A sizing composition for paper or cardboard

Abstract

The present invention relates to a surface sizing composition of paper or cardboard, as well as a sizing method using said composition. This sizing composition comprises a polymer of at least one hydrophobic monomer and one polyvinyl amine.

Description

[0001] A sizing composition for paper or cardboard

[0002] Technical field of the invention

[0003] The present invention relates to a paper or cardboard sizing composition, as well as a sizing method by using said composition.

[0004] Prior art

[0005] The paper industry is constantly working on improving its methods for manufacturing paper, cardboard and the like, in particular, regarding cost reduction, yield, productivity, or also the properties of the final product.

[0006] This is particularly the case for the packaging industry that is working on improving the performance of paper, cardboard and the like, including resistance to liquids (such as water, oils and greases) and printability, so as to meet current ecological challenges by replacing plastic packaging.

[0007] One of the main problems encountered with paper or cardboard packaging is the tendency of cellulosic fibres to absorb liquids. This results in a decrease in the strength properties of the paper or cardboard under humid conditions, and ink diffusion during printing, leading to a blurred or flowing pattern.

[0008] To counter this phenomenon, the paper or cardboard undergoes a sizing step, giving it a barrier effect against liquids.

[0009] The purpose of sizing is therefore double (1) by allowing increased moisture resistance and (2) by allowing the inks to remain on the surface of the paper or cardboard and to dry on it, rather than being absorbed.

[0010] There are two kinds of sizing, internal sizing and surface sizing. The main purpose of internal sizing is to improve moisture resistance, whereas the main purpose of surface sizing is to improve printability.

[0011] In the case of internal sizing, the sizing agent is added during the formation of the sheet of paper or cardboard, whereas, in the case of surface sizing, the sizing agent is applied in the form of a liquid composition onto the surface of paper or cardboard strips. Historically, the sizing agent is starch, that improves the strength properties and smoothes the surface of paper or cardboard. However, starch is hydrophilic, reducing the moisture resistance of paper or cardboard.

[0012] WO 98 / 32920 discloses a paper surface sizing composition comprising starch, a water-soluble polymer and a water-insoluble polymer. US 2007 / 167558 teaches a sizing composition comprising a cationic polymer having vinylamine units, an anionic dispersant and an alkyldiketene. WO 2005 / 012639 teaches a sizing composition comprising an aqueous mixture comprising of starch, an anionic polymer, and a cationic polymer. US 2012 / 0073774 relates to reducing stickies in the drying section of a papermaking method, wherein the following additives are added to the paper stock: (a) a water-soluble cationic polymer and (b) a polymer sizing agent.

[0013] Therefore, solutions have been developed which combine starch with hydrophobing agents. The most common hydrophobing agents are alkenyl succinic anhydride (ASA) and alkyl ketene dimer (AKD). Apart from these compounds, synthetic polymers have also been developed, among the most common examples are polystyrenes, in particular, polystyrene acrylate emulsions (SAE), polystyrene maleic anhydride polymers (SMA), styrene acrylic acid polymers (SAA) or polyurethane dispersions (PUD). Among these hydrophobing agents, alkenyl succinic anhydride (ASA) and alkyl ketene dimer (AKD) are mainly used for internal sizing, whereas synthetic polymers are mainly used for surface sizing, with polystyrene acrylate (SAE) emulsions being the most common.

[0014] The Applicant has discovered a new sizing composition providing better liquid resistance properties (such as water, oils or greases) and printability to paper or cardboard. The composition combines a hydrophobic polymer and a polyvinyl amine.

[0015] In addition, polyvinyl amine may partially replace the hydrophobic polymer, making it possible, during the recycling of the paper or cardboard obtained by sizing the composition according to the invention, to confer to the latter, better properties of repellency and mechanical strength, because polyvinyl amine remains fixed on recycled cellulose fibres, unlike the hydrophobic polymer, that, because of its hydrophobic nature, will tend to form insoluble aggregates of adhesive particles (“stickies"). Replacing a portion of the hydrophobic polymer with polyvinyl amine therefore also makes it possible to reduce the formation of stickies which are harmful during the preparation of recycled paper or cardboard. The composition of the invention therefore makes it possible to improve the liquid resistance properties (such as water, oils or greases) and printability, and also to improve the recycling of paper or cardboard that has undergone a sizing step.

[0016] The present invention falls under a principle of environmental awareness and of the impact of industries and mankind on the planet. Thanks to the sizing composition of the invention, it is possible to reduce the quantity of polymer used to obtain performance equivalent to prior art solutions, thus reducing greenhouse gas emissions such as CO2 associated with the manufacture of synthetic polymers.

[0017] Disclosure of the invention

[0018] The present invention relates to a paper or cardboard sizing composition comprising at least: [a] a polymer S2comprising at least 40 mol% of at least one hydrophobic monomer A selected from the group consisting of: i) monomers of formula I: wherein Ri and R2 are, independently, selected from the group consisting of a hydrogen atom, an alkyl chain of 1 to 4 carbon atoms, and a halogen (F, Cl, Br, I); ii) (meth)acrylic acid ester monomers; iii) vinyl ester monomers (-C=C-O-C(=O)-); iv) their mixtures;

[0019] [b] a polyvinyl amine.

[0020] The weight ratio between polymer S2and polyvinyl amine is between 55 / 45 and 99 / 1 and the weight-average molecular weight of the polyvinyl amine is between 30 000 and 300 000 g / mol. The monomer of formula I comprises a single R2 group, that is in the ortho, meta or para position with respect to the main substituent CRI=CH2.

[0021] The present invention also relates to a method for sizing paper or cardboard comprising the application of the sizing composition according to the invention on a sheet of paper or carboard.

[0022] Description of the invention

[0023] The term “sizing” means both sizing and bonding, each term being interchangeable.

[0024] The term “polymer” means a homopolymer prepared from a monomer or a copolymer prepared from at least two different monomers, monomers being selected from among: anionic hydrophilic monomers, cationic hydrophilic monomers, non-ionic hydrophilic monomers, zwitterionic hydrophilic monomers, hydrophobic monomers, and their mixtures.

[0025] The term “molecular weight” relates to the weight-average molecular weight.

[0026] The term “hydrophilic monomer” means a monomer that has an octanol-water partition coefficient, Kow, less than or equal to 1, wherein the partition coefficient Kowis determined at 25°C in an octanol-water mixture with a volume ratio of 1 / 1, at a pH of between 6 and 8.

[0027] The term “hydrophobic monomer” means a monomer that has an octanol-water partition coefficient, Kow, greater than 1, in which the partition coefficient Kowis determined at 25°C in an octanol-water mixture with a volume ratio of 1 / 1, at a pH of between 6 and 8.

[0028] The octanol-water partition coefficient, Kow, represents the ratio of concentrations (g / L) of a monomer between the octanol phase and the aqueous phase. It is defined as follows:

[0029] > [monomeroctanolow[monomer]water

[0030] The term “water-soluble polymer” means a polymer that gives an aqueous solution without insoluble particle, when it is dissolved under stirring at 25°C and with a concentration of 10g. I'1in deionised water.

