Polymer dispersions, their uses and methods for their manufacture

Abstract

The present invention relates to a water-soluble polymer dispersion and a method for preparing the same. The dispersion comprises a styrene acrylate polymer obtained by free radical polymerization of 1 to 90% by weight of monomer (a) containing at least one optionally substituted styrene, 10 to 99% by weight of monomer (b) containing at least one alkyl (meth)acrylate, and 0 to 9% by weight of monomer (c) containing at least one ethylenically unsaturated monomer different from monomer (b). The polymerization is carried out in a polymerization medium containing a cationic prepolymer obtained by free radical polymerization of 10 to 55% by weight of monomer (i) containing at least one ethylenically unsaturated quaternary amine and / or tertiary amine, 35 to 90% by weight of monomer (ii) containing at least one optionally substituted styrene, and 0 to 55% by weight of monomer (iii) containing at least one alkyl (meth)acrylate. The oligomer content in the polymer dispersion is 1.4% by weight or less, calculated from the dry polymer content.

Description

[Technical Field]

[0001] The present invention relates to a polymer dispersion, its use and a method for its preparation according to the preambles of the independent claims below. [Background technology]

[0002] Due to international supply chains and increasing online retail, the consumption of packaging materials is increasing. In particular, the consumption of paperboard for packaging purposes is increasing, and the properties of packaging board are becoming a matter of great interest. Among other things, the paperboard must protect the packaged goods from external impacts, i.e., have good strength properties, and at the same time protect the packaged goods from moisture and oil, i.e., have good barrier properties. Furthermore, the paperboard should also be suitable for food packaging, i.e., it must be hygienic and not contaminate the packaged food, e.g., by transferring chemical components from the paperboard.

[0003] In the production of paper or paperboard, the use of sizing reduces the water absorption of the paper or paperboard, making it more hydrophobic. Sizing can be performed as an internal sizing or a surface sizing. Traditionally, paperboard sizing has been performed as an internal sizing. However, in the production of paperboard, especially linerboard, there is an increasing trend toward using surface sizing due to various economic factors and wet-end processes. This means that there is a need for more efficient surface sizing agents that are also suitable for surface sizing paperboard and are safe for food contact applications. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE INVENTION It is an object of the present invention to minimize or even eliminate the disadvantages present in the prior art.

[0005] It is an object of the present invention to provide a polymer dispersion that imparts improved hydrophobizing properties when used as a surface sizing agent or as a component in a surface sizing composition.

[0006] Another object of the present invention is to provide a method for making a polymer dispersion that can be used to improve hydrophobing properties in the surface sizing of paper or paperboard.

[0007] It is yet another object of the present invention to provide a polymer dispersion that can be safely used for surface sizing of paperboard for food packaging. [Means for solving the problem]

[0008] These objects are achieved by a polymer dispersion and a method having the following characteristics, as presented in the characterizing parts of the independent claims. Some preferred embodiments of the invention are presented in the dependent claims.

[0009] The embodiments referred to herein relate to all aspects of the invention where applicable, even if not specifically mentioned. DETAILED DESCRIPTION OF THE INVENTION

[0010] Typical aqueous polymer dispersions of the present invention include: 1 to 90 wt. % of monomer (a) comprising at least one optionally substituted styrene; 10 to 99% by weight of a monomer (b) comprising at least one alkyl (meth)acrylate; 0 to 9% by weight of monomer (c) containing at least one ethylenically unsaturated monomer different from monomer (b); 1. A water-soluble polymer dispersion containing a styrene acrylate polymer obtained by free radical polymerization in a polymerization medium containing a cationic prepolymer, The cationic prepolymer comprises at least At least one ethylenically unsaturated quaternary Ammoniumand / or 10 to 55% by weight of a monomer (i) containing a tertiary amine; 35 to 90 wt. % of monomer (ii) comprising at least one optionally substituted styrene; with 0 to 55 wt. % of monomer (iii) comprising at least one alkyl (meth)acrylate; obtained by free radical polymerization, The oligomer content in the polymer dispersion is 1.4% by weight or less, calculated from the dry polymer content. (≦) is.

[0011] Typically, the aqueous polymer dispersions of the present invention are used for surface sizing of paper, paperboard and the like.

[0012] A typical process for preparing the aqueous polymer dispersion of the present invention comprises at least two polymerization stages: In the first polymerization step, at least At least one ethylenically unsaturated quaternary Ammonium and / or 10 to 55% by weight of a monomer (i) containing a tertiary amine; 35 to 90 wt. % of monomer (ii) comprising at least one optionally substituted styrene; 0 to 55 wt. % of monomer (iii) comprising at least one alkyl (meth)acrylate; wherein the free radical polymerization is carried out to obtain a polymerization medium comprising a cationic prepolymer formed from the monomer (i), the monomer (ii), and optionally the monomer (iii), In the second polymerization step, 1 to 90 wt. % of monomer (a) comprising at least one optionally substituted styrene; 10 to 99% by weight of a monomer (b) comprising at least one alkyl (meth)acrylate; 0 to 9 wt. % of monomer (c) comprising at least one ethylenically unsaturated monomer different from monomer (b); is carried out in said polymerization medium to obtain a styrene acrylate polymer, Preferably, the oligomer content in the polymer dispersion is 1.4% by weight or less, calculated from the dry polymer content. (≦) is.

[0013] It contains a styrene acrylate polymer obtained by polymerization in a polymerization medium containing a cationic prepolymer, and the oligomer content is 1.4% by weight or less calculated from the dry polymer content. (≦) It has been surprisingly found that polymer dispersions, such as those described above, exhibit unexpectedly good results in the surface sizing of paperboard, particularly linerboard. The low concentration of oligomers in the polymer dispersion is particularly advantageous for polymer dispersions used in the surface sizing of paper, paperboard, and the like, and is especially advantageous for use in the surface sizing of paperboard for food packaging. It has been unexpectedly realized that the low concentration of oligomers not only results in a polymer dispersion that is safe for food packaging applications, but can also further improve the sizing results, such as strength and barrier properties. Traditionally, a goal of many polymerization methods has been to minimize the amount of free monomer at the end of the process. This goal has been achieved by subjecting the reaction mixture to various post-polymerization steps. However, these traditional steps can lead to the formation of large or relatively large amounts of various oligomers, such as dimers, trimers, tetramers, or pentamers. It has now been surprisingly realized that by carefully controlling and selecting the polymerization conditions in the first polymerization stage, which involves the free radical polymerization of monomers (i), (ii), and optionally (iii) to obtain a prepolymer, low amounts of oligomers can be achieved, while at the same time the amount of free monomer can be maintained at low or substantially non-existent levels.

[0014] According to one preferred embodiment, the oligomer content in the polymer dispersion may be in the range of 0 to 1.4 wt.%, preferably 0.001 to 1.2 wt.%, more preferably 0.001 to 0.7 wt.%, and even more preferably 0.001 to 0.4 wt.%, calculated from the dry polymer content of the dispersion. The oligomer content in the polymer dispersion may be in the range of 0 to 1.0 wt.%, preferably 0.001 to 0.9 wt.% or 0.001 to 0.5 wt.%, calculated from the dry polymer content of the dispersion.

