EP1408171A1 - Glass fiber facing sheet and method of making same - Google Patents

Abstract

The invention provides a glass fiber facing sheet for engineered surfaces such as cement boards which reduces the pitting associated with open mesh glass scrims. The glass fiber facing sheet comprises an open mesh glass scrim having a plurality of intersecting continuous multifilament yarns which are bonded at their crossover points to provide dimensional stability to the scrim. A melt blown polymer web is preferably joined to one face of the glass scrim and covers the mesh openings in the scrim. The opposed face of the scrim defines an exposed grid profile surface which is available for mechanical interaction between the scrim and the cementitious slurry used in cement boards. In cement boards, the glass fiber facing sheet of the present invention is preferably mechanically integrated into a surface portion of the cement core along the exposed grid profile of the scrim. A second facing sheet may also be mechanically integrated into an opposed surface portion of the cement core and contain a melt blown polymer web joined to one face. The present invention further includes a method of making the glass fiber facing sheet of the invention and a method of making a smooth cement board containing the glass fiber facing sheet of the invention.

Description

Field of the Invention
• The invention relates to glass fiber facingsheets for cement boards and a method of making same,and more particularly, relates to nonwoven, open meshfacing sheets formed of continuous glass yarns, to amethod of making same and to engineered surfaces,specifically, cement boards including such facing sheetmaterial.
Background of the Invention
• Interior and exterior construction boardswith cores of plaster, cement, or hybrid materials,such as cement boards or gypsum boards, are used in awide variety of indoor and outdoor structuralapplications. For example, cement boards are used as asupport surface for overlying materials such as woodsiding, stucco, synthetic stucco, aluminum, brick,tile, stone aggregate and marble. In addition, cementboards are used in exterior insulating systems,commercial roof deck systems, and exterior curtainwalls.
• Generally, cement boards contain a coreformed of a cementitious material which is interposedbetween two layers of facing material. The facingmaterial advantageously contributes flexural and impactstrength to the high compressive strength but brittlematerial forming the hardened cementitious core. In addition, the facing material can provide a durablesurface and/or other desirable surface properties tothe cement board.
• One material which has been used to formfacing sheet material is glass fibers. In addition toincreased dimensional stability in the presence ofmoisture, glass fiber facings provide greater physicaland mechanical properties to the cement board. Asdescribed, for example, in U.S. Pat. No. 5,371,989 toLehnert et al., the method of making cement boardscontaining glass fiber facing sheets typically consistsof providing a continuous feed of the facing materialand depositing a cementitious slurry onto the topsurface of the facing material. A second continuousfeed of facing material is then applied to the topsurface of the slurry. The slurry is then dried toharden the cementitious composition and to integratethe facing material in the cement board. The cementboard is cut to a predetermined length for shipping andfor its eventual use.
• U.S. Pat. No. 4,647,496 to Lehnert et al.describes the use of randomly oriented fibrous glassmats as the facing material for gypsum boards.Additionally, U.S. Pat. No. 5,397,631 to Green et al.describes coating a gypsum board including a randomlyoriented glass mat with a water-resistant resinousbinder to prevent the deterioration of the bond betweenthe gypsum and the glass mat.
• An alternative to the randomly orientedfibrous glass mats to reinforce cement boards is theuse of open mesh glass scrims formed from continuousglass yarns. Because these scrims contain continuousyarns, they possess greater tensile strength than therandomly oriented fibrous glass mats. For example,U.S. Pat. No. 3,993,882 to Knauf et al. describes usinga facing sheet formed of a glass fabric. In addition,published European patent application 637,658 to Bay Mills Limited describes the use of glass rovings toform nonwoven scrims for stucco boards.
• In order to reduce glass usage, the mesh sizeof the glass scrims may be increased thus reducing thenumber of yarns or "picks per inch" in the transverseand/or the longitudinal direction without reducing thestrength of the cement board. Nevertheless, theresulting increase in the size of the mesh openings inthe glass fiber facing sheet causes other problems.Particularly, when the open mesh facing is applied to acementitious slurry, pitting or the formation ofindentations may occur in the center of the meshopenings which negatively affects the aestheticappearance and surface properties of the cement board.
Summary of the Invention
