Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
;37
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COMPOSITION
r~RouND OF T~E l~V~ih~ON
Thi~ inven~ion rela~es to thermoplas~ic resin
compo~i~ion~ and more particula~ly is conc~rned with
polyeax~onate resi~ mixture~ havi~g improved impact
~tre~g~h, espe~ia U ~ in thick ~ections, and good
re3ista~c~ to environmental stress crazing and
cracking~
Aromatic carbonate polymers are w~ll known commer-
cially available materials having a variety of appli-
cations in the ~lastics ar~. 5uch carbonate pol~m~rs
may be prepared by reac~ing a dihydric phenol, such as
~,2-bis~4-hydroxyphenyl)propane, with a car~nate pre-
cursor~ such as pho~gene, in the presence of an acid
binding agent~ Generally speaking, aromatlc polycar-
bonate resins offer a high resistance to the attac~ of
mineral acids, may be easily molded, a~d are physiolog~
ically harmles~ as well as stai~ resista~t. In addi-
tio~, such polymer~ have a high ~en~ile and impac~
strength, (except in thick molded sec~io~s), and a
~;~ensio~al stability surpassing that of other thermo-
2U plas~ic materials. ~owever, in certain applications,
~lZI~ 37
8C~-616
-2-
the use of aromatic polycarbonate re~in~ is limited
because they exhibit severe environmental ~kr~
crazing a~d cracking. "~nvironmen~al s~ress crazing
and cracking" refer~ to the type o ailure which is
has~e~ed by the presence o organic Qolven~s ~uch a~,
for example, gasoline, paxticularly ~igh octane no-lead
gasoline, acetone, heptane and carbon tetrachloride
when such sQlve~ts are in contac~ with stressed parts
fabricated from aromatic polycarbonate re~ins. The
mo~t ~ignifica~t effect i~ a loss in vital impact
~trength and al~o an increase in brittle-type failuxe.
Contact with such solvents may occur, for example, when
part~ are used under ~he hood of automobiles, or near
the ga~oline filler port~ thereof/ or when solvents are
used to clean or degrease ~tre~ ed parts made from
polycar~onate re3in~.
At present, no entiraly satis~actory mean~ is
available for reducing environmental stre3s cra~ing and
cracklng of polycarbonate re3ins, although a variety of
methods have been proposedO
Blends of aroma~i~ polycarbonate with butadiene
styrene and polyolefins are disclosed in European
Patent Application 28753, laid open May 20g 1981.
Among the pro~erties disclosed for the blends is reduc-
ed ~en~itivity to stress crackingO General proportions
of blend constituents are 80~96.5 weight percent aro-
matic polycar~onate, 1-10 weight perce~t polyolefin and
20 5-10 weight percent butadiene styrene polymer con-
taining 30-90% butadiene or a gra~t copolymer of 80~10
mixture of 50-100% styrene and 0-50% acrylonitrile on
90-0 percent polybutadiene.
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8CL-6165
U.A. Patent No. 3,239,582, issued March 8, 1966
to Keskkula et al, discloses blends of 95 to 80 weight
percent polycarbonate and 5 to 20 weight percent of
an alkenylaromatic polymer or copolymer. The term
"alkenyl aromatic" is defined and exemplified at
column 2, lines 10-47. The blends were disclosed
as having an improved melt viscosity compared with
polycarbonate itself. No mention of improved
resistance to stress cracking is made.
Still other modifiers have been proposed
for impact strength improvement, but none of them
provides optimum environmental stress crazing and
cracking resistance - applicant's earlier filed
commonly assigned Canadian Application Serial No.
399,992, filed March 31, 1982; U.S. Patent No. 4,430,476,
issed February 7, 1984 and U.S. Pakent No. 4,444,949,
issued ~pril 24, 1984. The above-mentioned Canadian
Application Serial No. 399,992 and U.S. Pa-tent
No. 4,444,949 described polycarbonates modified
with a combination of a butadiene-styrene block type
copolymer, an acrylate core shell interpolymer and,
optionally, an olefin/acrylate copolymer. Such
compositions process well and are toughened, but there
is no disclosure of significant solvent resistance and,
as will be shown later herein, by themselves, the block
type copolymers do not provide significant resistance
to environmental stress crazing and cracking at
relatively low and moderate levels, even in thin
sections. The above-mentioned U.S. Patent No.
4,430,476 describes polycarbonate resins modified
with a combination of the block type copolymers
and a linear low density polyolefin resin. There is no
mention that such modifier combinations will provide enhanced
resistance to environmental stress crazing and cracking.
