AU2007202503C1

AU2007202503C1 - A thermoformable acoustic sheet

Info

Publication number: AU2007202503C1
Application number: AU2007202503A
Authority: AU
Inventors: Michael William Coates; Marek Kierzkowski
Original assignee: Zephyros Inc
Current assignee: Zephyros Inc
Priority date: 2000-07-19
Filing date: 2007-05-31
Publication date: 2012-07-12
Anticipated expiration: 2021-07-19
Also published as: AU2010233029A1; AU2010233029C1; AU2007100274B4; AU2010233029B2; AU2007100274A5; AU2007202503B2; AU2007202503A1

Abstract

P \OPER\Sgw\2(X0\an-Jue\30236 5 Abmsra c .o /5/2007 A thermoformable acoustic sheet formed by a compressed fibrous web including 5 high melt and adhesive thermoplastic fibres in which the adhesive fibres are at least partially melted so that in the compressed web the adhesive fibres at least partially coat the high melt fibres and reduce the interstitial space in the fibre matrix. Also included is a method of producing a thermoformable acoustic sheet which includes the steps of heating a fibre web including high melt and adhesive 10 thermoplastic fibres to at least partially melt the adhesive fibres and compressing the web to form a sheet so that the adhesive fibres at least partially coat the high melt fibres to reduce the interstitial space in the fibre matrix.

Description

P/00/0Il Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT (ORIGINAL) Name of Applicant(s): I..N.C. Corporation Pty Ltd, ACN 005 302 250, 63-79 South Park Drive, Dandenong South Victoria, 3175 Australia Actual Inventor(s): Michael William COATES Marek KIERZKOWSKI Address for Service: DAVIES COLLISON CAVE, Patent & Trademark Attorneys, of I Nicholson Street, Melbourne, 3000, Victoria, Australia Ph: 03 9254 2777 Fax: 03 9254 2770 Attorney Code: DM Invention Title: "A thermoformable acoustic sheet" The following statement is a full description of this invention, including the best method of performing it known to us:- A THERMOFORMABLE ACOUSTIC SHEET BACKGROUND OF THE INVENTION 5 This invention relates to materials for acoustic absorption. More particularly it relates to thermoformable acoustic sheets. Sounds absorption is required in a wide variety of industrial and domestic applications. In many of these applications it is desirable that the acoustic 10 material conforms to the shape of a surface for example or otherwise retains a particular shape. In such applications it is desirable that the acoustic sheet can be heat moulded to the required shape to provide relative ease and speed of production. Sound absorption can be a function of depth of air space, air flow resistance, mass, stiffness and the acoustic impedance of any porous media 15 behind the acoustic sheet. Therefore, adding a third dimension for example by moulding to a required shape increases stiffness and can add practical and aesthetic value. Importantly a three dimensionally shaped material provides its, own air space. The shape therefore has a major influence on sound absorption and stiffness. One particular application for heat mouldable or thermoformable 20 acoustic sheets is in the automotive industry, in particular, in under bonnet insulators for motor vehicles. Existing under bonnet insulators use moulded fibreglass insulators for sound absorption. In these products resinated fibreglass, or felt is sandwiched between two layers of non-woven tissue and subsequently heat molded to form a so called "biscuit" with sealed edges. The 25 difficulties associated with this product include the fact that the moulding process is relatively slow taking up to 21/2 minutes per moulded part. Additionally, the use of resinated fibreglass is undesirable because of its inherent undesirable handling problems while the resins can release toxic gases during the moulding process. 30 C:\NRPonb\DCC\WAMu 982081.DOC-29)9/2010 -2 Other examples of applications for thermoformable sheets in the automotive industry include wheel arch linings, head linings and boot linings. Attempts to produce a suitable thermoformable material from thermoplastic textile 5 for underbonnet insulator have been unsuccessful due to one or more of the failure of the materials to meet requirements of low sag modulus typically encountered at operating temperatures, unsuitable moulding performance, and lack of uniformity of air flow resistance required for acoustic absorption performance. 10 One or more embodiments of the present invention may provide a thermoformable acoustic sheet and a method of producing such a sheet that will at least provide a useful alternative. 15 SUMMARY OF THE INVENTION In one aspect this invention provides a thermoformable acoustic sheet formed by a compressed fibrous web including high melt fibres and adhesive thermoplastic fibres in which the adhesive fibres are at least partially melted so that in the 20 compressed web the adhesive fibres at least partially coat the high melt fibres and reduce the interstitial space in the fibrous web to form paths for air flow through said sheet at a selected total air flow resistance; wherein the selected total air flow resistance is between 275 and 1100 mks Rayls and is substantially uniform across said sheet. 25 In one form of the invention, the thermoplastic fibres are treated with an adhesive coating to increase the airflow resistance. In another form of the invention, the thermoplastic fibres are treated with a coating 30 formed by one or more further webs of thermoplastic fibres to increase the air flow resistance.

