Thin fiber cement roof tile comprising a core-shell emulsion with improved impact resistance

Abstract

This invention provides fiber cement products, such as roof tiles, with improved impact and hail resistance, and methods for preparing these fiber cement products. These fiber cement products include: cement; optional fillers; reinforcing fibers, such as poly(vinyl alcohol) fibers or a mixture of cellulose fibers and synthetic fibers; one or more core-shell aqueous emulsion polymers having a crosslinked rubber core and at least partially grafted acrylic or vinyl shell polymers, the crosslinked rubber core having a calculated glass transition temperature (calculated Tg) of -20°C to -140°C, and the at least partially grafted acrylic or vinyl shell polymer having a calculated Tg of 20°C to 170°C and a Z-average primary particle size of 55 nm to 800 nm or preferably 140 nm to 650 nm. The solid weight ratio of the crosslinked rubber core to the shell of the core-shell aqueous emulsion polymer can range from 85:20 to 97:3.

Description

[0001] This invention relates to impact-resistant fiber cement products, including cement fiberboard and fiber cement roofing tiles. More specifically, this invention relates to fiber cement products comprising an aqueous core-shell emulsion polymer having a rubber core. Additionally, this invention relates to a method for preparing impact-resistant fiber cement products.

[0002] The use of corrugated fiber cement tiles for roofing residential and commercial buildings and cement fiber panels for exterior siding continues to grow. These roofing tiles and panels are constructed from cement and fillers and reinforced with fibers. However, recent health and safety restrictions regarding the use of asbestos fibers have led to an increasing use of alternative fibers, such as polyvinyl alcohol (PVOH). Unfortunately, cement fiber panels and roofing tiles made from alternative fibers exhibit limited mechanical properties, such as hail impact resistance, thus limiting their use in countries with stringent mechanical property standards (e.g., the United States). Hail resistance has previously been studied and classified according to the test method ANSI / UL 2218-2012 (Impact Resistance of Prepared Roof Covering Materials), American National Standards Institute, Washington, DC (2012), which includes impact energy derived from actual hail. However, there is no direct correlation between the impact resistance of roofing materials under hail and their performance under steel ball impact. Improved hail resistance fiber cement products remain needed to achieve acceptable durability.

[0003] Recent efforts to improve the crack resistance of fiber-reinforced cement composites have included attempts to incorporate elastomer particles into the cement matrix. However, hydrophobic elastomer particles are considered not to adhere to or bind to the polar and hydrophilic cement matrix. Therefore, the presence of unbonded particulate elastomers within the cement matrix has been found to generally prevent the effective transfer of stress from the cement matrix to the particulate elastomers dispersed therein. Nevertheless, no elastomer particles have yet been found to improve the impact resistance of fiber-reinforced cement products.

[0004] U.S. Patent No. 7,148,270B2, granted to Bowe, discloses a method for providing polymer-modified fiber-cement composites by forming an aqueous composition. The method includes mixing an emulsion polymer having a glass transition temperature (Tg) of -25°C to 150°C, cement, cellulose fibers, a siliceous material, and water; removing the water; and curing the cement. However, it does not disclose fiber cement products with sufficient impact resistance, such as those meeting the ANSI / UL 2218-2012 Class 4 hail resistance standard. Therefore, there remains a need for impact-resistant fiber cement products, such as fiber cement tiles and cement fiberboard.

[0005] The inventors have sought to address the problem of providing air-cured fiber cement products (e.g., fiber cement boards) that offer acceptable impact resistance for widespread use in roofs or walls, thereby improving nail / screw crack resistance when installing panels. Summary of the Invention

[0006] According to the present invention, a fiber cement product with improved impact resistance comprises: one or more core-shell aqueous emulsion polymers, based on the total solid weight of the fiber cement product, ranging from 1 wt.% to 25 wt.%, or preferably from 1.5 wt.% to 20 wt.%, or more preferably from 2.4 wt.% to 19 wt.%, wherein the one or more core-shell aqueous emulsion polymers have a crosslinked rubber core and at least partially grafted acrylic or vinyl shell polymers, wherein the crosslinked rubber core has a calculated glass transition temperature (calculated Tg) of -20°C to -140°C, preferably -35°C or lower, and the at least partially grafted acrylic or vinyl shell polymer has a calculated Tg of 20°C to 170°C, or preferably 45°C or higher, and the core-shell aqueous emulsion polymer also has a Z-average primary particle size of 55 nm to 800 nm, or preferably 110 nm to 800 nm, or more preferably 140 nm to 650 nm; cement; and further wherein the fiber cement product comprises reinforcing fibers. The shell polymer of the core-shell aqueous emulsion polymer may include one or more polymers comprising copolymer residues of one or more acrylic or vinyl monomers, such as copolymer residues of methyl methacrylate (MMA).

[0007] According to a first aspect of the invention, a fiber cement product with improved impact resistance comprises: 1 wt.% to 25 wt.%, or preferably 1.5 wt.% to 20 wt.%, or more preferably 2.4 wt.% to 19 wt.%, based on the total solid weight of the fiber cement product, wherein the one or more core-shell aqueous emulsion polymers have a crosslinked rubber core and a partially grafted acrylic or vinyl shell polymer, the crosslinked rubber core having a temperature range of -20°C to -140°C, or preferably -3°C. The calculated glass transition temperature (calculated Tg) is 5°C or lower, and the partially grafted acrylic or vinyl shell polymer has a calculated Tg of 20°C to 170°C, or preferably 45°C or higher, or more preferably 50°C to 150°C. Preferably, the shell polymer comprises copolymer residues of methyl methacrylate (MMA), and the core-shell aqueous emulsion polymer has a Z-average primary particle size of 55 nm to 800 nm, or preferably 110 nm to 800 nm, or more preferably 140 nm to 650 nm.

[0008] According to a first aspect of the invention, in a fiber cement article, the shell of at least one of the one or more core-shell aqueous emulsion polymers in the fiber cement article comprises one or more vinyl methacrylates or alkyl methacrylates, preferably, a vinyl methacrylate or C1 to C4 alkyl methacrylate, or more preferably, one or more vinyl methacrylates or C1 to C4 alkyl methacrylates, or even more preferably, copolymer residues of methyl methacrylate (MMA).

[0009] According to the fiber cement product of the present invention, the shell of at least one of the one or more core-shell aqueous emulsion polymers may further include one or more of the following: carboxylic acid monomers or salts thereof, such as (meth)acrylic acid; (alkyl)acrylamide; (alkyl)methacrylamide; silane monomers; phosphorous acid-containing monomers; or combinations thereof.

