Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-23
2003-06-03
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S047000, C524S539000, C524S605000, C525S444000, C525S450000, C525S452000, C525S540000, C428S480000
Reexamination Certificate
active
06573340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to biodegradable polymer blends. More particularly, the present invention relates to blends of two or more biopolymers, such as biodegradable polyesters and polyester amides, in order to yield sheets and films having improved physical properties such as flexibility and elongation. The biodegradable polymer blends may be suitable for a number of applications, such as in the manufacture of disposable wraps, bags and other packaging materials or as coating materials.
2. The Relevant Technology
As affluence grows, so does the ability to purchase and accumulate more things. Never before in the history of the world has their been such a large number of people with such tremendous buying power. The ability to purchase relatively inexpensive goods, such as books, tools, toys and food, is a luxury enjoyed by virtually all levels of society, even those considered to be at the poorer end of the spectrum. Because a large percentage of what is purchased must be prepackaged, there has been a tremendous increase in the amount of disposable packaging materials that are routinely discarded into the environment as solid waste. Thus, as society becomes more affluent, it generates more trash.
In many cases, packaging materials are intended for only a single use, such as boxes, cartons, pouches and wraps used to package many, if not most, commodities purchased from wholesale and retail outlets. Even the advent of computers and “paperless” transactions has not stemmed the rising tide of packaging wastes. Indeed, the onset of “e-commerce” has spawned a great mail-order fad, thus increasing, instead of decreasing, the amount of packaging materials being used as products must now be individually packed in boxes suitable for shipping.
Moreover, the incredibly fast-paced lifestyles now being pursued have greatly disrupted traditional eating routines in which people prepared their own meals and sat down as a family or group. Instead, people grab food on the run, thus creating ever-increasing amounts of fast food packaging materials being used and then immediately discarded. In view of the rising tide of disposable packaging materials, some countries, particularly those in Europe, have begun to mandate either the recycling of fast food generated wastes or the use of packaging materials which are “biodegradable” or “compostable”. Environmental activists have also entered the fray to put pressure on companies that generate solid waste. Thus, large fast food chains such as McDonald's have been essentially forced to discontinue nonbiodegradable packaging materials such as foamed polystyrene, either by government fiat or by pressure by environmental groups. There is therefore an ever-present need to develop biodegradable alternatives to nonbiodegradable paper, plastics and metals.
In response to the demand for biopolymers, a number of new biopolymers have been developed which have been shown to biodegrade when discarded into the environment. Some of the larger players in the biodegradable plastics market include such well-known chemical companies as DuPont, BASF, Cargill-Dow Polymers, Union Carbide, Bayer, Monsanto, Mitsui and Eastman Chemical. Each of these companies has developed one or more classes or types of biopolymers. For example, both BASF and Eastman Chemical have developed biopolymers known as “aliphatic-aromatic” copolymers, sold under the trade names ECOFLEX and EASTAR BIO, respectively. Bayer has developed polyesteramides under the trade name BAK. Du Pont has developed BIOMAX, a modified polyethylene terephthalate (PET). Cargill-Dow has sold a variety of biopolymers based on polylactic acid (PLA). Monsanto developed, but has since stopped the manufacture of, a class of polymers known as polyhydroxyalkanoates (PHA), which include polyhydroxybutyrates (PHB), polyhydroxyvalerates (PHV), and polyhydroxybutyrate-hydroxyvalerate copolymers (PHBV). Union Carbide manufactures polycaprolactone (PCL) under the trade name TONE.
Each of the foregoing biopolymers has unique properties, benefits and weaknesses. For example, biopolymers such as BIOMAX, BAK, PHB and PLA tend to be strong but also quite rigid or even brittle. This makes them poor candidates when flexible sheets or films are desired, such as for use in making wraps, bags and other packaging materials requiring good bend and folding capability. In the case of BIOMAX, DuPont does not presently provide specifications or conditions suitable for blowing films therefrom, thus indicating that it may not be presently believed that films can be blown from BIOMAX.
On the other hand, biopolymers such as PCL, ECOFLEX and EASTAR BIO are many times more flexible compared to the more rigid biopolymers discussed immediately above. However, they have relatively low melting points such that they tend to be self adhering when newly processed and/or exposed to heat. While easily blown into films, such films are difficult to process on a mass scale since they will tend to self adhere when rolled onto spools, which is typically required for sale and transport to other locations and companies. To prevent self-adhesion (or “blocking”) of such films, it is typically necessary to incorporate silica or other fillers.
Another important criteria for sheets and films used in packaging is temperature stability. “Temperature stability” is the ability to maintain desired properties even when exposed to elevated or depressed temperatures, or a large range of temperatures, which may be encountered during shipping or storage. For example, many of the more flexible biopolymers tend to become soft and sticky if heated significantly above room temperature, thus compromising their ability to maintain their desired packaging properties. Other polymers can become rigid and brittle upon being cooled significantly below freezing (i.e., 0° C.). Thus, a single homopolymer or copolymer may not by itself have sufficient stability within large temperature ranges.
In the case of the packaging of foods, such as refrigerated meats or fast foods, the packaging materials may be subjected to widely fluctuating temperatures, often being exposed to rapid changes in temperature. A biopolymer that may be perfectly suitable at room temperature, for example, may become completely unsuitable when used to wrap hot foods, particularly foods that emit significant quantities of hot water vapor or steam. In the case of meats, a wrapping that may be suitable when used at room temperature or below, such as at refrigeration or freezing temperatures, might become soft and sticky during microwave thawing of the meat. Of course, it would generally be unacceptable for a biopolymer to melt or adhere to the meat or fast food being served unless for some reason it was desired for the person to actually consume the biopolymer.
In view of the foregoing, it would be an advancement in the art to provide biodegradable polymers which could be readily formed into sheets and films that had strength and flexibility properties suitable for use as packaging materials.
In particular, it would be an advancement in the packaging art to provide improved biodegradable polymers which could be readily formed into sheets and films that were capable of being folded, sealed or otherwise manipulated in order to reliably enclose and seal a substrate therein.
It would be a further advancement in the art to provide improved biodegradable polymers which could be readily formed into sheets and films having sufficient flexibility while avoiding or minimizing problems such as undesired self-adhesion.
It would yet be an advancement in the art to provide improved biodegradable polymers which could be readily formed into sheets and films having increased temperature stability over a broad range of temperatures compared to existing biopolymers.
Such improved biopolymers are disclosed and claimed herein.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention encompasses biodegradable polymer blends having improved strength, flexibility, elongation an
Andersen Per Just
Hodson Simon K.
Khemani Kishan
Schmidt Harald
Acquah Samuel A.
Biotec Biologische Naturverpackungen GmbH & Co. KG
Workman & Nydegger & Seeley
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