WO1990008786A1

WO1990008786A1 - Sterically stabilised aqueous polymer dispersions

Info

Publication number: WO1990008786A1
Application number: PCT/EP1990/000146
Authority: WO
Inventors: Ralf Tatas; Horst Specht
Original assignee: Akzo N.V.
Priority date: 1989-01-28
Filing date: 1990-01-26
Publication date: 1990-08-09
Also published as: DE3902536A1; BR9007050A; JPH04503224A; EP0455729A1; CA2050305A1

Abstract

Sterically stabilised aqueous polymer dispersions, based on radically polymerised ethylenically unsaturated monomers and on a graft polymer used as a protective colloid, are produced by radically grafting the essentially hydrophobic ethylenically unsaturated monomers, such as alkylesters of acrylic or methacrylic acid, on the essentially water-soluble or water-dispersable polymeric protective-colloid preproduct by means of a graft initiator, and by polymerising, in the presence of the protective colloid thus obtained, radically polymerisable ethylenically unsaturated monomers in an aqueous medium by emulsion polymerisation in the presence of a usual initiator forming free radicals. The protective colloid preproducts are preferably polysaccharides and polymerisates of ethylenically unsaturated monomers, in particular polyvinylpyrrolidon and polyvinylalcohol. These aqueous polymer dispersions, which can be processed even at room temperature, are a suitable base for varnishes and coatings.

Description

Sterically stabilized aqueous polymer dispersions

Description:

The present invention relates to sterically stabilized aqueous dispersions of polymers based on free-radically polymerized ethylenically unsaturated monomers, their preparation and their use as film formers, for example for the production of coatings.

Polymer dispersions generally have the advantage over polymer solutions that they allow polymer preparations of surprisingly high solids content to be used with a relatively low proportion of solvents (dispersion medium) but nevertheless relatively low processing viscosities. The lower proportion of solvent required meets the requirements for air pollution control.

The increasingly strict air pollution control regulations and cost considerations eventually led to developments that largely rely on organic solvents, either

REPLACEMENT LEAF as a solvent or dispersion medium, and instead the environmentally safe and cheaper water is used.

Aqueous polymer dispersions have been widely described and are increasingly being used even where higher demands are placed on the end product, for example coatings.

The problem of the stability of these dispersions played a central role in the introduction of aqueous polymer dispersions. In general, the dispersion particles coagulated and settled after a relatively short service life. In the meantime, storage-stable polymer dispersions can be provided which have usable storage stability. It was particularly important to suitably coordinate the - generally anionic - emulsifier, the protective colloid or the so-called internal stabilizer, which was done more or less empirically. Useful results are usually only obtained if both the emulsifier and the protective colloid and inner stabilizer have relatively strongly polarized to ionic groups. The stabilization is based primarily on the electrostatic repulsion of polar charges of the same orientation on the surfaces of the dispersion particles. Dispersion systems stabilized in this way therefore have the following two serious disadvantages:

With regard to their stability, they are very sensitive to the addition of electrolyte.

REPLACEMENT LEAF Moldings made from them, for example paint films, are relatively unstable with regard to aqueous external influences.

The latter disadvantage is obviously caused by the fact that after the production of these aqueous polymer dispersions, for example, and after the dispersion medium has evaporated, no completely homogeneous layers are formed, but rather an inhomogeneous honeycomb structure predetermined by the dispersion particles and rather by insufficient coalescence. Structure is preserved. The polar to ionic originally stabilizing groups of emulsifier, protective colloid or inner stabilizer are enriched in the interfaces of these honeycombs, and along these hydrophilic interface structures, slightly polar substances of low molecular weight, such as e.g. Water, diffuse and thus render the coating unusable. In addition, the emulsifiers used in each case can either migrate (sweat out) or migrate to the substrate along these honeycomb surfaces. In the former case, the surface gets an undesirable stickiness; in the latter there is a loss of liability.

There was therefore a need for stable aqueous polymer dispersions which do not have these disadvantages. The object resulting therefrom is achieved according to the invention by sterically stabilized, emulsifier-free aqueous dispersions of polymers based on free-radically polymerized ethylenically unsaturated monomers and a protective colloid, which are characterized in that

(1) the dispersions are essentially free of organic solvents,

(2) the protective colloid consists essentially of a free radical with essentially hydrophobic chains

REPLACEMENT LEAF Basis of ethylenically unsaturated monomers grafted essentially saturated water-soluble or water-dispersible polymers and

(3) the protective colloid is essentially non-ionic

Contains groups.

There are thus provided stable dispersions available, which in the ^{"substantially} no ionic groups at the surface between Grenz¬ dispersion and an aqueous medium have, and their stabilization is based solely on steric effects.

A process for the preparation of sterically stabilized aqueous dispersions of polymers based on ethylenically unsaturated monomers is also described in US Pat. No. 4,453,261. According to this document, the sterically stabilizing aid can also be any grafted polymer, among other things. As can further be seen from this document, the preparation of the graft polymers is preferably only a polymerization of ethylenically unsaturated monomers, a long-chain hydrophilic monomer and a short-chain hydrophobic monomer leading to a hydrophobic main chain with hydrophilic side chains. The situation is quite different in the production of protective colloids according to the invention: This is a grafting in the narrower sense in which reactive centers are formed on a saturated polymer chain by radical formation and finally hydrophobic side chains on a hydrophilic main chain.

Accordingly, the side chains of the preferred protective colloids according to US Pat. No. 4,453,261 are oriented toward the aqueous phase, while those of the inventive ones

REPLACEMENT LEAF Protective colloids orient themselves into the interior of the dispersion particles. Thus, there are substantially different dispersion particle structures and, in accordance with the stabilization principle, organic, water-compatible solvents such as in US Pat. No. 4,453,261 do not necessarily have to be added to the dispersions according to the invention in order to actually obtain stable dispersions or to further process them into, for example, usable coating films. Obviously, the considerable amounts of solvent in the dispersions according to US Pat. No. 4,453,261 are required to increase their mobility by swelling of the polymers in the dispersion particles and thus to ensure sufficient dispersion stability but also sufficient coalescence of the particles during film formation to reach. In contrast, in the dispersion particles according to the invention, this function of the solvent is already taken over by the hydrophobic side chains aligned in the interior of the particles, so that additional coalescence aids are not required.

The sterically stabilized aqueous polymer dispersions according to the invention thus meet the maximum demand for environmentally friendly, that is to say as completely as possible solvent-free, coating systems in a substantially more advantageous and uncompromising manner.

