EP4688997A1

EP4688997A1 - Two-part thermally conductive silicone adhesive composition

Info

Publication number: EP4688997A1
Application number: EP23929070.3A
Authority: EP
Inventors: Wenting GAO; Yilei ZHU; Jingjing CHANG; Dan Li; Dan XIE
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2023-03-24
Filing date: 2023-03-24
Publication date: 2026-02-11
Also published as: WO2024197467A9; TW202446928A; CN120897973A; WO2024197467A1

Abstract

The present invention provides a two-part thermally conductive silicone adhesive composition featuring favorable storage stability and high dispensing stability while maintain good thermal conductivity.

Description

Two-part Thermally Conductive Silicone Adhesive Composition

Technical field

The present invention relates to a two-part thermally conductive silicone adhesive composition, and particularly relates to a two-part thermally conductive silicone adhesive composition exhibiting favorable storage stability and high dispensing stability while maintain good thermal conductivity, and use thereof.

Background of the invention

In recent years, along with size reduction and performance enhancement of electronic devices, there is an increasing demand for heat-dissipating compositions. Thermally conductive silicone adhesive compositions exhibiting good flowability and high thermal conductivity is widely used in electronic devices, especially the telecom and datacom devices, such as 5G station, or the like.
Such two-part thermally conductive silicone adhesive compositions may be exemplified by the following: a thermally conductive silicone adhesive composition comprising an organopolysiloxane having vinyl groups, an organohydrogenpolysiloxane, a thermally conductive filler, an adhesion-imparting agent selected from epoxy silane or alkyl titanate, and a platinum-type catalyst. In order to improve thermal conductivity in a cured body obtained from such thermally conductive silicone adhesive compositions, the compositions must incorporate a large amount of thermally conductive fillers.
However, prior products in the market usually show significant flow rate reduction and poor dispensing performance after storage for more than 4 months. When the dispenser is re-started, certain quantity of adhesive product will be waste. As a result, dispenser needs to be kept on with pressure. However, pressure hold may cause oil filler separation, which will lead to dispensing block in dispenser. This will lead to production disruptions and lower productivity.
In view of the above, it is an object of the present invention to provide a two-part thermally conductive silicone adhesive composition that has a favorable combination of properties including good flowability and dispensing stability after 6 month’s shelf life while maintain good thermal conductivity when cured.
Summary of the invention
Disclosed herein is a two-part thermally conductive silicone adhesive composition consisting of Part (I) comprising:
(A) at least one alkenyl group-containing organopolysiloxane, and
(B) at least one catalyst; and
Part (II) comprising:
(C) at least one organohydrogenpolysiloxane having an average of at least two hydrogen atoms directly bonded to a silicon atom in one molecule;
wherein the composition further comprises (D) at least one thermally conductive filler in Part (I) and/or Part (II) , which has a halogen content of less than 70ppm according to EN 14582: 2016 and a specific surface area of from 0.8 to 1.2 m² /g.
Also disclosed herein is the cured product of the two-part thermally conductive silicone adhesive composition according to the present invention.
Also disclosed herein is the use of the two-part thermally conductive silicone adhesive composition and the cured product of the thermally conductive silicone adhesive composition according to the present invention in heat dissipation material.
Other features and aspects of the subject matter are set forth in greater detail below.

