Water-redispersible polymer powder for dry building material formulations

Description

[0001] The invention relates to methods for producing polymers in the form of water-dispersible powders by adding alkali sulfates or sulfites, the polymer powders thus obtained, and their use, for example, in dry building material formulations such as tile adhesives, sealing slurries, self-leveling compounds or reinforcing compounds.

[0002] Polymers in the form of water-redispersible powders (polymer powders) are known to be powder compositions that can be obtained by drying the corresponding aqueous polymer dispersions in the presence of drying aids. Due to this manufacturing process, the finely divided polymer resin of the dispersion is coated with drying aids, which are usually water-soluble. During drying, the drying aid acts like a coating that prevents the particles from irreversibly sticking together. When the polymer powders are redispersed in water, the drying aid dissolves, and an aqueous redispersion is formed in which, as far as possible, the original polymer particles (primary polymer particles) are present again (Schulze J. in TIZ, No. 9, 1985).

[0003] To equip polymer powders with such redispersible properties, developments in various directions have taken place in the past, and a number of different drying aids have become established, particularly water-soluble organic polymers. For example, US 5567750 teaches polyvinyl alcohols as drying aids. US 5874524 recommends polyelectrolytes for this purpose, and EP 0078449 recommends vinylpyrrolidone-vinyl acetate polymers or (earth) alkali salts of naphthalenesulfonic acid-formaldehyde condensates. Such naphthalenesulfonic acid-formaldehyde condensates are also disclosed in EP 407889. Similarly, starch (derivatives) have found widespread use as drying aids, as described in EP 134451.

[0004] Polymer powders are widely used as additives in dry construction material formulations based on hydraulically setting binders, especially cement, as well as fillers and additives, as described in US2007037925, for example, in applications such as tile adhesives, joint fillers, leveling compounds, waterproofing slurries, plaster, or screed. The addition of polymer powders to these dry construction material formulations can improve the cohesive or adhesive properties of the cured building products, particularly their mechanical strength, such as tensile bond strength.

[0005] The tensile bond strength of building products is affected by heat. Sunlight and underfloor heating expose building products to thermal stress, leading to mechanical stresses and weakening their tensile bond strength. These products are expected to withstand such thermal stresses throughout their life cycle, often for many years. The tensile bond strength of building products after heat storage is an important measure of their resilience to thermal stress.While conventional polymer powders can already improve adhesion strengths after heat storage, there is a need to further improve adhesion strengths after heat storage, especially in light of climate change and the use of polymer-modified building material formulations in warmer countries, and to achieve this in the most efficient way possible, particularly when using small amounts of polymer powder.

[0006] Against this background, the task was to improve the tensile bond strength of construction products after heat storage. This was to be achieved preferably in the most efficient way possible, especially when using small amounts of polymer powder.

[0007] Surprisingly, the problem was solved with a polymer powder in the production of which alkali sulfates or alkali sulfites were used exclusively or to a significant extent as drying aids, and ≤ 40 wt% of water-soluble organic polymers were added as drying aids, based on the total weight of these water-soluble organic polymers and protective colloids. This was particularly surprising since the water-soluble organic polymers previously established as drying aids also have binder properties with a positive influence on tensile bond strengths, but according to the invention, alkali sulfates or sulfites were used at least partially as drying aids, which are not in themselves known to improve the tensile bond strengths of building products after heat storage.

[0008] WO21239234 improves the storage stability of polymer powders by adding alkali sulfates or magnesium sulfate, but uses established water-soluble organic polymers in standard quantities as drying aids. US2007037925 aims to produce accelerated-setting mortars and teaches the addition of polymer powder compositions modified with (earth)alkali salts of inorganic or organic acids. Here, too, standard water-soluble organic polymers are used in usual quantities as drying aids.In WO2017 / 178422, aqueous polymer dispersions are combined with a drying aid and water-soluble salts a) of multivalent metals, such as alkaline earth metals, aluminum, zirconium, iron, or zinc, and additionally with water-soluble salts b) of anions, such as aluminates, silicates, borates, sulfates, or carbonates. The multivalent metals of salt a) react with the anions of salt b) to form water-insoluble salts. The mixture is then dried, and the water-insoluble salts formed from salts a) and b) create a shell on the polymer particles that dissolves only in alkaline media or as a result of mechanical stress. The proportion of the inorganic shell is 10 to 50 wt.% or 10 to 20 wt.%, based on the polymer core. The shell of water-insoluble salts prevents the polymer particles from clumping together and acts as an antiblocking agent.

[0009] The polymerization of ethylene-unsaturated monomers is typically initiated using initiators, such as alkali persulfates. These initiators are known to decompose into radicals that add to the ethylene-unsaturated monomers, thereby initiating polymer chain growth. Consequently, the initiators are bound to the polymers formed during polymerization via covalent bonds and are therefore either not present in the polymer dispersion as inorganic low-molecular-weight compounds, such as alkali sulfates, or only present in negligible amounts.

