DESC:FIELD OF INVENTION
The present invention relates to silica-acrylic hybrid emulsion polymer with scrub resistance/anti-peel off performance and a process to synthesize such silica-acrylic hybrid emulsion having good colloidal stability while at the same time achieving enhanced interaction of silica with polymer particles in said emulsion.
BACKGROUND ART
Improvement of Dirt Pick Up Resistance (DPUR) along with better elongation is achieved by incorporation of silica (as a dispersion), during emulsion synthesis is a well-known art. Incorporation of alkoxy silane, along with silica (as a dispersion), during emulsion polymerization, to get water resistance and anti-peel effect is a challenge, as this results into unstable emulsion leading to gelation.
Reference to Patent no. WO2007072189A2 is invited teaching stable silylated polymer emulsion and its preparation method and uses. The emulsion of the prior art comprises a silylated polymer, water, nano silica and an optional emulsifying agent. By using the preparation method of the advancement, nano silica can be homogeneously dispersed in a silylated polymer. Without any surface modification, nano silica can be directly added to the silylated polymer and shows good compatibility with the silylated polymer. The prepared emulsion has a solid content of < 85%, a particle size of less than 3 µm, being of a low VOC content that well meets the environmental protection requirements, and a shelf life of over half a year when stored at room temperature. After volatilization of water, the emulsion can crosslink to form an elastomer, wherein nano silica can play a role of enhancing the mechanical strength of the crosslinked polymer. In use, the emulsion can be directly diluted with water. The emulsion can be used for formulating coatings, adhesives, sealants, inks, skin care products and detergents.
EP3060611B1 teaches an aqueous coating composition and a process of making such aqueous coating composition with a low VOC content that provides coating films with balanced properties of high hardness, high clarity, good water resistance, and good alcohol resistance
CN1654533A is directed to one kind of nanometer composite silica/acrylate emulsion and its preparation process, stating it superior to available technology, and the composite emulsion has dispersed nanometer inorganic silica phase in 0.1-5 % of the total weight of monomers for the acrylate copolymer emulsion. The preparation process includes the surface treatment of nanometer inorganic silica phase, and synthesizing nanometer inorganic phase/polymer emulsion in molecular level compounding through in-situ polymerization process or seed emulsion polymerization process. The composite emulsion of CN1654533A can form film with doubled tensile strength and breaking elongation. Adding nanometer silica in 0.2 % results in tensile strength of 5.25 MPa and breaking elongation of 1300 %.
KR100783051 teaches a method for preparing an acrylic silica hybrid emulsion resin and provides a water-soluble acrylic silica hybrid paint to improve contamination resistance and fire proofness. A method for preparing said acrylic silica hybrid emulsion resin comprises the steps of mixing 50-90 parts by weight of an acrylate-based monomer, 5-10 parts by weight of an aromatic vinyl-based monomer, and 5-10 parts by weight of a nitrile vinyl-based monomer; polymerizing 20-60 parts by weight of the obtained monomer mixture, 20-50 parts by weight of colloidal silica, 0.5-3 parts by weight of a surfactant, and 0.1-2 parts by weight of a radical polymerization initiator; and controlling the pH of the obtained polymer product at 6-10.
IN201821035940 teaches stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion and an emulsion polymerization process of making silica- organic hybrid latex particles with core-shell structure and a stable dispersion of the same out of said stable in-situ functionalized silica dispersion/emulsion, wherein said latex particles have silica core and polymer as organic shell. More particularly, a stable in-situ functionalized silica dispersion/emulsion comprising in-situ surface functionalized silica dispersion/emulsion is provided together with a process for manufacturing said in-situ surface functionalized stable aqueous silica dispersion at room temperature adapted for the manufacture of silica- organic hybrid latex particles with silica core and acrylic shell, preferably also provided as an emulsion. The emulsions are employed as binders for aqueous latex paints or can be used as alone to coat and protect various substrates including wood, paper, plastic, metal, concrete, ceramic
J. APPL. POLYM. SCI. 2012, DOI: 10.1002/APP.37582 teaches for a stable nano-dispersion involving functionalized fumed silica in water using a nonionic surfactant. This nano-dispersion was blended with an aqueous acrylic polymer dispersion to produce hybrid nanocomposite films. The silica particles were shown to be well dispersed in the polymer matrix, with little agglomeration. Further evidence of good compatibility between the silica and acrylic polymer was given by the improved thermal stability of the nanocomposite compared with the pristine polymer. The nanocomposite films exhibited significantly lower dirt pick-up behavior, which seems to be associated to the nano-roughness of the composite film surface observed in AFM analysis. This nanocomposite decreases the contact area between film and micrometric dirt particles. Surface tension and hardness do not seem to be significantly different in the composite and noncomposite materials. This approach may provide a strategy to obtain hybrid coatings with self-cleaning properties, taking advantage of the relatively low cost, and large availability of fumed silica.
Polymer International 51, no. 8 (2002): 693-698.,https://doi.org/10.1002/pi.968 is directed to acrylic/nano-silica composite latexes prepared by blending via high shear stirring (SS) or ball milling (BM) and in situ polymerization (IS). For comparison, composites filled with micro-silica were also prepared. The mechanical and optical properties of the polymers formed by the composite latex filled with nano- or micro-silica were investigated using an Instron testing machine, by dynamic mechanical analysis, ultraviolet–visible spectrophotometry and transmission electron micrography. The results showed that SS and BM methods could obtain better nanocomposite latex and polymers than the IS method, characterized by better dispersion of nanoparticles, higher tensile strength and Tg for SS and BM than for IS. The increase in absorbance and reduction in transmittance of UV (290–400?nm wavelength) were observed as nano-silica content increased, whereas the UV absorbance or transmittance basically were kept unchanged for the composites filled with micro-silica.
Reference is also drawn to the following prior arts:
JP2020147699A provides an acrylic resin composition capable of obtaining a cured product excellent in stain resistance. Title acrylic resin composition comprises a monomer (A) having a (meth)acryloyl group, at least one polymer (B) selected from the group consisting of (meth)acryloyl polymer and a polymer having (meth)acryloyl group, a surface conditioner (C) having a siloxane skeleton, which has a surface tension reduction rate of 10% or less, which is obtained by the following formula; surface tension reduction rate (%) = { (a1-a2)/a1} x 100, paraffin wax (D) and a reducing agent (E). Wherein, in formula, a1 is the surface tension of the composition (X) composed of 20 parts of a copolymer of Me methacrylate and Bu methacrylate, and 80 parts of Me methacrylate having a mass ratio of a monomer unit derived from Me methacrylate to a monomer unit derived from Bu methacrylate to be 60/40, having a mass average mol. weight of 42000 and the glass transition point of 65°, and a2 is the surface tension of the composition (Y) in which 0.5 parts of the surface conditioner (C) is mixed with 100 parts of the composition (X). Thus, 73 parts of Acryester M (Me methacrylate), 4 parts of Blemmer PDE 150, 23 parts of Bu methacrylate-Me methacrylate copolymer (preparation shown), 0.2 part of Byk 315N (surface conditioner), 0.12 parts of Paraffin Wax 115, 0.08 part of Paraffin Wax 130, 0.05 parts of Paraffin Wax 150, 0.8 part of N, N-di(2-hydroxyethyl)-p-toluidine (reducing agent) and 0.05 parts of H-BHT (polymerization inhibitor) were added to obtain the title acrylic resin composition.
