The present invention relates to sound insulators for automobiles and particularly relates to an improved sound insulator for automobiles.
Sound insulators for automobiles are already known in the art. However, known sound insulators are not completely effective for Indian conditions.
According to one such sound insulator is disclosed in European Patent No.EP 1623 777. According to this patent a sound absorbent, comprising two interconnected non-woven-fibre textiles (1,2), with thermoplastic or duroplastic bonding, whereby the non-woven-fibre textile (1), facing the acoustic emission source, has a layer thickness in the range of 2 to 15 mm, a density in the range of 50 to 500 kg/m<3>, a specific area weight in the range of 0.1 to 5 kg/m<2> and a flow resistance in the range of 50 to 1000 kNs/m4 and the non-woven-fibre textile (2), facing away from the acoustic emission source, has a layer thickness in the range of 10 to 100 mm, a density on the range of 20 to 100 kg/m<3>, a specific area weight in the range of 0.5 to 1 kg/m<2> and a flow resistance in the range of 10 to 40 kNs/m4 with a total thickness for the sound absorbent in the range of 12 to 30 mm and a total specific area weight for the sound absorbent in the range of 0.5 to 3 kg/m<2>.
In the corresponding US Patent under No.6145617 the details of such sound insulator are given. This sound insulator is less effective for Transmission Loss due to:
The sound insulator does not have any non porous layer in between or has only one air layer in between. The Transmission Loss property is less because of non existence of middle non porous film.

The applicants after various trials have found that the porous film layer in between two layers helps in achieving higher air flow resistance resulting in better Transmission Loss. Thus induction of non-porous layer in between absorbing layer has been found to provide effective sound insulation which can be used in automobiles.
Thus the present invention provides an improved sound insulators for automobiles which comprises first layer of non-woven open pored absorbent material having thickness of 5mm to 75 mm, a density in the range of 6 - 600 kg/cum and specific area weight of 0.5 kg-3.0 kg / sqmt, second layer of non porous film having thickness of 0.01 mm - 2 mm having a relatively higher airflow resistance and third layer of non-woven rigidly compressed fibrous layer having thickness of 1mm -10 mm, a density of 50 - 2000 kg / cum and specific weight area of 0.5 kg - 2.0 kg / sq mt.
According to the present invention there is provided an improved sound insulators for automobiles which comprises (i) first layer made of non - woven open pored absorbent material having thickness of 5 mm - 75 mm (ii) second layer of non porous film having thickness of 0.01 mm - 2mm and relatively higher air flow resistance and (iii) third layer of non-woven rigidly compressed fibrous layer having thickness of 1mm - 10 mm.
All three layers are sandwiched together by laminating and thermoforming

We shall now describe the present invention by way of illustration but does not restrict the scope of the present invention.
Fig. 1 of the accompanying drawing shows the classic construction of sound insulation of the present invention.
Referring to Fig. 1 the sound absorbent insulated material consists of (i) first layer made of non - woven open pored absorbent material having thickness of 5 mm ~ 75 mm (ii) second layer of non porous film having thickness of 0.01 mm ~ 2mm and relatively higher air flow resistance and (iii) third layer of non-woven rigidly compressed fibrous layer having thickness of 1mm ~ 10 mm.

WE CLAIM:
1. An improved sound insulators for automobiles which comprises (i) first layer made of non - woven open pored absorbent material having thickness of 5 mm ~ 75 mm (ii) second layer of non porous film having thickness of 0.01 mm ~ 2mm and relatively higher air flow resistance and (iii) third layer of non-woven rigidly compressed fibrous layer having thickness of 1mm -10 mm.
2. An improved sound insulators for automobiles as claimed in claim 1, wherein all three layers are sandwiched together by laminating and thermoforming.
3. An improved sound insulators for automobiles substantially as herein described and illustrated in the drawing.

An improved sound insulators for automobiles which comprises (i) first layer made of non - woven open pored absorbent material having thickness of 5 mm ~ 75 mm (ii) second layer of non porous film having thickness of 0.01 mm ~ 2mm and relatively higher air flow resistance and (iii) third layer of non-woven rigidly compressed fibrous layer having thickness of 1mm ~ 10 mm.