[0015] As used herein, the term "oligomer" refers to a polymer having a molecular weight of 1000 g / mol or less. (≦) The term "oligomer" includes low molecular weight structures such as those described above. Thus, the term "oligomer" not only includes the monomers but also at least the dimers, trimers, tetramers, and pentamers formed from the monomers used. In particular, the term "oligomer" includes structures formed from at least two monomers, such as dimers, trimers, tetramers, and pentamers, having a molecular weight of 100 to 1,000 g / mol, preferably 150 to 1,000 g / mol, and more preferably 200 to 1,000 g / mol.

[0016] According to one embodiment, the polymer dispersion has a molecular weight of 1,000 g / mol or less. (≦)The polymer dispersion may contain oligomers of the formula (I) in an amount of less than 1.4 wt.%, preferably less than 1.2 wt.%, or less than 1.0 wt.%, more preferably less than 0.7 wt.%, or less than 0.4 wt.%, calculated from the dry polymer content. In particular, the polymer dispersion may contain oligomers of molecular weight less than (<) 500 g / mol in an amount of less than 0.5 wt.%, preferably less than 0.4 wt.%, or less than 0.3 wt.%, more preferably less than 0.2 wt.%, calculated from the dry polymer content. The low oligomer content results in unexpected improvements in surface sizing properties. Without wishing to be bound by theory, it is believed that the relative absence of oligomers reduces polymer migration into the paperboard structure. Thus, the polymer dispersion of the present invention can provide better coverage of the paper or paperboard surface, which may be related to improved sizing results and / or barrier properties. At the same time, the risk of oligomer migration into the packaging article is reduced.

[0017] According to one embodiment of the present invention, the weight average molecular weight (MW) of the resulting polymer dispersion, as analyzed from the final dispersion, may be in the range of 20,000 to 300,000 g / mol, preferably 25,000 to 200,000 g / mol, more preferably 30,000 to 100,000 g / mol, and sometimes 40,000 to 70,000 g / mol. The MW can be measured, for example, by size exclusion chromatography.

[0018] According to one embodiment of the present invention, the number average molecular weight (Mn) of the polymer dispersion is 10,000 g / mol or more (Mn) as analyzed from the final dispersion. >The number average molecular weight (Mn) of the polymer dispersion, as determined from the final dispersion, may be, for example, in the range of 10,000 to 100,000 g / mol, preferably in the range of 11,000 to 50,000 g / mol, more preferably in the range of 12,000 to 40,000 g / mol, and even more preferably in the range of 13,000 to 30,000 g / mol.

[0019] According to one embodiment of the present invention, the molecular weight dispersity (D M ) is 4.5 or less (≦) may be, preferably 4 or less (≦) and more preferably 3.8 or less. (≦) According to one embodiment, the dispersity may be in the range of 1.0 to 4.5, preferably in the range of 1.5 to 4, and more preferably in the range of 1.5 to 3.8. In this specification, the molecular weight dispersity (D M ) is calculated by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn), i.e., the formula: D M When the polymer dispersion is used as a surface sizing agent or as a component in a surface sizing agent, if the molecular weight distribution is narrow, i.e., the molecular weight distribution (D M It has been found that a smaller value of ) results in a more advantageous effect on the hydrophobicity properties.

[0020] According to one embodiment, the polymer dispersion may have a particle size D50 of less than 70 nm, preferably less than 60 nm, and more preferably less than 40 nm, and / or a particle size D90 of less than 120 nm, preferably less than 90 nm, more preferably less than 70 nm, and even more preferably less than 50 nm. The D50 and D90 particle size values ​​represent the 50th and 90th percentiles of the volumetric particle size distribution, respectively. A relatively small particle size and narrow particle size distribution result in a polymer dispersion with good viscosity and a good size distribution on the surface, thereby improving the performance of the polymer dispersion in surface sizing applications. For example, the hydrophobicity and printing properties associated with surface sizing may be improved. Particle size can be measured, for example, by laser correlation spectroscopy or turbidity measurement.

[0021] The solid content of the polymer dispersion of the present invention may be 10 to 50% by weight, preferably 20 to 45% by weight, and more preferably 26 to 38% by weight.

[0022] The polymerization process for the polymer dispersion of the present invention is a two-stage process: in the first polymerization stage, a prepolymer is obtained by free radical polymerization of monomer (i), monomer (ii), and optional monomer (iii) in a polymerization solvent, and in the second polymerization stage, a styrene acrylate polymer is obtained by free radical polymerization of monomer (a), monomer (b), and optional monomer (c) in a polymerization medium containing the cationic prepolymer.

[0023] As used herein, the term "polymerization medium" includes the prepolymer obtained in the polymerization solvent, the polymerization solvent itself, any water, and any other additives that may be used. The polymerization medium does not include any monomers that are added and polymerized in the second polymerization stage of the process to form the styrene acrylate polymer.

[0024] The cationic monomer (i) is at least one ethylenically unsaturated quaternary Ammonium or at least one ethylenically unsaturated tertiary amine, or any mixture thereof. Monomer (i) may be, for example, a quaternary salt selected from the group consisting of N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylamide, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylamide, and any mixture thereof. AmmoniumThe cationic monomer (i) may be selected from 2-(dimethylamino)ethyl acrylate benzyl chloride, 2-(dimethylamino)ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate dimethyl sulfate, and diallyldimethylammonium chloride. Preferably, the monomer (i) may be selected from quaternary salts of N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylate, and any mixture thereof. More preferably, the monomer (i) may be selected from quaternary salts of N,N,N-trimethylamino C1-4 alkyl acrylate or N,N,N-trimethylamino C1-4 alkyl methacrylate with a mineral acid, for example, the quaternary salt of N,N,N-trimethylaminoethyl (meth)acrylate with HCl. Even more preferably, the monomer (i) is a quaternary ammonium chloride selected from [2-(methacryloyloxy)ethyl]trimethylammonium chloride and [2-(acryloyloxy)ethyl]trimethylammonium chloride. AmmoniumAlternatively or in addition, monomer (i) may comprise a tertiary amine selected from the group consisting of, for example, N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylamide, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylamide, and any mixture thereof, and preferably comprises a tertiary amine selected from the group consisting of N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylate, and any mixture thereof. Preferably, the monomer (i) may be a tertiary amine selected from N,N-dimethylamino C1-4 alkyl acrylate and N,N-dimethylamino C1-4 alkyl methacrylate, for example, N,N-dimethylaminoethyl (meth)acrylate. More preferably, the monomer (i) may contain a tertiary amine selected from dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl methacrylate, dimethylaminopropyl acrylamide, and dimethylaminopropyl methacrylamide. Preferably, the monomer (i) contains at least one ethylenically unsaturated quaternary amine. Ammonium and / or a mixture of at least one ethylenically unsaturated tertiary amine. Even more preferably, monomer (i) may be a mixture of N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylate and N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylamide, for example, a mixture of 2-(dimethylamino)ethyl methacrylate and N-[3-(dimethylamino)propyl]methacrylamide.

[0025] Monomer (ii) may comprise at least one optionally substituted styrene, which may be selected from α-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any mixture thereof.

[0026] Monomer (iii) may be selected from C1-4 alkyl (meth)acrylates and any combination thereof. Suitable C1-4 alkyl (meth)acrylates are C1-4 alkyl acrylates, C1-4 alkyl methacrylates, or mixtures thereof, such as n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, or 2-butyl acrylate, and the corresponding butyl methacrylates; methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, or propyl methacrylate. Other suitable ethylenically unsaturated monomers (iii) may be selected from the group including ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic acid or methacrylic acid with alcohols having more than 4 carbon atoms, acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate, and anionic comonomers (e.g., acrylic acid, methacrylic acid, styrene sulfonic acid). C1-4 alkyl (meth)acrylates are preferred.

