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WO2014060350A1 - Aqueous silicone resin emulsion and its application - Google Patents

Aqueous silicone resin emulsion and its application Download PDF

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Publication number
WO2014060350A1
WO2014060350A1 PCT/EP2013/071418 EP2013071418W WO2014060350A1 WO 2014060350 A1 WO2014060350 A1 WO 2014060350A1 EP 2013071418 W EP2013071418 W EP 2013071418W WO 2014060350 A1 WO2014060350 A1 WO 2014060350A1
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Prior art keywords
silicone resin
aqueous
latex
resin latex
aqueous silicone
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French (fr)
Inventor
Shenggang SHA
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Wacker Chemie AG
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Wacker Chemie AG
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
    • C09D183/04—Polysiloxanes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
    • C08L83/04—Polysiloxanes

Definitions

  • the present invention relates to an aqueous silicone resin latex and the use thereof in the field of building coatings.
  • Textured building coatings are widely used for an exterior wall of a building, and a thermal insulation system of the exterior wall.
  • the textured coating generally has an extremely rough surface, on which dust is prone to build up in the atmospheric environment, thereby impairing the aesthetic effect.
  • Aqueous acrylic varnish is a commonly used finishing coating for the textured coating, but being a thermoplastic polymer, is likely to be fouled by dust due to the tendency thereof to become soft at a high temperature in the summer, thus having a sub-optimal anti-fouling performance.
  • Other aqueous coatings having a certain anti-fouling performance are desired in the field of building coatings.
  • silicone resins are known to be able to be cross- linked after the film formation, so as to form a thermosetting polymer compound. Addition of the silicone resin to the aqueous acrylic varnish can greatly improve the anti-fouling performance, water-resistance, and aging tolerance of the product.
  • the silicone resin is generally used in the form of a silicone resin latex.
  • the solvents most commonly used in the formulation of the silicone resin latex are aromatic solvents with a low melting point, for example, toluene, xylene, trimethyl benzene, and the like. However, these solvents generally have an irritating odor, are volatile organics, and thus cannot meet the current demands for products with low VOC, and particularly zero VOC.
  • US5039724 discloses an aqueous silicone resin latex, in which a low molecular weight polysiloxane is used. Due to the slow cross-linking reaction between the polysiloxane of low molecular weight and the silicone resin, it takes a relatively long curing time (more than 20 days) for the latex to dry to form a film; however the film has a relatively low hardness, and still cannot meet the requirements in practical application .
  • an objective of the present invention is to provide an aqueous silicone resin latex which has an excellent anti-fouling performance, and is environmentally friendly and safe.
  • the inventor of this invention finds, after extensive and deep research in the field of aqueous silicone resin latexes, that the foresaid objectives can be achieved with an aqueous silicone resin latex containing a silicone resin with a melting point above 30°C and a particular alcohol ester.
  • the aqueous silicone resin latex of the present invention has an excellent anti-fouling performance, and is environmentally friendly and safe.
  • the inventor accomplishes the present invention based on the above findings .
  • An aqueous silicone resin latex comprising a silicone resin and an alcohol ester, wherein said silicone resin has a melting point above 30°C and a structural unit of general formula R a (R ⁇ O) b SiO( 4 _ ( a+ b) ) /2 , wherein R is C1-C14 hydrocarbyl, R 1 is C1-C4 alkyl or hydrogen, a is 0-3, preferably 0.75-1.5, and more preferably 0.9-1.1; and b is 0-3, preferably 0.01-1.1, and more preferably 0.01-0.07; and
  • said alcohol ester has a chemical general formula of:
  • R 4 , and R 6 are each independently C1-C6 alkyl, and preferably C3-C6 alkyl
  • R 5 is C1-C6 alkylene, preferably C3-C6 alkylene
  • the alcohol ester has a boiling point above 250 °C.
  • aqueous silicone resin latex of item 1 wherein R is selected from C1-C6 alkyl and C2-C6 alkenyl , more preferably from methyl, ethyl, propyl, and ethenyl, and most preferably from methyl, ethyl, and propyl; and R 1 is selected from methyl, ethyl, and propyl, and more preferably ethyl. 3.
  • the aqueous silicone resin latex of item 1 or 2 wherein the silicone resin has a weight average molecular weight of 5000-15000 g/mol and a polydispersity index of 3-5, and preferably has a weight average molecular weight of 8000-12000 g/mol and a polydispersity index of 3.5-4.5.
  • aqueous silicone resin latex of any one of items 1 to 4, wherein the amount of the alcohol ester is 5-20 wt%, and preferably 8-15 wt%, based on the total weight of the aqueous silicone resin latex.
  • aqueous silicone resin latex of any one of items 1 to 5, comprising 0.1-50 wt%, and preferably 1-10 wt% of an emulsifying agent, based on the total weight of the aqueous silicone resin latex.
  • said aqueous silicone resin latex has a particle size ranging between 100 and 1000 nm, and a D50 of 100-500 nm.
  • aqueous silicone resin latex of item 6 or 7 formed by emulsifying a silicone resin solution in water in the presence of an emulsifying agent, wherein the silicone resin solution comprises the silicone resin and the alcohol ester.
  • aqueous silicone resin latex of item 8 wherein the silicone resin solution further comprises an alkylalkoxysilane of general formula: R 2 m Si (OR 3 ) 4-m , wherein R 2 is C1-C16 alkyl, R 3 is C1-C4 alkyl or hydrogen; and m is an integer of 0-3, and preferably 1-3; and the alkylalkoxysilane is present in an amount of 1-20 wt%, preferably 2-15 wt%, and more preferably 5- 10 wt% of the total weight of the silicone resin solution.
  • R 2 is C1-C16 alkyl
  • R 3 is C1-C4 alkyl or hydrogen
  • m is an integer of 0-3, and preferably 1-3
  • the alkylalkoxysilane is present in an amount of 1-20 wt%, preferably 2-15 wt%, and more preferably 5- 10 wt% of the total weight of the silicone resin solution.
  • aqueous silicone resin latex of item 9 wherein the alkylalkoxysilane is one of or a mixture of more than one of: n-butyltriethoxysilane , iso-butyltriethoxysilane , n- octyltriethoxysilane , iso-octyltriethoxysilane , dodecyltriethoxysilane , and hexadecyltriethoxysilane ; and is preferably iso-octyltriethoxysilane .
  • aqueous silicone resin latex of any one of items 1 to 11, wherein the weight ratio of the alcohol ester to the silicone resin is 0.2-0.55, and preferably 0.25-0.45.
  • An aqueous coating comprising 5-25 wt% of the aqueous silicone resin latex of any one of items 1 to 12, and 5-25 wt of an aqueous acrylic latex.
