CA1094719A

CA1094719A - Process for the preparation of dispersible dispersion powders

Info

Publication number: CA1094719A
Application number: CA275,366A
Authority: CA
Inventors: Detlev Seip; Wolfgang Zimmermann
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-04-02
Filing date: 1977-04-01
Publication date: 1981-01-27
Also published as: BE853212A; CH628652A5; NL7703326A; DE2614261B2; FI64384C; DE2614261A1; JPS6050814B2; NO771166L; IE44732B1; SE7703815L; NO147031C; JPS52121092A; ATA230577A; FR2346379B1; GB1569637A; FI64384B; FR2346379A1; IT1075379B; DK143139C; IE44732L

Abstract

PROCESS FOR THE PREPARATION OF DISPERSIBLE DISPERSION
POWDERS
Abstract of the disclosure:

Dispersion powders having excellent properties for the production of synthetic resin-bound plasters in dry form are obtained by polymerizing vinyl acetate with other olefini-cally unsaturated monomers in the presence of an ionic emul-sifier, a non-ionic emulsifier and at least one polyvinyl alcohol and spray drying the copolymer dispersion in a spray tower with simultaneous introduction of an anti-caking agent to obtain a fine powder.

Description

` ``` ~ 1094719 `

~he inventio~ is concerned with a process for the preparation of dispersi~le polyvinyl acet &t6 copolymer disper-sion powders and the use thereof in the field of coating ~nd building.
Polyvinyl acetate homo- and co-polymer dispersion pot~ders dispersible with water are known. ~omopolymer dispersion powders are used chiefl~ in the adhesive field and copolymer dispersion powders are used chiefly in the coating and building field. In addition to the general requirements o~ a disper-sion powder, such as high stability in storage, good ~rining capacity and good dispersibility in water, there are furthsr special requirements for use in the coating and buildin~
field. Thus, dispersions o~t~ined with dispersion powders should have a minimum film-forming temperature of about 0C.
and the polymers should have a good stability to alkalies.
In combination ~Jith binding agents that set hydraulically dispersion powders should have a good compat~bility and bring about an improvement in the flexural strength and co~ression strength of test bodies. As the sole binding a~envs L or coating surfaces such, for exam~le, as asbestos ceme~t, wood ~nd masonry, there is required in so-called synthetic resin-bound plasters an especially high adhesion and abrasion resist-ance of the plaster s~stems bound by dispersion powders on all substrata, especially in the wet state.
In DAS 1l7199317 is described a process for prcducing non-blockin~, dispersible ~owders from poiymerisates and co~oly-merisates of vinyl acetate by the spr~ drying o~ dis~ersions~
The dispersions aré prepared with the use of polyvin~l alcohols as protectiYe colloids, at a conversion of mo~omers o~ 80 to ~0 9~ are added to the dispersion 0.5 to 4 parts by wei~ht OL

2 .