C.NRfnbl\DCC\WAM\3199219_ .DOC-299/201M -3 Preferably the further web contains a substantial amount of adhesive fibre. In another aspect this invention provides a method of producing a thermoformable 5 acoustic sheet including the steps of heating a fibrous web including high melt fibres and adhesive thermoplastic fibres to at least partially melt the adhesive fibres and compressing the web to form the thermoformable acoustic sheet at sufficient pressure so that the heated adhesive fibres flow to at least partially coat the high melt fibres and reduce the interstitial space in the fibrous web to create a 10 labyrinthine structure that forms a tortuous path for air flow through said sheet at a selected total air flow resistance; wherein the selected total air flow resistance is between 275 and 1100 mks Rayls and is substantially uniform across said sheet. In one form of the method of the present invention, the sheet is treated with an 15 adhesive coating to increase the air flow resistance. In another form of the method of the present invention, the thermoplastic fibres are treated with a coating formed by one or more further webs of thermoplastic fibres to increase the air flow resistance. 20 The compression of the fibrous material under heat and pressure results in the at least partial melting of the adhesive fibre which acts as a heat activatable binder to at least partially coat and join to the high melting fiber thus reducing interstitial space in the fibre matrix and creating a labyrinthine structure that forms a tortuous 25 path for air flow through the fiber matrix. The high melting fibre remains substantially intact, although some softening is acceptable and can act as a reinforcement in the acoustic sheet. The acoustic sheet has a total air flow resistance of between 275 and 1100 mks 30 Rayl, more preferably 600-1100 mks Rayl and even more preferably 900-1000 mks Rayl. Such air flow resistance values of the acoustic sheet result in effective C:\NRPonb\DCCMKA\9X62 18 DOC.M l/21112 -4 absorption of sound for applications such as hood or under bonnet insulation. In this regard the acoustic sheet produced in accordance with the present invention exhibit the acoustic behaviour of a porous limp sheet. Porous limp sheets display superior sound absorption at low frequencies. 5 Preferably, the thermoformable acoustic sheet has a low sag modulus at temperatures up to about 1500C. The fibrous material can be a combination of fibres of various denier. The high 10 melt fibres are 12 denier or below, 6 denier or below and/or 4 denier or below. The adhesive fibres are 8 denier or below, 6 denier or below, 4 denier or below and/or at about 2 denier. The fibrous material can be selected from, but not limited to, polyester, 15 polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene 1,4-cyclohexanedimethanol (PCT), polylactic acid (PLA) and/or polypropylene (PP). Fibre with special characteristics such as high strength or very high melting point can also be used. Examples include Kevlar T M , NomexTM and BasofilTM. Alternatively, the high melting point fibres may be natural fibre such as wool, 20 hemp, kenaf etc. The web of fibrous material used to produce the acoustic sheet of this invention can be produced from a non-woven vertically aligned high loft thermally bonded material formed by the STRUTO T M process under Patent WO 99/61693. Suitable 25 low and high melt materials can be used to provide the respective fibres. The web of fibrous material used to produce the acoustic sheet of this invention can also be produced by cross-lapping and thermal bonding. The web can also be produced by carding fibres and consolidation by needle punching. According to 30 another option the web can be produced by other non-woven textile manufacturing methods such as melt blown, spun bond etc.

