Electric heating – Microwave heating – Cookware
Reexamination Certificate
1999-06-11
2001-04-03
Walberg, Teresa (Department: 1714)
Electric heating
Microwave heating
Cookware
C524S128000
Reexamination Certificate
active
06211501
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. Nos. 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, mineral-filled polypropylene 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 further 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.
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 mineral-filled polypropylene food contact articles such as bowls or plates exhibit superior olfactory characteristics when prepared including a basic organic or inorganic compound.
There is provided in a first aspect of the present invention a method of preparing a microwaveable, mineral-filled polypropylene food contact article including the steps of: (a) preparing a melt-compounded composition with from about 40 to 90 percent by weight of a polypropylene polymer; from about 10 to about 50 percent by weight of a primary mineral filler and an effective odor-reducing amount of a basic organic or inorganic compound, the melt-compounded compositon exhibiting an odor index of less than about 0.75; (b) extruding the aforesaid melt comounded composition into sheet form; and (c) forming the food contact article from the sheet, wherein the basic organic or inorganic compound is operative to reduce undesireable odors in the melt-compounded composition to the aforesaid odor index value of 0.75 or less. The primary filler is mica, clay, a siliceous material, ceramics, glass, a sulfate mineral, or mixtures thereof.
Typically, the primary mineral filler is mica, talc, kaolin, bentonite, wollastonite, milled glass fiber, glass beads (solid or hollow), silica, or silicon carbide whiskers or mixtures thereof. We have discovered that when polypropylene is melt-compounded with acidic-type minerals the resulting mixture has a higher odor index (offensive odors) that would disqualify them from use in food service products.
Acidic type fillers such as mica; natural clay minerals such as kaolinite, bentonite, attapulgite, montmorillonite, clarite, or fuller's earth; and silica are particularly detrimental in generating odor compounds when processed under high shear and high temperature conditions experienced during twin screw compounding. We have found that changing the compounding process and adding a basic component to the primary acidic filler allows the production of low odor index compounds. The reason for this effect is unknown since the fundamental cause of the degradation in polypropylene may be due, in part, to catalysis effects caused by impurities in the mineral as well as its acidic or basic nature. In this regard, the addition of CaCo
3
to talc is beneficial whereas, it may be unnecessary when wollastonite is used as the primary filler.
The preferred primary fillers are mica, talc, kaolin, bentonite, milled glass fibers, and wollastonite or mixtures thereof. Of these milled glass fibers and wollastonite are basic in nature and may not necessarily require the addition of a secondary basic component.
As noted above, suitable mineral fillers include mica, talc, kaolin, bentonite, wollastonite, milled glass fiber, glass beads (hollow or solid), silica whiskers, silicon carbide whiskers and mixtures thereof as well as the mineral fillers recited herein, whereas the basic organic or inorganic compound is generally 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 silicon 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, aluminum oxide, 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 silicon 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, aluminum oxide, sodium silicate, sodium borosilicate, magnesium oxide, strontium oxide, barium oxide, zeolites, sodium phosphate, potassium phosphate, magnesium phosphate, mixtures of silicon 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
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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