[0027] The cationic prepolymer can be obtained by free radical polymerization of at least monomer (i), monomer (ii), and monomer (iii). Preferably, the first stage polymerization does not use an anionic monomer, which means that the cationic prepolymer does not contain structural units derived from an anionic monomer.

[0028] The cationic prepolymer can be obtained by free radical polymerization of at least 10 to 55% by weight of monomer (i), 35 to 90% by weight of monomer (ii), and 0 to 55% by weight of monomer (iii). According to one embodiment of the present invention, the cationic prepolymer can be obtained by polymerization of 15 to 55% by weight, preferably 15 to 49% by weight, more preferably 18 to 39% by weight of monomer (i), 51 to 85% by weight, preferably 61 to 82% by weight of monomer (ii), and 0 to 22% by weight, preferably 0 to 5% by weight of monomer (iii).

[0029] In the first polymerization stage, the polymerization solvent may contain, for example, at least one C1-C6 carboxylic acid, C1-C6 carboxylic anhydride, or any mixture thereof. The polymerization solvent may contain a saturated C1-C6 monocarboxylic acid and / or a saturated C1-C6 dicarboxylic acid, with a saturated C1-C6 monocarboxylic acid being preferred. The saturated C1-C6 carboxylic acid may optionally have one or more substituents, such as a hydroxyl group. The polymerization solvent may contain or be selected from formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, hydroxypropionic acid, hydroxybutyric acid, or any mixture thereof. Preferably, the polymerization solvent contains formic acid, acetic acid, propionic acid, hydroxypropionic acid, or any mixture thereof. Even more preferably, the polymerization solvent contains acetic acid. Alternatively, or in addition, the polymerization solvent may contain at least one C1-C6 carboxylic acid anhydride, which may be selected from formic anhydride, acetic anhydride, propionic anhydride, butyric anhydride, or any mixture thereof. The anhydride may also contain one or more substituents, such as hydroxyl groups. Preferably, the polymerization solvent contains a C1-C6 carboxylic acid anhydride, which is acetic anhydride. The polymerization solvent may be added to the polymerization reactor before adding the monomers and initiator for prepolymer polymerization. Alternatively, a portion of the polymerization solvent may be fed to the polymerization reactor together with the initiator.

[0030] According to one preferred embodiment, the polymerization solvent in the first polymerization stage does not interfere with the polymerization of the prepolymer. In particular, the polymerization solvent does not impart any chain transfer effect, such as reducing the polymer chain length and increasing the amount of oligomers formed during polymerization. The first polymerization stage is preferably carried out without the use of alcohol. In particular, the first polymerization stage is preferably carried out without the presence of isopropanol, which is known as a chain transfer agent in the polymerization of acrylate monomers.

[0031] According to one embodiment, the polymerization solvent in the first polymerization stage also contains water. The water in the polymerization solvent typically originates from the monomers, C1-C6 carboxylic acid, and / or initiator used. The water content in the polymerization solvent may be 0 to 25 wt %, preferably 0 to 15 wt %, calculated based on the total solvent weight. When water is present in the polymerization solvent, the polymerization solvent preferably contains at least one anhydride as described above to provide the corresponding acid. The content of the C1-C6 carboxylic anhydride in the polymerization solvent may preferably be greater than or at least equal to the amount of water, in molar terms. For example, the molar ratio of the C1-C6 carboxylic anhydride to water in the polymerization solvent may be 0.9:1.1 to 1.1 to 0.9, preferably 1:1.

[0032] The free radical polymerization of the cationic prepolymer in the first polymerization stage is carried out and initiated by the presence of a first free radical initiator. Suitable first free radical initiators may be peroxides such as hydrogen peroxide, alkyl hydroperoxides, or dialkyl peroxides. The first free radical initiator may be selected from hydrogen peroxide, sodium peroxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate, dibenzoyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl 2-ethylhexaneperoxyate, cumyl hydroperoxide, or biscyclohexyl peroxydicarbonate. According to one preferred embodiment, the first free radical initiator is a dialkyl peroxide or alkyl hydroperoxide. Preferably, the first free radical initiator is an alkyl hydroperoxide or dialkyl peroxide, more preferably tert-butyl hydroperoxide. The use of a peroxide as the first free radical initiator is believed to further reduce the oligomers formed during the first polymerization stage.

[0033] Peroxide initiators are typically used as part of a redox initiator system that also includes a reducing agent. Suitable combinations of peroxide-containing redox initiator systems include, for example, ascorbic acid and a heavy metal cation, such as iron, manganese, or cerium ions. According to one preferred embodiment, the redox initiator system includes tert-butyl hydroperoxide and an iron salt. Initiation occurs when the metal salt of the redox initiator system, e.g., an iron(II) salt, is added to the polymerization solvent prior to the start of the first polymerization stage. Here, the peroxide is added simultaneously but separately from the addition of the monomers. Iron(II) salts are typically used at iron(II) ion concentrations of 5 to 300 mg / L of the total dispersion, although higher or lower concentrations are possible. The first polymerization stage can also be initiated by a peroxide-containing free radical initiator without a reducing agent.

[0034] According to one embodiment, the free radical polymerization of the cationic prepolymer in the first polymerization stage can be initiated by the presence of at least two first free radical initiators. The main first free radical initiator can be selected from the peroxide initiators described above, and the auxiliary first free radical initiator can be selected from azo initiators such as 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), or dimethyl 2,2'-azobis(2-methylpropionate). The amount of the main first free radical initiator is at least 50 wt.%, at least 60 wt.%, or even at least 75 wt.%, based on the total amount of initiators. Preferably, the first polymerization stage does not include an azo initiator such as 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2-methylbutyronitrile), or dimethyl 2,2'-azobis(2-methylpropionate).

[0035] The first polymerization stage can be carried out either as a feed process or as a batch process. The polymerization temperature in the first polymerization stage may be in the range of 80 to 150°C or 80 to 140°C, preferably 107 to 140°C, more preferably 110 to 140°C, and even more preferably 115 to 130°C. It is preferable that the polymerization temperature in the first polymerization stage is not too high, since an uncontrolled polymerization reaction can easily result in increased oligomer formation.

[0036] The first polymerization stage is preferably carried out under standard atmospheric pressure, which is about 101 kPa or slightly higher, for example, in the range of 101 to 200 kPa or in the range of 101 to 150 kPa. Conducting the first polymerization stage under no pressure is believed to prevent significant formation of oligomers during the first polymerization stage, thereby further reducing the oligomer content in the final polymer dispersion.

