Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
2000-09-15
2002-09-03
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S286000, C428S703000
Reexamination Certificate
active
06443258
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of building materials, and more particularly to acoustical panels for walls, ceilings, movable partitions and other interior surfaces in commercial and residential construction. These are porous materials designed for acoustic absorbency.
BACKGROUND OF THE INVENTION
Acoustical panels for walls and ceilings provide sound absorption, aesthetics, and separate utility space in ceilings. Manufacturers strive to develop decorative acoustical ceiling panels at the lowest possible cost by continuously refining the manufacturing process in an effort to reduce energy use, materials costs and waste. While cost reduction is important, there is an inherent limit to how much the process can be simplified and still produce a panel that meets the requirements of acoustical performance, moisture resistance, and fire resistance.
Typical wallboard manufacturing begins with gypsum that is mined and crushed as gypsum rock or obtained synthetically from flu gas desulfurization plants. In the calcination process, the powdered gypsum is heated to dehydrate the gypsum to a hemihydrate. The calcined gypsum or hemihydrate is known as stucco. Fillers such as perlite and fiberglass are added to the stucco to achieve the desired properties of the finished wallboard. Other additives include starch to help adhere the core to the paper face. Retarders and accelerators may be added to adjust the reaction rate. These ingredients are combined with water and soap foam in a high speed or pin mixer. Although soap foam is added to lower the core density, the resulting structure may not have sufficient porosity to be considered acoustic. The resulting mixture is placed between two sheets of paper and sized for thickness by a roller. After the core sets up, the board is cut to length then transferred to an oven to dry.
Current methods of producing acoustical ceiling panels utilize various combinations of fibers, fillers, binders, water and surfactants mixed into a slurry which is processed into panels. This process is very similar to the methods used in papermaking. Examples of fibers used may include mineral fiber, fiberglass, and cellulosic material. Mineral wool is a lightweight, vitreous, silica-based material spun into a fibrous structure similar to fiberglass and may also be used. Mineral wool enhances acoustical performance, fire resistance, and sag resistance of an acoustic panel.
Fillers may include expanded perlite and clay. Expanded perlite reduces material density and clay enhances fire resistance of the acoustical panel. Examples of binders used in acoustical panels may include starch, latex and/or reconstituted paper products, which link together and create a binding system that locks all of the ingredients into a structural matrix.
The above ingredients, when combined and processed appropriately, produce a porous, sound absorbent panel suitable for use as acoustic ceiling panels and other types of construction panels. Today, such panels are manufactured using a high volume process that resembles paper production.
Traditional fabrication methods of forming panels incorporating a mineral wool fiber, perlite filler and cellulosic binders, rely upon aggregation and flocculation of the cellulosic ingredients. The resulting aqueous cellular foam is dried to provide a stable structure within which fiber, binders and fillers flocculate and bond to create a matrix. While an aqueous cellular foam mixture may include a surfactant to facilitate the entrainment of air into the mixture the traditional methods of fabrication rely upon flocculation. The structure of a typical ceiling panel material is shown in the 30×photomicrograph of FIG.
1
. The perlite particles are discernable as round nodules embedded in an interconnecting matrix of mineral wool and reconstituted newsprint fibers.
Current processes for manufacturing ceiling panels are complex, include many steps, and use large amounts of water and energy. During the process, water is progressively removed from the product through a combination of draining, pressing, and high-temperature oven heating. Some drained water may be recycled, but a majority is treated and released into the environment.
Different production processes and slurry recipes yield panels with differing acoustical and structural characteristics. There is a tradeoff between the acoustical performance and the durability. A highly porous, low-density material may exhibit the best acoustical performance. Unfortunately, a low-density material tends to be fragile and difficult to handle and exhibits low durability, low scrubability, and low tensile strength. For the purpose of this disclosure, the term durability refers to a panel's compressive yield strength which is a measure of how easily panel material deforms under compression. Resistance to finger indentation is an example of good compressive yield strength. Scrubability is the resistance to abrasion by repeated back and forth motion of a wet scrub brush. Tensile strength refers to the ability to lift or support a panel along one edge without the panel breaking.
Various processes and recipes are used to balance the tradeoffs inherent in the manufacture of acoustical ceiling panels. For example, one common structure for a ceiling panel is a laminate, using different layers of material, as shown in FIG.
2
. One layer
201
comprises a soft, acoustically absorbent material, while the other layer
202
, which faces into the room, is a more durable, sometimes structural material that is relatively transparent to sound. The acoustical performance of the panel is largely a function of the inner layer
201
, while the outer layer
202
enhances the durability, scrubability, and aesthetics. The outer layer
202
in
FIG. 2
may be a third-party supplied material. Normally, an adhesive attaches the overlay
202
to the inner layer
201
. Other steps involved in the manufacture of laminated panels include painting, cutting to size, and packaging.
Laminated panels provide a good balance between performance and durability. Such panels have the advantage of being susceptible to continuous manufacturing processing in certain steps, but require additional process steps and additional materials, e.g. the outer layer material and adhesive, which are not required when producing a homogeneous panel. Furthermore, the outer layer material usually is a high-cost constituent and the lamination process requires additional machinery, materials, and human resources. While the production of the acoustical material
201
component can typically be done in continuous fashion, the lamination step is not a continuous process. As a result, laminated panels are relatively expensive to manufacture.
Casting or molding processes are also used to create a panel structure as in FIG.
1
. Casting produces a homogeneous material that is very durable and has good acoustical properties. Cast materials generally have a much higher density, and do not require the additional layer present in laminated construction. Casting is essentially a batch process in which the material is poured into a mold. The bottom of the mold is typically lined with a carrier or release agent to prevent sticking. The materials are dried in the mold, the mold is removed, and the panel undergoes a finishing process. Molded panels usually have good mechanical strength properties and exhibit good durability but the acoustical performance is generally not as good as a laminated panel. Drawbacks to the molding process include: the requirement of moving molds continuously throughout the process, smaller panels resulting from mold size constraints; the requirement of the added step of panel removal from the molds; and higher material cost per panel because of increased panel density.
Another common method of producing a panel having the structure shown in
FIG. 1
is to extrude the slurry onto a wire belt, and allow the water to drain from the slurry. Other process steps include forming, drying, and surfacing or sanding resulting panels to c
Bischel Marsha Stalker
Moser Andrea M.
Putt Dean L.
Wiker Anthony L.
AWI Licensing Company
Dang Khanh
Womble Carlyle Sandridge & Rice PLLC
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