[0010] The invention relates to processes for the production of protective colloid-stabilized polymers based on ethylene-unsaturated monomers in the form of water-redispersible powders (polymer powders), by drying aqueous dispersions of protective colloid-stabilized polymers based on ethylene-unsaturated monomers (polymer dispersions) in the presence of one or more drying aids, characterized in that the drying aids comprise a) one or more inorganic salts selected from the group of alkali sulfates and alkali sulfites and b) optionally one or more water-soluble organic polymers, and the inorganic salts a) are present in dissolved form in the polymer dispersions after the addition of all drying aids, wherein the inorganic salts a) are used as drying aids in a quantity of ≥ 25 wt.%, based on the total weight of the drying aids, and wherein the proportion of any water-soluble organic polymers b) used as drying aids is ≤ 40 wt.-% is based on the total weight of protective colloids and any water-soluble organic polymers used as drying aids b). .

[0011] Another object of the invention is protective colloid-stabilized polymers based on ethylene-unsaturated monomers in the form of water-redispersible powders (polymer powders) obtainable according to the aforementioned inventive method.

[0012] The inorganic salts used as drying aids a) are preferably selected from the group consisting of lithium sulfate (Li₂SO₄), sodium sulfate (Na₂SO₄), potassium sulfate (K₂SO₄), lithium sulfite (Li₂SO₃), sodium sulfite (Na₂SO₃), and potassium sulfite (K₂SO₃). Sodium sulfate, sodium sulfite, potassium sulfate, and potassium sulfite are particularly preferred. Sodium sulfate and sodium sulfite are most preferred. Sulfates are more preferred in this context.

[0013] The inorganic salts a) are present in the polymer dispersions in dissolved form after the addition of all drying aids. The inorganic salts a) are preferably present in the polymer dispersions in dissolved form after the addition of the entire quantity of all drying aids. Generally, the inorganic salts a) are present in the polymer dispersions in dissolved form before drying and / or at the beginning of drying. However, this does not preclude the possibility that some of the inorganic salts a) are present in the polymer dispersions in undissolved form, for example, adhering to a component of the polymer dispersions. Preferably, at least the predominant part of the inorganic salts a) is present in the polymer dispersions in dissolved form. More preferably, > 50 wt.%, even more preferably ≥ 70 wt.%, particularly preferably ≥ 90 wt.%, and most preferably ≥ 99 wt.%.-% of the inorganic salts a) are present in the polymer dispersions in dissolved form, based on the total weight of the inorganic salts a) introduced into the polymer dispersions as drying aids. Most preferably, the inorganic salts a) introduced as drying aids are present in the polymer dispersions completely in dissolved form. All of this generally also applies if, in addition to the inorganic salts a), other organic or, in particular, inorganic salts are introduced into or are present in the polymer dispersions. When several inorganic salts a) are introduced into the polymer dispersions, no insoluble salts are generally formed from these salts.

[0014] A measure and a method according to the invention for determining the solubility of the inorganic salts a) in the polymer dispersions is their solubility in water. The inorganic salts a) or, in the case of the use of further organic or, in particular, inorganic salts, their mixtures with the inorganic salts a) exhibit a water solubility of preferably ≥ 1 g per liter of water, more preferably ≥ 3 g per liter of water, even more preferably ≥ 10 g per liter of water, particularly preferably ≥ 50 g per liter of water, and most preferably ≥ 100 g per liter of water, each under standard conditions (23°C / 50% relative humidity) according to DIN 50014. These values ​​preferably refer to neutral pH values, i.e., pH 7.

[0015] Preferably, the polymer dispersions and / or the polymer powders contain 0.1 to 20 wt.%, more preferably 0.2 to 10 wt.%, even more preferably 0.3 to 5 wt.%, even more preferably 0.4 to 4 wt.%, particularly preferably 0.5 to 3 wt.%, most preferably 1 to 2 wt.% and most preferably 1.1 to 2 wt.% of inorganic salts a), based on the total weight of the polymers based on ethylene unsaturated monomers.

[0016] The proportion of inorganic salts a), based on the total weight of the protective colloids, is preferably 2 to 50 wt.%, particularly preferably 3 to 30 wt.% and most preferably 5 to 20 wt.%.

[0017] The proportion of inorganic salts a), based on the total weight of the protective colloids and the water-soluble organic polymers b), is preferably 2 to 50 wt.%, particularly preferably 3 to 30 wt.% and most preferably 5 to 20 wt.%.

[0018] The proportion of inorganic salts a), based on the total weight of the drying aids, is preferably > 25 wt.%, more preferably ≥ 30 wt.%, even more preferably ≥ 40 wt.%, even more preferably ≥ 50 wt.%, even more preferably ≥ 60 wt.% and particularly preferably ≥ 80 wt.%.

[0019] Inorganic salts are the most preferred drying aids.

[0020] In the event that the polymer dispersions contain salts, in particular cations, which form water-insoluble salts with the anions of the inorganic salts a), in particular sulfate, the above wt.% values ​​regarding the amounts of inorganic salts a) according to the invention preferably refer to the proportions of the inorganic salts a) that are present in dissolved form in the polymer dispersions. This is particularly preferred in the event that the polymer dispersions contain alkaline earth metal, aluminum, zirconium, iron, or zinc cations.

[0021] The water-soluble organic polymers (b) used as drying aids have a water solubility of preferably ≥ 1 g per liter of water, particularly preferably ≥ 3 g per liter of water, and most preferably ≥ 10 g per liter of water, each under standard conditions (23°C / 50% relative humidity) according to DIN 50014. These values ​​preferably refer to neutral pH values, i.e., pH 7.

