RU2800147C2 - Borate and silicate coating for improving acoustic characteristics of panels and methods for its manufacture - Google Patents

Abstract

FIELD: fibrous panels.

SUBSTANCE: invention relates to coatings for improving the acoustic characteristics of panels and methods for their manufacture. The invention proposes is a fibrous panel containing starch and mineral wool fiber, having a rear surface and an opposite front surface, where the panel has a cured coating layer that contains from 10 to 100 wt.% of an inorganic binder, based on the total dry coating weight, while the specified inorganic binder comprises a borate salt and at least one of an alkali metal silicate or an alkaline earth metal silicate, and the inorganic binder is water soluble. A method for coating a fibrous panel is also proposed.

EFFECT: panel has improved acoustic performance and increased sag resistance.

10 cl, 1 dwg, 3 tbl, 2 ex

Description

FIELD OF TECHNOLOGY

[0001] This invention generally relates to a curable coating composition for acoustic panels, acoustic panels coated with a curable coating composition according to this invention, and methods of making the same. More specifically, this invention relates to a curable coating comprising an inorganic borate and silicate binder, said binder being water soluble.

BACKGROUND OF THE INVENTION

[0002] Acoustic panels (or slabs) are specially designed systems that are designed to improve acoustic properties by absorbing sound and/or reducing sound transmission in a room, such as a room, hallway, conference room, or the like. Although there are many types of acoustic panels, the general variety of acoustic panels typically consists of mineral wool fibers, fillers, dyes, and binders, as described in, for example, US Pat.

[0003] To make panels, fibers, fillers, bulking agents, binders, water, surfactants, and other additives are typically combined to form a slurry and processed. Cellulose fibers are usually supplied in the form of recycled newsprint. The bulking agent is typically expanded perlite. Fillers may include clay, calcium carbonate or calcium sulfate. Binders may include starch, latex, and reconstituted paper products bonded together to create a binder system that facilitates fixation of all ingredients in the desired structural matrix.

[0004] Organic binders, such as starch, are often the primary binder that provides structural adhesion to the panel. Starch is the preferred organic binder because, among other reasons, it is relatively inexpensive. For example, panels containing newsprint, mineral wool and perlite can be economically bonded together using starch. Starch gives strength and durability to the panel structure, but is susceptible to problems caused by moisture. Moisture can cause the panel to soften and sag, giving an unsightly appearance to the ceiling and may cause the panel to weaken.

[0005] One of the methods used to solve problems caused by moisture in the panels is to apply a melamine formaldehyde resin coating on the back of the panels with or without the addition of a urea formaldehyde component. When such a formaldehyde resin coating is exposed to moisture or humidity, it tends to resist back surface compressive forces resulting from downward sagging.

[0006] Cured melamine-formaldehyde resins, when properly cured, have a hard and brittle cross-linked structure. This rigid structure functions to withstand backside compressive forces resulting from downward sag. However, formaldehyde resins tend to release formaldehyde, which is a known environmental irritant.

[0007] In order to reduce formaldehyde emissions, formaldehyde-reactive agents such as urea were added to remove free formaldehyde. Unfortunately, such low molecular weight scavenging agents can block formaldehyde resin reactive groups and thus prevent significant levels of crosslinking from occurring. As a result, the desired polymer structure with a high level of cross-linking is never formed. The resulting coating is fragile and will not resist sagging.

[0008] While there are many commercially available acoustic panels classified as sources of low volatile organic chemical (VOC) emissions, these products nevertheless emit detectable levels of formaldehyde due to the presence of various formaldehyde releasing components that are used in these panels. Although formaldehyde emissions that are generated during heat exposure in the manufacturing process may be vented to exhaust pipes or thermal oxidizers, the resulting product will still contain residual formaldehyde that may be released after installation. Reducing or eliminating formaldehyde emissions will improve indoor air quality in areas where acoustic panels are installed, such as public buildings, including schools, healthcare facilities, or office buildings.

SUMMARY OF THE INVENTION

[0009] In one aspect of the present invention, a coated fibrous panel is provided comprising a fibrous panel having a back surface and an opposite front surface coated with a cured coating layer located on at least one surface of the panel, said cured coating layer being from about 10 to 100 wt. one of the group consisting of alkali metal silicates, alkaline earth metal silicates and combinations thereof, wherein said inorganic binder is water soluble.

[0010] In another aspect of the present invention, a method of coating a fibrous panel is provided, comprising providing a fibrous panel having a back surface and an opposite front surface, and applying a first coating layer to at least one surface of the fibrous panel, wherein said first coating layer contains an inorganic binder, wherein said inorganic binder is present in an amount of from about 10 to 100 wt.% based on the total weight of the dry first layer of coating, and while the specified inorganic binder includes a borate salt and a metal silicate selected from the group consisting of alkali metal silicate, alkaline earth metal silicate and combinations thereof, and said inorganic binder is water soluble.

[0011] In another aspect of the present invention, there is provided a curable coating composition for improving the sag resistance of a fibrous panel, wherein the curable coating composition contains from about 10 to 100 wt % of an inorganic binder based on the total dry weight of the coating formed therefrom, said inorganic binder comprising a borate salt and a metal silicate selected from the group consisting of alkali metal silicate, alkaline earth metal silicate and their combinations, wherein said inorganic binder is water soluble.

[0012] Additional aspects and advantages of the present invention will be apparent to those skilled in the art from a review of the following detailed description. Although the methods and compositions allow for embodiments of the present invention in various forms, the following description includes specific embodiments of the invention with the understanding that the description of the invention is illustrative and is not intended to limit the invention to the specific embodiments described herein.

BRIEF DESCRIPTION OF GRAPHICS

[0013] In FIG. 1 is a schematic perspective view of a coated panel having a coating according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] This description presents a coated fibrous panel, including a fibrous panel having a back surface and an opposite front surface coated with a layer of a cured coating located on at least one surface of the panel, while the specified layer of the cured coating includes from 10 to 100 wt.% of an inorganic binder based on the total weight of the dry coating, while the specified inorganic binder includes a borate salt and a metal silicate selected from the group, with consisting of an alkali metal silicate, an alkaline earth metal silicate, and combinations thereof, wherein said inorganic binder is water soluble.

[0015] In this context, the terms "panel" and "slab" should be considered interchangeable. Likewise, the terms "fibreboard", "ceiling board" and "acoustic board" should be considered interchangeable.

[0016] In this context, the terms "coating composition" and "coating layer" should be considered interchangeable, since the term "coating layer" is used to refer to the coating composition when applied or sprayed onto a fibrous panel. In this context, the terms "dry coating", "dry coating layer" or "cured coating layer" can be used interchangeably to refer to the final coating on the coated fibrous panel after any drying and/or curing steps. That is, any aqueous solvent used to mix the inorganic binders of this invention, such as water and the like, that may be present in the coating composition has been evaporated or dehydrated by heating, chemical curing, or any other process suitable for drying the coated fibrous panel.

[0017] Coated fibrous panels as described herein have the advantage of significantly less sag compared to uncoated fibrous panels, and fibrous panels coated with a metal silicate binder only (i.e., the inorganic binder does not include borate salt) have at least a similar, if not improved, sag resistance compared to finished fibrous panels having standard formaldehyde. cover.

