GB2543434A

GB2543434A - Improved fabric

Info

Publication number: GB2543434A
Application number: GB1619994.5A
Authority: GB
Inventors: Avril David; Galloway Keith; Baxter George
Original assignee: Don and Low Ltd
Current assignee: Don and Low Ltd
Priority date: 2011-10-13
Filing date: 2012-10-10
Publication date: 2017-04-19
Also published as: GB2495622A; GB201619994D0; GB201218165D0

Abstract

An air and/or moisture vapour permeable and/or liquid impermeable non-woven fabric, which may be used as a construction fabric, such as in the building industry as a housewrap walling fabric for timber frame houses or as a roof tile underlay, may be produced by calendering a precursor non-woven fabric with a flat roll 105,110 to uniformly apply pressure and/or heat. The precursor material may comprise a spunbond material. Alternatively the precursor material may be bonded by point embossed calendar bonding. The material may a comprise composite or laminate with a plurality of layers at least one of which is a nonwoven fabric layer. The nonwoven material may include a polyolefin spunbond material, which may be point-bonded and may include polypropylene homopolymer. The rollers may be heated metal rollers.

Description

IMPROVED FABRIC

FIELD OF INVENTION

The present invention relates generally to fabrics such as nonwoven fabrics. The invention also relates to breathable or permeable fabrics, or liquid impermeable and liquid vapour and/or gas permeable fabrics. The invention more particularly, though not exclusively, relates to air and/or moisture/water vapour permeable fabrics, such fabrics or materials may find particularly beneficial application as construction fabrics, such as in the building industry, e.g. as a housewrap walling fabric for timber frame houses or as a roof tile underlay.

BACKGROUND TO INVENTION

According to EDANA (the European Disposables and Nonwovens Association) nonwovens are engineered fabrics made from fibres and which are used across a wide range of applications and products.

Nonwovens typically have specific characteristics which can be selectably engineered dependent upon end use, e.g. moisture vapour permeability, gas/air permeability, liquid impermeability, resilience, stretch, softness, strength, flame retardancy, washability, cushioning, filtering. A nonwoven is a sheet of filaments (continuous filaments), fibres or chopped yarns of any nature or origin that have been formed into a web by any means, and bonded together by any means with the exception of weaving or knitting.

Composite structures or “laminates” are considered as nonwovens provided their mass is constituted of at least 50% of nonwoven or if the nonwoven component plays a prevalent role.

Also according to EDANA, a spunlaid nonwoven (also referred to herein as a spunbond fabric) comprises a spunlaid web bonded by one or more techniques to provide fabric integrity. Once such technique is point bonding (e.g. calender point bonding) which typically uses heat and pressure in a predetermined discrete (point) pattern to bind thermoplastic filaments or fibres to form a (self-supporting) nonwoven fabric. The filament or fibres of nonwoven fabrics typically comprise polymers or thermoplastics, e.g. polypropylene or alternatively polyethylene or polyester.

In the UK it is known to provide a wall breather membrane or a housewrap fabric comprising a single layer UV stabilised polypropylene based spunbond nonwoven fabric having a mass per unit area of 100g/m2 or 150g/m2. Both comprise an air and vapour permeable breather membrane.

Turning to laminate nonwoven fabrics EP 0 579 215 A, by the present Applicant, discloses use of a laminate as a roofing underlay material wherein said laminate comprises: a liquid impermeable and vapour permeable microporous membrane and a substrate, the membrane and substrate being intermittently bonded to preserve the liquid vapour transmission properties of the membrane. The laminate is provided with a supporting substrate on both sides of the membrane, the membrane and the substrates being intermittently bonded to preserve the liquid vapour transmission properties of the membrane. In one form one or both of the substrates of said laminate is a spunbonded polymeric nonwoven material.

The content of EP 0 570 215 A is incorporated herein by reference. EP 0 742 305 A, also by the present Applicant, discloses use as a building material (and particularly as a roofing underlay) of a laminated fabric comprising at least two layers of nonwoven sheet material, said fabric comprising: (1) a first layer of compressed meltblown material having an average pore size diameter in range from 1 pm to about 8pm; and (2) a second layer of a material having an open porous structure, and wherein the second layer of material is a spunbonded structure. The layers comprising the fabric are bonded by a point-bonding technique, such as a calendering treatment.

The content of EP 0 742 305 A is incorporated herein by reference. A commercially available SMS (Spunbond - Meltblown - Spunbond) laminate according to EP 0 742 305 A has a mass per unit area of 175g/m2

Other prior art is EP 1 400 248, also by the present Applicant, and EP 1 105 290 by Hunt Technology Limited.

It is an object of at least one embodiment of at least one aspect of the present invention to obviate or at least mitigate one or more problems in the prior art.

It is a further object of at least one embodiment of at least one aspect of the present invention to provide an improved nonwoven or spunbond fabric, such as a, particularly, though not exclusively, a single layer nonwoven or spunbond fabric, breathable building membrane suitable for use as a wall breather membrane or housewrap and/or for use as a roofing underlay.

It is an object of at least one embodiment of at least one aspect of the present invention to provide a lightweight nonwoven fabric shown in the prior art, e.g. a construction material such as a housewrap have a reduced mass per unit area as compared in the prior art, e.g. 50g/m2 instead of 100g/m2.

SUMMARY OF INVENTION

According to a first aspect of the present invention there is provided a method of manufacturing a nonwoven material or fabric, the method comprising: providing an initial or precursor nonwoven material or fabric; calendering the initial or precursor nonwoven material at least once using a calender comprising flat rollers (or bowls), e.g. a pair of flat rollers.

