GB2199052A - Making yarn containing glass fibre - Google Patents

Abstract

A process for the manufacture of a substantially untwisted glass fibre and man-made organic fibre blended yarn, comprises the steps of assembling together in side-by-side relation a core strand of relatively coarse glass fibre filaments of diameter 13 to 24 microns and a surface strand of relatively fine glass fibre filaments of diameter 6 to 10 microns, followed by subjecting the assembly to an air jet treatment in the absence of positive mechanical overfeed, wherein either the core or the surface strand or both contain organic fibres.

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.

Our patent 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.

According to the invention, some of the glass fibre in the substantially untwisted yarn just described is replaced by organic fibre. Replacement is preferably carried out prior to the side-by-side assembly stage, by substitution of man-made fibres, or filaments, or both, for some of the glass fibres in either or both of the initial strands.

Particularly preferred organic fibres are man-made fibres such as polyvinyl alcohol fibres, although polyamide fibres, polyester fibres, aramid fibres and viscose rayon fibres may be used. Natural organic fibres such as cotton may also be used. Blends of these fibres are also possible.

The absence of mechanical overfeed means that unlike certain prior art processes for combining filamentary strands, there is no mechanically-induced overfeed by way of feed rollers operating with different surface speeds. Instead, it is still preferred that for the purposes of this present invention the relative tensions of the relatively fine and coarse filaments should be adjusted so that a degree of self-induced overfeeding of the surface strand takes place solely under the influence of the aijet treatment.

It has been found that if the relative tensions are carefully adjusted the filaments of the surface strand and the core strand react to the air jet to form a composite strand which has the attributes of an effect yarn. Preferably some of the glass fibres in only the core strand are replaced by organic fibres and in such a case the interpenetration of the fine filaments into the mixed fibre filaments forming the core strand produces a coherent composite strand without spinning and/or twisting. Furthermore, the bulk generated in the surface strand filaments by the air jet treatment is retained by this interpenetration, even on stretching the product.

This is because the coarse core filaments resist practically all of the stretching force. Core strands of the referred filament 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 fine to coarse filaments being selected together with the organic fibre content to give satisfactory bulking, allied to high longitudinal strength. The relative poportions of the core strand and surface strand can be anywhere in the range from about 15 to about 981 percent by weight, with either one predominating. The process therefore has exceptional flexibility.

Conveniently, the tension in the individual bundles of filaments assembled together is adjusted by regulating the tension of each bundle as it is withdrawn from a creel and allowed to go forward to the assembly point, prior to the air jet treatment. The air jet is preferably a conventional venturi type bulking o texturing jet of the kind commonly used in the textile art for producing bulky yarns. The driven packages and/or differential rates of feed used for conventional core-effect yarns are not needed.

It has been found that the presence of even minor proportion of, for example, polyvinyl alcohol fibres in the core strand results in a notable increase in tensile strength, coupled with reduced elongation or break.

This is accompanied by a dramatic increase in impact strength when used as a reinforcement for a synthetic resin matrix, as for example in a pultruded product.

The relative proportions (by weight) of glass fibre to organic fibre may be selected from a wide range, up to say 50 percent of each, referred to the total product weight. Where the core strand alone contains the man-made component, the latter may be from as little as 3% by weight of the core, up to as much as 97% 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 3-30 percent by weight of the core strand.

Even at relatively low values, using polyvinyl alcohol fibres, the improvement in impact strength can be as much as 100% over the all-glass fibre product. There are however other advantages accruing from the invention, the most notable being an improvement in tensile strength, coupled with reduced elongation at break. However, possibly more significant than this, these improved properties are achieved despite a reduction in weight.

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 surface strand filaments is not pulled out during the pultrusion process, the unbulked core strand serving to prevent this. The surface strand filaments are available to provide reinforcement in directions transverse to the axis of the core strand.

Hitherto, this has been generally unobtainable in pultrusion reinforcement yarns.

A typical example of a process according to the invention is as follows. Three 300 tex wound packages of 13y diameter glass fibre were loaded onto a standard creel together with one 335 tex package of polyvinyl alcohol fibres. The four package ends were withdrawn as a parallel bundle and inserted into an air jet, as a 1200 tex core yarn.

Twenty 64 tex packages of 6y diameter glass fibre were also loaded onto the same creel, to give a total of 1280 tex, and all twenty ends were fed through the same air jet as before. The total of 2480 tex were then subjected to air treatment in a jet placed between the creel and the winder for the treated strand. 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 12 percent by weight of man-made fibres; its breaking load was 800N compared with 400 for the all-glass fibre equivalent, with an elongation at break of only 3%, compared with 48 for all-glass.

The same technique was used to make a 1500 tex yarn containing about 25% of polyvinyl alcohol fibres. The core was one strand of 335 tex polyvinyl alcohol fibres and one strand of 152 tex 13pu - glass fibres. These were loaded onto a creel with 6 strands of 170 tex (10y) glass fibres and processed as before. The product had a breaking load of 50 ON, compared with 300N for the all-glass equivalent. The elongation at break was also 3%.

When used as a pultrusion process reinforcement, about 100% improvement in impact strength was obtained.

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, say, aramid fibres, without the need for twisting/doubling operations and the relatively low throughput associated with the latter.

This means that glass-based blended weaving grade yarns can be made economically, thereby facilitating the production of specialist fabrics for safety garments such as flak jackets where impact strength is essential.

Very significantly, such products have reduced weight compared to the all-glass products previously available.

Likewise, flame resistant fabrics can be produced without the traditional (an expensive) steps of twisting/doubling yarns to form the desired blend.

Blends of the preferred organic fibres can be used, as previoulsly 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 (9)

CLAIMS:

1. A process for the manufacture of a substantially untwisted glass fibre and man-made organic fibre blended yarn, comprising the steps of assembling together in side-by-side relation a core strand of relatively coarse glass fibre filaments of diameter 13 to 24 microns and a surface strand of relatively fine glass fibre filaments of diameter 6 to 10 microns, followed by subjecting the assembly to an air jet treatment in the absence of positive mechanical overfeed, wherein either the core or the surface strand or both contain organic fibres.

2. A process according to claim 1 wherein the organic fibre component comprises up to 50% of the final product weight.

3. A process according to claim 1 or claim 2 wherein only the core strand contains organic fibre, in an amount of from 3 to 97% by weight of the strand.

4. A process according to claim 3 wherein the organic fibre constitutes from 3 to 30% by weight of the strand.

5. A process according to any preceding claim wherein the organic fibre is selected from polyvinyl alcohol fibres, polyester fibres, polyamide fibres, aramid fibres, viscose rayon fibres, cotton fibres, or a blend of two or more of these fibres.

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

7. A process according to claim 1 wherein the tensions in the fine and coarse filaments are respectively adjusted so as to permit a degree of overfeeding of the surface strand solely in response to the aijet treatment.

8. A process according to any preceding claim wherein the relative proportions of the core strand and surface strand are in the range from about 15 to about 98; percent 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.