Polymer dispersion

Abstract

A process for producing an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization, wherein: the overall monomer composition comprises a monomer composition A and a monomer composition B; the monomer composition B is dosed when dosing of the monomer composition A has been finished; and the ratio of monomer composition A to monomer composition B is 50:50 to 70:30. The invention also relates to the dispersion obtained by this process and to its use as a binder, adhesive, sizing agent for fibers, for producing coats or for producing a paper coating slip.

Description

[0001] polymer dispersion

[0002] The invention relates to a process for producing an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization of butyl acrylate, vinylaromatic compound, and conjugated aliphatic diene by a monomer feed process. The invention also relates to the aqueous polymer dispersions produced by the process and their use as binders, adhesives, sizing agents, for fibers, and coating materials.

[0003] Polymer dispersions containing copolymers of vinylaromatic compounds and aliphatic dienes are often chosen as binders for paper coating slips. For example, WO 2021 / 136703 teaches an aqueous polymer dispersion based on butyl acrylate, styrene, and butadiene as a binder for paper coating slips with good water resistance. Papers coated with this dispersion exhibit improved wet adhesion.

[0004] Furthermore, EP 2085409 teaches binders for paper coating slips that increase the printability of the papers using gravure printing processes. They are produced by polymerizing a composition of butyl acrylate, acrylic acid, and acrylonitrile in the presence of a styrene / butadiene / acrylonitrile / acrylic acid latex. According to the teaching of this document, both the acrylonitrile and the low glass transition temperatures in the range of -20 to -50°C of the second polymer result in a "soft" outer phase of the polymer particles, which improves printability.

[0005] Paper coating slips are used to refine base paper, for example, in the production of graphic paper. Such high-quality papers should be easy to print on and have a white, smooth surface. During the printing process, the paper is pressed at high speed onto the roller containing the viscous printing ink. It is therefore important that the binder ensures good adhesion of the coating to the base paper, preventing parts of the coating from detaching during the printing process, a process known as picking. Therefore, one object of the present invention was to find a good bonding force on paper for a wide variety of printing processes.

[0006] White pigments are typically added to paper coating slips. Nevertheless, paper coated with paper coating slips containing a styrene / butadiene dispersion as a binder tends to yellow. Therefore, the object of the present invention was to find styrene / butadiene-based binders that, when used in paper coating slips, exhibit less thermal and UV yellowing of the coated papers.

[0007] Furthermore, the papers coated with these paper coating slips should have good printability as well as good strength.

[0008] The object is achieved according to the invention by a process for producing an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization according to a monomer feed process, wherein the total monomer composition comprises a monomer composition A and a monomer composition B, and the monomer composition B is metered after the end of the metering of the monomer composition A, wherein the monomer composition A comprises

[0009] (a) 25 to 44 parts by weight of at least one conjugated aliphatic diene,

[0010] (b) 55 to 74 parts by weight of at least one vinyl aromatic compound, (c) 1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid

[0011] (d) 0 to 15 parts by weight of n-butyl acrylate and

[0012] (e) 0 to 5 parts by weight of acrylamide, each based on 100 parts by weight of monomer composition A, and the monomer composition B comprises

[0013] (b) 35 to 74 parts by weight of at least one vinyl aromatic compound and

[0014] (c) 1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid,

[0015] (d) 25 to 64 parts by weight of n-butyl acrylate and

[0016] (e) 0 to 5 parts by weight of acrylamide, each based on 100 parts by weight of monomer composition B, and the ratio of monomer composition A to monomer composition B is from 50:50 to 70:30.

[0017] The present invention further relates to the aqueous polymer dispersion obtained by the process according to the invention, as well as to its use as a binder, as an adhesive, as a fiber sizing agent, and for the production of coatings, in particular as a binder for two-component cementitious or one-component cementitious sealing slurries and as a binder for paper coating slips, as well as to the paper coating slips and the sealing slurries. Furthermore, it relates to the process for coating paper and cardboard, and to the coated paper or cardboard obtained thereby.

[0018] In the following, compounds derived from acrylic acid and methacrylic acid are sometimes abbreviated by inserting the syllable "(meth)" into the compound derived from acrylic acid.

[0019] The total amount of monomer is the total amount of all monomers used in the polymerization, which add up to 100 parts by weight.

[0020] The total dosing time of the monomers refers to the period of time required for the continuous dosing of monomers. Dosing can occur by adding a mixture or by adding separate monomers, which can also be staggered. The key point is that monomer is added at all times, meaning that the addition is continuous. Accordingly, the total dosing time begins with the start of the dosing of the first monomer / mixture and ends with the end of the last monomer / mixture.

[0021] Where the solids content of the aqueous dispersion is mentioned in wt%, it is based on the weight of the aqueous dispersion.

[0022] According to the invention, a monomer composition A is metered which contains at least one conjugated aliphatic diene, at least one vinylaromatic compound, and at least one ethylenically unsaturated carboxylic acid. N-butyl acrylate and acrylamide may also be present. Other monomers may also be present. According to the invention, a monomer composition B is metered which contains at least one vinylaromatic compound, at least one ethylenically unsaturated carboxylic acid, and n-butyl acrylate. Acrylamide may also be present. Other monomers may also be present.

[0023] Examples of conjugated aliphatic dienes (a) include 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-dimethylbutadiene, and cyclopentadiene. From this group of monomers, 1,3-butadiene and / or isoprene are preferred.

[0024] The amount of monomers (a) in the monomer composition A is 25 to 44 parts by weight, preferably 28 to 40 parts by weight, in particular 30 to 38 parts by weight, based on 100 parts by weight of monomer composition A.

[0025] The amount of monomers (a) is preferably 10 to 35 parts by weight, preferably 12 to 30 parts by weight and in particular 15 to 25 parts by weight, based on 100 parts by weight of total monomers.

[0026] Examples of suitable vinylaromatic compounds (b) include styrene, o-methylstyrene, and / or vinyltoluene. Styrene is preferably selected from this group of monomers.

[0027] The amount of monomers (b) in the monomer composition A is 55 to 74 parts by weight, preferably 57 to 72 parts by weight, in particular 60 to 70 parts by weight, based on 100 parts by weight of monomer composition A. The amount of monomers (b) in the monomer composition B is 35 to 74 parts by weight, preferably 38 to 70 parts by weight, in particular 42 to 65 parts by weight, based on 100 parts by weight of monomer composition B.

[0028] The monomers (b) preferably comprise a proportion of 45 to 70 parts by weight, preferably 48 to 65 parts by weight and in particular 51 to 62 parts by weight, based on 100 parts by weight of total monomers.