[0031] The term “X and / or Y” means, according to the invention, “X”, or “Y”, or “X and Y”. The invention also includes all possible combinations of the various embodiments disclosed, whether they are preferred embodiments or given by way of example. Furthermore, when ranges of values are indicated, the limit values are included in these ranges. The disclosure also includes all of the combinations between the limit values of these ranges of values. For example, the ranges of values “1-20, preferably 5-15” imply disclosure of the ranges “1-5”, “1-15”, “5-20” and “15-20” and the values 1, 5, 15 and 20.

[0032] The molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to a person skilled in the art and can be calculated from the reduced viscosity values for different polymer concentrations by a graphical method consisting in spotting the reduced viscosity values (y-axis) on the concentration (x-axis) and extrapolating the curve to zero concentration. The intrinsic viscosity value is spotted on the y-axis or by using the least-squares method. The molecular weight can then be determined using the Mark-Houwink equation: [r|] = K.M“

[0033] [q] represents the intrinsic viscosity of the polymer determined by the solution viscosity measurement method.

[0034] K represents an empirical constant.

[0035] M represents the molecular weight of the polymer, a represents the Mark-Houwink coefficient.

[0036] K and a depend on the particular polymer-solvent system.

[0037] All of the particular and / or preferred embodiments described in the invention may be combined provided that they are not incompatible.

[0038] Sizing composition

[0039] The present invention relates to a paper or cardboard sizing composition comprising at least: [a] a polymer S2comprising at least 40 mol% of a hydrophobic monomer A selected from: i) monomers of formula I:

[0040] wherein R1and R2are, independently, a hydrogen atom, an alkyl chain of 1 to 4 carbon atoms, or a halogen (F, Cl, Br, I); ii) (meth)acrylic acid ester monomers; iii) vinyl ester monomers (-C=C-O-C(=O)-); iv) their mixtures;

[0041] [b] a polyvinyl amine having a molecular weight of between 30 000 and 300 000 g / mol. The weight ratio between polymer S2and polyvinyl amine is between 55 / 45 and 99 / 1.

[0042] Polymer S2Polymer S2is a water-insoluble polymer.

[0043] The term “water-insoluble” means a polymer that, when placed in deionised water, does not completely dissolve and remains at least partly (at least 40% by weight) as solid particles in deionised water (after stirring for 1 hour at 200 rpm, at 25°C, and with a concentration of 5 g-L’1). Polymer S2may be non-ionic, cationic or anionic.

[0044] Polymer S2is obtained from at least 40 mol% of a hydrophobic monomer A selected from among: i) monomers of formula I:

[0045] wherein R1and R2are, independently, a hydrogen atom, an alkyl chain of 1 to 4 carbon atoms, or a halogen (F, Cl, Br, I); ii) (meth)acrylic acid ester monomers; iii) vinyl ester monomers (-C=C-O-C(=O)-); iv) their mixtures.

[0046] Hydrophobic monomer A is advantageously selected from (i) monomers of formula I, (ii) (meth)acrylic acid ester monomers, (iii) vinyl ester monomers (-C=C-O-C(=O)-), and (iv) their mixtures. The hydrophobic monomer may be of formula I: wherein R1and R2are, independently, a hydrogen atom, an alkyl chain of 1 to 4 carbon atoms, or a halogen (F, Cl, Br, I).

[0047] Advantageously, the hydrophobic monomer A of formula I is selected from styrene, ortho- chlorostyrene, meta-chlorostyrene, para-chlorostyrene, ortho-bromostyrene, meta- bromostyrene, para-bromostyrene, ortho-iodostyrene, meta-iodostyrene, para-iodostyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, ortho-ethyl styrene, metaethyl styrene, para-ethyl styrene, ortho-propyl styrene, meta-propyl styrene, para-propyl styrene, ortho-t-butyl styrene, meta-t-butyl styrene, para-t-butyl styrene, and their mixtures.

[0048] The quantity of hydrophobic monomer A of formula I in polymer S2is advantageously of at least 1 mol%, preferably of at least 5 mol%, more preferably of at least 10 mol%, even more preferably of at least 20 mol%; and advantageously of at most 99 mol%, preferably of at most 95 mol%, more preferably of at most 90 mol% and even more preferably of at most 80 mol% (with respect to the total quantity of monomers of polymer S2). It is advantageously of between 33 and 67 mol%, preferably between 40 and 60 mol%, more preferably between 45 and 55 mol%.

[0049] When the hydrophobic monomer A is a (meth)acrylic acid ester, it advantageously results from the reaction between (meth)acrylic acid and an alcohol having a Ci to C30 hydrocarbon group, preferably Ci to C25, more preferably Ci to C20, even more preferably Ci to C15, the hydrocarbon group of the alcohol may be saturated or unsaturated, linear, branched or cyclic, optionally substituted by one or more heteroatoms selected from among N, O, P and S, and / or optionally substituted by one or more groups selected from among acid, aryl, ester, amine, amide, carbamate, hydroxyl, ether (preferably C2 or C3 ether), nitrile, vinyl, allyl, thioether, sulphonic or halogen.

[0050] Advantageously, when the hydrophobic monomer A is a (meth)acrylic acid ester, it is selected from: methyl (meth)acrylate; ethyl (meth)acrylate; butyl (meth)acrylate; ter-butyl (meth)acrylate; isobutyl (meth)acrylate; 2-ethylhexyl (meth)acrylate; ethylene glycol (meth)acrylate; octyl (meth)acrylate; lauryl (meth)acrylate; stearyl (meth)acrylate; dialkyl aminoalkyl acrylates, such as dimethylaminoethyl (meth)acrylate, their acidified or quaternised salts, and their mixtures.

[0051] When the hydrophobic monomer A is a vinyl ester, it advantageously has a Ci to C30 hydrocarbon group, preferably Ci to C25, more preferably Ci to C20, even more preferably Ci to C15, the hydrocarbon group which may be saturated or unsaturated, linear, branched or cyclic, optionally substituted by one or more heteroatoms selected from among N, O, P and S, and / or optionally substituted by one or more groups selected from among acid, aryl, ester, amine, amide, carbamate, hydroxyl, ether (advantageously C2 or C3 ether), nitrile, vinyl, allyl, thioether, sulphonic or halogen.

[0052] Advantageously, when the hydrophobic monomer A is a vinyl ester, it is selected from vinyl acetate, vinyl propionate, vinyl laurate and vinyl versatates of formula (II) CH2=CH-0- C(=0)-C(CH3)(Rx)(Ry), with Rx+ Ryrepresenting a total number of carbon atoms of between 5 and 8.

[0053] In terms of vinyl versatate of formula (II), mention may be made, for example, of those of the Veova® range from Hexion, such as Veova® 9, 10 and 11.

