HK1139170B - Adhesive composition - Google Patents

Description

Adhesive composition

Technical Field

The present invention relates to an adhesive composition comprising a thermoplastic resin, a monofunctional acrylate and a radical polymerization initiator.

Background

In display devices such as liquid crystal display devices, plasma display devices, and organic EL display devices, most display panels are anisotropically and conductively connected to a flexible wiring board by thermocompression bonding via an anisotropic conductive film. As such an anisotropic conductive film, a film in which conductive particles are dispersed in an adhesive composition containing a thermoplastic resin, an epoxy resin, and an amine-based curing agent as main components is generally used, and the thermocompression bonding condition is generally 180 ℃ for 7 seconds.

However, in recent years, since the screen size of the display panel has increased, the influence of thermal stress on the display panel when thermocompression bonding is performed using the anisotropic conductive film cannot be ignored, and in order to eliminate the influence as much as possible, it is necessary to change the thermocompression bonding condition from 7 seconds at 180 ℃ to 4 seconds at 160 ℃ ± 20 ℃. Therefore, as an anisotropic conductive film that can be bonded at a relatively low temperature, a radical polymerizable anisotropic conductive film in which conductive particles are dispersed in a binder containing a thermoplastic resin, a polyfunctional acrylate, and a peroxide as main components to form a film can be used. Further, in the thermal curing process of such a radical polymerizable anisotropic conductive film, hydroxyl groups, which improve the adhesion to a display panel or a flexible wiring substrate, are not desired to be generated. Therefore, in order to improve the adhesiveness, a urethane acrylate having 2 or more highly polar urethane bonds in the molecule showing affinity for the polyimide surface or the metal is blended into the adhesive (patent document 1).

Patent document 1: japanese patent laid-open publication No. 2006 and 257208

Disclosure of Invention

Problems to be solved by the invention

In order to improve the adhesion with the anisotropic conductive film, the surface of the anisotropic conductive connection for the display panel or the flexible wiring board is subjected to surface roughening treatment with chemicals before thermocompression bonding, but with the recent densification of the wiring pitch, when the wiring metal surface of the flexible wiring board or the polyimide surface exposed between the wirings is subjected to surface roughening treatment with chemicals in the same manner as in the conventional art, adverse effects such as thinning of the wiring metal occur, and therefore it is difficult to perform surface roughening treatment on the same level as in the conventional art.

Therefore, there are problems as follows: it is necessary to perform thermocompression bonding with the anisotropic conductive film in a state where the surface roughening treatment is not sufficiently performed on the surfaces and the surfaces are kept relatively smooth, and even when the anisotropic conductive film of patent document 1 containing urethane acrylate is used, sufficient adhesive strength between the display panel and the flexible wiring board cannot be secured.

The present invention is intended to solve the above problems of the prior art, and has an object to: even if the wiring metal surface of the flexible wiring substrate or the polyimide surface exposed between the wirings is in a relatively smooth state, the adhesive composition comprising the thermoplastic resin, the polyfunctional acrylate and the radical polymerization initiator can exhibit good adhesive strength to these surfaces.

Means for solving the problems

The present inventors found that the conventional urethane acrylate blended into the adhesive composition comprising a thermoplastic resin, a polyfunctional acrylate and a radical polymerization initiator cannot ensure sufficient adhesive strength between a relatively smooth display panel and a flexible wiring substrate because the urethane bond of the urethane acrylate used in patent document 1 is not present at the molecular end but present inside, and thus the effect on the wiring metal surface of the flexible wiring substrate or the polyimide surface exposed between the wirings is suppressed due to the influence of steric hindrance or the like, and found that the above object can be achieved by using a monofunctional urethane acrylate having a urethane residue at the terminal instead of a urethane acrylate having 2 or more urethane bonds in the molecule, thereby completing the present invention.

