Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
ARC RESISTA~T COMPOSITION
Background _ the Invention
This invention relates to arc resistant compositions. In par-
ticular, it relates to arc resistant compositions having poly(arylene
sulfide)as their basic ingredlent.
In many commercial applications involving the use of high-voltage
electric current, such as electric power transmission, or electric
resistance heating, it is either necessary or desirable to employ com-
ponents made of materials which are arc resistant as defined in ASTM-D-
495-73. Even more desirable are arc resistant compositions which are
water resistant and which have acceptable physical properties.
The present invention provides an arc resistant composition which
is suitable for being made into electrical components.
It is therefore one object of the invention to provide an arc
resistant composition of matter and a process for making same.
Another object of the invention is to provide an arc resistant
composition which possesses acceptable physical properties.
; A further object of the invention is to provide an arc resistant
composition which is water resistant.
Still another object of the invention is to provide an arc re-
sistant composition which has an improved linear coefficient of expansion.
A still further object of the inven-tion is to provide articles
made of the arc resistant composition.
Still another object of the invention is to provide an arc re-
sistant article having acceptable physical properties and improved water
resistance and linear coefficient of expansion.
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Summary of the Invention
In accordance with one aspect of the invention, an arc
resistant composition comprises poly(arylene sulfide) and 30-60 percent
by weight of fillers comprising 0-30 wei~ht percent of glass, 0-20
weight percent of calcium carbonate, and the rest being at least one of
clay and talc. Preferably the content of clay and talc comprises from
about 20 to about 50 weight percent of the arc resistant composition.
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In accordance with another aspect of the invention, an arc
resistant composition having improved water resistance is provided. The
composition comprises poly(phenylene sulfide) and 30-60 percent by weight
of Eillers with the total amount of fillers comprised of 0-75 weight
percent of glass, 0-50 weight percent of calcium carbonate, and about
0.5-5 weight percent oE silanes, and the balance of at least one of clay
and talc.
In accordance with a further aspect of the invention, a method for
producing an arc resistant composition is provided. Uncured or partially
cured poly(phenylene sulfide) is placed in a suitable blender together with
30-60 weight percent of fillers with the total amount of filler comprised
of 0-75 weight percent of glass, 0-50 weight percent of calcium carbonate,
and at least one of clay and talc. The ingredients are mixed until a
homogeneous blend is produced. The blend is then injection molded to form
an arc resistant composition.
In accordance with still another aspect of the invention, a
method for producing an arc resistant composition which has improved water
resistance is provided. Uncured or partially cured poly(phenylene sulfide)
is blended in a tumbler together with about 30-60 percent by weight of fillers
with the amount of fillers comprised of 0-75 weight percent of glass, 0-50
weight percent of calcium carbonate, about 0.5-5 weight percent of silanes,
and a remainder including at least one of talc and clay. The blend is
then compression molded to form an arc resistant compositionofdesiredshape.
In accordance with still another aspect of the invention, an
article of manufacture is produced using the composition of this invention.
Further aspects of the invention will become apparent to those
skilled in the art upon study of this specification and the appended claims.
Detailed Description of the Invention
Poly(arylene sulfides) having no additives do not exhibit good
arc resistance properties. For example, poly(phenylene sulfide) has arc
resistance of about 10 seconds, measured in accordance with ASTM-D-495-73,
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whereas the minimum acceptable value for arc resistant materials is about
120 seconds.
Surprisingly, it was discovered that addition of large amounts of
fillers with the total amount of fillers comprised of 0-75 weight percent
glass, 0-50 weight percent calcium carbonate, and the remainder of at
least one of clay and talc to poly(arylene sulfide) produces a composition
which is arc resistant, i.e., has arc resistance equal to or greater than
120 seconds as measured by ASTM-D-495-73. Moreover, it was discovered that
addition of small amounts of silanes to the new arc resistant composition
imparts improved water resistance to the composition and decreases, or at
least stabilizes, its linear coefficient of expansion.
