CA1128233A - Reusable molded utensils having improved stress cracking resistance - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention pertains to a reusable molded utensil having residual molding stresses and which is subjected to repeated washing in an aqueous detergent solution, said utensil molded from a composition comprising an aromatic poly-carbonate having incorporated therein from about 3 to 7%
by weight of a saturated polyolefin polymer.

Description

1128Z33 Mo-1169-FC

REUSABLE MOLDED UTENS~S HAVING IMPROVED
: STRESS CRACKING RESISTANCE

FIELD OF ~HE INVENTION

This invention relates to reusable molded utensils, and more particularly to reusable molded utensils molded from an aromatic polycarbonate containing a saturated polyolefin polymer.

BACKGROUND OF THE INVENTION
Reusable m~lded plastic utensils having residual molding stresses have encountered wide acceptance and success since their introduction into the market place. However, after repeated washing in a detergent solution, many reusable molded plastic utensils have a tendency to stress crack in high stress areas, such as in the corners of the food service tray of Flgures 1 and 2 and at the base of the mug of Figures 3 and 4. Such reusable molded utensils have been m~lded from polycarbonate resins, but such utensils have been found to experience the same stress cracking problems encountered in reusable m~lded utensils molded from other non-polycarbonate plastics.
Canadian Patent 863,411 indicates that polycarbonate -materials may be rendered resistant to environmental stress crazing and cracking by the incorporation of from about 0.1 parts to 10 parts by weight, per 100 parts of the polycarbonate, of an unsaturated aliphatic polyolefin. However, this patent is limited to the use of unsaturated aliphatic polyolefins and is not directed to nor suggests reusable molded utensils pre-pared from its resin mixture.

In accordance with the present invention, reusable utensils having residualmDlding s-tresses m~lded from an aromatic polycarbonate containing a saturated polyolefin polymer are providea having improved stress cracking resistance.
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SUMMARY OF THE TNVENTION

The present in~ention comprises a reusable moldecl utensil haviny residual moldmg stresses which is intended to be subjected to repeated washing in an aqueous detergent solution and which is molded from a composition comprising an aro~atic polycarbonate having incorporated therein from about 3 to 7~ by weight of a saturated polyolefin polymer.

DESCRIPTION OF THE DRAWINGS

Figures 1 and 2 are directed to a top view and a side view, respectively,of a food service tray according to the invention.
Figures 3 and 4 are directed to a top view and a side view, respectively, of a mug according to the invention.
The arrows point to areas containing high residual molded stress.
DETAILED DESCRIPTION OF THE INVENTION
The polycarbonates suitable in the present invention are preferably those having a weight average molecular weight from about 10,000 to 200,000, most preferably from about 20,000 to 80,000, and most particularly a melt flow rate range of from about 1 to 24 g/10 min (ASTM D-1238) and are prepared by methods known to those skilled in the art and more particularly by methods disclosed in German Patent Nos. 926,274 and 1,046,311 and .in U. S. Patent Nos. 3,028,365, 2,999,846, PC-01~ - 2 -3,248,414, 3,153,008, 3,215,668, 3,187,065, 2,964,794,

2,970,131, 2,991,273 and 2,999,835.
The aromatic polycarbonates use~ul in practice of the invention are produced by reacting di-(monohydroxy-aryl)-alkanes or dihydroxybenzenes and substituted dihydroxy-benzenes with derivatives of carbonic acid such as carbonic acid diesters, phosgene, bis-chlorocarbonic acid esters of di-(monohydroxyaryl)-alkanes and the bis-chlorocarbonic acid esters of the dihydroxy-benzenes and the substituted dihydroxy-benzenes.
By aromatic polycarbonate, in the sense of thepresent invention, there are understood homopolycarbonate and copolycarbonate resins which are based, for example, on one or more of the following bisphenols~ hydroquinone, resorcinol, dihydroxydiphenyls, bis-(hydroxyphenyl)-alkanes, bis-(hydroxy-phenyl)-cycloalkanes, bis-(hydroxyphenyl)-sulphides, bis-~rq, (hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulphoxides, bis-(hydroxyphenyl)-sulphones and a,~bis-(hydroxyphenyl)-diisopropylbenzenes, as well as their nuclear-alkylated and nuclear-halogenated compounds.
These and further suitable aromatic dihydroxy compounds are described, for example, in U.S. Patent Nos. 31028r365 2,999,835, 3,148,172, 3,271,368, 2,991,273, 3,271l367,

