EMULSION COPOLYMERISATION

Abstract: Copolymers are formed under pressure, preferably in the presence of a surfactant having an alkylene moiety, and then post reacted with an epoxy silane. The resultant emulsion is usuable e.g. in tile adhesives and paints.

Description: Field of the invention: The invention relates to emulsion vinyl polymers intended principally, but not exclusively, for use in adhesive compositions, especially those intended for use with ceramic objects, for example tiles. Background to the invention: Aqueous emulsions of vinyl polymers are used as binders in adhesives, paints, pastes and coating materials. The adhesion of these emulsions after drying is not always satisfactory when in contact with mineral substrates, for example ceramics, bricks and glass. The film adhesion is, in particular, weakened when the use environment of the adhesive or other vinyl polymer based material contains moisture. The present invention is directed to improving the use properties of vinyl polymer emulsions intended for use as binders in ceramic tile adhesives. These adhesives are frequently used in high moisture environments, eg. kitchens and bathrooms. General description of the invention: The invention provides novel vinyl copolymer emulsions, processes for their manufacture and adhesive compositions containing them. The invention provides a process of preparing a copolymer emulsion wherein i) the monomer components are reacted under catalytic emulsion polymerisation conditions under a pressure from about 20 bar (2 x 10⁶ Nm⁻²) preferably from about 40 bar (4 x 10⁶ Nm⁻²) to about 100 bar (10⁷ Nm⁻²) to provide an emulsion of polymer particles with a surface capable of reacting with an epoxy moiety and ii) the emulsion is reacted chemically with from about 0.1% to about 3% by weight of an epoxy silane material usually at a temperature in the range 20°C to 60°C. Preferably the polymer is a vinyl acetate/vinyl chloride/ethylene terpolymer, more preferably having the composition ratio vinyl acetate: vinyl chloride 4.0 to 0.54:1 vinyl acetate: ethylene 13.3 to 1.5:1 vinyl chloride: ethylene 1.0 to 11.5:1 more preferably the weight percentages of the monomers are vinyl acetate (vinyl ester of C2 to C18 alkanoic acid) 30% to 70% vinyl chloride 15% to 60% ethylene (alkylene) 5% to 20% Additional monomers 0.1 to 10% Vinyl acetate is an example of a vinyl ester of a C2 to C18 alkanoic acid to which the invention is generally directed. A preferred class of epoxy silanes has the formula: X - Si (OR)3 wherein X is an alkyl group containing a reactive epoxy moiety and the three R radicals, which may be the same or different, are each hydrogen or a C1 to C4 alkyl radical with not more than two of the R radicals being hydrogen. The invention includes a copolymer emulsion post reacted with from about 0.1% to about 3% by weight of an epoxy silane. A feature of the invention is the use of a surfactant including a C14 to C20 unsaturated alkenylene moiety in the emulsion polymerisation. Examples of such surfactants are an oleyl propanol amide sulphosuccinate obtainable from Witco of USA under the trade name Emcol K8300 and the potassium salt of the sulphonation product of oleic acid obtainable from Lankro Chemicals of Manchester England under the trade name Lankropol OPA. The use of a surfactant of this class provides a marked enhancement of the effect obtained from the epoxy silane. There is no criticality in the monomers used in the manufacture of the copolymer emulsion. It is believed the external surface of the emulsion particles should include groups capable of reacting chemically with the epoxy silane component. In this description the preferred group is the carboxyl group which includes both the acidic group and the ionised, i.e. carboxylate, group. This reaction is an explanation of the technical benefit noted but is not presented as a proven reaction. The use of a post reaction step allows the preparation of necessary product amounts as required from a base stock of copolymer emulsion, the latter being usable for other applications. Thus the emulsion feedstock is available for use in a flexible manner. The monomer composition