Field of the Invention

[0001] The invention pertains to embossed non-woven fabrics, and methods of embossing non-woven fabrics for use as exterior sheets suitable for underlayments, such as roofing underlayments.

Background of the Invention

[0002] It is known in the art to emboss surfaces of fabrics. It is desirable for a method to emboss surfaces of fabrics having a wide range of weights and thicknesses. The present invention is directed to methods for making embossed non-woven fabric, and the use of such embossed non-woven fabric in underlayments.

Summary

[0003] One aspect of the invention provides a method for making an embossed nonwoven fabric from a plain, smooth surfaced non-woven fabric having a wide range of weights and thicknesses, particularly a non-woven fabric which has a weight of up to 400 grams per square meter, and a thickness of up to about 100 mils. A plain non-woven fabric is fed between a pair of heated rotating rollers, and is arranged to be pressed between the rollers as the fabric is being fed therebetween. One or both of the rotatable rollers include an embossing roller which has a surface with a texture formed of a plurality of raised and/or sunken features so as to provide the desired inverse texture on the plain non-woven fabric. The embossing process is performed on an embossing line which is separate from the fabric production line.

[0004] Another aspect of the invention provides an embossed non-woven fabric made by the method of the invention. The embossed non-woven fabric may be used as an exterior sheet suitable as roofing underlayments. The embossed non-woven fabric that makes up the exterior sheet comprises a spunbond fabric, for example polypropylene, polyester, nylon and the like. The embossed non-woven fabric may be reinforced by bonding (e.g., thermal bonding by a thermoplastic coating or an adhesive layer) to a woven scrim such as fiberglass, polypropylene and polyethylene. [0005] Further aspects of the invention and features of specific embodiments of the invention are described below.

Brief Description of the Drawings

[0006] Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

[0007] Figure 1 is a schematic diagram showing an embodiment of a method of embossing a non-woven fabric.

[0008] Figure 2 is a schematic diagram showing an embodiment of a method of embossing a plurality of layers of non-woven fabric.

[0009] Figure 3 is a schematic diagram of a roof underlayment which incorporates the embossed non-woven fabric produced by the method of Figure 1 .

[0010] Figure 4A is a photograph showing a first surface of a plain, smooth spunbound non-woven fabric. Figure 4B is a photograph showing an opposed second surface of the spunbound non-woven fabric of Figure 4A.

[0011] Figure 5A is a photograph showing a first surface of the embossed non-woven fabric produced by the method of Figure 1. Figure 5B is a photograph showing an opposed second surface of the embossed non-woven fabric of Figure 5A.

[0012] Figure 6A is a photograph showing a first surface of an embossed non-woven fabric produced by an on-line embossing method. Figure 6B is a photograph showing an opposed second surface of the embossed non-woven fabric of Figure 6A.

Detailed Description

[0013] The invention provides a method of embossing non-woven fabrics, such as a spunbond fabric. The embossed non-woven fabrics produced by embodiments of the method may be used as exterior sheets for underlayments, such as roofing underlayments. The method of the invention begins with a non-woven fabric which may be plain (e.g., a non-woven fabric with smooth surfaces), and in a rigid state, arranged to be fed through a hot embossing line to produce a non-woven fabric with an embossed surface. The nonwoven fabric may be a product which has been further treated chemically and/or physically by finishing processes such as calendering and fire retardant treatments. The plain nonwoven fabric may be a commercially purchased product made by a third party manufacturer. The fibers of the non-woven fabric may also include conventional additives such as dyes, pigments, antioxidants, UV stabilizers, hydrophobic or hydrophilic additives, fire retardant additives, anti-slip additives, anti-frost additives, inorganic fillers, and the like.

[0014] Referring to Figure 1 , the embossing line 20 includes a pair of spaced-apart rotatable rollers 22A, 22B through which a plain non-woven fabric 24 is fed therebetween. The embossing line 20 is separate from the fabric production line of the non-woven fabric 24, i.e. , the non-woven fabric 24 that is introduced to the embossing line 20 is removed from the fabric production line, and has been sufficiently cooled to be in a rigid state. The plain non-woven fabric 24 is arranged to be pressed between the rotating rollers 22A, 22B, which are heated, as the fabric 24 is being fed between them. One or both of the rollers 22A, 22B may be heated to and maintained at a temperature in a range of from about 50°C to about 120°C. The rollers 22A, 22B may be arranged to be separated by a gap of between 0.1 mm to about 5 mm so as to allow the non-woven fabric 24 to be pressed therebetween.

