Polymer dispersion and its use

Abstract

A polymer dispersion comprising an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase, comprises further a prepolymer of polyaminoamide-epichlorohydrin (PAE) as a stabilizing agent. The polymer dispersion is used as a sizing agent or a component in a sizing composition, preferably a surface sizing agent or a component in a surface sizing composition.

Description

[0001] POLYMER DISPERSION AND ITS USE

[0002] Field of the invention

[0003] The present invention relates to a polymer dispersion and its use according to the enclosed independent claims. The present invention further relates to a use of a prepolymer of polyaminoamide-epichlorohydrin (PAE) as a stabilizing agent in polymer dispersions.

[0004] Background of the invention

[0005] Various aqueous polymer dispersions are used in many industrial processes. For example, in pulp and paper industry polymer dispersions can be used as sizing agents.

[0006] Polymer dispersions are usually stabilized. In practice this means that the polymer dispersion contains a stabilizing agent that improves the stability of the dispersion and reduces or even eliminates the risk for particle aggregation and phase separation during the storage of the polymer dispersion. Stabilizing agent can be either mixed into the liquid phase of the polymer dispersion together with the polymer, or the stabilizing agent can be already present during the polymerisation of the dispersed polymer. Usually polymer dispersions, especially polymer dispersions with small particle size, are stabilized by using other polymers or surfactants. Starch has been used for stabilizing some polymer dispersions, for example polystyrene acrylate dispersions. Starch is produced from plants that could be used for feeding humans and animals, and growing plants for starch production use valuable farming land that could be used for food production instead. Therefore, it would be beneficial to find new stabilizers for polymer dispersions.

[0007] Cationic surface size polymer dispersions are used for hydrophobation in paper and paperboard manufacturing. Commonly used surface size compositions are polystyrene acrylates in aqueous dispersion including acetic acid as a cosolvent. Acetic acid is used in the first stage of the polymerisation to make a stabilizer polymer of tertiary amine (meth)acrylates and styrene, followed by a polymerisation of styrene and alkyl acrylates to form the surface size dispersion. The amount of acetic acid is typically 5 - 10weight-% contributing to volatile organic compounds (VOCs) and unpleasant odour of the product. Therefore, it would also be beneficial to find new ways to produce aqueous polystyrene acrylate dispersions, which are not stabilized with acetic acid.

[0008] Summary of the Invention

[0009] It is an object of the present invention to reduce or even eliminate the above-mentioned problems appearing in prior art.

[0010] An object of the present invention is to provide polymer dispersions which are stabilized by using a novel stabilizing agent.

[0011] An object is also to provide a polymer dispersion, which provides improved performance when used as a sizing agent or as a component in a sizing composition in paper or paperboard manufacturing.

[0012] These objects are attained with the invention having the characteristics presented below in the characterising parts of the independent claims.

[0013] Some preferred embodiments of the invention are presented in the dependent claims.

[0014] All the described embodiments and advantages apply all aspects of the present invention, i.e. the use of the prepolymer of polyaminoamideepichlorohydrin (PAE), the polymer dispersion and its use, when applicable, even if not always explicitly stated so.

[0015] A typical polymer dispersion according to the present invention comprises an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase, and a stabilizing agent in an amount of 25 - 50 weight-%, calculated from the total weight of polymer dispersion as dry, the stabilizing agent comprises a prepolymer of polyaminoamide-epichlorohydrin (PAE).

[0016] A polymer dispersion according to the present invention is typically used in a manufacture of a fibrous web, such as a paper, paperboard or the like. In a typical embodiment according to the present invention, a polymer dispersionis used as a sizing agent or a component in a sizing composition, preferably a surface sizing agent or a component in a surface sizing composition.

[0017] A typical use according to the present invention of a prepolymer of polyaminoamide-epichlorohydrin (PAE), is as a stabilizing agent in a polymer dispersion comprising polymer particles dispersed in an aqueous liquid phase.

[0018] Now it has been found that a polymer dispersion can be effectively stabilized by using a prepolymer of polyaminoamide-epichlorohydrin (PAE) wet strength resin. According to the present invention, a prepolymer of PAE refers to polyamidoamine (PAIM), and / or an adduct (PAE-CLH) obtained by reacting a polyamidoamine (PAIM) with epichlorohydrin. The polyamidoamine epichlorohydrin adduct PAE-CLH refers to a polymer before the ring-closure and cross-linking steps in wet strength PAE synthesis. Furthermore, it has been found that the use of a prepolymer of polyaminoamide-epichlorohydrin (PAE), when used as a stabilizing agent during polymerisation, may provide the polymer dispersion, which is advantageous for practical applications, e.g. in sizing of paper, board or the like.