~0~ 7~1 9 polyvinyl alcohols havi~g a viscosit~ of 3 to 13 cP and a degree o~ hydrolysis of 75 to ~5 mol~ he dispersion powders produced by DAS 1,719,317 do not fulfil the conditions required for producing sufficiently waterproof synthetic resin-bound plasters.
In DOS 2,214,410 is described a p~ocess for the production of a re-dispersible vinyl acetate/ethylene polymer dispersion powder by spray drying a vinyl acetate/ethylene polymer dispex-sion. ~he dispersions are prepared at ethylene pressures of up to 100 atmospheres and polymerisation temperatures of pref-erably 50 to 70C. with the use of small quantities of ionio emulsifiers and polyvinyl alcohol as a protective colloid.
The synthetic resin plasters prepared with these dispersion po~ders h~ve ~ good ~terproof chc~r~cter~ ~hen, however, ~he vinyl acetate/ethylene dispersions are prepared at polymeri-zation temperatures of above 70Q C~ in order to save time in polymerization, the syr~thetic resin-bound pl~sters prepared with the dispersion powders obtc~ined therefrom are not suf~ic-iently waterproof. Pol~merisztion temperatures above 70C.
are deslred for vinyl acetate/ethylene di~spers~ons, because 'hen the dispersions can be prepared more economically .;ith shorter monomer-dosing times.
There has now been discovered a process for the p.oduction of copolymer powders dispersible in water by spra~ drying c~
copolymerisate dispersio~ of vinyl acetate with other olefinic-ally unsaturated monomers in the presence of anti-caking agents, which is characterised in that the emulsion polymerisation of the monomers is carried out in the presenc~ of O.C2 to ,.~' l~y weight, calculated on the copolymer, of ionic emulsi~ie~s, 0.05 to ~D by weight, calculated on the copolymer, of non-~ionic , . . ., _ . , . ~ , e~ulsifiers containing oxethyl groups, 5 to 2CPo by weight, calculated on the copolymer,of at least one polyvinyl 2lcohol of which an aqueous solution of 4 per cent strength has a vis-cosity at 20C. of 3 to 45 mPas and an ester number of 90 to - 215 mg of KOH/g and also of a radical initiator at a polymer-isation temperature of 70 to 100C., and t-he copolymer disper~
sion so obtained is dried in a spray drying tower to form a fine powder with the simulta~eous but spatially separated do~ing of anti-caking agents having a particle siz~ of 0.01 ~0 to 0.5 ~, such as aluminium silicate, silicic acid or calci~m carbonate, in a quantity of 2 to 2~o by weight calculated on the content of solid matter in the aqueous dispersion.
The copolymer dis~ersion so prepared has preferably a vinyl acetate content exceeding 4G,~ by weight. As copol~mer components there come into consideration furth~r olefinically unsaturated monomers, su~h as vinyl esters of strai~ht-chained or branched carboxylic acids containing 3 to 18 carbon &toms, acrylic, methacrylic, maleic or fumaric ac~d esters of aliphatic alcohols containing 1 to 18 carbon atoms, vinyl chlori~e, etnylene? isobutylene or higher ~-olefines co~taining 4 ~o 1 carbon atoms. Suitable combi-nations of monomei~s are vinyl acetate/2-ethylhexanoic acid vinyl ester, vinyi acetate/vinyi laurate, vinyl acetate/vin~l esters of carboxylic acids branch-ed in the ~-position containing 10 c~rbon atoms, vinyl acetate~
ethylene, vi~l acetate/vi~yl pivalate/ethylene and ~inyl acetate/vinyl chloride~eth~lene.
Monomer combinations of which the correspondin~ disper-sions have a mi~imum film-forming temperature of about GG.
are preferred. Howe~er, there may also ~e used monomer combinations of vinyl acetate of which the correspoJIding 10~ 719 dispersions have a minimum film-forming temperature of abo~re 0C., aIld a further reduction to about 0C. can be achieved by the addition of external plasticizers, such as adipic and phthalic acid esters, trialkyl-- and triaryl-phosphoric acid esters or glycerine esters of long-chained carboxylic acids.
In addition to the monomers mentioned above there may also .
be used other ~onomers having a stabilizing action on the dis-persion such, for example, as sodium vinyl sulphonate, mono~rs containing carboxyl groups such as ~crylic, methacrylic, cro-tonic or itaconic acid or monoesters of maleic acid, of w~ich the alcohol components may contain 1 to 18 carbon atoms, acrylamide or methac~yl~mide in a conce~tration of up to 5~
by weight calculated on the total polymer. In addition there may also be used components havin~ a cross-linki~g ~^tiOIl~
for example, co~pounds containi.n~ methylol groups, such as N-methylol-acryla~ide or ~onomers colltaining two or mo~e unsaturated double bonds, such as ~iallyl maleate, tetra-allyloxyethane or adipic acid divinyl ester.
The emulsifier/protective colloid syste~ of the in~entiorl, which yields the vinyl acetate copol~ne.r dispersions used for the claimed d~spersio~ powders, is composed of ionic and non-ionic emulsi~iers and polyvinyl alcohols as protective colloi~s.
~he ionic emulsi~iers are used in quantities of OrO5 to 1C~
~y weight, preferably 0.05 to 0.5,. ~y .eight, calculated on the polymer. There are advantageously used emulsifiers of the type of alkyl sulphates containing ~0 to 16 carbon atoms.
Non-ionic oxethylated emulsifiers a~e used in qu~ntities ot`
.1 to ~0 by ~reight, preferably 0.1 to 1r., by weight, calculate~
on the pol~mer. ~refer~ed emulsifi.ers of` this type ~re