  • An aspect of the present invention relates to an aqueous silicone resin latex, which comprises a silicone resin and an alcohol ester, where said silicone resin has a melting point above 30°C and a structural unit of general formula R a (R 1 0)bSiO(4- (a+ ))/2, in which R is C1-C14 hydrocarbyl, R 1 is Cl- C4 alkyl or hydrogen, a is 0-3, preferably 0.75-1.5, and more preferably 0.9-1.1; and b is 0-3, preferably 0.01-1.1, and more preferably 0.01-0.07; and
  • said alcohol ester has a chemical general formula of:
  • R 4 , and R 6 are each independently C1-C6 alkyl, and preferably C3-C6 alkyl
  • R 5 is C1-C6 alkylene, and preferably C3-C6 alkylene
  • the alcohol ester has a boiling point above 250 °C.
  • R is preferably selected from C1-C6 alkyl and C2-C6 alkenyl, more preferably from methyl, ethyl, propyl, and ethenyl, and most preferably from methyl, ethyl, and propyl.
  • R 1 is preferably selected from methyl, ethyl, and propyl, and more preferably ethyl.
  • a suitable silicone resin preferably has a weight average molecular weight of 5000-15000 g/mol and a polydispersity index PD of 3-5, and preferably has a weight average molecular weight of 8000-12000 g/mol and a polydispersity index PD of 3.5-4.5.
  • the silicone resin has a structural unit of, for example, general formulas CH 3 SiOi. 97 (OC 2 H 5 ) 0 .o6 and
  • a suitable alcohol ester for the present invention is one of or a mixture of more than one of: 2 , 2 , 4 -trimethyl- 1 , 3 - pentanediol monoisobutyrate, 2 , 2 , 4 -triethyl- 1 , 3 -pentanediol monoisobutyrate, 2,2, 4-trimethyl- 1, 3-hexanediol monoisobutyrate, 2, 2, 4-triethyl-l, 3-hexanediol monoisobutyrate, and 2 , 4-dimethyl-l, 3-hexanediol monoisobutyrate.
  • the amount of the alcohol ester is preferably 5-20 wt%, and more preferably 8-15 wt%, based on the total weight of the aqueous silicone resin latex.
  • said aqueous silicone resin latex further comprises 0.1-50 wt%, and preferably 1-10 wt% of an emulsifying agent, based on the total weight of the aqueous silicone resin latex.
  • the emulsifying agent is a C1-C20 alkyl polyethylene oxide ether having 3-150 ethylene oxide units and/or a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-150 ethylene oxide units and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; and more preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-6 ethylene oxide units, an iso-tridecyl alcohol polyethylene oxide ether having 8-16 ethylene oxide units, and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units;
  • said aqueous silicone resin latex has a particle size ranging between 100 and 1000 nm, and a D50 of 100-500 nm.
  • said aqueous silicone resin latex is formed by emulsifying a silicone resin solution in water in the presence of an emulsifying agent, wherein the silicone resin solution comprises the silicone resin and the alcohol ester.
  • the alcohol ester is present in an amount of 15-35 wt%, and preferably 15-25 wt% of the weight of the silicone resin solution.
  • said silicone resin solution can further comprise an alkylalkoxysilane of general formula: R 2 m Si (OR 3 ) 4-m , wherein R 2 is C1-C16 alkyl, R 3 is C1-C4 alkyl or hydrogen; and m is an integer of 0-3, and preferably 1-3.
  • R 2 is preferably C4-C16 alkyl, and is more preferably selected from butyl, hexyl, octyl, dodecyl, and hexadecyl .
  • R 3 is preferably selected from methyl, ethyl, and propyl, and more preferably ethyl.
  • Said alkylalkoxysilane is present in an amount of 1-20 wt%, preferably 2-15 wt%, and most preferably 5-10 wt% of the total weight of the silicone resin solution.
  • said alkylalkoxysilane is one of or a mixture of more than one of: n-butyltriethoxysilane , iso- butyltriethoxysilane , n-octyltriethoxysilane , iso- octyltriethoxysilane , dodecyltriethoxysilane , and hexadecyltriethoxysilane; and is preferably iso- octyltriethoxysilane .
  • said silicone resin solution can further comprise 1-40 wt%, and preferably 5-10 wt% of an aromatic solvent and/or an aliphatic solvent, based on the total weight of the solution, said aromatic solvent or aliphatic solvent having a chemical general formula C p H q , wherein p is 9-15 and q is 12-32.
  • the aromatic solvent may be a mixture of C 9 -Ci aromatic hydrocarbons, and the aliphatic solvent may be a mixture of Ci 2 -C 15 aliphatic hydrocarbons.
  • the commercially available hydrocarbon solvents include, for example, Solvesso 150ND, Solvesso 200, and Solvesso 200ND having heavy aromatic hydrocarbon naphtha as a principal ingredient, or Exxsol D60 and Exxsol D80 having a hydrogenated light-weight ingredient of distilled petroleum as a principal ingredient.
  • the weight ratio of the alcohol ester to the silicone resin is 0.2- 0.55, and preferably 0.25-0.45.
  • the aqueous silicone resin latex according to the present invention can be prepared by dissolving the silicone resin in a mixed liquid of the above-mentioned alcohol ester, an optional alkylalkoxysilane , and an optional hydrocarbon solvent, to give a colorless and clear silicone resin solution, and then emulsifying the solution in water with the aid of an emulsifying agent. During this, depending on the characteristics of the emulsifying agent, the emulsifying agent can be added to the aqueous phase or the oil phase.
  • the silicone resin can also be dissolved in the alcohol ester first, and then an optional alkylalkoxysilane and an optional hydrocarbon solvent are added, to afford a colorless and clear silicone resin solution.
  • a standard stirrer for example, a high-speed disperser or a homogenizer. After emulsification, the latex can be diluted with water.
  • the solid content in the aqueous silicone resin latex according to the present invention is 1-80 wt%, preferably 30- 60 wt%, and more preferably 35-55 wt%.
  • the aqueous silicone resin latex according to the present invention can further comprise a small amount, for example, about 1-5 wt% based on the total weight of the latex, of conventional aids, for example, a preservative (e.g. an isothiazolinone preservative) and a pH regulator (e.g. a potassium methylsilanolate solution) .
  • a preservative e.g. an isothiazolinone preservative
  • a pH regulator e.g. a potassium methylsilanolate solution
  • Another aspect of the present invention relates to the use of the aqueous silicone resin latex according to the present invention in building coatings.
  • a further aspect of the present invention relates to an aqueous coating, which comprises about 5-25 wt% of the aqueous silicone resin latex according to the present invention and about 5-25 wt% of an aqueous acrylic latex.
  • Said aqueous coating can further comprise 1-5 wt% of an aid for coating.
  • the aqueous acrylic latex may be those commonly used in the art, for example, commercially available latexes for building coatings for exterior walls.
  • the acrylic latexes are for example those described in Acrylate Coating (ISBN: 9787502566319, Wang Changchun et al . , Chemical Industry Press, April 2005) .
  • Useful acrylate therein includes, for example, esters of (meth) acrylic acid and an alcohol.