CN108102027 teaches a preparation method including mixing of xylene and silane coupling agent KH-570, and then adding acrylonitrile, isooctyl methacrylate, isopentyl methacrylate, dodecyl methacrylate, hydroxypropyl acrylate, epoxy Pr acrylate and initiator azobisisobutyronitrile solution; stirring, heating to 72-75°C, holding for 0.5-1 h, performing polymerization reaction, heating to 80-85°C, holding for 2-3 h, dropwise adding hexafluorobutyl methacrylate at 80-85°C, heating to 85-90°C, and holding for 1.5-2 h ; and cooling to room temperature, and packaging. The synthesized fluorine-containing acrylate monomer modified styrene-acrylic copolymer has high bonding strength, surface hardness, wear resistance and washing resistance. The surface treatment agent has excellent film surface performance, and can be applied in surface treatment of cement concrete and ceramic.
CN107502118 A teaches for polymer cement waterproof coating prepared from (by weight parts) modified acrylate emulsion 80-90, cement 35-40, heavy calcium carbonate 25-33, quartz sand 19-27, vermiculite 12-15, o-cresol novolac epoxy resin 7-9, cyanite 6-8, film forming aid 4-6, dispersant 3-5 and water reducer 1-3. The film forming aid is propylene glycol Me ether acetate or alc. ester-12. The dispersant is stearamide and oxidized polyethlene wax. The water reducer is polycarboxylic acid water reducer. The acrylate emulsion is synthesized using Et acrylate and methacrylate as base raw materials, organosilicon monomer Me vinyl dichlorosilane is used for modification, silicon-oxygen bond is introduced, the bonding degree with cement is increased, the film performance and firmness are improved, under the effect of Lewis acid, unsaturated bond is introduced with maleic anhydride, the active group of emulsion is increased, the effect with calcium ion is increased, the water resistance is further improved, light sensitivity of emulsion is increased, the film flowability at early state is improved by complexing with butanol, and the performance of non-recovery of cyanite calcination is utilized to form pores in cement, thus increasing contact performance with emulsion. The emulsion is complexed with o-cresol novolac epoxy resin to increase self-curing film forming performance of coating, and prevent re-swelling of curing film by water.
CN105238126A is directed to multifunctional additive prepared from polyoxyethylene ether 20-44, acrylic acid monomer 1-3, ?-Pr methacrylate based trimethoxysilane 3, ammonium persulfate 0.5, mercaptopropionic acid 1, nano-silicon modified material 10, cellulose ether 0.02, and deionized water 20-80 weight part. The polyoxyethylene ether is from allyl alc. polyoxyethylene ether and/or isobutenyl alc. polyoxyethylene ether, the acrylic acid monomer is one or two of acrylic acid, methacrylic acid, methacrylate, maleic anhydride and sodium methallyl sulfonate, and the cellulose ether is from Me cellulose ether, hydroxyethyl Me cellulose ether, HPMC ether, CM-cellulose ether or Et cellulose ether. The nano-silicon modified material (its active ingredient content 1-5%) is prepared by dispersing nano silicon dioxide in ethanol under ultrasonic irradiation, adding 5 wt% ?-(2,3-epoxy propoxy) propyltrimethoxysilane, mixing for 30 min under ultrasonic irradiation, reacting for 24 h under stirring and refluxing, cooling to room temperature, and separating by ultrasonic irradiation and centrifugation. The multifunctional additive is prepared by (1) dissolving polyoxyethylene ether in deionized water under heating and N2 atmosphere, cooling to room temperature, adding acrylic acid monomer and ?-Pr methacrylate based trimethoxysilane, mixing uniformly under stirring to obtain mixed solution, (2) dissolving ammonium persulfate in deionized water to obtain 0.5% ammonium persulfate aqueous solution, (3) heating the mixed solution to 70°C under N2 atmosphere, dripping slowly 0.5% ammonium persulfate aqueous solution and mercaptopropionic acid in 1-1.5 h, reacting at 70-80°C for 24 h, cooling to room temperature in standing conditions to obtain polymer solution, adjusting pH to 6-7 with 30% NaOH solution, (4) dialyzing with distilled water in a dialysis bag (its mol. weight cut-off 10,000), collecting target polymer solution in the dialysis bag, concentrating to solid content 20-40%, and (5) adding nano-silicon modified material and cellulose ether, treating for 24 h under mech. stirring and ultrasonic dispersion. The multifunctional additive is used for concrete decoration and protective coating, which is prepared by mixing uniformly multifunctional additive 0.1-0.3, organosilicon defoaming agent 0.05-0.1 and water 5-10 into polymer emulsion 25-50 weight part in an elec. mixer under low-speed stirring, adjusting pH to 7-9, adding cement 25-40, composite filler 20-30 and pigment 2-5 weight part, stirring completely until the system is no obvious crude particles, defoaming under standing, and coating for 2-3 times to thickness 1.5±>0.2 mm. The polymer emulsion (its solid content 40-60%) is from acrylate emulsion and/or vinyl acetate-ethylene emulsion, the cement is P.O 32.5 ordinary Portland cement, the composite filler is mixture of quartz sand (its particle size 100-200 mesh) and heavy calcium carbonate (its particle size 400 mesh) at a mass ratio of 2-5:2, and the pigment is titanium dioxide powder. The multifunctional additive is used as coating addition in dam corridor concrete surface decoration and protection field, with improved liquid/powder system fluidity, homogeneity and stability, and increased adhesive property, mech. property and durability of coating film after film formation with moist base surface. The multifunctional additive is prepared from polyoxyethylene ether 20-44, acrylic acid monomer 1-3, ?-Pr methacrylate based trimethoxysilane 3, ammonium persulfate 0.5, mercaptopropionic acid 1, nano-silicon modified material 10, cellulose ether 0.02, and deionized water 20-80 weight part. The polyoxyethylene ether is from allyl alc. polyoxyethylene ether and/or isobutenyl alc. polyoxyethylene ether, the acrylic acid monomer is one or two of acrylic acid, methacrylic acid, methacrylate, maleic anhydride and sodium methallyl sulfonate, and the cellulose ether is from Me cellulose ether, hydroxyethyl Me cellulose ether, HPMC ether, CM-cellulose ether or Et cellulose ether. The nano-silicon modified material (its active ingredient content 1-5%) is prepared by dispersing nano silicon dioxide in ethanol under ultrasonic irradiation, adding 5 wt% ?-(2,3-epoxy propoxy)propyltrimethoxysilane, mixing for 30 min under ultrasonic irradiation, reacting for 24 h under stirring and refluxing, cooling to room temperature, and separating by ultrasonic irradiation and centrifugation. The multifunctional additive is prepared by (1) dissolving polyoxyethylene ether in deionized water under heating and N2 atmosphere, cooling to room temperature, adding acrylic acid monomer and?