Polymer dispersions, their uses and methods for their manufacture - Patents.com

Abstract

The present invention relates to a polymer dispersion comprising polymer particles dispersed in an aqueous continuous phase. The polymer particles can be obtained by radical polymerization of one or more vinyl monomers comprising alkyl (meth)acrylates. Prior to the radical polymerization of the vinyl monomers, a rosin component is dissolved in at least one of the vinyl monomers, and the radical polymerization is carried out in the presence of the rosin component. The present invention also relates to the use of the polymer dispersion for surface sizing of cellulose fibrous webs, and to a method for producing the polymer dispersion.

Description

[Technical field]

[0001] The present invention relates to a polymer dispersion according to the preamble of the attached independent claim, to its use and to a method for producing the polymer dispersion. [Background technology]

[0002] In the manufacture of cellulosic fibrous webs, such as paper, board, etc., the properties of the produced web are often improved by adding various chemicals during and after the formation of the cellulosic fibrous web. For example, surface sizing is commonly used to improve the strength and / or water resistance of the produced cellulosic fibrous web, or to otherwise improve the surface properties of such fibrous webs. In surface sizing, an aqueous solution or dispersion containing one or more sizing agents is applied onto the surface of the cellulosic fibrous web, and the web is then dried.

[0003] It is a general trend and requirement to reduce the use of materials based on non-renewable sources, especially petroleum-based raw materials. In the paper and paperboard industry, efforts are being made to reduce the use of synthetic polymers in the production of cellulose fiber webs, with the aim of making the entire process more sustainable. Sizing agents used for surface sizing often contain or are based on synthetic polymers, such as poly(styrene acrylate). It is desirable to reduce the amount of synthetic polymers, especially styrene, in the production of paper and paperboard. At the same time, it is desired to obtain at least similar, and preferably better, surface sizing results for the sized paper, paperboard, etc., in terms of strength, water resistance, and / or other surface properties.

[0004] Rosin, and even its derivatives, can be seen as a sustainable alternative to synthetic polymers. Aqueous dispersions of rosin and its derivatives are already used as hydrophobizing agents in papermaking. However, the use of rosin traditionally requires the use of alum. Furthermore, the softening points of rosin and its derivatives are generally too high in current surface sizing applications to obtain sufficient surface sizing results. The particle size of rosin dispersions is also often too large to obtain good surface sizing results. It has been shown that it is difficult to obtain rosin dispersions with small particle sizes by mechanical mixing and other corresponding techniques.

[0005] Therefore, there is a need for more sustainable alternatives suitable for surface sizing of cellulosic fibrous webs. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to minimize, or if possible even eliminate, the drawbacks present in the prior art.

[0007] Another object of the present invention is to provide a polymer dispersion which is more sustainable and gives good surface sizing results when used in the surface sizing of cellulosic fibrous webs.

[0008] It is yet another object of the present invention to provide a polymer dispersion preferably having a small particle size.

[0009] These objects are achieved according to the invention by means of the characteristics presented in the characterizing parts of the following independent claims.

[0010] Some preferred embodiments of the invention are set out in the dependent claims.

[0011] All described embodiments and advantages apply, where applicable, to all aspects of the present invention, i.e. the polymer dispersion, its uses, and its preparation process, even if not always explicitly stated. [Means for solving the problem]

[0012] A typical polymer dispersion according to the present invention comprises polymer particles dispersed in an aqueous continuous phase, said polymer particles being obtained by radical polymerization of one or more feeds of vinyl monomers in an aqueous polymerization medium comprising a polysaccharide, said vinyl monomers comprising at least one alkyl (meth)acrylate, and wherein prior to said radical polymerization of said vinyl monomers, a rosin component is dissolved in at least one of said feeds of said vinyl monomers.

[0013] A typical use according to the invention of the polymer dispersion according to the invention is for the surface sizing of cellulosic fibrous webs (e.g. paper or paperboard), preferably in an amount of 0.1 to 10 kg / t (more preferably 0.5 to 6 kg / t) of dry cellulosic fibrous web.

[0014] An exemplary process according to the present invention for the preparation of a polymer dispersion comprising polymer particles in an aqueous continuous phase for surface sizing of cellulosic fibrous webs such as paper, paperboard, etc., comprises the steps of: - obtaining a vinyl monomer solution comprising an alkyl (meth)acrylate monomer; - dissolving a rosin component in the vinyl monomer solution; - providing at least one feed of said vinyl monomer solution containing said rosin component and a polymerization initiator into an aqueous polymerization medium containing a polysaccharide; - radically polymerizing the vinyl monomer solution containing the rosin component; Includes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] It has now been surprisingly found that by dissolving a rosin component in a vinyl monomer solution prior to the radical polymerization of these vinyl monomers in an aqueous polymerization medium, it is possible to obtain a polymer dispersion that is more sustainable, since it is produced by reducing the use of synthetic petroleum-based monomers. The polymer dispersion can also show good, or even improved, surface sizing results when applied onto the surface of a cellulose fiber web during surface sizing. When the rosin component is first dissolved in a vinyl monomer solution, the radical polymerization of the vinyl monomer is carried out in the presence of the rosin component, which becomes part of the polymer particle. It is assumed that the rosin component becomes permanently incorporated into the structure of the polymer particle formed by the radical polymerization of the vinyl monomer feed. Without having a theoretical explanation of the reactions and mechanisms involved, it has been observed that the resulting polymer dispersion can provide an effective sizing effect without tackiness problems, when a rosin component is dissolved in at least one of the feeds of monomers used and is therefore present during the polymerization.