Japanese patent application 55-161 806 also describes hydrophilic polymers grafted with acrylate monomers as protective colloids for the emulsion polymerization of ethylenically unsaturated monomers. Starch products modified by grafting function here as protective colloids. With these protective colloids it should be achieved that usable aqueous polymer dispersions based on not only less selected ethylenically unsaturated monomers, but

REPLACEMENT LEAF have a much wider range of monomers produced by emulsion polymerization. Unlike the grafted hydrophobic monomers according to the invention, those according to Jap. -Kokai 55-161 806 grafted monomers but hydrophilic acrylates, as can be seen from the general chemical formula given there. Accordingly, the side chains formed by grafting these hydrophilic monomers onto the starch chain are oriented in the dispersion towards the aqueous phase, as is the case with the protective colloids according to US Pat. No. 4,453,261; this results in dispersions stabilized differently compared to the invention (see comments on this US patent).

Otherwise the subject of the Jap differs. Kokai 55-161 806 of the present invention in particular also due to the presence of emulsifiers which also carry ionic charges, while according to the invention, for the reasons mentioned above, such emulsifiers are dispensed with. It is therefore not to be expected that such emulsifier-containing dispersions are sufficiently stable to electrolytes or the resulting films are stable to aqueous media. The properties of these polyacrylate dispersions and their use are described in Jap. Kokai - 55-161 806 also stated nothing that goes beyond the storage stability. For the rest, the experimental examples given in Japanese Kokai prove not to be feasible: the grafted starch products A to C produced according to the working instructions given therein did not result in the emulsion polymerization of ethylhexyl acrylate in accordance with the working instructions of these Japanese. Kokai still in an embodiment of the emulsion polymerization according to the invention to stow dispersions.

REPLACEMENT LEAF It was extremely surprising that protective colloids according to the invention can actually be used to obtain stable dispersions without the presence of the apparently indispensable, in particular ionic emulsifier, which is a prerequisite for resulting stable dispersions in emulsion polymerizations.

At this point, it should be expressly pointed out that the term "emulsifier" is to be understood as meaning conventional emulsion stabilizers with surface-active properties, but not those stabilizers with the action of thickeners, which in the present case are referred to separately as protective colloids (cf. Classification of the emulsifiers in "Römpps Chemie-Lexikon, 8th edition, 1981, page 1126").

The protective colloids which sterically stabilize the aqueous polymer dispersions according to the invention are formed from protective colloid precursors, which can be water-soluble or water-dispersible natural or synthetic polymers, by grafting. Examples of such protective colloid precursors are, according to the invention, preferably polysaccharides and polymers made from ethylenically unsaturated monomers.

The naturally occurring, unmodified polysaccharides can preferably be used. Preferred naturally occurring polysaccharides or natural substances containing them are those from the group of poly-α-glycoses such as starches, amyloses, amylopectins, dextrins, dextrans and pullulans, from the group of polygalactoses such as gum arabic, agar agar, tragacanth, carrageenin and pectins , and from the group of polymannoses such as carubin, tara gum, algin, alginic acid and guar (galactomannose).

REPLACEMENT LEAF Among the polymers made from ethylenically unsaturated monomers, polyvinyl compounds in particular have proven to be suitable as protective colloid precursors, and among them polyvinyl pyrrolidone and polyvinyl alcohol are particularly suitable.

Those polymers are preferred as protective colloid precursors which have a polymer weight of 10,000 to 5,000,000 and in particular 50,000 to 500,000.

Suitable essentially hydrophobic ethylenically unsaturated monomers which can be grafted onto the protective colloid precursor to form hydrophobic side chains are those which can be attached to the radically activated centers of the saturated polymer.

Such monomers suitable for grafting are, in particular, those selected from the group of the alkyl esters of acrylic acid or methacrylic acid, the methacrylic acid benzyl ester, the dialkyl esters of itaconic acid, maleic acid or fumaric acid, acrylonitrile or methacrylonitrile, styrene or those with alkyl groups with 1 to 4 carbon atoms or styrene compounds substituted by a chlorine atom, the vinyl esters of aliphatic carboxylic acids having 2 to 12 carbon atoms. The alkyl groups of the esters and substituted styrene compounds mentioned can be straight-chain or branched. The graft monomers mentioned can be grafted on either alone or in a mixture. However, the free unsaturated acids, especially acrylic acid or methacrylic acid, acrylamide or methacrylamide, as well as hydroxyalkyl acrylates or methacrylates, each in small proportions in a mixture with one or more of the abovementioned monomers, can also be used advantageously.

REPLACEMENT LEAF Among the alkyl esters of acrylic acid and methacrylic acid mentioned and the dialkyl esters of ethylenically unsaturated dicarboxylic acids mentioned, preference is given to those having 1 to 18 carbon atoms and in particular having 1 to 8 carbon atoms in the alkyl group. Preferred graft monomers are also the monomers acrylonitrile, styrene, vinyl toluene, t-butyl styrene, vinyl acetate or vinyl propionate.

In most cases, the monomers which form the grafted-on side chains are also those monomers which are involved in the structure of the other dispersion polymers.

Preferred protective colloids are, moreover, those in which the average length of the grafted-on side chains is 10 to 100 monomer units or those in which the average number of grafted-on side chains is 50 to 1000 per main chain of the protective colloid.

The polymer weight of the grafted polymers can no longer be measured because it is already too high so that the polymers can no longer be dissolved.

It is not necessary to add conventional emulsifiers to produce the desired stable polymer dispersions according to the invention, and a low proportion of protective colloid is usually sufficient. In many cases, usable stabilities are already achieved with protective colloids which represent a proportion of protective colloid precursor of less than 1% by weight, based on the total weight of the ethylenically unsaturated monomers required for the structure of the graft and emulsion polymers. The upper limit for this level of protective colloid precursor can vary within wide limits, but the percentage will be off

REPLACEMENT LEAF For economic reasons or in view of the desired resistance of the resulting paint films to aqueous media, do not set them too high; however, it may well be 20% by weight. A particularly preferred range of the protective colloid content is between 1 and 10% by weight, based on the weight of non-volatile components of the polymer dispersion. A proportion of protective colloid precursor is preferably from 0.2 to 20% by weight and particularly preferably from 1 to 10% by weight, based in each case on the total weight of the monomers in the side chains of the graft polymer and in the emulsion polymer.