• The present invention provides a glass fiberfacing sheet for engineered surfaces such as formasonry applications, roofing applications, and thelike, preferably for cement board. The glass fiberfacing sheet provides a smooth surface which isessentially free of pitting. The glass fiber facingsheet is created from a minimal amount of materialcompared to glass fiber facing sheets that use aheavier weight scrim, thus reducing the cost and weightof the resulting cement board or other product butwithout significant negative impact on the physical andmechanical properties of the final product.
• In accordance with the present invention, theglass fiber facing sheet comprises an open mesh glassscrim having a plurality of intersecting glass yarnswhich are bonded at their crossover points to providedimensional stability to the scrim. The glass scrim ofthe present invention is preferably a nonwoven scrimcomprising generally transverse and generallylongitudinal yarns having less than 100 mesh openingsper square inch, i.e., less than 10 by 10 picks per inch. Preferably, the glass yarns are bonded throughthe use of a polymeric binder. A polymer web is joinedto one or both faces of the glass scrim and covers atleast a portion of the mesh openings in the scrim. Thepolymer web is formed of melt blown polymer fiberswhich are preferably formed directly on the surface ofthe scrim. The melt blown polymer web is generally alow strength web that does not contribute significantlyto the strength of the cement board. Nevertheless, thepolymer web causes a cementitious slurry or otherliquid used to form cement board, roofing materials andthe like, to window pane evenly over the mesh openingson the exterior of the scrim thus improving theappearance and, at least in some cases the strength ofthe final product, e.g., cement board, by improving theinteraction of the liquid or slurry and the glassscrim. Because the melt blown web is typically thinand is normally applied to only one face of the glassscrim, the opposed face of the scrim provides anexposed three-dimensional grid profile surface whichremains available to interact mechanically withhardenable liquids such as the cementitious slurry usedin the cement board. Accordingly, when used in formingcement board, the glass fiber facing sheet of thepresent invention is mechanically integrated into asurface portion of the cementitious core by virtue ofthe exposed grid profile surface of the scrim. Asecond open mesh glass scrim may be mechanicallyintegrated into the other surface of the cement core tofurther enhance the properties of the cement board andmay also include a melt blown polymer web on thesurface of the scrim.
• In one preferred embodiment of the invention,the melt blown polymer web applied to the surface ofthe glass scrim has a basis weight of between about 2and 30 g/m² (grams per square meters of scrim). Cementboard formed using this facing sheet has a smooth exterior surface with little or no pitting. In anotherpreferred embodiment of the invention, the melt blownpolymer web applied to the surface of the open meshglass scrim has a higher basis weight of between about10 and 50 g/m². The basis weight of the melt blownpolymer web in this embodiment provides variousdesirable surface properties including a smoothfinished exterior surface which can be painteddirectly.
• In yet another preferred embodiment of theinvention, the melt blown polymer web applied to thesurface of the glass scrim has an even higher basisweight of between about 45 and 75 g/m². The melt blownpolymer web may then be subjected to heat and pressureto melt and coalesce the fibers in the polymer web toform a microporous layer. The microporous layerprovides a water resistant surface which nonethelessallows gases such as water vapor to pass through theweb. Alternatively, a microporous film such as a highdensity polyethylene film may be applied to the facingsheet prior to or following deposition of the meltblown polymer web to provide essentially the sameresult.
• In a preferred method embodiment of theinvention, the present invention includes a method ofcreating a glass fiber facing sheet for engineeredsurfaces on products such as cement boards. Accordingto this preferred embodiment, the melt blown polymerweb is generally formed directly on the surface of thescrim and is preferably formed from an adhesive polymercomposition which adheres to the surface of the scrim.In another preferred method embodiment, the presentinvention includes a method of making an engineeredsurface comprising providing a method of making anengineered surface comprising providing a facing sheetcomprising an open mesh glass scrim defined by aplurality of intersecting, continuous filament glass yarns bonded at crossover points thereof and a meltblown polymer web joined to one face of the glass scrimand covering at least a portion of the mesh openingsthereon, the opposed face of the glass scrim definingan exposed grid profile surface, integrating theexposed grid profile surface of the facing sheet into asurface portion of a cementitious slurry layer, andallowing the cementitious slurry layer to harden toform the engineered surface.