[0010] According to a first aspect of the invention, in a fiber cement article, the crosslinked rubber core of at least one of the one or more core-shell aqueous emulsion polymers in the fiber cement article comprises at least one crosslinked polyene unsaturated monomer, preferably, allyl (meth)acrylate, one or more C2 to C8 alkyl acrylates, preferably, a C2 to C8 alkyl acrylate, or more preferably, a copolymer residue of ethyl acrylate (EA), butyl acrylate or ethylhexyl acrylate.

[0011] Preferably, in the fiber cement product according to the first aspect of the invention, based on the total weight of the monomers of the crosslinked rubber core used to prepare the core-shell aqueous emulsion polymer in the fiber cement product, the crosslinked rubber core comprises 0.2 wt.% to 2 wt.%, or preferably 0.25 wt.% to 1.4 wt.% of at least one copolymer residue of a crosslinked polyene unsaturated monomer.

[0012] Preferably, in the fiber cement product according to the first aspect of the invention, the weight ratio of the crosslinked rubber core of the core-shell aqueous emulsion polymer to the shell polymer of the core-shell aqueous emulsion polymer is in the range of 80:20 to 97:3, or preferably 87:13 to 94:6, or more preferably 85:20 to 97:3.

[0013] According to a first aspect of the invention, the fiber cement article wherein the reinforcing fibers are selected from cellulose fibers, synthetic fibers, or mixtures thereof.

[0014] According to the first aspect of the invention, the reinforcing fibers in the fiber cement product may be synthetic fibers selected from: polyester fibers, such as polyethylene terephthalate (PET); polyvinyl alcohol fibers; polyolefin fibers, such as PP (polypropylene); bicomponent polymer microfibers having a polyamide core or a polyolefin core; polymer blends of polyolefins, preferably polypropylene (PP) or maleic anhydride-grafted polypropylene (PP-g-MAH); polymer blends or polyamide and polyolefin minerals; acrylonitrile; and mineral wool.

[0015] According to the first aspect of the invention, the reinforcing fibers in the fiber cement product may be natural fibers selected from cellulose fibers derived from bamboo, wood (such as pine or eucalyptus), hemp, and sisal.

[0016] Preferably, in the fiber cement article according to the first aspect of the invention, the amount of these reinforcing fibers is in the range of 0.5 wt.% to 10.0 wt.%, or preferably 1.0 wt.% to 7.0 wt.%, or preferably 1.5 wt.% to 5.0 wt.%, based on the total solid weight of the fiber cement article.

[0017] According to a first aspect of the invention, the fiber cement product comprises the core-shell aqueous emulsion polymer, reinforcing fibers, and hydraulic cement, limestone, or cement curing agent in cured form, such as a basic salt or alkali metal salt, preferably calcium formate. The fiber cement product of the invention may or may not include one or more particulate fillers, preferably one or more fillers such as silica, sand, clay, or extenders such as CaCO3 aggregate.

[0018] Preferably, in the fiber cement products according to the invention, the hydraulic cement is selected from ordinary Portland cement, such as ASTM C-150 Type 3 or calcium silicate alite (3CaO·SiO2) or (C3S), belite (2CaO·SiO2) or simply (C2S), and a phase consisting of tricalcium aluminate (3CaO·Al2O3) or (C3A) followed by tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3) or C4AF, high-alumina cement and mixtures thereof.

[0019] Preferably, in the fiber cement product according to the first aspect of the invention, the amount of the cement curing agent in the cement is in the range of 50 wt.% to 80 wt.%, or preferably 65 wt.% to 75 wt.%, based on the total solid weight of the fiber cement product.

[0020] Preferably, in the fiber cement product according to the first aspect of the invention, the amount of filler or limestone aggregate (such as filler or limestone aggregate having a weight average particle size (DLS) of 10 micrometers to 100 micrometers (such as 20 micrometers to 60 micrometers)) is in the range of 12 wt.% to 35 wt.%, or preferably 16 wt.% to 30 wt.%, based on the total solid weight of the fiber cement product.

[0021] According to a first aspect of the invention, the fiber cement article, wherein the composition further comprises one or more of the following: a thickener, a plasticizer, or a pigment or colorant.

[0022] Preferably, the fiber cement product according to the first aspect of the invention comprises the core-shell aqueous emulsion polymer, reinforcing fibers, and one or more emulsifiers or coagulants, more preferably nonionic surfactants, poly(methyl methacrylate) (PMMA) particulate coagulants, or combinations thereof.

[0023] Preferably, the fiber cement product according to the first aspect of the invention comprises the core-shell aqueous emulsion polymer as aggregate or secondary particles having a weight-average particle size of 200 nm to less than 5,000 nm.

[0024] Preferably, the fiber cement product according to the first aspect of the invention comprises roofing tiles or cement fiberboard.

[0025] According to a second aspect of the present invention, a method for preparing fiber cement products includes:

[0026] An aqueous slurry mixture that forms solids is formed by adding, during mixing, a dry mixture comprising a clinker or cementitious agent and preferably another one or more inorganic fillers such as sand, silica, limestone, or clay to an aqueous mixture containing reinforcing fibers, 1 to 3 parts water (preferably 1.5 to 2 parts water) based on the total solid weight of the dry mixture, and one or more core-shell aqueous emulsion polymers, wherein the one or more core-shell aqueous emulsion polymers have a crosslinked rubber core and at least partially grafted acrylic or vinyl shell polymers, wherein the crosslinking... The rubber core has a calculated glass transition temperature (calculated Tg) of -20°C to -140°C or preferably -35°C or lower, the at least partially grafted acrylic or vinyl shell polymer has a calculated Tg of 20°C to 170°C or preferably 45°C or higher, the shell polymer preferably includes copolymer residues of methyl methacrylate (MMA), and the core-shell aqueous emulsion polymer also has a weight-average primary particle size of 55 nm to 800 nm or preferably 110 nm to 800 nm or more preferably 140 nm to 650 nm.

[0027] The aqueous slurry mixture is deposited onto a perforated shaped screen or belt, such as a felt or polymer screen, preferably an operating conveyor screen or belt, more preferably by suction to remove excess process water while retaining solids on the screen or belt, thereby forming an uncured composite precursor with a cementitious matrix; and

[0028] The uncured composite precursor is dried or cured under ambient conditions, at elevated temperatures, or in an autoclave to form a cured product.

[0029] According to a second aspect of the invention, in a method for preparing fiber cement products, the shell of the core-shell aqueous emulsion polymer in the aqueous slurry mixture comprises one or more vinyl (meth)acrylates or alkyl (meth)acrylates, preferably, a vinyl (meth)acrylate or a C1 to C4 alkyl (meth)acrylate, or more preferably, a vinyl methacrylate or a C1 to C4 alkyl methacrylate, or even more preferably, copolymer residues of methyl methacrylate (MMA).

