Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
The present invention relates to a process for minimizing
the mold deposit problem frequently encountered when polyoxymethylene
molding compositions are molded. Such deposits are detrimental
to the formation of a quality molded article having smooth and uniform
surface characteristics.
As is well known polyoxymethylene or polyacetal, is a thermo-
plastic resin which finds wide utility in the manufactureof shaped
articles by inJection molding or extrusion processes. Polyoxymethylene
has many excellent mechanical properties which result in shaped
articles characterized by their hardness, strength and toughness.
Polyoxymethylene resin, however, is subject to degradation
par-ticularly under the influence of heat, the amount of degradation
being a ~actor of -the method of preparation of the polyoxymethylene
and the like. The degradation may occur for example, as the result
of oxidative attack. The oxidative attack, which may lead to chain
scission and depolymerization, is often ret;arded by the addition of
antioxidants to the polyoxymethylene composition. Degradation is
also believed to occur as the result of acidolytic cleavage of the
polymer chain caused by acidic species present in the polymer. The
acidic species may be acidic catalyst residues derived from catalysts
used in the formation of the polymer or may be acetic acid generated ;
from acetate end groups when a given chain, so stabilized,
depolymerizes as a result of occasional oxidative or acidolytic
chain scission. To assist in minimizing such degradation of
polyoxymethylene especially during subsequent processing in the
hot, or melt, state, "acid scavengers" are often admixed with the
polymer composition.
~ ~ `
Albeit most commercially available polyoxymethylene is "pre-
stabilized" either by means of acetylation or hydrolysis treatments (see,
for example, United States Patent No. 3,839,267) or by the addition of
additives such as the above-mentioned antioxidants and/or acid scavengers,
it has been found that during the high-temperature molding, particularly,
injection molding of the non-fiber reinforced resin an objectionable film,
or mold deposit, commonly forms on the surface of the mold. The mold
deposit, which can lead to surface defects on the molded Tesin, is generally
believed to be of two types. One type of mold deposit is believed to be
caused by the use of certain antioxidants which plate out on the mold surface.
This type of mold deposit can be eliminated by using a less volatile anti-
oxidant. The second type of mold deposit is believed to be caused by
formaldehyde ~generated, for example, as a result of the chain scission o
the polyoxymethylene under the conditions of the molding process) condensing
on the mold su~face. The chain scission, in turn, is believed to be caused
by acidic residues present in the polyoxymethylene and which have not been
~'cleaned up" by the prior stabilization treatments.
Although tlle thermal stabilization, i.e., stabilization against
the effects of temperatures encountered in the melt state, of polyoxy-
methylene has heretofore been p~oposed in the art such as, for example, by
the addition to the polyoxymethylene of amino substituted amides (United
States Patent No. 3,274,149, issued September ~0, 1966, Frank M. Berardinelli),
carbamates ~United States Patent No. 3,144,431, issued August 11J 1964,
Thomas J. Dolce, Frank M. Berardinelli and Donald E. Hudgin)~ or severely
hindered carbodiimides (British Patent No. 993,60V, published May 26, 1965,
Farbenfarbriken Bayer Aktiengesellschaft), such stabilization has either
not been effective in removing the mold deposit tendency or results in
undesirable discoloration of the polymer.
_3
.: . . . ' . ,~ . , .
3~
Thc physical blending of polyoxymethylene with thern~,oplastic
resins, so as to improve the properties of a polycarbonate has also been
proposed. Such blending has not been directed at improving the properties
of the polyoxymethylene and has employed a relatively large quantity of the
polycarbonate. Thus, for example, United States Patent No. 3,646,159,
issued February 29, 1972, Gerald W. Miller, discloses the blending of poly-
oxymethylenes, or polyacetals with a polycarbonate to improve the properties
of the polycarbonate and to provide a polycarbonate mixture having improved
resistance to environmental stress cracking and crazing. Although Miller
suggests, inter alia, that the polyacetals may be employed in amounts of
from 25 to 95 percent by weight based on the combined weigh~ of the poly-
carbonate and polyacetal, the working examples are limited to blends con-
taining a maximum of about 50 percent by weight of polyacetal. United States
Patent No. 3,290,261, issued December 6, 1966, Kenneth B. Goldblum, discloses
the blending o~ polycarbonate and up to about 20 percent polyacetal to obtain
a foamed polycarbonate resin. Goldblum discloses that if the amount of
polyacetal exceeds 20 percent, then the blend begins to lose the beneficial
properties of the polycarbonate (Column 1, line 47).
