EP1771486A1

EP1771486A1 - Method for the production of aqueous styrol-butadiene polymer dispersions

Info

Publication number: EP1771486A1
Application number: EP05759051A
Authority: EP
Inventors: Wolfgang Gaschler; Christoph Hamers
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-07-20
Filing date: 2005-07-14
Publication date: 2007-04-11
Also published as: DE102004035075A1; US20070191531A1; WO2006008056A1

Abstract

Disclosed is a method for producing an aqueous styrol-butadiene polymer dispersion by means of radical aqueous emulsion polymerization of a monomer mixture M containing 30 to 80 percent by weight of styrol, 20 to 70 percent by weight of butadiene, and 0 to 40 percent by weight of at least one ethylenically unsaturated comonomer that is different from styrol and butadiene, the percentages being in relation to the total quantity of the monomer mixture M, according to a monomer feeding process in the presence of a non-copolymerizable hydroperoxide of general formula R-O-O-H as a regulator, the monomer mixture M being fed to the polymerization vessel within four hours.

Description

Process for preparing aqueous styrene-butadiene polymer dispersions

description

The present invention relates to a process for preparing an aqueous styrene-butadiene polymer dispersion by free-radical aqueous emulsion polymerization of a monomer mixture M comprising

From 30 to 80% by weight of styrene, from 20 to 70% by weight of butadiene and

0 to 40% by weight of at least one ethylenically unsaturated comonomer other than styrene and butadiene,

in each case based on the total amount of the monomer mixture M, according to a monomer feed process in the presence of a non-copolymerizable hydroperoxide of the general formula ROOH as regulator, where R is hydrogen, C 1 -C ₈ -alkyl, C ₇ -C ₂₂ -aralkyl and a saturated or unsaturated carbocyclic or heterocyclic rings having 3 to 18 carbon atoms, which is gekenn¬ characterized in that the monomer mixture M is supplied to the polymerization within 4 hours.

Aqueous styrene-butadiene polymer dispersions are used in a variety of ways, in particular as binders in coating compositions, such as dispersion paints and paper coating colors, in barrier coatings, as back coatings for carpets, as adhesive raw materials in carpet adhesives, in building adhesives, for modifying mortar , Cement and asphalt, for the consolidation of nonwovens, in Dicht¬ masses, in molded foam parts and as a binder for leather finishing.

The preparation of these dispersions is generally carried out by free-radical aqueous emulsion polymerization of styrene and butadiene-containing monomer mixtures. In these processes, chain transfer agents are frequently used in order to avoid excessive crosslinking of the polymers, which may adversely affect the performance properties of the dispersion. Such substances regulate the molecular weight of the forming polymer chains and are therefore also referred to as regulators.

In the prior art a wide variety of substances are proposed as regulators. Of commercial importance are compounds with thiol groups, in particular alkylmercaptans such as n- and tert-dodecylmercaptan (see, for example, Ullmann's Encyclopedia of Industrial Chemistry, 5th ed. On CD-ROM , Synthetic Rubber 2.1.2). However, these substances are disadvantageous in various respects, for example because of their unpleasant odor, they are difficult to handle both before and during the polymerization. Another disadvantage is their effect on the egg smell of the dispersions. This can not be completely suppressed even by extensive deodorizing measures.

To avoid the odor problem in the preparation and processing of aqueous polymer dispersions, in particular aqueous styrene-butadiene polymer dispersions, EP-A 1380597 discloses the use of peroxides, in particular organic hydroperoxides as sulfur and halogen-free regulators. However, the document does not disclose how and in what time the monomers and the regulators are fed to the polymerization medium. Also found in the aforementioned document no evidence to solve the problem of residual monomer minimization, especially on an industrial scale.

High residual monomer contents occur in particular when the content of styrene in the monomer mixture to be polymerized is 40% by weight and more, and become all the more serious at styrene contents from 45% by weight, in particular from 50% by weight and especially lower 55% by weight. Although high contents of volatile constituents can be partially removed by subsequent physical deodorization, the expense increases, not least the expenditure of time, and thus the costs with increasing residual monomer content. The residual monomer minimization by so-called chemical deodorization is costly and time consuming. By chemical deodorization, the person skilled in the art understands a radical-initiated postpolymerization under forced polymerization conditions (see, for example, DE-A 44 35423, DE-A 44 19 518, DE-A 44 35 422, DE-A 102 41 481 and literature cited therein). ,

It is an object of the present invention to provide a process which can be carried out well in industrial production scale for the preparation of aqueous styrene-butadiene polymer dispersions which have no disturbing mercaptan odor and a low residual monomer content, in particular a lower styrene content.

Accordingly, the method defined above was found.

The process according to the invention is carried out by a monomer feed process. This is understood to mean that the main amount, usually at least 70% by weight, preferably at least 80% by weight and in particular at least 90% by weight or the total amount of the total monomers to be polymerized are fed to the polymerization reaction under polymerization conditions. The term "polymerization conditions" is understood by the person skilled in the art to mean that the aqueous polymerization medium contains an amount of initiator sufficient to initiate the polymerization reaction and has a temperature at which the initiator has a decomposition rate sufficient to initiate the polymerization. The relationships between temperature and decay rate are the person skilled in the known polymerization initiators well known or can be determined in routine experiments.

The inventive method is particularly suitable for the preparation of aqueous styrene-butadiene polymer dispersions which by free-radically initiated aqueous emulsion polymerization of a monomer M, containing 30 to 80 wt .-%, often 35 to 75 wt .-% and often 40 to 70 Wt .-% styrene, 20 to 70 wt .-%, often 25 to 65 wt.% And often 30 to 60 wt .-% butadiene and 0 to 40 wt .-%, often 2 to 30 wt .-% and often 3 to 25 wt .-% of at least one of styrene and butadiene different ethylenically unsaturated comonomer, in each case based on the total amount of the monomer mixture M, are obtained.

At this point it should be noted that in this document butadiene stands for 1, 3-butadiene and that the amounts of the monomers contained in the monomer M are also to reflect the percentage of monomers copolymerized in the corresponding styrene-butadiene polymer.

With regard to the at least one comonomer, there are basically no restrictions in the process according to the invention. Rather, the type and amount of optionally used at least one comonomer primarily depend on the desired application. Examples of suitable comonomers are:

monoethylenically unsaturated monomers having an acid group such as monocarboxylic and dicarboxylic acids having 3 to 10 C atoms, such as acrylic acid, methacrylic acid, crotonic acid, acrylamidoglycolic acid, vinylacetic acid, maleic acid, itaconic acid and the half esters of maleic acid with C 1 -C ₄ -alkanols, ethylenically unsaturated sulfonic acids, such as vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, 2-acrylamidomethylpropanesulfonic acid, and ethylenically unsaturated phosphonic acids, for example 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 Acid. Such monomers may be included in the monomer mixture M 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 monoethylenically unsaturated carboxylic acids, such as acrylamide and methacrylamide, and the N- (hydroxy-C ₁ -C ₄ -alkyl) amides, preferably the N-methylolamides of ethylenically unsaturated carboxylic acids, such as N-methylolacrylamide and N-methylolmethacrylamide. Such monomers may be present in the monomer mixture M in an amount of up to 10% by weight, for example 0.1 to 10% by weight.