[0030] According to the method for preparing fiber cement products of the present invention, based on the total weight of the monomers in the shell, the shell of at least one of the one or more core-shell aqueous emulsion polymers may also contain any of the following copolymer residues: one or more carboxylic acid monomers or salts thereof, such as, for example, acrylic acid, methacrylic acid or itaconic acid; silane monomers, such as, for example, vinyltrimethoxysilane; one or more phosphorous acid-containing monomers or salts thereof, such as, for example, phosphate esters of 2-hydroxyethyl methacrylate or polyethylene glycol monomethacrylate; or combinations thereof.

[0031] In the shell of at least one of the core-shell aqueous emulsion polymers, based on the total weight of the monomers used to prepare the copolymer, one or more copolymer residues of carboxylic acid or salt monomers may be present, for example, in an amount of 0 wt.% to 5 wt.%, or preferably 0.2 wt.% to 3 wt.%.

[0032] In the shell of at least one of the one or more core-shell aqueous emulsion polymers, the copolymer residues of the one or more (alkyl) (meth)acrylamide monomers may be present in an amount from 0 wt.% to 3 wt.% based on the total weight of the monomers used to prepare the copolymer.

[0033] In the shell of at least one of the one or more core-shell aqueous emulsion polymers, the copolymer residues of the one or more phosphorous acid or salt-containing monomers may be present in an amount from 0 wt.% to 3 wt.% based on the total weight of the monomers used to prepare the copolymer.

[0034] In the shell of at least one of the one or more core-shell aqueous emulsion polymers, the copolymer residues of the one or more silane monomers may be present in an amount of 0 wt.% to 1 wt.% based on the total weight of the monomers used to prepare the copolymer.

[0035] According to a second aspect of the invention, in a method for preparing fiber cement products, the crosslinked rubber core of the core-shell aqueous emulsion polymer in the aqueous slurry mixture comprises a crosslinked polyene unsaturated monomer, preferably, allyl (meth)acrylate, one or more C2 to C8 alkyl acrylates, preferably, a C2 to C8 alkyl acrylate, or more preferably, a copolymer residue of ethyl acrylate (EA), butyl acrylate, or ethylhexyl acrylate.

[0036] Preferably, in the method for preparing fiber cement products according to the second aspect of the invention, based on the total weight of the monomers of the crosslinked rubber core of the core-shell aqueous emulsion polymer used to prepare the aqueous slurry mixture, the crosslinked rubber core comprises 0.1 wt.% to 1 wt.%, or preferably 0.25 wt.% to 0.8 wt.% of copolymer residues of crosslinked polyene unsaturated monomers.

[0037] Preferably, in the method for preparing fiber cement products according to the second aspect of the invention, the weight ratio of the crosslinked rubber core of the core-shell aqueous emulsion polymer to the shell polymer of the core-shell aqueous emulsion polymer in the aqueous slurry mixture is in the range of 85:20 to 97:3, or preferably 87:13 to 94:6.

[0038] A method for preparing fiber cement products according to a second aspect of the present invention, the method further comprising:

[0039] This allows the uncured composite precursor to dry and develop green strength.

[0040] Pressing an uncured composite precursor with green strength in a flat press or forming press to form a pressed article; and

[0041] The pressed product is dried or cured to form a fiber cement product.

[0042] A method for preparing a fiber cement article into a multilayer fiber cement article according to a second aspect of the present invention, wherein the process further includes:

[0043] The uncured composite precursor is dried until it becomes self-supporting to form the first self-supporting uncured composite precursor sheet.

[0044] The first self-supporting uncured composite precursor sheet is moved or conveyed to another forming screen or secondary forming screen to receive the self-supporting uncured composite precursor, such as a forming roller, as a layer or sheet.

[0045] The second uncured composite precursor sheet is formed by: forming an aqueous slurry mixture comprising hydraulic cement and reinforcing fibers to remove excess process water and form a second or subsequent self-supporting uncured composite precursor sheet; and depositing the aqueous slurry mixture onto a perforated forming screen or belt; and

[0046] Before drying or curing the first self-supporting uncured composite precursor sheet, the second uncured composite precursor sheet is stacked on top to form a stack of uncured composite precursor sheets. Optionally, the uncured composite precursor with green strength is pressed in a flatbed press or forming press to form a pressed article; and

[0047] The stacked or pressed product is dried or cured to form a multilayer fiber cement product.

[0048] Furthermore, according to the method for preparing a multilayer fiber cement article according to a second aspect of the present invention, the process further includes:

[0049] Before drying or curing the existing stack of uncured composite precursor sheets, the subsequent uncured composite precursor is formed by: forming an aqueous slurry mixture comprising hydraulic cement and reinforcing fibers to remove excess process water and form the subsequent self-supporting uncured composite precursor sheets; and depositing the aqueous slurry mixture onto a perforated forming screen or belt; and

[0050] The subsequent uncured composite precursor sheet is stacked on top of the existing stack of uncured composite precursor sheets to form a thickened existing stack; and

[0051] The resulting thickened existing stack is dried or cured to form fiber cement products.

[0052] Additionally, according to a method for preparing a multilayer fiber cement article according to a second aspect of the invention, the process further includes:

[0053] Before drying or curing the existing stack of thickened uncured composite precursor sheets, an additional uncured composite precursor is formed by: repeatedly forming an aqueous slurry mixture to remove excess process water and form an additional self-supporting uncured composite precursor sheet, and depositing the aqueous slurry mixture onto a perforated forming screen or belt; and

[0054] The additional self-supporting uncured composite precursor layer is stacked on top of the thickened existing stack of the uncured composite precursor layer to further increase the size of the stack.

[0055] If desired, repeat the forming and stacking steps used to prepare additional self-supporting uncured composite precursor material sheets and stack them onto the thickened existing stack of uncured composite precursor sheets until a stack with the desired or preset thickness is achieved.

[0056] The resulting stack is dried or cured to form a fiber cement product.

[0057] The method for preparing multilayer fiber cement products according to a second aspect of the present invention may further include:

[0058] The stacking of uncured composite precursor sheets is dried and green strength is generated;

[0059] Uncured composite precursor stacks with green strength are pressed in a flat press or forming press to form pressed multilayer fiber cement products; and

[0060] The pressed article is dried or cured to form a multilayer fiber cement article, wherein at least one of these uncured composite precursor sheets comprises hydraulic cement, one or more core-shell aqueous emulsion polymers of the present invention, and reinforcing fibers.

