Mineral wool-free acoustical tile composition

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FIELD OF THE INVENTION

This invention relates to acoustical tile compositions useful in manufacturing acoustical tiles and panels for ceiling applications. More particularly, this invention relates to acoustical tile compositions which do not contain mineral wool. The invention also relates to a novel combination of expanded perlite, reinforcing fibers and an inorganic filler in an acoustical tile composition.

BACKGROUND OF THE INVENTION

A commercially successful acoustical tile is marketed under the trademark ACOUSTONE and is made generally using the composition and procedures disclosed in U.S. Pat. No. 1,769,519. According to the teachings of this patent, a molding composition comprising granulated mineral wool fibers, fillers, colorants and a binder, in particular a starch gel, is prepared for molding or casting the body of the tile. This mixture or 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 pulp or composition are then placed in an oven for twelve (12) hours or more to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size.

The mineral wool acoustical tiles of the prior art, as disclosed in U.S. Pat. Nos. 3,246,063 and 3,307,651, generally used a starch gel as a binder for the mineral wool fibers. The gel may comprise a thick boiling starch composition combined with calcined gypsum (calcium sulfate hemihydrate) which are added to water and cooked at 180.degree. F.-195.degree. F. for several minutes to form the starch gel. Thereafter, the granulated mineral wool is mixed into the starch gel to form the aqueous composition which is used to fill the trays.

Mineral wool acoustical tiles are very 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 and provide light weight.

It is an object of this invention to provide an acoustical tile composition which contains no mineral wool.

It is another object of this invention to provide a mineral wool-free acoustical tile composition having acoustical properties comparable to the commercially available cast mineral wool tiles.

It is a further object of this invention to provide an acoustical tile composition comprising a combination of expanded perlite, a starch gel binder, reinforcing fibers, and an inorganic filler.

These and other objects will be apparent to persons skilled in the art in view of the description which follows.

SUMMARY OF THE INVENTION

It has been discovered that an expanded perlite can be combined with a standard starch gel binder, an inorganic mineral filler for texturability if desired, and a fiber reinforcing material (non-mineral wool), to provide a dough-like composition (hereinafter referred to as a "pulp") which can be used to cast an acoustical tile using equipment and procedures currently used to produce cast mineral wool tiles. The mineral wool-free pulp can be dried using less energy than employed in drying a mineral wool pulp. The dried product can be formed into tiles having comparable acoustical properties with commercially available acoustical tiles. Acoustical tiles made from the mineral wool-free pulp of this invention have acceptable physical properties for use in suspended ceiling systems.

DETAILED DESCRIPTION OF THE INVENTION

The mineral wool-free acoustical tile compositions of this invention are based on using an expanded perlite as a substitute for granulated mineral wool to provide porosity and good sound absorption properties preferably combined with an inorganic filler to provide texturability. These two ingredients when mixed with a starch gel binder, a fiber reinforcing material and water, provide a mineral wool-free pulp which can be cast or molded in trays using equipment and procedures currently used to produce cast mineral wool tiles.

It has been found that a medium grade expanded perlite provides sufficient porosity and acceptable texturability. The expanded perlite material is commercially available from Silbrico Corporation under the designation Perlite D-1. This medium grade expanded perlite contains perlite particles that are similar in size to granulated mineral wool. A finer grade of perlite (more than 60% by weight passed through a 100 mesh screen) was evaluated, but the pulps made with the finer perlite had a lower texture rating and the dried tiles showed more surface cracking. Other properties such as warpage, hardness and modulus of elasticity were improved by the finer grind. The finer grade perlite particles have greater surface area and require more starch gel binder to obtain texture ratings comparable to the medium grade expanded perlite. In addition, the finer grade perlite increased the criticality of the fiber reinforcement relative to providing an acceptable pulp texture. The range of expanded perlite in the pulp, on a dry solids basis, may be from about 10% by weight to about 85% by weight, with the preferred range being from about 25 to about 50 % by weight.