[0016] A typical polymer dispersion according to the present invention comprises polymer particles dispersed in an aqueous continuous phase. The polymer dispersion may comprise polymer particles having a particle size of D50≦200 nm, preferably ≦120 nm, more preferably ≦80 nm, even more preferably ≦55 nm, and even in some cases ≦45 nm. The particle size D50 of the polymer particles of the dispersion may be, for example, in the range of 10-200 nm, preferably 15-120 nm, more preferably 20-80 nm, even more preferably 25-55 nm, and even in some cases 25-45 nm. The polymer dispersion may comprise polymer particles having a particle size D90 of ≦500 nm, preferably ≦200 nm, more preferably ≦140 nm, and even more preferably ≦95 nm. The particle size D90 of the polymer particles of the dispersion may be, for example, in the range of 20-500 nm, preferably 25-200 nm, more preferably 30-140 nm, and even more preferably 35-95 nm. All particle sizes are measured using a Zetasizer Nano ZS, Malvern. In the context of the present invention, particle size D50 means the 50th percentile value of the volume-based distribution, and particle size D90 means the 90th percentile value of the volume-based distribution. Unexpectedly, it has been observed that when the rosin component is dissolved in the vinyl monomer solution before the radical polymerization, the resulting polymer dispersion has low particle size D50 and D90 values. The obtained values ​​also show that the particle size distribution is relatively narrow. All this is advantageous in terms of surface sizing results.

[0017] The polymer in the dispersion may have a weight average molecular weight Mw in the range of 1000 to 100,000 g / mol, preferably 5000 to 80,000 g / mol, more preferably 10,000 to 40,000 g / mol, as determined from the final dispersion. The polymer in the dispersion may have a number average molecular weight Mn in the range of 1000 to 20,000 g / mol, preferably 2000 to 15,000 g / mol, more preferably 3000 to 10,000 g / mol, as determined from the final dispersion. The weight average molecular weight and number average molecular weight can be determined, for example, by size exclusion chromatography.

[0018] The polymer dispersion has a glass transition temperature T in the range of 10 to 90° C., preferably 25 to 80° C., more preferably 35 to 75° C., or even more preferably 38 to 70° C., in a dry state. g may have:

[0019] The polymer dispersion according to the invention can be obtained by radical polymerization, preferably by free radical polymerization, of one or more feeds of vinyl monomers. The vinyl monomer comprises at least one alkyl (meth)acrylate. The polymer dispersion may be obtained by radical polymerization of one alkyl (meth)acrylate. Alternatively, the polymer dispersion may be obtained by radical polymerization of a plurality of different vinyl monomers, such as two, three or more, at least one of which is an alkyl (meth)acrylate. Preferably, the polymer dispersion is obtained by radical polymerization of a feed of two or three different vinyl monomers, at least one of which is an alkyl (meth)acrylate. The different vinyl monomers may be provided as separate feeds or one feed of vinyl monomers may comprise a mixture of two, three or more different vinyl monomers.

[0020] The vinyl monomers, at least one of which is an alkyl (meth)acrylate, are obtained in the form of a solution, i.e. in liquid form, or are prepared to form a solution. The vinyl monomer solution is fed to the aqueous polymerization medium as one or more feeds of vinyl monomer. The resin component is dissolved in at least one of the vinyl monomer solutions or feeds before the initiation of the radical polymerization of the vinyl monomer. The at least one solution or feed of vinyl monomer thus comprises a rosin component. The vinyl monomers to be used in the radical polymerization are in the form of a vinyl monomer solution, which may contain small amounts of water and / or other solvents. However, the amount of water and / or other solvents in the monomer solution, and thus in the monomer feed, is preferably minimized. Preferably, each vinyl monomer to be used in the radical polymerization is in the form of a monomer solution or feed, which is essentially free of water. Preferably, the vinyl monomer solution or feed is also essentially free of other solvents, for example organic solvents. In the context of the present invention, the term "essentially free" means that the vinyl monomer solution contains less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight of water and / or other solvents. It has been found that the rosin component can be effectively and uniformly dissolved in the vinyl monomer solution or feed, or at least one of the vinyl monomer solutions or feeds, prior to the radical polymerization in the aqueous medium. The vinyl monomer solution or feed serves as a solvent for the rosin component. The rosin component is preferably completely dissolved in the vinyl monomer solution or feed, and after the dissolution, no solid or semi-solid rosin component can be observed. By dissolving the rosin component in the vinyl monomer feed, it is possible to ensure that the rosin component is uniformly present during the polymerization and well integrated into the polymer structure. Furthermore, since the vinyl monomer solution or feed serves as a solvent for the rosin component, the use of additional organic solvents during the process can be avoided.This makes the preparation of the polymer dispersion simple and rapid, as no additional solvent needs to be removed from the aqueous phase of the polymer dispersion after the radical polymerization. Using a vinyl monomer solution or feed as a solvent for the rosin component can also provide benefits in the quality of the resulting polymer dispersion, such as reduced stickiness.

[0021] At least one feed of the vinyl monomer solution is fed into an aqueous polymerization medium along with at least one polymerization initiator, and radical polymerization of the vinyl monomer feed or feeds is carried out in the presence of the rosin component. Without wishing to be bound by theory at this time, it is believed that the rosin component may be at least partially integrated into the polymer structure formed during the polymerization. Thus, the rosin component may preferably become an inseparable part of the polymer particles formed.

[0022] According to one embodiment of the present invention, the aqueous polymerization medium may contain an additional solvent during the radical polymerization. The aqueous polymerization medium may contain up to 50% additional solvent other than water during the polymerization, preferably up to 35%, more preferably up to 15%. The additional solvent may be an alcohol, such as ethanol or isopropanol. The additional solvent may be removed from the polymer dispersion after the polymerization is completed, for example by distillation. According to one preferred embodiment, the obtained polymer dispersion may contain up to 10% additional solvent other than water, preferably up to 5%, more preferably up to 1%.

[0023] According to one particularly preferred embodiment, the aqueous polymerization medium is free of other solvents than water, ie, the aqueous polymerization medium is free of organic solvents such as alcohols, for example ethanol and isopropanol.

[0024] In the context of the present invention, the term "rosin component" refers to rosin and its derivatives. The rosin component is insoluble in water and is therefore dissolved in the solution of the vinyl monomer prior to the radical polymerization. The rosin component may be a mixture of different rosins. The rosin component used in the present invention may preferably comprise rosin and / or rosin derivatives, such as one or more rosin esters, dimerized rosin, polymerized rosin, hydrogenated rosin, fortified rosin, and unmodified rosin. According to one preferred embodiment of the present invention, the rosin component may be selected from the group consisting of tall oil rosin, wood rosin, gum rosin, derivatives thereof, and any mixtures thereof. For example, the rosin component may be a mixture of tall oil rosin and gum oil rosin. By using different rosins or mixtures thereof as the rosin component, the possibility of influencing, at least to some extent, the properties of the resulting polymer dispersion may be obtained.

