CA1259737A - Avoidance of colour shift in processed poly (arylene sulfide) compositions - Google Patents

Abstract

Abstract of the Disclosure Zinc oxide is used in combination with pigment and silane in poly(arylene sulfide) compositions to improve encapsulation properties and to inhibit color shift. The invention includes articles of manufacture comprising the poly(arylene sulfide) compositions containing zinc oxide, pigment and silane.

Description

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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, .

7~7 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 C

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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.
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(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.

Claims (22)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising (a) poly(arylene sulfide), (b) zinc oxide, present in an amount sufficient to inhibit a temperature caused color shift, (c) pigment selected from monoazo nickel complex pigment, iron oxide pigment, lead chromate pigment, cadmium sulfo-sulfide pigment, and combinations thereof, and, (d) silane selected from organomercaptosilane, organoaminosilane, and combinations thereof.

2. A composition according to claim 1 wherein the weight ratio of (a) to (b) is at least about 2.5 to 1 and less than about 2,500 to 1;
wherein the weight ratio of (a) to (c) is at least about 2.5 to 1 and less than about 2,500 to 1; and wherein the weight ratio of (a) to (d) is at least about 2.5 to 1 and less than about 2,500 to 1.

3. A composition according to claim 1 wherein the weight ratio of (a) to (b) is at least about 10 to 1 and less than about 100 to 1;
wherein the weight ratio of (a) to (c) is at least about 10 to 1 and less than about 100 to 1; and wherein the weight ratio of (a) to (d) is at least about 10 to 1 and less than about 100 to 1.

4. A composition according to claim 3 wherein (a) is poly(phenylene sulfide)

5. A composition according to claim 1 wherein (d) is 3-mercaptopropyltrimethoxysilane.

6. A composition according to claim 2 wherein (d) is organomercaptosilane.

7. A composition according to claim 2 wherein (d) is organoaminosilane.

8. A composition according to claim 2 wherein (c) is a monoazo nickel complex pigment.

9. An composition according to claim 2 wherein (c) is a combination of (i) iron oxide pigment and (ii) lead chromate pigment or cadmium sulfo-sulfide pigment.

10. A composition according to claim 4 further comprising calcium sulfate; wherein (c) is monoazo nickel complex pigment and (d) is N-{2-[3-(trimethoxysilyl)propylamino]ethyl}-p-vinylbenzylammonium chloride.

11. A composition according to claim 4 further comprising talc; wherein (c) is a combination of iron oxide pigment and cadmium sulfo-sulfide pigment and (d) is 3-mercaptopropyltrimethoxysilane.

12. An article of manufacture comprising an electronic component encapsulated with the composition of claim 1.

13. An article of manufacture according to claim 12 wherein the weight ratio of (a) to (b) is at least about 2.5 to 1 and less than about 2,500 to 1; wherein the weight ratio of (a) to (c) is at least about 2.5 to 1 and less than about 2,500 to 1; and wherein the weight ratio of (a) to (d) is at least about 2.5 to 1 and less than about 2,500 to 1.

14. An article of manufacture according to claim 12 wherein the weight ratio of (a) to (b) is at least about 10 to 1 and less than about 100 to 1; wherein the weight ratio of (a) to (c) is at least about 10 to 1 and less than about 100 to 1; and wherein the weight ratio of (a) to (d) is at least about 10 to 1 and less than about 100 to 1.

15. An article of manufacture according to claim 12, wherein (a) is poly(phenylene sulfide).

16. An article of manufacture according to claim 13 wherein (c) is a monoazo nickel complex pigment.

17. An article of manufacture according to claim 13 wherein (c) is a combination of (i) iron oxide pigment and (ii) lead chromate pigment or cadmium sulfo-sulfide pigment.

18. An article of manufacture according to claim 13 wherein (d) is organomercaptosilane.

19. An article of manufacture according to claim 13 wherein (d) is organoaminosilane.

20. An article of manufacture according to claim 12 wherein (d) is 3-mercaptopropyltrimethoxysilane.

21. An article of manufacture according to claim 15 further comprising calcium sulfate; wherein (c) is monoazo nickel complex pigment and (d) is N-{2-[3-(trimethoxysilyl)propylamino]ethyl}-p-vinylbenzylammonium chloride.

22. An article of manufacture according to claim 15 further comprising talc; wherein (c) is a combination of iron oxide pigment and cadmium sulfo-sulfide pigment and (d) is 3-mercaptopropyl-trimethoxysilane.