Detailed description of the invention

It is to be understood by one of ordinary skill in the art that the present invention is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention. 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.
Unless specified otherwise, in the context of the present invention, the terms used are to be construed in accordance with the following definitions.
Unless specified otherwise, as used herein, the terms “a” , “an” and “the” include both singular and plural referents.
The terms “comprising” and “comprises” 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 term "room temperature" as used herein refers to a temperature of about 20 ℃ to about 25 ℃, preferably about 25 ℃.
The molecular weights refer to weight average molecular weights (Mw) , unless otherwise stipulated.
All molecular weight data refer to values obtained by gel permeation chromatography (GPC) , unless
otherwise stipulated, e.g. according to DIN 55672.
Unless specified otherwise, 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 present invention, including technical and scientific terms, have the meaning as commonly understood by one of the ordinary skilled in the art to which this invention belongs.
In one aspect, the present disclosure is generally directed to a two-part thermally conductive silicone adhesive composition consisting of
Part (I) comprising:
(A) at least one alkenyl group-containing organopolysiloxane, and
(B) at least one catalyst; and
Part (II) comprising:
(C) at least one organohydrogenpolysiloxane having an average of at least two hydrogen
atoms directly bonded to a silicon atom in one molecule;
wherein the composition further comprises (D) at least one thermally conductive filler in Part (I) and/or Part (II) , which has a halogen content of less than 70ppm according to EN 14582: 2016 and a specific surface area of from 0.8 to 1.2 m² /g.
(A) Alkenyl group-containing organopolysiloxane
According to the present invention, Part (I) of the two-part thermally conductive silicone adhesive composition comprises (A) an alkenyl group-containing organopolysiloxane.
In some embodiments, Part (II) of the two-part thermally conductive silicone adhesive composition can further comprises at least one component (A) .
As used herein, “alkenyl” refers to a radical of a straight-chain or branched hydrocarbon group having from 2 to 40 carbon atoms and one or more carbon-carbon double bonds (e.g., 1, 2, 3, or 4 double bonds) ( “C_2-40 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 30 carbon atoms ( “C_2-30 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 20 carbon atoms ( “C_2-20 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 10 carbon atoms ( “C_2-10 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 9 carbon atoms ( “C_2-9 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 8 carbon atoms ( “C_2-8 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 7 carbon atoms ( “C_2-7 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 6 carbon atoms ( “C_2-6 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 5 carbon atoms ( “C_2-5 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 4 carbon atoms ( “C_2-4 alkenyl” ) . In some embodiments, an alkenyl group has 2 to 3 carbon atoms ( “C_2-3 alkenyl” ) . In some embodiments, an alkenyl group has 2 carbon atoms ( “C₂ alkenyl” ) . The one or more carbon-carbon double bonds can be internal (such as in 2-butenyl) or terminal (such as in 1-butenyl) . Examples of C_2- ₄ alkenyl groups include ethenyl (C₂) , 1-propenyl (C₃) , 2-propenyl (C₃) , 1-butenyl (C₄) , 2-butenyl (C₄) , butadienyl (C₄) , and the like. Examples of C_2-6 alkenyl groups include the aforementioned C_2- ₄ alkenyl groups as well as pentenyl (C₅) , pentadienyl (C₅) , hexenyl (C₆) , and the like. Additional examples of alkenyl include heptenyl (C₇) , octenyl (C₈) , octatrienyl (C₈) , and the like. Unless otherwise specified, each instance of an alkenyl group is independently unsubstituted (an “unsubstituted alkenyl” ) or substituted (a “substituted alkenyl” ) with one or more substituents. In certain embodiments, the alkenyl group is an unsubstituted C_2-30 alkenyl. In certain embodiments, the alkenyl group is a substituted C_2-30 alkenyl.
In some embodiments, the quantity of alkenyl groups is within a range from 0.01 to 10 wt%, and preferably from 0.1 to 5 wt%based on the total weight of the alkenyl group-containing organopolysiloxane. Furthermore, these alkenyl groups may be bonded to silicon atoms at the terminals of the molecular chain, to non-terminal silicon atoms within the molecular chain, or to both these types of silicon atoms, although from the viewpoints of ensuring a good curing rate for the composition and producing favorable physical properties for the cured product, the organopolysiloxane should comprise at least alkenyl groups bonded to a molecular chain terminal silicon atom, and preferably to the silicon atoms at both terminals of the molecular chain.
In some embodiments, the viscosity at 25℃ of the component (A) is within a range from 10 to 1000 mPa·s, and preferably from 10 to 500 mPa·s. If the viscosity at 25℃ is within the range defined above, then the physical characteristics of the cured silicone adhesive can be improved. The viscosity herein was measured with TA Rheometer parallel plate using spindle 25mm under 60 rpm, 25℃.
There are no particular restrictions on the molecular structure of the component (A) , including but not limited to straight chain structures, cyclic structures, branched chain structures, partially branched straight chain structures and three-dimensional network structures, although an essentially straight chain diorganopolysiloxane in which the principal chain is formed from repeating diorganosiloxane units, and both terminals of the molecular chain are blocked with triorganosiloxy groups, is preferred. Furthermore, the component (A) may be a single polymer with this type of molecular structure, a copolymer with this type of molecular structure, or a mixture of different polymers with this type of molecular structure.
Specific examples of the component (A) include the compounds represented by the general formulae (i) to (v) shown as below.
In the formulae (i) to (v) above, R each independently represents a substituted or unsubstituted monovalent hydrocarbon group bonded to a silicon atom, but excluding alkenyl groups, as described above, and is preferably a methyl group or a phenyl group. In the formulae (i) to (v) , n is an integer of from 0 to 5000, m is an integer of from 5 to 5000, and the sum of n and m ranges from 5 to 10000. In some embodiments, n ranges from as little as 0, 10, 50, 100, 200, 500, as great as 1000, 2000, 5000, or within any range defined between any two of the foregoing values; and m ranges from 5, 10, 50, 200, or as great as 500, 1000, 2000, 5000, or within any range defined between any two of the foregoing values. In addition, the sum of n and m ranges from as little as 5, 10, 30, 50, 100, 200, 500, or great as 1000, 2000, 5000, 10000, or within any range defined between any two of the foregoing values, such as between 10 and 10000, and between 1000 and 5000.
In some embodiments, the unsubstituted or substituted monovalent hydrocarbon group R in the formulae (i) to (v) above is each independently selected from straight-chain alkyl groups, preferably selected from methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, and n-eicosyl group; branched-chain alkyl groups, preferably selected from isopropyl group, t-butyl group, isobutyl group, 2-methylundecyl group, and 1-hexylheptyl group; cyclic alkyl groups, preferably selected from a cyclopentyl group, cyclohexyl group, and cyclododecyl group; aryl groups, preferably selected from a phenyl group, tolyl group, and xylyl group; aralkyl groups, preferably selected from a benzyl group, phenethyl group, and 2- (2, 4, 6-trimethylphenyl) propyl group; and halogenated alkyl groups, preferably selected from 3, 3, 3- trifluoropropyl group and 3-chloropropyl group; preferably selected from straight-chain alkyl groups and aryl groups; and more preferably selected from methyl group, ethyl group and phenyl groups.
In one preferred embodiment, component (A) is selected from vinyl terminated polydimethylsiloxane, vinyl terminated diphenylsiloxane-dimethylsiloxane copolymer, vinyl terminated polyphenylsiloxane, vinylbenzyl terminated vinylphenylsiloxane-phenylmethylsiloxane copolymer, vinyl terminated trifluoropropylmethylsiloxane-dimethylsiloxane copolymer, vinyl terminated diethylsiloxane-dimethylsiloxane copolymer, vinylmethylsiloxane-dimethylsiloxane copolymer, trimethylsilanyl terminated vinylmethylsiloxane-dimethylsiloxane copolymer, silanol terminated vinylmethylsiloxane-dimethylsiloxane copolymer, vinylmethylsiloxane homopolymer, vinylmethylsiloxane copolymer, vinyl terminated poly (methyl siloxane) copolymer, vinyl terminated poly (methyl siloxane) copolymer, vinyl terminated poly (methyl siloxane) copolymer, poly (vinyl terminated poly (methyl siloxane) copolymer, poly (vinyl terminated poly (vinyl siloxane) and poly (vinyl siloxane) copolymer, monovinyl-terminated polydimethylsiloxane, vinylmethylsiloxane terpolymers, vinylmethoxysilane homopolymers, or combination thereof.