%, preferably 0.1 to 4 wt .-%, be contained; Hydroxyalkyl esters of monoethylenically unsaturated carboxylic acids, in particular hydroxyethyl, and hydroxypropyl and hydroxybutyl, for example, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate and 3-hydroxypropyl methacrylate. Such monomers may be present in the monomer mixture M in an amount of up to 10% by weight, for example 0.1 to 10% by weight.

%, preferably 0.5 to 5 wt .-%, be contained;

ethylenically unsaturated nitriles having preferably 3 to 10 C atoms, such as acrylonitrile and methacrylonitrile. Such monomers may be present in the monomer mixture M in an amount of up to 30% by weight, for example from 1 to 30% by weight, preferably from 5 to 20% by weight;

Reactive monomers: The reactive monomers include those which have a reactive functionality suitable for crosslinking. These include, in addition to the aforementioned ethylenically unsaturated carboxylic acids, their N-

Alkylolamides and Hydroxyalkylesters Monomers having a carbonyl group or an epoxy group, for example N-diacetoneacrylamide, N-diacetone methacrylamide, acetylacetoxyethyl acrylate and acetylacetoxyethyl methacrylate, glycidyl acrylate and glycidyl methacrylate. Such monomers may be present in the monomer mixture M in an amount of up to 10% by weight, for example from 0.5 to 10% by weight

and Crosslinking Monomers: Crosslinking monomers include those having at least two non-conjugated ethylenically unsaturated bonds, e.g. the di- and tri-acrylates or methacrylates of difunctional and trifunctional alcohols, such as, for example, ethylene glycol diacrylate, diethylene glycol diglycol, triethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, trimethylolpropane triacrylate and tripropylene glycol diacrylate. Such monomers may be present in the monomer mixture M in an amount of up to 2% by weight, preferably not more than 1% by weight, e.g. 0.01 to 2 wt.%, Preferably 0.01 to 1 wt.

%, be included. In a preferred embodiment, the monomer mixture M contains no crosslinking monomer.

Preferred comonomers are the monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 10 C atoms, their amides, their hydroxy-C ₂ -C ₄ -alkyl esters, their N- (hydroxy-C ₁ -C ₄ -alkyl) amides and also the aforementioned ethylenically unsaturated nitriles. Particularly preferred comonomers are the monoethylenically unsaturated mono- and dicarboxylic acids, in particular acrylic acid, methacrylic acid and itaconic acid.

In a particularly preferred embodiment of the process according to the invention, the monomer mixture M to be polymerized comprises From 50 to 70% by weight of styrene, from 29 to 49% by weight of butadiene and

1 to 10 wt .-% of at least one comonomer, preferably at least one ethylenically unsaturated mono- or dicarboxylic acid.

In another preferred embodiment of this process, a portion of the styrene, preferably 5 to 20 wt .-%, based on the total amount of monomer M _{1 is} replaced by acrylonitrile and / or methacrylonitrile. In this preferred embodiment, the monomer mixture M to be polymerized contains, for example

From 40 to 65% by weight of styrene, from 29 to 44% by weight of butadiene,

5 to 25 wt .-% of acrylonitrile and / or methacrylonitrile and 1 to 10 wt .-% of an ethylenically unsaturated mono- or dicarboxylic acid.

With regard to the use of the styrene-butadiene polymers prepared by the process according to the invention as binders in coating compositions, in particular in paper coating slips, it has proved to be advantageous if the polymer resulting from the aqueous emulsion polymerization has a glass transition temperature in the range from -20 to 5O ⁰ C and preferably in the range of 0 to 3O ⁰ C auf¬. The glass transition temperature here is the so-called mid-point temperature, which can be determined according to ASTM 3418-82 by means of DSC.

The glass transition temperature can be controlled via the monomer mixture M used in a manner familiar to the person skilled in the art.

According to Fox (TG Fox, Bull. Am. Phys Soc. (Ser. II) 1 123 [1956] and Ullmann's Encyclopedia of Technical Chemistry, Weinheim (1980), pages 17, 18) applies to the glass transition temperature of Copolymers with large molar masses in good approximation X "T- +.

where X ¹ , X ² ,..., X ^{π are} the mass fractions 1, 2,..., n and T ₉ ¹ , T ₉ ² ,..., T ₉ ^{π are} the glass transition temperatures of only one of the Monomers 1, 2 n constructed polymers in degrees Kelvin. The latter are, for example, from Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, Vol. A 21 (1992) page 169 or from J. Brandrup, EH Immergut, Polymer Handbook 3 ^rd ed., J. Wiley, New York 1989 be¬ known. Polystyrene then has a T ₉ of 380 K and polybutadiene has a T ₉ of 171 K or 166 K. It is essential to the process that the free-radically initiated aqueous emulsion polymerization takes place in the presence of a non-copolymerizable hydroperoxide of the general formula ROOH as regulator, where R is hydrogen, C 1 -C ₈ -alkyl, C ₇ -C ₂₂ -aralkyl and a saturated or unsaturated carbocyclic or hetero - Rocyclic ring having 3 to 18 carbon atoms, and the radical R may optionally be substituted.

In this case, the radical R can be unbranched or branched as well as also substituted, for example with one or more substituents from the group comprising halo genes, hydroxyl, alkoxy, aryloxy, epoxy, carboxyl, ester, amide, Nitrile or cetane group. Preferred radicals R are hydrogen, isopropyl, tert-butyl or tert-pentyl radical and also 1,1-dimethylbutyl and 1,1-dimethylpentyl radicals, which may optionally be substituted by an OH group. Preferred aralkyl radical is the cumene radical. As Carbocyclische remainders the Menthol and the Pinenrest are preferential.

Particular preference is given to using at least one hydroperoxide as regulator, which is selected from the group comprising hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene monohydroperoxide, tert-pentyl hydroperoxide, 1,1-dimethylbutyl hydroperoxide, 1,1-dimethylpropyl hydroperoxide, 1,1-dimethyl- 3-hydroxybutyl hydroperoxide, 1, 1, 3,3-tetramethylbutyl hydroperoxide, p-menthyl hydroperoxide, pinanyl hydroperoxide, 1-methylcyclopentyl hydroperoxide, 2-hydroperoxy-2-methyltetrahydrofuran, 1-methoxycyclohexyl hydroperoxide, 1, 3,4,5,6,7-hexahydroxy 4a (2H) -naphthalenyl hydroperoxide, β-pinene hydroperoxide, 2,5-dihydro-2-methyl-2-furanyl hydroperoxide.

The non-copolymerizable hydroperoxides can be used as regulators in addition to a polymerization initiator ("initiator" for short) and simultaneously as regulator and initiator.

Suitable initiators or redox initiator combinations are in principle all those compounds which are known to the skilled man to initiate a free-radical watery emulsion polymerization of butadiene and styrene in the temperature range> 0 ⁰ C to <130 ⁰ C, often> 60 ⁰ C to <110 ⁰ C and often> 70 ° C to <100 ⁰ C are known. Preferred initiators are water-soluble. Examples of such initiators are the sodium, potassium or ammonium salts of peroxodisulfuric acid, hydrogen peroxide, tert-butyl peroxide, potassium peroxodiphosphate, tert-butyl peroxypivalate, cumene hydroperoxide, diisopropylbenzene monohydroperoxide or azoisobutyronitrile. The initiators mentioned are generally used in an amount of from 0.01 to 10% by weight and preferably from 0.1 to 5% by weight, in each case based on the total amount of the monomer mixture M. As redox initiators, the initiators mentioned are used in combination with a reducing agent. Suitable reducing agents are sulfites and bisulfites of Alkali metals and ammonium, for example sodium sulfite or sodium bisulfite, the derivatives of sulfoxylic acid such as zinc or Alkaliformaldehydsulfoxylate, for example Natriumhydroxymethansulfinat, and ascorbic acid. The amount of reducing agent is generally from 0.01 to 10% by weight and preferably from 0.1 to 5% by weight, in each case based on the total amount of the monomer mixture M. In a preferred embodiment, no further initiators are used apart from the non-copolymerizable hydroperoxide added.

