Stock material or miscellaneous articles – Structurally defined web or sheet – Weight per unit area specified
Reexamination Certificate
1998-12-28
2001-10-09
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Weight per unit area specified
C127S032000, C127S033000, C264S211000, C264S211110, C428S327000, C428S340000
Reexamination Certificate
active
06299969
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to expanded or foamed shaped starch products which are made by extrusion under select conditions using starch feed materials having a defined particle size.
Starch, a readily available known biodegradable material, has been used to prepare foamed; film and other shaped products for different purposes including selected packaging applications. Some of these starch products and their uses are described in U.S. Pat. Nos. 5,035,930 and 5,043,196.
Extrusion is a well known technique, widely used in forming plastic materials into various foamed and expanded products. More recently, the extrusion of starch into expanded articles has shown increased interest as noted in the aforementioned '930 and '196 U.S. patents which disclose the extrusion of low density, high amylose starch into packaging materials. Other disclosures of forming starch products by extrusion can be found in U.S. Pat. No. 5,248,702 directed to packaging fillers and in U.S. Pat. No. 5,314,754 involved with the formation of shaped products such as films, rods and sheets. Another disclosure, EP 0 544 234 shows the general process of starch extrusion. However, despite this background of extrusion as well as the known capability of using starch in forming expanded products, the ability to produce different large shaped or structured starch products such as flexible sheets and rigid boards or planks, has not been easily attained.
While much attention has been directed to finding different starch compositions including combinations with various synthetic polymers and additives such as plasticizers, only limited consideration has been given to the nature of the extrusion process itself. Extrusion and expansion of starch not only is different from plastics, but even varies in many respects when large structured products are formed as compared to the formation of smaller products such as cylinders, tubes, rope like products and narrow sheets. In order to produce large shaped products, the need to utilize extruder dies of different shapes and configurations is apparent. However, the ability to make large expanded starch products is complicated by the fact that most of the properties in the smaller formed products have to be maintained or improved while several other properties such as flexibility or rigidity have to be satisfied. The process of forming large structured foam products not only involves a change in the die configuration and size but has to overcome problems or variations caused by increased threshold throughput or feed rates and changes in processing pressure and product cell structure.
Accordingly, there is a need to define a method for producing structured shaped starch products, having the necessary properties such as flexibility or rigidity, and the products produced by this method.
SUMMARY OF THE INVENTION
The present invention provides a biodegradable, structured, shaped product having good flexibility or rigidity properties as well as compressibility and resilience comprising an expanded, closed cell starch product wherein the product is formed by extruding starch which has a selected particle size. More particularly, the expanded starch product of this invention is a structured, shaped product made by extruding starch having a particle size of from 400 to 1500 microns.
DETAILED DESCRIPTION OF THE INVENTION
The ability to provide large shaped or structured starch products for use in packaging or other applications is the main objective of this invention. The term “structured” product as used herein refers to products having relatively large configurations or shapes such as wide and/or thick sheets and planks. Typically this would include sheets, planks or board having thicknesses of several inches or more and more particularly up to 4″ and varying widths of 24″ to 48″ or more. Sheets which are usually flexible, typically have thicknesses of up to ¼″ while planks or boards, which are usually rigid or semi-rigid typically have thicknesses of ¼″ to 1″.
The formation of shaped starch products by extrusion is becoming of more interest and has been described many times in the recent literature as noted previously. Most of the disclosures have been involved with providing shaped fillers and random or smaller packaging materials such as discrete loosefill products, sometimes called peanuts, or very small sheets. The ability to extend this processing concept to the formation of bigger or larger starch shaped products has not been a simple or direct extension of the known technology. This is because the chemical nature of starch is quite different from the various plastic and synthetic materials, such as styrene and polyethylene, that have been extruded into shaped products for many years. Additionally, while the rheology of starch extrusion to form smaller loosefill type products is similar in some respects to the extrusion of larger structured products, it is also different or lacking in other properties or aspects. Along these lines it is noted that the extrusion of starch to produce the structured foamed products generally requires dies with large openings or increased cross sectional areas. This means higher throughput or feed rates to satisfy pressure, fill rates and other rheological properties needed to produce products with suitable properties. One significant variation is that of cell structure in the resulting product.
In order to provide suitable extrusion properties and particularly the needed high feed rates and threshold throughput in forming desired structured starch products it has been found that the feed starch particle size is an important factor. A significantly large and defined particle size has been found especially advantageous in providing desirable extrusion processing conditions and resulting product properties. The useful particle size is large and in a defined range of from about 400 to 1500 microns and more particularly from about 800 to 1200 microns. When using starch feed material with this defined particle size, the extrusion processing conditions including feed rate and pressure, plus needed cell structure in the formed product were more readily attainable to provide the structured product of suitable characteristics. Generally, essentially all of the starch feed will have the noted particle size, however, amounts of up to about 10 to 20% of the starch feed may have particle size outside the specified range without substantially affecting the process condition and/or product properties.
In order to obtain the starch feed material having the necessary particle size in accordance with this invention, a method known as compact granulating, commonly referred to as chilsonating, may be used. Other methods to attain desired starch particle size may also be used provided substantially all of the starch feed material is within the prescribed size range.
Another feature which improves processing and the properties of the resulting structures starch products is the addition of a nucleating agent or salt to the starting starch feed material. This is especially helpful when dies of increased and large open areas or cross section are used and particularly improves the cell structures of the expanded product. Various nucleating agents or salts may be used in this capacity including any inorganic, water soluble salt or mixtures thereof and especially an alkali metal or alkaline earth metal salt such as sodium sulfate and sodium chloride. Other nucleating agents such as microtalc can be used but the alkali metal or alkaline earth metal salts are preferred. The amount of nucleating agent used will depend on particular processing conditions and desired extruded product dimensions with at least 1%, more particularly at least 2% and preferably from 4% to 8% by weight of nucleating agent, based on the weight of starch in the feed composition, being used. When making flexible sheets it has been found desirable to use 2 to 5% by weight of nucleating agent and with rigid or semi-rigid planks it
Altieri Paul A.
Tormey Beth C.
Duncan, Esq. Lourcke A.
Le Hoa T.
National Starch & Chemical Investment Holding Corporation
Zagarella, Esq. Eugene
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