Stock material or miscellaneous articles – Hollow or container type article – Flexible food casing
Reexamination Certificate
2000-11-21
2004-11-23
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Flexible food casing
C138S118100, C428S035600, C428S036900, C428S346000, C452S030000, C452S035000
Reexamination Certificate
active
06821588
ABSTRACT:
The invention relates to a film containing thermoplastic starch and/or thermoplastic starch derivatives and is particularly suitable as food casing. In addition the invention relates to a process for producing this food casing and its use as packaging film, in particular as sausage casing.
Most sausage casings consist of animal gut, but also from fiber-reinforced regenerated cellulose, collagen or synthetic polymers. Although cellulose and collagen are of natural origin, the production of such sausage casings is carried out in complex and environmentally polluting processes. Casings made of other material, for example from protein-coated or acrylate-coated fabric, in contrast, are of only small importance.
Of the known casings, those made from cellulose hydrate have the broadest spectrum of applications. However, for some uses they have an excessive permeability to water vapor and/or oxygen. Collagen casings have a lower permeability, but are too labile in contrast. The casings made of synthetic polymers are unsuitable for producing long-keeping sausage. Although they may be produced inexpensively and simply, for example by extrusion, they are however not biodegradable, in contrast to the cellulose hydrate or collagen casings.
Although the sausage casing which is described in EP-A 0 709 030 and is produced by extrusion of thermoplastic starch is biodegradable, it still has deficiencies. It is, in particular, not sufficiently cooking-resistant and has a tendency to embrittlement after water treatment or due to plasticizer loss.
Finally, single-layer or multilayer tubular biaxially oriented food casings are also known which consist of a thermoplastic biodegradable polymer or
comprise at least one layer thereof (EP-A 0 820 698). They are produced by an extrusion process. Thermoplastic biodegradable polymers which can be used in this process are aliphatic or partially aromatic polyesters, thermoplastic aliphatic polyester urethanes, aliphatic-aromatic polyester carbonates and in particular aliphatic polyester amides. Tubular casings made of these polymers, in particular polyester urethanes, however, have a poor caliber constancy, which leads to problems during processing.
The object was therefore to develop a food casing which may be made from natural renewable raw materials in a simple and environmentally conserving manner, as far as possible by an extrusion process, and which is at the same time compostable or at least biodegradable. The casing is to be sufficiently permeable and usable for virtually all sausage types, that is to say for producing cooked-meat sausages and scalded-immersion sausages and for raw sausages.
The object is achieved by a mixture (blend) of a) thermoplastic starch and/or a thermoplastic starch derivative (both termed “TPS” hereinafter) and b) at least one polyester urethane.
The present application thus relates to a film which comprises thermoplastic starch and/or a thermoplastic starch derivative and which is produced from a thermoplastic mixture which comprises a) thermoplastic starch and/or a thermoplastic starch derivative and b) at least one polyester urethane, in which the weight ratio a):b) is in the range from 75:25 to 5:95, preferably from 30:70 to 60:40, and which has an area-based drawing ratio of from 2 to 70, preferably from 4 to 40, particularly preferably from 6 to 20. If appropriate, the film can also comprise native starch. For fine adjustment of the stress/strain pattern, organic or inorganic finely dispersed fillers can also be added to the blend. In the polymer blend, the polyester urethane forms the continuous matrix in which the thermoplastic starch or the thermoplastic starch derivative is embedded in microdisperse distribution in the form of discrete particles having a diameter d
p
of from 0.05 to 30 &mgr;m, preferably between 0.1 and 3.0 &mgr;m. In the drawn state, the film preferably has a thickness of from 30 to 120 &mgr;m, particularly preferably from 50 to 80 &mgr;m. It can be used as packaging film, in particular for foods, especially as seamless, tubular sausage casing.
The thermoplastic starch derivative is preferably a starch ester, as is described in detail in DE-A 195 15 477. The acid component in the ester is generally a (C
2
-C
10
)alkanoic acid which is preferably unbranched or has only a low degree of branching. A particularly preferred and inexpensive starch alkanoate is starch acetate having a degree of substitution of less than 3, in particular from 1.5 to 2.4. In contrast to starch itself, starch esters, such as starch acetate, are already thermoplastic as such and do not need to be plasticized first. Starch esters having a relatively long alkyl chain, for example starch hexanoates, starch octanoates or starch decanoates, cause a change in suppleness and toughness, and also in the permeation of the food casings. By combining various starch esters, casings can be produced having very specific properties. Starch ethers and thermoplastic starch derivatives which have cationic quatemary side groups having hydrophobic (C
2
-C
18
)alkyl groups, preferably (C
2
-C
12
)alkyl groups, are also suitable. Finally, anionic starch derivatives can also be used.
It has been found that casings which consist only of thermoplastic starch and/or thermoplastic starch derivatives do not yet have the desired extent of extensibility, strength, toughness, suppleness, but especially stability to hot or boiling water. Casings made of pure polyester urethane also do not have the desired properties.
Specifically they lack strength, temperature stability and caliber constancy. They cannot then be significantly improved even if other low molecular substances such as lubricants, plasticizers and fillers are added to the thermoplastic starch or the thermoplastic starch derivative.
Surprisingly, it has been found that a significant improvement occurs when the thermoplastic starch or the starch derivative is mixed with thermoplastic polyester urethanes.
The thermoplastic polyester urethane (also termed “TPU” hereinafter) consists of hard polyurethane and soft polyester segments, the segments being arranged in alternating sequence. “Soft” denotes segments having a glass transition temperature (T
g
) of −20° C. or below, in contrast “hard” denotes those having T
g
of +30° C. or above. The polyester urethane can be of aliphatic or aromatic nature. The proportion of polyurethane segments in the thermoplastic polyester urethane is in this case from 10 to 90% by weight, preferably from 20 to 50% by weight, in each case based on the total weight of the polyester urethane. They generally consist of diisocyanate and diol unites. The diisocyanate unites can be aliphatic, cycloaliphatic or aromatic. Examples of aliphatic diisocyanates are butane 1,4-diisocyanate and hexane 1,6-diisocyanate. Isophorone diisocyanate (=3-isocyanatomethyl-3,5,5-trimethylcyclohexane isocyanate) represents a cycloaliphatic diisocyanate. Toluene 2,4-diisocyante and 2,6-diisocyanate, diphenylmethane 2,2′-diisocyanatc, 2,4′-diisocyante, 2,6′-diisocyanate and 4,4′-diisocyanate, and naphthalene 1,5-diisocyanate are preferred aromatic diisocyanates.
The polyester segments generally have a mean molar mass M
w
of from 500 to 10,000 g/mol, preferably from 1000 to 4000 g/mol. They preferably consist of units of dihydric or polyhydric alcohols and units of dibasic or polybasic carboxylic acids. They may be prepared from said starting materials by condensation polymerization in the presence of catalysts such as titanium butoxide (=orthotitanic acid tetrabutyl ester). However, usually, the polyester segments consist of diol and dicarboxylic acid units. In the condensation reaction, instead of the free acids, obviously also corresponding acid derivatives, such as carbonyl halides (in particular carbonyl chlorides), carboxylic anhydrides or (C
1
-C
4
)alkyl esters of carboxylic acids can be used. The diols or polyols generally have an aliphatic or cycloaliphatic backbone. Preferred diols for preparing the ester segments are ethane-1,2-diol (
Ahlers Michael
Fritz Hans-Gerhard
Grolig Gerhard
Hammer Klaus-Dieter
Seidenstuecker Thomas
Connolly Bove & Lodge & Hutz LLP
Kalle GmbH & Co. KG
Nolan Sandra M.
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