Sound absorptive multilayer composite
A sound absorptive multilayer composite having an air-impermeable barrier, an air-permeable reinforcing core having an airflow resistance of at least about 100 mks Rayls and a thickness at least about ⅓ the final composite thickness, an air-permeable open cell foam or fibrous pad having an airflow resistance less than about 2000 mks Rayls and a thickness at least about 1/10 the final composite thickness and a semipermeable airflow-resistive membrane having an airflow resistance of about 500 to about 4000 mks Rayls can provide improved acoustic performance. For example, existing vehicular headliner designs may be improved by adding a properly chosen and properly positioned semipermeable airflow-resistive membrane, a properly chosen and properly positioned air-impermeable barrier, or a properly chosen and properly positioned open cell foam layer.
1. A method for making a multilayer sound absorptive composite comprising:
a) providing a stack of layers comprising in order an air-impermeable barrier, an air-permeable reinforcing core comprising a foam and having an airflow resistance of at least about 100 miks Rayls and a thickness at least about ⅓ the final composite thickness, an air-permeable open cell foam or fibrous pad having an airflow resistance less than about 2000 miks Rayls and a thickness at least about 1/10 the final composite thickness, and a semipermeable airflow-resistive membrane having an airflow resistance of about 500 to about 4000 miks Rayls, and
b) laminating the stack of layers together under sufficient heat and pressure to form a unitary sound absorptive multilayer composite.
2. A method according to claim 1 wherein the composite has a cavity depth at least 90% of the total composite thickness, with the cavity depth being measured from the air-impermeable barrier innermost side to the membrane outermost side.
3. A method according to claim 1 wherein the composite has a cavity depth at least 95% of the total composite thickness, with the cavity depth being measured from the air-impermeable barrier innermost side to the membrane outermost side.
4. A method according to claim 1 wherein the membrane has an airflow resistance of about 500 to about 1500 miks Rayls.
5. A method according to claim 1 wherein the membrane is an outermost layer of the composite.
6. A method according to claim 1 wherein the membrane is colored or textured to provide a decorative appearance.
7. A method according to claim 1 wherein the membrane comprises a nonwoven web.
8. A method according to claim 1 wherein the membrane comprises knit or woven fabric comprising microdenier yarns.
9. A method according to claim 1 wherein the membrane comprises multicomponent fibers.
10. A method according to claim 1 wherein the membrane comprises split or splittable bicomponent fibers.
11. A method according to claim 1 wherein the foam or fibrous pad has a thickness at least about ¼ the total composite thickness.
12. A method according to claim 1 wherein the foam or fibrous pad has a thickness at least about ½ the total composite thickness.
13. A method according to claim 1 wherein the foam or fibrous pad has an airflow resistance less than about 500 miks Rayls.
14. A method according to claim 1 wherein the core has a thickness less than about ⅔ the total composite thickness.
15. A method according to claim 1 wherein the core has a thickness less than about ½ the total composite thickness.
16. A method according to claim 1 wherein the core has an airflow resistance less than about 2000 miks Rayls.
17. A method according to claim 1 wherein the stack further comprises an outermost nonrestrictive air-permeable decorative layer adjacent the membrane.