WO2004101462A1

WO2004101462A1 - Method for producing polymer powders

Info

Publication number: WO2004101462A1
Application number: PCT/EP2004/004821
Authority: WO
Inventors: Markus Koppers; Joachim Pakusch; Heinrich Sack; Matthias Kroner; Matthias KLÜGLEIN; Matthias Laubender
Original assignee: Basf Aktiengesellschaft
Priority date: 2003-05-19
Filing date: 2004-05-06
Publication date: 2004-11-25
Also published as: DE10322786A1

Abstract

The invention relates to a method for producing polymer powders by vaporizing the volatile constituents out of aqueous dispersions consisting of film-forming polymers P. The inventive method is characterized in that the aqueous polymer dispersion contains, before vaporizing the volatile constituents, drying auxiliary agents T that are added in a quantity ranging from 0.1 to 80 % by weight with regard to the polymer P of the dispersion. Polymers are used as drying auxiliary agents T that are constituted of repetitive units containing carboxyl groups and of at least 5 mol %, with regard to the total quantity of polymers, of repetitive units with hydrophobic side groups.

Description

Process for the preparation of polymer powders

description

The present invention relates to a method for producing polymer powders

Evaporation of the volatile constituents from aqueous dispersions of film-forming polymers P, which is characterized in that the aqueous polymer dispersion also has drying aids T before the evaporation of the volatile constituents, in an amount of 0.1 to 80% by weight, based on the polymer P of the dispersion are present, the drying aids used being T polymers which are composed of monomers containing carboxyl groups and at least 5 mol%, based on the total amount of the polymers, of monomers having hydrophobic side groups.

The present invention further relates to the polymer powders obtainable by this process, their use as binders, adhesives, and mineral binder building materials which contain such polymer powders.

Aqueous dispersions of film-forming polymers are widely used, for example as cobinders for mineral building materials or as binders, in particular for synthetic resin plasters or highly pigmented interior paints, adhesives or coating agents. However, it is often desirable not to use the aqueous polymer dispersion itself, but rather the polymer contained therein in powder form.

In order to obtain the film-forming polymer in powder form, the dispersion is subjected to a drying process in which the volatile constituents of the dispersion are evaporated using a suitable method, for example by means of spray drying or freeze drying. It should be noted that the polymer particles of the aqueous dispersion can irreversibly aggregate with one another and form secondary particles when the aqueous dispersion medium evaporates. The secondary particle formation leads to poorer redispersibility, usually accompanied by poorer application technology

Properties of the powder. In addition, it leads to the formation of deposits on the dryer walls and thus reduces the powder yield.

To avoid these disadvantages, DE-A 4021216 recommends, in the production of redispersible polymer powder by spray drying, in addition to a film-forming dispersion polymer, a completely or partially neutralized water-soluble copolymer of an olefinically unsaturated mono- or dicarboxylic acid and a C ₃ -C ₁₂ Alk-1-en or styrene to use. In order to prevent or at least reduce the irreversible secondary particle formation during powder production, drying aids are also used. These are often referred to as spraying aids, since spray drying particularly promotes the formation of irreversibly agglomerated secondary particles. This effect is more pronounced the lower the glass transition temperature (and thus the softening temperature or the

Minimum film-forming temperature) of the polymer particles, especially if it is below the drying temperature.

At the same time, drying aids generally reduce the formation of polymer coating adhering to the dryer wall and thus increase the powder yield.

The drying aids used frequently, and not least because of their low price, are the salts, preferably the alkali metal, alkaline earth metal or ammonium salts of condensation products of aromatic sulfonic acids with formaldehyde (arylsulfonic acid-formaldehyde condensation products).

DE-A-2445 813 describes a pulverulent polymer which can be redispersed in aqueous systems and which, as drying aid, contains 1 to 20% by weight of a water-soluble condensation product of aromatic hydrocarbons and formaldehyde containing sulfonic acid or sulfonate groups, for example phenolsulfonic acid or naphthalenesulfonic acid-formaldehyde condensates, contains.

WO 98/03577 discloses salts of naphthalenesulfonic acid-formaldehyde condensation products with a number-average molecular weight Mn below 1500 daltons, which have particularly good spray auxiliary properties.

Similarly, EP-A-407 889 describes the use of a water-soluble alkali or alkaline earth metal salt of a phenolsulfonic acid-formaldehyde condensation product as a spraying aid for the preparation of polymer powders redispersible in water.

WO 98/03576 also discloses salts of phenolsulfonic acid-formaldehyde condensation products which have a number-average molecular weight Mn below 1500 daltons and particularly good spray auxiliary properties.

However, the use of drying agents, in particular arylsulfonic acid-formaldehyde condensation products, has the disadvantage that the film formation of the powder particles in the redispersed state required for the application is adversely affected. Furthermore, DE-A 10040826 discloses a process for drying dispersions based on styrene-butadiene copolymers, in which spray drying is carried out in the presence of salts of oligomeric arylsulfonic acid-formaldehyde condensates as drying aids. The dispersions described therein contain at least 1.5% by weight of an anionic surface-active compound with a C ₆ -C ₃₂ alkyl group. The process described there is distinguished, inter alia, by good redispersibility and filming of the powders obtained. However, these powders are not completely neutral to some materials, such as cement, and are therefore not very suitable for some applications.

EP-A 1036101 also relates to a process for the preparation of emulsifier-free, protective colloid-stabilized copolymers based on vinyl aromatics and 1,3-dienes. DE-A 19853450 also discloses emulsifier-free dispersion powders based on copolymers of styrene and butadiene. The emulsifier-free, protective colloid-containing styrene-butadiene dispersions obtained in this way are, however, very coarse and therefore have high concentrations of the malodorous Diels-Alder product 4-phenylcyclohexene.

Usual spraying aids (drying aids) such as polyvinyl alcohol, naphthalenesulfonic acid-formaldehyde condensates, phenolsulfonic acid form after

Spray drying with acrylamide-free dispersions based on copolymers of styrene and butadiene under the usual conditions with subsequent filming often cracked films. Flawless filming of the redispersed dispersion powder is important for use in many systems, for example in mortar modification or painting. In addition, it is sometimes necessary to add soap to the dispersion to be dried before spray drying. For procedural reasons, however, there is a desire not to add soap when spray drying.

