JP2926005B2 - Room temperature stable, one-component electrically conductive flexible epoxy adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to compositions used as adhesives. In particular, the invention relates to flexible epoxy compositions for use as electrically conductive adhesives designed to be stable at room temperature.

[0002]

BACKGROUND OF THE INVENTION The market for flexible polymers provides a wide range of adhesive polymers, including compounds such as polyurethanes, polysulfides, silicones, and epoxy compounds. In particular, epoxy compounds have been shown to have the ability to adhere strongly to a variety of materials, including metals, glass, plastics, wood, and fibers, and are therefore often used to adhere different materials. Further, epoxy compounds are known to exhibit excellent resistance to attack by many corrosive chemicals. Despite the ability to bind these different materials and their resistance to chemical attack, commercially available epoxy compounds lack certain properties required for use as electrically conductive adhesives in automated bonding processes. .
In particular, epoxy-based electrically conductive adhesives must also be convenient to store, can be easily cured, and form a sufficiently flexible bond. Currently, electrically conductive epoxy-based adhesives are available in two forms, two-component or one-component. None of these are convenient for storage and cannot be easily cured.

[0003] Two-component epoxy-based adhesives can be easily cured at room temperature, but are inconvenient to use and to store. The components in a two-component system must be accurately weighed and properly mixed immediately before use. Thus, the various components to be mixed have to be stored separately until use, and the producer has more responsibility for producing an epoxy-based adhesive with certain properties. Of course, two-component epoxy-based adhesives are not effective.

[0004] One-component epoxy-based adhesives are utilized in industrial applications as two basic forms, a rigid epoxy resin and a premixed, freeze-flexible adhesive. Such adhesive compositions are properly stored as a single component, but need to cure at elevated temperatures.
Hard epoxy resins include compounds such as bisphenol A epoxy adhesives and novolaks. These hard epoxy adhesives exhibit strong adhesion to many materials and can be stored properly at room temperature. But,
Rigid epoxy-based adhesives often form hard but brittle bonds that are inappropriate for bonding different materials.
For example, a brittle bond between different materials having different coefficients of thermal expansion cannot withstand the strain caused by thermal drift, and both bonded and non-bonded surfaces can be broken.

[0005] Premixed, freeze-flexible epoxy adhesives are also used industrially, but the use of such adhesives goes beyond that of hard epoxy adhesives. The premixed frozen flexible epoxy adhesive is
US Pat. No. 4,866,108 assigned to the current assignee.
Is disclosed. This includes frozen flexible epoxy adhesive compositions developed for application to spacecraft electronic components, which were later added to Flexipoxy 100 adhesive (Fl
exipoxy 100 Adhesive). ) Are disclosed and claimed. Compared to rigid epoxy adhesives, flexible epoxy adhesives form a more flexible bond that can well accommodate strains between different materials caused by different expansion rates. However, in contrast to hard epoxy adhesives, premixed freeze-flexible epoxy adhesives must be stored in a frozen state and must be thawed before use. In addition, frozen adhesives, once thawed, have a lifespan of only about 2
To 8 hours. However, in practice, typical automated bonding operations require a working life of at least one week. Thus, premixed freeze-flexible epoxy adhesives are difficult to schedule and are used in large volume automated processing due to the need to thaw the adhesive and the limited working life available after thawing. In order to do so, impracticality must be widely considered.

[0006]

Accordingly, there is also provided a flexible bond which can withstand the severities due to changes in the coefficient of expansion between the bonded materials, but provides the convenience of storage at room temperature and the rapid curing at low temperatures. There is a need for a one-component electrically conductive epoxy adhesive. This need is particularly urgent for large volume automated gluing operations that cannot tolerate either frequent breaks in thawing or waste of expensive glue at all. This need must be achieved without sacrificing good adhesive properties.

[0007]

The above object is achieved by the present invention described in the following embodiments.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, an epoxy adhesive composition that is electrically conductive, can be stored at room temperature, provides a brittle, flexible bond, exhibits strong adhesion, and has excellent processing characteristics is provided. Provided. Further, the compositions of the present invention can easily cure at relatively low temperatures (ranging from about 100 ° C to 140 ° C) within 2 hours. Thus, these compositions avoid the significant disadvantages of conventional compositions and still have most (but not all) of the advantages of the above-mentioned conventional compositions.

