THIN FIBER CEMENT ROOF TILES COMPRISING CORE-SHELL EMULSIONS HAVING IMPROVED IMPACT RESISTANCE

Abstract

The present invention provides fiber cement articles, such as roof tiles having improved impact and hail resistance and methods for making them. The fiber cement articles comprise cement, an optional filler, reinforcing fibers, such as poly(vinyl alcohol) fibers or a mixture of cellulosic and synthetic fibers, one or more core-shell aqueous emulsion polymers having a crosslinked rubbery core with a calculated glass transition temperature (calculated Tg) of from −20 to −140° C., and an at least partially grafted acrylic or vinyl shell polymer having a calculated Tg of from 20 to 170° C., and having a Z-average primary particle size of from 55 to 800 nm, or, preferably, from 140 to 650 nm. The solids weight ratio of the crosslinked rubbery core to the shell of the core-shell aqueous emulsion polymer may range from 85:20 to 97:3.

Claims

1. A fiber cement article having improved impact resistance comprising from 1 to 25 wt. %, based on the total solids weight of the fiber cement article, of one or more core-shell aqueous emulsion polymers having a crosslinked rubbery core with a calculated glass transition temperature (calculated Tg) of from −20 to −140° C., and an at least partially grafted acrylic or vinyl shell polymer having a calculated Tg of from 20 to 170° C., and a Z-average primary particle size of from 55 to 800 nm, cement, and, further wherein, the fiber cement article comprises reinforcing fibers.

2. The fiber cement article as claimed in claim 1, wherein the fiber cement article comprises from 2.4 to 19 wt. %, based on the total solids weight of the fiber cement article, of one or more core-shell aqueous emulsion polymers having a crosslinked rubbery core with a calculated glass transition temperature (calculated Tg) of −20° C., and an at least partially grafted acrylic or vinyl shell polymer having a calculated Tg of from 20 to 170° C.

3. The fiber cement article as claimed in claim 2, wherein at least one of the one or more core-shell aqueous emulsion polymer comprises an at least partially grafted acrylic or vinyl shell polymer having a calculated Tg of 45° C. or higher.

4. The fiber cement article as claimed in claim 1, wherein the shell polymer comprises the copolymerized residues of at least one of the one or more vinyl or C.sub.1 to C.sub.4 alkyl (meth)acrylates.

5. The fiber cement article as claimed in claim 1, wherein the shell polymer comprises the copolymerized residues of methyl methacrylate (MMA).

6. The fiber cement article as claimed in claim 1, wherein at least one of the one or more core-shell aqueous emulsion polymer has a Z-average primary particle size of from 110 to 800 nm.

7. The fiber cement article as claimed in claim 6, wherein at least one of the one or more core-shell aqueous emulsion polymers has a Z-average primary particle size of from 140 to 650 nm.

8. The fiber cement article as claimed in claim 1, wherein the weight ratio of the crosslinked rubbery core of the core-shell aqueous emulsion polymer to the shell polymer of the core-shell aqueous emulsion polymer ranges from 85:20 to 97:3.

9. The fiber cement article as claimed in claim 1, wherein the crosslinked rubbery core of at least one of the one or more core-shell aqueous emulsion polymer in the fiber cement article comprises the copolymerized residues of from 0.2 to 2 wt. % of a crosslinking multi-ethylenically unsaturated monomer, monomer, based on the total weight of monomers used to make the crosslinked rubbery core.

10. The fiber cement article as claimed in claim 1, wherein the reinforcing fibers are chosen from cellulosic fibers, synthetic fibers or mixtures thereof.

11. The fiber cement article as claimed in claim 10, wherein the reinforcing fibers are chosen from synthetic fibers comprising poly(vinyl alcohol) fibers.

Description

[0119] EXAMPLES: The following examples are used to illustrate the present invention without limiting it to those examples. Unless otherwise indicated, all temperatures are ambient temperatures (21-23° C.) and all pressures are 1 atmosphere.

[0120] Component proportions are indicated in the examples, below. The following abbreviations are used: Pbw: Parts by weight;

[0121] The materials used in the examples are, as follows:

[0122] Cellulose Fiber: Softwood pulp made of long fibers from coniferous tree species and used as an aqueous slurry, with a refining treatment with intensity level around 60-63 SR grade (w/units expressed in Schopper Riegler grade) in accordance with ISO 5267-1, 27.8 wt. % solids (PineCel™ fibers, Klabin S/A, Parand, Brazil) Cement: Type III Portland Cement comprising calcium silicate alite (3CaO SiO.sub.2) or (C3S) about 50-70 wt. %, and the remainder as belite (2CaO.Math.SiO.sub.2) or (C2S), and phases composed of tricalcium aluminate (3CaO.Math.Al.sub.2O.sub.3) or (C.sub.3A) and tetracalcium ferroaluminate (4CaO.Math.Al.sub.2O.sub.3.Math.Fe.sub.2O.sub.3) or C.sub.4AF.

