GB2132939A

GB2132939A - Sterilizable medical wrap

Info

Publication number: GB2132939A
Application number: GB08234010A
Authority: GB
Inventors: Thomas Ian Overthrow
Original assignee: WYCOMBE MARSH PAPER MILLS Ltd
Current assignee: WYCOMBE MARSH PAPER MILLS Ltd
Priority date: 1982-11-29
Filing date: 1982-11-29
Publication date: 1984-07-18

Abstract

A sterilizable medical wrap comprises a melt blown microfibre matt which at localised regions disposed thereacross is welded face-to-face to a non-woven reinforcing web of discontinuous fibres at least some of which are thermoplastic.

Description

SPECIFICATION Sterilizable medical wrap The present invention concerns a sterilizable medical wrap which includes as a bacterial probability filter a melt blown microfibre matt. The latter has insufficient inherent strength for use alone as a medical wrap, so that in practice the wrap has the matt spot-welded face-to-face to a reinforcing web. Heretofore, as taught in U.S. Patent No.2041 203, it has been considered essential, if the wrap is to have adequate strength and handling etc. properties, for the reinforcing web to be of randomnly deposited substantially continuous molecularly oriented filaments of thermoplastic polymer. U.S.Patent No. 4041 203 teaches that the continuous filaments of the reinforcing web should have an average diameter in excess of 12 microns; it teaches spot-welding of the matt to the reinforcing web by the localised application of heat and pressure between heated embossing rolls, it being necessary for this purpose for the softening temperature of the microfibres of the matt to be from 10 to 40 C less than that of the continuous filaments of the reinforcing web.

We have found, contrary to this previous teaching and understanding, that an excellent sterilizable medical wrap can be provided if the reinforcing web is of discontinuous fibres and that advantages are thereby obtainable which are not available with the prior wrap construction.

The sterilizable medical wrap according to the invention comprises a melt blown microfibre matt which at localised regions disposed thereacross (e.g. at discrete spots or zones or along intersecting or non-intersecting lines) is welded face-to-face to a non-woven reinforcing web of discontinuous fibres at least some of which are thermoplastic. Making the reinforcing web of discontinuous fibres facilitates the use of mixtures of different materials, making available a range of reinforcing web properties not obtainable or readily obtainable with a continuous filamentary web. The reinforcing web may for example include non-thermoplastic fibres, e.g. natural cellulosicfibres or synthetic or modified cellulosicfibres (for example of rayon, viscose, cellulose acetate etc.); the proportion of non-thermoplastic fibre may be substantial, e.g.

20 or 30 weight percent or more, but the thermoplastic fibre content of the reinforcing web is of course always enough for the localised welding of the web to the micro-fibre matt. The discontinuous thermoplastic fibres of the reinforcing web may be substantially uniform in composition and properties, or mixtures of different fibres may be used; the discontinuous fibres may for example be selected from polyester, polyamide, polyurethane and polyolefin (e.g. polypropylene) fibres. When natural, synthetic, or modified cellulosic fibres are included in the reinforcing web, these may be activated by steam autoclave sterilizing in use of the wrap to enhance the bacterial barrier properties of the wrap.

The melt brown microfibre (fibre diameter 10 microns or less) matt using the present invention is a known material. Such matts of thermoplastic microfibres suitable for localised bonding according to the invention are available commercially and are described for example in US Patent Nos. 4041 203 and in literature to which it refers - such as the article "Superfine Thermoplastic Fibres" in "Industrial and Engineering Chemistry", Vol.48 No.8, US Patents No. 715 251,3 704 198,3 676 242 and 3595245 and UK No. 1 217 892.

Manufacture may comprise melt extruding continuous micro filaments and breaking these by means of an air blast into microfibres which are deposited as a matt on a receiving surface, the deposited microfibres interlocking mechanically and to a certain extent by welding to provide a coherent matt. A wide variety of thermoplastic polymers can be used for the fibres of the matt, e.g. polyolefins such as polypropylene and polyethylene, polyamides, polyesters, polyurethanes, and various others; a matt may be composed of microfibres of two or more different polymer types. The matt and reinforcing web may employ fibres of the same thermoplastic.

