Internal lubricant for glass reinforced polyarylene sulfide

Polyarylene sulfide molding compositions are provided with improved mold release properties by the inclusion of an internal lubricant comprising pentaerythritol tetrastearate.

FIELD OF THE INVENTION 
This invention is directed to compositions containing polyarylene sulfide. 
More particularly, this invention is concerned with molding compositions 
comprising glass reinforced polyarylene sulfide which have improved mold 
release properties. 
BACKGROUND OF THE INVENTION 
Useful articles from various thermoplastic resins have been prepared from 
molds for many years. Polyarylene sulfide resins are among such moldable 
compositions and have been prepared, for example, as in U.S. Patent No. 
3,354,129. A relatively recent development has been the use of polyarylene 
sulfide compositions such as, for example, polyphenylene sulfide 
compositions, for molding electronic components and as encapsulating 
materials for electronic components. These compositions typically 
represent a carefully balanced blend of at least polyarylene sulfide, 
glass fibers, and filler such as silica or talc. In addition, relatively 
small amounts of other components such as, for example, colorants, flow 
improvers, processing aids, organosilanes and like are typically present. 
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 addressed by the present invention relates specifically to 
polyarylene sulfide compositions used to make molded electronic parts and 
to encapsulate electronic components. 
Polyarylene sulfide, in particular, polyphenylene sulfide compositions are 
used to form electronic components and often to encapsulate electronic 
components in accordance with any encapsulation method suitable for 
thermoplastic encapsulation compositions. Such methods are well known in 
the art. One particularly useful method involves introducing the 
polyarylene sulfide composition into an injection molding apparatus to 
produce a melt which is extruded into an injection mold wherein the melt 
is shaped or wherein the electronic component to be encapsulated is 
positioned. Injection molding provides a convenient way for preparing 
various articles from polyarylene sulfide, particularly objects of a 
relatively intricate nature, e.g., electronic components. 
In order to injection mold articles in an economic manner, the mold 
resident cycle time should be kept to a minimum. The shorter cycle time 
provides a shorter resin heat period with consequently less thermal damage 
to the resin and/or less thermal promoted interaction between the resin 
and various additives present in the resin. 
In order to accomplish a release of the resin from the mold, various mold 
release agents have been found which provide for a release of the resin 
with lower ejection pressure. Mold release agents to be effective should 
be chemically compatible with the resin as measured by the usual 
characteristics of the resin under normal conditions and heat treatments. 
Mold release of a thermoplastic resin from the mold is generally 
accomplished by the addition of a mold release spray applied to the mold 
to provide release of the part from the mold without sticking under 
standard molding conditions. Alternatively, the thermoplastic resin can be 
formulated with an internal lubricant which provides inherent mold release 
properties to the resin. There are many different internal mold release 
agents in practical use. However, these mold release agents are sometimes 
disadvantageous. For example, some commercial mold release agents highly 
effective for improving the mold release property of a thermoplastic resin 
decrease the mechanical strength of the molded article or discolor the 
molded article. Other mold release agents which do not degrade the 
mechanical strength and appearance of the mold article, do not 
satisfactorily improve the mold release property. Moreover, with respect 
to the molding or encapsulation of electronic components, it is important 
that the mold release agent and, generally, any additive, which is 
incorporated into the thermoplastic resin not add any ionic impurities 
such as Na, K, Li, Fe, Cl, etc. to the compounded product. There is a 
continuing need, therefore, to find useful internal lubricants to provide 
mold release properties to thermoplastic molding compositions. The present 
invention is directed to finding a useful internal lubricant for 
polyarylene sulfide. 
One particular commercially employed mold release agent for thermoplastic 
resins, in general, is pentaerythritol tetrastearate. Several U.S. patents 
have been granted to the use of pentaerythritol tetrastearate as a mold 
release agent for specific thermoplastic resins. 
U.S. Pat. No. 4,408,000 discloses a composition comprising a thermoplastic 
resin including among others polysulphones, polyethersulphones and 
polysulfides, a mold release agent such as PETS, and a mold release 
enhancing effective amount of a fatty acid. With regard to polycarbonate 
resins, it was found that a combination of PETS and a mixture of fatty 
acids showed greater mold release than an aromatic polycarbonate 
containing PETS alone as a mold release agent. 
U.S. Pat. No. 4,409,351 illustrates that a fatty acid provides greater mold 
release to an aromatic polycarbonate than does PETS. 
