HK1117208A - Interior wallboard and method of making same - Google Patents

Description

Interior wall panel and method of making same

Technical Field

The present invention relates to an improved gypsum wallboard faced on both major surfaces with a fiberglass mat. More particularly, the present invention relates to a gypsum wallboard suitable for interior use, which is covered on one major surface with a coated glass fiber mat of a specific diameter and length of glass fibers, such that the mat has a surface suitable for Level 4 finishing (GA-214-96), having a first basis weight, and on its other major surface with an optionally coated glass fiber mat of a second, usually higher basis weight and made of glass fibers of a larger diameter and longer length than the fibers of the coated glass fiber mat, such that the wallboard has acceptable flexural strength properties.

Background

The building industry has widely used gypsum wallboard, consisting of a set gypsum core sandwiched between two sheets of multi-ply paper facing materials, to construct residential houses, commercial buildings, and other structures. The use of paper-faced gypsum wallboard has become one of the most common ways to finish the internal structure of buildings. Paper faced gypsum wallboard, also known as paper faced gypsum board or drywall, is typically made (pre-cut) into 4ft x 8ft or 4ft x 12ft flat boards, typically having a thickness of 1/2 "or 5/8". Sheets of paper-faced gypsum wallboard are hung on wooden or metal studs to form interior partitions or walls of rooms, elevator shafts, stairwells, ceilings, and the like.

Conventional paper-faced gypsum wallboard is typically made from a stucco slurry (calcined gypsum slurry, gypsum hemihydrate slurry), wherein the stucco slurry is placed between two layers of the paper facing and allowed to set. In typical paper-faced gypsum wallboard, the two-ply, multi-ply paper facing holds/restrains the stucco slurry while it sets and provides the flexural strength required in installation and use. When calcined gypsum reacts with water to form calcium sulfate dihydrate, the resulting set gypsum is a hard and rigid product.

During wallboard manufacture, water in excess of that required to hydrate the calcined gypsum must be removed from the stucco slurry during curing. While a certain amount of water is required to hydrate the calcined gypsum, an excess of water is added, for example, about twice or more as much as is actually required to hydrate the calcined gypsum to obtain a smooth, free-flowing stucco slurry suitable for shipping and then deposited on the bottom facing sheet to form the board core. This excess water must evaporate primarily through the veneer when the panel is cured and dried.

Gypsum wallboard is typically manufactured as a continuous product on an endless conveyor belt using rolls of paper facing material. The board is cut into discrete lengths to accommodate subsequent processing and then dried in a heated dryer until the discrete boards are completely dried. The quality of the paper facing determines the type of application for which the board is suitable and the surface treatment that can be used on the board.

The paper facers commonly used to make paper-faced gypsum wallboard are generally composed of two types. The facings used on the sides of the wallboard intended to facing the interior of a room are multi-ply structures in which the outer ply is typically constructed of a better grade of paper. This enables the smooth surface board to be finished in a variety of aesthetically acceptable ways, especially by painting. The inner layer, including the layer in contact with the board core, is typically made of repulped newsprint and recycled corrugated boxes. Paper facers for use on the back of boards intended to be placed against studs are typically made from multiple layers of lower grade paper, such as repulped newsprint and corrugated boxes.

Multi-ply paper facings have long been used because they provide a unique combination of properties. The paper is capable of forming a satisfactory bond with set gypsum, particularly gypsum containing added binders such as starch, so that the facing does not readily delaminate from the set gypsum core. As described above, the water added to make the gypsum slurry and not chemically bound to the stucco slurry (calcined gypsum) must evaporate primarily through any of the facing sheets without causing delamination. The paper is sufficiently porous to allow water vapor to permeate through the paper during manufacture of the gypsum wallboard. The paper also has a smooth surface that can be easily finished in various ways, for example by applying wallpaper or in particular by painting, with minimal surface treatment.

Although paper is a relatively inexpensive facing material and can be readily used in the process of making wallboard, it also has some drawbacks, particularly in terms of moisture resistance. Moisture can have a deleterious effect on paper faced wallboard. In addition to degrading strength and other structural properties, moisture (in combination with other factors) can promote the growth of fungi (including, for example, mold). This problem can be particularly acute (in some cases) with respect to certain spaces that are sealed and difficult to access when installing the wall panels.

As an alternative to paper facing, gypsum wallboard can also be made using fibrous mats (e.g., glass fiber mats) as facing materials. Examples of such wall panels include those described in, for example, U.S. patent 3,993,822, U.S. patent 5,644,880, U.S. patent 5,791,109, U.S. patent 5,883,024, and U.S. patent 6,001,496. In addition to improved water resistance, fibrous mats, and particularly glass fiber mats, can provide significant improvements in strength and other desirable structural characteristics.

U.S. patent application serial No. 10/957,745, incorporated herein by reference, describes a recent development in gypsum wallboard technology for interior applications. According to this patent application, at least one major surface of gypsum wallboard is faced with a unique coated non-woven glass fiber mat suitable for producing a surface in the resulting glass fiber mat-faced gypsum board suitable for level 4 finishing, i.e., a very smooth surface, in the same manner as commercially available multi-ply paper-faced gypsum wallboard.

This result is achieved by using as facing material for making gypsum wallboard a coated non-woven glass fiber mat comprising and preferably consisting essentially of fibers having a diameter of no greater than about 11 microns and preferably no less than about 8 microns and a length of 1/4-3/4 inches, the fibers being bonded together primarily with an acrylic adhesive having a suitable softness. The coating on the glass fiber mat is produced by drying an aqueous mixture of (i) a mineral pigment, (ii) a polymeric binder (again preferably an acrylic binder) and optionally (iii) an inorganic binder. Preferably, the coating is applied to the glass fiber mat prior to use in the manufacture of gypsum wallboard. Such mats are referred to as pre-coated mats.

In the initial development of this product, a blend of 75 wt% 1/4 inches long and 25 wt% 3/4 inches long glass fibers (H fibers) of nominal 10-11 micron diameter bonded together with an acrylic adhesive was used to make the actual coated glass fiber mat facing material for the inside (smooth) face. The fiberglass mat had a basis weight (prior to application of the coating) of about 1.4 pounds per 100 square feet. The opposite surface of the gypsum board is also faced with a fiberglass mat. The fiberglass mat used on the opposite surface was also a coated fiberglass mat having a basis weight of about 1.4 pounds per 100 square feet (prior to coating). The glass fiber mats for the opposing surfaces were made using predominantly 3/4 inch long glass fibers (K fibers) of nominal diameter about 13 microns bonded together primarily with a urea-formaldehyde binder.

Two problems encountered during the development of this internal gypsum board product are (1) the unpredictable distortion of the board made with the above-described fiberglass mat on both major faces (primarily distortion that occurs as the board passes through the oven dryer), and (2) the inability to consistently produce a finished board with acceptable flexural strength.

