Multi-functional coating system for cementitious composite materials

Abstract

Improved coating formulations for cementitious composite building materials are disclosed herein. The coating formulations provide both sealer and primer functions, particularly for substrates in a high alkaline environment, such as fiber cement composite materials. The coating formulations can be applied in a cost-effective single step; exhibit improved adhesion, blocking resistance, water resistance characteristics

Claims

1. A multi-functional coating formulation for cementitious composite materials containing hydroxyl functional groups, comprising: 50% to 60% by weight of a thermoplastic polymer binder comprising an epoxy ester dispersion containing at least one reactive functional group, the thermoplastic polymer binder comprising a non-crosslinking polymer capable of bonding to the hydroxyl functional groups in the cementitious composite material in a manner so as to form a sealing film on a surface of the composite material; 25% to 35% by weight of a functional pigment dispersed in the thermoplastic polymer binder, the functional pigment being rutile TiO.sub.2 having an average particle size greater than 5 microns (m) and less than 12 microns (m), wherein the pigment volume concentration of the rutile TiO.sub.2 in the coating formulation is about 30%, said functional pigment formulated with an oil absorption level of less than or equal to 17, wherein the oil absorption level in combination with the pigment volume concentration provide the coating formulation with blocking resistance; 10% to 20% by weight of deionized water; and wherein the coating formulation functions as both a sealer and a primer for the cementitious composite material.

2. The coating formulation of claim 1, wherein the polymer binder of said coating formulation has an average particle size of 100 nanometers (nm) or less.

3. The coating formulation of claim 1, wherein the at least one reactive functional group of the epoxy ester dispersion is cross-linkable.

4. The coating formulation of claim 1, wherein the polymer binder comprises a cross-linking agent.

5. The coating formulation of claim 4, wherein the polymer binder further comprises an acrylic emulsion with aziridine crosslinker.

6. The coating formulation of claim 4, wherein the cross-linking agent comprises an amine crosslinker.

7. The coating formulation of claim 4, wherein the polymer binder further comprises an acrylic emulsion with a polycarbodiimide based crosslinking agent.

8. The coating formulation of claim 1, further comprising at least one filler, wherein the at least one filler comprises an inorganic compound having a particle size less than 12 m and an oil absorption less than about 17.

9. The coating formulation of claim 8, wherein said at least one filler is precipitate CaCO.sub.3.

10. The coating formulation of claim 1, wherein the non-crosslinking polymer bonds to the OH groups on the cementitious substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example of a fiber cement substrate having a coating formulation according to one embodiment of the invention.

DETAILED DESCRIPTION

(2) In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

(3) The present disclosure generally describes an improved coating system and formulation for cementitious composite materials that can achieve an appropriate balance between blocking moisture penetration and maintaining strong adhesion, thereby capable of functioning as both a sealer and primer in a highly alkaline environment. The coating formulation generally includes a polymer binder, functional pigments, and fillers having pre-selected properties. In various embodiments, the polymer binder has a pre-selected glass transition temperature and minimum film formation temperature; the functional pigments and fillers have a pre-selected particle size range and oil absorption properties. In one embodiment, the coating formulation comprises up to 80% of a polymer binder, up to 35% of at least one pigment, and up to 15% of at least one filler.

(4) The polymer binder may comprise thermosetting polymers that form cross-linking systems. Thermosetting polymers include, but are not limited to, aromatic or aliphatic epoxy emulsions; acrylate emulsions; a combination of epoxy emulsions and acrylate emulsions (such as reacting epoxy emulsion and an acrylate emulsion having a carboxylic group in the presence of a catalyst; cross-linking epoxy emulsions; mixtures of cross-linking acrylic emulsions with aziridine; mixtures of oxazaline monomers or polymers; polymers having carboxyl group, and amino salts of acidic compounds as catalysts; acrylic emulsions with polycarbodiimide based crosslinking agents; water based alkyd with driers such as hydrocure driers; and polyurethane (such as those with a hydroxyl group and isocyanate group).