By flat is or may be meant that the rollers are nonpatterned and/or nonembossed. Herein by "flat" is meant to include polished and/or matt and/or sand blasted (e.g. to provide a rough engraving, e.g. to a roughness value of 30pm to 45pm) surface finishes to the rollers.

Preferably the nonwoven material comprises a spunbond material.

Preferably the initial nonwoven material is self supporting.

The initial (precursor) nonwoven material may comprise at least one layer which is bonded, e.g. to provide (structural) integrity of said at least one layer.

The initial nonwoven material may comprise at least one layer which is point-bonded or embossed, e.g. calender point-bonded.

An embossed area of the surface of the initial nonwoven material may be in the range 7% to 35%, e.g. 15% to 25%, e.g. around 19% of the total surface area.

The emboss points may preferably be of diamond shape, square shape, or round shape, e.g. circular, oval or elliptical.

The emboss points may be uniformly distributed on the initial nonwoven material, e.g. in a repeating pattern.

The initial nonwoven material may comprise a single layer of nonwoven fabric. The initial nonwoven material or fabric may advantageously comprise a single layer of spunbond fabric or spunbond filamentous layer.

The initial nonwoven material may alternatively comprise a composite or laminate material comprising a plurality of layers, at least one of the layers comprising a nonwoven fabric layer. The nonwoven material or fabric layer may advantageously comprise a single layer of spunbond fabric or spunbond filamentous layer.

Calendering the initial nonwoven material at least once may comprise calendering the initial nonwoven material once or alternatively more than once.

The nonwoven material may be laminated with or to another material(s) or fabrics(s), e.g. on at least one side or on both sides of the nonwoven material. Advantageously, the nonwoven material may be laminated with or to another material(s) or fabric(s) simultaneously with the step of (flat) calendering the initial nonwoven material. By the present invention it is therefore possible to provide a laminate including a nonwoven material wherein the laminate is not formed using a point-emboss pattern. This avoids any problems associated with having a laminate having two point-emboss patterns.

Alternatively or additionally, the nonwoven material may be laminated with or to another material(s) or fabric(s) prior to and/or subsequent to the step of (flat) calendering the initial nonwoven material.

The another material may comprise a film, a woven material, a reflective (e.g. heat/IR reflective) material or film, reinforcing net, a spunbond material or another nonwoven material.

The nonwoven material and another material may be thermally laminated to one another; the nonwoven material and another material may be thermally compatible, e.g. have similar melting or softening points.

The nonwoven material may comprise or substantially comprise a polymeric material(s), e.g. a thermoplastic polymer. The polymeric material may advantageously comprise polypropylene. Alternatively the polymeric material may comprise polyethylene.

The nonwoven material may be formed of polymeric filaments, and optionally, each filament may comprise or consist of a single polymer or co-polymer. The nonwoven material may be formed of polyolefinic filaments, such as single component or monocomponent polyolefinic filaments. As used herein, a single component filament may be formed by extruding from a single homogeneous polymeric material. Polyolefinic filaments used in nonwoven materials of embodiments of the invention may comprise or consist of a single polyolefin homopolymer, such as a polypropylene homopolymer or a polyethylene homopolymer. Polyolefin filaments of the invention may consist of a polyolefin, such as polypropylene, or alternatively, polyethylene.

The polymeric material may comprise one or more additives, e.g. selected from ultraviolet (UV) stabilisers, hydrophobic additives, flame retardants, pigments, colour pigments and/or plasticisers.

The flat rollers may comprise a pair of flat rollers with a nip therebetween through which the initial nonwoven material is caused to pass.

Preferably heat or pressure or preferably both are applied to the (initial) nonwoven material passing through the nip. As the rollers are flat, the pressure and/or temperature applied to the (initial) nonwoven material will be substantially uniform or even across a width of the (initial) nonwoven material.

Advantageously, each of the flat rollers comprises a metal roller such as a steel roller, and optionally, each roller is heated or is provided with heating means.

Preferably the step of providing the (initial) nonwoven material is performed “online”, e.g. by a further calendar having a pair of rollers at least one of which provides an emboss pattern.

Preferably the step of calendering the initial nonwoven material is performed “off-line”. A filament diameter of the initial nonwoven material may be in the range 12pm to 25pm, and preferably around 20pm. A weight per unit area (g/m2) of the initial nonwoven material may be in the range 15g/m2 to 150g/m2, and preferably around 80g/m2.

An average pore size of the initial nonwoven material may be greater than around 100pm.

An average pore size of the nonwoven material may be in the range 50pm to 100pm, or 60pm or 90pm, and preferably around 78pm. A water hold-out (hydrostatic head) of the initial nonwoven material may be in the range 10cm to 30cm, and preferably around 20cm. A water hold-out (hydrostatic head) of the nonwoven material may be in the range 15cm to 60cm and preferably around 40cm. A moisture vapour transmission rate (MVTR) of the initial nonwoven material may be around 2500g/m2/24 hr. A moisture vapour transmission rate (MVTR) of the nonwoven material may be around 1000g/m2/24 hr. A pressure of 20N/mm to 200N/mm, and preferably around 80N/mm may be applied to the initial nonwoven material between the flat calender rollers.