The object of the present invention was therefore to remedy the disadvantages described and to develop a process for producing polymer powders which is as simple as possible to carry out and leads to polymer powders which, inter alia, are as odorless and colorless as possible and show good redispersibility and filming without the need to add soap after the polymerization and before spray drying.

This object was surprisingly achieved by a process for the production of polymer powders, in which the volatile constituents are first evaporated from aqueous dispersions of film-forming polymers P, which is characterized in that the aqueous polymer dispersion also contains drying agents T before the volatile constituents are evaporated has, which are present in an amount of 0.1 to 80 wt .-%, based on the polymer P of the dispersion, T polymerizates being used as drying aids, which are composed of repeat units containing carboxyl groups and at least 5 mol%, based on the Total amount of the polymers, on repeating units with hydrophobic side groups.

Film-forming means that the polymer particles of the aqueous dispersion or the powder particles in an aqueous redisperse melt when the water evaporates (drying) above a temperature specific for them, the minimum film-forming temperature MFT, and form a coherent polymer film. Aqueous redispersate means an aqueous dispersion of the polymer powder.

The copolymers of carboxyl group-containing monomers used as drying aids T are, according to the process of the invention, in an amount of 0.1 to 80% by weight, in particular in an amount of 1 to 50% by weight, preferably in an amount of 2 to 30% by weight .-% and particularly preferably in an amount of 5 to 20 wt .-%, based on the polymer of the dispersion.

It is advisable to use, as drying aids, in particular those polymers made from monomers containing carboxyl groups which have a molar mass (weight average) of 500 to 100000 g / mol, in particular 500 to 50,000 g / mol and particularly preferably 1000 to 30,000 g / mol, and which contain at least 10% by weight, based on the total amount of the polymers, of hydrophobic groups in the polymer chains.

Suitable drying aids T are hydrophobically modified polyelectrolytes

(a) 95-50 mol% of units of the formula (I)

etall or NH,

and (b) 5-50 mol% of units of the formula (II)

nyl

or NH ₄

and

(c) 0-30 mol% of other units obtained by radical polymerization of other monomers,

are set up.

CrC ₅ alkyl means a methyl, ethyl, propyl, i-propyl, n-butyl, i-butyl, t-butyl or a pentyl radical. Alkali metals are taken to mean Li, Na, K, Rb or Cs, alkaline earth metals can be Ca, Mg, Sr, Ba or Rb.

Examples of suitable drying aids include copolymers of olefinically unsaturated mono- and dicarboxylic acids or their anhydrides or mixtures of these monomers (monomers a) with copolymerized C ₂ -C ₀ -alk-1-enes (monomers b) and optionally further free-radically polymerizable monomers ( Monomers c).

It is recommended that the proportion of the monomers a in the copolymers to 30 to 95% by weight, in particular 50 to 90% by weight, that of the monomers b to 5 to 70% by weight, in particular 10 to 50 % By weight and that of the monomers c to 0 to 50% by weight.

Preferred monomers a are olefinically unsaturated C ₃ to C ₂ mono- and dicarboxylic acids or their anhydrides, the acrylic acid, methacrylic acid, maleic acid, fumaric acid and Itaconic acid and maleic anhydride are particularly preferred. Mixtures of several monomers a can also be used.

Preferred monomers b which carry hydrophobic groups are, in particular, C ₃ -C ₂₀ -alk-1-enes such as, for example, propylene, but-1-ene, pent-1-ene, hex-1-ene, hept-1 - s, oct-1-s, and styrene, isobutylene or diisobutylene, with propylene, isobutylene and diisobutylene being preferred. Of course, several different monomers b can also be used.

Suitable monomers c include Radically polymerizable monomers such as acrylonitrile, methacrylonitrile and esters or amides of olefinically unsaturated mono- and dicarboxylic acids. It is also possible to use several of these monomers c.

The drying aids T described include: can be obtained by customary polymerization processes, such as, for example, in EP 467103 or DE 19949591.

As drying assistant T is further homo- or copolymers are of hydrophobic substances with partial esters of olefinically unsaturated mono- or dicarboxylic acids, in particular homo- or copolymers of C ₃ - to C ₁₂ mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, maleic acid, fumaric acid, or of itaconic acid. Such copolymers preferably contain 50 to 99% by weight, in particular 55 to 95% by weight, of acrylic acid.

Partially esterified means a degree of esterification of the carboxyl groups of at least 5 mol%, in particular at least 10 mol%, and of at most 50 mol%, in particular of at most 40 mol%. Suitable hydrophobic substances for this are those that can form a covalent bond with carboxyl groups. Examples include fatty alcohols or alkylamines as well as ionic and non-ionic emulsifiers, the hydrophilic part of which is terminated by an NH ₂ or OH group. For this purpose, particularly preferred emulsifiers are ethoxylated or propoxylated fatty alcohols or alkylamines such as, for example, ethoxylated oleylamines, which are sold by BASF under the trade name Uniperoi ^® .

Suitable polymers for the process according to the invention and the polymer powder likewise according to the invention are essentially all film-forming polymers which form aqueous dispersions or can be prepared as an aqueous dispersion. These are usually polymers which are composed of ethylenically unsaturated monomers, for example from: (a) 80 to 100% by weight of at least one monomer which is selected from vinyl aromatic compounds, esters of α, β-monoethylenically unsaturated C ₃ -C ₆ carboxylic acids and d-C ₂ alkanols, preferably C ₈ -C ₈ Alkanols, vinyl and allyl esters of CrG ^ carboxylic acids and conjugated C -C ₁₀ diolefins, and

(b) 0 to 20% by weight of at least one other monomer which has at least one ethylenically unsaturated group.

All quantities for monomers are based on 100% by weight, i.e. based on the total amount of the monomers to be polymerized.

Examples of vinyl aromatic compounds are styrene, a-methylstyrene, -CC ₄ -alkylstyrenes such as o-vinyltoluene and tert-butylstyrene.

The esters of α, β-monoethylenically unsaturated carboxylic acids are, in particular, esters of acrylic acid and methacrylic acid. Examples of such esters are methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-decyl (meth) acrylate or dodecyl (meth) acrylate.

Usable vinyl and allyl esters are vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate and the corresponding allyl esters.