[0054] The quantity of hydrophobic monomer A (meth)acrylic acid ester in polymer S2is advantageously of at least 1 mol%, preferably of at least 5 mol%, more preferably of at least 10 mol%, even more preferably of at least 20 mol%; advantageously of at most 99 mol%, preferably of at most 95 mol%, more preferably of at most 90 mol% and even more preferably of at most 80 mol%, it is advantageously between 33 mol% and 67 mol%, preferably between 40 mol% and 60 mol%, more preferably between 45 mol% and 55 mol%.

[0055] The quantity of hydrophobic monomer A vinyl ester in polymer S2is advantageously of at least 1 mol%, preferably of at least 5 mol%, more preferably of at least 10 mol%, even more preferably of at least 20 mol%; advantageously of at most 99 mol%, preferably of at most 95 mol%, more preferably of at most 90 mol% and even more preferably of at most 80 mol%, it is advantageously between 33 mol% and 67 mol%, preferably between 40 mol% and 60 mol%, more preferably between 45 mol% and 55 mol%.

[0056] In some preferred embodiments, polymer S2consists of hydrophobic monomer A.

[0057] In some preferred embodiments, polymer S2consists of:

[0058] - 33 mol% to 67 mol% of monomer of formula I, preferably between 40 mol% and 60 mol%, more preferably between 45 mol% and 55 mol%; and

[0059] - 33 mol% to 67 mol% of monomer ester of (meth)acrylic acid and / or vinyl ester, preferably between 40 mol% and 60 mol%, more preferably between 45 mol% and 55 mol%.

[0060] In some preferred embodiments, polymer S2has a ratio between the monomer(s) of formula I and (meth)acrylic acid ester monomer(s), advantageously of between 2: 1 and 1 : 2, preferably between 1.5: 1 and 1 : 1.5, and more preferably the ratio is 1 : 1. In some preferred embodiments, polymer S2has a ratio between the monomer(s) of formula I and vinyl ester monomer(s) (-C=C-O-C(=O)-), advantageously of between 2: 1 and 1 : 2, preferably between 1.5: 1 and 1 : 1.5, and more preferably the ratio is 1 : 1.

[0061] In some preferred embodiments, polymer S2has a ratio between (1) the monomer(s) of formula I and (2) (meth)acrylic acid ester monomer(s) and vinyl ester monomer(s) (-C=C-O- C(=O)-), advantageously of between 2: 1 and 1 : 2, preferably between 1.5: 1 and 1 : 1.5, and more preferably the ratio is 1 : 1.

[0062] Polymer S2may also comprise at least one monomer B different from the hydrophobic monomer A, selected from among hydrophilic non-ionic monomers, hydrophilic anionic monomers, hydrophilic cationic monomers and hydrophilic zwitterionic monomers.

[0063] Advantageously, the non-ionic hydrophilic monomer(s) are selected, in particular, in the group comprising vinyl monomers which are soluble in water, such as, acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (for example, N,N-dimethylacrylamide or N,N-diethylacrylamide), N,N-dialkylmethacrylamides, acrylic acid alkoxylated esters, methacrylic acid alkoxylalted esters, N-vinylpyrrolidone, N- methylol(meth)acrylamide, N-vinyl caprolactame, N-vinylformamide (NVF), N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), glyceryl methacrylate, diacetone acrylamide, methacrylic anyhydride, maleic anhydride, itaconic anhydride, itaconamide, hydroxyalkyl (meth)acrylates, thioalkyl (meth)acrylates, isoprenol and its alcoxyl derivatives, hydroxyethyl(meth)acrylates and their alcoxyl derivatives, hydroxypropylacrylate and its alcoxyl derivatives, vinyl acetate, and their mixtures. Among these non-ionic monomers, the alkyl groups are advantageously C1-C5, and more advantageously C1-C3. Preferably, the hydrophilic nonionic monomers B are acrylamide and N-methylol acrylamide.

[0064] Advantageously, the other anionic hydrophilic monomer(s) may be selected from a large group. These monomers may have a vinyl function, in particular, acrylic, maleic, fumaric, itaconic, or allylic. They may also contain a carboxylate, phosphonate, phosphate, sulphonate, sulphate group, or another anionic filler group. Preferred monomers belonging to this class are, for example, acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; C1-C3 itaconic acid half-esters; acryloyl chloride; crotonic acid; maleic acid; fumaric acid; 3- acrylamido 3 -methylbutanoic acid; strong acid-type monomers having, for example, a sulphonic acid-type or phosphonic acid-type function, such as vinylsulphonic acid, vinylphosphonic acid, allylsulphonic acid, methallylsulphonic acid, 2-methylidenepropane- 1,3-disulphonic acid, 2-sulphoethylmethacrylate, sulphopropylmethacrylate, sulphopropylacrylate, allylphosphonic acid, ethylene glycol methacrylate phosphate, sulphonic styrene acid, 2-acrylamido-2-m ethylpropane sulphonic acid (ATBS), 2-acrylamido- 2 -methylpropane disulphonic acid 3 -allyloxy -2-hydroxypropane sulphonic acid, diethylallylphosphonate; water-soluble salts of all of these monomers, such as their alkaline metal salts, alkaline earth metal salts, or ammonium salts; and their mixtures. Also included are half-esters of maleic acid or itaconic acid, their salts and their mixtures. Preferably, the hydrophilic anionic monomer B is (meth)acrylic acid.

[0065] In some preferred embodiments of the invention, the hydrophilic anionic monomer(s) B may be salified. This may also be a mixture of acid form and salified form, for example, a mixture of acrylic acid and acrylate.

[0066] The term “salified” means the substitution of a proton of at least one acid function of the - Ra(=O)-OH type (with R= P, S or C) of the anionic monomer by a metal cation or organic cation to form a salt of the -Ra(=O)-OX type (X being a metal cation or organic cation). In other words, the non-salified form corresponds to the acid form of the monomer, for example, Rb-C(=O)-OH in the case of the carboxylic acid function, while the salified form of the monomer corresponds to the Rb-C(=O)-O- X+, X+ corresponding to an alkaline cation or an organic cation. The salification of the acid functions of polymer S2may be partial or total.

[0067] The salified form advantageously corresponds to the salts of alkaline metals (Li, Na, K, etc.), alkaline-earth metals (Ca, Mg, etc.), and the organic cation is advantageously the ammonium ion or a tertiary ammonium. The preferred salts are sodium salts.

[0068] The salification may take place before or after polymerisation.

