TWI866934B - Conductive adhesive composition - Google Patents

Abstract

The present invention provides a conductive adhesive composition that can be processed below 120°C and has both isotropic conductivity and excellent adhesion. A conductive adhesive composition, relative to 100 parts by mass of a resin component, contains 50 to 300 parts by mass of a dendritic conductive filler, and the resin component contains at least: a crystalline thermoplastic resin (A) with a melting point of more than 90°C, a carboxyl-modified polyester resin (B) and a urethane-modified polyester resin (C).

Description

Conductive adhesive composition

The present invention relates to a conductive adhesive composition.

Background technology As a method for electrically connecting electronic parts to substrates, a conductive adhesive composition in which a conductive filler is dispersed can be used. Regarding the above-mentioned conductive adhesive composition, for example, Patent Document 1 describes a thermoplastic resin composition, which is based on the purpose of providing a thermoplastic resin composition having excellent mechanical strength and heat resistance and excellent electrical properties such as conductivity and antistatic properties, and includes an amorphous thermoplastic resin (component A), a crystalline thermoplastic resin (component B), a conductive carbon black (component C), and a conductive carbon black or hollow carbon fiber having a larger specific surface area than the conductive carbon black of component C.

However, when a conductive adhesive composition that can obtain isotropic conductivity is sought according to different uses, the conductivity of the thermoplastic resin composition described in Patent Document 1 is anisotropic. If a high amount of conductive filler is added to make it isotropic, there is a risk that the adhesiveness will be impaired.

Furthermore, in recent years, conductive adhesive compositions used for connecting heat-sensitive components such as electronic parts, for example, electrodes of piezoelectric films, etc., are required to be processed at low temperatures, especially below 120°C. In view of the above problem, Patent Document 2 discloses an anisotropic conductive film that anisotropically connects a terminal of a first electronic part to a terminal of a second electronic part, and contains a film-forming resin, a curing resin, a curing agent, and conductive particles, and the film-forming resin contains a crystalline resin and an amorphous resin. Furthermore, Patent Document 3 discloses an anisotropic conductive film, which is used to anisotropically connect the terminal of a first electronic component to the terminal of a second electronic component, and is characterized in that it contains a crystalline resin, an amorphous resin, and conductive particles, and the crystalline resin contains a crystalline resin having a resin characteristic bond, and the resin characteristic bond is the same as the resin characteristic bond of the amorphous resin. However, all of the above are anisotropic conductive films.

Furthermore, Patent Document 4 discloses a bonding agent composition comprising: (a) a crystalline polyester resin having a melting point of 40°C to 80°C, (b) a free radical polymerizable compound, and (c) a free radical polymerization initiator; and in order to impart conductivity or anisotropic conductivity, it is disclosed that the bonding agent composition may further include (f) conductive particles.

However, as described above, in order to obtain isotropic conductivity, a high amount of conductive filler must be added, and there is room for further improvement in achieving both adhesion and isotropic conductivity.

Prior art documents Patent documents [Patent document 1] Japanese Patent Publication No. 2003-96317 [Patent document 2] Japanese Patent Publication No. 2014-102943 [Patent document 3] Japanese Patent Publication No. 2014-60025 [Patent document 4] International Publication No. 2009/038190

Summary of the invention Problems to be solved by the invention The present invention is completed in view of the above, and its purpose is to provide a conductive adhesive composition that can be processed at a low temperature below 120°C and has both isotropic conductivity and excellent adhesion.

Means for solving the problem To solve the above problem, the conductive adhesive composition of the present invention contains 50 to 300 parts by mass of a dendritic conductive filler relative to 100 parts by mass of a resin component, and the resin component contains at least: a crystalline thermoplastic resin (A) having a melting point of 90°C or above, a carboxyl-modified polyester resin (B) and a urethane-modified polyester resin (C).

The crystalline thermoplastic resin (A) may be a crystalline polyester resin.

The glass transition point of the carboxyl-modified polyester resin (B) may be 10-30°C.

The glass transition point of the urethane modified polyester resin (C) may be 80-120°C.