• The present invention further includes amethod of making a cement board using the glass fiberfacing sheet of the invention. The glass fiber facingsheets can be used to prepare cement boards of varioustypes using conventional cement board manufacturingapparatus and manufacturing layouts. The methodcomprises providing a first facing sheet, preferablyformed of glass fibers, and depositing a firstcementitious slurry onto and through the facing sheet.A second cementitious slurry typically varying inmaterial composition and/or viscosity from the firstcementitious slurry may optionally be deposited on thefirst cementitious slurry. A glass fiber facing sheetformed according to the method described above is thenapplied to the cementitious slurry with the exposedgrid profile directly contacting the cementitiousslurry. An additional cementitious slurry preferablyhaving a low viscosity may optionally be applied to thesurface of the glass fiber facing sheet. Thecementitious slurry(s) and the glass fiber facingsheet(s) are then preferably pressed to controlthickness and consolidate the materials and thecementitious material hardened, for example by heating,to mechanically integrate the exposed three-dimensionalgrid profile surface of the glass fiber facing sheetinto the cementitious core thereby forming the cementboard.
• Cement boards including the glass fiberfacing sheet of the present invention have a smoothfinish with little or no pitting. In addition, theseboards can be lighter and/or less expensive thanconventional cement boards while possessing mechanicaland physical properties comparable to or exceedingconventional boards.
Brief Description of the Drawings
• In the drawings which form a portion of theoriginal disclosure of the invention:
• Figure 1 illustrates a perspective view ofone glass fiber facing sheet of the invention includinga melt blown polymer web having a density of betweenabout 2 and 30 g/m² according to a preferred embodimentof the invention.
• Figure 2 illustrates a perspective view ofone glass fiber facing sheet of the invention includinga melt blown polymer web having a density of betweenabout 10 and 50 g/m² according to an alternativepreferred embodiment of the invention.
• Figure 3 illustrates a perspective view ofone glass fiber facing sheet of the invention includinga melt blown polymer web having a density of betweenabout 45 and 75 g/m² and which has been melted to form amicroporous film according to an alternative preferredembodiment of the invention.
• Figure 4 illustrates a plan view of the glassfiber facing sheet inFigure 1 taken from the bottomthereof and illustrates the exposed grid profile of thefacing sheet.
• Figure 5 schematically illustrates onepreferred method of forming the melt blown polymer webon one face of the glass scrim to form a glass fiberfacing sheet according to the invention.
• Figure 6 schematically illustrates onepreferred method of making a cement board including theglass fiber facing sheet of the invention.
• Figure 7 illustrates a perspective view of acement board including a glass fiber facing sheet ofthe invention.
• Figure 8 is a sectional view of the cementboard inFigure 7 along line8-8.
Detailed Description of the Preferred Embodiments
• In the following detailed description,preferred embodiments of the invention are describedand discussed in detail to enable practice of theinvention. It will be apparent that although specificterms are used to describe the preferred embodiments,these are used in the descriptive sense and not for thepurpose of limiting the invention thereto. It willalso be apparent that the invention is susceptible to awide variety of changes as will become apparent from aconsideration of the preferred embodiments of theinvention as shown in the attached drawings anddescribed in detail below.
• Figure 1 illustrates a glassfiber facingsheet10 for an engineered surface such as cement board12 according to one preferred embodiment of theinvention. The glassfiber facing sheet10 of theinvention comprises an open mesh glass scrim15 and amelt blownpolymer web20. The open mesh glass scrim15 is formed by a plurality of intersecting, continuousmultifilament,glass yarns25 and30 which are bondedat their crossover points35 to provide dimensionalstability to the glass scrim. Preferably, as shown inFigure 1, the open mesh glass scrim is formed by aplurality of generally transverse glass yarns25 and aplurality of generallylongitudinal glass yarns30which are bonded at their crossover points35 toprovide dimensional stability to the glass scrim. As will be apparent, the glass scrim 15 can be formed fromor include yarns of various orientations in place of orin addition to the generally transverse and generallylongitudinal yarns illustrated in Figure 1 includingdiagonally oriented yarns, randomly oriented yarns, andyarns in a 0°/60°/120° orientation, which intersect andare bonded at their crossover points and define agenerally open mesh scrim. The scrim15 can be woven,knitted or nonwoven. Preferably, scrims such as scrim15 comprising transverse yarns25 and thelongitudinalyarns30 are nonwoven. The glass scrim15 can beformed by the apparatus and process of U.S. Patent No.4,242,779 issued January 6, 1991 to Curinier et al.which is hereby incorporated by reference. Thisprocess involves using an apparatus for forming a webof transverse (weft) yarns25 for use in the scrim15and subsequently superimposing one or more webs oflongitudinal (warp)yarns30 on the web of weft yarnsto form the open mesh glass scrim.