U.S. Pat. No. 4,530,953 utilizes PETS as a mold release agent for 
polyesters such as polyethylene terephthalate resin. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a polyarylene sulfide 
resin molding composition reinforced with inorganic fibers and having 
improved mold release properties. 
Another object of the present invention is to provide a polyarylene sulfide 
resin composition useful for producing molded articles having a 
satisfactory mechanical strength and appearance. 
Still another object of this invention is to provide polyarylene sulfide 
molding and encapsulation compositions having improved mold release 
properties. 
The above-mentioned objects are attained by providing a polyarylene sulfide 
resin composition which comprises 25-75% by weight polyarylene sulfide, 5% 
to 60% by weight of glass or wollastonite fibers, 0-50% by weight filler 
and 0.01% to 2% by weight of an internal lubricant comprising 
pentaerythritol tetrastearate. 
DETAILED DESCRIPTION OF THE INVENTION 
Uncured or partially cured polyarylene sulfide polymers whether 
homopolymer, copolymer, terepolymer, and the like, or a blend of such 
polymers, can be used in the practice of this 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 crosslinking or 
by combination of both by supplying thereto sufficient energy, such as 
heat. Suitable polyarylene sulfide polymers include, but are not limited 
to, those described in U.S. Pat. No. 3,354,129, incorporated by reference 
herein. 
Some examples of polyarylene sulfide compositions suitable for the purposes 
of this invention include poly(2,4-tolylene sulfide), 
poly(4,4'-biphenylene sulfide) and polyphenylene sulfide. Because of its 
availability and desirable properties such as high chemical resistance, 
nonflammability, and high strength and hardness polyphenylene sulfide is 
the presently preferred polyarylene sulfide. The polyarylene sulfide 
composition may be a mixture of more than one polyarylene sulfide. 
Particularly preferred polyarylenesulfides for use in this invention are 
disclosed in U.S. Pat. No. 4,645,826, the entire content of which is 
herein incorporated by reference. As disclosed therein a linear PAS of a 
markedly high molecular weight with a melt viscosity of about some 
thousands to some tens of thousands poise can be readily produced without 
the use of an aid by forming a PAS prepolymer of low to medium molecular 
weight according to a preliminary polymerization, then elevating the 
temperature by heating the polymerization system under strongly alkaline 
conditions with addition of a phase separating agent to the polymerization 
system, thereby separating the system into two liquid phases of high 
viscosity phase (polymer solution phase) and low viscosity phase (solvent 
phase), and carrying out the reaction under such a state. 
The two-phase separated polymerization comprises dissolving an 
arylenesulfide prepolymer having a melt viscosity of 5 to 3,000 poise (at 
310.degree. C., shearing rate=200 (sec) .sup.-1) in a poor solvent under a 
strongly alkaline condition (in a pH range of from 9.5 to 14 of the 
reaction mixture when diluted 10-fold with water) in a temperature range 
of from 245.degree. C. to 290.degree. C. into a liquid-liquid two-phase 
separated state and maintaining this state for 1 to 50 hours to convert 
the arylenesulfide prepolymer into a high molecular weight polymer, then 
separating the polymer from the polymerization system and purifying the 
polymer after neutralization. 
The process for production of a high to ultra-high molecular weight PAS 
according to U.S. Pat. No. 4,645,826 comprises, basically, forming PAS 
molecules through bonding between an alkali metal sulfide and a 
dihalo-aromatic compound and/or converting the PAS molecules into a high 
molecular weight polymer. PPS having melt viscosities of at least 3,000 
poise can be produced by the process as disclosed therein including PPS 
having melt viscosities of at least 7,000 poise and much higher. 
The alkali metal sulfide used includes lithium sulfide, sodium sulfide, 
potassium sulfide, rubidium sulfide, cesium sulfide and mixtures thereof. 
These alkali metal sulfides can be used as hydrates or aqueous mixtures, 
or in anhydrous forms. Among these alkali sulfides, sodium sulfide is the 
least expensive and is commercially preferred. It is also possible to use 
a small amount of an alkali metal hydroxide in combination in order to 
neutralize an acidic salt (e.g., alkali metal disulfides and alkali 
bicarbonates) which may sometimes occur in minute amount in an alkali 
metal sulfide. 
The dihalo-aromatic compound used includes any of dihalo-aromatic compounds 
as disclosed in Japanese Laid-open Patent Publication No. 22926/1984. 