The content of the crystalline thermoplastic resin (A) can be 50-70 parts by mass in 100 parts by mass of the resin component.

The content of the carboxyl-modified polyester resin (B) can be 15-35 parts by weight based on 100 parts by weight of the resin component.

The content of the urethane modified polyester resin (C) can be 15-35 parts by weight based on 100 parts by weight of the resin component.

Effect of the invention The conductive adhesive composition of the present invention can be processed at a low temperature below 120°C, and can obtain isotropic conductivity and excellent adhesion.

The following is a more detailed description of the implementation of the present invention.

The conductive adhesive composition of this embodiment contains 50-300 parts by weight of a dendritic conductive filler relative to 100 parts by weight of a resin component, and the resin component contains at least a crystalline thermoplastic resin (A) having a melting point of 90°C or above, a carboxyl-modified polyester resin (B), and a urethane-modified polyester resin (C). Here, the so-called crystalline resin is a polymer having a crystalline portion after curing. The differential scanning calorimetry curve of such a crystalline resin obtained during the temperature increase process of differential scanning calorimetry (hereinafter also referred to as "DSC") is not a step-like endothermic change, but shows a clear endothermic peak. The melting point (Tm) of the crystalline resin refers to the peak temperature of the endothermic peak. In this specification, differential scanning calorimetry is measured using a differential scanning calorimeter (e.g., Seiko Instruments Inc., trade name "DSC220"), and the measurement conditions are that air is flowed at a flow rate of 10 mL/min, and after being maintained at 25°C, the temperature is raised to 200°C at a rate of 10°C/min. In this specification, the crystalline thermoplastic resin (A) does not include a carboxyl-modified polyester resin (B) and a urethane-modified polyester resin (C).

The crystalline thermoplastic resin (A) is not particularly limited, and examples thereof include polyester (PEs), polyethylene (PE), polypropylene (PP), polyamide (PA), polyimide (PI), polycarbonate (PC), polyacetal (POM), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), etc., and any one of them may be used alone or in the form of a mixture of two or more thereof. Among them, polyester resin is preferred from the viewpoint of processability at a low temperature of 120°C or less.

The number average molecular weight of the crystalline thermoplastic resin (A) is not particularly limited, and is preferably 8,000 to 30,000, and more preferably 10,000 to 25,000. When the number average molecular weight is within the above range, a suitable viscosity is formed and a film such as an electrode of a piezoelectric thin film is easily formed. In this specification, the number average molecular weight is a value measured using a gel permeation chromatography device (e.g., measuring device: "Lliance HPLC System" manufactured by Waters Corporation, column: "KF-806L" manufactured by Shodex), using tetrahydrofuran as a solvent, and converted based on standard polyethylene.

The melting point of the crystalline thermoplastic resin (A) is not particularly limited as long as it is 90°C or higher, but is preferably 90-140°C, and more preferably 90-130°C. In view of the use of the conductive adhesive composition of this embodiment to connect electronic parts and substrates, it is preferable to maintain adhesion below 85°C. When the melting point of the crystalline thermoplastic resin (A) is 90°C or higher, creep deformation at 85°C is unlikely to occur, and excellent adhesion is easily obtained. In addition, when the melting point of the crystalline thermoplastic resin (A) is 140°C or lower, it is not easy to gel even if it is dissolved in an organic solvent at room temperature, and excellent processability is easily obtained.

The carboxyl modified polyester resin (B) may be crystalline or amorphous, preferably amorphous. The so-called amorphous resin is a polymer substance that does not have a crystalline part after curing. The differential scanning calorimetry curve of the amorphous resin obtained during the temperature increase process of DSC usually does not show a clear endothermic peak.

The glass transition point of the carboxyl modified polyester resin (B) is not particularly limited, and is preferably 10-30°C, preferably 14-30°C. Here, the glass transition point in this specification refers to the temperature of the inflection point of the differential scanning calorimetry curve obtained by differential scanning calorimetry. When the glass transition point is within the above range, it is easy to obtain excellent low-temperature processability and softness, and it is easy to obtain excellent results in the 85°C creep strength test or the 90° peel strength test for evaluating adhesion.