Suitable ethylenically unsaturated monomers, which form the basis for the polymers of the aqueous dispersions according to the invention, are virtually all those monomers whose use in homo- or copolymerization by means of emulsion polymerization in aqueous medium has already been described or appears feasible. Please refer to the relevant literature, e.g. HOELSCHER, "Dispersions of Synthetic High Polymers", Part I, Springer-Verlag 1969, or H. WARSON, "The Application of Synthetic Resin Emulsions", Benn-Limited, London 1972. Many of these monomers can be made in such an emulsion polymerisation polymerize only to homopolymers or only to copolymers. In the case of copolymerizations, the type and proportion of the respective comonomers in particular have an influence on the feasibility of the emulsion polymerization or the stability of the resulting dispersions. However, restrictions in this regard can be found in the prior art. Which monomers will be chosen will also depend on the resulting polymer glass transition temperatures with regard to the intended field of application for the dispersions, which the person skilled in the art will find out about

REPLACEMENT LEAF can inform easily. Since the possible application of dispersions according to the invention is above all the production of coatings and the film production plays a central role in the field of the production of coatings, one will primarily choose those monomers or monomer combinations which result in polymers having glass transition temperatures lead, which in the resulting coating film sufficiently meet the requirements with regard to the film formation temperatures.

Part of the dispersion polymers according to the invention can be, for example, the following ethylenically unsaturated radically polymerizable monomers: alkyl esters of acrylic acid, such as _. For example, methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, decyl acrylate and dodecyl acrylate, benzyl acrylate, alkyl esters of methacrylic acid, such as, for example, methyl methacrylate, ethyl methacrylate and butyl methacrylate, dialkyl esters of itaconic acid, maleinic acid, maleinic acid, maleinic acid, maleinic acid, malemic acid, maleinic acid, maleinic acid, malemic acid, malemic acid, maleinic acid, maleinic acid, malemic acid, maleinic acid, malemic acid, maleinic acid, malemic acid, maleinic acid, malemic acid, malemic acid, maleinic acid, maleinic acid, maleinic acid, maleinic acid, maleinic acid, malemic acid, maleinic acid, maleinic acid, maleinic acid, maleinic acid, malemic acid, maleinic acid, maleinic acid, maleinic acid, maleinic acid, and malefic acid, for example and diethyl fumarate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, styrene, substituted styrene compounds such as, for example, vinyl toluene, chlorostyrene and t-butyl styrene, vinyl esters of saturated straight-chain or branched carboxylic acids, for example vinyl acetate, vinyl propionate, vinyl laate, or vinyl laurate or vinyl laurate or vinyl laurate or Vinyl ethers such as vinyl isobutyl ether, vinyl chloride, vinylidene chloride, chloroprene, isoprene, butadiene, ethylene, propylene, 2-butene and α-olefins with 4 to 12 carbon atoms, stilbenes, alkyl esters of crotonic acid and cinnamic acid and allyl ethers or mixtures of these monomers.

These monomers, like the graft monomers, can likewise contain the free unsaturated acid components of the abovementioned

REPLACEMENT LEAF Esters, acrylamide or methacrylamide and hydroxyalkyl acrylate or methacrylates, in each case in relatively small proportions in a mixture with one or more of the above-mentioned monomers.

Preferred ethylenically unsaturated monomers are those from the group of the alkyl esters of acrylic acid or methacrylic acid, the dialkyl esters of itaconic acid, maleic acid or fumaric acid, acrylonitrile or methacrylonitrile, styrene or those substituted by alkyl groups with 1 to 4 carbon atoms or by means of a chlorine atom Styrene compounds, the vinyl ester of aliphatic carboxylic acids with 2 to 12 carbon atoms or mixtures thereof. The alkyl groups of the esters and the substituted styrene compounds of these preferred monomers can be either straight-chain or branched.

Coatings with a high quality standard, e.g. With regard to appearance, mechanical properties and resistance to a wide variety of external influences, they are generally obtained especially with such polymers based on acrylic and methacrylic compounds, alone or in combination with styrene compounds and / or vinyl esters, which is why, in the context of the present invention, dispersion polymers in particular based on these monomers were examined in more detail. Among these monomers, the alkyl esters of acrylic acid and methacrylic acid having 1 to 18 carbon atoms and in particular 1 to 8 carbon atoms, acrylonitrile, acrylamide, methacrylamide, styrene, methylstyrene, t-butylstyrene, chlorostyrene, vinyl acetate and vinyl propionate or mixtures thereof are particularly preferred.

REPLACEMENT LEAF The present invention also relates to a process for the preparation of sterically stabilized emulsifier-free aqueous polymer dispersions, which is characterized in that one or more radically polymerizable ethylenically unsaturated monomers are used in an aqueous medium which is essentially free of organic solvents emulsion polymerized in the presence of a protective colloid and a conventional free radical initiator, the protective colloid consisting essentially of a free radical grafted with (a) essentially hydrophobic chains based on one or more ethylenically unsaturated monomers (b) essentially saturated water-soluble or water-dispersible polymers exists and contains essentially no ionic groups.

A process for the production of sterically stabilized, emulsifier-free aqueous polymer dispersions is advantageous, which is characterized in that a protective colloid which contains essentially no ionic groups is first prepared by free-radical grafting of (a) essentially hydrophobic chains based on a or more ethylenically unsaturated monomers on (b) essentially saturated water-soluble or water-dispersible polymers in an aqueous medium essentially free of organic solvents in the presence of a customary graft initiator and then in the presence of this protective colloid essentially one or more radically polymerizable ethylenically unsaturated ones Monomers are emulsion polymerized in an aqueous medium substantially free of organic solvents in the presence of a free radical initiator.

REPLACEMENT LEAF The known grafting reaction of ethylenically unsaturated monomers and polymers with activated, graftable hydrogen bonds is described, for example, in "Houben-Weyl, Methods of Organic Chemistry", volume E20 (1987).

Details on emulsion polymerization can also be found in the relevant literature, for example "Houben-Weyl, Methods of Organic Chemistry", Volume E20, or HOELSCHER, "Dispersions of Synthetic High Polymers", Part I, Springer-Verlag 1969.

In the process according to the invention for the preparation of the polymer dispersions it is preferred to use 0.5 to 20% by weight of the ungrafted and particularly preferably from 1 to 10% by weight protective colloid precursor, in each case based on the total weight of the ethylenically unsaturated monomers required for the graft and emulsion polymerizations .

It is advisable to first prepare the protective colloid precursor by stirring for several hours in water at room temperature and then to activate it by adding part of the amount of graft initiator at the process temperature. The graft polymerization can then be carried out by metering in the ethylenically unsaturated monomers and the remaining amount of graft initiator.

The process according to the invention can advantageously be carried out in such a way that the protective colloid is produced by grafting and the sterically stabilized polymer dispersions by emulsion polymerization of the ethylenically unsaturated monomers in direct succession without prior isolation of the graft polymer in the same reaction mixture

REPLACEMENT LEAF become. A two-stage process is then unnecessary; Graft polymerization and emulsion polymerization can be carried out in one reaction vessel.