Suitable conjugated C ₄ -C ₁₀ diolefins include butadiene and isoprene.

Examples of the monomers (b) are:

ethylenically unsaturated monomers with acid groups such as mono- and dicarboxylic acids with 3 to 8 carbon atoms such as acrylic acid, methacrylic acid, crotonic acid, acrylamidoglycolic acid, vinyl acetic acid, maleic acid, itaconic acid and the half esters of maleic acid with C | -C ₄ -

Alkanols, ethylenically unsaturated sulfonic acids such as vinylsulfonic acid, allylsulfonic acid, styrene sulfonic acid, 2-acrylamidomethylpropanesulfonic acid, and ethylenically unsaturated phosphonic acids, e.g. B. vinylphosphonic acid, allylphosphonic acid, styrenephosphonic acid and 2-acrylamido-2-methylpropanephosphonic acid and their water-soluble salts, for example their alkali metal salts, preferably acrylic acid and methacrylic acid.

Such monomers can be present in the polymers P in an amount of up to 10% by weight, for example 0.1 to 10% by weight, preferably 0.1 to 4% by weight; Amides of ethylenically unsaturated carboxylic acids, such as acrylamide and methacrylamide, and the N-alkylolamides, preferably the N-methylolamides of ethylenically unsaturated carboxylic acids, such as N-methylolacrylamide and N-methylolmethacrylamide. Such monomers can be present in the polymers P in an amount of up to 10% by weight, for example 0.1 to 10% by weight, preferably 0.1 to 4% by weight;

Hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, especially hydroxyethyl and hydroxypropyl esters, e.g. B. hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. Such monomers can be present in the polymers P in an amount of up to 10% by weight, for example 0.1 to 10% by weight, preferably 0.5 to 6% by weight

Acrylonitrile and methacrylonitrile. Such monomers can be contained in the polymers P in an amount of up to 10% by weight, for example 0.5 to 10% by weight.

Reactive monomers: reactive monomers include those that have a reactive functionality suitable for crosslinking. In addition to the aforementioned ethylenically unsaturated carboxylic acids, their N-alkylolamides and hydroxyalkyl esters, these include monomers which have a carbonyl group or an epoxy group, for example N-diacetone acrylamide, N-diacetone methacrylamide,

Acetylacetoxyethyl acrylate and acetylacetoxyethyl methacrylate, glycidyl acrylate and glycidyl methacrylate. Such monomers can be contained in the polymers P in an amount of up to 10% by weight, for example 0.5 to 10% by weight

- and crosslinking monomers. The crosslinking monomers include those which have at least two non-conjugated ethylenically unsaturated bonds, e.g. B. the di- and triacrylates or methacrylates of di- and trifunctional alcohols, for. B. ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, trimethylolpropane triacrylate and tripropylene glycol diacrylate. Such monomers can in the polymers P in one

Amount of up to 2% by weight, preferably not more than 1% by weight, for example 0.01 to 2% by weight, preferably 0.01 to 1% by weight, may be included. In a preferred embodiment, the polymers P contain no crosslinking monomer copolymerized.

The process according to the invention is preferably suitable for the production of polymer powders based on styrene-butadiene copolymers. In this context, the term copolymer is not to be understood as restrictive and also includes those polymers that in addition to styrene and butadiene also contain other ethylenically unsaturated monomers in copolymerized form. Styrene-butadiene copolymers are usually made up of:

10 to 90% by weight, preferably 20 to 80% by weight, in particular 40 to 75% by weight, of styrene and, if appropriate, one or more, different vinylaromatic

monomers

10 to 90% by weight, preferably 20 to 80% by weight, in particular 25 to 60% by weight 1,3-butadiene, optionally in a mixture with another conjugated diolefin such as isoprene and optionally

up to 20% by weight, preferably up to 10% by weight, e.g. 0.1 to 20% by weight, preferably 0.1 to 10% by weight, of one or more of the aforementioned monomers (b).

The weight ratio of vinyl aromatic monomers to butadiene is generally in the range from 1: 9 to 9: 1, in particular in the range from 4: 1 to 1: 4 and very particularly preferably in the range from 3: 1 to 1: 1.

In a preferred embodiment of the present invention, the polymer P is composed of:

20 to 80 wt .-%, in particular 40 to 75 wt .-% styrene

20 to 80 wt .-%, in particular 25 to 60 wt .-% butadiene, and optionally

0.1 to 10% by weight, preferably 0.1 to 5% by weight, of monomers containing carboxyl groups, in particular acrylic acid, methacrylic acid and / or itaconic acid.

The process according to the invention is particularly suitable for the production of polymer powders in which the polymer in the dispersion does not exceed a glass transition temperature (DSC, midpoint temperature, ASTM D 3418-82) of 65 ° C., in particular 50 ° C., particularly preferably 30 ° C. In general, the glass transition temperature of the polymers is at least -60 ° C, preferably at least -40 ° C and in particular at least -20 ° C. The glass transition temperature of a polymer approximately corresponds to or is slightly above the minimum film-forming temperature.

It is often helpful to estimate the glass transition temperature Tg of the dispersed polymer. After Fox (TG Fox, Bull. Am. Phys. Soc. (Ser. II) 1, 123 [1956] and Ullmanns Encyclopedia of Technical Chemistry, Weinheim (1980), pp. 17, 18) applies to the glass transition temperature of copolymers with large molar masses in good nutrition

where X ¹ , X ² , ..., X "the mass fractions of the monomers 1, 2, ..., n and T _g \ T _g ² , .... T _g ⁿ the glass transition temperatures of each of only one of the monomers 1, 2, ..., n mean polymers in degrees Kelvin, the latter being, for example, from Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, Vol. A 21 (1992) p. 169 or from J. Brandrup, EH Immergut, Polymer Handbook 3 ^rd ed., J. Wiley, New York 1989 known.

Preferred polymer dispersions are also those in which the weight-average diameter d _{w of} the dispersed polymer particles is> 100 nm. The weight-average diameter d _w is usually <2000 nm.

The d _w value of the particle size is, as usual, defined as the weight-average particle size, as determined using an analytical ultracentrifuge according to the method of W. Scholtan and H. Lange, Kolloid-Z. and Z.-Polymer 250 (1972) pages 782 to 796. The ultracentrifuge measurement provides the integral mass distribution of the particle diameter of a sample. From this it can be seen what percentage by weight of the particles have a diameter equal to or less than a certain size.