Particularly preferred are p-dichlorobenzene, m-dichlorobenzene, 
2,5-dichlorotoluene, 2,5-dichloro-p-xylene, p-dibromobenzene, 
1,4-dichloronaphthalene, 1-methoxy-2,5-dichlorobenzene, 
4,4'-dichlorobiphenyl, 3,5-dichlorobenzoic acid, 
p,p'-dichlorodiphenylether, p,p'-dichlorodiphenylsulfone, 
p,p'-dichlorodiphenylsulfoxide, p,p'-dichlorodiphenylketone, and the like. 
Among these, those composed mainly of para-dihalobenzene, typically 
p-dichlorobenzene, are especially preferred. 
By appropriate selection and combination of dihalo-aromatic compounds, a 
random or block copolymer containing two or more different reaction units 
can be obtained. For example, when employing p-dichlorobenzene in 
combination with m-dichlorobenzene or p,p'dichlorodiphenylsulfone, a 
random or block copolymer containing: 
##STR1## 
can be obtained. Further, a small amount of a polyhaloaromatic compound 
(e.g., trichlorobenzene) within the range which may provide some 
cross-linking but not substantially impair linearity may also be employed 
in combination, but no such compound is ordinarily required. 
The organic amide solvent used in the polymerization step for forming the 
prepolymer can be selected from N-methylpyrrolidone (NMP), 
N-ethyl-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 
N-methylcaprolactam, tetramethylurea, hexamethylphosphorotriamide, and 
mixtures thereof. Among these, N-methylpyrrolidone is particularly 
preferred from viewpoints such as chemical stability and ability to 
produce readily a high molecular weight polymer. The organic amide as the 
polymerization solvent is desirably an aprotic compound. In the 
polymerization step for forming an ultra-high molecular linear polymer 
from the prepolymer, the above organic amide can of course be used. 
Otherwise, it is also possible to employ, for example, aromatic 
hydrocarbons (C.sub.6 -C.sub.30), aliphatic hydrocarbons (C.sub.6 
-C.sub.30), ethers (C.sub.6 -C.sub.30), ketones (C.sub.5 -C.sub.30), 
pyridine or quinoline or derivatives of these (C.sub.5 -C.sub.30), and 
mixtures thereof as such or as mixtures with organic amides. 
The polymerization process as described in U.S. Pat. No. 4,645,826 is 
applicable for not only homopolymerization or random copolymerization but 
also for block copolymerization. For example, a purified p-phenylene 
prepolymer and a purified m-phenylene prepolymer can be dispersed in the 
same polymerization vessel to carry out the two-phase separated 
polymerization step, whereby a (p-phenylenesulfide)-(m-phenylenesulfide) 
block copolymer can readily be obtained. 
In accordance with a preferred concept of this invention, electronic 
components are molded or encapsulated with a polyarylene sulfide 
composition such as, for example, a polyphenylene sulfide composition, 
which contains fiber reinforcement. 
Suitable reinforcing fibers include fibers of glass or calcium silicate, 
e.g. wollastonite. Although not generally preferred, other reinforcements 
can be used including glass or calcium silicate in nonfibrous form, e.g. 
beads, powders, grains, etc., and fibers of other materials such as 
asbestos, ceramic, etc. 
In the present invention, it is essential that the polyarylene sulfide 
molding composition contain effective amounts of pentaerythritol 
tetrastearate to promote release of the molded article from the mold. 
When the amount of pentaerythritol tetrastearate mixed into the polyarylene 
sulfide resin composition is less than 0.01% by weight, the resultant 
composition exhibits an unsatisfactory mold release property. If the 
amount of pentaerythritol tetrastearate is more than 2% by weight, the 
resultant molded article may discolor and have a decreased mechanical 
strength. 
The scope of this invention also broadly allows for the inclusion of any 
desired filler. 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 
for the polyarylene sulfide compositions of this invention, in particular, 
compositions used for molding or encapsulating electronic components 
several factors should be considered. Among these include the electrical 
conductivity of the filler (the lower the better), tendency of the filler 
to decompose at molding temperatures, and the level of ionic impurities in 
the filler. 
Besides reinforcing agents and fillers, the compositions of this invention 
can optionally contain relatively small amounts of other ingredients such 
as, for example, pigments, flow improvers, and processing aids. 
In accordance with one aspect of this invention, the improved polyarylene 
sulfide compositions can be used to make electronic components such as, 
but certainly not limited to, connectors, bobbins, coils, relays, etc. 
This aspect of the invention includes all electronic components that can 
be at least partially made from a resinous composition such as a 
polyarylene sulfide composition. 
