Background Art Emulsion polymerization and copolymerization of vinylacetate, vinylesters of versatic acid and acrylate esters, either alone or as co-and terpolymers with various other monomers or mutually, is used for preparation of polymer dispersions for traditional and special applications.

One of the application fields of aqueous polymer dispersions is the field of building industry, where the polymer dispersions are used for outdoor, as well as for intdoor applications, particularly in coating compositions, further as additives to polymer-cement mortars, concretes, plaster materials, stuffs, pugging stuffs, binders and building adhesives.

Aqueous copolymer dispersions are also used in preparation of priming anticorrosive coating compositions.

The use of aqueous copolymer dispersions in external facade coating compositions, as well as in the coating compositions for anticorrosive protection, requires high quality of the dispersion and of the polymer contained therein. In the past mostly solvent coating systems were used in these applications, and they are partly used up to the present. But at present the most often used method of protection against external effects, including corrosive effects, is the application of organic coatings. The development and usage of permanently innovated systems for surface protection is influenced by a number of factors of which the most important are the effects on the environment and economy of surface finishing. In this respect the organic coating must fulfill the requirements of physiologically unexceptionable character, low or zero content of organic solvents, no toxic pigments, and an applicability which is independent of the environmental effects.

The ecological aspect has gained great importance in recent years, and in a number of countries it is a limiting factor. In the past, great attention was directed especially to volatile substances contained in the coating compositions. The fight against emissions of organic solvents has considerably limited manufacturers and those who process classical coating compositions which are now being replace by coating compositions which can be diluted by water, consist of powder or contain a great amount of dry substance.

Building paints constitute an important group of coating compositions which can be diluted by water. They are used for coating of plastes, concrete, of ceramic, wood-fibre or wooden walls, and gypsum wallboards. Both types of paints for the building industry-exterior and interior-are highly filled coating compositions in which the volume of pigments and fillers (VOF) is 50 to 80 %.

Thus, they are filled with a greater or equal amount as indicated by the value of critical volume concentration of pigment (CVCP) in the system. Content of the binder (aqueous dispersion) lies in the range from 5 to 25 % by weight. The actual amount of the binder depends on the ability of the binder to bind the particles of pigment and fillers.

Disperse coating compositions contain a number of components which influence properties of both the coating composition alone in the liquid state, and the film formed after drying out. Chemical composition influences the values Tg (glass-transition temperature), MFT (minimum film-forming temperature) which have an important influence on the applicability of the prepared coating composition. Composition of the polymer also influences physico-mechanical properties of dry films, like extensibility, thermal expansivity, elasticity, and so on.

The resulting properties of a film may be also influenced by the initiation system used. Also the protecting colloid or tenside may influence absorptivity of the disperse film to a certain degree. The choice of a suitable dispersion for a formulation of the coating composition must be performed taking into account the chemical composition of the dispersion, initiation system used, and the protecting colloid or tenside.

Besides the above given requirements which must be fulfilled by an aqueous polymer dispersion, used for preparation of building (facade) paints, this must contain a polymer which provides the film, formed after drying out the facade paint, with a required lustre, adherence and hardness, low diffusion resistance and absorptivity in water, good ability to be washed, and high abrasive resistance. A very important criterion is the resistance against the UV radiation which characterizes the environmental effects.

An aqueous polymer dispersion, suitable for the formulation of priming anticorrosive paints, should contain a polymer, intended to form a film after drying the applied paint out which film must fulfill the protection function under the effect of water and moisture, polluted atmosphere (S02, CI-), oxygen, increased temperature and UV radiation (for the top layers of the system).

