Note: Descriptions are shown in the official language in which they were submitted.
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FM/6-18531/A
Filler for heat-conductive plastics materials
The present invention relates to a formulation comprising three different fracdons of
alumina particles each having different particle diameters, which composition is suitable
as filler for the production of heat-conductive plastics materials, to a formulation
comprising a plastics material and said filler, and to the use of said formulation as
moulding material for the production of moulded parts and composites.
Plastics materials are known to have poor thermal conductivity. To enhance their thermal
conductivity therefore, finely particulate metallic or mineral fillers are blended into
plastics materials. It is, however, only possible to use metallic fillers if no electrical
insulating properties are required. Frequently used mineral fillers are quartz and silica,
with which a thermal conductivity of up to about 2.5 W/mK is achieved with at high
volume loadings or, preferably, alumina, with which it is possible tO achieve a thermal
conductivity of up to about 3.5 W/m. To avoid abrasion in moulds it is expedient to use
spherical particles. It is also known that abrasion can be reduced by choosing particles of
small size; but this also results in a reduction of volume loading and thus of thermal
conductivity.
CA 112: 57551r tl990) discloses thermally conductive polymers which contain
electrically fused alumina powder as filler. This filler is known to be abrasive, thereby
limiting its utilities.
CA112:57894e (1990) discloses epoxy resins containing a-alumina as filler having an
average particle diameter of S to 6011m. The volume loading and therrnal conductivity are
considered inadequate.
CA 111: 175480u (1989) discloses thermally conductive polymers which contain a
mixture of alumina and mainly spheAcal corundum having a very small particle diameter
from S to 10 ~lm. High volume loadings and hence high thermal conductivities cannot be
achieved with this filler.
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It has now been found that it is possible to to increase the volume loading further as well
as to achieve higher thermal conductivities, such that the thermal coefficients of expansion
are close to those of metals such as copper, silver or gold, by using as filler a mixture of
alumina fractions of different particle size and different shape. It has also been found that
this filler makes it possible to obtain low viscosity casting resins which have a very high
filler loading and excellent castability and hence processibility.
In one of its aspects, the invention accordingly relates to a powdered mixture of alumina
with fractions of different particle size and external shape, which mixture comprises:
(1) 55 to 75 % by volume of spherical ac-a1umina, at least 90 % by weight of which has an
average particle size of 20 to 120 llm,
(2) 35 to 20 % by volume of spherica1 alumina, at least 90 % by weight of which has an
average particle size of 3 to 25 ~m, and
(3) 10 to 1 % by volume of alumina, at least 90 % by weight of which has a particle size of
1 to7 ~m,
the percentages by volume adding up to 100 %.
The particle size distribution is determined with a laser scanner (CIS supplied by LOT
GmbH, Darmstadt, Germany). This is done by measuring the particles of the defined 90 %
by weight range withou~ the two tail ranges of the distribution curve. The percentages by
volume relate to the solids present in the powder mixture.
In a preferred embodiment of the formulation of the invention, the mixture comprises
a) 65 to 75 % by volume of component (1),
b) 35 to 22 % by volume of component (2), and
c) 7 to 1 % by volume of component (3),
the percentages by volume adding up to 100 %.
In a further preferred embodiment of the formulation of the invention, the mixture
comprises
a) 70 to 75 % by volume of component (1),
b) 30 to 22 % by volume of component (2), and
c) 7 to 1 % by volume of component (3),
the percentages by volume adding up to 100 %.
Irregular shape means particles which have not been subjected to an aftertreatment, for
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example the form in which Ihey are obtained after grinding.
The particle diameter of component (1) is preferably 30 to 100 ,lLm, that of component (2)
is preferably 3 to 20 ~,~m, and that of component (3) is preferably 1 to 5 ~m.
The remaining 10 % by weight of component (1) may contain particles having a diameter
larger than 120 ~lm and up to 200 llm, as well as smaller than 20 llm and up to 0.1 ~lm. The
remaining 10 % of component (2) may contain particles having a diameter larger than
25 ~m and up to 40 llm, as well as smaller than 3 llm and up to 0.01 ~,~m. And the
remaining 10 % of component (3) may contain particles having a diameter larger than
7 ,um and up to 20 llm, and smaller than 1 ~,~m and up to 0.001 ~Im.