[0018] Optionally, the coating layer is substantially free of formaldehyde and substantially free of organic polymeric binder(s). Similarly, in embodiments of the invention, the inorganic binder is substantially free of formaldehyde and substantially free of organic polymeric binders. When the coating layer(s) of the coated fibrous panels of this invention are substantially free of formaldehyde and/or organic polymeric binders, it has the advantage of a reduced risk of formaldehyde emission, even compared to known formaldehyde-free coatings. In particular, formaldehyde-free acoustic panel coatings typically include organic polymer binders. Some organic polymeric binders inherently contain, release, release or generate detectable and quantifiable levels of formaldehyde. Thus, even though formaldehyde may not be a component of the organic polymeric binder used in acoustic panel coating, the panel may still release, emit, or generate formaldehyde for a variety of reasons, including, for example, degradation of the organic polymeric binders. In embodiments of the present invention wherein the coating compositions as described are substantially free of organic polymeric binders, said coating compositions and coated fibrous panels do not contain or emit formaldehyde associated with degradation of such organic polymeric binders.

[0019] In alternative embodiments of this invention, the coating layer includes additional binders, including, but not limited to, organic polymeric binders.

[0020] In this context, the term "substantially free of formaldehyde" means that the coating layer and/or binder is not made with formaldehyde or formaldehyde-forming chemicals and will not emit formaldehyde under normal operating conditions. The term "substantially free of formaldehyde" may be further defined as meaning the absence of intentionally or intentionally added formaldehyde, such that an incidental or background amount of formaldehyde (eg, less than 100 ppb) may be present in the coating composition. Some additives, such as wet preservatives or biocides, included in surface treatments and back coatings can release, release, or generate detectable and quantifiable levels of formaldehyde. Thus, even though formaldehyde may not be a specially added component used in acoustic panels, said panel may still release, emit, or generate formaldehyde for a variety of reasons, including, for example, biocide degradation.

[0021] The amount of formaldehyde present in a coating composition can be determined in accordance with ASTM D5197 by heating dried coating samples to 115°C in a Markes humidified microchamber and then collecting emissions under controlled conditions using a 2,4-dinitrophenylhydrazine (DNPH) cartridge. After exposure, the DNPH cartridge is washed with acetonitrile, the acetonitrile wash solution is diluted to 5 ml, and the sample is analyzed by liquid chromatography. The results are presented in µg/mg of the coating sample and compared with a control sample. Samples that are within the experimental error of the control sample over a representative series of tests are clearly substantially free of formaldehyde.

[0022] In this context, the term "substantially free of organic polymeric binder" means that the inorganic binder does not contain an organic polymeric binder, and that the coating composition comprising the inorganic binder also does not contain significant amounts of specifically added organic polymeric binder. Thus, an occasional or background amount of organic polymeric binder (e.g., less than about 100 ppb) may be present in the coating compositions of this invention (e.g., leached from the panel core material) and is within the scope of this invention. As used herein, the term "organic polymeric binder" includes organic polymers and oligomers, and further includes organic monomers that can polymerize in situ (with or without curing) to form an organic polymer.

[0023] The specification also provides coating methods for fibrous panels and curable coating compositions for improving the sag resistance of fibrous panels.

inorganic binder

[0024] In general terms, the inorganic binder of this invention includes a curable borate salt and metal silicate compounds that are bonded together to form a binder system that assists in holding all ingredients of the coating composition in the desired structural matrix. The inorganic binder includes a borate salt and a metal silicate selected from the group consisting of alkali metal silicates, alkaline earth metal silicates, and combinations thereof. The inorganic binder according to this invention is water soluble. Typically, during drying, the coatings change from a liquid to a solid state due to solvent evaporation and/or due to physical and/or chemical reactions of the binder [Coatings Encyclopedic Dictionary, S. LeSota, Ed., Federation of Soc. for Coatings Technology, Blue Bell, PA., 1995].

[0025] The inorganic binder of this invention includes a borate salt. Any water soluble borate salt and combinations thereof are considered suitable for the coating composition of this invention. Suitable borate salts include, for example, sodium metaborate, sodium tetraborate, potassium tetraborate, potassium pentaborate, ammonium pentaborate, borax decahydrate, boron oxide, lithium borate, and combinations thereof. In embodiments of this invention, the borate salt is selected from the group consisting of sodium metaborate, sodium tetraborate, potassium tetraborate, potassium pentaborate, ammonium pentaborate, borax decahydrate, boron oxide, lithium borate, and combinations thereof. The borate salt may be an anhydrous borate salt or a hydrated borate salt. For example, as used herein, an inorganic binder comprising sodium tetraborate includes an inorganic binder including anhydrous sodium tetraborate, sodium tetraborate pentahydrate, or mixtures thereof.

[0026] The inorganic binder according to this description further includes a metal silicate. Any water soluble metal silicate and combinations thereof may be included in the coating compositions of this invention. In embodiments of this invention, the metal silicate is selected from the group consisting of alkali metal silicate, alkaline earth metal silicate, and combinations thereof. Specific metal silicates include, but are not limited to, sodium silicate, potassium silicate, lithium silicate, magnesium silicate, calcium silicate, beryllium silicate, and combinations thereof. In some embodiments of this invention, the metal silicate is an alkaline earth metal silicate. In embodiments of this invention, the alkaline earth metal silicate is selected from the group consisting of magnesium silicate, calcium silicate, beryllium silicate, and combinations thereof. In some embodiments of this invention, the metal silicate is an alkali metal silicate. In embodiments of this invention, the alkali metal silicate is selected from sodium silicate, potassium silicate, lithium silicate, and combinations thereof. In some embodiments of this invention, the alkali metal silicate includes sodium silicate.

[0027] Sodium silicate solutions may also be referred to as "water glass" and have the nominal formula Na ₂ O(SiO ₂ ) _x. Commercially available sodium silicate solutions have a SiO ₂ :Na ₂ O weight ratio in the range of about 1.5 to about 3.5. The specified ratio is an average value for silicates with different molecular weights. Suitable sodium silicate solutions have a SiO ₂ :Na ₂ O weight ratio in the range of about 1.5 to about 3.5, about 2 to about 3.2, about 2.5 to about 3.2, such as about 2.5, about 2.6, about 2.7, about 2.8, about 2.9, about 3.0, about 3.1, or about 3.2. In embodiments of this invention, the sodium silicate solution may have a SiO ₂ :Na ₂ O weight ratio in the range of about 3.0 to about 3.2.

[0028] Coating compositions containing borate salts in combination with alkali and/or alkaline earth metal silicates, in which the metal silicates are typically present as aqueous solutions/dispersions, have physical and chemical properties that are useful in coating applications. When thinly coated on a fibrous panel, the borate and silicate solution/dispersion dries to form a coating having one or more of the following advantages: low cost, non-flammable, temperature resistant up to 3000°F (about 1650°C), sag resistant, odorless, and non-toxic.

[0029] In embodiments of this invention, the inorganic binder includes sodium silicate and sodium tetraborate.

[0030] Optionally, the coating according to this invention essentially does not contain additional binders. That is, in embodiments of the invention, said coating is substantially free of non-borate salt binders, substantially free of non-alkali metal silicate binder, and substantially free of non-alkaline earth silicate binders. As used herein, the terms "substantially free of non-alkali metal silicates", "substantially free of non-alkali earth metal silicates" mean that the coating does not contain significant amounts of specially added non-alkaline earth metal silicate binders, non-alkaline earth metal silicate binders, or non-borate salt binders (e.g., less than 3 wt.%, less than 2 wt.%, or less than 1 wt.% based on the total weight of the dry coating may be present in the coating and be within the scope of this invention). Thus, in embodiments of this invention, the inorganic binder according to this invention may consist or consist essentially of one or more of the following agents: borate salts, alkali metal silicates, alkaline earth metal salts, and combinations thereof.