The problem of panel warping is particularly prevalent when making longer panels, such as 4ft by 12ft panels, having a thickness of 5/8 inches. The distortion manifests itself as a bending of the sheet in the Machine Direction (MD). In the case of 5/8 boards, the distortion was so severe that the end taping of the boards-the conventional practice of stacking the inside surfaces of two boards face-to-face could not be done without damaging the boards.

Based on additional developments, it was determined that the construction of the present invention can provide an untwisted interior gypsum wallboard product in a consistent manner having the desired flexural strength and having on both major surfaces a fiberglass mat facing, one of which is a pre-coated mat having a smooth surface suitable for a level 4 finish (GA-214-96).

Brief Description of Drawings

The features and advantages of the present invention will be apparent from the following more detailed description of certain embodiments of the invention, and are explained in the accompanying drawings, in which reference characters refer to the same parts throughout the various views. The drawings are not to scale and are intended to be illustrative of the features of the invention rather than limiting.

Fig. 1 is a highly schematic cross section of a coated fiberglass mat faced wallboard according to the present invention.

Figure 2 is a highly schematic illustration of a portion of a wallboard production line.

Detailed Description

In accordance with the present invention, gypsum wallboard suitable for finishing the interior spaces of residential houses, commercial buildings, and other structures is faced on both major surfaces with a non-woven glass fiber mat.

One of the major surfaces of the gypsum wallboard, i.e., the surface intended to face the interior space of a house, is faced with a coated non-woven fiberglass mat (i.e., a facing having a very smooth surface) (i.e., the first mat) suitable for a level 4 finish, having a smoothness comparable to commercially available multi-ply paper faced gypsum wallboard. This result is achieved by using as facing material for making gypsum wallboard a coated non-woven glass fiber mat comprising, and preferably consisting essentially of, fibers having a nominal diameter of no greater than about 11 microns, and preferably no less than about 8 microns, bonded together with an acrylic adhesive having suitable softness. The fibers comprising the coated fiberglass mat also have a fiber length of 1/4-3/4 inches, and the coated nonwoven fiberglass facing material has a basis weight of about 1.7-2.0 pounds per 100 square feet prior to application of the coating.

According to the present invention, the other major surface of the gypsum wallboard, i.e., the surface intended to face the supporting studs, is faced with an optionally coated non-woven glass fiber mat (i.e., a second mat) made of glass fibers having a nominal diameter of at least about 13 microns but not greater than about 16 microns, also bonded together with an acrylic binder. The fibers comprising the optionally coated fiberglass mat also have a fiber length of at least about 3/4 inches and typically no greater than about 1 inch, and the optionally coated nonwoven fiberglass facing material has a basis weight (prior to application of any coating) of about 1.8-2.2 pounds per 100 square feet, preferably at least 1.9 pounds per 100 square feet, and which is typically greater than the basis weight of the coated nonwoven fiberglass mat facing material (first mat) prior to application of its coating. Preferably, the basis weight of the second mat is at least about 0.5 pounds per 100 square feet, and more typically at least about 0.15 pounds per 100 square feet, greater than the uncoated basis weight of the coated nonwoven glass fiber mat facing material (first mat).

The term "nominal diameter" as used herein refers to the minimum thickness of the following fibers: it may not have a substantially circular cross-section and is intended to include fibers having a normal distribution of thickness around the mean.

The various grades of finished Gypsum Board are described in publications GA-214-96, Recommanded levels of Gypsum Board available from Gypsum Associates, Washington, D.C., the entire contents of which are incorporated herein by reference. When flat paint, lightweight structures or wall coverings are applied to a panel surface, a level 4 finish is typically specified. Thus, the surface must be suitably smooth so that the wall finishes can be applied with minimal handling and are aesthetically acceptable.

Non-woven glass fiber mats suitable for use on both major surfaces of gypsum board in the present invention may be made by a wet-laid process on equipment that can be considered as a modified papermaking machine. Descriptions of wet-laid processes for making glass fiber mats may be found in a number of U.S. patents, including U.S. patent nos.2,906,660, 3,012,929, 3,050,427, 3,103,461, 3,228,825, 3,760,458, 3,766,003, 3,838,995, 3,905,067, 4,112,174, 4,129,674, 4,681,802, and 4,810,576, all of which are incorporated herein by reference. The method of making the nonwoven glass fiber mat does not form part of the present invention.

In general, a wet-laid process for making a nonwoven glass fiber mat comprises: an aqueous slurry of short length glass fibers (referred to in the art as "white water") is first formed in a mixing tank with agitation, and then the slurry is fed onto a moving screen where the fibers wind themselves into a freshly made wet glass fiber mat while excess water is separated from the fiber mat.

Some machines such as wirestyle, Fourdrinier, Stevens Former, Hydroformer, rotoformer, Deltaformer, invader Former, and VentiFormer machines may be used to form the wet-laid mat. In these devices, a headbox deposits the slurry onto a moving wire screen. Suction or vacuum removes the water to form a wet laid mat.

Since glass fibers generally do not disperse well in water, industry practice provides suspension aids for glass fibers. Such suspending aids or dispersants are generally materials which increase the viscosity of the aqueous medium. Suitable dispersants conventionally used in the art include polyacrylamides, hydroxyethyl cellulose, ethoxylated amines and amine oxides. Other additives such as surfactants, lubricants, and defoamers are also conventionally added to the white water. These agents, for example, further promote the wettability and dispersibility of the glass fibers.

The fiber slurry deposited on the moving screen or cylinder is processed into a sheet-like nonwoven fiber mat by removing water, typically by suction and/or vacuum equipment, and a binder is typically subsequently coated on the mat. The binder composition is typically a water-based fluid and is impregnated directly into the fibrous mat and immediately thereafter set or cured to provide the desired mat integrity.

The present invention relies on the use of an acrylic binder in the glass fiber mat used on both major surfaces of the gypsum board. However, the actual structure of each of the pads themselves differs, except for the adhesive.

In the case of a non-woven mat (first mat) bonded to the major surface of the gypsum core intended to face the interior space of a room, the mat is made using glass fibers having a nominal diameter of preferably not less than about 8 microns and not greater than about 11 microns. The glass fibers may be E, C, T or S fibers or any known type of glass fiber having excellent strength and durability. Preferably, a major portion of the fibers, more preferably at least about 75 weight percent (wt%) of the fibers and even more preferably substantially all of the fibers (i.e., consisting essentially of) have a nominal diameter of no less than about 8 microns and no greater than about 11 microns. In addition, it is preferred that there be substantially no fibers in the nonwoven first mat having a nominal diameter greater than about 13 microns (i.e., no fibers larger than K fibers). For example, the first mat may be made from a blend of H and K fibers, provided that a greater weight percentage of H fibers, such as 75 wt% H fibers and 25 wt% K fibers, or the first mat may be made primarily from fibers having a nominal diameter of about 10-11 microns (i.e., greater than 95 wt% of the fibers have a nominal diameter of about 10-11 microns (i.e., 95 wt% H fibers)).