The novel mixtures can be prepared by mixing the three components. Particulate aluminas
are known and commercially available. FMctions having defined ranges of particle size
are obtainable by conventional separation methods. These separation methods also make it
possible to obtain fractions such that the percentage of the tail ranges of the distribution
curves is diminished or removed. Thus the three fractions of the novel powder mixture
comprise at least 95 % by weight or 100 % by weight of the particles having the particle
diameters previously defined. Spherical particles may typically be prepared by sintering or
melt processes. The preparation of different modifications of alumina particles is known in
the art. Components (2) and (3) can be in the form of different modifications.
The novel mixtures are admirably suited for use as fillers for polymers to enhance thermal
conductivity, and the abrasiveness of the formulation is of a low order.
In another of its aspects, the invention relates to a homogeneously blended formulation
comprising
a) 10 to 95 % by weight of a thermoplastic or structurally crosslinked polymer, and
b) 90 to 5 % by weight of the previously described powder mixture.
The formulation will norrnally comprise lO to 90 % by weight of polymer and 90 to 10 %
by weight of the powder mixture. Depending on the envisaged end use, the loading of the
powder mixture in the polymer can vary in volume. Thus for many moulded parts ofwhich no very high thermal conductivity is expected, a loading of 5 to 50 % by weight,
preferably 10 to 40 % by weight, of the powder mixture will meet the requirements of
articles of use in respect of thermal conductivity. It it is desired to achieve a very high
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thermal conducdvity, as for encapsulating electrical or electronic components, the loading
of powder mixture will normally be more than 50 % by weight, preferably 60 to 90 % by
weight and, most preferably, 70 to 90 % by weight,
The thermoplastic polymers may be selected from the following polymers, copolymers or
mixtures thereof:
1. Polymers of monoolefins and diolefins, for example polypropylene, polyisobutylene,
polybut- 1-ene, polymethylpent- 1-ene, polyisoprene or polybutadiene, as well as polymers
of cycloolefins, for example of cyclopentene or norbornene, polyethylene (which can be
uncrosslinked or crosslinked), for example high density polyethylene (EIDPE~,low density
polyethylene (LDPE and linear low density polyethylene (LLDPE).
2. Mixtllres of the polymers mentioned under 1), for example mixtures of polypropylene
with polyisobutylene, polypropylene with polyethylene (for example PP/~IDPE,
PP/LDPE) and mixtures of different types of polyethylene (for example LDPE/HDPE).
3. Copolymers of monoolefins and diolefins with each other or with other vinyl
monomers, for example ethylene/propylene copolymers linear low density polyethylene
(LLDPE) and mixtures thereof with low density polyethylene (LDPE),
propylene/but-1-ene copolymers, ethylene/hexene copolymers, ethylene/methylpentene
copolymers, ethylene/heptene copolymers, ethylene/octene copolymers,
propylene/butadiene copolymers, isobutylene/isoprene copolymers, ethylene/alkyl acrylate
copolymers, ethylene/alkyl methacrylate copolymers, ethylene/vinyl acetate or
ethylene/acrylic acid copolymers and their salts (ionomers), as well as terpolymers of
ethylene with propylene and a diene such as hexadiene, dicyclopentadiene or
ethylidenenorbornene; and also mixtures of such copolymers with each other and with
polymers mendoned in 1) above, for example polypropylene/ethylene propylene
copolymers, LDPE~VA,LDPE/EAA,LLDPE/EVA and LLDPE/EAA.
3a. Hydrocarbon resins (for example Cs-Cg), including hydrogenated modificationsthereof (for example tackifiers).