[0031] The amount of the inorganic binder in the coating composition or coating layer according to the present invention is not particularly limited. The inorganic binder may be present in an amount of from about 10 wt.% to about 100 wt.%, from about 25 wt.% to about 75 wt.%, from about 40 wt.% to about 60 wt.%, or from about 30 wt.%. up to about 50 wt.%, for example, about 10, 15, 20, 22, 25, 27, 30, 32, 35, 37, 40, 42, 45, 47, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 wt.% based on the total dry weight coverage.

inorganic filler

[0032] Optionally, the coating layer and/or coating composition of the coated fibrous panel according to this invention may include an inorganic filler. Generally, any inorganic solid, inert mineral, or mineral-like material can be added as the inorganic filler.

[0033] Suitable mineral and mineral-like fillers include, for example, clay (for example, kaolin clay or bentonite clay), mica, sand, barium sulfate, silica, talc, magnesia, olivine, dolomite, tremolite, xonolite, vermiculite, gypsum, perlite, limestone (calcite or aragonite), magnesite, wollastonite , zinc oxide, zinc sulfate, hollow granules, bentonite salts, fly ash, furnace ash, coal ash, metal slag, oxidizing slag, limestone slag, zeolite, and combinations thereof. In embodiments of this invention, said filler is selected from the group consisting of clay, mica, sand, barium sulfate, silica, talc, magnesia, olivine, dolomite, tremolite, xonolite, vermiculite, gypsum, perlite, limestone (calcite or aragonite), magnesite, wollastonite, zinc oxide, zinc sulfate, hollow granules, salt bentonite, fly ash, furnace ash, coal ash, metal-containing slag, oxidizing slag, limestone slag, zeolite, and combinations thereof. In embodiments of this invention, said filler comprises calcium carbonate. In embodiments of this invention, said filler includes calcium carbonate and kaolin clay.

[0034] The particle size of the inorganic filler is not particularly limited as long as the particle size does not adversely affect the binding properties of the inorganic binder of the coating. In embodiments of the present invention, the particle size of the inorganic filler may be in the range of about 1 µm to about 200 µm, about 10 µm to about 100 µm, or about 25 µm to about 75 µm. For example, the particle size of the inorganic filler may be about 1, about 5, about 10, about 15, about 20, about 25, about 30, about 40, about 50, about 60, about 70, about 75, about 80, about 85, about 90, about 100, about 110, about 120, about 130, about 140, about 150, about 160, about 170, about 180, about 190 or about 200 microns.

[0035] An inorganic filler is not the same as an inorganic binder. Thus, in embodiments of the invention, said inorganic filler is substantially free of borate salts, alkali metal silicates and alkaline earth metal silicates. As used herein, the terms "substantially free of borate salts,""substantially free of alkali metal silicates," and "substantially free of alkaline earth metal silicates" mean that the inorganic filler does not contain significant amounts of specifically added borate salts, such as sodium metaborate, sodium tetraborate, borax decahydrate, boron oxide, or lithium borate; a significant amount of specially added alkali metal silicates, for example sodium silicate, potassium silicate or lithium silicate; or a significant amount of specially added alkaline earth metal silicates, for example magnesium silicate, calcium silicate or beryllium silicate. Thus, random or background amounts of borate salts and metal silicates (e.g., less than 3 wt.%, less than 2 wt.%, or less than 1 wt.% based on the total dry weight of the coating) in the inorganic filler may be present, which is within the scope of this invention. Inorganic fillers containing glass and clays may include aluminum silicate and/or borosilicate and are within the scope of this invention.

[0036] The amount of inorganic filler in the composition or coating layer according to this invention is not particularly limited. In embodiments of the present invention, said inorganic filler may be included in an amount of up to about 90% by weight. For example, said inorganic filler may be included in an amount of from about 10 wt.% to about 90 wt.%, from about 25 wt.% to about 75 wt.%, from about 40 wt.% to about 60 wt.%, or from about 30 wt.% to about 50 wt.%, for example, about 5, about 10, about 15, about 20, about 22, about 25, about 27, about 30 , about 32, about 35, about 37, about 40, about 42, about 45, about 47, about 50, about 55, about 60, about 65, about 70, about 75, about 80, about 85 or about 90 wt.% based on the total weight of the dry coating.

[0037] The coating composition and coating layer may optionally further include one or more components such as dispersants, pigments, surfactants, pH modifiers, buffering agents, viscosity modifiers, stabilizers, defoamers, flow modifiers, and combinations thereof.

[0038] In some embodiments of this invention, the specified coating composition includes one or more dispersants. Suitable dispersants include, for example, tetrapotassium pyrophosphate (TKPP) (FMC Corp.), sodium polycarboxylates such as Tamol® 731A (Rohm & Haas), and non-ionic surfactants such as Triton™ CF-10 alkylaryl polyether (Dow Chemicals). In embodiments of the invention, said coating composition comprises a dispersant selected from nonionic surfactants such as Triton™ CF-10 alkylarylpolyether (Dow Chemicals).

[0039] Optionally, the coating composition and coating layer may further include minor amounts of a component to impart increased water resistance to the coating. For example, the component to impart increased water resistance may be included in the coating composition and/or coating layer in an amount of about 3 wt.% or less, about 2 wt.% or less, or about 1 wt.% or less. Suitable components which impart increased water resistance include, for example, siloxanes which impart hydrophobicity to the coating. Suitable siloxanes include, but are not limited to, polymethylhydrosiloxane, polydimethylsiloxane, and combinations thereof.

[0040] The curable coating composition can be prepared by mixing the inorganic binder and other optional components (eg, inorganic filler) using conventional mixing techniques. Typically, the coating particles or solid particles are suspended in an aqueous carrier. Typically, an inorganic binder, including a borate salt and a metal silicate, and optionally an inorganic filler, is added to and mixed with the aqueous carrier, followed by the other optional components in descending order according to percentage of dry weight. The coating composition can then be applied to the fibrous panel to form a coating layer.

[0041] Alternatively, said coating layer can be obtained by applying the inorganic binder and, if present, the inorganic filler in stages to the fibrous panel. In such embodiments of this invention, an inorganic binder is added and mixed with an aqueous carrier, and then with other optional components, as described above, to form a dispersion of the binder. Similarly, an inorganic filler may be added and mixed with an aqueous carrier and then with other optional components as described above to form a filler dispersion. The binder dispersion and the filler dispersion can then be applied to the fibrous panel in stages. For example, in some embodiments of the present invention, a binder dispersion is applied to the fibrous panel and then the filler dispersion is applied. In another embodiment of the present invention, a filler dispersion is applied to the fibrous panel and then a binder dispersion is applied.

