Process for the preparation of dispersions of ethylene-vinylester polymers.

p0001The present invention relates to a process for producing ethylene-vinyl ester graft copolymers, by the graft polymers produced in solution are transferred directly into stable dispersions.

p0002It is known to convert ethylene copolymers from their solution in finely divided dispersions. Thus, DE-AS 1,237,311 describes a process, ethylene-vinyl acetate copolymers from their solution in tert. Butanol or mixtures of tert. Butanol, woks if vinyl esters and an organic water-immiscible solvent having a boiling point above 50 ° C to disperse using a combination of anionic and nonionic emulsifiers dispersing aid in water and from this emulsion to remove the solvent by distillation. Although this process leads to finely divided ethylene-vinyl ester copolymer dispersions, but may be the addition of special emulsifying and dispersing agents, which are often undesirable and often lead to the formation of foam in the distillative removal of the solvent.

p0003It has now been found that finely divided without the use of such emulsifiers and dispersants and without the addition of water-immiscible solvents, stable dispersions are obtained from ethylene-vinyl ester graft when in the preparation of the graft polymers in organic solution after at least 25 wt. -% of the graft monomers are reacted, adding under the action of shearing forces, for example stirring, a precipitating agent for the reaction products. In general, adding the precipitating agents is still incomplete conversion of the graft monomers and to the polymerization during or after the formation of the dispersion to an end. Of course, it is also possible to first graft polymerization to the desired, eg complete monomer conversion to perform, and then to convert the reaction products in a dispersion.

p0004The invention provides a process for the preparation of stable, finely divided dispersions of optionally cross-linked ethylene-vinyl ester graft polymers, characterized in that<ul><li>_A) 95-25, preferably 90-50 wt .-% of an ethylene-vinyl ester copolymer with a Vinylesterge content of 25-75, preferably of 35-50 wt .-% as graft substrate and</li><li>B) 5-75, preferably 10-50 wt .-% of a vinyl ester of a C₁-C₁₈Carboxylic acid and / or a C₁-C₁₀Alkyl ester of acrylic and / or methacrylic acid and</li><li>C) 0-40, preferably 0-20 wt .-% of a two. or more cross-linking agent containing CC double bonds, the sum of components A) - C) wt .-% is always 100, in organic solution, to polymerize to a conversion of at least 25 wt .-% of component B) and then under the action of shear forces adding a precipitating agent, whereby the reaction product precipitates and at the same time passes over into a stable dispersion, and the polymerization before, during or after the formation of the dispersion is taken to completion.</li></ul>

p0005As graft substrates are ethylene vinyl acetate copolymers with from 25 to 75, preferably used with from 35 to 50 wt .-% polymerized vinyl ester. As the vinyl esters are vinyl esters of saturated organic, optionally substituted by halogen, especially by chlorine, substituted C₁-C₁₈Monocarboxylic acids in question, such as vinyl formate, vinyl acetate, vinyl propionate, vinyl chloropropionate, vinyl butyrate, vinyl isobutyrate, Vinyllaurinat, Vinylmyristinat, vinyl stearate, vinyl benzoate. Preferably ethylene-vinyl acetate copolymers are.

p0006The ethylene-vinyl acetate copolymers are prepared by the known methods of high and medium pressure synthesis, optionally in solvents such as tert-butanol, and, if desired, be completely or partially hydrolyzed. They have Mooney viscosities ia ML4 / 100 ° C, measured according to DIN 53 323, of 15 to 80, preferably 20 to 45, and intrinsic viscosities η of 0.5 to 1.8 dl / g, measured in THF.

p0007For the grafting suitable monomers already mentioned vinyl esters of C₁-C₁₈Carboxylic acids and / or C₁-C₁₀Alkyl esters of acrylic and / or methacrylic acid such as methyl (meth) acrylate, n- or isobutyl (meth) acrylate, ethyl (meth) acrylate, n- or isopropyl (meth) acrylate and 2-ethylhexyl (meth) acrylate , Preferably Vinylacetat.als graft monomer is used.