3,280,078, 3,014,891 and 2,999,846, in German Offenlegung-sschriften (German Published Specification) 1,570,703, 2,063,050, 2,063,052, 2,211,956 and 2,211,957, in French Patent Specification 1,561,518 and in the monograph "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publish-ers, New York, 1964".
Preferred bisphenols are those of the formula I

HO ~ X ~ / ~ ~ -OH ~I) ;~ in which R is identical or different and denotes H, Cl-C4-alkyl, Cl or Br, preferably H or Cl-C4-alkyl, and in which X is a bond, Cl-C~-alkylene, C2-C8-alkylidene, C5-C15-cycloalkylene, C5-C15-cycloalkylidene, -S-, -SO2-, -SO-, -CO- or - C - ~ CH3 ~, 3;3 ~xamples o~ these bisphenols are: 4,~'-clihydroxydi-phenyl, 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A~, 2,4-bis-(~~hydroxyphenyl)-2-methylbutane, l,l-bis-(~-hydroYy-phenyl)-cyclohexane, ~,~-his-(4-hydroxyphenyl)-p-diisoprop~l-benzene, 2,2-bis-(3-methyl-4-hydroxyphenyl)-propane, 2,2-bis-(3-chloro-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-methane, 2,2-bis-(3,5-dimethyl-4-hydroxy-phenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-sulphone, 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane, ~,~-bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropyl-benzene, 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane and 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane (tetrabromo bisphenol A).

Examples of particularly preferred bisphenols are:
2,2-bis-(4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dichloro-4-hydroxy-phenyl)-propane, 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane and l,l-bis-(4-hydroxyphenyl)-cyclohexane.

Preferred aromatic polycarbonates are those which ; are based on one or more of the bisphenols mentioned as being preferred. Particularly preferred copolycarbonates are those based on 2,2-bis-~4-hydroxyphenyl)-propane and one of the other bisphenols mentioned as being particularly preferred. Further particularly pre~erred polycarbonates are those based solely on 2,2-bis-(4-hydro~yphenyl)-propane or 2,2-bis-(3J5-dimethyl-4-hydroxyphenyl)-propane.

The aromatic high-molecular weight polycarbonates can be branched due to the incorporation of srnall amounts, preferably of between about 0.05 and 200 mol ~ (relative to diphenols employed), of trifunctional or more than trifunctional compounds, especially compounds with three or more phenol~c hydroxyl groups.
Polycarbonates o~ this type are described, ~or example, in German Offenlegungsschriften (German Published Specifications~ 1,570,533, 1,595,762, 2,116,97~ and 2,113,347, British Patent Specification 1,079,821 and U.S. Patent Specification 3,544,514.
Some examples of compounds with three or more than three phenolic hydroxyl groups which can be used are phloro-glucinoll 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane-2,4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 1,4,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tri-(~-hydroxyphenyl)-phenylmethane, 2,2-bis-[4,~-bis-(4-hydroxyphenyl)-cyclohexyl]-propane, 2,4-bis-(~-hydroxyphenyl-isopropyl)-phenol, 2,6-bis-(2-hydroxy-5'-methyl-benzyl)-4-- methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-~- propane, hexa(4-(4-hydroxyphenylisopropyl)phenyl) ortho-; terephthalic acid ester, tetra-(4-hydroxyphenyl)-methane, tetra-(4-(4-hydroxyphenylisopropyl)-phenoxy)-methane and 1,4-bis-((4',4"-dihydroxytriphenyl)-methyl)-benzene. Some of the other tri~unctional compounds are 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(4-hydroxy-~ phenyl)-2-oxo-2,3-dihydroindole.
In the preparation of polycarbonate compositions suitable for preparing the reusable molded utensils in accordance with this invention, any suitable saturated poly-olefin may be used such as, for example, polyethylene, poly-propylene, polybutylene, halogenated polyolefin mixtures and 30 copolymers thereof, such as described in U.S. Patent Nos.

~.