The number average molecular weight of the carboxyl-modified polyester resin (B) is not particularly limited, but is preferably 10,000 to 30,000, and more preferably 14,000 to 20,000. When the number average molecular weight is within the above range, excellent softness is easily obtained, and excellent results are also easily obtained in the 90° peel strength test for evaluating adhesion.

The acid value of the carboxyl-modified polyester resin (B) is not particularly limited, but is preferably 10-25 mgKOH/g, preferably 15-20 mgKOH/g. When the acid value is within the above range, it is easy to obtain excellent softness and also easy to obtain excellent results in the 90° peel strength test for evaluating adhesion.

The urethane-modified polyester resin (C) may be crystalline or amorphous, but is preferably amorphous.

The glass transition point of the urethane modified polyester resin (C) is not particularly limited, but is preferably 70-120°C, more preferably 75-110°C, and more preferably 80-110°C. When the glass transition point is within the above range, excellent low temperature processability and flexibility are easily obtained, and excellent results are easily obtained in the 85°C creep strength test or the 90° peel strength test for evaluating adhesion.

The number average molecular weight of the urethane modified polyester resin (C) is not particularly limited, and is preferably 10000 to 50000, and more preferably 20000 to 45000. When the number average molecular weight is within the above range, it is easy to obtain excellent softness and also easy to obtain excellent results in the 90° peel strength test for evaluating adhesion.

Without prejudice to the object of the present invention, the resin component of the conductive adhesive composition of the present embodiment may also include resins other than the above-mentioned crystalline thermoplastic resin (A), carboxyl-modified polyester resin (B), and urethane-modified polyester resin (C).

The content ratio of the crystalline thermoplastic resin (A) in 100 parts by mass of the resin component is not particularly limited, but is preferably 50 to 70 parts by mass, more preferably 50 to 60 parts by mass. When the content ratio is within the above range, it is easy to obtain excellent results in the 85° creep strength test for evaluating adhesion.

The content ratio of the carboxyl modified polyester resin (B) in 100 parts by weight of the resin component is not particularly limited, but is preferably 15 to 35 parts by weight, and more preferably 20 to 30 parts by weight. When the content ratio is within the above range, it is easy to obtain excellent results in the 90° peel strength test for evaluating adhesion.

The content ratio of the urethane modified polyester resin (C) in 100 parts by weight of the resin component is not particularly limited, but is preferably 15 to 35 parts by weight, and more preferably 20 to 30 parts by weight. When the content ratio is within the above range, it is easy to obtain excellent results in the 85° creep strength test for evaluating adhesion.

The content of the conductive filler is 50-300 parts by mass, preferably 50-280 parts by mass, and more preferably 50-250 parts by mass relative to 100 parts by mass of the resin component. When the content is 50 parts by mass or more, isotropic conductivity is easily obtained, and when the content is 300 parts by mass or less, both conductivity and adhesion are easily achieved.

The conductive filler is not particularly limited as long as it is in a tree-like shape. Examples thereof include copper particles, silver particles, gold particles, nickel particles, silver-coated copper particles, silver-coated copper alloy particles, and silver-coated nickel particles. From the perspective of reducing costs and improving conductivity, silver-coated copper particles, silver-coated copper alloy particles, and silver-coated nickel particles are preferred. Here, the so-called tree-like shape refers to a shape having one or more tree-like protrusions protruding from the surface of the particle. The tree-like protrusions may be only unbranched main branches, or may be a shape in which branch portions branch out from the main branches and grow in a planar or three-dimensional manner.

Silver-clad copper particles may include copper particles and a silver-containing layer covering the copper particles, silver-clad copper alloy particles may include copper alloy particles and a silver-containing layer covering the copper alloy particles, and silver-clad nickel particles may include nickel particles and a silver-containing layer covering the nickel particles. In addition, the copper alloy particles may have a nickel content of 0.5 to 20% by mass and a zinc content of 1 to 20% by mass. Nickel and zinc may also be contained within the above range, with the remainder being composed of copper, and the remainder of the copper containing unavoidable impurities.

