Improved multilayer laminate

Abstract

The multilayer fabric comprises a first meltblown layer 121 including a hydrophobic additive laminated to a second melt-blown layer 122 and a 1st outer, spunbond layer 111. The melt blown layers 121,

Description

Field of the Invention The present invention relates to a laminated fabric and a method of producing 5 same. In particular, but not exclusively, the invention relates to a laminated fabric suitable for use in building materials, such as a roofing underlay. Background Vapour-permeable fabrics known in the art as possessing good barrier properties 10 to water droplets and / or solid particles generally comprise co-extruded or monolayer films comprising a plurality of micropores or monolithic films. Such vapour permeable films may be used as roofing underlays due to their ability to assist in evacuating unwanted moisture from roof spaces. Generally these vapour permeable films that provide a barrier to the passage of water droplets are air barrier materials known as LO 15 vapour permeable / air barrier roofing underlays. C\l However, in the UK, it is increasingly acknowledged that roofing underlays that -j— are both vapour permeable and air permeable are very effective at evacuating large amounts of water from the roof space beneath the underlay. Air permeable and vapour permeable underlays are termed ‘breathable’ and are acknowledged to form an effective 20 alternative to traditional mechanical vents in ‘cold’ unoccupied roof spaces. That is to say that the underlay is sufficiently breathable such that any moisture entering the roofspace from the occupied living area underneath will be evacuated from the roofspace into the atmosphere through the underlay itself. There are two typical types of roof construction: 25 - ‘warm’ roofs - where the insulation is at rafter level with the roofspace itself being occupied, and - ‘cold’ roof spaces - where the insulation is laid on the floor of the roofspace and it is unoccupied. Traditionally, unwanted moisture is evacuated from ‘cold’ roof spaces via the 30 introduction of mechanical vents, typically at the eaves and the ridge. These mechanical vents allow atmospheric air to enter and leave the roofspace, which effectively transports unwanted moisture to the outside atmosphere. The use of mechanical vents at the eaves and / or ridge of a ‘cold’ unoccupied roof space can increase the heat losses from a property by various mechanisms including (i) increasing the temperature gradient 35 between the occupied and unoccupied spaces, and (ii) air entering the roof space via mechanical vents at the eaves can pass through the glass wool insulation laid on the floor of the roofspace, thus reducing the efficiency of the insulation. The use of an air and vapour permeable roofing underlay as an alternative to mechanical ventilation may reduce heat losses and improve the thermal efficiency of a property, whilst at the same time reducing the risk of condensation. The superior performance of air permeable fabrics when compared to air barrier materials to reduce condensation in energy efficient ‘cold’ (unoccupied) unventilated roofspaces has been acknowledged by the National House Building Council (NHBC) in the UK. This national body now insist that, for any new build domestic property that incorporates a nonventilated ‘cold’ roof space, i.e. where traditional mechanical vents are eliminated from the roof construction, only roofing underlays that are both air and vapour permeable are used. Whilst it is desirable that roofing underlays are air permeable to assist in moisture evacuation, at the same time, roofing underlays should also possess sufficient levels of water hold-out to be fit for purpose. For instance, roofing underlays are preferably resistant to wind-driven rain and sitting water. According to EDANA (the European Disposables and Nonwovens Association), a nonwoven fabric 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. 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 and / or filtering. A spunlaid nonwoven (also referred to herein as a spunbond fabric) comprises a spunlaid web. A spunbond or spunlaid nonwoven material is formed of continuous filaments, typically having a filament diameter greater than 15 micron (pm). A meltblown nonwoven material is comprised of discontinuous fibres, typically having a fibre diameter 2.5 micron (pm) or greater. The spunlaid web can be bonded by one or more techniques to provide fabric integrity. One such technique is point-bonding (e.g. thermal calender point bonding) which typically uses heat and pressure in a predetermined discrete (point) pattern to fuse 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. Air permeable roofing underlays typically comprise a meltblown layer. The weight, pore size and fibre diameter of the meltblown layer is the primary functional layer regulating the underlays vapour permeability, air permeability and water hold out. Typically, in order to provide support for the meltblown layer, the meltblown layer in combined with a one or more spunbond layers. An example of such a laminated fabrics is described in EP 0742305 B2 (Ferrar et al). In certain embodiments, the meltblown material is sandwiched between two layers of spunbond material. The layer(s) of spunbond material may define outer layers of the laminated fabric and may provide support to the meltblown layer. The spunbond material may act as an abrasion resistant, durable and / or protective cover for the meltblown material. This laminate structure is conveniently referred to an ‘SMS’ (spunbonded / meltblown / spunbonded) structure. The water hold-out performance of an SMS composite is conventionally dictated by the weight of the micro fibrous meltblown present in the SMS laminate: • The heavier the weight of meltblown present, the greater the water hold-out performance of the SMS laminate, i.e. the greater the hydrostatic head value. This is because there is more micro fibrous material present to resist the passage of water resulting in improved hydrostatic head values. The inclusion of higher weights of micro fibrous meltblown in laminates normally corresponds to a decrease in the fabric’s ability to breathe, as measured by air permeability, due to the heavier microfibrous meltblown layer offering a greater resistance to air flow through the fabric. • Conversely, it has been observed that a reduction in the weight of the micro fibrous meltblown layer in the laminate results in a reduction in water hold-out performance, i.e. a lower hydrostatic head value. This is because there is less micro fibrous material present to resist the passage of water hence the lower hydrostatic head values. However, a reduction in a weight of the meltblown layer should improve the breathability, or air permeability, of the laminate due to less microfibrous material resisting the passage of air flow through the fabric. The ability of the fabric to hold out water can be quantified by measuring the hydrostatic head of the fabric. Water hold-out is required to offer a weatherproof under tile layer. The ability of the fabric to hold out water can be quantified by measuring the hydrostatic head of the fabric. Hydrostatic head is quoted in either cm or metres and represents the pressure required to force a minimum of 3 drops of water through the fabric. A suitable European test method is laid out in EN 20811. Typically, air barrier, air permeable underlay fabrics have hydrostatic head