Aqueous polymer dispersions belong to a group of substances which fulfill completely the requirements for the formulation of building and anticorrosive priming coating compositions from the point of view of ecology. It has turned out that by suitable composition of a mixture of monomers and by suitable way of performing the polymerization conditions will be created under which the resulting polymeric particles and their distribution, as well as the polymer structure favourably influence homogeneity of the polymer film, formed from the dispersion, and, therefore, also its application properties in the direction required. The prepared aqueous copolymer dispersion is, as a result of its properties and the properties of the polymer contained therein, suitable to be used for preparation of exterior (facade) and interior building coating compositions, as well as for preparation of priming anticorrosive coating compositions.

Present invention solves the process of preparation of such an aqueous polymer dispersion.

Disclosure of invention Nature of the process of preparation of an aqueous copolymer dispersion, based on vinylester of versatic acid, vinylacetate and acrylate esters, consists according to this invention in that to an aqueous phase containing the components of the mulsion system and electrolyte, a mixture of monomers of the composition of 40 to 55 % by weight of vinylester of versatic acid (VeoVa 10), 20 to 40 % by weight of vinylacetate, 15 to 25 % by weight of methylmetacrylate, and 0 to 15 % by weight of 2-ethylhexylacrylate, is added.

The initiating system contains potassium, sodium or ammonium peroxodisulfate in an amount of 2.3 parts by weight, related to the whole polymerization charge which represents 1000 parts by weight.

Examples of Embodiments Example 1 A polymerization reactor is gradually fed by the components of the aqueous phase-18.0 weight parts, i. e. 18.0 g (as approximately 10% aqueous solution) of polyvinylalcohol having a molecular weight, given by the K-value of 45 to 55, calculated according to Fickentscher, and having the content of residual acetate groups of 10 to 15 % by weight, and conductivity of max. 200 IlS. cm~1 (trade name Duviol SP-1), 18.0 weight parts, i. e. 18.0 g (as approximately 13% aqueous solution) of alkylpolyglycolether, characterized by the content of ethylene oxide of 87 to 93 % by weight, and by a ratio number expressing the hydrophilic-lipophilic balance (HLB) of 16 to 20 (trade name Slovasol 2430), 1.5 weight parts, i. e. 1.5 g (as approximately 10% aqueous solution) of NaHCO3, and an amount of water which does not exceed its overall necessary amount of 478.5 weight parts, i. e. 478.5 g.

The aqueous phase, prepared in this way, is heated under permanent stirring to a temperature of 69 to 70 °C, and 23.8 weight parts, i. e. 23.8 g of a mixture of monomers, representing 5 % by weight of its overall amount (476.7 weight parts, i. e. 476.7 g), are supplie. The mixture of monomers has the following composition: 20 % by weight of vinylacetate, 45 % by weight of vinylester of versatic acid (trade name VeoVa 10), 20 % by weight of methylmetacrylate and 15 % by weight of 2-ethylhexylacrylate. After 5 to 10 minutes of emulsification the first dose of initiator is added in an amount of 1.5 weight parts, i. e. 1.5 g of potassium peroxodisulfate in the form of a 5% aqueous solution. After adding the initiator the temperature of the reaction mixture starts to be increased under the influence of the reaction. When a temperature of 72 to 73 °C is reached the rest of 452.9 weight parts, i. e. 452.9 g of a mixture of monomers is started to be continuously dosed. Until the 140th minute the mixture is dosed at a constant rate in an amount of 1.95 weight parts, i. e. 1.95 g per minute. In the 140th minute the dosed amount is decreased to 1.80 weight parts, i. e. 1.80 g per minute which dosing is then uniformly decreasing, so that within the last 10 minutes the mixture of monomers is dosed at a rate of 0.85 to 0.45 weight parts, i. e. 0.85 to 0.45 g per minute. Dosing of the mixture of monomers lasts 270 or 300 minutes on the whole.

Temperature of the reaction mixture is maintained at 74 to 76 °C during the whole period of dosing. In the 120th minute of dosing the mixture of monomers a second initiator dose is added to the polymerization charge in an amount of 0.4 weight parts, i. e. 0.4 g of potassium peroxodisulfate. Further parts are added in the 150th minute in an amount of 0.1 weight parts, i. e. 0.1 g, and then in the 180th, 210th, 240th and 270th minute, each time in an amount of 0.075 weight parts, i. e. 0.075 g of potassium peroxodisulfate, and always as a 5% aqueous solution.