[0029] Examples of ethylenically unsaturated carboxylic acids (monomers (c)) include o,β-monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 6 carbon atoms in the molecule. Examples include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinylacetic acid, and vinyllactic acid. Preferably, the at least one ethylenically unsaturated carboxylic acid is selected from acrylic acid, methacrylic acid, and itaconic acid.

[0030] The ethylenically unsaturated carboxylic acids can be used in the polymerization in the form of the free acids or in a form partially or completely neutralized with suitable bases. Sodium hydroxide solution, potassium hydroxide solution, and / or ammonia are preferably used as neutralizing agents.

[0031] The amount of monomers (c) in the monomer composition A is 1 to 10 parts by weight, preferably 2 to 8 parts by weight, in particular 3 to 6 parts by weight, based on 100 parts by weight of monomer composition A. The amount of monomers (c) in the monomer composition B is 1 to 10 parts by weight, preferably 1 to 8 parts by weight, in particular 2 to 6 parts by weight, based on 100 parts by weight of monomer composition B.

[0032] The monomers (c) preferably comprise a proportion of 1 to 10 parts by weight, preferably 1 to 8 parts by weight, and in particular 2 to 6 parts by weight, based on 100 parts by weight of total monomers. Furthermore, other monoethylenically unsaturated monomers (f) are optionally used to modify the polymers. Other monomers (f) are neither conjugated aliphatic dienes, vinylaromatic compounds, ethylenically unsaturated carboxylic acids, n-butyl acrylate, nor acrylamide.

[0033] Other monoethylenically unsaturated monomers (f) are preferably selected from acrylonitrile, methacrylonitrile, methacrylamide, N-methylolacrylamide, N-methylol(meth)acrylamide, vinyl esters of saturated C 1 - to C 6 -carboxylic acids, preferably vinyl acetate, and esters of acrylic acid and methacrylic acid with monohydric C 1 - to C 5 -alcohols such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate and isopropyl methacrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, sec.-butyl acrylate, sec.-butyl methacrylate, tert.-butyl acrylate, tert.-Butyl methacrylate, as well as esters of acrylic acid and methacrylic acid with monohydric Cs to Cw alcohols, such as pentyl acrylates, pentyl methacrylates, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, allyl esters of saturated carboxylic acids, vinyl ethers, vinyl ketones, dialkyl esters of ethylenically unsaturated carboxylic acids, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, N,N-dialkylaminoalkylacrylamides, N,N-dialkylaminoalkyl methacrylamides, N,N-dialkylaminoalkyl acrylates, N,N-dialkylaminoalkyl methacrylates, vinyl chloride and vinylidene chloride and mixtures thereof.

[0034] According to one embodiment, the proportion of monomers (f) in the monomer composition A is <10 parts by weight, preferably <5 parts by weight, in particular 0.1 to 3 parts by weight, based on 100 parts by weight of monomer composition A.

[0035] Furthermore, the proportion of the monomers (f) in the monomer composition B is <10 parts by weight, preferably <5 parts by weight, in particular 0.1 to 3 parts by weight, based on 100 parts by weight of monomer composition B.

[0036] According to a preferred embodiment, neither monomer composition A nor monomer composition B contains acrylonitrile.

[0037] According to a preferred embodiment, the monomer composition A consists of a) 25 to 44 parts by weight of at least one conjugated aliphatic diene,

[0038] (b) 55 to 74 parts by weight of at least one vinyl aromatic compound,

[0039] (c) 1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid

[0040] (d) 0 to 15 parts by weight of n-butyl acrylate and

[0041] (e) 0 to 5 parts by weight of acrylamide

[0042] (f) 0 to 10 parts by weight of other monomers, each based on 100 parts by weight of monomer composition A.

[0043] According to a further preferred embodiment, the monomer composition B consists of

[0044] (b) 35 to 74 parts by weight of at least one vinyl aromatic compound and

[0045] (c) 1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid,

[0046] (d) 25 to 64 parts by weight of n-butyl acrylate and

[0047] (e) 0 to 5 parts by weight of acrylamide

[0048] (f) 0 to 10 parts by weight of other monomers, each based on 100 parts by weight of monomer composition B. The emulsion polymerization takes place in an aqueous medium. This can be, for example, completely demineralized water or a mixture of water and a miscible solvent such as methanol, ethanol, ethylene glycol, glycerol, or sugar alcohols such as sorbitol or tetrahydrofuran. Preferably, this is water.

[0049] The total amount of aqueous medium is such that the resulting aqueous polymer dispersion has a solids content of preferably > 45 wt.%, particularly preferably 50 to 60 wt.%, in particular > 50 wt.%, based on the weight of the aqueous dispersion.

[0050] The process according to the invention is a monomer feed process. A person skilled in the art understands a monomer feed process to mean that the majority of the monomers to be polymerized, usually at least 80 parts by weight, preferably at least 85 parts by weight, are fed to the polymerization reaction under polymerization conditions continuously—i.e., without interruption of the flow of monomers A or B. The composition of the respective monomer stream can vary over time. Monomer composition A is the sum of all monomers A added in the first stage. Monomer composition B is the sum of all monomers B added in the second stage.

[0051] It is possible to initially charge a portion of the monomer composition A in the polymerization reactor before the start of polymerization (also referred to as a receiver). This can be one or more monomers A. Thus, the polymerization can be initiated in this receiver, which contains 1 to 10 parts by weight, preferably 1 to 7 parts by weight, of the total monomer amount, and monomers can then be continuously added.

[0052] The dosing of monomers A (first stage) ends with the end of the dosing of the conjugated aliphatic diene. The end of the dosing of the conjugated aliphatic diene is the earliest point at which the dosing of monomers B (second stage) can begin.

[0053] It is also possible to have a pause without any monomer dosing between the dosing of monomers A and B. Preferably, the dosing of monomers B starts no later than 60 minutes, particularly preferably 20 minutes, after the end of monomer A dosing.

[0054] According to a preferred embodiment, monomer dosing B follows immediately after monomer dosing A.

[0055] Polymerization conditions generally refer to the amounts of radical initiator, temperatures, and pressures under which the radically initiated aqueous emulsion polymerization does not stop. The polymerization rate generally depends on the type and amount of radical initiator used. The relationships between temperature and decomposition rate are well known to those skilled in the art for common polymerization initiators or can be determined in routine experiments.

[0056] The monomers are preferably added over a period of at least 100 minutes, particularly preferably over a period of 100 to 300 minutes, in particular over a period of 150 to 270 minutes (total metering time of the total monomers).