values that exceed 3 metres whilst air permeable, vapour permeable underlays typically exhibit hydrostatic head values of 1 metre to 1.5 metre. Water hold out performance of air permeable fabrics can also be further enhanced by hydrophobic treatments applied to the spunbond surface. The water vapour transmission rate (MVTR) of a breathable fabric can be quantified by measuring using an established gravimetric test method, such as EN ISO 12572 (Hygrothermal performance of building materials and products- Determination of water vapour transmission properties cup method), which quantifies the amount of moisture vapour passing through a set area of membrane under standard conditions over a 24-hour period. However, MVTR is a ‘passive’ test method and is not always an accurate measure of the ability of a fabric to dynamically allow the free passage of moisture. It is believed that measuring a fabric’s air permeability may be better at quantifying a fabric’s ‘breathability’ towards water vapour, i.e. air permeable fabrics are better able to dynamically allow large quantities of water vapour to pass through the material. Air permeability is quantified by measuring the quantity of air (measured in litres / m2 / second or l / m2 / s) that passes through a fixed area of fabric at a set pressure drop across the fabric. In Europe, a well-established air permeability test method has been developed by EDANA. This test method is EDANA 140.2 - 99 and measures the quantity of air (measured in l / m2 / s) passing through a 20cm2 fabric area at a pressure drop of 200 Pascals. Whilst the water hold-out performance of a non-woven laminated fabric may be increased by increasing the weight of the meltblown layer, the use of a heavier meltblown material can cause a decrease in air permeability, as the heavier meltblown layer offers greater resistance to air flow through the fabric. Heavier meltblown materials also may lead to heavier composite fabrics which are less easy to handle when in use on a building site. The use of heavier meltblown materials to obtain higher levels of water hold-out may also significantly add to the cost of the final product, as the meltblown layer is typically the most expensive component of such laminated fabrics. Attempts have been made to reduce the weight of the meltblown layer in order to, inter alia, reduce the costs of the final product and improve ease of handling, whilst maintaining satisfactory levels of water hold-out. Examples of such improved laminated fabrics are disclosed in GB 2494544 B (Avril et al). Typically, roofing laminates also comprise additives to impart advantageous functions to the laminate without increasing its weight. Examples of such conventional additives include hydrophobic melt additives, UV absorbers, flame retardants, pigments and / or plasticisers. In particular, air permeable roofing laminates typically use a hydrophobic additive in the meltblown layer to improve rain and chemical resistance. Such hydrophobic additives are conventionally based on fluorocarbon organic compounds, and include per-and poly-fluoroalkyl substances (PFAS), and perfluorooctane sulfonic acid derivatives (PFOS). However, due to environmental concerns, a number of fluorocarbon-based hydrophobic additives have been withdrawn from manufacture and restricted from use in the UK, the EU, and other parts of the world. Such banned compounds include for example C8 fluorocarbon hydrophobics, and certain C6 fluorocarbon hydrophobics. As a result, it has been necessary to replace those banned additives with more environmentally friendly hydrophobic compounds. A problem with such alternative compounds is that they are generally based on a less thermally stable chemistry, and, in particular, degrade at lower temperatures. This, in turn, means that the extrusion process to manufacture the meltblown layer must be carried out at lower temperature. For example, while a conventional extrusion temperature for the meltblown may be in the region of about 280 °C, the temperature stability of the replacement hydrophobic additives requires the use of lower temperatures, typically less than 260°C, preferably less than 250°C, e.g. about 220 °C-250°C. For health and safety reasons, maintaining the chemical stability of the additives is important in order to minimise the potential release of toxic hydrogen fluoride. A consequence of the reduced extrusion temperature is a radical change of the melt characteristics and of the extrusion performance, all of which change the filament geometry and other characteristics of the fabric web. In particular, reducing extrusion temperature, when seeking to otherwise maintain other extruding parameters, causes an increase in filament diameter due the lower viscosity of the polymeric material at lower temperatures. This also results in the overall meltblown layer of a given weight having increased air permeability but also decreasing its hydrostatic head value, which is undesirable. It is an object of the invention to address and / or mitigate one or more problems highlighted above and / or associated with the prior art. Summary The present invention is based on the finding that it is possible to replace existing hydrophobic additives in non-woven fabric laminates, e.g. roofing underlays, with less thermally stable additives by reducing the operating temperature during manufacture, whilst maintaining satisfactory air permeability and water hold-out properties. According to a first aspect, there is provided a roofing underlay comprising a laminated nonwoven fabric, wherein the laminated nonwoven fabric comprises: a first, outer, spunbond layer; a first meltblown layer, wherein the first meltblown layer is made of a meltblown material comprising at least one hydrophobic additive, and wherein the first meltblown layer has a basis weight less than approximately 30 g / m2; a second meltblown layer in contact with the first meltblown layer, wherein the second meltblown layer is made of a meltblown material, and wherein the second meltblown layer has a basis weight less than approximately 30 g / m2, wherein the first spunbond layer is laminated to the first meltblown layer or to the second meltblown layer, and wherein the hydrostatic head of the combined meltblown layers including the first meltblown layer and the second meltblown layer, of the laminated nonwoven fabric, is at least 70cm. Preferably, the laminated nonwoven fabric may further comprise a second, outer, spunbond layer. The second spunbond layer may be laminated to the first meltblown layer or to the second meltblown layer. The second spunbond layer may be provided opposite the first spunbond layer. In such instance, the laminated nonwoven fabric may have two outer spunbond layers, and at least two meltblown layers provided between the first and second spunbond layers. In an embodiment, there may be provided two meltblown layers, e.g. the first meltblown layer and the second meltblown layer. In such instance, the laminate may have an “SMMS” (spunbond-meltblown-meltblown-spunbond) structure. Advantageously, it was found that the problems associated with the defects resulting from manufacturing the meltblown layer at reduced temperature, may be overcome by providing a plurality of meltblown layers, at least one of which contains an environmentally acceptable hydrophobic additive. In such instance, the meltblown layer(s) comprising such additives may be extruded at lower temperature, e.g. at less than