Polymer dispersions

Abstract

A process for preparing an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization wherein the total monomer composition comprises a monomer composition A and a monomer composition B, and the monomer composition B is metered after the metering of the monomer composition A ends, and the ratio of monomer composition A to monomer composition B is 50: 50 to 70: 30, the invention also relates to the dispersions thus obtained and to the use of the dispersions as binders, binders, sizing agents for fibers, for the production of coatings or for the production of paper coating compounds.

Description

[0001] The present invention relates to a process for the preparation of aqueous polymer dispersions by radical initiated aqueous emulsion polymerization of butyl acrylate, a vinyl aromatic compound and a conjugated aliphatic diene according to a monomer feeding process. The present invention also relates to the aqueous polymer dispersions prepared by this process and to the use of these aqueous polymer dispersions as binders, adhesives, sizing agents for fibers, for coating compositions.

[0002] Polymer dispersions with copolymers of a vinyl aromatic compound and an aliphatic diene are often chosen as binders for paper coating compounds. For example, WO 2021 / 136703 teaches an aqueous polymer dispersion based on butyl acrylate, styrene and butadiene which is used as a binder for paper coating compounds with good water resistance. Paper coated with this dispersion has improved wet pick up.

[0003] Furthermore, EP 2085409 teaches binders for paper coating compounds which increase the printability of paper using the gravure printing method. They are produced by polymerizing a combination of butyl acrylate, acrylic acid and acrylonitrile in the presence of a styrene / butadiene / acrylonitrile / acrylic acid latex. According to the teachings of this document, both the low glass transition temperature in the range of -20°C to -50°C of the acrylonitrile and the second polymer cause a "soft" outer phase of the polymer particles which improves the printability.

[0004] Paper coating compounds are used for the final treatment of the base paper, for example for the production of drawing paper. Such high-quality papers have good printability and exhibit a smooth white surface. During the printing process, the paper is pressed at high speed onto a roller with adhesive ink. It is therefore important that the binder ensures good adhesion of the coating to the base paper so that during the printing process, no parts of the coating come off - so-called picking. It is therefore an object of the present invention to find good adhesion on paper for a wide variety of different printing methods.

[0005] Usually, white pigments are added to paper coating compounds. Nevertheless, papers coated with paper coating compounds with styrene / butadiene dispersions as binders tend to yellow. It is therefore an object of the present invention to find styrene / butadiene based binders which show lower thermal and UV yellowing of the paper coated with them when used in paper coating compounds.

[0006] Furthermore, papers coated with these paper coating compounds will also have good printability and good strength.

[0007] According to the present invention, this objective is achieved by a method for preparing an aqueous polymer dispersion by free radical-initiated aqueous emulsion polymerization according to a monomer feeding method, wherein the total monomer composition comprises monomer composition A and monomer composition B, and monomer composition B is metered in after the metering of monomer composition A is completed.

[0008] Wherein monomer composition A contains

[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,

[0011] (c) 1 to 10 parts by weight of at least one olefinically unsaturated carboxylic acid,

[0012] (d) 0 to 15 parts by weight of n-butyl acrylate, and

[0013] (e) 0 to 5 parts by weight of acrylamide,

[0014] In each case, based on 100 parts by weight of monomer composition A,

[0015] And monomer composition B contains

[0016] (b) 35 to 74 parts by weight of at least one vinyl aromatic compound and

[0017] (c) 1 to 10 parts by weight of at least one olefinically unsaturated carboxylic acid,

[0018] (d) 25 to 64 parts by weight of n-butyl acrylate, and

[0019] (e) 0 to 5 parts by weight of acrylamide,

[0020] In each case, based on 100 parts by weight of monomer composition B,

[0021] Furthermore, the ratio of monomer composition A to monomer composition B is 50:50 to 70:30.

[0022] The present invention further relates to aqueous polymer dispersions obtained according to the method of the invention, and to their use as binders, adhesives, sizing agents for fibers, and binders for the production of coatings, particularly for two-component or one-component cement-based sealants, and for paper coating blends, and to paper coating blends and sealants. The invention also relates to methods for coating paper and paperboard, and to the resulting coated paper or coated paperboard.

[0023] Some compounds derived from acrylic acid and methacrylic acid are referred to below as abbreviations by inserting the syllable "(meth)" into the names of compounds derived from acrylic acid.

[0024] "Total monomers" refers to the total amount of all monomers used in the polymerization, which sums up to 100 parts by weight.

[0025] The total metering time of a monomer refers to the period of time during which monomers are continuously metered and added. Metering can be performed by adding mixtures or by adding individual monomers, and its addition can also begin with a time delay. The key is that the monomers are metered and added at each point in time; that is, the addition is continuous. Accordingly, the total metering time begins when the first monomer (mixture) is metered and adds and ends when the last monomer (mixture) is metered and added.

[0026] Regarding the solids content (by weight %) of the aqueous dispersion, this is based on the weight of the aqueous dispersion.

[0027] According to the present invention, a monomer composition A comprising at least one conjugated aliphatic diene, at least one vinyl aromatic compound, and at least one olefinically unsaturated carboxylic acid is added in a metered manner. Additionally, n-butyl acrylate and acrylamide may be present. Furthermore, other monomers may be present.

[0028] According to the present invention, a monomer composition B comprising at least one vinyl aromatic compound, at least one olefinically unsaturated carboxylic acid, and n-butyl acrylate is added in a metered manner. Acrylamide may also be present. Other monomers may also be present.

[0029] Illustrative conjugated aliphatic dienes (a) include 1,3-butadiene, isoprene, 1,3-pentadiene, dimethyl-1,3-butadiene, and cyclopentadiene. From this group of monomers, 1,3-butadiene and / or isoprene are preferred.

[0030] The amount of monomer (a) in monomer composition A is 25 to 44 parts by weight, preferably 28 to 40 parts by weight, and particularly 30 to 38 parts by weight, based on 100 parts by weight of monomer composition A.

[0031] The amount of monomer (a) is preferably 10 to 35 parts by weight, more preferably 12 to 30 parts by weight, and especially 15 to 25 parts by weight, based on 100 parts by weight of total monomer.

[0032] Examples of suitable vinyl aromatic compounds (b) include styrene, α-methylstyrene, and / or vinyltoluene. From this group of monomers, styrene is preferred.

[0033] The amount of monomer (b) in monomer composition A is 55 to 74 parts by weight, preferably 57 to 72 parts by weight, and particularly 60 to 70 parts by weight, based on 100 parts by weight of monomer composition A. The amount of monomer (b) in monomer composition B is 35 to 74 parts by weight, preferably 38 to 70 parts by weight, and particularly 42 to 65 parts by weight, based on 100 parts by weight of monomer composition B.

