Patent Application
20080057318
The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, and any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references.
In the drawings, the thickness of the lines, layers, and regions may be exaggerated for clarity. It is to be noted that like numbers found throughout the figures denote like elements. The terms “top”, “bottom”, “side”, “upper”, “lower” and the like are used herein for the purpose of explanation only. It will be understood that when an element is referred to as being “on,” another element, it can be directly on or against the other element or intervening elements may be present. The terms “formulation” and “composition” may be used interchangeably herein. In addition, the terms “polymer” and “polymeric resin” may be used interchangeably. Further, the terms “filler” and “filler material” may be interchangeably used herein.
The present invention relates to a thin, lightweight drywall board that may or may not have a textured surface and a method of making the inventive lightweight drywall board. The drywall board is formed of alternating layers of a matrix formulation and a lightweight fibrous mat positioned on a gel coat. The gel coat may be utilized to pick up a desired design from a mold or other textured surface and becomes a top layer (e.g., viewable surface area) of the thin drywall board. The matrix composition forms a lightweight gypsum board that includes gypsum and a polymeric resin that is at least partially dispersible in water. The combination of the components in the matrix composition have a synergistic effect which creates a thin drywall board that is water resistant, fire resistant, and has improved mechanical properties. Additives such as a density reducing filler material and coupling agents may be added to the matrix composition.
The matrix composition includes one or more polymeric resins that are at least partially dispersible in water, and most preferably, fully dispersible in water. The polymeric resin provides strength, flexibility, toughness, durability, and water resistance to the final product. The polymer may be in the form of a liquid, an emulsion, and/or a powder. The polymeric resin is not particularly limited, so long as it is at least partially water dispersible. The polymer may or may not be self-crosslinking. An additional polymer such as melamine formaldehyde or urea formaldehyde, which acts as crosslinking agent, may be added to assist in the crosslinking reaction, regardless of whether or not the polymer is self-crosslinking. However, it is to be appreciated that if the polymer is not self-crosslinking, a crosslinking agent such as melamine formaldehyde is desirably added to catalyze and assist in the crosslinking reaction.
The crosslinking reaction may occur slowly over time at atmospheric conditions (typically over a period of approximately two weeks). As the crosslinking between the polymers occur and a polymeric network is formed around the gypsum, the molecular weight of the polymer increases. As the molecular weight of the polymer increases, the composition becomes more rigid. The crosslinking reaction may be accelerated upon heating the composition to a moderate temperature, such as to a temperature between about 140° F. to about 160° F. (between about 60° C. to about 71° C.), for a predetermined period of time. It is preferred, however, that the crosslinking reaction be permitted to occur over time at room temperature.
Suitable polymeric resins for use in the composition may include, but are not limited to, acrylic based polymers, polyester emulsions, vinylacetate emulsions, epoxy emulsions, and phenolic based polymers. Specific examples of polymers that may be used in the glass fiber based composition include polyvinyl alcohol (PVA), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyethylene, polypropylene, polycarbonates, polystyrene, styreneacrylonitrile, acrylonitrile butadiene styrene, acrylic/styrene/acrylonitrile block terpolymer (ASA), polysulfone, polyurethane, polyphenylenesulfide, acetal resins, polyamides, polyaramides, polyimides, polyesters, polyester elastomers, acrylic acid esters, copolymers of ethylene and propylene, copolymers of styrene and butadiene, copolymers of vinylacetate and ethylene, and combinations thereof. In addition, the polymeric resin may be post industrial or consumer grade (regrind).