The hydroperoxides used as regulators can be initially introduced into the aqueous polymerization medium, be metered in total or in proportions, frequently <30% by weight, <20% by weight or <10% by weight, based in each case on the hydroperoxide. Total, submitted and the remainder are added. If the hydroperoxides are used only as regulators and in conjunction with an initiator, it is possible to proceed in such a way that the total hydroperoxide is initially charged or is added together with monomer or initiator, or in part, frequently <30% by weight, <20% by weight .-% or <10 wt .-%, in each case based on the total amount of hydroperoxide, vor¬ laid and the remainder is added together with monomer or initiator. In the process variants in which the hydroperoxide is added in total or in part, the amounts added are preferably such that the initiator and in the course of the polymerization, the molar ratio of hydroperoxide to initiator 0.2 to 1 and often 0.3 to 0.9 or 0.4 to 0.8.

If the hydroperoxides are used both as regulators and as initiators, one of the abovementioned reducing agents is additionally used to form a redox initiator system. In this case, the hydroperoxide can be initially charged in total, metered in in total or partially charged, and the remainder added in the course of the polymerization. The abovementioned reducing agent can also be initially charged in its entirety, metered in in total amount or partially charged, and the remainder metered in during the course of the polymerization. Advantageously, however, the total amount of the reducing agent is added in the course of the polymerization reaction. This is particularly preferred

Hydroperoxide initially introduced or metered in such amounts that the molar ratio of hydroperoxide to reducing agent at initiation and in the course of the polymerization is 1, 2 to 20, in particular 1, 5 to 7.5.

The initiator can be used both as such or as a dispersion or solution in a suitable solvent. Suitable solvents are in principle all customary solvents which are able to dissolve the initiator. Preference is given to water and water-miscible organic solvents, for example C 1 -C ₄ -alcohols or mixtures thereof with water. In particular, the initiator is used as an aqueous solution. The completion of the addition of the initiator is preferably carried out when the addition of monomer has ended or at the latest 1 hour, in particular at the latest 0.5 hours after the end of the monomer addition. The polymerization temperature naturally depends on the decomposition characteristics of the polymerization initiator and is preferably at least 6O ⁰ C, more preferably at least 7O ⁰ C, more preferably at least 8O ⁰ C and most preferably at least 90 ⁰ C. Typically it will be a polymerization temperature of 12O ⁰ C and preferably do not exceed 110 ⁰ C to avoid expensive printing equipment. However, with a suitable choice of the reaction vessel, it is also possible to use temperatures above it. In the so-called cold mode, ie when using redox initiator systems, it is possible to polymerize even at lower temperatures, for example, already from 5 ⁰ C or 1O ⁰ C.

The inventive method is particularly suitable for the production of aqueous styrene-butadiene polymer dispersions on an industrial scale, for the production of a total amount of butadiene> 1000 kg,> 5000 kg or> 10000 kg are used.

Furthermore, aqueous styrene-butadiene polymer dispersions having a low residual monomer content, in particular a lower styrene content, are obtainable by the process according to the invention if the monomer mixture M is fed to the polymerization vessel within shorter dosing times, for example within 3.5 hours or within 3 hours.

As a rule, the process according to the invention is carried out exclusively in the presence of the above-mentioned hydroperoxides as a polymerization regulator. However, even small amounts of other compounds which are known to act as polymerization regulators can be tolerated. These include, for example, the abovementioned compounds with a thiol group, for example alkyl mercaptans, and also the compounds mentioned in EP-A 407 059 and DE-A 195 12 999. Their proportion will generally amount to less than 0.1% by weight of the monomers to be polymerized and preferably not exceed a proportion of 50 parts by weight, preferably 20 or 10 parts by weight, based on 100 parts by weight of total hydroperoxide used.

In addition, it has proven advantageous for the reduction of the residual monomer content, in particular of the residual styrene content, when the monomer mixture M is fed to the polymerization vessel in the form of the monomer feeds Mz1 and Mz2, the feed Mz1 comprising styrene, butadiene and optionally at least one comonomer, and Feed Mz2 exclusively consists of butadiene, wherein at a time when> 70% by weight of feed Mz1 has been fed to the polymerization vessel, the total feed time Tz1 of the feed Mz1 feed Mz2 is supplied for a period Tz2 of> 1%, and wherein feed Mz2 consists of <30 wt .-% of BuTadiengesamtmenge. Frequently, feed Mz2 is started after> 75% by weight or> 80% by weight, but often <99% by weight, <95% by weight or <90% by weight of feed Mz1 fed to the polymerization vessel have been.

Feed Mz2 corresponds to <30% by weight, frequently <25% by weight or <20% by weight and often <15% by weight or <10% by weight and> 0.1% by weight, frequently > 0.5% by weight or> 1% by weight and often> 1.5% by weight or> 5% by weight of the total amount of butadiene. Feed Mz2 advantageously corresponds to> 0.5 to <20% by weight or> 1 to <20% by weight of the total amount of butadiene.

The feed time Tz2 is often> 2%,> 5%,> 7% or> 10% and <40%, <30%, <20% or <15% of the total feed time Tz1 of the feed Mz1. Often the feed time Tz2> 5 to <40% or> 7 to <20% of the total feed time Tz1. The maximum total feed time Tz1 is <4 hours, <3.5 hours or <3 hours. Frequently, however, the total feed time Tz1 is <95%, <90%, <85% or <80% of the aforementioned times.

Advantageously, the process according to the invention takes place in such a way that feed Mz2 is started at a time at which> 80% by weight of feed Mz1 has been fed to the polymerization vessel, the period Tz2> 5 to <40% of the total feed time Tz1 of the feed Mz1 and the feed Mz2 consists of> 0.5 to <30 wt .-% of total butadiene.

It is essential for the invention that the inlets Mz1 and Mz2 at least partially overlap. In this case, feed Mz2 can be ended before, after or together with the completion of feed Mz1. However, it is essential that the termination of the last feed takes place within 4 hours, within 3.5 hours or within 3 hours. In accordance with the invention, feed Mz1 is advantageously completed after feed Mz2.

According to the invention, the feeds Mz1 and Mz2 can be fed to the polymerization vessel continuously or batchwise, in constant, increasing or decreasing flow rates. It is also possible in principle that the composition of the feed Mz1 changes in the course of the feed in the claimed composition range, for example by stepwise or gradient mode of operation. Advantageously, feed Mz1 is continuously fed to the polymerization vessel without changing the composition continuously with a constant flow rate and feed Mz2 at a constant flow rate.

