Plain surface acoustical product and coating therefor

Details Plain surface acoustical product and coating therefor Plain surface acoustical product and coating therefor

1999-03-24

2001-09-04

Cole, Elizabeth M. (Department: 1771)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S219000, C428S330000, C428S341000, C428S342000, C442S076000, C106S816000, C106S817000, C181S293000

Reexamination Certificate

active

06284351

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention is directed to an improved acoustical fiberboard and the coating therefor. Methods for obtaining high noise reduction coefficients (NRC) are well known. NRC values are secured by using ASTM test C423-90a to measure the NRC of a product. Fiberglass is known to be a good sound absorber since it has high porosity. It can be decorated with a surface layer of laminated fabrics or painted scrims requiring only a minimal openness in the surface layer for sound to pass through and be absorbed in the substrate.
To make an acoustically high NRC (= or >65) product using a wood or mineral fiberboard substrate, the board porosity must be high. Finish paint applied directly to the board also must not form a continuous film closing off the board surface. Normally this occurs thus lowering the NRC. A method generally used to increase the NRC is hole punching and surface perforations.
The desired product herein is to have a high NRC with a plain, fine textured, nonperforated surface visual. If a sanded and painted fiberboard without surface perforations and scrim is the construction, then the porosity of the paint layer must be equal or greater than the porosity of the board in order to retain the sound absorption properties of the board. The special paint that enables high application rates providing adequate coverage while remaining porous is the subject of this invention. Attaining a high porosity and NRC= or >65 is not easily accomplished with fiberboard without sacrificing other material properties such as strength and hardness.
If hole punching the fiberboard is needed to achieve the NRC= or >65, then a facing layer is necessary in order to make a plain, nonperforated surface visual. Porous nonwoven scrims are attached for this purpose. Again a special paint is necessary to cover the scrim to make it optically opaque. Opacity is needed to hide the holes yet it must be acoustically transparent. The combination of the scrim and special paint herein is also the subject of this invention.
SUMMARY OF THE INVENTION
This invention describes a plain, fine textured product consisting of a wood or mineral fiber substrate having a high NRC (= or >65) and a surfacing that does not alter the substrate sound absorption characteristics. The surfacing described herein is intended to render a product having a plain, fine textured surface without holes or surface perforations. This surface layer can be a directly applied paint or an attached painted nonwoven scrim. The critical characteristic of this surfacing is that it is acoustically transparent so that the sound can penetrate through the surface and be absorbed in the substrate.
Paints are generally designed and applied at sufficient rates to form a continuous film. Atomized paint droplets coalesce and normally flow, and wick on the substrate to spread over the surface forming a film. This same type of wicking and spreading occurs when painting porous scrims. Retaining acoustical transparency of the surface can be attained by applying small amounts of paint insufficient to form a film, but these small amounts are not optically opaque. Another method is to use a paint having minimal wicking and spreading characteristics. More paint can then be applied without closing off the surface. If hole perforations are needed to develop the desired NRC, these holes can be hidden by applying a porous nonwoven scrim to the board surface bridging the holes and then painted with an acoustically porous paint.
An invention herein describes a paint which has restricted flow properties and minimized coalescence when applied, thus retaining discrete paint droplets. This is accomplished with a critically high solids/low liquid suspension ranging from about 70-85% solids by weight which increases viscosity quickly with minimal water loss. The paint also has to have a greater affinity for itself than for the surface to which it is applied. By adding coarse limestone (ranging from 40 mesh to 150 mesh) to a more conventional fine particle paint, the total filler level can be increased to 82% solids while retaining a relatively low viscosity of about 1000-8000 cps. Other particles that can be used are glass beads, silica, perlite, etc. Using these coarse fillers in blends with very fine fillers and binders, causes the liquids and fine fillers to hold to the coarse limestone by surface tension. This prevents wicking of the droplets into the surface of the fiberboard or the scrim. The combination of the paint and scrim is another invention herein. The combination of the paint or paint and scrim on a fiberboard is another invention herein.
In all three inventions, since flow and coalescence of the paint droplets is minimal, this high solids coating remains discontinuous allowing heavier application rates while retaining an openness essential for air and sound passage.
If desired, the porosity of the paint coating could be used to reduce the sound absorption of the fiberboard.


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