[0022] Examples of water-soluble organic polymers suitable as drying aids (b) are polyvinyl alcohols, polyvinyl acetals, non-ionic polyvinylpyrrolidones, non-ionic poly(meth)acrylamides, polysaccharides, and proteins. The aforementioned water-soluble organic polymers (b) are accessible by methods known to those skilled in the art. Non-ionic water-soluble organic polymers (b) are preferred. The non-ionic water-soluble organic polymers (b), in particular the non-ionic polyvinylpyrrolidones and the non-ionic poly(meth)acrylamides, generally contain no ionic monomer units and generally do not bear any ionic groups, in particular no ammonium, carboxylic acid, or sulfonic acid groups. The non-ionic polyvinylpyrrolidones preferably consist of vinylpyrrolidone units. The non-ionic poly(meth)acrylamides preferably consist of (meth)acrylamide units.

[0023] Polyvinyl alcohols; polyvinyl acetals; polysaccharides, especially in water-soluble form such as starches (amylose and amylopectin), celluloses or their derivatives, such as carboxymethyl, methyl, hydroxyethyl, and hydroxypropyl derivatives; and proteins such as casein or caseinate, soy protein, and gelatin are preferred. Polyvinyl alcohols are particularly preferred. Most preferred is the use of no other water-soluble organic polymer (b) as a drying aid in addition to polyvinyl alcohols.

[0024] Preferred polyvinyl alcohols are partially or fully saponified polyvinyl alcohols with a degree of hydrolysis of preferably 80 to 100 mol%. Partially saponified polyvinyl alcohols with a degree of hydrolysis of 80 to 95 mol%, particularly with a Höppler viscosity, in a 4% aqueous solution of 1 to 30 mPas (Höppler method at 20°C, DIN 53015) are particularly preferred. Most preferred are polyvinyl alcohols with a degree of hydrolysis of 85 to 94 mol%, particularly with a Höppler viscosity, in a 4% aqueous solution of 3 to 15 mPas (Höppler method at 20°C, DIN 53015).

[0025] Preferably, the polymer dispersions and / or the polymer powders contain ≤ 15 wt.%, more preferably ≤ 10 wt.%, even more preferably ≤ 5 wt.%, even more preferably ≤ 3 wt.%, particularly preferably ≤ 0.9 wt.% and most preferably ≤ 0.5 wt.% of water-soluble organic polymers b) as drying aids, based on the total weight of the polymers based on ethylene unsaturated monomers.

[0026] Preferably, the polymer dispersions and / or the polymer powders contain < 40 wt.%, more preferably ≤ 30 wt.%, even more preferably ≤ 20 wt.%, even more preferably ≤ 10 wt.%, particularly preferably ≤ 5 wt.% and most preferably ≤ 1 wt.% of water-soluble organic polymers b) as drying aids, based on the total weight of the protective colloids.

[0027] Preferably, the polymer dispersions and / or the polymer powders contain < 40 wt.%, more preferably ≤ 30 wt.%, even more preferably ≤ 20 wt.%, even more preferably ≤ 10 wt.%, particularly preferably ≤ 5 wt.% and most preferably ≤ 1 wt.% of water-soluble organic polymers b) as drying aids, based on the total weight of protective colloids and any water-soluble organic polymers b).

[0028] The proportion of water-soluble organic polymers b) as drying aids is preferably ≤ 70 wt.%, more preferably ≤ 50 wt.%, even more preferably ≤ 30 wt.%, particularly preferably ≤ 10 wt.%, most preferably ≤ 5 wt.%, based on the total weight of the drying aids.

[0029] Water-soluble organic polymers are most preferably used as drying aids.

[0030] Any water-soluble organic polymers (b) used as drying aids are generally added to the polymer dispersions, that is, generally after their production by polymerization. Water-soluble organic polymers (b) used as drying aids are therefore generally added after polymerization has ended. The end of polymerization is known to be noticeable, for example, by the decreasing heat of the polymerization reaction. After polymerization has ended, the polymerization reaction generally no longer releases heat. Therefore, no ethylene-unsaturated monomers, protective colloids, or initiators are generally added to the polymer dispersions after their production by polymerization.The addition of the water-soluble organic polymers used as drying aids b) therefore takes place in particular after degassing or depressurizing the polymerization mixture, or after post-polymerization, or after removal of the residual monomers or preferably after preparation of the polymer dispersions, i.e. after the addition of additives such as preservatives or defoamers.

[0031] In contrast, protective colloids are known to be generally present during polymerization. The addition of protective colloids therefore generally occurs before or during polymerization, or before or during the addition of monomers or initiators, and in particular before the complete addition of the monomers or initiators. The addition of protective colloids also generally occurs before the removal of residual monomers, or before post-polymerization, i.e., generally before the end of polymerization.

[0032] These process steps inevitably affect the structural properties of the polymer powders. For example, protective colloids and water-soluble organic polymers used as drying aids are generally known to be incorporated into the polymer powders in completely different ways and fulfill completely different functions. Differences regarding the type or method of addition of protective colloids or drying aids thus justify process differences as well as material differences in the polymer powders.

[0033] Protective colloids generally stabilize the polymerization reaction during polymerization in aqueous media, as well as the polymer particles formed during polymerization. These polymer particles are also referred to as primary particles. Protective colloids are generally incorporated into the primary particles or bound to them physically or chemically, preferably irreversibly, for example by physical entanglement or covalent bonding, or encapsulated by the polymers formed during polymerization.