3~ oxethylatea aliphatic alcohols, oxethylated al~rl-~he~o.1.~ a~d 10~4719 oxethylated polyprGpylene glycols. One or more types of polyvinyl alcohol having an ester number of 90 to 215 mg of KOH per gram, preferably 90 to 160 mg of KOH per gram, and a viscosity of an aqueous solution of 4 % strength at 20 C of 3 to 45 mPas, and prefereably 4 to ~0 mPasJare used in quan-tities of 5 to 20 % by weight, calculated on the polymer, and preferably 7 to 15 ~ by weight. For preparing the disper-sion powder of the i~vention it is of advan~age for the poly-merisation liquor to contain at the beginning of the prepara-tion of the dispersion 50 to 9~, by weight of the pol~viny1 alcohol used and subsequently to add to the finished disper-sion 10 to 50~0 by weight in the form of an aqueous solution.
~he dispersion li~uor is adjusted to a ~I~-value within the range of 4 to 7.5. A suitable ~uXfer such, for exa~ple, as sodium acetate, sodi~m phosph~te or sodiu~ bicarbonate, may be added to the dispersion ~quor to control the p~-value.
The emulsifier/protective colloid system permits of ~sing the especially advantageous polymerisatio~l temperatures of above 70 to 100C. The hi~her the polymerisation tempera'ure the more economical is the process as the heat of polym~risa-tion can be more easily abstracted and in -~ s S`J~y the perio~l during which monomer is supplied and therewith the ~hole period of preparation can be shortened~
As pol~erisation initiators there are used the usual radical initiators, preferably ~Jater-~oluble per-compoun~s, but monomer-soluble compounds may also be used.
The vinyl acetate-copolymerisate dispersions have a con-tent of solid matter of about 30 to 6~/~ by weight. ~fter the polymerisation has ended, a content of solid matter favourable for spray drying of about 30 to 4~% by weight isadjuste~ by 10~`~719 the addition of water or an aqueous solution of polyvinyl alcohol.
The dispersion powders of the invention are prep~red from the a~ueous synthetic resin dispersions by spr~y dryin~.
If synthetic resin dispersions having a minimum film-forming temperature of around 0C. are used, it is necessary in the spray dr~ing to add an anti-cakinæ agentto ensure that the dis-persion powder has a good stability during storage. Suitable anti-caking a~ents are alumini~m silica~es, calcium carbonates or silicic acids having an average particle size of about 0.01 to 0.5 ~. Especially preferred anti-caking a~e~ts are silicic acids and aluminium silicates, and advantageous quan-tities are 2 to ~/o by weight calculated on the content of solid matter in the aqueous synthetic resin dispersions.
I'he anti-caking agent is introduced into the spray dryin~
tower simultaneously with but separately from the aqueous dispe~sion. This ~ethod ol supplyinbP the anti-caking a,~ent preve~ts to a great extent the formation of undesired coati~gs on the wall of the drier.
The dispersion powders prepared in accord?~n~e with th~
in~ention have a gOoa stability to storage, and run wall and can be stirred with water to form rapidly homogeneous disper-sions of stable viscosit~ and stable to storage. They are well suited for the production of adhesives, sizes and coa~ing preparations~ They axe outst~ndingly useful ~or the produe~or.
o~ s~nthetic resin-bound plasters in dry io~m. ~hese syntheti~
resin-bound plasters are prepared in the d~y st~te by intim~ e-- ly mixing v~rious granulated mineral additives ~ith the ~inyl acetate copolymerisation powders o~ the invention. At the place of use these dxy powders are st;irred with water and aPPlied in a suitable manner to a wall or masonry.