4. Polystyrene, poly-(p-methylstyrene), poly-(a-methylstyrene).
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5. Copolymers of styrene or a-methylstyrene with dienes or acrylic derivatives, for
example styrene/butadiene, styrene/acrylonitrile, styrene/alkylmethacrylate,
styrene/butadiene/aLlcylacrylate, styrenel maleic anhydride, styrene/acrylonitdle/methyl
acrylate; mixtures of high impact strength from styrene copolymers and another polymer,
for exarnple from a polyacrylate, a diene polymer or an ethylene/propylene/dieneterpolymer; and block copolymers of styrene, for example styrene/butadiene/styrene,
styrene/isoprene/styrene, styrenelethylene/butylenelstyrene or
styrenelethylenelpropylenelstyrene.
6. Graft copolymers of styrene or a-methylstyrene, for example styrene on polybutadiene,
styrene on polybutadienelstyrene or polybutadienelacrylonitrile; styrene and acrylonitrile
(or methacrylonitri1e) on polybutadiene; styrene and maleic anhydtide or maleimide on
polybutadiene; styrene, acrylonitrile and maleic anhydride or maleimide on polybutadiene;
styrene, acry10nitrile and methyl methacrylate on polybutadiene, styrene and alkyl
acrylates or methacrylates on polybutadiene, styrene and acrylonitrile on
ethylene/propylene/diene terpolymers, styrene and acrylonitrile on polyaLlcylacrylates or
po1yaL~tylmethacrylates, styrene and acrylonitrile on acrylate/butadiene copolymers, as
well as mixtures thereof with the copolymers listed under 5), for example the copolymer
mixtures known as ABS, MBS, ASA or AES polymers.
7. Halogenated polymers such as polychloroprene, chlorinated rubbers, chlorinated or
sulfochlorinated polyethylene, copolymers of ethylene and chlodnated ethylene,
epichlorohydrin homo- and copolymers, preferably polymers of halogenated vinyl
compounds, for example poly- vinylchlordde, polyvinylidene chlordde, polyvinyl fluoride,
polyvinylidene fluoride, as well as copolymers thereof, for example vinyl
chloridelvinylidene chloride, vinyl chloddelvinyl acetate or vinylidene chloridelvinyl
acetate copolymers.
8. Polymers derived from a,~-unsaturated acids and dedvatives thereof, such as
polyacrylates and polymethacrylates, polyacrylamides and polyacrylonitriles.
9. Copolymers of the monomers mentioned under 8) with each other or with other
unsaturated monomers, for example acrylonitdle/butadiene copolymers, acrylo-
nitrile/aL~ylacrylate copolymers, acrylonitrile/alkoxyalkylacrylate or acrylonitrile/vinyl
halide copolymers or acrylonitdlelalkylmethacrylate/butadiene terpolymers.
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10. Polymers derived from unsaturated alcohols and amines or the acyl derivatives or
acetals thereof, such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, polyvinyl
benzoate, polyvinyl maleate, polyvinylbutyrate, polyallyl phthalate or polyallylmelamine;
as well as their copo1ymers with the olefins mentioned in 1) above.
11. Homopolymers and copolymers of cyclic ethers such as polyalkylene glycols,
polyethylene oxide, polypropylene oxide or copolymers thereof with bisglycidyl ethers.
12. Polyacetals such as polyoxymethylene and those polyoxymethylenes which contain
ethylene oxide as a comonomer, polyacetals modified with thermoplasdc polyurethanes,
acrylates or MBS.
13. Polyphenylene oxides and sulfides and mixtures thereof with polystyrene or
polyamides.
14. Polyurethanes which are derived from polyethers, polyesters or polybutadienes
carrying terminal hydroxyl groups on the one hand and aliphatic or aromatic
polyisocyanates on the other, as well as precursors thereof.
15. Polyamides and copolyamides which are derived from diamines and dicarboxylicacids andl[ch]or from aminocarboxylic acids or the corre- sponding lactams, such as
polyamide 4, polyamide 6, polyamide 6/6, 6/10, 6/9, 6/12 and 4/6, polyamide 11,
polyamide 12, aromatic polyamides obtained by condensation of m-xylene, diamine and
adipic acid; polyamides prepared from hexamethylenediamine and isophthalic and/or
terephthalic acid, with or without an elastomer as modifier, for example poly-2,4,4,-
trimethylhexamethylene terephthalamide or poly-m-phenylene isophthalamide; blockcopolymers of the aforementioned polyamides with polyo1ef~ns, olefm copolymers,
ionomers or chemically bonded or grafted elastomers; or with polyethers, for example
with polyethylene glycol, polypropylene glycol or polytetramethylene glycol; and also
polyamides or copolyamides modi~led with EPDM or ABS, and polyamides condensed
during processing (RIM polyamide systems).