[0123] Limestone filler: Calcário Agricola—42-45 (wt. %) CaO (˜40 micron or 325 mesh, Votorantim, Itau de Minas—Minas Gerais, Brazil).

[0124] Synthetic Fiber: Polyvinyl alcohol (PVOH) microfibers: High tenacity and high modulus PVA fiber W1 6 mm (Anhui Wanwei Updated Hightech Material Industry Co. Ltd., Chao hu, Anhui, China). PVOH fiber properties are presented from the fiber producer data sheet in Table 1, below.

TABLE-US-00001 TABLE 1 Synthetic Fiber Properties Properties value Linear density (dtex*) 2 Tenacity (cN/dtex) 12.2 E-Modulus (cN/dtex) 275 Elongation (%) 6.8 Hot water solubility % (90° C., 1 h) 0.7 Dispersion grade (class)** 1 Length (mm) 6 *1dtex = 1 g per 10000 m; **1 best, 4 worst.

[0125] Aqueous emulsion Polymers 1, 2, 3 and 1A were made as set forth in the Synthesis Examples 1 and 1A, below.

[0126] Synthesis Example 1: Polymer 1 Core-shell (90//10 w/w) emulsion polymer of butyl acrylate (BA) (99.3%) crosslinked with allyl methacrylate (ALMA) (0.7%) and shell 100%, methyl methacrylate (MMA). Emulsion polymerization was carried out in a 5 liter 4-necked round bottom flask reactor equipped with a mechanical stirrer, heating mantel, thermometer, temperature controller and nitrogen (N2) inlet. To the reactor was charged 1019.61 g of deionized water, and 0.47 g of acetic acid. Under an N2 sweep, the reactor contents were heated to 40° C. A butyl acrylate (BA) monomer emulsion was prepared in a separate container with 189.67 g of deionized water, 46.67 g of sodium lauryl sulfate surfactant (SLS, 28 wt. % in water), 1497.42 g of BA and 10.55 g of allyl methacrylate (ALMA). Mechanical agitation was applied to effect emulsification. To the reactor was added 32.99 g of a 3 wt. % aqueous solution of sodium formaldehyde sulfoxylate (SFS) (reductant). To the reactor was added 535.34 g of the BA monomer emulsion with 0.38 g of a 70 wt. % aqueous solution of t-butyl hydroperoxide (t-BHP). After a couple of minutes, the observed exotherm resulted in a temperature increase of about 41° C. (to 81° C.). The reaction was then cooled to 40° C. To the reactor was added 697.73 g of the BA monomer emulsion with 0.52 g of a 70 wt. % aqueous solution of t-BHP. After a couple of minutes, the observed exotherm resulted in a temperature increase of about 41° C. The reaction was then cooled back to 56° C. To the reactor was added the remaining 513.85 g of the BA monomer emulsion with 0.35 g of a 70% aqueous solution of t-BHP. After a couple of minutes, the observed exotherm resulted in a temperature increase of about 38° C. The core stage was completed by adding 1.12 g of a 70 wt. % aqueous solution of t-BHP and 26.79 g of a 3 wt. % aqueous solution of SFS to the reactor, while cooling to 75° C. over a period of 20 minutes. To the reactor was added 11.03 g of sodium lauryl sulfate surfactant (28 wt. % in water) and 167.48 g of MMA monomer followed by 40 minute simultaneous feeds of sodium persulfate (NaPS) and SFS solutions. The NaPS feed was 32.5 g of a 3 wt. % aqueous solution and the SFS feed was 16.37 g of a 3 wt. % aqueous solution. The shell stage was completed by adding 0.59 g of a 70 wt. % aqueous solution of t-BHP and 6.98 g of a 3 wt. % aqueous solution of SFS to the reactor, while cooling to 60° C. over a period of 20 minutes. The reaction was then cooled to 40° C. and filtered through cheesecloth. The Z average particle size of the aqueous emulsion polymer was measured at 65 nm (by Malvern Instruments light scattering), and the solids content was 32.5% (by gravimetry). The calculated Tg of the rubbery core is from −20 to −140° C.