[0037] The first polymerization stage to produce the aqueous prepolymer composition may be carried out in the presence of one or more polymerization regulators, such as a chain transfer agent. The one or more polymerization regulators, such as a chain transfer agent, may be introduced into the reaction simultaneously with the monomers but separately. The polymerization regulator may also be introduced into the reaction as a mixture with the monomers. Suitable polymerization regulators may be, for example, sulfur compounds such as mercaptans, disulfides, polysulfides, esters and sulfides of thiocarboxylic acids, esters and sulfides of dithiocarboxylic acids, and enol sulfides. Examples of suitable mercaptans include ethyl mercaptan, n-butyl mercaptan, tert-butyl mercaptan, n-octadecyl mercaptan, n-dodecyl mercaptan, and tert-dodecyl mercaptan. Examples of other polymerization regulators based on sulfur-containing organic compounds include mercaptoethanol, mercaptopropanol, mercaptobutanol, thioglycolic acid, thioacetic acid, thiopropionic acid, 1-dodecanethiol, thioethanolamine, sodium dimethyldithiocarbamate, cysteine, ethyl thioglycolate, trimethylolpropane trithioglycolate, pentaerythrityl tetra(mercaptopropionate), pentaerythrityl tetrathioglycolate, trimethylolpropane tri(mercaptoacetate), butylmethylenebis(thioglycolate), thioglycerol, glyceryl monothioglycolate, thiophenol, mercaptotrimethoxysilane, and acetylcysteine.Halogen compounds, aldehydes, ketones, formic acid, enol ethers, enamines, hydroxylamines, halogenated hydrocarbons, alcohols, ethylbenzene, and xylene can also be used as polymerization regulators, as can terpenes (e.g., monocyclic terpenes such as terpinene). When a polymerization regulator is used, the amount of the polymerization regulator may be 0.01 to 5% by weight, preferably 0.01 to 1.0% by weight, more preferably 0.1 to 0.7% by weight, calculated from the weight of the monomers. In some cases, the polymerization medium may contain 0 to 1% by weight, preferably 0.05 to 1% by weight, of the polymerization regulator.Preferably, the amount of polymerization regulator, such as a chain transfer agent, in the polymerization medium is relatively low, or preferably no polymerization regulator is used at all. In fact, the use of a polymerization regulator can reduce the chain length of the prepolymer and, especially if used in large amounts, increase the oligomer content. According to one preferred embodiment, the first polymerization stage is carried out without the addition and / or use of any polymerization regulator, such as a chain transfer agent.

[0038] The first polymerization stage is typically completed by the addition of water to obtain the formed prepolymer as an aqueous prepolymer composition, either in the form of a dispersion or an aqueous solution. The concentration of the prepolymer prepared in the first polymerization stage in the aqueous prepolymer composition, after completion of the polymerization by the addition of water, may be 10 to 40% by weight or 5 to 30% by weight, preferably 13 to 24% by weight or 8 to 19% by weight. The aqueous prepolymer composition is then used as the polymerization medium in the second polymerization stage.

[0039] The weight average molecular weight (MW) of the cationic prepolymer prepared in the first polymerization stage may range from 5,000 to 200,000 g / mol, preferably from 10,000 to 100,000 g / mol. Molecular weight can be measured, for example, by size exclusion chromatography.

[0040] In the second polymerization stage, a polymer dispersion containing a styrene acrylate polymer is obtained by free radical polymerization of monomer (a), monomer (b), and optional monomer (c). Monomer (a), monomer (b), and optional monomer (c) may be added individually or as a mixture to the polymerization medium containing the cationic prepolymer. A suitable free radical initiator for initiating polymerization is added to the polymerization medium containing the cationic prepolymer.

[0041] Suitable monomers (a) may be styrene or substituted styrenes such as α-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene or any mixture thereof.

[0042] According to one preferred embodiment of the present invention, the monomer (b) in the second polymerization step may be selected from C1-C4 alkyl (meth)acrylates and any combination thereof. Suitable C1-C4 alkyl (meth)acrylates include C1-C4 alkyl acrylates, C1-C4 alkyl methacrylates, or mixtures thereof, such as n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, or 2-butyl (meth)acrylate; methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, or propyl methacrylate. The monomer (b) may also be a mixture of at least two butyl acrylate isomers. For example, the monomer (b) may be a mixture of n-butyl acrylate and methyl methacrylate, or a mixture of n-butyl acrylate and tert-butyl acrylate. The mixing ratio of the two monomers (b) may be 10:90 to 90:10.

[0043] The monomer (c) in the second polymerization stage comprises at least one ethylenically unsaturated monomer different from the monomers (a) and (b). Other suitable ethylenically unsaturated monomers (c) are ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic acid or methacrylic acid with alcohols having more than 4 carbon atoms, and also acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate, or anionic comonomers (e.g., acrylic acid, methacrylic acid, styrene sulfonic acid). Ethylhexyl acrylate and acrylonitrile are preferred as the monomer (c).

[0044] The styrene acrylate polymer is obtained by free radical polymerization of at least 1-90% by weight of monomer (a), 10-99% by weight of monomer (b), and 0-9% by weight of monomer (c) different from monomer (b), where the sum of monomers (a) + (b) + (c) is 100% by weight. According to one embodiment of the present invention, the polymer is obtained by free radical polymerization of 10-80% by weight, preferably 15-75% by weight, of monomer (a), 20-90% by weight, preferably 25-85% by weight, of monomer (b), and 0-7% by weight, preferably 0-5% by weight, of monomer (c), where the sum of monomers (a) + (b) + (c) is 100% by weight.

[0045] The monomers may be preferably selected so that the glass transition temperature of the polymer dispersion is in the range of +5°C to +85°C, preferably in the range of +30°C to +70°C, more preferably in the range of +42°C to +68°C.

[0046] In the second polymerization stage, a water-soluble redox system containing an oxidizing agent and a reducing agent can be used to initiate the polymerization of the styrene acrylate polymer. The oxidizing agent of the redox system can be selected from peroxides, such as hydrogen peroxide, sodium peroxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate, dibenzoyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl 2-ethylhexaneperoxyate, cumyl hydroperoxide, or biscyclohexyl peroxydicarbonate. The reducing agent of the redox system can be selected from sodium sulfite, sodium metabisulfite, sodium bisulfite, sodium dithionite, sodium hydroxymethanesulfinate, or ascorbic acid, or metal salts such as cerium salts, manganese salts, or iron(II) salts. According to one preferred embodiment, the second polymerization stage is typically carried out using a redox initiation system containing hydrogen peroxide and a metal salt. Metal salts, such as iron(II) salts, may be added to the polymerization medium prior to initiation of polymerization, with hydrogen peroxide being added simultaneously with but separately from the monomers. The iron(II) salts may be used at a concentration of 5 to 300 mg / L of iron(II) ions, based on the total dispersion weight, although higher or lower concentrations may also be used. Hydrogen peroxide (calculated as 100%) may be added at a concentration of 0.2 to 2.0 wt. % based on the weight of the monomers. Polymerization with a redox system containing hydrogen peroxide and a metal salt results in fine particle-sized dispersions with good sizing properties.

[0047] The second polymerization stage can be carried out either as a feed process or as a batch process. The polymerization temperature in the second polymerization stage can be in the range of 40 to 105°C, preferably in the range of 50 to 100°C.

[0048] A polymerization regulator may be used in the second polymerization stage. The polymerization regulator may be selected from the same group of compounds as in the first polymerization stage described above. The amount of polymerization regulator in the second polymerization stage may be the same as that in the first polymerization stage. According to one embodiment, the second polymerization stage does not contain a polymerization regulator, i.e., no polymerization regulator is added or used.