Specifically disclosed is an adhesive composition which is characterized by containing a thermoplastic resin, a polyfunctional acrylate and a radical polymerization initiator, and is characterized by containing a monofunctional urethane acrylate having a urethane residue at the end, which is represented by the formula (1).

CH₂＝CR₀-COO-R₁-NHCOO-R₂ (1)

In the formula (1), R₀Is hydrogen or methyl, R₁Is a divalent hydrocarbon radical, R₂Is optionally substituted lower alkyl.

Further, the present invention provides a connection structure formed by electrically connecting opposing electrodes with the above adhesive composition interposed therebetween, the adhesive composition containing conductive ions for anisotropic conductive connection.

Effects of the invention

The adhesive composition of the present invention comprising a thermoplastic resin, a polyfunctional acrylate and a radical polymerization initiator comprises a urethane acrylate having a urethane residue at the terminal. In this case, the acrylate residue is a polymerization site and is expected to exist at the molecular terminal, so the urethane acrylate having a urethane residue at the terminal must be monofunctional. Therefore, compared with urethane acrylate having 2 or more urethane bonds in the molecule, monofunctional urethane acrylate having a urethane residue at the end can reduce the molecular structure itself, and can sufficiently exert the affinity of the urethane bond to the wiring metal surface of the flexible wiring board or the polyimide surface exposed between the wirings, and therefore can exhibit good adhesive strength even when these surfaces are in a relatively smooth state.

Brief Description of Drawings

Fig. 1 is an explanatory view of an adhesive strength test (in the drawing, FPC is an abbreviation of flexible printed circuit, TAB is an abbreviation of tape automated bonding, and ACF is an abbreviation of anisotropic conductive film).

Best Mode for Carrying Out The Invention

The adhesive composition of the present invention is an adhesive composition comprising a thermoplastic resin, a polyfunctional acrylate and a radical polymerization initiator, and is characterized by comprising a monofunctional urethane acrylate having a urethane residue at the terminal represented by formula (1).

CH₂＝CR₀-COO-R₁-NHCOO-R₂ (1)

In the formula (1), R₀Is hydrogen or methyl. Herein, when R is₀When hydrogen, the terminal of the monofunctional urethane acrylate of the formula (1) has an acrylate residue more reactive than methacrylate, when R is₀When the group is a methyl group, the monofunctional urethane acrylate of the formula (1) has a methacrylate residue at the terminal. Therefore, when higher reactivity of the binder composition is required, R is preferable₀Is hydrogen, and R is preferred when lower reactivity of the binder composition is desired₀Is methyl.

R₁Is a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include an alkylene group such as a methylene group, an ethylene group, a propylene group, a butylene group, and a cyclohexylene group, an arylene group such as a phenylene group and a naphthylene group, and an aralkylene group such as a xylylene group. Among them, an alkylene group is preferable, particularly a methylene group and an ethylene group are preferable, and an ethylene group is more preferable, from the viewpoint of improving the adhesive strength.

R₂Is optionally substituted lower alkyl. Examples of the substituent include an alkoxy group such as a methoxy group or an ethoxy group, and an aryl group such as a phenyl group. Examples of the lower alkyl group include a methyl group, an ethyl group, an isopropyl group, a propyl group, a butyl group, an isobutyl group, a pentyl group, and a hexyl group,Hexyl, cyclohexyl, and the like. As R₂Preferable specific examples of (3) include methyl, ethyl, ethoxyethyl, butyl and hexyl groups, and among them, methyl or ethyl groups are more preferable in terms of the effect of improving the adhesive strength.

Therefore, preferable specific examples of the monofunctional urethane acrylate of the formula (1) include methyl N- (methacryloyloxyethyl) carbamate, ethyl N- (methacryloyloxyethyl) carbamate, ethoxyethyl N- (methacryloyloxyethyl) carbamate, butyl N- (methacryloyloxyethyl) carbamate, hexyl N- (methacryloyloxyethyl) carbamate, and the like. Methyl or ethyl N- (methacryloyloxyethyl) carbamate is particularly preferred.