The localised welding, e.g. spot-welding, of the microfibre matt to the reinforcing web may be by localised application of heat and pressure by means of embossing rolls, but ultrasonic welding is preferred. Suitable procedure and apparatus for such ultrasonic spot-welding is described in US Specification No. 3733 238 and is commercially available under the Trade Name "Pinsonic".The use of ultrasonic welding permits a wider choice of materials for the microfibre matt and reinforcing web since, compared with use of embossing rolls, it imposes little or no restriction on the softening point difference between the fibres of the two layers; for adequate ultrasonic spot-welding the softening point difference between microfibre matt and reinforcing web could for example be from 0 to 1 250C. If desired, the microfibres of the microfibre matt may themselves previously be bonded together at localised regions disposed across the matt, e.g. at discrete spots or zones along intersecting or non-intersecting lines. In the medical wrap according to the invention, the microfibre matt may have one or both faces welded to a reinforcing web.The reinforcing web of discontinuous fibres employed according to the invention may be a wet laid or dry laid non-woven. The reinforcing web may be substantially uniform, or it may be patterned with apertures or variation in fibre density across its area - e.g.

it may be a spunlace material, and can be produced as described for example in US Patent No. 2 862 251 or 3 485 706.

To improve the drape of a medical wrap according to the invention, the laminate of microfibre matt and reinforcing web or webs may be convoluted in three dimensions, an effect suitably produced by an embossing technique with co-operating embossing members (e.g. rollers), the procedure yielding an undulatory sheet which (apart possibly from the bonded regions) is of substantially constant density over its area. A suitable embossing apparatus for this purpose, described for example in US Patent No. 3673839, is available from M.Beidil Maskinfabrik of Nyholms Alle 26,2610 R~dovre, Denmark; this has co-operating patterned rollers with pyramidal surface projections whose heights can be regulated according to the depth of embossing required; the same emboss is provided on both sides of the material to give a three-dimensional effect; the embossing rollers do not mesh, embossing occurring by deformation of the substrate between the pyramids without compress.

The accompanying drawings illustrate diagrammatically two methods for spot-welding the microfibre matt to a reinforcing web in the production of a laminate medical wrap according to the invention.

Figure 1 illustrates an ultrasonic technique, and Figure 2 a heated roll embossing technique.

The Fig. 1 technique uses a driven pattern roll 2 upon which is engineered a series of pins set in relief across the whole width and circumference of the roll. Above this roll is fixed one or more sonic systems 4 fitted with horns 6 approximately 7-9 inches wide.

The plies of material to be bonded (microfibre matt 8, reinforcing web 10, and optionally further reinforcing web 12) pass between the horns and the roll. By means of compressed air the horn(s) may be loaded onto the pins via the substrate plies. The horn(s) vibrate at 20,000 c/s and when a pin passes underneath, a high level of energy develops which welds the two or more plies of thermoplastic containing material.

Neither the pattern roll nor horn(s) need be heated. Welding is achieved bythe absorption of energyfrom the vibrations within the material itself.

Another advantage in such a system is that webs of unlike thermoplastic materials can be welded together even though melting points are widely different- e.g. polypropylene to polyamide, polypropylene to polyester etc.

In the commercially available "Pinsonic" system the pattern roll has 10-200 pins per sq. centimetre. Fig. 1 shows the ultrasonically spot-welded laminate passing to treatment station 14for application of an aqueous treatment solution - for imparting, for example, one or more of bacteriocidal properties and water and alcohol repellency - then to an antistatic spray station 15, then to a heated (e.g.100 C)drying cylinder 16 and finally to reel up 18. It will be appeciated that stations 14 and 15 are each optional, and that treatment agent(s) may be applied in a variety of ways with different agents applied separately or together according to their compatibility and miscibility.

In Fig. 2, which employs the same reference numerals to indicate like items, the ultrasonic spot-welding equipment is replaced by a pair of co-operating hot embossing rolls, each heated for example to about 140 C; one roll (e.g. the upper one) is plain whilst the other has a patterned surface to effect the spot-welding.

The spot-welding laminate may be subjected to three-dimensional embossing (e.g. by means of the mentioned Beidil embossing units) immediately after the spot-welding, immediately after leaving the drying cylinder 16, or in a wholly separate operation.

The following Examples relate to currently preferred embodiments of the invention.

In the Examples the machine direction (MD) and cross direction (CD) tensile strength and stretch are measured on INSTRON TENSILE TESTER MODEL 1026, and parts and percentages are by volume unless otherwise specified.