[0061] A method for preparing fiber cement products according to a second aspect of the present invention, the method further comprising:

[0062] This allows the uncured composite precursor to dry and develop green strength.

[0063] Pressing uncured composite precursors or uncured composite precursor sheets with green strength to form pressed articles; and

[0064] The pressed product is dried or cured to form a fiber cement product.

[0065] Preferably, according to the method of the second aspect of the invention, the fiber cement product comprises roofing tiles or cement fiberboard.

[0066] Preferably, in the method for preparing fiber cement products according to the second aspect of the invention, in order to help the core-shell aqueous emulsion polymer penetrate into the cement matrix, deposition to remove excess process water includes applying a vacuum to a perforated forming screen or belt or providing a slowly running perforated forming screen or belt.

[0067] Unless otherwise specified, the temperature and pressure conditions are ambient temperature and standard pressure. All ranges listed are inclusive and combinable.

[0068] Unless otherwise specified, any term containing parentheses or alternatively refers to the entire term, as well as terms without parentheses and combinations of each alternative form. Thus, the term "(poly)ethylene glycol" refers to ethylene glycol, polyethylene glycol, or mixtures thereof.

[0069] All ranges are inclusive and composable. For example, the term “0.06 wt.% to 0.25 wt.%, or preferably 0.06 wt.% to 0.08 wt.%” will include each of 0.06 wt.% to 0.25 wt.%, 0.06 wt.% to 0.08 wt.%, and 0.08 wt.% to 0.25 wt.%.

[0070] As used in this article, the term "ANSI" refers to publications from the National Institute of Standards and Technology in Washington, D.C.

[0071] As used herein, the term "aqueous" refers to water or a mixture of most water with a small amount (>50 wt.%) of one or more water-miscible solvents.

[0072] As used herein, the term "aqueous slurry mixture" refers to a hydraulic binder composition used to prepare fiber cement products, tiles, or fiberboard.

[0073] As used in this article, the term "ASTM" refers to the publications of ASTM International, West Conshohocken, PA.

[0074] As used herein, the terms “calculated glass transition temperature” or “calculated Tg” refer to the value calculated using the Fox equation (Fox, Bulletin of the American Physical Society, Vol. 1, No. 3, p. 123 (1956)), which is as follows:

[0075] 1 / Tg(calculation)=Σw(M1) / Tg(M1)+w(M2) / Tg(M2)+…w(M n ) / Tg(M n Where Tg(calculated) is the glass transition temperature calculated for the copolymer.

[0076] w(M1) is the weight fraction of monomer M1 in the copolymer.

[0077] w(M2) is the weight fraction of monomer M2 in the copolymer.

[0078] w(M n () represents the weight fraction of monomer Mn in the copolymer.

[0079] Tg(M1) is the glass transition temperature of the homopolymer of M1.

[0080] Tg(M2) is the glass transition temperature of the homopolymer of M2, and

[0081] Tg(M n () is the glass transition temperature of the homopolymer of Mn.

[0082] All temperatures are in °K.

[0083] Glass transition temperatures of homopolymers can be found, for example, in the *Polymer Handbook*, edited by J. Brandrup and E. Himmergut, Interscience Publishers, New York, 1999.

[0084] As used herein, the term “fiber cement products” is used interchangeably with “cement fiberboard” or “fiberboard” and refers to the same thing as “cement fiberboard” or “fiberboard”.

[0085] As used herein, the term "hydraulic cement" includes substances that solidify and harden in the presence of water, such as Portland cement, silicate-based cement, aluminate-based cement or high-alumina cement, pozzolanic cement, and composite cement.

[0086] As used herein, the term “macrofiber” refers to a fiber having an average linear density of 580 denier and an equivalent diameter of ≥0.3 mm or ≥30 micrometers, in accordance with the ASTM D7508 / D7508M(2015) Standard Specification for Polyolefin Chopped Strands for Use in Concrete.

[0087] As used herein, the term “microfiber” refers to a fiber having a linear density of less than 580 denier and an equivalent diameter of <0.3 mm or less than 30 micrometers, according to the ASTM D7580 / D7580M (2015) standard specification for chopped polyolefin filaments used in concrete.

[0088] As used herein, the term "polymer" includes homopolymers (such as core homopolymers) and copolymers formed from two or more different monomer reactants or comprising two different repeating units.

[0089] As used herein, the term "surfactant" refers to a water-dispersible organic molecule containing both a hydrophilic phase (such as oligoethoxylates) and a hydrophobic group or phase (such as C8 alkyl or alkylaryl groups).

[0090] As used herein, the term “total solids” or “solids” means all materials in a given composition other than solvents, liquid carriers, non-reactive volatiles (including volatile organic compounds or VOCs), ammonia, and water.

[0091] As used herein, the term "weight-average molecular weight" or MW refers to the weight-average molecular weight distribution of a polymer or plasticizer material determined at room temperature using gel permeation chromatography (GPC) of a polymer dispersion in water or a suitable solvent for the analyte polymer or plasticizer and using appropriate conventional polyethylene glycol, vinyl, or styrene polymer standards.

[0092] As used herein, the term “weight-average particle size (DLS)” refers to the weight-average particle distribution of a pigment, filler, or extender as determined using dynamic light scattering.

[0093] As used herein, the term "Z-average primary particle size" refers to the Z-average of the particle size distribution of an indicator material, such as when using Malvern Mastersizer. TMThe light scattering measurement device (Malvern Instruments, Malvern, UK) determines the weight-average particle size distribution by means of light scattering and by mathematically measuring the Z-average of the particle size distribution thus measured. The term "weight-average particle size" refers to the result given by mathematically measuring the weight-average of the particle size distribution thus measured.

[0094] As used in this article, the phrase “weight%” refers to a percentage of weight.

[0095] According to the present invention, the inventors have discovered that fiber cement products further comprising a core-shell aqueous emulsion polymer exhibit improved impact resistance. Compared to conventional air-cured fiber cement roofing tiles without a core-shell aqueous emulsion polymer, the resulting fiber cement products exhibit significantly increased impact resistance. The present invention can improve impact resistance by, for example, 25% to 35%, measured according to ASTM D5420 using a Gardner Universal Impact Tester to evaluate the drop weight test of a 1.7 cm diameter sample area.

[0096] When used in fiber cement products, the rigid (meth)acrylate or (meth)acrylate alkyl acrylate shell of the core-shell aqueous emulsion polymer appears to minimize the tackiness of the rubbery polymer and its tendency to set. Furthermore, even if it does not contain acidic or hydrophilic groups in copolymer form, the shell in the aqueous emulsion polymer composition of the present invention allows the copolymer to be adequately dispersed in hydraulic cement. For the purpose of delaying setting time or promoting adhesion between the core-shell aqueous emulsion polymer and the cement matrix, additional monomers in copolymer form (such as (meth)acrylamide, carboxylic acid monomers, silane monomers, or phosphorous acid monomers, or combinations thereof) may be included in the shell.

