Note: Descriptions are shown in the official language in which they were submitted.
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31271US
ZINC OXIDE IN POLY(ARYLENE SULFIDE) COMPOSITIONS
This invention relates to poly(arylene sulfide) compositions.
In one aspect this invention relates to electronic components
encapsulated with poly(arylene sulfide) compositions. In another aspect
this invention relates to poly(arylene sulfide) compositions containing a
color shift inhibitor.
Background and Objects
The encapsulation of electronic components represents an art in
and of itself. Electronic components are encapsulated to maintain
electrical insulation, to provide mechanical protection and to otherwise
shield the component from exposure to its environment. As the evolution
of electronics continues its rapid advance it becomes increasingly
important that the art and technology of encapsulation keep pace. An
area of significant concern and interest relates specifically to the
compositions used to encapsulate electronic components. There is an
on-going effort to discover new and improved encapsulation materials. A
relatively recent development has been the use of poly(arylene sulfide)
compositions such as, for example, poly(phenylene sulfide) compositions,
as encapsulating materials.
The reliability and useful life of an electronic component
depends upon various factors. One important factor is the material used
to encapsulate the electronic component. It is desired to employ
encapsulation compositions which maximize the reliability and useful life
of electronic components.
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It is one object of this invention to improve the reliability
and increase the life of electronic components encapsulated with
poly(arylene sulfide) compositions. It is another object of this
invention to provide improved encapsulation compositions and electronic
components encapsulated therewith.
Pigmented poly(arylene sulfide) compositions are frequently
processed (e.g. molded, extruded, etc.) at elevated temperatures. The
presence of certain components in the composition may make the color of
the composition temperature sensitive. For example, if identical
compositions are processed at different temperatures the resultant
materials may have different colors, i.e. a color shift may occur at the
higher temperature.
It is a further object of this invention to provide
poly(arylene sulfide) compositions susceptible to color shift with a
lS color shift inhibitor. Poly(arylene sulfide) compositions so inhibited
are useful as laser printable materials and encapsulation materials and
for any other application where a pigmented poly(arylene sulfide) is
desired.
Other objects, advantages and aspects of this invention will
become apparent to persons skilled in the art upon study of this
disclosure and the appended claims.
Brief Summary of the Invention
It has been discovered that the addition of zinc oxide to
poly(arylene sulfide) compositions can improve the reliability and
lengthen the life of electronic components encapsulated therewith. It
has also been discovered that zinc oxide can inhibit the color shift
associated with poly(arylene sulfide) compositions containing certain
pigments and silanes. This invention is further, and more completely,
described in the disclosure that follows.
Description of the Invention~
In accordance with this invention an electronic component is
encapsulated with a composition containing poly(arylene sulfide) and zinc
oxide. This invention includes electronic components encapsulated with
the above-described composition as well as certain encapsulation
compositions that are especially well suited for the encapsulation of
electronic components.
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In accordance with another aspect of this invention a
composition containing poly(arylene sulfide), pigment and silane is
inhibited against color shift by the addition thereto of zinc oxide.
This invention includes the article of manufacture and the
compositions described and set forth as follows.
1. Article of Manufacture
The article of manufacture of this invention is an electronic
component encapsulated wi~h a composition containing poly(arylene
sulfide) and zinc oxide.
For the purposes of this entire disclosure and the appended
claims the term poly(arylene sulfide) is intended to designate arylene
sulfide polymers. Uncured or partially cured poly(arylene sulfide)
polymers whether homopolymer, copolymer, terpolymer, and the like, or a
blend of such polymers, can be used in the practice of my invention. The
uncured or partially cured polymer is a polymer 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. Suitable poly(arylene sulfide) polymers include,
but are not limited to, those described in U.S. 3,354,129.
Some examples of poly(arylene sulfide) suitable for the
purposes of our invention include poly(2,4-tolylene sulfide),
poly(4,4'-biphenylene sulfide) and poly(phenrlene sulfide). Because of
its availability and desir~ble properties (such as high chemical
resistance, nonflammability, and high stren~th and hardness)
poly(phenylene sulfide) is the presently preferred poly(arylene sulfide).
