CA1206673A - Polycarbonate resin mixtures - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Novel compositions with improved resistance to environmental stress cracking and crazing comprising (a) an aromatic carbonate polymer; and (b) a modifier combination therefor comprising (i) a thermoplastic olefin polymer insoluble therein; and (ii) a linear low density polyolefin /

Description

i~73 FOR: POLYCARBO ~TE RESIN MIXTURES
BACRGROUND OF THE INVENTION
This invention relates to thermoplastic resin com-positions and more particularly is concerned with poly-carbonate resin mixtures having extraordinary resistance to environmental stress crazing and cracking.
Aromatic carbonate polymers are well known, com-mercially available materials having a variety of applications in the plastics art. Such carbonate polymers may be prepared by reacting a dihydric phenol, such as

2,2-bis(4-hydroxyphenyl)-propane, with a carbonate pre-cursor, such as phosgene, in the presence of an acid binding agent. Generally speaking, aromatic poly-carbonate resins offer a high resistance to the attack of mineral acids, may be readily molded, and are physiolo-gically harmless as well as stain resistant. In addition, such polymers have a high tensile and impact strength (except in thick molded sections), and a dimensional stability surpassing that of other thermoplastic materials.
However, in certain applications, the use of aromatic polycarbonate resins is limited because they exhibit severe environmental stress crazing and cracking. "Environmental stress crazing and cracking" refers to the type of failure which is hastened by the presence of organic solvents such as, for example, gasoline, acetone, heptane and carbon tetrachloride when such solvents are in contact with stressed parts fabricated from aromatic polycarbonate~
~Y~

- ~ \
;73 resins. The most significant effect is a loss in impact strength and also an increase in brittle type failure.
Contact with such solvents may occur, for example, when parts are used under the hood of automobiles, or near the gasoline filler ports thereof, or near the gasoline filler ports thereof, or when solvents are used to clean or degrease stressed parts made from polycarbonate resins.
At present, no entirely staisfactory means is available for reducing environmental stress crazing and cracking of polycarbonate resins, although a variety of methods have been proposed.
In Goldblum, U~S. 3,431,224 dated March 4, 1969, assigned to the same assignee as this application, for example, it is proposed to addmodifiers to polycarbonates, in certain proportions, the modifiers comprising at least one member o~ the class consisting of polyethylene, polypropylene, polyisobutylene, a copolymer of ethylene and an ethyl acrylate, a copolymer of ethylene and propylene, a cellulose ester, a polyamide, a polyvinyl acetal, an alkyl cellulose ether, and a polyurethane elastomer. While the results with such modifiers are generally excellent, in thin sections, e.g, 1/8 inch, it has been found, as will be shown later herein, that the weld line strength i5 significangly improved by the compositions of this invention.
Another modifier proposed to be added to poly-carbonate is reported in Research Disclosure No. 20810, Dow Chemical Company, August 1981. Date are provided sho~iny that polycarbonates modified with a linear low

3~ density polyolefin, namely, ethylene/ octene-l copolymer, provided good impact strength at increased part thickness.
There is no suggestion therein that such a modifier will enhance resistance to environmental stress crazing and cracking, and, as will be shown hereinafter, soaking a composition modified with a linear low density copolymer ~.~~3 of ethylene and butene-l, even in thin sections, causes the impact strength to deteriorate substantially and results in brittle failure. Still other modifiers have been proposed for impact strength improvement, but none of then provides optimum environmental stress crazing and cracking resistance -- applicant's earlier filed commonly assigned Canadian patent applications, Serial Number 412,599, filed September 30, 1982, being expressly mentioned in this connectionO Serial No.
412, 599 describes polycarbonates modified with a linear low density polyolefin (LLDPE), e.g., a copolymer of ethylene and a small amount of butene-l. Such compositions process well and are toughened, but there is no disclo-sure of solvent resistance and, as will be shown later herein, the LIDPE's alone do not provide enhanced resistance to environmental stress crazing and cracking, even in thin sections.

SUMMARY OF THE_INVENTION

Unexpectedly, in ~iew of the foregoing, it has now been discovered that polycarbonate resins (a) may be rendered more resistant to environmental stress crazing and cracking by incorporating therewith, in certain pro-poxtions, a modifier combination comprising (b) (i), a thermoplastic olefin polymer insoluble in the said poly-carbonate and (b~ (ii) a linear low density polyolefin.