[0034] In contrast, water-soluble organic polymers used as drying aids (b) are generally not incorporated into the primary particles. Following their addition after polymerization, these water-soluble organic polymers (b) generally coat the primary particles. The powdery particles formed during drying are also referred to as secondary particles. After drying the aqueous polymer dispersions, the polymer primary particles are generally coated with a drying aid shell; this isolates the primary particles from one another, preventing irreversible agglomeration. Primary particles are generally released again after redispersing the polymer powders in water. Drying aids are generally also present at the particle-air interface, whereas protective colloids are generally not.

[0035] Due to the addition of water-soluble organic polymers used as drying aids (b) generally after polymerization, these water-soluble organic polymers (b) are generally not modified by radical-initiated polymerization, such as by grafting reactions or oxidation or reduction reactions by initiators like redox initiators, or saponification, such as the saponification of acetate units of partially saponified polyvinyl alcohols. Grafting reactions are known to attach chemical groups, such as monomers, to polymers, generally via covalent bonds. Grafting reactions occur particularly during the polymerization of vinyl acetate and / or ethylene. In contrast, protective colloids can generally undergo such modifications as a result of their presence during polymerization.

[0036] Aids or additives for polymerization, such as initiators, are generally either directly attached to the polymer chains via covalent bonds during polymerization, incorporated into the polymer particles, or encapsulated by the polymers.

[0037] The polymers of ethylene unsaturated monomers (base polymers) are based, for example, on one or more monomers selected from the group comprising vinyl esters, (meth)acrylic acid esters, vinyl aromatics, olefins, 1,3-dienes and vinyl halides.

[0038] Suitable vinyl esters include those of carboxylic acids with 1 to 15 carbon atoms. Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methyl vinyl acetate, vinyl pivalate, and vinyl esters of α-branched monocarboxylic acids with 9 to 11 carbon atoms, such as VeoVa9R or VeoVa10R (trade names of Resolution), are preferred. Vinyl acetate is particularly preferred.

[0039] Suitable monomers from the group of acrylic or methacrylic esters are, for example, esters of unbranched or branched alcohols with 1 to 15 carbon atoms. Preferred methacrylic or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, and 2-ethylhexyl acrylate. Methyl acrylate, methyl methacrylate, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate are particularly preferred.

[0040] Preferred vinyl aromatics are styrene, methylstyrene, and vinyltoluene. The preferred vinyl halide is vinyl chloride. Preferred olefins are ethylene and propylene, and preferred dienes are 1,3-butadiene and isoprene.

[0041] Optionally, 0 to 10 wt.%, preferably 0.1 to 5 wt.%, based on the total weight of the monomers, auxiliary monomers can be copolymerized. Examples of auxiliary monomers are ethylene-unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid, and maleic acid; ethylene-unsaturated carboxylic acid amides and nitriles, preferably acrylamide and acrylonitrile; mono- and diesters of fumaric acid and maleic acid, such as the diethyl and diisopropyl esters, as well as maleic anhydride; ethylene-unsaturated sulfonic acids or their salts, preferably vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid.Other examples include pre-crosslinking comonomers such as polyethylene unsaturated comonomers, for example diallyl phthalate, divinyl adipate, diallyl maleate, allyl methacrylate, or triallyl cyanurate, or post-crosslinking comonomers, for example acrylamidoglycolic acid (AGA), methyl methylacrylamidoglycolic acid ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide, N-methylolallylcarbamate, alkyl ethers such as the isobutoxy ether or esters of N-methylolacrylamide, N-methylolmethacrylamide, and N-methylolallylcarbamate. Epoxy-functional comonomers such as glycidyl methacrylate and glycidyl acrylate are also suitable. Other examples are silicon-functional comonomers, such as acryloxypropyltri(alkoxy) and methacryloxypropyltri(alkoxy) silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, where ethoxy and ethoxypropylene glycol ether residues may be present as alkoxy groups.Also mentioned are monomers with hydroxy or CO groups, for example methacrylic acid and acrylic acid hydroxyalkyl esters such as hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate, as well as compounds such as diacetone acrylamide and acetylacetoxyethyl acrylate or methacrylate.

[0042] In an alternative, preferred embodiment, no ethylene-unsaturated mono- and dicarboxylic acids, no mono- and diesters of fumaric acid and maleic acid, no maleic anhydride, and / or no ethylene-unsaturated sulfonic acids are polymerized into the copolymers. Particularly preferred is the polymerization of no auxiliary monomers into the copolymers.

[0043] Styrene-(meth)acrylic acid ester copolymers and especially vinyl acetate-ethylene copolymers are preferred.

[0044] The polymer powders preferably contain 50 to 90 wt.% of vinyl acetate-ethylene and / or styrene-(meth)acrylic acid ester copolymers, based on the total weight of the polymer powders.