[0015] One or both of the rotatable rollers 22A, 22B is an embossing roller which has a surface with a texture formed of a plurality of features that are raised (e.g., protrusions) and/or sunken (e.g., depressions) with respect to its surface so as to provide the desired embossed inverse texture on the plain non-woven fabric 24. In embodiments of the method which include two embossing rollers, both the first 28A and the opposite second 28B surfaces of the resulting embossed non-woven fabric 26 have an inverse texture corresponding to the textures on the surfaces of the respective embossing rollers 22A, 22B. In embodiments of the method which include a pair of rotatable rollers 22A, 22B with one embossing roller and one smooth surfaced pressure roller, only one of the surfaces 28A, 28B of the resulting embossed non-woven fabric 26 has an inverse texture disposed thereon, and the other surface 28A, 28B is smooth after the plain non-woven fabric 24 is being pressed between the rollers 22A, 22B. In some embodiments, the surface of the smooth surfaced pressure roller is wrapped with one or more layers of fabric to provide traction to the plain non-woven fabric 24 as it is being fed between the rollers 22A, 22B. Any types of heat-resistant fabric that can increase the friction of the pressure roller can be used including for example polyethylene terephthalate (PET), felt, fleece, and the like. The wrapping fabric preferably has a thermal resistance sufficient to withstand the temperature at which the rollers 22A, 22B are maintained.

[0016] The texture on the first and/or second surfaces 28A, 28B of the embossed nonwoven fabric 26 may include raised and/or sunken features of the same shape or varying shapes that are arranged adjacent to or spaced apart from each other to form an enhanced friction or slip-resistant surface. Any suitable shape to form a slip-resistant surface may be used, including for example ovals, diamonds, square, and triangle. Figures 4A and 4B are photographs showing top and bottom surfaces of an example plain, smooth surfaced, spunbound non-woven fabric (i.e. , a non-woven fabric that has not undergone an embossment step). Figures 5A and 5B are photographs showing an example embossed non-woven fabric 26 made by the method of this invention, i.e., an off-line embossing method. The embossed non-woven fabric 26 includes a plurality of raised portions 23, each of which are separated by depressed portions 25. The depressed portions 25 are joined to form a plurality of channels 27 which encircle the raised portions 23. The depressed portions 25 of the fabric 26 are formed with loose, unmelted, fibers. This is in contrast to the characteristics of the fibers formed within the depressed portions of the embossed fabric that is prepared by an on-line embossing method. For example, Figures 6A and 6B are photographs showing an example embossed non-woven fabric 50 prepared by an on-line embossing method. The embossed non-woven fabric 50 includes a plurality of raised portions 52, each of which are separated by depressed portions 54. The depressed portions 54 are joined to form a plurality of channels 56 which encircle the raised portions 52. The fibers within the depressed portions 54 of the embossed fabric 50 are melted, i.e., not loose as seen in the depressed portions 25 of the embossed fabric 26 prepared by the off-line embossing method. The loose, unmelted, fibers formed in the depressed portions 25 of the embossed fabric 26 created by an off-line embossing method results in a height difference between the depressed portions 25 and raised portions 23 that is less than the height difference between the melted fibers formed in the depressed portions 54 and the raised portions 52 of the embossed fabric 50 created by the on-line embossing method.

[0017] In some embodiments, the non-woven fabric that is being introduced to the embossing line 20 comprises an embossed surface on one or both of its surfaces. In such embodiments, the non-woven fabric is first fed through a pair of rotatable rollers, one or both of which is an embossing roller, on the fabric production line. The fabric is then introduced to the embossing line 20 for further embossment on one or both of its surfaces after the non-woven fabric has been cooled and removed from the fabric production line.

[0018] In some embodiments of the method, a plurality of layers of non-woven fabrics is thermally bonded by being pressed between the heated rotatable rollers 22A, 22B to produce an embossed non-woven fabric composite. The plurality of layers may comprise a non-woven fabric that is of the same or different material, colour, density or thickness.