The ratio of the silver coating in the silver-coated copper particles, silver-coated copper alloy particles or silver-coated nickel particles is preferably 1-30% by mass, more preferably 3-20% by mass. If the silver coating is 1% by mass or more, excellent conductivity is easily obtained. If the silver coating is 30% by mass or less, excellent conductivity can be maintained and the cost can be reduced compared with silver particles.

The average particle size of the conductive filler is not particularly limited, but is preferably 1 to 20 μm, more preferably 3 to 15 μm. When the particle size is 1 μm or more, excellent dispersibility is easily obtained, and when the particle size is 20 μm or less, excellent conductivity is easily obtained. Here, the average particle size in this specification refers to the particle size (primary particle size) at the cumulative value of 50% in the particle size distribution obtained by the laser diffraction scattering method.

In the conductive adhesive composition of this embodiment, silica or urethane beads can be appropriately added according to the required physical properties to adjust the hardness of the composition. By adding silica, the conductive adhesive composition can be made harder, and by adding urethane beads, the conductive adhesive composition can be made softer.

In addition to the above-mentioned components, the conductive adhesive composition of the present embodiment may also contain antioxidants, pigments, dyes, adhesive imparting resins, plasticizers, ultraviolet absorbers, defoamers, levelers, fillers, flame retardants, etc. within the scope that does not impair the purpose of the present invention.

The conductive adhesive composition of this embodiment can be produced by kneading in a conventional manner using a commonly used Banbury mixer, kneader, roll or other mixer.

The conductive adhesive composition of one embodiment can be used as an electrode of a piezoelectric film or an adhesive for heat-sensitive electronic parts.

The conductive adhesive composition of this embodiment can be coated with a desired film thickness on a film made of polyethylene terephthalate or the like that has been subjected to a mold release treatment to form a film to make a conductive adhesive film. Furthermore, for the purpose of protecting the conductive adhesive film, a mold release film can also be provided on one or both sides thereof.

[Example] The following is an example of the present invention, but the present invention is not limited to the following example. In addition, unless otherwise specified, the following mixing ratios are based on mass.

The conductive adhesive composition was prepared by mixing the components according to the formula shown in Table 1 below. The conductive adhesive composition was coated on a release-treated polyethylene terephthalate (PET) film (release film 18) to prepare a conductive adhesive film with a film thickness of 60 μm. The detailed description of the compounds listed in the table is as follows, Tm represents the melting point, Tg represents the glass transition point, and Mn represents the number average molecular weight.

･Crystalline thermoplastic resin 1: crystalline polyester, Tm=120℃, Mn=22000 ･Crystalline thermoplastic resin 2: crystalline polyester, Tm=92℃, Mn=36000 ･Crystalline thermoplastic resin 3: crystalline polyester, Tm=85℃, Mn=19000 ･Amorphous thermoplastic resin 1: amorphous polyester, Tg=65℃, Mn=16000 ･Carboxyl modified polyester resin: Tg=15℃, Mn=16000, Acid value = 18mgKOH/g ･Urethane modified polyester resin 1: Tg = 84℃, Mn = 40000 ･Urethane modified polyester resin 2: Tg = 106℃, Mn = 25000 ･Conductive filler 1: Silver-coated copper particles in the shape of dendrites, average particle size 5μm, silver coating 10 mass% ･Conductive filler 2: Spherical, silver-coated copper particles, average particle size 5μm ･Urethane beads: "Dynamic beads UCN-5050 CLEAR" manufactured by Dainichi Seika Co., Ltd.

The adhesive properties (85°C creep strength, 90° peel strength and tensile shear strength), surface resistivity and connection resistivity of the obtained conductive adhesive composition were measured, and the results are shown in Table 1. The measurement method is as follows.