  • Said alcohol is preferably C1-C12, preferably C1-C8, and particularly preferably C1-C4 alkanol, for example the methyl ester, ethyl ester, n-butyl ester, iso-butyl ester, and 2- ethylhexyl ester of acrylic acid, and the methyl ester, ethyl ester, n-butyl ester, iso-butyl ester, and 2-ethylhexyl ester of (meth) acrylic acid.
  • the most suitable carrier is water, and said aqueous coating contains about 50-75 wt% of water.
  • an aid for coating of about 1-5 wt%, based on the total weight of the coating may be used.
  • the aid for coating used includes a thickener (e.g. a cellulosic thickener), an anti-foaming agent (e.g. a silicone anti-foaming agent), a preservative (e.g. an isothiazolinone preservative), a H regulator (e.g. triethanolamine) , and an anti-freezing agent (e.g. 1 , 3 -propylene glycol), and the like.
  • a thickener e.g. a cellulosic thickener
  • an anti-foaming agent e.g. a silicone anti-foaming agent
  • a preservative e.g. an isothiazolinone preservative
  • H regulator e.g. triethanolamine
  • an anti-freezing agent e.g. 1 , 3 -propylene glycol
  • a silicone resin of empirical formula eSiOx.48 (OEt) 0.0 (trade name: SILRES ® MK powder, supplied by Wacker Chemie company, weight average molecular weight: about 10000 g/mol, polydispersity index PD: 4.3, melting point: 35°C- 55°C) was dissolved in a mixed liquid of 21 parts of 2,2,4- trimethyl-1 , 3 -pentanediol monoisobutyrate (trade name Texanol, provided by: Eastman company, boiling point: 255°C-261.5°C (102.4 kPa) ) and 7 parts of heavy aromatic solvent (trade name Solvesso 150ND, supplied by ExxonMobil company) .
  • a colorless and clear solution was obtained after uniformly stirring, which has a viscosity of about 10000 cps at 23°C.
  • a silicone resin of empirical formula MeSiOi.4 8 (OEt) 0.0 (trade name SILRES ® MK powder, supplied by Wacker Chemie company, weight average molecular weight: about 10000 g/mol, polydispersity index PD: 4.3, melting point: 35°C- 55°C) was dissolved in a mixed liquid of 21 parts of 2,2,4- trimethyl-1, 3 -pentanediol monoisobutyrate (trade name Texanol) and 7 parts of iso-octyltriethoxysilane (trade name SILRES ® BS1701, supplied by Wacker Chemie company) .
  • a colorless and clear solution was obtained after uniformly stirring, which has a viscosity of about 15600 cps at 23°C.
  • a silicone resin of empirical formula MeSiOi.48 (OEt) 0.0 (trade name SILRES ® MK powder, supplied by Wacker Chemie company, weight average molecular weight: about 10000 g/mol, polydispersity index PD: 4.3, melting point: 35°C- 55°C) was dissolved in 30 parts of 2 , 2 , 4 -trimethyl- 1 , 3 - pentanediol monoisobutyrate (trade name Texanol) .
  • a colorless and clear solution was obtained after uniformly stirring, which has a viscosity of about 18000 cps at 23°C.
  • silicone resin solution A colorless and clear appearance of the silicone resin solution suggests that the silicone resin is well dissolved; and a cloudy appearance, or the presence of a precipitate in the solution suggests that the silicone resin is poorly dissolved. It can be seen from Table 1 that the silicone resins are dissolved very well, and highly stable solutions are obtained .
  • a nonionic emulsifying agent iso- tridecyl alcohol polyethylene oxide ether (5 EOs , MULTISO 13/50, supplied by Sasol Chemical company) and 2.70 parts of C12 alkyl polyethylene oxide ether (containing 28 EOs, trade name Emulsogen ® LCN 287, supplied by Clariant company) were dissolved in 5.0 parts of deionized water. After the emulsifying agent was fully and uniformly dispersed in water, 54 parts of the silicone resin solution 1 was slowly added therein, stirring during addition, within a feeding time of about 35 minutes and at a stirring speed of about 1500 rpm.
  • a nonionic emulsifying agent iso-tridecyl alcohol polyethylene oxide ether (5 EOs, MULTISO 13/50, supplied by Sasol Chemical company)
  • 1.0 part of a nonionic emulsifying agent iso-tridecyl alcohol polyethylene oxide ether (10 EOs , MULTISO 13/100, supplied by Sasol Chemical company)
  • 2.0 parts of C13 alkyl polyethylene oxide ether containing 100 EOs, trade name Genapol X1005, supplied by Clariant company
  • silicone resin solution 2 was slowly added therein, stirring during addition, within a feeding time of about 35 minutes and at a stirring speed of about 1500 rpm. Then 38.0 parts of deionized water was added therein with stirring, until a uniform white latex was formed. Then 0.06 part of a preservative Rocima R550 and 0.12 part of a preservative Rocima R640 were added therein, and finally 0.1 part of potassium methyl silanolate solution SILRES ® BS168 was added therein to adjust to pH 7-8.
  • the particle size ranges between 100-500 nm and D50 is 313 nm, as measured by a Malvern particle- size- distribution analyzer.
  • a nonionic emulsifying agent iso- tridecyl alcohol polyethylene oxide ether (5 EOs, MULTISO 13/50, supplied by Sasol Chemical company)
  • 0.94 part of a nonionic emulsifying agent iso-tridecyl alcohol polyethylene oxide ether 10 EOs, MULTISO 13/100, supplied by Sasol Chemical company
  • 1.4 parts of a nonionic emulsifying agent castor oil polyethylene oxide ether 200 EOs, EtocasTM 200, supplied by Croda company
  • silicone resin solution 2 was slowly added therein, stirring during addition, within a feeding time of about 35 minutes and at a stirring speed of about 1500 rpm. Then, 38.31 parts of deionized water was added therein with stirring, until a uniform white latex was formed. Then, 0.06 part of a preservative Rocima R550 and 0.12 part of a preservative Rocima R640 were added therein, and finally 0.1 part of potassium methylsilanolate solution SILRES ® BS168 was added therein to adjust to pH 7-8.
  • the particle size ranges between 100-900 nm and D50 is 400 nm, as measured by a Malvern particle-size-distribution analyzer .
  • Varnish examples 1-3 and the comparative example were put in sealed plastic bottles, then placed in a thermostat oven at 50 °C, and examined for the occurrence of layering and precipitation after 1 month. The results are shown in Table 2. A satisfactory coating should experience no or slight layering without influencing the utility.
  • Varnish examples 1-3 and the comparative example were spread with a wire rod applicator on glass substrates, to give a wet film with a thickness of 100 ⁇ .
  • the samples were left for 24 hrs at 23 °C and 50% relative humidity, soaked for 96 hrs in deionized water, and then removed. The appearances of the samples after soaking and drying were observed. The results are shown in Table 3. A satisfactory sample should appear slightly white after soaking, and reappear transparent again after drying.
