GB1598430A - Coherent staple fibre webs - Google Patents

Description

(54) COHERENT STAPLE FIBRE WEBS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF a British Company do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to staple fibre webs having a high degree of longitudinal fibre orientation combined with sufficient lateral coherence to impart handleability.

Fibre webs, which are thin sheet like arrays of fibres, are the basic materials used for the production of non-woven fabrics. Arrays of both continuous filaments and staple fibres have been suggested as fibre webs and in particular carded fibre webs comprising a single web or a multiplicity of webs laid one on the other have commonly been used. Such carded fibre webs have only a limited degree of fibre orientation or parallelism and this introduces undesired limitations to the properties possible in a derived non-woven fabric. In US patents 3098265 and 3119152 methods of enhancing the degree of fibre orientation is a carded fibre web have been described wherein the carding machine in modified with additional roll or belt apparatus so as to doff the web while applying a small degree of drafting. While such webs have at least some enhanced fibre orientation they do not have this feature in combination with other desired properties such as a low but positive transverse coherence.

Accordingly the present invention p,rovides a staple fibre web having a fibre direction coherence of at least 1.0 g/cm per g/m-. a cross fibre direction coherence of less than 0.2 g/cm per g/m, preferably less than 0.1 g/cm per g/m2 and a tweezer separation distance of at least 5 cm.

The fibre coherence and tweezer distance properties together measure the fibre parallelism and handleability of a web and the three values are in some measure independent and in some measure interrelated. A web having a combination of the three values as hereinbefore specified is one having a very high order of fibre parallelism combined with sufficient coherence longitudinally and transversely to withstand the tensions occurring during subsequent processing as for example the laying up of several webs together and the bonding of a web or webs to form a useful non-woven fabric suitable for apparel or other textile purposes. Thus an oriented web of the desired degree of fibre parallelism should exhibit a low but measurable cross-fibre coherence, preferably more than 0.02 g/cm per git2, in order that the web has sufficient strength and integrity to be passed through subsequent processes without damage. Webs according to the invention which include a major proportion of synthetic thermoplastic fibres, may have the desired low cross fibre coherence associated with quite high values of fibre direction coherence but as the latter value increases such webs tend to become somewhat stiffer. It is therefore preferred that for these webs the fibre direction coherence does not exceed 50 g/cm per g/m2 or further preferably does not exceed 40 g/cm per git2. These upper values of fibre direction coherence may be exceeded in some cases since some of the stiffness of a web which passes through to a non-woven fabric made therefrom may be removed or reduced by mechanical or hot liquid treatments such as fulling, washing or dyeing. However if the stiffness is undesired in the greige state non-woven fabric then the foregoing upper limits of fibre direction coherence in the web should be adhered to.

As described in detail hereinafter the fibre direction coherence is measured using a test length of web greater than the mean fibre length and thus this property is influenced by the presence of any bonds between fibres resisting slippage of one fibre over the other. Such interfibre bonding may be present or deliberately introduced during the production of a coherent web, particularly if the web includes a large proportion of thermoplastic fibres and thermal treatments are included in the web making process. Undue stiffening in the web and a non-woven fabric is preferably avoided as this may interfere with the properties of the derived fabric or require additional fabric treatment.

The tweezer separation distance, the measurement of which is described hereinafter, is another measure of coherence particularly cross-fibre coherence and for webs of maximal parallelism and minimal but adequate cross fibre direction coherence, values of tweezer separation distance may be quite high. However the values of tweezer separation distance and fibre and cross-fibre coherence are sufficiently inter-related as to set an upper limit for tweezer separation distance. As this value increases one or both of the coherency values tend to decrease and eventually would reach an unacceptable level.

Web coherence is conveniently measured using a flexible tensile test machine such as the Instron machine. For both fibre and cross-fibre direction measurements a sample width of 2.5 cm equal to the width of the machine clamping jaws which are operated at a cross-head speed of 20 cm/min together with a chart speed of 10 cm/min. For fibre direction coherence samples having a length 1.5 times the nominal or mean fibre length plus the clamping length are cut and weighed carefully so as not to disturb the delicate fibre structure and then mounted in the test machine. For cross-fibre direction coherence measurements a test sample length of 1 cm (plus clamping length) is used and for both measurements the coherence is calculated from the measured breaking load as follows; B LW 1 Coherence = - x - x- X- g/cm per g/m2 2.5 100 100 M where B is the measured breaking load in g L is the sample length in cm W is the sample width in cm, and M is the sample weight in g For measurement of tweezer separation distance stainless steel tweezers are selected measuring 13 cm end to end and 11 cm from the hinge point to the tweezer tips, the hinge resilience being such that there is 1 cm separation of the tips from beginning to end of a test.