[0019] According to one preferable embodiment of the present invention, a prepolymer of polyaminoamide-epichlorohydrin (PAE) is used as a stabilizing agent in the polymer dispersion of alkyl acrylates and styrene. The present invention eliminates the need to use acetic acid or other organic cosolvent in polymerisation of polystyrene acrylate dispersions. The surface sizing performance has been tested to be similar or even better with the polystyrene acrylate dispersions according to the present invention as the reference product containing acetic acid as a cosolvent.

[0020] A polymer dispersion according to the present invention is cost-efficient and easy to produce. In the present invention, there is no need for starch as stabilizing agent.Detailed description of the invention

[0021] The polymer dispersion comprising an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase can be obtained or formed by using conventional techniques. A polymer dispersion may be formed by polymerising suitable monomers in an aqueous liquid phase, wherein the polymerisation leads to formation of polymer particles dispersed in the aqueous liquid phase. The forming of polymer particles may be performed either at an elevated pressure or at atmospheric pressure.

[0022] According to the present invention, the prepolymer of polyaminoamideepichlorohydrin (PAE) is present in the aqueous liquid phase during the polymerisation of monomers into the polymer particles, as the stabilizing agent. The prepolymer of polyaminoamide-epichlorohydrin (PAE) is added to the aqueous liquid phase, where the polymerisation is conducted. Typically, the prepolymer of polyaminoamide-epichlorohydrin (PAE) is added to the aqueous liquid phase before the polymerisation and / or at the beginning of the polymerisation. In this manner polymer dispersions with advantageously small particle size are easily and effectively obtained. Preferably, the prepolymer of polyaminoamide-epichlorohydrin (PAE) is a sole stabilizing agent present during the radical polymerisation. In addition to the prepolymer of polyaminoamide-epichlorohydrin (PAE) as the stabilizing agent, the aqueous liquid phase typically also comprises an acid for controlling pH of the dispersion during the polymerisation, for example sulphuric acid can be used for adjusting pH. According to one embodiment, the aqueous liquid phase is free of starch.

[0023] According to the present invention, a prepolymer of polyaminoamide-epichlorohydrin (PAE) comprises or consisting of polyamidoamine (PAIM), and / or an adduct (PAE-CLH) obtained by reacting polyamidoamine (PAIM) with epichlorohydrin. The polyamidoamine-epichlorohydrin adduct PAE-CLH refers to a polymer before the ring-closure and cross-linking steps in wet strength PAE synthesis. In one preferred embodiment of the invention, the polyamidoamine-epichlorohydrin adduct PAE-CLH does not contain covalently bound azetidinium groups. A prepolymer of polyaminoamide-epichlorohydrin suitable for use in the present invention comprises the water-soluble polyamide, which is obtained by reacting the dibasic carboxylic acidwith the polyalkylene polyamine, under conditions such as to produce a water-soluble polyamide containing the recurring groups

[0024] — NH(CnH2nNH)x— CORCO—

[0025] where n and x are each 2 or more, and R is a divalent hydrocarbon of the dibasic carboxylic acid. The dicarboxylic acids may be dibasic carboxylic acids containing from 3 to 10 carbon atoms such as succinic acid, glutaric acid, adipic acid, azelaic acid and the like, and / or dibasic acids having from 4 to 8 carbon atoms in the molecule such as adipic acid and glutaric acid. According to one preferred embodiment, the dicarboxylic acids may be saturated dibasic carboxylic acids containing from 3 to 10 carbon atoms, and / or saturated dibasic acids having from 4 to 8 carbon atoms in the molecule. Blends of two or more dibasic carboxylic acids may also be used, preferably blends of two or more saturated dibasic carboxylic acids. A variety of polyalkylene polyamines including polyethylene polyamines, polypropylene polyamines, polybutylene polyamines, polypentylene polyamines, polyhexylene polyamines and any combinations thereof may be employed. Preferably, polyethylene polyamines, such as diethylenetriamines are used. The water-soluble polyamide may comprise also monocarboxylic acid such as hexanoic acid or octanoic acid or tricarboxylic acid such as citric acid, or other amines than polyamines, for example diethylamine, diisopropylamine, piperazine, or aminoethylpiperazine. The amount of the other components than dicarboxylic acids and polyalkylene polyamines is typically less than 5 weight-% of polyamide. Preferably, the water-soluble polyamide is essentially free of the other components, such as monocarboxylic acids. According to the present invention, the prepolymer of polyaminoamide-epichlorohydrin comprises a water-soluble polyamide from dibasic carboxylic acid and polyalkylene polyamine, optionally reacted with epichlorohydrin. There is no reaction with monocarboxylic acids. The polyamidoamino is typically not further modified, such as hydrophobized and / or cationized.

