SAG RESISTANT, FORMALDEHYDE-FREE COATED FIBROUS SUBSTRATE

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 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.

Claims

1. A method of manufacture of a sag-resistant building panel comprising applying a coating composition to a major surface of a substrate, the coating composition comprising: a polymeric binder comprising carboxylic acid groups; a crosslinker; a neutralizing agent; and liquid carrier; wherein the coating composition is formaldehyde-free and has a pH of at least 6; and drying the coating composition applied to the substrate such that the liquid carrier is evaporated to form the sag-resistant building panel.

2. The method according to claim 1, wherein the liquid carrier comprises water.

3. The method according to claim 2, wherein the liquid carrier is present in an amount of about 45 wt. % to about 50 wt. % based on the total weight of the coating composition.

4. The method according to claim 1, wherein the coating composition has a metal ion concentration of less than 1000 ppm.

5. The method according to claim 1, wherein the substrate comprises a fibrous body

6. The method according to claim 1, wherein the crosslinker comprises a polyol.

7. The method according to claim 6, wherein the polyol comprises an amine group.

8. The method according to claim 6, wherein the polyol is selected from the group consisting of diethanolamine, triethanolamine, glycerol, dextrose, sucrose, fructose, sorbitol, and combinations thereof.

9. The method according to claim 1, wherein the blend further comprises a filler in a weight ratio of filler to polymeric binder ranges from about 1:1: to about 10:1.

10. A method of manufacture of a sag-resistant building panel comprising applying an aqueous coating composition to a major surface of a fibrous substrate, the coating composition comprising: a polymeric binder having carboxylic acid groups; a hydroxyl-functional crosslinker; a neutralizing agent; filler; and wherein a weight ratio of filler to polymeric binder ranges from about 1:1: to about 10:1, and the coating composition has a metal ion concentration of less than 1000 ppm; and drying the coating composition applied to the fibrous substrate such that the liquid carrier is evaporated to form the sag-resistant building panel.

11. The method composition of claim 10, wherein polymeric binder is a homopolymer.

12. The method composition of claim 10, wherein the polymeric binder is selected from the group consisting of polyacrylic acid, polymethacrylic acid, polystyrene maleic acid, polystyrene maleic anhydride, or combinations thereof.

13. The method composition of claim 12, wherein the neutralizing agent comprises a volatile base.

14. The method composition of claim 13, wherein the volatile base is aqueous ammonia.

15. The method composition of claim 10, wherein the filler is selected from inorganic fillers, organic fillers and combinations thereof.

16. The method composition of claim 15, wherein the filler comprises inorganic fillers selected from limestone powder, clay, sand, mica, perlite, diatomaceous earth, feldspar, talc and glass beads.

17. The method composition of claim 15, wherein the filler comprises organic filler that includes hard plastic powders.

18. A method of manufacture of a sag-resistant building panel comprising applying a coating composition to a major surface of a fibrous substrate, the coating composition comprising a blend of: a polymeric binder comprising carboxylic acid groups that are at least partially neutralized with a volatile base; a crosslinker; liquid carrier; filler; and wherein the coating composition is formaldehyde-free and is free of any single or multi-valence metal ions selected from sodium, potassium, and calcium, and the coating composition has a pH of at least about 6; and drying the coating composition applied to the fibrous substrate such that the liquid carrier is evaporated to form the sag-resistant building panel.

19. The method according to claim 19, wherein the volatile base is aqueous ammonia.

20. The method according to claim 18, wherein the crosslinker is selected from the group consisting of diethanolamine, triethanolamine, glycerol, dextrose, sucrose, fructose, sorbitol, and combinations thereof.

Description

DETAILED DESCRIPTION

[0013] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0014] As used throughout, ranges are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, all references cited herein are hereby incorporated by referenced in their entireties. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure controls.

[0015] Unless otherwise specified, all percentages and amounts expressed herein and elsewhere in the specification should be understood to refer to percentages by weight. The amounts given are based on the active weight of the material.

[0016] The present invention is 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.

[0017] 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 carboxyl groups include styrene, ethylene, propylene, acrylate esters, etc. The preferred polycarboxy polymers are polyacrylic acid which is synthesized from only acrylic acid monomer.

[0018] 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.

[0019] Aqueous ammonia is the preferred choice of volatile base because ammonia will evaporate quickly 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 was found to also hinder the crosslinking reaction. The coating binder therefore preferably has a metal ion concentration of less than 1000 ppm and more preferably less than 500 ppm.

[0020] Polyols from renewable resources are particularly preferred due to their renewability, low toxicity, and low cost. The most favorable renewable polyols includes glycerol, dextrose, fructose, sucrose, and sorbitol, etc. Polyols are polyhydric alcohols containing two or more hydroxyl groups. The polyol crosslinkers include secondary alkanolamine (such as diethanolamine, ethyl diethanolamine, methyl diethanolamine, etc.), tertiary alkanolamine (such as triethanolamine), glycerol, glucose (i.e., dextrose), fructose, sucrose, sorbitol, resorcinol, catechol, pyrogallol, glycollated ureas, polyvinyl alcohol, 1,4-cyclohexane diol, pentaerythritol, ethylene glycol, diethylene glycol, triethylene glycol, hydroxyl terminated polyethyleneoxide, trimethylol propane, or a mixture thereof.

