HK1026396A - Gypsum/fiber board with improved impact resistance - Google Patents

Description

Gypsum/fiber board with improved impact resistance

The present invention generally relates to a paperless gypsum/fiber board having improved impact resistance and a method of making such gypsum/fiber board. More particularly, the present invention relates to a multi-layer gypsum/fiber board having a fiberglass mesh embedded in the back to improve impact resistance.

Conventional gypsum wallboard or roofing shingles are typically prepared from a gypsum slurry in which a wet slurry of calcium sulfate hemihydrate (commonly referred to as calcined gypsum) is placed between two layers of paper and the slurry is allowed to harden. The hardened gypsum is a hard product obtained when calcined gypsum reacts with water to form calcium sulfate dihydrate. The calcined gypsum is calcium sulfate hemihydrate (CaSO)₄.1/2H₂O) or calcium sulfate anhydrous (CaSO)₄). When calcium sulfate dihydrate is heated sufficiently in a step known as calcination, the water of hydration is removed and calcium sulfate hemihydrate or calcium sulfate anhydrite is formed, depending on the temperature and exposure time. When water is added to calcined gypsum to harden the gypsum, in general, the calcined gypsum reacts with the water and the calcined gypsum rehydrates. In typical gypsum wallboard, a two-ply paper comprises the slurry and provides securityStrength required for loading and use. The wallboard is cut into various lengths for subsequent processing and then dried in an externally heated dryer until the board is dry. The bending strength of the wallboard is largely dependent on the tensile strength of the paper. The set gypsum is used as a core and for fire protection, and can be modified to have various uses. The paper determines the use characteristics of the board and the surface treatment that can be applied to the board.

While paper-covered wallboard has many uses and has been a popular building material for many years, it has been recognized in the art that it is advantageous for certain applications to use gypsum roof panels whose strength and other properties are not dependent on paper-covered sheet material. Several prior art fiber reinforced gypsum boards are as follows:

U.S. Pat. No. 5,320,677 to Baig, which is incorporated herein by reference in its entirety, describes a composite product and a method of making the product wherein a dilute slurry of gypsum particles and cellulose fibers are heated under pressure to convert the gypsum to alpha calcium sulfate hemihydrate. The cellulose fibers have pores or have voids at the surface, and the alpha hemihydrate crystals are formed in, on, or around the voids and pores of the cellulose fibers. The heated slurry is then dewatered to form a mat, preferably using equipment similar to paper making equipment, and the mat is pressed into a board having a desired structure before the slurry is cooled sufficiently to rehydrate the hemihydrate to gypsum. The pressed mat is cooled and the hemihydrate rehydrates to gypsum, thereby forming a dimensionally stable, strong and useful building board. The board is then trimmed and dried. The process described in patent No. 5,320,677 differs from previous processes in that the calcination of the gypsum is carried out in the presence of cellulose fibers while the gypsum is present in a dilute slurry, such that the slurry wets the cellulose fibers while carrying dissolved gypsum into the interstices of the fibers and the calcination forms acicular alpha hemihydrate crystals in situ in and around the interstices.

U.S. patent No. 5,135,805 to Sellers et al describes a water resistant gypsum product that is a "faceless" product, that is, it may not include a facing sheet made of paper, fiberglass mat, or similar material. Gypsum products described in us patent No. 5,135,805 generally contain reinforcing fibers, for example cellulose fibers such as wood or paper fibers, glass or other mineral fibers and polypropylene or other synthetic resin fibers. The reinforcing fiber is present in an amount of about 10 to about 20 weight percent of the dry weight of the composition from which the set gypsum product is made. The density of the product is generally from about 50 to about 80 pounds per cubic foot.