There are no particular restrictions on the molecular weight of component (A) , and preferably in the range of from 3000 to 20,000 g/mol.
The component (A) may be used either alone, or in combinations of two or more different compounds.
Such alkenyl group-containing organopolysiloxane used as component (A) can be produced using conventionally known methods. In a typical production method, the alkenyl group-containing organopolysiloxane is produced by conducting an equilibration reaction of an organocyclooligosiloxane and a hexaorganodisiloxane in the presence of either an alkali or acid catalyst.
Examples of commercially available products of the component (A) include vinyl terminated polydimethylsiloxane from RH Vi392, RH Vi393, RH Vi395, RH Vi321, RH Vi322, RH Vi311, RH Vi305, RH Vi70E, RH Vi100E, RH Vi500E, RH Vi1000E manufactured by Zhejiang Runhe Chemical New Material Co., Ltd; Andisil^TM VS 20, Andisil^TM VS 50, Andisil^TM VS 100, Andisil^TM VS 200, Andisil^TM VS 500, Andisil^TM VS 100 manufactured by AB Specialty Silicones.
According to the present invention, the component (A) may be present in an amount of from 0.2%to 6%, preferably 0.5 %to 4%by weight, based on the total weight of the Part (I) and Part (II) of the adhesive composition.
(B) Catalyst
In addition to the component (A) , the Part (I) of the two-part thermally conductive silicone adhesive composition also comprises (B) at least one catalyst.
The component (B) is a catalyst for promoting an addition reaction of an alkenyl group derived from the component (A) , and a -Si-H group derived from the component (C) as described below. A catalyst well-known as a catalyst used in a hydrosilylation reaction may be used.
Specific examples thereof include platinum group metal simple substance such as platinum (including platinum black) , rhodium, and palladium; platinum chloride, chloroplatinic acid and chloroplatinate such as H₂PtCl₄·nH₂O, H₂PtCl₆·nH₂O, NaHPtCl₆·nH₂O, KaHPtCl₆·nH₂O, Na₂PtCl₆·H₂O, K₂PtCl₄·nH₂O, PtCl₄·nH₂O, PtCl₂, and Na₂HPtCl₄·nH₂O (here, in the formula, n is an integer of 0 to 6, preferably alcohol-modified chloroplatinic acid) ; complexes of chloroplatinic acid and olefin; ones obtained by supporting a platinum group metal such as platinum black and palladium on a support such as alumina, silica or carbon; a rhodium-olefin complex, chlorotris (triphenylphosphine) rhodium (Wilkinson catalyst) ; and, complexes of platinum chloride, chloroplatinic acid or chloroplatinate and a vinyl group-containing siloxane, in particular, a vinyl group-containing cyclic siloxane may be used, preferably a platinum-based catalyst.
Suitable commercially available examples of catalysts include platinum-based catalyst under CATALYST 512 from Evonik and CAT-50 from Avantor.
According to the present invention, the component (B) may be present in an amount of from 0.001%to 0.1%by weight, preferably from 0.001%to 0.05%by weight, based on the total weight of the Part (I) and Part (II) of the adhesive composition.
(C) Organohydrogenpolysiloxane
According to the present invention, Part (II) of the two-part thermally conductive silicone adhesive composition comprises (C) an organohydrogenpolysiloxane having an average of at least two hydrogen atoms directly bonded to a silicon atom in one molecule, which works as a crosslinking agent to the component (A) to form silicone polymer matrix.
In one embodiment, the organohydrogenpolysiloxane has two or more -Si-H groups in one molecule. The -Si-H groups in the component (C) and alkenyl groups in the component (A) are added by a hydrosilylation reaction promoted by (B) catalyst described above to generate a three-dimensional network structure having a crosslinked structure.
The component (C) may have an average of at least two, and preferably three or more -Si-H groups per molecule, and these -Si-H groups may be positioned at the terminals of the molecular chain, at non-terminal positions, or at both these positions.
In one embodiment, the organohydrogenpolysiloxane is linear or branched, and in preferred embodiments, the organohydrogenpolysiloxane can be represented by the general formula (vi) :
In the above formula (vi) , R’ each independently represents a hydrogen atom or an unsubstituted or substituted monovalent hydrocarbon group excluding aliphatic unsaturated bonds and at least two R’ groups are hydrogen atoms. Index e represents an integer of 1 or more.
Suitable examples of the unsubstituted or substituted monovalent hydrocarbon group in the general formula (vi) is each independently selected from straight-chain alkyl groups, preferably selected from methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, and n-eicosyl group; branched-chain alkyl groups, preferably selected from isopropyl group, t-butyl group, isobutyl group, 2-methylundecyl group, and 1-hexylheptyl group; cyclic alkyl groups, preferably selected from a cyclopentyl group, cyclohexyl group, and cyclododecyl group; aryl groups, preferably selected from a phenyl group, tolyl group, and xylyl group; aralkyl groups, preferably selected from a benzyl group, phenethyl group, and 2- (2, 4, 6-trimethylphenyl) propyl group; and halogenated alkyl groups, preferably selected from 3, 3, 3-trifluoropropyl group and 3-chloropropyl group; preferably selected from straight-chain alkyl groups and aryl groups; and more preferably selected from methyl group, ethyl group and phenyl groups.
The functionality content of -Si-H groups in the component (C) is preferably in the range of from 0.1 to 10.0 mmol/g, more preferably from 0.1 to 5.0 mmol/g.
In preferred embodiments, the number of moles of the -Si-H groups contained in the component (C) is preferable in an amount that 0.1 to 5.0 times, more preferably from 0.5 to 2.0 times the number of moles of the alkenyl groups derived from the component (A) .
Specific examples of component (C) include but not limited to 1, 1, 3, 3-tetramethyldisiloxane, dimethylhydrosiloxane, methylhydrogencyclopolysiloxane, cyclic copolymers of methylhydrogensiloxane and dimethylsiloxane, methylhydrogenpolysiloxane with both terminals blocked with trimethylsiloxy groups, copolymers of dimethylsiloxane and methylhydrogensiloxane with both terminals blocked with trimethylsiloxy groups, dimethylpolysiloxane with both terminals blocked with dimethylhydrogensiloxy groups, copolymers of dimethylsiloxane and methylhydrogensiloxane with both terminals blocked with dimethylhydrogensiloxy groups, copolymers of methylhydrogensiloxane and diphenylsiloxane with both terminals blocked with trimethylsiloxy groups, copolymers of methylhydrogensiloxane, diphenylsiloxane and dimethylsiloxane with both terminals blocked with trimethylsiloxy groups, copolymers of methylhydrogensiloxane, dimethylsiloxane and diphenylsiloxane with both terminals blocked with dimethylhydrogensiloxy groups.
The component (C) can be produced using conventionally known methods. In a typical production method, octamethylcyclotetrasiloxane and/or tetramethylcyclodisiloxane, and a compound to from the terminal groups such as hexamethyldisiloxane or a compound incorporating a 1, 1'-dihydro-2, 2', 3, 3'-tetramethyldisiloxane unit are subjected to equilibration in the presence of a catalyst such as sulfuric acid, trifluoromethanesulfonic acid or methanesulfonic acid, at a temperature of -10℃ to 40℃.
Examples of commercially available products of the component (C) include dimethylhydrosiloxane from RH-H503, RH-H33, RH-H57, RH-H86, RH-DH02, RH-DH04, RH-DH07 manufactured by Zhejiang Runhe Chemical New Material Co., Ltd; Andisil^TM CE500, Andisil^TM CE 30LV, Andisil^TM CE XL 1B, Andisil^TM CE XL 12, Andisil^TM CE XL 17, Andisil^TM CE XL 1340 manufactured by AB Specialty Silicones.
According to the present invention, the component (C) may be present in an amount of from 0.01%to 5%, preferably 0.05 %to 3%by weight, based on the total weight of the Part (I) and Part (II) of the composition.
(D) Thermally conductive filler
According to the present invention, the two-part thermally conductive silicone adhesive composition comprises (D) at least one thermally conductive filler in Part (I) and/or Part (II) , wherein the component (D) has a halogen content of less than 70ppm according to EN 14582: 2016 and a specific surface area of from 0.8 to 1.2 m² /g.