2,825,721, 2,905,646, 2,912,424, 2,915,514, 2,~21,059, 2,949,4~7, 2,980,66~, 2,981,723, 2,981,726, 2,989,516, 3,024,226, 3,024,227, 3,0~9,529 and 3,06~,132.
Both high and low density polyethylene may be used.
Low density polyethylenes of up to 0.925 gram/cc. are pro-duced by the polymerization of ethylene at pressures in the range of 15,000 to about 45,000 p.s.i.g. and temper-atures of from about 100C. to about 300C. in the presence of free radical catalysts such as oxygen or peroxides. High density polyethylenes range from 0.93 to 0.965 gram/cc.
and are obtained from the polymerization of ethylene at moder-ate pressures and temperatures in a suitable solvent, and in the presence of a suitable catalyst. A polyethylene having a density of from about 0.93 to about 0.95 and a melt index of from about 0.6 to about 15 is preferred~
Any suitable polypropylene polymer may be used and preferably those having a melt index of from about 0.7 to about 15. These polypropylenes may be obtained in accordance with the procedure set forth in U.S. Patent No. 2,845,414 or in the manner described in the "Source Book of the New Plastics", volume 1, by Herbert R. Simonds, published by the Reinhold Publishing Corporation.
Any suitable butylene or isobutylene polymer may be used and preferably those having molecular weights greater than about 75,000 and most preferably of from about 100,000 to about 200,000 and a density of from about 0.8 to about 1.2 grams/cc.
In addition to those mentioned above, halogenated polyolefins such as polychlorotrifluoroethylenes, polytetra-~Z1~233 fluoroethylenes and the like may be used either alone or in admixture with other polyoleEins.

Polyethylene is the preferred saturated pol~ole~in polymer to be used with the polycarbonate in the present in-vention. High density polyethylene is most preferred.

The saturated polyolefin is incorporated into the aromatic polycarbonate in from about 3 to 7% b~ weight, pre-ferably about ~ to 7% by weight.

..
The reusable m~lded utensilsof the present invention may also be pigmented. The smallest amount of pigment possible to obtain the proper color is generally used. In general, ; less than about 5% by weight, based on the weight of the aromatic polycarbonate resin, of pigment is used. Preferably, less than about 3% by weight of pigment is used.

Any suitable pigment may be used, such as, for example, white opaque pigments; lead, zinc, titanium and antimony oxide pigments; red, maroon and brown inorganic pigments composed of the various oxides of iron; cadmium yellows, cadmium reds and cadmium maroons, such as cadmium sulfoselenides, cadmium sulfides, and the like; green pigments such as chrome greens, chromium oxides and the hydrated chromiwm oxides; blue pigments such as iron blues and ultra marine blues; carbon blacks, iron oxide blacks and the like.
Particular examples of suitable pigments include Pigment Blue 15 (C.I. 74160), Diluted Black-PDS 161 B-192 (Kohnstamm), Solvent Violet 13 (C.I. 60725), Yellow 37 (CoI~ 77199), Cadmium Red (C.I. 77196), Croton East Green Toner 4D-3600 (Harshaw Chemical Co.), Amaplast Yellow GEIS (Drakenfeld), PDS 987 Thermax Blue-Black (Kohnstamm), Marine Blue (Drak-enfeld), Scarlet Red 10177 (Drakenfeld), Scarlet Red 10051 PC-01~ - 8 -3~ 33 tBrakenfeld)l phthalocyanine pigments such as, or example, copper phthalocyanine (Monastral Fast Blue B or Helioyen Blue BA), chlorinated copper phthalocyanine (Monastral Fast Green G or Heliogen Green GA), sulfonated copper phthalo-cyanine, metal free phthalocyanine (Monastral Fast Blue G),and phthalocyanine derivatlves in which one or more of the external hydrogen atoms are replaced by other groups such as halogen, alkyl, aryl, amino, nitro, substituted amino, sulfo, carboxy, alkoxy, aryloxy, thiocyano and the like.

The combination of the polycarbonate resin, the saturated polyolefin and the optional pigment can be accom-plished by any suitable technique known in the art which will bring about the thorough distribution of the materials such as, for example, by the use of mixing rollers, dough mixers, Banbury mixers, extruders and the like.

In one technique for obtaining an intimate disper-sion of the polyolefin in the polycarbonate, the materials are blended in powder or granular form and thereafter extruded until pelletized.

In a second technique the polyolefin in the form of granules or pellets may be introduced simultaneously with a polycarbonate solution into a devolatilizing extruder contain-ing one or more vents to remove the solvent by evaporation, and the resulting material can then be extruded and pelletized if desired.

During the blending process, it is also possible to admix additional additives such as glass fibers, stabilizers, flame retardant agents, flow agents, lubricants and antistatic agents in a known manner.