The preparation of the polymer dispersions to be dried is known and is generally carried out in the case of polymers which are composed of ethylenically unsaturated monomers by means of a free-radical aqueous emulsion polymerization, i.e. the monomers are polymerized in an aqueous emulsion in the presence of surface-active substances and at least one radical initiator.

Free radical initiators (polymerization initiators) are all those compounds which are capable of triggering a free-radical, aqueous emulsion polymerization. These include both organic and inorganic peroxides and hydroperoxides as well as azo compounds. Also suitable are redox initiator systems which generally contain a peroxide compound and a reducing agent, for example ascorbic acid, hydroxymethanesulfinic acid, bisulfite adduct with acetone, sodium sulfite or sodium sulfite, and / or a transition metal ion which can change its valency, for example in the form of water-soluble salts such as iron -, vanadium or copper salts and water-soluble complexes thereof. Preferred initiator systems are the peroxides and hydroperoxides such as Hydrogen peroxide, tert-butyl hydroperoxide, and isopropyl hydroperoxide. Preferred initiators are also the salts of peroxidic sulfuric acid, especially their alkali metal salts (e.g. potassium and sodium salts) and / or their ammonium salts. The radical initiator is usually used in an amount of 0.1 to 3% by weight, based on the monomers to be polymerized.

Suitable surface-active substances are both protective colloids, ie water-soluble polymers with a molecular weight (number average) M _n > 2000, and also anionic or neutral surface-active compounds (emulsifiers) which, in contrast to the protective colloids, generally have a molecular weight Mn <2000 and in particular <1000. The surface-active substances are usually used in amounts of up to 10% by weight, preferably 0.1 to 5% by weight, based on the monomers to be polymerized, anionic emulsifiers (compounds AO) generally not more than 1% by weight .-%, for example 0.1 to 1% by weight of the monomers to be polymerized.

Suitable protective colloids are polyvinyl alcohols, starch and cellulose derivatives, polyacrylic acids, copolymers of acrylic acid and methacrylic acid with hydrophobic monomers and / or with hydroxyl group-containing monomers, polyacrylamide or vinylpyrrolidone-containing polymers.

Suitable anionic emulsifiers include salts of such compounds which have at least one C ₆ -C ₃₂ alkyl group, in particular a C ₈ -C ₂₂ alkyl group and a functionality suitable for salt formation with a base, for example a carboxyl, sulfonyl, phosphonyl, phosphate - Or have a sulfate group, preferably a sulfate or sulfonate group. Preferred salts have alkali metal, alkaline earth metal or ammonium ions as counterions and in particular sodium, potassium and calcium ions. Such compounds are known, inter alia, from Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 192-208.

Examples of suitable anionic emulsifiers are salts of alkyl sulfates which are derived from linear or branched alcohols, for example fatty or oxo alcohols (alkyl radical: C ₈ -C ₃₂ ), from sulfuric acid semiesters of ethoxylated alkanols, which are derived from linear or branched alcohols, for example fatty or Oxoalcohols are derived (EO grade: 2 to 50, alkyl radical: C ₈ to C ₃₂ ), from sulfuric acid semiesters of ethoxylated alkylphenols with preferably linear alkyl radicals (EO degree: 2 to 50, alkyl radical: C ₆ -C ₂₂ ), from alkyl sulfonic acids ( Alkyl radical: C ₈ -C ₃₂ ), of dialkyl esters of sulfosuccinic acid (alkyl radical: C ₆ to C ₃₂ ) and of alkylarylsulfonic acids with a preferably linear alkyl radical (alkyl radical: C ₆ to C ₃₂ ). The salts are also suitable anionic emulsifiers the di-C ₆ -C ₃₂ alkyl derivatives of bis (phenylsulfonyl) ether, and technical mixtures thereof, for example as DOWFAX ^® 2A1 from Dow Chemical Co. are commercially available.

Preferred anionic emulsifiers are also the compounds of the general formula III,

wherein

R ^{1 represents} a C ₆ -C ₃₂ alkyl and preferably a C _ß -C ^ alkyl group,

R ^{2 represents} hydrogen, CrC-alkyl, a fused benzene ring which is optionally substituted with dC ₄ -alkyl, or a phenoxy radical which optionally has a C ₆ -C ₃₂ -alkyl group and / or a sulfonate group, and

X is a cation equivalent, and is preferably an alkali metal cation, in particular a sodium or potassium ion, an equivalent of an alkaline earth metal cation, in particular 1/2 Ca ²⁺ or an ammonium ion.

R ² in formula III is particularly preferably hydrogen. R ¹ is particularly preferably bonded para to the sulfonate group.

In addition to the anionic emulsifiers mentioned, the polymer dispersion used in the process according to the invention can also contain nonionic surface-active compounds (nonionic emulsifiers). Preferred nonionic emulsifiers are araliphatic emulsifiers, for example ethoxylated mono-, di- and trialkylphenols (EO degree: 3 to 50, alkyl radical: C ₆ -C ₃₂ ), or aliphatic emulsifiers based on alkyl-substituted aromatics, for example ethoxylates of long-chain alcohols, for example from oxo - or fatty alcohols (EO grade: 3 to 50, alkyl radical: C ₈ -C ₃₂ ). These emulsifiers can be present in the polymer dispersion in amounts of up to 10% by weight, preferably up to 4% by weight and in particular up to 2% by weight, for example 0.1 to 10, preferably 0.1 to 4% by weight and in particular 0.2 to 2 wt .-% may be included.

The surface-active substances used can be added to the polymer dispersion to be dried during the drying process or, preferably, beforehand. It it is advisable to use the surface-active substances already during the preparation of the aqueous polymer dispersion.

The polymers of carboxyl group-containing monomers used according to the invention as drying aids T can be used both during the actual process

Drying process, as well as previously added to the aqueous polymer dispersion. The drying aids are preferably added to the drying process before the drying process, but after the aqueous polymer dispersion has been prepared. The addition of the polymers from monomers containing carboxyl groups to the aqueous polymer dispersion can also be carried out in portions at certain times after the end of the preparation of the aqueous polymer dispersion.