[0069] Advantageously, the cationic hydrophilic monomer(s) B may be chosen, in particular, from among the vinyl-type monomers, in particular, of the acrylamide, acrylic, allylic or maleic type having an ammonium function, advantageously quaternary ammonium. Mention may be made, in particular, and in a non-limiting manner, of diallyldialkyl ammonium salts, such as diallyl dimethyl ammonium chloride (DADMAC); acidified or quaternised dialkyl- aminoalkyl(meth)acrylamide salts, like for example, methacrylamido-propyl trimethyl ammonium chloride (MAPTAC), acrylamido-propyl trimethyl ammonium chloride (APTAC), acidified or quaternized dialkyl-aminoalkyl acrylate salts like quaternized or salified dimethylaminoethyl acrylate (DMAEA); acidified or quaternized dialkyl aminoalkyl methacrylate salts like quaternized or salified dimethylaminoethyl methacrylate (DMAEMA); acidified or quaternised N,N-dimethylallylamine salts, acidified or quaternised diallylmethylamine salts, acidified or quaternised diallylamine salts, vinylamine obtained by hydrolysis (basic or acid) of an amide group -N(R2)-C0-RI with Ri and R2 being, independently, a hydrogen atom or an alkyl chain of 1 to 6 carbon atoms, vinylamine obtained by Hofmann degradation, and their mixtures. Advantageously, the alkyl groups are C1-C7, preferably C1-C3 and may be linear, cyclic, saturated or unsaturated chains.

[0070] A person skilled in the art will know how to prepare the quaternised monomers, for example, by means of an R-X-type quatemisation agent, R being an alkyl group and X being a halogen or a sulphate.

[0071] The term “quatemisation agent” means a molecule being able to alkylate a tertiary amine.

[0072] The quatemisation agent may be selected from among dialkyl sulphates comprising 1 to 6 carbon atoms or alkyl halides comprising 1 to 6 carbon atoms. Preferably, the quatemisation agent is selected from among methyl chloride, benzyl chloride, dimethyl sulphate or diethyl sulphate. Furthermore, the present invention also covers DADMAC, APTAC and MAPTAC- type monomers in which the counterion is a sulphate, a fluoride, a bromide or an iodide instead of chloride.

[0073] The quantity of monomer B in polymer S2is advantageously 60 mol% or less, preferably 50 mol% or less, more preferably 40 mol% or less, more preferably 30 mol% or less, more preferably 20 mol% or less, more preferably 10 mol% or less. When present, the monomer B in polymer S2represents at least 1 mol%.

[0074] The quantity of monomers B will be adjusted depending on the preparation conditions of the polymer S2and on the use thereof so that it remains insoluble in water.

[0075] Polymer S2is conventionally obtained by direct emulsion polymerisation according to the general knowledge of a person skilled in the art.

[0076] Polymer S2may be linear, branched or cross-linked. The S2polymer may be branched or cross-linked, for example, using a branching agent and / or using a transfer agent. Polymer S2may comprise other hydrophobic monomers different from hydrophobic monomer A. Advantageously they represent at most 20 mol% of the polymer S2, preferably at most 15 mol%, more preferably at most 10 mol% and even more preferably at most 5 mol% with respect to the total number of monomers of the polymer S2.

[0077] The quantities of the different monomer(s) will be adjusted by a person skilled in the art so as to reach 100 mol% when preparing the polymer S2.

[0078] In some preferred embodiments, polymer S2consists of monomers A and B. Preferably polymer S2consists of monomers A.

[0079] In some preferred embodiments, the polymer S2may be structured with at least one branching agent. A structured polymer is a non-linear polymer with side chains.

[0080] The branching agent is advantageously selected from:

[0081] - structuring agents, which may be selected from the group comprising polyethylenically unsaturated compounds (having, at least two unsaturated functions) different from the monomers previously described, such as, vinyl functions, in particular, allylic or acrylic functions, and may include, for example, methylene bisacrylamide (MBA), triallyamine, tetraallylammonium chloride, 1,2 dihydroxy ethylene bis-(N-acrylamide), ethylene glycol (meth)acrylate, divinyl benzene;

[0082] - compounds having at least two epoxy functions;

[0083] - compounds having at least one unsaturated function and one epoxy function, such as glycidyl (meth)acrylate;

[0084] - macro-initiators, such as polyperoxides, polyazoics and transfer polyagents, such as polymercaptan polymers, and polyols;

[0085] - functionalised polysaccharides;

[0086] - water-soluble metal complexes composed:

[0087] * of a metal of valence greater than 3 such as, as an example and in a non-limiting manner, aluminium, boron, zirconium, or also titanium, and

[0088] * of a ligand carrying a hydroxyl function.

[0089] The quantity of branching agent in polymer S2is advantageously of between 1 ppm and 100 000 ppm, preferably between 10 ppm and 50 000 ppm, more preferably between 100 ppm and 10 000 ppm. In some preferred embodiments, the polymer S2is free of branching agent.

[0090] Polyvinyl amine

[0091] Polyvinyl amine is a water-soluble polymer.

[0092] Polyvinyl amine can be obtained by partial or total Hofmann rearrangement of acrylamide, methacrylamide, acrylonitrile, and their mixtures; or by partial or total hydrolysis of the amide group -N(R2)-C0-RI of a monomer of formula III: wherein R1and R2are, independently, a hydrogen atom or an alkyl chain of 1 to 6 carbon atoms.

[0093] Hofmann rearrangement

[0094] The Hofmann rearrangement reaction consists, in particular, of converting amide or nitrile functions into amine functions (for example, by formation of vinylamine monomeric units) by involving two main coefficients (expressed in molar ratios):

[0095] - Coefficient Alpha = hypo-halide (alkali metal hypohalite and / or alkaline earth metal hypohalite) / amide and / or nitrile functions;

[0096] - Coefficient Beta = hydroxide (alkali metal hydroxide and / or alkaline earth metal hydroxide) / hypo-halide (alkali metal hypohalite and / or alkaline earth metal hypohalite).

[0097] A hypohalite is an oxy-anion, for example, the hypochlorite CIO'. Preferably, it is sodium hypochlorite.

[0098] The term “alkali metal hypohalite” means a hypohalite of at least one alkali metal, for example, NaOCl, KOBr or NaOCl+KOBr. The same applies to an alkaline-earth hypohalite.

[0099] The term “alkali” means an alkali metal, advantageously lithium, sodium or potassium. The term “alkaline-earth” means an alkaline-earth metal, advantageously calcium or magnesium.

[0100] The term “alkali hydroxide” means a hydroxide (OH-) of at least one alkali metal, for example, NaOH, KOH or NaOH+KOH. The same applies to alkaline earth hydroxide. Preferably, it is sodium hydroxide.

[0101] The Hofmann rearrangement may be performed before, during or after polymerisation of monomers constituting a polymer Pl, comprising acrylamide, methacrylamide, acrylonitrile and / or their mixtures.

[0102] Advantageously, the Hofmann degradation reaction comprises at least the following steps:

[0103] 1) dilution (advantageously in water) of the solution comprising polymer Pl so as to form a dilute solution of the polymer (SD1);

[0104] 2) addition of hypohalite and hydroxide so as to form a dilute solution (SD2);

[0105] 3) reaction between polymer Pl, hypohalite and hydroxide so as to obtain a solution comprising polyvinyl amine (SD3).

[0106] Advantageously, in step 1), the concentration of polymer Pl in the dilute solution SD1 of polymer Pl is between 1% and 40% by weight with respect to the weight of the SD1, more preferably between 2% and 30% and even more preferably between 5% and 25%.