C:\NRPnb\DCC\WAAu19820X I. DOC-29A9/241 I - 4A Adhesive fibres are also known as low melt, bonding or binding fibres. Various material can be used for the high melt and adhesive fibres so long as the -5 adhesive fibre can be partially melted without substantially melting the high melt fibre. Some softening of the high melt fibre is acceptable. The high melt fibre preferably has a melting point above about 220 0 C. The adhesive fibre preferably has a melting point between 100 and 1600C, more preferably 120 5 150*C and even more preferably 135-145*C. It will be appreciated that thermoplastic fibres are available in mono and bi component form. A bicomponent fibre can be formed of discrete low and high melting point portions. Heating such a bicomponent fibre ("adhesive bicomponent fibre") results in at least partial melting of the low melting point portion leaving the 10 higher melting point portion intact. Therefore in the method of the present invention, heating a fibre web results in at least partial melting of the adhesive fibres and/or the low melting point portion of any adhesive bicomponent fibres present in the web to at least partially coat and join to the high melting fibre. The higher melting point fibres and high melting point portions of any adhesive 15 bicomponent fibre remain intact after the compaction process. The web of fibrous material used to produce the acoustic sheet preferably has a web weight 1000 g/m 2 or below, more preferably 800 g/m 2 or below, even more preferably 600 g/m 2 or below and even further preferably 400 g/m 2 or below. 20 The web is typically compressed by between 15 and 25 times. The compression step of the method of the present invention can be undertaken in any suitable known manner, for example in any flat bed laminator or calender. 25 In one embodiment, the fibrous material is produced as a single layer with a high proportion, preferably greater than 50% of adhesive and/or adhesive bicomponent fibre. This may be compacted in a MeyerP m flat bed laminator at 180-220"C, preferably at 190-200*C, for a period of 1-3 minutes, preferably 30 1.5-2 minutes. The processing conditions can be varied to alter the thickness -6 and/or other characteristics and the subsequent air flow resistance of the acoustic sheet. In one form of the invention, the thermoplastic fibres are treated with an 5 adhesive coating. The coating treatment can be effected in any suitable known manner, for example by the application of an adhesive film or an adhesive powder and subsequent heating. The amount of adhesive treatment can be adjusted to control the total air flow resistance of the thermoformable acoustic sheet. The adhesive can be a cross-linking adhesive powder. The application 10 rate of powder is dependent on particle size, melting point, melt flow properties and polymer type. These types of adhesive have an initial curing temperature that can be exceeded after curing and cooling without remelting of the adhesive. Suitable adhesives include the product SURLYNTM manufactured by i. Pont. Typical polymers for the adhesive film and/or powder are co-polyester, 15 polyethylene and/or polypropylene. In one form of the invention, where the adhesive coating is an adhesive powder, a layer of non-woven fabric or other material may be laminated to the compressed thermoplastic sheet using the adhesive powder. 20 Preferably the compression and coating treatment steps are performed in a single process. That is, heating required prior to the compression and for adhesive melting (to form the coating) can be a single step before compression. 25 In another form of the invention, the compression of the thermoplastic fibre and the lamination to the non-woven fabric are achieved in a single process. Preferably a compression and adhesive melting temperature of about 2000 C is used. 30 In another form of the invention, the coating by use of a web of thermoplastic -7 fibres may be effected by the application of multiple webs of fibrous material which are introduced in parallel into the compaction process, and compacted concurrently. Alternatively, the web(s) can be introduced in one or more further compacting steps after the first web of fibrous material including adhesive and 5 high melt thermoplastic fibres has been compacted. The further web(s) of fibrous material can include adhesive fibre, adhesive bicomponent fibre and/or high melt fibre. The amount and type of additional fibrous material can be adjusted to control the total air flow resistance of the thermoformable acoustic sheet. 10 In one form of the invention the thermoformable acoustic sheet can be formed from a first web preferably comprising 10-40%, further preferably 20% high melting point fibre and a second web of fibrous material, preferably comprising 60-100% further preferably more than 70%, even further preferably 100% 15 adhesive or adhesive melt bicomponent fibre. The two webs can be compacted concurrently and adhere to each other without the need for an adhesive layer. In another form of the invention the thermoformable acoustic sheet may be formed from two webs in which one of the webs may have a relatively low 20 proportion of adhesive or adhesive bicomponent fibre, such as 10-50% preferably 20-25%. The webs can be compacted as described above. However, in this embodiment, a thermoplastic adhesive layer may be required to be introduced between the two webs, in the form of a powder. The addition rate of the powder is preferably within the range 10 and 80 g/m 2 , more 25 preferably 40-60 g/m 2 . If a film is used rather than a powder it must be thin enough to become permeable during the compaction process, preferably from 15-25 microns thick. The adhesive may be required if the compressed webs exhibit recovery after compaction, or if they do not compact sufficiently for adequate sound absorption. 30 -8 The mouldable acoustic sheet according to this invention has been found to be particularly suitable for use in automotive applications and in particular as an under bonnet acoustic liner. The thermoformable acoustic sheet can be readily formed using a moulding temperature of between 1500 and 180 0 C and may 5 require use of flame retardant fibres or an additional flame retardant treatment. Suitable additives as flame retardants are deca-bromodiphenyloxide as supplied by Great Lake Chemicals. High melt fibres having improved inherent flame retardant characteristics may be used, for example a grafted polyester such as TreviraTM CS. The moulded sheet substantially retains the air flow 10 resistance of the unmoulded sheet and thus its acoustic properties. Moreover, the sheet has a low sag modulus at temperatures up to about 150 0 C and is suitable for use as an under bonnet insulator or liner. For hood insulator applications, the appearance must be consistent and low 15 gloss. Appearance can be influenced by the fibre properties and binder fibres tend to develop gloss during compaction and subsequent molding. To minimise gloss, the option of using an additional layer of fibrous material as the coating with each layer having significantly different fibre blend ratios is preferred. A face web should have a relatively low proportion of binder fibre, preferably 10 20 20% and a back web should have a very high binder ration, from 60-100%, preferably 80%. The back web will significantly contribute to flow resistance to assure excellent sound absorption, whilst the facing web assists in resisting marring during the process. 25 The thermoformable material of this invention is also suitable for use in wheel arch linings, head linings and boot linings. In most applications the selected air flow resistance of the moulded sheet can be used in combination with an acoustic cavity or space behind the sheet to achieve desired acoustic absorption. 30 C:\NRPonbl\DCC\WAM\ 3 19K2N_1 DOC-29AW201ln -9 In another form of the invention the uniform air flow resistance can be at least partially achieved by laminating a textile layer with selected air flow resistance to the compressed sheet. The layer can for example be a slit or perforated thermoplastic film or textile layer. 5 BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments of the invention will now be described by way of example only with reference to the accompanying drawings and examples, in which: 10 Figure 1 is a schematic diagram of a flat bed laminating machine; Figure 2 is a plot of normal incidence sound absorption coefficient against frequency for tested samples of this invention; Figure 3 is a plot of flow resistance versus fibre formulation for samples 15 having a high melt/adhesive fibre ratio of 1:1 and web weight of 600 g/m 2 ; Figure 4 is a plot of flow resistance versus powder additive weight for samples having a high melt (6 denier)/adhesive (4 denier) fibre ratio of 1:1, and a web weight of 600 g/m 2 Figure 5 is a plot of sound absorption versus flow resistance for a range of 20 samples with a web weight of 500 g/m 2 at a frequency of 1000 Hz and a 50 mm air gap; and Figure 6 is a plot of sound absorption versus product weight for a range of samples with an air flow resistance of 600 mks Rayls at a frequency of 500 Hz and an air gap 50 mm. 25 DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be implemented using a known laminating machine such as a Meyer laminating machine schematically illustrated in Figure 1. As 30 shown in the drawing the laminating machine 1 includes a web supply roll 2.