p0008The grafting reaction can optionally by adding 0-10, preferably 0.1-10 wt .-%, based on component B, of so-called. "Graft activators" favored. As graft activators are C readily copolymerizable unsaturated monomers, for example,₂-C₁₈-α-olefins, such as ethylene, propylene and isobutylene, allyl compounds such as diisobutylene, Isobutylendiacetat, isobutylenediol, vinyl ethylene carbonate, diallyl carbonate, 1-butene-3,4-diol, and 2-methylene-1,3-dihydroxipropan or 2-methylene-1,3 -diacetoxipropan, (meth) acrylic acid and (meth) acrylamide: ethylene is as Pfropfaktivator.

p0009For the preparation of crosslinked graft polymers suitable crosslinking agents include divinyl aromatics, divinyl ethers, divinyl esters of C₂-C₁₀Dicarboxylic acids, diallyl and triallyl ethers and esters, esters of diols mitcL, ß-unsaturated C₃-C₁₀Monocarboxylic acids and unsaturated polyesters. Examples include: divinylbenzene, butanediol diacrylate, Glykoldivinylether, divinyl, allyl vinyl ether, diallyl, triallyl and trimethylolpropane triallyl.

p0010The aliphatic or mixed aliphatic-aromatic polyesters used as cross-linking agents are prepared in per se known manner by esterification or transesterification of mixtures of aliphatic or aromatic dicarboxylic acids or their derivatives such as anhydrides or esters and aliphatic dialcohols (cf.. Ullmann's Encyclopedia of Industrial Chemistry, Volume 14;. Urban and Schwarzenberg, Munich, 1963, p 80 ff).

p0011Examples of preferably to be used for preparing the polyesters unsaturated dicarboxylic acids or their derivatives are maleic acid, maleic anhydride and fumaric acid. but can be used also mesaconic acid, citraconic acid, itaconic acid or chloromaleic acid. In addition, aromatic dicarboxylic acids or their derivatives, such as phthalic anhydride, isophthalic acid, terephthalic acid, hexa- or tetrahydrophthalic acid or their anhydrides, endomethylene or its anhydride and saturated dicarboxylic acids and their derivatives such as succinic acid or succinic anhydride and succinic acid ester and chloride, adipic acid and sebacic acid may be used , Preferably, polyesters are maleic acid, which may be replaced by phthalic acid or isophthalic% up to 25 mole sowie.von adipic acid, the maleic acid can be replaced by up to 30 mol%.

p0012Suitable dihydric alcohols for preparing the polyesters for example, ethylene glycol, propanediol-1,2, propanediol-1,3, diethylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, perhydrobisphenol and can be used , Preferably used are ethylene glycol, 1,2-propanediol, diethylene glycol and dipropylene glycol.

p0013For branched polyester of higher functionality carboxylic acids or alcohols are used, mention may be made of glycerol, 1,1,1-trimethylolpropane, hexanetriol and pentaerythritol (see. Eg DE-PS 1,105,106 and DE-AS 1,029,147). The molecular weights of the polyesters are between 800-10000, the OH numbers between 0.1 and 100, acid values ​​between 0.1 and 80. The residual water contents of the polyesters are generally below 0.1%. If desired, special polyester with, for example, narrow molecular weight distribution can be used, which are obtained by polymerization of lactones, such as beta-propiolactone, γ-butyrolactone or ε-caprolactone, or by copolymerization of epoxides with cyclic anhydrides (see FIG. K. Hamann , Makrom. Chem. 51 (1962) 53 and RF Fischer, J. poly. Sci. 44 (1960) 155).

p0014The polyesters may be used alone, possibly also polyethers are used in a mixture with other polyesters or.

p0015The unsaturated polyesters have the advantage that they are precipitated with the ethylene-vinyl acetate copolymers, and thus result in the dispersed particles to a high crosslink density compared to low molecular weight crosslinkers.

p0016Suitable solvents for the present process include cycloaliphatic and aromatic, optionally halogenated hydrocarbons, and straight and branched C₄-C_8th-monoalcohols. Preferred solvents for the purposes of the invention are water-miscible solvents such as dimethylformamide or tetrahydrofuran, preferably tert-butanol as well as mixtures of tert.-butanol containing up to 25% of its weight in water. As precipitating agent water or C1-C3-alcohols are generally used. The preferred precipitating agent according to the invention is water.