The use of mats made from glass fibers having a nominal diameter of less than about 8 microns is undesirable because it is believed that the peel strength, bonding ability, and possible porosity (particularly after coating) of such mats prevent the manufacture of acceptable gypsum wallboard. On the other hand, applicants anticipate that using a mat made with too many fibers having a nominal fiber diameter greater than about 11 microns will result in a nonwoven mat having a surface morphology that cannot be finished in an acceptable manner (i.e., the surface is not sufficiently smooth to be directly suitable for the level 4 finishing technique described above) even after application of a coating as described below. Suitable fibers having suitable diameters for making glass fiber mats suitable for use in the present invention may be obtained, for example, from Johns Manville and Owens-Corning.

Most, if not all, of the fibers used to make the first mat should also have a length of about one-quarter (1/4) to about three-quarters (3/4) of an inch, more preferably about one-quarter (1/4) to about one-half (1/2) of an inch. Shorter fibers make mat formation more difficult; while too high a proportion of longer fibers interferes with the manufacture of a mat having a suitable surface morphology (smoothness) for a level 4 finish. Preferably, at least about 75 wt% of the fibers used to make the mat have a length of about one-quarter (1/4) to about three-quarters (3/4) of an inch, and preferably about one-quarter (1/4) to about one-half (1/2) of an inch; and more preferably at least about 90 wt% of the fibers used to make the mat have a length of about one-quarter (1/4) to about three-quarters (3/4) of an inch, and preferably about one-quarter (1/4) to about one-half (1/2) of an inch. For example, a mat made using 75 wt% 1/4 inch H fibers (nominal diameter of about 10-11 microns) and 25 wt% 3/4 inch H fibers was observed to have a suitable surface smoothness.

In addition to the nominal fiber diameter and fiber length, the weight per unit surface area that the resulting nonwoven first glass fiber mat has also affects the surface properties (e.g., smoothness) and, in particular, the properties of the board made from the mat, and thus determines the suitability of the mat for use in making the gypsum wallboard of the present invention. More specifically, it is preferred that the non-woven glass fiber mat (first mat) be at least about 1.7lb/100ft²But not greater than about 2.0lb/100ft²And is manufactured at an uncompressed mat thickness of about 25 to about 40 mils, and most typically at a thickness of about 33 mils. Preferably about 1.8lb/100ft²About 1.9lb/100ft²And a basis weight of about 1.8lb/100ft²The basis weight of (b) appears to be suitable.

According to a particularly preferred embodiment of the present invention, the nonwoven fibrous mat used to make gypsum wallboard according to the present invention consists essentially of a substantially random distribution of fibers having a nominal diameter of about 10-11 microns (and not less than 8 microns) (preferably at least 90 wt% of the fibers have a diameter of about 10-11 microns), and at least 75 wt% of the fibers have a length of about 1/4 to about 3/4 inches, preferably a length of about 1/4 to about 1/2 inches (preferably at least 90 wt% of the fibers have a length of about 1/4 to about 3/4 inches and preferably about 1/4 to about 1/2 inches), and the mat has a length of about 1.8lb/100ft²Basis weight of (c). As shown in the examples below, a basis weight of about 1.8lb/100ft was made from 75 wt% 1/4 inch H fibers and 25 wt% 3/4 inch H fibers²The pad of (2) is particularly suitable.

The optionally coated nonwoven mat (second mat) bonded to the other major surface of the gypsum core intended to face the room stud is made using glass fibers having a nominal diameter of at least about 13 microns (K fibers) but typically no greater than about 16 microns (M fibers). Also, the glass fibers may be E, C, T or S fibers or any known type of glass fibers having excellent strength and durability. Preferably, a major portion of the fibers, more preferably at least about 75 wt% of the fibers and even more preferably substantially all of the fibers (i.e., consisting essentially of) have a nominal diameter of at least about 13 microns. Also, it is generally preferred that substantially no fibers having a nominal diameter greater than about 16 microns be present in the nonwoven second mat.

With respect to the second mat, in addition to the nominal fiber diameter and fiber length, the resulting optionally coated, non-woven glass fiber second mat has a weight per unit surface area that also affects the performance of the panel made from the mat. According to the present invention, the nonwoven glass fiber mat (second mat) has a weight per unit surface area (hereinafter also referred to as basis weight, and measured prior to providing the mat with an optional coating) of about 1.8-2.2 pounds per 100 square feet, preferably at least 1.9 pounds per 100 square feet, and the basis weight is generally greater than the basis weight of the coated nonwoven glass fiber mat facing material (first mat) prior to applying any coating. Preferably, the basis weight of the second mat is at least about 0.5 pounds per 100 square feet, and more typically at least about 0.15 pounds per 100 square feet, greater than the pre-coated basis weight of the coated nonwoven glass fiber mat facing material (first mat).

The second pad also has an uncompressed pad thickness of about 25 to about 40 mils, most typically a thickness of about 33 mils. As demonstrated by the examples, a basis weight of about 2.0lb/100ft made substantially from 3/4 inch long K fibers²The second pad of (a) appears to be suitable.

Nonwoven mats suitable for use in the present invention will typically have an air permeability of less than about 900cfm (cubic feet per minute), and even more preferably less than about 800cfm (as measured using test method FG436-910, which is incorporated herein by reference), but have an air permeability of at least about 100cfm, prior to application of any coating.

Although the first and second mats have been described as being made of glass fibers, a small amount of synthetic fibers of similar size, such as polyester fibers, may also be included as a substitute for some of the glass fibers in the mats. For example, 25 wt% of the glass fibers may be replaced with similarly sized polyester fibers. Within the meaning of the present description and claims, a glass fibre mat containing said small amount of synthetic fibres is also to be regarded as a glass fibre mat. Preference is given to mats made entirely of glass fibers, i.e. mats having exclusively glass fibers.

After the initial mat formation, an adhesive, preferably a water-based adhesive, is coated onto the nonwoven mat to create the completed structure. Although urea-formaldehyde (UF) resins are commonly used to make non-woven glass fiber mats, for the purposes of this invention, acrylic binders need to be used on both the first and second mats. For each mat that will facing both major surfaces of the gypsum board, the acrylic-based binder will comprise at least 50 wt%, preferably at least 75 wt%, more preferably at least 80 wt% and up to at least 90 wt%, and most preferably it is the entire glass fiber mat binder. The balance of the binder may be urea-formaldehyde resin or melamine-formaldehyde resin. However, for internal applications, it is generally desirable to minimize the possibility of formaldehyde being released from the mat or outgassing from the mat. In this case the mat binder is almost completely made using an acrylic binder, i.e. only a small amount of urea-formaldehyde resin can be used to crosslink the acrylic binder.