[0034] Monomer (b) together preferably comprises 45 to 70 parts by weight, more preferably 48 to 65 parts by weight and especially 51 to 62 parts by weight of the total monomers based on 100 parts by weight.

[0035] Examples of olefinically unsaturated carboxylic acids (monomers (c)) include α,β-monoolefinically unsaturated monocarboxylic acids and dicarboxylic acids having 3 to 6 carbon atoms in the molecule. Examples of these are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinylacetic acid, and vinyllactic acid. At least one olefinically unsaturated carboxylic acid is preferably selected from acrylic acid, methacrylic acid, and itaconic acid.

[0036] Unsaturated carboxylic acids with olefinic bonds can be used in polymerization as free acids or as partially or completely neutralized by a suitable base. Sodium hydroxide solution, potassium hydroxide solution, and / or ammonia are preferred as neutralizing agents.

[0037] The amount of monomer (c) in monomer composition A is 1 to 10 parts by weight, preferably 2 to 8 parts by weight, and particularly 3 to 6 parts by weight, per 100 parts by weight of monomer composition A. The amount of monomer (c) in monomer composition B is 1 to 10 parts by weight, preferably 1 to 8 parts by weight, and particularly 2 to 6 parts by weight, per 100 parts by weight of monomer composition B.

[0038] The monomer (c) together preferably comprises 1 to 10 parts by weight, more preferably 1 to 8 parts by weight, and especially 2 to 6 parts by weight of the total monomers based on 100 parts by weight.

[0039] In addition, alternatively, other mono-olefinic unsaturated monomers (f) may be added for polymer modification. These other monomers (f) are neither conjugated aliphatic dienes, vinyl aromatic compounds, olefinic unsaturated carboxylic acids, n-butyl acrylate, nor acrylamide.

[0040] Other mono-olefinic unsaturated monomers (f) are preferably selected from acrylonitrile, methacrylonitrile, methacrylamide, N-hydroxymethylacrylamide, N-hydroxymethyl(meth)acrylamide, and saturated C1 to C24 monomers. 18Vinyl esters of carboxylic acids, preferably vinyl acetate, and esters of acrylic acid and methacrylic acid with monocarboxylic C1 to C3 alcohols such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, and acrylic acid and methacrylic acid with monocarboxylic C5 to C3 alcohols. 10 Esters of alcohols such as amyl acrylate, amyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-octyl acrylate, allyl esters of saturated carboxylic acids, vinyl ethers, vinyl ketones, dialkyl esters of olefinically unsaturated carboxylic acids, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, N,N-dialkylaminoalkylacrylamide, N,N-dialkylaminoalkylmethylacrylamide, N,N-dialkylaminoalkylacrylate, N,N-dialkylaminoalkylmethylacrylate, vinyl chloride and vinylidene chloride, and mixtures thereof.

[0041] According to one embodiment, the fraction of monomer (f) in monomer composition A is ≤ 10 parts by weight, preferably ≤ 5 parts by weight, and particularly 0.1 to 3 parts by weight, based on 100 parts by weight of monomer composition A.

[0042] Furthermore, the fraction of monomer (f) in monomer composition B is based on 100 parts by weight of monomer composition B, ≤ 10 parts by weight, preferably ≤ 5 parts by weight, and particularly 0.1 to 3 parts by weight.

[0043] According to a preferred embodiment, neither monomer composition A nor monomer composition B contains acrylonitrile.

[0044] According to a preferred embodiment, monomer composition A comprises the following:

[0045] (a) 25 to 44 parts by weight of at least one conjugated aliphatic diene,

[0046] (b) 55 to 74 parts by weight of at least one vinyl aromatic compound,

[0047] (c) 1 to 10 parts by weight of at least one olefinically unsaturated carboxylic acid,

[0048] (d) 0 to 15 parts by weight of n-butyl acrylate, and

[0049] (e) 0 to 5 parts by weight of acrylamide,

[0050] (f) 0 to 10 parts by weight of other monomers,

[0051] In each case, the monomer composition A is based on 100 parts by weight.

[0052] According to another preferred embodiment, monomer composition B comprises the following:

[0053] (b) 35 to 74 parts by weight of at least one vinyl aromatic compound and

[0054] (c) 1 to 10 parts by weight of at least one olefinically unsaturated carboxylic acid,

[0055] (d) 25 to 64 parts by weight of n-butyl acrylate, and

[0056] (e) 0 to 5 parts by weight of acrylamide,

[0057] (f) 0 to 10 parts by weight of other monomers,

[0058] In each case, the monomer composition B is based on 100 parts by weight.

[0059] Emulsion polymerization is carried out in an aqueous medium. This can be, for example, completely softened water or a mixture of water and a solvent miscible with it (such as methanol, ethanol, ethylene glycol, glycerol, sugar alcohols such as sorbitol, or tetrahydrofuran). Preferably, the medium is water.

[0060] The total amount of the aqueous medium is proportional to such that the obtained aqueous polymer dispersion has a solid content of preferably ≥ 45% by weight, more preferably 50% to 60% by weight, and particularly ≥ 50% by weight, based on the weight of the aqueous dispersion.

[0061] The method of the present invention is a monomer feeding method. Through this monomer feeding method, those skilled in the art will understand that a major amount, typically at least 80 parts by weight, preferably at least 85 parts by weight, of the monomer to be polymerized is continuously supplied to the polymerization reaction under polymerization conditions, i.e., without interrupting the volumetric flow of monomer A or monomer B. The composition of the respective monomer flow 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.

[0062] A portion of monomer composition A (also known as the initial charge) may be included in the polymerization reactor before polymerization begins. This may include one or more monomers A. Polymerization can then be initiated in this initial charge, which contains 1 to 10 parts by weight, preferably 1 to 7 parts by weight, of the total amount of monomer, and then the monomers are continuously metered in.

[0063] The stoichiometric addition of monomer A (stage one) ends with the stoichiometric addition of the conjugated aliphatic diene. The end of the stoichiometric addition of the conjugated aliphatic diene is the earliest time at which the stoichiometric addition of monomer B (stage two) begins.

[0064] It is also possible to have an interruption between the metering of monomer A and monomer B without any metering of monomers being added. Preferably, the metering of monomer B begins no later than 60 minutes, more preferably 20 minutes, after the metering of monomer A has ended.

[0065] According to a preferred embodiment, the metered addition of monomer B immediately follows the metered addition of monomer A.