U.S. patent No. 5,342,566 to Schafer et al, which is incorporated herein by reference in its entirety, relates to a method of making a fibrous gypsum board comprising mixing predetermined amounts of fibers and water in an initial mixing step to form a wetted loose fiber mixture; mixing the wetted fibers with a predetermined amount of dried calcined gypsum in a mixing step; premixing the set accelerator with one of the dry calcined gypsum, fiber or water components; rapidly pressing the mixed composition into a mat; adding a predetermined amount of water to the mat obtained in the first compression step, i.e. degassing the mat; and immediately compressing the mat to form a board comprised of bonded fibers and gypsum. The method is also used to make a homogeneous board, preferably a fibre-reinforced gypsum board such as paper fibre, in which the materials forming the several layers of the board are laid on top of each other before the board is formed, pressed and dried, and the composition of each layer is the same. Schafer et al describe, inter alia, the production of three-layer sheets in which the composition of the central core layer differs from that of the outer layers.

A multi-layer paperless gypsum/fiber board and a method of making such a three-layer gypsum/fiber board is described in provisional application serial No. 60/073,503 to Carbo et al, wherein the composition of the middle core layer is different from the composition of the outer layers, which is incorporated herein by reference in its entirety.

The prior art gypsum/fiber board is improved by bonding a layer of mesh to the back of the board to improve impact resistance. Although such improved panels have improved impact resistance, the panels are produced at low speeds, with high energy consumption, increased material costs and increased labor costs because of the need to laminate the gypsum boards to the web in a separate step which presents control problems associated with the lamination process and bonding problems between the roof panels. The lamination step is difficult due to the varying thickness of the sheet covered by the mesh and solid reinforcement. The laminating step also has the problem of not being able to maintain a constant pressure across the roof panel as the thickness or profile of the laminating step varies. The problem of roofing sheets sticking to each other is a serious problem when laminating nets on a surface, because glue actually adheres the superposed roofing sheets and nets on the surface to each other.

It is an object of the present invention to provide a fiber reinforced gypsum board with improved impact resistance which avoids many of the problems associated with prior art gypsum/fiber boards. More specifically, the present invention provides a multi-layer gypsum/fiber board having a glass fiber web embedded in the back to improve impact resistance as measured by soft body impact resistance according to astm e695 method and hard body impact resistance according to USG method, which are described in reports HPWL1#7122 and HPWL #7811-02, respectively. Embedding the reinforcing mesh in the gypsum/fiber board according to the present invention has many advantages such as high production speed, better product appearance, integral reinforcement of the reinforcing mesh in the board, and cost reduction of the product. The embedded reinforcing mesh also improves the processability of the sheet and reduces the likelihood of sheet sticking (bonding of adjacent sheets when the sheets are stacked horizontally). The product of the invention may comprise a flush net which does not raise the surface of the panel on which it is placed and which improves the security of the reinforcement in the panel because it protects the surface from abrasion and friction. An additional advantage of the product is that the tension of the web in the product gives the board increased toughness. With the method of the invention there is no need to transport the board to the second process and the reinforced board is produced on a standard gypsum fiberboard production line.

The present invention generally relates to a paperless gypsum/fiber board having improved impact resistance and a method of making such gypsum fiber board. The term "paperless" gypsum/fiber board is used herein to distinguish the reinforced gypsum board to which the present invention relates from conventional gypsum board of the prior art, also referred to as "wallboard" or "panel wallboard", at least one surface of which is comprised of paper, including "wallboard" or "panel wallboard" having some fiber reinforcement in the core layer.

Paperless gypsum/fiber board having improved impact resistance is prepared by embedding a reinforcing mesh, preferably a flexible fiberglass mesh, in the back of a multi-layer gypsum fiber board. In this method, a mesh is loaded into a shaped area of the sheet material prior to pressing the roof panel prior to drying.

It is to be understood that both the foregoing general description and the following detailed description are explanatory and explanatory only and are not restrictive of the invention as claimed.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the operation of the invention.

FIG. 1 is a partial end view of a homogeneous single layer panel of the present invention;

FIG. 2 is a partial end view of a multi-layer plate of the present invention;

FIG. 3 is a schematic side view of a forming station of the production line of the present invention;

FIG. 3A is a schematic drawing of a partial side view of an improved forming station of the production line of the present invention;

FIG. 4 is a schematic illustration of a side view of a press area of the production line of the present invention; and

FIG. 5 is a schematic illustration in partial side view of another embodiment of a molding station of the manufacturing line of the present invention.