- 10 The web 3 is fed to a heat contact system 9 , which is readily known to those in the art as including heaters 10 positioned on either side of two opposed parallel belts 11 and 12. The belts 11, 12 are thus heated and in turn heat the web 3 to about 2000. A pair of adjustable pressure rollers 13, 14 bear against 5 the respective belts 11, 12 to compress the web 3. A subsequent cooling system 15 is provided to cool the compressed product. In the case of a product made using a thermoplastic adhesive powder, the web 3 is fed from the supply roller through a scatter head 4 which applies the 10 thermoplastic adhesive powder to the surface of the web 3. A winding system 5 for thermoplastic adhesive film 6 is also provided in the machine 1. It will be apparent td those skilled ir ne art one or other of the scatter head system 4 or unwinding system 5 for thermoplastic adhesive film 6 is to place adhesive in contact with web 3. As described above, the web 3 then continues through heat 15 contact system 9 where the thermoplastic adhesive powder is melted under the action of heated belts 11, 12 as the web 3 is simultaneously compressed under the action of pressure rollers 13, 14. Cooling system 15 cools the final product as described above. 20 Where a further fabric layer or web is to be provided, a supply of fabric or web 7 is stored on a roll 8 prior to entry into the heat contact system 9 so that the fabric web 7 is fed to the heat contact system 9 simultaneously with web 3. Where a thermoplastic adhesive has been deposited on web 3 by scatter head system 4 or unwinding system 5, the heated belts 11, 12 heat the fabric 7 and 25 web 3 to melt the adhesive. Pressure rollers 13, 14 bear against the respective belts 11, 12 to force fabric 7 into contact with web 3 and the melted adhesive. Again, as described above, the web 3 is compressed and the cooling system 15 cools the compressed and laminated product. 30 C:\NRPonbl\DCC\MXA\39862|_l DOC-18/1/2012 - 11 Test results 5 Example 1 A sample was prepared using the above described machine and tested using an impedance tube with a 50mm air gap to ASTM E 1050-90. The properties of the sample were: 10 " carrier formulation 30% polypropylene (adhesive fibre) and 70% polyester (high melt); * web material was a needle punched mixture in roll form; e carrier web weight 450g/m 2 ; and 15 . polyester non-woven fabric facing web weight 50g/m 2 adhered with a small (1 5-20g) of polypropylene powder. The average air flow resistance of the sample was 300-400 mks Rayls. Figure 2 is a plot of average incident sound absorption versus frequency for six randomly selected samples prepared according to this example. 20 Example 2 A sample was prepared and tested in the same manner as in Example 1 with the following specifications: 25 0 50% high melt fibre of 6 denier; * 50% adhesive fibre of 4 denier; and 0 web weight 700g/m 2 . 30 -12 The air flow resistance of the sample was in the range of 300-400 mks Rayls. Example 3 5 A sample was prepared and tested in the same manner as in Example 1 with the following specifications: 0 30% high melt polyester fibre of 6 denier; * 70% adhesive polyester fibre of 4 denier; 10 * web weight 600g/m 2 . The air flow resistance of the sample was in the range of 700-850 mks Rayls. Example 4 15 A sample was prepared and tested in the same manner as in Example 1 with the following specifications: e 50% high melt polyester fibre of 6 denier; * 50% adhesive bicomponent polyester fibre of 4 denier; and 20 9 web weight 600g/m 2 . As shown in figure 3, the air flow resistance of the sample was in the range of 275-375 mks Rayls. Example 5 25 A sample was prepared and tested in the same manner as in Example 1 with the following specifications: * 50% staple high melt polyester fibre of 6 denier; -13 * 50% adhesive bicomponent polyester fibre of 2 denier; and * web weight 600g/m2 As shown in figure 3, the air flow resistance of the sample was in the range of 450-600 mks Rayls. 5 Example 6 A sample was prepared and tested in the same manner as in Example 1 with the following specifications: 10 * 50% high melt polyester fibre of 3 denier; * 50% adhesive polyester fibre of 2 denier; and * web weight 600g/m 2 As shown in figure 3, the air flow resistance of the sample was in the range of 15 550-750 mks Rayls. Example 7 A sample was prepared and tested in the same manner as in Example I with 20 the following specifications: 0 30% high melt polyester fibre of 4 denier; * 70% adhesive bicomponent polyester fibre of 2 denier; 0 web weight 250g/m 2 ; 25 * spun bonded non-woven fabric polyester with a web weight of 1 OOg/m 2 , 0 polyethylene thermoplastic powder at an application rate of 20g/m 2 ; and * dibromophenyloxide flame retardant additive at an application of 25g/m 2 The air flow resistance of the sample was in the range of 700-900 mks Rayls.