According to the invention, the monomers forming the monomer mixture M or the corresponding monomer feeds Mz1 and Mz2 can be fed to the polymerization vessel via separate feeds. Of course it is also possible, the Monomer mixture M forming monomers or the corresponding Monzemenzuläufe Mz1 and Mz2 fed to the polymerization vessel via an inlet. If the monomer feed takes place via an inlet, then it has proved advantageous to mix the monomers forming the monomer mixture M or the corresponding monomer feeds Mz1 and Mz2 continuously before being introduced into the polymerization vessel. Particularly suitable for this purpose are static mixers.

If the monomer feed via an inlet, so the polymerization is first fed to the monomer Mz1. At a selected point in time at which> 70% by weight of feed Mz1 has already been fed to the polymerization vessel, the feed of butadiene is then increased for the selected period of time Tz2 in such a way that the additional amount of butadiene Mz2 is fed to the polymerization vessel.

Of course, it is also possible to feed the monomer mixture M or the corresponding monomer feeds Mz1 and Mz2 to the polymerization vessel in such a way that at a point in time> 70% by weight of the styrene and butadiene and of the optionally used at least one comonomer the polymerization vessel were fed, the flow rates of styrene and the optionally used at least one comonomer are reduced while maintaining the butadiene flow rate.

The addition of the monomer mixture M can be effected both in the form of the monomers as such and also in the form of an aqueous emulsion of the monomers, preference being given to the latter procedure as a rule.

If the monomers are added to the polymerization reaction as an aqueous emulsion, the monomer content is usually from 30 to 90% by weight, in particular from 40 to 80% by weight, of the total weight of the aqueous emulsion. In addition, the monomer emulsion generally contains at least one part, preferably at least 70% by weight, in particular at least 80% by weight, or the total amount of dispersants usually required for emulsion polymerization.

In the process according to the invention, at least one dispersing agent is used which keeps both the monomer droplets and the polymer particles formed during the polymerization dispersed in the aqueous phase and thus ensures the stability of the aqueous polymer dispersion produced. Suitable dispersants are both protective colloids and emulsifiers.

Examples of suitable protective colloids are polyvinyl alcohols, polyalkylene glycols, alkali metal salts of polyacrylic acids and polymethacrylic acids, cellulose, starch and gelatin derivatives or acrylic acid, methacrylic acid, maleic anhydride, 2-acrylamido-2-methylpropanesulfonic acid and / or 4-styrenesulfonic acid-containing Polymers and their alkali metal salts but also N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylcarbazole, 1-vinylimidazole, 2-vinylimidazole, 2-vinylpyridine, 4-vinylpyridine, acrylamide, methacrylamide, acrylates containing amine groups, methacrylates, acrylamides and / or methacrylamides homo - and copolymers. A detailed description of other suitable protective colloids can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Materials, Georg Thieme Verlag, Stuttgart, 1961, pages 411 to 420.

Of course, mixtures of emulsifiers and / or protective colloids can be used. Frequently used as dispersants are exclusively emulsifiers whose relative molecular weights, unlike the protective colloids, are usually below 1500. They may be anionic, cationic or nonionic in nature. Of course, in the case of the use of mixtures of surface-active substances, the individual components must be compatible with one another, which can be checked in case of doubt by means of fewer preliminary tests. In general, anionic emulsifiers are compatible with one another and with nonionic emulsifiers. The same applies to cationic emulsifiers, while anionic and cationic emulsifiers are usually incompatible with one another. An overview of suitable emulsifiers can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Materials, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 208.

Useful nonionic emulsifiers are for example ethoxylated mono-, di- and tri-alkylphenols (EO units: 3 to 50, alkyl radical: C ₄ to C ₂₎ and ethoxylated fatty alcohols (EO units: 3 to 80; alkyl radical: C ₈ to C ₃₆ ). Examples are the Lutensol ^® A grades (C ₁₂ C ₁₄ fatty alcohol ethoxylates, EO units: 3 to 8), Lutensol ^® AO-marks (C ₁₃ C ₁₅ - Oxoalkoholethoxilate, EO units: 3 to 30), Lutensol ^® AT grades (C ₁₆ C ₁₈ - fatty alcohol ethoxylates, EO grade: 11 to 80), Lutensol ^® ON grades (C ₁₀ - oxo alcohol ethoxylates, EO grade: 3 to 11) and the Lutensol ^® TO grades (C ₁₃ - Oxo alcohol ethoxylates, EO grade: 3 to 20) from BASF AG.

Typical anionic emulsifiers include alkali metal and ammonium salts of alkyl sulfates (alkyl radical: C ₈ to Ci _2), ethoxylated sulfuric acid monoesters of alkanols (EO units: 4 to 50, alkyl radical: C ₁₂ to C ₁₈₎ and of ethoxylated alkylphenols (EO degree: 3 to 50, Alkyirest: C ₄ to C _12), of alkylsulfonic acids (alkyl radical: C ₁₂ to C ₈₎ and of Al kylarylsulfonsäuren (alkyl radical: C ₉ to C _18).

Further anionic emulsifiers further compounds of general formula I have

wherein R ¹ and R ^{2 are} H atoms or C ₄ - to C ₂₄ alkyl and are not simultaneously H atoms, and A and B may be alkali metal ions and / or ammonium ions proved. In the general formula I, R ¹ and R ^{2 are} preferably linear or branched alkyl radicals having 6 to 18 C atoms, in particular having 6, 12 and 16 C atoms or -H, where R ¹ and R ^{2 are} not both simultaneously H Atoms are. A and B are preferably sodium, potassium or ammonium, with sodium being particularly preferred. Particularly advantageous are compounds I in which A and B are sodium, R ^{1 is} a branched alkyl radical having 12 C atoms and R ^{2 is} an H atom or R ¹ . Industrial mixtures are used which have a share of 50 to 90 wt .-% of the monoalkylated Pro¬ domestic product such as Dowfax ^® 2A1 (trademark of Dow Chemical Compa¬ ny). The compounds I are generally known, for example from US-A 4,269,749, and commercially available.

Suitable cationic emulsifiers are generally C ₆ -C ₁₈ -alkyl, aralkyl or heterocyclic radical-containing primary, secondary, tertiary or quaternary ammonium salts, alkanolammonium salts, pyridinium salts, imidazolinium salts, oxazolinium salts, morpholinium salts, thiazolinium salts and salts of amine oxides, quinolinium salts, isoquinolinium salts, tropylium salts, sulfonium salts and phosphonium salts. Dodecylammonium acetate or the corresponding hydrochloride, the chlorides or acetates of the various 2- (N ₁ N ₁ N-trimethylammonium-ethylparaffinate esters, N-cetylpyridinium chloride, N-laurylpyridinium sulfate and N-cetyl-N, N-trimethylammonium bromide, N-dodecyl-N, N, N-trimethylammoniumbrornid, N-octyl-N, N, N-trimethlyammoniumbromid, N ₁ N- distearyl-N, N-dimethylammonium chloride and also the gemini surfactant N ₁ N'-(lauryl) ethylendiamindibromid. Numerous other examples can be found in H. Stache, Tensid-Taschenbuch, Carl-Hanser-Verlag, Munich, Vienna, 1981, and McKincheon's, Emulsifiers & Detergents, MC Publishing Company, Glen Rock, 1989.

However, particularly suitable are nonionic and / or anionic emulsifiers.