Since the content of the monofunctional urethane acrylate in the adhesive composition is likely to cause a decrease in adhesive strength when it is too small and a decrease in cohesive force and conduction failure when it is too large, the content of the monofunctional urethane acrylate in the resin solid component (the total of the thermoplastic resin, the polyfunctional acrylate, the radical polymerization initiator, and the monofunctional urethane acrylate) is preferably 2% by mass to 20% by mass, and more preferably 5% by mass to 10% by mass.

Although commercially available products can be used as the monofunctional urethane acrylate, as disclosed in jp-a-54-005921, a monofunctional urethane acrylate can be synthesized by reacting a compound having a methacryloxy group and a terminal isocyanate group with an alcohol.

The thermoplastic resin constituting the adhesive composition of the present invention is a component for forming a film, and can be appropriately selected and used from thermoplastic resins generally used in the fields of anisotropic conductive adhesives, insulating adhesives, and the like. Specific examples of the thermoplastic resin include phenoxy resins, polyurethane resins, polyimides, polyamides, poly (meth) acrylates, polyether polyurethanes, NBR resins, and the like. The weight average molecular weight of these thermoplastic resins is usually 5000-150000 from the viewpoint of ensuring film-forming properties and ensuring compatibility with other components.

When the content of the thermoplastic resin in the binder composition is too small, it is difficult to form a film, and when too large, it is liable that the resin cannot be excluded at the time of connection to cause conduction failure, and therefore the content of the thermoplastic resin in the solid resin component (the total of the thermoplastic resin, the polyfunctional acrylate, the radical polymerization initiator, and the monofunctional urethane acrylate) is preferably 10% by mass to 60% by mass, more preferably 20% by mass to 50% by mass.

The multifunctional acrylate constituting the adhesive composition of the present invention is a component that introduces a three-dimensional network structure into the adhesive composition film and increases the cohesive force. The polyfunctional acrylate is a polymerizable compound having 2 or more acrylate residues or methacrylate residues in the molecule, and can be appropriately selected from polyfunctional acrylates generally used in the fields of anisotropic conductive adhesives, insulating adhesives, and the like. Specific examples of the polyfunctional acrylate include trimethylolpropane tri (meth) acrylate, polyethylene glycol di (meth) acrylate, polyalkylene glycol di (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, neopentyl glycol di (meth) acrylate, dipentaerythritol hexa (meth) acrylate, isocyanuric acid-modified 2-functional (meth) acrylate, isocyanuric acid-modified 3-functional (meth) acrylate, and the like.

When the content of the polyfunctional acrylate in the adhesive composition is too small, the cohesive force is insufficient, and the connection reliability is lowered, and when too large, the polyfunctional acrylate is hardened, and the stress relaxation effect is lowered, and the adhesive force tends to be lowered, so that the content of the polyfunctional acrylate in the resin solid component (the total of the thermoplastic resin, the polyfunctional acrylate, the radical polymerization initiator, and the monofunctional urethane acrylate) is preferably 10% by mass to 60% by mass, and more preferably 20% by mass to 50% by mass.