Herein, the "halogen content" represents the halogen content of the thermally conductive filler determined according to EN 14582: 2016. The halogen may be existed in the thermally conductive filler because the raw material used to produce the conductive filler may contain halogen, furthermore, additional halogen may be added during production of those fillers for the purpose of improving the crystallization of the fillers.
The component (D) of the present invention may be a mixture comprising at least two, preferably three, more preferably four, even more preferably five thermally conductive fillers in Part (I) and/or Part (II) , wherein the component (D) has a halogen content of less than 70 ppm according to EN 14582: 2016.
The expression “the component (D) has a halogen content of less than 70 ppm according to EN 14582: 2016” should be interpreted as follows. When the component (D) of the present invention is a mixture comprising at least two thermally conductive fillers having different halogen content, some thermally conductive filler (s) can contain a halogen content of higher than 70 ppm while others can contain a halogen content of lower than or equal to 70 ppm, provided that the thermally conductive filler mixture as a whole shall have a halogen content value of less than 70 ppm determined according to EN 14582: 2016.
In some embodments, when the component (D) of the present invention is a mixture comprising two thermally conductive fillers having different halogen content, the component (D) of the present invention may comprise:
0 to 9%by weight of one thermally conductive filler having a halogen content of more than 300 ppm, and
91%to 100%by weight of one thermally conductive filler having a halogen content of less than 10ppm,
based on the total weight of the component (D) .
In some embodments, when the component (D) of the present invention is a mixture comprising three thermally conductive fillers having different halogen content, the component (D) of the present invention may comprise:
0 to 9%by weight of thermally conductive filler having a halogen content of more than 300 ppm,
5 to 35%by weight of thermally conductive filler having a halogen content of from 10 ppm to less than 100 ppm, and
60%to 95%by weight of thermally conductive filler having a halogen content of less than 10 ppm, based on the total weight of the component (D) .
The component (D) of the present invention having a halogen content higher than the claimed range described above would cause flow rate reduction of the composition during storage and lead to poor dispensing performance.
Herein, the "D50 particle size" represents a median diameter in a volume-basis particle size distribution curve obtained by measurement with a laser diffraction particle size analyzer.
In some embodiment, the component (D) of the present invention may comprise:
(D-1) 10%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 2 μm,
(D-2) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 30 μm, and
(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm,
based on the total weight of the component (D) .
Further, the above component (D-1) may comprise (D-1 a) at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm, and (D-1 b) at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm. In such case, the component (D) of the present invention may comprise:
(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm,
(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm,
(D-2) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 30 μm, and
(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm,
based on the total weight of the component (D) .
Further, the above component (D-2) may comprise (D-2a) at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 10 μm, and (D-2b) at least one thermally conductive filler having a D50 particle size of from 10 μm to less than 30 μm. In such case, the component (D) of the present invention may comprise:
(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm,
(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm,
(D-2a) 10%to 40%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 10 μm,
(D-2b) 10%to 20%by weight of at least one thermally conductive filler having a D50 particle size of from 10 μm to less than 30 μm, and
(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm,
based on the total weight of the component (D) .
In some embodiment, the component (D) of the present invention may comprise:
(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm and a halogen content of from 10ppm to less than 100 ppm,
(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm and a halogen content of less than 10 ppm,
(D-2) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 30 μm and a halogen content of less than 10 ppm, and
(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm and a halogen content of less than 10 ppm,
based on the total weight of the component (D) , and the above halogen content is determined according to EN 14582: 2016.
In preferred embodiments, the component (D) of the present invention may comprise:
(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm and a halogen content of from 10ppm to less than 100 ppm,
(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm and a halogen content of less than 10 ppm,
(D-2a) 10%to 40%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 10 μm and a halogen content of less than 10 ppm,
(D-2b) 10%to 20%by weight of at least one thermally conductive filler having a D50 particle size of from 10 μm to less than 30 μm and a halogen content of less than 10 ppm, and
(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm and a halogen content of less than 10 ppm,
based on the total weight of the component (D) , and the above halogen content is determined according to EN 14582: 2016.
In addition to the halogen content, another important feaure of the component (D) of the present invention disclosed herein is the specific surface area.
Herein, the “specific surface area” ( “SSA” ) , defined as the total surface area of a solid filler material per unit of mass, deterimed by 3H-2000A Specific surface area Analyzer.
The component (D) of the present invention may be a mixture comprising at least two, preferably three, more preferably four, even more preferably five thermally conductive fillers in Part (I) and/or Part (II) , wherein the component (D) has a specific surface area of from 0.8 to 1.2 m² /g.
The expression “the component (D) has a specific surface area of from 0.8 to 1.2 m² /g” should be interpreted as follows. When the two-part thermally conductive silicone adhesive composition comprises a mixture of at least two thermally conductive fillers in different particle size distribution, the specific surface area of the two fillers refers to the calculated SSA according to the following modified Gordon-Taylor equation (I) , that is, these fillers as a whole have a calculated SSA of from 0.8 to 1.2 m² /g. In present invention, the calculated SSA of two or more fillers can be calculated according to the following modified Gordon-Taylor equation (I) :
SSA = W1×SSA₁ + W2×SSA₂ +…Wn×SSA_n (I)
Wherein:
-W1 is weight percentage of the first filler based on total fillers,
-SSA₁ is the SSA of the first filler deterimed by 3H-2000A Specific surface area Analyzer,
-W2 is weight percentage of the second filler based on total fillers,
-SSA₂ is the SSA of the second filler deterimed by 3H-2000A Specific surface area Analyzer,
-Wn is weight percentage of the n^th filler based on total fillers,
-SSA_n is the SSA of the n^th filler deterimed by 3H-2000A Specific surface area Analyzer.
When the component (D) of the present invention has a specific surface area of less than 0.8 m² /g, the composition will have dispensing block issue during dispensing process and lead to significant flow rate reduction during storage. When the component (D) has a specific surface area of larger than 1.2 m² /g, the flow rate of the adhesive composition is too low, and hence the adhesive composition is difficult to dispense.
In some embodiments, the component (D) can be selected from alumina particles, aluminum nitride particles, fumed silica particles, precipitated silica particles, fumed titanium oxide particles, diamonds and combinations thereof, preferably alumina particles, aluminum nitride particles and combinations thereof.
The shape of the component (D) used in the present invention is not particularly limited. They may have spherical, rod-like, needle-like, disc-like, or amorphous shape, preferably spherical shape. In this description, the term "spherical" refers to a shape in which the entire surface is formed from a convex smooth surface.
The component (D) can be surface treated or non-surface treated. It is preferably to use surface-treated particles as component (D) in the present invention to increase the compatibility with component (D) in silicone polymer matrix. The particle can be surface treated with a surface treating agent such as a silane compound, an organotitanium compound, an organoaluminum compound or a phosphate compound, and preferably with the silane compound.