Air permeability for the initial nonwoven material (e.g. 100g/m2 spunbond fabric) may be 700l/m2/second to 800l/m2/second; the air permeability of the nonwoven material may be less than 100 l/m2/second. A thickness of the initial nonwoven material (e.g. 100g/m2 spunbond material) may be around 0.5mm and a thickness of the nonwoven material may be around 0.2mm. A temperature of 90°C to 170°C, may be applied to the initial nonwoven material between the flat calender rollers.

Accordingly to a second aspect of the present invention there is provided a method of manufacturing a nonwoven material or fabric comprising: providing or forming a first nonwoven material or web; bonding said first nonwoven material so as to provide a second nonwoven material; calendering the second nonwoven material or web using a calender having flat rollers.

Preferably the step of bonding is made using another calender having at least one point embossing roller.

According to a third aspect of the present invention there is provided a method of manufacturing a nonwoven material or fabric comprising: providing or forming a first nonwoven material or web; bonding said first nonwoven material or web to provide a second nonwoven material; uniformly applying heat and/or pressure to the second nonwoven material.

Preferably the step of uniformly applying pressure also comprises heating the second nonwoven material.

Preferably the pressure (and temperature) is/are applied by a calender having flat rollers.

Preferably the step of bonding is carried out using another calender having at least one embossed or point embossed calender.

According to a fourth aspect of the present invention there is provided a nonwoven material made by the method of any of the first, second or third aspects of the present invention.

According to a fifth aspect of the present invention there is provided a nonwoven fabric which has been calendered by a calender having at least one embossed roller so as to form an emboss pattern on the nonwoven material and subsequently calendered by a calender having flat rollers.

According to a sixth aspect of the present invention there is provided use of a nonwoven material according to either of the fourth or fifth aspects of the present invention advantageously as a construction product such as a walling fabric or roofing fabric, or alternatively as a graphic display or printing substrate, single use fabric or product, packaging product, workwear product or filtration product.

It will be appreciated that any of the features, e.g. optional features, of any of the foregoing aspects of the present invention may be used in any of the other aspects of the present invention whether alone or in combination, and are not recited herein in full merely for reasons of brevity.

BRIEF DESCRIPTIONS OF DRAWINGS

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

Figure 1 a schematic diagram of an apparatus for manufacture of a precursor nonwoven fabric for use in the present invention;

Figure 2 an emboss pattern engraved on a roller of a calender of the apparatus of Figure 1;

Figure 3 an enlarged top view of a portion of the emboss pattern of Figure 2;

Figure 4 an enlarged cross-sectional side view of a portion of the emboss pattern of Figure 2;

Figure 5 a schematic diagram of a further apparatus for manufacture of a nonwoven material according to the present invention;

Figure 6 a cut-away perspective view of a wall including a nonwoven fabric according to the present invention; and

Figure 7 a schematic cross-sectional side view of a part of a roof including a nonwoven fabric according to the present invention.

DETAILED DESCRIPTION OF DRAWINGS

Referring initially to Figures 1 to 5 according to an embodiment of the present invention there is provided a method of manufacturing a nonwoven material or fabric, generally designated 5, the method comprising: providing an initial or precursor nonwoven material or fabric 10; and calendering the initial or precursor unwoven material 10 at least once with a calender 100 comprising flat rollers (or bowls), i.e. a pair of flat rollers 105, 110.

By flat is meant that the rollers 105, 110 are nonpatterned and/or unembossed. Herein by "flat" includes polished and/or matt and/or sand-blasted (e.g. to provide a rough engraving, e.g. to a roughness value of 30pm to 45pm) surface to the rollers.

The initial nonwoven material 10 is self supporting. The initial (precursor) nonwoven material 10 comprises at least one layer which is bonded to provide integrity of said at least one layer. The initial nonwoven material 10 comprises at least one layer which is point-bonded or embossed, in this embodiment, calender point-bonded.

An embossed area of the surface of the initial nonwoven material 10 is in the range 7% to 35%, typically 15% to 25%, and in this embodiment around 19%. The emboss points can be of diamond shape, square shape, or round shape, e.g. circular, oval or elliptical. The emboss points are uniformly distributed on the initial nonwoven material 10, i.e. in a repeating pattern.

In this embodiment the initial nonwoven material 10 comprises a single layer of nonwoven fabric. The initial nonwoven material 10 comprises a single layer of spunbond fabric or spunbond filamentous layer. The initial nonwoven material 10 alternatively comprises a composite or laminate material comprising a plurality of layers, at least one of the layers comprising a nonwoven fabric layer. The nonwoven material or fabric layer advantageously comprises a single layer of spunbond fabric or spunbond filamentous layer.

In this embodiment calendering the initial nonwoven material 10 at least once may comprise calendering the initial nonwoven material 10 once or in an alternative embodiment more than once.

The nonwoven material 5 can be laminated with or to another material(s) or fabrics(s), e.g. on at least one side or on both sides of the nonwoven material. Advantageously, the nonwoven material 5 can be laminated with or to another material(s) or fabric(s) simultaneously with the step of flat calendering the initial nonwoven material 10. Alternatively or additionally, the nonwoven material 5 can be laminated with or to another material(s) or fabric(s) prior to and/or subsequent to the step of flat calendering the initial nonwoven material 10.

The another material typically comprises a film, a woven material, a reflective (e.g. heat/IR reflective) material or film, reinforcing net, a spunbond material or another nonwoven material.

The nonwoven material 5 and another material are beneficially thermally laminated to one another; the nonwoven material 5 and another material being thermally compatible, having similar melting or softening points.

