Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1995-05-09
2001-12-25
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S359000, C428S397000, C428S400000, C264S171100
Reexamination Certificate
active
06333108
ABSTRACT:
This invention relates to regenerated cellulosic filaments, particularly viscose filaments, which have a multi-limbed cross-section, to fibre comprising such filaments and to products formed therefrom.
One advantage of multi-limbed viscose filaments over conventional circular cross-sectional viscose filaments is their greater bulk, because the circumferential area of the multi-limbed filaments is larger than their actual cross-sectional area. For example, Japanese Patent Application Kokai 61-113812 describes a filament yarn consisting of X- or Y-shaped continuous viscose filaments that is used in textile applications where bulk is important, for example in pile weaves.
Another advantage of multi-limbed viscose filaments is their increased absorbency over conventional filaments. Thus, multi-limbed filaments in staple fibre form are particularly useful for absorbent products, for example tampons, towels and swabs. Absorbent viscose fibre is described in UK Patent 1 333 047 in which the filaments have a collapsed hollow structure and a multi-limbed cross-section. Although these filaments have a relatively high absorbency compared with conventional viscose filaments, they have the disadvantage that they are complicated to manufacture, as the filaments must be formed with an inflated, hollow structure and subsequently collapsed. The process also has the disadvantage that the collapse of the fibre is difficult to control sufficiently to ensure a uniform filament cross-section, and therefore the resulting filaments have irregular multi-limbed cross-sectional shapes. The filaments also have a relatively low tenacity.
The present invention provides a solid filament of regenerated cellulosic material having a decitex of less than 5.0 and a multi-limbed cross-section, each limb having a length-to-width aspect ratio of at least 2:1.
The length-to-width aspect ratio of the filament limbs is generally from 2:1 to 10:1, preferably from 2:1 to 7:1, and more preferably from 3:1 to 5:1. In general, the higher the aspect ratio, the higher the degree of free volume of the filaments. This gives a high degree of absorbency when the filaments are in staple fibre form, provided that the limbs are not so long and thin that they bend back upon themselves.
The filament according to the invention preferably has 3 or 4 limbs, although it may have more than 4 limbs if desired, and also preferably has a cross-sectional shape that is generally (i.e. largely) symmetrical about at least one axis, as in a Y-, X-, H- or T-shaped filament cross-section, although other shapes are also included within the scope of the invention. Preferably, the filament has a Y-shaped cross-section. The angle between the limbs varies according to the cross-sectional shape and can be, for example, from 5 to 180°, although, it is preferred that the filament cross-section is as regular as possible.
As mentioned above, the filament according to the invention has a low decitex of less than 5.0, a low decitex being advantageous for high absorbency products. Generally the decitex is between 0.5 and 5.0, but more preferably is between 1.5 and 4.0.
Filaments according to the invention are advantageously produced in the form of staple fibre, and the invention further provides such staple fibre. The combination of the multi-limbed cross-sectional shape and the low decitex gives filaments which in staple fibre form exhibit a high absorbency. Surprisingly, we have found that, although the filaments have a solid structure as opposed to a collapsed hollow structure characteristic of the fibre of UK Patent 1,333,047 mentioned above, the fibre of the invention has an absorbency which can match and in some product forms exceed the absorbency of the fibre of the said UK patent, even though its water imbibition is considerable lower. Usually the fibre according to the invention has a total free absorbency (TFA) of at least 24 grams of water per gram of the fibre (g/g) using the test as set out in British Pharmacopoeia 1980, Standard Methods (BP 1980, SDM.) XI.A, p.928. For instance, a TFA in the range up to 28 g/g can be obtained. In addition the fibre of the invention has high bulk, a cotton-like handle, and a tenacity approximately equivalent to conventional circular cross-sectional viscose filaments for a given viscose composition and decitex.
The staple fibre according to the invention preferably comprises multi-limbed filaments substantially all of which have substantially the same cross-sectional shape. This enables the fibre properties, such as absorbency and bulk, to be more readily controlled. However, if desired, the staple fibre may comprise a mixture of filaments of two or more different cross-sectional shapes provided that at least some of the filaments have a multi-limbed cross-section characteristic of the filaments of the invention.
Preferably, the filaments according to the invention are viscose, and they are conveniently spun from a standard viscose composition using standard viscose spinning conditions, with the exception that multi-limbed shaped extrusion holes in the spinnerette are substituted for the conventional circular shaped holes. As the filaments produced have a solid rather than a hollow structure, the disadvantages involved in producing hollow filaments are avoided.
The viscose composition used for spinning the filaments of the invention may be a commonly used viscose, typically having a cellulose content of 5 to 12% by weight and a caustic soda content of 4 to 10%, preferably 5 to 7%, by weight. Filaments may be spun over the full range of salt figures, although viscose having a salt figure of 4.0 to 12.0 is generally used. The ball-fall viscosity of the viscose can be from 15 to 180 seconds at 18° C., but is preferred to be from 45 to 55 seconds.
The filaments are spun through extrusion holes having a multi-limbed shape similar to the desired shape of the filaments. Typically the spinnerette is made from a gold-platinum alloy and the extrusion holes formed by conventional methods such as spark erosion or mechanical punching. To achieve filament limb aspect ratios of at least 2:1 together with a filament decitex of less than 5.0 the dimensions of the limbs of the extrusion holes are preferably between 50 &mgr;m and 250 &mgr;m long and between 20 &mgr;m and 40 &mgr;m wide.
The filaments are spun into a spin bath which can conveniently be of a standard spin bath composition for viscose spinning. Typically this composition includes by weight zero to 3%, preferably 0.5 to 2%, zinc sulphate, 6 to 20%, preferably 7 to 10%, sulphuric acid and 10 to 28%, preferably 20 to 26%, sodium sulphate. The spin bath temperature is generally between 50 and 60° C., although higher and lower temperatures may be used.
We have found that, for absorbent products such as tampons, even higher absorbencies can be achieved by adapting the process to give a slower rate of filament regeneration. The regeneration rate can be slowed down by altering one or more or the spinning conditions, for example by decreasing the acid level and/or increasing the sulphate level. Alternatively, or in addition, the viscose can be modified by a viscose modifier which is usually added to the viscose prior to spinning. Any of the commonly available viscose modifiers may be employed, examples being polyalcohols, soluble dithiocarbonates, soluble aliphatic and alicyclic amines, oxyethanols and quinoline. Polyglycols are preferred, especially PEG-1500 (polyethylene glycol where 1500 indicates the average molecular weight of the chain).
After spinning, the filaments are stretched, and then preferably cut into staple lengths, washed and dried using conventional techniques to give staple fibre.
The low decitex, multi-limbed filaments in staple fibre form can be used in a wide range of textile and other applications which take advantage of the fibre's high absorbency, bulk, cover and/or cotton-like handle. These applications include, for example, tampons, swabs and waddings, woven fabrics, knitted fabrics and non-woven fabrics. Non-woven fabrics can be produced by, for
Bartholomew Alan John
Wilkes Andrew George
Acordis Kelheim GmbH
Edwards N.
Howson and Howson
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