DE19537936A1 - Process for the preparation of coagulate-free polymer dispersions - Google Patents

Abstract

The invention concerns a process for preparing aqueous polymer dispersions by the emulsion-polymerization of olefinically unsaturated compounds. The invention is characterized in that the water-soluble initiator used is added at least partially in the form of an aqueous initiator solution which comprises a surfactant and the initiator or, in the case of reduction-oxidation (redox) initiator system, at least one initiator component (emulsified initiator solution).

Description

In the case of emulsion polymerization, radical polymerization takes place bare compounds (monomers) in aqueous emulsion using a polymerized water-soluble initiator. For the emulsion poly In some cases, undesired coagulation occurs dispersed polymer particles.

With the different uses of the polymer obtained dispersions, e.g. B. as adhesives, paints, binders for Nonwovens or paper coating slips lead to such coagulum shares z. B. specks in the end product.

When carrying out emulsion polymerization in technical Benchmark is therefore a special requirement to coagulate polymerization, to avoid.

Coagulates contained in the dispersion must e.g. B. by Filtra tion of the polymer dispersion are separated. The proportion of coagulum determines the filtration effort.

A low coagulum content means a lower filtrate expenditure, that means shorter filtration times and a reduced graced number of filter changes. A low proportion of coagulum leads at reduced disposal costs for the filter residues. The The economic result is low costs and a higher one Plant availability.

The object of the present invention was therefore to reduce the Coagulate share in emulsion polymerization.

Accordingly, a process for the production of aqueous Polymer dispersions by emulsion polymerization of olefinic unsaturated compounds, characterized in that the ver partially used water-soluble initiator in the form an aqueous initiator solution, which is a surface-active Substance and the initiator, or in the case of a reduction oxide tion (Red-Ox) initiator system at least one initiator component, contains (emulsified initiator solution), added, found.

Processes for emulsion polymerization are sufficient for the person skilled in the art known. In emulsion polymerization polymeri sizable, olefinically unsaturated compounds (so-called monomers) in Emulsified water with the help of surface-active compounds  and using water-soluble initiators polymerized.

So-called Haupt are of particular technical importance monomers selected from C₁-C₂₀ alkyl (meth) acrylates, vinyl esters of up to 20 carbon atoms containing carboxylic acids, vinyl aromatics with up to 20 carbon atoms, ethylenically unsaturated nitriles, Vinyl halides, vinyl ethers containing 1 to 10 carbon atoms Alcohols, aliphatic hydrocarbons with 2 to 8 carbon atoms and 1 or 2 double bonds or mixtures of these monomers.

To mention are z. B. (meth) acrylic acid alkyl ester with a C₁-C₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

In particular, mixtures of the (meth) acrylic acid alkyl esters suitable.

Vinyl esters of carboxylic acids with 1 to 20 carbon atoms are e.g. B. Vinyl laurate, stearate, vinyl propionate, vinyl versatic acid and vinyl acetate.

Suitable vinyl aromatic compounds are vinyl toluene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of nitriles are Acrylonitrile and methacrylonitrile.

The vinyl halides are substituted with chlorine, fluorine or bromine ethylenically unsaturated compounds, preferably vinyl chloride and Vinylidene chloride.

Examples of vinyl ethers include B. vinyl methyl ether or vinyl isobutyl ether. Vinyl ether of 1 to 4 carbon atoms is preferred containing alcohols.

As hydrocarbons with 2 to 8 carbon atoms and two olefinic Double bonds are butadiene, isoprene and chloroprene.

In addition to these main monomers, other monomers, e.g. B. Hydro Monomers containing xyl groups, in particular C₁-C₁₀ hydroxy alkyl (meth) acrylates, (meth) acrylamide, ethylenically unsaturated Acids, especially carboxylic acids, such as (meth) acrylic acid or Itaconic acid, dicarboxylic acids and their anhydrides or half esters, e.g. B. maleic acid, fumaric acid and maleic anhydride in the polymer Find use.  

Customary emulsion polymers generally exist at least 40, preferably at least 60, particularly preferably at at least 80% by weight of the above main monomers.

Particularly preferred main monomers are (meth) acrylic acid esters and vinyl aromatic compounds and their mixtures.

In emulsion polymerization, ionic and / or not ionic emulsifiers and / or protective colloids or stabilizers used as surfactant compounds.