In a further advantageous embodiment, the preparation of the polymer dispersions can be carried out in a one-stage procedure in such a way that the grafting of the protective colloid precursor is carried out by means of the graft initiator until the monomer conversion has stagnated and immediately afterwards by adding an initiator for the customary polymerization changes the dispersion production by emulsion polymerization. As is known, the graft polymerization does not proceed until the complete conversion of the monomers; with polysaccharides as the graft base, it often stagnates - depending on the monomers - after only 25 to 30% conversion. To carry out the emulsion polymerization, these unreacted monomers can be left in the reaction mixture. However, they can also be removed from this prior to switching to emulsion polymerization, for example by distillation in vacuo. This will happen especially when the graft monomers and the monomer components of the emulsion polymer are not to be the same. In order to avoid the work involved in separating the monomers, it is therefore advantageous to prepare polymer dispersions in which the graft monomers can simultaneously be part of the emulsion polymer.

The ethylenically unsaturated monomers can be used alone or in a mixture in the process according to the invention. When using monomer mixtures, the various monomers can be introduced or metered side by side. You can also use the different monomers

REPLACEMENT LEAF Introduce the production process at different times, both for the grafting reaction and for the emulsion polymerization, as a result of which the properties of the resulting dispersions can be varied to a certain extent. For example, the respective polymerization can be started with a monomer M- or a monomer mixture consisting predominantly of M ₁ and ended with a monomer M_ or a mixture consisting predominantly of monomer M ~, the monomer ratio being able to be continuously shifted (so-called power feed).

The cheap graft initiator, its amount and the manner in which it is added depend in many cases on the graft base. Salts of polyvalent metals and / or peroxides are mostly used. Very suitable graft initiators are, for example, salts of tetravalent cerium.

Usual initiators for the emulsion polymerization are radical formers such as inorganic peroxides, for example hydrogen peroxide or peroxydisulfates, organic peroxides, for example t-butyl, cumyl or lauroyl peroxide, or azo compounds, for example azo-diisobutyronitrile, and can be used together with chain regulators, for example mercapto compounds, and other conventional polymerization aids are used.

Initiators and auxiliaries are used in the usual amounts.

The process according to the invention for the preparation of the aqueous, sterically stabilized polymer dispersions is preferably in the range from 40 to 100 ° C. and is particularly preferred

REPLACEMENT LEAF from 55 to 90 ° C, both in the graft polymerization section and in the emulsion polymerization section. Above the upper temperature limits, poor grafting efficiency is to be expected, the polymerization proceeds too quickly and problems can arise during process control. Below the preferred lower temperature limits, the polymerization process is delayed too much or the monomer conversion is no longer guaranteed. If, for certain reasons, a relatively low polymerization temperature is mandatory, a redox initiator system can be used in a known manner. It will also depend on the particular monomers to be polymerized which polymerization temperature is chosen; it should not be below the glass transition temperature of the resulting polymers.

It was further surprising that not only are stable dispersions obtained according to the invention, but that these stable dispersions actually do not have the shortcomings of dispersions of the prior art described at the outset, and are furthermore distinguished by other favorable performance properties.

The dispersions according to the invention prove to be stable with respect to strong electrolytes, for example salts of polyvalent cations. Addition of ferric chloride / calcium chloride did not lead to any precipitation. It was also found that the dispersions can also be mixed with the strongly alkaline water glass without the formation of precipitation. The processing of dispersions according to the invention together with, in particular, polar auxiliaries to be added, depending on the application, thus prepares

REPLACEMENT LEAF hardly any difficulties. Above all, the dispersions can also be pigmented.

The solids content, i.e. the proportion of non-volatile constituents in dispersions according to the invention is advantageously in the range from 40 to 60% by weight, based on the total weight of the respective dispersion. Towards higher proportions there are limits to the flowability of the dispersions. However, a proportion of up to 70% solids is quite possible, especially if the dispersions have a correspondingly favorable distribution of the particle diameters.

The viscosity of the dispersions according to the invention is in a low range which is favorable for further processing. It depends in part on the p "range of the dispersion medium, but in particular on the dispersion solids content, i.e. the proportion of non-volatile components. The standard specification for the preparation of dispersions in the context of the investigations according to the invention is based on a solids content of approx. 50% by weight and leads to acidic dispersions, with viscosities in a favorable low range of 18 to 100 mP-s being generally obtained also above 100 mP-s and up to 500 mP-s. - Dispersions according to the invention can therefore be used with conventional application techniques.

The average diameters of the individual particles of dispersions which were produced in the course of the investigations according to the invention are in the range from 250 to 2000 nm. These average particle diameters can easily be varied on the dispersion system according to the invention, if necessary, by appropriate polymerization technology. There

REPLACEMENT LEAF As is well known, the particle size and its distribution has a determining influence on a number of application properties, such as flow behavior, penetration into porous substrates, coalescence behavior and density, as well as smoothness or gloss of the resulting film surfaces, efforts will be made to determine the average particle size and its distribution in the to set one direction or another. For example, in order to obtain glossy, smooth film surfaces, dispersions with the smallest possible mean particle diameters and favorable distribution of larger and smaller particles will be used. The easy variability of particle size and size distribution in sterically stabilized dispersions according to the invention, which therefore makes it possible to provide “tailor-made” dispersions to a certain extent, depending on the technical application, can be illustrated in FIGS. 1 and 2. These relate to copolymer dispersions based on the monomer composition (parts by weight) 48 methyl methacrylate - 48 butyl acrylate - 1 methacrylamide - 1 methacrylic acid with guar as a protective colloid precursor according to the standard recipe, depending on the proportion by weight of guar (Fig. 1) or guar / cerium (IV) sulfate (Fig. 2) and the proportion of cerium (IV) sulfate in the template (Fig. 2).

It can be seen from these figures that if the proportion of graft initiator (Fig. 1; 1% by weight) is kept constant and the proportion of protective colloid precursor is very low, the mean particle diameters are initially relatively high and their distribution is very wide, then as the proportion increases but very small average diameters are obtained with an extremely narrow distribution and finally with a further increasing proportion (> 2% by weight) a trend towards bimodal distribution is evident. The biodiversity is particularly striking due to

REPLACEMENT LEAF 20th

a very narrow distribution for both particle sizes when the proportion of cerium (IV) sulfate is increased at the same time as the proportion of protective colloid precursor (Figures 2b). As can be seen from Fig. 2a and 2b, right curves, the distribution of the amount of graft initiator on the template and proportion of dosing has a significant influence on the size distribution and modality. It is therefore very surprising, according to the distribution curves in FIGS. 1 and 2, that under certain conditions there are sometimes very narrow distributions of the particle diameters, so that in practice one can speak of monodisperse systems. In general, polymer dispersions have more or less broadly dispersed particle diameters and the production of practically monodisperse dispersions according to the prior art was only successful in a few cases; and in these only with very special, simplified systems, in particular of homopolymers, mostly of styrene.