The nonwoven material 5 comprises or substantially comprises a polymeric material(s), such as a thermoplastic polymer. In this embodiment the polymeric material advantageously comprises polypropylene. In alternative embodiments the polymeric material can comprise polyethylene.

The polymeric material typically comprises one or more additives, e.g. selected from ultraviolet (UV) stabilisers, hydrophobic additives, flame retardants, pigments, colour pigments and/or plasticisers.

The flat rollers 105, 110 comprise a pair of flat rollers with a nip 115 therebetween through which the initial nonwoven material 10 is caused to pass.

Heat or pressure or beneficially both are applied to the initial nonwoven material 10 passing through the nip 115. As the rollers are flat, the pressure and/or temperature applied to the nonwoven material will be substantially uniform or even across a width of the nonwoven material. Each of the flat rollers 105,110 comprises a metal roller, and in this embodiment, a steel roller, and each roller 105,110 is heated, i.e. is provided with heating means.

Referring to Figure 1, the step of providing or producing the initial nonwoven material 10 is done “on-line”, while referring to Figure 5, the step of calendering the initial nonwoven material 10 is done “off-line”. A filament diameter of the initial nonwoven material 10 can be in the range 12pm to 25pm, and typically around 20pm. A weight per unit area (g/m2) of the initial nonwoven material 10 can be in the range 15g/m2 to 150g/m2, and typically around 80g/m2.

An average pore size of the initial nonwoven material 10 can be greater than 100pm.

An average pore size of the nonwoven material 5 can be in the range 50pm to 100pm, particularly 60pm to 90pm, and typically around 78pm.

The water hold-out (hydrostatic head) of the initial nonwoven material 10 can be in the range 10cm to 30cm, and typically around 20cm.

The water hold-out (hydrostatic head) of the nonwoven material 5 can be in the range 15cm to 60cm, and typically around 40cm.

The moisture vapour transmission rate (MVTR) of the initial nonwoven material 10 can typically be around 2500g/m2/24hr.

The moisture vapour transmission rate (MVTR) of the nonwoven material 5 can typically be around 1000g/m2/24hr A pressure of 20N/mm to 200N/mm, and typically around 80 N/mm may be applied to the initial nonwoven material 10 between the flat calender rollers 105, 110. A temperature of 90°C to 170°C may be applied to the initial nonwoven material 10 between the flat calender rollers 105, 110.

Air permeability for the initial nonwoven material 10 (e.g. 100g/m2 spunbond fabric) is typically 700l/m2/second to 800l/m2/second; the air permeability of the nonwoven material is typically less than 100 l/m2/second. A thickness of the initial nonwoven material 10 (e.g. 100g/m2 spunbond material) may be around 0.5 mm and a thickness of the nonwoven material 5 may be around 0.2mm.

From the foregoing it will be appreciated that the disclosed embodiment of the present invention provides a method of manufacturing a nonwoven material or fabric 5 comprising: providing or forming a first nonwoven material or web; bonding, particularly point embossed calendar bonding, said first nonwoven material or web to provide a second nonwoven material; calendering the second nonwoven material or web using a calender 100 having flat rollers 105, 110.

The step of bonding is performed using spunbond apparatus 200 comprising another calender 201 having at least one point embossing roller 205 and a flat roller 210.

From the foregoing it will also be appreciated that the disclosed embodiment of the present invention provides a method of manufacturing a nonwoven material or fabric 5 comprising: providing or forming a first nonwoven material or web; bonding, particularly point embossed calender bonding, said first nonwoven material or web to provide a second nonwoven material; uniformly applying pressure and/or heat to the second nonwoven material.

The step of uniformly applying pressure also advantageously comprises heating the second nonwoven material.

The pressure (and temperature) is/are applied by a calender 100 having flat rollers 105, 110.

The disclosed embodiment of the present invention therefore provides a nonwoven material 5 made by the foregoing method. The nonwoven material 5 has been calendered by a calender 200 having at least one embossed roller 205 so as to form an emboss pattern on the nonwoven material and subsequently calendered by a calender 100 having flat rollers 105, 110.

The nonwoven material 5 advantageously finds use as a construction product such as a walling fabric or roofing fabric, or alternatively as a graphic display or printing substrate, single use fabric or product, packaging product, workwear product or filtration product.

Referring to Figures 1 to 5 in one implementation (so-called “off-line”) the nonwoven fabric is formed and rolled prior to calendering. The nonwoven fabric is formed by spunbond apparatus 200 and calendered by calendar 100 as will hereinafter be described.

In such method, the step of providing or forming includes the steps of laying down filaments so as to form initial nonwoven fabric and calendering the nonwoven fabric, e.g. with a first point-emboss pattern. Calendering is a thermal bonding technique involving the application of a combination heat and pressure.

Further, in such method the step of calendering the initial nonwoven fabric is performed with the apparatus of Figure 5.

The spunbond apparatus 200 comprises a polymer feed 211 for forming filaments and a plurality of filament spinners 212. Additives can be introduced in the polymer feed prior to melting and subsequent mixing in an extruder 213. Filaments are cooled by cooling means and loose laid as a web on a spinbelt. A conveyor 215 conveys the web 216 to a point-bonding calendar 201. The calender 201 has three embossing bowls 205, a first embossing bowl with a 19% embossing area (so-called STANDARD-BOND) and a diamond embossing pattern, and a second bowl, which is smooth, and a third bowl with a 7½ % embossing area (so-called LOW-BOND) with a round embossing pattern. The web is selected to be passed between the first and second bowls or the second and third bowls dependent upon the embossing pattern to be selected. After calendering the web forms a spunbond fabric, i.e. the filamentous polymer fabric. The spunbond fabric 109 is then rolled on wind-up roller 220.