･85℃ creep strength: Sample 1 and sample 2 were prepared. Sample 1 was a PET film 10 on which a copper foil 12 was laminated via a double-sided adhesive tape 11, and sample 2 was a PET film 10 on which an aluminum vapor-deposited film 13 was laminated via a double-sided adhesive tape 11 with the aluminum vapor-deposited surface being the surface. Samples 1 and 2 were each cut into pieces of 50 mm × 20 mm in size. Then, the conductive adhesive film 14 with a film thickness of 60 μm made of the conductive adhesive composition obtained above was cut into pieces with a size of 20 mm×5 mm, and then laminated on the copper foil 12 of sample 1, and pressed at a temperature of 100°C and a pressure of 0.5 MPa for 30 seconds, and then the release film 18 was peeled off. Then, as shown in FIG. 1 , the aluminum vapor-deposited surface of the aluminum vapor-deposited film 13 of sample 2 was contacted with the conductive adhesive film 14, and pressed at a temperature of 100°C and a pressure of 0.5 MPa for 30 seconds to connect them. Hold the unjoined end of sample 1 and hang it in a ventilation oven. Add a weight of 500±2g to the unjoined end of sample 2, heat it at 85℃, and measure the time until sample 1 and sample 2 separate at the joint. If the time until separation is more than 500 hours, it is considered to be excellent in adhesion.

･90° peel strength (N/5mm): Prepare the sample 3 and the aluminum vapor-deposited film 13 on which the copper foil 12 is laminated via the double-sided tape 11 on the glass epoxy substrate 15, and cut each into pieces of 5mm×70mm. Then, as shown in FIG2, cut the conductive adhesive film 14 obtained above into pieces of 5mm×50mm, laminate it on the copper foil 12 of the sample 3, and press it at a temperature of 100℃ and a pressure of 0.5MPa for 30 seconds, then peel off the release film 18. Then, the aluminum vapor-deposited surface of the aluminum vapor-deposited film 13 is connected to the conductive adhesive film 14 by pressing at a temperature of 100°C and a pressure of 0.5 MPa for 30 seconds. The aluminum vapor-deposited film 13 connected to the sample 3 is peeled using a tensile tester (PT-200N manufactured by Minebea Co., Ltd.) at a tensile speed of 120 mm/min and a peeling direction of 90 degrees (the direction of the arrow in Figure 2), and the average value of the load until the film breaks is taken as the measured value. The film with a 90° peel strength of 3.5 N/5 mm or more is considered to have excellent adhesion.

･Tensile shear strength (N/20mm): Similar to the 85℃ creep strength, sample 1 and sample 2 were bonded together with a conductive adhesive film 14. According to JIS K6850, a tensile tester "AGS-X50S" manufactured by Shimadzu Corporation was used to perform a tensile test at a tensile speed of 200mm/min, and the maximum load at the time of fracture was measured. Those with a value of 60N/20mm or more were considered to have excellent adhesion.

･Surface resistivity (Ω/□): As shown in Figure 3, cubic electrodes A and B (electrode area: 1 cm ² (each side = 1 cm), electrode surface: gold-plated) are placed on the conductive adhesive film 14 prepared above. The distance between electrodes A and B is set to 10 mm. A load of 4.9 N is applied to each electrode in the vertical direction, and the resistance value between electrodes AB is measured by the two-terminal method. The value after 1 minute from the start of measurement is taken as the surface resistivity R ₁ .

･Connection resistivity: The connection resistivity with the aluminum vapor-deposited surface and the connection resistivity with the copper foil surface were measured. Specifically, as shown in FIG. 4 , an aluminum vapor-deposited film 17 having an aluminum vapor-deposited layer 16 formed on a PET film 10 was prepared, and the conductive adhesive film 14 having a film thickness of 60 μm and composed of the conductive adhesive composition obtained above was transferred to the aluminum vapor-deposited film 17 at a temperature of 100°C and a pressure of 0.5 MPa for 30 seconds, and the release film 18 was peeled off. Then, of the cubic electrodes C and D (electrode area: 1 cm ² (each side = 1 cm), electrode surface: gold-plated), electrode C is placed on the conductive adhesive film 14, and electrode D is placed on the aluminum vapor-deposited film 17. In addition, the connection resistance R ₂ between electrodes CD is measured in the same manner as the surface resistivity. In addition, the connection resistivity with the copper foil surface is measured in the same manner as above except that copper foil is used instead of the aluminum vapor-deposited film 17 and electrode D is placed on the copper foil.