[0066] Polymerization conditions should generally be understood to refer to the amounts of free radical initiator, temperatures, and pressures under which free radical-initiated aqueous emulsion polymerization will not cease. The polymerization rate typically depends on the nature and amount of the free radical initiator used. The relationship between temperature and decomposition rate for standard polymerization initiators is well known to those skilled in the art or can be determined in routine experiments.

[0067] The monomers are preferably metered over a period of at least 100 minutes, more preferably over a period of 100 to 300 minutes, and particularly over a period of 150 to 270 minutes (total metering time of total monomers).

[0068] Emulsifiers and / or protective colloids are commonly used to stabilize emulsions for free radical aqueous emulsion polymerization. A comprehensive description of suitable protective colloids can be found in Houben-Weyl, Methoden der organischen Chemie [Methodsof Organic Chemistry], Vol. XIV / 1, Makromolekulare Stoffe [Macromolecular Materials], Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411-420.

[0069] Technicians generally understand emulsifiers as emulsifying agents that maintain both monomer droplets and polymer particles dispersed in an aqueous phase and thus ensure the stability of the produced aqueous polymer dispersion. Useful emulsifiers include interfacial active substances having a number-average molecular weight typically below 2000 g / mol or preferably below 1500 g / mol.

[0070] Suitable emulsifiers include not only anionic and cationic emulsifiers, but also nonionic emulsifiers. The surfactants used are preferably emulsifiers with a relative molecular weight typically lower than that of the protective colloid.

[0071] Suitable anionic emulsifiers are, for example, alkyl sulfates (alkyl: C8-C). 22), ethoxylated alkanols (EO level: 2 to 50, alkyl: C 12 -C 18 ) and ethoxylated alkylphenols (EO levels: 3 to 50, alkyl: C4-C9) sulfate monoesters, alkyl sulfonic acids (alkyl: C 12 -C 18 ), alkyl aryl sulfonic acid (alkyl: C9-C) 18 ), and sulfosuccinic acid and C4-C 18 Alkali metal salts and ammonium salts of diesters of alkanols. Other suitable emulsifiers can be found in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Vol. XIV / 1, Makromolekulare Stoffe [Macromolecular Compounds], Georg-Thieme-Verlag, Stuttgart, 1961, pp. 192-208. Also suitable as anionic emulsifiers are those with C4-C4 rings on one or both aromatic rings. 24 Alkyl bis(phenylsulfonic acid) ethers and their alkali metal or ammonium salts. These compounds are generally known, for example from US-A-4,269,749, and are commercially available, for example as Dowfax® 2A1 (Dow Chemical Company).

[0072] Suitable nonionic emulsifiers are aryl or aliphatic nonionic emulsifiers, such as ethoxylated mono-, di-, and trialkylphenols (EO level: 3 to 50, alkyl: C4-C). 10 ), ethoxylated long-chain alcohols (EO level: 3 to 100, alkyl: C8-C) 36 ), as well as polyethylene oxide / polypropylene oxide homopolymers and copolymers. These may contain epoxy alkyl units copolymerized randomly or in block form. A very suitable example is EO / PO block copolymers. Ethoxylated derivatives of long-chain alkanols (alkyl: C1-C) are preferred. 30 (average ethoxylation level of 5 to 100), and among these, those with straight-chain C are particularly preferred. 12 -C 20 Alkyl groups and those with average ethoxylation levels of 10 to 50, as well as ethoxylated monoalkylphenols.

[0073] In the method of this invention, a free radical initiator (also known as a free radical polymerization initiator), i.e., an initiator that forms free radicals under reaction conditions, is used. These can be peroxides or azo compounds. Redox initiator systems are also suitable.

[0074] The peroxides used can, in principle, be inorganic peroxides and / or organic peroxides.

[0075] Examples of suitable inorganic peroxides include hydrogen peroxide and peroxydisulfate, such as mono- or dialkali metal salts or ammonium salts of peroxydisulfate, for example, its mono- and disodium salts, mono- and dipotassium salts, or ammonium salts. Examples of suitable organic peroxides are alkyl hydrogen peroxides such as tert-butyl hydrogen peroxide, aryl hydrogen peroxides such as p-menthyl or cumene hydrogen peroxide, and dialkyl or diaryl peroxides such as di-tert-butyl peroxide, dibenzoyl peroxide, or dicumene peroxide.

[0076] A redox initiator system is a combination system consisting of at least one organic or inorganic reducing agent and at least one peroxide. Suitable oxidants for redox initiator systems are essentially the peroxides mentioned above. Corresponding reducing agents that can be used are sulfur compounds in low oxidation states, such as alkali metal sulfites, for example, potassium sulfite and / or sodium sulfite; alkali metal bisulfites, for example, potassium bisulfite and / or sodium bisulfite; alkali metal metabisulfites, for example, potassium metabisulfite and / or sodium metabisulfite; acetone bisulfite; formaldehyde hyposulfite, for example, potassium formaldehyde hyposulfite and / or sodium formaldehyde hyposulfite; alkali metal salts, especially potassium and / or sodium salts of aliphatic sulfinic acids; and alkali metal hydrosulfides, for example, potassium and / or sodium hydrosulfide; salts of polyvalent metals, such as ferric(II) sulfate, ammonium ferric(II) sulfate, ferric(II) phosphate; olefinic alcohols, such as dihydroxymaleic acid, benzoin, and / or ascorbic acid; and reducing sugars, such as sorbitol, glucose, fructose, and / or dihydroxyacetone.

[0077] Preferred are inorganic and organic peroxides, especially ammonium or alkali metal salts of persulfate or peroxydisulfate, as well as tert-butyl hydroperoxide, p-menthyl hydroperoxide and cumyl hydroperoxide, particularly selected from sodium peroxydisulfate and potassium sodium peroxydisulfate, tert-butyl hydroperoxide and cumyl hydroperoxide.

[0078] At least one inorganic peroxide and at least one organic peroxide are used as preferred free radical initiators. Particularly preferred are at least one inorganic peroxide, preferably peroxydisulfate, especially sodium peroxydisulfate, and an organic peroxide, preferably alkyl hydroperoxide, especially tert-butyl hydroperoxide.

[0079] Polymerization is typically carried out using 0.1 to 5 parts by weight of a free radical initiator, preferably 0.5 to 4 parts by weight, based on 100 parts by weight of total monomers, and preferably at least one inorganic and organic peroxide. Dispersions produced by a combination of inorganic / organic free radical initiators are particularly preferred because the resulting polymer dispersions have particularly low odor.

