Aqueous polymer dispersion, process for its preparation and application.

The invention relates to an aqueous dispersion of polymers of at least two different mono-unsaturated free-radically polymerizable compounds, of which at least one is a monounsaturated monocarboxylic acid and a method for preparing the dispersion, and their use.

Aqueous dispersions of polymers of mono-carboxylic acids, in particular of copolymers and terpolymers of acrylic acid or of methacrylic acid are already known. It is in this context referred to the US Patent 3,980,602 in which a dispersing agent is described for an aqueous acrylic resin paint composition as well as to the European laid-open specification 0115694, the aqueous acrylic resin dispersions and their use for protective layers described.

Such dispersions s.ind partly very complicated construction, some of them are oriented only for very specific applications. Often, the dispersions contain ingredients that make an environmentally friendly use impossible.

The invention has for its object to provide aqueous dispersions of polymers containing carboxyl groups, which are simple in structure, are allowing an environmentally friendly application and easy to manufacture.

The dispersions of the invention are characterized in that the polymer is crosslinked, the aqueous medium is free of organic solvents and the carboxyl groups of the polymers are partially neutralized. -The Polymer is preferably free of cross-linkable groups.

Such polymer dispersions are extremely safe to use, because vaporize any organic solvents which may be harmful or dangerous due to their flammability. In the dispersions of the invention are 2 to 20 mol% in general, preferably n.eutralisiert 3 to 8 mol% of the carboxyl groups. Based on the weight of the copolymer, this preferably has from 0.1 to 1 wt .-%, neutralized carboxyl groups. This partial neutralization of the carboxyl groups, the polymers have an enhanced hydrophilic surface, but are not soluble in the aqueous medium. The electrical charge as a result of the dissociated carboxyl groups provides sufficient stabilization of the dispersed polymer particles in the aqueous medium. Suitable unsaturated carboxylic acids for the polymer, especially monocarboxylic acids such as acrylic acid and methacrylic acid are suitable. Methacrylic acid is preferred. Mixtures may also be used. The second monomer, that is, in the case of a copolymer, is preferably an ester of acrylic acid or of methacrylic acid with an alcohol having 1 to 4 C atoms, especially ethyl acrylate. Methacrylic acid and ethyl give each other particularly suitable copolymers for the dispersion of the invention. If the polymer is a terpolymer, then an ester of acrylic acid or methacrylic acid as the third monomer is preferably provided with an alcohol having 1 to 18 C-atoms, which is however different from the second monomer. As termonomer is suitable in particular butyl acrylate.

With particular advantage, the polymer is a copolymer of 2 to 6 moles, in particular 3.5 to 4 mol of comonomer per mole of methacrylic acid and / or acrylic acid. Also highly suitable are terpolymers of 2 to 6, preferably 3.5 to 4 moles of comonomer and 0.05 to 1, preferably 0.1 to 0.5 moles per mole of methacrylic acid termonomer and / or acrylic acid. For the inventive dispersion suitable polymers and their preparation 84 111 508.2 (Publication no. 0,143,935) are described in the European patent application, the contents of which incorporated herein by reference. The polymer is preferably a bulk polymer. When polymer is particularly advantageously a thermoplastic. These polymers can be readily prepared without solvent.

The carboxyl group content of the polymer is, based on the polymer weight, preferably from 5 to 15, in particular 8 to 12 wt .-%. The polymer is in the strongly acidic range insoluble in water, completely soluble in the alkaline range and suitable in the neutral to slightly acidic range for the formation of a dispersion. The polymer content of the dispersion is normally in the range of 5 to 75 wt .-%, especially 10 to 30 wt .-% (according to DIN 53189), based on the total weight of the dispersion. In particular, if the dispersion contains very little polymer, ie, about 5 to 30 wt .-%, then it preferably contains a thixotropic agent, in particular bentonite, to facilitate their environment to handle lo, eg in the production of coatings. For this purpose, ranging generally from 0.5 to 2 wt .-% thixotropic agent, based on the total weight of the dispersion.