The present invention generally relates to a paperless gypsum/fiber board having improved impact resistance and a method of making such gypsum/fiber board. Paperless gypsum/fiber boards having improved impact resistance are prepared by embedding a reinforcing web, preferably a flexible fiberglass web, in the back of a multi-layer gypsum/fiber board. In this method, the web is loaded into the forming zone of the board before pressing the board before drying.

The enhanced and improved impact resistance of gypsum/fiber board is obtained by embedding a reinforcing mesh in the back of the gypsum/fiber board. The web may be woven or non-woven, and may be made of a variety of different materials. Preferably the mesh is made of flat wire of non-elastic material, such as fiberglass mesh. The most preferred mesh is a fiberglass mesh having openings in the mesh, with the openings being of a size sufficient to allow a measured amount of dry gypsum/fiber mixture to pass through the mesh and embed the mesh in the set gypsum of the final product.

One effective glass fiber web is available from Bayex under number 0040/286. Bayex0040/286 is a Leno woven mesh having warp and weft yarns of 6/inch (ASTM D-3775), a weight of 4.5 ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and minimum tensions in the warp and weft yarns of 150 and 200 pounds per inch (ASTM D-5035), respectively. It is alkali resistant and hard to handle. Other fiberglass meshes of nearly the same size have openings of a size sufficient to allow a portion of the gypsum/fiber mixture to pass through the mesh during board formation and are equally useful.

Other useful woven glass fiber webs are available from Bayex under the number 0038/503. Bayex 0038/503 is a Leno woven mesh with 6/inch warp yarns and 5/inch weft yarns (ASTM D-3775), a weight of 4.2 ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and minimum tensions in the warp and weft yarns of 150 and 165 pounds per inch (ASTM D-5035), respectively. It is alkali resistant and hard to handle.

Another effective woven glass fiber web is available from Bayex under the number 0038/504. Bayex 0038/504 is a Leno woven mesh with 6/inch warp yarns and 5/inch weft yarns (ASTM D-3775), a weight of 4.2 ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and minimum tensions in the warp and weft yarns of 150 and 165 pounds per inch (ASTM D-5035), respectively. It is alkali resistant and hard to handle. Other fiberglass meshes of nearly the same size have openings of a size sufficient to allow a portion of the gypsum/fiber mixture to pass through the mesh during board formation and are equally useful.

Another effective woven glass fiber web is available from Bayex under the number 4447/252. Bayex 4447/252 is a Leno woven mesh with 2.6/inch warp yarns and 2.6/inch fill yarns (ASTM D-3775), a weight of 4.6 ounces per square yard (ASTM D-3776), a thickness of 0.026 inch (ASTM D-1777) and minimum tensions in the warp and weft yarns of 150 and 174 pounds per inch (ASTM D-5035), respectively. It is alkali resistant and hard to handle. Other fiberglass meshes of nearly the same size have openings of a size sufficient to allow a portion of the gypsum/fiber mixture to pass through the mesh during board formation and are equally useful.

The mesh is preferably embedded in the back of the three-layer plate with the warp oriented in the length direction of the plate. Because the board of the present invention expands in multiple directions during the pressing step, the use of an extensible web imparts better bonding to the gypsum/fiber board.

Preferably the mesh is substantially embedded in the board and covered by the gypsum/fibre mixture, as this can secure the mesh to the board. Additionally, embedding the mesh completely in the gypsum/fiber mixture may impart better impact resistance to the board. The complete embedment of the mesh in the gypsum/fiber mixture may also render the reinforcement imperceptible to the consumer.

Adhesive agent

In one embodiment, the web is treated with a binder to improve the bond between the web and the gypsum/fiber board. Suitable binders include polyvinyl acetate, polyvinyl alcohol, and specialty adhesives. Preferably the binder is water activated, i.e. activation is caused by wetting of the water in the board during the forming step of the board making process.

