Sound absorbing material, a method for production of the same and device for cutting apertures in the sound absorbing material

Abstract

Sound absorbing material for use in rooms inside buildings. The material comprises a continuous polymeric film (11) having smooth surfaces, said film having a thickness (t) of about 0.1 to 0.3 mm. The film is provided with numerous substantially parallel discontinuous microslits (12) with a degree of perforation of from 0.3-3%. The microslits are cut with laser devices to produce a highly smooth and level surface. The film is tensioned in a frame (16) with a level film surface or curved film surface.

Claims

1. A sound absorbing material suitable for use in rooms inside buildings for absorbing sound, said sound absorbing material comprising: a continuous substantially translucent polymeric film (11) arranged with a fastening device (15), said film having smooth surfaces, with a thickness (t) of about 0.1-0.3 mm and provided with numerous discontinuous laser cut microslits (12) with a degree of perforation of from 0.3-10%, said microslits (12) exhibiting a length (L) of about 10-20 mm and a width (d) of about 0.05 to 0.15 mm, microslit arranged in a substantially parallel pattern, wherein the mutual distance (b) between substantially parallel adjacent slits is about 4-8 mm and the distance (s) between the short ends of adjacent slits (12) is about 10-20 mm wherein the film (11) is attached to a curved frame and tensioned to form an uneven curved film surface.

2. The sound absorbing material of claim 1, wherein the fastening device (15) is a continuous frame (15) surrounding substantially the whole periphery of the film (11), wherein the film is tensioned within the frame.

3. The sound absorbing material of claim 1, wherein the film (11) thickness (t) is about 0.2 mm.

4. The sound absorbing material of claim 1, wherein the slit width (d) typically is about 100 m.

5. The sound absorbing material of claim 1, wherein the slit (12) length (L) is about 15 mm.

6. The sound absorbing material of claim 1, wherein the mutual distance (b) between substantially parallel slits (12) is about 6 mm.

7. The sound absorbing material of claim 1, wherein the distance (s) between adjacent slits (12) in their longitudinal direction is about 15 mm.

8. The sound absorbing material of claim 1, wherein the polymeric material is selected from the group consisting of PP, PE, PC and PS.

9. The sound absorbing material of claim 1, wherein the film is made of polypropylene comprising a halogen-free flame retardant containing calcium hydrophosphite as the main component.

10. A method of assembly of the sound absorbing material of claim 1 comprising: a) providing a sheet of the sound absorbing material; b) providing numerous mounting devices; c) tensioning the sound absorbing material within said mounting devices and affixing the sound absorbing material to the mounting devices; and d) attaching the mounting devices and sound absorbing material at a distance (D) from an object in the building.

11. The method of claim 10, wherein the distance (D) is about 50-200 mm, particularly about 100 mm.

12. The method of claim 10, wherein several sound absorbing material layers are arranged on top of each other.

13. The method of claim 10, wherein the sound absorbing material is mounted to a substantially vertical object, with its microslits arranged with their longitudinal axis in a substantially vertical direction.

Description

FIGURES

(1) The invention is now described in further details with reference to Figures, where

(2) FIG. 1a illustrates a frontal view of the film with dimensions indicated,

(3) FIG. 1b is a cross section through the film,

(4) FIG. 2 shows a top view of one embodiment of a sound absorbing film in accordance with the invention, and

(5) FIG. 3 shows another embodiment of a sound absorbing film in accordance with the invention in perspective.

(6) FIG. 1a illustrates a schematic section of a sound absorbing film 11 per se in accordance with the invention that illustrates one out of many different patterns for the microslits. Here, the microslits 12 are provided in a regular parallel pattern having a slit length L, a slit width d and a distance b to an adjacent (parallel) slit. The film thickness t is indicated in FIG. 1b and is typically within the range from about 0.1 to 0.3 mm, particularly about 200 m. The slit length L is typically about 10-20 mm, particularly about 15 mm. The distance b between adjacent parallel microslits is typically about 4-8 mm, particularly about 6 mm. The distance s from the end of one microslit to the end of another is typically about 10-20 mm, particularly about 15 mm. The slit width d is typically about 0.05 to 0.15 mm, particularly about 100 m.

(7) FIG. 1b illustrates a schematic partial cutout area in a cross-section of the film of FIG. 1 mounted to a surface 14 in a space to be sound dampened. The sound absorbing film is arranged at a distance D from said surface 14, e.g., a ceiling or a wall, with attachment means (not shown). Air space between the sound absorbing film 11 and the surface 14 is indicated at 13. The distance D may vary according to the film characteristics and the environments, but typical values may vary from 8 to 20 cm, for example 15 cm, more preferred about 10 cm.

(8) The degree of perforation calculated from the slit area to the total surface area of the film resides typically in the range of about 0.3-10%, preferably 0.3-5%, most preferably 0.3-3%. The figures above provide a proper sound dampening effect for most applications.