~,
37
8CI.-6165
5UMk~RY OF T~E LNV :N-1~1ON
Unexpectedly in view of the for~going, it has now
been discovered that polycar~or~at~ re~ins are rendered
more resistant to environmental str~ss cracking a~d
S crazing by incorporat:ing therewith certain quantities
o~ a coupled re~inou~ block copolymer havi~g bloclc~
compri~ing polymerized vinyl aroma~:ic units connected
to blocks comprising polymerized diene units.
D~ TT.~!n DESCR:~PTIO~ OF TEIE l~v~ ON
In accordance with the inven~iGn, there is a com-
po~ition comprising a blend of
( a ) all a~omatic car~onate polyliLer resin and
~ ~ ~ a~ amount of coupled re~inous bloc~c copolymer
having bloc3c~ comprising polymerized ~inyl a~:omatic
15 units connected to blocks compri~ing polymerized diene
units which imparts to the blend a resistance to
erlvironmental stre~s cracking and cxazing greater than
that pos~essed by the said aromatic carbonate polymer.
The amou~t of diene-vinyl aromatic polymer to be
20 employed varie~ widèly but the minimum amount is any
~antity which signiicantly increases the resistanc~
of aroma~ic carbonate polymer to environmental stress
cracking and crazing, particularly that caused by high
aromatic no-lead gasoline to aromatic carbona~e polymer
article u~der ~tress and then measured by an impac~
test. Clearly, this ~inirn~ amount will vary somewhat
depending upvn the specific diene-vinyl aromatic poly
mer and aromatic carbonate polymer employed. ~owever,
in general, a minimum amount of about 10 weight percent
of diene-vinyl aromatic should be pre~ent in the blend,
the percentage based on the sum of the aromatic carbon-
ate polymer and the diene-vinyl aromatic polymer. As
J~Z()~637
8CL-6165
--5--
long as the re~istance to environmental stre~s crazing
and cracking of the aromatic carbonate polymer article
is sig~ific~ntly enhanced, larger quantitie~ o~ diene-
vinyl aromatic may be employed. The prac~ical upper
limit of diene-vinyl aromatic polymer i~ that quantity
which allows the aromatic carbonate polymer ~o retain a
signiica~ number and proportion Q~ it~ desirable
propertis ~ Generally, depending upon the specific
aromatic carbonate poly~er and diene-vinyl aromatic
.employed, a ~; ~ amount o~ about 50 weight percent
of diene-vinyl aromatic polymer can be employed. A
range of from about 14 to ab~ut 35 weight perc~nt of
die~e vinyl aromatic in the blend is preferred.
Such addition may be accompli~hed in any ~nnpr so
long as a thorough distribution of the modifier in the
polycarbonate resin is obtained. For example, the
mixing of ~aterials may be accomplished by a variety of
meth~ds noxmally employed for incorporatio~ of plastic-
izers or fillers into thermo~lastic polymexs including
but not limited to mixing rolls, doughr;~rs~ Banbury
mixer~, extruders, and other mixing e~uipment. The
resulting mixtures may be handled in any conventional
mann~r employed for ~he fabrication or manipulation o~
thermo~lastic resins. T~e material~ may be formed or
molded using compression, injection, calendering,
extrusion and blow molding techniques, alone~ or in a~y
combination~ Also, multiprocessing methods, such as
ex~rusion-blow molding or coextrusionco-injection, can
be used, e.g., for multi-layer containers. It should
be understood that the aromatic carbonate polymer resin
mixture~ prepared in accordance with the invention may
also contain, in addition to the above-mentioned poly-
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8CL-6165
-6-
m~rs, other additives to lubricate, reinforce, prevent
oxidatio~, th~r~ y stabilize or le~d color to the
material. Other additives such as mold release agents
and ~lame retaxdant agents, particularly the metal
salt~ of various organic ~ul~onic acids, are well known
i~ th~ art, and may be incorporated without depaxting