Gypsum/fiber board compositions

The materials used for preparing the gypsum fiber board are conventional materials. As used herein, the term "gypsum" refers to calcium sulfate in the form of a stable dihydrate, CaSO₄.2H₂O and includes naturally occurring materials, synthetically prepared equivalents such as FGD gypsum (a synthetic gypsum that is a byproduct of flue gas desulfurization), and dihydrate materials formed by hydration of calcium sulfate hemihydrate (a mixture of gypsum hemihydrate and gypsum) or calcium sulfate anhydrite. The term "calcium sulfate material" as used herein refers to calcium sulfate in any of its forms, i.e., calcium sulfate anhydrite, calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof.

The fibers used to reinforce gypsum are organic fibers and preferably readily available cellulose fibers. For example, the cellulose fibers may be waste such as waste paper, used newspapers, inexpensive household waste paper, and waste fibers in pulp production.

Expanded perlite is used in the core of the product to reduce the density of the core layer. Conventional expanded perlite, preferably perlite, can be used to expand to a density of about 5 to 10 pounds per cubic foot.

Additional components conventionally used in gypsum/fiber board can be used in the board of the present invention. Such conventional components include set accelerators, wetting agents, biocides, and the like.

Multi-layer gypsum fiber board

The present invention contemplates the production of fiber reinforced gypsum board having a substantially uniform structure as shown in board 102 of fig. 1 and composite boards having two or more layers, each layer having a different composition 100 and 101 as shown in fig. 2. In a panel having a uniform structure, as shown in fig. 1, a reinforcing mesh 120 is embedded in the back surface of the panel. In a panel having a multilayer structure, the reinforcing mesh 120 is arranged between layers, for example between layers 100 and 101, but preferably the mesh 120 is embedded in the back of the outer layer 100 of the panel, as shown in fig. 2. The preparation of a multi-layer board having perlite and fiber with gypsum for the middle core layer will first be described. The method and equipment used to prepare the different panels of the invention will then be described.

The forming of the panel can be described with reference to fig. 3, which fig. 3 shows 3 forming lines. Each forming line has 3 preformed strips 3126, 3166 and 3136 on which wet fibers and dry calcined gypsum are made into a surface layer with an admixture and wet perlite, fiber (with or without) and dry calcined gypsum are made into a core layer. For the upper and lower surface layers, wet fibers from a mill (not shown) are conveyed by closed-loop pneumatic conveyors 2511, 2512 to a forming station where the fibers are separated from the air by cyclones. The separated fibers are deposited on a reciprocating conveyor at the top of the fiber forming apparatus 3114, 3134. The fiber forming apparatus spreads a predetermined amount of fiber on the preformed belts 3126, 3136 via the discharge rollers to form a mat according to the weight ratio of the preferred formulation.

Immediately following the discharge rolls are dressing rolls 3117 and 3137, respectively, which scrape off excess fibers and thus make the thickness of the mat uniform. The height of the dressing roll can be adjusted to ensure that the deposited fibrous mat has a uniform weight. A vacuum may be applied to the rollers to draw excess fiber by compressed air. The fibers scraped off by the dressing rolls are circulated by compressed air to the same reciprocating conveyors on top of the fiber forming apparatuses 3113 and 3134 by pneumatic conveyors 2513 and 2507. The preformed band is run at a constant speed.

The dried calcined gypsum admixture mixture from the batching bin (not shown) is added to the stucco shaping bins 3124, 3164, and 3144. Stucco, as explained below, is primarily calcined gypsum, although stucco may include other conventional additives for controlling chemical reactions. The gypsum is metered from the molding bin by conventional means such as a conveyor, chute or rollers. The bottom of these bins have adjustable speed belt conveyors and a full set of mat scales 3125, 3145 and 3165 for controlling the amount of lime mud deposited on the pre-form belt according to the recipe. The exact amount of stucco was added as a top layer on top of the fiber mat.

The continuous web 120, which may be secured to a transfer roll 126, is transferred to a forming belt 4010 as shown in fig. 3. Preferably, the warp yarns of web 120 are oriented parallel to the direction of movement of forming belt 4010.