[0057] Emulsifiers and / or protective colloids are typically used to stabilize radical aqueous emulsion polymerizations. A detailed description of suitable protective colloids can be found in Houben-Weyl, Methoden der organischen Chemie (Methods of Organic Chemistry), Volume XIV / 1, Macromolecular Materials, Georg-Thieme-Verlag, Stuttgart, 1961, pages 411 to 420.

[0058] The term emulsifier is usually understood by those skilled in the art to mean emulsifying aids that keep both the monomer droplets and polymer particles dispersed in the aqueous phase, thus ensuring the stability of the resulting aqueous polymer dispersion. Suitable emulsifiers are surfactants whose number-average molecular weight is typically below 2000 g / mol or preferably below 1500 g / mol.

[0059] Both anionic, cationic, and nonionic emulsifiers are suitable. Emulsifiers whose relative molecular weights are usually lower than those of protective colloids are preferably used as surfactants.

[0060] Suitable anionic emulsifiers include, for example, alkali and ammonium salts of alkyl sulfates (alkyl radical: C5-C22), of sulfuric acid half-esters of ethoxylated alkanols (EO degree: 2 to 50, alkyl radical: C12-C18) and ethoxylated alkylphenols (EO degree: 3 to 50, alkyl radical: C4-C9), of alkylsulfonic acids (alkyl radical: C12-C18), of alkylarylsulfonic acids (alkyl radical: C8-C18), and of diesters of sulfosuccinic acid with C4-C18 alkanols. Further suitable emulsifiers can be found in Houben-Weyl, Methoden der organischen Chemie, Volume XIV / 1, Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 192-208). Bis(phenylsulfonic acid) ethers or their alkali metal or ammonium salts, which bear a C4-C24 alkyl group on one or both aromatic rings, are also suitable as anionic emulsifiers. These compounds are well known, e.g., from US Pat. No. 4,269,749, and commercially available, for example, as Dowfax® 2A1 (Dow Chemical Company).

[0061] Suitable nonionic emulsifiers are araliphatic or aliphatic nonionic emulsifiers, for example, ethoxylated mono-, di-, and trialkylphenols (EO degree: 3 to 50, alkyl radical: C4-C10), ethoxylates of long-chain alcohols (EO degree: 3 to 100, alkyl radical: Cs-Cse), and polyethylene oxide / polypropylene oxide homo- and copolymers. These can contain the alkylene oxide units randomly distributed or polymerized in the form of blocks. EO / PO block copolymers, for example, are particularly suitable. Preference is given to ethoxylates of long-chain alkanols (alkyl radical C1-C30, average degree of ethoxylation 5 to 100), and among these, those with a linear C12-C20 alkyl radical and an average degree of ethoxylation of 10 to 50, as well as ethoxylated monoalkylphenols.

[0062] The process according to the invention uses radical initiators (also referred to as radical polymerization initiators), i.e., initiators that form radicals under the reaction conditions. These can be either peroxides or azo compounds. Redox initiator systems are also possible, of course.

[0063] In principle, inorganic peroxides and / or organic peroxides can be used as peroxides.

[0064] Suitable inorganic peroxides include, for example, hydrogen peroxide and peroxodisulfates, such as the mono- or di-alkali metal or ammonium salts of peroxodisulfuric acid, for example, its mono- and disodium, potassium, or ammonium salts. Suitable organic peroxides include, for example, alkyl hydroperoxides such as tert-butyl hydroperoxide, aryl hydroperoxides such as p-menthyl or cumene hydroperoxide, and dialkyl or diaryl peroxides such as di-tert-butyl, dibenzoyl, or di-cumene peroxide. Redox initiator systems are combined systems composed of at least one organic or inorganic reducing agent and at least one peroxide. The peroxides mentioned above are essentially suitable as oxidizing agents for redox initiator systems.Suitable reducing agents which can be used are sulfur compounds with a low oxidation state, such as alkali sulfites, for example potassium and / or sodium sulfite, alkali hydrogen sulfites, for example potassium and / or sodium hydrogen sulfite, alkali metabisulfites, for example potassium and / or sodium metabisulfite, acetone bisulfite, formaldehyde sulfoxylates, for example potassium and / or sodium formaldehyde sulfoxylate, alkali salts, especially potassium and / or sodium salts, aliphatic sulfinic acids and alkali metal hydrogen sulfides, such as potassium and / or sodium hydrogen sulfide, salts of polyvalent metals, such as iron(II) sulfate, iron(II) ammonium sulfate, iron(II) phosphate, enediols, such as dihydroxymaleic acid, benzoin and / or ascorbic acid, and reducing saccharides, such as sorbose, glucose, fructose and / or dihydroxyacetone.

[0065] Preferred inorganic and organic peroxides are preferably ammonium or alkali metal salts of peroxosulfates or peroxodisulfates, as well as tert-butyl, p-mentyl and cumyl hydroperoxide, in particular selected from sodium and potassium peroxodisulfate, tert-butyl hydroperoxide and cumyl hydroperoxide.

[0066] Preferred radical initiators are at least one inorganic peroxide and at least one organic peroxide. Particular preference is given to using at least one inorganic peroxide, preferably peroxodisulfate, especially sodium peroxodisulfate, and one organic peroxide, preferably alkyl hydroperoxide, especially t-butyl hydroperoxide.

[0067] The polymerization is generally carried out using 0.1 to 5 parts by weight of the radical initiator, preferably 0.5 to 4 parts by weight of the radical initiator, preferably at least one inorganic and organic peroxide, based on 100 parts by weight of total monomers. Dispersions prepared using an inorganic / organic radical initiator combination are particularly preferred, since the resulting polymer dispersions are particularly low in odor.

[0068] Initiation of the polymerization reaction is understood to mean the start of the polymerization reaction of the monomers present in the polymerization vessel through the decomposition of the radical initiator. Polymerization starts, for example, when the polymerization mixture contains monomers and inorganic peroxide and reaches a temperature in the range of > 80°C to < 95°C.

[0069] For example, to initiate the polymerization, an aqueous mixture is first prepared containing a portion of a protective colloid and / or an emulsifier in dissolved form, a portion of a monomer, and optionally a seed latex. This mixture is heated to a temperature above the decomposition temperature of the radical initiator, and a portion of the radical initiator is metered in. After a period of typically 1 to 15 minutes following the addition of the radical initiator, the monomers are metered in. Advantageously, another portion of radical initiator, preferably inorganic peroxide, is metered in at the same time as the monomers.