Referring to Figure 2, a first layer of a plain non-woven fabric 30 (e.g., with an area density of 50 grams per meter square) and a second layer of a plain non-woven fabric 32 (e.g., with an area density of 50 grams per square meter) are arranged to be pressed between the heated rotatable rollers 22A, 22B, and resulting from which is a composite fabric 34 (e.g., with an area density of 100 grams per meter square) comprising the thermally bonded first 30 and second 32 layers. One or both of the surfaces 36A, 36B of the composite fabric 34 may be embossed.

[0019] In some embodiments of the method, a plain non-woven fabric is first made on a fabric production line by any suitable conventional methods, such as chemical and thermal bonding, needle punching, and melt-blown extrusion. The fabric may be further treated on the production line, or in separate finishing operations. The finished non-woven fabric is cooled and removed from the production line, fed through a separate embossing line for embossment. Embodiments of the method involve a two-step process comprising two separate lines for producing the non-woven fabric and embossing the fabric.

[0020] The inventors have found that a two-step process of producing and embossing the non-woven fabric (an “off-line embossing method”), which is distinct from an “on-line embossing method” where the fiber web is formed and embossed on the fabric production line, permits the embossment of non-woven fabrics with a wide range of weights and thicknesses. Embodiments of the method can be used to emboss non-woven fabrics with an area density in the range of from about 20 grams per square meter to about 400 grams per square meter, and a thickness in the range of from about 3 mils to about 100 mils.

[0021] The embossed non-woven fabrics produced by the method of this invention can be used alone, or arranged in combination with other fabrics to form membrane composites which are useful for various applications, such as for flooring and roofing underlayments. In one embodiment, the embossed non-woven fabric is used as exterior sheets for roofing underlayments. The exterior sheets are arranged on the uppermost layer of roofing underlayments. Embossed exterior sheets increase the friction of its surfaces and thus provide a slip-resistant walking surface on roofing underlayments.

[0022] Referring to Figure 3, a roofing underlayment 40 includes an embossed exterior sheet 42 adhered to a substrate layer 44. The substrate layer 44 may include one or more layers of material (e.g., any suitable woven or non-woven materials, water-resistant materials, or slip resistant materials) that make up a membrane composite for forming a roofing underlayment. The embossed exterior sheet 42 may comprise a single layer made of the embossed non-woven fabric 26, or a plurality of layers which includes a top embossed non-woven fabric 26 being adhered to other woven and/or non-woven fabrics to form a composite exterior sheet. In an example embodiment, the embossed exterior sheet 42 includes one or more layers of polyester.

[0023] In one embodiment, a single layer exterior sheet 42 comprising the embossed non-woven fabric 26 can be arranged to adhere to a reinforcing material such as a fiberglass scrim. In another embodiment, a composite exterior sheet 42 includes two layers having an embossed non-woven fabric 26 coated with a layer of coating such as a polyolefin coating. In a further example embodiment, a composite exterior sheet 42 includes three layers having a woven or non-woven fabric (e.g., fiberglass or polyolefin) arranged between an uppermost layer comprising an embossed non-woven fabric 26 and a bottom layer comprising a plain or embossed non-woven fabric.

[0024] The embossed exterior sheet 42 may be produced by feeding a formed, rigid, plain non-woven fabric 24 between the rotatable rollers 22A, 22B, one of which is a smooth surfaced pressure roller arranged to contact the second surface 28B and the other is an embossing roller with the desired texture on its surface arranged to contact the first surface 28A. Referring to Figures 5A and 5B, the embossed non-woven fabric 26 has a first surface 28A with an embossed texture imprinted thereon, and a substantially smooth opposing second surface 28B with no to minimal signs of embossment by the embossing roller being transferred onto the second surface 28B. The texture of the second surface 25B of the embossed non-woven fabric 26 is comparable to the texture of the surfaces of a plain non- woven fabric, i.e. , one that has not undergone an embossing step (see Figures 4A and 4B). By contrast, embossed non-woven fabrics that are prepared using the on-line embossing method, i.e., on the fabric production line, show the embossed texture being imprinted on both the first and second surfaces, as shown in Figures 6A, 6B. Non-woven fabrics that are embossed using the off-line embossing method of this invention produces an embossed exterior sheet 42 that is able to provide for improved adhesion to the substrate layer 44, thereby increasing the lamination strength of the roofing underlayment 40.