-Pr methacrylate based trimethoxysilane, mixing uniformly under stirring to obtain mixed solution, (2) dissolving ammonium persulfate in deionized water to obtain 0.5% ammonium persulfate aqueous solution, (3) heating the mixed solution to 70°C under N2 atmosphere, dripping slowly 0.5% ammonium persulfate aqueous solution and mercaptopropionic acid in 1-1.5 h, reacting at 70-80°C for 24 h, cooling to room temperature under standing to obtain polymer solution, adjusting pH to 6-7 with 30% NaOH solution, (4) dialyzing with distilled water in a dialysis bag (its mol. weight cut-off 10,000), collecting target polymer solution in the dialysis bag, concentrating to solid content 20-40%, and (5) adding nano-silicon modified material and cellulose ether, treating for 24 h under mech. stirring and ultrasonic dispersion. The multifunctional additive is used for concrete decoration and protective coating, which is prepared by mixing uniformly multifunctional additive 0.1-0.3, organosilicon defoaming agent 0.05-0.1 and water 5-10 into polymer emulsion 25-50 weight part in an elec. mixer under low-speed stirring, adjusting pH to 7-9, adding cement 25-40, composite filler 20-30 and pigment 2-5 weight part, stirring completely until the system is no obvious crude particles, defoaming under standing, and coating for 2-3 times to thickness 1.5±>0.2 mm. The polymer emulsion (its solid content 40-60%) is from acrylate emulsion and/or vinyl acetate-ethylene emulsion, the cement is P.O 32.5 ordinary Portland cement, the composite filler is mixture of quartz sand (its particle size 100-200 mesh) and heavy calcium carbonate (its particle size 400 mesh) at a mass ratio of 2-5:2, and the pigment is titanium dioxide powder. The multifunctional additive is used as coating addition in dam corridor concrete surface decoration and protection field, with improved liquid/powder system fluidity, homogeneity and stability, and increased adhesive property, mech. property and durability of coating film after film formation with moist base surface. This prior art teaches modification of silica particles and covering up by polymer particles, for its usage in concrete protection. However, not related to any emulsion polymerization of acrylic monomer along with alkoxy silanes first, followed by addition of silica, in controlled manner so that the silica is adsorbed onto the polymer particles giving good cleanability when used in coatings system.
JP63248784 A teaches preparation of polymer-impregnated cement products by polymerization of cement impregnated with a surface tension reducing agent and monomer. Thus, a steel fiber-reinforced concrete specimen (10 × 10 × 20 cm) was dried at 150° for 24 h, and 5 faces of this rectangular prism was coated by epoxy resin. It was deaired and immersed in Me methacrylate monomer solution containing 1% silane coupling agent and 0.5% L-77 (surface tension reducing agent; polyether of modified dimethylsiloxane) under pressurized condition at 3 kg/cm2 for 4 h. The solution penetrated 200 mm deep from one face uncoated by epoxy resin of the specimen and the compressive strength after polymerization was 1840 kg/cm2, vs. 60 mm and 836 kg/cm2 without the surface tension reducing agent.
JP2013249389A is directed to cohydrolyzing and condensation polymerizing the organic silane and a metal alkoxide in a solution including an organic solvent, water with the control of the distance between the organosilanes to prepare coatings having contact angle hysteresis of the surface smaller than that for the surface of the organosilane coatings. Thus, a coating material contained decyltriethoxysilane-tetramethoxysilane copolymer, silica, and tolyltriazole.
JP2007070766A provides manufacturing method of sheets, useful as artificial leather, etc., includes dispersing recovered proteins containing fine a-keratoses in aqueous media, adding reductants and water-soluble substances with d (solubility parameter) 19.0-26.0, adding alkoxysilanes so as to form fibers, and adding transglutaminase, silane sol, and epoxy silanes so as to crosslink. Thus, feeding a-keratose powders 19.0, collagens (PK 100) 5.0, 10% solution of L-cysteine hydrochloride and acetylcysteine (22-SS-55) 5.0, ethanol 3.0, 3-methoxy-3-methyl-butanol (Solfit S 110) 3.0%, and water into a flask, dispersing, adding 1.5% (based on the dispersion) Si(OEt)4 hydrolyzate, stirring, adding 5 parts (based on 77.5 parts of the resultant fibers) crosslinker solution containing Si(OEt)4 and 3-(glycidoxy)propyltrimethoxysilane (KBM 403), and 2.5 parts (as above) aqueous solution of transglutaminase (Activa TGS), extruding into a sheet, and crosslinking at 30° for 40 h gave a 0.8 mm-thick protein sheet showing d. 1.35 g/cm2, similar texture to leather, and no crack after storing at 25° and RH 15% for 24 h.
In spite of the above known conventional knowledge flowing from the art on silica-acrylic hybrid emulsion polymer, there is still a need in the art to provide for select such emulsion polymers and process thereof enabling good colloidal stability that would be thus free of any unstable emulsion/ gel formation during synthesis so that silica-acrylic hybrid emulsion polymer so obtained would have efficient interaction of silica particles with polymer to enable emulsions usable for exterior applications to provide anti-peeling performance and water resistance.
OBJECTS OF THE INVENTION
The basic object of the present invention is to provide for silica-acrylic hybrid emulsion polymer with anti-peel off performance and the process of making thereof.
It is another object of the present invention to provide for said silica-acrylic hybrid emulsion polymer and a process of its attaining that would result in good colloidal stability by avoiding gelation.
It is yet another object of the present invention to provide for said silica-acrylic hybrid emulsion polymer which so obtained by multi-stage emulsion synthesis would have efficient interaction of silica particles with polymer to enable said emulsions usable for exterior applications as a coating to provide anti-peeling performance and water resistance.
It is still another object of the present invention to provide for said silica-acrylic hybrid emulsion polymer synthesis process for incorporation of alkoxy silane group along with silica dispersion via a multistage process technique by avoiding formation of unstable emulsion/gelation during synthesis while at the same time achieving enhanced interaction of silica with polymer particles.
SUMMARY OF THE INVENTION
It is a significant finding of the present invention to provide for silica-acrylic hybrid emulsion polymer with improved scrub resistance/ anti-peel off performance based on select stage wise emulsion polymerization process comprising copolymerizing acrylic monomer along with unsaturated hydrolyzed alkoxy silanes followed by addition of functionalized silica dispersion including epoxy silane modified/surface treated colloidal silica, in controlled manner so that the silica is adsorbed onto the polymer particles enabling good cleanability when involved in coating systems/ formulations.
The primary embodiment of the present invention is directed to provide a silica-acrylic hybrid emulsion polymer comprising unsaturated hydrolyzed alkoxy silane incorporated acrylic or vinyl monomer/s based emulsion polymer and co-acting functionalized silica dispersion including epoxy silane modified colloidal silica, free of gelation.
Another embodiment of the present invention is directed to provide said silica-acrylic hybrid emulsion polymer wherein said functionalized silica dispersion in 0.5-2.5 wt.% levels is grafted on appended functional groups of main chain of polymer particle including OH and carboxylic acid enabling improved cleanability in coating formulations comprising the same, and, obtained of stagewise emulsion polymerization of acrylic monomer with alkoxy silanes followed by addition of said silica dispersion in controlled manner.
Yet another embodiment of the present invention is directed to provide said silica-acrylic hybrid emulsion polymer wherein said unsaturated hydrolyzed alkoxy silane incorporated acrylic/vinyl monomers based emulsion polymer and functionalized silica dispersion includes Methyl Methacrylate (10.2-15.4 wt.%), 2-Ethyl hexyl acrylate (5.5-8.5 wt.%), Tert-Butyl Methacrylate (4.0-5.0 wt.%) Methacrylic Acid (0.55-0.85 wt.%) and Hydroxy Ethyl Methacrylate (1.6-2.4 wt.%); and
said alkoxy silanes include vinyl trimethoxy silane, vinyl triethoxy silane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane in an amount of 0.08-0.12 wt %. and 0.24-0.36 wt %.
Further embodiment of the present invention is directed to provide said silica-acrylic hybrid emulsion polymer having appearance of Bluish white free flowing liquid, % NVM-49.1%, viscosity 89 gm, pH- 9.1, tack free, clear, Tg (°C by DMA)- 51.6 and cross-linking density 3.18 X 10—5 XLD (mol/cm3).