Films with a smooth surface can easily be produced from the sterically stabilized dispersions according to the invention. It is very advantageous and surprising that film formation and film drying (hardening) in many cases take place relatively quickly even at room temperature. Most of the time, a thorough drying takes place after just a few hours.

Lacquer films obtained from dispersions according to the invention essentially prove to be stable against the action of water for 24 hours (water test), in contrast to films from comparable non-sterically stabilized dispersions. Dispersions according to the invention are therefore suitable as the basis of lacquers or coatings, in particular those for outdoor use.

REPLACEMENT LEAF The fact that they can be processed even at room temperature makes them interesting for do-it-yourself and painter paints.

In those cases in which dispersions within the scope of the invention do not lead to sufficiently cured and therefore insufficiently resistant films at room temperature, improvements can be achieved even at a slightly elevated drying temperature, for example already at 50 ° C. Dispersions according to the invention can also be processed as a thermosetting system, for example together with capped polyisocyanates or melamine resins. correspond

^• Appropriate tests with melamine resins of the Cymel type (Cymel 325 and Cymel 327) led to increased pendulum hardness values (around 50 to 200 ° C) at curing temperatures above 80 ° C, in particular between 90 and 130 ° C, and a curing time of only 30 minutes %) and strength. Yellowing is occasionally observed above 100 ° C in films of melamine resin-free dispersions based on grafted cellulose; corresponding dispersions containing melamine resin do not show this yellowing. The dispersions applied with the melamine resins also led to coatings with excellent adhesion to plastic substrates, such as, for example, to polybutylene terephthalate.

It goes without saying that if the maximum requirements with regard to environmental friendliness and workplace hygiene are met at the same time, the requirements for very high quality lacquers cannot be met at the same time, for the advantages achieved in terms of coating quality, e.g. a certain compromise can be made with the visual impression

REPLACEMENT LEAF got to. On the other hand, appropriate measures familiar to the person skilled in the art can optimize the paint quality in the desired direction if a portable compromise in environmental friendliness and workplace hygiene below the maximum requirement justifies this. For example, certain varnish properties can be improved by adding small amounts of volatile organic solvents as film-forming aids within the scope of the invention.

Experimental part

Standard recipe for the production of aqueous polymer dispersions according to the invention.

Unless otherwise stated, the procedure is as follows:

10 g of protective colloid precursor are dispersed or dissolved in 400 g of distilled water under nitrogen in a 1 liter flask with stirrer, reflux condenser, nitrogen supply and metering device. If dispersions are present, the mixture is stirred at room temperature for several hours, for example up to 10 hours in the case of polysaccharides as a precursor. The mixture is then heated to 70 ° C., 1 g of cerium (IV) sulfate, dissolved in 70 g of water, is added and the mixture is stirred at 70 ° C. for 1 hour. Then 490 g of ethylenically unsaturated monomers from a metering device and simultaneously 4 g of Ce (IV) sulfate, dissolved in 30 g of water, from another metering device are metered in at 70 ° C. for 1 hour.

After a reaction time of 1 hour at 70 ° C., 5 g of ammonium peroxydisulfate are finally dissolved in

REPLACEMENT LEAF 20 g of water, metered in for 10 minutes. The flask contents are kept at 70 ° C for 1 hour and then cooled.

The solids content of the aqueous, sterically stabilized polymer dispersion obtained in this way must be 49.3% by weight with 100% conversion of the monomers.

Unless otherwise stated, guar flour (food quality) from Roth, Karlsruhe, and a mixture of the following compositions are used as protective colloidal precursor guar meal (food grade): 240 g of methyl methacrylate / 240 g of butyl acrylate / 5 g of methacrylamide / 5 g of methacrylate crylic acid.

Testing the aqueous polymer dispersions according to the invention:

Solids content / conversion:

To determine the monomer conversion, the proportion of non-volatile dispersion components was determined by drying the dispersion at 150 ° C. to constant weight and comparing this with the value calculated for 100% conversion.

Viscosity:

The dynamic viscosity of the polymer dispersions was determined at 20 ° C. in a rotary viscometer ("Viskotester VT" 180 from Haake).

Storage stability:

For this purpose, the dispersions were stored at room temperature or in a so-called rapid test at 50 ° C. and the service life after which the respective dispersion had noticeably coagulated was recorded, and the coagulate was no longer

REPLACEMENT LEAF let stir. In the rapid test, those dispersions were classified as outstandingly stable which had not settled after 30 days or were no longer stirrable.

Electrolyte stability:

25 ml of the dispersion to be tested were diluted to 100 ml and titrated with a saturated solution of iron (III) chloride and calcium chloride (weight ratio 1: 1). A polymer dispersion was assessed as being stable to electrolytes if the dispersion did not coagulate when 25 ml of saline solution was consumed.

Particle size:

The mean diameters of the dispersion particles were determined by measuring the turbidity.

The distribution curves for the particle diameters were determined by transmission electron microscopy (TEM-Phillips device) with an automatic image analysis system (Quantimet device), the particle preparations being solidified with osmium tetroxide and steamed with carbon.

Film formation / hardening:

In order to assess the film-forming properties and the hardening of the resulting coating films of dispersions according to the invention, these were applied to glass plates and deformed thereon with a deep-drawing spiral to give wet films 150 μm thick. The curing process both at room temperature and at 50 ° C. drying was assessed by measuring the film hardness after 4 hours, 1 day, 15 and 30 days.

REPLACEMENT LEAF The film formation was assessed qualitatively by the optical impression (smoothness and homogeneity of the film surface, transparency of the film).

The films from mixtures of dispersions according to the invention with melamine resin were baked in the standard tests at 100 and 120 ° C. for 30 minutes. In the standard tests, these mixtures consisted of 100 g of dispersion and 25 g of Cymel 325 or Cymel 327 (from Cyanamid).

Film hardness:

The hardness of the films on the glass plates was determined as the pendulum hardness according to Koenig (DIN 53157).

Water test:

To determine the water resistance of the films, a cotton ball soaked in tap water was placed on the film on the glass plate and covered with a watch glass. After a standing time of 24 hours at room temperature, the appearance of the film was assessed (non-water-resistant films tarnish white). Both 1 day at room temperature and 50 ° C. and films cured for a further 29 days at room temperature were assessed.