In accordance with another aspect of this invention, electronic components 
can be encapsulated with the polyarylene sulfide composition of this 
invention. The electronic components to be encapsulated in accordance with 
this aspect of the invention broadly includes all electronic components, 
i.e. devices, parts, etc., for which encapsulation is desired. Many 
electronic components have been manufactured or encapsulated with 
polyarylene sulfide compositions or have been suggested as being capable 
of made or encapsulated with polyarylene sulfide compositions, and this 
invention is not intended to be narrow in scope to any specific components 
mentioned, but include any and all electronic components which can be 
manufactured from polyarylene sulfide molding compositions. 
The polyarylene sulfide compositions of the present invention will comprise 
in general about 25 to 75 weight percent polyarylene sulfide, 5 to 60 
weight percent reinforcing fibers, 0.01 to 2.0 weight percent of an 
internal lubricant comprising pentaerythritol tetrastearate and, 
optionally, 0 to 50 weight percent filler. 
A more preferred composition comprises from about 25 to 60 weight percent 
polyarylene sulfide, 10 to about 45 weight percent reinforcing fibers, 0.1 
to 0.8% by weight of the internal lubricant and 10 to 40 weight percent 
filler. 
The above weight percentages are based upon the total amount of the 
components as above listed for the composition. Other components, 
including those previous identified, can optionally be present. 
The polyarylene sulfide resin composition of the present invention can be 
prepared, for example, by mixing predetermined amounts of the polyarylene 
sulfide resin, preferably dried, fibers, and mold release agent by means 
of a usual mixer, for example, a tumbler mixer; by melt-kneading the 
mixture by means of a extruder or kneader, and if necessary, by 
pelletizing the melt-kneaded mixture. 
Once made, the composition of the present invention can be used to make 
molded parts or used to encapsulate electronic components in accordance 
with any method suitable for thermoplastic encapsulation compositions. 
Such methods are well known in the art. The composition can be heated to a 
temperature of at least about the melting point of the polyarylene sulfide 
and then used to mold the desired components or encapsulate as above 
described. The compositions of the present invention are especially suited 
for injection molding wherein the composition is introduced into an 
injection molding apparatus to produce a melt which is extruded into an 
injection mold which conforms to the part to be molded or, in the 
encapsulation method wherein the electronic component to be encapsulated 
is positioned. 
The following examples are presented to facilitate disclosure of this 
invention and should not be interpreted to unduly limit its scope.

EXAMPLE I 
Five glass reinforced Fortron.TM. polyphenylene sulfide compositions were 
prepared and molded into test samples to determine the physical properties 
thereof. Fortron.TM. is a commercial product made in accordance with the 
teachings of U.S. Pat. No. 4,645,826. Of the five compositions, four 
contained 0.3 weight percent of a specified commercially available 
pentaerythritol tetrastearate and the fifth was a control which did not 
contain the internal lubricant. All five compositions contained 40% by 
weight glass fibers. 
All compositions were prepared by compounding the components in a 30 
millimeter twin screw ZSK extruder. The compounded compositions were 
molded into test samples on an 8 ounce Reed injection molding machine at a 
mold temperature of 135.degree. C. The mechanical properties of each 
sample are shown in Table 1. The properties were determined by standard 
ASTM methods. 
As can be seen from Table I, all samples which contained the 
petraerythritol tetrastearate lubricant yielded physical properties 
substantially equivalent to the control sample. Use of the internal 
lubricant of this invention, therefor, does not degrade the properties of 
the resin. 
TABLE I 
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EFFECT OF LUBRICANTS ON PROPERTIES OF 40% 
GLASS REINFORCED POLYPHENYLENE SULFIDE 
LUBRICANT* PETS 
LOXL 
GLYC 
RIKS 
CONTROL 
__________________________________________________________________________ 
TENSILE 
Strength, PSI .times. 10.sup.3 
23.3 
23.7 
22.7 
23.1 
24.3 
Elongation, % 1.7 1.7 1.7 1.6 1.6 
FLEXURAL 
Strength, PSI .times. 10.sup.3 
32.8 
33.1 
31.9 
32.6 
34.9 
Modulus, PSI .times. 10.sup.6 
1.9 1.9 1.9 1.9 2.0 
IZOD IMT FT-LBS/IN. 
Notched 1.3 1.4 1.4 1.4 1.4 
Unnotched 9.8 9.9 9.1 8.8 10.1 
HEAT DISTORTION .degree.C. 
at 264 PSI 265 266 266 266 268 
at 66 PSI 279 278 278 279 279 
SPECIFIC GRAVITY 1.66 
1.67 
1.66 
1.65 
1.70 
WATER ABSORPTION, % 0.01 
0.01 
0.01 
0.01 
0.01 
ROCKWELL HARDNESS, M SCALE 
103 102 103 103 103 
__________________________________________________________________________ 
*PETS: Pentaerythritol Tetrastearate, Eastman Kodak 
LOXL: Loxiol H7119, Henkel Corp. 