At the end of the preform strip, a layer of fibrous stucco is directed down onto the mixing tubes 3129, 3148, and 3168. The mixing tube includes a set of spiked rollers (not shown) that thoroughly mix the fibers and stucco to achieve a homogeneous composition and transport the composition from the end of the preform belt (feed) to the discharge of the mixing tube above the web 120 of the forming belt 4010. A series of spiked rollers control the downward movement of the material depending on the distance from the end of the preform belt to the mixing tube. As the mesh moves over the forming belt 4010, a portion of the fiber/stucco mixture falls into the openings of the reinforcement mesh 120. The nozzles additionally water the bottom layer of the mat.

Fig. 3A shows another embodiment in which the net lifter bar 128 is disposed between the net 120 and the forming belt 4010. Preferably, the lifter bar 128 is up to the full width of the forming belt 4010. The lifter bars serve to space the mesh 120 upward about 2 inches from the surface of forming belt 4010 as the mesh 120 passes beneath mixing tube 3129. The spacing of mesh 120 upward from forming belt 4010 allows a portion of the fiber/gypsum mixture falling from mixing tube 3129 to pass through the mesh onto forming belt 4010 and embed the mesh (at least in part) in the finished board. If desired, the lifter bar 128 can be vibrated to move a substantial amount of the gypsum/fiber mixture through the mesh 120.

Fig. 5 shows another embodiment in which web 120 passes under tension roll 136 and over set point roll 138 before web 129 is moved down toward forming belt 4010. As mesh 120 passes under mixing tube 3129. The spot rolls 138 are used to space the web 120 up to several inches from the surface of the forming belt 4010. The spacing of mesh 120 upward from forming belt 4010 allows a portion of the fiber/gypsum mixture falling from mixing tube 3129 to pass through the mesh onto forming belt 4010 and embed the mesh (at least in part) in the finished board. The optimum spacing of the web 120 upwardly from the forming belt 4010 depends on the size of the openings in the web 120, the temperature content of the fiber/gypsum mixture, the speed of the forming belt 4010, and other operating conditions. In the embodiment shown in fig. 5, a spreading jaw 140, the length of which is the entire width of the forming belt 4010, is mounted on the discharge side of the mixing tube 3129. The spreading j aw 140 is used to spread the wet fiber and gypsum mixture across the width of the reinforcing mesh as the mesh 120 is raised above the forming belt 4010. The embodiment shown in fig. 5 can increase the amount of fiber/gypsum passing through the web onto the forming belt 4010 and result in a product in which the web is more completely embedded.

For multilayer boards, the core layer is formed in a manner similar to the surface layer. In the examples to be described, a low percentage of fibres is included in the core layer, because a volume of expanded perlite is used in the core layer. The core layer contains expanded perlite for reducing the specific gravity of the overall panel. The expanded perlite is combined with gypsum to obtain a noncombustible core material which allows the core layer to pass the ASTM E136 test method. Preferably, the mixture of wet paper fibers and perlite particles are wetted so that they will carry the water needed to hydrate the stucco used to form the core layer to optimum strength. As explained below, in a preferred embodiment, the binder, preferably liquid starch, is first mixed with water for warming the perlite and the fiber is separately mixed with water. The wet fiber and wet perlite are then mixed together to form a homogeneous mixture.

Referring again to fig. 3, the warm perlite, starch and fiber mix (from the conveyor shown) is deposited in a fiber former 3154, which is identical in construction and operation to the formers 3114, 3134. The perlite, starch and fiber mixture is deposited onto the preformed tape 3166 by a draw-off roll in the same way as the surface layer of the board. The pre-form belt 3166 stratifies the perlite, starch, and fiber mixture from the fiber former bin 3154 and the stucco from the forming bin 3164 and delivers these components into a mixing pipe 3168. The forming silo 3164 includes a complete mat scale 3165. The core layer forming line includes a trim roll 3157, a mat scale 3156, and a mixing tube 3168, which operate the same as those elements in the surface layer forming line.

