Note: Descriptions are shown in the official language in which they were submitted.
~045808
This invention relates generally to compositions which
contain high molecular weight aromatic polycarbonates based on
aromatic bis-hydroxy compounds, in particular on dihydroxydi-
aryl compounds, and more particularly to such polycarbonates
having improved electrical tracking resistance co~pared with
glass fiber reinforced high molecular weight, aromatic poly-
carbonate compositions.
~ ore and~more attention and consideration are being
given to the electrical tracking resistance of chemical
materials. An adequate electrical tracking resistance is
demanded of those synthetic substances which carry voltage-
conducting parts or are in contact with them. Since the sur-
face of a synthetic substance may come into contact with
moisture and dust, leakage current paths may form on such a
surface and, as a further consequence, leakage tracks, and
(surface) leakage currents may flow which, finally, may, in the
case of materials inadequately resistant to leakage current,
lead to breakdown and possibly to the starting of a fire.
Materials with low or inadequate resistance to (surface)
leakage current should therefore, for these fields of appli-
cation, be provided with a sufficiently electrical tracking
resistant finish.
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It is known that the electrical tracking resistance
of chemical materials which consist predominantly or exclusively
of aromatic polymers, such as polystyrene or aromatic poly-
sulphones, is not satisfactory. Although high-molecular-
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weight aromatic polycarbonates based on dihydroxydiaryl com-
pounds, in particular those based on bis-2-(4-hydroxyphenyl)-
propane(Bisphenol A) have a resistance to the flow of (sur-
face) leakage current when measured by the KB method with test
solution F according to VDE (Verband Deutsche`r Elektrotechniker,
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i.e. Association of German Electrical Engineers) Instruction
Sheet 0303, Part 1, of September 1964 of about 300 ~ 20, the
resistance to (surface) leakage current of high-molecular-
weight aromatic polycarbonates which are reinforced with glass
fibers is distinctly lower or only 180 + 20. Test solution F
is a 0.1~ aqueous ammonium chloride solution.
It is therefore an object of this invention to pro-
vide a high molecular weight, aromatic polycarbonate composition
having improved electrical tracking resistance to surface leakage
current in comparison with glass fiber reinforced, high molecular
weight aromatic polycarbonate compositions, whereas the good
mechanical and thermal properties of the glass fiber rein- .:
forced aromatic polycarbonate compositions are almost achieved;
another object of the invention is to provide a method for
improving the resistance of a polycarbonate composition to
surface leakage current having almost the good mechanical and
,
thermal properties of the glass fiber reinforced, high molecular
weight aromatic polycarbonate compositions; a further object
of the invention is to provide a molded polycarbonate composition
which has almost the good mechanical and thermal properties of
the glass fiber reinforced aromatic polycarbonate compositions
and which has a satisfactory resistance to flow of leakage
electric current and is suitable for molding parts which are
associated with electrical conductors.
The foregoing objects and others are accomplished in
accordance with this invention, generally speaking, by pro-
viding a high molecular weight polycarbonate composition
containing a silica flour of Farsil type respectively quartz
flour of Farsil type. Polycarbontes containing silica are known
in the art(compare the book "Polycarbonates", by Christopher and :~
Fox, Reinhold Publishing Corporation, New York, 1962, page 151);~
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1045808
but it has now been found that high molecular weight aromatic
polycarbonate compositions which have physical properties
approaching those of a fiber-gla~ reinforced polycarbonate and
having a better resistance to the flow of leakage current can
be prepared by dispersing silica flour of Farsil type respectively
quartz flour of Farsil type in the polycarbonate. A hydrophobic
pigment which is inèrt to the polycarbonate may be included with
the silica flour respectively quartz flour in the composition.
The polycarbonate compositions provided by the invention because
of their resistance to surface leakage current in combination
with other good physical properties are suitable for molding many
different products but are particularly well suited for making
parts for electrical appliances and electrical insulating compo-
nents to be used for electrical engineering purposes.