EXAMPLE 1 Construction Web of polypropylene microfibre matt 30 g/m2 (softening point 137 C) Web of wet laid nonwoven containing 24 g/m2 80% polyester staple fibre (20 mm, softening point 260 C) and 20% cellulose fibre (21/2-5mm).

This web can be water repellent or absorbent.

Laminating Conditions Ultrasonic technique (PINSONIC) - see Fig. 1 - with the microfibre matt web against the patterned roll having 30 "square impressions" per sq. cm.

Machine speed 30 mimin Pressure 3.0 kg/cm2.

Vibrating horn frequency 20,000 c/s.

Physical Properties Dry Tensile (N/15 mm) Stretch (%) MD CD MD CD unbonded polypropylene 8.4 6.2 30 70 microfibre matt unbondedwetlaidnon 17.7 5.8 15 25 woven Laminate product 29.5 15.0 18 22 EXAMPLE 2 Construction As Example 1 with a further web of the 24 g/m2 wet laid nonwoven bonded to the reverse side, i.e. against the other face of microfibre matt.

Laminating Conditions Ultrasonic technique (PINSONIC) Machine speed 25 m/min.

Pressure 3.5 kg/cm2.

Vibrating horn frequency 20,000 c/s.

Physical Properties of Laminate Product MD Tensile 43.7 N/15 mm CD Tensile 20.7N/15mm MD Stretch 20% CD Stretch 25% EXAMPLE 3 Construction Web of polypropylene microfibre matt 30 g/m2 (softening point 137 C) Web of wet laid nonwoven containing 20 g/m2 70% polyester and 30% cellulose fibres (softening point and fibre lengths as in Example 1) Laminating Conditions Ultrasonic technique (PINSONIC) with the microfibre matt web against the patterned roll having 30 "square impressions" per sq. cm.

Machine speed 35 m/min.

Pressure 2.5 kg/cm2.

Vibrating horn frequency 20,000 c/s.

Physical Properties Dry Tensile (N/15 mm) Stretch (%) MD CD MD CD unbonded polypropylene 8.4 6.2 30 70 microfibre matt unbonded wet laid 9.8 9.5 10 10 nonwoven Laminate product 25.1 14.7 20 15 EXAMPLE 4 Construction Web of polypropylene microfibre matt 30 g/m2 (softening point 137 C) Web of "Santara" spunlace material 56 g/m2 (Du Pont) containing 100% polyester fibre (softening point 260 C) - apertured Laminating Conditions Ultrasonic technique (PINSONIC) with the microfibre matt web against patterned roll having 30 "square impressions" per sq. cm.

Machine speed 25 m/min.

Pressure 3.5 kg/cm2.

Horn frequency 20,000 c/s.

Physical properties Dry Tensile (n/15 mm) Stretch (%) MD CD MD CD unbonded polypropylene 8.4 6.2 30 70 microfibre matt unbondedspunlacedweb 35.0 18.0 36 130 Laminate product 29.2 17.0 30 110 EXAMPLE 5 Construction Web of polypropylene microfibre matt 30 g/m2 (softening point 137 C) Web of 100% polypropylene dry laid 20 g/m2 nonwoven fibre- softening point 1370C Laminating Conditions Hot roll emobssing technique as in Fig. 2.

Patterned roll 140 C (patterned with 40 square impressions per sq. cm.) Plain roll 140 C Machine speed 50 m/min.

Roll 1/2 nip pressure 5 kg/cm2.

Physical Properties Dry Tensile (N/15 mm) Stretch (%) MD CD MD CD unbonded polypropylene 8.4 6.2 30 70 microfibre matt unbonded 100% 12.3 3.9 24 9 polypropylene nonwoven Laminate product 19.5 8.9 28 24 EXAMPLE 6 The products of Examples 1-5 were treated with aqueous applications providing: a) Antistatic properties.

b) Added water repellency.

c) Alcohol repellency.

d) Bacteriocidai properties.

The components for (b) to (d) are in this case applied together as a mixed aqueous solution, as at 14 in Fig.

1 or 2. The antistatic component is applied separately as an aqueous spray as at 15 in Fig. 1 or 2.