[0026] The polyamidoamine-epichlorohydrin adduct PAE-CLH is obtained by reacting the polyamidoamine (PAIM) with epichlorohydrin. The PAE-CLH is the polymer obtained before the ring-closure and cross-linking steps in wet strength PAE synthesis.According to an embodiment of the present invention, the prepolymer of polyaminoamide-epichlorohydrin (PAE) comprises < 1000 ppm, preferably < 500 ppm, more preferably < 300 ppm of impurities, such as residuals of the polymer synthesis, which include epichlorohydrin, 1,3-dichloro-2-propanol, 2, 3-dichloro-1 -propanol, and 3-monochloro-1,2-propanediol. In an embodiment according to the present invention, the prepolymer of polyaminoamide-epichlorohydrin (PAE) is membrane-filtrated prior to use as the stabilizing agent of the polymer dispersion, to remove impurities. According to an embodiment of the invention the membrane has pore size smaller than 1 pm. Advantageously the pore size is 9 x10’3to 7 x10’3pm, more advantageously 9 x 10’5to 7 x 10’3pm.

[0027] According to the present invention, a prepolymer of polyaminoamide-epichlorohydrin (PAE), i.e. water-soluble polyamidoamine (PAIM) and / or an polyamidoamine-epichlorohydrin adduct PAE-CLH is used as the stabilizing agent of the polymer dispersion.

[0028] According to an embodiment of the present invention, the prepolymer of polyaminoamide-epichlorohydrin (PAE) has a viscosity of < 200 mPas, preferably in a range of 1 - 200 mPas, measured at 20 °C with Brookfield DVEELVTJ0 viscometer, in a small sample adapter with spindle 61 at 100 rpm, measured at solids content of 20-30 weight-%.

[0029] The prepolymer of PAE is stable at high solid content. According to the present invention, the polymer dispersion comprises the prepolymer of polyaminoamide-epichlorohydrin (PAE), as the stabilizing agent, in an amount of 25 - 50 weight-%, preferably 30 - 45 weight-%, calculated from the total weight of polymer and stabilizing agent, as dry.

[0030] According to an embodiment of the present invention, the prepolymer of PAE comprising polyamidoamine (PAIM), and / or an adduct (PAE-CLH) obtained by reacting polyamidoamine (PAIM) with epichlorohydrin, has cationic charge of <0.5 meq / g dry measured at pH > 9.5 by colloidal titration, such as Mutek PCD 05 particle charge detector. The cationic charge may affect stability of the final product and therefore it is advantageous that the cationicity of the prepolymer of PAE is <0.5 meq / g dry, measured at pH > 9.5 by colloidal titration. According to one preferred embodiment of the present invention,the prepolymer of PAE comprising polyamidoamine (PAIM), and / or an adduct (PAE-CLH) obtained by reacting polyamidoamine (PAIM) with epichlorohydrin, is non-cationized. According to an embodiment of the present invention, the prepolymer of PAE has an acid index in the range IQ-30 mg KOH Zg product.

[0031] The aqueous liquid phase of polymer dispersion according to one preferred embodiment of the present invention may not comprise any other additional solvents other than water. According to one preferred embodiment of the present invention, the polymer dispersion is free of any organic solvents. According to an embodiment of the present invention, the aqueous liquid phase may comprise some impurities from degradation of monomers, for example organic alcohols, or solvents of other additives. The amount of the impurities may be less than 0.5 weight-%, calculated from the total weight of the aqueous liquid phase.

