Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ
Reexamination Certificate
1999-09-10
2001-07-10
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
C264S049000, C264S171100, C264S187000, C264S203000, C264S211160, C264S172130
Reexamination Certificate
active
06258304
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to modified lyocell fibre and film and to a process for the preparation of modified lyocell fibre or film. “Fibre” is used in this specification to include continuous filament yarns, tows of yarn for cutting into staple fibre and also staple Fibre formed from such a tow.
BACKGROUND ART
Lyocell fibre and film is produced by dissolving cellulose in a suitable solvent, for example a tertiary amine N-oxide such as N-methyl morpholine oxide mixed with water. A suitable method of manufacture is described in U.S. Pat. No. 4,416,698. The solution of cellulose in the amine oxide solvent, which is solid at ambient temperature, is extruded at a temperature of 95-1250° C. from a spinneret or film die through an air gap into a precipitation bath of water or dilute aqueous amine oxide, and the amine oxide solvent leaches into the bath, producing cellulose fibre or film.
JP-A-8-170224 discloses a biconstituent fibre of the islands-in-the-sea type in which the continuous “sea” component is a cellulose-type polymer spun from an organic solvent system and the “islands” are composed of a polymer dyeable by a disperse dye and are 0.01-34 &mgr;m in size and form 2-45% by weight of the fibre. The disperse dyeable polymer is for example a polyester such as polyethylene terephthalate, sulphonic acid-modified polyethylene terephthalate or polybutylene terephthalate.
GE-A-2121069 discloses cellulose-based (viscose rayon) fibres for the Production of nonwovens containing as mineral fillers barium sulphate, talcum, muskovite, or a mixture thereof, in an amount of from 15 to 60%, preferably 40 to 50%, of the total fibre mass, and, if desired, additionally hydrophobic, polymer or oligomer substances, such as polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyester, polytetrafluoroethylene or waxes, in an amount of from 1 to 60%, preferably 25 to 50%, of the total fibre mass. GB-A-2008126 discloses the use of polystyrene as a delustrant for viscose rayon fibres.
DISCLOSURE OF THE INVENTION
A process according to the in ention for the preparation of lyocell fibre or film by extruding a solution of cellulose in amine oxide through a spinneret or film die at elevated temperature via an air gas into an aqueous precipitation bath is characterised in that 0.1-60 wt % based on cellulose of a thermoplastic low-melting polymer is incorporated into the cellulose solution, the low-melting polymer having a melting point above 25° C. but below the extrusion temperature of the cellulose solution.
In the process of the invention, the thermoplastic low-melting polymer is in a melted state in the cellulose solution at the extrusion temperature and the melted polymer is aligned in the axial direction of the fibre or film as the solution is extruded. When fibre is extruded through a spinneret, the low-melting polymer generally forms particles or domains of aspect ratio at least 1.5 and usually at least 2 in the fiber.
The thermoplastic low-melting polymer should generally be sufficiently compatible with the cellulose solution that the polymer when molten does not agglomerate as a separate phase from the cellulose solution, but is is preferably not soluble either in amine oxide or in the solution of cellulose. One type of preferred low-melting polymer is a polyester.
In general, we have found that the presence of carboxylic acid groups in the low-melting polymer increases its compatibility with the cellulose solution, giving more thorough mixing of the cellulose and the low-melting polymer. For most uses, the polymer preferably has an acid value of at least 10, up to for example 50 or 100 or even 150. We also believe that a branched polymer structure may be advantageous. The melting point of the low-melting polymer is preferably at least 35° C. and up to 125° C., most preferably in the range 50 to 100° C., as measured by differential thermal analysis. The Tg of the polymer is preferably higher than 30° C. Examples of polyesters of this type having the required low melting point are formed from a mixture of aromatic dicarboxylic acids selected from isophthalic acid, terephthalic acid, and phthalic acid or anhydride, optionally with an aliphatic dicarboxylic acid such as adipic, succinic or sebacic acid, and one or more aliphatic diols such as neopentyl glycol, ethylene glycol, propylene glycol, propane-1,3-diol, butane-1,4-diol, butylene glycol or diethylene glycol. Branching can be introduced by a trifunctional reagent, for example trimellitic acid or anhydride or trimethylolprocane, glycerol or pentaerythritol. The required acid value can be obtained by using an appropriate excess of carboxylic acid-functional reagent. Such polyesters are sold for use in thermosetting powder coatings, for example under the Trade Marks “Alftalat 03258”, “Uralac P2980” or “Grilesta V76-12”.
Alternative thermoplastic low-melting polymers are polyamides, for example polyamides formed from fatty acid dimers and aliphatic diamines or the copolyamide sold under the Trade Mark “Griltex”, or olefin copolymers, for example ethylene/vinyl acetate or ethylene/butylene/butyl acrylate copolymers, preferably containing a small amount of acrylic acid comonomer to give the preferred acid value.
Thus, according to another aspect of the invention lyocell fibre is characterised in that the fibre contains elongated domains of polyester, polyamide or an olefin copolymer, the domains having an aspect ratio of at least 1.5 and being aligned substantially parallel to the axis of the fibre.
The concentration of cellulose in the solution to be extruded (otherwise known as the spinning solution) is generally 12 to 20% by weight, preferably at least 14 or 15% up to 17 or 18% by weight. We have found that the thermoplastic low-melting polymer tends to reduce the viscosity and shear resistance of the spinning solution, as evidenced by reduction in back-pressure during spinning, so that the concentration of cellulose can be increased compared to extrusion (spinning) without added polymer. The spinning solution preferably contains water, usually in the range 5-50% by weight, with the remainder, generally 65-83% by weight, being amine oxide. The extrusion temperature is generally 95 to 125° C.
The low-melting polymer can be added to the cellulose solution at any of various points during its preparation. The polymer can for example be premixed with cellulose pulp, the pulp then being mixed with amine oxide and water to form the swirling solution. The polymer can alternatively be added, preferably in molten form, to a preformed cellulose solution. In a further alternative, a relatively high proportion of low-melting polymer is premixed wish a preformed cellulose solution, for example forming 10 to 50% by weight of the mixture. The pulp can then be used as a masterbatch to add the low-melting polymer to cellulose solution at the required level.
The cellulose solution containing a low-melting polymer can be extruded to form fibres using the same spinneret, or to form film using the same extrusion die, at the same temperature as is conventionally used for forming lyocell fibre or film.
The domains or particles of low-melting polymer are distributed uniformly throughout the fibre or film as a separate phase. When a carboxy-functional polyester is included as low-melting polymer in a lyocell spinning solution, for example, the polyester phase appears as particles or domains of length 70 to 1000 nanometres (nm) and diameter 30 to 400 nm. Polyesters of higher carboxyl content tend to produce fibres with relatively small polyester domains whereas polyesters of low carboxyl content tend to produce fibres having relatively large polyester domains. The polyester phase cannot usually be seen by optical microscopy but can be seen by electron microscopy at x9000 enlargement. Fibre inspection by electron microscope in cross-section shows apparently spherical particles but a longitudinal view shows that the polyester domains are elliptical. The polyester domains generally have an aspect ratio (ratio of length to diameter) of at
Howson & Howson
Tencel Limited
Tentoni Leo B.
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