[0070] According to a preferred embodiment, the metering of the organic peroxide is started at a time at which at least 5 wt.%, preferably at least 8 wt.%, in particular at least 10 wt.%, and at most 30 wt.% of the vinylaromatic compound, based on total monomer, has already been metered in in a continuous flow. In general, it is advantageous in polymerization reactions if the initial charging of the reaction components, the metering / polymerization, and the subsequent reaction in the reaction vessel take place under an inert gas atmosphere, for example, under a nitrogen or argon atmosphere.

[0071] Preferred polymerization conditions are a temperature in the range of > 80°C to < 115°C, preferably > 85°C to < 110°C, in particular > 90°C to < 105°C.

[0072] The conjugated aliphatic diene is typically added at elevated pressure. The conjugated aliphatic diene is preferably added at a pressure in the range of 5 to 15 bar. The elevated pressure ensures that, for example, 1,3-butadiene, which is gaseous at atmospheric pressure and room temperature, is largely contained in the polymerization mixture.

[0073] According to a preferred embodiment, the polymerization is carried out in the presence of a seed latex - also referred to as seed polymer.

[0074] A person skilled in the art usually understands a seed latex to be a polymer dispersion whose seed particles act as centers of particle formation in the polymerization process.

[0075] According to a preferred process variant, an aqueous polymer dispersion with a weight-average particle size D w 50 in the range of 20 to 60 nm and a ratio D w 50 / D n50 < 2 used.

[0076] In this document, the weight-average particle diameter is defined as the weight-average D determined by the analytical ultracentrifuge method. w 50- value, and the number-average particle diameter is the number-average D determined by the same method N 50 value (cf. SE Harding et al., Analytical Ultracentrifugation in Biochemistry and Polymer Science, Royal Society of Chemistry, Cambridge, Great Britain 1992, Chapter 10, Analysis of Polymer Dispersions with an Eight-Cell-AUC-Multiplexer: High Resolution Particle Size Distribution and Density Gradient Techniques, W. Mächtle, pages 147 to 175). In the context of this document, a narrow particle size distribution is understood to mean that the ratio of the weight-average particle diameters D determined by the analytical ultracentrifuge method w 50 and number-average particle diameter DN50 [D W50 / DN50] is less than or equal to 2.0, preferably less than or equal to 1.5 and particularly preferably less than or equal to 1.2 or less than or equal to 1.1.

[0077] The production of a seed latex is known to those skilled in the art and is usually carried out in the presence of a large amount of emulsifier, resulting in small particle sizes and a narrow particle size distribution. It is generally observed that polymerizations carried out in the presence of such an exogenous seed latex—in contrast to an in-situ seed latex—are characterized by uniform particle growth. The seed latex, as the name suggests, is usually used in the form of an aqueous dispersion.

[0078] The seed latex is preferably a polymer based on styrene and / or methyl methacrylate with a glass transition temperature of > 50 °C, > 60 °C, > 70 °C, > 80 °C, or > 90 °C, measured according to DIN EN ISO 11357-2 (2013-09). Polystyrene is particularly preferred.

[0079] Preferably, 0.01 to 2.5 parts by weight, especially 0.02 to 2 parts by weight, of seed latex (calculated as solids), based on total monomers, are used. The polymerization is preferably initiated in a receiver containing up to 2.5 parts by weight of polystyrene seed latex (calculated as solids), based on 100 parts by weight of total monomers, and then monomers and emulsifier are continuously added.

[0080] To modify the properties of the polymers, the emulsion polymerization can optionally be carried out in the presence of at least one radical chain-transfer agent. These are typically used to reduce or control the molecular weight of the polymers obtainable by radical aqueous emulsion polymerization.

[0081] Radical chain transfer compounds (radical chain regulators) can be used to adjust the weight-average molecular weights of the polymers formed. Essentially, aliphatic and / or araliphatic halogen compounds are used, such as n-butyl chloride, n-butyl bromide, n-butyl iodide, methylene chloride, ethylene dichloride, chloroform, bromoform, bromotrichloromethane, dibromodichloromethane, carbon tetrachloride, carbon tetrabromide, benzyl chloride, benzyl bromide, organic thio compounds, such as primary, secondary or tertiary aliphatic thiols, such as ethanethiol, n-propanethiol, 2-propanethiol, n-butanethiol, 2-butanethiol, 2-methyl-2-propanethiol, n-pentanethiol, 2-pentanethiol, 3-pentanethiol, 2-methyl-2-butanethiol, 3-methyl-2-butanethiol, n-hexanethiol, 2-hexanethiol, 3-hexanethiol, 2-methyl-2-pentanethiol, 3-methyl-2-pentanethiol, 4-methyl-2-pentanethiol, 2-methyl-3-pentanethiol, 3-methyl-3-pentanethiol, 2-ethylbutanethiol, 2-ethyl-2-butanethiol,n-Heptanethiol and its isomeric compounds, n-Octanethiol and its isomeric compounds, n-Nonanthiol and its isomeric compounds, n-Decanethiol and its isomeric compounds, n-Undecanethiol and its isomeric compounds, n-Dodecanethiol and its isomeric compounds, in particular tert-Dodecanethiol, n-Tridecanethiol and its isomeric compounds, substituted thiols, such as 2-Hydroxyethanethiol, aromatic thiols, such as Benzenethiol, ortho-, meta-, or para-Methylbenzenethiol, Mercaptoalkanoic acid and its derivatives, such as 3-Mercaptopropionic acid-6-methyl Ihepty lester or 2-Mercaptoethanoic acid-2-ethylhexyl ester as well as all others in the Polymer Handbook 3rd edition, 1989, J. Brandrup and EH Immergut, John Wiley & Sons, Section II, pages 133 to 141 , but also aliphatic and / or aromatic aldehydes, such as acetaldehyde, propionaldehyde and / or benzaldehyde, unsaturated fatty acids, such as oleic acid,Dienes with non-conjugated double bonds, such as divinylmethane, vinylcyclohexane, or terpinoene, or hydrocarbons with easily abstractable hydrogen atoms, such as toluene, are used. However, it is also possible to use mixtures of the aforementioned non-interfering radical chain regulators.

[0082] According to a preferred variant, the monomer composition A is polymerized in the presence of one or more radical chain regulators selected from aliphatic and / or araliphatic halogen compounds, organic thio compounds and substituted thiols.

[0083] If a radical chain regulator is used in the polymerization, the amount used is, for example, 0.01 to 5, preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the monomers used in the polymerization.

[0084] It is possible to initially introduce radical chain regulators into the aqueous reaction medium before initiating the polymerization reaction. However, it is also possible to initially introduce only a portion of the radical chain regulator into the aqueous reaction medium before initiating the polymerization reaction and then add the entire amount or any remaining amount continuously or discontinuously as required under polymerization conditions during the radically initiated emulsion polymerization.

