Sound absorbing material

[0001] The invention relates to a sound absorbing material, made from a microfilament nonwoven fabric having a mass per unit area of 40 to 300 g/m².

[0002] Paneling parts for automobile interiors, such as roof linings, which possess sound absorbing properties, are known from the documents European Patent 0 909 680 and U.S. Pat. No. 4,851,283. They are made from a staple fiber nonwoven fabric layer in which preferably polyester fibers are bonded using binding fibers, and are coated with at least one foam material layer.

[0003] Furthermore, insulating and sound absorbing materials that are made from staple fiber nonwoven fabrics, particularly from polyester fibers, and are bonded using mechanical as well as thermal processes, are known from the documents DE 197 26 965 and DE 197 08 188.

[0004] In the course of ever greater requirements in the automobile industry, new demands are being made on the suppliers. For example, the paneling parts used in the interior of the automobile are supposed to demonstrate attractive optical and sensory properties of the decor. The parts are supposed to be capable of recycling, to possess a very high level of resistance to color fading especially under the effects of black-panel temperatures, a low tendency to become dirty, a high level of friction wear resistance, moisture resistance, fire resistance, cleanability, and a very good capacity for deep drawing, and furthermore to take into account the increasing requirements with regard to noise absorption, with the goal of increasing the comfort of automobile passengers.

[0005] The invention has set itself the task of indicating a sound absorbing material, as well as a method for its production, that take into account the stated requirements.

[0006] According to the invention, the task is accomplished by a sound absorbing material that is made from a microfilament nonwoven fabric having a mass per unit area of 40 to 300 g/m², the a nonwoven fabric being made from a melt-spun, drawn multi-component endless filament having a titer of 1.5 to 5 dtex, being directly laid up to form a fibrous web, and the multi-component endless filaments, optionally prebonded being split to micro-endless filaments having a titer of 0.1 to 1.2 dtex, up to at least 80%, and bonded. The sound absorbing material demonstrates a high level of specific fiber surface at a comparatively low mass per unit area, as well as high opacity. The fineness of the filaments permits good printability and embossability, and thereby decorative structuring of the material.

[0007] Preferably, the sound absorbing material is one in which the nonwoven fabric is made from melt-spun, aerodynamically stretched multi-component endless filaments and directly laid up to form a fibrous web, having a titer of 1.5 to 3 dtex, and the multi-component endless filaments are split to micro-endless filaments having a titer of 0.1 to 0.3 dtex, up to a degree of 80% and bonded. The sound absorbing material demonstrates an isotropic filament distribution in the web, making further processing relatively independent of the machine running direction and thereby very advantageous for material utilization.

[0008] Preferably, the sound absorbing material is one in which the multi-component endless filament is a bicomponent endless filament made from two incompatible polymers, particularly a polyester and a polyamide. Such a bicomponent endless filament demonstrates good splittability into micro-endless filaments and results in an advantageous ratio of strength to mass per unit area. At the same time, the sound absorbing material according to the invention is very easy to clean and wipe down, because of the polymers used and their filament structure, and demonstrates a high level of friction wear resistance, i.e. it is easy to take care of.

[0009] Preferably, the sound absorbing material is one in which the multi-component endless filaments have a cross-section having an orange-like multi-segment structure, also called a pie structure, the segments alternately containing one of the two incompatible polymers in each case. In addition to this orange-like multi-segment structure of the multi-component endless filaments, a side-by-side (s/s) arrangement of the incompatible polymers in the multi-component endless filaments is also possible, which arrangement is preferably used for the production of crimped filaments. Such segment arrangements of the incompatible polymers in the multi-component endless filament have proven to be very easy to split. The sound absorbing material possesses a good deep drawing capacity, or deformability, which is expressed in the average strength values at a high expansion capacity and comparatively low modulus values.

[0010] Preferably, the sound absorbing material is furthermore one in which at least one of the incompatible polymers forming the multi-component endless filament contains an additive, such as color pigments, permanently acting anti-statics, flame retarding agents and/or additives that influence the hydrophobic properties, in amounts up to 10 percent by weight. Static charges can be reduced or prevented with the additives, and the lightfastness under black-panel temperatures can be improved. Using overdyed products, values for lightfastness under black-panel temperatures of 6 have been achieved, determined according to DIN EN 20105-A02.

[0011] The method according to the invention, for the production of a sound absorbing material, is made up of the steps that multi-component endless filaments are spun from the melt, stretched, and directly laid up to form a web, that prebonding takes place, and that the nonwoven fabric is bonded using high-pressure fluid jets, and, at the same time, split into micro-endless filaments having a titer of 0.1 to 1.2 dtex. The sound absorbing material obtained in this way is very uniform with regard to its thickness, it demonstrates an isotropic filament distribution, and it possesses no tendency to delaminate.