[0042] The solids content of the coating composition of this invention, ie the binder dispersion and/or optional filler dispersion, can be as high as is practical for the particular application. The limiting factor regarding the choice and amount of liquid carrier used is the viscosity obtained with the required amount of solids. Spraying is the most sensitive to viscosity, while other application methods are less sensitive. An effective range of solids content in the coating composition is about 15 wt.% or more, for example, about 20 wt.% or more, about 25 wt.% or more, about 30 wt.% or more, about 35 wt.% or more, about 40 wt.% or more, or about 45 wt.% or more, based on the entire composition of the coating composition before any drying and/or curing step. That is, the effective range of solids content in the coating composition, as defined herein, includes any aqueous carrier or solvent, such as water, which typically evaporates from the final dry coating layer. Alternatively or additionally, the coating composition has a solids content of about 80 wt.% or less, or about 75 wt.% or less, or about 70 wt.% or less, based on the entire composition of the coating composition before any drying and/or curing step. Thus, the solids content of the coating composition may be limited by any two of the above limits specified for the solids content of the coating composition. For example, the solids content of the coating composition may be from about 15 wt.% to about 80 wt.%, from about 35 wt.% to about 80 wt.%, from about 45 wt.% to about 75 wt.%, or from about 45 wt.% to about 70 wt.%.

[0043] For example, a coating composition comprising a 60 wt.% solution of sodium silicate with a content of 37.5% solids, 5 wt.% sodium tetraborate and 35 wt.% additional water, has a solids content of about 27.5 wt.%, based on the entire composition of the coating composition before any stage of drying and / or curing, consisting of 100% inorganic binders (for example, sodium silicate and sodium tetraborate). Thus, when the coating is dried and/or cured, the inorganic binder makes up about 100% by weight of the coating, based on the total dry weight of the coating.

[0044] In an additional example in which an inorganic filler is included, the coating composition comprises a 60 wt.% solution of sodium silicate with a solids content of 37.5%, 5 wt.% sodium tetraborate, 5 wt.% kaolin clay, 20 wt.% calcium carbonate and 10 wt.% additional water, has a solids content of about 52.5 wt.% based on the entire composition of the coating composition before any drying and / or curing step, consists of about 27.5% inorganic binder (ie sodium silicate and sodium tetraborate) and about 25% inorganic filler (ie kaolin clay and calcium carbonate). Thus, when the coating is dried and/or cured, the inorganic binder makes up about 52.4% by weight of the coating, based on the total dry weight of the coating, and the inorganic filler makes up about 47.6% by weight of the coating, based on the total dry weight of the coating.

[0045] Thus, the specification provides a curable coating composition for improving the sag resistance of a fibrous panel, said curable coating composition comprising from about 10 to about 90 wt % of an inorganic binder based on total dry weight of the coating, said inorganic binder comprising a borate salt and a metal silicate selected from the group consisting of an alkali metal silicate, an alkaline earth metal silicate, and a combination thereof. th, and while the inorganic binder is water-soluble.

[0046] Optionally, a curable coating composition as described herein may further include up to about 90% by weight of an inorganic filler, based on total dry weight of the coating, where the inorganic binder and inorganic filler are not the same.

fiber panel

[0047] This document further describes a panel (eg, acoustic panel, ceiling tile) coated with a coating composition according to the present invention. Coated panel 10 according to one aspect of the present invention, as schematically illustrated in FIG. 1 comprises a panel core 20 having a back surface 30 and a front surface 40. The panel optionally further comprises a backing layer 35 in contact with the back surface 30 and/or a face layer 45 in contact with the front surface 40'. The back cover layer 50 is positioned, for example, in contact with the back surface 30 or optional underlayment 35. Optionally, an additional facing layer of cover 60 is located on or over, for example, front surface 40 or optional front layer 45.

[0048] The backsheet layer 50 advantageously resists sagging gravity in wet conditions, thus the backsheet is applied to the back surface 30 (or underlayment 35, if any) of the core of the panel 20. The back surface 30 may be a surface that is directed toward a high pressure area above the panel in a suspended ceiling tile system. The coated panel 10 may be an acoustic sound attenuation panel. The rear surface 30 may be a surface that is directed towards the wall behind the panel in the case where an acoustic panel is provided on the walls.

[0049] An exemplary procedure for making a panel core 20 is described in US Pat. No. 1,769,519. In one aspect, the panel core 20 comprises mineral wool fiber and starch. In another aspect of the present invention, the starch component may be a starch gel that acts as a binder for the mineral wool fiber as described in US Pat.

[0050] The core panel 20 of the coated panel according to this invention may also include a variety of other additives and agents. For example, the core of the panel 20 may include calcium sulfate material (such as stucco, gypsum and/or anhydrite), boric acid, and sodium hexametaphosphate (SHMP). In the manufacture of acoustic board, kaolin clay and guar gum can be replaced with stucco and boric acid.

[0051] The core of the coated panel according to this invention can be made using various methods. In one embodiment of the present invention, the panel core 20 is made by wet felting or water felting as described in US Pat. The resulting slurry is heated to boil the starch and form a starch gel, which is then mixed with mineral wool fiber. This combination of gel, additives and mineral wool fiber (called "pulp") is dosed into trays in a continuous process. The bottom of the trays into which pulp is dispensed may further comprise a backing layer 35 (e.g., bleached paper, unbleached paper, or kraft-based aluminum foil, hereinafter referred to as kraft/aluminum foil) which serves to facilitate material release from the tray, but also remains part of the finished product. The surface of the pulp may be patterned and the trays containing the pulp may be subsequently dried, for example by transporting them through a convection tunnel dryer. The dried product or sheet can then be fed to a finishing line where it can be cut to size to form a panel core 20. The panel core 20 can then be converted into a panel of the invention by applying the coating composition of the invention. The coating composition is preferably applied to the core of the panel 20 after said core has already been formed and dried. In yet another embodiment of this invention, the core of the panel 20 is made according to the method described in US patent No. 7 364 015, which is incorporated into this description by reference. In particular, the core of the panel 20 comprises an acoustic layer containing an interconnected matrix of set gypsum, which may be a monolithic layer or may be a multilayer composite. It is desirable that the core of the panel 20 can be made on the usual line of production of drywall, where the tape of the predecessor of the acoustic panel is formed by casting a mixture of water, calcified gypsum, a foaming agent and, not necessarily, pulp fiber (for example, paper fiber), light aggregate (for example, foamy polystyrene), binding substances (for example, Krahmala, lamasy, lakes. Tex) and/or improving material (for example, sodium trimetaphosphate) on the conveyor tape.

[0052] In embodiments of this invention, the core of the panel comprises an undersheet (e.g., paper, metal foil, or a combination thereof), optionally covered with a mesh scrim (e.g., paper, woven or non-woven glass fiber), and/or a densified layer precursor containing calcined gypsum, and having a density of at least 35 lb/ft ³ . In yet another embodiment of the present invention, the core of the panel 20 is made according to a wet felting process. In the wet felting process, an aqueous slurry of panel-forming materials, including mineral wool, expanded perlite, starch, and minor additives, is applied to a moving wire mesh, such as a Fourdrinier moulder or a cylinder moulder. On Fourdrinier wire mesh, a wet mat is formed by dewatering an aqueous suspension under gravity and then optionally by vacuum suction. The wet mat is pressed to the desired thickness between pressure rolls for additional dewatering. The pressed mat is dried in ovens and then cut to form acoustic panels. Then the core of the panel 20 can be converted into a panel according to this invention by applying the coating composition according to this invention. The coating composition is preferably applied to the core of the panel 20 after said core has already been formed and dried.