[0032] According to one preferable embodiment of the present invention the prepolymer of PAE may be used as the stabilizing agent in a polymer dispersion which comprises or consists of hydrophobic polymer particles obtained by radical polymerisation of one or more vinyl monomers comprising alkyl (meth)acrylates. The polymer dispersion may be obtained by a radical polymerisation of alkyl (meth)acrylate, for example C1-C8 alkyl (meth)acrylate, preferably C1-C4 alkyl (meth)acrylate, and any of their mixtures, as described below. Alternatively, the polymer dispersion may be obtained by a radical polymerisation of several, such as two, three or more, different vinyl monomers, of which at least one is alkyl (meth)acrylate. Preferably the polymer dispersion is obtained by a radical polymerisation of two or three different vinyl monomers, of which at least one is alkyl (meth)acrylate.

[0033] The polymer dispersion may comprise polymer particles, which are obtained by a radical polymerisation of vinyl monomers, such as alkyl (meth)acrylate, in the presence the prepolymer of PAE as a stabilising agent. According to an embodiment, the polymer dispersion comprises polymer particles, which are obtained by a radical polymerisation of vinyl monomers comprising alkyl (meth)acrylate, in the presence of the prepolymer of polyaminoamideepichlorohydrin (PAE) as a stabilizing agent. According to one preferableembodiment, the polymer dispersion may be obtained by a radical polymerisation of at least one first monomer (a) which is selected from C1-C8 alkyl (meth)acrylates and any of their mixtures; and optionally at least one second monomer (b) which is selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures.

[0034] According to one embodiment of the present invention the vinyl monomers may comprise at least one first monomer (a) which is selected from alkyl (meth)acrylates, such as C1-C8 alkyl (meth)acrylates, preferably C1-C4 alkyl (meth)acrylates, and any of their mixtures. Suitable first monomer (a) may be, for example, methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; n-propyl or iso-propyl acrylate and corresponding propyl methacrylates; n-butyl, iso-butyl, tert-butyl or 2-butyl acrylate and the corresponding butyl methacrylates; n-pentyl or neopentyl acrylate and the corresponding pentyl methacrylates; 2-hexyl or 2-ethylhexyl acrylate and corresponding methacrylates; n-octyl or isooctyl acrylate and corresponding methacrylates. According to one preferable embodiment the monomer (a) is selected from butyl (meth)acrylates. The first monomer (a) may be selected from C1-C4-alkyl acrylates, C1-C4-alkyl methacrylates or any of their mixtures, e.g. n-butyl, iso-butyl, tert-butyl or 2-butyl acrylate and the corresponding butyl methacrylates; 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.

[0035] According to one embodiment of the present invention the vinyl monomers may comprise at least one second monomer (b) which may be selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures.

[0036] The polymer dispersion may be obtained by radical polymerisation of 20 -100 weight-%, preferably 40 - 100 weight-%, more preferably 40 - 85 weight-% of the first monomer (a), and 0 - 80 weight-%, preferably 0 - 60 weight-%, more preferably 15 - 60 weight-% of the second monomer (b), calculated from the total dry solids content of the monomers (a) and (b). Insome embodiments according to the present invention, the polymer dispersion may be obtained by radical polymerisation of 40 - 60 weight-%, preferably 50 - 60 weight-% of the first monomer (a), and 40 - 60 weight-%, preferably 40 - 50 weight-% of the second monomer (b).

[0037] According to one embodiment of the invention the polymer particles in the polymer dispersion may be obtained by radical copolymerisation of at least first monomers (a), second monomers (b) and at least one third monomer (c), which is ethylenically unsaturated and different from first monomer (a) and second monomer (b) present simultaneously. Suitable ethylenically unsaturated third monomers (c) are ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic and methacrylic acid with alcohols which have more than four C atoms, and further acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate or anionic comonomers, such as acrylic acid, methacrylic acid, styrene sulphonic acid. Ethylhexyl acrylate and methacrylic acid may be preferred as third monomer (c). The amount of third monomer (c) may be 0 - 10 weight-%, preferably 0 - 5 weight-% calculated from the total dry solids content of the monomers (a), (b) and (c).

[0038] According to one embodiment of the present invention the prepolymer of PAE may be used as the stabilizing agent in a radical polymerisation, where at least one polymerisation regulator is employed. The one or more polymerisation regulators, such as chain transfer agents, may be introduced to the polymerisation reaction simultaneously, but separately, with the monomer feed(s), or as mixed into at least one of the monomer feed(s). Suitable polymerisation regulators may be, for example, sulphur compounds, e.g. mercaptans.

