Nonwoven fabric

Abstract

There is disclosed a nonwoven laminate (5) or laminate fabric comprising at least three layers (10, 20) comprising spunbond/meltblown/spunbond layers, wherein the laminate (5) has: an abrasion resistance of at least 5,000 rubs or higher, and a microbiological filtration performance measured as a log reduction factor (LRF) of 3 or higher. The laminate (5) comprises a medical and/or pharmaceutical fabric such as for medical and/or sterile packaging. Beneficially the laminate (5) has been flat calendared between flat heated metal rollers (105, 110) and further, the laminate (5) has been flat calendar laminated between flat heated metal rollers (105, 110).

Claims

1. A nonwoven laminate fabric comprising at least three layers comprising spunbond/meltblown/spunbond layers, wherein the laminate fabric has: an abrasion resistance of at least 5,000 rubs or higher (as measured by EDANA NWSP 020.5 RO); a microbiological filtration performance measured as a log reduction factor (LRF) of 3 or higher (as measured by ASTM F1608); and has been flat calendar laminated between flat heated metal rollers; and wherein the meltblown layer comprises polymeric fibres comprising polypropylene, the fibres of the meltblown layer have an average diameter between 0.5 μm and less than 2 μm, and the spunbond layers comprise respective outer layers of the laminate, wherein at least one or each of the spunbond layer(s) comprise polymeric filaments, wherein the filaments of the spunbond layers have a diameter or average diameter less than 19 and at least one of the outer layers is point-bonded or embossed.

2. A nonwoven laminate fabric as claimed in claim 1, wherein the laminate fabric comprises a fabric selected from one or more of: a medical fabric, a pharmaceutical fabric, a medical packaging fabric, a sterile packaging fabric.

3. A nonwoven laminate fabric as claimed in claim 1, wherein the laminate fabric has been calendered and/or laminated without the use of a calendering and/or lamination pattern.

4. A nonwoven laminate fabric as claimed in claim 1, wherein both of the spunbond outer layers are point-bonded or embossed.

5. A nonwoven laminate as claimed in claim 1, wherein the laminate fabric is at least partially permeable and/or transparent to at least one sterilisation means or agents, or at least one of: steam, ethylene oxide (EtO), electrons and gamma radiation.

6. A nonwoven laminate fabric as claimed in claim 1, wherein the layers of the laminate fabric are thermally laminated to one another.

7. A nonwoven laminate fabric as claimed in claim 1, wherein the air permeability of the laminate (measured by the Bendtsen method) is less than 670 ml/min, and/or the air resistance of the laminate material (measured by the Gurley method) is more than 40 s.

8. A nonwoven laminate fabric as claimed in claim 1, wherein the meltblown layer comprises polymeric fibres comprising a single polypropylene homopolymer.

9. A nonwoven laminate fabric as claimed in claim 1, wherein the meltblown layer comprise pores which have a diameter or average diameter in the range of 10 μm to 30 μm (as measured by BS3321).

10. A nonwoven laminate fabric as claimed in claim 1, wherein polymeric filaments of the spunbond layers comprise metallocene polymer/polypropylene or metallocene catalysed polymer/polypropylene.

11. A nonwoven laminate fabric as claimed in claim 1, wherein the laminate fabric has a microbiological filtration performance measured as a log reduction factor (LRF) of 4 or higher, 5 or higher, or 6 or higher.

12. A nonwoven laminate fabric as claimed in claim 1, wherein the laminate fabric has an abrasion resistance of at least 10,000 rubs or higher or around 25,000 rubs.

13. Use of a nonwoven laminate fabric of claim 1, wherein the laminate fabric is used as a component of a medical and/or pharmaceutical product or fabric, such as medical and/or sterile packaging.

14. A method of manufacturing a nonwoven laminate fabric as claimed in claim 1, wherein the method comprises: laminating the spunbond/meltblown/spunbond layers together, and calendering the laminate with a calendar; wherein the calendering of the laminate fabric is done between flat heated metal rollers.