[0053] In a further embodiment of this invention, the panel core 20 may include one or more formaldehyde-free biocides as a preservative, as described in US Patent Application Publication 2007/0277948 A1, which is incorporated herein by reference. Suitable formaldehyde-free biocides include 1,2-benzisothiazolin-3-one available as Proxel GXL (Proxel® GXL) or Proxel® CRL (ARCH Chemicals), Nalcon® (Nalco), Canguard™ BIT (Dow Chemical) and Rocima™ BT 1S (Rohm & Haas). Other isothiazolin-3-ones include mixtures of 1,2-benzisothiazolin-3-one and 2-methyl-4-isothiazolin-3-one available as MBS Acticide (Acticide® MBS) (Acti-Chem). Additional isothiazolin-3-ones include 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and mixtures thereof. Mixtures of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one are available as Kathon™ LX (Rohm & Haas), Mergal® K14 (Troy Chemical) and Amerstat® 251 (Drew Chemical). Another suitable formaldehyde-free biocide includes 1-hydroxy-2(1H)-zinc pyridinethione available as Zinc Omadine® (ARCH Chemicals) and is optimally effective both dry and wet. Zinc-1-hydroxy-2(1H)-pyridinethione can also be used with zinc oxide, available as Zinc Omadine® emulsion. Other suitable formaldehyde-free biocides include 2-n-octyl-4-isothiazolin-3-one available as Kathon™ 893 and Skane® M-8 (Rohm & Haas) and 2-(4-thiazolyl)-benzimidazole available as Metasol® TK-100 (LanXess).

[0054] As previously discussed, the coated panel of the present invention may optionally include a backing layer 35. A variety of materials can be used as the backing layer 35, including unbleached paper, bleached paper, kraft foil/aluminum foil, and the like. The flame retardant backcoat can optionally be applied in combination with bleached or unbleached paper liner to improve the burning characteristics of the surface of the products. The fire retardant backsheet may include a variety of components such as, for example, water, a fire retardant, and a biocide. The underlayment 35 may also be used to improve sag resistance and/or soundproofing. In addition, a filler coat or a plurality of filler coats can be applied to the underlayment 35. The fill coat may include a variety of components such as, for example, water, fillers, binders, and various other additives such as defoamers, biocides, and dispersants. Generally, when a filler coat is applied, said filler coat is usually applied after the metal silicate coat of the present invention.

[0055] The coating composition of this invention is suitable for use in coating the front and/or back of a panel, such as a fiber panel (eg, acoustic panel or ceiling tile). The coating composition of this invention can be used with acoustic panels known in the art and prepared by methods known in the art, including wet felted acoustic panels. For example, acoustic panels and their manufacture are described in, for example, U.S. Patent Nos. 1,769,519; 3,246,063; 3,307,651; 4,911,788; Suitable commercial ceiling tiles for use in the present invention include, for example, ^RadarTM ceiling tiles available from USG Interiors, Inc. of Chicago, Illinois. ^RadarTM trade name board is a 5/8'' thick slag or mineral wool fiber panel having the following composition: 1-75 wt.% slag wool fibers, 5-75 wt.% expanded perlite, 1-25 wt.% cellulose, 5-15 wt. .% calcium sulfate dehydrate, less than 2 wt.% limestone or dolomite, less than 5 wt.% crystalline silica and less than 2 wt.% vinyl acetate polymer or ethylene vinyl acetate polymer. The diameter of mineral wool fibers varies widely, for example from 0.25 to 20 microns, with most fibers having a diameter in the range of 3 to 4 microns. The length of the mineral fibers is from about 1 mm to about 8 mm.

Coating Methods for Fiber Panel

[0056] The present invention provides a method for coating a fibrous panel, comprising providing a fibrous panel having a back surface and an opposite front surface, and applying a coating layer to at least one surface of the fibrous panel, said coating layer comprising an inorganic binder, wherein said inorganic binder is present in an amount of from about 10 to 100 wt.% based on the total weight of the first dry coating layer, and wherein said inorganic binder includes a borate salt and a metal silicate selected from the group consisting of an alkali metal silicate, an alkaline earth metal silicate, and a combination thereof, wherein said inorganic binder is water soluble. In embodiments of the present invention, a coating is applied to the back surface of the fibrous panel to provide a back coating. In this context, the term "back coating" refers to a borate salt and metal silicate coating applied to the back surface of a ceiling tile or fibrous panel.

[0057] In embodiments of this invention, the coated fibrous panel includes a single coating layer containing an inorganic binder according to this invention. In embodiments of this invention, the coated fibrous panel includes at least 2, 3 or 4 layers of coating to 8, 9 or 10 layers of coating, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 layers of coating containing an inorganic binder according to this invention. Each coating layer according to this invention includes an inorganic binder, while the specified inorganic binder is present in an amount of from about 10 to 100 wt.% based on the total weight of the dry coating layer, and while the specified inorganic binder includes a borate salt and a metal silicate selected from the group consisting of alkali metal silicate, alkaline earth metal silicate and combinations thereof, and while the specified inorganic binder is water-soluble.

[0058] In embodiments of the present invention in which at least a second coating layer is applied to the fibrous panel, said coating method further comprises applying a second coating layer in contact with or over the first coating layer, wherein the second coating layer includes a second inorganic binder, and wherein the second inorganic binder is present in an amount of from 10 to 100 wt.% based on the total dry weight of the second layer, while the second inorganic binder includes a borate salt and a metal silicate selected from the group consisting of alkali metal silicate, alkaline earth metal silicate and combinations thereof, wherein the second inorganic binder is water soluble.

[0059] In embodiments of the present invention in which more than two coating layers are applied, a subsequent coating layer may be applied such that it is in contact with or over the previously applied coating layer. That is, for example, the third coating layer may be in contact with the second coating layer, the fourth coating layer may be in contact with the third coating layer, or the fifth coating layer may be in contact with the fourth coating layer.

[0060] In embodiments of this invention, the first and/or second coating layer(s) and any subsequent coating layer applied thereon (e.g., third, fourth, fifth, sixth, seventh, eighth, ninth, and/or tenth coating layers) may optionally further comprise an inorganic filler, wherein said inorganic filler is present in an amount of up to about 90 wt.% based on the weight of the dry coating layer, and the inorganic binder and not organic filler are not the same.

[0061] In embodiments of the present invention in which an inorganic filler is present in the coating layer, the method as described herein may further comprise mixing the inorganic binder and the inorganic filler to form a curable coating composition prior to applying the coating layer. That is, the inorganic binder and the inorganic filler, if present, may be pre-mixed and therefore applied simultaneously as a mixture. In other embodiments of this invention, in which an inorganic filler is present in the coating layer, the specified inorganic filler and inorganic binder is applied in stages from a dispersion of inorganic binder and a dispersion of inorganic filler. Optionally, the inorganic filler is first applied and then the inorganic binder is applied in contact with the first layer of inorganic filler. Without wishing to be bound by theory, it is believed that the application of an inorganic filler first improves the retention of the filler in the matrix formed by the cross-linking/dehydration of the borate and silicate binder, and further promotes the cross-linking/dehydration of the borate and silicate binder. In embodiments of this invention, the dispersant may be mixed with the curable coating composition and applied simultaneously with the inorganic binder and inorganic filler. The dispersant may also be included in the inorganic binder dispersion and/or the inorganic filler dispersion when the binder and filler are applied in stages.