~rom the scope o~ the invention~
The aromatic carbonate polym~rs (a) used to pro-
vide mixtures of the present inve~tion may be prepared
by reacting a ~ihydric phenol with a carbonate preeur-
sor, such as phosgene, a haloformate or a earbonate
ester. Generally speaking, ~uch carbonate polymers may
be ty~ified a~ possessing recurring structural units of
the onmula:
O-A-O-~
wherein A is a divalent aromatic radical of the di~
hydric phenol employed i~ the polymer producing reac-
tioQ~ Pxeferably, the aromatic carbonate polymers used
to provide th~ resinous mixtures of the invention have
an intrinsic viscosity (as measured in methylene
~hloride at 25C.) ranging from about 0.35 to about
0.75 dl./g. ThP dihydric phenols which may be employed
to provide such aromatic carbonate polymers are mono-
nuclear or polynuclear aromatic compounds, containing
as functional groups two hydroxy radicals, each of
which is attached directly to a carbon atom of an0 aromatic nucleus. Typical dihydric phenols are
2,2-bis-(4-hydroxyphenyl)propane;
hydroquinone;
;37
8CL-6165
--7--
resorcinol;
2,2-bis-(4-hydroxyphenyl)pentane;
2,4'-(dihydroxydiphenyl)methane;
. bis-(2-hydroxyphenyl)methane;
bis-(4-hydroxyphenyl)methane;
bis-(4-hydroxy-~-nitrophenyl)methane;
1,1-bi (4-hydroxyphenyl)etha~e;
3,3-~is(4-hydroxyphenyl)pentane;
2,2-dihydroxydiphenyl;
10 . 2,6-dihydroxynaphthalene;
bis-(4 hyaroxydiphenyl)sulfone;
bis-(3,5-diethyl-4-hydroxyphenyl)sulfone;
2,2-~is-(3,5-dimethyl 4-hydroxyphenyl)propa~e;
2,4'-dihydroxydipnenyl sulfone;
5'-chloro-2,4'-dihydroxydiphenyl sulfone;
bis-~4-hyroxyphe~yl)diphenyl sulfone;
4,~'-dihydroxydiphenyl ether;
4 ~ 4 ' -dihydroxy 3, 3 ' -dichlorodiphenyl ether;
4, 4 1 -dihydroxy 2, 5-dihydroxydiphenyl ether;
2û and the like.
A variety o~ additional dihydric phenols which may
: be employed to provide such carbonate polymers are dis-
closed in commo~ly assigned Goldberg, U.S. 2,999,835.
It is, of course, possible to employ two or moxe dif-
ferent dihydric phenols or a dihydric phenol in combi
nation with a glycol, a hydroxy terminated polyester,
or a dibasic acid in the event that a car~onate copoly-
mer rather than a homopolymer ls desired ~or use in the
prepar2tion of the polycarbonate mixtures o~ the inven-
tion. Branched polycar~onates are also useful.
637
8CL~616
8-
In any event, the ~referred aromatic carbonate polymer is
a homopolymer derived from 2,2-bis(hydr3xyphenyl)propane
(bis~henol-A).
Copolymer component "b" o~ the blend in accorda~ce
wi~h this invention comprises a coupled resinous block
copolymer having blocks comprising polymerized vinyl
aromatic units connec~ed to ~locks comprising polymer-
ized diene units. Exam~les of ~inyl aromatic units
include styrene, alpna methylstyrene, vinyl toluene,
para-methylstyrene ~Qd the like. The preferred unit is
styrene. Examples of diene units include butadiene,
isopre~e, 1,3-pentadiene, 2,3-dimethylbutadiene and the
li~e. Thus the pre~erred "b" csmpone~t of the blend is
a copolymer of pol~merized butadiene and s~yrene units.
i5 The bu~adi~e portion, based on the total weig~
of the copolymer can range from about 15 to about 40
weight percent. The s~yrene portion can range from
about 60 to about 8C-weight percent. In especially
preferred butadiene styrene copolymers, the weight
ratio of the styre~e fraction to the butadie~e fraction
ranges from about 2 ~o 1 to about 3 to l. ~he residual
dienic un~aturation can be partially or essentially
removed by selective hydrogenation if desired. The
copolymers may be made by procedures well known ,o
those skilled in the art. A suitable commercial
material is Phillips Petrole~m ~-~esin RRO3 BDS poly-
mer. This has a styrene-butadiene wei~ht ratio of
about 3:1 and a denslty of the order of about loOl
g/cm3, see ~.S. 3,639,517 and 4,0~1,053.
