GB2297564A

GB2297564A - Coated elastomeric polymer filaments

Info

Publication number: GB2297564A
Application number: GB9601776A
Authority: GB
Inventors: William Pigg
Original assignee: Smith and Nephew PLC; Smith and Nephew Inc
Current assignee: Smith and Nephew PLC; Smith and Nephew Inc
Priority date: 1995-01-31
Filing date: 1996-01-30
Publication date: 1996-08-07
Also published as: GB9501827D0; GB9601776D0

Abstract

A non-synthetic elastomeric polymer filament is coated with a protective barrier, eg. polyurethane layer, to prevent possible allergic responses to proteins contained in some non-synthetic polymers. The filaments can be used in bandages to provide elasticity.

Description

BANDAGES This invention relates to coated elastomeric polymer filaments, methods for their preparation and bandaging materials and articles 'prepared from them.

However, bandages containing elastomeric filaments whilst generally providing satisfactory elastomeric properties, may suffer from a number of disadvantages.

Most importantly non-synthetic elastomers can cause a Type IV allergic response. These allergic responses can be caused by the penetration of chemical additives added during processing or proteins contained in the non-synthetic elastomer, into the skin, thereby initiating an allergic response.

A possible approach to rendering for example natural rubber less likely to initiate an allergic response is to remove the proteins by extraction or by enzymatic dehydration. However, these methods are unlikely to remove all of the proteins and they would not deal with any substances added during processing.

Further, because the filaments may not possess a perfectly smooth surface, stress zones occur, particularly when the filaments are stretched and thus localised breaks may occur.

Thus the aim of the present invention is to provide hypoallergenic filaments with a protective barrier for preventing the penetration of chemical additives or proteins into the skin, whilst retaining the desired elasticity and other physical properties.

The use of coatings to render surgical gloves hypoallergenic is disclosed in Patent Application W088/08311, where the coating is ionic to avoid the use of donning powders which in themselves can cause skin irritations for the users and patients. Patent Application EP0249312 discloses fibreglass casting substrates which incorporate elastic fibres. There is also discussed that some elastic fibres contain chemicals which may cause the watercurable polyurethane prepolymers employed in the casting tape to gel prematurely, and that therefore the use of polyurethane fibres is preferred, which however swell in such prepolymers and the effect may be reduced by cross-linking or coating the fibres. US 3,501,741 describes coating elastomeric filaments with a polymeric foam, to protect the filaments and to hide from view any discolouration with age.

The abovementioned disclosures do not address the issue of allergic responses caused by non-synthetic filaments in articles such as for example bandages or articles of clothing. The present invention provides a solution to the problem of such allergic responses by producing a non-porous hypoallergenic coating for non-synthetic filaments.

According to the invention we provide a non-synthetic elastomeric polymer filament wherein the filament is coated with a barrier film to allergy causing substances. Such allergy causing substances may be chemical additives or proteins contained in nonsynthetic elastomers.

Further, in a preferred embodiment of the invention we provide a non-synthetic elastomeric polymer filament wherein the filament is coated with a barrier film which provides protection from chemical additives and proteins contained in non-synthetic elastomers.

The barrier film coating may comprise a synthetic polymeric material. Synthetic polymeric material includes for example polyurethanes and olefinic polymers, such as neoprenes. We especially prefer to use synthetic polymers, and especially polyurethanes.

Such polyurethanes must be sufficiently adhesive towards the elastomeric filament and preferably has extensional qualities which match the elastomeric filament. We have found that the most preferred polyurethane is a water borne emulsion sold by BIP Chemicals Ltd, Oldbury as Beetafin L9009.

In a further preferred embodiment the filament may be coated with a barrier film comprising at least a first and second layer which may be the same or different. Preferably a layer comprises a coagulant. We prefer the coagulant coating to be applied prior to the barrier coating. Ionic coagulants are preferred, and especially di- and tri- valent cations. The most preferred coagulant is calcium nitrate.

According to the invention we also provide a method for manufacturing a coated elastomeric polymer filament as hereinbefore described which comprises extruding an elastomeric polymer filament, dipping the filament into a barrier medium, and then drying the coated filament. The barrier medium may be a solution, suspension or emulsion. The barrier medium is preferably in the form of an emulsion and especially an aqueous emulsion.

Most preferably the barrier material is a polyurethane. The concentration of polyurethane in the emulsion may vary according to the type of filament desired, but may be from 1 to 40% w/w.

The method according to the invention may also include the step of first dipping the filament into a coagulant medium, drying and subsequently coating with a barrier medium. The coagulant medium may be a solution, suspension or emulsion. The coagulant is preferably a suspension of calcium nitrate in an alcohol, for example methanol, ethanol, isopropylalcohol, n-propylalcohol or n-hexylalcohol. The concentration of the coagulant suspension may be from 1 to 40% wiw, preferably 5 to 30% w/w, more preferably 5 to 20% wlw and especially 10% w/w.

The number of coatings of the barrier material and/or the coagulant layer may vary according to the nature of the proposed use of the resultant coated filament. However, the number of each of the coatings, which may be the same or different, may be from 1 to 4 and preferably 1 or 2.

The thickness of the coatings forming the barrier film of the invention may vary, however we prefer the thickness to be in the range of 1 to 100calm, preferably 1 to SOpm, more preferably 5 to 35cam, eg. 10 to 20pom.

The diameter of the uncoated filament may be from 0.2 to 0.7mm, preferably 0.3 to 0.6mm and more preferably 0.4 to 0.6mm.

The thickness of the coating on the filament may be measured as a % increase in the filament diameter. This increase is preferably from 0.1 to 30%, more preferably 0.1 to 20%, eg. 5 to 20%.