- 14 Example 8 A sample was prepared and tested in the same manner as in Example 1 using 5 two webs of fibrous material with the following specifications: * 180 g/m 2 30% bicomponent polyester fibre of 2 denier and 70% high melt black 4 denier polyester fibre; and * 300 g/m 2 100% 2 denier bicomponent fibre. 0 The two webs of the above specification were introduced to a Meyer laminator at the following settings. - pressure 15 KPa; - distance between top and bottom belt 1 mm; 5 - first bank of heaters temperature 1750C; and - second bank of heaters temperature 1900C. This resulted in a flow resistance of 900-1100 mks Rayls. 20 Example 9 A sample was prepared and tested in the same manner as in Example 8: Web 1 25 e 85% high melt polyester fibre with 4 denier; . 15% adhesive bicomponent polyester fibre of 2 denier; and 0 web weight 180g/m 2 . Web 2 30 e 30% staple high melt polyester fibre of 4 denier, -15 . 70% adhesive bicomponent polyester fibre of 2 denier; and * web weight 250g/m 2 . The air flow resistance of the sample was in the range of 700-900 mks Rayls. 5 Example 10 Samples were prepared and tested in the same manner as in Example 1 with the following specifications: 10 * 50% high melt polyester fibre of 6 denier; * 50% adhesive polyester fibre of 4 denier; * web weight 600g/m 2 ; and * varying application rates of LDPE adhesive powder. 15 Eight samples were made, each with the application rate of the adhesive powder varying from 1Og/m 2 to 80g/m 2 in 1Og/m 2 intervals. A plot of the resulting air flow resistance of each sample is shown in Figure 4. Test results for a range of acoustic sheets made in accordance with the 20 invention are illustrated in Figures 5 and 6. In Figure 5, a range of samples with a web weight 600g/m 2 were tested at a frequency of 1000Hz with a 50mm air gap between the sample and a solid surface for their sound absorption coefficient against the air flow resistance. Figure 6 illustrates the sound absorption coefficient against product weight (g/m 2 ) for a range of samples 25 having an air flow resistance of 600 mks Rayls. The sound absorption coefficients were measured at a frequency of 500Hz with a 50mm air gap between the samples and a solid surface. The air flow resistance is dependent on the ratio of binder matrix to high melt 30 fibre. If a low air flow resistance is required, then a smaller amount of binder is C:\NRPortbl\DCOWAMul9X2U_ I DOC-29A9/2010 - 16 required. For a high air flow resistance, the binder ratio is significantly higher. Air flow resistance can vary with fibre size and geometry. Larger diameter fibres result in lower air flow resistance through a higher porosity. 5 The foregoing describes a limited number of embodiments of the invention and modifications can be made without departing from the scope of the invention. Throughout this specification and the claims which follow, unless the context 10 requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 15 The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. 20