To set the desired molecular weight, small amounts, e.g. 0.01 to 2% by weight, based on the monomers to be polymerized, regulating substances are also used. Suitable controllers are e.g. Connections that a

Have thiol group and or a silane group (e.g. t-dodecyl, n-dodecyl mercaptan or mercaptopropyltrimethoxysilane), allyl alcohols or aldehydes such as formaldehyde, acetaldehyde and the like.

The emulsion polymerization can be carried out either continuously or according to the batch procedure, preferably according to a semi-continuous process. The monomers to be polymerized can be fed continuously to the polymerization batch, including step or gradient procedures. For this purpose, the monomers can be fed to the polymerization both as a monomer mixture and as an aqueous monomer emulsion.

In addition to the seed-free production method, the emulsion polymerization can be carried out by the seed latex process or in the presence of seed latex prepared in situ to set a defined polymer particle size. Methods for this are known and can be found in the prior art (see EP-B 40419 and “Cyclopedia of Polymer Science and Technology ', vol. 5, John Wiley & Sons Inc., New York 1966, p. 847).

In a preferred embodiment of the present invention, the polymerization is carried out in the presence of 0.01 to 3% by weight and in particular 0.05 to 1.5% by weight of a seed latex (solids content of the seed latex, based on the total amount of monomer), preferably with initially introduced Seed latex (master seed) carried out. The latex generally has a weight-average particle size of 10 to 400 nm, preferably 20 to 120 nm and in particular 20 to 50 nm. Its constituent monomers are, for example, styrene, Methyl methacrylate, n-butyl acrylate and mixtures thereof, the seed latex to a lesser extent also ethylenically unsaturated carboxylic acids, e.g. B. acrylic acid and / or methacrylic acid and / or their amides, preferably less than 10 wt .-%, based on the total weight of the polymer particles in the seed latex, may be copolymerized.

In general, polymerization temperatures between room temperature and 120 ° C, preferably at temperatures of 40 to 110 ° C and particularly preferably between 50 and 100 ° C at a pressure in the range of 1 to 10 bar.

Following the actual polymerization reaction, it may be necessary to make the aqueous polymer dispersions according to the invention largely free from odorants, such as residual monomers and other organic volatile constituents. This can be achieved physically in a manner known per se by removal by distillation (in particular by steam distillation) or by stripping with an inert gas. The lowering of the residual monomers can continue chemically through free radicals

Postpolymerization, in particular under the action of redox initiator systems, such as those described for. B. are listed in DE-A 4435423, DE-A 44 19518 and DE-A 4435422. The postpolymerization is preferably carried out using a redox initiator system composed of at least one organic peroxide and one organic sulfite.

In this way, polymer dispersions with polymer contents of up to 80% by weight, based on the total weight of the dispersion, are accessible. As a rule, the solids content of the polymer dispersions prepared in this way will be in the range from 40 to 60% by weight. The polymer dispersions thus obtainable can then, if necessary, be adjusted to the solids content desired for drying by dilution with a suitable solvent, for example with water or a water-emulsifier mixture and / or by adding an aqueous solution of the drying aid.

The solids content of the polymer dispersion to be dried, which is already the

Containing drying aids is usually in the range of 10 to 60 wt .-%, preferably in the range of 20 to 55 wt .-% (each calculated as polymer + drying aid, based on the total weight of the dispersion).

The volatile constituents are evaporated from the aqueous polymer dispersion (hereinafter also referred to as drying) in a conventional manner, for example by freeze drying or preferably by spray drying. In spray drying, the polymer dispersions to be dried are dried in the presence of the drying aid in a drying tower through which a stream of warm air is passed. The temperature of the warm air stream is generally 100 to 200 ° C., preferably 110 to 170 ° C. at the entrance to the drying tower, and approximately 30 to 100 ° C., preferably 50 to 80 ° C. at the tower exit. The polymer dispersion to be dried can be introduced into the hot air flow or preferably in parallel into the warm air flow. It can be added via single or multi-component nozzles or via a rotating disc. The polymer powders are separated in a conventional manner, for example using cyclones or filter separators.

In principle, the polymers of monomers containing carboxyl groups used as drying agent T can be added during the drying process in the form of solutions, for example as aqueous or aqueous-alcoholic solutions, to the polymer dispersion to be dried. The drying aid is preferably added to the polymer dispersion before drying. The drying agent can be used both as a solid or preferably as a solution, e.g. B. as an aqueous-alcoholic solution or in particular as an aqueous solution to the dispersion.

Furthermore, an anticaking agent (anti-caking agent) can be added to the polymer dispersion to be dried during the drying process. This is a fine-particle inorganic oxide, for example a fine-particle silica or a fine-particle silicate, e.g. B. talc. The finely divided inorganic oxide preferably has an average particle size in the range from 0.01 to 0.5 mm. Particularly preferred is finely divided silica with an average particle size in the range from 0.01 to 0.5 mm, which can be both hydrophilic and hydrophobic. Mixtures of hydrophilic and hydrophobized anti-caking agents are particularly preferably used. The anti-caking agent can be metered in before or during the drying of the polymer dispersion. In another embodiment, the anti-caking agent is added to the polymer powder in a mixing device suitable for solids, for example a vibrator, wheelchair screw mixer or the like.

If desired, the anti-caking agent is used in an amount of 0.5 to 15% by weight and preferably in an amount of 2 to 12% by weight, based on the polymer powder (or on the total amount of polymer P + drying aid in the aqueous polymer dispersion).

The polymer powders obtained by the process according to the invention are also the subject of the present invention. In the presence of water stand out aqueous Redispergate of the polymer powder, among other things, by an improved film-forming ability. Surprisingly, the method according to the invention also leads to better results in spray drying, for example to an increased powder yield and to a reduced deposit formation. Surprisingly, other application properties are not adversely affected.

The polymer powders obtained by the process according to the invention comprise:

i at least one film-forming polymer P,

ii 0.1 to 80% by weight, based on the polymer P, polymers of monomers containing carboxyl groups which contain at least 5% by weight, based on the total amount of the polymers, of hydrophobic groups in the polymer chains as drying aids T,

iii optionally surface-active compounds in an amount of up to 10% by weight, based on the polymer P, and

iv optionally fillers, pigments, anticaking agents and / or customary auxiliaries, e.g. State of the art drying aids, biocides and / or defoamers.