[0080] Initiation of a polymerization reaction should be understood as the polymerization of monomers present in the polymerization vessel beginning due to the decomposition of a free radical initiator. For example, polymerization is initiated when the polymerization mixture contains monomers and inorganic peroxides and reaches a temperature in the range of ≥ 80°C to ≤ 95°C.

[0081] For example, to initiate polymerization, an aqueous mixture comprising a portion of a protective colloid and / or emulsifier in dissolved form, a portion of monomer, and any seed latex is first prepared. This mixture is heated to a temperature above the decomposition temperature of the free radical initiator, and a portion of the free radical initiator is metered in. After a typical period of 1 to 15 minutes following the addition of the free radical initiator, the monomer is metered in. Advantageously, an additional amount of the free radical initiator, preferably an inorganic peroxide, is metered in simultaneously with the monomer.

[0082] According to a preferred embodiment, the addition of organic peroxide begins when at least 5%, preferably at least 8%, particularly at least 10% and at most 30% by weight of total monomers have been added in a continuous volumetric flow.

[0083] Generally, for polymerization reactions, it is advantageous if the initial charge, metered addition / polymerization, and post-reaction of the reactants are carried out in a reaction vessel under an inert gas atmosphere, such as nitrogen or argon.

[0084] Preferred polymerization conditions are temperatures in the range of ≥ 80°C to ≤ 115°C, preferably ≥ 85°C to ≤ 110°C, and especially ≥ 90°C to ≤ 105°C.

[0085] Conjugated aliphatic dienes are typically added in metering under high pressure. The metering addition of conjugated aliphatic dienes is preferably carried out at pressures in the range of 5 to 15 bar. The effect of high pressure is that, for example, 1,3-butadiene, which is gaseous at standard pressure and room temperature, is present in large quantities in the polymerization mixture.

[0086] According to a preferred embodiment, polymerization is carried out in the presence of seed latex (also known as seed polymer).

[0087] Seed latex is generally understood by those skilled in the art to mean a polymer dispersion in which seed particles act as particle-forming centers during polymerization.

[0088] In a preferred variation of the method, the seed latex used has a weight-average particle size D in the range of 20 to 60 nm. w 50 and ≤ 2 of D w 50 / D n A 50-ratio aqueous polymer dispersion.

[0089] In this paper, the weight-average particle diameter should be understood as the weight-average D measured by the analytical ultracentrifugation method. w 50, and the number-average particle diameter should be understood as the number-average D measured by the same method. N 50 (See SE Harding et al., Analytical Ultracentrifugation in Biochemistry 5, and Polymer Science, Royal Society of Chemistry, Cambridge, UK 1992, Chapter 10, Analysis of Polymer Dispersions with an Eight-Cell-AUC-Multiplexer: High-Resolution Particle Size Distribution and Density Gradient Techniques, W. Mächtle, pp. 147-175). In the context of this specification, a narrow particle size distribution should be understood as the weight-average particle diameter D determined by analytical ultracentrifugation. w 50 and number-average particle diameter D N 50% ratio [D] w 50 / D N 50] A particle size distribution of not more than 2.0, preferably not more than 1.5, and especially preferably not more than 1.2 or not more than 1.1.

[0090] The production of seed latex is common knowledge to those skilled in the art and is generally effective in the presence of a large amount of emulsifier, resulting in small particle size and narrow particle size distribution. It is typically observed that polymerization in the presence of such exogenous seed latex is characterized by uniform particle growth compared to in-situ seed latex. Seed latex, as its name suggests, is typically used in the form of aqueous dispersions.

[0091] The seed latex is preferably a styrene- and / or methyl methacrylate-based polymer having a glass transition temperature of ≥ 50°C, ≥ 60°C, ≥ 70°C, ≥ 80°C or ≥ 90°C as measured according to DIN EN ISO 11357-2 (2013-09). Polystyrene is particularly preferred.

[0092] It is preferred to use seed latex (in solids) based on 0.01 to 2.5 parts by weight of total monomers, and especially 0.02 to 2 parts by weight.

[0093] The polymerization is preferably initiated in an initial charge containing up to 2.5 parts by weight of polystyrene seed latex (in solids) based on 100 parts by weight of total monomers, and then monomers and emulsifiers are added continuously by metering.

[0094] To modify the properties of the polymer, emulsion polymerization can optionally be carried out in the presence of at least one compound used as a chain transfer agent. These chain transfer agents are typically used to reduce or control the molecular weight of polymers obtainable through free radical aqueous emulsion polymerization.

[0095] Free radical chain transfer compounds (chain transfer agents) can be used to adjust the weight-average molecular weight of the formed polymer. The compounds used here are primarily aliphatic and / or aryliphatic halogen compounds, such as n-butyl chloride, n-butyl bromide, n-butyl iodide, dichloromethane, dichloroethane, chloroform, bromoform, chloroform, dibromodichloromethane, carbon tetrachloride, carbon tetrabromide, benzyl chloride, benzyl bromide, and organothioides, 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 isomers, n-octanethiol and its isomers, n-nonanethiol and its isomers, n-decanethiol and its isomers, n-undecanethiol and its isomers, n-dodecanethiol and its isomers (especially tert-dodecanethiol), n-tridecanethiol and its isomers, substituted thiols, such as 2-hydroxyethylthiol, aromatic thiols, such as benzenethiol, o-methylbenzenethiol, m-methylbenzenethiol or p-methylbenzenethiol, mercaptoalkyl acids and their derivatives, such as 6-methylheptyl 3-mercaptopropionate or 2-ethylhexyl 2-mercaptoacetate, and in Polymer All other sulfur compounds described in *The Polymer Handbook*, 3rd edition, 1989, J. Brandrup and EH Immergut, John Wiley & Sons, Part II, pp. 133–141, as well as 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 terpinene; or hydrocarbons with readily abstractable hydrogen atoms, such as toluene. However, mixtures of the aforementioned chain transfer agents that do not interfere with each other may also be used.

[0096] According to a preferred variant, monomer composition A is polymerized in the presence of one or more chain transfer agents selected from aliphatic and / or aryliphatic halogen compounds, organothio compounds, and substituted thiols.

[0097] If a chain transfer agent is used during polymerization, the corresponding amount used is based on 100 parts by weight of monomer used during polymerization, for example, 0.01 to 5 parts by weight, preferably 0.1 to 3 parts by weight.

[0098] The chain transfer agent can be loaded into the aqueous reaction medium before initiating the polymerization reaction. Alternatively, it may be possible to include only a portion of the chain transfer agent in the initial charge in the aqueous reaction medium before initiating the polymerization reaction, and then, under polymerization conditions, add the total amount or any remaining residual amount in a continuous or discontinuous manner during radical-initiated emulsion polymerization as needed.