Polycarbonates have also been disclosed as additives or modifierc
or scavengers for polyester tire cord when added to the polyester prior to
fiber ormation ~see, for instance, United States Patent No. 3~563,847,
issued February 16, 1971, Grover W. Rye and Thomas E. Evans). `
In light of this prior art it is an object of the present invention
to provide a process for the preparation of an improved polyoxymethylene
molding composition which forms reduced mold deposits upon molding.
It is a further object of the invention to provide a polyoxy-
methylene n~lding composition having high stability when subjected to the
~ ~4-
3P3
influence of heat and particularly when sub~jected to the con~
ditions typically encountered during molding operations,
It is still another ob~ect of the pres~ent invention
to provide an improved non-reinforced polyoxymetl~ylene compos-
ition for an iniection molding process,
Another object of the present inventIon is the
provision for the preparation of a stabilized polyoxymethylene '-
molding composition employing an aromatic polycaraona~e addi~
tive, which stabllized polyoxymethylene IS not undesirably dis~
colored.
According to the present invention it has now been
found that certain aromatic polycarbonates Cas defined~ in~
crease the thermal stability of polyoxymethylenes ~ithout
severely discoloring the polyoxymethylenes,
Thus, the invention prov;ldes a process for produc~
ing an improved polyoxymethylene molding compos~tion comprising
heating a mixture o:
(1~ a polyoxymethylene polymer ~hich exhibits a
propensity to form mold deposits upon moldin~, and
~2~ a~out 1 to about 4 percent by ~eight based on
the ~eight o the polyoxymethylene polymer of an aromatic
polycarbonate having an intrinsic vlscosity of about 0,35 to
0.75 in methylene chloride at 25C which is derived from a non~
hindered non-halogenated dihydric phenol,
for at least about two minutes at a temperature at ~hi:ch the
polyoxymethylene polymer is molten to yIeld a molding compo~
sition which forms a reduced quantity of mold deposits upon
molding,
The addition of the aromatic polycarbonate to ~ ~ :
polyoxymethylene follo~ed by the appropriate thermal treatment
has been found to reduce the amount of formaldehyde generated
- 5 -
. ~
by the polyoxymethylene when subsequently subjected to the
influence of heat; particularly when subjected to conditions
which have heretofore resulted in the formation of objection-
able formaldehyde-type mold deposits.
As indicated, the improved molding compositions,
i.e., stabilized polyoxymethylene, is prepared by heating the
polyoxymethylene and the polycarbonate while in admixture for
at least about two minutes at a temperature at which the poly-
oxymethylene is molten ~generally above 160C). The amount
of polycarbonate used is from about 1 to about 4 percent by
weight, based upon the weight of the polyoxymethylene polymer.
Particularly satisfactory results are achieved if a
- 5a -
.~ ' ~ :
~J
minor quantity o~ malonamide also is admixed with the polyoxymethylene
polymer and the aromatic polycarbonate during heating.
Description of Preferred Embodiments
As used herein the term "polyoxymethylene" is intended
to include both homopolymers, including so-called capped homo-
polymers, i.e., acylated homopolymers, as well as copolymers
as will be defined more specifically below.
