Shaped microperforated polymeric film sound absorbers and methods of manufacturing the same

• US 6,598,701 B1
• Filed: 06/30/2000
• Issued: 07/29/2003
• Est. Priority Date: 06/30/2000
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Martinson, Paul A., Wood, Kenneth B.
• Primary Examiner(s): HSIEH, SHIH YUNG
• Application Number:
  US09/607,485
• Time in Patent Office: 1,124 Days
• Field of Search: 181/284, 181/286, 181/290, 181/292, 181/294, 181/296
• US Class Current: 181/290
• CPC Class Codes: G10K 11/162 Selection of materials
• CPC Class Codes: G10K 11/172 using resonance effects

Abstract

Shaped, microperforated sound absorbers and methods of making the same are herein provided. In one embodiment, the sound absorber is produced from a polymeric, typically plastic, film having a series of microperforations formed over all or a portion of the film surface. The film is then formed to produce the desired three-dimensional shape. The depth of the three-dimensional shape is controlled to provide the desired cavity depth which, in turn, influences the sound absorption spectrum. After forming, the three-dimensional shape is maintained without the need for additional supports or frames. Deformation of the microperforations due to the forming process does not substantially interfere with the sound absorption properties of the film. Further, film resonance over largely unsupported portions also has little effect on the sound absorption spectrum.

Claims

1. A sound absorbing body comprising:

a polymeric film comprising first and second major surfaces;

a plurality of microperforations extending between the first and second major surfaces of the polymeric film; and

a three-dimensional shape formed by the polymeric film, the three-dimensional shape comprising an interior surface and an exterior surface, wherein the interior surface defines a volume.

2. The sound absorbing body of claim 1, wherein the polymeric film has a bending stiffness of 10⁷ dyne-cm or less.

3. The sound absorbing body of claim 1, wherein the sound absorbing body comprises one or more substantially planar elements.

4. The sound absorbing body of claim 1, wherein the sound absorbing body comprises one or more non-planar elements.

5. The sound absorbing body of claim 1, further comprising a reflecting surface facing the interior surface of the three-dimensional shape, wherein the volume is further defined by the reflecting surface.

6. The sound absorbing body of claim 5, wherein the reflecting surface is substantially planar.

7. The sound absorbing body of claim 5, wherein the reflecting surface is non-planar.

8. The sound absorbing body of claim 5, wherein the sound absorbing body is proximate the reflecting surface.

9. The sound absorbing body of claim 5, wherein the sound absorbing body is attached to the reflecting surface.

10. The sound absorbing body of claim 5, wherein the sound absorbing body is semi-permanently attached to the reflecting surface.

11. The sound absorbing body of claim 1, wherein the thickness of the polymeric film varies over the three-dimensional shape.

12. The sound absorbing body of claim 1, wherein one or more of the plurality of microperforations has a diameter which varies between the first major surface and the second major surface.

13. The sound absorbing body of claim 1, wherein the film has sufficient stiffness to maintain the three-dimensional shape.

14. The sound absorbing body of claim 1, wherein a plurality of three-dimensional shapes are formed in a substantially unitary polymeric film.

15. The sound absorbing body of claim 1, wherein a plurality of substantially uniform three-dimensional shapes are formed in a substantially unitary polymeric film.

16. The sound absorbing body of claim 1, wherein a plurality of different three-dimensional shapes are formed in a substantially unitary polymeric film.

17. The sound absorbing body of claim 16, wherein the plurality of different three-dimensional shapes vary in size.

18. The sound absorbing body of claim 16, wherein the plurality of different three-dimensional shapes vary in shape.

19. The sound absorbing body of claim 16, wherein the plurality of different three-dimensional shapes vary in size and shape.

20. The sound absorbing body of claim 1, wherein at least one of the plurality of microperforations has a narrowest diameter less than a thickness of the polymeric film at its thickest portion.

21. The sound absorbing body of claim 1, wherein a majority of the plurality of microperforations are tapered between the first and second major surfaces of the polymeric film.

22. The sound absorbing body of claim 1, wherein a majority of the plurality of microperforations are tapered between the first and second major surfaces of the polymeric film, and wherein each of the tapered microperforations has a narrowest diameter less than a thickness of the polymeric film at its thickest portion.

23. The sound absorbing body of claim 1, wherein the microperforations comprise a narrowest diameter of about 20 mils or less.

24. The sound absorbing body of claim 1, wherein the plurality of microperforations are arranged in a pattern comprising a density of about 100 to about 4000 per square inch.

25. A sound absorbing body comprising:

a polymeric film comprising first and second major surfaces;

a plurality of microperforations extending between the first and second major surfaces of the polymeric film; and

a three-dimensional shape formed by the polymeric film, the three-dimensional shape comprising an interior surface and an exterior surface, wherein the interior surface defines a volume of the three-dimensional shape, and further wherein, in response to incident soundwaves at a particular frequency in the audible frequency spectrum, the sound absorbing body absorbs at least a portion of the incident soundwaves, and further wherein at least a portion of the three-dimensional shape vibrates in response to the incident soundwaves.