15. The method of claim 14, wherein the laminating of the layers is done between flat heated metal rollers.

Description

BRIEF DESCRIPTIONS OF DRAWINGS

(1) Embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings, which are:

(2) FIG. 1 a meltblown fabric according to a first embodiment of the present invention;

(3) FIG. 2 a schematic diagram of an apparatus for manufacture of the meltblown fabric of FIG. 1;

(4) FIGS. 3a and b a spunbond fabric of the art; and a spunbond fabric according to a second embodiment of the present invention, respectively;

(5) FIG. 4 a schematic diagram of an apparatus for manufacture of the spunbond fabric of FIG. 3b;

(6) FIG. 5 a laminate according to a third embodiment of the present invention; and

(7) FIG. 6 a schematic diagram of an apparatus for manufacture of the laminate of FIG. 5.

DETAILED DESCRIPTION OF DRAWINGS

First Embodiment (Meltblown)

(8) Referring initially to FIG. 1, according to a first embodiment of the present invention there is provided a meltblown fabric or material 10, such as a medical or sterile packaging fabric or material.

(9) The meltblown material 10 comprises fibres. The fibres have an average diameter in the range of 0.5 μm to 2 μm. The laminate containing the meltblown material 10 has a microbiological filtration performance measured as a log reduction factor of 3 or higher. The meltblown material 10 filters microscopic organism(s). The un-calendared meltblown material 10 comprises pores. The pores have a diameter or average diameter in the range of 20 μm to 25 μm. The meltblown material 10 comprises a polymeric material(s), e.g. a thermoplastic polymer. The meltblown material 10 is formed of polymeric fibres, and each fibre comprises a single polymer. The meltblown material 10 is, in this embodiment, formed of single component polypropylene homopolymer.

(10) The weight per unit area (g/m.sup.2) of the meltblown material 10 in this embodiment is around 30 g/m.sup.2. The water hold-out (hydrostatic head) of the meltblown material 10 in this embodiment is around 140 cm. The air permeability of the meltblown material 10 (e.g. 30 g/m.sup.2 meltblown fabric) is less than 150 I/m.sup.2/second.

(11) The meltblown material 10 is at least partially permeable and/or transparent to sterilisation means or agents, in this embodiment, steam, and/or ethylene oxide (EtO). Electron beam, or gamma radiation would degrade the polypropylene used in this embodiment. The meltblown material 10 allows sterilisation means to pass through the meltblown material. The meltblown material 10 is gas and air and liquid/moisture vapour permeable and liquid/moisture impermeable.

(12) Referring to FIG. 2, there is shown an apparatus, generally designated 300 for use in a method of manufacturing the meltblown fabric 10

(13) The method comprises meltblowing a molten material with an apparatus 300. The method comprises extruding a molten material from a polymer feed 311 through an extruder 313, then through a die with a plurality of spinnerets 312 into an airstream, producing a plurality of fibres. The plurality of fibres form a web 316, which is collected on a conveyor belt 315. The meltblown material is calendared between rollers 305 and 310, and is collected on a winder 320.

(14) The die is heated to a temperature of 275° C. The airstream is heated to a temperature of 295° C. The process air volume is 1800 m.sup.3/hr. The temperature of the molten polymer material at the nozzle of the die is around 268° C. The material throughput in this embodiment is 40 kg/hour. The distance from the die to the conveyor belt 315 in this embodiment 170 mm.

(15) Suction is applied through the conveyor belt 315 to collect the extruded fibres on the belt. In this embodiment around 95% of the collector area on the conveyor belt 315 has suction applied through it.

Second Embodiment (Spunbond)

(16) Referring to FIG. 3b, according to a second embodiment of the present invention there is provided a spunbond fabric or material 20, The spunbond material 20 comprises filaments. In this embodiment, the filaments have a diameter or average diameter in the range of 15 μm to 19 μm. The filaments of the spunbond material 20 have a smaller diameter or average diameter than the filaments of the spunbond material of the art 21 (see FIG. 3a).

(17) The spunbond material 20 has an abrasion resistance of 10,000 rubs or higher. The spunbond material 20 is self-supporting. The spunbond material 20 is point-bonded or embossed, e.g. calendar point-bonded 22. The embossed area of the surface of the spunbond material in this embodiment around 19% of the total surface area. The emboss points 22 are uniformly distributed on the spunbond material 20 in a repeating pattern.