Experimental Examples 1 to 6 and Comparative Example

Stable aqueous polyperdispersions with the following commercially available colloid precursors were prepared according to the standard recipe given on page 22:

1. Guar (guar flour from Roth, Karlsruhe)

2. Water soluble starch

3. Gum arabic (commercially available)

REPLACEMENT LEAF 4. Olibanum (commercially available)

5. Dextran (commercially available)

6. Polyvinylpyrrolidone (type PVP-K15 from GAF)

490 g of a mixture of methyl methacrylate (49% by weight), butyl acrylate (49% by weight), methacrylamide (1% by weight) and methacrylic acid (1% by weight) were used as ethylenically unsaturated monomers.

The procedure for producing a - non-sterically stabilized - comparative dispersion was as follows: 4.0 g of Natrosol 250 LS (Hercules hydroxyethyl cellulose from the Hercules company as a protective colloid) were placed in the 1-1 flask equipped as described in the standard recipe, 12.0 g of Triton X 165 (nonionic emulsifier from Rohm & Haas) and 9.0 g of sodium lauryl sulfate dissolved and heated to 70 ° C. The following three mixtures were also produced:

1) monomer mixture as in experimental examples 1 to 6; additionally 4 g t-dodecyl mercaptan as chain regulator

2) 4.0 g ammonium peroxydisulfate in 60 ml water

3) 4.0 g sodium bisulfite in 60 ml water

In each case 10% of these 3 mixtures were added to the contents of the flask heated to 70 ° C. and reacted for 20 minutes (seed). The remaining 90% of the three mixtures were then metered simultaneously from separate metering devices into the flask at 70 ° C. over a period of 2 hours. The contents of the flask were then kept at 70 ° C. for a further 2 hours and then cooled.

REPLACEMENT LEAF The essential properties of the polymer dispersions thus obtained and the resulting coating films are summarized in Tables 1 and 1a.

In all cases, a high conversion of the ethylenically unsaturated monomers is achieved (> 99%). The dispersions have a pH in the acidic range and, despite the high solids content, are of a low viscosity suitable for further processing into paints. The stability of the dispersions at room temperature storage and the average diameter of the dispersion particles are relatively different depending on the protective colloid precursor used.

Electron microscope images of the sterically stabilized dispersions show relatively uniformly large particles which agglomerate only slightly. The distribution of particle sizes can be determined very easily on the basis of such recordings. In contrast, the particles of conventional, non-sterically stabilized dispersions tend to agglomerate in the production of electron microscopic images, so also in the case of the present comparative experiment, so that a determination of the average particle diameter and its distribution is practically impossible in this way.

In contrast to the non-sterically stabilized dispersion according to the comparative experiment, the sterically stabilized dispersions of experiments 1 to 6 prove to be stable with respect to electrolyte additives.

The values given in Table la for the pendulum hardness of paint films from the dispersions after 4 hours and 1 day

REPLACEMENT LEAF Drying at room temperature and 50 ° C. and a further 29 days drying only at room temperature show that extensive hardening takes place after only a few hours and that in most cases the hardness values achieved after a day no longer increase or only increase significantly. In most cases the hardness values at 50 ° C are higher than those at room temperature. The more favorable film formation with the 50 ° C. drying can also be recognized by the appearance of the resulting lacquer films: films dried at 50 ° C. are almost clear, while the films dried at room temperature mostly remain white. In contrast to lacquer films from the non-sterically stabilized dispersion (comparative experiment), those from sterically stabilized dispersions are predominantly resistant to the action of water for 24 hours (experiments 1,2,5 and 6).

REPLACEMENT LEAF Experimental examples 7 to 11

According to the standard recipe, stable polymer dispersions with 490 g of different monomer compositions (as indicated in Table 2) and 10 g of guar as a protective colloid precursor (2%, based on the weight of monomers + precursor) were prepared. Turnover and properties of the dispersions are shown ⁱⁿ Table 2. In the case of experiment 8a with vinyl acetate as a comonomer, the acidic dispersion was neutralized after the polymerization (pH 7.5) in order to counteract the acidic hydrolysis of the acetyl group. The dispersions of experiments 8a and 8b turned out to be very viscous. Their repetition - with the difference that the solids content was set to approx. 40% by weight instead of approx. 49% by weight - led (with almost 100% monomer conversion) to lower-viscosity dispersions: 8a 480 mPa-s; 8b 570 mPa-s.

All dispersions are stable against the addition of electrolytes. Lacquer films dried both at room temperature and at 50 ° C proved to be resistant to water in the 24-hour test.

Experimental examples 12 to 18

According to the standard recipe, polymer dispersions with different proportions were made with the monomer composition consisting of methyl methacrylate (49% by weight), butyl acrylate (49% by weight), methacrylamide (1% by weight) and methacrylic acid (1% by weight) on guar as a protective colloid precursor, as indicated in Table 3. With a proportion of 10% or more by weight of guar, the dispersions become very viscous. In order to use this high guar content, dispersions of

REPLACEMENT LEAF To obtain usable viscosity, the solids content of the dispersions had to be set lower, ie a correspondingly lower monomer / water ratio had to be assumed. For dispersion 17 (10% guar) the solids content is 42% by weight and for dispersion 18.15% guar) it is around 26% by weight.

The dispersions turned out to be stable, even in the electrolyte stability test. The development of the particle size distribution of the dispersions with increasing guar content, which is shown in FIG. 2, is striking: dispersions with less than 1% by weight guar have a broad particle size distribution. With 1% by weight and 1.5% by weight guar, very narrow distributions are then to be registered, which become increasingly broader with higher proportions and finally become bimodal from a proportion of 4% by weight guar. Dispersions with 10 to 15% by weight guar, on the other hand, are monomodal again and have relatively small and very uniform particle diameters, the uniformity being so obvious that automatic image analysis was dispensed with.

Experimental examples 19 to 27

With these experiments, the influence of the cerium IV sulfate content and the time of its addition in the polymerization process on the properties of the polymer dispersions was investigated. It turned out to be favorable to also increase the guar proportion with an increasing proportion of cerium IV sulfate. Test conditions and dispersion properties are shown in Table 4. Unless otherwise stated in the table, the standard recipe was used. The “presented” cerium IV sulfate is to be understood as the proportion which is added before the monomers are metered in

REPLACEMENT LEAF (20% by weight according to the standard recipe), and under "metered" cerium IV sulfate is the portion which is metered in simultaneously with the monomers (but from another metering device) (80% by weight according to the standard recipe).

A favorable property profile can be seen from the information in the table. Only in the case of a very small proportion of cerium IV sulfate (which is only presented) according to trials 19 and 20, although the monomer conversion is very high, relatively highly viscous dispersions are obtained which, when stored at 50 ° C., only last up to 13 days remain stable.