  • the above-mentioned textured coating was evenly spread onto a cement fiberboard of 7 x 15 centimeters with a scraper, to give a consistent thickness controlled in the range of 2 to 3 mm, and dried for 7 days at 23 °C and 50% relative humidity to be ready for use.
  • Varnish example 2 and the comparative example were brushed onto the surface of the above-mentioned textured coating in an amount of 100 g/square meter, and fully dried after standing for 7 days at 23 °C and 50% relative humidity. Then, the whiteness of the resulting coating was measured. The tests were performed by using a Color-guide color-difference meter from BYK Company, Germany, to measure L, a, and b values of individual coating surfaces, wherein L denotes the whiteness. For each sample, three measurements were taken and averaged.
  • Formulated ash for testing the anti-fouling performance of coatings meets the requirements of GB/T 9780-2005, Test method for dirt pickup resistance of film of architectural coatings and paints, has graphite powder as a principal component, and has the following parameters: fineness: 0.045 mm; screen residue amount on square mesh sieve: (5.0 + 2.0)%, loss on ignition: (12 + 2)%, density: (2.7 + 0.2) g/cm 3 , specific surface area: (440 + 20) m 2 /kg, and reflective coefficient: (37 + 3)%.
  • the above-mentioned formulated ash was mixed with an equal amount of water, then brushed with a wool brush onto the coating surface formed with the coating from Varnish example 2 and the coating surface formed with the coating from the comparative example in an amount of 50-80 g/m 2 , followed by drying for 2 hours, and then washing with water for 1 min, and measuring for the whiteness after 24 hrs . Then, the fouling test was repeated, being performed a total of 5 times. The results are shown in Table 4.
  • Dc x L ! /L 0 *100%
  • Dc 2 L 2 /L 0 *100%
  • Dc 3 L 3 /L 0 *100%
  • Dc 4 L 4 /L 0 *100%
  • Dc 5 L 5 /L 0 *100%

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Abstract

The present invention relates to an aqueous silicone resin latex, which comprises a silicone resin and an alcohol ester, wherein said silicone resin has a melting point above 30°C and a structural unit of general formula Ra (R1O) bSiO(4- (a+b) ) /2 , wherein R is C1-C14 hydrocarbyl, R1 is C1-C4 alkyl or hydrogen, a is 0- 3, preferably 0.75-1.5, and more preferably 0.9-1.1; and b is 0-3, preferably 0.01-1.1, and more preferably 0.01-0.07; and said alcohol ester has a structure as defined in the specification; and preferably the alcohol ester has a boiling point above 250°C. The present invention also relates to the use of said aqueous silicone resin latex in building coatings and an aqueous coating comprising said aqueous silicone resin latex.

Description

Aqueous silicone resin emulsion and its application
Technical field
The present invention relates to an aqueous silicone resin latex and the use thereof in the field of building coatings.
Background
Textured building coatings are widely used for an exterior wall of a building, and a thermal insulation system of the exterior wall. The textured coating generally has an extremely rough surface, on which dust is prone to build up in the atmospheric environment, thereby impairing the aesthetic effect. Aqueous acrylic varnish is a commonly used finishing coating for the textured coating, but being a thermoplastic polymer, is likely to be fouled by dust due to the tendency thereof to become soft at a high temperature in the summer, thus having a sub-optimal anti-fouling performance. Other aqueous coatings having a certain anti-fouling performance are desired in the field of building coatings.
In order to achieve this, some literature (for example, Lin Xiaodan, "Preparation of Opacity Polymer and Its Application in Coatings", Paint and Coating Industry, 2004 (8)) discloses aqueous coatings containing a hollow polymer, which have a relatively good anti-fouling performance. However, the hollow polymer itself has a covering rate, and the addition of the hollow polymer cannot result in a transparent coating.
Some silicone resins are known to be able to be cross- linked after the film formation, so as to form a thermosetting polymer compound. Addition of the silicone resin to the aqueous acrylic varnish can greatly improve the anti-fouling performance, water-resistance, and aging tolerance of the product. The silicone resin is generally used in the form of a silicone resin latex. The solvents most commonly used in the formulation of the silicone resin latex are aromatic solvents with a low melting point, for example, toluene, xylene, trimethyl benzene, and the like. However, these solvents generally have an irritating odor, are volatile organics, and thus cannot meet the current demands for products with low VOC, and particularly zero VOC.
US5039724 discloses an aqueous silicone resin latex, in which a low molecular weight polysiloxane is used. Due to the slow cross-linking reaction between the polysiloxane of low molecular weight and the silicone resin, it takes a relatively long curing time (more than 20 days) for the latex to dry to form a film; however the film has a relatively low hardness, and still cannot meet the requirements in practical application .
Summary of the Invention
In view of the above state of the art, an objective of the present invention is to provide an aqueous silicone resin latex which has an excellent anti-fouling performance, and is environmentally friendly and safe. The inventor of this invention finds, after extensive and deep research in the field of aqueous silicone resin latexes, that the foresaid objectives can be achieved with an aqueous silicone resin latex containing a silicone resin with a melting point above 30°C and a particular alcohol ester. The aqueous silicone resin latex of the present invention has an excellent anti-fouling performance, and is environmentally friendly and safe. The inventor accomplishes the present invention based on the above findings .
The technical solutions for accomplishing the objective of the present invention can be summarized as follows:
1. An aqueous silicone resin latex, comprising a silicone resin and an alcohol ester, wherein said silicone resin has a melting point above 30°C and a structural unit of general formula Ra (R^O) bSiO(4_ (a+b) ) /2 , wherein R is C1-C14 hydrocarbyl, R1 is C1-C4 alkyl or hydrogen, a is 0-3, preferably 0.75-1.5, and more preferably 0.9-1.1; and b is 0-3, preferably 0.01-1.1, and more preferably 0.01-0.07; and
said alcohol ester has a chemical general formula of:
Figure imgf000004_0001
wherein R4, and R6 are each independently C1-C6 alkyl, and preferably C3-C6 alkyl, R5 is C1-C6 alkylene, preferably C3-C6 alkylene; and preferably, the alcohol ester has a boiling point above 250 °C.
2. The aqueous silicone resin latex of item 1, wherein R is selected from C1-C6 alkyl and C2-C6 alkenyl , more preferably from methyl, ethyl, propyl, and ethenyl, and most preferably from methyl, ethyl, and propyl; and R1 is selected from methyl, ethyl, and propyl, and more preferably ethyl. 3. The aqueous silicone resin latex of item 1 or 2 , wherein the silicone resin has a weight average molecular weight of 5000-15000 g/mol and a polydispersity index of 3-5, and preferably has a weight average molecular weight of 8000-12000 g/mol and a polydispersity index of 3.5-4.5.
4. The aqueous silicone resin latex of any one of items 1 to 3, wherein the alcohol ester is one of or a mixture of more than one of: 2 , 2 , 4 -trimethyl- 1 , 3 -pentanediol monoisobutyrate , 2 , 2 , 4 -triethyl-1 , 3 -pentanediol monoisobutyrate, 2,2,4- trimethyl - 1 , 3 -hexanediol monoisobutyrate, 2 , 2 , -triethyl- 1 , 3 - hexanediol monoisobutyrate, and 2 , 4 -dimethyl- 1 , 3 -pentanediol monoisobutyrate .