As a rule, a total of 0.05 to 20 parts by weight, often 0.1 to 10 parts by weight and often 0.2 to 7 parts by weight of dispersant, each based on 100 parts by weight of aqueous polymerization , formed from the total amounts of deionized water and the at least one dispersant. The total amount of the dispersant may be initially charged in the reaction vessel prior to the addition of the monomer mixture M. However, it is also possible to introduce only a partial amount of the dispersant prior to the addition of the monomer mixture M in the reaction vessel and to add the remaining amount during the polymerization. If necessary, however, the total amount of the dispersant may be added in the course of the polymerization. Frequently, the total amount or at least the main amount of the dispersant in the course of the polymerization, in particular in the form of an aqueous monomer emulsion, the Po lymerisationsgefäß supplied.

Furthermore, it has proved to be advantageous if the reaction mixture is subjected to thorough mixing during the polymerization. Intensive mixing can be achieved, for example, by using special stirrers in conjunction with high stirring speeds, by combining stirrers with stators or by rapid circulation, e.g. Circulating the reaction mixture via a bypass, the bypass in turn being equipped with devices for generating shear forces, e.g. fixed installations such as shear or perforated sheets, can be equipped. Special stirrers are understood to mean those stirrers which, in addition to a tangential flow component, also generate an axial flow field. Such stirrers are e.g. described in DE-A 197 11 022. Particularly preferred are multistage stirrers. Examples of special stirrers for generating tangential and axial flow components are cross-bar stirrers, MIGR and INTERMIGR stirrers (multi-stage impulse countercurrent stirrers and interference multi-stage impulse countercurrent stirrers from EKATO), axial flow turbine stirrers, wherein the abovementioned stirrers are constructed in one or more stages and can also be combined with conventional stirrers, furthermore helical stirrers, preferably in wall-mounted design, coaxial stirrers, which have an armature-shaped wall-mounted stirrer and a one-stage or multistage, high-speed central stirrer, as well as multiple-blade stirrers. Also suitable are the types of stirrers described in DE-C1 4421949, JP-A 292002, WO 93/22350.

Furthermore, it has proved to be advantageous to carry out the process according to the invention in such a way that the particle density of the polymer particles in the finished aqueous dispersion does not fall below a value of about 5 × ^{10 16} particles per kg of aqueous dispersion and in particular in the range from 10 ¹⁷ to 3 x 10 ¹⁹ particles / kg dispersion. The particle density naturally depends on the average particle diameter of the polymer particles in the aqueous dispersion. Preferably, the average particle diameter of the polymer particles will be below 300 nm, and preferably in the range of 50 to 200 nm. The average particle diameter is defined as usual as the weight-average particle size, as determined by means of an analytical ultracentrifuge according to the method of W. Scholtan and H. Lange, Kolloid-Z. and Z.-Polymere 250 (1972) pages 782 to 796 (see also W. Mächtle in "Analytical Ultracentrifugation in Biochemistry and Polymer Scien", SE Harding et al (ed.), Cambridge: Royal Society of Chemistry, 1992, pp. 147-175). The ultracentrifuge measurement provides the integral mass distribution of the particle diameter of a sample. From this it can be seen how many percent by weight of the particles have a diameter equal to or below a certain size. Similarly, the weight-average particle diameter can also be determined by dynamic or quasi-elastic light scattering of laser light (see H. Wiese in D. Distler (ed.) "Aqueous Polymer Dispersions", Wiley-VCH, Weinheim 1999, p. 40 ff there quoted literature). Measures for adjusting the particle density and the average particle diameter of aqueous polymer dispersions are known to the person skilled in the art, for example from N. Dezelic, JJ. Petres, G. Dezelic, Colloid-Z. u. Z. Polymere, 1970, 242, pages 1142-1150. It can be controlled both by the amount of surface-active substances and by using seed polymers, so-called seed latices, with high emulsifier concentrations and / or high concentration of seed polymer particles usually resulting in small particle diameters.

In general, it proves to be advantageous to carry out the emulsion polymerization in the presence of one or more very finely divided polymers in the form of aqueous latices (so-called seed latices). Preference is given to using 0.1 to 10 wt .-% and in particular 0.2 to 5 wt .-% of at least one seed latex (solids content of the seed latex, based on the total amount of monomer). The seed latex may be partially or completely supplied with the monomers of the polymerization reaction. Preferably, however, the process is carried out with seed latex present (master seed). The latex generally has a weight-average particle size of 10 to 200 nm, preferably 20 to 100 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 also to a lesser extent including ethylenically unsaturated carboxylic acids, e.g. Acrylic acid and / or methacrylic acid and / or their amides, preferably less than 10 wt .-%, based on the total weight of the polymer in the seed latex, in copolymerized form.

When using a seed latex, it will often be the case that the seed latex is partially or completely, preferably at least 80%, introduced into the polymerization vessel, a portion of the initiator / regulator, preferably in the abovementioned shares, and optionally a part of adding polymerizing monomers and heated to the desired polymerization temperature. Of course, the introduction of the initiator / regulator and the seed latex can also be done in reverse order. The addition of the monomers preferably takes place only under polymerization conditions. Usually, the template contains, in addition to the initiator / regulator and the seed latex, water and optionally some of the surface-active compounds. As a rule, a pH of 9 will not be exceeded during the polymerization. The control of the pH is carried out in a simple manner by adding a neutralizing agent in the course of the polymerization reaction. Suitable examples are Ba¬ sen such as alkali metal hydroxide, carbonate or bicarbonate and alkali phosphates or condensed phosphates, if the pH drops during the polymerization. This is the case, for example, when using peroxodisulfates as polymerization initiators.

Subsequent to the polymerization reaction, postpolymerization is frequently still carried out to reduce the unreacted monomers in the aqueous polymer dispersion (so-called residual monomers). This postpolymerization is frequently also referred to as chemical deodorization. The chemical deodorization is generally carried out by radical postpolymerization, in particular under the action of redoxiniti- atorsystemen, as described for example in DE-A 44 35 423, DE-A 44 19 518, DE-A 44 35 422 and in DE-A 102 41 481 are listed. The postpolymerization is preferably carried out with a redox initiator system comprising at least one organic peroxide and a reducing agent, preferably an inorganic sulfite or the salt of an α-hydroxysulfone or sulfinic acid (hydrogen sulfite adduct of carbonyl compound). The amounts of initiator for the postpolymerization are generally in the range of 0.1 to 5 wt .-%, preferably in the range of 0.2 to 3 wt .-% and in particular in the range of 0.3 to 2% by weight, based on the total amount of the monomer mixture M. In the case of initiator systems comprising a plurality of components, for example the redox initiator systems, the amounts given relate to the total amount of these components. The chemical deodorization is preferably carried out at temperatures in the range of 60 to 10O ⁰ C and in particular in the range of 70 to 95 ⁰ C. The amount of initiator used for the chemical deodorization can be added in one portion or over a prolonged period continuously with a constant or variable, eg increasing feed rate of the dispersion. The duration of the addition is then usually in the range of 10 minutes to 5 hours and in particular in the range of 30 minutes to 4 hours. The total duration of the chemical post-polymerization is usually in the range of 15 minutes to 5 hours, and preferably in the range of 30 minutes to 4 hours.