[0099] To complete the polymerization reaction, it is advantageous to continue stirring the reaction mixture for 0.5 to 3 hours, for example, at the polymerization temperature, after the monomer metering has been completed. Typically, this method can achieve a conversion rate of approximately 95%.

[0100] To further improve the conversion and thus reduce the residual monomer content, for example, additional radical initiators from the group of initiators described above can be added to the reaction mixture or their addition can be extended and so-called "post-polymerization" can be carried out, i.e., polymerization that achieves a conversion of >95% to 99%.

[0101] This post-polymerization can be carried out at the same temperature as, or at a lower or higher temperature than, the primary polymerization. For example, in this stage, 0.1 to 1.5 parts by weight of an inorganic peroxide, preferably sodium peroxydisulfate, optionally in combination with tert-butyl hydroperoxide, is metered in based on 100 parts by weight of the monomer used in the polymerization as an initiator, and the polymerization temperature is set in the range of 80°C to 120°C.

[0102] During polymerization, the pH can be, for example, between 1 and 5. After polymerization with a conversion rate > 95% is completed, the pH is adjusted, for example, to a value between 6 and 7.

[0103] In addition, chemical deodorization can be performed. If trace amounts of residual monomers still need to be removed, this can also be done chemically using the redox initiator systems described above, as well as those described in DE-A 44 35 423, DE-A 44 19 518, and DE-A 44 35 422.

[0104] The treatment using the redox initiator system is carried out in a temperature range of 60°C to 115°C, preferably 80°C to 100°C. Redox pairs can be added independently, in whole, in batches, or continuously over a period of 10 minutes to 4 hours. To improve the post-polymerization effect of the redox initiator system, a soluble salt of a metal with variable valence, such as an iron salt, copper salt, or vanadium salt, can also be added to the dispersion. A complexing agent that keeps the metal salt in a soluble state under reaction conditions is also typically added.

[0105] Following the polymerization reaction (primary polymerization + post-polymerization) and optional chemical deodorization, it may be necessary to render the aqueous polymer dispersion substantially free of odorous compounds, such as residual monomers and other volatile organic components, which is also known as physical deodorization. This can be achieved either by distillation (particularly via steam distillation) or by physical means such as stripping with an inert gas, in ways known per se.

[0106] The present invention also relates to polymer dispersions obtainable by the method according to the invention.

[0107] These are noteworthy because they are actually aqueous dispersions free of condensates. The amount of condensate is in the ppm range and preferably less than 2000 ppm, especially less than 1000 ppm.

[0108] Furthermore, the polymer dispersion of the present invention preferably has a solids content of ≥ 40% by weight based on the weight of the aqueous polymer dispersion, more preferably ≥ 50% by weight, and most preferably in the range of 50% to 60% by weight.

[0109] The aqueous polymer dispersions of the present invention can be used as binders, adhesives, sizing agents for fibers, for the production of coatings, or for the production of paper coating blends. The aqueous polymer dispersions of the present invention are suitable for sizing textile fibers and for sizing mineral fibers, especially glass fibers. Due to their good adhesive strength, particularly when using comonomers that result in low glass transition temperatures (e.g., less than 20°C) in the copolymer, they can also be used as adhesives, for example, for the production of laminates and for the production of coatings such as barrier coatings.

[0110] Furthermore, the polymer dispersions according to the invention, or the water-redispersible powder thereof, are suitable for use in 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 mortar or tile elements) from water ingress and other environmental influences.

[0111] In principle, the following sealing grouts are preferred:

[0112] A) A two-component (2K) cement-based sealant comprising a hydraulic mineral binder and a polymer dispersion according to the invention;

[0113] B) A one-component (1K) cement-based sealant comprising at least one hydraulic mineral binder and a polymer dispersion according to the invention.

[0114] In addition, the sealant may contain one or more additives, which may be needed to fine-tune specific properties of the final product.

[0115] The term "cement-based" refers to a composition containing a hydraulic mineral binder. As used herein, the term "mineral binder" is intended to refer to calcium silicate cement, ordinary Portland cement, pozzolanic cement, aluminate cement, calcium sulfoaluminate cement, slag cement, white Portland cement, masonry cement, waterproof cement, mixtures of different types of cement, and similar hydraulic binder materials. Pozzolanic cement includes siliceous or siliceous and depleted materials, such as volcanic-derived materials like volcanic ash or pumice, or obtained from clay, calcined oil shale, or sedimentary acidic rocks, and also from industrial sources such as fly ash, to name just a few of the materials used as additives in building mixtures with hydraulic binder properties.

[0116] Such sealant grouts are known in principle to those skilled in the art and are described in WO 2016 / 142339, which specifically and explicitly refers to the description of hydraulics, mineral binders, additives and compositions.

[0117] The aqueous polymer dispersion of the present invention is preferably used as a binder in paper coating formulations.

[0118] The present invention also provides a paper coating compound comprising:

[0119] (i) Inorganic pigments, and

[0120] (ii) The above-mentioned aqueous polymer dispersion that can be obtained by the method of the present invention

[0121] (iii) and optionally additional adjuvants.

[0122] Besides water, paper coating formulations typically contain pigments, binders, and additives (such as thickeners) to establish the desired rheological properties. Pigments are typically dispersed in water. Paper coating formulations contain pigments in an amount preferably at least 80% by weight, for example, 80% to 95% by weight or 80% to 90% by weight, based on the total solids content.

[0123] White pigments are particularly suitable. Examples of suitable pigments are metal salt pigments, such as calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate, and calcium carbonate, among which carbonate pigments, and especially calcium carbonate, are preferred. Calcium carbonate can be ground calcium carbonate (GCC, naturally ground calcium carbonate), precipitated calcium carbonate (PCC), lime, or chalk. Suitable calcium carbonate pigments are, for example, Covercarb. ® 60. Hydrocarb ® 60 or Hydrocarb ®90 ME is available. Other suitable pigments are, for example, silicon oxides, aluminum oxides, aluminum hydroxides, silicates, titanium dioxide, zinc oxides, kaolin, alumina, talc, or silica. Other suitable pigments are, for example, Capim. ® MP 50 (Clay), Hydragloss ® It can be obtained with 90 (clay) or Talcum C10.

[0124] Paper coating formulations contain a polymer dispersion produced according to the present invention as the sole binder or in combination with other binders. The most important function of the binder in the paper coating formulation is to bind the pigment to the paper and to bind the pigments together, as well as to fill the cavities between the pigment particles to a certain extent.

