The Field of the Invention
The present invention relates to compositions, methods for manufacturing sheets, and articles of manufacture having a highly inorganically filled organic polymer matrix. Sheets and articles of manufacture having such a matrix can vary greatly in thickness, stiffness, flexibility, toughness, and strength and can be used in a dry or moist state to form a variety of objects, including printed sheets, containers and other packaging materials. Such sheets are less expensive and are more environmentally friendly than sheets made from conventional materials (such as paper, plastic, or metal) and are especially useful in the manufacture of disposable food and beverage containers used by the fast food industry.
The Relevant Technology.
A. Sheets, Containers, and Other Packaging Materials.
Thin, flexible sheets made from materials such as paper, paperboard, plastic, polystyrene, and even metals are presently used in enormous quantity as printed materials, labels, mats, and in the manufacture of other objects 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, t and photocopying, magazines, newspapers, books, wrappers, and other flat items made from primarily from tree derived paper sheets are also manufactured each year in enormous quantities. In the United States alone, approximately 51/2 million tons of paper are consumed each year for packaging purposes, which represents only about 15% of the total annual domestic paper a production.
B. The Impact of Paper, Plastic, Glass and Metal.
Recently there has been a debate as to which of these materials (e.g., paper, paperboard, plastic, polystyrene, glass, 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. In fact, paper, paperboard, plastic, polystyrene, glass, and metal materials each has its own unique environmental weaknesses.
Polystyrene products have more recently attracted the ire of environmental groups, particularly containers and other packaging materials. While polystyrene itself is a relatively inert substance, its manufacture involves the use of a variety of hazardous chemicals and starting materials. Unpolymerized styrene is very reactive and therefore presents a health problem to those who must handle it. Because styrene is manufactured from benzene (a known mutagen and probably a carcinogen), residual quantities of benzene can be found in styrene. More potentially damaging has been the use of chloro-fluorocarbons (or "CFCs") in the manufacture of "blown" or "expanded" polystyrene products. This is because CFCs have been linked to the destruction of the ozone layer. In the manufacture of foams, including blown polystyrene, CFCs (which are highly volatile liquids) have been used to "expand" or "blow" the polystyrene into a foamed material, which is then molded into the form of cups, plates, trays, boxes, "clam-shell" containers, spacers, or packaging materials. Even the substitution of less "environmentally damaging" blowing agents (e.g., HCFC, CO.sub.2, and pentanes) are still significantly harmful and their elimination would be beneficial.
As a result, there has been widespread pressure for companies to stop using polystyrene products in favor of more environmentally safe materials. Some environmental groups have favored a temporary return to the use of more "natural" products such as paper or other products made from wood pulp, which are believed to be biodegradable. Nevertheless, other environmental groups have taken the opposite view in order to minimize the cutting of trees and depletion of forests.
Although paper products are ostensibly biodegradable and have not been linked to the destruction of the ozone layer, recent studies have shown that the manufacture of paper probably more strongly impacts the environment than does the manufacture of polystyrene. In fact, the wood pulp and paper industry has been identified as one of the five top polluters in the United States. For instance, products made from paper require ten times as much steam, fourteen to twenty times the electricity, and twice as much cooling water compared to an equivalent polystyrene product. Various studies have shown that the effluent from paper manufacturing contains ten to one hundred times the amount of contaminants produced in the manufacture of polystyrene foam.
In addition, a by-product of paper manufacturing is that the environment is impacted by dioxin, a harmful toxin. Dioxin, or more accurately, 2,3,7,8-tetrachlorodibenzo[b,e]-[1,4]dioxin, is a highly toxic contaminant, and is extremely dangerous even in very low quantities. Toxic effects of dioxin in animals and humans include anorexia, severe weight loss, hepatoxicity, hematoporphyria, vascular lesions, chloracne, gastric ulcers, porphyrinuria, porphyria, cutanea tarda, and premature death. Most experts in the field believe that dioxin is a carcinogen.
Another drawback of the manufacture of paper and paper board is the relatively large amount of energy that is required to produce paper. This includes the energy required to process wood pulp to the point that the fibers are sufficiently delignified and fray that they are essentially self-binding under the principles of web physics. In addition, a large amount of energy is required in order to remove the water within conventional paper slurries, which contain water in amounts of up to about 99.5% by volume. Because so much water must be removed from the slurry, it is necessary to literally suck water out of the slurry even before heated rollers can be used to dry the sheet. Moreover, much of the water that is sucked out of the sheets during the dewatering processes is usually discarded into the environment.