In preferred embodiments, the amount of the surface treating agent adhered to the thermal particles is, with respect to the weight of thermal particles, for example, from 0.01%to 2%by weight, preferably from 0.02%to 1.5%by weight, more preferably from no less than 0.03%to 1%by weight. If the content of surface treating agent is within the range defined above, the thermal particles will have improved compatibility with other thermal particles.
The silane compound to be used for the surface treatment is not especially limited, and examples thereof include alkoxysilanes and chlorosilanes; and the alkoxysilanes are preferable. When the thermal particles surface-treated with the silane compound, it is easy to conform to the silicone polymer matrix, making it easy for the amount of the thermal particles blended in the thermally conductive composition to be increased.
Examples of the alkoxysilanes include alkoxysilanes having a reactive group and alkoxysilanes having no reactive group. The reactive group of the alkoxysilanes having a reactive group is selected, for example, from an epoxy group, a (meth) acryloyl group, an amino group, a vinyl group, a ureido group, a mercapto group and an isocyanate group.
Examples of alkoxysilanes having an epoxy group include 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane and 3-glycidoxypropyltriethoxysilane. Examples of alkoxysilanes having a (meth) acryloyl group include 3- (meth) acryloxypropylmethyldimethoxysilane, 3- (meth) acryloxypropyltrimethoxysilane, 3-(meth) acryloxypropylmethyldiethoxysilane and 3- (meth) acryloxypropyltriethoxysilane. Examples of silane compounds having an amino group include alkoxysilanes such as N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane. Examples of silane compounds having a vinyl group include vinyltrimethoxysilane and vinyltriethoxysilane. Examples of alkoxysilanes having a mercapto group include 3-mercaptopropyltrimethoxysilane and 3-mercaptopropylmethyldimethoxysilane. Examples of alkoxysilanes having a ureido group include 3-ureidopropyltrimethoxysilane. Examples of alkoxysilanes having an isocyanate group include 3-isocyanatopropyltriethoxysilane. Further, Examples of the alkoxysilanes having no reactive group include trialkoxysilanes such as aryltrialkoxysilanes, alkyltrialkoxysilanes, and dialkoxysilanes such as dialkyldialkoxysilanes and diaryldialkoxysilanes, and among these, trialkoxysilanes such as alkyltrialkoxysilanes are preferable. Examples of the alkyltrialkoxysilanes include alkyltrialkoxysilanes in which the number of carbon atoms of the alkyl group is about 1 to 10, such as methyltrimethoxysilane, methyltriethoxysilane, n-proyltrimethoxysilane, n-propyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-octyltriethoxysilane and n-decyltrimethoxysilane. Further, Examples of the aryltrimethoxysilanes include aryltrimethoxysilanes in which the number of carbon atoms of the aryl group is about 6 to 10, such as phenyltrimethoxysilane, benzyltrimethoxy silane and tolyltrimethoxysilane. Further, Examples of the dialkoxysilanes include dimethyldimethoxysilane and dimethyldiethoxysilane. As a preferable aspect of the silane compounds, there is used a polymeric silane compound being a reaction product of an alkoxysilane having a reactive group with a polyorganosiloxane having a functional group reactive with the reactive group.
The suitable polymeric silane compound can be obtained, for example, by mixing the alkoxysilane having a reactive group with the polyorganosiloxane and allowing these to react under heating in the presence of a catalyst such as a platinum-based catalyst, a palladium-based catalyst or a rhodium-based catalyst. As the alkoxysilane having a reactive group, the ones listed in the above can be used, but among the above, it is preferable to use triakoxysilanes. As the alkoxysilane having a reactive group, silane compounds having a (meth) acryloyl group or a vinyl group are preferable, and trialkoxysilanes having a (meth) acryloyl group are more preferable. When a silane compound having a (meth) acryloyl group or a vinyl group is used, since the silane compound easily reacts with an organopolysiloxane having hydrosilyl groups (-SiH) described later, a polymeric silane compound can be obtained by a simple method. The polyorganosiloxane having a functional group to be used for the polymeric silane compound may have one functional group or may have two or more functional groups. In the case of having two or more functional groups, two or more molecules of the alkoxysilane having a reactive group may be bonded to one molecule of the polyorganosiloxane. The polyorganosiloxane having a functional group is preferably an organopolysiloxane having hydrosilyl groups (-SiH) . Examples of the organopolysiloxane having hydrosilyl groups (-SiH) include methylhydrosiloxane-dimethylsiloxane copolymers and methylhydrosiloxane-phenylmethylsiloxane copolymers. These may contain hydrosilyl groups on the terminals, or may not. The weight-average molecular weight of the polyorganosiloxane having a functional group is preferably 800 to 5000 and more preferably 1500 to 4000. Here, the weight-average molecular weight is a value in terms of polystyrene measured by GPC.
A method of the surface treatment using the silane compound is not especially limited, and may be a well-known method; and there can be used, for example, a wet treatment method, a dry treatment method or a pretreatment method. In the present invention, among these, the wet treatment method is preferable. In the wet treatment method, the surface treatment can be made, for example, by adding the thermal particles in a solution in which the silane compound is dispersed or dissolved, mixing the mixture, and thereafter heat-treating the mixture to bond or adhere the silane compound to the surface of the thermal particles. The dry treatment method is a method of the surface treatment using no solution, and specifically, is a method in which the thermal particles are mixed with the silane compound and stirred by a mixer or the like, and thereafter heat-treated to bond or adhere the silane compound to the surface of the thermal particles.
Suitable commercially available examples of the component (D) include BAK-1, BAK-3, BAK-5, BAK-10, BAK-20, NSAR-05, NSM-1S/2S, TA-F01, TA-F02, TA-F03, TA-F80, TA-F100 from Bestry; AO-502 from Admatechs; ASFP-03S, ASFP-05S, DAW-01, DAW-03, DAW-05, DAW-07, DAW-10, DAW-20 from Denka; AA-03F, AA-03NF, AA-03, AA-04, AA-05, AA-07, AA-2, AA-3, AA-5, AA-10, AA-18 from Sumitomo; AN2, AN3, AN5, AN20, AN30, AN80, AN100 from Ginet; and AlN020AW, AlN 050AW, AlN 300RW, AlN 800RW from Thurtek.
In particular preferred embodiments, the component (D) in Part (I) and/or Part (II) may be present in an amount of from 80%to 99%, preferably from 85%to 97%by weight, based on the total weight of the Part (I) and Part (II) of the adhesive composition.
(E) Non-reactive dimethylpolysiloxane
According to the present invention, the two-part thermally conductive silicone adhesive composition may further optionally comprise (E) at least one non-reactive dimethylpolysiloxane in Part (I) and/or Part (II) . The purpose of adding component (E) is to adjust the flow rate of the composition.
Suitable non-reactive dimethylpolysiloxane used in the present invention includes dimethylpolysiloxanes having both ends blocked by an alkoxysilyl group and/or an alkyl group. Examples of an alkyl group may include ethyl group, propyl group, hexyl group and octyl group. Examples of an alkoxysilyl group may include methyldimethoxy group, trimethoxy group and the like.
In some embodiments, the viscosity at 25℃ of the component (E) is within a range from 10 to 1000 mPa·s, and preferably from 20 to 500 mPa·s.
Examples of commercially available examples of component (E) include Andisil^TM SF 20, Andisil^TM 50, Andisil^TM 100, Andisil^TM 200, Andisil^TM 500 and Andisil^TM 100 from AB Specialty Silicones, H201-20, H201-50, H201-100, H201-200, H201-500 and H201-1000 from Sinopharm Chemical Reagent.
In particular preferred embodiments, the component (E) may be present in an amount of from 0.1%to less than 5%by weight, preferably from 0.5%to less than 3%by weight, based on the total weight of the Part (I) and Part (II) of the adhesive composition.
(F) Additive
In some embodiments, the two-part thermally conductive silicone adhesive composition may further optionally comprise additive in Part (I) and/or Part (II) , selected from filler treatment agent, inhibitors, pigments, dyes, fluorescent dyes, heat resistant additives, flame retardants, plasticizers, adhesion-imparting agents and combination thereof, provided that the inclusion of these additives does not impair the object of the present invention.