16. Polyureas, polyimides and polyamide-imides and polybenzimidazoles.
17. Polyesters derived from dicarboxylic acids and diols and/or from hydroxycarboxylic
acids or the corresponding lactones, such as poly-ethylene terephthalate, polybutylene
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terephthalate, poly-1,4-dimethylolcyclohexane terephthalate, polyhydroxybenzoates as
well as block-copolyether esters derived from hydroxyl-terrninated polyethers; and also
polyesters modified with polycarbonates or MBS.
18. Polycarbonates and polyester carbonates.
19. Polysulfones, polyether sulfones and polyether ketones.
20. Polyethers of diglycidyl compounds, including diglycidyl ethers and diols, for example
of bisphenol A diglycidyl ether and bisphenol A.
21. Natural polymers such as cellulose, rubber, gelatine and chemically modifiedhomologous derivatives thereof such as cellulose acetates, cellulose propionates and
cellulose butyrates, or the cellulose ethers, such as methylcellulose; as well as rosins and
their derivatives.
22. Mixtures (polyblends) of the aforementioned polymers, for example PP/EPDM,
Polyamide 6/EPDM or ABS, PVCIEVA, PVS/ABS, PVC/MBS, PC/ABS, PBTP/ABS,
PC/ASA, PC/PBT, PVC/CPE, PVC/acrylates, POM/therrnoplastic PUR, PC/thermoplasticPUR, POM/acrylate, POM/MBS, PPE/HIPS, PPE/PA 6.6 and copolymers, PA/HDPE,
PA/PP, PA/PPO.
The structurally crosslinked polymers may be typically the following polymers:
1. Crosslinked polymers which are derived from aldehydes on the one hand and phenols,
ureas and melamines on the other hand, such as phenoVformaldehyde resins,
urea/formaldehyde resins and melamine/formaldehyde resins.
2. Drying and non-drying alkyd resins.
3. Unsaturated polyester resins which are derived from copolyesters of saturated and
unsaturated dicarboxylic acids with polyhydric alcohols and vinyl compounds as
crosslinking agents, and also halogen-containing modifications thereof of low
flammability.
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4. Crosslinkable acrylic resins derived from substituted acrylic esters such as epoxy
acrylates, urethane acrylates or polyester acrylates.
5. Alkyd resins, polyester resins or acrylate resins which are cr~ss-linked with melamine
resins, urea resins, polyisocyanates or epoxy resins.
6. Rubber derived from crosslinked polydienes, for example butadiene or isoprene; silicon
rubber.
7. Crosslinked epoxy resins which are derived from polyepoxides, for exampb frombisglycidyl ethers or from cycloaliphatic diepoxides.