[0021] The molar ratio between carboxyl groups in the polycarboxy polymer to hydroxyl 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 to optimize the desired end properties. The preferred carboxyl to hydroxyl molar ratio is from about 1:0.2 to about 1:8.

[0022] Hygroscopic expansion and sag resistant properties can be further modulated with filler addition level. The fillers should be insensitive to moisture which can then dampen the hygroscopic expansion at 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 fillers include limestone, clay, sand, mica, perlite, diatomaceous earth, feldspar, tale, glass beads, etc. Suitable organic fillers include hard plastic powders such as polycarbonate, polyesters, nylon, polypropylene, polyethylene, etc.

EXAMPLES

Example 1

[0023] The waterborne coating BC #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 TMN-6 (wetting agent), 2.6 g defoamer, 1.2 g biocide, and 1519.7 g filler slurry were added in sequence to the mixer. The finished coating had solids content of 55%, Brookfield viscosity of 3,4(0) cps, pH of 8.9, and filler to binder (F:B) ratio of 6:1.

[0024] The coating was applied by spray to the back side of three types of ceiling panels. They all contain different levels of reinforcing fibers (either mineral wool or glass fiber). Panel #3 was a kilned product containing additional clays. The dry application weight was 10 grams per square foot. In order to balance the ceiling tile stress caused by drying the back coating a prime coating (PC #1) comprising 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° F. 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 RH loop of 35% to 90% to 35% for 2 cycles (24 hours per cycle). The final sag is a projected value at 4.sup.th cycle. The sag data were then converted using empirical factors to 2′×2′ and 2′×4′ of full panel sizes.

[0025] As shown in Table I are modulus of elasticity (MOE), modulus of rupture (MOR), formaldehyde emission (CA 1350), and sag data of all three base panels before coating applications. It is shown in Table I that modulus of rupture (MOR) and modulus of elasticity (MOE) increase with increasing the level of mineral wool fiber or glass fiber. That clearly indicates that the panel gets stronger as increasing reinforcing fibers. The kilned panel #3 (containing most wool fiber and additional clays) is the strongest of all. The bare Panel #1 with minimal reinforcing fiber sagged the worst. Sag of bare panels was improved as the mechanical strength was improved. Panel #3 had no sag since it is essentially non-hygroscopic. Therefore, the panels with poor mechanical property will need special coatings to improve their sag resistance while there is no such need for kilned Panel #4.

TABLE-US-00001 TABLE I Summary of test results for Examples 1-2 and Comparative Examples 1-2 Panel ID Bare Panel Property Panel #1 Panel #2 Panel #3 Panel Construction Ca. 10% Ca. 30% Ca. 40-50% (Reinforcing Fiber %) (Kilned w/clay) MOE (psi) 15480 19180 116500 MOR (psi) 76 96 223 Formaldehyde Emission Factor — — Non-detectable (CA-1350 μg/m.sup.2hr) Sag (2′ × 4′) −598 −404 −75 Example 1 (BC #1/PC #1) (BC #1/PC #1) (BC #1/PC #1) Coatings F:B Ratio 6:1 6:1 6:1 Sag (2′ × 2′) −98 −103 −8 (Requirement => −150) Sag (2′ × 4′) −210 −186 −21 (Requirement => −200) Example 2 (BC #2/PC #1) (BC #2/PC #1) (BC #2/PC #1) Coatings F:B Ratio 2:1 2:1 2:1 Formaldehyde Emission Factor — — Non-detectable (CA-1350 μg/m.sup.2hr) Sag (2′ × 2′) −52 −32 −15 (Requirement => −150) Sag (2′ × 4′) −131 −72 −38 (Requirement => −200) Comparative Example 1 (BC#3/PC #1) (BC #3/PC #1) (BC #3/PC #1) Coatings F:B Ratio 0:1 0:1 0:1 Sag (2′ × 2′) −228 −219 −16 (Requirement => −150) Sag (2′ × 4′) −489 −367 −39 (Requirement => −200) Comparative Example 2 (BC #4/PC #2) Coatings F:B Ratio 0:1 Sag (2′ × 2′) −212 (Requirement => −150) Sag (2′ × 4′) −535 (Requirement => −200)

[0026] When panels were coated with BC #1 and PC #1 their sag behaviors changed depending on the level of reinforcing fibers. As before sag results improved with increasing reinforcing fibers in the panel. Table 1 shows that for Panel #2 the BC #1 coating satisfied sag resistance for both the 2×2′ and 2×4′ sizes. For Panel #1, the BC #1 coating satisfied sag resistance for 2×2′, but did not provide enough sag resistance for the 2′×4′ panel size due to its wider span.