[0062] The coating composition can be applied to one or more surfaces of the panel, preferably the fibrous acoustic panel or ceiling tile substrate, by a variety of methods well known and available to those skilled in the art. Such methods include, for example, airless spray systems, air assisted spray systems, and the like. The coating, depending on the method of application, can be a roller coating, a flow coating, a flow coating, a spray coating, a curtain coating, an extrusion coating, a knife coating, and combinations thereof. The borate salt and metal silicate coating may be applied to give a coating weight on a wet weight basis of from about 10 g/ft ² to about 40 g/ft ² , from about 15 g/ft ² to about 35 g/ft ² , and from 15 g/ft ² to about 25 g/ft ² . The aqueous coating composition may have any suitable solids content, for example, in the range of from about 15 wt.% to about 80 wt.%, from about 35 wt.% to about 80 wt.%, from about 45 wt.% to about 75 wt.%, or from about 45 wt.% to about 70 wt.%. The borate salt and metal silicate coating can be applied from a 65% solids composition to give a coating weight on a dry basis of about 0.014 lb/ft ² (about 6.5 g/ft ² ) to about 0.065 lb/ft ² (about 29.3 g/ft ² ), from about 0.020 lb/ft ² (about 9.8 g/ft ² ) to about 0.050 lb/ft ^{2 (about 22.8 g/ft 2 ) or from about 0.020 lb/ft 2 ( about} 9.8 g/ft ² ) to about 0.036 lb/ft ² (about 16.3 g/ft ² ). In embodiments of the present invention, a borate salt and metal silicate coating may be applied from a 45 wt.% solids composition to provide a coating weight on a dry weight basis from about 0.010 lb/ft ² (about 4.5 g/ft ² ) to about 0.040 lb/ft ² (about 18 g/ft ² ), from about 0.015 lb/ft ² (about 6.8 g/ft ² ) to about 0.035 lb/ft ² (about 15.8 g/ft ² ) or from about 0.015 lb/ft ² (about 6.8 g/ft ² ) to about 0.025 lb/ft 2 (about 11.3 ^g /ft ² ). In one embodiment of the present invention, the coating composition according to the present invention is applied to the back surface 30 of the panel. In another embodiment of the present invention, the coating composition according to the present invention is applied to the underlying layer 35 of the panel.

[0063] After the curable coating composition of the present invention has been applied to the panel, either as a pre-blended curable composition or by stepwise application of an inorganic binder and an optional inorganic filler, the coated fibrous panel may be dried or cured. In this context, the term "curing" refers to any chemical or morphological change that is sufficient to change the properties of the binder, for example, through a covalent chemical reaction (eg, condensation reaction), hydrogen bonding, and the like. The coated fibrous panel may be dried after applying each individual layer of coating (for example, after a single application of a premixed composition of inorganic binder and inorganic filler) or after applying all layers of the coating (for example, after several applications of a premixed composition of inorganic binder and inorganic filler, or after adding compositions containing an inorganic binder or inorganic filler in stages). Drying the fibrous panel promotes the formation of a crosslinked/dehydrated solid coating layer of borate salt and metal silicate. In some embodiments of the present invention, the coated fibrous panel is dried by air drying. That is, the fibrous panel is allowed to dry under ambient and room temperature conditions without the use of heat or forced air. In alternative or additional embodiments of this invention, the composition can be dried by heating the coated fibrous panel. Without wishing to be bound by any theory, it is believed that heating affects the curing and cross-linking/dehydration of the inorganic borate and silicate binder, thereby strengthening the borate-silicate structural matrix. In addition, when an inorganic filler is present, it is believed that heating improves the retention of the inorganic filler in the borate and silicate structural matrix. Drying the resulting product removes all water used as a carrier for the coating composition or any of its components and converts the inorganic boratosilicate binder into a structurally rigid network capable of providing increased structural rigidity to the panel.

[0064] When the coated fibrous panel is dried by heating, the duration and temperature of the heating will affect the drying rate, ease of processing or handling, and the formation of the properties of the heated substrate. Heat treatment temperatures from about 100°C to about 500°C (e.g., about 120°C, from about 150°C to about 500°C, or from about 175°C to about 400°C, or from about 200°C to about 300°C, or from about 300°C to about 500°C) for a period of about 3 seconds to about 15 minutes are suitable for drying the coated fibrous panel(s) according to the invention. For acoustic panels, suitable temperatures may be in the range of about 300°C to about 500°C, or about 350°C to about 450°C (about 600 to about 800°F). Typically, heating is continued until a coating surface temperature of at least about 200° C. to 240° C. (about 390 to about 465° F.) is reached, as this indicates complete cure. In embodiments of the present invention, said method includes heating the coated fibrous panel to a surface temperature of at least about 250°F (about 120°C), at least 300°F (about 150°C), at least 350°F (about 175°C), to about 400°F (about 205°C), about 450°F (about 230°C), or about 500°F. (about 260°C).

[0065] If desired, the drying and curing functions can be performed in two or more separate steps. For example, the curable coating composition may first be heated to a temperature for a period of time sufficient to substantially dry but not substantially cure the composition, and then heated a second time at a higher temperature and/or for a longer period of time to fully cure. Such a procedure, referred to as "transition to the B-stage", can be used to obtain coated panels according to this invention.

[0066] In some embodiments of this invention, this method further includes applying a layer of chemical curing. The methods of this invention may use chemical curing in addition to or even instead of drying and/or heat curing. Chemical curing may include precipitating a multivalent metal compound or an acidic solution to form cured borate salt and metal silicate coatings by precipitating insoluble metal silicate compounds from solution to form a solid layer. In embodiments of the present invention, the coating layer(s) may be further coated with a multivalent metal or acid solution. In embodiments of the invention in which the inorganic binder and optional inorganic filler are applied in stages, the polyvalent metal or acid may be provided with and/or applied simultaneously with the inorganic filler and/or inorganic binder. In embodiments of the present invention in which multiple premixed coating layers are applied, a chemical cure layer may be applied between each coating layer.

[0067] Without wishing to be bound by theory, the multivalent metal is believed to displace any monovalent cations (eg, sodium, lithium, or potassium) in the interstitial spaces of the inorganic network, accelerating curing and forming an insoluble silicate coating. The polyvalent metal may be present as a divalent and/or trivalent metal salt. Suitable polyvalent metals include, but are not limited to, Be ²⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Zn ²⁺ , Cu ²⁺ , Fe ²⁺ , Fe ³⁺ and Al ³⁺ . In embodiments of this invention, the multivalent metal includes a metal salt having a cation selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, zinc, copper, iron, aluminum, and combinations thereof. In embodiments of this invention, the multivalent metal includes a metal salt having a cation selected from the group consisting of calcium, magnesium, zinc, copper, iron, aluminum, and combinations thereof. In embodiments of this invention, the multivalent metal includes an alkaline earth metal salt having a cation selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, and combinations thereof. Suitable salts include borates, chlorides, carbonates, sulfates, and combinations thereof. In embodiments of this invention, the multivalent metal is provided in the form of oxide, hydroxide, or combinations thereof. Without wishing to be bound by theory, it is believed that slower dissolving compounds, eg carbonate salts, oxides, hydroxides, and the like, can be used to obtain stable formulations.