The thermal stability provided by the addition of the
aromatic polycarbonates to the polyoxymethylene according to the
present invention is stability against degradation when the poly-
oxymethylene is subjected to the influence of heat. The aromatic
polycarbonate is believed to provide stability against any o~ the
degradative effects of heat including, for example, aging of molded
polyoxymethylene articles at temperatures of from 100 to 140C.,
but is particularly useful in providing stability against degradation
when the polyoxymethylene is subjected to the temperatures and
conditions typically encountered during t,he molding of the poly-
oxymethylene into shaped articles, i.e., temperatures of from
about 185C. to about 240C. for a period of several minutes.
A particularly preferred application of the present invention
is in the injec-tion molding of polyoxymethylene because the mani-
festations oftheinstabili-ty, or degradation, of polyoxymethylene are more
troubleseome in this type of operation than in, for example, an extru-
sion operation. In the extrusion of polyoxymethylene, formaldehyde
which may be generated during degradation of the polymer does not
have an opportunity to condense on a mold surface and may escape
through vents provided on the extruder.
InJection molding is intended to refer to any of the well-known
processes wherein a polyoxymethylene molding composition is heated
in a preheating zone to a plastic melt, and is thereafter forced
through a nozzle into a closed mold. Heating of the polyoxymethylene
is typically to a temperature of from about lôO C. to about 2~0C. The ;
temperature of the mold is generally substantially lower, e.g., about
lOO C. lower, although the exact relationship between the melt
temperature andthe mold temperatureis dependent on factors such
as the desired surface characteristics of the shaped article as will
be appreciated by the art-skilled person. Mold deposit can be noticed
at any of the recommended molding temperatures when a poor quality ~-
polyoxymethylene copolymer is employed (usually after 25-50 shots) `~
and tends to be greater with higher melt temperatures and lower mold
temperatures. The tendency toward mold deposit varies according
to the particular polyoxymethylene, prestabilization treatment and the `~
like. Thus for example, acylated homopolymer generally produces
mold deposit problems less frequently than a melt hydrolyzed
copolymer. The occurrence of the mold-deposit problems depends
additionally on the size of the molded part, gating and venting. Small
parts, small gates and inadequate venting give the most problems. The
mold deposit tends to cause imperfections on the surface of the molded `~ ;
parts. Such parts must be ground up and remolded.
The addition of the polycarbonates to the polyoxymethylene
according to the present invention is effective in providing thermal ;~`
stabilization at the molding (mèlt) temperatures, but may not be
effective above temperatures of about 2~19 C. because of the degradation
of the polyoxymethylene.
:
8~
The injection molding may be carried out in conventional
injection-molding apparatus having, for example, a preheating
cylinder, plunger, or reciprocating screw, torpedo, nozzle and mold
including a sprue, runners, gates and mold cavities. Cylinder
temperatures are usually between about 180 C. and about 240C.
and molding pressures are usually between about 5,000 and 20jO00
psi. Acutal molding temperatures and pressures will vary depending
on the type of machine, i.e., plunger injection molding machine or
screw inJection molding machine, employed or on the desired shape
and size of the molded article. Cycle times are usually between about
30 and about 110 seconds.
Polyoxymethylene polymer which may be stabilized with the
aromatic polycarbonate in accordance with the present invention, as
stated above, includes both homopolymers and copolymers. Such
polymers, which may be produced according to methods well-known
in the art have recurring -OCH2- units and are typically prepared by
-the polymerization of anhydrous formaldehycLe or by the polymerization
of` trioxane.
Particularly useful in this invention is polyoxymethylene
copolymer having at least one chain containing recurring oxymethylene
(-OCH2-) units interspersed with -OR- groups in the main polymer
chain where R is a divalent radical containing at least two carbon atoms
directly linked to each other and positioned in the chain between the
two valences with any substituents on said R radical being inert, i.e.,
substituents which will not induce undesirable reactions. Preferred
copolymers contain from 60 to 99.6 mole percent of recurring
oxymethylene groups. In a preferred embodiment R may be, for ;~
example, an alkylene or substituted alkylene group containing at least
~6~
two carbon atoms.