The spunbond processing thus involves passing a polymer melt through a die with a plurality of holes to form a mass of filaments. The filaments are stretched, cooled, and formed into a loose web on a conveyor belt, and then passed through a calendar. The calender comprises a smooth roller and an embossed roller, the embossing pattern of which may typically cover from 7% to 35% of the surface area, and which may be a diamond, round or other shape. The smooth bowl of the calender should be of the swim roll type, i.e. is capable of being ‘bent’ to accommodate variations in thickness of the web. Both bowls of the calender 201 should be heated, the temperature selected being dependent on the type of polymer being processed, and on the balance of properties required in the end product.

The calender 100 can also operate as a laminator. A reel of spunbond fabric and optionally further material(s), e.g. membrane, are unrolled and passed through calendar 100. The calendar 100 has two smooth bowls, a first bowl 105 which is smooth and a second bowl 110 which is smooth. The calender 100 can also comprise an accumulator and a winder (not shown). Both bowls 105,110 are heated steel bowls.

The Inventors have found that by taking point embossed spunbond and subjecting it to a subsequent thermal consolidation, across 100% of the fabric area (i.e. flat calendering), certain fabric properties can be enhanced, in particular: improvement in water resistance (whilst maintaining moisture vapour permeability); improving fabric smoothness and flatness; reduction in fabric thickness; increased robustness; improved abrasion resistance; substantially reduced air permeability (whilst maintaining moisture vapour permeability).

This subsequent thermal consolidation step is across the complete area of the fabric (i.e. not point-bonding) and is achieved by passing the spunbond fabric through two flat thermal calender rollers at elevated temperature and pressure (see Figure 5).

The invention alters certain properties of point-bonded spunbond by imparting an additional thermal treatment through two flat rollers using pressure and heat. This process further consolidates the fabric, reducing pore size whilst maintaining the fabric structure. It is presently believed that an advantage of using flat thermal rollers is that it maximises consolidation by achieving a high amount of fibre to fibre bonding.

The reduction in pore size has the effect of significantly enhancing the fabrics water hold out characteristics whilst the pores still allow breathability of water vapour through the fabric structure. This can be witnessed by a substantial increase in hydrostatic head; see Table 1 below. This is particularly desirable for construction applications. In addition this additional thermal process, and resultant reduction in pore size, can have the impact of converting the nonwoven fabric from an air permeable material to effectively an air barrier material, with a much reduced air permeability, see Table 1 below. This is again desirable for construction applications as specifiers seek additional measures to reduce air leakage from a building. However, this reduction in air permeability is not achieved at the expense of moisture vapour permeability. This is because, whilst the fabric is thermally consolidated across its entire surface, it maintains it fibrous nature, hence retaining the ability to allow the transmission of moisture vapour.

The fully thermally consolidated spunbond is also extremely tough, being considerably more robust than conventional spunbond. This makes it particularly suited for tear resistant packaging applications, such as tear resistant envelopes.

In addition the additional thermal consolidation produces a much flatter surface which makes the resultant fabric particularly suitable as a printing substrate. The print quality is unaffected by the depressions in the fabric surface, caused by the original point-bonding of the spunbond, as the subsequent thermal consolidation ‘flattens’ these out to produce a flat, smooth surface for printing

This invention relates specifically to additional thermal treatment of a polyolefin spunbond substrate that has already been point-bonded. Normally in the art such thermal treatments are applied to unbonded fabric mats during production of the fabric, not as an additional, subsequent operation.

Advantages of applying an additional thermal treatment to 100% of the fabric area in a second ‘off line’ calendering process, that has already been point-bonded, are numerous.

The initial calender point-bonding of the spunbond substrate can be optimised for the final application. For instance the spunbond substrate can be produced with a lower percentage point-bond area and/or reduced calender point-bonding when producing the spunbond substrate. This produces a much smoother surface when this spunbond is subjected to a subsequent, 100% coverage thermal calendering step. This is important in applications where a smooth surface is desirable, such as for use as a substrate for printing.

The operating conditions of the second thermal consolidation step (such as temperature, pressure or throughput) can be optimised to produce a fully consolidated fabric with the required physical properties. The process conditions are not dictated by other factors such as rate of production of the spunbond, as would be the case if this thermal consolidation step were integrating into the spunbond process itself.

By conducting the subsequent calender process as a second step (‘off line’) the production of spunbond substrate can be produced on a variety of different production lines. This allows the spunbond substrate to be produced on the most appropriate production line to optimise its properties, prior to 100% thermal consolidation.

By conducting the 100% thermal consolidation off-line multiple layers of spunbond can be combined to produce a composite spunbond material, e.g. spunbond materials of different colours can be combined to form a 100% consolidated fabric where each side is a different colour. Combining multiple layers of spunbond also gives more even fibre distribution resulting in a more consistent fabric with improved appearance.

Conducting 100% thermal consolidation ‘off-line’ also allows spunbond to be combined with other types of substrate, such as nets, films and other nonwovens, to produce a 100% consolidated composite product with differentiated properties.

Spunbond produced using a variety of polyolefin polymers can be enhanced via this subsequent 100% thermal consolidation step.