[0045] Preferably, copolymers of vinyl acetate with 1 to 50 wt% ethylene are used; copolymers of vinyl acetate with 1 to 50 wt% ethylene and 1 to 50 wt% of one or more further comonomers from the group consisting of vinyl esters with 1 to 12 carbon atoms in the carboxylic acid residue, such as vinyl propionate, vinyl laurate, vinyl esters of alpha-branched carboxylic acids with 9 to 13 carbon atoms, such as VeoVa9, VeoVa10, VeoVa11; copolymers of vinyl acetate, 1 to 50 wt% ethylene, and preferably 1 to 60 wt% (meth)acrylic acid esters of unbranched or branched alcohols with 1 to 15 carbon atoms, in particular n-butyl acrylate or 2-ethylhexyl acrylate; and copolymers with 30 to 75 wt% vinyl acetate, 1 to 30 wt% vinyl laurate or vinyl ester of an alpha-branched carboxylic acid with 9 to 11 carbon atoms, as well as 1 to 30 wt% (meth)acrylic acid esters of unbranched or branched alcohols with 1 to 15 carbon atoms, in particular n-butyl acrylate or 2-ethylhexyl acrylate, which contain 1 to 40 wt%.-% ethylene contained; copolymers with vinyl acetate, 1 to 50 wt% ethylene and 1 to 60 wt% vinyl chloride; wherein the copolymers may also contain the aforementioned auxiliary monomers in the aforementioned quantities, and the values ​​in wt% add up to 100 wt% each.

[0046] (Meth)acrylic acid ester polymers are also preferred, such as copolymers of n-butyl acrylate or 2-ethylhexyl acrylate or copolymers of methyl methacrylate with n-butyl acrylate and / or 2-ethylhexyl acrylate; styrene-acrylic acid ester copolymers with one or more monomers from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; vinyl acetate-acrylic acid ester copolymers with one or more monomers from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, and optionally ethylene; styrene-1,3-butadiene copolymers; wherein the polymers may also contain the aforementioned auxiliary monomers in the specified amounts, and the values ​​in wt.% add up to 100 wt.% each.

[0047] Most preferred are copolymers with vinyl acetate and 5 to 50 wt% ethylene; or copolymers with vinyl acetate, 1 to 50 wt% ethylene and 1 to 50 wt% of a vinyl ester of α-branched monocarboxylic acids with 9 to 11 carbon atoms; or copolymers with 30 to 75 wt% vinyl acetate, 1 to 30 wt% vinyl laurate or vinyl ester of an α-branched carboxylic acid with 9 to 11 carbon atoms, and 1 to 30 wt% (meth)acrylic acid esters of unbranched or branched alcohols with 1 to 15 carbon atoms, which also contain 1 to 40 wt% ethylene; or copolymers with vinyl acetate, 5 to 50 wt% ethylene and 1 to 60 wt% vinyl chloride.

[0048] The selection of monomers or the weight fractions of comonomers is carried out such that a glass transition temperature Tg of preferably -50°C to +35°C, particularly preferably -30°C to +25°C, and most preferably -10°C to +20°C results. The glass transition temperature Tg of the polymers can be determined in a known manner using differential scanning calorimetry (DSC). Tg can also be approximately predicted using the Fox equation. According to Fox TG, Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1 / Tg = x1 / Tg1 + x2 / Tg2 + ... + xn / Tgn, where xn represents the mass fraction (wt% / 100) of monomer n, and Tgn is the glass transition temperature in Kelvin of the homopolymer of monomer n. Tg values ​​for homopolymers are listed in Polymer Handbook 2nd Edition, J. Wiley & Sons, New York (1975).

[0049] The polymers are preferably obtained by emulsion polymerization or suspension polymerization of one or more ethylene-unsaturated monomers in an aqueous medium. Preferably, the polymers are produced by the emulsion polymerization process.

[0050] The polymerization temperature is preferably between 40°C and 110°C, particularly preferably between 60°C and 90°C. The copolymerization of gaseous comonomers such as ethylene, 1,3-butadiene, or vinyl chloride can also be carried out under pressure, generally between 5 bar and 100 bar.

[0051] The polymerization is initiated using water-soluble or monomer-soluble initiators or redox-initiator combinations commonly used for emulsion or suspension polymerization. Examples of water-soluble initiators include the sodium, potassium, and ammonium salts of peroxodisulfuric acid, hydrogen peroxide, tert-butyl peroxide, tert-butyl hydroperoxide, potassium peroxodiphosphate, tert-butyl peroxopivalate, cumene hydroperoxide, isopropylbenzene monohydroperoxide, and azobisisobutyronitrile. Examples of monomer-soluble initiators include dicetyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, and dibenzoyl peroxide. The aforementioned initiators are generally used in an amount of 0.001 to 1.0 wt.%, preferably 0.0015 to 0.7 wt.%, particularly preferably 0.002 to 0.4 wt.% and most preferably 0.0025 to 0.3 wt.%, in each case based on the total weight of the monomers.

[0052] Redox initiators are combinations of the aforementioned initiators and reducing agents. Suitable reducing agents include the sulfites and bisulfites of alkali metals and ammonium, for example, sodium sulfite; sulfoxylic acid derivatives such as zinc or alkali formaldehyde sulfoxylates, for example, sodium hydroxymethane sulfinate; and ascorbic acid. The amount of reducing agent is generally 0.001 to 1.0 wt.%, preferably 0.0015 to 0.7 wt.%, particularly preferably 0.002 to 0.4 wt.%, and most preferably 0.0025 to 0.3 wt.%, in each case based on the total weight of the monomers.

[0053] To control the molecular weight, regulating substances can be used during polymerization. If regulators are used, they are typically added in amounts between 0.01 and 5.0 wt%, based on the monomers to be polymerized, and dosed separately or premixed with reaction components. Examples of such substances are n-dodecyl mercaptan, tert-dodecyl mercaptan, mercaptopropionic acid, methyl mercaptopropionic acid ester, isopropanol, and acetaldehyde.