[0025] In some embodiments, the second surface of an embossed non-woven fabric that is prepared using the on-line embossing method has a coefficient of friction of at least about 9% to 16% greater than the coefficient of friction of the second surface of the embossed non-woven fabric that is prepared using the off-line embossing method. The transfer of the embossed texture from the embossing roller to the second surface 28B using the on-line embossing method results from embossing the fabric while the fabric is still in a molten state when the fibers contained therein can be easily shaped, as opposed to the fabric being in a rigid state as used in the off-line embossing method. An embossed exterior sheet 42 with a smooth back surface has the advantage of allowing a bonding material (e.g., adhesive, asphalt, butyl, etc.) to be coated evenly thereon, resulting in a stronger lamination between the embossed exterior sheet 42 and the substrate layer 44. In addition, the lack of texture imprinted on the back surface of the embossed exterior sheet 42 reduces the likelihood of water travelling or being trapped within the depressions of the texture, further improving the adhesion and increasing the lamination strength between the embossed exterior sheet 42 and the substrate layer 44.

Examples

Example 1: Embossed Spunbond Non-Woven Fabric

[0026] A plain, smooth surfaced spunbond non-woven fabric with a weight of about 65 gsm and a thickness of about 16.6 mils was fed through a hot embossing line consisting of two rotatable rollers, one of which is an embossing roller and the other is a smooth surfaced roller, to produce an embossed spunbond fabric. The smooth surfaced roller was wrapped with a layer of PET fleece which has a thickness of 140 gsm. The height of the raised portions of the embossed texture is about 0.51 mm. The kinetic and static coefficients of friction (COF) for the machine direction (MD) and cross machine direction (CD) were measured on the embossed spunbond non-woven fabric and the plain spunbond nonwoven fabric in accordance with ASTM D1894. The measurements are shown in the table below:

Table 1. Comparison of Coefficients of Friction between the Embossed Fabric and the Plain Fabric

[0027] A series of slip resistance tests were performed on the embossed and plain spunbond non-woven fabrics. The slip resistance test involves measuring the frictional force necessary to keep a shoe heel from slipping on a wet or dry walking surface that is inclined at various angles (the “Dry Shoe Test” or the “Wet Shoe Test”). The results from the Dry Shoe Test and the Wet Shoe Test are shown in the table below:

Table 2. Comparison of Frictional Force Results between the Embossed Fabric and the

Plain Fabric

Example 2: Comparison of Coefficients of Friction between Surfaces of Spunbond Non- Woven Fabric Prepared Using Off-line and On-line Embossing Methods

[0028] An embossed spunbound fabric was prepared using an on-line embossing method by extruding a polypropylene resin through a die to produce thin strands. The thin strands are pressed between two heated rotatable rollers, one of which is an embossing roller and the other is a smooth surfaced roller to create an embossed non-woven fabric with a weight of about 65 gsm and a thickness of about 19.1 mils. .

[0029] The kinetic and static coefficients of friction (COF) for the machine direction (MD) and cross machine direction (CD) were measured on each of the first and second surfaces of the embossed spunbond non-woven fabrics and the plain spunbond non-woven fabric in accordance with ASTM D1894. Three measurements were taken for each test, and the values presented in Table 3 are the average numbers of the three measurements.

Table 3. Comparison of Coefficients of Friction between Surfaces of Embossed Fabrics Prepared Using the On-line versus Off-line Methods

[0030] The results show that the second surface of the embossed non-woven fabric that is prepared using the on-line embossing method has a coefficient of friction of at least about 9% to 16% greater than the coefficient of friction of the second surface of the embossed non-woven fabric that is prepared using the off-line embossing method. As compared to the plain, smooth, non-woven fabric, the second surface of the embossed non-woven fabric that is prepared using the off-line embossing method has a coefficient of friction of about 2% to 13% greater than the second surface of the plain fabric. The coefficient of friction between the first and second surfaces of the embossed non-woven fabric that is prepared using the off-line embossing method has a difference of about 1 % to 7%.

[0031] Throughout the foregoing description and the drawings, in which corresponding and like parts are identified by the same reference characters, specific details have been set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail or at all to avoid unnecessarily obscuring the disclosure.

[0032] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.