Preferred polymers come from the family of acrylic latexes. Acrylic monomers used to make acrylic latexes include methyl acrylate, ethyl acrylate, butyl acrylate, and acrylic acid. Combinations of these monomers may be emulsion polymerized to make acrylic resins. These polymers typically contain hydroxyethyl acrylate monomers to impart hydroxyl groups along the polymer chain. These hydroxyl containing polymers are called thermoset acrylics. The acrylic (R—OH) permits crosslinking with other polymers such as melamine formaldehyde or urea formaldehyde. In a preferred embodiment, the crosslinking occurs through both the hydroxyl and ether groups in melamine formaldehyde, and are catalyzed by an acid. Acids and acid producing agents such asp-toluenesulfonic acid and ammonium chloride, which forms hydrochloric acid, are suitable catalysts for the crosslinking reaction. Combinations of melamine formaldehyde resin and acrylic resin produce good quality coatings and give good water resistance and chemical resistance to the drywall board. The use of these polymers allows the drywall board formed by the present invention to be manufactured without styrene and the requisite environmental controls. The polymeric resin(s) may be present in the matrix composition in an amount from about 5.0% to about 35% by weight of the active solids in the composition, preferably from about 15% to about 25% by weight of the active solids.
A second component of the inventive matrix composition is gypsum. Gypsum, also known as calcium sulfate dihydrate (CaSO4.2H2O), is a natural mineral derived from the earth. When calcined, three quarters of the water of crystallization is driven off to produce calcium sulfate hemihydrate (CaSO4.½H2O). If the calcination is carried out under pressure, an α-form of gypsum is produced. α-gypsum has regular, needle (acicular), or rod shaped particles. On the other hand, if the calcination is conducted at atmospheric pressure, a β-form of gypsum is produced with porous, irregularly-shaped particles. Although the gypsum used in the inventive composition may be α-gypsum, β-gypsum, or a combination thereof, β-gypsum is more preferred due to its lower cost and increased ability to absorb water as compared to α-gypsum. One advantage of gypsum-based materials in general is that they can be shaped, molded, and processed within a short period of time due to gypsum's naturally occurring rapid setting and hardening characteristics. In addition, the gypsum provides a fire resistance property to the drywall board. In the inventive matrix composition, the gypsum absorbs water and goes from a partially hydrated state (naturally occurring state) to a fully hydrated state and hardens. Gypsum may be present in the matrix formulation in an amount from about 35% to about 65% by weight of the active solids in the composition, preferably from about 40% to about 60% by weight of the active solids.
Additional components may be added to the matrix composition to modify properties of the drywall board. For example, low density fillers may be added to reduce the cost, the overall density of the drywall board, and may also be used as an extender. If a denser drywall board is desired, a more dense filler, such as calcium carbonate may be used. Non-limiting examples of suitable fillers that may be used in the matrix formulation include perlite (expanded perlite), calcium carbonate, sand, talc, vermiculite, aluminum trihydrate, recycled polymer materials, microspheres, microbubbles, wood flour, natural fibers, clays, calcium silicate, graphite, kaolin, magnesium oxide, molybdenum disulfide, slate powder, zinc salts, zeolites, calcium sulfate, barium salts, diatomaceous earth, mica, wollastonite, expanded shale, expanded clay, expanded slate, pumice, round scrap glass fibers, flaked glass, nano-particles (such as nano-clays, nano-talcs, and nano-TiO2), and/or finely-divided materials that react with calcium hydroxide and alkalis to form compounds possessing cementitious properties such as fly ash, coal slag, and silica. The term “natural fiber” as used in conjunction with the present invention refers to plant fibers extracted from any part of a plant, including, but not limited to, the stem, seeds, leaves, roots, or phloem. Examples of natural fibers suitable for use as the reinforcing fiber material include cotton, jute, bamboo, ramie, bagasse, hemp, coir, linen, kenaf, sisal, flax, henequen, and combinations thereof. Low density fillers are preferred for use in the matrix formulation to reduce the weight of the drywall board. Perlite is a preferred density reducing filler material due to its low cost. In at least one exemplary embodiment, the perlite utilized in the matrix composition has a density from 0.18 g/cc to 0.30 g/cc. Perlite, or another low density filler or fillers, may be present in the matrix formulation in an amount from about 0% to about 10.0% by weight of the active solids in the composition, preferably from about 4.0% to about 8.0% by weight of the active solids in the composition.