[0039] The radical polymerisation, during which the prepolymer of PAE is present as a stabilizing agent, may be carried out in the presence of a free radical initiator. Suitable free radical initiators may be, for example, peroxides such as hydrogen peroxide, sodium peroxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate, or tert-butyl hydroperoxide. Peroxide initiator is usually used as part of a redox initiator system comprising also a reducing agent. Suitable combinations for the redox initiator systems comprising a peroxide may comprise, for example, ascorbic acid, and a heavy metal cation, such as iron, manganese, or cerium ions.The radical polymerisation process may also comprise an additional postpolymerisation step, after termination of the monomer and initiator feed(s). During the post-polymerisation step the amount residual monomers in the obtained polymer dispersion is further reduced, for example, by addition of further initiator amount or a second initiator.

[0040] The radical polymerisation may be performed at a temperature in range of 50 - 100 °C, preferably 70 - 98 °C, more preferably 80 - 97 °C, to ensure the polymerisation of the monomers into small particle size polymer dispersion and low residual monomer level. In one preferable embodiment, the pH is adjusted to be in <3 during the polymerisation of polymer dispersion for avoiding crosslinking steps in PAE synthesis.

[0041] In a typical method for producing a polymer dispersion according to the present invention, the method comprises two-stage polymerisation process. In the first stage, a prepolymer of PAE wet strength resin comprising polyamidoamine (PAIM) or polyamidoamine-epichlorohydrin adduct PAE-CLH is polymerised. In the second stage the polymer particles are polymerised in the presence of the said prepolymer of PAE. PAIM and PAE-CLH are stable over time and there are no need to run both steps right one after another.

[0042] According to an embodiment of the present invention, the polymer dispersion comprises polymer particles, which have a particle size D10 < 100 nm. The polymer dispersion may comprise polymer particles having a particle size D50 < 150 nm, preferably < 125 nm. The particle size D50 for the polymer particles of the dispersion may be, for example, in a range of 10 - 150 nm, preferably 10 - 125 nm. The polymer dispersion may comprise polymer particles, which have a particle size D90 < 250 nm, preferably < 200 nm. The particle size D90 for the polymer particles of the dispersion may be, for example, in a range of 10 - 250 nm, preferably 50 - 200 nm. The polymer dispersion may comprise polymer particles, which have a particle size D95 < 350 nm. All particle sizes are measured by using Dynamic Light Scattering Particle Size Distribution Analyzer. In the present context D10, D50, D90 and D95 are so-called percentile values. These are statistical parameters that can be read from a volume-based cumulative particle size distribution. Theyindicate the size below which 10%, 50%, 90% or 95% of all particles are found.

[0043] The obtained polymer dispersion may have a solids content of at least 5 weight-%, preferably at least 15 weight-%. According to one embodiment the solids content of the polymer dispersion may be in a range of 5 - 60 weight-%, preferably 15 - 50 weight-%, even more preferably 20 - 40 weight-%.

[0044] According to an embodiment of the present invention, the obtained polymer dispersion has a cationic charge in a range of 0.25 - 2.0 meq / g (dry), measured at pH 7 by colloidal titration, such as Mutek PCD 05 particle charge detector.

[0045] According to an embodiment of the present invention, the polymer dispersion has glass transition temperature (Tg) in a range from -20 °C to +90 °C, preferably from 0 °C to +70 °C, more preferably from +20 °C to +70 °C, measured by a differential scanning calorimeter (DSC).

[0046] In one embodiment pH of the aqueous polymer dispersion according to the present invention is 3 - 7, preferably 3 - 6, more preferably 3 - 5 measured at 20 °C.

[0047] In one embodiment viscosity of the aqueous polymer dispersion according to the present invention is < 500 mPas, such as 1 - 500 mPas or 1 - 100 mPas or 1 - 50 mPas. The viscosity values are measured at 20 °C, with Brookfield DVEELVTJ0 in a small sample adapter with spindle 61 at 100 rpm viscometer at solids content of 20 - 30 weight-%.

[0048] The polymer dispersion according to the present invention may contain in addition to the stabilizing agent comprising the prepolymer of PAE also other additives, such as defoamers, co-surfactants, plasticizers, biocides and / or pH adjustment chemicals.

[0049] The polymer dispersion according to the present invention stabilized with the prepolymer of PAE is especially suitable for use in a manufacture of a fibrous web, such as paper, board, tissue, non-woven or other cellulosic product. The polymer dispersion may be used as a sizing agent or as a component ina sizing composition for paper or paperboard. Especially, the polymer dispersion may be used as a surface sizing agent or as a component in a surface sizing composition for paper or paperboard. A method according to an embodiment of the present invention for producing a surface sized paper or paperboard comprises applying a polymer dispersion according to the present invention as a surface size into a paper or paperboard. The polymer dispersion of the present invention may improve the barrier properties, such as water resistance, of the formed paper or paperboard. It has been observed that the use of the prepolymer of PAE provides the polymer dispersion with hydrophobic properties.