Among the cross1inked polymers, crosslinked epoxy resins are preferred which, as poly-
epoxides, are derived preferably from glycidyl compounds which contain on average two
epoxy groups in the molecule. Particularly suitable glycidyl compounds are those which
conhin t~vo glycidyl groups, B-methylglycidyl groups or 2,3-epoxycyclopentyl groups
athched to a hetero atom (e.g. sulfur, preferaUy oxygen or nitrogen), in particular
bis(2,3-epoxycyclopentyl) ether, diglycidyl ethers of polyhydric aliphatic alcohols, such as
1~4buhnediol~ or polyalkylene glycols, such as polypropylene glycols; diglycidyl ethers
of cycloaliphadc polyols, such as 2,2-bis(4-hydroxycyclohexyl)propane; diglycidyl ethers
of polyhydric phenols, such as resorcinol, bis(p-hydroxyphenyl)methane, 2,2-bis-(p-hydroxyphenyl)propane (= diomethane), 2,2-bis(4'-hydroxy-3',5'-dibromophenyl)-
propane, 1,3-bis(p-hydroxyphenyl)ethane; bis(l3-methylglycidyl) ethers of the above
dihydric alcohols or dihydric phenols; diglycidyl esters of dicarboxylic acids, such as
phthalic acid, terephthalic acid, 4-tetrahydrophthalic acid and hexahydrophthalic acid;
N,N-diglycidy1 derivadves of primary amines and amides and heterocyclic nitrogen bases
which contain two N-atoms, and N,N'-diglycidyl derivadves of disecundary diamides and
diamines, such as N,N-diglycidylaniline, N,N-diglycidyltoluidine, N,N-diglycidyl-
p-aminophenyl methyl ether, N,N'-dimethyl-N,N'-diglycidylbis(p-aminophenyl)methane;
N',N"-dig1ycidyl-N-phenyl-isocyanurah; N,N'-diglycidyl ethyleneurea; N,N'-diglycidyl-
5,5-dimethylhydantoin, N,N'-diglycidyl-5-isopropyl-hydantoin, N,N-methylenebis-
(N',N'-diglycidyl-5,5-dimethylhydantoin), 1,3-bis(N-glycidyl-5,5-dimethylhydantoin)-
2-hydroxypropane; N,N'-diglycidyl-5,5-dimethyl-6-isopropyl-5,6-dihydrouracil, tri-
glycidyl isocyanurate.
A preferred group of epoxy resins comprises glycidylated novolaks, hydantoins,
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aminophenols, bisphenols and aromatic diamines or cycloaliphatic epoxy compounds.
Particularly preferred epoxy resins are glycidylated cresol novolaks, bisphenol A and
bisphenol F diglycidyl ether, hydantoin-N~Nubisglycide~ p-aminophenol triglycide,
diaminodiphenylmethane tetraglycide, vinylcyclohexene dioxide, 3,4-epoxycyclohexyl-
methyl-3,4-epoxycyclohexanecarboxylate or mixtures thereof.
Further suitable epoxy resins are prereacted adducts of such epoxy compoundc with epoxy
hardeners, for example an adduct of bisphenol A diglycidyl ether and bisphenol A, or
adducts which have been prereacted with oligoesters which carry two terminal carboxyl
groups and epoxides.
Suitable hardeners for epoxy resins are acid or basic compounds. Illustradve examples of
suitable hardeners are: amines, including aliphatic, cycloaliphatic or aromatic, primary,
se~ondary and tertiary amines, ethylenediamine, hexamethylenediamine, trimethylhexa-
methylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine,
N,N-dimethylpropylene- 1 ,3-diamine, N,N-diethylpropylene- 1 ,3-diamine, 2,2-bis-
(4'-aminocyclohexyl)propane, 3,3,5-trimethyl-3-(aminomethyl)cyclohexylamine (iso-
phoronediamine), Mannich bases such as 2,4,6-tris(dimethylaminomethyl)phenol,
m-phenylenediamine, p-phenylenediamine, bis(4-aminophenyl)methane, bis(4-amino-
phenyl)sulfone, xylylenediamine; aminoalcohols, such as aminoethanol, 1,3-amino-propanol, diethanolamine or triethanolamine; adducts of acrylonitrile with polyalkyl-
enepolyamines or monoepoxides (ethylene oxide, propylene oxide) with polyalkylene-
polyamines (diethylenetriamine, triethylenetetramine); adducts of an excess of polyamines
(diethylenetriamine, triethylenetetramine) and polyepoxides such as bisphenol A di-
glycidyl ethers; polyamides, preferably those from aliphatic polyamines (diethylene-
triamine, triethylenetetramine) and di- or trimerised unsaturated fatty acids (dimerised
linseed oil fatty acid, Versamid~9); dicyandiamide; polysulfides (Thiokol(g)); aniline-form-
aldehydes; polyhydric phenols (resorcinol, 2,2-bis(4-hydroxyphenyl)propane) or phe-
nol-formaldehyde resins; polybasic carboxylic acids and the anhydrides thereof, such as
phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-
hexahydrophthalic anhydride, 3,6-endomethylene-tetrahydrophthalic anhydride,
4-methyl-3,6-endomethylen-tetrahydrophthalic anhydride (methylnadic anhydride),
3,4,5,6,7,7-hexachloroendomethylene-tetrahydrophthalic anhydride, succinic anhydride,
adipic anhydride, trimethyladipic anhydride, sebacic anhydride, maleic anhydride,
dodecylsuccinic anhydride, pyromellitic dianhydride, trimellitic anhydride, benzo-
phenonetetracarboxylic dianhydride, or mixtures of such anhydrides.