Claims

1. A thermoformable acoustic sheet formed by a compressed fibrous web including high melt fibres and adhesive thermoplastic fibres in which the adhesive 5 fibres are at least partially melted so that in the compressed web the adhesive fibres at least partially coat the high melt fibres and reduce the interstitial space in the fibrous web to form paths for air flow through said sheet at a selected total air flow resistance; wherein the selected total air flow resistance is between 275 and 1100 mks Rayls and is substantially uniform across said sheet. 10

2. A thermoformable acoustic sheet according to claim 1 wherein the high melt fibres and adhesive fibres are treated with an adhesive coating.

3. A thermoformable acoustic sheet according to claim 1 wherein the high melt 15 fibres and adhesive fibres are treated with a coating formed by one or more further webs of thermoplastic fibres.

4. A thermoformable acoustic sheet according to claim 1, 2 or 3 wherein the total air flow resistance is between 550 and 900 mks Rayls. 20

5. A thermoformable acoustic sheet according to claim 4 wherein the total air flow resistance is between 700 and 900 mks Rayls.

6. A thermoformable acoustic sheet according to claim 4 wherein the total air 25 flow resistance is between 550 and 750 mks Rayls.

7. A thermoformable acoustic sheet according to claim 1, 2 or 3 wherein the total air flow resistance is between 450 and 600 mks Rayls. 30

8. A thermoformable acoustic sheet according to any preceding claim having a low sag modulus at temperatures up to 150 0 C. C:\NRPonblDCC\MKA096218_1 DOCK1Wj/2012 - 18

9. A thermoformable acoustic sheet according to any preceding claim wherein the high melt fibres have a melting point above about 200*C.

10. A thermoformable acoustic sheet according to any preceding claim wherein 5 the adhesive fibres have a melting point between 100 and 160*C.

11. A thermoformable acoustic sheet according to any preceding claim wherein the high melt fibres are 12 denier or below. 10

12. A thermoformable acoustic sheet according to claim 11 wherein the high melt fibres are about 6 denier or below.

13. A thermoformable acoustic sheet according to any preceding claim wherein the adhesive fibres are 8 denier or below. 15

14. A thermoformable acoustic sheet according to claim 13 wherein the adhesive fibres are about 6 denier or below.

15. A thermoformable acoustic sheet according to any preceding claim wherein 20 the compressed fibrous web is produced from non-woven vertically aligned high loft thermally bonded fibres.

