NO133597B - - Google Patents

Description

Method for producing a stable dispersion of an acrylic polymer in an organic liquid.

The present invention relates to new dispersions of synthetic polymers i

organic liquids, new methods for producing such dispersions and coating mixtures produced from the dispersions.

Although it is well known to polymerize monomers in an aqueous phase and form a stable dispersion of polymer in this aqueous phase, it is common in practice, when a dispersion of polymer in an organic liquid is needed, to disperse an already prepared polymer in the liquid, for example in painting processes similar to those used when dispersing a pigment in an organic liquid. Better dispersion of the dispersions can be achieved by adding a common stabilizing agent, for example polyethylene glycol monolaurate or -stearate, to the organic liquid, the agent presumably being absorbed on the surface of the already formed particles so that a partially protective layer of "solvated " groups.

Although it is possible to polymerize a

monomer in an organic liquid, the polymer does not form a uniform dispersion, but a sticky or glassy layer or mass, if it is insoluble in the liquid. A similar result is obtained by attempting to prepare a dispersion by precipitating the polymer from a solution in organic liquid. Addition of a common stabilizing agent to the organic liquid does not in any of the cases produce a sufficient one

stabilization of a dispersion of polymer in organic liquid. This is presumably due to the fact that the adsorption energy cannot be made large enough to form a sufficient protective layer of solvated groups on the polymer particles during their formation and thus prevent coagulation.

The present invention provides stable dispersions of acrylic polymers in organic liquids, characterized in that stabilizing solvated components are linked by primary chemical bonds to the molecules and form an integral part of the dispersed particles. This is in contrast to the use of conventional stabilizing agents, in which the stabilizing solvated groups are indirectly linked to the disperse particles by groups which themselves are only adsorbed to the surface of the disperse particles by secondary valence forces.

According to the present invention, a method is provided for producing a stable dispersion of acrylic polymer in an organic liquid in which it is insoluble, characterized in that an acrylic monomer is polymerized in the organic liquid in the presence of denatured natural or synthetic rubber which is dissolved in the organic liquid .

The solvated groups in common stabilizing agents usually have a chain of approx. 10 carbon atoms, i.e. that their molecular weight is approx. 250. While solvated groups of this size can in some cases be used to stabilize the dispersions according to the present invention, we prefer to use solvated denatured natural or synthetic rubber with a molecular weight of at least 1000, the advantages of which are explained in the following.

By "solvated" is meant solvated by the organic liquid (solvent) in which the polymer is dispersed.

The polymeric dispersions according to the present invention are of particular value in coating mixtures since they are substantially well dispersed compared to dispersions, which previously had to be prepared by forming a polymer in an aqueous phase and then dispersing it in an organic liquid. Consequently, the rheological properties of coating agents based on dispersions according to the present invention are substantially improved. In addition, they offer wider ranges for particle size and molecular weight than those available in the previous method, as these two factors are also of particular importance in that, together with the improved rheological properties, they enable recipes for coating mixtures that give glossy pigment-containing Movies. Pigments and plasticizers can be mixed into the coating compositions in the various commonly used ways.

Furthermore, in contrast to dispersions formed by polymer isation in an aqueous medium which are contaminated by common emulsifying and stabilizing agents, often of an ionic nature, the dispersion polymers according to the invention mostly contain only small amounts of copolymer. They can therefore be precipitated, dried or otherwise separated from the liquid phase to produce polymers with improved physical and electrical properties.

To prepare a dispersion, the polymer must be substantially insoluble in the organic liquid, and consequently the nature of the polymer to be dispersed must determine the nature of the organic liquid. For example where the polymer is strongly polar, e.g. methylacrylate, (3-ethoxyethyl methacrylate or acrylonitrile, the organic liquid must be non-polar, e.g. aliphatic hydrocarbons such as "white spirit" or iso-octane, or in connection with the more insoluble polymers such as acrylonitrile, aromatic hydrocarbons such as, eg ben-zen.

The disperse acrylic polymer produced by the method according to

invention, may be a homopolymer or copolymer, but it is referred to throughout the description as the polymer or the polymeric. By "acryl-" is meant acrylic or methacrylic acid or esters, amides or nitriles of one of these acids.

Mixtures of different monomers can be used. Typical substances which are suitable monomers according to the invention include styrene, vinyltoluene, divinylbenzene, diisopropenylbenzene, allyl acetate, diallyl adipate, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl propionate, vinyl acetate, vinyl stearate and acrylates and methacrylates of aliphatic alcohols such as ethyl, acrylic, lauryl and natural fatty alcohols. The preferred monomers for use in the production of polymers for use in coating compositions by this process are methyl methacrylate, (3-ethoxyethyl methacrylate, ethyl acrylate, vinyl acetate, acrylonitrile, methacrylic acid and acrylic acid and the amides of these acids. Combinations of the aforementioned monomers may be used and other typical substances suitable for use as comonomers include dimethyl itaconate, diethyl meleate, maleic anhydride and allyl alcohol.