subjected to emulsion polymerisation may be consistant during polymerisation or may be varied so that the component providing the external groups reacting with the epoxy groups is only present during the final stage of the polymerisation process. Examples of the vinyl monomers usable in the preparation of the emulsions of the invention are vinyl esters of C2 to C18 carboxylic acids eg. vinyl acetate and vinyl propionate, vinyl chloride, alkylenes eg. propylene and ethylene, vinyl mono-carboxylic C2 to C10 acids eg. acrylic acid, alkyl acrylates, hydroxy acrylates, methacrylates, diacrylates, and crosslinking agents eg. diallyl phthalate and N-methylolacrylamide. The epoxy silane is preferably a gamma glycidoxy silane. Examples of silanes are gamma - glycidoxy propyl trimethoxy silane and gamma - glycidoxy propyl methoxy diethoxy silane. The copolymer emulsions are usable as components in structural adhesives used, for example as tile adhesives, emulsion based paints, emulsion based plasters and other compositions. Structural adhesives will generally comprise:- i) from 5% to 40% by weight of the copolymer solids, usually 10% to 25%, ii) from 15% to 85% by weight, usually 40% to 70%, of particulate filler, and iii) from 15% to 45%, usually 20% to 40% by weight of aqueous phase which amount includes the water in the copolymer emulsion. Examples of the fillers are quartz powder, kaolin, silica and milled minerals eg. feldspar, gypsum, chalk and talc. The adhesive is obtained by simple mixing of the components, usually by adding the solid components into the mixed liquid materials. Wetting agents, fungicides and thickeners may be added. Emulsion based paints will usually comprise: i) 5% to 35% by weight of copolymer solids, ii) 5% to 35% by weight of aqueous phase including water present in the emulsion, iii) 5% to 55% by weight of filler, and iv) 5% to 30% by weight of pigment. The fillers will include those listed for adhesive use and the pigments will include titanium dioxide, zinc oxide and zinc sulphide. Optional components such as wetting agents, thickeners, fungicides, anti-foaming agents and film forming auxiliaries may be present. Emulsion based plasters include coarse fillers, eg. stone fragments of size 0.2mm to 5mm, in addition to the copolymer emulsion solids and water. Literature: Copolymerisation of an organo-silicon compound with polymerisable monomers to form a silanol containing emulsion is disclosed in GB 1407827 (Wacker). This emulsion is disclosed as giving improved wet strength to ceramic tile adhesives. EP 0195406 (Mitsubishi Petrochemical) discloses the reaction of a water absorbing polymer with a silane coupling agent to improve the water absorption properties of the polymer. EPA 0214696 (DSM) describes reaction of a low pressure copolymer with an epoxy silane. Test Procedures: The utility of the emulsion vinyl polymers of the invention is demonstrated by testing the wet strength of bonds obtained using adhesives containing the polymers. A standard tile adhesive of formula: Filler sand (HPF3) 600g Water 140g Polymer Emulsion (ca 50% non-volatile content) 100g Formalin (fungicide) 2g Antifoam (Hercules 1512M) 0.5g Coalescing solvent (Dalpad A) 5g Thickener (Celacol HPM 5000 DS) 3g was prepared by mixing antifoam and fungicide in the water base and then the solvent and thickener with slow stirring. When these additives had been dispersed the emulsion was mixed in. When a homogeneous mixture was obtained the filler was added with rapid stirring over a short period. The adhesive composition was left for a day and then used to prepare test bonds. Ceramic tile test pieces using standard tiles were prepared and tested in accordance with BS 5980:1980. Those used for the dry test were conditioned in air for 14 days at 20°C and 65% RH and the samples for the wet test conditioned for 7 days at 20°C and 65% RH in air and then immersed in water for 7 days at 20°C. Specific Description of the Invention: Examples of the polymers and process of the invention will now be given to illustrate but not limit the invention. Example 1 This example describes a silanised terpolymer of vinyl acetate, vinyl chloride and ethylene. The polymer was produced from a monomer composition of:- Vinyl acetate 1052 g Vinyl chloride 412 g Ethylene 165 g Acrylic acid 4.1 g An aqueous solution with the composition listed below was prepared and loaded into a stirred pressure reactor (3.7 l capacity). The reactor was flushed first with nitrogen and then with ethylene. The agitator was then started, the vessel contents heated to 30°C and part of the ethylene component introduced into the vessel to give a pressure of 28 bar (2.8 x 10⁶ Nm⁻²). 