[0097] Furthermore, it has been shown that the incorporation of core-shell aqueous emulsion polymers increases Gardner impact-resistant air-cured fiber cement tiles proportionally to the range of core-shell aqueous emulsion polymer loadings, and is improved with smaller rubber particle sizes. Therefore, the fiber cement articles of the present invention comprise core-shell aqueous emulsion polymers formed by conventional emulsion polymerization and which increase their Z-average primary particle size without any further processing.

[0098] Fiber cement products according to the invention can be formed by methods known in the art, such as the Hatschek, Magnani process, flow-on process, or any other water-based fiber cement forming process known in the art. Typically, the process involves forming an aqueous slurry mixture, forming the aqueous slurry mixture into layers or sheets and removing water therefrom, stacking more than one sheet on top of each other, if desired, to form an uncured composite precursor, then optionally, pressing the uncured composite precursor, any further shaping (such as cutting and / or embossing), and drying and / or curing, such as under ambient conditions or at elevated temperatures or in an autoclave, followed by cutting the cured product to the desired size and / or further shaping other than embossing. Typically, water removal involves depositing the aqueous slurry mixture as a layer onto a porous sieve (such as felt) to allow water removal therefrom. In the flow process, pulp sheets are pulped and hydrated in water until the hydrated pulp becomes a pulp slurry, which is then mixed with cement and filler and the mixture is transferred to a felt to be dehydrated. Water is removed from the mixture using a vacuum pump, and the mixture is formed by forming and pressure rollers until it becomes a film layer with a thickness ranging from 0.40 mm to 0.70 mm. Thick fiber cement boards can be produced in this flow process.

[0099] Another process used to produce fiber cement composites includes extrusion. Because it is continuous, extrusion allows for a wide range of cross-sections when forming extruded products, uses simpler machinery for continuous production, and has a low water / cement ratio, which enables the production of fiber cement with less liquid and solid waste.

[0100] The surface of the product can be further finished using methods such as sanding, brushing, sandblasting, stamping, embossing or machining.

[0101] The product may be air-cured, cured in an autoclave, or cured by another known or available curing method or system. The product may be treated with one or more coatings.

[0102] Before or after curing, fiber cement products can be further shaped and sized or cut into desired shapes and sizes. For example, the resulting cured material can then be periodically cut to produce products with desired lengths.

[0103] In one example of the process according to the invention, the aqueous slurry mixture is formed by adding cement and inorganic fillers (such as sand or silica) to a mixture of fibers, water, and emulsion polymers during mixing. The aqueous slurry mixture is collected in a large drum or container and deposited onto a forming screen or an operating conveyor (such as felt or such as NYLON). TMThe polyamide polymer mesh (perforated belt) is filtered through the forming screen or an operating conveyor, optionally using suction, to remove excess process water and form an uncured composite precursor. The process may include the use of additional forming screens or secondary forming screens (such as forming rollers) to accept the self-supporting uncured composite precursor as layers or sheets, wherein one or more uncured composite precursor sheets can be accumulated on the forming roller screen, and if there are multiple sheets, these multiple sheets are stacked until the desired total material thickness is achieved. One or more layers of the uncured composite precursor may be further pressed and then cured under ambient conditions, at elevated temperatures, or in an autoclave.

[0104] Using a vacuum or slowly running screen or a low-viscosity water-based emulsion polymer during dewatering helps the polymer penetrate into the cement matrix.

[0105] In the process according to the invention, prior to dehydration, an aqueous slurry mixture of hydraulic cement, limestone or cement curing agent, any filler (such as silica), fiber, aqueous core-shell emulsion polymer, reinforcing fiber and any thickener (if used) is dispersed in water at a solids concentration of 250 g to 300 g solids / 1000 g total mass.

[0106] According to the method of the invention, an aqueous slurry mixture can be formed by mixing a hydraulic cement mixture with an aqueous slurry of fiber and core-shell aqueous emulsion polymer. The aqueous slurry mixture according to the invention is prepared using techniques well known in the field of fiber-cement. The components are mixed together to facilitate effective dispersion without pretreatment or balancing any components with each other. For use with machinery commonly used to form fiber cement products, such as through the Hatschek process and its modifications, the aqueous slurry mixture can have a solids level of 10 wt.% to 30 wt.%, or preferably 10 wt.% to 20 wt.%.

[0107] A method for forming an aqueous slurry mixture includes mixing hydraulic cement, limestone, or cementitious agent and filler with a mixture of aqueous emulsion polymer and polymer fibers for 10 seconds to 20 minutes. Preferably, the mixing time is at least 30 seconds, or more preferably at least 1 minute and at most 10 minutes, or most preferably 1 minute to 5 minutes.

[0108] Fiber cement products (such as cement fiberboard and roofing tiles) typically consist of cement, fillers, and reinforcing fibers, such as cellulose or synthetic fibers. These fiber cement products are formed by mixing these materials with other components in an aqueous slurry.

[0109] According to the present invention, fiber cement products comprise core-shell aqueous emulsion polymers having a crosslinked rubber core and an acrylic or vinyl shell polymer, preferably comprising at least partially grafted copolymer residues of methyl methacrylate (MMA).

[0110] According to the aqueous slurry mixture of the present invention, the core-shell aqueous emulsion polymer comprises a rubber core, and the shell polymer is separable by coagulation into powder, and provides improved compatibility with cementitious matrices compared to the rubber core alone.

[0111] In the core-shell aqueous emulsion polymer of the present invention, the weight ratio of the core polymer to the shell polymer is 85:20 to 97:3, or preferably 87:13 to 94:6.