The solvated deconstructed natural or synthetic rubber can have a molecular weight from the equivalent of a normal stabilizer and up to a molecular weight of 10". Since, however, chain lengths with a molecular weight below about 1000 mean that relatively larger proportions of solvated component are needed, and even then leads to dispersions which are often quite coarse, it is preferred to use solvated components with a molecular weight of at least 1,000. Particularly satisfactory dispersions are achieved by using solvated components with molecular weights from 1,000 to 100,000, preferably 1,500 to 10,000.

Where a free radical catalyst such as a peroxide is used in the dispersion polymerization, the solvated component should contain an unsaturated carbon-carbon bond, a tertiary carbon atom or other equally reactive groups, which are capable of being activated under the reaction conditions. The unsaturated carbon-carbon-carbon bond can also be activated by free radical catalysts, which are not of the peroxide type, such as e.g. azodiisobu-thyronitrile, under oxidizing conditions. For example when methyl methacrylate is dispersion-polymerized in a liquid hydrocarbon, an unsaturated rubber with a low molecular weight can be added.

The nature of the solvated component is determined from the nature of the organic liquid in which the polymer is to be dispersed. In contrast to the disperse polymer, this component should be of the same type as the solvent, i.e. both should be non-polar. Suitable combinations are polyisoprene with white spirit, and polyisobutylene with paraffin hydrocarbons.

The organic liquid used as polymerization and/or dispersion medium does not necessarily have to be a single liquid in all cases, but may well be a mixture of two or more. This can be an important factor when the dispersions are to be used as, for example, coating mixtures and it is desirable to be able to control the volatility of the liquid. Suitable combinations that can be used are isooctane with high-boiling neutroleum fractions (kerosene).

The amount of solvated constituents needed to stabilize the dispersion will also depend on the nature and molecular weight of the solvated constituent, the desired particle size, the final polymer concentration, etc.

Where polymeric solvated components such as denatured natural rubber and polyisobutylene are introduced, proportions now from 0.10 to 10 percent by weight of the polymer to be dispersed are appropriate.

Other surfactants can be used in the processes according to the present invention, but are not necessary to achieve stable dispersions.

The quantity ratio of polymer that can be obtained in the final polymer dispersion after this process can be varied over a wide range, e.g. within the range 5-65 percent of polymeric substances in the final dispersion. The dispersions preferably have a solids content of between 25 and 50 percent. If a higher solids content is needed, it is possible to increase the amount of solids in a dispersion by evaporating part of the liquid, if necessary under reduced pressure .

Dispersions with average particle size varying from 0.05 micron to 2.0 micron can be prepared and the molecular weight of the dispersed polymer can vary from less than 20,000 to 1,000,000 or more.

Dispersions of polymers with a molecular weight varying from 50,000 to 250,000 are particularly useful for use in coating compositions. In coating compositions to be oven dried at 100-150°C, dispersions of polymers with molecular weights from 100,000 to 250,000 are suitable. In coating compositions to be oven dried at 75-100° C, dispersions of polymers with molecular weights from 60,000 to 100,000 are suitable.

For use in coating compositions, we prefer dispersions of a polymer of acrylic acid or methacrylic acid or of an ester, amide or nitrile of such an acid, in which the organic liquid is hydrocarbon, either aliphatic or a mixture of aliphatic and aromatic. The stabilizing solvated component is made from degraded natural rubber or an unsaturated synthetic rubber.

The invention is illustrated by the following examples, where all parts are indicated as parts by weight.

Example 1.

1,500 parts of commercial methyl methacrylate monomer, 3,000 parts of white spirit and 75 parts of a denatured rubber solution prepared by grinding crepe rubber in a heated rolling mill until it was reduced to the consistency of a viscous liquid (molecular weight approx. 30,000 when measuring viscosity), cooling and dilution with an equal weight of white spirit, was placed in a reaction vessel equipped with a stirrer, cooling coil, thermometer and reflux cooler with outlet to the atmosphere. The contents of the container were heated to 85° C. and 5 parts of a 65% paste of benzoyl peroxide in dimethyl phthalate were added. After 30 minutes the portion began to whiten and it was then boiled at 85°C for 5 hours with the necessary use of the cooling coil during the exothermic phase of the reaction. A thin, creamy dispersion with 32% solids was formed.

The particle size in the dispersion, judged from electron microscope photography, was in the range 0.1 n to 0.5 n with the main amount of approx. 0.25 li. The molecular weight of the disperse polymer judged from viscosity measurement was 350,000.

Example 2.

Example 1 was repeated using only 16 parts of the degraded rubber solution. The finished product was a very thin, whitish dispersion containing small amounts of granulated polymer. The range of particle size was from 0.3 li to 1.2 ii with the main amount of approx. 0.8 u. The molecular weight of the disperse polymer was 380,000.

Example 3.