[0127] Synthesis Example 2: Polymer 2 Core-shell (90//10 w/w) emulsion polymer of butyl acrylate (BA) (99.3%) crosslinked with allyl methacrylate (ALMA) (0.7%) and shell 100%, methyl methacrylate (MMA). Synthesis Example 1 was repeated except that the amount of SLS surfactant in the monomer emulsion was 1.35 wt. %, based on the total weight of monomers polymerized. Further, 360 g of a crosslinked poly(BA) latex (seed, 32 wt. % polymer in water; Z-average particle size of 55 nm) was charged to the reactor along with the SFS reductant. The Z average particle size of the aqueous emulsion polymer was measured at 162 nm (by Malvern Instruments light scattering), and the solids content was 46.0% (by gravimetry). The calculated Tg of the rubbery core is −20 to −140° C.

[0128] Synthesis Example 3: Polymer 3 Core-shell (90//10 w/w) emulsion polymer of butyl acrylate (BA) (99.3%) crosslinked with allyl methacrylate (ALMA) (0.7%) and shell 100%, methyl methacrylate (MMA). Synthesis Example 1 was repeated except that the amount of SLS surfactant in the monomer emulsion was 0.50 wt. %, based on the total weight of monomers polymerized. Further, 360 g of a crosslinked poly(BA) latex (seed, 32 wt. % polymer in water; Z-average particle size of 236 nm) was charged to the reactor along with the SFS reductant. The Z average particle size of the aqueous emulsion polymer was measured at 550 nm (by Malvern Instruments light scattering), and the solids content was 52.0% (by gravimetry). The calculated Tg of the rubbery core is −20 to −140° C.

[0129] Synthesis Example 1A: Single Stage Aqueous Emulsion Polymer 1A. An emulsion polymerization was carried out in a conventional manner by gradual addition polymerizing a monomer emulsion in the presence of an anionic surfactant and a 15% sodium persulfate solution as in Example 2 of U.S. Patent Publication no. 2018/0327310 A1, to Evans et al. The properties of the aqueous emulsion polymers are set forth in Table 2, below.

TABLE-US-00002 TABLE 2 Aqueous Emulsion Polymers and Properties Product Polymer 1A* Polymer 1, 2 and 3 Appearance Milky white Milky white Polymer Styrene acrylic Core-Shell Solid, by weight, % 56 Indicated above pH 6 2.0-6.0 MFFT, ° C. <0 n/a** Calculated Tg −8 n/a  *Denotes Comparative Example.

[0130] Roof Tile preparation: Flat multilayer roof tiles were prepared from the indicated wet formulations as set forth in Table 3, below, by a pulp screen dewatering process. The cement and limestone filler were dispersed in approximately 200 mL of water for 2 min at 2,000 rpm. In another container, cellulose was pre-dispersed in water (150 mL) during 1 min at same stirring speed. Cellulose fiber was then added to the cementitious slurry, synthetic fiber, previous dispersed in 150 mL of water was added and mixed for 2 min at 1,000 rpm. After this period, if included, the indicated aqueous emulsion polymer and the remaining (200 mL) water was added to form an aqueous slurry mixture at 27.8 wt. % dry material content by mixing for 2 min at 1,000 rpm. After that, the aqueous slurry mixture was subject to dewatering using a molding chamber equipped with a perforated screen covered with a 80 g/cm.sup.2 paper filter and applying vacuum (200-300 mmHg). Fiber cement boards were cast in 4 layers of which only the top layer of the boards comprised the indicated emulsion polymer, wherein each layer was pressed in the molding chamber described before for 2 min at 3.2 MPa. The resulting board was finally pressed for 5 min at 3.2 MPa. Fiber cement boards were then “plastic sealed” (wrapped) in polyvinylidene fluoride wrap and left in an oven for 24h at 50° C.; after this period, the cement fiberboard (160×200×5) mm.sup.3 was removed from the oven and let sit at room temperature (28 d/23±2° C.) for curing. Upon completing the curing period, the resulting fiber cement board was subject to impact testing. The amount of polymer in the resulting multilayer article listed in Table 3, below, represents the amount of polymer solids weight based on the weight of the entire multilayer article.

TABLE-US-00003 TABLE 3 Formulations for Polymer Containing Fiber Cement Roof Tiles PVOH Polymer Polymer Cement Limestone Fiber Cellulose Particle Rubbery Shell Amount Example wt. % wt. % wt. % wt. % size (nm) core ratio ratio (Solids wt. %) 1* 74.4 22.5 0 3.1 none None None None 0 2* 73 22.1 1.9 3 none None None None 0 3* 71.2 21.6 1.9 2.9   1A 290 None None 2.4 4 71.6 21.7 1.9 2.9 1 65 90 10 2 5 71 21.5 1.8 2.9 1 65 90 10 2.8 6 71.6 21.7 1.9 2.9 3 550 90 10 2 7 71.6 21.7 1.9 2.9 2 160 90 10 2 8 71.6 21.7 1.9 2.9 2 160 80 20 2 *Denotes Comparative Example.

