AU2015203105C1

AU2015203105C1 - Sag resistant, formaldehyde-free coated fibrous substrate

Info

Publication number: AU2015203105C1
Application number: AU2015203105A
Authority: AU
Inventors: Kenneth G. Caldwell; Lida Lu
Original assignee: Armstrong World Industries Inc
Current assignee: Armstrong World Industries Inc
Priority date: 2010-12-16
Filing date: 2015-06-10
Publication date: 2017-05-04
Anticipated expiration: 2031-12-15
Also published as: AU2015203105B2; AU2015203105A1

Abstract

The present invention relates to an improved formaldehyde-free coated fibrous substrate. The coating includes a crosslinked binder system which forms three dimensional networks when heat cured. After the coating is applied to the back of the fibrous substrate and cured, the coating is capable of hygroscopic expansion which imparts excellent anti-sag properties. The coating is compatible with other coating systems with neutral or mild alkaline pH. The improvement being the binding system is neutralized with a volatile base so that it evaporates quickly so as not to hinder the cross-linking reaction. 2885497_1.docx

Description

2015203105 10 Jun2015

SAG RESISTANT, FORMAU?£HY0E-FREE COATEE* FISRQtiS SUSSTRATE

BACKGROUND OF THE INVENTION fOOOl] The present invention is related to coated panels, and, in particular, to a formaldehyde-free coating that is applied to a major exterior surface of a fibrous panel to resist sag.

[0002] Fibrous substrates are light weight, porous composite materials which are used for many;: different purposes including panels in suspended ceiling systems. They are produced from a water bped slurry mixture containing fibers, a binding system and other additives. Fibers, which are typically used as reinforcing materials, include minerai wool, glass and celfulosic fibers. Binding systems, which hold the fibers and other additives together, include starches, lati% reconstituted paper productsand other polymeric materials. Other additives include fillers such as expanded perlite, clay, etc. £0003] It is widely known in the art that varying the material percentages of the aforementioned;; components ultimately impacts the physical and mechanical properties of the fibrous substrate, particularly when the fibrous substrate is installed in a horizontally extending suspended ceiling system. For exam pie, It is well Ιηο^η to those skilled in the art that after installation into a suspended ceiling framework, a fibrous substrate has a tendency to sag when exposed to high humidity environment due to the hydropitlc nature olcertam^ e.g. water soluble polymer binders: (e.g. starch) and celfulosic fibers (e.g. newsprint). More specifically, alter absorbing moisture, the substrate loses its modulus and sags by its gravity. Thus, conventional wisdom is that as the material percentages of these hydrophilic components are increased, the sag performance of the substrate decreases.

[0004] ϊ here have been various attempts to improve or even eliminate sag in these conventional fibrous substrates. One known method is to apply a hygroscopic coating on one of the major exterior surfaces of the substrate. More specifically, such coating includes a binder system which is hydrophilic end capable of absorbing moisture with rising humidity and desorbing moisture with decreasing * 2015203105 18 Nov 2016 humidity. Thus, when humidity rises, the hygroscopic coating absorbs moisture and expands in its volume and dimension, thus creating an expansion force on the surface of the substrate to which the coating is applied. In essence, the coating counter-acts the compressive force caused by the humid conditions.

[0005] In order to resist the compressive force from the underlying fibrous acoustic panel at high relative humidity, not only must the back coating be hygroscopic and create an expansion force, it is further required for the coating to maintain a high modulus. It is well understood in the art that polymer modifications are necessary for the hydrophilic polymer to maintain a high modulus after absorbing high level of moisture. One known method of polymer modification is by means of crosslinking. Once the polymer is properly crosslinked, the polymer matrix expansion will be limited, and, in turn, the polymer softening, i.e. loss of modulus, at high humidity conditions will be minimized.

