Patent Application
20220002607
This invention relates to a thermally conductive potting composition, comprising a first part comprising at least one epoxy resin; at least one thermally conductive filler; and at least one metal complex; and a second part comprising at least one curing agent. The first part of the thermally conductive potting composition exhibits high thixotropic index and therefore the first part is easily stored. After the first part and the second part are mixed, the thermally conductive potting composition exhibits low thixotropic index and the meets the requirement for potting process.
With the development of transportation, electronic, general industry, it is desirable to have smaller and lighter electrical parts, such as battery, motor, and generator. Insolation materials are often used to encapsulate the sensitive components of the electrical parts in order to keep them from moisture and provide cushions to avoid damages from external impacts, such as shaking and bumping. One challenge is to develop an insulation material that is able to conduct the heat efficiently from the sensitive components of the electrical parts.
Potting compositions are commonly introduced to fill in the electrical parts and cured as insulation materials to encapsulate the sensitive components of the electrical parts. The potting composition often comprises two parts. One part contains resin and thermally conductive fillers to enhance the thermal conductivity of the potting composition, and the other part contains curing agent for the resin. However, most thermally conducive fillers tend to subside after the part that contains the thermally conductive fillers is stored for a certain period of time. The traditional method adds fumed silica in the potting composition to solve the filler sedimentation problem. Fumed silica functions to reduce the mobility of the thermally conductive fillers in the liquid system by increasing the yield value of the liquid system. However, after the first part and the second part are mixed, the potting composition shows poor flowability due to the incorporation of fumed silica and is hard to process for potting.
Therefore, there is a need to develop a potting composition that has no or little filler sedimentation issue during storage and good flowability when needs to be applied to encapsulate the sensitive components of the electrical parts.
The present invention relates to a thermally conductive potting composition, comprising:
wherein * represents a coordinating position of the metal atom in the metal complex; and R1 and R2 are identical or different, and independently represent optionally substituted univalent organic groups.
The first part of the thermally conductive potting composition of the invention exhibits no or little filler sedimentation during storage and the thermally conductive potting composition has good flowability after the two parts are mixed.
The present invention also relates to a cured product of the thermally conductive potting composition.
The present invention also relates to an article bonded, coated, or filled with the cured thermally conductive potting composition.
The present invention also relates to a process of making a thermally conductive potting composition comprising steps of:
wherein * represents a coordinating position of the metal atom in the metal complex; and R1 and R2 are identical or different, and independently represent optionally substituted univalent organic groups.
In the following passages the present invention is described in more detail. Each aspect so described may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.
In the context of the present invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.
As used herein, the singular forms “a”, “an” and “the” include both singular and plural referents unless the context clearly dictates otherwise.
The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or process steps.
The recitation of numerical end points includes all numbers and fractions subsumed within the respective ranges, as well as the recited end points.
All references cited in the present specification are hereby incorporated by reference in their entirety.
Unless otherwise defined, all terms used in the disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of the ordinary skill in the art to which this invention belongs to. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.
In the context of this disclosure, a number of terms shall be utilized.
The term “diameter” means the longest length as measured in a straight line passing through the center of gravity of the thermally conductive filler.
The term “metal complex” refers to chemical complex compounds comprising a central metal atom or ion complexed with at least one ligand.
The term “organic group” refers to a group that includes at least one carbon atom. Exemplary of the organic group includes but not limited to an alkyl group, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, tertiary butyl, isobutyl, chloromethyl, 3,3,3-trifluoropropyl and the groups alike; an alkenyl group, such as vinyl, allyl, butenyl, pentenyl, hexenyl and the groups alike; an aralkyl group, such as benzyl, phenethyl, 2-(2,4,6-trimethylphenyl)propyl and the groups alike; or an aryl group, such as phenyl, tolyl, xyxyl and the groups alike; and an alkoxyl group, such as methoxyl, ethoxyl, butoxyl and the groups alike.
The first part of the present invention comprises at least one epoxy resin. The epoxy resin of the first part refers to any common epoxy resin containing at least one epoxy group per molecule, and preferably containing multiple epoxy groups per molecule. Exemplary of the epoxy resin includes but not limited to bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, diphenyl ether epoxy resins, diphenyl thioether epoxy resins, hydroquinone epoxy resins, biphenyl novolac epoxy resins, cresol novolac epoxy resins, phenol novolac epoxy resins, bisphenol A novolac epoxy resins, trisphenol epoxy resins, tetraphenylolethane epoxy resins, and any combination thereof.
Examples of commercially available epoxy resins are, for example, D.E.R. 331 from Olin Corporation; EPIKOTE 240 from Hexion; and EPICLON N-665 from Dainippon Ink and Chemicals Inc.