Acrylic adhesives (or acrylic polymers) are polymers or copolymers containing units of acrylic acid, methacrylic acid, and their esters and related derivatives. Such polymers and copolymers may be thermosetting acrylic latexes or thermoplastic acrylic latexes (also known as elastomeric acrylic latexes). Blends of thermoset and thermoplastic acrylic polymers, for example, blends of equal weight thermoplastic and thermoset polymers, may be advantageously used as binders for the first and second mats. Such polymers and copolymers are well known and widely commercially available. Thus, such polymers need not be described in detail. Such polymers and copolymers can generally be placed in aqueous solution or provided as an aqueous latex emulsion.

For example, it is contemplated that suitable binders, particularly the preferred water-based latex binders, may be made by emulsion polymerization using the following monomers: (meth) acrylic acid (wherein conventional (meth) acrylic acid is intended to include acrylic acid and methacrylic acid), 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, cyclohexyl (meth) acrylate, heptyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, hexyl (meth), Isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, octadecyl (meth) acrylate, stearyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiglycol (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, phenoxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxyethylene glycol (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, dicyclopentadiene (meth) acrylate, dicyclopentyl (meth) acrylate, dodecyl (meth) acrylate, tricyclodecyl (meth) acrylate, isobornyl (meth) acrylate, and bornyl (meth) acrylate. Other monomers copolymerizable with the (meth) acrylic monomer, generally in minor amounts, include: styrene, diacetone (meth) acrylamide, isobutoxymethyl (meth) acrylamide, N-vinylpyrrolidone, N-vinylcaprolactam, N-dimethyl (meth) acrylamide, tert-octyl (meth) acrylamide, N-diethyl (meth) acrylamide, N' -dimethyl-aminopropyl (meth) acrylamide, (meth) acryloylmorpholine; vinyl ethers such as hydroxybutyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether and 2-ethylhexyl vinyl ether; a maleate ester; a fumarate; and similar compounds.

Acrylic polymers and copolymers particularly useful in making glass fiber mats suitable for making glass fiber mat-faced gypsum boards of the present invention are provided as latex materials and have a Glass Transition Temperature (GTT) of at least about 20 ℃, but not greater than about 115 ℃ in use. Thus, acrylic polymers and copolymers having a Glass Transition Temperature (GTT) of at least about 30 ℃, but not greater than about 85 ℃, would be particularly suitable. Acrylic polymers and copolymers with a GTT of about 40 ℃ are particularly useful. Although the same acrylic adhesive is preferably used for both pads, so long as each acrylic adhesive has a Glass Transition Temperature (GTT) of at least about 20 ℃, but not greater than about 115 ℃. The adhesive should have sufficient flexibility to enable the objectives of the present invention to be achieved.

One class of suitable acrylic polymers or copolymers available as thermoplastic acrylic latex or elastomeric acrylic latex are all Rhoplex ® polymers such as Rhoplex ® GL-618 available from Rohm and Haas Company. Rhoplex ® GL-618 had a GTT of about 36 ℃. Rohm & HassTSet ® acrylic latex polymers that are thermosetting acrylic polymers may also be used, especially when possibly blended with thermoplastic or elastomeric acrylic latexes at equal weights. These thermosets may also be referred to as formaldehyde-free polyacrylic thermosets. Suitable thermosetting acrylic latexes can have a GLT of about 100 ℃ +.

The acrylic binder, preferably a water-based binder, may be coated onto the wet-laid nonwoven glass fiber mat using any suitable equipment such as curtain coaters or dip and squeeze coaters. In the drying and curing oven, the glass fiber mat is heated to a temperature of up to about 250-300 ° f for a period of time generally not exceeding 1 or 2 minutes and generally less than 30-50 seconds to effect drying and, if desired, drying the binder and, if desired, curing the binder. The adhesive is applied in an amount sufficient to provide a complete self-supporting mat. Suitable amounts are described in the aforementioned patents and may in certain cases be determined by routine experimentation.

After forming the non-woven glass fiber mat, the mat to be bonded on the major surface of the panel facing the room interior space (i.e., the first mat) is provided on one side with a coating of a dried, preferably aqueous mixture of: (i) a mineral (inorganic) pigment or filler, (ii) a polymeric (organic) binder and optionally (iii) an inorganic binder. The other (second) pad is optionally provided with the coating. Preferably, the coating is applied to one side (surface) of the glass fiber mat prior to using the mat to make the glass fiber mat-faced gypsum board of the present invention. Generally, the coating is applied by contacting the pad with an aqueous mixture containing the ingredients and then drying/curing the mixture.

The organic binder, typically a latex binder, and preferably an acrylic binder, constitutes at least about 1 wt% of the coating, and typically no more than about 20 wt%, and most typically less than about 17 wt%, based on the dry weight (100%) of the two essential components, the mineral pigment and the organic binder, the balance being an inorganic mineral pigment or filler. Optionally, an inorganic binder, preferably comprising at least about 0.5 wt% but not more than about 20 wt% of the total weight of the dried (cured) coating, may also be present. The weight ratio of mineral pigment or filler to polymeric (organic) binder may exceed 15: 1, but in some cases may exceed 20: 1, but is usually at least about 5: 1.

Thus, based on the dry weight of the three components (100%), a suitable coating composition for making a coating pad may comprise about 75-99% mineral pigment or filler, more typically about 80-95% mineral pigment or gown, about 0-20% inorganic binder, more typically about 0-10%, and about 1-20% polymeric binder (organic binder), typically about 1-17% and more typically about 1-12%.

As mentioned above, mineral pigments or fillers constitute the main component of the coating composition. Examples of mineral pigments suitable for making coated pads useful in the present invention include, but are not limited to, ground limestone (calcium carbonate), clay, sand, mica, talc, gypsum (calcium sulfate dihydrate), Aluminum Trihydrate (ATH), antimony oxide, or a combination of any two or more of these.

Mineral pigments are usually provided in particulate form. To be an effective mineral pigment for making the coated mat used as the first mat in the present invention, the pigment preferably has a particle size such that at least about 95% of the pigment particles pass through a 100 mesh wire screen. Preferably, most, if not all, of the fine particles of the pigment are removed. It has been observed that the presence of an excess of fine particles in the coating composition negatively affects the porosity of the coated mat. One preferred mineral pigment is limestone having an average particle size of about 40 microns. Alternatively, throughout the remainder of this application, the material is referred to collectively and individually as mineral pigment or "filler".

The resins used in the coating must also meet a certain degree of porosity when used in combination with mineral fillers for making coated glass fiber mats. Porosity tests were performed with a coated test pad made by coating a glass fiber mat with an aqueous coating formulation and drying it at 230 ° f (110 ℃) for 20 minutes. The coating formulation is made by mixing and thoroughly blending the filler, resin (typically a latex, and preferably an acrylic latex), and any optional inorganic binder, for example, for about 30 seconds. The aqueous formulation can be coated on the mat using a simple knife coater to obtain about 22g coating/ft on the glass fiber mat²Dry basis weight of (a).