The room temperature stable, one-component flexible epoxy-based adhesive composition of the present invention comprises: (a) (i) a stoichiometric amount of diethylenetriamine ("D
Durometer Shore D when cured with ETA ")
A polymer mixture containing at least one polyepoxide resin having a hardness not exceeding 45 and (ii) a substantially stoichiometric amount of at least one latent epoxy curing agent; and A conductive filler, wherein the adhesive composition cures to about 10% when cured.
^It shows a volume resistivity of less than ^-2 ohm-cm and a durometer Shore A of less than about 95.

[0010] The polyepoxide resin component of the composition of the present invention is a flexible epoxy resin. A flexible epoxy resin is even defined in the present invention as an epoxy resin having a durometer Shore D measurement of 45 or less when cured with DETA. For comparison, a semi-flexible epoxy resin is defined as an epoxy resin having a durometer Shore D value in the range of about 45 to 75 when cured with DETA, and a hard epoxy resin cured with DETA. An epoxy resin with a durometer Shore D value of more than 75 is defined in some cases.

The epoxy resin curing agent used to cure the epoxy resin is latent curable. Thus, the reaction between the curing agent and the epoxy resin composition does not occur at room temperature. Rather, the epoxy resin composition cures when exposed to elevated temperatures in the presence of a curing agent. The formulation of the epoxy resin, latent epoxy resin curing agent, and filler of the present invention remains uncured, is rheologically stable at room temperature for weeks or even months, and is therefore prolonged for automated bonding processes. Storage life.

The electrically conductive filler is used in sufficient volume percent to allow electricity to flow through the adhesive composition.
In particular, the filler must be present in a sufficient amount such that the filler particles are in the range of Angstroms of each other, thereby providing a path for electrons to travel through the adhesive composition.

Except for the epoxy resin, the latent hardener, and the filler component, other components that may optionally be added to the adhesive composition of the present invention include processing such as diluents, flexibilizers and antioxidants. Additives are included.

The epoxy resins and latent hardeners selected and listed are completely compatible with each other with respect to curing and incorporation of suitable fillers, and are about 10 ^-2 ohm-at room temperature.
A flexible adhesive having a volume resistivity of less than cm is formed.
Thus, the adhesive formulation of the present invention has both electrical conductivity and sufficient flexibility to withstand strain due to thermal shear.

The adhesive composition of the present invention firstly mixes the following components to form a completely wet mass. The components are:
(1) a liquid component containing an epoxy resin component and an optional flexibilizer and diluent; and (2) a solid component containing a latent epoxy resin curing agent, a filler, and optional processing additives. Next, the completely wet mass is reacted at a temperature in the range of about 100 ° C. to 170 ° C. to form the cured flexible epoxy adhesive of the present invention. However, the present compositions are designed to cure within two at relatively low temperatures ranging from about 100 ° C to 140 ° C.

In summary, the adhesives of the present invention are rheologically stable at room temperature for weeks or months at room temperature as a single component mixture, and at low temperatures (about 100 ° C. to 140 ° C.).
Provides an epoxy-based electrically conductive composition that can be cured within 2 hours and is flexible with respect to curing to temperatures as low as -50 ° C. Thus, the adhesives of the present invention exhibit the most excellent properties of the prior art adhesives. Like the premixed freeze-flexible epoxy adhesive, the adhesive of the present invention forms a flexible bond that is resistant to distortion due to thermal misalignment. Like hard epoxy adhesives, the compositions of the present invention can be conveniently stored at room temperature and can be easily processed. The adhesive of the present invention, which can provide a strong flexible electrically conductive bond without disrupting the production schedule, facilitates the use of epoxy-based adhesives in automated bonding processes due to its ability. Briefly, these adhesives can take advantage of the superior bonding qualities associated with epoxy compounds in the industry without sacrificing the benefits of automation. Importantly, the compositions of the present invention exhibit these advantages without the use of solvent components, thus preserving environmental integrity.