Suitable examples of inhibitor used in the present invention, including but not limited to an acetylene-based compound such as 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, or 1-ethynyl-1-cyclohexanol; ahydrazine-based compound; a phosphine-based compound; or a mercaptan-based compound, in order to regulate the curing rate of the composition, thereby enabling an improvement in the flowability and workability properties.
Suitable commercially available examples of the inhibitor include 1, 3, 5, 7-tetramethyl-1, 3, 5, 7-tetravinyl-cyclotetrasiloxane from Evonik.
Suitable commercially available examples of the filler treatment agent include Loctite Pre-mix W1 from Henkel.
Suitable commercially available examples of the pigment include red pigment manufactured by Lanxess.
In those cases where the composition of the present invention comprises additive, there are no particular restrictions on the quantity of the additive, although a quantity within a range from 0.0001 to 1.0%by weight, based on the total weight of the Part (I) and Part (II) of the adhesive composition is preferred.
In particular preferred embodiments, the two-part thermally conductive silicone adhesive composition, consisting of
Part (I) comprising:
from 0.2%to 6%, preferably 0.5%to 4%by weight of (A) at least one alkenyl group-containing organopolysiloxane, and
from 0.001%to 0.1%, preferably from 0.001%to 0.05%by weight of (B) at least onecatalyst; and
Part (II) comprising:
from 0.01%to 5%, preferably 0.05 %to 3%by weight of (C) at least an organohydrogenpolysiloxane having an average of at least two hydrogen atoms directly bonded to a silicon atom in one molecule;
wherein the composition further comprises from 80%to 99%, preferably from 85%to 97%by weight of (D) at least one thermally conductive filler in Part (I) and/or Part (II) ,
all above ratio is based on the total weight of the composition;
wherein the component (D) has a halogen content of less than 70 ppm according to EN 14582: 2016 and a specific surface area of from 0.8 to 1.2 m² /g.
In preferred embodiments, the mixing ratio by weight of Part (I) and Part (II) is from 0.7 to 1.2, preferably from 0.8 to 1.1.
A further aspect of the present invention relates to a method for preparing a two-part thermally conductive silicone adhesive composition, comprising the following steps:
1) mixing the component (A) , component (D) (if any) , component (E) (if any) and additive (if any) according to the present invention at room temperature, and then mixing in vacuum for at least 90 minutes; then mixing in vacuum at temperature of 85℃ to 150℃ for 60 minutes; after cooling to room temperature, adding the component (B) and further mixing in vacuum for 10 to 30 minutes, to obtain Part (I) ;
2) mixing the component (C) , the component (D) (if any) and additive (if any) at room temperature and then mixing in vacuum for at least 90 minutes; then mixing in vacuum at temperature of 85 to 150℃ for 60 minutes; after cooling to room temperature to obtain Part (II) ; and
3) Mixing Part (I) and Part (II) prior to use.
The two-part thermally conductive silicone adhesive composition of the present invention has a good flowability when cured with the thermally conductive filler loading of more than 80%, for example, having a flow rate more than 30 g/min, defined as the adhesive composition weight dispensed under a pressure of 90 psi per minute using dispenser machine Nordson Ultimus-I equipped with a 30cc plastic tube having a nozzle in a diameter of 2.54±5%mm. Having such flow rate, especially more than 30g/min, ensures that the nozzle of conventional adhesive dispensers will not be blocked by the adhesive composition after mixing. Furthermore, the two-part thermally conductive silicone adhesive composition of the present invention has a flow rate reduction of less than 20%after 6 months.
In preferred embodiments, the thermally conductive silicone adhesive composition can cure at room temperature for no more than 7 days. Curing can be accelerated by applying heat, for example, by heating from 60 to 200 ℃ for from 30 minutes to 2 hours.
In the present invention, the two-part thermally conductive silicone adhesive composition can be applied to the desired substrate by any convenient technique. It can be applied cold or be applied warm if desired. It can be applied by extruding or pasting it onto the substrate or other mechanical application methods such as a caulking gun. Generally, the two-part thermally conductive silicone adhesive composition of the present invention is applied to one surface of a pair of substrates, and then the substrates are contacted each other to be bonded together. After application, the two-part thermally conductive silicone adhesive composition of the present invention cures at room temperature, optionally followed by curing at elevated temperature.
In another aspect of the present invention, provided is an article comprising a first substrate, a cured adhesive, and a second substrate bonded to the first substrate through the cured adhesive comprising a cured product derived from two-part thermally conductive silicone adhesive composition according to the present invention.
The first substrate and/or second substrate can be of a single material and a single layer or can include multiple layers of the same or different material. The layers can be continuous or discontinuous.
The substrates of the article descried herein can have a variety of properties including rigidity (e.g., rigid substrates (i.e., the substrate cannot be bent by an individual using two hands or will break if an attempt is made to bend the substrate with two hands) , flexibility (e.g., flexible substrates (i.e., the substrate can be bent using no greater than the force of two hands) , porosity, conductivity, lack of conductivity, and combinations thereof.
The substrates of the article can be in a variety of forms including, e.g., fibers, threads, yarns, wovens, nonwovens, films (e.g., polymer film, metallized polymer film, continuous films, discontinuous films, and combinations thereof) , foils (e.g., metal foil) , sheets (e.g., metal sheet, polymer sheet, continuous sheets, discontinuous sheets, and combinations thereof) , and combinations thereof.
Useful substrate material used in the present invention include, e.g., polymer (e.g., polycarbonate, ABS resin (Acrylonitrile-Butadiene-Styrene resin) , liquid crystal polymer, polyolefin (e.g., polypropylene, polyethylene, low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, and oriented polypropylene, copolymers of polyolefins and other comonomers) , polyether terephthalate, ethylene-vinyl acetate, ethylene-methacrylic acid ionomers, ethylene-vinyl-alcohols, polyesters, e.g. polyethylene terephthalate, polycarbonates, polyamides, e.g. Nylon-6 and Nylon-6, 6, polyvinyl chloride, polyvinylidene chloride, cellulosics, polystyrene, and epoxy) , polymer composites (e.g., composites of a polymer and metal, cellulose, glass, polymer, and combinations thereof) , metal (aluminum, copper, zinc, lead, gold, silver, platinum, and magnesium, and metal alloys such as steel (e.g., stainless steel) , tin, brass, and magnesium and aluminum alloys) , carbon-fiber composite, other fiber-based composite, graphene, fillers, glass (e.g., alkali-aluminosilicate toughened glass and borosilicate glass) , quartz, boron nitride, gallium nitride, sapphire, silicon, carbide, ceramic, and combinations thereof, preferably liquid crystal polymer, glass and combinations thereof.
The cured product of the two-part thermally conductive silicone adhesive composition of the present invention has a thermal conductivity of more than 8 W/ (m·K) , measured according to ASTM-D5470.
A further aspect in connection with the present invention relates to the use of the two-part thermally conductive silicone adhesive composition and the cured product of the two-part thermally conductive silicone adhesive composition according to the present invention in heat dissipation material which can be used in electronic devices, especially telecom and datacom devices, such as 5G station, or the like.
Exemplary electronic devices encompass computers and computer equipment, such as telecom and datacom devices, such as 5G station, or the like; printers, fax machines, scanners, keyboards and the like; medical sensors; automotive sensors and the like; wearable electronic devices (e.g., wrist watches and eyeglasses) and their integrated circuit elements, handheld electronic devices (e.g., phones (e.g., cellular telephones and cellular smartphones) and their integrated circuit elements, cameras, tablets, electronic readers, monitors (e.g., monitors used in hospitals, and by healthcare workers, athletes and individuals) , watches, calculators, mice, touch pads, and joy sticks) , computers (e.g., desk top and lap top computers) and their integrated circuit elements, computer monitors, televisions, media players, household appliances (e.g., refrigerators, washing machines, dryers, ovens, and microwaves) , light bulbs (e.g., incandescent, light emitting diode, and fluorescent) , and articles that include a visible transparent or transparent component, glass housing structures, protective transparent coverings for a display or other optical component.