PC-012 _9_ Examples of suitable reusable molded utensils in accordance with the present invention include, bllt are not limited to, food service trays, glasses, bottles, cups, mugs, plates, saucers, knives, forks, spoons, medicine dispensers and medical specimen containers.

A preferred reusable molded utensil is a food service tray.
In a particularly preferred embodiment, the reusable molded utensil of the present invention is in the form of a food service tray which comprises a moldeci toP ancl a molded bottom joined by connective means having foamed insulation between said top and bottom. The top and bottom ~ay be molded by any forming process including injection molding, blow molding and thermoforming. Preferably, the top anc~ bo-ttom of the food service tray are thermoformed from an aromatic polycarbonate, ; preferably a bisphenol A polycarbonate, containing about 3 to 7 by weight of a saturated polyolefin polymer, preferably poly-ethylene. The foamed insulation is preferably polyurethane foam.
Aqueous detergent solutions in which the reusable molded utensils of the present invention are repeatedly washed include both acidic and alkaline detergent aqueous solutions. Preferably the concentration of such detergent aqueous solutions is less than 30 wt. % and most preferably from 0.5 to 10 wt. %.
In order to test the compatibility of reusable molded utensils molded from an aromatic polycarbonate containing about 3 to 7% by weight of a saturated polyolefin polymer as com pared to reusable molded utensils molded from an aromatic polycarbonate alone under various environmental conditions or chemicals, the quantitative method pu~lished in Kunststoff, Vol.
65, March 1975, pages 155-157, entitled 'Determination of .

Chemical Resistance of Plastics Under Mechnical Stress" b~
Dr. W. Kaufmann was used.
In principle, the test consists of clamping a tensile specimen to a jig with a circular arc segment and immersing the assembly into the desired test environment. After the immersion period, the specimen is tested in any appropriate tensile machine tester. The test jigs are made to various radii, calculated to result in several levels of outer fiber strain using the formula:

max S X 100 in % where S is the section thickness R is the radius of curvature for the arc E is the outer fiber strain rate.

3L~L2~3~3~

The stress jig can he machined to fit any suitable specimen. In the present comparisons, the stress jiy ls machined to accept a DIN 53-455 (ASTM D-638) specimen. For this specimen, Table 1 gives the radius of curvature and the 5 calculated outer fiber stress within the usual range used with aromatic polycarbonate.

The invention will be further illustrated, but is not intended to be limited, by the following examples.

EXAMæLE5 Test specimens in accordance with DIN 53-455 ~ASTM
D-638) having a thickness of 0. 080 inches (2mm) were molded from a bisphenol A polycarbonate having a melt flow rate of from about 6 to 11.9 gms/10 min. at 300C (ASTM D-1238) and 15 having incorporated therein about 5% by weigllt of high density polyethylene. The resulting test specimens were exposed for 16 hours at 65.5C in three different alkaline industrial detergent aqueous solutions (desiynated industrial detergent solutions A, B and C) at concentrations of 2 wt. %, 1 wt. % and 1/2 wt. % and then tested for tensile elongation at break expressed in percent. The test results are reported in Tables 2, 3 and

4.

; EXAMPLE 2 Test specimens in accordance with DIN 53-A55 ~ASTM
D-638) having a thickness of 0. 080 inches (2m~) were molded from a bisphenol A polycarbonate having a melt flow rate of from about 3.0 to 5. g gms/10 min~ at 300C accordiny to ASTM
D-1238. The resulting test specimens were then exposed at the same conditions as in Example 1 in industrial detergent ~215~233 solutions A, B and C and then tested for tensile elongation at break expressed in percent. The test results are reported in Tables 2, 3 and 4.

45 food service trays were molded from a bisphenol A
polycarbonate having a melt flow rate of from about 6 to 11.9 gms/10 min. (ASTM D-1238) having incorporated therein about

5% by weight of high density polyethylene. These food service trays were sent to a medical institution for use and testing.
It was found that all but 17 of the original food service trays were free from stress cracking after 600 uses and washings.