The adhesive composition of the present invention provides an industrial product capable of storing an uncured epoxy-based adhesive at room temperature, as well as good adhesive properties, electrical conductivity,
It was developed to provide a cured epoxy-based adhesive with flexibility and easy processability. In particular, the adhesive composition of the present invention can be cured within a temperature range of about 100 ° C. to 140 ° C. within 2 hours, and when cured, at about 1 room temperature.
0 ^-2 ohm -cm or less of the volume resistivity and in Shore A durometer show the flexibility which is measured as about 95 or less.

The composition of the present invention is based on the use of a blend of selected epoxy resins, hardeners and fillers that will provide a flexible electrically conductive product,
It can be stored at room temperature in an uncured state. The choice of the particular epoxy resin and curing agent is strictly defined to provide the desired flexibility in the final adhesive product.

The composition of the present invention uses at least one polyepoxide resin classified as a so-called "flexible epoxy resin". The phrase "flexible epoxy resin"
It is meant to include epoxy resins whose durometer Shore D value does not exceed 45 when cured with diethylenetriamine ("DETA"). The internal flexibility exhibited by a suitable flexible epoxide resin can be attributed to long aliphatic chains, ether and ester linkages within the polymer chain, which increase flexibility by increasing the rotation of adjacent carbon-carbon single bonds, and Derived from properties such as carbon-carbon double bonds.

The polyepoxy resin or mixture of polyepoxy resins used in the practice of the present invention should have a weight corresponding to more than 250 epoxides. Therefore,
The volume ratio of resin: hardener is increased to the maximum for the following reasons. Polyepoxide resins having an epoxide equivalent weight greater than 250 that are suitably used in the practice of the present invention as primary resins include the following compounds.
(1) Two moles of bisphenol A added to one mole of linoleic acid dimer. It has an epoxy equivalent weight of about 700 and is commercially available under the trade name EPON 872 from Shell Chemical Company, Houston, Texas. (2) Cardolite
) Corp.). Newark, N from New Jersey
A trifunctional novolak epoxy of cardanol having an epoxy equivalent weight of about 600 available under the trade name C-547. (3) Cardolite Corp. A difunctional novolak epoxy of cardanol having an epoxy equivalent weight of about 350 available under the trade name NC-514. (4) Diglycidyl ether of polyoxypropylene glycol having an epoxy equivalent weight of about 320, commercially available under the trade name DER732 from Dow Chemical, Midland, Michigan. (5)
Diepoxide of polyoxypropylene diol. It has an epoxy equivalent weight in the range of about 290 to 325 and is available from Shell Chemical Co. From Heloxy 50
It is commercially available under the trade name No. 2. (6) Polyglycidyl ethers of aliphatic polyols. This is about 650
Having an epoxy equivalent weight of Shell Chemical Co. Is commercially available under the trade name HEROXY 84. What
Contact the above polyepoxy resin or polyepoxy resin
The products are all stoichiometric amounts of diethylenetriamine
About 45 Durome when cured with ("DETA")
With a hardness not exceeding the Shore D reading
You.

Flexible polyepoxy resins having an epoxy equivalent weight of about 250 or less are not properly used as primary resins, but they are secondary resins as long as the average epoxide equivalent weight of the mixture of polyepoxide resins exceeds about 250. Can be used as a resin. Secondary resins are used to enhance certain properties of the adhesive composition, such as flexibility and lap shear strength. Examples of the secondary resin that can be used as the secondary resin include the following compounds.
(1) Diglycidyl ether of 1,4-butanediol. It has an epoxy equivalent weight of about 130 and is available from Houston Shell Chemical Co. , TX to herooxy 67
Available under the trade name (2) Diglycidyl ether of neopentyl glycol. It has an epoxy equivalent weight of about 135 and is available from Shell Chemical Co. Available under the trade name HEROXY 68. (3) Diglycidyl ether of cyclohexanedimethanol. This is about 160
Having an epoxy equivalent weight of Shell Chemical Co. Is available under the trade name of HEROXY 107. (4) Diglycidyl ether of polyoxypropylene glycol.
It has an epoxy equivalent weight of 190 and is commercially available from Dow Chemical, Midland, Michigan under the trade name DER736. The maximum acceptable concentration of the secondary resin can vary with the composition of the adhesive, but as a general rule, the amount of secondary resin present in the adhesive composition should be 40 wt% of the polyepoxy resin component. Not exceed.

