Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2000-01-11
2001-05-15
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C106S145100, C106S206100, C106S217900, C524S047000, C525S054240, C536S102000
Reexamination Certificate
active
06231970
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to compositions and methods for manufacturing thermoplastic starch compositions and articles made therefrom. More particularly, the present invention relates to thermoplastic starch compositions that include a particulate filler component. The thermoplastic starch compositions may optionally include one or more additional thermoplastic polymers blended therewith and fibers for reinforcement.
2. The Relevant Technology
A. Sheets, Containers, and Other Articles Made From Paper, Plastic, Glass and Metal.
Materials such as paper, paperboard, plastic, polystyrene, and metals are presently used in enormous quantity as printed materials, labels, mats, and in the manufacture of other articles such as containers, separators, dividers, envelopes, lids, tops, cans, and other packaging materials. Advanced processing and packaging techniques presently allow an enormous variety of liquid and solid goods to be stored, packaged, or shipped while being protected from harmful elements.
Containers and other packaging materials protect goods from environmental influences and distribution damage, particularly from chemical and physical influences. Packaging helps protect an enormous variety of goods from gases, moisture, light, microorganisms, vermin, physical shock, crushing forces, vibration, leaking, or spilling. Some packaging materials also provide a medium for the dissemination of information to the consumer, such as the origin of manufacture, contents, advertising, instructions, brand identification, and pricing.
Typically, most containers and cups (including disposable containers) are made from paper, paperboard, plastic, polystyrene, glass and metal materials. Each year over 100 billion aluminum cans, billions of glass bottles and thousands of tons of paper and plastic are used in storing and dispensing soft drinks, juices, processed foods, grains, beer, etc. Outside of the food and beverage industry, packaging containers (and especially disposable containers made from such materials are ubiquitous. Paper for printing, writing, and photocopying, as well as magazines, newspapers, books, wrappers, and other flat items made primarily from tree derived paper sheets are also manufactured each year in enormous quantities. In the United States alone, approximately 5½ million tons of paper are consumed each year for packaging purposes, which represents only about 15% of the total annual domestic paper production.
Recently there has been a debate as to which of these materials (e.g., paper, paperboard, plastic, polystyrene, or metal) is most damaging to the environment. Consciousness-raising organizations have convinced many people to substitute one material for another in order to be more environmentally “correct.” The debate often misses the point that each of these materials has its own unique environmental weaknesses. One material may appear superior to another when viewed in light of a particular environmental problem, while ignoring different, often larger, problems associated with the supposedly preferred material (e.g., whereas paper is more biodegradable than plastics and polystyrene, paper is far more polluting to the environment to manufacture).
The debate should not be directed to which of these materials is more or less harmful to the environment, but rather toward asking whether an alternative material can be developed which will solve most, if not all, of the various environmental problems associated with each of these presently used materials.
B. Starch.
Starch is a plentiful, inexpensive and renewable material that is found in a large variety of plant sources, such as grains, tubers, fruits, and the like. In many cases, starch is discarded as an unwanted byproduct of food processing. However, because starch is readily biodegradable it does not persist in the environment as a harmful material when disposed of. Perhaps the only harm that starch might cause is that it can put unwanted nutrients into the water or soil into which it is discarded, which could attract and facilitate the proliferation of certain unwanted organisms. It is this quality as a nutrient, though, that greatly facilitates the breakdown and elimination of starch from the environment.
Because of the biodegradable nature of starch many have attempted to incorporate starch into a variety of materials in order to improve the environmental desirability of such materials. Starch has been incorporated into multi-component compositions in various forms, including as a filler, binder, or as a constituent within thermoplastic polymer blends. In addition, some have attempted to utilize starch alone as a thermoplastic material, although with limited success due to the tendency of starch to form retrograde crystallization products upon resolidifying, which crystallization products often lack appropriate mechanical properties.
Starch may be added as an inert filler, typically in its native, unmodified state, which is a generally water-insoluble, granular material. In such cases, the starch granules will normally behave as any other solid particulate filler and will contribute little, if any, in terms of improving the mechanical properties of the resulting material. Alternatively, starch that has been gelatinized, dried, and then ground into a powder may also be added as a particulate filler. Although starch may be added as a filler, its more interesting and technologically challenging uses have been in the area of using starch as a binder, as a thermoplastically processible constituent within thermoplastic polymer blends, and as a thermoplastic material by itself.
Although the alternative uses of starch as a water-soluble binder or as a thermoplastic material generally require significantly different compositional formulations and process conditions in order to successfully process them as intended, they have the common requirement that the native starch granules must in some way be transformed or altered from being in a granular or particulate state to being in a molten or plastic state, such as be dissolution or gelation within a solvent or by being heated to form a starch melt. Because native starch has a melting point that approaches the decomposition temperature, it is virtually impossible to form a starch melt without the addition of plasticizers, solvents or other components that allow the starch to become molten, solvated or otherwise liquified into a plastic state at a temperature that is safely below the decomposition temperature.
Starch can be used as a “binder” in order to glue or otherwise adhere other solid constituents together to form a heterogenous mixture of different components. At some point before or during the molding phase, the starch is typically dissolved or gelatinized in an appropriate solvent, such as water, in order for it to become a liquid or gel. This allows the initially granular starch to become a flowable or plastic material into which the other components can be dispersed. Upon resolidification of the gelatinized starch, typically by removing enough of the water by evaporation so that the starch recrystallizes or otherwise dries out, the starch forms a solid or semi-solid binding matrix that can bind the remaining components together. Examples of patents that teach the use of starch as a binder and, in particular, processes for molding articles from aqueous starch mixtures include U.S. Pat. No. 5,660,900 to Andersen et al.; U.S. Pat. No. 5,683,772 to Andersen et al.; U.S. Pat. No. 5,709,827 to Andersen et al.; U.S. Pat. No. 5,868,824; and U.S. Pat. No. 5,376,320 to Tiefenbacher et al. For purposes of disclosing compositions, methods, and systems for molding aqueous starch mixtures that are subsequently dried so as to form a binding matrix of dried starch which binds together discrete solid materials such as fibers and/or particulate fillers, the foregoing patents are incorporated herein by specific reference.
Related to the process of molding aqueous starch mixtures is the formation of sheets havin
Andersen Per Just
Hodson Simon K.
Copenheaver Blaine
E. Khashoggi Industries, LLC
Workman & Nydegger & Seeley
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