[0054] The same polymers described above as water-soluble organic polymers b) are suitable and preferred as protective colloids for polymerization. Polyvinyl alcohols are therefore preferred.

[0055] The protective colloids are added during polymerization in an amount of preferably 1 to 20 wt.%, particularly preferably 2 to 15 wt.% and most preferably 3 to 10 wt.%, based on the total weight of the monomers.

[0056] When polymerizing in the presence of emulsifiers, their amount is 0.5 to 5 wt% based on the amount of monomer. Suitable emulsifiers include anionic, cationic, and non-ionic emulsifiers, for example, anionic surfactants such as alkyl sulfates with a chain length of 8 to 18 carbon atoms, alkyl or alkylaryl ether sulfates with 8 to 18 carbon atoms in the hydrophobic residue and up to 40 ethylene or propylene oxide units, alkyl or alkylaryl sulfonates with 8 to 18 carbon atoms, esters and semi-esters of sulfosuccinic acid with monohydric alcohols or alkylphenols, or non-ionic surfactants such as alkyl polyglycol ethers or alkylaryl polyglycol ethers with 8 to 40 ethylene oxide units.

[0057] Polymerization is particularly preferred in the absence of emulsifiers. The aqueous dispersions and / or the polymer powders preferably contain no emulsifiers.

[0058] After completion of the polymerization, residual monomers can be removed by post-polymerization using known methods, generally by post-polymerization initiated with a redox catalyst. Volatile residual monomers can also be removed by distillation, preferably under reduced pressure, and optionally by passing or over inert carrier gases such as air, nitrogen, or steam.

[0059] The polymers obtained in this way are preferably in the form of aqueous dispersions, in particular aqueous dispersions stabilized with protective colloid.

[0060] The addition of the inorganic salts a) used as drying aids can take place before, during, or preferably after the production of the polymers by polymerization. Chemical substances that are converted into the inorganic salts a) according to the invention by chemical reaction can also be used.

[0061] For example, the inorganic salts can be mixed with the ethylene unsaturated monomers before initiating the polymerization. Alternatively, the inorganic salts can be added during the polymerization of the ethylene unsaturated monomers. Likewise, a portion of the inorganic salts can be added to the ethylene unsaturated monomers before initiating the polymerization, and the remaining portion can be added during the polymerization.

[0062] Preferably, the inorganic salts a) are added to the corresponding polymer dispersion after completion of the polymerization. Particularly preferably, the inorganic salts a) are added before drying the aqueous polymer dispersion. For this purpose, one or more inorganic salts a) are preferably added to the aqueous polymer dispersions, and the resulting mixtures are then dried. Preferably, no inorganic salts a) are added during the drying of the aqueous polymer dispersions.

[0063] Any water-soluble organic polymers used as drying aids b) are generally added to the polymer dispersions, for example spatially or temporally together with the inorganic salts a) or separately from the inorganic salts a).

[0064] The drying of the polymer dispersions can be carried out, for example, by fluidized bed drying, freeze-drying, or spray drying. Preferably, the dispersions are spray-dried. Spray drying is performed in conventional spray drying systems, with atomization being achieved using single-, dual-, or multi-component nozzles or a rotating disc. The outlet temperature is generally selected in the range of 45°C to 120°C, preferably 60°C to 90°C, depending on the system, the temperature of the resin, and the desired degree of dryness. The viscosity of the atomized product is adjusted via the solids content to achieve a value preferably < 10,000 mPas, more preferably < 5,000 mPas, and particularly preferably < 1,000 mPas (Brookfield viscosity at 20 revolutions and 23°C). The solids content of the dispersion to be atomized is preferably 30 to 75 wt.% and particularly preferably 50 to 60 wt.%.

[0065] In many cases, an antifoam concentration of up to 1.5% by weight, based on the polymer, has proven advantageous. The antifoam is preferably added during atomization.

[0066] To increase shelf life by improving blocking stability, particularly in polymer powders with low glass transition temperatures, the resulting polymer powder can be equipped with one or more antiblocking agents. The antiblocking agents are preferably not added to the aqueous polymer dispersions, i.e., preferably not before drying, but rather during or after drying, especially during drying in the spray drying system. Preferred polymer powders contain antiblocking agents, in particular 1 to 30 wt.%, based on the total weight of the polymeric components. Examples of antiblocking agents are calcium or magnesium carbonate, talc, gypsum, silica, kaolins such as metakaolin, and silicates, preferably with particle sizes in the range of 10 nm to 10 µm. Antiblocking agents are typically water-insoluble.

[0067] To improve the application-related properties, further additives can be added during drying. Other components of polymer powder contained in preferred embodiments include, for example, pigments, fillers, foam stabilizers, water repellents, or cement plasticizers.

[0068] The polymer powders preferably do not contain a polyelectrolyte. Polyelectrolytes generally refer to polymers with ionically dissociable groups in aqueous media, which can be components or substituents of the polymer chain. The number of ionically dissociable groups is generally large enough that the polymers are completely soluble in water in their dissociated form. Polyelectrolytes can be, for example, polyacids or polybases.

[0069] The polymer powders preferably do not contain water-soluble halide salts, in particular no water-soluble chloride salts. Water-soluble halide salts have a water solubility of preferably ≥ 1 g per liter of water under standard conditions (23 / 50) according to DIN 50014.