The preparation of aqueous styrene-butadiene copolymer dispersions using a non-copolymerizable hydroperoxide by the novel process gives aqueous polymer dispersions having a significantly lower proportion of residual monomers than the processes of the prior art for the preparation of comparable dispersions. After the chemical desorption, which is usually carried out, it is possible to obtain dispersions whose content of volatile organic compounds is markedly below 10000 ppm (parts per million), preferably below 3000 ppm, in particular below 2500 ppm, and especially below 2000 ppm. Of course, it is possible to further reduce the content of volatile organic constituents by known methods. This can be carried out in a manner known per se physically by distillative removal (in particular by steam distillation) or by stripping with an inert gas, or by adsorption (see R. Racz, Macromol., Symp., 155, 2000, pp. 171-180). be achieved. Preferably, after the polymerization reaction, first a chemical deodorization and then a physical deodorization will be carried out. Both measures can also be carried out simultaneously.

The aqueous styrene-butadiene polymer dispersions obtained according to the invention usually have solids contents of from 30 to 70% by weight, frequently from 40 to 60% by weight and often from 45 to 55% by weight.

The process according to the invention makes it possible to provide aqueous styrene-butadiene polymer dispersions on an industrial scale with short cycle times, small amounts of regulator and, at the same time, low residual monomer contents, in particular low styrene and optionally comonomer contents.

In addition, the aqueous styrene-butadiene polymer dispersions obtainable by the process according to the invention have no disadvantageous or unpleasant odors, which is why they are used as components in emulsion paints, paper coating compositions, barrier coatings, adhesives, sealants, leather finishes, molded foam, backing coatings for carpets, and the like for the modification of mortar, cement and Asphaltinsbesondere and in particular as a binder in Papierstreich¬ masses are suitable.

Examples:

analytics

The weight-average particle diameter (D ₅₀ value) were determined in an analytical ultracentrifuge (AUC) according to W. Mächtle, Makromolekulare Chemie 185, 1984, pages 1025 to 1039.

The average particle diameter of the styrene-butadiene polymer particles were% aqueous dispersion at 23 ⁰ C using an Autosizer IIC from. Malvern Instruments, England, determined by dynamic light scattering on a 0.005 to 0.01 wt .-. The average diameter of the cumulant evaluation (cumulant z-average) of the measured autocorrelation function is given (ISO standard 13 321). The solids contents were determined by a defined amount (about 5 g) of watery polymer dispersion at 140 ⁰ C in a drying cabinet to Gewichtskon¬ substance was dried. Two separate measurements were carried out in each case. The value given in the respective examples represents the mean value of the two measurement results.

The glass transition temperature was determined by the DSC method, 20 K / min, midpoint measurement, by means of a DSC apparatus DSC822 (TA8000 series) from Mettler-Toledo, Germany, according to DIN 53765.

The residual monomer contents of the aqueous dispersions were determined by means of gas chromatography. The device was used Perkin bucket HS 40, with a column DB1 from J & W Scientific, USA. Nitrogen was used as the carrier gas. The calibration of the measurements was carried out with aqueous polymer dispersions, with a known content of butadiene and styrene.

I. Preparation of the Aqueous Polymer Dispersions

Dispersion 1 (D 1)

300 g of deionized water and 83 g of a 33% strength by weight aqueous polystyrene latex having a weight-average particle diameter D ₅₀ of 30 nm and 10% by weight were introduced into a 2 l polymerization vessel at room temperature (20 ° to 25 ° C.) under a nitrogen atmosphere. % of feed 2 and heated to 90 ⁰ C heated with stirring. Subsequently, two feeds were added simultaneously, starting at the same time within 3 hours, feed 1 and the remainder of feed 2 continuously in constant mass flows while maintaining the temperature in the polymerization vessel.

After completion of the aforementioned feeds, the polymerization mixture was stirred for 30 minutes at 90 ° C, then cooled to 85 ⁰ C and then at the same time on separate feeds starting a solution of 8 g of tert-butyl hydroperoxide and 80 g of deionized water and a solution, consisting of 3.5 g of acetone, 5.7 g of sodium disulfite (Na ₂ S ₂ O ₅ ) and 76 g of deionized water, continuously in constant Men¬ genströmen while maintaining the temperature within 2 hours. Thereafter, 22 g of a 25% strength by weight aqueous solution of sodium hydroxide were added to the polymerization mixture in one shot and the aqueous polymer dispersion was cooled to room temperature. Feed 1:

490 g of deionized water

9.9 g of a 45 wt .-% aqueous solution of Dowfax 2A1 ^® 23.1 g of a 15 wt .-% aqueous solution of sodium dodecylbenzenesulfonate

(Lutensit® ^® A-LBN 50, BASF AG trademark of., Germany)

19.3 g of a 70 wt .-% aqueous solution of tert-butyl hydroperoxide

730 g of styrene

580 g of butadiene 41.0 g of acrylic acid

10.0 g of a 25% strength by weight aqueous solution of sodium hydroxide

Feed 2 consisted of a solution of 13.6 g of sodium peroxodisulfate in 230 g of deionized water.

The solids content of the resulting aqueous polymer dispersion was 50.2 wt .-%, the average particle diameter was 125 nm and the glass transition temperature was determined to 6 ⁰ C. The residual styrene content was 1200 ppm and the residual butadiene content 160 ppm.

Dispersion 2 (D2)

300 g of deionized water and 83 g of a 33% strength by weight aqueous polystyrene latex having a weight-average particle diameter D ₅₀ of 30 nm and 10% by weight of feed 2 were initially charged at room temperature under nitrogen in a 2 l polymerization vessel and heated to 90 ⁰ C with stirring. Subsequently, over two separate feeds at the same time beginning within 3 hours feed 1 and the remainder of feed 2 continuously in constant flow rates while maintaining the temperature in the polymerization vessel. 145 minutes after the start of feeds 1 and 2, 29 g of butadiene were added continuously to the polymerization mixture over a wide feed rate within 20 minutes in a constant stream.

After completion of feeds 1 and 2, the polymerization was stirred for 30 minutes at 90 ⁰ C, then cooled to 85 ° C and then at the same time on separate feeds starting a solution of 8 g of tert-butyl hydroperoxide and 80 g of deionized water and a solution consisting of 3.5 g of acetone, 5.7 g of sodium disulfite and 76 g of deionized water, continuously in constant flow rates while maintaining the temperature within 2 hours. Thereafter, 22 g of a 25% strength by weight aqueous solution of sodium hydroxide were added to the polymerization mixture in one shot and the aqueous polymer dispersion was cooled to room temperature. Feed 1:

490 g deionized water 9.9 g of a 45 wt .-% aqueous solution of Dowfax ^® 2A1

23, 1 g of a 15 wt .-% aqueous solution of Lutensit ^® A-LBN 50

19.3 g of a 70 wt .-% aqueous solution of tert-butyl hydroperoxide

730 g of styrene

551 g of butadiene 41.0 g of acrylic acid

10.0 g of a 25% strength by weight aqueous solution of sodium hydroxide

The solids content of the resulting aqueous polymer dispersion was 50.1 wt .-%, the average particle diameter was 123 nm and the glass transition temperature was determined to be 6 ° C. The residual styrene content was 800 ppm and the residual butadiene content was 120 ppm.

Comparative dispersion 1 (V1)

The preparation of comparative dispersion 1 was carried out analogously to dispersion 1 with the difference that feed 1 and the remainder of feed 2 were not metered in within 3 hours but within 6 hours.