~2~;~33 Outer fiber strain for DIN 53-455 speclmen, 0.080 inch thickness (2mm) E~lax 2R~S where S = 0.080 inch R, inches max %
9.835 0.4

6.544 0.6 4.898 0.8 3.910 1.0 3.252 1.2 2.782 1.4 2.429 1.6 Measurement of Tensile Elongation at Break (%) After 16 Hours at 65.5C In Industrial Detergent "A"
Detergent Concen- outer Fiber Strain t ~
tration Example 0 .4 .6 .8 1.0 1.2 1.4 1.6 2% 1 70 5 2 2 202~ 2 80 5 B B B B B B
1% 1105 105 65 10 10 8 7 10 1% 2115 115 100 10 B B B B
1/2% 1110 95 85 50 40 5 6 5 1/2% 2115 110 105 95100 2 B
B = Breaks 31 ~2E~

Measurement of Tensile Elongation at Break (~) After 16 Hours At 65.5C In Industrial Detergent "B"
Detergent 5Concen- Outer Fiber Strain, ~
tration Example 0 .4 .6 .8 1.0 1.2 1.4 1.6 -2% 1 80 80 5 2 B B B B
2% 2 100 90 B B B B B B
1% 1 85 90 20 4 2 5 2 2 10 1% 2 110 100 B B B B B B
1/2% 1 110 90 100 10 5 2 5 5 1/2% 2 115 110 100 B B B B B

B = Breaks Measurement of Tensile Elongation at Break (%) After 16 ~ours At 65.5C In Industrial Detergent "C"
Detergent Outer Fiber Strain, %
Concen-tration Example 0 4 .6 _ .8 1.0 1.2 1.4 1.6 2% 1 70 5 2 2 2 2 2 2 2% 2 80 5 B B B B B B
1% 1 70 5 3 2 2 5 2 2 1% 2 90 10 B B B B B B
1/2% 1 80 30 10 5 5 3 2 3 1/2% 2100 50 B B B B B B

B = Breaks ~3L2~ 3~

A review of the data contained in Tables 2, 3 and 4 indicates that the stressed kest specimens molded ~rom bis-phenol A polycarbonate alone, rather than from bisphenol A
polycarbonate containing about 5% by weight of high density polyethylene, had a definite tendency to stress crack and break after being exposed for 16 hours at 65.5C in industrial detergent solutions of various concentrations and could not ; subsequently be tested for tensile elongation at bxeak. It is noted that the compatibility test developed by Dr. W.
Kaufmann is an "extreme torture" washing test and not one generally encountered in actual use. However, the results of the compatibility tests are a true reflection of the improved stress cracking resistance-of reusable molaed utensils molded from bisphenol A polycarbonate containing about 5%
by weight of high density polyethylene as compared to the stress cracking resistance of reusable molded utensils m~lded from bisphenol A polycarbonate alone.

The tensile elongation at break percentages re~
ported in the Tables for the stressed test specimens molded from bisphenol A polycarbonate containing high density poly-ethylene may not at first glance appear to be significant, but these figures in fact do reflect an improvement in ductility of a stressed test specimen that has been exposed for 16 hours at 65.5C in an industrial solvent solution. Such an improve-ment is magnifie~ in the extended service life of reusable utensilsmolded from this composition.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the inven-tion except as it may be limited by the claims.

Claims (8)

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

1. A reusable, molded food service tray having improved stress cracking resistance in an aqueous detergent solution molded from a composition comprising an aromatic polycarbonate having incorporated therein from about 3 to 7%
by weight of a saturated polyolefin polymer.

2. The reusable molded food service tray of Claim 1 wherein the saturated polyolefin polymer is incorporated in about 5% by weight.

3. The reusable molded food service tray of Claim 1 wherein the saturated polyolefin polymer is polyethylene.

4. The reusable molded food service tray of Claim 1 wherein the aromatic polycarbonate is a bisphenol A
polycarbonate.

5. The reusable molded food service tray of Claim 1 wherein less than about 5% by weight of pigment is incorporated into the composition.

6. A reusable, molded food service tray having improved stress cracking resistance in an aqueous detergent solution comprising a molded top and a molded bottom joined by connective means and having foamed insulation between said top and bottom wherein (i) said top and bottom are molded from an aromatic polycarbonate having incorporated therein from about 3 to 7%
by weight of a saturated polyolefin polymer, and (ii) said foamed insulation is polyurethane foam.

7. The molded food service tray of Claim 6 wherein the top and bottom are thermoformed from a bisphenol A
polycarbonate having incorporated therein about 5%
by weight of polyethylene.

8. A process for making a reusable, molded food service tray having improved stress cracking resistance in an aqueous detergent solution comprising molding said food service tray from a composition comprising an aromatic polycarbonate having incorporated therein from abut 3 to 7%
by weight of a saturated polyolefin polymer.