[0107] Advantageously, in step 2), the coefficient Alpha = hypohalite / amide and / or nitrile functions is between 0.1 and 1.0, preferably between 0.3 and 1.0 and more preferably between 0.5 and 1.0.

[0108] Advantageously, in step 2), the coefficient Beta = hydroxide / hypohalite is between 0.5 and 4.0.

[0109] Advantageously, in step 3), the reaction between the polymer Pl, hypohalite and hydroxide lasts between 10 seconds and 180 minutes, preferably between 1 minute and 120 minutes, more preferably between 10 minutes and 90 minutes, and even more preferably between 30 minutes and 75 minutes.

[0110] Advantageously, in step 3), the reaction between the polymer Pl, hypohalite and hydroxide is performed at a temperature of between 10°C and 30°C, preferably between 15°C and 25°C. At the end of step 3), polyvinyl amine according to the invention is obtained.

[0111] In some preferred embodiments according to the invention, at the end of step 3), poly vinylamine may be functionalised with an aldehyde to give an aldehyde polyvinyl amine.

[0112] Aldehyde is advantageously selected from glyoxal, glutaraldehyde, furan-dialdehyde, adipaldehyde, succinaldehyde, starch dialdehyde, 2,2-dimethoxyethanal, diepoxy compounds, and their mixtures. Preferably, this is glyoxal.

[0113] So as to stabilise the amine functions produced, a person skilled in the art may use at least one quaternary ammonium derivative as described in document JP 57077398. The purpose of this quaternary ammonium derivative is to avoid the reaction between the amine functions and the residual amide functions. These agents may be added separately, simultaneously, mixed or not, in any order of introduction, and at one or more injection points. Advantageously, these agents are added in step 1).

[0114] During the Hofmann rearrangement, the cationicity of the polymer increases by the use / consumption, in whole or in part, of an alkali or alkaline earth hypohalite.

[0115] Hydrolysis of the monomer of formula (III)

[0116] Advantageously, the monomer(s) of formula (III) are selected from: N-vinylformamide, N- vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N- ethylacetamide, N-vinylpropianamide, N-vinyl-N-methylpropianamide and N- vinylbutyramide. Preferably, it is N-vinylformamide.

[0117] Hydrolysis of the monomer of formula (III) may be performed under the action of an acid (acid hydrolysis) or a base (basic hydrolysis). Preferably, it is a basic hydrolysis.

[0118] Acid hydrolysis may be performed using any Bronsted acid known to a person skilled in the art, by way of example and in a non-limiting manner, mention may be made, in particular, of hydrochloric acid, sulphuric acid, nitric acid or phosphoric acid.

[0119] Acid hydrolysis is advantageously performed at a pH of between 0 and 2, preferably between 0 and 1.

[0120] Acidic hydrolysis is advantageously performed at a temperature of between 60°C and 100°C, preferably between 70°C and 90°C, more preferably between 75°C and 85°C. The acidic hydrolysis step advantageously lasts between 120 minutes and 720 minutes, preferably between 180 minutes and 600 minutes, more preferably between 300 minutes and 540 minutes.

[0121] Basic hydrolysis may be performed using any base known to a person skilled in the art, by way of example and in a non-limiting manner, mention may be made in particular of sodium hydroxide, potassium hydroxide or ammonia.

[0122] Basic hydrolysis is advantageously performed at a pH of between 8 and 14, preferably between 8 and 13, more preferably between 9 and 12.

[0123] Basic hydrolysis is advantageously performed at a temperature of between 60°C and 100°C, preferably between 70°C and 90°C, more preferably between 75°C and 85°C.

[0124] The acidic hydrolysis step advantageously lasts between 60 minutes and 480 minutes, preferably between 120 minutes and 420 minutes, more preferably between 240 minutes and 360 minutes.

[0125] Depending on the quantity of acid or base added, the monomers of formula (III) are partially or totally converted to an amine function.

[0126] Once the hydrolysis reaction is complete, the pH is advantageously adjusted between 6 and 9.

[0127] Polyvinyl amine

[0128] The quantity of amine functions (-CH2-CH(NH2)- group) in polyvinyl amine is between 1 mol% and 100 mol%, preferably between 10 mol% and 90 mol%, more preferably between 20 mol% and 80 mol%, more preferably between 30 mol% and 70 mol%, and even more preferably between 35 mol% and 60 mol%. The quantity of amine functional groups in polyvinyl amine may, in particular, be between 30 mol% and 100 mol%.

[0129] Polyvinyl amine may also comprise at least one monomer selected from hydrophilic non-ionic monomers other than acrylamide, methacrylamide, acrylonitrile and monomer of formula (III); hydrophilic anionic monomers; hydrophilic cationic monomers different from amines obtained after the Hofmann rearrangement of acrylamide, methacrylamide, acrylonitrile or hydrolysis of the compound(s) of formula (III); hydrophilic zwitterionic monomers; and hydrophobic monomers. Advantageously, the non-ionic hydrophilic monomer(s) (other than acrylamide, methacrylamide, acrylonitrile and the monomer of formula (III)) are chosen, in particular, in the group comprising vinyl monomers which are soluble in water, such as N- alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (for example, N,N- dimethylacrylamide or N,N-di ethyl acrylamide), N,N-dialkylmethacrylamides, acrylic acid alkoxylated esters, methacrylic acid alkoxylalted esters, N-vinylpyrrolidone, N- methylol(meth)acrylamide, N-vinyl caprolactame, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, methacrylic anyhydride, maleic anydride, itaconic anhydride, itaconamide, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate, isoprenol and its alcoxyl derivatives, hydroxyethyl(meth)acrylates and their alcoxyl derivatives, hydroxypropylacrylate and its alcoxyl derivatives, vinyl acetate and their mixtures. Among these non-ionic monomers, the alkyl groups are advantageously C1-C5, and more advantageously C1-C3. They are preferably linear alkyls.

[0130] Polyvinyl amine advantageously comprises less than 50 mol% of hydrophilic non-ionic monomer (different from acrylamide, methacrylamide, acrylonitrile and monomer of formula (III)), preferably less than 40 mol% and more advantageously less than 30 mol%.

[0131] Advantageously, the other anionic hydrophilic monomer(s) may be selected from a large group. These monomers may have a vinyl function, in particular, acrylic, maleic, fumaric, malonic, itaconic, or allylic. They may also contain a carboxylate, phosphonate, phosphate, sulphonate group, or another anionic filler group. Preferred monomers belonging to this class are, for example, acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; C1-C3 itaconic acid half-esters; acryloyl chloride; crotonic acid; maleic acid; fumaric acid; 3- acrylamido 3 -methylbutanoic acid; strong acid-type monomers having, for example, a sulphonic acid-type or phosphonic acid-type function, such as vinylsulphonic acid, vinylphosphonic acid, allylsulphonic acid, methallylsulphonic acid, 2-methylidenepropane- 1,3-disulphonic acid, 2-sulphoethylmethacrylate, sulphopropylmethacrylate, sulphopropylacrylate, allylphosphonic acid, ethylene glycol methacrylate phosphate, sulphonic styrene acid, 2-acrylamido-2-m ethylpropane sulphonic acid (ATBS), 2-acrylamido- 2-methylpropane disulphonic acid, 3-allyloxy-2-hydroxypropane sulphonic acid, diethylallylphosphonate, carboxyethyle acrylate; water-soluble salts of all of these monomers, such as their alkaline metal salts, alkaline earth metal salts, or ammonium salts; and their mixtures. Also included are monoesters of maleic acid or itaconic acid, their salts, and their mixtures.