Dispersion stability against electrolyte addition and film stability against 24 hours exposure to water are good in all cases.

The influence of the graft initiator on the size distribution of the dispersion particles is very pronounced, as can be seen in Figure 2 for experiments 21 to 24 (increasing bimodality with increasing cerium IV sulfate / guar fraction or increasing fraction cerium IV sulfate in the template).

Experimental Examples 28 and 29

These tests relate to the preparation of polymer dispersions according to the standard recipe, but at temperatures 10 ° C. below (test 28) and 10 ° C. above (test 29) the standard temperature of 70 ° C. Dispersions with a property profile such as those produced at 70 ° C. are obtained. The polymerization at 60 ° C, however, leads to a conversion of only 88% of the monomers; however, sales can increase to 98.2%

REPLACEMENT LEAF are used if - in deviation from the standard recipe - 1.5% by weight ammonium peroxydisulfate (instead of 1% by weight) is used and polymerization is carried out for 3 hours (instead of 2 hours).

Experimental examples 30 to 33

These experiments relate to the preparation of stable polymer dispersions with variations in the metering of monomers in such a way that one of the two main monomers, butyl acrylate and methyl methacrylate, was metered in in excess at the start of metering and the other in excess at the end of metering or vice versa. The procedure according to the standard recipe was followed, except that only one of these main monomers is present in the usual metering device at the beginning of the monomer metering, while the other monomer is only added dropwise to this metering device at the same time and within the same metering period of 1 hour . The aim of this procedure was to form a graft polymer rich in butyl acrylate and main polymers rich in methyl methacrylate, or conversely a graft polymer rich in methyl methacrylate and main polymers rich in butyl acrylate.

These experiments are summarized in Table 5. In the evaluated basic properties of these polymer dispersions there were no noteworthy changes compared to the comparable standard tests (tests 21 and 23). The dispersions are stable to the addition of electrolytes and paint films produced therefrom are resistant to the action of water (water test).

Experimental examples 34 to 36

REPLACEMENT LEAF In these experiments, the polymer dispersions were prepared by initially forming a graft polymer as usual, but then polymerizing to form the main polymer while metering in the further monomers.

In the case of experiment 34, the procedure was such that only two thirds of the total monomer mixture were metered in for 1 hour in the preparation of the graft polymers according to the standard recipe (2% by weight guar, 2% by weight cerium IV sulfate) , and after 1 hour of post-reaction to the main polymerization with ammonium peroxydisulfate was switched over by metering for 1 hour - separately and simultaneously - the ammonium peroxydisulfate solution and the remaining third of the monomer mixture.

In the case of experiments 35 and 36, the standard recipe (2% by weight guar, 2% by weight cerium IV sulfate) was used as usual until the end of the after-reaction after the graft polymerization; but then the monomers not reacted in the graft polymerization were separated off by distillation. The resulting aqueous dispersion of the graft polymer with a solids content of 16% by weight was then separated after heating to 70 ° C. and, at the same time, a further monomer mixture and an aqueous ammonium peroxydisulfate solution were metered in. The amount of the monomer mixture was chosen so that at the end of the polymerization there was a dispersion with the usual solids content of 49% by weight. As usual, the proportion of ammonium peroxydisulfate was 1% by weight, based on the weight of the metered monomers. In the case of experiment 35, the monomer mixture contained 55% by weight of methyl methacrylate, 43% by weight of butyl acrylate, 1% by weight of methacrylamide and 1% by weight of methacrylic acid, and in the case

REPLACEMENT LEAF of experiment 36 27.5% by weight of methyl methacrylate, 43% by weight of butyl acrylate, 27.5% by weight of styrene, 1% by weight of methacrylamide and 1% by weight of methacrylic acid.

In the stable polymer dispersions 34 to 36 obtained in this way, there were no noteworthy changes in the basic properties assessed compared with comparable other polymer dispersions according to the invention. Their electrolyte stability and the resistance of corresponding paint films to the effects of water are good. A particularly narrow distribution of the dispersion particle diameters could be determined on the dispersion of experiment 34, so that in this case one can speak practically of a monodisperse system.

Experimental example 37

This example relates to the curing of polymer dispersions according to the invention in the presence of melamine resins. The dispersions of experiments 15, 19, 24, 30 and 33 and the melamine resins Cymel 325 and Cymel 327 (from Cyanamid) were used for this. 100 g of dispersion and 25 g of the melamine resin were mixed together. The paint films produced from this were cured at 100 ° C. for 30 minutes. The resulting film hardness values are shown in Table 6 and compared with the hardness values of melamine-free films dried at room temperature. For comparison, Table 6 also contains the hardness values at 100 ° C. without films hardened from melamine resin.

REPLACEMENT LEAF ω

>

N 03 r

>

] based on the weight of the ethylenically unsaturated monomers + precursor] coagulates after the first drops of the solution have been added

Table la: drying and water resistance of paint films from dispersions according to Table 1 upper numerical values: room temperature drying lower numerical values: 50 ° C - drying

(up to 1 day, then room temperature)

Test drying film resistance no. Hardness [see] against 24 h water exposure

4h ld 30d

REPLACEMENT LEAF Table 2: Experiments with various ethylenically unsaturated monomers 2% by weight guar as a protective colloid precursor

Experiment Mono erenzomposition conversion viscous particle storage stabili

8a> 30 +

8b> 30

8c 17 + 9> 30 + 10a> 30 +

10b> 30

Table 3: Experiments with increasing proportion of protective colloid precursor (guar) monomer composition: 49% MMA - 49% BA

1% MAA - 1% MAS

*) based on the weight of the monomers **) 42% solids ***) 26% solids

REPLACEMENT LEAF Table 4: Experiments with different proportions of graft initiator (Ccr-IV sulfate) and different distributions of the same on presentation and dosage

Monomer composition: 49% MMA - 49% BA - 1% MAA - 1% MAS

*) based on total weight of protective colloid precursor + unsaturated. Monomers based on total cerium IV sulfate

Table 5: Variations in the monomer dosage

Monomer composition: 49% MMA - 49% BA MAA - 1 MAS

Trial distribution of MMA and BA Cer-IV guar conversion viscous particle

No. sulfate percentage [%] diam.

Start of dosing Dosing proportion [%] [mPa •] [n] [% 1 *) *)

ispersion table, film hardness (see.) request which the r. Dispersion without melamine resin Cymel 325 Cymel 327 describes RT (ld) 100 ° C (30 min.) 100 ° C (30 min.) 100 ° C (30 min.)

