example 17] (System without conductive particles)
An adhesive composition was prepared and an adhesive film was produced in the same manner as in Example 1, except that no conductive particles (product name: Micropearl, manufactured by Sekisui Chemical Co., Ltd., Ni resin particles having an average particle size of 4 μm) were used.

The test and evaluation methods are explained below.

<Evaluation of adhesive strength>
- Fabrication of connection structure -
The adhesive film prepared in the examples and comparative examples was slit to a width of 1.0 mm, and then the cover film was peeled off. Next, the adhesive film was attached to the edge of the glass substrate (thickness 0.7 mm) so that the exposed surface of the adhesive layer was bonded to the glass substrate, and a force was applied uniformly on a hot plate at 45 ° C. Then, the peeling base material was peeled off, and the gold wiring part of the flexible printed circuit board (FPC; thickness 50 μm) was connected and bonded so that the exposed surface of the adhesive layer was completely covered. The FPC and the glass substrate were thermocompression bonded with the adhesive layer between them, and all the opposing conductive parts of the FPC and the glass substrate were bonded with the cured product of the adhesive layer to obtain a connected connection structure. The thermocompression bonding conditions were 160 ° C, 3 MPa, and 5 seconds.

The connection structures were made using (1) adhesive film immediately after production (initial), (2) adhesive film stored for 14 days in a room temperature environment of 25°C and 65% RH after production, and (3) adhesive film stored for one month in a refrigerated environment at 5°C after production.

- Measurement and evaluation of adhesive strength -
The adhesive strength of the resulting connection structure was measured by a 90-degree peel test. In detail, the FPC and the cured product were cut to a length of 10 mm, and the 10 mm-long FPC was gripped with a gripper, and the load (N/cm) was measured when the FPC was peeled off in the vertical direction at room temperature (25°C) at a speed of 50 mm/min until it peeled off from the glass substrate. A Tensilon tester (STA-1150, manufactured by Orientec Co., Ltd.) was used for the measurement.

<Evaluation of Conduction Resistance>
- Fabrication of connection structure -
The adhesive film immediately after being produced in the examples and comparative examples was slit to a width of 1.0 mm, and then the cover film was peeled off. Next, the adhesive film was attached to the edge of the ITO glass substrate (thickness 0.7 mm) so that the exposed surface of the adhesive layer was bonded to the ITO glass substrate, and a force was applied uniformly on a hot plate at 45 ° C. Then, the peeling base material was peeled off, and the gold wiring part of the FPC (thickness 50 μm) was connected and bonded so that the exposed surface of the adhesive layer was completely covered. The FPC and the ITO glass substrate were thermocompression bonded with the adhesive layer interposed therebetween to obtain a connection structure. The thermocompression bonding conditions were 160 ° C, 3 MPa, and 5 seconds.

-Measurement and evaluation of conduction resistance-
The conductive resistance of the obtained connection structure was measured immediately after bonding and after being held for 32 hours under high temperature and high humidity conditions of 110° C. and 85% RH, and was evaluated according to the following criteria. Note that this evaluation was not performed for Example 17, which did not contain conductive particles.

Regarding the initial continuity, an index was set as a performance comparison index, not as a practical evaluation standard. Note that if the reliability test is rated B or higher, there is no problem in practical use, and a rating of A is preferable.
Initial (evaluation criteria)
A: Less than 0.5Ω B: 0.5Ω or more and less than 1.0Ω C: 1.0Ω or more After reliability test (evaluation criteria)
A: Less than 1.0 Ω B: 1.0 Ω or more but less than 5.0 Ω C: 5.0 Ω or more

The evaluation results for the examples and comparative examples are shown in Tables 1 to 3.

The results in Table 1 (comparison between Comparative Example 1 and Reference Example 1) show that when a quaternary ammonium salt-based thermal acid generator is used instead of a sulfonium salt-based thermal acid generator, the adhesive strength is reduced under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used.

The results in Table 1 (comparison between Example 1 and Comparative Example 1) show that when a bifunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound are used as radical polymerizable components in combination with a quaternary ammonium salt-based thermal acid generator, not only is the decrease in adhesion suppressed due to storage at room temperature or in a refrigerated environment, but the adhesive strength is also significantly improved even under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used. In Comparative Example 1, it was confirmed that when the entire amount of the bifunctional alicyclic epoxy compound, which is the cationic polymerizable component, is replaced with a tetrafunctional alicyclic epoxy compound (i.e., when a tetrafunctional alicyclic epoxy compound is used alone as the cationic polymerizable component), the adhesive layer does not stick to the glass substrate in the first place.