The polymer powders according to the invention are suitable as cobinders in mineral binders and ready-to-use binders, as binders in paints, varnishes, adhesives, coating and sealants, construction adhesives, e.g. Floor adhesive and especially tile adhesive, as well as in synthetic resin plasters.

The polymer powders obtainable according to the invention are particularly suitable as cobinders in mineral binding building materials or in ready-to-use preparations of these building materials, and in building adhesives. These are also the subject of the present invention.

Mineral binder building materials or their preparations are understood to mean compositions which contain at least one mineral binder such as lime, gypsum, clay and / or cement and, if appropriate, mineral additives. The ready-to-use preparation is converted into the actual building material preparation by stirring with water, which, if left to its own devices, solidifies in stone or in air or under water, possibly under the influence of elevated temperature. In addition to the Mineral supplements also contain mineral building material preparations, such as conventional aids. B. Depending on the application, thickeners or plasticizers and defoamers.

Preferred mineral binders contain 70 to 100% by weight of cement and 0 to 30% by weight of gypsum. In particular, cement is the sole mineral binder. The effect according to the invention is essentially independent of the type of cement. Depending on the project, blast furnace cement, oil shale cement, Portland cement, hydrophobized Portland cement, quick cement, swelling cement or alumina cement can be used, with the use of Portland cement proving to be particularly favorable.

The dry compositions of mineral binder building materials typically contain, based on the amount of mineral binder, 0.1 to 20% by weight, in particular 0.5 to 10% by weight, of modifying polymer powder. The weight fraction of polymer to mineral binder is usually in the range from 1: 100 to 1: 1.

To improve their processing properties, cellulose derivatives and microsilica are often added to the mineral binders. The former usually have a thickening effect, and the latter normally form thixotropic agents which additionally reduce the flowability of the aqueous mortar before it solidifies in the applied retirement. By adding defoamers (in terms of "dry mortar" preferably in

Powder form) in the solidified state, a practical air pore content (5 to 20 vol .-%) of the solidified cementitious mortar can be achieved.

Sand, e.g. Quartz sand, as well as fillers such as calcium carbonate and pigments such as titanium dioxide or iron oxide, natural and synthetic fibers usually form the other additives.

Construction adhesives include e.g. B. Floor adhesive and tile adhesive. They contain as an adhesive component at least one polymer powder according to the invention and, depending on the type of formulation, plasticizers, fillers, dispersing aids, biocides and, if appropriate, water, defoamers, thickeners, thioxotropic agents and other additives. In a preferred embodiment, they also contain a mineral binder, e.g. B. cement. Such preparations are used in particular as tile adhesives. Due to the mineral binder, they are also among the mineral binders.

Typical mineral binders and other construction adhesives such as tile adhesives, especially as mineral binders dry preparations, (based on the total weight of the solids contained in them): 10 to 60, preferably 15 to 50% by weight of mineral binder (preferably exclusively cement, in particular Portland cement)

0.1 to 20 frequently 0.2 to 15% by weight, in particular 0.5 to 10% by weight, especially 2 to 8% by weight, of polymer powder according to the invention,

up to 25% by weight of conventional auxiliaries, for example defoamers, thickeners, plasticizers and thixotropic agents, and as a residual amount 30 to 80% by weight of additives, for example sand, fillers (for example CaC0 ₃ ), pigments (for example Ti0 ₂ ) natural and / or synthetic fibers. Defoamers are generally used in an amount of 0.1 to 2% by weight, thixotropic agents to 2% by weight, plasticizers to 1% by weight.

Typical embodiments of mineral binders are cementitious repair or reinforcement mortar. Common reinforcing mortars have natural or synthetic fibers made of materials such as e.g. Dralon (length e.g. 1 to 10 mm, length-related mass e.g. 3 to 10 dtex) in an amount of up to 10% by weight. H. Reul gives an overview of auxiliaries and supplements in "Handbuch der Bauchemie, Verlag für chemischen Industrie, H. Zielkowsky KG, Augsburg, 1991.

A further preferred embodiment of mineral binder building material preparations is tile adhesive. Typical tile adhesives contain as a dry preparation, in addition to the polymer powder, which, based on 100% by weight of dry preparation, generally makes up 0.5 to 10% by weight, in particular 2 to 8% by weight, of 15 to 50% by weight of mineral binder , in particular cement, 30 to 80% by weight of the usual additives, in particular quartz sand, e.g. B. with a sieve line of 0.063-0.4 mm, and / or calcium carbonate, and conventional auxiliaries such as thickeners, defoamers, biocides, dispersing aids, plasticizers (plasticizers), film-forming aids, etc. in an amount of 0.1 to 25% by weight %.

The process according to the invention for the production of polymer powders can be carried out industrially without great effort, resulting in polymer powders which, inter alia, are only colored white and are odorless and show good redispersibility and filming, without the addition of soap being necessary. Examples

I feed materials:

i Polymer dispersion D1: aqueous styrene-butadiene dispersion containing 50% by weight

Polymer with a glass transition temperature T _g of 4 ° C. which contains 52.3% by weight of styrene, 43.2% by weight of butadiene and 4.5% by weight of acrylic acid and which contains 0.5% by weight, based on the polymer of a nonionic emulsifier (C ₁₂ alkanol ethoxylate with a degree of ethoxylation of 2 to 3) is stabilized.