[0132] In some preferred embodiments, the hydrophilic anionic monomer(s) may be salified. This may also be a mixture of acid form and salified form, for example, a mixture of acrylic acid and acrylate.

[0133] The term “salified” means the substitution of a proton of at least one acid function of the - Ra(=O)-OH type (with R= P, S or C) of the anionic monomer by a metal cation or organic cation to form a salt of the -Ra(=O)-OX type (X being a metal cation or organic cation). In other words, the non-salified form corresponds to the acid form of the monomer, for example Rb-C(=O)-OH in the case of the carboxylic acid function, while the salified form of the monomer corresponds to the Rb-C(=0)-0‘ X+form, X+corresponding to an alkaline cation or an organic cation. The salification of the acid functions of the polymer may be partial or total.

[0134] The salified form advantageously corresponds to the salts of alkali metals (Li, Na, K, etc.), alkaline-earth metals (Ca, Mg, etc.), and the organic cation is advantageously the ammonium ion or a tertiary ammonium. The preferred salts are sodium salts.

[0135] The salification may take place before or after polymerisation.

[0136] The polyvinyl amine advantageously comprises less than 50 mol% of hydrophilic anionic monomer, preferably less than 40 mol% and more advantageously less than 30 mol%.

[0137] Advantageously, the hydrophilic cationic monomer(s) (different from the monomer that has undergone the Hofmann degradation reaction or hydrolysis) are selected from monomers derived from vinyl-type units (advantageously of the acrylamide, acrylic, allylic or maleic type), these monomers having a quaternary ammonium function. In particular and in a nonlimiting manner, mention may be made of diallyldialkyl ammonium salts such as diallyldimethyl ammonium chloride (DADMAC); quatemised salts of dialkylaminoalkylacrylamides; quaternised salts of dialkylaminoalkyl methacrylamides such as methacryl amido-propyl trimethyl ammonium chloride (MAPTAC), aery 1 amido-propyl trimethyl ammonium chloride (APTAC), quatemised salts of dialkyl aminoalkyl acrylate, such as quaternised dimethylaminoethyl acrylate, quatemised salts of dialkyl aminoalkyl methacrylate, such as quaternised dimethylaminoethyl methacrylate, acidified or quatemised salts of N,N-dimethylallylamine; acidified or quaternised salts of diallylmethylamine; acidified or quaternised salts of diallylamine, and their mixtures. Advantageously, the alkyl groups are C1-C3. Preferably, the monomer having a quaternary amine function is diallyl dimethyl ammonium chloride (DADMAC).

[0138] A person skilled in the art will know how to prepare the quaternised monomers, for example, by means of an R-X-type quatemisation agent, R being an alkyl group and X being a halogen or a sulphate.

[0139] The term “quatemisation agent” means a molecule being able to alkylate a tertiary amine.

[0140] The quatemisation agent may be selected from among dialkyl sulphates comprising 1 to 6 carbon atoms or alkyl halides comprising 1 to 6 carbon atoms. Preferably, the quatemisation agent is selected from among methyl chloride, benzyl chloride, dimethyl sulphate or diethyl sulphate. Furthermore, the present invention also covers DADMAC, APTAC and MAPTAC monomers in which the counterion is sulphate, fluoride, bromide or iodide instead of chloride.

[0141] The polyvinyl amine advantageously comprises less than 50 mol% of hydrophilic cationic monomer (different from the monomer that has undergone the Hofmann degradation reaction or hydrolysis), preferably less than 40 mol% and more advantageously less than 30 mol%.

[0142] The quantities of different monomers will be adjusted by a person skilled in the art, so as to not exceed 100 mol% during the preparation of the polyvinyl amine.

[0143] Polyvinyl amine has a weight-average molecular weight of between 30 000 g / mol and 300 000 g / mol, preferably between 50 000 g / mol and 300 000 g / mol, more preferably between 50 000 and 250 000 g / mol, more preferably between 50 000 g / mol and 200 000 g / mol, more preferably between 100 000 g / mol and 250 000 g / mol and even more preferably between 100 000 g / mol and 200 000 g / mol.

[0144] The polyvinyl amine may further be structured by at least one branching agent. A structured polymer is a non-linear polymer that has side chains.

[0145] The branching agent is advantageously selected from:

[0146] - structuring agents, which may be selected from the group comprising polyethylenically unsaturated compounds (having, at least two unsaturated functions) different from the previously described monomers, such as vinyl functions, in particular allylic or acrylic functions, and may include, for example, methylene bisacrylamide (MBA), triallyamine, or tetraallylammonium chloride, 1,2 dihydroxy ethylene bis-(N-acrylamide), ethylene glycol (meth)acrylate;

[0147] - compounds having at least two epoxy functions;

[0148] - compounds having at least one unsaturated function and one epoxy function, such as glycidyl (meth)acrylate;

[0149] - macro-initiators, such as polyperoxides, polyazoics and transfer polyagents, such as polymercaptan polymers, and polyols;

[0150] - functionalised polysaccharides;

[0151] - water-soluble metal complexes composed:

[0152] * of a metal of valence greater than 3 such as, as an example and in a non-limiting manner, aluminium, boron, zirconium, or also titanium, and

[0153] * of a ligand carrying a hydroxyl function.

[0154] In some preferred embodiments, the polyvinyl amine is free of branching agent.

[0155] In some preferred embodiments, the polyvinyl amine comprises a transfer agent.

[0156] The transfer agent is advantageously selected from among methanol; isopropyl alcohol; sodium hypophosphite; calcium hypophosphite; magnesium hypophosphite; potassium hypophosphite; ammonium hypophosphite; formic acid; sodium formiate; calcium formiate; magnesium formiate; potassium formiate; ammonium formiate; 2-mercaptoethanol; 3- mercaptopropanol; glycol dithiopropylene; thioglycerol; thioglycolic acid; thiohydracrylic acid; thiolactic acid; thiomalic acid; cysteine; aminoethanethiol; thioglycolates; allyl phosphites; allyl mercaptans; sodium methallysulphonate; calcium methally sulphonate; magnesium methallysulphonate; potassium methallysulphonate; ammonium methallysulphonate; polythiols, and their mixtures. Preferably, the transfer agent is sodium hypophosphite, sodium formate or a mixture of them.

[0157] In some preferred embodiments, the polyvinyl amine is free of transfer agent.

[0158] In some preferred embodiments, polyvinyl amine is prepared according to the process described by the Applicant in document FR2305149.

