BANDAGES

Abstract: An elastic filament formed from an elastomeric material wherein the filament achieves an effective compressive force at an extension between 20 to 60 % after which any further extension of the filament up to an extension of 100 % is accompanied by only a small increase in compressive force wherein the elastic filament is resistant to degradation by hydrocarbon oils and the elastomeric material comprises heterochain segmented block copolymers.

Description: BANDAGES This invention relates to elastic fliaments, formed from an elastomeric material, that is suited for use in woven or knitted elastic compression bandages for application to a body portion. Woven or knitted elastic bandages are used to provide support and to assist in the repair of soft tissues such as the healing of strained muscles and in the treatment of various venous conditions. It is important that such bandages are applied at the correct tension which is sufficiently high to enable them to maintain an effective level of compressive force under the bandage over a period of time. However, a disadvantage associated with known woven or knitted bandages is that if they are stretched too much during the application to a body portion the compression under the bandage may be overly great and cause damage, for example by restriction of the blood supply. As a result such bandages are usually applied with too little tension thus resulting in ineffective treatment. EP-A-0460040 discloses a bandage which generates the required compressive force at low extensions. The bandage contains both elastic and inelastic yarns, which show a large rate of increase in compressive force with extension at low extensions until the required extension is reached after which the force increases only slightly even though there may be a large increase in extension. However the elastic yarns employed in compression bandages are susceptible to degradation when they come into contact with hydrocarbon oils for example paraffins such as white oil or mineral oil contained in creams and pastes which are used to treat for example many venous conditions. As a result the bandages lose their effectiveness over time and may not be suitable for washing and re-use. Currently such problems are overcome by the use of interleaving layers and extra bandage layers which however increase the cost of treatment and reduce the ease of application. It is an object of the invention to overcome the problem of degradation of elastomeric filaments coming into contact with hydrocarbon oils. According to the present invention there is provided an elastic filament formed from an elastomeric material wherein the filament achieves an effective compressive force at an extension between 20 to 60% after which any further extension of the filament up to an extension of 100% is accompanied by only a small increase in compressive force characterized in that the elastic filament has a resistance to degradation by hydrocarbon oils of at least 24 hours and the elastomeric material comprises heterochain segmented block copolymers. The measurement of resistance to degradation by hydrocarbon oils is determined when the filaments are tested under the conditions described in Example 1 herein. The filaments of the invention have a resistance to degradation of at least 24 hours and preferably at least 48 hours. Surprisingly we have found that the use of elastic filaments comprising heterochain segmented block copolymers have a greatly improved resistance to hydrocarbon oils and thus the employment of such filaments in bandage decreases the degree of degradation on exposure to such oils dramatically. According to a further embodiment of the present invention there is provided an elastic bandage which comprises a fabric containing both inelastic and elastic filaments in accordance with this invention. The elastic filaments preferably comprise hydrocarbon elastomeric based A-B-A tri-block copolymers substituted with heterochain segmented block copolymers. The elastic yarns may comprise synthetic elastomeric heterochain segmented block copolymers. The molecular weight of a segment for a segmented block copolymer is typically from 400 to 6000g/mol. Furthermore the segments are preferably chemically incompatible so that the segmented block copolymers are likely to form phases. For example, hard block may form a glassy or crystalline phase and the soft block may form a rubbery phase. The exact morphology depends on the nature of the polymer molecular structure and on the processing history. The copolymers used in the present invention preferably comprise but are not limited to urethane and or amide based polymers. Urethane based polymers aptly consist of two types of segment: a) a soft block segment, for example a hydroxy terminated species of a low molecular weight, typically in the range from 600 to 6000g/mol such as a polyether or polyester. Other examples include hydroxy terminated siloxane, butadiene and isobutylene polymers. Suitable materials include poly(ethylene adipate) glycol, poly(tetra-methylene adipate) glycol, poly(hexamethylene adipate) glycol, poly(tetramethylene glycol) and poly(propylene glycol). b) a hard block segment, for example difunctional isocyanates reacted with chain extenders such as difunctional amines, alcohols and acids to give hard block segments with molecular weights up to 600g/mol. Examples of suitable isocyanates include, but are not limited to p-phenyl diisocyanate, diphenylmethane-pp'-diisocyanate, m-phenyl diisocyanate, 2,4-toluene diisocyanate. Amide based polymers are aptly composed of hard polyamide blocks and a soft block typically comprising polyethers, polyesters and polyether esters. Other suitable polymers include polyetheresters and polysiloxane ureas. Rubber/olefin blends and elastomeric alloys may also separate out into hard and soft blocks. Rubber/olefin blends may typically contain a crystalline hard block consisting of isotactic polypropylene and a soft block consisting of EPR (ethylene propylene rubber) or EPDM (ethylene propylene diene monomer) rubber. Elastomeric alloy thermoplastic vulcanisates may typically consist of a hard block containing polyethylene or polypropylene and a soft block containing a vulcanised diene or EPDM rubber. The heterochain segmented block copolymers as hereinbefore described are formed from many hard and soft block segments along the polymer chain. Suitably the molecular weight for the heterochain segmented block copolymers is up to 400,000g/mol. The copolymers used in the present invention are formed into elastic filaments prior to their being knitted or woven into bandages. The elastic filaments of the present invention may be prepared by extrusions methods known to those skilled in the art. Apt filament diameters are from 0.1mm to 4mm, preferably from 0.1mm to 2mm. The copolymers for use in the present invention may be blended with other additives in order to aid processing; for example lubricants and or plasticisers. Lubricants may include but are not limited to hydrocarbon waxes, such as low molecular weight polyethylene; metal soaps such as zinc, magnesium and calcium stearate; silicone oils such as poly(dimethylsiloxane); molybdenum disulphide powder and graphite powder. Plasticisers may include but are not limited to esters of diacids such as esters of alkanedioic acids and esters of dibenzoic acids; dipropylene glycol esters and dipropylene glycol dibenzoate. These are particularly suitable for polyurethanes. An apt polyamide plasticiser includes a mixture of o- and p-toluene ethyl sulphonamide. The bandage may be knitted or woven using methods known to those skilled in the art, furthermore the bandage may comprise a tubular bandage. The elastic filaments in accordance with the invention and for use in bandages of the invention have a force-extension relationship where at low extensions the rate of increase of compressive force with extension is large until an extension is reached after which any further extension is accompanied by only a small increase in compressive force. The force extension relationship of such yarns may be measured by stretching a sample of the yarn using an INSTRON Tensile Testing Machine, and representing the results graphically. The elastic filaments may be used as monofilaments or multifilaments. The ratio of elastic filaments into elastic yarns or filaments may vary depending on the nature of the fabric. Preferably the ratio will be between 1:1 and 1:2. Accordingly the present invention provides an elastic bandage which comprises a fabric containing both inelastic and elastic filaments in which the ratio of elastic filaments to inelastic filaments is from 1:1 to 1:12 and in which the bandage achieves an effective compressive force at an extension between 20 to 60% after which any further extension of the bandage up to an extension of 100% is accompanied by only a small increase in compressive force wherein the elastic filaments comprise an elastomeric heterochain segmented block copolymer. According to the present invention there is also provided, the use of a bandage as hereinbefore described for the treatment of various venous disorders using compression therapy. The elastic filaments may also be further suitable for use in other materials such as compression bandages, compression hosiery, hosiery, garments and clothing. The invention will now be described by way of example only. Suitable materials were obtained and extruded into filaments with a diameter of 0.43mm. Tensile tests were performed on the filaments using a crosshead speed of 500mm/min on a Zwick 1435 tensometer. In the tests 5 lengths of filaments were stuck on a card template which is then mounted in a set of pneumatic grips. 8 Subsequently the filaments were tested for their resistance to hydrocarbon oils. Example 1 Immersion tests are performed by suspending the filaments (3 for each material) between the sides of a box with dimensions such that when the filaments were weighed down to the bottom of the box they were at 50% extension. Box dimensions were 15cm x 25cm x 10cm deep, with the filaments mounted across the 15cm side. The box was then filled with 750cl of white oil and the time to failure of the filaments was measured. Test Results