(5) The polymer binder may also comprise non-crosslinking polymers. Functional groups of the polymers can then subsequently react with, for example, hydroxyl groups on the surface of the building materials, thus creating a strong reinforcement on the top surface of the building materials. Examples of a non-crosslinking polymer capable of reacting with the surface of the building materials include, but are not limited, to blocked isocyanates and isocyanate dispersions. Non-limiting examples of a cross-linking polymer system capable of reacting with the surface of the building materials include blocked isocyanate with acrylic emulsions and isocyanate dispersions with acrylic emulsions. Thermoplastic systems include, but are not limited to, polyurethane (such as those with a hydroxyl group and isocyanate group); polyurethane hybrids with acrylic emulsions; epoxy ester dispersions; and combination of epoxy ester dispersion and acrylate emulsions.

(6) The polymer binder may also be hydrophobic and thus have a low acidic content (e.g. low number of acidic groups). However, the acidic groups may be used to react with other functional groups within the polymer itself to form cross-linking systems or with functional groups on the building composite materials to form a reinforced surface.

(7) The polymer binder may also have a particle size of up to about 500 nm. In some embodiments, the particle size may be less than about 400 nm, less than about 300 nm, less than about 200 nm, or less than about 100 nm.

(8) It is desirable that the polymer binder have a higher glass transition temperature (Tg) and yet lower minimum film formation temperature (MFFT). The larger differences between Tg and MFFT will improve film formation and blocking resistance. Polymers used in the disclosed formulations may have a Tg of about 50 C. to about 70 C. and a MFFT of about 30 C. or less than about 30 C. Non-limiting examples of such polymers include acrylic emulsions that have a Tg of 56 C. and MFFT at 26 C.

(9) In some embodiments, the coating formulation has a pre-selected pigment volume concentration (PVC), which may be dependent on the type of polymer used in the coating formulation. The inventors have discovered that if PVC is too high, a loss of adhesion may occur; on the other hand, if PVC is too low, blocking resistance may be compromised. The coating formulation preferably has a PVC of 0% to 40%, or 0% to 30%, or 10% to 20%, or 10% to 30%, or 20% to 30%, or 12% to 40%.

(10) In some embodiments, the coating formulation includes pigments and fillers that typically exhibit low oil absorption, which allows the polymer to achieve better integrity after film formation. Pigments may include organic or inorganic pigments. The pigment may be an inorganic compound having a particle size less than about 12 m and oil absorption of less than about 17. Non-limiting examples of pigments include rutile TiO.sub.2, Fe.sub.2O.sub.3 (yellow), Fe.sub.2O.sub.3 (black), zinc phosphate, zinc polyphosphate, modified orthophosphates, other phosphate related compounds, phthalocyanine blue, phthalocyanine green, Diarylide yellow, alkali blue, Toluidine red, polymeric amine salt, amino carboxylate and organic acid amine, zinc stearate, calcium stearate, other stearate-related compounds, and any combinations thereof. In one implementation, the coating formulation may include up to about 35% of at least one pigment.

(11) In some embodiments, the coating formulation includes fillers that are inorganic compounds having a particle size less than about 12 m and oil absorption of less than about 17. The fillers with oil absorption at or lower than 17 is preferred since it provides better film integrity for better blocking performance while good adhesion is still achieved. Non-limiting examples of fillers include CaCO.sub.3, talc, silica, clay, calcined clay, wallostonite, mica, feldspar, calcium silicate, barium sulfate, zinc oxide and any combination thereof. In one implementation, the coating formulations may include up to about 15% of at least one filler.

(12) In some embodiments, the coatings formulation further includes anti-blocking agents that may be used to improve blocking resistance of the coating. Antiblocking agents include but are not limited to, natural and synthetic wax dispersions, potassium silicate, silicon and fluoropolymer related oligomer or polymer. In one implementation, the coating formulation may include up to about 1% of at least one antiblocking agent.

(13) In some embodiments, the coating formulation further includes thickeners. Non-limiting examples of thickeners include conventional polymers (e.g., cellulose ether), associative polymers (hydrophobically modified ethylene oxide urethane, hydrophobically modified alkali soluble emulsion and hydrophobically modified hydroxyl ethyl cellulose), thixotropes (attapulgite and bentonite caly), and metal chelates. In one implementation, the coating formulation may include up to about 5% of at least one thickener.

