Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1998-10-20
2001-04-10
Edwards, Newton (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S364000
Reexamination Certificate
active
06214464
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to compositions tor obtaining regenerated cellulose articles, particularly fibres or films, to processes for obtaining these articles, and to the cellulose fibres themselves.
The production of viscose and rayon fibres by a wet process has been known for a very long time, in which the formation of the fibre in the coagulation bath is accomplished by coagulation resulting from the dehydrating action of a solution of electrolytes and extraction of the solvent (see “Cellulose Chemistry and its Applications”, Ed. T. P. Nevell and S. H. Zeronian, Ellis Horwood Limited, 1985, Chapter 18; and “Physics and Chemistry of Cellulose Fibers” by P. H. Hermans, Elsevier. 1949, Part 3, for example). This process employs a succession of complex steps which have characteristics which are significant as regards pollution.
Various processes have been described aimed at remedying this pollution disadvantage; these are summarised below.
It has been proposed that cellulose be dissolved directly in tertiary amine N-oxides, particularly N-methylmorpholine N-oxide, as described for example in the patents U.S. Pat. Nos. 4,416,698, 4,734,239, and DD 298 653. These solvents have the property of decomposing readily, forming peroxides which can lead to explosions and cause degradation of the cellulose. Moreover, the fibres resulting from this process exhibit a marked tendency to fibrillation.
It is known that cellulose fibres can be prepared by dissolving cellulose in a mixture of N,N-dimethylacetamicle (DMAC) and LiCl, as described for example in U.S. Pat. No. 4,302,252 and in European Patent Application EP-A-178 293, but this process necessitates prior activation of the cellulose.
Japanese Patent Applications JP-A-60/199 912 and JP-A-60/209 006 describe the production of fibres by employing solutions of cellulose in organic solvents containing halogenated tetraalkylammonium compounds. This process does not permit a concentration of 6% by weight of dissolved cellulose to be exceeded.
Patent Application WO-A-85/05115 and the equivalent patents EP-B-179822 and U.S. Pat. No. 4,839,113 describe the production of cellulose formate fibres from anisotropic solutions of cellulose formate in formic acid and 99% crystalline phosphoric acid, wherein these fibres can be regenerated. The process for obtaining fibres is non-polluting, and the regenerated cellulose fibres thus obtained are characterised by very high mechanical property values; the initial modulus and the tenacity in particular have high values. However, the fibres obtained in this manner have a very ordered structure and a particular morphology which reflect the anisotropic character of the starting solutions, which makes them unsuitable for textile use.
Patent Application WO-A-94/17136 describes regenerated cellulose fibres which are obtained from isotropic solutions of cellulose formate in suitable solvents. The process described in this patent application is non-polluting, and it is very flexible since it enables what are termed “technical” fibres (rayon type) as well as what are termed “textile” fibres (viscose type) to be obtained. The fibres obtained are characterised in particular by a less ordered structure and by a morphology which exhibits greater continuity in the transverse direction compared with the fibres described in WO-A-85/05115. However, the values of their elongation at break remain moderate in the majority of cases, which can be troublesome for certain applications, particularly for textile applications.
SUMMARY OF THE INVENTION
The particular object of the present invention is to remedy the aforementioned disadvantages or to limit these disadvantages by proposing a composition comprising a cellulose derivative, a process for obtaining regenerated cellulose articles, particularly fibres or films, from the said composition. and a regenerated cellulose fibre.
The composition according to the invention is characterised by the following points:
a) it contains cellulose formate and a system, termed “solvent system”, capable of dissolving the said formate:
b) at a temperature at least equal to a value T
f
, the composition is a solution;
at a temperature appreciably less than T
f
, the composition is an elastic, thermoreversible gel.
The process according to the invention for preparing a regenerated cellulose article is characterised by the following points:
a) the composition defined above is transformed into a liquid object having the shape of the desired article, at a temperature such that the composition is a solution;
b) the said liquid object is subjected to thermal quenching by rapid cooling of the solution in a medium of gelation, the temperature of which is appreciably less than T
f
, so as to obtain an elastic, thermoreversible gel;
c) the article in the form of the said gel is washed to remove the whole or the major part of the solvent system;
d) the cellulose of the article is regenerated;
e) the article which is thus regenerated is washed and dried.
The process according to the invention is used in particular in order to obtain a fibre or a film by transformation of the composition, particularly by extrusion, during step a) above, into a liquid object having the form of a fibre or a film.
The regenerated cellulose fibre according to the invention, which consists of at least one filament, is characterised in that it has the following properties:
a) the degree of substitution of the cellulose by formate groups, denoted by DS
f
and expressed in %, complies with the following relationship: 0<DS
f
<5;
b) the filament has a morphology in cross-section which is practically continuous from the periphery up to the core;
c) the filament does not fibrillate. or practically does not;
d) the fibre has an initial modulus at least equal to 500 cN/tex, an elongation at break at least equal to 5% and a tenacity at least equal to 15 cN/tex.
In particular, the fibre according to the invention is a monofilament fibre, the diameter of which is greater than 40 &mgr;m, and the titre of which is greater than 2.0 tex.
The present invention also relates to regenerated cellulose articles, particularly fibres and films, obtained by the process according to the invention, and to assemblies comprising at least one fibre and/or one film according to the invention, wherein such assemblies may for example be cables, for example monofilament cables, plied yarns, or multifilament fibres which are twisted on themselves, wherein such articles or assemblies may for example be hybrids or composites, namely comprising elements of a different nature, optionally not according to the present invention.
The articles and/or assemblies according to the invention may be used in particular in packaging (in the food packaging sector, for example), in the textile industry, and also as technical reenforcements, for example for reinforcing articles made of rubber or of plastics materials, particularly belts, hoses or tires, the present invention relating also to these reinforced articles.
The solvent system is preferably formed from at least one constituent (I) which is an aprotic solvent for cellulose formate and of at least one constituent (II) which is a non-solvent for cellulose formate, the amount of the said non-solvent, or of the totality of the said nonsolvents, being at least equal to 10% by weight and at most equal to 40% by weight of the total weight of the solvent system.
Advantageously:
the aprotic solvent constituent is selected from the group (I) comprising alkyl sulphoxides, lactams, acyclic amides, and cyclic derivatives of urea having a methyl substituent on the nitrogen, wherein the lactams and acyclic amides may be substituted or unsubstituted, and
the non-solvent constituent is selected from the group (II) comprising water and alcohols.
Examples of compounds of groups (I) include &ggr;-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulphoxide. tetramethylene sulphoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-formylmorpholine, N-formylpyrrolidine, &egr;-caprolactam, N-methylca
Esnault Philippe
Huston Rima
Meraldi Jean-Paul
BakerBotts L.L.P.
Edwards Newton
Michelin Recherche & Technique
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