Patent Application
20070145644
1. Field of the Invention
The present invention relates to methods of forming sound absorbing composite structures have an acoustic tuning layer.
2. Background Art
There is an increasing demand for the reduction of sound levels to improve perception in the passenger compartments of automobiles. Development of methods and systems that accomplish such reductions require an understanding of the potential internal and external noise sources in an automobile as well as the effect of various automobile components in masking or attenuating such noise. Moreover, reduction of noise in the 1 KHZ to 5 KHz frequency range is particularly desirable due to the increased sensitivity of vehicle passengers in that range for speech intelligibility and speech clarity.
Some sound insulating components such as dash insulators and vehicle passenger floor components act as acoustic tuning layers by controlling the air permeability of a single layer within a composite. Examples of such acoustic tuning layers include perforated films or fabrics that resist air flow. In other variations, the layer may be coated with a material such as a sintered or powder coated thermoplastic. These layers shift the sound absorption of a composite to lower frequencies than it would have if impermeable to air. A problem sound absorbing component having such layers is that after the component is formed into a shape the air permeability of the acoustic tuning layer is altered.
Accordingly, there is a need in the prior art for improved methods of forming sound insulating automobile components with adjustable air permeability.
The present invention solves one or more problems of the prior art by providing in at least one embodiment a method of making a sound insulating layered composite structure. In the method of the invention, a sound insulating layered composite structure is formed from a padding layer. The padding layer has a preformed shaped corresponding to the automobile component which is ultimately formed. The padding layer is contacted with a curable liquid composition to form an uncured or partially cured cap layer disposed over at least a portion of the padding layer. Uncured or partially cured cap layer is cured to form the sound insulating composite structure of the present embodiment. Advantageously, the sound insulating layered composite structure of the present embodiment is useful for making a variety of sound insulating automotive components such as dash insulators.
Reference will now be made in detail to presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventors.
In an embodiment of the present invention, a method of making a sound insulating layered composite structure is provided. With reference to
The method of the present invention advantageously allows for a tailoring of the air flow resistance of the formed sound insulating composite structure. In a variation of the present embodiment, the air flow resistance is determined as in ASTM C522-03. The entire disclosure of ASTM C522-03 is hereby incorporated by reference. Typically, the air flow resistance set by the method of the present embodiment is from about 300 to about 6000 rayl. Sound insulating layered composite 10 is also characterized by the position of its peak sound absorption. In one variation of the present embodiment, sound insulating layered composite structure 10 has a peak sound absorption at a sound frequency from about 500 and 6,400 Hz. In another variation of the present embodiment, sound insulating layered composite structure has a peak sound absorption at a sound frequency from about 1500 and 5000 Hz.
With reference to
With reference to
The curable liquid compositions used in the present invention may be thermally and/or photochemically cured. Uncured or partially cured cap layer 16 is substantially fully cured by heating. In one variation, the curable liquid composition comprises a latex or polyurethane. Examples include acrylic latex, ethylene vinyl acetate latex, and styrene butadiene rubber latex. In another variation, the curable liquid composition comprises cross-linkable polymer precursors. In general, polymer precursors are cross-linking agents, oligomers, and monomers. Suitable polymer precursors for the methods of the invention include the curable liquid composition comprises latex precursors or polyurethane precursors. Specific examples include, but are not limited to, acrylic latex precursors, ethylene vinyl acetate latex precursors, styrene butadiene rubber latex precursors, and the like. In a further refinement of the invention, the curable comprises a two component system that is mixed prior to or during the step in which liquid composition 14 is contacted with padding layer 12. Accordingly, cap layer 18 includes the polymer residues of the polymer precursors. Typically, cap layer 18 has a thickness from about 0.3 mil to about 0.25 mm. In another variation, cap layer 14 has a thickness from about 2 mil to about 10 mil.
Padding layer 14 is made from any of the materials typically used for sound insulating automotive components. In a variation, padding layer 14 comprises a component selected from the group consisting of fibrous padding and open cell foams. Such fibrous padding includes padding that comprises cotton (e.g., cotton shoddy) or polyester (e.g., polyethylene terephthalate) or polyolefin (e.g., polypropylene) fibers. Padding layer 14 optionally further comprises an additive selected from the group consisting of glass fibers, fire retardants, and combinations thereof.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