In some embodiments of the present invention, the amount of epoxy resin in the first part is preferably from 2 to 70%, more preferably from 5 to 50%, and even more preferably from 7 to 20% by weight based on the total weight of the first part.
The first part of the present invention comprises at least one thermally conductive filler. The thermally conductive filler of the present invention may be selected from a metal oxide, such as aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, and the like; a metal nitride, such as boron nitride, and aluminum nitride, magnesium nitride, and the like; a metal hydroxide, such as aluminum hydroxide, magnesium hydroxide, and like; a metal powder, such as copper powder, aluminum powder, and the like; other common thermally conductive fillers, such as silicon carbide, silicon boride, graphite, carbon nanotube, carbon fiber, and the like. The thermally conductive fillers can be used alone or in combination. Preferably, the thermally conductive filler is selected from at least one of metal oxides, metal hydroxides, and metal nitrides. More preferably, the thermally conductive filler is at least one of metal oxides. Even more preferably, the thermally conductive filler contains at least one aluminum oxide to avoid filler sedimentation problem in the first part.
The shape of the thermally conductive filler of the present invention may be a regular or irregular shape and includes but is not limited to polygon, cube, oval, sphere, needle, flake, plate or any combination thereof. The thermally conductive filler may also be in the form of aggregated particles. Preferably, the thermally conductive filler is in a spherical shape.
The average diameter of the thermally conductive filler of the present invention is from 0.01 to 150 μm, preferably from 2 to 70 μm, and more preferably from 5 to 50 μm. The average diameter of the thermally conductive filler can be measured with any diameter analyzer known in the art. The average diameter of the thermally conductive filler is preferably measured by light scattering method using LS-POP(6) available from Zhuhai OMEC Instruments Co., Ltd.
In some embodiments of the present invention, the first part comprises a first thermally conductive filler and a second thermally conductive filler which have different average diameters. The first thermally conductive filler has an average diameter greater than or equal to 0.01 μm and less than 20 μm, preferably from 2 to 15 μm, and more preferably from 4 to 10 μm; and the second thermally conductive filler has an average diameter from 20 to 150 μm, preferably from 20 to 70 μm, and more preferably from 20 to 50 μm.
In preferred embodiments of the present invention, the first part comprises a first spherical aluminum oxide filler with an average diameter from 2 to 15 μm, and a second spherical aluminum oxide filler with an average diameter from 20 to 70 μm. In further embodiments, the first part comprises a first spherical aluminum oxide filler with an average diameter from 4 to 10 μm, and a second spherical aluminum oxide filler with an average diameter from 20 to 50 μm.
Examples of commercially available thermally conductive fillers are, for example, BAK 10 and BAK 40 from Shanghai Bestry Performance Materials Co., Ltd.; RY20 and CF5 from Shanghai Yu Rui New Material technology Co., Ltd.; SJR4 and SJR20 from Anhui Estone Materials technology Co., Ltd.
In some embodiments of the present invention, the amount of thermally conductive filler in the first part is preferably from 20 to 95%, and more preferably from 50 to 70% by weight based on the total weight of the first part.
The first part of the present invention comprises at least one metal complex comprising at least one organic ligand represented by the following general formula (1) which is coordinatively bounded to a metal atom in the metal complex,
wherein * represents a coordinating position of a metal atom in the metal complex; and R1 and R2 are identical or different, and independently represent optionally substituted univalent organic groups. Preferably, R1 and R2 are optionally substituted C1 to C20 alkyl groups, alkenyl groups, or alkoxyl groups. One specific example of the metal complex comprising at least one organic ligand represented by the general formula (1), aluminum acetylacetonate, is shown below as formula (2).
The metal atom in the metal complex comprising at least one organic ligand represented by the general formula (1) is not particularly limited, and includes, for example, aluminum, titanium, and zinc. Preferably, the metal atom is aluminum or titanium.
In some embodiments of the present invention, the metal complex comprising at least one organic ligand represented by the general formula (1) is preferably in a liquid form. For example, the metal complex comprising at least one organic ligand represented by the general formula (1) has a viscosity less than or equal to 1000 cps at 25° C. measured according to ASTM D 2983-04.
In preferred embodiments, the metal complex comprises only one organic ligand represented by the general formula (1). Surprisingly, the first part containing metal complex comprising only one organic ligand represented by the general formula (1) has less filler sedimentation during storage than those containing metal complex comprising multiple organic ligands represented by the general formula (1). The thermally conductive potting composition comprising the first part that contains metal complex comprising only one organic ligand represented by the general formula (1) also shows better flowability after the first part and the second part are mixed.
Examples of commercially available metal complex compound comprising at least one organic ligand represented by the general formula (1) are, for example, Plenact AL-M from Ajinomoto fine-techno Co., Inc.; and ACA-AA2 from Nanjing Capature Chemical Co. Ltd.