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A preferred group of hardeners comprises polyamines, novolaks, polyaminoamides and
polycarboxylic anhydrides.
The epoxy resins can also be additionally cured with curing accelerators or only with
thermal curing catalysts. Exemplary of curing accelerators and catalysts are tertiary
amines, salts thereof or quaternaly ammonium compounds (2,4,6-tris(dimethylamino-
methyl)phenol, benz~l dimethylamine, 2-ethyl-4-methylimidazole, triamylammonium
phenolate); mono- or polyphenols (phenol, diomethane, salicylic acid); boron trifluoride
and the complexes thereof with organic compounds, such as boron trifluoride ether
complexes and boron trifluoride amine complexes (BF3/monoethylamine complex);
phosphoric acid and triphenylphosphite.
Curing accelerators and catalysts are normally added in an amount of 0.1 to 10 % by
weight, based on the epoxy resin. Hardeners for epoxy resins are normally used in
equimolar amounts, based on the epoxy groups and funcdonal groups of a hardener.
Further additives for enhancing processing properties, the mechanical, electrical and
thermal properties, surface properties and light stability can be blended into the novel
formulation. Exemplary of such additives are finely pardculate fillers, reinforcing fillers,
plasdcisers, lubricants and mould release agents, adhesion promoters, andoxidants, heat
and light stabilisers, pigments and dyes. The maximum amount of additional fillers and/or
reinforcing fillers concurrently used is conveniently, together with the novel powder
mixture, not more than 95 % by weight, preferably not more than 90 % by weight, based
on the formulation.
The novel formulatdon can be prepared by methods known in plasdcs technology,
conveniently by blending the fnely particulate thermally conducdve filler with the
p1astics material before, during or after its producdon, by plasdcising the plastics material
and blending it with the filler by calendering, extrusion or injecdon moulding tO prepare
granulates or mouldings. It is also possible to make a dry blend of the powdered plastics
material with the filler or to suspend the filler in a solution of the plastics material and
then to remove the solvent.
When using thermoset resins and structurally crosslinked polymers, the finely particu1ate
filler is conveniently added prior to shaping and to curing or crosslinking, typiucally by
"' ,;
jointly blending the resin components with the filler, which may be incorporated before-
hand in one component.
The powder mixture can be blended into the plastics material in the form of the mixture
itself, in a combination of two components, followed by addition of the third component,
or by the addition of the individual components in succession.
The novel mixture is especially suitable for the producdon of epoxy casting resins having
a high-volume loading of filler such that moulded articles prepared therefrom have
thermal conductivities at fairly low temperature of more than 3.2 and even more than
4 W/mK. Despite the high-volume loading, the viscosity of the casting resins is still so
low that they are in some cases pourable when subjected to heat and/or vibration and can
be readily processed to moulded articles.
The invention further relates to an epoxy casting resin formulation which comprises 70 to
90 % by weight, preferably 75 to 90 % by weight and, most preferably, 80 to 90 % by
weight, of the novel powder mixture of aluminas.
Suitable epoxy resins are those previously mentioned above. Preferred epoxy resins are
those based on bisphenol diglycidyl ethers or advanced bispbenol diglycidyl ethers,
typically bisphenol A and bisphenol P diglycidyl ether, and a polycarboxylic anhydride,
such as phthalic anhydride or hydrophthalic anhydride, as hardener, which epoxy resins
are preferably cured in the presence of a hardening accelerator such as
N-methylimidazole.