[0125] 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 of the present invention (in solid terms, i.e., without water or other solvents that are liquid at 21°C and 1 bar) are used per 100 parts by weight of pigment.

[0126] Preferably, the paper coating compound contains 1 to 50 parts by weight of the polymer of the aqueous polymer dispersion according to the invention, based on the total amount of pigment. Furthermore, the paper coating compound preferably contains 80 to 95 parts by weight of pigment based on the total solids content, and at least one additive.

[0127] The pigments are selected from the following groups: calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate, calcium carbonate, silicon oxide, aluminum oxide, hydrated alumina, silicate, titanium dioxide, zinc oxide, kaolin, alumina, talc, and silicon dioxide.

[0128] Suitable additives are selected from the group consisting of: thickeners, additional polymer binders, co-binders, optical brighteners, fillers, flow control aids, dispersants, surfactants, lubricants, neutralizers, defoamers, degassing agents, preservatives, and dyes.

[0129] Other synthetic binders, unlike those produced by the polymers according to the present invention, are common knowledge 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 and thereafter, the disclosure of which is expressly incorporated by reference.

[0130] Other useful binders include binders with natural bases, particularly starch-based binders, and synthetic binders other than those produced according to the invention, especially emulsion polymers that can be produced by emulsion polymerization. In this context, "starch-based binder" should be understood to mean any natural, modified, or degraded starch. Natural starch can consist of amylose, amylopectin, or mixtures thereof. Modified starch can be oxidized starch, starch esters, or starch ethers. The molar mass of starch can be reduced by hydrolysis (degraded starch). Oligosaccharides or dextrins are possible degradation products. Preferred starches are cereal starches, corn starch, and potato starch. Cereal starches and corn starch are particularly preferred, with corn starch being very particularly preferred.

[0131] The paper coating formulations according to the invention may additionally contain other additives, such as fillers, co-binders, and thickeners for further optimizing viscosity and water retention, optical brighteners, dispersants, surfactants, lubricants (e.g., calcium stearate and waxes), neutralizers for pH adjustment (e.g., NaOH or ammonium hydroxide), defoamers, degassing agents, preservatives (e.g., biocides), flow control aids, dyes (especially soluble dyes), etc. Useful thickeners include not only synthetic polymers (e.g., cross-linked polyacrylates) but also, in particular, cellulose, preferably carboxymethyl cellulose. Optical brighteners are, for example, fluorescent or phosphorescent dyes, especially piracetam.

[0132] The paper coating compound is preferably an aqueous paper coating compound; it contains water, particularly directly through the formulation of the components (aqueous polymer dispersions, aqueous pigment pastes); the desired viscosity can be set by adding additional water. The conventional solids content of the paper coating compound is in the range of 30% to 80% by weight. The pH of the paper coating compound is preferably set to a value of 6 to 11, particularly 7 to 10.

[0133] The present invention also provides paper or board coated with the paper coating compound of the present invention, and a method for coating paper or board, wherein,

[0134] - To produce an aqueous polymer dispersion according to the present invention; and

[0135] - To produce a paper coating compound using the polymer dispersion, at least one pigment and optional additional additives; and to apply the paper coating compound to at least one surface of paper or board.

[0136] Preferably, the paper coating compound is applied to uncoated base paper or uncoated board. The amount applied is typically 1 to 50 g per square meter, preferably 5 to 30 g (in solids, i.e., without water or other solvents that are liquid at 21°C and 1 bar). Coating can be carried out by conventional application methods, such as by sizing press, film pressing, doctor blade coating, air brush, knife coating, curtain coating, or spraying. Depending on the pigment system, aqueous dispersions of water-soluble copolymers can be used in the paper coating compound for use as a base coat and / or for use as a top coat.

[0137] The paper coating formulations of this invention possess excellent properties. They exhibit good flow characteristics and high levels of adhesion in paper coating methods. The coated paper and board exhibit good surface strength, especially very high wet and dry fuzzing resistance. They are highly suitable for printing using conventional printing methods such as relief printing, gravure printing, offset printing, digital printing, inkjet printing, flexographic printing, newsprint printing, letterpress printing, sublimation printing, laser printing, electrostatic copying, or combinations of these methods. Furthermore, the coated paper and board exhibit lower thermal yellowing and lower UV yellowing.

[0138] Example

[0139] Unless the context otherwise indicates, percentages are always expressed as a weight percentage. The reported content refers to the content in aqueous solutions or dispersions. When water is used in this example, softened water is used.

[0140] Measurement methods

[0141] Determination of the viscosity of dispersions:

[0142] The viscosity of the dispersion was determined according to ASTM D2196 using a Brookfield viscometer with RV rotor 3 at 100 rpm and at a temperature of 23°C.

[0143] Solid content:

[0144] The solids content of the polymer dispersion was determined by distributing 0.5 to 1.5 g of the polymer dispersion in a metal plate cap with a diameter of 4 cm and then drying it in an air-circulating drying oven at 140°C for 30 minutes. The solids content of the polymer dispersion was given by the ratio of the mass of the sample after drying under the above conditions to the mass of the sample taken.

[0145] The following ingredients are used in the example:

[0146] Emulsifier A: Sodium lauryl sulfate in the form of a 15% solution by weight (from BASF's Disponil® SDS).

[0147] Emulsifier B: Sodium dodecyl diphenyl ether disulfonate in the form of a 45% solution by weight (Dowfax 2A1 from Dow).

[0148] Complexing agent: EDTA (Trilon® BX from BASF) in the form of a 2% solution by weight.

[0149] Seed latex: Polystyrene seeds with a particle size of approximately 30 nm in the form of a dispersion of 29.7% by weight (determined by analytical ultracentrifugation).

[0150] Initiator A: 7% sodium persulfate (NaPS) solution by weight

[0151] Initiator B: 10% by weight tert-butyl hydrogen peroxide solution

[0152] Reducing agent: 13% acetone bisulfite solution by weight

[0153] In all instances, unless otherwise stated, the feed is metered in at a uniform mass flow rate.

[0154] Production of emulsion polymers

[0155] The following quantities, expressed in pphm (parts per hundred parts of monomer), are based on 100 parts by weight of total monomer.

[0156] Example 1: According to the present invention

[0157] Initial loading:

[0158] 425.67 g water

[0159] 150.00 g of 7% itaconic acid aqueous solution (0.5 pphm) by weight

[0160] 41.72 g by weight of a dispersion of polystyrene latex with an average particle size of 30 nm (0.6 pphm), representing 29.7% by weight.