Huh

(a) 2% guar / 2% cerium (TV) sulfate

H = frequency

_A bb.2: Dependence of particle diameter [µm] distribution of dispersions according to standard recipe depending on the weight fraction of protective colloid precursor

( _G uar) / Pfrop initiator (cerium (IV) sulfate), based on non-volatile dispersion constituents, or on the proportion of total cerium (IV) sulfate amount in the initial charge.

Claims

Sterically stabilized aqueous polymer dispersions Patent claims:

1. Sterically stabilized emulsifier-free aqueous dispersions of polymers based on free-radically polymerized ethylenically unsaturated monomers and a protective colloid, characterized in that

(1) the dispersions are essentially free of organic solvents,

(2) the protective colloid consists essentially of a substantially saturated water-soluble or water-dispersible polymer grafted free radically with essentially hydrophobic chains based on ethylenically unsaturated monomers and

(3) the protective colloid contains essentially no ionic groups.

REPLACEMENT SHEET . Dispersions according to claim 1, characterized in that the water-soluble or water-dispersible natural or synthetic polymers are those from the group of modified or unmodified polysaccharides or polymers made from ethylenically unsaturated monomers.

3. Dispersions according to claim 2, characterized in that the polysaccharide is a naturally occurring, unmodified polysaccharide.

4. Dispersions according to claims 2 or 3, characterized in that the polysaccharide is a poly-α-glucose, a polygalactose or a polymannose.

5. Dispersions according to claim 2, characterized in that the polymer of ethylenically unsaturated monomers is a polyvinyl compound and preferably polyvinylpyrrolidone and polyvinyl alcohol.

6. Dispersions according to one or more of claims 1 to 5, characterized in that the water-soluble or water-dispersible polymers forming the protective colloid precursor have a polymer weight of 10,000 to 5,000,000 and in particular of 50,000 to 500,000.

7. Dispersions according to one or more of claims 1 to 6, characterized in that the essentially hydrophobic ethylenically unsaturated monomers radically grafted onto the polymeric protective colloid precursor are selected from the group of the alkyl esters of acrylic acid and / or methacrylic acid, des

REPLACEMENT SHEET Benzyl methacrylate, the dialkyl ester of itaconic acid, maleic acid and/or fumaric acid, acrylonitrile and/or methacrylonitrile, styrene and/or styrene compounds substituted by alkyl groups with 1 to 4 carbon atoms or by a chlorine atom, the vinyl ester of aliphatic carboxylic acids 2 to 12 carbon atoms or mixtures of these monomers.

8. Dispersions according to claim 7, characterized in that the alcoholic component in the alkyl esters and dialkyl esters mentioned has 1 to 18 carbon atoms and preferably 1-8 carbon atoms.

9. Dispersions according to claim 7, characterized in that the substituted styrene compounds are vinyl toluene, t-butylstyrene and the vinyl esters are vinyl acetate or vinyl propionate.

10. Dispersions according to one or more of claims 1 to 9, characterized in that the average length of the grafted side chains in the protective colloid corresponds to 10 to 100 monomer units.

11. Dispersions according to one or more of claims 1 to 10, characterized in that the average number of grafted side chains is in the range from 50 to 1000 per protective colloid main chain.

12. Dispersions according to one or more of claims 1 to 11, characterized in that the proportion of protective colloid precursor is 0.5 to 20% by weight and preferably 1 to 10% by weight, based in each case

REPLACEMENT SHEET Total weight of the monomers in the side chains of the graft polymer and in the emulsion polymer.

13. Dispersions according to one or more of claims 1 to 12, characterized in that the radically polymerized ethylenically unsaturated monomers, which form the basis of the polymers in the aqueous dispersions, monomers from the group of alkyl esters of acrylic acid and / or methacrylic acid, the dialkyl esters of itaconic acid, maleic acid and/or fumaric acid, the acrylonitrile and/or methacrylonitrile, the styrene and/or the styrene compounds substituted by alkyl groups with 1 to 4 carbon atoms or by means of a chlorine atom, the vinyl esters of aliphatic carboxylic acids with 2 to 12 carbon atoms or mixtures of these monomers.

14. Dispersions according to claim 13, characterized in that the ethylenically unsaturated monomers are alkyl esters and dialkyl esters with 1 to 8 carbon atoms in the alcoholic component, vinyl toluene, t-butylstyrene, chlorostyrene, vinyl acetate, vinyl propionate and / or vinyl laurate.

15. Process for the production of sterically stabilized emulsifier-free aqueous polymer dispersions, characterized in that one or more radically polymerizable ethylenically unsaturated monomers are emulsion-polymerized in an aqueous medium essentially free of organic solvents in the presence of a protective colloid and a usual free radical-forming initiator, where the protective colloid essentially consists of a free radical with (a) im

REPLACEMENT SHEET Essential hydrophobic chains based on one or more ethylenically unsaturated monomers grafted (b) consists of essentially saturated water-soluble or water-dispersible polymers and essentially contains no ionic groups.

16. Process for the production of sterically stabilized emulsifier-free aqueous polymer dispersions, characterized in that a protective colloid containing essentially no ionic groups is first produced by free radical grafting of (a) essentially hydrophobic chains based on one or more ethylenically unsaturated monomers onto ( b) essentially saturated water-soluble or water-dispersible polymers in an aqueous medium essentially free of organic solvents in the presence of a conventional graft initiator and then in the presence of essentially this protective colloid one or more free-radically polymerizable ethylenically unsaturated monomers in an essentially of orga ¬ Niche solvent-free aqueous medium in the presence of an initiator that forms free radicals.

17. Process for the production of aqueous polymer dispersions according to claim 15 or 16, characterized in that 0.5 to 20% by weight and preferably 1 to 10% by weight of the ungrafted protective colloid precursor, based in each case Total weight of the monomers in the side chains of the graft polymers and in the emulsion polymer can be used.

REPLACEMENT SHEET

18. Process for the production of aqueous polymer dispersions according to claim 15 or 16, characterized in that the production of the protective colloid by grafting and the production of the sterically stabilized polymer dispersions by emulsion polymerization of the ethylenically unsaturated monomers in direct succession without prior isolation of the Graft polymers are carried out in the same reaction mixture.

19. The method according to claim 18, characterized in that the grafting of the protective colloid precursor is carried out using the grafting initiator until the monomer conversion stagnates and then switched directly to dispersion production by emulsion polymerization by adding an initiator for the usual polymerization.

20. A process for producing aqueous polymer dispersions according to one or more of claims 15 to 19, characterized in that both the graft polymerization to produce the protective colloid and the emulsion polymerization to produce the polymer dispersions are carried out at temperatures in the range of 40 to 100 ° C and preferably in the range from 55 to 90 ° C.

21. Use of aqueous polymer dispersions according to one or more of claims 1 to 20 for producing coatings.

REPLACEMENT SHEET