[0068] In embodiments of the present invention in which an acid is used for chemical curing, said acid may be any acid, such as an organic acid or a mineral acid, including, but not limited to, organic acids and mineral acids selected from the group consisting of acetic acid, sulfuric acid, phosphoric acid. acid and their combinations.

[0069]In embodiments of the present invention, the multivalent metal compound or acid may be present in the composition for forming the chemical cure layer in any suitable amount to enhance the curing of the coating layer(s), for example, in an amount from about 5 wt.% to about 30 wt.%, from about 10 wt.% to about 25 wt.%, or from about 15 wt.% to about 20 wt.%, for example, about 5 wt.%, about 10 wt.%, about 11 wt.%, about 12 wt.%, about 13 wt.%, about 14 wt.%, about 15 wt.%, about 16 wt.%, about 17 wt.%, about 18 wt.%, about 19 wt.%, about 20 wt.%, about 25 wt.% or about 30 wt.% based on the weight of the composition for forming the layer of chemical curing (before any drying and/or curing step).

[0070] In embodiments of the present invention, the chemical curing composition may further include an inorganic filler. Suitable inorganic fillers include those which may be included in the coating layers such as, for example, clay (eg kaolin clay or bentonite clay), mica, sand, barium sulfate, silica, talc, magnesia, olivine, dolomite, tremolite, xonolite, vermiculite, gypsum, perlite, limestone (calcite or aragonite), magnesite, wollastonite, zinc oxide, zinc sulfate, hollow granules, bentonite salts, fly ash, furnace ash, coal ash, metal slag, oxidizing slag, limestone slag, zeolite, and combinations thereof.

[0071] In embodiments of the present invention, the inorganic filler may be present in the composition for forming the chemical curing layer in an amount of up to about 50 wt.%, from about 5 wt.% to about 45 wt.%, from about 10 wt.% to about 40 wt.%. from about 15 wt.% to about 25 wt.%, for example, about 5 wt.%, about 10 wt.%, about 15 wt.%, about 20 wt.%, about 25 wt.%, about 30 wt.%, about 35 wt.%, about 40 wt.%, about 45 wt.% or about 50 wt.%, based on the weight of the composition for forming the layer of chemical curing (before any stage of drying and / or from statements).

[0072] In embodiments of this invention, the chemical cure layer includes calcium chloride and an inorganic filler such as clay.

[0073] The hardener composition containing the multivalent metal compounds can be applied by any method known in the art, such as airless spray systems, air assisted spray systems, and the like. The multivalent metal compound coating, depending on the method of application, can be a roller coating, a flow coating, a flow coating, a spray coating, a curtain coating, an extrusion coating, a knife coating, and combinations thereof. Solutions of multivalent metal compounds, including but not limited to calcium chloride, magnesium chloride, and combinations thereof, can be sprayed onto a hot panel coated with a curable coating composition. Without wishing to be bound by theory, it is believed that there is a minimum amount of polyvalent metal salt required to complete the chemical curing reaction. A suitable weight of the multivalent metal salt coating to complete the chemical curing reaction is at least about 2.5 mmol/ft ² or at least about 5 mmol/ft ² on a wet or dry basis. The polyvalent metal can be deposited as a salt at a coating weight (wet or dry weight) in the range of about 2.5 mmol/ft ² to about 35 mmol/ft ² , or about 5 mmol/ft ² to about 30 mmol/ft ² , about 7 mmol/ft ² to about 20 mmol/ft ² , or about 9 mmol/ft ² to about 15 mmol/ft ² .

[0074] Необязательно, после того, как раствор соединения многовалентного металла распылен на панель, указанную панель можно высушить и снова нагреть, например, до температуры в диапазоне от 100°F до 600°F (от около 35°C до около 315°C), от около 200°F до около 500°F (от около 90°C до около 260°C), от около 300°F до около 400°F (от около 150°C до около 205°C), например, около 100°F (около 35°C), около 200°F (около 90°C), около 300°F (около 150°C), около 400°F (около 205°C), около 450°F (около 230°C), около 500°F (около 260°C), около 550°F (около 290°C) или около 600°F (около 315°C) в течение 20 от секунд до пяти минут. Alternatively, or in combination with heat, after the polyvalent metal compound solution has been sprayed onto the panel, said panel can be air dried.

[0075] The coated panel of this invention has improved resistance to permanent deformation (sag resistance), as determined in accordance with ASTM C367M-09.

Sag Test - ASTM C367M-09

[0076] Ceiling slab sag can be measured in accordance with ASTM C367M-09. Briefly, ceiling tiles are placed in a test rack that mimics a ceiling grid. The vertical position of the geometric center of the panel mounted on the rack is measured to determine the initial position of the product after 1 hour of adaptation to conditions at 70°F (21°C)/50% RH. Once the initial position of the slab has been measured, the slab is subjected to various environmental conditions which constitute one test cycle. In particular, in the examples described below, a cycle of 12 hours at 104°F (40°C)/50% RH followed by 12 hours at 70°F (21°C)/50% RH is completed 3 times, with the center position being measured after completion of each cycle. Sagging is described in two ways. "Total movement" is defined as the difference in vertical position between the initial position of the ceiling slab and the final position of the slab after the completion of three cycles. The "final position" is defined as the final vertical position of the slab. Unless otherwise noted, sag is in inches for 2´ × 4´ slabs. Suitable boards of this invention exhibit less sag than uncoated tiles, such as less than about 1.0 inch (about 2.5 cm) sag, or less than about 0.8 inch (about 2.0 cm), or less than about 0.6 inch (about 1.5 cm), or less than about 0.5 inch (about 1.3 cm), or less than about 0.4 inch (about 1.0 cm), or less than about 0.3 inch (about 0.75 cm) or less than about 0.2 inch (about 0.50 cm) or less than about 0.1 inch (about 0.25 cm).

[0077] The foregoing description is for clarity of understanding only and is not intended to be undue limitation, as modifications within the scope of the invention may be apparent to those skilled in the art.

[0078] Compositions, panels and methods according to this invention can be better understood in light of the following examples, which are intended only to illustrate the compositions, panels and methods according to this invention and are not intended to limit its scope in any way.

EXAMPLES

Example 1 - Manufacture of coated fiber panel

[0079] A series of coated acoustic ceiling tiles were manufactured and tested for sag resistance. Unless otherwise noted, all ceiling tiles used in the examples are Radar ^™ brand ceiling tiles available from USG Interiors, Inc., Chicago, Illinois. ^RadarTM trade name board is a 5/8'' thick slag or mineral wool fiber panel having the following composition: 1-75 wt.% slag wool fibers, 5-75 wt.% expanded perlite, 1-25 wt.% cellulose, 5-15 wt. .% calcium sulfate dehydrate, less than 2 wt.% limestone or dolomite, less than 5 wt.% crystalline silica and less than 2 wt.% vinyl acetate polymer or ethylene vinyl acetate polymer. The diameter of mineral wool fibers varies widely, for example from 0.25 to 20 microns, with most fibers having a diameter in the range of 3 to 4 microns. The length of the mineral fibers is from about 1 mm to about 8 mm.

[0080] The ceiling tiles were cut and divided into 6" x 24" panel samples. Half of the panel samples were coated with a coating composition comprising an inorganic binder as described (Example 1), while the other half of the panel samples were coated with a comparative coating composition containing alkali metal silicate but no borate salt (Comparative Example 1). After applying the roller coating to all samples of panels to obtain a back coating, they were dried for 3 minutes at 550°F (about 290°C).