The invention thus provides compostions which con-
tain high-molecular weight aromatic polycarbonates based on
aromatic bis-hydroxy compounds, in particular on dihydroxy-
diaryl compounds, and which are characterized in that they
have a content of a silica flour of Farsil type respectively
quartz flour of Farsil type of about 10 percent to about 60
percent by weight, preferably of about 20 percent to about
40 percent by weight. These compositions may additionally
contain a hydrophobic inert pigment, such as TiO2 or Cr203,
in an amount of from about 2 percent to 20 percent by weight,
preferably about 5 percent to about 10 percent by weight,
the percentages by weight being in each case with respect
to the weight of high-molecular-weight polycarbonate. -
The compositions of the invention thus obtained have
an electrical tracking resistance to surface leakage current
which is at least 260 + 20 when measured by the KB method with
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test solution F according to VDE Instruction Sheet 0303,
Part 1 of September 1964.
Accordingly, the present invention pertains to a
composition comprising
(a) a high molecular weight aromatic polycarbonate
and
(b) about 10 to 60 weight percent, based on the
high molecular weight polycarbonate, of silica
flour of a maximum particle size less than 100
~m and an alkali metal oxide or alkali earth
metal oxide content of less than 1 weight
percent, based on the silica flour, wherein the
flour is prepared by heating quartz materials
to between 1400C and 1600C for several hours,
15 cooling them and comminuting them to size.
The present invention further pertains to a process
for improving the resistance of a high molecular weight,
aromatic polycarbonate to leakage current comprising dispersing
in the polycarbonate about 10 to 60 weight percent, based on
` 20 the weight of the polycarbonate, of a silica flour having a
particle size of less than 100 ~m and an alkali metal oxide
or alkali earth metal oxide content of less than 1 weight
percent based on the silica flour wherein the flour is
prepared by heating quartz materials to between 1400C and
1600C for several hours, cooling them and comminuting them
to size.
The present invention also pertains to an electrical
insulator shaped from the composition of the invention and
having a minimum tracking resistance of 260 + 20 volts and
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a minimum impact strength of about 70 kpcm/cm2.
The polycarbonates, useful for the instant invention,
are those prepared by reaction of aromatic bis~hydroxy
compounds, particularly of dihydroxydiarylalkanes, with
phosgene or diesters of carbonic acid. Polycarbonates
prepared from unsubstituted dihydroxydiarylalkanes or
those prepared from dihydroxydiarylalkanes having acyl
radicals which carry methyl groups or halogen atoms in
the ortho- or meta-position to the hydroxyl group are
included. Branched polycarbonates are also suitable.
The polycarbonates may have an average molecular
weight between about 10,000 and about 100,000, preferably
between about 20,000 and 40,000.
Examples of suitable aromatic bis-hydroxy compounds
for preparing the polycarbonates are hydroquinone, resorcinol,
4,4'-dihydroxydiphenyl, bis-(hydroxyphenyl)-alkanes as for
example Cl-C8-alkylene- or C2-C8-alkylidene-bisphenols,
bis~hydroxyphenyl)cycloalkanes such as, for example, C5-C15-
cycloalkylene- or C5-C15-cycloalkylidene-bisphenols, bis-
(hydroxyphenyl)-sulphides, -ethers, -ketones, -sulphoxides or
-sulphones. Further, a,~'-bis-thydroxyphenyl)-diisopropyl-
benzene as well as the corresponding nuclearly alkylated or
nuclearly halogenated compounds and the like. Preferred are
polycarbonates based on bis-(4-hydroxyphenyl)-propane-2,2
(bisphenol A), bis-(4-hydroxy-3,5-dichlorophenyl)-propane-
2,2 (bisphenol A), bis-(4-hydroxy-3,5-dichlorophenyl)-propane-
2,2 (tetrachlorobisphenyl A), bis-(4-hydroxy-3,5-dibromophenyl)-
propane-2,2 (tetrabromobisphenol A), bis-(4-hydroxy-3,5-di-
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1~)45808
methylphenyl)-propane-2,2 (tetramethylbisphenol A), bis-(4-
hydroxyphenyl)-cyclohexane-l,l (bisphenol Z) and based on
tri-nuclear bisphenols such as a,~'-bis-(~-hydroxyphenyl)-p-
diisopropylbenzene.
Additional aromatic bis-hydroxy compounds suitable
for the preparation of the polycarbonate are described in
U. S. Patents 3,028,365; 2,999,835; 3,148,172; 3,271,368;
2,970,137; 2,991,273; 3,271,367; 3,280,078; 3,014,891; and
2,999,846.