The radical polymerization initiator constituting the adhesive composition of the present invention is an initiator for radical polymerization of a multifunctional acrylate and a monofunctional urethane acrylate, and can be appropriately selected from radical polymerization initiators which are generally used in the fields of anisotropic conductive adhesives, insulating adhesives, and the like and hardly generate gas during polymerization. From the viewpoint of stability, reactivity, compatibility, as a specific example of the radical polymerization initiator, an organic peroxide having a 1-minute half-life temperature of 90 ℃ to 175 ℃ and a molecular weight of 180-1,000 can be preferably used. Specific examples of such organic peroxides include benzoyl peroxide, cumyl peroxyneodecanoate, 1, 3, 3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, tert-hexyl peroxyneodecanoate, tert-butyl peroxypivalate, 1, 3, 3-tetramethylbutyl peroxy2-ethylhexanoate, 2, 5-dimethyl-2, 5-bis (2-ethylperoxyhexanoyl) hexane (2, 5- ジメチル -2, 5- ジ (2- エチルヘキサノイルパ - オキシ) ヘキサン), tert-hexyl peroxy2-ethylhexanoate, tert-butyl peroxypivalate, and the like, Tert-butyl peroxyneoheptanoate, tert-amyl peroxy-2-ethylhexanoate, di-tert-butyl peroxyhexahydroterephthalate, tert-amyl peroxy-3, 5, 5-trimethylhexanoate, 3-hydroxy-1, 1-dimethylbutyl peroxyneodecanoate, tert-amyl peroxy-2-ethylhexanoate, tert-hexyl peroxyisopropylmonocarbonate, tert-butyl peroxymaleate, tert-butyl peroxy-3, 5, 5-trimethylhexanoate, tert-butyl peroxylaurate, 2, 5-dimethyl-2, 5-bis (3-methylperoxybenzoyl) hexane (2, 5- ジメチル -2, 5- ジ (3- メチルベンソイルパ - オキシ) ヘキサン), T-butyl peroxy-2-ethylhexyl monocarbonate, t-hexyl peroxybenzoate, 2, 5-dimethyl-2, 5-di (benzoyl peroxide) hexane (2, 5- ジメチル -2, 5- ジ (ベンソイルパ - オキシ) ヘキサン), t-butyl peroxybenzoate, dibutyl trimethyl peroxyadipate, t-amyl n-octanoate peroxide, t-amyl peroxyisononanoate, t-amyl peroxybenzoate, and the like. These compounds may be used in combination of two or more.

Since the curing is insufficient when the content of the radical polymerization initiator in the adhesive composition is too small and the resin exclusivity and the connection resistance tend to be decreased and increased when the content is too large at the time of heating and pressurizing, the content of the radical polymerization initiator in the resin solid component (the total of the thermoplastic resin, the polyfunctional acrylate, the radical polymerization initiator, and the monofunctional urethane acrylate) is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 8% by mass.

The adhesive composition of the present invention may contain, as required, conductive particles such as nickel particles having a particle diameter of 0.1 to 10 μm, anisotropic conductive particles such as resin-coated nickel particles having a particle diameter of 2 to 10 μm, and insulating fillers such as silica having a particle diameter of 0.01 to 1 μm. If the conductive particles are contained, they can be used as a conductive adhesive composition. If the anisotropic conductive particles are contained, they can be used as an anisotropic conductive adhesive. In this case, the anisotropic conductive particles are blended in the resin solid content (the total of the thermoplastic resin, the polyfunctional acrylate, the radical polymerization initiator, and the monofunctional urethane acrylate) preferably at 1% by mass to 50% by mass, more preferably at 1% by mass to 40% by mass. Further, if a filler is contained, the mechanical strength of the cured product can be improved. In addition, various rubber materials may be included for stress relaxation at the time of hardening. Further, if necessary, general-purpose solvents such as alcohols such as methanol, ethanol, and butanol, esters such as ethyl acetate, and ketones such as acetone and methyl ethyl ketone can be appropriately blended. These solvents are preferably contained when the adhesive composition is made into a film.

The binder composition of the invention can be formulated as follows: the thermoplastic resin, the polyfunctional acrylate, the radical polymerization initiator, the monofunctional urethane acrylate having a urethane residue at the terminal represented by formula (1), and other additive components or solvents as needed are uniformly mixed by a conventional method.

The binder composition of the present invention can be used as a paste or a film according to a known method. For example, the adhesive composition of the present invention is sandwiched between opposing electrodes as a paste or a film and thermocompression bonded to obtain a connection structure in which the electrodes are electrically connected to each other. The opposed electrodes include, but are not limited to, a combination of electrodes of a display panel and electrodes of a flexible wiring board. In a preferred embodiment, one of the opposing electrodes is an electrode pad of a semiconductor device.

