GB2023684A - Cored yarn - Google Patents

Abstract

The invention is a method of preparing a yarn wherein fibers, filaments or yarn adhere to a central core by means of a polymeric material which comprises a polymeric material having as a first component a thermoplastic material and as a second component a vinyl acetate material particularly an ethylene vinyl acetate copolymer. The use of an ethylene vinyl acetate copolymer improves the manufacturing conditions of the yarn and imparts desirable characteristics to the final product.

Description

SPECIFICATION Eva yarn compositions The present invention relates to yarns and more particularly, relates to yarn compositions and a method of manufacturing said yarns.

Recent technology in the field of textiles and particularly yarns has included the development of what have become known as "composite" yarns. These composite yarns are manufactured by several different processes which have been described in the art and in this respect, reference may be had, for example, to Canadian Patents 883,443; 880,988 and 983,694, among others. These patents describe various processes and apparatuses for manufacturing composite yarns.

A first method for manufacturing a composite yarn, as taught in the art, comprises extending a filament of a tacky material such as a molten polymeric material and subsequently juxtaposing fibers thereto such that the fibers adhere to and are embedded in the polymeric material which acts as a binder. In a second method of manufacturing composite yarns, a carrier material, which may be any suitable material, either single or multi-filament, is coated with a tacky binder substance such as a molten polymeric material by passing the same through an extrusion die whereby a sheath of molten polymeric material is extruded thereabout, and subsequently fibers are juxtaposed to the coated carrier to form the final yarn product which has the fibers adhering to and embedded in the polymeric sheath about the carrier.

The advantages of composite yarn manufactured according to the above-described processes have been multifold. Thus, the methods and apparatuses permit manufacture of yarn at substantially greater speeds then were previously obtainable by conventional techniques such as rotor spinning or ring spinning. Futhermore, the multi-component yarns permit one to "engineer" the desired properties into the final yarn product and in some instances, have permitted the use of certain material previously not suitable for yarn products.

With the manufacture of the yarn occurring at high speeds, certain problems are encountered.

Thus, the use of certain polymeric material as the binding material for the fibers introduces a limitation to the speed at which the process can be run. Furthermore, the use of certain materials, in certain required percentages, has been found to impart some undesirable characteristics to the final yarn products such as stiffness, limited dyeability, etc.

It is an object of the present invention to provide a method for the manufacture of a composite yarn, which method provides better processability of the yarn and further provides a yarn having an increased fiber loading.

According to one aspect of the present invention, in a yarn product wherein an outer yarn component adheres to a center core of the yarn product by means of a binding material, there is provided the improvement wherein said binding material comprises an alloy having as a first component thereof a polymeric material and a second component thereof a vinyl acetate.

In a further aspect of the present invention, in a method of manufacturing a yarn product wherein an outer yarn component is placed in contact with a center core having a tacky surface, there is provided the improvement comprising the step of contacting said outer yarn component with a binding material comprising an alloy having as a first component thereof a polymeric material and as a second component thereof a vinyl acetate.

In greater detail, the present invention provides a polymeric "alloy" which is suitable for use in the manufacture of composite yarn as a binding material. The polymeric alloy comprises a first polymeric material to which is added a vinyl acetate preferably in the form of an ethylene vinyl acetate copolymer.

In this specification, the term "composite yarn" refers to a yarn which is manufactured of two or more components. This includes yarns having a central core, a polymeric sheath or binder thereabout, with fibers adhered to or embedded in the polymeric sheath. In this embodiment, three "different" components are employed although they may all be of the same material. The center core component may comprise, in one aspect, one or more single or multi-filament bundles or a "yarn" or like carrier material. The outer yarn component "fibers" may be either in the form of individual discrete fibers such as staple fibers or in the form of "filaments"; still futher, the term fibers includes the use of material in the form of a yarn which may then be further treated to achieve the desired effect.

Still further, the center core of the yarn may comprise an extruded filament of the polymeric alloy discussed herein. An outer yarn component comprising fibers or filaments as discussed above will then be adhered to the filament, at least the outer surface of which is in a tacky condition when contacted with the outer yarn component.

The polymeric "alloy" used as a binding material comprises a first polymeric material, which material may be any of the conventional resins employed for use in the formation of composite yarns. For example, resins such as polypropylene, polyethylene, polyurethane, nylon, polyester, "SARAN" etc., may be employed. The polymeric alloy further includes a vinyl acetate compound preferably in the form of an ethylene vinyl acetate (EVA) copolymer. It has been found that the use of an EVA copolymer imparts substantial advantages both to the final product and to a method of manufacturing a composite yarn. The term "EVA" is in this specification used to designate a group of EVA copolymers, which copolymers are commercially available in various grades with different ratios in the copolymer itself.Such EVA materials are known, for example, under the trade mark "ULTRATHENE"designating the ethylene vinyl acetate family of polyoflefin copolymers developed by U. S. Industrial Chemicals Co. The copolymers are available ranging from a few percent by weight of vinyl acetate or up to and in excess of 50% vinyl acetate.

