GB2214937A - Glass fibre yarn - Google Patents

Abstract

A substantially untwisted glass fibre yarn containing at least one metal filament is made by the steps of assembling together in side-by-side relation glass fibre filaments and at least one metal filament followed by subjecting the assembly to an air jet treatment in the absence of positive mechanical overfeed. The air jet treatment preferably comprises passing the assembled filaments through a confined passageway at from 150 to 300 metres/minute, whilst air is introduced into the passageway at from 0.5 to 1.5 cubic metres/minute under a pressure of from 400 to 600 KN/metre<2>. The yarn may be used as reinforcement in a puttrusion process or can be woven to give a fabric for eg flak-jackets or flame-resistant use.

Description

Improvements in and relating to glass fibre products This invention relates to substantially untwisted glass fibre yarns particularly but more exclusively useful in pultrusion processess, where they form the major (if not only) reinforcement for a resin matrix, for example as used in the manufacture of reinforced plastics such as fibre optics cables.

Specification EP-A-0045560 discloses a method of producing a coherent untwisted continuous multifilament glass fibre roving, the method being characterised by the steps of withdrawing individual continuous multifilament glass fibre strands from each of a plurality of creel packages, assembling them side-by-side to form a single roving, passing said roving at a rate of from 150 to 300 metres/minute through an air treatment zone constituted by a confined passageway into which air is introduced at 0.5 to 1.5 cubic metres/minute, under a pressure of from 400 to 600 KN/metre2 without positive overfeed, and thereafter winding the treated roving into a package.

GB-B-2123446 discloses that a substantially untwisted glass fibre yarn may be made by the step of assembling together in side-by-side relation a core strand of relatively coarse filaments of diameter 13 to 24 microns and a surface strand of relatively fine filaments of diameter 6 to 10 microns, followed by subjecting the assembly to an air jet treatment in the absence of positive mechanical overfeed.

The air jet treatment preferred is that of EP-A-0045560 in which the assembled strand is passed at from 150 to 300 metres/minute through an air treatment zone constituted by a confined passageway into which air is introduced at 0.5 to 1.5 cubic metres/minute, under a 2 pressure of from 400 to 600 KN/metre2, According to this invention, some of the glass fibre in either of the prdcess yarns just described is replaced by at least one metal filament. This may be in conjunction with the (optional) replacement of some of the glass fibres by man-made organic fibre. Replacement is preferably carried out prior to the side-by-side assembly stage, by substitution of at least one metal filament for some of the glass fibres. In the second process, this may be in either or both of the initial strands.

If man-made fibres are also present, particularly preferred fibres are polyvinyl alcohol fibres, although polyamide fibres, polyester fibres, aramid fibres and viscose rayon fibres may be used. Blends of these man-made fibres are also possible.

Particularly preferred metal filaments have diameters in the range 5 to 200 microns. The amount of the metal filament component is preferably below about 20% by weight, amounts of from less than about 1% to say 10% by weight being preferred for some end uses.

The absence of mechanical overfeed means that unlike other well-known prior art processes for combining rilamentary strands - by twisting, there is no mechanically-induced overfeed by way of feed rollers operating with different surface speeds. This makes it possible to avoid using the multiple changes of direction, including impingement on baffles immediately following the texturing jet outlet, which are characteristic of conventional texturing processes/ apparatus. It has been found that these changes of direction effectively prevent the introduction of metal filaments in such conventional processes.

Instead, it is still preferred that for the purposes of this present invention the relative tensions of the glass filaments together with that of the metal filament or filaments should be adjusted so that a degree of self-induced overfeed takes place solely under the influence of the air jet treatment.

Where the optional man-made fibres are included, the interpenetration of these man-made filaments into the glass fibre strand produces a coherent composite strand without spinning and/or twisting, whilst the metal filament/filaments increase the longitudinal strength of the product. Furthermore, the bulk generated in the glass fibre component by the air jet treatment is retained by this interpenetration, even on stretching the product. This is because the metal filament/ filaments resist practically all of the stretching force. Metal filaments of the preferred diameter range are relatively unaffected by air jet bulking treatments.

The products may have a linear density in the range of from 300 to in excess of 9600 tex, the ratio of metal to glass filaments being selected together with the metal filament diameter and the optional man-made fibre content to give satisfactory bulking, allied to high longitudinal strength. The relative proportions of the metal filament to glass fibre can be anywhere in the range from about 20% to about 80% by weight. The process therefore has exceptional flexibility.

The tension in the glass filaments may be adjusted by regulating the tension of the or each strand as it is withdrawn from a creel and allowed to go forward to the air jet treatment. Likewise, the metal filament(s) are introduced under controlled tension, prior to the air jet treatment. The air jet is preferably a bulking or texturing jet of the kind disclosed in EP-A-0045560. The driven packages and/or differential rates of feed used for conventional core-effect yarns are not needed. Nor is there any need for baffles, the use of which is in any event undesirable.