The thermocompression bonding conditions include curing conditions at a relatively low temperature for a short time, usually 100 ℃ to 200 ℃ for 3 seconds to 10 seconds, preferably 130 ℃ to 200 ℃ for 3 seconds to 6 seconds. Thus, a wide bonding temperature limit can be achieved.

Examples

The present invention will be specifically described below by way of examples.

Example 1

100 parts by mass of methanol was added to 10 parts by mass of isocyanatoethyl methacrylate, and stirred at 60 ℃ for 10 hours to obtain a methanol solution of N- (methacryloyloxyethyl) carbamic acid methyl ester. 40 parts by mass of phenoxy resin (YP50, Tokyo chemical Co., Ltd.), 40 parts by mass of diacrylate (ライトエステル 3EG, Kyoto chemical Co., Ltd.), 10 parts by mass of polyester polyurethane (ニツポラン 3113, Japan ポリウレタン, Ltd.), 3 parts by mass of benzoyl peroxide (Japan oil & fat Co., Ltd.) and a mixed solvent of ethyl acetate and toluene (1: 1 (volume ratio) in such an amount that the solid content of the resin becomes 50% by mass) were uniformly mixed with the methanol solution containing 10 parts by mass of methyl N- (methacryloyloxyethyl) carbamate to obtain an adhesive composition.

Example 2

The same operation as in example 1 was repeated except that 100 parts by mass of ethanol was used instead of 100 parts by mass of methanol to prepare an ethanol solution of N- (methacryloyloxyethyl) urethane, thereby obtaining an adhesive composition.

Example 3

The same operation as in example 1 was repeated except that 100 parts by mass of ethoxyethanol was used instead of 100 parts by mass of methanol to prepare an ethoxyethanol solution of ethoxyethyl N- (methacryloyloxyethyl) carbamate, thereby obtaining an adhesive composition.

Example 4

The same operation as in example 1 was repeated except that 100 parts by mass of butanol was used instead of 100 parts by mass of methanol to prepare a butanol solution of N- (methacryloyloxyethyl) butyl carbamate, thereby obtaining an adhesive composition.

Example 5

The same operation as in example 1 was repeated except that 100 parts by mass of hexanol was used instead of 100 parts by mass of methanol to prepare a hexanol solution of hexyl N- (methacryloyloxyethyl) carbamate, thereby obtaining an adhesive composition.

Comparative example 1

The same operation as in example 1 was repeated except that 100 parts by mass of phenol was used instead of 100 parts by mass of methanol to prepare a phenol solution of phenyl N- (methacryloyloxyethyl) carbamate, thereby obtaining a binder composition.

Comparative example 2

10 parts by mass of 2-functional urethane acrylate (U-ZPP A, Mitsumura chemical Co., Ltd.) was uniformly mixed with 40 parts by mass of phenoxy resin (YP50, Tokyo chemical Co., Ltd.), 40 parts by mass of diacrylate (ライトエステル 3EG, Kyowa chemical Co., Ltd.), 10 parts by mass of polyester polyurethane (ニツポラン 3113, Japan ポリウレタン Co., Ltd.), 3 parts by mass of benzoyl peroxide (Japan oil & fat Co., Ltd.) and a mixed solvent of ethyl acetate and toluene (1: 1 (volume ratio) in an amount such that the solid content of the resin became 50 mass%) to obtain an adhesive composition.

Comparative example 3

40 parts by mass of a phenoxy resin (YP50, Tokyo chemical Co., Ltd.), 40 parts by mass of a diacrylate (ライトエステル 3EG, Kyoho chemical Co., Ltd.), 10 parts by mass of a polyester polyurethane (ニツポラン 3113, Japan ポリウレタン Co., Ltd.), and 3 parts by mass of benzoyl peroxide (Japan oil & fat Co., Ltd.) and a mixed solvent of ethyl acetate and toluene (1: 1 (volume ratio) in an amount such that the solid content of the resin becomes 50% by mass) were uniformly mixed to obtain a binder composition.