GLYC: Glyco Lube P Beads, Glyco 
RIKS: Rikester EW400, Falek Chemical Co. 
EXAMPLE II 
Three 40 weight percent glass reinforced Fortron.TM. polyphenylene sulfide 
compositions were prepared and molded into test samples to determine the 
physical properties thereof as well as the mold release properties of the 
composition. A control did not include a lubricant while the other two 
compositions contained an internal lubricant comprising pentaerythritol 
tetrastearate and stearyl erucamide, respectively. Compounding of the 
compositions was done on a twin screw 53 millimeter ZSK extruder while 
molding was done on an 8 ounce Reed at a mold temperature of 135.degree. 
C. The amount of lubricant and the physical properties of the test samples 
are shown in Table II. 
As can be seen from Table II, the two samples which contained the internal 
lubricants did not stick to the mold in contrast to the control which was 
found to stick to the mold. The physical properties of all the samples are 
essentially equivalent indicating that the internal lubricant does not 
adversely effect the physical properties of polyphenylene sulfide. Tables 
III and IV show that the electric and flow properties, respectively, of 
the polyphenylene sulfide are also not adversely affected by addition of 
the lubricants. 
TABLE II 
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EFFECT OF LUBRICANTS ON PROPERTIES OF 40% 
GLASS REINFORCED POLYPHENYLENE SULFIDE 
LUBRICANT* NONE 
PETS (0.2%) 
SE (0.5%) 
__________________________________________________________________________ 
MOLD STICKING YES NO NO 
TENSILE 
Strength, PSI .times. 10.sup.3 
24.1 
24.9 25.0 
Elongation, % 1.7 1.8 1.9 
FLEXURAL 
Strength, PSI .times. 10.sup.3 
36.3 
37.3 37.3 
Modulus, PSI .times. 10.sup.6 
2.0 2.0 2.0 
IZOD IMT FT-LBS/IN. 
Notched 1.8 1.7 1.7 
Unnotched -- 11.8 11.4 
HEAT DISTORTION .degree.C. 
at 264 PSI 258 259 259 
at 66 PSI 277 278 278 
SPECIFIC GRAVITY 1.65 
1.65 1.65 
WATER ABSORPTION, % 0.02 
0.02 0.02 
ROCKWELL HARDNESS, M SCALE 
96 99 100 
__________________________________________________________________________ 
*PETS = Pentaerythritol Tetrastearate 
SE = Stearyl Erucamide. 
TABLE III 
__________________________________________________________________________ 
ENGINEERING PROPERTIES OF PPS COMPOSITIONS 
PETS SE 
PROPERTY CONTROL 
(0.2%) 
(0.5%) 
__________________________________________________________________________ 
DIELECTRIC STRENGTH, V/MIL 
400 464 438 
DIELECTRIC CONSTANT, 25.degree. C. 
1 .multidot. KHZ 3.6 3.5 3.5 
10.sup.2 .multidot. KHZ 
3.6 3.5 3.4 
DISSIPATION FACTOR, 25.degree. C. 
1 .multidot. KHZ 0.0020 0.0010 
0.0013 
10.sup.2 .multidot. KHZ 
0.0010 0.0009 
0.0011 
VOLUME RESISTIVITY, 
1 .times. 10.sup.16 
1 .times. 10.sup.16 
1 .times. 10.sup.16 
OHM-CM 
ARC RESISTANCE, SEC. 
136 134 136 
__________________________________________________________________________ 
PETS (PENTAERYTHRITOL TETRASTEARATE). 
SE (STEARYL ERUCAMIDE). 
TABLE IV 
______________________________________ 
EFFECT OF LUBRICANTS ON SPIRAL FLOW LENGTH 
FLOW LENGTH, 
LUBRICANT INCHES 
______________________________________ 
None 13.0 
STEARYL ERUCAMIDE (0.5%) 
13.0 
PENTAERYTHRITOL 13.3 
TETRASTEARATE (0.2%) 
INJ MOLD: 
SPIRAL FLOW 
MOLD TEMP: 275.degree. F. (135.degree. C.) 
MELT TEMP: 590.degree. F. (310.degree. C.) 
PRESSURE: 8000 PSI 
RESULTS ARE AVERAGE OF 10 SHOTS. 
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