[0131] TEST METHODS: The following test methods were used in the Examples.

[0132] Gardner Universal Impact Test: To measure impact resistance in fiber cement roof tiles a Gardner Universal Impact Tester (GARDCO™ IM-IG-1120 Heavy-Duty Impact Tester, Paul N. Gardner Co., Pompano Beach, Fla.) having a graduated 102 cm (40 inch) guide tube, a 0.91 kg (2 lb) weight to measure a maximum force of (80 inch-lb*f), a 12.7 mm (0.500 in) diameter punch, 16.3 mm (0.640 in) die ASTM D5420 to evaluate a falling weight over a sample piece of roof tile having an area of 1.7 cm. The indicated sample roof tile was centered on a base plate over an opening of the 12.7 mm diameter punch. The die impactor with a nose of the 16.3 mm was placed in contact with the center of the roof tile sample. The weight, centered above the impactor was raised inside a guide tube to the indicated height and was then released to drop onto the top of the impactor, forcing the nose through the sample roof tile. The Gardner Impact energy (force) at which the tile broke was reported in Tables 4 and 5 below. For each roof tile tested, 2 trials were measured and the best result taken and reported. The pass/fail criteria are reported visual by detecting cracks formation after the impact to the tile. To approximate a correlation between results from tests in accordance with ANSI/UL 2218-2012 using hail balls and Gardner impact testing using steel balls, the percentage in the improvement of the impact resistance has been expressed as an incremental % using Comparative Example 2 in Tables 4 and 5, below, as a control of 100%.

TABLE-US-00004 TABLE 4 Gardner Impact Testing Report Maximum energy in Joules (in/lb*f) 1.12 1.35 1.57 1.81 1.5 2.25 Example (10) (12) (14) (16) (18) (20) 1* nm nm nm nm nm nm 2* met met met nm nm nm 3* met met nm nm nm nm 4 met nm nm nm nm nm 5 met met met met met met 6 met met met met met nm 7 met met met met met met 8 met met nm nm nm nm *Denotes Comparative Example; nm: not met.

TABLE-US-00005 TABLE 5 Impact resistance point per sample Polymer Particle Rubbery Kinetic Example size.sup.1 (nm) core Shell wt. % Energy Data 1* none None None None 0 less than example 2 representing space without fibers 2* none None None None 0 100% 3*   1A 290 None None 2.4  85% 4 1 65 90 10 2  72% 5 1 65 90 10 2.8 142% 6 1 550 90 10 2 128% 7 1 160 90 10 2 142% 8 1 160 80 20 2  85% .sup.1Z-average of the particle size; *Denotes Comparative Example.

[0133] As shown in Tables 4 and 5, above, the Gardner impact resistance measurement performed in Comparative Example 1 with no synthetic fibers provides a result of less than 10 in/lb*f and represents conventional cement articles without fibers. Comparative Example 2, 2 with 1.9 wt. % solids PVOH fibers had an impact resistance of 14 in/lb*f and represents conventional fiber cement articles used to normalized the results for the examples on this invention. Comparative Example 3 with 1.9% weight solids PVOH fibers, 2.9 wt. % solids of cellulose fibers and 2.4 wt. % solids of a conventional one stage aqueous emulsion polymer 1 A exhibits an inferior impact resistance compared to Comparative Example 2. Accordingly, inclusion of a polymer in a conventional form may decrease the impact resistance properties of fiber cement articles made therefrom even at low concentration. Meanwhile, as shown in inventive Example 5 the presence of a core-shell aqueous emulsion polymer having a crosslinked rubbery core and a Z-average particle size of 65 nm at a loading of 2.8 wt. % of dry solids results in a dramatic improvement in impact resistance to a rating of 142%; in inventive Examples 4 and 8, at a 2.0 wt. % dry solids loading, the indicated polymer did not give improved impact result at break but did perform better than Comparative Examples 1, 2, and 3 as the visually observed cracks were shallower and narrower than in the comparative examples, especially in Example 8 where the polymer had a larger Z-average particle size. As shown in inventive Examples 6, and 7, an increased average particle size of the core-shell aqueous emulsion polymer enables improvement in the Gardner impact resistance.