Evaluation of

The adhesive compositions of examples and comparative examples were coated on a release-treated polyethylene terephthalate film having a thickness of 50 μm to a dry thickness of 50 μm, and were dried in an oven at 80 ℃ for 5 minutes to prepare adhesive films. The adhesive strength was measured as follows using the obtained adhesive film.

(bond Strength test: refer to FIG. 1)

An ITO glass substrate on which an ITO film was formed and a polyimide flexible wiring substrate (40 mm in width) having a pitch of 50 μm (25 μm in width of copper wiring and 8 μm in thickness of copper wiring) were prepared on a glass substrate having a thickness of 0.7mm, and electrodes of the wirings were respectively opposed to each other with an adhesive film interposed therebetween, and thermocompression-bonded under conditions of 160 ℃ and 4MPa for 4 seconds. After the thermocompression bonding, the polyimide flexible wiring substrate was cut to a cut of the adhesive film with a width of 10mm, and was peeled at 90 degrees at a speed of 50mm/min by a tensile tester (テンシロン, オリエンテツク). The values of the adhesion strength obtained at this time are shown in table 1. In addition, from the viewpoint of practicality, it is desirable that the adhesive strength is 5N/cm or more.

[ Table 1]

As shown in Table 1, the adhesive compositions of examples 1 to 5 are preferably 5N/cm or more in adhesive strength from the viewpoint of practical use, and particularly, the adhesive strength is high when R2 is a methyl group or an ethyl group.

On the other hand, in the case of comparative example 1 in which R2 is a phenyl group, in the case of comparative example 2 in which a 2-functional urethane acrylate is used, or in the case of comparative example 3 in which no urethane acrylate is used, the adhesive strength is not 5N/cm or more.

Industrial applicability of the invention

The adhesive composition of the present invention comprising a thermoplastic resin, a polyfunctional acrylate and a radical polymerization initiator comprises a monofunctional urethane acrylate having a urethane residue at the terminal. This makes it possible to sufficiently exert affinity of urethane bonds to the wiring metal surface of the flexible wiring board or the polyimide surface exposed between the wirings, and thus to exhibit good adhesive strength even when these surfaces are in a relatively smooth state. Therefore, the method can be used for connecting electronic materials with dense intervals and smooth bonding surfaces.

Claims (8)

1. An adhesive composition comprising a thermoplastic resin, a polyfunctional acrylate and a radical polymerization initiator, characterized by comprising a monofunctional urethane acrylate having a urethane residue at the terminal represented by formula (1),

CH₂＝CR₀-COO-R₁-NHCOO-R₂ (1)

wherein R is₀Is hydrogen or methyl, R₁Is a divalent hydrocarbon radical, R₂Is optionally substituted methyl, ethyl, isopropyl, propyl, butyl, isobutylA radical, a pentyl radical, a hexyl radical or a cyclohexyl radical,

the resin solid content contains 2 to 20 mass% of the monofunctional urethane acrylate.

2. The binder composition of claim 1, wherein R₁Is an alkylene group.

3. The binder composition of claim 2, wherein the alkylene group is ethylene.

4. The binder composition of any one of claims 1-3, wherein R₂Is methyl, ethyl, ethoxyethyl, butyl or hexyl.

5. The binder composition of claim 4, wherein R₂Is methyl or ethyl.

6. The adhesive composition of any one of claims 1-3, wherein the adhesive composition comprises conductive particles for anisotropic conductive connection.

7. A connecting structure formed by electrically connecting opposing electrodes with the adhesive composition of claim 6 interposed therebetween.

8. The connection structure of claim 7, wherein one of the opposing electrodes is an electrode pad of the semiconductor element.