[0070] The polymer powders preferably do not contain polyfunctional alcohols, in particular no alcohols bearing at least one alcohol group and optionally one or more further functional groups selected from the group comprising amine, carbamic, mercaptan, sulfonic, sulfuric, halide, carboxyl, alkoxy, phosphinic, phosphonic, and phosphoric acid groups, wherein the sum of the number of alcohol groups and the number of further functional groups of the alcohols is ≥ 2. The polymer powders preferably do not contain alcohols with ≤ 20, particularly preferably ≤ 15 carbon atoms or > 2 carbon atoms.

[0071] The polymer powders preferably do not contain any polyalkylene polyamines, in particular no polyethyleneimine, especially not with a molecular weight of 300 to 10,000,000. Polyalkylene polyamines are generally based on ethylene-unsaturated monomers bearing amine, ammonium or amide groups and optionally further ethylene-unsaturated monomers.

[0072] Preferably no salts of multivalent metals are added to the polymer dispersions, in particular no salts of magnesium, calcium, barium, aluminium, zirconium, iron or zinc.

[0073] Another object of the invention is dry building material formulations containing one or more hydraulically setting binders, one or more fillers, one or more polymer powders according to the invention and optionally one or more additives.

[0074] The dry building material formulations preferably contain 0.1 to 30 wt.%, particularly preferably 0.3 to 12.0 wt.% and most preferably 0.5 to 5.0 wt.% polymer powders according to the invention, in each case based on the total weight of the dry building material formulations.

[0075] Suitable hydraulically setting binders include, for example, cements, in particular Portland cement, aluminate cement, trass cement, blast furnace cement, magnesia cement, phosphate cement, or blast furnace cement, as well as blended cements, filler cements, fly ash, microsilica, hydraulic lime, and gypsum. Portland cement, aluminate cement, and blast furnace cement, as well as blended cements, filler cements, hydraulic lime, and gypsum, are preferred. Mixtures of two or more hydraulically setting binders, especially those containing cement and hydraulic lime, are also preferred.

[0076] In general, dry building material formulations contain 5 to 50 wt.%, preferably 10 to 30 wt.%, hydraulically setting binders, based on the total weight of the dry building material formulations.

[0077] Examples of suitable fillers include quartz sand, quartz flour, calcium carbonate, dolomite, aluminum silicates, clay, chalk, hydrated lime, talc, or mica, as well as lightweight fillers such as pumice, foam glass, aerated concrete, perlite, vermiculite, and carbon nanotubes (CNTs). Any mixture of the aforementioned fillers can also be used. Quartz sand, quartz flour, calcium carbonate, chalk, or hydrated lime are preferred. Fillers are generally, or implicitly, water-insoluble.

[0078] In general, dry building material formulations contain 30 to 90 wt.%, preferably 40 to 85 wt.% fillers, based on the total weight of the dry building material formulations.

[0079] Other common additives for dry building material formulations include thickeners, such as polysaccharides like cellulose ethers and modified cellulose ethers, starch ethers, guar gum, xanthan gum, layered silicates, polycarboxylic acids like polyacrylic acid and their partial esters, as well as polyvinyl alcohols, which may be acetalized or hydrophobically modified, casein, and associative thickeners. Common additives also include retarders, such as hydroxycarboxylic acids or dicarboxylic acids or their salts, saccharides, oxalic acid, succinic acid, tartaric acid, gluconic acid, citric acid, sucrose, glucose, fructose, sorbitol, and pentaerythritol. Setting accelerators, such as alkali or alkaline earth salts of inorganic or organic acids, are also a common additive. In addition, the following should be mentioned: hydrophobing agents, preservatives, film-forming aids, dispersing agents, foam stabilizers, defoamers and flame retardants (e.g. aluminium hydroxide).

[0080] The additives are used in the usual quantities, which depend on the type of additive. Generally, the quantities range from 0.01 to 10% by weight, based on the total weight of the dry building material formulations.

[0081] Dry construction material formulations are generally produced by mixing and homogenizing one or more hydraulically setting binders, one or more fillers, one or more polymer powders, and optionally one or more additives into a dry mixture. The production of these dry formulations can be carried out in a conventional manner using standard equipment. The amount of water required for processing the dry formulations is typically added immediately before application.

[0082] Dry formulations of building materials are suitable, for example, for the production of reinforcing compounds for external thermal insulation composite systems (ETICS), or for the production of adhesives or coatings. Examples of adhesives include adhesives for thermal insulation boards and soundproofing boards, tile adhesives, and adhesives for bonding wood and wood-based materials. Examples of coatings include mortars, self-leveling compounds, waterproofing slurries, screeds, and plasters.

[0083] Surprisingly, by adding the polymer powders according to the invention to dry building material formulations, building products with improved tensile bond strengths are obtained after heat storage. Particularly surprising was the fact that this was achieved by using alkali sulfates or sulfites as drying aids, which are not inherently known to improve the tensile bond strengths of building products after heat storage.

[0084] Advantageously, the tensile adhesion strength can be significantly improved after heat storage even with relatively small amounts of polymer powders according to the invention.

[0085] The following examples serve to further illustrate the invention. Production of the polymer powders:

[0086] The same standard polymer dispersion of a vinyl acetate-ethylene copolymer with a glass transition temperature (Tg) of 17°C was used for the production of the polymer powders. The polymer dispersion was prepared conventionally by emulsion polymerization and contained 6 wt% polyvinyl alcohol as a protective colloid.