[0049] According to one embodiment, the polymerization of styrene acrylate polymer in the second polymerization stage is completed by adding a second initiator. The completion of the second polymerization stage can be ensured by adding, for example, a second initiator. Suitable free radical initiators used as the second initiator include, for example, organic peroxides such as dibenzoyl peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, cumyl hydroperoxide, dilauroyl peroxide, 1,1,3,3-tetramethylbutyl 2-ethylhexane peroxyate, or biscyclohexyl peroxydicarbonate. According to one preferred embodiment, the second free radical initiator is a dialkyl peroxide or alkyl hydroperoxide, more preferably tert-butyl hydroperoxide or di-tert-butyl hydroperoxide. The second free radical initiator is preferably added after the addition of monomer (a), monomer (b), and optional monomer (c) and after the polymerization with the aqueous redox system in the second polymerization stage to subsequently activate any residual monomers present and complete the polymerization. In this case, the second polymerization stage is first carried out, for example, with the redox initiator system described above (e.g., containing hydrogen peroxide and iron(II) sulfate). The second free radical initiator, e.g., organic peroxide, is then added for subsequent activation. The initiator may be added directly after the monomer feed or after the mixing period. Polymer conversions greater than 99% (>), preferably greater than 99.5% (>), and even more preferably greater than 99.9% (>), and residual monomer contents of the dispersion less than 1000 ppm (<) can be achieved, eliminating the need for monomer removal. Preferably, the residual monomer content of the dispersion is less than (<) 500 ppm, preferably less than (<) 300 ppm, and even more preferably less than (<) 100 ppm. The residual monomer content includes all monomers in the final polymer dispersion, i.e., both monomers from the first polymerization stage and monomers from the second polymerization stage. The residual monomer content can be analyzed by chromatographic methods such as HPLC.

[0050] The first and second polymerization stages are usually carried out in the absence of oxygen, preferably under an inert gas atmosphere, for example under a nitrogen atmosphere. During both polymerization stages, thorough mixing is preferably ensured by the use of any suitable stirrer.

[0051] In the first and / or second polymerization stages, an emulsifier is used only if necessary. Examples of emulsifiers that can be used include sodium alkanesulfonates, sodium alkyl sulfates, sulfosuccinates, and quaternary alkylammonium salts. It is preferred not to use any emulsifier in the first and / or second polymerization stages.

[0052] The resulting polymer dispersion preferably has a solids content in the range of 10 to 50% by weight, preferably 25 to 40% by weight or 26 to 38% by weight. The viscosity of the polymer dispersion is 50 mPas or less at 25°C, measured using a Brookfield LVDV viscometer, spindle 18. (≦) The viscosity may be less than 200 mPas (<), preferably in the range of 0.1 to 100 mPas, more preferably in the range of 1 to 50 mPas, when measured at 60 rpm in the case of a viscosity above 50 mPas (>), or at 30 rpm in the case of a viscosity above 50 mPas (>) to 200 mPas. The pH value of the polymer dispersion may be in the range of 2 to 5, preferably in the range of 2.5 to 4.5.

[0053] The amount of cationic prepolymer may typically be in the range of 20 to 60% by weight, preferably 30 to 50% by weight, calculated from the dry solid content of the total amount of the polymer dispersion.

[0054] The polymer dispersions of the present invention are particularly suitable for use as sizing agents or as components of surface sizing compositions. The surface sizing compositions may further contain other additives conventionally used in the surface sizing of paper, paperboard, and other cellulosic products. Such additives, known in the art, include, but are not limited to, dispersants, antifoaming agents, colorants, inorganic pigments and fillers, anti-curl agents, antistatic agents, and additional conventional components such as surfactants, plasticizers, humectants, defoamers, UV absorbers, lightfastness promoters, polymeric dispersants, dye mordants, fluorescent dyes, leveling agents, rheology modifiers, and force enhancers. Additives may be used to further enhance sizing properties, improve runnability through the size press, or to adjust the surface properties of the final paper, paperboard, etc.

[0055] The surface sizing composition may further contain starch and / or a starch derivative, such as dextrin. The starch may be modified, for example, into starch hydrolysates, starch oxides, or cationized starch. Typically, the aqueous polymer dispersion of the present invention is mixed with a solution of starch and / or starch derivative and applied to the surface of paper or paperboard. The concentration of starch and / or starch derivative in the sizing composition may range from 1 to 30% by weight, preferably from 5 to 25% by weight, and more preferably from 8 to 20% by weight, and the concentration of the polymer dispersion (as dry matter) may be from 0.1 to 20% by weight, preferably from 0.5 to 5.0% by weight, based on the dry weight of starch.

[0056] The temperature of the surface sizing composition during sizing may be in the range of 50 to 85°C.

[0057] The surface sizing composition containing the polymer dispersion of the present invention is suitable for surface sizing cellulosic products, particularly all paper and paperboard qualities, whether unsized or presized with, for example, alkyl ketene dimer, alkenyl succinic anhydride, or rosin. Specific techniques used to size paper and other cellulosic products, such as paperboard, include, but are not limited to, techniques commonly employed in papermaking for applying a sizing composition to a cellulosic product. The surface sizing composition can be applied to the cellulosic product as a liquid or foam. For example, an aqueous sizing composition can be applied to the paper surface using a paddle or a film size press or a size press using a roll or doctor knife blade. Alternatively, the sizing composition can be sprayed onto a paper web, or the paper can be immersed in the aqueous surface sizing composition. The paper or other cellulosic product treated with the surface sizing solution is then dried at elevated temperatures, typically at paper temperatures of 80 to 110°C.

[0058] Surface sizing compositions containing the polymer dispersions of the present invention are particularly suitable for surface sizing cellulosic products when the cellulosic products contain recycled fibers.

[0059] Example The following methods were used in the examples to characterize the polymer dispersions.

[0060] particle size Particle size measurements were performed using a Malvern Zetasizer Nano-device.

[0061] solids content The solids content was determined using a Mettler Toledo Halogen Moisture Analyzer.

[0062] viscosity Viscosity was measured with a Brookfield LVDV small sample adapter using spindle 18 at 60 rpm and 25°C.

[0063] Number average molecular weight (Mn), weight average molecular weight (Mw), dispersity (D M ) and oligomer content Molecular weights were determined by size exclusion chromatography (SEC) using an Agilent 1100 HPLC system integrated with an autosampler, degasser, column oven, and refractive index detector. The eluent was N,N-dimethylformamide (DMF) containing 5 g / L lithium chloride. The flow rate was 0.6 ml / min at 45 °C (column oven and RI detector). The column set consisted of three GRAM columns (1000 Å + two 30 Å columns) from Polymer Standard Service. Samples were lyophilized before analysis. The injection volume was 50 μl at a sample concentration of 4 mg / ml. Conventional column calibration was performed using narrow molecular weight distribution polystyrene standards (Polymer Standard Service) over the molecular weight (MW) range of 266 to 1,210,000 g / mol. Calibration curves were generated using Agilent's GPC Addon software.

[0064] The oligomer content was defined as the percentage of the signal intensity area below (<) 1000 g / mol compared to the total signal area of ​​the polymer.

[0065] test The sizing properties of the surface size dispersions were tested on internally unsized linerboard. The surface size was added to a 12% solution of surface-sized starch (C*film07312). The temperature of the surface size mixture was set at 65°C. The sheets were passed through a Mathis horizontal pound size press, model 5607, at 2 m / min (2 bar). The size press nip temperature was set at 65°C. The sheets were dried at 95°C for 1 minute per side using a PTI laboratory sheet dryer or at 95°C for a drying time of 1.5 minutes using an AMC drum dryer (speed 50). Sizing efficiency was determined by measuring the degree of sizing to Cobb 60 according to standard ISO 535.

