Note: Descriptions are shown in the official language in which they were submitted.
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EM/K-188 19/A
Epoxv novolaks stabilised with or~anic phosphorus compounds
The present invention relates to novel compositions comprising an epoxidised novolak and
at least one speci~lc organic phosphorus compound as flame retardant, and to the use of
said compositions in encapsulating systems and laminating resins.
The flame resistance of polymers can be enhanced in different ways, for example by
reducing the organic polymer component by adding fillers of low flammability such as
quartz flour, glass or wollastonite, and also by the addition of flame retardants such as
boron compounds, metal hydroxides, brominated compounds, halogenated phosphoric
acid esters or specific organic phosphorus compounds as disclosed in European patent
application 0 456 605.
The flame retardants currently added to the epoxy novolaks which are used in
encapsulating systems and in laminating resins and which have to be made flame resistant
are usually combinations of brominated organic compounds in admixture with antimony
trioxide, the brominated organic compound normally being a brominated and glycidylised
novolak.
For some time there have been ongoing efforts to develop replacement products for
antimony trioxide for ecological and industrial health reasons, all the more so as antimony
trioxide is preferably used in the ~me (dust) form in which it has the best flame retardant
effect. If the antimony trioxide component is eliminated, then it is observed that the
thermostability of encapsulating compositions is markedly impaired.
Surprisingly, it has now been found that specific combinations of epoxidised novolaks and
specific sterically hindered organic (thio)phosphates, without the use of antimony trioxide
and with a low halogen concentration in the encapsulating and laminating systems, ensure
excellent flame resistance without the other performance properties such as thermal
resistance, mechanical strength, dielectric constant or water absorption, being materially
influenced.
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Specifically, the invention relates to compositions comprising
a) an epoxidised novolak, and
b) 0.1 to 100 parts by weight, based on 100 parts by weight of component a), of at least
one compound of formula I
X1~0- 1 -Y (I),
R4
R2
wherein ~1 is chloro or bromo,
X2 is chloro, bromo or hydrogen, and
Y is OorS, and
Rl and R2 are each independently of the other Cl-C4alkyl, and
R3 and R4 are a group of formula II
R,l
_o~X1 (II),
R2 x2
wherein Rl, R2, Xl and X2 are as defined above, which group calTies identical or different
substituents, or R3 and R4, when taken together, forrn a group of formula m
R2~R1
~o~
CH2 (III),
C~'
R2 R1
208~0~
wherein Rl and R2 are as defined above.
Xl and X2 are chloro and, preferably, bromo. X2 is preferably hydrogen. Y is preferably
oxygen.
Rl and R2 as aLkyl substituents may each independently of the other typically be methyl,
ethyl, propyl, isopropyl, butyl or tert-butyl. Rl in ~ormulae I and Il is preferably methyl or
tert-butyl and, in formula III, is preferably tert-butyl. The preferred meaning of 1~2 is
methyl.
In preferred compounds of formula I, Xl is bromo, X2 is hydrogen and Y is oxygen.
In particularly preferred compounds of formula I, Xl is bromo, X2 is hydrogen, Y is
oxygen, Rl is methyl or tert-butyl, R2 is methyl, and R3 and R4 are each an identically
substituted group of -formula I~, and Xl, X2, Rl and R2 are as defined above.
Further preferred compounds of forrnula I are those wherein R3 and R4, when taken
together, form a group of formula III, and Xl is bromo, X2 is hydrogen, Y is oxygen, Rl
and R2 in formula I are rnethyl, and Rl in formula UI is tert-butyl, and R2 in formula III is
methyl.
The compounds of forrnula I and the preparation thereof are known and disclosed in
European patent application 0 456 605 referred to above.
Suitable epoxidised novolaks are typically epoxy phenol novolak and epoxy cresolnovolak resins which may be obtained by condensing phenolic compounds with
aldehydes. Owing to their high functionality - usually 2 to 6 epoxy groups per molecule -
they are capable, in conjunction with the customary crosslinking agents, preferably at
elevated temperature, of constructing a very compact macromolecular ne~work.