~fter dl~ing these synthetic resin-bound plasters fulfil to a high degree the necessary requirements, such as a good w~t and dry adhesive power and good resistance to water.
~he following Examples illustrate the invention.
Example I
1. ~he ~roduction of a vinyl acetate/eth~lene copolymer dis~ersion.
Into a pressure reaction vessel haviI~ a capacity of 30 parts by ~olume provided with a temperature regulating device and stirring means is introduced a solution, adjusted to a pH-value of 6.0, of 7 parts by weight of sodium lauryl sulph-ate, 76 parts by weight of oxethyl~ted nonyl-phenol contai~ing 30 mol of ethylene oxide per mol of non~l-phenol, 680 parts by weight of polyvinyl alcohol of which an aqueous solution ~5 of 4yo strength at 20C. has a viscosity of about 8 m~as a~d ~ich has an ester n~er of 14Q n~ per KOH/c~, 139 r~arts bv ~i~h~ of polyvinyl alcohol o~ which an aqueous solution of 4Cb strengtn at 20 C has a viscositv or a}:~ut 18 Irpas ~d ~ic.h has an ester nu~er of 140 mg of KOH/g, 15.3 parts by weight of anhydrous sodiu~
acetate and 7700 parts by weight o~ water. The reactor is ~cavenged with nitrogen and ethylene in order to remove practically all the oxygen r The stirrin~ ~eans is then adjusted to 150 revolutions per mi~ute, 760 parts ~y ~ei~st of ~inyl acetate are added to the mixture, the contents of 2~ the vessel are heated to 60C., ~t 60C. a solution o~ ~ ~ar'~
by wei~ht of a~lmonium persulphate in 500 parts by ~eight of wat`er is added, and the contents o~ the vessel are further heated to 80C. During the heating-up process ethylene - is introduced up to a pressure of 20 bar. When the internal temperature o~ 80C. is reached, the introduction o~er a 109`~7~,9 .

period of 5 hours of 6880 parts by weight of vinyl acetate and a solution of 4.2 parts by weight of ~nonium persulphate in 350 parts by weight of water at an internal temper~ture of 80C. and a pressure of ethylene of cO bar is comme~ced.
When the introduction is complete, there is added to ~he mix-ture a solution of 1.8 parts by ~eight of ammonium persulphate in 150 parts by weight of water, and the whole is further heated for 1.5 hours at an external temperature of 85C.
The supply of ethylene is then cut off and the dispersion is cooled to room temperature. There is then added tc the dis-persion a solution of 220 parts by weight of polyvinyl alcoh~l~
of which an aqueous solution of 4C~o stren~h at 2CC. ha~ a viscosity of about 4 ~as and ~hich has an ester n~er of 140 m~ of ~0~/g)in 1280 parts by weigh-E of water. ~he ~inyl ac~tate/
ethylene copolymer dispersion of 50,~ stren~th is then dra~n off and has an ethylene content of about 14~ by weight9 a residual monomer content sf less than 0.5% by weight, a latex viscosity (~pprecht-rheometer C/II) of 1.5 Pas and a ~in~m~
film-forming temperature belo~ 0C.
2. The production ol the vinYl acetate/e ~h~lene copol~mer __ ~o~der.
~he vinyl acetate/ethylene copol~mer dispersion pr~pared in Example I~1 is diluted ~lith ate~ to a content of solid matter of 4~' by weight, before ~he spray dryintt. ~s the drying ap~aratus there is used an ~ onising tower, of which the cylindrical part h~s a diameter of 1.6 metres and a l~n~h of 4 metres and of which the conical part has ~ len~th o 2 metresc The dispersion is supplied b~J !~eans oî ar eccentric sc~ pump to a two-component a~omising noæ~le ha~in,~
3 a pxoduct bore 3 L~ in diameter. ~he drying is cs-~ried GU`~