(9) FIG. 2 show a schematic top view of one embodiment of a sound absorbing film 1 in accordance with the invention deployed as a rectangular sheet. The film 11 is provided with numerous microslits 12 arranged across a substantial part of the surface of the film 11. The film is tensioned within one or more fastening devices 16. The fastening device may be a frame or frame element, e.g. of wood or metal, or may advantageously be a resilient material, e.g. a flexible polymer sheet or textile. When being tensioned, the flexible fastening device which at least in part is encircling the film 11 will make the film more uniform and planar. Accordingly, the use of a resilient frame or sheet attached to the film along at least a part of the periphery of the film (at least at two opposite sides of the film) is a preferred embodiment. In the embodiment shown in FIG. 2, the film is provided with two fastening/mounting devices 15 at two sides of the film. Then, the microslits are preferably arranged with their longitudinal axis towards the fastening device 15. In other words, having a square or rectangular film 11, the longitudinal axis of the fastening devices 15 extend substantially perpendicular to the longitudinal axis of the microslits. However, the fastening device 16 may also surround the sound absorbing film 11. Further details of the fastening device should be within the scope of a person skilled in the art with support in the present specification. In this embodiment, the film surface is substantially level.

(10) When mounting the sound absorbing material according to the invention on a wall, the slits are advantageously arranged with their longitudinal axis vertically. In this way, less area will be available for dust collection compared to a horizontal arrangement of the slits or a film having a large number of hole perforations.

(11) Now referring to FIG. 3, another embodiment of the sound absorbing material is shown in perspective. Here the film material 11 is attached to and tensioned within a curved frame 16 attached to a surface 14 of a structural object in the building and at a distance therefrom via support and attachment means 16. Numerous substantially mutually parallel slits are indicated at 12.

(12) Assembly

(13) A method of assembling a sound absorbing film in a room in a building can be summarized as follows a) providing a sheet of the sound absorbing film provided with microslits, b) providing one or more mounting devices, c) tensioning the film within said mounting devices and affixing the film to the mounting devices to obtain a substantially level sheet, and e) attaching the microperforated film and mounting device to an object in the building, located at a distance D (FIG. 1b) from the object.

(14) The distance D is typically about 50-200 mm, particularly about 100 mm.

(15) Further details regarding mounting of the pre-fabricated versions of the sound absorbing films tensioned in a frame has been omitted here since it is considered to be within the reach of a person skilled in the art.

EXAMPLE

(16) The effect of the present invention compared to prior art sound absorbing materials is presented in an example below. A sound absorbing test was conducted in accordance with ISO354 where sound absorbing effect of a sound absorbing material arranged at a certain distance from a hard surface, such as a wall or ceiling. The test is performed in a compartment having the required dimension and a known reverbation (which intentionally has been made longer than normal). Then, a minimum of a sound absorbing material is inserted, normally 10 m.sup.2 whereupon a loudspeaker applies (white) nose into the room. Measurements performed on how fast all frequencies are dampened at 60 dB in the room. A similar measurement must be performed prior to insertion of the sound material to be tested for calibration purposes. The sound absorbing effect of the materials is calculated from the difference in reverbation with and without the sound absorbing material at the frequencies in question. The test is repeated numerous times to provide an average effect recalculated from reduced reverbation into a percentage sound absorption effect ranging from 0 to 100%, alternatively as a factor (in the table below referred to as Absorption Coefficient) ranging from 0 to 1 where 1 represents complete absorption and 0 represents no absorption.

(17) An exception from ISO354 in this test was that the distance between the sound absorbing material and the hard surface of practical reasons was changed from 100 mm to 70 mm. The sound absorbing effect is practically the same.

(18) A prior art sound absorbing material of polymeric material was provided. Its physical figures are summarized follows: thickness: 0.1 mm; hole diameter: 0.2 mm; hole spacing: 2.0 mm; and weight of the foil: 0.14 kg/m.sup.2.

(19) The sound absorbing material in accordance with the present invention had the physical figures as set forth below. Reference is made to the FIGS. 1a and 1b as well. Film Thickness: t=180 m Slit Length: L=8 mm Center-to-Center Distance Between Slits (y-direction): b=9 mm Distance Between Adjacent Slits (x-direction): s=4 mm Center-to-Center Distance Between Slits (x-direction): B=L+s=12 mm Depth of Air Cavity Behind Panel: D=100 mm Slit width is d=90 m

(20) TABLE-US-00001 Absorption Coefficient Absorption (The invention) Coefficient Frequency 100 mmbuild height (Prior art) (Hz) from reflective surface 100 mm 125 0 0.05 250 0 0.1 500 0.2 0.45 1000 0.5 0.6 2000 0.6 0.35 4000 0.4 0.5

(21) As can be seen from the table above, the sound absorbing material in accordance with the present invention exhibit an acceptable and competitive sound absorbing effect within the frequency range which is typical for noise within buildings from normal human activity, e.g. within a shopping mall.

(22) Whereas the present invention has been described in the form of a single layered sound absorbing film, it should be noted that the invention is not limited to one single layer of the sound absorbing film and arrangement of multiple layers of the sound absorbing film is also conceivable. Moreover, the attachment means described in the embodiments above, such attachment frames, is not limited to the examples described. Any other attachment means can be used and will be within the reach of a person skilled in the art, such as double-sided tape attached to the sound absorbing film, welding of the film to another material, e.g. to a silicon list to be clamped to some other attachment means or object. Moreover, the fastening device may be provided in the form of a shade, including means to suspend the material from an object, and means to allow the polymer film to be drawn down from a rolled-up configuration to an extended configuration and fixed by fastening means or one or more weights. A configuration of this type provides stepless adjustable acoustics, e.g. in a room, with no sound dampening effect by the present invention in a fully uprolled configuration, to full sound dampening effect by the present invention in a fully extended configuration.