about 260°C, e.g. less than about 250°C, e.g. at about 220 °C-250°C, to generate a meltblown layer, e.g. the first meltblown layer, with a basis weight typically less than approximately 30 g / m2, e.g. less than approximately 25 g / m2, e.g. between 5 g / m2 and 25 g / m2 , e.g. between 10 g / m2 and 25g / m2, e.g. between 15 g / m2 and 20g / m2, e.g. around 17g / m2. Whilst a person of skill in the art would typically expect such a meltblown layer to be incapable of exhibiting sufficient water hold-out properties, it was surprisingly found that this problem can be overcome by providing a plurality of meltblown layers which, when combined, provide the laminate with adequate and / or superior air permeability and water hold-out, particular when intended for use as a roofing underlay. The laminated nonwoven fabric may comprise or may be a building material such as a roofing underlay, a flooring underlay, a wall membrane, or the like. In an embodiment, the laminated nonwoven fabric may comprise or may be a roofing underlay. The laminated nonwoven fabric may comprise one or more further meltblown layers, e.g. provided between the first spunbond layer and the second spunbond layer. The laminated nonwoven fabric may comprise one or more further spunbond layers, e.g. provided on an outer surface or on an inner surface of the first spunbond layer and / or of the second spunbond layer. The material of the first meltblown layer and of the second meltblown layer may be the same or may be different. The first meltblown layer, second meltblown layer, first spunbond layer and / or second spunbond layer may comprise a base polymer. Examples of polymers from which meltblown and spunbond materials may be made include polyolefinic polymers such as polyethylene and polypropylene homopolymers and co-polymers thereof, and of mixtures of homopolymers and co-polymers thereof. Preferably, the first meltblown layer, second meltblown layer, first spunbond layer and / or second spunbond layer may comprise a base polymer consisting of polypropylene. Other polymeric materials may also be found suitable as will be apparent to the skilled reader. As stated above, the first meltblown layer comprises at least one hydrophobic additive. The second meltblown layer may comprise at least one hydrophobic additive. The second meltblown layer may be devoid of a hydrophobic additive. When present, the at least one hydrophobic additive of the second meltblown layer may be the same, or may be different from, the at least one hydrophobic additive of the first meltblown layer. The at least one hydrophobic additive may comprise one or more environmentally acceptable hydrophobic additives, such as a fluorocarbon wax, a fluorinated C6 compound, or other fluorinated or fluorine-free hydrophobic compounds. 10 15 Basis weight The first meltblown layer may have a basis weight less than approximately 25 g / m2, e.g. between 5 g / m2 and 25 g / m2, e.g. between 10 g / m2 and 25g / m2, e.g. between 15 g / m2 and 20g / m2, e.g. around 17g / m2. The second meltblown layer may have a basis weight less than approximately 25 g / m2, e.g. between 5 g / m2 and 25 g / m2, e.g. between 10 g / m2 and 25g / m2, e.g. between 15 g / m2 and 20g / m2, e.g. around 17g / m2. Thus, at least one, e.g. each, of the meltblown layers may have a basis weight less than the typical basis weight of a corresponding meltblown layer of a building material, e.g. roofing underlay, comprising a single meltblown layer. The basis weight of the combined meltblown layers of the laminated nonwoven fabric, may be greater than 25 g / m2, e.g. may be between about 26 and 50g / m2, e.g. between about 30 and 40g / m2, e.g. around 34g / m2. Thus, the basis weight of the combined meltblown layers of the laminated nonwoven fabric may be similar to the typical basis weight of a corresponding meltblown layerof a building material, e.g. roofing underlay, comprising a single meltblown layer. Hydrostatic head At least one, e.g. each, of the meltblown layers, e.g. the first meltblown layer and the second meltblown layer, may have a hydrostatic head less than the typical 25 hydrostatic head of a corresponding meltblown layer of a building material, e.g. roofing underlay, comprising a single meltblown layer. The hydrostatic head of the combined meltblown layers of the laminated nonwoven fabric, is at least 70cm, e.g. may be between about 70 and 80cm. Thus, the hydrostatic head of the combined meltblown layers of the laminated nonwoven fabric 30 may be similar to or greater than the typical hydrostatic head of a corresponding meltblown layer of a roofing underlay comprising a single meltblown layer. It will be appreciated that, depending on the manufacturing process, it may not be possible to measure the hydrostatic head of each meltblown layer, e.g. of the first meltblown layer and of the second meltblown layer, separately. This may be the case, 35 for example, when the if the first meltblown layer and the second meltblown layer are extruded in series via a “twin beam” apparatus, where the second meltblown layer may be applied or “blown” directly on a surface of the first meltblown layer, and the first and second meltblown layers may be bound together without the need for lamination. In such instance, both layers are intermingled and / or fused during the twin beam extrusion process, and the hydrostatic head of each meltblown layer may not be measured individually. Air permeability At least one, e.g. each, of the meltblown layers, e.g. the first meltblown layer and the second meltblown layers, may have air permeability less than the typical air permeability of a corresponding meltblown layer of a building material, e.g. roofing underlay, comprising a single meltblown layer. The air permeability of the combined meltblown layers of the laminated nonwoven fabric, may be at least 300 l / m2 / s, e.g. may be at least 320 l / m2 / s, e.g. may be at least 330 l / m2 / s, e.g. may be between about 330 and 350 l / m2 / s . Thus, the air permeability of the combined meltblown layers of the laminated nonwoven fabric may be similar to or greater than the typical air permeability of a corresponding meltblown layer of a roofing underlay comprising a single meltblown layer. It will be appreciated that, depending on the manufacturing process, it may not be possible to measure the air permeability of each meltblown layer, e.g. of the first meltblown layer and of the second meltblown layer, separately. This may be the case, for example, when the if the first meltblown layer and the second meltblown layer are extruded in series via a “twin beam” apparatus, where the second meltblown layer may be applied or “blown” directly on a surface of the first meltblown layer, and the first and second meltblown layers may be bound together without the need for lamination. In such instance, both layers are intermingled and / or fused during the twin beam extrusion process, and the air permeability of each meltblown layer may not be measured individually. Fiber diameter At least one of the meltblown layers, e.g. at least the first meltblown layer, may have a fibre diameter greater than the typical fibre diameter of a corresponding meltblown layer of a building material, e.g. roofing underlay, comprising a single meltblown layer. Whilst a person of skill in the art would typically expect such fibre diameter to lead to a meltblown layer exhibiting insufficient water hold-out properties, it was surprisingly found