[0085] To complete the polymerization reaction, it is advantageous to stir the reaction mixture at the polymerization temperature for, for example, 0.5 to 3 hours after the monomer addition has been completed. Typically, a conversion of around 95% can be achieved this way.

[0086] In order to further increase the conversion and thus reduce the residual monomer content, one can, for example, add additional radical initiators from the group of initiators mentioned above to the reaction mixture or extend their addition and carry out a so-called "post-polymerization", i.e. a polymerization, in order to achieve conversions of >95% up to 99%.

[0087] Such a post-polymerization can be carried out at the same, lower, or higher temperature than the main polymerization. For example, 0.1 to 1.5 parts by weight, based on 100 parts by weight of the monomers used in the polymerization, of inorganic peroxide, preferably sodium peroxodisulfate, optionally in combination with t-butyl hydroperoxide as initiator, are added in this phase, and the polymerization temperature is set to a temperature in the range of 80 to 120 °C.

[0088] The pH value during polymerization can be, for example, 1 to 5. After polymerization at a conversion of >95%, the pH value is adjusted to a value between 6 and 7, for example.

[0089] Chemical deodorization can also be performed. If traces of residual monomers still need to be removed, this can also be done chemically using the redox initiator systems mentioned above and systems such as those listed in DE-A 44 35 423, DE-A 44 19 518, and DE-A 44 35 422.

[0090] Treatment with the redox initiator system is carried out in the temperature range of 60 to 115°C, preferably at 80 to 100°C. The redox partners can be added to the dispersion independently of one another, completely, in portions, or continuously over a period of 10 minutes to 4 hours. To improve the post-polymerization effect of the redox initiator systems, soluble salts of metals of varying valence, such as iron, copper, or vanadium salts, can also be added to the dispersion. Complexing agents are also frequently added to keep the metal salts in solution under the reaction conditions.

[0091] Following the polymerization reaction (main polymerization + post-polymerization) and, if necessary, chemical deodorization, it may be necessary to render the aqueous polymer dispersions largely free of odor carriers, such as residual monomers and other organic volatile components, a process also referred to as physical deodorization. This can be achieved in a conventional manner by distillative removal (particularly via steam distillation) or by stripping with an inert gas.

[0092] The present invention also relates to the aqueous polymer dispersions obtainable by the process according to the invention.

[0093] These are characterized by being virtually coagulum-free aqueous dispersions. The amount of coagulum is in the ppm range and is preferably less than 2000 ppm, in particular less than 1000 ppm. Furthermore, the polymer dispersions according to the invention preferably have a solids content of >40% by weight, particularly preferably >50% by weight, preferably in the range from 50 to 60% by weight, based on the weight of the aqueous polymer dispersion.

[0094] The aqueous polymer dispersions of the invention are used as binders, adhesives, fiber sizing agents, for the production of coatings, or for the production of paper coating slips. The aqueous polymer dispersions of the invention are suitable both for sizing textile fibers and for sizing mineral fibers, especially glass fibers. Due to their good adhesive strength, particularly when comonomers are used that result in a low glass transition temperature of the copolymer (e.g., less than 20°C), they can also be used as adhesives, for example, for the production of laminates and for the production of coatings such as barrier coatings.

[0095] Furthermore, the polymer dispersions according to the invention or their water-redispersible powders are suitable for the production of sealing slurries. Sealing slurries used in the construction industry are used, for example, to seal and protect surfaces such as masonry or concrete, as well as screed or tile bodies, from water penetration and other environmental influences.

[0096] In principle, the following sealing slurries are preferred:

[0097] A) Two-component (2K) cementitious sealing slurry comprising hydraulic, mineral binders and the polymer dispersion according to the invention;

[0098] B) One-component (1 K) cementitious sealing slurry comprising at least one hydraulic, mineral binder and a powder of the polymer dispersion according to the invention.

[0099] Furthermore, the sealing slurries may contain one or more additives that may be required to fine-tune specific properties of the final product.

[0100] The term "cementitious" refers to compositions containing hydraulic, mineral binders. The term "mineral binder," as used herein, refers to calcium silicate cements, ordinary Portland cements, pozzolanic cements, aluminate cements, calcium sulfoaluminate cements, slag cement, white Portland cement, masonry cement, waterproof cement, mixtures of various cement types, and similar hydraulic binder materials. Pozzolanic cements contain siliceous or siliceous and exhausted materials, e.g., of volcanic origin, such as volcanic ash or pumice, or are obtained from clays, calcined oil shale, or sedimentary rock, as well as from industrial sources such as fly ash, to name just a few of the materials used as additives in construction mixtures with hydraulic binder properties.

[0101] Such sealing slurries are known in principle to the person skilled in the art and are described in WO2016 / 142339, to whose description in particular of the hydraulic, mineral binders, auxiliary materials and compositions is expressly referred.

[0102] The aqueous polymer dispersions according to the invention are preferably used as binders in paper coating slips. The invention therefore also provides a paper coating slip comprising

[0103] (i) inorganic pigment and

[0104] (ii) an aqueous polymer dispersion as described above and obtainable by the process according to the invention

[0105] (ill) and, if necessary, other excipients.

[0106] In addition to water, paper coating slips generally contain pigments, binders, and auxiliaries for adjusting the required rheological properties, such as thickeners. The pigments are usually dispersed in water. The paper coating slip contains pigments in an amount of preferably at least 80 wt.%, e.g., 80 to 95 wt.% or 80 to 90 wt.%, based on the total solids content.

[0107] White pigments are particularly suitable. Suitable pigments include, for example, metal salt pigments such as calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate and calcium carbonate, of which carbonate pigments, in particular calcium carbonate, are preferred. The calcium carbonate can be ground calcium carbonate (GCC, natural ground calcium carbonate), precipitated calcium carbonate (PCC, precipitated calcium carbonate), lime or chalk. Suitable calcium carbonate pigments are available, for example, as Covercarb® 60, Hydrocarb® 60 or Hydrocarb® 90 ME. Other suitable pigments include, for example, silicas, aluminum oxides, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, clay, talc or silicon dioxide. Other suitable pigments are available, for example, as Capim® MP 50 (Clay), Hydragloss® 90 (Clay) or Talcum C10.

[0108] The paper coating slip contains the polymer dispersion prepared according to the invention as the sole binder or in combination with another binder. The most important functions of binders in paper coating slips are to bond the pigments to the paper and the pigments to each other, and to partially fill voids between pigment particles.

[0109] For example, 1 to 50 parts by weight, preferably 1 to 25 parts by weight or 5 to 20 parts by weight of the polymer according to the invention (solid, ie without water or other solvents which are liquid at 21 °C, 1 bar) are used per 100 parts by weight of pigments.