Among the copolymers which are utilized in accordance with the
invention are those having a structure comprising recurring ~mits of the
formula:
1 Rl~ ~
wherein n is zeTo or an integer of fro~ 1 to 5 and wherein n is zero in
from 60 to 99.6 percent of the recurring units. Rl and R2 are inert
substituents, that is, substituents which will not cause undesirable
reactions.
~ preferred class of copolymers are those having a structure com-
prising recurring units wherein from 60 to 99.6 percent of the recurring
units are oxymethylene units. These copolymers are prepared by copolymerizing
tr:ioxane with a cyclic ether having the structure: -
:
CH 0
1 2
CH2 - CCH2)n
wherein n is 0, 1 or 2.
Examples of other preferred polymers include copolymers of
triox~ne and cyclic ethers containing at least two adjacent carbon atoms ~ ;
such as the copolymers disclosed in United States Patent No. 3,027,352,
issued March 27, 1962, Cheves T. Walling, Frank Brown and Kenneth William
Bartz.
Among the specific ethers which may be used are ethylene oxide,
1,3-dioxolane, 1,3,5-trioxepane, 1,3-dioxane, trimethylene oxide, penta-
methylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, neopentyl `~
formal, pentaerythritol diformal paraldehyde7 tetra-
g_
hydrofuran~ and butadiene monoxide.
The preferred polymers treated in accordance with the invention
aTe moldable thermoplastic materials having a weight average molecular
weight of at least about 35,000, a melting point of at least about 150C.
and an inherent viscosity of at least about 0.~ ~measured at 60C. in a 0.1
weight percent solution in p-chlorophenol containing 2 weight percent of
alpha-pinene).
As understood by those skilled in the art, the polyoxymethylene
should be pre-stabilized prior to being heated in admixture with the poly-
carbonate. Such prestabili7ation may take the form of stabilization by
degradation of the molecular ends of the polymer chain to a point where a
relatively stable carbon-to-carbon linkage exists at each end. For example,
such degradation may be effected by melt hydrolysis such as that disclosed
in United States Patent No. 3,318,8~8, issued May 9, 1967, Charles ~1. Clsrke
or by solution hydrolysis such as that disclosed in United States Patent
3,219,623, issued No~ember 23, 1965, Frank M. ]Berardinelli. ~lixtures of
polyoxymethylenes stabili~ed by melt hydrolysis and by solution hydrolysis
may, of course, be used. The polyoxymethylene may also be pre-stabilized by
admixing with con~entional stabilizers such as an antioxidant (e.g. in a
concentration of about 0.2 to 2.0 percent by weight) andfor an acid
scavenger (e.g. in a concentration of about 0.05 to 1.0 percent by weight).
Generally, these stabilizers will be present in a total amount of less than
about 3 percent by weight based on the weight of the polyoxymethylene polymer.
Generally speaking, the aTomatic polycarbonates that are employed
according to the present invention are well known, commercially a~ailable
thermoplastic resin materials. In general, such aromatic polycarbonates may
be described as polymers containing recurring structural units of the
formula:
I O
- t ~ A - O - ~ - -
~10-`
wheTe A is a divalent aromatic radical derived from a non-hindered non-
halogenated dihydric phenol. Specific processes for preparing such poly-
carbonates as well as starting materials and polymers prepared therefrom
are described in well known texts such as "Chemistry and Physics of Poly- -
carbonates" by Hermann Schnell and "Polycarbonates" by William F.
Christopher, and in the patent literature, such as United States Patent
Nos. 2,970,137, issued January 31, 1961~ Herbert E. Whitlock; 2,991,273,
issued July 4, 1961, Wilhelm ~lechelhan~er and Gunter Peilstocker; 2,999,846,
issued September 12, 1961, Hermann Schnell and Heinrich Krimm; 2,999,835,
issued September 12, 1961, Eugene P. Goldberg; 3,014,891, issued December
26, 1961, Kenneth B. Goldblum; 3,028,365, issued April 3, 1962, Hermann
Schnell, Ludwig Bottenbruch and HeinTich Krimm; 3,030,331, issued April
17, 1~62, Eugene P. Goldberg.