[0025] According to one preferred embodiment of the present invention, the rosin component may be a fortified rosin. The fortified rosin is obtained by adding an unsaturated carboxylic acid to the rosin. Suitable carboxylic acids are, for example, fumaric acid, acrylic acid, maleic acid, or itaconic acid. Maleic acid and fumaric acid are preferred. It has been observed that the fortified rosin dissolves very effectively in the vinyl monomer solution, which makes the preparation of the polymer dispersion easy and efficient.

[0026] According to one preferred embodiment of the present invention, the rosin component may have a softening point in the range of 15 to 150° C., preferably 40 to 140° C., more preferably 55 to 130° C., and even more preferably 75 to 125° C. According to one embodiment, the rosin component is essentially free of monocyclic terpene compounds.

[0027] The rosin component may be in liquid or solid form when dissolved or added to the vinyl monomer solution. The rosin component may be dissolved in the vinyl monomer solution at a temperature of 15-40° C. or 20-40° C. In general, the dissolution of the rosin component may be achieved without external heating of the vinyl monomer solution or feed. The dissolution time can be easily determined with a few experiments and usually depends on the monomer used, the rosin component used, and the amount of the rosin component to be dissolved. Typical dissolution times vary between 15-60 minutes.

[0028] The final polymer dispersion may contain the rosin component in an amount of 0.01 to 70% by weight (preferably 1 to 60% by weight, more preferably 1.5 to 49% by weight) calculated on a dry basis from the total weight of the vinyl monomer and the rosin component. In the present invention, the rosin component can be used within a wide range, which allows the flexible production of polymer dispersions with different properties.

[0029] According to one embodiment of the present invention, the polymer dispersion may contain 5 to 70% by weight (preferably 7.5 to 49% by weight, more preferably 10 to 35% by weight, and even more preferably 15 to 34% by weight) of the rosin component, calculated on a dry weight basis from the total weight of the vinyl monomer and the rosin component. By dissolving the rosin component in the vinyl monomer solution prior to the polymerization, it is possible to increase the amount of rosin in the resulting polymer dispersion without compromising the properties of the polymer dispersion, e.g., the particle size of the dispersion, and the resulting surface sizing effect.

[0030] According to another embodiment of the present invention, the polymer dispersion may contain 0.05-4.5 wt. % (preferably 0.5-3.5 wt. %, more preferably 1.5-3.0 wt. %) of the rosin component, calculated on a dry weight basis from the total weight of the vinyl monomer and the rosin component. Even when used in a relatively small amount, the rosin component effectively influences the properties of the resulting polymer dispersion. It is currently assumed that the rosin component can act as a chain transfer agent during the radical polymerization, and thus controls the structure and molecular weight of the polymer formed by the radical polymerization.

[0031] The vinyl monomer may comprise or consist of an alkyl (meth)acrylate, which may be selected from C1 to C18 alkyl (meth)acrylates, preferably C1 to C12 alkyl (meth)acrylates, more preferably C1 to C4 alkyl (meth)acrylates, and any mixture thereof. The vinyl monomers may be selected from methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; n-propyl or isopropyl acrylate and the corresponding propyl methacrylate; n-butyl, isobutyl, tert-butyl, or 2-butyl acrylate and the corresponding butyl methacrylate; n-pentyl or neopentyl acrylate and the corresponding pentyl methacrylate; 2-hexyl or 2-ethylhexyl acrylate and the corresponding methacrylate; n-octyl or isooctyl acrylate and the corresponding methacrylate; decyl acrylate; decyl methacrylate; dodecyl acrylate; dodecyl methacrylate; lauryl acrylate; lauryl methacrylate; stearyl acrylate; stearyl methacrylate. Preferably, the vinyl monomer may be selected from C1-C4 alkyl acrylates, C1-C4 alkyl methacrylates, or any mixture thereof, such as n-butyl, isobutyl, tert-butyl, or 2-butyl acrylate and the corresponding butyl methacrylate; methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, or propyl methacrylate. It is possible that the vinyl monomer may comprise or consist of a mixture of at least two isomeric butyl acrylates, such as a mixture of n-butyl acrylate and methyl methacrylate, or a mixture of n-butyl acrylate and tert-butyl acrylate.

[0032] According to one embodiment of the present invention, the vinyl monomer may comprise at least one first monomer (a) selected from alkyl (meth)acrylates, such as C1 to C18 alkyl (meth)acrylates, preferably C1 to C12 alkyl (meth)acrylates, more preferably C1 to C4 alkyl (meth)acrylates, and any mixture thereof. Suitable first monomers (a) may be, for example, methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; n-propyl or isopropyl acrylate and the corresponding propyl methacrylate; n-butyl, isobutyl, tert-butyl, or 2-butyl acrylate and the corresponding butyl methacrylate; n-pentyl or neopentyl acrylate and the corresponding pentyl methacrylate; 2-hexyl or 2-ethylhexyl acrylate and the corresponding methacrylate; n-octyl or isooctyl acrylate and the corresponding methacrylate; decyl acrylate; decyl methacrylate; dodecyl acrylate; dodecyl methacrylate; lauryl acrylate; lauryl methacrylate; stearyl acrylate; stearyl methacrylate. According to one preferred embodiment, the first monomer (a) is selected from C1-C4 alkyl acrylates, C1-C4 alkyl methacrylates, or any mixture thereof, such as n-butyl, isobutyl, tert-butyl, or 2-butyl acrylate and the corresponding butyl methacrylate; methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, or propyl methacrylate. The first monomer (a) may be a mixture of at least two isomeric butyl acrylates. For example, the first monomer (a) may be a mixture of n-butyl acrylate and methyl methacrylate, or a mixture of n-butyl acrylate and tert-butyl acrylate.

[0033] According to one embodiment of the present invention, the vinyl monomer may further comprise at least one second monomer (b) which may be selected from styrene, α-methylstyrene, vinyltoluene, ethylvinyltoluene, substituted styrenes such as chloromethylstyrene, and any mixture thereof.