[0066] Example Polymerization Example 1 73.2 g of glacial acetic acid was weighed into a 1 L glass reactor equipped with a cooling / heating jacket. The reactor was heated to 118°C. A nitrogen atmosphere was maintained within the reactor, and stirring was continued throughout the reaction. After the reactor reached temperature, chemical feeds into the reactor were started. A monomer feed of 76.2 g of styrene, 4.1 g of 3-dimethylaminopropyl methacrylamide, 20.5 g of 2-(dimethylamino)ethyl methacrylate, and 0.50 g of dodecyl mercaptan was fed over 90 minutes. A second feed of 11.9 g of glacial acetic acid and 3.96 g of tert-butyl hydroperoxide (70%) was fed simultaneously during the monomer feed and continued for 3 minutes after the monomer feed was completed.

[0067] The temperature in the reactor was maintained at 118°C during the feeds and for 90 minutes after the feeds were completed, after which cooling to 76°C was initiated. 437 g of heated demineralized water was then added to the reactor, and a 94.1 g sample of prepolymer was withdrawn. After the temperature stabilized at 76°C, 7.30 g of a 2.9% strength aqueous solution of ammonium iron(II) sulfate hexahydrate was added to the reactor. After 15 minutes, an initiator feed of 41.9 g of a 3.2% solution of hydrogen peroxide was started. After 5 minutes, a monomer mix of 6.3 g of n-butyl acrylate, 57.7 g of tert-butyl acrylate, 0.70 g of dodecyl mercaptan, and 64.0 g of styrene was started. The monomer mix was fed over 230 minutes. The initiator feed was continued for 25 minutes after the monomer feeds were completed. The temperature was maintained at 76°C during the feeds and for 45 minutes after the feeds were completed. Cooling to room temperature was then effected. Filtration was carried out using a 100 μm filter cloth. A finely divided polymer dispersion was obtained. The polymer dispersion had a solids content of 30.2 wt %, a pH of 3.2, and a viscosity of 20 mPas. Other properties are listed in Table 1.

[0068] Polymerization Example 2 73.2 g of glacial acetic acid was weighed into a 1 L glass reactor equipped with a cooling / heating jacket. The reactor was heated to 118°C. A nitrogen atmosphere was maintained within the reactor, and stirring was continued throughout the reaction. After the reactor reached temperature, chemical feeds into the reactor were started. A monomer feed of 76.2 g of styrene, 4.1 g of 3-dimethylaminopropyl methacrylamide, 20.5 g of 2-(dimethylamino)ethyl methacrylate, and 0.50 g of dodecyl mercaptan was fed over 90 minutes. A second feed of 11.9 g of glacial acetic acid and 3.96 g of tert-butyl hydroperoxide (70%) was fed simultaneously during the monomer feed and continued for 3 minutes after the monomer feed was completed.

[0069] The temperature in the reactor was maintained at 118°C during the feeds and for 90 minutes after the end of the feeds, after which cooling to 76°C was initiated. Then, 437 g of heated demineralized water was added to the reactor, and a 94.1 g sample of prepolymer was withdrawn. After the temperature stabilized at 76°C, 7.30 g of a 2.9% strength aqueous solution of ammonium iron(II) sulfate hexahydrate was added to the reactor. After 15 minutes, an initiator feed of 41.9 g of a 3.2% solution of hydrogen peroxide was started. After 5 minutes, a monomer mix of 6.3 g of n-butyl acrylate, 57.7 g of tert-butyl acrylate, 0.70 g of dodecyl mercaptan, and 64.0 g of styrene was started. The monomer mix was fed simultaneously with the initiator feed over 285 minutes. The temperature was maintained at 76°C during the feeds and for 45 minutes after the end of the feeds. Cooling was then effected to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely divided polymer dispersion was obtained with a solids content of 30.2% by weight, a pH of 3.3, and a viscosity of 27 mPas. Other properties are listed in Table 1.

[0070] Polymerization Example 3 73.2 g of glacial acetic acid was weighed into a 1 L glass reactor equipped with a cooling / heating jacket. The reactor was heated to 118°C. A nitrogen atmosphere was maintained within the reactor, and stirring was continued throughout the reaction. After the reactor reached temperature, chemical feeds into the reactor were started. A monomer feed of 76.2 g of styrene, 4.1 g of 3-dimethylaminopropyl methacrylamide, 20.5 g of 2-(dimethylamino)ethyl methacrylate, and 0.50 g of dodecyl mercaptan was fed over 90 minutes. A second feed of 11.9 g of glacial acetic acid and 3.96 g of tert-butyl hydroperoxide (70%) was fed simultaneously during the monomer feed and continued for 3 minutes after the monomer feed was completed.

[0071] The temperature in the reactor was maintained at 118°C during the feeds and for 90 minutes after the end of the feeds, after which cooling to 76°C was initiated. Then, 437 g of heated demineralized water was added to the reactor, and a 94.1 g sample of prepolymer was withdrawn. After the temperature stabilized at 76°C, 7.30 g of a 2.9% strength aqueous solution of ammonium iron(II) sulfate hexahydrate was added to the reactor. After 15 minutes, an initiator feed of 41.9 g of a 3.2% solution of hydrogen peroxide was started. After 5 minutes, a monomer mix of 6.3 g of n-butyl acrylate, 57.7 g of tert-butyl acrylate, 0.70 g of dodecyl mercaptan, and 64.0 g of styrene was started. The monomer mix was fed over 200 minutes. The initiator feed was continued for 25 minutes after the end of the monomer feeds. The temperature was maintained at 76°C during the feeds and for 90 minutes after the end of the feeds. Cooling to room temperature was then effected. Filtration was carried out using a 100 μm filter cloth. A finely divided polymer dispersion was obtained. The polymer dispersion had a solids content of 30.8 wt %, a pH of 3.3, and a viscosity of 20 mPas. Other properties are listed in Table 1.

[0072] [Table 1]

[0073] Application example 1 The sizing properties of the surface size polymer dispersions were tested on internally unsized linerboard. Each surface size polymer dispersion was added to a 12% solution of surface-sized starch (C*film07312). The temperature of the resulting surface size mixture containing the polymer dispersion and starch was set to 65°C. The sheets were passed through a Mathis horizontal pound size press, model 5607, at 2 m / min (2 bar). The size press nip temperature was set to 65°C. The sheets were dried at 95°C for 1 minute per side using a PTI laboratory sheet dryer or at 95°C for 1.5 minutes using an AMC drum dryer (speed 50). Sizing efficiency was determined by measuring the Cobb 60 sizing degree according to standard ISO 535.

[0074] Three polymer dispersions were tested: Polymer Dispersion 1 in Polymerization Example 1, Polymer Dispersion 2 in Polymerization Example 2, and Polymer Dispersion 3 in Polymerization Example 3.

[0075] The results are shown in Table 2.