Polymer dispersion D2: A mixture of

150 g water

5.6 g of a 20% by weight aqueous solution of an ethoxylated p-isooctylphenol (EO grade 25),

0.48 g of a 35% by weight aqueous solution of a sodium salt of a sulfated and ethoxylated p-isooctylphenol (EO grade 25),

3.9 g of a 10% by weight aqueous formic acid solution,

1.7 g of sodium hydrogen carbonate and 3.4 g of a 20% by weight aqueous polyacrylamide solution

was heated to 90 ° C. 742.8 g of an aqueous mixture were then added to this mixture at the same time and while maintaining the internal temperature at 90 ° C. in 2 h

Monomer emulsion consisting of

403.2 g of n-butyl acrylate,

140.0 g styrene,

11.2 g acrylamide,

5.6 g methacrylamide, 8.4 g of a 20% by weight aqueous solution of an ethoxylated p-isooctylphenol (EO-

Grade 25),

11.5 g of a 35% by weight aqueous solution of a sodium salt of a sulfated and ethoxylated p-isooctylphenol (EO grade 25) and

162.9 water

and in 2.5 h a solution of 3.3 g of sodium peroxodisulfate in 90 g of water was continuously added dropwise. The reaction mixture was then stirred for a further 120 min at 90 ° C. and cooled to 60 ° C. After adding a solution of 1.1 g of t-butyl hydroperoxide in 5.5 g A solution of 0.6 g of sodium hydroxymethanesulfinate in 15 g of water was added to water at this temperature in the course of 1 h and the mixture was subsequently stirred for 0.5 h. After 15 minutes, the mixture was cooled to room temperature and neutralized with 4 ml of a 20% by weight aqueous calcium hydroxide slurry. After filtration, a dispersion with a solids content of 55.3%, a light transmittance of 0.01

% By weight dispersion at 20 ° C. and a layer thickness of 2.5 cm (“LD value”) of 8% and a pH value of 8.7. The glass transition temperature (DSC midpoint) of the polymer was -15 ° C.

Production of the polymer powder

The polymer dispersions of Examples 1 to 5 according to the invention and of Comparative Examples A to D were spray-dried in a pilot dryer. No soap was added. The drying aid T was added in each case in an amount of 10% by weight, based on the polymer P of the aqueous dispersion, as

A conventional antiblocking agent based on silica gel was used for the flow aid. The solids content of the spray food was 30% by weight. The atomization was carried out via a Teflon two-component nozzle (gap width 1.3 mm), the inlet temperature was 130 ° C, the outlet temperature 60 ° C.

T- _\ : polymer of 3 parts of carboxylic acid monomers and 1 part of ethoxylated oleylamine

15.2 parts by weight of fully demineralized water, 6.73 parts by weight of maleic anhydride, and also were in a pressure reactor (anchor stirrer, 2 feed points)

22.16 parts by weight of Lutensol ^® FA (ethoxylated oleylamine Fa. BASF AG). If necessary, 0.3% (based on monomers) of phosphorous acid was added as a corrosion inhibitor.

The mixture was heated to 120 to 125 ° C. under a nitrogen atmosphere. After this temperature had been reached, feed 1, consisting of 17.46 parts by weight of fully demineralized water and 18.60 parts by weight of acrylic acid, and, within 5 h, feed 2, of 3.44 parts by weight of fully demineralized water and 2.13 parts by weight of hydrogen peroxide (30% strength) ), evenly dosed. After feed 1 had ended, a further 2.88 parts by weight of fully demineralized water were added. During the polymerization, the pressure was kept at 2 to 3 bar by carefully releasing the pressure. After the end of the reaction, 30 cooled to 35 ° C and 11, 40 parts by weight of triethanolamine carefully stirred in with cooling. The finished polymer solution was filled into containers via a filter.

pH value: 3.5, surface tension: 43 mN / m, viscosity: 595 mPas

T ₂ : polymer of 3 parts of carboxylic acid monomers and 1 part of ethoxylated oleylamine

In a pressure reactor (anchor stirrer, 2 feed ports) were 152.0 kg of demineralized water, 67.3 kg of maleic anhydride, 0.88 kg Antifoam TEGO ^® 730 (defoamer from. Goldschmidt) and 221.6 kg Lutensol ^® FA 12 (ethoxylated oleylamine from BASF AG). If necessary, 0.3% by weight (based on the total amount of monomers) of phosphorus-containing inorganic acids was added as a corrosion inhibitor.

The mixture was heated to 120 to 125 ° C. under a nitrogen atmosphere. After this temperature had been reached, feed 1, consisting of 174.6 kg of fully demineralized water and 186.0 kg of acrylic acid, and within 5 hours of feed 2, consisting of 34.4 kg of fully demineralized water and 21.3 kg of a 30% by weight, % aqueous solution of hydrogen peroxide, evenly metered. To

At the end of feed 1, a further 28.8 kg of fully demineralized water were added to the reaction mixture. During the polymerization, the pressure was kept at 2 to 3 bar by carefully releasing the pressure. After the end of the reaction, the reaction mixture was let down to atmospheric pressure and cooled to 30 to 35 ° C., which took about 15 minutes. 114.0 kg of triethanolamine were then added to the reaction mixture with cooling.

The finished polymer solution had a pH of 3.5 and a viscosity of 598 mPa * s and could be filled into containers within 10 minutes using a filter.

T ₃ : polymer of 3 parts of carboxylic acid monomers and 1 part of ethoxylated oleylamine

In a pressure reactor (anchor stirrer, 2 feed points) 152.0 kg of demineralized

Water, 67.3 kg of maleic anhydride and 221.6 kg of Lutensol ^® FA 12 are presented. If necessary, 0.3% by weight (based on the total amount of monomers) of phosphorus-containing inorganic acids was added as a corrosion inhibitor. The mixture was heated to 120 to 125 ° C. under a nitrogen atmosphere. After reaching this temperature, feed 1, consisting of 174.6 kg of fully demineralized water, 186.0 kg of acrylic acid and 0.88 kg of TEGO Antifoam ^® 730, and feed 2, consisting of 34.4 kg of fully demineralized water and 21.3 kg of a 30% by weight aqueous solution of hydrogen peroxide, metered in uniformly. After feed 1 had ended, a further 28.8 kg of fully demineralized water were added to the reaction mixture. During the polymerization, the pressure was kept at 2 to 3 bar by carefully releasing the pressure. After the end of the reaction, the reaction mixture was opened

Atmospheric pressure relaxed and cooled to 30 to 35 ° C, which took about 15 minutes. 114.0 kg of triethanolamine were then added to the reaction mixture with cooling.

The finished polymer solution had a pH of 3.5 and a viscosity of 584 mPa * s and could be filled into containers within 10 minutes using a filter.

A general manufacturing specification for the drying aids T4-T6 is described in EP 467 103 (column 9, “Dispersion I”).

T ₄ : copolymer of 50% by weight of maleic anhydride and 50% by weight of diisobutylene, neutralized with NaOH, M _w (GPC) approx. 12000 g / mol.

T ₅ : copolymer of 72% by weight of maleic anhydride and 28% by weight of isobutylene, with

NaOH neutralized, M _w (GPC) approx. 4000 g / mol.