that this problem can be overcome by providing a plurality of meltblown layers which, when combined, provide the laminate with adequate and / or superior air permeability and water hold-out, particular when intended for use as a roofing underlay. Pore size The compositions of the meltblown layers, e.g. the compositions of the first meltblown layer and of the second meltblown layer, may be the same or may be different. One or more properties, e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size, of the meltblown layers, e.g. of the first meltblown layer and of the second meltblown layer, may be the same or may be different. In an embodiment, the first and second meltblown layers may have the same compositions, e.g. may each comprise a hydrophobic additive, typically in an amount of about 4-20 wt%. In such instance, the meltblown layers, e.g. of the first and second meltblown layers, may be extruded using similar parameters and / or may have similar properties, e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size. For example, if the target basis weight of the meltblown layer of a laminate having a single meltblown layer was approximately 34g / m2, the basis weight of each of the first meltblown layer and of the second meltblown layer, may each be approximately 17g / m2. This may ensure that each meltblown layer may be extruded at a temperature below the degradation temperature of the environmentally friendly hydrophobic additive, whilst providing the laminated fabric with adequate and / or superior air permeability and water hold-out. In another embodiment, the first and second meltblown layers may have different compositions. For example, the first and second meltblown layers may have different concentrations of hydrophobic additive. In such instance, the meltblown layers, e.g. of the first and second meltblown layers, may be extruded using different parameters and / or may have properties, e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size. For example, the second meltblown layer may have a concentration of hydrophobic material less than that of the first meltblown layer. The second meltblown layer may not contain any hydrophobic material. By such provision, the manufacture of the second meltblown layer may not be restricted to the same temperature limitations as the first meltblown layer, which may allow a higher throughput for the second meltblown layer, and / or may allow the properties of the second meltblown layer to be adjusted relative to the properties of the first meltblown layer. Advantageously, this may allow the overall properties e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size, of the laminate, e.g. of the combined meltblown layers, to be selected 5 by tailoring the properties e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size, of each meltblown layer, e.g. of the first and second meltblown layers. 10 15 30 Spunbond layer(s) One of more spunbond layer, e.g. the first and / or second spunbond layers, may have a basis weight between 15 and 150 g / m2, or between 40 and 100 g / m2. The spunbond layers, e.g. first and / or second spunbond layers, may have the same, or may have different, basis weights. For example, when used as a roofing underlay, the layer of spunbond material comprising the underside (i.e. the layer facing the roofspace) may have a lower basis weight than the opposing layer of spunbond material facing outwards. Structure The laminated nonwoven fabric may typically comprise a “SMMS” laminate. The laminate may be prepared by one or of the following methods: Providing a double meltblown layer (herein described as “MM”), e.g. comprising the first and second meltblown layers (for example via twin beam meltblown manufacture), and laminating such to the first spunbond layer, and to the second spunbond layer. This may be referred to as a “S(MM)S” structure. Extruding each of the first meltblown layer and second meltblown layer separately, and laminating each of the first meltblown layer and second meltblown layer to a relative spunbond layer, thereby preparing two separate “SM” laminates, and laminating the two “SM” laminates via their respective meltblown layers to provide a “(SM)(MS)” structure. Extruding each of the first meltblown layer and second meltblown layer separately, and each spunbond layer separately, followed by laminating these layers together, thereby providing a “SMMS” structure. - Extrusion of all four layers in series on a single line and then calendering all layers together, thereby providing a “SMMS” structure. According to a second aspect, there is provided a method for manufacturing a laminated nonwoven fabric, the method comprising: extruding a first composition through a meltblown die at a first temperature, wherein the first composition comprises a first base polymer material and a hydrophobic additive, to form a first meltblown layer having a basis weight less than approximately 30 g / m2, extruding a second composition through a meltblown die at a second temperature, wherein the second composition comprises a base polymer material, to form a second meltblown layer having a basis weight less than approximately 30 g / m2, and contacting the first meltblown layer and the second meltblown layer together, wherein the first temperature is less than about 250°C. Advantageously, this may prevent degradation of environmentally friendly hydrophobic additives, which typically not stable at conventional extrusion temperatures of about 270°C. The first temperature may be about 220°C-250°C, e.g. about 230cC-250 C. The term “contacting” will be herein understood to mean that the first meltblown layer and the second meltblown layer are bonded together, e.g. via their respective contacting surfaces. This can cover a number of mechanisms which may depend on the method by which the fabric is made. In an embodiment, if the first meltblown layer and the second meltblown layer are extruded separately, the first meltblown layer and the second meltblown layer may be brought together and may be laminated, e.g. by bonding the layers together by feeding them through a heated calendaring apparatus. In another embodiment, if the first meltblown layer and the second meltblown layer are extruded in series via a “twin beam” apparatus, the second meltblown layer may be applied or “blown” directly on a surface of the first meltblown layer, and the first and second meltblown layers may be bound together without the need for lamination. The method may comprise laminating a first spunbond layer to the first meltblown layer or to the second meltblown layer. The method may comprise extruding a third composition through a spunbond die, to form the first spunbond layer. The method may comprise laminating a second, outer, spunbond layer to the first meltblown layer or to the second meltblown layer. 