[0159] In some preferred embodiments, polyvinyl amine may react with a,P-unsaturated alkylcarbonyl compounds, including amides, esters and acids under acidic conditions to form a Michael adduct. Composition

[0160] The quantity of polymers S2and polyvinyl amine advantageously represents between 1% and 100% by weight of the active material of the sizing composition, preferably between 5% and 100% by weight, more preferably between 20% and 100% by weight.

[0161] The quantity of polymers S2and polyvinyl amine advantageously represents between 0.5% and 15% by weight with respect to the total weight of the sizing composition, preferably between 1% and 10% by weight, more preferably between 1.5% and 8% by weight.

[0162] The term “active material” of the sizing composition means the polymers S2and polyvinyl amine and, when it is present, starch, with the exception of the solvent(s) and optional other additives, the solvent advantageously corresponding to water.

[0163] The weight ratio between polymer S2and polyvinyl amine is between 55 / 45 and 99 / 1, more preferably between 60 / 40 and 99 / 1, more preferably between 80 / 20 and 95 / 5.

[0164] The sizing composition may also comprise starch.

[0165] The quantity of starch in the sizing composition is advantageously between 0% and 99% by weight with respect to the active material of the sizing composition, preferably between 0% and 80%, preferably between 10% and 80% by weight, more preferably between 10% and 75% by weight.

[0166] In addition to polymer S2and polyvinyl amine, the sizing composition may comprise additives conventionally used for sizing paper or cardboard by a person skilled in the art; mention may be made, by way of example, of aluminium chloride, enzymes, dyes, optical brighteners, an anti-foaming agent, paraffin, mineral or vegetable waxes, surfactants, polysaccharides other than starch, other polymers (e.g., polyvinyl alcohol or polyvinyl acetate).

[0167] The quantity of additives in the sizing composition generally does not exceed 50% by weight, preferably not 40% by weight and more preferably not 30% by weight, with respect to the total weight of the active material of the sizing composition.

[0168] Waxes of mineral or vegetable origin advantageously have a melting point of between 40°C and 65°C, preferably between 45°C and 60°C, more preferably between 50°C and 55°C. The surfactants may be non-ionic, anionic or cationic, they are preferably non-ionic.

[0169] As surfactants, mention may be made, by way of example, of polyesters having a molecular weight of between 1 000 g / mol and 3 000 g / mol, condensation products between a poly(isobutenyl) succinic acid or its anhydride and a polyethylene glycol, block polymers having a molecular weight of between 2 500 g / mol and 3 500 g / mol, for example, those sold under the names Hypermer®, sorbitan extracts, such as sorbitan monooleate or sorbitan polyoleates, sorbitan isostearate or sorbitan sesquioleate, poly ethoxylated sorbitan esters, or diethoxylated oleocetyl alcohol or tetraethoxylated lauryl acrylate, condensation products of fatty alcohols greater than ethylene, like reaction product of oleyl alcohol with 2 ethylene oxide units; condensation products of alkylphenols and ethylene oxide, such as the reaction product of nonyl phenol with 4 ethylene oxide units. Preferably, it is sorbitol palmitate, optionally oxyethylenated, sorbitol stearic.

[0170] As polysaccharides, mention may be made, by way of example, of carboxymethylcellulose or any other chemically-modified polysaccharide derivative.

[0171] The quantity of the various constituents of the sizing composition of the invention will be adjusted by a person skilled in the art so as to reach 100% by weight.

[0172] The present invention also relates to a method for sizing paper or cardboard comprising the application of the sizing composition according to the invention on a sheet of paper or cardboard.

[0173] In some preferred embodiments, the sizing composition is applied on a surface sizing.

[0174] The invention and its advantages will be better shown by the following examples given to show the invention, without however limiting it.

[0175] Examples

[0176] List of abbreviations:

[0177] PVAM: Polyvinyl amine

[0178] AMD: Acrylamide

[0179] AA: Sodium acrylate NVF : N-vinylformamide VA: Vinyl amine APTAC: Aery 1 amido-propyl trimethyl ammonium chloride ADC: Dimethylaminoethyl acrylate methyl chloride DMAEMA: Dimethylaminoethyl methacrylate

[0180] Description of products used:

[0181] Product A (PA): Polyvinyl amine (PVAM) from polyNVF, 50% hydrolysed, with a molecular weight of 275 000 g / mol.

[0182] Product B (PB): Polyvinyl amine (PVAM) resulting from Hofmann rearrangement on polyacrylamide, 100% acrylamide conversion, with a molecular weight of 150 000 g / mol. Product C (PC): Polyvinyl amine (copolymer NVF / AA 70 / 30 mol%) of which 50% hydrolysed NVF (i.e. NVF / VA / AA 35 / 35 / 30 mol%), having a molecular weight of 225 000 g / mol.

[0183] Product D (PD): Polyvinyl amine (copolymer NVF / APTAC 50 / 50 mol%), obtained by Michael’s reaction with a 100% hydrolysed poly(NVF), having a molecular weight of 235 000 g / mol.

[0184] Polymer S2-A (cationic) (SAE A): Product sold by Axchem under the name Axsize SS 8100 (styrene / n-butyl acrylate / tert-butyl acrylate / DMAEMA - 55 / 23 / 20 / 2).

[0185] Polymer S2-B (anionic) (SAE B): Product sold by Axchem under the name Axsize SS 2765 EP (styrene / n-butyl acrylate / tert-butyl acrylate - 50 / 45 / 5).

[0186] Comparative Product E (PE-CE): Polyvinyl amine (PVAM) from polyNVF 100% hydrolyzed, with a molecular weight of 400 OOOg / mol (PVAM).

[0187] Comparative Product F (PF-CE): Cationic polyacrylamide (AMD / ADC 65 / 35 mol% copolymer), with a molecular weight of 1 100 OOOg / mol.

[0188] Product G (PG): Polyvinyl amine (PVAM) from polyNVF 100% hydrolyzed, with a molecular weight of 300 OOOg / mol (PVAM).

[0189] Product H (PH): Polyvinyl amine (PVAM) from polyNVF 90% hydrolyzed, with a molecular weight of 300 OOOg / mol (PVAM).

[0190] Product I (PI): Polyvinyl amine (PVAM) from polyNVF 80% hydrolyzed, with a molecular weight of 300 OOOg / mol (PVAM).

[0191] Comparative Product J (PJ-CE): Polyvinyl amine (PVAM) from Hofmann rearrangement on poly AMD, 100% AMD conversion, with a molecular weight of 20 000 g / mol (PVAM).

[0192] Product K (PK): Polyvinyl amine (PVAM) from Hofmann rearrangement on poly AMD, 100% AMD conversion, with a molecular weight of 50 000 g / mol (PVAM). Preparation of sizing compositions 1 to 14

[0193] In a reactor, 586 g of water, 80 g of native potato starch and 0.04 g of amylase enzyme are weighed. This solution is heated at 72°C for 3 minutes, and then at 85°C for 6 minutes. After that, 0.6 g of zinc sulphate is added so as to remove the enzymes and then heated at 93°C to 95°C for 12 minutes.