p0017The graft copolymerization process of the invention can be generally carried out without the use of dispersants, since the ethylene-vinyl ester copolymers and the graft polymers themselves act as dispersants. In certain cases, however, such adjuvants may optionally be added.

p0018Particularly effective dispersants are soluble high molecular weight polymers in vinylaromatics, in unsaturated polyesters or a polyester / vinyl aromatic mixture. Very particularly preferred dispersants are ethylene-vinyl acetate copolymers with more than 60 wt .-%, preferably 65-75 wt .-% of vinyl acetate content and a Mooney viscosity of at least 15, preferably from 40 to 65 Mooney, measured according to DIN 53 523 (1-4), and polyvinyl acetate.

p0019Furthermore, polymers of (meth) acrylic acid esters containing 1 to 24 carbon atoms in the alcohol component, or their copolymers are suitable with vinyl esters of organic mono or dicarboxylic acids having 1 to 18 carbon atoms, and hydrolysis products thereof, as dispersants, however. Very good dispersants are graft polymers with polymers mentioned as a graft substrate. Suitable dispersants are also cellulose derivatives such as methylcellulose, hydroxyethylcellulose or cellulose ester -, - for example, cellulose acetate, cellulose acetopropionate, cellulose acetobutyrate or nitrocellulose.

p0020Mention may also exemplified styrene-acrylic acid or hydrolyzed styrene-maleic anhydride copolymers, polyethylene oxide, polyacrylamide or polyacrylic acid. The dispersion auxiliaries are on the total solids content of the dispersion, added in amounts of O to 10 wt .-%, preferably from 0.5 to 2 wt .-%, based.

p0021After addition of the graft and optionally the crosslinking agent and graft activators induce the polymerization by irradiation or radikalliefernde initiators. Initiator radicals can also known redox systems are generated by means of UV irradiation or actinic light or accelerated electrons.

p0022As polymerization catalysts can be used per- or azo compounds or radical yielding highly substituted ethane derivatives such as Benzpinacol. Examples include: benzoyl peroxide. tert. Perpivalate, lauroyl peroxide, tert. Peroctoate, tert. Butyl perbenzoate, di-tert. Butyl peroxide, tert. Butylperisononanat, diisopropyl, dicumyl peroxide, tert-butyl perneodecanoate, azobisisobutyronitrile or esters of Azobisisobuttersäure such as Bisethylester.

p0023The polymerization can before, during or added after dissolving or mixing the polymerization. The catalysts are preferably added after preparation of the homogeneous Pfropfsubstratlösung with the monomers or separately from the monomers in the reaction mixture.

p0024The polymerization catalysts are expediently used in an amount of 0.001 to 2 wt .-%, based on the sum of graft substrate and grafting. This amount can of course far exceeded or undershot.

p0025The graft polymerization is preferably carried out depending on the initiators used at temperatures between 20 and 250 ° C in the temperature interval from 50 to 150 ° C. There are pressures from 1 to 400 bar, preferably applied by 1 to 25 bar.

p0026The graft and disper inventive alloy can be carried out either continuously or intermittently. The graft substrate is dissolved in a solvent or solvent mixture precipitant. Or after addition of the graft monomers, optionally one or more cross-linking components, possibly graft activators as well as in special cases, dispersing aids, the polymerization is started. After at least 25 wt .-% are converted to the graft, metered to a precipitant and falls from the reaction products.

p0027For carrying out the process it is of advantage to carry out the addition of the precipitant in a zone of high turbulence. To prepare the dispersion in a zone of high turbulence, use is generally well-known devices, for example, conventional stirred tank. The specific mixing performance in an intensively stirred stirred vessel is usually 10^-1 to 10-3 watts / cm³,

p0028Much better than conventional stirred tank are equipped with rotors provided pumps, especially because in them the residence time in the zone of high turbulence is sharply restricted. A specifically developed to high turbulence special type of so-called Kreiselhomogenisiermaschinen works with very high throughput; its specific mixing performance is about 5-25 watts / cm³, So please allow a particularly intensive mixing in a very short residence time and are therefore preferably used.