The novel formulation is a useful moulding material for the production of thermally
conductive moulded articles of aII kinds, including films, sheets, ribbons, fibres, boards,
semi-finished products, shaped articles and casings. The conventional techniques of
plastics processing can be used, typically casting, calendering, injection moulding,
extruding, deep drawing, compression moulding and sintering. The novel folmulation is
especially suitaUe for the production of heating elements, resin adhesives and hot melt
adhesives, preferably for bonding metals, and also as thermally conductive sealing
material especially for electrical and electronic components.
The invention further relates to the use of the novel formulation or of the casting resin
formulation for the production of thermally conductive moulded articles and composites.
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In yet another of its aspects, the invention relates to the use of the casting resin
formulation as resin adhesive for bonding metals or as sealing material for electrical and
electronic components.
The following Examples illustrate the invention in more detail. The thermal conductivity
is measured by the thermal comparison method using Pyroceram~ 9606 as reference
material. The method is described by L. C. Hulstrom et al. in "Round-Robin Testing Of
Thermal Conductivity Reference Materials", Proceedings of Thermal Conductivity 19,
October 20-23, 1985, Cookevelli, Tennessee, edited by D.W. Yarbrough.
Example 1: The following alumina fractions are chosen to prepare a casting resinformulation:
1. Sintered, spherical a-AI203, median diameter 47 llm, particle diameter of the defined
90 % by weight range from 30 to 100 ~m.
2. Comsnercial spherical a- and ~-AI203 (Alunabeads CBA-10~, Showa Denko, Japan),
median diameter 9 llm, particle diameter of the defined 90 % by weight range from 3 to
20 ~m.
3. Commercial Al2O3 (CTB 5/6FG(g), Alcoa), median diameter 3.5 llm, particle diarneter
of the defined 90 % by weight range from 1 to 5 ~,lm
71 % by weight (70 % by volume) of component 1 and 28 % by weight (29 % by volume)
component 2 are stirred for 7 hours in a polypropylene bottle (stirrer with mobile blades).
Afterwards 1 % by weight (1 % by volume) of component 3 are added and stirring is
continued for 1 hour. With stirring, the powder mixture is homogeneously blended at 80C
into an epoxy casting resin comprising 50.9 % by weight of bisphenol F diglycidyl ether,
48.9 % by weight of hexahydrophthalic anhydride and 0.2 % by weight of N-methyl-imidazole. The amount is chosen such that the formulation is still pourable under
vibration. The formulation is poured into an aluminium mould and then cured for 4 hours
at 80C and for 18 hours at 120C. The loading of the powder rnixture is determined from
the density and is 73 % by volume (84 % by weight). The thermal conductivity of the
cured specimen at 40C is 4.05 W/mK.
Example 2: In accordance with the procedure described in Example 1, an epoxy casting
resin containing 88 % by weight (70.2 % by volume) of the following filler formulation is
prepared:
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72.9 % by weight (70.2 % by volume) of component 1 according to Example l;
23.1 % by weight (24 % by volume) of component 2 according to Example l;
4 % by weight (4 % by volume) of component 3 according to Example 1.
The thermal conductivity is 3.6 W/mK.
Example 3: In accordance with the procedure described in Example 1, an epoxy casting
resin containing 87.6 % by weight (69.3 % by volume) of the following filler formulation
is prepared:
73.8 % by weight (73 % by volume) of component 1 according to Example l;
22.2 % by weight (23 % by volume) of component 2 according to Example l;
4 % by weight (4 % by volume) of component 3 according to Exarnple 1.
The thermal conductivity is 3.3 W/mK.
Example 4: In accordance with the procedure described in Example 1, an epoxy casting
resin containing 88.4 % by weight (70.9 % by volume) of the following filler forrnulation
is prepared:
59 % by weight (58 % by volume) of component 1 according to Example l;
35 % by weight (34 % by volume) of component 2 according to Example l;
7 % by weight (4 % by volume) of component 3 according to Example 1.
The therrnal conductivity is 3.8 W/mK.