• Preferably, the quantity of glass yarns usedto form the glass scrim15 is minimal, thereby reducingthe cost and the weight of the resulting cement boardusing the glassfiber facing sheet10. Nevertheless,the amount of continuous glass yarns used in the glassscrim15 are sufficient to impart the desired physicaland mechanical properties to the scrim15 and the glassfiber facing sheet10. Therefore, scrims havinggenerally transverse25 and generallylongitudinalyarns30 are preferred. The amount of generallytransverse yarns25 and generallylongitudinal yarns30may be defined by the "picks per inch" or pick count ofthe scrim15. Alternatively, the number of transverseyarns25 andlongitudinal yarns30 may be defined bythe number ofmesh openings40 in the glass scrim15.Preferably, the glass scrim15 has less than about 100mesh openings per square inch (i.e, a pick count ofless than 10 by 10). More preferably, the glass scrim 15 has less than about 70 mesh openings per square inchor even less than about 50 mesh openings per squareinch. Generally, the individual yarns used to form thescrim can have a size ranging from about 900 yds/lb toabout 9,000 yds/lb.
• The transverse yarns25 and thelongitudinalyarns 30 are bonded at their crossover points35 toprovide dimensional stability to the scrim15 andtherefore to the glassfiber facing sheet10.Preferably, the transverse yarns25 and thelongitudinal yarns30 are bonded at their crossoverpoints35 by a polymeric binder. The polymeric binderis preferably applied as a low viscosity coating sothat it can uniformly penetrate into the transverseyarns25 andlongitudinal yarns30 and coat thefilaments forming the yarns. Numerous differentpolymeric binders capable of penetrating the transverseyarns25 and thelongitudinal yarns30 and interlockingthe transverse yarns and longitudinal yarns together attheir crossover points35 can be used in the invention.Preferably, the polymeric binder is an alkali andmoisture resistant thermoplastic or thermosettingpolymer coating which can, in addition to providingdimensional stability to the scrim, also preventchemical interaction between the cementitious materialsforming the core of the cement board and the glassfilamentary material, particularly when an alkalineand/or silicious cementitious material, e.g. Portlandcement, is contained in the core of the cement board.Exemplary moisture resistant materials for thepolymeric binder include polyvinyl chloride, polyvinylacetate, polyvinylidene chloride, polyvinyl alcohol,styrene butadiene rubber, urethane, silicone, metallicresinates, wax, asphalt, acrylic resins, styreneacrylate copolymers, aromatic isocyanates anddiisocyanates, organohydrogenpolysiloxenes, thermosetresins such as epoxies and phenolics, mixtures thereof, and the like. The preferred polymeric binder forbinding the transverse yarns25 and thelongitudinalyarns30 is polyvinyl chloride (PVC) which is appliedas a plastisol. Preferably, the polymer coating isapplied to the scrim in between about 5 and 150 partsdry weight of resin to 100 parts by weight of fabric.In other words, the coating is applied at 5% to 150%dry weight pick-up.
• A melt blownpolymer web20 is preferablyjoined to the glass scrim15 on one face45 of thescrim, but may be applied on both faces of the scrim.The melt blownpolymer web20 covers at least a portionof themesh openings40 in the glass scrim15,preferably, a significant portion (e.g. most, if notall) of the mesh openings. The term "covers" as usedin this context includes both partial and completecoverage of the mesh openings. Thepolymer web20 ispreferably composed of a plurality of randomly orientedmelt blown polymer fibers. Preferably, the melt blownweb partially and uniformly covers the mesh openings,i.e., each opening includes a porous web that onlypartially covers the scrim opening because of theopenings in the porous web. The melt blown polymerfibers preferably are formed from an adhesive polymerso that the web adheres to the face45 of the glassscrim15 without requiring application of a separateadhesive layer. Therefore, the polymer used for themelt blownpolymer web 20 is typically a polymer whichpossesses a certain tackiness to the glass surface orthe polymeric binder, at least when the fibers are at atemperature above their softening point (e.g. 350° to400°F). Such materials include polyolefins such aspolypropylene, polyethylene and amorphous poly(α-olefins);ethylene copolymers such as ethylene vinylacetate or ethylene methacrylate copolymers, polyesterssuch as polyethylene terephthalate; polyamides;polyacrylates; polystyrene; styrene block copolymers; thermoplastic elastomers; mixtures thereof; and otherknown fiber forming thermoplastic materials.Preferably, the polymer used to form the melt blownpolymer web 20 is not tacky at temperaturesconsiderably below its softening point (e.g. at roomtemperature) to allow the facing sheet to be rolled andunrolled without sticking to itself, i.e., withoutadherence between the opposed face of the scrim and themelt blown polymer web. Preferred melt blown polymersinclude amorphous poly(α-olefin) polymers (e.g. 8494-36Gfrom National Starch and Chemical Co.) andpolyamides (e.g. HL-6520-X from HB Fuller Co.)