in parallel flow, and as the drying gas there is used nitro~cn having a throughput of 750 cubic metres per hour. The temper-ature o~ the drying gas at the in]et of the tower is 115C. and in the cyclone separator 65C. he throughput of atomising air for the product nozzle is 70 parts by weight at a pressure in frbnt of the nozzle of 5 bar and a temperature of 23C.
Through æ second two-component nozzle, which is situated in the ~icinit~ of the wall of the tower only a little below the product nozzle, is introduced as an anti-cc~king a~ent a finely di~ided powder of silicic acid having an SiO2 content of 92,~"
a surface area a~cording to BE~ of 250 square metres per gram and an average size of the primary particles of 0.018 ~ in quantity of 5C~ calcul~ted on the content of solid matter of the aqueous dispersion, into the spraying to~er simultaneo~sly with the dispersion. The dispersion powder so obtained has a good running capacity and a good stability to storage, that is to say, a sc~mple of the powder even after being stored for 24 hours at 50C under a load of 200 gra~ per square cen,i~etre can easily be loosened up. ~he ~pparent density ol the powder is ~80 ~rams per litre, the volume after ~haking is 81f,~ and the compression density is 470 gr~ms per litre. '~he po~.~der can easil~ be stirred with water to form a stable dispersicn, of which the viscosity, measured wit'l a dispersion of 5~r~`
strength and accordin~ to Epprecht/me~suring system C 2, is 7.3 P~s.
In æddition to its suit,ability for preparing sizes, adhesives ~nd coating preparations tllis po~der can be used as the sole binding a~ent Ior the p-~oduction o~ synth_tic resin d~y plasters having excellent properties, A selec-tion of various recipes for the production of syn~hetic resir 109`~719 plasters is given in the accompan~ing Table. The preparation of the plasters is carried out by intense mixing of the solid constituents, then adding water, again thoroughly mixing and applying the plasters with a wiper or trowel to test plates of asbestos cement having a thickness of about 5 mm.
~he dried out plasters are distinguished by a very good resist-ance to water and a very good adhesive power on the underlying material, ~fter storing the plates in wa~er the plasters remain practically unaffected. ~heir adhesi.on to asbestos cement i5 very good and detrition in the wet state is insig-ni~icant.