Example 2

[0027] The waterborne coating BC #2 was made in the following procedure: 576.0) g ammonium polyacrylic acid (38% w/w) was added into a mixer containing 387.8 g water. While mixing, 239.3 g Dextrose, 1.0 g Tergitol TMN-6, 2.6 g defoamer, 1.2 g biocide, and 1187.5 g tiller slurry were added in sequence to the mixer. The finished coating had solids content of 55%. Brookfield viscosity of 1,100 cps, pH of 8.9, and filler to binder (F:B) 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 1.

[0028] Formaldehyde emission testing using the California CA 1350 method has shown that Panel #3 with BC #2 coating and bare Panel #3 both had non-detectable emissions levels. Therefore, the BC #2 coating did not add detectable formaldehyde emissions in this test. These panels would easily met the formaldehyde emission limit of 18.9 μg/m.sup.2 hr in the Collaborative for High Performance Schools (CHPS) code. From Table I it has clearly shown that BC #2 formula has better sag resistance than BC #1 formula for the 2′×4′ panels. However, panel cupping became an issue if BC #2 formula is used for the 2′×2′ panel size.

Comparative Example 1

[0029] The waterborne coating BC #3 was made in the following procedure: 1557.6 g ammonium polyacrylic acid (38% 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 50%, Brookfield viscosity of 170 cps, pH of 9.6, and filler to binder (F:B) ratio of 0:1. 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.

[0030] 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 sag performance. This clearly indicates that fillers are very helpful to reinforce the strength of the binder.

Comparative Example 2

[0031] The waterborne coating BC #4 was made in the following procedure: 265.3 g Rhoplex GL 720 latex (acrylic base, Tg=95° C., 50% solids) was added into a mixer containing 81.2 g water. While mixing, 0.1 g tetra-sodium polyphosphate, 1568.2 g Kaolin clay slurry (70% solids), 81.1 Mica, 0.8 g biocide, 1.0 g Rhoplex RM 232 thickener, and 3.2 g defoamer were added in sequence to the mixer. The finished coating had solids content of 65%. Brookfield viscosity of 520 cps, pH of 6.6, and filler to binder (F:B) ratio of about 8:1. Following the same coating application, coating curing, and panel sag testing procedure as described in Example 1 Panel #1 was evaluated using this back coating. A new prime coating PC #2 (16:1 F:B ratio and 50% solids) was used in this comparative example. The converted sag data are shown in Table I.

[0032] Panel #1 failed the sag test at both panel sizes although the 2′×2′ panels did better than 2′×4′ panels. Therefore, on the same cost base the latex based back coating BC #4 had higher sag values than BC #1 and BC #2 and was not adequate enough to resist humidity sag.

TABLE-US-00002 TABLE II Sage results on Panel #1 coated with various coatings Bare Panel Property Example 3 Example 4 Example 5 Example 6 Coating ID BC #5/PC #1 BC #6/PC #1 BC #7/PC #1 BC #8/PC #1 F:B ratio 2:1 2:1 2.7:1 2.5:1 Sag (2′ × 4′) −198 −188 −180 −126 (Requirement => −200)

Example 3

[0033] The waterborne coating BC #5 was made in the following 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 defoamer, 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. Following the same coating application, coating curing, and panel sag testing procedure as described in Example 1 Panel #1 (with about 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 II.

Example 4

[0034] The waterborne coating BC #6 was made in the following procedure: 227.2 g SMA-1000H was added into a mixer containing 352.7 g water. While mixing, 76.6 g dextrose (glucose), 1.0 g defoamer, 1.0 g biocide, and 340.0 g Kaolin clay were added into the mixer. The resulting coating had 50% solids, 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 #1 was tested using this coating. This coated panel had a sag value of −188 mils after 4 humidity cycles as shown in Table II.

Example 5

[0035] The waterborne coating BC #7 was made in the following procedure: 346.8 g SMA1000H was added into a mixer containing 377.9 g water. While mixing, 22.1 g triethanolamine (TEA), 1.0 g defoamer, and 440.9 g Kaolin clay were added into the container. 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 Table II.

Example 6

[0036] The waterborne coating BC #8 using a commercial thermoset binder GP364G17 from Georgia-Pacific. Inc. based on polycarboxy polymer and polyol was made as follows: 449.4 g GP364G17 was added into a mixer containing 445.0 g water. While mixing, 1.2 g defoamer, 1.0 biocide, and 503.0 g kaolin clay were added into the mixer. The resulting coating had filler to binder ratio of 2.5:1, 50% solids, 720 cps Brookfield viscosity, and 8.0 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 −126 mils after 4 humidity cycles as shown in Table II.

[0037] The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. For example, although the coating is described herein as being incorporated in a ceiling tile structure, it will be appreciated by those skilled in the art, however, that the coating may have other applications, for example, in the 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 full range of equivalents