(14) In some embodiments, the coating formulation may also include a solvent. The solvent may be hydrophilic. In some variations, the solvent is deionized water. In some implementations, the coating formulations may include up to about 50% of solvent.

(15) In some embodiments, the coating formulation also may include a catalyst. A non-limiting example of a suitable catalyst is a hydrocure catalyst and boroacylate driers. In some implementations, the coating formulation may include up to about 1% of catalyst.

(16) Additives may also be added to the coating formulations. Additives that can be used include, but are not limited to, one or more diluents, coalescents, surfactants, dispersion agents, defoamers, leveling agents, biocides, and pH adjusters. The additive(s) used will depend on performance requirements of the formulation. In some embodiments, the coating formulations may include diluents comprising small molecules that can react with the polymers over a time period, such as within a few days. In one implementation, coating formulations disclosed herein may include up to about 10% by weight of-diluent. Examples of diluents include, but are not limited to, oxazolidines and epoxy diluent (for epoxy systems). In some embodiments, the coating formulations may include coalescents. Non-limiting examples of coalescents include ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol 2-ethylhexyl ether and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate. Desirable coalescents may also react with the polymers during mixing or after application of the coating formulation to building materials; a non-limiting example of such a suitable coalescent is a propylene glycol monoester of corn oil fatty acid. In one implementation, the coating formulations may include up to about 3% by weight of coalescents.

(17) In some embodiments, the coating formulation may include dispersants. Suitable dispersion agents may be organic or inorganic, including but not limited to polyacid, hydrophobic copolymer polyelectrolyte, block copolymer with pigment affinic groups and phosphates.

(18) In some embodiments, the coating formulation may include surfactants. Non-limiting examples of surfactants include polyether modified dimethylpolysiloxane, benzyl ether, octyl phenoxy polyethoxy ethanol, octylphenol ethoxylate, sulfosuccinate and nonionic surfactants. A hydrophilic lipophilic balance (HLB) nonionic surfactant may be added to improve shelf-life/stability, oven aging, or resistance to freeze-thaw cycling. In one implementation, the coating formulations may include up to about 1% of surfactants.

(19) In some embodiments, the coating formulation may include biocides, mildewcides, and/or algicides, such as families of dioxabicyclo octane, azoniaadamantane chloride, 2-methyl-4-isothiazolin-3-one, and 1,2-Benzisothiazolin-3-one. In one implementation, the coating formulations may include up to about 1% of biocides.

(20) In some embodiments, the coating formulation may include suitable defoamers, which may be silicon based, mineral oil based, and combinations thereof. In one implementation, the coating formulations may include up to about 1% of dispersants.

(21) The coating formulations disclosed herein may also include pH adjusters. Non-limiting examples of pH adjusters include ammonium water solution, ethanol amine, trimine and ethylene diamine. In one implementation, the coating formulations may include up to about 1% of pH adjusters.

(22) The following examples provide greater detail of useful coating formulations for cementitious composite building materials. The examples are not to be construed as limiting the scope of the invention described.

(23) Examples of coating formulations having a PVC of 0 were prepared by mixing all the components for 10 minutes. Two representative examples of such formulations are shown in Table 1.

(24) TABLE-US-00001 TABLE 1 Example 1 (Thermoplastic) Example 2 (Thermosetting) Acceptable Acceptable Wet Wet Exemplary Weight % Exemplary Weight % Component Component Range Component Component Range Polymer Epoxy ester 70-80 Polymer Epoxy 30-40 emulsion Dry Catalyst Hydrocure 0-5 Crosslinker Amine 15-25 catalyst Solvent Deionized 20-30 Solvent Deionized 40-50 water water

(25) To study adhesion, the coating formulation was applied onto a fiber cement surface at approximately 12.5 m dry film thickness and dried in an over until the surface temperature reached at least 160 F. A top coat was then applied to reach the appropriate dry film thickness and subsequently dried in an oven until the surface temperature reached at least 160 F. or was left at room temperature until fully dried, depending on the top coat applied therein.