EXAMPLES

Examples of materials made according to the present invention will now be given. EXAMPLE 1

Table 1 below compares properties of conventional point-bonded (or point embossed) polypropylene spunbond with the same fabric that has been subjected to subsequent flat calendering, i.e. additional 100% thermal consolidation, at different temperatures:

Table 1

It can be seen from Table 1 that the fabric subjected to additional thermal consolidation: • Is over 50% thinner than conventional spunbond resulting in increased density. • Has reduced air permeability, which can effectively make the fabric an air barrier. • Has improved water hold-out, as can be seen from the higher hydrostatic head values.

• Retains its fibrous structure allowing the fabric to maintain its water vapour permeability. • Has increased machine-direction strength with improved resistance to surface abrasion.

It can also be seen from Table 1 that the greater the degree of this subsequent calendering or thermal consolidation the greater the impact on the properties of the resultant fabric. A number of variables that can influence the extent of this subsequent thermal consolidation step are: • Machine throughput - the slower the speed of the fabric through the process the greater the degree of thermal consolidation. • Roller temperature - the higher the temperature of the calender rollers the greater the degree of thermal consolidation. • Nip pressure (between the calender rollers) - increasing calender roller nip pressure increases heat transfer through the fabric and increases the degree of bonding at the contact points between filaments, increasing the degree of thermal consolidation.

It should also be noted that passing spunbond through this 100% consolidation step more than once can further influence the fabric properties, e.g. passing spunbond through 100% thermal consolidation will influence fabric properties as indicated in Table 1, and by taking this consolidated spunbond and passing back through this 100% thermal consolidation process again, i.e. repeating the flat calendering step, will further influence the fabric properties, which can be advantageous in certain situations. EXAMPLE 2 A standard method of assessing the suitability of a fabric for use as a housewrap fabric for the UK construction marker is the Mason Jar test, as defined in BS 4016. This test measures the ability of a fabric to withstand a standing head of water without leakage over a 24 hour period. For conventional, point-embossed polypropylene spunbond the minimum fabric weight that can pass the Mason jar test is 100g/m2. As such this weight of fabric has become the minimum weight for spunbond housewrap fabrics in the UK. Table 2 below demonstrates the practical advantages that an additional 100% thermal consolidation step can have on spunbond fabric. It can be seen from Table 2 that subjecting spunbond to 100% thermal consolidation reduces the pore size to such an extent that 60g/m2 fabric now passes the Mason jar test. This improvement in water hold out is achieved whilst retaining the ability of the fabric to transmit water vapour. The Moisture Vapour Transmission Rate (MVTR) only reduces to 1000g/m2/day which is well above the minimum breathability for a housewrap fabric in the UK (as defined in BS4016) of 342g/m2/day.

Table 2

EXAMPLE 3

The additional flat calendering or thermal consolidation step, as described above, can also be used effectively to advantageously modify the properties of nonwoven composites such as spunbond/meltblown/spunbond (S/M/S) composites to improve water hold out properties whilst retaining moisture vapour permeability. See Table 3 below:

Table 3

In Table 3 the SMS laminate has been produced by combining the various components of the composite on a conventional ‘point-bonding’ thermal lamination calender. The composite has then been passed through a second flat calendering or thermal consolidation step, as previously described.

In addition a 100% thermally consolidated spunbond can itself be used as part of nonwoven composite. In this example the fully consolidated spunbond can be combined with other nonwovens, either fabric, net or film, in a variety of different ways to produce a composite fabric with enhanced properties.

Examples of how differentiated composite fabrics can be produced using a 100% thermal consolidation process are: • A spunbond that has been subjected to subsequent 100% thermal consolidation can then be laminated with other materials using a conventional point-bonding calender (either thermal or ultrasonic).

• Another option is to take the composite produced above (through a point-bonding lamination process) and passing the composite back through the 100% thermal consolidation unit. • Alternatively conventional point-bonded spunbond can be combined with other substrates in a single step through the 100% thermal consolidation process. • There are also benefits in subjecting spunbond to 100% thermal consolidation then subsequently combining this material into a composite with other materials via the same 100% thermal consolidation process.

There may also be situations where a ‘smooth and flat’ composite surface is desirable, as opposed to an uneven ‘point-bonded’ surface. An example would be thermally bonding a reflective material to spunbond to produce a reflective housewrap composite fabric where a ‘flatter’ reflective surface will give a lower emissivity (higher reflectance). This ‘flatter’ fabric offers a superior thermal performance when used as part of a thermal insulation system in, for instance, a timber frame house. Thus, according to the invention a point-embossed spunbond may therefore be flat calendar laminated to a reflective film. EXAMPLE 4

Various current construction products were flat calendered to evaluate changes to the physical properties as detailed in Table 4.

Table 4

Effect on key properties is as shown in Table 5.

Table 5

Potential construction related applications for flat calendered nonwoven fabrics according to the invention include: • Lighter Weight Single Layer Air Breather Walling Fabric (for UK) - the increase in water hold should allow a lighter weight fabrics to pass Mason Jar. Despite the lower nail tear values the fabrics are very ‘tough’. • Single Layer Air Barrier Walling Fabric - currently there is a requirement in mainland Europe and US for an air barrier walling fabric, this is currently met with air barrier spunbond laminates containing microporous film. This could be substituted with a single layer fabric providing the single layer flat calendered product is an air barrier. EXAMPLE 5

According to an embodiment of the invention there is provided a nonwoven product comprising a spunbond fabric with differentiated appearance and properties. These include: • Over 50% thinner than conventional spunbond resulting in an increased density giving a dramatic reduction in air permeability, effectively making the fabric an air barrier, along with improved water hold out; • Retention of fibrous structure allowing the fabric to maintain water vapour permeability; • A smoother surface providing a superior substrate for printing; • Greater thermal processing gives improved resistance to abrasion and increased strength.