[0087] The amounts of drying aids listed in Table 1 were added to this polymer dispersion.

[0088] The resulting spray feeds were dried in a conventional manner using spray drying for all (comparative) examples, resulting in a redispersible polymer powder.

[0089] 20% by weight of anti-caking agent was added to each of the polymer powders produced in this way during spray drying.

[0090] The polymer powders were tested in cementitious tile adhesives of the following formulations: Tile adhesive 1 with 3 wt% polymer powder: 420 g Milke CEM I, 460 g quartz sand (medium grain size), 81 g calcium carbonate, 4 g Tylose, 5 g accelerator, 30 g polymer powder of the respective (comparative) example, 310 g water Tile adhesive 2 with 6 wt% polymer powder: 400 g Milke CEM I, 265.5 g coarse quartz sand, 265.5 g fine quartz sand, 4 g Tylose, 5 g accelerator, 60 g polymer powder of the respective (comparative) example, 270 g water

[0091] The tile adhesives 1 and 2 were applied using conventional methods. The adhesion values ​​after heat curing were tested according to EN1348.

[0092] The results of the testing are summarized in Table 1. Table 1: drying aid Tensile adhesion value after heat storage [N / mm²< ] PVOH (04 / 88) a,b)< inorganic salt a)< Tile adhesive 1 Tile adhesive 2 VBsp. 1 - - 0, 47 1,07 Example 2 - 1.3 wt% Na₂SO₄ 1,63 2,70 Example 3 - 1.3 wt% Na₂SO₃ 1,39 2,24 Example 4 1 wt.% - 0,60 1,26 Example 5 1 wt.% 0.6 wt% Na₂SO₄ 1,44 2,13 Example 6 1 wt.% 1.3 wt% Na₂SO₄ 1,48 2,46 Example 7 1 wt.% 1.3 wt% Na₂SO₃ 1,48 2,31 a) wt% based on the polymer content of the dispersion (solid solid); b) PVOH (04 / 88): Polyvinyl alcohol with a Höppler viscosity of 4 mPas and a degree of saponification of 88%.

[0093] The test results in Table 1 show that the addition of inorganic salts a) as drying aids improves the tensile adhesion values ​​after heat storage.

Claims

1. A process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders, by producing aqueous dispersions of protective-colloid-stabilized polymers based on ethylenically unsaturated monomers by polymerization of one or more ethylenically unsaturated monomers in an aqueous medium and drying said dispersions in the presence of one or more drying aids, characterized in that the drying aids include a) one or more inorganic salts selected from the group of alkali metal sulfates and alkali metal sulfites and b) optionally one or more water-soluble organic polymers and the inorganic salts a) are present in the aqueous dispersions of the protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in dissolved form after all drying aids have been added, wherein the inorganic salts a) are employed as drying aids to an extent of ≥ 25% by weight based on the total weight of the drying aids, and wherein the proportion of any water-soluble organic polymers b) employed as drying aids is ≤ 40% by weight based on the total weight of protective colloids and any water-soluble organic polymers b) employed as drying aids, with the proviso that the protective colloids are added before or during the polymerization, and that any water-soluble organic polymers b) employed as drying aids are added to the aqueous dispersions of the protective-colloid-stabilized polymers after production of said aqueous dispersions by polymerization, and that the protective colloids stabilize the polymerization batch during the polymerization in an aqueous medium and also the polymer particles formed in the course of the polymerization and that the protective colloids are incorporated into the polymer particles formed in the course of the polymerization, and that any water-soluble organic polymers b) employed as drying aids, as a result of their addition after the polymerization, encase the polymer particles formed in the course of the polymerization.

2. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claim 1, characterized in that 0.1% to 20% by weight of inorganic salts a) are used, based on the total weight of the polymers based on ethylenically unsaturated monomers.

3. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claim 1 or 2, characterized in that 2% to 50% by weight of inorganic salts a) are used, based on the total weight of the protective colloids.

4. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claims 1 to 3, characterized in that 2% to 50% by weight of inorganic salts a) are used, based on the total weight of the protective colloids and the water-soluble organic polymers b).

5. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claims 1 to 4, characterized in that sodium sulfate, sodium sulfite, potassium sulfate and / or potassium sulfite are used as inorganic salts a).

6. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claims 1 to 5, characterized in that one or more water-soluble organic polymers b) are selected from the group comprising polyvinyl alcohols, polyvinyl acetals, nonionic polyvinylpyrrolidones, nonionic poly(meth)acrylamides, polysaccharides, and proteins.

7. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claims 1 to 6, characterized in that exclusively inorganic salts a) are employed as drying aids.

8. The process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders as claimed in claims 1 to 6, characterized in that the inorganic salts a) are employed as drying aids to an extent of ≥ 40% by weight based on the total weight of the drying aids.

9. A protective-colloid-stabilized polymer based on ethylenically unsaturated monomers in the form of water-redispersible powders obtainable by the process as claimed in claims 1 to 8.

10. A protective-colloid-stabilized polymer based on ethylenically unsaturated monomers in the form of water-redispersible powders obtainable by the process as claimed in claim 7.

11. A building material dry formulation comprising one or more hydraulically setting binders, one or more fillers, one or more protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders from claim 9 or 10, and optionally one or more additives.

12. The use of the building material dry formulation from claim 11 for the production of reinforcing compounds for thermal insulation composite systems or for the production of adhesives or coating materials.