[0076] [Table 2]

[0077] Although the present invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it should be understood that the present invention is not limited to the above-described embodiments, and the present invention is intended to encompass various modifications and equivalent technical solutions within the scope of the appended claims. <Additional Notes> Aspects of the present invention include the following. <Section 1> 1 to 90 wt. % of monomer (a) comprising at least one optionally substituted styrene; 10 to 99% by weight of a monomer (b) comprising at least one alkyl (meth)acrylate; 0 to 9% by weight of monomer (c) containing at least one ethylenically unsaturated monomer different from monomer (b); 1. A water-soluble polymer dispersion containing a styrene acrylate polymer obtained by free radical polymerization in a polymerization medium containing a cationic prepolymer, The cationic prepolymer comprises at least 10 to 55% by weight of a monomer (i) containing at least one ethylenically unsaturated quaternary ammonium and / or tertiary amine; 35 to 90 wt. % of monomer (ii) comprising at least one optionally substituted styrene; with 0 to 55 wt. % of monomer (iii) comprising at least one alkyl (meth)acrylate; obtained by free radical polymerization, An aqueous polymer dispersion, wherein the oligomer content in said polymer dispersion is 1.4% by weight or less (≦) calculated from the dry polymer content. <Section 2> Item 1. The polymer dispersion according to item 1, wherein the oligomer content in the polymer dispersion is in the range of 0 to 1.4 wt %, preferably in the range of 0.001 to 1.2 wt %, more preferably in the range of 0.01 to 0.7 wt %, and even more preferably in the range of 0.001 to 0.4 wt %, calculated from the dry polymer content of the dispersion. <Section 3> the polymer dispersion comprises oligomers with a molecular weight of less than (<) 1,000 g / mol in an amount of less than 1.4% by weight, preferably less than 1.2% by weight, calculated on the dry polymer content; and / or Item 1 or Item 2. The polymer dispersion according to item 1 or 2, characterized in that the polymer dispersion contains oligomers having a molecular weight of less than (<) 500 g / mol in an amount of less than 0.5 wt.%, preferably less than 0.3 wt.%, more preferably less than 0.2 wt.%, calculated from the dry polymer content. <Section 4> Item 4. The polymer dispersion according to any one of Items 1 to 3, wherein the weight average molecular weight (MW) of the polymer dispersion is in the range of 20,000 to 300,000 g / mol, preferably in the range of 25,000 to 200,000 g / mol, more preferably in the range of 30,000 to 100,000 g / mol, and even more preferably in the range of 40,000 to 70,000 g / mol. <Section 5> Item 5. The polymer dispersion according to any one of Items 1 to 4, wherein the number average molecular weight of the polymer dispersion is in the range of 10,000 to 100,000 g / mol, preferably in the range of 11,000 to 50,000 g / mol, more preferably in the range of 12,000 to 40,000 g / mol, and even more preferably in the range of 13,000 to 30,000 g / mol. <Section 6> Item 6. The polymer dispersion according to any one of items 1 to 5, wherein the particle size D50 of the polymer dispersion is less than 70 nm, preferably less than 60 nm, more preferably less than 40 nm, and / or the particle size D90 of the polymer dispersion is less than 120 nm, preferably less than 90 nm, more preferably less than 70 nm, and even more preferably less than 50 nm. <Section 7> The styrene acrylate polymer comprises at least 1 to 90% by weight, preferably 10 to 80% by weight, more preferably 15 to 75% by weight of monomer (a); 10 to 99% by weight, preferably 20 to 90% by weight, preferably 25 to 85% by weight of monomer (b); with 0 to 9% by weight, preferably 0 to 7% by weight, preferably 0 to 5% by weight of a monomer (c) different from the monomer (b); obtained by free radical polymerization, Item 7. The polymer dispersion according to any one of items 1 to 6, wherein the total of the monomers (a)+(b)+(c) is 100% by weight. <Section 8> 8. The polymer dispersion according to any one of items 1 to 7, wherein the monomer (b) is selected from C1 to C4 alkyl methacrylates and any combination thereof. <Section 9> The polymer dispersion according to any one of items 1 to 8, characterized in that the monomer (c) is selected from ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic acid or methacrylic acid with alcohols having more than 4 carbon atoms, acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate, or anionic comonomers (e.g., acrylic acid, methacrylic acid, styrene sulfonic acid). <Section 10> The cationic prepolymer comprises at least 15 to 55% by weight, preferably 15 to 49% by weight, more preferably 18 to 39% by weight of monomer (i); 35 to 90% by weight, preferably 51 to 85% by weight, more preferably 61 to 82% by weight of monomer (ii); 0 to 55% by weight, preferably 0 to 20% by weight, more preferably 0 to 5% by weight of monomer (iii), Item 10. The polymer dispersion according to any one of items 1 to 9, which is obtained by free radical polymerization. <Section 11> the monomer (i) is a quaternary ammonium selected from the group consisting of N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylamide, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylamide, and a quaternary salt of any mixture thereof; and / or Item 11. The polymer dispersion according to any one of items 1 to 10, wherein the monomer (i) is a tertiary amine selected from the group consisting of N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylamide, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylamide, and any mixture thereof. <Section 12> Item 12. The polymer dispersion according to any one of items 1 to 11, wherein the monomer (iii) is selected from the group consisting of n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate. <Section 13> Item 13. The polymer dispersion according to any one of items 1 to 12, wherein the monomer (ii) or the monomer (a) is selected from styrene, α-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any mixture thereof. <Section 14> Item 14. Use of the aqueous polymer dispersion according to any one of items 1 to 13 for surface sizing of paper, paperboard, and the like. <Section 15> Item 14. A method for producing an aqueous polymer dispersion according to any one of items 1 to 13, comprising at least two polymerization stages: In the first polymerization step, at least 10 to 55% by weight of a monomer (i) containing at least one ethylenically unsaturated quaternary ammonium and / or tertiary amine; 35 to 90 wt. % of monomer (ii) comprising at least one optionally substituted styrene; 0 to 55 wt. % of monomer (iii) comprising at least one alkyl (meth)acrylate; wherein the free radical polymerization is carried out to obtain a polymerization medium comprising a cationic prepolymer formed from the monomer (i), the monomer (ii), and optionally the monomer (iii), In the second polymerization step, 1 to 90 wt. % of monomer (a) comprising at least one optionally substituted styrene; 10 to 99% by weight of a monomer (b) comprising at least one alkyl (meth)acrylate; 0 to 9 wt. % of monomer (c) comprising at least one ethylenically unsaturated monomer different from monomer (b); is carried out in said polymerization medium to obtain a styrene acrylate polymer, The manufacturing method. <Section 16> Item 16. The method according to Item 15, wherein the polymerization solvent in the first polymerization stage contains at least one C1-C6 carboxylic acid, at least one C1-C6 carboxylic acid anhydride, or any mixture thereof. <Section 17> Item 17. The method according to Item 15 or 16, wherein the polymerization temperature in the first polymerization stage is in the range of 80 to 150°C, preferably in the range of 107 to 140°C, and more preferably in the range of 115 to 130°C. <Section 18> Item 18. The method according to Item 15, Item 16, or Item 17, wherein the polymerization temperature in the second polymerization stage is in the range of 40 to 105°C, preferably in the range of 50 to 100°C. <Section 19> the polymerization of the styrene acrylate polymer in the second polymerization stage is initiated by an aqueous redox system comprising an oxidizing agent and a reducing agent; and Item 19. The method according to any one of items 15 to 18, wherein the polymerization of the styrene acrylate polymer in the second polymerization stage is completed by the addition of a second initiator. <Section 20> Item 19. The method according to any one of items 15 to 19, wherein in the first polymerization step, the free radical polymerization is initiated in the presence of a first free radical initiator selected from peroxides such as hydrogen peroxide, alkyl hydroperoxides, or dialkyl peroxides.