It is important to note that all so-called flexible polyepoxy resins having an epoxy equivalent weight greater than 250 are not suitable for the practice of the present invention. For example, certain flexible epoxy resins do not cure in an adequate time using available latent epoxy resin curing agents. An example is an epoxy equivalent weight of about 600, available from Shell Chemical Co. of Houston, Texas. From herooxy 5
There is a polyglycidyl ether of castor oil commercially available under the trade name No. 05. However, heroxy 505 can be used as a secondary resin to increase the flexibility of the present adhesive composition.

The curing agent that can be used in the present invention is selected to provide a flexible product from the selected epoxy resin. The curing agents of the present invention are characterized by long aliphatic moieties within these structures that are compatible with the selected resin at the curing temperature. The curing agent of the present invention further comprises a “latent”
Characterized as a curing agent. Latent curing agents are those that come into contact with the target epoxy resin but do not cure the epoxy resin until dissolved at the elevated temperature during the curing process. In addition, the curing agents preferably used in the practice of the present invention have two or more active hydrogen atoms per mole, have a melting point or softening point between about 60 ° C and 150 ° C, and are finely dispersed. Should be available as a powder.

Achieving a flexible epoxy adhesive (in view of the selected class of epoxy resins, selected curing temperatures ranging from about 100 ° C. to 140 ° C., and selected curing times within 2 hours). Examples of curing agents that may be suitably used in the practice of the present invention include dihydrazide curing agents. Examples of dihydrazide curing agents suitably used in the practice of the present invention include Azinomoto Co., Tynek, New Jersey. , Inc. Includes the following compounds available from

(1) having an active hydrogen equivalent weight of 134;
Diuron available under the trade names Ajicure AH-122 and Ajicure AH-123
n) accelerator (3- (3,4-dichlorophenyl) -1,
Aliphatic dihydrazide having 1-dimethylurea).

(2) A diuron accelerator (3- (3,4-dichlorophenyl) -1,1-1-) having an active hydrogen equivalent weight of 49 and available under the trade name of ACIDURE AH-127.
Adipic dihydrazide having dimethyl urea).

(3) Eicosandioic acid dihydrazide (C ₂₀ H ₄₂ N) having a caustic hydrogen equivalent weight of 92.5
₄ O ₂ ). It is available under the trade name LDH and contains about 10% of a compound sold as hexadecandionic dihydrazide according to the Azinomoto Material Stability Data Sheet ("MSDS").

(4) 7,11-octadecadien-1,18-dicarboxylic acid dihydrazide (C ₂₀ H ₃₈ N ₄ O ₂ ) having an active hydrogen equivalent weight of 91.5. This is UDH
Available under the trade name

(5) A valine hydrazide having an active hydrogen equivalent weight of 78.5. It is available under the trade name VDH.

AH-122 and AH-127 can be preferably used in the practice of the present invention.

In addition, there are certain latent hardeners that cannot induce cure at 100 ° C. for one hour, but are used with the proviso that the upper limit of the listed range of cure temperature and cure time is used. . Polyamine adducts of epoxy resins (commercially available from Air Products, Allentown, Pa. Under the trade name Ancmine 2014), and epoxyamine adducts (e.g., trade names of Adicure PN-23). Commercially available from Azinomoto Co., Inc.)
May suitably be used at a curing temperature of over 120 and a curing time of about 2 hours.

The amount of the latent hardener is preferably in stoichiometric proportion to the epoxy resin used. Generally, the amount of hardener may vary from stoichiometric by about ± 15 percent. This is an amount that does not adversely affect the final product. The terrible adverse effects derived from using more or less than the net stoichiometric amount of the hardener are the functionalities of the components used (eg, trifunctional epoxy resins are better than difunctional epoxy resins). And the curing temperature used (eg, a resin cured at a higher temperature is better than one cured at a lower temperature).