In some embodiments of the present invention, the amount of metal complex compound comprising at least one organic ligand represented by the general formula (1) in the first part is preferably from 0.01 to 10%, more preferably from 0.4 to 5%, and even more preferably from 0.8 to 2% by weight based on the total weight of the first part.
The second part of the present invention comprises at least one curing agent. The curing agent of the second part refers to any commonly used curing agent for epoxy systems, and includes but is not limited to polyamide, amine, imidazole and the derivatives thereof. Illustrative curing agent include polyamide resin based on dimerized fatty acid and polyamines, methyldiethanolamine, triethanolamine, diethylaminopropylamine, benzyldimethyl amine, m-xylylenedi(dimethylamine), benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, 1-methylimidazole, 2-methylimidazole and 2,4-diethylimidazole. The curing agent can be used alone or in any combination.
Examples of commercially available curing agent, for example, are Versamid 140 from
Gabriel Performance Products; Ancamine TEPA from Evonik; Ajicure PN-H from Ajinomoto Fine-Techno
Co., Ltd.; Fujicure-FXR-1090FA from T&K Toka; 1,2-dimethyl imidazole from Shikoku
Chemicals Corporation; 2E4MI from Evonik; D230 and DMP30 from Huntsman; and Gaskamine 240 from Mitsubishi Gas Chemical.
In some embodiments of the present invention, the amount of the curing agent in the second
part is from 5 to 100%, preferably from 10 to 70%, and more preferably from 10 to 50% by weight
based on the total weight of the second part.
Reactive diluent may be presented in the first part of the thermally conductive potting composition as an optional additive to control the flowability. Suitable reactive diluent includes but is not limited to diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol, and triglycidyl ether of trimethylolpropane. The reactive diluent can be used alone or in combination.
Examples of commercially available reactive diluents are, for example, Modifier 48 from Hexion Specialty Chemical; and EPODIL 747, EPODIL 748, EPODIL 757 from Air Products and Chemical Inc.
In some embodiments of the present invention, the amount of the reactive diluent in the first part is preferably from 0 to 60%, and more preferably from 5 to 40% by weight based on the total weight of the first part.
In a preferred embodiment, the thermally conductive potting composition comprises:
a first part comprising:
from 2 to 70% by weight of the first part of at least one epoxy resin;
from 20 to 80% by weight of the first part of at least one first thermally conductive filler having an average diameter greater than or equal to 0.01 μm and less than 20 μm;
from 20 to 80% by weight of the first part of at least one second thermally conductive filler having an average diameter from 20 to 150 μm;
from 0.01 to 10% by weight of the first part of at least one metal complex; and
from 0 to 60% by weight of the first part of at least one reactive diluent; wherein the weight percentages of all components in the first part add up to 100%; wherein the metal complex comprises at least one organic ligand represented by the following general formula (1) which is coordinatively bounded to a metal atom in the metal complex,
wherein * represents a coordinating position of the metal atom in the metal complex; and R1 and R2 are identical or different, and independently represent optionally substituted univalent organic groups.
a second part comprising at least one curing agent.
The thermally conductive potting composition of the present invention may be prepared by the steps of:
preparing a first part by mixing at least one epoxy resin, at least one thermally conductive filler and at least one metal complex;
preparing a second part by mixing at least one curing agent; and
mixing the first part and the second part at a desired ratio;
wherein the metal complex in the first part comprises at least one organic ligand represented by the following general formula (1) which is coordinatively bounded to a metal atom in the metal complex,
wherein * represents a coordinating position of the metal atom in the metal complex; and R1 and R2 are identical or different, and independently represent optionally substituted univalent organic groups.
Preferably, the thermally conductive potting composition of the present invention may be prepared by the steps of:
preparing a first part by:
mixing at least one epoxy resin with at least one reactive diluent homogenously;
adding at least one metal complex to the mixture from step i), and mixing the mixture to homogeneity; and
adding at least one thermally conductive filler to the mixture from step ii), and mixing the mixture to homogeneity;
preparing a second part by mixing at least one curing agent homogenously; and
mixing the first part and the second part at a desired ratio homogenously; wherein the metal complex in the first part comprises at least one organic ligand represented by the following general formula (1) which is coordinatively bounded to a metal atom in the metal complex,
wherein * represents a coordinating position of the metal atom in the metal complex; and R1 and R2 are identical or different, and independently represent optionally substituted univalent organic groups.
The first part should be used in a weight ratio to the second part, in the range of 0.7:1 to 1.3:1, and preferably from 0.9:1 to 1.1:1. A person skilled in the art will be able to make appropriate choices among the varies components based on the description, representative examples and guidelines of the present invention to prepare a composition to achieve desired effects.
The first part and the second part prefers to be combined 1 to 10 minutes prior to the use of the thermally conductive potting composition.