One limb of the tweezers is attached rigidly to the measuring arm of a rotary tensiometer for example of the "Zivy" type having a full scale deflection of 30g. To effect a measurement the tweezers tips (sharpened to fine points if necessary) are inserted in the closed position into the web sample to the specified depth, the sample having been suitably supported in a horizontal plane under slight tension. The tips are then allowed to open to 1 cm separation in the cross fibre direction and the gauge moved horizontally and parallel to the fibre direction along the web until the initial zero reading rises to 20 g. The distance moved in cm between these points is the tweezer separation distance which is approximately independent of the web weight at least for values in the range 40 + 10 g/m2.

For webs of the invention weighing 10-100 g/m2 the product of tweezer separation distance and web weight should be at least 200 cm git2.

A useful visual assessment of web orientation may be carried out using a pin-hole camera method. A strong source of illumination as for example a mercury vapour lamp and appropriate filter are used to illuminate a pin hole in an opaque screen which is parallel to and spaced 45 cm from the web sample which is positioned close enough to a camera preferably a camera of the Polaroid Land type giving direct prints, so that a sharp image of the pin hole as diffracted by the web is projected onto the film.

Fabrics according to this invention are characterised by a diffraction pattern showing two opposed lobes. The attached figures illustrate diffraction patterns of prior art webs and webs according to this invention wherein.

Figure 1 is the diffraction pattern of a normal card web of polyester fibres.

Figure 2 is the diffraction pattern of a continuous polyester filament web produced as described in UK patent specification 1001813.

Figure 3 is the diffraction pattern of a web according to the invention made from bicomponent polyester fibres having an eccentric sheath/core configuration and Figure 4 is the diffraction pattern of a web also according to the invention of bicomponent polyester fibres in a side by side configuration.

Referring to Figure 1 it is seen that a substantially uniform diffraction pattern is produced exhibiting no lobes.

In Figure 2 the diffraction pattern exhibits four substantially uniformly spaced lobes in conformity with a high degree of parallelism between the continuous filaments.

In Figure 3 and Figure 4 bilobate patterns result from the high fibre parallelism and small cross-fibre orientation characteristic of webs according to this invention proposed as hereinafter described in Examples 3 and 2 respectively. The pattern in Figure 3 is sharper and narrower than that of Figure 4, and this is believed to be due to the presence of a finer and tighter helical crimp in the Figure 4 web prepared from side-by-side bicomponent fibres which may also influence the relative coherency values of these two webs.

Highly ordered webs according to this invention may be produced by any method wherein the requisite high degree of fibre parallelism together with the low cross-fibre orientation or coherence is induced in a staple fibre web. A very effective method for the production of highly ordered webs having the desired properties from staple fibre slivers consisting of or including some thermoplastic crimpable fibres is a process wherein a plurality of staple fibre slivers are spread and merged into a thin web by passage between a series of fluted drafting roller pairs and the web is then subjected to a heat treatment which induces crimping and the formation of a coherent highly ordered web.

The fibres of a web may include natural or artificial fibres or synthetic fibres spun from linear organic polymeric materials, as for example, melt spinnable polyesters, polyamides and copolymers of these classes of organic linear polymers. It is preferred that at least some of the fibres in a web should be synthetic thermoplastic fibres since these may be readily produced in both staple fibre and potentially crimpable forms, as for example bicomponent fibres in which at least part of one component present at the surface of the fibres is of lower softening or melting point and different shrinkage propensity than the other component.

Such bicomponent fibres are commonly of the side-by-side or sheath and core configuration.

The invention is illustrated in the following examples: EXAMPLE 1 A quantity of polyethylene terephthalate fibres (3.3 decitex 90 mm length) was assembled into a sliver weighing 2 g/metre. Seven of such slivers were introduced side-by-side at a spacing of 1 cm into a drafting frame having five successive pairs of wide drafting rolls which spread and merge the slivers into a web of substantially parallel fibres at a total draft of 4.0 the web being overfed to the last stage at a draft of 0.73 and being treated with a stream of hot air at a temperature of 220"C between the two pairs of rolls in this last stage. The resulting highly ordered coherent web weighs 40 g/m2 and has the following coherency values.

Fibre direction coherence 1.3 g/cm per g/m2 Cross fibre direction coherence 0.04 g/cm per g/m2 Tweezer separation distance 40 cm The web exhibits a bilobate diffraction pattern.

EXAMPLE 2 A highly ordered coherent web was prepared as in Example 1 using 9 slivers weighing 1.9 g/metre composed of 3.3 decitex 49 mm staple bicomponent fibres with the components arranged side-by-side one being polyethylene terephthalate and the other a copolymer of 15 mole percent ethylene isophthalate and 85 mole percent ethylene terephthalate. The overall draft applied was 3.75, that of the heating stage (145"C) being 0.60. The resulting web weighing 40 g/m2 had the following coherency values.

Fibre direction coherence 3.0 g/cm per g/m2 Cross-fibre direction coherence 0.06 g/cm per g/m2 Tweezer separation distance 7.5 cm The web exhibits a diffraction pattern as in Figure 4.