[0050] According to an embodiment of the present invention, a polymer dispersion may be used in combination of metal salts. Examples of metal salts are selected from the group aluminium sulfate, alum, aluminium chloride, aluminium nitrate, polyaluminium sulfate (PAS), polyaluminium chloride (PAC), and polyaluminium chloride sulfate (PACS), polyaluminium formiate, polyaluminum nitrate, and any combination thereof. Preferred metal salts are polyaluminium sulfate, aluminium sulfate, and / or polyaluminium chloride.

[0051] A surface sizing composition comprising the polymer dispersion according to the present invention may further comprise polysaccharide such as starch and / or starch derivative. The starch may be modified starch, for example, degraded, oxidized or cationized starch, or dextrin. Typically, the polymer dispersion of the present invention may be applied on the paper or paperboard surface mixed with a solution of starch and / or starch derivative. The starch and / or starch derivative concentration in the surface sizing composition may be in the range of 1 - 30 weight-%, preferably 5 - 25 weigh-%, more preferably 8 -20 weight-%. The concentration of the polymer dispersion as dry content may be 0.1 - 20 weight-%, preferably 0.5 - 5.0 weight-%, based on the weight of dry starch. The dosage of the polymer dispersion according to the present invention may be from 0.1 to 20% by weight, preferably from 0.2 to 10.0 weight-%, even more preferably from 0.5 to 8 weight-%, based on the weight of dry starch. The polymer dispersion according to the present invention may be applied also without starch or starch derivative.The surface sizing composition may further comprise other additives used in surface sizing of paper, paperboard and other cellulosic products. Such additives include, but are not limited to, dispersing agents, antifoaming agents, colorants, inorganic pigments, rheology modifiers and antistatic agents.

[0052] The surface sizing composition may be provided as a liquid or a foam. For instance, the sizing composition may be applied to the surface of the paper, paperboard or other cellulosic product using a puddle or film size press or curtain application. Alternatively, the sizing composition may be sprayed onto the fibrous web. The paper, paperboard or other cellulosic product is typically dried after the surface sizing composition is applied.

[0053] Surface sizing composition comprising the polymer dispersion according to the present invention is particularly suitable for surface sizing of cellulosic products when the cellulosic product comprises recycled fibres.

[0054] EXPERIMENTAL

[0055] Some embodiments of the invention are described more closely in the following examples. Examples 1 and 2 describe the methods for producing a polymer dispersion according to the present invention. Example 3 is an application example for using a polymer dispersion according to the present invention as a surface sizing agent.

[0056] Methods

[0057] The following measurement methods and conditions have been used in the examples:

[0058] The viscosity values are measured at 20 °C, with Brookfield DVEELVTJ0 viscometer, in a small sample adapter with spindle 61 at 100 rpm, measured at solids content of 20 - 30 weight-%.

[0059] pH values are measured at 20 °C by using laboratory pH meter.The particle size measurements are done by using with Dynamic Light Scattering Particle Size Distribution Analyzer Horiba LB 500.

[0060] The glass transition temperatures (Tg) are measured by using DSC device.

[0061] Cationic charges are measured with particle charge detector Mutek PCD 05.

[0062] Dry contents are calculated based on the measurements before and after the drying: 1 g, 1 h at 125°C.

[0063] PAIM acid index is measured by a titration method using methanol and propanol as solvents and tetrabutylammonium hydroxide as titration agent.

[0064] Example 1: PAIM as a stabilizer

[0065] At first polyamidoamine (PAIM) is synthetized in the following manner. Diethylenetriamine (DETA) and adipic acid are mixed under stirring in water (1% of adipic acid amount) in a glass reactor. The ratios of raw materials are 58 weight-% of adipic acid and 42 weight-% of DETA. The reaction is exothermic, and temperature increases up to 130 °C. When no more exothermic reaction is observed, external heating is switched on. Heating is continued with the following manner (temperature / holding time): 130 °C / 1h, 152 °C / 1h, 157 °C / 1h, 162 °C / 1h, 168 °C / 1h and 170 °C / 1h. When 92 % of theoretical water is distilled, the external heating is switched off. Water is added to decrease the solids from 100 % to about 45%. Agitation is continued at least 30 min.