26. The sound absorbing body of claim 25, wherein the particular frequency is a fundamental resonant frequency of the polymeric film with the microperforations formed therein.

27. The sound absorbing body of claim 25, wherein the sound absorbing body has a sound absorption coefficient of 0.4 or greater at the fundamental resonant frequency.

28. The sound absorbing body of claim 25, wherein the three-dimensional shape comprises one or more curvilinear surfaces.

29. The sound absorbing body of claim 25, wherein the three-dimensional shape comprises a smooth, continuous surface.

30. The sound absorbing body of claim 25, wherein the three-dimensional shape comprises one or more planar surfaces.

31. The sound absorbing body of claim 25, wherein the sound absorbing body is proximate a reflecting surface which further defines the volume.

32. The sound absorbing body of claim 31, wherein the three-dimensional shape further comprises coupling portions for coupling the three-dimensional shape to the reflecting surface.

33. The sound absorbing body of claim 25, wherein the plurality of microperforations are formed over substantially all of the three-dimensional shape.

34. The sound absorbing body of claim 25, wherein the plurality of microperforations are formed over a portion of the three-dimensional shape.

35. A sound absorbing body comprising:

a polymeric film comprising first and second major surfaces;

a plurality of microperforations extending between the first, and second major surfaces of the polymeric film;

a three-dimensional shape formed by the polymeric film, the three-dimensional shape comprising an interior surface and an exterior surface, wherein the interior surface defines a volume of the three-dimensional shape; and

fibrous sound absorbing material proximate the polymeric film.

36. The sound absorbing body of claim 35, wherein the fibrous sound absorbing material is attached to the polymeric film.

37. The sound absorbing body of claim 35, wherein the fibrous sound absorbing material is located within the volume defined by the interior surface of the three-dimensional shape.

38. The sound absorbing body of claim 35, wherein the fibrous sound absorbing material is coupled to the polymeric film.

39. A method of manufacturing a sound absorbing body comprising:

providing a sheet of polymeric film comprising first and second major surfaces, the polymeric film comprising a plurality of microperforations extending between the first and second major surfaces of the polymeric film; and

deforming the sheet to form a three-dimensional shape, the three-dimensional shape comprising an interior surface and an exterior surface, wherein the interior surface defines a volume of the three-dimensional shape.

40. The method of claim 39, wherein the deforming comprises heating the sheet of polymeric film.

41. The method of claim 39, wherein the deforming comprises forcing the sheet of polymeric film against a mold surface.

42. The method of claim 39, wherein the deforming comprises heating the sheet of polymeric film and forcing the sheet of polymeric film against a mold surface.

43. The method of claim 39, wherein the deforming comprises heating the sheet of polymeric film and forcing the sheet of polymeric film against a mold surface after heating the sheet.

44. The method of claim 39, wherein the deforming comprises forcing the sheet of polymeric film against a heated mold surface.

45. The method of claim 39, wherein the deforming comprises forming a plurality of the three-dimensional shapes in the sheet of polymeric film.

46. The method of claim 39, further comprising attaching a reflecting surface to the sheet of polymeric film after the deforming, the reflecting surface facing the interior surface of the three-dimensional shape, wherein the volume defined by the interior surface of the three-dimensional shape is further defined by the reflecting surface.

47. The method of claim 46, wherein the reflecting surface is substantially planar.

48. A sound absorbing body comprising:

a polymeric film comprising first and second major surfaces;

a plurality of microperforations extending between the first and second major surfaces of the polymeric film; and

a three-dimensional shape formed by the polymeric film, the three-dimensional shape comprising an interior surface and an exterior surface, wherein the interior surface defines a volume of the three-dimensional shape, and further wherein, in response to incident soundwaves at a particular frequency in the audible frequency spectrum, the sound absorbing body absorbs at least a portion of the incident soundwaves, and further wherein at least a portion of the three-dimensional shape vibrates in response to the incident soundwaves, and still further wherein the sound absorbing body operates to cause a normal incidence sound absorption spectrum to exhibit a notch.

49. The sound absorbing body of claim 48, wherein the particular frequency is a fundamental resonant frequency of the polymeric film with the microperforations formed therein.

50. The sound absorbing body of claim 49, wherein the sound absorbing body has a sound absorption coefficient of 0.4 or greater at the fundamental resonant frequency.

51. The sound absorbing body of claim 48, wherein the three-dimensional shape comprises one or more curvilinear surfaces.

52. The sound absorbing body of claim 48, wherein the three-dimensional shape comprises a smooth, continuous surface.

53. The sound absorbing body of claim 48, wherein the three-dimensional shape comprises one or more planar surfaces.

54. The sound absorbing body of claim 48, wherein the sound absorbing body is proximate a reflecting surface which further defines the volume.

55. The sound absorbing body of claim 54, wherein the three-dimensional shape further comprises coupling portions for coupling the three-dimensional shape to the reflecting surface.

56. The sound absorbing body of claim 48, wherein the plurality of microperforations are formed over substantially all of the three-dimensional shape.

57. The sound absorbing body of claim 48, wherein the plurality of microperforations are formed over a portion of the three-dimensional shape.