The dihyclric phenol is non-hindered in the sense no ortho
substitution is present on the aromatic ring adjacent either of the hydroxy
groups. Such substitution will prevent the resulting polycarbonates from
efectively f~mctioning in tl-e process of the present invention. Para-
su~stituted dihydric phenols are preferred; however, meta-substituted
dihydric phenols are acceptable for use. Also, the dihydric phenol is
fre0 of halogens or any other functional groups including sulfone linkages
which would interfere with the desired results. Preferably only hydrogens
are present on the aromatic rings of the dihydric phenol other than the
hydroxyl groups.
Representative non-hindered, non-halogenated dihydric phenols
from which the aromatic polycarbonate can be derived include:
HO ~ C ~ OH
',
0~1 ~
8~3
HO ~ ~ ~ ~ OH
HO ~ C ~ ~ ~ OH
HO ~ H
~ '
A hindered dihydric phenol such as 2,2'-dihydroxydiphenyl, i.e.,
,PH ~O
V ~ should not be employed.
For exampleJ the yreferred aromatic polycarbonate may be produced
from a dihydroxydiaryl alkane such as 2,2-bis-~4-hydroxyphenyl)propane
~i.e. bisphenol A) and phosgene, a haloformate or a diester of carbonic acid
as described in United States Patent No. 3,028,365, issued April 3, 1962,
Herman Schnell, Ludwig Bottenbruch and Heinrich Krimm. Homopolymers derived
from 2,2-bis-~4-hydroxyphenyl) propane are pa~ticularly preferTed. Such
materials are marketed commercially under the trademark "Merlon" by the
Mbbay Chemical Corporation and "Lexan" by the General Electric Company.
Preferred aromatic polyca~bonate copolymers are derived fro~ at least 80
~ole percent of 2,2-bis-(4-hydroxyphenyl) propane.
The aromatic polycarbonate selected for use in the present
process is miscible with the polyoxymethylene polymer while in the molten ~;
state so as to insure good mixing or blending, and additionally should
not volatilize under the conditions of mixing and subsequent
molding. Typically the aromatic polycarbonate has an intrinsic
viscosity of about 0.35 -to 0.75 in methylene chloride at 25C., and
preferably an intrinsic viscosity of about 0.35 to o.6 under the same
conditions.
The aromatic polycarbonate is mixed or blended with the poly-
oxymethylene composition (i.e. pre-stabilized polyoxymethylene)
in an amount of from about 1 to about 4 percent by weight based on the
weight of the polyoxymethylene polymer and more preferably in an
amount of from about 1 to about 2 percent by weight. Amounts of ;~
aromatic polycarbonate much less than about 1 percent by weight may re-
quire extensive mixing with the polyxoymethylene to achieve a desired
stabiliztion whereas amounts much greater than about 4 percent
by weight tend to significantly adversely alter the physical properties,
i.e., tensile strength, Izod impact values and the like, of a molded
article formed from the composition. Any of` the aromatic poly-
carbonates included within the description presented above can be
used alone or in mixture with other of the aromatic polycarbonates
to achieve the desired results.
The polyoxSrmethylene and polycarbonate are heated to a
temperature at which the polyoxymethylene is molten or in the melt
state. Generally, a temperature above about 160 C. is required,
preferably above about 180C., and morepreferably between about
180C. and about 240C. Temperatures much higher than about 240C.
may lead to degradation of the materials and/or possible adverse
side reactions. Thus, the temperature range is one which will main-
tain the polyoxymethylene polymer in melt form, but not cause
significant degradation or adverse side reactions.
The polyoxymethylene polymer and aromatic polycarbonate
are maintained at these -temperatures for at least about 2 minutes and
-, :
.