(26) Wet adhesion was evaluated using a modified ASTM D3359, which differed in that samples did not receive an X cut and cross cut. The adhesive was a 1 inch wide adhesive of 3M Scotch tape No. 250 applied directly to a coated surface (e.g., primed and/or painted) after the surface (typically the entire sample) was soaked in tap water for about 24 hours (each specimen was weighed before and after soaking in water, and paper towels were used to remove the water from the surface of each sample after soaking). The top surface of the tape was rolled with a 10 lb. rubber roller at for 10 cycles to promote adhesion. Tape was then removed quickly at a 90 angle. Dry adhesion was also evaluated using the same method as wet adhesion except the samples were soaked in water before tape test.

(27) The pot life of the coating formulations was also evaluated. Pot life refers to the time period (after mixing the reactive components of the coating system) during which the coating can be applied to a substrate without degradation.

(28) Blocking capabilities of the coating formulations were also evaluated. For blocking, a modified ASTM D2793 was used. The specimens were stacked and pressed at about 70 PSI at 125 F. for about 5 minutes. A pressure of 70 PSI is similar to a typical weight of about 10 pallets of composite building materials stacked on top of each other. The elevated temperature is similar to the highest temperature that such a material may be stacked. A value of 1 after blocking testing indicates there is no interaction related bonding between boards. A value of 2 correlates to some blocking issue (boards stick to each other and do not separate automatically). The code of 2(X)s refers to blocking with very minor force to take specimen apart. The code of 2(X)m refers to blocking with moderate force to take specimens apart while 2(X)l refers to blocking with large force to take specimens apart. The minimum requirement is 2(X)s for commercial practice.

(29) Example 1 in Table 1 exhibited a 6% wet adhesion, 0 dry adhesion, blocking at 2(5)m, and no pot life issues. Example 2 in Table 1 exhibited a 3% wet adhesion, 0 dry adhesion, blocking at 2(5)m, and a pot life of 4 hours.

(30) Representative Examples 3 and 4 of coating formulations having a PVC of 30% are shown in Table 2. To prepare these formulations, the pigment paste components were mixed and ground until the particle size dropped to less than 45 The pigment paste was then agitated while all of the letdown components except the thickener was added. Then, the thickener was added while the mixture was slowly agitated.

(31) Example 3 exhibited a 7% wet adhesion, 0 dry adhesion, blocking at 2(3)s, and no pot life issue. Example 4 exhibited a 10% wet adhesion, 0 dry adhesion, blocking at 2(1)s, and a pot life of less than 4 hours.

(32) TABLE-US-00002 TABLE 2 Example 3 (Thermoplastic) Example 4 (Thermosetting) Acceptable Acceptable Exemplary Wet Weight % Exemplary Wet Weight % Components Component Range Components Component Range Pigment Solvent Deionized 10-20.sup. Pigment Solvent Deionized 10-20.sup. Paste water Paste water Components Dispersant Tamol 165A <about 1% Components Dispersant Tamol 165A <about 1% Surfactant Byk 348 <about 1% Surfactant Byk 348 <about 1% Biocide Nuosept 095 <about 1% Biocide Nuosept 095 <about 1% Defoamer Defoamer <about 1% Defoamer Defoamer <about 1% Pigment TiO.sub.2 25-35% Pigment TiO.sub.2 25-35% Letdown Polymer Epoxy ester 50-60% Letdown Polymer Epoxy 50-60% components dispersion components emulsion Crosslinker Amine Defoamer Defoamer <about 1% Defoamer Defoamer <about 1% pH adjuster NH.sub.3H.sub.2O <about 1% pH adjuster NH.sub.3H.sub.2O <about 1% Antiblocking Antiblocking <about 1% Antiblocking Antiblocking <about 1% agent agent agent agent Thickener Thickener 0-5% Thickener Thickener 0-5% Solvent Deionized 0-5% Solvent Deionized 0-5% water water

(33) Representative Examples 5 and 6 of coating formulations having a PVC of 20% and with color are shown in Table 3. To prepare these formulations, the pigment paste components were mixed and ground until the particle size dropped to less than 45 m. The pigment paste was then agitated while all of the letdown components except the thickener were added. Then, the thickener was added while the mixture was slowly agitated.