[0006] Additionally, there are several known formaldehyde-free compositions for use as binders for making fibrous substrates. For example, U.S. Pat. Nos. 6,221,973 and 6,331,350 describe a formaldehyde-free fiberglass binder including a polyacid, such as polyacrylic acid, and a polyol, such as glycerol, diethanolamine, triethanolamine, sorbitol, or ethylene glycol. However, the main drawback of these formaldehyde-free binder solutions is their low pH which is often not compatible with other coatings and/or causes corrosion of processing equipment.

[0007] Thus, what is needed is an improved coated fibrous substrate which: does not emit environmental irritants such as formaldehyde; is sag resistant while at the same time maintains a high modulus; is compatible with other coatings and fillers; and avoids corroding processing equipment.

[0007A] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

[0007B] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 2 2015203105 18 Nov 2016

SUMMARY

[0008] Disclosed herein is a coated fibrous panel comprising a fibrous substrate and a formaldehyde-free coating applied to a major surface of the fibrous substrate. The coating includes a binder system having a neutralized polycarboxy polymer and a polyol crosslinker. The coating has a pH of 6 or greater and is capable of hygroscopic expansion at high humidity to resist sag. The improvement is that the coating is neutralized with a volatile base which evaporates quickly so as not to hinder the crosslinking reaction.

[0008A] Specific embodiments of the invention are described as items 1-17.

Item 1 A coated fibrous substrate comprising: a fibrous substrate comprising reinforcing fiber in an amount of equal to or less than 40 wt. % based on the total weight of the fibrous substrate; and a formaldehyde-free coating applied to a major surface of the fibrous substrate, the formaldehyde-free coating comprising a binder system and a filler, the binder system comprising: a polycarboxy polymer and a polyol crosslinker selected from the group consisting of glycerol, dextrose, fructose, sucrose, and sorbitol; and a volatile base, wherein the formaldehyde-free coating has a pH of from about 6 or greater and hygroscopic expands and wherein the filler and the binder system are present in a weight ratio ranging from about 3.0:1.0 to about 10:1.

Item 2. The coated fibrous substrate of item 1, wherein the formaldehyde-free coating has a pH of from about 6 to about 10.

Item 3. The coated fibrous substrate of item 1 or 2, wherein the binder system has a metal ion concentration of less than 1000 ppm.

Item 4. The coated fibrous substrate of any one of items 1 to 3, wherein the binder system has a metal ion concentration of less than 500 ppm.

Item 5. The coated fibrous substrate according to any one of items 1 to 4, wherein the coating further comprises a filler and the filler is selected from: an inorganic filler, an organic filler, and a combination thereof.

Item 6. The coated fibrous substrate of item 1, wherein the polycarboxy polymer is a homopolymer.

Item 7. The coated fibrous substrate of item 1, wherein the polycarboxy polymer is polyacrylic acid, polymethacrylic acid, polystyrene maleic acid, polystyrene maleic anhydride, or a combination thereof.

2A 2015203105 18 Nov 2016

Item 8. The coating fibrous substrate of item 1, wherein the inorganic fillers include limestone powder, clay, sand, mica, perlite, diatomaceous earth, feldspar, talc, and glass beads.

Item 9. A method of forming a coated fibrous substrate comprising: providing a formaldehyde-free coating composition comprising a binder system, the binder system comprising a polyol crosslinker and a polycarboxy polymer neutralized with a volatile base; applying the formaldehyde-free coating composition to a major surface of a fibrous substrate; curing the binder system such that the volatile base evaporates from the formaldehyde-free coating composition and the polycarboxy polymer reacts with the polyol crosslinker; wherein the formaldehyde-free coating composition has a pH of from about 6 or greater and hygroscopic expands and the binder system.

Item 10. The method according to item 9, wherein the polyol crosslinker is free of alkanolamine compounds.

Item 11. The method according to any one of items 9 to 10, wherein the polyol crosslinker selected from the group consisting of glycerol, dextrose, fructose, sucrose, and sorbitol.

Item 12. The method according to any one of items 9 to 11, wherein the formaldehyde-free coating composition has a pH of from about 6 to about 10.

Item 13. The method according to any one of claims 9 tol2 wherein the binder system has a metal ion concentration of less than 1,000 ppm.