The latent epoxy curing agent used in the present invention is:
It is commercially available as a solid powder. If other components such as fillers are also in special forms, and if the liquid content of the adhesive composition is limited to hold a finite volume of solid particles, the volume of the particulate hardener will be Other particle components should have sufficient space in the adhesive composition and be minimized to perform their expected function. Thus, it is preferred that the volume ratio of resin: hardener is increased to the utmost to exert these expected functions at the minimum concentration optimal for fillers and other solid components. The epoxy resins and hardeners selected for use in the practice of the present invention reflect attempts to maximize the resin: hardener volume ratio, whereby the hardener has the lowest possible amount. On the other hand, the epoxy resin has the highest possible epoxy equivalent weight. Thus, the adhesive composition of the present invention can maximize the resin: cured product volume ratio while substantially maintaining the stoichiometric ratio.

The filler component is added to make the adhesive composition of the present invention electrically conductive. In order to achieve electrical conductivity, the filler must be incorporated such that the filler particles are in the range of a few Angstroms from each other, thereby forming a path for electron transfer. Until the concentration of the filler reaches this essential level, the volume resistivity of the adhesive composition will remain high (eg, 10 ¹² ohm-cm) and its electrical conductivity will remain negligible. Once the requisite filler concentration level is achieved, the adhesive composition can be reduced to about 10 ^-2 at room temperature.
The volume resistivity is less than ohm-cm. The essential filler concentration generally amounts to about 40% by volume of the total adhesive composition. In particular, the essential filler concentration is lower when fillers composed of spherical particles are used than when fillers composed of particles having a higher aspect ratio such as flakes and rods are used. Because the different fillers have different densities, the essential weight percentages for each filler will vary, but can be calculated to find the essential volume percentages.

The electrically conductive filler component can contain any metal and can take the form of metal powder, metal flakes, or non-metallic particles that are coated on the outside with a metal. Preferably, noble metals are used to maintain electrical conductivity for long periods. Examples of noble metals suitably used in the practice of the present invention include gold, silver, and platinum.
Examples of outer metal-coated particles that are acceptable in the practice of the present invention include silver-plated copper beads and silver-plated glass beads.

The particle size of the filler material should be considered when formulating the adhesive composition of the present invention. As discussed in connection with the choice of curing agent, the filler and the curing agent are both solid, and thus have limited space within the adhesive composition. In addition to maximizing the resin: hardener volume ratio, this overcrowding problem also results in choosing different particle sizes for the hardener and filler so that smaller particles fit into the gap between the larger particles Can be avoided.

If desired, the composition of the present invention preferably comprises a non-reactive flexible material not exceeding 50 wt% of the total liquid of the adhesive, including the epoxy resin and the flexibilizer. An agent is included. In general, the flexibilizer effectively increases the liquid content of the adhesive composition, thereby allowing more electrically conductive filler to be added to the adhesive composition, thereby providing the essential filler concentration Guaranteed to reach level. In particular, the non-reactive flexibilizer does not chemically bond to the polymer network, but acts as an external plasticizer that is retained in the network by Van der Waals forces and / or hydrogen bonds. Therefore, they must have a chemical structure that is consistent with the epoxy / curative structure in order for these to not be discharged. Higher molecular weight plasticizers are desirable because they increase chain entanglement between the plasticizer and the epoxy / hardener structure and reduce plasticizer migration. Simple experiments to determine a compatible plasticizer are performed, for example, formulating the polymer with the proposed plasticizer and observing whether compatibility exists. Such experiments are considered to be routine efforts within the ability of those skilled in the art and are not considered to be inappropriate. At least 1,0
Polyols having a molecular weight of 00 and triols having a molecular weight in the range of 1,500 to 6,000 may generally be used as non-reactive plasticizers. Examples of high molecular weight triols that may be suitably used in the practice of the present invention include high molecular weight poly (oxypropylene) triol (available from Union Carbide, Danbury, Conn. Under the trade name LHT-28) and terminal. Polybutadiene having hydroxyl groups (from Atochem to poly B
It is available under the trade name DR45HT. ).
In addition, the latter is a preferable flexible agent in the practice of the present invention. Other examples of suitable non-reactive flexibilizers include phthalates, adipates and methyl lineolate.

The adhesive composition may also contain a diluent as needed. The diluent can include any monofunctional material that reduces viscosity (ie, one with one active hydrogen per mole). The diluent includes any material for this purpose, such as a monoepoxide and a secondary amine. A simple experiment will readily determine the appropriate amount of diluent in the adhesive composition. The range of experiments required to determine the appropriate concentration of diluent is considered reasonable by one of ordinary skill in the art and is not considered inappropriate.