[0161] 4.67 g of 45% Dowfax 2A1 solution (0.10 pphm) by weight

[0162] 31.50 g of 2% EDTA solution (complexing agent) (0.03 pphm) by weight

[0163] 21.00 g butadiene (1 pphm)

[0164] 42.00 g styrene (2 pphm)

[0165] Add to:

[0166] 60.00 g of 7% sodium persulfate solution (initiator A) (0.2 pphm)

[0167] Feed 1 A:

[0168] 44.55 g acrylic acid (2.12 pphm)

[0169] 749.07 g styrene (35.68 pphm)

[0170] Feed 1 B:

[0171] 24.75 g acrylic acid (1.18 pphm)

[0172] 416.43 g styrene (19.82 pphm)

[0173] Feed 2:

[0174] 28.00 g of 45% Dowfax 2A1 solution (0.60 pphm) by weight

[0175] 42.00 g of 15% sodium lauryl sulfate solution (0.3 pphm) by weight

[0176] 690.48 ml water

[0177] Feed 3:

[0178] 350.7 g butadiene (16.7 pphm)

[0179] Feed 4:

[0180] 21.00 g styrene (1 pphm)

[0181] 25.2 g tert-dodecyl mercaptan (1.2 pphm)

[0182] Feed 5:

[0183] 420.00 g n-Butyl acrylate (20 pphm)

[0184] Feed 6:

[0185] 285.00 g of 7% sodium persulfate solution (initiator A) (0.95 pphm)

[0186] Feed 7:

[0187] 84.00 g of 10% tert-butyl hydrogen peroxide solution (initiator B) (0.4 pphm)

[0188] Feed 8:

[0189] 44.10 g of 10% tert-butyl hydrogen peroxide solution (initiator B) (0.21 pphm)

[0190] Feed 9:

[0191] 49.15 g of 13.1% acetone bisulfite solution (0.33 pphm) by weight

[0192] (Phase A)

[0193] The initial charge components were placed in a 6 L pressure reactor and mixed. The initial charge was heated to 95°C. When 90°C was reached, initiator A was slowly added (added) and polymerization began.

[0194] Immediately afterwards, feeds 1A, 2, 3, 4, and 6 were initiated. Feed 2 was initiated over 3 hours and 30 minutes. Feed 1A was initiated over 2 hours and 15 minutes. Feeds 3 and 4 were initiated over a period of 1 hour and 55 minutes. Feed 6 (initiator A) was initiated over 3 hours and 30 minutes. Feed 7 (initiator B) was initiated 30 minutes after feeds 1, 2, 3, 4, and 6 and was initiated over a period of 1 hour and 25 minutes.

[0195] (Phase B)

[0196] Feeds 1B and 5 are started 20 minutes after the metered addition of feed 3, or immediately after the completion of feed 1A, and carried out for 1 hour and 15 minutes. After the metered addition of feeds 1B, 5, and 6 (initiator A) is complete, the polymerization mixture is heated to 90°C and then 117 ml of water (5.6 pphm) is added. Feeds 8 and 9 are then started and carried out over an additional 1.5 hours. After the completion of feeds 8 and 9, the polymerization mixture is cooled to room temperature and 84 g of a 15% sodium hydroxide solution (0.6 pphm) by weight is added.

[0197] The solids content of the dispersion is 50% by weight.

[0198] Example 2 is not based on the present invention (similar to Example 2 of WO 2021 / 136703).

[0199] Initial loading:

[0200] 523.79 g water

[0201] 149.47 g of 7% itaconic acid aqueous solution (0.52 pphm) by weight

[0202] 39.40 g by weight of a dispersion of polystyrene latex with an average particle size of 30 nm (0.59 pphm), representing 29.7% by weight.

[0203] 6.26 g of 45% Dowfax 2A1 solution (0.142 pphm) by weight

[0204] 30.27 g of 2% EDTA solution (complexing agent) (0.03 pphm) by weight

[0205] 2.44 g terpinene (0.12 pphm)

[0206] 24.65 g butadiene (1.23 pphm)

[0207] 32.4 g styrene (1.62 pphm)

[0208] 0.58 g tert-dodecyl mercaptan (0.03 pphm)

[0209] 2.14 g acrylic acid (0.10 pphm)

[0210] Add to:

[0211] 28.57 g of 7% sodium persulfate solution (initiator A) (0.1 pphm)

[0212] Feed 1 A:

[0213] 34.07 g acrylic acid (1.70 pphm)

[0214] 105.90 g of 7% itaconic acid aqueous solution (0.37 pphm) by weight

[0215] 967.60 g styrene (48.37 pphm)

[0216] 17.41 g tert-dodecyl mercaptan (0.87 pphm)

[0217] Feed 1 B:

[0218] 9.77 g acrylic acid (0.49 pphm)

[0219] 31.78 g of 7% itaconic acid aqueous solution (0.11 pphm) by weight

[0220] Feed 2:

[0221] 38.13 g of 45% Dowfax 2A1 solution (0.86 pphm) by weight

[0222] 485.6 ml water

[0223] Feed 3:

[0224] 849.35 g butadiene (42.46 pphm)

[0225] Feed 4:

[0226] 60.00 g n-Butyl acrylate (3.00 pphm)

[0227] Feed 5:

[0228] 271.43 g of 7% sodium persulfate solution (initiator A) (0.95 pphm)

[0229] Feed 6:

[0230] 42.00 g of 10% tert-butyl hydrogen peroxide solution (initiator B) (0.21 pphm)

[0231] Feed 7:

[0232] 46.24 g of 13.1% acetone bisulfite solution (0.33 pphm) by weight

[0233] (Phase A)

[0234] The initial charge components are placed in a 6 L pressure reactor and mixed. The initial charge is heated to 90°C. When 85°C is reached, initiator A (added) is slowly added and polymerization begins.

[0235] Immediately afterwards, feeds 1A, 2, 3, and 5 were started. Feed 2 was carried out over 4 hours and 30 minutes. Feeds 1A and 3 were carried out over 3 hours and 30 minutes. Feed 5 (initiator A) was carried out over 4 hours and 45 minutes.

[0236] (Phase B)

[0237] After the metered addition of feeds 1A, 2, and 3 is completed, feeds 1B and 4 are immediately started and carried out for 1 hour. After the metered addition of feed 5 (initiator A) is completed, the polymerization mixture is stirred for another 30 minutes. Thereafter, the reactor temperature is adjusted from 90°C to 85°C and then 117 ml of water (5.6 pphm) is added. Feeds 6 and 7 are then started and carried out over another 1.5 hours. After feeds 6 and 7 are completed, the polymerization mixture is cooled to room temperature and 185.0 g of water (9.25 pphm) and 80 g of a 15% sodium hydroxide solution (0.6 pphm) by weight are added.