The presence of at least one coupling agent in the matrix formulation may also provide added desirable attributes. For example, the presence of a coupling agent helps to bond the organic (polymeric resin) and inorganic (perlite) components of the matrix formulation. In particular, the addition of a coupling agent to the composition increases the bond strength between the perlite and the polymer. Silane coupling-agents are preferred due to their ability to distribute quickly into water. Examples of silane coupling agents that may be used in the matrix composition may be characterized by the functional groups amino, epoxy, vinyl, methacryloxy, ureido, and isocyanato. In preferred embodiments, the silane coupling agents include silanes containing one or more nitrogen atoms that have one or more functional groups such as amine (primary, secondary, tertiary, and quaternary), amino, imino, amido, imido, ureido, or isocyanato. Suitable silane coupling agents include, but are not limited to, aminosilanes, silane esters, vinyl silanes, methacryloxy silanes, epoxy silanes, sulfur silanes, ureido silanes, and isocyanato silanes. When silane coupling agents are used, a small amount of an organic acid (such as acetic acid, formic acid, succinic acid, and/or citric acid) may be added to regulate the pH of the composition, preferably to a pH of about 3 to about 6.5. Acetic acid is the most preferred organic acid for use in the inventive matrix composition.
Specific non-limiting examples of silane coupling agents for use in the inventive composition include γ-aminopropyltriethoxysilane (A-1100), n-trimethoxy-silyl-propyl-ethylene-diamine (A-1120), and γ-glycidoxypropyltrimethoxysilane (A-187). Other non-limiting examples of suitable silane coupling agents are set forth in Table 1. All of the coupling agents identified above and in Table 1 are available commercially from GE Silicones.
Preferably, the silane coupling agent is an aminosilane or a diaminosilane. The coupling agent may be present in the composition in an amount from about 0% to about 5.0% by weight of the active solids in the composition, preferably from about 0.01% to about 2.0% by weight of the active solids.
An accelerator may be added to the matrix composition to increase the rate at which the gypsum hardens or sets. A preferred accelerator is aluminum sulfate. However, any suitable accelerator identifiable by one skilled in the art may be used, such as, for example, potassium sulfate, terra alba, sodium hexafluorosilicate, sodium chloride, sodium fluoride, sodium sulfate, magnesium sulfate, and magnesium chloride. The accelerator may be present in the matrix formulation in an amount up to about 1.0% by weight of the active solids in the composition, preferably up to about 0.5% by weight of the active solids in the composition. It is to be appreciated that the amount or quantity of accelerator added to the composition may dramatically affect how quickly the gypsum hardens. For example, a large amount of accelerator added to the matrix composition will cause the gypsum to set more quickly than if a smaller amount of accelerator was added to the composition. In other words, a larger amount of accelerator will more quickly increase the speed at which the gypsum hardens compared to a smaller amount of added accelerator.
In addition, a hardener or hardening agent such as ammonium sulfate or ammonium chloride may be added to the composition to increase both the rate of crosslinking and the crosslink density. The hardener may be present in the matrix composition in an amount up to about 1.0% by weight of the active solids in the composition. Additional additives such as dispersants, antifoaming agents, viscosity modifiers, and/or other processing agents may be added to the matrix composition.