Preferred embodiment of the present invention is directed to provide a multi stage process for manufacturing the silica-acrylic hybrid emulsion comprising the stages of incorporation of unsaturated alkoxy silane and copolymerizing with acrylic/vinyl monomers, followed by addition of functionalized silica dispersion including epoxy silane modified colloidal silica in the final stage at higher temperature of 70-80 deg C and at acidic pH between 3.5 to 5.5 and alkaline pH 8.5 to 9.5, enabling effective interaction of surface modified epoxy silane silica dispersion with thus formed copolymers.

Further embodiment of the present invention is directed to provide said multi stage process for manufacturing the silica-acrylic hybrid emulsion wherein said stage wise process includes the following:
a. first stage alkoxy silanes generate in-situ silanols which undergoes self-crosslinks thereby reducing the probability of interaction of formed silanols with silica dispersion;
b. second stage includes initiation of copolymerization with acrylic/vinyl monomers with formed silanols in step (a) to result in a copolymer with >99% monomer conversion/ reaction completion;
c. third stage includes addition of functionalized silica dispersion post >99% monomer conversion/ reaction in step (b) at elevated temperature range of 70 to 80°C and in acidic pH between 3.5 to 5.5 and alkaline pH 8.5 to 9.5 leading to predominant interaction of copolymer functionalities including hydroxyl, carboxyl with functionalized silica preferably epoxy silane modified/ surface treated colloidal silica, thereby grafting of silica dispersion on polymers promoting enhanced crosslinking and Tg together with adhesion of the emulsion on substrate resulting in water resistance and anti-peel off/ scrub resistance performance of the emulsion polymer.
Still further embodiment of the present invention is directed to provide said multi stage process for manufacturing the silica-acrylic hybrid emulsion wherein addition of an alkoxy silane in the first stage includes 50-60% monomer pre-mixture addition.
DETAILED DESCRIPTION OF THE INVENTION
As discussed hereinbefore, the present invention relates to silica-acrylic hybrid emulsion polymer with scrub resistance/ anti-peel off performance and a process to synthesize such silica-acrylic hybrid emulsion having good colloidal stability.
The approach of the present invention, in one of its aspects is to provide for said silica-acrylic hybrid emulsion polymer comprising incorporation of alkoxy silane group along with silica dispersion, by involving a multistage process technique, which avoids formation of unstable emulsion/gelation during synthesis.
In a preferred aspect said multistage polymer synthesis is followed by incorporation of alkoxy silane in the first stage of polymerization, followed by copolymerizing with acrylic/vinyl monomers and further addition of silica dispersion in the final stage, at higher temperature of 70 - 80 deg C and at pH between 3.5 to 5.5, for effective interaction of surface modified (epoxy silane) silica with thus formed copolymers.
Polymer coagulation or gelation is avoided in the following aspects of the process embodiment:
a. Alkoxy silane undergoes hydrolysis in the first stage and self-crosslinks, reducing the probability of interaction of in-situ formed silanols (post hydrolysis) with silica dispersion;
b. initiating copolymerization with acrylic/vinyl monomers to result in a copolymer;
c. Addition of silica dispersion at elevated temperature (70 to 80°C) leading to predominant interaction with functionalities like hydroxyl, carboxyl of the copolymer etc. in acidic pH (3.5-5.5) with functionalized silica preferably epoxy silane functionalized silica,
thereby enhancing interaction of silica with polymer particles, to result in enhanced adhesion and hence water resistance of the emulsion polymer so synthesized.
In another aspect of the present invention the silica-acrylic hybrid emulsion polymer and a multistage process of its synthesis includes addition of an alkoxy silane in the first stage of the synthesis, i.e. 50-60% monomer pre-mixture addition.
Preferably another aspect of the present invention is directed to silica-acrylic hybrid emulsion polymer and its multistage process of synthesis that includes alkoxy silane like vinyl trimethoxy silane, vinyl triethoxy silane, methacryloxy -proprytrimethoxysilane, methacryloxypropyltriethoxysilane etc.
Preferably in another preferred aspect of the present invention there is provided a multistage process including addition of silica dispersion in the reactor after >99% reaction completion.
More preferably in said multistage process maintains temperature of the reactor between 70-80°C and pH between 3.5-5.5 during silica dispersion addition to achieve efficient interactions of silica particles with copolymer to form silica-acrylic hybrid emulsion polymer.
Advantages of the present invention is that it could provide a silica-acrylic hybrid emulsion polymer and a multistage process of its synthesis for incorporation of alkoxy silane group along with silica dispersion which avoids formation of unstable emulsion/gelation during synthesis.
Examples:
The objective of the present invention is to prepare silica-acrylic hybrid emulsion polymer with anti-peel off performance and a process to synthesize such silica-acrylic hybrid emulsion having good colloidal stability wherein incorporation of alkoxy silane group along with silica dispersion is carried out by involving a multistage process technique, which avoids formation of unstable emulsion/gelation during synthesis.
Hence multiple experiments were carried out keeping the same reaction protocol varying only the silica addition at different stages of the multistage process.
General method for the preparation of hybrid emulsion polymer

