Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
1999-12-02
2003-02-18
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S051000, C264S053000, C264S211110, C264S328180
Reexamination Certificate
active
06521147
ABSTRACT:
The invention relates to a method for manufacturing foamed products according to the preamble of claim 1. Such a method is known from International patent application WO 96/05254. The invention further relates to an apparatus that can be used therefor and to products that can be obtained according to this method.
The products to be manufactured according to the invention have a foamy structure. More particularly, the foamy material always comprises at least three parts: two relatively dense layers on the outside, which, as it were, form a skin, and between them a foam structure as core. The dense layers are firm and strong and consist of substantially closed, small cells. The foam structure of the core is generally open, which means that the cells have burst to allow the gasses evolving during the manufacture, for instance water vapour or carbon dioxide, to escape. The cells generally have a firm and solid cell wall due to the relatively high pressure and temperature during the process. In the manufactured product, the fibers extend between and possibly partly through the cells and are mainly intricately connected to the material of the cells.
In this description, “gelatinization” is understood to mean a change of a natural polymer from a slightly or completely loose granular or comparable granulate form into a cohesive form which may or may not be dry and/or foamed, in which stretched polymers are present. That is to say, a transition occurs from a solid substance, a colloidal solution or suspension to a more homogenous fluid mass. Depending on the polymers used, “gelatinization” should therefore be understood to include, for instance, gelling, gellating and the like.
In foamed products where only gelatinization occurs, as a result of gas evolution, bubbles are formed in the mass to be foamed, substantially after gelatinization. This process occurs at relatively lower temperatures and pressures. Over the entire cross section, such products have approximately the same structure of relatively small cells with walls of substantially uncross-linked natural polymers.
In this description, “baking” is understood to mean a method in which both gelatinization and cross-linking occur, at relatively high temperatures and/or pressure. As a result, the formation of gas arises relatively soon, so that bubbles are already formed prior to or during gelatinization. As a result of inter alia the high pressure adjacent strongly heated parts, the polymers cross-link quickly when using a mould or like baking form with a temperature at or above the baking temperature.
These baked products have a core with relatively large cells, enclosed between skin parts with relatively small cells. The cell walls have a relatively high density and the natural polymers included therein are cross-linked to a high extent, which means that they have entered into mutual chain bonds. Such a baked product therefore has a sandwich-like structure.
In the method known from WO 96/05254 and WO 95/20628, an open platen set is employed, wherein products are manufactured from a batter comprising natural polymers, inorganic filler, water and fibers. The batter is introduced into the bottom half of an open platen set, for instance a baking iron, after which the platen set is closed and heated, so that the batter is gelantinized. The products obtained are thin-walled and biodegradable, which is advantageous from an environmental point of view. The fibers added have the advantage that an increase of the product strength is thereby obtained relative to products wherein such fibers have not been added. Such products are for instance known from WO91/12186.
A disadvantage of the use of platen sets is that the batter is introduced into an open mould which is subsequently closed and, for instance, is passed through a continuous oven, where it is heated, for instance by gas burners. Energetically speaking, this is little efficient and moreover the temperature in the baking mould is not properly controllable and may vary strongly during the baking process, which is not beneficial to the quality of the products. Moreover, the products which are obtained according to this method are not particularly dimensionally stable and allow no or only very slight differences in wall thickness, because otherwise no homogenous structure can be obtained. A further disadvantage of this method is that the introduction of the batter and the removal of the product is very laborious and will often lead to failure in the production. Moreover, with this method no products can be manufactured that are non-withdrawable, so that the freedom of design is limited.
In a further method according to WO 96/05254 a powderlike mixture of natural polymers, inorganic filler, water and fibers is introduced into a conventional EPS mould by use of an airstream through said mould. The mixture is heated inside the mould by use of heated steam, in order to provide for gelatinization and foaming of the mixture for forming the desired article.
In this method the mixture is introduced into the mould relatively slowly, which results in relatively long production times and can only be used with moulds having relatively easy designs and short flow paths. Furthermore, the products resulting from this method have to be stabilized by conditioning them, resulting in even longer production cycles.
European patent application 0 118 240 discloses a method for manufacturing biodegradable medicament capsules and like products by injection-moulding from a starch composite. To that end, a starch mixture with a low water content is introduced into a closed space, in particular the hopper of an injection-moulding machine, where plasticization of the mixture is provided for at a suitable specific temperature, pressure and humidity. The temperature and pressure are increased to such an extent that the mixture is adjusted to above the verification point. Thereafter the plasticized mixture is forced into a cooled mould and maintained under pressure, until the or each product has cooled off sufficiently, whereafter the mould is opened and emptied.
The advantage of this known method is that dimensionally stable biodegradable products can be manufactured relatively fast. However, the possible dimensions of products that can be manufactured with this method are limited, owing to the flow path in the mould. In fact, the plasticized mass forced into the mould is cooled directly, which gives rise to solidification and prevents flow of the mass relatively soon after entry of the mould. Moreover, no cross-linking of the starch in the mass occurs, so that the products have relatively weak strength properties and exhibit relatively poor resistance to water and moist conditions in general. In a moist environment the products will take up a great deal of water and thereby become slack; conversely, in a dry environment moisture will evaporate from the products, so that they become hard and brittle. The products obtained with this method have a high density and have no foamy structure.
International patent application 95/04104 discloses a method for manufacturing foamed, biodegradable products from starch-containing raw materials, in which an amount of a starch is liquefied in a pre-stage by heating to a temperature far above the gelatinization temperature, whereafter an amount of water-saturated ramie fibers is admixed. This mixture is thereafter passed into or through the mould or converted to a dry granulate. Upon heating of the mixture, the water is to escape from the ramie fibers and to function as blowing agent. When using this known method, a substantially dry granulate of starch is to be strongly heated in the pre-stage, which granulates therefore cannot form a liquid batter. This known method has the disadvantage that the raw materials are to be supplied in relatively dry form and in the pre-stage are to be mixed with the moist fibers under simultaneous increase of the temperature in the tank, whereby the desired gelatinization occurs. To that end, the mixture must be heated, which is difficult to effect h
Arentsen Jan Hendrik Adolf
Huisman Jan Wietze
Kuhns Allan R.
Michaelson Peter L.
Michaelson & Wallce
Murray Jeremiah G.
Vertis B. V.
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