After termination of dosing the mixture of monomers the polymerization charge is maintained at a temperature of 78 to 80 °C for 30 to 45 minutes.

Within this time interval all free monomers react, and then the reactor content is cooled down to 30 to 35 °C. After the dispersion is cooled down, it is treated by adding 5.0 weight parts, i. e. 5.0 g of ethylene glycol, and after its perfect mixing up the dispersion is filled to containers.

The amounts of individual components, given in weight parts or in g, are related to 1000.0 weight parts of the polymerization charge, i. e. 1000.0 g.

The dispersion, prepared by the above given process, shows the following quality: -dry matter-min. 50.0 % by weight -viscosity (Rheostat)-2 to 3 Pa. s -particle size-120 to 150 nm -pH-4 to 5 -temperature of film formation (MFT)-4 to 6 °C -absorptivity-10 to 30 % by weight -degree of alkaline hydrolysis-0 % by weight -abrasive resistance-> 45 minutes -extensibility-800 to 1500 % The facade coating composition, prepared from the dispersion, has the followingproperties: -adherence-1St degree -diffusion resistance-65 to 80 -absorptivity-0.02 to 0.06 kg/m2 -hardness-19 to 25 % -wet abrasion-about 5000 cycles -After a 1000 hours exposure to an alternating action of UV radiation, rinsing by water, action of temperatures of-20 and +50 °C the composition has shown no change in lustre, colour shade, adherence and weight, compared with the original values.

Example 2 Process of preparation the same as in Example 1 with the difference that a mixture of monomers having the composition of 40 % by weight of vinylacetate, 40 % by weight of vinylester of versatic acid (VeoVa 10), 15 % by weight of methylmetacrylate and 5 % by weight of 2-ethylhexylacrylate is used. The mixture of monomers is dosed at a constant rate of 1.89 weight parts, i. e. 1.89 g per minute, while the dosing lasts 235 to 245 minutes. The initiator, peroxodisulfate, is added in three parts, the first dose consists of 1.5 weight parts, i. e. 1.5 g. Next part is used in the 120t minute of dosing in an amount of 0.5 weight parts, i. e. 0.5 g, and the last one in an amount of 0.3 weight parts, i. e. %. 3 g is added after termination of dosing the mixture of monomers. It is always used in the form of 5 % aqueous solution.

The prepared dispersion, as well as a facade coating composition, formulated from it, have shown similar properties as given in Example 1.

Example 3 Process of preparation and the amounts of individual components of the polymerization system as in Example 1 and 2 with the difference that the composition of the mixture of monomers is as follows: 20 % by weight of vinylacetate, 55 % by weight of vinylester of versatic acid (VeoVa 10), and 25 % by weight of methylmetacrylate.

The prepared dispersion, as well as a facade coating composition, formulated from it, have shown similar properties as given in Example 1.

Example 4 Process of preparation and the amounts of individual components of the polymerization system as in Example 1 and 2 with the difference that the composition of the mixture of monomers is as follows: 20 % by weight of vinylacetate, 50 % by weight of vinylester of versatic acid (VeoVa 10), 25 % by weight of methylmetacrylate, and 5 % by weight of 2-ethylhexylacrylate.

The prepared dispersion shows similar properties as given in Example 1, and a priming anticorrosive paint, formulated on its basis, fulfills besides the basic properties the demands, put on the paint in accelerated tests of exposition to the fog of NaCI, and to the atmosphere of S02.

Industrial Applicability The polymer dispersions, based on vinylester of versatic acid, vinylacetate and acrylate esters, prepared according to this invention, extend the possibilities of preparation of polymer aqueous dispersions, and they can be used in the industry of coating compositions and in building industry.