16. A thermoformable acoustic sheet according to any preceding claim wherein the high melt fibres and/or adhesive fibres are selected from polyethylene 25 terephthalate (PET), polybutylene terephthalate (PBT), polyethylene 1,4 cyclohexanedimethanol (PCT), polylactic acid (PLA) and/or polypropylene (PP).

17. A thermoformable acoustic sheet according to any one of claims 1 to 15 wherein the high melt fibres are natural fibres. 30

18. A thermoformable acoustic sheet according to any preceding claim wherein C:\NRPonbl\DCC\MKA39K62 I _ IDOC- I /0 1/2(12 - 19 the adhesive fibres are bicomponent fibres.

19. A thermoformable acoustic sheet according to any preceding claim wherein the web of high melt fibres and adhesive fibres has a web weight of about 5 1 000g/m 2 or below.

20. A thermoformable acoustic sheet according to any preceding claim further including a flame retardant. 10

21. A thermoformable acoustic sheet according to claim 1 wherein the web of high melt fibres and adhesive fibres has 50% or more of adhesive fibre or adhesive bicomponent fibre and is formed by heating a fibrous web to a temperature between 180-2001C and compressing said web. 15

22. A thermoformable acoustic sheet according to claim 1 and having a sound absorption coefficient of about 0.6 or greater at a frequency of 1000 Hz as measured in accordance with ASTM E 1050-90 using an impedance tube with a 50 mm air gap.

23. A thermoformable acoustic sheet according to claim 1, wherein the 20 adhesive fibres are bicomponent polyester fibres.

24. A thermoformable acoustic sheet according to claim 1 and substantially as hereinbefore described with reference to the Examples and/or accompanying drawings. 25

25. A method of producing a thermoformable acoustic sheet including the steps of heating a fibrous web including high melt fibres and adhesive thermoplastic fibres to at least partially melt the adhesive fibres and compressing the web to form the thermoformable acoustic sheet at sufficient pressure so that the heated 30 adhesive fibres flow to at least partially coat the high melt fibres and reduce the interstitial space in the fibrous web to create a labyrinthine structure that forms a C:\NRPonblDCC\MKAu3986218_ I DOC-I1/)1/2012 - 20 tortuous path for air flow through said sheet at a selected total air flow resistance; wherein the selected total air flow resistance is between 275 and 1100 mks Rayls and is substantially uniform across said sheet. 5

26. A method of producing a thermoformable acoustic sheet according to claim 25 further including the step of treating the high melt fibres and adhesive fibres are treated with an adhesive coating to increase the air flow resistance.

27. A method of producing a thermoformable acoustic sheet according to claim 10 26 wherein the adhesive coating is applied as a powder at a rate of from 10 to 80g/m 2 .

28. A method of producing a thermoformable acoustic sheet according to claim 25 further including the step of treating the high melt fibres and adhesive fibres 15 with a coating formed by one or more further webs of thermoplastic fibres.

29. A method of producing a thermoformable acoustic sheet according to claim 28 wherein the fibrous web and the coating formed by one or more further webs of thermoplastic fibres are compressed concurrently. 20

30. A method of producing a thermoformable acoustic sheet according to any one of claims 25 to 29 wherein the web is compressed at a temperature between 180 and 200 0 C. 25

31. A method of producing a thermoformable acoustic sheet according to any one of claims 25 to 30 wherein the sheet is a thermoformable acoustic sheet according to any one of claims 4 to 24.

32. A method of producing a thermoformable acoustic sheet according to claim 30 25 and substantially as hereinbefore described with reference to the examples and/or accompanying figures. C:\NRPorbnDCOWAP1 99209_1DOC-29/ 2 01M -21

33. A thermoformed acoustic article produced by thermoforming a thermoformable acoustic sheet according to any one of claims 1 to 24. 5

34. A thermoformed acoustic article according to claim 33 and selected from the group consisting of under bonnet insulators, wheel arch linings, head linings and boot linings.

35. Use of a thermoformed acoustic article according to claim 33 or 34 in 10 automotive applications.

36. Use according to claim 35 wherein said article is mounted to a motor vehicle with an acoustic cavity or space behind the article.