Preferred in accordance with the invention is the use of the embodiments identified earlier on above as being preferred or more preferred, for the thermally conductive silicone adhesive composition of the present invention, where preferably two or more of the aspects or corresponding features described for the thermally conductive silicone adhesive composition are combined with one another.
Examples
The following examples are intended to assist one skilled in the art to better understand and practice the present invention. The scope of the invention is not limited by the examples but is defined in the appended claims. All parts and percentages are based on weight unless otherwise stated.
Raw materials:
Component (A)
Component a-1: RH-Vi100E is vinyl terminated polydimethylsiloxane having viscosity of 100 mPa·s, manufactured by Zhejiang Runhe Chemical New Material Co., Ltd.
Component (B)
Component b-1: CATALYST 512 is a divinyl tetramethyl disiloxane complex having 2%by weight of platinum, manufactured by Evonik.
Component (C)
Component c-1: RH-H86 is dimethylhydrosiloxane, manufactured by Zhejiang Runhe Chemical New Material Co., Ltd.
Component c-2: RH-DH04 is dimethylhydrosiloxane, manufactured by Zhejiang Runhe Chemical New Material Co., Ltd.
Component (D)
Component d-1a: AA-03NF is alumina powder (D50=0.1 μm to less than 0.6 μm, halogen content of from 10ppm to less than 100 ppm) , manufactured by Sumitomo.
Component d-1a’: ASFP-05S is alumina powder (D50=0.1 μm to less than 0.6 μm, halogen content more than 300 ppm) , manufactured by Denka.
Component d-1b: AN 2 is aluminum nitride powder (D50=0.6 μm to less than 2 μm, halogen content less than 10 ppm) , manufactured by Ginet.
Component d-2a: BAK-5 is aluminum powder (D50=2 μm to less than 10 μm, halogen content less than 10 ppm) , manufactured by Bestry.
Component d-2b: DAW-20 is aluminum powder (D50=10 μm to less than 30 μm, halogen content less than 10 ppm) , manufactured by Denka.
Component d-3: TA-F80 is aluminum nitride powder (D50=50 μm to less than 120 μm, halogen content less than 10 ppm) , manufactured by Bestry.
Component (E)
Component e-1: Andisil^TM SF 50 is dimethylpolysiloxane, manufactured by AB Specialty Silicone.
Component e-2: Andisil^TM SF 100 is dimethylpolysiloxane, manufactured by AB Specialty Silicone.
Component (F)
Component f-1 is Loctite Pre-mix W1 (filler treatment agent) , manufactured by Henkel.
Component f-2 is 1, 3, 5, 7-tetramethyl-1, 3, 5, 7-tetravinyl-cyclotetrasiloxane (inhibitor) , manufactured by Evonik.
Test Methods:
Flow Rate:
The flow rate of the two-part thermally conductive silicone adhesive composition of the present invention and samples of the comparative examples were tested by a dispenser machine (Nordson Ultimus^TM -I) . The dispenser machine contains a 30cc plastic tube having a nozzle in a diameter of 2.54±5%mm and the tube is connected to a pressurization unit. When testing, the sample was dispensed under a pressure of 90psi in 1 minute into a balance tray. The weight of sample dispensed in 1 minute was measured and recorded as flow rate value in Table 1. A larger flow rate value indicates greater flowability for the thermally conductive silicone adhesive composition and superior handling characteristics. The flow rate of more than 30 g/min can be acceptable.
Flow rate reduction ratio:
The flow rate reduction ratio after 6 months shelf life (%) of the two-part thermally conductive silicone adhesive composition of the present invention and samples of the comparative examples were determined by the following equation:
The initial flow rate was tested according to the procedure of Flow Rate described above. After testing, the samples were sealed in a dry box at room temperate for preservation for 6 months. After that, the flow rate was tested again and recorded as Flow Rate after 6 month shelf life. The Flow Rate Reduction Ratio of less than 20%can be acceptable.
Dispensing stability:
The dispensing stability of the two-part thermally conductive silicone adhesive composition of the present invention and samples of the comparative examples were tested by a dispenser machine (Scheugenpflug DispensingCell DC803) . Firstly, the dispenser was flushed until it can stably dispense, and then each sample was dispensed under the pressure of 5 to 6 bars, if it was hard to dispense, recorded as “x” ; otherwise, dispensing to draw a pattern before stop dispensing for half an hour under the pressure to simulate the actual production situation, and then resume dispensing to draw a pattern, if dispenser clogs up, recorded as “▲” ; otherwise, continuing dispensing to run the 2^nd cycle, i.e. dispensing to draw a pattern before stop for another one hour under the pressure and then resume to dispense, if dispenser clogs up, recorded as “⊙” ; otherwise continuing dispensing to run the 3^rd cycle i.e. dispensing to draw a pattern before stop for another two hours under the pressure and resume to dispense, if it can be stably dispensed still, recorded as “○” , otherwise recorded as “⊙” .
After testing, all the samples were sealed in a dry box at room temperate for preservation for 6 months. The dispensing stability after 6 months shelf life of the samples was evaluated again based on the above measurement and evaluation scale.
Thermal conductivity:
The two-part thermally conductive silicone adhesive composition of the present invention and comparative examples were cured at 125℃ for 1 hour. The cured samples of the present invention and comparative examples were tested under temperature of 80℃ and pressure of 40 psi by LW 9389 manufactured by Longwin according to ASTM-D5470.
The thermal conductivity of more than 8 W/ (m·K) can be acceptable.
Examples 1 to 5 (Ex. 1 to Ex. 5) and Comparative Examples 1 to 4 (CEx. 1 to CEx. 4)
The inventive and comparative two-part thermally conductive silicone adhesive compositions were prepared by the following steps:
1) mixing the component (A) , component (D) and component (E) (if any) by weight of mass according to Table 1 at room temperature, and then mixing in vacuum for at least 90 minutes; then mixing in vacuum at temperature of 85 to 150℃ for 60 minutes; after cooling to room temperature, adding the component (B) and further mixing in vacuum for 10 to 30 minutes, to obtain Part (I) ;
2) mixing the component (C) , the component (D) and component (F) by weight of mass according to Table 1 at room temperature and then mixing in vacuum for at least 90 minutes; then mixing in vacuum at temperature of 85 to 150℃ for 60 minutes; after cooling to room temperature to obtain Part (II) ; and
3) Mixing Part (I) and Part (II) prior to use.
Prior to mixing, the specific surface area of each thermally conducive filler used in each Example and Comparative Example was tested by 3H-2000A Specific surface area Analyzer and the weight of each thermally conducive filler was weighed. And then the aforementioned tested value was applied into the equation (I) described herein, to calculate the specific surface area of the component (D) for each sample, recorded in Table 1 as below.
The halogen content (ppm) of the component (D) for each Example and Comparative Example was determined according to EN 14582: 2016, specifically, the thermally conductive fillers were mixed with respective weights shown as Table 1 at room temperature, and then the filler mixture was combusted in an oxygen bomb, after combustion, the mixture is dissolved in an absorption solution and filtrated for analyzing by ion chromatography, to obtain the halogen content of the component (D) for each sample, recorded in Table 1 as below.
The properties were tested using the methods stated above, and the results of evaluations are shown in Table 1 as below.
As can be seen from Table 1, the two-part thermally conductive silicone adhesives of the present invention (Ex. 1 to Ex. 5) showed excellent flowability and dispensing stability after 6 month’s shelf life and good thermal conductivity when cured. However, in the cases where the components of the present invention were not used as in Comparative Examples 1 to 4 (CEx. 1 to CEx. 4) , it showed unsatisfied flow rate or dispensing stability compared to the two-part thermally conductive silicone adhesive composition of the present invention, indicating that such adhesive compositions may readily cause nozzle blocking of conventional adhesive dispensers after relatively long shelf life.
Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.