Any uncured or partially cured poly(arylene sulfide), whether
homopolymer, copolymer, terpolymer, and the like, or a blend of such
polymers, can be used in the practice of this invention. In this application
an uncured or partially cured polymer is a polymer and the molecular weight
of which can be increased by either lengthening of a molecular chain or by
cross-linking or by combination of both by supplying thereto sufficient
energy, such as heat, preferably in the presence of oxygen. The process
which increases the molecular weight of the polymer shall be designated
as a curing process. Particularly suited for use in this invention are
those poly(arylene sulfides) having inherentviscosities in chloronaphthalene
(0.2 gram polymer in 100 cc chloronaphthalene) at 206C (402.8F) of at
least about 0.08, preferably between about 0.1 and about 0.3, and more
preferably about 0.13 and 0.23. Examples of polymers which can be used in
this inventionare disclosed in U.~.3,354,129, James T. Edmonds, Jr. et al,
issued November 21, 1967. Other examples of poly(arylene sulfides) are
poly(4,4'--biphenylene sulfide); poly(2,4-tolylene sulfide); a copolymer
from p-dichlorobenzene, 2,4-dichloratoluene, and sodium sulfide, and blends
thereof. Of all of the poly(arylene sulfides) poly(phenylene sulf~ide)
(PPS~ polymers are presently preferred for use with the invention.
Any commercially available clay, talc, calcium carbonate, or
glass can be used as fillers; high purity of these ingredients is not required.
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Although it is believed that any silane can be utilized to impart
improved water resistance and linear coefficient of expansion to the new
arc resistant composition, presently preferred are the alkylsilanes, alkoxy-
silanes, and polymers thereof. Examples of these are: Y-glycidoxypropyl-
trimethoxysilane, methyltrimethoxysilane, and polyisoxymethoxysilane.
The proportion oE fillers added to poly(arylene sulfide) can vary
from about 30 to about 60 weight percent of the total composition. The
fillers comprise 0-30 weight percent of glass, 0-20 weight percent of
calcium carbonate, and the remainder at least one of talc and clay. One
presently preferred arc resistant composition comprises:
PPS 45 weight percent
Clay 17.5 weight percent
Talc 17 5 weight percent
Glass 20.0 wei~ht percent
The concentration of silanes that can optionally be incorporated
into the improved arc resistant composition can vary between about 0.5 and
about 5 weight percent, usually between about 0.5 and about 1 weight percent
of the total composition.
The method for producing the improved arc resistant composition
is best explained by following in sequence the steps of the process.
If the composition is made by injection molding, i-t is desirable
to partially cure the polymer to reduce its melt flow to a value below
75 g/10 minutes according to ASTM Method D-1238-74 (343C and 5 kg load).
The polymers having melt flow below that level can be injection molded
with greater efficiency. The curing process is accomplished by subjecting
the uncured or partially cured polymer, preferably in air, to elevated
temperatures until desired melt flow is obtained. Elevated temperatures
of at least 500F (2~0C) are normally used; the preferred temperature
ranges from 550-900F (288-482C).
The uncured or partially cured polymer is placed in a tumbler or
other suitable mixer together with preselected amounts of a filler or fillers,
and, opt~onally, a predetermined amount of silanes. The ingredients are
compounded in accordance with a known process until a homogeneous blend
is produced.
The blend is then introduced into an injection molding apparatus
to form, upon processing, an arc resistant composition. The product of
the injection molding step can be shaped to a desired form during injection
molding or it can be machine- or otherwise-shaped after the injection
molding step is completed.
When the composition is not produced by injection molding,
but instead by a process such as compression molding, the melt flow character-
istics of the poly(arylene sulfide) are normally not as important. Any
solid or liquid, uncured or partially cured poly(arylene sulfide) can be
blended with the enumerated fillers and the composition cured by application
of energy such as heat without first bringing the melt flow of the
poly(arylene sulfide) to a preferred minimum level.
The follo~ing examples are provided merely to illustrate the
practice of the invention rather than to in any way limit the scope of the
invention.
EX~MPLE I
Powder poly(phenylene sulfides), known under the trademark
Ryto ~ P3 and having a density of 1.3 measured in accordance with ASTM
D 1505-68 and a melt flow of 75 g/10 minutes measured in accordance with
ASTM D 1238-74, (343C and 5 kg load) was blended with varying amounts of
clay, talc, calcium carbonate9 mica, and fiberglass. The weight percentage
of each filler in each one of -the blends is shown in Table I. The blending
was performed by tumbling the ingredients of each sample in a rotating drum
blender.