(18) The spunbond material 20 is formed of polymeric filaments, and each filament comprises a single polymer. The spunbond material 20 is formed of single component metallocene catalysed polypropylene homopolymer.

(19) The weight per unit area (g/m.sup.2) of the spunbond material 20 in this embodiment is around 35 g/m.sup.2.

(20) The spunbond material 20 is at least partially permeable and/or transparent to sterilisation means or agents 50, such as steam, and ethylene oxide (EtO). The spunbond material 20 allows sterilisation means 50 to pass through the spunbond material 20.

(21) Referring to FIG. 4, there is shown an apparatus, generally designated 200 for use in a method of manufacturing the spunbond fabric or material 20.

(22) The method of manufacturing the spunbond material 20 comprises melt spinning a molten material with an apparatus 200. The method comprises extruding a molten polymer from a polymer feed 211 through an extruder 213, then a die with a plurality of filament spinnerets 212, producing a plurality of filaments. The plurality of filaments form a web 216, which is collected on a conveyor belt 215. The web 216 is calendared between an embossing calendar 205 and a flat roller 210 of a calendar 201, producing the spunbond material 20. The spunbond material 20 is collected on a winder 220.

(23) The die is heated to a temperature in this embodiment of 245° C. The temperature of the molten material at the nozzle of the die in this embodiment is 246° C. The material throughput in this embodiment is 320 kg/hour.

Third Embodiment (Laminate)

(24) Referring to FIG. 5, according to a third embodiment of the present invention there is provided a laminate 5, such as a medical or sterile packaging laminate material, the laminate 5 comprising the meltblown material 10, and the further spunbond material 20, for example, of the first and second embodiments of the present invention, respectively.

(25) The layers of the laminate material 5 are nonwoven materials 10, 20. The laminate material 5 comprises a meltblown material 10 of the first aspect/first embodiment of the present invention laminated between spunbond materials 20 of the third aspect/second embodiment of the present invention.

(26) The laminate 5 comprises three layers. The outermost layers of the laminate 5 comprise the same material 20. The layers of the laminate 5, therefore, have a spunbond/meltblown/spunbond structure or configuration.

(27) The SMS laminate 5, when (subsequently) flat calendared, has an abrasion resistance of 10,000 rubs or higher. The abrasion resistance of the nonwoven is measured using EDANA NWSP 020.5 RO.

(28) The SMS laminate when (subsequently) flat calendared has a microbiological filtration performance measured as a log reduction factor of 4 or higher. The laminate 5 filters microscopic organism(s).

(29) The laminate 5 is at least partially permeable and/or transparent to at least one sterilisation means or agents 50, such as at least one of steam and ethylene oxide (EtO). The laminate 5 allows sterilisation means to pass through the laminate 5. The laminate 5 is at least partially microscopic organisms impermeable. The laminate 5 is gas and/or air and/or liquid/moisture vapour permeable and/or liquid/moisture impermeable.

(30) The laminate 5 has the properties of the layers of the laminate 5. In this embodiment, the laminate 5 comprises the features of the first aspect of the present invention, by incorporation of a meltblown material 10 of the first aspect/first embodiment of the present invention in the laminate 5. The laminate 5 similarly has the features of the spunbond material 20 of the third aspect/second embodiment of the present invention.

(31) Layers of the laminate 5 are thermally laminated to one another between flat calendar rollers. The layers of the laminate 5 are thermally compatible; in this embodiment the layers of the laminate 5 have similar melting or softening points. In this way the layers are autogenously bonded.

(32) Referring to FIG. 6, according to an embodiment of the present invention, there is provided a method of manufacturing the laminate 5 comprising:

(33) step 1—laminating together one nonwoven layer 10 and two other nonwoven layers 20 using a calendar 100 comprising flat rollers (or bowls) e.g. a pair of flat (heated) rollers 105, 110; and

(34) step 2—calendaring the resulting laminate 5 with a calendar comprising flat rollers (or bowls) e.g. a/the pair of flat rollers 105, 110.