It has been found that the presence of even a very minor proportion of metal filament in the strand results in a notable increase in tensile strength, coupled with reduced elongation at break. If accompanied by the inclusion of organic fibres such as polyvinyl alcohol fibres, there is also a dramatic increase in impact strength when used as a reinforcement for a synthetic resin matrix, as for example in a pultruded product, such as a fibre optics cable.

The relative proportions (by weight) of glass fibre to metal filament may be selected as indicated above, up to, say, 20% of metal filament referred to the total product weight. Where a yarn of the kind disclosed in GB-A-2123446 are being manufactured, and the core strand alone contains the metal filaments, optionally in admixture with a man-made fibre component, the metal filaments may be from less than 1% by weight of the core, up to as much as 10% by weight of the core.

However, the best results in terms of both relative cost and enhanced properties appear to be in the range of 1-10% by weight of the core strand. Even at relatively low values, using drawn metal filament of 6-150 micron diameter, the improvement in tensile strength is substantial, possibly over 50% greater than the all-glass fibre product. There are however other advantages accruing from the invention, the most notable being the creation of an electrically-conductive strand.

It has been found that yarns made by the present method have exceptional utility in the pultrusion process. It is thought that this is due to the fact that the bulkiness of the glass filaments is not pulled out during the pultrusion process. The glass filaments are available to provide reinforcement in directions transverse to the axis of the metal filament. The inclusion of at least one metal filament increases the axial strength, as well as conferring electrical conductivity. Hitherto, the resultant combination of properties has been generally unobtainable in pultrusion reinforcement yarns.

A typical example of a process according to the invention is as follows. Four 154 tex wound packages of 10 micron diameter glass fibre were loaded onto a standard creel together with one package of 130 micron diameter copper filament, (equivalent to 118 tex). The five package ends were withdrawn as a parallel bundle and inserted into an air jet, to produce a 734 tex product, (allowing for the bulk.) The jet was constructed and operated in accordance with EP-A-45560.

The winding speed was 200-300 metres/minute, the air jet pressure being in the range 60-100 p.s.i.g.

The end product contained about 19% by weight of copper filament; its breaking load was in excess of 600N compared with 40 for all-glass fibre equivalent, with an elongation at break of only 2%, compared with 4% for all-glass.

The same technique was used to make a 1200 tex yarn also containing about 25% of polyvinyl alcohol fibres. The product had a breaking load of well over 500N, compared with 300N for the all-glass equivalant. The elongation at break was also 2%.

When used as a pultrusion process reinforcement, over 100% improvement in tensile strength was obtained, accompanied by excellent impact strength.

The benefits of the invention are not confined to resin reinforcement. The process is relatively inexpensive and therefore provides a cost-effective way of combining glass fibres with both metal filaments and say, aramid fibres, without the need for twisting/doubling operations and the relatively low throughput associated with the latter.

This means that glass-based, metal filament reinforced blended weaving grade yarns can be made economically, thereby facilitating the production of specialist fabrics for safety garments such flak jackets where impact strength is essential. Likewise, flame resistant fabrics can be produced without the traditional (and expensive) steps of twisting/doubling yarns to form the desired blend.

Blends of the prefe'rred man-made organic fibres can be used, as previously noted and it will be apparent that blending can also be carried out within the process of the invention, thereby, eliminating yet another traditional processing operation of twisting/doubling.

Claims (14)

1. A process for the manufacture of a blended yarn comprising substantially untwisted glass fibres and at least one metal filament, optionally also containing man-made organic fibres, comprising the steps of assembling together in side-by-side relation glass fibre filaments and at least one metal filament followed by subjecting the assembly to an air jet treatment in the absence of positive mechanical overfeed.

2. A process according to claim 1 wherein the metal filament component comprises up to 20% of the final product weight.

3. A process according to claim 1 or claim 2 wherein metal filament comprises from 1 to 10% by weight of the strand.

4. A process according to claim 3 wherein the metal filament has a diameter in the range 5 to 200 microns.

5. A process according to any preceding claim wherein man-made organic fibre selected from polyvinyl alcohol fibres, polyester fibres, polyamide fibres, aramid fibres, viscose rayon fibres, or a blend of two or more of these fibres are also present.

6. A process according to claim 5 wherein two or more man-made fibres are blended within the process, without preliminary twisting/doubling.

7. A process according to claim 1 wherein the tensions in the glass and metal filaments are respectively adjusted so as to permit a degree of overfeeding solely in response to the air jet treatment.

8. A process according to any preceding claim wherein the relative- proportions of glass to metal are in the range from about 20% to about 80% by weight.

9. A process according to any preceding claim wherein the tex of the treated strand is in the range from about 300 to at least 9600 tex.

10. Substantially untwisted glass fibre strand made by the process of any of claims 1 to 9 inclusive.

11. Reinforced plastics artefacts made by subjecting the strand of claim 10 to a pultrusion process.

12. Textile fabrics made from the strand of claim 10 by weaving or like processes.

13. Electrically-conductive products incorporating a glass fibre strand made by the process of any preceding claim.

14. A process for the production of glass fibre strands substantially as hereinbefore described.