~Z~6~i73 ~CL-6119 When the above-mentioned modifier combination is added to the polycarbonate resin, within a certain range~ the resultant mixture possesses a resistance to environmental stress crazing and cracking greater than that possessed by the polycarbonate resin itself. This result is entire.ly unexpected because the prior art would indicate that high crystallinity is necessary for solvent resistance whereas and, in fact, partially ~rystalline modifiers are employed herein, as component (b)~ , reducing crystallinity but inducing solvent resistance.

DE~SCRIPTION OF THE INVENTION

In accordance with the invention there are provided resin admixtur~s comprising (a) an aromatic polycarbonate resin; and ~bl a modifier combination therefor comprising (i) a thermoplastic olefin polymer insoluble in the said polycarbonate resin; and (ii) a linear low density polyolefin resin, said modifier being present in an amount sufficient to impart to said mixture a resistance to environmental stress crazing and cracking greater than that possessed by said polycarbonate resin alone, and enhanced weld line strength compared to polycarbonate resin plus (b) (i).
The amounts of modifier combination to be empolyed vary broadly but, in general, best results will be obtained when the modifier is added to the polycarbonate .resin in amounts ranging from about 4 parts to about 50 ' ~2~6673 parts by weight per lO0 parts by weight of the poly-carbonate res;n and the modifier. When less than 4.0 parts are used, the improvement in the craze resistance of the polycarbonate is not readily detectable and, where the amount exceeds abou-t 50 parts, the mixture begins to lose the beneficial properties of the poly-carbonate. Preferably, the modifier is added in amounts ranging from about 5.0 to 15 parts per hundred of combined ~a) and (b). Such addition may be accomplished in any manner so long as a thorough distribution of the modifier in the polycarbonate resin is obtained. For example, the mixing of materials may be accomplished by a variety of methods normally employed for incorporation of plasticizers or fillers into thermoplastic polymers including but not limited to mixing rolls, doughmixers, Banbury mixers, extruders, and other mixing equipment. The resulting mixtures may be handled in any conventional manner employed for the fabrication or manipulation of thermoplastic resins. The materials may be formed or molded using compression~ injection, calendering, extrusion, blow molding, etc. techniques, alone, or in any combination.
Also, multiforming methods such as extrusion-blow molding, ox co-extrusion-coinjection can be used, e.g., for multi-layer containers. It should be understood that the ~5 polycarbonate resin mixtures prepared in accordance with the invention may also contain, in addition to the above-mentioned polymers, other additives to lubricate, rein-force, prevent oxidation, or lend color to the material.
Such additives are well known in the art, and may be incorporated without departing from the scope of the invention.

6~3 The fact that the addition of the combination of components specified above to a polycarbonate resin system provides a resinous mixture having an improved resistance to environm~ntal stress crazing and cracking with respect to polycarbonate and enhanced weld line strength compared to polycarbonate resin plus (b)(i) is totally unexpected and not fully understood.
The aromatic carbonate polymers (a) used to provide polycarbonate mixtures of the present invention may be prepared by reacting a dihydric phenol with a carbonate precursor such as phosgene, a haloformate or a carbonate ester. Generally speaking, such carbonate polyrners may be typified as possessing recurring structural units of the formula:
_ -;

~ O - A ~ O - C _ _ __ _ where A is a divalent aromatic radical of the dihydric phenol employed in the polymer producing reaction.
PreEerably, the carbonate polymers used to provide the resinous mixtures of the invention have an intrinsic ~2~6673 _ 7 _ viscosity (as measured in methylene chloride in deciliters per gram at 25C) r~ging from about ~ . 3Q
to about 1Ø The dihydric phenols which may be ~m~loyed to ~roYide such aromatic car~o~ate polymers ar~ mononuclear or po}ynuc~ea~ aromatic compounds, containi~g as functional groups, two hydroxy radicals, each o~ which is attached directly to a carbon atom Qf an aromatic nucleus. Ty~ical dihydric phenols are 2,2-bis-(4-hydrox~phe~yl~ropane;
hydroquino~e;
resorci~ol;
2,2-bis-~4-hydroxyphenyl)pentane;
2,4'-(dihydroxydiph~nyl)methane;
: ~is-(2-~ydroxyphenyl)methane;
~is-~4-hydroxyphe~yl~metha~e;
bi~-~4-hydroxy-~-n~rophenyl~methane;
i5 (4~hydroxyphenylte~hane;
3,3-bis~4-hydroxyphenyl~penta~e;
2,2-dihydroxydiphen~l;
2~ 2,6-dihydroxynaphthalene;
bis-~4-hydroxydiphe~yl)sulfone;
bis-(3,5- ethyl-4-hydroxyphenyl)sulfone;
2,2-bis-~3,5-dimethyl-4-hydroxyphen~})propane;
2,4'-dihydroxydiphenyl sulfone;
5'-chloro-Z,4'-dihydroxydiphenyl sulfone;
bis-(4-hydroxyphenyl)dipheny} sul~one;