Prevoiusly, problems of adhesion of the molten polymer to the carrier, when the carrier is passed through the extruder, have been present due to the high speed at which such composite yarns are formed. However, it has been found that the inclusion of an EVA copolymer in the met significantly improves the processing and permits higher production speeds without breaks in the polymeric sheath about the carrier. Naturally, this leads to improved properties for the yarn itself such as increased fiber coverage and a more uniform fiber coverage.

It has further been found that the use of a polymeric alloy having therein an EVA copolymer reduces the stiffness of the yarn and as a consequence, fabrics made therefrom. Still further, the hand of a fabric knitted from the yarn has been found to be improved. Other advantages include a improvement of colour uniformity as the amount of EVA copolymer (i.e. the amount of vinly acetate) present in the alloy increases. Utilizing this, slightly darker shades of the yarn can be achieved utilizing the same dyeing conditions or, in other words, less dye is needled for the same shade. Also, generally, the dyeability of the fabric is improved with increasing amounts of EVA until a maximum effect is achieved-further increase in the EVA copolymer content has a diminishing effect on uniformity or dye pick-up.

The use of an EVA copolymer in a polymeric alloy also results in a more reliable spinning.

Stability in the spinning zone has generally been found to improve and the number of polymer breaks reduced. In addition, EVA copolymer blend alloys can in general be run about 40"C lower in temperature than, for example, a straight polypropylene resin. The bonding of the resin to a fiber as well as to the carrier is improved.

As aforementioned, the particular resin to which the EVA copolymer is added may vary.

However, it is a condition, as will be understood by those skilled in the art, that the resin which is employed must be one with which the EVA copolymer is compatible or, in other words, is "soluble" in.

The ratio of resin to EVA copolyrner will vary depending on the specific properties of the yarn desired and as well, the particular resin or resins employed in the polymeric alloy. In certain instances, the EVA copolymer is only soluble in the resin to a certain extent as is the case, for example, with condensation polymers. Thus, with certain resins, a maximum of 10% of the EVA copolymer with respect to the remaining resin or resins may be employed before the polymers separate and the melt will appear as a two-phase system. On the other hand, with resins such as ethylene and vinyl polymers, any ratio of EVA to resin may be employed without separation problems. Naturally, as will be understood by those skilled in the art, a single phase alloy system is employed with the present invention.

As will be appreciated, for each resin or resins employed, there is a range within which the benefits and the advantages outlined above are maximized. Thus, for resins such as polypropylene and polyethylene, a 20 to 70% EVA content has been found to be generally most suitable with a 40 to 60% range being preferred. Naturally, the amount of EVA can be varied, as previously mentioned, depending on the specific properties desired and on the amount of vinyl acetate in the EVA.

It will understood, in the above context, that the term "ethylene vinyl acetate" includes copolymers wherein the percentage of vinyl acetate may vary. Thus, in commercially availabe EVA copolymers, the vinyl acetate percentage generally varies between 9 and 55%. For the practice of the present invention, a 20 to 28% vinyl acetate content has been found to be suitable.

The present invention also includes the embodiment, as discussed previously, wherein the centre core of the composite yarn comprises an extruded filament of the binding material per se.

It has been found that not only does the binding material act as in the above-mentioned yarns (better adhesion and fiber coverage), but also provides increased processability. In this embodiment, the polmyer alloy is as defined above.

Having thus generally described the invention, reference will be made to the accompanying Examples illustrating embodiments thereof.

EXAMPLES 1 TO 7 Seven different composite yarns were manufactured with varying compositions as shown in Table I. These yarns were produced on a Bobtex Mark I ICS Machine produced for the manufacture of composite yarns by The Bobtex Corporation. In each instance, the carrier was fed through an extruder die wherein it was coated with the binder. The fibers were then juxtaposed to the coated carrier.

TABLE I EVA ALLOY BASED ICS YARNS SAMPLE NO. 1 2 3 4 5 6 7 Count(tex) 190 215 75 115 115 140 100 Composition1 Fibers % V60 A/W 64 W55 A50 A50 W/MA 72 V40 Carrier % PET 26 PET 22 PET22 PET 26 PET 29 GLASS PET 33 24 Binder % 14 13 23 21 21 49 27 Binder Composition Resin Name PP PP PP PP PP SARAN PP Resin % 33 33 25 50 75 97 100 EVA3 % 66 66 75 50 25 3 0 Running Speed 2040 2000 1450 2010 2010 2040 2000 (Ft/min) Break Strength(g) 1050 1550 633 1400 1400 2500 1320 Elongation (%) 46 22 30 35 35 3 32 Adhesion Index2 5 5 4 4 4 5 1 'W-wool V-viscose MA-modacrylic PP-Polypropylene PPEL--PP alloy PET-polyester EVA EVA/PP copolymer A-acrylic SPcSARAN alloy 2Adhesion Index-measure of ability to strip fiber/polymer sheath from the carrier core filament, scale 1 to 5; 1-easy sliding off, 5-no stripping, force to strip exceeds strength of yarn.