Claims: CLAIMS 1. An elastic filament formed from an elastomeric material wherein the filament achieves an effective compressive force at an extension between 20 to 60% after which any further extension of the filament up to an extension of 100% is accompanied by only a small increase in compressive force characterized in that the elastic filament has a resistance to degradation by hydrocarbon oils of at least 24 hours and the elastomeric material comprises heterochain segmented block copolymers. 2. An elastic filament as claimed in claim 1 wherein the elastic filaments comprise hydrocarbon based A-B-A tri-block copolymers substituted with heterochain segmented block copolymers. 3. An elastic filament as claimed in claim 1 or 2 wherein the segmented block copolymers are chemically incompatible. 4. An elastic filament as claimed in any preceding claim wherein the heterochain segmented block copolymers are formed from hard and soft block segments. 5. An elastic filament as claimed in any preceding claim wherein the heterochain segmented block copolymers have a molecular weight of between 400 and 6000g/mol. 6. An elastic filament as claimed in any preceding claim wherein the heterochain segmented block copolymers are substantially urethane and or amide based polymers. 7. An elastic filament as claimed in any preceding claim wherein the heterochain segmented block copolymer is a hydroxy terminated species. 8. An elastic filament as claimed in any preceding claim wherein the heterochain segmented block copolymer contains at least polyether, polyester, polyether ester, polysiloxane urea, hydroxy terminated siloxane, butadiene, isobutylene polymers or a difunctional isocyanate. 9. An elastic filament as claimed in any preceding claim wherein the heterochain segmented block copolymers contain rubber/ olefin blends and or elastomeric alloys. 10. A yarn which contains an elastic filament as claimed in any perceding claim. 11. A garment which contains an elastic filament as claimed in any one of claims 1 to 9 or which contains a yarn as claimed in claim 10. 12. An elastic bandage which contains an elastic filament as claimed in any one of claims 1 to 9 or which contains a yarn as claimed in claim 10 or which contains a garment as claimed in claim 11. 13. An elastic bandage as claimed in claim 12 which comprises a fabric containing both inelastic and elastic filaments in which the ratio of elastic filaments to inelastic filaments is from 1:1 to 1:12. 14. The use of an elastic bandage as claimed in claim 12 or 13 or the treatment of venous disorders by compression therapy.

Inventors: HARDWICK STEVEN THOMAS, HARDWICK, STEVEN, THOMAS
Applicants: HARDWICK STEVEN THOMAS, SMITH & NEPHEW, HARDWICK, STEVEN, THOMAS, SMITH & NEPHEW PLC
Application year: 1998
Main classification: D01F6
IPC codes: A61F13, A61L15, D01F6