Surfactants and other dispersion stabilizers may be provided, but are not required. Particularly advantageously, the dispersion is even free of surfactants and dispersion stabilizers. In a preferred embodiment of the invention, the dispersion is essentially free, preferably completely free of non-polymer belonging anions, apart from the course always present low content of OH - ions of water. With particular advantage the polymer itself does not contain any hydrophilic groups or charged residues other than those derived from the mono-carboxylic acid carboxyl groups. This simple charge and solubility are created that have an advantageous effect on handling. By ester groups the solubility properties can be varied to some extent.

The pH of the dispersion depends on the number of carboxyl groups present and the amount of the neutralized carboxyl groups. In typical dispersion according to the invention, the pH is less than 7 and preferably between 4 and 6.5, in particular between 5 and 6 (according to DIN 53785).

preferably monovalent ions are provided for the neutralization of the carboxyl groups, in particular sodium or ammonium ions. The viscosity of the dispersion may be adjusted within wide ranges and depends inter alia on the content of polymer, the particle size of the polymer and the preparation of the dispersion from. The particle size of the polymer particles is less than 20 pm and is preferably in the range of 0.1 to 10_Nm, particularly 0.1 to 5 pm. The viscosity is usually in the range of 10 to 50 sec flow time from a cup 48540th

The dispersions of the invention are particularly suitable for the production of coatings, primarily those that by applying a weakly alkaline aqueous medium to be detachable again after its intended use. They are suitable for producing temporary protective coatings for motor vehicles instead of the previous use of waxy coatings. The dispersions are also suitable for other applications where objects and materials from air, light are und_Feuchtigkeit protect. If desired, the dispersions of pigments and stabilizers and the like to light. be offset.

The dispersions of the invention result after its application even at low temperatures between 0 ° C and ambient temperature homogeneous closed films. Etc. There are various forms of application for the inventive dispersions, such as brushing, troweling, rolling, dipping, flooding, pouring, spraying. Due to their defined electrical charge dispersions of the invention are also particularly suitable for electric coating operations, and not only for the electrostatic spraying, but also in particular for application by electrophoresis and the Chemiphorese (Autophoresis). Also, a baking of the coating at an elevated temperature is possible.

The polymers of the dispersions of the invention may be prepared in part in a conventional manner, for example by emulsion polymerization or suspension. However, particularly suitable are dispersions which are prepared from the finished solid or molten polymer, because here the carrying of foreign substances in the dispersion, which originate from the preparation of the polymers, can be avoided. Through bulk erhalte- ne, especially thermoplastic, produced in the extruder polymers are particularly suitable as starting material. This manufacturing method allows a variety of variations in the composition of the polymers as they can not be obtained by emulsion or dispersion polymerization.

The comminution of the polymers is preferably carried out starting from a granulate, powder or a melt. Although the polymers can be mechanically ground to the desired fineness, but other methods have proved to be advantageous. Preferably, the comminution of the dry polymer previously prepared is carried out in an aqueous medium, which is in particular alkaline, so that during the comminution takes place at least partially neutralizing the carboxyl groups of the polymer. The inventive polymer is neutralized at least partially with advantage before it is converted into the dispersion.

In a particularly preferred embodiment of the method according to the invention the polymer is added in the form of a partially neutralized melt with the aqueous medium and mixed under crushing. It is the partial neutralization of the melt, advantageously lower than in the final dispersion, and-the aqueous medium contains the remaining amount of basischwirkender substance to achieve the desired degree of neutralization. The partial neutralization of the not yet shredded polymer and the content of the aqueous medium are thus preferably matched to one another that, dispersions are obtained in the desired pH range.

