CA1200637A - Polycarbonate resin mixtures having improved impact strength - Google Patents

Abstract

COMPOSITION
ABSTRACT OF DISCLOSURE

A composition with increased resistance to environmental stress cracking and crazing comprising a blend of (a) an aromatic carbonate polymer resin and (b) an effective amount of a coupled resin block co-polymer of polymerized vinyl aromatic units connected to polymerized diene units.

Description

;37 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.

~Z0l~i3'7 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.

~, 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 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-~IL2~30~7 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 an 0 aromatic nucleus. Typical dihydric phenols are 2,2-bis-(4-hydroxyphenyl)propane;
hydroquinone;

;37 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.

8CL~616 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.

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 ~ 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.

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.

Claims (11)

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

1. A composition comprising a blend of (a) an aromatic carbonate polymer resin derived from a carbonate precursor and a dihydric phenol, said dihydric phenol being unsubstituted on its aryl grouping or groupings and (b) from about 10 to about 50 weight percent based on the weight percent of copolymer and aromatic carbonate polymer of coupled resinous block copolymer having blocks comprising polymerized vinyl aromatic units connected to blocks comprising polymerized diene units, the residual diene unsaturation being essentially non-hydrogenated, and said 10 to about 50 weight percent of copolymer imparting to the blend a resistance to environmental stress cracking and crazing greater than that possessed by the said aromatic carbonate polymer the amount of copolymer based upon the weight percent of copolymer and aromatic carbonate polymer.

2. A composition in accordance with claim 1 wherein A is derived from bisphenol-A.

3. A composition in accordance with claim 1 or 2 wherein "b" copolymer comprises polymerized styrene units and polymerized butadiene units.

4. A composition in accordance with claim 1 or 2 wherein "b" copolymer comprises polymerized styrene units and polymerized butadiene units and is present in quantities of from about 13 to 35 weight percent.

5. A composition in accordance with claim 1 or 2 wherein a reinforcing amount of a filler is present.

6. A composition in accordance with claim 1 or 2 wherein a reinforcing amount of a glass fiber is present.

7. A composition in accordance with claim 1 or 2 wherein a flame retardant effective amount of a metal salt of an organic sulfonic acid is present.

8. A composition in accordance with claim 1 wherein the polymerized dienic units are from about 15 to 40 weight percent of the "b" copolymer and the vinyl aromatic units are from about 60 to 85 weight percent of the "b" copolymer.

9. A composition in accordance with claim 8 wherein the "b" copolymer is from about 13 to 35 weight percent.

10. A composition in accordance with claim 2 wherein the "b" copolymer is from about 13 to 35 weight percent.

11. A composition in accordance with claim 10 wherein the polymerized diene units are butadiene units and are from about 15 to 40 weight percent of the copolymer and the polymerized vinyl aromatic units are styrene units and are from about 60 to 85 weight percent of the copolymer.