A detailed description of suitable protective colloids can be found Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular substances, Georg-Thieme-Verlag, Stuttgart, 1961, Pp. 411 to 420. Emulsifiers include both anionic, cationic as well as nonionic emulsifiers. Before are also used as accompanying surfactants only emulsifiers are used, the molecular weights of which difference to the protective colloids usually below 2000 g / mol lie. Of course, in the case of using Mixtures of surface-active substances the individual components be compatible with each other, which is less if in doubt Preliminary tests can be checked. Anionic are preferred and non-ionic emulsifiers as surfactants used. Common accompanying emulsifiers are e.g. B. ethoxylated fatty alcohols (EO grade: 3 to 50, alkyl radical; C₈- bis C₃₆), ethoxylated mono-, di- and tri-alkylphenols (EO grade: 3 to 50, alkyl radical: C₄- to C₉), alkali metal salts of dialkyl esters of sulfosuccinic acid and alkali and ammonium salts of Alkyl sulfates (alkyl radical: C₈ to C₁₂), of ethoxylated Alkanols (EO grade: 4 to 30, alkyl radical: C₁₂- to C₁₈), from ethoxylated alkylphenols (EO grade: 3 to 50, alkyl radical: C₄ bis C₉), of alkyl sulfonic acids (alkyl radical: C₁₂- to C₁₈) and of Alkylarylsulfonic acids (alkyl radical: C₉ to C₁₈).

Other suitable emulsifiers are compounds of the general Formula II

wherein R⁵ and R⁶ are hydrogen or C₄ to C₁₄ alkyl and are not hydrogen at the same time, and X and Y are alkali metals can be ions and / or ammonium ions. Preferably mean R⁵, R⁶ linear or branched alkyl radicals with 6 to 18 carbon atoms or hydrogen and in particular with 6, 12 and 16 carbon atoms, where R⁵ and R⁶ are not both hydrogen at the same time. X and Y are preferably sodium, potassium or ammonium ions, with sodium is particularly preferred. Are particularly advantageous Compounds II in which X and Y are sodium, R⁵ is a branched one Alkyl radical with 12 carbon atoms and R⁶ is hydrogen or R⁵. Often technical mixtures are used, the proportion of 50 to 90% by weight of the monoalkylated product, for example Dowfax® 2A1 (trademark of Dow Chemical Company).

Suitable emulsifiers can also be found in Houben-Weyl, Methods der organic chemistry, volume 14/1, macromolecular substances, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 208.

Trade names of emulsifiers are e.g. B. Dowfax® 2 A1, Emulan® NP 50, Dextrol® OC 50, Emulsifier 825, Emulsifier 825 S, Emulan® OG, Texapon® NSO, Nekanil® 904 S, Lumiten® I-RA, Lumiten E 3065 Etc.

The surfactant is usually used in amounts of 0.1 to 10 wt .-%, based on the monomers to be polyinerized used.

Water-soluble initiators for emulsion polymerization are e.g. B. ammonium and alkali metal salts of peroxidic sulfuric acid, e.g. As sodium peroxodisulfate, hydrogen peroxide or organic Peroxides, e.g. B. tert-butyl hydroperoxide.

So-called reduction, Oxidation (Red-Ox) initiator systems.

The Red-Ox initiator systems usually consist of at least one inorganic reducing agent and an inorganic or orga African oxidizing agent.

The oxidation component is e.g. B. the already Above initiators for emulsion polymerization.

The reduction components are e.g. B. Alkali metal salts of sulfurous acid, such as. B. sodium sulfite, Sodium hydrogen sulfite, alkali salts of disulfuric acid such as Sodium disulfite, bisulfite addition compounds more aliphatic Aldehydes and ketones such as acetone bisulfite or reducing agents such as  Hydroxymethanesulfinic acid and its salts, or ascorbic acid. The Red-Ox initiator systems can be more soluble when used Metal compounds, their metallic component in several people skill levels can be used.

Common Red Ox initiator systems are e.g. B. Ascorbic acid / egg sen (II) sulfate / sodium peroxydisulfate, tert-butyl hydroperoxide / Na trium disulfite, tert-butyl hydroperoxide / Na hydroxymethanesulfine acid. The individual components, e.g. B. the reduction component, can also be mixtures z. B. a mixture of sodium salt of hydroxymethanesulfinic acid and sodium disulfite.

The compounds mentioned are mostly in the form of aqueous solutions gene used, the lower concentration by the in the Dispersion acceptable amount of water and the upper concentration by the solubility of the compound in question in water is determined.