Item 14. The method according to any one of items 9 to 13, wherein the formaldehyde-free coating composition further comprises a filler selected from an inorganic filler, an organic filler, and a combination thereof.

Item 15. The method according to any one of items 9 to 14, wherein the polycarboxy polymer is a homopolymer.

Item 16. The method according to any one of items 9 to 15, wherein the polycarboxy polymer is polyacrylic acid, polymethacrylic acid, polystyrene maleic acid, polystyrene maleic anhydride, or a combination thereof.

Item 17. The method according to item 14, wherein the filler and the binder system are present in a weight ratio ranging from about 3.0:1.0 to about 10:1.0.

2B 2015203105 18 Nov 2016

DETAILED DESCRIPTION

[0009] The present disclosure provides a formaldehyde-free coating that can be applied to a major surface of a fibrous substrate to impart resist sag resistance while maintaining a high modulus. The coating has neutral or mild alkaline pH of about 6 or greater, and preferable from about 6 to about 10, such that the coating is compatible with other coatings, various fillers, and processing equipment. The preferred coating binder system includes at least one polycarboxy polymer neutralized with a volatile base and at least one polyol capable of crosslinking the neutralized polycarboxy polymer. More specifically, the polyol crosslinks the polycarboxy polymer to form three dimensional networks which have a high modulus and are capable of hygroscopic expansion to inhibit sag. The molar ratio between carboxyl groups in the polycarboxy polymer to hydroxyl groups in the polyol is from about 1:0.2 to about 1:8.

[0010] The polycarboxy polymers are homopolymers or copolymers which contain multi carboxyl groups. The polycarboxy polymers are synthesized from monomers with at least one monomer containing carboxyl groups. Suitable monomers containing carboxyl groups include acrylic acid, methacrylic acid, maleic acid, fumaric acid, maleic anhydride, etc. Suitable monomers containing no 3 2015203105 10 Jun2015 carboxyl groups include styrene, ethylene, propylene, acrylate esters, etc. The preferred polycarboxy polymers are pofyscrylic acid which is synthesized from only acrylic acid monomer. (0011 j The polycarboxy polymers are neutralized in aqueous solutions with a volatile base so as not to hinder the crosslinking reaction and, thus, avoiding any detriment to sag performance. Aqueous ammonia is the preferred choice of volatile base because ammonia will evaporate qeickiy and will allow faster curing. Additionally, the coating binder should be free from any single or multi-valence metal ions such as sodium, potassium, calcium, etc. Unexpectedly, any significant amount of those ions in the coating wasifound: to a iso hinder the crossiinking reaction. The coating binder therefore preferably has a mets! ion concentration of less than 1000 ppm and more preferably less than 500 ppm. |0012] Polydls ffom renewable resources are particularly preferred due to their renewability, low toxicity, and low cost The most favorable renewable polyols includes glycerol, dextrose, fructose, sucrpSe* and sorbitol, etc, Polyols are poiyhydric alcohols containing two or more hydroxyl groups. The polyol cross Sinkers Include secondary' alkanoiamine (such as diethanolamine, ethyl diethanolamine, methyl diethanolamine, etc,}, tertiary alkanoiamine {such as triethanolamihej* glycerol, glucose (i>e., dextrosej, fructose, sucrose, sorbitol, resorcinol, catechol, pyrogalloi, giycollated ureas, polyvinyl alcohol 1,4-cyclohexane efiol, pentaerythritol, ethylene glycol, dietbyiene glycol, triethylene glycol, hydroxyl terminated poiyethyleneoxide, trimsthyloi propane, or a mixture thereof! (9013) The mbipr ratio ^tvyeen carfeo*¥i gfOUps in the poiycarboxy polymer to hydroxy! groups in the polyol affect the crosslinking density, coating modulus, coating hygroscopic properties, and the sag resistance property,: Therefore, the carboxyl to hydroxyl molar ratio of can be manipulated fp the desired end properties. The preferred carboxyl to hydroxyl molar ratio is from about 1:0.2 to aMbt 1:8. {0014) Hygmsecilpfe sag resistant properties can be further modulated with filler addition level, The fillers should be insensitive to moisture 'Which can then darhpefiithb hygroscopic ^pansier a t 2015203105 10 Jun2015 high humidity. Also, the fillers preferably have a high modulus which, in turn, can improve the cured coating modulus. A variety of fillers can be used either organic or inorganic. Suitable inorganic fitters Include limestone, day, sand, mica, perlite, diatomaceous earth, feldspar, talc, glass beads, etc. Suitable organic fillers include hard plastic powders such as polycarbonate, polyesters, nylon, poiyprccy'sre ipolyethylene, etc,· EXAMPLES Example 1 fOOlSf The waterborne coating SC #1 was made in the following procedure: 247.0 g ammonium polyacrylic acid (38%w/w) was added into a mixer containing 521,8 g water. While mixing, 102.5 g Dextrose, 1.0 g Tergitol TMfcMs Iptting agent), 2,6 g defcamer, 1,2 g biodicfe, and 1519.7 g filler slurry, were added in sequence to the mixer. The finished coating had solids content of 55%, Brookfield viscosity of 3,400 cps, pH of 8.9, and filler to binder (F:8) ratio of 6:1. (O01f>| The coating was applied by spray to the back side of three types of ceiling panels. They ail contain different levels of reinforcing fibers (either mineral wool or glass fiber). Panel S3 was a kilned product containing additional elay&Thte dry application weight was 10 grams per square foot, in order to balance the ceiling tile stfefe caUfed by drying the back coating a prime coating {PC #1) comprisfhg a filler to binder ratio of 5:1 and 50% solids was also applied to the face of ceiling panel with dry: application weight at about 10 grams per square foot. The sprayed panel was then dried and cured at 410*8 for 10 minutes in an oven. The coated panels were then cut into 24" by 3" strips to test for sag at 82“F and ftH loop of 35% to 90% to 35% for 2 cycles (24 hours per cycle). The final sag is a projected value at 4lh cycle. The sag data were then converted using empirical factors to 2'x2' and 2'x4' of full (Sizes,. |001?| As shown in Table 1 are modulus of elasticity (MOP), modulus of rupture (MOR), formaldehyde f mission (CA135$), andseg data of ail three base panels before coating applications, it is shown in