The partially neutralized melt can be prepared by basic substances, in particular sodium carbonate, in the previously prepared polymer, and in particular in the molten state, are mixed, which can be done for example in an extruder or kneader. It is with particular advantage, however, also possible to carry out the partial neutralization already during or before the production of the polymers, ie, during or before the polymerization. This is possible by removing a part of the unsaturated monocarboxylic acids used as the monomer in salt form, particularly as a sodium salt, and used as such, is copolymerized. This can preferably be made using an apparatus and by the method as described in the European patent application 84 109 569.8 (Publication No. 0142894). In the partially neutralized "dry" polymer are preferably from 0.1 to 1 wt .-%, in particular 0.3 to 0.7 wt .-% of carboxyl groups, based on the total weight of the polymer is neutralized. This typically corresponds to about 2 to 20, preferably 4 to 6% of the carboxyl groups present. As the aqueous medium is a sodium carbonate solution is preferably added. The mixing of previously partially neutralized polymer and the alkaline solution or water can be carried out continuously so far, until the desired degree of dispersion is achieved. There the finished dispersion is obtained in one go. It is also a preswelling at room temperature or in the heat with a portion of the aqueous medium possible.

The dispersion is thus carried out with adjustment of the pH and that in the case described above by preferably constant increase of the pH value. In another embodiment, however, the preparation of the dispersion is also carried out by adjusting the pH by the continual lowering des.pH value, by starting from a solution of the polymer and by lowering the pH to the desired level the polymer precipitates and the dispersion forms. To carry out this embodiment, it is preferable from the not pre-neutralized polymer, for example, of granules, as is in particular obtained by bulk. The polymer is then dissolved in an aqueous alkaline medium, preferably containing a volatile base, in particular ammonium hydroxide, wherein the lowering of the pH of the solution is preferably carried out by partially removing, in particular by evaporation of the base. In contrast to a simple neutralization by addition of acid, the removal of the base has the advantage that a dispersion is obtained which is free of salt in a similar manner as the dispersion prepared according to the above-described embodiment by increasing the pH. This means that no free salts in an aqueous medium are present except the salt formation at the polymer itself by the partial neutralization of the carboxyl groups.

The removal of the base may take place in various ways. Is appropriate to remove by ion exchange using an ion exchanger. However, particularly preferred evaporation of the volatile base, in particular at elevated temperature. The base can be removed with, for example, by distilling off a portion of the aqueous phase to a sufficient extent, so that a reduction is achieved in the desired pH range. A pressure distillation at temperatures above 100 ° C, in particular in the range of 120 to 150 ° C results, in particular when distillative removal of ammonia, rapidly to the desired result. Optionally, the medium again water are supplied in order to maintain a desired ratio of polymer to dispersing medium. The addition of water can share or continuously. Generally used ent ionized water according to the invention, the possibly required chemicals are added. In this way the introduction is avoided of undesirable foreign ions.

Further features, details and advantages of the invention will become apparent from the following description of preferred embodiments in conjunction with the subclaims.

example 1

Producing Disperionen from the polymer melt after partial neutralization.

For this example, an ethyl acrylate-acrylic acid copolymer was einem.Mol ratio of 3.5: 1 is used, which was produced by polymerization in the extruder (melt index 12 g per 10 minutes at 150 ° C - DIN 53 735 -, acid number 127 ). Granules of this polymer was melted in a kneader at 120 to 130 ° C and kneaded with about 5 mol% of the theoretically necessary for complete salt formation amount of soda. There was soda (sieve fraction 63-125 pm) used. After mixing the Sodapulvers the polymer Soda mixture was cooled to below 100 ° C, then it was still molten. The mass was then diluted successively to the desired concentration by adding water. The addition of water at elevated temperature is especially preferred because of the low viscosity and the resulting good mixing.