After the screened mat is formed on forming belt 4010, the three-layer mat is pressed in a press line as shown in fig. 4. In one embodiment, the forming belt 4010 is also part of the press line and extends through the press and calibration area. In another embodiment (not shown), there is an open gap between the degassing position and the compression position. After the last compression roll in the degassing position, spray nozzles were installed for additional addition of water for wetting the upper surface of the felt.

The press line includes three main sections, a degassing location 4012, a pressing location 4013, and a calibration location 4014. These positions can be adjusted to vary the spacing between the belts and the pressure exerted on the mat or gypsum, fibers, additives and other materials. Adjustment of the position thus enables the user to vary the thickness of the panel.

Initially, the mat is pre-compressed at a degassing location 4012 to remove air from the mat. For standard board, this position reduces the thickness of the mat from a few inches to a final thickness that may vary, for example, between 3/8 to 3/4 inches. The tapered belt is directed to the pressing location along the outside edges and center of the mat. These tapered strips taper the pressed sheets along the edge of the roof panel. The degassed mat is then compressed in a compression station 4013, where the mat is subjected to a high load and pressed to the final board thickness. The mat then passes through a calibration location 4014 which maintains the thickness of the board to allow the hardening process to proceed.

After pressing and before drying, the board was cut and prepared to enter a dryer. These permanently formed and pressed panels are pre-trimmed and cut into sheets, for example, 24 feet in length. High pressure water jets may be used to cut and trim the edge. For example, the edge may be trimmed using 2 stationary jets, while the cutting plate is hydraulically jetted to the desired length using a moving cross. At the cutting zone or slightly before, the plate is supported by the conveyor belt moving forward. Also, air jets or similar devices (not shown) may provide the air cushion, as is well known in the art. The belt conveyor (not shown in fig. 4) achieves a higher conveying speed of the sheet thickness.

Non-combustible plate

In a preferred embodiment, a three-layer fiber reinforced panel is prepared in which the core layer has a low content of organic material that allows the core layer to pass the ASTM E136 test method. The improved fiber reinforced panel of the present invention may be classified as a noncombustible panel because various specific standards, such as BOCA, specify that 1/8 inches are cut from the top and lower layers of the panel before the core layer of the panel is subjected to the ASTM test method. The remaining part, i.e. the core layer, becomes non-combustible due to the removal of the surface layer of the paper having a relatively high fibre content. Prior art fiberboards are relatively non-combustible because they employ non-combustible fibers such as asbestos and minerals such as aluminum trihydrate that reduce the release of heat during testing. The panels of the invention pass ASTM E136 testing because the composition of the core layer includes a total of no more than 2% organic material and also includes a minimal amount of 0.6% starch sprayed onto the perlite, with the paper content not exceeding 1.4%, the paper including paper from scrap (fiber) and from recycled board material. The board of the invention, however, has a high strength, which is provided by the high paper fibre content in the surface layer.

In this embodiment, the compositions of the three layers, i.e., the lower surface layer ("SLB"), the upper surface layer ("SLT"), and the intermediate core layer ("CL"), are shown in table 1 below.

Table 1 Components SLB SLT CL size paper fiber 18181.4% stucco 828262% perlite 0036% starch 000.6%

Reinforcing procedure

The strengthening procedure consisted of the following steps: the glass fiber web is spread on a forming belt, and a lower surface layer of mixed paper fibers and stucco is spread over the fiber web, followed by spraying additional water required for hydration. Once the relative position of the surface layer/web has been determined, the core layer and the top layer are mixed, spread and deposited on the lower surface layer. At this point, a three-layer mat is formed and sent to a precompressor to remove the remaining air and add additional water to the upper surface layer required for hydration and convey the mat through a press. The material is pressed in a press and the stucco hardens, binding all of the material in the green sheet together. While the fibre web is firmly embedded in the lower surface layer of the green sheet,

the continuous green sheet exits the press, is cut to the desired size using high pressure water jets, and the individual sheets are transported to a dryer. The free water after hydration is removed and the board is transported to a coating line where a sealing layer is applied to the upper surface of the board. The board is then transported to a second dryer to remove the remaining moisture from the upper surface of the board. The sheet is transported to a finishing line, cut to size, rated and boxed for shipment.