[0238] The solids content of the dispersion is 50% by weight.

[0239] Table 1: Monomer composition of the dispersion

[0240]

[0241] Production of paper coating compound:

[0242] The reported quantities are based on solids content in each case.

[0243] 100 parts by weight of precipitated calcium carbonate (Opacarb A40 from Specialty Minerals)

[0244] 9.5 parts by weight of the corresponding example of emulsion polymer

[0245] 0.25 parts by weight of rheological additive (Sterocoll FS from BASF SE)

[0246] Solid content = 64%-66%

[0247] Viscosity (Brookfield RVT, rotor 4, 100 rpm) = 500-1000 mPas at 20°C-25°C

[0248] pH = 8.8-9.2

[0249] Paper coating compound is prepared in a mixing device by sequentially feeding individual components into the mixing device.

[0250] Add the pigment (precipitated calcium carbonate) in a pre-dispersed form (slurry). Add the other components in the order listed above. Set the final solids content by adding water.

[0251] Paper coating:

[0252] The coating compound was applied to approximately 58 g / m² of wood-free pulp standard Magnostar base paper. The coating compound 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 radiant heaters. Application was performed by a doctor blade method. The coating weight was 10-12 g / m². 2 (solid).

[0253] Determination of thermal yellowing

[0254] Thermal yellowing was measured on coated paper. The paper coating mixture to be tested was applied to one side of the base paper using a laboratory coating machine and dried by an IR lamp. The applied coating weight was 10 g / m². 2The CIE whiteness of the coated side of the paper produced in this manner was determined. It was then stored in an air-circulating drying oven at 120°C for 8 hours. The R457 whiteness of the stored paper was then measured. Yellowing was given by the difference (Δ) between the two measurements. A value of 0 indicates no yellowing. The smaller the value, the lower the degree of yellowing.

[0255] Measurement of UV yellowing

[0256] UV yellowing was measured on coated paper. The paper coating mixture to be tested was applied to one side of the base paper using a laboratory coating machine and dried under an IR lamp. The applied coating weight was 10 g / m². 2 The CIE whiteness of the coated side of the paper produced in this manner was determined. It was then exposed to UV radiation at SUNTEST XLS+ (765 W / m² radiation) for 8 hours. The CIE whiteness of the stored paper was then measured. Yellowing was given by the difference (Δ) between the two measurements. A value of 0 indicates no yellowing. The smaller the value, the lower the degree of yellowing.

[0257] Dry fuzz resistance was measured using an IGT test printing press (IGT dry type):

[0258] The coated paperboard to be tested was cut into strips and printed using an IGT test printing press. The printing ink used was a specific test ink from Lorilleux that transmits different tensile forces. The test strips were guided through the printing press at a continuously increasing speed (maximum speed 200 cm / s). The results were evaluated by measuring the number of 10 fuzzing points appearing on the paper surface of the printed sample strip after printing began. The dry fuzzing resistance measurement mentioned refers to the speed (in cm / s) present during printing and the test ink used. A higher printing speed at the tenth fuzzing point (PA) indicates a better evaluation of the paper surface quality.

[0259] Table 2: Performance data of coated paper

[0260]

[0261] ni: Not in accordance with the present invention

[0262] These examples demonstrate that paper coated with paper coating blends containing polymers according to the invention exhibits lower yellowing and better dry linting resistance than those of the prior art.

Claims

1. A method for preparing an aqueous polymer dispersion via free radical-initiated aqueous emulsion polymerization according to a monomer feeding method, wherein the total monomer composition comprises monomer composition A and monomer composition B, and monomer composition B is metered in after the metering of monomer composition A is completed. Wherein the monomer composition A contains (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 olefinically unsaturated carboxylic acid, (d) 0 to 15 parts by weight of n-butyl acrylate, and (e) 0 to 5 parts by weight of acrylamide, In each case, based on 100 parts by weight of monomer composition A, And the monomer composition B contains (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 olefinically unsaturated carboxylic acid, (d) 25 to 64 parts by weight of n-butyl acrylate, and (e) 0 to 5 parts by weight of acrylamide, In each case, based on 100 parts by weight of monomer composition B, Furthermore, the ratio of monomer composition A to monomer composition B is 50:50 to 70:

30.

2. The method according to claim 1, wherein, The conjugated aliphatic diene is 1,3-butadiene and / or isoprene.

3. The method according to claim 1 or 2, wherein, The vinyl aromatic compound is styrene.

4. The method according to any one of claims 1 to 3, wherein, Neither monomer composition A nor monomer composition B contains acrylonitrile.

5. The method according to any one of claims 1 to 4, wherein, At least one inorganic peroxide and at least one organic peroxide are used as free radical initiators.

6. The method according to any one of claims 1 to 5, wherein, Use at least one peroxydisulfate and alkyl hydrogen peroxide.

7. The method according to any one of claims 1 to 6, wherein, Polymerization is carried out at temperatures ranging from ≥ 80°C to ≤ 115°C.

8. The method according to any one of claims 1 to 7, wherein, The monomer composition A is polymerized in the presence of one or more chain transfer agents selected from aliphatic and / or aryliphatic halogen compounds, organothio compounds, and substituted thiols.

9. An aqueous polymer dispersion, which can be obtained by free radical-initiated emulsion polymerization according to any 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 formulations.

11. The use of the aqueous polymer dispersion according to claim 9 or its redispersible powder in water as a binder in two-component cement-based or one-component cement-based sealant slurries.

12. A paper coating compound comprising (i) an inorganic pigment and (ii) an aqueous polymer dispersion according to claim 9, and optionally additional additives.

13. The paper coating compound according to the preceding claim, wherein, The polymer in the aqueous polymer dispersion is used in an amount of 1 to 50 parts by weight based on the total amount of pigments, wherein 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, silicon oxide, aluminum oxide, hydrated alumina, silicate, titanium dioxide, zinc oxide, kaolin, alumina, talc, and silicon dioxide.

14. A paper or paperboard coated with a paper coating compound according to any one of the preceding two claims.

15. A method for coating paper or paperboard, wherein, - Provides the aqueous polymer dispersion according to claim 9; and - To produce paper coating formulations using this aqueous polymer dispersion, at least one pigment, and optional additional additives; and - Apply the paper coating compound to at least one surface of paper or paperboard.

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