Technical data includes:

Table 6

EXAMPLE 6

Referring to Figure 6 there is shown a schematic cut-away perspective view of part of a building construction 300 comprising a cavity wall 305 of a timber frame 310, including a nonwoven fabric 5 as a “housewrap”, i.e. an outermost skin 315 of a timber frame. The building construction 300 is finished by external skin 320 comprising bricks 320 or the like. The building construction 300 is typically constructed by erecting the timer frame 310 with outermost skin 315 and thereafter finishing with the external skin 320. EXAMPLE 7

Referring now to Figure 7, there is shown a schematic cross-sectional side view of part of a building construction comprising a roof 400, e.g, a pitched tiled roof, including a nonwoven fabric 5 as a roofing underlay and a plurality of tiles 405. As can be seen, the roof may include a plurality of overlapping lengths of fabric.

The fabric may span between adjacent structural members (now shown), e.g. A-frame rafters, battens or the like. Further as can be seen there are provided counter battens 410 spanning between and fixed to the structural members, the counter battens supporting the tiles 405 in a conventional way.

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

It will be understood that although the fabrics of the present invention find particularly advantageous use in the building and/or construction industry, the fabrics of the invention may also find use in other sectors.

Key properties of flat calendered 100g/m2 and 150g/m2 single layer point-embossed spunbond have been found to be:

Table 7

Possible use of the flat calendered nonwoven fabrics includes: • Substrate for printing, e.g. banners, of advertising displays/billboards, material for use as targets. • Air barrier walling fabric (for UK) - possible alternative to 100g/m2 to 150g/m2 single layer walling fabric, increased water hold out may allow weight reduction. • air barrier walling fabric (for Europe) - walling fabrics for the continent and Europe have to be airtight. This nonwoven fabric can provide an airtight single layer walling fabric. • Packaging - flat calendered spunbond resembles TYVEK®, and is therefore useful in ‘tough’ durable envelopes or the like. • Workwear - flat calendered fabric could offer a single layer alternative to in line SMS laminated fabric. TYVEK® is a single layer workwear fabric, which resembles flat calendered spunbond. Could also be used as a stiffener in clothing components. • Filtration - Controlled porosity materials for industrial filtration.

• Covers - e.g. for building, vehicles of the like.

Other potential uses are flat calender laminates, include: • lower emissivity reflective products - initial indications are that flatter reflective products have lower emissivity; • potential application of full width adhesive to construction products; • reinforced membranes - calendering reinforcing net with flat bowl should give reduced damage (no embossed points) and result in a stronger fabric, with possibility to reduce weight. Also possible use of woven products e.g. leno’s for high strength reinforced fabrics; • new laminates - possible use of tie layers for joining dissimilar materials together.

It will be appreciated that the characteristics of flat calendered point-embossed spunbond according to the invention suggest that for a given water hold-out or water resistance a reduced weight fabric can be used. This may be of particular benefit in some applications, e.g. construction such as walling or roofing.

Claims

1. A method of manufacturing a nonwoven material or fabric, the method comprising: providing an initial or precursor nonwoven material or fabric, wherein the nonwoven material comprises a spunbond material; calendering the initial or precursor nonwoven material at least once using a calender comprising flat rollers.

2. A method as claimed in claim 1, wherein the initial nonwoven material comprises at least one layer which is point-bonded or embossed, such as calender point-bonded.

3. A method as claimed in any preceding claim, wherein the nonwoven material comprises or substantially comprises a polymeric material(s), such as a thermoplastic polymer, e.g. a polyolefin.

4. A method as claimed in claim 3, wherein the polymeric material comprises or consists of polypropylene or polyethylene.

5. A method as claimed in any preceding claim, wherein the nonwoven material is formed of polyolefinic filaments, such as single component or monocomponent polyolefinic filaments.

6. A method as claimed in any preceding claim, wherein the nonwoven material is formed of polymeric filaments which comprise or consist of a single polyolefin homopolymer, such as a polypropylene homopolymer or a polyethylene homopolymer.

7. A method as claimed in any preceding claim, wherein the initial nonwoven material is self supporting.

8. A method as claimed in any preceding claim, wherein the initial (precursor) nonwoven material comprises at least one layer which is bonded to provide integrity of said at least one layer.

9. A method as claimed in any of claims 2 to 8, wherein an embossed area of the surface of the initial nonwoven material is in the range 7% to 35%, or 15% to 25%, or around 19%.

10. A method as claimed in any of claims 2 to 9, wherein the emboss points are of diamond shape, square shape, round shape, or are circular, oval or elliptical.

11. A method as claimed in any of claims 2 to 10, wherein the emboss points are uniformly distributed on the initial nonwoven material, such as in a repeating pattern.

12. A method as claimed in any preceding claim, wherein the initial nonwoven material comprises a single layer of nonwoven fabric.

13. A method as claimed in any of claims 2 to 11, wherein the initial nonwoven material comprises a composite or laminate material comprising a plurality of layers, at least one of the layers comprising a nonwoven fabric layer.

14. A method as claimed in any preceding claim, wherein the nonwoven material or fabric layer comprises a single layer of spunbond fabric or spunbond filamentous layer.

15. A method as claimed in any preceding claim, wherein calendering the initial nonwoven material at least once comprises calendering the initial nonwoven material once or more than once.