3"ULTRATHENE"-28% vinyl acetate content.

As will be evident from Table I, the use of EVA in the binder composition substantially improved the adhesion of the fibers to the carrier. As little as 25% EVA, which translates to a 7% vinyl acetate content, substantially improved the adhesion of the fibers to the binder and carrier. With certain resins, such as is the case with SARAN, as little as 3% EVA content provides not only perfect adhesion but greatly improved processability.

Thus, the use of the EVA provides an extremely high adhesion characteristic while it has been found that the same polyester filaments with pure polypropylene (as in Examples 1 to 5 and 7) has resin yield adhesion indices in the range of 1 and 2. Within the operating EVA range, there does not appear to be high sensitivity to the level of EVA content versus the adhesion index.

EXAMPLES 8 TO 12 In these Examples, a yarn was manufactured as described above with reference to Examples 1 to 7. In each instance, the carrier was a polyester with fibers being of an acrylic material. The resin was polypropylene with the percentage of EVA being varied as set forth in Table II.

TABLE II EVA ALLOYING CHARACTERISTICS EVA2 % Process Draw Down Softness Fiber Loading Temp. oF Ratio Index Index Index 0% 550 60 .35 48% 25% 525 90 .45 53% 50% 475 95 .70 57% 75% 450 95 .70 60% 100% 450 10 .70 60% 'The Softness Index is an arbitrary dimensionless subjective index with 1.0 representing maximum softness and .1 representing a very stiff yarn.

2Vinyl acetate content-28%.

As will be seen from Table II, the increase in EVA content permits an increased number of fibers to be adhered to the core of the yarn. An increased number of adhered fibers is naturally desirable to give any desired surface effect in a textile product.

As will be seen from Example 8, and as has been established, 48% represent the approximate maximum, in a practical sense, of the fiber loading with pure polypropylene. It will also be noted that the maximum fiber loading was achieved with a 21 % vinyl acetate content-further increase in the vinyl acetate content did not further improve the fiber loading index. The maximum softness was achieved with a 14% vinyl acetate content.

As will be further noted, the process temperature can be substantially reduced with the increase in the vinvyl acetate content.

EXAMPLES 13 TO 14 Yarns were manufactured according to Table Ill and as in previous Examples with a carrier of glass material and fibers of a viscose/modacrylic material.

TABLE III ALLOYING EFFECT ON PROCESSABILITY Example Resin Process Draw Down Process Alloy Temp. Ratio ability %/% F Index Index 13 SARAN 100/EVAO 390 20 1 14 SARAN 96/EVA 4 385 40 4 fon a scale of 1 to 5 with 5 indicating maximum processability-i.e. the most desirable.

As will be seen, the use of even a small percentage of EVA results in a dramatic increase in the processability of the yarn. The EVA yarn provides twice the draw down and at a lower temperature, the processability increased dramatically.

As will be seen from the above Examples, the use of an EVA copolymer in the binder material leads to substantial advantages. With the processability, the high strains placed upon the liquid extrudate in the process for manufacturing composite yarns makes the yarn path highly sensitivie to breakage. Use of the EVA alloying has permitted greater line stability, reduction or elimination of melt resonance, processing reliability, and the attainment of efficiency levels not otherwise attainable.

It will be understood that the above-described embodiments are for purposes of examplification only and are not limiting.

Claims (14)

1. In a composite yarn product wherein an outer yarn component adheres to a centre core of the yarn product by means of a binding material, the improvement wherein said binding material comprises an alloy having as a first component thereof a polymeric material and as a second component thereof a vinyl acetate material.

2. The yarn product of claim 1 wherein said centre core comprises a carrier material formed of one or more filaments.

3. The yarn product of claim 2 wherein said outer yarn component comprises fiber partially embedded in said binding material.

4. The yarn product of claim 1 wherein said fibers are staple fibers.

5. The yarn product of claim 2 wherein said centre core comprises a carrier of a polyester or glass material.

6. The yarn product of claim 1 wherein said polymeric material is polypropylene.

7. The yarn product of claim 1 wherein said vinyl acetate comprises between 2 and 35% of the binding material.

8. In a method of manufacturing a composite yarn product wherein an outer yarn component is placed in contact with a centre core having a tacky surface, the improvement comprising the step of contacting said outer yarn component with a binding material comprising an alloy having as a first component thereof a polymeric material and as a second component thereof a vinyl acetate.

9. The method of claim 8 wherein said centre core comprises a carrier coated with said binding material.

10. The method of claim 8 wherein said centre core comprises an extruded filament of said binding material.

11. The method of claim 8 wherein said outer yarn component comprises fibers.

1 2. The method of claim 8 wherein the step of contacting said outer yarn component with a binding material comprises the step of contacting the same with a binding material comprising polypropylene and vinyl acetate.

1 3. The method of claim 8 wherein said vinyl acetate comprises between about 2% and 35% of vinyl acetate.

14. The method of claim 9 including the step of passing said carrier through an extruder to coat the carrier with said binding material.