10 15 25 30 This may result in a laminated nonwoven fabric having two outer spunbond layers, and at least two meltblown layers provided between the first and second spunbond layers. In an embodiment, there may be provided two meltblown layers, e.g. the first meltblown layer and the second meltblown layer. In such instance, the laminate may have an “SMMS” (spunbond-meltblown-meltblown-spunbond) structure. Advantageously, it was found that the problems resulting from manufacturing the meltblown layer at reduced temperature, may be overcome by providing a plurality of meltblown layers, at least one of which contains an environmentally acceptable hydrophobic additive. In such instance, the meltblown layer(s) comprising such additives may be extruded at lower temperature, e.g. at less than about 250°C, e.g. may about 220°C-250°C, e.g. about 230°C-250°C, to generate a meltblown layer, e.g. the first meltblown layer, with a basis weight typically less than approximately 30 g / m2, e.g. less than approximately 25 g / m2, e.g. between 5 g / m2 and 25 g / m2 , e.g. between 10 g / m2 and 25g / m2, e.g. between 15 g / m2 and 20g / m2, e.g. around 17g / m2. Whilst a person of skill in the art would typically expect such a meltblown layer to be incapable of exhibiting sufficient water hold-out properties, it was surprisingly found that this problem can be overcome by providing a plurality of meltblown layers which, when combined, provided the laminate with adequate and / or superior air permeability and water hold-out, particular when intended for use as a roofing underlay. The method may comprise manufacturing a laminated nonwoven fabric having a “SMMS” structure. In an embodiment, the method may comprise preparing a double meltblown layer (herein described as “MM”), e.g. comprising the first meltblown layer and the second meltblown layer. The method may comprise using a twin beam meltblown method. The method may comprise laminating the “MM” structure to at least one spunbond layer, e.g. the first spunbond layer, and optionally to the second spunbond layer, typically on a side opposite the first spunbond layer. This may result in a “S(MM)S” structure. In another embodiment, the method may comprise extruding each of the first meltblown layer and the second meltblown layer separately. The method may comprise laminating each of the first meltblown layer and second meltblown layer to a respective spunbond layer, thereby preparing two separate “SM” laminates. 10 15 The method may comprise laminating the two “SM” laminates, e.g. via their respective meltblown layers, to provide a “(SM)(MS)” structure. In another embodiment, the method may comprise extruding each of the first meltblown layer and second meltblown layer separately. The method may comprise extruding each spunbond layer, e.g. each of the first spunbond layer and second spunbond layer, separately. The method may comprise laminating a plurality of layers, e.g. the first spunbond layer, first meltblown layer, second meltblown layer, and second spunbond layer, to provide a “SMMS” structure. The method may comprise extruding one or more further meltblown layers. The method may comprise extruding one or more further spunbond layers. The method may comprise providing the one or more further meltblown layers and / or the one or more further spunbond layers in the laminated nonwoven fabric, thereby providing a structure such as a “SSMMS”, “SMMMS”, “SSMMMS” or the like. The features described in relation to any aspect of the invention may equally apply to any other aspect and, merely for brevity, are not repeated. For example, features described in relation to apparatus or products can apply in relation to methods, and vice versa. Brief Description of Drawings 25 Embodiments of the invention are described with reference to the accompanying drawings, in which: Figure 1 shows a laminated fabric according to the prior art; Figure 2 shows a laminated fabric according to a first embodiment; Figure 3 shows a schematic representation of an unsupported roof; 30 Figure 4 shows a schematic representation of a fully supported or sarked roof; Figure 5 shows a perspective view of a laminated fabric according to an embodiment of the present invention; Figure 6 is a schematic view of a twin beam process for making a double layer meltblown laminate according to an embodiment. 10 15 Detailed Description In the present disclosure, reference is made to a number of terms, which have the meanings provided below, unless a context indicates to the contrary. The nomenclature used herein for defining compounds, in particular the compounds according to the invention, is in general based on the rules of the IUPAC organisation for chemical compounds, specifically the “IUPAC Compendium of Chemical Terminology (Gold Book)”. For the avoidance of doubt, if a rule of the IUPAC organisation is in conflict with a definition provided herein, the definition herein is to prevail. Furthermore, if a compound structure is in conflict with the name provided for the structure, the structure is to prevail. The term “comprising” or variants thereof is to be understood herein to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The term “consisting” or variants thereof is to be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, and the exclusion of any other element, integer or step or group of elements, integers or steps. The term “about” herein, when qualifying a number or value, is used to refer to values that lie within ± 5% of the value specified. For example, if a temperature is specified to be about 5 to about 13 °C, temperatures of 4.75 to 13.65 °C are included. Reference to physical states of matter (such as liquid or solid) refer to the matter’s state at 25 °C and atmospheric pressure unless the context dictates otherwise. Figure 1 shows a laminated fabric 5 according to the prior art. 25 The fabric 5 comprises a first layer of a meltblown material 21 sandwiched between a first spunbond layer 11 and a second spunbond layer 12. The first spunbond layer 11 and a second spunbond layer 12 act as an abrasion resistant, durable and protective cover for the meltblown material 21. The meltblown material layer 21 is typically laminated to the layers of spunbond material 11,12 by passing the sheet 30 materials simultaneously through, for example, a point bonding calendering process. In this process, which is known in the art, a combination of heat and pressure is applied in an intermittent pattern known as point bonding. The area of such bond points is typically 5% to 40% of the total area of the bonded materials and may preferably be in the range 15% to 20%. In this laminate 5, the meltblown layer 21 is the primary functional layer 35 regulating the underlay’s vapour permeability and water hold-out properties. This type of laminate 5, as well as the embodiments of laminates according to the invention described below such as laminate 105, may be used as building materials, for example, as roofing underlays. Typical roof constructions for ‘cold’ unoccupied roof spaces are shown in Figures 3 and 4. Figure 3 shows an unsupported roof, wherein the underlay, for example a laminated fabric 5,105 is draped between the rafters 30. Battens 42 are placed on top of the underlay 5,105 and the tiles or slates 40 are secured onto these battens. An alternative construction is a fully supported or sarked roof as is shown in Figure 4. In this type of construction, boards or sheets 44 are placed on the rafters 30. These boards or sheets 44 are commonly known in the art as sarking and are typically made out of timber or fibreboard, such as oriented strand board (OSB). An underlay, such as a laminated fabric 5,105, is laid directly onto the sarking 44. Tiles or slates 40 are secured directly through the underlay to the sarking (as shown in Figure 4). Alternatively battens may be laid on top of the underlay and secured to the sarking and the tiles or slates secured to these battens. The roofing laminate 5 typically preferably requires the use of hydrophobic additives in the meltblown layer 21 to improve rain and chemical