Example 1 was repeated using 160 parts of denatured rubber solution. The finished product was a thick creamy dispersion with a tendency to form a weak gel on standing. The particle size ranged from 0.05 µl to 0.3 µl with the bulk at 0.2 µl.

Example 4.

Example 1 was repeated using a mixture of 1000 parts of (3-ethoxyethyl methacrylate, 400 parts of ethyl acrylate and 100 parts of maleic acid in place of the methyl methacrylate. The weight of catalyst paste was also increased to 7.5 parts. A good, ash-thin, yellow-white dispersion was formed with a solids content of 31 percent and a particle size of approximately 0.5 l. The molecular weight was not determined.

Example 5.

Example 4 was repeated using 800 parts of acrylonitrile instead of the f5-ethoxyethyl methacrylate. The boiling temperature was further reduced to 75° C, the system flowed through with inert gas and the amount of catalyst paste increased to 15 parts. After 4 hours, a yellowish, opalescent dispersion with 28% dry matter content had formed, even though deposits of coagulated polymer had formed on the reaction vessel. The dispersion had the fine average particle size of 0.08 µl.

Example 6.

Example 1 was repeated using 1500 parts of petroleum ether with a boiling range of 100-120° C and 1500 parts of an industrial kerosene which boils above 170° C instead of white spirit. At the end of the reaction, however, the vessel was placed under water pump vacuum and approx. 1400 parts of the diluent distilled over the temperature range 37 to 55° C. so that a fairly thick dispersion with 49 percent solids was formed. The particle size and molecular weight of the dispersed polymer in the final dispersion with a high content of solids were not significantly different from the corresponding values for the polymer in example 1.

Example 7.

Example 3 was repeated using 80 parts of a low molecular weight synthetic polybutadiene (about 1500 by viscosity measurement) in place of the degraded rubber solution. A product essentially similar to that in Example 3, but somewhat coarser in particle size and with a much lower viscosity, was formed.

Example 8.

Example 1 was repeated using 37.5 parts of solid gutta-percha in place of the decomposed gum solution. A product essentially the same as in example 1 was obtained.

Example 9.

200G parts of petroleum ether with a boiling range of 60-80° C and 1000 parts of white spirit were introduced, together with 20 parts of non-volatilely decomposed rubber (molecular weight 23,000 when measuring viscosity) and 50 parts of benzoyl peroxide paste with a 65% solids content in dimethyl phthalate, in the apparatus according to example 1. The temperature was raised to 65° C. and 1000 parts of methyl methacrylate were dripped into the reaction mixture at a rate of 200 parts per hour. After all the monomer had been added, the Dorsjonen was boiled for a further 30 minutes. About. 1500 parts of diluent were then distilled off to a final boiling point of 88° C. at atmospheric pressure. The resulting dispersion was quite thick, had an average particle size of approx. 0.2 ii and a molecular weight of 103,000.

Example 10.

This example illustrates the use of the dispersions according to the invention in coating mixtures.

A coating mixture was prepared based on the following composition: Dispersion according to example 9 100 parts methylcyclohexanyl phthalate 24 parts Titanium oxide rutile 18 parts Dispersing aid 0.5 parts Aliphatic hydrocarbon is added to spray viscosity.

The pigment was dispersed in 8 parts of the phthalate plasticizer using oil alkyd resin with a high oil content as a dispersing aid. Sufficient aliphatic hydrocarbon was added for

that the pigment dispersion should be able to

be carried out in a ball mill. The other 16 parts of the plasticizer were stirred in

the polymer dispersion, into which the pigment dispersion was then mixed. The mixture was

filtered and diluted to spray viscosity

with aliphatic hydrocarbon.

The mixture was applied by spraying

on a primed metal plate, quickly dried

and then oven-dried for 30 minutes in wood

135° C. The resulting film was tough and

blank.

Dispersions of other polymers can

used in coating mixtures in it

polymers of acrylic or methacrylic acid of

an ester, amide or nitrile of such an acid

are particularly applicable.

Other plasticizers and pigments can of course be used.

Claims (4)

1. Method for the production of a stable dispersion of an acrylic polymer such as methyl methacrylate, in an organic liquid in which it is insoluble, especially for the production of coating agents, characterized in that an acrylic monomer is polymerised in the organic liquid in the presence of degraded natural or synthetic rubber which is dissolved in the organic liquid under such conditions that the rubber molecules are linked by primary chemical bonds to the polymer during its formation. 2. Method as stated in claim 1, characterized in that a rubber with a molecular weight of from 1,000 to 100,000 is used. 3. Method as stated in claim 1 or 2, characterized in that the rubber is used in an amount of 0.1 to 10 per cent, preferably 0.5 to 5 per cent, based on the weight of the disperse polymer. 4. Method as stated in one of the preceding claims, characterized in that the acrylic monomer and the rubber components are polymerized into a polymer with a molecular weight in the range from 20,000 to 1,000,000, preferably 50,000 to 250,000.