The solid content of the obtained aqueous polymer dispersion was 50.0 wt%, the average particle diameter was 127 nm, and the glass transition temperature was determined to be 9 ° C. The residual styrene content was 700 ppm and the residual butadiene content 100 ppm.

Comparative dispersion 2 (V2)

Comparative dispersion 2 was prepared analogously to comparative dispersion 1 with the difference that feed 1 contained 28.9 g instead of 19.3 g of a 70% strength by weight aqueous solution of tert-butyl hydroperoxide.

The solid content of the obtained aqueous polymer dispersion was 50.1 wt%, the average particle diameter was 125 nm, and the glass transition temperature was determined to be 5 ° C. The residual styrene content was 3100 ppm and the residual butadiene content was 400 ppm. Dispersion 3 (D3)

In a 18 m ³ -Polymerisationsreaktor, with a ratio of internal height to Innen¬ diameter of 2.1, equipped with a 4-stage MIG stirrer, with a diameter ratio of stirrer blade to reactor internal diameter of 0.85, were at room temperature under Nitrogen atmosphere 1700 kg of deionized water, 100 kg of a 2% strength by weight aqueous solution of sodium ethylenediaminetetraacetate (Na EDTA) and 498 kg of a 33% strength by weight aqueous polystyrene latex having a weight average particle diameter D ₅₀ of 30 nm and 10% by weight .-% of feed 2 and heated with stirring (35 revolutions per minute) to 90 ° C. An¬ closing metered via two separate feeds simultaneously starting within 3 hours feed 1 and the remainder of feed 2 continuously in constant flow rates while maintaining the temperature in the polymerization reactor.

After completion of the aforementioned feeds, the polymerization mixture was stirred for 30 minutes at 90 ⁰ C, then cooled to 85 ⁰ C and then at the same time on separate feeds starting a solution of 54 kg of tert-butyl hydroperoxide and 480 kg of deionized water and a solution, consisting of 21 kg of acetone, 34.2 kg of sodium disulphite and 456 kg of deionized water, continuously in constant flow rates while maintaining the temperature within 2 hours. Thereafter, 132 kg of a 25% by weight aqueous solution of sodium hydroxide in one shot was added to the polymerization mixture and the aqueous polymer dispersion was cooled to room temperature.

Feed 1:

2940 kg of deionized water

59.4 kg of a 45 wt .-% aqueous solution of Dowfax ^® 2A1 138.6 kg of a 15 wt .-% aqueous solution of Lutensit ^® A-LBN 50 115.8 kg of a 70 wt .-% aqueous solution tert-butyl hydroperoxide 4380 kg styrene 3480 kg butadiene 246.0 kg acrylic acid

60.0 kg of a 25 wt .-% aqueous solution of sodium hydroxide

Feed 2 consisted of a solution of 81.6 kg of sodium peroxodisulfate in 1380 kg of deionized water.

The solids content of the resulting aqueous polymer dispersion was 50.0 wt .-%, the average particle diameter was 129 nm and the glass transition temperature was determined to be 6 ⁰ C. The residual styrene content was 900 ppm and the residual butadiene content was 220 ppm. Dispersion 4 (D4)

In a 18 m ³ -Polymerisationsreaktor, with a ratio of internal height to inner diameter of 2.1, equipped with a 4-stage MIG stirrer, with a Durch¬ knife ratio of stirrer blade to reactor internal diameter of 0.85, were at room temperature under Nitrogen atmosphere 1700 kg of deionized water, 100 kg of a 2% by weight aqueous solution of Na-EDTA and 498 kg of a 33% by weight aqueous polystyrene latex having a weight-average particle diameter D ₅₀ of 30 nm and 10% by weight of feed 2 and heated with stirring (35 revolutions per minute) to 90 ⁰ C. Subsequently, feed 2 was metered in via two separate feeds simultaneously starting within 3 hours and the residual amount of feed 2 was continuously in constant flow rates while maintaining the temperature in the polymerization reactor. 160 minutes after the start of feeds 1 and 2, 360 kg of butadiene were continuously added to the polymerization mixture via a further feed as feed 3 within 30 minutes in a constant stream.

After completion of feed the polymerization mixture 3 was stirred for 30 min- utes at 90 ⁰ C, then cooled to 85 ⁰ C, and then starting gave separate Zuläu¬ fe at the same time a solution of the 54 kg of tert-butyl hydroperoxide and 480 kg ent ¬ ionized water and a solution consisting of 21 kg of acetone, 34.2 kg of sodium disulfite and 456 kg of deionized water continuously in constant flow rates while maintaining the temperature within 2 hours. Thereafter, 132 kg of a 25% strength by weight aqueous solution of sodium hydroxide were added in one shot to the polymerization mixture and the aqueous polymer dispersion was cooled to room temperature.

Feed 1:

2940 kg of deionized water

59.4 kg of a 45 wt .-% aqueous solution of Dowfax ^® 2A1 138.6 kg of a 15 wt .-% aqueous solution of Lutensit ^® A-LBN 50 115.8 kg of a 70 wt .-% aqueous solution tert-butyl hydroperoxide 4380 kg styrene 3120 kg butadiene 246.0 kg acrylic acid 60.0 kg of a 25% strength by weight aqueous solution of sodium hydroxide

Feed 2 consisted of a solution of 81.6 kg of sodium peroxodisulfate in 1380 kg of deionized water. The solids content of the resulting aqueous polymer dispersion was 50.2 wt .-%, the average particle diameter was 123 nm and the glass transition temperature was determined to be 5 ° C. The residual styrene content was 750 ppm and the residual butadiene content was 250 ppm.

Comparative dispersion 3 (V3)

Comparative dispersion 3 was prepared analogously to dispersion 3 with the difference that feed 1 and the remainder of feed 2 were not metered in within 3 hours but within 6 hours.

The solids content of the resulting aqueous polymer dispersion was 49.9 wt .-%, the average particle diameter was 132 nm and the glass transition temperature was determined to be 8 ° C. The residual styrene content was 600 ppm and the residual butadiene content was 150 ppm.

II. Application testing

For the investigation, wood-free base paper (basis weight 70 g / m ² ) from the company Scheufeien, Germany, was coated on one side with 10 g / m ^{2 of} a paper coating slip (calculated as solid) consisting of

70 parts by weight Hydrocarb® ^® 90 (Calcium carbonate from. Omya AG, Switzerland), 30 parts by Amazon Plus ^® (kaolin from the company. CADAM SA, Brazil), 0.33 parts by weight Polysalt ^® S (45 % by weight aqueous solution of a polyacrylic acid

Sodium salt from BASF AG, Germany),

20 parts by weight of the aqueous dispersions D1 to D4 and V1 to V3, 1, 2 parts by weight of Sterocoll FD ^® (25 wt .-% aqueous ethyl acrylate / acrylic acid / methacrylic acid dispersion from. BASF AG, Germany),

0.2 parts by weight of a 25% strength by weight aqueous solution of sodium hydroxide and 49 parts by weight of deionized water,

by means of a DT Laboratory Coater Fa. DT Paper Science Oy Ab, Finland at 30 ⁰ C and atmospheric pressure coated (Stiffblade mm with a thickness of 0.3). The paper web was dried by means of an IR drying unit and air drying (8 IR emitters each with 650 watts, throughput speed 30 m per minute). Subsequently, the paper strips were calendered at room temperature by means of the bench laboratory calender K8 / 2 from Kleinenefers Anlagen GmbH, Germany. The line pressure between the rollers was 200 kN / cm paper width and the speed 10 m per minute. The process was carried out a total of four times. Depending on the binder used for the production of the respective paper coating slip aqueous polymer dispersion D1 to D4 and V1 to V3, the papers obtained were referred to as PD1, PD2, PD3, PD4, PV1, PV2 or PV3.