5. The aqueous silicone resin latex of any one of items 1 to 4, wherein the amount of the alcohol ester is 5-20 wt%, and preferably 8-15 wt%, based on the total weight of the aqueous silicone resin latex.
6. The aqueous silicone resin latex of any one of items 1 to 5, comprising 0.1-50 wt%, and preferably 1-10 wt% of an emulsifying agent, based on the total weight of the aqueous silicone resin latex.
7. The aqueous silicone resin latex of item 6, wherein said emulsifying agent is a C1-C20 alkyl polyethylene oxide ether having 3-150 ethylene oxide units and/or a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-150 ethylene oxide units and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; and more preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-6 ethylene oxide units, an iso-tridecyl alcohol polyethylene oxide ether having 8-16 ethylene oxide units, and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units;
and said aqueous silicone resin latex has a particle size ranging between 100 and 1000 nm, and a D50 of 100-500 nm.
8. The aqueous silicone resin latex of item 6 or 7, formed by emulsifying a silicone resin solution in water in the presence of an emulsifying agent, wherein the silicone resin solution comprises the silicone resin and the alcohol ester.
9. The aqueous silicone resin latex of item 8, wherein the silicone resin solution further comprises an alkylalkoxysilane of general formula: R2 mSi (OR3 ) 4-m, wherein R2 is C1-C16 alkyl, R3 is C1-C4 alkyl or hydrogen; and m is an integer of 0-3, and preferably 1-3; and the alkylalkoxysilane is present in an amount of 1-20 wt%, preferably 2-15 wt%, and more preferably 5- 10 wt% of the total weight of the silicone resin solution.
10. The aqueous silicone resin latex of item 9, wherein the alkylalkoxysilane is one of or a mixture of more than one of: n-butyltriethoxysilane , iso-butyltriethoxysilane , n- octyltriethoxysilane , iso-octyltriethoxysilane , dodecyltriethoxysilane , and hexadecyltriethoxysilane ; and is preferably iso-octyltriethoxysilane .
11. The aqueous silicone resin latex of any one of items 8 to 10, wherein the silicone resin solution further comprises 1-
40 wt%, and preferably 5-10 wt% of an aromatic solvent and/or an aliphatic solvent, based on the total weight of the solution, said aromatic solvent or aliphatic solvent having a chemical general formula CpHq, wherein p is 9-15 and q is 12-32.
12. The aqueous silicone resin latex of any one of items 1 to 11, wherein the weight ratio of the alcohol ester to the silicone resin is 0.2-0.55, and preferably 0.25-0.45.
13. Use of the aqueous silicone resin latex of any one of items 1 to 12 in building coatings.
14. An aqueous coating, comprising 5-25 wt% of the aqueous silicone resin latex of any one of items 1 to 12, and 5-25 wt of an aqueous acrylic latex.
Specific Embodiments
An aspect of the present invention relates to an aqueous silicone resin latex, which comprises a silicone resin and an alcohol ester, where said silicone resin has a melting point above 30°C and a structural unit of general formula Ra(R10)bSiO(4-(a+ ))/2, in which R is C1-C14 hydrocarbyl, R1 is Cl- C4 alkyl or hydrogen, a is 0-3, preferably 0.75-1.5, and more preferably 0.9-1.1; and b is 0-3, preferably 0.01-1.1, and more preferably 0.01-0.07; and
said alcohol ester has a chemical general formula of:
Figure imgf000007_0001
wherein R4, and R6 are each independently C1-C6 alkyl, and preferably C3-C6 alkyl, R5 is C1-C6 alkylene, and preferably C3-C6 alkylene; and preferably the alcohol ester has a boiling point above 250 °C. Regarding the silicone resin according to the present invention, R is preferably selected from C1-C6 alkyl and C2-C6 alkenyl, more preferably from methyl, ethyl, propyl, and ethenyl, and most preferably from methyl, ethyl, and propyl. According to an embodiment of the present invention, R1 is preferably selected from methyl, ethyl, and propyl, and more preferably ethyl.
A suitable silicone resin preferably has a weight average molecular weight of 5000-15000 g/mol and a polydispersity index PD of 3-5, and preferably has a weight average molecular weight of 8000-12000 g/mol and a polydispersity index PD of 3.5-4.5. Preferably, the silicone resin has a structural unit of, for example, general formulas CH3SiOi.97 (OC2H5) 0.o6 and
CH3SiOi, 8 (OC2H5) 0,04 ·
A suitable alcohol ester for the present invention is one of or a mixture of more than one of: 2 , 2 , 4 -trimethyl- 1 , 3 - pentanediol monoisobutyrate, 2 , 2 , 4 -triethyl- 1 , 3 -pentanediol monoisobutyrate, 2,2, 4-trimethyl- 1, 3-hexanediol monoisobutyrate, 2, 2, 4-triethyl-l, 3-hexanediol monoisobutyrate, and 2 , 4-dimethyl-l, 3-hexanediol monoisobutyrate.
In the aqueous silicone resin latex according to the present invention, the amount of the alcohol ester is preferably 5-20 wt%, and more preferably 8-15 wt%, based on the total weight of the aqueous silicone resin latex.
In an embodiment of the present invention, said aqueous silicone resin latex further comprises 0.1-50 wt%, and preferably 1-10 wt% of an emulsifying agent, based on the total weight of the aqueous silicone resin latex. According to an embodiment of the present invention, the emulsifying agent is a C1-C20 alkyl polyethylene oxide ether having 3-150 ethylene oxide units and/or a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-150 ethylene oxide units and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; and more preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-6 ethylene oxide units, an iso-tridecyl alcohol polyethylene oxide ether having 8-16 ethylene oxide units, and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units;
and said aqueous silicone resin latex has a particle size ranging between 100 and 1000 nm, and a D50 of 100-500 nm.
According to an embodiment of the present invention, said aqueous silicone resin latex is formed by emulsifying a silicone resin solution in water in the presence of an emulsifying agent, wherein the silicone resin solution comprises the silicone resin and the alcohol ester.
In a preferred embodiment, the alcohol ester is present in an amount of 15-35 wt%, and preferably 15-25 wt% of the weight of the silicone resin solution.
According to an embodiment of the present invention, said silicone resin solution can further comprise an alkylalkoxysilane of general formula: R2 mSi (OR3) 4-m, wherein R2 is C1-C16 alkyl, R3 is C1-C4 alkyl or hydrogen; and m is an integer of 0-3, and preferably 1-3. R2 is preferably C4-C16 alkyl, and is more preferably selected from butyl, hexyl, octyl, dodecyl, and hexadecyl . R3 is preferably selected from methyl, ethyl, and propyl, and more preferably ethyl. Said alkylalkoxysilane is present in an amount of 1-20 wt%, preferably 2-15 wt%, and most preferably 5-10 wt% of the total weight of the silicone resin solution.