a. Anionic migratory surfactant and de-mineralized water were charged into a kettle with a three necked lid and the assembly was heated to 80-90°C.

b. In a separate pre-emulsion flask filled with anionic migratory and/or non-migratory surfactant or migratory non-ionic surfactant dissolved in de-mineralized water, acrylic/vinyl functional monomers were added and stirred to form a milky white pre-emulsion-I (as per Table 1).
c. Adding Methacrylic acid and potassium per sulphate into pre-emulsion, just prior to addition of 3-7% Pre emulsion into the reactor kettle.
d. Adding 3-7% of pre-emulsion into reactor followed by addition of buffer solution and potassium per sulphate solution into the reactor wherein start of the reaction is indicated by the exotherm.
e. To the reaction mixture, the pre-emulsion was added for a period of 145-160 minutes, by maintaining the temperature at 70-90°c.
f. Adding silane monomer into the pre-emulsion after 25-35% completion of pre-emulsion-I addition and continued the addition
g. After the completion of pre-emulsion-I addition, de-mineralised water was employed to flush the peristaltic pump used to pump the pre-emulsion mixture into the reactor.
h. In a separate pre-emulsion flask filled with anionic migratory and/or non-migratory surfactant or migratory non-ionic surfactant dissolved in de-mineralized water, select quantities of acrylic/vinyl functional monomers were added and stirred to form a milky white pre-emulsion-II (as per Table 1).
I. Adding the pre-emulsion-II spanning over a period of 100-120 minutes, by maintaining the temperature at 70-90°c.
J. sodium formaldehyde sulphoxylate (SFS) in de-mineralized water was added to the reaction mixture after completion of pre-emulsion-II addition, followed by addition of mixture of tert-butyl hydroperoxide & fluro-surfactant dissolved in de-mineralized water and digestion process continued for one hour.
cooling the reaction mass below 50°C and adding in-can preservative in reactor vessel, followed by addition of liquor ammonia to make the pH of the reaction mass alkaline.