On-pad paintAfter coating and curing, the test for porosity is a modification of TAPPI T460, the procedure of Gurley method, for measuring the air resistance of paper. In this procedure, a sample of the coated pad (about 2 inches by 5 inches) was clamped to a lin of a Gurley air permeability tester (model 4110)²Between the orifice plates. The inner cylinder was released and allowed to descend under its own weight only (i.e. by gravity alone) and the time (measured in seconds) elapsed from the instant the inner cylinder entered the outer cylinder of the device until the 100ml mark on the inner cylinder reached (entered) the outer cylinder was recorded. The test was then repeated with the sample facing (oriented) in the opposite direction.

The porosity reported in seconds consists of the average of two replicate tests for each sample. Suitable pre-coated glass fiber mats exhibit a porosity of less than about 45 seconds, preferably less than about 30 and more preferably less than about 20 seconds. At porosities above about 45 seconds, the coated mat-gypsum core interface is at much higher risk of delamination (i.e., pore formation) because water vapor seeks a path to escape during board curing. Preferably, the porosity is also greater than about 2 seconds so as to minimize bleeding (bleedthreough) of the gypsum slurry during board manufacture.

Filler materials that inherently contain some naturally occurring inorganic binders can be used to make coated mats. Examples of such fillers, some with naturally occurring binders, include (but are not limited to) the following: limestone containing quicklime (CaO), clay containing calcium silicate, sand containing calcium silicate, aluminum trihydrate containing aluminum hydroxide, cement fly ash containing magnesium sulfate or chloride, or both, and magnesium oxide. Depending on its degree of hydration, gypsum can be both a mineral pigment and an inorganic binder, but it is only slightly soluble in water and the solid form is crystalline, making it brittle and weak as a binder. Therefore, gypsum is not generally preferred for use as an inorganic binder.

Fillers that inherently include an inorganic binder as a component and cure by hydration also advantageously act as burn inhibitors. By way of example, Aluminum Trihydrate (ATH), calcium sulfate (gypsum), and magnesium oxychloride and oxysulfate (oxysulfate) all carry water molecules bound in their molecular structure. This water, known as crystal water or water of hydration, is released when heated sufficiently, actually inhibiting combustion.

Thus, such low cost inorganic mineral pigments having the properties described in the preceding paragraph can provide three (3) important contributions to the coating mixture: fillers, binders and burn inhibitors.

Examples of polymeric binders for use in the coating composition include, but are not limited to: styrene-butadiene rubber (SBR), styrene-butadiene-styrene (SBS), ethylene-vinyl chloride (EVCl), polyvinylidene chloride (PVdCl) and polyvinylidene (certain) copolymers, modified polyvinyl chloride (PVC), polyvinyl alcohol (PVOH), ethylene-vinyl acetate (EVA), polyvinyl acetate (PVA) and polymers and copolymers comprising units of acrylic acid, methacrylic acid, their esters and derivatives thereof (acrylic polymers), for example styrene-acrylate copolymers. Most, if not all, of these materials are available as latex formulations. Acrylic latex polymers are generally preferred.

In addition to the two essential components and one optional component, the aqueous coating composition will include water in an amount sufficient to provide the composition with the desired rheological properties (e.g., viscosity), as well as other optional ingredients such as colorants (e.g., pigments), thickeners or rheology control agents, defoamers, dispersants and preservatives, suitable for the selected composition coating form and suitable for retention on the surface of the glass fibers of the mat (including the fibers within the interstices of the glass fiber mat). Generally, the solids content of the aqueous coating formulation is about 45 wt% to 85 wt%. When used, the total amount of these other ingredients in the coating composition is typically from 0.1 to 5% of the main three said components, and typically does not exceed about 2%.

Any suitable method for applying the aqueous coating composition to the fibrous mat substrate may be used to produce the coated mat, such as roll coating, curtain coating, knife coating, spray coating, and the like, including combinations of the above. To obtain the best performance in the coated mat and the resulting gypsum board, the coating is applied such that it penetrates to a depth of about 30% to about 50% of the thickness of the coated glass fiber mat and encapsulates the fibers of the glass fiber mat. In this regard, reference is made to U.S. application Ser. No. 10/798,891 entitled "Use of Pre-Coated Mat for Preparing Gypsum Board" filed on 3, 12, 2004, which is incorporated herein by reference. After the aqueous coating composition is applied to the mat, the composition is dried (cured), typically by heating, to form a coated glass fiber mat.

In order to maximize the applicability of the pre-coated mat to the manufacture of mat-faced gypsum board of the present invention, it is preferred that the pre-coated mat be sufficiently flexible to enable winding into a roll of continuous sheet material. Thus, the pre-coated mats should not be so rigid and brittle that they will break when bent. To achieve this, it is clear that the inorganic binder content of the mat coating should generally not exceed about 20% by weight of the total dry weight of the coating, and is generally less than 10%. Also, as previously mentioned, polymeric binders have a practical upper limit due to cost and the desire to limit the flammability of the coating.

The amount of coating applied to the surface of the fiber mat should generally be sufficient to coat the surface of the mat (i.e., the fibers comprising the mat surface) with the coating composition. In the case of the first mat (i.e., the mat intended to face the interior of a room), sufficient paint will be applied to make the surface of the mat directly suitable for level 4 finishing. The amount of coating required depends in part on the thickness of the mat. It is difficult to measure the thickness of the coating due to the uneven nature of the fibrous mat substrate on which the coating is applied. Roughly speaking, the depth of the coating should be at least about 10 mils, but when the glass fiber mat is relatively thin and the coating is sufficiently dry, a coating as thin as 4 mils may be sufficient. Generally, the depth or thickness of the coating need not exceed about 30 mils.

Can be prepared by combining an aqueous coating composition containing the solid component to an amount equivalent to at least about 15lb/1000ft on a dry weight basis²Pads, more typically about 30-60lb/1000ft²The amount of mat is coated on the fiber mat to produce a coated glass fiber mat for use in the present invention. Typically, the dry coating is applied at a rate equivalent to at least about 40lb/1000ft, depending on the thickness of the fiberglass mat²Pads, most typically about 35-55lb/1000ft²The amount of pad present. Although higher or lower amounts of coating may be used in any particular case, it is believed that for most applications, the amount of coating will fall within the range of about 30 to about 60lb/1000ft²Pads (dry basis).

After the aqueous coating composition is applied to the mat, the composition is dried (cured), typically by heating, to form a coated mat. Coated mats made according to these teachings allow water vapor to pass through. A pre-coated mat suitable for use as the first mat according to the present invention is made by coating a glass fiber mat with an aqueous coating composition containing an acrylic binder and a platy clay filler. Made solely of H-fibers, the glass fiber mat has about 1.8lb/100ft²A 75 wt% of 1/4 inch length and a 25 wt% of 3/4 inch length, and using an elastomeric acrylic latex (e.g., Rhoplex ® GL-618 acrylic latex) and a thermosetting acrylic latex (e.g., Rohm)&Haas TSet ® acrylic latex) that is crosslinked with a small amount of U-F resin. The binder constitutes about 20 wt% of the glass fiber mat before the coating is applied.