The concentration is generally 0.1 to 30% by weight, preferably 0.5 to 2.0% by weight, particularly preferably 1.0 to 10 wt .-%, based on the solution.

The amount of initiators is generally 0.1 to 10 wt .-%, preferably 0.5 to 5 wt .-%, based on the poly merizing monomers. There can also be several different ones Initiators are used in emulsion polymerization.

The emulsion polymerization usually takes place at 30 to 95 preferably 50 to 90 ° C. The polymerization medium can both only from water, as well as from mixtures of water and thus miscible liquids such as methanol exist. Preferably only water is used. The emulsion polymerization can be both Batch process as well as in the form of a feed process Lich step or gradient style. The feed process is preferred, in which part of the Submits the polymerization approach to the polymerization temperature heated, polymerized and then the rest of the bottom lymerization approach, usually over several ge separated feeds, one or more of which the monomers in contained in pure or in emulsified form, continuously, gradually or with a concentration gradient superimposed while maintaining the polymerization of the polymerization zone feeds.

The way in which the initiator in the course of the radika Mix aqueous emulsion polymerization the polymerization vessel is added is known to those of ordinary skill in the art. It can  both completely placed in the polymerization vessel, as also according to its consumption in the course of the radical aqueous emulsion polymerization continuously or in stages be used. In detail, this depends on the through itself Cutters known way of both chemical nature the initiator system as well as the polymerization temperature from. A part is preferably submitted and the rest made to measure surrender of consumption to the polymerization zone.

The removal of the residual monomers is usually also carried out after End of actual emulsion polymerization, d. H. after one Conversion of the monomers of at least 95%, initiator added.

The individual components can the reactor in the feed process from above, in the side or from below through the reactor floor are given.

The aqueous polymer dispersions of the polymer are in the Usually with solids contents of 15 to 75% by weight, preferably of 40 to 60 wt .-% produced.

The method according to the invention is compared to the above characterized methods of emulsion polymerization thereby records that the water-soluble initiator in whole or in part Form of an aqueous solution, which is the initiator of an initia gate component, e.g. B. the reduction or oxidation component a red-ox initiator, and at least one surfactant Contains substance, (hereinafter briefly "emulsified initiator solution "called) is added.

It is the initiator and the surfactant around the initiators and limits already described above surface-active substances.

Suitable surface-active compounds are e.g. B. alkylphenol ethoxylates, alkyl ethoxylates, alkanesulfonates, alkylphenol ethers sulfates, sodium lauryl sulfate, sodium lauryl ether sulfate, sodium maloate, alkali metal salts of phosphated alkylphenoxy ethoxy alkanol compounds.

With the initiator, which is in the form of the emulsified initiator solution is added, it is preferably a Red-Ox initiator, one or both components being emulsified Solution can be added. Re is particularly preferred duction component in the form of the emulsified initiator solution puts.  

Alkaline metal salts of sulphurous ones should be mentioned here in particular Acid, e.g. B. sodium sulfite and bisulfite addition compounds ali phatic aldehydes with ketones such as acetone bisulfite.

The emulsified initiator solution is prepared by Solution of the initiator or the initiator components in the water, the surfactant being placed in the water or can be added during or after the dissolving process.

For the content of the initiator or the initiator components in For the emulsified solution, what has already been said above applies.

The content of the surfactant in the emulsified Solution is preferably 0.05 to 50, particularly preferably 0.5 up to 20 and very particularly preferably 1 to 10% by weight, based on the dissolved initiator or the dissolved initiator component.

Use all or part of the emulsion polymerization The initiator can be used as an emulsified solution of the initiator or at least one of the components are added, the emulsified solution e.g. B. can be presented in part or while rend emulsion polymerization can be added, as in individual above in the description of the emulsion polymerization is listed.

A preferred embodiment of the method according to the invention is, the initiators or initiator components that are against or after the end of the emulsion polymerization to be added to the Lower residual monomer content in the polymer dispersion, in Add form of the emulsified initiator solution.

The emulsified initiator solution is therefore preferred after a Conversion of the monomers of 95 wt .-%, d. H. after 95% by weight of Total amount of monomers bound in the polymer is added.

The emulsified initiator solution is particularly preferably after a conversion of 98% by weight, very particularly preferably 99% by weight and in particular after a conversion of the monomers of 99.8% by weight, added.