[0112] The core-shell aqueous emulsion polymer according to the invention can be formed by conventional polymerization techniques, wherein one of the polymer stages is prepared in the presence of a previously prepared polymer stage. These stages are at least partially grafted together by one or more covalent bonds. Due to the grafting, the core-shell aqueous emulsion polymer acts as a polymer but has the rubbery properties of the core and the hard polymer properties of the shell. In the polymerization, each polymer stage, core, and shell is prepared independently, which means that surfactants, initiators, and other additives are selected independently, and for each polymer, their types and amounts can be the same or different. In the emulsion polymerization process, conventional amounts of conventional surfactants, such as, for example, anionic and / or nonionic emulsifiers, such as, for example, alkali metal salts or ammonium salts of alkyl, aryl, or alkylaryl sulfates, can be used. In the emulsion polymerization process, free radical polymerization initiators can be used, including, for example, thermal initiators or redox initiators. Thermal initiators may include, in conventional amounts, peroxides, such as tert-butyl hydroperoxide; ammonium and / or alkali metal persulfates; sodium perborate; and other peracids. Redox initiators include one or more oxidizing agents and suitable reducing agents, such as, for example, sodium formaldehyde sulfoxylate; ascorbic acid; isoascorbic acid; alkali metal salts and ammonium salts containing sulfuric acid, such as sodium sulfite or sodium bisulfite, and the salts of the aforementioned acids can be used in conventional amounts. Chain transfer agents, such as, for example, thiols, such as alkyl esters of thioglycolate, alkyl esters of mercaptoalkylate, and C4-C... 22Linear or branched alkyl thiols can be used independently to reduce the molecular weight of the first and second polymer stages formed, and / or to provide a molecular weight distribution different from that obtained with any radical generation initiator. Chain transfer agents can be added once or multiple times, or continuously, linearly, or non-linearly, during most or all of the reaction time or during a limited portion of the reaction time. Monomers, or combinations thereof, can be added purely (i.e., not in aqueous emulsion form) or in aqueous emulsion form, either once or multiple times, or continuously, linearly, or non-linearly, during the reaction time.

[0113] During processing, the adhesion or attraction between the core-shell aqueous emulsion polymer, the cement matrix, and the reinforcing fibers remains critical for fiber cement products produced by processes such as the Hatschek process, which requires dehydrating the composition without losing materials other than water.

[0114] Cement-instable core-shell aqueous emulsion polymers can be used, which will slightly coagulate without migrating during dewatering. Examples of such core-shell aqueous emulsion polymers can include any aqueous emulsion polymer having a shell that is unstable in alkaline pH or high Ca++ ion content environments, including uncharged polymers that do not contain more than 0.5 wt.% nonionic surfactants based on total polymer solids. Core-shell aqueous emulsion polymers containing some coagulant (such as PMMA) are also included.

[0115] In contrast, waterborne emulsion polymers are considered "cement-stabilized" if they neither flocculate nor shorten the pot life or workability of the mortar when mixed with cement. During the dewatering process, cement-stabilized waterborne emulsion polymers with a Z-average primary particle size of less than 500 nanometers can pass through the perforated screen of the wet fiber cement matrix and the fiber cement product molding machine, resulting in the removal of most of the polymer.

[0116] In contrast to cement-stabilized aqueous emulsion polymers, core-shell aqueous emulsion polymers that can cause cement instability predictably flocculate at any point in the material flow leading to the molding machine in the fiber cement wet mixture. These flocs can take the form, for example, primary particle clusters with a Z-average primary particle size of, for example, 1 micrometer (nm) to less than 20 micrometers. The flocculated core-shell polymers can also, or additionally, precipitate onto any other component in the mixture besides water (such as extenders). In any such case, after removing excess process water, the flocculated core-shell polymers will be more completely retained in the uncured composite precursor.

[0117] Preferably, in order to help retain the core-shell aqueous emulsion polymer in the fiber cement product, the aqueous slurry mixture may contain 2 wt.% to 20 wt.% of an emulsifier, such as preferably a nonionic surfactant, or a coagulant, preferably poly(methyl methacrylate), based on the total core-shell aqueous emulsion polymer solids.

[0118] The aqueous slurry mixture according to the invention comprises reinforcing fibers, such as synthetic fibers or natural fibers, such as cellulose fibers, such as cellulose fibers from eucalyptus or pine, or as a sieve for retaining solids during dehydration. Fibers suitable for preparing fiber cement products according to the invention may include, for example, natural fibers (such as cellulose fibers from bamboo, wood, or hemp) or synthetic fibers other than cellulose fibers (such as, for example, mineral wool, polyester fibers, polyvinyl alcohol fibers); polyolefin fibers, such as PP (polypropylene); bicomponent polymer microfibers having a polyamide core or a polyolefin core; polymer blends of polypropylene (PP) and maleic anhydride-grafted PP (PP-g-MAH); and polymer blends of polyester polymers (such as polyethylene terephthalate (PET)) or polyolefins (preferably polypropylene, maleic anhydride-grafted polypropylene).

[0119] A suitable aqueous slurry mixture composition according to the invention may contain 0.5 wt.% to 10.0 wt.%, or preferably 1.0 wt.% to 5.0 wt.%, or more preferably 1.5 wt.% to 5.0 wt.% of fibrous solids.

[0120] According to the aqueous slurry mixture of the present invention, based on the total solid weight of the fiber cement product, the hydraulic cement may include an amount of ordinary Portland cement in the aqueous slurry mixture ranging from 60 wt.% to 80 wt.%, or preferably from 65 wt.% to 75 wt.%.

[0121] The aqueous slurry mixture also contains limestone or finely ground calcium carbonate or another cementitious agent, such as calcium formate, and, if necessary, a thickener, such as CaCO3 aggregate.

[0122] According to the present invention, the aqueous slurry mixture further comprises fillers such as fumed silica, slag, fly ash, limestone or ceramic microspheres; and corrosion inhibitors.

[0123] In accordance with the aqueous slurry mixture of the present invention, to ensure a uniform fiber cement product, the filler or additive should have a weight-average particle size of 300 micrometers or less. Therefore, the aqueous slurry mixture composition according to the present invention is essentially composed of materials having a weight-average particle size of 300 micrometers or less.

[0124] The aqueous slurry mixture according to the invention may contain other components, such as, for example, water-reducing agents, such as superplasticizers; defoamers; neutralizers; thickeners or rheology modifiers; wetting agents; dampening agents; biocides; plasticizers; pigments; colorants; waxes; and antioxidants.

[0125] The fiber cement products according to the invention can be used as building products, such as tile backing layers, wall panels, panels, decorations, trims, roofs, crown moldings, cover plates, and fences.

[0126] Example: The following examples are for illustrative purposes only and are not intended to limit the invention to these examples. Unless otherwise stated, all temperatures are ambient temperatures (21°C to 23°C), and all pressures are 1 atmosphere.

[0127] The component proportions are shown in the following examples. Use the following abbreviations: Pbw: parts by weight;

[0128] The materials used in the example are as follows:

[0129] Cellulose fibers: Cork pulp, made from long fibers from coniferous species and used as an aqueous pulp, refined according to ISO 5267-1, having a strength level of approximately 60 to 63 SR (w / unit as Schopper-Riegler grade), and 27.8 wt.% solids (PineCel from Klabin S / A, Paraná, Brazil). TM fiber).