The manufacturing processes of forming metal sheets into containers (particularly cans made of aluminum and tin), blowing glass bottles, and shaping ceramic containers utilize high amounts of energy because of the necessity to melt and then separately work and shape the raw metal into an intermediate or final product. These high energy and processing requirements not only utilize valuable energy resources, but they also result in significant air, water, and heat pollution to the environment. While glass can be recycled, that portion that ends up in landfills is essentially non-degradable. Broken glass shards are very dangerous and can persist for years.
Some of these pollution problems are being addressed; however, the result is the use of more energy, as well as the significant addition to the capital requirements for the manufacturing facilities. Further, while significant efforts have been expended in recycling programs, only a portion of the raw material needs come from recycling--most of the raw material still comes from nonrenewable resources.
Even paper or paperboard, believed by many to be biodegradable, can persist for years, even decades, within landfills where they are shielded from air, light, and water--all of which are required for normal biodegradation activities. There are reports of telephone books and newspapers having been lifted from garbage dumps that had been buried for decades. This longevity of paper is further complicated since it is common to treat, coat, or impregnate paper with various protective materials which further slow or prevent degradation.
Another problem with paper, paperboard, polystyrene, and plastic is that each of these requires relatively expensive organic starting materials, some of which are nonrenewable, such as the use of petroleum in the manufacture of polystyrene and plastic. Although trees used in making paper and paperboard are renewable in the strict sense of the word, their large land requirements and rapid depletion in certain areas of the world undermines this notion. Hence, the use of huge amounts of essentially nonrenewable starting materials in making sheets and objects therefrom cannot be sustained and is not wise from a long term perspective. Furthermore, the processes used to make the packaging stock raw materials (such as paper pulp, styrene, or metal sheets) are very energy intensive, cause major amounts of water and air pollution, and require significant capital requirements.
In light of the foregoing, the debate should not be directed to which of these materials is more or less harmful to the environment, but rather toward asking: Can we discover or develop an alternative material which will solve most, if not all, of the various environmental problems associated with a each of these presently used materials?
C. Inorganic Materials.
Man has made great use of essentially nondepletable inorganic materials such as clay, natural minerals, or stone for millennia. Clay has found extensive use because of its ready moldability into a variety of articles including containers, tiles, and other useful objects. However, some of the drawbacks of clay include the time it takes for clay to harden, the need to fire or sinter clay in order for it to achieve its optimum strength properties, and its generally large, heavy, and bulky nature. Unfired clay, in particular, has low tensile strength and is very brittle. Nevertheless, clay has found some use in the manufacture of other materials as a plentiful, inexhaustible, and low-cost filler, such as in paper or paperboard. However, because of the brittle and non-cohesive nature of clay when used as a filler, clay has generally not been included in amounts greater than about 20% by weight of the overall paper material.
Man has also made extensive use of stone in the manufacture of buildings, tools, containers, and other large, bulky objects. An obvious drawback of stone, however, is that it is very hard, brittle, and heavy, which limits its use to large, bulky objects of relatively high mass. Nevertheless, smaller or crushed stone can be used as an aggregate material in the manufacture of other products, such as hydraulically settable, or cementitious materials.
Hydraulically settable materials such as those that contain hydraulic cement or gypsum (hereinafter "hydraulically settable," "hydraulic," or "cementitious" compositions, materials, or mixtures) have been used for thousands of years to create useful, generally large, bulky structures that are durable, strong, and relatively inexpensive.
For example, cement is a hydraulically settable binder derived from clay and limestone, and it is essentially nondepletable and very inexpensive compared to the other materials discussed above. Hydraulic cement can be mixed with water and an aggregate material such as crushed stone or pebbles in order to create concrete. However, concrete has found commercial application only in the manufacture of large, bulky structural objects.
Although hydraulically settable materials have heretofore found commercial application only in the manufacture of large, bulky structural type objects, hydraulically settable mixtures have been created using a microstructural engineering approach which can be molded or shaped into relatively small, thin-walled objects. Indeed, such mixtures, which were developed by the inventors hereof, have been found to be highly moldable and can be extruded and/or rolled into thin-walled sheets, even as thin as 0.1 mm. Such mixtures and methods used to manufacture sheets therefrom are set forth more fully in copending U.S. patent application Ser. No. 08/101,500, entitled "Methods and Apparatus for Manufacturing Moldable Hydraulically Settable Sheets Used in Making Containers, Printed Materials, and other Objects," and filed Aug. 3, 1993, in the names of Per Just Andersen, Ph.D., and Simon K. Hodson (hereinafter the "Andersen-Hodson Technology").