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Comparison Exc~mple I
.
In accordance with the procedure gi~en in Exa~ple I
is prepared a vinyl acetate/ethylene copol~mer dispersion at a pol~erisation temperature of 60C. and an eth~lene pressure of ~0 bar ~rith the difference ~s co~pared with Ex~mple I that the poly~erisation liquor contains no oxeth~l-ated nonyl-phenol. Owing to the low pol~erisation ~emper-ature of 60C. ~d the diffic~lty connected there~iith in abstracting the heat cf pol~Jmerisation, the period of in'rc-ducin~ the monomers, as distinct from ~x~ple I, must be extended from 5 to 8.hours. ~he vinyl acetate/e~hylene copolymer dispersion of 50% strerl~rth so obtained san be spr~r dried, as in ~xample I, in the presence of the anti-c~kinfr a~ent described thexein t~ form a dispersion powder stable to stora~e, which is also suitab'e for the production of synthetic resin-bourld plasters havin~r a good ~aterproo~
character.
C~omp~ri son Ex<~lple IX
~he procedure for preparing a vinyl acetatc/ethyle~e copolymer dispersion is the same as in Gonpa-ison E~a~ple I, except that as in 3x~mple I the desirably high ~ol~merisL-atiQn temperature of 80~C. is used. ~he period of irtrocLuctlon of the monomers was 5 kours ~s in E~2-Ijle T. m~e ~i~l acetate~ethylene copolymer ~ispersion so ob~ai~ed ws s r~--dried by the procedure given in ExL~ple I in ~he presence of the c~ti-cakin~ agent, silicic acid, to lorm a dispersion powder, which was worked up accord ill{~, to the directio~ s gi ~;en in Example I to form s~nthetic res`n-bo~ d plasters, but which ~!Jere insufficiently ~aterproof nnd had a poor wet 3 adhesive power on asbestos cement. ~fter sto~ ; .,he through-dried plaster in water the plaster could easil~ be separatcd t`rom the underlying material and on the surface it could be easily rubbed off. The comparison Exa~les T
and II make clear that at lo~ poly~erisation tem~eratur~s, which lead to unavoidably lo~g and economically unfavou-able periods of pol~meri~ation, the use of the emulsifier/~rot~ctive colloid system in accordance with the invention can be dispens-ed ~ith fo~ attaining the ob~ect aimed at, namely the pro~uc-tion of waterproof synthetic resin plasters. ~owever, -t the economically favourable hinh pol~merisation te~peraJ1res the desired aim can be achieved only by the use of the e;~
sifier/pro~ective colloid syste~ of the inven ion.
xample II
In a polymsrisation vessel having a capacity of 1Co parts by volum.e, provided with a horseshoe mixer and re~.L~
condenser, a vinyl acetate copolymsr dispersion is pre~ red with the use of a polymerisation liquor contai.ning ~0,~00 parts by weight of water, 2~700 p~rts by weigh~ of pol~ri~y~
alcohol of which an aqueous solution of 4~ strength ~t 2C~.
l~as a viscosity of a~out 8 n~as and which has an ester nu~e:r of 14r~ T~ r .-o~/g~ 150 parts by wei~ht of oxe~hylated polypropylcne gl~col havin~ a molecular weicrht of about 200C ~nd cn e ~'l!
o~ide content of about 40,b b~T ~ei~ht, 24 parts by weigh~ o~
sodium lauryl sulphate an~ 60 parts b~ ~reight of anhydrcus sodiu~ aG~tate~ a moncmer mixture of 1~,C00 parts by ~;e ~t of vinyl acetate and 12~000 parts b~ eight Gf a vi~l es~er of carbo~ylic acids containin~ 10 carbon ato~s and br--n&l~ed in the ~~position a~d a catalyst solu-tion containirl~ 47 ~_rts by weight of ammonium p~rsulphat~ and 8C0 parts by wei~lt of water, at a polymerisation temperature of 8QC. and a pe~io~

109~719 of introduction of the monomers o~ 2.5 hours. After the preparation, there are added to the dispersion 990 p~rts by weight of phthalic acid dibutyl ester and a solution of 750 parts by weight of polyvinyl alcohol of which an aqueous solution Of 4C~ strength has at 20C. ~ viscosity of 4 mPas and~ich has an ester n~r of 140l~`of KO~per ~ram in 3000 u~ts by weight of water. ~he vinyl acetate copolymer dispersion of about 5~c s~rength so obtained has a ~inimum film-forming temperature of 0C. and a latex viscosi~r measured in the Epprech~-rheometer C/2 of 2.5 Pas.
The spr~v dryinG of the dispersion diluted with wa-ter to a content of solid matter of 4~,~ by ~Jeight is carried out according to the data ~ n ~n ~x~mple I,~ with &~,~, calcv.lated on the content of solid matter i~ the dispersion, of sy~thetic silicic acid as a~ti-caking agent ka~ing an ~iO2-ccntent of 93,h, a surface area according to BE~ of 230 square metres per gram and an average size of the primar.~y particles o~ OoO1 ~, resulted in a flo~able dispersion powder o~ good sbabili.ty to storage, ~hich was outstandingly suitable for the produc~
~0 tion of waterproof plasters.