TABLE NO. 1: Experiments
Sr. No. Chemical Example 1
(Emulsion-A) Example 2
(Emulsion-B) Example 3
(Emulsion-C) Example 4
(Emulsion-D) Example 5
(Emulsion-E) Example 6
(Emulsion-F) Example 7
(Emulsion-G)
Silica dispersion addition stage In reactor from initial stage During PE-I addition, simultaneously in reactor During PE-II addition, simultaneously in reactor After monomer pre-mix addition completion, in reactor at temperature 70-80°C After complete reaction & additive addition, at Room temperature, in reactor After monomer pre-mix addition completion, in reactor at temperature 70-80°C After complete reaction, at Room temperature, in reactor
pH of reactor charge during silica addition Acidic Alkaline Alkaline Acidic
Migratory sulphonate based anionic surfactant 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12
Neutral dispersion of epoxy silane surface treated colloidal silica 0.5-2.5 0.5-2.5 0.5-2.5 0.5-2.5 0.5-2.5 0.5-2.5 0.5-2.5
Ammonia 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24
DM water 0.5-1.0 0.5-1.0 0.5-1.0 0.5-1.0 0.5-1.0 0.5-1.0 0.5-1.0
1 Reactor charge-I (80 deg C)
DM water 14.2-21.4 14.2-21.4 14.2-21.4 14.2-21.4 14.2-21.4 14.2-21.4 14.2-21.4
migratory sulphonate based anionic surfactant 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24
2 3-7% pre-emulsion-I seed
Buffer 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24
DM water 1.7-2.6 1.7-2.6 1.7-2.6 1.7-2.6 1.7-2.6 1.7-2.6 1.7-2.6
Initiator 0.1-0.14 0.1-0.14 0.1-0.14 0.1-0.14 0.1-0.14 0.1-0.14 0.1-0.14
DM water 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4
3 Rest of Pre-emulsion-I
DM water 9.5-14.2 9.5-14.2 9.5-14.2 9.5-14.2 9.5-14.2 9.5-14.2 9.5-14.2
Sulphonate based non-migratory Surfactant 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12
Non-polymerizable Sulphonate based anionic surfactant 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24
Non-polymerizable non-ionic surfactant 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75
Methyl Methacrylate 10.2-15.4 10.2-15.4 10.2-15.4 10.2-15.4 10.2-15.4 10.2-15.4 10.2-15.4
2-Ethyl hexyl acrylate 5.5-8.5 5.5-8.5 5.5-8.5 5.5-8.5 5.5-8.5 5.5-8.5 5.5-8.5
Tert-Butyl methacrylate 4.0-5.0 4.0-5.0 4.0-5.0 4.0-5.0 4.0-5.0 4.0-5.0 4.0-5.0
Methacrylic Acid 0.55-0.85 0.55-0.85 0.55-0.85 0.55-0.85 0.55-0.85 0.55-0.85 0.55-0.85
Hydroxy Ethyl Methacrylate 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4
Coalescing solvent 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75
Initiator 0.06-0.1 0.06-0.1 0.06-0.1 0.06-0.1 0.06-0.1 0.06-0.1 0.06-0.1
4 Pre-emulsion-II
DM water 6.0-9.0 6.0-9.0 6.0-9.0 6.0-9.0 6.0-9.0 6.0-9.0 6.0-9.0
Sulphonate based non-migratory Surfactant 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12
Non-polymerizable sulphonate based anionic surfactant 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12
Non-polymerizable non-ionic surfactant 0.32-0.48 0.32-0.48 0.32-0.48 0.32-0.48 0.32-0.48 0.32-0.48 0.32-0.48
Difunctional monomer 0.26-0.4 0.26-0.4 0.26-0.4 0.26-0.4 0.26-0.4 0.26-0.4 0.26-0.4
Methyl Methacrylate 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2
2-Ethyl hexyl acrylate 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2 5.4-8.2
Hydroxy Ethyl Methacrylate 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4
UV crosslinker 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4 1.6-2.4
UV stabiliser 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12
Alkoxy Silane monomer 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 - -
Coalescing solvent 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75 0.45-0.75
Initiator 0.032-0.048 0.032-0.048 0.032-0.048 0.032-0.048 0.032-0.048 0.032-0.048 0.032-0.048
5 Pre-emulsion-I Addition stage (feed over 145-160 minutes at uniform rate)
6 After 25% pre-emulsion-I addition
Silane Monomer 0.24-0.36 0.24-0.36 0.24-0.36 0.24-0.36 0.24-0.36 - -
DM water 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 - -
7 Pre-emulsion-II Addition stage (feed over 100-120 minutes at uniform rate)
8 DM water For flushing 1.00 1.00 1.00 1.00 1.00 1.00 1.00
9 Digestion catalysts
Tertiary butyl hydroperoxide 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06
Fluro surfactant 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12 0.08-0.12
DM water 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6
Sodium formaldehyde Sulphoxy late 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06 0.04-0.06
DM water 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6
10 Additives
Biocide 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24 0.16-0.24
Defoamer 0.016-0.024 0.016-0.024 0.016-0.024 0.016-0.024 0.016-0.024 0.016-0.024 0.016-0.024
Ammonia 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6 0.4-0.6
DM water 2.4-3.6 2.4-3.6 2.4-3.6 2.4-3.6 2.4-3.6 2.4-3.6 2.4-3.6