[0066] The properties of the obtained PAIM are measured. The properties are presented in Table 1 below.

[0067] Table 1. PAIM properties.

[0068]

[0069] After PAIM synthesis, the polymer dispersion of alkyl acrylates and styrene is prepared by using PAIM as a stabilizing agent. PAIM is mixed with water under stirring (350 rpm for 10 min) in a double jacket reactor. The final dry content of the mixture is adjusted between 9.0 - 11.0 %. pH of this PAIM mixture is adjusted to pH 3.0 with 38% sulphuric acid. The PAIM mixture is heated to 85 °C. 0.13 g of heptahydrate iron sulphate is added to the reactor. Hold time is 5 min. A feed of 3.8 g of hydrogen peroxide 50 % is started to the reactor and continued for 165 min on a constant feed rate. Then after 15 min from the beginning of hydrogen peroxide feed, the monomer mixture including styrene, tert-butyl acrylate, n-butyl acrylate and n-dodecyl mercaptan (n-ddm; chain transfer agent), is fed to the reactor during 120 min at a constant feed rate. The amounts of PAIM, styrene, tert-butyl acrylate, n- butyl acrylate and n-ddm are presented at Table 2.

[0070] The reactor temperature is kept at 85 °C during these feeds. After that the obtained polymer dispersion is cooled to a room temperature, followed by pH adjustment to pH 3.8 with 25% sodium hydroxide. The properties of the obtained polymer dispersion are measured. The properties are presented in Table 3 below.

[0071] Table 2. The amount of PAIM and monomers used in the polymer dispersions

[0072]

[0073] Table 3. Properties of the polymer dispersions having PAIM as a stabilizer.

[0074]

[0075] Example 2: PAE-CLH as a stabilizer

[0076] At first PAIM is synthesized as described in Example 1. 250g of the obtained PAIM is added under stirring in a glass reactor with a cooling / heating jacket. Temperature is fixed at 15 °C. Epichlorohydrine (ECH) is added to the reactor a feed rate of 1.64 ml / min and continued for 30 minutes. Temperature is controlled to be below 20 °C. When ECH addition is completed, the mixture is left T< 20°C for 21 hours. 385g of water purified by reverse osmosis is added. The properties of the obtained PAE-CLH are measured. The properties are presented in Table 4 below.

[0077]

[0078] After PAE-CLH synthesis, the polymer dispersion of alkyl acrylates and styrene is prepared by using PAE-CLH as a stabilizing agent. The method for producing polymer dispersion of alkyl acrylates and styrene is performed as described in Example 1, only difference is that PAE-CLH is used as a stabilizing agent instead of PAIM. The amounts of PAE-CLH, styrene, tert-butyl acrylate, n-butyl acrylate and n-ddm are presented as Table 5. The properties of the obtained polymer dispersions are measured. The properties are presented in Table 5 below.

[0079] Table 5. The amount of PAE-CLH and monomers used in the polymer dispersions

[0080]

[0081] Table 6. Properties of the polymer dispersions having PAE-CLH as a stabilizer.

[0082]

[0083] Example 3

[0084] Surface sizing of linerboard was done with nonionic starch on a laboratory puddle size press. The reference product was an aqueous dispersion of poly(styrene butyl acrylate) stabilized with a polymer of styrene, 3- dimethylaminopropyl methacrylamide (D MAP MA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The reference dispersion contained 9 weight-% of acetic acid as a cosolvent. The products according to the invention were Example 1.1 (including PAIM emulsifier) and Example 2.1 (including PAE- CLH emulsifier).Sizing performance of the surface size compositions were tested on an internally unsized recycled fibre linerboard, which had a base weight of 140 g / m2. The sheets were run through Mathis horizontal pond size press type 5607 at 2 m / min (2 Bar). The temperature of surface size composition and the size press nip was adjusted to 65 °C. The sheets were dried at 95 °C using an AMC drum dryer at speed 50, giving drying time of 1.5 minutes. Sizing efficiency was determined by measuring Cobbeo sizing degree according to standard ISO 535.

[0085] Sizing performance of the polymer dispersions was tested with and without polyaluminum chloride.