The following examples will illustrate the method of making a gypsum/fiber board product of the present invention wherein the gypsum/fiber board is a three-ply fiber reinforced board having a core layer with a relatively low level of organic material so as to be classified as a non-combustible building material as specified by various building standards (e.g., BOCA) and as a result of testing in accordance with ASTM E136. The board of the invention has a non-combustible rating because the board contains less than about 2% total organic material, also includes a small amount of 0.6% starch sprayed on perlite, and the paper content (including paper from scrap (fiber) and from recycled board material) does not exceed 1.4%. However, the board of the present invention has a high strength, which is provided by the paper content in the surface layer. However, it should be understood that this example is for illustrative purposes only and that many other gypsum fiber products are within the scope of the present invention.

Examples

A composite paperless fiber reinforced gypsum board was prepared in the following manner. Calcined gypsum (hemihydrate gypsum) is mixed with recycled paper fiber, expanded perlite, starch, water and potassium sulfate to make a three-layer board. As shown in table 2 below, three fiber and gypsum formulations were formulated as a lower surface layer ("SLB"), an upper surface layer ("SLT"), and a middle layer ("CL"). These formulations were used to prepare 3-ply gypsum/fiber board having a thickness of 5/8 inches, using the continuous process and equipment described under the heading "multi-ply gypsum fiber board" above.

TABLE 2

SLB% Dry weight SLT% Dry weight CL% Dry weight component fiber 18.018.01.4 Gypsum 82.082.061.4 perlite 0036.6 starch 000.6 Dry weight Total layer 100100100 Water Wet based Total layer in part% 28.028.0 layer of the Board

The fibres used are waste paper fibres from magazines, newspapers and similar materials. "stucco" is about 97% calcium sulfate hemihydrate, the balance being inert impurities. The stucco requires about 18% water by weight to completely form the hydrate. The reinforcing mesh is Bayex 0038/503 described above.

The resulting three-layer panel had a thickness of 5/8 inches and a density of 55 pounds per cubic foot, with the middle layer being 44% and the surface layers each being 28%. Due to the relatively low paper content of the intermediate layer, panels obtained according to the regulations of various building standards (e.g. BOCA) can be classified as non-combustible building materials. The improved fiber reinforced panel of the present invention may achieve a non-combustible rating because 1/8 inches may be cut from both the upper and lower layers of the panel prior to fire testing in accordance with building standards (e.g., BOCA). The remaining part, i.e. the core layer, is non-combustible when tested according to ASTM, due to the removal of the surface layer, which has a relatively high fiber content of the paper. Prior art fiberboards are relatively non-combustible because they employ non-combustible fibers such as asbestos and minerals such as aluminum trihydrate that reduce the release of heat during testing. The board of the invention achieves a non-combustible rating because the composition of the core layer includes a total of no more than about 2% organic material, and also includes a minimal amount of 0.6% starch sprayed onto the perlite, and the content of paper, including paper from scrap (fiber) and from recycled board material, is no more than 1.4%. The board of the invention, however, has a high strength, which is provided by the high paper fibre content in the surface layer. The panels of the invention have superior impact resistance compared to similar panels without the mesh reinforcement, as shown in ASTM test E-695.

The impact resistance of the panels prepared in the following examples was tested according to the test method described under ASTM E695. Several commercially available 5/8 inch thick plaques were also tested according to ASTM E695. The test results are listed in table 3 below.

Table 3 board type impact strength X type gypsum board 120FIBEROCK AR 150 example boards greater than 250

The gypsum board type X is a conventional gypsum board. FIBERROCK AR is a commercial product known as AbuseResistant, which is prepared without a fiberglass mesh. The impact strength of the example panels exceeded the maximum limit of the equipment used to test the panels.

The forms of the invention herein shown and described are to be taken as illustrative only. It will be apparent to those skilled in the art that many changes can be made without departing from the spirit of the invention and the scope of the claims.