Fig. 1 is a cross-section of a wall panel 10 made in accordance with the present invention. FIG. 1 is not to scale; various angles, thicknesses, and other dimensions are exaggerated for the purpose of clarity and illustration of the present invention. Wallboard 10 has a gypsum board core 12. The wall panel 10 has a first major face 14, two edges 16 and a second major face 18. The entire (or substantially the entire) surface area of the first major face 14 is covered by a coated non-woven fiberglass mat 22 (the first fiberglass mat). The second major face 18 is also covered by a non-woven glass fiber mat 24 (second glass fiber mat). The non-woven glass fiber mat 22 is a pre-coated non-woven glass fiber mat-with a coating on the surface of the mat opposite the gypsum core (i.e., on the free surface of the mat), as described below.

In making wall panels for interior finishing applications, particularly for residential dwellings, the first major face 14 preferably has a shaped area 20 formed along a side portion of the first major face 14 adjacent the edge 16. Although wall panel 10 is shown with one particular tapered configuration, alternative shapes including square edges, beveled surfaces, rounded edges, and other shapes (not shown) may be used. The entire (or substantially the entire) surface area of the first major face 14 is covered by the coated fiberglass mat 22. The second major face 18 is covered by a glass fiber mat material 24. The mat material 24 may also optionally be a coated glass fiber mat with a coating on the mat surface opposite the gypsum core (i.e., on the free surface). A mat material 24 overlies a portion of first mat 22 surrounding margin 16. Obviously, other alternatives for connecting the mat facings together are possible.

As is known, wall panels 10 of varying thickness and varying lengths and widths can be manufactured. Generally, two thicknesses of wallboard were made, 1/2 inches and 5/8 inches, and were typically 4 feet wide and 8 or 12 feet long. For a wall panel of nominal thickness of 1/2 inches, the taper by way of example may have a width w of about 2.5 inches and a height h of about 0.075 inches.

The gypsum core 12 of the wallboard 10 of the present invention is primarily of the type used in gypsum building products commonly known as paper-faced gypsum wallboard, drywall, gypsum board, gypsum laths and gypsum sheathing. The present invention is not limited to any particular core layer composition. The core layer of such gypsum products is formed by combining water with powdered calcium sulfate anhydrite or calcium sulfate hemihydrate (CaSO)₄·1/2H₂O) (also known as calcined gypsum) to form an aqueous gypsum slurry, and then hydrating or setting the gypsum slurry mixture to calcium sulfate dihydrate (CaSO)₄·2H₂O) (a relatively hard material). The core of the product will typically comprise at least about 85 wt% set gypsum, although the invention is not limited to any particular gypsum content in the core.

The composition from which the set gypsum core of the building board is made may include various optional additives including, for example, those conventionally included in gypsum wallboard and well known to the skilled artisan. Also, the present invention is not so limited and does not exclude any known gypsum core additives. Examples of such additives include set accelerators, set retarders, foaming agents, reinforcing fibers, and dispersing agents. Fungicides may be added if deemed necessary. To improve the water resistance of the core layer, the gypsum composition from which the core layer is made may also include one or more additives to improve the ability of the set gypsum composition to resist being broken down by water (e.g., resist dissolving).

The wallboard may contain wax or a wax emulsion as an additive to improve the water resistance of the gypsum core. However, the present invention is not so limited, and examples of other materials reported as being effective for improving the water resistance of gypsum products include the following: poly (vinyl alcohol) with or without a small amount of poly (vinyl acetate); a metal resinate; waxes or bitumens or mixtures thereof, usually provided as emulsions; waxes and/or bitumens and mixtures of cornflower and potassium permanganate; water-insoluble thermoplastic organic materials such as petroleum and natural pitches, coal tar, and thermoplastic synthetic resins such as poly (vinyl acetate), poly (vinyl chloride), and copolymers of vinyl acetate and vinyl chloride and acrylic resins; a mixture of a metal rosin soap, a water-soluble alkaline earth metal salt and residual fuel oil; a mixture of petroleum wax and residual fuel oil, pine tar or coal tar in the form of an emulsion; a mixture comprising residual fuel oil and rosin; aromatic isocyanates and diisocyanates; organohydrogenpolysiloxanes, such as the types mentioned in U.S. Pat. nos.3,455,710, 3,623,895, 4,136,687, 4,447,498, and 4,643,771; a siliconate, such as available from Dow Corning as Dow Corning 772; wax emulsions and wax-asphalt emulsions, each with or without materials such as potassium sulfate, alkali and alkaline earth metal aluminates, and portland cement; a wax-asphalt emulsion produced by adding an oil-soluble water-dispersible emulsifier to a molten wax and asphalt blend and mixing the foregoing with a casein solution containing an alkali metal sulfonate salt of a polyarylalmethylene condensation product as a dispersant. Mixtures of these additives may also be used. Of these types of materials, poly (methylhydro-siloxane) is particularly preferred. When used, the amount of organopolysiloxane should be at least about 0.2 wt%. As noted above, any particular water-proofing additive is optionally used.

Generally, the core layer of the nonwoven glass fiber mat-faced gypsum wallboard has from about 40 to about 55lb/ft³More typically from about 46 to about 50lb/ft³The density of (c). Of course, core layers having higher and lower densities may be used in particular applications, if desired. The manufacture of a core layer of a predetermined density can be accomplished by using known techniques, for example by introducing a suitable amount of foam material (soap) into the aqueous gypsum slurry from which the core layer is formed or by molding.

In accordance with the present invention and as shown in fig. 1, one surface of the core layer 12 of the gypsum board 10 is faced with a non-woven glass fiber mat 22. The non-woven glass fiber mat is first manufactured as described above and then pre-coated to make it directly suitable for a level 4 finishing technique. Simultaneously, the coating may also make the veneer and resulting panel moisture resistant. The coating is sufficiently porous to allow water in the aqueous gypsum slurry from which the gypsum core is made to evaporate in its vapor state therethrough during manufacture of the board. The coated mat is prefabricated and used to make the board.

A surprising aspect of the present invention is that the first and second mats of the fibers (nominal fiber diameter and fiber length and preferred basis weight) bonded together with an acrylic binder, one of which is coated and preferably both of which are coated, can provide a suitable degree of porosity to enable continuous manufacture of gypsum board by conventional commercial operations without experiencing excessive delamination of the fiber mat facing and without experiencing board distortion, while yielding a finished board having surface characteristics (e.g., smoothness) that make it directly suitable for use in a level 4 finishing technique.

As described in more detail below, wallboard can be efficiently manufactured by: an aqueous gypsum slurry containing excess water is formed and placed on a horizontally oriented moving web of a coated glass fiber mat. Another horizontally oriented moving glass fiber web (second mat) was then placed on the upper free surface of the aqueous gypsum slurry. After initial hydration and eventually with the aid of heat, excess water evaporates through the pad as the calcined gypsum hydrates and sets.