[0086] Surface size compositions were prepared by dissolving starch (C*Film 07312) first into water according to conventional starch cooking procedure. The starch solution was then mixed with a polymer dispersion to be tested. For each polymer dispersion three different dosages 1 weight-%, 2 weight-%, 3 weight-% were tested, the percentages calculated from weight of dry starch. The starch concentration was 12 weight-%. The tested polymer dispersions can be seen in Table 7 as well as the sizing results, given as Cobbeo g / m2values. Cobbeo indicates water absorption capacity of the sample, smaller values are better. The polymer dispersions used in this Example are the same as prepared in the preceding polymer dispersion examples. Polyaluminum chloride (PAC), when used as indicated in Table 7, was added to the surface size composition in amount of 1 weight-%, calculated from dry starch, prior to the surface sizing.

[0087] It can be seen from Table 7 that the polymer dispersions according to the invention provide at least similar or even better sizing performance than the reference polymer dispersion.able 7. Sizing performance results.

[0088]

[0089] * weight-% of starch as dry solids

Claims

Claims1. A polymer dispersion, which comprises an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase, characterised in that the polymer dispersion further comprises a stabilizing agent in an amount of 25 - 50 weight-%, calculated from the total weight of polymer dispersion as dry, the stabilizing agent comprises a prepolymer of polyaminoamide-epichlorohydrin (PAE).

2. Polymer dispersion according to claim 1, characterised in that the prepolymer of PAE comprises polyamidoamine (PAIM) and / or an adduct (PAE-CLH) obtained by reacting a polyamidoamine (PAIM) with epichlorohydrin.

3. Polymer dispersion according to claim 1 or 2, characterised in that the polymer dispersion comprises the stabilizing agent in an amount of 30 - 45 weight-%, calculated from the total weight of polymer dispersion, as dry.

4. Polymer dispersion according to any one of preceding claims, characterised in that the prepolymer of PAE has cationic charge of <0.5 meq / g dry, measured at pH > 9.5 by colloidal titration.

5. Polymer dispersion according to any one of preceding claims, characterised in that the polymer dispersion comprises polymer particles, which are obtained by a radical polymerisation of vinyl monomers comprising alkyl (meth)acrylate, in the presence of the prepolymer of polyaminoamide-epichlorohydrin (PAE) as a stabilizing agent.

6. Polymer dispersion according to claim 5, characterised in that the vinyl monomers comprise at least one first monomer (a) which is selected from C1 - C8 alkyl (meth)acrylates and any of their mixtures.

7. Polymer dispersion according to claim 6, characterised in that the monomer (a) is selected from butyl (meth)acrylates.

8. Polymer dispersion according to any one of the preceding claims 5 - 7, characterised in that the vinyl monomers comprise at least one secondmonomer (b) which is selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures.

9. Polymer dispersion according to any one of the preceding claims 5 - 8, characterised in that the vinyl monomers comprise 0 - 100 weight-%, preferably 40 - 100 weight-%, more preferably 40 - 85 weight-% of the first monomer (a), and 0 - 80 weight-%, preferably 0 - 60 weight-%, more preferably 15 - 60 weight-% of the second monomer (b), calculated from the total dry solids content of the monomers (a) and (b).

10. Polymer dispersion according to any one of the preceding claims 6 - 9, characterised in that the polymer particles are obtained by radical polymerisation of at least the first monomers (a), the second monomers (b) and at least one third monomer (c), which is ethylenically unsaturated and different from the first monomers (a) and the second monomers (b).

11. Polymer dispersion according to any one of preceding claims, characterised in that the polymer dispersion has a cationic charge in a range of 0.25 - 2.0 meq / g (dry), measured at pH 7 by colloidal titration.

12. Polymer dispersion according to any one of preceding claims, characterised in that the polymer dispersion comprises polymer particles having a particle size D50 <150 nm, preferably <125 nm, and / or a particle size D90 <250 nm, preferably <200 nm.

13. Use of a polymer dispersion according to any one of claims 1 - 12 in a manufacture of a fibrous web, such as paper, paperboard or the like.

14. Use according to claim 13, characterised in that the polymer dispersion is used as a sizing agent or a component in a sizing composition, preferably a surface sizing agent or a component in a surface sizing composition.

15. Use of a prepolymer of polyaminoamide-epichlorohydrin (PAE) comprising polyamidoamine (PAIM) and / or an adduct obtained by reacting a polyamidoamine (PAIM) with epichlorohydrin (PAE-CLH), as a stabilizingagent in a polymer dispersion comprising polymer particles dispersed in an aqueous liquid phase.

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