• The amount of melt blown fibers forming thepolymer web20 and applied to the face45 of the glassscrim15 is normally described in terms of basisweight, or grams of melt blown fibers per square metersof glass scrim surface. Preferably, the basis weightof the melt blownpolymer web20 is between about 1 and100 g/m². In one preferred embodiment, illustrated inFigure 1, the basis weight of the melt blownpolymerweb20 is about 2 and 30 g/m².
• The melt blownpolymer webs20 illustrated inFigure 1 have very little inherent strength and areessentially nonstructural. Nevertheless, as describedherein, the melt blown polymer web prevents pitting(i.e. indentations caused when the slurry used to formthe cementitious core sinks into the mesh openings ofthe glass scrim). This is particularly a problem inthe large open mesh glass scrims that are used inpreferred embodiments of the present invention. Themelt blownpolymer web20 maintains a portion of thecementitious slurry on the surface of the glassfiberfacing sheet10 and causes the slurry to "window pane"themesh openings40 of the glass scrim15 therebyforming a substantially planar bridge surface betweenthe transverse andlongitudinal yarns 25 and 30.Accordingly, at least in some cases, the melt blownpolymer web20 increases the composite strength of thecement board12 by improving the mechanical integrationof the facingsheet10 into the cement board 12.
• Figure 2 illustrates a glass fiber facingsheet110 according to an alternative preferredembodiment of the invention. In Figure 2, the basisweight of the melt blown polymer web120 is betweenabout 10 and 50 g/m². The increased basis weight of themelt blown polymer web120 over the embodimentillustrated in Figure 1 provides a correspondingincrease in the inherent strength of the web.Nevertheless, the majority of the strength provided bythe facing sheet110 in the cement board12 is providedby the glass scrim15. In the embodiment shown inFigure 2, the higher basis weight melt blown polymerweb120, which by itself is relatively weak, combineswith the cementitious slurry to provide variousdesirable surface properties including a smoothfinished exterior surface which can be painted directlywithout requiring any additional material on thesurface of the cement board.
• Figure 3 illustrates a glassfiber facingsheet210 according to yet another embodiment of theinvention. In Figure 3, the melt blown polymer web220applied to the surface of the glass scrim 15 has aneven higher basis weight of between about 45 and 75g/m². As in Figure 2, the increased basis weight overthe embodiment illustrated in Figure 1 does increasethe inherent strength of the web220 but the majorityof the strength provided by the facingsheet210 isstill provided by glass scrim15. The melt blownpolymer web220 may be subjected to heat and pressureto melt and coalesce the melt blown fibers in thepolymer web to form a microporous layer220. Themicroporous layer220 provides a water resistantsurface which nonetheless allows gases such as watervapor to pass through the facingsheet210. The microporosity of the layer220 can be particularlydesirable in the formation of cement boards because thecement used in the core of the cement board is ahydrated compound and therefore water vapor may beevaporated from the hydrated cement. The microporouslayer 220 allows the water vapor to pass through theglass scrim 15 thus preventing the buildup of moistureon the interior of the facingsheet210 and theeventual corrosion of the cement board.
• In the embodiments illustrated in Figures 1-3,the glass fiber facing sheet may additionallyinclude a microporous film (not shown) either betweenthe glass scrim15 and the melt blownpolymer web20,120, 220 or on top of the melt blown polymer web. Themicroporous layer provides all the benefits describedwith respect to the embodiment of Figure 3. Suitablemicroporous films include the polymers described foruse as melt blown polymer fibers. Preferably, themicroporous layer is a microporous high densitypolyethylene film.
• As described above, the melt blownpolymerweb20 is preferably applied to one face45 of theglass scrim15 to form the glassfiber facing sheet10.The opposed face50 of the glass scrim15 is preferablynot covered by the melt blownpolymer web20 anddefines an exposed three-dimensional grid profilesurface55 as illustrated in Figure 4. The gridprofile surface55 is available to interactmechanically with a cementitious slurry used in thecement board12. As described below, this allows theglassfiber facing sheet10 to be mechanicallyintegrated into a surface portion of the cementitiouscore by virtue of the exposed grid profile surface55of the scrim15.