The thermally conductive potting composition of the present invention may be cured in a temperature range from 0 to 200° C. and applied to substrates by a mixing device.
The thixotropic index of the first part of the thermally conductive potting composition is calculated by dividing the viscosity of the first part measured at shear rate of 1 s−1 by the viscosity of the first part measured at shear rate of 10 s−1. The viscosity of the first part may be determined according to ASTM D3835-16 at 25° C.
The first part of the thermally conductive potting composition of the present invention preferably has a thixotropic index greater than or equal to 1.2, more preferably greater or equal to 1.6 and even more preferably greater than or equal to 2 at 25° C. With higher thixotropic index, the first part can be stored for a longer period of time with little or no filler sedimentation issue.
The thixotropic index of the thermally conductive potting composition is calculated by dividing the viscosity of the thermally conductive potting composition measured at shear rate of 1 s−1 by the viscosity of the thermally conductive potting composition measured at shear rate of 10 s−1. The viscosity of the thermally conductive potting composition may be determined according to ASTM D3835-16 at 25° C.
The thermally conductive potting composition of the present invention preferably has a thixotropic index less than or equal to 1.4, and more preferably less or equal to 1.2 at 25° C. With lower thixotropic index, the thermally conductive potting composition has good flowability and can be processed easily for potting.
The lap shear strength of the thermally conductive potting composition of the present invention may be assessed according to ASTM D1002 by bonding aluminum substrates.
The thermally conductive potting composition of the present invention preferably has a lap shear strength greater than or equal to 8 Mpa, and more preferably greater than or equal to 9 Mpa when it is applied to aluminum substrates.
The present invention will be further described and illustrated in detail with reference to the following examples. The examples are intended to assist one skilled in the art to better understand and practice the present invention, however, are not intended to restrict the scope of the present invention. All numbers in the examples are based on weight unless otherwise stated.
The thixotropic index of the first part of the thermally conductive potting composition was calculated by dividing the viscosity of the first part measured at shear rate of 1 s−1 by the viscosity of the first part measured at shear rate of 10 s−1. The viscosity of the first part was determined according to ASTM D3835-16 at 25° C. using Rheometer MCR 301, from Anton Paar.
The thixotropic index of the thermally conductive potting composition was calculated by dividing the viscosity of the thermally conductive potting composition measured at shear rate of 1 s−1 by the viscosity of the thermally conductive potting composition measured at shear rate of 10 s−1. The viscosity of the thermally conductive potting composition was determined according to ASTM D3835-16 at 25° C. using Rheometer MCR 301, from Anton Paar.
The lap shear strength of the thermally conductive potting composition of the present invention was assessed according to ASTM D1002 by bonding two aluminum substrates at 25° C., using INSTRON 5569 from company INSTRON. The size of the aluminium substrate was 254×150mm and the thickness of the aluminium substrate was 2 mm. The control speed was 10 mm/min.
A first part of the adhesive composition sample was prepared according to Table 1 by the steps of:
mixing EPIKOTE 240 with Modifier 48 for 2 minutes under 2000 rpm;
adding Plenact AL-M, ACA-AA2, or ACA-EAA1 to the mixture from step i), and mixing the mixture for 2 minutes under 2000 rpm; and
adding thermally conductive fillers of BAK 40 and BAK 10, or RY 20 and CF 5 to the mixture from step ii) and mixing the mixture for 2 minutes under 2000 rpm.
The first part of the thermally conductive potting composition was subjected to the thixotropic index test mentioned above.
A second part of the adhesive composition sample was prepared according to Table 2 by mixing DMP30 and DH230 for 2 minutes under 2000 rpm.
The first part and the second part of the thermally conductive potting composition sample were mixed in a weight ratio of 1:1 and were mixed for 2 minutes under 2000 rpm. The thermally conductive potting composition was then subjected to the thixotropic index and lap shear strength test mentioned above.
The mixing apparatus used in preparing the first part, the second part and the thermally conductive potting composition was SpeedMixers DAC600, from FlackTek.
In Table 3, the thixotropic index of the first part of the thermally conductive potting composition is reported. Through Examples 1 to 6, all the samples of the first part showed high thixotropic index, and therefore, they had little or no filler sedimentation even after a long period time of storage. On the contrary, samples of the first part in Example 7 and 8 exhibited severe filler sedimentation. Additionally, the thixotropic index of the thermally conductive potting composition after the first part and the second part were mixed and tested is also reported. Through Examples 1 to 6, all the samples of the thermally conductive porting composition showed low thixotropic index, and therefore the thermally conductive potting composition had good flowability and could be easily used for the potting process.
In Table 4, the lap shear strength of the thermally conductive potting composition is reported. The thermally conductive potting composition samples in Examples 1 to 6 had good lap shear strength to aluminum substrate.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2019/078237 | Mar 2019 | US |
| Child | 17475548 | US |
