Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
2000-12-27
2002-09-03
Fletcher, Marlon T. (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S290000
Reexamination Certificate
active
06443256
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an acoustical ceiling tile having an improved sound absorption value. More particularly, this invention relates to a dual layer acoustical ceiling tile having a low or no mineral wool base mat layer and a high mineral wool overlay surface layer which provides improved sound absorption values with or without perforating or fissuring the tile. The invention also relates to a dual layer acoustical tile which is manufactured using a high speed, water-felting process. A pattern can be applied before drying the tile (wet end embossing), or the pattern can be formed in the tile after the drying.
BACKGROUND OF THE INVENTION
The water-felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a commercial process for manufacturing acoustical ceiling tile. In this process, a dispersion of mineral wool, lightweight aggregate, binder and other ingredients as desired or necessary is flowed onto a moving foraminous support wire, such as that of a Fourdrinier or Oliver mat forming machine, for dewatering. The dispersion is first dewatered by gravity and then vacuum suction is applied. After vacuum dewatering, the wet mat is dried in heated convection drying ovens, and the dried mat is cut to the desired panel or tile dimensions. If desired, the panels or tiles can be top coated with paint.
Acoustical ceiling tiles can also be made by a wet pulp molding or cast process such as described in U.S. Pat. No. 1,769,519. In accordance with this process, a molding composition comprising granulated mineral wool fibers, fillers, colorants and a binder (e.g. starch gel), is prepared for molding or casting the tile. The composition is placed upon suitable trays which have been covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the mineral wool composition are then placed in an oven to dry or cure.
In U.S. Pat. No. 5,250,153, issued Oct. 5, 1993, a process is disclosed for making mineral wool panels on a foraminous support wire by forming a dilute aqueous dispersion of mineral wool fibers and/or aggregate and an anionically stabilized latex binder. The binder is deposited onto the mineral wool fibers by adding a small amount of a cationic flocculant. Substantially all of the binder latex becomes coupled to the mineral wool fibers. The wet mat can be dried quickly by passing heated air through the mat that is capable of maintaining its structure.
In my U.S. Pat. No. 5,558,710, issued Sep. 24, 1996, I disclose a gypsum/cellulosic fiber composition that can replace all or a portion of the mineral wool normally present in acoustical ceiling tiles. The gypsum/cellulosic fiber composition is combined with a lightweight aggregate material and a binder to form a composition that is used in a water-felting process to manufacture acoustical ceiling tiles.
As disclosed in Example 1 of U.S. Pat. No. 5,558,710, a water-felting process was used to make the acoustical tiles. The feed slurry during mat formation was held at 4% solids, and this 4% solids consistency was also used in making the control tile. The control tile, using 100% mineral fiber (i.e. no gypsum/wood fiber) had the following formulation:
Weight %
Mineral Fiber
37.58
Expanded Perlite
34.83
Newspaper
15.91
CTS-1 Clay
3.54
Starch
8.01
Flocculant
0.06
Surfactant
0.08
Samples of the control tile were tested for NRC (noise reduction coefficient) using the Impedance tube method. The samples were not perforated, fissured or painted. The control tiles had an average NRC value of only 0.434.
In general, acoustical tiles made using a water-felting process have a hard surface that does not have good sound absorption properties. The sound absorption is substantially improved by fissuring and/or perforating the surface that increases the NRC value. However, many purchasers prefer a smooth, unperforated acoustical ceiling tile for its aesthetic appearance.
As disclosed in U.S. Pat. No. 5,250,153, acoustical ceiling tiles having an average NRC equivalent to commercially available cast ceiling tiles can be made by using an anionically stabilized latex binder and a cationic flocculant to couple the latex binder onto the mineral fiber materials. In the acoustical tiles made by this process, the mineral fibers constitute about 50% or more of the total dry solids, preferably from about 60 to about 95 weight % of the acoustical panel. However the tiles made by this process are quite soft compared to the water-felted tiles having a starch binder. In addition, the tiles made with a latex binder have lower structural strength and are made in thicknesses of at least about ½ inch and frequently have a woven scrim applied thereto to increase strength. These acoustical tiles do have smooth surfaces and higher NRC values resulting from the higher mineral wool content.
Mineral wool acoustical tiles are porous which is necessary to provide good sound absorption. The prior art (U.S. Pat. Nos. 3,498,404, 5,013,405 and 5,047,120) also discloses that mineral fillers, such as expanded perlite, may be incorporated into the composition to improve sound absorbing properties.
It is an object of this invention to provide an acoustical tile having a dual layer of acoustical materials both of which contain mineral fibers or having a base mat with no mineral fibers.
It is another object of this invention to provide a water-felted base mat having a relatively low mineral fiber content or no mineral fibers and a surface layer having a high mineral fiber content to form an acoustical tile with improved sound absorbing properties.
It is a further object of this invention to provide a dual layer acoustical ceiling tile having a smooth, unperforated surface and also good sound absorbing properties.
It is a still further object of this invention to provide a dual layer acoustical ceiling tile having a sound absorption value (NRC) of at least about 0.50.
These and other objects will be apparent to persons skilled in the art in view of the description that follows.
SUMMARY OF THE INVENTION
It has been discovered that a dual layer acoustical ceiling tile having an improved sound absorption value (NRC) can be made in a water-felting process wherein a base mat layer has a relatively low mineral fiber content, and a surface layer having a high mineral fiber content is overlaid onto the base mat. The base mat layer is made from a low mineral fiber content or no mineral fiber material which has relatively low NRC values unless its surface is perforated and/or fissured. The mineral fiber-rich surface layer that has a thickness of about ¼ inch or less also has a relatively low NRC value at such thickness. It was discovered that these two low NRC value materials could be combined to provide a dual layer ceiling tile having a high NRC value.
DETAILED DESCRIPTION OF THE INVENTION
The acoustical ceiling tiles of this invention are based on the discovery that two acoustical materials having relatively low NRC values can be combined to form a dual layer acoustical ceiling tile having excellent sound absorption values (NRC). These ceiling tiles are made using a water-felting process to form both the base mat layer and the fiber-rich surface layer. In carrying out the process, two head boxes are used to feed the acoustical materials to the production line.
One head box feeds the base mat material, having a relatively low mineral fiber content (less than about 50% by weight of mineral fiber) or it may contain no mineral fiber, to a moving foraminous support wire, such as that of a Fourdrinier or Oliver mat forming machine for dewatering. After water is removed through the support wire by gravity, additional water can be removed by applying a vacuum to the wet base mat, but depending upon the consistency of the base mat material in the head box, the line speed and other considerations, it may not be necessary to use vacuum for dewatering purposes
Fletcher Marlon T.
Janci David F.
Lockett Kim
Lorenzen John M.
Robinson Robert H.
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