As already stated preparation of the silica-acrylic hybrid emulsion polymer is a multistage reaction in accordance to the present invention. The steps of said multistage reaction includes
1. Reactor charge-I (80 deg C);
2. 3-7% pre-emulsion-I seed;
3. Pre-emulsion-I Addition stage (feed over 145-160 minutes at uniform rate);
4. After 25% Pre-emulsion-I silane monomer is added into the pre-emulsion;
7. Pre-emulsion-II Addition stage (feed over 100-120 minutes at uniform rate);
8. De-mineralized water for flushing;
9. Digestion catalysts;
10. Additives.
While carrying out the synthesis of the silica-acrylic hybrid emulsion polymer, silica dispersion is added at different stages (Table-1) of the multistage reaction and evaluation of the properties of the formulated final emulsions are provided in Table-2

TABLE 2: Emulsion properties

Sr. No. Chemical Example 1
(Emulsion-A) Example 2
(Emulsion-B) Example 3
(Emulsion-C) Example 4
(Emulsion-D) Example 5
(Emulsion-E) Example 6
(Emulsion-F) Example 7
(Emulsion-G)
Silica dispersion addition stage In reactor from initial stage During PE-I addition, simultaneously in reactor During PE-II addition, simultaneously in reactor After monomer Pre-mix-II addition completion, in reactor at temperature 70-80°C After complete reaction & additive addition, at Room temperature, in reactor After monomer Pre-mix-II addition completion, in reactor at temperature 70-80°C After complete reaction, at Room temperature, in reactor
pH of reactor charge during silica addition acidic pH between 3.5 to 5.5 Alkaline
pH 8.5 to 9.5 Alkaline
pH 8.5 to 9.5 Acidic pH between 3.5 to 5.5
Reactor hygiene Gelled after 30 minutes of PE-I addition Gelled after 10 minutes of PE-II addition Gelled after PE-I & PE-II addition, during digestion stage Acceptable processing with negligible grit content Acceptable processing with negligible grit content Acceptable processing with negligible grit content Acceptable processing with negligible grit content
% Yield - - - > 99% > 99% > 99% > 99%
Appearance - - - Bluish white free flowing liquid Bluish white free flowing liquid Bluish white free flowing liquid Bluish white free flowing liquid
% NVM - - - 49.1 49.3 48.9 48.7
Viscosity (g) fresh - - - 89 91 88 90
Viscosity (g) after 6 months 89.5 90.5 88.5 89
pH - - - 9.1 8.9 9.2 9.2
Tack - - - Tack free Tack free Tack free Tack free
Bits - - - No bits No bits No bits No bits
Clarity - - - Clear Clear Clear Clear
Tg (°C by DMA) - - - 51.6 48.5 49.7 48.7
XLD (mol/cm3) - - - 3.18 X 10-5 2.25 X 10-5 2.88 X 10-5 1.96 X 10-5
Scrub resistance (as per ASTM D2486 500 cycles 500 cycles 500 cycles 500 cycles

For the conducted experiments, the processing conditions were kept similar. The data recorded for reactor hygiene (in the context of chemical processes, reactor hygiene refers to maintaining the cleanliness, safety, and optimal conditions within a reactor during chemical reactions. % Yield, ease of processing and coagulum generation. When silica dispersion is added during initial stage of synthesis e.g. in reactor before addition of monomer seed or simultaneous addition in reactor along with Pre-emulsion-I, or, simultaneous addition in reactor along with Pre-emulsion-II, emulsion polymerisation led to gelation. The processing pH during synthesis ranges between 3-5 and presence of alkoxy silane at said pH, viz. is favourable condition for agglomeration of silica particles resulted in gelation. Interaction of silica particles with the in-situ generated silanol from silane monomer in presence of water in acidic condition, lead to the hydrogen bonding and re-agglomeration.