• The present invention also includes a methodof making a glassfiber facing sheet10 for anengineered surface such as the surface of cement board12 according to the invention. First, the glass scrim15 is created from a plurality of intersecting yarnssuch as generally transverse yarns25 and generallylongitudinal yarns30. As stated above, the glassscrim15 may include other yarn orientations.Typically, the scrim15 is created by forming a web ofweft yarns and then superimposing one or more webs ofwarp yarns as described in U.S. Patent No. 4,242,779.Alternatively, the generally transverse yarns25 andgenerallylongitudinal yarns30 can be woven or knittedto form the glass scrim15. Once the glass scrim15 isformed, the transverse yarns25 andlongitudinal yarns30 are interlocked at their crossover points35 toprovide dimensional stability to the glass scrim15.As described above, preferably this is accomplished byapplying a polymer coating to the scrim15. Generally,the glass scrim15 is coated by the polymer coating bypassing the glass scrim through a resinous bathcontaining the coating and then allowing the coating toharden on the surface and throughout the transverseyarns25 andlongitudinal yarns30 of the glass scrim.Typically, the coating is hardened on the scrim15 byheating the coated glass scrim to set the polymericbinder.
• Once the glass scrim15 is formed and coatedwith the polymeric binder, the melt blownpolymer web20 is preferably formed onto one face45 of the glassscrim15 to cover themesh openings40 thereon. Thisprovides an exposed grid profile surface55 on theopposed face of the glass scrim15 for mechanicalinteraction with the cementitious composition of thecement board. The melt blownpolymer web20 can beformed onto the face45 of the glass scrim15 in an"on-line" process prior to taking the coated glassscrim up on rolls (e.g. roll60 in Figure 5) oralternatively, the melt blown polymer web can be formed on the face of the coated glass scrim 15 after it istaken up on rolls in an "off-line" process.
• Figure 5 schematically illustrates theapplication of the melt blownpolymer web 20 to theface 45 of the glass scrim 15 to form the glassfiberfacing sheet 10 of the invention by forming a meltblown web directly on the glass scrim using aconventional melt blowing apparatus. Melt blowingapparatus are known to the skilled artisan and aredisclosed, for example, in U.S. Patent No. 3,849,241 toBuntin et al. and U.S. Patent No. 4,048,364 to Hardinget al. The melt blowing process involves supplyingpolymeric pellets or other polymer materials to amelting apparatus 64 such as an extruder, melting themolten polymeric material in the melting apparatus, andpumping it to melt blowing heads 66. The filamentarystreams exit theheads 66 where high velocityconverging streams of a heated gas, typically air, aresupplied from nozzles. The converging streams of highvelocity heated gas attenuate the polymer streams anddeposit same on the surface of glass scrim 15. Thefibers are randomly oriented and together form the meltblownpolymer web 20. Once the melt blownpolymer web20 has been formed on the surface of the glass scrim15, the web/scrim laminate constituting the facingsheet 10 of the invention, may be taken up on acollectingroll 70. Alternatively, the facingsheet 10can be formed "on-line" in a process of forming anengineered surface such as cement board without beingcollected on rolls prior to use in forming the finalproduct, e.g. cement board.
• In the event that the melt blownpolymer web20 is to be melted to form a microporous layer 220 asdescribed with respect to the embodiment in Figure 3,the process of making the glassfiber facing sheet 10can include a heater (not shown) or alternative meansfor melting and coalescing the melt blown fibers to form the microporous layer. Alternatively, if aseparate microporous film is to be applied to thesurface of the glass scrim15 prior to applying themelt blownpolymer web20, then an additional meltblown apparatus and head (not shown) can be providedbefore themelt blowing apparatus62 to form a lightweight tacky web on the surface of the glass scrim15thereby allowing the microporous film to bond thereto.Additionally, it may be advantageous to apply aseparate microporous layer on the melt blown polymerweb, in which case, the additional melt blown apparatusand head would be provided after themelt blowingapparatus62.
• Figure 6 illustrates formation of a cementboard12 employing the glassfiber facing sheet10 ofthe invention using conventional cement boardmanufacturing apparatus and layouts. As shown inFigure 6, a first facing sheet72 having any of variousconstructions is provided and the cement board12formed thereon. The first facing sheet72 can, forexample, be an open mesh glass scrim comprising aplurality of generally transverse yarns and generallylongitudinal yarns optionally containing a melt blownpolymer web as described above or any other materialwhich can be used as a facing material for the cementboard12. The first facing sheet72 is typicallyformed of glass fibers and supplied by a roll74 orother suitable means and a firstcementitious slurry76is provided from a mixer78 and deposited onto thesurface of the facing sheet72. Thecementitiousslurry76 can be formed of numerous differentcompositions of varying moisture content. Exemplarycementitious materials include hydraulic cements suchas aluminous cement, Portland cement, gypsum cements,mixtures thereof with aggregates or polymer binders,and the like as will be known to the skilled artisan.Additional mixers such as mixer92 can be installed between mixer78 andpressing rolls80 for theapplication of an additional cementitious material suchasslurry93 which may differ in viscosity and/orcomposition from the firstcementitious slurry76.Preferably, a secondcementitious slurry93 when usedhas a higher viscosity and generally contains largeraggregate particles thanslurry76.