EXAMPLE 3 A highly ordered coherent web was prepared as in Example 1 using 15 slivers weighing 2 gimetre composed of 3.3 decitex 100 mm staple bicomponent fibres with the components arranged in eccentric sheath/core fashion the core being polyethylene terephthalate and the sheath a copolymer fo 15 mole percent ethylene isophthalate with 85 mole percent ethylene terephthalate having a lower melting point than the homopolymer. The overall draft applied was 3.96. that of the heating stage (180 ) being 0.67. In the resulting web as in that of Example 2 some interfibre bonding was present, the web weighing 40 g/m2 and having the following coherency values.

Fibre direction coherence 27 g/cm per g/m2 Cross fibre direction coherence 0.04 g/cm per g/m2 Tweezer separation distance 19 cm The web exhibits a diffraction pattern as in Figure 3.

COMPARA TIVE EXAMPLES A AND B A normal carded web (Web A) prepared from the eccentric sheath/core bicomponent fibres as used in Example 3 and a web (Web B) prepared according to the method of UK patent specification 1001813 from polyethylene terephthalate continuous filament tow were submitted to the foregoing coherency tests with the following results.

WEB A WEBB Fibre direction coherence 0.2 -* g/cm per g/m2 Cross fibre direction coherence 2.1 0.25 g/cm per g/m2 Tweezer separation distance 3 3.5 cm * Not measured because web of continuous filaments.

Both these webs exhibit an undesirably high cross fibre coherence and low-separation distance. In addition Web A exhibits a very low fibre direction coherence.

WHAT WE CLAIM IS: 1. A staple fibre web having a fibre direction coherence of at least 1.0 g/cm per g/m2, a cross fibre direction coherence of less than 0.2 g/cm per g/m2 and a tweezer separation distance of at least 5 cm.

2. A web according to claim 1 wherein the cross fibre direction coherence is less than 0.1 g/m per g/cm2.

3. A web according to claim 1 or claim 2 wherein the cross fibre direction coherence is more than 0.02 g/cm per g/m2.

4. A web according to any one of claims 1-3 wherein the product of tweezer separation distance in centimetres and the web weight in g/m2 is at least 200.

5. A web according to any one of the preceding claims wherein the pin-hole diffraction pattern measured as hereinbefore described is bilobate.

6. A web according to any one of claims 1-5 comprising a major proportion of synthetic thermoplastic fibres.

7. A web according to claim 6 wherein at least some of the synthetic fibres are side-by-side or sheath/core bicomponent fibres.

8. A web according,to claim 6 or claim 7 wherein the fibre direction coherence does not exceed 50 g/cm per g/m .

9. A web according to claim 6 or claim 7 wherein the fibre direction coherence does not exceed 40 g/cm per g/m 10. A staple fibre web substantially as hereinbefore described with reference to and as illustrated in Examples 1-3.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   COMPARA TIVE EXAMPLES A AND B A normal carded web (Web A) prepared from the eccentric sheath/core bicomponent fibres as used in Example 3 and a web (Web B) prepared according to the method of UK patent specification 1001813 from polyethylene terephthalate continuous filament tow were submitted to the foregoing coherency tests with the following results.

   WEB A WEBB Fibre direction coherence 0.2 -* g/cm per g/m2 Cross fibre direction coherence 2.1 0.25 g/cm per g/m2 Tweezer separation distance 3 3.5 cm * Not measured because web of continuous filaments.

   Both these webs exhibit an undesirably high cross fibre coherence and low-separation distance. In addition Web A exhibits a very low fibre direction coherence.

   WHAT WE CLAIM IS: 1. A staple fibre web having a fibre direction coherence of at least 1.0 g/cm per g/m2, a cross fibre direction coherence of less than 0.2 g/cm per g/m2 and a tweezer separation distance of at least 5 cm.
2. 2. A web according to claim 1 wherein the cross fibre direction coherence is less than 0.1 g/m per g/cm2.
3. 3. A web according to claim 1 or claim 2 wherein the cross fibre direction coherence is more than 0.02 g/cm per g/m2.
4. 4. A web according to any one of claims 1-3 wherein the product of tweezer separation distance in centimetres and the web weight in g/m2 is at least 200.
5. 5. A web according to any one of the preceding claims wherein the pin-hole diffraction pattern measured as hereinbefore described is bilobate.
6. 6. A web according to any one of claims 1-5 comprising a major proportion of synthetic thermoplastic fibres.
7. 7. A web according to claim 6 wherein at least some of the synthetic fibres are side-by-side or sheath/core bicomponent fibres.
8. 8. A web according,to claim 6 or claim 7 wherein the fibre direction coherence does not exceed 50 g/cm per g/m .
9. 9. A web according to claim 6 or claim 7 wherein the fibre direction coherence does not exceed 40 g/cm per g/m
10. 10. A staple fibre web substantially as hereinbefore described with reference to and as illustrated in Examples 1-3.