To create the matrix composition that may be utilized to form the lightweight drywall board, the dry components of the composition, such as, for example, melamine formaldehyde, gypsum, and filler (e.g., perlite) may be dry blended in a container to form a dry mixture. Wet components of the composition, such as water, the emulsion polymer, and coupling agent(s) are stirred in a second container until they are blended. The dry mixture may be slowly added to the wet components in the second container with stirring until all the dry mixture is added and the resulting composition is well blended. The amount of water in the matrix composition may vary dramatically based the desired mechanical properties of the drywall board, but water is typically present in the matrix composition in an amount of approximately ⅓ of the amount of gypsum present. It is to be appreciated, however, that the amounts of one or more of the components of the matrix composition may vary outside the ranges recited above and the amounts of the components of the matrix composition are ultimately dependent upon the intended use of the drywall board, such as, for example, if the drywall board is intended for use as an internal drywall board, an external sheathing, a large, continuous sheet of drywall board (e.g., 8 feet high by 40 feet in length), or a lumber board. Not wishing to be bound by theory, it is believed that the mechanical properties may be optimized for these various uses by the chemistry of the matrix composition.
The composition of the gel coat may be formed of at least one water soluble polymer, gypsum, one or more crosslinking agents (each of which is described in detail above with respect to the matrix composition), and water. Additionally, a coupling agent such as is described above may be added to the gel coat composition to assist in releasing the gel coat from a mold or textured surface. Further, the gel coat composition may optionally include an accelerator and/or a hardening agent. The gel coat composition preferably contains melamine formaldehyde as a crosslinking agent to assist in crosslinking the polymer(s) in the gel coat composition. The water soluble polymer, gypsum, crosslinking agent, and coupling agent(s) in the gel coat composition may or may not be the same compound as is utilized in the matrix composition.
The water soluble polymer may be present in the gel coat composition in an amount from about 10% to about 30% by weight of the active solids in the gel coat composition, preferably in an amount from about 15% to about 25% by weight of the active solids. The gypsum may be present in the gel coat composition in an amount from about 40% to about 70% by weight of the active solids in the gel coat composition, preferably in an amount from about 50% to about 60% by weight of the active solids. The crosslinking agent may be present in the gel coat composition in an amount from 0% to about 15% by weight of the active solids in the gel coat composition, preferably in an amount from about 4.5% to about 6.5% by weight of the active solids. An accelerator may be present in the gel coat composition in an amount from 0% to about 0.1% by weight of the active solids in the gel coat composition, preferably in an amount from about 0.01 to 0.1% by weight of the active solids. In addition, a hardening agent may be present in the gel coat composition in an amount from 0% to about 0.1% by weight of the active solids in the gel coat composition, preferably in an amount from about 0.01 to 0.1% by weight of the active solids. The coupling agent may be present in an amount up to about 1.0% by weight of the active solids of the gel coat composition. The gel coat composition may be mixed in a manner consistent with that of the matrix composition in which the dry components (e.g., melamine formaldehyde and gypsum) are separately mixed and are added to a mixture of the wet components (e.g., water and coupling agent(s)) in a separate container until the wet and dry components of the gel coat composition are well blended.
In one exemplary embodiment of the invention, a lightweight, multilayered drywall board is made by an open mold, hand lay-up process. A lightweight drywall board 10 that includes a dry gel coat and alternating layers of the matrix composition described above and glass mat layers is illustrated in
Once the gypsum in the gel coat composition of the gel coat 12 has hardened, a layer or layers formed of the matrix composition are alternately layered with a glass fiber layer or layers 16 on the gel coat 12, with the matrix composition being applied on the gel coat 12. The matrix formulation forms a polymer/gypsum layer 14 in the drywall board 10. It is to be noted that it is not necessary that the crosslinking of the polymer(s) in the gel coat composition be complete when the matrix composition is applied thereto. In addition, it is desirable that the matrix formulation be in a liquid or semi-liquid state so that the matrix formulation can at least partially saturate the wet glass fiber layer 16. Once the matrix formulation (i.e., the polymer/gypsum layer(s)) has reached a sufficient green strength, the drywall board is removed from the mold or other releasable surface. It is not required that the crosslinking reaction between the polymers be complete before the drywall board is removed from the mold or releasable surface. In fact, the crosslinking reaction between the polymers in the matrix composition typically occurs for a period of time after the drywall board has been removed from the mold or releasable surface.