4,4'-dihydrox~diphenyl ether;
4,4'-dihydroxy 3,3'-dichlorodiphenyl ether;
4,4'-dihydrox~-2,~-dihydroxydiphenyl ether;
and the like.

A variety of additional dihydric phenols which may be employed to provide ~uch carbonate polymers are 1 disclosed in commonly assigned Goldberg, U.S. 2,999,835.
3~ It is, of course, possible to employ tWQ or more different .. .. . . .

2(~667;~

dihydric phenols or a dihydric phenol in combination with a glycol, a hydroxy terminated polyester, or a dibasic acid in the event that a carbonate copolymer rather than a homopolymer is ~esired for use in the preparation of the polycarbonate mixtures of the invention. Branched poly-carbonates are also useful. To avoid unnecessarily detailed description, the disclosures of U.S. Patent No 3,028,365 to Schnell dated April 3, 1962, 3,334,154 dated August 1, 1967 to K;m, 4,001,184 dated January 4, 1977 to Scott, 4,131,575 dated ~ecember 26, 1978 to Adelmann et al. In any event, the preferred aromatic carbonate polymer is a homopolymer derived from 2 r 2-bis(4-hydroxyphenyl) propane (bisphenol Al.
Generally speaking, the modifier combination com-ponents (b) (i) and (b) (ii) which are admixed with polycarbonate resins to provide the resin mixtures of the in~ention are themsel~es well known commercially availab]e thermoplastic resin materials.
Thermoplastic polyolefin resin component (b~ (i) will comprise a polymer of ethylene, propylene, ethylene-ethyl acrylate copolymer, ethylene propylene copolymer and other copolymers of ethylene with monomers polymeriz-able with ethylene. The polymers are to be insoluble in polycarbonake. By "insoluble" is meant at least essentially insoluble in polycarbonate at ordinary temperature. It is desirable but not essential that they have a melt viscosity within 50 percent of that of the polycarbonate selected at the melt blending temperature and shear rate employed in mixing.

6~73 _ g In any case, where ethylene i5 copolymerized with an alpha-olefin, component (b) (i) will be destin-guishable from component (b) (ii) because the former may have random and side chain branchiny, and the latter will be predominantly linear with controlled side chains links. Especially preferred for component (~b) (i) are polyethylene, polypropylene, polyisobutylene, a copolymer of ethylene and ethyl acrylate, a copolymer of ethylene and propylene and mixtures of any of the foregoing. Especially preferred is polypropylene, which is readily available from a number of commercial sources.

Linear low density polyolefin component (b) (ii) may be prepared by state of-the-art polymerization pro-cesses such as those described in U.S. Patent Number 4,Q76,698 to Anderson et al dated February 28, 1978 and Eur.Pat. Appl. 4,6~5. The polymer may have a density between 0.8g and Q.96 g./cc. and a controlled concentration of simple side chain branching which distinguishes it from polymers such as high pressure low density poly-eth~lene and high density polyethylene. The preferred range of density is 0.915 to 0.945 g./cu. The linear low density polymers preferably are made fxom ethylene and an alpha olefin of C3 to C8 carbon content, e.g., butene-l and octene-l, or mixtures of such alpha-olefins. The comonomer is used in a minor amount, e.g.,10 mol ~ or less of the total amount of monomers. A
preferred range is 1-3 mol~. The preferred copolymer is a copolymer made from ethylene and butene-l such as Escorene LPX-15 of Exxon, ~ouston, Texas.