(35) By flat it is meant that the rollers 105, 110 are non-patterned and/or non-embossed. Herein by “flat” is meant to include polished and/or matt and/or sand blasted (e.g. to provide a rough engraving, in this embodiment to a roughness value of 30 μm to 45 μm) surface finishes to the rollers.

(36) The plurality of layers 10, 20 and/or the laminate 5 are passed through a pair of flat rollers 105, 110 with a nip 115 therebetween.

(37) Both heat and pressure are applied to the plurality of layers 10, 20 and the laminate 5 passing through the nip 115. As the rollers 105, 110 are flat, the pressure and temperature applied to the plurality of layers 10, 20 and the laminate 5 are substantially uniform across the width of the plurality of layers 10, 20 and the laminate 5.

(38) Each of the flat rollers 105, 110 comprises a steel roller, and each roller 105, 110 is provided with heating means.

(39) In this example the step of laminating the plurality of layers 10, 20 is performed “off-line”, i.e. in this embodiment the step of laminating the plurality of layers 10, 20 is not done on apparatus 200. It is, therefore, laminated on apparatus 100.

(40) The step of calendaring the laminate 5 is performed “off-line”. The steps of laminating and calendaring are performed with the same flat rollers 105, 110. The steps of laminating and calendaring are performed under different conditions.

(41) A pressure of 100 N/mm is applied to the plurality of layers 10, 20 during the lamination between the flat calendar rollers 105, 110. A temperature of 135° C. is applied to the plurality of layers 10, 20 during the lamination between the flat calendar rollers 105, 110.

(42) A pressure of 130 N/mm is applied to the laminate 5 during the calendaring between the flat calendar rollers 105, 110. A temperature of 154° C. is applied to the laminate 5 during the calendaring between the flat calendar rollers 105, 110.

(43) The speed of the first pass is 10 m/min. The speed of the second pass is 7.5 m/min.

EXAMPLES

(44) Examples of the present invention will now be given.

Example 1 (Fine Fibred Meltblown)

(45) Table 1 below compares standard processing parameters for manufacturing a meltblown fibre with the processing properties for manufacturing a meltblown fabric according to an embodiment of the present invention.

(46) TABLE-US-00001 TABLE 1 Meltblown Process Conditions Process Standard parameters of process the present parameters invention Die Temperature (° C.) 270 275 Process Air Set Temperature (° C.) 290 295 Process Air Volume (%) 55 62 Nozzle Melt Temperature (° C.) 258 268 Suction Zone 2 (%) 55 95 Polymer throughput (kg/hour) 100 40 Die to Collection Belt Distance 220 170 DCD (mm)

(47) It has been discovered that finer fibred polypropylene meltblown can be achieved with the meltblown process through changes to process settings that result in: (i) reduced polymer throughput per hole of the die, (ii) increased air speed at the die to increase draw on the polymer, (iii) increased polymer temperature to reduce viscosity and hence increase ability to increase attenuation of fibres, and (iv) less fibre entanglement.

(48) (i) Reduced polymer throughput per hole of the die—reduction in throughput (mass) of polymer passing through each die hole yields a reduction in the diameter of the resultant fibre produced. This reduction in polymer throughput means that there is less polymer to draw (attenuate) resulting in a finer fibre. It has been discovered that a reduction of 60% throughput yields the finest fibre whilst maintaining process integrity.

(49) (ii) Increased air speed at the die to increase draw on the polymer—process air is the air directed at molten polymer leaving the die. Increasing process air flow rate increases attenuation of the fibre. Increased process air flow also increases fibre velocity and thus reduces fibre travel time to the collection belt. Because it takes time for fibre entanglement to occur (resulting in coarse fibre agglomerations (bundles)), any process change that decreases fibre travel time reduces fibre entanglement, thus decreasing the number of coarse fibre agglomerations (bundles).

(50) (iii) Increased polymer temperature to reduce viscosity—increasing melt temperature through an increase in extruder, die, and process air temperature results in lower material viscosity: allowing material to flow more easily and for fibres to attenuate further.