In a preferred embodiment, three layers of the glass fiber layer 16 are utilized to form the textured, thin drywall board. One of the glass fiber layers 16 is positioned on an external surface of the thin, drywall board. The glass fiber layer 16 preferably contains wet glass fibers and is desirably in the form of a wet formed mat that includes wet used chopped strand glass fibers (WUCS). Preferred mats for use as the wet glass layer 16 include WUCS-based shingle mats available from Owens Corning (Toledo, Ohio, USA) with weights between about 0.5 lb/100 ft2 and about 5.0 lb/100 ft2, preferably between about 1.5 lb/100 ft2 and about 2.5 lb/100 ft2, more preferably less than about 2 lb/100 ft2, and most preferably between about 1.75 lb/100 ft2 and about 1.95 lb/100 ft2. According to the present invention, it is not necessary to utilize “A” grade fiberglass mats. “B” grade mats, or mats with a non-structural defect of some kind (e.g., a visual defect) which would cause the mat to be otherwise be disposed of, may be utilized in forming the thin drywall board, without any reduction in strength or other mechanical/physical properties. Utilizing “B” grade mats in the drywall boards of the present invention helps to reduce the overall manufacturing costs and reduces the amount of waste generated and introduced into the environment. Although the glass fiber layer 16 is described herein with reference to a wet formed glass mat, a preferred embodiment, the glass fiber layer 16 may be formed of mats composed of other types of fibers, such as, but not limited to, synthetic fibers such as polypropylene or polyethylene, natural fibers, a continuous strand mat, or a chopped strand glass mat that is not formed of WUCS fibers. The physical characteristics of the drywall board 10 are at least partially dependent upon the type of mat chosen to form layer 16, and it is to be appreciated that not all mats will provide the same physical characteristics of the glass fiber mats.
The drywall board 10 illustrated in
Unlike conventional drywall, the thin drywall board 10 of the present invention may be attached to the studs of a house, office building, or other desired surface by an adhesive. By attaching the thin drywall board 10 to a designated surface by an adhesive, both time and cost can be saved. It is possible to affix the inventive thin drywall board 10 to a surface with conventional mechanical fasteners such as nails, screws, and/or staples. The strength of the fiberglass mat forming the wet glass layer 16 provides sufficient strength to hold the mechanical fastener and securely affix the inventive drywall board to the designated surface. However, this is not a preferred method of attachment due to the fact that the nail holes or screw holes would have to be filled in and smoothed over to provide a finished, paintable surface, unlike when an adhesive is used to attach the thin drywall board 10 to a surface. Further, in an embodiment where the drywall board 10 is formed in a large size (e.g., 8 feet by 40 feet), the large size of the thin drywall board 10 would permit, for example, an entire wall of a house to be drywalled at one time. By not having to piece together shorter, conventional drywall boards, installation of the large sheets of inventive drywall board is easier and faster. In addition, a wall containing a large, thin sheet of inventive drywall 10 would not contain any seams. The seams connecting the pieces of drywall would be present at the corners of the room, and not positioned intermittently along the wall as with conventional drywall boards.
Other embodiments of the present invention include composite boards 25 such as is illustrated in
In another alternate embodiment, a composite board may be formed utilizing more than three layers of the wet glass fiber layer 16. For example, a composite board may be formed of multiple stratum (layers) formed of the polymer/gypsum layer 14 alternating with the wet glass fiber layer 16. As shown in the example depicted in
The thin lightweight drywall board 10 may be used as replacements for conventional gypsum boards such as the conventional drywall board 20 depicted in
Unlike conventional drywall boards 20, the thin drywall board 10 has the advantages of being lightweight and having increased strength, increased impact resistance, increased water resistance, and it may be adhered to a surface by an adhesive. Additionally, the thin drywall board 10 can achieve these advantageous properties at lower weights than conventional drywall. The thin drywall board 10 may be produced either in-line (e.g., in a continuous manner), or off-line. Preferably, the manufacturing of the thin drywall board 10 is conducted in-line to increase manufacturing efficiency.