637
8C~-~165
_9_
The resistance to environmental stres~ crazing and
cracking of the polycarbonate resin mixtures prepared
in ac~ordance with the invention wa~ determined by
subjecting ~tressed specimens to gasoline soaking and
5 then measuring their impact strength~ with special
atte~ion to the mode of failure, ductile failure being
preerable. Th~ specimens are ASTM D-256 impact test
bars o two size~: 2 1/2" x lJ2" x 1/8" a~d 2 1~2" x
L/2" x 1/4". Values o~ the desired stress were appLied
to each teqt bar by mounting on an ASTM stress jig ~1
percent strain). The m~unted bar~ were so~ked 24 hours
at room temperature in AMOCO~ unleaded premium grad~
gasolinq. They ~ere the~ removed from the jig, th~
gasoline e~aporated and the bars dried ~or 24 hours7
Izod impact strength~ were then aetermined according to
ASTM D256 procadures on n~tched spQcimens. In all
cases, the proper~ies are compared with those of
identical unsoaked, molded mix~ures. Those which
retain a substantia-l amount of impact resistance after
20 soaking obviously are ~he best at resisting
environmental stress cracking.
D~SC~IPTION OF T~E PREFERRED ~BODIMENTS
In order that those skilled in the art may better
understand how the present invention may ~e practiced,
the following ~rl es are given by way o~ illustration
and not by way of limitationl All parts and percent-
ages are by weight unless otherwis~ noted. The various
polycarbonate resin mixtures were molded into the test
specimens in a 3 oz. Van Dorn injection molding
machine. The temperatures used were 270C on the
cylinder and nozzle with a range o~ from 265C to
285C
~ 637 8C~-61~5
--10~
EXA~oeLES 1 AND 2
A~ aromatic polycarbonate derived from 2,2-bis(4~
hydroxyphe~yl~propane and having an intrinsic visco~ity
(I.V.) in the range of from abcut 0.46 to about 0.49
dl/g as deterr; ne~ in methylene chLoride qolutio~ at
25C, was mixed with a bu~adie~e-~tyr~ne polymer
(Phillips Petroleum RR-03, hereinafter referred to as
BDS), said copolymer ~aving a weight ratio of styrene
~o butadie~e of abou~ 3:1. The ingredient~ were ~he~
blended together by mQcha~ically mixing them in a
laborator~ tumbler and the resulting mixtures were fed
to an ex~ruder which wa~ opera~ed at about 255~C. The
re~ulting extrudate~ were comminuted into pellets. The
p~llet~ were i~jection molded a.t abou~ 265C. to abou~
285C. into te~t specimens of about 2 l/Z" ~ 1/2" x
l/4" and 2 1/2" x 1/2" x 1/8", the latter dimension
bei~g specimen thick~ess. Some of the specimens were
mounted o~ an ASTM stress jig tl% strain) and soaked in
AMOCO~ premium u~leaded gasoline for 24 hours. They
were removed from the jig, th~ gasoline allowed to
evaporate at room temperature for 24 hours, and then
they were testedO Where indica~ed, Izod impact
strengths o~ these spe~i -n-~ were measured according to
the notched Izod test~ ASTM D256, and are set foxth in
Table Io The superscript refers to the percent ductil
ity at the foot/lb. value. The samples labeled con-
trol was ~he bisphenol A polycarbonate, u~modified~ or
modified as i~dicated. The formulations used, and the.
results obtained are set forth in Table l:
~Z~U~i3~
8CI~-6165
T~BLE I
POliYCARBONATE MODIEIED WIT~
BUTADIE~E ST~rRENE COPOI.YM13R
;
EXA~L13 A* B* C* 1 2
Compositio~ ( pl~w)
Polyc rbonate 100 95.7 9403 80 84
BD--S Copolymex --- 40 3 5 . 7 20 16
PRO~
Notched Impac:t Stre~gth
l/a~ f~. lb. iI~, 14.~t 15.2 14~,3 13~8 1~.6
l/4" ft. lb. in. 1. 68 . 960 ll. 2 10 . 4 10 . 5
SO~ED IN GASOLINE
Notched Impact Streng~h
l/8" ft. lb. i~. broke0.5 1.0 13.3 13.6
1/4" ft. lb. in. ~ 10 . 4 4. 5
~Can~rol
Unless otherwise ~pecified by superscript aLl were ductile
25 at failure.
637
8CL-6165
-12-
As is observed ~rom the above data, the polycar-
bonate alone has ~o resi~tance to gasoline u~der the
te~t condition~. Those e~ample~ with relatively small
quantities of butadiene-styren~, B and C, show virt-
S ually no improv. ~nt in resistance to ga~oline and abrittla failure mode~ ~owever those example3 with ~ub-
stantially increased quantities of butadiene-skyrene, 1
and 2I show substankially increased re~istance to
ga~olin~ a~d a ductile failure mode. In fact, Example
1 show~ a complete retainment of impact properties and
ductile failure mode under the test conditio~s.