[0130] Cement: Type III Portland cement, comprising about 50 wt.% to 70 wt.% of calcium silicate alite (3CaO·SiO2) or (C3S), and the balance being belite (2CaO·SiO2) or (C2S), and a phase consisting of tricalcium aluminate (3CaO·Al2O3) or (C3A) and tetracalcium aluminoferrite (4CaO·Al2O3 Fe2O3) or C4AF.

[0131] Limestone filler: Agricultural lime (Calcário Agrícola) - 42 to 45 (wt.%) CaO (approximately 40 microns or 325 mesh, Votorantim, Itau de Minas–Minas Gerais, Brazil).

[0132] Synthetic Fiber: Polyvinyl alcohol (PVOH) microfiber: High-toughness and high-modulus PVA fiber W1 6mm (Anhui Wanwei Updated Hightech Material Industry Co., Ltd., Chaohu, Anhui, China). PVOH fiber properties are given in the fiber manufacturer data sheet in Table 1 below.

[0133] Table 1: Properties of Synthetic Fibers

[0134] characteristic value Linear density (dtex*) 2 Toughness (cN / dtex) 12.2 E-modulus (cN / dtex) 275 Elongation (%) 6.8 Hot water solubility % (90℃, 1 hour) 0.7 Dispersion level (level)** 1 Length (mm) 6

[0135] *1 dtex = 1 g / 10000 m; **1 is the best, 4 is the worst.

[0136] Aqueous emulsion polymers 1, 2, 3 and 1A were prepared as shown in the following synthesis examples 1 and 1A.

[0137] Synthesis Example 1: A core-shell (90 / / 10 w / w) emulsion polymer of polymer 1 crosslinked with butyl acrylate (BA) (99.3%) and shell 1 of 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 mantle, thermometer, temperature controller, and nitrogen (N2) inlet. 1019.61 g of deionized water and 0.47 g of acetic acid were added to the reactor. The reactor contents were heated to 40 °C under N2 purging. In a separate vessel, a butyl acrylate (BA) monomer emulsion was prepared using 189.67 g of deionized water, 46.67 g of sodium lauryl sulfate (SLS, 28 wt.) surfactant in water, 1497.42 g of BA, and 10.55 g of allyl methacrylate (ALMA). Mechanical stirring was applied to achieve emulsification. 32.99 g of a 3 wt.% aqueous solution of sodium formaldehyde sulfoxylate (SFS) (reducing agent) was added to the reactor. 535.34 g of BA monomer emulsion and 0.38 g of a 70 wt.% aqueous solution of tert-butyl hydroperoxide (t-BHP) were added to the reactor. After a few minutes, an exothermic reaction was observed, causing the temperature to rise by approximately 41 °C (to 81 °C). The reaction was then cooled to 40 °C. 697.73 g of BA monomer emulsion and 0.52 g of a 70 wt.% aqueous solution of t-BHP were added to the reactor. After a few minutes, an exothermic reaction was observed, causing the temperature to rise by approximately 41 °C. The reaction was then cooled back to 56 °C. The remaining 513.85 g of BA monomer emulsion and 0.35 g of a 70% aqueous solution of t-BHP were added to the reactor. After a few minutes, an exothermic reaction was observed, causing the temperature to rise by approximately 38 °C. The core stage was completed by adding 1.12 g of a 70 wt.% t-BHP aqueous solution and 26.79 g of a 3 wt.% SFS aqueous solution to the reactor, while simultaneously cooling to 75°C over a 20-minute period. The shell stage was completed by adding 11.03 g of sodium lauryl sulfate surfactant (28 wt.% in water) and 167.48 g of MMA monomer to the reactor, followed by simultaneous feeding of sodium persulfate (NaPS) and SFS solution over a 40-minute period. 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.% t-BHP aqueous solution and 6.98 g of a 3 wt.% SFS aqueous solution to the reactor, while simultaneously cooling to 60°C over a 20-minute period. The reaction was then cooled to 40°C and filtered through coarse cotton cloth. The Z-average particle size of the aqueous emulsion polymer was measured at 65 nm (by Malvern Instruments light scattering), with a solids content of 32.5% (by gravimetric analysis). The calculated Tg of the rubber core ranged from -20°C to -140°C.

[0138] Synthesis Example 2: A core-shell (90 / / 10 w / w) emulsion polymer of polymer 2 crosslinked with butyl acrylate (BA) (99.3%) and shell of 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 the polymerized monomers. Additionally, 360 g of the crosslinked poly(BA) latex (seed, 32 wt.% aqueous solution of polymer; Z-average particle size 55 nm) along with the SFS reducing agent was charged into the reactor. 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 gravimetric analysis). The calculated Tg of the rubber core was -20 °C to -140 °C.

[0139] Synthesis Example 3: A core-shell (90 / / 10 w / w) emulsion polymer of polymer 3 crosslinked with butyl acrylate (BA) (99.3%) and shell of 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 the polymerized monomers. Additionally, 360 g of the crosslinked poly(BA) latex (seed, 32 wt.% aqueous solution of polymer; Z-average particle size 236 nm) along with the SFS reducing agent was charged into the reactor. 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 gravimetric analysis). The calculated Tg of the rubber core was -20 °C to -140 °C.

[0140] Synthesis Example 1A: Single-stage aqueous emulsion polymer 1A. As in Example 2 of U.S. Patent Publication No. 2018 / 0327310A1 to Evans et al., emulsion polymerization was carried out in a conventional manner by gradually adding the monomer emulsion in the presence of an anionic surfactant and a 15% sodium persulfate solution. The properties of the aqueous emulsion polymer are listed in Table 2 below.

[0141] Table 2: Aqueous Emulsion Polymers and Properties

[0142] product Polymer 1A* Polymers 1, 2 and 3 Appearance milky milky polymer Styrene Acrylic Core-shell Solids, by weight % 56 As shown above pH 6 2.0-6.0 MFFT, ℃ <0 n / a** Calculated Tg -8 n / a

[0143] * indicates a comparison example.