"` IL2(~6~;73 - lO - 8CL 6119 Within the broad composition ranges specified ahove, the following have been found to provide desirable properties for the mixtures: polycarbonate component (a) comprises from about 84 to about 96

5 parts by weight; polyolefin component (b) (i) comprises from about 2 to about 8 parts by weight; and linear low density polyolefin component (b) (ii) comprises from about 2 to about 8 parts by weight, per 100 parts by weight of components (a), (b) (i) and lO (b) (ii~ combined.
The resistance to environmental stress crazing and cracking of the polycarbonate resin mixtures prepared in accordance with the invention was determined by subjecting stressed specimens to 15 gasoline soaking and than measuring their impact strengths with special attention to the mode of failure, ductile failure being preferable. The specimens were ASTM D 256 impact test bars of two sizes: 2l2 x l/2" x 1/8" and 2l2 x 1/2" x l/4".
20 Values of the desired stress were applied to each test bar by mounting on an ASTM stress jig at 0.3 percent strain. The mounted bars were soaked 4 hours at room temperature in AMOCO~) unleaded premium grade gasoline. They were ~hen removed from the jig, the 25 gasoline evaporated and the bars dried for 24 hours.
Izod impact strengths were then determined according to ASTM D 256 procedures on notched specimens. In all cases, the properties are compared with those of identical unsoaked, molded mixtures. Those which 30 retains a substantial amount of impact resistance after soaking obviously are the best at resisting environmental stress cracking. Additionally, the weld line strength of the compositions was measured with specimens prepared in a double gate mold and 3S tested ~cco~ding to ASTM D 256.

lZ~6673 - 11 ~ 8CL 6119 DESCRIPTION OF THE PREFERRED EMBODIMENTS
In order that those skilled in the art may better understand how the present invention may be practiced~ the following examples are given by ~ay of illustration and not by way of limitation.
All parts and percentages are by weight unless otherwise 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 275C. on the cylinder and nozzle with a range of from 265C. to 282C.

EXAMPLES 1~3 An aromatic polycarbonate derived from 2,2-bis(4-hydroxyphenyl) propane and having an intrinsic viscosity (i.v.) in the range of from about 0.46 to about 0.49 dl/g as determined in methylene chloride solution at 25C. was mixed with polypropylene (Escorene PP1012) and a linear low density polyclefin resin which is a copolymer of ethylene and butene-l (Escorene~ LPX-15). The ingredients were then blended together by mechanically mixing them in a laboratory tumbler and the resulting mixture was fed to an extruder which was operated at about 255C. The resulting extrudates were comminuted into pellets.
The pellets were injection molded at 265C. to 282C. into test specimens of about 21 by 1/2" by 1/4"
and 212 by 1/2" by 1/8", the lattex dimension being specimen thickness. Some of the specimens were mounted on an ASTM stress jig at .3% strain and soaked in ~ lZ(~6~i~73 8cL-6 o AMOCO ~ ~remium unleaded gasoline for 4 hours, remDved ~rom ~he jig, the gasoline allowed to evaporate and dry at room temperature f~r-2~ hours. ~here indicated, Izoa impact s~rengths of these s~ecimens were measured accord-ing to the notched Izod test, ASTM D 256, and are set forth i~ Table 1.. ~he weld li~e strength was determined as pre~iously mentioned. The super.~cript refers to the per~en~ ductility at the foot lb. ~alue. Th~ samples labeled control were the bisphenol ~ polycarbonate, un-modified, or modified as indicated. The formulationsused, and ~he results obtained are set for~h in Table I:.

TABLE I. POLYCARBONATE ~ODIFID WIT~ A POLYOLEFIN
AND A LINEAR L~W D~NSITY PO~YOLEFI~_ _ EXAMPLE A* B* C* 1 2 3 ComDositio~ (~bw) .
oolyc~rbonate 100 90 90 91 92 91 ~olypropylene - - 10 - 6 4 3 20linear low density polyethylene - - 10 3 4 6 .. .
PROPE~TIES:
Notched Impact S~rength 1/8n ~t. Lbs.-in. 14.8** 10.7 12.4 12.0 12.7 12.0 1/4" ~t. lbs.-in. 1.6 7.98-8~ 8 2208 7~o 7-8 Weld line strength ~4.0 4-7~ 4.3 5.4 6.6- 6.7 SOAXED IN GASOLINE
Notched Impact Strength 1/8' ft. lbs.-in. 6.6 10.5 0.9 i~ o12.5 12.a *Control **Unless otherwise specified, all were ductile at failure.