Exemplary of phenolic compounds are phenol, alkylphenols containing up to 9 carbon
atoms in the alkyl moiety, typically cresols, xylenols, ethyl-, propyl- and butylphenols,
and also phenylphenols, resorcinol, pyrocatechol, hydroquinone, bisphenol A and pyro-
gallol.
Exemplary of aldehydes are formaldehyde, acetaldehyde, benzaldehyde and
2 ~ g ~
teraphthalaldehyde .
It is preferred to use phenol-foremaldehyde resins and, more particularly,
cresol-formaldehyde resins, for the preparation of which o-, m- or p-cresol or mixtures of
these isomers have been used in any or in given rados. The preparation of such resins is
known.
It is preferred to use 0.5 to 30 parts by weight and, more particularly, 2 to 20 parts by
weight, of a sompound of formula I, based on 100 parts by weight of component a). The
optimum amount will depend on the nature of component a) and on the type of compound
of formula I, and can be easily computed by simple experimentation.
As the compounds of ~ormula I are ordinarily effective in minor amounts and, in addition,
are of low halogen content, they give rise to virtually no undesirable effects in the novolak
compared with other known flame retardants.
The compounds of formula I may be used in different physical forms, depending on the
type of epoxidised novolak used and on the desired properties. Thus they may be milled to
a finely particulate form to enable better dispersion throughout the novolak. Mixtures of
different compounds of formula I may also be used.
The novel compositions are suitable for fabricating cured products, typically for
encapsulations, for exarnple of electronic components, as of integrated circuits, or for
making laminates, in which case a hardener is used for component a).
Mixtures of different novel compositions andlor hardeners may be used. Suitable
hardeners are any epoxy resin hardeners, typically cyanamide, dicyandiamide,
polycarboxylic acids, polycarboxylic anhydrides, polyamines, polyaminoamides, adducts
of amines and polyepoxides, and polyols.
Suitable polycarboxylic acids and their anhydrides are typically phthalic anhydride or
tetrahydro- and hexahydrophthalic anhydride, and the acids from which these anhydrides
are derived.
Exemplary of polyamines which may suitably be used as hardeners are aliphatic,
cycloaliphatic, aromatic and heterocyclic polyamines, such as hexamethylenediarnine,
2 ~ 3
diethylenetriamine, m-xylylenediamine, bis(4-aminocyclohexyl)methane, m- and p-phen-
ylenediamine, bis(4-aminophenyl)methane, bis(4-aminophenyl)sulfone and
aniline-formaldehyde resins. Suitable polyaminoamides are typically those which are
prepared from aliphatic polyamines and dimerised or trimerised unsaturated fatty acids.
Particularly suitable polyol hardeners are mononuclear or polynuclear aromatic polyols,
including novolaks, typically resorcinol~ hydroquinone, 2,6-dihydroxytoluene, pyrogallol,
1,1,3-tris(hydroxyphenyl)propane, bis(4-hydroxyphenyl)methane, 2,2-bis(4-hydroxy-
phenyl)propane, bis(4-hydroxyphenyl)sulfone and 4,4'-dihydroxybiphenyl, as well as
novolaks from formaldehyde or acetaldehyde and phenol, chlorophenol or aLtcylphenols
containing up to ~ carbon atoms in the alkyl moiety, preferably phenol and cresol
novolaks.
PrefeIred hardeners are polycarboxylic anhydrides, such as tetrahydro- and
hexahydrophthalic anhydride, as well as aromatic polyainines, preferably
bis(4-aminophenyl)methane, bis(4-aminophenyl)sulfone and m- or p-phenylenediamine,
and also, most preferably, polyol hardeners based on novolaks, more particularlycresol-novolaks or phenol-novolaks.
The novel compositions may also contain further conventional modifiers, typically an
accelerator and/or other modifiers.