(51) (iv) Less fibre entanglement—fibres commonly become entangled during processing into tight fibre agglomerations (bundles); these may be composed of single fibres or a large number of fibres. When fibre entanglement is reduced, the number and size of agglomerations (bundles) is reduced. Reducing the DCD (Die to Collection belt Distance) has the effect by reducing fibre travel time to the collection belt, which reduces coarse fibre agglomerations (bundles), for the reasons described above.

(52) Suction onto the collection belt is also increased to address the problem of fibre fly during production. Due to the low mass of these fibres, they are likely to be blown off the collection belt before having time to stick and crystallise. Greater belt suction applies more downward force on the fibres to encourage these finer fibres to be drawn to and remain on the belt.

(53) Table 2 below compares the properties of meltblown fibres made by the standard method with the properties of meltblown fibres of an embodiment of the present invention.

(54) TABLE-US-00002 TABLE 2 Meltblown Properties Air Permeability Pore Fibre l/m.sup.2/second diameter Area weight diameter (EDANA (μm g/m.sup.2 (μm) NWSP.070.1) BS3321) Conventional 30 2.53 237 34 Polypropylene Meltblown ‘Fine Fibred’ 30 1.24 131 22 Polypropylene meltblown

(55) It has been found that the microbiological barrier performance (measured as LRF) of the spunbond/meltblown/spunbond (SMS) laminate can be positively influenced by reducing the fibre diameter of the meltblown layer used. The finer fibred meltblown layer yields a lower pore size.

(56) This lower pore size, created by using the finer fibred meltblown, yields a much higher microbiological barrier performance, whilst retaining fabric breathability. Surprisingly LRF values of up to 6.1 have been obtained in laminates incorporating this finer fibred meltblown fabric.

(57) Such a meltblown material can be used as the inner layer in a spunbond/meltblown/spunbond (SMS) structure nonwoven laminate. Table 3 below compares the properties of a SMS laminate made with conventional meltblown layer and conventional spunbond layer with the properties of a SMS laminate made with a meltblown layer and spunbond layer both according to the present invention. The meltblown layer in each laminate is 30 gsm.

(58) TABLE-US-00003 TABLE 3 Laminate Properties Microbiological Air Barrier Meltblown Permeability Performance weight g/m.sup.2 (ml/min) Pore (Log (incorporated Fibre (Bendtsen diameter Reduction into diameter method (μm Factor) laminate) (μm) ISO 5636-3) BS3321) ASTM F1608 Conventional 30 2.53 60 12 3.1 Polypropylene Meltblown ‘Fine Fibred’ 30 1.24 55 <12 4.6 Polypropylene Meltblown

Example 2 (Fine Fibred Metallocene Spunbond)

(59) The abrasion resistance/fibre shedding properties of a spunbond fabric can be improved by increasing the extent of filament/filament bonding by decreasing filament diameter. This increases the length of filament for a given weight of fabric, and hence increases the number of filament/filament intersections that can be bonded. Increasing the number of filament/filament bond points results in a considerable increase in abrasion resistance (over 2 orders of magnitude increase), with a resultant decrease in fibre shedding.

(60) The filament diameter of spunbond filaments produced using conventional polypropylene homopolymer cannot be decreased beyond a certain point—due to filament breaking when trying to increase the draw on molten polypropylene polymer during extrusion, i.e. the filament diameter is restricted by the rheology of the polypropylene polymer as the rheology dictates the melt strength of the polymer during extrusion. The stronger the melt strength on the molten polymer, the greater draw one can apply, and hence the finer filaments that can be produced.

(61) Producing spunbond using metallocene, controlled rheology, polypropylene polymer allows increased draw during extrusion due to higher strength of this polymer in its molten state. By combining a lower throughput through each spinneret hole, combined with higher draw results in the production of finer fibres.