The solution for application at flooded nip 14 is as follows: 10 parts Scotchban FC 808 (3M) (water dispersible fluorochemical copolymer for water and alcohol repellency).

5 parts Antimicrobial agent 5700 (DOW CORNING) (Silicone quaternary ammonium salt).

900 parts Water.

2 parts Triton X-155 (ROHM & HAAS) (wetting agent).

The solution for spraying at 15 is 1 part ZELEC DP (antistatic quaternary ammonium salt from Du Pont) in 750 parts water.

After application of these solutions the treated web is dried over hot cylinders at 1 OO"C. The effect of the applications was as follows: a. Antistatic Properties Surface resistivity was reduced from the order of 10ie ohms/sq. to 1010 ohms/sq. - as measured using 6105 resistivity adaptor ex Keithly Instruments Inc., Cleveland, Ohio, USA.

b. Water Repellency To assess this the sample was stretched across the top of a Mason Jar (Kilner Jar type) containing a 10 cm head of water. The jar was then inverted and the time taken for the first drops of water to penetrate was noted. The product of each of Examples 1 to 5 passed the minimum requirement of 30 mins. without water penetration.

c. Alcohol Repellency Drops of a 70%/30% (v/v) ethanol/water mixture were applied to the exposed face of the sample supported by a glass plate; the underside of the plate was viewed and the time for initial penetration recorded. The product of each of Examples 1 to 5 met the minimum requirements of 5 mins. withut liquid penetration.

EXAMPLE 7 Bacterial Barrier Checks Three methods have been used on the product of Example 1 (without application of bacteriocidal agent).

1. Methylene Blue Test (Spec TSS/S/33aO(}5Appendix BJ This test is based on the simulation of bacteria by a cloud of dry methylene blue particles of the following distribution: Particle Diameter % by mass up to (microns) stated size 0.05 0.15 0.10 1.80 0.20 12.0 0.40 37.5 0.60 64.2 0.80 85.0 1.00 96.3 1.50 100.0 At a linear flow of 30 cm/min through the Example 1 product 15% of methylene blue particles passed through. This equates to a particular size up to 0.25 microns approx. Bacteria, however, as individual organisms range in size from 0.3 - 14 microns. This demonstrates that the sample is an effective barrier to particles directly related in size to airborne bacteria.

2. Wet Bacteria Challenge Test 5 drops of 0.1 ml. each of a suspension of 107 staph/ml in distilled water are placed on the sample (either side). After natural drying the underside of the sample is placed in contact with agar nutrient. After 10 seconds the sample is disposed of. The agar plate is then incubated t 500C in the normal manner. Using the Example 1 product as sample, absolutely no growth was noted.

3. Dry Bacteria Challenge Test The sample is stretched across the top of a Mason Jar, in the bottom of which is agar nutrient media. The jar is sterilized at 120 C. The top of the sample is then coated with bacteria contaminated dust at a known concentration. Air is then made to flow into and out of the jar by subjecting it to alternate heating and cooling. After six cycles the jar with agar is incubated under standard conditions and inspected for bacterial growth. 30 samples of Example 1 product were tested and in no case was bacterial growth observed.

EXAMPLE 8 The product of Example 1 was three-dimensionally embossed with Beidil embossing units, the drape being measured before and after embossing according to TAPPI standard T-451 M-60. The results were as follows: Before embossing - MD 12.8 cm, CD 9.0 cm; After embossing - MD 10.4cm, CD 7.3cm.

Claims

1. A sterilizable medical wrap comprising a melt blown microfibre matt which at localised regions disposed thereacross is welded face-to-face to a nonwoven reinforcing web of discontinuous fibres at least some of which are thermoplastic.

2. A wrap according to claim 1 wherein the discontinuous fibres of the reinforcing web include non-thermoplastic fibres.

3. A wrap according to claim 2 wherein said non-thermoplastic fibres are selected from natural, synthetic and modified cellulosic fibres.

4. A wrap according to any of claims 1 to 3 having a reinforcing web locally welded to each face of the microfibre matt.

5. A wrap according to any preceding claim wherein the microfibre matt is ultrasonically spot-welded to the or each reinforcing web.

6. Awrap according to any preceding claim having a three-dimensional emboss.

7. A wrap according to any preceding claim bearing at last one agent selected from antistatic, water-repellent, alcohol-repellent and bacteriocidal agents.