At higher temperature, in acidic pH, when silica dispersion is added into the reactor during digestion stage, silica interacts with hydroxyl/carboxyl functional groups present in acrylic/ vinyl functional monomers under acidic condition, resulting in the increased crosslinking density and Tg (Example 4). When the silica dispersion is added at room temperature under acidic condition, extent of crosslinking reduces. It may be due to unavailability of free carboxyl groups to interact with silica (Example 7).

When the silica dispersion added in alkaline condition at high temperature (Example 6) slightly reduced crosslinking density & Tg compared to Example 4 are obtained. Low crosslinking tendency observed in example 5, i.e., addition of silica at room temperature in alkaline condition.

From the Table 2, it is evident that synergistic effect of acidic pH and high temperature (70-80°C) provides highly crosslinked polymer with high Tg as compared to rest polymers. At elevated temperature (70 to 80°C), surface modified silica may predominantly interact with carboxyl group in acidic pH (3.5-5.5) at elevated temperature, thereby enhancing inter-particle (polymer particle) crosslinking, which has led to increase in the Tg of the polymer and extent of crosslinking. The extent of cross-linking is provided by XLD (mol/cm3) values. Scrub resistance (as per ASTM D2486) of the paint prepared using the silica modified emulsion showed better resistance (more than 500 cycles) reflecting the proper adherence of paint. The viscosity of the formulations from Ex4- Ex 7 remain unaffected for minimum 6 months.

Advantageously, it is thus possible by way of the present invention to provide for said silica-acrylic hybrid emulsion polymer and a multistage process of its synthesis by avoiding unstable emulsion/ gel formation during synthesis thereby providing for said emulsion polymer with anti-peel off performance, as a result of achieving enhanced interaction of silica with polymer particles.
,CLAIMS:We Claim:

1. Silica-acrylic hybrid emulsion polymer comprising unsaturated hydrolyzed alkoxy silane incorporated acrylic or vinyl monomer/s based emulsion polymer and co-acting functionalized silica dispersion including epoxy silane modified colloidal silica, free of gelation.
2. The silica-acrylic hybrid emulsion polymer as claimed in claim 1 wherein said functionalized silica dispersion in 0.5-2.5 wt.% levels is grafted on appended functional groups of main chain of polymer particle including OH and carboxylic acid enabling improved cleanability in coating formulations comprising the same, and, obtained of stagewise emulsion polymerization of acrylic monomer with alkoxy silanes followed by addition of said silica dispersion in controlled manner.
3. The silica-acrylic hybrid emulsion polymer as claimed in claims 1 or 2 wherein said unsaturated hydrolyzed alkoxy silane incorporated acrylic/vinyl monomers based emulsion polymer and functionalized silica dispersion includes Methyl Methacrylate (10.2-15.4 wt.%), 2-Ethyl hexyl acrylate (5.5-8.5 wt.%), Tert-Butyl Methacrylate (4.0-5.0 wt.%) Methacrylic Acid (0.55-0.85 wt.%) and Hydroxy Ethyl Methacrylate (1.6-2.4 wt.%); and
said alkoxy silanes include vinyltrimethoxysilane, vinyltriethoxysilane, methacryl -oxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane in an amount of 0.08-0.12 wt %. and 0.24-0.36 wt %.
4. The silica-acrylic hybrid emulsion polymer as claimed in claims 1-3 having appearance of Bluish white free flowing liquid, % NVM-49.1%, viscosity 89 gm, pH- 9.1, tack free, clear, Tg (°C by DMA)- 51.6 and cross-linking density 3.18 X 10—5 XLD (mol/cm3).
5. A multi stage process for manufacturing the silica-acrylic hybrid emulsion as claimed in claims 1-4 comprising the stages of incorporation of unsaturated alkoxy silane and copolymerizing with acrylic/vinyl monomers, followed by addition of functionalized silica dispersion including epoxy silane modified colloidal silica in the final stage at higher temperature of 70-80 deg C and at acidic pH between 3.5 to 5.5 and alkaline pH 8.5 to 9.5, enabling effective interaction of surface modified epoxy silane silica dispersion with thus formed copolymers.
6. The multi stage process for manufacturing the silica-acrylic hybrid emulsion as claimed in claim 5 wherein said stage wise process includes the following:
a. first stage alkoxy silanes generate in-situ silanols which undergoes self-crosslinks thereby reducing the probability of interaction of formed silanols with silica dispersion;
b. second stage includes initiation of copolymerization with acrylic/vinyl monomers with formed silanols in step (a) to result in a copolymer with >99% monomer conversion/ reaction completion;
c. third stage includes addition of functionalized silica dispersion post >99% monomer conversion/ reaction in step (b) at elevated temperature range of 70 to 80°C and in acidic pH between 3.5 to 5.5 and alkaline pH 8.5 to 9.5 leading to predominant interaction of copolymer functionalities including hydroxyl, carboxyl with functionalized silica preferably epoxy silane modified/ surface treated colloidal silica, thereby grafting of silica dispersion on polymers promoting enhanced crosslinking and Tg together with adhesion of the emulsion on substrate resulting in water resistance and anti-peel off/ scrub resistance performance of the emulsion polymer.
7. The multi stage process for manufacturing the silica-acrylic hybrid emulsion as claimed in claims 4-6 wherein addition of an alkoxy silane in the first stage includes 50-60% monomer pre-mixture addition.

Dated this the 27th day of March, 2024 Anjan Sen
(Anjan Sen and Associates)
(Applicants Agent)
IN/PA-199