[0144] Roofing Tile Preparation: Flat, multi-layered roofing tiles were prepared using a pulp screen dewatering process from the wet formulations indicated in Table 3 below. Cement and limestone filler were dispersed in approximately 200 mL of water at 2,000 rpm for 2 minutes. In another container, cellulose was pre-dispersed in water (150 mL) at the same stirring speed for 1 minute. The cellulose fibers were then added to the cement slurry, along with the synthetic fibers previously dispersed in 150 mL of water, and mixed at 1,000 rpm for 2 minutes. After this period, if applicable, the indicated aqueous emulsion polymer and the remaining (200 mL) water were added, and the mixture was stirred at 1,000 rpm for 2 minutes to form an aqueous slurry mixture with a dry material content of 27.8 wt.%. Following this, a coating of 80 g / cm³ was used. 2 The perforated screen of the paper filter was molded in a vacuum chamber (200 mmHg to 300 mmHg) to dehydrate the aqueous slurry mixture. Fiber cement board was cast into four layers, with only the top layer of the board comprising the indicated emulsion polymer, each layer being pressed for 2 minutes at 3.2 MPa in the previously described molding chamber. The resulting board was then pressed for 5 minutes at 3.2 MPa. The fiber cement board was then “plastic-sealed” (wrapped) in a polyvinylidene fluoride (PVDF) enclosure and placed in an oven at 50°C for 24 hours; after this period, the cement fiber board (160 × 200 × 5 mm) was... 3 Remove from the oven and allow to stand at room temperature (28 days / 23±2℃) to harden. After the curing period is complete, the resulting fiber cement board is subjected to an impact test. The amounts of polymer in the resulting multilayer products listed in Table 3 below represent the amount of polymer solids based on the total weight of the multilayer product.

[0145] Table 3: Formulation of Polymer-Containing Fiber Cement Roofing Tiles

[0146]

[0147]

[0148] * indicates a comparison example.

[0149] Testing method: The following testing method is used in the example.

[0150] Gardner Universal Impact Tester: To measure the impact resistance of fiber cement roofing tiles, the Gardner Universal Impact Tester (Paul N. Gardner Co., Pompano Beach, FL) is used. TMThe IM-IG-1120 Heavy Impact Tester features a 102 cm (40 inch) graduated conduit, a 0.91 kg (2 lb) weight to measure the maximum force (80 inch-lb*f), a 12.7 mm (0.500 inch) diameter punch, and a 16.3 mm (0.640 inch) die (ASTM D5420) to evaluate the drop weight over a sample of a roof tile with an area of ​​1.7 cm². The indicated sample roof tile is centered on a base plate above the opening of the 12.7 mm diameter punch. The die impactor with the 16.3 mm nose is positioned in center contact with the roof tile sample. The weight centered above the impactor is raised within the conduit to the indicated height and then released to fall onto the top of the impactor, forcing the nose through the sample roof tile. The Gardner impact energy (force) at tile breakage is reported in Tables 4 and 5 below. For each roof tile tested, two tests were performed, and the best result was taken and reported. The pass / fail criterion is visually reported by detecting crack formation after impact with the tile. To approximate the correlation between results from tests using hailballs according to ANSI / UL 2218-2012 and Gardner impact tests using steel balls, the percentage improvement in impact resistance is expressed as an increment (%), using Comparative Example 2 in Tables 4 and 5 below as a 100% control.

[0151] Table 4: Gardner Impact Test Report

[0152]

[0153]

[0154] * indicates a comparison example; nm: not satisfied.

[0155] Table 5: Impact resistance points for each sample

[0156]

[0157] 1. Z-average particle size; *- indicates a comparison example.

[0158] As shown in Tables 4 and 5 above, the Gardner impact resistance measurement performed in Comparative Example 1, which does not contain synthetic fibers, yielded a result of less than 10 in / lb*f, representing a conventional cement product without fibers. Comparative Examples 2,2, having 1.9 wt.% solid PVOH fibers, exhibited an impact resistance of 14 in / lb*f, representing a conventional fiber cement product used to normalize the results of the various examples of the invention. Compared to Comparative Example 2, Comparative Example 3, having 1.9 wt.% solid PVOH fibers, 2.9 wt.% solid cellulose fibers, and 2.4 wt.% solid conventional primary aqueous emulsion polymer 1A, showed poorer impact resistance. Therefore, including polymers in conventional forms can also reduce the impact resistance of fiber cement products made therefrom, even at low concentrations. Meanwhile, as shown in Example 5 of the present invention, at a dry solids loading of 2.8 wt.%, the presence of a core-shell aqueous emulsion polymer with a crosslinked rubber core and a Z-average particle size of 65 nm significantly improves the impact resistance to a level of 142%. In Examples 4 and 8 of the present invention, at a dry solids loading of 2.0 wt.%, the indicated polymers did not give improved fracture impact results, but performed better than Comparative Examples 1, 2, and 3 because the visually observed cracks were shallower and narrower than those observed in the comparative examples, especially in Example 8 where the polymer had a larger Z-average particle size. As shown in Examples 6 and 7 of the present invention, the increased average particle size of the core-shell aqueous emulsion polymer enables improved Gardner impact resistance.

Claims

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

2. The fiber cement product according to claim 1, wherein, based on the total solid weight of the fiber cement product, the fiber cement product comprises 2.4 wt.% to 19 wt.% of one or more core-shell aqueous emulsion polymers, the one or more core-shell aqueous emulsion polymers having a crosslinked rubber core and at least partially grafted acrylic or vinyl shell polymers, the crosslinked rubber core having a calculated glass transition temperature Tg of -20°C, and the at least partially grafted acrylic or vinyl shell polymer having a calculated glass transition temperature Tg of 20°C to 170°C.

3. The fiber cement product according to claim 2, wherein at least one of the one or more core-shell aqueous emulsion polymers comprises at least partially grafted acrylic or vinyl shell polymers, wherein the at least partially grafted acrylic or vinyl shell polymers have a calculated glass transition temperature Tg of 45°C or higher.

4. The fiber cement product according to claim 1, wherein the shell polymer comprises at least one copolymer residue of one or more vinyl methacrylates or C1 to C4 alkyl methacrylates.

5. The fiber cement product according to claim 1, wherein the shell polymer comprises copolymer residues of methyl methacrylate (MMA).

6. The fiber cement product according to claim 1, wherein at least one of the one or more core-shell aqueous emulsion polymers has a Z-average primary particle size of 110 nm to 800 nm.

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

8. The fiber cement product according to claim 1, wherein the weight ratio of the crosslinked rubber core of the core-shell aqueous emulsion polymer to the shell polymer of the core-shell aqueous emulsion polymer is in the range of 85:20 to 97:

3.

9. The fiber cement product according to claim 1, wherein, based on the total weight of monomers of at least one of the one or more core-shell aqueous emulsion polymers used to prepare the fiber cement product, the crosslinked rubber core comprises 0.2 wt.% to 2 wt.% copolymer residues of crosslinked polyene unsaturated monomers.

10. The fiber cement product according to claim 1, wherein the reinforcing fiber is selected from cellulose fibers, synthetic fibers, or mixtures thereof.

11. The fiber cement product according to claim 10, wherein the reinforcing fiber is selected from synthetic fibers including polyvinyl alcohol fibers.

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