[0034] The polymer dispersion can be obtained by radical polymerization of one or more feeds of vinyl monomers containing 51 to 100% by weight (preferably 55 to 99.5% by weight, more preferably 60 to 99% by weight, or 65 to 99% by weight) of the first monomer (a) and / or 0 to 49% by weight (preferably 0.5 to 45% by weight, more preferably 1 to 40% by weight, or 1 to 35% by weight) of the second monomer (b), calculated on a dry weight basis from the total weight of the monomers.

[0035] According to one preferred embodiment of the present invention, the polymer dispersion is obtained by radical polymerization of at least one feed of vinyl monomers, including, for example, alkyl (meth)acrylates as defined above, in the absence of styrene and substituted styrene monomers. The polymer dispersion can thus be obtained without a second monomer (b) selected from styrene, α-methylstyrene, vinyltoluene, ethylvinyltoluene, substituted styrenes such as chloromethylstyrene, and any mixtures thereof. The resulting polymer dispersion can thus be free of structural units derived from monomers selected from styrene, α-methylstyrene, vinyltoluene, ethylvinyltoluene, substituted styrenes such as chloromethylstyrene, and any mixtures thereof. It has been observed that when the radical polymerization is carried out in the presence of the rosin component, the resulting polymer dispersion acquires a glass transition temperature that makes it suitable for use in surface sizing of paper, paperboard, and the like. It is therefore even possible to completely replace styrene in the polymer dispersion, the polymer dispersion thus being free of styrene residues.

[0036] The resulting polymer dispersion may have a solids content of at least 10% by weight, preferably at least 20% by weight, and possibly even at least 25% by weight. According to one embodiment, the solids content of the polymer dispersion may be in the range of 10-60% by weight, preferably 20-55% by weight, and more preferably 25-45% by weight.

[0037] The monomer solution, i.e. the vinyl monomer feed, or the aqueous polymerization medium may contain a regulator useful in the polymerization, such as a chain transfer agent. The regulator may be introduced into the polymerization medium simultaneously with the vinyl monomer, but separately. Alternatively, or in addition, the regulator may be introduced as a mixture with the monomer solution or feed. If a regulator is used, the amount may be 0.01-5% by weight, preferably 0.01-1.0% by weight, more preferably 0.1-0.7% by weight, calculated from the weight of the vinyl monomer. In some cases, the aqueous polymerization medium may contain 0-2% by weight, preferably 0.05-2% by weight, or 0.05-1% by weight of a regulator. According to one embodiment, the polymerization is carried out without the addition and / or use of a regulator. Suitable regulators may be, for example, sulfur-containing organic compounds, such as mercaptans, di- and polysulfides, sulfides, or esters of thio- and dithiocarboxylic acids; halogen compounds, alcohols, or aldehydes. According to one preferred embodiment, the modulating agent may be a terpene-containing compound, such as terpinolene.

[0038] The continuous aqueous phase of the polymer dispersion can further comprise a stabilizer. The stabilizer can be selected from synthetic, natural, electrostatically charged and surface active stabilizers. The stabilisers can be anionic, cationic, amphoteric or non-ionic. The stabilising effect can be based, for example, on steric stabilisation, electrosteric stabilisation, electrostatic stabilisation or Pickering stabilisation.

[0039] The aqueous polymerization medium comprises a polysaccharide. The polysaccharide is added to the aqueous polymerization medium before the start of the polymerization, and the polysaccharide is present during the radical polymerization. The polysaccharide may function as a protective colloid for the polymer particles in the resulting polymer dispersion. It has been observed that the presence of the polysaccharide results in an unexpectedly stable dispersion with a narrow particle size distribution, even when the polymerization is carried out in the presence of the rosin component. The polysaccharide may be added in an amount of 10-45% by weight, preferably 15-40% by weight, more preferably 20-35% by weight, calculated on a dry basis from the total weight of the polymer dispersion. According to one preferred embodiment, the polysaccharide is selected from the group comprising polysaccharide derivatives, degraded polysaccharides, derivatives of degraded polysaccharides, and any mixtures thereof. The polysaccharide may be selected, for example, from starch, substituted starch, cellulose, substituted cellulose, hemicellulose, substituted hemicellulose, chitosan, glucan derivatives, dextrin, degraded starch, and any mixtures thereof, preferably degraded starch. Preferably, the polysaccharide is essentially water-soluble. The polysaccharide preferably has an average molecular weight Mn in the range of 500 to 10,000 g / mol. The polysaccharide, such as starch or degraded starch, may be anionic, cationic, amphoteric or nonionic, preferably anionic.

[0040] According to one embodiment, the polymer dispersion may include one or more surfactants, which may function as stabilizers.

[0041] A water-soluble redox system comprising an oxidizing agent and a reducing agent can be used to initiate the radical polymerization of the feed of vinyl monomer. 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-tetramethylbutylperoxy-2-ethylhexanoate, cumyl hydroperoxide, or bis-cyclohexyl peroxydicarbonate. The reducing agent of the redox system can be selected from sodium sulfite, sodium pyrosulfite, sodium bisulfite, sodium dithionite, sodium hydroxymethanesulfinate, or ascorbic acid, or metal salts such as cerium, manganese, or iron (II) salts. According to one preferred embodiment, the radical polymerization may be carried out using a graft-linking water-soluble redox initiator system comprising hydrogen peroxide and a metal salt, such as an iron(II) salt, which may be added to the aqueous polymerization medium prior to the initiation of the polymerization, while hydrogen peroxide is added simultaneously but separately from the addition of the monomers.

[0042] The polymer particles in the polymer dispersion are formed directly by the radical polymerization of the monomer in the aqueous polymerization medium containing polysaccharide. The radical polymerization can be carried out by a feed process, in which the one or more feeds of vinyl monomer are fed into the aqueous polymerization medium during the polymerization time, or by a batch process, in which the entire feed of vinyl monomer is added to the aqueous polymerization medium at once at the beginning of the polymerization, the feed process being preferred. A continuous polymerization process in a series of stirred kettles or a flow tube is also possible. In a preferred feed process, a continuous feed of at least one vinyl monomer and a free radical initiator is metered uniformly into the aqueous polymerization medium, preferably containing degraded starch, in a stirred reactor. During the entire production and polymerization process, sufficient mixing is maintained with the aid of any suitable stirring or mixing unit so that the added monomer feeds and other components are homogeneously distributed as quickly as possible.