. . .

~:06673 The results demonstrate ~hat the imp~c~
strengths o the new compositions of Examples i throug~
3 were retained in comparison with ~he controls i~ the 1/8 n samples and that impact strengths in the 1/4ff samples are substantially Lmproved over the poly-S car~onate alone con~rols. Furthermore, after soakingi~ gasoline, the i~ention Examples show a retention of stre~gth and desirable duc~ile failure mode~ The w~ld line strengths ~f ~he invention Ex~mples are si~nifican~ly higher ~hen ei~h~r polycarbonate with polypropylene or polycarbonat~ with linear low densit~
polyethylene~at comparable total quan~i~ies. It is also intexes~ing to note that although polycar~onate with linear low density polyethylen~ loces significaDt ~ act resis~ance at 1~" ~hen soaked Ln ~asoline, lg ~h~ in~ent~o~ ~xamples show compl~te re~eation of i~p~c~ re~ a~c~ whe~ si~ ica~t ~u~tit'es af li~ear low ~n~it~ polyethyle~e ar~ incDr~r~e~ t~rein.

Th~ above-mentioned patents, applic~tions, and publications are incorporatea herein by reference.
Ob~iously, many variations wil~ sugyest themselves to those skilled in this art in light of ~he de$ailed de-scription herein. For exzmple, instead of a bisphenol-A
polycarbonate, one containing units derived from tetra-methylbisphenol-~ or from dixylenol sulfone can be used.
Instead of polypropylene, a copolymer of ethylene and propylene can be used. Instead of a linear low density polyethylene comprising units of ethylene and butene-l, there can be substituted one comprising units of ethy-3G lene and octene-l. The compositions can be provided in reinforced modifications, e.g., those reinforced with chopped glaqs filaments, or in flame retardant modifications. ~11 such obvious variations are with- -in ~he full intended scope of the appended claims.

Claims (9)

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

1. A resin mixture comprising (a) an aromatic polycarbonate resin, and (b) a modifier combination therefor comprising (i) a thermoplastic olefin polymer insoluble in said polycarbonate resin excluding a linear low density polyolefin; and (ii) a linear low density polyolefin resin, said modifier being present in an amount sufficient to impart to said mixture a resistance to environmental stress crazing and cracking greater than that possessed by said polycarbonate resin (a) alone, and enhanced weld line strength compared to polycarbonate resin plus (b)(i) wherein said component (a) comprises from 84 to about 96 parts by weight, component (b)(i) comprises from about 2 to about 8 parts by weight and component (b)(ii) comprises from about 2 to about 8 parts by weight, per 100 parts by weight of components (a), (b)(i) and (b)(ii) combined.

2. A resin mixture as defined in claim 1 wherein the amount of modifier combination (b) ranges from about 4 to about 50 parts by weight per 100 parts by weight of resin (a) and modifier combination (b) together.

3. A resin mixture as defined in claim 1 wherein the aromatic carbonate polymer comprises recurring structureal units of the formula:

wherein A is a divalent aromatic radical of a dihydric phenol.

4. A resin mixture as defined in claim 3 wherein in said formula, A is derived from a 4,4'-dihydroxy-di(mononuclear aryl)alkane.

5. A resin mixture as defined in claim 1 wherein said aromatic polycarbonate (a) comprises poly(2,2-diphenyl-propane)carbonate.

6. A resin mixture as defined in claim 1 wherein said thermoplastic olefin polymer (b)(i) comprises at least one member selected from the class consisting of polyethylene, polypropylene, polyisobutylene, a copolymer of ethylene and ethyl acrylate and a copolymer of ethylene and propylene.

7. A resin mixture as defined in claim 6 wherein said thermoplastic olefin polymer (b)(i) comprises polymerized propylene units.

8. A resin mixture as defined in claim 1 wherein said linear low density polyolefin resin (b)(ii) is a linear low density polyethylene resin.

9. A resin mixture as defined in claim 8 wherein said linear low density polyolefin resin is a copolymer of ethylene and butene-l.