From the results in Table 2, it can be seen that when the tetrafunctional/bifunctional mass ratio is in the range of 0.1 to 0.85, excellent adhesive strength is exhibited. It was also confirmed that when the tetrafunctional/bifunctional mass ratio is in the range of 0.1 to 0.85, the occurrence of lifting at the connection points of the connection structure can be significantly suppressed even after reliability testing in a high-temperature, high-humidity environment. Furthermore, it can be seen that when the tetrafunctional/bifunctional mass ratio is in the range of 0.1 to 0.4, significantly excellent adhesive strength is achieved.

The results in Table 3 (comparison of Examples 7 to 11 and Comparative Example 3) show that in adhesive compositions using sulfonium salt-based thermal acid generators, the addition of a thiol compound not only does not improve adhesive strength, but rather reduces adhesive strength. In contrast, in the adhesive composition of the present invention, which uses a combination of a quaternary ammonium salt-based thermal acid generator and a specific cationic polymerizable component (a combination of a bifunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound), the further inclusion of a thiol compound dramatically improves adhesive strength.

The results in Table 3 (Examples 12 to 16 (compared to Example 1)) show that even when the composition of the film-forming components is changed, good adhesive strength is exhibited under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used. It was also confirmed that the inclusion of a phenoxy resin with Mw 30,000 as the film-forming component significantly suppresses the occurrence of lifting at the connection points of the connection structure even after reliability testing in a high-temperature, high-humidity environment.

Furthermore, the results in Table 3 (Example 17) show that even when no conductive particles are added, good adhesive strength is exhibited under the same adhesive conditions as when a sulfonium salt-based thermal acid generator is used.

Regarding the initial conductivity and conductivity after reliability testing, all examples showed values that were practically acceptable.

Claims (15)

An adhesive composition comprising a binder composition containing a cationic polymerizable component and a film-forming component, and a cationic polymerization initiator,
the cationic polymerization initiator is a quaternary ammonium salt-based thermal acid generator;
An adhesive composition, wherein the cationically polymerizable component comprises a difunctional alicyclic epoxy compound and a tetrafunctional alicyclic epoxy compound, and the tetrafunctional alicyclic epoxy compound comprises a tetrafunctional alicyclic epoxy compound comprising a structural unit represented by formula (1) .

(In the formula, R ¹ represents a monovalent organic group having an epoxy C ₃ -C ₁₀ cycloalkyl group, and R ² represents a hydrogen atom, a hydrocarbon group, or an alkoxy group.) The adhesive composition according to claim 1, in which the mass ratio of the tetrafunctional alicyclic epoxy compound to the difunctional alicyclic epoxy compound [tetrafunctional alicyclic epoxy compound/difunctional alicyclic epoxy compound] (hereinafter referred to as the "tetrafunctional/difunctional mass ratio") is less than 1.0. The adhesive composition according to claim 1 or 2, wherein the tetrafunctional/difunctional mass ratio is 0.1 or more and 0.85 or less. The adhesive composition according to any one of claims 1 to 3, wherein the difunctional alicyclic epoxy compound has an epoxy C ₃ -C ₁₀ cycloalkyl group. The adhesive composition according to any one of claims 1 to 4 , wherein the tetrafunctional alicyclic epoxy compound containing a structural unit represented by formula (1) has four structural units represented by formula (1) in one molecule. The adhesive composition according to any one of claims 1 to 5 , further comprising a thiol compound. The adhesive composition according to claim 6 , wherein the thiol compound contains the same number of carbonyloxy groups as the number of mercapto groups in one molecule. The adhesive composition according to claim 6 or 7 , wherein the functionality of the thiol compound is 2 or more. The adhesive composition according to any one of claims 6 to 8 , wherein the thiol compound contains a structural unit represented by formula (2).

The adhesive composition according to any one of claims 6 to 9 , wherein a mass ratio of the thiol compound to the quaternary ammonium salt-based thermal acid generator [thiol compound/quaternary ammonium salt-based thermal acid generator] is 0.1 or more. The adhesive composition according to any one of claims 1 to 10 , wherein the film-forming component comprises a phenoxy resin. The adhesive composition according to claim 1 , further comprising conductive particles. An adhesive film comprising the adhesive composition according to any one of claims 1 to 12 . A connection structure in which a first electronic component and a second electronic component are connected with the adhesive composition according to any one of claims 1 to 12 or the adhesive film according to claim 13 . A method for producing a connection structure, comprising a step of pressure-bonding a first electronic component and a second electronic component with the adhesive composition according to any one of claims 1 to 12 or the adhesive film according to claim 13 interposed therebetween.