5% by weight of each of the vinyl acetate, vinyl chloride and acrylic acid monomers were added at this stage to form an initial monomer charge. Initiator containing solutions having the compositions A and B had been prepared. A. Ammonium persulphate 6.6g Sodium bicarbonate 6.6g Water 250 g B. Sodium formaldehyde sulphoxylate dihydrate 2.6g Sodium vinyl sulphonate (25% aq) 66.0g Water 200 g When the monomeric first stage had been completely added, the continous additions of these initiator containing solutions were commenced along side the remainder of the monomers. The monomer components were added continuously over a period of 5 hrs whilst the initiator solutions were added over 6 hrs. Once the reaction had begun the internal tempeature was raised to 60°C over 3 hrs; and after 30 mins at 60°C ethylene was added to maintain a pressure of 28 bar (2.8 x 10⁶ Nm⁻²) for 4 hrs. When the additions were complete the reactor contents were cooled to ambient temperature while adding final stage initiator containing solutions C and D over a period of 1 hr. C. t-butyl hydroperoxide 5.0g Disodium phosphate dihydrate 4.2g Water 40.0g D. Sodium metabisulphite 5.0g Water 40.0g When the emulsion had been cooled and 4.0 g of preservative added, 1.0% on emulsion weight of gamma-glycidoxypropyl trimethoxysilane (obtained from Dow Corning of Michigan USA under the Trade Name Z-6040) was added dropwise to the polymer at ambient temperature. When the silane had been added the blend was stirred for 30 minutes and then allowed to stand for 24 hours before use. The polymer emulsion product from Example I was formulated into tile adhesives having the Test Procedure compositions. Comparison adhesives were prepared using i) the emulsion from Example I which had not been post reacted with epoxy silane and ii) emulsions formed by copolymerising the base monomers with an equivalent amount of a vinyl silane in accordance with the process generally described in GB1407827 (Wacker). The Dry bond and Wet bond strengths were measured as described previously and are quoted in Table I. All the adhesive compositions prepared were stable and suitable for their intended use. It will be seen the use of post-reacted emulsions of the invention provide improved dry and wet bond strengths compared with the unreacted base terpolymer and copolymer and these polymer compositions subjected to copolymerisation with vinyl silane. The adhesives using the emulsions of the invention also satisfy the appropriate British Standard. Example II This example compares the bond strengths of adhesives formed from emulsions A and B whose preparation was identical except for the use of two surfactants during polymerisation. A copolymer with the composition vinyl acetate 39.5%, vinyl chloride 50%, ethylene 10% and acrylic acid 0.5% was prepared in a redox initiated system using sodium persulphate (0.75%) and sodium formaldehyde sulphoxylate dihydrate (0.25%). The surfactants used were Lankropol OPA (emulsion A) and GAFAC RE-610, an ethoxylated alkyl phenol ester of phosphoric acid obtainable from GAF Chemicals of New York USA (emulsion B). The monomers were added over 4 hours at 50°C with 35% of the monomers, other than vinyl chloride, present initially. The initiator was added over 4.5 hours at 50°C. The emulsions obtained were formulated into tile adhesives and test for bond strength as given in Table II. Epoxy silane (Z6040) was added to the emulsions at the levels shown on the emulsion weight before formulating. The use of the preferred surfactant provides improved bond strengths, and this is particularly seen with the wet bond strength. Example III This example