Accordingly, poly(phenylene sulfide) compositions are the preferred
encapsulation compositions of our invention.
In accordance wi~h this invention electronic components are
encapsulated with a poly(arylene sulfide) composition (such as, for
example, a poly(phenylene sulfide) composition) containing zinc oxide.
The poly(arylene sulfide) composition can ~e, but is not required to be,
a mixture of more than one type of poly(arylene sulfide). The
poly(arylene sulfide) composition can contain, in addition to zinc oxide,
other components although the broad concept of our invention is not
limited thereto.
Our invention also includes electronic components encapsulated
with more detailed poly(arylene sulfide) compositions which are
- especially well suited for successful use as encapsulation compositions.
These compositions are described later in this disclosure.
Zinc oxide is a material well known by, and readily available
to, persons skilled in the art. This invention is not limited to any
particular type or grade of zinc oxide. For a more detailed discussion
of zinc oxide any one of numerous references can be consulted. One such
reference is the Kirk-Othmer Encyclopedia of Technology, Second Edition,
Volume 22, pages 609~.
Broadly this invention is not limited to any ranges of
materials. It is contemplated, however, that the ratio of (a) the weight
of poly(arylene sulfide) in the composition to (b) the weight of zinc
oxide in the composition will generally be at least about 2.5 to 1 and
less than about 2,500 to 1. This ratio, called the weight ratio, is
calculated with disregard to the presence or absence of other components
in the composition. We prefer a weight ratio (i.e. (a) to (b) of at
least about 10 to 1 and less than about 100 to 1. Good results within
this range have been obtained. It should be noted that the choice of a
particular weight ratio will be greatly influenced by the presence and
relative amounts of other components in the composition.
The electronic components to be encapsulated in accordance with
our invention broadly include all electronic components (i.e. devices,
parts, etc.) for which encapsulation is desired. The term electronic
component is intended to be broadly construed and includes, by way of
non-limiting example, the following:
capacitors,
resistors,
resistor networks,
integrated circuits,
transistors,
diodes,
triodes,
thyristors,
coils,
varistors,
connectors,
condensers,
transducers,
crvstal oscillators,
fuses,
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rectifiers,
power supplies, and
microswitches.
The definition of each of the above-identified electronic
components is similarly intended to be broad and comprehensive. The
term integrated circuit, for example, is intended to include, but is
not limited to
large scale integrated circuits,
TTL (transistor transistor logic),
hybrid .:tegrated circuits,
linear amplifiers,
operational amplifiers,
instrumentation amplifiers,
isolation amplifiers,
multipliers and dividers,
log/antilog amplifiers,
RhS-to-DC converters,
voltage references,
transducers,
conditioners,
instrumentation,
dig:tal-to-analog converters,
analog-to-digital converters,
voltage/frequency converters,
synchro-digital converters,
sample~track-hold amplifiers,
CMOS switches and multiplexers,
data-acquisition subsystems,
power supplies,
memory integrated circuits,
microprocessors,
and so on.
The scope of this invention broadly allows the inclusion of
fillers and reinforcements in the encapsulation composition. Fillers
can be used to improve the dimensional stability, thermal conductivity
and mechanical strength of the composition. Some suitable fillers
include, for example, talc, silica, clay, alumina, calcium sulfate,
calcium carbonate, mica and so on. The fillers can be in the form of,
for example, powder, grain or fiber. In selecting a filler the
following factors should be considered:
(1) the electrical conductivity of the filler (the lower
the better.
(2) the thermal stability of the filler at encapsulation
temperatures; and ~ 259737
(3) the level of ionic impurities in the filler.
Suitable reinforcements i~clude fibers of glass or calcium
silicate (e.g. wollastonite). Examples of other reinforcements include
glass or calcium silicate in nonfibrous form (e.g. beads, powders,
grains, etc.) and fibers of other materials such as asbestos, ceramics,
etc.
Although this invention is not limited thereto, a
hydrogenated conjLgated dienetmonovinyl-substituted aromatic copolvmer
can be included in the poly(arylene sulfide) composition. An example
of such a copolymer is hydrogenated butadiene/styrene copolymer.
O~hers are known to persons skilled in the art.