resistance. Such hydrophobic additives are conventionally based on fluorocarbon organic compounds, and include per- and poly-fluoroalkyl substances (PFAS), and perfluorooctane sulfonic acid derivatives (PFOS). However, due to environmental concerns, a number of fluorocarbon-based hydrophobic additives have been restricted in the UK, the EU, and other parts of the world. Such banned compounds include for example C8 fluorocarbon hydrophobics, and certain C6 fluorocarbon hydrophobics. Replacing those banned additives involves the use of alternative hydrophobic compounds. These include for example fluorocarbon waxes, fluorinated C6 compounds, or other fluorinated or fluorine-free hydrophobic compounds. A problem with such compounds is that they are generally based on a less stable chemistry, and, in particular, degrade at lower temperatures. This, in turn, means that the extrusion process to manufacture the meltblown layer must be carried out at lower temperature. For example, while a conventional extrusion temperature for the meltblown lay 21 of laminate 5 may be in the region of about 270°C, the temperature stability of the replacement hydrophobic additives requires the use of lower temperatures, typically less than 260°C, preferably less than 250°C, e.g. about 220°C-250°C, e.g. about 230°C -250°C.. For health and safety reasons, maintaining the chemical stability of the additives is important in order to minimise the potential release of toxic hydrogen fluoride. A consequence of the reduced extrusion temperature is a radical change of the melt characteristics and of the extrusion performance, all of which change the filament geometry. In particular, reducing extrusion temperature, when seeking to otherwise maintain other extruding parameters, causes an increase in filament diameter due the lower viscosity of the polymeric material at lower temperatures. This also results in the overall meltblown layer having increased air permeability but also decreasing its hydrohead value, which is undesirable. Figure 2 shows a laminated fabric 105 according to a first embodiment. In this embodiment, the laminate 105 includes outer layers made of a first spunbond layer 111 and a second spunbond layer 112. Sandwiched between the spunbond layers 111,112 is a meltblown structure 120, which in this embodiment is made of two meltblown layers 121,122. The first meltblown layer 121 is made of a meltblown material comprising a base polymer, typically polypropylene, and a hydrophobic additive, which in this embodiment is a fluorinated C6 compound or a fluorinated wax. Because of the lower thermal stability of these additives, the first meltblown layer 121 is extruded at a lower temperature than conventionally, e.g. less than about250°C, e.g. about 230°C-250°C. To overcome the changes in physical properties of the material during manufacture, e.g. a reduction in viscosity, the first meltblown layer 121 is manufactured to have a basis weight lower than in the prior art, typically less than approximately 30 g / m2, e.g. less than approximately 25 g / m2, e.g. between 5 g / m2 and 25 g / m2 , e.g. between 10 g / m2 and 25g / m2, e.g. between 15 g / m2 and 20g / m2, e.g. around 17g / m2. Whilst a person of skill in the art would typically expect such a meltblown layer to be incapable of exhibiting sufficient water hold-out properties in applications such as a roofing underlay, it was surprisingly found that this problem can be overcome by providing a plurality of meltblown layers 121,122 which, when combined, provide the laminate 105 with adequate and / or superior air permeability and water hold-out, particular when intended for use as a roofing underlay. The compositions of the meltblown layers, e.g. the compositions of the first meltblown layer 121 and of the second meltblown layer 122, may be the same or may be different. In an embodiment, the first and second meltblown layers 121,122 may have the same compositions, e.g. may each comprise a hydrophobic additive. In such instance, the meltblown layers 121,122 may be extruded using similar parameters and / or may have similar properties, e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size. For example, if the target basis weight of the meltblown layer of a laminate having a single meltblown layer was approximately 34g / m2, the basis weight of each of the first meltblown layer 121 and of the second meltblown layer 122, may each be approximately 17g / m2. This may ensure that each meltblown layer 121,122 may be extruded at a temperature below the degradation temperature of the environmentally friendly hydrophobic additive, whilst providing the laminated fabric 105 with adequate and / or superior air permeability and water hold-out. For example, when the first meltblown layer and the second meltblown layer are made using a twin beam apparatus, one or more of the extrusion parameters may be as follows: Temperature : 230°C; Working pressure : 15 bar; Spin pump : 40 rpm In another embodiment, the first meltblown layer and the second meltblown layer 122 may have different compositions. For example, the first meltblown layer 121 and the second meltblown layer 122 may have different concentrations of hydrophobic additive(s). In such instance, the meltblown layers 121,122 may be extruded using different parameters and / or may have different properties, e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size. For example, the second meltblown layer 122 may have a concentration of hydrophobic material less than that of the first meltblown layer 121. The second meltblown layer 122 may not contain any hydrophobic material. By such provision, the manufacture of the second meltblown layer 122 may not be restricted to the same temperature limitations as the first meltblown layer 121, which may allow a higher throughput for the second meltblown layer 122, and / or may allow the properties of the second meltblown layer 122 to be adjusted relative to the properties of the first meltblown layer 121. Advantageously, this may allow the overall properties e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size, of the laminate 105, and in particular of the combined meltblown layers 121,122, to be selected by tailoring the properties e.g. basis weight, hydrostatic head, air permeability, fibre diameter, and / or pore size, of each meltblown layer 121,122. Figure 5 shows a perspective view of the laminated fabric 105 according to an embodiment of the present invention, illustrating some its properties. As explained above, the laminate 105 is air permeable and vapour permeable. Thus, air and vapour are able to pass through the membrane as illustrated by arrows ‘B’ in Figure 5. As is also illustrated on Figure 5, the laminated fabric 105 offers satisfactory or improved water hold-out properties meaning that the fabric resists the passage of water droplets (as shown by arrows ‘A’). Figure 6 is a schematic view of a twin beam process for making a double layer meltblown laminate according to an embodiment. As explained above, in the laminate 105 of Figure 2, the meltblown structure is made of two separate meltblown layers 121,122. Figure 6 illustrates an embodiment of a process to make such a structure 120. The first meltblown unit or “beam” 50 forms the first meltblown layer 121. In the first hopper 51, a first composition including a first polymer, typically polypropylene, and an environmentally friendly hydrophobic additive such as a fluorinated C6 compound or a fluorinated