S 2015203105 10 Jun2015

Table ! that modulus of rupture | MO R) and modulus of elasticity (MOEj increase with increasing the level of mineral wool fiber or glass fiber. That dearly indicates that ihepanei gets stronger as increasing reinforcing fibers. The kilned panel #3 (containing most wool fiber and additional days) is the strongest of all. The ha-e Panel 81 with minimal reinforcing fiber sagged the worst. Sag of bare panels was fmpfbyed ds· the mechanical strength was improved. Pane! #3 had no sag since it is essentially non-hygroscopic. Therefore, the panels with poor mechanical property will need special costings to improve their sag resistance while there is no such need for kilned Panel #4,

Table i. Summary of test results for Examples 1-2 and Comparative Examples 1-2

Pane! ID Panel #1 Panel#2 Panel #3 Bare Panel Property' Pane! Construction (Reinforcing Fiber %} Ca. 10% Ca. 30% Ca. 40-50% (Kilned w/ clay) MOE (psi) 15480 19180 116500 76 96 223 Formaldehyde Emission Factor (CA-135G) pg/m’hr - -- Mon-detectable Sag (2'χΛ1) :-598 -404 -75 I Example 1 \ Coatings F:B Ratio (BC ffl/PC#2) 6:1 (8C8l/PC#X) m (Bcii/pcm) ' m 1 (Requirement = > -150} -98 -loa; -8 1 Sag (2'x4;) (Requirement = > -200} |210....... -186 -21 Example 2 Coatings F:B Ratio (BC #2/PC Hi} 1:1 (BC P2/PC #1} 2:1 (BC S2/PC Ul) 2:1 Formaldehyde Emission Factor (CA-1350) pg/nr'hr --: Non-detectable Sag (2.’x2'} (Requirement ~ > -iso) *52 -3| •15 | ":M{2'x4') ........................ (Requirement ~ > -200) yiSi -7| -38 Comparative Example 1 Coatings F;8 Ratio (Bcei/pc#i) .,,..,.:6::1 (BC #3/PC f#l) ,, Oil,. ., {BCifS/PCSX} 0:1 Sag (2'x2'j (Requirement -* > -150} *228 -219 -16 Sag {2fx4'.j (Requirement = > -200} *489 :-36f -35 5