The electrical resistance and hydrolytic stability of the
encapsulation compositions of this i~vention can be improved by the
addition of an organosilane. Many suitable organosilanes are known in
the art. Good results can be obtained wi~h, for example, N-{2-[3-
(trimethoxysi~yl)propylamino]ethyl}-p-vinylbenzylammonium chloride.
Organomercaptosilanes can also be used for this purpose.
3-Mercaptopropyltrimethoxysilane, HSCH2CH2CH2Si(OCH3)3, is most
preferred because of its high utility in improving electrical
resistance and hydrolytic stability.
Besides reinforcements, fillers, copolymers and silanes the
compositions can optionally contain relatively small amounts of other
ingredien~s such as, but not llmited to, pigments, flow improvers, and
processing aids.
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2. _mpositio_ Inhibited ~gainst Col_r Shift
It has been discovered tha-t æinc oxide can be used to inhibit the
color shift associated with the high temperature processing of a
poly(arylene sulEide) composition con-tain:ing a pigment and a silflne. In
the absence of the silane a color shift does not occur over a
normal range of processing temperatures. The presence of the
silane~ however, can cause a temperature-sensi-tive shift of color
to occur. To avoid -this color shift, processing temperatures must
be held lower than otherwise deslred. Z:inc oxide inhibits the
color shift and allows higher -temperature processing of the
composition.
The pigment, in this aspect of the inven-tion, is any pigment
selected from monoazo nickel complex pigments ~see, for example U.S.
patent 2,396,327), iron oxide pigments, lead chromate pigmen-ts, cadmium
i5 sulfo-sulfide pigmen-ts, and combinations of any two or more thereof
(e.g. a combinfltion of an iron oxide pigment and a lead chromate
pigment; a combination of an iron oxide pigment and a cadmium
sulfo-sulfide pigment; e-tc.).
The silane in this aspect of the invention is any silane selected
from the organomercaptosilarles, the organoaminosilanes and any
combination thereof. An organomercaptosilane is an organosilane
characterized by a mercapto (-SH) functionality in i-ts chemical formula.
An example is 3-mercaptopropyltrimethoxysilane. An organoaminosilane is
an organosilane characterized by an amino functionality in its chemical
formula. Examples include 3-aminopropyltrimethoxysilane and
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N-{2-[3-(trimethox~silyl)propylamino]ethyl}-p-vinylbenzylammonium
chloride.
Poly(arylene sulfide) compositions containing the
above-identified silanes and pigments are laser printable and are
useful for the encapsulation of electronic components. This aspect of
the invention, although not limited thereto, has applicability to the
compositions described in 1 and 2 above wherein those compositions
further contain a pigment and a silane as identified above. This aspect
of the invention is not limited to encapsulation compositions but
includes any application wbere it is desired to inhibit color shift.
Although this invention is not limited thereto it is
contemplated that the invention will usually be practiced within the
ranges provided below.
Weight Ratio of Poly(arylene sulfide)
15 Component to Component
zinc oxide: at lea~t about 2.5 to 1 (broad range)
less than about 2,500 to 1
at least 10 to 1 (narrow range)
less than about 100 to 1
20 pigment: at least about 2.5 to 1 (broad range)
less than about 2,500 to I
at least about 10 to 1 (narrow range)
less than about 100 to 1
silane: at least about 2.5 to 1 (broad range)
less than about 2,500 to 1
at least about 10 to 1 (narrow range)
less than abo~t 100 to 1
The above weight ratios are calculated with disregard ~o the
presence or ab~ence of other co~ponents in the composition. The narrow
ranges are preferred because good results have been obtained within
those ranges.
The use of zinc oxide as a color shift inhibitor is desirable
when the poly(arylene sulfide) compo5ition is subjected to a
temperature at which a ~clor shift would occur in ~he absence of the
zinc oxide. This color shift inhibiting aspect of the invention is
further illus~rated in Example ~.
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3. w to Make
The cornpositions of this invention can be made in accordance
with any method whe,rein the poly(arylene sulEide), zinc oxide and
other components (if flny) are combined -to form a mixture. Many
sui-table methods are well known to -those of skill :in the art. By way
of example, the components oE the composi-tion can be mixed together at
room temperflture in a rotating drum blender or in an intensive mixer
such as a Henschel mixer and then extrusion compounded at a
tempera-ture above about the melting point of -the poly(arylene sulfide)
to produce a uniform blend.