wax, is fed in an amount of about 4-20 wt%. The composition is extruded in first extruder 52 and the meltblown fibres are generated through first meltblown die 53, forming a first meltblown layer 121 which is collected on first collector 54 and is then passed through a series of rollers 55. Because the presence of the environmentally friendly hydrophobic additive, the maximum temperature used in the first beam, e.g. in the first extruder 52 and in the first meltblown die 53, is less than about 250°C, e.g. may about 230°C-250°C. In this embodiment, the temperature was 230°C. The first meltblown layer 121 has a basis weight less than approximately 30 g / m2, in this embodiment about 17 g / m2. The second meltblown unit or “beam” 60 forms the second meltblown layer 122. In the second hopper 61, a second composition including a second polymer, typically polypropylene, and an environmentally friendly hydrophobic additive such as a fluorinated C6 compound or a fluorinated wax, is fed in an amount of about 4-20 wt%. The composition is extruded in second extruder 62 and the meltblown fibres are generated through second meltblown die 63, forming a second meltblown layer 122 which is combined with first meltblown layer 121 on second collector 64 to form meltblown structure 120 and is then passed through a series of rollers 65 and stored on a winder 70. Because the presence of the environmentally friendly hydrophobic additive, the maximum temperature used in the second beam 60, e.g. in the second extruder 62 and in the second meltblown die 63, is less than about 250°C, e.g. may about 230°C-250°C. In this embodiment, the temperature was 230°C The second meltblown layer 122 has a basis weight less than approximately 30 g / m2, in this embodiment about 17 g / m2. The meltblown structure 120 combining first meltblown layer 121 and second meltblown layer 122 typically has: a hydrostatic head typically between 65cm and 85cm. air permeability between 300 l / m2 / s and 350 l / m2 / s. The laminated fabric 105 is then prepared by laminating the meltblown structure 120 with a first spunbond layer 111 and a second spunbond layer 112 to yield an “SMMS” laminate. As explained above, in other embodiments, the first composition and the second composition may be different. For example, the second composition may have less hydrophobic additive than the first composition. The second composition may have no hydrophobic additive. In such instance, the parameter of the second beam 60 may be different from the parameters of the first beam 50. It will be appreciated that other methods for combining multiple meltblown layers may be used, for example: - By extruding each of the first meltblown layer 121 and the second meltblown layer 121 separately, and laminating each of the first meltblown layer 121 and second meltblown layer 122 to a respective spunbond layer, thereby preparing two separate “SM” laminates. The two “SM” laminates may then be laminated together to provide a “(SM)(MS)” structure. By extruding each of the first meltblown layer 121 and second meltblown layer 122 separately, and extruding each of the first spunbond layer 111 and second spunbond layer 112, separately. The first spunbond layer 111, first meltblown layer 121, second meltblown layer 122, and second spunbond layer 112 are then laminated to provide a “SMMS” structure. It will be understood that the present embodiments are provided by way of example only, and that various modifications can be made to the present embodiments without departing from the scope of the invention. Examples Comparative Example 1: Single beam meltblown properties (containing a C8 fluorinated hydrophobic additive which is no longer available due to 5 environmental restrictions - Perfluorooctanoic acid (PFOA - CAS number: 335-67-1): 10 15 A single meltblown layer was manufactured using a conventional process using the following parameters: - Weight: 34g - Throughput: 109 kg / h Extrusion temperature: 280°C Line speed: 32m / min - Working pressure: 18 bar Spin pump: 34.3 rpm - Quench air temperature: 18°C - Suction air: 55% The properties of the resulting meltblown layer were measured and corresponding SMS laminate are as follows: Original Composition (containing PFOA) Meltblown Laminat e Hydro Head Air Perm Hydro Head Air Perm cm l / m2 / s cm l / m2 / s 300 Comparative Example 2: Single beam meltblown properties (with new generation 25 hydrophobic additive): A single meltblown layer was manufactured using the following process, to take account of the temperature stability of the new generation hydrophobic additive. The parameters of the process were as follows: 30 - Extrusion temperature: 230°C Line speed 14 m / min Spin pump: 15 rpm - Throughput: 48 kg / h Quench air temperature: 20°C - Suction air: 50% The properties of the resulting meltblown layer were measured as follows: Hydrostatic head (cm): 55 Air permeability (l / m2 / sec): 378 Throughput (kg / hr): 50 Line speed (metres / min): 14 Therefore, it can been seen that, because of the necessary adjustments in the process to account for the temperature stability of the new generation hydrophobic additive, the resulting meltblown layer has a lower hydrostatic head than the corresponding single meltblown layer of comparative example 1, and the process is also associated with lower throughput and line speed, making the manufacturing process less efficient Example 3: Double beam meltblown properties (with new generation hydrophobic in both meltblown layers): A double meltblown layer was manufactured using the process described in Figure 6. The parameters of the “twin beam” process were as follows: Beam A Extruder temperature: 230°C Die temperature: 230°C - Extruder revolutions: 29rpm - Extruder pressure: 21 bar Spin pump temperature: 238°C Spin pump revolutions: 40 rpm - Working pressure: 15 bar Die pressure: 14 bar - Die melt temperature: 235°C - Die tip temperature: 230°C - Process air temperature: 250°C Process air flow rate: 1900 m3 / hr 5 Quench cooling air temperature: 35°C Suction fan pressure: 6343 pascals (85%) - Une speed: 25 m / min - Die to collector distance (DCD): 150mm - Web forming longitudinal adjustment: -74mm - Throughput (total): 91 kg / hr (45.5 kg / hr per beam) - Weight: 17 gsm 10 Beam B - Extruder temperature: 230°C Die temperature: 230°C Extruder revolutions: 26 rpm Extruder pressure: 20 bar 15 Spin pump temperature: 224°C LO CM - Spin pump revolutions: 40 rpm - Working pressure: 15 bar Die pressure: 15 bar Die melt temperature: 240°C 20 Die tip temperature: 235°C - Process air temperature: 250°C - Process air flow rate: 1900 m3 / hr - Quench cooling air temperature: 35°C Suction fan pressure: 7935 pascals (89%) 25 Line speed: 25 m / min Die to collector distance (DCD): 150mm - Web forming longitudinal adjustment: -74mm - Throughput (total): 91 kg / hr (45.5 kg / hr per beam) - Weight: 17 gsm 30 The properties of the resulting double meltblown layer structure and corresponding SMMS laminate were measured as follows: New generation hydrophobic - twinbeam Meltblown Laminate Hydro Head Air Perm Hydro Head Air Perm cm l / m2 / s cm l / m2 / s iiM 340 105 Throughput (kg / hr): 91 Line speed (metres / min): 25 5 Therefore, it can been seen that, because of the present process provides a meltblown structure having similar hydrostatic head to a conventional meltblown (see comparative example 1), while improving air permeability, and maintain satisfactory throughput and line speed. LD CM