The inorganic mineral filler provides texturability. Tabular acicular gypsum is the preferred filler. Other materials, such as kaolin clay (in natural hydrous form, or a calcined anhydrous form), Gardner ball clay, stucco (calcium sulfate hemihydrate), gypsum (calcium sulfate dihydrate), and fibrous calcium sulfate hemihydrate (FRANKLIN FIBER filler), have been evaluated as fillers. The evaluations indicated that the presence of a filler in the formulation causes a decrease in the final physical properties of the acoustical tile. The filler appeared to contribute to the formation of undesirable surface cracks, particularly in the absence of a fiber reinforcement. The filler also adversely affected acoustical properties. However, the filler has a marked effect upon the texturability of the resultant pulp and is critical in providing a pulp which can be processed on equipment which is currently used to make acoustical tile out of mineral wool pulp. The tabular acicular gypsum filler provided a pulp which had properties most similar to a standard mineral wool pulp. Other fillers which might be used include limestone (calcium carbonate), Feldspar, Nepheline, talc, mica, Wollastonite, synthetic silicates, hydrous alumina, and silica.

The tabular acicular gypsum is made in accordance with the process disclosed in U.S. Pat. Nos. 4,801,355 and 5,106,600. The disclosure in said U.S. Patents is incorporated herein by reference. It is generally preferred that the inorganic mineral filler be present in the pulp, on a dry solids basis, in amounts ranging from about 10% by weight to about 60% by weight, with a range of about 35% to about 50% by weight being particularly preferred.

When the inorganic mineral filler contains water of hydration, e.g. tabular acicular gypsum, the filler may be calcined during the drying of the tile which may be carried out at 350.degree. F. If the gypsum is calcined to a hemihydrate or soluble anhydrite, the tile product may not be stable under high humidity conditions and may sag excessively.

The first step in the preparation of an acoustical tile is the preparation of the starch gel. In general, only the starch is dispersed in water, and the slurry is heated until the starch is fully cooked and the slurry thickens to a viscous gel. In the event a cellulosic fiber is used as a reinforcing agent, it may be incorporated into the starch slurry prior to cooking. The cooking temperature of the starch slurry should be closely monitored to assure full swelling of the starch granules. A representative cooking temperature for corn starch is about 180.degree. F. (82.degree. C.)to about 195.degree. F.(90.degree. C.). The starch gel binder in the pulp may range from about 5% to about 25% on a dry solids basis.

Several types of fiber reinforcing agents have been evaluated in the mineral wool-free acoustical tile compositions of this invention. In general, the fiber reinforcing agents may be selected from cellulosic fibers, polymeric fibers and vitreous (glassy) fibers. Examples of cellulosic fibers are softwood and hardwood fibers and paper fibers. Polyester fibers have been used to prepare a pulp, but the dried product was difficult to cut and to kerf. In addition, E-glass fibers have also been used, but the preferred E-glass fibers require special handling procedures. The fiber reinforcing agent is present in only minor amounts, generally ranging from about 2% to about 10% by weight on a dry solids basis. Other examples of polymeric fibers include rayons, polyolefins, polyamides, nylons, acetates and aramid fibers.

The initial development efforts to produce a starch-based, cast acoustical ceiling product without using mineral wool were directed to developing a product requiring reduced drying energy. The following formulation was developed to provide optimum texturability:

______________________________________ Ingredient Amount (grams) % Solids ______________________________________ Expanded Perlite (medium grade) 500 42.4 Tabular Acicular Gypsum Filler 500 42.4 Starch Gel Binder 130 11 Cellulosic Fiber 50 4.2 Water 2,500 0 ______________________________________

The procedure used in preparing the starch-based acoustical tile was very similar to the manufacturing methods used to prepare a standard cast mineral wool tile. The reason for the similarity was the intention to use existing equipment to make the mineral wool-free acoustical tile. It was the basic cast process wherein a starch gel binder was mixed with an expanded perlite and an inorganic filler (preferably tabular acicular gypsum) to produce a dough-like pulp.