[0012] It is advantageous if the method for the production of the sound absorbing material is carried out in such a manner that the multi-component endless filaments are bonded and split in that the nonwoven fabric, which has been prebonded, if necessary, is impacted at least once on each side with high-pressure water jets. As a result, the sound absorbing material demonstrates a good surface and a degree of splitting of the multi-component endless filaments >80%.

[0013] It is advantageous if the sound absorbing material according to the invention is subjected to spot calendering in order to increase its friction wear resistance. For this purpose, the split and bonded nonwoven fabric is passed through heated rollers, at least one of which has elevations that result in melt-bonding of the filaments to one another at certain points.

[0014] The sound absorbing material according to the invention is suited for the production of car roof linings, door paneling, column paneling, rear window shelves and/or trunk paneling, as well as wheel box paneling, because of its properties, such as good printability, a high level of friction wear resistance, as well as its good lightfastness under black-panel temperatures, its thermoformability in the deep-drawing process, and its sensory properties. In this connection, it is possible to do without an additional foam material coating, without suffering major losses in sound absorbing properties, if very high levels of weight savings are a concern.

[0015] The sound absorbing material is suitable as a sound absorbing material in the construction of roof linings, in the construction of column, door, and trunk linings, in the construction of dashboards, in the area of the engine compartment and/or floor linings, the material demonstrating good sound absorbing values at a low mass per unit area as compared with known materials.

[0016] In particular, the sound absorbing material is suited as a tuft carrier for automobile carpeting, which possesses sound absorbing properties that are at least as good as those of conventional automobile carpeting, with a significantly lower amount of material being required, since heavy-carpet backing coatings can be eliminated.

[0017] A filament sheet having a mass per unit area of 138 g/m² is produced from a side-by-side (s/s) polyester-polyamide 6.6 (PES-PA6.6) bicomponent endless filament having a titer of 2.3 dtex and a weight ratio of PES/PA6.6 of 60/40, and is subjected to water-jet needlepunching at pressures up to 230 bar, on both sides. The bicomponent endless filaments have a titer of <1.2 dtex and a thickness of 0.73 mm after the water-jet needlepunching process, which results in splitting of the starting filaments, at the same time. Values of 391 N in the machine running direction and 372 N in the crosswise direction were determined for the tear strength.

[0018] A filament sheet having a mass per unit area of 115 g/m² is produced from a 16 segment (pie) polyester-polyamide 6.6 (PES-PA6.6) bicomponent endless filament having a titer of 2.4 dtex and a weight ratio of PES/PA6.6 of 55/45, and is subjected to water-jet needlepunching at pressures up to 230 bar, on both sides. The bicomponent endless filaments have a titer of <0.15 dtex after the water-jet needlepunching process, which results in splitting of the starting filaments, at the same time, and a thickness of 0.48 mm after a final smoothing process. Values of 302 N in the machine running direction and 303 N in the crosswise direction were determined for the tear strength.

[0019] A commercially available single-layer needlepunched nonwoven fabric made from polyester (car roof lining material) having a thickness of approximately 1.1 mm was used.

[0020] A laminate of a knitted fabric (approximately 0.6 mm thick) and a foam material substratum (approximately 1.6 mm thick), which is typically used as a car roof lining material, was tested.

[0021] A laminate made up of a knitted fabric (approximately 0.6 mm thick) and a polyester needlepunched nonwoven fabric (approximately 1.9 mm thick), which is typically used as a car roof lining material, was tested.

[0022] A laminate made up of a knitted fabric (approximately 0.6 mm thick), a foam material intermediate layer (approximately 4.4 mm thick), and a nonwoven fabric substratum (approximately 0.3 mm thick), which is typically used as a car roof lining material, was tested.

[0023] The results of the sound absorbing properties (measured in a pipe according to DIN 52215) at different frequencies are listed in Table 1.

TABLE 1
Ex.	500	625	800	900	1000	1120	1250	1400	1600
No.	Hz	Hz	Hz	Hz	Hz	Hz	Hz	Hz	Hz
1	6%	12%	28%	33%	39%	46%	51%		70%
2	1%	8%	24%	34%	50%	74%	91%	95%	95%
Cl	1%	5%	10%	12%	14%	16%	21%		29%
C2	2%	6%	11%	12%	14%	16%	10%		27%
C3	5%	11%	20%	24%	28%	35%	38%		54%
C4	5%	10%	20%	25%	30%	33%	34%	71%	76%