- .. . . :, .
usually fox about 2 to a~out 20 minutes. Caution should be employed when
longer times are used particulaTly much ab~e about 20 minutes as the polymer
materials may tend to degrade.
The exact time employed will depend primarily on the particular
apparatus in which the polymers aTe heated ~hile in admixture. More efficient
mixing and heating devices such as a Werner-Pfleiderer ZSK* twin screw
extruder will of course require less time than, for example, devices such as
a Brabender plastograph.
In general, the polyoxymethylene and polycarbonate may be mixed
or blended and heated in any convenient manner or apparatus as long as the
polyoxymethylene polymer is molten and in intimate contact with the aromatic
polycarbonate for at least about 2 minutes while in such a state. If desired
the polymers can first be dry blended and thereafter heated or they can be
initially admixed in the heating apparatus.
It is believed that the aromatic polycarbonate reacts with the
acid residues in the polyoxymethylene polymer during the heating step, thus
stabilizing the polyoxymethylene when it is subsequently molded, i.e.
formaldehyde mold deposit is decreased. Accordingly the most eficient
means of heating and mixing the polymers are clesirable to assure complete
polycarbonate-acid residue reaction and hence substantial elimination of
the formaldehyde mold deposit during subsequent molding.
For this reason direct addition of the polycarbonate to the
polyoxymethylene in the molding apparatus is not recommended unless
suffiGient preheat time is provided for the materials to be mixed and
for the aTomatic polycarbonate acid Tesidue reaction to occur before the
molding composition enters the mold cavity.
*Trademark
,. ..
" ,: ,
I~ d2sired, the polyoxymethylene and polycarbonate may be mixed
and hea~ed as set forth abo~e, pelleted and stored for later use in the
molding process~
Polyoxymethylene molding compositions of the present invention,
in addition to including the polyoxymethylene and the polycarbonate,
optionally may also include a minor quantity of additives conventionally
employed in polyoxymethylene molding compositions both polymeric and non-
polymeric, such as lubricity agentsJ dyes, and conventional antioxidants
and acid scavengersJ etc.J as discussed above. In a preferred embodiment
ibrous reinforcement is omitted from the molding composition since it is
in such a system that mold deposit problems have more commonly been observed
in the prior art.
The aromatic polycarbonates utilized in the present process are
believed to be somewhat unique in that the mold deposit problem is effectively
eliminated. Excessive color formation, as often encountered if large amounts
of conventional basic acid scavengers are employed, is not a factor. Also,
as discussed below theTe is no signiicant reduction in molded article
properties as is commonly encountered if particulate non-polymeric additives
are utilized.
In a particularly preferred aspect according to the present
invention, the aromatic polycarbonate is employed in combination with a
minor quantity of malonamide (i.e. carboamidoacetamide) to provide an
effective theImal stabilization of polyoxymethylenes a~d, particularly, to
reduce the mold deposit tendencies of the polyoxymethylene. Malonamide is
a known and effective thermal stabilizer for polyoxymethylene polymer, but
is not widely used because it adversely discolors the polyoxymethylenes
and tends to be expensive. See, for instance, United States Patent No.
3,116,267, issued December 31, 1963, Thomas J. Dolce. In combination
with the aromatic polycarbonate, however,
-15-
. . , - . -.
;........ , ,. .
the discoloration of the polyoxymethylene surprisingly is substantially
reduced and at the same time the desired thermal stabilization is
provided. The presence of the aromatic polycarbonate permits the
utilization of lesser levels of malonamide. For instance, malonamide
may be present in a concentration of about 0.1 to 1 percent by weight
based on the weight of the polyoxymethylene polymer, and preferably
in a concentration of about 0.1 to about 0.5 percent by weight.
Molded articles prepared from the aromatic polycarbonate-
stabilized polyoxymethylene molding composition according to the
present invention show only a slight decrease, typically less
than 10 percent, in physical properties (tensile, modulus, impact
strengths, and the like) as compared to articles prepared from
polyoxymethylene compositions not including the aromatic polycarbonate.