Con Coa rparative Kxample 2 tings F:8 Ratio |8C 44/PC 42) m r 1 Sag (2'x2'J (Requirement = > 150) -212 1 Sag {2'x4'j i {Requirements > -200} -535 ] 2015203105 10 Jun2015 18] When panels were coated with BC #1 and PC SI their sag behaviors changed depending on the level of reinforcing fibers. As before sag fesPtts impfbveci with increasing reinforcing fibers in the pane! Table 1 shows that for Panel tf2 the BC til coating satisfied sag resistance for both the 2x2' and 2x4' sizes, for Panel 41, the BC Pi costing satisfied sag resistance for 2x2', but did not provide enough sag resistance for the 2'x4' panel size due to its wider span. :j£gam:oie2 [0019] The waterborne coating BC 42 was made ih tbe fdifowlng procedure' 576.0 g ammonium poiyacrylic acid 08%w/w) was added into SshdxPf to mixing, 239.3 g

Dextrose, 1.0 g Tergitol TMN-6, 2.6 g defoarner, 1.2 g biocide, and 1X87.5 g filler slurry were added in sequence to the mixer. The finished coating had solids content of 55%, Brookfield viscosity of 1,100 eps, pH of 8.9, and filler to binder {F:8} ratio of 2:1. Following the same coating application, coating curing, and panel sag testing procedure as described In Example 1 three different ceiling panels were evaluated using this back coating, The converted sag data are shown in Table i, p028f Formaldehyde emission testing using the California CA 13SO method has shown that Pane! #3 With BC 42 coating and bare Panel #3 both had non-detectabfe emissions levels. Therefore, the BC 42 coating did not add oetectable formaldehyde emissions in this test. These panels would easily met the formaldehyde emission limit of 18.9 pg/rrAtr in the Collaborative for High Performance Schools iCHPS) code. From ; able i it has cfeariy shown that BC if2 formula has better sag resistance than BC 41 formula 7 2015203105 10 Jun2015 for the 2*x4- panels. However, panel cupping became art issue if BC 82 formula is used for the 2'x?‘ pane)

Comparative Example 1 [0021} The waterborne coating 1C #3 was made in the following procedure: 1557.6 g ammonium pofyacryiic acid {|S%w/w) was added into a mixer containing 177.4 g water. While mixing, 647.0 g Dextrose, 2,6 g defoamer, and 1.2 g biocide were added to the mixer. The finished coating had solids content of:5056, Brookfield viscosity of 170 cps, pH of 9.6, and filler to binder {F: 8) ratio of 0:1. FoiSowing the same coating application, coating curing, and panel sag testing procedure as described in Example 1 three differenCceliing panels were evaluated using this back coating. The converted sag data are shown in Table k [0022] When a formula without fillers was used in ceiling Panels #1 and #2, the reinforcing effect of fillers was lost.and the coating did not provide the panels with adequate panel sdg piffdrrnance. This clearly indicates that fillers are very helpful to reinforce the strength ipf the binder,