• As shown in Figure 6, the glassfiber facingsheet10 of the invention can be supplied from a roll70 ("off-line") or formed on-line. Anadditional mixer90 can be used to apply a low viscosity cementitiousslurry91 to facingsheet10. The low viscosity slurry91 will generally pass through the glassfiber facingsheet10 but will also window pane over themeshopenings40 to create a smooth surface on the cementboard. The glassfiber facing sheet10 is then appliedto the cementitious slurry76 (and optionallycementitious slurry93) such that the exposed threedimensional grid profile surface55 on the lower face50 of the glass scrim15 directly contacts thecementitious slurry(s). The glassfiber facing sheet10, thecementitious slurry76 or slurries and thefacing sheet72 are then pressed together such as byone or morepressing rolls80, a doctor blade or anyother suitable means. When the glassfiber facingsheet10 is pressed into thecementitious slurry76 orslurries, the cementitious slurry is forced up throughthemesh openings40 of the glassfiber facing sheet10. The force of gravity then causes thecementitiousslurry76 to sink back down away from the glassfiberfacing sheet10 and form meniscuses within the meshopenings. Nevertheless, the melt blownpolymer web20prevents thecementitious slurry76 from sinking intothelarge mesh openings40 of the glassfiber facingsheet10. Instead, the melt blownpolymer web20maintains a portion of thecementitious slurry76 onthe surface of the glassfiber facing sheet10 and causes the slurry to window pane themesh openings40of the glass scrim15 thereby forming a substantiallyplanar bridge surface between the transverse andlongitudinal yarns,25 and30. As a result, the glassfiber facing sheet10 becomes mechanically integratedinto the cement board12 once thecementitious slurry76 or slurries harden to thereby provide a generallyuniform planar exterior surface on the cement board12.
• In the hardening of thecementitious slurry76 or slurries, the cementitious material becomeshydrated. This process can be accelerated by theapplication of heat such as from heater82. Duringhardening of theslurry76, the exposed threedimensional grid profile surface55 of the glassfiberfacing sheet10 becomes mechanically interlocked intothe cement board12 since the grid profile surfaceallows the fluid slurry to intimately contact thefilament yarns25 and30 forming the scrim15 around asubstantial portion of their cross-sections.Preferably thecementitious slurry76 substantiallyfully surrounds the cross-section of the longitudinalandtransverse yarns25 and30 to achieve a high levelof mechanical integration of the facingsheet10 intothe core when the slurry hardens. Once the cementboard is formed, it may be cut by appropriate means84into boards such as 4' x 8' x 7/16" boards. Theresulting cement board is illustrated in Figure 7.
• Figure 8 illustrates a cross-section of thecement board12 illustrated in Figure 7 along line 8-8.As shown in Figure 8, the glassfiber facing sheet10comprising the glass scrim15 and the melt blownpolymer web20 is mechanically integrated into asurface portion86 of thecementitious core80 formingthe cement board. In addition, the facing sheet72 ismechanically integrated into anopposed surface portion90 of thecementitious core80.
• As will be apparent from the foregoing, theglassfiber facing sheet10 of the present inventionprovides a smooth cement board12 which is essentiallyfree of pitting. The glassfiber facing sheet10 canbe constructed using fewer continuous glass yarns perunit length of the scrim fabric, thus reducing the costof the resulting cement board12 but without negativelyaffecting the physical and mechanical properties of thecement board.
• The cement boards including the glass fiberfacing sheet of the invention can be used in a widevariety of indoor and outdoor structural application.For example, cement boards are used as a supportsurface for overlying materials such as wood siding,stucco, synthetic stucco, aluminum, brick, tile, stoneaggregate and marble. In addition, cement boards areused in exterior insulating systems, commercial roofdeck systems, and exterior curtain walls. In additionto cement boards, the facing sheet of the invention canbe used with other engineered surfaces in masonryapplications, roofing applications and the like.
• The invention has been described inconsiderable detail with particular reference topreferred embodiments. However, numerous variationsand modifications can be made without departing fromthe spirit and scope of the invention as described inthe foregoing specification and shown in the drawingsand defined in the following claims.