Other optional additives to the flexible epoxy adhesive composition include UV stabilizers, antioxidants, and other processing aids such as wetting agents, defoamers, and dispersants. Is included. These are all known and commonly used in the art. Processing aids are preferably used at concentrations up to 5 wt% of the total adhesive composition.

Another novel property of the present invention is that the uncured formulation of epoxy resin, latent hardener, and filler is stable at room temperature. In particular, uncured formulations are rheologically stable at room temperature for weeks or even months. This means that the formulation does not cure at room temperature and is stable in terms of viscosity. Thus, unlike premixed frozen flexible epoxy compounds, the compositions of the present invention do not need to be thawed prior to curing and are used for curing as is on a required basis. The formulation cures easily within 2 hours in a temperature range of about 100 ° C to 140 ° C. Upon curing, the compositions of the present invention are flexible and reworkable, having a durometer Shore A value of 95 or less. Other properties of the composition of the present invention has a flexibility, as measured by glass transition temperature T _g is that spread to minus 50 ° C. (-50 ° C.) of about low.
This is in contrast to typical glass transition temperatures for hard epoxy adhesives of over + 100 ° C. Finally, the adhesive composition of the present invention has about 10 ^-2 ohm-c at room temperature.
The volume resistivity is less than m. Therefore, the adhesive composition of the present invention is capable of soft and strong bonding, and is subjected to an automatic bonding operation due to its stability at room temperature and easy curability,
A current can flow through the electronic device.

The adhesive of the present invention comprises a liquid component (ie, epoxy resin, non-reactive flexibilizer, and diluent) and a dry component (ie, hardener, filler, and processing aid).
Formulated by mixing at these appropriate concentrations until the dry ingredients are completely wetted. Preferably, the dry ingredients are ground and mixed with the liquid ingredients, for example using a 3-roll mill. By pulverizing and mixing, the resin and the curing agent can be mixed well, whereby the adhesive obtained becomes uniform as a composition and therefore exhibits high quality as a whole.
Once the dry ingredients have been completely wetted, the air is removed from the adhesive mixture by mixing it under reduced pressure. The resulting uncured composition can be stored at room temperature for weeks or even months. When a mixture containing the composition of the present invention is used as an adhesive, the mixture must be cured. First, the mixture is placed in contact with the material and glued in the desired way. Then, both the adhered material and the introduced mixture are cured by heating at an elevated curing temperature. A curing temperature of about 175 ° C. is used depending on individual electronic components,
The adhesive composition of the present invention is designed to cure in a reasonable time in a temperature range of about 100 ° C to 140 ° C. Although the curing time varies with the melting point and molecular weight of the curing agent, the curing time of the adhesive of the present invention is designed to be within 2 hours within the selected temperature range. In most cases, the required cure time is expected to be only about 30 minutes. Upon curing, the composition of the present invention forms a strong and flexible bond between the materials, while remaining flexible,
The glass transition temperature T _g (the exact minimum T _g depends on the adhesive formulation) can be reduced to as low as -50 ° C.

[0042]

EXAMPLES Examples 1 to 3 show adhesive compositions prepared according to the present invention. The formulations of Examples 1-3 are reported in Table I below. In each case, the polymer mixture is about 15 parts by weight of the adhesive composition (PBW), while the filler is about 85 parts by weight of the adhesive composition. The filler used in each example is a silver flake powder, which is commercially available from DuPont under the trade name V9. The amount of filler used is about 35% by volume of the adhesive composition.

The adhesive compositions of Examples 1-3 are formulated by mixing a liquid epoxy resin, a solid curing agent and a filler until the dry ingredients are completely wetted and blended. The blend blended in each case is about 120
Cured after exposure to a temperature of ° C. Examples 1 to 3
The liquid epoxy resins used in
Cured with stoichiometric amount of diethylenetriamine ("DETA")
When read about 45 durometer Shore D
It has a hardness not exceeding. Also, a set of Examples 1 to 3
All products are rheologically stable at room temperature.
Was.