Per se known compounds can also be used as accelerators. Typical examples are:
complexes of amines, preferably tertiary amines such as monoethylamine with boron
trifluoride or boron trichloride, tertiary amines such as benzyldimethylamine, urea
derivatives such as N-4-chlorophenyl-N',N'-dimethylurea (monuron), unsubstituted or
substituted imidazoles such às imidazole or 2-phenylimidazole, and sulfonium salts and
tertiary phosphines.
The hardeners are used in the usual effective amounts, i.e. in the amounts suff1cient to
cure the novel compositions. The ratio of component a) to the hardener will depend on the
type of compounds used, on the requisite curing rate, and on the desired properties of ;he
final product, and can be easily determined by those skilled in the art of curing epoxy
resins. lf the hardener is an amine, then it will be expedient to use 0.75 to 1.25 equivalents
of active hydrogen bound to amino nitrogen per 1 epoxide equivalent. If the hardener is a
polycarboxylic acid or an anhydride thereof, then usually 0.4 to 1.1 equivalents of
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carboxyl or anhydride groups will be used per 1 epoxide equivalent. If the hardener is a
polyo1, then it will be expedient to use 0.75 to 1.25 equivalents of phenolic hydroxyl
groups per 1 epoxide equivalent.
The accelerators may generally be used in amounts of 0.1 to 5 % by weight, based on the
epoxy novolak resin a).
If desired, reactive diluents may be added to the curable compositions to reduce the
viscosity. Exemplary of reactive diluents are styrene oxide, butyl glycidyl ether,
2,2,4-trimethylpentyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ethers or
glycidyl esters of synthetic, highly branched, mainly tertiary aliphatic monocarboxylic
acids. The novel compositions may also contain as additional customary modifiersplasticisers, extenders, fillers and reinforcing agents, including bitumenous coal tar,
bitumen, textile fibres, glass fibres, asbestos fibres, boron fibres, carbon fibres, mineral
silicates, mica, quartz flour, hydrated alumina, bentonites, kaolin, silica aerogel or me~al
powders such as aluminium powder or iron powder, and also pigments and dyes such as
carbon black, oxide pigments and titanium dioxide, additional flame retardants,
thixotropic agents, flow control agents such as silicones, waxes and stearates, some of
which are also used as mould release agents, adhesion promoters, antioxidants and light
stabilisers, and also foaming agents, fungicides or antistatic agents.
Additional flame retardants which may conveniently be used together with the compounds
of formula I are phosphorus-containing salts such as ammonium polyphosphates, and also
alumina, bismuth oxide, molybdenum oxide or mixtures of these compounds with zinc
and/or magnesium oxide or salts, but preferably non-halogenated triphenylphosphates.
Non-halogenated triphenylphosphates may carry sterically hindered phenyl radicals,
typically with at least one tert-butyl group, but also at least one methyl group, in
ortho-position to the phenolic hydroxyl group.
The novel compositions are used for fabricating cured products such as laminates, but
preferably for encapsulating electronic components, typically of electronic c*cuits. They
may be used in a formulation adapted to suit each speci~lc end use, in the filled or unfilled
state, typically as moulding compounds, dipping resins, casting resins, impregnating
resins, laminating resins and matrix resins.
The cure of the novel compositions may be carried out in a manner known per se in one or
two steps. The cure is normally carried out by heating to temperatures in the range from
80 to 200C, preferably from 100 to 180C.
The cured products fabricated with the polyepoxides obtainable in the practice of this
invention are distinguished by good mechanical, therrnal and chemical properties.
In the preparation of laminating resins, typically of fibrous composite systems, the fibres
conventionally used for reinforcing moulding compounds may suitably be used as
reinforcing fibres. These fibTes may be organic or inorganic fibres, natural or synthetic
fibres such as aramide fibres, and be in the forrn of fibre bundles or continuous fibres. The
fibres typically used as reinforcing fibres are glass, asbestos, boron, carbon and metal
fibres, preferably carbon and metal fibres. Such fibres and fabrics made theTefrom are
commercially available.
The following Examples illustrate the invention in more detail.