;~ Each of the blends and a batch of pure poly(phenylene sulfide)
of the typP used for making the blends were injection molded into bar
specimens having dimensions (8.5 inch x 1/2 inch x 125 mils) and shape
suitable for ASTM tensile strength. Each specimen was then tested to
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determine its tensile strength, % elongation, arc resistance (in accordance
with ASTM D 495-73). The results are shown in Table I.
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The results indicate that addition of the enumerated fillers
decreases the tensile strength of poly(phenylene sulfide) and the % elongation.
However, each one of the fillers improved the arc resistance of the polymer.
The degree to whlch the arc resistance was improved varied greatly depending
on the amount and type of the fil]er. The best arc resistance was obtained
with blends A, B, and I. Considerably less improvement in arc resistance
was observed with blends G and H. Othex blends specifled in Table I resulted
in only slight improvement of arc resistance, not sufficient to satisfy the
minimum 120 second arc resistance as measured by ASTM D 495-73.
It should be noted that blend I composed of 17% of clay, 17% of
talc, and 20% of iberglass resulted in a composition having not only vastly
improved arc resistance but also having tensile strength reduced least of any
of the other compositions formed through compounding poly(phenylene sulfide).
EXAMPLE II
Since talc and clay in combination with poly(phenylene sulfide)
appeared to have good arc resistance, another series of tests was made using
varying amounts of these two fillers. The tests were conducted by procedures
outllned in Example I. The results are summarized below.
TABLE II
Filler, Wt. % Melt Flow( )
Talc Clay Arc Resistance, seconds g~10 minutes
132 93.6
183 68.1
188 37.
193 10.7
(1) ASTM ~ 1238-7~, 3~3C and 5 kg load
The data show that all the blends exceed the minimum accepted value
for arc resistance of 120 seconds but that the blends containing 15 wt. % of
each filler have by far superior combined properties of arc resistance and
melt flow. Good melt flow properties are required for good processability
of the composition especially by injection molding.
_ ~ _
EXAMPLE III
A blend of the following ingredients at specified concentrations
was produced by mixing in a tumbler:
Ingredient Concentration (wt. %)
Partially cured
pol.y(phenylene sulfide) 45
Clay 17.5
Talc 17.5
- Glass 20.0
The blend was then subdivided into seven samples. Six of the
samples were compounded with 0.8 weight percent of various silanes as
follows:
Sample 1 Control, no silane
Sample 2 ~-glycidoxypropyltrimethoxysilane (Union
Carbide)
Sample 3 ~-glycidoxypropyltrimethoxysilane (Dow)
Sample 4 methyltrimethoxysilane (Dow)
: Sample 5 polyisoxymethoxysilane (Dow)
Sample 6 methy.lmethoxysilane (Union Carbide)
Sample 7 long chain alkyl silane (Experimental) (Dow)
The samples were injection molded to produce specimens of a shape suitable
for testing. The physical and electrical properties and coefficients of
- linear thermal expansion of each specimen were then tested. The results
of the tests appear in Tables III-V.
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From the results in Table III it can be concluded that the addition
of the silanes did not materially affect the physical properties of the
samples.
The tests of electrical properties in Table IV reveal that all samples
had good arc resistance. The dielectric constants of the samples were of
the same order of magnitude for all samples but after 7 day-immersion in
water, dielectric constants of silane containing samples were about 10-20%
lower than that of the control sample. Volume resistivity of the control
after immersion was poorer by a factor of 1000 (103) whereas the silane
treated samples showed comparatively little change.
TABLE _
Coefficient of Linear Thermal Expansion
Temperature Range: All values x 106/degree C
Property -30 to +30C +70C +125C +140C +225C
Sample 1 20.7 21.8 13.4 23.8 42.7
2 20.1 18.2 22.4 21.6 32.3
3 16.8 14.9 17.5 17.5 17.4
4 19.4 erratic 10.7 16.9 39.6
17.1 17.1 17.4 17.4 16.9
6 16.9 9.9 15.6 17.8 22.2
7 23.7 19.2 31.3 28.3 58.9
The results indicate that silanes contained in samples 3, 5 and 6
cause a significantly lower coefficient of th rmal linear expansion. Silanes
in samples 3 and 5 resulted in stabilizing the coefficient of thermal linear
expansion over the temperature range of the tests.
Only the silane in sample 7 resulted in increasing the coefficient
above that of the control sample (sample 1~. The effect on the coefficient
of linear expansion was totally unexpected and no explanation for this
effect is offered.
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