[0081] Coating compositions are shown in volume % aqueous coating composition and corresponding wt % aqueous coating composition in Table 1 below:

Table 1. Aqueous compositions for coatings

Ingredient Example 1 (vol.%) Example 1 (wt.% solids) Comparative Example 1 (vol.%) Comparative Example 1 (wt% solids) Sodium silicate solution
(37.5% solids) 59.0 22.1 41.0 15.4 Sodium tetraborate pentahydrate 2.2 2.2 0 - Calcium carbonate 20.0 20.0 40.0 40.0 Kaolin clay 5.0 5.0 5.0 5.0 Dispersant 0.2 - 0.2 - Water 13.6 - 13.8 -

[0082] The inorganic binder from Example 1 included sodium tetraborate pentahydrate and sodium silicate solution (sodium silicate solution, 3.22 SiO ₂ :Na ₂ O, 37.5% solids, PQ Corporation, Valley Forge, PA). An inorganic binder was used in combination with an inorganic filler and a dispersant. The coating composition of Example 1 included 59% sodium silicate solution with 37.5% solids, 2.20% sodium tetraborate pentahydrate, 20% calcium carbonate, 5% kaolin clay, 0.20% dispersant and 13.6% additional water.

[0083] Thus, the coating composition of Example 1 had a solids content of about 49.3 wt.%, based on the entire composition of the coating composition before any drying and / or curing step, consisting of 24.3% inorganic binder (i.e. sodium silicate and sodium tetraborate) and 25% inorganic filler (for example, calcium carbonate and kaolin clay). Thus, when the coating was dried and/or cured, the inorganic binder made up about 49.3% by weight of the coating, based on the total dry weight of the coating, and the inorganic filler made up about 50.7% by weight of the coating, based on the total dry weight of the coating.

[0084] In Comparative Example 1, the coating composition included a 41% sodium silicate solution with a solids content of 37.5%, calcium carbonate 40%, kaolin clay 5%, a dispersant 0.20%, and an additional 13.8% water.

[0085] Thus, the coating composition of comparative example 1 had a solids content of about 60.4 wt.%, based on the entire composition of the coating composition before any drying and / or curing step, consisting of about 15.4% inorganic binder (i.e. sodium silicate), and 45% inorganic filler (for example, calcium carbonate and kaolin clay). Thus, when the coating was dried and/or cured, the inorganic binder made up about 25.5% by weight of the coating, based on the total dry weight of the coating, and the inorganic filler made up about 74.5% by weight of the coating, based on the total dry weight of the coating.

[0086] The amounts of inorganic binder and inorganic filler in the two coatings, based on the total dry weight of the coating, are compared in Table 2 below.

Table 2 Dried Coating Compositions

Coating component Example 1 (wt.%, total weight of dry coating) Comparative Example 1 (wt.%, total weight of dry coating) inorganic binder 49.3 25.5 inorganic filler 50.7 74.5

[0087] After drying for 3 minutes at 550°F (about 290°C), the boards were coated with a chemical cure layer consisting of a solution of 15 wt.% calcium chloride and 20 wt.% clay, and dried at 550°F (about 290°C) for 30 seconds.

Example 2 - Testing coated fiber panels for sag resistance

[0088] The fiber panels from Example 1 were tested for sag according to ASTM C367M-09 as described above using a total of 100 sample panels for each coating composition. The sag test results are shown in Table 3 below.

Table 3. Sag resistance data

Coating composition Test No. (50 samples each) Total movement (inches) Example 1 1 0.37 2 0.30 Comparative Example 1 1 0.76 2 0.57

[0089] As shown in Table 1, coated panels having an inorganic binder, including the borate salt and metal silicate of the present invention, exhibited at least about 35% (and up to about 60%) sag reduction compared to coated panels containing only metal silicate and an inorganic binder.

[0090] Thus, Examples 1 and 2 demonstrate coated fibrous panels and methods for their manufacture, as well as curable coating compositions for improving the sag resistance of a fibrous panel according to this invention. In addition, Examples 1 and 2 demonstrate that the coated fibrous panel of the present invention has a significantly improved sag resistance compared to a similar coated fibrous panel containing no inorganic borate salt binder.

Claims (19)

1. A coated fiber panel comprising: a fibrous panel containing starch and mineral wool fiber and having a back surface and an opposite front surface, where the fibrous panel has a cured coating layer located on at least one surface of the panel, while said cured coating layer contains: from 10 to 100 wt.% inorganic binder based on the total weight of the dry coating, wherein said inorganic binder comprises a borate salt and a metal silicate selected from the group consisting of alkali metal silicates, alkaline earth metal silicates, and combinations thereof, and wherein said inorganic binder is water soluble. 2. The panel according to claim 1, wherein said coating layer further comprises up to 90% by weight of an inorganic filler based on the total dry weight of the coating, wherein the inorganic binder and the inorganic filler are not the same. 3. The panel according to any one of the preceding claims, wherein the alkali metal silicate or alkaline earth metal silicate is selected from the group consisting of sodium silicate, potassium silicate, lithium silicate, magnesium silicate, calcium silicate, beryllium silicate, and combinations thereof; and characterized in that the borate salt is selected from the group consisting of sodium metaborate, sodium tetraborate, potassium tetraborate, potassium pentaborate, ammonium pentaborate, borax decahydrate, boron oxide, lithium borate, and combinations thereof. 4. A panel according to any one of the preceding claims, wherein the inorganic binder comprises sodium silicate and sodium tetraborate. 5. A panel according to any one of the preceding claims, wherein the cured coating layer is located on the back surface of the panel, the back surface being directed towards the pressurized area above the fibrous panel in the suspended ceiling board system, the fibrous panel being the ceiling board. 6. A method of coating a fibrous panel, including: providing a fibrous panel containing starch and mineral wool fiber and having a back surface and an opposite front surface; applying a first coating layer to at least one surface of the fibrous panel, wherein said first coating layer contains an inorganic binder, wherein said inorganic binder is present in an amount of from about 10 to 100 wt.% based on the total dry weight of the first coating layer, and wherein said inorganic binder includes a borate salt and a metal silicate selected from the group consisting of alkali metal silicate, alkaline earth metal silicate, and combinations thereof, and when this specified inorganic binder is water-soluble. 7. The method according to p. 6, in which the first coating layer additionally contains an inorganic filler, while the specified inorganic filler is present in an amount of up to 90 wt.% based on the weight of the dry first coating layer, and the inorganic binder and inorganic filler are not the same; And further comprising mixing an inorganic binder and an inorganic filler to form a curable coating composition prior to application of the first coating layer. 8. The method according to any one of paragraphs. 6, 7, further comprising: applying a second coating layer in contact with the first coating layer, wherein the second coating layer includes a second inorganic binder, and wherein the second inorganic binder is present in an amount of from 10 to 100 wt.% based on the total dry weight of the second layer, while the second inorganic binder includes a borate salt and a metal silicate selected from the group consisting of alkali metal silicate, alkaline earth metal silicate and combinations thereof, and the second inorganic binder the substance is water soluble. 9. The method according to any one of paragraphs. 6-8, further comprising applying a layer of chemical curing, wherein said chemical curing layer comprises a solution of a polyvalent metal or acid. 10. Method according to claim 9, characterized in that said chemical curing layer contains calcium chloride and clay.