The starch gel binder was prepared as set forth above. When cellulosic fibers were used for reinforcement, they were incorporated into the starch gel prior to cooking. Mixing the cooked starch gel with the expanded perlite and the inorganic filler is the final step in preparing the pulp. In the laboratory, the mixing step was carried out in a Hobart (Model A-200) mixer. A mix time of 1 minute at speed No. 1 was determined to be suitable to attain complete mixing of all of the ingredients without breaking down the starch gel and the fragile perlite particles.

Physical testing of laboratory boards was conducted according to established procedures. In most instances, three 10 inch.times.3 inch samples were cut from each 12 inch.times.12 inch or 12 inch.times.24 inch board and tested in a flexural mode using an Instron Model 1130 test instrument. Data normally measured included density (lb./ft..sup.3), the modulus of rupture (MOR) in psi, the modulus of elasticity (in psi) and the hardness (in lbs. using the 2 inch Janka ball hardness method).

EXAMPLE 1

A series of inorganic fillers were evaluated to determine which filler provided the best texturability. The following fillers were tested: Gardner Ball Clay; Kaolin Clay; Stucco (calcium sulfate hemihydrate); Tabular Acicular Gypsum; and Fibrous Calcium Sulfate Hemihydrate (Franklin Fiber Brand). The formulation used to carry out the evaluation was as follows:

______________________________________ Total Ingredient Amount (grams) % Solids ______________________________________ Expanded Perlite (Slibrico D-1) 600 78.4 Starch Gel 100 15.7 Paper Fiber 37.5 5.9 Filler Variable 0-300 -- Water 2,000 0 ______________________________________

TABLE 1 ______________________________________ Filler Type Filler % Density (lb./ft..sup.3 MOR(psi) ______________________________________ Ball Clay 13.6 14.1 174 Ball Clay 23.9 14.3 148 Ball Clay 32.0 16.1 215 Kaolin Clay 13.6 13.7 151 Kaolin Clay 23.9 14.8 166 Kaolin Clay 38.6 19.1 170 Stucco 13.6 13.7 117 Stucco 23.9 16.0 110 Stucco 32.0 17.1 115 Acicular Gypsum 13.6 14.1 150 Acicular Gypsum 23.9 15.2 146 Acicular Gypsum 32.0 16.6 133 Franklin Fiber 5.2 12.7 130 Franklin Fiber 9.9 13.7 115 ______________________________________

The tabular acicular gypsum provided pulp properties most similar to those of granulated mineral wool and the best texturability.

EXAMPLE 2

A variety of cellulosic fiber types were evaluated in a mineral wool-free pulp. The following cellulosic fibers were used in the pulp formulations which did not contain an inorganic filler:

1) a medium wood fiber type

2) a coarse wood fiber type

3) pulped fly leaf--a highly refined bleached fiber obtained by hydropulping waste office paper

4) bleached softwood kraft--a long fibered, bleached, softwood kraft fiber

The following formulation was used:

______________________________________ Ingredient Total Amount (grams) % Solids ______________________________________ Expanded Perlite (D-1) 500 83.3 Starch Gel 100 16.7 Cellulosic Fiber Variable 0-66.67 -- Filler 0 -- Water 2,000 0 ______________________________________

The acoustical tiles made from this pulp formulation using the various cellulosic fibers were evaluated and yielded the following results:

______________________________________ % Density MOR MOE Fiber Type Fiber (lb./ft..sup.3) (psi) (psi) ______________________________________ Medium Wood Fiber 2.0 11.4 82.5 14,400 Medium Wood Fiber 4.0 11.8 107 13,800 Medium Wood Fiber 6.0 12.1 120 15,900 Medium Wood Fiber 7.6 12.2 133 16,800 Medium Wood Fiber 10 12.4 152 17,500 Coarse Wood