The silica flour respectively quartz flour of Farsil
type are SiO2 flours having an alkali metal oxide content or
alkaline earth metal oxide content which is not greater than
1% by weight and which were obtained with the aid of a so-
called sintering process and whose particle size lies between
15 0 and 100 ~m, preferably between 0 and 10 ~m. The silica
flour of Farsil type respectively quartz flour of Farsil
type may be prepared by a sintering process wherein quartz
materials are heated for several hours to about 1400C to
1600C, cooled and comminuted (cf. French Patent Specifica-
20 tion 1,288,904). (Suitable are e.g. the Grénette Farsil
types 44 and 28 of the firm S.A.N.S.O.N., Cayeux-sur-Mer/
France.) A small particle size is necessary, among other
reasons, to avoid damage to the screws of the extruder or
injection molding machine because of the hardness of the
silica flour. Unsuitable are, for example, silica flours
of a particle size between 0 and 100 ~m which after grinding
were calcined for 2 hours at 1000C (e.g. the types W 6,
W 12 and Sikron(R) 100 of Quarzwerke GmbH, Cologne)
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10458~D8
Any suitable pigment which is hydrophobic and inert
to high-molecular-weight aromatic polycarbonates, for example
TiO2, Cr203, in the form of powder may be used.
A~ suitable process may be used to disperse the silica
flour respectively quartz flour of Farsil type in the
preparation of the compositions, according to the high-
molecular-weight aromatic polycarbonates such as, for example:
1. The silica flour respectively quartz flour and, optionally,
the pigment may be introduced into the polycarbonate melt.
Mixing may be effected by any known process and the mixture
may be extruded or injection molded according to any known
process.
2. The silica flour respectively quartz flour and, optionally,
the pigment may be introduced into a solution of the poly-
carbonate, the solvent evaporated as usual from the solution
and the residue dried.
The compositions provided by the invention may be -
used in the elctrical filed, especially for the production
of articles which carry ~oltage-conducting parts or come into -
contact with voltage-conducting parts.
The following Examples illustrate the improved tracking
resistance, with respect to a glass reinforced polycarbonate
composition, and the good physical-technological properties
picture of the compositions provided by the invention and
simultaneously show that other silica flours are not as well
suited in this respect. I
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Example 1
About 40~ by weight of silica ~lour is added to a
high-molecular-weight polycarbonate melt based on Bisphenol A
(prepared according to the process of interface condensation
with phosgene, and having a rel. solution viscosity of 1.320)
with the aid of a twin screw extruder. The polycarbonate bristles
obtained are drawn off via a water- and air-cooled through and
immediately granulated.
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Example 2
According to the process described under Example 1,
a mixture of 20% by weight of silica flour and 10% by weight
of pigment is added to the polycarbonate.
Some selected values of the physical~technological
properties in dependence on the silica flour type used and,
in some cases, pigment addition, are recorded in the following
Table:
Example 3
- The polycarbonate of Example 1 containing in`stead
of 40 % by weight of silica flour 20 % by w~ight of milled
glass i~iber.
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1~)45808
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O '-I ~1 ~ U') O O ~ D h :
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tq o ~ U ~ ~ h ~q O O ~ ~ g O~ î~
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16~45808
. Farsil-44 has the following chemical analysis and the
.:
. .ollowing particle sizes. ~ .
.. Farsil-44 100 % finer than 60 Micron
. 96 % finer than 40 Micron
. 92 % finer than 28 Micron
84 % finer than 20 Micron
60 % finer than 10 Micron
34 % ~iner than 5 Micron
26 % finer than 3 Micron
14 % finer than 2 Micron
10 % finer than l Micron
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Chemical Analysis: SiO2 : 99.03% Al2O3 : 0-18% :
Fe2O3 : 0.02~ CaO : 0.5 % :
MgO : 0.I % Na2O : 0.07%
. 10 K2O : 0.03% . -
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Although the invention is described in detail for
~j the purpose of illustration it is to be understood that such
detail is solely for that purpose and that variations can be
made therein by those skilled in the art without departing
from the spirit and scope of the invention except as it may
be limited by the claims.
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