[0110] A preferred paper coating slip contains the inventive polymers of the aqueous polymer dispersion in an amount of 1 to 50 parts by weight, based on the total amount of pigments. Furthermore, the paper coating slip preferably contains pigments in an amount of 80 to 95 parts by weight, based on the total solids content, and at least one auxiliary agent.

[0111] The pigments are selected from the group consisting of calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate, calcium carbonate, silicic acids, aluminum oxides, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, clay, talc and silicon dioxide.

[0112] Suitable auxiliaries are selected from the group consisting of thickeners, other polymeric binders, co-binders, optical brighteners, fillers, flow control agents, dispersants, surfactants, lubricants, neutralizing agents, defoamers, deaerating agents, preservatives and dyes.

[0113] The other synthetic binders different from the polymers prepared according to the invention are generally known and are described, for example, in D. Urban and K. Takamura, Polymer Dispersions and Their Industrial Applications, 2002, Wiley-VCH Verlag GmbH, Weinheim, Chapter 4.4.4, page 90 ff., the disclosure of which is expressly incorporated by reference.

[0114] Other suitable binders include natural-based binders, in particular starch-based binders, as well as synthetic binders different from the polymers produced according to the invention, in particular emulsion polymers producible by emulsion polymerization. Starch-based binders in this context are understood to mean any native, modified, or degraded starch. Native starches can consist of amylose, amylopectin, or mixtures thereof. Modified starches can be oxidized starch, starch esters, or starch ethers. The molecular weight of the starch can be reduced by hydrolysis (degraded starch). Suitable degradation products are oligosaccharides or dextrins. Preferred starches are cereal, corn, and potato starch. Cereal and corn starch are particularly preferred, and corn starch is most preferably used.

[0115] Paper coating slips according to the invention can additionally contain other auxiliaries, e.g. fillers, co-binders and thickeners for further optimizing viscosity and water retention, optical brighteners, dispersants, surfactants, lubricants (e.g. calcium stearate and waxes), neutralizing agents (e.g. NaOH or ammonium hydroxide) for pH adjustment, defoamers, deaerating agents, preservatives (e.g. biocides), flow control agents, dyes (especially soluble dyes), etc. Suitable thickeners include synthetic polymers (e.g. cross-linked polyacrylate), especially celluloses, preferably carboxymethylcellulose. Optical brighteners include, for example, fluorescent or phosphorescent dyes, especially stilbenes.

[0116] It is preferably an aqueous paper coating slip; it already contains water, particularly due to the preparation of the components (aqueous polymer dispersions, aqueous pigment slurries); the desired viscosity can be adjusted by adding additional water. Typical solids contents of paper coating slips are in the range of 30 to 80 wt.%. The pH of the paper coating slip is preferably adjusted to values ​​of 6 to 11, especially 7 to 10.

[0117] The invention also relates to paper or board coated with a paper coating slip according to the invention, and to a process for coating paper or board, wherein an aqueous polymer dispersion is prepared according to the invention; and a paper coating slip is prepared using this polymer dispersion, at least one pigment and optional further auxiliaries; and the paper coating slip is applied to at least one surface of paper or board.

[0118] The paper coating slip is preferably applied to uncoated base paper or uncoated cardboard. The application rate is generally 1 to 50 g, preferably 5 to 30 g (solid, i.e., without water or other solvents liquid at 21 °C, 1 bar) per square meter. Coating can be carried out using conventional application methods, e.g., size press, film press, blade coater, air brush, doctor blade, curtain coating, or spray coater. Depending on the pigment system, the aqueous dispersions of the water-soluble copolymers in paper coating slips can be used for the base coat and / or the top coat.

[0119] The paper coating slips of the invention have good performance properties. They exhibit good runnability in paper coating processes and high bond strength. The coated papers and boards have good surface strength, in particular very high wet and dry pick resistance. They are readily printable using conventional printing processes, such as letterpress, gravure, offset, digital, inkjet, flexographic, newsprint, letterpress, sublimation, laser, electrophotographic, or a combination of these processes. Furthermore, the coated papers and boards exhibit reduced thermal yellowing and low UV yellowing.

[0120] Examples

[0121] Unless otherwise indicated by the context, percentages always refer to percentages by weight. The stated content refers to the content in an aqueous solution or dispersion. Where water was used in the examples, demineralized water was used.

[0122] Measurement methods

[0123] Determination of the viscosity of the dispersion:

[0124] The viscosity of the dispersion was determined according to ASTM D2196 using a Brookfield viscometer with RV spindle 3 at 100 rpm and a temperature of 23°C.

[0125] Solids content:

[0126] The solids content of the polymer dispersions was determined by distributing 0.5 to 1.5 g of the polymer dispersion in a 4 cm diameter metal lid and then drying it in a forced-air drying cabinet at 140°C for 30 minutes. The ratio of the mass of the sample after drying under the above conditions to the mass at sampling gives the solids content of the polymer dispersion.

[0127] The following materials were used in the examples:

[0128] Emulsifier A: Sodium lauryl sulfate in the form of a 15 wt.% solution (Disponil® SDS from BASF)

[0129] Emulsifier B: Dodecyldiphenyl ether disulfonic acid sodium salt in the form of a 45 wt.% solution (Dowfax 2A1 from Dow)

[0130] Complexing agent: EDTA in the form of a 2 wt.% solution (Trilon® BX from BASF)

[0131] Seed latex: Polystyrene seed in the form of a 29.7 wt.% dispersion with a particle size of approximately 30 nm (determined by analytical ultracentrifuge)

[0132] Initiator A: 7 wt.% solution of sodium peroxodisulfate (NaPS)

[0133] Initiator B: 10 wt.% solution of tert-butyl hydroperoxide

[0134] Reducing agent: 13 wt.% solution of acetone bisulfite

[0135] In all examples, the feeds were metered in a uniform flow rate, unless otherwise stated.