According to the procedure give in Example I.1 there was p.repared a vi~yl acetate/vi~Yl chloride/ethylene terpol,~
mer dispersion at a pol~erisation te~pe~ature of 8CC. arld an ethylene pressure ol 45 bar with the difference ~ro~.
~xample I.1 that there were used, instead of 7640 ~ar~s b~
weight of vinyl acetate, a mixture of 5350 parts by weight o.f vinyl acetate and 2290 parts by ~eigbt of vinyl ~hlorîàe Rlld, instead of 76 paI~ts by weight of oxethyl~at~d nonyl-p~l~nol, 57 parts by weight of' oxethylated ste~ryl alcohol oon 10~7~9 20 mol of et-hyl~ne oxide per mol of stearyl alcohol.
The vinyl acetate/vinyl chloride/ethylene terpoly~er dispe~-si.on, after dilution to a content of solid m~tter of 4~j~
by weight, was spray dried in accordance w~th the prescrip-tion given in Ex~mple I.2 to form a flowable dispersion powder stable to storage, ~Jhich by usin~ the recipes formu-lated ~n the ~able is outstandingly suitable for the produc-tion of haterproof synthetic resin plasters~
xample IV
In accordance with the ~rocedure given in Ex~le II
a ~inyl acetlte/2-ethylhexanoic acid vinyl ester copolymer dispersion is prepared with the difference from ~xa.~.)le II
that, instead of the monomer mixture given in Exam-ele II, there is used a mixture of 21000 parts by we.ight of vinyl acetate and 9000 parts by wéight of 2-ethylhexanoic acid vinyl`ester, and no phthalic acid dibutyl ester is subse-que~tly added to the dispersion. ~he dispersion ca~ be spray dried, as described in Exa~ple II, to form a flowable dispersion powder stable to st~ra,~e, ~hich is outstandin~ly suiGabIe for the production of ;~aterprooi syrthetic resin plasters.
Ex~mple V
In accorda~ce with the prescri."tion given in Exæaple TI
a vinyl acetate/dibutyl maleate copolymer dispersion ,:~s prepared with the dif~erence from Exc~nple II that. there were ~sed, instead of the ~ono~ler mixt:ure give~ in Ex~aple 11, a mixture of 20,100 parts by weight of vinyl acetate and -~ 9900 parts by weight of dibutyl maleate and, ins~ead o~ t`~le oxethyla~ed polyprop~lene glycol used in E~a~ple II, cne ~0 havi~g an ethylene oxide content of 2~' by weight.

10~4719 The dispers~on powder ob~ained from this dispersion by spray drying is also outstandingly suitable for the production of waterproof synthetic resin plasters.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED OR DEFINED AS FOLLOWS:

1. A process for the preparation of a dispersion powder which is dispersible in water and is suitable for use as a binding agent for synthetic resin-bound plasters, in which a mixture of vinyl acetate with at least one other olefinically unsaturated monomer is subjected to emulsion polymerisation in the presence of (a) 0.02 to 1.0% by weight of at least one ionic emulsifier, calculated on the copolymer, (b) 0.05 to 2.0% by weight of at least one non-ionic emul-sifier containing oxethyl groups, calculated on the copolymer, (c) 5 to 20% by weight, calculated on the copolymer, of at least one polyvinyl alcohol, an aqueous solution of which having 4% strength has at 20°C a viscosity of 3 to 45 mPas and which has an ester number of 90 to 215 mg of KOH/g, and (d) a radical initiator, at a polymerisation temperature of 70 to 100°C, and the resultant copolymer dispersion is spray-dried in a drying tower to form a fine powder with the simultaneous, but spatially separated introduction of at least one anti-caking agent having a particle size of 0.01 to 0.5 µ, in a quantity of 2 to 20% by weight, calculated on the content of solid matter of the aqueous dispersion.

2. A process as claimed in claim 1 in which the anti-caking agent is selected from the group of aluminium silicate, silicic acid and calcium carbonate.

3. A process as claimed in claim 1, in which the non-ionic emulsifier is selected from the group of oxethylated alkyl-phenols, oxethylated alcohols and oxethylated polypropyl glycols.

4. A process as claimed in claim 1, claim 2 or claim 3 in which the olefinically unsaturated monomers are selected from the group of vinyl esters of straight chain or branched carboxylic acids containing 3 to 18 carbon atoms, acrylic, methacrylic, maleic and fumaric acid esters of aliphatic alcohols containing 1 to 18 carbon atoms, vinyl chloride, ethylene, isobutene and higher .alpha.-olefins having 4 to 12 carbon atoms.