One advantage of the gel coat composition and the matrix composition of the present invention is they form a thin drywall board that is Class A fire resistant. For example, the gypsum provides fire resistance to the inventive drywall board. A Class A fire rating means that a thin drywall board formed from the inventive gel coat and matrix compositions will not support the spread or propagation of flames.
In addition, the matrix formulation of the present invention imparts improved physical properties, such as improved strength, stiffness, and increased impact resistance to the finished lightweight drywall board.
It is also advantageous that the polymeric resin provides strength, flexibility, toughness, durability, and water resistance to the inventive drywall board. In particular, combinations of melamine formaldehyde resin and acrylic resin produce good quality coatings and give good weather resistance, water resistance, and chemical resistance to the final drywall board or composite board as described herein.
Having generally described this invention, a further understanding can be obtained by reference to the specific example illustrated below which is provided for purposes of illustration only and is not intended to be all inclusive or limiting unless otherwise specified.
Example: Thin Drywall Board
Small samples of thin drywall boards were prepared by forming (1) a gel coat composition formed of α-gypsum, a polyacrylic latex emulsion, an epoxy silane coupling agent, and melamine formaldehyde and (2) a matrix formulation formed of α-gypsum, a polyacrylic latex emulsion, a silane coupling agent, melamine formaldehyde, and an accelerator (ammonium sulfate) in accordance with the present invention. The gel coat composition and the matrix composition were each individually formed by dry mixing the dry components (α-gypsum, melamine formaldehyde, and ammonium sulfate (only in the instance of the matrix composition)) were dry mixed in a container. The wet components (the polyacrylic latex emulsion and coupling agent) were mixed in a mixing container. The dry components were then added gradually to the mixing container until the wet and dry components were fully mixed. The resulting gel coat composition and matrix composition were used to manufacture 12″×12″ samples of thin drywall boards that included between 1 to 5 layers of Owens Corning's 1.95 lb/ft2 shingle mat. The gel coat composition was applied to the mold and permitted to harden prior to the application of the matrix composition. Alternating layers of glass mat and matrix composition were then applied, with a glass mat forming the external surface of the drywall board opposing the gel coat. After sufficient time had passed, the samples of thin drywall were removed from the mold. The physical properties of the various drywall samples are shown in Table 1.
Two-ply and three-ply inventive thin drywall samples were tested for various mechanical properties, including tensile strength (ASTM D638), tensile modulus (ASTM D638), and Izod impact strength (unnotched) (ASTM D4812). These two- and three-ply thin drywall samples were also tested for water absorption following the testing procedures set forth in ASTM D570. The results of the mechanical testing are set forth in Table 2.
It can be concluded from Table 2 that the two- and three-ply thin drywall samples possessed a much larger tensile strength than the tested conventional drywall. In addition, the glass reinforcement in drywall samples caused a vast increase in the impact strengths of the inventive drywall board over the tested conventional drywall. Further, as the amount of plies of the glass mats increased from two to three plies, the tensile strengths substantially increased. It is believed that as more glass mats are added to the inventive drywall board in a layered fashion with the matrix composition, the impact resistance of the inventive drywall board will continue to increase. Additionally, it can be seen from Table 2 that both the two- and three-ply drywall board samples absorbed significantly less water than the conventional drywall. This decrease in water absorption is significant in that the inventive drywall boards may be used in areas prone to receiving a lot of water, such as in a flood plain or a hurricane zone without ruining the inventive drywall board. Also, it is to be noted that both the all of the tested inventive drywall board samples were thinner than the conventional drywall (Panel 5). One advantage provided by the thinness of the inventive drywall board is that more product may be transported at one time, thereby saving in transportation costs. Thus, it can be concluded from Table 2 that the inventive drywall boards have increased impact strength, improved tensile strength, and decreased water absorption in products and are thinner than conventional drywall.
The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below.