[0194] Water at 80°C is added to dilute this starch solution to 9% by weight.

[0195] A starch solution is thus obtained having a concentration of 9% by weight for a viscosity measured with a Brookfield LV1 viscometer, speed 100 rpm, at 50 cps at 50°C.

[0196] To this starch solution are added the polymer S2(SAE) and polyinyl amine (PVAM) to obtain the sizing composition.

[0197] For sizing compositions 9 to 14, 0.4% by weight of poly-aluminium chloride was added.

[0198] Sizing compositions 1 to 14 are summarised in Table 1.

[0199] Preparation of sizing compositions 15 to 28

[0200] Polymer S2and polyvinyl amine are mixed in a reactor. For sizing compositions 17 to 21, 0.4% by weight of poly-aluminium chloride was added.

[0201] Cationic polyacrylamide (AMD / ADC 65 / 35 mol% copolymer) (Comparative product F (PF- CE)) was used instead of polyvinyl amine for sizing composition 23.

[0202] Sizing compositions 15 to 28 are summarised in Table 1.

[0203]

[0204] Table 1 - Active ingredient of sizing compositions 1 to 28 (CE = comparative example, Inv = invention); * Cationic polyacrylamide (AMD / ADC 65 / 35 mol% copolymer) was used instead ofPVAM

[0205] Sizing method Two sizing methods were performed to demonstrate the effect of the composition of the invention.

[0206] - In a first series of tests, a Mathis AG is used for sizing, the speed of the rollers being 1 rpm, the pressure between the rollers being 2 bars and the temperature of the sizing composition being 60°C. The sizing composition is applied onto a sheet of paper (100% recycled fibres), 90 g / m2, placed in the direction of travel.

[0207] The coated sheet of paper is dried on a dryer at 117°C for 5 minutes.

[0208] - In a second series of tests, a K303 multi-coater is used for sizing, the speed being 8m / min, and the rod used being a 10 pm threaded rod.

[0209] The sizing composition is applied onto a sheet of paper (100% recycled fibres), 90 g / m2, placed in the direction of travel.

[0210] The coated sheet of paper is dried on a dryer at 117°C for 5 minutes.

[0211] Tests

[0212] The different sizing compositions prepared above are tested according to two parameters, the rate of deposition of the sizing composition on the paper sheet and the Cobb 60 parameter, allowing the absorption of the treated water sheet to be measured. The results are summarised in Table 2.

[0213] Deposition rate

[0214] The deposition rate is calculated by measuring the quantity of sizing composition that attaches to the sheet of paper by measuring the weight of the sheet before deposition and after deposition plus drying of the sheet. The higher the deposition rate, the better the sizing.

[0215] Cobb 60

[0216] Cobb 60 corresponds to the quantity of water absorbed by the coated sheet of paper after a period of 60 seconds of contact with water (g / m2).

[0217] The lower the quantity of water absorbed by the sheet of paper, the better the sizing.

[0218] Results

[0219]

[0220] Table 2 - Deposition rate and Cobb 60 results for sizing compositions 1 to 28

Claims

CLAIMS1. A sizing composition for paper or cardboard comprising at least:[a] a polymer S2comprising at least 40 mol% of at least one hydrophobic monomer A selected from the group consisting of: i) monomers of formula I:wherein Ri and R2 are, independently, selected from the group consisting of a hydrogen atom, an alkyl chain of 1 to 4 carbon atoms, and a halogen; ii) (meth)acrylic acid ester monomers; iii) vinyl ester monomers; iv) mixtures thereof;[b] a polyvinyl amine having a weight-average molecular weight of between 30 000 and 300 000 g / mol, the polymer S2and polyvinyl amine having a weight ratio of from 55 / 45 to 99 / 1.

2. Sizing composition according to claim 1, characterised in that the at least one hydrophobic monomer A of formula (I) is selected from styrene, ortho-chlorostyrene, metachlorostyrene, para-chlorostyrene, ortho-bromostyrene, meta-bromostyrene, parabromostyrene, ortho-iodostyrene, meta-iodostyrene, para-iodostyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, ortho-ethyl styrene, meta-ethyl styrene, paraethyl styrene, ortho-propyl styrene, meta-propyl styrene, para-propyl styrene, ortho-t- butylstyrene, meta-t-butyl styrene, para-t-butyl styrene, and their mixtures.

3. Sizing composition according to any one of claims 1 to 2, characterised in that the at least one hydrophobic monomer A (meth)acrylic acid ester is an ethylenically unsaturatedester resulting from the reaction between (meth)acrylic acid with an alcohol having a Ci to C30 hydrocarbon group, the hydrocarbon group of the alcohol may be saturated or unsaturated, linear, branched or cyclic, optionally substituted by one or more heteroatoms selected from N, O, P and S, and / or optionally substituted by one or more groups selected from acid, aryl, ester, amine, amide, carbamate, hydroxyl, ether, nitrile, vinyl, allyl, thioether, sulphonic or halogen.

4. Sizing composition according to any one of claims 1 to 3, characterised in that hydrophobic monomer A vinyl ester has a Ci to C30 hydrocarbon group on the ester group, the hydrocarbon group being saturated or unsaturated, linear, branched or cyclic, optionally substituted by one or more heteroatoms selected from among N, O, P and S, and / or optionally substituted by one or more groups selected from among acid, aryl, ester, amine, amide, carbamate, hydroxyl, ether, nitrile, vinyl, allyl, thioether, sulphonic or halogen groups.

5. Sizing composition according to any one of claims 1 to 4, characterised in that the polymer S2has a quantity of monomer B of less than 60 mol%, said monomer B being selected from hydrophilic non-ionic monomers, hydrophilic anionic monomers, hydrophilic cationic monomers and hydrophilic zwitterionic monomers.

6. Sizing composition according to any one of claims 1 to 5, characterised in that the polyvinyl amine is obtained by partial or total Hofmann rearrangement of a polymer of acrylamide, methacrylamide, acrylonitrile or their mixtures; or by partial or total hydrolysis of the amide group -N(R2)-CO-RI of a polymer of a monomer of formula III:wherein R1and R2are, independently, a hydrogen atom or an alkyl chain of 1 to 6 carbon atoms.

7. Sizing composition according to any one of claims 1 to 6, characterised in that polyvinyl amine has a weight-average molecular weight of between 50 000 g / mol and 300 000 g / mol.

8. Sizing composition according to any one of claims 1 to 7, characterised in that the polymer S2and polyvinyl amine have a ratio by weight of between 80 / 20 et 95 / 5.

9. Sizing composition according to any one of claims 1 to 8, characterised in that the composition comprises a quantity of starch of between 10% and 80% by weight, with respect to the total weight of the sizing composition.

10. Method for sizing paper or cardboard comprising the application of the sizing composition according to any one of claims 1 to 9 on a sheet of paper or cardboard.

11. Method according to claim 10, characterised in that the sizing is a surface sizing.

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