Once made, the composition can be used to encapsulate elec-
-tronic components in accordance wi-th any encapsulation method sui-table
for thermoplastic encapsulation compositions. Such methods are well
known in the art. The composition can be heated to a temperature of
flt least about the melting point of the poly(arylene sulfide) and then
used to encapsulate electronic components. The composition can, for
example, be introduced into an lnjection molding apparatus to produce
a melt which is extruded into an injection mold where;n the electronic
componen-t to be encapsulated is positioned. Transfer molding
processes are also acceptable.
The following examples are presented to facilitate
disclosure of th;s invention and should not be interpreted to unduly
limit its scope.
EXAMP E I
This example shows the color shift problem associated
with organomercaptosilane-con-taining poly(arylene sulfide)
compositions and demonstrates the color shift inhibiting utility
of zinc oxide. Three compositions, C, ~ and E~ were prepared in
accordance with Table l.
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Table 1 (compositions-wel~t pe entagesi)
C D E
poly(pheny~ene sulfide) 35~ 35% 35%
fiberglass 35% 35% 35%
talcC d 12.75% 11.75% 9.75~
titanium dio~ide 15% 15% 15%
3-merca~topropyltrimethoxysilanee 1% 1%
pigment 2% 2% 2%
processinghaidg .25% .25% .25%
10 zinc oxide 2b
100% 100%100,'
(a) PPS, from Phillips Chemical Company, having a viscosity of
about 210 poise as tested on a capillary1rheometer at
650F and at a shear rate of 1000 (Sec)
(b) Fiberglass Grade 197 from Owens-Corning, Amarillo, Texas.
(c) Talc type 2620 from Pioneer Talc Co., Van Horn, Texas.
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(d) Titanium dioxide, Unitane 0-110 from American Cyanamid Co.
lM
(e) A-189 from Union Carbide Corp.
(f) Yellow pig~ent, Harmon Y-5694 from ~armon Chemical Co.,
Hawthorne, New Jersey.
(g) Polyethylene, Marlex~ EMN-TR885 from Phillips Chemical
Company.
(h) Zinc oxide, U.S.P. grade, from Mallinkrodt, Inc.
(i) The percentages given in Table l are weight percentages and
are based upon the total weight of the composition.
Each composition was separately prepared as follows. The
composition components were mixed together in a Xenschel mixer until the
components were co~pletely dispersed. The resultant mixture was passed
through a Buss-Condux cokneader extruder at 570-600F and pelletized.
Each composition thuR produced was u3ed to ~a~e disc~ (2 -
1/8 inch diameter, 1/16 inch thick) i~ the following manner. The
pelletized material was i~jection molded, nsing an Arburg molding
machine, into the discs. From composition C a first disc was molded at
575F and a second disc was molded at 650F. From composition D a
first disc was molded at 600F and a second disc was molded at 650F.
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From compos:;tion E a fLrst disc was molded at 600F and a
second disc was molded at 650F. Each disc was carefully observed for
color. The observed color corresponding to each disc is reported in
Tflble 2 below.
s
_able 2~ e Disc Col~
Composition 575F _ 600F 650F
tO C yellow gold - yellow gold
D - yellow gold green gold
E - yellow gold yellow gold
Composition C was color stable over the temperatures tested.
There was no significant difference Ln color between the first (S75F)
and second (650F) discs. Composition D, containing the silane,
exhibited a color shift. The Eirst disc (600F) was ye]low gold,
however, the second disc (650 F) was green gold. Composition E,
containing both the silane and zinc oxide, was color stable, i.e.
there was no signLficant dlfference in color between the first (600F)
and sacond (650F) discs. The results associated with composition E
demonstrate the utility of zinc oxide in inhibiting color shift in
organomercaptosilane-containing poly(arylene sulfide) compositions.
Composition E represents a material suitable for the
encapstllation of electronic components. It can be used, for example,
to encapsulate capacitors. Gomposition E is also a laser printable
material.