[0136] Production of emulsion polymers

[0137] The following quantities in pphm (parts per hundred monomer) are based on 100 parts by weight of total monomer. Example 1: according to the invention

[0138] Template:

[0139] 425.67 g water

[0140] 150.00 g of a 7 wt.% aqueous solution of itaconic acid (0.5 pphm)

[0141] 41.72 g of a 29.7 wt.% dispersion of a polystyrene latex with an average particle size of 30 nm (0.6 pphm)

[0142] 4.67 g of a 45 wt% solution of Dowfax 2A1 (0.10 pphm)

[0143] 31.50 g of a 2 wt.% solution of EDTA (complexing agent) (0.03 pphm)

[0144] 21.00 g butadiene (1 pphm)

[0145] 42.00 g styrene (2 pphm)

[0146] Encore:

[0147] 60.00 g of a 7% w / w solution of sodium peroxodisulfate (initiator A) (0.2 pphm)

[0148] Inlet 1 A:

[0149] 44.55 g acrylic acid (2.12 pphm)

[0150] 749.07 g styrene (35.68 pphm)

[0151] Inlet 1 B:

[0152] 24.75 g acrylic acid (1.18 pphm)

[0153] 416.43 g styrene (19.82 pphm)

[0154] Inlet 2:

[0155] 28.00 g of a 45 wt% solution of Dowfax 2A1 (0.60 pphm)

[0156] 42.00 g of a 15 wt.% solution of sodium lauryl sulfate (0.3 pphm)

[0157] 690.48 ml water

[0158] Inlet 3:

[0159] 350.7 g butadiene (16.7 pphm)

[0160] Inlet 4:

[0161] 21.00 g styrene (1 pphm)

[0162] 25.2 g tert-dodecyl mercaptan (1.2 pphm)

[0163] Inlet 5:

[0164] 420.00 g n-butyl acrylate (20 pphm)

[0165] Inlet 6:

[0166] 285.00 g of a 7% w / w solution of sodium peroxodisulfate (initiator A) (0.95 pphm) Feed 7:

[0167] 84.00 g of a 10% w / w solution of tert-butyl hydroperoxide as (Initiator B) (0.4 pphm)

[0168] Inlet 8:

[0169] 44.10 g of a 10% w / w solution of tert-butyl hydroperoxide as (initiator B) (0.21 pphm)

[0170] Inlet 9:

[0171] 49.15 g of a 13.1% w / w solution of acetone bisulfite (0.33 pphm)

[0172] (Level A)

[0173] The components of the initial mixture were placed in a 6-liter pressure reactor and mixed. The initial mixture was heated to 95°C. When 90°C was reached, initiator A (additive) was slowly added, and polymerization was initiated.

[0174] Immediately afterward, feeds 1A, 2, 3, 4, and 6 were started. Feed 2 was administered over 3 hours 30 minutes. Feed 1A was administered over 2 hours 15 minutes. Feeds 3 and 4 were administered over a period of 1 hour 55 minutes. Feed 6 (initiator A) was administered over 3 hours 30 minutes. Feed 7 (initiator B) was initiated 30 minutes after the start of feeds 1, 2, 3, 4, and 6 and was administered over 1 hour 25 minutes.

[0175] (Level B)

[0176] 20 minutes after the end of feed 3, or immediately after the end of feed 1A, feeds 1B and 5 began and were added over 1 hour 15 minutes. After the end of feeds 1B, 5, and 6 (initiator A), the polymerization mixture was heated to 90°C, and 117 ml of water (5.6 pphm) were added. Feeds 8 and 9 were then started and were added over a further 1.5 hours. After the end of feeds 8 and 9, the polymerization mixture was cooled to room temperature, and 84 g of 15 wt% sodium hydroxide solution (0.6 pphm) were added.

[0177] The solids content of the dispersion was 50 wt%.

[0178] Example 2: not according to the invention (analogous to Example 2 of WO 2021 / 136703)

[0179] Template:

[0180] 523.79 g water

[0181] 149.47 g of a 7 wt% aqueous solution of itaconic acid (0.52 pphm)

[0182] 39.40 g of a 29.7 wt.% dispersion of a polystyrene latex with an average particle size of 30 nm (0.59 pphm)

[0183] 6.26 g of a 45 wt% solution of Dowfax 2A1 (0.142 pphm)

[0184] 30.27 g of a 2 wt.% solution of EDTA (complexing agent) (0.03 pphm)

[0185] 2.44 g terpinoiene (0.12 pphm)

[0186] 24.65 g butadiene (1.23 pphm)

[0187] 32.4 g styrene (1.62 pphm)

[0188] 0.58 g tert-dodecyl mercaptan (0.03 pphm)

[0189] 2.14 g acrylic acid (0.10 pphm) Addition:

[0190] 28.57 g of a 7% w / w solution of sodium peroxodisulfate (initiator A) (0.1 pphm)

[0191] Inlet 1 A:

[0192] 34.07 g acrylic acid (1.70 pphm)

[0193] 105.90 g of a 7 wt.% aqueous solution of itaconic acid (0.37 pphm)

[0194] 967.60 g styrene (48.37 pphm)

[0195] 17.41 g tert-dodecyl mercaptan (0.87 pphm)

[0196] Inlet 1 B:

[0197] 9.77 g acrylic acid (0.49 pphm)

[0198] 31.78 g of a 7 wt% aqueous solution of itaconic acid (0.11 pphm)

[0199] Inlet 2:

[0200] 38.13 g of a 45 wt% solution of Dowfax 2A1 (0.86 pphm)

[0201] 485.6 ml water

[0202] Inlet 3:

[0203] 849.35 g butadiene (42.46 pphm)

[0204] Inlet 4:

[0205] 60.00 g n-butyl acrylate (3.00 pphm)

[0206] Inlet 5:

[0207] 271.43 g of a 7% w / w solution of sodium peroxodisulfate (initiator A) (0.95 pphm)

[0208] Inlet 6:

[0209] 42.00 g of a 10% w / w solution of tert-butyl hydroperoxide as (initiator B) (0.21 pphm)

[0210] Inlet 7:

[0211] 46.24 g of a 13.1% w / w solution of acetone bisulfite (0.33 pphm)

[0212] (Level A)

[0213] The components of the reaction mixture were placed in a 6-liter pressure reactor and mixed. The reaction mixture was heated to 90°C. When 85°C was reached, initiator A (addition) was slowly added, and polymerization was initiated.

[0214] Immediately thereafter, feeds 1A, 2, 3, and 5 were started. Feed 2 was administered over 4 hours 30 minutes. Feeds 1A and 3 were administered over 3 hours 30 minutes. Feed 5 (initiator A) was administered over 4 hours 45 minutes.

[0215] (Level B)

[0216] Immediately after the end of the metered addition of feeds 1A, 2, and 3, feeds 1B and 4 began and took place over 1 hour. After the end of the metered addition of feed 5 (initiator A), the polymerization mixture was stirred for a further 30 minutes. The reactor temperature was then adjusted from 90°C to 85°C, and 117 ml of water (5.6 pphm) were added. Feeds 6 and 7 were then started and took place over a further 1.5 hours. After the end of feeds 6 and 7, the polymerization mixture was cooled to room temperature, and 185.0 g of water (9.25 pphm) and 80 g of 15 wt% sodium hydroxide solution (0.6 pphm) were added.