According to a preferred embodiment of the present invention, said alkylalkoxysilane is one of or a mixture of more than one of: n-butyltriethoxysilane , iso- butyltriethoxysilane , n-octyltriethoxysilane , iso- octyltriethoxysilane , dodecyltriethoxysilane , and hexadecyltriethoxysilane; and is preferably iso- octyltriethoxysilane .
According to an embodiment of the present invention, said silicone resin solution can further comprise 1-40 wt%, and preferably 5-10 wt% of an aromatic solvent and/or an aliphatic solvent, based on the total weight of the solution, said aromatic solvent or aliphatic solvent having a chemical general formula CpHq, wherein p is 9-15 and q is 12-32. The aromatic solvent may be a mixture of C9-Ci aromatic hydrocarbons, and the aliphatic solvent may be a mixture of Ci2-C15 aliphatic hydrocarbons. The commercially available hydrocarbon solvents include, for example, Solvesso 150ND, Solvesso 200, and Solvesso 200ND having heavy aromatic hydrocarbon naphtha as a principal ingredient, or Exxsol D60 and Exxsol D80 having a hydrogenated light-weight ingredient of distilled petroleum as a principal ingredient.
In a preferred embodiment of the present invention, the weight ratio of the alcohol ester to the silicone resin is 0.2- 0.55, and preferably 0.25-0.45. The aqueous silicone resin latex according to the present invention can be prepared by dissolving the silicone resin in a mixed liquid of the above-mentioned alcohol ester, an optional alkylalkoxysilane , and an optional hydrocarbon solvent, to give a colorless and clear silicone resin solution, and then emulsifying the solution in water with the aid of an emulsifying agent. During this, depending on the characteristics of the emulsifying agent, the emulsifying agent can be added to the aqueous phase or the oil phase. Of course, during the preparation of the silicone resin solution, the silicone resin can also be dissolved in the alcohol ester first, and then an optional alkylalkoxysilane and an optional hydrocarbon solvent are added, to afford a colorless and clear silicone resin solution.
For dissolving the silicone resin and preparing the latex, a standard stirrer can be used, for example, a high-speed disperser or a homogenizer. After emulsification, the latex can be diluted with water.
The solid content in the aqueous silicone resin latex according to the present invention is 1-80 wt%, preferably 30- 60 wt%, and more preferably 35-55 wt%.
The aqueous silicone resin latex according to the present invention can further comprise a small amount, for example, about 1-5 wt% based on the total weight of the latex, of conventional aids, for example, a preservative (e.g. an isothiazolinone preservative) and a pH regulator (e.g. a potassium methylsilanolate solution) .
Another aspect of the present invention relates to the use of the aqueous silicone resin latex according to the present invention in building coatings.
A further aspect of the present invention relates to an aqueous coating, which comprises about 5-25 wt% of the aqueous silicone resin latex according to the present invention and about 5-25 wt% of an aqueous acrylic latex. Said aqueous coating can further comprise 1-5 wt% of an aid for coating.
In the present invention, the aqueous acrylic latex may be those commonly used in the art, for example, commercially available latexes for building coatings for exterior walls. The acrylic latexes are for example those described in Acrylate Coating (ISBN: 9787502566319, Wang Changchun et al . , Chemical Industry Press, April 2005) . Useful acrylate therein includes, for example, esters of (meth) acrylic acid and an alcohol. Said alcohol is preferably C1-C12, preferably C1-C8, and particularly preferably C1-C4 alkanol, for example the methyl ester, ethyl ester, n-butyl ester, iso-butyl ester, and 2- ethylhexyl ester of acrylic acid, and the methyl ester, ethyl ester, n-butyl ester, iso-butyl ester, and 2-ethylhexyl ester of (meth) acrylic acid.
In the aqueous coating according to the present invention, the most suitable carrier is water, and said aqueous coating contains about 50-75 wt% of water.
In the aqueous coating, an aid for coating of about 1-5 wt%, based on the total weight of the coating, may be used. The aid for coating used includes a thickener (e.g. a cellulosic thickener), an anti-foaming agent (e.g. a silicone anti-foaming agent), a preservative (e.g. an isothiazolinone preservative), a H regulator (e.g. triethanolamine) , and an anti-freezing agent (e.g. 1 , 3 -propylene glycol), and the like.
For the formulation of said aqueous coating, the components above are only required to be simply mixed and stirred.
Examples
In the examples below, the parts are weight parts, unless specifically indicated otherwise.
Silicone resin solution 1
About 72 parts of a silicone resin of empirical formula eSiOx.48 (OEt) 0.0 (trade name: SILRES® MK powder, supplied by Wacker Chemie company, weight average molecular weight: about 10000 g/mol, polydispersity index PD: 4.3, melting point: 35°C- 55°C) was dissolved in a mixed liquid of 21 parts of 2,2,4- trimethyl-1 , 3 -pentanediol monoisobutyrate (trade name Texanol, provided by: Eastman company, boiling point: 255°C-261.5°C (102.4 kPa) ) and 7 parts of heavy aromatic solvent (trade name Solvesso 150ND, supplied by ExxonMobil company) . A colorless and clear solution was obtained after uniformly stirring, which has a viscosity of about 10000 cps at 23°C.
Silicone resin solution 2
About 72 parts of a silicone resin of empirical formula MeSiOi.48 (OEt) 0.0 (trade name SILRES® MK powder, supplied by Wacker Chemie company, weight average molecular weight: about 10000 g/mol, polydispersity index PD: 4.3, melting point: 35°C- 55°C) was dissolved in a mixed liquid of 21 parts of 2,2,4- trimethyl-1, 3 -pentanediol monoisobutyrate (trade name Texanol) and 7 parts of iso-octyltriethoxysilane (trade name SILRES® BS1701, supplied by Wacker Chemie company) . A colorless and clear solution was obtained after uniformly stirring, which has a viscosity of about 15600 cps at 23°C.
Silicone resin solution 3
About 70 parts of a silicone resin of empirical formula MeSiOi.48 (OEt) 0.0 (trade name SILRES® MK powder, supplied by Wacker Chemie company, weight average molecular weight: about 10000 g/mol, polydispersity index PD: 4.3, melting point: 35°C- 55°C) was dissolved in 30 parts of 2 , 2 , 4 -trimethyl- 1 , 3 - pentanediol monoisobutyrate (trade name Texanol) . A colorless and clear solution was obtained after uniformly stirring, which has a viscosity of about 18000 cps at 23°C.
The solubility results of the silicone resins are summarized in Table 1 below.
Figure imgf000014_0001
A colorless and clear appearance of the silicone resin solution suggests that the silicone resin is well dissolved; and a cloudy appearance, or the presence of a precipitate in the solution suggests that the silicone resin is poorly dissolved. It can be seen from Table 1 that the silicone resins are dissolved very well, and highly stable solutions are obtained .