FIG. 2 is a schematic view of a portion of a conventional manufacturing line for making gypsum wallboard according to the present invention. In a conventional manner, the dry ingredients from which the gypsum core is formed can be pre-mixed and then fed into a type of mixer commonly referred to as a pin mixer (not shown). The water and other liquid components used to make the core layer, such as soap, are metered into the pin mixer, whereupon they are mixed with the desired dry ingredients to form an aqueous gypsum slurry 41 which is discharged from the discharge tube(s) 40 of the pin mixer. The foam material (soap) is typically added to the gypsum slurry, for example in a pin mixer, to control the density of the resulting core layer. Also, the method of making the core material for the gypsum board is not a critical part of the invention and a wide variety of methods may be advantageously employed.

The gypsum slurry is deposited through one or more outlets of the discharge conduit 40 onto a horizontally moving continuous web of fibrous mat material 22 (the coated first glass fiber mat). The amount of deposition can be controlled in a manner known in the art. The mat material 22 is fed from a roll (not shown) with the coated side down, i.e., away from the deposited gypsum slurry. Prior to receiving the gypsum slurry 41, the web of mat material 22 is flattened by rollers (not shown) and scored by one or more scoring devices (not shown). The score lines enable the sides of mat material 22 to be folded upwardly to form the edges of the panel, as described below.

The mat material 22 (first mat) and the deposited gypsum slurry 41 move in the direction of arrow B. The moving web of mat 22 forms the first veneer of the wallboard being manufactured and the gypsum slurry at least partially (and preferably only partially) penetrates into the thickness of the mat and cures. When set, a strong adhesive bond is formed between the set gypsum and the glass fiber mat. The partial penetration of the gypsum slurry into the pad can be controlled according to methods known in the art, such as controlling the viscosity of the gypsum slurry.

In conventional wallboard manufacture, it is also known to apply a relatively thin coating of higher density aqueous calcined gypsum slurry to the interior surface of either or both facings prior to application of the aqueous gypsum slurry forming the core layer. The veneer with the thin gypsum slurry coating is then sandwiched with the main core gypsum slurry to form a wet board. In a similar manner, it is also known to coat higher density aqueous calcined gypsum slurries along both edges (16 in fig. 1) of gypsum wallboard. These features may optionally be used to make gypsum wallboard according to the present invention.

After the gypsum slurry 41 is deposited on the web of mat material 22, the edges of the web are gradually folded around the edges of the formed wallboard (using equipment well known to those skilled in the art) and terminate along the sides at the upper surface of the gypsum slurry. A second glass fiber mat 22, fed from a roll (not shown) in the direction of arrow C, is applied to the upper surface of the gypsum slurry 41 and generally only slightly overlaps the folded-around edges of the (bottom) web of the first mat material 22.

Glue may be applied to the second web along the portion that will overlap and contact the folded edge of the first pad (glue application not shown) before the (top) second pad 24 is applied to the upper surface of the gypsum slurry. Although the invention is not limited by the type of glue used, it is preferred to use a non-starch based glue. One suitable glue is a poly (vinyl alcohol) latex glue. Glues based on vinyl acetate polymers, especially vinyl acetate that is hydrolyzed to form polyvinyl alcohol, are widely commercially available as white glues. After the (top) web 24 is applied, a "sandwich" of glass fiber mat, gypsum slurry and glass fiber mat is pressed between the boards 50 and 52 to the desired wallboard thickness. Alternatively, the web and gypsum slurry may be rolled or otherwise pressed to a desired thickness. The continuous sandwich of gypsum slurry and applied facing material is then carried by conveyor belt 54 (one or more) in the direction of arrow D. The gypsum slurry 41 sets as it is carried along the conveyor belt.

Conventional methods for interior wallboard manufacture form a shaped zone at the bottom surface edge of the formed wallboard as it moves below the production line.

After forming and after the gypsum has set sufficiently, the wallboard is typically cut to the desired length and dried. To prevent the quality of the tapered edges from degrading during drying, the plate is typically turned over prior to drying.

Although not so limited, commercial drying conditions typically used in conventional continuous gypsum board manufacture may also be used to manufacture wallboard according to the present invention. Exemplary drying conditions include a temperature of about 200 to about 600 degrees Fahrenheit at a line speed of about 70 to about 600 linear feet per minute, and a drying time of about 30 to about 60 minutes.

Examples

A variety of glass fiber mats were used as the first and second mats on a conventional wallboard manufacturing line to make a nominal 5/8 inch gypsum wallboard (4 'x 12'). Boards were made using the same gypsum core furnish throughout the test to evaluate the effect of different fiberglass mat facing structures on the performance of the resulting wallboard.

6 different first pad configurations were used throughout the test, identified in the accompanying Table 1 as pads 1, 2, 3,4, 5 and 6. Pad 1 at 1.5lb/100ft²Was made with H fibers only (10-11 micron nominal diameter, 25 wt% of which is 3/4 inches long and 75 wt% of which is 1/4 inches long) at a basis weight, and an acrylic adhesive comprising a 50-50 (wt%) blend of an elastomeric acrylic latex crosslinked with a small amount of urea-formaldehyde resin and a thermosetting acrylic latex was used. Acrylic resins from Rohm&Haas. Pad 2 is also at 1.5lb/100ft²Was made with H fibers having the same distribution for the pad 1 at a basis weight of (a), and used as a fiber obtained from Rohm&Addition of Melamine-Elastomeric acrylic latex of formaldehyde resin (also 50-50 blend). Pad 3 at 1.5lb/100ft²Was made with 75 wt% H fibers and 25 wt% K fibers (13 micron nominal diameter) at basis weight of (c), and used as a fiber obtained from Rohm&Haas's elastomer acrylic latex and added melamine-formaldehyde resin. The H fibers were 1/4 inches long and the K fibers were 3/4 inches long. Pad 4 is at 1.8lb/100ft²Was made with 75 wt% H fibers and 25 wt% K fibers at basis weight of (c), and used as a fiber obtained from Rohm&Haas's elastomer acrylic latex and added melamine-formaldehyde resin. Likewise, the H fibers were 1/4 inches long and the K fibers were 3/4 inches long. Pad 5 at 1.8lb/100ft²Was made with 75 wt% H fibers and 25 wt% K fibers at basis weight of (c), and used as a fiber obtained from Rohm&50-50 wt.% blends of Haas's elastomeric acrylic latex crosslinked with a small amount of urea-formaldehyde resin and thermosetting acrylic latex. Likewise, the H fibers were 1/4 inches long and the K fibers were 3/4 inches long. Finally, the pad 6 is at 1.8lb/100ft²Was made with only H fibers (25 wt% of which was 3/4 inches long and 75 wt% of which was 1/4 inches long) and a blend of elastomeric acrylic latex and thermosetting acrylic latex was used.

All first mats were coated with the same coating formulation at about the same coating basis weight.