16. A method as claimed in any preceding claim, wherein the nonwoven material is laminated with or to another material(s) or fabrics(s), such as on at least one side or on both sides of the nonwoven material.

17. A method as claimed in any preceding claim, wherein the nonwoven material is laminated with or to another material(s) or fabric(s) simultaneously with the step of (flat) calendering the initial nonwoven material.

18. A method as claimed in any preceding claim, wherein the nonwoven material is laminated with or to another material(s) or fabric(s) prior to and/or subsequent to the step of (flat) calendering the initial nonwoven material.

19. A method as claimed in any of claims 16 to 18, wherein the another material comprises a film, a woven material, a reflective material or film, reinforcing net, a spunbond material, another nonwoven material, or another nonwoven material according to claim 1.

20. A method as claimed in any of claims 16 to 19, wherein the nonwoven material and another material are thermally laminated to one another; the nonwoven material and another material being thermally compatible, having similar melting or softening points.

21. A method as claimed in any of claims 3 to 20, wherein the polymeric material comprises one or more additives, optionally selected from ultraviolet (UV) stabilisers, hydrophobic additives, flame retardants, pigments, colour pigments and/or plasticisers.

22. A method as claimed in any preceding claim, wherein the flat rollers comprise a pair of flat rollers with a nip therebetween through which the initial nonwoven material is caused to pass.

23. A method as claimed in claim 22, wherein heat or pressure or both are applied to the initial nonwoven material passing through the nip.

24. A method as claimed in claim 23, wherein the rollers are flat, the pressure and/or heat applied to the nonwoven material is substantially uniform or even across a width of the (initial) nonwoven material.

25. A method as claimed in any preceding claim, wherein each of the flat rollers comprises a metal roller such as a steel roller, and optionally, each roller is heated or provided with heating means.

26. A method as claimed in any preceding claim, wherein the step of providing the initial nonwoven material is performed on-line on a spunbond apparatus comprising a/the further calender.

27. A method as claimed in any preceding claim, wherein the step of calendering the initial nonwoven material is performed off-line using the calender.

28. A method as claimed in any preceding claim, wherein a filament diameter of the initial nonwoven material is in the range 12pm to 25pm, or around 20pm.

29. A method as claimed in any preceding claim, wherein a weight per unit area (g/m2) of the initial nonwoven material is in the range 150g/m2 to 180g/m2, or around 80g/m2.

30. A method as claimed in any preceding claim, wherein an average pore size of the initial nonwoven material is greater than 100pm.

31. A method as claimed in any preceding claim, wherein an average pore size of the nonwoven material is in the range 60pm to 90pm.

32. A method as claimed in any preceding claim, wherein a water hold-out (hydrostatic head) of the initial nonwoven material is in the range 10cm to 30cm, or around 20cm.

33. A method as claimed in any preceding claim, wherein a water hold-out (hydrostatic head) of the nonwoven material is in the range 15cm to 60cm, or around 40cm.

34. A method as claimed in any preceding claim, wherein a moisture vapour transmission rate (MVTR) of the initial nonwoven material is around 2500g/m2/24hr.

35. A method as claimed in any preceding claim, wherein a moisture vapour transmission rate (MVTR) of the nonwoven material is around 1000g/m2/24hr.

36. A method as claimed in any preceding claim, wherein a pressure of 20N/mm to 200N/mm, or around 80N/mm is applied to the initial nonwoven material between the flat calender rollers.

37. A method as claimed in any preceding claim, wherein an air permeability of the initial nonwoven material is greater than 700 l/m2/second and/or the air permeability of the nonwoven material is less than 100 l/m2/second.

38. A method as claimed in any preceding claim, wherein the thickness of the nonwoven material is less than or equal to 70% or 50% of the thickness of the initial nonwoven material.

39. A method as claimed in any preceding claim, wherein a temperature of 90°C to 170°C is applied to the initial nonwoven material between the flat calender rollers.

40. A method of manufacturing a nonwoven material or fabric comprising: providing or forming a first nonwoven material or web; bonding said first nonwoven material so as to provide a second nonwoven material; calendering the second nonwoven material or web using a calender having flat rollers.

41. A method as claimed in claim 340, wherein the step of bonding is made using another calender having at least one point embossed roller.

42. A method of manufacturing a nonwoven material or fabric comprising: providing or forming a first nonwoven material or web; bonding, particularly point embossed calender bonding, said first nonwoven material or web to provide a second nonwoven material; uniformly applying pressure and/or heat to the second nonwoven material.

43. A method as claimed in claim 42, wherein the step of uniformly applying pressure also comprises heating the second nonwoven material.

44. A method as claimed in either of claims 42 or 43, wherein the pressure or temperature is/are applied by a calender having flat rollers.

45. A nonwoven material made by the method of any of claims 1 to 44.

46. A nonwoven fabric which has been calendered by a calender having at least one embossed roller so as to form an emboss pattern on the nonwoven material and subsequently calendered by a calender having flat rollers.

47. Use of a nonwoven material according to either of claims 45 or 46 as a construction product such as a walling fabric or roofing fabric, or alternatively as a graphic display or printing substrate, packaging product, workwear product or filtration product.

48. A method of manufacturing a nonwoven material or fabric as hereinbefore described with reference to the accompanying drawings.

49. A nonwoven material or fabric as hereinbefore described with reference to the accompanying drawings.

50. Use of a nonwoven material or fabric as hereinbefore described with reference to the accompanying drawings.