[0043] The radical polymerization can be carried out at a polymerization temperature within the range of 50 to 100°C, preferably 60 to 90°C, and more preferably 70 to 90°C.

[0044] The resulting polymer dispersion may have a viscosity of ≦500 mPas, preferably ≦200 mPas, more preferably ≦50 mPas. The viscosity may be in the range of 1-500 mPas, preferably 1-200 mPas, more preferably 2-50 mPas. All viscosity values ​​are measured at 25° C. at 25% solids by weight using a Brookfield LVDV viscometer in a small sample adapter equipped with spindle 18.

[0045] According to one embodiment of the present invention, the polymer dispersion is used together with an aluminum compound such as alum or polyaluminum chloride in surface sizing. However, the use of alum is not essential, and sufficient surface sizing results can be easily obtained with the polymer dispersion of the present invention even in the absence of alum.

[0046] The polymer dispersion according to the present invention is particularly suitable for use in the surface sizing of cellulose webs. In addition to the polymer dispersion, the surface sizing composition may further comprise surface sizing starch and other additives conventionally used in the surface sizing of paper, paperboard and other cellulose products. Such additives, which are generally known in the art, include, but are not limited to, dispersants, defoamers, colorants, inorganic pigments and fillers, anti-curl agents, antistatic agents, further conventional components surfactants, plasticizers, wetting agents, defoamers, UV absorbers, lightfastness improvers, polymer dispersants, mordants, optical brighteners, leveling agents, rheology modifiers and strength additives. The above additives may be used to further improve the sizing performance obtained with the polymer dispersion according to the present invention.

[0047] The polymer dispersion can be applied to a cellulose fiber web (e.g. paper, paperboard, etc.) in an amount of 0.1 to 10 kg / t, preferably 0.5 to 6 kg / t, of the dried cellulose fiber web. The polymer dispersion according to the invention is suitable for surface sizing of all paper and paperboard qualities. The polymer dispersion according to the invention is particularly suitable for surface sizing of cellulose fiber webs containing recycled fibers. EXAMPLES

[0048] Some embodiments of the invention are described in greater detail in the following non-limiting examples.

[0049] The following methods were used in the examples to evaluate the dispersion properties.

[0050] <Particle size> Particle size measurements of the polymer dispersions were performed using a Malvern Zetasizer Nano instrument. Particle size measurements of the rosin dispersions were performed by a Malvern MasterSizer 2000.

[0051] <Solid content> Solids content was measured using a Mettler Toledo Halogen moisture meter.

[0052] <Viscosity> Viscosity was measured using a Brookfield LVDV viscometer in a small volume sample adapter equipped with spindle 18 at 60 rpm and 25°C.

[0053] <Number average molecular weight (M n ), weight average molecular weight (M w )> Molecular weights were determined by size-exclusion chromatography (SEC) using an Agilent 1100 HPLC system equipped with an integrated 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 Polymer Standard Service GRAM columns (1000 Å + 2 × 30 Å columns). Samples were lyophilized prior to analysis. The injection volume was 50 μl and the sample concentration was 4 mg / ml. For conventional column calibration, the system was calibrated over the Mw range of 266-1210000 g / mol using narrow molecular weight distribution poly(styrene) standards (Polymer Standards Service). Calibration curves were generated using Agilent's GPC Addon software.

[0054] < Glass transition temperature (T g )> The glass transition temperatures were measured from freeze-dried samples using a differential scanning calorimeter Mettler Toledo DSC 3+.

[0055] <Production Example of Polymer Dispersion> The tall oil rosin was obtained commercially and had the properties of a softening point of approximately 65° C. and a rosin acid content of 86%.

[0056] The modified rosins were tall oil rosins with added fumaric acid prepared from the tall oil rosins described above. Modified rosin 1 had a softening point of approximately 115°C, and modified rosin 2 had a softening point of approximately 95°C.

[0057] Example 1: Preparation of polymer dispersion containing tall oil rosin 78.7 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 550 g of demineralized water in a 1 L glass reactor with cooling / heating jacket under stirring and nitrogen atmosphere. The mixture was heated to 95° C. and the starch was dissolved by heat treatment at 95° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.74% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.4 g of a 30% strength hydrogen peroxide was added. After 40 minutes at 95° C., starch decomposition was complete.

[0058] While the starch was breaking down, in a separate container, a mixture was made by blending together 159g of tert-butyl acrylate, 8.4g of n-butyl acrylate, and 16.7g of the tall oil rosin. The tall oil rosin was dissolved in the monomer.

[0059] The temperature of the degraded starch-containing reactor was cooled to 85° C., after which the chemical feeds were started simultaneously. 184.1 g of a mixture (solution) of monomers and tall oil rosin were fed during 120 minutes. 74.7 g of a 5.5% hydrogen peroxide solution were fed during 165 minutes. The reactor temperature was kept at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C., and 5.2 g of a 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was kept at 60° C. for another 60 minutes. The resulting polymer dispersion was then cooled to 50° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjusting the pH to 3.8 with a 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0060] Example 2: Preparation of polymer dispersion containing tall oil rosin The polymer dispersion of Example 2 was prepared using the same procedure as in Example 1, except that the amount of tert-butyl acrylate was 140.0 g, the amount of n-butyl acrylate was 7.4 g, and the amount of tall oil rosin was 36.8 g. The amounts of other materials and reaction conditions were kept the same as in Example 1. The properties of the polymer dispersion are shown in Table 1.

[0061] Example 3: Preparation of polymer dispersion containing tall oil rosin The polymer dispersion of Example 3 was prepared using the same procedure as in Example 1, except that the amount of tert-butyl acrylate was 117.9 g, the amount of n-butyl acrylate was 29.5 g, and the amount of the tall oil rosin was 36.8 g. The amounts of other materials and reaction conditions were kept the same as in Example 1. The properties of the polymer dispersion are shown in Table 1.