Determination of dry picking strength with the IGT test printing device (IGT dry)

From the coated papers PD1 to PD4 and PV1 to PV3 test strips were cut out with a size of 33 x 3 cm and stored for 15 hours in a Kli¬ makammer at 27 ° C and a relative humidity of 50%.

The test strips were subsequently printed at increasing speed in a printing unit (IGT printability tester AC2 / AIC2) with a standard color (printing ink 3808 from Lorilleux-Lefranc). The maximum printing speed was 200 cm / s. The paint was applied at a line pressure of 350 N / cm.

As a measure of the dry picking strength, the speed is given in "cm / sec", at which 10 out breaks from the paper coating slip (picking points) are carried out after the start of printing, the result being all the better the higher this printing speed at the tenth picking point The results of the tests carried out on the different coated papers are listed in Table 1.

Determination of wet pick resistance

The test strips were prepared and prepared as described for testing the dry picking strength.

The printing unit (IGT Printability Verifier AC2 / AIC2) has been set up so that the test strips are moistened with water before printing.

The pressure was carried out at a constant speed of 0.6 cm / sec.

Tears from the paper are visible as unprinted areas. To determine the wet pick resistance, the color density is therefore determined with a color densitometer in comparison to the full hue in%. The higher the specified color density, the better the wet pick resistance. The results of tests conducted on the different coated papers are also listed in Table 1. Table 1 Summary of results

It is clear from the results that the residual contents of styrene and butadiene of comparative dispersions V1 and V3 are below the respective contents of the corresponding dispersions D1 and D2 or D3 and D4 according to the invention. The comparative dispersion V2, on the other hand, has significantly higher residual contents of styrene and butadiene than the dispersions D1 and D2 according to the invention. Of particular importance, however, is that the performance properties of the coated papers PV1 and PV3, which are coated with the comparative dispersions V1 or V3 formulated Papierstreich¬ masses, are significantly poorer compared to the coated papers PD1 and PD2 or PD3 and PD4, which are coated with the dispersions D1 and D2 or D3 and D4 formulated paper coating slips.

By increasing the amount of regulator in the preparation of comparative dispersion 2, it was possible to produce a coated paper PV2 whose performance properties are comparable to the properties of the papers PD1 and PD2 according to the invention, but the comparison dispersion 2 obtained has the same properties as compared to the dispersions 1 and 2 according to the invention also for comparison dispersion 1 significantly higher residual monomer contents.

Claims

claims

1. A process for preparing an aqueous styrene-butadiene polymer dispersion by free-radical aqueous emulsion polymerization of a monomer mixture M containing

From 30 to 80% by weight of styrene,

From 20 to 70% by weight of butadiene and

in each case based on the total amount of the monomer mixture M, according to a monomer feed process in the presence of a non-copolymerizable hydroperoxide of the general formula ROOH as regulator, where R is hydrogen, C ₁ -C ₁₈ alkyl, C ₇ -C ₂₂ aralkyl and a saturated or unsaturated carbocyclic or heterocyclic ring having 3 to 18 carbon atoms, characterized in that the monomer mixture M is fed to the polymerization vessel within 4 hours.

2. The method according to claim 1, characterized in that the Gesamtad Butadienge¬ is> 1000 kg.

3. Process according to claim 1 or 2, characterized in that the total amount of butadiene is> 5000 kg.

4. The method according to any one of claims 1 to 3, characterized in that the monomer mixture M is led to the polymerization within 3.5 hours zu¬.

5. The method according to any one of claims 1 to 4, characterized in that the monomer mixture M is the polymerization within 3 hours zuge¬ leads.

6. The method according to any one of claims 1 to 5, characterized in that prior to the start of the polymerization reaction <30 wt .-% of the hydroperoxide are placed in the polymerization vessel ris¬ and the remaining amount of the polymerization vessel is supplied in the course of the polymerization reaction.

7. The method according to any one of claims 1 to 6, characterized in that the polymerization reaction is carried out in the presence of at least one seed latex.

8. The method according to any one of claims 1 to 7, characterized in that the radical R is hydrogen, tert-butyl, tert-pentyl, 1, 1-dimethylbutyl or 1, 1-dimethylpentyl, wherein said organic radicals may optionally be substituted with a hydroxy group.

9. The method according to any one of claims 1 to 8, characterized in that at least one hydroperoxide is used as regulator, which is selected from the group comprising hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene monohydroperoxide, tert-pentyl hydroperoxide, 1, 1 Dimethylbutyl hydroperoxide, 1, 1-dimethylpropyl hydroperoxide, 1,1-dimethyl-3-hydroxybutyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, p-menthyl hydroperoxide, pinanyl hydroperoxide, 1-methylcyclopentyl hydroperoxide, 2-hydroperoxy-2-methyltetrahydrofuran, 1-methoxycyclohexyl hydroperoxide , 1, 3,4,5,6,7-hexahydro-4a (2H) -naphthalenyl hydroperoxide, β-pinene hydroperoxide, 2,5-dihydro-2-methyl-2-furanyl hydroperoxide.

10. The method according to any one of claims 1 to 9, characterized in that the hydroperoxide is used only as a regulator and in combination with an initiator, wherein the molar ratio of hydroperoxide to the initiator 0.2 to 1 is.

11. The method according to any one of claims 1 to 9, characterized in that the hydroperoxide is used simultaneously as a regulator and initiator without the use of a further free radical initiator.

12. The method according to claim 11, characterized in that in addition to the hydro perperoxide, a reducing agent is used.

13. The method according to claim 12, characterized in that the molar ratio of hydroperoxide to reducing agent is 1, 2 to 20.

14. The process as claimed in claim 1, wherein the monomer mixture M is fed to the polymerization vessel in the form of the monomer feeds Mz1 and Mz2, the feed Mz1 comprising styrene, butadiene and optionally at least one comonomer and the feed Mz2 exclusively from butadiene, wherein at a time when> 70 wt .-% of feed Mz1 have been supplied to the polymerization, for a period Tz2 of> 1% of the total feed time Tz1 of the feed Mz1 Zu¬ run Mz2 is supplied, and wherein feed Mz2 consists of <30% by weight of the total amount of butadiene.

15. The method according to claim 14, characterized in that

a) with feed Mz2 is started at a time at> 80 wt .-% of feed Mz1 have been supplied to the polymerization vessel, b) the period Tz2> 5 to <40% of the total feed time Tz1 of the feed

Mz1, and c) feed Mz2 consists of> 0.5 to <30 wt .-% of total butadiene.

16. The method according to claim 14 or 15, characterized in that feed Mz1 is terminated after feed Mz2.

17. Aqueous styrene-butadiene polymer dispersion obtainable by a process according to any one of claims 1 to 16.

18. Use of an aqueous styrene-butadiene polymer dispersion according to claim 17 as a component in emulsion paints, paper coating slips, barrier coatings, adhesives, sealants, leather finishes, molded foam parts, backings for carpets and for the modification of mortar, cement and asphalt.