All the measured gas environment temperatures were set to room temperature (18~28℃), and the average values of the test number set to n=5 are shown in Table 1. Those with a resistance value of 10Ω/□ or less can be judged to have excellent conductivity. At this time, the evaluation of whether the electrical connection is anisotropic or isotropic was also carried out, and the evaluation of the surface resistivity _R1 of the anisotropic ones was set to blank (-).

[Table 1]

As shown in Table 1, the adhesion (85°C creep strength, 90° peel strength and tensile shear strength), surface resistivity and connection resistivity of Examples 1 to 7 are all excellent.

Comparative Example 1 is an example in which a crystalline thermoplastic resin having a melting point of 85°C is used to replace the crystalline thermoplastic resin (A), and the creep strength at 85°C is poor.

Comparative Example 2 is an example in which an amorphous thermoplastic resin is used to replace the carboxyl-modified polyester resin (B), and the 90° peel strength is poor.

Comparative Example 3 is an example without the urethane-modified polyester resin (C), and the creep strength at 85°C is poor.

Comparative Example 4 is an example in which the content of the conductive filler is lower than the lower limit, and the surface resistivity and the connection resistivity with the aluminum vapor-deposited surface are poor.

Comparative Example 5 is an example in which the content of the conductive filler exceeds the upper limit, and the 85°C creep strength and 90° peel strength are poor.

Comparative Example 6 is an example in which the conductive filler is spherical in shape, the electrical connection is anisotropic, and the connection resistivity with the aluminum vapor-deposited surface and the connection resistivity with the copper foil surface are different.

1: Sample 2: Sample 3: Sample 10: PET film 11: Double-sided tape 12: Copper foil 13: Aluminum vapor-deposited film 14: Conductive adhesive film 15: Glass epoxy substrate 16: Aluminum vapor-deposited film 17: Aluminum vapor-deposited film 18: Release film A: Electrode B: Electrode C: Electrode D: Electrode R ₁ : Surface resistivity R ₂ : Connection resistivity

Figure 1 is a schematic cross-sectional view of a sample used for 85°C creep strength and tensile shear strength measurement. Figure 2 is a schematic cross-sectional view of a sample used for 90° peel strength measurement. Figure 3 is a schematic cross-sectional view for illustrating a method for measuring surface resistivity _R1 . Figure 4 is a schematic cross-sectional view for illustrating a method for measuring connection resistivity _R2 .

(without)

Claims (7)

A conductive adhesive composition contains 50-300 parts by mass of a dendritic conductive filler relative to 100 parts by mass of a resin component, wherein the resin component contains at least: a crystalline thermoplastic resin (A) having a melting point of 90-140°C, a carboxyl-modified polyester resin (B), and a urethane-modified polyester resin (C). The conductive adhesive composition of claim 1, wherein the aforementioned crystalline thermoplastic resin (A) is a crystalline polyester resin. As in the conductive adhesive composition of claim 1 or 2, the glass transition point of the aforementioned carboxyl-modified polyester resin (B) is 10~30℃. The conductive adhesive composition of claim 1 or 2, wherein the glass transition point of the aforementioned urethane-modified polyester resin (C) is 80~120℃. For example, in the conductive adhesive composition of claim 1 or 2, the content of the aforementioned crystalline thermoplastic resin (A) is 50-70 parts by mass in 100 parts by mass of the resin component. For example, in the conductive adhesive composition of claim 1 or 2, the content of the carboxyl-modified polyester resin (B) is 15 to 35 parts by weight in 100 parts by weight of the resin component. For example, in the conductive adhesive composition of claim 1 or 2, the content of the aforementioned urethane modified polyester resin (C) is 15 to 35 parts by weight in 100 parts by weight of the resin component.