Sound absorbent thin-layer laminate

[0002] The present invention relates to a sound-absorbing thin-layer laminate according to the precharacterising clause of claim 1, having at least an open-cell backing layer of foam or nonwoven and an open-cell fibre layer, and to a process for the production thereof.

[0003] Sound-absorbing thin-layer laminates are used principally in the automobile industry, which is increasingly seeking to produce light, low-cost, low-noise vehicles. This makes it essential to use cheap, thin, light components, which simultaneously exhibit good sound-absorbing properties.

[0004] Thus, ultralight sound-insulating vehicle trim is currently known for example from WO-A-98/18656, which is 50% lighter than conventional sound insulation assemblies while retaining identical acoustic efficiency. These sound insulation assemblies substantially comprise an open-cell foam layer, to which a microporous reinforcing layer is applied. In these components, the foam layer, made from thermoformed foam or PU foam, exhibits a thickness of from 10 to 25 mm and the reinforcing layer, made from a thermoplastic mixed fibre nonwoven, exhibit a thickness of from 1.3 to 2.5 mm.

[0005] U.S. Pat. No. 5,298,694 describes thin nonwoven laminates for lining vehicle doors. These laminates comprise a nonwoven at least 5 mm thick consisting of thermoplastic fibres and laminated with a thin woven fabric, a fibrous web, a film or a foil. The nonwoven, which is at least 5 mm thick, consists of a mixture of melt-blown microfibres and crimped bulking fibres. Owing to the relatively large diameter of the microfibres (up to 15 μm) and the fact that air flow resistance in the individual layers is not regulated or specified, the sound-absorbing properties of these materials are not optimised and these materials do not take account of sound absorption in particular in relation to lower frequencies.

[0006] Air flow resistance may be unambiguously determined using measuring methods as stated in DIN standard 52 213.

[0007] Owing to the relatively large diameter of the fibres used (5-15 μm), these nonwoven laminates essentially exhibit a backing function and are distinguished by their mechanical properties, the sound-absorbing performance thereof being rather average.

[0008] The object of the present invention is to provide in a simple, low-cost manner, an acoustically highly effective, ultralight thin-layer laminate. In particular, a laminate is to be provided which exhibits excellent sound-absorbing properties (with comparable thickness) at lower frequencies while at the same time exhibiting a certain degree of structural stability.

[0009] This object is achieved according to the invention by a sound-absorbing thin-layer laminate having the features of claim 1 and in particular by a thin-layer laminate consisting of two different materials. The laminate according to the invention comprises a thin layer of microfibres, which is bonded to a backing layer consisting of an low-density open-cell nonwoven. In a preferred embodiment, the microfibres consist of melt-blown polypropylene and comprise a fibre diameter of approximately 2-5 μm. It goes without saying that these microfibres may also be produced from a different polyolefin, polyester, polyurethane or nylon. The microfibre layer attains a thickness of only 0.2 to 1.0 mm, and in particular 0.3 to 0.7 mm and has a weight per unit area of 20 to 200 g/m², and in particular 30 to 100 g/M². The backing layer used according to the invention comprises a weight per unit area of less than 2000 g/m²and a thickness of up to 50 mm and may be made of cotton fibres, synthetic fibres or another fibre mixture. According to the invention, if the backing layer consists of an open-cell foam, it exhibits a low density of from 1 to 2 lb/ft³(16 to 32 kg/m³) and may be made from polyurethane or another foamed plastics. The microfibre layer is adhered in simple manner to the nonwoven or foam layer.

[0010] It has emerged that coating an open-cell, “low density” foam or an open-cell, sparingly compacted nonwoven layer with an extremely thin layer of microfibres, in accordance with the invention, produces a component which exhibits a surprisingly high absorption coefficient. This results in highly effective sound-absorbing thin-layer components with low weight per unit area. Furthermore, the microfibre layer has proven to be water-repellent and thus also allows use of the thin-layer laminates according to the invention in a moist or wet environment.

[0011] Thin-layer laminates are hereinafter understood to be laminates which comprise a thin microfibre layer 0.2 to 1.0 mm, in particular 0.3 to 0.7 mm thick.

[0012] The sparingly compacted nonwoven backing layer advantageously comprises fibres which are bonded with thermoplastic fibres or thermosetting plastic resins, to enable sound-absorbing vehicle parts, in particular carpets or dashboard trim, to be formed during manufacture into specified shapes by means of treatment with pressure and heat.

[0013] In modifications of the thin-layer laminate according to the invention, a third layer of nonwoven may be applied over the microfibre layer. This third nonwoven layer may further improve the sound-absorption capacity of the thin-layer laminate and protects the extremely thin microfibre layer from possible abrasion.