(62) Decreasing filament diameter using metallocene polypropylene has a number of positive impacts on the abrasion performance, and hence improvement in fibre shedding, for example: the lower melting point of metallocene polypropylene spunbond increases the degree of thermal consolidation for a given thermal calendar setting (temperature, pressure and throughput), hence improved bonding at the filament/filament intersection is observed; finer filaments have physically less mass to melt, during the thermal calendaring process, at filament/filament intersection, hence improving bonding; finer filaments mean that for a given weight of fabric there are considerably more filaments per unit area hence there are considerably more filament/filament intersections, giving more thermal bond points and hence improved abrasion resistance and significantly reduced fibre shedding; when incorporated into a spunbond/meltblown/spunbond laminate, the lower melting point of the outer spunbond layers (produced using metallocene polypropylene) is better able to bond to the other layers of the laminate. Hence the individual layers of the laminate are more firmly bonded together and less liable to delaminate when peeled away from another substrate to which it is bonded. This better laminate integrity also reduces the amount of fibre shedding as the individual layers of the laminate are less liable to peel apart.

(63) An improvement in abrasion resistance from 100 rubs (before fabric pilling occurred) to greater than 10,000 rubs has been found. This dramatic improvement in abrasion resistance effectively eliminates fibre shedding when the fabric is peeled from another substrate. Such a spunbond material can be used as the outer layers in a spunbond/meltblown/spunbond (SMS) structure nonwoven laminate. Table 4 below compares properties of SMS laminates not according to the invention (Comparative Example Sample A and Example Sample B) with one according to the present invention (Embodiment Sample C). Table 4 compares the properties of SMS laminates made with conventional spunbond layers and fine fibred meltblowns with the properties of an SMS laminate made with spunbond layers and with fine fibred meltblown according to the present invention. The laminate of the invention was laminated between flat rollers and subsequently flat calendared.

(64) TABLE-US-00004 TABLE 4 Abrasion Filament Resistance Spunbond Diameter EDANA Spunbond Melt Point μm Calender NWSP Fibre Polymer ° C. BS3321 Conditions 020.5.RO Shedding Sample A: 163 Average Embossed 800 rubs Considerable Conventional 20.87 Bowl 136° C. Polypropylene Range Smooth Homopolymer 19.5-23.5 Bowl 166° C. Pressure 32 N/mm Sample B: 163 Average Flat Bowl 100 rubs Considerable Conventional 20.87 147° C. Polypropylene Range Smooth Homopolymer 19.5-23.5 Bowl 147° C. Pressure 100 N/mm Sample C: 151 Average Flat Bowl >10,000 rubs None Metallocene 16.98 154° C. Polypropylene Range Smooth 15.0-18.5 Bowl 154° C. Pressure 130 N/mm

(65) 10,000 rub abrasion resistance is consistent with other medical packaging materials on the market. A fabric with an abrasion resistance of 10,000 rubs yields a material with an acceptable level of abrasion resistance for medical and/or sterile packaging

Example 3 (Two Pass Laminate)

(66) The degree of thermal consolidation, and hence abrasion resistance/fibre shedding and microbiological filtration performance of a spunbond/meltblown/spunbond laminate can be improved by conducting the initial lamination calendaring step through heated flat steel rollers (as opposed to conventional embossing rollers).

(67) Table 5 below compares the properties of a spunbond/meltblown/spunbond structure laminate made by the standard method (lamination through conventional embossed/flat roll calendar then subsequent flat calendaring of laminate) with the properties of similar laminate made with flat calendar lamination and subsequent flat roller calendaring of the spunbond/meltblown/spunbond structure laminate of an embodiment of the present invention.

(68) TABLE-US-00005 TABLE 5 Abrasion Resistance EDANA NWSP Fibre Process Route 020.5.RO Shedding Embossed Lamination followed 900 Rubs Considerable by Flat Calendering of Resultant Laminate Flat Calender Lamination >10,000 Rubs None followed by Flat Calendering of Resultant Laminate

(69) It has been established the degree of thermal consolidation, and hence abrasion resistance/fibre shedding along with microbiological filtration performance, can be improved by conducting the initial lamination calendaring step through flat bowls (as opposed to conventional embossed roller/flat roller calendar).

(70) It will be appreciated that the embodiments of the present invention herebefore described are given by way of example only, and are not meant to limit the scope of the invention in any way.

(71) It will also be appreciated that the term “medical” used herein is meant to include both human and animal medicine and surgery. It will be further appreciated that any ranges mentioned include within the range the end points of the range.