Claims

A two-part thermally conductive silicone adhesive composition consisting of Part (I) comprising:

(A) at least one alkenyl group-containing organopolysiloxane, and

(B) at least one catalyst; and

Part (II) comprising:

(C) at least one organohydrogenpolysiloxane having an average of at least two hydrogen atoms directly bonded to a silicon atom in one molecule;

wherein the composition further comprises (D) at least one thermally conductive filler in Part (I) and/or Part (II) , which has a halogen content of less than 70ppm according to EN 14582: 2016 and a specific surface area of from 0.8 to 1.2 m² /g.
The two-part thermally conductive silicone adhesive composition according to claim 1, wherein Part (II) further comprises (A) at least one alkenyl group-containing organopolysiloxane.
The two-part thermally conductive silicone adhesive composition according to claim 1 or 2, wherein the component (B) is a platinum-based catalyst.
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

0 to 9%by weight of one thermally conductive filler having a halogen content of more than 300 ppm, and

91%to 100%by weight of one thermally conductive filler having a halogen content of less than 10ppm,

based on the total weight of the component (D) .
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

0 to 9%by weight of thermally conductive filler having a halogen content of more than 300 ppm,

5 to 35%by weight of thermally conductive filler having a halogen content of from 10 ppm to less than 100 ppm, and

60%to 95%by weight of thermally conductive filler having a halogen content of less than 10 ppm,

based on the total weight of the component (D) .
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

(D-1) 10%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 2 μm,

(D-2) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 30 μm, and

(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm,

based on the total weight of the component (D) .
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm,

(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm,

(D-2) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 30 μm, and

(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm,

based on the total weight of the component (D) .
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm,

(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm,

(D-2a) 10%to 40%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 10 μm,

(D-2b) 10%to 20%by weight of at least one thermally conductive filler having a D50 particle size of from 10 μm to less than 30 μm, and

(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm,

based on the total weight of the component (D) .
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm and a halogen content of from 10ppm to less than 100 ppm,

(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm and a halogen content of less than 10 ppm,

(D-2) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 30 μm and a halogen content of less than 10 ppm, and

(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm and a halogen content of less than 10 ppm, based on the total weight of the component (D) , and the above halogen content is determined according to EN 14582: 2016.
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) comprises:

(D-1a) 5%to 30%by weight of at least one thermally conductive filler having a D50 particle size of from 0.01 μm to less than 0.6 μm and a halogen content of from 10ppm to less than 100 ppm,

(D-1b) 0 to 15%by weight of at least one thermally conductive filler having a D50 particle size of from 0.6 μm to less than 2 μm and a halogen content of less than 10 ppm,

(D-2a) 10%to 40%by weight of at least one thermally conductive filler having a D50 particle size of from 2 μm to less than 10 μm and a halogen content of less than 10 ppm,

(D-2b) 10%to 20%by weight of at least one thermally conductive filler having a D50 particle size of from 10 μm to less than 30 μm and a halogen content of less than 10 ppm, and

(D-3) 20%to 60%by weight of at least one thermally conductive filler having a D50 particle size of from 30 μm to less than 120 μm and a halogen content of less than 10 ppm, based on the total weight of the component (D) , and the above halogen content is determined according to EN 14582: 2016.
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the component (D) is selected from alumina particles, aluminum nitride particles, fumed silica particles, precipitated silica particles, fumed titanium oxide particles, diamonds and combinations thereof, preferably alumina particles, aluminum nitride particles and combinations thereof.
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the composition further comprises (E) at least one non-reactive dimethylpolysiloxane in Part (I) and/or Part (II) .
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the composition further comprises (F) at least one additive in Part (I) and/or Part (II) , selected from filler treatment agent, inhibitors, pigments, dyes, fluorescent dyes, heat resistant additives, flame retardants, plasticizers, adhesion-imparting agents and combinations thereof.
The two-part thermally conductive silicone adhesive composition according to any of the preceding claims, wherein the composition has a flow rate reduction ratio after 6 months of less than 20%.
A cured product of the two-part thermally conductive silicone adhesive composition according to any of the claims 1 to 14.
Use of the two-part thermally conductive silicone adhesive composition according to any one of claims 1 to 14 or the cured product according to claim 15 in heat dissipation material.