The specific procedure was as follows: 570 g of the polymer (carboxyl group content 10.2 wt .-%, based on the weight of the polymer) were first homogenized at 120 ° C in a kneader. Thereafter, the melt at 120 to 130 ° C 5 g crystal soda ash powder were (sieve fraction 63-135 gm) added and incorporated into the polymer. The mass was then cooled to 80 to 85 ° C, with 450 ml of deionized water was added proportionately or continuously with simultaneous thorough mixing. Thereafter, the mixture obtained was diluted with deionized water to a solids content of 40 wt .-%. Here, a very fine low viscous dispersion was obtained with a pH of 6.2.

example 2

570 g of the granules according to Example 1 were melted at 120 ° C on a Kenter. Thereafter, 4 mol% of the carboxyl groups by adding 4 g anhydrous sodium carbonate (sieve fraction 63-125 pm) and mixing of soda were neutralized in the melt. Subsequently, the mass was cooled to 80 to 90 ° C, with strength in the melt successively 0.005% aqueous sodium carbonate solution was incorporated, to a solids content of about 40% was achieved. The final dispersion had a pH value of 6.2. The particle size of the dispersion particles was 90% to under 4th

example 3

Preparation of the dispersion from the polymer melt after salt-copolymerization.

In this example was the preparation of the carboxyl-containing polymer in which a part, namely 5 mol% of methacrylic acid were replaced by sodium acrylate or sodium. The preparation of the polymer in the extruder was carried out in the same manner as the preparation of the polymer according to Example 1. The final polymer but corresponded by the Copolymerization of the salt of the carboxylic acid be already the partially neutralized product of the preceding examples after incorporation of the sodium carbonate. The polymer was homogenized in the kneader at 100 ° C and again dispersed at 80 to 90 ° C with deionized water. However, it may also direct the polymer obtained after polymerization, still molten processed with water to disperse.

Depending on the proportion of the salt used as the monomer of the carboxylic acid, the dispersion can be performed with pure water or with alkaline water, for example, soda water, occur, wherein the amounts of base used for partial neutralization are each matched to one another such that a stable dispersion is obtained.

example 4

The preparation of the dispersion by pressure distillation.

In ammoniacal solutions of carboxyl-containing polymers, a balance between ammonia and ammonium ions as a result of hydrolysis vor..Es is has been found that under pressure of this equilibrium can be shifted by removal of ammonia in the manner by distillation at elevated temperature, that progressively less carboxyl groups in salt form present.

In a pressure cooker, fitted with pressure gauges, thermometers, air valve, relief valve and safety valve, 200 g of ethyl acrylate-methacrylic acid copolymer were with a carboxyl group content of 10.4% in 1800 ml of deionized water and 12 ml of 30% ammonia (40% of salt formation theoretically required amount) while heating up to 127 to 128 ° C. dissolved. A pressure of about 1.5 bar was established, and it was through the secure safety valve distilled off a mixture of water vapor and ammonia. twice there were distilled 1000 ml water, 1000 ml were replaced. After cooling to about 60 ° C, the final dispersion was filtered through a sieve of 71 pm. The dispersion obtained had at a density of 1.03 g / cm³ a solids content of 20% and a pH of 5.5.

example 5

The procedure of Example 4 was repeated except that the pellets in 1800 ml of deionized water and 21 ml of 30% ammonia (70% of the theoretically required amount) was dissolved. The solution was heated to 120 to 122 ° C, resulting in a pressure of 1.2 bar being established. Through the safety valve, a mixture of ammonia and water was distilled off. There were continuous 2000 ml of ammonia-water mixture is removed, of which 1000 ml were replaced by continuous addition of deionized water. The pH of the last 100 ml of distillate was 10.3 at 20 ° C.

After cooling to about 60 ° C, the final dispersion was filtered through a 71 micron steel mesh. The dispersion obtained had a density of 1.03 g / cm³, A solids content of 20% and a pH of 5.5. The particle size of the dispersion particles was about 90% less than 1 .mu.m.

The company resulting from the specification and claims, individual features can advantageous either alone or with others, for example in the form of subcombinations and represent in themselves protectable constructions for which protection is claimed here.