[0217] The solids content of the dispersion was 50 wt%.

[0218] Table 1 : Monomer composition of the dispersions

[0219] Production of paper coating slips:

[0220] The quantities given refer to the solid content.

[0221] 100 parts by weight of precipitated calcium carbonate (Opacarb A 40 from Specialty Minerals)

[0222] 9.5 parts by weight of emulsion polymer of the respective example

[0223] 0.25 parts by weight of rheology aid (Sterocoll FS from BASF SE)

[0224] Solids content = 64 - 66%

[0225] Viscosity (Brookfield RVT, spindle 4, 100 rpm) = 500 - 1000 mPas at 20 - 25 °C pH = 8.8 - 9.2

[0226] The paper coating slip was prepared in a stirring unit into which the individual components were added one after the other.

[0227] The pigment (precipitated calcium carbonate) was added in predispersed form (slurry). The other components were added in the order above. The final solids content was adjusted by adding water.

[0228] Paper coating:

[0229] A standard paper Magnostar base paper wood-free approx. 58 g / m 2 The coating was applied to one side of the paper using a laboratory coating machine at a pressure of approximately 1.45 bar and a speed of 3 m / min. The coating was dried using three 650 W heaters. The application was carried out using the blade coating method. The coating weight was 10-12 g / m 2 (firmly).

[0230] Determination of thermal yellowing

[0231] Thermal yellowing was determined on coated paper. The paper coating slip to be tested was applied to one side of a coated paper base using a laboratory coating machine and dried using an IR lamp. The weight of the applied coating layer was 10 g / m 2The CIE whiteness of the coated side of the paper produced in this way was determined. It was then stored in a forced-air drying cabinet at 120 °C for 8 hours. The R457 whiteness of the stored paper was then measured. The difference (A) between the two measurements indicates the yellowing. A value of 0 indicates no yellowing. The lower the value, the less yellowing.

[0232] Determination of UV yellowing

[0233] UV yellowing was determined on coated paper. The paper coating slip to be tested was applied to one side of a coated paper base using a laboratory coating machine and dried using an IR lamp. The weight of the applied coating layer was 10 g / m². 2 The CIE whiteness of the coated side of the paper produced in this way was determined. It was then exposed to UV radiation using the SUNTEST XLS+ (765 W / m 2Radiation). The exposure time was 8 hours. The CIE whiteness of the stored paper was then measured. The difference (A) between the two measurements indicates the yellowing. A value of 0 means no yellowing. The lower the value, the less yellowing.

[0234] Measurement of dry pick resistance with IGT test printer (IGT dry):

[0235] Strips were cut from the coated board to be tested and printed using the IGT test printer. The printing inks used were specific test inks from Lorilleux, which transmit different tensile forces. The test strips were passed through the press at continuously increasing speeds (maximum speed 200 cm / s). To evaluate the results, the point on the sample print strip at which 10 picking points appeared on the paper surface after the start of printing was determined. The measurement given for dry picking resistance is the speed in cm / s present at this point during printing, as well as the test ink used. The higher the printing speed at the tenth picking point (PA), the better the quality assessment of the paper surface.

[0236] Table 2: Application data of the coated paper ne: not according to the invention

[0237] The examples show that papers coated with paper coating slips containing the polymers according to the invention exhibit less yellowing and better dry-pick resistance than those of the prior art.

Claims

Claims 1. A process for the preparation of an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization according to a monomer feed process, characterized in that the total monomer composition comprises a monomer composition A and a monomer composition B, and the monomer composition B is metered after the end of the metering of the monomer composition A, wherein the monomer composition A comprises (a) 25 to 44 parts by weight of at least one conjugated aliphatic diene, (b) 55 to 74 parts by weight of at least one vinyl aromatic compound, (c) 1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid (d) 0 to 15 parts by weight of n-butyl lacry lat and (e) 0 to 5 parts by weight of acrylamide, each based on 100 parts by weight of monomer composition A, and the monomer composition B comprises (b) 35 to 74 parts by weight of at least one vinyl aromatic compound and (c) 1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid, (d) 25 to 64 parts by weight of n-butyl acrylate and (e) 0 to 5 parts by weight of acrylamide, each based on 100 parts by weight of monomer composition B, and the ratio of monomer composition A to monomer composition B is from 50:50 to 70:

30.

2. Process according to claim 1, characterized in that the conjugated aliphatic diene is 1,3-butadiene and / or isoprene.

3. Process according to claim 1 or 2, characterized in that the vinyl aromatic compound is styrene.

4. Process according to one of claims 1 to 3, characterized in that neither the monomer composition A nor the monomer composition B contains acrylonitrile.

5. Process according to one of claims 1 to 4, characterized in that at least one inorganic peroxide and at least one organic peroxide are used as radical initiators.

6. Process according to one of claims 1 to 5, characterized in that at least one peroxodisulfate and one alkyl hydroperoxide are used.

7. Process according to one of claims 1 to 6, characterized in that polymerization is carried out at a temperature in the range from > 80°C to < 115°C.

8. Process according to one of claims 1 to 7, characterized in that the monomer composition A is polymerized in the presence of one or more radical chain regulators selected from aliphatic and / or araliphatic halogen compounds, organic thio compounds and substituted thiols.

9. Aqueous polymer dispersion obtainable by radically initiated emulsion polymerization according to one of claims 1 to 8.

10. Use of the aqueous polymer dispersion according to claim 9 as a binder, adhesive, sizing agent for fibers, for the production of coatings or for the production of paper coating slips.

11. Use of the aqueous polymer dispersion according to claim 9 or its water-redispersible powder as a binder in two-component cementitious or one-component cementitious sealing slurries.

12. Paper coating slip containing (i) inorganic pigments and (ii) an aqueous polymer dispersion according to claim 9 and optionally further auxiliaries.

13. Paper coating slip according to the preceding claim, characterized in that the polymers of the aqueous polymer dispersion are used in an amount of 1 to 50 parts by weight, based on the total amount of pigments, and that the pigments are present in an amount of 80 to 95 parts by weight, based on the total solids content, and are selected from the group consisting of calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate, calcium carbonate, silicic acids, aluminum oxides, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, alumina, talc and silicon dioxide.

14. Paper or cardboard coated with a paper coating slip according to one of the two preceding claims.

15. A process for coating paper or board, wherein an aqueous polymer dispersion according to claim 9 is provided; and a paper coating slip is prepared using the aqueous polymer dispersion, at least one pigment, and optionally further auxiliaries; and the paper coating slip is applied to at least one surface of paper or board.

Images