As indicated hereinabove, the po]yoxymethylene molding
compositions o~ the present invention show increased -thermal
stability when heated to temperatures of from about 180C. to about
240C. The thermal stability can be measured by heating the poly-
oxymethylene composition in an all glass apparatus at a temperature
of either 218C. or 228 C. + 2C. for 30 minutes. ~t the end
of this time a vacuum is applied to the system and the liberated
formaldehyde is drawn through two sodium sulfite traps. The
quantity of formaldehyde in the traps is then determined by titration
with a standard acid. The amount of formaldehyde given off is a
reasonable measure of the thermal stability and of the tendency of
the composition to form mold deposits. `
The invention thus provides a means for thermally stabilizing
polyoxymethylene polymer in a short time while employing small
concentrations of a particular class of aromatic polycarbonate or of
- 16 -
aromatic polycar~onate in combination with malonamide.
The invention is additionally illustrated in connection with the
following examples which are to be considered as illustrative of the present
invention. It should be understood, however, that the invention is not
li~ited to the specific details of the examples.
Examp1es
The thermal s~ability of various polyoxy~ethylene molding com-
positions in accordance with the present invention aTe shown in the Table.
The molding compositions were prepared by mixing 50 grams of the
polyoxymethylene polymer with the additives in a Brabender Plasticorder*
plastigraph (200 C~ and 35 RPM). Additives WeTe blended in -for twenty
minutes from the time the polyoxymethylene polymer appeared to be completely
melted. Controls were milled for similar times in the absence of any
additives. No torque increases were observed for any o the blends.
Polymers I and II were each polyoxymethylene copolymers prepaTed
in the same manner from trioxane and ethylene oxide (2 percent by weight).
Each had a weight average molecular weight of 68,000. Polymer I had been
melt hydrolyzed according to the technique of United States Patent No.
3~219,623, issued November 23, 1965, ~rank M. BeTardinelli. Each of the
polymers also had been "stabili~ed" OT "pre-stabili7ed" prior to compolmding
with the polycarbonate with a standard additive package including O.S ;
percent 2,2'-methylene-bis-~4-methyl-6-tertiaTy butyl phenol) antioxidant,
0.1 percent cyanoguanidine acid scavenger~ and about 0.2 percent diamide
synthetic wax lubricant available from Glyco Chemicals, Inc. under the
designation Acrawax* C lubricant.
*Trademark .
~.
B -17-
Aromatic polycarbonate I was non-hindered and non-halogenated and
was commercially available under the trademark "Merlon", type M39F, from the
Mobay Chemical Company. It was derived from 2,2-bis(4-hydroxyphenyl) propane
and exhibited an intrinsic viscosity in methylene chloride at 25 C. of 0.5.
Generated formaldehyde was determined according to the procedure
described above by heating the samples at 228C. for 30 minutes~ and is
based on the initial weight of the sample.
TABLE
Example Molding Percent Generated Color of
No. Composition Formaldehyde Molded Article
1 Polymer I Control 0.28 white
2 Polymer II Control 0.10 white
3 Polymer I + 1% malon- 0.02 pale yellow
amide
l~ Polymer I + 1% Polycar- 0.12 white
bonate I
Polymer I + 1% malon- <0.01 sligh-tly
amide + 1% Polycar- off-white
bonate I
It is readily seen that an aroma-tic polycarbonate defined accord-
ing to this invention provides eff`ective stabilization against degradationof the polyoxymethylene under the test conditions and without imparting
objectionable discloration to the polyoxymethylene.
The principles, preferred embodiments and modes of operation of
the present invention have been described in the foregoing specification.
The invention which is intended to be protected herein, however, is not
to be construed as limited to the particular forms disclosed, since these
are to be regarded as illustrative rather than restrictive. Variations and
changes may be made by those skilled in the art without departingfrom the
spirit of the invention.
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