demonstrates the improvement in the properties of a paint formulation when formulated with an emulsion of the invention. The copolymer was produced from a monomer composition of vinyl acetate 1135g vinyl chloride 380g 2-ethylhexyl acrylate 133g ethylene 228g acrylic acid 4.75g An aqueous solution with the composition below was prepared, loaded into a stirred tank reactor (3.71 capacity) and heated to 40°C. Lankropol OPA (50% aq) 114g Formic acid 4mls (pH 3.5 to 4.0) Ferric chloride (1% aq) 0.95mls Distilled water 940g After purging with nitrogen and ethylene the vessel was pressurised with 55 bar (5.5 x 10⁶ Nm⁻²) ethylene. Initiator solutions A and B had been prepared. A Sodium persulphate 7.6g Sodium bicarbonate 7.6g Distilled water 200g B Sodium formaldehyde sulphoxylate dihydrate 3g Sodium vinyl sulphonate (25% aq) 76g Distilled water 132g. 285g of the monomer mixture, excluding ethylene, was pumped into the vessel and held for 10 minutes. The remainder of the monomers was added over 4 hours. The solutions A and B were added over 6 hours with the first 15 minutes and final 45 minutes added at double rate. During the first 30 minutes addition the temperature was raised to 50°C and maintained thereafter. After these additions the reaction mass was held for 30 minutes and then the solutions t-butyl hydroperoxide 5.7g Distilled water 50g and Sodium metabisulphite 3.6g Distilled water 50g Added over 30 minutes while cooling. Silane Z6040 was then added at a level of 1% on the emulsion and the emulsion left for 24 hours before formulating a test paint. This paint comprised (in parts by weight) The paints were at 82% PVC made by appropriate adjustment of the above formulation. Paint A contained a non-silanised emulsion and paint B the silanised (1% level) emulsion. Test pieces were made by drawing down a 5 micron (5 x 10⁻⁶ m) wet film of the paint onto a plastic foil. The panels were allowed to dry for 7 days and then scrubbed on a sheen apparatus using water as medium. Paint A required 2,000 scrubs to produce significant failure while Paint B after 4,500 scrubs did not show so much damage.

Claims: A process of preparing a vinyl copolymer emulsion wherein i) the monomer components are reacted under pressure emulsion polymerisation conditions at a pressure of from about 20 bar in the presence of a surfactant including a C14 to C20 unsaturated alkenylene moiety to provide an emulsion of vinyl polymer particles with a surface capable of reacting with an epoxy moiety, and ii) the emulsion is reacted chemically with from about 0.1% to about 3% by weight of an epoxy silane material. A process according to claim 1 wherein the vinyl polymer is a vinyl C2 to C18 alkanoate/vinyl chloride/alkylene terpolymer. A process according to claim 1 or 2 wherein the epoxy silane has the formula: X - Si (OR)3 wherein X is an alkyl group containing a reactive epoxy moiety and the three R radicals, which may be the same or different, are each hydrogen or a C1 to C4 alkyl radical with not more than two of the R radicals being hydrogen. A process according to any preceding claim wherein the polymerisation is performed at a pressure of from about 40 bar to about 100 bar. A process according to any preceding claim wherein the surfactant containing an unsaturated alkenylene moiety is selected from oleyl propanol amide sulphosuccinate and a potassium oleic acid sulphonate. A pressure vinyl copolymer emulsion prepared as in claim 1 part (i) chemically post reacted with from about 0.1% to about 3% by weight of an epoxy silane. A tile adhesive comprising i) from about 15% to about 85% of solid particulate filler, ii) from about 5% to about 40% of copolymer emulsion particles as defined in claim 6, and iii) from about 15% to about 45% of aqueous phase, which amount includes the water in the copolymer emulsion. An emulsion based paint based on the emulsion of claim 6 comprising by weight Copolymer solids 5% to 35%, Aqueous phase 5% to 35%, Filler 5% to 55%, and Pigment 5% to 30%

Inventors: LEWIS, IAN DOUGLAS
Applicants: UNILEVER N.V., UNILEVER PLC
Application year: 1988
Main classification: C08F8
IPC codes: C09J201, C09D5, C09J151, C09J9, C08F8, C09J131