Claims (27)

1. A method of making a cement board comprising:

   providing a first facing sheet;

   depositing a first cementitious slurry on the firstfacing sheet to form a first cementitious slurry layer incontact with said first facing sheet on one side thereof;

   applying a second facing sheet to the opposed sideof said slurry layer, said second facing sheet comprisingan open mesh glass scrim defined by a plurality ofintersecting, continuous filament glass yarns bonded atcrossover points thereof and a melt blown polymer webjoined to one face of the glass scrim and covering atleast a portion of the mesh openings thereon, the opposedface of the glass scrim defining an exposed grid profilesurface, said second facing sheet being applied to saidslurry layer such that said exposed grid profile surfaceis orientated in a direction toward said slurry and isapplied to the first cementitious slurry; and

   allowing the cementitious material to harden to formthe cement board so that said open mesh profile surfaceof said second facing sheet mechanically interlocks saidsecond facing sheet in the cement board.
2. The method according to claim 1, wherein saidapplying step comprises a second facing sheet comprisingan open mesh glass scrim defined by a plurality generally transverse and generally longitudinal, continuousfilament yarns.
3. The method according to claim 1, wherein saidproviding step includes providing a first facing sheetcomprising an open mesh glass scrim.
4. The method according to claim 3, wherein said openmesh glass scrim is defined by a plurality of generallytransverse and generally transverse longitudinal,continuous filament glass yarns bonded at crossoverpoints thereof.
5. The method according to claim 3, wherein said firstfacing sheet further comprises a melt blown polymer webjoined to one face of the glass scrim and uniformlycovering at least a portion of the mesh openings thereon.
6. The method according to claim 1, wherein saiddepositing step comprises depositing a material selectedfrom the group consisting of hydraulic cement and gypsumcement.
7. The method according to claim 1, further comprisingdepositing a second cementitious slurry on the firstcementitious slurry layer prior to said applying step, said second cementitious slurry having at least one of adifferent viscosity and a different composition than thefirst cementitious slurry.
8. The method according to claim 1, further comprisingdepositing a low viscosity cementitious slurry on saidsecond facing sheet after said applying step.
9. The method according to claim 1, further comprisingthe step of pressing the first and second facing sheetsinto the cement slurry.
10. The method according to claim 1, wherein saidallowing step comprises heating the slurry to allow theslurry to harden.
11. The method according to claim 1, further includingthe steps of:

    providing an open mesh glass scrim from a pluralityof intersecting, continuous filament glass yarns;

    applying a polymer coating to said scrim tointerlock the yarns at their crossover points; and

    forming a melt blown polymer web onto one face ofthe open mesh glass scrim over at least a portion of themesh openings thereon to provide an exposed grid profilesurface on the opposed side of said scrim for mechanical interaction with a cementitious composition of saidcement board.
12. A method of making a glass fiber facing sheet for anengineered surface comprising:

    providing an open mesh glass scrim defined by aplurality of intersecting, continuous filament glassyarns;

    applying a polymer coating to said scrim tointerlock the intersecting yarns at their crossoverpoints; and

    forming a melt blown polymer web onto one face ofthe open mesh glass scrim to cover at least a portion ofthe mesh openings on said one face and to provide anexposed grid profile surface on the opposed face of theopen mesh glass scrim for mechanical interaction with acementitious composition.
13. The method according to claim 11 or 2, wherein saidstep of providing an open mesh glass scrim comprisesproviding a glass scrim comprising a plurality ofgenerally transverse and generally longitudinal yarns.
14. The method according to claim 11 or 12, furthercomprising the step of heating the scrim after said stepof applying a polymer coating.
15. The method according to claim 14, wherein thepolymer coating comprises polyvinyl chloride.
16. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webhaving a basis weight between about 2 and 30 g/m².
17. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webhaving a basis weight between about 45 and 50 g/m².
18. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webhaving a basis weight between about 10 and 75 g/m².
19. The method according to claim 18, further comprisingmelting the polymer to form a microporous layer on oneface of the scrim.
20. The method according to claim 11 or 12, furthercomprising the step of applying a microporous layer ontothe glass scrim prior to forming the melt blown polymerweb.
21. The method according to claim 11 of 12, furthercomprising the step of applying a microporous layer ontothe melt blown polymer web after said forming step.
22. The method according to claim 13, wherein said stepof providing an open mesh glass scrim comprises providinga scrim having less than about 100 mesh openings persquare inch.
23. The method according to claim 13, wherein said stepof providing an open mesh glass scrim comprises providinga scrim having less than about 70 mesh openings persquare inch.
24. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webconsisting of a material which is tacky at a temperatureabove its softening point to facilitate adhesion betweensaid melt blown polymer web and said glass scrim butwhich is essentially free of tackiness at temperaturesconsiderably below its softening point to thereby allowsaid facing sheet to be rolled and unrolled withoutadherence between said opposed face and said melt blownpolymer web.
25. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webcomprising a polymer selected from the group consistingof polyolefins ethylene copolymers, polyesters,polyamides, polyacrylates, polystyrene, styrene blockcopolymers, thermoplastic elastomers, and mixturesthereof.
26. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webcomprising an amorphous poly (α-olefin) polymer.
27. The method according to claim 11 or 12, wherein saidforming step comprises forming a melt blown polymer webcomprising a polyamide.

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