The addition can be made directly at the end of the actual emulsion polymer rization or at a later date. The The temperature of the polymer dispersion is 30 to 95 preferably 50 to 90 ° C.  

The amount of added in the form of the emulsified initiator solution Initiators are preferably at least 0.05 to 30, especially preferably at least 0.1 to 10% by weight of the total in the emul sion polymerization used amount of initiator (will only an In itiator component of a Red-Ox initiator system in the form of the emul added solution, applies when calculating the above the weight advantage, the corresponding amount of Red-Ox Initiator system, as in the form of the emulsified initiator solution added).

In the processes according to the invention, polymer dispersions are used receive a significantly reduced coagulum content point.

Examples Example I

It became an emulsion polymer by emulsion polymerization from ethylhexyl acrylate, styrene, acrylamide, methacrylamide under Made using 2.5% sodium persulfate solution.

After carrying out the main reaction were to lower the Residual monomers alternatively followed steps A) to D) leads.

• A) At 70 ° C was a 10% solution of tert-butyl hydroperoxide and then a 10% solution of sodium disulfite was added and stirred for 2 hours.
• B) The procedure was as under A, but after the addition the 10% tert-butyl hydroperoxide solution contains 10% sodium sulfite solution added, the 0.5% of an alkylphenol ethoxylate contained.
• C) Experiment A was with a 5% sodium disulfite solution repeated.
• D) Experiment B was with a 5% sodium disulfite solution repeated, also 0.5% of the same alkylphenol contained ethoxylates.

Test series II

The test series I was repeated, but became a manufacturer a 2.5% sodium persulfate solution used the 0.5% of the alkylphenol ethoxylate as an emulsifier contained.

Determination of sieve residue (analogous to DIN 53 786)

In a modification of DIN 53 786, 1 kg each was the above placed dispersions over a sieve with a mesh size of 0.125 mm filtered. The residue was washed with deionized water washed out and dried. Then the sieve residue balanced. The information is given in percent coagulate, based on the dispersion.

Test results

The results clearly show the advantageous use of emulsifier-containing initiator solutions, or of emulsifier-containing Redox component solutions.

Test series III Experiment A: (for comparison)

In a reactor equipped with a MIG stirrer 16 t of an approx. 50% dispersion o.g. Monomers together Settlement established after the addition of the Mono with a 7% sodium persulfate solution Depletion of the residual monomers was aftertreated. For this, first at 70 ° C 395 l of a 10% tert-butyl hydroperoxide  stirred in solution and then a solution of 33.5 kg Sodium disulfite in 288 l of deionized water. After be The reaction ended with a sieve basket filter filtered, which has a sieve insert with a mesh size of Contained 0.5 mm. The number of filter changes and the filtration time.

Attempt B

The experiment described above was repeated, but the Solution of 33.5 kg sodium disulfite in 288 l water, 1.02 kg one added ethoxylated alkylphenol.

Attempt C

Experiment B was repeated, but the solution of 33.5 kg of sodium disulfite in 380 l of deionized water 2.0 kg of a sulfated alkylphenol ethoxylate were added used.

table

Test results of the 3rd test series

The test results of the Ver Suchs clearly show the economic importance of the Erfin dung. With the method according to the invention, the koa can be Reduce the amount of gulate significantly, reducing the number of filters change and the filtration times are significantly reduced.

Claims (6)

1. A process for the preparation of aqueous polymer dispersions by emulsion polymerization of olefinically unsaturated compounds, characterized in that the water-soluble initiator used is at least partially in the form of an aqueous initiator solution which is a surface-active substance and the initiator, or in the case of a reduction oxi dation (Red -Ox) initiator system contains at least one initiator component is added. 2. The method according to claim 1, characterized in that the Initiator solution 0.05 to 50 wt .-% of a surfactant Substance based on the dissolved initiator or the dissolved Initiator component. 3. The method according to claim 1 or 2, characterized in that at least 0.05 to 30 wt .-% of the total in the Emul Sion polymerization used amount of initiator in the mold is added to the emulsified initiator solution. 4. The method according to any one of claims 1 to 3, characterized records that the initiator solution is added after a Sales of at least 95 wt .-%, based on the total amount of the monomers to be polymerized has been reached. 5. The method according to any one of claims 1 to 4, characterized records that it is the emulsified initiator solution the aqueous solution of the oxidation or reduction compo nents of a Red-Ox initiator system. 6. The method according to claim 5, characterized in that it the emulsified initiator solution is the solution of the Reduction components.