Claims (23)

1. A method of making a gypsum/fiber board having improved impact resistance, said method comprising the steps of:

mixing predetermined amounts of fiber, calcined gypsum and water to form a wet loose fiber mixture;

laying a reinforcing net on the upper surface of the forming belt;

depositing said mixture onto said web to form said mixture layer, said mixture layer having a substantially uniform consistency; and

pressing said mesh and said mixture together to embed said mesh in a lower surface of said mixture layer to form a panel of bonded fibers and gypsum with said surface embedded mesh; and

drying the board to obtain a finished board.

2. A method of making a gypsum/fiber board having improved impact resistance, said method comprising the steps of:

mixing predetermined amounts of fiber and water to form a wet loose fiber mixture;

mixing said warm fibers with a predetermined amount of dry calcined gypsum to form a mixed composition;

laying a reinforcing net on the upper surface of the forming belt;

depositing said mixed composition on said web to form said mixed composition layer, said mixed composition layer having a substantially uniform consistency; and

pressing said mesh and said mixed composition together to embed said mesh in the lower surface of said mixed layer to form a sheet comprised of bonded fibers and gypsum with said mesh embedded in the surface thereof; and

drying the board to obtain a finished board.

3. The method of claim 2, further comprising the step of passing a portion of said mixed composition through said mesh openings prior to said pressing step.

4. The process of claim 2 wherein said web is spaced above said forming belt, and said mixed composition is deposited on said web.

5. The method of claim 2, wherein the web is vibrated while the mixed composition is deposited on the web.

6. The method according to claim 2, further comprising the step of adding water to said stacked mixed composition layer.

7. A gypsum/fiber board product made according to the method of claim 2.

8. The gypsum/fiber board product of claim 7 wherein said web is completely embedded in said gypsum/fiber board.

9. The gypsum/fiber board product of claim 7 wherein said web is non-elastic.

10. The gypsum/fiber board product of claim 9 wherein the web is fiberglass.

11. The gypsum/fiber board product of claim 7 wherein said web is woven.

12. The gypsum/fiber board product of claim 11, wherein said woven web is a Leno weave.

13. A method of making a gypsum/fiber board having improved impact resistance, said method comprising the steps of:

mixing predetermined amounts of fiber and water to form a wet loose fiber mixture;

mixing said wet fibers with a predetermined amount of dry calcined gypsum to form a mixed composition;

laying a reinforcing net on the upper surface of the forming belt;

depositing said mixed composition on said web to form a layer of said mixed composition having a substantially uniform consistency;

mixing the low density porous particulate mixture with water to form a warm low density particulate material;

mixing the wet low density porous particles with a predetermined amount of dried calcined gypsum to form a second composition;

depositing a second composition on the first layer to form a second layer having a substantially uniform consistency;

mixing the wet fibers with a predetermined amount of dried calcined gypsum to form a third composition;

depositing the third composition on the second layer to form a third layer having a substantially uniform consistency; and

pressing said mesh and said three layers together to embed said mesh in the surface of said first layer to form a panel of bonded fibers and gypsum with said embedded-in-surface mesh; and

drying the board to obtain a finished board.

14. The method of claim 13, further comprising the step of passing a portion of said blended composition through said mesh openings prior to said pressing step.

15. The process according to claim 13, wherein said web is spaced above said forming belt, and said first mixed composition is deposited on said web.

16. The method of claim 13, wherein the web is vibrated while the first mixed composition is deposited on the web.

17. The method of claim 13, further comprising the step of adding water to said stacked first mixture layer.

18. A gypsum/fiber board product made according to the method of claim 13.

19. The gypsum/fiber board product of claim 18, wherein said mesh is completely embedded in said gypsum/fiber board.

20. The gypsum/fiber board product of claim 18 wherein said web is non-elastic.

21. The gypsum/fiber board product of claim 20 wherein said web is fiberglass.

22. The gypsum/fiber board product of claim 18 wherein said web is woven.

23. The gypsum/fiber board product of claim 22, wherein said woven web is a Leno weave.