Comparative Example 2 (0023| The waterborne coating BC #4 was made in the following procedure: 266,3 g Rhoplex Cl 720 latex (acrylic base, Tg*95 X 50% solids) was added into a mixer containing SI.2 g water. While mixing, 0,1 g tetra-sodium polyphosphate, 1568,2 g Kaolin day slurry (70% solids), 81.1 Mica, 0.8 g biocide, 10 g Rhoplex SM 232 thickener, and 3.2 g defoamer were added in sequence to the mixer. The finished fpating had solids content of 65%, Brookfield viscosity of 520 cps, pH of 6.6, and filler to binder (F:B) ratio pfabout 8:1, Following the same coating application, coating curing, 3nd pane! sag testing procedure as described In Example 1 Panel i! was evaluated uibithis back coating: ^ new prime: coating PC #2 {16:1 FtB ratis and 50% solids) was used in this comparative example. The converted sag data are shown in Table I. 8 2015203105 10 Jun2015

Pane! #2 failed the sag test at both panel sites although the 2**2' panels did better than 2'χ4' panels. Therefore, on the same cost base the latex based back coating 8C #4 had higher sag values than 8C #1 and BC #2 and was not adequate enough to resist humidity sag.

Table IS. Sag results on Panel #1 coated with various coatings

Example ID jpExInipile' 3' | Example 4 Example 5 Example 6 Coating ID | BC#5/PCffl | BC #6/PC #1 BC #7/PC #1 BC #8/PC M F:8 ratio 1 2:1 ΐ 2:1 2.7:1 2.5:1 Sig:i2i*4fv"" (Requirement = > -200) -198 *188 -180 -126·

Example 3 [0025] The waterborne coaling BC #5 was made in the fd!l!Mi| procedure: 328.0 g SMA-1000H from

Sartomer Co. was added into a mixer containing 291.0 g water. While mixing, 38,0 g glycerol, 1,0 g: defoamec 1.0 g biocide, and 340.0 g Kaolin clay were added into the mixer. The resulting coating had 50% solids, 630 cps Brookfield viscosity, and filler to binder ratio of 2:1. application, coating curing, and panel sag testing procedure as described in Example 1 Panel STHwith abbot 10% reinforcing fiber) was tested using this coating. The coated panel had a sag value of -198 mils after 4 humidity cycles as shown in Table if.

Example^ [0026] The waterborne coating BC86 was hiMein the following procedure: 227.2 g SMA-1Q00H was added into a mixer containing 352,7 g water. While;musing, 76.& g dextrose (glucose), 1,0 g defoamer, 1.0 g biocide, and 340.0 g Kaolin ciaywtre added into the rbixer. The resulting coating' haliSiMsbilds, 2700 cps Brookfield viscosity, 8,9 pH, and filler to binder ratio of 2:1. Following the same coating application, coating curing, and panel sag testing procedure as described in Example 1 Panel ffl was 9 2015203105 10 Jun2015 be appreciated by those skilled fhfhdAri:, hdwd very that the tested using this costing. This coated panes had 2 sag value c? -188 mils site? 4 humidity cycles as shown in Table Si.

Exa m ole : ¾ [0027) The waterborne coating BC #7 was made in the following procedure* 346.8 g SMAiOOOH was added into a mi%rcontaining 377.9 g water. While mixing,: 22-1 g triethanolamine {TEA), 1.0 g defoamer, and 440,9g Kaolin clay were added into thecontainer. The finished coating had filler to binder ratio of 2,7:1, 50% solids, 1260 cps Brookfield viscosity, and 8,9 pH, following the same coating application, coating curing, and panel sag testing procedure as described in Example 1 Panel #1 was tested using: this coating. This coated tile had a sag value of -180 mils after 4 humidity cycles as shown in Tabie 11. rxampie 8 {6028) The waterborne coating BC#8 using a commercial thermoset binder <39164617 from Georgia-Pacific, inc. based on poiycarboxy polymer and polyol was made as follows: 449.4 g GP364G17 was added into s mixer containing 445.0 g water. While mixing, 1.2 g defoamer, 1.0 biocide, and 503.0 g kaolin day were added into the mixer. The resulting coating had filler to binder ratio of 2,5.1, 50% solid 720 cps Brookfield viscosity, and S.O pH. following the same coating application, coating curing, and panel sag testing procedure as described in Example 1 Panel dl was tested using this coating. This Coated tile had a sag value of -126 mils after 4 humidity eyeifS:as shown in Tabie 11.