Claims

1. 1 to 90% by weight of monomer (a) comprising at least one optionally substituted styrene; 10 to 99% by weight of monomer (b) comprising at least one alkyl (meth)acrylate; 0 to 9% by weight of monomer (c) comprising at least one ethylenically unsaturated monomer different from monomer (b); An aqueous polymer dispersion containing a styrene acrylate polymer obtained by a second free radical polymerization in a polymerization medium containing a cationic prepolymer, The cationic prepolymer comprises at least 10 to 55 wt. % of monomer (i) comprising at least one ethylenically unsaturated quaternary ammonium and / or tertiary amine; 35 to 90 wt. % of monomer (ii) comprising at least one optionally substituted styrene; with 0 to 55 wt. % of monomer (iii) comprising at least one alkyl (meth)acrylate; a first free radical polymerization initiated by the presence of a first free radical initiator selected from peroxides; the polymerization solvent in the first free radical polymerization stage is alcohol-free and comprises at least one C1-C6 carboxylic acid, at least one C1-C6 carboxylic acid anhydride, or any mixture thereof, and 0 to 25 wt. % water, calculated on the total polymerization solvent weight; An aqueous polymer dispersion, wherein the content of oligomer in said aqueous polymer dispersion is 1.4% by weight or less (≦) calculated from the dry polymer content, and the molecular weight of said oligomer is 100 to 1,000 g / mol.

2. 2. The aqueous polymer dispersion according to claim 1, wherein the content of said oligomer in said aqueous polymer dispersion is in the range of 0 to 1.4% by weight, calculated from the dry polymer content of said aqueous polymer dispersion.

3. the aqueous polymer dispersion contains oligomers with a molecular weight of less than (<) 1,000 g / mol in an amount of less than 1.4% by weight, calculated on the dry polymer content; and / or 3. Aqueous polymer dispersion according to claim 1 or claim 2, characterized in that the aqueous polymer dispersion contains oligomers with a molecular weight of less than (<) 500 g / mol in an amount of less than 0.5% by weight, calculated from the dry polymer content.

4. 4. The aqueous polymer dispersion according to claim 1, wherein the weight average molecular weight (MW) of the styrene acrylate polymer in the aqueous polymer dispersion is in the range of 20,000 to 300,000 g / mol.

5. 5. The aqueous polymer dispersion according to claim 1, wherein the number average molecular weight of the styrene acrylate polymer in the aqueous polymer dispersion is in the range of 10,000 to 100,000 g / mol.

6. 6. The aqueous polymer dispersion according to claim 1, wherein the styrene acrylate polymer in the aqueous polymer dispersion has a particle size D50 of less than 70 nm and / or a particle size D90 of less than 120 nm.

7. The styrene acrylate polymer comprises at least 10 to 80% by weight of monomer (a); 20 to 90% by weight of monomer (b); with 0 to 7% by weight of a monomer (c) different from the monomer (b), obtained by said second free radical polymerization, 7. Aqueous polymer dispersion according to claim 1, wherein the sum of the monomers (a)+(b)+(c) is 100% by weight.

8. The aqueous polymer dispersion according to any one of claims 1 to 7, characterized in that the monomer (b) is selected from C1 to C4 alkyl methacrylates and any combination thereof.

9. 9. The aqueous polymer dispersion according to claim 1, wherein the monomer (c) is selected from ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic or methacrylic acid with alcohols having more than 4 carbon atoms, acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate, or an anionic comonomer selected from the group consisting of acrylic acid, methacrylic acid, and styrene sulfonic acid.

10. The cationic prepolymer comprises at least 15 to 49% by weight of monomer (i); 51 to 85% by weight of monomer (ii); 0 to 20% by weight of monomer (iii), 10. Aqueous polymer dispersion according to any one of claims 1 to 9, characterized in that it is obtained by said first free radical polymerization.

11. the monomer (i) is a quaternary ammonium selected from the group consisting of N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylate, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl acrylamide, N,N,N-tri(C1-4 alkyl)amino C1-4 alkyl methacrylamide, and quaternary salts of any mixture thereof; and / or 11. The aqueous polymer dispersion of claim 1, wherein the monomer (i) is a tertiary amine selected from the group consisting of N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylate, N,N-di(C1-4 alkyl)amino C1-4 alkyl acrylamide, N,N-di(C1-4 alkyl)amino C1-4 alkyl methacrylamide, and any mixture thereof.

12. 12. The aqueous polymer dispersion according to any one of claims 1 to 11, characterized in that the monomer (iii) is selected from the group consisting of n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate and propyl (meth)acrylate.

13. 13. The aqueous polymer dispersion according to any one of claims 1 to 12, characterized in that the monomer (ii) or the monomer (a) is selected from styrene, α-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any mixture thereof.

14. Use of the aqueous polymer dispersion according to any one of claims 1 to 13 for the surface sizing of paper or paperboard.

15. A method for producing the aqueous polymer dispersion according to any one of claims 1 to 13, comprising the steps of: The content of oligomer in the aqueous polymer dispersion is 1.4% by weight or less (≦) calculated from the dry polymer content, and the molecular weight of the oligomer is 100 to 1,000 g / mol; The method comprises at least two polymerization stages, In the first polymerization stage, at least 10 to 55 wt. % of monomer (i) comprising at least one ethylenically unsaturated quaternary ammonium and / or tertiary amine; 35 to 90 wt. % of monomer (ii) comprising at least one optionally substituted styrene; 0 to 55 wt. % of monomer (iii) comprising at least one alkyl (meth)acrylate; subjecting the resulting mixture to a first free radical polymerization in the presence of a first free radical initiator selected from a peroxide in a polymerization solvent comprising at least one C1-C6 carboxylic acid, at least one C1-C6 carboxylic acid anhydride, or any mixture thereof, and 0 to 25 wt. % water, calculated on the total polymerization solvent weight, wherein the first free radical polymerization step does not use an alcohol, and the first free radical polymerization is for obtaining a polymerization medium comprising a cationic prepolymer formed from the monomer (i), the monomer (ii), and optionally the monomer (iii); In the second polymerization stage, 1 to 90% by weight of monomer (a) comprising at least one optionally substituted styrene; 10 to 99% by weight of monomer (b) comprising at least one alkyl (meth)acrylate; 0 to 9 wt. % of monomer (c), which comprises at least one ethylenically unsaturated monomer different from monomer (b); is carried out in said polymerization medium to obtain a styrene acrylate polymer. The manufacturing method.

16. 16. The method according to claim 15, wherein the polymerization temperature in the first polymerization stage is in the range of 80 to 150°C.

17. The method according to claim 15 or 16, wherein the polymerization temperature in the second polymerization stage is in the range of 40 to 105°C.

18. the polymerization of the styrene acrylate polymer in the second polymerization stage is initiated by an aqueous redox system comprising an oxidizing agent and a reducing agent; and The process according to any one of claims 15 to 17, wherein the polymerization of the styrene acrylate polymer in the second polymerization stage is completed by the addition of a second initiator.

19. The method according to any one of claims 15 to 18, wherein the first free radical initiator selected from the peroxides is selected from the group consisting of hydrogen peroxide, sodium peroxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate, dibenzoyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl 2-ethylhexaneperoxyate, cumyl hydroperoxide, and biscyclohexyl peroxydicarbonate.

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