[0062] Example 4: Preparation of polymer dispersion containing fortified tall oil rosin 57.3 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 329 g of demineralized water under stirring in a 1 L glass reactor with cooling / heating jacket under nitrogen atmosphere. The mixture was heated to 85° C. and the starch was dissolved by heat treatment at 85° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.66% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.3 g of a 30% strength hydrogen peroxide was added. After 10 minutes at 85° C., starch decomposition was complete.

[0063] While the starch was disintegrating, in a separate container, a mixture was made by blending together 90.4 g of tert-butyl acrylate, 6.7 g of n-butyl acrylate, 70.3 g of styrene, and 16.1 g of Modified Rosin 1. Modified Rosin 1 was dissolved in the monomers.

[0064] The temperature of the degraded starch reactor was maintained at 85° C. and the chemical feeds were started. 183.5 g of the monomer and modified tall oil rosin mixture (solution) and 167.4 g of dilution water as a separate feed were fed during 160 minutes. A feed of 74.8 g of a 5.5% hydrogen peroxide solution was started simultaneously with the monomer and water feeds and continued for 200 minutes. The reactor temperature was maintained at 85° C. during the feeds and for the following 15 minutes for post polymerization. The mixture was then cooled to 60° C. and 5.2 g of an 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was maintained at 60° C. for another 60 minutes. The dispersion was then cooled to 40° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjusting the pH to 4.5 with 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0065] Example 5: Preparation of polymer dispersion containing tall oil rosin 67.0 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 372.1 g of demineralized water in a 1 L glass reactor with cooling / heating jacket under stirring and nitrogen atmosphere. The mixture was heated to 85° C. and the starch was dissolved by heat treatment at 85° C. for 30 minutes. After the completion of starch dissolution, 28.6 g of a 0.66% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.9 g of a 30% strength hydrogen peroxide was added. After 10 minutes at 85° C., the starch decomposition was complete.

[0066] While the starch was breaking down, in a separate container, a mixture was made by blending together 117.2 g of tert-butyl acrylate, 50.2 g of styrene, and 25.1 g of the tall oil rosin. The tall oil rosin was dissolved in the monomer.

[0067] The temperature of the reactor containing the degraded starch was maintained at 85° C. and the chemical feeds were started. 192.5 g of a mixture (solution) of monomer and tall oil rosin, as well as 167.4 g of dilution water as a separate feed, were fed during 120 minutes. A feed of 74.8 g of a 5.5% hydrogen peroxide solution was started simultaneously with the monomer and water feeds and continued for 165 minutes. The reactor temperature was maintained at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C. and 5.2 g of an 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was maintained at 60° C. for another 60 minutes. The dispersion was then cooled to 40° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjusting the pH to 4.5 with 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0068] Example 6: Preparation of polymer dispersion containing modified tall oil rosin 67.0 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 372 g of demineralized water under stirring in a 1 L glass reactor with cooling / heating jacket under nitrogen atmosphere. The mixture was heated to 85° C. and the starch was dissolved by heat treatment at 85° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.66% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.9 g of a 30% strength hydrogen peroxide was added. After 10 minutes at 85° C., starch decomposition was complete.

[0069] While the starch was disintegrating, in a separate container, a mixture was made by blending together 90.4 g of tert-butyl acrylate, 6.7 g of n-butyl acrylate, 70.3 g of styrene, and 25.1 g of Modified Rosin 1. Modified Rosin 1 was dissolved in the monomers.

[0070] The temperature of the reactor containing the degraded starch was maintained at 85° C. and the chemical feeds were started. 192.5 g of the monomer and modified rosin mixture (solution) and also 167.4 g of dilution water as a separate feed were fed during 160 minutes. A feed of 73.2 g of a 5.5% hydrogen peroxide solution was started simultaneously with the monomer and water feeds and continued for 200 minutes. The reactor temperature was maintained at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C. and 5.2 g of an 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was maintained at 60° C. for another 60 minutes. The dispersion was then cooled to 40° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjusting the pH to 4.5 with 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0071] Example 7: Preparation of polymer dispersion containing tall oil rosin 67.0 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 372 g of demineralized water under stirring in a 1 L glass reactor with cooling / heating jacket under nitrogen atmosphere. The mixture was heated to 85° C. and the starch was dissolved by heat treatment at 85° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.66% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.9 g of a 30% strength hydrogen peroxide was added. After 10 minutes at 85° C., starch decomposition was complete.

[0072] While the starch was breaking down, in a separate container, a mixture was made by blending together 90.4 g of tert-butyl acrylate, 6.7 g of n-butyl acrylate, 70.3 g of styrene, and 24.1 g of the tall oil rosin. The tall oil rosin was dissolved in the monomers.

[0073] The temperature of the reactor containing the degraded starch was maintained at 85° C. and the chemical feeds were started. 191.5 g of a mixture (solution) of monomer and tall oil rosin, as well as 167.4 g of dilution water as a separate feed, were fed during 120 minutes. A feed of 74.8 g of a 5.5% hydrogen peroxide solution was started simultaneously with the monomer and water feeds and continued for 165 minutes. The reactor temperature was maintained at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C. and 5.2 g of an 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was maintained at 60° C. for another 60 minutes. The dispersion was then cooled to 40° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjusting the pH to 4.5 with 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0074] Example 8: Preparation of polymer dispersion containing tall oil rosin 63.2 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 351.2 g of demineralized water in a 1 L glass reactor with cooling / heating jacket under stirring and nitrogen atmosphere. The mixture was heated to 85° C. and the starch was dissolved by heat treatment at 85° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.66% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.7 g of a 30% strength hydrogen peroxide was added. After 10 minutes at 85° C., starch decomposition was complete.

[0075] While the starch was breaking down, in a separate container, a mixture was made by blending together 85.3 g of tert-butyl acrylate, 6.3 g of n-butyl acrylate, 66.4 g of styrene, and 33.5 g of the tall oil rosin. The tall oil rosin was dissolved in the monomers.