Although the hydraulically settable binder is believed to impart a significant amount of strength, including tensile and (especially) compressive strengths, such materials have been found in lower quantities to act less as a binding agent and more like an aggregate filler. As a result, studies have conducted to determine whether sheets which do not necessarily use a hydraulically settable binder (or which only use such a binder in low enough quantities so that it will act mainly as an aggregate material) but which incorporate high concentrations of inorganic material can be manufactured. Such sheets would likewise have the advantages of hydraulically settable sheets over prior art paper, plastic, and metal materials in terms of their low cost, low environmental impact, and the ready availability of abundant starting materials.
Due to the more recent awareness of the tremendous environmental impacts of using paper, paperboard, plastic, polystyrene, and metals for a variety of single-use, mainly disposable, items such as printed sheets or containers made therefrom (not to mention the ever mounting political pressures), there has been an acute need (long since recognized by those skilled in the art) to find environmentally sound substitute materials. In particular, industry has sought to develop highly inorganically filled materials for these high waste volume items.
In spite of such economic and environmental pressures, extensive research, and the associated long-felt need, the technology simply has not existed for the economic and feasible production of highly inorganically filled, organic polymer bound materials which could be substituted for paper, paperboard, plastic, polystyrene, or metal sheets, or container products made therefrom Some attempts have been made to fill paper with inorganic materials, such as kaolin and/or calcium carbonate, although there is a limit (about 20-35% by volume) to the amount of inorganics that can be incorporated into these products. In addition, there have been attempts to fill certain plastic packaging materials with clay in order to increase the breathability of the product and improve the ability of the packaging material to keep fruits or vegetables stored therein fresh. In addition, inorganic materials are routinely added to adhesives and coatings in order to impart certain properties of color or texture to the cured product.
Nevertheless, inorganic materials only comprise a fraction of the overall material used to make such products, rather than making up the majority of the packaging mass. Because highly inorganically filled materials essentially comprise such environmentally neutral components as rock, sand, clay, and water, they would be ideally suited from an ecological standpoint to replace paper, paperboard, plastic, polystyrene, or metal materials as the material of choice for such applications. Inorganic materials also enjoy a large advantage over synthetic or highly processed materials from the standpoint of cost.
Such materials not only use significant amounts of nondepletable components, they do not impact the environment nearly as much as do paper, paperboard, plastic, polystyrene, or metal. Another advantage of highly inorganically filled materials is that they are far less expensive than paper, paperboard, plastic, polystyrene, or metals. As set forth above, highly inorganically filled material require far less energy to manufacture.
Based on the foregoing, what is needed are improved compositions and methods for manufacturing highly inorganically filled organic polymer mixtures that can be formed into sheets and other objects presently formed from paper, paperboard, polystyrene, plastic, glass, or metal.
It would be a significant improvement in the art if such compositions and methods yielded highly inorganically filled sheets which had properties similar to paper, paperboard, polystyrene, plastic, or metal sheets. It would also be a tremendous improvement in the art if such sheets could be formed into a variety of containers or other objects using existing manufacturing equipment and techniques presently used to form such objects from paper, paperboard, polystyrene, plastic, or metal sheets.
It would yet be an advancement in sheet making if the sheets could be formed from moldable mixtures which contain only a fraction of the water of typical slurries used to make paper and which did not require extensive dewatering during the sheet forming process. In addition, it would be a significant improvement in the art if such sheets, as well as containers or other objects made therefrom, were readily degradable into substances which are commonly found in the earth.
From a practical point of view, it would be a significant improvement if such materials and methods made possible the manufacture of sheets, containers, and other objects therefrom at a cost that is comparable or even superior to existing methods of manufacturing paper, plastic, or metal products. Specifically, it would be desirable to reduce the energy requirements and initial capital investment costs for making products having the desirable characteristics of paper, plastic, or metals.
From a manufacturing perspective, it would be a significant advancement in the art of shaping highly inorganically filled materials to provide compositions and methods for mass producing highly inorganically filled sheets which can rapidly be formed and substantially dried within a matter of minutes from the beginning of the manufacturing process.
It would also be a tremendous advancement in the art to provide compositions and methods which allow for the production of highly inorganically filled materials having greater flexibility, tensile strength, toughness, moldability, and mass-producibility compared to materials having a high content of inorganic filler.
Such compositions and methods are disclosed and claimed herein.