Silicone resin latex 1
About 1.89 parts of a nonionic emulsifying agent iso- tridecyl alcohol polyethylene oxide ether (5 EOs , MULTISO 13/50, supplied by Sasol Chemical company) and 2.70 parts of C12 alkyl polyethylene oxide ether (containing 28 EOs, trade name Emulsogen® LCN 287, supplied by Clariant company) were dissolved in 5.0 parts of deionized water. After the emulsifying agent was fully and uniformly dispersed in water, 54 parts of the silicone resin solution 1 was slowly added therein, stirring during addition, within a feeding time of about 35 minutes and at a stirring speed of about 1500 rpm. Then 36.4 parts of deionized water was added therein with stirring, until a uniform white latex was formed. Then, 0.06 part of a preservative Rocima R550 (a methylisothiazolinone preservative, available from Dow Chemicals) and 0.12 part of a preservative Rocima R640 (phenylisothiazolinone preservative, available from Dow Chemicals) were added therein, and finally 0.1 part of a potassium methylsilanolate solution (SILRES® BS168, available from Wacker Chemie company) was added therein to adjust to pH 7-8. The particle size ranges between 100-500 nm and D50 is 152 nm, as measured by a Malvern particle-size- distribution analyzer. Silicone resin latex 2
About 1.0 part of a nonionic emulsifying agent iso-tridecyl alcohol polyethylene oxide ether (5 EOs, MULTISO 13/50, supplied by Sasol Chemical company), 1.0 part of a nonionic emulsifying agent iso-tridecyl alcohol polyethylene oxide ether (10 EOs , MULTISO 13/100, supplied by Sasol Chemical company), and 2.0 parts of C13 alkyl polyethylene oxide ether (containing 100 EOs, trade name Genapol X1005, supplied by Clariant company) were dissolved in 3.75 parts of deionized water. After the emulsifying agent was fully and uniformly dispersed in water, 54 parts of silicone resin solution 2 was slowly added therein, stirring during addition, within a feeding time of about 35 minutes and at a stirring speed of about 1500 rpm. Then 38.0 parts of deionized water was added therein with stirring, until a uniform white latex was formed. Then 0.06 part of a preservative Rocima R550 and 0.12 part of a preservative Rocima R640 were added therein, and finally 0.1 part of potassium methyl silanolate solution SILRES® BS168 was added therein to adjust to pH 7-8. The particle size ranges between 100-500 nm and D50 is 313 nm, as measured by a Malvern particle- size- distribution analyzer.
Silicone resin latex 3
About 1.17 parts of a nonionic emulsifying agent iso- tridecyl alcohol polyethylene oxide ether (5 EOs, MULTISO 13/50, supplied by Sasol Chemical company), 0.94 part of a nonionic emulsifying agent iso-tridecyl alcohol polyethylene oxide ether (10 EOs, MULTISO 13/100, supplied by Sasol Chemical company), and 1.4 parts of a nonionic emulsifying agent castor oil polyethylene oxide ether (200 EOs, Etocas™ 200, supplied by Croda company) were dissolved in 3.9 parts of deionized water. After the emulsifying agent was fully and uniformly dispersed in water, 54 parts of silicone resin solution 2 was slowly added therein, stirring during addition, within a feeding time of about 35 minutes and at a stirring speed of about 1500 rpm. Then, 38.31 parts of deionized water was added therein with stirring, until a uniform white latex was formed. Then, 0.06 part of a preservative Rocima R550 and 0.12 part of a preservative Rocima R640 were added therein, and finally 0.1 part of potassium methylsilanolate solution SILRES® BS168 was added therein to adjust to pH 7-8. The particle size ranges between 100-900 nm and D50 is 400 nm, as measured by a Malvern particle-size-distribution analyzer .
Varnish example 1
15 parts of the silicone resin latex 2, 15 parts of an acrylic latex (trade name Primal 261P, available from Dow Chemicals, 100% acrylate polymer, solid content: 50 wt%, density: 1.06 g/ml, viscosity: below 300 cps (at 60 rpm with No. 2 rotor of Brookfield viscometer)) and 70 parts of deionized water were uniformly mixed, and then a small amount of aids, namely 0.1 part of a preservative Kathon LXE (isothiazolinone preservative, available from Dow Chemicals) , 0.5 part of a thickener Acrysol RM-2020 NPR (a polyurethane thickener, available from Dow Chemicals), 0.2 part of an anti- foaming agent SILFOAM® SD 860 (a silicone anti-foaming agent, commercial products from Wacker Chemie company), 0.1 part of a pH regulator triethanolamine , and 1.0 part of an anti-freezing agent 1,3-proplene glycol, were added therein and mixed uniformly to obtain a coating. Varnish example 2
15 parts of the silicone resin latex 3, 15 parts of an acrylic latex (trade name Primal 261P) , and 70 parts of deionized water were uniformly mixed, and then a small amount of the same aids as those used in Varnish example 1, namely a preservative, a thickener, an anti- foaming agent, a pH regulator, and an anti- freezing agent, were added therein and uniformly mixed, to obtain a coating.
Varnish example 3
15 parts of the silicone resin latex 3, 15 parts of an acrylic copolymer latex (trade name NaPoly 2800, commercial product from Henkel company, acrylic copolymer latex, soap- free polymerization, solid content: about 47 wt%, viscosity: 1000- 4000 cps (at 60 rpm with No. 4 rotor of Brookfield viscometer)) and 70 parts of deionized water were uniformly mixed, and then a small amount of the same aids as those used in Varnish example 1, namely a preservative, a thickener, an anti-foaming agent, a pH regulator, and an anti- freezing agent, were added therein and uniformly mixed, to obtain a coating.
Comparative example
30 parts of an acrylic latex (trade name Primal 261P) and 70 parts of deionized water were uniformly mixed, and then a small amount of the same aids as those used in Varnish example 1, namely a preservative, a thickener, an anti-foaming agent, a pH regulator, and an anti-freezing agent, were added therein and uniformly mixed, to obtain a coating. Thermal storage stability of the coatings
The coatings formulated in Varnish examples 1-3 and the comparative example were put in sealed plastic bottles, then placed in a thermostat oven at 50 °C, and examined for the occurrence of layering and precipitation after 1 month. The results are shown in Table 2. A satisfactory coating should experience no or slight layering without influencing the utility.
Table 2
Figure imgf000019_0001
Water resistance of the coatings
The coatings from Varnish examples 1-3 and the comparative example were spread with a wire rod applicator on glass substrates, to give a wet film with a thickness of 100 μηα. The samples were left for 24 hrs at 23 °C and 50% relative humidity, soaked for 96 hrs in deionized water, and then removed. The appearances of the samples after soaking and drying were observed. The results are shown in Table 3. A satisfactory sample should appear slightly white after soaking, and reappear transparent again after drying.
