Electric heating – Microwave heating – Cookware
Reexamination Certificate
2000-03-13
2001-07-03
Walberg, Teresa (Department: 3742)
Electric heating
Microwave heating
Cookware
C219S725000, C428S308400
Reexamination Certificate
active
06255636
ABSTRACT:
BACKGROUND OF THE INVENTION
Filled polypropylene articles have been observed to exhibit undesirable odors, particularly upon heating. In this respect, see U.S. Pat. No. 5,023,286 to Abe et al., wherein phenolic antioxidants are suggested to control the odor problem. Other polypropylene compositions may be found in U.S. Pat. No. 4,734,450 to Kawai et al.; U.S. Pat. No. 5,045,369 to Kobayashi et al.; U.S. Pat. No. 5,300,747 of Simon; U.S. Pat. No. 5,439,628 of Huang and U.S. Pat. No. 4,933,526 of Fisher et al.
This invention relates to disposable, polypropylene/mica microwaveable containers having suitable food contact compatible olfactory properties including cups, trays, soufflé dishes, lids, plates, bowls, and related articles of manufacture useful for preparation, storage, delivery, and serving of food, wherein convenience and low cost are of paramount importance. Nevertheless, suitable food contact compatible olfactory properties, appearance, and tactile characteristics of the plate, container, etc., are important for consumer preference. The suitability of these disposable articles of manufacture for microwave cooking, or heating of food, has an important place in today's marketplace. Both the commercial and retail market components need an aesthetically pleasing microwaveable, disposable, rigid and strong container, plate, or cup, and related articles of manufacture which also have suitable food contact compatible olfactory properties.
These disposable microwaveable containers and plates exhibit a melting point of no less than about 250° F., the containers or plates being dimensionally stable and resistant to grease, sugar and water at temperatures up to at least 220° F. and exhibiting sufficient toughness to be resistant to cutting by serrated polystyrene flatware and also exhibiting food contact compatible olfactory properties. The preferred containers and plates exhibit both suitable food contact compatible olfactory properties and at least one micronodular surface on the food contact side of the container or plate.
SUMMARY OF THE INVENTION
Microwaveable, disposable, rigid and strong containers and plates having suitable food contact compatible olfactory properties have been prepared. These disposable and microwaveable articles of manufacture exhibit (a) suitable food contact compatible olfactory properties; and (b) a melting point of not less than 250° F., suitably 250° F. to 330° F. In preferred embodiments these articles of manufacture exhibit a micronodular surface on the side coming in contact with food. These microwaveable, food contact compatible containers and plates are dimensionally stable and resistant to grease, sugar and water at temperatures of at least 220° F. and are of sufficient toughness to be resistant to cutting by serrated polystyrene flatware. The containers and plates of this invention answer a long felt need for products which can withstand the severe conditions of a microwave oven when common foods such as beans and pork, pancakes with syrup, pepperoni pizza, and broccoli with cheese are microwaved during food cooking and reconstituting processes.
It has been found in accordance with the present invention that polypropylene/mica food contact articles such as bowls or plates exhibit suitable olfactory characteristics when prepared by a low temperature process and/or when prepared including a basic organic or inorganic compound. There is provided in a first aspect of the present invention, a microwaveable, disposable food service article having food contact compatible olfactory properties formed of a melt processed polyolefin/mica composition wherein the composition includes from about 40 to about 90% by weight of a polypropylene polymer and from about 10 to about 50% by weight mica where the melt processed composition exhibits low odor as characterized by a relative aroma intensity index of less than about 1.6. Less than about 1.5 is more preferred and, as a practical matter, the lower limit of the relative aroma intensity index for the inventive composition is believed to be about 0.1.
Typically, the melt processed composition from which the microwaveable article is formed also includes a basic organic or inorganic compound including the reaction product of an alkali metal or alkaline earth element with carbonates, phosphates, carboxylic acids as well as alkali metal and alkaline earth element oxides, hydroxides, or silicates and basic metal oxides including mixtures of silicone dioxide with one or more of the following oxides: magnesium oxide, calcium oxide, barium oxide, and mixtures of the foregoing. More specifically, the basic organic or inorganic compound may be selected from the group consisting of: calcium carbonate, sodium carbonate, potassium carbonate, barium carbonate, sodium silicate, sodium borosilicate, magnesium oxide, strontium oxide, barium oxide, zeolites, sodium citrate, potassium citrate, calcium stearate, potassium stearate, sodium phosphate, potassium phosphate, magnesium phosphate, mixtures of silicone dioxide with one or more of the following oxides: magnesium oxide, calcium oxide, barium oxide, and mixtures of one or more of the above. Furthermore, hydroxides of the metals and alkaline earth elements recited above may be utilized.
Where a basic inorganic odor suppressing compound is chosen, generally such compound is selected from the group consisting of calcium carbonate, sodium carbonate, potassium carbonate, barium carbonate, sodium silicate, sodium borosilicate, magnesium oxide, strontium oxide, barium oxide, zeolites, sodium phosphate, potassium phosphate, magnesium phosphate, mixtures of silicone dioxide with one or more of the following oxides: magnesium oxide, calcium oxide, barium oxide, and mixtures of one or more of the basic inorganic compounds set forth above. The amount of a basic inorganic compound is generally from about 2 to 20 weight percent, but is usually from about 5 to about 15 weight percent of the article. Most preferably the basic inorganic compound selected is calcium carbonate; typically present from about 5 to about 20 weight percent.
Where an organic compound is chosen, it is typically selected from the group consisting of sodium stearate, calcium stearate, potassium stearate, sodium citrate, potassium citrate, and mixtures of these where the amount of such compound is from about 0.5 to about 2.5 weight percent of the article.
Typically, microwaveable articles produced in accordance with the present invention exhibit a relative aroma intensity index of less than about 1.0; preferably less than about 0.7; with a practical lower limit being 0.1 or so.
As shown below in connection with microwaveability testing, and summarized in Table 20, competing commercial polystyrene type plates cannot withstand the high temperatures generated in the microwave oven during food contact and either significantly warp or deform when the aforementioned food products were heated on them. Under the usual microwaving conditions with high grease content foods, the prior art plates tend to deform and flow to the point where parts of the plate become adhered to the inside of the microwave oven. For disposable plates and containers, having suitable food contact olfactory properties, appearance and feel are important attributes. The micronodular surface of the plates and containers of this invention where mica and the basic inorganic compound or basic organic compound are used in combination with polypropylene or polypropylene polyethylene copolymers or blends tend to give these products the pleasing appearance, feel of stoneware or a pottery-like look and suitable food contact olfactory properties. Another significant property of the containers and plates of this invention is their cut resistance. These rigid articles of manufacture are of sufficient toughness to be resistant to cutting by serrated polystyrene flateware. In normal usage they are also resistant to cutting by regular metal flatware.
Whereas any microwaveable article may be produced in accordance with the invention, most typically the article is a
Cochran, II Ronald L.
Littlejohn Mark B.
McCarthy Donald C.
Neculescu Cristian M.
Patterson Robert
Ferrell Michael W.
Fort James Corporation
Van Quang
Walberg Teresa
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