(34) Example 5 exhibited a 6% wet adhesion, 0 dry adhesion, and blocking at 2(5)s, no pot life issue. Example 6 exhibited a 5% wet adhesion, 0 dry adhesion, blocking at 2(4)s, and a pot life of less than 4 hours.

(35) TABLE-US-00003 TABLE 3 Example 5 (Thermoplastic) Example 6 (Thermosetting) Acceptable Acceptable Exemplary Wet Weight % Exemplary Wet Weight % Components Component Range Components Component Range Pigment Solvent Deionized 10-20.sup. Pigment Solvent Deionized 10-20.sup. Paste water Paste water Components Dispersant Tamol 165A <about 1% Components Dispersant Tamol 165A <about 1% Surfactant Byk 348 <about 1% Surfactant Byk 348 <about 1% Biocide Nuosept 095 <about 1% Biocide Nuosept 095 <about 1% Defoamer Defoamer <about 1% Defoamer Defoamer <about 1% Pigment TiO.sub.2 <about 5% Pigment TiO.sub.2 <about 5% Pigment Zinc stearate <about 1% Pigment Zinc stearate <about 1% Pigment Fe.sub.2O.sub.3 <about 1% Pigment Fe.sub.2O.sub.3 <about 1% (yellow) (yellow) Pigment Fe.sub.2O.sub.3 <about 1% Pigment Fe.sub.2O.sub.3 <about 1% .sub.(black) .sub.(black) Filler Talc 0-5% Filler Talc 0-5% Filler CaCO.sub.3 0-10% Filler CaCO.sub.3 0-10% Filler clay 0-5% Filler Clay 0-5% Letdown Polymer Epoxy ester 60-70% Letdown Polymer Epoxy 60-70% components dispersion components emulsion and amine Defoamer Defoamer <about 1% Defoamer Defoamer <about 1% pH adjuster NH.sub.3H.sub.2O <about 1% pH adjuster NH.sub.3H.sub.2O <about 1% Antiblocking Antiblocking <about 1% Antiblocking Antiblocking <about 1% agent agent agent agent Thickener Thickener 0-5% Thickener Thickener 0-5%

(36) The coating formulations disclosed herein may be used for application to various types of building composite materials, such as cementitious material, gypsum, or other inorganic composite material.

(37) Some embodiments provide a coating formulation suitable for use on a fiber cement substrate. In some embodiments, the coating formulations disclosed herein exhibit a pre-selected amount of binder and filler to allow the coating formulations to maintain both adhesion and blocking when applied to fiber cement substrates. Moreover, in some embodiments, the disclosed coating formulations may be applied to fiber cement substrates in a cost-effective single step and without applying a sealer in a second application step.

(38) The coating formulations disclosed herein may be applied to cementitious building composite materials using any method known in the art, including but not limited to brushing, spraying, dabbing, and any combinations thereof. The coating formulation may be applied to the entire surface or portions of the surface of these building composite materials. As a non-limiting example, FIG. 1 shows a fiber cement composite material 100 incorporating a single layer of protective coating that functions as both a primer and sealer. The fiber cement composite material 100 comprises a fiber cement substrate 100 having a layer of coating material 120 formed on the upper surface of the substrate 100. The layer of coating material 100 is formulated in accordance with the formulations disclosed herein. The fiber cement material 100 can be configured as a plank, siding board, or other building components.

(39) Although the foregoing description of the preferred embodiments has shown, described and pointed out certain novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form of the detail as illustrated as well as the uses thereof, may be made by those skilled in the art, without departing from the scope of the invention. Particularly, it will be appreciated that the preferred embodiments may manifest itself in other shapes and configurations as appropriate for the end use of the article made thereby.

(40) As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as up to, at least, greater than, less than, and the like include the number recited and refer to ranges which can be subsequently broken down into sub-ranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 articles refers to groups having 1, 2, or 3 articles. Similarly, a group having 1-5 articles refers to groups having 1, 2, 3, 4, or 5 articles, and so forth.