[0029] The foregoing illustrates some of the possibilities for practicing the invention. Many other pm bid i mete ere: possible Within the scope ah| spiHt pf the invention. For example, although the costing is described herein as being incorporated in a ceiling tile structure, it will coating may have other applications, for exampie, In fie; 10 2015203105 10 Jun2015 building, furniture, or automotive industry. It is, therefore, intended that the Foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their Ml range Of equivalents. 11

Claims

Claims

1. A coated fibrous substrate comprising: a fibrous substrate comprising reinforcing fiber in an amount of equal to or less than 40 wt. % based on the total weight of the fibrous substrate; and a formaldehyde-free coating applied to a major surface of the fibrous substrate, the formaldehyde-free coating comprising a binder system and a filler, the binder system comprising: a polycarboxy polymer and a polyol crosslinker selected from the group consisting of glycerol, dextrose, fructose, sucrose, and sorbitol; and a volatile base, wherein the formaldehyde-free coating has a pH of from about 6 or greater and hygroscopic expands and wherein the filler and the binder system are present in a weight ratio ranging from about 3.0:1.0 to about 10:1.
2. The coated fibrous substrate of claim 1, wherein the formaldehyde-free coating has a pH of from about 6 to about 10.
3. The coated fibrous substrate of claim 1 or 2, wherein the binder system has a metal ion concentration of less than 1000 ppm.
4. The coated fibrous substrate of any one of claims 1 to 3, wherein the binder system has a metal ion concentration of less than 500 ppm.
5. The coated fibrous substrate according to any one of claims 1 to 4, wherein the coating further comprises a filler and the filler is selected from: an inorganic filler, an organic filler, and a combination thereof.
6. The coated fibrous substrate of claim 1, wherein the polycarboxy polymer is a homopolymer.
7. The coated fibrous substrate of claim 1, wherein the polycarboxy polymer is polyacrylic acid, polymethacrylic acid, polystyrene maleic acid, polystyrene maleic anhydride, or a combination thereof.
8. The coating fibrous substrate of claim 1, wherein the inorganic fillers include limestone powder, clay, sand, mica, perlite, diatomaceous earth, feldspar, talc, and glass beads.
9. A method of forming a coated fibrous substrate comprising: providing a formaldehyde-free coating composition comprising a binder system, the binder system comprising a polyol crosslinker and a polycarboxy polymer neutralized with a volatile base; applying the formaldehyde-free coating composition to a major surface of a fibrous substrate; curing the binder system such that the volatile base evaporates from the formaldehyde-free coating composition and the polycarboxy polymer reacts with the polyol crosslinker; wherein the formaldehyde-free coating composition has a pH of from about 6 or greater and hygroscopic expands.
10. The method according to claim 9, wherein the polyol crosslinker is free of alkanolamine compounds.
11. The method according to any one of claims 9 to 10, wherein the polyol crosslinker selected from the group consisting of glycerol, dextrose, fructose, sucrose, and sorbitol.
12. The method according to any one of claims 9 to 11, wherein the formaldehyde-free coating composition has a pH of from about 6 to about 10.
13. The method according to any one of claims 9 tol2 wherein the binder system has a metal ion concentration of less than 1,000 ppm.
14. The method according to any one of claims 9 to 13, wherein the formaldehyde-free coating composition further comprises a filler selected from an inorganic filler, an organic filler, and a combination thereof.
15. The method according to any one of claims 9 to 14, wherein the polycarboxy polymer is a homopolymer.
16. The method according to any one of claims 9 to 15, wherein the polycarboxy polymer is polyacrylic acid, polymethacrylic acid, polystyrene maleic acid, polystyrene maleic anhydride, or a combination thereof.
17. The method according to claim 14, wherein the filler and the binder system are present in a weight ratio ranging from about 3.0:1.0 to about 10:1.0.