T ₆ : copolymer of 50% by weight of maleic anhydride and 50% by weight of one

Mixture of 1 part by weight of C ₁₂ alk-1-ene and 1 part by weight of C ₂₀ alk-1-ene; M _w (GPC) approx. 4000 g / mol.

T ₇ : naphthalenesulfonic acid-formaldehyde condensation product as calcium salt, corresponds to example S1 from EP-B 914366 (p. 8 / line 24 ff.).

T ₈ : copolymer of 50% by weight of acrylic acid and 50% by weight of maleic anhydride, with

NaOH partially neutralized, M _w (GPC) approx. 3000 g / mol. The table below summarizes the results of spray drying and redispersion.

Results

The results of Examples 1 to 5 according to the invention and of Comparative Examples A to D are shown in Table 1 below.

Table 1

Benotunq - powder Benotunq - film formation

1 = no clumping 1 = filmed without errors

2 = minimal clumping, easily pulverizable 2 = filmed with scars

3 = slight clumping, moderately pulverizable 3 = shrinkage cracks at the edge

4 = larger clumping, easy to pulverize 4 = large-scale shrinkage cracks

5 = larger clumping, difficult to pulverize 5 = totally cracked

6 = greater clumping, not pulverizable 6 = no filming

Table 1 shows the results of spray drying. The powders produced with the spraying aid according to the invention could be spray-dried in high yield without problems, are readily redispersible and show faultless filming. In particular, the comparison of Examples 1 with Comparative Examples B to D shows that a minimum concentration of hydrophobic, aliphatic groups is necessary for the carboxylates. The hydrophobic groups can be polymerized alpha-olefins or else they are ester groups, which can also be connected to the main chain by means of a hydrophilic spacer.

Redispersibility: 30 g of the polymer powder prepared according to II was dispersed in a standing cylinder in 70 ml of deionized water and left for 4 hours at room temperature and then assessed visually how strongly the polymer phase had separated from the water phase.

Filming: A polymer film was cast from the redispersed dispersions and then dried at room temperature for 4 days. The quality of the film was assessed visually as shown in Table 1.

Claims

claims

1. A process for the preparation of polymer powders by evaporating the volatile constituents from aqueous dispersions of film-forming polymers P, characterized in that the aqueous polymer dispersion, prior to the evaporation of the volatile constituents, also has drying aids T which are present in an amount of 0.1 to 80% by weight. %, based on the polymer P of the dispersion, are used as drying aids T polymers which are composed of repeat units containing carboxyl groups and at least 5 mol%, based on the total amount of the polymers, of repeat units with hydrophobic

Page groups are built.

2. The method according to claim 1, characterized in that the polymers used as drying aids T are present in an amount of 1 to 50% by weight, based on the polymer P, of the dispersion.

3. Process according to claims 1 or 2, characterized in that the polymers used as drying aids T are present in an amount of 5 to 20% by weight, based on the polymer, of the dispersion.

4. The method according to claims 1 to 3, characterized in that the polymers used as drying aids T have a molar mass (weight average Mw) of 500 g / mol to 50,000 g / mol.

5. The method according to any one of claims 1 to 4, characterized in that as

Drying aids T hydrophobically modified polyelectrolytes are used, which are made from

(a) 95 - 50 mol% of repeating units of the formula (I) with

-C5 alkyl -CH2-CO-OY

all, alkaline earth metal or NH ₄

and

(b). 5 - 50 mol% repeat units of the formula (II) with

and

(c) 0-30 mole% of other monomers obtained by radical polymerization,

are set up.

6. The method according to claims 1 to 5, characterized in that as

Drying aids T copolymers of olefinically unsaturated mono- or dicarboxylic acids, or an anhydride of these acids or a mixture of these monomers (monomers a) with copolymerized C ₂ - to C ₀ -alk-1-enes (monomers b) and optionally further free-radically polymerizable monomers ( Monomers c) are used.

7. The method according to claims 1 to 6, characterized in that as drying aids T homo- or copolymers of olefinically unsaturated mono- or dicarboxylic acids esterified in whole or in part with emulsifiers.

8. The method according to any one of claims 1 to 7, characterized in that the polymer in the dispersion is a styrene-butadiene copolymer.

9. The method according to any one of claims 1 to 8, characterized in that the

Polymer in the dispersion has a glass transition temperature Tg below 65 ° C.

10. The method according to any one of claims 1 to 9, characterized in that the

Polymer dispersion additionally contains at least one emulsifier in an amount of up to 10% by weight, based on the polymer.

11. The method according to any one of claims 1 to 10, characterized in that the evaporation of the volatile constituents from the aqueous polymer dispersion is carried out by a spray drying process.

12. Polymer powder obtainable by a process according to one of claims 1 to 11.

13. The polymer powder according to claim 12, comprising:

i at least one film-forming polymer P, ii 0.1 to 80% by weight, based on the polymer P, drying aid T, which consists of monomers containing carboxyl groups and at least 5 mol% based on the

Total amount of the polymers of monomers with hydrophobic side groups are built up, iii optionally neutral surface-active compounds in an amount of up to 10% by weight, based on the polymer P, and iv optionally fillers, pigments, anticaking agents and / or conventional auxiliaries.

14. Use of the polymer powder according to claim 12 or 13 as a cobinder in mineral binders and ready-to-use binders or as a binder in paints, varnishes, adhesives, coating and sealing compounds, construction adhesives and in synthetic resin plasters.

15. Mineral binder building material containing a polymer powder according to one of claims 12 or 13.

16. Mineral binder building material according to claim 15 in the form of a dry mortar preparation consisting of

10 to 60% by weight of mineral binder,

0.1 to 30% by weight of polymer powder according to one of claims 12 or 13, up to 25% by weight of auxiliaries customary for mineral binders and additives, such as sand, fillers, pigments, natural fibers and / or synthetic fibers.

7. Mineral binder building material according to claim 15 in the form of a construction adhesive dry preparation consisting of

15 to 50 wt .-% mineral binder

0.5 to 10% by weight of polymer powder, according to one of claims 12 or 13

0.1 to 25% by weight of auxiliaries usual for construction adhesives

30 to 80 wt% surcharges customary for construction adhesives