Table I below lists various properties observed for the cured adhesive compositions of Examples 1-3. In particular, the volume resistivity, glass transition temperature, durometer hardness value, and overlap shear strength of each example were described. The lap shear strength is described for both the 1 hour and 2 hour curing times. Volume resistivity was measured by the American Society for Testing and Materials ("ASTM") as specified in ASTM D257. The measurement of the glass transition temperature is
Performed according to ASTM E831. Shore-A and Shor
The eD durometer test was performed on an adhesive composition that was cured as specified by ASTM D2240, "Durometer Indentation Hardness of Rubber and Plastics". Finally, the lap shear strength is ASTM D1
Measured as specified by 002.

For comparison, Examples 4 to 6 show formulations outside the scope of the present invention. Each of these formulations does not meet one or more of the requirements of the present invention, as shown in Table II.

[0046]

[Table 1]

[Table 2] The formulations of Examples 1-3 were made according to the present invention. Their volume resistivity is less than 10 ^-2 ohm-cm each, their glass transition temperatures are close to -50 ° C, their durometer hardness values are each less than 95 Shore A, and their lap shear strengths are less than 95 Shore A. The value was high enough to serve the purpose as an adhesive.

In contrast, the formulations of Examples 4-6 did not meet at least one objective of the present invention. The formulation of Example 4 exhibits a volume resistivity greater than 10 ^-2 ohm-cm,
This is due to too little silver flake filler. The adhesive formulation of Example 5 did not cure within 2 hours at 120 ° C. This is due to its improper height of the heloxy 505 from the secondary resin to the primary resin. The adhesive formulation of Example 6 exhibits a volume resistivity greater than 10 ^-2 ohm-cm. This is due to the use of too little filler. However, a high level of solid curing agent must be used for the effect of lowering the volume resistivity,
Large amounts of silver cannot be added.

Thus, the adhesive compositions formulated in accordance with the present invention are electrically conductive and at relatively low temperatures (about 100 ° C).
(In the range of 140 ° C. to 140 ° C.) within 2 hours, with a durometer Shore A value of less than 95 at room temperature for curing, indicating a glass transition temperature close to −50 ° C. In addition, the adhesive compositions of the present invention exhibit the necessary lap shear strength to provide a sufficiently strong bond in an industrial setting.

The cured adhesives of the present invention are flexible and electrically conductive over a wide temperature range. Furthermore, the uncured adhesives of the invention are rheologically stable at room temperature for a measurement period of several months. Given these properties, the electrically conductive adhesives of the present invention require very automatic bonding of different materials, including the manufacture of products such as automobiles, trucks, aircraft, boats, and buildings. Can be successfully used for many industrial applications.

Thus, a composition and method for producing an electrically conductive flexible epoxy adhesive that is stable at room temperature in the uncured state is disclosed. It will be readily apparent to those skilled in the art that various changes and modifications of obvious nature can be made. Also, all such changes and modifications are considered to be within the scope of the invention as defined in the following claims.

[0051]

The adhesives of the present invention are rheologically stable at room temperature for weeks or months at room temperature as a single component mixture and exhibit a low temperature (from about 100 ° C. to 140 ° C.).
It provides a new epoxy-based electrically conductive composition that can cure within hours and is flexible with respect to curing to temperatures as low as -50C. The adhesive of the present invention forms a flexible bond that is resistant to distortion due to thermal misalignment, such as a pre-mixed frozen-flexible epoxy adhesive, and, like a hard epoxy adhesive, The composition can be conveniently stored at room temperature and can be easily processed. The adhesives of the present invention can provide strong flexible electrically conductive bonds without disrupting the production schedule.
Also, the adhesives of the present invention can utilize the superior bonding qualities associated with epoxy compounds in the industry without sacrificing the benefits of automation. Furthermore, since the composition of the present invention does not use a solvent component, environmental preservation can be maintained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-114641 (JP, A) JP-A-49-43912 (JP, A) JP-A-48-56797 (JP, A) 217854 (JP, A) JP-A-9-104855 (JP, A) JP-A-9-100458 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09J 163/00-163 / 10 C09J 9/02 C08G 59/20-59/32

Claims (8)