p0029The precipitated according to the inventive reaction products are present in the form of stable, finely divided dispersions of homogeneous particle size distribution. The particle size varies between 0.1 and 10 microns, preferably in the range between 0.2 and 2 microns. The shelf life is at least six months.

p0030The ethylene produced by the novel vinyl ester graft polymer dispersions suitable for coating paper and fabrics of all kinds, as binders for fiber webs of natural or synthetic origin, as well as binders for paints.

p0031The following examples illustrate the invention. It is an ethylene-vinyl acetate copolymer (EVA copolymer) having a vinyl acetate content of 45%, a Mooney viscosity of 18-25 and an intrinsic viscosity η of 1.2 [d1 / g], measured in toluene, is used. Percentages always relate to the weight. As the crosslinking agent used is a polyester referred to as A, using 0.5 mole of butanediol, 0.5 mol of ethylene glycol, 0.7 mole adipic acid and 0.3 mole of maleic acid synthesized polyester having an OH number of 53, an acid number of 0.8 and has a viscosity at 75 ° C of 1890 mPas. The experiments described in the examples are in with an anchor Impellrührer fitted 12 or 20 1 Autoklavenduchgeführt; the stirrer speed is 240 or 180 U / min.

example 1

p00322₀₀0 g of EVA copolymer are dissolved in a stirred vessel 6000 g of tert-butanol and 1000 g of water. For this purpose 500 g of vinyl acetate are metered. After addition of 5 g of tert-butyl perpivalate dissolved in 100 g of a 4: 1 mixture of tert-butanol and water, is 30 min, and then polymerized at a temperature of 80 ° C over a period of 1 h at the same 45 g perpivalate dissolved in 300 g of a 4: 1 mixture of tertiary butanol and water and 1500 grams of water was pumped into the stirred tank. Then again 1000 g of water are added and polymerized until the complete consumption of the initiator. A stable, finely divided dispersion having a solids content of about 20%.

example 2

p00332000 g EVA copolymer be supported in a stirred tank in 6000 g. Butanol and 1000 g of water. These 1000 g of vinyl acetate are metered. After addition of 2 g of tert-butyl perpivalate, the reaction solution for 1 h at a temperature of 80 ° C and then pumped within 1 hour 1500 g of water. Then again 1000 g of water are added and polymerized until the complete consumption of the initiator. A stable, finely divided dispersion having a solids content of about 24%.

example 3

p00342000 g EVA copolymer and 100 g of Polyester A are dissolved in a stirred vessel 6000 g in tert-butanol. For this purpose 500 g of vinyl acetate are metered. After addition of 5 g of tert-butyl perpivalate dissolved in 100 g of a 4: 1 mixture of tert-butanol and water, the reaction solution at a temperature of 80 ° C is stirred for 30 minutes. Thereafter, simultaneously over a period of 1 hour 45 g of tert-butyl perpivalate dissolved in 500 g of a 4: 1 mixture of tert. Butanol and water and 2500 grams of water was pumped into the stirred tank. Then again 1000 g of water are added and polymerized until the complete consumption of the initiator. A stable, finely divided dispersion having a solids content of about 20%.

example 4

p00352000 g EVA copolymer be supported in a stirred tank in 6000 g. Butanol. For this purpose, 800 g of vinyl acetate and 200 g of n-butyl acrylate are metered. the reaction solution is stirred at a temperature of 80 ° C for 3 hours until complete consumption of the initiator after addition of 2 g of tert-butyl perpivalate. Subsequently, the reaction solution is transferred by the addition of 4000 g of water with stirring in a stable, finely divided dispersion having a solids content of about 25%.

example 5

p00362000 g EVA copolymer are dissolved in a stirred vessel 2000 g in tert-butanol. For this purpose 500 g of vinyl acetate are metered and 1 g ethylene. After adding 5 g of dicumyl peroxide for 30 minutes is polymerized and then at a temperature of 150 ° C at the same time 15 g of dicumyl peroxide dispersed in 150 g of a 4: 1 mixture of tert-butanol and water, and 1500 g of water within 2 hours in pressed the stirred tank and polymerized until the complete consumption of the initiator. A stable, finely divided dispersion having a solids content of about 40%.