The coated elastomeric polymer filaments may be processed into threads or yarns and subsequently may be woven or knitted into bandages, dressings or articles.

The elastic bandage may be in the form of a woven or knitted fabric. Woven fabrics may have any of the weaving patterns which are conventionally used for making elastic bandages. The woven fabric comprises warp and weft threads. The coated elastomeric polymer filament of the invention can be present in the warp wherein only a proportion of the warp threads are elastic yarn. Thus depending upon the weight of coated elastomeric polymer required in the bandage every 2nd, 3rd, 4th, 5th etc., warp thread may be a coated elastomeric polymer filament yarn. Suitably the coated elastomeric polymer filament is woven into the fabric under tension and the woven material is allowed to relax. When in use the bandage is re-extended and applied to the affected part it provides the required compressive force.

The knitted fabrics may be in the form of conventional linear bandages or of tubular bandages. When a linear bandage is required the fabric can be in the form of a warp knitted fabric, for example one based on a 3- or 4-bar Raschel knitting pattern. The knitting of the yarns may be arranged so that bar 1 forms the chain stitches from the ground yarn, usually a cotton or cottoniviscose yarn and bars 2 and 3 lay in a ground yarn and the elastic yarn respectively. Aptly the knit has about 80 to 120 wales/lOcm width and 120 to 160 courses/lOcm length. The weight of the fabric may be altered in a conventional manner such as by changing the thickness of the yarn or changing the number of needles over which bar 2 inlays the ground yarn.In another pattern, the knitting of the yarns may be arranged so that bar 1 knits the chain stitches from the elastic yarn and the ground yams are inlaid from the other guide bars.

The dressing fabrics according to the invention when prepared as linear bandages may vary in width, although generally and by way of example only, a width of 1 00mm may be employed. For a dressing fabric of 1 00mm width the number of coated filaments required to be effective may be from 25 to 50, preferably 30 to 40.

Tubular bandages may be knitted on a conventional circular knitting machine. The coated elastomeric polymer filament of the invention can be knitted into the bandage in various ways, for example, if the coated elastomeric polymer filament forms the stitches then a tubular bandage is formed which has two-way stretch characteristics or the coated elastomeric polymer filament may be laid into the bandage so as to provide only radial stretch. The ground yarn in tubular bandages may be a cotton/viscose. The ratio of coated elastomeric polymer filament to ground yarn can suitably be in the ratio of 1:2 to 1:4.

Thus, according to the invention we also provide an article comprising coated filaments as hereinbefore described. Such articles may include "linear" bandages, tubular bandages and articles of clothing.

According to the invention we provide a bandage comprising a fabric which fabric contains one or more filaments of a coated elastomeric polymer according to the invention.

The invention will now be described by way of the accompanying drawing in which, Figure 1 is a cross section of a coated filament according to the invention.

With reference to Figure 1, a coated filament (1) comprises a non-synthetic elastomeric polymer filament (2), coated with a layer (3) of calcium nitrate coagulant and a polyurethane polymer (4).

Claims

1. A non-synthetic elastomeric polymer filament wherein the filament is coated with a barrier film to allergy causing substances.

2. A filament according to claim 1 wherein the filament comprises a natural rubber.

3. A filament according to claim I wherein the barrier film comprises a synthetic polymeric material.

4. A filament according to claim 3 wherein the synthetic polymeric material comprises a polyurethane.

5. A filament according to claim 1, wherein the barrier film comprises at least a first and a second layer, which may be the same or different.

6. A filament according to claim 5 wherein the first layer comprises a coagulant.

7. A filament according to claim 5 wherein the second layer comprises a barrier to allergy causing substances.

8. A filament according to claim 5 wherein the barrier film comprises up to four layers which may be the same or different.

9. A filament according to claim 6 wherein the coagulant comprises ionic cations with a valency of 2 to 3.

10. A filament according to claim 6 wherein the coagulant comprises calcium nitrate.

11. A filament according to claim 1 wherein the thickness of the barrier film is from 1 to 100calm.

12. A filament according to claim 1 wherein the thickness of the barrier film is from 1 to SOpm.

13. A filament according to claim 1 wherein the diameter of the uncoated filament is from 0.2 to 0.7mm.

14. A method for making a filament according to claim 1, wherein the filament is dipped into a barrier medium followed by drying the coated filament.

15. A method for making a filament according to claim 14, wherein the barrier medium is a solution, suspension or emulsion.

16. A method for making a filament according to claim 5 wherein the filament is dipped into a coagulant medium, dried and dipped into a barrier medium followed by drying the coated filament.

17. A method for making a filament according to claim 16 wherein the coagulant medium is a solution, suspension or emulsion.

18. A method for making a filament according to claim 14 wherein the barrier medium is in an emulsion.

19. A method for making a filament according to claim 18 wherein the emulsion is an aqueous emulsion of polyurethane.

20. A method for making a filament according to claim 18 wherein the concentration of the emulsion is from 1 to 40% w/w.

21. A method for making a filament according to claim 16 wherein the coagulant comprises a suspension at a a concentration of 1 to 40% wlw.

22. A method for making a filament according to claim 16 wherein the coagulant comprises a suspension at a concentration of 5 to 20% w/w.

23. A method for making a filament according to claim 16 wherein the coagulant comprises a suspension of calcium nitrate in alcohol.

24. A method for making a filament according to claim 23 wherein the alcohol is selected from the group consisting of methanol, ethanol, isopropylalcohol, n-propylalcohol, n-hexylalcohol.

25. An article comprising one or more coated filaments according to claim 1.

26. An article according to claim 25 which is a bandage.

27. An article according to claim 25 which is an article of clothing.

28. An article according to claim 25 which is woven.