(57) [Claims] 1. A flexible electrically conductive epoxy adhesive composition comprising a blend of the following components: (a) (i) a stoichiometric amount of diethylene triamine ("D
About 45 durometer when cured with "ETA")
Hardness not exceeding Shore D's reading, 2 moles of bisphenol A added to 1 mole of linoleic acid dimer, cardanol trifunctional novolak epoxy, cardanol difunctional novolak epoxy, polyoxypropylene glycol At least one polyepoxide resin selected from the group consisting of diglycidyl ethers, diepoxides of polyoxypropylene diols, and polyglycidyl ethers of aliphatic polyols; and (ii) a substantially stoichiometric amount of at least one latent epoxy. A polymer mixture containing a curing agent, and (b) an electrically conductive filler containing a metal, wherein the electrically conductive epoxy adhesive composition is rheologically stable at room temperature, and when cured, at about 95% at room temperature. the following following durometer Shore a and about 10 ^-2 ohm -cm It indicates the volume resistivity. 2. The flexible electrically conductive epoxy adhesive composition of claim 1, wherein said at least one polyepoxide resin has an epoxy equivalent weight greater than 250. 3. The flexible electrically conductive epoxy adhesive composition of claim 1, wherein said at least one latent epoxy curing agent is dihydrazide, a polyamine adduct of an epoxy resin, and an epoxyamine adduct. Wherein the hydrazide is an aliphatic dihydrazide,
Selected from the group consisting of adipic dihydrazide, icosandioic dihydrazide, 7,11-octadecadien-1,18-dicarboxylic dihydrazide, and valine dihydrazide, wherein the aliphatic dihydrazide and the adipic dihydrazide optionally further comprise an accelerator. What to do. 4. The flexible electrically conductive epoxy adhesive composition according to claim 1, wherein the electrically conductive filler contains a noble metal selected from silver, gold, and platinum. 5. The flexible electrically conductive epoxy adhesive composition of claim 1, wherein the electrically conductive filler is about 40 vo of the flexible electrically conductive epoxy adhesive composition.
l What is present in%. 6. The flexible electrically conductive epoxy adhesive composition of claim 1, wherein the polymer mixture comprises:
Diglycidyl ether of 1,4-butanediol, diglycidyl ether of neopentyl glycol, diglycidyl ether of cyclohexanedimethanol, diglycidyl ether of polyoxypropylene glycol, and polyglycidyl ether of castor oil. Those further containing one secondary epoxy resin. 7. The flexible electrically conductive epoxy adhesive composition according to claim 1, further comprising at least one component selected from the group consisting of a non-reactive flexibilizer and a diluent. Wherein said non-reactive flexibilizer comprises at least 1,0
A polyol having a molecular weight of 00 and a triol having a molecular weight in the range of about 1,500 to 6,000, wherein said diluent is selected from the group consisting of monoepoxides and secondary amines. 8. A method for producing a flexible electrically conductive epoxy adhesive composition according to claim 1, wherein: (a) mixing the following components to form a completely wet mass: (I) stoichiometric amounts of diethylenetriamine ("DET
A)), when cured with a durometer Shore D reading of not more than 45 and 2 moles of bisphenol A
Added to 1 mol of linoleic acid dimer,
Dananol trifunctional novolak epoxy, cardanol
Novolak epoxy, polyoxypropylene
Diglycidyl ether of glycol, polyoxypropyl
Of dienoxides of rangeols and aliphatic polyols
It contains at least one polyepoxide resin selected from the group consisting of polyglycidyl ethers and, optionally, at least one component selected from the group consisting of non-reactive flexibilizers and diluents. A liquid component, and (ii) a solid component containing a substantially stoichiometric amount of at least one latent epoxy resin curing agent, a metal-containing electrically conductive filler, and a processing aid, wherein said solid component comprises: The wetted mass is rheologically stable at room temperature; and (b) removing the completely wet mass from about 100 ° C to 175 ° C.
A cured, electrically conductive epoxy adhesive composition that has been reacted and cured at a temperature in the range of up to 0 ° C., wherein the cured electrically conductive epoxy adhesive composition has a durometer Shore A at room temperature of about 95 or less. And forming a material having a volume resistivity of 10 ⁻² ohm-cm or less.