[0076] The temperature of the reactor containing the degraded starch was maintained at 85° C. and the chemical feeds were started. 191.5 g of a mixture (solution) of monomer and tall oil rosin, as well as 158 g of dilution water as a separate feed, were fed during 120 minutes. A feed of 74.8 g of a 5.5% hydrogen peroxide solution was started simultaneously with the monomer and water feeds and continued for 165 minutes. The reactor temperature was maintained at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C. and 5.2 g of an 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was maintained at 60° C. for another 60 minutes. The dispersion was then cooled to 40° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjusting the pH to 4.5 with 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0077] Example 9: Preparation of polymer dispersion containing modified tall oil rosin 78.7 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 550 g of demineralized water in a 1 L glass reactor with cooling / heating jacket under stirring and nitrogen atmosphere. The mixture was heated to 95° C. and the starch was dissolved by heat treatment at 95° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.74% strength aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.4 g of a 30% strength hydrogen peroxide was added. After 40 minutes at 95° C., starch decomposition was complete.

[0078] While the starch was disintegrating, in a separate container, a mixture was made by blending together 140.0 g of tert-butyl acrylate, 7.4 g of n-butyl acrylate, and 36.8 g of Modified Rosin 2. Modified Rosin 2 was dissolved in the monomers.

[0079] The temperature of the reactor containing the degraded starch was cooled to 85° C., after which the chemical feeds were started simultaneously. 184.2 g of the mixture (solution) of monomer and modified rosin were fed during 120 minutes. 69.2 g of a 5.5% hydrogen peroxide solution were fed during 165 minutes. The reactor temperature was kept at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C., and 5.2 g of an 11.7% strength tert-butyl hydroperoxide solution was added dropwise to the reactor. The temperature was kept at 60° C. for another 60 minutes. The dispersion was then cooled to 50° C., 5.9 g of a 10% strength ethylenediaminetetraacetic acid sodium salt (EDTA-Na) solution was added, followed by adjustment of the pH to 3.8 with a 25% strength sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0080] Comparative Example 1: Preparation of polymer dispersion not containing tall oil rosin 78.7 g of oxidatively degraded potato starch (Perfectamyl A 4692) was dispersed in 550 g of demineralized water under nitrogen atmosphere and stirring in a 1 L glass reactor with cooling / heating jacket. The mixture was heated to 95° C. and the starch was dissolved by stirring at 95° C. for 30 minutes. After complete starch dissolution, 28.6 g of a 0.74% strength by weight aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 3.4 g of a 30% strength by weight hydrogen peroxide was added. After 40 minutes, starch decomposition was complete.

[0081] While the starch was decomposing, 159.0 g of tert-butyl acrylate, 8.4 g of n-butyl acrylate, and 2.5 g of 1-dodecyl mercaptan were mixed.

[0082] The temperature of the reactor containing the degraded starch was cooled to 85° C., after which the chemical feeds were started simultaneously. The mixture of the monomers and 1-dodecyl mercaptan was fed during 120 minutes. 74.7 g of a 5.5% by weight hydrogen peroxide solution was fed during 165 minutes. The reactor temperature was kept at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C., and 5.2 g of an 11.7% by weight tert-butyl hydroperoxide solution was added to the reactor. The temperature was kept at 60° C. for another 60 minutes. The polymer dispersion was then cooled to 50° C., 5.9 g of a 10% by weight ethylenediaminetetraacetic acid sodium salt solution was added, followed by adjusting the pH to 3.8 with sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1.

[0083] Comparative Example 2: Preparation of polymer dispersion containing no tall oil rosin 57.7 g of oxidized degraded potato starch (Perfectamyl A 4692) was dispersed in 346 g of demineralized water in a 1 L glass reactor with cooling / heating jacket under stirring under nitrogen atmosphere. The mixture was heated to 95° C. and the starch was dissolved by stirring at 95° C. for 30 minutes. After completion of starch dissolution, 8.8 g of a 2.17% by weight aqueous solution of iron(II) sulfate heptahydrate was added to the reactor. After 10 minutes, 6.0 g of a 15% by weight hydrogen peroxide was added. After 40 minutes, the starch solution was diluted by adding 167 g of demineralized water.

[0084] While the starch was decomposing, 98.9 g of tert-butyl acrylate, 8.2 g of n-butyl acrylate, 57.7 g of styrene, and 2.4 g of 1-dodecyl mercaptan were mixed.

[0085] The temperature of the reactor containing the degraded starch was cooled to 85° C., after which the chemical feeds were started simultaneously. The mixture of the monomers and 1-dodecyl mercaptan was fed during 135 minutes. 56.0 g of a 2.7% by weight hydrogen peroxide solution was fed during 137 minutes. The reactor temperature was kept at 85° C. during the feeds and for the following 15 minutes for post-polymerization. The mixture was then cooled to 60° C., and 4.5 g of an 11.7% by weight tert-butyl hydroperoxide solution was added to the reactor. The temperature was kept at 60° C. for another 60 minutes. The polymer dispersion was then cooled to 40° C., 5.2 g of a 10% by weight ethylenediaminetetraacetic acid sodium salt solution was added, followed by adjusting the pH to 4.5 with sodium hydroxide solution and cooling to room temperature. Filtration was carried out using a 100 μm filter cloth. A finely dispersed polymer dispersion was obtained. The properties of the polymer dispersion are shown in Table 1. [Table 1]

[0086] <Application Examples> The sizing performance of the declared size composition is shown in Table 1. 2The tests were carried out on recycled fibre linerboard with no internal sizing. The sheets were passed through a Mathis horizontal pound size press type 5607 at 2 m / min (2 bar). The temperature of the surface size composition and the size press nip was adjusted to 60°C. The sheets were dried at 95°C using an AMC drum dryer at speed 50 with a drying time of 1.5 minutes. The sizing efficiency was measured according to standard ISO 535 using a Cobb 60 The degree of sizing was determined by measuring.

[0087] <Application Example 1: Sizing performance without alum> The surface size composition was prepared by first dissolving starch in water according to its general starch heat treatment instructions. The dissolved starch in the form of a solution was then blended with a polymer dispersion as specified in Table 2.

[0088] Tests were performed with an 8% solution of Raisamyl 01121 starch.