Two different second pads were used in the test. Both mats were made using 3/4 inch K fibers bonded with the same acrylic adhesive. The binder is obtained mainly from Rohm&Haas's 50: 50 blend of elastomeric acrylic latex and thermosetting acrylic latex. The second pad identified as pad A in Table 1 is at 1.4lb/100ft²Is made at a base weight of (1). The second pad identified as pad B in Table 1 is at 2.0lb/100ft²Is made at a base weight of (1). Both mats were also coated with the same coating formulation.

All of the gypsum boards described were made with 12 different mat combinations. Table 1 reports the difference between the average of the flexural properties and the acceptable standard values for 5 tested gypsum board samples for each of the 12 mat combinations produced; tested under 4 test conditions: test I-the first pad faces upward against the plate to which pressure is applied in the transverse direction (pass standard value 140); test II-the first pad is facing down against the plate with pressure applied in the cross direction (pass standard value 140); test III-the first pad facing up against the plate exerting pressure in the longitudinal direction (normalized acceptable value 100) and test IV-the first pad facing down against the plate exerting pressure in the longitudinal direction (normalized acceptable value 100) (note: for the plate of pad 5-pad a combination, only 4 samples were tested in tests I and II). The panels were tested according to ASTM Standard 1178 using United tester method B.

The hatched boxes in table 1 represent those cases where the average of the tested replicate tests meets the passing standard value of the respective test. Among the combinations tested and as described in table 1, the only ones that most consistently provided suitable results are the following combinations: pad 4-pad B, pad 5-pad B, and pad 6-pad B. In the case of pad 2-pad B and pad 3-pad B, the magnitude of the deviation from the standard value observed in test II showed unacceptable consistency.

TABLE 1

First pad	Second pad	Test I	Test II	Experiment III	Test IV
						1	A	-31	-21	-16	-14
2	A	-29	-24	-7	+9
						3	A	-6	-29	+6	+16
4	A	-23	-4	-21	+28
						5	A	-16	+2	-14	+30
6	A	-35	+2	-16	+11
						1	B	-9	-17	+6	-9
2	B	+9	-28	+11	+15
						3	B	+2	-16	-2	0
4	B	+17	-3	+22	+32
						5	B	+16	-3	+14	+32
6	B	+5	+17	-1	+15

It should be understood that while the invention has been described in conjunction with specific embodiments thereof, the foregoing description and examples are intended to illustrate, but not limit the scope of the invention. Other aspects, advantages and modifications will be apparent to those skilled in the art to which the invention relates, and these aspects and modifications are within the scope of the invention, which is defined solely by the appended claims. All percentages are by weight unless otherwise specifically indicated. Throughout this specification and in the claims, the term "about" is intended to include + or-5%.

Claims (18)

1. A gypsum wallboard, comprising:

a gypsum core having a planar first major face and a planar second major face;

a coated nonwoven first glass fiber mat facing material suitable for a level 4 finish bonded to and covering the flat first major face of the gypsum core layer by an uncoated side, wherein the coated nonwoven first glass fiber mat facing material comprises a majority of glass fibers having a nominal fiber diameter of about 8 to about 11 microns and a fiber length of 1/4 to 3/4 inches, the glass fibers of the coated nonwoven first glass fiber mat facing material bonded together with a binder comprising an acrylic binder, wherein the coated nonwoven first glass fiber mat facing material has a coating comprising a dried aqueous mixture comprising: (i) a mineral pigment, (ii) a polymeric binder, and optionally (iii) an inorganic binder, and wherein the coated nonwoven first glass fiber mat facing material has a basis weight of from about 1.7 to about 2.0 pounds per 100 square feet prior to application of the coating;

an optionally coated nonwoven second glass fiber mat facing material bonded to and covering the flat second major face of the gypsum core layer by an uncoated side, wherein the optionally coated nonwoven second glass fiber mat facing material comprises a majority of glass fibers having a nominal fiber diameter of at least about 13 microns but not greater than about 16 microns and a fiber length of at least about 3/4 inches but not greater than about 1 inch, the glass fibers of the coated nonwoven second glass fiber mat facing material bonded together with a binder comprising an acrylic binder, and wherein the optionally coated nonwoven second glass fiber mat facing material has a basis weight of 1.8-2.2 pounds per 100 square feet prior to application of the optional coating.

2. The gypsum wallboard of claim 1, wherein the gypsum core includes a water-resistant additive in an amount sufficient to increase the water-resistance of the core.

3. The gypsum wallboard of claim 2, wherein the water-resistant additive comprises at least one of a wax emulsion, an organopolysiloxane, and a silicate.

4. The gypsum wallboard of claim 1, wherein the gypsum core further comprises a fungicide.

5. The gypsum wallboard of claim 1, wherein at least about 75% of the glass fibers of the coated nonwoven first glass fiber mat facing material have a nominal fiber diameter of about 8 to about 11 microns and at least about 75% of the glass fibers of the coated nonwoven first glass fiber mat facing material have a fiber length of about 1/4 to about 1/2 inches.

6. The gypsum wallboard of claim 1, wherein the coated non-woven first glass fiber mat facing material has 1.75-2.0lb/100ft prior to coating any coating²Basis weight of (c).

7. The gypsum wallboard of claim 6, wherein the coated nonwoven first glass fiber mat facing material has about 1.85lb/100ft²Basis weight of (c).

8. The gypsum wallboard of claim 1, wherein at least 90 wt% of the glass fibers of the coated nonwoven first glass fiber mat facing material have a nominal fiber diameter of about 11 microns and at least 90 wt% of the fibers of the coated nonwoven first glass fiber mat facing material have a fiber length of 1/4-3/4 inches.

9. The gypsum wallboard of claim 6, wherein the acrylic binder has a glass transition temperature of at least about 20 ℃, but not greater than about 115 ℃.

10. The gypsum wallboard of claim 9, wherein the acrylic binder has a glass transition temperature of at least about 30 ℃ but not greater than about 55 ℃.

11. The gypsum wallboard of claim 8, wherein the acrylic binder has a glass transition temperature of at least about 20 ℃, but not greater than about 115 ℃.

12. The gypsum wallboard of claim 11, wherein the acrylic binder has a glass transition temperature of at least about 30 ℃ but not greater than about 55 ℃.

13. The gypsum wallboard of claim 1 wherein the basis weight of the second mat is greater than the basis weight of the first mat.

14. The gypsum wallboard of claim 13, wherein the basis weight of the second mat is 0.05 pounds per 100 square feet greater than the basis weight of the first mat.

15. The gypsum wallboard of claim 14, wherein the basis weight of the second mat is 0.15 pounds per 100 square feet greater than the basis weight of the first mat.

16. The gypsum wallboard of claim 1, wherein the first glass fiber mat is free of fibers having a nominal fiber diameter greater than about 13 microns.

17. The gypsum wallboard of claim 16, wherein the second glass fiber mat facing material has a basis weight of about 1.9-2.2 pounds per 100 square feet.

18. The gypsum wallboard of claim 17, wherein the second glass fiber mat is free of fibers having a nominal diameter greater than about 16 microns.