Table 3
Figure imgf000020_0001
Anti-fouling performance of the coatings
Preparation of the textured coatings is as follows:
10 parts of water, 15 parts of an acrylic latex POLYSOL AP4765 (available from Showa chemical company, solid content: about 46 wt%, viscosity at 23°C: 3500 mPa.s), 1.0 part of 2 , 2 , 4 -trimethyl-1, 3 -pentanediol monoisobutyrate , 0.1 part of a preservative Kathon LXE (Dow Chemicals), 0.5 part of a thickener Acrysol TT-935 (Dow Chemicals), 0.1 part of an anti- foaming agent SILFOAM® SD 860 (commercial product from Wacker Chemie company) , and 0.1 part of a pH regulator triethanolamine were uniformly mixed, and then 75 parts of white quartz sand of 20-100 mesh was added therein and uniformly mixed, to obtain a textured coating.
The above-mentioned textured coating was evenly spread onto a cement fiberboard of 7 x 15 centimeters with a scraper, to give a consistent thickness controlled in the range of 2 to 3 mm, and dried for 7 days at 23 °C and 50% relative humidity to be ready for use.
The coatings from Varnish example 2 and the comparative example were brushed onto the surface of the above-mentioned textured coating in an amount of 100 g/square meter, and fully dried after standing for 7 days at 23 °C and 50% relative humidity. Then, the whiteness of the resulting coating was measured. The tests were performed by using a Color-guide color-difference meter from BYK Company, Germany, to measure L, a, and b values of individual coating surfaces, wherein L denotes the whiteness. For each sample, three measurements were taken and averaged.
Formulated ash for testing the anti-fouling performance of coatings (supplied by Shanghai Academy of Building Science Research) meets the requirements of GB/T 9780-2005, Test method for dirt pickup resistance of film of architectural coatings and paints, has graphite powder as a principal component, and has the following parameters: fineness: 0.045 mm; screen residue amount on square mesh sieve: (5.0 + 2.0)%, loss on ignition: (12 + 2)%, density: (2.7 + 0.2) g/cm3, specific surface area: (440 + 20) m2/kg, and reflective coefficient: (37 + 3)%. The above-mentioned formulated ash was mixed with an equal amount of water, then brushed with a wool brush onto the coating surface formed with the coating from Varnish example 2 and the coating surface formed with the coating from the comparative example in an amount of 50-80 g/m2, followed by drying for 2 hours, and then washing with water for 1 min, and measuring for the whiteness after 24 hrs . Then, the fouling test was repeated, being performed a total of 5 times. The results are shown in Table 4.
Table 4
Figure imgf000022_0001
Fouling index: Dcx= L!/L0*100%; Dc2= L2/L0*100%; Dc3= L3/L0*100%; Dc4= L4/L0*100%; and Dc5= L5/L0*100%;
L0 -the whiteness before fouling; Li - the whiteness after the first fouling; L2 - the whiteness after the second fouling; L3 -the whiteness after the third fouling; L4 - the whiteness after the fourth fouling; L5 - the whiteness after the fifth fouling.
The greater the value of the fouling index is, the better the anti-fouling performance of the coating is. It can be seen from the results in Table 4 that after 5 times of repeated fouling, the coating from Varnish example 2 still maintains a high anti-fouling capability.

Claims

Claims
1. An aqueous silicone resin latex, comprising a silicone resin and an alcohol ester, wherein said silicone resin has a melting point above 30°C and a structural unit of general formula Ra (R^O) bSiO(4_ (a+b) > /2 , wherein R is C1-C14 hydrocarbyl, R1 is C1-C4 alkyl or hydrogen, a is 0-3, preferably 0.75-1.5, and more preferably 0.9-1.1; and b is 0-3, preferably 0.01-1.1, and more preferably 0.01-0.07; and
said alcohol ester has a chemical general formula of :
Figure imgf000023_0001
wherein R4, and R6 are each independently C1-C6 alkyl, and preferably C3-C6 alkyl, R5 is C1-C6 alkylene, and preferably C3-C6 alkylene; and preferably the alcohol ester has a boiling point above 250 °C.
2. The aqueous silicone resin latex of claim 1, wherein R is selected from C1-C6 alkyl and C2-C6 alkenyl, more preferably from methyl, ethyl, propyl, and ethenyl, and most preferably from methyl, ethyl, and propyl; and R1 is selected from methyl, ethyl, and propyl, and more preferably ethyl.
3. The aqueous silicone resin latex of claim 1 or 2, wherein the silicone resin has a weight average molecular weight of 5000-15000 g/mol and a polydispersity index of 3-5, and preferably has a weight average molecular weight of 8000- 12000 g/mol and a polydispersity index of 3.5-4.5.
4. The aqueous silicone resin latex of any one of claims 1 to 3, wherein the amount of the alcohol ester is 5-20 wt%, and preferably 8-15 wt%, based on the total weight of the aqueous silicone resin latex.
5. The aqueous silicone resin latex of any one of claims 1 to 4, comprising 0.1-50 wt%, and preferably 1-10 wt% of an emulsifying agent, based on the total weight of the aqueous silicone resin latex.
6. The aqueous silicone resin latex of claim 5, wherein said emulsifying agent is a C1-C20 alkyl polyethylene oxide ether having 3-150 ethylene oxide units and/or a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-150 ethylene oxide units and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units; and more preferably a mixture of an iso-tridecyl alcohol polyethylene oxide ether having 3-6 ethylene oxide units, an iso-tridecyl alcohol polyethylene oxide ether having 8-16 ethylene oxide units, and a castor oil polyethylene oxide ether having 150-250 ethylene oxide units;
and said aqueous silicone resin latex has a particle size ranging between 100 and 1000 nm, and a D50 of 100-500 nm.
7. The aqueous silicone resin latex of claim 5 or 6 , formed by emulsifying a silicone resin solution in water in the presence of an emulsifying agent, wherein the silicone resin solution comprises the silicone resin and the alcohol ester.
8. The aqueous silicone resin latex of claim 7, wherein the silicone resin solution further comprises an alkylalkoxysilane of general formula: R2 mSi (OR3) 4-m, wherein R2 is C1-C16 alkyl, R3 is C1-C4 alkyl or hydrogen; and m is an integer of 0-3, and preferably 1-3; and the alkylalkoxysilane is present in an amount of 1-20 wt%, preferably 2-15 wt%, and more preferably 5- 10 wt% of the total weight of the silicone resin solution.
9. The aqueous silicone resin latex of any one of claims 7 to 8 , wherein the silicone resin solution further comprises 1- 40 wt%, and preferably 5-10 wt% of an aromatic solvent and/or an aliphatic solvent based on the total weight of the solution, said aromatic solvent or aliphatic solvent having a chemical general formula CpHq, wherein p is 9-15 and q is 12-32.
10. Use of the aqueous silicone resin latex of any one of claims 1 to 9 in building coatings.
11. An aqueous coating, comprising 5-25 wt% of the aqueous silicone resin latex of any one of claims 1 to 9, and 5-25 wt% of an aqueous acrylic latex.
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