Claims

1. A roofing underlay comprising a laminated nonwoven fabric, wherein the laminated nonwoven fabric comprises:5 a first, outer, spunbond layer;a first meltblown layer, wherein the first meltblown layer is made of a meltblown material comprising at least one hydrophobic additive, and wherein the first meltblown layer has a basis weight less than 30 g / m2; anda second meltblown layer in contact with the first meltblown layer, wherein the 10 second meltblown layer is made of a meltblown material, and wherein the second meltblown layer has a basis weight less than 30 g / m2,wherein the first spunbond layer is laminated to the first meltblown layer or to the second meltblown layer, andwherein the hydrostatic head of the combined meltblown layers including the first LO 15 meltblown layer and the second meltblown layer, of the laminated nonwoven fabric, is at CM least 70cm.CM2. A roofing underlay according to claim 1, wherein the laminated nonwoven fabric further comprises a second, outer, spunbond layer laminated to the first meltblown layer CM 20 or to the second meltblown layer, wherein the second spunbond layer is provided opposite the first spunbond layer.

3. A roofing underlay according to any preceding claim, wherein the laminated nonwoven fabric further comprises one or more further meltblown layers.

254. A roofing underlay according to any preceding claim, wherein the laminated nonwoven fabric further comprises one or more further spunbond layers.

5. A roofing underlay according to any preceding claim, wherein the material of the 30 first meltblown layer and of the second meltblown layer is the same.

6. A roofing underlay according to any one of claims 1 to 5, wherein the material of the first meltblown layer and of the second meltblown layer is different.

7. A roofing underlay according to any preceding claim, wherein the first meltblown layer, second meltblown layer, first spunbond layer and / or second spunbond layer comprises a base polymer, the base polymer being a polyolefinic polymer5 8. A roofing underlay according to claim 7, wherein the polyolefinic polymercomprises or consists of polypropylene.

9. A roofing underlay according to any preceding claim, wherein the second meltblown layer comprises at least one hydrophobic additive.1010. A roofing underlay according to any preceding claim, wherein the at least one hydrophobic additive comprises one or more environmentally acceptable hydrophobic additive selected from the list consisting of a fluorocarbon wax, and / or a fluorinated C6 compound.1511. A roofing underlay according to any preceding claim, wherein the first meltblown layer has a basis weight less than 25 g / m2, and / or wherein the second meltblown layer has a basis weight less than 25 g / m2.20 12. A roofing underlay according to any preceding claim, wherein the basis weight ofthe combined meltblown layers of the laminated nonwoven fabric is greater than 25 g / m2.

13. A roofing underlay according to any preceding claim, wherein the air permeability of the combined meltblown layers of the laminated nonwoven fabric is at least 300 l / m2 / s.2514. A roofing underlay according to any one of claims 2 to 13, wherein the first spunbond layer is laminated to the first meltblown layer or to the second meltblown layer, and wherein the second spunbond layer is laminated to the other of the first meltblown layer or second meltblown layer.3015. A method for manufacturing a roofing underlay comprising a laminated nonwoven fabric, the method comprising:extruding a first composition through a meltblown die at a first temperature, wherein the first composition comprises a first base polymer material and a hydrophobic 35 additive, to form a first meltblown layer having a basis weight less than 30 g / m2,extruding a second composition through a meltblown die at a second temperature, wherein the second composition comprises a second base polymer material, to form a second meltblown layer having a basis weight less than 30 g / m2, andcontacting the first meltblown layer and the second meltblown layer together, 5 wherein the first temperature is less than 250°C.

16. A method according to claim 15, wherein the first meltblown layer and the second meltblown layer are extruded separately, and wherein the first meltblown layer and the second meltblown layer are laminated together.1015CM2017. A method according to any of claims 15 to 16, wherein the first meltblown layer and the second meltblown layer are extruded in series via a “twin beam” apparatus, and wherein the second meltblown layer is applied directly on a surface of the first meltblown layer.

18. A method according to any of claims 15 to 17, wherein the method comprises laminating a first spunbond layer to the first meltblown layer or to the second meltblown layer.

19. A method according to claim 18, wherein the method comprises laminating a second, outer, spunbond layer to the other of the first meltblown layer or second meltblown layer.

20. A method according to any one of claims 15 to 19, wherein the first base polymer25 material and the second base polymer material comprises or consists of polypropylene.

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