[0089] The results are shown in Table 2. It can be seen that the sizing efficiency does not decrease with decreasing amount of polymer in the sizing composition. It can also be seen that alum is not required for good sizing efficiency. [Table 2]

[0090] <Application Example 2: Sizing Performance> A surface size composition was prepared similarly to Application Example 1. Alum, if used, was added to the surface size composition prior to surface sizing in an amount of 1% by weight calculated on dry starch.

[0091] In Comparative Tests 3 and 4, a rosin dispersion was prepared by dispersing fumaric tall oil rosin having a softening point of approximately 95° C. in water. The rosin dispersion had a particle size D90 of 1.3 μm and a particle size D50 of 0.5 μm as measured by a Mastersizer. The rosin content of the rosin dispersion was 84% ​​by weight of its dry solids.

[0092] The results of Application Example 2 are shown in Table 3. It can be seen that a polymer dispersion in which the tall oil rosin is dissolved in the monomer before polymerization gives better sizing results than the rosin dispersed in water. [Table 3]

[0093] Although the present invention has been described in connection with what is believed to be the most practical and preferred embodiments at present, it is understood that the present invention is not limited to the above-mentioned embodiments, and the present invention is intended to encompass various modifications and equivalent technical solutions within the scope of the appended claims.

Claims

1. A polymer dispersion comprising polymer particles dispersed in an aqueous continuous phase, wherein the polymer particles are obtained by radical polymerization of one or more feeds of vinyl monomers in an aqueous polymerization medium containing a polysaccharide, and the vinyl monomers include at least one alkyl (meth)acrylate, and a rosin component is dissolved in at least one of the feeds of the vinyl monomers prior to the radical polymerization of the vinyl monomers, characterized in that it is a polymer dispersion.

2. The polymer dispersion according to claim 1, characterized in that the rosin component comprises rosin and / or a rosin derivative (such as one or more rosin esters, dimerized rosin, polymerized rosin, hydrogenated rosin, fortified rosin, and non- modified rosin).

3. The polymer dispersion according to claim 1 or claim 2, characterized in that the rosin component is selected from the group consisting of tall oil rosin, wood rosin, gum rosin, derivatives thereof, and any mixtures thereof.

4. The polymer dispersion according to claim 1 or claim 2, characterized in that the rosin component is contained in an amount of 0.01 to 70% by weight (preferably 1 to 60% by weight, more preferably 1.5 to 49% by weight), calculated from the total weight of the vinyl monomer and the rosin component on a dry weight basis.

5. The polymer dispersion according to claim 4, characterized in that the rosin component is contained in an amount of 10 to 35% by weight (preferably 15 to 34% by weight), calculated from the total weight of the vinyl monomer and the rosin component on a dry weight basis.

6. The vinyl monomer is at least one first monomer (a) selected from alkyl (meth)acrylates (such as C1-C18 alkyl (meth)acrylates) and any mixtures thereof, styrene, substituted styrenes (such as α-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene), and at least one second monomer (b) selected from any mixtures thereof, and the polymer dispersion according to claim 1 is characterized by containing the same.

7. On a dry weight basis, the vinyl monomer is calculated from the total weight of the monomers, 51 to 100% by weight (preferably 55 to 99.5% by weight, more preferably 60 to 99% by weight, or 65 to 99% by weight) of said first monomer (a), and / or 0 to 49% by weight (preferably 0.5 to 45% by weight, more preferably 1 to 40% by weight, or 1 to 35% by weight) of said second monomer (b), The polymer dispersion according to claim 6, characterized by comprising.

8. The polymer dispersion according to claim 1, characterized in that the polysaccharide is selected from polysaccharide derivatives, degraded polysaccharides, derivatives of degraded polysaccharides, and any mixtures thereof.

9. The polymer dispersion according to claim 8, characterized in that the polysaccharide is selected from starch, substituted starch, cellulose, substituted cellulose, hemicellulose, substituted hemicellulose, chitosan, glucan derivatives, dextrin, degraded starch, and any mixtures thereof.

10. The polymer dispersion according to claim 1, characterized by comprising polymer particles having a particle size D50 of ≦ 200 nm (preferably ≦ 120 nm, more preferably ≦ 80 nm, even more preferably ≦ 55 nm).

11. The polymer dispersion according to claim 1, characterized by comprising polymer particles having a particle size D90 of ≦ 500 nm (preferably ≦ 200 nm, more preferably ≦ 140 nm, even more preferably ≦ 95 nm).

12. The polymer dispersion according to claim 10 or claim 11, characterized by comprising polymer particles having a particle size D50 within the range of 10 to 200 nm (preferably 15 to 120 nm, more preferably 20 to 80 nm) and / or a particle size D90 within the range of 20 to 500 nm (preferably 25 to 200 nm, more preferably 30 to 140 nm).

13. The polymer dispersion according to claim 1, characterized by having a weight average molecular weight Mw within the range of 1000 to 100,000 g / mol (preferably 5000 to 80,000 g / mol, more preferably 10,000 to 40,000 g / mol).

14. Use of the polymer dispersion according to claim 1 for surface sizing of a cellulose fiber web (such as paper, paperboard, etc.), preferably in an amount of 0.1 to 10 kg / t (preferably 0.5 to 6 kg / t) when the cellulose fiber web is dry.

15. The use according to claim 14, characterized in that the polymer dispersion is used together with an aluminum compound (such as alum or polyaluminum chloride, etc.) in the surface sizing.

16. A method for producing a polymer dispersion containing polymer particles in an aqueous continuous phase for surface sizing of a cellulose fiber web (such as paper, paperboard, etc.), obtaining a vinyl monomer solution containing an alkyl (meth)acrylate monomer, dissolving a rosin component in the vinyl monomer solution, feeding at least one feed of the vinyl monomer solution containing the rosin component and a polymerization initiator into an aqueous polymerization medium containing a polysaccharide, performing radical polymerization of the vinyl monomer solution containing the rosin component, comprising the method.

17. The method according to claim 16, characterized in that the radical polymerization is carried out at a polymerization temperature in the range of 50 to 100 ° C (preferably 60 to 90 ° C, more preferably 70 to 90 ° C).