Examples 1-3: Test specimens are prepared from the following epoxy cresol novolak
having an epoxy value of 200 eq/kg (EOCN 1020, Nippon Kayaku Co.) with the addition
of flame retardant A or B or a combination of flame retardant B in admixture with a
non-halogenated organic phosphate, and with the addition of the further modi~lers listed in
the following Table.
The test specimens contain a silicon chip having an aluminium strip structure (5 ~,lm wide,
1 llm thick) on a thermally oxidised SiO2 substrate. This chip is bonded with an epoxy
adhesive to a leadframe made of metal alloy (Alloy 42), and the adhesive is then thermally
cured. The contact points of the aluminium strips are then bonded to the leadframe with
gold wire, and the structured material so obtained as a whole is subsequently encapsulated
with an epoxy novolak system (q.v. the Table). Moulding temperature: 175C for
2 minutes; moulding pressure: 700 NT/cm2. Postcure temperature: 1 80C for ~ hours.
After removal from the mould, the test specimens are tested for the~r conductivity (in
ohn~) after storage at 200C. A conductivity greater than 10 ohm is counted as failure.
Test bars are prepared from the same epoxy cresol novolak composition (moulding
temperature: 175C for 2 minutes; moulding pressure: 700 NT/cm2; postcure temperature:
180C for 4 hours) and tested for their flammability in accordance with Standard UL 94,
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3rd edition (revised) of September 25, 1987 (vertical flammability test) of Underwriter
Laboratories Ltd.
Table (the amounts are given in parts by weight):
Examples:
Components of the
epoxy novolak system 1 2 3
-
a) epoxidised novolak 393.6 393.6 393.6
b) novolak (hardener) 206.4 206.4 206.4
A) comp. of formula I 101.4
B) comp. of formula I 48.6 32.4
c) non-halogenated phosphate
derivative 48.6 48.6
d) silane derivative 6 6 6
e) wax 6 6 6
f) carbonblack 6 6 6
g) phosphine derivative 4.B 4.8 4.8
h) RD-8 (filler) 2400 2400 2400
Bromine content~ based on the total amount of novolak resin (a+b):
Examples 1 and 3 : 2 % by weight in each;
Example 2 : 3 % by weight.
Kev to Table 1:
a) epoxy cresol novolak resin having an epoxy value of 200 eq~g; [EOCN 1020;
supplier: Nippon Kayaku Co];
b) phenol novolak resin TD 2093 [supplier Dainippon Lnk Co];
c) non-halogenated organic phosphate FY 511 [Ciba-Geigy AG; structure according to
formula I, wherein Xl and X2 are hydrogen, Y is oxygen and Rl and R2 are methyl,and R3 and R4 together form a group of formula III, wherein Rl is tert-butyl and R2 is
methyl];
d) 3-glycidyloxypropyl trimethoxysilane [KBM 403; supplier Shin-Etsu Chem.];
e) camauba resin;
f) carbon black;
g) triphenylphosphine;
h) silicate powder (silica~ having an avera~e particle diameter of 13 ~lm [RD-8; supplier
Tatsumori Co];
H3C
A) =P ~ ~ Br)
C(CH3)3 3
H3C
B) O=P~o~Br)
~13C 3
Test results:
inflammability according
to Example 1 2 3
(UL 94/2 mm) V-O V-O V-O
conductivity failure rate a~ter
storage at 200C for
141 hours 0/15 0/15 0/15
338 hours 0/15 0/15 0/15
It is evident from this Table that the inventive compositions, when tested in accordance
with Examples 1, 2 and 3, exhibit excellent inflammability (V-O) and that still no failure
in conductivity occurs after 141 and 338 hours at 200C when using a strongly reduced
bromine concentration in the resin formulations (2 % and 3 %, respectively). In contrast,
comparable tests made without the use of a compound of formula I, but using a
corresponding amount of a brominated epoxy novolak resin in admixture with a
percentage of Sb203, display a markedly poorer conductivity.
